JP2024076974A - Inkjet recording method, inkjet recording apparatus, and set of aqueous ink and aqueous reaction liquid - Google Patents

Abstract

[Problem] To provide an inkjet recording method and the like that can record images with excellent image clarity and moisture absorption resistance while suppressing bleeding, even when recording on a non-absorbent recording medium using an aqueous reaction liquid. [Solution] An inkjet recording method that records an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink. The aqueous ink contains a pigment that is dispersed by the action of carboxylic acid groups, specific resin particles, and a specific water-soluble organic solvent, and when contacted with the aqueous reaction liquid, the particle size increase rate of the pigment that is dispersed by the action of the carboxylic acid groups is 8.0 times or more. The recording medium absorbs 10 mL/m2 or less of water from the start of contact until 30 msec1/2 in the Bristow method. [Selected Figures] None

Description

The present invention relates to an inkjet recording method, an inkjet recording device, and a set of an aqueous ink and an aqueous reaction liquid.

In recent years, inkjet recording methods have been increasingly used in the field of sign and display, such as printing posters and large-format advertisements. In this field, inkjet recording devices are characterized by a larger recording area compared to home inkjet recording devices. In addition, because images need to be eye-catching, inks that can record images with high color development are required.

In the sign and display field, non-absorbent recording media are often used, whose surfaces are made of polyvinyl chloride (PVC) or polyethylene terephthalate (PET), which have almost no ink absorption. For this reason, it is necessary to suppress bleeding of images on non-absorbent recording media. Hereinafter, recording media whose surfaces have almost no ink absorption will also be referred to as "non-absorbent recording media." In the inkjet recording method for recording on non-absorbent recording media, it is important to suppress bleeding by preventing ink dots from being repelled by the recording medium. To do this, it is necessary to rapidly thicken and fix the ink after it is applied to the recording medium.

Methods for recording on non-absorbent recording media include those using solvent-based inks that contain organic solvents as the main component, and those using curable inks that contain polymerizable monomers. However, in recent years, from the standpoint of environmental impact and safety, there has been an increasing need for a recording method that can record on non-absorbent recording media using water-based inks.

Methods for recording on non-absorbent recording media using aqueous ink include evaporating the water content of the ink on the surface of the non-absorbent recording media, and using a reaction liquid that causes the ink components to coagulate. The former is advantageous in terms of running costs because there is no need to provide a means for applying the reaction liquid, but it requires a slower recording speed, making it less productive. For this reason, methods that use a reaction liquid are being considered.

Some recording media have a glossy surface, and high image clarity is required for such recording media in order to record high-quality images. "Image clarity" refers to the sharpness of an image when projected onto the surface of the image; low image clarity results in a blurred image, whereas high image clarity results in a clear image. Furthermore, in sign and display applications, recorded images are displayed in a variety of environments, including outdoor and indoor environments, so environmental resistance is also important. Specifically, there is the issue of "moisture absorption resistance," where an image absorbs moisture and loses brightness when displayed in a humid environment.

To date, in order to obtain images with high gloss using an aqueous reaction liquid, an inkjet recording method that can reduce the amount of reaction liquid applied (see Patent Document 1) and an ink composition that contains a resin with low coagulation properties against the reaction liquid (see Patent Document 2) have been proposed. In addition, in order to obtain images with excellent abrasion resistance and high image quality, an inkjet recording method that also uses a clear ink that does not contain a coloring material has been proposed (see Patent Document 3). Furthermore, an inkjet recording method that adjusts the coagulation properties of the ink against the reaction liquid has been proposed (see Patent Documents 4 and 5). And, in order to record images with excellent image fixation properties and suppressed image bleeding and cracking, a set of a treatment liquid (reaction liquid) and ink that controls the maximum tensile stress of the ink film has been proposed (see Patent Document 6).

JP 2018-165029 A JP 2019-157064 A JP 2019-155852 A JP 2021-030613 A JP 2019-147339 A JP 2022-186629 A

The present inventors have investigated various performances of images recorded using the inkjet recording methods described in Patent Documents 1, 3, 4, and 5, the ink composition described in Patent Document 2, and the ink set described in Patent Document 6. As a result, it was not possible to suppress bleeding of the images in the images recorded using the inkjet recording method described in Patent Document 1 and the ink set described in Patent Document 6. Furthermore, although images having a certain degree of image clarity could be recorded using the ink composition described in Patent Document 2 and the inkjet recording methods described in Patent Documents 3 to 5, the moisture absorption resistance of the images was insufficient.

Therefore, an object of the present invention is to provide an inkjet recording method that can suppress bleeding and record images that have excellent image clarity and moisture absorption resistance, even when recorded on a non-absorbent recording medium. Another object of the present invention is to provide an inkjet recording device for use in this inkjet recording method, and a set of an aqueous ink and an aqueous reaction liquid.

That is, according to the present invention, there is provided an inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink, the method comprising: a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium; and an ink applying step of applying the aqueous ink so as to overlap at least a part of an area of the recording medium to which the aqueous reaction liquid is applied, the aqueous ink containing a pigment that is dispersed by the action of a carboxylic acid group, resin particles, and a water-soluble organic solvent, and the aqueous ink containing a pigment that is dispersed by the action of a carboxylic acid group when it comes into contact with the aqueous reaction liquid, The inkjet recording method is characterized in that the pigment dispersed by the action of an acid group has a particle diameter increase rate of 8.0 times or more, the resin particles include first resin particles having a particle diameter increase rate of 3.0 times or less when contacted with the aqueous reaction liquid, the content (mass %) of the first resin particles in the aqueous ink is 1.2 times or more and 25.0 times or less in mass ratio to the total content (mass %) of the second resin particles having a particle diameter increase rate of more than 3.0 times when contacted with the aqueous reaction liquid and the content (mass %) of the pigment dispersed by the action of the carboxylic acid group, the water-soluble organic solvent includes a first water-soluble organic solvent having a vapor pressure of 1.0 × 10 ^-2 kPa or more, the proportion (mass %) of the first water-soluble organic solvent in the water-soluble organic solvent in the aqueous ink is 50.0 mass % or more, and the recording medium has an absorption amount of water of 10 mL/m ² or less from the start of contact until 30 msec ^1/2 in the Bristow method.

According to the present invention, it is possible to provide an inkjet recording method that can suppress bleeding and record images that have excellent image clarity and moisture absorption resistance, even when recorded on a non-absorbent recording medium. In addition, according to the present invention, it is possible to provide an inkjet recording device used in this inkjet recording method, and a set of an aqueous ink and an aqueous reaction liquid.

1 is a perspective view illustrating an embodiment of an inkjet recording apparatus of the present invention. 1 is a side view diagrammatically illustrating an embodiment of an inkjet recording apparatus of the present invention.

The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, the aqueous ink and reaction liquid for inkjet printing may be simply referred to as "ink" and "reaction liquid." Unless otherwise specified, the physical property values are values at room temperature (25°C) and normal pressure (1 atm). When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

First, the inventors of the present invention investigated the reason why it is not possible to simultaneously suppress bleeding and improve image clarity when using a reactive liquid, as described in Patent Documents 1 and 2. The reactive liquid contains a reactant that reacts with the ink components (pigment, resin, etc.) and causes the above components to aggregate. Therefore, when the reactive liquid and the ink come into contact with the surface of a non-absorbent recording medium, the ink components rapidly aggregate as described above, and an image is recorded. At this time, the components that rapidly aggregate due to the reactant are likely to form unevenness as aggregates on the surface of the non-absorbent recording medium, reducing the smoothness of the image surface and reducing the image clarity.

To improve the smoothness of the image surface, the reactivity between the reactant and the ink components can be adjusted to make it difficult for aggregates to form. On the other hand, if the reactivity is reduced to make it difficult for aggregates to form, the ink components will not be reliably fixed to the surface of the recording medium, making it impossible to record a high-quality image. In particular, in images in which a large amount of ink is applied, even slight movement of the ink components is visible as bleeding. Therefore, it is difficult to achieve both image bleeding suppression and image clarity with the method of adjusting the amount of reaction liquid applied as described in Patent Document 1, or the method of adding components to adjust the reactivity with the reaction liquid as described in Patent Document 2.

The inventors therefore considered the following configuration to achieve both suppression of image bleeding and image clarity. First, they considered using a pigment that is highly reactive with the reactant in the reaction liquid to suppress image bleeding, and using resin particles that are less reactive with the reactant to improve image clarity. However, the image clarity of the resulting image was insufficient. This is thought to be because, even if the reactivity of the resin particles with the reactant was reduced, the pigment's reactivity with the reactant was still high, resulting in the formation of aggregates and insufficient smoothness.

Next, the inventors investigated adjusting the ratio of resin particles to pigment. As a result, they found that by setting the ratio of resin particles to pigment within a certain range, it is possible to suppress bleeding in the image and improve image clarity at the same time. However, while it is possible to suppress bleeding in the image and improve image clarity at the same time by adjusting the ratio of resin particles to pigment, it was found that a new problem described below occurs when the resulting image is displayed for a long period of time. Specifically, when the resulting image is displayed for a long period of time, a phenomenon occurs in which numerous small droplets adhere to the surface of the image, reducing color development. Hereinafter, this problem is referred to as "moisture absorption resistance."

The inventors analyzed the cause of the phenomenon in which numerous small droplets adhere to the surface of an image when it is displayed for a long period of time. As a result, they discovered that the reaction liquid and the liquid components of the ink applied to the non-absorbent recording medium remain inside the image even when the surface of the image appears dry, and that the remaining liquid components attract water vapor from the air and form droplets over a long period of display. They also discovered that the decrease in color development due to the adhesion of droplets does not occur when highly reactive pigments and highly reactive resin particles are used, but occurs significantly when highly reactive pigments and less reactive resin particles are used.

The inventors speculate that the cause of the deterioration of the moisture absorption resistance of the image is as follows. Since non-absorbent recording media are difficult to absorb liquid components, the liquid components in the reaction liquid and ink hardly penetrate the recording media, and even if the image is dried by heating, etc., some of the liquid components remain inside the image. The remaining liquid components are easily compatible with water vapor in the air. Here, if the reactivity of the pigment and resin particles is high, the aggregates formed are bulky and have many gaps, so the liquid components remaining inside the image gradually evaporate even while the image is displayed. However, resin particles with low reactivity are difficult to aggregate, and the resin particles spread to fill the gaps in the pigment aggregates and are fixed to the recording medium. As a result, the evaporation of the liquid components remaining inside the image is prevented by the resin particles, and it is thought that the liquid components attract water vapor in the air when the image is displayed for a long period of time, causing the phenomenon of droplets adhering to the surface of the image.

In light of the above-mentioned causes, the inventors have investigated ways to avoid leaving liquid components inside the image as much as possible. As a result, they have discovered that the moisture absorption resistance of the image can be improved by setting the ratio of water-soluble organic solvents with high vapor pressure to a certain level or higher.

That is, the inkjet recording method of the present invention has the following characteristics. First, the aqueous ink contains a pigment dispersed by the action of a carboxylic acid group, resin particles, and a water-soluble organic solvent. The particle size increase rate of the pigment dispersed by the action of a carboxylic acid group when contacted with an aqueous reaction liquid is 8.0 times or more. The resin particles contain first resin particles having a particle size increase rate of 3.0 times or less when contacted with an aqueous reaction liquid. The content (mass%) of the first resin particles in the aqueous ink is 1.2 times or more and 25.0 times or less in mass ratio to the total content (mass%) of the second resin particles having a particle size increase rate of more than 3.0 times when contacted with an aqueous reaction liquid and the content (mass%) of the pigment dispersed by the action of a carboxylic acid group. The water-soluble organic solvent contains a first water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more, and the proportion (mass%) of the first water-soluble organic solvent in the water-soluble organic solvent in the aqueous ink is 50.0 mass% or more. The recording medium has a water absorption amount of 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method. The aqueous reaction liquid and the above-mentioned aqueous ink are applied to the recording medium so that they at least partially overlap. The present inventors speculate as follows about the mechanism by which the above-mentioned configuration suppresses bleeding and enables recording of an image with excellent image clarity and moisture absorption resistance.

The ink contains a pigment that is dispersed by the action of carboxylic acid groups. Therefore, when it comes into contact with the reaction liquid described below, the pigment reacts with the reactant in the reaction liquid through electrostatic interaction and aggregates. If the colorant is dispersed by the action of a nonionic group such as an ethylene oxide group or an anionic group other than a carboxylic acid group, the aggregation of the colorant does not progress easily, and bleeding of the image cannot be suppressed.

In addition, the particle size increase rate of the pigment dispersed by the action of the carboxylic acid group when it comes into contact with the aqueous reaction liquid is 8.0 times or more. The "particle size increase rate of the pigment" is an index of the tendency of the pigment to aggregate when it comes into contact with the reaction liquid, and the higher the value, the higher the aggregation tendency. The definition and measurement method of the "particle size increase rate of the pigment" will be described later. When the reaction liquid and the ink come into contact on the recording medium, if the particle size increase rate is 8.0 times or more, the reactivity of the pigment with the reactant is sufficiently high, and an image with suppressed bleeding can be recorded. If the particle size increase rate is less than 8.0 times, even if the reaction liquid and the ink come into contact on the surface of the recording medium, the pigment does not sufficiently aggregate, and bleeding of the image cannot be suppressed.

The ink contains first resin particles having a particle diameter increase rate of 3.0 times or less when in contact with a reaction liquid. The "particle diameter increase rate of resin particles" is an index of the tendency of resin particles to aggregate when in contact with a reaction liquid, and the larger the value, the higher the aggregation tendency. The definition and measurement method of the "particle diameter increase rate of resin particles" will be described later. When the reaction liquid and the ink come into contact with each other on a recording medium, if the particle diameter increase rate is 3.0 times or less, the reactivity of the resin particles with the reactant is sufficiently low, and an image with excellent image clarity can be recorded. Even if the ink contains resin particles, if the particle diameter increase rate is more than 3.0 times, the aggregation of the resin particles is likely to progress when the reaction liquid and the ink come into contact with each other on the surface of the recording medium. As a result, image clarity cannot be obtained. In addition, the content (mass%) of the first resin particles must be 1.2 times or more and 25.0 times or less in mass ratio to the total content (mass%) of the second resin particles having a particle diameter increase rate of more than 3.0 times and the content (mass%) of the pigment dispersed by the action of the carboxylic acid group. Here, the content (mass %) of the second resin particles in the ink may be 0% based on the total mass of the ink. In other words, the ink may not substantially contain the second resin particles. If the mass ratio is less than 1.2 times, the ink contains many components that are highly reactive with the reactant, and aggregates are likely to cause unevenness on the surface of the image, making it difficult to obtain image clarity. If the mass ratio is more than 25.0 times, the ink contains too many components that are less reactive with the reactant, and the movement of the less reactive resin particles tends to cause the pigment to move, making it difficult to suppress bleeding of the image.

The water-soluble organic solvent in the ink includes a first water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more, and the proportion (mass %) of the first water-soluble organic solvent in the water-soluble organic solvent in the ink must be 50.0 mass % or more. The first water-soluble organic solvent evaporates easily in a general environment such as room temperature (25° C.) and normal pressure (1 atm). By setting the proportion of the first water-soluble organic solvent in the water-soluble organic solvent in the ink to the above range, it is possible to prevent liquid components from remaining inside the recorded image, thereby improving the moisture absorption resistance of the image.

<Inkjet recording method, inkjet recording device, and set of aqueous ink and aqueous reaction liquid>
The inkjet recording method of the present invention is a method of ejecting an aqueous ink and an aqueous reaction liquid from an inkjet recording head by the action of thermal energy, and applying the aqueous ink and the aqueous reaction liquid to a recording medium to record an image. The inkjet recording method of the present invention includes a reaction liquid applying step of applying the aqueous reaction liquid to a recording medium, and an ink applying step of applying the aqueous ink so as to overlap at least a part of the area of the recording medium to which the aqueous reaction liquid is applied. The aqueous ink contains a pigment dispersed by the action of a carboxylic acid group, resin particles, and a water-soluble organic solvent. The particle size increase rate of the pigment dispersed by the action of the carboxylic acid group when contacted with the aqueous reaction liquid is 8.0 times or more. The resin particles include first resin particles having a particle size increase rate of 3.0 times or less when contacted with the aqueous reaction liquid. The content (mass%) of the first resin particles in the aqueous ink is 1.2 times or more and 25.0 times or less in mass ratio to the total content (mass%) of the second resin particles having a particle size increase rate of more than 3.0 times when contacted with the aqueous reaction liquid and the content (mass%) of the pigment dispersed by the action of the carboxylic acid group. The water-soluble organic solvent includes a first water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more, and the proportion (mass %) of the first water-soluble organic solvent in the water-soluble organic solvent in the aqueous ink is 50.0 mass % or more. The aqueous reaction liquid includes a reactant that reacts with the aqueous ink. The recording medium is a recording medium in which the amount of water absorbed from the start of contact until 30 msec ^1/2 in the Bristow method is 10 mL/m ² or less.

The inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method in which an aqueous ink and an aqueous reaction liquid are ejected from an inkjet recording head by the action of thermal energy and applied to a recording medium to record an image. The apparatus is suitable for use in the above-mentioned recording method. In the inkjet recording method and inkjet recording apparatus of the present invention, it is not necessary to cure the image by irradiation with active energy rays or the like.

The set of aqueous ink and aqueous reaction liquid of the present invention is a set used in an inkjet recording method in which an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink are ejected from a recording head to record an image on a recording medium. The set is suitable for use in the above recording method. The form of the set includes a set of multiple ink cartridges each containing multiple inks (reaction liquids) independently, and an ink cartridge formed integrally by combining multiple ink storage sections each containing multiple inks (reaction liquids). The set of the present invention is not limited to the above form and may be in any form as long as it is configured so that the inks and reaction liquids can be used in combination.

The inkjet recording method and inkjet recording device of the present invention (hereinafter, simply referred to as the "recording method and recording device") will be described in detail below.

FIG. 1 is a perspective view showing an embodiment of the inkjet recording apparatus of the present invention. FIG. 2 is a side view showing an embodiment of the inkjet recording apparatus of the present invention. As shown in FIGS. 1 and 2, the recording apparatus of this embodiment includes an inkjet recording head 22 that ejects ink. The recording head 22 is a recording head that ejects ink by the action of thermal energy. A recording head that ejects ink by the action of thermal energy applies thermal energy to the ink by applying an electric pulse to an electrothermal conversion element, thereby ejecting the ink from the ejection port. Here, a recording head that ejects ink by the action of thermal energy is given as an example, but a recording head that ejects ink by the action of mechanical energy may also be used. The recording head may include a mechanism (temperature control mechanism) that heats the water-based ink ejected from the recording head. When the recording head includes a temperature control mechanism, the temperature of the ink ejected from the recording head is preferably 35° C. or higher and 70° C. or lower.

[Heating process]
The recording method of the present invention may include a step of heating (heat treatment) the recording medium to which the ink (and the reaction liquid) has been applied. By heating the recording medium to which the ink has been applied, it is possible to promote drying and increase the strength of the image. Examples of the means for heating the recording medium include known heating means such as a heater, air blowing means using air blowing such as a dryer, and heating means such as a combination of these. Examples of the heating means include the above-mentioned heating means, air blowing means, and a combination of these. Examples of the heat treatment method include a method of applying heat from the opposite side (back side) of the recording surface (ink application surface) of the recording medium using a heater, a method of applying warm or hot air to the recording surface of the recording medium, and a method of heating from the recording surface or back side using an infrared heater. A combination of these methods may also be used.

The heating temperature of the recording medium to which the ink has been applied is preferably 50°C or higher and 90°C or lower, in order to increase the abrasion resistance of the image. The heating temperature of the recording medium to which the ink has been applied may be read by a sensor incorporated in a position corresponding to the heating means of the recording device, or may be determined from the relationship between the amount of heat and the temperature of the recording medium, which is determined according to the type of ink and recording medium.

In the recording device shown in Figures 1 and 2, a heater 25 supported by a frame (not shown) is disposed downstream in the sub-scanning direction A from the position where the recording head 22 reciprocates in the main scanning direction B. The recording medium 1 to which ink has been applied is heated by the heater 25. Examples of the heater 25 include a sheath heater and a halogen heater. The heater 25 is covered by a heater cover 26. The heater cover 26 is a member for efficiently irradiating the heat generated by the heater 25 to the recording medium 1. Furthermore, the heater cover 26 is also a member for protecting the heater 25. The recording medium 1 to which ink has been applied ejected from the recording head 22 is wound by a winding spool 27 to form a roll-shaped wound medium 24.

(recoding media)
In the recording method and recording device of the present invention, a low-absorbency or non-absorbency recording medium (low to non-absorbency recording medium) is used. A low to non-absorbency recording medium is a recording medium having a water absorption amount of 0 mL/ ^m2 or more and 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method described in JAPAN TAPPI Paper Pulp Test Method No. 51 "Liquid Absorbency Test Method for Paper and Paperboard". In the present invention, a recording medium that satisfies the above water absorption amount condition is defined as a "low to non-absorbency recording medium". A recording medium for inkjet recording (glossy paper, matte paper, etc.) having a coating layer (ink receiving layer) formed of inorganic particles, and plain paper without a coating layer are "absorbency recording media" having the above water absorption amount of more than 10 mL/ ^m2 .

Examples of low to non-absorbent recording media that can be used include plastic films; recording media in which a plastic film is adhered to the recording surface side of a substrate; and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp. Of these, plastic films are preferred, and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp are also preferred.

When ink containing resin particles is applied to a non-absorbent recording medium, the water, water-soluble organic solvent, and other components evaporate, concentrating the resin particles. This promotes adhesion between the concentrated resin particles, improving the strength of the recorded image. In contrast, when ink is applied to a recording medium that has high absorbency of liquid components, it is difficult to promote adhesion between the resin particles, and the strength of the image does not improve. Note that the recording medium in this specification does not refer to a transfer body, but rather to a recording medium on which an image is recorded as a recorded matter.

(Reaction solution)
The recording method of the present invention has a reaction liquid applying step of applying an aqueous reaction liquid containing a reactant that reacts with an aqueous ink to a recording medium. In particular, it is preferable to have a reaction liquid applying step before the ink applying step, or to perform the ink applying step and the reaction liquid applying step in parallel. Each component used in the reaction liquid will be described in detail below.

[Reactants]
The reaction liquid reacts with the ink when it comes into contact with the ink, and aggregates the components in the ink (components having anionic groups, such as resins, surfactants, and self-dispersing pigments), and contains a reaction agent. When the reaction agent is present, the state of existence of the components having anionic groups in the ink can be destabilized when the ink and the reaction agent come into contact with each other on the recording medium, and the aggregation of the ink can be promoted. Examples of the reaction agent include cationic components such as polyvalent metal ions and cationic resins, and organic acids. The reaction agent may be used alone or in combination of two or more.

[Organic acids]
The reaction liquid containing an organic acid has a buffering ability in the acidic region (less than pH 7.0, preferably pH 2.0 to 5.0), and thus efficiently converts the anionic groups of the components present in the ink into an acid form and causes aggregation. The pigment is dispersed by the action of the carboxylic acid group, and when it comes into contact with the organic acid, it loses its dispersing ability and aggregation proceeds. Examples of the organic acid include monocarboxylic acids and salts thereof, such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrole carboxylic acid, furan carboxylic acid, picolinic acid, nicotinic acid, thiophene carboxylic acid, levulinic acid, and coumaric acid; dicarboxylic acids and salts and hydrogen salts thereof, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid, sebacic acid, phthalic acid, malic acid, and tartaric acid; tricarboxylic acids and salts and hydrogen salts thereof, such as citric acid and trimellitic acid; and tetracarboxylic acids and salts and hydrogen salts thereof, such as pyromellitic acid.

When an organic acid is used as a reactant, it is preferable to use a polycarboxylic acid from the viewpoint of more effectively suppressing image bleeding. In other words, it is preferable that the organic acid used as the reactant is a polycarboxylic acid. When a monocarboxylic acid with low water solubility is used as a reactant, it is easy to precipitate due to evaporation of the liquid components of the ink before it is applied to the recording medium, and it may not be possible to fully exert the effect of converting the anionic group to an acid form. As a result, it may not be possible to fully suppress image bleeding. In addition, even if a monocarboxylic acid with high water solubility is used as a reactant, it may not be possible to fully exert the effect of converting the anionic group to an acid form, as described above, because it is highly volatile. As a result, it may not be possible to fully suppress image bleeding.

The acid dissociation constant (pKa) of the organic acid at 25°C is preferably 5.0 or less. pKa represents the ease of dissociation of the proton of the acid. When the organic acid has multiple anionic groups (carboxylic acid groups), it has multiple pKas, but the amount of the organic acid dissociated in the reaction solution can be said to depend on the first acid dissociation constant (pKa ₁ ) representing the ease of dissociation of the proton of the first stage acid. Therefore, in this specification, the acid dissociation constant in the case of an organic acid having multiple anionic groups refers to the first acid dissociation constant. If the pKa of the organic acid is more than 5.0, the effect of aggregating the pigment is weakened, and image bleeding may not be sufficiently suppressed. In addition, from the viewpoint of reactivity with the resin particles, the pKa of the organic acid at 25°C is preferably 0 or more. Furthermore, in the case of resin particles in which the resin particles in the ink are dispersed by the action of carboxylic acid groups, the pKa of the organic acid at 25°C is preferably 3.2 or more. In particular, the pKa of the organic acid at 25° C. is more preferably 3.5 or more. If the pKa of the organic acid is less than 3.2, the action of aggregating the resin particles becomes too strong, and sufficient image clarity may not be obtained. The content (mass %) of the organic acid in the reaction liquid is preferably 1.0 mass % or more and 10.0 mass % or less, and more preferably 1.0 mass % or more and 5.0 mass % or less, based on the total mass of the reaction liquid.

Here, the acid dissociation constant is defined as follows. For example, the ionization equilibrium of an acid represented by HA can be expressed as HA⇔H ⁺ +A ^- , and the equilibrium constant Ka is expressed as Ka = [H ⁺ ] x [A ^- ] / [HA]. The acid dissociation constant pKa is the negative common logarithm of this equilibrium constant, and is defined as pKa = -log ₁₀ Ka. The acid dissociation constant (pKa) of an organic acid at 25°C can be calculated by neutralization titration using a pH meter (for example, trade name "Metrohm 798 MPT Titrino", manufactured by Metrohm) or the like.

[Polyvalent metal salt]
The polyvalent metal salt is a compound formed of a divalent or higher metal ion (polyvalent metal ion) and an anion. The polyvalent metal salt dissociates in the aqueous reaction liquid to become a polyvalent metal ion, and the carboxylic acid group in the ink acts to aggregate the dispersed pigment. The polyvalent metal salt may be a hydrate.

Examples of polyvalent metal ions constituting the polyvalent metal salt include divalent metal ions such as Ca2 ⁺ , Cu2 ⁺ , Ni2 ⁺ , Mg2 ⁺ , Sr2 ⁺ , Ba2 ⁺ , and Zn2 ⁺ , and trivalent metal ions such as Fe3 ⁺ , Cr3 ⁺ , Y3 ⁺ , and Al3 ⁺ . Among these, from the viewpoint of image clarity, it is preferable to use at least one metal ion selected from the group consisting of ^Ca2+ and Mg2 ⁺ .

Examples of anions constituting polyvalent metal salts include inorganic anions such as Cl ^- , Br ^- , I ^- , ClO ^- , ClO ₂ ^- , ClO ₃ ^- , ClO ₄ ^- , NO ₂ ^- , NO ₃ ^- , SO ₄ ^2- , CO ₃ ^2- , HCO ₃ ^- , PO ₄ ^3- , HPO ₄ ^2- , and H ₂ PO ₄ ^- ; HCOO ^- , (COO ^- ) ₂ , COOH(COO ^- ), CH ₃ COO ^- , C ₂ H ₅ COO ^- , CH ₃ CH(OH)COO ^- , C ₂ H ₄ (COO ^- ) ₂ , C ₆ H ₅ COO ^- , C ₆ H ₄ (COO ^- ) ₂ , and CH and organic anions such as _3SO3- . These polyvalent metal salts may be used alone or in combination of two or more. Among them, it is preferable to use at least one compound selected from the group consisting of ^{calcium lactate (a combination of Ca2+} _and ^CH3CH ₍ OH) ^COO- ) and magnesium sulfate (a combination of ^{Mg2+ and SO42- )} _as the polyvalent metal salt in the reaction solution. By using the above polyvalent metal salt, the image clarity can be further improved.

When polyvalent metal ions are used as reactants, the content (mass %) of the polyvalent metal salt in the reaction solution is preferably 1.0 mass % or more and 20.0 mass % or less based on the total mass of the reaction solution. In this specification, when the polyvalent metal salt is a hydrate, the "content (mass %) of the polyvalent metal salt in the reaction solution means the "content (mass %) of the anhydrous polyvalent metal salt" excluding water as a hydrate.

[Cationic Resin]
The cationic resin has a cationic site in the resin structure, and aggregates the pigment dispersed by the action of the carboxylic acid group in the ink. Examples of the cationic resin include resins having a primary to tertiary amine structure and resins having a quaternary ammonium salt structure. Specific examples include resins having structures such as vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensate. In order to increase the solubility in the reaction liquid, the cationic resin can be used in combination with an acidic compound, or the cationic resin can be subjected to a quaternary treatment.

When a cationic resin is used as the reactant, the weight average molecular weight of the cationic resin is preferably 500 to 10,000. The weight average molecular weight of the cationic resin can be measured, for example, as a pullulan equivalent value measured by gel permeation chromatography. In particular, the weight average molecular weight of the cationic resin is more preferably 5,000 or less. If the weight average molecular weight exceeds 5,000, the aggregates with the ink components may become too large, and sufficient image clarity may not be obtained. The content (mass %) of the cationic resin in the reaction liquid is preferably 0.1 mass % to 10.0 mass % and more preferably 0.1 mass % to 5.0 mass % based on the total mass of the reaction liquid.

The cationic resin preferably has a cationic degree of 3 meq/g or more and 7 meq/g or less. If the cationic degree is less than 3 meq/g, the effect of aggregating the pigment described below is weakened, and image bleeding may not be sufficiently suppressed. On the other hand, if the cationic degree is more than 7 meq/g, the effect of aggregating the resin particles described below is weakened, and image clarity may not be sufficient. The cationic degree is an index showing the degree of cationicity of the resin, and a higher cationic degree means a larger number of moles of cationic groups.

The cationic degree of the cationic resin can be measured by colloid titration at 25°C using an automatic potentiometric titrator (product name "AT-510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) and a 1/400N potassium polyvinyl sulfate solution (manufactured by Fujifilm) as the titration reagent. The aqueous solution of the cationic resin used in the titration can be prepared by dissolving the cationic resin appropriately extracted from the reaction solution in water.

[Aqueous medium]
The reaction liquid is an aqueous reaction liquid containing at least water as an aqueous medium. The aqueous medium used in the reaction liquid can contain a water-soluble organic solvent, which can be contained in the ink, as described below. The reaction liquid further contains a second water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more, and the ratio (mass %) of the second water-soluble organic solvent to the water-soluble organic solvent in the reaction liquid is preferably 90.0 mass % or more. If the ratio is less than 90.0 mass %, the liquid component remaining inside the recorded image becomes large, and the moisture absorption resistance of the image may not be sufficiently obtained. The ratio may be 100.0 mass %, that is, all of the water-soluble organic solvent in the reaction liquid may be the second water-soluble organic solvent. As the second water-soluble organic solvent, the same one as the first water-soluble organic solvent described below can be used. In this specification, the vapor pressure is a value at 25° C. and 1 atm.

[Other ingredients]
The reaction liquid may contain various other components as necessary. Examples of the other components include the same components as those that can be contained in the ink, which will be described later.

In addition, when the reaction liquid contains resin particles as described below, the content (mass %) is preferably 1.0 mass % or less based on the total mass of the reaction liquid. If the content exceeds 1.0 mass %, when the reaction liquid and the ink come into contact on the recording medium, the reactant may be prevented from coming into contact with the ink components, and image bleeding may not be sufficiently suppressed. The content (mass %) of resin particles in the reaction liquid is preferably 0.0 mass %. In other words, it is preferable that the reaction liquid does not substantially contain resin particles.

[Properties of reaction solution]
The reaction liquid used in the recording method of the present invention is an aqueous reaction liquid applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical property values. Specifically, the surface tension of the reaction liquid at 25°C is preferably 20 mN/m or more and 60 mN/m or less. In addition, the viscosity of the reaction liquid at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the reaction liquid 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.

<Ink>
The ink used in the recording method of the present invention is a water-based ink for ink-jet recording, which contains a pigment dispersed by the action of a carboxylic acid group, resin particles, and a water-soluble organic solvent. Each component constituting the ink will be described in detail below.

[Pigment]
The ink contains a pigment as a coloring material. This pigment is dispersed by the action of a carboxylic acid group, and aggregates with the reactant in the reaction liquid. The particle size increase rate of the pigment dispersed by the action of the carboxylic acid group when it comes into contact with the reaction liquid is 8.0 times or more. The particle size increase rate is preferably 50.0 times or less. Here, the particle size increase rate of the pigment is the particle size increase rate of the pigment when a dispersion of the pigment dispersed by the action of the carboxylic acid group is mixed with the reaction liquid in a mass ratio of 1:1. Specifically, it is a value calculated by (D ₅₀ of the pigment after mixing with the reaction liquid) / (D ₅₀ of the pigment in the pigment dispersion). Here, the content (mass %) of the pigment in the pigment dispersion is 1.0 mass %. D ₅₀ is the cumulative 50% particle size based on volume, and details will be described later. The D ₅₀ of the pigment after mixing with the reaction liquid is measured after the reaction has progressed sufficiently. For example, the reaction liquid and the pigment dispersion are mixed and thoroughly stirred, and then the measurement is performed. As long as the reaction can proceed sufficiently, any stirring method may be used, such as using a stirrer. In the examples described later, the reaction solution and the pigment dispersion were placed in a beaker, stirred with a stirrer for 30 seconds, and then the cumulative 50% particle size based on volume of the pigment was measured.

The particle size increase rate of the pigment dispersed by the action of the carboxylic acid group can be adjusted, for example, in the case of a self-dispersed pigment, by the density of the carboxylic acid group bonded directly or via another atomic group to the pigment particle surface. In the case of a resin-dispersed pigment, it can be adjusted by the acid value of the resin dispersant used. To increase the particle size increase rate, there are methods such as increasing the density of the carboxylic acid group of the self-dispersed pigment or increasing the acid value of the resin dispersant of the resin-dispersed pigment. When the pigment dispersion method is fixed, the particle size increase rate also differs depending on the type of reactant in the reaction solution used in combination. The content (mass %) of the pigment in the ink is preferably 0.1 mass % or more and 15.0 mass % or less, based on the total mass of the ink, and more preferably 1.0 mass % or more and 10.0 mass % or less.

Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, and dioxazine. One type of pigment may be used alone, or two or more types may be used in combination.

As the dispersion method of the pigment, a resin-dispersed pigment using a resin as a dispersant, a self-dispersed pigment in which a hydrophilic group is bonded to the pigment particle surface, etc. can be used. In addition, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the pigment particle surface, and a microcapsule pigment in which the surface of the pigment particle is coated with a resin, etc. can be used. It is also possible to use a combination of pigments with different dispersion methods among these. Among them, it is preferable to use a resin-dispersed pigment in which a resin as a dispersant is physically adsorbed on the pigment particle surface, rather than a resin-bonded pigment or a microcapsule pigment. In other words, it is preferable that the pigment is a pigment that is dispersed by the action of a resin (resin dispersant) having a carboxylic acid group. If the pigment is a self-dispersed pigment, the reactivity with the reactant is likely to increase, and the image clarity may not be sufficient. As the resin dispersant, a resin such as that described later, especially a water-soluble resin, can be used. The content (mass%) of the pigment in the ink is preferably 0.3 times or more and 10.0 times or less in terms of the mass ratio to the content of the resin dispersant.

As the self-dispersing pigment, at least a carboxylic acid group may be bonded to the surface of the pigment particles directly or via another atomic group (-R-). An anionic group other than the carboxylic acid group (sulfonic acid group, sulfate ester group, phosphonic acid group) may be bonded to the surface of the pigment particles. The anionic group such as the carboxylic acid group may be either an acid type or a salt type, and if it is a salt type, it may be either a partially dissociated state or a completely dissociated state. When the anionic group is a salt type, examples of the cation that serves as the counter ion include an alkali metal cation, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include a linear or branched alkylene group having 1 to 12 carbon atoms; an arylene group such as a phenylene group or a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; and an ether group. A group that is a combination of these groups may also be used.

The volume-based cumulative 50% particle diameter ( _D50 ) of the pigment is preferably 10 nm or more and 300 nm or less, and more preferably 20 nm or more and 200 nm or less. The volume-based cumulative 50% particle diameter of the pigment is the diameter of the particle that is 50% of the total volume of the measured particles when integrated from the small particle diameter side in the particle diameter integration curve. The volume-based cumulative 50% particle diameter of the pigment can be measured using a particle size analyzer and measurement conditions described in the resin section below. In addition, the particle diameter increase rate of the pigment can also be measured by this method, but the measured value may vary due to the influence of pigment aggregation, etc. Therefore, it is preferable to make appropriate adjustments such as shortening the measurement time.

As mentioned above, a carboxylic acid group is used as the functional group for dispersing the pigment. When a resin having a carboxylic acid group is used as a pigment dispersant (resin dispersant), it is preferable to use a (meth)acrylic resin having a unit having a carboxylic acid group and a hydrophobic unit.

The unit having a carboxylic acid group is a hydrophilic unit, and those described in the specific examples of the resin section described later can be used in the same way. The hydrophobic unit can also be those described in the specific examples of the resin section described later.

The acid value of the resin having a carboxylic acid group (resin dispersant) is preferably 100 mgKOH/g or more. If the acid value of the resin is less than 100 mgKOH/g, the reactivity with the reactant decreases, and the pigment becomes less likely to aggregate. As a result, image bleeding may not be sufficiently suppressed. The acid value of the resin having a carboxylic acid group (resin dispersant) is preferably 200 mgKOH/g or less.

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

In this specification, "resin particles" refers to a resin that does not dissolve in the aqueous medium that constitutes the ink, specifically, a resin that can exist in the aqueous medium in a state in which it forms particles whose particle diameter can be measured by dynamic light scattering. On the other hand, "water-soluble resin" refers to a resin that can dissolve in the aqueous medium that constitutes the ink, specifically, a resin that can exist in the aqueous medium in a state in which it does not form particles whose particle diameter can be measured by dynamic light scattering. "Resin particles" can also be called "water-dispersible resin (water-insoluble resin)." A method for determining whether a resin is a water-soluble resin or a resin particle using dynamic light scattering will be described later.

As described above, the resin particles must include those that are not easily aggregated by the reactant in the reaction liquid. Specifically, the resin particles include first resin particles having a particle diameter increase rate of 3.0 times or less when contacted with the reaction liquid. In particular, the particle diameter increase rate of the first resin particles is preferably 1.2 times or less. The particle diameter increase rate of 1.2 times or less means that the resin particles are hardly aggregated by the reactant. Therefore, the image clarity can be further improved. The particle diameter increase rate is preferably 1.0 times or more. The particle diameter increase rate of the resin particles is the particle diameter increase rate when the aqueous dispersion of the resin particles and the reaction liquid are mixed at a mass ratio of 1:1. Specifically, it is a value calculated by (D ₅₀ of the resin particles after mixing with the reaction liquid) / (D ₅₀ of the resin particles in the aqueous dispersion of the resin particles). Here, the content (mass %) of the resin particles in the aqueous dispersion of the resin particles is 1.0 mass % based on the total mass of the aqueous dispersion. _D50 is the cumulative 50% particle diameter based on volume, and details will be described later. The _D50 of the resin particles after mixing with the reaction liquid is measured after the reaction has progressed sufficiently. For example, the reaction liquid and the aqueous dispersion of the resin particles may be mixed and thoroughly stirred before measurement. As long as the reaction can be sufficiently progressed, any method of stirring may be used, such as using a stirrer. In the examples described later, the reaction liquid and the aqueous dispersion of the resin particles are placed in a beaker, stirred with a stirrer for 30 seconds, and then the cumulative 50% particle diameter based on volume of the resin particles is measured.

The particle size increase rate of the resin particles can be adjusted, for example, by the density of the anionic groups on the surface of the resin particles or the acid value of the resin particles. To reduce the particle size increase rate, there are methods such as reducing the density of the carboxylic acid groups of the resin particles or reducing the acid value of the resin particles. When the type of resin particles is fixed, the particle size increase rate also differs depending on the type of reactant in the reaction solution used in combination. Hereinafter, the "first resin particles" may be referred to as "resin particles".

The content (mass%) of the first resin particles in the aqueous ink is 1.2 times or more and 25.0 times or less in mass ratio to the sum of the content (mass%) of the second resin particles having a particle diameter increase rate of more than 3.0 times and the content (mass%) of the pigment. In particular, the content (mass%) of the first resin particles in the aqueous ink is preferably 1.5 times or more and 6.0 times or less in mass ratio to the sum of the content (mass%) of the second resin particles and the content (mass%) of the pigment. If the mass ratio is less than 1.5 times, the resin particles may not be able to fully smooth the image, and the image clarity may not be sufficient. On the other hand, if the mass ratio is more than 6.0 times, the proportion of components in the ink that are difficult to aggregate becomes too high, and the aggregated pigment is likely to move along with the movement of the resin particles on the surface of the recording medium. As a result, the bleeding of the image may not be sufficiently suppressed.

The resin particles can be dispersed in an emulsion type that uses an emulsifier or in a self-dispersion type that can be dispersed without using an emulsifier. In the case of emulsion type resin particles, the resin forming the resin particles may have a hydrophilic group, but does not necessarily have to have a hydrophilic group, and it is sufficient that the resin particles are dispersed by the action of an emulsifier that has a hydrophilic group. In the case of self-dispersion type resin particles, the resin forming the resin particles has a hydrophilic group. The hydrophilic group can be at least one selected from the group consisting of a hydroxy group, an ethylene oxide group, a propylene oxide group, a sulfonic acid group, a sulfate ester group, a phosphonic acid group, and a carboxylic acid group.

The hydrophilic groups of the resin particles may be nonionic hydrophilic groups such as hydroxyl groups, ethylene oxide groups, and propylene oxide groups, or anionic hydrophilic groups such as sulfonic acid groups, sulfate ester groups, phosphonic acid groups, and carboxylic acid groups. However, in order to adjust the particle size increase rate of the resin particles, it is preferable to match the type of reactant used in combination. When the reactant is an organic acid, the first resin particles are preferably resin particles dispersed by the action of at least one hydrophilic group selected from the group consisting of hydroxyl groups, ethylene oxide groups, propylene oxide groups, sulfonic acid groups, sulfate ester groups, phosphonic acid groups, 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 ionized, so they can be considered to be resin particles dispersed by the action of the sulfonic acid groups.

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 mgKOH/g or less. In particular, the acid value of the resin particles (first resin particles) dispersed by the action of carboxylic acid groups is more preferably 5 mgKOH/g or less. By setting the acid value of the resin particles dispersed by the action of carboxylic acid groups to the above range, the reactivity with the reactant is suppressed, and the image clarity can be further improved. The acid value of the resin particles (first resin particles) dispersed by the action of carboxylic acid groups is preferably 1 mgKOH/g or more. The acid value of the resin particles can be measured, for example, by potentiometric titration.

When the reactant is a polyvalent metal salt, the first resin particles are preferably resin particles dispersed by the action of at least one hydrophilic group selected from the group consisting of hydroxyl groups, ethylene oxide groups, propylene oxide groups, sulfonic acid groups, sulfate ester groups, and phosphonic acid groups. When the reactant is a cationic resin, the first resin particles are preferably resin particles dispersed by the action of at least one hydrophilic group selected from the group consisting of hydroxyl groups, ethylene oxide groups, and propylene oxide groups. By using resin particles dispersed by the action of a specific hydrophilic group according to the type of reactant, the reactivity with the reactant can be reduced, and as a result, the clarity of the image can be improved.

The resin particles in the aqueous ink preferably have at least one anionic group selected from the group consisting of sulfonic acid groups, sulfate ester groups, and phosphonic acid groups. When the hydrophilic groups of the resin particles in the aqueous ink are only nonionic hydrophilic groups such as hydroxyl groups, ethylene oxide groups, and propylene oxide groups, the resin particles do not have a surface charge. Therefore, the reactivity with the reactant may not be sufficiently obtained, and the bleeding of the image may not be sufficiently suppressed. In addition, even if the resin particles have anionic groups, if they only have carboxylic acid groups, the resin particles may tend to aggregate, and the image clarity may not be sufficiently obtained. In addition, the first resin particles in the aqueous ink preferably have at least one anionic group selected from the group consisting of sulfonic acid groups, sulfate ester groups, and phosphonic acid groups.

The particle size increase rate of the resin particles can be adjusted by changing the type and ratio of the hydrophilic groups of the resin particles, assuming that the resin particles are dispersed with hydrophilic groups according to the type of reactant as described above. 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 addition to at least one hydrophilic group selected from the group consisting of a hydroxyl group, an ethylene oxide group, a propylene oxide group, a sulfonic acid group, a sulfate ester group, and a phosphonic acid group. Nonionic hydrophilic groups tend to reduce reactivity, while anionic hydrophilic groups tend to increase reactivity. In addition, the particle size increase rate of the resin particles dispersed by the action of the carboxylic acid group can be adjusted, for example, by the acid value of the resin particles. Specifically, the particle size increase rate can be reduced by reducing the acid value of the resin particles. Of course, as in the case of pigments, when the dispersion method of the resin particles is fixed, the particle size increase rate also differs depending on the type of reactant in the reaction solution used in combination.

The constituent unit of the resin forming the resin particles can be appropriately selected from the same as the units constituting the resin described later. The acid value of the resin constituting the resin particles is preferably 5 mgKOH/g or more and 100 mgKOH/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, and more preferably 100,000 or more and 3,000,000 or less. The volume-based cumulative 50% particle diameter (D ₅₀ ) of the resin particles measured by dynamic light scattering is preferably 50 nm or more and 500 nm or less, and more preferably 100 nm or more and 300 nm or less. The volume-based cumulative 50% particle diameter of the resin particles is the diameter of the particles that is 50% of the total volume of the measured particles when integrated from the small particle diameter side in the particle diameter integration curve. The volume-based cumulative 50% particle diameter of the resin particles can be measured under the same measurement conditions using a particle size analyzer by dynamic light scattering method described in the resin section described later. In addition, whether or not a certain resin is a resin particle can be determined by whether or not the cumulative 50% particle diameter based on volume is measured in the above measurement. The glass transition temperature of the resin particle is preferably 40°C or more and 120°C or less, and more preferably 50°C or more and 100°C or less. The glass transition temperature (°C) of the resin particle can be measured using a differential scanning calorimeter (DSC). The resin particle does not need to contain a coloring material.

[Composition analysis of resin particles]
The resin constituting the resin particles can be determined, for example, by the following method. First, the resin particles are dissolved in an organic solvent capable of dissolving the resin particles, such as tetrahydrofuran, to prepare a sample. The resin particles used in this case may be in the form of an aqueous dispersion or in a dried state. The obtained sample is analyzed by nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), or the like. This makes it possible to know the type and ratio of the units (monomers) constituting the resin. In addition, the resin particles themselves can be analyzed by pyrolysis gas chromatography to detect the units (monomers) constituting the resin. In addition, when insoluble matter that does not dissolve in the organic solvent is generated during the preparation of the above sample, the insoluble matter can be analyzed by pyrolysis gas chromatography to detect the units (monomers) constituting the resin.

[Surfactant]
The ink may contain a surfactant. By containing a surfactant, the surface tension of the ink is reduced, the ink is easily wetted and spread on the surface of the recording medium, and the image clarity can be improved. The content (mass %) of the surfactant in the ink is preferably 0.1 mass % or more and 5.0 mass % or less, and preferably 0.1 mass % or more and 2.0 mass % or less. Examples of the surfactant include anionic surfactants, cationic surfactants, and nonionic surfactants. It is preferable to use a nonionic surfactant because it is less likely to affect the reactivity of the pigment and resin particles with the reactant. Among them, it is preferable that the aqueous ink further contains at least one surfactant selected from the group consisting of fluorine-based nonionic surfactants and silicone-based nonionic surfactants. The surfactant can effectively reduce the surface tension of the ink without destabilizing the dispersion state of the pigment and resin particles, and therefore the image clarity can be further improved.

In addition to the above surfactants, the aqueous ink preferably contains a hydrocarbon-based nonionic surfactant. By using a hydrocarbon-based surfactant in combination, the wettability of the ink can be further improved, thereby further improving the clarity of the image.

Silicone-based nonionic surfactants are surfactants in which hydrophilic groups such as ethylene oxide groups are introduced into polyorganosiloxanes whose main skeleton is a siloxane bond (SiO) in which silicon (Si) and oxygen atoms (O) are alternately linked. Examples of silicone-based surfactants include polyether-modified siloxane compounds, alkyl-polyether-modified siloxane compounds, alkyl silicone dendron polyether-modified siloxane compounds, and alkyl silicone dendron diglycerin-modified siloxane compounds. Depending on the site where the hydrophilic group is introduced, they can be broadly classified into side chain type and straight chain type. In this specification, the side chain type refers to a polyorganosiloxane in which a hydrophilic group is introduced to a silicon atom other than the terminal. The straight chain type refers to a polyorganosiloxane in which a hydrophilic group is introduced to a silicon atom at one terminal or both terminals. Examples of hydrophilic groups include alkylene oxide groups and hydroxyl groups. Examples of the alkylene oxide group include an ethylene oxide group, a propylene oxide group, and a butylene oxide group. Of these, an ethylene oxide group and a propylene oxide group are preferred. An example of a side chain type structure is shown in the following formula (1), and an example of a straight chain type structure is shown in the following formula (2).

(In formula (1) and formula (2), m, n, X, and Y represent natural numbers. R ₁ , R ₂ , and R ₃ each independently represent an alkylene group, and EO represents an ethylene oxide group.)

Fluorine-based nonionic surfactants are surfactants that have a perfluoroalkyl group as the main skeleton and hydrophilic groups such as ethylene oxide groups introduced into them. Examples of fluorine-based surfactants include perfluoroalkyl ethylene oxide adducts.

A hydrocarbon-based nonionic surfactant is a surfactant in which a hydrophilic group such as an ethylene oxide group is introduced to a hydrocarbon chain as the main skeleton. Examples of hydrocarbon-based nonionic surfactants include polyoxyethylene alkyl ethers, ethylene oxide adducts of acetylene glycol, polyethylene glycol polypropylene glycol block copolymers, and ethylene oxide adducts of polyhydric alcohols. Hydrocarbon-based nonionic surfactants can be broadly classified into side chain type and straight chain type depending on the site of introduction of the hydrophilic group. In this specification, the side chain type refers to one in which a hydrophilic group is introduced to a carbon atom other than the terminal of the hydrocarbon chain, and the straight chain type refers to one in which a hydrophilic group is introduced to one or both terminals of the hydrocarbon chain. An example of the side chain type structure is shown in the following formula (3), and an example of the straight chain type structure is shown in the following formula (4).

CH ₃ -(CH ₂ ) _m -O-(EO) _n -H (4)

(In formula (3) and formula (4), m, n, X, and Y represent natural numbers. EO represents an ethylene oxide group.)

The silicone-based nonionic surfactant is preferably a compound having a structure in which at least one hydrophilic group selected from the group consisting of an alkylene oxide group and a hydroxyl group is substituted on a silicon atom other than the terminal of a polyorganosiloxane chain having a repeating siloxane structure as the main skeleton. The hydrocarbon-based nonionic surfactant is preferably a compound having a structure in which at least one hydrophilic group selected from the group consisting of an alkylene oxide group and a hydroxyl group is substituted on a carbon atom other than the terminal of the hydrocarbon chain, which is the main skeleton. In other words, the silicone-based nonionic surfactant and the hydrocarbon-based nonionic surfactant of the water-based ink are preferably side-chain type. A linear type surfactant is more easily adsorbed to the pigment than a side-chain type, and therefore it is easier to suppress the reaction between the pigment and the reactant. As a result, there are cases in which image bleeding cannot be sufficiently suppressed.

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

Resins can be added to inks (i) to stabilize the dispersion state of pigments, i.e., as resin dispersants or their assistants, or (ii) to improve various characteristics of the recorded image. Examples of the resin form include block copolymers, random copolymers, graft copolymers, and combinations of these.

[Composition of Water-Soluble Resin]
Examples of the water-soluble resin include acrylic resins, urethane resins, and olefin resins. Among them, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are more preferred. The water-soluble resin is preferably at least one selected from the group consisting of (i) a water-soluble resin containing a unit having at least one selected from the group consisting of an ethylene oxide group and a propylene oxide group, and (ii) a block copolymer containing a block composed of a unit not having an acid group. By using the water-soluble resin, the image clarity of the image can be further improved. The content (mass%) of the water-soluble resin in the ink is preferably 0.1 mass% or more based on the total mass of the ink.

As the acrylic resin, one having a hydrophilic unit and a hydrophobic unit as constituent units is preferable. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer is preferable. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene is preferable. These resins are easily interacted with pigments, and therefore can be suitably used as a resin dispersant for dispersing pigments.

The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of hydrophilic monomers having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Specific examples of hydrophobic monomers include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and the like.

Urethane-based resins can be obtained, for example, by reacting polyisocyanate with polyol. They may also be obtained by further reacting a chain extender. Examples of olefin-based resins include polyethylene and polypropylene.

[Properties of water-soluble resin]
In this specification, "a resin is water-soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, the resin is present in an aqueous medium in a state in which no particles whose particle size can be measured by a dynamic light scattering method are formed. Whether or not a resin is water-soluble can be determined according to the following method. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by a dynamic light scattering method, if no particles having a particle size are measured, the resin can be determined to be water-soluble. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. In addition, as a particle size distribution measurement device, a particle size analyzer using a dynamic light scattering method (for example, the product name "UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution measurement device and measurement conditions used are not limited to those described above.

The acid value of the water-soluble resin is preferably 10 mgKOH/g or more and 200 mgKOH/g or less, and more preferably 50 mgKOH/g or more and 150 mgKOH/g or less. The weight average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less. The weight average molecular weight of the water-soluble resin can be measured as a polystyrene-equivalent value measured by gel permeation chromatography.

[Wax particles]
The ink may contain particles formed of wax (wax particles). By using an ink containing wax particles, an image with further improved abrasion resistance can be recorded. In this specification, the wax may be a composition containing components other than wax, or the wax itself. The wax particles may be dispersed by a dispersant such as a surfactant or a water-soluble resin. The wax may be used alone or in combination of two or more kinds. The content (mass %) of the wax particles in the ink is preferably 0.1 mass % or more and 10.0 mass % or less, and more preferably 1.0 mass % or more and 5.0 mass % or less, based on the total mass of the ink.

In the narrow sense, wax is an ester of a water-insoluble higher monohydric or dihydric alcohol and a fatty acid, and includes animal waxes and vegetable waxes, but does not include oils and fats. In the broad sense, wax includes high-melting-point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the recording method of the present invention, any wax in the broad sense can be used without particular restrictions. Wax in the broad sense can be classified into natural waxes, synthetic waxes, blends of these (blended waxes), and modified products of these (modified waxes).

Examples of natural waxes include animal waxes such as beeswax, spermaceti, and wool wax (lanolin); vegetable waxes such as wood wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral waxes such as montan wax; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes such as Fischer-Tropsch wax and polyolefin wax (e.g., polyethylene wax and polypropylene wax). The blended wax is a mixture of the above-mentioned various waxes. The modified wax is a wax obtained by subjecting the above-mentioned various waxes to a modification treatment such as oxidation, hydrogenation, alcohol modification, acrylic modification, and urethane modification. One of the above waxes may be used alone, or two or more may be used in combination. The wax is preferably at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and modified or blended products thereof. Among these, a blend of multiple types of wax is more preferable, and a blend of petroleum-based wax and synthetic wax is especially preferable.

The wax is preferably solid at room temperature (25°C). The melting point (°C) of the wax is preferably 40°C or higher and 120°C or lower, and more preferably 50°C or higher and 100°C or lower. The melting point of the wax can be measured in accordance with the test method described in 5.3.1 (melting point test method) of JIS K2235:1991 (petroleum wax). In the case of microcrystalline wax, petrolatum, and a mixture of multiple types of wax, the test method described in 5.3.2 can be used to measure more accurately. The melting point of the wax is easily affected by characteristics such as molecular weight (the higher the molecular weight, the higher the melting point), molecular structure (the higher the melting point if the chain is straight, and the lower the melting point if the chain is branched), crystallinity (the higher the crystallinity, the higher the melting point), and density (the higher the density, the higher the melting point). Therefore, by controlling these characteristics, it is possible to obtain a wax having a desired melting point. The melting point of the wax in the ink can be measured in accordance with the above test method, for example, after the ink is subjected to ultracentrifugation, the wax separated is washed and dried.

[Aqueous medium]
The ink used in the recording method of the present invention is an aqueous ink containing at least water as an aqueous medium. The ink may contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the aqueous ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. In addition, the content (mass%) of water-soluble organic solvent in the aqueous ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink.

The water-soluble organic solvent includes a first water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more, and the ratio (mass%) of the first water-soluble organic solvent to the water-soluble organic solvent in the aqueous ink is 50.0% by mass or more. In particular, the ratio (mass%) of the first water-soluble organic solvent to the water-soluble organic solvent in the aqueous ink is preferably 90.0% by mass or more. If the ratio is less than 90%, the liquid component remaining inside the recorded image becomes large, and the moisture absorption resistance of the image may not be sufficient. The ratio (mass%) of the first water-soluble organic solvent to the water-soluble organic solvent in the aqueous ink may be 100.0% by mass, that is, the water-soluble organic solvent in the ink may be the first water-soluble organic solvent. Examples of the first water-soluble organic solvent include 1,2-butanediol (2.0×10 ⁻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 −2 kPa} ), and diethylene glycol monomethyl ether (2.4×10 ⁻² kPa). As the water-soluble organic solvent other than the first water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing solvents, and sulfur-containing solvents, can be used. The water-soluble organic solvent may be used alone or in combination of two or more.

[Other ingredients]
The ink may contain various other components as necessary. Examples of other components include various additives such as defoamers, surfactants, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and reduction inhibitors. However, it is preferable that the ink does not contain a reactant to be contained in the reaction liquid.

[Ink properties]
The ink is an aqueous ink applied to an inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property values. Specifically, the surface tension of the ink at 25° C. is preferably 20 mN/m or more and 60 mN/m or less, and more preferably 20 mN/m or more and 30 mN/m or less. In addition, the viscosity of the ink at 25° C. is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25° C. is preferably 7.0 or more and 9.5 or less, and more preferably 8.0 or more and 9.5 or less.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to the following examples as long as it does not deviate from the gist of the invention. Unless otherwise specified, the terms "parts" and "%" used to describe the amounts of components are based on mass.

<Preparation of reaction solution>
The components (unit: %) shown in Tables 1 and 2 were mixed and thoroughly stirred, and then pressure filtration was performed using a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare each reaction solution. In Table 1, "Catiomaster PDT-2", "Catiomaster PD-7", and "Catiomaster PD-30" are trade names of aqueous solutions of amine-epichlorohydrin condensation polymers manufactured by Yokkaichi Chemicals. "Acetylenol E60" is the trade name of a side-chain type hydrocarbon-based nonionic surfactant manufactured by Kawaken Fine Chemicals. "Proxel GXL (S)" is the trade name of a preservative manufactured by Arch Chemicals. The vapor pressure is the value at 25° C. and 1 atm. Details of the cationic resins used in the preparation of the reaction solutions listed in Table 1 are shown below.
Catiomaster PDT-2 (product name): manufactured by Yokkaichi Chemical Co., Ltd., weight average molecular weight: 1,000, cationic degree: 7 meq/g, resin content: 60.0%
Catiomaster PD-7 (product name): manufactured by Yokkaichi Chemical Co., Ltd., weight average molecular weight: 5,000, cationic degree: 7 meq/g, resin content: 50.0%
Catiomaster PD-30 (product name): manufactured by Yokkaichi Chemical Co., Ltd., weight average molecular weight: 9,000, cationic degree: 7 meq/g, resin content: 50.0%
PAS-2401 (product name): manufactured by Nittobo Medical, weight average molecular weight: 2,000, cationic degree: 2 meq/g, resin content: 25.0%
PAS-A-5 (product name): manufactured by Nittobo Medical, weight average molecular weight: 4,000, cationic degree: 3 meq/g, resin content: 40.0%
PAA-HCL-01 (product name): manufactured by Nittobo Medical, weight average molecular weight: 1,600, cationic degree: 9 meq/g, resin content: 33.0%
Polyquat 40u05NV (product name): manufactured by Katpol GmbH, average molecular weight: 4,000, cationic degree: 6 meq/g, resin content: 40.0%

<Preparation of Pigment Dispersion>
(Pigment Dispersion 1)
A styrene-ethyl acrylate-acrylic acid copolymer (resin 1) with an acid value of 160 mgKOH/g and a weight average molecular weight of 8,000 was prepared. 20.0 parts of resin 1 were neutralized with potassium hydroxide in an amount equimolar to the acid value, and then an appropriate amount of pure water was added to prepare an aqueous solution of resin 1 with a resin (solid content) content of 20.0%. 15.0 parts of pigment (carbon black (specific surface area: 200 m ² /g), 37.5 parts of the aqueous solution of resin 1, and 47.5 parts of pure water were mixed to obtain a mixture. The obtained mixture and 200 parts of zirconia beads with a diameter of 0.3 mm were placed in a batch-type vertical sand mill (manufactured by Imex) and dispersed for 5 hours while cooling with water. After centrifugal separation to remove coarse particles, the mixture was pressure-filtered with a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare pigment dispersion 1 with a pigment content of 15.0% and a resin dispersant (resin 1) content of 7.5%.

(Pigment Dispersion 2)
Pigment dispersion 2 having a pigment content of 15.0% and a resin dispersant (resin 2) content of 7.5% was prepared in the same manner as in the above-mentioned pigment dispersion 1, except that resin 1 was changed to a resin (resin 2) having an acid value of 60 mgKOH/g and a weight average molecular weight of 7,000.

(Pigment Dispersion 3)
Pigment dispersion 3 having a pigment content of 15.0% and a resin dispersant (resin 3) content of 7.5% was prepared in the same manner as in the above-mentioned pigment dispersion 1, except that resin 1 was changed to a resin (resin 3) having an acid value of 50 mgKOH/g and a weight average molecular weight of 7,500.

(Pigment Dispersion 4)
Pigment dispersion 4 was prepared in the same manner as in the above-described pigment dispersion 1, except that resin 1 was changed to a resin (resin 4) having an acid value of 100 mgKOH/g and a weight average molecular weight of 7,000. The pigment dispersion 4 had a pigment content of 15.0% and a resin dispersant (resin 4) content of 7.5%.

(Pigment Dispersion 5)
Pigment dispersion 5 was prepared in the same manner as in the above-described pigment dispersion 1, except that resin 1 was changed to a resin (resin 5) having an acid value of 92 mgKOH/g and a weight average molecular weight of 8,400. The pigment dispersion 5 had a pigment content of 15.0% and a resin dispersant (resin 5) content of 7.5%.

(Pigment Dispersion 6)
20.0 g of carbon black (specific surface area: 200 m ² /g), 13.3 mmol of p-aminobenzoic acid, 13.3 mmol of nitric acid, and 200 mL of pure water were mixed. Using a rotary laboratory mixer (trade name "SILVERSON L5M-A", manufactured by Silverson), mixing was performed at room temperature at 6,000 rpm to obtain a mixture. After 30 minutes, potassium nitrite (equimolar to the (total) amount of the treatment agent) dissolved in a small amount of water was slowly added to the mixture and mixed. The temperature of the mixture reached 60°C by this mixing, and the mixture was reacted in this state for 1 hour. Thereafter, the pH of the mixture was adjusted to 10 using an aqueous potassium hydroxide solution. After 30 minutes, 20 mL of pure water was added, and diafiltration was performed using a spectrum membrane to prepare a self-dispersing pigment. Water was added to the prepared self-dispersing pigment to prepare pigment dispersion 6 with a pigment content of 10.0%. The surface charge amount of the pigment in Pigment Dispersion 6 was 3.0 μmol/ ^m2 . Here, the surface charge amount of the pigment was measured by colloid titration utilizing potential difference using an automatic potentiometric titrator (product name "AT-510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500). Specifically, the pigment dispersion was diluted about 300 times (by mass) with pure water, and the pH was adjusted to about 10 with potassium hydroxide as necessary, and potentiometric titration was performed using 5 mmol/L methyl glycol chitosan as a titration reagent.

(Pigment Dispersion 7)
Pigment dispersion 7 having a pigment content of 10.0% was prepared in the same manner as in Pigment Dispersion 6, except that p-aminobenzoic acid was changed to p-aminobenzenesulfonic acid in the preparation of Pigment Dispersion 6. The surface charge amount of the pigment in Pigment Dispersion 7 was 3.0 μmol/ ^m2 .

(Pigment Dispersion 8)
Pigment dispersion 8 having a pigment content of 10.0% was prepared in the same manner as in Pigment Dispersion 6, except that the amount of p-aminobenzoic acid was changed to 8.7 mmol in Pigment Dispersion 6. The surface charge amount of the pigment in Pigment Dispersion 8 was 2.0 μmol/ ^m2 .

(Pigment Dispersion 9)
A pigment dispersion 9 having a pigment content of 15.0% and a resin dispersant (resin 1) content of 7.5% was prepared in the same manner as in the pigment dispersion 1 described above, except that the pigment was changed to C.I. Pigment Blue 15:3.

<Analysis of resin particles>
(Cumulative 50% Particle Diameter Based on Volume of Resin Particles)
The volume-based cumulative 50% particle diameter (D ₅₀ ) of the resin particles was measured as follows. First, a liquid containing resin particles (aqueous dispersion of resin particles) was diluted with ion-exchanged water to prepare a sample with a resin particle content of about 1.0%. The particle diameter of this sample was measured using a particle size distribution meter (product name "Nanotrac WAVEII-Q", manufactured by Microtrac Bell) using a dynamic light scattering method. The measurement conditions were SetZero: 30 s, number of measurements: 3, measurement time: 180 s, shape: spherical, refractive index: 1.6, and density: 1.0.

(Acid value of resin particles)
The acid value of the resin particles was measured as follows. The resin particles were separated from a liquid containing the resin particles, and washed with 1.0 mol/L hydrochloric acid and then with ion-exchanged water. The resin particles were added to 60 mL of a liquid in which water and tetrahydrofuran were mixed in a mass ratio of 1:6, and the resin was dissolved at 25°C to prepare a sample. Neutralization titration was performed on this sample to measure the acid value of the resin. For the neutralization titration, a potentiometric automatic titrator (trade name "AT510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a composite glass electrode (trade name "C-171", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) was used. As a titration reagent, a 0.5 mol/L ethanol solution of potassium hydroxide was used.

<Preparation of Resin Particles>
(Resin particles 1 to 6)
Ion-exchanged water and 0.2 parts of potassium persulfate were mixed in a four-neck flask equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet tube. The amount of ion-exchanged water used was adjusted so that the total content including each component described below was 100.0 parts. In addition, an emulsion was prepared by mixing each component listed in Table 3. Under a nitrogen atmosphere, the prepared emulsion was dropped into the four-neck flask over 1 hour, and a polymerization reaction was carried out for 2 hours while stirring at 80°C. After cooling to 25°C, ion-exchanged water and an aqueous solution containing potassium hydroxide in an amount equimolar to the acid value of the resin particles were added to prepare an aqueous dispersion of resin particles 1 to 6 having a resin particle (solid content) content of 25.0%. In Table 3, "ADEKA REASOAP ER-20" is the trade name of a nonionic surfactant (addition mole number of ethylene oxide groups: 20) manufactured by ADEKA. "Aqualon KH-05" is the trade name of an anionic surfactant manufactured by Daiichi Kogyo. "Blemmer PME1000" is the trade name of polyethylene glycol monomethacrylate (number of moles of ethylene oxide group added: 23) manufactured by NOF Corp. The hydrophilic group that contributes to the dispersion of each resin particle is shown in the "Type of hydrophilic group" column. Resin particles 1 to 5 have sulfonic acid groups and carboxylic acid groups, and considering the acid dissociation constant, they are considered to be resin particles that are dispersed by the action of the sulfonic acid groups.

(Resin particles 7 to 10)
A mixture of the components (units: parts) listed in the "esterification reaction" section of Table 4 was placed in a reaction vessel installed in an autoclave, and heated at 220°C for 4 hours to carry out an esterification reaction. The temperature was then raised to 240°C, and the pressure in the autoclave was reduced to 13 Pa over 90 minutes. The esterification (dehydration condensation) reaction was continued by maintaining the reduced pressure of 240°C and 13 Pa for 5 hours, and then nitrogen gas was introduced into the autoclave to return to normal pressure. The temperature in the reaction vessel was lowered to 220°C, and a catalyst (tetra-n-butyl titanate) and the components (units: parts) listed in the "ester exchange reaction" section of Table 4 were added, and the mixture was heated at 220°C for 2 hours to carry out an ester exchange reaction. The amount of catalyst used (mol) was 3 x 10 ^-4 x the total amount of polyvalent carboxylic acid used (mol). Nitrogen gas was then introduced into the autoclave to create a pressurized state, and a sheet-shaped resin was taken out. The resin was cooled to 25°C and then crushed with a crusher.

A stirrer (product name "Tornado Stirrer Standard SM-104", manufactured by AS ONE) was set in a 2.0 L beaker. The resins synthesized above and tetrahydrofuran were placed in this beaker, and the resins were dissolved by stirring at 25 ° C. Next, a 5.0% aqueous solution of sodium hydroxide was added in an amount equivalent to the neutralization rate (mol%) based on the acid value of the resin, and the mixture was stirred for 30 minutes. 900 parts of ion-exchanged water was dripped into the beaker at a rate of 20 mL / min while stirring at 10 ° C and 150 rpm. The temperature was then raised to 60 ° C, tetrahydrofuran was distilled off under reduced pressure, and some of the water was also distilled off. The beaker was placed in a water bath, and stirring was continued under the conditions described in the "Heat Treatment" section of Table 4 at 85 ° C, and heat treatment was performed. The contents of the beaker were filtered using a 150 mesh wire mesh (a filter in which 150 stainless steel wires are woven vertically and horizontally in a 1-inch square). An appropriate amount of ion-exchanged water was added to adjust the resin particle content, and an aqueous dispersion of resin particles 7 to 10 with a resin particle content of 25.0% was obtained. The properties of the synthesized resin particles are shown on the right side of Table 4. In Table 4, the abbreviations for each component are EG: ethylene glycol, BPA: bisphenol A, tPA: terephthalic acid, iPA: isophthalic acid, and BTA: trimellitic acid. The hydrophilic groups that contribute to the dispersion of each resin particle are listed in the "Type of hydrophilic group" column.

<Preparation of Water-Soluble Resin>
(Water-soluble resin 1)
Using each component shown in Table 5, water-soluble resin 1, which is a block copolymer, was prepared. First, the monomer of the A block (unit: parts) was synthesized by living radical polymerization. Specifically, under a nitrogen atmosphere and at a temperature of -50°C, 30 parts of n-butyl lithium was added to 1,600 parts of tetrahydrofuran to which 4.7 parts of lithium had been added, and then 60.0 parts of benzyl methacrylate was added and stirred for 40 minutes. Next, 30.0 parts of diethyl zinc was added and stirred for 1 minute to obtain a liquid containing a polymer corresponding to the A block composed of hydrophobic monomer units.

Separately, 30.0 parts of n-butyl acrylate and 10.0 parts of acrylic acid were polymerized by a conventional method to polymerize a random copolymer corresponding to the B block. The random copolymer corresponding to the B block and 45.0 parts of diethyl zinc were added to 110 parts of tetrahydrofuran to obtain a liquid containing a hydrophilic monomer unit as a random copolymer corresponding to the B block.

This liquid was added dropwise to a liquid containing the polymer corresponding to the A block, and after stirring for 60 minutes, 1.3 parts of acetic acid was added to stop the reaction. 30.0 parts of a 35.0% aqueous solution of acetic acid was added to this liquid and stirred for 10 minutes. Water-soluble resin 1 was obtained by washing three times with pure water and drying the precipitated resin. Neutralization was performed with potassium hydroxide in an amount equimolar to the acid value, and an appropriate amount of ion-exchanged water was added to obtain a liquid containing water-soluble resin 1 with a resin content of 10.0%. Water-soluble resin 1 is a block copolymer having an A block composed only of units derived from hydrophobic monomers, and a B block which is a random copolymer.

(Water-soluble resin 2)
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 by a conventional method to obtain a random copolymer, water-soluble resin 2. The mixture was neutralized with potassium hydroxide in an amount equimolar to the acid value, and an appropriate amount of ion-exchanged water was added to obtain a liquid containing water-soluble resin 2 with a resin content of 10.0%. Here, Blemmer PME-400 is the trade name of polyethylene glycol monomethacrylate (number of moles of ethylene oxide groups added: 9) manufactured by NOF Corp.

(Water-soluble resin 3)
A liquid containing water-soluble resin 3 was obtained 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, 5.0 parts of acrylic acid, and 10.0 parts of Blemmer PME-400 were 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 water-soluble resins that contain units having ethylene oxide groups (nonionic units) and also have anionic groups.

(Water-soluble resin 4)
As the liquid containing the water-soluble resin 4, the aqueous solution of the resin 1 used in the preparation of the pigment dispersion liquid was used.

<Preparation of Silicone Surfactant>
(Silicone-based surfactant 1)
Silicone surfactant 1 was synthesized as follows, using a glass vessel equipped with a thermometer and a stirring means. In the vessel, a polysiloxane compound represented by the following formula (A) and a polyoxyethylene compound represented by the following formula (B) were added in the presence of a platinum catalyst to synthesize silicone surfactant 1. The addition reaction was continued until a surfactant having a weight-average molecular weight described below was obtained. The obtained silicone surfactant 1 was a nonionic compound corresponding to a side chain type having a structure in which X=2, Y=1, n=13, and R ₃ =n-propylene group in formula (1). The weight-average molecular weight of this surfactant was about 1,000.
Si(CH3) ₃ -O-(Si( _CH3 ) ₂ -O) ₂ -Si( _CH3 )H-O-Si( _CH3 ) ₃ ... (A)
CH ₂ ═CHCH ₂ —O—(C2H4O) ₁₃ —H...(B)

(Silicone-based surfactant 2)
Silicone surfactant 2 was prepared in the same manner as silicone surfactant 1, except that the polysiloxane compound and polyoxyethylene compound were changed to those of the following formula (C) and formula (D), respectively. The obtained surfactant was a straight-chain nonionic compound having a structure in formula (2) where X=4, m=6, n=6, R ₁ =n-propylene group, and R ₂ =n-propylene group. The weight-average molecular weight of this surfactant was about 900.
H-(Si( _CH3 ) ₂ -O) ₅ -Si( _CH3 ) ₂ -H... (C)
CH ₂ ═CHCH ₂ -O-(CH ₂ H ₄ O) ₆ -H... (D)

<Ink Preparation>
Each ink was prepared by mixing the components (unit: %) shown in Tables 5 to 8, thoroughly stirring, and then filtering under pressure using a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm. "Capstone FS3100" is the trade name of a fluorine-based nonionic surfactant manufactured by LEHVOSS Group. "NIKKOL BL4.2" is the trade name of a straight-chain hydrocarbon-based nonionic surfactant manufactured by Nikko Chemicals.

<Preparing the recording medium>
The following recording media 1 to 3 were prepared.
Recording medium 1: Product name "Scotchcal Graphic Film IJ1220-10" (manufactured by 3M, material: polyvinyl chloride, in the Bristow method, the amount of water absorbed from the start of contact to 30 msec ^1/2 is in the range of 0 mL/ ^m2 to 10 mL/ ^m2 )
Recording medium 2: Product name "Canon Photo Paper Glossy Pro [Platinum Grade] PT-201" (Canon, in the Bristow method, the amount of water absorbed from the start of contact to 30 msec ^1/2 is more than 10 mL/m ² )
Recording medium 3: Product name "GIY-0305" (manufactured by Lintec, material: PET, the amount of water absorbed from the start of contact to 30 msec ^1/2 in the Bristow method is in the range of 0 mL/ ^m2 to 10 mL/ ^m2 ).

<Evaluation>
The prepared reaction liquid and ink were filled in a cartridge, and the cartridge was set in an inkjet recording device (product name "imagePROGRAF PRO-2000", manufactured by Canon) equipped with a recording head that ejects ink by thermal energy. In this recording device, a heating device for drying the recording medium to which the reaction liquid and ink were applied was incorporated at a position downstream of the recording head in the conveying direction of the recording medium. The surface temperature of the recording medium was set to 80°C by heating with the heating device. The recording environment was set to a temperature of 25°C and a relative humidity of 50%. In this example, an image recorded under the condition that one drop of 4.0 ng of ink was applied to a unit area of 1/1200 inch x 1/1200 inch is defined as having a recording duty of 100%. A solid image was recorded by applying the reaction liquid and ink shown in Tables 9 and 10 to the recording medium shown in Tables 9 and 10 in layers with a recording duty of 40% for the reaction liquid and a recording duty of 200% for the ink. Thereafter, a solid image was recorded adjacent to the above solid image under the same conditions as above, except that ink 4 was used. An evaluation image was obtained by drying at 25° C. for 24 hours. In the present invention, in the evaluation criteria for each item below, "AA", "A" and "B" were defined as acceptable levels, and "C" was defined as an unacceptable level. The evaluation results are shown in Table 11.

When the ink contains resin particles with a particle size increase rate of more than 3.0 times, the content is shown in the "Other resin particles (%)" column in Tables 9 and 10. Ink 26 of Example 39 contains two types of resin particles, but resin particles 7 correspond to other resin particles (second resin particles), and when used together with reaction liquid 1, the particle size increase rate was about 40.0 times.

(Image bleeding suppression)
For the obtained evaluation images, the lagnetness value of the boundary between adjacent solid images was measured using a handheld image quality analyzer (product name "PIAS-II", manufactured by Quality Engineering Associates). The lagnetness value is a value defined in ISO-13660, and the measurement mode used was edge measurement. Then, bleeding suppression was evaluated according to the evaluation criteria shown below. A low lagnetness value at the boundary means that color mixing of adjacent images is suppressed, that is, bleeding of images is suppressed.
AA: The lajetness value was 50 or less. A: The lajetness value was more than 50 and less than 60. B: The lajetness value was more than 60 and less than 70. C: The lajetness value was more than 70.

(Imageability)
The obtained evaluation images were attached to test benches with radii of curvature of 200 mm, 60 mm, and 45 mm, and two fluorescent lamps spaced 10 cm apart were used as observation light sources to project the fluorescent lamps onto the images from a position 2 m away. The shapes of the fluorescent lamps projected onto the areas of the evaluation images recorded with the inks shown in Tables 9 and 10 were visually confirmed under conditions of an illumination angle of 45 degrees and an observation angle of 45 degrees, and the image clarity of the images was evaluated according to the evaluation criteria shown below.
AA: The boundary between the two projected fluorescent lights was visible in the images attached to either test stand. A: The boundary between the two fluorescent lights was not visible in the image attached to the test stand with a curvature radius of 200 mm, but was visible in the images attached to the test stands with a curvature radius of 60 mm and 45 mm. B: The boundary between the two fluorescent lights was not visible in the images attached to the test stands with a curvature radius of 200 mm and 60 mm, but was visible in the image attached to the test stand with a curvature radius of 45 mm. C: The boundary between the two projected fluorescent lights was not visible in the images attached to either test stand.

(Moisture absorption resistance)
The lightness L ^* of the obtained evaluation image was measured under the conditions of light source D50, viewing angle 2 degrees, incident angle 45 degrees, reflection angle 0 degrees, and filter: ANSI A. The solid image was then placed in an environment of temperature 30°C and humidity 80% for 7 days, and the lightness L ^* was measured in the same manner. Here, the lightness L ^* is a value in the L ^* a ^* b ^* color system defined by CIE (Commission Internationale de l'Eclairage). The difference in L ^* before and after placement was calculated, and the moisture absorption resistance of the image was evaluated according to the following evaluation criteria.
AA: The difference in brightness L ^* before and after placement was 1 or less. A: The difference in brightness L ^* before and after placement was more than 1 and 2 or less. B: The difference in brightness L ^* before and after placement was more than 2 and 3 or less. C: The difference in brightness L ^* before and after placement was more than 3.

The image clarity of Example 15 was rated "A" like Example 13, but Example 13 was superior. In Table 11, those marked "AA+" were superior to those marked "AA" with the same rating.

The disclosure of this embodiment includes the following methods and configurations:

(Method 1) An inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink, comprising the steps of:
a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium;
an ink applying step of applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied,
the aqueous ink contains a pigment dispersed by the action of a carboxylic acid group, resin particles, and a water-soluble organic solvent;
the particle size increase rate of the pigment dispersed by the action of the carboxylic acid group when contacted with the aqueous reaction liquid is 8.0 times or more;
the resin particles include first resin particles having a particle diameter increase rate of 3.0 times or less when contacted with the aqueous reaction liquid,
a content (mass%) of the first resin particles in the aqueous ink is 1.2 times or more and 25.0 times or less in mass ratio to the sum of a content (mass%) of the second resin particles having a particle diameter increase rate of more than 3.0 times when contacted with the aqueous reaction liquid and a content (mass%) of the pigment dispersed by the action of the carboxylic acid group,
the water-soluble organic solvent includes a first water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more;
a ratio (mass %) of the first water-soluble organic solvent to the water-soluble organic solvent in the aqueous ink is 50.0 mass % or more;
The ink-jet recording method according to claim 1, wherein the recording medium has an absorption amount of water of 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method.

(Method 2) The reactant of the aqueous reaction solution is an organic acid,
The inkjet recording method according to Method 1, wherein the first resin particles in the aqueous ink are resin particles dispersed by the action of at least one hydrophilic group selected from the group consisting of a hydroxy group, an ethylene oxide group, a propylene oxide group, a sulfonic acid group, a sulfate ester group, and a phosphonic acid group.

(Method 3) The reactant of the aqueous reaction solution is an organic acid having a pKa of 3.2 or more at 25° C.,
The inkjet recording method according to Method 1, wherein the first resin particles in the aqueous ink are resin particles dispersed by the action of a carboxylic acid group and have an acid value of 11 mgKOH/g or less.

(Method 4) The inkjet recording method according to Method 3, in which the organic acid has a pKa of 3.5 or more at 25°C.

(Method 5) The inkjet recording method according to Method 3 or 4, in which the acid value of the first resin particles is 5 mg KOH/g or less.

(Method 6) The inkjet recording method according to any one of Methods 2 to 5, in which the organic acid is a polycarboxylic acid.

(Method 7) The reactant of the aqueous reaction liquid is a polyvalent metal salt,
The inkjet recording method according to Method 1, wherein the first resin particles in the aqueous ink are resin particles dispersed by the action of at least one hydrophilic group selected from the group consisting of a hydroxy group, an ethylene oxide group, a propylene oxide group, a sulfonic acid group, a sulfate ester group, and a phosphonic acid group.

(Method 8) The inkjet recording method according to Method 7, in which the polyvalent metal salt is at least one compound selected from the group consisting of calcium lactate and magnesium sulfate.

(Method 9) The reactant of the aqueous reaction liquid is a cationic resin,
The inkjet recording method according to Method 1, wherein the first resin particles in the aqueous ink are resin particles dispersed by the action of at least one hydrophilic group selected from the group consisting of a hydroxy group, an ethylene oxide group, and a propylene oxide group.

(Method 10) The inkjet recording method according to Method 9, in which the weight average molecular weight of the cationic resin is 5,000 or less.

(Method 11) The inkjet recording method according to Method 9 or 10, in which the cationic resin has a cationic degree (meq/g) of 3 meq/g or more and 7 meq/g or less.

(Method 12) The inkjet recording method according to any one of Methods 1 to 11, in which the pigment is a pigment dispersed by a resin having a carboxylic acid group.

(Method 13) The inkjet recording method according to Method 12, in which the acid value of the resin having a carboxylic acid group is 100 mg KOH/g or more.

(Method 14) The inkjet recording method according to any one of Methods 1 to 13, wherein the aqueous ink further contains at least one surfactant selected from the group consisting of fluorine-based nonionic surfactants and silicone-based nonionic surfactants.

(Method 15) The inkjet recording method according to Method 14, wherein the aqueous ink further contains a hydrocarbon-based nonionic surfactant.

(Method 16) The silicone-based nonionic surfactant of the water-based ink is a compound having a structure in which at least one hydrophilic group selected from the group consisting of an alkylene oxide group and a hydroxy group is substituted on a silicon atom other than the terminal of a polyorganosiloxane chain having a siloxane repeating structure as a main skeleton,
16. The inkjet recording method according to claim 15, wherein the hydrocarbon-based nonionic surfactant of the aqueous ink is a compound having a structure in which at least one hydrophilic group selected from the group consisting of an alkylene oxide group and a hydroxy group is substituted on a carbon atom other than the terminal carbon atom of a hydrocarbon chain that is the main skeleton.

(Method 17) The inkjet recording method according to any one of Methods 1 to 16, wherein the content (mass%) of the first resin particles in the aqueous ink is 1.5 to 6.0 times the total content (mass%) of the second resin particles and the pigment.

(Method 18) The inkjet recording method according to any one of Methods 1 to 17, wherein the resin particles in the aqueous ink have at least one anionic group selected from the group consisting of a sulfonic acid group, a sulfate ester group, and a phosphonic acid group.

(Method 19) The inkjet recording method according to any one of Methods 1 to 18, in which the particle diameter increase rate of the first resin particles is 1.2 times or less.

(Method 20) The inkjet recording method according to any one of Methods 1 to 19, wherein the proportion (mass %) of the first water-soluble organic solvent in the water-based ink is 90.0 mass % or more.

(Method 21) The aqueous reaction liquid further contains a second water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more;
21. The inkjet recording method according to any one of Methods 1 to 20, wherein the proportion (mass %) of the second water-soluble organic solvent in the water-soluble organic solvent in the aqueous reaction liquid is 90.0 mass % or more.

(Method 22) The inkjet recording method according to any one of Methods 1 to 21, in which the content (mass%) of resin particles in the aqueous reaction liquid is 1.0 mass% or less based on the total mass of the reaction liquid.

(Method 23) The water-based ink further contains a water-soluble resin,
the water-soluble resin is at least one selected from the group consisting of (i) a water-soluble resin including a unit having at least one selected from the group consisting of an ethylene oxide group and a propylene oxide group, and (ii) a block copolymer including a block composed of a unit having no acid group,
23. The inkjet recording method according to any one of Methods 1 to 22, wherein the content (mass %) of the water-soluble resin in the aqueous ink is 0.1 mass % or more based on the total mass of the ink.

(Configuration 1) An inkjet recording apparatus used for recording an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink, comprising:
a reaction liquid applying means for applying the aqueous reaction liquid to the recording medium;
an ink applying means for applying the water-based ink so as to overlap at least a portion of an area of the recording medium to which the water-based reaction liquid is applied,
the aqueous ink contains a pigment dispersed by the action of a carboxylic acid group, resin particles, and a water-soluble organic solvent;
the particle size increase rate of the pigment dispersed by the action of the carboxylic acid group when contacted with the aqueous reaction liquid is 8.0 times or more;
the resin particles include first resin particles having a particle diameter increase rate of 3.0 times or less when contacted with the aqueous reaction liquid,
a content (mass%) of the first resin particles in the aqueous ink is 1.2 times or more and 25.0 times or less in mass ratio to the sum of a content (mass%) of the second resin particles having a particle diameter increase rate of more than 3.0 times when contacted with the aqueous reaction liquid and a content (mass%) of the pigment dispersed by the action of the carboxylic acid group,
the water-soluble organic solvent includes a first water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more;
a ratio (mass %) of the first water-soluble organic solvent to the water-soluble organic solvent in the aqueous ink is 50.0 mass % or more;
13. An ink jet recording apparatus, comprising: a recording medium having an amount of water absorption of 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method.

(Configuration 2) A set of an aqueous ink and an aqueous reaction liquid used in an inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink, comprising:
the inkjet recording method includes a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium;
an ink applying step of applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied,
the aqueous ink contains a pigment dispersed by the action of a carboxylic acid group, resin particles, and a water-soluble organic solvent;
the particle size increase rate of the pigment dispersed by the action of the carboxylic acid group when contacted with the aqueous reaction liquid is 8.0 times or more;
the resin particles include first resin particles having a particle diameter increase rate of 3.0 times or less when contacted with the aqueous reaction liquid,
a content (mass%) of the first resin particles in the aqueous ink is 1.2 times or more and 25.0 times or less in mass ratio to the sum of a content (mass%) of the second resin particles having a particle diameter increase rate of more than 3.0 times when contacted with the aqueous reaction liquid and a content (mass%) of the pigment dispersed by the action of the carboxylic acid group,
the water-soluble organic solvent includes a first water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more;
a ratio (mass %) of the first water-soluble organic solvent to the water-soluble organic solvent in the aqueous ink is 50.0 mass % or more;
A set of an aqueous ink and an aqueous reaction liquid, characterized in that the recording medium has an absorption amount of water of 10 mL/ ^m2 or less from the start of contact until 30 msec ^1/2 in the Bristow method.

Claims (25)

An inkjet recording method for recording an image on a recording medium using an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, comprising:
a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium;
an ink applying step of applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied,
the aqueous ink contains a pigment dispersed by the action of a carboxylic acid group, resin particles, and a water-soluble organic solvent;
the particle size increase rate of the pigment dispersed by the action of the carboxylic acid group when contacted with the aqueous reaction liquid is 8.0 times or more;
the resin particles include first resin particles having a particle diameter increase rate of 3.0 times or less when contacted with the aqueous reaction liquid,
a content (mass%) of the first resin particles in the aqueous ink is 1.2 times or more and 25.0 times or less in mass ratio to the sum of a content (mass%) of the second resin particles having a particle diameter increase rate of more than 3.0 times when contacted with the aqueous reaction liquid and a content (mass%) of the pigment dispersed by the action of the carboxylic acid group,
the water-soluble organic solvent includes a first water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more;
a ratio (mass %) of the first water-soluble organic solvent to the water-soluble organic solvent in the aqueous ink is 50.0 mass % or more;
The ink-jet recording method according to claim 1, wherein the recording medium has an absorption amount of water of 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method. the reactant of the aqueous reaction liquid is an organic acid,
2. The inkjet recording method according to claim 1, wherein the first resin particles in the aqueous ink are resin particles dispersed by the action of at least one hydrophilic group selected from the group consisting of a hydroxy group, an ethylene oxide group, a propylene oxide group, a sulfonic acid group, a sulfate ester group, and a phosphonic acid group. the reactant in the aqueous reaction solution is an organic acid having a pKa of 3.2 or more at 25° C.,
2. The ink jet recording method according to claim 1, wherein the first resin particles in the water-based ink are resin particles dispersed by the action of a carboxylic acid group and have an acid value of 11 mgKOH/g or less. The inkjet recording method according to claim 3, wherein the organic acid has a pKa of 3.5 or more at 25°C. The inkjet recording method according to claim 3, wherein the acid value of the first resin particles is 5 mg KOH/g or less. The inkjet recording method according to claim 2, wherein the organic acid is a polycarboxylic acid. the reactant of the aqueous reaction liquid is a polyvalent metal salt,
2. The inkjet recording method according to claim 1, wherein the first resin particles in the aqueous ink are resin particles dispersed by the action of at least one hydrophilic group selected from the group consisting of a hydroxy group, an ethylene oxide group, a propylene oxide group, a sulfonic acid group, a sulfate ester group, and a phosphonic acid group. The inkjet recording method according to claim 7, wherein the polyvalent metal salt is at least one compound selected from the group consisting of calcium lactate and magnesium sulfate. the reactant in the aqueous reaction liquid is a cationic resin,
2. The inkjet recording method according to claim 1, wherein the first resin particles in the aqueous ink are resin particles dispersed by the action of at least one hydrophilic group selected from the group consisting of a hydroxy group, an ethylene oxide group, and a propylene oxide group. The inkjet recording method according to claim 9, wherein the weight average molecular weight of the cationic resin is 5,000 or less. The inkjet recording method according to claim 9, wherein the cationic resin has a cationic degree (meq/g) of 3 meq/g or more and 7 meq/g or less. The inkjet recording method according to claim 1, wherein the pigment is a pigment dispersed by a resin having a carboxylic acid group. The inkjet recording method according to claim 12, wherein the acid value of the resin having a carboxylic acid group is 100 mg KOH/g or more. The inkjet recording method according to claim 1, wherein the aqueous ink further contains at least one surfactant selected from the group consisting of fluorine-based nonionic surfactants and silicone-based nonionic surfactants. The inkjet recording method according to claim 14, wherein the aqueous ink further contains a hydrocarbon-based nonionic surfactant. the silicone-based nonionic surfactant of the water-based ink is a compound having a structure in which at least one hydrophilic group selected from the group consisting of an alkylene oxide group and a hydroxy group is substituted on a silicon atom other than that at the terminal of a polyorganosiloxane chain having a siloxane repeating structure as a main skeleton,
16. The inkjet recording method according to claim 15, wherein the hydrocarbon-based nonionic surfactant of the aqueous ink is a compound having a structure in which at least one hydrophilic group selected from the group consisting of an alkylene oxide group and a hydroxy group is substituted on a carbon atom other than the terminal carbon atom of a hydrocarbon chain that is a main skeleton. The inkjet recording method according to claim 1, wherein the content (mass%) of the first resin particles in the aqueous ink is 1.5 to 6.0 times the total content (mass%) of the second resin particles and the pigment. The inkjet recording method according to claim 1, wherein the resin particles in the aqueous ink have at least one anionic group selected from the group consisting of a sulfonic acid group, a sulfate ester group, and a phosphonic acid group. The inkjet recording method according to claim 1, wherein the particle diameter increase rate of the first resin particles is 1.2 times or less. The inkjet recording method according to claim 1, wherein the proportion (mass %) of the first water-soluble organic solvent in the water-based ink is 90.0 mass % or more. the aqueous reaction liquid further contains a second water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more;
The inkjet recording method according to claim 1, wherein a ratio (mass %) of the second water-soluble organic solvent to the water-soluble organic solvent in the aqueous reaction liquid is 90.0 mass % or more. The inkjet recording method according to claim 1, wherein the content (mass %) of resin particles in the aqueous reaction liquid is 1.0 mass % or less based on the total mass of the reaction liquid. The water-based ink further contains a water-soluble resin,
the water-soluble resin is at least one selected from the group consisting of (i) a water-soluble resin including a unit having at least one selected from the group consisting of an ethylene oxide group and a propylene oxide group, and (ii) a block copolymer including a block composed of a unit having no acid group,
The inkjet recording method according to claim 1, wherein the content (mass %) of the water-soluble resin in the aqueous ink is 0.1 mass % or more based on the total mass of the ink. An inkjet recording apparatus used to record an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink, comprising:
a reaction liquid applying means for applying the aqueous reaction liquid to the recording medium;
an ink applying means for applying the water-based ink so as to overlap at least a portion of an area of the recording medium to which the water-based reaction liquid is applied,
the aqueous ink contains a pigment dispersed by the action of a carboxylic acid group, resin particles, and a water-soluble organic solvent;
the particle size increase rate of the pigment dispersed by the action of the carboxylic acid group when contacted with the aqueous reaction liquid is 8.0 times or more;
the resin particles include first resin particles having a particle diameter increase rate of 3.0 times or less when contacted with the aqueous reaction liquid,
a content (mass%) of the first resin particles in the aqueous ink is 1.2 times or more and 25.0 times or less in mass ratio to the sum of a content (mass%) of the second resin particles having a particle diameter increase rate of more than 3.0 times when contacted with the aqueous reaction liquid and a content (mass%) of the pigment dispersed by the action of the carboxylic acid group,
the water-soluble organic solvent includes a first water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more;
a ratio (mass %) of the first water-soluble organic solvent to the water-soluble organic solvent in the aqueous ink is 50.0 mass % or more;
13. An ink jet recording apparatus, comprising: a recording medium having an amount of water absorption of 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method. A set of an aqueous ink and an aqueous reaction liquid used in an inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink, comprising:
the inkjet recording method includes a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium;
an ink applying step of applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied,
the aqueous ink contains a pigment dispersed by the action of a carboxylic acid group, resin particles, and a water-soluble organic solvent;
the particle size increase rate of the pigment dispersed by the action of the carboxylic acid group when contacted with the aqueous reaction liquid is 8.0 times or more;
the resin particles include first resin particles having a particle diameter increase rate of 3.0 times or less when contacted with the aqueous reaction liquid,
a content (mass%) of the first resin particles in the aqueous ink is 1.2 times or more and 25.0 times or less in mass ratio to the sum of a content (mass%) of the second resin particles having a particle diameter increase rate of more than 3.0 times when contacted with the aqueous reaction liquid and a content (mass%) of the pigment dispersed by the action of the carboxylic acid group,
the water-soluble organic solvent includes a first water-soluble organic solvent having a vapor pressure of 1.0×10 ⁻² kPa or more;
a ratio (mass %) of the first water-soluble organic solvent to the water-soluble organic solvent in the aqueous ink is 50.0 mass % or more;
A set of an aqueous ink and an aqueous reaction liquid, characterized in that the recording medium has an absorption amount of water of 10 mL/ ^m2 or less from the start of contact until 30 msec ^1/2 in the Bristow method.

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