Ink jet recording method and ink jet recording apparatus

Abstract

To provide an ink jet recording method which suppresses non-discharge and is excellent in the discharge recovery property even when recording an image by discharging aqueous fluorescent ink by using an ink jet recording apparatus having a recovery mechanism that recovers a discharge state of ink by applying pressure to an ink flow path in a recording head.SOLUTION: Provided is an ink jet recording method including recording an image on a recording medium through use of an ink jet recording apparatus, the ink jet recording apparatus including: an aqueous ink; a recording head including an ink flow path in which the aqueous ink flows and including an ejection orifice configured to eject the aqueous ink; and a recovery mechanism configured to recover an ejection state of the aqueous ink from the ejection orifice by applying a pressure to the ink flow path inside the recording head. The aqueous ink contains resin particles each dyed with a basic dye exhibiting fluorescence and a water-soluble resin. The resin particles are each formed of a resin having an anionic group-containing unit. The water-soluble resin has an anionic group-containing unit.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an inkjet recording method and an inkjet recording apparatus. [Background technology]

[0002] According to the inkjet recording method, it is possible to record images such as photographs and documents on various recording media. In addition, various inks have been proposed according to the purpose, such as inks suitable for recording photographic quality images on glossy paper and inks suitable for recording documents on plain paper. In recent years, there has been an increasing demand for recorded matter on which highly colored images, such as fluorescent images, are recorded for posters and signage applications. As an ink for recording fluorescent images, an ink containing a fluorescent dye has been proposed (Patent Document 1).

[0003] There is also an increasing demand for efficient use of ink. In response to such demands, a recording device has been proposed that incorporates a pressurized recovery system that performs a recovery operation by applying pressure in order to reduce the amount of waste ink (ink used for purposes other than recording) (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-113332 A [Patent Document 2] JP 2000-238277 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have investigated the use of a recording device equipped with a pressurized recovery system to eject fluorescent ink containing a fluorescent dye to record an image, and have found that non-ejection of the ink is likely to occur, and the recorded image is likely to be distorted.

[0006] Therefore, an object of the present invention is to solve the problems that arise when an inkjet recording device is used that has a recovery mechanism that applies pressure to the ink flow path in the recording head to recover the ink ejection state, and ejects a water-based fluorescent ink to record an image. That is, an object of the present invention is to provide an inkjet recording method that suppresses ejection failures and has excellent ejection recovery properties even in such a case. Another object of the present invention is to provide an inkjet recording device used in the above inkjet recording method. [Means for solving the problem]

[0007] That is, according to the present invention, there is provided an inkjet recording method comprising a step of recording an image on a recording medium using an inkjet recording device comprising: an aqueous ink; a recording head having an ejection port for ejecting the aqueous ink, the ejection port including an ink flow path through which the aqueous ink flows; and a recovery mechanism for applying pressure to the ink flow path in the recording head to recover the ejection state of the aqueous ink from the ejection port, wherein the aqueous ink contains resin particles dyed with a fluorescent basic dye and a water-soluble resin, the resin particles are formed of a resin having an anionic group-containing unit, and the water-soluble resin has an anionic group-containing unit. Effect of the Invention

[0008] According to the present invention, it is possible to solve the problems that arise when recording an image by ejecting a water-based fluorescent ink using an inkjet recording device provided with a recovery mechanism that applies pressure to the ink flow path in the recording head to restore the ink ejection state. That is, even in such a case, it is possible to provide an inkjet recording method that suppresses ejection failures and has excellent ejection recovery properties. Furthermore, according to the present invention, it is possible to provide an inkjet recording device used in the above inkjet recording method. [Brief description of the drawings]

[0009] [Figure 1] 1 is a perspective view illustrating an embodiment of an inkjet recording apparatus of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating an example of an ink supply system. [Diagram 3] FIG. 4 is a schematic diagram illustrating an example of a pressurized recovery mechanism. [Figure 4] FIG. 4 is a schematic diagram illustrating an example of a pressurized recovery mechanism. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, water-based ink for inkjet printing may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified. In the present invention, the "unit" constituting the resin means a repeating unit derived from one monomer.

[0011] The present inventors first studied fluorescent inks capable of recording images with excellent color development. As a result, it was found that when inks with a simple increased content of fluorescent dyes are used, the saturation of the recorded image is improved, but the brightness is significantly reduced. This is believed to be due to the concentration quenching characteristic of fluorescent materials. Further studies revealed that the use of resin particles dyed with fluorescent dyes can suppress the decrease in brightness, making it possible to record images with the desired color development.

[0012] Next, we investigated the recording of images by ejecting fluorescent ink from an inkjet recording device equipped with a recovery mechanism (pressure recovery mechanism) that applies pressure to the ink flow path in the recording head to restore the ink ejection state. As a result, we found that non-ejection of ink is likely to occur after the recovery operation by the pressure recovery mechanism is performed, and that this can cause distortion in the resulting image. When using conventional dye ink or pigment ink other than fluorescent ink, non-ejection of ink does not occur or is so minor that it is not a problem, even when using an inkjet recording device equipped with the above-mentioned pressure recovery mechanism.

[0013] The present inventors speculate as follows about the reason why ink non-ejection is likely to occur when fluorescent ink is ejected from an inkjet recording device equipped with a pressurized recovery mechanism. When a recovery operation is performed by the pressurized recovery mechanism, the ink flows with force, and gas such as air that was present in the ink flow path is entrained, generating air bubbles in the ink flow path. If the generated air bubbles are carried by the ink flow during recording and reach the recording head, it becomes difficult for the ink to be ejected from the ejection port, and it is thought that ink non-ejection is likely to occur. In contrast, when conventional dye ink or pigment ink is used, the air bubbles break as the ink flows, making it difficult for them to reach the ejection port, and therefore ink non-ejection is thought to be unlikely to occur.

[0014] On the other hand, when an ink containing resin particles dyed with a fluorescent basic dye is used as a coloring material, the bubbles are less likely to break and are more likely to reach the ejection port. The basic dye has a basic group, which is a cationic portion, and an anionic portion, such as a chloride ion, which is a counter to the cationic portion. When the resin particles are dyed with such a basic dye, the anionic portion of the resin particles and the cationic portion of the basic dye interact with each other. Most of the basic dyes are present in the ink in a state where they interact with the resin particles, but it is believed that some of the basic dyes are present in the ink in a state where they are separated from the resin particles. It is believed that when the basic dyes separated from the resin particles are present in the ink, the cationic concentration increases locally. When the cationic concentration increases, the resin particles having an anionic group tend to gather together, and the distance between the resin particles becomes shorter. The anionic groups of the resin particles act hydrophilically in the ink, and the portions other than the anionic groups act hydrophobically. As a result, the hydrophilic portions of the resin particles interact with each other and the hydrophobic portions of the resin particles interact with each other, which is believed to cause the resin particles to behave like surfactants.

[0015] When the pressurized recovery operation is performed with a high cation concentration, the resin particles behave like surfactants in the fast-flowing ink, generating bubbles. It is believed that the resin particles around the generated bubbles strongly interact with each other, making it difficult for the bubbles to break. It is believed that the bubbles that are difficult to break ride the ink flow and travel through the ink flow path in the recording head to the ejection port, reducing the ejection performance of the ink and causing image disturbances.

[0016] Based on this understanding, the present inventors have further studied. As a result, it has been found that non-ejection after the pressurized recovery operation can be suppressed by using an ink further containing a water-soluble resin having an anionic group-containing unit. The cationic portion of the basic dye released from the resin particles interacts with the anionic group of the water-soluble resin, thereby suppressing a local increase in the cationic concentration in the ink. Even if bubbles are generated by the pressurized recovery operation, if the local increase in the cationic concentration is suppressed, the strength of the bubbles is reduced because the interaction between the resin particles is weakened, and the bubbles are likely to break. As a result, it is believed that the bubbles that have passed through the ink flow path in the recording head break before moving to the ejection port, thereby suppressing non-ejection of the ink.

[0017] In ink that does not contain a water-soluble resin having an anionic group-containing unit, it is believed that the cationic component increases locally. During an actual recording operation, the concentration of resin particles in the ink increases with the evaporation of water from the tip of the ejection port, and the cationic concentration increases. When the concentration of resin particles in the ink increases, the resin particles interact with each other and tend to aggregate. As a result, the ink viscosity increases near the tip of the ejection port, and the ejection properties of the ink decrease. When the ejection properties of the ink decrease and the ejection interval becomes longer, it may become difficult for the ink to be ejected normally even by the ejection operation. In order to suppress such a decrease in the ejection properties of the ink, it is necessary to increase the number of ejection operations that eject the ink to a place other than the recording medium (for example, the ejection port) and refresh the state near the ejection port of the ink flow path.

[0018] On the other hand, in an ink containing a water-soluble resin having an anionic group-containing unit, the resin particles and the water-soluble resin interact with each other. As a result, the interaction between the resin particles is suppressed, and the aggregation of the resin particles at the tip of the ejection port is suppressed. This allows the ink to be ejected normally by normal ejection operation even if the ejection interval becomes long. This makes it possible to reduce the number of ejection operations to refresh the condition near the ejection port of the ink flow path, thereby reducing the amount of waste ink.

[0019] <Inkjet recording method and inkjet recording apparatus> In the inkjet recording method of the present invention, an inkjet recording device is used that includes an aqueous ink, a recording head having an ejection port for ejecting the aqueous ink, and a recovery mechanism for recovering the ejection state of the aqueous ink from the ejection port. The recording head includes an ink flow path through which the aqueous ink flows. The recovery mechanism is a mechanism for applying pressure to the ink flow path in the recording head to recover the ejection state of the aqueous ink from the ejection port. The inkjet recording method of the present invention includes a step of recording an image on a recording medium using the inkjet recording device (hereinafter, also referred to as a "recording step"). The aqueous ink contains resin particles dyed with a fluorescent basic dye and a water-soluble resin. The resin particles are formed of a resin having an anionic group-containing unit, and the water-soluble resin has an anionic group-containing unit.

[0020] The inkjet recording apparatus of the present invention is an apparatus suitable for use in the inkjet recording method, and includes an aqueous ink, a recording head, and a recovery mechanism. The aqueous ink contains resin particles dyed with a fluorescent basic dye and a water-soluble resin. The resin particles are formed of a resin having an anionic group-containing unit, and the water-soluble resin has an anionic group-containing unit.

[0021] FIG. 1 is a perspective view showing a schematic diagram of an embodiment of an inkjet recording apparatus of the present invention. The inkjet recording apparatus of this embodiment is a so-called serial type inkjet recording apparatus that performs a recording operation by reciprocating a recording head in an X direction (main scanning direction). A recording medium 101 is intermittently transported in a Y direction (sub-scanning direction) by a transport roller 107. A recording unit 102 mounted on a carriage 103 is reciprocally scanned in an X direction (main scanning direction) that is a direction perpendicular to the Y direction that is the transport direction of the recording medium 101. A recording operation is performed by transporting the recording medium 101 in the Y direction and reciprocating scanning of the recording unit 102 in the X direction. The recording unit 102 is composed of an inkjet type recording head 203 (FIG. 2) that ejects ink from a plurality of ejection ports, and a subtank 202 (FIG. 2) as a second ink storage section, and is mounted on the carriage 103. The carriage 103 is supported so as to be movable along a guide rail 105 arranged along the X direction, and is fixed to an endless belt 106 that moves in parallel with the guide rail 105. The endless belt 106 reciprocates due to the driving force of a motor, thereby causing the carriage 103 to scan back and forth in the X direction.

[0022] A main tank 201 (FIG. 2) serving as a first ink storage section is stored inside the main tank storage section 108. The main tank 201 stored in the main tank storage section 108 and a sub-tank 202 of the recording unit 102 are connected via an ink supply tube 104. Ink is supplied from the main tank 201 to the sub-tank 202 (FIG. 2) via the ink supply tube 104, and then ejected from the ejection opening of the recording head 203. The main tank 201, the ink supply tube 104, and the sub-tank 202 can each be provided in numbers corresponding to the type of ink. It is preferable that the main tank 201 and the sub-tank 202 are connected by the ink supply tube 104 without going through another ink storage section.

[0023] The main tank housing section 108 is provided with an ink inlet 210 for injecting ink into the main tank 201 from outside the inkjet recording device. When using the inkjet recording device for the first time, or when the amount of ink has decreased, ink is injected from an ink bottle into the main tank placed inside the inkjet recording device. The user can open the ink inlet 210 and inject ink into the main tank 201. In other words, the main tank is left inside the inkjet recording device and is not replaced itself.

[0024] 2 is a schematic diagram showing an example of an ink supply system. Ink (shown by hatching) stored in a main tank 201 is supplied to a sub tank 202 via an ink supply tube 104, and then supplied to a print head 203. A gas introduction tube 204 serving as an air communication section is connected to the main tank 201. When printing is performed and ink is consumed, ink is supplied from the main tank 201 to the sub tank 202, and the ink in the main tank 201 decreases. Then, air is introduced into the main tank 201 from the gas introduction tube 204, one end of which is open to the atmosphere, so that the internal negative pressure for holding the ink is kept substantially constant in the ink supply system.

[0025] The recording unit 102 is composed of a recording head 203 and a subtank 202. The subtank 202 may be attached to the recording unit 102, which is a head cartridge in which the recording head 203 is built, and the recording unit 102 with the subtank 202 attached may be attached to the carriage 103. Furthermore, the recording unit 102 integrally composed of the subtank 202 and the recording head 203 may be attached to the carriage 103. Among these, it is preferable to adopt a configuration in which the recording unit 102 with the subtank 202 attached is set in the carriage 103 as shown in Figures 1 and 2.

[0026] The ink ejection method of the recording head 203 may be a method of applying mechanical energy to the ink or a method of applying thermal energy to the ink. Among these, it is preferable to adopt a method of ejecting ink by applying thermal energy to the ink.

[0027] 2, the inkjet recording apparatus of this embodiment includes a recording unit 102 that is composed of a sub-tank 202, which is a second ink storage section, and a recording head 203. Inside the sub-tank 202 and the recording head 203 that constitute the recording unit 102, an ink flow path that supplies ink is formed, which communicates from the upstream end of the sub-tank 202 to the downstream end, which is the ejection port of the recording head 203.

[0028] The inkjet recording device is provided with a recovery mechanism (pressure recovery mechanism) that applies pressure to the ink flow path in the recording head to recover the ink ejection state from the ejection port. This pressure recovery mechanism may be any mechanism that is capable of applying pressure to the ink flow path in the recording head. For example, the mechanisms described in JP-A-2000-238294, JP-A-2000-238277, and JP-A-2000-033711 may be adopted.

[0029] 3 and 4 are schematic diagrams showing an example of a pressurized recovery mechanism. To perform a recovery operation for recovering the ink ejection state from the ejection ports of the print head 203 mounted on the carriage 103 (FIG. 1), a pump 303 is first connected to an air vent 304 provided in the subtank 202 via an air tube, as shown in FIG. 3. A flexible bag 301 housed in the subtank is connected to the air vent 304. Next, the pump 303 is operated to pressurize and inject a predetermined volume of air into the bag 301, causing the bag 301 to expand in the subtank 202. As the bag 301 expands, the pressure in the ink flow path of the print head 203 increases, causing a flow of ink 305 to the ejection ports of the print head 203, and ink is discharged from the ejection ports, thereby recovering the ejection state of the ink 305 from the ejection ports.

[0030] The pressure applied to the ink flow path during the recovery operation is preferably 20 kPa or more, more preferably 30 kPa or more, and even more preferably 40 kPa or more. By applying a pressure of 20 kPa or more to the ink flow path to perform the recovery operation, the ejection recovery of the ink can be further improved. The pressure applied to the ink flow path during the recovery operation is preferably 80 kPa or less.

[0031] After the recovery operation is performed, the air tube 302 is removed from the ventilation hole 304 as shown in Fig. 4. This allows the air injected into the bag 301 to flow out from the ventilation hole, and the internal pressure of the bag 301 returns to atmospheric pressure, allowing the bag 301 to contract and deform inside the subtank 202.

[0032] In the inkjet recording method of the present invention, an inkjet recording device that is small but has excellent ink ejection stability is used, so that images can be recorded with high productivity. The moving speed of the recording head when recording an image is preferably 30 inches / second or more, more preferably 35 inches / second or more. The moving speed of the recording head when recording an image is preferably 70 inches / second or less.

[0033] Any recording medium may be used for recording an image by the inkjet recording method of the present invention. In particular, it is preferable to use permeable paper such as recording media without a coating layer, such as plain paper or uncoated paper, or recording media with a coating layer, such as glossy paper or art paper.

[0034] (ink) In the inkjet recording method of the present invention, a water-based ink for inkjet use containing resin particles dyed with a fluorescent dye and a water-soluble resin is used. Hereinafter, each component constituting the ink used in the inkjet recording method of the present invention will be described in detail.

[0035] [Resin particles dyed with fluorescent dye] The ink contains resin particles (fluorescent particles) dyed with a fluorescent dye. The fluorescent dye is a basic dye that exhibits fluorescence. In this specification, the term "fluorescent dye" refers to a dye that emits fluorescence when excited by ultraviolet or visible light. Whether a certain dye is a "fluorescent dye" that exhibits fluorescence can be determined, for example, according to the method shown below. A sample obtained by dissolving a dye in a liquid that can dissolve the dye is irradiated with ultraviolet light (ultraviolet light) of a long wavelength (about 315 to 400 nm) that is barely visible to the naked eye using a black light or the like. If light of a color different from the ultraviolet light irradiated by the black light can be visually observed, the dye can be determined to be a "fluorescent dye" that exhibits fluorescence. As the black light, a commercially available product (for example, the product name "SLUV-4" (manufactured by AS ONE) or the like) can be used. Fluorescence can also be measured using a spectrofluorometer or the like. As the spectrofluorometer, for example, the product name "FP-8050 series" manufactured by JASCO or the like can be used.

[0036] The fluorescent dye in the resin particles dyed with the fluorescent dye can be analyzed, for example, according to the following procedure. Resin particles extracted from the ink according to a conventional method are dissolved in an organic solvent such as chloroform to prepare a sample. The fluorescent dye is isolated from the prepared sample using HPLC (high performance liquid chromatography). The isolated dye is analyzed by common structural analysis methods such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS).

[0037] A basic dye is a fluorescent compound having a basic group, such as an amino group or an imino group (which may form a salt), in its molecular structure. Examples of compounds having an amino group or an imino group in their molecular structure include "dyes whose names in the Colour Index include 'basic'". The Colour Index is a database of colouring materials constructed by the British Society of Dyes and Colourants and others. Examples of the skeleton of the dye include xanthene, azine, azole, thiazole, azo, diarylmethane, triarylmethane, acridine, coumarin, methine and the like. Among these, compounds having a skeleton such as xanthene or coumarin are preferred, and compounds having a xanthene skeleton are even more preferred.

[0038] Specific examples of fluorescent basic dyes, expressed by CI number or general name, include CI Basic Red 1, 1:1, 2, 4, 8, 11, 12, 13; CI Basic Violet 1, 3, 10, 11, 11:1, 14; Rhodamine 19, 575; CI Basic Yellow 1, 2, 9, 13, 24, 37, 40, 96; CI Basic Blue 7; CI Basic Green 1; and CI Fluorescent Brightener 363. Among these, CI Basic Red 1, 1:1; CI Basic Violet 11, 11:1; and CI Basic Yellow 40 are preferred because of their excellent color development.

[0039] The fluorescent dye preferably contains two or more kinds of fluorescent dyes. The presence of multiple fluorescent dyes in the resin particles inhibits the crystallization of the fluorescent dyes, so that the fluorescent dyes can efficiently interact with the resin particles at the molecular level and can be stably dyed.

[0040] The content (mass%) of the fluorescent dye in the ink is preferably 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink. The ratio (mass%) of the fluorescent dye in the resin particles is preferably 1.0% by mass or more and 15.0% by mass or less, and more preferably 3.0% by mass or more and 8.0% by mass or less. If the ratio of the fluorescent dye in the resin particles is too low, the color development (saturation) of the image may be slightly decreased. On the other hand, if the ratio of the fluorescent dye in the resin particles is too high, the color development (brightness) of the image may be slightly decreased due to concentration quenching. In addition to the resin particles dyed with a fluorescent basic dye, other color materials such as dyes and pigments may be used.

[0041] [Resin particles] In this specification, the term "resin particles" refers to a resin that can be present in an aqueous medium in a state of being dispersed in the aqueous medium and having a particle size. Therefore, the resin particles are present in a dispersed state in the ink, i.e., in a state of a resin emulsion.

[0042] Whether or not a certain resin is a "resin particle" can be determined according to the following method. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by dynamic light scattering, if particles having a particle size are measured, the resin can be determined to be a "resin particle". A particle size analyzer (for example, product name "UPA-EX150", manufactured by Nikkiso) can be used as a particle size distribution measuring device using the dynamic light scattering method. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: spherical, refractive index: 1.59. Of course, the particle size distribution measuring device and measurement conditions used are not limited to those described above. The particle size is measured using neutralized resin in order to confirm that particles are formed even when the resin is sufficiently neutralized to make it more difficult to form particles. Even under such conditions, resins that have a particulate shape exist in the form of particles in the water-based ink.

[0043] The resin particles are formed of a resin having an anionic group-containing unit. Examples of the resin forming the resin particles include acrylic resins and polyester resins. As the polyester resin, polyester resins having sulfonic acid groups are preferable. As the acrylic resin, acrylic resins having carboxylic acid groups are preferable. Among them, acrylic resins are preferable as the resin forming the resin particles.

[0044] As the resin particles, it is preferable to use resin particles having a so-called core-shell structure, which has a core portion and a shell portion covering the core portion. The core portion preferably contains an aromatic group-containing unit and a cyano group-containing unit. By the core portion containing an aromatic group-containing unit and a cyano group-containing unit, the resin particles are efficiently dyed with the fluorescent dye, and the color development of the fluorescent dye itself is efficiently exhibited, thereby improving the color development of the image. The shell portion preferably contains an aromatic group-containing unit and an anionic group-containing unit.

[0045] As the monomer that becomes the aromatic group-containing unit by polymerization, it is preferable that the monomer has one polymerizable functional group such as an ethylenically unsaturated bond in the molecule.Specific examples include styrene, vinyltoluene, p-fluorostyrene, p-chlorostyrene, α-methylstyrene, 2-vinylnaphthalene, 9-vinylanthracene, 9-vinylcarbazole, phenyl(meth)acrylate, benzyl(meth)acrylate, 2-phenoxyethyl(meth)acrylate, 2,4-diamino-6-((meth)acryloyloxy)ethyl-1,3,5-triazine, 2-naphthyl(meth)acrylate, 9-anthryl(meth)acrylate, (1-pyrenyl)methyl(meth)acrylate, etc.As the monomer that becomes the aromatic group-containing unit by polymerization, it is preferable that the monomer does not have an anionic group or a cyano group, or that the molecular weight is 300 or less, and more preferably that the molecular weight is 200 or less. Among these, styrene and its derivatives are more preferred, and styrene and vinyltoluene are particularly preferred, since they have good reactivity during polymerization and the stability of the resulting resin particles is excellent.

[0046] As the monomer that becomes a cyano group-containing unit by polymerization, one having one polymerizable functional group such as an ethylenically unsaturated bond in the molecule is preferable. Specific examples include acrylonitrile, methacrylonitrile, chloroacrylonitrile, and 2-cyanoethyl (meth)acrylate. As the monomer that becomes a cyano group-containing unit by polymerization, one having no anionic group or aromatic group, or one having a molecular weight of 300 or less is preferable, and one having a molecular weight of 200 or less is more preferable. Among them, acrylonitrile and methacrylonitrile are particularly preferable because they have good reactivity during polymerization and the stability of the obtained resin particles is excellent.

[0047] The anionic group in the anionic group-containing unit is preferably one having one polymerizable functional group such as an ethylenically unsaturated bond in the molecule. Specifically, carboxylic acid groups, phenolic hydroxy groups, phosphate groups, etc. can be mentioned. Among them, carboxylic acid groups are preferred because the stability of the resin particles in the ink is good. Examples of monomers that become an anionic group-containing unit by polymerization include (meth)acrylic acid, p-vinylbenzoic acid, 4-vinylphenol, β-carboxyethyl (meth)acrylate, (methacrylic acid-2-hydroxyethyl) phosphate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, etc. As monomers that become an anionic group-containing unit by polymerization, those that do not have an aromatic group or a cyano group, and those that have a molecular weight of 300 or less are preferred, and those that have a molecular weight of 200 or less are more preferred. Among them, (meth)acrylic acid is particularly preferred. In addition, it is preferred that the anionic group in the anionic group-containing unit is only a carboxylic acid group. The anionic group may be either an acid type or a salt type, and when it is a salt type, it may be either a partially dissociated state or a completely dissociated state. When the anionic group is a salt type, examples of the cation that serves as the counter ion include an alkali metal cation, ammonium, and organic ammonium.

[0048] The shell part preferably contains a unit derived from a crosslinking agent. As the crosslinking agent constituting the unit derived from the crosslinking agent, at least one kind may be used, and it is preferable to use two or more kinds of crosslinking agents. As the crosslinking agent, a compound having two ethylenically unsaturated bonds in the molecule is preferable. By using a compound having two ethylenically unsaturated bonds in the molecule as a crosslinking agent, aggregation of resin particles caused by excessive crosslinking is suppressed, and resin particles with a more uniform particle size can be obtained. Among the compounds having two ethylenically unsaturated bonds in the molecule, divinylbenzene and ethylene glycol di(meth)acrylate are more preferable.

[0049] A surfactant can be used when producing resin particles. It is preferable to produce resin particles in the presence of a surfactant, since the particle size and shape of the resulting resin particles are likely to be stable. However, non-reactive surfactants may be easily peeled off from the resin particles. If the surfactant peels off in the ink, it may affect the physical properties of the ink, and the ejection stability may be easily reduced. For this reason, reactive surfactants are preferable as surfactants used when producing resin particles.

[0050] As the reactive surfactant, it is preferable to use a compound in which a polymerizable functional group such as a (meth)acryloyl group, a maleyl group, a vinyl group, or an allyl group is bonded to the inside or end of a molecule composed of a hydrophilic part and a hydrophobic part. Examples of the hydrophilic part include polyoxyalkylene chains such as an ethylene oxide chain and a propylene oxide chain. Examples of the hydrophobic part include structures such as alkyl, aryl, and combinations thereof. The hydrophilic part and the hydrophobic part may be bonded via a linking group such as an ether group. As the reactive surfactant, those having a molecular weight of more than 200 are preferable, those having a molecular weight of more than 300 are more preferable, and those having a molecular weight of 400 or more are particularly preferable.

[0051] The core and shell of the resin particles may each contain a unit other than the above units, as long as the effect of the present invention is not impaired. As the unit other than the above units, those having one polymerizable functional group in the molecule are preferable, and specifically, a unit derived from an ethylenically unsaturated monomer can be mentioned.

[0052] The volume-based cumulative 50% particle diameter (D50) of the resin particles is preferably 250 nm or less. If the volume-based cumulative 50% particle diameter (D50) of the resin particles exceeds 250 nm, the resin particles may be prone to settling inside the ink cartridge, ink supply system, recording head, etc., and may be prone to deviation from the desired color tone. The volume-based cumulative 50% particle diameter (D50) of the resin particles is preferably 50 nm or more. The volume-based cumulative 50% particle diameter (D50) of the resin particles can be measured by the same method as the above-mentioned method for determining whether or not the resin particles are resin particles.

[0053] The content (mass%) of the resin particles in the ink is preferably 1.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. If the content of the resin particles is less than 1.0% by mass, the color development of the image may be slightly decreased. On the other hand, if the content of the resin particles is more than 10.0% by mass, the ejection stability of the ink may be slightly decreased.

[0054] [Method of manufacturing dyed resin particles] The resin particles can be produced according to a conventionally known method such as emulsion polymerization, mini-emulsion polymerization, seed polymerization, and phase inversion emulsification. Examples of the dyeing method for the resin particles include a method of polymerizing a monomer mixture in which a fluorescent dye is dissolved to form resin particles; a method of adding a fluorescent dye to resin particles and heating the particles; and the like. Among them, the method of adding a fluorescent dye to resin particles and heating the particles is preferred because it can be applied to a wider variety of fluorescent dyes. It is preferable not to add a dyeing assistant (water-soluble resin, surfactant, etc.) during heating. If a water-soluble resin is used as a dyeing assistant, the water-soluble resin may form a film and inhibit the redispersion of the resin particles, which may slightly reduce the fixation recovery of the ink. In addition, if a surfactant is used as a dyeing assistant, the physical properties of the ink may be affected, and the ejection stability of the ink may slightly decrease.

[0055] [Verification method for resin particles] The composition of the resin particles can be verified according to the following methods (i) to (iii). Below, a method for extracting resin particles from ink and analyzing and verifying them will be described, but resin particles extracted from an aqueous dispersion or the like can also be analyzed and verified in the same manner.

[0056] (i) Extraction of resin particles Density gradient centrifugation can be used to separate and extract resin particles from ink that contains them. Among density gradient centrifugation methods, density gradient sedimentation velocity separates and extracts resin particles based on the difference in sedimentation coefficient of components. Also, among density gradient centrifugation methods, density gradient sedimentation equilibrium separates and extracts resin particles based on the difference in density of components.

[0057] (ii) Confirmation and separation of layer structure First, the resin particles are stained and fixed with ruthenium tetroxide, and then embedded in epoxy resin to stably hold them. Next, the resin particles embedded in epoxy resin are cut with an ultramicrotome, and the cross section is observed using a scanning transmission electron microscope (STEM). By observing the cross section cut through the center of gravity of the resin particles, the layer structure of the resin particles can be confirmed. The resin particles embedded in epoxy resin are used as an analysis sample, and the elements contained in the layers (core and shell) that make up the resin particles can be quantitatively analyzed by STEM-EDX, which is equipped with energy dispersive X-ray spectroscopy (EDX).

[0058] (iii) Analysis of the units (monomers) that make up the resin of each layer The resin particles to be used as a sample for separating the resin of each layer may be in the form of a dispersion liquid. Alternatively, the resin particles may be dried to form a film to be used as a sample. After dissolving the resin particles to be used as a sample in an organic solvent, the layers are separated by gel permeation chromatography (GPC), and the resins constituting each layer are separated. The separated resin is then subjected to elemental analysis by a combustion method. Separately, the separated resin is pretreated by an acid decomposition (addition of hydrofluoric acid) method or an alkali fusion method, and then the inorganic components are quantitatively analyzed by an inductively coupled plasma optical emission spectrometry method. By comparing the results of the elemental analysis and the quantitative analysis of the inorganic components with the results of the quantitative analysis of the elements by STEM-EDX obtained in (ii) above, the layer of the resin particles that constituted the separated resin can be known.

[0059] The fractionated resin is analyzed by nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS). This allows the types and ratios of the units (monomers) and crosslinking components that make up the resin to be known. Furthermore, the monomers generated by depolymerization can be directly detected by analyzing the fractionated resin by pyrolysis gas chromatography.

[0060] (Water-soluble resin) The water-soluble resin has an anionic group-containing unit. The water-soluble resin is preferably an acrylic resin or a urethane resin, and more preferably an acrylic resin. The anionic group in the anionic group-containing unit interacts with the cationic portion of the basic dye released from the resin particle, suppressing or mitigating local aggregation of the cationic portion. As a result, as described above, the interaction between the resin particles is weakened, and bubbles generated during the pressurized recovery operation are easily broken.

[0061] The anionic group-containing unit in the water-soluble acrylic resin may be the above-mentioned anionic group-containing unit. The water-soluble acrylic resin may further have units (other units) other than the anionic group-containing unit. Examples of monomers constituting the other units include the above-mentioned monomers which become aromatic group-containing units by polymerization; those having a substituent such as an alkoxy group or a hydroxy group, such as 2-hydroxyethyl (meth)acrylate; 3-hydroxypropyl (meth)acrylate; methoxy (mono-, di-, tri-, or poly)ethylene glycol (meth)acrylate; alkenes such as ethylene and propylene; methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, lauryl (meth)acrylate, and hexadecyl (meth)acrylate. Examples of the water-soluble acrylic resin include alkyl (meth)acrylates such as cyclopropyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, and cyclodecyl (meth)acrylate; monocyclic (meth)acrylates such as isobornyl (meth)acrylate and norbornyl (meth)acrylate; and tricyclic (meth)acrylates such as adamantyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate. The water-soluble acrylic resin may be any of a random copolymer, a block copolymer, and a graft copolymer.

[0062] As the water-soluble urethane resin, a product obtained by reacting polyisocyanate with a component that reacts therewith (such as a polyol having an acid group, a polyol not having an acid group, or a polyamine) can be used. In addition, a product obtained by further reacting a chain extender or a crosslinking agent can also be used. At least one of these components has an anionic group.

[0063] The acid value of the water-soluble resin is preferably 60 mgKOH / g or more and 250 mgKOH / g or less. If the acid value of the water-soluble resin is less than 60 mgKOH / g, the ejection stability of the ink may decrease. On the other hand, if the acid value of the water-soluble resin is more than 250 mgKOH / g, the aggregation of the resin particles on the recording medium may not progress easily, and the color development of the image may decrease.

[0064] The weight-average molecular weight of the water-soluble resin is preferably 5,000 or more and 50,000 or less. If the weight-average molecular weight of the water-soluble resin is less than 5,000, the effect of improving the ejection stability of the ink may be slightly reduced. On the other hand, if the weight-average molecular weight of the water-soluble resin is more than 50,000, the viscosity of the ink is likely to increase, and the effect of improving the ejection stability of the ink may be slightly reduced.

[0065] The content (mass%) of the water-soluble resin in the ink is preferably 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink. The content (mass%) of the water-soluble resin is preferably 0.1 times or more, more preferably 0.5 times or more, in terms of mass ratio to the content (mass%) of the resin particles. When the mass ratio is 0.1 times or more, the interaction between the water-soluble resin and the resin particles is enhanced, and bubbles generated during the pressurized recovery operation are more likely to break. Furthermore, when the mass ratio is 0.5 times or more, the effect is further improved. On the other hand, the content (mass%) of the water-soluble resin is preferably 2.0 times or less, more preferably 1.0 times or less, in terms of mass ratio to the content (mass%) of the resin particles. When the mass ratio is more than 2.0 times, the viscosity of the ink increases, and the ejection stability may decrease.

[0066] The composition, weight average molecular weight, acid value, and other physical properties of the water-soluble resin can be measured according to a conventional method. Specifically, the ink is centrifuged to obtain a precipitate and a supernatant, and the physical properties of the water-soluble resin can be measured. Although the water-soluble resin can be analyzed in the ink state, it is preferable to analyze the water-soluble resin extracted from the ink, since the measurement accuracy can be improved. Specifically, it is preferable to add an excess of acid (such as hydrochloric acid) to the supernatant obtained by centrifuging the ink at 75,000 rpm, and then dry the precipitated resin and analyze it.

[0067] By analyzing the resin separated from the ink using a high-temperature gas chromatography / mass spectrometer (high-temperature GC / MS), it is possible to confirm the types of units that make up the water-soluble resin. 13 Quantitative analysis using C-NMR or Fourier transform infrared spectroscopy (FT-IR) can confirm the molecular weight and type of monomers that make up each unit.

[0068] The acid value of the water-soluble resin can be measured by a titration method. Specifically, the water-soluble resin is dissolved in tetrahydrofuran (THF) to prepare a measurement sample. The prepared measurement sample is then subjected to potentiometric titration using an automatic potentiometric titrator with a potassium hydroxide ethanol titrant, thereby measuring the acid value of the water-soluble resin. As the automatic potentiometric titrator, for example, a product name "AT510" (manufactured by Kyoto Electronics Manufacturing Co., Ltd.) can be used.

[0069] The weight average molecular weight of the water-soluble resin can be measured by gel permeation chromatography (GPC). The GPC measurement conditions can be as follows: Apparatus: Alliance GPC 2695 (manufactured by Waters) Column: Shodex KF-806M 4-column (Showa Denko) ·Mobile phase: THF (special grade) ·Flow rate: 1.0mL / min Oven temperature: 40.0℃ -Amount of sample solution injected: 0.1mL Detector: RI (Refractive Index) Polystyrene standard samples: PS-1 and PS-2 (manufactured by Polymer Laboratories, molecular weights: 7,500,000, 2,560,000, 841,700, 377,400, 320,000, 210,500, 148,000, 96,000, 59,500, 50,400, 28,500, 20,650, 10,850, 5,460, 2,930, 1,300, 580, 17 types).

[0070] [Aqueous medium] The ink is an aqueous ink containing at least water as an aqueous medium. The ink may further contain a water-soluble organic solvent as an aqueous medium. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. In addition, as the water-soluble organic solvent, any of those generally used in inks can be used. Examples include alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink.

[0071] [Surfactants] The ink preferably further contains a surfactant. As the surfactant, any of anionic, cationic, and nonionic surfactants can be used. Among them, nonionic surfactants are preferable. As the nonionic surfactant, various surfactants such as hydrocarbon-based, fluorine-based, and silicone-based surfactants can be mentioned. The nonionic surfactant is preferably at least one selected from the group consisting of hydrocarbon-based surfactants and silicone-based surfactants. The surfactant acts in a direction to weaken the interaction between the resin particles, and bubbles generated by the pressurized recovery operation are easily broken, thereby improving the ejection stability of the ink. The content (mass %) of the surfactant in the ink is preferably 0.1 mass % or more and 5.0 mass % or less, and more preferably 0.2 mass % or more and 1.5 mass % or less, based on the total mass of the ink.

[0072] Examples of the hydrocarbon-based nonionic surfactant include polyoxyethylene alkyl ether, ethylene oxide adduct of acetylene glycol, polyethylene glycol polypropylene glycol block copolymer, and ethylene oxide adduct of polyhydric alcohol. Examples of the fluorine-based nonionic surfactant include perfluoroalkyl ethylene oxide adduct. Examples of the silicone-based nonionic surfactant include polyether-modified siloxane compounds.

[0073] [Other additives] In addition to the above-mentioned components, the ink may contain, as necessary, water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols, such as trimethylolpropane and trimethylolethane, and urea derivatives, such as urea and ethyleneurea. Furthermore, the ink may contain, as necessary, various additives, such as other surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, reduction inhibitors, evaporation promoters, chelating agents, and other resins. EXAMPLES

[0074] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples without departing from the gist of the invention. "Parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0075] <Preparation of Water Dispersion of Resin Particles> (Aqueous dispersion of resin particles 1) A reaction vessel equipped with a stirrer was set in a hot water bath. 1,178 parts of water was placed in the reaction vessel, and the internal temperature was maintained at 70°C. 219.0 parts of styrene, 233.0 parts of acrylonitrile, and 14.0 parts of a reactive surfactant (trade name "ADEKA REASOAP SR-10", manufactured by ADEKA) were mixed to prepare a monomer mixture for the core part. In addition, 1.9 parts of potassium persulfate and 659 parts of water were mixed to prepare an aqueous solution of polymerization initiator 1. The monomer mixture for the core part and the aqueous solution of polymerization initiator 1 were dropped into the reaction vessel in parallel over 60 minutes. After the dropping was completed, stirring was continued to react for another 30 minutes to synthesize particles that would become the core part of the resin particles.

[0076] Next, 15.2 parts of styrene, 12.0 parts of methacrylic acid, 32.0 parts of ethylene glycol dimethacrylate, 20.0 parts of ethylene glycol diglycidyl ether, and 0.8 parts of reactive surfactant were mixed to prepare a monomer mixture for the shell part. EX-810 (trade name "Denacol EX-810", manufactured by Nagase Chemtex) was used as the ethylene glycol diglycidyl ether. The reactive surfactant was the same as that used for the synthesis of the core part. 0.1 parts of potassium persulfate and 133 parts of water were mixed to prepare an aqueous solution of polymerization initiator 2. The monomer mixture for the shell part and the aqueous solution of polymerization initiator 2 were dropped in parallel over 10 minutes into a reaction vessel containing particles that would become the core part. After the dropwise addition was completed, the mixture was stirred at 80°C for 10 minutes to continue the reaction to synthesize the shell part, and resin particles having a core-shell structure in which the particles that would become the core part were coated with the resin that would become the shell part were synthesized.

[0077] Then, an appropriate amount of 8 mol / L potassium hydroxide aqueous solution was added to the reaction vessel, and the pH of the liquid was adjusted to 8.5. Furthermore, 23.2 parts of CI Basic Red 1 (powder) and 5.8 parts of CI Basic Violet 11 (powder) were added, and the temperature was raised to 80°C. After that, the mixture was stirred for 2 hours to dye the resin particles with the fluorescent dye. Next, an appropriate amount of 8 mol / L potassium hydroxide aqueous solution was added to the reaction vessel, and the pH of the liquid was adjusted to 8.5. An appropriate amount of water was further added to obtain an aqueous dispersion of resin particles 1 with a resin particle content of 20.0%. The particle diameter of the obtained resin particles 1 (cumulative 50% particle diameter on a volume basis) was 80 nm. The particle diameter of the resin particles 1 was measured using a dynamic light scattering particle size analyzer (trade name "UPA-EX150", manufactured by Nikkiso) under the conditions of SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: spherical, and refractive index: 1.59.

[0078] (Aqueous dispersion of resin particles 2) A reaction vessel equipped with a stirrer was set in a hot water bath. 1,178 parts of water was placed in the reaction vessel, and the internal temperature was maintained at 70°C. 256.6 parts of styrene, 273.0 parts of acrylonitrile, and 16.4 parts of a reactive surfactant (trade name "ADEKA REASOAP SR-10", manufactured by ADEKA) were mixed to prepare a monomer mixture. 1.9 parts of potassium persulfate and 659 parts of water were mixed to prepare an aqueous solution of polymerization initiator 3. The monomer mixture and the aqueous solution of polymerization initiator 3 were dropped into the reaction vessel in parallel over 60 minutes. After the dropwise addition, stirring was continued to react for another 30 minutes to synthesize particles.

[0079] Then, an appropriate amount of 8 mol / L potassium hydroxide aqueous solution was added to the reaction vessel, and the pH of the liquid was adjusted to 8.5. Furthermore, 23.2 parts of CI Basic Red 1 (powder) and 5.8 parts of CI Basic Violet 11 (powder) were added, and the temperature was raised to 80°C. After that, the mixture was stirred for 2 hours to dye the resin particles with the fluorescent dye. Next, an appropriate amount of 8 mol / L potassium hydroxide aqueous solution was added to the reaction vessel, and the pH of the liquid was adjusted to 8.5. An appropriate amount of water was further added to obtain an aqueous dispersion of resin particles 2 with a resin particle content of 20.0%. The particle diameter of resin particles 2 (cumulative 50% particle diameter based on volume), measured in the same manner as resin particles 1, was 80 nm.

[0080] (Aqueous dispersion of resin particles 3) Polyester resin particles (polyester resin particles 1) were prepared with reference to the method described in JP 2020-50874 A. Except for using the prepared polyester resin particles, an aqueous dispersion of resin particles 3 colored with a basic dye and having a resin particle content of 20.0% was obtained in the same manner as the aqueous dispersion of resin particles 1 described above. The particle diameter (cumulative 50% particle diameter on a volume basis) of resin particles 3 measured in the same manner as resin particles 1 was 80 nm.

[0081] (Aqueous dispersion of resin particles 4) Instead of CI Basic Red 1 (powder) and CI Basic Violet 11 (powder), 29.0 parts of CI Disperse Red 58 (powder) were used. Except for this, an aqueous dispersion of resin particles 4 with a resin particle content of 20.0% was obtained in the same manner as the aqueous dispersion of resin particles 2 described above. The CI Disperse Red 58 used does not fall under the category of "basic dye exhibiting fluorescence". The particle diameter of resin particles 4 (cumulative 50% particle diameter based on volume), measured in the same manner as resin particles 1, was 80 nm.

[0082] <Preparation of dye aqueous solution> CI Basic Red 1 was dissolved in water at 80° C. to prepare an aqueous solution of CI Basic Red 1 (fluorescent dye content: 10.0%). Furthermore, CI Basic Violet 11 was dissolved in water at 80° C. to prepare an aqueous solution of CI Basic Violet 11 (fluorescent dye content: 10.0%). In addition, the concentration of a commercially available dye aqueous solution (product name "Projet Fast Black 2", Fujifilm) was adjusted to prepare an aqueous solution of Projet Fast Black 2 with a dye content of 10.0%.

[0083] <Preparation of pigment dispersion> (Pigment dispersion 1) A solution of 70.6 mmol of concentrated hydrochloric acid in 5.5 g of water was cooled to a temperature of 5°C, and 9.8 mmol of 4-aminophthalic acid was added. The container containing this solution was placed in an ice bath and the liquid was stirred to keep the solution at 10°C or less. A solution of 24.9 mmol of sodium nitrite in 9.0 g of water at 5°C was added to this. After stirring for another 15 minutes, 6.0 g of pigment was added under stirring. Carbon black (product name "Black Pearls 880", manufactured by Cabot) was used as the pigment. Then, the mixture was stirred for another 15 minutes to obtain a slurry. The obtained slurry was filtered with filter paper (product name "Standard Filter Paper No. 2", manufactured by Advantec), thoroughly washed with water, and dried in an oven at 110°C to obtain a self-dispersing pigment. The pigment content was adjusted using ion-exchanged water to obtain pigment dispersion 1. Pigment dispersion 1 contained a self-dispersing pigment in which a phthalic acid group having a sodium ion as a counter ion was bonded to the particle surface, and the pigment content was 10.0%.

[0084] (Pigment dispersion 2) A mixture was obtained by mixing 10.0 parts of pigment, 20.0 parts of an aqueous solution of a resin dispersant (resin (solid content) content 20.0%), and 70.0 parts of ion-exchanged water. Carbon black (trade name "Black Pearls 880", manufactured by Cabot) was used as the pigment. In addition, as the aqueous solution of the resin dispersant, a styrene-acrylic acid copolymer (weight average molecular weight 10,000, acid value 200 mgKOH / g), which is a water-soluble resin, was dissolved in ion-exchanged water using sodium hydroxide in an amount equimolar to the acid value. The obtained mixture was dispersed for 3 hours using a batch-type vertical sand mill, and then pressure-filtered with a microfilter (manufactured by Fujifilm) having a pore size of 1.2 μm. Next, ion-exchanged water was added to adjust the pigment content, and pigment dispersion liquid 2 was obtained. Pigment dispersion liquid 2 contained a pigment dispersed by a water-soluble resin (resin dispersant), and the pigment content was 10.0% and the water-soluble resin content was 4.0%.

[0085] <Preparation of acrylic resin aqueous solution> The types and amounts of monomers shown in Table 1 were polymerized by a conventional method to synthesize water-soluble acrylic resins 1 to 5, which are random copolymers. Water containing potassium hydroxide in an amount equimolar to the acid value was added to neutralize the anionic groups, and then an appropriate amount of water was further added to obtain an aqueous solution of each acrylic resin with a resin content of 10.0%. The obtained acrylic resin was dissolved in tetrahydrofuran to prepare a measurement sample, and the acid value was measured by potentiometric titration using an automatic potentiometric titrator (product name "AT510", manufactured by Kyoto Electronics Co., Ltd.) with a potassium hydroxide ethanol titrant. The weight average molecular weight in terms of polystyrene measured by GPC was 25,000 for each. The abbreviations in Table 1 are St: styrene, BzMA: benzyl methacrylate, nBA: n-butyl acrylate, and MAA: methacrylic acid.

[0086] TIFF2024000521000001.tif56170

[0087] <Preparation of aqueous solution of urethane resin> 41.9 parts of polypropylene glycol with a number average molecular weight of 2,000 was dissolved in methyl ethyl ketone. Then, 46.1 parts of isophorone isocyanate and 12.0 parts of dimethylolpropionic acid were added and reacted at 75 ° C for 1 hour to obtain a urethane prepolymer solution. The obtained urethane prepolymer solution was cooled to 60 ° C, and water containing potassium hydroxide equimolar to the acid value was added to neutralize the carboxylic acid group. It was cooled to 40 ° C, ion-exchanged water was added, and the mixture was emulsified by high-speed stirring with a homomixer. 2.1 parts of ethylenediamine was added, and a chain extension reaction was carried out at 30 ° C for 12 hours. After confirming that the isocyanate group was no longer present by FT-IR, the mixture was heated and reduced pressure to distill off methyl ethyl ketone, and an aqueous solution of urethane resin with a resin content of 20.0% was obtained. The weight average molecular weight of the urethane resin, measured in the same manner as the acrylic resin, was 30,000 and the acid value was 50 mgKOH / g.

[0088] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in the upper rows of Tables 2-1 to 2-3, thoroughly stirring, and then filtering under pressure using a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. In the tables, "hydantoin" is 1,3-bis(2-hydroxyethyl)-5,5-dimethylhydantoin. The lower rows of Tables 2-1 to 2-3 show the properties of the ink. The trade names of the surfactants used in preparing the inks are as follows: Surfynol 465 (trade name, manufactured by Evonik Operations GmbH): a nonionic hydrocarbon surfactant BYK3420, BYK348, BYK3456 (product names, manufactured by BYK): nonionic silicone surfactants Capstone FS-3100 (product name, manufactured by Chemours): a nonionic fluorosurfactant

[0089] TIFF2024000521000002.tif205170

[0090] TIFF2024000521000003.tif190170

[0091] TIFF2024000521000004.tif218170

[0092] <Evaluation> An inkjet recording device having the main components shown in FIG. 1 and incorporating an ink supply system having the configuration shown in FIG. 2 and a pressurization recovery mechanism including a sub-tank shown in FIG. 3 was prepared. This recording device is a serial type recording device in which a recording head 203 is incorporated and a recording unit 102 having a sub-tank 202 is mounted on a carriage 103. A tube (ink supply tube 104) made of a styrene-based thermoplastic elastomer and having an inner diameter of 2 mm and an outer diameter of 4 mm was used to connect the main tank 201 and the sub-tank 202. The ink capacity of the main tank was 150 mL, and the ink capacity of the sub-tank was 7 mL. In this example, the recording duty of a solid image recorded under the condition that two ink droplets with a mass of 5 ng per droplet are applied to a unit area of ​​1 / 600 inch x 1 / 600 inch is defined as 100%. Using this device, the following items were evaluated. In the present invention, in the evaluation criteria shown below, "AA", "A" and "B" were considered to be acceptable levels, and "C" was considered to be an unacceptable level. The evaluation results are shown in Table 3.

[0093] (Color development) The prepared ink was poured into the main tank of the inkjet recording device, and the ink was supplied to the sub-tank and recording head. After that, the pressure was monitored and adjusted to a specified pressure, and the recovery operation shown in Table 3 was carried out. After that, a solid image with a recording duty of 100% was recorded on a recording medium (glossy paper, product name "Canon Photo Paper Glossy Pro [Platinum Grade] PT-201", manufactured by Canon). After drying the recorded image for one day, a spectrophotometer (product name "X-Rite eXact" (M1 light source), manufactured by X-Rite) was used to measure the chroma (C * ), and lightness (L *) was measured. The color development of the image was evaluated according to the following evaluation criteria. In this example, the ink using the black color material did not exhibit fluorescence, so the color development was not evaluated. A: Saturation was 30 or more and brightness was 50 or more. C: Saturation was less than 30 or brightness was less than 50.

[0094] (Dischargeability after recovery operation) The prepared ink was poured into the main tank of the inkjet recording device, and the ink was supplied to the sub-tank and recording head. After that, the pressure was monitored and adjusted to a predetermined pressure, and the recovery operation shown in Table 3 was performed. After that, a solid image was recorded on the entire surface of an A4-sized plain paper (product name "GF-500", manufactured by Canon) with a recording duty of 50%. The recorded solid image was visually checked, and the ejection performance after the recovery operation was evaluated according to the evaluation criteria shown below. AA: There were no unevenness in the solid image. A: Unevenness was observed in an area of ​​5% or less of the total area of ​​the solid image. B: Unevenness was observed in an area exceeding 5% and not exceeding 10% of the total area of ​​the solid image. C: Unevenness was observed in an area exceeding 10% of the total area of ​​the solid image.

[0095] (Discharge recovery) The prepared ink was poured into the main tank of the inkjet recording device, and the ink was supplied to the sub-tank and the recording head. After that, the pressure was monitored and adjusted to a predetermined pressure, and the recovery operation shown in Table 3 was performed. Then, an evaluation pattern was recorded on A4-sized plain paper (product name "GF-500", manufactured by Canon) to check whether ink was normally ejected from each nozzle. As the evaluation pattern, a ruled line pattern having multiple ruled lines with different line widths in the conveying direction and width direction of the paper was used. A cycle was set in which a 1.6 cm x 5 cm solid image with a recording duty of 1% was recorded until the evaluation pattern became normal (normal ejection from all ejection ports was possible), and then a nozzle check pattern was recorded. Then, the ejection recovery property was evaluated according to the evaluation criteria shown below based on the number of sheets of the nozzle check pattern recorded. AA: The nozzle check pattern was restored to a normal state by printing one solid image. A: By printing two solid images, the nozzle check pattern was restored to a normal state. B: By printing three solid images, the nozzle check pattern was restored to a normal state. C: It took four or more solid images to be printed before the nozzle check pattern returned to a normal state.

[0096] TIFF2024000521000005.tif239170

[0097] In Reference Example 1, where a recovery operation was performed by suction, the flow of ink was weak, so no non-ejection occurred after the recovery operation. However, the recovery operation took a long time, and the amount of ink wasted by the recovery operation increased. In Reference Example 2, where a fluorescent dye that does not fall under the category of "basic dye that exhibits fluorescence" was used, the level of color development was insufficient. Also, in Reference Examples 3 to 6, where no fluorescent dye was used, no non-ejection occurred after the recovery operation, but the level of color development was insufficient.

Claims

1. An inkjet recording method comprising the steps of recording an image on a recording medium using an inkjet recording apparatus comprising: an aqueous ink; a recording head having an ejection port for ejecting the aqueous ink, including an ink channel through which the aqueous ink flows; and a recovery mechanism that applies pressure to the ink channel within the recording head to restore the ejection state of the aqueous ink from the ejection port, wherein the method includes the steps of recording an image on a recording medium using an inkjet recording apparatus, The aqueous ink contains resin particles dyed with a fluorescent basic dye and a water-soluble resin. The resin particles are formed from a resin having anionic group-containing units. An inkjet recording method characterized in that the water-soluble resin has an anionic group-containing unit.

2. The inkjet recording method according to claim 1, wherein the pressure applied to the ink channel is 20 kPa or more.

3. The inkjet recording method according to claim 1, wherein the pressure applied to the ink channel is 40 kPa or more.

4. The inkjet recording method according to claim 1, wherein the content (mass%) of the water-soluble resin in the aqueous ink is 0.1 times or more by mass ratio to the content (mass%) of the resin particles.

5. The inkjet recording method according to claim 1, wherein the content (mass%) of the water-soluble resin in the aqueous ink is 0.5 times or more by mass ratio to the content (mass%) of the resin particles.

6. The inkjet recording method according to any one of claims 1 to 5, wherein the water-soluble resin further comprises aromatic group-containing units.

7. The inkjet recording method according to any one of claims 1 to 5, wherein the resin particles are acrylic resin.

8. The inkjet recording apparatus further comprises a pump, The inkjet recording method according to claim 1, wherein pressure is applied to the ink channel in the recording head using the pump.

9. The inkjet recording method according to claim 8, wherein the recovery mechanism is a mechanism that uses the pump to apply pressure from the upstream side of the ink flow path in the recording head toward the discharge port to restore the discharge state of the aqueous ink from the discharge port.

10. The inkjet recording device further comprises an ink storage section, The inkjet recording method according to claim 8, wherein the pump is configured to be connectable to the ink storage section.

11. The inkjet recording method according to claim 10, wherein the recovery mechanism is a mechanism that applies pressure to the ink flow path in the recording head by applying pressure to the ink storage section using the pump, thereby restoring the discharge state of the aqueous ink from the discharge port.

12. The inkjet recording device further comprises a bag-shaped bag housed in the ink storage section, The inkjet recording method according to claim 11, wherein the recovery mechanism is a mechanism that uses the pump to pressurize and inject air into the bag, thereby applying pressure to the ink storage section, and thereby applying pressure to the ink flow path in the recording head, and restoring the ejection state of the aqueous ink from the ejection port.

13. The inkjet recording apparatus further comprises a first ink storage unit and a second ink storage unit which together with the recording head constitutes a recording unit, The inkjet recording method according to claim 1, wherein the first ink storage unit and the second ink storage unit are connected via an ink supply tube.

14. An inkjet recording apparatus comprising: an aqueous ink; a recording head having an ejection port for ejecting the aqueous ink, including an ink channel through which the aqueous ink flows; and a recovery mechanism that applies pressure to the ink channel within the recording head to restore the ejection state of the aqueous ink from the ejection port, The aqueous ink contains resin particles dyed with a fluorescent basic dye and a water-soluble resin. The resin particles are formed from a resin having anionic group-containing units. An inkjet recording apparatus characterized in that the water-soluble resin has an anionic group-containing unit.

Images