JP7575941B2 - Water-based dispersion - Google Patents

Description

The present invention relates to an aqueous dispersion and an aqueous ink containing the same.

Inkjet recording is a method of printing characters and images by ejecting ink droplets from extremely fine nozzles directly onto a recording medium. This method has become extremely popular due to its many advantages, including the ease of full-color printing, low cost, the ability to use plain paper as a recording medium, and no contact with the substrate.
In recent years, water-based pigment inks that use pigments as colorants and polymers to disperse the pigments have been attracting attention from the perspective of imparting weather resistance and water resistance to printed matter and reducing the burden on the working environment and the natural environment.

On the other hand, water-based pigment dispersions and water-based pigment inks have problems such as poor storage stability due to the presence of coarse particles derived from pigments and polymers.
Furthermore, in the commercial printing and industrial printing markets, low liquid-absorbent recording media such as resin films are widely used, but water-based pigment inks have poor adhesion to low liquid-absorbent recording media, particularly to polar resin films such as polyvinyl chloride (PVC), and the ink coating is prone to peeling off from the recording medium, impairing the aesthetic appeal of the recorded matter.
Therefore, various proposals have been made to improve these problems.
For example, Patent Literature 1 discloses an aqueous pigment dispersion having excellent storage stability and having a high print density while maintaining excellent adhesion to a non-water-absorbent print medium when used in an aqueous ink, the aqueous pigment dispersion being obtained by dispersing a pigment in an aqueous medium with a polymer dispersant, the polymer dispersant containing a (meth)acrylic resin and a polyester resin.

JP 2019-119890 A

Since the inkjet recording method is suitable for recording a wide variety of products in small quantities, the range of recording media for which it is applicable is expanding. As the range of applications expands, there is a demand for improved recording density and solvent resistance in commercial and industrial printing using low-absorbency resin films, etc.
Conventional water-based pigment dispersions and water-based inks using the same described in Patent Document 1 and the like have been desired to be further improved in terms of storage stability, adhesion to low-liquid-absorbent recording media, recording density, and solvent resistance.
An object of the present invention is to provide an aqueous dispersion and an aqueous ink which, when incorporated into an aqueous ink, can give recorded matter which has excellent storage stability, adhesion to low water-absorbent recording media, recording density, and solvent resistance.

The present inventors have found that the above-mentioned problems can be solved by using a composite resin containing a polyester resin segment and a (meth)acrylic resin segment as a pigment-dispersed polymer, and by including 3-methyl-1,5-pentanediol in an alcohol component constituting the polyester resin segment.
That is, the present invention provides the following [1] and [2].
[1] An aqueous dispersion of composite resin particles containing a pigment,
The composite resin contains a polyester resin (A) segment and a (meth)acrylic resin (B) segment, and the alcohol component constituting the polyester resin (A) contains at least 3-methyl-1,5-pentanediol.
[2] A water-based ink comprising an aqueous dispersion of composite resin particles containing the pigment according to [1] above and a water-soluble organic solvent.

Water-based inks containing the water-based dispersion of the present invention have excellent storage stability and can produce printed matter that has excellent adhesion to low-water-absorbency recording media, recording density, and solvent resistance.

[Aqueous Dispersion]
The aqueous dispersion of the present invention is an aqueous dispersion of composite resin particles containing a pigment,
The composite resin contains a polyester resin (A) segment and a (meth)acrylic resin (B) segment, and the alcohol component constituting the polyester resin (A) contains at least 3-methyl-1,5-pentanediol.
The aqueous ink containing the aqueous dispersion of the present invention can exhibit the above-mentioned effects on low water-absorbent recording media, and can therefore be used for inkjet recording, flexographic printing, gravure printing, and the like, but is preferably used for inkjet recording.
In this specification, the term "recording" refers to a concept that includes printing and printing out characters and images, and the term "recorded matter" refers to a concept that includes printed matter and printed matter on which characters and images are recorded.
By "water-based" it is meant that water constitutes the largest proportion of the medium contained in the ink.
In addition, the term "low water absorption" is a concept that includes low liquid absorption and non-liquid absorption, and means that the amount of water absorption of the recording medium when the recording medium is in contact with pure water for 100 ms is 0 g/m2 or ^more and 10 g/m2 ^or less.

The aqueous ink containing the aqueous dispersion of the present invention has excellent storage stability and can provide recorded matter having excellent adhesion to low water-absorbent recording media, recording density, and solvent resistance. The reason for this is unclear, but is thought to be as follows.
In aqueous pigment dispersions and aqueous inks, when a polyester resin is used as a pigment dispersion polymer, the main chain of the polyester resin is cut due to hydrolysis, and the molecular weight is significantly reduced over time. As a result, even if the polyester resin is adsorbed to the pigment, the adsorption state cannot be stably maintained for a long period of time, and the pigment and polymer gradually aggregate, resulting in the problem of generating coarse particles. As a means for preventing aggregation due to hydrolysis of the polyester resin, a composite with another polymer is considered, but for example, in the case of a composite of a polyester resin and a (meth)acrylic resin, there is a problem that the desired effect cannot be obtained because hydrolysis is unavoidable with a general polyester resin.

The present inventors have found that by using a composite resin containing a polyester resin (A) segment and a (meth)acrylic resin (B) segment as a pigment-dispersing polymer, and by including 3-methyl-1,5-pentanediol in the alcohol component constituting the polyester resin (A), the generation of coarse particles due to aggregation can be suppressed.
This is believed to be because the methyl group at the center of 3-methyl-1,5-pentanediol suppresses the affinity with the aqueous medium and also suppresses hydrolysis of the polyester resin (A), stabilizing the composite resin.
This allows the pigment to be uniformly covered with the composite resin having the polyester resin (A) segment, and the polymer is firmly fixed to the pigment. Therefore, when the water-based ink is applied to a low water-absorbent recording medium or the like, the composite resin having the polyester resin (A) segment is dried to form a resin coating film that exhibits high affinity with the low water-absorbent recording medium, and is thought to improve adhesion.
In addition, the composite resin has excellent solvent resistance, and the (meth)acrylic resin (B) segment is considered to enhance the dispersion stability of the composite resin particles in the ink vehicle. As a result, it is considered that the aqueous ink containing the aqueous dispersion of the present invention has excellent storage stability, and can provide a recorded matter having excellent adhesion to a low water-absorbent recording medium, recording density, and solvent resistance.

<Composite Resin Particles Containing Pigments>
The pigment used in the present invention is contained as composite resin particles containing a pigment, from the viewpoints of improving the storage stability of the resulting water-based ink and obtaining recorded matter that is excellent in adhesion to low water-absorbent recording media, recording density, and solvent resistance.
In this specification, "composite resin particles containing a pigment" includes particles in a form in which the composite resin encompasses the pigment, particles made of a composite resin and a pigment in which part of the pigment is exposed on the surface, particles in which the composite resin is adsorbed to part of the pigment, and particles in a mixture of these forms, with the form of composite resin particles that encompass the pigment being more preferred.
Moreover, the "pigment-containing composite resin particles" are more preferably "pigment-containing crosslinked composite resin particles" which are further crosslinked with a crosslinking agent.

[Pigments]
The pigment used in the present invention may be either an inorganic pigment or an organic pigment, and may also be a lake pigment or a fluorescent pigment. If necessary, these pigments may also be used in combination with an extender pigment.
Specific examples of inorganic pigments include carbon black, metal oxides such as titanium oxide, iron oxide, red iron oxide, and chromium oxide, and pearlescent pigments. In particular, carbon black is preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black.
Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments.

The hue is not particularly limited, and any of achromatic pigments such as white, black, and gray; and chromatic organic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used.
Specific examples of preferred organic pigments include one or more product numbers selected from C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green.
Examples of the extender pigment include silica, calcium carbonate, and talc.
The above pigments may be used alone or in combination of two or more.

<Polymer Constituting Composite Resin Particles Containing Pigment>
The polymer constituting the pigment-containing composite resin particles is a composite resin containing a polyester resin (A) segment and a (meth)acrylic resin (B) segment.
The composite resin is a polymer having a pigment dispersing ability, and is preferably a water-insoluble polymer. Even if the polymer is a water-soluble polymer, it becomes a water-insoluble polymer by a crosslinking treatment.
Here, the term "water-insoluble" of a polymer means that when a polymer that has been dried at 105° C. for 2 hours and has reached a constant weight is dissolved in 100 g of water at 25° C., the amount of dissolution is 10 g or less, and the amount of dissolution of the polymer is preferably 5 g or less, more preferably 1 g or less. When the polymer is an anionic polymer, the amount of dissolution is the amount of dissolution when the anionic groups of the polymer are 100% neutralized with sodium hydroxide.

The mass ratio [(A)/(B)] of the polyester resin (A) segment to the (meth)acrylic resin (B) segment in the composite resin is preferably 50/50 or more, more preferably 52/48 or more, even more preferably 55/45 or more, still more preferably 58/42 or more, from the viewpoint of improving the storage stability of the resulting water-based ink and obtaining a recorded matter having excellent adhesion to low water-absorbent recording media, recording density, and solvent resistance, and is preferably 98/2 or less, more preferably 95/5 or less, even more preferably 90/10 or less, and still more preferably 85/15 or less.

[Polyester Resin (A) Segment]
The polyester resin (A) segment contains a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid component, and can be obtained by polycondensation of the alcohol component and the carboxylic acid component.

(Alcohol content)
The alcohol component, which is a raw material monomer constituting the polyester resin (A), contains at least 3-methyl-1,5-pentanediol from the viewpoint of improving the storage stability of the resulting water-based ink and obtaining a recorded matter having excellent adhesion to low water-absorbency recording media, recording density, and solvent resistance. 3-methyl-1,5-pentanediol is a diol that is an isomer of 1,6-hexanediol, and is non-crystalline due to the influence of the methyl group at its center, suppressing affinity with water-based media and also suppressing hydrolysis of the polyester resin (A), which is thought to stabilize the composite resin.
From the same viewpoints as above, the content of 3-methyl-1,5-pentanediol in the alcohol component is preferably 30 mol% or more, more preferably 35 mol% or more, even more preferably 40 mol% or more, still more preferably 45 mol% or more, and preferably 85 mol% or less, more preferably 80 mol% or less, even more preferably 75 mol% or less, and still more preferably 70 mol% or less.

The alcohol component, which is a raw material monomer for the polyester resin (A), may contain other alcohol components in addition to 3-methyl-1,5-pentanediol.
As the other alcohol component, an aromatic diol is preferable, and an alkylene oxide adduct of bisphenol A is more preferable.
The alkylene oxide adduct of bisphenol A is a compound having a structure in which an oxyalkylene group is added to 2,2-bis(4-hydroxyphenyl)propane, and specifically, a compound represented by the following general formula (I) is preferred.

In formula (I), OR ¹ and R ² O each independently represent an oxyalkylene group having from 1 to 4 carbon atoms, and are preferably an oxyethylene group or an oxypropylene group.
x and y are the number of moles of alkylene oxide added, and each is independently a positive number of 0 or more. From the viewpoint of reactivity with the carboxylic acid component, the average value of the sum of x and y is preferably 2 or more, and is preferably 7 or less, more preferably 5 or less, and further preferably 3 or less.
Furthermore, x OR ¹ 's and y R ² O's may be the same or different, but are preferably the same from the same viewpoint as above.
The alkylene oxide adduct of bisphenol A is preferably a propylene oxide adduct of bisphenol A or an ethylene oxide adduct of bisphenol A, and more preferably a propylene oxide adduct of bisphenol A.
From the same viewpoints as above, the content of the alkylene oxide adduct of bisphenol A in the alcohol component is preferably 70 mol % or less, more preferably 65 mol % or less, even more preferably 60 mol % or less, still more preferably 55 mol % or less, and preferably 15 mol % or more, more preferably 20 mol % or more, even more preferably 25 mol % or more, and still more preferably 30 mol % or more.

Examples of other alcohol components include ethylene glycol, propylene glycol (1,2-propanediol), glycerin, pentaerythritol, trimethylolpropane, hydrogenated bisphenol A, sorbitol, and alkylene oxide adducts (having a carbon number of 2 to 4) thereof (average number of moles added: 1 to 16).
The alcohol components may be used alone or in combination of two or more.

(Carboxylic Acid Component)
The carboxylic acid component which is a raw material monomer of the polyester resin (A) includes carboxylic acid, its acid anhydride, and its alkyl (having 1 to 3 carbon atoms) ester.
Examples of the carboxylic acid component include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and trivalent or higher polycarboxylic acids.
As the aromatic dicarboxylic acid, phthalic acid, isophthalic acid and terephthalic acid are preferred, and terephthalic acid is more preferred.
The aliphatic dicarboxylic acid may be unsaturated or saturated, and the unsaturated aliphatic dicarboxylic acid may be fumaric acid or maleic acid, more preferably fumaric acid. The saturated aliphatic dicarboxylic acid may be adipic acid or succinic acid, more preferably adipic acid.
As the alicyclic dicarboxylic acid, cyclohexanedicarboxylic acid, decalindicarboxylic acid, and tetrahydrophthalic acid are preferred.
As the trivalent or higher polyvalent carboxylic acid, trimellitic acid and pyromellitic acid are preferred, and trimellitic anhydride is also preferred.
The carboxylic acid components may be used alone or in combination of two or more kinds.
From the viewpoints of improving the storage stability of the resulting aqueous ink and obtaining a recorded matter that is excellent in adhesion to a low water-absorbent recording medium, recording density, and solvent resistance, the above-mentioned carboxylic acid component preferably contains one or more selected from aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and tri- or higher polycarboxylic acids, and it is more preferable to use these in combination.

(Production of Polyester Resin (A))
The polyester resin (A) can be obtained by polycondensing the alcohol component and the carboxylic acid component in an appropriate combination, for example, by polycondensing the alcohol component and the carboxylic acid component in an inert gas atmosphere at a temperature of 150° C. to 250° C. using an esterification catalyst as necessary.
Examples of the esterification catalyst include tin catalysts, titanium catalysts, and metal compounds such as antimony trioxide, zinc acetate, and germanium dioxide, and from the viewpoint of esterification reaction efficiency, tin catalysts are preferred. As the tin catalyst, dibutyltin oxide, tin(II)(2-ethylhexanoate), and salts thereof are preferred, and tin(II)(2-ethylhexanoate) is more preferred. If necessary, an esterification promoter such as gallic acid may be further used.
A radical polymerization inhibitor such as 4-tert-butylcatechol may also be used in combination.

The polyester resin (A) preferably has an acid group, from the viewpoints of improving the storage stability of the resulting water-based ink and obtaining a recorded matter having excellent adhesion to a low water-absorbency recording medium, recording density, and solvent resistance.
The acid value of the polyester resin (A) is preferably 10 mgKOH/g or more, more preferably 12 mgKOH/g or more, even more preferably 15 mgKOH/g or more, and is preferably 90 mgKOH/g or less, more preferably 70 mgKOH/g or less, even more preferably 50 mgKOH/g or less.
From the same viewpoints as above, the softening point of the polyester resin (A) is preferably 85°C or higher, more preferably 90°C or higher, even more preferably 95°C or higher, and is preferably 180°C or lower, more preferably 160°C or lower, even more preferably 140°C or lower.

From the same viewpoints as above, the glass transition temperature of the polyester resin (A) is preferably 38° C. or higher, more preferably 40° C. or higher, even more preferably 42° C. or higher, and is preferably 80° C. or lower, more preferably 70° C. or lower, even more preferably 60° C. or lower.
From the same viewpoints as above, the number average molecular weight of the polyester resin (A) is preferably 2,000 or more, more preferably 3,000 or more, even more preferably 3,500 or more, and preferably 10,000 or less, more preferably 7,000 or less, even more preferably 5,000 or less.
The acid value, softening point, glass transition temperature, and number average molecular weight of the polyester resin can be measured by the method described in the Examples. These physical properties can be adjusted to the desired values by appropriately adjusting the type and blending ratio of the monomers used, the polycondensation temperature, and the reaction time.

[(Meth)acrylic resin (B) segment]
The (meth)acrylic resin (B) segment is a vinyl polymer containing a structural unit derived from (meth)acrylic acid, where (meth)acrylic acid means one or more selected from acrylic acid and methacrylic acid.
The (meth)acrylic resin (B) segment contains a structural unit derived from (meth)acrylic acid, and preferably further contains a structural unit derived from a hydrophobic monomer.
Here, the term "hydrophobic" in the hydrophobic monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of the monomer dissolved is less than 10 g.
Specific examples of hydrophobic monomers include those described in paragraphs [0020] to [0022] of JP-A-2018-83938. Among these, one or more selected from alkyl (meth)acrylates having an alkyl group with 1 to 22 carbon atoms, styrene, α-methylstyrene, and benzyl (meth)acrylate are preferred, and one or more selected from alkyl (meth)acrylates having an alkyl group with 1 to 6 carbon atoms, styrene, and α-methylstyrene are more preferred.

The (meth)acrylic resin segment (B) may further contain a structural unit derived from a nonionic monomer.
Specific examples of the nonionic monomer include those described in paragraph [0018] of JP-A-2018-83938. Among these, one or more selected from methoxypolyethylene glycol (n = 1 to 30) (meth)acrylate and polypropylene glycol (n = 2 to 30) (meth)acrylate are preferred.
From the above viewpoints, it is more preferable that the (meth)acrylic resin (B) segment is a (meth)acrylic resin having a constituent unit derived from (meth)acrylic acid and a constituent unit derived from an alkyl (meth)acrylate having an alkyl group having 1 to 6 carbon atoms, or a constituent unit derived from one or more selected from styrene and α-methylstyrene.

(Content of each structural unit in (meth)acrylic resin (B) segment)
The content of each of the constituent units constituting the (meth)acrylic resin (B) segment is as follows, from the viewpoints of improving the storage stability of the resulting aqueous ink and obtaining a recorded matter having excellent adhesion to a low water-absorbent recording medium, recording density, and solvent resistance.
The content of the constituent units derived from (meth)acrylic acid in all monomer constituent units constituting the (meth)acrylic resin (B) segment is preferably 10 mass% or more, more preferably 15 mass% or more, even more preferably 20 mass% or more, and is preferably 50 mass% or less, more preferably 45 mass% or less, even more preferably 40 mass% or less.
The content of the structural units derived from hydrophobic monomers in all monomer structural units constituting the (meth)acrylic resin (B) segment is preferably 90 mass% or less, more preferably 85 mass% or less, even more preferably 80 mass% or less, and is preferably 50 mass% or more, more preferably 55 mass% or more, even more preferably 60 mass% or more.
When a nonionic monomer constituent unit is contained, the content thereof is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or less.

The content of the structural units derived from (meth)acrylic acid and hydrophobic monomer in the (meth)acrylic resin (B) segment can be determined by measurement, or can be substituted by the charging ratio of the raw material monomers containing (meth)acrylic acid and hydrophobic monomer during the production of the (meth)acrylic resin (B).

(Production of (meth)acrylic resin (B))
The (meth)acrylic resin (B) can be produced by copolymerizing a monomer mixture of (meth)acrylic acid and a hydrophobic monomer by a known polymerization method, preferably a solution polymerization method.
There is no limitation on the solvent used in the solution polymerization method, but polar solvents such as water, lower aliphatic alcohols, ketones such as methyl ethyl ketone, ethers, and esters are preferred.
In the polymerization, a polymerization initiator such as an azo compound or a persulfate, or a polymerization chain transfer agent such as a mercaptan, can be used. The polymerization temperature varies depending on the type of polymerization initiator, monomer, and solvent used, but is preferably 30° C. or higher, more preferably 50° C. or higher, and is preferably 95° C. or lower, more preferably 80° C. or lower.
After removing the organic solvent used in the production, the (meth)acrylic resin (B) is preferably dispersed in water to form an aqueous dispersion, which is then used in the production of an aqueous dispersion of pigment-containing composite resin particles, which will be described later.
Commercially available products may also be used as the (meth)acrylic resin (B), such as styrene-acrylic resins such as JONCRYL 67, 678, 683, and 690 manufactured by BASF Japan Ltd.

From the viewpoints of improving the storage stability of the resulting water-based ink and obtaining a recorded matter having excellent adhesion to a low water-absorbent recording medium, recording density, and solvent resistance, the acid value of the (meth)acrylic resin (B) is preferably 150 mgKOH/g or more, more preferably 170 mgKOH/g or more, even more preferably 180 mgKOH/g or more, and is preferably 300 mgKOH/g or less, more preferably 280 mgKOH/g or less, even more preferably 260 mgKOH/g or less.
From the same viewpoints as above, the number average molecular weight of the (meth)acrylic resin (B) is preferably 3,000 or more, more preferably 5,000 or more, even more preferably 8,000 or more, and is preferably 100,000 or less, more preferably 80,000 or less, even more preferably 50,000 or less.
The acid value and number average molecular weight of the (meth)acrylic resin (B) can be measured by the method described in the Examples.

<Production of aqueous dispersion of pigment-containing composite resin particles>
The production of the aqueous dispersion of the composite resin particles containing a pigment can be carried out by any known method such as bulk polymerization, seed polymerization, dispersion treatment, etc., either alone or in combination as appropriate, without any particular limitation. Among these, the dispersion treatment is preferred from the viewpoint of operability.
The dispersion treatment method is a method in which, for example, a polyester resin, a (meth)acrylic resin and a pigment are dispersed in an aqueous medium, and if necessary, a crosslinking treatment is further carried out to produce a composite resin dispersion containing the pigment.

The dispersion treatment method is preferably a method having the following steps I to III. If necessary, it is preferable to further carry out a crosslinking step IV.
Step I: A step of dispersing a pigment mixture containing a polyester resin (A), an organic solvent, a pigment, and water to obtain a dispersion of polyester resin particles containing a pigment (hereinafter also referred to as "pigment-containing polyester resin particles"). Step II: A step of dispersing the dispersion obtained in Step I and an aqueous dispersion of a (meth)acrylic resin (B) to obtain a dispersion of composite resin particles containing a pigment (hereinafter also referred to as "pigment-containing composite resin particles"). Step III: A step of removing the organic solvent from the pigment dispersion obtained in Step II to obtain an aqueous dispersion of pigment-containing composite resin particles. Step IV: A step of crosslinking the aqueous dispersion obtained in Step III with a crosslinking agent (C) to obtain an aqueous dispersion of crosslinked composite resin particles containing a pigment (hereinafter also referred to as "pigment-containing crosslinked composite resin particles"). The "aqueous dispersion of the present invention" encompasses the aqueous dispersion of pigment-containing composite resin particles obtained in Step III and the aqueous dispersion of pigment-containing crosslinked composite resin particles obtained in Step IV.

(Step I)
In step I, a method is preferred in which the polyester resin (A) is first dissolved in an organic solvent, and then the pigment, water, a neutralizing agent, and optionally a surfactant, etc. are added to the obtained polymer solution and mixed to obtain an oil-in-water dispersion.
There are no limitations on the organic solvent in which the polyester resin (A) can be dissolved. However, aliphatic alcohols, ketones, ethers, esters, and the like having 1 to 3 carbon atoms are preferred, ketones having 4 to 8 carbon atoms are more preferred, and methyl ethyl ketone is even more preferred.

At least a part of the acid groups of the polyester resin (A) is preferably neutralized with a neutralizing agent. When neutralizing, it is preferable to neutralize so that the pH is 6 or more and 10 or less.
As the neutralizing agent, from the viewpoint of improving storage stability, etc., an alkali metal compound or the like is preferable, an alkali metal hydroxide is more preferable, and sodium hydroxide is further preferable.
Furthermore, prior to step I, the polyester resin (A) may be neutralized in advance.
From the same viewpoints as above, the amount of the neutralizing agent used is preferably 20 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, and is preferably 150 mol% or less, more preferably 120 mol% or less, even more preferably 100 mol% or less.
Here, the equivalent amount of the neutralizing agent used can be calculated by the following formula, where polymer a before neutralization is "polymer a'".
Equivalent amount of neutralizing agent used (mol %)=[{weight (g) of neutralizing agent added/equivalent amount of neutralizing agent}/[{acid value of polymer a' (mg KOH/g) x weight (g) of polymer a'}/(56 x 1,000)]] x 100
The dispersion treatment in step I can be carried out by a known method. As a dispersing machine, a commonly used mixing and stirring device such as an anchor blade or a disperser blade can be used.

(Step II)
In step II, the dispersion obtained in step I and an aqueous dispersion of the (meth)acrylic resin (B) are subjected to a dispersion treatment to obtain a dispersion of pigment-containing composite resin particles.
As the aqueous dispersion of the (meth)acrylic resin (B), those described in the section (Production of the (meth)acrylic resin (B)) can be used.
Examples of the dispersing machine used in step II include kneading machines such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersing machines such as paint shakers and bead mills. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment.
When the dispersion treatment is carried out using a high-pressure homogenizer, the average particle size of the pigment particles in the pigment aqueous dispersion can be adjusted by controlling the treatment pressure and the number of passes.
From the viewpoints of productivity and economy, the treatment pressure is preferably 60 MPa or more and 300 MPa or less, and the number of passes is preferably 3 or more and 30 or less.

(Step III)
In step III, the organic solvent is removed from the dispersion obtained in step II by a known method to obtain the aqueous dispersion of the present invention. It is preferable that the organic solvent in the obtained aqueous dispersion of the present invention is substantially removed, but it may remain as long as it does not impair the object of the present invention.

(Step IV)
Step IV is a step of crosslinking the aqueous dispersion of pigment-containing crosslinked composite resin particles obtained in step III with a crosslinking agent (C) to obtain an aqueous dispersion of pigment-containing crosslinked composite resin particles.
Step IV is an optional step, but it is preferable to carry out Step IV from the viewpoints of improving the storage stability of the resulting water-based ink and obtaining a recorded matter that has excellent adhesion to low water-absorbent recording media, recording density, and solvent resistance.
By carrying out step IV, at least a part of the acid groups of the polyester resin (A) segment and the (meth)acrylic resin (B) segment constituting the composite resin is crosslinked with the crosslinking agent (C) through a chemical reaction, and a crosslinked structure is formed in the surface layer portion of the pigment-containing composite resin particle. That is, the aqueous dispersion of the present invention is preferably an aqueous dispersion of pigment-containing crosslinked composite resin particles in which the composite resin constituting the pigment-containing composite resin particles is crosslinked with the crosslinking agent (C).

(Crosslinking Agent (C))
The crosslinking agent (C) is preferably a polyfunctional epoxy compound having two or more epoxy groups, preferably a glycidyl ether group, in the molecule, and more preferably a glycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 8 carbon atoms.
The number of epoxy groups in the polyfunctional epoxy compound is 2 or more, preferably 3 or more, per molecule from the viewpoint of efficiently reacting with the carboxy groups to enhance the storage stability, etc., of the pigment-containing crosslinked composite resin particles, and is preferably 6 or less, per molecule, and more preferably 4 or less from the viewpoint of market availability.
From the same viewpoints as above, the epoxy equivalent of the polyfunctional epoxy compound is preferably 100 or more, more preferably 110 or more, even more preferably 120 or more, and preferably 300 or less, more preferably 270 or less, even more preferably 250 or less.

Specific examples of polyfunctional epoxy compounds include polyglycidyl ethers such as polypropylene glycol diglycidyl ether, glycerin polyglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, 1,6-hexanediol diglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether. Among these, one or more selected from trimethylolpropane polyglycidyl ether, 1,6-hexanediol diglycidyl ether, and pentaerythritol polyglycidyl ether are preferred.

The crosslinking reaction of the pigment-containing composite resin is preferably carried out after dispersing the pigment in the composite resin. From the viewpoints of completion of the reaction and economic efficiency, the reaction temperature is preferably 50° C. or higher, more preferably 60° C. or higher, and preferably 95° C. or lower, more preferably 85° C. or lower.
The reaction time is preferably 0.5 hours or more, more preferably 1 hour or more, and is preferably 12 hours or less, more preferably 10 hours or less.

From the viewpoints of improving the storage stability of the resulting water-based ink and obtaining a recorded matter having excellent adhesion to a low water-absorbency recording medium, recording density, and solvent resistance, the degree of crosslinking of the resulting pigment-containing crosslinked composite resin is preferably 10 mol % or more, more preferably 20 mol % or more, even more preferably 30 mol % or more, and is preferably 70 mol % or less, more preferably 60 mol % or less, even more preferably 50 mol % or less.
The crosslinking degree of the pigment-containing crosslinked composite resin is an apparent crosslinking degree calculated from the acid values of the polyester resin (A) and the (meth)acrylic resin (B) and the equivalent weight of the epoxy group of the polyfunctional epoxy compound. That is, the crosslinking degree is calculated by "the mole number of epoxy groups of the crosslinker (C) segment of the pigment-containing crosslinked composite resin in the aqueous dispersion of the present invention / the total mole number of carboxy groups of the polyester resin (A) segment and the (meth)acrylic resin (B) segment in the aqueous dispersion of the present invention".
From the same viewpoint as above, the degree of neutralization of the pigment-containing composite resin that constitutes the pigment-containing crosslinked composite resin particles is preferably 40 mol % or more, more preferably 50 mol % or more, even more preferably 60 mol % or more, and is preferably 80 mol % or less, more preferably 70 mol % or less.
The above-mentioned degree of neutralization is calculated by "the number of moles of the neutralizing agent in the aqueous dispersion of the present invention / the total number of moles of the carboxy groups in the polyester resin (A) segment and the (meth)acrylic resin (B) segment in the aqueous dispersion of the present invention".

The average particle size of the pigment-containing (crosslinked) composite resin particles in the aqueous dispersion of the present invention is, from the viewpoints of reducing coarse particles and improving the adhesion of aqueous inks, preferably 80 nm or more, more preferably 85 nm or more, even more preferably 90 nm or more, and is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less.
The average particle size of the pigment-containing (crosslinked) composite resin particles in the water-based ink of the present invention is substantially the same as the average particle size of the pigment-containing (crosslinked) composite resin particles in the water-based dispersion of the present invention.
The non-volatile component concentration (solids concentration) of the obtained aqueous dispersion of the present invention is, from the viewpoint of improving storage stability and facilitating preparation of an aqueous ink, preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 30% by mass or less, more preferably 25% by mass or less.
The average particle size and solid content are measured by the methods described in the Examples.

(Content of each component in the aqueous dispersion of the present invention)
The contents of the respective components in the aqueous dispersion of the present invention are as follows, from the viewpoints of improving the storage stability of the aqueous dispersion and aqueous ink of the present invention and obtaining recorded matter having excellent adhesion to a low water-absorbent recording medium, recording density, and solvent resistance.
(Pigment content)
The content of the pigment in the aqueous dispersion of the present invention is preferably 2% by mass or more, more preferably 4% by mass or more, even more preferably 6% by mass or more, and is preferably 20% by mass or less, more preferably 18% by mass or less, even more preferably 16% by mass or less.
The content of the pigment-containing composite resin particles in the aqueous dispersion of the present invention is preferably 3% by mass or more, more preferably 6% by mass or more, even more preferably 10% by mass or more, and is preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less.

The content of the composite resin in the aqueous dispersion of the present invention is preferably 2 mass% or more, more preferably 4 mass% or more, even more preferably 5 mass% or more, and is preferably 20 mass% or less, more preferably 18 mass% or less, even more preferably 15 mass% or less.
The content of the polyester resin (A) segment in the aqueous dispersion of the present invention is preferably 2 mass% or more, more preferably 4 mass% or more, even more preferably 6 mass% or more, and is preferably 20 mass% or less, more preferably 18 mass% or less, even more preferably 15 mass% or less.
The content of the (meth)acrylic resin (B) segment in the aqueous dispersion of the present invention is preferably 0.5 mass% or more, more preferably 1 mass% or more, even more preferably 1.5 mass% or more, and is preferably 10 mass% or less, more preferably 8 mass% or less, even more preferably 15 mass% or less.

The mass ratio of the pigment to the (meth)acrylic resin (B) segment in the aqueous dispersion of the present invention [pigment/(pigment + (meth)acrylic resin (B) segment)] is preferably 0.7 or more, more preferably 0.75 or more, even more preferably 0.8 or more, and is preferably 0.98 or less, more preferably 0.95 or less, even more preferably 0.92 or less.
The mass ratio can be calculated from the charge amount ratio.
The pH of the aqueous dispersion of the present invention is, from the viewpoints of storage stability, reduced corrosiveness, and the like, preferably 7.0 or more, more preferably 7.2 or more, even more preferably 7.5 or more, and is preferably 11 or less, more preferably 10 or less, even more preferably 9.5 or less.

[Water-based ink]
The water-based ink of the present invention contains an aqueous dispersion of composite resin particles containing the pigment of the present invention and a water-soluble organic solvent.
The water-based ink of the present invention can be efficiently produced by mixing the water-based dispersion containing the pigment-containing composite resin particles and/or the pigment-containing crosslinked composite resin particles obtained above, a water-soluble organic solvent, water, and, as necessary, various additives such as a surfactant.
There is no particular limitation on the method for mixing the above components.

(Water-soluble organic solvent)
The water-soluble organic solvent used may be either liquid or solid at 25° C., but when the organic solvent is dissolved in 100 mL of water at 25° C., the amount of the dissolved organic solvent is 10 mL or more.
From the viewpoint of improving the wetting and spreading properties of the ink, the boiling point of the water-soluble organic solvent is preferably 100° C. or higher, more preferably 120° C. or higher, even more preferably 140° C. or higher, still more preferably 150° C. or higher, and preferably 250° C. or lower, more preferably 245° C. or lower, even more preferably 240° C. or lower, and still more preferably 235° C. or lower.
Examples of the water-soluble organic solvent include glycol ethers such as alkylene glycol ethers, polyhydric alcohols, amide compounds, etc. Among these, alkylene glycol ethers and polyhydric alcohols are preferred.

Examples of alkylene glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monobutyl ether, and dipropylene glycol monomethyl ether.
Among these, one or more selected from diethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol isobutyl ether, diethylene glycol monomethyl ether, and dipropylene glycol monomethyl ether are preferred, and diethylene glycol monoisobutyl ether is more preferred.

Examples of polyhydric alcohols include propylene glycol, ethylene glycol, butanediol, diethylene glycol, dipropylene glycol, glycerin, etc. Among these, propylene glycol is preferred.
It is more preferable that the water-based ink of the present invention uses diethylene glycol monoisobutyl ether and propylene glycol in combination.

<Surfactant>
The water-based ink of the present invention preferably contains a surfactant from the viewpoints of maintaining the surface tension of the ink at an appropriate level and improving the wettability of the ink to a recording medium.
The surfactant is not particularly limited, but a nonionic surfactant is preferred, and one or more surfactants selected from acetylene glycol surfactants and silicone surfactants are more preferred.
Examples of acetylene glycol surfactants include acetylene diols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, 2,4-dimethyl-5-hexyne-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, and ethylene oxide adducts thereof.
Commercially available examples of acetylene glycol surfactants include the "Surfynol" series and "Olfine" series manufactured by Nissin Chemical Industry Co., Ltd., and the "Acetylenol" series manufactured by Kawaken Fine Chemicals Co., Ltd.

(Silicone surfactant)
Examples of silicone surfactants include dimethylpolysiloxane, polyether-modified silicone, amino-modified silicone, and carboxy-modified silicone, with polyether-modified silicone being preferred from the same viewpoint as above.
The HLB (hydrophilic lipophilic balance) value of the polyether-modified silicone surfactant is preferably at least 2, more preferably at least 3, and even more preferably at least 4. Here, the HLB value can be determined by the Griffin method.
Specific examples of polyether-modified silicones include PEG-3 dimethicone, PEG-9 dimethicone, PEG-9PEG-9 dimethicone, PEG-9 methyl ether dimethicone, PEG-10 dimethicone, PEG-11 methyl ether dimethicone, PEG/PPG-20/22 butyl ether dimethicone, PEG-32 methyl ether dimethicone, PEG-9 polydimethylsiloxyethyl dimethicone, and the like.
Examples of commercially available polyether-modified silicones include the silicone KF series manufactured by Shin-Etsu Chemical Co., Ltd.
The above surfactants may be used alone or in combination of two or more.

Other additives that may be used in the water-based ink of the present invention include fixing aids, humectants, wetting agents, penetrating agents, viscosity adjusters, defoamers, preservatives, antifungal agents, and rust inhibitors.
The fixing aid may be an emulsion containing water-insoluble polymer particles. Examples of the water-insoluble polymer particles include particles of condensation resins such as polyurethane and polyester; and vinyl resins such as (meth)acrylic resins, styrene resins, styrene-(meth)acrylic resins, butadiene resins, styrene-butadiene resins, vinyl chloride resins, vinyl acetate resins, and acrylic silicone resins.

(Content of each component in the water-based ink of the present invention)
The contents of the various components in the water-based ink of the present invention are as follows, from the viewpoints of improving storage stability and obtaining recorded matter that is excellent in adhesion to low water-absorbent recording media, recording density, and solvent resistance.
(Pigment content)
The content of the pigment in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 2.5% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less.
The content of the pigment-containing composite resin particles in the water-based ink is preferably 3% by mass or more, more preferably 4% by mass or more, even more preferably 5% by mass or more, and is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less.

The content of the polyester resin (A) segment in the water-based ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less.
The content of the (meth)acrylic resin (B) segment in the water-based ink is preferably 0.1 mass % or more, more preferably 0.2 mass % or more, even more preferably 0.3 mass % or more, and is preferably 4 mass % or less, more preferably 2 mass % or less, even more preferably 1 mass % or less.

The total content of the water-soluble organic solvents in the water-based ink is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and is preferably 45% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less.
The content of the system surfactant in the water-based ink is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and is preferably 3% by mass or less, more preferably 2% by mass or less, even more preferably 1.5% by mass or less.
The water content in the water-based ink is preferably 5% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, and is preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less.
The water-based ink of the present invention may contain various additives such as preservatives, pH adjusters, viscosity adjusters, antifoaming agents, and rust inhibitors as optional components depending on the application.

(Physical properties of the water-based ink of the present invention)
The viscosity of the water-based ink of the present invention at 32°C is preferably 2 mPa·s or more, more preferably 2.5 mPa·s or more, and is preferably 12 mPa·s or less, more preferably 9 mPa·s or less, from the viewpoint of adhesion to low water-absorbent recording media, etc.
The pH of the water-based ink of the present invention is preferably 7.0 or more, more preferably 7.2 or more, and is preferably 11 or less, more preferably 10 or less, from the viewpoints of storage stability, reduction in corrosiveness, etc.

The water-based ink of the present invention can be loaded into a known inkjet printing device and ejected as ink droplets onto a recording medium having low water absorption or the like to record an image or the like.
There are three types of ink droplet ejection methods: piezo, thermal, and electrostatic, with the piezo method being the most preferable. In the piezo method, a large number of nozzles are each connected to a pressure chamber, and ink droplets are ejected from the nozzles by vibrating the walls of the pressure chambers with a piezo element.

Examples of low water-absorbent recording media include low water-absorbent coated paper, art paper, and resin films.
Examples of coated paper include general-purpose glossy paper and multi-color form glossy paper.
The resin film may be a transparent synthetic resin film, such as a polyester film, a polyvinyl chloride film, a polypropylene film, a polyethylene film, a nylon film, etc. These films may be biaxially oriented films, uniaxially oriented films, or non-oriented films.

In the following manufacturing examples, preparation examples, working examples, and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

(1) Number average molecular weight (Mn) of resin
The number average molecular weight was determined by the following gel permeation chromatography (GPC) method.
(1-1) Preparation of sample solution A sample was dissolved in tetrahydrofuran at 40° C. to a concentration of 0.5 g/100 mL. Next, this solution was filtered using a PTFE-type membrane filter "DISMIC-25JP" (manufactured by Toyo Roshi Kaisha, Ltd.) with a pore size of 0.20 μm to remove insoluble components, thereby obtaining a sample solution.
(1-2) Molecular weight measurement Using the following measurement device and analytical column, tetrahydrofuran was passed as an eluent at a flow rate of 1 mL per minute, and the column was stabilized in a thermostatic bath at 40°C. 100 μL of the sample solution was injected therein and measurement was performed. The molecular weight of the sample was calculated based on a calibration curve prepared in advance.
Measuring device: HLC-8220GPC (manufactured by Tosoh Corporation)
Analytical column: TSKgel GMHXL + TSKgel G3000HXL (Tosoh Corporation)
For the calibration curve, several types of monodisperse polystyrene (A-500 (5.0× ¹⁰² ), A-1000 (1.01× ¹⁰³ ), A-2500 (2.63× ¹⁰³ ), A-5000 (5.97× ¹⁰³ ), F-1 (1.02× ¹⁰⁴ ), F-2 (1.81× ¹⁰⁴ ), F-4 (3.97× ¹⁰⁴ ), F-10 (9.64× ¹⁰⁴ ), F-20 (1.90× ¹⁰⁵ ), F-40 (4.27× ¹⁰⁵ ), F-80 (7.06× ¹⁰⁵ ), F-128 (1.09× ¹⁰⁶ ) manufactured by Tosoh Corporation) were used as standard samples. The molecular weight is shown in parentheses.

(2) Measurement of Resin Acid Value The acid value of the resin was measured based on the method of JIS K0070: 1992. However, the measurement solvent was changed from the mixed solvent of ethanol and ether specified in JIS K0070: 1992 to a mixed solvent of acetone and toluene (acetone:toluene = 1:1 (volume ratio)).

(3) Measurement of resin softening point Using a flow tester "CFT-500D" (manufactured by Shimadzu Corporation), a part of the sample was heated at a temperature increase rate of 6°C/min while applying a load of 1.96 MPa with a plunger, and extruded from a nozzle with a diameter of 1 mm and a length of 1 mm. The plunger descent amount of the flow tester was plotted against the temperature, and the temperature at which half of the sample flowed out was taken as the softening point.

(4) Measurement of glass transition temperature of resin Using a differential scanning calorimeter "Q-100" (manufactured by TA Instruments Japan), 0.01 to 0.02 parts of a sample was weighed into an aluminum pan, heated from room temperature (20°C) to 200°C at a heating rate of 10°C/min, and cooled from that temperature to 0°C at a heating rate of 10°C/min. The sample was then heated to 180°C at a heating rate of 10°C/min, and the temperature at the intersection of the extension of the baseline below the highest endothermic peak temperature and the tangent showing the maximum slope from the rising part of the peak to the apex of the peak was taken as the glass transition temperature.

(5) Measurement of average particle size of pigment-containing (crosslinked) composite resin particles The particle size was measured by dynamic light scattering using a laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd., product name: ELS-8000), and calculated by cumulant method analysis.
The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measurement sample was weighed into a screw tube, water was added so that the solid concentration was 5 x ^10-3 mass%, and the sample was stirred with a magnetic stirrer at 25°C for 1 hour.

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

(7) Measurement of pH Using a pH meter (manufactured by DKK-TOA Corporation, product name: HM-20P), the measurement was performed at 25° C. after calibration with standard buffer solutions of pH 6.86 and pH 9.18 (manufactured by DKK-TOA Corporation).

Production Example I-1 (Production of Acrylic Resin A1)
60 parts of acrylic acid, 130 parts of styrene, and 10 parts of α-methylstyrene were mixed to prepare a monomer mixture. 20 parts of methyl ethyl ketone (MEK), 0.3 parts of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the monomer mixture were mixed in a reaction vessel, and nitrogen gas replacement was performed thoroughly. Meanwhile, a mixture of the remainder of the monomer mixture (90% of the monomer mixture), 0.27 parts of the polymerization chain transfer agent, 60 parts of MEK, and 2.5 parts of an azo-based radical polymerization initiator (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: V-65, 2,2'-azobis(2,4-dimethylvaleronitrile)) was placed in a dropping funnel, and the monomer mixture in the reaction vessel was heated to 65°C while being stirred under a nitrogen atmosphere, and the mixture in the dropping funnel was dropped over 3 hours. After 2 hours had elapsed at 65° C. from the end of the dropwise addition, a solution in which 0.3 parts of the polymerization initiator was dissolved in 5 parts of MEK was added, and the mixture was further aged at 65° C. for 2 hours and at 70° C. for 2 hours to obtain a solution of acrylic resin A1. The results are shown in Table 1.

Production Example I-2 (Production of Acrylic Resin A2)
Acrylic resin A2 was obtained in the same manner as in Production Example I-1, except that the conditions in Production Example I-1 were changed to those shown in Table 1. The results are shown in Table 1.

Production Examples II-1 to II-7 (Production of Composite Resin)
Trimellitic anhydride, fumaric acid, and raw material monomers for polyester resin other than acrylic resin, an esterification catalyst, and an esterification promoter shown in Table 2 were placed in a 10 L four-neck flask equipped with a thermometer, a stainless steel stirring rod, a downflow condenser, and a nitrogen inlet tube, and the temperature was raised to 235° C. in a mantle heater in a nitrogen atmosphere, and polycondensation was carried out at 235° C. for 10 hours.
Next, after lowering the temperature to 200° C., trimellitic anhydride, fumaric acid, and acrylic resin A1 or A2 obtained by drying the polymer solution obtained in Production Example I-1 or I-2 under reduced pressure were added, and the reaction was carried out at 200° C. and 8.0 kPa until the softening point shown in Table 2 was reached, thereby obtaining composite resins H1 to H7. The results are shown in Table 2.

Production Examples III-1 to III-4 (Production of Polyester Resins P1 to P4)
In a 10 L four-neck flask equipped with a nitrogen inlet tube, a stirrer, and a thermocouple, raw material monomers other than trimellitic anhydride and fumaric acid, an esterification catalyst, and an esterification co-catalyst shown in Table 3 were placed, and the temperature was raised to 235° C. under a nitrogen atmosphere, and polycondensation was carried out at 235° C. for 10 hours.
Next, after lowering the temperature to 200° C., trimellitic anhydride and fumaric acid shown in Table 1 were added and reacted at 200° C. for 1 hour. Next, the reaction was continued at 200° C. and 8 kPa until the softening point shown in Table 3 was reached, to obtain polyester resins P1 to P4. The results are shown in Table 3.

Comparative Production Example III-1
The raw material monomers, esterification catalyst, and polymerization inhibitor shown in Table 3 were placed in a 10 L four-neck flask equipped with a nitrogen inlet tube, a stirrer, and a thermocouple, and the temperature was raised to 210° C. over 10 hours under a nitrogen atmosphere. Polycondensation was then carried out at 210° C. for 1 hour, and the reaction was continued at 40 kPa until the softening point shown in Table 3 was reached, to obtain polyester resin P5. The results are shown in Table 3.

Preparation Examples I-1 to I-2 (Preparation of Acrylic Resin Aqueous Dispersions 1 and 2)
The acrylic resin A1 solution obtained in Production Example I-1 was added with MEK to prepare a solid content of 40%. 250 parts of the obtained resin solution were placed in a 2L four-neck flask equipped with a nitrogen inlet tube, a reflux condenser, a stirrer (manufactured by Shinto Scientific Co., Ltd., product name: Three-One Motor BL300) and a thermocouple, and stirred at 25°C. Next, a 48% aqueous sodium hydroxide solution in the amount shown in Table 4 was added and stirred for 30 minutes, and then the entire amount of ion-exchanged water shown in Table 4 was dropped at 25°C under stirring at a rate of 20mL/min. Next, the temperature was raised to 60°C, and MEK was distilled off while gradually reducing the pressure from 80kPa to 30kPa, and some water was further distilled off. After cooling to 25°C, ion-exchanged water was added, and the mixture was filtered using a 25 mL syringe (manufactured by Terumo Corporation) equipped with a filter having a pore size of 5 µm (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) to obtain acrylic resin aqueous dispersions 1 and 2 (solid content concentration: 30%).
The results are shown in Table 4.

Preparation Example II-1 (Preparation of Water-Based Dispersion 1 of Pigment-Containing Crosslinked Composite Resin Particles)
66.7 parts of the composite resin H1 obtained in Production Example II-1 was dissolved in 198.6 parts of MEK, and 3.4 parts of a 48% aqueous sodium hydroxide solution (neutralization degree of the composite resin: 60 mol%) as a neutralizing agent and 390.5 parts of ion-exchanged water were added, and the mixture was stirred and mixed for 15 minutes at 1,500 rpm using a disper blade at 10° C. to 15° C. Next, 100 parts of carbon black (manufactured by Cabot Corporation, product name: Monarch 717) was added, and the mixture was stirred and mixed for 2 hours at 6,500 rpm using a disper blade at 10° C. to 15° C.
The obtained dispersion liquid was filtered through a 200 mesh filter, diluted with 36.1 parts of ion-exchanged water, and then subjected to a dispersion treatment at a pressure of 150 MPa using a high-pressure homogenizer (manufactured by Microfluidics, product name: Microfluidizer (model: M-110K)).
The entire amount of the obtained dispersion was placed in a 2 L eggplant flask, ion-exchanged water was added so that the solid concentration became 15%, and the organic solvent was removed by keeping the temperature at 32° C. and a pressure of 0.09 MPa (abs) for 3 hours at a rotation speed of 50 r/min using a rotary distillation apparatus (manufactured by Tokyo Rikakikai Co., Ltd., product name: Rotary Evaporator N-1000S) in a warm bath adjusted to 32° C. The temperature of the warm bath was further adjusted to 62° C., the pressure was reduced to 0.07 MPa (abs), and the mixture was concentrated until the solid concentration became 25%, to obtain a concentrate.

The concentrate obtained was placed in a 500 mL angle rotor and centrifuged at 3,660 r/min for 20 minutes using a high-speed cooling centrifuge (Hitachi Koki Co., Ltd., product name: himac CR22G, set temperature 20°C). The liquid layer was then filtered through a membrane filter with a pore size of 5 μm (Sartorius, product name: Minisart) and diluted with water to a solids concentration of 22%. The amount of aqueous dispersion shown in Table 5 was placed in a screw-top glass bottle, a crosslinking agent (trimethylolpropane polyglycidyl ether, Nagase Chemtex Co., Ltd., product name: Denacol EX-321L) was added, the bottle was sealed, and the bottle was heated at 70°C for 5 hours while stirring with a stirrer. After that, the temperature was lowered to room temperature and the solids content was adjusted to 22% with ion-exchanged water. The mixture was filtered using a 25 mL syringe (Terumo Corporation) equipped with a 5 μm pore size filter (acetyl cellulose membrane, outer diameter: 2.5 cm, Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain aqueous dispersion 1 of pigment-containing crosslinked composite resin particles (solids concentration: 22%, pigment: 13%, polymer: 9%, average particle size: 98.4 nm). The results are shown in Table 5.

Preparation Examples II-2 to II-7 (Preparation of Water-Based Dispersions 2 to 7 of Pigment-Containing Crosslinked Composite Resin Particles)
Aqueous dispersions 2 to 7 of pigment-containing crosslinked composite resin particles were obtained in the same manner as in Preparation Example II-1, except that the conditions in Preparation Example II-1 were changed to those shown in Table 5. The results are shown in Table 5.

Preparation Example II-8 (Preparation of Water-Based Dispersion 8 of Pigment-Containing Crosslinked Composite Resin Particles)
66.7 parts of polyester resin P1 obtained in Production Example III-1 was dissolved in 198.6 parts of MEK, and 1.2 parts of a 48% aqueous sodium hydroxide solution (neutralization degree: 60 mol%) as a neutralizing agent and 390.5 parts of ion-exchanged water were further added, followed by stirring and mixing for 15 minutes at 1,500 rpm using a disper blade at 10 to 15° C. Next, 100 parts of carbon black (manufactured by Cabot Corporation, product name: Monarch 717) was added, followed by stirring and mixing for 2 hours at 6,500 rpm using a disper blade at 10° C. to 15° C.
To the resulting mixture, 55.6 parts of the acrylic resin aqueous dispersion 1 (solid content: 30%) obtained in Preparation Example I-1, 7.5 parts of MEK, and 16.3 parts of ion-exchanged water were added to obtain a pigment mixture.
The resulting pigment mixture was filtered through a 200 mesh filter, diluted with 36.1 parts of ion-exchanged water, and then subjected to a dispersion treatment at a pressure of 150 MPa using a high-pressure homogenizer (manufactured by Microfluidics, product name: Microfluidizer (model: M-110K)).
The entire amount of the obtained dispersion was placed in a 2 L eggplant flask, ion-exchanged water was added so that the solid concentration became 15%, and the organic solvent was removed by keeping the temperature at 32° C. and a pressure of 0.09 MPa (abs) for 3 hours at a rotation speed of 50 r/min using a rotary distillation apparatus (manufactured by Tokyo Rikakikai Co., Ltd., product name: Rotary Evaporator N-1000S) in a warm bath adjusted to 32° C. The temperature of the warm bath was further adjusted to 62° C., the pressure was reduced to 0.07 MPa (abs), and the mixture was concentrated until the solid concentration became 25%, to obtain a concentrate.

The obtained concentrate was placed in a 500 mL angle rotor and centrifuged at 3,660 r/min for 20 minutes using a high-speed refrigerated centrifuge (manufactured by Hitachi Koki Co., Ltd., product name: himac CR22G, set temperature 20° C.), and the liquid layer was then filtered through a membrane filter having a pore size of 5 μm (manufactured by Sartorius, product name: Minisart) and diluted with water to a solid concentration of 22%, to obtain an aqueous dispersion of pigment-containing composite resin particles (neutralization degree of pigment-containing composite resin particles: 60%).
100 parts of the obtained dispersion was taken in a screw-top glass bottle, a crosslinking agent (trade name: Denacol EX-321L) was added, the bottle was sealed, and the bottle was heated at 70°C for 5 hours while stirring with a magnetic stirrer. After that, the temperature was lowered to room temperature, and ion-exchanged water was added to adjust the solid content concentration to 22%. The mixture was filtered with a 25 mL syringe (manufactured by Terumo Corporation) equipped with a filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) having a pore size of 5 μm, to obtain an aqueous dispersion 8 of pigment-containing crosslinked composite resin particles (solid content concentration: 22%, pigment: 11.7%, polymer: 10.3% (polyester resin (A) segment: 8.23%, (meth)acrylic resin (B) segment: 2.06%), average particle size of pigment-containing crosslinked composite resin particles: 103.1 nm). The results are shown in Table 6.

Preparation Examples II-9 to II-12 (Preparation of Water-Based Dispersions 9 to 12 of Pigment-Containing Crosslinked Composite Resin Particles)
Aqueous dispersions 9 to 12 of pigment-containing crosslinked composite resin particles were obtained in the same manner as in Preparation Example II-8, except that the conditions in Preparation Example II-8 were changed to those shown in Table 6. The results are shown in Table 6.

Preparation Example II-13 (Preparation of Water-Based Dispersion 13 of Pigment-Containing Composite Resin Particles)
After carrying out the same procedures as in Preparation Example II-10 up to centrifugation, the liquid layer was filtered through a membrane filter (manufactured by Sartorius, product name: Minisart) having a pore size of 5 μm without carrying out a crosslinking treatment, and the liquid layer was diluted with water to obtain an aqueous dispersion 13 of pigment-containing composite resin particles (solid concentration: 22%, pigment: 12%, polymer: 10%, average particle size of pigment-containing composite resin particles: 101.6 nm). The results are shown in Table 6.

Comparative Preparation Examples II-1 to II-3 (Preparation of Water-Based Dispersions 21 to 23 of Pigment-Containing (Crosslinked) Composite Resin Particles)
Using 66.7 parts of Resin P5 obtained in Comparative Production Example III-1, the same procedure as in Preparation Example II-8 was repeated except that the resin type and various blending amounts were changed to those shown in Table 6, and the solid content was diluted with water to 22%, thereby obtaining an aqueous dispersion 21 (solid content: 22%, pigment: 13.2%, polymer: 8.8%), an aqueous dispersion 22 (solid content: 22%, pigment: 11.6%, polymer: 10.4%), and an aqueous dispersion 23 (solid content: 22%, pigment: 13.2%, polymer: 8.8%) of pigment-containing (crosslinked) composite resin particles.
The results are shown in Table 6.

Example 1 (Preparation of Water-Based Ink 1)
A 100 mL screw tube was charged with 10.0 parts of propylene glycol, 15.0 parts of diethylene glycol monoisobutyl ether (iBDG), 1.0 part of an acetylene glycol surfactant (manufactured by Nissin Chemical Industry Co., Ltd., product name: Olfine E1010), 1.0 part of a polyether-modified silicone surfactant (PEG-11 methyl ether dimethicone, manufactured by Shin-Etsu Chemical Co., Ltd., product name: KF-6011), and 42.9 parts of ion-exchanged water, and the mixture was stirred at room temperature for 15 minutes using a magnetic stirrer to obtain a mixed solution.
Next, 31.0 parts of the aqueous dispersion 1 of the pigment-containing crosslinked composite resin particles obtained in Preparation Example II-1 was added to the above mixed solution while stirring with a magnetic stirrer (total 100 parts). Then, the mixture was filtered through a filter having a pore size of 5.0 μm (manufactured by Sartorius Stedim Biotech, product name: Minisart) to obtain an aqueous ink 1 (solid content concentration: 6.8%, pigment: 4.0%, polymer: 2.4% (polyester resin (A) segment: 1.9%, (meth)acrylic resin (B) segment: 0.5%)).

Examples 2 to 13 and Comparative Examples 1 to 3 (Preparation of Water-Based Inks 2 to 13 and 21 to 23)
Water-based inks 2 to 13 and 21 to 23 (pigment: 4.0%) were obtained in the same manner as in Example 1, except that the conditions in Example 1 were changed to those shown in Table 7.
Using each of the obtained water-based inks, storage stability, resin film adhesion after long-term storage, print density, and solvent (alcohol) resistance were evaluated by the following methods. The results are shown in Table 7.
The amount of each component in Table 7 is the effective amount (solid content).

(1) Evaluation of storage stability 1 (average particle size change rate) The water-based ink was stored in a sealed container in a thermostatic chamber at 60°C, and after 28 days, it was removed and the average particle size after storage was measured. The average particle size change rate after storage at 60°C for 28 days was calculated using the following formula (rounded down to the nearest whole number), and the storage stability was evaluated according to the following evaluation criteria.
Rate of change in average particle size (%) = [(average particle size after storage/average particle size before storage) - 1] x 100
(Evaluation Criteria)
A: The absolute value of the rate of change in average particle size is less than 5%.
B: The absolute value of the rate of change in average particle size is 5% or more and less than 15%.
C: The absolute value of the rate of change in average particle size is 15% or more and less than 30%. D: The absolute value of the rate of change in average particle size is 30% or more and less than 50%.
E: The absolute value of the rate of change in average particle size is 50% or more, or the water-based ink has lost fluidity and is not in a state where the average particle size can be measured.
If the evaluation result is B or above, there is no problem in practical use.

(2) Evaluation of storage stability 2 (pH ratio) The water-based ink was stored in a sealed container in a constant temperature room at 60° C., and after 28 days, it was taken out and the pH of the water-based ink was measured. The ratio of the pH of the water-based ink after storage to the pH of the water-based ink before storage (pH after storage/pH before storage) was calculated.
The closer the pH ratio is to 1, the better the storage stability is, and if it is 0.8 or higher, there is no problem in practical use.

(3) Evaluation of resin film (PVC) adhesion after long-term storage The aqueous ink obtained above after 28 days of storage at 60°C was filled into an inkjet printer (manufactured by Ricoh Co., Ltd., product name: IPSiO GX 2500, piezoelectric type), and an A4 solid image was printed on a polyvinyl chloride (PVC) film (product name: 3M ^TM Scotchcal ^TM Graphic Film IJ40-10R (white gloss)). Then, it was dried for 5 minutes in a dryer at 80°C, and left to stand for 1 day in an environmental chamber at room temperature of 25°C and relative humidity of 50%, to obtain a print for evaluation.
A cutter knife was used to make 11 vertical and horizontal cuts (1 mm apart) on the printed surface of the evaluation print that reached the PVC film base, creating a grid of 100 squares. Cellotape (registered trademark) (product name: CT15) was then attached to the grid, and the tape was peeled off at an angle of 90° at a speed of 10 cm/sec, and the number of squares that did not peel off was visually confirmed.
Table 7 shows the number of squares that did not peel off per 100 squares.
The greater the number of squares that are not peeled off, the better the adhesion to the resin film (PVC). If the number is 70 or more, there is no problem in practical use.

(4) Evaluation of print density after long-term storage A print for evaluation was obtained in the same manner as in the evaluation of adhesion in (3) above. The print obtained was measured at five points, the center and four corners, using a Macbeth densitometer (manufactured by GretagMacbeth, product number: Spectroeye), and the average value was calculated.
The larger the value, the better the print density of the ink after long-term storage, and a value of 1.6 or more poses no problem in practical use.

(5) Evaluation of Solvent (Alcohol) Resistance After Long-Term Storage Printed materials for evaluation were obtained in the same manner as in the evaluation of adhesion in (3) above.
Ethanol was diluted with ion-exchanged water to prepare aqueous ethanol solutions with different mass concentrations of ethanol for evaluation (aqueous solutions were prepared in 10% increments in the range of 0 to 100%). Next, a cotton swab impregnated with the aqueous ethanol solution (each mass concentration) was used to gently rub the printed surface back and forth 10 times at a speed of one back and forth per second with a width of 2 to 3 cm. The state of the rubbed printed surface was visually observed, and the highest mass concentration of ethanol at which no changes such as scratches, peeling, or cloudiness were observed on the printed surface is shown in Table 7 as an index of solvent (alcohol) resistance.
The higher the mass concentration of ethanol, the better the alcohol resistance. If it is 50% or more, there is no problem in practical use, but it is preferably 60% or more.

From Table 7, it can be seen that the water-based inks obtained in Examples 1 to 13 have superior storage stability in a hydrophobic system, and are superior in adhesion of the ink to a resin film after long-term storage, print density of printed matter, and solvent resistance (alcohol) compared to the water-based inks obtained in Comparative Examples 1 to 3.
The water-based inks obtained in Comparative Examples 1 and 2 did not contain 3-methyl-1,5-pentanediol in the alcohol component constituting the polyester resin (A), and the water-based ink obtained in Comparative Example 3 did not contain a (meth)acrylic resin (B) segment, so they were inferior in storage stability, adhesion of the ink to the resin film after long-term storage, print density of printed matter, and solvent (alcohol) resistance.

Claims (7)

An aqueous dispersion of pigment-containing composite resin particles,
The composite resin contains a polyester resin (A) segment and a (meth)acrylic resin (B) segment, the alcohol component constituting the polyester resin (A) contains at least 3-methyl-1,5-pentanediol, and the content of 3-methyl-1,5-pentanediol in the alcohol component is 30 mol % or more and 85 mol % or less . An aqueous dispersion of composite resin particles containing the pigment according to claim 1, in which the content of the (meth)acrylic acid-derived constituent units constituting the (meth)acrylic resin (B) segment is 10% by mass or more and 50% by mass or less of all monomer constituent units constituting the (meth)acrylic resin (B) segment. An aqueous dispersion of composite resin particles containing the pigment according to claim 1 or 2, in which the acid value of the (meth)acrylic resin (B) is 150 mg KOH/g or more and 300 mg KOH/g or less. An aqueous dispersion of composite resin particles containing the pigment according to any one of claims 1 to 3, in which the mass ratio [(A)/(B)] of the polyester resin (A) segment to the (meth)acrylic resin (B) segment is 50/50 or more and 98/2 or less. An aqueous dispersion of composite resin particles containing the pigment according to any one of claims 1 to 4, in which the composite resin is a crosslinked composite resin particle formed by crosslinking with a crosslinking agent (C). An aqueous dispersion of composite resin particles containing the pigment according to any one of claims 1 to 5, for use in inkjet recording. A water-based ink containing a water-based dispersion of composite resin particles containing the pigment according to any one of claims 1 to 6 and a water-soluble organic solvent.