Inkjet recording method, inkjet recording device, and water-based ink

Abstract

This invention provides an inkjet recording method that enables more efficient recording of images with excellent opacity and scratch resistance, even when heated at low temperatures for a short time. [Solution] An inkjet recording method comprising the step of ejecting aqueous ink from an inkjet recording head and applying it to a recording medium. The aqueous ink is a white ink containing metal oxide particles, first resin particles, and second resin particles formed of crystalline resin, the glass transition temperature of the first resin particles is 50°C or higher, the onset temperature To(°C) of the maximum endothermic peak of the second resin particles is 50°C or higher and 80°C or lower, the endset temperature Te(°C) and onset temperature To(°C) of the maximum endothermic peak of the second resin particles satisfy the relationship in formula (1) below, and further comprising the step of heating the recording medium to which the aqueous ink has been applied to a temperature of To(°C) or higher than the onset temperature of the second resin particles. Te ≤ (To + 20) ... (1)

Description

Technical Field

[0001] The present invention relates to an inkjet recording method, an inkjet recording apparatus, and an aqueous ink.

Background Art

[0002] In recent years, papers, resin films, etc. have been used as recording media for advertisements and exhibits, and inkjet recording apparatuses are widely used to record images on these recording media. In order to record a clear color image on a transparent recording media, white ink is used in combination with black or basic color inks (hereinafter, black and basic color inks are also collectively referred to as "color inks" for convenience). Specifically, after performing a base treatment of previously applying white ink to a location including an area for recording an image on a transparent recording media, color ink is applied thereon to record an image. Also, an image is recorded by so-called backprinting, in which the application order of white ink and color ink is reversed. Note that titanium oxide is widely used as a coloring material constituting white ink because it is low cost and has high whiteness and hiding power, etc.

[0003] When recording an image using white ink on a recording media such as a resin film with low absorbency and transparency, an ink added with resin particles is used to fix metal oxide particles used as a coloring material on the recording media. And after applying an ink added with resin particles on the recording media, a method has been proposed in which heating is performed at a temperature higher than the glass transition temperature (Tg) of the resin particles to form a film of the resin particles and record an image (Patent Document 1).

[0004] On the other hand, it is known that sharp melting resins such as waxes and crystalline resins rapidly form a film when the temperature exceeds the melting point, that is, the onset temperature (To) measured by differential scanning calorimetry (DSC) analysis, and can form a film by heating at a lower temperature and for a shorter time than resins. And white inks containing such sharp melting resins have been proposed (Patent Documents 2 and 3).

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the case of the method proposed in Patent Document 1, when a resin with a high glass transition temperature is used, it is necessary to raise the maximum temperature reached during heat drying, and there is a problem that a long time is required for the process from recording to film formation (that is, printing throughput). On the other hand, if a resin with a low glass transition temperature (for example, 50°C or lower) is used, film formation can be achieved even when the maximum temperature reached during heat drying is lowered, so the printing throughput can be shortened. However, when an ink containing a resin with a low glass transition temperature is used, problems such as deterioration of characteristics such as the rub resistance of the image are likely to occur.

[0007] In addition, when the white ink proposed in Patent Documents 2 and 3 is used, the film formed of a resin with sharp meltability rapidly softens as it approaches the onset temperature To. For this reason, there is a problem that the rub resistance of the image is likely to decrease, such as the entire image collapsing at once due to the heat generated during rubbing.

[0008] Therefore, an object of the present invention is to provide an inkjet recording method capable of more efficiently recording an image excellent in concealability and rub resistance even by heating at a low temperature for a short time. Another object of the present invention is to provide an inkjet recording apparatus and an aqueous ink used in this inkjet recording method.

Means for Solving the Problems

[0009] In other words, according to the present invention, an inkjet recording method comprising the step of ejecting aqueous ink from an inkjet recording head and applying it to a recording medium, wherein the aqueous ink is a white ink containing metal oxide particles, first resin particles, and second resin particles formed of crystalline resin or wax, wherein the content (mass%) of the second resin particles contained in the aqueous ink is 0.05 times or more and 0.35 times or less in mass ratio to the total content (mass%) of the first resin particles and the second resin particles, and the total content (mass%) of the first resin particles and the second resin particles contained in the aqueous ink is the metal oxide particles An inkjet recording method is provided, characterized in that the mass ratio of the first resin particles to the content (mass%) is 0.3 times or more and 1.0 times or less, the glass transition temperature of the first resin particles is 50°C or higher, the onset temperature To(°C) of the maximum endothermic peak of the second resin particles in differential scanning calorimetry is 50°C or more and 80°C or less, the endset temperature Te(°C) and onset temperature To(°C) of the maximum endothermic peak of the second resin particles in differential scanning calorimetry satisfy the relationship of formula (1) below, and further comprising the step of heating the recording medium to which the aqueous ink has been applied to a temperature of To(°C) or higher than the onset temperature of the second resin particles. Te ≤ (To + 20) ... (1) [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an inkjet recording method that enables more efficient recording of images with excellent opacity and scratch resistance even by heating at a low temperature for a short time. Furthermore, according to the present invention, it is possible to provide an inkjet recording apparatus and an aqueous ink used in this inkjet recording method. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram illustrating one example of the image formation process. [Figure 2] This is a schematic diagram illustrating one example of the image formation process. [Figure 3]This is a schematic perspective view showing one embodiment of the inkjet recording apparatus of the present invention. [Figure 4] This is a schematic side view showing one embodiment of the inkjet recording apparatus of the present invention. [Modes for carrying out the invention]

[0012] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists dissociated as ions in the ink and reaction solution, but for convenience, it will be expressed as "contains a salt." Also, the aqueous ink and aqueous reaction solution for inkjet printers may be simply referred to as "ink" and "reaction solution." Unless otherwise specified, the physical properties are values ​​at room temperature (25°C) and normal pressure (1 atm). When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0013] The inventors investigated an inkjet recording method that could more efficiently record images with excellent opacity and scratch resistance even with only low-temperature, short-time heating. As a result, they found that by satisfying the following requirements (i) to (vii), it is possible to efficiently record images with excellent opacity and scratch resistance in a short time even with only low-temperature, short-time heating, leading to the present invention. (i) The ink is a white ink containing metal oxide particles, first resin particles, and second resin particles formed of crystalline resin or wax. (ii) The content (mass%) of the second resin particles contained in the ink is 0.05 times or more and 0.35 times or less in mass ratio to the total content (mass%) of the first and second resin particles. (iii) The total content (mass%) of the first resin particles and the second resin particles contained in the ink is 0.3 times or more and 1.0 times or less in mass ratio to the content (mass%) of the metal oxide particles. (iv) The glass transition temperature of the first resin particle is 50°C or higher. (v) The onset temperature To(°C) of the maximum endothermic peak of the second resin particle in differential scanning calorimetry (DSC) measurement is between 50°C and 80°C. (vi) The end-set temperature Te(°C) and on-set temperature To(°C) of the maximum endothermic peak of the second resin particle in differential scanning calorimetry satisfy the relationship (1): Te≦(To+20). (vii) The process includes the steps of ejecting ink from an inkjet recording head and applying it to a recording medium, and heating the ink-covered recording medium to a temperature equal to or greater than the onset temperature To (°C) of the second resin particles.

[0014] Figures 1 and 2 are schematic diagrams illustrating an example of the image formation process. As shown in Figure 1(a), when a recording medium coated with ink is heated, volatile components such as water and water-soluble organic solvents evaporate, causing the ink to dry. This forms a densely packed film of metal oxide particles 1, first resin particles 2, and second resin particles 3 in the ink. Subsequently, when the recording medium is heated to a temperature above the onset temperature (To) of the second resin particles (the temperature at which the second resin particles melt), as shown in Figure 1(b), the second resin particles 3 melt, generating molten resin or molten wax. The generated molten resin or molten wax begins to permeate the surfaces of the metal oxide particles 1 and the first resin particles 2. Further heating of the recording medium causes the first resin particles 2 to soften, and as shown in Figure 1(c), the molten resin or molten wax fills the gaps between the metal oxide particles 1 and the first resin particles 2, forming a film overall.

[0015] The mass ratio of the second resin particles contained in the ink is between 0.05 and 0.35 times the total mass ratio of the first and second resin particles. When the recording medium is heated to an onset temperature To (°C) or higher, the second resin particles melt rapidly and permeate the surface of the metal oxide particles 1 and the first resin particles as described above. If the mass ratio of the second resin particle content is less than 0.05 times the total mass ratio of the first and second resin particles, the amount of second resin particles that permeate the surface of the metal oxide particles and the first resin particles will be insufficient. As a result, the gaps between the particles will not be sufficiently filled, and the desired opacity will not be obtained. On the other hand, if the mass ratio of the second resin particle content is greater than 0.35 times the total mass ratio of the first and second resin particles, the abrasion resistance of the film will decrease and the desired abrasion resistance will not be obtained.

[0016] Furthermore, the desired scratch resistance and opacity can be obtained when the total mass content (%) of the first and second resin particles in the ink is between 0.3 and 1.0 times the mass content (%) of the metal oxide particles. If the total mass content (%) of the first and second resin particles is less than 0.3 times the mass content (%) of the metal oxide particles, the amount of resin in the film will be insufficient, reducing the strength of the film and preventing the desired scratch resistance from being achieved. On the other hand, if the total mass content (%) of the first and second resin particles is greater than 1.0 times the mass content (%) of the metal oxide particles, the amount of metal oxide particles in the film will be insufficient, preventing the desired opacity from being achieved.

[0017] As shown in Figure 2(a), when the particle size of the metal oxide particles 1 is small, they tend to aggregate in the reaction solution to which they are applied, forming aggregates 4. Since there are gaps inside the formed aggregates 4, the molten resin and molten wax present in the surrounding area are drawn into these gaps by capillary action. Average primary particle size D of the metal oxide particles 1 P0When the (nm) is 150 nm or less, the total amount of voids in the entire film is large, and because the voids are narrow, the capillary force also tends to increase, making it easier for molten resin or molten wax to be drawn into the voids. When molten resin or molten wax is drawn into these narrow voids, relatively large pores 5 with a diameter of about 200-300 nm are formed in the film, as shown in Figure 2(b). The refractive index (≒1.0) of the formed pores 5 is lower than that of the surrounding resin or metal oxide particles, so it is thought that it scatters light more strongly, and the opacity of the image is further improved.

[0018] <Inkjet recording method, inkjet recording device, and water-based ink> The present invention relates to an inkjet recording method comprising the step of ejecting ink from an inkjet recording head and applying it to a recording medium. The ink is a white ink containing metal oxide particles, first resin particles, and second resin particles formed of crystalline resin or wax. The content (mass%) of the second resin particles in the ink is 0.05 to 0.35 times the mass ratio of the total content (mass%) of the first and second resin particles. The total content (mass%) of the first and second resin particles in the ink is 0.3 to 1.0 times the mass ratio of the content (mass%) of metal oxide particles. The glass transition temperature of the first resin particles is 50°C or higher. The onset temperature To (°C) of the maximum endothermic peak of the second resin particles in differential scanning calorimetry is 50°C to 80°C. In differential scanning calorimetry, the end-set temperature Te(°C) and on-set temperature To(°C) of the maximum endothermic peak of the second resin particle satisfy the relationship given by equation (1) below. Furthermore, the inkjet recording method of the present invention further includes a step of heating the ink-coated recording medium to a temperature equal to or greater than the on-set temperature To(°C) of the second resin particle. The inkjet recording method of the present invention does not require a step of curing the image by irradiation with active energy rays or the like. Te ≤ (To + 20) ... (1)

[0019] The inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method which has a step of ejecting ink from an inkjet recording head and applying it to a recording medium, and is an apparatus that is suitably used in the above-described inkjet recording method.

[0020] Furthermore, the ink of the present invention is an aqueous ink used in an inkjet recording method that has a step of ejecting aqueous ink from an inkjet recording head and applying it to a recording medium, and is an ink that is suitably used in the above-mentioned inkjet recording method.

[0021] The inkjet recording method of the present invention (hereinafter also simply referred to as the "recording method") will be described in detail below.

[0022] (Inkjet recording device) Figure 3 is a schematic perspective view showing one embodiment of the inkjet recording apparatus of the present invention. Figure 4 is a schematic side view showing one embodiment of the inkjet recording apparatus of the present invention. As shown in Figures 3 and 4, the recording apparatus of this embodiment includes an inkjet recording head 1 that ejects ink. Examples of recording heads include recording heads that eject ink and reaction liquid by the action of mechanical energy, and recording heads that eject ink and reaction liquid by the action of thermal energy. Among these, recording heads that eject ink and reaction liquid by the action of thermal energy are preferred. A recording head that ejects ink and reaction liquid by the action of thermal energy is a thermal recording head that imparts thermal energy to the ink and reaction liquid by applying an electric pulse to an electrothermal conversion element, and ejects the ink and reaction liquid from the ejection port. It is preferable to include a mechanism (temperature control mechanism) that heats the aqueous ink ejected from the recording head and applied to the recording medium to a predetermined temperature. When a temperature control mechanism is included, it is preferable that the temperature of the ink ejected from the recording head be 35°C or higher and 70°C or lower.

[0023] It is preferable to apply ink to a unit area of ​​the recording medium by multi-pass recording, which is performed by dividing the process into multiple relative scans between the recording head and the recording medium. In particular, it is preferable to apply white ink and color ink to the unit area using different relative scans. This increases the time until the inks come into contact with each other, making it easier to suppress mixing. The unit area can be set to any area, such as one pixel or one band.

[0024] [Heating process] The recording method of the present invention includes a step of heating (heat treatment) a recording medium to which ink has been applied (heat step). In the heating step, the recording medium to which ink has been applied is heated to melt the second resin particles in the ink. This allows the image to be fixed to the recording medium. When the recording medium to which ink has been applied is heated, volatile components (solvents) in the ink, such as water and water-soluble organic solvents, evaporate, and an ink film is formed in which metal oxide particles, first resin particles, and second resin particles, which are solid components dispersed in the ink, are densely packed. Subsequently, the heated second resin particles melt to form a film. This allows the image to be fixed to the recording medium.

[0025] In the heating process, the ink is heated to a temperature above the onset temperature To (°C) of the second resin particles in order to melt the second resin particles. That is, heating temperature T H (°C) can be appropriately set according to the onset temperature To(°C) of the second resin particles. Specifically, the heating temperature T in the heating process H From the viewpoint of shortening the printing throughput, the heating temperature (°C) is preferably 50°C or higher, more preferably 70°C or higher, and particularly preferably around 80°C. H (°C) represents the highest temperature reached on the surface of the recording medium during the heating process. Heating temperature T HThe temperature in degrees Celsius (°C) can be measured using, for example, a contact thermometer that brings a thermocouple or the like into contact with the surface of the recording medium, or a non-contact infrared thermometer. In the embodiment described later, a non-contact infrared digital radiation temperature sensor (product name "FT-H20", manufactured by Keyence), not shown in the figure, was used to measure the surface temperature of the recording medium from a position 10 cm vertically above the surface of the recording medium.

[0026] By heat treatment, the second resin particles are melted, allowing the film to be formed at a lower temperature. Average primary particle diameter D of metal oxide particles P0 When the (nm) value is 150 nm or less, it is possible to record images containing relatively large pores with a diameter of approximately 200-300 nm.

[0027] Examples of heating means for the recording medium include known heating means such as heaters, air blowing means such as dryers, and means combining these. Examples of heating means include the above-mentioned heating means, air blowing means, and means combining these. Examples of heating methods include applying heat from the side (back side) opposite to the recording surface (ink application surface) of the recording medium with a heater, applying warm air or hot air to the recording surface of the recording medium, and heating from the recording surface or back side using an infrared heater. Multiple of these may also be combined. Furthermore, the recording surface or back side of the recording medium may be heated by bringing a heated component into contact with it. The duration of the heating process should be sufficient to melt the second resin particles. For example, when heating the recording medium with an air blowing means, the temperature of the airflow can be 80°C or higher and 120°C or lower.

[0028] The velocity (wind speed) of the airflow, such as warm air, is preferably between 1 m / s and 100 m / s. The temperature of the airflow can be measured using, for example, a K-type thermocouple thermometer. A specific measuring instrument is, for example, the "AD-5605H" (manufactured by A&D). If necessary, the airflow may be directed to the back surface of the recording medium, but it is preferable to direct the airflow to the front surface (recording surface) of the recording medium. The distance from the air-blowing device to the recording medium is preferably between 5 mm and 50 mm.

[0029] In the recording apparatus shown in Figures 3 and 4, a heater 25 supported by a frame (not shown) is positioned downstream in the sub-scanning direction A from the position where the recording head 1 reciprocates in the main scanning direction B. The recording medium P to which ink has been applied can be heated by the heater 25. Specific examples of the heater 25 include sheath heaters and halogen heaters. The heater 25 is covered by a heater cover 26. The heater cover 26 is a component that efficiently irradiates the recording medium P with the heat generated from the heater 25. Furthermore, the heater cover 26 also serves as a component that protects the heater 25. The recording medium P to which ink has been applied, ejected from the recording head 1, is wound up by a take-up spool 27 to form a roll-shaped winding medium 24. The highest temperature reached on the surface of the recording medium P is the temperature near the exit of the heater cover 26, measured by a radiation thermometer (not shown).

[0030] [Reaction solution application process] The inkjet recording method of the present invention preferably further includes a reaction liquid application step of applying an aqueous reaction liquid containing a reactant that reacts with the ink to a recording medium. The reaction liquid application step is preferably carried out before the step of applying ink to the recording medium (ink application step) or in parallel with the ink application step. Further, when the reaction liquid application step is included, it is preferable to carry out a heating step after the reaction liquid application step. When the reaction liquid is applied to the recording medium, as shown in FIGS. 1(a) and 2(a), the metal oxide particles 1, the first resin particles 2, and the second resin particles 3 in the ink can be aggregated more densely. Thereby, the molten resin generated by melting the second resin particles 3 can be more surely impregnated into the surfaces of the metal oxide particles 1 and the first resin particles 2. Furthermore, when the average primary particle diameter D P0 (nm) of the metal oxide particles 1 is 150 nm or less, an image including pores 5 as shown in FIG. 2(b) can be easily formed.

[0031] [Recording medium] The type of the recording medium for recording an image is not particularly limited, and any recording medium may be used. Among them, since a white ink capable of recording an image such as white with excellent hiding property is used, it is preferable to use a recording medium other than white such as a transparent film, a translucent film, and colored paper. That is, as the recording medium, it is preferable to use a non-absorbent recording medium. A non-absorbent recording medium (low to non-absorbent recording medium) has a water absorption amount of 0 mL / m 1 / 2 or more and 10 mL / m 2 or less from the start of contact to 30 msec in the Bristow method. The Bristow method is described in the "Liquid Absorbency Test Method for Paper and Paperboard" of JAPAN TAPPI Paper Pulp Test Method No. 51. An inkjet recording medium (such as glossy paper and matte paper) having a coat layer (ink receiving layer) formed of inorganic particles or ordinary paper having no coat layer is an "absorbent recording medium" in which the above water absorption amount exceeds 10 mL / m 2 .

[0032] ​​As low-to-non-absorbent recording media, the following can be used: plastic films; recording media in which a plastic film is bonded to the recording surface of a substrate; and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp. Among these, plastic films are preferred, and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp are also preferred.

[0033] (ink) The ink is an aqueous white inkjet ink containing metal oxide particles, first resin particles, and second resin particles. White inks include those that can record (form) a white image even if they do not appear white in their ink state. White refers to a lightness (L). * ) and chromaticity (a * , b * ) are, respectively, 70 ≤ L * ≤100, -4.5 ≤a * ≤ 2, and -6 ≤ b * This means it is within the range of ≤2.5. The components that make up the ink will be explained in detail below.

[0034] [Metal oxide particles] The ink contains metal oxide particles. The content of metal oxide particles in the ink (volume %) is preferably 1.2% to 16.3% by volume, based on the total volume of the ink. It is even more preferably 1.8% to 12.7% by volume, and particularly preferably 1.5% to 5.0% by volume. If the content of metal oxide particles is less than 1.5% by volume, sufficient voids for melting and permeating the second resin particles may not be formed, which may reduce the amount of voids formed and decrease the image opacity. On the other hand, if the content of metal oxide particles exceeds 5.0% by volume, the viscosity of the ink tends to increase, which may slightly increase the likelihood of ejection failure and decrease the image opacity.

[0035] Metal oxide particles are typically dispersed in ink in the form of secondary aggregates (secondary particles) where two or more primary particles are aggregated. The average primary particle size D of the metal oxide particles to be included in the ink.P0 The (nm) is preferably 250 nm or less, more preferably 150 nm or less, and particularly preferably 50 nm or less. Average primary particle diameter D of metal oxide particles P0 The lower limit of (nm) is not particularly limited, but it is preferably 5 nm or greater. The primary particle diameter of metal oxide particles can be measured by observing the particles using a scanning electron microscope. The average primary particle diameter D of the metal oxide particles is then... P0 (nm) is the average value of the primary particle diameters of multiple particles (e.g., 100 particles).

[0036] Furthermore, in this specification, "average particle size D P "(nm)" represents the cumulative 50% particle size in the volume-based particle size distribution. P This means "(nm)". Cumulative 50% particle size D in volume-based particle size distribution. P (nm)(Average particle diameter D P (nm) is the diameter of the particle that reaches 50% of the total volume of the measured particles in the particle diameter integration curve, starting from the smallest particle diameter. P The particle size distribution (nm) can be measured using a particle size distribution analyzer based on dynamic light scattering. Possible measurement conditions include, for example, SetZero: 30 seconds, Number of measurements: 3, Measurement time: 180 seconds, Shape: Non-spherical. A particle size distribution analyzer based on dynamic light scattering (e.g., product name "UPA-EX150," manufactured by Nikkiso) can be used. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those mentioned above.

[0037] The metal oxide particles are preferably at least one selected from the group consisting of titanium dioxide, calcium carbonate, calcium phosphate, barium sulfate, zirconium oxide, and silicon dioxide. The surface of the titanium dioxide particles may be coated with inorganic oxides such as alumina, silica, zinc oxide, and zirconia; or organic substances such as polyols. By using titanium dioxide with a coated surface as metal oxide particles, it is expected that the photocatalytic activity will be suppressed and the dispersibility will be improved. There are three crystalline forms of titanium dioxide: rutile, anatase, and brookite. Among these, it is preferable to use rutile titanium dioxide, which has low photocatalytic activity. Industrial methods for producing titanium dioxide include the sulfuric acid method and the chlorine method. Titanium dioxide produced by either method can be used.

[0038] The titanium dioxide particle content (mass%) in the ink is preferably 5.0% by mass or more and 45.0% by mass or less, and more preferably 7.0% by mass or more and 38.0% by mass or less, based on the total mass of the ink.

[0039] Average primary particle size D of titanium dioxide P0 The (nm) is preferably 250 nm or less, and more preferably 30 nm or less. Also, the average particle size D of titanium dioxide. P The (nm) wavelength is preferably 250 nm or less, more preferably 150 nm or less, and particularly preferably 5 nm or more and 50 nm or less.

[0040] As for calcium carbonate, it is preferable to use cubic light calcium carbonate because it has relatively uniform particle size and shape, and can form a film with appropriate voids.

[0041] The zirconium oxide is of fine particle grade, with an average primary particle size (D P0The nanoparticle size is preferably 250 nm or less, more preferably 150 nm or less, and particularly preferably 5 nm to 50 nm. Examples of commercially available fine particle grade zirconium oxide include Nissan Chemical's "Nano-Use Series."

[0042] Silicon dioxide can be synthesized by the Stober method, and the average primary particle size can be controlled by adjusting the content of the organic solvent. Average primary particle size D of silicon dioxide P0 The wavelength is preferably 250 nm or less, more preferably 150 nm or less, and particularly preferably 5 nm to 50 nm.

[0043] [First resin particle] The ink contains first resin particles. When the liquid medium in the ink applied to the recording medium evaporates, the metal oxide particles, the first resin particles, and the second resin particles become closely adhered to each other. The total content (mass%) of the first resin particles and the second resin particles in the ink is preferably 2.5% by mass or more and 17.0% by mass or less, and more preferably 2.5% by mass or more and 14.0% by mass or less, based on the total mass of the ink. The glass transition temperature (Tg) of the first resin particles is preferably 50°C or higher. By using first resin particles with a glass transition temperature (Tg) of 50°C or higher, the effect of improving the scratch resistance of the image can be further enhanced.

[0044] Examples of resins that form the first resin particles include vinyl chloride resins, styrene resins, urethane resins, acrylic resins, and polyester resins. Among these, acrylic resins, polyester resins, and urethane resins are preferred from the viewpoint of inkjet properties. If the first resin particles are formed from resins other than those mentioned above, the ink ejection may become somewhat unstable, and as a result, the effect of improving the opacity of the image may be slightly reduced. Among these, the resin that forms the first resin particles is preferably an acrylic resin, and more preferably an acrylic resin that contains units derived from styrene.

[0045] As for acrylic resins, those having hydrophilic units and hydrophobic units as constituent units are preferred. In particular, resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one selected from the group consisting of monomers having aromatic rings and (meth)acrylic acid ester monomers are preferred. Especially preferred are resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene. Because these resins readily interact with metal oxide particles, they can be suitably used as resin dispersants for dispersing metal oxide particles.

[0046] Hydrophilic units are units that have hydrophilic groups, such as anionic groups. Hydrophilic units can be formed, for example, by polymerizing hydrophilic monomers that have hydrophilic groups. Specific examples of hydrophilic monomers that have hydrophilic groups include acidic monomers having carboxylic acid groups, such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; anionic monomers such as anhydrides and salts of these acidic monomers; and so on. Cationic ions that constitute salts of acidic monomers include lithium, sodium, potassium, ammonium, and organic ammonium ions. Hydrophobic units are units that do not have hydrophilic groups, such as anionic groups. Hydrophobic units can be formed, for example, by polymerizing hydrophobic monomers that do not have hydrophilic groups, such as anionic groups. Specific examples of hydrophobic monomers include monomers having aromatic rings, such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and so on.

[0047] Urethane resins can be obtained, for example, by reacting polyisocyanate with a polyol. Alternatively, they may be obtained by further reacting a chain extender. Examples of olefin resins include polyethylene and polypropylene.

[0048] Polyester resins are typically composed of units derived from polyhydric alcohols and units derived from polyhydric carboxylic acids. Examples of polyhydric alcohols include dihydric to tetrahydric polyhydric alcohols. Examples of polyhydric alcohols include polyhydric alcohols having aliphatic groups, polyhydric alcohols having aromatic groups, and sugar alcohols.

[0049] Examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol (1,2-ethanediol), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,3-propanediol, 1,4-butanediol, benzenediol, and 2,2-bis(4-hydroxyphenyl)propane (bisphenol A); trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; and tetrahydric alcohols such as pentaerythritol. Oligomers (low-molecular-weight polymers with a molecular weight of 1,000 or less) can also be used as polyhydric alcohols. It is preferable to use dihydric or trihydric polyhydric alcohols because it facilitates the adjustment of the weight-average molecular weight of the polyester resin.

[0050] Examples of polycarboxylic acids include divalent to tetravalent polycarboxylic acids. Examples of polycarboxylic acids include polycarboxylic acids having aliphatic groups, polycarboxylic acids having aromatic groups, and nitrogen-containing polycarboxylic acids. Examples of polycarboxylic acids include divalent carboxylic acids such as glutaric acid, adipic acid, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; trivalent carboxylic acids such as trimellitic acid; and tetravalent carboxylic acids such as ethylenediaminetetraacetic acid. Furthermore, oligomers (low molecular weight polymers with a molecular weight of 1,000 or less) can also be used as polycarboxylic acids. It is preferable to use divalent or trivalent polycarboxylic acids because it is easy to adjust the weight-average molecular weight and acid value of the polyester resin.

[0051] In this specification, "resin particles" refers to resins that exist in an insoluble state in the aqueous medium of the ink, and more specifically, resins that can exist in the aqueous medium in a state in which particles whose particle size can be measured by dynamic light scattering are formed. In contrast, "water-soluble resin" refers to resins that exist in a dissolved state in the aqueous medium of the ink.

[0052] Whether a resin qualifies as "resin particles" can be determined according to the following method. First, a liquid containing the resin to be evaluated is prepared and diluted with pure water to a resin content of approximately 1.0% to prepare a sample. Then, the particle size of the resin in the sample is measured by dynamic light scattering. If particles with a particle size are measured, the resin is determined to be "resin particles" (i.e., a "water-dispersible resin"). On the other hand, if no particles with a particle size are measured, the resin is determined not to be "resin particles" (i.e., a "water-soluble resin"). The measurement conditions in this case can be, for example, SetZero: 30 seconds, Number of measurements: 10 times, Measurement time: 120 seconds, Shape: Spherical, Refractive index: 1.5, Density: 1.0.

[0053] As a particle size distribution measuring device, a particle size analyzer using the dynamic light scattering method (for example, product name "UPA-EX150," manufactured by Nikkiso) can be used. Of course, the particle size distribution measuring device and measurement conditions used are not limited to those mentioned above. The first resin particles do not need to contain a colorant.

[0054] [Second resin particle] The ink contains second resin particles formed from crystalline resin or wax. The onset temperature To (°C) of the maximum endothermic peak of the second resin particles in differential scanning calorimetry (DSC) measurement is between 50°C and 80°C. Furthermore, the endset temperature Te (°C) and onset temperature To (°C) of the maximum endothermic peak of the second resin particles in differential scanning calorimetry satisfy the relationship given by equation (1) below. Te ≤ (To + 20) ... (1)

[0055] Crystalline resins are resins that, after being heated and melted, solidify as the temperature drops, forming a crystalline region where molecules are regularly arranged. Crystalline resins typically have two temperature characteristics: a glass transition temperature (Tg) and a melting point. The melting point is a physical property value corresponding to the onset temperature (To) of the maximum endothermic peak in differential scanning calorimetry. The glass transition temperature (Tg) is usually 60°C or more lower than the onset temperature (To).

[0056] Whether the resin constituting the resin particles is a crystalline resin can be determined by measuring the degree of crystallinity of the resin using a differential scanning calorimeter. If no melting peak is observed using a differential scanning calorimeter, the resin can be determined to be amorphous. On the other hand, if a melting peak is observed, the resin can be determined to be crystalline. In the case of crystalline resins, the heat of fusion can be determined from the peak area, and the degree of crystallinity can be calculated from the ratio of the determined heat of fusion to the heat of fusion of a perfect crystal with 100% crystallinity calculated by theoretical calculation.

[0057] The crystalline resin is preferably at least one selected from the group consisting of crystalline polyester and crystalline urethane. The crystalline resin can be used in the form of an aqueous dispersion. As the aqueous dispersion of the crystalline resin, an aqueous dispersion of polyester resin or an aqueous dispersion of polyurethane resin can be used. Examples of aqueous dispersions of polyester resin include KA3556 (To=64℃, Te=81℃), KA5071s (To=60℃, Te=80℃), and KT8803 (To=56℃, Te=70℃) (all manufactured by Unitika), which are listed below by trade name.

[0058] The wax may be either a natural wax or a synthetic wax. Examples of waxes include rice wax, paraffin wax, microcrystalline wax, montan wax, polyethylene wax, and Fischer-Tropsch wax. In particular, it is preferable that the wax be at least one selected from the group consisting of rice wax and paraffin wax.

[0059] The wax can be used in aqueous dispersion form. Commercially available aqueous dispersions of rice wax include XAQUASPROUT-0009, XAQUASPROUT-0015, and XAQUASPROUT-0016 (all with To=73℃, Te=82℃, manufactured by Nippon Seiro), under the following product names.

[0060] Commercially available aqueous dispersions of paraffin wax include the following products: EMUSTAR-1155 (To=54℃, Te=71℃, manufactured by Nippon Seiro); AQUACER 497 (To=60℃, Te=73℃, manufactured by Bic Chemie); SELOSOL R-582 (To=70℃, Te=80℃, manufactured by Chukyo Oil & Fat Co., Ltd.).

[0061] Whether or not the second resin particles melt during the heating process can be easily determined, for example, by observing the cross-sections formed by cutting the recording medium before and after the heating process using a scanning electron microscope. The second resin particles do not need to contain a colorant.

[0062] In the ink, the content of the second resin particles (mass%) relative to the total content (mass%) of the first and second resin particles is preferably 5% by mass or more and 35% by mass or less. Furthermore, the total content (volume%) of the first and second resin particles in the ink is preferably 1.3 to 5.0 times, and more preferably 2.0 to 4.0 times, relative to the content (volume%) of metal oxide particles. If the above volume ratio exceeds 5.0 times, the ink tends to become highly viscous, which can easily lead to dispensing problems.

[0063] When the metal oxide particles are titanium dioxide, the total content (mass%) of the first and second resin particles in the ink is preferably 0.3 to 1.0 times the mass ratio of the titanium dioxide content (mass%). It is even more preferably 0.4 to 0.6 times.

[0064] [Water-soluble resin] The ink may further contain a water-soluble resin that can dissolve in an aqueous medium. The water-soluble resin can be added to the ink (i) to stabilize the dispersion state of the metal oxide, i.e., as a resin dispersant or its auxiliary agent. It can also be added to the ink (ii) to improve various properties of the recorded image. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. The amount of water-soluble resin to be contained in the ink should be set considering the total amount of first and second resin particles. Specifically, the content (mass%) of water-soluble resin in the ink is preferably 0.1% by mass or more and 10.0% by mass or less, and more preferably 0.5% by mass or more and 8.0% by mass or less, based on the total mass of the ink. If the content of water-soluble resin is too high, the ink tends to become highly viscous, which can easily lead to dispensing problems.

[0065] Examples of water-soluble resins include acrylic resins, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred, and acrylic resins containing units derived from (meth)acrylic acid or (meth)acrylate are even more preferred.

[0066] As for acrylic resins, those having hydrophilic units and hydrophobic units as constituent units are preferred. In particular, resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one selected from the group consisting of monomers having aromatic rings and (meth)acrylic acid ester monomers are preferred. Especially preferred are resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene. Because these resins readily interact with metal oxide particles, they can be suitably used as resin dispersants for dispersing metal oxide particles.

[0067] Hydrophilic units are units that have hydrophilic groups, such as anionic groups. Hydrophilic units can be formed, for example, by polymerizing hydrophilic monomers that have hydrophilic groups. Specific examples of hydrophilic monomers that have hydrophilic groups include acidic monomers having carboxylic acid groups, such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; anionic monomers such as anhydrides and salts of these acidic monomers; and so on. Cationic ions that constitute salts of acidic monomers include lithium, sodium, potassium, ammonium, and organic ammonium ions. Hydrophobic units are units that do not have hydrophilic groups, such as anionic groups. Hydrophobic units can be formed, for example, by polymerizing hydrophobic monomers that do not have hydrophilic groups, such as anionic groups. Specific examples of hydrophobic monomers include monomers having aromatic rings, such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and so on.

[0068] The acid value of the water-soluble resin is preferably 100 mg KOH / g or more and 250 mg KOH / g or less. The weight-average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less.

[0069] [Aqueous medium] The ink is an aqueous ink containing at least water as an aqueous medium. The ink may contain an aqueous medium which is water or a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass%) in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. The water-soluble organic solvent content (mass%) in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable in inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used.

[0070] [Other ingredients] The ink may further contain water-soluble organic compounds that are solid at 25°C, such as urea and its derivatives, trimethylolpropane, and trimethylolethane. The content (by mass) of the water-soluble organic compounds in the ink is preferably 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the ink. In addition to the above components, the ink may also contain various other components as needed. Examples of other components include various additives such as surfactants, defoamers, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, fungicides, antioxidants, and reduction inhibitors. However, it is preferable that the ink does not contain the reactants included in the reaction solution.

[0071] [Ink properties] The ink is an aqueous ink for use in inkjet systems. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the ink at 25°C is preferably 20 mN / m or more and 60 mN / m or less. The viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25°C is preferably 7.0 or more and 9.5 or less, and more preferably 8.0 or more and 9.5 or less.

[0072] (Reaction solution) The recording method of the present invention preferably further comprises a reaction solution application step of applying an aqueous reaction solution containing a reactant that reacts with aqueous ink to a recording medium. The components used in the reaction solution will be described in detail below.

[0073] [Reactive agent] The reaction solution reacts with the ink upon contact, causing the components in the ink (components with anionic groups, such as resins and metal oxide particles) to aggregate, and contains a reactant. Examples of reactants include organic acids, polyvalent metal salts, and cationic resins.

[0074] The reaction solution containing organic acids has buffering capacity in the acidic range (pH less than 7.0, preferably pH 2.0 to 5.0), which efficiently converts the anionic groups of components present in the ink into acidic forms and aggregates them. Examples of organic acids include monocarboxylic acids and their salts such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrole carboxylic acid, furanic acid, picolinic acid, nicotinic acid, thiophene carboxylic acid, levulinic acid, and coumaric acid; dicarboxylic acids and their salts or hydrogen salts such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid, sebacic acid, phthalic acid, malic acid, and tartaric acid; tricarboxylic acids and their salts or hydrogen salts such as citric acid and trimellitic acid; and tetracarboxylic acids and their salts or hydrogen salts such as pyromellitic acid. The content (by mass) of organic acids in the reaction solution is preferably 1.0% by mass or more and 50.0% by mass or less, based on the total mass of the reaction solution.

[0075] Polyvalent metal salts are compounds composed of two or more valent metal ions (polyvalent metal ions) and anions. In a reaction solution, polyvalent metal salts dissociate into polyvalent metal ions, which then aggregate pigments and other materials dispersed by the anionic groups in the ink. Examples of polyvalent metal ions include Ca 2+ Cu 2+ Ni 2+ Mg 2+ Sr2+ Ba 2+ , and Zn 2+ Divalent metal ions such as Fe 3+ , Cr 3+ , Y 3+ , and Al 3+ Examples of trivalent metal ions include Cl. - , Br - , I - , - ClO2 - ClO3 - ClO4 - NO2 - NO3 - SO4 2- CO3 2- , HCO3 - , PO4 3- HPO4 2- , and H2PO4 - Inorganic anions such as HCOO - , (COO - )2, COOH(COO - ), CH3COO - CH3CH(OH)COO - , C2H4(COO - )2, C6H5COO - , C6H4(COO - )2, and CH3SO3 - Examples of organic anions include the following.

[0076] Specific examples of polyvalent metal salts include calcium carbonate such as heavy calcium carbonate and light calcium carbonate, calcium nitrate, calcium chloride, calcium sulfate, magnesium sulfate, calcium hydroxide, magnesium chloride, magnesium carbonate, barium sulfate, barium chloride, zinc carbonate, zinc sulfide, aluminum silicate, calcium silicate, magnesium silicate, copper nitrate, calcium acetate, magnesium acetate, aluminum acetate, aluminum sulfate, calcium methanesulfonate, calcium lactate, magnesium lactate, calcium propionate, calcium acetate, calcium pantothenate, and calcium gluconate. These polyvalent metal salts may contain water of hydration. The content (mass%) of polyvalent metal salts in the reaction solution is preferably 1.0% by mass or more and 20.0% by mass or less, based on the total mass of the reaction solution.

[0077] Cationic resins have cationic moieties in their structure and aggregate pigments and other materials dispersed in ink through the action of anionic groups. Examples of cationic resins include resins having primary to tertiary amine structures and resins having quaternary ammonium salt structures. Specifically, examples include resins having vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensate structures. To improve solubility in the reaction solution, cationic resins can be used in combination with acidic compounds, or the cationic resins can be subjected to quaternization treatment. The content (mass%) of cationic resin in the reaction solution is preferably 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the reaction solution.

[0078] [Aqueous medium] The reaction solution is an aqueous reaction solution containing at least water as the aqueous medium. Examples of aqueous mediums used in the reaction solution include those similar to the aforementioned aqueous mediums that can be incorporated into ink.

[0079] [Other ingredients] The reaction solution may contain various other components as needed. Examples of other components include those similar to those mentioned above that can be included in the ink.

[0080] [Physical properties of the reaction solution] The reaction solution is an aqueous reaction solution applied to an inkjet system. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the reaction solution at 25°C is preferably 20 mN / m or more and 60 mN / m or less. The viscosity of the reaction solution at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the reaction solution at 25°C is preferably 5.0 or more and 9.5 or less, and more preferably 6.0 or more and 9.0 or less. [Examples]

[0081] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0082] <Preparation of metal oxide particles> Aqueous dispersions of metal oxide particles of the types shown in Table 1 (metal oxide dispersions) were prepared.

[0083] TIFF2026090912000001.tif46170

[0084] For metal oxide particle 1 in Table 1, the content of metal oxide particle 1 was adjusted to 30.0% by adding an appropriate amount of deionized water or by evaporating the liquid component, thereby obtaining an aqueous dispersion of metal oxide particle 1. For metal oxide particles 2 and 4 in Table 1, 10.0 parts of each particle, 0.8 parts of DISPERBYK-154, and 100 parts of 0.1 mm zirconia beads were mixed and dispersed in a bead mill for 6 hours. After filtering off the zirconia beads, an appropriate amount of deionized water was added as needed to obtain aqueous dispersions of metal oxide particle 2 and metal oxide particle 4 with a metal oxide particle content of 30.0%.

[0085] For metal oxide particles 3 in Table 1, the dispersion was prepared as follows: First, 10.0 parts of calcium carbonate (Viscal), 1.0 part of DISPERBYK-154, and 100 parts of 0.1 mm zirconia beads were mixed and dispersed in a bead mill for 6 hours. After that, the zirconia beads were filtered off, and an appropriate amount of deionized water was added to obtain an aqueous dispersion of metal oxide particles 3 with a metal oxide particle content of 30.0%.

[0086] Average primary particle diameter (D) of metal oxide particles P0 The average primary particle diameter (D) was measured using the following method. First, a scanning electron microscope (product name "S-4700", manufactured by Hitachi High-Tech) was used to photograph the sample at a magnification of 100,000x. Next, the diameter of the circle circumscribing 100 primary particles of metal oxide was measured, and the average value was taken as the "average primary particle diameter (D)". P0 )” was also stated. In addition, the average particle size of metal oxide particles (D P The particle size was measured using a dynamic light scattering particle size analyzer (product name "UPA-EX150", manufactured by Nikkiso). The average particle size of the resin particles (cumulative 50% particle size in the volume-based particle size distribution), which will be described later, was also measured using the above particle size analyzer. In Table 1, the refractive index of each titanium oxide particle was between 2.5 and 2.8. The refractive index of particle 3 was between 1.5 and 2.2.

[0087] <Preparation of the first resin particles> Aqueous dispersions of the first type of resin particles shown in Table 2 were prepared.

[0088] TIFF2026090912000002.tif86170

[0089] The first resin particle 1 was synthesized by a soap-free emulsion polymerization method. Specifically, 400 g of deionized water, 12 g of styrene, 11.5 g of methyl methacrylate, and 0.044 g of sodium styrene sulfonate were placed in a 500 mL separatory flask and stirred at 50 rpm while the temperature was raised to 70°C with nitrogen gas bubbling. After stirring for 30 minutes, 0.8 g of polymerization initiator (potassium peroxodisulfate, manufactured by Fujifilm Wako Pure Chemical Industries) dissolved in 20 g of deionized water was added, and the mixture was reacted at 70°C for 8 hours with stirring at 200 rpm to form resin particles, obtaining an aqueous dispersion of the first resin particle 1.

[0090] The glass transition temperature (Tg) of the first resin particle was measured using a differential scanning calorimeter (DSC). Specifically, 2 mg of resin particles obtained by drying an aqueous dispersion of resin particles under reduced pressure at 80°C was placed in an aluminum container and sealed to prepare a sample for measurement. The prepared sample was subjected to thermal analysis using a differential scanning calorimeter (product name "DSC-2500", manufactured by TA instruments) according to the temperature program shown below. In this specification, the glass transition temperature of the resin particle is defined as follows: That is, the temperature at the intersection of a straight line extended from two points on the low-temperature side of the heating curve (horizontal axis: temperature, vertical axis: heat) in the temperature program (3) below to the high-temperature side, and a tangent line drawn at the point where the slope of the step-like change portion of the curve is maximum is determined. The temperature obtained in this way was defined as the "glass transition temperature (Tg) of the resin particle". [Temperature Program]: (1) Increase the temperature from 20°C to 200°C at a rate of 10°C / min. (2) Defrost from 200°C to -50°C at a rate of 5°C / min (3) Heat from -50°C to 200°C at a rate of 10°C / min.

[0091] <Preparation of the second resin particle> Aqueous dispersions of the second type of resin particles shown in Table 3 were prepared.

[0092] TIFF2026090912000003.tif67170

[0093] The second resin particle 3 was synthesized by the following method. 300 g of sebaciic acid and 170 g of 1,6-hexanediol were mixed and heated to 190°C over 1 hour while stirring. After adding 0.01 g of tetrabutyl orthotitanate, polymerization was carried out by raising the internal temperature to 240°C over 6 hours while distilling off the generated water, obtaining a crystalline polyester resin. 50 g of the obtained polyester resin was placed in a 300 mL four-necked flask equipped with a nitrogen inlet tube, stirrer, and thermocouple. After adding 50 g of methyl ethyl ketone, the polyester resin was dissolved by heating to 40°C under a nitrogen stream. 1.2 g of triethylamine was further added and stirred for 1 hour, then 106 g of deionized water was added dropwise at a rate of 7.5 g / min and stirred for 30 minutes. Next, the methyl ethyl ketone was removed under reduced pressure to obtain an aqueous dispersion of the second resin particle 3 with a resin particle content of 20.0%. The average particle size (D) of the second resin particle 3 E The wavelength was 190 nm. Furthermore, the onset temperature (To) of the second resin particle 3, measured using a differential thermal analyzer, was 67°C, and the endset temperature (Te) was 77°C.

[0094] <Ink preparation> Each component (unit: mass%) shown in Tables 4-1 to 4-3 was mixed. After adding potassium hydroxide to adjust the pH to a range of 8 to 9, each ink was prepared by pressure filtration through a 3.0 μm pore size microfilter (manufactured by Fujifilm). In Tables 4-1 to 4-3, "Acetylenel E100" is the trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals.

[0095] TIFF2026090912000004.tif194170

[0096] TIFF2026090912000005.tif194170

[0097] TIFF2026090912000006.tif207170

[0098] <Preparation of reaction solution> Reaction solution 1 was obtained by mixing 10.0 parts of magnesium sulfate heptahydrate, 2.0 parts of glycerin, 7.0 parts of ethylene glycol, 0.5 parts of a nonionic surfactant, and an amount of deionized water totaling 100 parts of the components. The nonionic surfactant used was "Acetylenel E100" (manufactured by Kawaken Fine Chemicals).

[0099] <Rating> Each ink obtained as described above was evaluated for the following items. In this invention, "AA," "A," and "B" were considered acceptable levels in the evaluation criteria for each item shown below, and "C" was considered an unacceptable level. The evaluation results are shown in Table 5.

[0100] (Image recording) An inkjet recording device (product name "PIXUS PRO-10S", manufactured by Canon) equipped with a recording head that ejects liquid using thermal energy was prepared. This inkjet recording device is defined as having a recording duty cycle of 100% when recording an image under the condition that 8 ink droplets with a mass of 3.5 ng each are applied to a unit area of ​​1 / 600 inch x 1 / 600 inch. Reaction solution 1 and the inks shown in Tables 4-1 to 4-3 were filled into cartridges and set in the above inkjet recording device. Using this inkjet recording device, ink was ejected from the lower half of the recording head in the longitudinal direction, and reaction solution 1 was applied to the recording medium to record an image (50 mm x 50 mm) with a recording duty cycle of 400% on the recording medium. The recording duty cycle of reaction solution 1 was set to 40%. As the recording medium, a PET film (product name "LLRPCF1372", manufactured by Sakurai) cut to A4 size was used. This PET film was measured from the start of contact 30 msec as measured by the Bristow method. 1 / 2 The amount of water absorbed up to 0 mL / m³ is 0 mL / m³. 2 More than 10mL / m 2 It falls within the following range.

[0101] The transport speed of the recording medium was adjusted so that the time required to dry the leading edge of the recording medium in the transport direction from the upstream end to the downstream end of the heater cover 26 (Figures 3 and 4) was 1 minute. Inside the heater cover 26, hot air was blown at a maximum airflow speed of 20 m / s to dry the image. The airflow speed of the hot air was adjusted so that the temperature of the recorded recording medium downstream of the heater cover 26 reached the heating temperature (°C) shown in Tables 4-1 to 4-3. The temperature of the recorded recording medium was measured using a radiation thermometer (FT-H10, manufactured by Keyence).

[0102] (Film forming property) After leaving the recording medium on which the image was recorded at room temperature (25°C) for 30 minutes, the image surface was lightly wiped with a black cloth. The surface of the black cloth used to wipe the image surface was observed, and the film-forming properties of the ink were evaluated according to the evaluation criteria shown below. A: No white clumps originating from metal oxide particles were found adhering to the surface of the black cloth. C: White clumps, originating from metal oxide particles, were found adhering to the surface of the black cloth.

[0103] (Concealing ability) The opacity of the recorded images was measured and calculated according to a method compliant with ISO 2471:2008, and the opacity of the images was evaluated according to the evaluation criteria shown below. In ISO 2471:2008, opacity test paper (white board and black board, manufactured by TP Giken, with inspection certificate from the Japan Paint Inspection Association) is placed on the back of the paper to be tested, and the reflectance is measured, and the opacity is calculated from the following formula (A). Concealment rate (%) = (R0 / R ∞ ) × 100 ···(A) R0: Reflectance measured with a black board placed behind it. R ∞ Reflectance measured with a white board placed behind it. AA: The concealment rate was 60% or higher. A: The concealment rate was between 55% and 60%. B: The concealment rate was between 45% and 55%. C: The concealment rate was less than 45%.

[0104] (Abrasion resistance) A friction test was conducted using a Japan Society for the Promotion of Science (JSPS) type abrasion resistance tester (manufactured by Tester Sangyo Co., Ltd.) conforming to JIS L0849, with a white friction cloth (cotton) specified in JIS L0803, applying a load of 600g to the image surface and performing 150 back-and-forth cycles. After the friction test, the image was visually inspected, and its abrasion resistance was evaluated according to the evaluation criteria shown below. AA: Abrasion marks were observed in the image after 300 back-and-forth passes, but no abrasion marks were observed in the image after 150 back-and-forth passes. A: Abrasion marks were observed in the image after 150 back-and-forth passes, but no abrasion marks were observed in the image after 50 back-and-forth passes. B: Scratch marks were observed in the image after 50 round trips, but the white background of the recording medium was not visible. C: After 50 round trips, abrasion marks were observed in the image, and the white background of the recording medium was visible.

[0105] TIFF2026090912000007.tif232170

[0106] This embodiment includes the following methods and configurations. (Method 1) An inkjet recording method comprising the step of ejecting aqueous ink from an inkjet recording head and applying it to a recording medium, The aqueous ink is a white ink containing metal oxide particles, first resin particles, and second resin particles formed of crystalline resin or wax. The content (mass%) of the second resin particles contained in the aqueous ink is such that, in terms of mass ratio, it is 0.05 times or more and 0.35 times or less the total content (mass%) of the first resin particles and the second resin particles. The total content (mass%) of the first resin particles and the second resin particles contained in the aqueous ink is such that the mass ratio to the content (mass%) of the metal oxide particles is 0.3 times or more and 1.0 times or less. The glass transition temperature of the first resin particle is 50°C or higher. The onset temperature To(°C) of the maximum endothermic peak of the second resin particle in differential scanning calorimetry is between 50°C and 80°C. In differential scanning calorimetry, the end-set temperature Te(°C) and on-set temperature To(°C) of the maximum endothermic peak of the second resin particle satisfy the following relationship (1): Furthermore, the inkjet recording method is characterized by comprising the step of heating the recording medium to which the aqueous ink has been applied to a temperature equal to or greater than the onset temperature To (°C) of the second resin particles. Te ≤ (To + 20) ... (1) (Method 2) The crystalline resin is at least one selected from the group consisting of crystalline polyester and crystalline urethane. The inkjet recording method according to Method 1, wherein the wax is at least one selected from the group consisting of rice wax and paraffin wax. (Method 3) The inkjet recording method according to Method 1 or 2, wherein the total content (volume %) of the first resin particles and the second resin particles contained in the aqueous ink is 1.3 times or more and 5.0 times or less in volume ratio to the content (volume %) of the metal oxide particles. (Method 4) The average primary particle diameter D of the metal oxide particles P0 An inkjet recording method according to any one of methods 1 to 3, wherein (nm) is 150 nm or less. (Method 5) The inkjet recording method according to any one of Methods 1 to 4, wherein the metal oxide particles are at least one selected from the group consisting of titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, zirconium oxide, and silicon dioxide. (Method 6) The inkjet recording method according to any one of Methods 1 to 5, further comprising a reaction solution application step of applying an aqueous reaction solution containing a reactant that reacts with the aqueous ink to the recording medium. (Configuration 1) An inkjet recording apparatus used in an inkjet recording method which has a step of ejecting aqueous ink from an inkjet recording head and applying it to a recording medium, The aqueous ink is a white ink containing metal oxide particles, first resin particles, and second resin particles formed of crystalline resin or wax. The content (mass%) of the second resin particles contained in the aqueous ink is such that, in terms of mass ratio, it is 0.05 times or more and 0.35 times or less the total content (mass%) of the first resin particles and the second resin particles. The total content (mass%) of the first resin particles and the second resin particles contained in the aqueous ink is such that the mass ratio to the content (mass%) of the metal oxide particles is 0.3 times or more and 1.0 times or less. The onset temperature To(°C) of the maximum endothermic peak of the second resin particle in differential scanning calorimetry is between 50°C and 80°C. In differential scanning calorimetry, the end-set temperature Te(°C) and on-set temperature To(°C) of the maximum endothermic peak of the second resin particle satisfy the following relationship (1): The glass transition temperature of the first resin particle is 50°C or higher. The inkjet recording apparatus is characterized in that the inkjet recording method further comprises a step of heating the recording medium to which the aqueous ink has been applied to a temperature equal to or greater than the onset temperature To(°C) of the second resin particles. Te ≤ (To + 20) ... (1) (Configuration 2) An aqueous ink used in an inkjet recording method which has a step of ejecting aqueous ink from an inkjet recording head and applying it to a recording medium, A white ink containing metal oxide particles, first resin particles, and second resin particles formed of crystalline resin or wax. The content (mass%) of the second resin particles is 0.05 times or more and 0.35 times or less in mass ratio to the total content (mass%) of the first resin particles and the second resin particles. The total content (mass%) of the first resin particles and the second resin particles is 0.3 times or more and 1.0 times or less in mass ratio to the content (mass%) of the metal oxide particles. The onset temperature To(°C) of the maximum endothermic peak of the second resin particle in differential scanning calorimetry is between 50°C and 80°C. In differential scanning calorimetry, the end-set temperature Te(°C) and on-set temperature To(°C) of the maximum endothermic peak of the second resin particle satisfy the following relationship (1): The glass transition temperature of the first resin particle is 50°C or higher. The water-based ink is characterized in that the inkjet recording method further comprises a step of heating the recording medium to which the water-based ink has been applied to a temperature equal to or greater than the onset temperature To(°C) of the second resin particles. Te ≤ (To + 20) ... (1)

Claims

1. An inkjet recording method comprising the step of ejecting aqueous ink from an inkjet recording head and applying it to a recording medium, The aqueous ink is a white ink containing metal oxide particles, first resin particles, and second resin particles formed of crystalline resin or wax. The content (mass%) of the second resin particles in the aqueous ink is 0.05 times or more and 0.35 times or less in mass ratio to the total content (mass%) of the first resin particles and the second resin particles. The total content (mass%) of the first resin particles and the second resin particles contained in the aqueous ink is 0.3 times or more and 1.0 times or less in mass ratio to the content (mass%) of the metal oxide particles. The glass transition temperature of the first resin particle is 50°C or higher. The onset temperature To (°C) of the maximum endothermic peak of the second resin particle in differential scanning calorimetry is 50°C or higher and 80°C or lower. In differential scanning calorimetry, the end-set temperature Te (°C) and on-set temperature To (°C) of the maximum endothermic peak of the second resin particle satisfy the following relationship (1): Furthermore, the inkjet recording method is characterized by comprising the step of heating the recording medium to which the aqueous ink has been applied to a temperature equal to or greater than the onset temperature To (°C) of the second resin particles. Te≦(To+20)...(1)

2. The crystalline resin is at least one selected from the group consisting of crystalline polyester and crystalline urethane. The inkjet recording method according to claim 1, wherein the wax is at least one selected from the group consisting of rice wax and paraffin wax.

3. The inkjet recording method according to claim 1, wherein the total content (volume %) of the first resin particles and the second resin particles contained in the aqueous ink is 1.3 times or more and 5.0 times or less in volume ratio to the content (volume %) of the metal oxide particles.

4. The average primary particle diameter D of the metal oxide particles Ｐ０ The inkjet recording method according to claim 1, wherein the (nm) is 150 nm or less.

5. The inkjet recording method according to any one of claims 1 to 4, wherein the metal oxide particles are at least one selected from the group consisting of titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, zirconium oxide, and silicon dioxide.

6. Furthermore, the inkjet recording method according to any one of claims 1 to 4, further comprising a reaction solution application step of applying an aqueous reaction solution containing a reactant that reacts with the aqueous ink to the recording medium.

7. An inkjet recording apparatus used in an inkjet recording method that includes a step of ejecting aqueous ink from an inkjet recording head and applying it to a recording medium, The aqueous ink is a white ink containing metal oxide particles, first resin particles, and second resin particles formed of crystalline resin or wax. The content (mass%) of the second resin particles in the aqueous ink is 0.05 times or more and 0.35 times or less in mass ratio to the total content (mass%) of the first resin particles and the second resin particles. The total content (mass%) of the first resin particles and the second resin particles contained in the aqueous ink is 0.3 times or more and 1.0 times or less in mass ratio to the content (mass%) of the metal oxide particles. The onset temperature To (°C) of the maximum endothermic peak of the second resin particle in differential scanning calorimetry is 50°C or higher and 80°C or lower. In differential scanning calorimetry, the end-set temperature Te (°C) and on-set temperature To (°C) of the maximum endothermic peak of the second resin particle satisfy the following relationship (1): The glass transition temperature of the first resin particle is 50°C or higher. The inkjet recording apparatus is characterized in that the inkjet recording method further comprises a step of heating the recording medium to which the aqueous ink has been applied to a temperature equal to or greater than the onset temperature To (°C) of the second resin particles. Te≦(To+20)...(1)

8. A water-based ink used in an inkjet recording method that includes a step of ejecting water-based ink from an inkjet recording head and applying it to a recording medium, A white ink containing metal oxide particles, first resin particles, and second resin particles formed of crystalline resin or wax. The content (mass%) of the second resin particles is 0.05 times or more and 0.35 times or less in mass ratio to the total content (mass%) of the first resin particles and the second resin particles. The total content (mass%) of the first resin particles and the second resin particles is 0.3 times or more and 1.0 times or less in mass ratio to the content (mass%) of the metal oxide particles. The onset temperature To (°C) of the maximum endothermic peak of the second resin particle in differential scanning calorimetry is 50°C or higher and 80°C or lower. In differential scanning calorimetry, the end-set temperature Te (°C) and on-set temperature To (°C) of the maximum endothermic peak of the second resin particle satisfy the following relationship (1): The glass transition temperature of the first resin particle is 50°C or higher. The water-based ink is characterized in that the inkjet recording method further comprises the step of heating the recording medium to which the water-based ink has been applied to a temperature equal to or greater than the onset temperature To (°C) of the second resin particles. Te≦(To+20)...(1)

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