WO2024158051A1

WO2024158051A1 - Aqueous pigment dispersion and aqueous ink

Info

Publication number: WO2024158051A1
Application number: PCT/JP2024/002443
Authority: WO
Inventors: 真澄高村
Original assignee: 国立大学法人山形大学
Priority date: 2023-01-27
Filing date: 2024-01-26
Publication date: 2024-08-02

Abstract

An aqueous pigment dispersion containing water, a pigment and a dispersant, wherein: the dispersant includes a main chain structure and terminal structures bonded to at least two terminals of the main chain structure; the main chain structure is a living radical polymer of a radical-polymerizable unsaturated monomer having a group compatible with the water; and the terminal structures have adsorption groups for the pigment.

Description

Water-based pigment dispersion and water-based ink

The present invention relates to an aqueous pigment dispersion and an aqueous ink. The present invention also relates to an ink cartridge for an inkjet printer that contains the aqueous ink. Furthermore, the present invention also relates to inkjet printing that uses the aqueous ink.

In recent years, digital printing using desktop publishing (DTP) inks containing pigments has become popular. To produce high-quality images, the particle size of the pigments needs to be reduced from micrometer to nanometer size, but this can lead to problems as the pigment particles tend to aggregate.

To solve the above problems, a copolymer consisting of a radically polymerizable unsaturated monomer having a compatible group for the dispersion medium of the ink and a radically polymerizable unsaturated monomer having an adsorptive group for the pigment is used as a dispersant.

Furthermore, Patent Document 1 discloses a pigment whose surface is coated with a composition containing a living radical polymer having a specific functional group at its end, with the aim of improving the properties of the ink composition.

International Publication No. 2022/163542

Many attempts have been made to improve the dispersibility of pigments, but there is still room for improvement. Therefore, the present invention provides water-based pigment dispersions and the like that have excellent pigment dispersibility.

As a result of extensive research, the inventors have discovered that the dispersibility of pigments can be improved by using a polymer that has adsorptive groups for pigments at at least two ends as a dispersant.

The present invention includes the following embodiments.
[1]
A water-based pigment dispersion comprising water, a pigment, and a dispersant,
The dispersant comprises a main chain structure and a terminal structure bonded to at least two terminals of the main chain structure,
the main chain structure is a living radical polymer of the radically polymerizable unsaturated monomer having a water-compatible group,
the terminal structure has an adsorptive group for the pigment;
Water-based pigment dispersion.
[2]
each of the terminal structures is independently composed of one or more constitutional units;
The aqueous pigment dispersion according to [1], wherein 60% or more of the structural units constituting the terminal structure have the adsorptive group.
[3]
The aqueous pigment dispersion according to [2], wherein the number of the structural units constituting the terminal structure is 1 to 10.
[4]
The aqueous pigment dispersion according to any one of [1] to [3], wherein the surface of the pigment is nonionic, and the adsorptive group is an aromatic hydrocarbon group and/or an aliphatic hydrocarbon group having 6 or more carbon atoms.
[5]
The aqueous pigment dispersion according to any one of [1] to [3], wherein the surface of the pigment is cationic, and the adsorptive group is an anionic group.
[6]
The aqueous pigment dispersion according to any one of [1] to [3], wherein the surface of the pigment is anionic, and the adsorptive group is a cationic group.
[7]
The aqueous pigment dispersion according to any one of [1] to [6], wherein the living radical polymer has a number average molecular weight of 6,000 or more.
[8]
The aqueous pigment dispersion according to any one of [1] to [7], wherein all of the monomers constituting the living radical polymer are radically polymerizable unsaturated monomers having the compatible group.
[9]
The aqueous pigment dispersion according to any one of [1] to [8], wherein the radically polymerizable unsaturated monomer having a compatible group is a polyalkylene glycol mono(meth)acrylate or an alkoxy polyalkylene glycol mono(meth)acrylate.
[10]
The aqueous pigment dispersion according to any one of [1] to [9], wherein the radically polymerizable unsaturated monomer having a compatible group is methoxypolyethylene glycol mono(meth)acrylate.
[11]
A water-based ink comprising the water-based pigment dispersion according to any one of [1] to [10].
[12]
12. The water-based ink according to claim 11, for use in inkjet printing.
[13]
An ink cartridge for an inkjet printer, comprising the water-based ink according to [11] or [12].
[14]
A printing method comprising ejecting the water-based ink according to [11] or [12] by an inkjet system.

The present invention can provide water-based pigment dispersions with excellent pigment dispersibility.

FIG. 1 shows an outline of the synthetic routes for the dispersants of Preparation Examples 1 to 5. FIG. 2 shows an outline of the synthetic route for the dispersants of Preparations 6 and 7. FIG. 3 shows an outline of the synthetic route for the dispersant of Preparation Example 15. FIG. 4 shows an outline of the synthetic route for the dispersant of Preparation Example 8. FIG. 5 outlines the synthetic routes for the dispersants of Preparations 9 and 16. FIG. 6 shows an outline of the synthetic route for the dispersant of Preparation Example 10. FIG. 7 shows an outline of the synthetic route for the dispersant of Preparation Example 17. FIG. 8 shows an outline of the synthetic route for the dispersants of Preparations 11 and 12. FIG. 9 shows an outline of the synthetic route for the dispersants of Preparations 13 and 14.

The following provides a detailed description of the embodiments of the present invention, but the present invention is not limited to these, and various modifications are possible without departing from the spirit of the invention.

<Water-based pigment dispersion>
One embodiment of the present invention is a water-based pigment dispersion comprising water, a pigment, and a dispersant,
The dispersant comprises a main chain structure and a terminal structure bonded to at least two terminals of the main chain structure,
the main chain structure is a living radical polymer of the radically polymerizable unsaturated monomer having a water-compatible group,
The present invention relates to an aqueous pigment dispersion, wherein the terminal structure has an adsorptive group for the pigment.

The aqueous pigment dispersion according to this embodiment contains a dispersant with a specific structure, and therefore has excellent pigment dispersibility.

The reason for the excellent dispersibility of the pigment is assumed to be that the main chain structure of the dispersant is compatible with the aqueous dispersion medium, while at least two ends of the dispersant are adsorbed to the pigment, but the present invention is not limited in any way to the assumed reason.

The amount of dispersant is preferably 0.1 to 60% by mass, more preferably 1 to 40% by mass, and even more preferably 1 to 20% by mass, based on the mass of the pigment.

[Dispersant]
The water-based pigment dispersion according to this embodiment contains a dispersant that includes a main chain structure and terminal structures bonded to at least two ends of the main chain structure.

(Main Chain Structure of Dispersant)
The main chain structure of the dispersant is a living radical polymer of a radically polymerizable unsaturated monomer having a water-compatible group (hereinafter also referred to as a "compatible monomer").

The main chain structure may be linear or branched. When the main chain structure is linear, the main chain structure has two ends. When the main chain structure is branched, the main chain structure has three or more ends. Although not particularly limited, it is preferable that the main chain structure is linear.

The water-compatible group is not particularly limited as long as it is a hydrophilic group. Examples of the compatible group include polyalkylene glycol groups. Examples of the polyalkylene glycol group include polyethylene glycol groups, polypropylene glycol groups, and polyethylene glycol-propylene glycol groups. From the viewpoint of improving pigment dispersibility, the number of oxyalkylene units in the polyalkylene glycol group is preferably 2 to 20, more preferably 3 to 15, and even more preferably 3 to 9.

Examples of compatible monomers constituting the main chain structure include polyalkylene glycol mono(meth)acrylates and alkoxy polyalkylene glycol mono(meth)acrylates. The alkylene portion of the compatible monomer is preferably ethylene or propylene. The alkoxy portion of the compatible monomer is preferably methoxy, ethoxy, or propoxy.

The polyalkylene glycol mono(meth)acrylate is preferably polyethylene glycol (meth)acrylate, polypropylene glycol mono(meth)acrylate, or polyethylene glycol-propylene glycol mono(meth)acrylate, and more preferably polyethylene glycol mono(meth)acrylate.

The alkoxy polyalkylene glycol mono(meth)acrylate is preferably methoxy polyethylene glycol mono(meth)acrylate or methoxy polypropylene glycol mono(meth)acrylate, and more preferably methoxy polyethylene glycol mono(meth)acrylate.

The proportion of compatible monomers constituting the main chain structure is preferably 30% or more, more preferably 50% or more, and even more preferably 80% or more, based on the number of all monomers constituting the main chain structure (excluding residues of polymerization initiators). The main chain structure may contain residues of polymerization initiators in addition to the monomers that are its constituent units.

The number average molecular weight of the living radical polymer, which is the main chain structure, is preferably 6,000 or more, more preferably 7,000 to 30,000, and even more preferably 9,000 to 20,000, from the viewpoint of improving pigment dispersibility. The number average molecular weight can be determined by the method described in the examples below.

(End structure of dispersant)
The terminal structure of the dispersant (hereinafter also referred to as "adsorptive terminal structure") has an adsorptive group for the pigment and is bonded to the terminal of the main chain structure.

The number of adsorbent terminal structures should be at least two or more, and may be determined appropriately depending on the shape of the main chain structure (in other words, the number of ends of the main chain structure). Although not particularly limited, it is preferable that the shape of the main chain structure is linear (i.e., the number of ends is two) and the number of adsorbent terminal structures is two.

The adsorption groups for pigments vary depending on the performance of the pigment (especially the pigment surface).

When the surface of the pigment is nonionic, examples of the adsorption group include nonionic groups. Examples of the nonionic group include aromatic hydrocarbon groups and aliphatic hydrocarbon groups having 6 or more carbon atoms. All of the adsorption groups may be aromatic hydrocarbon groups. All of the adsorption groups may be aliphatic hydrocarbon groups having 6 or more carbon atoms. The adsorption groups may be a combination of aromatic hydrocarbon groups and aliphatic hydrocarbon groups having 6 or more carbon atoms. The aliphatic hydrocarbon groups may be linear, branched, or cyclic.
The aromatic hydrocarbon group preferably has 6 to 14 carbon atoms, more preferably 6 to 10 carbon atoms, and even more preferably 6 carbon atoms (ie, a phenyl group).
The aliphatic hydrocarbon group preferably has 6 to 22 carbon atoms, more preferably 8 to 18 carbon atoms, and further preferably 12 to 16 carbon atoms.

When the surface of the pigment is cationic, examples of the adsorption groups include anionic groups. Examples of the anionic groups include carboxyl groups, phosphate groups, and sulfonate groups.

When the surface of the pigment is anionic, examples of the adsorption groups include cationic groups. Examples of the cationic groups include amino groups (primary, secondary, and tertiary amines) and quaternary ammonium groups.

Each of the adsorbent end structures is independently composed of one or more structural units (which may be not only monomers but also residues of polymerization initiators or residues of modifiers), and it is preferable that 40% or more of the structural units have an adsorbent group. For example, when the adsorbent end structure is composed of 10 structural units, it is preferable that 4 or more of the structural units have an adsorbent group. Note that when the adsorbent end structure is composed of 10 structural units, these structural units are the 10 structural units at the ends of the dispersant.

The number of constituent units constituting the adsorbent end structure can be, for example, 1 to 20, 1 to 15, 1 to 10, 2 to 20, 2 to 15, 2 to 10, 3 to 20, 3 to 15, 3 to 10, 4 to 20, 4 to 15, 4 to 10, 5 to 20, 5 to 15, and 5 to 10. Two or more adsorbent end structures may each independently be composed of a different number of constituent units. For example, the first adsorbent end structure may be composed of one constituent unit, and the second adsorbent end structure may be composed of 2 to 10 constituent units.

Among the constituent units constituting the adsorptive terminal structure, the proportion of the number of constituent units having an adsorptive group is more preferably 50% or more, even more preferably 60% or more, and particularly preferably 70% or more.

The constituent units that make up the adsorptive end structure include, for example, a radically polymerizable unsaturated monomer having an adsorptive group (hereinafter also referred to as an "adsorbable monomer"), an adsorptive group-containing residue of a polymerization initiator, and an adsorptive group-containing residue of a modifier. In this specification, the "residue" of a polymerization initiator or a modifier means a part of the polymerization initiator or modifier that is incorporated in the dispersant.

An example of an adsorptive monomer is mono(meth)acrylate having an adsorptive group.

The polymerization initiator is preferably one that can initiate living radical polymerization and at least a portion of which has an adsorption group is incorporated into the adsorption terminal structure. Examples of the polymerization initiator include those described in pages 2-34 of "Precise Radical Polymerization Handbook" published by Sigma-Aldrich in July 2012, pages 365-367 of "Living Radical Polymerization 2. Polymerization Mechanism and Method 2" in Journal of the Society of Rubber Science and Technology of Japan (No. 82) published in August 2009, pages 6610-6618 of Macromolecules (No. 47) published by ACS Publishing in September 2014, and pages 5177-5185 of Polymer (No. 49) published by ELSEVIER Publishing in September 2008.

The modifier is preferably one that reacts with the end of the living radical polymer, which is the main chain structure, so that at least a portion of the adsorbent group is incorporated into the adsorbent end structure. An example of the modifier is a compound of the formula: Y-C(=O)-O-O-C(=O)-Y (wherein Y is an adsorbent group-containing group).

(Overall structure of dispersant)
The overall structure of the dispersant may be roughly as follows:
[X ² ]-{AX ¹ -A}-[X ² ]
[X ² -B]-{A-X ¹ -A}-[B-X ² ]
[X ¹ -B]-{A}-[X ² ]
[M]-{AX ¹ -A}-[M]
[ ]: Adsorptive end structure { }: Main chain structure A: Compatible monomer or a repeat thereof B: Adsorptive monomer or a repeat thereof X ¹ : Residue of polymerization initiator not containing an adsorptive group X ² : Residue of polymerization initiator containing an adsorptive group M: Residue of modifier containing an adsorptive group

Specific examples of the overall structure of the dispersant include the following structure:

1-1. Nonionic adsorbent-containing symmetric dispersant (one adsorbent at each end structure)

[Wherein,
Each R ₁ is independently hydrogen or methyl;
Each _R2 is independently hydrogen or methyl;
Each R ₃ is independently hydrogen or alkyl having 1 to 3 carbon atoms;
Each _R4 is independently hydrogen or methyl;
Each 1 is independently an integer of 7 or greater;
Each m is independently an integer from 3 to 12.

1-2. Nonionic adsorbent-containing symmetric dispersant (multiple adsorbent groups at each end structure)

[Wherein,
R ₁ to R ₄ , l, and m are as defined above;
Each n is independently an integer from 1 to 9.

2-1. Symmetrical dispersant containing anionic adsorbent groups (one adsorbent group at each end structure)

2-2. Symmetrical dispersant containing anionic adsorbent groups (multiple adsorbent groups at each end structure)

[In the formula, R ₁ to R ₄ , l, m and n are as defined above.]

3-1. Symmetrical dispersant containing cationic adsorbent groups (one adsorbent group at each end structure)

[In the formula, R ₁ to R ₄ , l, and m are as defined above.]

3-2. Symmetrical dispersant containing cationic adsorbent groups (multiple adsorbent groups at each end structure)

[In the formula, R ₁ to R ₄ , l, m and n are as defined above.]

4. Nonionic adsorptive group-containing asymmetric dispersants (one or more adsorptive groups at each end structure)

[In the formula, R ₁ to R ₄ , l, m, and n are as defined above.]

5. Anionic Adsorbent-Containing Asymmetric Dispersants (One or More Adsorbents at Each Terminal Structure)

[Wherein,
R ₁ to R ₄ , l, m, and n are as defined above;
Each _R5 is independently hydrogen or methyl;
h is independently an integer from 1 to 9;
-r- indicates that the adsorptive monomers bonded to both ends of r form a random copolymer;
Among the structural units (h+n) constituting the adsorptive terminal structure, the ratio of the number of structural units (n) having an adsorptive group is 50% or more.]

6. Cationic adsorbent-containing asymmetric dispersant (one or more adsorbents at each end structure)

[In the formula, R ₁ to R ₄ , l, m, and n are as defined above.]

(Method of producing dispersant)
The method for producing the dispersant is not particularly limited, and the known synthesis method of living radical polymers may be appropriately used. Examples of known synthesis methods include nitroxide-mediated radical polymerization (NMP method), atom transfer radical polymerization (ATRP method), radical polymerization using reversible addition-fragmentation reaction (RAFT method), radical polymerization using organic tellurium (TERP method), and radical polymerization using iodine (RCMP method and RTCP method). Specific production methods include the methods described in the examples below, and the raw materials may be appropriately changed according to the structure of the target dispersant.

Examples of the method for producing the dispersant include the following methods. The details of the structure of the dispersant are as described above.
A method for producing a dispersant comprising: a main chain structure; and a terminal structure bonded to at least two terminals of the main chain structure, the method comprising the steps of:
the main chain structure is a living radical polymer of a radically polymerizable unsaturated monomer having a water-compatible group,
the terminal structure has an adsorptive group for a pigment,
The manufacturing method comprises:
a polymerization step of performing living radical polymerization using a polymerization initiator having a dormant at at least two ends and the radically polymerizable unsaturated monomer having the compatible group to form a main chain structure having the dormant at at least two ends;
an introduction step of reacting a main chain structure having the dormant at at least two ends with the terminal modifier having the adsorptive group to introduce the terminal structure having the adsorptive group into at least two ends of the main chain structure;
A manufacturing method comprising:

The polymerization initiator having dormant groups at at least two ends (hereinafter referred to as "multifunctional dormant initiator") is not particularly limited, and examples thereof include the initiators described in Macromolecules (No. 47), a journal published by ACS in September 2014, pp. 6610-6618, and Polymer (No. 49), a journal published by ELSEVIER in September 2008, pp. 5177-5185.

The dormant is preferably iodine. The number of dormants in the multifunctional dormant initiator is preferably 2. An example of a bifunctional dormant initiator is a compound of the formula: D-X ¹ -D (wherein D is a dormant and X ¹ is a residue of the polymerization initiator that does not contain an adsorptive group).

An example of a main chain structure having dormant groups at two ends is a compound of the formula: D-{A-X ¹ -A}-D (wherein D is a dormant group, { } is a main chain structure, A is a compatible monomer or a repeating unit thereof, and X ¹ is a residue of a polymerization initiator that does not contain an adsorptive group).

An example of a terminal modifier having an adsorptive group (hereinafter referred to as an "adsorbent terminal modifier") is a compound of the formula: Y-C(=O)-O-O-C(=O)-Y (wherein Y is an adsorptive group-containing group).

As a modification method that can obtain a more efficient modification rate, it is preferable to add a terminal modifier continuously after the polymerization of the main chain structure having dormant at two ends is completed, without isolating or purifying the polymer.

Examples of dispersants include compounds of the formula: [M]-{A-X ¹ -A}-[M] (wherein [ ] is an adsorptive terminal structure, M is an adsorptive group-containing residue of a modifying agent, { } is a main chain structure, A is a compatible monomer or a repeating monomer thereof, and X ¹ is an adsorptive group-free residue of a polymerization initiator).

[Pigment]
The type of pigment is not particularly limited, and any known pigment can be used. The pigment is preferably one that can be used for inkjet printing. The surface of the pigment may be modified to have a predetermined property.

Examples of pigments include the following:

Cyan copper phthalocyanine (CI Pigment Blue 15)
・Aluminum phthalocyanine (CI Pigment Blue 79)

Magenta dimethylquinacridone pigment (CI Pigment Red 122)
- Unsubstituted quinacridone (CI Pigment Violet 19)
-Dichloroquinacridone (CI Pigment Red 202)
・Carmine 6B (CI Pigment Red 57)
・Diaminoanthraquinonyl Red (CI Pigment Red 177)
・Benzimidazolone Red (CI Pigment Red 185)
・Dibromoanthanthron (CI Pigment Red 168)

Yellow Monoazo Yellow (CI Pigment Yellow 74)
- Condensed azo yellow (CI Pigment Yellow 128)
・Azomethine Yellow (CI Pigment Yellow 150)
・Benzimidazolone Yellow (CI Pigment Yellow 151, 154, 155)
・Isoindolinone Yellow (CI Pigment Yellow 109, 110)
・Isoindoline Yellow (CI Pigment Yellow 139, 185)
・Quinoxaline Yellow (CI Pigment Yellow 213)

White Titanium Dioxide (CI Pigment White 6)

Black/Carbon Black (CI Pigment Black 7)

The pigment should be selected appropriately depending on the type of adsorption group of the dispersant.

When the adsorptive group of the dispersant is a nonionic group, it is preferable to use a pigment having a nonionic group on the surface. Examples of the nonionic group on the pigment surface include aromatic hydrocarbon groups and aliphatic hydrocarbon groups having 6 or more carbon atoms. The aliphatic hydrocarbon group may be linear, branched, or cyclic.
The aromatic hydrocarbon group preferably has 6 to 14 carbon atoms, more preferably 6 to 10 carbon atoms, and even more preferably 6 carbon atoms (ie, a phenyl group).
The aliphatic hydrocarbon group preferably has 6 to 22 carbon atoms, more preferably 8 to 18 carbon atoms, and further preferably 12 to 16 carbon atoms.

An example of an organic pigment having a nonionic group on its surface is an organic pigment that has not been subjected to a surface treatment. The surface of an organic pigment that has not been subjected to a surface treatment is generally nonionic.
Examples of inorganic pigments having a nonionic group on the surface include inorganic pigments having an aromatic hydrocarbon group and/or an aliphatic hydrocarbon group having 6 or more carbon atoms on the surface.

When the adsorptive group of the dispersant is a cationic group, it is preferable to use a pigment having an anionic group on the surface. Examples of anionic groups include carboxyl groups, phosphate groups, sulfonic acid groups, and phenolic hydroxyl groups.

Examples of organic pigments having an anionic group on the surface include organic pigments having at least one anionic group selected from the group consisting of a carboxyl group, a phosphoric acid group, and a sulfonic acid group on the surface.
Examples of inorganic pigments having an anionic group on the surface include inorganic pigments having a carboxyl group and/or a phenolic hydroxyl group on the surface (for example, carbon black (black), neutral to weakly alkaline).
Furthermore, when the inorganic pigment is a metal oxide having an isoelectric point at pH lower than 7 (for example, titanium oxide (isoelectric point: about 5), silica (isoelectric point: about 3), and zirconia (isoelectric point: about 4)) or a pigment whose surface is coated with such a metal oxide, the hydroxyl groups on the surface of such pigments can be included as anionic groups. That is, when the pH of the inkjet printing ink is neutral to weakly alkaline (pH: 7 to 8), if the isoelectric point of the metal oxide is lower than the pH of the ink, the hydroxyl groups (-OH) on the surface of the metal oxide will become " ^-O- (negative)".

When the adsorption group of the dispersant is an anionic group, it is preferable to use a pigment having a cationic group on the surface. Examples of cationic groups include amino groups (primary, secondary, and tertiary amines) and quaternary ammonium groups.

Examples of organic pigments having cationic groups on the surface include organic pigments having amino groups (primary, secondary, and tertiary amines) and/or quaternary ammonium groups on the surface.
When the inorganic pigment is a metal oxide having an isoelectric point at pH higher than 7 (for example, alumina (isoelectric point: about 9)) or a pigment having a surface coated with such a metal oxide, the hydroxyl groups on the surface of the pigment can be included as cationic groups. That is, while the pH of the ink for inkjet printing is neutral to weakly alkaline (pH: 7 to 8), if the isoelectric point of the metal oxide is higher than the pH of the ink, the hydroxyl groups (-OH) on the surface of the metal oxide will become "-OH ₂ ⁺ (plus)."

<Water-based ink>
One embodiment of the present invention relates to a water-based ink comprising the water-based pigment dispersion described above. The water-based ink according to this embodiment is preferably used in ink-jet printing applications.

The water-based ink may contain other components in addition to the water-based pigment dispersant. Examples of other components include binder resins, photosensitizers, photoacid generators, plasticizers, surface conditioners, UV inhibitors, antioxidants, hydrolysis inhibitors, and drying accelerators.

The viscosity of the water-based ink at 25°C is preferably 0.1 to 50 mPa·s, more preferably 0.5 to 30 mPa·s, and even more preferably 1 to 10 mPa·s, for suitable use in inkjet printing. The viscosity can be determined by the method described in the examples below.

<Ink cartridges for inkjet printers>
One embodiment of the present invention relates to an ink cartridge for an inkjet printer, which contains the above-mentioned water-based ink. The ink cartridge according to this embodiment is not particularly limited, and may be any ink cartridge capable of storing water-based ink and capable of being installed in an inkjet printer.

<Printing method>
One embodiment of the present invention relates to a printing method that includes ejecting the above-mentioned water-based ink by an inkjet method. The printing method according to this embodiment is not particularly limited, and any known inkjet method may be used as appropriate.

The present invention will be described in more detail below using examples and comparative examples, but the technical scope of the present invention is not limited to these.
Various values in the examples may be used as preferred lower or upper limits in the embodiment of the present invention. Two values of the same type in the examples may be appropriately combined to form a preferred numerical range.

＜Terminology＞

AIBN: 2,2'-azobis(isobutyronitrile)
ACVN: 4,4'-azobis(4-cyanopentanoic acid)
DBTC: S,S-dibenzyl trithiocarbonate BDMAT: S,S-bis(α,α'-dimethyl-α''-acetic acid) trithiocarbonate BDCPT: S,S-bis(2-cyano-2-propyl)trithiocarbonate CPBD: 2-cyano-2-propyl benzodithioate CPDT: 2-cyano-2-propyl dodecyl trithiocarbonate CCPA: 4-[(2-carboxyethylsulfanylthiocarbonyl)sulfanyl)-4-cyanopentanoic acid

EBIP: ethylene bis(2-iodopropanoate)
BNI: Tetrabutylammonium iodide

BPO: Dibenzoyl peroxide LPO: Dilauryl peroxide SAPO: Disuccinic acid peroxide APPO: Di(3-aminopropionic acid) peroxide

PEGMEA-1: methoxypolyethylene glycol acrylate (n=9) (molecular weight: 480 g/mol)
PEGMEA-2: methoxypolyethylene glycol acrylate (n=3) (molecular weight: 188 g/mol)
PEGMEMA: methoxypolyethylene glycol methacrylate (n=9) (molecular weight: 500 g/mol)

BzA: benzyl acrylate (molecular weight: 162 g/mol)
BzMA: benzyl methacrylate (molecular weight: 176 g/mol)
AA: acrylic acid (molecular weight: 72 g/mol)

<Analysis method>
[Polymerization conversion rate]
The polymerization conversion rate was determined by dissolving the polymer after polymerization in deuterated chloroform containing tetramethylsilane (TMS) as a standard substance, measuring the area 1 (molar conversion) of the proton peak derived from the residual monomer and the area 2 (molar conversion) of the proton peak derived from the polymer by ^1H -NMR, and calculating the following value.
Polymerization conversion rate (mol %)=area 2 of proton peak derived from polymer (molar conversion)/(area 1 of proton peak derived from residual monomer (molar conversion)+area 2 of proton peak derived from polymer (molar conversion))×100

[Number average molecular weight (Mn) and dispersity (Mw/Mn)]
The number average molecular weight (Mn), weight average molecular weight (Mw) and dispersity (Mw/Mn) of the polymer are values measured under the following measurement conditions by size exclusion chromatography in accordance with general rules (JIS K 7252-1 (2016)) and ISO 16014-1 (2012).
Measurement equipment: EXTREMA size exclusion chromatography (GPC/SEC) system manufactured by JASCO Corporation Column: SHODEX manufactured by Showa Denko K.K. Sample side: K-803, KF-804L, KF-806F (three columns connected), Reference side: KF-800RH
Eluent: Tetrahydrofuran (hereinafter referred to as THF)
・Calibration curve standard material: Polymethyl methacrylate (non-styrene polymer), polystyrene (styrene polymer)
Preparation of a measurement sample: A polymer is dissolved in an eluent (THF) to prepare a solution with a polymer concentration of 0.1% by weight, and the solution is filtered through a filter to obtain a filtrate.

<Preparation of Dispersant>
[Production Example 1]
In a 30 ml Schlenk flask, 0.087 g (0.3 mmol) of S,S-dibenzyltrithiocarbonate (DBTC, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., used as is) was weighed out as a RAFT agent (polymerization initiator), 4.32 g (9 mmol) of methoxypolyethylene glycol acrylate-1 (PEGMEA-1 (n=9); manufactured by Tokyo Chemical Industry Co., Ltd., purified by column chromatography in a conventional manner) was weighed out as a monomer 1 (hydrophilic monomer), and 0.855 g of diethylene glycol dimethyl ether (DEGDME; manufactured by Tokyo Chemical Industry Co., Ltd., used as is) was weighed out and dissolved, and 0.0099 g (0.06 mmol) of 2,2'-azobis(isobutyronitrile) (AIBN; manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., purified by recrystallization in a conventional manner) was weighed out and dissolved as a free radical polymerization initiator. The molar ratio of the materials charged was AIBN:DBTC:PEGMEA-1=1:5:150. After the inner space of the Schlenk flask was replaced with nitrogen gas, the contents were stirred at 60° C. for 2 hours under a nitrogen atmosphere, and then rapidly cooled to room temperature, and diluted with 1.5 ml of acetone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).
The resulting solution was dropped into hexane (Kanto Chemical Co., Ltd.)/acetone = 630 ml/70 ml to effect reprecipitation, and the solution was filtered through a PTFE membrane filter (pore size: 0.45 μm) to obtain a powder, which was then vacuum dried at 40°C for 8 hours to obtain a PEGMEA-1 polymer having aromatic groups at both the α-terminus and the γ-terminus (hereinafter, aromatic-P(PEGMEA-1)-aromatic) (polymerization conversion of PEGMEA-1 = 57%). The number average molecular weight of the resulting polymer was 7,600 g/mol, and the polydispersity (Mw/Mn) was 1.11. The theoretical molar ratio of the polymer calculated from the molar ratio of the polymerization initiator (DBTC) and hydrophilic monomer 1 (PEGMEA-1) (DBTC:PEGMEA-1=1:30) and the polymerization conversion rate of PEGMEA-1 (57%) was calculated to be DBTC:PEGMEA-1 polymer=1:(30×0.57)=1:17 (number of monomers), and the theoretical molecular weight was calculated to be 17×480=8,200 g/mol.

[Production Examples 2 and 3]
A dispersant was prepared in the same manner as in Production Example 1, except that the polymerization time of PEGMEA was changed.

[Production Example 4]
A polymer was prepared in the same manner as in Production Example 1, except that the monomer 1 (hydrophilic monomer) was changed to 1.05 g (6.5 mmol) of benzyl acrylate (BzA; manufactured by Tokyo Chemical Industry Co., Ltd., which was distilled and purified by a conventional method) as monomer 2 (pigment-adsorbing monomer), the solvent was changed to 1,4-dioxane (manufactured by Tokyo Chemical Industry Co., Ltd., which was used as is), the amount of AIBN was changed to 0.011 g (0.065 mmol), and the polymerization conditions were changed to 60° C. for 0.5 hours.
0.17 g (0.325 mmol) of the obtained polymer was weighed out, and 9.75 g (6.5 mmol) of PEGMEA-1 and 0.007 g (0.043 mmol) of AIBN were added as monomer 1 (hydrophilic monomer). The molar ratio of the materials charged was AIBN: obtained polymer: PEGMEA-1 = 1:5:150. After replacing the inner space of the Schlenk flask with nitrogen gas, the contents were stirred at 60°C for 4 hours under a nitrogen atmosphere, then rapidly cooled to room temperature, and diluted with 13 ml of DEGDME.
The resulting solution was added dropwise to a mixture of 630 ml of hexane and 70 ml of acetone to effect reprecipitation, and after standing, the upper layer was discarded, and the solution remaining in the lower layer was dissolved in 200 ml of chloroform (Kanto Chemical Co., Ltd.). The resulting solution was concentrated using a rotary evaporator and then vacuum dried at 60° C. for 2 hours to obtain a block copolymer having benzene rings at both extreme ends (polymerization conversion of PEGMEA-1=75%). The number average molecular weight of the resulting block copolymer was 10,700 g/mol, and the polydispersity (Mw/Mn) was 1.13.

[Production Example 5]
A dispersant was prepared in the same manner as in Production Example 4, except that the amount of BzA and the polymerization time were changed.

[Production Example 6]
A dispersant was prepared in the same manner as in Production Example 1, except that the RAFT agent was changed to BDMAT.

[Production Example 7]
A dispersant was prepared in the same manner as in Production Example 4, except that the RAFT agent was changed to BDMAT and Monomer 2 (pigment-adsorbing monomer) was changed to acrylic acid (AA).

[Production Example 8]
In a 30 ml Schlenk flask, 0.031 g (0.1867 mmol) of AIBN as a free radical polymerization initiator and 2.467 g (same weight as Monomer 2) of diethylene glycol dimethyl ether (DEGDME; manufactured by Tokyo Chemical Industry Co., Ltd., used as is) as a solvent were weighed and dissolved.
Next, 0.124 g (0.56 mmol) of 2-cyano-2-propylbenzodithioate (CPBD, manufactured by Sigma-Aldrich Japan (same company) was used as it is) as a RAFT agent (polymerization initiator), and 2.467 mg (14 mmol) of benzyl methacrylate (BzMA; manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. and purified by distillation in a conventional manner) as a monomer 2 (pigment adsorption monomer) were weighed and dissolved in a 5 ml sample bottle 1, and then charged into the above-mentioned Schlenk flask. The molar ratio of the materials charged was CPBD:AIBN:BzMA=3:1:75. After replacing the internal space of the above-mentioned Schlenk flask with nitrogen gas, the contents were stirred at 70° C. for 0.5 hours under a nitrogen atmosphere, and then rapidly cooled to room temperature, and 13 ml of DEGDME was added to dilute.
The resulting solution was dropped into 700 ml of hexane (Kanto Chemical Co., Ltd.) to cause reprecipitation, and the solution was filtered through a PTFE membrane filter (pore size: 0.45 μm) to obtain a powder, which was then vacuum dried at 40° C. for 8 hours to obtain a BzMA polymer having benzocyanoate at one extreme end (hereinafter, PBzMA-CPBD) (polymerization conversion rate of BzMA=20. The number average molecular weight of the obtained polymer was 900 g/mol, and the dispersity (Mw/Mn) was 1.13.
Next, 0.175 g (0.195 mmol) of the above-mentioned PBzMA-CPBD was weighed out into a 30 ml Schlenk flask, and 2.438 g (4.875 mmol) of methoxypolyethylene glycol methacrylate (PEGMEMA; Tokyo Chemical Industry Co., Ltd., purified by column purification in a conventional manner, n=9) as monomer 1 (hydrophilic monomer) and 0.011 g (0.065 mmol) of AIBN were added thereto. The molar ratio of the materials charged was AIBN:PBzMA-CPBD:PEGMEMA=1:3:75. After replacing the internal space of the above-mentioned Schlenk flask with nitrogen gas, the contents were stirred at 70° C. for 1.25 hours under a nitrogen atmosphere, and then rapidly cooled to room temperature, and 13 ml of DEGDME was added to dilute.
The obtained solution was dropped into a mixture of 630 ml of hexane and 70 ml of acetone to perform reprecipitation, and after standing, the upper layer was discarded, and the solution remaining in the lower layer was dissolved in 200 ml of chloroform. The obtained solution was concentrated with a rotary evaporator and then vacuum dried at 70°C for 2 hours to obtain a block copolymer having benzocyanoate at one end and a short-chain aliphatic at the other end (polymerization conversion rate of PEGMEMA = 88%). The number average molecular weight of the obtained block copolymer was 10,800, and the dispersity (Mw/Mn) was 1.114.

[Production Example 9]
A dispersant was prepared in the same manner as in Production Example 8, except that the RAFT agent was changed to CPDT.

[Production Example 10]
A dispersant was prepared in the same manner as in Production Example 8, except that AIBN was replaced with ACVN, the solvent was replaced with 1,4-dioxane, the RAFT agent was replaced with CCPA, and the molar ratio of AA to BzA as monomer 2 (pigment-adsorbing monomer) was 1:1.

[Production Example 11]
In a 30 ml Schlenk flask, 0.167 g (0.383 mmol) of ethylene bis(2-iodopropanoate) (EBIP; Fujifilm Wako Pure Chemical Industries, Ltd., used as is) was weighed and dissolved as an RCMP initiator, 5.020 g (23 mmol) of methoxypolyethylene glycol acrylate (PEGMEA-2 (n=3); Tokyo Chemical Industry Co., Ltd., purified by a column in a conventional manner) was weighed and dissolved as a monomer 1 (hydrophilic monomer), and 0.567 g (1.533 mmol) of tetrabutylammonium iodide (BNI; Tokyo Chemical Industry Co., Ltd., used as is) was weighed and dissolved as a catalyst. The molar ratio of the materials charged was EBIP:BNI:PEGMEA=1:4:60. After replacing the inner space of the Schlenk tube with nitrogen gas, the contents were stirred at 110 ° C. for 10 hours under a nitrogen atmosphere, and then the polymer was not purified. While stirring, a mixture of 0.928 g (3.83 mmol) of dibenzoyl peroxide (BPO, manufactured by NOF Corp., used as is) dissolved in 12.8 g of toluene was added and modified at 110 ° C. for 1 hour. The polymer was rapidly cooled to room temperature, and the toluene solution was placed in a centrifuge tube and centrifuged at 3000 rpm for 5 minutes in order to remove unreacted BNI. The supernatant was concentrated and reprecipitated by dropping it into hexane (manufactured by Kanto Chemical Co., Ltd.) / acetone = 700 ml / 50 ml. The polymer obtained by removing the supernatant was vacuum dried at 40 ° C. for 8 hours to obtain a PEGMEA-2 polymer having aromatic groups at both the α-terminus and the γ-terminus (hereinafter, aromatic-P (PEGMEA-2)-aromatic). The number average molecular weight of the resulting polymer was 7,400, and the polydispersity (Mw/Mn) was 1.12.

[Production Examples 12, 13 and 14]
Instead of BPO in Production Example 11, LPO (Production Example 12), SAPO (Production Example 13), or APPO (Production Example 14) was used to modify the ends of the dispersant.

[Production Example 15]
A dispersant was prepared in the same manner as in Production Example 2, except that the RAFT agent was changed to BDCPT, and a PEGMEA-1 polymer having short-chain aliphatic groups at both the α-terminus and the γ-terminus (hereinafter, short-chain aliphatic-P(PEGMEA-1)-short-chain aliphatic group) was obtained.

[Production Example 16]
To 0.3 g of the dispersant produced in Production Example 9, 0.002 g of 1,1'-azobis(cyclohexane-1-carbonitrile) (V-40; manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., used as is) as a radical generator and 0.054 g of 1-ethylpiperidine hypophosphite (EPHP; manufactured by Tokyo Chemical Industry Co., Ltd., used as is) as a hydrogen donor were added, and 1 ml of toluene was added as a solvent. The molar ratio of the charges was 0.3 mol of V-40 and 10 mol of EPHP relative to 1 mol of the block copolymer obtained in Production Example 9.
The contents were reacted at 100° C. for 4 hours to obtain a dispersant having a short-chain aliphatic group at one extreme end and hydrogen at the other extreme end.

[Production Example 17]
The dispersant of Production Example 17 is the polymer of Production Example 12 before being terminally modified with LPO.

The dispersants produced in the above Production Examples are shown in Tables 1-1 and 1-2 below.

<Preparation of Water-Based Pigment Dispersion>
As shown in Tables 2-1 and 2-2 below, a pigment, an aqueous solvent, and a dispersant were mixed to prepare an aqueous pigment dispersion. The prepared aqueous pigment dispersion was evaluated as described below. The results are shown in Tables 2-1 and 2-2.

<Evaluation of Water-Based Pigment Dispersions>
[Standing stability (25°C, 90 days)]
The aqueous pigment dispersion was left to stand in an incubator at 25° C. for 90 days, and the state of pigment separation was visually observed. The dispersion in which no pigment separation was observed was rated as “good”, and the dispersion in which pigment separation was observed was rated as “poor”.

[Dispersion average particle size]
The dispersion average particle size was measured by a dynamic light scattering method in accordance with general rules (JIS Z 8828 (2019) and ISO 22412 (2017)) under the following measurement conditions.
The obtained aqueous pigment dispersion was diluted with an aqueous solvent and a dispersant to a pigment concentration of 0.05%, and the average particle size (D50: cumulative 50% value calculated from the small particle side in the frequency distribution of scattering intensity) at 25° C. was measured using the following device. Also, CV (%) indicates (standard deviation/average particle size)×100, and the smaller the value, the smaller the particle size distribution.
Particle size measuring device: Zeta potential, particle size, and molecular weight measuring system (ELSZ-2000Z manufactured by Otsuka Electronics Co., Ltd.), number of accumulations: 70 times

[Dispersibility (dispersion average particle size/primary particle average particle size)]
The obtained dispersion average particle size is divided by the average particle size of the primary particles of each pigment, and the closer the value is to 1, the better the dispersibility. The particle size of the particles produced as powder can be measured by known means such as SEM observation. The primary particle average particle size of the pigment used in this example is as follows: It is.
Cyan (both unmodified and modified): 110 nm
Magenta (denatured): 120 nm
Yellow (denatured): 120 nm
White (denatured): 210 nm
Black (denatured): 135 nm

<Preparation of Water-Based Ink>
100 parts by weight of the pigment dispersion having the composition shown in Tables 2-1 and 2-2 and 400 parts by weight of zirconia beads having a diameter of 0.3 mm were placed in a 250 ml plastic bottle with a lid, and the mixture was permeated for 2 to 4 hours at 600 rpm in a rocking mill (manufactured by Seiwa Giken Co., Ltd.) to obtain a water-based pigment dispersion having a pigment concentration of 13.5% by weight. The obtained content was filtered through a nylon mesh having an opening of 150 μm to obtain a pigment dispersion.
Next, 20 parts by weight of propylene glycol, 2 parts by weight of triethylene glycol-n-butyl ether, 6.2 parts by weight of a urethane binder (Takelac W-6061T, manufactured by Mitsui Chemicals, Inc., solid content: 31% by weight), 0.8 parts by weight of a nonionic surfactant (Olfine 1010, manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol-10% EO adduct), and 26.6 parts by weight of ion-exchanged water were mixed in a 250 ml disposable beaker, and a magnetic stirrer was placed in the mixture. 44.4 parts by weight of the above pigment dispersion was then dropped therein at 500 rpm for 10 minutes, and the mixture was mixed at 500 rpm for 30 minutes to obtain an ink with a pigment concentration of 6% by weight.

<Evaluation of Water-Based Inks>
[Standing stability (60°C, 30 days)]
The water-based ink was left to stand in an incubator at 60° C. for 30 days, and the state of pigment separation was visually observed. The ink in which no pigment separation was observed was rated as “good”, and the ink in which pigment separation was observed was rated as “poor”.

[Viscosity (25°C)]
The ink viscosity is a value measured under the following measurement conditions by a viscosity measurement method in accordance with general rules (JIS K 5600-2-3 (2004)).
That is, immediately after preparation of each ink, the viscosity value was measured using an E-type rotational viscometer (TVE-25 manufactured by Toki Sangyo Co., Ltd., rotation speed 100 rpm, 25° C.).

[Inkjet Discharge Evaluation]
The ink was measured using an inkjet ejection evaluation device (JETXPERT-2 and IJ-scope, manufactured by ImageXpert Co., Ltd.) and an inkjet head (MH2420 (Gen4, for low to high viscosity, manufactured by Ricoh Co., Ltd.)) and evaluated according to the following criteria.
◯: Discharge is stable at each frequency, and no noticeable mist is seen. ×: Discharge is unstable at each frequency, and noticeable mist is seen.

Claims

A water-based pigment dispersion comprising water, a pigment, and a dispersant,
The dispersant comprises a main chain structure and a terminal structure bonded to at least two terminals of the main chain structure,
the main chain structure is a living radical polymer of the radically polymerizable unsaturated monomer having a water-compatible group,
the terminal structure has an adsorptive group for the pigment;
Water-based pigment dispersion.
each of the terminal structures is independently composed of one or more constitutional units;
The water-based pigment dispersion according to claim 1 , wherein 60% or more of the number of the structural units constituting the terminal structure have the adsorptive group.
The aqueous pigment dispersion according to claim 2, wherein the number of structural units constituting the terminal structure is 1 to 10.
3. The aqueous pigment dispersion according to claim 1, wherein the surface of the pigment is nonionic, and the adsorptive group is an aromatic hydrocarbon group and/or an aliphatic hydrocarbon group having 6 or more carbon atoms.
The aqueous pigment dispersion according to claim 1 or 2, wherein the surface of the pigment is cationic, and the adsorptive group is an anionic group.
The aqueous pigment dispersion according to claim 1 or 2, wherein the surface of the pigment is anionic, and the adsorptive group is a cationic group.
The aqueous pigment dispersion according to claim 1 or 2, wherein the number average molecular weight of the living radical polymer is 6,000 or more.
The aqueous pigment dispersion according to claim 1 or 2, wherein all of the monomers constituting the living radical polymer are radically polymerizable unsaturated monomers having the compatible group.
The aqueous pigment dispersion according to claim 1 or 2, wherein the radically polymerizable unsaturated monomer having a compatible group is a polyalkylene glycol mono(meth)acrylate or an alkoxy polyalkylene glycol mono(meth)acrylate.
The aqueous pigment dispersion according to claim 1 or 2, wherein the radically polymerizable unsaturated monomer having a compatible group is methoxypolyethylene glycol mono(meth)acrylate.
An aqueous ink containing the aqueous pigment dispersion according to claim 1 or 2.
The water-based ink of claim 11 for use in inkjet printing.
An ink cartridge for an inkjet printer, comprising the water-based ink according to claim 11 or 12.
A printing method comprising ejecting the water-based ink according to claim 11 or 12 by an inkjet system.