JP7761869B2 - Aqueous dispersion, method for producing aqueous dispersion, and ink - Google Patents

Description

The present invention relates to an aqueous dispersion, a method for producing the aqueous dispersion, and an ink.

Inkjet recording devices have advantages such as low noise, low running costs, and easy color printing, and are widely used in ordinary homes as digital signal output devices. In recent years, inkjet technology has been used not only for home use but also for commercial and industrial applications. Furthermore, in commercial and industrial applications, low-ink-absorbent coated printing paper (coated paper) and non-ink-absorbent plastic media are used as recording media, and there is a demand for inkjet recording methods to achieve image quality on par with conventional offset printing even for these media.

For example, Patent Document 1 discloses an aqueous pigment dispersion in which a pigment is mixed with an aqueous solution of a polymeric dispersant, and the pigment is dispersed with an adsorptive dispersant.
Patent Documents 2 and 3 disclose water-based pigment dispersions in which a resin solution containing a pigment is mixed and dispersed in water and/or an aqueous medium.
Patent Document 4 discloses an aqueous pigment dispersion in which pigment particles are coated with a specific resin by an acid precipitation method.

However, even with this technology, it is difficult to completely encapsulate the pigment in the resin. Furthermore, there are issues such as the high hydrophilicity of the resin coating the pigment, which makes the resin prone to detachment from the pigment surface. As a result, the stability of the pigment composite resin particles is poor, and for example, heat drying can cause the pigment to aggregate, which can deteriorate the uniform dispersion of the pigment or the surface roughness of the coating film, resulting in a decrease in image density compared to before heat drying. Therefore, the above-mentioned water-based inks cannot satisfy the recent demand for high image density.
An object of the present invention is to provide an aqueous dispersion containing pigment composite resin particles, which has good dispersion stability and can provide images with excellent image density.

The present invention, which solves the above problems, relates to an aqueous dispersion as described below.
An aqueous dispersion containing emulsion resin particles as a dispersoid,
the emulsion resin particles include pigment-encapsulated emulsion resin particles that encapsulate an inorganic pigment and non-pigment-encapsulated emulsion resin particles that do not encapsulate an inorganic pigment,
the emulsion resin particles have a volume-based cumulative 50% particle diameter (D50) of 40 nm or more and 150 nm or less, a volume-based cumulative 90% particle diameter (D90) of 70 nm or more and 300 nm or less, as measured by a laser diffraction scattering method, and an average aspect ratio of 1.0 or more and 1.5 or less, and the primary particle diameter of the inorganic pigment is smaller than the minimum particle diameter of the non-pigment-encapsulated emulsion resin particles;
An aqueous dispersion characterized by:

The present invention aims to provide an aqueous dispersion containing pigment composite resin particles that has good dispersion stability and can provide images with excellent image density.

FIG. 1 is a TEM image (magnification: 40,000 times) of the aqueous dispersion containing the pigment-encapsulated emulsion resin particles obtained in Example 1. FIG. 2 is a TEM image (magnification: 40,000 times) of the aqueous dispersion containing the pigment-encapsulated emulsion resin particles obtained in Comparative Example 1. FIG. 3 is a schematic diagram illustrating an example of a recording apparatus. FIG. 4 is a perspective view illustrating an example of a recording apparatus. FIG. 5 is a perspective view illustrating an example of a main tank.

An example of an embodiment of the present invention will be described below. However, the following description is intended to illustrate an example of an embodiment of the present invention and is not intended to limit the scope of the present invention.

<Pigment-encapsulated emulsion resin particles>
The pigment-encapsulating emulsion resin particles of the present invention are in the form of a resin emulsion.
By incorporating pigments into a resin emulsion, it is possible to prevent the resin from escaping into the medium. An emulsion is a state in which particles are dispersed in water or ink, regardless of whether the particles are solid or liquid.

The pigment-encapsulated emulsion resin particles (hereinafter also referred to as "pigment-encapsulated resin particles") refer to a form in which a pigment is encapsulated within emulsion resin particles of a resin emulsion. It is preferable that the pigment is not encapsulated within emulsion resin particles and dispersed in a dispersion medium, or that the pigment is not partially exposed on the surface of emulsion resin particles. Furthermore, it is preferable that the pigment-encapsulated resin particles are spherical.

In this invention, pigment-encapsulated emulsion resin particles refer to pigments contained within a resin emulsion. For example, Patent Documents 1 to 4 propose coated pigments and microencapsulated pigments, but these do not involve pigments being covered within a resin emulsion and are therefore different from pigment-encapsulated emulsion resin particles.

When producing pigment-encapsulated resin particles, emulsion resin particles in which no pigment is encapsulated (hereinafter also referred to as "non-pigment-encapsulated resin particles") are also produced together with the pigment-encapsulated resin particles.
The amount of pigment-encapsulated resin particles present can be adjusted by appropriately selecting the ratio between the pigment-encapsulated resin particles and the pigment-free emulsion resin particles depending on the purpose.

The amount of pigment-encapsulated resin particles present can be determined by taking five or more images of a field of view containing three or more particles with a particle size of 50 nm or more at randomly changed locations, and calculating the proportion of the number of pigment-encapsulated resin particles to the number of particles with a particle size of 50 nm or more for each image.The average value is preferably 30% or more, and more preferably 50% or more. Furthermore, it is preferable that each pigment-encapsulated resin particle contains two or more primary pigment particles. In this way, increasing the pigment density within the particle improves image density. Pigment-encapsulated resin particles can be observed, for example, using a transmission electron microscope (TEM).

The observation of the pigment-encapsulating resin particles using a transmission electron microscope (TEM) is carried out, for example, as follows.
First, a sample solution was prepared by diluting an aqueous dispersion containing pigment-encapsulated resin particles with ion-exchange water to a solids concentration of 0.1% by mass. Next, 1 μL of the sample solution was placed using a micropipette on a hydrophilically treated collodion-coated mesh (Nisshin EM Co., Ltd., Collodion-coated mesh, Cu150 mesh). The sample solution was then immediately absorbed with triangular filter paper. Next, 1 μL of 10-fold diluted EM stainer was placed using a micropipette, and the sample solution was immediately absorbed with triangular filter paper. After drying under reduced pressure, the sample was observed using a transmission electron microscope (JEOL Ltd., JEM-2100F) at an accelerating voltage of 200 kV and a magnification of 40,000x.

The encapsulated form of the pigment is a spherical emulsion in which the entire surface of the pigment is covered with the resin, and it is preferable that there is no form in which the unencapsulated pigment is dispersed in the dispersion medium of the aqueous dispersion, or a form in which the pigment is partially exposed on the surface of the emulsion resin particle. The encapsulated form of the pigment can be observed using the above-mentioned transmission electron microscope (TEM).
In order to obtain a spherical emulsion in which the entire surface of the pigment is covered with resin, it is preferable that the minimum particle size of the non-pigment-encapsulated resin particles is larger than the primary particle size of the inorganic pigment. If the primary particle size of the inorganic pigment is larger than the minimum particle size of the non-pigment-encapsulated resin particles, the entire surface of the pigment cannot be uniformly covered with the resin emulsion, and part of the pigment may be exposed to the surface by heat drying after printing, resulting in a decrease in image density.

The minimum particle size of the non-pigment-encapsulated resin particles is evaluated as follows: When observing the pigment-encapsulated resin particles using the transmission electron microscope (TEM), five or more images of a field of view containing five or more non-pigment-encapsulated resin particles are obtained from randomly changed locations, and the minimum particle size of the non-pigment-encapsulated resin particles is calculated for each image, and the average value is used as the particle size of the non-pigment-encapsulated resin particles.

The minimum particle size of the non-pigment-encapsulated resin particles is preferably 20 nm or more and 200 nm or less, and more preferably 40 nm or more and 150 nm or less. When the minimum particle size of the non-pigment-encapsulated resin particles is 20 nm or more, multiple pigment particles are encapsulated within a spherical emulsion, resulting in good image density. Furthermore, when the minimum particle size of the non-pigment-encapsulated resin particles is 200 nm or less, particle settling is suppressed, resulting in good storage stability as particles.

The primary particle size of the pigment was evaluated as follows.
The primary particle size of the pigment is measured using a transmission electron microscope (TEM) and processed with image analysis software (ImageJ, manufactured by the National Institutes of Health, USA). 20 primary particles are randomly selected by image analysis, their particle sizes are measured, and the average is calculated. If the particles have a major axis and a minor axis, the major axis is used for calculation.

The aspect ratio of pigment-encapsulated resin particles is determined by image processing of images obtained by observing the pigment-encapsulated resin particles using the transmission electron microscope (TEM) described above. Specifically, the observation position is arbitrarily changed to obtain multiple images of the field of view that includes the pigment-encapsulated resin particles. Pigment-encapsulated resin particles that do not overlap with other particles are extracted by binarization using image analysis software (ImageJ, manufactured by the National Institutes of Health, USA) and particle analysis is performed. The major axis/minor axis of the closest-fitting ellipse is used as the aspect ratio, and the average value for 20 particles is calculated.

The degree of pigment encapsulation is evaluated by quantifying the amount of pigment that is not encapsulated and is exposed (pigment exposure rate). The pigment exposure rate can be calculated, for example, using a scanning electron microscope (SEM). The specific method for calculating the pigment exposure rate is as follows.
An aqueous dispersion containing pigment-encapsulated resin particles was prepared using ion-exchanged water to a solids concentration of 10.75% by mass. The dispersion was then coated onto coated paper (Lumia Art Gloss 130) using a 0.15 mm bar coater and dried at 25°C. This coating film was cut out and attached to a SEM observation stub using carbon tape. This was then observed without any conductive treatment using a scanning electron microscope (ZEISS Merlin) at an accelerating voltage of 0.75 kV, a backscattered electron detector, and a magnification of 2000 to 20,000 times. This observation method allows the exposed pigment to be distinguished from the carbon black and the resin due to the difference in the backscattered electron emission amount, based on the difference in contrast in the SEM image.

At 20,000x magnification, the proportion of the area occupied by the pigment on the coating film surface (pigment exposure rate) is preferably 8% or less of the total, and more preferably 5% or less. The area occupied by the pigment on the coating film surface is determined by binarizing the SEM observation image, and is preferably the average of three or more fields of view observed at random locations. Under these observation conditions, objects that are unobservable due to charging tend to have a low pigment exposure rate, and are easily observed when the pigment area rate is 3% or less.

By covering two or more primary pigment particles with a spherical resin, it is possible to achieve uniform pigment dispersion in the film after heat drying and reduce the surface roughness of the film. Reducing the surface roughness of the coating film can improve the image OD. The surface roughness of the coating film is preferably 20 nm or less, more preferably 10 nm or less, and even more preferably 5 nm or less. By keeping it 20 nm or less, it is possible to suppress a decrease in image density after heat drying.

<Surface roughness>
The surface roughness of the coating film is calculated for the printed image or coating film using a scanning probe microscope (SPM). In the case of a coating film, for example, first, an aqueous dispersion containing pigment-encapsulated resin particles is prepared using ion-exchanged water to a solids concentration of 10.75% by mass, and then coated onto coated paper (Lumia Art Gloss 130) using a 0.15 mm bar coater. The coating film is then dried by heating in an oven at 100°C for 5 minutes to obtain a coating film. This coating film is cut out and observed under the following conditions to calculate the surface roughness. Observation is performed in three fields of view at random locations, and the average surface roughness is calculated. In the case of a printed image, a solid image prepared using an inkjet device is observed in the same manner as for the coating film, and the average surface roughness is calculated.
Apparatus: Scanning probe microscope (Dimension Icon manufactured by Bruker)
Cantilever: Olympus OMCL-AC240TS
Measurement mode: Tapping mode Observation range: 2 μm square

The particle size of the pigment-encapsulating resin particles is preferably a volume-based cumulative 50% particle size (D50) of 40 nm to 150 nm, more preferably 60 nm to 150 nm, and even more preferably 70 nm to 100 nm. Hereinafter, the volume-based 50% particle size (D50) will be referred to as "D50," and the volume-based cumulative 90% particle size (D90) will be referred to as "D90."
When D50 is 40 nm or more, the liquid viscosity is reduced, resulting in excellent dispersion stability, and the encapsulation of a plurality of pigment primary particles results in good image density. Furthermore, when D50 is 150 nm or less, particle sedimentation is suppressed, resulting in good storage stability of the particles.

Furthermore, D90 is preferably 70 nm or more and 300 nm or less, and more preferably 150 nm or less.
When D90 is 70 nm or more, the pigment can be efficiently encapsulated, and when it is 300 nm or less, sedimentation of the particles is suppressed, resulting in good storage stability of the particles.

Coarse particles refer to particles of 1 μm or larger in the aqueous dispersion. The number of coarse particles in the present invention refers to the number of particles of 1 μm or larger contained in 5 μL of the aqueous dispersion when converted into a solids concentration of 1%.
The number of coarse particles of the pigment-encapsulating resin particles is preferably 1 million or less, more preferably 500,000 or less, and even more preferably 200,000 or less, of particles having a size of 1 μm or more in 5 μL of a dispersion having a solid content of 1%. By reducing the number of coarse particles, particle sedimentation is less likely to occur, and storage stability is improved.

The number of coarse particles is measured, for example, using an AccuSizer particle size distribution analyzer manufactured by PSS Japan, as follows: First, an aqueous dispersion containing pigment-encapsulated resin particles is diluted with ion-exchanged water until it falls within the measurable range, and then measured. From the measurement results, the number of particles 1 μm or larger in 5 μL of the aqueous dispersion, converted to a solids concentration of 1%, is calculated and this is taken as the number of coarse particles.

<Method of producing aqueous dispersion containing pigment-encapsulated resin particles>
The pigment-encapsulated resin particles of the present invention are pigment-encapsulated emulsion resin particles in which a pigment is encapsulated in a resin. A method for producing an aqueous dispersion containing pigment-encapsulated emulsion resin particles is not particularly limited, and may include, for example, the following steps 1 to 4.
Step 1: Mixing a pigment, a pigment dispersant, and an organic solvent to obtain a pigment pre-dispersion in which the volume-based cumulative 50% particle size (D50) of the pigment is 30 nm or more and 120 nm or less. Step 2: Mixing the pigment pre-dispersion obtained in Step 1 with a self-emulsifying resin to obtain a pigment dispersion resin solution. Step 3: Mixing the pigment dispersion resin solution obtained in Step 2 with water to obtain a dispersion containing pigment-encapsulated emulsion resin particles in which the pigment is encapsulated in the resin. Step 4: Removing the organic solvent from the dispersion containing pigment-encapsulated emulsion resin particles obtained in Step 3 to obtain an aqueous dispersion containing pigment-encapsulated emulsion resin particles. Each of Steps 1 to 4 above will be described in detail below.

(Step 1)
Step 1 is a step of obtaining a pigment pre-dispersion.
The pigment pre-dispersion obtained in step 1 is obtained by dispersing the pigment using an organic solvent, a pigment, and optionally a pigment dispersant and other components, and adjusting the particle size. There are no particular restrictions on the apparatus used in step 1, but it is preferable to use a disperser for dispersion.

The organic solvent used in the pigment pre-dispersion is not particularly limited as long as it can dissolve the resin in step 2. However, solvents with high affinity for water are preferred, and organic solvents that are miscible with water are more preferred. The water-miscible organic solvent is an organic solvent that can be dissolved in any ratio with water, and examples include alcohols (specifically, methanol, ethanol, propanol, isopropanol, tert-butyl alcohol, ethylene glycol, etc.); ethers (specifically, 1,2-dimethoxyethane, tetrahydrofuran, 1,4-dioxane, etc.); ketones (specifically, acetone, etc.); amines (specifically, pyridine, N-methylpyrrolidone, triethylamine, dimethylformamide, etc.); and others such as acetonitrile. The water-miscible organic solvent is not particularly limited, but is preferably a cyclic compound, and more preferably a cyclic ether compound. Tetrahydrofuran is a particularly preferred cyclic ether compound.

The particle size of the pigment in the pigment pre-dispersion is not particularly limited, but from the viewpoint of enabling the particle size of the pigment-encapsulated resin particles to be small, D50 is preferably 30 nm or more and 120 nm or less, and more preferably 40 nm or more and 100 nm or less. The particle size of the pigment can be measured using a zeta potential particle measurement system (ELSZ-1000, manufactured by Otsuka Electronics Co., Ltd.). The content of the pigment in the pigment pre-dispersion is not particularly limited and can be appropriately selected depending on the purpose.
It is preferable to filter the pigment pre-dispersion using a filter, a centrifugal separator or the like, if necessary, to remove coarse particles.

The pigment pre-dispersion can be produced by dissolving or suspending the pigment dispersant in an organic solvent as needed, adding the pigment and stirring, and then using a commonly used, known disperser. Known dispersers include, for example, anchor blades, disperser blades, homomixers, ball mills, roll mills, bead mills, sand mills, attritors, pearl mills, Dyno-mills, high-pressure homogenizers, ultrasonic dispersers, agitator mills, paint shakers, grain mills, Cobol mills, and jet mills. Among these, roll mills, bead mills, sand mills, Dyno-mills, high-pressure homogenizers, and paint shakers are preferred in terms of dispersion efficiency.

(Step 2)
Step 2 is a step of mixing the pigment pre-dispersion and a resin to obtain a pigment-dispersed resin solution.
The pigment-dispersed resin solution is obtained by mixing and stirring the pigment pre-dispersion obtained in step 1 with a resin, and optionally a basic compound, an organic solvent, and additives. There are no particular restrictions on the mixing and stirring device used in step 2, but examples include the devices described in step 1. Among these, a high-speed stirring device equipped with anchor blades or disper blades is preferably used in terms of uniformly stirring a high-viscosity solution and efficiently dissolving the resin powder.

There is no particular limitation on the procedure for preparing the pigment-dispersed resin solution. The resin may be added to the pigment pre-dispersion obtained in step 1, or may be added after the resin has been solubilized in an organic solvent.
The particle size of the pigment in the pigment dispersion resin solution is preferably the same as that of the pigment particles in the pigment pre-dispersion obtained in step 1 above, and more preferably does not change between steps 1 and 2.

The water content of the pigment dispersion resin solution is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 3% by mass or less. If the water content of the pigment dispersion resin solution is greater than 20% by mass, the dispersion stability of the pigment may deteriorate, causing agglomerations, and the pigment-encapsulated resin particles obtained in step 3 may become coarse.

The resin is used to encapsulate the pigment in step 3 and is preferably a self-emulsifying resin. A self-emulsifying resin is a resin that can form an emulsified state by stirring and mixing a resin solution with water, and the self-emulsifying resin preferably has a nonionic, anionic, or cationic hydrophilic group, and more preferably is anionic.
When the resin is an anionic self-emulsifying resin, it is preferable that the resin forms an emulsion in an aqueous medium and that some or all of the anionic groups are neutralized with a basic compound in order to maintain dispersion stability in the aqueous medium.

The mass ratio (P/R) of the pigment (P: Pigment) to the resin (R: Resin) is preferably 0.20 or more and 0.75 or less, more preferably 0.30 or more and 0.60 or less, and even more preferably 0.35 or more and 0.50 or less, relative to 1 part resin. When the pigment to resin ratio is 0.20 or more, the pigment concentration is appropriate and the printed image density is excellent. Furthermore, when the pigment to resin ratio is 0.75 or less, most of the pigment can be encapsulated in the resin, suppressing the surface roughness of the coating film after heat drying and improving the image density. The pigment to resin ratio can be calculated from the charge ratio or the obtained dispersion.

The ratio can be calculated from the dispersion by thermal analysis of a dried-solid dispersion film using, for example, a thermogravimetric differential thermal analyzer (TG-DTA). Specifically, a dried-solid dispersion film is heated to the thermal decomposition temperature of the resin in a nitrogen gas atmosphere using a thermogravimetric differential thermal analyzer, and the decomposed weight is calculated as the resin, and the weight of the residue as the pigment. Furthermore, for highly heat-resistant resins that cannot be completely decomposed by thermal decomposition in a nitrogen gas atmosphere, the heat loss and pigment to resin ratio can be calculated using a calibration curve of the heat loss and resin to pigment ratio. Specifically, multiple mixtures of pigment and resin at arbitrary ratios are prepared, and each mixture is heated to a fixed temperature and held at that temperature to create the calibration curve. The ratio of pigment to resin can then be calculated based on the weight loss rate obtained from the measurement results of unknown samples.

The mass ratio (R/S) of resin (R: Resin) to organic solvent (S: Solvent) in the pigment dispersion resin solution is preferably 1.2 or more and 3.0 or less, more preferably 1.4 or more and 2.5 or less, and even more preferably 1.6 or more and 2.0 or less. When the ratio of resin to organic solvent is 1.2 or more, the emulsification rate of the resin in step 3 increases, making it possible to reduce the particle size of the pigment-encapsulated resin particles. Furthermore, when the ratio of resin to organic solvent is 3.0 or less, high viscosity in the reaction system is suppressed, and stirring efficiency is improved, thereby suppressing the generation of coarse particles.

(Step 3)
Step 3 is a step of obtaining a dispersion containing pigment-encapsulated emulsion resin particles.
The dispersion liquid is obtained by mixing the pigment-dispersed resin solution obtained in step 2 with water. There are no particular restrictions on the mixing and stirring device used in step 3, and examples include the devices described in step 1. Among these, a high-speed stirring device equipped with an anchor blade or a disper blade is preferred from the viewpoint of uniform stirring in a highly viscous solution; if the energy required for dispersion is high, the resulting pigment-encapsulated resin particles may be crushed, making it impossible to maintain the encapsulated form.

There are no particular restrictions on the procedure for mixing the pigment dispersion resin solution and water, but it is preferable to add water to the pigment dispersion resin solution. The water addition rate is preferably 10 to 1,000 parts by mass/min, and more preferably 30 to 500 parts by mass/min, per 100 parts by mass of resin. Adding water at a rate of 10 to 1,000 parts by mass/min suppresses pigment aggregation within the system, thereby preventing coarsening of the pigment-encapsulated resin particles.

From the viewpoint of the dispersion stability of the pigment-encapsulated resin particles, the amount of water added is preferably 70 parts by mass or more and 700 parts by mass or less, and more preferably 100 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of the resin used in step 2.
The reaction temperature in step 3 is preferably 20°C or higher and 80°C or lower, more preferably 30°C or higher and 60°C or lower.

(Step 4)
Step 4 is a step of obtaining an aqueous dispersion containing pigment-encapsulated emulsion resin particles.
The aqueous dispersion can be obtained by removing a part or all of the organic solvent from the dispersion containing the pigment-encapsulated resin particles obtained in step 3.
The method for removing the organic solvent from the dispersion obtained in step 3 is not particularly limited, and a known removal device can be used. Examples include a method of removing the organic solvent by heating at a temperature above the boiling point of the organic solvent under reduced pressure using a rotary evaporator, and a method of replacing the organic solvent with water using an ultrafiltration device. The reduced pressure is preferably 200 mmHg or less, more preferably 100 mmHg or less. The heating temperature is preferably 20°C or higher and 80°C or lower, more preferably 30°C or higher and 60°C or lower.
If necessary, the aqueous dispersion containing the pigment-encapsulating resin particles can be filtered using a filter, a centrifugal separator, or the like to remove coarse particles.

<Resin>
The resin is not particularly limited, but a self-emulsifying resin is preferred, and examples thereof include polyester, polyurethane, and acrylic resin. The self-emulsifying resin preferably has an anionic group, and examples of the anionic group include a carboxyl group, a carboxylate group, a sulfonic acid group, and a sulfonate group. Among these, it is preferred to use a carboxylate group or a sulfonate group that has been partially or completely, particularly preferably completely, neutralized with a basic compound or the like.

Neutralizing agents that can be used to neutralize anionic groups include, for example, organic amines such as ammonia, triethylamine, pyridine, and morpholine, basic compounds such as alkanolamines such as monoethanolamine, and metal base compounds containing sodium, potassium, lithium, calcium, etc.

The acid value of the self-emulsifying resin is preferably 10 mgKOH/g or more and 50 mgKOH/g or less, and more preferably 15 mgKOH/g or more and 25 mgKOH/g or less. When the acid value is 10 mgKOH/g or more, dispersion stability is excellent, and as a result, particle size is uniform and dispersion and ejection properties are good. Furthermore, when the acid value is 30 mgKOH/g or less, hydrophilicity is appropriate, water resistance is improved, and stability as particles is good.

The acid value may be a catalog value or may be calculated by measurement. The acid value can be measured, for example, by placing the polyester in a tetrahydrofuran (THF) solution and titrating it with a 0.1 M solution of potassium hydroxide in methanol. When the carboxyl groups in the resin in the aqueous dispersion are neutralized, for example, an excess of aqueous hydrochloric acid is added to make an acidic solution, and the resin is then extracted with chloroform. The pigment is then removed by filtration, centrifugation, or the like, and the resulting resin is then dried by heating or drying under reduced pressure to obtain a dried resin. The acid value can also be measured by dissolving the resulting resin in THF and titrating it with a 0.1 M solution of potassium hydroxide in methanol.
Hereinafter, polyester will be described in detail as an example of the self-emulsifying resin.

(polyester)
The polyester is obtained by polycondensation of a polyhydric alcohol with a polycarboxylic acid, such as a polycarboxylic acid, a polycarboxylic anhydride, or a polycarboxylic ester, and/or a derivative thereof, and contains an aromatic unit in part or all of its composition. That is, the aromatic-containing polyester has a polyhydric alcohol and a polycarboxylic acid, such as a polycarboxylic acid, a polycarboxylic anhydride, or a polycarboxylic ester, and/or a derivative thereof as constituent components.

-Polyhydric alcohol component-
The polyhydric alcohol component may be a dihydric alcohol (diol), specifically, alkylene glycols having 2 to 36 carbon atoms (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexanediol, trimethylolpropane, etc.); alkylene ether glycols having 4 to 36 carbon atoms (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, etc.); Examples of suitable alicyclic diols include alicyclic diols having from 1 to 36 carbon atoms (1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.); adducts (number of moles added: 1 to 30) of the above-mentioned alicyclic diols with alkylene oxides having from 2 to 4 carbon atoms (ethylene oxide (hereinafter abbreviated as EO), propylene oxide (hereinafter abbreviated as PO), butylene oxide (hereinafter abbreviated as BO), etc.); and adducts (number of moles added: 2 to 30) of bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.) with alkylene oxides having from 2 to 4 carbon atoms (EO, PO, BO, etc.).

In addition to the dihydric diols, trihydric or higher (tri- to octahydric or higher) alcohol components may also be contained. Specifically, tri- to octahydric or higher aliphatic polyhydric alcohols having 3 to 36 carbon atoms (alkane polyols and their intramolecular or intermolecular dehydration products, such as glycerin, triethylolethane, trimethylolpropane, pentaerythritol, sorbitol, sorbitan, polyglycerin, dipentaerythritol; sugars and their derivatives, such as sucrose and methyl glucoside; etc.) ); adducts (1 to 30 moles added) of alkylene oxides (EO, PO, BO, etc.) having 2 to 4 carbon atoms of the above-mentioned aliphatic polyhydric alcohols; adducts (2 to 30 moles added) of alkylene oxides (EO, PO, BO, etc.) having 2 to 4 carbon atoms of trisphenols (such as trisphenol PA); adducts (2 to 30 moles added) of alkylene oxides (EO, PO, BO, etc.) having 2 to 4 carbon atoms of novolak resins (such as phenol novolak and cresol novolak; average degree of polymerization 3 to 60). These may be used alone or in combination of two or more.

- Polycarboxylic acid component -
Examples of the polycarboxylic acid component include dicarboxylic acids (dicarboxylic acids), specifically, alkanedicarboxylic acids having 4 to 36 carbon atoms (such as succinic acid, apidic acid, and sebacic acid), alkenylsuccinic acids (such as dodecenylsuccinic acid), alicyclic dicarboxylic acids having 4 to 36 carbon atoms (such as dimer acids (dimerized linoleic acid)), alkenedicarboxylic acids having 4 to 36 carbon atoms (such as maleic acid, fumaric acid, citraconic acid, and mesaconic acid), and aromatic dicarboxylic acids having 8 to 36 carbon atoms (such as phthalic acid, isophthalic acid, terephthalic acid, or derivatives thereof, and naphthalenedicarboxylic acid). Among these, alkanedicarboxylic acids having 4 to 20 carbon atoms and aromatic dicarboxylic acids having 8 to 20 carbon atoms are preferred. Examples of the polycarboxylic acid component include acid anhydrides and lower alkyl (1 to 4 carbon atoms) esters (such as methyl esters, ethyl esters, and isopropyl esters) of the above-mentioned compounds. These may be used alone or in combination of two or more.
In addition, ring-opening polymerization systems such as polylactic acid and polycarbonate diol can also be suitably used.

The polyester can be isolated, for example, by heating and drying an aqueous dispersion containing pigment-encapsulated resin particles, and then placing the resulting dried product in a tetrahydrofuran (THF) solution to dissolve the polyester. The pigment is then removed by centrifugation, filtration, or other methods, and the THF is then removed to isolate the polyester. Recycling GPC can also be used if necessary.

The molecular weight of the polyester can be selected appropriately depending on the purpose, but a weight-average molecular weight (Mw) of 7,000 to 15,000 is preferred, and 9,000 to 13,000 is more preferred, as measured by GPC. A weight-average molecular weight of 7,000 or more suppresses the formation of a fine particle emulsion during the emulsification process, allowing the entire surface of the pigment to be covered. Furthermore, a weight-average molecular weight of 15,000 or less enables emulsification at a low water content, allowing the pigment to be retained within the resin emulsion.

The glass transition temperature (Tg) of the polyester is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 30°C to 100°C, and more preferably 50°C to 80°C.

The softening temperature of the polyester is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 60°C to 180°C, more preferably 80°C to 150°C.
The molecular structure of the polyester can be confirmed by NMR measurement using a solution or solid, as well as GC/MS, LC/MS, IR measurement, and the like.

The polyester can be produced by a conventional method, for example, the following method.
First, the polyol and the polycarboxylic acid are polycondensed in the absence of a solvent or in the presence of an organic solvent.
The acid value of the polyester can be adjusted by any method. For example, the acid value can be imparted by reacting the obtained polyester with a polycarboxylic acid or a carboxylic acid anhydride.

<Pigments>
As the pigment, inorganic pigments can be used, such as titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, and chrome yellow, as well as carbon blacks (C.I. Pigment Black 7) produced by known methods, such as furnace black, lamp black, acetylene black, and channel black, and metals such as copper and iron (C.I. Pigment Black 11).

The primary particle size of the carbon black is preferably 10 nm or more and 50 nm or less, and more preferably 10 nm or more and 35 nm or less. By keeping the primary particle size within this range, the number of coarse particles in the aqueous dispersion containing the pigment-encapsulated resin particles is reduced, resulting in good storage stability and improved color development.

The primary particle size of the carbon black was measured using a transmission electron microscope (TEM) and image analysis software (ImageJ, manufactured by the National Institutes of Health, USA). 20 primary particles were randomly selected through image analysis, their particle diameters were measured, and the average was calculated. If the particles had a major and minor diameter, the major diameter was used for the calculation.

The pH of the carbon black is preferably 2 or more and 12 or less, and more preferably 7 or more and 10 or less. By keeping the pH within this range, the amount of coarse particles in the aqueous dispersion containing the pigment-encapsulated resin particles is reduced.

The DBP (dibutyl phthalate) absorption of the carbon black is preferably 30 mL/100 g or more and 150 mL/100 g or less. By keeping it in this range, pigment dispersibility in organic solvents can be improved. The DBP oil absorption of the carbon black can be measured using the method of JIS K6217.

Self-dispersing pigments may also be used. These self-dispersing pigments are pigments whose dispersion has been stabilized by introducing functional groups directly onto the pigment surface or via other atomic groups. As the pigment before dispersion stabilization, various conventionally known pigments, such as those listed in WO 2009/014242, can be used.

<Pigment dispersant>
It is preferable to add a pigment dispersant to the pigment pre-dispersion in order to improve the dispersibility of the pigment. The pigment dispersant is not particularly limited, and surfactants, polymer dispersants, and the like can be appropriately selected depending on the purpose. Examples of pigment dispersants that can be used include (meth)acrylic resins, styrene-(meth)acrylic resins, hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high-molecular-weight acid esters, salts of high-molecular-weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high-molecular-weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalenesulfonic acid-formalin condensate salts, aromatic sulfonic acid-formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ethers, and stearylamine acetate.

The hydrophilicity/hydrophobicity of the pigment dispersant is not particularly limited and can be selected appropriately depending on the purpose, but a hydrophobic dispersant is preferred because it makes it easier for the pigment to be encapsulated in the resin and improves image density. Regarding the hydrophilicity/hydrophobicity of the pigment dispersant, if the pigment dispersant is insoluble in water it is hydrophobic, and if it is soluble in water it is hydrophilic.

The turbidity point of the pigment dispersant is preferably 2.0 to 3.5. By keeping it within this range, the number of coarse particles in the aqueous dispersion containing the pigment-encapsulated resin particles is reduced, resulting in good storage stability. The turbidity point is evaluated by dissolving 0.5 g of the dispersant in 10 ml of THF, followed by dropwise addition of ion-exchanged water while stirring. This solution is placed in a quartz cell and measured using a spectrophotometer (Spectrophotometer U-3900H, Hitachi High-Tech Science Corporation) with a slit of 2 nm, a WI lamp as the light source, and THF as the reference. The turbidity point is determined as the weight of ion-exchanged water added dropwise until the absorbance (abs) at a wavelength of 660 nm reaches 0.1 or greater.

The ratio of pigment to pigment dispersant in the pigment pre-dispersion is not particularly limited, but a ratio of pigment to pigment dispersant of 4:0.2 to 4:4 is preferred, 4:0.5 to 4:3 is more preferred, and 4:0.8 to 4:2.0 is even more preferred. By adding the pigment dispersant in this range, the dispersibility of the pigment pre-dispersion is improved, the number of coarse particles in the aqueous dispersion containing the pigment-encapsulated resin particles is reduced, and storage stability is improved.

Specific examples of pigment pre-dispersants include Joncryl (manufactured by Johnson Polymers), Anti-Terra-U (manufactured by BYK Chemie), Disperbyk (manufactured by BYK Chemie), Efka (manufactured by Efka Chemicals), Flourene (manufactured by Kyoeisha Chemical Co., Ltd.), Disparlon (manufactured by Kusumoto Chemicals Co., Ltd.), Ajisper (manufactured by Ajinomoto Fine-Techno Co., Ltd.), Demol, Homogenol, Emulgen (all manufactured by Kao Corporation), Solsperse (manufactured by Lubrizol Japan Co., Ltd.), and Nikkol (manufactured by Nikko Chemicals Co., Ltd.).

<Ink>
The organic solvent, water, coloring material, resin, additives, etc. used in the ink will be described below.

<Organic solvent>
The organic solvent used in the present invention is not particularly limited, and any water-soluble organic solvent can be used, including, for example, polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.
Specific examples of the water-soluble organic solvent include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, and the like. polyhydric alcohols such as pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, and petriol; ethylene glycol monoethyl ether; and ethylene glycol monobutyl ether. polyhydric alcohol alkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol; propylene carbonate; and ethylene carbonate.
It is preferable to use an organic solvent having a boiling point of 250° C. or less, since it not only functions as a wetting agent but also provides good drying properties.

Polyol compounds having 8 or more carbon atoms and glycol ether compounds are also preferably used. Specific examples of polyol compounds having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.
Specific examples of glycol ether compounds include polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; and polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

Polyol compounds with 8 or more carbon atoms and glycol ether compounds can improve the permeability of ink when paper is used as the recording medium.

There are no particular restrictions on the content of organic solvent in the ink and it can be selected appropriately depending on the purpose. However, from the viewpoint of the drying properties and ejection reliability of the ink, it is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 60% by mass or less.

<Water>
The water content in the ink is not particularly limited and can be selected appropriately depending on the purpose. From the viewpoint of the drying properties and ejection reliability of the ink, however, the water content is preferably 10% by mass or more and 90% by mass or less, and more preferably 20% by mass to 60% by mass.

There are no particular restrictions on the particle size of the solids in the ink and it can be selected appropriately depending on the purpose. However, to improve image quality such as ejection stability and image density, the maximum frequency, calculated as the maximum number, is preferably 20 nm or more and 1000 nm or less, and more preferably 20 nm or more and 150 nm or less. The solids include resin particles, pigment particles, etc. Particle size can be measured using a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

<Additives>
If necessary, surfactants, antifoaming agents, antiseptics, antifungals, rust inhibitors, pH adjusters, etc. may be added to the ink.

<Surfactant>
As the surfactant, any of silicone surfactants, fluorine surfactants, amphoteric surfactants, nonionic surfactants and anionic surfactants can be used.
Silicone surfactants are not particularly limited and can be appropriately selected depending on the purpose.Among them, those that do not decompose even at high pH are preferred, for example, side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, side-chain both-end modified polydimethylsiloxane, etc., and those having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as aqueous surfactants.In addition, polyether-modified silicone surfactants can also be used as the silicone surfactant, for example, compounds in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylsiloxane, etc.
As fluorine-based surfactants, for example, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chain are particularly preferred because of their low foaming properties. Examples of the perfluoroalkyl sulfonic acid compounds include perfluoroalkyl sulfonic acids and perfluoroalkyl sulfonate salts. Examples of the perfluoroalkyl carboxylic acid compounds include perfluoroalkyl carboxylic acids and perfluoroalkyl carboxylate salts. Examples of the polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chain include sulfate ester salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups on the side chains, and salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups on the side chains. Counter ions of the _salts in these fluorine-based _surfactants include Li, Na, K, _{NH4 , NH3CH2CH2OH , NH2} ( _CH2CH2OH ) ₂ , NH( _CH2CH2OH ) ₃ , and the like.
Examples of amphoteric surfactants include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.
Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adducts of acetylene alcohol.
Examples of anionic surfactants include polyoxyethylene alkyl ether acetates, dodecylbenzenesulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates.
These may be used alone or in combination of two or more.

The silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples include side-chain-modified polydimethylsiloxane, both-end-modified polydimethylsiloxane, one-end-modified polydimethylsiloxane, and both-end-modified side-chain polydimethylsiloxane. Polyether-modified silicone surfactants having a polyoxyethylene group or a polyoxyethylene-polyoxypropylene group as the modifying group are particularly preferred because they exhibit good properties as aqueous surfactants.
Such surfactants may be synthesized appropriately or commercially available products, such as those available from BYK Corporation, Shin-Etsu Chemical Co., Ltd., Dow Corning Toray Silicone Co., Ltd., Nippon Emulsion Co., Ltd., and Kyoeisha Chemical Co., Ltd.
The polyether-modified silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples include surfactants represented by general formula (S-1), in which a polyalkylene oxide structure is introduced into the Si moiety side chain of dimethylpolysiloxane.
(In the general formula (S-1), m, n, a, and b each independently represent an integer, R represents an alkylene group, and R′ represents an alkyl group.)
As the polyether-modified silicone surfactant, commercially available products can be used, and examples thereof include KF-618, KF-642, KF-643 (Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602, SS-1906EX (Nippon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (Dow Corning Toray Silicone Co., Ltd.), BYK-33, BYK-387 (BYK-Chemie Co., Ltd.), TSF4440, TSF4452, TSF4453 (Toshiba Silicon Co., Ltd.), and the like.

The fluorine-based surfactant is preferably a compound having 2 to 16 fluorine-substituted carbon atoms, more preferably a compound having 4 to 16 fluorine-substituted carbon atoms.
Examples of fluorine-based surfactants include perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in the side chains. Among these, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in the side chains are preferred because they have low foaming properties, and fluorine-based surfactants represented by general formula (F-1) and general formula (F-2) are particularly preferred.
In the compound represented by the above general formula (F-1), m is preferably an integer of 0 to 10, and n is preferably an integer of 0 to 40 in order to impart water solubility.
General formula (F-2)
C _n F _2n+1- CH ₂ CH(OH)CH ₂ -O-(CH ₂ CH ₂ O) _a -Y
In the compound represented by the general formula (F-2), Y is H, or CmF _2m+1 where m is an integer from 1 to 6, or CH ₂ CH(OH)CH ₂ -CmF _2m+1 where m is an integer from 4 to 6, or CpH _2p+1 where p is an integer from 1 to 19. n is an integer from 1 to 6. a is an integer from 4 to 14.
Commercially available fluorine-based surfactants may be used, such as Surflon S-111, S-112, S-113, S-121, S-131, S-132, S-141, and S-145 (all manufactured by Asahi Glass Co., Ltd.); Fullard FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, and FC-431 (all manufactured by Sumitomo 3M Limited); Megafa F-470, F-1405, F-474 (all manufactured by Dainippon Ink and Chemicals, Inc.); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, UR, Capstone FS-30, FS-31, FS-3100, FS-34, FS-35 (all manufactured by Chemours); FT-110, FT- 250, FT-251, FT-400S, FT-150, FT-400SW (all manufactured by Neos Co., Ltd.), Polyfox PF-136A, PF-156A, PF-151N, PF-154, PF-159 (manufactured by Omnova), Unidyne DSN-403N (manufactured by Daikin Industries, Ltd.), and among these, those with good print quality, particularly color development and paper adhesion are preferred. In view of the remarkable improvement in permeability, wettability and dyeing levelness, particularly preferred are FS-3100, FS-34 and FS-300 manufactured by Chemours Corporation, FT-110, FT-250, FT-251, FT-400S, FT-150 and FT-400SW manufactured by Neos Co., Ltd., Polyfox PF-151N manufactured by Omnova, and Unidyne DSN-403N manufactured by Daikin Industries, Ltd.

There are no particular restrictions on the content of surfactant in the ink and it can be selected appropriately depending on the purpose, but from the viewpoint of achieving excellent wettability and ejection stability as well as improved image quality, a content of 0.001% by mass or more and 5% by mass or less is preferred, and 0.05% by mass or more and 5% by mass or less is even more preferred.

<Antifoaming agent>
The defoaming agent is not particularly limited, and examples thereof include silicone-based defoaming agents, polyether-based defoaming agents, and fatty acid ester-based defoaming agents. These may be used alone or in combination of two or more. Among these, silicone-based defoaming agents are preferred because of their excellent foam-breaking effect.

<Preservative and fungicide>
The antiseptic and antifungal agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one.

<Rust inhibitor>
The rust inhibitor is not particularly limited, and examples thereof include acid sulfites and sodium thiosulfate.

<pH adjuster>
There are no particular limitations on the pH adjuster, as long as it can adjust the pH to 7 or higher, and examples thereof include amines such as diethanolamine and triethanolamine.

The physical properties of the ink are not particularly limited and can be appropriately selected depending on the purpose. For example, it is preferable that the viscosity, surface tension, pH, etc. are within the following ranges.
The viscosity of the ink at 25°C is preferably 5 mPa·s or more and 30 mPa·s or less, and more preferably 5 mPa·s or more and 25 mPa·s or less, from the viewpoint of improving print density and character quality and obtaining good ejection properties. Here, the viscosity can be measured using, for example, a rotational viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.). Measurement conditions include 25°C, a standard cone rotor (1°34' x R24), a sample liquid volume of 1.2 mL, a rotation speed of 50 rpm, and 3 minutes.
The surface tension of the ink is preferably 35 mN/m or less, and more preferably 32 mN/m or less at 25° C., in order to ensure that the ink is properly leveled on the recording medium and the drying time of the ink is shortened.
The pH of the ink is preferably 7 to 12, and more preferably 8 to 11, from the viewpoint of preventing corrosion of metal members that come into contact with the ink.

<Pretreatment liquid>
The pretreatment liquid contains a flocculant, an organic solvent, and water, and may also contain surfactants, antifoaming agents, pH adjusters, antiseptics, antifungals, antirust agents, and the like, as required.
The organic solvent, surfactant, antifoaming agent, pH adjuster, antiseptic/fungal agent, and antirust agent may be the same as those used in ink, and other materials used in known treatment liquids may also be used.
The type of flocculant is not particularly limited, and examples thereof include water-soluble cationic polymers, acids, and polyvalent metal salts.

<Post-processing solution>
The post-treatment liquid is not particularly limited as long as it can form a transparent layer. The post-treatment liquid can be obtained by selecting and mixing organic solvents, water, resins, surfactants, antifoaming agents, pH adjusters, antiseptic and antifungal agents, anti-rust agents, etc. as needed. The post-treatment liquid may be applied to the entire recording area formed on the recording medium, or may be applied only to the area where the ink image is formed.

<Recording Media>
There are no particular limitations on the recording medium, and although plain paper, glossy paper, special paper, cloth, etc. can be used, good image formation is also possible using an impermeable substrate.
The non-permeable substrate is a substrate having a surface with low water permeability and low absorbency, and includes materials that have many cavities inside but are not open to the outside. More quantitatively, it refers to a substrate whose water absorption amount from the start of contact to 30 msec ^1/2 in the Bristow method is 10 mL/m ² or less.
As the impermeable substrate, for example, a plastic film such as a vinyl chloride resin film, a polyethylene terephthalate (PET) film, a polypropylene film, a polyethylene film, or a polycarbonate film can be suitably used.

The recording medium is not limited to commonly used recording media, but can also be wallpaper, flooring, building materials such as tiles, cloth for clothing such as T-shirts, textiles, leather, etc., as appropriate. Furthermore, by adjusting the configuration of the path along which the recording medium is transported, ceramics, glass, metal, etc. can also be used.

<Recorded materials>
The ink recorded matter of the present invention comprises an image formed on a recording medium using the ink of the present invention.
Recording can be performed using an inkjet recording apparatus and an inkjet recording method to produce a recorded product.

<Recording device and recording method>
The ink of the present invention can be suitably used in various recording devices using the ink jet recording method, such as printers, facsimile machines, copying machines, printer/fax/copier combination machines, and three-dimensional modeling devices.
In the present invention, the term "recording apparatus" and "recording method" refer to an apparatus capable of ejecting ink or various treatment liquids onto a recording medium, and a method of recording using the apparatus. The term "recording medium" refers to an object onto which ink or various treatment liquids can be attached, even if only temporarily.
This recording device can include not only the head portion that ejects ink, but also means related to feeding, transporting, and discharging the recording medium, as well as other devices called pre-processing devices and post-processing devices.
The recording apparatus and recording method may have a heating means used in the heating step and a drying means used in the drying step. The heating means and drying means include, for example, means for heating and drying the printed surface and back surface of the recording medium. The heating means and drying means are not particularly limited, but for example, a hot air heater or an infrared heater can be used. Heating and drying can be carried out before, during, or after printing.
Furthermore, the recording device and recording method are not limited to those that visualize meaningful images such as letters and figures using ink. For example, those that form patterns such as geometric designs and those that create three-dimensional images are also included.
Furthermore, unless otherwise specified, the recording apparatus includes both a serial type apparatus in which the ejection head moves and a line type apparatus in which the ejection head does not move.
Furthermore, this recording device includes not only desktop types, but also wide-width recording devices that can print on A0-sized recording media, and continuous feed printers that can use continuous paper wound into a roll as a recording medium, for example.
An example of a recording apparatus will be described with reference to FIGS. 4 and 5. FIG. 4 is a perspective view of the apparatus. FIG. 5 is a perspective view of a main tank. An image forming apparatus 400, serving as an example of a recording apparatus, is a serial-type image forming apparatus. A mechanism unit 420 is provided within an exterior 401 of the image forming apparatus 400. Each ink storage unit 411 of the main tanks 410 (410k, 410c, 410m, 410y) for each color, black (K), cyan (C), magenta (M), and yellow (Y), is formed from a packaging material such as aluminum laminate film. The ink storage unit 411 is housed in a storage container case 414 made of, for example, plastic. As a result, the main tanks 410 are used as ink cartridges for each color.
On the other hand, a cartridge holder 404 is provided at the back of the opening when the cover 401c of the device body is opened. A main tank 410 is detachably attached to the cartridge holder 404. This allows each ink outlet 413 of the main tank 410 to communicate with an ejection head 434 for each color via a supply tube 436 for each color, making it possible to eject ink from the ejection head 434 onto a recording medium.

This recording device can include not only a part that ejects ink, but also devices called pre-processing devices and post-processing devices.
As an example of a pre-treatment device or a post-treatment device, a liquid storage unit containing a pre-treatment liquid or a post-treatment liquid and a liquid ejection head are added, as in the case of inks such as black (K), cyan (C), magenta (M), and yellow (Y), and the like, and the pre-treatment liquid or the post-treatment liquid is ejected by an inkjet recording method.
Other embodiments of the pre-treatment device and post-treatment device include those using a method other than the inkjet recording method, such as a blade coating method, a roll coating method, or a spray coating method.

The ink can be used in a wide variety of ways, not just inkjet recording. Other methods include blade coating, gravure coating, bar coating, roll coating, dip coating, curtain coating, slide coating, die coating, and spray coating.

The use of the ink of the present invention is not particularly limited and can be appropriately selected depending on the purpose, and can be applied to, for example, printed matter, paint, coating material, base, etc. Furthermore, the ink of the present invention can be used not only to form two-dimensional characters and images but also as a material for three-dimensional modeling for forming three-dimensional solid images (three-dimensional models).
Known 3D modeling devices can be used for forming 3D objects, and are not particularly limited. For example, devices equipped with ink storage means, supply means, discharge means, drying means, etc. can be used. 3D models include those obtained by applying ink multiple times. They also include molded products obtained by processing a structure on a substrate, such as a recording medium, to which ink has been applied. The molded products are, for example, records or structures formed in a sheet or film form that have been subjected to molding processes such as heat stretching or punching, and are suitable for use in applications where the surface is decorated and then molded, such as meters and operation panel panels for automobiles, office automation equipment, electrical and electronic devices, cameras, etc.

In the terminology of this invention, image formation, recording, printing, printing, etc. are all synonymous.

Recording medium, media, and printed material are all synonymous terms.

FIG. 3 shows an embodiment of a printing device using the ink of the present invention.
The printing device 1 includes an input unit 10, a pre-processing unit 50, a printing unit 20, a drying unit 30, and an output unit 40. In the printing device 1, a treatment liquid is applied to the sheet material P input from the input unit 10 in the pre-processing unit 50, the liquid is then applied in the printing unit 20 to perform the required printing, the liquid adhering to the sheet material P is dried in the drying unit 30, and the sheet material P is then discharged to the output unit 40.

The carry-in section 10 includes an input tray 11 on which multiple sheets P are stacked, a feeding device 12 that separates and feeds the sheets P one by one from the input tray 11, and a pair of registration rollers 13 that feed the sheets P into the printing section 20.

The feeding device 12 can be any type of feeding device, such as a device using rollers or a device that uses air suction. The leading edge of the sheet material P fed from the input tray 11 by the feeding device 12 reaches the pair of registration rollers 13, and then the pair of registration rollers 13 is driven at a predetermined timing to feed the sheet to the printing unit 20.

The pre-treatment section 50 has a treatment liquid container 51 that contains a treatment liquid that reacts with the liquid to suppress bleeding, and a pre-coating treatment rotor that serves as a treatment liquid application means that applies the treatment liquid to the sheet material P. The pre-coating treatment rotor has a draw-up roller that draws up the treatment liquid, an application roller 52 that receives the treatment liquid adhering to the draw-up roller and applies the treatment liquid to the surface of the sheet material being transported, and a roller 53 that clamps the sheet material by being pressed against the application roller.
After the treatment liquid is applied to the lower surface of the sheet material P by the application roller 52 , the sheet material P is turned upside down and conveyed to a pair of registration rollers 13 that constitutes the conveying section 10 .

The printing unit 20 includes a sheet conveying device 21 that conveys the sheet material P. The sheet conveying device 21 includes a belt that supports and conveys the sheet material P, a suction device that generates a suction force on the belt surface, and the like.
The printing unit 20 also includes a liquid ejection unit 22 that ejects and applies liquid onto the treatment liquid-applied surface of the sheet material P that is carried and transported by the belt of the sheet transport device 21 .
The liquid discharge section 22 is equipped with discharge units 23 (23A to 23F) which are liquid application means. For example, discharge unit 23A discharges cyan (C) liquid, discharge unit 23B discharges magenta (M) liquid, discharge unit 23C discharges yellow (Y) liquid, and discharge unit 23D discharges black (K) liquid. Discharge units 23F and 23F are used to discharge any of YMCK liquids, or special liquids such as white or gold (silver). Furthermore, a discharge unit that discharges a treatment liquid such as a surface coating liquid can also be provided.

The ejection unit 23 is, for example, a full-line type head made up of a plurality of liquid ejection heads (hereinafter simply referred to as "heads") each having a nozzle row in which a plurality of nozzles are arranged.
The ejection operation of each ejection unit 23 of the liquid ejection section 22 is controlled by a drive signal corresponding to the printing information. When the sheet material P carried on the drum passes through an area facing the liquid ejection section 22, liquid of each color is ejected from the ejection unit 23, and an image corresponding to the printing information is printed.

The sheet material P onto which the liquid has been applied by the liquid discharge unit 22 is delivered to the suction transport mechanism unit 31 of the drying unit 30 .
The drying section 30 includes a suction conveying mechanism section 31, which is a conveying means for conveying (suction conveying) the sheet material P in a suctioned state, and a drying mechanism section 32 for drying the liquid on the sheet material P being conveyed by the suction conveying mechanism section 31.

The sheet material P to which the liquid has been applied in the printing unit 20 is dried by the drying unit 32 while being transported by the suction transport mechanism 31 and then delivered to the discharge unit 40 .
The discharge section 40 includes a discharge tray 41 on which a plurality of sheet materials P are stacked. The sheet materials P conveyed from the drying section 30 are successively stacked and held on the discharge tray 41.

Note that while the pre-treatment unit 50 is configured to apply treatment liquid to one side of the sheet material P, this is not limited to this. Another treatment liquid container may be provided downstream in the transport direction from the treatment liquid container 51 to apply treatment liquid to the back side of the sheet material P, or the sheet material P that has passed through the treatment liquid container 51 may be turned over and passed through the treatment liquid container 51 again to apply treatment liquid to the back side of the sheet material P.

The following describes examples of the present invention, but the present invention is not limited to these examples. In the following description, "parts" means "parts by mass" unless otherwise specified, and "%" means "% by mass" unless otherwise specified.

First, we will explain how to evaluate various physical properties in the synthesis examples, production examples, preparation examples, working examples, and comparative examples described below.

[Production Example]
<Self-emulsifying resin: polyester synthesis example>
(Synthesis of Polyester A)
In a 500 mL four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, 262 parts of bisphenol A ethylene oxide 2-mol adduct (Fujifilm Wako Chemical Co., Ltd.: 4,4'-isopropylidenebis(2-phenoxyethanol)) and 75 parts of bisphenol A propylene oxide 2-mol adduct (Nippon Nyukazai Co., Ltd.: BA-P2 glycol) were mixed as diols, 4 parts of trimethylolpropane as a triol, and 146 parts of dimethyl terephthalate and 33 parts of dimethyl adipate as dicarboxylic acid components. After the atmosphere in the reaction vessel was thoroughly purged with nitrogen gas, 300 ppm (relative to the monomer) of titanium tetraisopropoxide was added, and the mixture was heated to 200°C under a nitrogen gas stream over about 4 hours, then to 230°C over 2 hours, and the reaction was continued until no effluent was observed. Thereafter, the mixture was reacted for 1.5 hours under a reduced pressure of 5 mmHg to 30 mmHg to obtain a polyester.
The resulting resin had an acid value (AV) of 0.5 mgKOH/g, a glass transition temperature (Tg) of 58°C, and a weight average molecular weight (Mw) of 8,900.
160 parts of the polyester obtained above was melted at 180°C under a nitrogen stream, and then 5.5 parts of trimellitic anhydride was added and stirred for 40 minutes to adjust the acid value of the resin, thereby obtaining [Polyester A] with an acid value (AV) of 20 mgKOH/g, a glass transition temperature (Tg) of 60°C, and a weight average molecular weight (Mw) of 9,000.

(Synthesis of Polyester B)
The same procedure as in the synthesis of Polyester A was carried out, except that the amount of trimellitic anhydride added was changed to 3.8 parts, to obtain Polyester B having an acid value (AV) of 14 mg KOH/g, a glass transition temperature (Tg) of 59°C, and a weight average molecular weight (Mw) of 9,000.

(Synthesis of Polyester C)
The same procedure as in the synthesis of Polyester A was carried out, except that the amount of trimellitic anhydride added was changed to 8.5 parts, to obtain [Polyester C] having an acid value (AV) of 30 mgKOH/g, a glass transition temperature (Tg) of 60°C, and a weight average molecular weight (Mw) of 9,000.

(Synthesis of Polyester D)
In a 1 L four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, 358 parts of propylene glycol as a diol, 731 parts of dimethyl terephthalate as a dicarboxylic acid, and 111 parts of succinic acid were mixed. After thoroughly purging the atmosphere in the reaction vessel with nitrogen gas, 300 ppm (relative to the monomer) of titanium tetraisopropoxide was added, and the mixture was heated to 200°C over about 4 hours under a nitrogen gas stream, then heated to 230°C over 2 hours, and reacted until no effluent remained. The mixture was then reacted for 1.0 hour under a reduced pressure of 5 mmHg to 30 mmHg to obtain a polyester.
The resulting resin had an acid value (AV) of 0.5 mgKOH/g, a glass transition temperature (Tg) of 59°C, and a weight average molecular weight (Mw) of 11,800.
160 parts of the polyester obtained above was melted at 180°C under a nitrogen stream, and then 4.5 parts of trimellitic anhydride was added and stirred for 40 minutes to adjust the acid value of the resin, thereby obtaining [Polyester D] with an acid value (AV) of 17 mgKOH/g, a glass transition temperature (Tg) of 60°C, and a weight average molecular weight (Mw) of 12,000.

(Synthesis of Polyester E)
In a 500 mL four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, 275 parts of bisphenol A ethylene oxide 2-mol adduct (Fujifilm Wako Chemical Co., Ltd.: 4,4'-isopropylidenebis(2-phenoxyethanol)) and 79 parts of bisphenol A propylene oxide 2-mol adduct (Nippon Nyukazai Co., Ltd.: BA-P2 glycol) as diols, as well as 140 parts of dimethyl isophthalate and 26 parts of adipic acid as dicarboxylic acids, were mixed. Then, after thoroughly replacing the atmosphere inside the reaction vessel with nitrogen gas, 300 ppm (relative to the monomer) of titanium tetraisopropoxide was added, and the mixture was heated to 200°C under a nitrogen gas flow over about 4 hours, then heated to 230°C over 2 hours, and reacted until no effluent was observed. The mixture was then reacted for 1 hour under a reduced pressure of 5 mmHg to 30 mmHg to obtain a polyester.
The resulting resin had an acid value (AV) of 0.5 mgKOH/g, a glass transition temperature (Tg) of 47°C, and a weight average molecular weight (Mw) of 4,800.
160 parts of the polyester obtained above was melted at 180°C under a nitrogen stream, and then 6 parts of trimellitic anhydride was added and stirred for 40 minutes to adjust the acid value of the resin, thereby obtaining [Polyester E] having an acid value (AV) of 20 mgKOH/g, a glass transition temperature (Tg) of 50°C, and a weight average molecular weight (Mw) of 4,900.

(Synthesis of Polyester F)
The same procedure as in the synthesis of Polyester A was carried out, except that the amount of trimellitic anhydride added was changed to 2.4 parts, to obtain [Polyester F] having an acid value (AV) of 9 mg KOH/g, a glass transition temperature (Tg) of 59°C, and a weight average molecular weight (Mw) of 9,000.

(Synthesis of Polyester G)
The same procedure as in the synthesis of Polyester A was carried out, except that the amount of trimellitic anhydride added was changed to 15 parts, to obtain [Polyester G] having an acid value (AV) of 52 mg KOH/g, a glass transition temperature (Tg) of 62°C, and a weight average molecular weight (Mw) of 9,000.

(Synthesis of Polyester H)
In a 500 mL four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, 146 parts of propylene glycol as a diol, 54.6 parts of bisphenol A ethylene oxide 2-mol adduct (manufactured by Fujifilm Wako Chemical Co., Ltd.: 4,4'-isopropylidenebis(2-phenoxyethanol)), and 250.7 parts of bisphenol A propylene oxide 2-mol adduct (manufactured by Nippon Nyukazai Co., Ltd.: BA-P2 glycol), 6.4 parts of trimethylolpropane as a triol, and 193.7 parts of dimethyl terephthalate as a dicarboxylic acid were mixed. Then, after thoroughly replacing the atmosphere in the reaction vessel with nitrogen gas, 300 ppm (relative to the monomer) of titanium tetraisopropoxide was added, and the temperature was raised to 200°C under a nitrogen gas stream over about 4 hours, and then raised to 230°C over 2 hours, and the reaction was continued until no effluent was observed. Thereafter, the mixture was reacted for 4 hours under a reduced pressure of 5 mmHg to 30 mmHg to obtain a polyester.
The resulting resin had an acid value (AV) of 0.4 mgKOH/g, a glass transition temperature (Tg) of 80°C, and a weight average molecular weight (Mw) of 24,500.
150 parts of the polyester obtained above was melted at 180°C under a nitrogen stream, and then 4.2 parts of trimellitic anhydride was added and stirred for 40 minutes to adjust the acid value of the resin, thereby obtaining [Polyester H] having an acid value (AV) of 20 mgKOH/g, a glass transition temperature (Tg) of 81°C, and a weight average molecular weight (Mw) of 25,000.

<Pigment pre-dispersion>
(Preparation of Pigment Pre-Dispersion α)
The ingredients in the following formulation were mixed and poured into a 110 ml glass screw cap bottle. 170 parts of 2.0 mm diameter zirconia balls (YTZ balls, manufactured by Nikkato Corporation) were then added, and the bottle was attached to a shaker (Vibrax VXR basic, manufactured by IKA Corporation) and dispersed at 1000 rpm for 24 hours. The media and dispersion were then separated by filtration, and the mixture was filtered through a PTFE membrane filter with an average pore size of 5.0 μm to produce [Pigment Pre-Dispersion α]. The D50 of this Pigment Pre-Dispersion α in ELSZ-1000 was 90 nm.
Carbon black: 15.0 parts (NIPEX 35, manufactured by Orion Engineered Carbons, primary particle size: 31 nm, pH: 9.0, DBP absorption: 42 mL/100 g)
Pigment dispersant: 3.8 parts (Solsperse J200, manufactured by Lubrizol Corporation, hydrophobic, cloud point: 3.1 g)
Tetrahydrofuran: 41.2 parts

(Preparation of Pigment Pre-Dispersion β)
The ingredients according to the following formulation were mixed and poured into a 110 ml glass screw cap bottle. 170 parts of 2.0 mm diameter zirconia balls (YTZ balls, manufactured by Nikkato Corporation) were then added, and the bottle was attached to a shaker (Vibrax VXR basic, manufactured by IKA Corporation) and dispersed at 1000 rpm for 24 hours. The media and dispersion were then separated by filtration, and the mixture was filtered through a PTFE membrane filter with an average pore size of 5.0 μm to produce pigment pre-dispersion β. The D50 of this pigment pre-dispersion in ELSZ-1000 was 110 nm.
Carbon black: 15.0 parts (NIPEX 35, manufactured by Orion Engineered Carbons, primary particle size: 31 nm, pH: 9.0, DBP absorption: 42 mL/100 g)
Pigment dispersant: 3.8 parts (Ajisper PB821, manufactured by Ajinomoto Fine-Techno Co., Ltd., hydrophobic, cloud point: 2.9 g)
Methyl ethyl ketone: 41.2 parts

Below, examples and comparative examples are shown of the preparation of aqueous dispersions 1 to 11, and examples of the preparation of inks 1 to 11 using these aqueous dispersions 1 to 11.
The evaluation results of the properties of the aqueous dispersion and the ink are shown in Table 1.

[Example 1]
(Preparation of Aqueous Dispersion 1)
A 0.3 L separable flask equipped with a three-one motor, anchor blades, and thermocouple was charged with 60 g of pigment pre-dispersion α and 30 g of polyester A, and the mixture was stirred at 40 ° C. to obtain a pigment dispersion resin solution, so that the mass ratio (P / R) of the pigment (P: Pigment) to the polyester (R: Resin) was 0.5. Next, tetrahydrofuran was removed under reduced pressure so that the mass ratio (R / S) of the polyester to tetrahydrofuran (S: Solvent) was 1.8. Then, 1.2 g of triethylamine (1.1 equivalents relative to the carboxyl group) was added to neutralize the acid value of the polyester, and the mixture was stirred for 0.5 hours. While stirring at a speed of 350 rpm, 64 g of ion-exchanged water was added dropwise at a rate of 30 ml / min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, the tetrahydrofuran was removed under reduced pressure, and the mixture was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 40% with ion-exchanged water to obtain [Water-based Dispersion 1] containing pigment-encapsulated resin particles each containing two or more pigment primary particles.
FIG. 1 is a TEM image (magnification: 40,000 times) of [Aqueous Dispersion 1].

(Preparation of Ink 1)
An ink having the following formulation was prepared using the [Aqueous Dispersion 1] obtained above. The viscosity at 25°C was adjusted to 7.5 mPa s, and then the ink was filtered through a membrane filter having an average pore size of 10 μm to prepare [Ink 1].
Ink prescription
Aqueous dispersion 1 (as solid content) ... 10.75%
Propylene glycol (adjusted to a viscosity of 7.5 mPa·s) ... approximately 40%
Silicone surfactant: 1.0%
(Silface SAG503A manufactured by Nissin Chemical Industry Co., Ltd.)
・Aliphatic dialcohol surfactant: 0.1%
(Surfynol AD01 manufactured by Nissin Chemical Industry Co., Ltd.)
・Water... remaining amount
(Total: 100%)

[Example 2]
(Preparation of Aqueous Dispersion 2)
A 0.3 L separable flask equipped with a three-one motor, anchor blades, and thermocouple was charged with 60 g of pigment pre-dispersion α and 30 g of polyester B, and the mixture was stirred at 40 ° C. to obtain a pigment dispersion resin solution, so that the mass ratio (P / R) of the pigment (P: Pigment) to the polyester (R: Resin) was 0.5. Next, tetrahydrofuran was removed under reduced pressure to obtain a mass ratio (R / S) of the polyester to tetrahydrofuran (S: Solvent) of 1.8. Then, 0.84 g of triethylamine (1.1 equivalents relative to the carboxyl group) was added and mixed and stirred for 0.5 hours to neutralize the acid value of the polyester. While stirring at a speed of 350 rpm, 64 g of ion-exchanged water was added dropwise at a rate of 30 ml / min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, the tetrahydrofuran was removed under reduced pressure, and the mixture was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 40% with ion-exchanged water to obtain [Water-based Dispersion 2] containing pigment-encapsulated resin particles each containing two or more pigment primary particles.
(Preparation of Ink 2)
[Ink 2] was prepared in the same manner as [Ink 1], except that [Aqueous Dispersion 2] was used instead of [Aqueous Dispersion 1].

[Example 3]
(Preparation of Aqueous Dispersion 3)
A 0.3 L separable flask equipped with a three-one motor, anchor blades, and thermocouple was charged with 60 g of pigment pre-dispersion α and 30 g of polyester C, and the mixture was stirred at 40 ° C. to obtain a pigment dispersion resin solution, so that the mass ratio (P / R) of the pigment (P: Pigment) to the polyester (R: Resin) was 0.5. Next, tetrahydrofuran was removed under reduced pressure so that the mass ratio (R / S) of the polyester to tetrahydrofuran (S: Solvent) was 1.8. Then, 1.8 g of triethylamine (1.1 equivalents relative to the carboxyl group) was added to neutralize the acid value of the polyester, and the mixture was stirred for 0.5 hours. While stirring at a speed of 350 rpm, 64 g of ion-exchanged water was added dropwise at a rate of 30 ml / min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, the tetrahydrofuran was removed under reduced pressure, and the mixture was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 40% with ion-exchanged water to obtain [Water-based Dispersion 3] containing pigment-encapsulated resin particles each containing two or more pigment primary particles.
(Preparation of Ink 3)
[Ink 3] was prepared in the same manner as [Ink 1], except that [Aqueous Dispersion 3] was used instead of [Aqueous Dispersion 1].

[Example 4]
(Preparation of Aqueous Dispersion 4)
A 0.3 L separable flask equipped with a three-one motor, anchor blades, and thermocouple was charged with 60 g of pigment pre-dispersion α and 30 g of polyester D, and the mixture was stirred at 40 ° C. to obtain a pigment dispersion resin solution, so that the mass ratio (P / R) of the pigment (P: Pigment) to the polyester (R: Resin) was 0.5. Next, tetrahydrofuran was removed under reduced pressure so that the mass ratio (R / S) of the polyester to tetrahydrofuran (S: Solvent) was 1.8. Then, 1.0 g of triethylamine (1.1 equivalents relative to the carboxyl group) was added to neutralize the acid value of the polyester, and the mixture was stirred for 0.5 hours. While stirring at a speed of 350 rpm, 64 g of ion-exchanged water was added dropwise at a rate of 30 ml / min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, the tetrahydrofuran was removed under reduced pressure, and the mixture was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 40% with ion-exchanged water to obtain [Water-based Dispersion 4] containing pigment-encapsulated resin particles each containing two or more pigment primary particles.
(Preparation of Ink 4)
[Ink 4] was prepared in the same manner as [Ink 1], except that [Aqueous Dispersion 4] was used instead of [Aqueous Dispersion 1].

[Example 5]
(Preparation of Aqueous Dispersion 5)
A 0.3 L separable flask equipped with a three-one motor, anchor blades, and thermocouple was added with 60 g of pigment pre-dispersion β and 30 g of polyester A, and the mixture was stirred at 40 ° C. to obtain a pigment dispersion resin solution so that the mass ratio (P / R) of the pigment (P: Pigment) to the polyester (R: Resin) was 0.5. Next, tetrahydrofuran was removed under reduced pressure so that the mass ratio (R / S) of the polyester to tetrahydrofuran (S: Solvent) was 1.8. To neutralize the acid value of the polyester, 1.2 g of triethylamine (1.1 equivalents relative to the carboxyl group) was added and mixed and stirred for 0.5 hours. While stirring at a speed of 350 rpm, 64 g of ion-exchanged water was added dropwise at a rate of 30 ml / min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, the tetrahydrofuran was removed under reduced pressure, and the mixture was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 40% with ion-exchanged water to obtain [Water-based Dispersion 5] containing pigment-encapsulated resin particles each containing two or more pigment primary particles.
(Preparation of Ink 5)
[Ink 5] was prepared in the same manner as [Ink 1], except that [Aqueous Dispersion 5] was used instead of [Aqueous Dispersion 1].

[Comparative Example 1]
(Preparation of Aqueous Dispersion 6)
A 0.3 L separable flask equipped with a three-one motor, anchor blades, and thermocouple was charged with 60 g of pigment pre-dispersion α and 30 g of polyester E, and the mixture was stirred at 40 ° C. to obtain a pigment dispersion resin solution, so that the mass ratio (P / R) of the pigment (P: Pigment) to the polyester (R: Resin) was 0.5. Next, tetrahydrofuran was removed under reduced pressure so that the mass ratio (R / S) of the polyester to tetrahydrofuran (S: Solvent) was 1.8. Then, 1.2 g of triethylamine (1.1 equivalents relative to the carboxyl group) was added to neutralize the acid value of the polyester, and the mixture was stirred for 0.5 hours. While stirring at a speed of 350 rpm, 64 g of ion-exchanged water was added dropwise at a rate of 30 ml / min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, the tetrahydrofuran was removed under reduced pressure, and the mixture was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 40% with ion-exchanged water to obtain "Aqueous Dispersion 6" containing pigment-encapsulated resin particles each containing two or more pigment primary particles.
FIG. 2 is a TEM image (magnification: 40,000 times) of [Aqueous Dispersion 6].
(Preparation of Ink 6)
[Ink 6] was prepared in the same manner as [Ink 1], except that [Aqueous Dispersion 6] was used instead of [Aqueous Dispersion 1].

[Comparative Example 2]
(Preparation of Aqueous Dispersion 7)
A 0.3 L separable flask equipped with a three-one motor, anchor blades, and thermocouple was charged with 60 g of pigment pre-dispersion α and 30 g of polyester F, and the mixture was stirred at 40 ° C. to obtain a pigment dispersion resin solution, so that the mass ratio (P / R) of the pigment (P: Pigment) to the polyester (R: Resin) was 0.5. Next, tetrahydrofuran was removed under reduced pressure so that the mass ratio (R / S) of the polyester to tetrahydrofuran (S: Solvent) was 1.8. Then, 0.54 g of triethylamine (1.1 equivalents relative to the carboxyl group) was added and mixed and stirred for 0.5 hours to neutralize the acid value of the polyester. While stirring at a speed of 350 rpm, 64 g of ion-exchanged water was added dropwise at a rate of 30 ml / min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, the tetrahydrofuran was removed under reduced pressure, and the mixture was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 40% with ion-exchanged water to obtain [Aqueous Dispersion 7].
(Preparation of Ink 7)
An attempt was made to prepare [Ink 7] using the same procedure as for [Ink 1], except that [Aqueous Dispersion 7] was used instead of [Aqueous Dispersion 1]. However, filtration through a membrane filter with an average pore size of 10 μm was difficult, and printing evaluation was not possible.

[Comparative Example 3]
(Preparation of Aqueous Dispersion 8)
A 0.3 L separable flask equipped with a three-one motor, anchor blades, and thermocouple was charged with 60 g of pigment pre-dispersion α and 30 g of polyester G, and the mixture was stirred at 40 ° C. to obtain a pigment dispersion resin solution, so that the mass ratio (P / R) of the pigment (P: Pigment) to the polyester (R: Resin) was 0.5. Next, tetrahydrofuran was removed under reduced pressure so that the mass ratio (R / S) of the polyester to tetrahydrofuran (S: Solvent) was 1.8. Then, 3.1 g of triethylamine (1.1 equivalents relative to the carboxyl group) was added and mixed and stirred for 0.5 hours to neutralize the acid value of the polyester. While stirring at a speed of 350 rpm, 64 g of ion-exchanged water was added dropwise at a rate of 30 ml / min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, the tetrahydrofuran was removed under reduced pressure, and the mixture was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 40% with ion-exchanged water to obtain aqueous dispersion 8 containing pigment-encapsulating resin particles containing two or more pigment primary particles.
(Preparation of Ink 8)
[Ink 8] was prepared in the same manner as [Ink 1], except that [Aqueous Dispersion 8] was used instead of [Aqueous Dispersion 1].

[Comparative Example 4]
(Preparation of Aqueous Dispersion 9)
A 0.3 L separable flask equipped with a three-one motor, anchor blades, and thermocouple was charged with 10.5 g of carbon black (NIPEX 35, manufactured by Orion Engineered Carbons, primary particle size: 31 nm, pH: 9.0, DBP absorption: 42 mL/100 g), 30 g of polyester A, and 21.4 g of tetrahydrofuran, with a pigment (P: Pigment) to polyester (R: Resin) mass ratio (P/R) of 0.35. The resulting mixture was stirred at 40 ° C to obtain a pigment dispersion resin solution. Next, to neutralize the acid value of the polyester, 1.2 g of triethylamine (1.1 equivalents relative to the carboxyl group) was added and the mixture was stirred for 0.5 hours. 64 g of ion-exchanged water was added dropwise at a rate of 30 ml/min while stirring at 350 rpm, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, tetrahydrofuran and methyl ethyl ketone were removed under reduced pressure, and the residue was purified by filtration using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 40% with ion-exchanged water to obtain [Aqueous Dispersion 9].
(Preparation of Ink 9)
An attempt was made to prepare [Ink 9] using the same procedure as for [Ink 1], except that [Aqueous Dispersion 9] was used instead of [Aqueous Dispersion 1]. However, filtration through a membrane filter with an average pore size of 10 μm was difficult, and printing evaluation was not possible.

[Comparative Example 5]
(Preparation of Aqueous Dispersion 10)
A 0.3L separable flask equipped with a three-one motor, anchor blades, and a thermocouple was charged with 10.5g of carbon black (NIPEX 35, manufactured by Orion Engineered Carbons, primary particle size: 31nm, pH: 9.0, DBP absorption: 42mL/100g), 30g of polyester H, and 21.4g of tetrahydrofuran, with a mass ratio (P/R) of pigment (P: Pigment) to polyester (R: Resin) of 0.35. The resulting mixture was stirred at 40°C to obtain a pigment dispersion resin solution. Next, to neutralize the acid value of the polyester, 1.2g of triethylamine (1.1 equivalents relative to the carboxyl group) was added and the mixture was stirred for 0.5 hours. While stirring at 350 rpm, 64g of ion-exchanged water was added dropwise at a rate of 30ml/min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, tetrahydrofuran and methyl ethyl ketone were removed under reduced pressure, and the residue was purified by filtration using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 30% with ion-exchanged water to obtain [Aqueous Dispersion 10].
(Preparation of Ink 10)
An attempt was made to prepare [Ink 10] using the same procedure as for [Ink 1], except that [Aqueous Dispersion 10] was used instead of [Aqueous Dispersion 1]. However, filtration through a membrane filter with an average pore size of 10 μm was difficult, and printing evaluation was not possible.

[Comparative Example 6]
(Preparation of Masterbatch (M.B.))
570 parts of polyester H and 430 parts of carbon black (NIPEX 35, manufactured by Orion Engineered Carbons, primary particle size: 31 nm, pH: 9.0, DBP absorption: 42 mL/100 g) were premixed in a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.), and then the mixture was melt-kneaded using a twin-screw kneading extruder and then crushed to obtain a masterbatch (M.B.).
(Preparation of Aqueous Dispersion 11)
A 0.3 L separable flask equipped with a three-one motor, anchor blades, and thermocouple was charged with 13 g of masterbatch (M.B.) (component materials: 5.6 g of pigment and 7.4 g of polyester), 8.6 g of polyester A, and 12 g of tetrahydrofuran, and the mixture was stirred at 40 ° C. to obtain a pigment dispersion resin solution with a pigment (P: Pigment) to polyester (R: Resin) mass ratio (P/R) of 0.35. To neutralize the acid value of the polyester, 1.1 g of triethylamine (1.1 equivalents relative to the carboxyl group) was added and the mixture was stirred for 0.5 hours. While stirring at 350 rpm, 65 g of ion-exchanged water was added dropwise at a rate of 16 ml/min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, methyl ethyl ketone was removed, and the mixture was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 40% with ion-exchanged water to obtain [Water-based Dispersion 11] containing pigment-encapsulating resin particles each containing two or more pigment primary particles.
(Preparation of Ink 11)
[Ink 11] was prepared in the same manner as [Ink 1], except that [Aqueous Dispersion 11] was used instead of [Aqueous Dispersion 1].

[Comparative Example 7]
Instead of the pigment-encapsulated resin particles, the following polyester single resin emulsion and water-based pigment dispersion were prepared to prepare inks.
(Polyester single resin emulsion)
A 0.3L separable flask equipped with a three-one motor, anchor blades, and thermocouple was charged with 25g of polyester A and 14g of tetrahydrofuran, and the mixture was stirred at 40°C to obtain a resin solution. Next, to neutralize the acid value of the polyester, 0.99g of triethylamine (1.1 equivalents relative to the carboxyl group) was added and stirred for 20 minutes. While stirring at 350 rpm, 53g of ion-exchanged water was added dropwise at a rate of 25ml/min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, the tetrahydrofuran was removed under reduced pressure, and the mixture was filtered and purified using a nylon mesh with a 67μm mesh size. The solid content was adjusted to 30% with ion-exchanged water to obtain a polyester-only resin emulsion with a D50 of 95nm in ELSZ-1000.

(Preparation of Aqueous Dispersion 12)
62.0 parts of 1,6-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in 700 ml of dichloromethane, and 20.7 parts of pyridine (manufactured by Tokyo Chemical Industry Co., Ltd.) were added and stirred. To this solution, a solution prepared by dissolving 2-naphthalenecarbonyl chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) in 100 ml of dichloromethane was added dropwise over 2 hours, and the mixture was stirred at room temperature for 6 hours. The resulting reaction solution was washed with water, and the organic layer was isolated and dried over magnesium sulfate, and the solvent was distilled off. The residue was purified by silica gel column chromatography using a mixed solvent of dichloromethane/methanol (volume ratio 98/2) as an eluent to obtain a compound.
Next, 42.1 parts of the obtained compound was dissolved in 80 ml of dry methyl ethyl ketone and heated to 60°C while stirring. A solution of 24.0 parts of Karenz MOI (Showa Denko K.K.) dissolved in 20 ml of dry methyl ethyl ketone was added dropwise to this solution over 1 hour, and the mixture was stirred at 70°C for 12 hours. After cooling to room temperature, the solvent was distilled off. The residue was purified by silica gel column chromatography using a mixed solvent of dichloromethane/methanol (volume ratio 99/1) as an eluent to obtain a monomer.
Next, 2.30 parts of acrylic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 8.54 g of the monomer, and 0.31 parts of 2,2'-azobis(isobutyronitrile) (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in 100 ml of methyl ethyl ketone, and the mixture was stirred for 5 hours at a temperature of 75°C under a nitrogen gas stream. Thereafter, the reaction solution was cooled to room temperature, and reprecipitation was repeated five times using hexane to purify the copolymer. After the purification treatment, the copolymer was filtered off and dried under reduced pressure to obtain a pigment dispersant.
3.8 parts of the resulting pigment dispersant was dissolved in 30.0 parts of a diethanolamine aqueous solution to a pH of 8.0. Further, ion-exchanged water was added to bring the total amount of the aqueous solution to 45.0 parts. Next, 15.0 parts of carbon black (NIPEX 35, manufactured by Orion Engineered Carbons, primary particle size: 31 nm, pH: 9.0, DBP absorption: 42 mL/100 g) was mixed and poured into a 110 ml glass screw cap bottle. 170 parts of 2.0 mm diameter zirconia balls (manufactured by Nikkato Corporation, YTZ balls) were then poured into the bottle. The bottle was then attached to a shaker (manufactured by IKA Corporation, Vibrax VXR basic) and dispersed at 1000 rpm for 24 hours. The media and dispersion were then separated by filtration, and the mixture was filtered through a cellulose acetate membrane filter with an average pore size of 5.0 μm to produce [Aqueous Dispersion 12]. This [Aqueous Dispersion 12] had a D50 of 100 nm in ELSZ-1000.
(Preparation of Ink 12)
An ink having the following formulation was prepared using the [Polyester Single Resin Emulsion] and [Aqueous Dispersion 12] obtained above. The viscosity at 25°C was adjusted to 7.5 mPa s, and then the ink was filtered through a membrane filter having an average pore size of 10 μm to prepare [Ink 12].
Ink prescription
Polyester single resin emulsion (as solids) ... 5.375%
Water-based pigment dispersion (as solids) ... 5.375%
Propylene glycol (adjusted to a viscosity of 7.5 mPa·s) ... approximately 40%
Silicone surfactant: 1.0%
(Silface SAG503A manufactured by Nissin Chemical Industry Co., Ltd.)
・Aliphatic dialcohol surfactant: 0.1%
(Surfynol AD01 manufactured by Nissin Chemical Industry Co., Ltd.)
・Water remaining amount
(Total: 100%)

[Evaluation method for aqueous dispersions]
The prepared aqueous dispersions were evaluated for D50, the mass ratio of pigment (P) to resin (R) (P/R), the pigment exposure rate, the unencapsulated resin rate, and the number of coarse particles. The evaluation results are shown in Table 1.
<Molecular weight>
Apparatus: GPC (manufactured by Tosoh Corporation), detector: RI, measurement temperature: 40°C
Mobile phase: tetrahydrofuran, flow rate: 0.45 mL/min.
The number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw/Mn) are the number average molecular weight, weight average molecular weight, and molecular weight distribution measured by GPC (gel permeation chromatography) using a calibration curve prepared using polystyrene samples of known molecular weight as a standard. Columns with exclusion limits of 60,000, 20,000, and 10,000 connected in series were used.

<voiced mark>
The dispersant clouding point was evaluated by dissolving 0.5 g of the pigment dispersant in 10 ml of THF, then adding ion-exchanged water dropwise while stirring. The solution was placed in a quartz cell and measured using a spectrophotometer (Spectrophotometer U-3900H, manufactured by Hitachi High-Tech Science Corporation) with a slit of 2 nm, a WI lamp as the light source, and THF as the reference. The weight of ion-exchanged water added dropwise until the absorbance (abs) at a wavelength of 660 nm reached 0.1 or more was taken as the clouding point.

<Volume-based cumulative 50% particle size>
The D50 of the pigment pre-dispersion was measured by dynamic light scattering using a zeta potential/particle size measurement system (ELSZ-1000, manufactured by Otsuka Electronics Co., Ltd.). Specifically, the sample was diluted with ion-exchanged water or, if necessary, an organic solvent so that the solids concentration of the measurement sample was 0.01 wt %, and a portion of the resulting solution was placed in a quartz cell and set in a sample holder. Measurement was then performed under the following conditions: temperature: 25°C, dust cut (number of times: 5, upper: 5, lower: 100), cumulative number: 70.
Furthermore, the D50, D90, and volume frequency (%) in the range of 1 μm to 50 μm of the aqueous dispersion containing the pigment-encapsulated resin particles were measured using a laser diffraction/scattering particle size distribution analyzer (LA-960, manufactured by Horiba, Ltd.) Specifically, the sample was diluted with ion-exchanged water so that the transmittance (R) and transmittance (B) during measurement with the above-mentioned analyzer were 30% to 70%, and a portion of the obtained solution was placed in a batch-type cell (spacer: 50 μm), which was then set in a sample holder and measured.

<Number of coarse particles>
The number of coarse particles was measured using an AccuSizer particle size distribution analyzer manufactured by PSS Japan as follows. First, an aqueous dispersion containing pigment-encapsulated resin particles was diluted with ion-exchanged water until it was within the measurable range, and then the measurement was performed. From the measurement results, the number of particles of 1 μm or more in 5 μL of the aqueous dispersion, converted to a solids concentration of 1%, was calculated and this was defined as the number of coarse particles.
Note that particles with large sizes and large amounts of coarse particles could not be measured due to problems with the structure of the measuring device, AccuSizer, and are therefore indicated in Table 1 as "impossible to measure."

<Dispersion Stability of Aqueous Dispersion>
Each aqueous dispersion was placed in a glass screw tube and adjusted with ion-exchanged water to a solids concentration of 10.75%. The tube was left standing at 40°C for one week, and the precipitate present at the bottom of the screw tube was evaluated according to the following criteria. The presence of precipitate was confirmed by slowly inverting the screw tube without shaking, leaving it standing for one hour, and then visually observing the bottom. Redispersibility was also confirmed by setting the dial to 4 on a VORTEX Genius 3 (manufactured by IKA) and shaking for 10 seconds.
(Evaluation criteria)
◎: No precipitate ○: Some granular precipitate can be seen, but it can be redispersed △: There is a lot of granular precipitate, but it can be redispersed ×: There is precipitate that cannot be redispersed

<Pigment exposure rate>
The pigment exposure rate was calculated by observing the amount of exposed pigment on the coating film surface using a scanning electron microscope (SEM). Specifically, an aqueous dispersion or ink was first prepared using ion-exchanged water to a solids concentration of 10.75%. Next, the coating was applied to coated paper (Lumia Art Gloss 130) using a 0.15 mm bar coater and dried overnight at 25°C. This coating film was cut out and fixed to an SEM observation stub using carbon tape. This was then observed without any conductive treatment using a scanning electron microscope (ZEISS Merlin) at an accelerating voltage of 0.75 kV, a backscattered electron detector, and a magnification of 2000 to 20,000 times. This observation method made it possible to distinguish exposed pigment from the difference in the amount of backscattered electrons emitted by the carbon black and the resin. The pigment exposure rate was defined and calculated as the area occupied by the pigment relative to the entire coating film at a magnification of 20,000 times. The proportion of the area occupied by the pigment on the coating film surface was determined by binarizing the SEM observation image, and the average of the values from three visual fields observed at randomly changed locations was calculated.

<Ratio of pigment-encapsulated resin particles>
The abundance of pigment-encapsulated resin particles in emulsion resin particles was observed as follows. First, an emulsion containing pigment-encapsulated resin particles was diluted with ion-exchange water to a solids concentration of 0.1% to prepare a sample solution. Next, 1 μL of the sample solution was placed using a micropipette on a hydrophilically treated collodion film-attached mesh (Nisshin EM Co., Ltd., Collodion Film-attached Mesh, Cu150 Mesh), and the sample solution was immediately absorbed with triangular filter paper. Next, 1 μL of 10-fold diluted EM stainer was placed using a micropipette, and the sample solution was immediately absorbed with triangular filter paper. After drying under reduced pressure, the sample was observed with a transmission electron microscope (JEOL Ltd., JEM-2100F) at an accelerating voltage of 200 kV and a magnification of 40,000 times. Using this observation method, five or more images of a field of view containing three or more particles of 50 nm or larger were acquired at random locations, and the ratio of the number of pigment-encapsulated resin particles to the number of particles of 50 nm or larger was calculated for each image, and the average of these was calculated. This ratio was defined as the abundance ratio of pigment-encapsulated resin particles among the particles.

<Average aspect ratio>
The average aspect ratio was determined by image processing of images obtained by observing the pigment-encapsulated resin particles using the transmission electron microscope (TEM). Specifically, multiple images of the field of view including the pigment-encapsulated resin particles were obtained by arbitrarily changing the observation position, and pigment-encapsulated resin particles that did not overlap with other particles were extracted by binarization using image analysis software (ImageJ, manufactured by the National Institutes of Health, USA), and particle analysis was performed. The major axis/minor axis of the closest-fitting ellipse was used as the aspect ratio, and the average value for 20 particles was calculated.
In addition, when the "abundance ratio of pigment-encapsulated resin particles" is 0%, the aspect ratio (major axis/minor axis of pigment-encapsulated resin particles) cannot be measured, and therefore this is indicated as "-" in Table 1.

<Minimum particle size of resin particles not encapsulating pigment>
The minimum particle size of non-pigment-encapsulated resin particles was calculated as follows. First, an emulsion containing pigment-encapsulated resin particles was diluted with ion-exchange water to a solids concentration of 0.1% to prepare a sample solution. Next, 1 μL of the sample solution was placed using a micropipette on a hydrophilically treated collodion film-attached mesh (Nisshin EM Co., Ltd., Collodion Film-Attached Mesh, Cu150 Mesh), and the sample solution was immediately absorbed with triangular filter paper. Next, 1 μL of 10-fold diluted EM stainer was placed using a micropipette, and the sample solution was immediately absorbed with triangular filter paper. After drying under reduced pressure, the sample was observed with a transmission electron microscope (JEOL Ltd., JEM-2100F) at an accelerating voltage of 200 kV and a magnification of 40,000 times. Using this observation method, five or more images of a field of view containing five or more non-pigment-encapsulated resin particles were obtained by arbitrarily changing the location. The minimum particle size of the resin particles not encapsulating a pigment was calculated for each image, and the average value was taken as the minimum particle size of the resin particles not encapsulating a pigment.

[Ink evaluation method]
Next, the image density of each of the prepared inks was evaluated as follows.
<Image output method>
The exterior of an inkjet printer (IPSiO GXe5500 manufactured by Ricoh) was removed, a rear multi-manual feeder was attached, and pure water was passed through the ink supply path including the print head to clean it. The water was passed through sufficiently until the cleaning liquid was no longer colored, and then the cleaning liquid was completely drained from the device, and this was used as a printing device for evaluation.
The prepared ink was then filled into an ink cartridge to prepare an ink cartridge for evaluation. A filling operation was performed, and it was confirmed that all nozzles were filled with the evaluation ink and that no abnormal images were produced. After selecting the glossy paper clean mode in the printer driver, the user set the print mode to color matching off. In this mode, the ejection volume was adjusted by changing the head drive voltage so that the amount of ink deposited on the recording medium for a solid image was 20 g/ ^m² . Lumi Art Gloss 130 was used as the recording medium.

<Image Density>
A solid image was printed using the above image output method, and then dried at room temperature (25° C.) for 1 day and in an oven at 100° C. for 5 minutes to prepare images.
With a sheet of white plain paper placed under the printed image, the total density was measured using a spectrodensitometer X-Rite 939, and the K value was taken as the image density.
Further, the difference ΔOD (=OD ₂₅ −OD ₁₀₀ ) between the image density (OD ₂₅ ) obtained by drying at 25° C. and the image density (OD ₁₀₀ ) obtained by drying at 100° C. was calculated, and this ΔOD was evaluated according to the following evaluation criteria.
(Evaluation criteria)
〇: Less than 0 △: 0
×: greater than 0

<Surface roughness>
The surface roughness was calculated using a scanning probe microscope (SPM) as follows. First, a solid image was printed using the image output method described above, and then heated and dried in an oven at 100°C for 5 minutes. This coating film was cut out and observed under the following conditions to calculate the surface roughness. Observation was performed in three fields of view at randomly changed locations, and the average surface roughness (Ra) was calculated.
Apparatus: Scanning probe microscope (Dimension Icon manufactured by Bruker)
Cantilever: Olympus OMCL-AC240TS
Measurement mode: Tapping mode Observation range: 2 μm square

The present invention relates to the aqueous dispersion of (1) below, but also includes the following embodiments (2) to (10).
(1) An aqueous dispersion containing emulsion resin particles as a dispersoid,
the emulsion resin particles include pigment-encapsulated emulsion resin particles that encapsulate an inorganic pigment and non-pigment-encapsulated emulsion resin particles that do not encapsulate an inorganic pigment,
the emulsion resin particles have a volume-based cumulative 50% particle diameter (D50) of 40 nm or more and 150 nm or less, a volume-based cumulative 90% particle diameter (D90) of 70 nm or more and 300 nm or less, as measured by a laser diffraction scattering method, and an average aspect ratio of 1.0 or more and 1.5 or less, and the primary particle diameter of the inorganic pigment is smaller than the minimum particle diameter of the non-pigment-encapsulated emulsion resin particles;
An aqueous dispersion characterized by:
(2) The aqueous dispersion according to (1) above, wherein the emulsion resin particles contain a polyester, and the weight-average molecular weight of the polyester is 7,000 or more and 15,000 or less.
(3) The aqueous dispersion according to (1) or (2) above, wherein the number of coarse particles in the aqueous dispersion obtained by the following measurement method is 200,000 or less.
(Measurement method)
The aqueous dispersion is diluted with ion-exchanged water until it falls within a measurable range, and the particle size distribution is measured using an AccuSizer number count particle size distribution analyzer manufactured by PSS Japan.
From the measurement results, the number of particles of 1 μm or more in 5 μL of the aqueous dispersion before dilution is calculated.
(4) The aqueous dispersion according to any one of (1) to (3), wherein the mass ratio of the inorganic pigment to the resin in the aqueous dispersion (pigment/resin) is 0.20 or more and 0.75 or less, and the pigment exposure rate calculated under the following conditions is 8% or less.
(Pigment exposure rate calculation conditions)
An aqueous dispersion containing pigment-encapsulated emulsion resin particles is prepared to a solids concentration of 10.75% by mass. The aqueous dispersion is then applied to coated paper and dried at 25°C. The resulting film is observed under a scanning electron microscope (accelerating voltage 0.75 kV, backscattered electron detector, magnification 20,000x) without any conductive treatment. The pigment area is calculated by binarizing the observed image, and the proportion of the pigment on the coating film surface is taken as the pigment exposure rate.
(5) The aqueous dispersion according to any one of (1) to (4) above, wherein the cumulative volume frequency of particles having a particle size of 1 μm or more and 50 μm or less, as determined by a laser diffraction scattering method, of the emulsion resin particles is 1.0% or less.
(6) The aqueous dispersion according to any one of (1) to (5) above, wherein the inorganic pigment is carbon black.
(7) The aqueous dispersion according to any one of (1) to (6) above, wherein the proportion of the number of the pigment-encapsulating emulsion resin particles to the number of the emulsion resin particles having a particle diameter of 50 nm or more is 30% or more.
(8) The aqueous dispersion according to any one of (1) to (7) above, wherein the emulsion resin particles contain a polyester, the polyester having a carboxyl group, and is a self-emulsifying resin.
(9) A method for producing the aqueous dispersion according to any one of (1) to (8) above, comprising the following steps 1 to 4:
Step 1: A step of mixing a pigment, a pigment dispersant, and an organic solvent to obtain a pigment pre-dispersion in which the volume-based cumulative 50% particle diameter (D50) of the pigment is 30 nm or more and 120 nm or less. Step 2: A step of mixing the pigment pre-dispersion obtained in Step 1 with a self-emulsifying resin to obtain a pigment dispersion resin solution. Step 3: A step of mixing the pigment dispersion resin solution obtained in Step 2 with water to obtain a dispersion containing pigment-encapsulated emulsion resin particles in which the entire pigment is encapsulated in the self-emulsifying resin. Step 4: A step of removing the organic solvent from the dispersion containing pigment-encapsulated resin particles obtained in Step 3 to obtain an aqueous dispersion containing pigment-encapsulated resin particles. (10) An ink containing emulsion resin particles as a dispersoid in an aqueous medium,
An ink containing pigment-encapsulated emulsion resin particles encapsulating an inorganic pigment as a dispersoid,
the emulsion resin particles include pigment-encapsulated emulsion resin particles that encapsulate an inorganic pigment and non-pigment-encapsulated emulsion resin particles that do not encapsulate an inorganic pigment,
The pigment-encapsulated emulsion resin particles have a volume-based cumulative 50% particle diameter (D50) of 40 nm or more and 150 nm or less, a volume-based cumulative 90% particle diameter (D90) of 70 nm or more and 300 nm or less, as measured by a laser diffraction scattering method, and an average aspect ratio of 1.0 or more and 1.5 or less, and the primary particle diameter of the inorganic pigment is smaller than the minimum particle diameter of the non-pigment-encapsulated emulsion resin particles.
An ink characterized by:

1 Printing device 10 Intake section 11 Intake tray 12 Feeding device 13 Pair of registration rollers 20 Printing section 21 Sheet conveying device 22 Liquid ejection section 23, 23A, 23B, 23C, 23D, 23E, 23F Ejection unit 30 Drying section 31 Suction conveying mechanism section 32 Drying mechanism section 40 Outlet section 41 Outlet tray 50 Pre-processing section 51 Treatment liquid container 52 Application roller 53 Roller 400 Image forming device 401 Exterior 401c of image forming device Cover of device main body 404 Cartridge holder 410 Main tanks 410k, 410c, 410m, 410y Main tanks 411 for each color of black (K), cyan (C), magenta (M), and yellow (Y) Ink storage section 413 Ink outlet 414 Storage container case 420 Mechanism 434 Discharge head 436 Supply tube P Sheet material

Japanese Patent Application Laid-Open No. 2016-196621 Japanese Patent Application Laid-Open No. 2002-322396 Japanese Patent Application Laid-Open No. 2019-99819 Japanese Patent Application Laid-Open No. 2017-014337

Claims (7)

An aqueous dispersion containing emulsion resin particles as a dispersoid,
the emulsion resin particles include pigment-encapsulated emulsion resin particles that encapsulate an inorganic pigment and non-pigment-encapsulated emulsion resin particles that do not encapsulate an inorganic pigment,
the emulsion resin particles have a volume-based cumulative 50% particle size (D50) of 40 nm or more and 150 nm or less, a volume-based cumulative 90% particle size (D90) of 70 nm or more and 300 nm or less, as measured by a laser diffraction scattering method, and an average aspect ratio of 1.0 or more and 1.5 or less, and the primary particle size of the inorganic pigment is smaller than the minimum particle size of the pigment-unencapsulated emulsion resin particles;
a mass ratio of the inorganic pigment to the resin (pigment/resin) in the aqueous dispersion is 0.20 or more and 0.75 or less, and a pigment exposure rate calculated under the following conditions is 8% or less;
An aqueous dispersion characterized by:
(Pigment exposure rate calculation conditions)
An aqueous dispersion containing pigment-encapsulated emulsion resin particles is prepared to a solids concentration of 10.75% by mass. The aqueous dispersion is then applied to coated paper and dried at 25°C. The resulting film is observed under a scanning electron microscope (accelerating voltage 0.75 kV, backscattered electron detector, magnification 20,000x) without any conductive treatment. The pigment area is calculated by binarizing the observed image, and the proportion of the pigment on the coating film surface is taken as the pigment exposure rate. The aqueous dispersion according to claim 1, wherein the emulsion resin particles contain polyester, and the weight-average molecular weight of the polyester is 7,000 or more and 15,000 or less. 3. The aqueous dispersion according to claim 1, wherein the number of coarse particles in the aqueous dispersion obtained by the following measurement method is 200,000 or less.
(Measurement method)
The aqueous dispersion is diluted with ion-exchanged water until it falls within a measurable range, and the particle size distribution is measured using an AccuSizer number count particle size distribution analyzer manufactured by PSS Japan.
From the measurement results, the number of particles of 1 μm or more in 5 μL of the aqueous dispersion before dilution is calculated. 4. The aqueous dispersion according to claim 1, wherein the cumulative volume frequency of particles having a particle size of 1 μm or more and 50 μm or less, obtained by a laser diffraction scattering method, of the emulsion resin particles is 1.0% or less. The aqueous dispersion according to claim 1 , wherein the inorganic pigment is carbon black. 6. The aqueous dispersion according to claim 1, wherein the proportion of the number of the pigment-encapsulating emulsion resin particles to the number of the emulsion resin particles having a particle diameter of 50 nm or more is 30% or more. The aqueous dispersion according to claim 1 , wherein the emulsion resin particles contain a polyester, the polyester having a carboxyl group, and the polyester is a self-emulsifying resin.