Aqueous ink, ink cartridge, and inkjet recording method

Abstract

The present invention relates to an aqueous ink, an ink cartridge, and an inkjet recording method. An aqueous ink which inhibits fogging and is excellent in storage stability is provided. The aqueous ink is an aqueous ink which is ejected from a recording head of an inkjet system by the action of thermal energy. The aqueous ink contains a first surfactant and a second surfactant. The first surfactant contains a compound represented by the following general formula (1) (in general formula (1), "m" and "n" each independently represent an integer of 1 or more and satisfy a relationship of m + n ≤ 10, and "a" represents an integer of 10 or more and 20 or less). The second surfactant contains an acetylenic diol compound.

Description

Technical Field

[0001] This invention relates to water-based ink, ink cartridges, and inkjet recording methods. Background Technology

[0002] In recent years, inkjet recording methods have enabled the recording of images with the same high resolution achieved through silver halide photography or offset printing. Furthermore, with the diversification of applications, such as photographic printing and graphic arts printing, there is a need for improved image quality using coated recording media, such as glossy paper. Systems that eject ink from the recording head of an inkjet system using thermal energy (thermal inkjet systems) are well-suited for improving image quality because they enable high-density recording.

[0003] In recent years, there has been a demand for inkjet recording methods to record images with higher resolution than ever before. Research has been conducted to improve the image quality of recording media, including coated media such as glossy paper. For example, an ink capable of recording images has been proposed that improves gloss by using a low molecular weight surfactant to reduce the surface tension of the ink, thereby effectively improving the ink's permeability in the recording medium (Japanese Patent Application Publication No. 2004-115649). Furthermore, an ink capable of recording images has been proposed that improves gloss by using an organosilicon (polysiloxane) surfactant to improve the wettability of the ink in the recording medium (Japanese Patent Application Publication No. 2006-233083). Additionally, a dye ink has been proposed that improves wettability and defoaming properties in the recording medium by using an acetylene glycol surfactant (Japanese Patent Application Publication No. 2005-103457).

[0004] The inventors of this invention have researched a recording method by which the image quality of coated recording media, such as glossy paper, can be improved by using a thermal inkjet system. Referring to the description in Japanese Patent Application Publication No. 2006-233083, the inventors have used a low surface tension ink with a silicone-based surfactant as the ink. As a result, the inventors have disclosed that image quality can be improved using silicone-based surfactants, but have found the following problems.

[0005] First, the following phenomenon was observed: when ink is stored for a long time, the surface tension of the ink increases over time due to the decomposition of silicone-based surfactants. When using ink with increased surface tension due to long-term storage during recording, a significant decrease in image quality was observed compared to recording with ink before storage. Furthermore, while the use of silicone-based surfactants can improve ink storage stability, the following phenomenon was observed: during image recording, fine droplets (hereinafter referred to as "mist") adhered to the recording head or the inside of the recording device. Mist consists of extremely fine droplets compared to the main ink droplets used for image recording. When recording continues in a misted state, the mist may adhere to various sensors in the recording device, thereby reducing the sensitivity of each sensor or causing them to malfunction. In addition, the adhesion of mist to the recording medium also affects the image. In other words, when attempting to obtain satisfactory image quality using a thermal inkjet system, suppressing mist formation and improving ink storage stability become problems. Therefore, further research is needed to address these issues. Summary of the Invention

[0006] Therefore, one object of the present invention is to provide a water-based ink that suppresses fogging and exhibits excellent storage stability. Another object of the present invention is to provide ink cartridges and inkjet recording methods using the water-based ink.

[0007] The above objective is achieved by the present invention described below. That is, according to the present invention, an aqueous ink ejected from the record head of an inkjet system by the action of thermal energy is provided, the aqueous ink comprising: a particulate component; a first surfactant; and a second surfactant, wherein the particulate component comprises at least one selected from the group consisting of pigments and resin particles, wherein the first surfactant comprises a compound represented by the following general formula (1), and wherein the second surfactant comprises an acetylene glycol compound:

[0008]

[0009] In general formula (1), "m" and "n" each independently represent integers above 1 and satisfy the relationship m+n≤10, and "a" represents integers above 10 and below 20.

[0010] Further features of the invention will become apparent from the following description of exemplary embodiments, with reference to the accompanying drawings. Attached Figure Description

[0011] Figure 1 This is a schematic cross-sectional view of an ink cartridge according to one embodiment of the present invention.

[0012] Figure 2A and Figure 2BThis is a view used to schematically illustrate an example of an inkjet recording device used in the inkjet recording method of the present invention, wherein... Figure 2A This is a perspective view of the main parts of an inkjet recording device, and Figure 2B This is a perspective view of the head box. Detailed Implementation

[0013] The invention is described in more detail below through exemplary embodiments. In this invention, when the ink contains salt, the salt exists in the ink in a dissociated ionic state; however, for convenience, the term "contains salt" is used. Furthermore, water-based inks used for inkjet printing are sometimes simply referred to as "ink". Unless otherwise stated, physical property values ​​are values ​​at room temperature (25°C).

[0014] To improve the image quality of recording media including coated materials such as glossy paper, the inventors of this invention have studied low surface tension inks that use silicone-based surfactants as surfactants introduced into water-based inks. As a result, the inventors observed that the surface tension of the ink increases over time when stored for an extended period. This phenomenon is caused by the decomposition of the silicone-based surfactants in the ink. When using ink with increased surface tension due to long-term storage during recording, a significant decrease in image quality was observed compared to recording with ink before storage.

[0015] The decomposition of silicone surfactants in water-based inks may be due to the fact that the siloxane portion, which acts as the hydrophobic part of the silicone surfactant, is easily hydrolyzed. Furthermore, the increased surface tension of the ink due to the decomposition of silicone surfactants may be due to the fact that the hydrolysis of the silicone surfactant separates the hydrophobic and hydrophilic parts of the surfactant, resulting in a loss of its surface activity.

[0016] In water-based inkjet inks, silicone surfactants are typically used. These surfactants have a siloxane structure as their basic framework, modified with polyether chains. Depending on the type of modification of the siloxane structure (-Si-O-) with polyether chains, these surfactants are broadly classified into single-terminal modified, two-terminal modified, ABn type, side-chain modified, and two-terminal modified side-chain types. The inventors of this invention have conducted various studies on the structures of the following silicone surfactants: even when using silicone surfactants, the increase in ink surface tension due to long-term storage can be suppressed. As a result, the inventors have found that, among silicone surfactants, two-terminal modified surfactants, ABn type surfactants (linear block copolymers), and surfactants obtained by alkylating the ethylene oxide chain ends of the side chains of side-chain modified surfactants can all improve the storage stability of ink.

[0017] The reason why end-modified and ABn-type organosilicon surfactants can suppress the increase in surface tension is that their surface activity is hardly lost even when the individual siloxane skeletons of the surfactants are separated by hydrolysis, because the hydrophobic and hydrophilic parts exist in their separated molecules. Furthermore, the reason why organosilicon surfactants obtained by alkylating the ethylene oxide chain ends of the side chains of side-chain modified surfactants can suppress the increase in surface tension of ink is as follows. Hydroxide ions in the ink are given as one reason for the hydrolysis reaction of the siloxane skeleton of the organosilicon surfactant. Carboxylic acid ions generated by the oxidation of hydroxyl groups at the ethylene oxide chain ends of the organosilicon surfactant are also given as one reason. Carboxylic acid ions can nucleophilically attack the intramolecular or intermolecular siloxane skeleton to promote hydrolysis. Therefore, it is speculated that the increase in surface tension is suppressed because the alkylation at the ethylene oxide chain ends inhibits the hydrolysis of the siloxane skeleton.

[0018] The inventors of this invention have studied the ejection characteristics of ink in a thermal inkjet system, which improve storage stability through the selection of its silicone-based surfactant. As a result, the inventors have discovered that when each of the aforementioned silicone-based surfactants that can individually improve the storage stability of the ink is used, a large amount of fogging is generated. This large amount of fogging is a phenomenon that does not occur when using silicone-based surfactants that have a low effect on improving the storage stability of the ink, or in ejection systems other than thermal inkjet systems.

[0019] This section describes mist in inkjet systems. Inkjet systems are broadly classified into piezoelectric inkjet systems and thermal inkjet systems. A piezoelectric inkjet system involves ejecting ink from an ejection orifice of a record head equipped with piezoelectric elements. A thermal inkjet system involves applying heat energy to the ink to eject it from an ejection orifice of a record head. In both piezoelectric and thermal inkjet systems, energy is applied to a liquid near the ejection orifice of the record head, and thus the ink is ejected from the orifice in droplet form.

[0020] Preferably, one droplet is ejected when jet energy is applied to the ink once. However, droplets can be split into multiple droplets by various factors, such as the physical properties of the ink, the shape of the ejection orifice, and the amount of jet energy. Among the split droplets, the droplet with the largest volume (the master droplet) adheres to the intended location on the recording medium. Meanwhile, droplets with smaller volumes may adhere to unintended locations on the recording medium, degrading the image quality of the image on the medium, or they may float in the recording device without adhering to the recording medium, and then adhere to the inside of the device, causing contamination or device malfunction. The split droplets that do not adhere to the intended location on the recording medium are referred to as "fog". It is known that ink splitting tends not to occur when the surface tension of the ink is high, and tends to occur when the surface tension of the ink is low. The term "surface tension" used herein refers to the surface tension (dynamic surface tension) over the time scale of ink droplets ejected from the ejection orifice of the recording head. The amount of fog is related to the ease with which a state appears to be established where the droplets leave a trail during ejection. It is known that this amount tends to be large when the ink viscosity is high, and small when the ink viscosity is low.

[0021] For example, acetylene glycol-based surfactants rapidly orient to the gas-liquid interface. When acetylene glycol-based surfactants are used in ink, the surfactant can rapidly orient to the surface of droplets formed by ink jetting, reducing the surface tension of the droplets and thus promoting droplet splitting. In contrast, it is assumed that silicone-based surfactants orient to the gas-liquid interface less rapidly, so as not to reduce the surface tension of the droplets formed by jetting, and therefore droplet splitting hardly occurs. Surfactants reduce the tension of the gas-liquid interface as follows: surfactant molecules desorb from micelles formed by the surfactant in the liquid and orient to the gas-liquid interface to reduce the tension. The rate of orientation depends on the strength of micelle association. Therefore, it is assumed that strong association forces acting between the molecules of silicone-based surfactants inhibit the desorption of surfactant molecules from the formed micelles, thereby slowing down the orientation to the gas-liquid interface, and therefore droplet splitting hardly occurs. However, contrary to this assumption, the inventors of the present invention have discovered that when ink using silicone-based surfactants that can improve the storage stability of ink is jetted through a thermal inkjet system, a particular increase in the amount of fog is produced. The inventors of this invention have speculated on the reasons for the generation of large amounts of fog as follows.

[0022] First, let's assume the reason for the increased fogging when using bi-terminated or ABn-type silicone surfactants is as follows. Due to the molecular structure of the surfactant, the viscosity of ink containing bi-terminated or ABn-type silicone surfactants may easily increase through evaporation at the ejection orifice of the record head. Therefore, the ink droplets appear to leave a trail during ejection, then break into spherical shapes. Fogging is likely generated for the reasons described above.

[0023] Next, when using silicone-based surfactants obtained by alkylating the ethylene oxide chain ends of the side chains of side-chain modified surfactants, the increased amount of fog is presumably due to the following reasons. It is expected that alkylation at the ethylene oxide chain ends lowers the cloud point of the silicone-based surfactant. Therefore, in thermal inkjet systems, micelles formed from silicone-based surfactants are hydrophobized by heating, and the hydrophobized micelles immediately migrate to the gas-liquid interface to reduce the surface tension of the ink droplets containing the surfactant, thereby breaking the droplets. Fogging is likely generated for the reasons described above.

[0024] Based on the above speculation, the inventors of this invention further investigated the composition that enables both fog suppression and ink storage stability when using a thermal inkjet system. As a result, the inventors discovered an ink composition that combines a particulate component (pigment or resin particles), a compound represented by general formula (1) as described later, and an acetylene glycol compound. By using ink with this composition, fog formation can be suppressed even when using a thermal inkjet system, and furthermore, high-level ink storage stability can be achieved. Hereinafter, the compound represented by general formula (1) is also referred to as the "first surfactant," and the acetylene glycol compound is also referred to as the "second surfactant."

[0025] The inventors of this invention have deduced the mechanism by which both fog suppression and ink storage stability can be achieved by introducing particulate components, a compound represented by general formula (1) (first surfactant), and an acetylene glycol compound (second surfactant) into ink, as described below. First, when the ink contains particulate components, the first surfactant, and the second surfactant, both fog suppression and ink storage stability can be achieved. When a combination of a two-terminal modified or ABn-type silicone surfactant and a second surfactant, other than the first surfactant which is a side-chain modified silicone surfactant, is used, fog formation during ink ejection cannot be suppressed. Furthermore, fog formation during ejection cannot be suppressed in the following cases: when the first surfactant and the second surfactant are used but the particulate component is absent; when a dye is used instead of the pigment used as the particulate component; and when a water-soluble resin is used instead of the resin particles used as the particulate component. Based on the foregoing, it is deduced that the specific actions of the particulate component, the first surfactant, and the second surfactant contribute to achieving both fog suppression and storage stability.

[0026] It is known that when multiple nonionic surfactants coexist in a liquid, mixed micelles can be formed based on their structure and the relationship between their hydrophilic and lipophilic balance (HLBs). This effect is likely due to: the formation of mixed micelles through a first surfactant and a second surfactant; and the coexistence of particulate components.

[0027] In the case of forming mixed micelles, even when heating based on a thermal inkjet system lowers the cloud point of the first surfactant to hydrophobize it, the hydrophobicity of the surface of the mixed micelles can be suppressed by the hydrophilic portion of the second surfactant adjacent to the first surfactant within the mixed micelles. Simultaneously, the interior of the mixed micelles is in a state where hydrophobic and hydrophilic portions coexist, because the mixed micelles contain not only the second surfactant but also the first surfactant, which has been hydrophobized by heating based on the thermal inkjet system. From the foregoing, it is conceivable that although the hydrophobicity of the mixed micelles is reduced to suppress its movement to the gas-liquid interface of the ink droplets, the hydrophobic portion exists on the surface of the mixed micelles, thus allowing the mixed micelles to move to the gas-liquid interface of the droplets. The surface of the pigment or resin particles used as particulate components has hydrophobic portions; therefore, the hydrophobic portion of the mixed micelles allows the mixed micelles and particulate components to interact effectively with each other, limiting the movement of the mixed micelles towards the gas-liquid interface. As a possible result, the mixed micelles are almost absent at the gas-liquid interface of the droplets, thus suppressing the reduction of the droplet's surface tension and thereby suppressing fogging. Furthermore, the ink includes a first surfactant that has been desorbed from the mixed micelles to exist in a unimolecular state. This first surfactant, desorbed from the mixed micelles, can be hydrophobized by heating based on a thermal inkjet system to reduce the surface tension of the droplets, thereby promoting fog formation. However, it is conceivable that fog formation can also be suppressed by adsorbing the particulate components of the already hydrophobized first surfactant.

[0028] As described above, the suppression of fogging cannot be achieved by using dyes or water-soluble resins instead of particulate components. The possible reasons for this are as follows: Unlike pigment or resin particles, dyes or water-soluble resins do not contain hydrophobic portions that can form particles. Therefore, the interaction between the dye or water-soluble resin and the mixed micelles is weak, and thus the movement of the mixed micelles towards the gas-liquid interface of the droplets cannot be suppressed. It is possible that the suppression of fogging is not achieved for the above reasons. Furthermore, when only the second surfactant is used as the surfactant in the ink, fogging is expected to occur easily. In contrast, the ink of the present invention can suppress fogging because of the fact that the strong association of the first surfactant traps the second surfactant, thus suppressing its desorption from the mixed micelles.

[0029] Furthermore, it is speculated that the reason why inks using silicone surfactants other than the first surfactant do not provide a suppressive effect on fogging is as follows: Silicone surfactants other than the first surfactant hardly form mixed micelles with the second surfactant because the chain length of the siloxane backbone of the surfactant and the balance between its hydrophilic and hydrophobic portions differ from those of the first surfactant. Therefore, silicone surfactants other than the first surfactant hardly form mixed micelles with the second surfactant, and a portion of the silicone surfactants other than the first surfactant exists as individual molecules or forms individual micelles instead of mixed micelles. It is possible that fogging cannot be suppressed for the above reasons.

[0030] Furthermore, the inventors have discovered that the above-described configuration improves the storage stability of the ink. A possible reason is that hydroxide ions, which are a cause of hydrolysis of organosilicon surfactants, are captured by hydrogen bonding with the hydroxyl groups of the second surfactant in the mixed micelles. In addition to the above, the following reasons are conceivable: the mixed micelles adsorb onto the particulate components to suppress nucleophilic attack on the siloxane backbone in the mixed micelles.

[0031] Water-based ink

[0032] As described above, ink is a water-based ink ejected from the record head of an inkjet system by the action of heat energy. The ink contains particulate components (pigment or resin particles) and surfactants. The surfactants include a first surfactant and a second surfactant. The ink of the present invention does not need to be a so-called "curable ink." Therefore, the ink of the present invention may not contain compounds such as polymerizable monomers that can be polymerized by applying external energy. The various components used to form the ink, etc., are described in detail below.

[0033] (Particulate components)

[0034] The ink contains at least one particulate component selected from the group consisting of pigments and resin particles. Preferably, the ink contains at least one pigment as a particulate component. The content (mass %) of the particulate component in the ink is preferably 0.10% by mass or more and 10.00% by mass or less relative to the total mass of the ink. In the ink, the mass ratio of the content (mass %) of the particulate component to the total content (mass %) of the first surfactant and the second surfactant is preferably 0.01 times or more and 10.00 times or less. More preferably, this mass ratio is 0.10 times or more and 5.00 times or less, and even more preferably 0.10 times or more and 2.00 times or less.

[0035] [pigment]

[0036] When pigment is used as a particulate component, the pigment content (by mass%) in the ink is preferably 0.10% by mass or more and 10.00% by mass or less, more preferably 0.50% by mass or more and 6.00% by mass or less, relative to the total mass of the ink. Ink that does not contain pigment as a particulate component can be used, for example, as a transparent ink that does not contain coloring materials or as a dye ink that contains dye as its coloring material.

[0037] Specific examples of pigments can include: inorganic pigments, such as carbon black and titanium dioxide; and organic pigments, such as azo, phthalocyanine, quinacridone, isoindolineone, imidazolineone, diketopyrrolopyrrole, and dioxazine.

[0038] Products that can be used individually as pigments are classified according to their dispersion system into, for example, resin-dispersed pigments that use resin as their dispersant and self-dispersed pigments having hydrophilic groups bonded to their particle surface. Furthermore, for example, resin-bonded pigments having resins containing organic groups chemically bonded to the particle surface and microencapsulated pigments with the particle surface coated with resin, etc., can each be used. Pigments of any dispersion system can be used in inks. Furthermore, pigments that are different from each other in the dispersion system can be used in combination. Preferably, a system (resin-dispersed pigment) is included where the pigment is dispersed by the action of a resin dispersant (e.g., a water-soluble resin comprising units having acid groups and units not having acid groups) that causes it to be physically adsorbed onto the surface of the pigment particles. The same units selected from those listed as examples of units used to form resin particles, which will be described later, can be used as units for forming the water-soluble resin used as a resin dispersant.

[0039] [Resin particles]

[0040] When resin particles are used as a particulate component, any type of resin with any structure can be used to form the resin particles, as long as the resin can be used in water-based inks. Examples include acrylic resins, polyurethane resins, polyamide resins, polyester resins, polyvinyl alcohol resins, and polyolefin resins. Resin particles formed from one or more of these resins can be introduced into the ink. When resin particles are used as a particulate component, the content (by mass%) of resin particles in the ink relative to the total mass of the ink is preferably 0.10% by mass or more and 5.00% by mass or less, more preferably 0.10% by mass or more and 3.00% by mass or less. In particular, this content is even more preferably 0.50% by mass or more and 2.00% by mass or less.

[0041] The term "resin particles" refers to resins that are insoluble in the aqueous medium used to form ink, and more specifically, resins that can exist in the aqueous medium in a state where their particle size can be measured by dynamic light scattering. Meanwhile, the term "water-soluble resin" refers to resins that are soluble in the aqueous medium used to form ink, and more specifically, resins that can exist in the aqueous medium without forming particles whose particle size can be measured by dynamic light scattering. The term "resin particles" can be replaced by the term "water-dispersible resin (water-insoluble resin)".

[0042] Whether a resin is a "resin particle" can be determined using the following method. First, prepare a liquid containing resin neutralized with a base (e.g., sodium hydroxide or potassium hydroxide) corresponding to its acid value (resin solids content: 10% by mass). Next, dilute the prepared liquid 10 times (by volume) with pure water to prepare a sample solution. Then, measure the particle size of the resin in the sample solution using dynamic light scattering. In this case, when particles with this particle size are observed, the resin can be determined to be a "resin particle" (water-dispersible resin). Conversely, when no particles with this particle size are observed, the resin can be determined not to be a "resin particle" (but rather a "water-soluble resin"). As a particle size distribution measurement device based on dynamic light scattering, a particle size analyzer (e.g., an analyzer purchased from Nikkiso Co., Ltd. under the trade name "UPA-EX150") can be used. The measurement conditions can be set as follows, for example: Set Zero: 30 seconds, Number of measurements: three, Measurement time: 180 seconds, Shape: true spherical shape, and Refractive index: 1.59. The particle size distribution measurement equipment and measurement conditions used are, of course, not limited to those described above. Particle size is measured using neutralized resin for the following purpose: even when the resin is fully neutralized to a state where particle formation is less likely, particle formation is still identified. Resin that exhibits a particulate shape even under these conditions also exists in the water-based ink in a particulate state.

[0043] The resin particles are preferably particles having a so-called core-shell structure, comprising a core and a shell covering the core. Among these particles, resin particles preferably include a core formed only of units without acid groups and a shell formed to contain units with acid groups; and the resin particles contain specific units. Specifically, at least one of the units for forming the core and the units for forming the shell preferably contains units derived from (meth)acrylates. When resin particles with this core-shell structure are used, the resin particles readily maintain their shape within ink droplets. Therefore, the mixed micelles of the first and second surfactants can be effectively adsorbed onto the resin particles, thus readily exhibiting a suppressive effect against fogging. When the core contains only units without acid groups, in other words, when the core does not contain any units with acid groups, the hydrophilicity of the resin used to form the core is reduced, thus the resin particles readily maintain their shape within droplets ejected by a thermal inkjet system. Therefore, the suppressive effect against fogging can be improved. Furthermore, when the shell portion is formed from resins with acidic groups, the resin particles are less prone to aggregation because their hydrophilicity is higher than that of resin particles whose shell portions are formed solely from units without acidic groups. Therefore, mixed micelles can be effectively adsorbed onto the resin particles, thereby improving the suppression of fogging. Moreover, when at least one of the units used to form the core and the units used to form the shell contains units derived from (meth)acrylates, the aggregation of resin particles in the ink is easily suppressed, thus further improving the ink's storage stability.

[0044] The resin used to form resin particles with a core-shell structure can be, for example, an acrylic resin obtained by (co)polymerization of acrylic monomers such as (meth)acrylic acid or (meth)acrylate. As used herein, the term "unit" in resin refers to a repeating unit derived from a monomer. Furthermore, the description of "(meth)acrylic acid" means "acrylic acid or methacrylic acid," and the description of "(meth)acrylate" means "acrylate or methacrylate."

[0045] Examples of monomers without acid groups that can be polymerized into units without acid groups include: monomers each having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 3-methyl-5-hydroxypentyl (meth)acrylate; monomers each having an aromatic group, such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and alkyl (meth)acrylates, such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Monomers without acid groups can be used alone or in combination.

[0046] Examples of monomers having acid groups that are polymerized into units having acid groups include: monomers each having a carboxylic acid group, such as (meth)acrylic acid, maleic acid, itaconic acid, and fumaric acid; monomers each having a sulfonic acid group, such as styrene sulfonic acid; monomers each having a phosphonate group, such as ethyl 2-phosphonate (meth)acrylate; and anhydrides and salts of these monomers. Examples of salts include: alkali metal salts, such as lithium, sodium, and potassium salts; ammonium salts; and organic ammonium salts. Monomers each having an acid group can be used alone or in combination.

[0047] (surfactant)

[0048] The ink contains a first surfactant, namely a compound represented by the following general formula (1). The compound represented by general formula (1) is an organosilicon surfactant having a structure obtained by introducing a terminally methylated ethylene oxide chain into a side chain of a polydimethylsiloxane structure. The ink may contain one or more compounds, each represented by general formula (1), as the first surfactant.

[0049]

[0050] In general formula (1), "m" and "n" each independently represent an integer greater than or equal to 1 and satisfy the relationship m+n≤10, and "a" represents an integer greater than or equal to 10 and less than 20. "m" and "n" each independently represent an integer greater than or equal to 1 and less than 9, preferably an integer greater than or equal to 1 and less than 8, as long as the relationship m+n≤10 is satisfied. It is more preferred that "m" represents an integer greater than or equal to 1 and less than 8 and "n" represents 1 or 2.

[0051] The weight-average molecular weight (Mw) of the compound represented by general formula (1) is preferably 800 or more and 12,000 or less, more preferably 800 or more and 2,000 or less, and even more preferably 1,000 or more and 1,500 or less. The weight-average molecular weight (Mw) can be measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the mobile phase. The method for measuring the Mw of the compound represented by general formula (1) is specifically described below. The Mw of surfactants S1 to S5 and S8 to S16 used in the examples described later is measured by the preferred measurement method described below. The measurement conditions, such as filters, columns, and standard polystyrene samples and their molecular weights, are not limited to those described below.

[0052] The weight-average molecular weight (Mw) of compounds represented by general formula (I) can be measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the mobile phase. Measurement conditions, such as filters, columns, and standard polystyrene samples and their molecular weights, are not limited to those described below. First, the sample to be measured is loaded into tetrahydrofuran (THF) and allowed to stand for several hours to dissolve. This prepares a solution. The solution is then filtered through a solvent-resistant membrane filter with a pore size of 0.2 μm to provide the sample solution. The concentration of the sample in the sample solution is adjusted so that the content of the organosilicon surfactant can be from 0.1% to 0.3% by mass. A refractive index detector (RI detector) is used in GPC. Furthermore, for accurate measurement of 10... 3 Up to 2×10 6 For a given molecular weight range, it is preferable to combine multiple commercially available polystyrene gel columns. For example, four products of Shodex LF-804 (manufactured by Showa Denko KK) can be used in combination, or corresponding products can be used. THF is used as the mobile phase and flowed at a rate of 1 mL / min through a column stabilized in a 40°C hot chamber. Approximately 0.1 mL of the above sample solution is injected into the column. The weight-average molecular weight of the sample is determined using a molecular weight calibration curve generated from a standard polystyrene sample. The molecular weight is approximately 10. 2 To about 10 7 A sample (manufactured by, for example, Polymer Laboratories) is used as a standard polystyrene sample. Furthermore, it is appropriate to use at least about 10 standard polystyrene samples.

[0053] The compound represented by general formula (1) is obtained by, for example, an addition reaction between a compound represented by general formula (A) and a compound represented by general formula (B).

[0054]

[0055] In general formula (A), “m” and “n” have the same meaning as “m” and “n” in general formula (1), respectively.

[0056]

[0057] In general formula (B), "a" has the same meaning as "a" in general formula (1).

[0058] The compound represented by general formula (A) is a polysiloxane compound having n hydrogen atoms bonded to the n Si atoms in general formula (A). Furthermore, the compound represented by general formula (B) is a methoxy-polyethylene glycol-allyl ether having an ethylene oxide unit, an allyloxy group (CH2=CH-CH2-O-) at one end, and a methyl group (-CH3) at the other end.

[0059] The content (by mass%) of the first surfactant in the ink is preferably 0.05% by mass or more and 4.00% by mass or less relative to the total mass of the ink. The above-mentioned content (by mass%) of the first surfactant in the ink is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, more preferably 2.00% by mass or less, and even more preferably 1.00% by mass or less.

[0060] The ink contains a second surfactant, namely an acetylenic diol compound. An acetylenic diol compound is a compound having an acetylene skeleton substituted with multiple hydroxyl groups, and an ethylene oxide chain may be present between the acetylene skeleton and the hydroxyl groups. A compound represented by the following general formula (2) is preferably used as the second surfactant. The ink may contain one or more acetylenic diol compounds, such as those represented by general formula (2), as the second surfactant.

[0061]

[0062] In general formula (2), "b" and "c" each independently represent positive integers.

[0063] In general formula (2), "b" and "c" each represent the number of additions to the ethylene oxide group (-CH2CH2O-) used as a hydrophilic group, and each independently represents a positive integer. "b" and "c" each preferably independently represent an integer of 1 or more and 50 or less, more preferably an integer of 1 or more and 20 or less. The sum "b+c" is preferably 4 or more, more preferably 6 or more. Furthermore, the sum "b+c" is preferably 50 or less, more preferably 20 or less.

[0064] Commercially available products can be used as acetylene glycol compounds (second surfactants). Specific examples of second surfactants may include products available under the following product names: ACETYLENOL E60 and ACETYLENOL E100 (each manufactured by Kawaken Fine Chemicals Co., Ltd.); and SURFYNOL 104, SURFYNOL 465 and SURFYNOL 485 (each manufactured by Nissin Chemical Industry Co., Ltd.).

[0065] The content (by mass%) of the second surfactant in the ink is preferably 0.10% by mass or more and 3.00% by mass or less relative to the total mass of the ink. More preferably, the content (by mass%) of the second surfactant in the ink is 0.20% by mass or more and 3.00% by mass or less, and even more preferably, 0.50% by mass or more and 2.50% by mass or less.

[0066] In the ink, the mass ratio of the content (mass%) of the first surfactant to the content (mass%) of the second surfactant is preferably 0.05 times or more and 3.00 times or less, particularly preferably 0.05 times or more and 2.00 times or less. When the above mass ratio is 0.05 times or more, fogging is easily suppressed. This is likely because the second surfactant is sufficiently captured by the strong association force of the first surfactant in the mixed micelles of the first and second surfactants. From the viewpoint of easier fog suppression, the above mass ratio is more preferably 0.10 times or more. At the same time, when the above mass ratio is 2.00 times or less, fogging is easily suppressed and the storage stability of the ink is easily improved. This is likely because it prevents the first surfactant from forming micelles alone.

[0067] (Other resins)

[0068] In addition to resin dispersants suitable for dispersing pigments and resin particles used as particulate components, any other resin (water-soluble resin) can be incorporated into the ink. Resins of any structure can be used as other resins, as long as they are suitable for use in water-based inks. Examples include acrylic resins, polyurethane resins, polyamide resins, polyester resins, polyvinyl alcohol resins, and polyolefin resins. One or more of these resins can be incorporated into the ink.

[0069] The ink preferably comprises a polyurethane resin, and more preferably a polyurethane resin having units derived from polyisocyanates, units derived from polyols without acid groups, and units derived from polyols with acid groups. The urethane or urea bonds in the polyurethane resin induce hydrogen bonding interactions with hydroxide ions in the ink, thereby reducing the reactivity of the hydroxide ions. Therefore, it is conceivable that the decomposition of the compound represented by general formula (1) hardly occurs, thus further improving the storage stability of the ink. The polyurethane resin may be a water-soluble polyurethane resin dissolved in an aqueous medium used to form the ink, or it may be a water-dispersible polyurethane resin dispersed in an aqueous medium used to form the ink. Water-soluble polyurethane resins are preferred.

[0070] Polyisocyanates are compounds that have two or more isocyanate groups in their molecular structure. Examples of polyisocyanates can include aliphatic polyisocyanates and aromatic polyisocyanates.

[0071] Examples of aliphatic polyisocyanates may include: polyisocyanates, each having a chain structure, such as tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, and 3-methylpentane-1,5-diisocyanate; and polyisocyanates, each having a cyclic structure, such as isophorone diisocyanate, hydrogenated xylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexene diisocyanate, and 1,3-bis(isocyanate methyl)cyclohexane.

[0072] Examples of aromatic polyisocyanates may include toluene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, phenyl dimethyl diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyl diphenylmethane diisocyanate, tetraalkyl diphenylmethane diisocyanate, and α,α,α',α'-tetramethylphenyl dimethyl diisocyanate. These polyisocyanates may be used alone or in combination.

[0073] Examples of polyols without acid groups include polyether polyols, polyester polyols, and polycarbonate polyols. Polyols without acid groups can be used alone or in combination. The number average molecular weight of polyols without acid groups is preferably 400 or more and 4,000 or less. Furthermore, polyether polyols are preferred.

[0074] Examples of polyether polyols may include polyalkylene glycols and products obtained by addition polymerization of alkylene oxides and diols or polyols with three or more alkylene groups. Examples of polyalkylene glycols may include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and ethylene glycol-propylene glycol copolymers. Examples of alkylene oxides may include ethylene oxide, propylene oxide, butane oxide, and oxidized α-olefins. Examples of diols may include hexamethylene glycol, tetramethylene glycol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 4,4-dihydroxyphenylpropane, and 4,4-dihydroxyphenylmethane. Examples of polyols with three or more alkylene groups may include glycerol, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, and pentaerythritol.

[0075] Examples of polyols having acid groups may include polyols each having an acid group such as a carboxylic acid group, a sulfonic acid group, a phosphate ester group, or a phosphonate ester group. The acid group is preferably a carboxylic acid group. Examples of polyols having carboxylic acid groups may include dimethylolacetic acid, dimethylolpropionic acid, and dimethylolbutyric acid. The acid group of a polyol having an acid group may be salt-type. As cations for forming the salt, examples include ions of alkali metals such as lithium, sodium, and potassium; ammonium ions; and cations of organic amines such as dimethylamine. Polyols each having an acid group may be used alone or in combination.

[0076] Furthermore, more preferably, in the polyurethane resin, the proportion of units derived from polyols having acid groups present at the molecular ends to all units derived from polyols having acid groups is 30 mol% or less. The terminal acid groups are more readily accessible to the compound represented by general formula (1) than the acid groups in the main chain of the polyurethane resin. Therefore, when the aforementioned proportion of units derived from polyols having acid groups present at the molecular ends is reduced to 30 mol% or less, it is easier to suppress the decomposition of the compound represented by general formula (1) by the acid groups. Therefore, it is easier to improve the storage stability of the ink. This proportion is preferably 0 mol% or more.

[0077] The ratio of units derived from polyols having acid groups at the molecular ends present in polyurethane resins to all units derived from polyols having acid groups can be verified by the following method. Polyurethane resin prepared for ink production or appropriately removed polyurethane resin from ink can be used as the polyurethane resin to be verified. First, the types of polyisocyanates, polyols without acid groups, and polyols with acid groups are identified by analyzing the polyurethane resin using pyrolysis gas chromatography. Next, the reaction product of the polyisocyanate and the identified polyols with acid groups is dissolved in deuterated dimethyl sulfoxide (deuterated DMSO) and analyzed by carbon nuclear magnetic resonance spectroscopy (CNMR spectroscopy). 13 C-NMR analysis of the solution. Therefore, the chemical shift of the carbonyl carbon in units of polyols having acid groups present at the molecule's ends was identified (in a lower magnetic field). Furthermore, the chemical shift of the carbonyl carbon in units of polyols having acid groups present in the molecule was identified (in a higher magnetic field).

[0078] Next, the ratio of the peak integral value of the carbonyl carbon originating from a polyol unit having an acidic group present at the molecule's end to the sum of the peak integral values ​​of the carbonyl carbon originating from a polyol unit having an acidic group is calculated. Thus, the ratio of the unit originating from a polyol having an acidic group present at the molecule's end to all units originating from polyols having acidic groups can be determined. For example, when using dimethylolpropionic acid (DMPA), a peak of the carbonyl carbon originating from a polyol unit having an acidic group present at the molecule's end is detected at approximately 176 ppm, although some deviations may occur depending on the measurement conditions. Furthermore, a peak of the carbonyl carbon originating from a polyol unit having an acidic group present in the molecule is detected at approximately 175 ppm. Similarly, when using dimethylolbutyric acid (DMBA), a peak of the carbonyl carbon originating from a polyol unit having an acidic group present at the molecule's end is detected at approximately 175 ppm. Furthermore, a peak of the carbonyl carbon originating from a polyol unit having an acidic group present in the molecule's end is detected at approximately 174 ppm. The number-average molecular weight of the polyol can be determined by the above... 13 The number of repeats of units derived from polyols is calculated by C-NMR analysis.

[0079] Chain extenders with bifunctionality or higher can be used to impart crosslinking structures to polyurethane resins. Examples of chain extenders include trimethylol melamine and its derivatives, dimethylol urea and its derivatives, dimethylol ethylamine, diethanolmethylamine, dipropanol ethylamine, dibutanol methylamine, ethylenediamine, propylenediamine, diethylenetriamine, hexamethylenediamine, triethylenetetramine, tetraethylenepentamine, isophorone diamine, phenylenediamine, diphenylmethane diamine, hydrogenated diphenylmethane diamine, hydrazine, polyamide polyamine, polyethylene polyimide, trimethylol melamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. These chain extenders can be used alone or in combination.

[0080] The content (by mass%) of other resins in the ink is preferably 0.10% by mass or more and 5.00% by mass or less relative to the total mass of the ink, more preferably 0.50% by mass or more and 5.00% by mass or less. In particular, this content is even more preferably 1.00% by mass or more and 4.00% by mass or less. Among these, the content (by mass%) of water-soluble polyurethane resin in the ink is preferably 0.40% by mass or more and 3.50% by mass or less relative to the total mass of the ink, more preferably 0.50% by mass or more and 3.00% by mass or less.

[0081] (Aqueous medium)

[0082] The ink is an aqueous ink that contains at least water as an aqueous medium. Deionized water (ion-exchanged water) is preferably used as the water. The water content (mass%) in the ink is preferably 10.00% by mass or more and 90.00% by mass or less relative to the total mass of the ink, more preferably 50.00% by mass or more and 90.00% by mass or less.

[0083] (Water-soluble organic solvent)

[0084] The aqueous medium may further contain a water-soluble organic solvent. Examples of water-soluble organic solvents that can be used include monohydric alcohols, polyhydric alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing polar solvents, and sulfur-containing polar solvents. One or more water-soluble organic solvents may be used.

[0085] In water-soluble organic solvents, a first water-soluble organic solvent and a second water-soluble organic solvent are preferably used. The first water-soluble organic solvent is an alkanediol with a relative permittivity of 28.0 or less and hydroxyl groups at both ends of its hydrocarbon chain, and the second water-soluble organic solvent has a relative permittivity of 40.0 or more. Using an ink that also contains the aforementioned first and second water-soluble organic solvents further promotes the suppression of fogging. The reason for this is speculated as follows: Water-soluble organic solvents with low relative permittivity readily interact with the polysiloxane sites of the first surfactant, and water-soluble organic solvents with high relative permittivity readily interact with the polyoxyethylene sites of the first surfactant. Therefore, it is speculated that the interactions between the sites are weakened. Furthermore, the first water-soluble organic solvent, with hydrophilic groups present at both ends of its alkyl chain, causes almost no steric hindrance to the first surfactant, and therefore easily approaches the surfactant. Therefore, the hydrophobic portion of the solvent's main chain readily interacts with the polysiloxane sites. Therefore, the molecules of the first surfactant are less likely to aggregate, thus facilitating the formation of mixed micelles of the first and second surfactants. As a result of the above, the effect of suppressing fog formation may be improved.

[0086] Examples of the first water-soluble organic solvent may include 1,5-pentanediol (27.0), 3-methyl-1,5-pentanediol (23.9), and 1,6-hexanediol (7.1), wherein the values ​​in parentheses represent the relative permittivity at 25°C. One or more first water-soluble organic solvents may be used. The relative permittivity of the first water-soluble organic solvent is preferably 3.0 or higher. Examples of the second water-soluble organic solvent may include glycerol (42.3) and ethylene glycol (40.4), wherein the values ​​in parentheses represent the relative permittivity at 25°C. One or more second water-soluble organic solvents may be used. The relative permittivity of the second water-soluble organic solvent is preferably 120.0 or lower.

[0087] The relative permittivity of water-soluble organic solvents can be measured individually using a dielectric constant meter (e.g., a product manufactured by Brookhaven Instruments Corporation and available under the product name "BI-870") at a frequency of 10 kHz. The relative permittivity of a water-soluble organic solvent that is a solid at 25°C is calculated by the following equation (I) after measuring the relative permittivity of its 50% by mass aqueous solution. Although the term "water-soluble organic solvent" generally refers to a liquid, in this invention, solvents that are solid at 25°C (room temperature) are also included in the category of water-soluble organic solvents.

[0088] ε sol =2ε 50％ -ε 水 ……(I)

[0089] ε sol Relative permittivity of a water-soluble organic solvent that is a solid at 25°C

[0090] ε 50％ The relative permittivity of a 50% by mass aqueous solution of a water-soluble organic solvent that is a solid at 25°C.

[0091] ε 水 The relative permittivity of water

[0092] Water-soluble organic solvents commonly used in water-based inks and which are solid at 25°C can be, for example, 1,6-hexanediol, trimethylolpropane, ethylidene urea, urea, or polyethylene glycol with a number-average molecular weight of 1,000. The reason why the relative permittivity of water-soluble organic solvents solid at 25°C is determined by the relative permittivity of their 50% by mass aqueous solution is as follows. Among water-soluble organic solvents that are solid at 25°C, some solvents that can be used as components of water-based inks have the following difficulties: it is difficult to prepare aqueous solutions with concentrations higher than 50% by mass. At the same time, in aqueous solutions with concentrations as low as 10% by mass or less, the relative permittivity of water becomes dominant, thus hindering the acquisition of possible (effective) values ​​of the relative permittivity of each water-soluble organic solvent. In view of the above, the inventors of the present invention conducted research. As a result, the inventors have disclosed that most solvents that are solid at 25°C and can be used in inks enable the preparation of aqueous solutions to be measured, and the relative permittivity of each solvent to be measured is consistent with the effects of the present invention. Therefore, the inventors decided to use a 50% by mass aqueous solution. In the case of a water-soluble organic solvent that is a solid at 25°C, the solubility of this solvent in water is so low that a 50% by mass aqueous solution cannot be prepared. For convenience, an aqueous solution with a saturated concentration was used, and the solution was prepared according to the measured ε... solThe value of its relative permittivity is calculated under the following conditions.

[0093] The content (by mass%) of water-soluble organic solvent in the ink is preferably 50.00% by mass or less relative to the total mass of the ink, more preferably 3.00% by mass or more and 30.00% by mass or less. The content (by mass%) of the first water-soluble organic solvent in the ink is even more preferably 1.00% by mass or more and 10.00% by mass or less relative to the total mass of the ink. The content (by mass%) of the second water-soluble organic solvent in the ink is even more preferably 2.00% by mass or more and 25.00% by mass or less relative to the total mass of the ink.

[0094] (Other additives)

[0095] In addition to the components mentioned above, inks may contain various additives as needed, such as surfactants, pH adjusters, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, evaporation promoters, and chelating agents.

[0096] (Compounds represented by general formula (3))

[0097] The ink preferably contains a compound represented by the following general formula (3):

[0098]

[0099] In general formula (3), “o” represents an integer greater than 1 and less than 10.

[0100] It is speculated that the compound represented by general formula (3) readily interacts with the polysiloxane site of the compound represented by general formula (1) to mitigate the decomposition of the polysiloxane site caused by hydroxide ions in the ink. Therefore, the storage stability of the ink can be further improved. In particular, it is preferable that the "o" in general formula (3) represents 1 or more, as the storage stability of the ink is further improved. Meanwhile, it is preferable that the "o" in general formula (3) represents 10 or less, as the suppression effect on fogging can be sufficiently obtained. Furthermore, it is more preferable that the mass ratio of the content (mass%) of the compound represented by general formula (3) to the content (mass%) of the first surfactant in the ink is 0.01 times or less, as the suppression effect on fogging can be sufficiently obtained. The aforementioned mass ratio is preferably 0.0005 times or more.

[0101] The content (mass%) of the compound represented by general formula (3) in the ink is preferably 0.040% by mass or less relative to the total mass of the ink. More preferably, the content (mass%) of the compound represented by general formula (3) in the ink is 0.0001% by mass or more and 0.020% by mass or less, and even more preferably 0.0001% by mass or more and 0.010% by mass or less.

[0102] (Physical properties of ink)

[0103] The viscosity of the ink at 25°C is preferably 1.0 mPa·s or higher and 10.0 mPa·s or lower, more preferably 1.0 mPa·s or higher and 5.0 mPa·s or lower, and particularly preferably 1.0 mPa·s or higher and 3.0 mPa·s or lower. The surface tension (static surface tension) of the ink at 25°C is preferably 10.0 mN / m or higher and 60.0 mN / m or lower, more preferably 20.0 mN / m or higher and 60.0 mN / m or lower, and particularly preferably 30.0 mN / m or higher and 50.0 mN / m or lower. The pH of the ink at 25°C is preferably 5.0 or higher and 10.0 or lower, more preferably 7.0 or higher and 9.5 or lower.

[0104] <Ink cartridge>

[0105] The ink cartridge of the present invention includes ink and an ink storage section configured to store the ink. Furthermore, the ink stored in the ink storage section is the water-based ink of the present invention described above. Figure 1 This is a schematic cross-sectional view of an ink cartridge according to one embodiment of the present invention. Figure 1 As shown, an ink supply port 12 for supplying ink to the recording head is arranged on the bottom surface of the ink cartridge. The interior of the ink cartridge is an ink storage section for storing ink. The ink storage section includes an ink storage chamber 14 and an absorbent storage chamber 16, and these chambers are connected to each other via a communication port 18. Furthermore, the absorbent storage chamber 16 is connected to the ink supply port 12. While liquid ink 20 is stored in the ink storage chamber 14, absorbents 22 and 24, each configured to hold the ink in a state of impregnation, are stored in the absorbent storage chamber 16. The ink storage section may be in a form that does not include an ink storage chamber configured to store liquid ink and is configured to retain the entire amount of ink stored in absorbent. Alternatively, the ink storage section may be in a form that does not contain absorbent and is configured to store the entire amount of ink in a liquid state. Furthermore, an ink cartridge formed to include an ink storage section and a recording head can be used.

[0106] <Inkjet Recording Methods>

[0107] The inkjet recording method of the present invention includes a method of ejecting the aqueous ink of the present invention described above from the recording head of an inkjet system to record an image on a recording medium. As the inkjet system, a system involving the application of heat energy to the ink is utilized. Apart from using the ink of the present invention, the steps of the inkjet recording method can be known steps. In the present invention, only the step of applying ink to the recording medium is required, and other processing (e.g., the step of applying a reaction solution that reacts with the ink, the step of curing the image by applying, for example, active energy rays, or the step of heating the image) is unnecessary.

[0108] Figure 2A and Figure 2BThis is a view used to schematically illustrate an example of an inkjet recording device used in the inkjet recording method of the present invention, wherein... Figure 2A This is a perspective view of the main parts of an inkjet recording device, and Figure 2B This is a perspective view of the head cartridge. In an inkjet recording device, a transport unit (not shown) and a carriage shaft 34 configured to transport the recording medium 32 are arranged. The head cartridge 36 can be mounted to the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40 and is configured to house ink cartridges 42 therein. While the head cartridge 36 is transported along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. The recording medium 32 is then transported by the transport unit (not shown) in the sub-scanning direction. Thus, an image is recorded on the recording medium 32.

[0109] Any recording medium can be used as a recording medium on which the ink of the present invention is recorded. However, it is preferred to use a recording medium with ink permeability, such as plain paper or a recording medium including a coating (glossy paper or coated paper). The use of a coated recording medium is preferred because it allows at least some of the pigment particles in the ink to be present on or near the surface of the recording medium. Such a recording medium can be selected according to the intended use of, for example, a recording product on which an image is recorded. Examples include: glossy paper suitable for obtaining an image with a glossy finish of photographic quality; and coated paper for representing, according to preference, the texture of the substrate (e.g., drawing paper texture, canvas texture, or Japanese paper texture) of images, photographs, and graphic images. Glossy paper, in which the surface of its coating is glossy, is particularly preferred.

[0110] [Example]

[0111] The invention is described in more detail below with reference to examples and comparative examples. However, the invention is by no means limited to the examples below, but is to be understood without departing from its spirit. In the description of the amounts of the components, unless otherwise stated, "parts" and "%" are by mass.

[0112] <Analytical conditions for resin>

[0113] The acid value of the resin was measured by dissolving the resin in tetrahydrofuran and using a 0.5 mol / L solution of potassium hydroxide in ethanol as a titrant and an automatic potentiometric titrator (product name: "AT-510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.). The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the resin were measured using polystyrene as a standard, tetrahydrofuran as a solvent, and a gel permeation chromatography system including a differential refractive index detector (product name: "Alliance GPC 2695", manufactured by Waters Corporation).

[0114] <Preparation of Water-Soluble Resins>

[0115] (Acrylic Resin 1)

[0116] Acrylic resin 1 was synthesized by copolymerizing 80.7 parts styrene and 19.3 parts acrylic acid using conventional methods. Acrylic resin 1 is a water-soluble resin with an acid value of 150 mg KOH / g and a weight-average molecular weight of 8,000. The resulting acrylic resin 1 was dissolved in ion-exchanged water by adding potassium hydroxide, the molar amount of which was equal to the acid value. Thus, an aqueous solution of acrylic resin 1 with a content of 20.0% was prepared.

[0117] (Acrylic resin 2)

[0118] Acrylic resin 2 was synthesized by copolymerizing 80.7 parts styrene and 19.3 parts acrylic acid using conventional methods. Acrylic resin 2 is a water-soluble resin with an acid value of 150 mg KOH / g and a number-average molecular weight of 1,600. The resulting acrylic resin 2 was dissolved in ion-exchanged water by adding potassium hydroxide, the molar amount of which was equal to the acid value. Thus, an aqueous solution of acrylic resin 2 with a content of 20.0% was prepared.

[0119] <Preparation of Pigment Dispersion>

[0120] (Pigment Dispersion 1)

[0121] A mixture of 15.0 parts carbon black (pigment), 30.0 parts an aqueous solution of acrylic resin 1, and 55.0 parts water was loaded into a sand mill and dispersed for 1 hour. Then, it was centrifuged to remove coarse particles, and the residue was filtered under pressure using a microfilter with a pore size of 3.0 μm (manufactured by FUJIFILM Corporation). An appropriate amount of deionized water was then added. This yielded pigment dispersion 1. Pigment dispersion 1 contained 10.0% pigment and 3.0% resin.

[0122] (Pigment Dispersion 2)

[0123] Except for changing the type of pigment to CI Pigment Blue 15:3, pigment dispersion 2 was obtained through the same steps as the preparation of pigment dispersion 1. Pigment dispersion 2 contained 10.0% pigment and 3.0% resin.

[0124] (Pigment Dispersion 3)

[0125] Except for changing the pigment type to CI Pigment Red 122, pigment dispersion 3 was obtained through the same steps as the preparation of pigment dispersion 1. Pigment dispersion 3 contains 10.0% pigment and 3.0% resin.

[0126] (Pigment Dispersion 4)

[0127] Except for changing the pigment type to CI Pigment Yellow 74, pigment dispersion 4 was obtained through the same steps as the preparation of pigment dispersion 1. Pigment dispersion 4 contains 10.0% pigment and 3.0% resin.

[0128] (Pigment Dispersion 5)

[0129] A solution obtained by dissolving 2.5g of concentrated hydrochloric acid in 5.5g of water was cooled to 5°C, and then 0.7g of 4-aminophthalic acid was added to it at this temperature. The container holding the solution was placed in an ice bath. While maintaining the temperature of the solution below 10°C by stirring, a solution obtained by dissolving 0.9g of sodium nitrite in 9.0g of ion-exchanged water at 5°C was added. After stirring the mixture for 15 minutes, 10.0g of carbon black (specific surface area: 220m²) was added while stirring. 2 / g, DBP oil absorption: 105mL / 100g), and further stirred the mixture for 15 minutes to obtain a slurry. The resulting slurry was filtered through filter paper (product name: "STANDARD FILTER PAPER No.2", manufactured by Advantec Corporation), and the particles were thoroughly washed with water and dried in an oven at 110°C. Then, sodium ions were replaced with potassium ions by ion exchange. Thus, a self-dispersible pigment with -C6H3-(COOK)2 groups bonded to the surface of carbon black particles was obtained. An appropriate amount of water was added to adjust the pigment content. Thus, a pigment dispersion 5 with a pigment content of 10.0% was obtained.

[0130] Synthesis of Resin Particles

[0131] (Resin particles 1-5)

[0132] A mixture was prepared by mixing 2.0 parts of n-hexadecane, 1.0 part of polymerization initiator (2,2'-azobis-(2-methylbutyronitrile)), and the core monomers shown in Table 1 (unit: parts) and stirring for 30 minutes. The monomer abbreviations have the following meanings: nBA represents n-butyl acrylate; St represents styrene; and AA represents acrylic acid. The resulting mixture was added dropwise to 229.5 parts of water in which 0.27 parts of sodium dodecyl sulfate were dissolved, and the mixture was stirred for 30 minutes to provide a core monomer mixture. The core monomer mixture was then ultrasonically homogenized using an ultrasonic homogenizer (product name: "S-150DDIGITAL SONIFIER", manufactured by Branson Ultrasonics Corporation) at 400W output, 20kHz frequency, and for 3 hours to disperse the components. The dispersed product was then polymerized at 80°C for 4 hours under a nitrogen atmosphere to synthesize a resin. Thus, a dispersion of an acrylic resin containing a core as resin particles was obtained.

[0133] Next, 200.0 parts of deionized water, 0.1 parts of potassium persulfate, 8.0 parts of sodium dodecyl sulfate, and the shell monomers (unit: parts) shown in Table 1 were emulsified to provide a monomer emulsion product for the shell. The monomer abbreviations have the following meanings: MMA represents methyl methacrylate; nBA represents n-butyl acrylate; St represents styrene; AA represents acrylic acid; and StSA represents styrene sulfonic acid. 0.1 parts of potassium persulfate and 600.0 parts of deionized water were added to 240.0 parts of a pre-prepared dispersion containing the resin used as the core, and the mixture was heated to 75°C under a nitrogen atmosphere. 350.0 parts of the monomer emulsion product for the shell were added dropwise to the dispersion over 3 hours. The mixture was then heated to 85°C and stirred for 2 hours to allow the monomers to polymerize. Thus, an acrylic resin used as the shell of the resin particles was synthesized. The resin was then cooled to 25°C, and an appropriate amount of deionized water and potassium hydroxide with a molar amount equal to the acid value of the resin were added. Thus, a liquid containing resin particles 1 to 5, each having a pH of 8.5 and a resin content of 10.0%, is obtained. Each of the resin particles 1 to 5 comprises a core and a shell.

[0134] Table 1: Synthesis conditions and characteristics of resin particles 1 to 5

[0135]

[0136] (Resin Particles 6)

[0137] 9.0 parts styrene, 1.5 parts acrylic acid, 0.1 parts sodium dodecyl sulfate, and 100.0 parts distilled water were mixed in a 300 mL four-necked flask containing a stirring seal, a stirrer, a reflux condenser, a rubber septum, and a nitrogen inlet tube. The flask was placed in a thermostat at 70 °C. While stirring the contents at 300 rpm, nitrogen was introduced into the flask to purge its interior for 1 hour. Then, potassium persulfate dissolved in 100.0 parts distilled water was injected into the flask using a syringe to initiate polymerization. The termination of polymerization was identified by monitoring the molecular weight of the resulting polymer using gel permeation chromatography. After purifying the polymer by ultrafiltration, an appropriate amount of ion-exchanged water and a molar amount of potassium hydroxide equal to the polymer's acid value were added to provide a liquid containing resin particles 6 with a pH of 8.5 and a resin content of 10.0%. Resin particles 6 are monolayer resin particles containing acrylic resin.

[0138] (Resin particles 7)

[0139] According to the description in Preparation Example 10 of Japanese Patent Application Publication No. 2017-019990, acrylic-organosilicon polymer fine particles were synthesized as resin particles 7, and a liquid in which the content of resin particles 7 was 40.0% was obtained.

[0140] Synthesis of Polyurethane Resins

[0141] Prepare a four-necked flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux tube. Add the polyisocyanate, a polyol without acid groups, one part (a) of dimethylolpropionic acid (types and amounts shown in Table 2), and 200.0 parts of methyl ethyl ketone to the four-necked flask. Then, allow the contents to react with each other at 80°C for 6 hours under a nitrogen atmosphere. Next, add another part (b) of dimethylolpropionic acid, ethylenediamine (chain extender), and methanol (terminating agent) (types and amounts shown in Table 2), and 100.0 parts of methyl ethyl ketone to the result. Determine the residual ratio of isocyanate groups by FT-IR, and allow the contents to react with each other at 80°C until the desired residual ratio is obtained. This yields a reaction solution. Cool the resulting reaction solution to 40°C, and then add deionized water. While stirring the mixture at high speed with a homogenizer, add an appropriate amount of deionized water and potassium hydroxide (molar amount equal to the acid value of the resin) to provide liquid. Methyl ethyl ketone was evaporated from the resulting liquid under reduced pressure during heating. This yielded a liquid containing water-soluble polyurethane resins 1 to 7, each comprising 20.0% of the polyurethane resin content. All of the resulting polyurethane resins 1 to 7 are water-soluble. The abbreviations in Table 2 have the following meanings: IPDI represents isophorone diisocyanate; HDI represents hexamethylene diisocyanate; MDI represents diphenylmethane diisocyanate; PPG represents polypropylene glycol with a number average molecular weight of 2,000; and PTMG represents polytetramethylene glycol with a number average molecular weight of 2,000.

[0142] Hydrochloric acid was added to each liquid containing polyurethane resin to precipitate the polyurethane resin. The resin was dried and dissolved in deuterated DMSO to prepare the measurement sample. Then, by... 13 The prepared samples were analyzed by C-NMR (equipment name: "Avance 500", manufactured by BRUKER BioSpin Corporation). The peak integral value of the carbonyl carbon originating from a unit of a polyol having an acidic group present at the molecule's end was then calculated as a ratio to the sum of the peak integral values ​​of the carbonyl carbon originating from units of polyols having acidic groups. This calculated value (ratio) is defined as "the proportion of units originating from polyols having acidic groups present at the molecule's end". For example, when dimethylolpropionic acid was used, a peak of the carbonyl carbon originating from a unit of a polyol having an acidic group present at the molecule's end was detected at approximately 176 ppm, although some deviations may occur depending on the measurement conditions. Furthermore, a peak of the carbonyl carbon originating from a unit of a polyol having an acidic group present in the molecule's end was detected at approximately 175 ppm. The results are respectively shown in Table 2 as "Terminal Acid Group Ratio (mol%)".

[0143] Table 2: Synthesis conditions and properties of polyurethane resins

[0144]

[0145] <Preparation of Surfactants>

[0146] (surfactants S1 to S5 and S8 to S16)

[0147] Polysiloxane and polyoxyethylene compounds were placed in a glass container including a thermometer and a stirring unit. The compounds were subjected to an addition reaction in the presence of a platinum catalyst to synthesize surfactants S1 to S5 and S8 to S16 respectively. As the aforementioned polysiloxane compounds, each was represented by the following general formula (A-1), wherein "m" and "n" in general formula (A-1) each represent the numbers shown in Table 3. Furthermore, as the aforementioned polyoxyethylene compounds, each was represented by the following general formula (B-1), wherein "a", R1, and R2 in general formula (B-1) each represent the numbers or structures shown in Table 3. The surfactants obtained by the above synthesis were each represented by the following general formula (1-1), wherein R3 in general formula (1-1) represents the structure shown in Table 3. In general formula (1-1), “m”, “n”, “a” and R2 correspond to “m”, “n”, “a” and R2 in general formulas (A-1) and (B-1) representing the structures of the compounds used in the synthesis, respectively. The weight-average molecular weights of the corresponding surfactants are also shown in Table 3.

[0148]

[0149] Table 3: Synthesis conditions and properties of surfactants S1 to S5 and S8 to S16

[0150]

[0151] (Surfactant S6)

[0152] A polysiloxane compound represented by the following general formula (C) and a polyoxyethylene compound represented by the following general formula (D) were placed in a glass container including a thermometer and a stirring unit. The compounds were subjected to an addition reaction in the presence of a platinum catalyst to synthesize surfactant S6. Surfactant S6 has the structure of a bi-terminated modified organosilicon compound represented by general formula (4). In general formula (4), “d”, “p”, “R6”, and “R5” correspond to “d”, “p”, “R4”, and “R5” in general formulas (C) and (D) representing the structures of the compounds used in the synthesis, respectively. “d” is 10, “p” is 5, R6 represents propylene, R5 represents methyl, and R4 represents propyl.

[0153]

[0154]

[0155] (Surfactant S7)

[0156] A polysiloxane compound represented by the following general formula (E) and a polyoxyethylene compound represented by the following general formula (F) were placed in a glass container including a thermometer and a stirring unit. The compounds were subjected to an addition reaction in the presence of a platinum catalyst to synthesize surfactant S7. Surfactant S7 has the structure of an ABn type organosilicon compound represented by general formula (5). In general formula (5), “e”, “q”, “R7”, and “R9” correspond to “e”, “q”, “R7”, and “R8” in general formulas (E) and (F) representing the structures of the compounds used in the synthesis, respectively. “e” is 10, “q” is 5, “r” is 2, R7 represents methyl, R9 represents propylene, and R8 represents propyl.

[0157]

[0158] (surfactant F1)

[0159] Prepare and use a fluorinated surfactant, which is available under the product name "MEGAFACE F-410" (manufactured by DICCorporation), as surfactant F1.

[0160] (surfactants C1 to C7)

[0161] Surfactants C1 to C6 are acetylenic diol compounds and surfactant C7 is a polyoxyethylene alkyl ether. Surfactants C1 to C3 and C5 are each acetylenic diol compounds represented by general formula (2).

[0162] Surfactant C1: Product name: “ACETYLENOL E60” (in general formula (2), b+c=6, manufactured by Kawaken Fine Chemicals Co., Ltd.)

[0163] Surfactant C2: Product name: “ACETYLENOL E40” (in general formula (2), b+c=4, manufactured by Kawaken Fine Chemicals Co., Ltd.)

[0164] Surfactant C3: Product name: “ACETYLENOL E100” (in general formula (2), b+c=10, manufactured by Kawaken Fine Chemicals Co., Ltd.)

[0165] Surfactant C4: Product name: “SURFYNOL 104” (in general formula (2), b = c = 0, manufactured by Nissin Chemical Industry Co., Ltd.)

[0166] Surfactant C5: Product name: "OLFINE E1010" (in general formula (2), b+c=10, manufactured by Nissin Chemical Industry Co., Ltd.)

[0167] Surfactant C6: Ethoxylated form of 2,4,7,9-tetramethyl-5-decyn-4,7-diol (in general formula (2), b+c = 50)

[0168] Surfactant C7: Product Name: "NIKKOL BC-20" (Polyoxyethylene cetyl ether, manufactured by Nikko Chemicals Co., Ltd.)

[0169] <Preparation of Compounds>

[0170] Siloxane compounds were synthesized by conventional methods to obtain compounds 1 to 6, each represented by general formula (3), wherein “o” in general formula (3) represents a number shown in Table 4 below.

[0171] Table 4: Structure of the compounds

[0172] 1 5 2 0 3 1 4 10 5 11 6 8

[0173] <Ink Preparation>

[0174] (Ink 1 to 67)

[0175] The components (unit: %) shown in the middle sections of each of Tables 5 (Tables 5-1 to 5-10) were mixed and thoroughly stirred. The mixture was then filtered under pressure using a microfilter (manufactured by FUJIFILM Corporation) with a pore size of 3.0 μm to prepare various inks. The materials whose numbers are shown in the upper section of each of Tables 5 are respectively used as “pigment dispersion,” “liquid containing resin particles,” “aqueous solution of polyurethane resin,” “surfactant S,” “surfactant C,” and “compound” shown in the middle section of each of Tables 5. However, the symbol “-” in the upper section of Table 5 indicates that the corresponding material was not used. The values ​​in parentheses attached to the water-soluble organic solvents in the middle section of each of Tables 5 represent the relative permittivity at 25°C. The amount of ion-exchanged water used was set such that the total amount of components was 100.00% of the margin. The pigment content P (%), resin particle content R (%), and particulate component content C (%) in each ink are shown as characteristics of the ink in the lower section of each of Tables 5. Similarly, the contents of the first surfactant (any one of surfactants S1 to S5, S15 and S16), A (%) of the second surfactant (any one of surfactants C1 to C6), and T (%) of the surfactants (any one or two of surfactants S1 to S16, F1 and C1 to C7) in each ink are shown. Similarly, the contents of the compound represented by general formula (3) (compound 1, 3, 4 or 6), the value of the ratio "S / A" (times), the value of the ratio "C / T" (times), and the value of the ratio "D / S" (times) in each ink are shown.

[0176] Table 5-1: Composition and Properties of Ink

[0177]

[0178] Table 5-2: Composition and Properties of Ink

[0179]

[0180] Table 5-3: Composition and Properties of Ink

[0181]

[0182] Table 5-4: Composition and Properties of Ink

[0183]

[0184] Table 5-5: Composition and Properties of Ink

[0185]

[0186] Table 5-6: Composition and Properties of Ink

[0187]

[0188] Table 5-7: Composition and Properties of Ink

[0189]

[0190] Table 5-8: Composition and Properties of Ink

[0191]

[0192] Table 5-9: Composition and Properties of Ink

[0193]

[0194] Table 5-10: Composition and Properties of Ink

[0195]

[0196] (Ink 68)

[0197] The following components were mixed and stirred thoroughly, and then filtered under pressure using a microfilter with a pore size of 3.0 μm (manufactured by FUJIFILM Corporation). This yielded Ink 68, an ink free of a second surfactant.

[0198] • Pigment dispersion 1:15.00%

[0199] • Aqueous solution of acrylic resin 2: 32.00%

[0200] Dipropylene glycol: 3.00%

[0201] ·1,2-Hexanediol: 0.50%

[0202] ·1,2-Octanediol: 1.00%

[0203] Surfactant S1: 0.10%

[0204] • Ion-exchanged water: 48.40%

[0205] (Ink 69)

[0206] The following components were mixed and stirred thoroughly, and then filtered under pressure using a microfilter with a pore size of 3.0 μm (manufactured by FUJIFILM Corporation). Thus, ink 69, which is an ink without a second surfactant, was prepared.

[0207] • Pigment dispersion 1:15.00%

[0208] • Liquid containing resin particles 7: 8.75%

[0209] 3-Ethyl-3-hydroxymethyloxetane: 30.00%

[0210] • Propylene glycol monomethyl ether: 10.00%

[0211] 2-Ethyl-1,3-hexanediol: 2.00%

[0212] ·2,4,7,9-Tetramethyldecane-4,7-diol: 0.50%

[0213] ·2-Amino-2-ethyl-1,3-propanediol: 0.20%

[0214] Surfactant S15: 2.00%

[0215] • Ion-exchanged water: 31.55%

[0216] (Ink 70)

[0217] The following components were mixed and stirred thoroughly, and then filtered under pressure using a microfilter (manufactured by FUJIFILM Corporation) with a pore size of 3.0 μm. This yielded ink 70, which is an ink free of the first surfactant.

[0218] • Pigment dispersion 1:15.00%

[0219] • Glycerin: 10.00%

[0220] Ethylene glycol: 20.00%

[0221] • Triethylene glycol monobutyl ether: 15.00%

[0222] Surfactant C5: 0.60%

[0223] • Ion-exchanged water: 39.40%

[0224] (Ink 71)

[0225] The following components were mixed and stirred thoroughly, and then filtered under pressure using a microfilter with a pore size of 3.0 μm (manufactured by FUJIFILM Corporation). This yielded Ink 71, an ink without a second surfactant. KF-353A is a side-chain silicone oil (product name, manufactured by Shin-Etsu Chemical Co., Ltd.).

[0226] • Pigment dispersion 1:15.00%

[0227] • Glycerin: 20.00%

[0228] ·1,2-Hexanediol: 10.00%

[0229] Triethanolamine: 0.90%

[0230] KF-353A: 0.10%

[0231] • Ion-exchanged water: 54.00%

[0232] (Ink 72)

[0233] The following components were mixed and thoroughly stirred, and then filtered under pressure using a microfilter with a pore size of 3.0 μm (manufactured by FUJIFILM Corporation). This yielded Ink 72, an ink free of particulate components.

[0234] • Cibafix Direct Black 19 (manufactured by Ciba-Geigy Japan Ltd.): 5.00%

[0235] • Glycerin: 15.00%

[0236] Propylene glycol: 0.05%

[0237] • Polyethylene glycol (number average molecular weight 200): 10.00%

[0238] Surfactant S16: 0.40%

[0239] Surfactant C6: 0.50%

[0240] Compound 6: 0.0025%

[0241] • Ion-exchanged water: 69.0475%

[0242] <Evaluation>

[0243] The following evaluations were conducted using the prepared inks. The evaluation results are shown in Table 6.

[0244] (Storage stability)

[0245] The surface tension (static surface tension) of each of the inks obtained above was measured. The surface tension of the inks was measured at 25°C using a Wilhelmy surface tension meter (product name: "Automatic Surface Tensiometer CBVP-Z", manufactured by Kyowa Interface Science Co., Ltd.). Each ink was placed in a sealed container and stored in an oven at 70°C for one week. The storage stability of the inks was evaluated by subtracting the surface tension of the ink before storage from the surface tension value of the ink after storage, according to the following evaluation criteria.

[0246] A: The difference in surface tension is less than 1.0 mN / m.

[0247] B: The difference in surface tension is greater than 1.0 mN / m and less than 2.0 mN / m.

[0248] C: The difference in surface tension is greater than 2.0 mN / m.

[0249] (Inhibition of fog formation)

[0250] The inks prepared as described above are each loaded into ink cartridges and placed in an inkjet recording device (product name: "TM-300", manufactured by Canon Inc., described as "heat" in the "Ejection System" item in Table 6) where ink is ejected from the recording head by thermal energy. In embodiments of the invention, a recording task of recording a solid image is defined as 100% under the following conditions: four ink droplets, each with a mass of 4.0 ng ± 5%, are applied to a unit area of ​​1 / 600 inch by 1 / 600 inch. In each of Reference Examples 1 and 2, an inkjet recording device is used that ejects ink from the recording head using a piezoelectric element (product name: "SC-T5255", manufactured by SeikoEpson Corporation; described as "piezoelectric" in the "Ejection System" item in Table 6). Solid images measuring 36 inches × 48 inches, representing 30% of the recording task, were recorded onto heavyweight coated paper (product name: "Heavyweight Coated Paper HG", manufactured by Canon Inc.) using the inkjet recording devices described above. The suppression effect on fog formation was then evaluated according to the following criteria. Recording was stopped when the device's sensors detected an error during continuous recording in foggy conditions. Therefore, a higher number of records that can be successfully recorded indicates a greater suppression effect on fog formation.

[0251] AA: Recording can be performed normally even when the number of records exceeds 50,000.

[0252] A: Stop recording during a time period when the number of records is between 40,000 and 50,000.

[0253] B: Stop recording during a time period when the number of records is more than 30,000 but less than 40,000.

[0254] C: Stop recording when the number of records is less than 30,000.

[0255] Table 6: Evaluation Criteria and Evaluation Results

[0256]

[0257] According to the present invention, a water-based ink that suppresses fogging and exhibits excellent storage stability can be provided. Furthermore, according to the present invention, ink cartridges and inkjet recording methods using the water-based ink can be provided respectively.

[0258] While the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to cover all such modifications and equivalent structures and functions.

Claims

1. An aqueous ink which is ejected from a recording head of an inkjet system by the action of thermal energy, characterized in that, The water-based ink comprises: Particulate components; The first surfactant; and The second surfactant, The particulate component comprises at least one selected from the group consisting of pigments and resin particles. The first surfactant comprises a compound represented by the following general formula (1), and The second surfactant contains an acetylene glycol compound: In general formula (1), "m" and "n" each independently represent integers above 1 and satisfy the relationship m+n≤10, and "a" represents integers above 10 and below 20.

2. The aqueous ink according to claim 1, wherein In the water-based ink, the mass ratio of the content of the first surfactant (in mass%) to the content of the second surfactant (in mass%) is more than 0.05 times and less than 3.00 times.

3. The water-based ink according to claim 1, wherein In the water-based ink, the mass ratio of the content of the first surfactant (in mass%) to the content of the second surfactant (in mass%) is more than 0.05 times and less than 2.00 times.

4. The water-based ink according to claim 1, The water-based ink further comprises: First water-soluble organic solvents with a relative permittivity of 28.0 or less; and A second water-soluble organic solvent with a relative permittivity of 40.0 or higher, and The first water-soluble organic solvent is an alkanediol having hydroxyl groups at both ends of the hydrocarbon chain.

5. The water-based ink according to claim 1, The aqueous ink further comprises a compound represented by the following general formula (3), and wherein In the water-based ink, the mass ratio of the compound represented by the general formula (3) to the content of the first surfactant (in mass percentage) is less than 0.01 times: In the general formula (3), "o" represents an integer greater than 1 and less than 10.

6. The water-based ink according to claim 1, wherein the particulate component comprises pigment.

7. The water-based ink according to claim 1, wherein the particulate component comprises the resin particles, and The resin particles comprise a core formed only of units without acid groups and a shell formed of units containing acid groups, and at least one of the units for forming the core and the units for forming the shell comprises units derived from (meth)acrylates.

8. The water-based ink according to claim 1, The water-based ink further comprises a polyurethane resin, and The polyurethane resin described herein has units derived from polyisocyanates, units derived from polyols without acid groups, and units derived from polyols with acid groups.

9. The water-based ink according to claim 8, wherein in the polyurethane resin, the proportion of units derived from polyols having acid groups present at the molecular ends to all units derived from polyols having acid groups is 30 mol% or less.

10. An ink cartridge comprising: ink; and An ink storage section is configured to store the ink. The ink is characterized in that it comprises the water-based ink according to claim 1.

11. An inkjet recording method, comprising ejecting ink from a recording head of an inkjet system by means of thermal energy to record an image on a recording medium, characterized in that, The ink comprises the water-based ink according to claim 1.

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