JP2023068767A - Inkjet ink and method for producing inkjet ink - Google Patents

Abstract

To provide an inkjet ink which is excellent in discharge stability and storage stability and can form an image excellent in fixability while suppressing occurrence of nozzle clogging.SOLUTION: The inkjet ink contains colored particles and an aqueous medium. The colored particles contain a carboxy group-containing vinyl resin and pigment particles dispersed in the carboxy group-containing vinyl resin. The pigment particles contain a pigment and a specific resin. The specific resin has a ring-unopened oxazoline group and an amide ester group.SELECTED DRAWING: Figure 1

Description

The present invention relates to an inkjet ink and a method for producing the inkjet ink.

Inkjet inks are required to be excellent in ejection stability and storage stability, and to be capable of forming images with excellent fixability while suppressing the occurrence of nozzle clogging. In response to such demands, for example, modified resin particles obtained by reacting resin particles containing a pigment with a compound having a reactive group that reacts with the functional groups of the resin particles in an aqueous medium are included. An inkjet ink has been proposed (Patent Document 1). The inkjet ink described above is said to be capable of forming an image with excellent fixability.

WO2016/104505

However, the inkjet ink described in Patent Literature 1 cannot satisfy all of ejection stability, storage stability, suppression of nozzle clogging, and fixability of formed images.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an inkjet ink which is excellent in ejection stability and storage stability and capable of forming an image with excellent fixability while suppressing the occurrence of nozzle clogging. That is.

The inkjet ink according to the present invention contains colored particles and an aqueous medium. The colored particles include a carboxy group-containing vinyl resin and pigment particles dispersed in the carboxy group-containing vinyl resin. The pigment particles contain a pigment and a specific resin. The specific resin has an unopened oxazoline group and an amide ester group.

A method for producing an inkjet ink according to the present invention is a method for producing an inkjet ink containing colored particles and an aqueous medium, wherein a pigment and an unopened ring oxazoline group-containing resin are subjected to a salt milling treatment to produce pigment particles. a salt milling step of obtaining the above; a melt-kneading step of obtaining a melt-kneaded product by melt-kneading the pigment particles and the carboxyl group-containing vinyl resin; a pulverizing step of obtaining a pulverized product by pulverizing the melt-kneaded product; and a dispersing step of dispersing the pulverized material in the aqueous medium.

INDUSTRIAL APPLICABILITY The inkjet ink and the method for producing the inkjet ink according to the present invention can provide an inkjet ink that is excellent in ejection stability and storage stability, and capable of forming an image with excellent fixability while suppressing the occurrence of nozzle clogging.

FIG. 2 is a diagram showing an example of colored particles contained in ink according to the present invention; FIG. 2 is a diagram showing another example of colored particles different from FIG. 1;

Embodiments of the present invention will be described below. In the following, unless otherwise specified, the measured value of the volume median diameter (D ₅₀ ) is measured using a dynamic light scattering particle size distribution analyzer ("Zetasizer Nano ZS" manufactured by Malvern). is the value In this specification, acryl and methacryl may be collectively referred to as "(meth)acryl".

The acid value can be determined according to the method described in JIS (Japanese Industrial Standard) K0070-1992.

The glass transition point (Tg) was measured according to "JIS (Japanese Industrial Standard) K7121-2012" using a differential scanning calorimeter (for example, "DSC-60" manufactured by Shimadzu Corporation) unless otherwise specified. value. In the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) measured with a differential scanning calorimeter, the temperature at the inflection point caused by the glass transition (specifically, the extrapolated line of the baseline and the falling edge The temperature at the intersection of the line with the extrapolated line) corresponds to Tg (glass transition point).

Unless otherwise specified, the number average primary particle diameter of the powder is the circle-equivalent diameter of the primary particles measured using a scanning electron microscope (Heywood diameter: a circle having the same area as the projected area of the primary particles diameter). The number average primary particle diameter of the powder is, for example, the number average value of equivalent circle diameters of 100 primary particles. The number average primary particle size of particles refers to the number average primary particle size of particles in powder unless otherwise specified.

Each component described in this specification may be used alone or in combination of two or more.

<First embodiment: inkjet ink>
The inkjet ink (hereinafter sometimes referred to as ink) according to the first embodiment of the present invention contains colored particles and an aqueous medium. The colored particles include a carboxy group-containing vinyl resin and pigment particles dispersed in the carboxy group-containing vinyl resin. Pigment particles include a pigment and a specific resin. The specific resin has an unopened oxazoline group and an amide ester group.

Applications of the ink of the present invention are not particularly limited, but for example, it can be used for image formation on permeable or non-permeable recording media. A permeable recording medium has excellent ink permeability. Permeable recording media include, for example, printing paper and fiber-based media (eg, fabric). Examples of printing paper include plain paper, copy paper, recycled paper, thin paper, thick paper, and glossy paper.

A non-permeable recording medium is inferior to a permeable recording medium in ink permeability. In the non-permeable recording medium, the absorption amount of the aqueous medium is, for example, 1.0 g/m ² or less. Impermeable recording media include, for example, resin recording media, metal recording media, and glass recording media. Examples of resin recording media include resin sheets and resin films. The resin contained in the resin-made recording medium is preferably a thermoplastic resin. Specific resins include, for example, polyethylene, polypropylene, polyvinyl chloride, and polyethylene terephthalate (PET). Examples of resin-made recording media include OPP films. When an image is formed on a resin recording medium with the ink of the present invention, the surface (printing surface) of the recording medium may be subjected to corona treatment.

Since the ink of the present invention has the above-described structure, it has excellent ejection stability and storage stability, and can form an image with excellent fixability while suppressing the occurrence of nozzle clogging. The reason is presumed as follows. The ink of the present invention contains colored particles as a coloring agent. The colored particles have a structure in which pigment particles are dispersed in a carboxy group-containing vinyl resin. Carboxy group-containing vinyl resins tend to have excellent affinity with aqueous media. The colored particles can be stably dispersed in an aqueous medium by containing the carboxy group-containing vinyl resin having the properties described above. As a result, the ink of the present invention can suppress the occurrence of nozzle clogging and is excellent in ejection stability.

Pigment particles also include a pigment and a specific resin. Pigment particles have, for example, a structure in which fine particles of pigment are coated with a specific resin, or a structure in which fine particles of pigment are dispersed in a specific resin. The specific resin contained in the pigment particles is covalently bonded to the carboxy group-containing vinyl resin via an amide ester group, for example. The specific resin suppresses detachment of the pigment particles from the coloring particles by covalently bonding with the carboxy group-containing vinyl resin. In the ink of the present invention, since the pigment particles are less likely to be detached from the colored particles, aggregation of the detached pigment particles in the aqueous medium can be suppressed. Furthermore, carboxy group-containing vinyl resins are chemically stable compared to other resins having carboxy groups (eg, polyester resins). Therefore, the ink of the present invention has excellent storage stability. Furthermore, after the ink of the present invention has landed on a recording medium, the carboxyl group-containing vinyl resin functions like a binder resin and protects the pigment particles by covering them. Therefore, the ink of the present invention can form an image having excellent scratch resistance. The details of the ink of the present invention are described below.

[Colored particles]
The colored particles include a carboxy group-containing vinyl resin and pigment particles dispersed in the carboxy group-containing vinyl resin. The colored particles preferably contain only the carboxy group-containing vinyl resin and the pigment particles. In the colored particles, the total content of the carboxy group-containing vinyl resin and the pigment particles is preferably 90% by mass or more, more preferably 100% by mass. _D50 of the colored particles is preferably 70 nm or more and 130 nm or less.

In the ink of the present invention, the content of the colored particles is preferably 3.0% by mass or more and 20.0% by mass or less, more preferably 6.0% by mass or more and 12.0% by mass or less. By setting the content ratio of the colored particles to 3.0% by mass or more, the ink of the present invention can form an image having a desired image density. By setting the content ratio of the colored particles to 20.0% by mass or less, the ink of the present invention can more reliably suppress the occurrence of nozzle clogging and exhibit even better ejection stability.

The colored particles will be described below with reference to the drawings. FIG. 1 shows colored particles 1, which are an example of colored particles contained in the ink of the present invention. The colored particles 1 include a large number of aggregated pigment particles 2 and a carboxy group-containing vinyl resin 3 covering the pigment particles 2 . In colored particles 1 , pigment particles 2 are completely coated with carboxy group-containing vinyl resin 3 .

FIG. 2 shows colored particles 11 which are another example of the colored particles shown in FIG. The colored particles 11 contain a relatively small number of pigment particles 12 and a carboxy group-containing vinyl resin 13 covering the pigment particles 12 . In the colored particles 11 , the pigment particles 12 are completely covered with the carboxy group-containing vinyl resin 13 .

The colored particles have been described above with reference to the drawings. However, in the ink of the present invention, the colored particles may have a structure different from that of the colored particles 1 shown in FIG. 1 and the colored particles 11 shown in FIG. Specifically, the number of pigment particles contained in one colored particle is arbitrary. Moreover, in the colored particles, the pigment particles may not be completely coated with the carboxy group-containing vinyl resin. That is, part of the pigment particles may be exposed on the surface of the coloring particles. In addition, in the colored particles, a plurality of pigment particles may be dispersed in the carboxy group-containing vinyl resin while being separated from each other.

(pigment particles)
Pigment particles include a pigment and a specific resin. The pigment particles preferably contain only the pigment and the specific resin, but may further contain other components (eg, unopened ring oxazoline group-containing resin). Pigment particles WHEREIN: As a total content rate of a pigment and specific resin, 90 mass % or more is preferable, and 100 mass % is more preferable. Although the number average primary particle diameter of the pigment particles is not particularly limited, it is, for example, 10 nm or more and 50 nm or less.

The content of the pigment particles in the colored particles is preferably 10% by mass or more and 60% by mass or less, more preferably 25% by mass or more and 40% by mass or less. By setting the content of the pigment particles to 10% by mass or more, the ink of the present invention can form an image having a desired image density. By setting the content ratio of the pigment particles to 60% by mass or less, it is possible to more reliably suppress detachment of the pigment particles from the colored particles.

(pigment)
Pigments include, for example, yellow pigments, orange pigments, red pigments, blue pigments, purple pigments, and black pigments. Examples of yellow pigments include C.I. I. Pigment Yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193). Examples of orange pigments include C.I. I. Pigment Orange (34, 36, 43, 61, 63, and 71). Examples of red pigments include C.I. I. Pigment Reds (122 and 202). Examples of blue pigments include C.I. I. Pigment Blue (15, more specifically 15:3). Examples of purple pigments include C.I. I. Pigment Violet (19, 23, and 33). Examples of black pigments include C.I. I. Pigment Black (7) (carbon black) may be mentioned. Examples of carbon black include acidic carbon black and neutral carbon black.

Acidic carbon black is preferred as the pigment. Acidic carbon black can form a covalent bond with a specific resin via an amide ester group. Therefore, by using acidic carbon black as the pigment, the pigment, the specific resin, and the carboxyl group-containing vinyl resin are integrated through covalent bonds. This makes it possible to more reliably prevent the pigment particles from detaching from the colored particles.

The pigment content in the ink of the present invention is preferably 0.5% by mass or more and 10.0% by mass or less, more preferably 2.0% by mass or more and 6.0% by mass or less. By setting the content of the pigment in the ink of the present invention to 2.0% by mass or more, the ink of the present invention can form an image having a desired image density. By setting the content of the pigment in the ink of the present invention to 2.0% by mass or more and 10.0% by mass or less, it is possible to suppress detachment of the pigment from the colored particles.

The content of the pigment in the pigment particles is preferably 70.0% by mass or more and 99.0% by mass or less, more preferably 85.0% by mass or more and 95.0% by mass or less. By setting the content of the pigment in the pigment particles to 70.0% by mass or more and 99.0% by mass or less, the ink of the present invention can form an image having a desired image density. By setting the content of the pigment in the pigment particles to 99.0% by mass or less, it is possible to suppress detachment of the pigment from the colored particles.

(specific resin)
The specific resin has an unopened oxazoline group and an amide ester group. The specific resin preferably has a repeating unit (1) represented by the following general formula (A) and a repeating unit (2) represented by the following general formula (B). Repeating unit (1) has an unopened oxazoline group. Repeating unit (2) has an amide ester group.

In general formula (A), R ¹ represents a hydrogen atom or an alkyl group having from 1 to 10 carbon atoms which may be substituted with a phenyl group. In general formula (B), R ² represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms which may be substituted with a phenyl group. * represents a bonding site with an atom contained in a carboxy group-containing vinyl resin or pigment (eg, acidic carbon black).

In general formula (A) or (B), the alkyl group having 1 to 10 carbon atoms represented by R ¹ or R ² includes, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n -butyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, 1,2-dimethylpropyl group, linear or branched hexyl group, linear or branched A branched heptyl group, a straight or branched octyl group, a straight or branched nonyl group, and a straight or branched decyl group are included.

In general formula (A), R ¹ preferably represents a hydrogen atom, a methyl group, an ethyl group or an isopropyl group. In general formula (B), R ² preferably represents a hydrogen atom, a methyl group, an ethyl group or an isopropyl group.

The specific resin may further have a repeating unit (3) derived from a vinyl compound. Examples of vinyl compounds include ethylene, propylene, butadiene, vinyl chloride, (meth)acrylic acid, (meth)acrylic acid esters (preferably (meth)acrylic acid alkyl esters), acrylonitrile, and styrene.

The specific resin preferably further has, as the repeating unit (3), a repeating unit derived from a (meth)acrylic acid alkyl ester or a repeating unit derived from styrene.

The specific resin preferably has only repeating units (1), repeating units (2) and repeating units (3). However, the specific resin may further have repeating units other than the repeating unit (1), the repeating unit (2) and the repeating unit (3).

The content of the specific resin in the ink of the present invention is preferably 0.05% by mass or more and 2.0% by mass or less, more preferably 0.1% by mass or more and 0.7% by mass or less. By setting the content ratio of the specific resin in the ink of the present invention to 0.05% by mass or more and 2.0% by mass or less, the ink of the present invention can further reliably suppress detachment of the pigment particles from the colored particles. .

The content of the specific resin in the pigment particles is preferably 1.0% by mass or more and 30.0% by mass or less, more preferably 5.0% by mass or more and 15.0% by mass or less. By setting the content ratio of the specific resin in the pigment particles to 1.0% by mass or more and 30.0% by mass or less, it is possible to further reliably suppress detachment of the pigment particles from the colored particles.

[Carboxy group-containing vinyl resin]
A carboxy group-containing vinyl resin is a vinyl resin having a carboxy group. A vinyl resin is a polymer having repeating units derived from a vinyl group-containing monomer. The carboxy group-containing vinyl resin exists, for example, on the surface of the colored particles. A carboxy group-containing vinyl resin has, for example, a repeating unit derived from a carboxy group-containing monomer. Carboxy group-containing monomers include, for example, (meth)acrylic acid and unsaturated carboxylic acids. Specific carboxy group-containing vinyl resins include, for example, (meth)acrylic resins and styrene-(meth)acrylic resins, with styrene-(meth)acrylic resins being preferred.

(Styrene-(meth)acrylic resin)
A styrene-(meth)acrylic resin is a resin having styrene units, repeating units derived from (meth)acrylic acid alkyl esters, and repeating units derived from (meth)acrylic acid. The styrene-(meth)acrylic resin preferably further has a repeating unit derived from a (meth)acrylic acid aryl ester.

(Meth)acrylic acid alkyl esters include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate and butyl (meth)acrylate. Examples of (meth)acrylic acid aryl esters include phenyl (meth)acrylate and benzyl (meth)acrylate.

In the styrene-(meth)acrylic resin, the content of styrene units relative to all repeating units is preferably 15.0% by mass or more and 60.0% by mass or less, more preferably 20.0% by mass or more and 45.0% by mass or less. preferable.

In the styrene-(meth)acrylic resin, the content ratio of repeating units derived from (meth)acrylic acid to all repeating units is preferably 2.0% by mass or more and 20.0% by mass or less, and 6.0% by mass or more. 14.0% by mass or less is more preferable. By setting the content of repeating units derived from (meth)acrylic acid to 2.0% by mass or more and 20.0% by mass or less, it is possible to impart an appropriate acid value to the carboxy group-containing vinyl resin.

In the styrene-(meth)acrylic resin, the content ratio of the repeating unit derived from the (meth)acrylic acid alkyl ester to the total repeating units is preferably 15.0% by mass or more and 65.0% by mass or less, and 25.0% by mass. % or more and 55.0 mass % or less is more preferable.

In the styrene-(meth)acrylic resin, the content of the repeating unit derived from the (meth)acrylic acid aryl ester relative to the total repeating units is preferably 10.0% by mass or more and 50.0% by mass or less, and 25.0% by mass. % or more and 35.0 mass % or less is more preferable.

As raw material monomers for the styrene-(meth)acrylic resin, the following combination (I) or (II) is preferred, and combination (Ia), (Ib) or (IIa) is more preferred.
Combination (I): styrene, (meth) acrylic acid, methyl (meth) acrylate, n-butyl (meth) acrylate and benzyl (meth) acrylate Combination (II): styrene, (meth) acrylic acid, (meth) ) Methyl acrylate and n-butyl (meth)acrylate Combination (Ia): styrene, acrylic acid, methyl methacrylate, n-butyl acrylate, and benzyl methacrylate Combination (Ib): styrene, methacrylic acid, methacrylic acid Methyl, n-butyl acrylate and benzyl methacrylate Combination (IIa): Styrene, acrylic acid, methyl methacrylate and n-butyl acrylate

The acid value of the carboxy group-containing vinyl resin is preferably 60 mgKOH/g or more and 120 mgKOH/g or less, more preferably 60 mgKOH/g or more and 100 mgKOH/g or less, and still more preferably 70 mgKOH/g or more and 95 mgKOH/g or less. By setting the acid value of the carboxyl group-containing vinyl resin to 60 mgKOH/g or more, it is possible to more reliably suppress detachment of the pigment particles from the colored particles. By setting the acid value of the carboxy group-containing vinyl resin to 120 mgKOH/g or less, the storage stability of the ink of the present invention can be further optimized.

The glass transition point of the carboxy group-containing vinyl resin is preferably 50° C. or higher and 80° C. or lower, more preferably 70° C. or higher and 80° C. or lower. By setting the glass transition point of the carboxy group-containing vinyl resin to 50° C. or higher, the storage stability of the ink of the present invention can be further optimized. By setting the glass transition point of the carboxy group-containing vinyl resin to 80° C. or lower, the fixability of the image formed by the ink of the present invention can be further optimized.

The content of the carboxy group-containing vinyl resin in the colored particles is preferably 40% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 75% by mass or less. By setting the content ratio of the carboxyl group-containing vinyl resin in the colored particles to 40% by mass or more, it is possible to more reliably suppress the separation of the pigment particles from the colored particles. By setting the content of the carboxy group-containing vinyl resin in the colored particles to 60% by mass or less, the ink of the present invention can form an image having a desired image density.

The content of the carboxy group-containing vinyl resin in the ink of the present invention is preferably 2.0% by mass or more and 15.0% by mass or less, more preferably 4.0% by mass or more and 9.0% by mass or less. By setting the content of the carboxy group-containing vinyl resin in the ink of the present invention to 2.0% by mass or more, the fixability of the image formed by the ink of the present invention can be further optimized. By setting the content ratio of the carboxy group-containing vinyl resin in the ink of the present invention to 15.0% by mass or less, the ink of the present invention exhibits even better ejection stability and more reliably prevents nozzle clogging. can be suppressed.

In the colored particles, the ratio (B/A) of the mass B of the carboxy group-containing vinyl resin to the mass A of the pigment particles is preferably 1.4 or more and 3.1 or less, more preferably 1.8 or more and 2.3 or less. . By setting the ratio (B/A) to 1.4 or more, the fixability of the image formed by the ink of the present invention can be further optimized. By setting the ratio (B/A) to 3.1 or less, the ink of the present invention can more reliably suppress the occurrence of nozzle clogging while exhibiting even better ejection stability.

[Aqueous medium]
The aqueous medium contained in the ink of the present invention is a medium containing water. The aqueous medium may function as a solvent or as a dispersion medium. Specific examples of the aqueous medium include an aqueous medium containing only water and an aqueous medium containing water and a water-soluble organic solvent.

(water)
In the ink of the present invention, the content of water is preferably 30.0% by mass or more and 80.0% by mass or less, more preferably 40.0% by mass or more and 60.0% by mass or less.

(Water-soluble organic solvent)
Examples of water-soluble organic solvents include glycol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerin and dimethylsulfoxide.

Examples of glycol compounds include ethylene glycol, 1,3-propanediol, propylene glycol, 1,2-pentanediol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3- Methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol and tetraethylene glycol.

Examples of glycol ether compounds include diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, and triethylene glycol monoethyl. Ethers, triethylene glycol monobutyl ether and propylene glycol monomethyl ether.

Lactam compounds include, for example, 2-pyrrolidone and N-methyl-2-pyrrolidone.

Nitrogen-containing compounds include, for example, 1,3-dimethylimidazolidinone, formamide and dimethylformamide.

Acetate compounds include, for example, diethylene glycol monoethyl ether acetate.

As the water-soluble organic solvent, a glycol compound is preferable, and ethylene glycol or diethylene glycol is more preferable.

The content of the water-soluble organic solvent in the ink of the present invention is preferably 10.0% by mass or more and 50.0% by mass or less, more preferably 30.0% by mass or more and 40.0% by mass or less.

[Surfactant]
The ink of the invention preferably further contains a surfactant. Surfactants allow the ink of the present invention to exert its permeability (wettability) to the recording medium. Surfactants include, for example, anionic surfactants, cationic surfactants and nonionic surfactants. A nonionic surfactant is preferred as the surfactant.

Examples of nonionic surfactants include polyoxyethylene dodecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene sorbitan monooleate ether, monodecanoyl sucrose, and ethylene oxide of acetylene glycol. adducts. As the nonionic surfactant, an ethylene oxide adduct of acetylene glycol is preferred.

The content of the surfactant in the ink of the present invention is preferably 0.05% by mass or more and 3.0% by mass or less, more preferably 0.2% by mass or more and 1.0% by mass or less.

[Other ingredients]
The ink of the present invention may further contain known additives (more specifically, for example, dissolution stabilizers, antidrying agents, antioxidants, viscosity modifiers, pH modifiers, and antifungal agents). may contain.

The ink of the present invention may contain a free resin (a resin that does not form a complex with a pigment or the like) present in an aqueous medium in a free state. When the ink of the present invention contains a large amount of free resin, the fixability of the image formed by the ink of the present invention is further optimized, but on the other hand, it is difficult for the ink of the present invention to exhibit sufficient ejection stability. tend to become From the above, the ink of the present invention preferably contains no free resin or contains a small amount of free resin. When the ink of the present invention contains a free resin, the content of the free resin with respect to the total mass of the resin components (the carboxy group-containing vinyl resin, the specific resin and the free resin) of the ink of the present invention is more than 0.0% by mass. Less than 0.0 mass % is preferred.

<Second Embodiment: Method for Producing Inkjet Ink>
A method for producing an inkjet ink according to a second embodiment of the present invention (hereinafter sometimes referred to as a method for producing an ink) will be described below. The method for producing an ink of the present invention is a method for producing an ink containing colored particles and an aqueous medium, and includes a salt milling step for obtaining pigment particles by subjecting a pigment and an unopened oxazoline group-containing resin to a salt milling treatment. a melt-kneading step of obtaining a melt-kneaded product by melt-kneading the pigment particles and the carboxyl group-containing vinyl resin; a pulverizing step of pulverizing the melt-kneaded product to obtain a pulverized product; and dispersing the pulverized product in an aqueous medium. and a dispersing step. According to the ink manufacturing method of the present invention, the ink according to the first embodiment can be manufactured easily and reliably. Details of each step will be described below.

[Salt milling process]
In this step, a salt milling treatment is performed on the pigment and the unopened oxazoline group-containing resin. In the salt milling treatment, for example, a mixture is obtained by mixing a pigment and an unopened ring oxazoline group-containing resin, a water-soluble inorganic salt, and optional additives (for example, a kneading aid). Next, the mixture is kneaded using a kneader (for example, a double-arm kneader). Next, the kneaded mixture is washed with water to remove water-soluble inorganic salts and additives, and then dried and pulverized as necessary. Pigment particles are thus obtained. Pigment particles include a pigment and an unopened oxazoline group-containing resin.

The kneading conditions are, for example, a temperature of 50° C. or higher and 100° C. or lower, a rotational speed of 1000 rpm or higher and 4000 rpm or lower, and a treatment time of 1 hour or longer and 10 hours or shorter.

(pigment)
Pigments used in this step include, for example, compounds similar to the pigments described in the first embodiment.

(Unopened oxazoline group-containing resin)
The unopened ring oxazoline group-containing resin used in this step has, for example, the repeating unit (1) described above. It is preferable that the unopened oxazoline group-containing resin further has the repeating unit (3).

As the unopened oxazoline group-containing resin, for example, "Epocross (registered trademark) WS-300" or "Epocross (registered trademark) WS-700" manufactured by Nippon Shokubai Co., Ltd. can be used. "Epocross (registered trademark) WS-300" contains a copolymer of 2-vinyl-2-oxazoline and methyl methacrylate (an unopened oxazoline group-containing resin). The mass ratio of the monomers constituting this copolymer was (2-vinyl-2-oxazoline):(methyl methacrylate)=9:1. "Epocross (registered trademark) WS-700" contains a copolymer of 2-vinyl-2-oxazoline, methyl methacrylate and butyl acrylate (unopened oxazoline group-containing resin). The mass ratio of the monomers constituting the copolymer was (2-vinyl-2-oxazoline):(methyl methacrylate):(butyl acrylate)=5:4:1. 2-vinyl-2-oxazoline is a compound represented by the following chemical formula (A-1).

The amount of the unopened ring oxazoline group-containing resin to be used is preferably 2.0 parts by mass or more and 20.0 parts by mass or less, more preferably 5.0 parts by mass or more and 12.0 parts by mass or less, relative to 100 parts by mass of the pigment. .

(Water-soluble inorganic salt)
Examples of water-soluble inorganic salts used in salt milling include sodium chloride, calcium chloride and potassium chloride, with sodium chloride being preferred. The amount of the water-soluble inorganic salt used is preferably 400 to 1,500 parts by mass, more preferably 800 to 1,200 parts by mass, based on a total of 100 parts by mass of the pigment and the unopened oxazoline group-containing resin.

(Kneading aid)
Examples of kneading aids used in salt milling include water-soluble organic solvents. Examples of the water-soluble organic solvent include compounds similar to the water-soluble organic solvent described in the first embodiment. As the kneading aid, a glycol compound is preferable, and diethylene glycol is more preferable. The amount of the kneading aid used is preferably 100 parts by mass or more and 500 parts by mass or less, more preferably 200 parts by mass or more and 300 parts by mass or less, with respect to a total of 100 parts by mass of the pigment and the unopened ring oxazoline group-containing resin.

[Melt-kneading process]
In this step, a melt-kneaded product is obtained by melt-kneading the pigment particles and the carboxy group-containing vinyl resin. In this step, the pigment particles are dispersed in the carboxy group-containing vinyl resin by melt-kneading, and the oxazoline groups of the unopened oxazoline group-containing resin contained in the pigment particles and the carboxy group-containing vinyl resin is covalently bonded with the carboxy group of As a result, at least part of the unopened oxazoline group-containing resin contained in the pigment particles is changed to a specific resin having an unopened ring oxazoline group and an amide ester group. When the pigment contained in the pigment particles contains acidic carbon black, in this step, the oxazoline groups of the unopened ring oxazoline group-containing resin contained in the pigment particles and the carboxyl groups of the pigment are separated by the high temperature during melt-kneading. Covalently bond.

In melt-kneading, for example, a melt-kneading device (eg, a single-screw or twin-screw extruder) can be used. Melt-kneading conditions may be, for example, a temperature of 120° C. or higher and 200° C. or lower.

[Pulverization process]
In this step, a pulverized material is obtained by pulverizing the melt-kneaded material. In this step, the melt-kneaded material may be coarsely pulverized to obtain a coarsely pulverized material, and then the coarsely pulverized material may be further pulverized to obtain a pulverized material. In addition, in this step, the obtained pulverized material may be subjected to a classification treatment, if necessary.

[Dispersion step]
In this step, the pulverized material is dispersed in an aqueous medium. In this step, the pulverized material may be further pulverized in order to disperse the pulverized material in the aqueous medium.

Examples of the method for dispersing the pulverized material in an aqueous medium include wet dispersion using a media type disperser or a medialess type disperser. As the aqueous medium used in this step, water is preferred. In this step, a surfactant may be added to the aqueous medium in order to uniformly disperse the pulverized material in the aqueous medium. Examples of surfactants include anionic surfactants, cationic surfactants, and nonionic surfactants, with nonionic surfactants being preferred. Specific examples of nonionic surfactants include compounds similar to the nonionic surfactants described in the first embodiment. In this step, a base may be added to the aqueous medium in order to neutralize the carboxy group-containing vinyl resin contained in the pulverized product. The amount of the base to be added is, for example, 0.8 to 1.1 times the neutralization equivalent of the carboxy group-containing vinyl resin contained in the pulverized material. Bases include, for example, sodium hydroxide.

In this step, the pulverized material may be dispersed in an aqueous medium and then filtered using a filter (for example, a filter with a pore size of 0.1 μm). Thereby, free resin and impurities can be removed. By performing such filtration, free resin is not contained or a small amount of free resin (for example, the content of free resin with respect to the total mass of resin is more than 0.0% by mass and less than 3.0% by mass). You can get the ink containing

In this step, the components may be adjusted by adding water or other components after dispersing the pulverized material in the aqueous medium. This gives an ink with the desired composition. Other ingredients include, for example, water-soluble organic solvents and surfactants. Examples of the water-soluble organic solvent and surfactant include the same compounds as the water-soluble organic solvent and surfactant described in the first embodiment. In this step, if necessary, foreign substances and coarse particles may be removed by a filter. As a result, an ink containing colored particles derived from the pulverized material and an aqueous medium can be obtained by this step.

Examples of the present invention will be described below. However, the present invention is not limited to the following examples.

[Method for measuring acid value]
The acid value in the examples was measured according to JIS (Japanese Industrial Standard) K-0070:1992. Specifically, 1.0 g of sample (mass of sample M) and 25 mL of a mixed solution of tetrahydrofuran and ethanol (tetrahydrofuran: ethanol = 2:1) are put into a beaker, and the sample is dissolved in the mixed solution to obtain a sample solution. was prepared. Next, using a potentiometric titration measurement device ("COM-2500" manufactured by HIRANUMA Co., Ltd.), neutralization titration was performed on the above sample solution with a 0.1 mol/L KOH ethanol solution. The amount of KOH ethanol solution used to neutralize the sample solution was designated as "S". Separately, neutralization titration of the mixed solution (blank for calibration) was performed using the above-described potentiometric titration measuring apparatus and KOH ethanol solution. The amount of KOH ethanol solution used for neutralizing the mixed solution was designated as "B". The acid value of the sample was calculated by applying "M", "S" and "B" to the following formula. In the formula below, "f" is a factor specific to the KOH solution.
Acid value [mgKOH/g] = (SB) x f x 5.61/M

[Measurement of glass transition point]
The glass transition point in the examples was measured by a method based on JIS (Japanese Industrial Standards) K7121-2012 using a differential scanning calorimeter ("DSC-60" manufactured by Shimadzu Corporation).

[Salt milling treatment]
340 g of pigment (“Carbon Black #970”, acidic carbon black manufactured by Mitsubishi Chemical Corporation), 3400 g of sodium chloride as a water-soluble inorganic salt, and 850 g of diethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a kneading aid. was put into a double-arm kneader (“S5-2” manufactured by Moriyama Co., Ltd.) and kneaded (salt milling) for 5 hours under conditions of a temperature of 50° C., normal humidity, and a rotation speed of 2000 rpm. Next, a treatment agent containing an unopened ring oxazoline group-containing resin and water (“Epocross (registered trademark) WS-500” manufactured by Nippon Shokubai Co., Ltd., an active ingredient: an acrylic resin having an oxazoline group, Active ingredient concentration: 40% by mass) 75 g (active ingredient amount: 30 g) was further added, and kneaded (salt milling) again for 5 hours under the conditions of temperature of 50°C, normal humidity, and rotation speed of 2000 rpm. Next, ion-exchanged water was added to the resulting mixture to prepare a slurry (A) containing the mixture and water. Next, using a Buchner funnel, the above slurry (A) was filtered to obtain a filter cake. Next, ion-exchanged water is added to the filter cake to prepare a slurry (B) containing the filter cake and water, and then the slurry (B) is filtered using a Buchner funnel to obtain the filter cake. Multiple washing treatments were performed. The washing treatment was repeated until the electric conductivity of the filtrate generated during filtration became 5 μS/cm or less. Next, using a dryer, the filtered material after the washing treatment was dried at 90° C. for 16 hours to obtain a dried material. Next, using a grinder (“Sample Mill SK-M2” manufactured by Kyoritsu Riko Co., Ltd.), the dried product was ground. As a result, pigment particles (P-1) containing a pigment and an unopened oxazoline group-containing resin were obtained.

Pigment particles (P-2) to (P-2) to ( P-6) was prepared.

A description of Table 1 below is provided below.
#970: Acidic carbon black ("Carbon black #970" manufactured by Mitsubishi Chemical Corporation)
MOGUL (R) L: acidic carbon black (“MOGUL (registered trademark) L” manufactured by Cabot)
MA600: Neutral carbon black (“MA600” manufactured by Mitsubishi Chemical Corporation)
P. B. 15:3: "Lionol (registered trademark) Blue FG-7330" manufactured by Toyocolor Co., Ltd., component: copper phthalocyanine, color index: pigment blue 15:3
WS-500: A treatment agent containing an unopened ring oxazoline group-containing resin and water ("Epocross (registered trademark) WS-500" manufactured by Nippon Shokubai Co., Ltd., active ingredient: acrylic resin having an oxazoline group, active ingredient concentration: 40 mass %)
WS-700: A treatment agent containing an unopened ring oxazoline group-containing resin and water (“Epocross (registered trademark) WS-700” manufactured by Nippon Shokubai Co., Ltd., active ingredient: acrylic resin having an oxazoline group, active ingredient concentration: 25 mass %)

[Synthesis of Resin Used as Carboxy Group-Containing Vinyl Resin]
Resins (R-1) to (R-6) were synthesized by the following method. Resins (R-1) to (R-6) were used as carboxy group-containing vinyl resins or their substitutes in Examples and Comparative Examples. Table 2 below shows the raw materials, glass transition point and acid value of each resin.

(Synthesis of resin (R-1))
A four-necked flask equipped with a stirrer, nitrogen inlet tube, condenser and dropping funnel was used as the reaction vessel. 100 parts by mass of isopropyl alcohol and 250 parts by mass of methyl ethyl ketone were put into a reaction vessel. Separately, 25 parts by mass of methyl methacrylate, 25 parts by mass of styrene, 10 parts by mass of n-butyl acrylate, 10 parts by mass of acrylic acid, 30 parts by mass of benzyl methacrylate, and azobisisobutyronitrile (AIBN , polymerization initiator) were mixed with 0.3 parts by mass to obtain a monomer solution. Next, nitrogen was introduced into the reaction vessel to create a nitrogen atmosphere, and then the temperature of the contents of the reaction solution was heated to 70° C. to bring it into a heating reflux state. Next, while the content of the reaction vessel was heated to reflux at 70° C., the dropping funnel was used to supply the entire amount of the monomer solution into the reaction vessel over about 2 hours. After the monomer solution was supplied, the contents of the reaction vessel were heated to reflux at 70° C. and maintained for an additional 6 hours. Separately, 150 parts by mass of methyl ethyl ketone and 0.1 part by mass of AIBN were mixed to obtain a methyl ethyl ketone solution. Next, while the content of the reaction vessel was heated to reflux at 70° C., the dropping funnel was used to supply the entire amount of the methyl ethyl ketone solution into the reaction vessel over 15 minutes. After feeding the methyl ethyl ketone solution, the contents of the reaction vessel were heated to reflux at 70° C. and maintained for an additional 5 hours. Next, an excess amount of hexane was added to the reaction solution to precipitate a solid content (resin (R-1)). The precipitated solid was then washed multiple times with hexane and then dried to remove the hexane. As a result, a resin (R-1), which is a styrene-acrylic resin having a carboxyl group, was obtained. Resin (R-1) had a glass transition point (Tg) of 63° C. and an acid value of 78 mgKOH/g.

(Synthesis of resins (R-2) to (R-4) and (R-6))
The resin (R-2 ) to (R-3) and (R-6), and resin (R-4), which is a styrene-acrylic resin having no carboxy group, were synthesized.

(Synthesis of resin (R-5))
A four-necked flask equipped with a distillation tube, a nitrogen inlet tube, a thermometer and a stirrer was used as a reaction vessel. 550 parts by mass of terephthalic acid, 340 parts by mass of isophthalic acid, 60 parts by mass of trimellitic acid, 300 parts by mass of ethylene glycol, 20 parts by mass of diethylene glycol, and 650 parts by mass of bisphenol A PO adduct (bisphenol A propylene oxide adduct) were added to a reaction vessel. , 20 parts by mass of pentaerythrol, and 1 part by mass of tetrabutoxytitanium as a reaction catalyst were added. The reaction vessel was then heated to bring the temperature of the contents of the reaction vessel to 130°C. Next, the reaction vessel was further heated to raise the temperature of the contents of the reaction vessel from 130° C. to 170° C. over 2 hours. Next, the reaction vessel was further heated and the pressure inside the reaction vessel was reduced. As a result, the temperature of the contents of the reaction vessel was set to 250° C. and the internal pressure of the reaction vessel was set to 666 Pa or less, and the polycondensation reaction was carried out under these conditions. The reaction time of the polycondensation reaction was the time required for the glass transition point of the polyester resin produced by the reaction to reach 55°C. Next, the contents of the reaction vessel were filtered and washed using filter paper, and then dried under reduced pressure. As a result, a resin (R-5), which is a polyester resin having a carboxyl group, was obtained. Resin (R-5) had a glass transition point (Tg) of 55° C. and an acid value of 65 mgKOH/g.

<Ink preparation>
Inks of Examples 1 to 9 and Comparative Examples 1 to 4 were prepared by the following method. Details of each ink are shown in Table 3 below.

[Example 1]
(Melting kneading treatment)
Using an FM mixer (“FM-10B” manufactured by Nippon Coke Kogyo Co., Ltd.), 200 parts by mass of resin (R-1) as a carboxy group-containing vinyl resin and 100 parts by mass of pigment particles (P-1) are mixed. to obtain a mixture. Next, using a twin-screw extruder ("PCM-30" manufactured by Ikegai Co., Ltd.), the mixture was melt-kneaded at a kneading speed of 30 rpm to obtain a melt-kneaded product. The ratio (B/A) of the mass B of the resin (R-1) to the mass A of the pigment particles (P-1) was 2.0.

(Pulverization process)
Next, the resulting melt-kneaded product was coarsely pulverized to a particle size of 2 mm or less with a pulverizer ("Rotoplex (registered trademark)" manufactured by Hosokawa Micron Corporation) to obtain a coarsely pulverized product. Next, using a pulverizer (“Turbo Mill” manufactured by Freund Turbo Co., Ltd.), the coarsely pulverized material was pulverized under the condition of a set particle size of 6 μm to obtain a pulverized material.

(Distributed processing)
Next, 69.5 parts by mass of ion-exchanged water, 30.0 parts by mass of the above-mentioned pulverized product, and a nonionic surfactant (Nihon 0.5 parts by mass of "OLFINE (registered trademark) E1004" manufactured by Shinkagaku Kogyo Co., Ltd., acetylene glycol surfactant) was added. In addition, the above vessel was filled with media (zirconia beads with a diameter of 1.0 mm). The filling amount of the media was set to 70% by volume with respect to the volume of the vessel.

Next, 1M NaOH aqueous solution was added to the vessel (neutralization treatment). The amount of the 1M NaOH aqueous solution added was an amount equivalent to 1.0 times the neutralization equivalent of the carboxy group-containing vinyl resin (resin (R-1) in Example 1) contained in the pulverized product in the vessel. This neutralized the carboxy group-containing vinyl resin contained in the pulverized material in the vessel. Next, using the above-mentioned media-type dispersing machine, the above-mentioned pulverized material was subjected to a wet dispersion treatment under the conditions of a discharge rate of 300 g/min and the number of passes of 1 pass to obtain a dispersion liquid. Next, the dispersion liquid was filtered using a filtration device ("LV Centramate Tangential Flow System" manufactured by Nippon Pall Co., Ltd.). In the filtration, a filter (“SUPORE MEMBRANE” manufactured by Nippon Pall Co., Ltd., pore size 0.1 μm) was used, and the filtration rate was set at 150 mL/min. This removed free resin and impurities from the dispersion. Next, ion-exchanged water was added to the filtrate after filtration. As a result, a colored particle dispersion liquid containing colored particles derived from the pulverized material and water was obtained. The amount of ion-exchanged water added was such that the solid content concentration of the colored particle dispersion liquid was 15% by mass.

(addition treatment)
Next, using a stirrer ("Three One Motor BL-600" manufactured by Shinto Kagaku Co., Ltd.) at a rotation speed of 400 rpm, 60.0 parts by mass of the colored particle dispersion (9 parts by mass of colored particles) and ethylene glycol 20.0 parts by mass, 15.0 parts by mass of diethylene glycol, nonionic surfactant (Nissin Chemical Industry Co., Ltd. "Olfine (registered trademark) E1004", acetylene glycol surfactant) 0.3 parts by mass, and ion Exchanged water was stirred to obtain a mixed liquid. The amount of ion-exchanged water added was such that the total amount of the mixed solution was 100 parts by mass. The obtained mixture was filtered using a filter (pore size: 5 μm) to remove coarse particles. Thus, the ink of Example 1 was obtained.

[Examples 2 to 9 and Comparative Example 3]
The inks of Examples 2 to 9 and Comparative Example 3 were prepared in the same manner as the inks of Example 1, except that the types of resin and pigment particles used in the melt-kneading process were changed as shown in Table 3 below. was prepared.

[Comparative Example 1]
In the melt-kneading process, as materials to be melt-kneaded, 200 parts by mass of resin (R-1) as a carboxyl group-containing vinyl resin and 100 parts by mass of pigment ("Carbon Black #970" manufactured by Mitsubishi Chemical Corporation, acidic carbon black). The ink of Comparative Example 1 was prepared in the same manner as the preparation of the ink of Example 1, except that the ink of Comparative Example 1 was used. The colored particles of the ink of Comparative Example 1 contained pigment itself instead of containing pigment particles.

[Comparative Example 2]
(Melting kneading treatment and pulverization treatment)
In the preparation of the ink of Comparative Example 2, first, the same melt-kneading treatment and pulverization treatment in the preparation of the ink of Example 1 were performed, except that the resin (R-4) was used instead of the resin (R-1). was carried out to obtain a pulverized product.

(Distributed processing)
Next, in the preparation of the ink of Comparative Example 2, a colored particle dispersion liquid was obtained by carrying out the same dispersion treatment as in the preparation of the ink of Example 1, except for the following changes. In the preparation of the ink of Comparative Example 2, in the dispersion treatment, 62.0 parts by mass of ion-exchanged water and 25.0 parts of the pulverized material were placed in a vessel of a media-type dispersing machine (“Dynomill” manufactured by Willie & E. Bakkofen). Parts by mass, pigment-coated resin-containing dispersion (“DISPERBYK (registered trademark) 193” manufactured by BYK Chemie, active ingredient concentration 40% by mass) 12.5 parts by mass, nonionic surfactant (manufactured by Nissin Chemical Industry Co., Ltd. “ Olfine (registered trademark) E1004", acetylene glycol surfactant) and 0.5 parts by mass were added. Further, in the preparation of the ink of Comparative Example 2, the neutralization treatment was not performed in the dispersion treatment. Thus, a colored particle dispersion liquid used for preparing the ink of Comparative Example 2 was obtained.

(addition treatment)
Next, an ink of Comparative Example 2 was obtained by carrying out the same addition treatment as in the preparation of the ink of Example 1, except that the above colored particle dispersion liquid was used.

[Comparative Example 4]
(Distributed processing)
A colored particle dispersion liquid used for preparing the ink of Comparative Example 4 was obtained by carrying out the same operation as the dispersion treatment in preparing the ink of Example 1, except that the following points were changed. In addition, in the preparation of the ink of Comparative Example 4, the melt-kneading treatment and the pulverization treatment were not performed.

In the dispersion treatment of Comparative Example 4, 69.5 parts by mass of ion-exchanged water and acidic carbon black ("Carbon Black #970”) 15.0 parts by mass, a pigment-coated resin-containing dispersion (“DISPERBYK (registered trademark) 193” manufactured by BYK Chemie Co., Ltd., active ingredient concentration 40% by mass) 15.0 parts by mass, and a nonionic surfactant ( Nissin Kagaku Kogyo Co., Ltd. "OLFINE (registered trademark) E1004", acetylene glycol surfactant) and 0.5 parts by mass were added. Further, in the dispersion treatment of Comparative Example 4, no neutralization treatment was performed. Thus, a colored particle dispersion liquid used for preparing the ink of Comparative Example 4 was obtained.

(addition treatment)
Next, an ink of Comparative Example 4 was obtained by performing the same addition treatment as in the preparation of the ink of Example 1, except that the above colored particle dispersion liquid was used. The ink of Comparative Example 4 contained the pigment itself instead of the colored particles.

<Evaluation>
By the following methods, the inks of Examples 1 to 9 and Comparative Examples 1 to 4 were evaluated for the presence or absence of nozzle clogging, the ejection stability (whether or not ejection distortion occurred), the fixability of the formed image, Long-term storage stability and short-term storage stability were evaluated. Evaluation was performed at a temperature of 25° C. and a humidity of 60% RH unless otherwise specified. The evaluation results are shown in Table 3 below.

[Evaluation machine]
As an evaluation machine, an inkjet recording apparatus (prototype manufactured by Kyocera Document Solutions Co., Ltd.) equipped with a piezo system line type recording head was used. After an object to be evaluated (specifically, one of the inks of Examples 1 to 9 and Comparative Examples 1 to 4) was put into the ink tank of the evaluation machine, the ink installation operation was performed using the evaluation machine. As a result, the recording head of the evaluation machine was filled with the object to be evaluated. In addition, the ejection conditions of the evaluation machine were set so that the volume of one ink droplet ejected from the evaluation machine was 11 pL.

[Nozzle clogging]
In the evaluation of nozzle clogging, A4 size inkjet matte paper ("Super Fine Paper" manufactured by Seiko Epson Corporation) was used as evaluation paper. A solid image of 150 mm×200 mm was continuously printed on 100 sheets of evaluation paper using an evaluation machine. Next, the evaluation target was purged from the recording head of the evaluation machine. Next, the ink ejection surface of the recording head of the evaluation machine was wiped to clean the recording head. Hereinafter, the operation of cleaning the print head by purging and wiping may be referred to as cleaning processing. Next, an evaluation machine was used to form a nozzle check pattern image on the evaluation paper. As a result, regardless of which evaluation target was used, the evaluation target was ejected from all nozzles (the number of non-ejection nozzles was 0). Next, the recording head was subjected to cleaning processing again. Next, the evaluation machine was allowed to stand for 7 days without attaching the cap to the recording head. Next, the recording head was subjected to cleaning processing again. Next, an evaluation machine was used to form a nozzle check pattern image (evaluation image) on an evaluation sheet. The evaluation image was checked, and the ratio of the number of ejection failure nozzles to all nozzles (7968 nozzles) was calculated. The calculated ratio of the number of non-ejection nozzles was used as an evaluation value for nozzle clogging. Whether or not the object to be evaluated causes nozzle clogging was evaluated according to the following criteria.

(Criteria for nozzle clogging)
A (Good): Evaluation value less than 10% B (Poor): Evaluation value 10% or more

[Ejection stability]
In the evaluation of ejection stability, A4 size inkjet matte paper ("Super Fine Paper" manufactured by Seiko Epson Corporation) was used as evaluation paper. A solid image of 150 mm×200 mm was continuously printed on 5,000 sheets of evaluation paper using the evaluation machine. Next, cleaning processing was performed on the recording head of the evaluation machine.

Next, using an evaluation machine, a stripe image formed by a plurality of parallel fine lines was formed on the recording medium. In forming the stripe image, the line width of the fine lines was set to 1 pixel, and the interval between adjacent fine lines (interline pitch) was set to 3 pixels. Next, the stripe image formed on the evaluation paper was read with a microscope. Specifically, the distance A between a specific fine line a and a fine line b located 16 pixels away from the fine line a was measured at 204 points. In addition, there were three separate thin lines between the thin line a and the thin line b. Variation (3σ) of the measured distance A was calculated using image processing software (manufactured by Kyocera Document Solutions Co., Ltd.). The calculated variation (3σ) of the interval A was used as the ejection stability evaluation value. Ejection stability was determined according to the following criteria.

A (good): 3σ is less than 15 B (bad): 3σ is 15 or more

[Fixability]
As a recording medium, an A4 size OHP sheet (“Espet (registered trademark) E5200” manufactured by Toyobo Co., Ltd., a biaxially stretched polyester film with a corona treatment on the surface, thickness 0.10 mm) was used. A solid image (size: 2 cm x 2 cm, print rate: 100%) was formed on the recording medium using the evaluation machine. Next, the above recording medium was dried at 60° C. for 2 hours using a dryer. Next, the solid image was fixed on the above recording medium at a fixing temperature of 160° C. using a fixing device provided in a multifunction machine (“TASKalfa2551ci” manufactured by Kyocera Document Solutions Inc.).

Next, a rubbing test was performed on the recording medium described above. Specifically, a metal weight (50 mm in diameter, 1 kg in mass) whose bottom surface was covered with cloth was placed on the solid image formed on the recording medium. Then, the solid image was rubbed back and forth 10 times with a weight of 1 kg. Next, the solid image was visually observed to confirm whether or not the solid image was peeled off from the OHP sheet. Fixability was determined according to the following criteria.

(Determination of fixability)
A (Good): Peeling of the solid image was not observed.
B (defective): Peeling of the solid image was confirmed.

[Storage stability]
(Long-term storage stability)
Using a vibrating viscometer ("VM-200T" manufactured by Nittetsu Hokkaido Control System Co., Ltd.), the viscosity (initial viscosity V ₁ ) was measured. Next, about 30 g of the object to be evaluated was placed in a container with a volume of 50 mL and sealed. The container described above was placed in a thermostat set at an internal temperature of 60° C. and kept warm for 3 months (long-term storage). After that, the above-mentioned container was taken out from the thermostat, and then the above-mentioned container was allowed to stand at room temperature for 3 hours. After that, the object to be measured was taken out from the above container, and the viscosity (post-treatment viscosity V ₂ ) was measured using the above vibration viscometer. Based on the measured initial viscosity _V1 and post-treatment viscosity _V2 , the viscosity change rate [%] was calculated (the following formula). The calculated viscosity change rate was used as an evaluation value for the long-term storage stability of the ink to be measured. Long-term storage stability was evaluated according to the following criteria.
Viscosity change rate [%] = 100 x ( _V1 - _V2 )/ _V1

(Criteria for long-term storage stability)
A (good): the absolute value of the viscosity change rate is 5% or less B (slightly good): the absolute value of the viscosity change rate is more than 5% and 10% or less C (poor): the absolute value of the viscosity change rate is more than 10%

(Short-term storage stability)
Evaluation of short-term storage stability by the same method as evaluation of long-term storage stability, except that the storage period in the thermostatic chamber (internal temperature 60 ° C) of the container into which the evaluation target was put was changed to 2 weeks (short-term storage). was performed to obtain the viscosity change rate [%] as an evaluation value. Short-term storage stability was evaluated according to the following criteria.

(Criteria for short-term storage stability)
A (good): the absolute value of the viscosity change rate is 5% or less B (slightly good): the absolute value of the viscosity change rate is more than 5% and 10% or less C (poor): the absolute value of the viscosity change rate is more than 10%

In Table 3 below, "Ox group-containing resin" indicates an oxazoline group-containing resin.

As shown in Tables 1-3, the inks of Examples 1-9 contained colored particles and an aqueous medium. The colored particles contained a carboxy group-containing vinyl resin and pigment particles dispersed in the carboxy group-containing vinyl resin. Pigment particles contained a pigment and a specific resin. The specified resin had an unopened oxazoline group and an amide ester group. The inks of Examples 1 to 9 were excellent in ejection stability and storage stability, and could form images with excellent fixability while suppressing the occurrence of nozzle clogging.

On the other hand, in the ink of Comparative Example 1, the colored particles contained not the pigment particles but the pigment itself. The ink of Comparative Example 1 was judged to have poor storage stability because the pigment easily detached from the colored particles.

In the ink of Comparative Example 2, the colored particles contained a vinyl resin having no carboxy instead of a vinyl resin containing a carboxy group. Since the ink of Comparative Example 2 had low dispersion stability of the colored particles, it was determined that the suppression of nozzle clogging, ejection stability, and storage stability were poor.

In the ink of Comparative Example 3, the colored particles contained a polyester resin instead of the carboxy group-containing vinyl resin. The ink of Comparative Example 3 was judged to have poor storage stability due to hydrolysis of the polyester resin.

Since the ink of Comparative Example 4 contained the pigment itself instead of the colored particles, it is judged that the fixability and storage stability of the formed image were poor.

Inks according to the present invention can be used to form images. The method for producing ink according to the present invention can be used for producing ink.

1, 11 colored particles 2, 12 pigment particles 3, 13 carboxy group-containing vinyl resin

Claims (8)

containing colored particles and an aqueous medium,
The colored particles include a carboxy group-containing vinyl resin and pigment particles dispersed in the carboxy group-containing vinyl resin,
The pigment particles contain a pigment and a specific resin,
The inkjet ink, wherein the specific resin has an unopened ring oxazoline group and an amide ester group. The inkjet ink according to claim 1, wherein the carboxy group-containing vinyl resin includes a styrene-(meth)acrylic resin. 3. The inkjet ink according to claim 1, wherein the pigment comprises acidic carbon black. The inkjet ink according to any one of claims 1 to 3, wherein the carboxy group-containing vinyl resin has an acid value of 60 mgKOH/g or more and 120 mgKOH/g or less. The inkjet ink according to any one of claims 1 to 4, wherein the carboxy group-containing vinyl resin has a glass transition point of 50°C or higher and 80°C or lower. 6. The colored particles according to any one of claims 1 to 5, wherein the ratio (B/A) of the mass B of the carboxy group-containing vinyl resin to the mass A of the pigment particles is 1.4 or more and 3.1 or less. 10. The inkjet ink according to Item 1. The aqueous medium does not contain a free resin present in a free state, or the free resin is contained, and the content ratio of the free resin with respect to the total mass of the carboxy group-containing vinyl resin, the specific resin and the free resin is 0.5. The inkjet ink according to any one of claims 1 to 6, which is more than 0% by mass and less than 3.0% by mass. A method for producing an inkjet ink containing colored particles and an aqueous medium, comprising:
A salt milling step of obtaining pigment particles by subjecting the pigment and the unopened ring oxazoline group-containing resin to a salt milling treatment;
a melt-kneading step of obtaining a melt-kneaded product by melt-kneading the pigment particles and the carboxy group-containing vinyl resin;
A pulverizing step of pulverizing the melt-kneaded product to obtain a pulverized product;
and a dispersing step of dispersing the pulverized material in the aqueous medium.

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