JP7340444B2 - pigment water dispersion - Google Patents

Description

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

The inkjet recording method is a recording method in which ink droplets are directly ejected from very fine nozzles using heat or mechanical vibration onto a recording medium, and the ink droplets adhere to the recording medium to obtain a printed matter on which characters or images are recorded. This method has become extremely popular because it has many advantages, such as being easy to produce full color, being inexpensive, being able to use plain paper as a recording medium, and being non-contact with the printing material.
In particular, thermal inkjet recording devices, which boil water by heating a heater and eject ink using the bubbling pressure, can produce inkjet heads using MEMS (micro electro mechanical system) technology, are inexpensive, and can print at high speeds. Because it is possible, it is becoming widely popular. In recent years, inks using pigments as colorants have been widely used to impart weather resistance and water resistance to printed matter.
In the case of pigment ink for inkjet recording, the pigment is dispersed in the vehicle using a dispersant, but with the remarkable increase in printing speed in recent years, the thermal and mechanical stress on the ink has increased, making it difficult to continuously Improving the ejection stability (continuous ejection stability) for stable ejection is being studied. In particular, in the case of a thermal inkjet recording device, the temperature of the ejection heater of the thermal head instantaneously reaches a high temperature of 300° C. or more, and ink components such as pigments burn on the heater and deposits are deposited. So-called kogation occurs, which reduces foaming pressure and impairs discharge performance. Therefore, attempts have been made to improve the thermal stability of colloids in order to suppress aggregation and deposition of colloids near the heater surface.

For example, Patent Document 1 describes a pigment aqueous dispersion that has excellent thermal stability when mixed with ink and printed, particularly suppresses the occurrence of kogation in the heater portion of a thermal head, and has excellent continuous ejection stability. An aqueous pigment dispersion comprising pigment-containing crosslinked polymer particles, wherein the crosslinked polymer contained in the particles has an ethyleneoxy group or a propyleneoxy group of a specified chain length. A pigment aqueous dispersion, etc., which is a polymer crosslinked with a compound represented by the following and whose pigment is carbon black, is described.

JP2017-165965A

Typical inkjet recording methods employ inks that use the three basic primary colors of yellow, magenta, and cyan and a coloring material of black, and various colors are reproduced by subtractively mixing the three basic primary colors of ink on the recording medium. However, so-called special color inks using coloring materials having hues other than the three basic primary colors such as orange, red, violet, green, and blue are sometimes added to expand the color reproducibility range.
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 special color inks.
The present invention aims to improve continuous ejection stability by suppressing the occurrence of kogation, especially in the heater part of a thermal head, in an inkjet recording system, while maintaining the excellent storage stability of the ink when blended with the ink. An object of the present invention is to provide an aqueous pigment dispersion, a method for producing the aqueous pigment dispersion, and an aqueous inkjet recording ink containing the aqueous pigment dispersion.

The present inventors have developed an aqueous pigment dispersion in which an organic pigment is dispersed with a crosslinked polymer, the organic pigment is a specific pigment, and the crosslinked polymer is a polymer crosslinked with a specific crosslinking agent. It has been found that the above problem can be solved.
That is, the present invention provides the following [1] to [3].
[1] A pigment aqueous dispersion in which organic pigment A is dispersed with a crosslinked polymer,
The organic pigment A is one or more selected from disazopyrazolone pigments, perinone pigments, dioxazine pigments, and copper phthalocyanine pigments,
A pigment aqueous dispersion, wherein the crosslinked polymer is a polymer crosslinked with 1,4-butanediol diglycidyl ether as a crosslinking agent.
[2] An aqueous ink for inkjet recording, comprising the aqueous pigment dispersion described in [1] above and a solvent.
[3] A method for producing an aqueous pigment dispersion in which organic pigment A is dispersed in a crosslinked polymer,
The organic pigment A is one or more selected from disazopyrazolone pigments, perinone pigments, dioxazine pigments, and copper phthalocyanine pigments,
A method for producing a pigment aqueous dispersion, including the following steps 1 and 2.
Step 1: A step of dispersing a pigment mixture containing a water-dispersible polymer, organic pigment A, and water to obtain an aqueous pigment dispersion. Step 2: Adding the aqueous pigment dispersion obtained in step 1 and the aqueous pigment dispersion as a crosslinking agent. 1,4-butanediol diglycidyl ether and reacting the water-dispersible polymer with the crosslinking agent to form a crosslinked polymer to obtain a pigment water dispersion.

According to the present invention, when blended into ink, while maintaining the excellent storage stability of the ink, it suppresses the occurrence of kogation, especially in the heater part of the thermal head, and improves continuous ejection stability in the inkjet recording method. It is possible to provide an aqueous pigment dispersion, a method for producing the same, and an aqueous inkjet recording ink containing the aqueous pigment dispersion.

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

In the aqueous pigment dispersion of the present invention, water occupies the largest proportion of the medium in which organic pigment A is dispersed by the crosslinked polymer. That is, the medium has water as a main component, but may contain components other than water. Components other than water include organic solvents that dissolve in water, such as alcohol solvents such as methanol, ethanol, isopropanol, and butanol; ketone solvents such as acetone and methyl ethyl ketone; and 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.

The aqueous pigment dispersion of the present invention can provide good printed matter when mixed with water-based ink and printed, so it is suitably used as an aqueous pigment dispersion for flexographic printing, gravure printing, or inkjet recording. be able to. The aqueous pigment dispersion of the present invention is preferably used as an aqueous pigment dispersion for inkjet recording because it has excellent continuous ejection stability in an inkjet recording method when mixed with aqueous ink and printed. It is more preferable to use it as a pigment aqueous dispersion for thermal inkjet recording because it suppresses this.

When the aqueous pigment dispersion of the present invention is blended into an ink, it maintains the excellent storage stability of the ink while suppressing the occurrence of kogation, especially in the heater part of a thermal head, in an inkjet recording system, allowing continuous ejection. Stability can be improved. Although the reason is not certain, it is thought to be as follows.
The aqueous pigment dispersion of the present invention has a specific type of organic pigment, that is, one or more types selected from disazopyrazolone pigments, perinone pigments, dioxazine pigments, and copper phthalocyanine pigments, and further includes one or more as a crosslinking agent. , 4-butanediol diglycidyl ether. It is presumed that the crosslinked polymer has a crosslinked structure derived from the crosslinking agent and has a specific strong affinity with the above specific type of organic pigment, so that it can efficiently exist in the vicinity of the pigment. . Therefore, even if the liquid medium evaporates in the heater part of a thermal inkjet printer and the pigments become close to each other, it has excellent dispersion stability and can suppress pigment aggregation. Since the amount of coarse particles of crosslinked polymer floating without adsorption can be reduced, the occurrence of kogation can be suppressed, and it is thought that continuous ejection stability can be improved.
In addition, in the pigment aqueous dispersion, by having a crosslinked structure derived from the crosslinking agent in the crosslinked polymer in which the organic pigment is dispersed, the organic pigment particles dispersed with 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 also increases. Therefore, even if the ink is maintained at a high temperature for a long period of time, organic pigments dispersed with a crosslinked polymer having a crosslinked structure derived from the crosslinking agent can maintain high dispersion stability and have excellent storage properties. It is assumed that stability can be maintained.

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

The organic pigment A according to the present invention is one or more selected from disazopyrazolone pigments, perinone pigments, dioxazine pigments, and copper phthalocyanine pigments.
Examples of disazopyrazolone pigments include C.I. I. Disazopyrazolone orange pigments such as Pigment Orange 34 and Pigment Orange 13; C.I. I. Examples include disazopyrazolone red pigments such as Pigment Red 37, Pigment Red 38, Pigment Red 41, and Pigment Red 111. Among these, disazopyrazolone orange pigments are preferred from the viewpoint of improving continuous discharge stability.
Perinone pigments include C.I. I. Pigment Orange 43 and other perinone orange pigments; C.I. I. Examples include perinone red pigments such as Pigment Red 194. Among these, perinone orange pigments are preferred from the viewpoint of improving continuous discharge stability.
As the dioxazine pigment, C.I. I. Examples include dioxazine violet pigments such as Pigment Violet 23.
Examples of copper phthalocyanine pigments include C.I. I. Pigment Green 7 (copper phthalocyanine green), C.I. I. Copper phthalocyanine green pigments such as Pigment Green 36 (copper phthalocyanine green); C.I. I. Examples include copper phthalocyanine blue pigments such as Pigment Blue 15 (copper phthalocyanine blue). Among these, copper phthalocyanine green pigments are preferred from the viewpoint of improving continuous discharge stability.
The above pigments can be used alone or in a mixture of two or more in any proportion.
From the viewpoint of improving continuous discharge stability, 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. .

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

[Water dispersible polymer]
In the present invention, "water-dispersible polymer" means a polymer before crosslinking, and the water-dispersible polymer is a polymer that has the ability to disperse an organic pigment in water or a medium mainly composed of water at room temperature. means.
Examples of water-dispersible polymers include polyester, polyurethane, vinyl polymers, and the like. One type of water-dispersible polymer can be used alone or two or more types can be used in combination.
From the viewpoint of improving continuous discharge stability, the water-dispersible polymer is preferably a vinyl polymer obtained by addition polymerization of vinyl monomers.
The water-dispersible polymer has a reactive group (crosslinkable functional group) that can react with the crosslinking agent. Examples of the reactive group include hydrophilic functional groups such as a carboxy group, a sulfonic acid group, a phosphoric acid group, an amino group, and a hydroxyl group, and from the viewpoint of reaction stability, a carboxy group is preferable. Examples of the vinyl polymer having a carboxyl group used in the water-dispersible polymer include (meth)acrylic acid polymers.
In this specification, "(meth)acrylic acid" means "one or more types selected from acrylic acid and methacrylic acid.""(Meth)acrylicacid" below also has the same meaning.

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

(ionic monomer)
The water-dispersible polymer is preferably an ionic monomer from the viewpoint of improving the dispersion stability of the pigment water dispersion, suppressing the occurrence of kogation, improving continuous discharge stability, and improving storage stability. Contains structural units derived from
The ionic monomer is a monomer having a group that can become an ion under acidic, neutral, or alkaline conditions.
The ionic monomer has a reactive group capable of reacting with the crosslinking 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 anionic monomers and cationic monomers having the reactive group. Among these, anionic monomers having the above-mentioned reactive group are preferred from the viewpoint of improving continuous discharge stability and storage stability.
Examples of the anionic monomer having a reactive group include carboxylic acid monomers, sulfonic acid monomers, phosphoric acid monomers, and the like. Among these, carboxylic acid monomers are more preferred.
Examples of carboxylic acid monomers include (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid. Among them, (meth)acrylic acid is more preferred.

(hydrophobic monomer)
The water-dispersible polymer preferably contains a structural unit derived from a hydrophobic monomer from the viewpoint of adsorption of the polymer onto 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. to saturation, 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 adsorption of the polymer to the pigment surface.
The hydrophobic monomer is preferably one or more selected from aromatic group-containing monomers and (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols.
As used herein, "(meth)acrylate" means "one or more types selected from acrylate and methacrylate."

The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group having 6 to 22 carbon atoms, and more preferably one or more selected from styrene monomers and aromatic group-containing (meth)acrylates. . The molecular weight of the aromatic group-containing monomer is preferably less than 500.
The styrenic monomer is preferably one or more selected from styrene and 2-methylstyrene, more preferably styrene. Further, 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 monomers are preferred, and styrene is more preferred, from the viewpoint of adsorption of the polymer onto 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, more preferably an alkyl group having 1 or more and 22 or less carbon atoms. More preferably, it has an alkyl group having 6 or more and 18 or less carbon atoms.
Examples include (meth)acrylates having a straight chain alkyl group, (meth)acrylates having a branched chain alkyl group, (meth)acrylates having an alicyclic alkyl group, and the like.

A macromonomer can also be used as the hydrophobic monomer.
A 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 100,000 or more from the viewpoint of improving continuous discharge stability and storage stability. ,000 or less. The number average molecular weight is a value measured by gel permeation chromatography using chloroform containing 1 mmol/L of dodecyldimethylamine as a solvent, using polystyrene as a standard substance.
The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, more preferably a methacryloyloxy group.
The macromonomer is preferably one or more selected from aromatic group-containing monomer-based macromonomers and silicone-based macromonomers, and more preferably aromatic group-containing monomer-based macromonomers, from the viewpoint of adsorption of the polymer onto the pigment surface. It is a monomer.
The aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer includes the aromatic group-containing monomers described in the hydrophobic monomer section, with styrene and benzyl (meth)acrylate being preferred, and styrene being more preferred.
Specific examples of styrenic macromers include AS-6(S), AN-6(S), and HS-6(S) (all trade names manufactured by Toagosei Co., Ltd.).
Examples of silicone macromonomers include organopolysiloxanes having a polymerizable functional group at one end.

The hydrophobic monomer is preferably an aromatic monomer, from the viewpoints of improving the dispersion stability of the aqueous pigment dispersion, suppressing the occurrence of kogation, improving the continuous ejection stability of the ink, and improving the storage stability. One or more selected from group group-containing monomers, (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols, and aromatic group-containing monomer-based macromers, more preferably aromatic group-containing monomers, even more preferably It is one or more selected from styrene monomers and aromatic group-containing (meth)acrylates, and styrene monomers are even more preferred.

(Nonionic monomer)
The nonionic monomer is a monomer that does not have the above-mentioned ionic group and has a solubility in 100 g of ion-exchanged water at 25° C. of 10 g or more.
Examples of the nonionic monomer include monomers having at least one of a hydroxyl group and a polyalkyleneoxy group.
The nonionic monomers 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); Indicates the number of moles. The following n indicates the average number of moles added of the oxyalkylene group.) Polyalkylene glycol (meth)acrylate such as (meth)acrylate; Methoxypolyethylene glycol (n = 1 to 30) (meth)acrylate , alkoxypolyethylene glycol (meth)acrylate such as octoxypolyethylene glycol (n = 1 to 30) (meth)acrylate; phenoxy (ethylene glycol/propylene glycol copolymerization) (n = 1 to 30, ethylene glycol among them: n =1 to 29) (meth)acrylate, etc.
Specific examples of commercially available nonionic monomers include NK Ester M-20G, 40G, 90G, NK Ester EH-4E (trade names manufactured by Shin-Nakamura Chemical Co., Ltd.), and Blenmar PE- 90, 200, 350; Blenmar PME-100, 200, 400; Blenmar PP-500, 800; Blenmar AP-150, 400, 550; Blenmar 50PEP-300, 50POEP-800B, 43PAPE -600B (the above are product names manufactured by NOF Corporation), etc.

The above ionic monomers, hydrophobic monomers, and nonionic monomers 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 structural units derived from one or more ionic monomers selected from acrylic acid and methacrylic acid, and carbonized units derived from an aromatic group-containing monomer and an aliphatic alcohol. A vinyl polymer containing a structural unit derived from one or more hydrophobic monomers selected from (meth)acrylates having a hydrogen group, more preferably one or more carboxylic acid monomers selected from acrylic acid and methacrylic acid. It is a vinyl polymer containing a structural unit derived from an aromatic group-containing monomer and a structural unit derived from an aromatic group-containing monomer, and more preferably a constitutional unit derived from one or more carboxylic acid monomers selected from acrylic acid and methacrylic acid, and a styrene-containing monomer. It is a vinyl polymer containing structural units derived from system monomers, and is even more preferably an acrylic acid/styrene copolymer.

When a vinyl polymer is used as the water-dispersible polymer, the content of structural units derived from ionic monomers and structural units derived from hydrophobic monomers in the vinyl polymer is as follows.
The content of the ionic monomer improves the dispersion stability of the pigment aqueous dispersion, suppresses the occurrence of kogation, improves the continuous ejection stability of the ink, and improves the storage stability. From the viewpoint of the % by 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 is 90% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less.
The total content of structural units derived from ionic group-containing monomers and structural units derived from hydrophobic monomers in the vinyl polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass. or more, and preferably 100% by mass or less.
The content of the structural units derived from each monomer in the above-mentioned vinyl polymer can be measured by analysis such as NMR. In addition, the preferred range of the content (content as unneutralized amount) of each monomer in the raw material monomer according to the present invention during production of the vinyl polymer is the content of the constituent units derived from each monomer in the vinyl polymer described above. It can be regarded as the same as the preferred range of content.

As the water-dispersible polymer, a synthesized one or a commercially available product may be used.
When a water-dispersible polymer is obtained by synthesis, it can be produced by copolymerizing the raw material monomers according to the present invention by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. . Furthermore, there is no restriction on the chaining mode of the polymerized monomers, and any polymerization mode such as random, block, or graft may be used.
Examples of commercially available water-dispersible polymers include acrylic acid/styrene copolymers such as Joncryl 67, Joncryl 611, Joncryl 678, Joncryl 680, Joncryl 690, and Joncryl 819 (manufactured by BASF Japan Co., 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, from the viewpoint of improving continuous discharge stability and storage stability, and , preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less.
Note that 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, and even more preferably It is 220 mgKOH/g or more, and preferably 320 mgKOH/g or less, more preferably 300 mgKOH/g or less, and even more preferably 280 mgKOH/g or less.
Note that 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 a crosslinking agent.
As a commercially available product of the crosslinking agent, "Denacol EX-214L" (manufactured by Nagase ChemteX Co., Ltd.) is mentioned. Since the crosslinking agent is usually manufactured using epichlorohydrin, chlorine ( Contains chlorine ions). However, from the viewpoint of suppressing corrosion of recording devices such as inkjet recording devices, suppressing kogation in the heater part of the thermal head when the ink ejection method in the inkjet recording method is a thermal method, and improving continuous ejection stability. It is preferable to use a crosslinking agent with a reduced chlorine content. From this point of view, the content of chlorine ions (chlorine content) as an impurity in the crosslinking agent is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, and even more preferably 0. .7% by mass or less, and from the viewpoint of productivity of the crosslinking agent, it is 0% by mass or more, preferably 0.1% by mass or more.
It is believed that chlorine in the crosslinking agent exists as an impurity chlorine ion (Cl ^- ). The content of chlorine ions in the crosslinking agent can be determined from the chloride ion concentration measured by titration or ion chromatography.

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 improves the dispersion stability of the pigment aqueous dispersion, suppresses the occurrence of kogation, and improves the continuity of 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, even more preferably 3 mol% or more, and preferably 20 mol%. The content is more preferably 17 mol% or less, still more preferably 15 mol% or less.

[Method for producing pigment water dispersion]
The aqueous pigment dispersion of the present invention is preferably produced efficiently by a production method including Step 1 and Step 2 below.
Step 1: A step of dispersing a pigment mixture containing a water-dispersible polymer, organic pigment A, and water to obtain an aqueous pigment dispersion. Step 2: Adding the aqueous pigment dispersion obtained in step 1 and the aqueous pigment dispersion as a crosslinking agent. 1,4-butanediol diglycidyl ether and reacting the water-dispersible polymer with the crosslinking agent to form a crosslinked polymer to obtain a pigment water dispersion.

<Step 1>
Step 1 is a step of dispersing a pigment mixture containing a water-dispersible polymer, organic pigment A, and water to obtain an aqueous pigment dispersion.
In step 1, a water-dispersible polymer, organic pigment A, water, and if necessary, a neutralizing agent, a surfactant, etc. are added and mixed to obtain a pigment mixture, and then the mixture is dispersed to form a pigment. The process of obtaining an aqueous dispersion is preferred. Although there is no restriction on the order of addition, it is preferable to obtain a pigment mixture by adding the pigment to an aqueous solution of a water-dispersible polymer prepared using a neutralizing agent if necessary.

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 storage stability. When using a neutralizing agent, it is preferable to neutralize the aqueous pigment dispersion so that the pH thereof is 7 or more and 11 or less.
Examples of neutralizing agents that can be used include alkali metal hydroxides, ammonia, and organic amines. One or more selected from metal hydroxides and ammonia are preferred, alkali metal hydroxides are more preferred, and sodium hydroxide is even more preferred.
The neutralizing agent is preferably used as a neutralizing agent aqueous solution from the viewpoint of sufficiently promoting neutralization. The neutralizing agents may be used alone or in combination of two or more.
The mass ratio of organic pigment A to the mass of 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, in the pigment mixture, preferably 1 or more, 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, more preferably 4 or less, even more preferably 3.5 or less.

There is no particular restriction on the method of dispersion treatment in step 1. Although it is possible to finely refine the average particle size of organic pigment A particles to a desired particle size only by main dispersion using shear stress, main dispersion is further performed after preliminary dispersion to reduce the average particle size of organic pigment A particles. The particle size may be controlled to a desired particle size.
Examples of means for applying shear stress for main dispersion include media type dispersion machines such as paint shakers and bead mills; kneading machines such as roll mills and kneaders; and high-pressure homogenizers such as microfluidizers (trade name, manufactured by Microfluidics).
The nonvolatile component concentration (solid content concentration) of the aqueous pigment dispersion obtained in Step 1 is preferably 10 from the viewpoint of improving the dispersion stability of the aqueous pigment dispersion and from the viewpoint of facilitating the preparation of the aqueous pigment dispersion. It is at least 15% by mass, more preferably at least 15% by mass, and preferably at most 30% by mass, more preferably at most 25% by mass.

<Step 2>
Step 2 is a step of mixing the aqueous pigment dispersion obtained in Step 1 with the crosslinking agent, reacting the water-dispersible polymer with the crosslinking agent to form a crosslinked polymer, and obtaining an aqueous pigment dispersion. It is.
In step 2, 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 as described above.
The temperature of the crosslinking 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 crosslinking reaction time is preferably 1 hour or more and 10 hours or less.

The aqueous pigment 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, as long as the particles are formed of at least the organic pigment A and the crosslinked polymer. Examples include particle forms in which organic pigment A is encapsulated in a crosslinked polymer, particle forms in which organic pigment A is uniformly dispersed in a crosslinked polymer, particle forms in which organic pigment A is exposed on the particle surface of a crosslinked polymer, etc. , mixtures thereof are also included.

(Composition and physical properties of pigment water dispersion)
The content of organic pigment A is determined from the viewpoints of improving the dispersion stability of the pigment water dispersion, suppressing the occurrence of kogation, improving continuous discharge stability, and improving 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, even more preferably 13% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or more. It is not more than 18% by mass, more preferably not more than 18% by mass.
The content of the crosslinked polymer is determined from the viewpoints of improving the dispersion stability of the pigment water dispersion, suppressing the occurrence of kogation, improving continuous discharge stability, and improving storage stability. Among them, preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass. It is as follows.
From the viewpoint of improving continuous discharge stability and storage stability, the content of water in the aqueous pigment dispersion is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more. , 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 organic pigment A to crosslinked polymer in the pigment aqueous dispersion [organic pigment A/crosslinked polymer] is preferably 1 or more from the viewpoint of improving continuous discharge stability and storage stability, and from the viewpoint of improving print 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.

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

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

The aqueous pigment dispersion of the present invention contains additives such as solvents, penetrants, dispersants, surfactants, viscosity modifiers, antifoaming agents, rust preventives, preservatives, and antifungal agents that are commonly used in water-based inks. It 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 aqueous inkjet recording ink of the present invention preferably contains the aqueous pigment dispersion and a solvent. In addition to solvents, water-based inks are added with penetrants, dispersants, surfactants, viscosity modifiers, antifoaming agents, rust preventives, preservatives, antifungal agents, etc., and are further filtered using filters. be able to.

<Solvent>
In the present invention, the term "solvent" refers to something other than water.
As the solvent, it is preferable to contain an organic solvent from the viewpoint of suppressing excessive viscosity increase due to the crosslinked polymer, and from the viewpoint of preventing ink drying and improving continuous ejection stability and storage stability.
The organic solvent includes monohydric alcohols having 1 to 4 carbon atoms, polyhydric alcohols, polyhydric alcohol alkyl ethers, ketones, cyclic ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, etc. be able to. From the viewpoint of improving continuous discharge stability and storage stability, the organic solvent is preferably one or more selected from polyhydric alcohols, polyhydric alcohol alkyl ethers, and nitrogen-containing heterocyclic compounds.

Examples of polyhydric alcohols 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 include 1,2,3-butanetriol, petriol, triethylene glycol, tripropylene glycol, and glycerin.
Examples of polyhydric alcohol alkyl ethers 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 include monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, triethylene glycol monobutyl ether, and the like.
Examples of the nitrogen-containing heterocyclic compound include N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethylimidazolidinone, and ε-caprolactam.
The above organic solvents can be used alone or in combination of two or more.

From the viewpoint of improving continuous discharge stability and storage stability, the solvent is preferably a polyhydric alcohol, more preferably one or more selected from propylene glycol and polyethylene glycol, and even more preferably polyethylene glycol.
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, nonionic surfactants are preferred.
Nonionic surfactants include (1) saturated or unsaturated, linear or branched higher alcohols, polyhydric alcohols, or aromatic alcohols having 8 or more carbon atoms and 22 or less carbon atoms; and these alcohols, ethylene oxide, Alkyl ether, alkenyl ether, alkynyl ether or aryl ether of polyoxyalkylene to which propylene oxide or butylene oxide (hereinafter collectively referred to as "alkylene oxide") has been added; (2) saturated or unsaturated polyoxyalkylene having 8 to 22 carbon atoms; Ester of a higher alcohol having a saturated, linear or branched hydrocarbon group and a polyhydric fatty acid; (3) polyoxy having a linear or branched alkyl group or alkenyl group having 8 to 20 carbon atoms; Examples include alkylene aliphatic amines, (4) higher fatty acids having 8 to 22 carbon atoms, ester compounds of polyhydric alcohols, or compounds obtained by adding alkylene oxides thereto.
Commercially available nonionic surfactants include, for example, the Surfynol series manufactured by Nissin Chemical Industry Co., Ltd., the acetylenol series manufactured by Kawaken Fine Chemicals Co., Ltd., and Emulgen 120 (polyoxyethylene lauryl ether) manufactured by Kao Corporation. etc.

The content of each component and the ink physical properties of the aqueous ink of the present invention are as follows.
The total content of organic pigment A and 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, 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. It is as follows.

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

The content of the surfactant in the aqueous 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. More preferably, it is 0.3% by mass or more, and preferably 3% by mass or less, more preferably 2% by mass or less, and still more preferably 1% by mass or less.

It is preferable that the particles of organic pigment A dispersed in the crosslinked polymer (pigment A-containing crosslinked polymer particles) in the aqueous ink of the present invention do not cause swelling or contraction of the particles or aggregation between the particles. It is more preferable that the average particle size of the organic pigment A particles is the same as the average particle size of the organic pigment A particles in the aqueous pigment dispersion. The preferred average particle size of the organic pigment A particles in the aqueous ink is the same as the preferred average particle size of the organic pigment A particles in the aqueous pigment dispersion described above. The average particle size of organic pigment A particles in the water-based ink can be measured by the method described in Examples below.

The static surface tension of the aqueous 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.
Static surface tension at 20° C. can be measured by the method described in Examples below.

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, and even more preferably 2.0 mPa·s, from the viewpoint of improving continuous ejection stability and storage stability. or more, 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 below.

Inkjet recording methods include a piezo method that uses mechanical energy and a thermal method that uses thermal energy as ink ejection methods. The aqueous pigment dispersion of the present invention can particularly suppress the occurrence of kogation in the heater portion of a thermal head and improve continuous ejection stability, so it can be used in thermal inkjet recording methods where the ink ejection method is a thermal method. It is preferable to use The thermal method is a method in which ink subjected to the action of thermal energy undergoes a rapid volume change, and the acting force resulting from this state change causes the ink to be ejected from a nozzle. For example, U.S. Pat. Preferably, the method is carried out using the basic principle disclosed in No. 4,740,796. More specifically, the method described in Japanese Patent Publication No. 61-59911 can be mentioned.
The aqueous ink containing the aqueous pigment dispersion of the present invention can achieve continuous ejection stability even if the ink ejection method is a thermal method, and can be suitably used for inkjet recording using a thermal method. can. The reason for this is that the aqueous pigment dispersion of the present invention has a specific strong affinity between the polymer crosslinked by the crosslinking agent and a specific type of organic pigment A, and the aqueous pigment dispersion of the present invention has Even if the liquid medium evaporates and the pigments become close to each other, it has excellent dispersion stability and can suppress pigment aggregation. Since the amount of particulate crosslinked polymer can be reduced, it is possible to suppress the occurrence of kogation 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.
Note that measurements of various physical properties were performed by the following methods.

(1) Weight average molecular weight of water-dispersible polymer Gel permeation chromatography was performed using a solution in which phosphoric acid and lithium bromide were dissolved in N,N-dimethylformamide to a concentration of 60 mmol/L and 50 mmol/L, respectively, as an eluent. Graphic method [GPC device (model: HLC-8320GPC, manufactured by Tosoh Corporation), column (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H, all trade names manufactured by Tosoh Corporation), flow rate: 0. 5 mL/min], 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), the above are trade names manufactured by Tosoh Corporation.
The measurement sample was prepared by mixing 0.1 g of the water-dispersible polymer with 10 mL of the eluent in a glass vial, stirring with a magnetic stirrer at 25°C for 10 hours, and using a syringe filter (product name: DISMIC-13HP, membrane filter material). : Hydrophilic PTFE, pore size 0.2 μm, manufactured by Advantech Co., Ltd.) was used.

(2) Measurement of solid content concentration 10.0 g of sodium sulfate, which had been made constant in a desiccator, was weighed into a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), and about 1.0 g of the sample was added thereto. After mixing, the mixture was accurately weighed, maintained at 105° C. for 2 hours to remove volatile components, and further left in a desiccator for 15 minutes to measure the mass. The mass of the sample after removal of volatile matter was taken as solid content, and the solid content concentration was obtained by dividing by the mass of the added sample.

(3) Average particle size of organic pigment A particles dispersed with crosslinked polymer in pigment aqueous dispersion and water-based ink (pigment A-containing crosslinked polymer particles) Laser particle analysis system "ELS-8000" (Otsuka Electronics Co., Ltd. ) (cumulant analysis) was taken as the average particle size of the pigment A-containing crosslinked polymer particles in the pigment aqueous dispersion or 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 integrations, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measurement 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 was measured in a cylindrical polyethylene container (diameter 3.6 cm x The static surface tension of the aqueous pigment dispersion or aqueous ink was measured at 20°C.

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

<Production of pigment aqueous dispersion>
Example 1-1
(Step 1)
As organic pigment A, C.I. I. 165 parts of Pigment Orange 34 (disazopyrazolone orange pigment), acrylic acid/styrene copolymer "Joncryl 690" (weight average molecular weight: 16,500, acid value: 240 mgKOH/g) as a water-dispersible polymer (BASF) 55 parts as a solid content of an aqueous solution (concentration 20%) of a water-dispersible polymer, and 33 parts of a 5N aqueous sodium hydroxide solution (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., reagent) as a neutralizing agent for water-dispersible polymers. After obtaining the mixture, the pigment mixture was subjected to a dispersion treatment 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 Co., Ltd., 1,4-butanediol diglycidyl ether, epoxy equivalent: 120, chlorine content: 0.4%) 4.0 parts (ratio of the number of moles of epoxy groups in the crosslinking agent to the number of moles of carboxyl groups in the water-dispersible polymer: 14 mol%) and 12.2 parts of ion-exchanged water were added, and while stirring. Heated at 70°C for 6 hours.
Next, after cooling to room temperature, coarse particles are removed by filtration with a filter "Mini Sarto Syringe Filter" (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate), and a pigment aqueous dispersion containing pigment A-containing crosslinked polymer particles is obtained. 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 pigment aqueous dispersion (I-1).

Example 1-2
In step 2 of Example 1-1, 4.0 parts of Denacol EX-214L was added to 2.0 parts as a crosslinking agent (ratio of the number of moles of epoxy groups in the crosslinking agent to the number of moles of carboxyl groups in the water-dispersible polymer: 7). A pigment aqueous dispersion (I-2) containing pigment A-containing crosslinked polymer particles 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 (mol%). Table 1 shows the characteristics of the pigment aqueous 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. The pigment aqueous dispersions (I-3) to (I-5) and (I -C1), (I-C2), and (I-C7) were obtained. Table 1 shows the characteristics of each pigment water dispersion.

Comparative example 1-3
In step 2 of Example 1-1, 4.0 parts of Denacol EX-214L as a crosslinking agent was added to Denacol 810 (manufactured by Nagase ChemteX Co., Ltd., ethylene glycol diglycidyl ether, epoxy equivalent: 113, chlorine content: 0.6 %) 3.8 parts (Ratio of the number of moles of epoxy groups in the crosslinking agent to the number of moles of carboxyl groups in the water-dispersible polymer: 14%) Containing pigment A in the same manner as in Example 1-1 A pigment aqueous 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 crosslinking agent was added to Denacol EX-850L (manufactured by Nagase ChemteX Co., Ltd., diethylene glycol diglycidyl ether, epoxy equivalent: 145, chlorine content: 0.6). %) 4.8 parts (Ratio of the number of moles of epoxy groups in the crosslinking agent to the number of moles of carboxyl groups in the water-dispersible polymer: 14%) Containing pigment A in the same manner as in Example 1-1 A pigment aqueous 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 crosslinking agent was mixed with 5.0 parts of Epolite 70P (manufactured by Kyoeisha Chemical Co., Ltd., propylene glycol diglycidyl ether, epoxy equivalent: 140-160) (water A pigment aqueous dispersion containing pigment A-containing crosslinked polymer particles ( IC5) was obtained. Table 1 shows the characteristics of each pigment water dispersion (IC5).

Comparative example 1-6
In step 2 of Example 1-1, 4.0 parts of Denacol EX-214L as a crosslinking agent was added to Denacol EX-321L (manufactured by Nagase ChemteX Co., Ltd., trimethylolpropane polyglycidyl ether, epoxy equivalent: 130, chlorine content: Pigment A was prepared in the same manner as in Example 1-1, except that the amount was changed to 4.3 parts (ratio of the number of moles of epoxy groups to the number of moles of carboxyl groups in the water-dispersible polymer: 14 mol%). A pigment aqueous dispersion (IC6) containing crosslinked polymer particles was obtained. Table 1 shows the characteristics of each pigment water dispersion (IC6).

Comparative example 1-8
In Step 2 of Example 1-1, 4.0 parts of Denacol EX-214L as a crosslinking agent was added to Denacol EX-212L (manufactured by Nagase ChemteX Co., Ltd., 1,6-hexanediol diglycidyl ether, epoxy equivalent: 135, chlorine Content: 0.4%) 4.6 parts (Ratio of the number of moles of epoxy group to the number of moles of carboxyl group in the water-dispersible polymer: 14 mol%) The same method as in Example 1-1. A pigment aqueous dispersion (IC8) containing pigment A-containing crosslinked polymer particles was obtained. Table 1 shows the characteristics of each pigment water dispersion (IC8).

Each notation in Table 1 is as follows.
(organic pigment)
PO34:C. I. Pigment Orange 34 (disazopyrazolone orange pigment, manufactured by Dainichiseika Industries Co., Ltd.)
PO43:C. I. Pigment Orange 43 (Perinone orange pigment, manufactured by Dainichiseika Kagyo Co., Ltd.)
PV23:C. I. Pigment Violet 23 (dioxazine violet pigment, manufactured by Dainichiseika Industrial Co., Ltd.)
PG7:C. I. Pigment Green 7 (copper phthalocyanine green, manufactured by Clariant Japan Co., Ltd.)
PV19:C. I. Pigment Violet 19 (quinacridone pigment) (manufactured by Dainichiseika Kagyo Co., Ltd.)
PR122:C. I. Pigment Red 122 (quinacridone pigment) (manufactured by Dainichiseika Kagyo Co., Ltd.)
M717: Carbon black (manufactured by Cabot Specialty Chemicals, product 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 diglycidyl ether Denacol EX-850L: Diethylene glycol diglycidyl ether Denacol EX-321L: Trimethylolpropane polyglycidyl ether Denacol EX-212L: 1 ,6-hexanediol diglycidyl ether Epolite 70P: Propylene glycol diglycidyl ether

<Manufacture of water-based ink>
Example 2-1
24.8 parts of the pigment aqueous dispersion (I-1) obtained in Example 1-1, polyethylene glycol 400 (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., reagent, number average molecular weight 360 to 440 (catalog value)) 10 1 part, Surfynol 104PG-50 (manufactured by Nissin Chemical Industry Co., Ltd., propylene glycol solution of acetylene glycol surfactant, effective content: 50%), 1 part of Emulgen 120 (manufactured by Kao Corporation, ether-based nonionic interface) Activator) 0.5 parts and ion-exchanged water was further added so that the total amount of ink was 100 parts, and the mixture was stirred, and then filtered with a 0.3 μm filter "20L-MBP-003XS" (manufactured by ROKI), Aqueous ink (II-1) of Example 2-1 (total content of pigment and crosslinked polymer in aqueous ink: 5.46%) was obtained.

Examples 2-2 to 2-5 and Comparative Examples 2-1 to 2-8
In Example 2-1, water-based inks (II-2) to (II-5) and comparative examples (II-C1) to (II -C8) water-based ink was obtained.

The following evaluations were performed 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 Table 1.
<Evaluation of continuous discharge stability>
The results obtained in Examples and Comparative Examples were applied to a printing machine modified so that printing could be performed by pulling out the liquid feeding tube of an inkjet recording device "LPP-6010N" (manufactured by LG Electronics) having a thermal head and inserting the tube into an ink tank. An A4 size regular image was filled with water-based ink and printed at a resolution of 1,600 dpi (vertical) x 1,600 dpi (horizontal) and a duty of 100% in the best mode at a temperature of 25 ± 1°C and a relative humidity of 30 ± 5%. Continuous printing was performed on paper "All-in-One paper" (manufactured by Office Max), and the number of sheets printed until the print density became 0.05 lower than the first sheet was measured, and the results were evaluated according to the following evaluation criteria. evaluated.
The print density is determined by measuring the print density (value output as black optical density) of the obtained printed matter using a spectrophotometer/densitometer "Spectro Eye" (manufactured by X-Rite Co., Ltd.) under measurement conditions. Measurements were made at five points in total (observation viewing angle: 2 degrees, observation light source: D65, white reference: Abs, polarizing filter: none, density reference: DIN), and the average value was used as the print density of the printed matter. If the following evaluation criterion A is satisfied, it is suitable as a water-based ink. Evaluation criteria B or C below poses a practical problem.
(Evaluation criteria)
A: 15,000 sheets or more of A4 paper B: 10,000 sheets or more of A4 paper but less than 15,000 sheets C: Less than 10,000 sheets of A4 paper

<Evaluation of storage stability>
40 g of the water-based ink obtained in the Examples and Comparative Examples was sealed in a 50 cc screw tube (manufactured by Maruem Co., Ltd., screw tube bottle No. 7) and placed in a constant temperature and humidity machine (ESPEC) set at a temperature of 70°C (no humidity setting). 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 below is to 100%, the better the storage stability is.
Particle size change rate (%) = [(average particle size of crosslinked polymer particles containing pigment A in aqueous ink after storage/initial average particle size of crosslinked polymer particles containing pigment A in aqueous ink) - 1] x 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 refers to the average particle size of the crosslinked polymer particles containing pigment A in the water-based ink obtained in the examples and comparative examples shown in Table 2. This is the average particle size of the included crosslinked polymer particles. If the following evaluation criterion A is satisfied, it is suitable as a water-based ink. Evaluation criterion B poses no practical problem, but evaluation criterion C poses 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 inks containing each pigment aqueous dispersion of Examples 1-1 to 1-5 use a specific organic pigment and 1,4-butanediol diglycidyl ether as a crosslinking agent. It can be seen that kogation is sufficiently suppressed and the continuous ejection stability is excellent compared to the aqueous inks containing each of the aqueous pigment dispersions of Comparative Examples 1-1 to 1-8.
The aqueous inks containing the aqueous pigment dispersions of Comparative Examples 1-1, 1-2 and Comparative Example 1-7 use quinacridone pigment or carbon black as the organic pigment, and therefore have poor continuous ejection stability.
The water-based inks containing each of the aqueous pigment dispersions of Comparative Examples 1-3 to 1-6 and 1-8 use a crosslinking agent other than 1,4-butanediol diglycidyl ether as a crosslinking agent, and therefore cannot be continuously discharged. Less stable.

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. It can be suitably used as a pigment aqueous dispersion, can sufficiently suppress kogation, and has excellent continuous ejection stability, so it can be particularly suitably used as a pigment aqueous dispersion for thermal inkjet recording. .

Claims (7)

A pigment aqueous dispersion in which organic pigment A is dispersed with a crosslinked polymer,
The organic pigment A is one or more selected from disazopyrazolone pigments, perinone pigments, dioxazine pigments, and copper phthalocyanine pigments,
The crosslinked polymer is a crosslinked product of a water-dispersible polymer using 1,4-butanediol diglycidyl ether as a crosslinking agent,
The water-dispersible polymer is a vinyl polymer containing a structural unit derived from one or more carboxylic acid monomers selected from acrylic acid and methacrylic acid, and a structural unit derived from a styrene monomer,
The acid value of the water-dispersible polymer is 200 mgKOH/g or more and 280 mgKOH/g or less,
A pigment aqueous dispersion, 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 3 mol% or more and 20 mol% or less. The pigment aqueous dispersion according to claim 1, wherein the styrenic monomer is one or more selected from styrene and 2-methylstyrene . The pigment aqueous dispersion according to claim 1 or 2, wherein the water-dispersible polymer has a weight average molecular weight of 5,000 or more and 30,000 or less . The pigment aqueous dispersion according to any one of claims 1 to 3 , wherein the content of the organic pigment A is 5% by mass or more and 20% by mass or less in the pigment aqueous dispersion. The pigment aqueous dispersion according to any one of claims 1 to 4, wherein the mass ratio of organic pigment A to crosslinked polymer [organic pigment A/crosslinked polymer] in the pigment aqueous dispersion is 1 or more and 5 or less. An aqueous ink for inkjet recording, comprising the aqueous pigment dispersion according to any one of claims 1 to 5 and a solvent. A method for producing an aqueous pigment dispersion in which organic pigment A is dispersed with a crosslinked polymer, the method comprising:
The organic pigment A is one or more selected from disazopyrazolone pigments, perinone pigments, dioxazine pigments, and copper phthalocyanine pigments,
Including the following steps 1 and 2,
Step 1: A step of dispersing a pigment mixture containing a water-dispersible polymer, organic pigment A, and water to obtain an aqueous pigment dispersion. Step 2: Adding the aqueous pigment dispersion obtained in step 1 and the aqueous pigment dispersion as a crosslinking agent. 1,4-butanediol diglycidyl ether and reacting the water- dispersible polymer with the crosslinking agent to form a crosslinked polymer to obtain a pigment water dispersion.
The water-dispersible polymer is a vinyl polymer containing a structural unit derived from one or more carboxylic acid monomers selected from acrylic acid and methacrylic acid, and a structural unit derived from a styrene monomer,
The acid value of the water-dispersible polymer is 200 mgKOH/g or more and 280 mgKOH/g or less,
A method for producing a pigment aqueous dispersion, 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 3 mol% or more and 20 mol% or less.