Aqueous ink, ink cartridge, and inkjet recording method

Abstract

Provided is an aqueous ink which is capable of suppressing deterioration of filterability even when microorganisms are present in the aqueous ink, and which has good ejection stability by a recording head even when applied to an inkjet aqueous ink.　Specifically provided is an aqueous ink which contains a coloring material, a quorum sensing (QS) inhibitor, and water. The QS inhibitor is at least one compound that is selected from the group consisting of aromatic amide compounds, furanone compounds, phenol compounds, histidine compounds, pyrimidine compounds, sugar ester compounds, lactam compounds, thiohydantoin compounds, and thiazolidinedione compounds. The QS inhibitor has a common logarithm Log S of the solubility in water at 25°C of -2.2 or more. The content of water in the ink is 50.00 mass% or more based on the total mass of the aqueous ink.

Description

Water-based ink, ink cartridge, and inkjet recording method

[0001] The present invention relates to a water-based ink, an ink cartridge, and an inkjet recording method.

[0002] Inks generally used for office equipment and printing purposes are designed to remove contaminants such as dust, and are finished into final products by passing through filters. In the case of water-based inks, unlike non-aqueous inks, microorganisms may grow in the ink. And when there are many biofilms produced by microorganisms growing in the ink, the property of the ink passing through the filter (hereinafter referred to as "filterability") may decrease. As a result, it may cause a decrease in the productivity of the ink. To avoid this problem, biocides are contained in the ink to suppress the growth of microorganisms (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2018-522956

[0004] However, due to recent regulations on biocides, the allowable amount of biocides contained in inks tends to decrease. As a result, the growth of microorganisms may not be completely suppressed, and furthermore, biofilms may not be suppressed.

[0005] Therefore, an object of the present invention is to suppress a decrease in filterability even when microorganisms are present in the water-based ink, and also to provide a water-based ink with good ejection stability by a recording head even when applied to a water-based ink for inkjet. Another object of the present invention is to provide an ink cartridge and an inkjet recording method using the above water-based ink.

[0006] In other words, the present invention provides an aqueous ink containing a colorant, a quorum sensing inhibitor, and water, wherein the quorum sensing inhibitor is at least one compound selected from the group consisting of aromatic amide compounds, furanone compounds, phenol compounds, histidine compounds, pyrimidine compounds, sugar ester compounds, lactam compounds, thiohydantoin compounds, and thiazolidinedione compounds, and the common logarithm LogS of its solubility in water at 25°C is -2.2 or higher, and the water content is 50.00% by mass or more based on the total mass of the aqueous ink.

[0007] According to the present invention, even when microorganisms are present in the aqueous ink, a decrease in filterability can be suppressed, and even when applied to aqueous ink for inkjet applications, an aqueous ink with good ejection stability by the recording head can be provided. Furthermore, according to the present invention, an ink cartridge using the above aqueous ink and an inkjet recording method can be provided.

[0008] This is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. This is a perspective view of the main part of an inkjet recording device used in the inkjet recording method of the present invention. This is a perspective view of the head cartridge of an inkjet recording device used in the inkjet recording method of the present invention.

[0009] The present invention will be further described in detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, water-based ink for inkjet applications may be simply referred to as "ink." Unless otherwise specified, physical properties are given at room temperature (25°C), normal pressure (1 atmosphere = 101,325 Pa), and normal humidity (50% relative humidity). In addition, "unit" in resins, polymers, and copolymers, unless otherwise specified, refers to the unit structure corresponding to one monomer. When "(meth)acrylic acid" or "(meth)acrylate" is written, it refers to "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0010] The inventors investigated the filterability of an aqueous ink using pigments as a coloring agent (hereinafter sometimes referred to as aqueous pigment ink) after reducing the amount of biocide to a level generally found in conventional inks and allowing microorganisms to proliferate in the ink. As a result, no particular problems occurred immediately after preparing the aqueous pigment ink. However, when the aqueous pigment ink was stored for about a month without filtration and then filtered, a tendency was observed for the filterability to decrease as the biocide content decreased. The inventors' analysis of the filter revealed that the cause of the decreased filterability was biofilm. From this, the inventors surmise that the reduction in biocide content allowed microorganisms to proliferate during ink storage, and that these proliferated microorganisms produced biofilm. Next, the aqueous pigment ink from which the biofilm and microorganisms suspended in the ink had been removed by filtration was ejected from an inkjet recording head. As a result, no problems occurred immediately after preparing the aqueous pigment ink. However, it was found that when the water-based pigment ink was ejected from the recording head again after being left for about a month, the ink flow path became blocked, causing ejection failure. The inventors investigated the reason why biofilm reappeared when the ink was stored, even though the biofilm and microorganisms floating in the ink had been removed, and found the following: Microorganisms that have the characteristic of oriented towards the interface exist in the form of adsorption on the surface of pigment particles, so even if the water-based pigment ink was filtered, it was not possible to completely remove the microorganisms. As a result, it was found that during the process of storing the water-based pigment ink, biofilm was produced from the microorganisms adsorbed on the surface of the pigment particles, and this clogged the filter of the liquid passage in the recording head. In other words, it was found that when using water-based pigment ink for inkjet applications, it is difficult to improve ejection stability unless the microorganisms adsorbed on the surface of the pigment are completely sterilized, or unless the ink has a function that prevents the production of biofilm even if microorganisms are present. However, as mentioned above, in recent years, the amount of biocides contained in water-based inks has had to be reduced due to regulations.In other words, it is extremely difficult to maintain a state free of microorganisms when storing water-based ink for a long period of time. Therefore, the inventors proceeded with their research based on a new idea: even if microorganisms are present, it is sufficient to prevent them from producing the problematic biofilm. As a result, the inventors found that the above problem can be solved by incorporating a quorum sensing inhibitor, which can suppress the production of biofilm even in the presence of microorganisms, into the water-based ink.

[0011] Next, we will explain how incorporating a quorum sensing inhibitor into an aqueous pigment ink can suppress the production of biofilms, even if microorganisms are present. Microorganisms produce biofilms by transmitting self-inducing substances to other microorganisms. A quorum sensing inhibitor is a material that blocks or captures self-inducing substances, preventing their transmission to other microorganisms. Therefore, the inventors hypothesize that incorporating a quorum sensing inhibitor into an aqueous pigment ink can suppress the production of biofilms, even if microorganisms are present. Furthermore, the quorum sensing inhibitor is at least one compound selected from the following group, and its common logarithm of solubility in water at 25°C (LogS) is -2.2 or higher. That is, the above group of compounds consists of aromatic amide compounds, furanone compounds, phenol compounds, histidine compounds, pyrimidine compounds, sugar ester compounds, lactam compounds, thiohydantoin compounds, and thiazolidinedione compounds. The inventors have found that by using the above-mentioned quorum sensing inhibitor, it can fully exhibit its function as a quorum sensing inhibitor even in aqueous ink. While the inclusion of the above-mentioned compound in ink has been proposed before, it has been used for other purposes and not as a quorum sensing inhibitor. For example, Japanese Patent Publication No. 2007-100018 describes the inclusion of sucrose fatty acid ester, a sugar ester compound, in an oil-based marking pen ink composition. However, in this patent document, sucrose fatty acid ester is used to improve the drying resistance of the pen tip, and there is no disclosure regarding its use as a quorum sensing inhibitor. Furthermore, oil-based marking pen ink compositions contain a high amount of organic solvent, creating conditions where microorganisms cannot easily survive, thus preventing problems caused by biofilms.

[0012] <Water-based ink> As described above, water-based ink contains a colorant, a quorum sensing inhibitor, and water. Water-based ink is preferably for inkjet use. The components that make up water-based ink will be described in detail below.

[0013] (Quorum Sensing Inhibitors) Quorum sensing inhibitors are compounds that inhibit quorum sensing in microorganisms. This can suppress the formation of biofilms by microorganisms such as bacteria.

[0014] The following compounds are used as quorum sensing inhibitors: at least one compound selected from the group consisting of aromatic amide compounds, furanone compounds, phenol compounds, histidine compounds, pyrimidine compounds, sugar ester compounds, lactam compounds, thiohydantoin compounds, and thiazolidinedione compounds. One or more of these quorum sensing inhibitors can be used. According to the inventors' studies, quorum sensing inhibitors other than the above compounds could not sufficiently suppress the production of biofilm in aqueous ink. Furthermore, the quorum sensing inhibitor must be a compound with a common logarithm of solubility in water at 25°C (LogS) of -2.2 or higher. This is because, in order to exert its effect as a quorum sensing inhibitor in aqueous ink, it is necessary to dissolve it in water, which is the solvent of the aqueous ink. By using a water-soluble quorum sensing inhibitor, the quorum sensing inhibitor can move more easily through the aqueous ink, thereby blocking or capturing self-inducing factors released by microorganisms. If the quorum sensing inhibitor is a compound with a common logarithm of its solubility in water at 25°C (LogS) of -2.3 or less, the efficiency of blocking or capturing self-inducing factors released by microorganisms will be drastically reduced. Therefore, in this case, if microorganisms are present in the aqueous ink, the production of biofilm cannot be sufficiently suppressed. The above LogS of the quorum sensing inhibitor is the common logarithm of the amount (solubility) S (g / 100g) of the quorum sensing inhibitor that dissolves in 100g of water at 25°C and pH 7. When using two or more compounds selected from the above group as quorum sensing inhibitors, it is sufficient that the above LogS of at least one compound is -2.2 or higher, but preferably the above LogS of each compound is -2.2 or higher. When the colorant of the aqueous ink is a pigment, aromatic amide compounds are preferred among the above compounds that can be used as quorum sensing inhibitors. In aqueous inks, aromatic amide compounds have a δ+ charge and tend to be present near pigments that have a δ- charge, resulting in microorganisms in the pigment and quorum sensing inhibitors being in close proximity.As a result, it is believed that the blocking or capture of self-inducing factors released by microorganisms is promoted, further suppressing the production of biofilms. For this reason, the quorum sensing inhibitor preferably contains an aromatic amide compound, and more preferably is an aromatic amide compound.

[0015] Examples of aromatic amide compounds include benzamide, bromobenzamide, hydroxybenzamide, aminobenzamide (2-aminobenzamide, 3-aminobenzamide, and 4-aminobenzamide), nitrobenzamide, nicotinamide, and pyrazineamide. One or more of these aromatic amide compounds can be used.

[0016] Examples of furanone compounds include furanone, methylfuranone (e.g., 5-methyl-2-furanone and 5-methyl-3-furanone), methoxyfuranone (e.g., 4-methoxy-2-furanone), dimethylfuranone (e.g., 2,5-dimethyl-3-furanone, 3,4-dimethyl-2-furanone, and 5,5-dimethyl-2-furanone), and bromofuranone. One or more of these furanone compounds can be used.

[0017] Examples of phenol compounds include vanillin, vanillic acid, and pyrogallol. One or more of these phenol compounds can be used. Examples of histidine compounds include histidine. Examples of pyrimidine compounds include pyrimidine.

[0018] Examples of sugar ester compounds include sucrose laurate, sucrose myristic acid, sucrose palmitate, and sucrose oleate. One or more of these sugar ester compounds can be used.

[0019] Examples of lactam compounds include pterolactam. Examples of thiohydantoin compounds include 2-thiohydantoin. Examples of thiazolidinedione compounds include thiazolidinedione.

[0020] The content (by mass%) of the quorum sensing inhibitor in the aqueous ink is preferably 0.02% by mass or more and 4.00% by mass or less, based on the total mass of the aqueous ink. When the content (by mass%) of the quorum sensing inhibitor in the aqueous ink is 0.02% by mass or more, quorum sensing by microorganisms can be sufficiently captured, and the effect of suppressing biofilm production can be further improved. Furthermore, when the content of the quorum sensing inhibitor in the aqueous ink is 4.00% by mass or less, the quorum sensing inhibitor can be sufficiently dissolved in the aqueous ink, and the decrease in filterability due to the quorum sensing inhibitor can be suppressed. In aqueous ink, the content of the quorum sensing inhibitor is preferably 0.025 times or more and 1.000 times or less by mass, relative to the content of the colorant. When the above mass ratio is 0.025 times or more, the quorum sensing inhibitor is more likely to exert an inhibitory effect on quorum sensing by microorganisms in the ink. On the other hand, if the above mass ratio is 1.000 times or less, it is easier to improve the dispersion stability of the pigment in the ink when using pigment as a colorant, and as a result, it is easier to suppress the increase in viscosity. The mass ratio of the quorum sensing inhibitor content to the colorant content can be determined by {mass of quorum sensing inhibitor / mass of colorant} (times) in the case of water-based ink. For the mass of the colorant and quorum sensing inhibitor, the respective mass-based usage amounts (parts by mass or mass %) of the colorant and quorum sensing inhibitor used when manufacturing water-based ink can be used.

[0021] (Colorants) As a colorant, at least one selected from the group consisting of pigments and dyes can be used. Among these, pigments are preferred from the viewpoint of lightfastness, and it is preferable that the colorant contains a pigment, and more preferably that it be a pigment. However, as mentioned above, in the case of pigments, microorganisms are easily adsorbed to the pigment, and it is difficult to remove microorganisms from the ink, so it is more difficult to improve the filterability and discharge stability of pigments than dyes. The content of colorants in water-based ink can be adjusted according to the application and form of the water-based ink.

[0022] Examples of dyes include direct dyes, acid dyes, basic dyes, disperse dyes, and food dyes. Among these, it is preferable to use dyes having anionic groups. Specific examples of dye skeletons include azo, triphenylmethane, phthalocyanine, azaphthalocyanine, xanthene, and anthrapyridone. Dyes may be used individually or in combination of two or more.

[0023] Specific examples of pigments include inorganic pigments and organic pigments. Examples of inorganic pigments include carbon black and titanium dioxide. Examples of organic pigments include azo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, isoindolinone pigments, imidazolon pigments, diketopyrrolopyrrole pigments, and dioxazine pigments. Among pigments, it is preferable to use condensed aromatic pigments. Condensed aromatic pigments are rich in π electrons and have a high negative charge, so it is thought that they can attract quorum sensing inhibitors, which are mostly positively charged materials, and thus suppress quorum sensing by microorganisms such as bacteria present near the pigment. For this reason, it is preferable that the pigment includes condensed aromatic pigments, and it is more preferable that the pigment is a condensed aromatic pigment. Specific examples of condensed aromatic pigments include phthalocyanine pigments, quinacridone pigments, and perylene pigments. The pigment may be used individually or in combination of two or more types. Furthermore, it is preferable that the pigment has been treated to sterilize and decompose any attached microorganisms or biofilms. Qualum sensing inhibitors are effective in suppressing the production of new biofilms, but they have little effect in removing microorganisms and biofilms that are already attached to the pigment. Therefore, by using pigments that have undergone sterilization and decomposition treatment, it is possible to reduce the amount of microorganisms and biofilms that are already attached to the pigment before preparing the water-based ink, thereby reducing the amount of microorganisms and biofilms that are introduced from the pigment into the water-based ink. Sterilization and decomposition treatment of pigments can be performed, for example, by immersing the pigment in an alkaline solution and heating it. As for the dispersion method of the pigment, resin-dispersed pigments using a resin (resin dispersant) as a dispersant, and self-dispersing pigments in which hydrophilic groups are bound to the surface of the pigment particles can be used. In addition, resin-bonded pigments in which organic groups containing resin are chemically bound to the surface of the pigment particles, and microcapsule pigments in which the surface of the pigment particles is coated with resin can be used. It is also possible to use a combination of pigments with different dispersion methods.As a resin dispersant for dispersing pigments in an aqueous medium, it is preferable to use a resin having anionic groups that can disperse pigments in an aqueous medium by the action of anionic groups. As a self-dispersing pigment, one can be used in which the anionic group is directly bonded to the particle surface of the pigment or via other atomic groups (-R-). Specific examples of other atomic groups (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene and naphthylene groups; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; ether groups, etc. Alternatively, combinations of these groups may also be used. Examples of the anionic groups mentioned in the descriptions of the resin dispersant, self-dispersing pigment, and dye include carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups. The anionic group may be either acidic or salt-type, and in the case of the salt-type, it may be in a partially dissociated state or a completely dissociated state. When the anionic group is in the salt form, examples of cations that become counterions include alkali metal cations, ammonium, and organic ammonium.

[0024] The content (mass%) of colorants in the aqueous ink is preferably 0.50% by mass or more and 15.00% by mass or less, more preferably 0.80% by mass or more and 12.00% by mass or less, and even more preferably 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the aqueous ink. (Resin) The ink may contain resin. Resin can be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary. It can also be added to the ink (ii) to improve various properties of the recorded image. The content (mass%) of resin in the aqueous ink is preferably 0.10% by mass or more and 20.00% by mass or less, and even more preferably 0.50% by mass or more and 15.00% by mass or less, based on the total mass of the aqueous ink. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may also be a water-soluble resin that can dissolve in an aqueous medium, or it may be resin particles dispersed in an aqueous medium. As the resin, a copolymer having units derived from each monomer is preferred, using two or more of the monomers listed below. Examples of the monomers include hydrophobic monomers and hydrophilic monomers. Examples of hydrophobic monomers include styrene monomers and (meth)acrylic acid esters. Examples of styrene monomers include styrene, α-methylstyrene, 4-methylstyrene, p-fluorostyrene, and p-chlorostyrene. Examples of (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and benzyl (meth)acrylate.Examples of hydrophilic monomers include hydrophilic monomers having a carboxyl group such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, and 4-vinylbenzoic acid; hydrophilic monomers having a sulfonic acid group such as styrene sulfonic acid, (meth)acrylic acid 2-sulfoethyl, and (meth)acrylamide t-butylsulfonic acid (also known as 2-(meth)acrylamide-2-methylpropanesulfonic acid); and hydrophilic monomers having a phosphonic acid group such as (meth)acrylic acid 2-phosphonoethyl (also known as 2-((meth)acryloyloxy)ethylphosphonic acid) and (meth)acrylic acid 2-phosphonooxyethyl (also known as 2-(meth)acryloyloxyethyl phosphoric acid). Among the above copolymers, copolymers having units derived from styrene monomers and units derived from (meth)acrylic acid monomers are preferred. Furthermore, it is preferable that the content of units derived from (meth)acrylic acid monomers in this copolymer is 20% by mass or more and 40% by mass or less based on the total mass of the copolymer. By having a copolymer content of 20% to 40% by mass of units derived from (meth)acrylic acid monomers, the resin is adsorbed appropriately onto the pigment, allowing for a large amount of quorum sensing inhibitors to be present near the pigment. This is presumed to make it easier for the quorum sensing inhibitors to capture self-inducing factor substances released by microorganisms present inside or on the surface of the pigment. Any of the styrene monomers listed above can be used as the styrene monomers that can be used in the copolymer. Furthermore, in this disclosure, (meth)acrylic acid monomers refer to polymerizable monomers that include (meth)acrylic acid and (meth)acrylic acid ester monomers. (Meth)acrylic acid ester monomers are polymerizable monomers having at least one of an acryloyloxy group and a methacryloyloxy group. As described above, by having a copolymer content of (meth)acrylic acid monomers in the copolymer within the range of 20% to 40% by mass, it is thought that the production of biofilms by microorganisms can be further suppressed. The resin is thought to have properties that make it easy to adsorb quorum sensing inhibitors.Therefore, in order to ensure that quorum sensing inhibitors are present near microorganisms on the surface of pigment particles, the resin (polymer) is preferably a resin dispersant. Furthermore, the weight-average molecular weight (Mw) of the resin dispersant is preferably 5,000 or more and 20,000 or less. By keeping the weight-average molecular weight (Mw) of the resin dispersant within the above range, the resin dispersant is adsorbed onto the pigment in an appropriate amount. As a result, the probability of microorganisms present on the surface of pigment particles and quorum sensing inhibitors that readily adsorb to resin being present in the vicinity increases, and the rate at which the quorum sensing inhibitor captures self-inducing factor substances released by microorganisms can be improved. The weight-average molecular weight of the resin dispersant can be taken as a value equivalent to standard polystyrene measured using gel permeation chromatography (GPC). In addition, the acid value (mgKOH / g) of the resin dispersant is preferably 80 mgKOH / g or more and 200 mgKOH / g or less. When the acid value of the resin dispersant is 80 mg KOH / g or higher, there are many water-soluble parts of the resin adsorbed onto the pigment, improving the dispersion stability of the pigment in the ink and making pigment aggregation less likely. As a result, it is possible to suppress the widening of the distance between microorganisms incorporated into the pigment aggregates and quorum sensing inhibitors that readily adsorb to the resin, creating a state where quorum sensing inhibitors are more likely to be present near the microorganisms. Furthermore, when the acid value of the resin dispersant is 200 mg KOH / g or lower, its strong hydrophobicity leads to a large amount of adsorption to the pigment, increasing the probability that microorganisms on the surface of the pigment particles and quorum sensing inhibitors that readily adsorb to the resin are present in close proximity. As a result, it is thought that the proportion of self-inducing factor substances released by microorganisms that are captured by quorum sensing inhibitors increases. The acid value of the resin dispersant can be measured using a potentiometric titrator with potassium hydroxide-methanol titration solution. The content of the resin dispersant in the aqueous ink is preferably 10% by mass or more and 50% by mass or less, based on the pigment content.

[0025] (Biocide) Water-based inks preferably contain a biocide. Among biocides, those with a common logarithm of solubility in water at 25°C (LogS) of -0.6 or higher are more preferable. When the common logarithm of solubility of the biocide in water at 25°C (LogS) is within the above range, the solubility of the biocide in water-based ink is improved, making it easier to exert an effect of suppressing the growth of microorganisms. The above LogS of the biocide is the common logarithm of the amount of biocide that dissolves in 100g of water at 25°C and pH 7 (solubility) S (g / 100g). A smaller LogS value indicates that it is less soluble in water. Biocides with a LogS of -0.6 or higher have the characteristics of being less adsorbed to colorants and less likely to aggregate with other biocides, making it easier to fully exert effects such as suppressing the production of biofilms and inhibiting the growth of microorganisms mixed into water-based inks.

[0026] Examples of biocides include thiazoline biocides, triazine biocides, morpholine biocides, paraben biocides, and methylbenzimidazole carbamate (MBC) biocides. One or more of these can be used.

[0027] Examples of thiazoline biocides include 1,2-benzoisothiazone-3-one. Examples of triazine biocides include hexahydro-1,3,5-triazine. Examples of morpholine biocides include morpholine. Examples of paraben biocides include methylparaben. Examples of MBC biocides include thiabendazole.

[0028] Among the biocides mentioned above, it is preferable to use a biocide containing at least one selected from the group consisting of thiazoline biocides, triazine biocides, and paraben biocides, from the viewpoint of being able to more easily suppress the growth of microorganisms, and it is more preferable to use a biocide containing at least one selected from the group consisting of thiazoline biocides and paraben biocides. In particular, it is preferable to use a biocide containing at least one selected from the group consisting of 1,2-benzoisothiazone-3-one (LogS = 0.3), hexahydro-1,3,5-triazine (LogS = 0.3), and methylparaben (LogS = -0.6), and it is more preferable to use a biocide containing at least one selected from the group consisting of 1,2-benzoisothiazone-3-one (LogS = 0.3) and methylparaben (LogS = -0.6).

[0029] The biocide may be supported on a carrier. Examples of carriers include zeolites; montmorillonite; activated carbon; calcium phosphate compounds such as hydroxyapatite; oxides such as silicon dioxide, aluminum oxide, magnesium oxide, titanium dioxide, and zirconium oxide; nitrides such as silicon nitride, titanium nitride, aluminum nitride, and zirconium nitride; non-oxide ceramics such as silicon carbide; calcium silicate, aluminum silicate, and magnesium silicate. One or more of these can be used.

[0030] Biocides come into contact with and inactivate self-inducing factors released by microorganisms, exhibiting an effect similar to that of quorum sensing inhibitors. Therefore, the biocide content (mass%) in the aqueous ink is preferably 0.02% by mass or more and 0.09% by mass or less, based on the total mass of the aqueous ink. A content of 0.02% by mass or more makes it difficult for the biocide to adsorb to the hydrophobic parts of the pigments and resins in the aqueous ink, thus suppressing the reduction in opportunities for contact with self-inducing factors. Furthermore, a content of 0.09% by mass or less makes it difficult for the biocide to adsorb to quorum sensing inhibitors, suppressing the reduction in the self-inducing factor capture function of quorum sensing inhibitors, and thus further suppressing biofilm production by microorganisms. The biocide content in the aqueous ink is preferably 0.010 times or more and 0.900 times the mass ratio of the quorum sensing inhibitor content.

[0031] When the above mass ratio is 0.010 or higher, the quorum sensing inhibitor is not in excess of the biocide, and the biocide is present in an appropriate amount relative to the quorum sensing inhibitor, making it easier for the biocide to come into contact with the microbial cell membrane. As a result, the biocide destroys the microbial cell membrane, strengthening the inhibitory effect on microbial growth, making it difficult for microbial growth to occur, thereby further suppressing the production of biofilms and further reducing the decrease in continuous ejection from the recording head.

[0032] On the other hand, if the above mass ratio is 0.900 times or less, the adsorption ratio of the biocide to the self-inducing factor substances released by microorganisms will not become too high, but will be moderately suppressed. In other words, the adsorption ratio of the quorum sensing inhibitor to quorum sensing will not become too low, but will be moderately high, and the shielding effect on information transmission between microorganisms and quorum sensing will be strengthened, making it easier to suppress the production of biofilm by microorganisms. As a result, biofilm is less likely to adhere to the filter installed in the recording head and is less likely to block the ink flow path, so the phenomenon of non-ejection during continuous ejection is less likely to occur, and continuous ejection performance from the recording head tends to be better.

[0033] The mass ratio of the biocide content to the quorum sensing inhibitor content can be determined using the formula {mass of biocide / mass of quorum sensing inhibitor} (times) in the aqueous ink. The masses of the quorum sensing inhibitor and biocide can be the respective mass-based usage amounts (parts by mass or mass %) of the quorum sensing inhibitor and biocide used in the manufacture of the aqueous ink.

[0034] (Aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. The ink may contain an aqueous medium which is water or a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferred as the water. The water content (mass%) in the aqueous ink is 50.00% by mass or more, preferably 50.00% by mass or more and 95.00% by mass or less, and more preferably 55.00% by mass or more and 84.00% by mass or less, based on the total mass of the aqueous ink. The water-soluble organic solvent content (mass%) in the aqueous ink is preferably 3.00% by mass or more and 48.00% by mass or less, and more preferably 15.00% by mass or more and 40.00% by mass or less, based on the total mass of the aqueous ink. A water-soluble organic solvent content of 15.00% by mass or more in the ink makes it possible to suppress the growth of microorganisms and the production of biofilms, and improves filterability. Furthermore, by keeping the content of water-soluble organic solvents in the ink at 40.00% by mass or less, the storage stability of the ink can be further improved.

[0035] As the water-soluble organic solvent, for example, one or more selected from the group consisting of the following water-soluble organic solvents can be used: Glycol ethers such as diethylene glycol monomethyl (or ethyl) ether and triethylene glycol monoethyl (or butyl) ether; C1 to C4 alkanols such as methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, isobutanol, and tert-butanol; Carboxylic acid amides such as N,N-dimethylformamide and N,N-dimethylacetamide; Ketones or keto alcohols such as acetone, methyl ethyl ketone, and 2-methyl-2-hydroxypentan-4-one; Cyclic ethers such as tetrahydrofuran and dioxane; Ethylene glycol, diethylene glycol, triethylene glycol, Examples of water-soluble organic solvents include glycols such as tetraethylene glycol, propylene glycol, butylene glycol, and hexylene glycol; polyethylene glycols with an average molecular weight of 200 to 2,000, specifically those with average molecular weights of 200, 400, 600, 1,000, and 2,000; acetylene glycol derivatives; polyhydric alcohols such as glycerin, 3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,2,6-hexanetriol; heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and N-methylmorpholine; and sulfur-containing compounds such as thiodiglycol and dimethyl sulfoxide. Among these water-soluble organic solvents, it is preferable that the ink contains a water-soluble organic solvent with an SP value of 12.8 or less, from the viewpoint of suppressing microbial growth and biofilm formation. When the colorant is a pigment, the surface of the pigment has not only smooth areas but also uneven areas, so it is thought that microorganisms and quorum sensing released by microorganisms can enter the recesses. Water-based inks contain water-soluble organic solvents with an SP value of 12.8 or less, so it is thought that quorum sensing inhibitors can enter the recesses of the pigment, making it easier to capture quorum sensing near the recesses.

[0036] Preferred water-soluble organic solvents with an SP value of 12.8 or less include alkanediols and ethers. Examples of alkanediols include 1,2-hexanediol (SP value 11.8), 1,2-pentanediol (SP value 12.2), and 1,2-butanediol (SP value 12.8). Examples of ethers include ethylene glycol monoethyl ether (SP value 11.5), triethylene glycol monoethyl ether (SP value 10.6), and polyethylene glycol with a number average molecular weight of 1,000 (SP value 10.1). These water-soluble organic solvents may be used individually or in combination of two or more.

[0037] (Surfactants) Water-based inks preferably contain surfactants. Furthermore, from the viewpoint of suppressing the growth of microorganisms and the production of biofilms, it is preferable that the surfactants include surfactants with an SP value of 12.8 or less. Nonionic surfactants can be suitably used as surfactants with an SP value of 12.8 or less. Examples of nonionic surfactants include a silicone-based surfactant represented by the following structural formula (1) (SP value 8.7) and a fluorine-based surfactant represented by the following structural formula (2) (SP value 8.7). In addition, acetylene-based nonionic surfactants with an SP value of 12.8 or less (for example, "Acetylenel E60" manufactured by Kawaken Fine Chemicals) can also be used. One or more types of surfactants can be used.

[0038]

[0039]

[0040] In this specification, the SP value (δ) is a value calculated by the Fedors method based on the following formula. Units are omitted in this specification, but the unit of the SP value (δ) is (cal / cm³). ３ ) １／２ ) is the case. δ = (ΔE ｖａｐ / V) １／２ (In the formula, ΔE ｖａｐrepresents the molar heat of vaporization (cal / mol), and V represents the molar volume (cc / mol) at 25°C.) (Other components) In addition to the above-described components, the ink may contain various additives such as a pH adjuster, a rust inhibitor, a preservative, a fungicide, an antioxidant, and an anti-reducing agent, as necessary.

[0041] <Method for producing ink> The aqueous ink can be prepared using a dye aqueous solution or an aqueous pigment dispersion described later. Specifically, an aqueous ink can be produced by having a mixing step of adding and mixing deionized water such as ion-exchanged water or pure water, and further, if necessary, a water-soluble organic solvent or the like to the dye aqueous solution or the aqueous pigment dispersion. Further, if necessary, a filtering step of filtering after the mixing step may be provided.

[0042] (Method for producing a dye aqueous solution) The method for producing a dye aqueous solution includes a dissolution step in which a dye as a colorant and an aqueous medium containing water are mixed and the dye is dissolved. Through this dissolution step, a dye aqueous solution containing the dye and the aqueous medium can be prepared. It is preferable to mix a quorum sensing inhibitor together in this dissolution step. This can further enhance the effect of suppressing microbial growth and biofilm formation. The reason for this is as follows: When a dye aqueous solution is left standing for a certain period of time, microorganisms that have come into contact with the dye or otherwise mixed into the dye aqueous solution will grow. These grown microorganisms then form aggregates. It is thought that self-inducing factor substances generated inside the microbial aggregates are less susceptible to adsorption by quorum sensing inhibitors. Therefore, it is presumed that by adding the quorum sensing inhibitor at the timing when it enters the inside of the microbial aggregate, i.e., during the dissolution step, the effect of the quorum sensing inhibitor can be more easily exerted inside the microbial aggregate. It is also preferable to mix a biocide together in the dissolution step. This can further enhance the effect of suppressing microbial growth. The dye content (mass%) in the aqueous dye solution is preferably 1.00% by mass or more and 30.00% by mass or less, and more preferably 5.00% by mass or more and 20.00% by mass or less, based on the total mass of the aqueous dye solution. The aqueous medium may also contain a water-soluble organic solvent. In addition, a surfactant may be mixed in during this dissolution step as needed. The water-soluble organic solvent, surfactant, and biocide can be the same as those contained in the aqueous ink described above.

[0043] (Method for producing aqueous pigment dispersion) The method for producing aqueous pigment dispersion includes a kneading step in which a pigment as a colorant, a water-soluble inorganic salt, and a water-soluble organic solvent are mixed and kneaded in a kneading device to obtain a colorant composition. It also includes a dispersion step in which the colorant composition obtained in the kneading step, a dispersant, and an aqueous medium containing water are mixed and dispersed. Through this kneading step and dispersion step, an aqueous pigment dispersion containing a pigment, a dispersant, and an aqueous medium can be prepared. Of these, it is preferable to mix a quorum sensing inhibitor together in the kneading step. This can further enhance the effect of suppressing microbial growth and biofilm production. The reason for this is as follows: Pigments form aggregates, and microorganisms exist not only on the surface of these aggregates but also inside them. Therefore, it is presumed that by adding the quorum sensing inhibitor at the timing when the pigment enters the inside of the aggregates, i.e., in the kneading step, the effect of the quorum sensing inhibitor can be more easily exerted inside the aggregates. Examples of water-soluble inorganic salts used in the kneading process include sodium chloride, potassium chloride, sodium sulfate, zinc chloride, calcium chloride, and magnesium chloride, as well as mixtures of two or more of these. A single water-soluble inorganic salt may be used, or two or more may be used in combination. Examples of water-soluble organic solvents used in the kneading process include the aforementioned water-soluble organic solvents that can be incorporated into the ink. A single water-soluble organic solvent may be used, or two or more may be used in combination. The aqueous pigment dispersion can be manufactured by a manufacturing method in which the dispersion conditions, such as the dispersion method of the dispersion apparatus used in the dispersion process, dispersion time, peripheral speed, and, if necessary, the type and particle size of the media used, are appropriately determined. Examples of dispersion apparatus include roll mills, bead mills, paint shakers, sand mills, agitator mills, nanomizers (registered trademark), homogenizers, microfluidizers, ultimateizers, and ultrasonic dispersers. Furthermore, it is preferable to mix a biocide together with the pigment in the kneading process. This enhances the effect of inhibiting microbial growth.The content (mass %) of the pigment in the aqueous pigment dispersion is preferably 1.00 mass % or more and 35.00 mass % or less, more preferably 5.00 mass % or more and 25.00 mass % or less, based on the total mass of the aqueous pigment dispersion. Also, in the dispersion step, the aqueous medium may contain a water-soluble organic solvent. Further, in this dispersion step, a surfactant may be mixed together as needed. Note that the water-soluble organic solvent, surfactant, and biocide can be the same as those contained in the above-described aqueous ink. Also, a resin dispersant contained in the above-described aqueous ink can be used as the dispersant.

[0044] <Ink Cartridge> The ink cartridge of the present invention includes ink and an ink storage unit for storing this ink. And the ink stored in this ink storage unit is the aqueous ink of the present invention described above. FIG. 1 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage unit for storing ink. The ink storage unit is composed of an ink storage chamber 14 and an absorber storage chamber 16, which communicate with each other through a communication port 18. Also, the absorber storage chamber 16 communicates with the ink supply port 12. A liquid ink 20 is stored in the ink storage chamber 14, and absorbers 22 and 24 that hold the ink in an impregnated state are stored in the absorber storage chamber 16. The ink storage unit may be in a form that does not have an ink storage chamber for storing liquid ink and holds the entire amount of the stored ink by the absorber. Also, the ink storage unit may be in a form that does not have an absorber and stores the entire amount of the ink in a liquid state. Furthermore, an ink cartridge configured to have an ink storage unit and a recording head may also be used.

[0045] <Inkjet Recording Method> The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the aqueous ink of the present invention described above from an inkjet recording head. Methods for ejecting the ink include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. In the present invention, it is particularly preferable to employ a method that imparts thermal energy to the ink to eject it. Aside from using the ink of the present invention, the steps of the inkjet recording method may be those of known sources.

[0046] Figures 2A and 2B schematically show an example of an inkjet recording apparatus used in the inkjet recording method of the present invention. Figure 2A is a perspective view of the main part of the inkjet recording apparatus, and Figure 2B is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting the recording medium 32, and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 comprises recording heads 38 and 40, and is configured to hold an ink cartridge 42. 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. Then, the recording medium 32 is transported in the sub-scanning direction by the transport means (not shown), and an image is recorded on the recording medium 32.

[0047] Any recording medium may be used as the recording medium for recording using the ink of the present invention. Recording media with ink absorption properties can be used, such as recording media without a coating layer, such as plain paper, and recording media with a coating layer, such as glossy paper or matte paper. In addition, recording media with low ink absorption or no ink absorption properties, such as printing paper, coated paper, resin sheets, and resin films, can be used.

[0048] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0049] <Preparation of Resin Aqueous Solutions> (Resin Aqueous Solutions 1-13) 400.0 parts of ethylene glycol monobutyl ether were placed in a four-necked flask equipped with a stirrer, nitrogen inlet tube, and reflux tube, and nitrogen gas was introduced. The temperature was raised to 130°C under stirring. A mixture of the monomers used in the amounts listed in Table 1 (in parts) and 4.0 parts of polymerization initiator (t-butyl peroxide) was added dropwise to the flask over 3 hours. After that, aging was performed for 2 hours, and the ethylene glycol monobutyl ether was removed by reduced pressure to obtain a solid resin (polymer). Potassium hydroxide and deionized water in an amount equivalent to the acid value of the obtained resin were added and dissolved at a temperature of 80°C to obtain resin aqueous solutions 1-13, each containing resin 1-13 with a resin content of 20.0%. Table 1 lists the properties of the resin, including the percentage (%) of units derived from (meth)acrylic acid monomers in the resin (polymer), the acid value of the resin (mgKOH / g), and the weight-average molecular weight Mw. The acid value and weight-average molecular weight of the obtained resin were measured using the method described above. In Table 1, St in the styrene monomer column represents styrene, and AMS represents α-methylstyrene. AA in the acrylic acid monomer column represents acrylic acid, and BA represents n-butyl acrylate. MAA in the methacrylic acid monomer column represents methacrylic acid, and MMA represents methyl methacrylate.

[0050] <Preparation of Aqueous Pigment Dispersion> (Pigment Dispersion 1) 20.00 parts of pigment, 60.00 parts of water-soluble inorganic salt, 16.00 parts of water-soluble organic solvent, and 4.00 parts of 2-aminobenzamide as a quorum sensing inhibitor were mixed and kneaded for 8 hours using a planetary mixer (product name "Trimix", manufactured by Inoue Seisakusho). The resulting mixture was thoroughly washed, ultrafiltered, and dried to obtain a pigment composition containing the pigment and the quorum sensing inhibitor. Copper phthalocyanine (product name "Fastogen Blue 5380 E", manufactured by DIC) was used as the pigment. An aqueous potassium hydroxide solution was added to the above pigment composition to adjust the pH to 12.0 or higher, and the mixture was heat-treated at 80°C for 2 hours (alkaline heat treatment). After that, the alkaline component was removed by ultrafiltration to prepare a mixture containing the pigment and the quorum sensing inhibitor. Ultrafiltration was performed using an ultrafiltration device (product name "Centramate Low Volume", manufactured by PALL) and a filter with a molecular weight cutoff of 300,000 until the conductivity of the filtrate was 200 μS / cm or less. To this mixture containing the pigment and quorum sensing inhibitor, resin aqueous solution 1 and water were added so that the pigment content was 10.00%, the quorum sensing inhibitor content was 2.00%, and the resin content was 3.00%. Then, the mixture to which resin aqueous solution 1 and water were added was dispersed using a batch-type vertical sand mill (manufactured by AIMEX) until the average particle size of the pigment was 80 nm, thereby obtaining pigment dispersion 1 containing resin-dispersed pigment.

[0051] (Pigment Dispersions 2-39) Pigment dispersions 2-36 were obtained in the same manner as pigment dispersion 1, except that the type and content of the pigment, quorum sensing inhibitor, and resin, the water content, and the presence or absence of alkaline heat treatment were changed, as shown in Table 2 (Tables 2-1 to 2-5). The numerical values ​​for each component shown in Table 2 represent the component content (unit: %) in each obtained pigment dispersion. For the monoazo yellow pigment in Table 2, the product name "Seikafast Yellow 2054" manufactured by Dainichi Seika Kogyo was used. Furthermore, the pigment dispersion containing carbon black, a self-dispersing pigment in pigment dispersion 37 in Table 2, was prepared as follows: A solution obtained by dissolving 2.5 g of concentrated hydrochloric acid in 5.5 g of water was cooled to 5°C, and 0.7 g of 4-aminophthalic acid was added at this state. The container of this solution was placed in an ice bath and stirred to maintain the solution temperature below 10°C, while a solution obtained by dissolving 0.9 g of sodium nitrite in 9.0 g of ion-exchanged water at 5°C was added. After stirring for 15 minutes, 10.0 g of carbon black (product name "EC300J", manufactured by Cabot) was added under stirring, and the mixture was stirred for another 15 minutes to obtain a slurry. The obtained slurry was filtered through filter paper (product name "Standard Filter Paper No. 2", manufactured by Advantec), the particles were thoroughly washed with water, and the mixture was dried in an oven at 110°C to obtain a pigment. 20.00 parts of the obtained pigment, 60.00 parts of a water-soluble inorganic salt, 16.00 parts of a water-soluble organic solvent, and 4.00 parts of 2-aminobenzamide as a quorum sensing inhibitor were mixed and kneaded for 8 hours using a planetary mixer (product name "Trimix", manufactured by Inoue Seisakusho). The resulting mixture was thoroughly washed, ultrafiltered, and dried to obtain a pigment composition containing the pigment and the quorum sensing inhibitor. An aqueous potassium hydroxide solution was added to the above pigment composition to adjust the pH to 12.0 or higher, and the mixture was subjected to a heat treatment (alkaline heat treatment) at 80°C for 2 hours. Subsequently, the alkaline components were removed by ultrafiltration to prepare a mixture containing the pigment and quorum sensing inhibitor. Ultrafiltration was performed using an ultrafiltration apparatus (product name "Centramate Low Volume", manufactured by PALL) and a filter with a molecular weight cutoff of 300,000 until the conductivity of the filtrate was 200 μS / cm or less.Water was added to the mixture containing the pigment and the quorum sensing inhibitor so that the pigment content was 10.00% and the quorum sensing inhibitor content was 2.00%. Then, the mixture with added water was dispersed using a batch-type vertical sand mill (manufactured by AIMEX) until the average particle size of the pigment was 80 nm, thereby obtaining pigment dispersion 37. Furthermore, pigment dispersion 38 was prepared in the same manner as pigment dispersion 37, except that the quorum sensing inhibitor was not added and 90.00 parts of deionized water were used instead. Pigment dispersion 39 was also prepared in the same manner as pigment dispersion 37, except that alkaline heat treatment was not performed. In the quorum sensing (QS) inhibitors shown in Table 2 and Table 3 below, "2-aminobenzamide" and "benzamide" are types of aromatic amide compounds, and "furanone" is a type of furanone compound. Similarly, "vanillin" and "eugenol" are types of "phenol compounds," and "sucrose lauryl ester" and "sucrose oleate" are types of sugar ester compounds. Also, "histidine" is a histidine compound, "pyrimidine" is a pyrimidine compound, "pterolactam" is a lactam compound, "2-thiohydantoin" is a thiohydantoin compound, and "thiazolidinedione" is a type of thiazolidinedione compound. Furthermore, "γ-caprolactone" is a type of lactone compound, and rhodanine is a type of rhodanine compound.

[0052] <Ink Preparation> Each component (unit: %) shown in Table 3 (Tables 3-1 to 3-7) was mixed and thoroughly stirred to prepare inks 1 to 55. The lower section of Table 3 shows the characteristics of the inks, specifically the mass ratio (times) of the biocide content to the QS inhibitor content, and the mass ratio (times) of the QS inhibitor content to the colorant content.

[0053] <Evaluation> (Filtration Performance) 10 kg of each prepared ink was pressure filtered through a filter with a pore size of 5.0 μm, and the filtration performance of the ink was evaluated according to the evaluation criteria shown below, based on the mass of the ink that passed through the filter and the filtration rate. The results are shown in Table 4. In the evaluation criteria shown below, "A", "B", and "C" were considered acceptable levels, and "D" was considered an unacceptable level. A: The entire 10 kg of ink could pass through, and the filtration rate after the entire 10 kg of ink had passed through did not change from the initial filtration rate. B: The entire 10 kg of ink could pass through, but the filtration rate after the entire 10 kg of ink had passed through decreased by 1-20% compared to the initial filtration rate. C: The entire 10 kg of ink could pass through, but the filtration rate after the entire 10 kg of ink had passed through decreased by 21-50% compared to the initial filtration rate. D: The entire 10 kg of ink could be passed through, but the filtration rate after passing the entire 10 kg of ink through decreased by more than 51% compared to the initial filtration rate, or the ink could no longer be passed through at any point.

[0054] (Continuous Discharge Performance) Each prepared ink was pressure filtered through a pore size 5.0 μm filter and stored for one month. The stored ink was filled into an ink cartridge and set in an inkjet recording device (product name "PIXUS 960i", manufactured by Canon, discharge volume 2 pL). 1,000 solid images with a recording duty cycle of 50% were continuously recorded on a recording medium (glossy paper, product name "Canon Photo Paper Gloss Gold GL-101", manufactured by Canon), and then a total of 20 cycles were performed in which images containing a grid pattern were recorded. For the images containing the grid pattern recorded in the 20th cycle, the discharge status from each nozzle was checked, and the percentage of nozzles that failed to discharge was calculated. Continuous discharge performance was evaluated from the average value of the 20 images according to the evaluation criteria shown below. The results are shown in Table 4. In the evaluation criteria shown below, "A", "B", and "C" were considered acceptable levels, and "D" was considered an unacceptable level. A: Ink was ejected normally from all nozzles. B: Ink was ejected normally from 90% to less than 100% of the nozzles. C: Ink was ejected normally from 80% to less than 90% of the nozzles. D: Ink was ejected normally from 50% to less than 80% of the nozzles.

[0055] The present invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of the invention public.

[0056] This application claims priority based on Japanese Patent Application No. 2024-199053, No. 2024-199052, No. 2024-199051, and No. 2025-192165, both filed on November 14, 2024, and all of their contents are incorporated herein by reference.

Claims

1. An aqueous ink comprising a colorant, a quorum sensing inhibitor, and water, wherein the quorum sensing inhibitor is at least one compound selected from the group consisting of aromatic amide compounds, furanone compounds, phenol compounds, histidine compounds, pyrimidine compounds, sugar ester compounds, lactam compounds, thiohydantoin compounds, and thiazolidinedione compounds, and has a common logarithm LogS of solubility in water at 25°C of -2.2 or higher, and the water content is 50.00% by mass or more based on the total mass of the aqueous ink.

2. The aqueous ink according to claim 1, wherein the quorum sensing inhibitor comprises the aromatic amide compound.

3. The aqueous ink according to claim 1 or 2, wherein the coloring material comprises a pigment.

4. The aqueous ink according to claim 3, wherein the pigment comprises a condensed aromatic pigment.

5. An aqueous ink according to any one of claims 1 to 4, comprising a copolymer having units derived from styrene monomers and units derived from (meth)acrylic acid monomers, wherein the content of the units derived from the (meth)acrylic acid monomers in the copolymer is 20% by mass or more and 40% by mass or less, based on the total mass of the copolymer.

6. The aqueous ink according to any one of claims 1 to 5, wherein the content of the quorum sensing inhibitor is 0.025 times or more and 1.000 times or less by mass ratio to the content of the colorant.

7. An aqueous ink according to any one of claims 1 to 6, containing a biocide.

8. The aqueous ink according to claim 7, wherein the biocide has a common logarithm of solubility in water at 25°C, LogS, of -0.6 or higher.

9. The aqueous ink according to claim 7 or 8, wherein the biocide content is 0.02% by mass or more and 0.09% by mass or less, based on the total mass of the aqueous ink.

10. The aqueous ink according to any one of claims 7 to 9, wherein the content of the biocide is 0.010 times or more and 0.900 times or less by mass ratio to the content of the quorum sensing inhibitor.

11. An aqueous ink according to any one of claims 1 to 10, which is for inkjet use.

12. An ink cartridge comprising ink and an ink storage section for storing the ink, wherein the ink is an aqueous ink according to any one of claims 1 to 11.

13. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, characterized in that the ink is an aqueous ink according to any one of claims 1 to 11.

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