JP7567286B2 - Aqueous dispersion and method for producing the same, as well as ink, printing method and printing device - Google Patents

Description

The present invention relates to an aqueous dispersion and its manufacturing method, as well as an ink, a printing method, and a printing device.

In recent years, inkjet technology has been used not only for home use but also for commercial and industrial use. In commercial and industrial use, low ink-absorbent coated paper for printing and non-ink-absorbent plastic film are used as recording media. Therefore, it is required to realize the same level of image quality as conventional offset printing by using inkjet recording methods for such recording media.
For example, Patent Documents 1 to 3 propose water-based pigment dispersions in which pigment particles are coated with a specific resin.

The present invention aims to provide an aqueous dispersion that can obtain high image density and suppress the decrease in image density during heating and drying.

The aqueous dispersion of the present invention as a means for solving the above-mentioned problems contains pigment-encapsulated resin particles that encapsulate a pigment and a surfactant, and the pigment-encapsulated resin particles have a cumulative 50% volume particle size ( _D50 ) of 200 nm or more and 500 nm or less, and an aspect ratio of the pigment-encapsulated resin particles of 1.0 or more and 1.5 or less.

The present invention provides an aqueous dispersion that can obtain high image density and suppress the decrease in image density during heating and drying.

FIG. 1 is a schematic diagram showing an example of a printing apparatus according to the present invention. FIG. 2 is a TEM image of the aqueous dispersion containing the pigment-encapsulated resin particles obtained in Example 1. FIG. 3 is a TEM image of the aqueous dispersion obtained in Comparative Example 2. FIG. 4 is a TEM image of the aqueous dispersion obtained in Comparative Example 3.

(Aqueous Dispersion)
The aqueous dispersion of the present invention contains pigment-encapsulated resin particles that encapsulate a pigment and a surfactant, the pigment-encapsulated resin particles have a cumulative 50% volume particle size ( _D50 ) of 200 nm or more and 500 nm or less, and an aspect ratio of 1.0 or more and 1.5 or less, and further contains other components as necessary.

In conventional technology, it is difficult to achieve both the formation of pigment-encapsulated resin particles in which a pigment is encapsulated in a resin and the particle size of the pigment-encapsulated resin particles suitable for inkjet recording methods. In addition, in pigment-encapsulated resin particles, the resin that coats the pigment is highly hydrophilic, so the resin is easily detached from the pigment surface, reducing the stability of the pigment composite resin particles, and 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. As a result, there is a problem that conventional water-based inks cannot satisfy the high image density that has been required in recent years.

In the present invention, by using an aqueous dispersion containing pigment-encapsulated resin particles that encapsulate a pigment and a surfactant, in which the pigment-encapsulated resin particles have a cumulative 50% volume particle size ( _D50 ) of 200 nm or more and 500 nm or less and an aspect ratio of 1.0 or more and 1.5 or less, a high image density can be obtained and a decrease in image density during heating and drying can be suppressed.

<Pigment-encapsulated resin particles>
The pigment-encapsulated resin particles are resin particles in which the entire surface of the pigment is coated with resin, and do not have any unencapsulated pigment dispersed therein or any part of the pigment exposed on the surface of the resin particles. The pigment-encapsulated resin particles are preferably spherical.
In this specification, the term "pigment-encapsulated resin particles" means that the pigment is entirely contained (encapsulated) in the resin particles in the resin emulsion. For example, JP-A-2016-196621, JP-A-2002-322396, JP-A-2019-099819, and JP-A-2005-120136 propose coated pigments and microencapsulated pigments, but these are not in the form of a pigment encapsulated in a resin particle in a resin emulsion, and are different from pigment-encapsulated resin particles.
The pigment-encapsulated resin particles are preferably in the form of a resin emulsion from the viewpoint of ease of handling. By encapsulating the pigment in the resin particles in the resin emulsion, it is possible to suppress the detachment of the pigment dispersion resin into the medium. The resin emulsion refers to a state in which the resin particles are dispersed in water or ink, and it does not matter whether the resin particles are solid or liquid.

The method of confirming that the particles are pigment-encapsulating resin particles can be performed by observation with a transmission electron microscope (TEM) as described below.
First, a water-based dispersion containing pigment-encapsulated resin particles is diluted with ion-exchanged water to a solid content concentration of 0.1% by mass to prepare a sample solution. Next, 1 μL of the sample solution is placed on a hydrophilically treated collodion membrane-attached mesh (manufactured by Nissin EM Co., Ltd., collodion membrane-attached mesh Cu150 mesh) using a micropipette, and the sample solution is immediately absorbed with a triangular 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 filter paper. After drying under reduced pressure, observation is performed with a transmission electron microscope (manufactured by JEOL Ltd., JEM-2100F) at an acceleration voltage of 200 kV and a magnification of 40,000 times. As a result of the observation, if a resin layer is present so as to completely cover the pigment (the pigment is encapsulated in the resin particles in the resin emulsion) (for example, see FIG. 2), it can be confirmed that the pigment-encapsulated resin particles of the present invention are the same.

The cumulative 50% volume particle diameter ( _D50 ) of the pigment-encapsulating resin particles is 200 nm to 500 nm, preferably 200 nm to 400 nm, and more preferably 200 nm to 300 nm. When the cumulative 50% volume particle diameter ( _D50 ) is 200 nm to 500 nm, a plurality of pigment primary particles can be encapsulated, thereby increasing image density.
The cumulative 50% volume particle size (D ₅₀ ) of the pigment-encapsulating resin particles can be measured, for example, by using a zeta potential particle measuring system (ELSZ-1000, manufactured by Otsuka Electronics Co., Ltd.).

The ratio of pigment-encapsulated resin particles is not particularly limited, and the ratio of pigment-encapsulated resin particles to resin particles that do not contain pigment can be appropriately selected. The amount of pigment-encapsulated resin particles is determined by taking five or more images of a field of view containing three or more particles with a volume diameter of 100 nm or more at any position, and the ratio of the pigment-encapsulated resin particles to the total particles with a volume diameter of 100 nm or more for each image, and the average value is preferably 30% or more, more preferably 50% or more. When the ratio of pigment-encapsulated resin particles is 30% or more, the image density can be increased by increasing the ratio of pigment-encapsulated resin particles.
The pigment-encapsulating resin particles preferably contain two or more primary pigment particles, and thus the pigment density in the pigment-encapsulating resin particles is increased, thereby making it possible to increase the image density.

The aspect ratio of the pigment-encapsulated resin particles is determined by taking multiple images of a field of view including the pigment-encapsulated resin particles, calculating the ratio of the major axis to the minor axis (major axis/minor axis) of 20 arbitrarily selected pigment-encapsulated particles, and averaging the ratios (average aspect ratio) to be in the range of 1.0 to 1.5, preferably 1.0 to 1.2. When the aspect ratio of the pigment-encapsulated resin particles is 1.0 to 1.5, there is an advantage in that the smoothness of the coating surface is improved and the image density is improved. In calculating the major axis/minor axis, the length of the particle along the axis that is the longest from end to end (major axis) is taken as the major axis, and the length of the particle in the direction perpendicular to the major axis at the center of the major axis is taken as the minor axis.

The degree of pigment encapsulation in the pigment-encapsulated resin particles can be evaluated by quantifying the amount of pigment that is exposed without being encapsulated (pigment exposure rate).
The pigment exposure rate can be calculated, for example, using a scanning electron microscope (SEM). The specific calculation method for the pigment exposure rate is as follows. An aqueous dispersion containing pigment-encapsulated resin particles is prepared using ion-exchanged water so that the solid content concentration is 10.75% by mass. Then, coated paper (Lumia Art Gloss 130, manufactured by STORA ENSO) is coated using a bar coater having a diameter of 0.15 mm, and dried at 25°C to form a coating film having an average thickness of 2 μm. This coating film is cut out and fixed to a stub for SEM observation using carbon tape. This is observed using a scanning electron microscope (manufactured by ZEISS, Merlin) without conducting a conductive treatment, with an accelerating voltage of 0.75 kV, a backscattered electron detector, and a magnification of 2,000 to 20,000 times. This observation method makes it possible to distinguish the exposed pigment from the difference in the contrast of the SEM image due to the difference in the amount of backscattered electrons emitted by the carbon black and the resin.
The ratio of the area occupied by the pigment on the coating surface at 20,000 times magnification (pigment exposure rate) is preferably 8% or less, more preferably 5% or less, and even more preferably 0% to 3%. The area occupied by the pigment on the coating surface is determined by binarizing the SEM observation image, and it is preferable to take the average of three or more visual fields observed at arbitrarily changed locations. 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.

By covering two or more primary pigment particles into a spherical shape with resin, it is possible to make the pigment dispersion in the coating film after heat drying uniform and reduce the surface roughness of the coating film, thereby improving the image density (OD) of the image.
The surface roughness of the coating film is preferably 20 nm or less, and more preferably 15 nm or less. By making the surface roughness of the coating film 20 nm or less, a decrease in image density after heat drying can be suppressed.
The surface roughness of the coating film is calculated, for example, using a scanning probe microscope (SPM) as follows. First, an aqueous dispersion containing pigment-encapsulated resin particles is prepared using ion-exchanged water so that the solid content concentration is 10.75% by mass. Then, coated paper (Lumia Art Gloss 130, manufactured by STORA ENSO) is coated with a 0.15 mm bar coater, and heated and dried in an oven at 100° C. for 5 minutes to form a coating film with an average thickness of 2 μm. This coating film is cut out and observed under the following conditions to calculate the surface roughness. Observation is performed in three fields of view to determine the average surface roughness.
[Measurement conditions]
Apparatus: Scanning probe microscope (Dimension Icon, manufactured by Bruker)
Cantilever: Olympus Corporation, OMCL-AC240TS
Measurement mode: Tapping mode Observation range: 2 μm square

<Resin>
The resin preferably has an anionic group. Examples of the anionic group include a carboxyl group, a carboxylate group, a sulfonic acid group, and a sulfonate group. Among these, a carboxylate group or a sulfonate group partially neutralized with a basic compound is preferred.
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 basic compounds including Na, K, Li, Ca, and the like.
The resin is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof include polyester resin, polyurethane resin, acrylic resin, etc. Among these, polyester resin is particularly preferred.

- Polyester resin -
The polyester resin 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.

-Polyhydric alcohol component-
The polyhydric alcohol component may be a dihydric alcohol (diol), specifically, an alkylene glycol having 2 to 36 carbon atoms (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexanediol, trimethylolpropane, etc.); an alkylene ether glycol having 4 to 36 carbon atoms (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, etc.); Examples of the alkylene oxide include alicyclic diols (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 (ethylene oxide (hereinafter abbreviated as "EO"), propylene oxide (hereinafter abbreviated as "PO"), butylene oxide (hereinafter abbreviated as "BO"), etc.); and adducts (number of moles added: 2 to 30) of bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.) with alkylene oxides having 2 to 4 carbon atoms (EO, PO, BO, etc.).
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.) ); an adduct of the aliphatic polyhydric alcohol with an alkylene oxide (EO, PO, BO, etc.) having 2 to 4 carbon atoms (number of moles added: 1 to 30); an adduct of a trisphenol (trisphenol PA, etc.) with an alkylene oxide (EO, PO, BO, etc.) having 2 to 4 carbon atoms (number of moles added: 2 to 30); an adduct of a novolak resin (phenol novolak, cresol novolak, etc.: average degree of polymerization: 3 to 60) with an alkylene oxide (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.

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

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

The molecular weight of the polyester resin is not particularly limited and may be appropriately selected depending on the purpose. 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.
The glass transition temperature (Tg) of the polyester resin is not particularly limited and may be appropriately selected depending on the purpose, but is preferably from 30° C. to 100° C., and more preferably from 50° C. to 80° C.
The softening temperature of the polyester resin is not particularly limited and may be appropriately selected depending on the purpose, but is preferably from 60° C. to 180° C., and more preferably from 80° C. to 150° C.
The molecular structure of the polyester resin can be confirmed by NMR measurement of a solution or solid, as well as GC/MS, LC/MS, IR measurement, and the like.

The polyester resin can be synthesized by a method that has been generally used, for example, the following method.
First, the polyhydric alcohol and the polycarboxylic acid can be polycondensed in the absence of a solvent or in the presence of an organic solvent.

<Pigments>
Examples of the pigment include organic pigments and inorganic pigments. Among these, inorganic pigments are preferred.
Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, carbon black (C.I. Pigment Black 7) produced by a known method such as furnace black, lamp black, acetylene black, channel black, and metals such as copper and iron (C.I. Pigment Black 11). Of these, carbon black is preferred.

The carbon black preferably has a primary particle size of 15 nm or more and 100 nm or less. By setting the primary particle size in the above range, color development is improved.
The DBP absorption of carbon black is preferably 30 mL/100 g or more and 150 mL/100 g or less. By setting the DBP absorption in the above range, the pigment dispersibility in an organic solvent can be improved.
A self-dispersing pigment may also be used, and the self-dispersing pigment refers to a pigment that 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 described in International Publication No. 2009/014242 can be used.

<Pigment dispersant>
In order to improve the dispersibility of the pigment-encapsulated resin particles, it is preferable to add a pigment dispersant to the aqueous dispersion.

The hydrophilicity/hydrophobicity of the pigment dispersant is not particularly limited and can be appropriately selected depending on the purpose, but it is preferable to use a hydrophobic pigment dispersant because the pigment is easily encapsulated in the resin and image density is improved. The hydrophilicity/hydrophobicity of the pigment dispersant is such that if the pigment dispersant is insoluble in water, it is hydrophobic, and if it is soluble in water, it is hydrophilic.

The pigment dispersant is not particularly limited and can be appropriately selected depending on the purpose. For example, a polymer dispersant can be used.
Examples of pigment dispersants include (meth)acrylic resins, styrene-(meth)acrylic resins, hydroxyl group-containing carboxylates, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylates, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalenesulfonic acid-formalin condensate salts, aromatic sulfonic acid-formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, stearylamine acetate, etc. These may be used alone or in combination of two or more.
Commercially available pigment dispersants can be used, and examples of the commercially available products include Joncryl (manufactured by Johnson Polymers), Anti-Terra-U (manufactured by BYK Chemie), Disperbyk (manufactured by BYK Chemie), Efka (manufactured by Efka Chemicals), Flourene (manufactured by Kyoeisha Chemical Co., Ltd.), Disparlon (manufactured by Kusumoto Chemicals Co., Ltd.), Ajisper (manufactured by Ajinomoto Fine-Techno Co., Ltd.), Demol (manufactured by Kao Corporation), Homogenol, Emulgen (all manufactured by Kao Corporation), Solsperse (manufactured by Lubrizol Corporation), and Nikkol (manufactured by Nikko Chemical Co., Ltd.). These may be used alone or in combination of two or more.

<Surfactant>
Examples of the surfactant include anionic surfactants such as alkylbenzenesulfonates, α-olefinsulfonates, and phosphoric acid esters; amine salt-type surfactants such as alkylamine salts, aminoalcohol fatty acid derivatives, polyamine fatty acid derivatives, and imidazolines; cationic surfactants of quaternary ammonium salt-type surfactants such as alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkyldimethylbenzylammonium salts, pyridinium salts, alkylisoquinolinium salts, and benzethonium chloride; and nonionic surfactants such as fatty acid amide derivatives and polyhydric alcohol derivatives, for example, alanine, dodecyldi(aminoethyl)glycine, di(octylaminoethyl)glycine, and N-alkyl-N,N-dimethylammonium betaine. Among these, anionic surfactants are preferred, and alkylbenzenesulfonates are more preferred from the viewpoint of increasing dispersion stability.

The content of the surfactant is preferably from 1% by mass to 20% by mass, and more preferably from 2% by mass to 10% by mass, based on the total amount of the aqueous dispersion.
When the surfactant content is within the above range, the dispersion stability is good. Inks using aqueous dispersions with a surfactant content of 20% by mass or more tend to have poor ejection stability due to nozzle clogging, ejection deflection, etc.
The method for measuring the content of the surfactant in the aqueous dispersion is not particularly limited and may be appropriately selected depending on the purpose. For example, the content of the surfactant can be measured using a high performance liquid chromatograph (LC-20, manufactured by Shimadzu Corporation).

<Other ingredients>
The other components are not particularly limited and may be appropriately selected depending on the purpose. Examples of the other components include organic solvents, antioxidants, and ultraviolet protection agents.

(Method for producing pigment-encapsulated resin particles)
The method for producing pigment-encapsulated resin particles of the present invention includes a step of mixing an organic solvent and a pigment to prepare a pigment pre-dispersion (hereinafter referred to as the "pigment pre-dispersion preparation step"), a step of mixing the obtained pigment pre-dispersion with a resin to prepare a pigment dispersion resin solution (hereinafter referred to as the "pigment dispersion resin solution preparation step"), a step of mixing the obtained pigment dispersion resin solution with a surfactant-containing liquid to prepare a pigment-encapsulated resin particle dispersion liquid (hereinafter referred to as the "pigment-encapsulated resin particle dispersion preparation step"), and a step of removing the organic solvent from the obtained pigment-encapsulated resin particle dispersion liquid (hereinafter referred to as the "organic solvent removal step"), and may further include other steps as necessary.

<Pigment pre-dispersion preparation step>
The pigment pre-dispersion preparation step is a step of mixing an organic solvent and a pigment to prepare a pigment pre-dispersion.
As the pigment, the same pigment as that in the above-mentioned aqueous dispersion can be used.
The organic solvent is not particularly limited as long as it can dissolve the resin in the next pigment dispersion resin solution preparation step, and can be appropriately selected depending on the purpose, and examples thereof include ethyl acetate, methyl ethyl ketone, acetone, etc. Among these, ethyl acetate is preferred.
The apparatus used in the pigment pre-dispersion preparation step is not particularly limited and can be appropriately selected depending on the purpose. For example, a dispersing machine can be used.

The cumulative volume particle size 50% (D ₅₀ ) of the pigment in the pigment pre-dispersion is preferably 10 nm or more and 150 nm or less, and more preferably 20 nm or more and 120 nm or less, from the viewpoint of making it possible to reduce the particle size of the pigment-encapsulating resin particles.
The cumulative volume particle size 50% (D ₅₀ ) of the pigment can be measured, for example, by using a zeta potential particle measuring 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.
In the pigment pre-dispersion preparation step, it is preferable to use a pigment dispersant. As the pigment dispersant, the same pigment dispersant as that in the above-mentioned aqueous dispersion can be used, and a hydrophobic pigment dispersant is particularly preferable.
The ratio of the pigment to the pigment dispersant in the pigment pre-dispersion is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoint of improving 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 that the pigment pre-dispersion is filtered, if necessary, with a filter, a centrifugal separator or the like to remove coarse particles.

The pigment pre-dispersion can be produced by dissolving or suspending a pigment dispersant in an organic solvent as necessary, adding a resin and a pigment, stirring the mixture, and then using a commonly used known dispersing machine.
The dispersing machine is not particularly limited and may be appropriately selected depending on the purpose, and examples thereof 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, jet mills, etc. Among these, from the viewpoint of dispersion efficiency, roll mills, beads mills, sand mills, Dyno Mills, high-pressure homogenizers, and paint shakers are preferred.

<Pigment dispersion resin solution preparation step>
The pigment dispersion resin solution preparation step is a step of mixing the obtained pigment pre-dispersion with a resin to prepare a pigment dispersion resin solution.
The pigment dispersion resin solution can be obtained by mixing and stirring the pigment pre-dispersion obtained in the pigment pre-dispersion preparation step, a resin, and, if necessary, a basic compound, an organic solvent, and additives.
As the resin, the same resin as that in the above-mentioned aqueous dispersion can be used.
The mixing and stirring device used in the pigment dispersion resin solution preparation step is not particularly limited and can be appropriately selected depending on the purpose, but examples thereof include the devices described in the pigment pre-dispersion preparation step. Among these, a homomixer or a high-speed stirring device equipped with a dispersing blade is preferably used from the viewpoints of uniform stirring of a high-viscosity solution and efficient dissolution of the resin powder.
The procedure for preparing the pigment dispersion resin solution is not particularly limited, and the resin may be added to the pigment pre-dispersion obtained in the pigment pre-dispersion preparation step, or may be added after the resin is solubilized in an organic solvent.
The cumulative volume particle size 50% ( _D50 ) of the pigment in the pigment dispersion resin solution is preferably the same as the cumulative volume particle size 50% ( _D50 ) of the pigment in the pigment pre-dispersion obtained in the above-mentioned pigment pre-dispersion preparation step, and it is more preferable that there is no change between the pigment pre-dispersion preparation step and the pigment dispersion resin solution preparation step.
The resin is used to encapsulate the pigment in the pigment-encapsulated resin particle dispersion preparation step, and preferably has a nonionic, anionic or cationic hydrophilic group, and more preferably has an anionic hydrophilic group.
When the resin is an anionic resin, it is preferable that the resin forms an emulsion in an aqueous medium and that a part or all of the anionic groups are neutralized with a basic compound in order to maintain dispersion stability in the aqueous medium.

The ratio of the pigment to the resin is preferably 0.2 or more and 0.75 or less, more preferably 0.3 or more and 0.6 or less. When the ratio of the pigment to the resin is 0.2 or more, the pigment concentration is appropriate, and the image density of the printed matter is high. 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 can be suppressed, thereby improving the image density. The ratio of the pigment to the resin can be calculated from the charge ratio or the obtained dispersion.
The calculation method from the aqueous dispersion can be, for example, calculation by thermal analysis of the dried and solidified film of the aqueous dispersion using a thermogravimetric differential thermal analyzer (TG-DTA). Specifically, the dried and solidified film of the aqueous dispersion can be heated and held in a nitrogen gas atmosphere to the thermal decomposition temperature of the resin using a thermogravimetric differential thermal analyzer, and the decomposed weight can be calculated as the resin and the weight of the residue as the pigment. In addition, a highly heat-resistant resin that cannot be completely decomposed by thermal decomposition in a nitrogen gas atmosphere can be calculated using a calibration curve of the heat loss and the pigment ratio to the resin. 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, to create the above calibration curve, and the ratio of pigment to resin can be calculated based on the weight loss rate obtained from the measurement results of the unknown sample.

<Step of preparing a dispersion of pigment-encapsulated resin particles>
The pigment-encapsulated resin particle dispersion liquid preparation step is a step of mixing the obtained pigment dispersion resin solution with a surfactant-containing liquid to prepare a pigment-encapsulated resin particle dispersion liquid.
The mixing and stirring device used in the pigment-encapsulated resin particle dispersion preparation step is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include the devices described in the pigment pre-dispersion preparation step. Among these, a high-speed stirring device equipped with a homomixer or a dispersing blade is preferred in terms of uniform stirring in a high-viscosity solution, and the higher the energy required for dispersion, the smaller the particle size of the generated pigment-encapsulated resin particles can be, but if the energy is too high, the generated pigment-encapsulated resin particles may be crushed and the encapsulation state may not be maintained.
There is no particular limitation on the procedure for mixing the pigment dispersion resin solution and the surfactant-containing liquid. The surfactant-containing liquid may be added to the pigment dispersion resin solution, or the pigment dispersion resin solution may be added to the surfactant-containing liquid.
As the surfactant, the same surfactant as that in the above-mentioned aqueous dispersion can be used.
From the viewpoint of dispersion stability of the pigment-encapsulated resin particles, the content of the surfactant-containing liquid 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 the pigment dispersion resin solution preparation process.
From the viewpoint of dispersion stability, the surfactant is preferably added to a solvent in an amount of 1.0% by mass to 20% by mass with respect to the aqueous dispersion, and then added to the pigment dispersion resin solution.

<Organic solvent removal process>
The organic solvent removing step is a step of removing the organic solvent from the obtained pigment-encapsulated resin particle dispersion liquid. By removing the organic solvent from the pigment-encapsulated resin particle dispersion liquid, the aqueous dispersion of the present invention is obtained.
The method for removing the organic solvent is not particularly limited, and any known removal device can be used. 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, and examples of such devices include a rotary evaporator.
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.
If necessary, the obtained aqueous dispersion may be filtered to remove coarse particles using a filter, a centrifugal separator, etc. Furthermore, if necessary, it is also possible to remove the surfactant using an ultrafiltration device.

(ink)
The ink of the present invention contains water, pigment-encapsulated resin particles that encapsulate a pigment, a surfactant, and an organic solvent, and further contains other components as required.

<Pigment-encapsulated resin particles containing pigment>
The pigment-encapsulating resin particles encapsulating the pigment are the same as the pigment-encapsulating resin particles encapsulating the pigment in the aqueous dispersion of the present invention.
The pigment-encapsulating resin particles have a cumulative 50% volume particle size (D ₅₀ ) of 200 nm or more and 500 nm or less, and an aspect ratio of the pigment-encapsulating resin particles of 1.0 or more and 1.5 or less.

<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.
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 diol, 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, ethylene glycol monobutyl ether, diene Examples of the alkyl ethers include polyhydric alcohols such as ethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; polyhydric alcohols such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol, propylene carbonate, and ethylene carbonate.
It is preferable to use an organic solvent having a boiling point of 250° C. or less, since this not only functions as a wetting agent but also provides good drying properties.

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

Polyol compounds with 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 selected appropriately depending on the purpose, but from the viewpoint of the drying property and ejection reliability of the ink, it is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 60% by mass or less.

<Water>
The water is not particularly limited and can be appropriately selected depending on the purpose. Examples of the water include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, and ultrapure water.
The water content in the ink is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoints of the drying property and ejection reliability of the ink, however, the water content is preferably from 10% by mass to 90% by mass, and more preferably from 20% by mass to 60% by mass.

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

<Surfactant>
As the surfactant, any of silicone-based surfactants, fluorine-based surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used.
The silicone surfactant is not particularly limited and can be appropriately selected according to the purpose. Among them, those that do not decompose even at high pH are preferable. Examples of silicone surfactants include side chain modified polydimethylsiloxane, both end modified polydimethylsiloxane, one end modified polydimethylsiloxane, and both end modified polydimethylsiloxane of side chain. Those having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modified group are particularly preferable because they show good properties as an aqueous surfactant. In addition, polyether modified silicone surfactants can also be used as silicone surfactants, and examples thereof include compounds in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylpolysiloxane.
As the fluorine-based surfactant, for example, perfluoroalkyl sulfonic acid compound, perfluoroalkyl carboxylic acid compound, perfluoroalkyl phosphate compound, perfluoroalkyl ethylene oxide adduct and polyoxyalkylene ether polymer compound having perfluoroalkyl ether group in the side chain are particularly preferred because they have low foaming properties.As the perfluoroalkyl sulfonic acid compound, for example, perfluoroalkyl sulfonic acid, perfluoroalkyl sulfonate, etc. can be mentioned.As the perfluoroalkyl carboxylic acid compound, for example, perfluoroalkyl carboxylic acid, perfluoroalkyl carboxylate, etc. can be mentioned.As the polyoxyalkylene ether polymer compound having perfluoroalkyl ether group in the side chain, for example, sulfate ester salt of polyoxyalkylene ether polymer having perfluoroalkyl ether group in the side chain, salt of polyoxyalkylene ether polymer having perfluoroalkyl ether group in the side chain, etc. can be mentioned. Examples of counter ions of the salts in these fluorosurfactants include Li, Na, _K , _{NH4 , NH3CH2CH2OH} , _NH2 ( _CH2CH2OH ) ₂ , _and NH( _{CH2CH2OH ) 3} .
Examples of amphoteric surfactants include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine.
Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adducts of acetylene alcohol.
Examples of the anionic surfactant include polyoxyethylene alkyl ether acetates, dodecylbenzene sulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates.
These may be used alone or in combination of two or more.

The silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples of the silicone surfactant include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, and both-end side-chain modified polydimethylsiloxane. Polyether-modified silicone surfactants having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as an aqueous surfactant.
Such surfactants may be synthesized appropriately or may be commercially available products, such as those available from BYK-Chemie Co., Ltd., Shin-Etsu Chemical Co., Ltd., Dow Corning Toray Silicone Co., Ltd., Nippon Emulsion Co., Ltd., and Kyoeisha Chemical Co., Ltd.
The polyether-modified silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be a surfactant represented by the general formula (S-1), in which a polyalkylene oxide structure is introduced into the Si part side chain of dimethylpolysiloxane.

（ただし、前記一般式（Ｓ－１）中、ｍ、ｎ、ａ、及びｂは、それぞれ独立に、整数を表し、Ｒは、アルキレン基を表し、Ｒ’は、アルキル基を表す。）

(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 (manufactured by Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602, SS-1906EX (manufactured by Nippon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164 (manufactured by Dow Corning Toray Silicone Co., Ltd.), BYK-33, BYK-387 (manufactured by BYK-Chemie Co., Ltd.), TSF4440, TSF4452, TSF4453 (manufactured by Toshiba Silicon Co., Ltd.), etc.

The fluorine-based surfactant is preferably a compound having 2 to 16 fluorine-substituted carbon atoms, and more preferably a compound having 4 to 16 fluorine-substituted carbon atoms.
Examples of the fluorine-based surfactant include perfluoroalkyl phosphate compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chains.
Among these, polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group in the side chain are preferred because they have little foaming property, and in particular, fluorine-based surfactants represented by any one of general formula (F-1) and general formula (F-2) are preferred.

上記一般式（Ｆ－１）で表される化合物において、水溶性を付与するためにｍは０～１０の整数が好ましく、ｎは０～４０の整数が好ましい。

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+ -CH ₂ CH(OH)CH ₂ -O-(CH ₂ CH ₂ O) _a -Y
In the compound represented by the above general formula (F-2), Y is H, or C _m F _2m+1 where m is an integer from 1 to 6, or CH ₂ CH(OH)CH ₂ -C _m F _2m+1 where m is or C _p H _2P+1 , where p is an integer from 1 to 19. n is an integer from 1 to 6. a is an integer from 4 to 14.
As the above fluorosurfactant, a commercially available product may be used.

Examples of commercially available products include Surflon S-111, S-112, S-113, S-121, S-131, S-132, S-141, and S-145 (all manufactured by Asahi Glass Co., Ltd.); Fullard FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430, and FC-431 (all manufactured by Sumitomo 3M Limited); Megaf FAC F-470, F-1405, F-474 (all manufactured by DIC Corporation); Zonyl TBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300, UR, Capstone FS-30, FS-31, FS-3100, FS-34, FS-35 (all manufactured by Chemours); FT-110, FT-250, Examples of such inks include FT-251, FT-400S, FT-150, and FT-400SW (all manufactured by Neos Co., Ltd.), Polyfox PF-136A, PF-156A, PF-151N, PF-154, and PF-159 (manufactured by Omnova), and Unidyne DSN-403N (manufactured by Daikin Industries, Ltd.). Among these, inks that have good print quality, particularly color development and paper penetration, are preferred. In terms of significantly improving wettability and uniformity, FS-3100, FS-34, and FS-300 manufactured by Chemours, 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. are particularly preferred.

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

<Other ingredients>
Examples of other components include, as required, antifoaming agents, antiseptic and antifungal agents, rust inhibitors, and pH adjusters.

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

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

- Rust inhibitor -
The rust inhibitor is not particularly limited, and examples thereof include acid sulfite and sodium thiosulfate.

- pH adjuster -
There are no particular limitations on the pH adjuster, so long as it is capable of adjusting the pH to 7 or higher, and examples of the pH adjuster include amines such as diethanolamine and triethanolamine.
isn't it.

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

<Pretreatment solution>
The pretreatment liquid contains a flocculant, an organic solvent, and water, and may contain, as necessary, a surfactant, an antifoaming agent, a pH adjuster, an antiseptic/fungal agent, an antirust agent, and the like.
The organic solvent, surfactant, defoamer, pH adjuster, antiseptic and antifungal 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.

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

<Recording media>
There are no particular limitations on the recording medium, and although plain paper, glossy paper, special paper, cloth, etc. can be used, good image formation is also possible using a non-permeable substrate.
The non-permeable substrate is a substrate having a surface with low water permeability and absorbency, and includes materials that have many cavities inside but are not open to the outside. More quantitatively, the non-permeable substrate is a substrate having a water absorption amount of 10 mL/m2 ^{or less} from the start of contact to 30 msec ^1/2 in the Bristow method.
As the impermeable substrate, for example, a plastic film such as a polyvinyl chloride resin film, a polyethylene terephthalate (PET) film, a polypropylene film, a polyethylene film, or a polycarbonate film can be suitably used.

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

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

<Recording device and recording method>
The ink of the present invention can be suitably used in various recording devices using the ink jet recording method, such as printers, facsimile machines, copying machines, printer/fax/copier combination machines, and three-dimensional modeling devices.
In the present invention, the recording apparatus and recording method refer to an apparatus capable of ejecting ink, various treatment liquids, etc. onto a recording medium, and a method of recording using the apparatus. The recording medium refers to an object onto which ink or various treatment liquids can be attached even temporarily.
This recording device can include not only 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 or an infrared heater can be used. Heating and drying can be performed before, during, or after printing.
Furthermore, the recording device and recording method are not limited to those that visualize meaningful images such as characters and figures with ink. For example, those that form patterns such as geometric designs and those that form three-dimensional images are also included.
Furthermore, unless otherwise specified, the recording apparatus includes both a serial type apparatus in which the ejection head moves and a line type apparatus in which the ejection head does not move.
Furthermore, this recording device includes not only desktop types, but also wide-width recording devices that can print on A0-sized recording media, and continuous-feed printers that can use, for example, continuous paper wound into a roll as a recording medium.

An example of a recording device will be described with reference to FIG. 1. FIG. 1 is a schematic diagram of a printing device that ejects liquid.

The printing device 1 comprises an input section 10, a pre-processing section 50, a printing section 20, a drying section 30, and an unloading section 40. In the printing device 1, a treatment liquid is applied to the sheet material P that is input from the input section 10 in the pre-processing section 50, the printing section 20 applies liquid to the sheet material P to perform the required printing, the drying section 30 dries the liquid adhering to the sheet material P, and the sheet material P is then discharged to the unloading section 40.

The loading section 10 includes an input tray 11 on which multiple sheets of material P are stacked, a feeding device 12 that separates and sends out the sheet materials P one by one from the input tray 11, and a pair of registration rollers 13 that sends the sheet materials P to the printing section 20.

The feeding device 12 can be any type of feeding device, such as a device using rollers or a device using air suction. After the leading edge of the sheet material P sent out from the input tray 11 by the feeding device 12 reaches the pair of registration rollers 13, the pair of registration rollers 13 are driven at a predetermined timing to send the sheet material P to the printing unit 20.

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

The printing unit 20 is equipped with a sheet conveying device 21 that conveys the sheet material P. The sheet conveying device 21 has a belt that carries and conveys the sheet material P, and a suction device that generates a suction force on the belt surface.

The printing unit 20 also includes a liquid ejection unit 22 that ejects and applies liquid toward the treatment liquid-applied surface of the sheet material P that is carried and transported by the belt of the sheet transport device 21.

The liquid ejection section 22 is equipped with ejection units 23 (23A to 23F) which are liquid application means. For example, ejection unit 23A ejects cyan (C) liquid, ejection unit 23B ejects magenta (M) liquid, ejection unit 23C ejects yellow (Y) liquid, and ejection unit 23D ejects black (K) liquid. Furthermore, ejection units 23F, 23F are used to eject any of the colors YMCK, or special liquids such as white or gold (silver). Furthermore, an ejection unit that ejects a treatment liquid such as a surface coating liquid can also be provided.

The ejection unit 23 is, for example, a full-line type head consisting of multiple liquid ejection heads (hereinafter simply referred to as "heads") each having a nozzle row in which multiple nozzles are arranged.

The ejection operation of each ejection unit 23 of the liquid ejection section 22 is controlled by a drive signal corresponding to the printing information. When the sheet material P supported on the drum passes through the area facing the liquid ejection section 22, liquid of each color is ejected from the ejection unit 23, and an image corresponding to the printing information is printed.

The sheet material P to which liquid has been applied by the liquid discharge unit 22 is passed to the suction transport mechanism unit 31 of the drying unit 30.

The drying section 30 includes a suction transport mechanism 31, which is a transport means that transports the sheet material P under suction (suction transport), and a drying mechanism 32 that dries the liquid on the sheet material P transported by the suction transport mechanism 31.

The sheet material P to which liquid has been applied in the printing unit 20 is dried by the drying mechanism 32 while being transported by the suction transport mechanism 31, and then transferred to the discharge unit 40.

The discharge section 40 is equipped with a discharge tray 41 on which multiple sheet materials P are stacked. The sheet materials P conveyed from the drying section 30 are stacked and held on the discharge tray 41 in sequence.

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

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

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

In the present invention, the terms image formation, recording, printing, printing, etc. are all synonymous.
Recording medium, media, and printed material are all synonymous.

The following describes examples of the present invention, but the present invention is not limited to these examples. The following describes the methods for measuring various physical properties in the examples.

<Measurement of number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw/Mn)>
Apparatus: GPC (manufactured by Tosoh Corporation)
Detector: RI
Measurement temperature: 40°C
Mobile phase: tetrahydrofuran Flow rate: 0.45 mL/min.
The number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw/Mn) are the number average molecular weight, weight average molecular weight, and molecular weight distribution measured by GPC (gel permeation chromatography) using a calibration curve prepared from polystyrene samples of known molecular weight as a standard. Note that columns with exclusion limits of 60,000, 20,000, and 10,000 connected in series were used.

(Synthesis Example 1 of Polyester Resin)
-Synthesis of polyester resin α-
In a 1 L four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, 280 parts by mass of propylene glycol as a diol, 611 parts by mass of terephthalic acid as a dicarboxylic acid, and 109 parts by mass of succinic acid were mixed.
Next, the inside of the reaction vessel was thoroughly replaced with nitrogen gas, and then 300 ppm (based on the monomer) of titanium tetraisopropoxide was added, and the temperature was raised to 200° C. in a nitrogen gas flow for about 4 hours.
Next, the temperature was raised to 230° C. over 2 hours, and the reaction was continued until no outflow occurred. After that, the reaction was continued for 1 hour under reduced pressure of 5 mmHg to 30 mmHg to obtain polyester.

(Preparation Example of Pigment Pre-Dispersion A)
The following materials were mixed and poured into a 110 mL glass screw tube bottle, after which 170 parts by mass of zirconia balls with a diameter of 2.0 mm (YTZ balls, manufactured by Nikkato Corporation) were poured in, the bottle was fixed to a shaker (Vibrax VXR basic, manufactured by IKA Corporation) and dispersed at 1,000 rpm for 24 hours. Thereafter, the media and the dispersion were separated by filtration, and the mixture was filtered through a PTFE membrane filter with an average pore size of 5.0 μm to prepare pigment pre-dispersion A.
The resulting pigment pre-dispersion A had a cumulative 50% volume particle size (D ₅₀ ) of 112 nm in ELSZ-1000.
[Pigment pre-dispersion formulation]
Carbon black (SBX45, manufactured by Asahi Carbon Co., Ltd., primary particle size: 22 nm, DBP absorption: 55 mL/100 g): 15.0 parts by mass Pigment dispersant (Ajisper PB821, manufactured by Ajinomoto Fine-Techno Co., Ltd., hydrophobic): 3.8 parts by mass Ethyl acetate: 41.2 parts by mass

(Preparation Example of Pigment Pre-Dispersion B)
The following materials were mixed and poured into a 110 mL glass screw tube bottle, after which 170 parts by mass of zirconia balls with a diameter of 2.0 mm (YTZ balls, manufactured by Nikkato Corporation) were poured in, the bottle was fixed to a shaker (Vibrax VXR basic, manufactured by IKA Corporation) and dispersed at 1,000 rpm for 24 hours. Thereafter, the media and the dispersion were separated by filtration, and the mixture was filtered through a PTFE membrane filter with an average pore size of 5.0 μm to prepare pigment pre-dispersion B.
The resulting pigment pre-dispersion B had a cumulative 50% volume particle size (D ₅₀ ) of 113 nm in ELSZ-1000.
[Pigment pre-dispersion formulation]
Carbon black (SBX45, manufactured by Asahi Carbon Co., Ltd., primary particle size: 22 nm, DBP absorption: 55 mL/100 g): 15.0 parts by mass Pigment dispersant (BYKJET-9151, manufactured by BYK Chemie, hydrophilic): 3.8 parts by mass Ethyl acetate: 41.2 parts by mass

(Preparation Example of Pigment Pre-Dispersion C)
The following materials were mixed and poured into a 110 mL glass screw tube bottle, after which 170 parts by mass of zirconia balls with a diameter of 2.0 mm (YTZ balls, manufactured by Nikkato Corporation) were poured in, the bottle was fixed to a shaker (Vibrax VXR basic, manufactured by IKA Corporation) and dispersed at 1,000 rpm for 24 hours. Thereafter, the media and the dispersion were separated by filtration, and the mixture was filtered through a PTFE membrane filter with an average pore size of 5.0 μm to prepare pigment pre-dispersion C.
The resulting pigment pre-dispersion C had a cumulative 50% volume particle size (D ₅₀ ) of 159 nm in ELSZ-1000.
[Pigment pre-dispersion formulation]
Carbon black (Asahi #15, manufactured by Asahi Carbon Co., Ltd., primary particle size: 122 nm, DBP absorption: 41 mL/100 g): 15.0 parts by mass Pigment dispersant (Ajisper PB821, manufactured by Ajinomoto Fine-Techno Co., Ltd., hydrophobic): 3.8 parts by mass Ethyl acetate: 41.2 parts by mass

Example 1
<Preparation of Aqueous Dispersion (1)>
26.7 g of the pigment pre-dispersion A, 13.4 g of the polyester resin α, 0.27 g of bis(2-morpholinoethyl)ether (manufactured by Tokyo Chemical Industry Co., Ltd.), and 5.19 g of ethyl acetate were placed in a container and stirred at 3,000 rpm for 1 minute using a T. K. Robomix (manufactured by Primix Corporation) to obtain a pigment dispersion resin solution.
Next, 39.6 g of ion-exchanged water, 7.06 g of a 50% by mass aqueous solution of sodium dodecyl phenyl ether disulfonate (Eleminol MON-7, manufactured by Sanyo Chemical Industries, Ltd.), and 3.7 g of ethyl acetate were mixed to prepare an aqueous layer, to which 29.6 g of the pigment dispersion resin solution prepared above was added, and the mixture was stirred at 5,000 rpm for 10 minutes using a T. K. Robomix (manufactured by Primix Corporation).
Finally, the ethyl acetate was removed, and the mixture was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 30% by mass with ion-exchanged water to obtain an aqueous dispersion (1) containing pigment-encapsulated resin particles containing two or more primary pigment particles. FIG. 2 shows a TEM image of the aqueous dispersion (1) containing the pigment-encapsulated resin particles obtained in Example 1. From FIG. 2, it can be seen that the pigment is encapsulated in the spherical resin particles in the aqueous dispersion (1).

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

Example 2
<Preparation of Aqueous Dispersion (2)>
An aqueous dispersion (2) containing pigment-encapsulated resin particles containing two or more pigment primary particles was obtained in the same manner as in Example 1, except that the amount of a 50 mass% aqueous solution of sodium dodecyl phenyl ether disulfonate (ELEMINOL MON-7, manufactured by Sanyo Chemical Industries, Ltd.) was changed from 7.06 g to 1.2 g.

<Preparation of Ink 2>
Ink 2 was prepared in the same manner as in Example 1, except that the aqueous dispersion (2) obtained above was used instead of the aqueous dispersion (1) in Example 1.

Example 3
<Preparation of Aqueous Dispersion (3)>
An aqueous dispersion (3) containing pigment-encapsulated resin particles containing two or more pigment primary particles was obtained in the same manner as in Example 1, except that the amount of a 50 mass% aqueous solution of sodium dodecyl phenyl ether disulfonate (ELEMINOL MON-7, manufactured by Sanyo Chemical Industries, Ltd.) was changed from 7.06 g to 12.2 g.

<Preparation of Ink 3>
Ink 3 was prepared in the same manner as in Example 1, except that the aqueous dispersion (3) obtained above was used instead of the aqueous dispersion (1).

Example 4
<Preparation of Aqueous Dispersion (4)>
An aqueous dispersion (4) containing pigment-encapsulated resin particles containing two or more pigment primary particles was obtained in the same manner as in Example 1, except that the amount of a 50 mass% aqueous solution of sodium dodecyl phenyl ether disulfonate (ELEMINOL MON-7, manufactured by Sanyo Chemical Industries, Ltd.) was changed from 7.06 g to 24.6 g.

<Preparation of Ink 4>
Ink 4 was prepared in the same manner as in Example 1, except that the aqueous dispersion (4) obtained above was used instead of the aqueous dispersion (1) in Example 1.

Example 5
<Preparation of Aqueous Dispersion (5)>
An aqueous dispersion (5) containing pigment-encapsulated resin particles containing two or more pigment primary particles was obtained in the same manner as in Example 1, except that the amount of pigment pre-dispersion A was changed from 26.7 g to 18.7 g.

<Preparation of Ink 5>
Ink 5 was prepared in the same manner as in Example 1, except that the aqueous dispersion (5) obtained above was used instead of the aqueous dispersion (1).

Example 6
<Preparation of Aqueous Dispersion (6)>
An aqueous dispersion (6) containing pigment-encapsulated resin particles containing two or more pigment primary particles was obtained in the same manner as in Example 1, except that the amount of pigment pre-dispersion A was changed from 26.7 g to 10.7 g.

<Preparation of Ink 6>
Ink 6 was prepared in the same manner as in Example 1, except that the aqueous dispersion (6) obtained above was used instead of the aqueous dispersion (1).

(Example 7)
<Preparation of Aqueous Dispersion (7)>
An aqueous dispersion (7) containing pigment-encapsulated resin particles containing two or more pigment primary particles was obtained in the same manner as in Example 1, except that the amount of a 50 mass% aqueous solution of sodium dodecyl phenyl ether disulfonate (ELEMINOL MON-7, manufactured by Sanyo Chemical Industries, Ltd.) was changed from 7.06 g to 0.84 g.

Preparation of Ink 7
Ink 7 was prepared in the same manner as in Example 1, except that the aqueous dispersion (7) obtained above was used instead of the aqueous dispersion (1).

(Example 8)
<Preparation of Aqueous Dispersion (8)>
An aqueous dispersion (8) containing pigment-encapsulated resin particles containing two or more pigment primary particles was obtained in the same manner as in Example 1, except that the amount of pigment pre-dispersion A was changed from 26.7 g to 40.0 g.

Preparation of Ink 8
Ink 8 was prepared in the same manner as in Example 1, except that the aqueous dispersion (8) obtained above was used instead of the aqueous dispersion (1) in Example 1.

(Comparative Example 1)
<Preparation of Aqueous Dispersion (9)>
An aqueous dispersion (9) containing pigment-encapsulated resin particles containing two or more pigment primary particles was obtained in the same manner as in Example 1, except that a 50 mass% aqueous solution of sodium dodecyl phenyl ether disulfonate (ELEMINOL MON-7, manufactured by Sanyo Chemical Industries, Ltd.) was not added.

Preparation of Ink 9
Ink 9 was prepared in the same manner as in Example 1, except that the aqueous dispersion (9) obtained above was used instead of the aqueous dispersion (1).

(Comparative Example 2)
<Preparation of Aqueous Dispersion (10)>
An aqueous dispersion (10) containing pigment-encapsulated resin particles containing two or more pigment primary particles was obtained in the same manner as in Example 1, except that the amount of a 50% by mass aqueous solution of sodium dodecyl phenyl ether disulfonate (Eleminol MON-7, manufactured by Sanyo Chemical Industries, Ltd.) was changed from 7.06 g to 37.2 g in Example 1. FIG. 3 shows a TEM image of the aqueous dispersion (10) obtained in Comparative Example 2. FIG. 3 shows that the aqueous dispersion (10) has a form in which the pigment is encapsulated in non-spherical resin particles.

<Preparation of Ink 10>
Ink 10 was prepared in the same manner as in Example 1, except that the aqueous dispersion (10) obtained above was used instead of the aqueous dispersion (1).

(Comparative Example 3)
<Preparation of Aqueous Dispersion (11)>
An aqueous dispersion (11) was obtained in the same manner as in Example 1, except that the pigment pre-dispersion A in Example 1 was replaced with the pigment pre-dispersion B. Fig. 4 shows a TEM image of the aqueous dispersion (11) obtained in Comparative Example 3. Fig. 4 shows that in the aqueous dispersion (11), the pigment is not encapsulated in the resin particles.

<Preparation of Ink 11>
Ink 11 was prepared in the same manner as in Example 1, except that the aqueous dispersion (11) obtained above was used instead of the aqueous dispersion (1).

(Comparative Example 4)
<Preparation of Aqueous Dispersion (12)>
An aqueous dispersion (12) containing pigment-encapsulated resin particles containing two or more pigment primary particles was obtained in the same manner as in Example 1, except that the pigment pre-dispersion A in Example 1 was changed to the pigment pre-dispersion C.

<Preparation of Ink 12>
Ink 12 was prepared in the same manner as in Example 1, except that the aqueous dispersion (12) obtained above was used instead of the aqueous dispersion (1).

(Comparative Example 5)
Instead of the pigment-encapsulated resin particles, the following resin-only emulsion and water-based pigment dispersion were prepared to prepare Ink 13.

<Preparation of Polyester Sole Resin Emulsion>
13.4 g of the polyester resin α, 0.27 g of bis(2-morpholinoethyl)ether (manufactured by Tokyo Chemical Industry Co., Ltd.), and 5.19 g of ethyl acetate were placed in a container and stirred for 1 minute at 3,000 rpm with a T. K. Robomix (manufactured by Primix Corporation) to obtain a resin solution. Next, 29.6 g of the pigment dispersion resin solution prepared above was added to an aqueous layer prepared by mixing 39.6 g of ion-exchanged water, 7.06 g of a 50% by mass aqueous solution of sodium dodecyl phenyl ether disulfonate (Eleminol MON-7, manufactured by Sanyo Chemical Industries Co., Ltd.), and 3.7 g of ethyl acetate, and the mixture was stirred for 10 minutes at 5,000 rpm with a T. K. Robomix.
Finally, the ethyl acetate was removed, and the residue was filtered and purified using a nylon mesh with a mesh size of 67 μm. The solid content was adjusted to 30 mass % with ion-exchanged water, and a polyester single resin emulsion having a cumulative 50% volume particle size (D ₅₀ ) of 257 nm was obtained.

(Production Example of Pigment Dispersant)
62.0 parts by mass of 1,6-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 700 mL of dichloromethane, and 20.7 parts by mass of pyridine (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred. A solution of 2-naphthalenecarbonyl chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved in 100 mL of dichloromethane was dropped into this solution over 2 hours, and then the mixture was stirred at room temperature for 6 hours. The resulting reaction solution was washed with water, and then the organic layer was isolated and dried over magnesium sulfate, and the solvent was distilled off. The residue was purified by silica gel column chromatography using a mixed solvent of dichloromethane/methanol (volume ratio 98/2) as an eluent to obtain a compound.
Next, 42.1 parts by mass of the obtained compound was dissolved in 80 mL of dry methyl ethyl ketone, and heated to 60° C. while stirring. A solution in which 24.0 parts by mass of Karenz MOI (manufactured by Showa Denko K.K.) was dissolved in 20 mL of dry methyl ethyl ketone was dropped into this solution over 1 hour, and then stirred at 70° C. for 12 hours. After cooling to room temperature, the solvent was distilled off. The residue was purified by silica gel column chromatography using a mixed solvent of dichloromethane/methanol (volume ratio 99/1) as an eluent to obtain a monomer.
Next, 2.30 parts by mass of acrylic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 8.54 parts by mass of the monomer, and 0.31 parts by mass of 2,2'-azobis(isobutyronitrile) (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in 100 mL of methyl ethyl ketone, and the mixture was stirred for 5 hours under a nitrogen gas flow at a temperature condition of 75°C. Thereafter, the reaction solution was cooled to room temperature, and reprecipitation was repeated five times using hexane to purify the copolymer. After the purification treatment, the copolymer was filtered off and dried under reduced pressure to obtain a pigment dispersant.

<Preparation of Water-Based Pigment Dispersion>
3.8 parts by mass of the pigment dispersant was dissolved in 30.0 parts by mass of an aqueous diethanolamine solution so that the pH was 8.0. Ion-exchanged water was further added to make the total amount of the aqueous solution 45.0 parts by mass.
Next, the materials in the following formulation were mixed and charged into a 110 mL glass screw tube bottle, after which 170 parts by mass of 2.0 mm diameter zirconia balls (YTZ balls, manufactured by Nikkato Corporation) were charged, the bottle was fixed to a shaker (Vibrax VXR basic, manufactured by IKA Corporation) and dispersed at 1,000 rpm for 24 hours. Thereafter, the media and the dispersion were separated by filtration, and filtered through a cellulose acetate membrane filter with an average pore size of 5.0 μm to produce an aqueous pigment dispersion. The cumulative 50% volume particle size (D ₅₀ ) of this aqueous pigment dispersion in ELSZ-1000 was 120 nm.
[Formulation of Water-Based Pigment Dispersion]
Carbon black (SBX45, manufactured by Asahi Carbon Co., Ltd.): 15.0 parts by mass Aqueous pigment dispersant solution: 45.0 parts by mass

<Preparation of Ink 13>
An ink having the following formulation was prepared using the polyester single resin emulsion and the aqueous pigment dispersion obtained above. The viscosity at 25° C. was adjusted to 7.5 mPa s, and then the ink was filtered through a membrane filter having an average pore size of 10 μm to prepare Ink 13.
"Ink prescription"
Polyester single resin emulsion: 5.375% by mass as solid content
Water-based pigment dispersion: 5.375% by mass as solid content
Propylene glycol: 40% by mass (adjusted to a viscosity of 7.5 mPa·s)
Silicone surfactant (Silface SAG503A, manufactured by Nissin Chemical Industry Co., Ltd.): 1.0% by mass
Aliphatic dialcohol surfactant (Surfynol AD01, manufactured by Nissin Chemical Industry Co., Ltd.): 0.1% by mass
Water: remaining amount (total: 100% by mass)

Next, the properties of each aqueous dispersion and each ink prepared were evaluated as follows. The results are shown in Tables 1 to 4.

<Cumulative 50% volume particle size (D ₅₀ ) of resin particles>
The cumulative 50% volume particle size (D ₅₀ ) of the resin particles was measured by a dynamic light scattering method using a zeta potential/particle size measuring system (ELSZ-1000, manufactured by Otsuka Electronics Co., Ltd.).
Specifically, the sample was diluted with ion-exchanged water or, if necessary, an organic solvent so that the solid content concentration of the measurement sample was 0.01 mass %, and a part of the obtained solution was placed in a quartz cell and set in a sample holder. Then, the measurement was performed under the conditions of temperature: 25°C, dust cut (number of times: 5, Upper: 5, Lower: 100), and cumulative number of times: 70.

<Pigment exposure rate>
The pigment exposure rate on the coating surface was calculated by observing with a scanning electron microscope (SEM).
Specifically, first, an aqueous dispersion was prepared using ion-exchanged water so that the solid content concentration was 10.75% by mass. Then, the dispersion was applied to coated paper (Lumia Art Gloss 130, manufactured by STORA ENSO) using a bar coater having a diameter of 0.15 mm, and dried overnight at 25° C. to form a coating film having an average thickness of 2 μm.
The coating film was cut out and fixed to a stub for SEM observation with carbon tape. This was observed without any conductive treatment using a scanning electron microscope (ZEISS, Merlin) at an acceleration voltage of 0.75 kV, a backscattered electron detector, and a magnification of 2,000 to 20,000 times. This observation method makes it possible to distinguish the exposed pigment from the difference in the amount of backscattered electrons emitted by carbon black and resin. The pigment exposure rate was defined as the area occupied by the pigment relative to the entire coating film at a magnification of 20,000 times, and the pigment exposure rate was classified as follows. The ratio of the area occupied by the pigment on the coating film surface was determined by binarizing the SEM observation image, and the average of three visual fields observed at random locations was taken to determine the pigment exposure rate, which was then evaluated according to the following criteria.
[Evaluation Criteria]
◎: 0% or more and 3% or less ○: 3% or more and 5% or less △: 5% or more and 8% or less ×: More than 8%

<Surface roughness of coating film>
The surface roughness of the coating film was calculated using a scanning probe microscope (SPM) as follows. First, an aqueous dispersion was prepared using ion-exchanged water so that the solid content concentration was 10.75% by mass. Then, the coating was applied to coated paper (Lumia Art Gloss 130, manufactured by STORA ENSO) using a bar coater with a diameter of 0.15 mm, and heated and dried in an oven at 100°C for 5 minutes. This coating film was cut out and observed under the following conditions to calculate the surface roughness. The observation was performed by arbitrarily changing the location and taking the average of three visual fields observed to obtain the average surface roughness.
[Measurement conditions]
Apparatus: Scanning probe microscope (Dimension Icon, manufactured by Bruker)
Cantilever: Olympus Corporation OMCL-AC240TS
Measurement mode: Tapping mode Observation range: 2 μm square

<Proportion of pigment-encapsulated resin particles>
First, each of the obtained aqueous dispersions was diluted with ion-exchanged water so that the solid content concentration was 0.1% by mass to prepare a sample solution.
Next, 1 μL of the sample liquid was placed on a hydrophilized collodion film-attached mesh (Nisshin EM Co., Ltd., collodion film-attached mesh, Cu150 mesh) using a micropipette, and the sample liquid was immediately absorbed with a triangular filter paper. Next, 1 μL of EM stainer diluted 10 times was placed using a micropipette, and the sample liquid 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 acceleration voltage of 200 kV and a magnification of 40,000 times. By this observation method, five or more images of a field of view containing three or more particles with a volume particle size of 100 nm or more were obtained by arbitrarily changing the location, and the ratio of the number of pigment-encapsulated resin particles to the total number of particles with a volume particle size of 100 nm or more was calculated for each image, and the average value was calculated. The obtained ratio was defined as the presence ratio of pigment-encapsulated resin particles, and was evaluated according to the following criteria.
[Evaluation Criteria]
◎: 50% or more 〇: 30% or more but less than 50% △: 10% or more but less than 30% ×: 0% or more but less than 10%

<Aspect ratio of resin particles>
The aspect ratio was determined by measuring the long and short sides of 20 pigment-encapsulated resin particles observed according to the above-mentioned observation method for pigment-encapsulated resin particles using a transmission electron microscope (TEM), calculating the average value, and calculating the aspect ratio from the average value of the long sides/average value of the short sides.

<Image Formation>
The exterior of an inkjet printer (IPSiO GXe5500, manufactured by Ricoh Company, Ltd.) was removed, a rear multi-manual feeder was attached, and pure water was passed through the ink supply path including the print head to clean it. The cleaning liquid was passed through sufficiently until it was no longer colored, and then the cleaning liquid was completely drained from the device to prepare a printing device for evaluation.
The prepared ink was filled into an ink cartridge to prepare an ink cartridge for evaluation.
A filling operation was performed, and it was confirmed that all nozzles were filled with the evaluation ink and 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 the print mode with color matching off.
In this mode, the ejection amount was adjusted by changing the head drive voltage so that the amount of ink deposited on the recording medium for a solid image was 20 g/m ² .

<Image Density>
A solid image was printed by the above image output method, and then dried at room temperature (25° C.) for 1 day and in an oven at 100° C. for 5 minutes to prepare images.
With a sheet of white plain paper placed under the printed image, the total density was measured using a spectrophotometric densitometer (X-Rite 939, manufactured by X-Rite Corporation), and the black (K) value was taken as the image density.
In addition, the difference in image density between the image obtained by drying at 25°C and the image obtained by drying at 100°C (ΔOD = "OD of image obtained by drying at 25°C" - "OD of image obtained by drying at 100°C") was calculated and evaluated according to the following criteria.
[Evaluation Criteria]
◯: ΔOD is less than 0% △: ΔOD is 0%
×: ΔOD is greater than 0%

＊表３中の比較例１～４における「－」は測定不能であることを意味する。

* In Table 3, "-" in Comparative Examples 1 to 4 means that measurement was not possible.

From the results in Tables 1 to 4, it is clear that in all of Examples 1 to 8, high image density was obtained and the decrease in image density during heating and drying could be suppressed.
In contrast, in Comparative Example 1, numerous nozzle clogging occurred in the inkjet evaluation, making it difficult to print solid images (image density could not be measured).
In addition, in Comparative Example 2, numerous nozzle clogging and deflection of ink ejection occurred in the inkjet evaluation, making it difficult to print solid images (image density could not be measured).
In Comparative Example 3, the surface smoothness of the coating film after drying at 100° C. was low, and high image density could not be obtained after drying at 100° C.
In addition, in Comparative Example 4, numerous nozzle clogging occurred in the inkjet evaluation, making it difficult to print solid images (image density could not be measured).
In Comparative Example 5, the surface smoothness of the coating film after drying at 100° C. was low, and high image density could not be obtained after drying at 100° C.

For example, aspects of the present invention are as follows.
<1> A pigment-encapsulated resin particle containing a pigment and a surfactant,
the pigment-encapsulating resin particles have a cumulative 50% volume particle size ( _D50 ) of 200 nm or more and 500 nm or less;
The aqueous dispersion is characterized in that the aspect ratio of the pigment-encapsulating resin particles is 1.0 or more and 1.5 or less.
<2> The aqueous dispersion according to <1>, wherein the content of the surfactant is 1% by mass or more and 20% by mass or less.
<3> The aqueous dispersion according to any one of <1> and <2>, wherein the surfactant is an anionic surfactant.
<4> The aqueous dispersion according to any one of <1> to <3>, wherein the pigment is an inorganic pigment, and the inorganic pigment is carbon black.
<5> The aqueous dispersion according to any one of <1> to <4>, wherein the pigment-encapsulating resin particles contain a polyester resin.
<6> The aqueous dispersion according to any one of <1> to <5>, wherein a mass ratio of the pigment to the resin (pigment/resin) in the pigment-encapsulating resin particles is 0.2 to 0.75.
<7> The aqueous dispersion according to any one of <1> to <6>, wherein a coating film having an average thickness of 2 μm formed using the aqueous dispersion has a pigment exposure rate of 8% or less on a surface thereof.
<8> The aqueous dispersion according to any one of <1> to <7>, wherein a coating film having an average thickness of 2 μm formed using the aqueous dispersion has a surface roughness of 20 nm or less.
<9> The aqueous dispersion according to any one of <1> to <8>, wherein the pigment-encapsulating resin particles account for 30% or more of the total number of particles having a volume particle size of 100 nm or more.
<10> A step of mixing an organic solvent and a pigment to prepare a pigment pre-dispersion;
A step of mixing the obtained pigment pre-dispersion with a resin to prepare a pigment dispersion resin solution;
A step of mixing the obtained pigment-dispersed resin solution with a surfactant-containing liquid to prepare a pigment-encapsulated resin particle dispersion liquid;
removing the organic solvent from the obtained pigment-encapsulated resin particle dispersion;
The present invention relates to a method for producing an aqueous dispersion comprising the steps of:
<11> The method for producing an aqueous dispersion according to <10>, wherein the pigment in the pigment pre-dispersion has a cumulative volume particle size of 50% (D ₅₀ ) of 10 nm or more and 150 nm or less.
<12> The method for producing an aqueous dispersion according to any one of <10> and <11>, wherein a hydrophobic pigment dispersant is added in the step of preparing the pigment pre-dispersion.
<13> A pigment-encapsulated resin particle that encapsulates a pigment, a surfactant, and an organic solvent,
the pigment-encapsulating resin particles have a cumulative 50% volume particle size ( _D50 ) of 200 nm or more and 500 nm or less;
The ink is characterized in that the aspect ratio of the pigment-encapsulating resin particles is 1.0 or more and 1.5 or less.
<14> A printing method, comprising: an ink applying step of applying the ink according to <13>.
<15> An ink storage section that stores the ink according to <13>;
an ink applying means for applying the ink;
The printing device is characterized by having:

The aqueous dispersion described in any one of <1> to <9>, the method for producing the aqueous dispersion described in any one of <10> to <12>, the ink described in <13>, the printing method described in <14>, and the printing device described in <15> can solve the problems of the prior art and achieve the object of the present invention.

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

JP 2016-196621 A JP 2002-322396 A JP 2019-099819 A

Claims (13)

The ink contains a hydrophobic pigment dispersant, pigment-encapsulated resin particles that encapsulate the pigment, and a surfactant,
the pigment-encapsulating resin particles have a cumulative 50% volume particle size ( _D50 ) of 200 nm or more and 500 nm or less;
The aspect ratio of the pigment-encapsulated resin particles is 1.0 or more and 1.5 or less,
The aqueous dispersion has a surfactant content of 1% by mass or more and 20% by mass or less . The aqueous dispersion according to claim 1 , wherein the surfactant is an anionic surfactant. 3. The aqueous dispersion according to claim 1 , wherein the pigment is an inorganic pigment, and the inorganic pigment is carbon black. The aqueous dispersion according to claim 1 , wherein the pigment-encapsulating resin particles contain a polyester resin. 5. The aqueous dispersion according to claim 1 , wherein the mass ratio of the pigment to the resin (pigment/resin) in the pigment-encapsulating resin particles is 0.2 or more and 0.75 or less. 6. The aqueous dispersion according to claim 1 , wherein a coating film having an average thickness of 2 μm formed using the aqueous dispersion has a pigment exposure rate of 8% or less on the surface thereof. 7. The aqueous dispersion according to claim 1 , wherein a coating film having an average thickness of 2 μm formed using the aqueous dispersion has a surface roughness of 20 nm or less. 8. The aqueous dispersion according to claim 1 , wherein the pigment-encapsulating resin particles account for 30% or more of the total number of particles having a volume particle size of 100 nm or more. mixing an organic solvent and a pigment to prepare a pigment pre-dispersion;
A step of mixing the obtained pigment pre-dispersion with a resin to prepare a pigment dispersion resin solution;
A step of mixing the obtained pigment-dispersed resin solution with a surfactant-containing liquid to prepare a pigment-encapsulated resin particle dispersion liquid;
removing the organic solvent from the obtained pigment-encapsulated resin particle dispersion;
Including,
In the step of preparing the pigment pre-dispersion, a hydrophobic pigment dispersant is added,
A method for producing an aqueous dispersion, wherein the amount of the surfactant added is 1.0% by mass or more and 20% by mass or less based on the aqueous dispersion obtained in the step of removing the organic solvent . The method for producing an aqueous dispersion according to claim 9 , wherein the pigment in the pigment pre-dispersion has a cumulative volume particle size of 50% (D ₅₀ ) of 10 nm or more and 150 nm or less. The ink contains water, a hydrophobic pigment dispersant, pigment-encapsulated resin particles that encapsulate a pigment , and a surfactant, and an aqueous dispersion containing the surfactant and an organic solvent;
the pigment-encapsulating resin particles have a cumulative 50% volume particle size ( _D50 ) of 200 nm or more and 500 nm or less;
The aspect ratio of the pigment-encapsulated resin particles is 1.0 or more and 1.5 or less,
The ink is characterized in that the surfactant contained in the aqueous dispersion is from 1% by mass to 20% by mass . A printing method comprising the step of applying the ink according to claim 11 . an ink storage section that stores the ink according to claim 11 ;
an ink applying means for applying the ink;
A printing device comprising: