Ink jet recording method and ink jet recording apparatus

Abstract

To provide an ink jet recording method capable of recording an image having suppressed granularity and excellent color development on a low- to non-absorbent recording medium.SOLUTION: The invention provides an ink jet recording method by ejecting an aqueous ink and an aqueous reaction liquid from an ink jet recording head and applying it to a non-absorbent recording medium to record an image. The method has the steps of: ejecting a reaction liquid from a recording head and applying it to a recording medium; and ejecting and applying an aqueous ink from the recording head so as to overlap at least a part of an area of the recording medium to which the reaction liquid is applied. The aqueous ink contains resin particles, a surfactant A represented by the general formula (1), and a water-soluble organic solvent having a permittivity of 31.5 or less, and a content (mass%) of the surfactant A in the aqueous ink is 0.01 times or more to 0.08 times or less in a mass ratio with respect to a content (mass%) of the resin particles.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, inkjet recording methods have been increasingly used in the sign and display field, such as for recording posters and large-sized advertisements. In this field, polyvinyl chloride sheets and polyethylene terephthalate (PET) sheets are often used as recording media due to their durability and cost. These recording media have no or almost no aqueous ink absorption layer on the recording surface, and are known as non-absorbent recording media (recording media that do not absorb aqueous ink) or low-absorbent recording media (recording media that have low absorbency for aqueous ink). Conventionally, solvent-based inks and curable inks have been used to record images on these recording media. However, there is a growing need for aqueous inks that use aqueous media to reduce environmental impact and odor.

[0003] In the field of signs and displays, there is a demand for the ability to record excellent, high-quality images with good color development and reduced unevenness even on the above-mentioned non-absorbent recording media and low-absorbent recording media (hereinafter collectively referred to as "non-absorbent recording media"). To meet this demand, for example, a method has been proposed for recording images on non-absorbent recording media using a set of an aqueous ink containing resin particles and a nonionic surfactant and a reaction liquid that has the effect of aggregating the components in the ink (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-165314 Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have studied images recorded on a non-absorbent recording medium using the set proposed in Patent Document 1. As a result, they have found that the quality (image quality) of the recorded images is not necessarily sufficiently high. Specifically, they have found that it is difficult to simultaneously suppress graininess in areas where a small amount of ink is applied and improve color development in areas where a large amount of ink is applied.

[0006] Therefore, an object of the present invention is to provide an inkjet recording method capable of recording an image with reduced graininess and excellent color development on a low- to non-absorbent recording medium. Another object of the present invention is to provide an inkjet recording apparatus used in this inkjet recording method. [Means for solving the problem]

[0007] That is, according to the present invention, there is provided an inkjet recording method for recording an image by ejecting an aqueous ink and an aqueous reaction liquid that reacts with the aqueous ink from an inkjet recording head and applying the reaction liquid to a recording medium, the method comprising the steps of: ejecting the reaction liquid from the recording head and applying it to the recording medium; and ejecting the aqueous ink from the recording head and applying it so as to overlap at least a part of an area of ​​the recording medium to which the reaction liquid is applied, the aqueous ink comprising resin particles, a surfactant A represented by the following general formula (1), and a water-soluble organic solvent having a relative dielectric constant of 31.5 or less, the content (mass %) of the surfactant A in the aqueous ink being 0.01 times or more and 0.08 times or less in mass ratio to the content (mass %) of the resin particles, and the recording medium being in a state where the reaction liquid is applied to the recording medium within 30 msec from the start of contact in a Bristow method. 1 / 2 Water absorption up to 10mL / m 2 An inkjet recording method is provided, characterized in that:

[0008] TIFF2025169905000001.tif27170 (in the general formula (1), R1 represents a chain hydrocarbon group having 12 to 24 carbon atoms, and a represents an integer of 1 to 10) [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an inkjet recording method capable of recording an image with reduced graininess and excellent color development on a low- to non-absorbent recording medium, and an inkjet recording apparatus used in the inkjet recording method. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. [Figure 2] 1 is a side view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink as dissociated ions, but for convenience it will be expressed as "containing a salt." In addition, aqueous inkjet ink and reaction liquid may be simply referred to as "ink" and "reaction liquid." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified. When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0012] The present inventors first investigated why it is difficult to simultaneously suppress graininess and improve color development in images recorded on non-absorbent recording media. It is known that when recording an image on a non-absorbent recording medium, the ink is brought into contact with a reaction liquid on the recording medium to aggregate the ink dots in order to properly pin (fix) the ink dots on the recording medium. Components in the ink that rapidly aggregate upon contact with the reaction liquid are likely to form aggregates that cause irregularities on the surface of the recording medium. This makes it easier for light to scatter on the dot surfaces, reducing the color development of the image.

[0013] To improve the smoothness of the dot surface and the color development of the image, it is effective to, for example, reduce the amount of reactive liquid relative to the amount of ink, or to reduce the components in the ink that react with the reactive liquid (pigments or resins), but this also reduces the pinning force of the ink dots. As a result, in areas where the amount of ink applied is small, dots that land on the recording medium tend to move, and large dots formed by adjacent dots merging become visible, making the graininess more noticeable. Therefore, it has been found that simply controlling the cohesion of the components in the ink is difficult to achieve both the suppression of graininess and the improvement of color development, which are in a trade-off relationship.

[0014] After further investigation, the present inventors discovered that an ink containing a phosphate ester surfactant (surfactant A) represented by the following general formula (1) and a water-soluble organic solvent having a dielectric constant of 31.5 or less can be used. As a result, they discovered that an image that achieves both suppressed graininess and improved color development can be recorded on a non-absorbent recording medium, leading to the present invention. Specifically, the ink used in the inkjet recording method of the present invention contains resin particles and surfactant A represented by the following general formula (1). The content (mass %) of surfactant A in the ink is 0.01 to 0.08 times the mass ratio of the content (mass %) of the resin particles. The ink is then applied so as to overlap at least a portion of the area of ​​the recording medium to which the reaction liquid is applied. The present inventors speculate as follows about the mechanism by which the above configuration enables images that achieve both suppressed graininess and improved color development to be recorded on a non-absorbent recording medium.

[0015] TIFF2025169905000002.tif27170 (in the general formula (1), R1 represents a chain hydrocarbon group having 12 to 24 carbon atoms, and a represents an integer of 1 to 10)

[0016] Surfactant A, represented by general formula (1), has a hydrophobic portion represented by R1, a nonionic portion having a repeating unit of ethylene oxide, and an anionic portion that is a phosphate group. It is believed that the resin particles interact with the hydrophobic portion (R1) of surfactant A in the ink. The nonionic portion (repeating unit of ethylene oxide) of surfactant A reduces the aggregation of the resin particles that have interacted with the hydrophobic portion (R1) of surfactant A upon contact with the reaction liquid. It is believed that the time from when the ink and the reaction liquid come into contact on the surface of the recording medium until the unevenness of the dot surface is formed is within several hundred milliseconds. Within this time scale, it is believed that the time it takes for the resin particles to come into contact with the reaction liquid and aggregate increases, improving the smoothness of the dot surface.

[0017] On the other hand, the dots move and merge on the recording medium by several tens of micrometers, causing noticeable graininess. The time it takes for the dots to move by several tens of micrometers is several seconds. During these few seconds, it is important to allow the reaction between the pigments and acid groups of the resin particles in the ink and the reactive liquid (reactant) to proceed, increasing the cohesive viscosity of the dots and enhancing the pinning force. During this time scale, the resin particles that interact with the hydrophobic portion (R1) of surfactant A further react with the anionic portion (phosphate group) of surfactant A, increasing the final cohesive viscosity of the dots. This is thought to sufficiently increase the pinning force of the dots and suppress graininess.

[0018] Furthermore, the content (mass%) of surfactant A in the ink is 0.01 to 0.08 times the mass ratio of the content (mass%) of resin particles. When the content (mass%) of surfactant A is 0.01 or more times the mass ratio of the content (mass%) of resin particles, the aggregation relaxation of the resin particles is facilitated several hundred milliseconds after the ink and reaction liquid come into contact, improving color development. On the other hand, when the content (mass%) of surfactant is 0.08 or less times the mass ratio of the content (mass%) of resin particles, the resin particles aggregate several seconds after the ink and reaction liquid come into contact, sufficiently increasing viscosity. This can suppress graininess.

[0019] The ink also contains a water-soluble organic solvent with a dielectric constant of 31.5 or less. Compared to water, water-soluble organic solvents with a dielectric constant of 31.5 or less have a higher affinity with the hydrophobic portion (R1) of surfactant A and the hydrophobic portion of the resin particles. Therefore, by including a water-soluble organic solvent with a dielectric constant of 31.5 or less in the ink, the hydrophobic portion (R1) of surfactant A can interact more strongly with the functional groups present near the surface of the resin particles. This is thought to enable surfactant A to exist in the vicinity of the resin particles.

[0020] <Inkjet recording method and inkjet recording apparatus> The inkjet recording method of the present invention is a method of recording an image by ejecting an aqueous ink and an aqueous reaction liquid that reacts with the aqueous ink from an inkjet recording head and applying them to a recording medium. The inkjet recording method of the present invention includes a step of ejecting the reaction liquid from the recording head and applying it to the recording medium, and a step of ejecting the aqueous ink from the recording head and applying it so as to overlap at least a portion of the area of ​​the recording medium to which the reaction liquid is applied. The aqueous ink contains resin particles, surfactant A represented by the following general formula (1), and a water-soluble organic solvent having a relative dielectric constant of 31.5 or less. The content (mass %) of surfactant A in the aqueous ink is 0.01 to 0.08 times the mass ratio of the content (mass %) of the resin particles. The recording medium is then subjected to a Bristow method for 30 msec from the start of contact.1 / 2 Water absorption up to 10mL / m 2 The following is the result.

[0021] TIFF2025169905000003.tif27170 (in the general formula (1), R1 represents a chain hydrocarbon group having 12 to 24 carbon atoms, and a represents an integer of 1 to 10)

[0022] 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 that reacts with the aqueous ink are ejected from an inkjet recording head and applied to a recording medium to record an image. The inkjet recording apparatus of the present invention is an apparatus that is suitably used in the above-mentioned recording method. It is not necessary to provide a step of applying a coating liquid that does not contain a coloring material other than the ink, or a step of curing the image by irradiating with active energy rays. The inkjet recording method and inkjet recording apparatus of the present invention (hereinafter also simply referred to as "recording method and recording apparatus") will be described in detail below.

[0023] (Inkjet recording device) FIG. 1 is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. FIG. 2 is a side view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. The recording apparatus of the embodiment shown in FIGS. 1 and 2 includes an inkjet recording head 22 that ejects ink and a reaction liquid. Examples of the recording head include a recording head that ejects ink and a reaction liquid by the action of mechanical energy and a recording head that ejects ink and a reaction liquid by the action of thermal energy. Of these, a recording head that ejects ink and a reaction liquid by the action of thermal energy is preferred. A recording head that ejects ink and a reaction liquid by the action of thermal energy is a thermal recording head that applies thermal energy to the ink and the reaction liquid by applying an electric pulse to an electrothermal conversion element, thereby ejecting the ink and the reaction liquid from the ejection openings. This thermal recording head preferably includes a mechanism (temperature control mechanism) that heats the aqueous ink to a predetermined temperature before being ejected from the recording head and applied to the recording medium.

[0024] [Heating process] The recording method of the present invention preferably further comprises a step of heating (heat treating) the recording medium to which the ink has been applied. Heating the recording medium to which the ink and reaction liquid have been applied promotes film formation of the resin particles, making it possible to record an image with excellent scratch resistance.

[0025] The means for heating the recording medium is not particularly limited, and examples thereof include known heating means such as a heater, air blowing means using air such as a dryer, and a combination of these. That is, the inkjet recording apparatus preferably includes a mechanism (heating means) for heating the recording medium to which the ink and reaction liquid have been applied. Examples of heating means include the above-mentioned heating means, air blowing means, and a combination of these. Examples of heat treatment methods include applying heat from the side (backside) opposite to the recording surface (ink-applied surface) of the recording medium using a heater or the like, applying warm or hot air to the recording surface of the recording medium, and heating from the recording surface or backside using an infrared heater.

[0026] In the recording device shown in FIGS. 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 can be heated by the heater 25. Specific 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 onto the recording medium 1. The heater cover 26 also serves as a member for protecting the heater 25. The recording medium 1 to which ink ejected from the recording head 22 has been applied is wound up by a take-up spool 27 to form a roll-shaped wound medium 24.

[0027] (Recording medium) In the recording method and recording device of the present invention, a non-absorbent recording medium (a low to non-absorbent recording medium) is used as the recording medium. The non-absorbent recording medium is a recording medium that is absorbed within 30 msec from the start of contact in the Bristow method described in JAPAN TAPPI Paper Pulp Test Method No. 51, "Liquid Absorbency Test Method for Paper and Paperboard." 1 / 2 Water absorption up to 0mL / m 2 More than 10mL / m 2 In the present invention, a recording medium that satisfies the above-mentioned condition of water absorption amount is defined as a "low to non-absorbent recording medium." Inkjet recording media (glossy paper, matte paper, etc.) having an ink-receiving layer formed of inorganic particles and plain paper having no coating layer have a water absorption amount of 10 mL / m or less. 2 It is an "absorbent recording medium" that exceeds this.

[0028] Examples of non-absorbent recording media that can be used include plastic films, recording media in which a plastic film is bonded to the recording surface of a substrate, and recording media in which an organic 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 an organic resin coating layer is provided as an organic resin layer on the recording surface of a substrate containing cellulose pulp are also preferred.

[0029] When the ink used in the recording method and recording apparatus of the present invention is applied to a non-absorbent recording medium, components such as water and water-soluble organic solvents volatilize, concentrating the resin particles. This promotes fusion between the concentrated resin particles, improving the abrasion resistance of the recorded image. In contrast, when the ink is applied to a recording medium with high liquid component absorption, fusion between the resin particles is less likely to be promoted, resulting in insufficient improvement in the abrasion resistance of the image. Note that the recording medium in this specification does not refer to a transfer medium, but rather to a recording medium on which an image is recorded as a recorded product.

[0030] (ink) The ink is a water-based ink for inkjet printing that contains resin particles and a surfactant A represented by general formula (1). Each component of the ink will be described in detail below.

[0031] [Resin particles] The ink contains resin particles. The charge amount of the resin particles (μmol / m 2 ) is 1.0 μmol / m from the viewpoint of suppressing graininess and improving color development. 2 More than 2.4μmol / m 2 The charge amount of the resin particles is preferably 2.4 μmol / m or less. 2 If the charge amount of the resin particles is more than 1.0 μmol / m, the resin particles may be strongly aggregated by the reaction solution, making it difficult to sufficiently fill the irregularities on the dot surface, and the effect of improving color development may be reduced. 2 If it exceeds this value, the aggregation of resin particles by the reaction liquid may be weakened, and the effect of suppressing graininess may be reduced.

[0032] Charge amount of resin particles (μmol / m 2 ) can be measured by colloid titration using potential difference. In the examples described below, an automatic potentiometric titrator (product name "AT-510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500) was used to measure the charge amount of resin particles by colloid titration using potential difference. The pH of the resin particle dispersion used for measurement was adjusted to 8 to 9, and methyl glycol chitosan was used as the titration reagent.

[0033] The content (mass %) of resin particles in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. The content (mass %) of resin particles in the ink is preferably 1.5 times or more, and more preferably 1.7 times or more, the mass ratio relative to the pigment content (mass %). Furthermore, the above mass ratio is preferably 10.0 times or less. The resin particles exist in the ink in a dispersed state, i.e., in the form of a resin emulsion.

[0034] In this specification, "resin particles" refers to a resin that is present in a state in which it is not dissolved in the aqueous medium of the ink, and more specifically, refers to a resin that can be present in the aqueous medium in the form of particles whose particle diameter can be measured by dynamic light scattering. In contrast, "water-soluble resin" refers to a resin that is present in a state in which it is dissolved in the aqueous medium of the ink. "Resin particles" can also be referred to as "water-dispersible resin (water-insoluble resin)."

[0035] Whether a certain resin corresponds to "resin particles" can be determined according to the method shown below. First, a liquid containing the resin to be determined is prepared and diluted with pure water so that the resin content is approximately 1.0% to prepare a sample. Then, when the particle size of the resin in the sample is measured by dynamic light scattering, if particles having a particle size are measured, the resin is determined to be "resin particles" (i.e., a "water-dispersible resin"). On the other hand, if particles having a particle size are not measured, the resin is determined not to be "resin particles" (i.e., a "water-soluble resin"). The measurement conditions in this case can be, for example, as follows: [Measurement conditions] SetZero: 30 seconds Number of measurements: 10 Measurement time: 120 seconds Shape: true spherical Refractive index: 1.5 Density: 1.0

[0036] As a particle size distribution measuring device, a particle size analyzer using dynamic light scattering (for example, the product name "UPA-EX150" manufactured by Nikkiso) can be used. Of course, the particle size distribution measuring device and measurement conditions used are not limited to those described above. Furthermore, the average particle diameter (50% cumulative particle diameter on a volume basis) of pigment or wax particles can be measured using the device and conditions described above. The average particle diameter of resin particles is the diameter of the particle that is 50% cumulative from the smallest particle diameter side on a particle size cumulative curve, based on the total volume of the measured particles.

[0037] 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 2,000,000 or less. The average particle diameter of the resin particles measured by dynamic light scattering is preferably 50 nm or more and 500 nm or less. The resin particles do not need to contain a colorant.

[0038] The constituent units of the resin constituting the resin particles can be appropriately selected from the same units constituting the water-soluble resins described below. Specific examples include acrylic resins, urethane resins, polyester resins, and various copolymers. Examples of copolymers include styrene-acrylic resins, styrene-butadiene resins, polyether-polyurethane resins, and polyester-polyurethane resins.

[0039] [Surfactant A] The ink contains a surfactant A represented by the following general formula (1).

[0040] TIFF2025169905000004.tif27170 (in the general formula (1), R1 represents a chain hydrocarbon group having 12 to 24 carbon atoms, and a represents an integer of 1 to 10)

[0041] If the phosphate group in general formula (1) is a carboxylic acid group or a sulfonic acid group, the color development of the image cannot be improved. Considering the reactivity between the ionized acid group and the cationic component in the reaction solution that functions as a reactant, the phosphate group, which has the largest number of anions, takes the longest time to neutralize. It is believed that using a surfactant containing a phosphate group can reduce the aggregation of resin particles several hundred milliseconds after the ink and reaction solution come into contact on the surface of the recording medium.

[0042] In general formula (1), if the carbon number of the chain hydrocarbon group represented by R1 is 11 or less or 25 or more, it does not sufficiently interact with the resin particles, and the effect of suppressing graininess and improving color development cannot be achieved. If a in general formula (1) is 0, the aggregation of the resin particles cannot be alleviated several hundred milliseconds after the ink and reaction liquid come into contact, and color development cannot be improved. On the other hand, if a in general formula (1) is 11 or more, even if the resin particles aggregate several seconds after the ink and reaction liquid come into contact, the large repeating structure of ethylene oxide in general formula (1) makes it difficult to sufficiently increase the aggregation viscosity, and graininess cannot be suppressed.

[0043] The surfactant A is preferably a compound represented by the following general formula (2), since this can further enhance the effect of suppressing graininess and the effect of improving color development.

[0044] TIFF2025169905000005.tif29170 (in the general formula (2), a represents an integer of 1 or more and 10 or less)

[0045] The content (mass%) of surfactant A in the ink is 0.01 to 0.08 times the mass of the content (mass%) of resin particles. The content (mass%) of surfactant A in the ink is preferably 0.02 to 0.06 times the mass of the content (mass%) of resin particles. If the mass ratio is too small, the amount of surfactant A is relatively small, resulting in insufficient relaxation of the resin particle aggregation several hundred milliseconds after contact between the ink and the reaction solution, which may reduce the effect of improving color development. On the other hand, if the mass ratio is too large, even if the resin particles aggregate several seconds after contact between the ink and the reaction solution, the relatively large amount of surfactant A makes it difficult to sufficiently increase the viscosity, which may reduce the effect of suppressing graininess. Regarding the numerical range of the mass ratio of surfactant A content (mass%) to the content (mass%) of resin particles in the ink of the present invention, if no value is specified to the third decimal place, it means that the third decimal place is 0. For example, the above "0.01 times or more and 0.08 times or less" means "0.010 times or more and 0.080 times or less."

[0046] [Other surfactants] The ink may further contain surfactants other than surfactant A (other surfactants). From the viewpoint of further improving color development, silicone-based surfactants are preferred as the other surfactants. Silicone-based surfactants can efficiently reduce the contact angle of the ink with the recording medium with smaller amounts than acetylene glycol-based surfactants. Therefore, the use of silicone-based surfactants facilitates the wetting and spreading of ink dots, further improving color development. However, adding an acetylene glycol-based surfactant to sufficiently reduce the contact angle of the ink results in an increased amount being added. Therefore, excess acetylene glycol-based surfactants are more likely to interact with the resin particles and may inhibit the interaction between surfactant A and the resin particles, potentially reducing the effects of suppressing graininess and improving color development.

[0047] Furthermore, fluorosurfactants tend to be more lipophobic and hydrophobic than silicone surfactants, which means that they are more likely to interact with resin particles and may also inhibit the interaction between surfactant A and the resin particles, reducing the effects of suppressing graininess and improving color development.

[0048] [Colorant] The ink may contain a pigment as a coloring material. The content (mass %) of the coloring material in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

[0049] 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, dioxazine, and perinone.

[0050] Pigment dispersion methods that can be used include resin-dispersed pigments that use a resin as a dispersant and self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface. Also available are resin-bonded pigments in which organic groups containing a resin are chemically bonded to the pigment particle surface, and microencapsulated pigments in which the pigment particle surface is coated with a resin or the like. Among these, it is preferable to use resin-dispersed pigments in which a resin as a dispersant is physically adsorbed onto the pigment particle surface, rather than resin-bonded pigments or microencapsulated pigments. In other words, it is preferable for the pigment to be one that is dispersed by the action of a resin dispersant.

[0051] As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of anionic groups. As the resin dispersant, a resin described below, particularly a water-soluble resin, can be used. The content (mass %) of the pigment in the ink is preferably 0.3 to 10.0 times the mass ratio of the content of the resin dispersant.

[0052] Self-dispersing pigments can be used in which anionic groups such as carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups are bonded to the surface of pigment particles directly or via another atomic group (-R-). The anionic group can be either an acid type or a salt type. If the anionic group is a salt type, it can be either partially dissociated or completely dissociated. When the anionic group is a salt type, examples of the cation that serves as the counter ion include alkali metal cations, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene and naphthylene; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; and ether groups. Furthermore, combinations of these groups may also be used.

[0053] [resin] The ink may contain a resin. The content (mass %) of the resin in the ink is preferably 0.1% to 20.0% by mass, and more preferably 0.5% to 15.0% by mass, based on the total mass of the ink.

[0054] Resins can be added to inks (i) to stabilize the dispersion state of pigments, i.e., as a resin dispersant or its auxiliary. Resins can also be added to inks (ii) to improve various properties of the printed image. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. Resins can be water-soluble resins that can be dissolved in aqueous media, or resin particles that can be dispersed in aqueous media.

[0055] [Resin Composition] Examples of the resin include acrylic resins, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are more preferred.

[0056] The acrylic resin is preferably one having a hydrophilic unit and a hydrophobic unit as constituent units. Among these, 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-based monomer is preferred. 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 particularly preferred. These resins are likely to interact with pigments, and can therefore be suitably used as resin dispersants for dispersing pigments.

[0057] 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 not having a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer not having 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; and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0058] The urethane resin can be obtained by reacting, for example, polyisocyanate with a polyol. Alternatively, a chain extender may be further added to the urethane resin. Examples of the olefin resin include polyethylene and polypropylene.

[0059] [Resin properties] The water-soluble resin preferably has an acid value of 100 mgKOH / g or more and 250 mgKOH / g or less, and a weight-average molecular weight of 3,000 or more and 15,000 or less.

[0060] [Water-soluble organic solvent] The ink contains a water-soluble organic solvent (hereinafter also referred to as "first water-soluble organic solvent") having a relative dielectric constant of 31.5 or less at 25°C. The relative dielectric constant of the water-soluble organic solvent can be measured using a dielectric constant meter (for example, a "BI-870" (manufactured by BROOKHAVEN INSTRUMENTS CORPORATION)) at a frequency of 10 kHz. The relative dielectric constant of a water-soluble organic solvent that is solid at 25°C is determined by measuring the relative dielectric constant of a 50% by mass aqueous solution and calculating the value from the following formula (A). Usually, the term "water-soluble organic solvent" refers to a liquid, but in the present invention, the term "water-soluble organic solvent" also refers to a solvent that is solid at 25°C (room temperature). ε sol =2ε 50% -ε water (A) ε sol : Dielectric constant of solid water-soluble organic solvent at 25℃ ε 50% : Relative dielectric constant of a 50% by mass aqueous solution of a solid water-soluble organic solvent at 25°C ε water : relative dielectric constant of water

[0061] Specific examples of water-soluble organic solvents that are solid at 25° C. and are generally used in aqueous inks include 1,6-hexanediol, trimethylolpropane, ethylene urea, urea, and polyethylene glycol with a number average molecular weight of 1,000.

[0062] The reason for calculating the dielectric constant of a water-soluble organic solvent that is solid at 25°C from the dielectric constant of a 50% by mass aqueous solution is as follows. Among water-soluble organic solvents that are solid at 25°C and can be used as components of aqueous inks, it is difficult to prepare a high-concentration aqueous solution exceeding 50% by mass. On the other hand, in a low-concentration aqueous solution of 10% by mass or less, the dielectric constant of water becomes dominant, making it difficult to obtain a reliable (effective) dielectric constant value of the water-soluble organic solvent. Therefore, the inventors conducted an investigation and found that it is possible to prepare an aqueous solution to be measured from most of the water-soluble organic solvents that are solid at 25°C used in ink, and the calculated dielectric constant is consistent with the effects of the present invention. For the above reasons, in the present invention, the dielectric constant of a water-soluble organic solvent that is solid at 25°C is calculated and used from the dielectric constant of a 50% by mass aqueous solution. Even if a water-soluble organic solvent is solid at 25°C, if its solubility in water is low and it is not possible to prepare a 50% by mass aqueous solution, a saturated aqueous solution is used, and the above-mentioned ε sol For convenience, the value of the relative permittivity calculated in accordance with the calculation of

[0063] Specific examples of the first water-soluble organic solvent having a relative dielectric constant of 31.5 or less include 1,4-butanediol (31.1), 1,3-butanediol (30.0), 3-methylsulfolane (29.0), 1,2-propanediol (28.8), 1,2,6-hexanetriol (28.5), 2-methyl-1,3-propanediol (28.3), 2-pyrrolidone (28.0), 1,5-pentanediol (27.0), 1,2-pentanediol (17.4), 3-methyl-1,3-butanediol (24.0), 3-methyl-1,5-pentanediol (23.9), ethanol (23.8), 1-(hydroxymethyl)-5,5-dimethylhydantoin (23.7), triethylene glycol (22.7). ), tetraethylene glycol (20.8), polyethylene glycol (18.9) having a number average molecular weight of 200, 2-ethyl-1,3-hexanediol (18.5), isopropanol (18.3), 1,2-hexanediol (14.8), n-propanol (12.0), polyethylene glycol (11.4) having a number average molecular weight of 600, triethylene glycol monobutyl ether (9.8), tetraethylene glycol monobutyl ether (9.4), tripropylene glycol monomethyl ether (8.5), 1,6-hexanediol (7.1), polyethylene glycol (4.6) having a number average molecular weight of 1,000 (the numbers in parentheses are the relative dielectric constants at 25°C). The relative dielectric constant of the first water-soluble organic solvent is preferably 3.0 or more.

[0064] Among the first water-soluble organic solvents, it is preferable to use one having a relative dielectric constant of 29.0 or less. The content (mass%) of the first water-soluble organic solvent in the ink is preferably 0.10% by mass or more and 20.00% by mass or less, and more preferably 0.20% by mass or more and 10.00% by mass or less, based on the total mass of the ink. By keeping the content of the first water-soluble organic solvent in the ink within the above range, the interaction between the surfactant A and the first water-soluble organic solvent can be further improved. The content (mass%) of the first water-soluble organic solvent in the ink is preferably 0.10 times or more the mass ratio of the pigment content (mass%).

[0065] [Aqueous medium] The ink 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 ink is preferably 50.0 mass % or more and 95.0 mass % or less based on the total mass of the ink.

[0066] The water-soluble organic solvent also includes a water-soluble organic solvent having a relative dielectric constant of 31.5 or less. The content (mass %) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less, based on the total mass of the ink. There are no particular restrictions on the water-soluble organic solvent as long as it is water-soluble, and any solvent that can be used in inkjet inks, such as alcohols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The content (mass %) of the water-soluble organic solvent (including the first water-soluble organic solvent) in the ink is preferably 3.00% by mass or more and 50.00% by mass or less, based on the total mass of the ink.

[0067] Specific examples of water-soluble organic solvents (including specific examples having a dielectric constant of 31.5 or less) include monohydric alcohols having 1 to 4 carbon atoms, such as methanol (33.1), ethanol (23.8), n-propanol (12.0), isopropanol (18.3), n-butanol, sec-butanol, and tert-butanol; 1,2-propanediol (28.8), 1,3-butanediol (30.0), 1,4-butanediol (31.1), 1,5-pentanediol (27.0), 1,2-pentanediol (17.4), and 1,2-pentanediol. Dihydric alcohols such as hexane (17.4), 1,2-hexanediol (14.8), 1,6-hexanediol (7.1), 2-methyl-1,3-propanediol (28.3), 3-methyl-1,3-butanediol (24.0), 3-methyl-1,5-pentanediol (23.9), and 2-ethyl-1,3-hexanediol (18.5); polyhydric alcohols such as 1,2,6-hexanetriol (28.5), glycerin (42.3), trimethylolpropane (33.7), and trimethylolethane; and ethylene glycol (40. 4), diethylene glycol (31.7), triethylene glycol (22.7), tetraethylene glycol (20.8), butylene glycol, hexylene glycol, thiodiglycol and other alkylene glycols; diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether (9.8) and other glycol ethers; polyethylene glycol (18.9) with a number average molecular weight of 200, polyethylene glycol (18.9) with a number average molecular weight of 600 Polyalkylene glycols with a number average molecular weight of 200 to 1,000, such as ethanol (11.4), polyethylene glycol (4.6) with a number average molecular weight of 1,000, and polypropylene glycol; 2-pyrrolidone (28.0), N-methyl-2-pyrrolidone (32.0), 1-(2-hydroxyethyl)-2-pyrrolidone (37.6), 1,3-dimethyl-2-imidazolidinone, N-methylmorpholine, urea (110.3), ethylene urea (49.7), triethanolamine (31.9), 1-hydroxymethyl-5,5-dimethylhydantoin (23.Examples of suitable dielectric constants include nitrogen-containing compounds such as dimethyl sulfoxide (48.9) and bis(2-hydroxyethyl)-5,5-dimethylhydantoin (16.0); sulfur-containing compounds such as dimethyl sulfoxide (48.9) and bis(2-hydroxyethyl sulfone); and cyclic ethers such as γ-butyrolactone (41.9) (the numbers in parentheses are the relative dielectric constants at 25°C). The relative dielectric constant of the water-soluble organic solvent (excluding the first water-soluble organic solvent) is preferably 3.0 or higher. The water-soluble organic solvent contained in the ink preferably has a vapor pressure lower than that of water at 25°C.

[0068] [Other ingredients] The ink may contain various other components as needed. Examples of other components include various additives such as antifoaming agents, surfactants, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and antireducing agents. However, it is preferable that the ink does not contain the reactants contained in the reaction liquid.

[0069] [Ink properties] The ink is an aqueous ink used in inkjet printing. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the ink at 25°C is preferably 20 mN / m or more and 60 mN / m or less. Furthermore, 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.

[0070] (Reaction solution) The reaction liquid used in the recording method of the present invention is a liquid containing a reactant that reacts with the ink, and is an aqueous reaction liquid for inkjet use that is used together with the ink. The recording method of the present invention, for example, includes a step of applying the reaction liquid to a recording medium. In particular, it is preferable to apply the reaction liquid before applying the ink to the recording medium, or to apply the ink and the reaction liquid in parallel. Each component used in the reaction liquid will be described in detail below.

[0071] [Reactant] The reaction liquid reacts with the ink upon contact with it to aggregate the components in the ink (resin particles, surfactants, and components having anionic groups such as self-dispersing pigments), and contains a reactant such as an organic acid, a polyvalent metal salt, or a cationic resin.

[0072] [Organic acid] The organic acid-containing reaction solution has buffering properties in the acidic range (less than pH 7.0, preferably pH 2.0 to 5.0), thereby efficiently converting anionic groups present in the ink into the acid form and causing them to aggregate. Examples of organic acids include monocarboxylic acids and salts thereof, such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrolecarboxylic acid, furancarboxylic acid, picolinic acid, nicotinic acid, thiophenecarboxylic acid, levulinic acid, and coumaric acid; dicarboxylic acids and 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 thereof, such as citric acid and trimellitic acid; and tetracarboxylic acids and salts thereof, such as pyromellitic acid. The content (mass %) of the organic acid in the reaction liquid is preferably 1.0 mass % or more and 50.0 mass % or less based on the total mass of the reaction liquid.

[0073] [Polyvalent metal salts] Polyvalent metal salts are compounds composed of divalent or higher metal ions (polyvalent metal ions) and anions. Polyvalent metal salts dissociate in the reaction solution to form polyvalent metal ions, which aggregate dispersed pigments and other materials by the action of anionic groups in the ink. Examples of polyvalent metal ions include Ca 2+ , Cu 2+ , Ni 2+ , Mg 2+ , Sr 2+ , Ba 2+ , and Zn 2+ Divalent metal ions such as Fe 3+ , Cr3+ , Y 3+ , and Al 3+ Examples of anions constituting polyvalent metal salts include trivalent metal ions such as Cl. - , Br - , I - , ClO - , ClO2 - , ClO3 - , ClO4 - , NO2 - , NO3 - , SO4 2- , CO3 2- , HCO3 - , PO4 3- , HPO4 2- , and H2PO4 - Inorganic anions such as HCOO - , (COO - )2, COOH(COO - ), CH3COO - , CH3CH(OH)COO - , C2H4(COO - )2, C6H5COO - , C6H4(COO - )2, and CH3SO3 - Examples of organic anions include:

[0074] Specific examples of polyvalent metal salts include calcium carbonate, such as heavy calcium carbonate and light calcium carbonate, calcium nitrate, calcium chloride, calcium sulfate, magnesium sulfate, calcium hydroxide, magnesium chloride, magnesium carbonate, barium sulfate, barium chloride, zinc carbonate, zinc sulfide, aluminum silicate, calcium silicate, magnesium silicate, copper nitrate, calcium acetate, magnesium acetate, aluminum acetate, aluminum sulfate, calcium methanesulfonate, calcium lactate, magnesium lactate, calcium propionate, calcium acetate, calcium pantothenate, and calcium gluconate. These polyvalent metal salts may contain water of hydration. The content (mass %) of the polyvalent metal salt in the reaction solution is preferably 1.0% by mass or more and 20.0% by mass or less, based on the total mass of the reaction solution.

[0075] [Cationic Resin] Cationic resins have cationic moieties in their structure and aggregate dispersed pigments and other components via the action of anionic groups in the ink. Examples of cationic resins include resins with primary, secondary, or tertiary amine structures and resins with quaternary ammonium salt structures. Specific examples include resins with structures of vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensates. To enhance solubility in the reaction solution, the cationic resin can be used in combination with an acidic compound or subjected to a quaternization treatment. The content (mass %) of the cationic resin in the reaction solution is preferably 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the reaction solution.

[0076] The reaction liquid preferably contains at least one reactant selected from the group consisting of polyvalent metal salts and organic acids, as this can further improve the color development of the image. A cationic resin has multiple cationic units in one molecule. Therefore, if only a cationic resin is used as the reactant, the resin particles tend to aggregate strongly, which can make it difficult to alleviate the aggregation of the resin particles several hundred milliseconds after the ink comes into contact with the reaction liquid, thereby reducing the effect of improving color development.

[0077] The reaction liquid preferably contains a reactant containing at least one selected from the group consisting of polyvalent metal salts and organic acids, and a cationic resin. Polyvalent metal salts and organic acids have smaller atomic or molecular sizes than cationic resins, resulting in a smaller number of cationic valences per atom or molecule, and therefore have lower aggregating reactivity with resin particles. Therefore, if at least one selected from the group consisting of polyvalent metal salts and organic acids is used as a reactant without using a cationic resin, even if the resin particles aggregate several seconds after contact between the ink and the reaction liquid, it may be difficult to sufficiently increase the agglomeration viscosity. This may result in a reduced effect of suppressing graininess.

[0078] The cationic resin is preferably polydiallyldimethylammonium chloride, as this further enhances the graininess suppression effect. Unlike, for example, alkylamine-epichlorohydrin condensates, polydiallyldimethylammonium chloride has a molecular structure in which quaternary ammonium cations are located in the side chain, making it more susceptible to reaction with resin particles and pigments. Therefore, polydiallyldimethylammonium chloride also easily reacts with resin particles whose aggregation has been suppressed by surfactant A, effectively promoting the aggregation reaction and further improving the graininess suppression effect.

[0079] [Aqueous medium] The reaction liquid is an aqueous reaction liquid containing at least water as an aqueous medium. Examples of the aqueous medium used in the reaction liquid include the same aqueous media as those that can be contained in the ink.

[0080] [Other ingredients] The reaction liquid may contain various other components as needed, including the same components as those that can be contained in the ink.

[0081] [Physical properties of reaction solution] The reaction liquid is an aqueous reaction liquid applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the reaction liquid at 25°C is preferably 20 mN / m or more and 60 mN / m or less. Furthermore, 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, and more preferably 6.0 or more and 9.0 or less. [Example]

[0082] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0083] <Preparation of pigment dispersion> (Pigment dispersion 1) A styrene-ethyl acrylate-acrylic acid copolymer (resin dispersant) with an acid value of 150 mgKOH / g and a weight-average molecular weight of 8,000 was prepared. 20.0 parts of the resin dispersant were neutralized with potassium hydroxide equivalent in moles to the acid value, and an appropriate amount of pure water was added to prepare an aqueous solution of the resin dispersant with a resin (solids) content of 20.0%. A mixture was obtained by mixing 20.0 parts of carbon black (trade name "MCF88" manufactured by Mitsubishi Chemical Corporation), 30.0 parts of the resin dispersant aqueous solution, and 50.0 parts of ion-exchanged water. The resulting mixture was dispersed 50 times using a Nanomizer (manufactured by Yoshida Kikai Kogyo) at a pressure of 150 MPa. After 30 minutes of centrifugation at 5,000 rpm to remove coarse particles, the mixture was pressure-filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm. The mixture was diluted with ion-exchanged water to obtain Pigment Dispersion Liquid 1 having a pigment content of 10.0% and a resin dispersant content of 3.0%.

[0084] (Pigment dispersions 2 to 4) Pigment dispersions 2 to 4 were prepared in the same manner as for the pigment dispersion 1 described above, except that the compositions shown in Table 1 were used.

[0085] TIFF2025169905000006.tif75170

[0086] <Production of resin particles> (Resin particles 1 to 5) 1,160 mL of water was heated in a reactor to the polymerization temperature shown in Table 2. An initiator solution was prepared by mixing 160 mL of water and 1.39 g of potassium persulfate. 32 mL of the prepared initiator solution was added to the reactor and stirred. A monomer mixture was prepared by mixing 159.4 mL of water, the monomers (types and amounts shown in Table 2), 1.6 g of isooctyl thioglycolate, and 9.98 g of a 30% aqueous solution of an emulsifier. The emulsifier used was Rhodafac RS 710 (manufactured by Rhodia Novecare). The prepared monomer mixture was added dropwise to the reactor over 30 minutes, and simultaneously, 129.4 g of the initiator solution was added dropwise to the reactor over 30 minutes and stirred. The reaction mixture was stirred at the polymerization temperature shown in Table 2 and maintained for 3 hours. After cooling to 50°C, the pH was adjusted to 8.5 by adding a 50% aqueous potassium hydroxide solution. The contents were cooled to ambient temperature and then filtered through a 200-mesh filter. Deionized water was added to dilute the contents, yielding aqueous dispersions of resin particles 1 to 5 (resin particle content: 20.0%). The properties of the resin particles in the resulting aqueous dispersions are shown in Table 2. The abbreviations for the monomers in Table 2 are as follows: ·MAA: methacrylic acid MMA: Methyl methacrylate HMA: Hexyl methacrylate nBMA: n-butyl methacrylate

[0087] TIFF2025169905000007.tif63170

[0088] <Surfactant A> The type of surfactant A shown in Table 3 was prepared.

[0089] TIFF2025169905000008.tif101170

[0090] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in Tables 4-1 to 4-3, thoroughly stirring, and then filtering under pressure through a membrane filter with a pore size of 4.5 μm (product name "HDC II filter", manufactured by Pall). Details of each component in Tables 4-1 to 4-3 are shown below. BYK349: Silicone surfactant, manufactured by BYK Japan Acetylenol E60: Acetylene glycol surfactant, manufactured by Kawaken Fine Chemicals FS3100: Fluorosurfactant, manufactured by Capstone Emulgen 320P: Polyoxyethylene stearyl ether, manufactured by Kao

[0091] TIFF2025169905000009.tif169170

[0092] TIFF2025169905000010.tif166170

[0093] TIFF2025169905000011.tif153170

[0094] <Preparation of reaction solution> Each reaction solution was prepared by mixing the components (unit: %) shown in Table 5, thoroughly stirring, and then filtering under pressure through a membrane filter with a pore size of 4.5 μm (product name "HDCII filter", manufactured by Pall). Details of each component in Table 5 are shown below. FLOQUAT FL2350: Cationic polymer (condensation product of dimethylamine and epichlorohydrin) aqueous solution, 50% concentration, manufactured by SNF POLYQUAT 40u05: Cationic resin (polydiallyldimethylammonium chloride) aqueous solution, 50% concentration, manufactured by KATPOL Chemie Dynol 607: Acetylene glycol surfactant, manufactured by Nissin Chemical Industry Co., Ltd.

[0095] TIFF2025169905000012.tif115170

[0096] <Preparing the recording medium> The following recording media 1 and 2 were prepared. Recording media 1 was used for recording 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 10mL / m 2 On the other hand, recording medium 2 was measured at 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 10mL / m 2 It is a recording medium that exceeds the Recording medium 1: Product name "Scotchcal Graphic Film IJ1220", manufactured by 3M, material: polyvinyl chloride Recording medium 2: High-quality dedicated paper, product name "HR-101S", manufactured by Canon

[0097] <Evaluation> An inkjet recording device having the configuration shown in FIG. 1 was prepared. This inkjet recording device was used to record an image under the condition of depositing eight 4.0 ng ink droplets per 1 / 600 inch x 1 / 600 inch unit area, with the recording duty defined as 100%. The ink and reaction liquid combinations shown in Table 7 were filled into the ink depositing device and reaction liquid depositing device, respectively. Ten solid images were recorded on the recording media shown in Table 7, with the reaction liquid recording duty set to 20% and the recording duty varied in 10% increments between 10 and 100%, and then heated to 80°C with heater 25 to dry. In the present invention, the following evaluation criteria for each item were used: "A" and "B" were considered acceptable levels, and "C" was considered unacceptable. The evaluation results are shown in Table 7. In Table 7, Comparative Examples 12 and 13 correspond to Example 18 and Comparative Example 4, respectively, described in Patent Document 1 (JP 2018-165314 A).

[0098] (Suppression of graininess) Using the inkjet recording device described above, images were recorded with a recording duty of 30% by applying the reaction liquid and ink in this order to a recording medium, and the recorded images were observed from distances of 20 cm, 30 cm, and 50 cm. The suppression of graininess was evaluated according to the following evaluation criteria. AA: Even when observed from a distance of 20 cm, no roughness due to granularity was observed, and the image was uniformly visible. A: When observed from a distance of 20 cm, roughness due to granularity was observed, but when observed from a distance of 30 cm, roughness due to granularity was not observed and the surface was visible uniformly. B: When observed from a distance of 50 cm, no roughness due to granularity was observed and the surface was uniform, but when observed from a distance of 30 cm, roughness due to granularity was observed. C: Roughness due to granularity was observed even when observed from a distance of 50 cm.

[0099] (Color development) Using the inkjet recording device, the reaction liquid and ink were applied to the recording medium in this order to record 10 types of solid images with the concentration varying in 10% increments between 10 and 100%. The brightness (L * ) and saturation (C * ) was measured, and the color development of the image was evaluated according to the evaluation criteria shown in Table 6. * and C * is based on the color difference display method specified by CIE. In this example, when the colorant is carbon black, it is referred to as black ink, and when the colorant is CI Pigment Blue 15:3, it is referred to as cyan ink. Furthermore, when the colorant is CI Pigment Red 122, it is referred to as magenta ink, and when the colorant is CI Pigment Yellow 74, it is referred to as yellow ink. In the case of black ink, the smaller the value of lightness, the darker the image and the better the color development. Furthermore, in the case of color inks (cyan, magenta, and yellow inks), the larger the value of saturation, the more vivid the image and the better the color development.

[0100] TIFF2025169905000013.tif95170

[0101] TIFF2025169905000014.tif255158

Claims

1. An inkjet recording method in which an aqueous ink and an aqueous reaction liquid that reacts with the aqueous ink are ejected from an inkjet recording head and applied to a recording medium to record an image, comprising: a step of ejecting the reaction liquid from the recording head and applying it to the recording medium; and applying the aqueous ink from the recording head so as to overlap at least a portion of the region of the recording medium onto which the reaction liquid is applied, the aqueous ink contains resin particles, a surfactant A represented by the following general formula (1), and a water-soluble organic solvent having a relative dielectric constant of 31.5 or less, the content (mass%) of the surfactant A in the aqueous ink is 0.01 times or more and 0.08 times or less in mass relative to the content (mass%) of the resin particles, The recording medium is １／２ Water absorption up to 10 mL / m ２ An inkjet recording method characterized by the following: (In the general formula (1), R １ represents a chain hydrocarbon group having 12 to 24 carbon atoms, and a represents an integer of 1 to 10.

2. 2. The inkjet recording method according to claim 1, wherein the content (mass %) of the surfactant A in the aqueous ink is 0.02 to 0.06 times the content (mass %) of the resin particles in terms of a mass ratio.

3. 2. The ink jet recording method according to claim 1, wherein the surfactant A is represented by the following general formula (2): (In the general formula (2), a represents an integer of 1 or more and 10 or less.)

4. 2. The ink jet recording method according to claim 1, wherein the water-based ink further contains a silicone surfactant.

5. 5. The inkjet recording method according to claim 1, wherein the reaction liquid contains at least one reactant selected from the group consisting of polyvalent metal salts and organic acids.

6. 5. The inkjet recording method according to claim 1, wherein the reaction liquid contains a reactant containing at least one selected from the group consisting of a polyvalent metal salt and an organic acid, and a cationic resin.

7. 7. The ink jet recording method according to claim 6, wherein the cationic resin is polydiallyldimethylammonium chloride.

8. The amount of electric charge of the resin particles (μmol / m ２ ) is 1.0 μmol / m ２ 2.4 μmol / m or more ２ The inkjet recording method according to any one of claims 1 to 4, wherein the inkjet recording method is as follows:

9. An inkjet recording apparatus used in an inkjet recording method in which an aqueous ink and an aqueous reaction liquid that reacts with the aqueous ink are ejected from an inkjet recording head and applied to a recording medium to record an image, comprising: the aqueous ink contains resin particles, a surfactant A represented by the following general formula (1), and a water-soluble organic solvent having a relative dielectric constant of 31.5 or less, the content (mass%) of the surfactant A in the aqueous ink is 0.01 times or more and 0.08 times or less in mass relative to the content (mass%) of the resin particles, The recording medium is １／２ Water absorption up to 10 mL / m ２ An inkjet recording apparatus characterized by the following: (In the general formula (1), R １ represents a chain hydrocarbon group having 12 to 24 carbon atoms, and a represents an integer of 1 to 10.

Images