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

Abstract

This invention provides an inkjet recording method that allows for the recording of images with excellent opacity while using water-based ink with excellent resistance to settling. [Solution] An inkjet recording method comprising, in this order, an ink application step of applying ink to a recording medium, and a drying step of drying the recording medium to which the ink has been applied. The ink contains particles, resin particles, and a first water-soluble organic solvent whose boiling point is higher than that of water, and the average primary particle diameter of the particles is 150 nm or less. The resin particles include first resin particles whose glass transition temperature in a dry state is 50°C or higher, and whose glass transition temperature in the first water-soluble organic solvent is less than 50°C. The glass transition temperature or melting point of the particles is higher than the glass transition temperature of the first resin particles in a dry state. In the drying step, the recording medium is dried at a temperature below the glass transition temperature of the first resin particles in a dry state to melt the first resin particles and create voids.

Description

[Technical Field]

[0001] This invention relates to an inkjet recording method, an inkjet recording apparatus, and an aqueous ink. [Background technology]

[0002] In recent years, the application of inkjet recording methods to fields such as commercial and industrial printing has been explored. In these fields, white ink is used when recording white images on non-white recording media such as colored paper, or when recording white images on recording media such as transparent or translucent films as a base for inks of a different color than white ink. Conventionally, white pigments such as titanium dioxide have been mainly used as colorants for white inks from the standpoint of material stability and cost.

[0003] However, the density of titanium dioxide is particularly high compared to the materials used in inks of colors other than white ink. Therefore, the density difference between titanium dioxide and the liquid components that make up the ink becomes large, leading to the problem of it being prone to sedimentation in the ink. In particular, if titanium dioxide with a larger particle size is used or the titanium dioxide content is increased in order to improve the opacity and whiteness of the recorded image, the titanium dioxide becomes even more prone to sedimentation. A white ink containing rutile-type titanium dioxide with an average particle size of 300 nm or more and urethane resin has been proposed as an ink that can record images with excellent whiteness and is easy to redisperse even if the pigment has settled (Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2013-060513 [Overview of the project] [Problems that the invention aims to solve]

[0005] The settling velocity V of particles in ink can be calculated using the following formula (A) (Stokes' formula). V={g(ρ S -ρ)d 2} / 18μ···(A) d: Particle size g:Gravity acceleration ρ S : Particle density ρ: Density of the dispersed medium μ: Viscosity of the dispersion medium

[0006] According to Stokes' equation, the sedimentation velocity V increases in proportion to the square of the particle diameter; that is, the larger the particle diameter, the easier it is for the particles to settle. Titanium dioxide has a higher density than other common materials used in inks, and therefore settles quickly. For this reason, the titanium dioxide used as a pigment in the white ink proposed in Patent Document 1 was relatively prone to settling.

[0007] On the other hand, in images recorded with ink containing titanium dioxide, which has small particle sizes, visible light is easily transmitted without scattering. Therefore, as the particle size decreases, the scattering intensity decreases rapidly, and the opacity of the image tends to decrease. In other words, there is a trade-off relationship between the particle settling velocity and the opacity of the recorded image.

[0008] Therefore, an object of the present invention is to provide an inkjet recording method that can record images with excellent opacity while using an aqueous ink with excellent sedimentation resistance. 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 problem]

[0009] That is, according to the present invention, there is provided an inkjet recording method for recording an image by applying an aqueous ink to a recording medium, comprising an ink application step of applying the aqueous ink to the recording medium, and a drying step of drying the recording medium to which the aqueous ink has been applied, in this order. The aqueous ink contains particles, resin particles, and a water-soluble organic solvent containing a first water-soluble organic solvent having a boiling point higher than that of water. The average primary particle diameter D P (nm) of the particles is 150 nm or less, and the resin particles have a glass transition temperature Tg Rd (°C) in the dry state of 50°C or higher, and the resin particles include first resin particles having a glass transition temperature Tg Rs (°C) in the first water-soluble organic solvent of less than 50°C. The glass transition temperature Tg P (°C) or melting point Tm P (°C) of the particles is higher than the glass transition temperature Tg Rd (°C) of the first resin particles in the dry state. In the drying step, the recording medium is dried at a temperature of the glass transition temperature Tg Rd (°C) or lower of the first resin particles in the dry state to melt the first resin particles and generate voids. An inkjet recording method is provided.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an inkjet recording method capable of recording an image with excellent concealability while using an aqueous ink having excellent sedimentation resistance. Further, according to the present invention, an inkjet recording apparatus and an aqueous ink used in this inkjet recording method can be provided.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic diagram for explaining an example of the image recording process. [Figure 2] It is a schematic diagram for explaining an example of the image recording process. [Figure 3] It is a perspective view schematically showing an 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 this invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, water-based inkjet inks and water-based reaction solutions may be simply referred to as "ink" and "reaction solution," respectively. Unless otherwise specified, physical properties are values ​​at room temperature (25°C) and normal pressure (1 atm). In this invention, for convenience, the density of the water-based ink will be set to 1 g / cm³. 3 Treat as (1g / mL).

[0013] The inventors investigated an inkjet recording method that can record images with excellent opacity while using ink with excellent settling resistance. As a result, they found that by satisfying the requirements (i) to (vi) below, it is possible to record images with excellent opacity while using ink with excellent settling resistance, leading to the present invention. (i) The process includes, in this order, an ink application step of applying ink to a recording medium and a drying step of drying the recording medium to which the ink has been applied. (ii) The ink contains a water-soluble organic solvent which includes particles, resin particles, and a first water-soluble organic solvent whose boiling point is higher than that of water. (iii) Mean primary particle size D of the particles P The (nm) value is 150 nm or less. (iv) The glass transition temperature Tg of the resin particles in a dry state Rd The temperature (°C) is 50°C or higher, and the glass transition temperature Tg in the first water-soluble organic solvent is Rs It contains first resin particles whose temperature (°C) is less than 50°C. (v) Glass transition temperature Tg of the particle P (°C) or melting point Tm P (°C) is the glass transition temperature Tg of the first resin particles in a dry state. Rd Higher than (°C). (vi) In the drying process, the recording medium is subjected to the glass transition temperature Tg of the first resin particles in the dry state. Rd The first resin particles are dried at a temperature below (°C) to melt them and create voids.

[0014] Figures 1 and 2 are schematic diagrams illustrating an example of the image recording process. When ink is applied to the recording medium, as shown in Figure 1, the liquid component evaporates and the ink dries, forming an ink film in which particles 1 and first resin particles 2 are densely packed. Since the ink contains a first water-soluble organic solvent whose boiling point is higher than that of water, water evaporates preferentially from the liquid component, and the ink film becomes rich in the first water-soluble organic solvent. Subsequently, the glass transition temperature Tg of the first resin particles 2 in the dry state... Rd The image (recording medium) is dried at a temperature of (°C) or lower. During drying, the resin generated by the melting of the first resin particles 2 penetrates into the voids formed by the multiple particles 1, and voids 4 are formed where the first resin particles 2 were located (Figure 2). At this time, the glass transition temperature Tg of the particles P (°C) or melting point Tm P (°C) is the glass transition temperature Tg of the first resin particles in a dry state. Rd (°C) is higher than the drying temperature T D (°C) represents the glass transition temperature Tg of the first resin particle in its dry state. Rd The temperature is below (°C). Therefore, particle 1 does not melt during the drying process. As the amount of the first water-soluble organic solvent in the ink film decreases during the drying process, the glass transition temperature Tg of the first resin particles, which had been lowered by the action of the water-soluble organic solvent, rises, and the resin produced by the melting of the first resin particles 1 hardens, increasing the strength of the ink film. In addition, the resin produced by the melting of the first resin particles penetrates into the voids formed by multiple particles 1, forming a binder 3 which is a mixture of particle 1 and melted resin. Here, the average primary particle diameter D of particle 1 is PSince the (nm) is 150 nm or less, visible light is hardly scattered by particle 1. However, low refractive index air is present in the vacancy 4. Therefore, the refractive index of vacancy 4 is relatively lower than that of binder 3. Under these conditions, incident light is scattered due to the difference in refractive index between binder 3 and vacancy 4. Therefore, it is possible to record highly opaque images without using components that tend to settle, such as titanium dioxide with large particle sizes.

[0015] As described above, it is necessary to melt the first resin particles through a drying process. For example, the glass transition temperature Tg of the first resin particles in the first water-soluble organic solvent. Rs If (°C) is higher than the drying temperature of the recording medium, the first resin particles will not melt. As a result, scattering due to the refractive index difference between the binder 3 and the pores 4 does not occur, and highly opaque images cannot be recorded. Also, as described above, the ink film will begin to dry with the first water-soluble organic solvent still present. Therefore, the glass transition temperature Tg of the first resin particles in the dry state is affected. Rd If drying is performed at a temperature higher than (°C), the first resin particles may begin to melt before a dense ink film is formed in which the particles and first resin particles are packed together. In this case, the particles become dispersed in the resin generated by the melting of the first resin particles, and the particles do not become the "skeleton of the voids," so no voids are formed. Furthermore, if drying is performed at a temperature that causes even the particles to melt during the drying process, not only the first resin particles but also the particles melt, and no voids are formed. As a result, the above-mentioned scattering does not occur, and it is not possible to record images with high opacity. Note that the scattering of light caused by the difference in refractive index between the binder and the voids is easily visible with bright white ink and can significantly improve opacity, but the scattering of light is relatively less visible with inks of colors other than white ink.

[0016] As described above, the ink contains a water-soluble organic solvent, including a first water-soluble organic solvent whose boiling point is higher than that of water. When the liquid components in the ink evaporate, water evaporates before the first water-soluble organic solvent, which has a higher boiling point than water. As the amount of water decreases, the concentration of the first water-soluble organic solvent relatively increases. Glass transition temperature Tg in the first water-soluble organic solventRs The first resin particles, whose temperature (°C) is less than 50°C, have a glass transition temperature (Tg) in the dry state during the drying process. Rd When the temperature drops below (°C), swelling occurs due to the first water-soluble organic solvent. In other words, as the concentration of the first water-soluble organic solvent in the liquid component relatively increases, the glass transition temperature of the first resin particles decreases, making it easier for the resin particles to change to a glassy state. As the glass transition temperature of the first resin particles decreases, the glass transition temperature Tg of the first resin particles in the dry state decreases. Rd It changes to a glassy state even at temperatures lower than (°C). In this way, the first resin particles change to a glass transition temperature Tg in their dry state. Rd (°C)2 or its melting point T M It can melt even at drying temperatures lower than (°C). Therefore, the glass transition temperature Tg in the dry state is low. Rd Even if (°C) is 50°C or higher, the glass transition temperature Tg in the first water-soluble organic solvent Rs By keeping the temperature (°C) below 50°C, it is possible to record highly opaque images while keeping the energy required for drying low. However, if an ink is used that contains an excess of a water-soluble organic solvent relative to the first resin particles, such that the glass transition temperature of the solvent is below 50°C when coexisting with the first resin particles, pores may not be formed. This is thought to be because some of the first resin particles melt before an ink film is formed in which the particles and the first resin particles are densely packed.

[0017] As shown by Stokes' equation (Equation (A)), the smaller the particle size, the slower the sedimentation. Therefore, the mean primary particle size D P By using particles with a relatively small particle size of 150 nm or less (nm), sedimentation is slowed, resulting in an ink with excellent sedimentation resistance. Average primary particle size D of particles PWhen the (nm) is greater than 150 nm, scattering of visible light is more likely to occur, which improves opacity, but also accelerates sedimentation, resulting in a lack of sedimentation resistance. Furthermore, as the particles become larger, when the image layer is formed, it is difficult for the first resin particles to be uniformly distributed around the particles as shown in Figure 1, making it impossible to record images with high opacity.

[0018] <Inkjet recording method, inkjet recording device, and water-based ink> The present invention relates to an inkjet recording method that records an image by ejecting aqueous ink from an inkjet recording head and applying it to a recording medium. The present invention relates to an ink application step of applying aqueous ink to a recording medium, and a drying step of drying the recording medium to which the aqueous ink has been applied, in that order. The aqueous ink contains a water-soluble organic solvent which includes particles, first resin particles, and a first water-soluble organic solvent whose boiling point is higher than that of water. The average primary particle diameter D of the particles is also specified. P The (nm) is 150 nm or less. Furthermore, the resin particles have a glass transition temperature Tg in the dry state. Rd The temperature (°C) is 50°C or higher, and the glass transition temperature Tg in the first water-soluble organic solvent is Rs It contains first resin particles whose temperature (°C) is less than 50°C. In addition, the glass transition temperature Tg of the particles is also included. P (°C) or melting point Tm P (°C) represents the glass transition temperature Tg of the first resin particles in a dry state. Rd (°C) is higher. And, in the drying process, the recording medium is subjected to the glass transition temperature Tg of the first resin particles in their dry state. Rd The first resin particles are dried at a temperature below (°C) to melt them and create voids.

[0019] The inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method in which aqueous ink is ejected from an inkjet recording head and applied to a recording medium to record an image, and is an apparatus suitably used in the above-described recording method. In the present invention, it is not necessary to cure the image by irradiation with active energy rays or the like.

[0020] Furthermore, the aqueous ink of the present invention is an ink used in an inkjet recording method in which aqueous ink is ejected from an inkjet recording head and applied to a recording medium to record an image. It is an ink that is preferably used in the above-described recording method.

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

[0022] Figure 3 is a schematic perspective view showing one embodiment of the inkjet recording apparatus of the present invention. Figure 4 is a side view of the recording apparatus shown in Figure 3. The recording apparatus of the embodiments shown in Figures 3 and 4 includes an inkjet recording head 22 that ejects ink. The recording head 22 may be equipped with a mechanism (temperature control mechanism) for heating the ink ejected from the recording head. If a temperature control mechanism is provided, the heating temperature of the ink ejected from the recording head is preferably 35°C or higher and 70°C or lower.

[0023] The inkjet recording apparatus shown in Figure 3 is capable of so-called multi-pass recording, in which ink is applied to a unit area of ​​the recording medium by multiple relative scans between the recording head and the recording medium. The unit area can be set to any area, such as one pixel or one band. When recording an image using an ink (white ink) containing particles, first resin particles, and first water-soluble organic solvent, in addition to an ink of a different color from the white ink, it is preferable to apply the white ink and the different colored ink using different relative scans.

[0024] (drying process) The recording method of the present invention includes a drying step of drying a recording medium to which ink has been applied. In the drying step, the recording medium to which ink has been applied is dried, causing the first resin particles in the ink to melt. This allows an image including voids created by melting to be fixed to the recording medium. In the ink, the particles behave as solids, but the first resin particles are affected by the glass transition temperature (glass transition temperature Tg in the dry state) of the resin particles themselves due to the influence of the coexisting first water-soluble organic solvent.Rd The effective glass transition temperature is lower compared to (°C). Therefore, during the ink drying process, the first resin particles behave like a low-viscosity fluid.

[0025] When an ink-coated recording medium is dried, as drying progresses, liquid components in the ink, such as water and water-soluble organic solvents, evaporate, forming an ink film in which solid particles and first resin particles that were dispersed in the ink are densely packed. Subsequently, the first resin particles, which behave as a low-viscosity fluid, penetrate into the voids formed by the multiple particles by capillary action. As a result, voids are formed where the first resin particles were located, and the resin generated by the melting of the first resin particles penetrates into the voids formed by the multiple particles. This forms a binder, which is a mixture of particles and resin, and an image containing voids can be fixed to the recording medium. As drying progresses further, the glass transition temperature Tg (°C) of the resin that has penetrated between the particles rises, and the glass transition temperature Tg in the dry state Rd The temperature returns to (°C). As a result, the viscosity of the resin melted by the first resin particles increases, which enhances the strength of the ink film and improves the scratch resistance of the image. The voids are formed when the resin generated by the melting of the first resin particles penetrates into the gaps formed by multiple particles. They are formed by replacing the areas where resin particles were present with voids, and are therefore different from voids formed by the expansion or foaming of resin particles.

[0026] In the drying process, the glass transition temperature Tg of the first resin particles in the dry state. Rd The recording medium is dried at a temperature of (°C) or lower to melt the first resin particles. The drying temperature is the glass transition temperature Tg of the first resin particles in the first water-soluble organic solvent. RsThe temperature can be set according to (°C). Specifically, the drying temperature in the drying process is preferably 50°C or lower, more preferably 40°C or lower. The drying temperature is preferably 20°C or higher, more preferably 25°C or higher, and particularly preferably 30°C or higher. The drying temperature refers to the highest temperature reached by the surface of the recording medium during the drying process. The drying temperature 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, the temperature on the surface of the recording medium was measured from a position 10 cm vertically upward from the surface of the recording medium using a product name "Non-contact infrared thermometer digital radiation temperature sensor FT-H20" (manufactured by Keyence).

[0027] The drying process melts the first resin particles, creating voids, which in turn allows for the recording of an image containing these voids. The drying process may be performed alone or in combination with other processes. Examples of drying means for the recording medium include known heating means such as heaters, blowing means such as hair dryers, and combinations thereof. Examples of drying methods include applying heat from the side (back side) opposite to the recording surface (ink application surface) of the recording medium using a heater, or blowing air onto the recording surface of the recording medium. Another example is drying using an infrared heater from the recording surface (ink application surface) or the back side of the recording medium. A combination of these methods may also be used. Furthermore, drying may be performed by bringing a heated component into contact with the recording surface or back side of the recording medium.

[0028] From the viewpoint of efficiently eliminating the liquid component in the ink, the drying process is preferably carried out by blowing air onto the recording medium. When blowing air onto the recording medium, it is even more preferable to blow air onto the surface of the recording medium from the viewpoint of efficiency. The time of the drying process is not particularly limited as long as the first resin particles can be melted. For example, when the drying process is carried out by blowing air, the temperature of the recording medium is the glass transition temperature Tg of the first resin particles in the dry state. RdThe wind temperature should be set within a range of (°C) or less. Specifically, it is preferable to set the wind temperature to 20°C or more and 60°C or less, and more preferably to 25°C or more and 50°C or less.

[0029] The recording method involves recording the glass transition temperature (Tg) of the first resin particles in their dry state after the drying process. Rd The process may include a heating step that involves heating to a temperature exceeding (°C). The heating means can be the same as the drying means.

[0030] In the recording apparatus shown in Figures 3 and 4, a blower 25 supported by a frame (not shown) is positioned downstream in the sub-scanning direction A from the position where the recording head 22 reciprocates in the main scanning direction B. The ink-coated recording medium 1 can be dried by the blower 25. The blower 25 is covered by a blower cover 26. The blower cover 26 is a component that protects the blower 25. The blower 25 may also have a function to heat the air it blows. The ink-coated recording medium 1 ejected from the recording head 22 is wound up by a take-up spool 27 to form a roll-shaped winding medium 24.

[0031] Prior to the drying process, it is preferable to further include a step of forming an ink film in which particles and first resin particles are densely packed, as shown in Figure 1. By including such a step, it becomes possible to more reliably penetrate the voids formed by multiple particles, and it becomes easier to create an image containing voids as shown in Figure 2. That is, it is preferable that the inkjet recording method further includes a reaction solution application step of applying an aqueous reaction solution containing a reactant that reacts with the ink to the recording medium. When the reaction solution is applied to the recording medium together with the ink, the ink particles and first resin particles can be efficiently aggregated, so that an ink film in which particles and first resin particles are densely packed can be formed. Details of the reaction solution will be described later. It is preferable to perform the reaction solution application step prior to the ink application step. In other words, it is preferable to perform the steps in the order of reaction solution application step, ink application step, drying step, and heating step. Also, when blowing air onto the recording medium, it is preferable to blow air onto the surface (recording surface) of the recording medium from the viewpoint of drying efficiency.

[0032] The drying process is preferably carried out immediately following the ink application process. If the ink film is dried by airflow while liquid components of the ink remain on the surface of the recording medium and thickening due to evaporation has not progressed sufficiently, the image may become distorted. For this reason, the airflow speed is preferably 1 m / s to 100 m / s. The temperature of the air, such as hot air, can be measured using a K-type thermocouple thermometer. A specific measuring instrument is, for example, the "AD-5605H" (manufactured by A&D). If necessary, the air may be directed to the back surface of the recording medium, but it is preferable to direct the airflow to the surface of the recording medium (the side to which the ink has been applied). The distance from the air-blowing device to the recording medium is preferably 5 mm to 50 mm. From the viewpoint of improving the water resistance of the recorded image, a process of applying a liquid containing a silicone-based resin or a process of attaching a film or the like to the image may be provided after the drying process.

[0033] (Recording medium) The type of recording medium used to record the image is not particularly limited, and any recording medium may be used. Since it is preferable to use a white ink capable of recording images such as white, it is preferable to use a recording medium other than white, such as transparent film, translucent film, or colored paper. Here, "white" refers to the same characteristics as the "white" ink described later. Furthermore, it is preferable to use a low-to-non-absorbent recording medium. In this specification, a "low-to-non-absorbent recording medium" refers to a recording medium that is 30 msec from the start of contact in the Bristow method. 1 / 2 Up to 10 mL / m² of water absorption capacity 2 The following recording media are referred to. The Bristow method is a widely used method for measuring the amount of liquid absorbed in a short time and is also adopted by the Japan Paper & Pulp Technology Association (JAPANTAPPI). Details of the test method are described in Standard No. 51, "Paper and Paperboard - Liquid Absorbency Test Method - Bristow Method," of the "JAPAN TAPPI Paper & Pulp Test Methods 2000 Edition." Recording media with an ink-receiving layer for inkjet recording (glossy paper, matte paper, etc.) and plain paper without a coating layer have a water absorption capacity of 10 mL / m². 2 It is a "highly absorbent recording medium" that exceeds [a certain limit].

[0034] Examples of low-absorption recording media include recording media without an ink-receiving layer and recording media with a thin ink-receiving layer. Examples of printing papers include art paper, fine coated paper, medium coated paper, fine lightweight coated paper, medium lightweight coated paper, lightly coated paper, and cast coated paper. Examples of non-absorbent recording media include recording media without an ink-receiving layer and recording media with a thin ink-receiving layer. Examples of plastics include plastic films and materials such as paper on which plastic is coated. Examples of plastics include polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyethylene, and polypropylene. Other examples include glass, metal, and ceramic. Among these, materials such as plastic films and materials such as paper on which plastic is coated are preferred. In this specification, "recording media" means an object on which an image is recorded as a recording, not a transfer medium.

[0035] (Water-based ink) The ink used in the recording method is an inkjet-compatible aqueous ink containing particles, first resin particles, and a first water-soluble organic solvent. This ink is preferably white. Here, "white ink" includes inks that do not appear white in their ink state but are capable of recording white images. White refers to CIEL * a * b * Lightness (L) in a color system * ) and chromaticity (a * , b * ) are, respectively, 70 ≤ L * ≤100, -4.5 ≤a * ≤2.0, -6.0 ≤b * This means the value is within the range of ≤2.5. The components that make up the ink will be explained in detail below.

[0036] In this specification, "resin particles" refers to resins that exist in an insoluble state in the aqueous medium of 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 resins" refer to resins that exist in a dissolved state in the aqueous medium of ink. Whether or not a resin qualifies as "resin particles" can be determined according to the method shown below. First, a liquid containing the resin to be judged is prepared and diluted with pure water to prepare a sample so that the resin content is approximately 1.0%. Then, when 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., "water-dispersible resin"). On the other hand, if particles with a particle size are not measured, the resin is determined not to be "resin particles" (i.e., "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. As a particle size distribution analyzer, a dynamic light scattering particle size analyzer (for example, 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] [particle] The ink contains particles. These particles may be colorants or non-colored particles such as resin particles. In particular, when recording a white image, it is preferable to use colorless or white particles. The particles have a glass transition temperature Tg so that they do not melt during the drying process that melts the first resin particles. P (°C) or melting point Tm P (°C) represents the glass transition temperature Tg of the first resin particles in a dry state. Rd The temperature must be higher than (°C), i.e., 50°C or higher. Specifically, the glass transition temperature Tg of the particles. P (°C) or melting point Tm PThe glass transition temperature (Tg) of the particles is preferably 100°C or higher, more preferably 200°C or higher, and preferably 3,000°C or lower. P (°C) and melting point Tm P The temperature (°C) can be measured using differential scanning calorimeter (DSC) or laser heating. Furthermore, if the particles are inorganic, the melting point Tm of the inorganic particles is also measured. P (°C) represents the glass transition temperature Tg of the first resin particles in a dry state. Rd Since the temperature is sufficiently high compared to (°C), general values ​​such as those from literature may be used. Whether a particle is amorphous or crystalline can be determined by measuring its degree of crystallinity using a differential scanning calorimeter. Particles in which no melting peak is observed with a differential scanning calorimeter are judged to be amorphous. Particles in which a melting peak is observed are judged to be crystalline. If the particle is crystalline, the heat of fusion can be determined from the peak area, and the degree of crystallinity can also be determined from the ratio of this heat of fusion to the heat of fusion of a perfect crystal with a degree of crystallinity of 100%, which is obtained from theoretical calculations.

[0038] [Content] Particle content in ink V P The particle content (volume %) is preferably 1.5 volume% or more, based on the total volume of ink. If the particle content is less than 1.5 volume%, the voids formed by multiple particles will be substantially reduced, and the volume through which the resin generated by the melting of the first resin particles penetrates will also be reduced, making it difficult to create large voids, and the opacity of the image may not be sufficient. The particle content (volume %) in the ink is preferably 5.0 volume% or less, based on the total volume of ink. Furthermore, the particle content (mass %) in the ink is preferably 5.0 mass% or more and 45.0 mass% or less, and more preferably 5.0 mass% or more and 40.0 mass% or less, based on the total mass of ink.

[0039] [Average primary particle size] Particles are typically dispersed in ink in the form of secondary particles, which are aggregates of two or more primary particles. The average primary particle diameter D of the particles. P0The (nm) must be 150 nm or less, preferably 50 nm or less, and more preferably 30 nm or less. Average primary particle diameter D P0 The (nm) is preferably 5 nm or greater. The average primary particle diameter of the particles can be measured by observing the particles using a scanning electron microscope. Average primary particle diameter D P0 (nm) can be calculated as the average value of the primary particle diameters of multiple particles (for example, 100 particles).

[0040] [Cumulative 50% particle size based on volume] Particles are typically dispersed in ink as secondary particles, which are aggregates of two or more primary particles. Cumulative 50% particle diameter D50 based on particle volume. P The (nm) is preferably 200 nm or less, more preferably 150 nm or less, and particularly preferably 100 nm or less. By using particles whose volume-based cumulative 50% particle diameter is within the above range, light scattering due to fine voids formed between aggregated particles is effectively suppressed, and the refractive index difference with respect to the voids becomes larger, further improving the opacity of the image. In addition, the settling of the particles becomes slower, further improving the resistance to settling. On the other hand, D50 P If the particle size (nm) exceeds 200 nm, the particles are too large, making it difficult for them to surround the first resin particles. This weakens the inter-particle bonding force that forms the framework of the voids, and may prevent efficient void formation. Also, the cumulative 50% particle size D50 based on particle volume... p (nm) is preferably 5 nm or greater, and more preferably 10 nm or greater.

[0041] In this specification, "cumulative 50% particle size by volume (D50)" PThe particle size distribution analyzer is defined as the diameter of the particle that reaches 50% of the total volume of the measured particles when accumulated from the smallest particle size side, and can be measured using a particle size distribution analyzer based on the dynamic light scattering method. For example, measurement conditions include SetZero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: non-spherical. As for the particle size distribution analyzer, a particle size analyzer based on the dynamic light scattering method (for example, 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 described above.

[0042] 〔density〕 The density of the particles is preferably the same as or greater than that of the first resin particles. In particular, the density of the particles is preferably greater than that of the first resin particles. 3 ) is 1.00 g / cm³ 3 More than 5.00g / cm 3 Preferably, the following is true: 2.00 to 5.00 g / cm³ 3 It is even more preferable that the following is true: 4.00 to 5.00 g / cm³ 3 The following is particularly preferable:

[0043] [Refractive index] Since the particles become part of the material that makes up the binder, it is preferable to use particles with a high refractive index. Specifically, the refractive index of the particles is preferably 1.2 to 3.0, and more preferably 2.0 to 3.0. Among these, it is preferable to use titanium dioxide, which has a relatively high refractive index, as the particles. The refractive index of titanium dioxide is preferably 2.1 or higher, and more preferably 2.5 to 2.8.

[0044] Suitable specific examples of particles include at least one selected from the group consisting of titanium dioxide, calcium carbonate, calcium phosphate, barium sulfate, zirconium oxide, silicon dioxide, kaolin, clay, and second resin particles. Among these, white pigments such as titanium dioxide, calcium carbonate, calcium phosphate, barium sulfate, zirconium oxide, silicon dioxide, kaolin, and clay are preferred, with titanium dioxide being particularly preferred.

[0045] Titanium dioxide exists in three crystalline forms: rutile, anatase, and brookite. Among these, rutile titanium dioxide, which has low photocatalytic activity, is preferred. Industrial methods for producing titanium dioxide include the sulfuric acid method and the chlorine method; titanium dioxide produced by either method can be used. The particle surface of titanium dioxide may be coated with alumina or zirconia. Alternatively, the particle surface may be coated with inorganic oxides such as silica, zinc oxide, and zirconia; or organic substances such as polyols. Using titanium dioxide with such coated particle surfaces is expected to suppress photocatalytic activity and improve dispersibility.

[0046] Calcium carbonate particles can be cubic or spindle-shaped. Among these, cubic calcium carbonate with a uniform shape is preferred. Examples of calcium phosphate include monocalcium phosphate (Ca(H2PO4)2), dicalcium phosphate (CaHPO4), and tricalcium phosphate (Ca3(PO)2). Among these, apatite-type calcium phosphate is preferred, particularly hydroxyapatite (Ca 10 (PO6)(OH)2) is even more preferable.

[0047] Barium sulfate is broadly classified into extirpated barium sulfate and precipitated barium sulfate. Precipitated barium sulfate allows for control of particle size through synthesis conditions, enabling the production of barium sulfate with appropriate particle sizes. Zirconium oxide, also known as zirconia, is known as a highly tough ceramic. Pure zirconia is susceptible to degradation due to changes in its crystalline structure and volume with temperature fluctuations. Therefore, it is preferable to use stabilized zirconia, which has volume changes suppressed by the addition of stabilizers.

[0048] For example, silicon dioxide synthesized by the Stober method can be used. The Stober method is a method in which the hydrolysis and polycondensation reaction of alkoxysilane, which is the silica source, proceeds in a mixed aqueous solution of water, ethanol, and ammonia. By changing the concentration of each reactant, it is possible to control the particle size of the resulting spherical particles.

[0049] Kaolin is a clay mineral containing multiple inorganic components. Specifically, it is a clay composed of kaolinite, hydrated halloysite, and the crystalline structure of halloysite. Clay, in addition to the components of kaolin, contains ilmenite, montmorillonite, and vermiculite. When using kaolin or clay to make white ink, it is preferable to select particles with high whiteness.

[0050] The second resin particles are different from the first resin particles, and in order to prevent them from melting during the drying process that melts the first resin particles, the glass transition temperature Tg of the second resin particles is set. P (°C) or melting point Tm P The temperature (°C) must be higher than the drying process temperature. In other words, the glass transition temperature Tg of the second resin particle. P (°C) or melting point Tm P (°C) represents the glass transition temperature Tg of the first resin particles in a dry state. RdIt is required to be higher than (°C). The second resin particles only need to satisfy this condition, and the resin for forming the resin particles can be selected from the same ones as those of the first resin particles described later. Among them, resin particles formed of a crosslinked resin are preferable, and resin particles formed of a crosslinked acrylic resin are more preferable. Particularly, crosslinked particles of poly(meth)acrylic acid methyl, crosslinked particles of polystyrene, etc. are preferable. The second resin particles do not need to encapsulate a colorant.

[0051] Examples of the method for dispersing the particles include a method of adding energy (mechanical, thermal) to the liquid medium containing the particles for dispersion. Also, from the viewpoint of stably maintaining the dispersed state of the particles, it is preferable to use a dispersant. For example, as a dispersant for particles having a low isoelectric point like dry silica and having a negative charge on the particle surface in an aqueous medium, it is preferable to use a cationic resin. Also, as a dispersant for particles having a positive surface charge like aluminum hydroxide hydrate, it is preferable to use an anionic component. The dispersant can also be physically adsorbed on the surface of the particles for dispersion. The dispersant is suitable because it can effectively suppress the aggregation of the particles by the electrical repulsion generated between molecules and the steric hindrance of the molecules. The dispersant can be appropriately selected according to the characteristics of the particles, such as an acid, an alkali, a resin, etc. The content (mass%) of the dispersant in the ink is preferably 0.5 mass% or more and 15.0 mass% or less, and more preferably 1.0 mass% or more and 10.0 mass% or less, based on the content (mass%) of the particles. When the content of the dispersant is less than 0.5 mass%, the dispersed state of the particles is likely to be destabilized and may aggregate easily. Also, when the content of the dispersant exceeds 15.0 mass%, the dispersant becomes excessive, and instead, the dispersed state of the particles may be destabilized and may aggregate easily.

[0052] [First Resin Particles] The ink contains the first resin particles. The first resin particles melt and generate voids when dried at a temperature of (°C) or lower, which is the glass transition temperature Tg in the dry state, in the drying process. The resin particles do not need to be "hollow particles" having voids inside. Rd by being dried at a temperature lower than (°C). The resin particles do not need to be "hollow particles" having voids inside.

[0053] It is preferable that the first resin particles maintain their shape and are not melted before the heating process. If the first resin particles melt before the heating process, mixing of the particles and the first resin particles will not proceed quickly, or the first resin particles will easily fuse together, making it difficult to form the desired pores, resulting in reduced light scattering efficiency and insufficient opacity. For this reason, the glass transition temperature Tg of the first resin particles in the dry state is preferable. Rd The temperature (°C) must be 50°C or higher. Furthermore, by reducing the amount of the first water-soluble organic solvent in the ink film through the drying process, the glass transition temperature of the resin generated by the melting of the first resin particles is increased, hardening the resin and improving the scratch resistance of the image. For this reason, the glass transition temperature Tg in the first water-soluble organic solvent is required. Rs (°C) must be less than 50°C. Glass transition temperature Tg of the first resin particles in dry state. Rd The temperature (°C) is preferably 100°C or lower, and more preferably 80°C or lower.

[0054] Glass transition temperature Tg of the first resin particle in a dry state Rd (°C), and the glass transition temperature Tg in the first water-soluble organic solvent. RsThe temperature (°C) can be measured using a differential scanning calorimeter (DSC). An example of the measurement method is shown below. Resin particles separated from the ink are allowed to dry. These resin particles are placed in an aluminum container and sealed to prepare a sample for measuring the glass transition temperature in a dry state. Resin particles obtained by drying an aqueous dispersion of resin particles used in ink preparation may also be used. Alternatively, resin particles separated from the ink are allowed to dry, and the resin particles and a first water-soluble organic solvent are mixed in a 1:1 ratio (by mass) to prepare a sample for measuring the glass transition temperature in the first water-soluble organic solvent. Using a differential scanning calorimeter, the temperature difference with a reference substance is measured according to the temperature program shown below, and the glass transition temperature is measured by observing the endothermic and exothermic reactions due to the change in the state of the sample. In the examples described later, a differential scanning calorimeter (product name "DSC600", manufactured by Hitachi High-Tech) was used to measure the glass transition temperature of the first resin particles. Of course, the differential scanning calorimeter and measurement conditions used are not limited to this. Glass transition temperature Tg of particles P (°C) can also be measured using a similar method.

[0055] [Measurement conditions] Heating conditions: 30℃~150℃ Heating rate: 10°C / min After heating: Hold at 150°C for 5 minutes.

[0056] Whether the first resin particles have melted during the drying process can be easily determined, for example, by cutting the recording medium on which images were recorded before and after the drying process and observing it with a scanning electron microscope. Alternatively, by measuring the particle size of the first resin particles in the image before the drying process, if the difference between the size of the voids in the image after the drying process and the particle size of the first resin particles is small (for example, within 10%), it can be determined that the first resin particles have melted and voids have formed. More simply, if spherical first resin particles disappear from the image after the heating process, and voids approximately the same size as the first resin particles or where particles are connected are observed, it can be determined that the first resin particles have melted and voids have formed.

[0057] [Content] The content (mass %) of the first resin particles in the ink is preferably 2.5 mass % or more and 17.0 mass % or less, more preferably 2.5 mass % or more and 14.0 mass % or less, based on the total mass of the ink. Further, the content (volume %) of the first resin particles in the ink is preferably 2.5 volume % or more and 17.0 volume % or less, more preferably 2.5 volume % or more and 14.0 volume % or less, based on the total volume of the ink.

[0058] In the ink, the content V of the first resin particles R (volume %) is the volume ratio to the content V of the particles P (volume %) and is preferably 1.3 times or more and 5.0 times or less, more preferably 2.0 times or more and 4.0 times or less. When the above volume ratio exceeds 5.0 times, the first resin particles become relatively numerous, so the amount of fusion of the first resin particles increases and it becomes difficult to form pores of a desired size. As a result, the concealability of the image may not be sufficiently obtained. Also, the refractive index of the melted first resin particles and the binder composed of particles tends to become small, and the light scattering efficiency decreases, and the concealability may not be sufficiently obtained. On the other hand, when the above mass ratio is less than 1.3 times, the pores formed decrease, and the concealability may not be sufficiently obtained.

[0059] When the particles are titanium oxide, in the ink, the content (mass %) of the first resin particles is preferably 0.30 times or more and 1.00 times or less, more preferably 0.40 times or more and 0.60 times or less, as the mass ratio to the content (mass %) of titanium oxide. By the mass ratio being within the above range, the concealability of the image can be further improved.

[0060] [Cumulative 50% particle diameter based on volume] The voids formed during the heating process are generated when the first resin particles melt and the molten resin penetrates the gaps formed by multiple particles. Therefore, the size of the formed voids is greatly influenced by the particle size of the first resin particles. On the other hand, the light scattering efficiency is also greatly influenced by the size of the formed voids. For this reason, from the viewpoint of further improving the light scattering efficiency, the cumulative 50% particle diameter D50 of the first resin particles is determined based on volume. R The (nm) range is preferably 80 nm to 400 nm, and more preferably 100 nm to 400 nm. Of these, 150 nm to 250 nm is particularly preferred. D50 R If (nm) is outside the above range, the effect of further improving opacity may not be sufficiently obtained, and D50 R If the (nm) value exceeds 400 nm, the effect of further improving the scratch resistance of the image may not be sufficiently obtained.

[0061] [Apparent density] The volume-based content of the first resin particles in the ink corresponds to the volume occupied by the first resin particles in the ink. If the first resin particles have pores or internal voids, the volume occupied by the first resin particles in the ink includes these pores and internal voids. The first resin particles in the ink film are directly replaced by voids. Therefore, the apparent density ρ of the first resin particles R (g / cm 3 ) is 0.8 g / cm³ 3 The above is preferable. The apparent density is the density estimated by considering the total volume of the solid, pores, and internal voids. Apparent density ρ R (g / cm 3 ) is 0.8 g / cm³ 3 If the apparent density is less than 2.0 g / cm³, the resin generated by the melting of the resin particles does not adequately fill the voids formed by multiple particles. Therefore, the refractive index of the binder composed of the molten first resin particles tends to decrease, reducing the light scattering efficiency and potentially resulting in insufficient opacity. Furthermore, because the amount of resin constituting the binder decreases, the image may not exhibit sufficient scratch resistance. The apparent density of the first resin particles is 2.0 g / cm³. 3 The following is preferable:

[0062] Apparent density ρ of the first resin particle R (g / cm 3 For example, it can be measured by following these steps: Allow the resin particles separated from the ink to dry. Approximately 30 cm 3 The first resin particles are in a volume of 100 cm 3 Place the first resin particles in a volumetric flask and weigh their mass. Then, fill the volumetric flask with isopropanol up to the mark. Weigh the mass of the isopropanol added to the volumetric flask and calculate the apparent density of the first resin particles (g / cm³) from formula (B) below. 3 The apparent density ρ of the first resin particle is calculated using the Le Chatelier specific gravity bottle method in accordance with JIS Z 8807. R (g / cm 3 It can also measure ). Apparent density ρ of the first resin particle R (g / cm 3 ) = A / (100-B) / C ···(B) A: Mass of the first resin particle (g) B: Mass of isopropanol (g) C: Density of isopropanol at 25℃

[0063] [Refractive index] From the viewpoint of forming a binder with a high refractive index, it is preferable to use first resin particles with a sufficiently high refractive index. The refractive index of the first resin particles is preferably 1.5 or higher, more preferably 1.6 or higher, and preferably 2.5 or lower.

[0064] [Acid value, weight average molecular weight] The acid value of the resin constituting the first resin particles is preferably 5 mg KOH / g or more and 100 mg KOH / g or less. The weight-average molecular weight of the resin constituting the first resin particles is preferably 1,000 or more and 3,000,000 or less, and more preferably 100,000 or more and 3,000,000 or less. The resin particles do not need to contain a colorant.

[0065] [Preferred materials] Examples of resins that form the first resin particles include vinyl chloride resins, styrene resins, urethane resins, acrylic resins, and polyester resins. These resins are suitable because they easily form stable particles suitable for addition to water-based inks. Among these, acrylic resins, polyester resins, and urethane resins are preferred from the viewpoint of inkjet properties. If first resin particles formed from resins other than those mentioned above are used, the ejection tends to be unstable, and as a result, sufficient opacity may not be obtained. Acrylic resins are particularly suitable because they have a high affinity for the first water-soluble organic solvent. The acrylic resin may be a homopolymer formed from only one type of monomer unit, or a copolymer formed from multiple types of monomer units. The resin that forms the first resin particles may be crystalline or amorphous. If first resin particles formed from resins other than those mentioned above are used, the ejection tends to be unstable, and as a result, sufficient opacity may not be obtained. Furthermore, as the resin that forms the resin particles, acrylic resins having styrene-derived units are particularly preferred. The resin that forms the first resin particles can be appropriately selected from the same resin compositions as those described later for "other resins".

[0066] [Other resins] The ink may further contain a resin other than the first resin particles described above (other resins). The content (mass%) of the resin (other resins) in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, and more preferably 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the ink.

[0067] Other resins can be added to the ink (i) to stabilize the dispersion state of the pigment, i.e., as a resin dispersant or its auxiliary agent; or (ii) to improve various properties of the recorded image. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. Other resins may be either water-soluble resins or resin particles, but water-soluble resins are preferred.

[0068] [Composition of the resin] Examples of resins include acrylic resins, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are even more preferred. Examples of resin properties include crystalline resins, amorphous resins, and waxes.

[0069] 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 pigments, they can be suitably used as resin dispersants for dispersing pigments.

[0070] 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; acidic monomers having sulfonic acid groups, such as styrenesulfonic acid; and anionic monomers such as anhydrides and salts of these acidic monomers. 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. Furthermore, monomers having a silicone structure can also be used.

[0071] 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.

[0072] Polyester resins are typically composed of units derived from polyhydric alcohols and units derived from polyhydric carboxylic acids. Examples of polyhydric alcohols that become units constituting polyester resins through reaction include dihydric to tetrahydric polyhydric alcohols. Examples of polyhydric alcohols include polyhydric alcohols having aliphatic groups, polyhydric alcohols having aromatic groups, and sugar alcohols.

[0073] 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.

[0074] Polycarboxylic acids that form units derived from polycarboxylic acids that constitute polyester resins through reactions include divalent to tetravalent polycarboxylic acids. Examples of polycarboxylic acid structures 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. 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.

[0075] [Physical properties of other resins] 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. Furthermore, the acid value of the resin constituting the resin particles is preferably 5 mg KOH / g or more and 100 mg KOH / g or less. The weight-average molecular weight of the resin constituting the resin particles is preferably 100,000 or more and 3,000,000 or less. The resin particles do not need to contain a colorant.

[0076] [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 aqueous 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 aqueous 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, it can be appropriately selected and used from those that can be used in inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing solvents, and sulfur-containing solvents.

[0077] The water-soluble organic solvent in the ink includes a first water-soluble organic solvent with a boiling point higher than water. The boiling point of the first water-soluble organic solvent must be above 100°C, preferably above 150°C, and preferably below 350°C. The content (mass%) of the first water-soluble organic solvent 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. Furthermore, the content (volume%) of the first water-soluble organic solvent in the ink is preferably 1.0% by volume or more and 50.0% by volume or less, based on the total volume of the ink. All of the water-soluble organic solvent in the ink may be the first water-soluble organic solvent. The ink may contain multiple types of the first water-soluble organic solvent.

[0078] In order to efficiently melt the first resin particles during the drying process, it is preferable that the first resin particles swell due to the first water-soluble organic solvent remaining in the ink film during the drying process in which the ink film is formed, and that the effective glass transition temperature of the first resin particles rapidly decreases. For this purpose, the content V of the first water-soluble organic solvent in the ink is S (Volume %) represents the content of the first resin particles V R The volume ratio to (volume %) is preferably 1.0 times or more. When the volume ratio is 1.0 times or more, voids are efficiently generated, and the opacity can be further improved. The volume ratio is preferably 3.0 times or less, and preferably 2.0 times or less.

[0079] It is preferable to increase the affinity between the first water-soluble organic solvent and the first resin particles, thereby causing the first resin particles to swell. This allows for a more efficient reduction of the glass transition temperature during the drying process. For this purpose, it is preferable that the SP values ​​of the first water-soluble organic solvent and the first resin particles are close to each other. S , and the SP value P of the first resin particle R The absolute value of the difference is preferably between 1.5 and 5.0. Being within this range further improves the image's opacity. Also, the SP value P of the first resin particle is important. R It is preferable that the value is between 9.0 and 12.5.

[0080] In this specification, the SP value (δ: solubility parameter) is calculated by the Fedors method based on the following formula (B) (RFFedors: Polym.Eng.Sci.,14[2],147-154(1974)). ΔE in formula (B) vap V represents the molar heat of vaporization of the compound (cal / mol), and V is the molar volume of the compound at 25°C (cm³). 3 This represents the molar heat of vaporization (ΔE) of a compound. The smaller the difference between the SP value of the solute and the SP value of the solvent, the greater the affinity of the solute to the solvent tends to be. vapThe SP value and the molar volume (V) of a compound at 25°C can both be determined by summing up fixed values ​​attributed to atoms and groups in the molecule. The unit "cal" is commonly used for SP values. When converting to the SI unit system, use "(cal / cm²)". 3 ) 1 / 2 = 2.046 × 10 3 (J / m 3 ) 1 / 2 The relationship between "[ ]" can be used. In this specification, the unit of the SP value may be omitted.

[0081]

number

[0082] If the water-soluble organic solvent in the ink contains multiple types of first water-soluble organic solvents, the SP value P of the first water-soluble organic solvent is... S The SP value is calculated as a volume-weighted value. Normally, "water-soluble organic solvents" are liquids, but in this invention, for convenience, substances that are solid at 25°C (room temperature) are also included as water-soluble organic solvents. Examples of water-soluble organic solvents that are commonly used in water-based inks and are solid at 25°C include 1,6-hexanediol, trimethylolpropane, ethylene urea, urea, and polyethylene glycol with a number average molecular weight of 1,000. Furthermore, if the resin particles are composed of multiple layers rather than a single layer, it is sufficient to consider only the layer in contact with the first water-soluble organic solvent, and the SP value is calculated for the resin constituting the surface layer of the resin particles.

[0083] The SP values ​​for major water-soluble organic solvents are shown in parentheses. Specifically, glycerin (16.4), N-hydroxy-2-pyrrolidone (16.4), 1,3-propanediol (16.1), trimethylolpropane (15.9), 1,4-butanediol (15.0), diethylene glycol (15.0), ethylene glycol (14.8), 1,3-butanediol (14.8), 2-methyl-1,3-propanediol (14.8), urea (14.4), ethyleneurea (14.2), 1,5-pentanediol (14.2), N-(hydroxymethyl)-2-pyrrolidone (14.2), triethanolamine (13.7), triethylene glycol (13.6), 1,6-hexanediol (13.5), 1,2-propanediol (13.5), 3-methyl-1,5-pentanediol ( Examples include 13.4), 2-ethylpropane-1,3-diol (13.2), 2-methylpentane-2,4-diol (13.1), tetraethylene glycol (12.8), 1,2-butanediol (12.8), 2-pyrrolidone (12.6), 1,2-pentanediol (12.2), ethylene glycol monomethyl ether (12.0), 1,2-hexanediol (11.8), isopropanol (11.6), triethylene glycol monoethyl ether (10.6), diethylene glycol monobutyl ether (10.5), triethylene glycol monobutyl ether (10.3), polyethylene glycol with a number average molecular weight of 1,000 (10.1), γ-butyrolactone (9.9), toluene (9.1), and others. As the first water-soluble organic solvent, it is preferable to use glycerin, 1,3-propanediol, ethylene glycol, 1,2-butanediol, 1,2-hexanediol, isopropanol, or diethylene glycol monobutyl ether.

[0084] [Other ingredients] In addition to the components mentioned above, the ink may 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. Generally, these additives are present in very small amounts in the ink and have little "direct" effect on the swelling of the first resin particles. For this reason, in this invention, these additives are not included in the "water-soluble organic solvent" and are not included in the calculation of the SP value. However, it is preferable that the ink does not contain the reactants included in the reaction solution.

[0085] [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 6.0 or more and 9.5 or less, and more preferably 7.0 or more and 8.5 or less.

[0086] (Reaction solution) The recording method of the present invention preferably further includes a reaction solution application step of applying an aqueous reaction solution containing a reactant that reacts with aqueous ink to a recording medium. In particular, it is preferable to have the reaction solution application step before the ink application step, or to perform the ink application step and the reaction solution application step in parallel. The components used in the reaction solution will be described in detail below.

[0087] [Reactive agent] The reaction solution reacts with the ink upon contact, causing the components in the ink (components with anionic groups, such as resins) to aggregate, and contains a reactant. The presence of the reactant destabilizes the state of the components with anionic groups in the ink when the ink and reactant come into contact on the recording medium, thereby promoting ink aggregation. Examples of reactants include organic acids, polyvalent metal salts, and cationic resins.

[0088] Examples of polyvalent metal ions that make up polyvalent metal salts include Ca 2+ Cu 2+ Ni 2+ Mg 2+ Sr 2+ 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 the following. To include polyvalent metal ions in the reaction solution, a water-soluble polyvalent metal salt (which may also be a hydrate) composed of a polyvalent metal ion and an anion can be used. Examples of anions that make up a polyvalent metal salt 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 - C2H5COO - CH3CH(OH)COO - CH3CH(OH)COO -, C2H4(COO - )2, C6H5COO - , C6H4(COO - )2, and CH3SO3 - Examples of organic anions include the following. When polyvalent metal ions are used as a reactant, the content (mass%) of the polyvalent metal salt in the reaction solution is preferably 1.0% by mass or more and 40.0% by mass or less, based on the total mass of the reaction solution. In this specification, when the polyvalent metal salt is a hydrate, the "content (mass%) of the polyvalent metal salt" in the reaction solution means the "content (mass%) of the anhydrous polyvalent metal salt" excluding water as the hydrate.

[0089] The reaction solution containing an organic acid 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. When using an organic acid as a reactant, the content (by mass) of the organic acid 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.

[0090] Examples of cationic resins include resins having the structure of primary to tertiary amines and resins having the structure of quaternary ammonium salts. Specifically, examples include resins having the structures of vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensates. To improve solubility in the reaction solution, cationic resins can be used in combination with acidic compounds, or cationic resins can be subjected to quaternization treatment. When a cationic resin is used as a reactant, the content (mass%) of the 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.

[0091] [Aqueous medium] The reaction solution is an aqueous reaction solution containing at least water as an aqueous medium. The aqueous medium used in the reaction solution may contain the aforementioned water-soluble organic solvent that can be incorporated into the ink.

[0092] [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.

[0093] [Physical properties of the reaction solution] The reaction solution is an aqueous 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]

[0094] 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.

[0095] <Measurement of physical properties> (Particle primary mean particle diameter D) P ) A scanning electron microscope (product name "S-4700," manufactured by Hitachi High-Tech) was used to image the sample at a magnification of 100,000x. The diameter of 100 circles circumscribing the primary particles was then measured, and the average value was calculated. The average value was then used to determine the average primary particle diameter D of the particles. P That's what I decided.

[0096] (Cumulative 50% particle size based on volume) Using a particle size analyzer based on dynamic light scattering (product name "UPA-EX150", manufactured by Nikkiso), the cumulative 50% particle size (D50) based on particle volume was determined. P The cumulative 50% particle diameter (D50) of resin particles based on volume was measured. P D50 R The above-mentioned device was also used for the measurement of ).

[0097] (Glass transition temperature, melting point) Using a differential scanning calorimeter (DSC), the glass transition temperature (Tg) of resin particles is measured. Rd and Tg Rs , and the glass transition temperature Tg of the particles PThe following measurements were taken. First, the glass transition temperature of the resin particles will be explained. Two mg of resin particles obtained by drying a dispersion of resin particles at 60°C were placed in an aluminum container and sealed to prepare a sample for measuring the "glass transition temperature in a dry state". In addition, two mg of resin particles obtained by drying a dispersion of resin particles at 90°C, and three mg of the water-soluble organic solvent shown in Table 5 were placed in an aluminum container and sealed to prepare a sample for measuring the "glass transition temperature in the first water-soluble organic solvent". Thermal analysis was performed on the prepared samples 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 resin particles 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 quantity) in the following temperature program (4) or (5) 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 of the resin particles". Glass transition temperature Tg of resin particles in a dry state Rd (°C) was calculated from the measurement results of the second cycle after running the temperature program for two cycles. Also, the glass transition temperature Tg of the resin particles in the first water-soluble organic solvent was calculated. Rs The temperature (°C) was calculated from the measurement results of the first cycle.

[0098] The glass transition temperature of the particles can be measured using the same method as for measuring the glass transition temperature of resin particles in a dry state. The melting points of the particles were determined using the values ​​shown in Table 1.

[0099] [Temperature Program] • Glass transition temperature (Tg) of resin particles in a dry state Rd (°C) Temperature measurement program: (1) Heat from -40°C to 200°C at a rate of 10°C / min. (2) Hold at 200°C for 5 minutes (3) Cooling from 200°C to -40°C at a rate of 10°C / min (4) Heat from -40°C to 200°C at a rate of 10°C / min. • Glass transition temperature (Tg) of resin particles in the first water-soluble organic solvent. Rs(°C) Temperature measurement program: (5) Heat from -40°C to 150°C at a rate of 10°C / min

[0100] (density) The particle density was measured using the Le Chatelier-type specific gravity bottle method in accordance with JIS Z 8807.

[0101] (Apparent density of resin particles) The apparent density of the resin particles was measured as follows: Volume 100 cm³ 3 Approximately 30 cm in a volumetric flask 3 The resin particles were packed into the volumetric flask, and the mass A (g) of the packed resin particles was weighed using an electronic balance (product name "GH-202", manufactured by A&D). Next, isopropanol was added to the mark in the volumetric flask containing the resin particles, taking care to avoid introducing air bubbles. The mass B (g) of isopropanol added to the volumetric flask was accurately weighed, and the apparent density (g / cm³) was calculated using formula (C). 3 ) was calculated. (Apparent density) = (Mass of resin particles A (g)) / (100 - (Mass of isopropanol B (g)) / (Density of isopropanol at 25°C)) (C)

[0102] <Particle preparation> The following particles were prepared. The properties of the particles are shown in Table 1. The refractive index of each titanium dioxide particle was in the range of 2.5 to 2.9, and the refractive index of particles other than titanium dioxide was in the range of 1.3 to 2.2.

[0103] (particles 1, 5, 9, 20, 21, 24) 35.0 parts of the particles of the type shown in Table 1, 1.2 parts of triethanolamine, and 63.8 parts of deionized water were mixed and pre-dispersed using a homogenizer to obtain a pre-dispersion. The obtained pre-dispersion and 100 parts of 0.05 mm zirconia beads were mixed and dispersed using a bead mill for 5 hours. The cumulative 50% particle size based on particle volume was adjusted by the peripheral speed of the bead mill. The zirconia beads were filtered off, and an appropriate amount of deionized water was added to obtain dispersions of particles 1, 5, 9, 20, 21, and 24.

[0104] (particle 2) 38.0 parts of the particles of the type shown in Table 1, 4.4 parts of a water-soluble acrylic acid-based dispersant (product name "Aron T-50", manufactured by Toagosei, resin content 43.0%), and 52.8 parts of deionized water were mixed and pre-dispersed using a homogenizer to obtain a pre-dispersion. The obtained pre-dispersion and 100 parts of 0.05 mm zirconia beads were mixed and dispersed using a bead mill for 10 hours. The dispersion obtained by filtering off the zirconia beads was subjected to ultrasonic treatment. The cumulative 50% particle size based on particle volume was adjusted by the peripheral speed of the bead mill and the ultrasonic treatment. To this dispersion, 4.8 parts of a water-soluble acrylic acid-based dispersant (product name "Aron A-6330", manufactured by Toagosei, resin content 40.0%) and an appropriate amount of deionized water were added to obtain a particle 2 dispersion.

[0105] (particle 3) 38.0 parts of the particles of the type shown in Table 1, 4.4 parts of a water-soluble acrylic acid dispersant (product name "Aron T-50", manufactured by Toagosei, resin content 43.0%), and 53.1 parts of deionized water were mixed and pre-dispersed using a homogenizer to obtain a pre-dispersion. The obtained pre-dispersion and 100 parts of 0.05 mm zirconia beads were mixed and dispersed using a bead mill for 5 hours. The cumulative 50% particle size based on particle volume was adjusted by the peripheral speed of the bead mill. The zirconia beads were filtered off, and 4.8 parts of a water-soluble acrylic acid dispersant (product name "Aron A-6330", manufactured by Toagosei, resin content 40.0%) and an appropriate amount of deionized water were added to obtain a dispersion of particle 3.

[0106] (particle 4) 38.0 parts of the particles of the type shown in Table 1, 3.8 parts of polycarboxylic acid polymer (product name "Aqualic GL-366", manufactured by Nippon Shokubai, resin content 50.0%), and 58.2 parts of deionized water were mixed and pre-dispersed using a homogenizer to obtain a pre-dispersion. The obtained pre-dispersion and 100 parts of 0.05 mm zirconia beads were mixed and dispersed using a bead mill for 5 hours. The cumulative 50% particle size based on particle volume was adjusted by the peripheral speed of the bead mill. The zirconia beads were filtered off, and 5.1 parts of polycarboxylic acid polymer (product name "Aqualic TL-37", manufactured by Nippon Shokubai, resin content 37.0%) and an appropriate amount of deionized water were added to obtain a dispersion of particle 4.

[0107] (particle 6) A commercially available dispersion containing the types of particles shown in Table 1 was used as the dispersion for particle 6.

[0108] (particle 7) 38.0 parts of the particles of the type shown in Table 1, 9.6 parts of a water-soluble acrylic acid dispersant (product name "Aron A-6330", manufactured by Toagosei, resin content 40.0%), and 52.4 parts of deionized water were mixed and pre-dispersed using a homogenizer to obtain a pre-dispersion. The obtained pre-dispersion and 100 parts of 0.05 mm zirconia beads were mixed and dispersed using a bead mill for 10 hours. The dispersion obtained after filtering off the zirconia beads was subjected to ultrasonic treatment. The cumulative 50% particle size based on particle volume was adjusted by the peripheral speed of the bead mill and the ultrasonic treatment. An appropriate amount of deionized water was added to this dispersion to obtain a dispersion of particle size 7.

[0109] (particle 8) 38.0 parts of the particles of the type shown in Table 1, 4.8 parts of a water-soluble acrylic acid dispersant (product name "Aron A-6330", manufactured by Toagosei, resin content 40.0%), and 57.2 parts of deionized water were mixed and pre-dispersed using a homogenizer to obtain a pre-dispersion. The obtained pre-dispersion and 100 parts of 0.05 mm zirconia beads were mixed and dispersed using a bead mill for 5 hours. The cumulative 50% particle size based on particle volume was adjusted by the peripheral speed of the bead mill. The zirconia beads were filtered off, and an appropriate amount of deionized water was added to obtain a dispersion of particle 8.

[0110] (Particles 10 and 16) 40.0 parts of the particles of the type shown in Table 1, 1.1 parts of a wetting dispersant (product name "BYK-154", manufactured by Bic Chemie, resin content 42.0%), and 58.9 parts of deionized water were mixed and pre-dispersed using a homogenizer to obtain a pre-dispersion. The obtained pre-dispersion and 100 parts of 0.1 mm zirconia beads were mixed and dispersed using a bead mill for 6 hours. The cumulative 50% particle size based on particle volume was adjusted by the peripheral speed of the bead mill. The zirconia beads were filtered off, and an appropriate amount of deionized water was added to obtain dispersions of particles 10 and 16.

[0111] (particle 11) 35.0 parts of the particles of the type shown in Table 1, 3.0 parts of a water-soluble acrylic acid dispersant (product name "Aron A-6330", manufactured by Toagosei, resin content 40.0%), and 62.0 parts of deionized water were mixed and pre-dispersed using a homogenizer to obtain a pre-dispersion. The obtained pre-dispersion and 100 parts of 0.1 mm zirconia beads were mixed and dispersed using a bead mill for 6 hours. The cumulative 50% particle size based on particle volume was adjusted by the peripheral speed of the bead mill. The zirconia beads were filtered off, and an appropriate amount of deionized water was added to obtain a dispersion of particle 11.

[0112] (Particles 12, 13, and 15) 27.0 parts of the particles of the type shown in Table 1, 0.8 parts of a wetting dispersant (product name "BYK-154", manufactured by Bic Chemie, resin content 42.0%), and 72.2 parts of deionized water were mixed and pre-dispersed using a homogenizer to obtain a pre-dispersion. The obtained pre-dispersion and 100 parts of 0.1 mm zirconia beads were mixed and dispersed using a bead mill for 6 hours. The cumulative 50% particle size based on particle volume was adjusted by the peripheral speed of the bead mill. The zirconia beads were filtered off, and an appropriate amount of deionized water was added to obtain dispersions of particles 12, 13, and 15.

[0113] (particle 14) A commercially available dispersion containing the types of particles shown in Table 1 was used as a dispersion of particle 14 by adding an appropriate amount of deionized water.

[0114] (particle 17) Particle 17 was prepared by the Stober method. A solution was obtained by dissolving 6.3 g of tetraethyl orthosilicate in a mixture of 75.0 g of ethanol, 25.0 g of methanol, and 18.0 g of deionized water. 2.2 g of 28% aqueous ammonia was added to the obtained solution, and the mixture was stirred at 25°C for 24 hours to obtain a dispersion. The obtained dispersion was centrifuged, the liquid medium was replaced with water, and the content was adjusted to obtain a dispersion of particle 17.

[0115] (particle 18) A mixture of 32.4 parts of the types of particles shown in Table 1 and 67.6 parts of deionized water was subjected to sonication to obtain a dispersion of particle 18.

[0116] (particle 19) 1.6 parts of 3-aminophthalic acid and 10.0 parts of 6 mol / L hydrochloric acid were mixed and cooled to 5°C. Then, 1.8 parts of sodium nitrite were added under stirring. 5.0 parts of carbon black (product name "Printex95", manufactured by Orion Engineered Carbons) were added, and the mixture was heated to 80°C and maintained at 80°C under stirring until the generation of nitrogen gas stopped. After the reaction mixture cooled, acetone was added and the separated pigment was washed by filtration. Subsequently, the mixture was purified by ion exchange, ultrafiltration, and removal of coarse particles by centrifugation. An appropriate amount of ion-exchanged water was added to obtain a dispersion of 19 particles.

[0117] (particle 22) A mixture of 7.0 parts methyl methacrylate, 2.0 parts t-butyl methacrylate, 1.0 part n-butyl methacrylate, and 400 parts deionized water was prepared (mixture of monomers for the core). The mixture was placed in a nitrogen-purged reaction vessel and heated to 70°C under stirring. A mixed solution of 5.0 parts potassium peroxodisulfate and 20.0 parts deionized water was added to the reaction vessel and stirred at 70°C for 10 hours. Next, 0.2 parts methyl methacrylate, 0.08 parts t-butyl methacrylate, 0.8 parts n-butyl methacrylate, and 0.05 parts methacrylic acid (monomers for the shell) were added. Furthermore, a mixed solution of 0.08 parts potassium peroxodisulfate and 2.0 parts deionized water was added to the reaction vessel and stirred at 70°C for 3 hours. After that, the reaction product was filtered and concentrated in an evaporator to obtain a dispersion of 22 particles.

[0118] (particle 23) A commercially available dispersion containing the types of particles shown in Table 1 was used as the dispersion for particle 23.

[0119] [Table 1]

[0120] <Preparation of resin particles> The following resin particles were prepared. The preparation conditions for the resin particles are shown in Table 2, and the properties of the resin particles are shown in Tables 3 and 4. ρ in Table 3 R D50 R , and TgRd ρ is the apparent density R (g / cm 3 ), volume-based cumulative 50% particle size D50 R (nm), glass transition temperature Tg in dry state Rd The temperature is shown in (°C). In Table 4, "mixed solvent" refers to a mixed solvent obtained by mixing each water-soluble organic solvent in the ratios (by mass) shown below Table 4. The abbreviations for monomers shown in Tables 2 and 3 are as follows: MMA: methyl methacrylate, MA: methyl acrylate, EA: ethyl acrylate, nBMA: n-butyl methacrylate, StSANa: sodium parastyrene sulfonate, CHMA: cyclohexyl methacrylate, 2EHA: 2-ethylhexyl acrylate, MAA: methacrylic acid, St: styrene, EMA: ethyl methacrylate, tBMA: t-butyl methacrylate, AN: acrylonitrile, 2EHMA: 2-ethylhexyl methacrylate.

[0121] (Resin particles 1, 2, 4-8, 10-13, 16-19) A mixture of monomers (in parts) and 400 parts of deionized water, as shown in Table 2, was prepared. The mixture was placed in a nitrogen-purged reaction vessel and heated to 70°C under stirring. A mixed solution of 0.8 parts of potassium peroxodisulfate and 20.0 parts of deionized water was added to the reaction vessel and stirred at 70°C for 10 hours. After that, the reaction product was filtered, concentrated using an evaporator, and the pH of the dispersion was adjusted to within the range of 7-8 using an 8 mol / L potassium hydroxide aqueous solution to obtain aqueous dispersions of each resin particle.

[0122] (Resin particles 3) 65.0 parts methyl methacrylate, 31.0 parts 2-ethylhexyl acrylate, 2.0 parts methacrylic acid, 3.0 parts reactive surfactant (product name "Adekaria Soap SR-10", manufactured by ADEKA), and 152.0 parts deionized water were mixed in a homomixer to obtain an emulsion for the core. 89.0 parts deionized water was placed in a nitrogen-purged reaction vessel and the temperature was raised to 70°C. Then, 0.8 parts of a 10% aqueous solution of the reactive surfactant (product name "Adekaria Soap SR-10", manufactured by ADEKA), the previously prepared emulsion, and 180 parts of a 5% aqueous solution of potassium peroxodisulfate were added dropwise over 2.5 hours. The mixture was stirred at 70°C for 2 hours to synthesize the resin particle core. Furthermore, 4.8 parts of methyl methacrylate, 4.3 parts of 2-ethylhexyl acrylate, 0.2 parts of methacrylic acid, and 3.9 parts of a reactive surfactant (product name "Adekaria Soap SR-10", manufactured by ADEKA) were mixed in a homomixer to obtain an emulsion for the shell. The emulsion for the shell and 18 parts of a 5% potassium peroxodisulfate aqueous solution were added dropwise to the above reaction vessel over 0.5 hours, and the mixture was stirred at 70°C for 2 hours. After cooling, the pH of the dispersion was adjusted to a range of 7-8 using an 8 mol / L potassium hydroxide aqueous solution, and then concentrated in an evaporator to obtain an aqueous dispersion of resin particles 3.

[0123] (Resin particles 9) A mixture of 170.0 parts terephthalic acid, 50.0 parts propylene glycol, 70.0 parts bisphenol A, and 14.5 parts dibutyltin oxide was placed in a three-necked flask and stirred at 230°C for 24 hours under a nitrogen atmosphere. Then, 12.0 parts trimellitic acid was added to the flask and stirred at 200°C for 30 minutes. Polyester resin A was synthesized by stirring under reduced pressure of 5 mmHg for 1 hour while maintaining the reaction system at 200°C. A dispersion was prepared by dissolving 5.4 parts anionic surfactant (trade name "Neogen RK", manufactured by Daiichi Kogyo Seiyaku), 8.46 parts N,N-diethylaminoethanol, and 0.80 parts sodium chloride (an amount equivalent to 0.10 mol / L) in 142 parts ion-exchanged water. This dispersion was placed in a 350 mL pressure-resistant round-bottom stainless steel container, and then 108.0 parts polyester resin A was added and mixed. A high-speed shear emulsifier (product name "Cleamix CLM-2.2S", manufactured by M-Technique) was sealed and connected to a pressure-resistant round-bottom stainless steel container. The mixture in the container was heated to 140°C and stirred for 10 minutes while applying shear force at a rotor speed of 20,000 r / min. While maintaining the rotation speed of 20,000 r / min, it was cooled at a rate of 1.0°C / min to 50°C, and an appropriate amount of deionized water was added to obtain an aqueous dispersion of resin particles 9.

[0124] (Resin particles 14) 5.0 parts vinyl acetate, 10.0 parts chloroethylene, and 0.75 parts benzoyl peroxide (polymerization initiator) were mixed and reacted at 170°C for 5 hours. The reaction mixture was then removed from the container, the solids were cooled and pulverized to obtain vinyl resin B. Vinyl resin B and 0.05 parts anionic surfactant (product name "Neogen SC-A", manufactured by Daiichi Kogyo Seiyaku) were dissolved in 240 parts tetrahydrofuran. Equimolar amounts of dimethylaminoethanol were added to this mixture and stirred for 10 minutes. Then, using a homogenizer (product name "Ultra-Turrax T50", manufactured by IKA), 200 parts of deionized water were added dropwise while stirring at 5,000 rpm to obtain the mixture. The resulting mixture was adjusted in concentration by removing the tetrahydrofuran by reducing the pressure to 50 mmHg at 50°C to obtain an aqueous dispersion of resin particles 14.

[0125] (Resin particles 15) 20.0 parts terephthalic acid, 70.0 parts isophthalic acid, 10.0 parts adipic acid, 40.0 parts neopentyl glycol, and 20.0 parts ethylene glycol were dissolved in 800 parts toluene to obtain a mixture. 30.0 parts dimethyl(methylenebis(4,1-phenylene)) dicarbamate were added to this mixture and the mixture was reacted at 110°C for 5 hours to obtain a reaction product. The toluene was removed from the reaction product by reducing the pressure to 20 mmHg at 50°C to obtain urethane resin C. The obtained urethane resin C and 0.05 parts anionic surfactant (trade name "Neogen SC-A", manufactured by Daiichi Kogyo Seiyaku) were dissolved in 240 parts tetrahydrofuran to obtain a solution. To the obtained solution, dimethylaminoethanol in an equimolar amount to urethane resin A was added and the mixture was stirred for 10 minutes. Subsequently, using a homogenizer (product name "Ultra-Turrax T50," manufactured by IKA), 200 parts of deionized water were added dropwise while stirring at a rotation speed of 5,000 rpm to obtain a mixture. The obtained mixture was then subjected to reduced pressure of 50 mmHg at 50°C to remove tetrahydrofuran and obtain an aqueous dispersion of 15 resin particles.

[0126] [Table 2]

[0127] [Table 3]

[0128] [Table 4]

[0129] <Preparation of water-soluble organic solvents> The water-soluble organic solvents shown in Table 5 were prepared.

[0130] [Table 5]

[0131] <Ink preparation> The components (in %) shown in the upper part of Tables 6-10 were mixed. Potassium hydroxide was added to adjust the pH to a range of 8-9. Each ink was prepared by pressure filtration through a 3.0 μm pore size microfilter (manufactured by Fujifilm). In Tables 6-10, "Acetylenel E100" is the trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals. The properties of the prepared inks are shown in the lower part of Tables 6-10. Ink 47 was a black ink, and all other inks were white inks.

[0132] [Table 6]

[0133] [Table 7]

[0134] [Table 8]

[0135] [Table 9]

[0136] [Table 10]

[0137] <Preparation of reaction solution> (Reaction solution 1) 10.0 parts magnesium sulfate heptahydrate, 2.0 parts glycerin, 7.0 parts ethylene glycol, 0.5 parts nonionic surfactant (product name "Acetylenel E100", manufactured by Kawaken Fine Chemicals), and 80.5 parts deionized water were mixed and thoroughly stirred. Then, reaction solution 1 was prepared by pressure filtration through a cellulose acetate filter with a pore size of 3.0 μm (manufactured by Advantec).

[0138] (Reaction solution 2) 37.0 parts of a liquid containing a cationic resin, 2.0 parts of glycerin, 7.0 parts of ethylene glycol, 0.5 parts of a nonionic surfactant (product name "Acetylenel E100", manufactured by Kawaken Fine Chemicals), and 53.5 parts of deionized water were mixed and thoroughly stirred. As the cationic resin, "Unisense FPA100L" (manufactured by Senka, cationic resin content: 27.0%) was used. Subsequently, reaction solution 2 was prepared by pressure filtration through a cellulose acetate filter with a pore size of 3.0 μm (manufactured by Advantec).

[0139] <Rating> The reaction solution and ink obtained above were used to evaluate 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 conditions and evaluation results are shown in Tables 11 and 12.

[0140] (Recording of images for evaluation) 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. The types of reaction liquids and inks shown on the left side of Tables 11 and 12 were filled into ink cartridges and set in the prepared inkjet recording device. In this embodiment, the recording duty cycle of a solid image recorded at a resolution of 600 dpi x 600 dpi, with 8 ink droplets having a mass of 3.5 ng per droplet applied to a unit area of ​​1 / 600 inch x 1 / 600 inch, is defined as 100%.

[0141] Using this inkjet recording device, a reaction solution and ink were ejected from the lower half of the longitudinal nozzle of the recording head, and an image (50mm x 50mm) with a reaction solution recording duty cycle of 40% and an ink recording duty cycle of 400% was recorded on a recording medium. The recording medium used was PET film (product name "LLRPCF1372", manufactured by Sakurai, 30 msec from the start of contact in the Bristow method). 1 / 2 The amount of water absorbed up to this point is 0 mL / m².2 More than 10mL / m 2 A sheet cut to A4 size (within the following range) was used. In the examples where "Air drying" is indicated in "Drying method" in Tables 11 and 12, after applying the reaction solution and ink, the recording medium was transported for a length equivalent to half the length of the recording head, and then the recording medium was dried by blowing air at the temperature shown in "Drying temperature" in Tables 11 and 12 for 5 minutes. In the examples where "Natural drying" is indicated, after applying the reaction solution and ink, the recording medium was left in a 25°C environment for 1 day to dry the image. The image was fixed to the recording medium by these drying methods. The drying temperature is the temperature of the air at the air outlet measured using a molded surface sensor (product name "MF-OK", manufactured by Toa Electric).

[0142] (Formation of voids) The melting of resin particles and the formation of voids were confirmed by the following method. The recording medium on which images were recorded before and after the drying process was cut, and the cross-section was observed with a scanning electron microscope (product name "S-4700 scanning electron microscope," Hitachi High-Tech, magnification 100,000x). The particle size of the first resin particles in the cross-section before the drying process was measured. In addition, if voids were observed in the cross-section after the drying process, the size of the voids was measured. If the difference between the particle size of the first resin particles and the size of the voids in the image was 10% or less, it was determined that the first resin particles had melted and voids had formed during the drying process. The particle size and void size were the average of 10 measured values. These evaluation results are recorded in the "Void Formation" column in Tables 11 and 12.

[0143] (Concealing ability) The opacity of the recorded images was evaluated by measuring and calculating the opacity of the recorded images according to a method compliant with ISO 2471:2008. ISO 2471:2008 measures the reflectance by placing a white plate and a black plate on the back of the recording medium (paper) under test, and calculates the opacity from the following formula (D). Concealment ratio = (R0 / R ∞ ) × 100···(D) R0: Reflectance measured with a black board placed behind it. R ∞ Reflectance measured with a white board placed behind it.

[0144] In this example, the opacity of images recorded using opacity test paper (white and black boards, manufactured by TP Giken, with inspection certificate from the Japan Paint Inspection Association) was measured and calculated in accordance with this method. The opacity was then evaluated according to the evaluation criteria shown below. 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%.

[0145] (Sinking resistance) The prepared ink was poured into a cylindrical sample container to a height of 24 mm, sealed, and left in a 25°C environment for one week. The height (mm) of the transparent portion of the supernatant after the period was measured, and the ink's sedimentation resistance was evaluated according to the evaluation criteria shown below. A smaller transparent portion indicates that particle sedimentation is suppressed and that the ink has good sedimentation resistance. A: The height of the clear supernatant was 2 mm or less. B: The height of the clear supernatant was greater than 2 mm and less than or equal to 10 mm. C: The height of the clear supernatant portion exceeded 10 mm.

[0146] (Abrasion resistance) The recording medium on which the image was recorded was fixed to a Japan Society for the Promotion of Science (JSPS) friction tester (product name "Friction Tester Type II," manufactured by Yasuda Seiki Seisakusho). A white cotton friction cloth (product name "Kanakin No. 3," manufactured by the Japanese Standards Association Group) was set on the friction element of the tester, and the image and the white cotton cloth were rubbed together for a predetermined number of back-and-forth strokes. After that, the image was visually inspected, and the abrasion resistance of the image was evaluated according to the evaluation criteria shown below. A: After 10 round trips, the image was free of scratches, but after 15 round trips, the image was scratched. B: After 5 round trips, the image was free of scratches, but after 10 round trips, the image was scratched. C: The image was damaged after 5 round trips.

[0147] [Table 11]

[0148] [Table 12]

[0149] Furthermore, the disclosure of embodiments of the present invention includes the following methods and configurations.

[0150] (Method 1) An inkjet recording method for recording an image by applying water-based ink to a recording medium, An ink application step of applying the aqueous ink to the recording medium, The process includes, in this order, a drying step of drying the recording medium to which the aqueous ink has been applied, The aforementioned water-based ink contains particles, resin particles, and a water-soluble organic solvent which includes a first water-soluble organic solvent whose boiling point is higher than that of water. The average primary particle diameter D of the aforementioned particles P (nm) is 150nm or less, The resin particles have a glass transition temperature Tg in a dry state. Rd The temperature (°C) is 50°C or higher, and the glass transition temperature Tg in the first water-soluble organic solvent is Rs It contains first resin particles whose temperature (°C) is less than 50°C. Glass transition temperature Tg of the aforementioned particles P (°C) or melting point Tm P (°C) is the glass transition temperature Tg of the first resin particles in a dry state. Rd Higher than (°C), In the drying step, the recording medium is subjected to the glass transition temperature Tg of the first resin particles in the dry state. Rd An inkjet recording method characterized by drying the first resin particles at a temperature of (°C) or lower to melt them and create voids.

[0151] (Method 2) The cumulative 50% particle diameter D50 based on the volume of the aforementioned particles P The inkjet recording method according to Method 1, wherein (nm) is 200 nm or less.

[0152] (Method 3) The cumulative volume-based 50% particle diameter D50 of the particles P The inkjet recording method according to Method 1, wherein (nm) is 150 nm or less.

[0153] (Method 4) The content V of the first resin particles R (volume %) is a ratio to the content V of the particles P (volume %), and is 1.3 times or more and 5.0 times or less. The inkjet recording method according to any one of Methods 1 to 3.

[0154] (Method 5) The content V of the first water-soluble organic solvent S (volume %) is a volume ratio to the content V of the first resin particles R (volume %), and is 1.0 times or more. The inkjet recording method according to any one of Methods 1 to 4.

[0155] (Method 6) The cumulative volume-based 50% particle diameter D50 of the first resin particles R (nm) is 80 nm or more and 400 nm or less. The inkjet recording method according to any one of Methods 1 to 5.

[0156] (Method 7) The cumulative volume-based 50% particle diameter D50 of the first resin particles R (nm) is 100 nm or more and 400 nm or less. The inkjet recording method according to any one of Methods 1 to 5.

[0157] (Method 8) The resin forming the first resin particles is at least one selected from the group consisting of an acrylic resin, a polyester resin, and a urethane resin. The inkjet recording method according to any one of Methods 1 to 7.

[0158] (Method 9) The resin forming the first resin particles is an acrylic resin. The inkjet recording method according to any one of Methods 1 to 7.

[0159] (Method 10) The inkjet recording method according to any one of methods 1 to 9, wherein the particle is at least one selected from the group consisting of titanium dioxide, calcium carbonate, calcium phosphate, barium sulfate, zirconium oxide, silicon dioxide, kaolin, clay, and second resin particles.

[0160] (Method 11) The apparent density ρ of the first resin particles R (g / cm 3 ) is 0.8 g / cm³ 3 The inkjet recording method described in any one of the methods 1 to 10 above.

[0161] (Method 12) SP value P of the first water-soluble organic solvent S , and the SP value P of the first resin particle R An inkjet recording method according to any one of methods 1 to 11, wherein the absolute value of the difference is 1.5 or more and 5.0 or less.

[0162] (Method 13) The inkjet recording method according to any one of methods 1 to 12, wherein the aqueous ink is a white ink.

[0163] (Method 14) The inkjet recording method according to any one of methods 1 to 13, wherein the drying temperature (°C) of the recording medium in the drying step is 50°C or less.

[0164] (Method 15) Furthermore, the inkjet recording method according to any one of methods 1 to 14, 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.

[0165] (device 1) An inkjet recording apparatus used in an inkjet recording method for recording an image by applying an aqueous ink containing particles, resin particles, and a first water-soluble organic solvent having a boiling point higher than that of water to a recording medium, An ink application means for applying the aqueous ink to the recording medium, The system comprises a drying means for drying the recording medium to which the aqueous ink has been applied, The average primary particle diameter D of the aforementioned particles P (nm) is 150nm or less, The resin particles have a glass transition temperature Tg in a dry state. Rd The temperature (°C) is 50°C or higher, and the glass transition temperature Tg in the first water-soluble organic solvent is Rs It contains first resin particles whose temperature (°C) is less than 50°C. Glass transition temperature Tg of the aforementioned particles P (°C) or melting point Tm P (°C) is the glass transition temperature Tg of the first resin particles in a dry state. Rd Higher than (°C), The drying means allows the recording medium to reach the glass transition temperature Tg of the first resin particles in the dry state. Rd An inkjet recording apparatus characterized by a means of drying at a temperature of (°C) or lower to melt the first resin particles and create voids.

[0166] (Composition 1) A water-based ink used in an inkjet recording method that applies water-based ink to a recording medium to record an image, The inkjet recording method includes an ink application step of applying the aqueous ink to the recording medium, The process includes, in this order, a drying step of drying the recording medium to which the aqueous ink has been applied, The aforementioned water-based ink contains particles, resin particles, and a water-soluble organic solvent which includes a first water-soluble organic solvent whose boiling point is higher than that of water. The average primary particle diameter D of the aforementioned particles P (nm) is 150nm or less, The resin particles have a glass transition temperature Tg in a dry state. RdThe temperature (°C) is 50°C or higher, and the glass transition temperature Tg in the first water-soluble organic solvent is Rs It contains first resin particles whose temperature (°C) is less than 50°C. Glass transition temperature Tg of the aforementioned particles P (°C) or melting point Tm P (°C) is the glass transition temperature Tg of the first resin particles in a dry state. Rd Higher than (°C), In the drying step, the recording medium is subjected to the glass transition temperature Tg of the first resin particles in the dry state. Rd A water-based ink characterized by drying at a temperature of (°C) or lower to melt the first resin particles and create voids. [Explanation of symbols]

[0167] 1 particle 2 First resin particle 3 Binders 4. Holes

Claims

1. An inkjet recording method for recording an image by applying water-based ink to a recording medium, An ink application step of applying the aqueous ink to the recording medium, The process includes, in this order, a drying step of drying the recording medium to which the aqueous ink has been applied, The aforementioned water-based ink contains particles, resin particles, and a water-soluble organic solvent which includes a first water-soluble organic solvent whose boiling point is higher than that of water. The average primary particle diameter D of the aforementioned particles Ｐ (nm) is 150 nm or less, The glass transition temperature Tg of the resin particles in a dry state Ｒｄ The temperature (°C) is 50°C or higher, and the glass transition temperature Tg in the first water-soluble organic solvent is Ｒｓ It contains first resin particles whose temperature (°C) is less than 50°C. Glass transition temperature Tg of the aforementioned particles Ｐ (°C) or melting point Tm Ｐ (°C) is the glass transition temperature Tg of the first resin particles in a dry state. Ｒｄ Higher than (°C), In the drying process, the recording medium is subjected to the glass transition temperature Tg of the first resin particles in the dry state. Ｒｄ An inkjet recording method characterized by drying the first resin particles at a temperature of (°C) or lower to melt them and create voids.

2. The cumulative 50% particle diameter D50 based on the volume of the aforementioned particles. Ｐ The inkjet recording method according to claim 1, wherein the (nm) is 200 nm or less.

3. The volume-based cumulative 50% particle diameter D50 of the particles Ｐ The inkjet recording method according to claim 1, wherein (nm) is 150 nm or less.

4. Content V of the first resin particles Ｒ (Volume %) is the content of the particles V Ｐ The inkjet recording method according to claim 1, wherein the ratio to (volume %) is 1.3 times or more and 5.0 times or less.

5. Content V of the first water-soluble organic solvent Ｓ (Volume %) is the content of the first resin particles V Ｒ The inkjet recording method according to claim 1, wherein the volume ratio to (volume %) is 1.0 times or more.

6. The cumulative 50% particle size D50 of the first resin particles based on volume. Ｒ The inkjet recording method according to claim 1, wherein the (nm) is 80 nm or more and 400 nm or less.

7. The cumulative 50% particle size D50 of the first resin particles based on volume. Ｒ The inkjet recording method according to claim 1, wherein (nm) is 100 nm or more and 400 nm or less.

8. The inkjet recording method according to claim 1, wherein the resin forming the first resin particles is at least one selected from the group consisting of acrylic resins, polyester resins, and urethane resins.

9. The inkjet recording method according to claim 1, wherein the resin forming the first resin particles is an acrylic resin.

10. The inkjet recording method according to claim 1, wherein the particles are at least one selected from the group consisting of titanium dioxide, calcium carbonate, calcium phosphate, barium sulfate, zirconium oxide, silicon dioxide, kaolin, clay, and second resin particles.

11. The apparent density ρ of the first resin particle Ｒ (g / cm ３ ) is 0.8 g / cm³ ３ The inkjet recording method according to claim 1, wherein the above is true.

12. SP value P of the first water-soluble organic solvent Ｓ , and the SP value P of the first resin particle Ｒ The inkjet recording method according to claim 1, wherein the absolute value of the difference is 1.5 or more and 5.0 or less.

13. The inkjet recording method according to claim 1, wherein the aqueous ink is white ink.

14. The inkjet recording method according to claim 1, wherein the drying temperature (°C) of the recording medium in the drying step is 50°C or less.

15. Furthermore, the inkjet recording method according to claim 1, 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.

16. An inkjet recording apparatus used in an inkjet recording method for recording an image by applying an aqueous ink containing particles, resin particles, and a first water-soluble organic solvent having a boiling point higher than that of water to a recording medium, An ink application means for applying the aqueous ink to the recording medium, The system comprises a drying means for drying the recording medium to which the aqueous ink has been applied, The average primary particle diameter D of the aforementioned particles Ｐ (nm) is 150 nm or less, The glass transition temperature Tg of the resin particles in a dry state Ｒｄ The temperature (°C) is 50°C or higher, and the glass transition temperature Tg in the first water-soluble organic solvent is Ｒｓ It contains first resin particles whose temperature (°C) is less than 50°C. Glass transition temperature Tg of the aforementioned particles Ｐ (°C) or melting point Tm Ｐ (°C) is the glass transition temperature Tg of the first resin particles in a dry state. Ｒｄ Higher than (°C), The drying means brings the recording medium to the glass transition temperature Tg of the first resin particles in the dry state. Ｒｄ An inkjet recording apparatus characterized by a means of drying the first resin particles at a temperature of (°C) or lower to melt them and create voids.

17. A water-based ink used in an inkjet recording method that applies water-based ink to a recording medium to record an image, The inkjet recording method includes an ink application step of applying the aqueous ink to the recording medium, The process includes, in this order, a drying step of drying the recording medium to which the aqueous ink has been applied, The aforementioned water-based ink contains particles, resin particles, and a water-soluble organic solvent which includes a first water-soluble organic solvent whose boiling point is higher than that of water. The average primary particle diameter D of the aforementioned particles Ｐ (nm) is 150 nm or less, The glass transition temperature Tg of the resin particles in a dry state Ｒｄ The temperature (°C) is 50°C or higher, and the glass transition temperature Tg in the first water-soluble organic solvent is Ｒｓ It contains first resin particles whose temperature (°C) is less than 50°C. Glass transition temperature Tg of the aforementioned particles Ｐ (°C) or melting point Tm Ｐ (°C) is the glass transition temperature Tg of the first resin particles in a dry state. Ｒｄ Higher than (°C), In the drying process, the recording medium is subjected to the glass transition temperature Tg of the first resin particles in the dry state. Ｒｄ A water-based ink characterized by drying at a temperature of (°C) or lower to melt the first resin particles and create voids.

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