JP7636711B2 - Aqueous dispersion, method for producing aqueous dispersion, ink and printed matter - Google Patents

Description

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

Inkjet recording devices have advantages such as low noise, low running costs, and easy color printing, and are widely used in ordinary households as digital signal output devices. In recent years, inkjet technology has been used not only for household use but also for commercial and industrial purposes. In commercial and industrial applications, low ink-absorbent coated paper for printing and non-ink-absorbent plastic media are used as recording media, and it is therefore required to achieve image quality on a par with that of conventional offset printing using inkjet recording methods for these media.
For example, Patent Documents 1 to 4 disclose water-based pigment dispersions in which pigment particles are coated with a specific resin.

However, even with such a technique, it is difficult to completely encapsulate the pigment. In addition, there are problems such as the high hydrophilicity of the resin that coats the pigment, which makes the resin easily detach from the pigment surface. As a result, the stability of the pigment composite resin particles is poor, and for example, the pigment aggregates due to heat drying, which deteriorates 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 ink cannot satisfy the recent user demand for images with high image density.
An object of the present invention is to provide an aqueous dispersion which has excellent dispersion stability and is capable of giving an image exhibiting high 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 encapsulating an inorganic pigment,
An aqueous dispersion characterized in that a pigment exposure rate calculated under the following pigment exposure rate calculation conditions is 8% or less, and a ratio of emulsion resin particles not encapsulating a pigment, as defined below, is 1.0 or less.
(Calculation conditions for pigment exposure rate)
An aqueous dispersion containing pigment-encapsulated emulsion resin particles is prepared so that the solid content concentration is 10.75% by mass. The aqueous dispersion is then applied to a coated paper, and the film obtained by drying at 25° C. is observed under a scanning electron microscope (accelerating voltage 0.75 kV, backscattered electron detector, magnification 20,000 times) without conducting a conductive treatment. The pigment area is calculated by binarizing the observed image, and the ratio of the pigment to the surface of the coating film is defined as the pigment exposure rate.
(Ratio of emulsion resin particles not containing pigment)
The aqueous dispersion containing the pigment-encapsulated emulsion resin particles is placed on a collodion film-attached mesh, and the dried sample is observed under a transmission electron microscope at an acceleration voltage of 200 kV and a magnification of 40,000 times. By this observation method, five or more images of a field of view containing three or more particles of 50 nm or more are obtained at any position. For each image, the number of pigment-encapsulated emulsion resin particles and the number of non-pigment-encapsulated emulsion resin particles are counted, and the ratio of non-pigment-encapsulated emulsion resin particles is calculated by the following formula (1), and the average value is taken as the ratio of non-pigment-encapsulated emulsion resin particles.

The present invention provides an aqueous dispersion that has excellent dispersion stability and can produce images with high image density.

FIG. 1 is a TEM image (magnification: 10,000 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 Example 1. FIG. 3 is an SEM image of the aqueous dispersion containing the pigment-encapsulated emulsion resin particles obtained in Example 1. FIG. 4 is an EFM image of the aqueous dispersion containing the pigment-encapsulated emulsion resin particles obtained in Example 1. FIG. 5 is a TEM image (magnification: 10,000 times) of the aqueous dispersion containing the pigment-encapsulated emulsion resin particles obtained in Comparative Example 1. FIG. 6 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. 7 is a TEM image (magnification: 40,000 times) of the ink obtained in Comparative Example 5. FIG. 8 is an SEM image of the ink obtained in Comparative Example 5. FIG. 9 is an EFM image of the ink obtained in Comparative Example 5. FIG. 10 is a perspective view illustrating an example of a recording apparatus. FIG. 11 is a perspective view illustrating an example of a main tank.

An example of an embodiment of the present invention will be described below. The following description is merely an example of an embodiment of the present invention and does not limit the scope of the present invention.

<Pigment-encapsulated emulsion resin particles>
The pigment-encapsulated emulsion resin particles in the present invention are in the form of a resin emulsion. By containing the pigment in the emulsion resin particles, it is possible to suppress the detachment of the resin from the pigment surface. The emulsion refers to 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 refer to a form in which the pigment is encapsulated in the emulsion resin particles of the resin emulsion, and the entire surface of the pigment is covered with the resin. It is preferable that the pigment is not encapsulated in the emulsion resin particles and dispersed in the dispersion medium, or that the pigment is partially exposed on the surface of the emulsion resin particles does not exist. In addition, it is preferable that the pigment-encapsulated emulsion resin particles are spherical.
In the aqueous dispersion, the pigment is encapsulated in the resin, so that the pigment does not aggregate, and an image in which the pigment is uniformly distributed can be obtained.

The phrase "the entire surface of the pigment is covered with resin" means that the distance from the outer edge (particle surface) of the pigment-encapsulated emulsion resin particle to the pigment, i.e., the thickness of the resin, is 5 nm or more, and is preferably 5 nm or more and 50 nm or less, and more preferably 10 nm or more and 30 nm or less. The thickness of the resin is determined by observing 10 or more pigment-encapsulated emulsion resin particles using the above-mentioned observation method of pigment-encapsulated emulsion resin particles using a transmission electron microscope (TEM), measuring the thickness from the resin surface layer on the outer edge of each particle to the pigment at 10 random locations, and calculating the average value.

Patent documents 1 to 4 propose coated pigments and microencapsulated pigments, but these are not pigments covered in a resin emulsion and are different from the pigment-encapsulated emulsion resin particles of the present invention.

When producing pigment-encapsulated emulsion resin particles, in addition to the pigment-encapsulated emulsion resin particles, emulsion resin particles that do not have a pigment (hereinafter referred to as "non-pigment-encapsulated emulsion resin particles") are also produced. The amount of pigment-encapsulated emulsion resin particles can be adjusted by appropriately selecting the ratio of pigment-encapsulated emulsion resin particles to non-pigment-encapsulated emulsion resin particles depending on the purpose. The amount of pigment-encapsulated emulsion resin particles is preferably 30% or more, more preferably 50% or more, by obtaining five or more images of a field of view that includes three or more particles of 50 nm or more. In addition, it is preferable that the pigment-encapsulated emulsion resin particles contain two or more primary pigment particles. In this way, the pigment density in the particles increases, thereby improving the image density.

The morphology of the pigment-encapsulating emulsion resin particles can be observed, for example, with a transmission electron microscope (TEM).
Observation of pigment-encapsulated emulsion resin particles using a transmission electron microscope (TEM) is performed, for example, as follows. First, a water-based dispersion containing pigment-encapsulated emulsion resin particles is diluted with ion-exchanged water so that the solid content concentration is 0.1% by mass to prepare a sample solution. Next, 1 μL of the sample solution is 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 is immediately absorbed with a triangular cut filter paper. Next, 1 μL of EM stainer diluted 10 times is placed using a micropipette, and the sample solution is immediately absorbed with a triangular cut filter paper. After drying under reduced pressure, observation is performed using a transmission electron microscope (JEM-2100F manufactured by JEOL Ltd.) at an accelerating voltage of 200 kV and a magnification of 40,000 times.

顔料未内包エマルション樹脂粒子比率は１．０以下であることが好ましい。顔料未内包エマルション樹脂粒子が少ないことで、粒径や粒子の密度が均一であるため、粒子の浮上や沈降といった分散不安定化が起きづらい。 The ratio of the pigment-encapsulated emulsion resin particles to the pigment-not-encapsulated emulsion resin particles is defined as the pigment-not-encapsulated emulsion resin particle ratio, and is calculated as follows.
According to the above-mentioned observation method of pigment-encapsulated emulsion resin particles by transmission electron microscope (TEM), five or more images of a field of view including three or more particles of 50 nm or more are obtained. For each image, the number of pigment-encapsulated emulsion resin particles and the number of non-pigment-encapsulated emulsion resin particles are counted, and the ratio of non-pigment-encapsulated emulsion resin particles is calculated by the following formula (1).

The ratio of non-pigment-containing emulsion resin particles is preferably 1.0 or less. When the amount of non-pigment-containing emulsion resin particles is small, the particle size and density are uniform, and dispersion instability such as floating or settling of particles is unlikely to occur.

The pigment-encapsulating emulsion resin particles are preferably spherical, and the aspect ratio of the particles is preferably in the range of 1.0 to 1.7, more preferably 1.0 to 1.5, and even more preferably 1.0 to 1.2.
The aspect ratio of the pigment-encapsulated emulsion resin particles was determined by image processing of the image obtained by observing the pigment-encapsulated emulsion resin particles using the above-mentioned transmission electron microscope (TEM). Specifically, the observation position was arbitrarily changed to obtain multiple images of the visual field including the pigment-encapsulated emulsion resin particles, and the pigment-encapsulated emulsion 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 most approximate ellipse was taken as the aspect ratio, and the average value of 20 particles was calculated.

The number of primary pigment particles contained in each particle of the pigment-encapsulated emulsion resin particles is preferably two or more. By containing multiple pigments in one particle, a dispersion that can achieve sufficient image density can be produced.

<Pigment exposure rate>
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 emulsion resin particles is prepared so that the solid content concentration is 10.75% by mass. The aqueous dispersion is then applied to coated paper and dried at 25° C. to obtain a film, which is observed under a scanning electron microscope (accelerating voltage 0.75 kV, backscattered electron detector, magnification 20,000 times) without being subjected to a conductive treatment.
This observation method makes it possible to distinguish the exposed pigment from the contrast of the SEM image due to the difference in the amount of reflected electron emission between the carbon black and the resin. The ratio of the area occupied by the pigment on the coating film surface at 20,000 times magnification is preferably 8% or less of the total area, and more preferably 5% or less.
The area of the coating film surface occupied by the pigment is determined by binarizing the SEM observation image, and it is preferable to take the average of three or more visual fields. Under these observation conditions, those that cannot be observed due to charge-up tend to have a low pigment exposure rate, and are easily observed when the pigment exposure rate is 3% or less.

The degree of pigment exposure can also be confirmed using an electric force microscope (EFM) as follows.
An aqueous dispersion containing pigment-encapsulated emulsion resin particles is prepared using ion-exchanged water so that the solid content concentration is 10.75% by mass. Then, the dispersion is coated on coated paper (Lumia Art Gloss 130) using a 0.15 mm bar coater and dried at 25° C. The coating film is cut out and observed under the following conditions using a scanning probe electron microscope (SPM).
Equipment: Bruker Dimension Icon
Cantilever: Olympus OMCL-AC240TM
Measurement mode: Electric force microscope (EFM) mode TipBias: 5V
Lift: 20 nm
Observation area: 5 μm square

This observation technique makes it possible to distinguish exposed pigments from carbon black and resins due to differences in the electrical properties and the difference in the contrast of the electric force image. It is preferable that the proportion of the area of the coating film surface occupied by pigments in a 5 μm square is 8% or less of the total area, and more preferably 5% or less.

In an image formed using the pigment-encapsulated emulsion resin particles, the pigment is not exposed. Therefore, in the heat drying process after image formation, the pigment does not aggregate, and the surface roughness of the coating film can be reduced. 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 making it 20 nm or less, light scattering can be suppressed and image density can be improved.

<Surface roughness>
The surface roughness of the coating film is calculated using a scanning probe microscope (SPM) as follows. First, an aqueous dispersion containing pigment-encapsulated emulsion resin particles is prepared using ion-exchanged water so that the solid content concentration is 10.75%. Next, the coating is applied to coated paper (Lumia Art Gloss 130) using a 0.15 mm bar coater, and heated and dried in an oven at 100°C for 5 minutes. 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 to determine the average surface roughness.
Equipment: Scanning probe microscope (Dimension Icon manufactured by Bruker)
Cantilever: Olympus OMCL-AC240TS
Measurement mode: Tapping mode Observation range: 2 μm square

<Number of coarse particles>
The term "coarse particles" refers to particles having a size of 1 μm or more in an aqueous dispersion. The number of coarse particles in the present invention refers to the number of particles having a size of 1 μm or more contained in 5 μL of the aqueous dispersion when converted into a solid content concentration of 1%.
The number of coarse particles in the aqueous dispersion containing the pigment-encapsulated emulsion resin particles is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 10,000 or less, of particles of 1 μm or more in 5 μL of the dispersion with a solid content concentration of 1%. By reducing the number of coarse particles, the particles are less likely to settle, and the storage stability is improved. The number of coarse particles is measured, for example, using a number-counting particle size distribution device AccuSizer manufactured by Nippon Integris LLC as follows. First, the aqueous dispersion containing the pigment-encapsulated emulsion resin particles is diluted with ion-exchanged water until it is within the measurable range, and then measured. From the measurement results, the number of particles of 1 μm or more in 5 μL of the aqueous dispersion when converted to a solid content concentration of 1% is calculated, and this is the number of coarse particles.

<50% cumulative volume particle size (D50)>
The particle diameter of the pigment-encapsulated emulsion resin particles is preferably 30 nm or more and 300 nm or less, more preferably 60 nm or more and 200 nm or less, and even more preferably 70 nm or more and 150 nm or less, in terms of 50% cumulative volume particle diameter (D50). When the particle diameter is 30 nm or more, the liquid viscosity is reduced, resulting in excellent dispersion stability. Furthermore, when the particle diameter is 300 nm or less, the settling of the particles is suppressed, resulting in good storage stability as particles. There are no particular limitations on the device for evaluating the particle diameter of the pigment-encapsulated emulsion resin particles, but it is preferable to measure the 50% cumulative volume particle diameter (D50) using, for example, a laser diffraction/scattering type particle size distribution measuring device (LA-960, manufactured by Horiba, Ltd.).
Hereinafter, "50% cumulative volume particle size (D50)" may be referred to as "D50".

<Method for producing aqueous dispersion containing pigment-encapsulated emulsion resin particles>
The pigment-encapsulated emulsion resin particles in the present invention are emulsion resin particles in which a pigment is encapsulated in a resin. The 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 5.
Step 1: A step of mixing a pigment, an organic solvent, and, if necessary, a pigment dispersant to obtain a pigment pre-dispersion having a pigment D50 of 10 nm or more and 150 nm or less. Step 2: A step of mixing the pigment pre-dispersion obtained in step 1 with a 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 liquid containing pigment-encapsulated emulsion resin particles in which the pigment is encapsulated in the resin. Step 4: A step of removing the organic solvent from the dispersion liquid containing pigment-encapsulated emulsion resin particles obtained in step 3 to obtain an aqueous dispersion containing pigment-encapsulated emulsion resin particles. Step 5: A step of separating and removing non-pigment-encapsulated emulsion resin particles and coarse particles from the aqueous dispersion obtained in step 4.

Next, each of the above steps 1 to 5 will be described in detail.
(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 limitations on the device used in step 1, but it is preferable to use a dispersing machine for dispersion.
The organic solvent used for the pigment pre-dispersion is not particularly limited as long as it can dissolve the resin in step 2. As the organic solvent, for example, ketones such as methyl ethyl ketone and acetone, and ethers such as tetrahydrofuran are preferable.

The particle size of the pigment in the pigment pre-dispersion is not particularly limited, but from the viewpoint of reducing the particle size of the pigment-encapsulated emulsion resin particles, D50 is preferably 10 nm or more and 150 nm or less, and more preferably 20 nm or more and 120 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. The ratio of the pigment to the pigment dispersant in the pigment pre-dispersion is not particularly limited, but from the viewpoint of increasing the dispersibility of the pigment pre-dispersion, the ratio of the pigment to the pigment dispersant is preferably 4:0.2 to 4:4, and more preferably 4:0.5 to 4:3.
It is preferable to separate and remove coarse particles from the pigment pre-dispersion using a filter, a centrifugal separator or the like, as necessary.

The pigment pre-dispersion can be produced by dissolving or suspending the pigment dispersant in an organic solvent as necessary, adding the pigment and stirring, and then using a commonly used known dispersing machine. Examples of known dispersing machines include anchor blades, dispersing blades, homomixers, ball mills, roll mills, beads mills, sand mills, attritors, pearl mills, dyno mills, high-pressure homogenizers, ultrasonic dispersers, agitator mills, paint shakers, grain mills, cobol mills, and jet mills. Of these, roll mills, beads mills, sand mills, dyno mills, high-pressure homogenizers, and paint shakers are preferably used in terms of dispersion efficiency.

(Step 2)
Step 2 is a step of mixing the pigment pre-dispersion obtained in step 1 with a resin to obtain a pigment dispersion resin solution.
The pigment dispersion resin solution obtained in step 2 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 an additive. There are no particular limitations on the mixing and stirring device used in step 2, but examples include the devices described for step 1. Among these, a high-speed stirring device equipped with an anchor blade or a dispersing blade is preferably used in terms of uniform stirring of a high-viscosity solution and efficient dissolution of resin powder.

The procedure for preparing the pigment dispersion resin solution is not particularly limited. The resin may be added to the pigment pre-dispersion obtained in step 1, or may be added after the resin is 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 it is more preferable that there is no 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 more than 20% by mass, the dispersion stability of the pigment may deteriorate, causing aggregates to form, and the pigment-encapsulated emulsion 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. The 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 of the pigment to the resin (P/R) is preferably 0.2 to 0.75, more preferably 0.3 to 0.6, relative to 1 resin. When the pigment to resin ratio is 0.2 or more, the pigment concentration is appropriate and the printed image density is excellent. When the pigment to resin ratio is 0.75 or less, most of the pigment can be encapsulated in the resin, and the surface roughness of the coating film after heat drying is suppressed, resulting in good image density. The pigment to resin ratio can be calculated from the charge ratio or the obtained dispersion.

The mass ratio (P/R) of the pigment to the resin from the dispersion can be calculated by, for example, thermal analysis of the dried-solid dispersion film using a thermogravimetric differential thermal analyzer (TG-DTA). Specifically, the dried-solid dispersion film can be heated to the thermal decomposition temperature of the resin in a nitrogen gas atmosphere using a thermogravimetric differential thermal analyzer, and the decomposed weight can be calculated as the resin and the residual weight as the pigment. In addition, for highly heat-resistant resins that cannot be completely decomposed by thermal decomposition in a nitrogen gas atmosphere, the heat loss can be calculated using a calibration curve of the heat loss and the pigment to resin ratio. Specifically, multiple mixtures of pigment and resin mixed at any ratio are prepared, and each mixture is heated to a certain temperature and maintained at that temperature, and the above calibration curve can be created, and the ratio of pigment to resin can be calculated based on the weight loss rate obtained from the measurement results of unknown samples.

The mass ratio (R/S) of the resin (R: resin) to the 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 2.0 or less. When the ratio of resin to the organic solvent is 1.2 or more, the emulsification speed of the resin in step 3 is increased, making it possible to reduce the particle size of the pigment-encapsulated emulsion resin particles. Furthermore, when the ratio of resin to the organic solvent is 3.0 or less, the increase in viscosity in the reaction system is suppressed, and the stirring efficiency is improved, thereby suppressing the generation of coarse particles.

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

There are no particular limitations on the procedure for mixing the pigment dispersion resin solution with water, but it is preferable to add water to the pigment dispersion resin solution. The rate at which water is added is preferably 10 parts by mass/min or more and 1,000 parts by mass/min or less, and more preferably 30 parts by mass/min or more and 500 parts by mass/min or less, relative to 100 parts by mass of resin. When the rate at which water is added is 10 parts by mass/min or more and 1,000 parts by mass/min or less, pigment aggregation in the system can be suppressed, thereby suppressing coarsening of the pigment-encapsulated emulsion resin particles.

From the viewpoint of dispersion stability of the pigment-encapsulated emulsion 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, and 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 obtained in the step 4 is obtained by removing the organic solvent from the dispersion liquid containing the pigment-encapsulated emulsion resin particles obtained in the 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. However, it is preferable to heat the organic solvent at a temperature equal to or higher than the boiling point of the organic solvent under reduced pressure. For example, a rotary evaporator can be used.
The reduced pressure is preferably 200 mmHg or less, more preferably 100 mmHg or less, and the heating temperature is preferably 20° C. or more and 80° C. or less, more preferably 30° C. or more and 60° C. or less.

(Step 5)
Step 5 is a step of separating and removing the emulsion resin particles not encapsulating the pigment and coarse particles from the aqueous dispersion obtained in step 4.
The method for separation and removal is not particularly limited and any known method can be used, but a combination of filtration through a membrane filter and centrifugation is preferred.
Filtration through a membrane filter can ensure stability during inkjet ejection. The pore size of the membrane filter is selected according to the nozzle diameter of the inkjet head to be used.
By using centrifugation, it is possible to remove resin particles not containing pigment and coarse particles from the system, which makes the particle size and density of the particles contained in the aqueous dispersion uniform, and makes it difficult for dispersion instability, such as floating or settling of particles, to occur.
As another method, separation using an ultrafiltration membrane or a microfiltration membrane can also be suitably used.

<Resin>
The resin is not particularly limited, but a self-emulsifying resin is preferred, and examples of the resin include polyester, polyurethane, and acrylic resins. 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 is partially or completely, particularly preferably completely, neutralized with a basic compound or the like.

Examples of neutralizing agents that can be used to neutralize the anionic groups include basic compounds such as organic amines such as ammonia, triethylamine, pyridine, and morpholine, and alkanolamines such as monoethanolamine, and metal base compounds including Na, K, Li, and Ca.
The acid value of the self-emulsifying resin is preferably 5 mgKOH/g or more and 50 mgKOH/g or less, more preferably 10 mgKOH/g or more and 30 mgKOH/g or less. When the acid value is 5 mgKOH/g or more, the dispersion stability is excellent, and the particle size is uniformed due to the effect, and the dispersion and ejection properties are good. Also, when the acid value is 50 mgKOH/g or less, the hydrophilicity is appropriate, the water resistance is improved, and the stability as a particle 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 putting the polyester into a tetrahydrofuran (THF) solution and titrating it with a 0.1M solution of potassium hydroxide in methanol. In addition, when the carboxyl group in the resin in the aqueous dispersion is neutralized, for example, an excess of hydrochloric acid is added to make an acidic solution, and then the resin is extracted with chloroform. Next, the pigment is removed by filtration, centrifugation, or the like, and then the resin is dried by heating or drying under reduced pressure to obtain a dried resin. The obtained resin can also be measured by dissolving it in THF and titrating it with a 0.1M solution of potassium hydroxide in methanol.
Hereinafter, a detailed description will be given of a self-emulsifying resin, for example, polyester.

(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 has an aromatic unit in a 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, an alkylene glycol 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.); an alkylene ether glycol having 4 to 36 carbon atoms (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, etc.); Examples of the alicyclic diols include: alicyclic diols having a carbon number of 2 to 36 (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 a carbon number of 2 to 4 (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 a carbon number of 2 to 4 (EO, PO, BO, etc.).

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

-Polycarboxylic acid component-
The polyvalent carboxylic acid component includes divalent carboxylic acids (dicarboxylic acids), specifically, alkane dicarboxylic acids having 4 to 36 carbon atoms (succinic acid, apidic acid, sebacic acid, etc.), alkenyl succinic acids (dodecenyl succinic acid, etc.); alicyclic dicarboxylic acids having 4 to 36 carbon atoms (dimer acids (dimerized linoleic acid), etc.); alkene dicarboxylic acids having 4 to 36 carbon atoms (maleic acid, fumaric acid, citraconic acid, mesaconic acid, etc.); aromatic dicarboxylic acids having 8 to 36 carbon atoms (phthalic acid, isophthalic acid, terephthalic acid or derivatives thereof, naphthalenedicarboxylic acid, etc.). Among these, alkane dicarboxylic acids having 4 to 20 carbon atoms and aromatic dicarboxylic acids having 8 to 20 carbon atoms are preferred. The polyvalent carboxylic acid component also includes anhydrides or lower alkyl (having 1 to 4 carbon atoms) esters (methyl esters, ethyl esters, isopropyl esters, etc.) 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.

As a method for isolating the polyester, for example, an aqueous dispersion containing pigment-encapsulated emulsion resin particles is dried by heating and drying, and the resulting dried product is placed in a tetrahydrofuran (THF) solution to dissolve the polyester. The pigment contained is then removed by centrifugation, filtration, etc., and the THF is then removed to isolate the polyester. In addition, recycled GPC can also be used if necessary.

The molecular weight of the polyester is not particularly limited and can be appropriately selected depending on the purpose, but the weight average molecular weight (Mw) measured by GPC is preferably 2,000 to 15,000, and more preferably 4,000 to 12,000.

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

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

The polyester can be produced by a method that has been generally used in the past, and examples of the method include the following.
First, the polyhydric alcohol and the polyvalent carboxylic 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 polyvalent carboxylic acid or a carboxylic acid anhydride.

<Pigments>
Although there is no particular limitation on the type of pigment, it is preferable to use an inorganic pigment. For example, in addition to titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, and chrome yellow, 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) can be used.

The carbon black preferably has a primary particle size of 15 nm or more and 100 nm or less, and by setting it in this range, the color development is improved. The DBP absorption is preferably 30 mL/100 g or more and 150 mL/100 g or less, and by setting it in this range, the pigment dispersibility in the organic solvent can be improved. Self-dispersing pigments may also be used, and the self-dispersing pigment refers to a pigment whose dispersion has been stabilized by introducing a functional group directly or via another atomic group onto the pigment surface. As the pigment before dispersion stabilization, for example, various conventionally known pigments such as those listed in the pamphlet of International Publication No. 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 can be appropriately selected according to the purpose from surfactants, polymer dispersants, etc. Examples of the pigment dispersant 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, naphthalene sulfonic 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 appropriately selected 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. The hydrophilicity/hydrophobicity of the pigment dispersant is such that if the pigment dispersant is insoluble in water, it is hydrophobic, and if it is soluble in water, it is hydrophilic.

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

<Ink>
The pigment-encapsulating emulsion resin particles can be mixed with an organic solvent, water, additives, and the like to obtain an ink.
The content of the pigment-encapsulated emulsion resin particles in the ink is preferably from 5% by mass to 20% by mass, and more preferably from 8% by mass to 15% by mass, from the viewpoints of improving image density, good fixing property, and ejection stability.
The organic solvent, water, 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. Examples of the organic solvent include 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 this 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 suitably 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 the glycol ether compound 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 having 8 or more carbon atoms and glycol ether compounds can improve the permeability of the ink when paper is used as the recording medium.
The content of the organic solvent in the ink is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoints of the drying property and ejection reliability of the ink, however, the content is preferably from 10% by mass to 60% by mass, and more preferably from 20% by mass to 60% by mass.

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

<Resin>
In addition to the resin contained in the pigment-encapsulated emulsion resin particles, another resin may be added to the ink. The type of resin to be added is not particularly limited, and examples thereof include urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin, acrylic styrene resin, and acrylic silicone resin.

Resin particles made of these resins may also be used. The resin particles are dispersed in water as a dispersion medium to form a resin emulsion, and the resin particles containing the pigment encapsulated in the emulsion and organic solvents are mixed together to obtain an ink. The resin particles may be appropriately synthesized or may be commercially available. These may be used alone or in combination of two or more types of resin particles.

The volume average particle size of the resin particles is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of obtaining good fixing property and high image hardness, the volume average particle size is preferably 10 nm or more and 1,000 nm or less, more preferably 10 nm or more and 200 nm or less, and particularly preferably 10 nm or more and 100 nm or less.
The volume average particle size can be measured, for example, by using a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).
The resin content is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of fixation property and storage stability of the ink, however, the total amount of the resin contained in the pigment-encapsulated emulsion resin particles and any resin added later is preferably 1% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 20% by mass or less, relative to the total amount of the ink.

<Additives>
If necessary, surfactants, antifoaming agents, antiseptic and antifungal agents, rust inhibitors, pH adjusters, and the like may be added to the ink.

<Surfactant>
As the surfactant, any of silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used.
Silicone surfactants are not particularly limited and can be appropriately selected according to purpose. Among them, those that do not decompose even at high pH are preferred, such as side chain modified polydimethylsiloxane, both end modified polydimethylsiloxane, one end modified polydimethylsiloxane, side chain both end modified polydimethylsiloxane, etc., and those having polyoxyethylene group or polyoxyethylene polyoxypropylene group as modified group are particularly preferred because they show good properties as aqueous surfactants. In addition, polyether modified silicone surfactants can also be used as the silicone surfactant, such as a compound in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylsiloxane.
As the fluorine-based surfactant, for example, perfluoroalkyl sulfonic acid compound, perfluoroalkyl carboxylic acid compound, perfluoroalkyl phosphate compound, perfluoroalkyl ethylene oxide adduct, and polyoxyalkylene ether polymer compound having perfluoroalkyl ether group in the side chain are particularly preferred because they have low foaming properties.As the perfluoroalkyl sulfonic acid compound, for example, perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, etc. can be mentioned.As the perfluoroalkyl carboxylic acid compound, for example, perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate, etc. can be mentioned.As the polyoxyalkylene ether polymer compound having perfluoroalkyl ether group in the side chain, for example, sulfate ester salt of polyoxyalkylene ether polymer having perfluoroalkyl ether group in the side chain, salt of polyoxyalkylene ether polymer having perfluoroalkyl ether group in the side chain, etc. can be mentioned. Examples of counter ions of the salts in these fluorosurfactants include _Li , Na, K, _NH4 , _NH3CH2CH2OH , _NH2 ( _{CH2CH2OH ) 2} , and _NH ( _CH2CH2OH ) _{3 .}
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 the anionic surfactant include polyoxyethylene alkyl ether acetates, dodecylbenzene sulfonates, laurates, and polyoxyethylene alkyl ether sulfates.
These may be used alone or in combination of two or more.

（但し、一般式（Ｓ－１）式中、ｍ、ｎ、ａ、及びｂは、それぞれ独立に、整数を表わし、Ｒは、アルキレン基を表し、Ｒ’は、アルキル基を表す。）
上記のポリエーテル変性シリコーン系界面活性剤としては、市販品を用いることができ、例えば、ＫＦ－６１８、ＫＦ－６４２、ＫＦ－６４３（信越化学工業株式会社）、ＥＭＡＬＥＸ－ＳＳ－５６０２、ＳＳ－１９０６ＥＸ（日本エマルジョン株式会社）、ＦＺ－２１０５、ＦＺ－２１１８、ＦＺ－２１５４、ＦＺ－２１６１、ＦＺ－２１６２、ＦＺ－２１６３、ＦＺ－２１６４（東レ・ダウコーニング・シリコーン株式会社）、ＢＹＫ－３３、ＢＹＫ－３８７（ビックケミー株式会社）、ＴＳＦ４４４０、ＴＳＦ４４５２、ＴＳＦ４４５３（東芝シリコン株式会社）などが挙げられる。 The silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the silicone surfactant include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, and both-end side-chain modified polydimethylsiloxane. Polyether-modified silicone surfactants having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as an aqueous surfactant.
Such surfactants may be synthesized appropriately or may be commercially available products, such as those available from BYK-Chemie Co., Ltd., 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. For example, it can be a surfactant represented by the general formula (S-1) in which a polyalkylene oxide structure is introduced into the Si part 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, for example, KF-618, KF-642, KF-643 (Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602, SS-1906EX (Nihon 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.

上記一般式（Ｆ－１）で表される化合物において、水溶性を付与するためにｍは０～１０の整数が好ましく、ｎは０～４０の整数が好ましい。
一般式（Ｆ－２）
Ｃ_ｎＦ_{２ｎ＋１－}ＣＨ_２ＣＨ（ＯＨ）ＣＨ_２－Ｏ－（ＣＨ_２ＣＨ_２Ｏ）_ａ－Ｙ
上記一般式（Ｆ－２）で表される化合物において、ＹはＨ、又はＣｍＦ_２ｍ＋１でｍは１～６の整数、又はＣＨ_２ＣＨ（ＯＨ）ＣＨ_２－ＣｍＦ_２ｍ＋１でｍは４～６の整数、又はＣｐＨ_２ｐ＋１でｐは１～１９の整数である。ｎは１～６の整数である。ａは４～１４の整数である。
上記のフッ素系界面活性剤としては市販品を使用してもよい。この市販品としては、例えば、サーフロンＳ－１１１、Ｓ－１１２、Ｓ－１１３、Ｓ－１２１、Ｓ－１３１、Ｓ－１３２、Ｓ－１４１、Ｓ－１４５（いずれも、旭硝子株式会社製）；フルラードＦＣ－９３、ＦＣ－９５、ＦＣ－９８、ＦＣ－１２９、ＦＣ－１３５、ＦＣ－１７０Ｃ、ＦＣ－４３０、ＦＣ－４３１（いずれも、住友スリーエム株式会社製）；メガファックＦ－４７０、Ｆ－１４０５、Ｆ－４７４（いずれも、大日本インキ化学工業株式会社製）；ゾニール（Ｚｏｎｙｌ）ＴＢＳ、ＦＳＰ、ＦＳＡ、ＦＳＮ－１００、ＦＳＮ、ＦＳＯ－１００、ＦＳＯ、ＦＳ－３００、ＵＲ、キャプストーンＦＳ－３０、ＦＳ－３１、ＦＳ－３１００、ＦＳ－３４、ＦＳ－３５（いずれも、Ｃｈｅｍｏｕｒｓ社製）；ＦＴ－１１０、ＦＴ－２５０、ＦＴ－２５１、ＦＴ－４００Ｓ、ＦＴ－１５０、ＦＴ－４００ＳＷ（いずれも、株式会社ネオス社製）、ポリフォックスＰＦ－１３６Ａ，ＰＦ－１５６Ａ、ＰＦ－１５１Ｎ、ＰＦ－１５４、ＰＦ－１５９（オムノバ社製）、ユニダインＤＳＮ-４０３Ｎ（ダイキン工業株式会社製）などが挙げられ、これらの中でも、良好な印字品質、特に発色性、紙に対する浸透性、濡れ性、均染性が著しく向上する点から、
Ｃｈｅｍｏｕｒｓ社製のＦＳ－３１００、ＦＳ－３４、ＦＳ－３００、株式会社ネオス製のＦＴ－１１０、ＦＴ－２５０、ＦＴ－２５１、ＦＴ－４００Ｓ、ＦＴ－１５０、ＦＴ－４００ＳＷ、オムノバ社製のポリフォックスＰＦ－１５１Ｎ及びダイキン工業株式会社製のユニダインＤＳＮ-４０３Ｎが特に好ましい。 The fluorine-based surfactant is preferably a compound having 2 to 16 fluorine-substituted carbon atoms, and more preferably a compound having 4 to 16 fluorine-substituted carbon atoms.
Examples of the fluorine-based surfactant include perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group on the side chain, etc. Among these, polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group on the side chain are preferred because they have low foaming properties, and the fluorine-based surfactants represented by the general formulas (F-1) and (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 above 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.
As the fluorine-based surfactant, commercially available products 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); Megafac F-470, F-1405, and F-474 (all manufactured by Dainippon Ink and Chemicals, Inc.); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, and FS-30. 0, 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 the like are particularly preferred. Among these, the following are particularly preferred from the viewpoint of excellent printing quality, particularly color development, penetration into paper, wettability, and uniform dyeing.
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.

The content of the surfactant in the ink is not particularly limited and can be selected appropriately depending on the purpose, but from the viewpoint of excellent wettability, ejection stability, and improved image quality, it is preferably 0.001% by mass or more and 5% by mass or less, and more preferably 0.05% by mass or more and 5% by mass or less.

<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.

<Anti-septic and anti-fungal agents>
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 sulfite and sodium thiosulfate.

<pH Adjuster>
There are no particular limitations on the pH adjuster, so long as it is capable of adjusting the pH to 7 or higher, and examples of the pH adjuster 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, in terms of improving the 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.). The measurement conditions are 25°C, a standard cone rotor (1°34'×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 appropriately leveled on the recording medium and the drying time of the ink is shortened.
The pH of the ink is preferably from 7 to 12, and more preferably from 8 to 11, from the viewpoint of preventing corrosion of metal members that come into contact with the ink.

<Pretreatment solution>
The pretreatment liquid contains a flocculant, an organic solvent, and water, and may contain, as necessary, a surfactant, an antifoaming agent, a pH adjuster, an antiseptic/fungal agent, an antirust agent, and the like.
The organic solvent, surfactant, defoamer, pH adjuster, antiseptic/fungal agent, and antirust agent can be the same as those used in ink, and other materials used in known treatment liquids can also be used.
The type of the 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 is obtained by selecting and mixing organic solvents, water, resins, surfactants, defoamers, pH adjusters, antiseptics, antifungals, rust inhibitors, etc. as necessary. 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 a non-permeable substrate.
The non-permeable substrate is a substrate having a surface with low water permeability and absorbency, and includes materials that have many cavities inside but are not open to the outside. More quantitatively, the non-permeable substrate is a substrate having a water absorption amount of 10 mL/m2 or ^less from the start of contact to 30 msec ^1/2 in the Bristow method.
As the non-permeable substrate, for example, a plastic film such as a polyvinyl 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 those generally used as recording media, but may be wallpaper, flooring, building materials such as tiles, cloth for clothing such as T-shirts, textiles, leather, etc., as appropriate. In addition, by adjusting the configuration of the path for transporting the recording medium, ceramics, glass, metal, etc. may also be used.

<Recordings>
The ink recorded matter of the present invention comprises an image formed on a recording medium using the ink of the present invention.
A recorded matter can be obtained by recording using an inkjet recording apparatus and an inkjet recording method.

<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 recording apparatus and recording method refer to an apparatus capable of ejecting ink, various treatment liquids, etc. onto a recording medium, and a method of recording using the apparatus. The recording medium refers to an object onto which ink or various treatment liquids can be attached even 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, and other devices called pre-processing devices and post-processing devices.
The recording apparatus and the 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 the drying means include, for example, a means for heating and drying the printed surface and the back surface of the recording medium. The heating means and the 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 performed before, during, or after printing.
Furthermore, the recording device and recording method are not limited to those that visualize meaningful images such as characters and figures with ink. For example, those that form patterns such as geometric designs and those that form three-dimensional images are also included.
Furthermore, unless otherwise specified, the recording apparatus includes both a serial type apparatus in which the discharge head moves and a line type apparatus in which the discharge 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.
An example of a recording apparatus will be described with reference to Figs. 10 and 11. Fig. 10 is a perspective view of the apparatus. Fig. 11 is a perspective view of a main tank. An image forming apparatus 400 as an example of a recording apparatus is a serial type image forming apparatus. A mechanism section 420 is provided in an exterior 401 of the image forming apparatus 400. Each ink storage section 411 of the main tanks 410 (410k, 410c, 410m, 410y) for each color of black (K), cyan (C), magenta (M), and yellow (Y) is formed of a packaging material such as an aluminum laminate film. The ink storage section 411 is stored in a storage container case 414 made of plastic, for example. As a result, the main tanks 410 are used as ink cartridges of each color.
On the other hand, a cartridge holder 404 is provided at the rear of the opening when the cover 401c of the apparatus 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 apparatus can include not only a portion that ejects ink, but also devices called pre-processing devices and post-processing devices.
As an embodiment of the pre-treatment device and the post-treatment device, a liquid storage section having a pre-treatment liquid and a liquid ejection head, similar to the case of inks such as black (K), cyan (C), magenta (M), and yellow (Y), and the like, are added, and the pre-treatment liquid and the post-treatment liquid are ejected by an inkjet recording method.
As another embodiment of the pre-treatment device and the post-treatment device, there is an embodiment in which a pre-treatment device and a post-treatment device using a method other than the inkjet recording method, for example, a blade coating method, a roll coating method, or a spray coating method, are provided.

The ink can be used in a wide variety of ways, not just inkjet recording. In addition to 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, undercoat, etc. Furthermore, the ink can be used not only as an ink for forming two-dimensional characters and images, but also as a material for three-dimensional modeling for forming three-dimensional solid images (three-dimensional objects).
A known three-dimensional modeling device for forming a three-dimensional object can be used, and is not particularly limited. For example, a device equipped with an ink storage means, supply means, discharge means, drying means, etc. can be used. The three-dimensional object includes a three-dimensional object obtained by applying ink over and over. Also included is a molded product obtained by processing a structure to which ink is applied on a substrate such as a recording medium. The molded product is, for example, a recorded matter or structure formed in a sheet or film shape, which is molded by heat stretching, punching, etc., and is preferably used for applications in which the surface is molded after decoration, such as meters and operation panels for automobiles, office automation equipment, electric and electronic devices, and cameras.

In the present invention, the terms image formation, recording, printing, printing, etc. are all synonymous.

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

Examples of the present invention will be described below, 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, examples of synthesis of raw materials constituting the ink, preparation of a pigment pre-dispersion, preparation of an aqueous dispersion and an ink are shown below. Methods for evaluating the physical properties of the aqueous dispersion and the ink are described later.

[Production Example]
<Self-emulsifying resin: polyester synthesis example>
(Synthesis of polyester α)
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 mole adduct (manufactured by Fuji Film Wako Chemical Co., Ltd.: 4,4'-isopropylidenebis(2-phenoxyethanol)) and 79 parts of bisphenol A propylene oxide 2 mole adduct (manufactured by Nippon Nyukazai Co., Ltd.: BA-P2 glycol) as diols, and 140 parts of dimethyl isophthalate and 26 parts of adipic acid as dicarboxylic acids were mixed. Then, after the inside of the reaction vessel was sufficiently replaced with nitrogen gas, 300 ppm (relative to the monomer) of titanium tetraisopropoxide was added, and the temperature was raised to 200°C in about 4 hours under a nitrogen gas flow, and then the temperature was raised to 230°C over 2 hours, and the reaction was carried out until no effluent was observed. Then, the reaction was carried out 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 5,000.
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 α] having an acid value (AV) of 20 mg KOH/g, a glass transition temperature (Tg) of 51° C., and a weight average molecular weight (Mw) of 5,100.

(Synthesis of polyester β)
In a 1L four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, 280 parts of propylene glycol as a diol, 611 parts of terephthalic acid as a dicarboxylic acid, and 109 parts of succinic acid were mixed. Then, after the inside of the reaction vessel was sufficiently replaced with nitrogen gas, 300 ppm (relative to the monomer) of titanium tetraisopropoxide was added, and the temperature was raised to 200°C in about 4 hours under a nitrogen gas flow, and then the temperature was raised to 230°C over 2 hours, and the reaction was carried out until no effluent was observed. Then, the reaction was carried out for 1 hour under a reduced pressure of 5 mmHg to 30 mmHg to obtain [polyester β].
The obtained [polyester β] had an acid value (AV) of 19 mgKOH/g, a glass transition temperature (Tg) of 57° C., and a weight average molecular weight (Mw) of 6,000.

<Preparation of Pigment Pre-Dispersion>
(Pigment Pre-Dispersion A)
The following materials were mixed and poured into a 110 ml glass screw tube bottle, after which 170 parts of 2.0 mm diameter zirconia balls (Nikkato Corporation, YTZ balls) were poured in, the bottle was fixed to a shaker (IKA Corporation, Vibrax VXR basic), and dispersed at 1000 rpm for 24 hours. Thereafter, the media and the dispersion were separated by filtration, and filtered through a PTFE membrane filter with an average pore size of 5.0 μm to produce [Pigment Pre-Dispersion A]. The D50 of this [Pigment Pre-Dispersion A] in ELSZ-1000 was 110 nm.
Carbon black: 15.0 parts (SBX45, manufactured by Asahi Carbon Co., Ltd., primary particle size: 22 nm, DBP absorption: 55 mL/100 g)
Pigment dispersant: 3.8 parts (Ajisper PB821, manufactured by Ajinomoto Fine-Techno Co., Ltd., hydrophobic)
Methyl ethyl ketone: 41.2 parts

In the following, preparation examples of aqueous dispersions 1 to 11 and inks 1 to 11 using these aqueous dispersions will be shown as examples and comparative examples.
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 0.3L separable flask equipped with a three-one motor, an anchor blade, and a thermocouple was added with 60 g of [pigment pre-dispersion A] and 30 g of [polyester α], and mixed and stirred at 40 ° C. so that the mass ratio (P / R) of the pigment (P: Pigment) and the polyester (R: Resin) was 0.5, to obtain a pigment dispersion resin solution. Next, methyl ethyl ketone was removed under reduced pressure so that the ratio (R / S) of the polyester (R: Resin) and the methyl ethyl ketone (S: Solvent) was 1.4, and then 1.1 g of triethylamine was added to the carboxyl group in an amount equivalent to neutralize the acid value of the polyester, and mixed and stirred for 0.5 hours. 64 g of ion-exchanged water was dropped at a rate of 15 ml / min while stirring at a speed of 350 rpm, and an emulsion was prepared by stirring for 20 minutes. Finally, methyl ethyl ketone was removed, and the residue was purified by filtration using a nylon mesh with 67 μm openings, and the solid content was adjusted to 30% with ion-exchanged water.
Next, the mixture was centrifuged at 4000 rpm for 5 hours using a centrifugal separator, and the upper 10 vol % and the lower 20 vol % of the cell were removed to obtain [Aqueous Dispersion 1], which contained pigment-encapsulated emulsion resin particles in which the entire surface of the pigment was covered with a resin layer of 5 nm or more and which contained two or more primary pigment particles.
1, 2, 3 and 4 are a TEM image (magnification: 10,000 times), a TEM image (magnification: 40,000 times), a SEM image and an EFM image of [Aqueous Dispersion 1], respectively.

(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 formula-
Aqueous dispersion 1 (as solid content): 10.75%
Propylene glycol (adjusted to viscosity 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]
Except for recovering only 5 vol% of the upper part and 10 vol% of the lower part of the cell after centrifugation, [Water-based Dispersion 2] containing pigment-encapsulated emulsion resin particles was obtained in the same manner as in Example 1. [Ink 2] was also prepared in the same manner as [Ink 1], except for using [Water-based Dispersion 2] instead of [Water-based Dispersion 1].

[Example 3]
Except for using [Polyester β] instead of [Polyester α], [Water-based Dispersion 3] containing pigment-encapsulated emulsion resin particles was obtained in the same manner as in Example 1. Also, [Ink 3] was prepared in the same manner as in [Ink 1], except for using [Water-based Dispersion 3] instead of [Water-based Dispersion 1].

[Example 4]
Except for using [Polyester β] instead of [Polyester α], [Water-based Dispersion 4] containing pigment-encapsulated emulsion resin particles was obtained in the same manner as in Example 2. Also, [Ink 4] was prepared in the same manner as in [Ink 1], except for using [Water-based Dispersion 4] instead of [Water-based Dispersion 1].

[Example 5]
[Ink 5] was prepared in the same manner as [Ink 1], except that [Aqueous Dispersion 5] prepared as described below was used instead of [Aqueous Dispersion 1].
(Preparation of Aqueous Dispersion 5)
A 0.3L separable flask equipped with a three-one motor, anchor blade, and thermocouple was charged with 40g of polycarbonate diol (Asahi Kasei Duranol T5651) and 1.69g of 2,2-bis(hydroxymethyl)propionic acid, and the water in the system was removed by reducing the pressure while stirring. Next, while introducing nitrogen, 36g of methyl ethyl ketone, 2.93g of triethylamine, and 23.7g of dicyclohexylmethane-4,4'-diisocyanate were charged as an organic solvent, 0.2mL of di-(2-ethylhexanoic acid)tin(II) was added as a catalyst, and the temperature was raised to 60°C and refluxed for 2 hours to obtain a polycarbonate-based polyurethane resin solution with a solid content concentration of 65%, NCO of 0.9%, and a weight average molecular weight (Mw) of 6,500. 22g of [pigment pre-dispersion A] was added thereto and mixed and stirred at 40°C to obtain a pigment dispersion resin solution. Next, 0.2 g of diethylenetriamine was added and mixed and stirred at 40° C. for 30 minutes, and then 78 g of ion-exchanged water was added dropwise at a rate of 15 ml/min while stirring at a speed of 350 rpm, and stirred for 20 minutes to prepare an emulsion. Finally, methyl ethyl ketone was removed, and the mixture was filtered and purified using a nylon net with a mesh size of 67 μm, and the solid content was adjusted to 30% with ion-exchanged water.
Next, the mixture was centrifuged at 4000 rpm for 5 hours using a centrifugal separator. The upper 20 vol % and the lower 40 vol % of the cell were removed and collected to obtain [Aqueous Dispersion 5] containing pigment-encapsulated emulsion resin particles.

[Example 6]
[Ink 6] was prepared in the same manner as [Ink 1], except that [Aqueous Dispersion 6] prepared as described below was used instead of [Aqueous Dispersion 1].
(Preparation of [Aqueous Dispersion 6])
After centrifugation, the same procedure as in Example 5 was repeated, except that the upper 10 vol % and the lower 20 vol % of the cell were removed and collected, to obtain [Water-based Dispersion 6] containing pigment-encapsulated emulsion resin particles.

[Comparative Example 1]
Except for not performing centrifugation, [Water-based Dispersion 7] containing pigment-encapsulated emulsion resin particles was obtained in the same manner as in Example 1. In addition, [Ink 7] was prepared in the same manner as in "Ink 1" except for using [Water-based Dispersion 7] instead of [Water-based Dispersion 1].
5 and 6 are TEM images (magnification: 10,000 times) and TEM images (magnification: 50,000 times) of [Aqueous Dispersion 7], respectively.

[Comparative Example 2]
Except for recovering only the bottom 50 vol% of the cell after centrifugation, an [Aqueous Dispersion 8] containing pigment-encapsulated emulsion resin particles was obtained in the same manner as in Example 1. In addition, [Ink 8] was prepared in the same manner as [Ink 1], except for using [Aqueous Dispersion 8] instead of [Aqueous Dispersion 1].

[Comparative Example 3]
Except for excluding and recovering the upper 50 vol% of the cell after centrifugation, [Water-based Dispersion 9] containing pigment-encapsulated emulsion resin particles was obtained in the same manner as in Example 1. Also, [Ink 9] was prepared in the same manner as [Ink 1], except for using [Water-based Dispersion 9] instead of [Water-based Dispersion 1].

[Comparative Example 4]
Except for not performing centrifugation, [Water-based Dispersion 10] containing pigment-encapsulated emulsion resin particles was obtained in the same manner as in Example 5. [Ink 10] was also prepared in the same manner as [Ink 1], except for using [Water-based Dispersion 10] instead of [Water-based Dispersion 1].

[Comparative Example 5]
Instead of the pigment-encapsulated emulsion resin particles, the following [Polyester Sole Resin Emulsion] and [Water-Based Pigment Dispersion 11] were prepared to prepare [Ink 11].
(Polyester single resin emulsion)
25g of polyester α and 14g of methyl ethyl ketone were added to a 0.3L separable flask equipped with a three-one motor, anchor blades, and a thermocouple, and the mixture was stirred at 40°C to obtain a resin solution. Next, in order to neutralize the acid value of the polyester, 0.84g of triethylamine was added in an amount equivalent to the carboxyl group and stirred for 20 minutes. While stirring at a speed of 350 rpm, 53g of ion-exchanged water was dripped at a rate of 15ml/min, and the mixture was stirred for 20 minutes to produce an emulsion. Finally, the methyl ethyl ketone was removed, and the mixture was filtered and purified using a nylon net with a mesh size of 67μm. The solid content was adjusted to 30% with ion-exchanged water to obtain a polyester-only resin emulsion with a D50 of 78nm.

(Water-based pigment dispersion)
3.8 parts of [pigment dispersant I] synthesized as follows was dissolved in 30.0 parts of diethanolamine aqueous solution so that the pH was 8.0. Further, ion-exchanged water was added to make the total amount of the aqueous solution 45.0 parts. Next, the materials of the following formulation were mixed and poured into a 110 ml glass screw tube bottle, and then 170 parts of zirconia balls (manufactured by Nikkato Corporation, YTZ balls) having a diameter of 2.0 mm were poured, and the bottle was fixed to a shaker (manufactured by IKA Corporation, Vibrax VXR basic) and dispersed for 24 hours at 1000 rpm. Thereafter, the media and the dispersion were separated by filtration, and the mixture was filtered through a cellulose acetate membrane filter having an average pore size of 5.0 μm to prepare [water-based pigment dispersion 11]. The D50 of this [water-based pigment dispersion 11] in ELSZ-1000 was 120 nm.
Carbon black (SBX45, manufactured by Asahi Carbon Co., Ltd.): 15.0 parts Pigment dispersant I aqueous solution: 45.0 parts

(Synthesis of Pigment Dispersant I)
62.0 parts of 1,6-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 700 ml of dichloromethane, and 20.7 parts of pyridine (manufactured by Tokyo Chemical Industry Co., Ltd.) was added thereto and stirred.
A solution of 2-naphthalenecarbonyl chloride (Tokyo Chemical Industry Co., Ltd.) dissolved in 100 ml of dichloromethane was added dropwise to this solution over 2 hours, and the mixture was stirred at room temperature for 6 hours. The resulting reaction solution was washed with water, and then 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 above compound obtained 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 then 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 (Tokyo Chemical Industry Co., Ltd.), 8.54 g of the monomer, and 0.31 parts of 2,2'-azobis(isobutyronitrile) (Tokyo Chemical Industry Co., Ltd.) were dissolved in 100 ml of methyl ethyl ketone, and the mixture was stirred for 5 hours at 75°C under a nitrogen gas flow. The reaction solution was then cooled to room temperature, and reprecipitation was repeated five times using hexane to purify the copolymer. After the purification process, the copolymer was filtered off and dried under reduced pressure to obtain pigment dispersant I.

(Preparation of Ink 11)
An ink having the following formulation was prepared using the [Polyester single resin emulsion] and [Water-based pigment dispersion 11] 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 11.
7, 8 and 9 are a TEM image (magnification: 40,000 times), a SEM image and an EFM image of [Ink 11], respectively.
-Ink formula-
Polyester single resin emulsion (as solid content): 5.375%
Water-based pigment dispersion 11 (as solid content): 5.375%
Propylene glycol (adjusted to viscosity 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 dispersion was evaluated for D50, the mass ratio (P/R) of pigment (P) to resin (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 from a polystyrene sample with a known molecular weight as a standard. Note that columns with exclusion limits of 60,000, 20,000, and 10,000 connected in series were used.

<Cumulative 50% volume average particle size (D50)>
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, with an organic solvent so that the solid content concentration of the measurement sample was 0.01 wt%, and a portion of the obtained solution was placed in a quartz cell and set in a sample holder. Then, the measurement was performed under the following conditions: temperature: 25°C, dust cut (number of times: 5, Upper: 5, Lower: 100), and cumulative number: 70.

The D50 of the emulsion resin particles of the aqueous dispersion containing the pigment-encapsulated emulsion resin particles was 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 device were 30% to 70%, and a portion of the resulting solution was placed in a batch-type cell (spacer: 50 μm), which was then set in the sample holder and measured.

<Mass ratio (P/R) of pigment (P) to resin (R)>
P/R (Pigment/Resin ratio) was calculated by thermal analysis of the dried product of the aqueous dispersion. Specifically, the aqueous dispersion was first heated and dried at 130°C for 5 hours to obtain a dried product. 10 mg of the obtained dried product was heated to 150°C in a nitrogen gas (200mL/L) atmosphere using a thermogravimetric differential thermal analyzer (EVO2G-TG-03 manufactured by Rigaku Corporation) and held for 10 minutes, then heated to 500°C at 20°C/min and held for 30 minutes. The weight after holding at 150°C for 10 minutes was the weight of the dried product, and the weight after holding at 500°C for 30 minutes was the weight of the pigment remaining after the resin was decomposed. The P/R (Pigment/Resin ratio) was calculated from a calibration curve prepared by similarly analyzing a mixture of known pigment/resin ratios in advance.

<Pigment exposure rate>
An aqueous dispersion containing pigment-encapsulated emulsion resin particles was prepared so that the solid content concentration was 10.75% by mass. The aqueous dispersion was then applied to a coated paper, and the film obtained by drying at 25° C. was observed under a scanning electron microscope (accelerating voltage 0.75 kV, backscattered electron detector, magnification 20,000 times) without conducting a conductive treatment. The pigment area was calculated by binarizing the observed image, and the ratio of the pigment to the surface of the coating film was taken as the pigment exposure rate.

This observation method makes it possible to distinguish between exposed pigment due to the difference in the amount of reflected electron emission between carbon black and resin, and the ratio of the area of exposed pigment to the entire observation range is defined as the pigment exposure rate. Exposed pigment is an area that is observed to have a bright contrast to the resin particles, and is determined by comparing with the results of observing a dispersion made by mixing a single resin particle with a pigment dispersion. The pigment exposure rate was calculated by averaging three visual fields measured at randomly changed locations.

<Ratio of emulsion resin particles not containing pigment>
The ratio of non-pigment-encapsulated emulsion resin particles was calculated as follows. First, an emulsion containing pigment-encapsulated emulsion resin particles was diluted with ion-exchanged water so that the solid content concentration was 0.1% to prepare a sample solution. Next, 1 μL of the sample solution was placed on a hydrophilically treated collodion film-attached mesh (Nisshin EM Co., Ltd. Collodion film-attached mesh Cu150 mesh), using a micropipette, and the sample solution was immediately absorbed with a triangular filter paper. Next, 1 μL of EM stainer diluted 10 times was placed on a micropipette, and the sample solution was immediately absorbed with a triangular filter paper. After drying under reduced pressure, observation was performed with a transmission electron microscope (JEM-2100F, JEOL Ltd.) at an accelerating voltage of 200 kV and a magnification of 40,000 times. By this observation method, five or more images of a field of view containing three or more particles of 50 nm or more were obtained at arbitrary locations. For each image, the number of pigment-encapsulated emulsion resin particles and the number of non-pigment-encapsulated emulsion resin particles were counted, and the ratio of non-pigment-encapsulated emulsion resin particles was calculated by the following formula (1), and the average was obtained.

<Number of coarse particles>
The number of coarse particles was measured using a particle size distribution analyzer, AccuSizer, manufactured by Nippon Entegris LLC, as follows. First, the aqueous dispersion containing the pigment-encapsulated emulsion resin particles was diluted with ion-exchanged water until it was within the measurable range, and then measured. From the measurement results, the number of particles of 1 μm or more in 5 μL of the aqueous dispersion when converted to a solids concentration of 1% was calculated, and this was taken as the number of coarse particles.

<Surface roughness>
The surface roughness was calculated using a scanning probe microscope (SPM) as follows. First, an aqueous dispersion containing pigment-encapsulated emulsion resin particles was prepared using ion-exchanged water so that the solid content concentration was 10.75%. Next, the coating was applied to coated paper (Lumia Art Gloss 130) using a 0.15 mm bar coater, and 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 random locations, and the average surface roughness was calculated.
Equipment: Scanning probe microscope (Dimension Icon manufactured by Bruker)
Cantilever: Olympus OMCL-AC240TS
Measurement mode: Tapping mode Observation range: 2 μm square

[Ink evaluation method]
Next, the prepared inks were evaluated for image density, sedimentation resistance, and floating resistance as described below. The results are shown in Table 1.

(Image output method)
The ink supply path including the print head of an inkjet printer (IPSiO GXe5500 manufactured by Ricoh) was cleaned by passing pure water through it until the cleaning liquid was no longer colored, and then the cleaning liquid was completely drained from the device to prepare a printing device for evaluation.
The prepared ink was 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 no abnormal images were produced. After selecting the glossy paper clean mode in the driver attached to the printer, the user settings were changed to the print mode with color matching off. In this mode, the ejection amount was adjusted by changing the head drive voltage so that the amount of ink attached to the recording medium for a solid image was 20 g/ ^m2 .
<Image Density>
A solid image was printed on recording paper (Lumia Art Gloss 130 manufactured by Premier Paper) using the image output method described below, and then heated and dried in an oven at 100° C. for 5 minutes to prepare each image.
With a sheet of white plain paper placed under the printed image, the total density was measured using a spectrophotometric densitometer X-Rite 939, and the K value was taken as the image density.

<Sedimentation resistance>
Each aqueous dispersion was placed in a glass screw cap bottle and allowed to stand at 40° C. for one week, and the precipitate present at the bottom of the screw cap bottle was evaluated according to the following criteria.
The presence of precipitate was confirmed by slowly turning the screw cap upside down without shaking and leaving it to stand for 1 hour, and then visually checking. The redispersibility was confirmed by shaking for 10 seconds with a VORTEX Genius 3 (manufactured by IKA) at a dial value of 4.
[Evaluation Criteria]
◯: No precipitate; △: Granular precipitate is present but can be redispersed; ×: Presence of precipitate that cannot be redispersed

<Floating resistance>
Each aqueous dispersion was subjected to an accelerated dispersion stability test at 2000 rpm using a centrifugal acceleration type dispersion stability measuring device LUMiSizer, and the floating of particles was observed and evaluated according to the following criteria.
[Evaluation Criteria]
○: No floating occurred 5 hours after the start of the test △: Floating occurred 1 hour to 5 hours after the start of the test ×: Floating occurred less than 1 hour after the start of the test

（２）前記水系分散体について、下記で定義される粗大粒子数が１０万個以下である、上記（１）に記載の水系分散体。
（粗大粒子数）
日本インテグリス合同会社製個数カウント粒度分布装置ＡｃｃｕＳｉｚｅｒを用いて、前記水系分散体を測定可能範囲内に入るまでイオン交換水で希釈し、粒度分布を測定する。測定結果より、固形分濃度１％に換算したときの前記水系分散体５μＬ中に１μｍ以上の粒子が何個あったかを算出し、これを「粗大粒子数」とする。
（３）前記水系分散体のレーザー回折散乱法により得られるエマルション樹脂粒子の５０％累積体積粒径（Ｄ５０）が３０ｎｍ以上３００ｎｍ以下であることを特徴とする上記（１）又は（２）に記載の水系分散体。
（４）前記顔料内包化エマルション樹脂粒子の平均アスペクト比が１．０以上１．７以下である、上記（１）乃至（３）のいずれか１項に記載の水系分散体。
（５）前記無機顔料がカーボンブラックである、上記（１）乃至（４）のいずれか１項に記載の水系分散体。
（６）前記顔料内包化エマルション樹脂粒子が前記無機顔料の一次粒子を二個以上包含する、上記（１）乃至（５）のいずれか１項に記載の水系分散体。
（７）前記水系分散体における前記無機顔料と樹脂との質量比（無機顔料／樹脂）が０．２５以上１．０以下である、上記（１）乃至（６）のいずれか１項に記載の水系分散体。
（８）前記エマルション樹脂粒子がポリエステルを含む、上記（１）乃至（７）のいずれか１項に記載の水系分散体。
（９）前記ポリエステルがカルボキシル基を有し、自己乳化型樹脂である、上記（１）乃至（８）のいずれか１項に記載の水系分散体。
（１０）上記（１）乃至（９）のいずれか１項に記載の水系分散体を製造する方法であって、下記工程１～工程５を含むことを特徴とする水系分散体の製造方法。
工程１：顔料と有機溶剤とを混合し、顔料の５０％累積体積粒径（Ｄ５０）が１０ｎｍ以上１５０ｎｍ以下である顔料プレ分散体を得る工程
工程２：工程１で得られた顔料プレ分散体と樹脂とを混合して、顔料分散樹脂溶液を得る工程
工程３：工程２で得られた顔料分散樹脂溶液と水とを混合して、顔料を樹脂で内包化した顔料内包化エマルション樹脂粒子を含む分散液を得る工程
工程４：工程３で得られた顔料内包化エマルション樹脂粒子を含む分散液から有機溶剤を除去して顔料内包化エマルション樹脂粒子を含む水系分散体を得る工程
工程５：工程４で得られた水系分散体から、顔料未内包エマルション樹脂粒子および粗大粒子を分離除去する工程
（１１）前記顔料未内包エマルション樹脂粒子および前記粗大粒子を分離除去する工程を遠心分離によって行う、上記（１０）に記載の水系分散体の製造方法。
（１２）上記（１）乃至（９）のいずれか１項に記載の水系分散体を成分として含有することを特徴とするインク。
（１３）上記（１２）に記載のインクの印刷層を含むことを特徴とする印刷物。 The present invention relates to the following aqueous dispersion (1), but also includes the following embodiments (2) to (13).
(1) An aqueous dispersion containing emulsion resin particles as a dispersoid,
the emulsion resin particles include pigment-encapsulated emulsion resin particles encapsulating an inorganic pigment,
An aqueous dispersion characterized in that a pigment exposure rate calculated under the following pigment exposure rate calculation conditions is 8% or less, and a ratio of emulsion resin particles not encapsulating a pigment, as defined below, is 1.0 or less.
(Calculation conditions for pigment exposure rate)
An aqueous dispersion containing pigment-encapsulated emulsion resin particles is prepared so that the solid content concentration is 10.75% by mass. The aqueous dispersion is then applied to a coated paper, and the film obtained by drying at 25° C. is observed under a scanning electron microscope (accelerating voltage 0.75 kV, backscattered electron detector, magnification 20,000 times) without conducting a conductive treatment. The pigment area is calculated by binarizing the observed image, and the ratio of the pigment to the surface of the coating film is defined as the pigment exposure rate.
(Ratio of emulsion resin particles not containing pigment)
The aqueous dispersion containing the pigment-encapsulated emulsion resin particles is placed on a collodion film-attached mesh, and the dried sample is observed under a transmission electron microscope at an acceleration voltage of 200 kV and a magnification of 40,000 times. By this observation method, five or more images of a field of view containing three or more particles of 50 nm or more are obtained at any position. For each image, the number of pigment-encapsulated emulsion resin particles and the number of non-pigment-encapsulated emulsion resin particles are counted, and the ratio of non-pigment-encapsulated emulsion resin particles is calculated by the following formula (1), and the average value is taken as the ratio of non-pigment-encapsulated emulsion resin particles.

(2) The aqueous dispersion according to (1) above, wherein the number of coarse particles defined as below is 100,000 or less.
(Number of large particles)
The aqueous dispersion is diluted with ion-exchanged water until it falls within the measurable range, and the particle size distribution is measured using an AccuSizer, a particle size counting device manufactured by Nippon Entegris LLC. From the measurement results, the number of particles of 1 μm or more in 5 μL of the aqueous dispersion converted into a solids concentration of 1% is calculated, and this is taken as the "number of coarse particles."
(3) The aqueous dispersion according to (1) or (2), wherein the 50% cumulative volume particle size (D50) of the emulsion resin particles obtained by a laser diffraction scattering method of the aqueous dispersion is 30 nm or more and 300 nm or less.
(4) The aqueous dispersion according to any one of (1) to (3) above, wherein the pigment-encapsulating emulsion resin particles have an average aspect ratio of 1.0 or more and 1.7 or less.
(5) The aqueous dispersion according to any one of (1) to (4) above, wherein the inorganic pigment is carbon black.
(6) The aqueous dispersion according to any one of (1) to (5) above, wherein the pigment-encapsulating emulsion resin particles contain two or more primary particles of the inorganic pigment.
(7) The aqueous dispersion according to any one of (1) to (6), wherein a mass ratio of the inorganic pigment to the resin in the aqueous dispersion (inorganic pigment/resin) is 0.25 or more and 1.0 or less.
(8) The aqueous dispersion according to any one of (1) to (7) above, wherein the emulsion resin particles contain a polyester.
(9) The aqueous dispersion according to any one of (1) to (8) above, wherein the polyester has a carboxyl group and is a self-emulsifying resin.
(10) A method for producing the aqueous dispersion according to any one of (1) to (9) above, comprising the following steps 1 to 5:
Step 1: mixing a pigment with an organic solvent to obtain a pigment pre-dispersion having a 50% cumulative volume particle size (D50) of the pigment of 10 nm or more and 150 nm or less. Step 2: mixing the pigment pre-dispersion obtained in step 1 with a 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. Step 5: separating and removing non-pigment-encapsulated emulsion resin particles and coarse particles from the aqueous dispersion obtained in step 4. (11) A method for producing an aqueous dispersion according to the above (10), wherein the step of separating and removing the non-pigment-encapsulated emulsion resin particles and the coarse particles is performed by centrifugation.
(12) An ink comprising the aqueous dispersion according to any one of (1) to (9) above as a component.
(13) A printed matter comprising a printed layer of the ink according to (12) above.

400 Image forming apparatus 401 Exterior of image forming apparatus 401c Cover of apparatus main body 404 Cartridge holder 410 Main tank 410k, 410c, 410m, 410y Main tanks for each color of black (K), cyan (C), magenta (M), and yellow (Y) 411 Ink storage section 413 Ink discharge port 414 Storage container case 420 Mechanical section 434 Discharge head 436 Supply tube

JP 2016-196621 A JP 2002-322396 A JP 2019-99819 A JP 2005-120136 A

Claims (3)

A method for producing an aqueous dispersion containing, as a dispersoid, emulsion resin particles including pigment-encapsulated emulsion resin particles that encapsulate an inorganic pigment , the method comprising the following steps 1 to 5:
Step 1: A step of mixing a pigment with an organic solvent to obtain a pigment pre-dispersion having a 50% cumulative volume particle size (D50) of the pigment of 10 nm or more and 150 nm or less. Step 2: A step of mixing the pigment pre-dispersion obtained in step 1 with a 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 liquid containing pigment-encapsulated emulsion resin particles in which the pigment is encapsulated in the resin. Step 4: A step of removing the organic solvent from the dispersion liquid containing pigment-encapsulated emulsion resin particles obtained in step 3 to obtain an aqueous dispersion containing pigment-encapsulated emulsion resin particles. Step 5: A step of separating and removing non-pigment-encapsulated emulsion resin particles and coarse particles from the aqueous dispersion obtained in step 4. The method for producing an aqueous dispersion according to claim 1 , wherein the step of separating and removing the non-pigment-containing emulsion resin particles and the coarse particles is carried out by centrifugation. The method for producing an aqueous dispersion according to claim 1 or 2, wherein the coarse particles have a particle size of 1 μm or more.

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