Inkjet recording method, inkjet recording apparatus, and aqueous ink and aqueous reaction liquid kit

Abstract

This invention relates to an inkjet recording method, an inkjet recording apparatus, and a kit of aqueous ink and aqueous reactive solution. An inkjet recording method is provided that records images on a recording medium using an aqueous ink and an aqueous reactive solution containing a reactant that reacts with the aqueous ink. The aqueous ink comprises pigments dispersed by carboxylic acid groups, resin particles, and a water-soluble organic solvent. The pigments dispersed by carboxylic acid groups exhibit a particle size increase of more than 8.0 times upon contact with the aqueous reactive solution. In the Bristow method, from the start of contact to 30 msec... 1 / 2 The amount of water absorbed by the recording medium is 10 mL / m 2 the following.

Description

Inkjet recording methods, inkjet recording equipment, and kits for water-based inks and water-based reaction solutions. Technical Field

[0001] This invention relates to inkjet recording methods, inkjet recording devices, and kits for water-based inks and water-based reaction solutions. Background Technology

[0002] In recent years, inkjet recording methods have been increasingly used in fields such as signage and displays, including posters and large-format advertising. Inkjet recording devices used in this field are characterized by having a wider recording area compared to household inkjet recording devices. Furthermore, the images need to be eye-catching; therefore, inks capable of recording images with high color rendering are required.

[0003] In the field of signage and display, non-absorbent recording media with surfaces that are substantially non-absorbent and made of materials such as vinyl chloride (PVC) or polyethylene terephthalate (PET) are frequently used. Therefore, it is necessary to suppress blurring of images on non-absorbent recording media. Hereinafter, recording media with surfaces that are substantially non-absorbent are also referred to as "non-absorbent recording media." In inkjet recording methods on non-absorbent recording media, it is important to suppress blurring by preventing ink droplets from being repelled on the recording medium. For this purpose, it is necessary to rapidly thicken and fix the ink after it has been applied to the recording medium.

[0004] Recording methods using solvent-based inks containing organic solvents as the main component or curable inks containing polymerizable monomers are known as methods for recording on non-absorbent recording media. From the viewpoint of environmental impact and safety, there has been an increasing demand recently for recording methods that can use water-based inks to record on non-absorbent recording media.

[0005] Examples of methods for recording on non-absorbent recording media using water-based inks include: methods in which water in the ink evaporates on the surface of the non-absorbent recording medium; and methods in which a reaction solution is used to aggregate the components of the ink. The former is advantageous from an operating cost perspective because it eliminates the need to provide a unit for applying the reaction solution, but it suffers from poor productivity because it necessitates a reduction in printing speed. For this reason, methods using reaction solutions have been investigated.

[0006] Some recording media have a glossy surface. From the viewpoint of recording high-quality images, such recording media also require high image sharpness. The term "image sharpness" refers to the clarity of the image when it is projected onto the surface on which the image is recorded. When image sharpness is low, the image appears blurry. When image sharpness is high, the image appears clear. In signage and display applications, recorded images are displayed in a variety of environments, including outdoor and indoor environments; therefore, environmental resistance is also important. Specifically, there is a problem with "moisture absorption resistance," that is, for example, when images are displayed in a humid environment, the images absorb moisture, thereby reducing their brightness.

[0007] To obtain images with high gloss using aqueous reaction solutions, inkjet recording methods that reduce the amount of reaction solution applied have been proposed, such as Japanese Patent Application Publication No. 2018-165029, and ink compositions in which a resin with low aggregation relative to the reaction solution is added, such as Japanese Patent Application Publication No. 2019-157064. As described in Japanese Patent Application Publication No. 2019-155852, inkjet recording methods that combine the use of clear ink without coloring materials have been proposed to obtain images with excellent scratch resistance and high image quality. As described in Japanese Patent Application Publication Nos. 2021-030613 and 2019-147339, inkjet recording methods that adjust the aggregation of ink relative to the reaction solution have been proposed. As described in Japanese Patent Application Publication No. 2022-186629, a processing liquid (reaction liquid) and a set of inks for controlling the maximum tensile stress of the ink film and having excellent image fixing properties have been proposed in order to record images that suppress blurring and cracking.

[0008] The inventors have investigated various properties of recorded images using inkjet recording methods described in Japanese Patent Application Publication Nos. 2018-165029, 2019-155852, 2021-030613, and 2019-147339, ink compositions described in Japanese Patent Application Publication No. 2019-157064, and complete sets of inks described in Japanese Patent Application Publication No. 2022-186629. Regarding images recorded using the inkjet recording method described in Japanese Patent Application Publication No. 2018-165029 and images recorded using the complete sets of inks described in Japanese Patent Application Publication No. 2022-186629, image blurring was not suppressed. Images recorded by using ink compositions described in Japanese Patent Application Publication No. 2019-157064 and images recorded by inkjet recording methods described in Japanese Patent Application Publication Nos. 2019-155852, 2021-030613 and 2019-147339 have a certain degree of image clarity, but their moisture resistance is insufficient.

[0009] This invention provides an inkjet recording method that can record images with excellent image sharpness and moisture resistance, even when recording on non-absorbent recording media, while suppressing blur. This invention also provides an inkjet recording apparatus for this inkjet recording method, as well as a kit for water-based ink and water-based reaction solution. Summary of the Invention

[0010] One aspect of the present invention relates to an inkjet recording method for recording images on a recording medium using an aqueous ink and an aqueous reactive solution comprising a reactant that reacts with the aqueous ink. The method includes: a reactive solution application step of applying the aqueous reactive solution to the recording medium; and an ink application step of applying the aqueous ink in such a manner that the aqueous ink overlaps with at least a portion of an area of ​​the recording medium on which the aqueous reactive solution has been applied. The aqueous ink comprises pigment dispersed by the action of carboxylic acid groups, resin particles, and a water-soluble organic solvent. The pigment dispersed by the action of carboxylic acid groups exhibits a particle size increase of 8.0 times or more upon contact with the aqueous reactive solution. The resin particles include first resin particles, the first resin particles exhibiting a particle size increase of 3.0 times or less upon contact with the aqueous reactive solution. In the water-based ink, the total mass ratio of the first resin particles (mass%) to the second resin particles (mass%) and the pigment dispersed by the carboxylic acid groups (mass%) is 1.2 times to 25.0 times, and the particle size increase rate of the second resin particles when in contact with the water-based reaction liquid is greater than 3.0 times. The water-soluble organic solvent comprises substances with a vapor pressure of 1.0 × 10⁻⁶. -2 The first water-soluble organic solvent has a pressure of kPa or higher. The proportion (mass%) of the first water-soluble organic solvent in the water-soluble organic solvent of the water-based ink is 50.0% by mass or higher. In the Bristow method, from the start of contact to 30 msec... 1 / 2 The amount of water absorbed by the recording medium is 10 mL / m 2 the following.

[0011] Further features of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0012] Figure 1 is a schematic perspective view illustrating an inkjet recording device according to an embodiment of the present invention.

[0013] Figure 2 is a schematic side view illustrating an inkjet recording device according to an embodiment of the present invention. Detailed Implementation

[0014] The present invention will be described in more detail below with reference to embodiments. In embodiments of the present invention, when the compound is a salt, the salt dissociates into ions in the ink, but for convenience, it is expressed as "containing salt". Aqueous inks and aqueous reaction solutions used for inkjet recording are also simply referred to as "ink" and "reaction solution", respectively. Physical property values ​​are at room temperature (25°C) and atmospheric pressure (1 atm), unless otherwise stated. The term "(meth)acrylic acid" includes acrylic acid and methacrylic acid. The term "(meth)acrylate" includes acrylates and methacrylates.

[0015] As described in Japanese Patent Application Publication Nos. 2018-165029 and 2019-157064, the inventors have investigated the reasons why image sharpness and image blur suppression cannot be simultaneously achieved when using a reactive liquid. The reactive liquid includes a reactant that reacts with components in the ink, such as pigments or resins, to cause the components to aggregate. Therefore, when the reactive liquid and ink come into contact with each other on the surface of a non-absorbent recording medium, the ink components rapidly aggregate as described above to record an image. At this time, the components rapidly aggregated by the reactant are likely to form unevenness as aggregates on the surface of the non-absorbent recording medium, thereby degrading the smoothness of the image surface and the image sharpness.

[0016] To improve the smoothness of the image surface, the reactivity between the reactant and the ink components can be adjusted to prevent the formation of aggregates. When the reactivity decreases to the point that aggregates are less likely to form, the ink components cannot be reliably fixed to the surface of the recording medium, thus preventing the recording of high-quality images. In particular, in images with a large amount of ink applied, even slight movement of the ink components is visually perceived as blurry. Therefore, it is difficult to simultaneously achieve image sharpness and suppression of image blur by using methods such as those described in Japanese Patent Application Publication No. 2018-165029, which involve adjusting the amount of reactant applied, or methods such as those described in Japanese Patent Application Publication No. 2019-157064, which involve adding components to adjust the reactivity with the reactant.

[0017] The inventors have investigated the following configuration to simultaneously achieve image sharpness and image blur suppression. Specifically, they investigated using pigments with high reactivity with the reactants in the reaction solution to suppress image blur, and using resin particles with low reactivity with the reactants to improve image sharpness. However, the resulting images lacked sufficient image sharpness. This is presumably because, although the reactivity of the resin particles with the reactants is reduced, the pigments retain high reactivity, leading to the formation of aggregates that fail to adequately improve smoothness.

[0018] The inventors have conducted research to adjust the ratio of resin particles to pigment and have discovered that when the ratio is within a specific range, both image sharpness and image blur suppression can be achieved. It has been found that while adjusting the resin particle to pigment ratio ensures both image sharpness and image blur suppression, a new problem arises when the resulting image is displayed for an extended period. Specifically, when the resulting image is displayed for a long time, a large number of small droplets adhere to the surface of the image, causing a deterioration in color rendering. This problem will be referred to below as "hygroscopicity."

[0019] The inventors have analyzed the reasons for the phenomenon of numerous small droplets adhering to the surface of an image during long-term display and discovered that even when the image surface appears dry, liquid components of the reactive liquid or ink applied to the non-absorbent recording medium remain inside the image. Furthermore, during long-term display, these residual liquid components attract water vapor from the air to form droplets. The inventors have also found that when highly reactive pigments and highly reactive resin particles are used, color development degradation due to droplet adhesion does not occur, while when highly reactive pigments and low-reactive resin particles are used, significant color development degradation occurs.

[0020] The inventors have hypothesized that the degradation of moisture resistance is due to the following: Non-absorbent recording media have difficulty absorbing liquid components; therefore, liquid components in the reaction solution or ink have difficulty penetrating into the recording medium, and even when the image is dried by heating or other means, some liquid components remain inside the image. These remaining liquid components have a high affinity for water vapor in the air. When pigments and resin particles have high reactivity, the resulting aggregates are large and have numerous gaps. Therefore, while the image is being displayed, the liquid components remaining inside the image gradually evaporate. However, resin particles with low reactivity do not easily aggregate. The resin particles expand, filling the gaps between the pigment aggregates and fixing the image on the recording medium. As a result, it is believed that the evaporation of the liquid components remaining inside the image occurs through the resin particles, and thus, due to prolonged display, the liquid components attract water vapor from the air, resulting in droplets adhering to the surface of the image.

[0021] For the reasons mentioned above, the inventors have studied how to minimize the presence of liquid components inside the image and have found that moisture resistance can be improved by setting the proportion of water-soluble organic solvents with high vapor pressure to a certain value or higher.

[0022] In other words, the inkjet recording method according to an embodiment of the present invention has the following characteristics. The water-based ink comprises pigment dispersed by the action of carboxylic acid groups, resin particles, and a water-soluble organic solvent. The pigment dispersed by the action of carboxylic acid groups exhibits a particle size increase rate of 8.0 times or more upon contact with the water-based reaction liquid. The resin particles include first resin particles, the first resin particles exhibiting a particle size increase rate of 3.0 times or less upon contact with the water-based reaction liquid. In the water-based ink, the mass ratio of the content (mass%) of the first resin particles to the total content (mass%) of the second resin particles and the content (mass%) of the pigment dispersed by the action of carboxylic acid groups is 1.2 times or more and 25.0 times or less, and the second resin particles exhibiting a particle size increase rate greater than 3.0 times upon contact with the water-based reaction liquid. The water-soluble organic solvent comprises a vapor pressure of 1.0 × 10⁻⁶. -2 The first water-soluble organic solvent has a pressure of kPa or higher. The proportion (mass%) of the first water-soluble organic solvent in the water-based ink is 50.0% or higher. In the Bristow method, from the start of contact to 30 msec... 1 / 2 The amount of water absorbed by the recording medium is 10 mL / m 2 The following describes the process of applying an aqueous reaction solution and an aqueous ink to a recording medium such that they at least partially overlap. The inventors have hypothesized that an image with excellent image sharpness and moisture resistance can be recorded using the above configuration, and that blurring is suppressed by the following mechanism.

[0023] Ink contains pigments dispersed by the action of carboxylic acid groups. For this reason, when the pigments come into contact with the reaction solution, they react with the reactants in the solution through electrostatic interactions and aggregate. When the coloring material is dispersed by nonionic groups such as vinyl oxides and anionic groups other than carboxylic acid groups, aggregation of the coloring material is not easy to occur, and therefore image blurring cannot be suppressed.

[0024] The pigment dispersed by the action of carboxylic acid groups exhibits a particle size increase of 8.0 times or more when it comes into contact with an aqueous reaction solution. "Particle size increase rate" is an indicator of the ease with which the pigment aggregates when in contact with the reaction solution. A higher value indicates higher aggregation. The definition and measurement method of "pigment particle size increase rate" will be described below. When the particle size increase rate is 8.0 times or more when the reaction solution and ink come into contact with each other on the recording medium, the reactivity of the pigment with the reactant is sufficiently high, and a blurred image can be recorded. When the particle size increase rate is less than 8.0 times, even when the reaction solution and ink come into contact with each other on the surface of the recording medium, pigment aggregation is not sufficient, and thus image blur cannot be suppressed.

[0025] The ink contains first resin particles, the particle size increase rate of which is 3.0 times or less when the first resin particles come into contact with the reaction liquid. "Particle size increase rate" is an indicator of the ease with which resin particles aggregate when in contact with the reaction liquid. A higher value indicates higher aggregation. The definition and measurement method of "particle size increase rate" will be described below. When the particle size increase rate is 3.0 times or less when the reaction liquid and ink come into contact with each other on the recording medium, the reactivity of the resin particles with the reactant is sufficiently low, and images with excellent image sharpness can be recorded. Even if the ink contains resin particles, a particle size increase rate greater than 3.0 times is likely to lead to aggregation of resin particles when the reaction liquid and ink come into contact with each other on the surface of the recording medium, thereby failing to obtain image sharpness. The total mass ratio of the first resin particle content (mass%) to the amount of second resin particles with a particle size increase rate greater than 3.0 times (mass%) and the amount of pigment dispersed by the action of carboxylic acid groups (mass%) needs to be 1.2 times or more and 25.0 times or less. The amount (mass%) of the second resin particles contained in the ink can be 0%, based on the total mass of the ink. The ink may be essentially devoid of second resin particles. A mass ratio of less than 1.2 times results in a large amount of highly reactive components with the reactants in the ink. Consequently, aggregates easily lead to unevenness on the surface of the image, resulting in a lack of image sharpness. A mass ratio greater than 25.0 times results in an excessive amount of low-reactivity components with the reactants in the ink. The movement of low-reactivity resin particles easily causes pigment migration, thereby failing to suppress image blurring.

[0026] The water-soluble organic solvent in the ink contains a vapor pressure of 1.0 × 10⁻⁶. -2 The first water-soluble organic solvent has a pressure of kPa or higher. The proportion (mass%) of the first water-soluble organic solvent in the ink's water-soluble organic solvent needs to be 50.0% by mass or higher. The first water-soluble organic solvent is easily evaporated under normal conditions, such as at room temperature (25°C) and normal pressure (1 atm). When the proportion of the first water-soluble organic solvent in the ink's water-soluble organic solvent is within the above range, the liquid component is less likely to remain inside the recorded image, thereby improving the image's moisture resistance.

[0027] Inkjet recording methods, inkjet recording equipment, and kits for water-based inks and water-based reaction solutions.

[0028] An inkjet recording method according to an embodiment of the present invention is a method in which aqueous ink and an aqueous reactive liquid are ejected from the recording head of an inkjet system and applied to a recording medium by the action of thermal energy to record an image. The inkjet recording method according to an embodiment of the present invention includes: a reactive liquid application step of applying the aqueous reactive liquid to the recording medium; and an ink application step of applying the aqueous ink in such a way that the aqueous ink overlaps with at least a portion of the area of ​​the recording medium to which the aqueous reactive liquid has been applied. The aqueous ink includes pigments dispersed by carboxylic acid groups, resin particles, and a water-soluble organic solvent. The pigments dispersed by carboxylic acid groups have a particle size increase rate of 8.0 times or more upon contact with the aqueous reactive liquid. The resin particles include first resin particles, the first resin particles having a particle size increase rate of 3.0 times or less upon contact with the aqueous reactive liquid. In water-based inks, the total mass ratio of the first resin particles (mass%) to the second resin particles (mass%) and the pigment dispersed by carboxylic acid groups (mass%) is 1.2 to 25.0 times, and the particle size increase rate of the second resin particles upon contact with the water-based reaction solution is greater than 3.0 times. Water-soluble organic solvents include those with a vapor pressure of 1.0 × 10⁻⁶. -2 The first water-soluble organic solvent has a pressure of kPa or higher. The proportion (mass%) of the first water-soluble organic solvent in the water-based ink is 50.0% or higher. The aqueous reaction solution contains the reactant that reacts with the water-based ink. In the Bristow method, from the start of contact to 30 msec... 1 / 2 The amount of water absorbed by the recording medium is 10 mL / m 2 the following.

[0029] The inkjet recording apparatus according to an embodiment of the present invention is an apparatus for an inkjet recording method in which aqueous ink and aqueous reactive liquid are ejected from the recording head of an inkjet system by the action of heat energy and applied to a recording medium to record an image. The apparatus can be used in the recording method. In the inkjet recording method and inkjet recording apparatus according to an embodiment of the present invention, it is not necessary to cure the image by using, for example, active energy rays for radiation.

[0030] According to an embodiment of the present invention, the kit of water-based ink and water-based reactive liquid is a kit for an inkjet recording method, which records images on a recording medium by discharging water-based ink and an water-based reactive liquid containing a reactant that reacts with the water-based ink from a recording head. This kit can be used in the recording method. Examples of the kit's configuration include: a kit comprising multiple ink cartridges independently containing various inks (reactive liquids); and an ink cartridge integrated by combining multiple ink reservoirs containing various inks (reactive liquids). The kit according to an embodiment of the present invention is not limited to the above configuration, as long as the ink and reactive liquid can be used in combination, and the kit can be of any configuration.

[0031] The inkjet recording method and inkjet recording apparatus according to embodiments of the present invention (hereinafter also referred to as "recording method and recording apparatus") will be described in detail below.

[0032] Figure 1 is a schematic perspective view showing an inkjet recording apparatus according to an embodiment of the present invention. Figure 2 is a schematic side view showing an inkjet recording apparatus according to an embodiment of the present invention. As shown in Figures 1 and 2, the recording apparatus according to this embodiment includes a recording head 22 configured to eject ink from an inkjet system. The recording head 22 is configured to eject ink by the action of thermal energy. In the recording head configured to eject ink by the action of thermal energy, an electrical pulse is applied to an electrothermal conversion element to apply thermal energy to the ink, thereby ejecting the ink from the ejection port. Here, a recording head configured to eject ink by the action of thermal energy is given as an example. However, a recording head configured to eject ink by the action of mechanical energy can be used. The recording head may include a mechanism (temperature control mechanism) configured to heat the water-based ink ejected from the recording head. When a temperature control mechanism is provided, the temperature of the ink ejected from the recording head can be above 35°C and below 70°C.

[0033] Heating process

[0034] A recording method according to an embodiment of the present invention may include a step of heating (heat treatment) a recording medium on which ink (and a reaction solution) has been applied. Heating the recording medium on which ink has been applied can promote drying and increase the intensity of the image.

[0035] Examples of units constituting a heated recording medium include: a heating unit, such as a known heating unit, like a heater; a blowing unit using air, such as a dryer; and a unit obtained by combining these units. Examples of heating units include the aforementioned heating unit; a blowing unit; and a unit obtained by combining these. Examples of heat treatment methods include: a method in which heat is applied from a side (back side) opposite to the recording surface (ink application surface) of the recording medium using, for example, a heater; a method in which warm air or hot air is applied to the recording surface of the recording medium; and a method in which heat is applied from the recording surface or back side using an infrared heater. Furthermore, two or more of these methods can be combined together.

[0036] The heating temperature of the recording medium with ink applied can be above 50°C and below 90°C, because this improves the scratch resistance of the image. The heating temperature of the recording medium with ink applied is read by a sensor introduced at a location corresponding to the heating unit of the recording device, or it can be determined from the relationship between the amount of heat and the temperature of the recording medium, which has been determined according to the type of ink and recording medium.

[0037] In the recording apparatus shown in Figures 1 and 2, a heater 25, supported by a frame (not shown), is positioned downstream of the location in the sub-scanning direction A relative to where the recording head 22 performs reciprocating scanning in the main scanning direction B. The recording medium 1, to which ink has been applied, is heated by the heater 25. Examples of heaters 25 include sheath heaters and halogen heaters. The heater 25 is covered by a heater cover 26. The heater cover 26 is a component for effectively irradiating the recording medium 1 using the heat generated from the heater 25. The heater cover 26 also serves to protect the heater 25. The recording medium 1, to which ink has been applied from the recording head 22, is wound by a winding spool 27 to form a roll-shaped wound medium 24.

[0038] Recording media

[0039] In the recording method and recording apparatus according to embodiments of the present invention, a low-absorbency or non-absorbent recording medium (low to non-absorbent recording medium) is used. Low to non-absorbent recording medium is defined as the recording medium used in the Bristow method, "Liquid Absorbency Test Method for Paper and Paperboard," as described in JAPAN TAPPI Paper and Pulp Test Method No. 51, from the start of contact to 30 msec. 1 / 2 The water absorption rate is 0 mL / m 2 Above and 10mL / m 2 The following are recording media. In embodiments of the present invention, a recording medium that meets the requirement of water absorption is defined as a "low to non-absorbent recording medium". Recording media for inkjet recording, such as glossy paper and matte paper, having a coating (ink receiving layer) formed of inorganic particles, and ordinary paper without a coating are defined as "absorbent recording media", wherein the water absorption is greater than 10 mL / m 2 .

[0040] Examples of low- to non-absorbent recording media that can be used include: plastic films; recording media having a recording surface side of the plastic film adhered to a substrate; and recording media having a resin coating on a substrate containing cellulose pulp for the recording surface. Among these, plastic films can be used. Recording media having a resin coating on a recording surface of a substrate containing cellulose pulp can also be used.

[0041] When ink containing resin particles is applied to a non-absorbent recording medium, components such as water and water-soluble organic solvents evaporate, causing the resin particles to concentrate. This promotes the fusion of the concentrated resin particles, thereby improving the intensity of the recorded image. Conversely, when ink is applied to a recording medium with highly absorbent liquid components, the fusion of resin particles is less likely to be promoted, and the image intensity cannot be improved. The recording medium in this specification does not refer to a transfer medium, but rather to the target recording medium on which the image is recorded as the object being recorded.

[0042] reaction solution

[0043] The recording method according to an embodiment of the present invention includes a reaction liquid application step of applying an aqueous reaction liquid containing a reactant that reacts with an aqueous ink to a recording medium. The reaction liquid application step may be performed before the ink application step. Optionally, the ink application step and the reaction liquid application step may be performed simultaneously. Components used in the reaction liquid, etc., will be described in detail below.

[0044] reactants

[0045] When the reaction solution comes into contact with ink, the reaction solution reacts with the ink, causing components in the ink, such as those containing anionic groups (e.g., resins, surfactants, or self-dispersing pigments), to aggregate. The reaction solution contains a reactant. When the ink and the reactant come into contact with each other in the recording medium, the presence of the reactant destabilizes the state of the components in the ink containing anionic groups, thereby promoting ink aggregation. Examples of reactants include: polyvalent metal ions; cationic components, such as cationic resins; and organic acids. These reactants can be used alone or in combination of two or more.

[0046] organic acids

[0047] The reaction solution containing organic acids has buffering capacity in the acidic region (pH less than 7.0, preferably 2.0–5.0) and thus effectively converts the anionic groups of components present in the ink into acidic forms to produce aggregates. Pigments are dispersed by the action of carboxylic acid groups. When pigments come into contact with organic acids, they lose their dispersibility and aggregate. Examples of organic acids include: monocarboxylic acids, such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrolic acid, furanic acid, pyridinecarboxylic acid, nicotinic acid, thiophenic acid, levulinic acid, and coumaric acid, and their salts; dicarboxylic acids, 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, and their salts and hydrogen salts; tricarboxylic acids, such as citric acid and trimellitic acid, and their salts and hydrogen salts; and tetracarboxylic acids, such as pyromellitic acid, and their salts and hydrogen salts.

[0048] When organic acids are used as reactants, polyvalent carboxylic acids can be used from the viewpoint of more effectively suppressing image blur. In other words, the organic acid used as a reactant can be a polyvalent carboxylic acid. When monocarboxylic acids with low water solubility are used as reactants, they readily precipitate through the evaporation of liquid components, such as ink, before being applied to the recording medium. For this reason, in some cases, the effect of converting the anionic group to the acid form is not sufficiently realized. This will not adequately suppress image blur. When monocarboxylic acids with high water solubility are used as reactants, as mentioned above, in some cases, the effect of converting the anionic group to the acid form is not sufficiently realized because of the high volatility of the monocarboxylic acid itself. This will not adequately suppress image blur.

[0049] The acid dissociation constant (pKa) of an organic acid at 25°C can be 5.0 or less. pKa represents the ease with which the protons of the acid dissociate. When an organic acid has multiple anionic groups (carboxylic acid groups), it has multiple pKa values. However, it can be said that the amount of organic acid dissociated in the reaction solution depends on the first acid dissociation constant (pKa1), which represents the ease with which the protons of the acid dissociate in the first stage. In this specification, the acid dissociation constant in the case where the organic acid has multiple anionic groups refers to the first acid dissociation constant. When the pKa of the organic acid is greater than 5.0, the effect of pigment aggregation weakens, and image blurring cannot be adequately suppressed in some cases. From the viewpoint of reactivity with resin particles, the pKa of the organic acid at 25°C can be 0 or more. When the resin particles in the ink are resin particles dispersed by the action of carboxylic acid groups, the pKa of the organic acid at 25°C is preferably 3.2 or more. More preferably, the pKa of the organic acid at 25°C is 3.5 or more. The pKa of organic acids is less than 3.2, resulting in an excessively strong effect on the aggregation of resin particles. This will not allow for adequate image sharpness. The organic acid content (mass%) of the reaction solution is preferably 1.0% or more and 10.0% or less, more preferably 1.0% or more and 5.0% or less, based on the total mass of the reaction solution.

[0050] The acid dissociation constant is defined as follows. For example, the ionic equilibrium of an acid represented by HA can be expressed by... The equilibrium constant Ka is expressed as Ka = [H]. + ]×[A - [HA] represents the acid dissociation constant. The acid dissociation constant pKa is the negative common logarithm of the equilibrium constant and is defined as pKa = -log[HA]. 10 Ka. The acid dissociation constant (pKa) of organic acids at 25°C can be calculated by neutralization titration using a pH meter (e.g., "Metrohm 798, MPT Titrino", available from Metrohm) or similar means.

[0051] polyvalent metal salts

[0052] Polyvalent metal salts are compounds formed by divalent or higher-valent metal ions (polyvalent metal ions) and anions. In aqueous reaction solutions, polyvalent metal salts dissociate into polyvalent metal ions and cause pigments dispersed in inks via carboxylic acid groups to aggregate. Polyvalent metal salts can also be hydrates.

[0053] Examples of polyvalent metal ions that constitute polyvalent metal salts include divalent metal ions, such as Ca. 2+ Cu 2+ Ni 2+ Mg 2+ 、Sr 2+ Ba 2+ and Zn 2+ ; and trivalent metal ions, such as Fe 3+ Cr 3+ Y 3+ And Al 3+ Of these, from the perspective of image sharpness, one can use a selection of Ca... 2+ and Mg 2+ At least one metal ion that makes up the group.

[0054] Examples of anions that constitute polyvalent metal salts include inorganic anions, such as Cl-. - ,Br - I - ,ClO - ClO2 - ClO3 - ClO4 - NO2 - NO3 - SO4 2- CO3 2- HCO3 - PO4 3- HPO4 2- and H2PO4 - ; and organic anions, such as HCOO - (COO) - 2. COOH (COO) - CH3COO - C2H5COO - CH3CH(OH)COO - C2H4(COO) - 2. C6H5COO - C6H4(COO) - )2 and CH3SO3 -These polyvalent metal salts can be used alone or in combination of two or more. Among these, calcium lactate (Ca) is selected. 2+ and CH3CH(OH)COO - (a combination of) and magnesium sulfate (Mg) 2+ and SO4 2- At least one compound from the group consisting of (a combination of) can be used as a polyvalent metal salt in the reaction solution. The use of calcium lactate or magnesium sulfate ensures further improvement in image sharpness.

[0055] When polyvalent metal ions are used as reactants, the ion content (mass%) of the reaction solution, converted to polyvalent metal salts, can be 1.0% by mass or more and 20.0% 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 "polyvalent metal salt content (mass%)" of the reaction solution refers to the "anhydrous polyvalent metal salt content (mass%)" excluding water as a hydrate.

[0056] cationic resins

[0057] Cationic resins have cationic sites in their structure and aggregate pigments dispersed in inks through the action of carboxylic acid groups. Examples of cationic resins include resins with primary to tertiary amine structures and resins with quaternary ammonium salt structures. Specific examples include resins each having the following structures: for example, vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, or alkylamine-epimyl condensates. To increase solubility in the reaction solution, cationic resins and acidic compounds can be used in combination, or cationic resins can be quaternized.

[0058] When a cationic resin is used as a reactant, the weight-average molecular weight of the cationic resin is preferably 500 or more and 10,000 or less. The weight-average molecular weight of the cationic resin can be measured, for example, by gel permeation chromatography converted to pullulan. More preferably, the weight-average molecular weight of the cationic resin is 5,000 or less. A weight-average molecular weight greater than 5,000 can lead to excessive aggregation with the ink components, resulting in insufficient image sharpness. The cationic resin content (mass%) of the reaction solution is preferably 0.1% or more and 10.0% or less, more preferably 0.1% or more and 5.0% or less, based on the total mass of the reaction solution.

[0059] The degree of cationization of cationic resins can be above 3 meq / g and below 7 meq / g. A degree of cationization less than 3 meq / g leads to a decrease in the aggregation of the following pigments, thus failing to adequately suppress image blur. A degree of cationization greater than 7 meq / g leads to a decrease in the aggregation of the following resin particles, thus failing to achieve sufficient image sharpness. The degree of cationization is an index representing the degree of cationicity of the resin. A higher degree of cationization indicates a greater amount of cationic groups on a molar basis.

[0060] The degree of cationization of the cationic resin can be measured at 25°C using an automatic potentiometric titrator for colloid titration (trade name: AT-510, available from Kyoto Electronics Manufacturing Co., Ltd.) with 1 / 400N potassium polyvinyl sulfate solution (available from Fujifilm Corporation) as the titrant. The aqueous solution of the cationic resin used for titration can be prepared by dissolving an appropriate amount of the cationic resin taken from the reaction solution in water.

[0061] Aqueous media

[0062] 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 include a water-soluble organic solvent that can be contained in the ink and will be described below. The reaction solution may further contain a vapor pressure of 1.0 × 10⁻⁶. -2 A second water-soluble organic solvent with a pressure of kPa or higher. The proportion (mass%) of the second water-soluble solvent in the water-soluble organic solvent of the reaction solution can be 90.0% by mass or more. A proportion less than 90.0% by mass will result in an increase in the amount of liquid components remaining inside the recorded image, thus failing to provide sufficient moisture resistance to the image. The proportion can be 100.0% by mass, that is, all the water-soluble organic solvent in the reaction solution can be the second water-soluble organic solvent. As the second water-soluble organic solvent, the same solvent as the first water-soluble organic solvent described below can be used. In this specification, the vapor pressure is the value at 25°C and 1 atm.

[0063] Other components

[0064] The reaction solution may contain various other components as needed. Examples of other components include those that may be contained in the ink and will be described below.

[0065] When the reaction solution contains resin particles, the resin particle content (mass%) can be less than 1.0% by mass, based on the total mass of the reaction solution. A resin particle content greater than 1.0% by mass will inhibit the contact between the reactant and ink components when the reaction solution and ink come into contact with each other on the recording medium, thereby failing to adequately suppress image blurring. The resin particle content (mass%) of the reaction solution can be 0.0% by mass. In other words, the reaction solution can be substantially free of resin particles.

[0066] Physical properties of the reaction solution

[0067] The reaction solution used in the recording method according to an embodiment of the present invention is an aqueous reaction solution for inkjet systems. Therefore, from a reliability point of view, the physical properties can be appropriately controlled. Specifically, the surface tension of the reaction solution at 25°C can be 20 mN / m or more and 60 mN / m or less. The viscosity of the reaction solution at 25°C can be 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, more preferably 6.0 or more and 9.0 or less.

[0068] ink

[0069] The ink used in the recording method according to an embodiment of the present invention is an aqueous ink for inkjet recording. This aqueous ink comprises pigments, resin particles, and a water-soluble organic solvent dispersed by the action of carboxylic acid groups. The components contained in the ink will be described in detail below.

[0070] pigment

[0071] The ink contains pigment as a coloring material. The pigment is dispersed by the action of carboxylic acid groups and aggregated by a reactant in the reaction solution. The pigment dispersed by the action of carboxylic acid groups exhibits a particle size increase of 8.0 times or more upon contact with the reaction solution. The particle size increase can be less than 50.0 times. The particle size increase rate is the rate of increase in pigment particle size when the dispersion of the pigment dispersed by the action of carboxylic acid groups and the reaction solution are mixed at a mass ratio of 1:1. Specifically, this ratio is the increase in pigment particle size through (the pigment after mixing with the reaction solution)... 50 ) / (D of pigment in dispersion 50 The calculated value. The pigment content (mass%) of the pigment dispersion is 1.0% by mass. D 50 The cumulative particle size is based on 50% of the volume, and its details will be described below. The D of the pigment after mixing with the reaction solution. 50Measurements are taken after the reaction has proceeded sufficiently. For example, measurements are taken after the reaction solution and pigment dispersion have been mixed and thoroughly stirred. Any stirring method can be used, such as using a stir bar, as long as the reaction proceeds sufficiently. In the examples described below, the reaction solution and pigment dispersion were placed in a beaker and stirred with a stirrer for 30 seconds, and then the 50% cumulative particle size of the pigment was measured based on volume.

[0072] For example, in the case of self-dispersible pigments, the particle size increase rate of pigments dispersed by the action of carboxylic acid groups can be adjusted, for example, by the density of carboxylic acid groups directly or by means of other atomic groups bonded to the surface of the pigment particles. In the case of resin-dispersed pigments, the acid value can be adjusted by the acid value of the resin dispersant used. The particle size increase rate can be increased, for example, by increasing the density of carboxylic acid groups in self-dispersible pigments, or by increasing the acid value of the resin dispersant in resin-dispersed pigments. When a fixed method is used to disperse pigments, the particle size increase rate also varies depending on the type of reactants in the reaction solution used in combination. The pigment content (mass%) of the ink is preferably 0.1% or more and 15.0% or less, more preferably 1.0% or more and 10.0% or less, based on the total mass of the ink.

[0073] Specific examples of pigments include: inorganic pigments, such as carbon black and titanium dioxide; and organic pigments, such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolide, diketopyrrolopyrrole, and dioxazine pigments. These pigments can be used alone or in combination of two or more.

[0074] Regarding the dispersion mode of the pigment, for example, a resin-dispersed pigment using a resin as a dispersant or a self-dispersing pigment in which hydrophilic groups are bound to the surface of the pigment particles can be used. Alternatively, for example, a resin-bonded pigment obtained by chemically binding resin-containing organic groups to the surface of the pigment particles or a microcapsule pigment obtained by coating the surface of the pigment particles with resin, etc., can be used. Combinations of pigments with different dispersion systems can also be used. Among these, instead of resin-bonded pigments or microcapsule pigments, a resin-dispersed pigment in which the resin as a dispersant is physically adsorbed onto the surface of the pigment particles can be used. In other words, the pigment can be a pigment dispersed by the action of a resin having carboxylic acid groups (resin dispersant). When the pigment is a self-dispersing pigment, the reactivity with the reactant can easily increase, thus failing to obtain sufficient image sharpness. As a resin dispersant, resins such as water-soluble resins can be used. The mass ratio of the pigment content (mass %) of the ink to the resin dispersant content can be 0.3 times or more and 10.0 times or less.

[0075] As self-dispersing pigments, pigments in which at least a carboxylic acid group is directly or by means of other atomic groups (-R-) can be bonded to the surface of the pigment particles. Anionic groups other than the carboxylic acid group (sulfonic acid group, sulfate ester group, or phosphonic acid group) can be further bonded to the pigment particle surface. Anionic groups such as carboxylic acid groups can be in any acidic or salt form. In the case of a salt form, the anionic group can be in any partially dissociated or fully dissociated state. When the anionic group is in salt form, examples of cations as counterions include: alkali metal cations; ammonium; and organic ammonium. Specific examples of other atomic groups (-R-) include straight-chain or branched alkylene groups having 1 to 12 carbon atoms; aryl groups, such as phenylene or naphthylene; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; and ether groups. Combinations of these groups can also be used.

[0076] The 50% cumulative particle size of the pigment based on volume (D) 50 Preferably, the particle size is 10 nm or more and 300 nm or less, more preferably 20 nm or more and 200 nm or less. The 50% volume-based cumulative particle size of the pigment is the diameter of the particle at which the cumulative value from the smallest particle size side reaches 50% of the total volume of the measured particles in the particle size accumulation curve. The 50% volume-based cumulative particle size of the pigment can be measured using a particle size analyzer with dynamic light scattering under the measurement conditions described in the following resin items. The particle size increase rate of the pigment can also be measured by this method. However, the measured value can vary due to, for example, the effect of pigment aggregation. Therefore, adjustments can be made appropriately, for example, by reducing the measurement time.

[0077] As described above, the carboxylic acid group is a functional group used for dispersing pigments. When a resin having a carboxylic acid group is used as a pigment dispersant (resin dispersant), a (meth)acrylic resin having a unit with a carboxylic acid group and a hydrophobic unit can be used.

[0078] The unit having a carboxylic acid group is a hydrophilic unit, and those described in the specific examples in the following resin items can be used. As a hydrophobic unit, those described in the specific examples in the following resin items can be used.

[0079] Resins with carboxylic acid groups (resin dispersants) can have an acid value of 100 mg KOH / g or higher. An acid value less than 100 mg KOH / g leads to decreased reactivity with reactants, making pigment aggregation less likely. This will not adequately suppress image blurring. Resins with carboxylic acid groups (resin dispersants) can have an acid value of 200 mg KOH / g or lower.

[0080] resin particles

[0081] The ink contains resin particles. The resin particle content (by mass%) of the ink is preferably 0.1% by mass or more and 15.0% by mass or less, more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. The resin particles are in a dispersed state, in other words, in the form of a resin emulsion in the ink.

[0082] As used in this specification, the term "resin particles" refers to resins that are insoluble in the aqueous medium constituting the ink; specifically, it refers to resins that can exist in the aqueous medium in the form of particles having a particle size that can be measured by dynamic light scattering. The term "water-soluble resin" refers to resins that are soluble in the aqueous medium constituting the ink; specifically, it refers to resins that can exist in the aqueous medium in a state where the resin does not form particles having a particle size that can be measured by dynamic light scattering. "Resin particles" can also be referred to as "water-dispersible resins (water-insoluble resins)." The method for determining whether a resin is a water-soluble resin or resin particles using dynamic light scattering will be described below.

[0083] As described above, the resin particles are required to contain particles that do not readily aggregate with the reactants in the reaction solution. Specifically, the resin particles include first resin particles whose particle size increase rate upon contact with the reaction solution is 3.0 times or less. The particle size increase rate of the first resin particles can be 1.2 times or less. A particle size increase rate of 1.2 times or less indicates that the resin particles are difficult to aggregate with the reactants. Therefore, the image clarity can be further improved. The particle size increase rate can be 1.0 times or more. The particle size increase rate of the resin particles is the particle size increase rate when the aqueous dispersion of the resin particles and the reaction solution are mixed at a mass ratio of 1:1. Specifically, this ratio is the ratio of the particle size increase rate of the resin particles after mixing with the reaction solution (D...). 50 ) / (D of resin particles in the dispersion of resin particles 50 The calculated value. Here, the resin particle content (mass%) of the resin particle dispersion is 1.0% by mass, based on the total mass of the aqueous dispersion. D 50 The cumulative particle size is based on 50% of the volume, and its details will be described below. The D of the resin particles after mixing with the reaction solution... 50 Measurements are taken after the reaction has proceeded sufficiently. For example, measurements can be taken after the reaction solution and the aqueous dispersion of resin particles have been mixed and thoroughly stirred. Any stirring method can be used, such as using a stir bar, as long as the reaction proceeds sufficiently. In the examples described below, the reaction solution and the aqueous dispersion of resin particles were placed in a beaker and stirred with a stirrer for 30 seconds, and then the 50% cumulative particle size of the resin particles was measured based on volume.

[0084] The particle size increase rate of resin particles can be adjusted, for example, by adjusting the density of anionic groups on the surface of the resin particles or the acid value of the resin particles. The particle size increase rate can be reduced, for example, by reducing the density of carboxylic acid groups in the resin particles or by reducing the acid value of the resin particles. When the type of resin particles is fixed, the particle size increase rate varies depending on the type of reactants used in the reaction solution. Hereinafter, "first resin particle" is also referred to as "resin particle".

[0085] In water-based inks, the total mass ratio of the content (mass%) of the first resin particles to the total mass ratio of the content (mass%) of the second resin particles (mass%) with a particle size increase rate greater than 3.0 times and the content (mass%) of pigment is 1.2 times or more and 25.0 times or less. The total mass ratio of the content (mass%) of the first resin particles to the total mass ratio of the content (mass%) of the second resin particles and the content (mass%) of pigment can be 1.5 times or more and 6.0 times or less. When the mass ratio is less than 1.5 times, the smoothing effect of the resin particles on the image is not sufficiently achieved. Therefore, in some cases, sufficient image sharpness is not obtained. When the mass ratio is greater than 6.0 times, the proportion of components in the ink that do not easily aggregate increases excessively, and the aggregated pigment does not easily move along with the movement of resin particles on the surface of the recording medium. This fails to adequately suppress image blurring.

[0086] As a type of resin particle dispersion, emulsions utilizing emulsifiers or self-dispersible resins that can be dispersed without emulsifiers can be used. In the case of emulsion-type resin particles, the resin forming the resin particles may have hydrophilic groups, but it is not necessary for it to have hydrophilic groups. The resin particles can be dispersed by the action of an emulsifier having hydrophilic groups. In the case of self-dispersible resin particles, the resin forming the resin particles has hydrophilic groups. Examples of hydrophilic groups include at least one selected from the group consisting of hydroxyl, vinyl oxide, propylene oxide, sulfonic acid, sulfate, phosphonic acid, and carboxylic acid groups.

[0087] The hydrophilic groups of the resin particles can be nonionic hydrophilic groups such as hydroxyl, vinyl oxide, or propylene oxide groups, or anionic hydrophilic groups such as sulfonic acid groups, sulfate groups, phosphonic acid groups, or carboxylic acid groups. The particle size increase rate of the resin particles can be adjusted according to the types of reactants used in combination. When the reactant is an organic acid, the first resin particle can be a resin particle dispersed by the action of at least one hydrophilic group selected from the group consisting of hydroxyl, vinyl oxide, propylene oxide, sulfonic acid, sulfate, phosphonic acid, and carboxylic acid groups. Here, when the resin particles have carboxylic acid groups in addition to sulfonic acid groups, most of the sulfonic acid groups are in an ionized state. For this reason, the resin particles can be considered as resin particles dispersed by the action of sulfonic acid groups.

[0088] When the first resin particles are resin particles dispersed by the action of carboxylic acid groups, the acid value of the resin particles is preferably 11 mg KOH / g or less. More preferably, the acid value of the resin particles dispersed by the action of carboxylic acid groups (the first resin particles) is 5 mg KOH / g or less. When the acid value of the resin particles dispersed by the action of carboxylic acid groups is within the above range, the reactivity with the reactant can be reduced, thereby further improving the image clarity. The acid value of the resin particles dispersed by the action of carboxylic acid groups (the first resin particles) can be 1 mg KOH / g or more. The acid value of the resin particles can be measured, for example, by potentiometric titration.

[0089] When the reactant is a polyvalent metal salt, the first resin particles can be resin particles dispersed by at least one hydrophilic group selected from the group consisting of hydroxyl, vinyl oxide, propylene oxide, sulfonic acid, sulfate, and phosphonic acid groups. When the reactant is a cationic resin, the first resin particles can be resin particles dispersed by at least one hydrophilic group selected from the group consisting of hydroxyl, vinyl oxide, and propylene oxide groups. Using resin particles dispersed by specific hydrophilic groups, depending on the type of reactant, ensures reduced reactivity with the reactant, thereby improving image sharpness.

[0090] The resin particles in water-based inks may have at least one anionic group selected from the group consisting of sulfonic acid groups, sulfate groups, and phosphonic acid groups. When the hydrophilic groups of the resin particles in water-based inks are only nonionic hydrophilic groups such as hydroxyl, vinyl oxide, or propylene oxide groups, the resin particles do not have a surface charge. Therefore, in some cases, the resin particles do not have sufficient reactivity with the reactant or sufficient resistance to bleed-out. Even if the resin particles have anionic groups, when the resin particles only have carboxylic acid groups, the resin particles can easily aggregate, thus failing to obtain sufficient image sharpness. The first resin particles in the water-based ink may have at least one anionic group selected from the group consisting of sulfonic acid groups, sulfate groups, and phosphonic acid groups.

[0091] As described above, when resin particles are dispersed by hydrophilic groups corresponding to the type of reactant, the particle size increase rate can be adjusted by changing the type or proportion of the hydrophilic groups in the resin particles. For example, when the reactant is a polyvalent metal salt, the particle size increase rate can be changed by using a carboxylic acid group in combination with at least one hydrophilic group selected from the group consisting of hydroxyl, vinyl oxide, propylene oxide, sulfonic acid, sulfate, and phosphonic acid groups. Nonionic hydrophilic groups tend to decrease reactivity. Anionic hydrophilic groups tend to increase reactivity. The particle size increase rate of resin particles dispersed by the action of carboxylic acid groups can be adjusted, for example, by adjusting the acid value of the resin particles. Specifically, a decrease in the acid value of the resin particles ensures a decrease in the particle size increase rate. In the case of pigments, when a fixation method is used to disperse resin particles, the particle size increase rate varies depending on the type of reactant used in the reaction solution.

[0092] The constituent units of the resin forming the resin particles may suitably be selected from those units constituting the resin described below. The acid value of the resin constituting the resin particles may be 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 1,000 or more and 3,000,000 or less, more preferably 100,000 or more and 3,000,000 or less. The volume-based 50% cumulative particle size (D) of the resin particles, measured by dynamic light scattering, is... 50 Preferably, the particle size is 50 nm or more and 500 nm or less, more preferably 100 nm or more and 300 nm or less. The 50% cumulative particle size based on volume of the resin particles is the diameter of the particles at which the cumulative value from the smallest particle size side reaches 50% of the total volume of the measured particles in the cumulative particle size curve. The 50% cumulative particle size based on volume of the resin particles can be measured using a particle size analyzer with dynamic light scattering under the measurement conditions described in the following resin items. Whether a particular resin is a resin particle can be determined by whether the 50% cumulative particle size based on volume is measured in the above measurements. The glass transition temperature of the resin particles is preferably 40 °C or more and 120 °C or less, more preferably 50 °C or more and 100 °C or less. The glass transition temperature (°C) of the resin particles can be measured using a differential scanning calorimeter (DSC). The resin particles do not need to contain coloring materials.

[0093] Compositional analysis of resin particles

[0094] The resin constituting the resin particles can be determined, for example, by the following method: The resin particles are dissolved in an organic solvent capable of dissolving resin particles, such as tetrahydrofuran, to prepare a sample. The resin particles used can be in the form of an aqueous dispersion or in a dried state. The resulting sample is analyzed, for example, by nuclear magnetic resonance (NMR) spectroscopy or matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS). This allows the type and proportion of the units (monomers) constituting the resin to be determined. Selectively, the resin particles themselves can be analyzed by pyrolysis gas chromatography to detect the units (monomers) constituting the resin. When insoluble components that are insoluble in the organic solvent are generated during sample preparation, the units (monomers) constituting the resin can also be detected by analyzing the insoluble components using pyrolysis gas chromatography.

[0095] surfactants

[0096] Ink may contain surfactants. The introduction of surfactants into the ink can reduce the surface tension of the ink, thereby facilitating wetting and spreading of the ink on the surface of the recording medium, and thus improving image sharpness. The surfactant content (by mass%) of the ink is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.1% by mass or more and 2.0% by mass or less. Examples of surfactants include anionic surfactants, cationic surfactants, and nonionic surfactants. Nonionic surfactants can be used because they are less likely to affect the reactivity of pigment and resin particles with the reactants. In particular, water-based inks may further contain at least one surfactant selected from the group consisting of fluorinated nonionic surfactants and silicone nonionic surfactants. Surfactants can effectively reduce the surface tension of the ink without destabilizing the dispersion of pigment and resin particles, thus further improving image sharpness.

[0097] In addition to the surfactants mentioned above, water-based inks may also contain hydrocarbon-based nonionic surfactants. Using hydrocarbon-based surfactants in combination with the aforementioned surfactants can further improve the wettability of the ink, thereby further improving image sharpness.

[0098] Organosilicon-based nonionic surfactants are surfactants obtained by introducing hydrophilic groups, such as vinyl oxides, into polyorganosiloxanes having siloxane bonds (SiO) in which silicon (Si) atoms and oxygen atoms (O) are alternately linked as the main backbone. Examples of organosilicon surfactants include polyether-modified siloxane compounds, alkyl polyether-modified siloxane compounds, alkyl organosilicon dendritic polyether-modified siloxane compounds, and alkyl organosilicon dendritic diglyceride-modified siloxane compounds. Based on the site of introduction of the hydrophilic group, they can be roughly classified into side-chain and linear types. In this specification, side-chain type refers to polyorganosiloxanes in which hydrophilic groups are introduced into silicon atoms other than the terminals of the polyorganosiloxane. Linear type refers to polyorganosiloxanes in which hydrophilic groups are introduced into silicon atoms at one or more terminals of the polyorganosiloxane. Examples of hydrophilic groups include alkenyl oxide and hydroxyl groups. Examples of alkenyl oxides include vinyl oxide, propylene oxide, and butenyl oxide. Among these, vinyl oxide and propylene oxide can be used. Examples of side-chain structures are shown in equation (1) below, and examples of linear structures are shown in equation (2) below:

[0099]

[0100] In each of formulas (1) and (2), m, n, X and Y are each natural numbers, R1, R2 and R3 are each independently alkylene groups, and EO is vinyl oxide.

[0101] Fluorinated nonionic surfactants are surfactants with a perfluoroalkyl group, such as vinyl oxide, as the main backbone. Examples of fluorinated surfactants include perfluoroalkyl vinyl oxide adducts.

[0102] Hydrocarbon-based nonionic surfactants are surfactants having a hydrocarbon as the main backbone in which a hydrophilic group, such as vinyl oxide, is introduced. Examples of hydrocarbon-based nonionic surfactants include polyoxyethylene alkyl ethers, ethylene oxide adducts of ethynyl glycol, polyethylene glycol-polypropylene glycol block copolymers, and ethylene oxide adducts of polyols. Hydrocarbon-based nonionic surfactants can be roughly classified into side-chain and linear types based on the site of introduction of the hydrophilic group. In this specification, side-chain type means that the hydrophilic group is introduced into a carbon atom of the hydrocarbon chain other than the terminal atom. Linear type means that the hydrophilic group is introduced into one or more ends of the hydrocarbon chain. Examples of side-chain structures are shown in the following formula (3), and examples of linear structures are shown in the following formula (4):

[0103]

[0104] CH3-(CH2) m-O-(EO) n -H(4)

[0105] In equations (3) and (4), m, n, X and Y are each natural numbers, and EO is vinyl oxide.

[0106] Organosilicon-based nonionic surfactants can be compounds with the following structure: silicon atoms in a polyorganosiloxane chain with a repeating siloxane structure as the main backbone are substituted with at least one hydrophilic group selected from the group consisting of oxidized alkenyl and hydroxyl groups at positions other than the terminal ends. Hydrocarbon-based nonionic surfactants can be compounds with the following structure: carbon atoms in a hydrocarbon chain with a main backbone are substituted with at least one hydrophilic group selected from the group consisting of oxidized alkenyl and hydroxyl groups at positions other than the terminal ends. In other words, both the organosilicon-based and hydrocarbon-based nonionic surfactants in water-based inks can be side-chain type. When the surfactant is a linear surfactant, it adsorbs onto the pigment more readily than a side-chain surfactant. Therefore, it easily inhibits the reaction between the pigment and the reactant. This may not sufficiently suppress image blurring.

[0107] Water-soluble resin

[0108] The ink may further contain a water-soluble resin. The water-soluble resin content (by mass%) of the ink is preferably 0.1% by mass or more and 15.0% by mass or less, based on the total mass of the ink. More preferably, the water-soluble resin content (by mass%) of the ink is 0.5% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

[0109] Resins can be added to inks to: (i) stabilize the dispersion of pigments, in other words, act as resin dispersants or their additives. Additionally, resins can be added to inks to: (ii) improve various properties of the recorded image. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof.

[0110] Composition of water-soluble resins

[0111] Examples of water-soluble resins include acrylic resins, polyurethane resins, and olefin resins. Among these, acrylic resins or polyurethane resins may be used. Acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate may be used. The water-soluble resin may be at least one selected from the group consisting of: (i) water-soluble resins comprising units having at least one selected from the group consisting of vinyl oxide and propylene oxide groups, and (ii) block copolymers comprising blocks composed of units without acid groups. The use of water-soluble resins can further improve image sharpness. The water-soluble resin content (mass %) of the ink may be 0.1% by mass or more, based on the total mass of the ink.

[0112] Acrylic resins can have both hydrophilic and hydrophobic units as constituent units. Resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one monomer selected from the group consisting of aromatic ring-containing monomers and (meth)acrylate monomers can be used. In particular, 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 can be used. These resins readily interact with pigments and can therefore be used as resin dispersants for dispersing pigments.

[0113] A hydrophilic unit is a unit having hydrophilic groups, such as anionic groups. Hydrophilic units can be formed, for example, by polymerizing hydrophilic monomers having hydrophilic groups. Specific examples of hydrophilic monomers having hydrophilic groups include: acidic monomers each having carboxylic acid groups such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; and anionic monomers, such as anhydrides and salts of those acidic monomers. Examples of cations constituting the salts of acidic monomers include lithium ions, sodium ions, potassium ions, ammonium ions, and organic ammonium ions. A hydrophobic unit is a unit without 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 that each have an aromatic ring, such as styrene, α-methylstyrene, and benzyl methacrylate; and (meth)acrylate monomers, such as methyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate.

[0114] Polyurethane resins can be prepared, for example, by reacting polyisocyanates with polyols. Polyurethane resins can also be prepared by further reacting a chain extender with polyisocyanates and polyols. Examples of olefin-based resins include polyethylene and polypropylene.

[0115] Performance of water-soluble resins

[0116] In this specification, "the resin is water-soluble" means that when the resin is neutralized with an alkali equal to its acid value, it exists in an aqueous medium in a state in which the resin does not form particles with a particle size that can be measured by dynamic light scattering. Whether a resin is water-soluble can be determined by the following method. First, prepare a liquid containing resin neutralized with an alkali such as sodium hydroxide or potassium hydroxide equal to its acid value (resin solids content: 10% by mass). Next, dilute the prepared liquid 10 times (based on volume) with pure water to prepare a sample solution. Then, if the particle size of the resin in the sample solution is measured by dynamic light scattering and no particles with that particle size are measured, the resin can be determined to be water-soluble. The measurement conditions at this time can be as follows: for example, Set Zero: 30 seconds; measurement factor: 3 times; and measurement time: 180 seconds. A particle size analyzer based on dynamic light scattering (e.g., trade name: "UPA-EX150", available from Nikkiso Co., Ltd.) can be used as a particle size distribution measurement device. Of course, particle size distribution measurement devices and measurement conditions are not limited to those mentioned above.

[0117] The acid value of the water-soluble resin is preferably 10 mg KOH / g or higher and 200 mg KOH / g or lower, more preferably 50 mg KOH / g or higher and 150 mg KOH / g or lower. The weight-average molecular weight of the water-soluble resin can be 3,000 or higher and 15,000 or lower. The weight-average molecular weight of the water-soluble resin can be measured by gel permeation chromatography converted to polystyrene.

[0118] wax particles

[0119] The ink may contain particles composed of wax (wax particles). Using ink containing wax particles can record images with further improved abrasion resistance. The wax in this specification may be a composition in which components other than wax are blended, or it may be wax itself. The wax particles may be dispersed by a dispersant such as a surfactant or a water-soluble resin. Wax may be used alone or in combination of two or more. The wax particle content (by mass%) of the ink is preferably 0.1% by mass or more and 10.0% by mass or less, more preferably 1.0% by mass or more and 5.0% by mass or less, based on the total mass of the ink.

[0120] In a narrow sense, wax is an ester of fatty acids and higher monohydric or dihydric alcohols that is insoluble in water, and includes animal and plant waxes, but excludes oils or fats. In a broad sense, wax includes high-melting-point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the recording method according to embodiments of the present invention, any wax in the broad sense can be used without particular limitation. Any wax in the broad sense can be classified as natural wax, synthetic wax, its blends (blended waxes), and its modified products (modified waxes).

[0121] Examples of natural waxes include: animal-based waxes, such as beeswax, whale wax, or lanolin; plant-based waxes, such as Japanese wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, or rice wax; mineral-based waxes, such as lignite wax; and petroleum-based waxes, such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes, such as Fischer-Tropsch wax, and polyolefin waxes such as polyethylene wax and polypropylene wax. Blended waxes are mixtures of the various waxes mentioned above. Modified waxes are prepared by modifying the various waxes mentioned above through processes such as oxidation, hydrogenation, alcohol modification, acrylic modification, or polyurethane modification. These waxes can be used alone or in combination of two or more. The wax can be at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, their modified products, and their blends. Blends of multiple waxes can be used. Blends of petroleum-based waxes and synthetic waxes can be used.

[0122] The wax can be solid at room temperature (25°C). The melting point (°C) of the wax is preferably above 40°C and below 120°C, more preferably above 50°C and below 100°C. The melting temperature of the wax can be determined according to the test method described in 5.3.1 (Test Method for Melting Point) of JIS K2235:1991 (Petroleum Wax). For microcrystalline waxes, petrolatum, and mixtures of various waxes, the melting point can be measured more accurately by the test method described in 5.3.2. The melting point of a wax is easily affected by characteristics such as molecular weight (higher molecular weight leads to a higher melting point), molecular structure (straight-chain structures have higher melting points, and branched-chain structures have lower melting points), crystallinity (higher crystallinity leads to a higher melting point), and density (higher density leads to a higher melting point). Therefore, waxes with a desired melting point can be produced by controlling these characteristics. The melting point of the wax in the ink can be determined, for example, by subjecting the ink to ultracentrifugation, washing and drying the separated wax, and then measuring it according to the test method described above.

[0123] Aqueous media

[0124] The ink used in the recording method according to an embodiment of the present invention is an aqueous ink containing at least water as an aqueous medium. The ink may contain water or be an aqueous medium that is a mixture of water and a water-soluble organic solvent. Deionized water or ion-exchanged water may be used as water. The water content (mass%) of the aqueous ink may be 50.0% or more and 95.0% or less, based on the total mass of the ink. The water-soluble organic solvent content (mass%) of the aqueous ink may be 3.0% or more and 50.0% or less, based on the total mass of the ink.

[0125] Water-soluble organic solvents contain substances with a vapor pressure of 1.0 × 10⁻⁶. -2The first water-soluble organic solvent has a strength of kPa or higher. The proportion (mass%) of the first water-soluble organic solvent in the water-soluble organic solvent of the water-based ink is 50.0% or more. The proportion (mass%) of the first water-soluble organic solvent in the water-soluble organic solvent of the water-based ink can be 90.0% or more. A proportion less than 90% by mass leads to an increase in the amount of liquid components remaining inside the recorded image, thus failing to provide sufficient moisture resistance to the image. The proportion (mass%) of the first water-soluble organic solvent in the water-soluble organic solvent of the water-based ink can be 100.0% by mass. In other words, all water-soluble organic solvents in the ink can be the first water-soluble organic solvent. Examples of the first water-soluble organic solvent include 1,2-butanediol (2.0 × 10⁻⁶ kPa). -2 kPa), propylene glycol (1,2-propanediol) (1.8×10 -2 kPa), ethylene glycol (1,2-ethanediol) (1.2×10 -2 kPa), diethylene glycol monoethyl ether (1.7×10 kPa) -2 kPa) and diethylene glycol monomethyl ether (2.4 × 10 kPa) -2 Examples of water-soluble organic solvents other than the first water-soluble organic solvent include alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing solvents, and sulfur-containing solvents, which can be used in inkjet recording inks. These water-soluble organic solvents can be used alone or in combination of two or more.

[0126] Other components

[0127] Ink may contain various other components as needed. Examples of other components include various additives, such as defoamers, surfactants, pH adjusters, viscosity modifiers, rust inhibitors, preservatives, antifungals, antioxidants, and reduction inhibitors. However, ink may not contain reactants included in the reaction solution.

[0128] The physical properties of ink

[0129] The ink is a water-based ink for use in inkjet systems. Therefore, from a reliability point of view, the physical properties can be appropriately controlled. The surface tension of the ink at 25°C is preferably 20 mN / m or more and 60 mN / m or less, more preferably 20 mN / m or more and 30 mN / m or less. The viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25°C is preferably 7.0 or more and 9.5 or less, more preferably 8.0 or more and 9.5 or less.

[0130] Example

[0131] While the present invention will be described in more detail with reference to embodiments and comparative examples, the invention is not limited to the following embodiments without departing from the spirit of the invention. Regarding the amount of components, "parts" and "%" are based on mass unless otherwise stated.

[0132] Preparation of reaction solution

[0133] The components (in %) given in Tables 1 and 2 were mixed. The resulting mixtures were thoroughly stirred and pressure filtered using a 3.0 μm cellulose acetate filter (available from Toyo Roshi Kaisha, Ltd.) to prepare the various reaction solutions. In Table 1, "Catiomaster PDT-2", "Catiomaster PD-7", and "Catiomaster PD-30" are trade names for aqueous solutions of amine-epimercohydrin condensation polymers available from Yokkaichi Chemical Co., Ltd. "Acetylenol E60" is a trade name for a side-chain hydrocarbon-based nonionic surfactant available from Kawaken Fine Chemicals Co., Ltd. "Proxel GXL(S)" is a trade name for a preservative available from Arch Chemicals Inc. Vapor pressures are values ​​at 25°C and 1 atm. Details of the cationic resins used to prepare the reaction solutions listed in Table 1 are described below.

[0134] • Catiomaster PDT-2 (trade name): Available from Yokkaichi Chemical Co., Ltd., weight average molecular weight: 1,000, degree of cationization: 7 meq / g, resin content: 60.0%

[0135] • Catiomaster PD-7 (trade name), available from Yokkaichi Chemical Co., Ltd., weight average molecular weight: 5,000, degree of cationization: 7 meq / g, resin content: 50.0%.

[0136] • Catiomaster PD-30 (trade name), available from Yokkaichi Chemical Co., Ltd., weight average molecular weight: 9,000, degree of cationization: 7 meq / g, resin content: 50.0%.

[0137] PAS-2401 (trade name), available from Nittobo Medical Co., Ltd., weight average molecular weight: 2,000, degree of cationization: 2 meq / g, resin content: 25.0%.

[0138] PAS-A-5 (trade name), available from Nittobo Medical Co., Ltd., weight average molecular weight: 4,000, degree of cationization: 3 meq / g, resin content: 40.0%.

[0139] PAA-HCL-01 (trade name), available from Nittobo Medical Co., Ltd., weight average molecular weight: 1,600, degree of cationization: 9 meq / g, resin content: 33.0%.

[0140] Polyquat 40 u 05 NV (trade name), available from Katpol-Chemie GmbH, average molecular weight: 4,000, degree of cationization: 6 meq / g, resin content: 40.0%.

[0141] Table 1: Composition of the reaction solution

[0142]

[0143] Table 2: Composition of the reaction solution

[0144]

[0145] Preparation of pigment dispersion

[0146] Pigment Dispersion 1

[0147] A styrene-ethyl acrylate-acrylic acid copolymer (resin 1) with an acid value of 160 mg KOH / g and a weight-average molecular weight of 8,000 was prepared. Then, 20.0 parts of resin 1 were neutralized with potassium hydroxide in an equimolar amount to its acid value. Afterwards, an appropriate amount of pure water was added to prepare an aqueous solution of resin 1 with a resin content (solid content) of 20.0%. This was achieved by adding 15.0 parts of pigment (carbon black, specific surface area: 200 m² / g)... 2 A mixture was prepared by mixing 37.5 parts of an aqueous solution of resin 1 and 47.5 parts of pure water. The resulting mixture was then placed in a batch vertical sand mill (available from Aimex Co., Ltd.) with 200 parts of 0.3 mm diameter zirconia beads and dispersed for 5 hours while the mill was cooled with water. After removing coarse particles by centrifugation, pressure filtration was performed using a 3.0 μm cellulose acetate filter (available from Toyo Roshi Kaisha, Ltd.) to prepare a pigment dispersion 1 with a pigment content of 15.0% and a resin dispersant (resin 1) content of 7.5%.

[0148] Pigment Dispersion 2

[0149] Except that resin 1 is changed to resin (resin 2) with an acid value of 60 mg KOH / g and a weight average molecular weight of 7,000, pigment dispersion 2 with a pigment content of 15.0% and a resin dispersant (resin 2) content of 7.5% is prepared by the same procedure as for pigment dispersion 1.

[0150] Pigment Dispersion 3

[0151] Except that resin 1 is changed to resin (resin 3) with an acid value of 50 mg KOH / g and a weight average molecular weight of 7,500, pigment dispersion 3 with a pigment content of 15.0% and a resin dispersant (resin 3) content of 7.5% is prepared by the same procedure as for pigment dispersion 1.

[0152] Pigment Dispersion 4

[0153] Except that resin 1 is changed to resin (resin 4) with an acid value of 100 mg KOH / g and a weight average molecular weight of 7,000, pigment dispersion 4 with a pigment content of 15.0% and a resin dispersant (resin 4) content of 7.5% is prepared by the same procedure as for pigment dispersion 1.

[0154] Pigment Dispersion 5

[0155] Except that resin 1 is changed to resin (resin 5) with an acid value of 92 mg KOH / g and a weight average molecular weight of 8,400, pigment dispersion 5 with a pigment content of 15.0% and a resin dispersant (resin 5) content of 7.5% is prepared by the same procedure as for pigment dispersion 1.

[0156] Pigment Dispersion 6

[0157] First, take 20.0g of carbon black (specific surface area: 200m²) 213.3 mmol of p-aminobenzoic acid, 13.3 mmol of nitric acid, and 200 mL of pure water were mixed. These were mixed at 6,000 rpm and room temperature using a laboratory rotary mixer (Silverson L5M-A, available from Silverson) to prepare a mixture. After 30 minutes, potassium nitrite dissolved in a small amount of water (equimolar to the total amount of the treatment agent) was slowly added to the mixture and mixed. This mixing brought the temperature of the mixture to 60°C, and the reaction was carried out under these conditions for 1 hour. The pH of the mixture was then adjusted to 10 using an aqueous solution of potassium hydroxide. After 30 minutes, 20 mL of pure water was added, and the mixture was permeated using a spectral membrane to prepare a self-dispersible pigment. Water was added to the prepared self-dispersible pigment to prepare pigment dispersion 6 with a pigment content of 10.0%. The surface charge of the pigment in pigment dispersion 6 was 3.0 μmol / m³. 2 The surface charge of the pigment was measured using an automated potentiometric titrator (trade name: AT-510, available from Kyoto Electronics Manufacturing Co., Ltd.) equipped with a flowing potentiometric titration unit (PCD-500) for colloidal titration. Specifically, the pigment dispersion was diluted with pure water to approximately 300 times, by weight. The pH of the pigment dispersion was then adjusted to approximately 10 with potassium hydroxide as needed. The pigment dispersion was potentiometrically titrated using 5 mmol / L methyl ethylene glycol chitosan as the titrant.

[0158] Pigment Dispersion 7

[0159] Except for replacing p-aminobenzoic acid with p-aminobenzenesulfonic acid, pigment dispersion 7, with a pigment content of 10.0%, was prepared in the same manner as pigment dispersion 6. The surface charge of the pigment in pigment dispersion 7 was 3.0 μmol / m³. 2 .

[0160] Pigment Dispersion 8

[0161] Except for a change in the amount of para-aminobenzoic acid to 8.7 mmol, pigment dispersion 8, with a pigment content of 10.0%, was prepared in the same manner as pigment dispersion 6. The surface charge of the pigment in pigment dispersion 8 was 2.0 μmol / m 2 .

[0162] Pigment Dispersion 9

[0163] Except that the pigment is changed to CI Pigment Blue 15:3, a pigment dispersion 9 with a pigment content of 15.0% and a resin dispersant (resin 1) content of 7.5% is prepared by the same procedure as for pigment dispersion 1.

[0164] Analysis of resin particles

[0165] 50% cumulative particle size based on volume of resin particles

[0166] The 50% cumulative particle size (D) of the resin particles based on volume 50 The measurements were performed as follows. A liquid containing resin particles (an aqueous dispersion of the resin particles) was diluted with deionized water to prepare a sample with a resin particle content of approximately 1.0%. The particle size of this sample was measured using a particle size distribution analyzer (trade name: "Nanotrac WAVE II-Q", available from MicrotracBEL Corp.) via dynamic light scattering. The measurement conditions were as follows: Set Zero: 30 seconds, Number of measurements: 3, Measurement time: 180 seconds, Shape: True spherical, Refractive index: 1.6, and Density: 1.0.

[0167] Acid value of resin particles

[0168] The acid value of the resin particles was measured as follows. The resin particles were recovered from the liquid containing them and washed with 1.0 mol / L hydrochloric acid and then with deionized water. The resin particles were added to 60 mL of liquid to dissolve the resin at 25°C, thereby preparing a sample. This liquid was prepared by mixing water and tetrahydrofuran at a mass ratio of 1:6. The sample was then subjected to neutralization titration to measure the acid value of the resin. For the neutralization titration, an automatic potentiometric titrator (trade name "AT-510", available from Kyoto Electronics Manufacturing Co., Ltd.) equipped with a combined glass electrode (trade name "C-171") was used. The titrant used was a 0.5 mol / L ethanol solution of potassium hydroxide.

[0169] Preparation of resin particles

[0170] Resin particles 1-6

[0171] In a four-necked flask equipped with a stirrer, reflux condenser, and nitrogen inlet, ion-exchanged water and 0.2 parts of potassium persulfate were mixed. The amount of ion-exchanged water used was adjusted so that the total amount of the mixture containing the following components was 100.0 parts. The components given in Table 3 were mixed to prepare an emulsion. Under a nitrogen atmosphere, the prepared emulsion was added dropwise to the four-necked flask over 1 hour. The polymerization reaction was carried out with stirring at 80°C for 2 hours. After cooling to 25°C, ion-exchanged water and an aqueous solution containing potassium hydroxide in an amount equal to the acid value of the resin particles were added. Thus, aqueous dispersions of resin particles 1 to 6 were prepared, each with a resin particle content (solid content) of 25.0%. In Table 3, "Adeka Reasoap ER-20" is the trade name of a nonionic surfactant available from ADEKA Corporation (based on the molar amount of vinyl oxide added: 20). "Aqualon KH-05" is the trade name of an anionic surfactant available from DKS Co., Ltd. "BlemmerPME-1000" is the trade name of polyethylene glycol monomethacrylate available from NOF Corporation (based on the molar addition of vinyl oxide: 23). Hydrophilic groups that contribute to the dispersion of each resin particle are listed in the "Type of Hydrophilic Group" column. Resin particles 1-5 have sulfonic acid and carboxylic acid groups, and considering the acid dissociation constant, they are considered to be resin particles dispersed through the action of sulfonic acid groups.

[0172] Table 3: Composition of Resin Particles

[0173]

[0174] 7-10 resin particles

[0175] The mixture of components (parts) listed in Table 4 under "Esterification" was placed in a reaction vessel within an autoclave and heated at 220°C for 4 hours to carry out the esterification reaction. The temperature was then increased to 240°C, and the autoclave pressure was reduced to 13 Pa over 90 minutes. The esterification (dehydration condensation) reaction was continued at 240°C for 5 hours while maintaining a reduced pressure of 13 Pa. Nitrogen gas was then introduced into the autoclave to bring the pressure to normal. The temperature in the reaction vessel was reduced to 220°C. A catalyst (tetrabutyl titanate) and components (parts) listed in Table 4 under "Transesterification" were added. The mixture was heated at 220°C for 2 hours to carry out transesterification. The amount of catalyst used (mol) was 3 × 10⁻⁶. -4 × Total amount of polyvalent carboxylic acids used (mol). Nitrogen gas was then introduced into the autoclave to create pressure, and the sheet resin was removed. The resin was cooled to 25°C and then pulverized using a pulverizer.

[0176] A 2.0 L beaker equipped with a stirrer (trade name: "Tornado Stirrer Standard SM-104", available from As One Corporation) was used. The synthesized resin and tetrahydrofuran were placed in the beaker. The mixture was stirred at 25 °C to dissolve the resin. A 5.0% aqueous solution of sodium hydroxide was added in an amount equal to the neutralization rate (mol%) based on the resin's acid value. The mixture was stirred for 30 minutes. Then, 900 parts of deionized water were added dropwise to the beaker at a rate of 20 mL / min while the mixture was stirred at 150 rpm and 10 °C. The mixture was then heated to 60 °C. The tetrahydrofuran was distilled off under reduced pressure. Further, water was partially distilled off. The beaker was placed in a water bath. Stirring was continued at 85 °C under the conditions specified in the "Heat Treatment" section of Table 4 for heat treatment. The contents of the beaker were filtered using a 150-mesh wire mesh (a filter obtained by weaving 150 stainless steel wires vertically and horizontally in a 1-inch square). An appropriate amount of deionized water was added to adjust the resin particle content. Thus, aqueous dispersions of 7–10 resin particles were prepared, each with a resin particle content of 25.0%. The properties of the synthesized resin particles are described on the right side of Table 4. In Table 4, the components are abbreviated as follows: EG: ethylene glycol, BPA: bisphenol A, tPA: terephthalic acid, iPA: isophthalic acid, and BTA: trimellitic acid. Hydrophilic groups that contribute to the dispersion of each resin particle are listed in the "Type of Hydrophilic Group" column.

[0177] Table 4: Synthesis conditions and characteristics of resin particles

[0178]

[0179] Preparation of water-soluble resins

[0180] Water-soluble resin 1

[0181] The water-soluble resin 1, as a block copolymer, was prepared using the components given in Table 5. The monomers of block A (in parts) were synthesized by living radical polymerization. Specifically, under a nitrogen atmosphere at -50°C, 30 parts of n-butyllithium were added to 1,600 parts of tetrahydrofuran in which 4.7 parts of lithium had already been added, followed by the addition of 60.0 parts of benzyl methacrylate, and then stirring for 40 minutes. Then, 30.0 parts of diethylzinc were added, and the mixture was stirred for 1 minute to prepare a liquid containing a polymer corresponding to the block A composed of hydrophobic monomer units.

[0182] Individually, 30.0 parts of n-butyl acrylate and 10.0 parts of acrylic acid were polymerized in a conventional manner to prepare a random copolymer corresponding to the B-block. The random copolymer corresponding to the B-block and 45.0 parts of diethylzinc were added to 110 parts of tetrahydrofuran to prepare a liquid containing a random copolymer corresponding to the B-block composed of hydrophilic monomer units.

[0183] The liquid was added dropwise to a liquid containing the polymer corresponding to block A. After stirring the mixture for 60 minutes, 1.3 parts of acetic acid were added to terminate the reaction. 30.0 parts of a 35.0% aqueous solution of acetic acid were added to the liquid, followed by stirring for 10 minutes. The mixture was washed three times with pure water, and the precipitated resin was dried to obtain water-soluble resin 1. The mixture was neutralized with potassium hydroxide in an equimolar amount of acid value. An appropriate amount of deionized water was added to prepare a liquid containing water-soluble resin 1, the resin content of which was 10.0%. Water-soluble resin 1 is a block copolymer having blocks A consisting only of units derived from hydrophobic monomers and blocks B as random copolymers.

[0184] Water-soluble resin 2

[0185] First, 60.0 parts of benzyl acrylate, 30.0 parts of n-butyl acrylate, 5.0 parts of acrylic acid, and 5.0 parts of Blemmer PME-400 were polymerized in a conventional manner to prepare a water-soluble resin 2 as a random copolymer. The mixture was neutralized with potassium hydroxide in an equimolar amount of acid value. An appropriate amount of deionized water was added to prepare a liquid containing water-soluble resin 2, the resin content of which was 10.0%. Blemmer PME-400 is a trade name for polyethylene glycol monomethacrylate (in molar amounts of vinyl oxide added: 9) available from NOF Corporation.

[0186] Water-soluble resin 3

[0187] The liquid containing water-soluble resin 3 is prepared in the same manner as in the preparation method of water-soluble resin 2, except that 60.0 parts of benzyl acrylate, 30.0 parts of n-butyl acrylate, and 10.0 parts of Blemmer PME-400 are used instead of 60.0 parts of benzyl acrylate, 30.0 parts of n-butyl acrylate, 5.0 parts of acrylic acid, and 5.0 parts of Blemmer PME-400. Water-soluble resins 2 and 3 are each water-soluble resins containing units having vinyl oxide (nonionic units) and having anionic groups.

[0188] Water-soluble resin 4

[0189] As a liquid containing water-soluble resin 4, an aqueous solution of resin 1 used to prepare the pigment dispersion is used.

[0190] Preparation of organosilicon surfactants

[0191] Organosilicon surfactant 1

[0192] Organosilicon surfactant 1 was synthesized using a glass container equipped with a thermometer and a stirrer. In this container, a polysiloxane compound represented by formula (A) and a polyethylene oxide compound represented by formula (B), as the main components, underwent an addition reaction in the presence of a platinum catalyst to synthesize organosilicon surfactant 1. The addition reaction continued until a surfactant with the following weight-average molecular weight was obtained. The prepared organosilicon surfactant 1 is a nonionic compound having a structure in formula (1) where X = 2, Y = 1, n = 13, and R3 = n-propylidene, corresponding to a side-chain type. The weight-average molecular weight of this surfactant is approximately 1,000.

[0193] Si(CH3)3-O-(Si(CH3)2-O)2-Si(CH3)HO-Si(CH3)3···(A)

[0194] CH2=CHCH2-O-(C2H4O) 13 -H···(B)

[0195] Organosilicon surfactant 2

[0196] Except for changing the polysiloxane compound and the polyethylene oxide compound to formulas (C) and (D) below, organosilicon surfactant 2 was prepared in the same manner as in the preparation of organosilicon surfactant 1. The resulting surfactant has a structure having X = 4, m = 6, n = 6, R1 = n-propylidene and R2 = n-propylidene in formula (2) and corresponds to a linear nonionic compound. The weight-average molecular weight of this surfactant is approximately 900.

[0197] H-(Si(CH3)2-O)5-Si(CH3)2-H···(C)

[0198] CH2=CHCH2-O-(CH2H4O)6-H···(D)

[0199] Ink preparation

[0200] Mix the components given in Tables 5-8 (unit: %). Thoroughly stir the resulting mixture and pressure filter it using a 3.0 μm cellulose acetate filter (available from Toyo Roshi Kaisha, Ltd.) to prepare the inks. "Capstone FS3100" is a trade name for a fluorinated nonionic surfactant available from LEHVOSS Group. "NIKKOL BL4.2" is a trade name for a linear hydrocarbon nonionic surfactant available from Nikko Chemicals Co., Ltd.

[0201] Table 5: Composition and Properties of Ink

[0202]

[0203] Table 6: Composition and Properties of Ink

[0204]

[0205] Table 7: Composition and Properties of Ink

[0206]

[0207] Table 8: Composition and Properties of Ink

[0208]

[0209] Preparation of recording media

[0210] Prepare the following recording media 1 to 3.

[0211] • Recording medium 1: Trade name "Scotchcal Graphic Film IJ1220-10" (available from 3M, material: polyvinyl chloride), in the Bristow method from contact start to 30 msec 1 / 2 The amount of water absorbed is 0 mL / m 2 Above and 10mL / m 2 the following)

[0212] • Recording medium 2: Trade name "Canon Photo Paper, Gloss Professional [Platinum Grade] PT-201" (available from CANON KABUSHIKI KAISHA, in the Bristow method from contact start to 30msec) 1 / 2 The amount of water absorbed is greater than 10 mL / m 2 )

[0213] • Recording medium 3: Trade name "GIY-0305" (available from Lintec Corporation, material: PET, from contact start to 30 msec in the Bristow method) 1 / 2 The amount of water absorbed is 0 mL / m 2 Above and 10mL / m 2 the following)

[0214] evaluate

[0215] The prepared reaction solution and ink were filled into each cartridge. The cartridges were placed in an inkjet recording device (trade name "imagePROGRAF PRO-2000", available from CANON KABUSHIKIKAISHA) equipped with a recording head configured to eject ink using heat. In this recording device, a heating device configured to dry the recording medium to which the reaction solution and ink were applied was introduced at a position downstream of the recording head in the direction of medium transport. The surface temperature of the recording medium was then set to 80°C by heating with the heating device. The recording environment was: temperature 25°C, relative humidity 50%. In the embodiment, an image recorded under the condition that a droplet of ink weighing 4.0 ng was applied to a unit area of ​​1 / 1,200 inch × 1 / 1,200 inch was defined as a 100% recording task. Solid images were recorded on the recording media given in Tables 9 and 10 by applying the reaction solution and ink given in Tables 9 and 10 in an overlapping manner with a 40% recording task of the reaction solution and a 200% recording task of the ink. Subsequently, under the same conditions as above, except using ink 4, a solid image was recorded at a position adjacent to the solid image. The image was then dried at 25°C for 24 hours to obtain an evaluation image. In embodiments of the present invention, in the evaluation criteria for the following items, "AA", "A", and "B" are considered acceptable levels, and "C" is considered an unacceptable level. Table 11 shows the evaluation results.

[0216] When the ink contains resin particles with a particle size increase rate greater than 3.0 times, its content is recorded in the "Other Resin Particles R (%)" column in Tables 9 and 10. The ink 26 in Example 39 contains two types of resin particles. Resin particle 7 corresponds to the other resin particles (second resin particles). The particle size increase rate when used with reaction solution 1 is approximately 40.0 times.

[0217] Image blur suppression

[0218] For the obtained evaluation images, a handheld image quality analyzer (trade name "PIAS-II", available from Quality Engineering Associates Inc.) was used to measure the roughness values ​​of the boundary between adjacent solid images. The roughness values ​​were defined in ISO 13660, and edge measurement was used as the measurement mode. Blur suppression was evaluated according to the following criteria: a low roughness value at the boundary indicates that color mixing between adjacent images is suppressed; in other words, image blur is suppressed.

[0219] AA: Roughness value below 50.

[0220] A: The roughness value is greater than 50 and less than 60.

[0221] B: Roughness value is greater than 60 and less than 70.

[0222] C: Roughness value is greater than 70.

[0223] Image clarity

[0224] The resulting evaluation images were affixed to test stands with radii of curvature of 200 mm, 60 mm, and 45 mm. Two fluorescent lamps spaced 10 cm apart served as the observation light source. The images were illuminated by the fluorescent lamps from a distance of 2 m. Under illumination and observation angles of 45°, the shape of the fluorescent lamps projected onto the areas in the evaluation images recorded in ink as described in Tables 9 and 10 was visually observed. The image sharpness was evaluated according to the following criteria.

[0225] AA: Identify the boundary between two projected fluorescent lamps on each image attached to the test bench.

[0226] A: The boundary between the two projected fluorescent lamps was not identified on the image attached to the test stage with a curvature radius of 200 mm, but it was identified on the images attached to the test stages with curvature radii of 60 mm and 45 mm.

[0227] B: No boundary between the two projected fluorescent lamps was found on the images attached to the test benches with curvature radii of 200 mm and 60 mm, but the boundary between the two projected fluorescent lamps was identified on the image attached to the test bench with a curvature radius of 45 mm.

[0228] C: The boundary between the two projected fluorescent lamps was not identified on any image attached to the test bench.

[0229] Moisture resistance

[0230] The obtained evaluations were measured using the image luminance L* under conditions of a D50 light source, a viewing angle of 2°, an incident angle of 45°, a reflection angle of 0°, and a filter of ANSI A. The solid image was then placed in an environment with a temperature of 30°C and a humidity of 80% for 7 days, and the luminance L* was measured again in the same manner. Here, luminance L* is the value in the L*a*b* color characteristic system specified by Commission Internationale de l'Eclairage (CIE). The difference in luminance L* before and after placement was calculated, and the image's moisture resistance was evaluated according to the following criteria.

[0231] AA: The difference in brightness L* before and after placement is less than 1.

[0232] A: The difference in brightness L* before and after placement is greater than 1 and less than 2.

[0233] B: The difference in brightness L* before and after placement is greater than 2 and less than 3.

[0234] C: The difference in brightness L* before and after placement is greater than 3.

[0235] Table 9: Evaluation Criteria

[0236]

[0237] Table 10: Evaluation Criteria

[0238]

[0239] Table 11: Evaluation Results

[0240]

[0241] The image sharpness rating in Example 15 is "A", the same as in Example 13, but the image sharpness in Example 13 is better than that in Example 15. In Table 11, under the same rating, the sample rated "AA+" is better than the sample rated "AA".

[0242] According to embodiments of the present invention, an inkjet recording method can be provided that records images with excellent image clarity and moisture resistance, and suppresses blurring, even when recording on non-absorbent recording media. Furthermore, according to embodiments of the present invention, an inkjet recording apparatus for this inkjet recording method, as well as a kit for water-based ink and water-based reactive liquid, can be provided.

[0243] While the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims is accorded the broadest interpretation, thereby covering all such modifications and equivalent structures and functions.

Claims

1. An inkjet recording method, characterized in that, It records images on a recording medium using water-based ink and an aqueous reaction solution containing a reactant that reacts with the water-based ink. The method includes: an application step of applying the aqueous reaction solution to the recording medium; and an ink application step of applying the water-based ink in such a way that it overlaps with at least a portion of the area of ​​the recording medium on which the aqueous reaction solution has been applied. The water-based ink comprises pigments dispersed by carboxylic acid groups, resin particles, and a water-soluble organic solvent, wherein the particle size increase of the pigments dispersed by carboxylic acid groups upon contact with the aqueous reaction solution is 8.0 times or more. The resin particles include first resin particles, wherein the particle size increase rate of the first resin particles upon contact with the aqueous reaction liquid is less than 3.0 times; in the aqueous ink, the total mass ratio of the content of the first resin particles (by mass%), the content of the second resin particles (by mass%), and the content of the pigment dispersed by the action of carboxylic acid groups (by mass%) is more than 1.2 times and less than 25.0 times; the particle size increase rate of the second resin particles upon contact with the aqueous reaction liquid is greater than 3.0 times; and the water-soluble organic solvent comprises a vapor pressure of 1.0 × 10⁻⁶. -2 The first water-soluble organic solvent has a pressure of kPa or higher, and the proportion of the first water-soluble organic solvent in the water-based ink is 50.0% by mass or higher, and in the Bristow method, from the start of contact to 30 msec... 1 / 2 The amount of water absorbed by the recording medium is 10 mL / m 2 the following.

2. The inkjet recording method according to claim 1, wherein the reactant in the aqueous reaction solution comprises an organic acid, and the first resin particles in the aqueous ink comprise resin particles dispersed by at least one hydrophilic group selected from the group consisting of hydroxyl, vinyl oxide, propylene oxide, sulfonic acid, sulfate ester, and phosphonic acid groups.

3. The inkjet recording method according to claim 1, wherein the reactant in the aqueous reaction solution comprises an organic acid with a pKa of 3.2 or higher at 25°C, and the first resin particles in the aqueous ink comprise resin particles dispersed by the action of carboxylic acid groups and have an acid value of less than 11 mg KOH / g.

4. The inkjet recording method according to claim 3, wherein the pKa of the organic acid at 25°C is 3.5 or higher.

5. The inkjet recording method according to claim 3, wherein the acid value of the first resin particles is below 5 mg KOH / g.

6. The inkjet recording method according to claim 2, wherein the organic acid includes polyvalent carboxylic acids.

7. The inkjet recording method according to claim 1, wherein the reactant in the aqueous reaction solution comprises a polyvalent metal salt, and the first resin particles in the aqueous ink comprise resin particles dispersed by at least one hydrophilic group selected from the group consisting of hydroxyl, vinyl oxide, propylene oxide, sulfonic acid, sulfate ester, and phosphonic acid groups.

8. The inkjet recording method according to claim 7, wherein the multivalent metal salt comprises at least one compound selected from the group consisting of calcium lactate and magnesium sulfate.

9. The inkjet recording method according to claim 1, wherein the reactant in the aqueous reaction solution comprises a cationic resin, and the first resin particles in the aqueous ink comprise resin particles dispersed by the action of at least one hydrophilic group selected from the group consisting of hydroxyl, vinyl oxide, and propylene oxide.

10. The inkjet recording method according to claim 9, wherein the cationic resin has a weight-average molecular weight of 5,000 or less.

11. The inkjet recording method according to claim 9, wherein the degree of cationization of the cationic resin, expressed in meq / g, is 3 meq / g or more and 7 meq / g or less.

12. The inkjet recording method of claim 1, wherein the pigment comprises a pigment dispersed using a resin having a carboxylic acid group.

13. The inkjet recording method according to claim 12, wherein the acid value of the resin having carboxylic acid groups is 100 mg KOH / g or higher.

14. The inkjet recording method according to claim 1, wherein the aqueous ink further comprises at least one surfactant selected from the group consisting of fluorinated nonionic surfactants and organosilicon nonionic surfactants.

15. The inkjet recording method according to claim 14, wherein the aqueous ink further comprises a hydrocarbon-based nonionic surfactant.

16. The inkjet recording method according to claim 15, wherein the organosilicon-based nonionic surfactant in the aqueous ink comprises a compound having the following structure: silicon atoms at positions other than the ends of a polyorganosiloxane chain having a repeating siloxane structure as the main backbone are replaced by at least one hydrophilic group selected from the group consisting of oxidized alkenyl and hydroxyl groups, and the hydrocarbon-based nonionic surfactant in the aqueous ink comprises a compound having the following structure: carbon atoms at positions other than the ends of the hydrocarbon chain serving as the main backbone are replaced by at least one hydrophilic group selected from the group consisting of oxidized alkenyl and hydroxyl groups.

17. The inkjet recording method according to claim 1, wherein in the water-based ink, the mass ratio of the content of the first resin particles (in mass%) to the total content of the second resin particles (in mass%) and the content of the pigment (in mass%) is more than 1.5 times and less than 6.0 times.

18. The inkjet recording method according to claim 1, wherein the resin particles in the water-based ink comprise anionic groups selected from the group consisting of sulfonic acid groups, sulfate groups, and phosphonic acid groups.

19. The inkjet recording method according to claim 1, wherein the particle size increase rate of the first resin particles is less than 1.2 times.

20. The inkjet recording method according to claim 1, wherein the proportion of the first water-soluble organic solvent in the water-soluble organic solvent of the water-based ink is 90.0% by mass or more.

21. The inkjet recording method according to claim 1, wherein the aqueous reaction solution further comprises a vapor pressure of 1.0 × 10⁻⁶. -2 The second water-soluble organic solvent has a pressure of kPa or higher, and the proportion of the second water-soluble organic solvent in the water-soluble organic solvent of the aqueous reaction solution is 90.0% by mass or higher.

22. The inkjet recording method according to claim 1, wherein the amount of resin particles in the aqueous reaction solution is less than 1.0% by mass, based on the total mass of the reaction solution.

23. The inkjet recording method of claim 1, wherein the aqueous ink further comprises a water-soluble resin, the water-soluble resin comprising at least one selected from the group consisting of: (i) a water-soluble resin comprising units having at least one of the group consisting of vinyl oxide and propylene oxide groups, and (ii) a block copolymer comprising blocks formed of acid-free units, and the amount of the water-soluble resin in the aqueous ink is 0.1% by mass or more, based on the total mass of the ink.

24. An inkjet recording device, characterized in that, The inkjet recording device is used to record images on a recording medium using water-based ink and an aqueous reaction solution containing a reactant that reacts with the water-based ink. The inkjet recording device includes: a reaction solution application unit configured to apply the aqueous reaction solution to the recording medium; and an ink application unit configured to apply the water-based ink in such a manner that it overlaps with at least a portion of the area of ​​the recording medium on which the aqueous reaction solution has been applied. The water-based ink comprises pigments dispersed by carboxylic acid groups, resin particles, and a water-soluble organic solvent, wherein the particle size of the pigments dispersed by carboxylic acid groups increases by 8.0 times upon contact with the aqueous reaction solution. The resin particles described above include first resin particles, wherein the particle size increase rate of the first resin particles upon contact with the aqueous reaction solution is less than 3.0 times; in the aqueous ink, the total mass ratio of the first resin particles (by mass%) to the second resin particles (by mass%) and the pigment dispersed by the carboxylic acid groups (by mass%) is more than 1.2 times and less than 25.0 times; the particle size increase rate of the second resin particles upon contact with the aqueous reaction solution is greater than 3.0 times; and the water-soluble organic solvent comprises a vapor pressure of 1.0 × 10⁻⁶. -2 The first water-soluble organic solvent has a pressure of kPa or higher, and the proportion of the first water-soluble organic solvent in the water-based ink is 50.0% by mass or higher, and in the Bristow method, from the start of contact to 30 msec... 1 / 2 The amount of water absorbed by the recording medium is 10 mL / m 2 the following.

25. A kit for a water-based ink and a water-based reaction solution, characterized in that, The kit is used in an inkjet recording method that records images on a recording medium using an aqueous ink and an aqueous reaction solution containing a reactant that reacts with the aqueous ink. The method includes: an application step of applying the aqueous reaction solution to the recording medium; and an ink application step of applying the aqueous ink in such a manner that it overlaps at least a portion of the area of ​​the recording medium on which the aqueous reaction solution has been applied. The aqueous ink comprises pigments dispersed by carboxylic acid groups, resin particles, and a water-soluble organic solvent. The particle size increase rate of the pigments dispersed by carboxylic acid groups upon contact with the aqueous reaction solution is... The resin particles, comprising first resin particles, exhibit a particle size increase rate of less than 3.0 times when in contact with the aqueous reaction liquid. In the water-based ink, the total mass ratio of the first resin particles (by mass%) to the second resin particles (by mass%) and the pigment dispersed by the carboxylic acid groups (by mass%) is greater than 1.2 times and less than 25.0 times. The particle size increase rate of the second resin particles when in contact with the aqueous reaction liquid is greater than 3.0 times. The water-soluble organic solvent comprises a vapor pressure of 1.0 × 10⁻⁶. -2 The first water-soluble organic solvent has a pressure of kPa or higher, and the proportion of the first water-soluble organic solvent in the water-based ink is 50.0% by mass or higher, and in the Bristow method, from the start of contact to 30 msec... 1 / 2 The amount of water absorbed by the recording medium is 10 mL / m 2 the following.

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