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

Abstract

This water-based ink can suppress the decrease in filterability even when microorganisms are present in the water-based ink, and also provides a water-based ink that exhibits good ejection stability by the recording head when applied to water-based inkjet inks. [Solution] The invention provides an aqueous ink containing a colorant, a quorum sensing (QS) inhibitor, and water. The QS inhibitor is at least one 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. Furthermore, the common logarithm LogS of the solubility of the QS inhibitor in water at 25°C is -2.2 or higher. The water content in the ink is 50.00% by mass or more, based on the total mass of the aqueous ink.

Description

Technical Field

[0001] The present invention relates to an aqueous ink, an ink cartridge, and an inkjet recording method.

Background Art

[0002] Generally, inks used for office equipment and printing applications are intended to remove contaminants such as dust, and are passed through filters and finished into final products. In the case of aqueous 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 to pass 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, a biocide is contained in the ink to suppress the growth of microorganisms (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0005] Therefore, an object of the present invention is to provide an aqueous ink that can suppress a decrease in filterability even when microorganisms are present in the aqueous ink, and that exhibits good ejection stability by the recording head even when applied to an aqueous ink for inkjet printing. Another object of the present invention is to provide an ink cartridge using the above-mentioned aqueous ink, and an inkjet recording method. [Means for solving the problem]

[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 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. [Effects of the Invention]

[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. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. [Figure 2] This figure schematically shows an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. [Modes for carrying out the invention]

[0009] The present invention will be described in more 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 printers 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 means the unit structure corresponding to one monomer unless otherwise specified. 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 biocides 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 led to the proliferation of microorganisms during ink storage, and that these proliferating microorganisms produced a biofilm.

[0011] 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 the aqueous pigment ink was prepared. However, it was found that when the aqueous 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 after the ink was stored, even though the biofilm and microorganisms suspended 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 aqueous pigment ink was filtered, the microorganisms could not be completely removed. As a result, it was found that during the process of storing the aqueous 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 aqueous 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 the ink has a function that prevents the production of biofilm even if microorganisms are present.

[0012] However, as mentioned above, in recent years, regulations have made it necessary to reduce the amount of biocides contained in water-based inks. In other words, it is extremely difficult to maintain a state in which water-based inks are free of microorganisms when stored for long periods 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 biofilms that cause problems. As a result, the inventors found that the above problem can be solved by including a quorum sensing inhibitor in the water-based ink that can suppress the production of biofilms even in the presence of microorganisms.

[0013] 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 these 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.

[0014] Furthermore, the quorum sensing inhibitor is at least one compound selected from the following group, and its common logarithm LogS of solubility in water at 25°C is -2.2 or higher. That is, the 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 quorum sensing inhibitor, it is possible to fully exhibit its function as a quorum sensing inhibitor even in aqueous ink. It should be noted that while the inclusion of the above-mentioned compounds 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 of its use as a quorum sensing inhibitor. Furthermore, oil-based marking pen ink compositions contain a high amount of organic solvents, creating conditions in which microorganisms cannot easily survive, thus preventing problems caused by biofilms.

[0015] <Water-based ink> As described above, the water-based ink contains a colorant, a quorum sensing inhibitor, and water. The water-based ink is preferably for inkjet applications. The components of the water-based ink are described in detail below.

[0016] (Quorum sensing inhibitor) Quorum sensing inhibitors are compounds that inhibit quorum sensing in microorganisms. This can suppress the formation of biofilms by microorganisms such as bacteria.

[0017] 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 compounds listed above were unable to sufficiently suppress the production of biofilm in aqueous inks.

[0018] Furthermore, quorum sensing inhibitors must be compounds with a common logarithm of solubility in water at 25°C (LogS) of -2.2 or higher. This is because, in order to exert their effect as quorum sensing inhibitors in aqueous inks, they need to be soluble in water, which is the solvent for aqueous inks. By using water-soluble quorum sensing inhibitors, the inhibitors can move more easily through aqueous inks, thereby blocking or capturing self-inducing substances released by microorganisms. If the quorum sensing inhibitor is a compound with a common logarithm of solubility in water at 25°C (LogS) of -2.3 or lower, the efficiency of blocking or capturing self-inducing substances released by microorganisms decreases drastically. Therefore, in this case, if microorganisms are present in the aqueous ink, the production of biofilms cannot be sufficiently suppressed.

[0019] The LogS of the quorum sensing inhibitor is the common logarithm of the amount S (g / 100 g) of the quorum sensing inhibitor dissolved in 100 g of water at a temperature of 25°C and a pH of 7 (solubility). When using two or more compounds selected from the above group as the quorum sensing inhibitor, it is sufficient that the LogS of at least one compound is -2.2 or more, but preferably the LogS of each compound is -2.2 or more.

[0020] When the coloring material of the aqueous ink is a pigment, among the above compounds that can be used as the quorum sensing inhibitor, an aromatic amide compound is preferable. In the aqueous ink, the aromatic amide compound has a δ+ charge and is likely to be present in the vicinity of the pigment having a δ- charge. As a result, the quorum sensing inhibitor and the microorganisms in the pigment are present at a short distance. It is considered that this promotes the blocking or capture of the autoinducer substance released by the microorganisms, and further suppresses the production of biofilms. Therefore, the quorum sensing inhibitor preferably contains an aromatic amide compound, and more preferably is an aromatic amide compound.

[0021] Examples of the aromatic amide compound 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.

[0022] Examples of the furanone compound 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.

[0023] Examples of phenol compounds include vanillin, vanillic acid, and pyrogallol. One or more of these phenol compounds can be used.

[0024] Examples of histidine compounds include histidine.

[0025] Examples of pyrimidine compounds include pyrimidines.

[0026] 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.

[0027] Examples of lactam compounds include pterolactams.

[0028] Examples of thiohydantoin compounds include 2-thiohydantoin.

[0029] Examples of thiazolidinedione compounds include thiazolidinedione itself.

[0030] 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, microbial quorum sensing 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.

[0031] In water-based inks, the content of the quorum sensing inhibitor is preferably 0.025 to 1.000 times the mass ratio of the colorant content. When the mass ratio is 0.025 or higher, the quorum sensing inhibitor is more likely to exert an inhibitory effect on quorum sensing by microorganisms in the ink. On the other hand, when the mass ratio is 1.000 or lower, when a pigment is used as the colorant, the dispersion stability of the pigment in the ink is more easily improved, and as a result, the increase in viscosity is more easily suppressed.

[0032] The mass ratio of the quorum sensing inhibitor content to the colorant content can be determined using the formula {mass of quorum sensing inhibitor / mass of colorant} (times) in the aqueous ink. The masses of the colorant and quorum sensing inhibitor can be the respective mass-based usage amounts (parts by mass or mass %) used when manufacturing the aqueous ink.

[0033] (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 the colorant preferably contains a pigment, and more preferably is 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 colorant in the water-based ink can be adjusted according to the application and form of the water-based ink.

[0034] Examples of dyes include direct dyes, acid dyes, basic dyes, disperse dyes, and food dyes. Among these, dyes having anionic groups are preferred. 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.

[0035] 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. Pigments may be used individually or in combination of two or more types.

[0036] Furthermore, it is preferable that the pigment has been treated to sterilize and decompose any attached microorganisms or biofilms. While quorum sensing inhibitors are effective in suppressing the production of new biofilms, they have little effect in removing microorganisms or biofilms that are already attached to the pigment. Therefore, by using pigments that have been treated to sterilize and decompose, it is possible to reduce the amount of microorganisms and biofilms already attached to the pigment before preparing the water-based ink, thereby reducing the amount of microorganisms and biofilms that are brought from the pigment into the water-based ink. Examples of pigment sterilization and decomposition treatment include immersing the pigment in an alkaline solution and heating it.

[0037] As for pigment dispersion methods, resin-dispersed pigments using a resin (resin dispersant) as a dispersant, and self-dispersing pigments in which hydrophilic groups are bonded to the surface of the pigment particles can be used. In addition, resin-bonded pigments in which organic groups containing resin are chemically bonded to the surface of the pigment particles, and microcapsule pigments in which the surface of the pigment particles is coated with resin or the like can be used. It is also possible to use a combination of pigments with different dispersion methods from among these.

[0038] 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 the aqueous medium through the action of anionic groups. As a self-dispersing pigment, one can be used in which the anionic groups are bonded directly to the surface of the pigment particles 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.

[0039] Examples of the anionic groups described in the descriptions of resin dispersants, self-dispersing pigments, and dyes include carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups. The anionic group may be either an acid type or a salt type, and if it is a salt type, it may be in a partially dissociated state or a fully dissociated state. When the anionic group is a salt type, examples of cations that become counterions include alkali metal cations, ammonium, and organic ammonium.

[0040] The colorant content (by mass) in the water-based ink is preferably 0.50% by mass or more and 15.00% by mass or less, based on the total mass of the water-based ink. More preferably, the colorant content in the water-based ink is 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.

[0041] (resin) The ink may contain a resin. The resin can be added to the ink (i) to stabilize the dispersion state of the pigment, i.e., as a resin dispersant or its auxiliary agent. It can also be added to the ink (ii) to improve various properties of the recorded image. The resin content (mass%) in the aqueous ink is preferably 0.10% by mass or more and 20.00% by mass or less, and 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 be a water-soluble resin that can dissolve in an aqueous medium, or it may be resin particles dispersed in an aqueous medium.

[0042] 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 above 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)acrylate 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)acrylate 2-phosphonoethyl (also known as 2-((meth)acryloyloxy)ethylphosphonic acid) and (meth)acrylate 2-phosphonooxyethyl (also known as 2-(meth)acryloyloxyethyl phosphoric acid); and others.

[0043] Among the copolymers described above, 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. When the content of units derived from (meth)acrylic acid monomers in the copolymer is 20% by mass or more and 40% by mass or less, the resin is adsorbed appropriately onto the pigment, so that a large amount of quorum sensing inhibitors can 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.

[0044] Any of the styrene monomers listed above can be used as the styrene monomers that can be used in the above copolymer. Furthermore, in this disclosure, (meth)acrylic acid monomers mean 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.

[0045] As described above, it is believed that the production of biofilms by microorganisms can be further suppressed if the content of (meth)acrylic acid monomers in the copolymer is within the range of 20% by mass to 40% by mass.

[0046] The above-mentioned resin is thought to have the property of readily adsorbing quorum sensing inhibitors. Therefore, in order to ensure that quorum sensing inhibitors are present near microorganisms on the surface of pigment particles, the above-mentioned resin (polymer) is preferably a resin dispersant.

[0047] Furthermore, the weight-average molecular weight (Mw) of the resin dispersant is preferably between 5,000 and 20,000. 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 the pigment particles being in close proximity to quorum sensing inhibitors that readily adsorb to the resin increases, thereby improving the rate at which quorum sensing inhibitors capture self-inducing factors released by microorganisms. 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).

[0048] Furthermore, the acid value (mgKOH / g) of the resin dispersant is preferably between 80 mgKOH / g and 200 mgKOH / g. When the acid value of the resin dispersant is 80 mgKOH / 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, and to create a state where quorum sensing inhibitors are more likely to be present near the microorganisms. Also, when the acid value of the resin dispersant is 200 mgKOH / g or lower, it is highly hydrophobic and adsorbs a large amount onto the pigment, so the probability of microorganisms on the surface of the pigment particles being near quorum sensing inhibitors that readily adsorb to the resin increases. 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.

[0049] (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. Having the common logarithm of solubility in water at 25°C (LogS) within this range improves the solubility of the biocide in the water-based ink, making it easier to exert an effect that suppresses microbial growth.

[0050] The LogS value for biocides is the common logarithm of the solubility (S) (g / 100g) of the biocide dissolved in 100g of water at 25°C and pH 7. A smaller LogS value indicates less solubility in water. Biocides with a LogS of -0.6 or higher have characteristics such as being less adsorbed to colorants and less likely to aggregate with other biocides, making them more effective in suppressing biofilm formation and inhibiting the growth of microorganisms mixed into water-based inks.

[0051] 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.

[0052] 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.

[0053] 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. Furthermore, it is even 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). Among these, it is even 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).

[0054] 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.

[0055] 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 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.

[0056] The biocide content in the aqueous ink is preferably 0.010 to 0.900 times the mass ratio of the quorum sensing inhibitor content.

[0057] 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 biofilm formation and reducing the decrease in continuous ejection from the recording head.

[0058] 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.

[0059] 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 %) used when manufacturing the aqueous ink.

[0060] (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. It is preferable to use deionized water or ion-exchanged water 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.

[0061] 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 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.

[0062] 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 depressions. It is thought that by containing a water-soluble organic solvent with an SP value of 12.8 or less in the water-based ink, quorum sensing inhibitors can enter the depressions of the pigment, making it easier to capture quorum sensing near the depressions.

[0063] 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.

[0064] (Surfactants) Water-based inks preferably contain surfactants. Furthermore, from the viewpoint of inhibiting microbial growth and suppressing biofilm formation, it is preferable that the surfactants contain surfactants with an SP value of 12.8 or less. Nonionic surfactants are 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 Chemical Co., Ltd.) can also be used. One or more surfactants can be used.

[0065] TIFF2026086379000001.tif51170

[0066] TIFF2026086379000002.tif19170

[0067] 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 / cm²). 3 ) 1 / 2) δ=(ΔE vap / V) 1 / 2 (In the formula, ΔE vap (where V represents the molar heat of vaporization (cal / mol), and V represents the molar volume at 25°C (cc / mol).)

[0068] (Other ingredients) Furthermore, in addition to the components mentioned above, the ink may contain various additives as needed, such as pH adjusters, rust inhibitors, preservatives, fungicides, antioxidants, and reduction inhibitors.

[0069] <Ink manufacturing method> Water-based inks can be prepared using aqueous dye solutions or aqueous pigment dispersions as described below. Specifically, water-based inks can be manufactured by a mixing step in which deionized water, such as ion-exchanged water or pure water, and optionally a water-soluble organic solvent are added to the aqueous dye solution or aqueous pigment dispersion and mixed. A filtration step may also be included after the mixing step, if necessary.

[0070] (Method for producing an aqueous dye solution) The method for producing an aqueous dye solution includes a dissolution step in which a dye as a colorant and an aqueous medium containing water are mixed to dissolve the dye. This dissolution step allows for the preparation of an aqueous dye solution containing the dye and the aqueous medium. It is preferable to mix a quorum sensing inhibitor together with the solution in this dissolution step. This further enhances the effect of suppressing microbial growth and biofilm formation. The reason for this is as follows: When an aqueous dye solution is left standing for a certain period of time, microorganisms that have become mixed into the aqueous dye solution by attaching to the dye will grow. These grown microorganisms then form aggregates. It is thought that self-inducing factor substances generated inside these 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 with the solution in this dissolution step. This further enhances the effect of suppressing microbial growth.

[0071] 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.

[0072] (Method for producing aqueous pigment dispersion) A method for producing an 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 these kneading and dispersion steps, 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 further enhances the effect of suppressing microbial growth and biofilm formation. 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 adding the quorum sensing inhibitor at the timing when the pigment enters the interior of the aggregates, i.e., during the kneading step, makes it easier for the quorum sensing inhibitor to exert its effect inside the aggregates.

[0073] 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 method of the dispersion apparatus used in the dispersion process, the 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.

[0074] The pigment content (mass%) in the aqueous pigment dispersion is preferably 1.00% by mass or more and 35.00% by mass or less, and more preferably 5.00% by mass or more and 25.00% by mass or less, based on the total mass of the aqueous pigment dispersion. In addition, the aqueous medium may contain a water-soluble organic solvent in the dispersion process. Furthermore, a surfactant may be mixed in with the dispersion process as needed. The water-soluble organic solvent, surfactant, and biocide can be the same as those contained in the aqueous ink described above. In addition, the resin dispersant contained in the aqueous ink described above can be used as the dispersant.

[0075] <Ink Cartridge> The ink cartridge of the present invention comprises ink and an ink storage section for storing this ink. The ink stored in this ink storage section is the aqueous ink of the present invention as described above. Figure 1 is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. As shown in Figure 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 section for storing ink. The ink storage section consists of an ink storage chamber 14 and an absorbent storage chamber 16, which are in communication with each other via a communication port 18. The absorbent storage chamber 16 is also in communication with the ink supply port 12. Liquid ink 20 is stored in the ink storage chamber 14, and absorbent materials 22 and 24 that hold the ink in an impregnated state are stored in the absorbent storage chamber 16. The ink storage section may not have an ink storage chamber for storing liquid ink, and the entire amount of ink to be stored may be held by an absorbent. Alternatively, the ink storage section may not have an absorbent, and the entire amount of ink may be stored in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

[0076] <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 origin.

[0077] Figure 2 is a schematic diagram showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) 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.

[0078] 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. [Examples]

[0079] 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.

[0080] <Preparation of resin aqueous solution> (Resin aqueous solution 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. Nitrogen gas was introduced, and 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 aging for 2 hours, the ethylene glycol monobutyl ether was removed by reduced pressure to obtain a solid resin (polymer). Equimolar amounts of potassium hydroxide and deionized water were added to the obtained resin and dissolved at 80°C to obtain resin aqueous solutions 1 to 13, each containing 20.0% resin. Table 1 lists the resin properties, 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 resins were measured using the methods described above.

[0081] In Table 1, in the column for styrene monomers, St represents styrene and AMS represents α-methylstyrene. In the column for acrylic acid monomers, AA represents acrylic acid and BA represents n-butyl acrylate. In the column for methacrylic acid monomers, MAA represents methacrylic acid and MMA represents methyl methacrylate.

[0082] TIFF2026086379000003.tif108170

[0083] <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 (trade 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 (trade name "Fastogen Blue 5380 E", manufactured by DIC) was used as the pigment.

[0084] Potassium hydroxide aqueous 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). Subsequently, the alkaline components were removed by ultrafiltration to prepare a mixture containing the pigment and the 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.

[0085] To the mixture containing the above-mentioned 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.

[0086] (Pigment dispersions 2-39) Pigment dispersions 2 to 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 values ​​for each component shown in Table 2 represent the component content (unit: %) in each obtained pigment dispersion. As the monoazo yellow pigment in Table 2, the product name "Seikafast Yellow 2054" manufactured by Dainichi Seika Kogyo Co., Ltd. was used.

[0087] 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 to this solution. 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 the pigment.

[0088] 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 quorum sensing inhibitor.

[0089] Potassium hydroxide aqueous 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). Subsequently, the alkaline components were removed by ultrafiltration to prepare a mixture containing the pigment and the 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.

[0090] Water was added to the mixture containing the above-mentioned pigment and 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.

[0091] Furthermore, pigment dispersion 38 was prepared in the same manner as pigment dispersion 37, except that 90.00 parts of deionized water were used instead of quorum sensing inhibitor. Pigment dispersion 39 was also prepared in the same manner as pigment dispersion 37, except that alkaline heat treatment was not performed.

[0092] 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. In addition, "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.

[0093] TIFF2026086379000004.tif243170

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[0096] TIFF2026086379000007.tif243170

[0097] TIFF2026086379000008.tif243170

[0098] <Ink preparation> Inks 1 to 55 were prepared by mixing each component (in %) shown in Table 3 (Tables 3-1 to 3-7) and stirring thoroughly. The lower part 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.

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[0105] TIFF2026086379000015.tif243170

[0106] <Rating> (filtration) Each prepared ink (10 kg) was pressure filtered through a 5.0 μm pore size filter, and the filterability of the ink was evaluated according to the following evaluation criteria 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 below, "A," "B," and "C" were considered acceptable levels, and "D" was considered an unacceptable level. A: The entire 10 kg of ink could be passed through, and the filtration rate after passing the entire 10 kg of ink through did not change compared to 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 10kg of ink could pass through, but the filtration rate after passing the entire 10kg of ink through decreased by 21-50% compared to the initial filtration rate. D: The entire 10kg of ink could pass through, but the filtration rate after passing the entire 10kg of ink decreased by more than 51% compared to the initial filtration rate, or the ink could no longer pass through at any point.

[0107] (Continuous dispensing) Each prepared ink was pressure-filtered through a 5.0 μm pore size filter and stored for one month. The stored ink was then filled into ink cartridges and set in an inkjet recorder (product name "PIXUS960i", Canon, ejection 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", Canon), followed by recording images containing a grid pattern. This cycle was repeated a total of 20 times. For the grid pattern image recorded in the 20th cycle, the ejection status from each nozzle was checked, and the percentage of nozzles with non-ejection was calculated. Continuous ejection 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 between 90% and 100% of the nozzles. C: Ink was ejected normally from between 80% and 90% of the nozzles. D: Ink was ejected normally from between 50% and 80% of the nozzles.

[0108] TIFF2026086379000016.tif174170

Claims

1. A water-based ink containing a colorant, a quorum sensing inhibitor, and water, 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 of solubility in water at 25°C, LogS, is -2.2 or higher. An aqueous ink characterized in that 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, wherein the coloring material includes a pigment.

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

5. It contains a copolymer having units derived from styrene monomers and units derived from (meth)acrylic acid monomers, The aqueous ink according to claim 1, wherein the content of units derived from the (meth)acrylic acid monomer 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 claim 1, 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. The aqueous ink according to claim 1, which contains 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, wherein the content of the biocide 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 claim 7, 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. The water-based ink according to claim 1, which is for inkjet use.

12. An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is the water-based ink described in any one of claims 1 to 11.

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

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