Aqueous dispersion, method for producing aqueous dispersion, ink and printed matter

Abstract

To provide an aqueous dispersion excellent in dispersion stability and capable of obtaining an image showing high image concentration.SOLUTION: An aqueous dispersion containing emulsion resin particles as a dispersoid, wherein the emulsion resin particles include pigment-encapsulated emulsion resin particles encapsulating an inorganic pigment, the pigment exposure rate is 8% or less, and the pigment non-encapsulated emulsion resin particle ratio calculated by [pigment non-encapsulated emulsion resin particle ratio=number of non-pigment-encapsulated emulsion resin particles / number of pigment-encapsulated emulsion resin particles] is 1.0 or smaller.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous dispersion, a method for producing the aqueous dispersion, an ink, and a printed matter. [Background technology]

[0002] Inkjet recording devices have the advantages of 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 printing paper and non-ink-absorbent plastic media are used as recording media, and there is a demand for inkjet recording methods to achieve image quality on a par with that of conventional offset printing. For example, Patent Documents 1 to 4 disclose water-based pigment dispersions in which pigment particles are coated with a specific resin. Summary of the Invention [Problem to be solved by the invention]

[0003] 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. [Means for solving the problem]

[0004] 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 pigment exposure rate calculation conditions below is 8% or less, and a ratio of emulsion resin particles not encapsulating a pigment, as defined below, is 1.0 or less. (Pigment exposure rate calculation conditions) An aqueous dispersion containing pigment-encapsulated emulsion resin particles is prepared so that the solid content is 10.75% by mass. The aqueous dispersion is then applied to 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 any 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 taken 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. Using 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 desired location. 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 using the following formula (1), and the average value is taken as the ratio of non-pigment-encapsulated emulsion resin particles.

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[0005] According to the present invention, it is possible to provide an aqueous dispersion which has excellent dispersion stability and is capable of obtaining images exhibiting high image density. [Brief description of the drawings]

[0006] [Figure 1] 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. [Diagram 2] 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. [Diagram 3] FIG. 3 is an SEM image of the aqueous dispersion containing the pigment-encapsulated emulsion resin particles obtained in Example 1. [Figure 4] FIG. 4 is an EFM image of the aqueous dispersion containing the pigment-encapsulated emulsion resin particles obtained in Example 1. [Diagram 5] 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. [Figure 6] 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. [Figure 7] FIG. 7 is a TEM image (magnification: 40,000 times) of the ink obtained in Comparative Example 5. [Figure 8] FIG. 8 is an SEM image of the ink obtained in Comparative Example 5. [Figure 9] FIG. 9 is an EFM image of the ink obtained in Comparative Example 5. [Figure 10] FIG. 10 is a perspective view illustrating an example of a recording apparatus. [Figure 11] FIG. 11 is a perspective explanatory view showing an example of the main tank. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] An example of an embodiment of the present invention will be described below. However, the following description is merely an example of an embodiment of the present invention and is not intended to limit the scope of the present invention.

[0008] <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.

[0009] 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.

[0010] 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, preferably 5 nm to 50 nm, and more preferably 10 nm to 30 nm. 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 arbitrary points, and calculating the average value.

[0011] Patent Documents 1 to 4 propose coated pigments and microencapsulated pigments, but these do not have a form in which the pigment is covered in a resin emulsion and are different from the pigment-encapsulated emulsion resin particles of the present invention.

[0012] When producing pigment-encapsulated emulsion resin particles, in addition to the pigment-encapsulated emulsion resin particles, emulsion resin particles not having 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 the pigment-encapsulated emulsion resin particles to the non-pigment-encapsulated emulsion resin particles according to 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 including 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 is increased, thereby improving the image density.

[0013] 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 sample solution is prepared by diluting an aqueous dispersion containing pigment-encapsulated emulsion resin particles with ion-exchanged water so that the solid content concentration is 0.1% by mass. Next, 1 μL of the sample solution is placed on a hydrophilically treated collodion membrane-attached mesh (Nisshin EM Co., Ltd. collodion membrane-attached mesh Cu150 mesh), using a micropipette, and the sample solution is immediately absorbed with a triangular piece of 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 piece of filter paper. After drying under reduced pressure, observation is performed with a transmission electron microscope (JEM-2100F, JEOL Ltd.) at an accelerating voltage of 200 kV and a magnification of 40,000 times.

[0014] 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).

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[0015] 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 images 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 field of view 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.

[0016] The number of primary particles of the pigment contained in one particle of the pigment-encapsulated emulsion resin particle is preferably 2 or more. By containing a plurality of pigments in one particle, a dispersion capable of achieving a sufficient image density can be prepared.

[0017] <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 between the exposed pigments from the contrast of the SEM images due to the difference in the amount of backscattered electrons emitted by the carbon black and the resin. At 20,000x magnification, the proportion of the area of ​​the coating film surface occupied by the pigment is preferably 8% or less of the total, 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 fields of view. 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.

[0018] 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 (Lumiart Gloss 130) using a 0.15 mm bar coater and dried at 25° C. The coated film is cut out and observed under the following conditions using a scanning probe electron microscope (SPM). Equipment: Bruker DimensionIcon Cantilever: Olympus OMCL-AC240TM Measurement mode: Electrical force microscopy (EFM) mode Tip Bias: 5V Lift: 20nm Observation area: 5μm square

[0019] This observation method makes it possible to distinguish between exposed pigments from carbon black and resins due to the difference in the contrast of the electric force image, which is due to the difference in the electrical properties of the resin. The ratio of the area of ​​the coating film surface occupied by the pigment in a 5 μm square is preferably 8% or less of the total area, and more preferably 5% or less.

[0020] In the image formed using the pigment-encapsulated emulsion resin particles, the pigment is not exposed. Therefore, in the heat drying process after the 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.

[0021] <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 the coating is dried by heating 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, and the average surface roughness is calculated. Equipment: Scanning probe microscope (Bruker DimensionIcon) Cantilever: Olympus OMCL-AC240TS Measurement mode: Tapping mode Observation area: 2μm square

[0022] <Number of large 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 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.

[0023] <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. When the particle diameter is 300 nm or less, the settling of the particles is suppressed, resulting in good storage stability as particles. There is no particular restriction 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".

[0024] <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: 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 the pigment-encapsulated emulsion resin particles obtained in step 3 to obtain an aqueous dispersion containing the pigment-encapsulated emulsion resin particles. Step 5: A step of separating and removing non-pigment-containing emulsion resin particles and coarse particles from the aqueous dispersion obtained in step 4.

[0025] Next, each of the above steps 1 to 5 will be described in detail. (Process 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 in the pigment pre-dispersion is not particularly limited as long as it can dissolve the resin in step 2. Preferred examples of the organic solvent include ketones such as methyl ethyl ketone and acetone, and ethers such as tetrahydrofuran.

[0026] 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.

[0027] The pigment pre-dispersion can be produced by dissolving or suspending a pigment dispersant in an organic solvent as necessary, adding a pigment and stirring the mixture, and then using a known dispersing machine that is generally used. 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. Among these, roll mills, beads mills, sand mills, Dyno Mills, high-pressure homogenizers, and paint shakers are preferably used in terms of dispersion efficiency.

[0028] (Process 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.

[0029] 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 has been solubilized in an organic solvent. The particle size of the pigment in the pigment dispersion resin solution is preferably the same as that of the pigment particles in the pigment pre-dispersion obtained in step 1 above, and it is more preferable that there is no change between steps 1 and 2.

[0030] 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 is deteriorated, which may cause aggregation, and the pigment-encapsulated emulsion resin particles obtained in step 3 may become coarse.

[0031] 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.

[0032] The mass ratio (P / R) of the pigment to the resin is preferably 0.2 to 0.75, more preferably 0.3 to 0.6, relative to 1 resin. When the ratio of the pigment to the resin is 0.2 or more, the pigment concentration is appropriate and the printed image density is excellent. When the ratio of the pigment to the resin 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 ratio to the resin can be calculated from the charge ratio or the obtained dispersion.

[0033] 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 is heated to the thermal decomposition temperature of the resin under a nitrogen gas atmosphere and held at that temperature, and the decomposed weight is calculated as the resin and the residual weight is calculated as the pigment. In addition, for highly heat-resistant resins that cannot be completely decomposed by thermal decomposition under a nitrogen gas atmosphere, the P / R ratio can be calculated using a calibration curve of the heat loss and the pigment to resin ratio. Specifically, a plurality of mixtures of pigment and resin mixed at any ratio are prepared, and each mixture is heated to a certain temperature and held at that temperature, and the calibration curve is prepared, and the ratio of the pigment to the resin can be calculated based on the weight loss rate obtained from the measurement results of the unknown sample.

[0034] 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 to 3.0, more preferably 1.4 to 2.0. When the ratio of the 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. In addition, when the ratio of the 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, making it possible to suppress the generation of coarse particles.

[0035] (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 dispersing 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 and the encapsulation form may not be maintained.

[0036] There is no particular restriction 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 water addition rate is preferably 10 parts by mass / min to 1000 parts by mass / min, more preferably 30 parts by mass / min to 500 parts by mass / min, relative to 100 parts by mass of resin. When the water addition rate is 10 parts by mass / min to 1000 parts by mass / min, the pigment aggregation in the system is suppressed, thereby suppressing the coarsening of the pigment-encapsulated emulsion resin particles.

[0037] 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.

[0038] (Step 4) Step 4 is a step of obtaining an aqueous dispersion containing pigment-encapsulated emulsion resin particles. The aqueous dispersion obtained in step 4 is obtained by removing the organic solvent from the dispersion liquid containing the pigment-encapsulated emulsion resin particles obtained in step 3. The method for removing the organic solvent from the dispersion obtained in step 3 is not particularly limited, and any 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.

[0039] (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.

[0040] <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.

[0041] 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 discharge 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.

[0042] 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.

[0043] (polyester) The polyester is obtained by polycondensation of a polyhydric alcohol with a polycarboxylic acid, a polycarboxylic anhydride, a polycarboxylic ester, or the like, 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, a polycarboxylic anhydride, a polycarboxylic ester, or the like, and / or a derivative thereof, as constituent components.

[0044] -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.); an alkylene ether glycol having 6 carbon atoms (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, etc.); Examples of the alkylene oxide adducts include alicyclic diols having 2 to 4 carbon atoms (e.g., 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 2 to 4 carbon atoms (e.g., ethylene oxide (hereinafter abbreviated as EO), propylene oxide (hereinafter abbreviated as PO), butylene oxide (hereinafter abbreviated as BO)); and adducts (number of moles added: 2 to 30) of bisphenols (e.g., bisphenol A, bisphenol F, bisphenol S) with alkylene oxides having 2 to 4 carbon atoms (e.g., EO, PO, BO, etc.).

[0045] In addition to the dihydric diol, the alcohol component 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 dehydration products, for example, glycerin, triethylolethane, trimethylolpropane, pentaerythritol, sorbitol, sorbitan, polyglycerin, dipentaerythritol; sugars and their derivatives, for example, sucrose and methyl glucoside; etc. ); adducts of the above aliphatic polyhydric alcohols with alkylene oxides (EO, PO, BO, etc.) having 2 to 4 carbon atoms (number of moles added: 1 to 30); adducts of trisphenols (trisphenol PA, etc.) with alkylene oxides (EO, PO, BO, etc.) having 2 to 4 carbon atoms (number of moles added: 2 to 30); adducts of 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 (number of moles added: 2 to 30). These may be used alone or in combination of two or more.

[0046] -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 the acid 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.

[0047] The method of isolating the polyester may be, for example, to dry the aqueous dispersion containing the pigment-encapsulated emulsion resin particles by heating and drying, and then to dissolve the polyester in a tetrahydrofuran (THF) solution. The pigment is then removed by centrifugation, filtration, or the like, and the THF is then removed to isolate the polyester. In addition, recycled GPC can be used as necessary.

[0048] 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 from 2,000 to 15,000, and more preferably from 4,000 to 12,000.

[0049] The glass transition temperature (Tg) of the polyester is not particularly limited and can be appropriately selected depending on the purpose, but is preferably from 30° C. to 100° C., more preferably from 50° C. to 80° C.

[0050] 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., 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 by GC / MS, LC / MS, IR measurement, and the like.

[0051] 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 polycarboxylic acid or a carboxylic anhydride.

[0052] <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 (CI 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 (CI Pigment Black 11) can be used.

[0053] The carbon black preferably has a primary particle size of 15 nm or more and 100 nm or less, and color development is improved by adjusting the particle size within this range. The DBP absorption is preferably 30 mL / 100 g or more and 150 mL / 100 g or less, and pigment dispersibility in organic solvents can be improved by adjusting the particle size within this range. 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.

[0054] <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. As the pigment dispersant, (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, stearylamine acetate, etc. can be used.

[0055] 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 the pigment is easily encapsulated in the resin and the image density is improved. The hydrophilicity / hydrophobicity of the pigment dispersant is hydrophobic if the pigment dispersant is insoluble in water, and hydrophilic if the pigment dispersant is soluble in water.

[0056] Specific examples of pigment dispersants include Joncryl (manufactured by Johnson Polymers), Anti-Terra-U (manufactured by BYK Chemie), Disperbyk (manufactured by BYK Chemie), Efka (manufactured by Efka Chemicals), Florene (manufactured by Kyoeisha Chemical Co., Ltd.), Disparlon (manufactured by Kusumoto Chemicals Co., Ltd.), Ajisper (manufactured by Ajinomoto Fine-Techno Co., Ltd.), Demol (manufactured by Kao Corporation), Homogenol, Emulgen (all manufactured by Kao Corporation), Solsperse (manufactured by Lubrizol Corporation), and Nikkol (manufactured by Nikko Chemical Co., Ltd.).

[0057] <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.

[0058] <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.

[0059] 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.

[0060] Polyol compounds having 8 or more carbon atoms and glycol ether compounds can improve the permeability of 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.

[0061] <Water> The water content in the ink is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of the drying property and ejection reliability of the ink, however, it is preferably from 10% to 90% by mass, and more preferably from 20% to 60% by mass.

[0062] <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.

[0063] Resin particles made of these resins may 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 the organic solvent 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 kinds of resin particles.

[0064] 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, however, it is preferably from 10 nm to 1,000 nm, more preferably from 10 nm to 200 nm, and particularly preferably from 10 nm to 100 nm. The volume average particle size can be measured, for example, 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.

[0065] <Additives> If necessary, surfactants, antifoaming agents, antiseptics, antifungals, rust inhibitors, pH adjusters, etc. may be added to the ink.

[0066] <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 fluorosurfactant, for example, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chain are particularly preferred because they have low foaming properties. As the perfluoroalkyl sulfonic acid compounds, for example, perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, etc. are included. As the perfluoroalkyl carboxylic acid compounds, for example, perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate, etc. are included. As the polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chain, for example, sulfate ester salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups on the side chains, salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups on the side chains, etc. are included. As counter ions of the salts in these fluorosurfactants, Li, Na, K, NH4, NH3CH2CH2OH, NH2(CH2CH2OH)2, NH(CH2CH2OH)3, etc. are included. 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.

[0067] 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 appropriately synthesized or 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. [ka] (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, such as 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.

[0068] 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 fluorine-based surfactants include perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in side chains, etc. Among these, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in side chains are preferred because they have low foaming properties, and fluorine-based surfactants represented by general formula (F-1) and general formula (F-2) are particularly preferred. [ka] 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- CH2CH(OH)CH2-O-(CH2CH2O) a -Y In the compound represented by the above general formula (F-2), Y is H or CmF 2m+1where m is an integer from 1 to 6, or CH2CH(OH)CH2-CmF 2m+1 where m is an integer between 4 and 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. The fluorine-based surfactant may be a commercially available product, such as Surflon S-111, S-112, S-113, S-121, S-131, S-132, S-141, S-145 (all manufactured by Asahi Glass Co., Ltd.); Fullard FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, FC-431 (all manufactured by Sumitomo 3M Limited); Megafac F-470, F-1405, F-474 (all manufactured by Dainippon Ink and Chemicals, Inc.); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-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.), etc., among these, from the viewpoint of excellent printing quality, especially 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.

[0069] The content of the surfactant in the ink is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoints of excellent wettability and ejection stability and improved image quality, the content is preferably from 0.001% by mass to 5% by mass, and more preferably from 0.05% by mass to 5% by mass.

[0070] <Defoaming agent> There are no particular restrictions on the defoaming agent, and examples thereof include silicone-based defoaming agents, polyether-based defoaming agents, fatty acid ester-based defoaming agents, etc. These may be used alone or in combination of two or more. Among these, silicone-based defoaming agents are preferred because of their excellent defoaming effect.

[0071] <Antiseptic and antifungal agent> There are no particular restrictions on the antiseptic and antifungal agent, and examples thereof include 1,2-benzisothiazolin-3-one, etc.

[0072] <Rust inhibitor> There are no particular restrictions on the rust inhibitor, and examples thereof include acid sulfite, sodium thiosulfate, etc.

[0073] <pH adjuster> There are no particular restrictions on the pH adjuster as long as it can adjust the pH to 7 or higher, and examples thereof include amines such as diethanolamine and triethanolamine.

[0074] There are no particular restrictions on the physical properties of the ink, and it can be appropriately selected according to the purpose. For example, it is preferable that the viscosity, surface tension, pH, etc. are in the following ranges. The viscosity of the ink at 25°C is preferably 5 mPa·s or more and 30 mPa·s or less, more preferably 5 mPa·s or more and 25 mPa·s or less, from the viewpoints of improving the printing density and character quality and obtaining good ejection properties. Here, for example, a rotational viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.) can be used to measure the viscosity. The measurement conditions are as follows: at 25°C, using a standard cone rotor (1°34’×R24), a sample liquid volume of 1.2 mL, a rotation speed of 50 rpm, and it can be measured in 3 minutes. The surface tension of the ink is preferably 35 mN / m or less, more preferably 32 mN / m or less at 25°C, from the viewpoints of the ink being preferably leveled on the recording medium and shortening the drying time of the ink. The pH of the ink is preferably 7 to 12, more preferably 8 to 11, from the viewpoint of preventing corrosion of the metal members in contact with the liquid.

[0075] <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 rust inhibitor may be the same as those used in ink, and other materials used in known treatment liquids may be used. The type of the flocculant is not particularly limited, and examples thereof include water-soluble cationic polymers, acids, and polyvalent metal salts.

[0076] <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.

[0077] <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, in the Bristow method, 1 / 2 Water absorption up to 10mL / m 2 The term "substrate" refers to a substrate that is: 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.

[0078] The recording medium is not limited to those generally used as recording media, and may be wallpaper, flooring, building materials such as tiles, cloth for clothing such as T-shirts, textiles, leather, etc. By adjusting the configuration of the path for conveying the recording medium, ceramics, glass, metal, etc. may also be used.

[0079] <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.

[0080] <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 a head portion that ejects ink, but also means related to feeding, transporting, and discharging the recording medium, as well as other devices called pre-processing devices and post-processing devices. The recording apparatus and 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 and an infrared heater can be used. Heating and drying can be performed before, during, or after printing. In addition, 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 create three-dimensional images are also included. Furthermore, unless otherwise specified, the recording apparatus includes both a serial type apparatus in which the ejection head moves and a line type apparatus in which the ejection head does not move. Furthermore, this recording device includes not only desktop types, but also wide-width recording devices capable of printing 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 device will be described with reference to Figs. 10 and 11. Fig. 10 is a perspective view of the device. Fig. 11 is a perspective view of a main tank. An image forming device 400 as an example of a recording device is a serial type image forming device. A mechanism unit 420 is provided in an exterior 401 of the image forming device 400. Each ink storage unit 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 unit 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 back side 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. As a result, each ink outlet 413 of the main tank 410 communicates with an ejection head 434 for each color via a supply tube 436 for each color, and ink can be ejected from the ejection head 434 to a recording medium.

[0081] 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 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.

[0082] The ink can be used in a wide variety of ways, including, but not limited to, inkjet recording, blade coating, gravure coating, bar coating, roll coating, dip coating, curtain coating, slide coating, die coating, and spray coating.

[0083] The application 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 to form two-dimensional characters and images when used as an ink, but also as a material for three-dimensional modeling to form 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 recording material 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 panel of automobiles, office automation equipment, electric and electronic equipment, cameras, etc.

[0084] In the present invention, the terms image formation, recording, printing, printing, etc. are all synonymous.

[0085] Recording medium, media, and printed material are all synonymous. EXAMPLES

[0086] 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.

[0087] [Production Example] <Self-emulsifying resin: polyester synthesis example> (Synthesis of polyester α) In a 500mL 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 continued until no effluent was observed. After that, the reaction was carried out for 1 hour under a reduced pressure of 5mmHg to 30mmHg 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] with an acid value (AV) of 20 mgKOH / g, a glass transition temperature (Tg) of 51°C, and a weight average molecular weight (Mw) of 5,100.

[0088] (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. After that, the reaction was carried out for 1 hour under a reduced pressure of 5mmHg to 30mmHg 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.

[0089] <Preparation of pigment pre-dispersion> (Pigment pre-dispersion A) The following ingredients were mixed and poured into a 110ml glass screw bottle, after which 170 parts of 2.0mm diameter zirconia balls (Nikkato Corporation, YTZ balls) were poured in, the bottle was attached to a shaker (IKA Corporation, Vibrax VXR basic) and dispersed at 1000 rpm for 24 hours. The media and dispersion were then 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, 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

[0090] In the following, preparation examples of aqueous dispersions 1 to 11 and inks 1 to 11 using these aqueous dispersions are shown as examples and comparative examples. The evaluation results of the properties of the aqueous dispersion and the ink are shown in Table 1.

[0091] [Example 1] (Preparation of Aqueous Dispersion 1) In a 0.3L separable flask equipped with a three-one motor, anchor blades, and a thermocouple, 60g of [pigment pre-dispersion A] and 30g of [polyester α] were added and mixed and stirred at 40°C so that the mass ratio (P / R) of the pigment (P: Pigment) and 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 methyl ethyl ketone (S: Solvent) was 1.4, and then 1.1g of triethylamine was added in an amount equivalent to the carboxyl group to neutralize the acid value of the polyester, and mixed and stirred for 0.5 hours. 64g of ion-exchanged water was dropped at a rate of 15ml / 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 mixture was filtered and purified using a nylon net with an opening of 67μm, 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 centrifuge. The upper 10 vol% and the lower 20 vol% of the cell were removed and collected to obtain [Aqueous Dispersion 1], in which the entire surface of the pigment was covered with a resin layer of 5 nm or more and which contained pigment-encapsulated emulsion resin particles containing 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), an SEM image and an EFM image of [Aqueous Dispersion 1], respectively.

[0092] (Preparation of Ink 1) Using the [Aqueous Dispersion 1] obtained above, an ink was prepared according to the following formulation. The viscosity at 25°C was adjusted to 7.5 mPa s, and then the ink was filtered through a membrane filter with an average pore size of 10 μm to prepare [Ink 1]. -Ink formula- Aqueous dispersion 1 (as solids): 10.75% Propylene glycol (adjusted to a viscosity of 7.5 mPa·s): approx. 40% Silicone surfactant: 1.0% (Nissin Chemical Industry Silface SAG503A) Aliphatic dialcohol surfactant: 0.1% (Surfynol AD01 manufactured by Nissin Chemical Industry Co., Ltd.) Water: remaining (Total: 100%)

[0093] [Example 2] Except for recovering only the upper 5 vol% and the lower 10 vol% 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 prepared in the same manner as [Ink 1], except for using [Water-based Dispersion 2] instead of [Water-based Dispersion 1].

[0094] [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].

[0095] [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 [Ink 1], except for using [water-based dispersion 4] instead of [water-based dispersion 1].

[0096] [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) In a 0.3L separable flask equipped with a three-one motor, anchor blade, and thermocouple, 40g of polycarbonate diol (Asahi Kasei Duranol T5651) and 1.69g of 2,2-bis(hydroxymethyl)propionic acid were added, 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 organic solvents, 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 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 to this 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, after which 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 produce 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, after which 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 [Water-based Dispersion 5] containing pigment-encapsulated emulsion resin particles.

[0097] [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 upper 10 vol % and the lower 20 vol % of the cell were removed and collected, and the same procedure as in Example 5 was used to obtain [Water-based Dispersion 6] containing pigment-encapsulated emulsion resin particles.

[0098] [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. Also, [Ink 7] was prepared in the same manner as "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.

[0099] [Comparative Example 2] Except for recovering only the bottom 50 vol% of the cell after centrifugation, [Water-based Dispersion 8] containing pigment-encapsulated emulsion resin particles was obtained in the same manner as in Example 1. [Ink 8] was also prepared in the same manner as [Ink 1], except for using [Water-based Dispersion 8] instead of [Water-based Dispersion 1].

[0100] [Comparative Example 3] Except for recovering only the top 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. [Ink 9] was also prepared in the same manner as [Ink 1], except for using [Water-based Dispersion 9] instead of [Water-based Dispersion 1].

[0101] [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. Also, [Ink 10] was prepared in the same manner as [Ink 1], except for using [Water-based Dispersion 10] instead of [Water-based Dispersion 1].

[0102] [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 blade, and thermocouple, and mixed and 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, an equal amount 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 15 ml / 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 67 μm. The solid content was adjusted to 30% with ion-exchanged water, and a polyester-only resin emulsion with a D50 of 78 nm was obtained.

[0103] (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 put into a 110 ml glass screw tube bottle, after which 170 parts of zirconia balls (Nikkato Corporation, YTZ balls) with a diameter of 2.0 mm were put in, the bottle was fixed to a shaker (IKA Corporation, Vibrax VXR basic), and dispersed at 1000 rpm for 24 hours. After that, the media and the dispersion were separated by filtration, and filtered with a cellulose acetate membrane filter with 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, Asahi Carbon Co., Ltd.): 15.0 parts Pigment dispersant I aqueous solution: 45.0 parts

[0104] (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 a period of 2 hours, and the mixture was stirred at room temperature for 6 hours. The resulting reaction solution was washed with water, and the organic layer was isolated, 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.

[0105] Next, 42.1 parts of the above-obtained compound was dissolved in 80 ml of dry methyl ethyl ketone, and heated to 60° C. while stirring. A solution of 24.0 parts of Karenz MOI (Showa Denko K.K.) dissolved in 20 ml of dry methyl ethyl ketone was added dropwise to this solution over 1 hour, and 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.

[0106] 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 a temperature of 75°C under a nitrogen gas flow. After that, the reaction solution was cooled to room temperature, and reprecipitation was repeated five times using hexane to purify the copolymer. After the purification process, the copolymer was filtered and dried under reduced pressure to obtain pigment dispersant I.

[0107] (Preparation of Ink 11) Using the [Polyester single resin emulsion] and [Water-based pigment dispersion 11] obtained above, an ink was prepared according to the following formulation. The viscosity at 25°C was adjusted to 7.5 mPa s, and then the ink was filtered through a membrane filter with an average pore size of 10 μm to prepare Ink 11. 7, 8 and 9 are a TEM image (magnification: 40,000 times), an SEM image and an EFM image of [Ink 11], respectively. -Ink formula- Polyester only resin emulsion (as solids): 5.375% Water-based pigment dispersion 11 (as solids): 5.375% Propylene glycol (adjusted to a viscosity of 7.5 mPa·s): approx. 40% Silicone surfactant: 1.0% (Nissin Chemical Industry Silface SAG503A) Aliphatic dialcohol surfactant: 0.1% (Surfynol AD01 manufactured by Nissin Chemical Industry Co., Ltd.) Water: remaining (Total: 100%)

[0108] [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.

[0109] <Molecular weight> Apparatus: GPC (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 made from a polystyrene sample of known molecular weight as the standard. Note that columns with exclusion limits of 60,000, 20,000, and 10,000 connected in series were used.

[0110] <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 resulting 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.

[0111] In addition, 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 type particle size distribution measuring device (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 device were 30% to 70%, and a part of the obtained solution was placed in a batch type cell (spacer: 50 μm), which was then set in a sample holder and measured.

[0112] <Mass ratio of pigment (P) to resin (R) (P / 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.

[0113] <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 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 any 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.

[0114] 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.

[0115] <Ratio of emulsion resin particles not containing pigment> The ratio of pigment-free emulsion resin particles was calculated as follows. First, the emulsion containing pigment-encapsulated emulsion resin particles was diluted with ion-exchanged water so that the solid concentration was 0.1% to prepare a sample solution. Next, 1 μL of the sample solution was placed on a hydrophilically treated collodion membrane-attached mesh (Nisshin EM Co., Ltd. Collodion membrane-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. Using 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 any desired location. For each image, the number of pigment-encapsulated emulsion resin particles and non-pigment-encapsulated emulsion resin particles were counted, and the ratio of non-pigment-encapsulated emulsion resin particles was calculated using the following formula (1), and the average was obtained.

number

[0116] <Number of large 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.

[0117] <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 (Lumiart 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, and the surface roughness was calculated. Observation was performed in three fields of view at random locations, and the average surface roughness was calculated. Equipment: Scanning probe microscope (Bruker DimensionIcon) Cantilever: Olympus OMCL-AC240TS Measurement mode: Tapping mode Observation area: 2μm square

[0118] [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.

[0119] (Image output method) The ink supply path including the print head of an inkjet printer (RICOH IPSiO GXe5500) 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 to confirm that all nozzles were filled with the evaluation ink and that no abnormal images were produced. After selecting the glossy paper clean mode in the driver attached to the printer, the user settings were changed to color matching off as the print mode. In this mode, the amount of ink adhering to the recording medium for a solid image was 20 g / m 2 The discharge amount was adjusted by changing the head drive voltage so as to obtain the following. <Image density> A solid image was printed on recording paper (Lumi 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 produce 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.

[0120] <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, then visually inspecting it. 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 ×: Precipitates that cannot be redispersed are present

[0121] <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 surface emergence 5 hours after the start of the test △: Floating occurred between 1 hour and 5 hours after the start of the test ×: Floating occurred within 1 hour of starting the test

[0122] [Table 1]

[0123] 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 pigment exposure rate calculation conditions below is 8% or less, and a ratio of emulsion resin particles not encapsulating a pigment, as defined below, is 1.0 or less. (Pigment exposure rate calculation conditions) An aqueous dispersion containing pigment-encapsulated emulsion resin particles is prepared so that the solid content is 10.75% by mass. The aqueous dispersion is then applied to 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 any 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 taken 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. Using 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 desired location. 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 using the following formula (1), and the average value is taken as the ratio of non-pigment-encapsulated emulsion resin particles.

number

[0124] 400 Image forming device 401 Exterior of image forming device 401c Device body cover 404 Cartridge Holder 410 Main Tank 410k, 410c, 410m, 410y Main tanks for black (K), cyan (C), magenta (M), and yellow (Y) 411 Ink storage unit 413 Ink outlet 414 Storage container case 420 Mechanism Department 434 Discharge Head 436 Supply Tube [Prior art documents] [Patent documents]

[0125] [Patent Document 1] JP 2016-196621 A [Patent Document 2] JP 2002-322396 A [Patent Document 3] JP 2019-99819 A [Patent Document 4] JP 2005-120136 A

Claims

1. A method for producing an aqueous dispersion containing emulsion resin particles as a dispersoid, 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: 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 the pigment-encapsulated emulsion resin particles obtained in step 3 to obtain an aqueous dispersion containing the pigment-encapsulated emulsion resin particles. Step 5: A step of separating and removing the emulsion resin particles not containing the pigment and the coarse particles from the aqueous dispersion obtained in step 4.

2. 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.

3. A method for producing an aqueous dispersion as described in claim 1 or 2, wherein the coarse particles have a particle size of 1 μm or more.

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