Inkjet recording method, inkjet recording apparatus, and set of aqueous ink and aqueous reactive liquid

Abstract

To provide an inkjet recording method that suppresses image irregularity and allows recording of an image with reduced graininess.SOLUTION: An inkjet recording method for recording an image on a low- to non-absorptive recording medium using an ink and a reactive liquid, wherein the ink contains a pigment dispersed by the action of an anionic group, resin particles, a silicone-based surfactant, and a hydrocarbon-based surfactant. The resin particles are at least one kind of resin particles selected from the group consisting of acrylic resins, urethane resins, and polyester resins. The hydrocarbon-based surfactant has an HLB value by the Griffin method of 4 or more and 8 or less. The static surface tension γi of the ink and the static surface tension γr of the reactive liquid satisfy the relation of the following formula (1). |γi-γr|≤3.8 (1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording method, an inkjet recording apparatus, and a set of an aqueous ink and an aqueous reaction liquid. [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] However, compared to recording an image on a recording medium having an absorbing layer, when recording an image on the above-mentioned low-absorbency or non-absorbency recording medium, there are problems such as low color development or insufficient image quality being obtained with the above-mentioned water-based ink. To address this, a printing method has been proposed in which printing is performed using a color ink consisting of a colorant, a resin component, a water-soluble solvent, and a surfactant, and a reactive ink containing a reactive agent that aggregates the components of the color ink, and then drying the ink (Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-115854 [Patent Document 2] Japanese Patent Application Laid-Open No. 2023-154399 [Patent Document 3] Japanese Patent Publication No. 2023-101528 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when images were recorded on low-absorbency or non-absorbency recording media using the ink sets described in Patent Documents 1 to 3, streak-like unevenness occurred in the recorded material. This is thought to be caused by the following phenomenon: Advection occurs during the drying process of the ink and reactive ink liquid components applied to the low-absorbency or non-absorbency recording media. When the next ink is applied to this state, the ink moves due to the influence of advection and cannot be fixed in the correct position, resulting in uneven density in the recorded material and appearing as streaks.

[0006] Furthermore, when an image was recorded on a low-absorbency or non-absorbency recording medium using the ink sets described in Patent Documents 1 and 2, in solid image areas with low recording duty, there were some areas where no ink was present and the underlying recording medium was visible, and graininess could not be suppressed. The inventors believe that this is because the ink does not spread on the low-absorbency or non-absorbency recording medium, causing the dots to shrink as they dry.

[0007] Therefore, an object of the present invention is to provide an inkjet recording method capable of recording images with reduced image unevenness and graininess. Another object of the present invention is to provide an inkjet recording apparatus used in the inkjet recording method, and a set of an aqueous ink and an aqueous reaction liquid. [Means for solving the problem]

[0008] That is, according to the present invention, there is provided an inkjet recording method for recording an image on a recording medium by ejecting from a recording head 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 the area of the recording medium to which the aqueous reaction liquid is applied, and the ink is applied within 30 msec from the start of contact of the recording medium in a Bristow method. 1 / 2 Water absorption up to 10mL / m 2 the aqueous ink contains a pigment dispersed by the action of an anionic group, resin particles, a silicone surfactant, and a hydrocarbon surfactant, the resin particles being formed of at least one resin selected from the group consisting of an acrylic resin, a urethane resin, and a polyester resin, the hydrocarbon surfactant having an HLB value according to the Griffin method of 4 or more and 8 or less, and the static surface tension γ of the aqueous ink is i and the static surface tension γ of the aqueous reaction liquid r The inkjet recording method is characterized in that the relationship of the following formula (1) is satisfied. |γ i -γ r |≦3.8 (1) [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 image unevenness and reduced graininess, and also to provide an inkjet recording apparatus used in the inkjet recording method, and a set of an aqueous ink and an aqueous reaction liquid. [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 conducted the following evaluations using reaction liquids and inks, with reference to the descriptions in Patent Documents 1 to 3. The inks used contained a combination of a silicone surfactant and an acetylene surfactant. The results of this test revealed that unevenness in images could occur due to differences in color density. Furthermore, in solid image areas with low printing duty, the ink was sometimes repelled by the recording medium, resulting in a grainy appearance. Therefore, the causes of each of these issues were investigated.

[0013] First, the inventors observed the image surface using an optical microscope and found that the ink dots had moved from their intended application positions on the recording medium, resulting in density differences. Furthermore, traces of ink dots running were observed in the thinner areas. This indicated that the ink dots were applied to the correct locations on the recording medium, but had moved without settling after application, resulting in density differences and image unevenness. This is thought to be due to advection occurring when there is a difference in static surface tension between the ink and the reaction liquid applied to a low-absorbency or non-absorbency recording medium, causing the ink dots applied to the areas where advection occurred to move from their intended application positions and set due to the influence of advection. This movement of ink dots is called the "beading phenomenon," and images with this phenomenon appear uneven.

[0014] Here, similar printing was performed on low-absorbency or non-absorbency recording media using ink and reaction liquid adjusted so that the static surface tensions of the ink and reaction ink were similar. Advection was successfully suppressed. This allowed the next applied ink dot to be fixed without moving from its original application position, improving image unevenness. Specifically, by setting the absolute value of the difference between the static surface tension of the ink and the static surface tension of the reaction liquid to 3.8 or less, advection was suppressed, thereby reducing image unevenness. However, the suppression of image unevenness and graininess had not yet reached the level desired by the inventors.

[0015] Next, the inventors investigated the cause of the graininess. When they checked the application of ink to low-absorbency or non-absorbency recording media, they found that after ink dots were applied to the recording medium, they did not spread but instead shrunk as they dried, leaving the underlying recording medium visible in places. Therefore, they added a hydrocarbon-based surfactant, which is expected to orient at solid-liquid interfaces and reduce static surface tension, and a silicone-based surfactant, which is likely to orient at gas-liquid interfaces, to the ink. As a result, they were able to improve the wetting and spreading of the ink onto the recording medium, uniformly filling the underlying recording medium with ink, and suppress the graininess.

[0016] Furthermore, graininess can be suppressed by using a hydrocarbon surfactant with a low HLB value, specifically, a hydrocarbon surfactant with an HLB value of 4 to 8 (measured by the Griffin method). This is thought to be because such surfactants quickly orient at solid-liquid interfaces, reducing the contact angle of the ink on the recording medium and improving ink wetting and spreading. If the HLB value of a hydrocarbon surfactant is less than 4, it is less soluble in the ink and easily separates, making it difficult to demonstrate its surfactant properties. On the other hand, if the HLB value of a hydrocarbon surfactant is greater than 8, it is slow to orient at the solid-liquid interface, making it prone to ink beading. As a result, graininess in the image cannot be suppressed. Furthermore, if a silicone surfactant is used alone, the wettability to the recording medium is insufficient, making it impossible to suppress graininess. Furthermore, if a hydrocarbon surfactant is used alone, the effect of suppressing image unevenness cannot be achieved.

[0017] The ink must contain resin particles formed of at least one resin selected from the group consisting of acrylic resins, urethane resins, and polyester resins. In inks that do not contain resin particles, the reaction between the pigment and the reactant tends to proceed rapidly, causing the pigment to aggregate before the ink wets and spreads on the recording medium, making it impossible to suppress graininess.

[0018] Resin particles formed from at least one resin selected from the group consisting of acrylic resins, urethane resins, and polyester resins have polarity and can exist stably in ink. Therefore, compared to other resin particles (e.g., wax particles), the resin particles are less likely to interact with the pigment particle surface. Therefore, the resin particles are less likely to inhibit the reaction between the pigment and the reactant and the fixation of the pigment, allowing the pigment to be fixed in a fixed position on the recording medium, thereby suppressing graininess and image unevenness. If wax particles were used instead of the resin particles, neither image unevenness nor graininess could be suppressed. Because wax particles have low polarity, they are more likely to interact with the pigment particle surface. Therefore, the wax particles inhibit the reaction between the pigment and the reactant, making it difficult to fix the pigment in a fixed position on the recording medium, and image unevenness cannot be suppressed. Furthermore, because the ink is difficult to fix in a fixed position, ink droplets tend to coalesce, making it difficult to suppress graininess.

[0019] Furthermore, when the ink and reaction liquid described above were used to print on an absorbent recording medium, no image unevenness occurred. This is because the ink and reaction liquid do not remain on the surface of the absorbent recording medium, and no advection occurs in the first place. In other words, the problem of image unevenness is a problem that occurs specifically with low-absorbency or non-absorbency recording media.

[0020] <Inkjet recording method, inkjet recording apparatus, and set of aqueous ink and aqueous reaction liquid> The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting an aqueous ink and an aqueous reaction liquid from a recording head. This inkjet recording method includes a step of applying the aqueous reaction liquid to the recording medium (a reaction liquid applying step) and a step of applying the aqueous ink to the recording medium so as to overlap at least a part of the area on the recording medium where the aqueous reaction liquid has been applied (an ink applying step).

[0021] The inkjet recording apparatus of the present invention is an apparatus used to eject an aqueous ink and an aqueous reaction liquid from a recording head to record an image on a recording medium. It is also an apparatus suitable for use in the inkjet recording method. This inkjet recording apparatus includes a means for applying the aqueous reaction liquid to the recording medium (reaction liquid applying means) and a means for applying the aqueous ink (ink applying means) so as to overlap at least a portion of the area of the recording medium to which the aqueous reaction liquid is applied. The inkjet recording method and inkjet recording apparatus of the present invention do not require curing the image by irradiation with actinic energy rays or the like.

[0022] The set of aqueous ink and aqueous reaction liquid of the present invention is used in an inkjet recording method in which the aqueous ink and aqueous reaction liquid are ejected from a recording head to record an image on a recording medium, and is suitably used in the inkjet recording method. The set can take the form of a set of multiple ink cartridges, each containing a plurality of inks (reaction liquids) independently, or an ink cartridge formed by combining multiple ink reservoirs, each containing a plurality of inks (reaction liquids). The set of the present invention is not limited to the above form and may take any form as long as it is configured to allow the inks and reaction liquids to be used in combination.

[0023] The above recording medium is a recording medium that is measured 30 msec after contact with the Bristow method. 1 / 2 Water absorption up to 10mL / m 2 The following recording medium (low-absorbency or non-absorbency recording medium) is used. The aqueous reaction liquid contains a reactant that reacts with the aqueous ink. The aqueous ink contains a pigment dispersed by the action of an anionic group, resin particles, a silicone surfactant, and a hydrocarbon surfactant. The resin particles are formed of at least one resin selected from the group consisting of acrylic resins, urethane resins, and polyester resins. The hydrocarbon surfactant has an HLB value of 4 or more and 8 or less according to the Griffin method. The static surface tension γ of the aqueous ink is i and the static surface tension γ of the aqueous reaction liquid rsatisfies the relationship of the following formula (1). |γ i -γ r |≦3.8 (1)

[0024] The inkjet recording method and inkjet recording apparatus (hereinafter also simply referred to as "recording method and recording apparatus") of the present invention will be described in detail below.

[0025] [Ink application process and reaction liquid application process] The recording method of the present invention includes a reaction liquid applying step of applying a reaction liquid to a recording medium, and an ink applying step of applying ink so as to overlap at least a portion of the area of the recording medium to which the reaction liquid is applied. The ink applying means and the reaction liquid applying means of the recording device use inkjet recording heads. The recording device may be configured to eject the ink and the reaction liquid from separate recording heads to record an image, or may be configured to eject the ink and the reaction liquid from each of a plurality of ejection port arrays provided on a single recording element substrate to record an image.

[0026] 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. 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, causing the ink to be ejected from the ejection opening. While a recording head that ejects ink by the action of thermal energy has been described as an example here, a recording head that ejects ink by the action of mechanical energy may also be used. The recording head may be equipped with a mechanism (temperature control mechanism) that heats the aqueous ink ejected from the recording head. If a temperature control mechanism is provided, the temperature of the ink ejected from the recording head is preferably set to 35°C or higher and 70°C or lower.

[0027] The recording head 22 preferably has a first nozzle array in which nozzles for ejecting aqueous ink are arranged along the sub-scanning direction, and a second nozzle array in which nozzles for ejecting aqueous reaction liquid are arranged along the sub-scanning direction. In this case, in the reaction liquid application process and the ink application process, the recording head is scanned N times (N is an integer of 2 or greater) in the main scanning direction intersecting the sub-scanning direction to eject the aqueous ink and aqueous reaction liquid from the recording head and apply them to a unit area on the recording medium. Of the N scans, the total amount of aqueous reaction liquid applied to the recording medium in the first N / 2 scans is preferably greater than the total amount of aqueous reaction liquid applied to the recording medium in the latter N / 2 scans. If N is an odd number, the first N / 2 is rounded up to the nearest whole number, and the latter N / 2 is rounded down to the nearest whole number. This control allows the ink to be piled up on top of the reaction liquid on the recording medium, suppressing beading and more effectively reducing graininess in the image. In particular, it is more preferable that the total amount of aqueous reaction liquid applied to the recording medium in the first N / 2 scans is 60% or more of the total amount of aqueous reaction liquid applied to the recording medium in N scans. The term "unit area" can be defined as various areas, such as one pixel or one band, as needed. One pixel refers to one pixel corresponding to the resolution of the recording head, and one band refers to the area that can be printed in one printing scan in the main scanning direction of the recording head.

[0028] [Heating process] In one embodiment, the recording method of the present invention may include a step of heating (heat treatment) the recording medium to which the ink and reaction liquid have been applied. Heating the recording medium to which the ink and reaction liquid have been applied can promote drying and increase the strength of the image.

[0029] Examples of means for heating the recording medium include known heating means such as heaters, air blowing means using air such as dryers, and combinations of these. That is, the inkjet recording apparatus may be equipped with 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 combinations 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. A combination of these methods may also be used.

[0030] In order to improve the scratch resistance of the image, the heating temperature of the recording medium to which the ink and reaction liquid have been applied is preferably 50°C or higher and 90°C or lower. Here, the heating temperature of the recording medium to which the ink and reaction liquid have been applied can also be rephrased as the temperature of the recorded image or the temperature reached by heating the recording medium to which the ink and reaction liquid have been applied. The heating temperature of the recording medium to which the ink and reaction liquid have 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 in advance depending on the type of ink and recording medium.

[0031] 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.

[0032] [Recording medium] In the recording method and recording device of the present invention, a low-absorbency or non-absorbent recording medium (low to non-absorbent recording medium) is used. The low-absorbency to non-absorbent recording medium is a recording medium that is measured by the Bristow method described in JAPAN TAPPI Paper Pulp Test Method No. 51, "Liquid Absorbency Test Method for Paper and Paperboard," and is measured within 30 msec from the start of contact. 1 / 2 Water absorption up to 10mL / m 2 That is, in the recording method and recording device of the present invention, the recording medium is a recording medium having a recording time of 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 0mL / m 2 More than 10mL / m 2 The following recording media are used. In this specification, 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 a coating layer (ink receiving layer) formed of inorganic particles, and plain paper without a coating layer, have a water absorption amount of 10 mL / m or more. 2 It is an "absorbent recording medium" that exceeds

[0033] Examples of low to non-absorbent recording media that can be used include plastic films, recording media having a plastic film bonded to the recording surface side of a substrate, and recording media having a resin coating layer provided on the recording surface of a substrate containing cellulose pulp. Of these, plastic films are preferred, and recording media having a resin coating layer provided on the recording surface of a substrate containing cellulose pulp are also preferred.

[0034] When an ink containing resin particles 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 strength of the recorded image. In contrast, even when the ink is applied to a recording medium with high absorbency of liquid components (an absorbent recording medium), it is difficult to promote fusion between the resin particles, making it difficult to improve the strength 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.

[0035] [Reaction solution] The recording method of the present invention includes a reaction liquid application step of applying an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to a recording medium. It is particularly preferred to have the reaction liquid application step before the ink application step, or to perform the ink application step and the reaction liquid application step in parallel. The components used in the reaction liquid are described in detail below.

[0036] [Reactant] The reaction liquid reacts with the ink upon contact with it, causing the components in the ink (components having anionic groups, such as resins, surfactants, and self-dispersing pigments) to aggregate, and contains a reactant. The presence of the reactant destabilizes the state of the components in the ink having anionic groups when the ink and the reactant come into contact on the recording medium, thereby promoting the aggregation of the ink. Examples of the reactant include cationic components such as polyvalent metal ions and cationic resins, and organic acids. One reactant may be used alone, or two or more may be used in combination.

[0037] Examples of polyvalent metal ions that constitute polyvalent metal salts include Ca. 2+ , Cu 2+ , Ni 2+ , Mg 2+ , Sr 2+ , Ba 2+ , and Zn 2+ Divalent metal ions such as Fe 3+ , Cr 3+ , Y 3+ , and Al 3+Examples of the trivalent metal ions include trivalent metal ions such as Cl. To add polyvalent metal ions to the reaction solution, a water-soluble polyvalent metal salt (which may be a hydrate) formed by combining a polyvalent metal ion with an anion can be used. Examples of the anion include 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 - , C2H5COO - , CH3CH(OH)COO - , C2H4(COO - )2, C6H5COO - , C6H4(COO - )2, and CH3SO3 - and other organic anions.

[0038] When a polyvalent metal ion is used as a reactant, the content (% by 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. In this specification, when the polyvalent metal salt is a hydrate, the "content (% by mass) of the polyvalent metal salt" in the reaction solution means the "content (% by mass) of the anhydrous polyvalent metal salt," excluding water as the hydrate.

[0039] Examples of cationic resins include resins having a primary, secondary, or 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 condensates. To enhance solubility in the reaction solution, the cationic resin can be used in combination with an acidic compound or the cationic resin can be subjected to a quaternization treatment. When a cationic resin is used as a reactant, the content (mass %) of the cationic resin in the reaction solution is preferably 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the reaction solution.

[0040] 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. When an organic acid is used as a reactant, 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.

[0041] [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 described below that can be contained in the ink. The water content (mass %) in the reaction liquid is preferably 50.0 mass % or more, more preferably 60.0 mass % or more, and preferably 90.0 mass % or less, based on the total mass of the reaction liquid.

[0042] [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, which will be described later.

[0043] [Physical properties of reaction solution] The reaction liquid is an aqueous reaction liquid used in inkjet printing. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the static surface tension of the reaction liquid at 25°C is preferably 20.0 mN / m or more and 60.0 mN / m or less, and more preferably 20.0 mN / m or more and 35.0 mN / m or less. The static surface tension of the reaction liquid can be measured by the platinum plate method. 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 viscosity of the reaction liquid can be measured in accordance with JIS Z 8803. For example, it can be measured using a rotational viscometer. The pH of the reaction liquid at 25°C is preferably 5.0 to 9.5, and more preferably 6.0 to 9.0.

[0044] The static surface tension of the ink is γ i , the static surface tension of the reaction solution is γ r When |γ i -γ r |≦3.8. In particular, the static surface tension γ r is the static surface tension of the ink γ i That is, the static surface tension γ i is the static surface tension of the reaction solution γ rThat is, γ i ≦γ r It is preferable that the following relationship be satisfied. When adjacent dots of ink and reaction liquid are applied to a recording medium, the ink flows into the reaction liquid with a greater static surface tension, reducing white voids and more effectively suppressing graininess. The static surface tensions of the ink and reaction liquid are all values at 25°C.

[0045] The contact angle of the ink with respect to the recording medium is preferably equal to or larger than the contact angle of the reaction liquid. i , the contact angle of the reaction liquid is θ r When this is done, θ i ≧θ r It is preferable that the relationship θ i ≧θ r By satisfying the relationship, when the ink and the reaction liquid are applied to the recording medium, the reaction liquid dots tend to flow toward the ink dots. This makes it easier for the ink to settle without moving from the applied position, so that graininess can be more effectively suppressed. In particular, θ r is θ i When the distance is smaller than 1 / 2 mm, the wettability of the reaction liquid to the recording medium is better than that of the ink, and the probability of contact between the reaction liquid and the ink increases, so that the ink can be reliably fixed at the intended position and graininess can be particularly effectively suppressed.

[0046] In addition, the contact angle θ of the ink with respect to the recording medium i is less than 55°, that is, θ i It is more preferable that the relationship θ≦55° is satisfied, and 30°≦θ i It is more preferable that the relationship θ≦55° is satisfied. i When the contact angle θ of the reaction liquid to the recording medium is ≦55°, the recording medium is less likely to repel ink, and image unevenness is more easily suppressed. r is less than 25°, that is, θ r It is more preferable that the relationship θ≦25° is satisfied, and 10°≦θ r It is more preferable that the relationship θ≦25° is satisfied.r By ensuring that the angle is ≦25°, the probability of contact between the reaction liquid and the ink increases, making it easier to suppress image unevenness and more effectively suppressing graininess. In the examples described below, the contact angles of the ink and reaction liquid with the recording medium were measured using a contact angle meter (trade name "DropMaster DMo-701", manufactured by Kyowa Interface Science). Of course, the contact angle meter that can be used in the present invention is not limited to this.

[0047] [ink] The recording method of the present invention includes an ink application step of applying an ink to a recording medium so as to overlap at least a portion of an area to which a reaction liquid is applied. The ink used in this recording method is an aqueous inkjet ink containing a pigment dispersed by the action of anionic groups, resin particles, a silicone surfactant, and a hydrocarbon surfactant. Each component of the ink will be described in detail below.

[0048] [Pigments] The ink contains a pigment as a colorant that is dispersed by the action of anionic groups. The content (mass %) of the pigment in the ink is preferably 0.1% to 15.0% by mass, and more preferably 1.0% to 10.0% by mass, 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, etc. One type of pigment may be used alone, or two or more types may be used in combination.

[0050] Pigment dispersion methods include resin-dispersed pigments that use a resin (resin dispersant) as a dispersant, and self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface. Other methods that can be used include 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. It is also possible to combine these pigments with different dispersion methods. 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.

[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 having anionic groups can be used, and the resins described below, especially water-soluble resins, 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 an anionic group such as a carboxylic acid group, sulfonic acid group, or phosphonic acid group is bonded to the surface of the pigment particle directly or via another atomic group (-R-). The anionic group may be either an acid type or a salt type, and if it is a salt type, it may 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, polyester 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] [Acrylic resin] 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, hexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0058] [Urethane resin] The urethane resin can be obtained, for example, by reacting polyisocyanate with a component that reacts with it (such as a polyol or a polyamine). Furthermore, a crosslinking agent or a chain extender may be further reacted. Among these, it is preferable to use a urethane resin obtained by polymerizing at least a polyisocyanate, a polyol having no acid groups, and a polyol having acid groups.

[0059] Polyisocyanates are compounds having two or more isocyanate groups in their molecular structure. Examples of polyisocyanates include aliphatic polyisocyanates and aromatic polyisocyanates. Examples of aliphatic polyisocyanates include polyisocyanates having a chain structure such as tetramethylene diisocyanate and hexamethylene diisocyanate; and polyisocyanates having a cyclic structure such as isophorone diisocyanate and hydrogenated xylylene diisocyanate. Examples of aromatic polyisocyanates include tolylene diisocyanate and 1,5-naphthylene diisocyanate. Of these, isophorone diisocyanate is preferred as the polyisocyanate.

[0060] A polyol is a compound having two or more hydroxy groups in its molecular structure. Examples of polyols include polyols without acid groups, such as polyether polyols, polyester polyols, and polycarbonate polyols; and polyols with acid groups. Examples of polyether polyols include addition polymers of alkylene oxides and polyols; and glycols such as (poly)alkylene glycols. Examples of polyester polyols include acid esters. Examples of polycarbonate polyols include alkanediol-based polycarbonate diols. The number-average molecular weight of the polyol without acid groups is preferably 400 or more and 4,500 or less. Examples of polyols with acid groups include those with acid groups such as carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, and phosphonic acid groups. The acid groups may form salts, and examples of the salts include alkali metal salts such as lithium, sodium, and potassium, ammonium salts, and organic ammonium salts. The polyol having an acid group is preferably a polyol having a carboxylic acid group such as dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, or dimethylolbutyric acid, with dimethylolpropionic acid and dimethylolbutanoic acid being more preferred.

[0061] Polyamines are compounds with two or more amino or imino groups in their molecular structure. Examples of polyamines include monoamines with multiple hydroxyl groups, such as dimethylolethylamine and diethanolmethylamine; bifunctional polyamines, such as ethylenediamine and propylenediamine; and trifunctional or higher polyamines, such as diethylenetriamine and triethylenetetramine. For convenience, compounds with multiple hydroxyl groups and one amino or imino group are also listed as "polyamines."

[0062] When synthesizing a urethane resin, a crosslinking agent or a chain extender can be used. Typically, a crosslinking agent is used when synthesizing a prepolymer, and a chain extender is used when carrying out a chain extension reaction on a prepolymer that has already been synthesized. Basically, the crosslinking agent or chain extender can be appropriately selected from water, polyisocyanate, polyol, polyamine, etc. depending on the purpose, such as crosslinking or chain extension.

[0063] [Olefin Resin] Examples of olefin resins include polyethylene and polypropylene.

[0064] [Polyester Resin] Polyester resins can be obtained by reacting a polyhydric alcohol with a polycarboxylic acid. Examples of polyhydric alcohols include dihydric, dihydric, and tetrahydric alcohols. Examples of polyhydric alcohol structures include polyhydric alcohols with aliphatic groups, polyhydric alcohols with aromatic groups, and sugar alcohols. Specific examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol (1,2-ethanediol), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,3-propanediol, 1,4-butanediol, benzenediol, and 2,2-bis(4-hydroxyphenyl)propane (bisphenol A); trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; and tetrahydric alcohols such as pentaerythritol. Furthermore, oligomers (low-molecular polymers with a molecular weight of 1,000 or less) can also be used as polyhydric alcohols. Examples of polycarboxylic acids that form the polycarboxylic acid-derived units that constitute the polyester resin through reaction include divalent to tetravalent polycarboxylic acids. Examples of the structure of the polycarboxylic acid include polycarboxylic acids having an aliphatic group, polycarboxylic acids having an aromatic group, and nitrogen-containing polycarboxylic acids. Specific examples of the polycarboxylic acid include dicarboxylic acids such as glutaric acid, adipic acid, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; tricarboxylic acids such as trimellitic acid; and tetracarboxylic acids such as ethylenediaminetetraacetic acid. Furthermore, oligomers (low-molecular polymers having a molecular weight of 1,000 or less) can also be used as the polycarboxylic acid.

[0065] (Resin properties) The acid value of the water-soluble resin is preferably 100 mgKOH / g or more and 250 mgKOH / g or less. Herein, the acid value of the resin can be a value measured by a potentiometric titrator using a potassium hydroxide-methanol titrant. The weight-average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less. Herein, the weight-average molecular weight of the resin can be measured as a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0066] [Resin particles] The ink contains resin particles formed of at least one resin selected from the group consisting of acrylic resins, urethane resins, and polyester resins. By using resin particles formed of at least one resin selected from the group consisting of acrylic resins, urethane resins, and polyester resins, it is possible to suppress graininess and image unevenness.

[0067] 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.

[0068] 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.

[0069] Whether a resin is a "resin particle" can be determined according to the following method. 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 using dynamic light scattering, if particles having a particle size are measured, the resin is determined to be a "resin particle" (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 a "resin particle" (i.e., a "water-soluble resin"). The measurement conditions for this can be, for example, Set Zero: 30 seconds, number of measurements: 10, measurement time: 120 seconds, shape: spherical, refractive index: 1.5, and density: 1.0.

[0070] As the particle size distribution measuring 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 measuring device and measurement conditions used are not limited to those described above. Furthermore, the average particle size (50% cumulative particle size on a volume basis) of the pigment can be measured using the device and conditions described above.

[0071] The acid value of the resin forming the resin particles is preferably 5 mgKOH / g or more and 100 mgKOH / g or less. The weight average molecular weight of the resin forming the resin particles is preferably 1,000 or more and 3,000,000 or less, more preferably 100,000 or more and 3,000,000 or less. The volume-based cumulative 50% particle diameter (D 50) is preferably 50 nm or more and 500 nm or less. The volume-based cumulative 50% particle diameter of resin particles is the diameter of the particles that is 50% when integrated from the small particle diameter side based on the total volume of the measured particles in a particle diameter integration curve. The volume-based cumulative 50% particle diameter of resin particles can be measured using the particle size analyzer and measurement conditions described above using the dynamic light scattering method. The glass transition temperature of the resin particles is preferably 40°C or more and 120°C or less, more preferably 50°C or more and 100°C or less. The glass transition temperature (°C) of the resin particles can be measured using a differential scanning calorimeter (DSC). The resin particles do not need to contain a colorant.

[0072] The resin forming the resin particles can be appropriately selected from the acrylic resins, urethane resins, and polyester resins described in the above resin section. Among them, the resin forming the resin particles is preferably an acrylic resin, and more preferably a copolymer having a first unit derived from (meth)acrylic acid and a second unit derived from a (meth)acrylic acid ester.

[0073] [Surfactant] The ink contains a silicone surfactant and a hydrocarbon surfactant. The silicone surfactant quickly orients at the gas-liquid interface, which is expected to reduce the static surface tension of the liquid. The hydrocarbon surfactant quickly orients at the solid-liquid interface, which is expected to improve the wettability of the liquid to the recording medium.

[0074] The content (mass %) of the silicone surfactant in the ink is preferably 0.2% by mass or more and 2.0% by mass or less, and more preferably 0.4% by mass or more and 1.0% by mass or less, based on the total mass of the ink. Having a silicone surfactant content of 0.2% by mass or more in the ink facilitates wetting and spreading of the ink on the recording medium, making it easier to suppress beading and more effectively reducing graininess in the image. On the other hand, having a silicone surfactant content of 2.0% by mass or less in the ink makes it easier to ensure the storage stability of the ink.

[0075] Silicone surfactants are surfactants in which hydrophilic groups such as ethylene oxide groups are introduced into polyorganosiloxanes, whose main chain consists of siloxane bonds (SiO) consisting of alternating silicon (Si) and oxygen (O) atoms. Examples of silicone surfactants include polyether-modified siloxane compounds, alkyl-polyether-modified siloxane compounds, alkylsilicone dendron polyether-modified siloxane compounds, and alkylsilicone dendron diglycerin-modified siloxane compounds. Silicone surfactants preferably contain propylene oxide units in their side chains. Here, "containing propylene oxide units in the side chain" refers to the introduction of propylene oxide units to silicon atoms other than those at the terminals of the polyorganosiloxane. While silicone surfactants generally contain ethylene oxide-modified side chains, the more hydrophobic propylene oxide-modified side chains can suppress thermal hydrolysis. This is thought to improve the storage stability of inks.

[0076] Among these, the silicone surfactant is preferably a compound represented by the following general formula (1). In other words, the silicone surfactant preferably has both a propylene oxide unit and an ethylene oxide unit in the side chain. Silicone surfactants having units with different hydrophilic properties in the side chain quickly adsorb to pigments and resin particles in aqueous inks, appropriately destabilizing the dispersion state and thereby enhancing the cohesion with reactants. Furthermore, they quickly orient to the interface and can quickly reduce static surface tension, thereby improving the wettability of the aqueous ink to the recording medium. This allows for more effective suppression of graininess in images.

[0077] TIFF2025115371000001.tif36170 (In general formula (1), k represents an integer of 1 to 3, l represents an integer of 1 to 4, and m+n represents integers of 8 to 15. m and n are natural numbers.)

[0078] The hydrocarbon surfactant used has an HLB value of 4 or more and 8 or less, as determined by the Griffin method. Hydrocarbon surfactants with an HLB value of less than 4 are difficult to dissolve stably in ink and tend to separate easily, making it difficult to eject the ink stably. On the other hand, hydrocarbon surfactants with an HLB value of more than 8 are slow to orient to the solid-liquid interface, are prone to causing beading of the ink, and are unable to suppress the graininess of the image. The HLB value of the hydrocarbon surfactant, as determined by the Griffin method, is preferably 4 or more and 6 or less. By setting the HLB value of the hydrocarbon surfactant, as determined by the Griffin method, to 4 or more and 6 or less, the graininess of the image can be more effectively suppressed.

[0079] Hydrocarbon-based nonionic surfactants are surfactants that have a hydrocarbon chain as the main backbone and have hydrophilic groups such as ethylene oxide groups introduced into them. Examples of hydrocarbon-based nonionic surfactants include polyoxyethylene alkyl ethers; acetylene-based surfactants such as ethylene oxide adducts of acetylene diols and acetylene glycols; polyoxyethylene-polyoxypropylene block copolymers; and ethylene oxide adducts of polyhydric alcohols.

[0080] Among hydrocarbon surfactants with an HLB value of 4 to 8, acetylene surfactants such as acetylene diols and ethylene oxide adducts of acetylene glycols are preferred. Acetylenic surfactants have a hydrocarbon main chain containing an acetylene structure (-C≡C-) and a hydrophilic group such as a hydroxyl group or an ethylene oxide group attached to the main chain. Acetylene surfactants are less likely to form micelles and quickly orient at interfaces, resulting in a small contact angle with the recording medium, improving ink spread and effectively suppressing graininess. Furthermore, acetylene surfactants are thought to be less likely to adsorb to pigments or resin particles, making it easier to obtain inks with excellent storage stability.

[0081] The content (mass %) of the hydrocarbon surfactant in the ink is preferably 0.01% by mass or more and 1.5% by mass or less, based on the total mass of the ink. It is more preferably 0.05% by mass or more and 1.5% by mass or less, and even more preferably 0.2% by mass or more and 1.5% by mass or less. By having the content of the hydrocarbon surfactant in the ink be 0.05% by mass or more, or even 0.2% by mass or more, the ink tends to wet and spread evenly on the recording medium, which makes it easier to suppress white voids and image unevenness. Meanwhile, having the content of the hydrocarbon surfactant in the ink be 1.5% by mass or less makes it easier to ensure the storage stability of the ink.

[0082] [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. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass %) in the ink is preferably 40.0% to 95.0% by mass, and more preferably 50.0% to 90.0% by mass, based on the total mass of the ink.

[0083] The water-soluble organic solvent may be any solvent that can be used in inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing solvents, and sulfur-containing solvents. The water-soluble organic solvent may be used alone or in combination of two or more. The content (mass %) of the water-soluble organic solvent in the ink is preferably 2.0% by mass or more and 50.0% by mass or less, and more preferably 3.0% by mass or more and 45.0% by mass or less, based on the total mass of the ink.

[0084] [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.

[0085] [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 static surface tension of the ink at 25°C is preferably 20.0 mN / m or more and 60.0 mN / m or less, and more preferably 20.0 mN / m or more and 35.0 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 static surface tension and viscosity of the ink can be measured using the same method as for measuring the static surface tension and viscosity of the reaction liquid described above. 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. [Example]

[0086] 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.

[0087] <Preparation of reaction solution> Each reaction solution was prepared by mixing the components (unit: %) shown in Table 1, thoroughly stirring, and then filtering under pressure through a 4.5 μm pore-size membrane filter (trade name "HDCII filter," manufactured by Pall). "Catiomaster PD-7" shown in Table 1 is the trade name of an aqueous solution (solid content 50.0%) of dimethylamine-epichlorohydrin condensate, a cationic resin manufactured by Yokkaichi Synthetic. Also shown in Table 1 is "Acetylenol E60" which is the trade name of a surfactant manufactured by Kawaken Fine Chemicals, and "Surfynol 420" which is the trade name of a surfactant manufactured by Nissin Chemical Industry. The bottom row of Table 1 shows the static surface tension γ of each reaction solution at 25°C. r The static surface tension of the reaction solution was measured by the platinum plate method using a surface tensiometer (product name "Automatic Surface Tensiometer DY-300 Type", manufactured by Kyowa Interface Science Co., Ltd.).

[0088] TIFF2025115371000002.tif70170

[0089] <Preparation of pigment dispersion> (Preparation of resin dispersant) A styrene-ethyl acrylate-acrylic acid copolymer (Resin 1) with an acid value of 150 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 an appropriate amount of ion-exchanged water was added to prepare an aqueous solution of Resin 1 with a resin (solid content) content of 20.0%.

[0090] In addition, a butyl acrylate / benzyl methacrylate / methoxypolyethylene glycol monomethacrylate copolymer (resin 2, water-soluble resin, composition (molar) ratio = 30.0 / 60.0 / 10.0, acid value 0 mgKOH / g) was prepared. An appropriate amount of ion-exchanged water was added to 20.0 parts of resin 2 to prepare an aqueous solution of resin 2 with a resin (solids) content of 20.0%. As the methoxypolyethylene glycol monomethacrylate, a product called "Blemmer PME-400" (manufactured by NOF Corp., number of moles of ethylene oxide groups added: approximately 9) was used.

[0091] (Pigment dispersions 1 to 5) A mixture of the components (unit: %) shown in the upper row of Table 2 was subjected to a dispersion treatment using a Nanomizer (Yoshida Kikai Kogyo) at a pressure of 150 MPa for 50 passes. After centrifuging at 5,000 rpm for 30 minutes to remove coarse particles, the mixture was filtered under pressure using a cellulose acetate filter (Advantec) with a pore size of 3.0 μm. An appropriate amount of ion-exchanged water was added for dilution, yielding pigment dispersions 1 to 5 with a pigment content of 10.0% and a resin dispersant content of 3.0%.

[0092] TIFF2025115371000003.tif76170

[0093] <Preparation of resin particles> (Resin particles 1) 1,160 parts of ion-exchanged water was placed in a reactor and heated to 90°C. An initiator solution was prepared by dissolving 1.39 parts of potassium persulfate in 160 parts of ion-exchanged water. 32.0 parts of the prepared initiator solution was added to the reactor and stirred. A monomer solution was prepared by mixing 159.4 parts of ion-exchanged water, 1.0 part of methacrylic acid, 49.5 parts of methyl methacrylate, 23.5 parts of n-hexyl methacrylate, 26.0 parts of n-butyl methacrylate, 1.6 parts of isooctyl thioglycolate, and 9.98 parts of an aqueous solution of an emulsifier. The emulsifier used was Rhodafac RS 710 (manufactured by Rhodia Novecare). An appropriate amount of ion-exchanged water was added to prepare an aqueous solution of the emulsifier with a content of 30.0%. The prepared aqueous monomer solution and 129.4 parts of the initiator solution were added dropwise in parallel to the reactor over 30 minutes and stirred, and then maintained at 90°C for 3 hours to obtain a reaction product. The resulting reaction product was cooled to 50°C, and then a 50% aqueous potassium hydroxide solution was added to adjust the pH to 8.5. After cooling to 25°C, the reaction product was filtered through a 200-mesh wire mesh (a filter with 200 stainless steel wires woven vertically and horizontally per square inch). An appropriate amount of ion-exchanged water was added to obtain an aqueous dispersion of resin particles 1 with a resin particle content of 30.0%. The volume-based cumulative 50% particle diameter D of resin particles 1 was 50 was 90 nm.

[0094] (Resin particles 2) A commercially available aqueous dispersion of urethane resin particles (product name "Takelac W-6010", manufactured by Mitsui Chemicals, volume-based cumulative 50% particle diameter D 50 : 60 nm, resin particle content: 30.0%) was used as an aqueous dispersion of resin particles 2.

[0095] (Resin particles 3) A reaction vessel was placed in an autoclave. A mixture of 90.0 parts ethylene glycol, 20.0 parts bisphenol A, 45.0 parts terephthalic acid, 45.0 parts isophthalic acid, and 7.0 parts trimellitic acid was placed in the reaction vessel. The mixture was then heated at 220°C for 4 hours to carry out an esterification (dehydration condensation) reaction. The temperature was then raised to 240°C, and the pressure inside the autoclave was reduced to 13 Pa over 90 minutes. This reduced pressure at 240°C and 13 Pa was maintained for 5 hours. Nitrogen gas was introduced into the reaction vessel to return it to atmospheric pressure, after which the temperature inside the reaction vessel was lowered to 220°C. A catalyst (tetra-n-butyl titanate) and 3.0 parts trimellitic acid were added, and the mixture was heated at 220°C for 2 hours to carry out a transesterification reaction. The amount of catalyst used (mol) was 3 x 10 -4 × The same amount as the total amount (mol) of polycarboxylic acid used. Nitrogen gas was then introduced into the reaction vessel to create a pressurized state, and a sheet-like resin was removed. This resin was cooled to 25 ° C and then crushed in a crusher to obtain a polyester resin.

[0096] A stirrer (product name: "Tornado Stirrer Standard SM-104" manufactured by AS ONE) was placed in a 2.0 L beaker. The polyester resin obtained above and tetrahydrofuran were placed in the beaker and stirred at 25 °C to dissolve the resin. Next, a 5.0% aqueous solution of sodium hydroxide was added in an amount corresponding to the neutralization rate (mol %) based on the acid value of the resin, and the mixture was stirred for 30 minutes. While stirring at 10 °C and 150 rpm, 900 parts of ion-exchanged water was added dropwise to the beaker at a rate of 20 mL / min. The mixture was then heated to 60 °C, and the tetrahydrofuran was distilled off under reduced pressure, followed by partial distillation of the water. The beaker was placed in a water bath and stirred at 85 °C and 300 rpm for 2 hours. The contents of the beaker were filtered using a 150-mesh wire mesh (a filter with 150 stainless steel wires woven vertically and horizontally per square inch). An appropriate amount of ion-exchanged water was added to adjust the content of the resin particles, and an aqueous dispersion of resin particles 3 with a resin particle content of 25.0% was obtained. 50 was 120 nm.

[0097] (Resin particles 4) A mixture was obtained by mixing 25.0 parts wax, 5.0 parts nonionic dispersant, 1.0 part anionic dispersant (ethylene acrylic acid copolymer), 1.0 part triethanolamine, and 68.0 parts water. The wax used was Fischer-Tropsch wax (trade name "FT-0165", melting point 73°C, manufactured by Nippon Seiro). The nonionic dispersant used was polyoxyethylene cetyl ether (trade name "NIKKOL BC-15", manufactured by Nikko Chemicals). This mixture was dispersed and pressure filtered through a 3.0 μm pore size cellulose acetate filter (manufactured by Advantec). The mixture was then diluted with ion-exchanged water to obtain an aqueous dispersion of resin particles 4 with a resin particle content of 25.0%. The volume-based cumulative 50% particle diameter of resin particles 4 was 180 nm.

[0098] <Preparation of water-soluble resin> A resin was synthesized according to the manufacturing example of "Binder Resin 28" described in JP 2020-180178 A to obtain an aqueous solution containing 30.0% water-soluble resin. This water-soluble resin was a random copolymer of methacrylic acid / 2-hydroxyethyl methacrylate / methyl methacrylate / butyl methacrylate / styrene (mass ratio: 4.5 / 5.0 / 55.5 / 20.0 / 15.0).

[0099] <Preparation of surfactant> A compound of the following formula (1A) and a compound of the following formula (2), both of which are silicone surfactants, were prepared.

[0100] TIFF2025115371000004.tif34170

[0101] TIFF2025115371000005.tif34170

[0102] The hydrocarbon surfactants shown in Table 3 were also prepared. The product name "NIKKOL BS-4" is a surfactant manufactured by Nikko Chemicals, and all others are surfactants manufactured by Nissin Chemical Industry Co., Ltd. Table 3 also shows the HLB values measured by the Griffin method.

[0103] TIFF2025115371000006.tif62170

[0104] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in the middle of Table 4 (Table 4-1 to Table 4-3), thoroughly stirring, and then filtering under pressure using a membrane filter with a pore size of 4.5 μm (product name "HDCII filter", manufactured by Pall). The static surface tension γ of each ink at 25°C is shown in the bottom of Table 4. i The static surface tension of the ink was measured by the platinum plate method using a surface tensiometer (product name "Automatic Surface Tensiometer DY-300 Type", manufactured by Kyowa Interface Science Co., Ltd.).

[0105] TIFF2025115371000007.tif166170

[0106] TIFF2025115371000008.tif165170

[0107] TIFF2025115371000009.tif166170

[0108] <Method of applying reaction solution> A recording head (see reference numeral 22 in FIG. 1) was used, which had a first nozzle array in which nozzles for ejecting ink were arranged along the sub-scanning direction (see arrow A in FIG. 1) and a second nozzle array in which nozzles for ejecting reaction liquid were arranged along the sub-scanning direction (see arrow A in FIG. 1). This recording head was scanned N times (N is an integer greater than or equal to 1) in the main scanning direction (see arrow B in FIG. 1) intersecting the sub-scanning direction (see arrow A in FIG. 1), and the ink and reaction liquid were ejected from the recording head and applied to a unit area on a recording medium (see reference numeral 1 in FIG. 1). In this example, the unit area was set to 1 / 1,200 inch x 1 / 1,200 inch. Reaction liquid application methods 1 to 7 were employed, with the amounts of reaction liquid applied to the recording medium in the first N / 2 scans and the latter N / 2 scans being the percentages shown in Table 5.

[0109] TIFF2025115371000010.tif62170

[0110] <Preparing the recording medium> The following recording media 1 and 2 were prepared. Recording medium 1: Product name "Scotchcal Graphic Film IJ1220N", manufactured by 3M, material = polyvinyl chloride, 30 msec from the start of contact in the Bristow method 1 / 2 Water absorption rate up to 10 mL / m 2 below. Recording medium 2: High-quality dedicated paper, product name "HR-101S", manufactured by Canon, 30 msec from the start of contact in the Bristow method 1 / 2 Water absorption rate up to 10 mL / m 2 Super.

[0111] <Evaluation> Each prepared reaction liquid and each ink was filled into a cartridge and set in an inkjet recording device (product name "imagePROGRAF PRO-2000" manufactured by Canon) equipped with a recording head that ejects ink using thermal energy. A heating device for drying the recording medium to which the reaction liquid and ink had been applied was incorporated into this recording device, located downstream of the recording head in the recording medium transport direction. The recording head of this recording device also had a first nozzle array in which nozzles for ejecting ink were arranged along the sub-scanning direction, and a second nozzle array in which nozzles for ejecting the reaction liquid were arranged along the sub-scanning direction. The recording environment was a temperature of 25°C and a relative humidity of 50%. In this example, a recording duty of 100% was defined as an image recorded under the condition of applying one droplet of 4.0 ng of ink to a unit area of 1 / 1,200 inch x 1 / 1,200 inch.

[0112] After an image was recorded on the recording medium, hot air was applied to the recording medium, and the recording medium was heated and dried so that the surface temperature of the recording medium reached 80°C. The heating temperature was measured using a radiation thermometer. In this example, the evaluation criteria for each item shown below were "AA", "A", and "B" as acceptable levels, and "C" as unacceptable level. The evaluation conditions and evaluation results are shown in Table 6. Table 6 shows the evaluation conditions, including the static surface tension γ of the ink at 25°C. i , the static surface tension of the reaction solution γ r , and |γ i -γ r and the contact angle θ of the ink on the recording medium shown in Table 6. i and the contact angle θ of the reaction liquid r showed.

[0113] (Suppression of image unevenness) Using the inkjet recording device described above, a 2 cm x 2 cm solid image with a recording duty of 100% was recorded on the recording medium shown in Table 6 using the reaction liquid and ink according to the reaction liquid application method shown in Table 6. Ten dark and light areas of the recorded image were randomly selected and the lightness (L * ) was measured using a fluorescence spectrodensitometer (product name "FD-7", manufactured by Konica Minolta).* is based on the color difference display method specified by CIE. * The difference between the lowest and highest values (ΔL * The value of ) determines whether image unevenness can be recognized, and the suppression of image unevenness was evaluated according to the following evaluation criteria. A:ΔL * was below 0.20. B:ΔL * was greater than 0.20 and less than 0.30. C:ΔL * was above 0.30.

[0114] (Suppression of graininess) Using the inkjet recording device described above, a 2 cm x 2 cm solid image with a recording duty of 100% and a 2 cm x 2 cm solid image with a recording duty of 70% were recorded on the recording medium shown in Table 6 using the reaction liquid and ink according to the reaction liquid application method shown in Table 6. The recorded images were observed visually and under an optical microscope, and the presence or absence of white spots was judged according to the evaluation criteria shown below, and the graininess was evaluated based on the presence or absence of white spots. AA: In the solid images of the two types of recording duty, no white spots were observed even when observed under a microscope. A: When observed under a microscope, white spots were observed in a solid image with a recording duty of 70%, but no white spots were observed visually. When observed under a microscope, white spots were not observed in a solid image with a recording duty of 100%. B: In the solid images of both recording duties, white spots were observed under a microscope, but no white spots were observed visually. C: White spots were observed by visual observation in the solid image of at least one of the printing duties.

[0115] TIFF2025115371000011.tif228170

[0116] In Comparative Example 1, when an image was recorded, the ink did not adhere and moved, making it impossible to perform the above evaluation. Furthermore, the acetylene surfactant separated from the ink 21 used in Comparative Example 7, making it impossible to perform the above evaluation. Therefore, the evaluation results for Comparative Examples 1 and 7 are marked with "-."

Claims

1. An inkjet recording method for recording an image on a recording medium by ejecting an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink from a recording head, 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 part of an area of the recording medium to which the aqueous reaction liquid is applied, 30 msec from the start of contact of the recording medium in the Bristow method １／２ Water absorption up to 10 mL / m ２ is as follows: the aqueous ink contains a pigment dispersed by the action of an anionic group, resin particles, a silicone surfactant, and a hydrocarbon surfactant; the resin particles are formed of at least one resin selected from the group consisting of an acrylic resin, a urethane resin, and a polyester resin, the hydrocarbon surfactant has an HLB value according to the Griffin method of 4 or more and 8 or less, The static surface tension γ of the water-based ink ｉ and the static surface tension γ of the aqueous reaction liquid ｒ and the ink jet recording method satisfies the following formula (1): |c ｉ -c ｒ |≦3.8 ・・・(1)

2. 2. The ink jet recording method according to claim 1, wherein the hydrocarbon surfactant is an acetylene surfactant.

3. 2. The ink jet recording method according to claim 1, wherein the hydrocarbon surfactant has an HLB value of 4 or more and 6 or less according to the Griffin method.

4. the recording head comprises a first ejection port array in which ejection ports for ejecting the water-based ink are arranged along a sub-scanning direction, and a second ejection port array in which ejection ports for ejecting the water-based reaction liquid are arranged along the sub-scanning direction, In the reaction liquid applying step and the ink applying step, the recording head is scanned N times (N is an integer of 2 or more) in a main scanning direction intersecting a sub-scanning direction, and the aqueous ink and the aqueous reaction liquid are ejected from the recording head and applied to a unit area of the recording medium, 2. The inkjet recording method according to claim 1, wherein the total amount of the aqueous reaction liquid applied to the recording medium in the first N / 2 scans of the N scans is greater than the total amount of the aqueous reaction liquid applied to the recording medium in the latter N / 2 scans.

5. The contact angle of the water-based ink with respect to the recording medium is θ ｉ , the contact angle of the aqueous reaction liquid is θ ｒ When this is done, θ ｉ ≧θ ｒ The ink jet recording method according to claim 1, wherein the following relationship is satisfied:

6. The contact angle of the water-based ink with respect to the recording medium is θ ｉ , the contact angle of the aqueous reaction liquid is θ ｒ When this is done, θ ｉ ≦55°, and θ ｒ The ink jet recording method according to claim 1, wherein the relationship of ≦25° is satisfied.

7. The static surface tension γ of the water-based ink ｉ is the static surface tension γ of the aqueous reaction liquid ｒ 2. The ink jet recording method according to claim 1, wherein:

8. 2. The ink jet recording method according to claim 1, wherein the silicone surfactant is a compound represented by the following general formula (1): (In the general formula (1), k represents an integer of 1 to 3, l represents an integer of 1 to 4, and m+n represents an integer of 8 to 15. m and n are natural numbers.)

9. An inkjet recording apparatus used to record an image on a recording medium by ejecting from a recording head an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, a reaction liquid applying means for applying the aqueous reaction liquid to the recording medium; an ink applying means for 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, 30 msec from the start of contact of the recording medium in the Bristow method １／２ Water absorption up to 10 mL / m ２ is as follows: the aqueous ink contains a pigment dispersed by the action of an anionic group, resin particles, a silicone surfactant, and a hydrocarbon surfactant; the resin particles are formed of at least one resin selected from the group consisting of an acrylic resin, a urethane resin, and a polyester resin, the hydrocarbon surfactant has an HLB value according to the Griffin method of 4 or more and 8 or less, The static surface tension γ of the water-based ink ｉ and the static surface tension γ of the aqueous reaction liquid ｒ and the ink jet recording apparatus is characterized in that the relationship of the following formula (1) is satisfied: |c ｉ -c ｒ |≦3.8 ・・・(1)

10. A set of an aqueous ink and an aqueous reaction liquid 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, comprising: 30 msec from the start of contact of the recording medium in the Bristow method １／２ Water absorption up to 10 mL / m ２ is as follows: the inkjet recording method includes 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 to the recording medium so as to overlap at least a portion of an area onto which the aqueous reaction liquid is applied, the aqueous ink contains a pigment dispersed by the action of an anionic group, resin particles, a silicone surfactant, and a hydrocarbon surfactant; the resin particles are formed of at least one resin selected from the group consisting of an acrylic resin, a urethane resin, and a polyester resin, the hydrocarbon surfactant has an HLB value according to the Griffin method of 4 or more and 8 or less, The static surface tension γ of the water-based ink ｉ and the static surface tension γ of the aqueous reaction liquid ｒ A set of an aqueous ink and an aqueous reaction liquid, characterized in that the relationship of the following formula (1) is satisfied: |c ｉ -c ｒ |≦3.8 ・・・(1)

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