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

Abstract

To provide an aqueous ink capable of recording an image excellent in light resistance, as well as capable of suppressing accumulation in a waste ink absorber.SOLUTION: An aqueous ink for inkjet includes a coloring material and a water-soluble organic solvent. The coloring material includes a compound expressed by a general formula (I). The water-soluble organic solvent includes a water-soluble organic solvent X with LogPX of -0.97 or more. A content (mass%) of the water-soluble organic solvent X is 0.20 to 0.45 time the content (mass%) of the water-soluble organic solvent in a mass ratio, based on an entire ink mass. The water-soluble organic solvent has LogPS of -1.60 to -1.10. A content (ppm) of a sodium ion is 150 to 1500 ppm, based on the entire ink mass.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Inkjet recording is a method of forming an image by applying ink droplets to a recording medium. Its popularity has been rapidly increasing due to its falling cost and improved recording speed. Generally, dye inks produce images with superior gloss compared to pigment inks, but the image's storage stability is poor. This is because prolonged exposure of the image to light, humidity, heat, and environmental gases such as ozone gas present in the air can cause the coloring material to deteriorate, resulting in changes in color tone and fading. Among the inks containing the basic colors cyan, magenta, and yellow, yellow dyes have a relatively small molecular weight, making them less susceptible to molecular aggregation. This tends to result in poor lightfastness of the image, and improvements in this area are therefore needed.

[0003] To address these technical challenges, an ink containing a yellow colorant having a bisazo skeleton has been proposed as a means for improving the lightfastness of images (see Patent Document 1). It has also been proposed that the ink contains ethylene urea or the like in addition to the bisazo compound described in Patent Document 1, thereby improving the coagulation properties of the bisazo compound and improving the lightfastness of images (see Patent Document 2).

[0004] On the other hand, to maintain normal ink ejection, inkjet recording devices are equipped with a mechanism for forcibly discharging ink from the ejection ports of the recording head, and a waste ink storage unit for storing waste ink generated by the ejection of ink. Typically, the waste ink storage unit has a waste ink absorber that absorbs and retains the ink, and functions to retain the waste ink in the waste ink absorber. Since the ink in the waste ink storage unit exists in an evaporated state, it tends to solidify and accumulate. Because the accumulated material inhibits ink absorption, ink overflow can occur depending on the operating environment of the inkjet recording device. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-083903 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-051648 Summary of the Invention [Problem to be solved by the invention]

[0006] The inks proposed in Patent Documents 1 and 2 have been shown to produce images with improved lightfastness compared to conventional dye inks developed prior to those technologies. However, there is a demand for even higher levels of lightfastness in images. Furthermore, as a result of the inventors' investigations, it was found that even with improvements in the shape of the waste ink absorber, it is difficult to sufficiently enhance the deposition suppression effect for inks containing dyes with enhanced coagulation properties to improve lightfastness, and there is room for improvement.

[0007] Therefore, an object of the present invention is to provide an aqueous ink that can record images with excellent lightfastness and can suppress accumulation of the waste ink on a waste ink absorber. Another object of the present invention is to provide an ink cartridge and an inkjet recording method that use this aqueous ink. [Means for solving the problem]

[0008] The above object can be achieved by the present invention, which provides a water-based inkjet ink containing a colorant and a water-soluble organic solvent, wherein the colorant contains a compound represented by the following general formula (I), and the water-soluble organic solvent is: At 25°C LogP X The ink contains a water-soluble organic solvent X having a mass ratio of -0.97 or more, the mass ratio (mass %) of the water-soluble organic solvent X to the mass (mass %) of the water-soluble organic solvent being 0.20 times or more and 0.45 times or less, based on the total mass of the ink. At 25°C LogP S is -1.60 or more and -1.10 or less, and the sodium ion content (ppm) based on the total mass of the ink is 150 ppm or more and 1500 ppm or less.

[0009] TIFF0007718833000001.tif30170 (In the general formula (I), R1 represents a monovalent group, R2 represents -OR3 or -NHR4 (R3 and R4 represent a hydrogen atom or a monovalent group), R5 represents an alkyl group, an aryl group, or a monovalent triazine ring group having an ionic group as a substituent, R6 represents an arylene group or a divalent heterocyclic group, R7 represents a divalent linking group, and m represents 0 or 1.) [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an aqueous ink that can record images with excellent lightfastness and that can suppress accumulation of the ink on a waste ink absorber. Furthermore, according to the present invention, it is possible to provide an ink cartridge and an inkjet recording method that use the aqueous ink. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view schematically illustrating an embodiment of an ink cartridge of the present invention. [Figure 2]1A and 1B are diagrams schematically illustrating an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, in which FIG. 1A is a perspective view of the main part of the inkjet recording apparatus, and FIG. 1B is a perspective view of a head cartridge. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink as dissociated ions, but for convenience, it will be expressed as "containing a salt." Furthermore, aqueous inkjet inks may be simply referred to as "ink." Physical property values are values at room temperature (25°C) unless otherwise specified.

[0013] As described above, the compound represented by general formula (I) is a colorant (dye) with enhanced coagulation properties due to its structural innovation. In inks containing a compound represented by general formula (I) with such properties, there is a trade-off between the lightfastness of the printed image and the suppression of deposition in the waste ink absorber. The lightfastness of the image is related to the aggregation that occurs after the ink is applied to the recording medium, when water, which has a high vapor pressure among the liquid components, evaporates and the proportion of water-soluble organic solvent near the colorant rapidly increases. Meanwhile, the suppression of deposition in the waste ink absorber is related to the aggregation that occurs when a certain amount of liquid components, including water, are present near the colorant. In other words, factors that affect the aggregation of the colorant when different components are present near the colorant must be considered. Based on this point, the inventors conducted research and found that precise control of the polarity of the water-soluble organic solvent and the aggregation caused by monovalent cations is necessary to achieve both lightfastness of the image and suppression of deposition in the waste ink absorber.

[0014] Specifically, we found that the following four conditions must be satisfied. The background to the discovery of these conditions is explained below. (1) The ink contains a water-soluble organic solvent X having a LogP of −0.97 or more. (2) The ink further contains a water-soluble organic solvent Y having a LogP of less than −0.97, and the content (mass %) of the water-soluble organic solvent X is 0.20 to 0.45 times the mass ratio of the content (mass %) of the water-soluble organic solvent. (3) The sodium ion content is 150 ppm or more and 1500 ppm or less. (4) The LogPs of the water-soluble organic solvents as a whole, including the water-soluble organic solvents X and Y, is −1.60 or more and −1.10 or less.

[0015] Due to its structure, the compound represented by general formula (I) has a high affinity with low-polarity water-soluble organic solvents. The inventors conducted research focusing on LogP, a parameter that indicates the polarity of a water-soluble organic solvent. As a result, they found that adding a water-soluble organic solvent having a LogP of -0.97 or more to an ink is important for improving the lightfastness of images recorded with ink containing the compound represented by general formula (I). Hereinafter, the water-soluble organic solvent having a LogP of -0.97 or more will be referred to as "water-soluble organic solvent X," and its LogP will be referred to as "LogP X Here, we will explain LogP (Log Pow), which is an index showing the polarity of water-soluble organic solvents. LogP is the partition coefficient between water and octanol (1-octanol). LogP is a physical property value related to the affinity of the target substance with water; the higher this value, the lower the polarity and hydrophilicity.

[0016] The inventors have used LogP X The mechanism by which the lightfastness of an image is improved by using a water-soluble organic solvent X with a LogP of -0.97 or more is thought to be as follows: Consider the state after the ink is applied to a recording medium. Dye ink absorbs light and develops color as the coloring material remains near the surface of the recording medium. As time passes after the ink is applied to the recording medium, an image is formed through the process of drying of the liquid components and fixing of the dye. During this process, when water, which has a high vapor pressure among the liquid components that make up the water-based ink, begins to evaporate, the compound represented by general formula (I) approaches the water-soluble organic solvent, which has a higher affinity. As a result of the inventors' investigations, it was found that the LogPX The lightfastness was particularly improved when a water-soluble organic solvent X with a polarity of -0.97 or more was used. From this, it is thought that the compound represented by general formula (I) becomes less susceptible to deterioration by light, as it is fixed to the recording medium in an aggregated state by coming close to the water-soluble organic solvent with low polarity, thereby improving the lightfastness of the image.

[0017] On the other hand, when the water-soluble organic solvent Y having a LogP of less than -0.97 was used alone as the water-soluble organic solvent to be contained in the ink, the lightfastness was insufficient. This is thought to be because the affinity between the water-soluble organic solvent Y having a LogP of less than -0.97 and the compound represented by general formula (I) is low, making it difficult for the compound represented by general formula (I) to approach the water-soluble organic solvent, and therefore aggregation did not occur.

[0018] As mentioned above, LogP X The use of a water-soluble organic solvent X with a LogP of -0.97 or greater can improve the lightfastness of images. However, it has been found that the use of water-soluble organic solvent X also increases the coagulation of dyes in the waste ink absorber of an inkjet recording device, potentially resulting in deposition. Therefore, the present inventors investigated a method for suppressing deposition while using water-soluble organic solvent X to improve the lightfastness of images. As a result, they found that a certain degree of deposition suppression effect can be achieved when the content (mass%) of water-soluble organic solvent X is 0.20 to 0.45 times the content (mass%) of the water-soluble organic solvent, based on the total mass of the ink. In other words, in addition to water-soluble organic solvent X, a water-soluble organic solvent Y with a LogP of less than -0.97 must be used, and the mass ratio of water-soluble organic solvent X must be within the above range.

[0019] As described above, a water-soluble organic solvent Y having a LogP of less than -0.97 has low affinity with the compound represented by general formula (I) and is therefore less likely to aggregate the dye. Compared to when the ink is applied to a recording medium to form an image, a large amount of water remains when the ink is discharged into the waste ink absorber. The presence of a water-soluble organic solvent Y having a LogP of less than -0.97 and water having excellent affinity with it suppresses rapid aggregation of the dye even in the presence of the water-soluble organic solvent X. During this time, the ink penetrates the waste ink absorber, making it easier to suppress deposition. If the mass ratio is less than 0.20, the amount of water-soluble organic solvent X required to aggregate the dye is too small, resulting in insufficient lightfastness of the image. On the other hand, if the mass ratio is more than 0.45, the amount of water-soluble organic solvent X is too high, making the dye more likely to aggregate, and thus failing to suppress deposition in the waste ink absorber.

[0020] Furthermore, in order to improve the lightfastness of the image and to reliably suppress deposition on the waste ink absorber, in addition to the two conditions mentioned above, the sodium ion content in the ink must be 150 ppm or more and 1500 ppm or less. The reason for this is explained below.

[0021] The compound represented by general formula (I) contains an ionic group. The dye exists in a dissolved state in the aqueous medium that constitutes the ink due to the ionic dissociation of the ionic group. The intermolecular distance between dye molecules varies depending on the type of monovalent cation present in the ink, which has a significant impact on dye aggregation. Monovalent cations exist in the ink primarily as counter ions of the anionic groups of the dye, but in addition to the counter ions, there are also monovalent cations that are derived from other components. Some of the counter ions of the anionic groups of the dye can be exchanged with monovalent cations derived from other components. Therefore, dye aggregation can be controlled by utilizing the monovalent cations present in the ink.

[0022] Sodium ions have a smaller atomic radius than potassium ions. The presence of sodium ions in ink reduces the intermolecular distance between compounds represented by general formula (I), facilitating dye aggregation and improving image lightfastness. On the other hand, if only lithium ions are used as alkali metal ions, the intermolecular distance becomes too small, causing the dye to rapidly aggregate in the waste ink absorber, making it impossible to suppress deposition. Therefore, sodium ions are considered to be the optimal monovalent cation for achieving both image lightfastness and ink deposition suppression. When the sodium ion content in the ink was less than 150 ppm, image lightfastness was not achieved. This is believed to be because the compound represented by general formula (I) did not sufficiently aggregate on the recording medium to which the ink was applied. Furthermore, when the sodium ion content in the ink exceeded 1500 ppm, ink deposition could not be suppressed. This is believed to be because the presence of a large amount of sodium ions in the ink made the compound represented by general formula (I) more likely to rapidly aggregate in the waste ink absorber.

[0023] As a result of investigations by the present inventors, it was found that the ink described in Patent Document 2 was unable to achieve both the lightfastness of the image and the suppression of deposition in the waste ink absorber to a level that meets the recent demands. In particular, the ink described in Patent Document 2 contains too little water-soluble organic solvent X for aggregating the dye, resulting in insufficient lightfastness of the image. In addition, it is believed that the ethylene urea contained in the ink described in Patent Document 2 becomes solid when the liquid component evaporates, which prevents the ink from sufficiently penetrating into the waste ink absorber and makes it prone to precipitation.

[0024] Therefore, the inventors of the present invention have conducted research to more reliably suppress the accumulation of ink on the waste ink absorber. As a result, the LogP S It was found that the effect of suppressing ink deposition can be reliably obtained by setting LogP to be between -1.60 and -1.10. S is the sum of the LogP values of each water-soluble organic solvent in the ink weighted by its content (mass %).

[0025] Compared to the ink applied to the recording medium, the ink has a higher moisture content when it is discharged into the waste ink absorber. However, compared to the ink before it is ejected or discharged, the ink discharged into the waste ink absorber has had most of its moisture evaporated. Therefore, the ease with which the waste ink is absorbed depends on the ease with which the liquid component made up of the water-soluble organic solvent that remains after the moisture has evaporated. In this case, the greater the LogP of the liquid component made up of the water-soluble organic solvent, the lower the polarity of the liquid component and the weaker the intermolecular forces, thereby lowering the surface energy. Therefore, it is thought that the liquid component becomes more compatible with the components of the waste ink absorber, making it easier for the waste ink to penetrate into the waste ink absorber. On the other hand, the LogP of the water-soluble organic solvent in the ink S When LogP of the water-soluble organic solvent was set to less than -1.60, deposition could not be suppressed. This is thought to be because the liquid component consisting of the water-soluble organic solvent is not easily compatible with the waste ink absorber, and the waste ink does not easily penetrate into the waste ink absorber. S When the ratio was greater than -1.10, the ink deposition could not be suppressed. This is thought to be because the polarity of the liquid component composed of the water-soluble organic solvent was significantly reduced, making the compound represented by general formula (I) more likely to aggregate.

[0026] Furthermore, the LogP of water-soluble organic solvents S It was also found that the lightfastness of the image can be improved by setting the LogP of the water-soluble organic solvent to -1.60 or more. In the dots immediately after the ink is applied to the recording medium, the ink is likely to separate into two layers, a water layer and a water-soluble organic solvent layer, due to the difference in polarity. At this time, the LogP of the water-soluble organic solvent S By making the value of the water-soluble organic solvent layer -1.60 or more, the polarity of the water-soluble organic solvent layer decreases, and the compound represented by general formula (I) present in the water layer is more likely to migrate from the water layer to the water-soluble organic solvent layer side. As a result, it is thought that the aggregation of the compound represented by general formula (I) is promoted in the process of fixing the dye, and the lightfastness of the image is improved.

[0027] <Ink> The components constituting the ink of the present invention and the physical properties of the ink will be described in detail below.

[0028] (Colorant: Compound represented by general formula (I)) The ink of the present invention contains a compound represented by the following general formula (I) as a coloring material (dye). This ink may contain other coloring materials in addition to the compound represented by general formula (I), for example, for the purpose of toning.

[0029] TIFF0007718833000002.tif30170

[0030] In general formula (I), R1 represents a monovalent group, R2 represents -OR3 or -NHR4 (R3 and R4 represent a hydrogen atom or a monovalent group), R5 represents an alkyl group, an aryl group, or a monovalent triazine ring group having an ionic group as a substituent, R6 represents an arylene group or a divalent heterocyclic group, R7 represents a divalent linking group, and m represents 0 or 1.

[0031] R1 in general formula (I) represents a monovalent group. Examples of the monovalent group include a halogen atom, an alkyl group, a cycloalkyl group, an aralkyl group, an alkenyl group, an alkynyl group, an aryl group, a heterocyclic group, a cyano group, a hydroxy group, a nitro group, a carboxylic acid group (which may be in the form of a salt), an alkoxy group, an aryloxy group, a silyloxy group, a heterocyclic oxy group, an acyloxy group, a carbamoyloxy group, an alkoxycarbonyloxy group, an aryloxycarbonyloxy group, an amino group, an alkylamino group, an anilino group, an acylamino group, an aminocarbonylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfamoyl Examples of the alkyl group include an arylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a mercapto group, an alkylthio group, an arylthio group, a heterocyclic thio group, a sulfamoyl group, a sulfonic acid group (which may be in the form of a salt), an alkylsulfinyl group, an arylsulfinyl group, an alkylsulfonyl group, an arylsulfonyl group, an acyl group, an aryloxycarbonyl group, an alkoxycarbonyl group, a carbamoyl group, an imido group, a phosphino group, a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, a silyl group, a phosphoric acid group (which may be in the form of a salt), and a phosphonic acid group (which may be in the form of a salt).

[0032] Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0033] The alkyl group includes a substituted or unsubstituted alkyl group. The substituted or unsubstituted alkyl group is preferably an alkyl group having 1 to 30 carbon atoms. Examples of the substituent include the same groups as those listed above for the monovalent group. Among these, a hydroxy group, an alkoxy group, a cyano group, a halogen atom, a sulfonic acid group (which may be in a salt form), a carboxylic acid group (which may be in a salt form), a phosphoric acid group (which may be in a salt form), and a phosphonic acid group (which may be in a salt form) are preferred. The "substituted" group described below also includes groups substituted with the same substituents as those listed above. Examples of the alkyl group include methyl, ethyl, butyl, t-butyl, n-octyl, eicosyl, 2-chloroethyl, hydroxyethyl, cyanoethyl, 4-sulfobutyl, and 4-carboxybutyl.

[0034] The cycloalkyl group includes a substituted or unsubstituted cycloalkyl group. As the substituted or unsubstituted cycloalkyl group, a cycloalkyl group having 5 to 30 carbon atoms is preferable. Examples of the cycloalkyl group include cyclohexyl, cyclopentyl, and 4-n-dodecylcyclohexyl.

[0035] The aralkyl group includes a substituted or unsubstituted aralkyl group. As the substituted or unsubstituted aralkyl group, an aralkyl group having 7 to 30 carbon atoms is preferable. Examples of the aralkyl group include benzyl and 2-phenethyl.

[0036] The alkenyl group includes linear, branched, or cyclic, substituted or unsubstituted alkenyl groups. As the substituted or unsubstituted alkenyl group, an alkenyl group having 2 to 30 carbon atoms is preferable. Examples of the alkenyl group include vinyl, allyl, prenyl, geranyl, oleyl, 2-cyclopenten-1-yl, and 2-cyclohexen-1-yl.

[0037] The alkynyl group includes substituted or unsubstituted alkynyl groups. As the substituted or unsubstituted alkynyl group, an alkynyl group having 2 to 30 carbon atoms is preferable. Examples of the alkynyl group include ethynyl and propargyl.

[0038] The aryl group includes a substituted or unsubstituted aryl group. The substituted or unsubstituted aryl group is preferably an aryl group having 6 to 30 carbon atoms. Examples of the aryl group include phenyl, p-tolyl, naphthyl, m-chlorophenyl, and o-hexadecanoylaminophenyl.

[0039] The heterocyclic group includes a monovalent group obtained by removing one hydrogen atom from a substituted or unsubstituted, aromatic or non-aromatic heterocyclic compound. As the substituted or unsubstituted heterocyclic group, a 5- or 6-membered aromatic heterocyclic group having 3 to 30 carbon atoms is preferred. Examples of such an aromatic heterocyclic group include 2-furyl, 2-thienyl, 2-pyrimidinyl, and 2-benzothiazolyl.

[0040] The alkoxy group includes a substituted or unsubstituted alkoxy group. As the substituted or unsubstituted alkoxy group, an alkoxy group having 1 to 30 carbon atoms is preferable. Examples of the alkoxy group include methoxy, ethoxy, isopropoxy, n-octyloxy, methoxyethoxy, hydroxyethoxy, and 3-carboxypropoxy.

[0041] The aryloxy group includes a substituted or unsubstituted aryloxy group. The substituted or unsubstituted aryloxy group is preferably an aryloxy group having 6 to 30 carbon atoms. Examples of the aryloxy group include phenoxy, 2-methylphenoxy, 4-t-butylphenoxy, 3-nitrophenoxy, and 2-tetradecanoylaminophenoxy.

[0042] The silyloxy group is preferably a silyloxy group having a carbon number of 3 to 20. Examples of the silyloxy group include trimethylsilyloxy and t-butyldimethylsilyloxy.

[0043] The heterocyclic oxy group includes a substituted or unsubstituted heterocyclic oxy group. The substituted or unsubstituted heterocyclic oxy group is preferably a heterocyclic oxy group having 2 to 30 carbon atoms. Examples of the heterocyclic oxy group include 1-phenyltetrazol-5-oxy and 2-tetrahydropyranyloxy.

[0044] The acyloxy group is preferably a formyloxy group, a substituted or unsubstituted alkylcarbonyloxy group having 2 to 30 carbon atoms, or a substituted or unsubstituted arylcarbonyloxy group having 6 to 30 carbon atoms. Examples of the acyloxy group include formyloxy, acetyloxy, pivaloyloxy, stearoyloxy, benzoyloxy, and p-methoxyphenylcarbonyloxy.

[0045] The carbamoyloxy group includes a substituted or unsubstituted carbamoyloxy group. As the substituted or unsubstituted carbamoyloxy group, a carbamoyloxy group having 1 to 30 carbon atoms is preferable. Examples of the carbamoyloxy group include N,N-dimethylcarbamoyloxy, N,N-diethylcarbamoyloxy, morpholinocarbonyloxy, N,N-di-n-octylaminocarbonyloxy, and Nn-octylcarbamoyloxy.

[0046] The alkoxycarbonyloxy group includes a substituted or unsubstituted alkoxycarbonyloxy group. As the substituted or unsubstituted alkoxycarbonyloxy group, an alkoxycarbonyloxy group having 2 to 30 carbon atoms is preferable. Examples of the alkoxycarbonyloxy group include methoxycarbonyloxy, ethoxycarbonyloxy, t-butoxycarbonyloxy, and n-octylcarbonyloxy.

[0047] The aryloxycarbonyloxy group includes a substituted or unsubstituted aryloxycarbonyloxy group. As the substituted or unsubstituted aryloxycarbonyloxy group, an aryloxycarbonyloxy group having 7 to 30 carbon atoms is preferable. Examples of the aryloxycarbonyloxy group include phenoxycarbonyloxy, p-methoxyphenoxycarbonyloxy, p-(n-hexadecyloxy)phenoxycarbonyloxy, etc.

[0048] The alkylamino group includes a substituted or unsubstituted alkylamino group. The substituted or unsubstituted alkylamino group is preferably an alkylamino group having 1 to 30 carbon atoms. Examples of the alkylamino group include methylamino and dimethylamino.

[0049] The anilino group includes a substituted or unsubstituted anilino group. The substituted or unsubstituted anilino group is preferably an anilino group having 6 to 30 carbon atoms. Examples of the anilino group include anilino, N-methylanilino, and diphenylamino.

[0050] The acylamino group is preferably a formylamino group, a substituted or unsubstituted alkylcarbonylamino group having 1 to 30 carbon atoms, or a substituted or unsubstituted arylcarbonylamino group having 6 to 30 carbon atoms. Examples of the acylamino group include formylamino, acetylamino, pivaloylamino, lauroylamino, benzoylamino, and 3,4,5-tri-n-octyloxyphenylcarbonylamino.

[0051] The aminocarbonylamino group includes a substituted or unsubstituted aminocarbonylamino group. The substituted or unsubstituted aminocarbonylamino group is preferably an aminocarbonylamino group having 1 to 30 carbon atoms. Examples of the aminocarbonylamino group include carbamoylamino, N,N-dimethylaminocarbonylamino, N,N-diethylaminocarbonylamino, and morpholinocarbonylamino.

[0052] The alkoxycarbonylamino group includes a substituted or unsubstituted alkoxycarbonylamino group. The substituted or unsubstituted alkoxycarbonylamino group is preferably an alkoxycarbonylamino group having 2 to 30 carbon atoms. Examples of the alkoxycarbonylamino group include methoxycarbonylamino, ethoxycarbonylamino, t-butoxycarbonylamino, n-octadecyloxycarbonylamino, and N-methyl-methoxycarbonylamino.

[0053] The aryloxycarbonylamino group includes a substituted or unsubstituted aryloxycarbonylamino group. The substituted or unsubstituted aryloxycarbonylamino group is preferably an aryloxycarbonylamino group having 7 to 30 carbon atoms. Examples of the aryloxycarbonylamino group include phenoxycarbonylamino, p-chlorophenoxycarbonylamino, and m-(n-octyloxy)phenoxycarbonylamino.

[0054] The sulfamoylamino group includes a substituted or unsubstituted sulfamoylamino group. As the substituted or unsubstituted sulfamoylamino group, a sulfamoylamino group having 0 to 30 carbon atoms is preferable. Examples of the sulfamoylamino group include sulfamoylamino, N,N-dimethylaminosulfonylamino, and N,N-octylaminosulfonylamino.

[0055] The alkylsulfonylamino group includes a substituted or unsubstituted alkylsulfonylamino group. The substituted or unsubstituted alkylsulfonylamino group is preferably an alkylsulfonylamino group having 1 to 30 carbon atoms. Examples of the alkylsulfonylamino group include methylsulfonylamino and butylsulfonylamino.

[0056] The arylsulfonylamino group includes a substituted or unsubstituted arylsulfonylamino group. The substituted or unsubstituted arylsulfonylamino group is preferably an arylsulfonylamino group having 6 to 30 carbon atoms. Examples of the arylsulfonylamino group include phenylsulfonylamino, 2,3,5-trichlorophenylsulfonylamino, and p-methylphenylsulfonylamino.

[0057] The alkylthio group includes a substituted or unsubstituted alkylthio group. As the substituted or unsubstituted alkylthio group, an alkylthio group having 1 to 30 carbon atoms is preferable. Examples of the alkylthio group include methylthio, ethylthio, and n-hexadecylthio.

[0058] The arylthio group includes a substituted or unsubstituted arylthio group. The substituted or unsubstituted arylthio group is preferably an arylthio group having 6 to 30 carbon atoms. Examples of the arylthio group include phenylthio, p-chlorophenylthio, and m-methoxyphenylthio.

[0059] The heterocyclic thio group includes a substituted or unsubstituted heterocyclic thio group. The substituted or unsubstituted heterocyclic thio group is preferably a heterocyclic thio group having 2 to 30 carbon atoms. Examples of the heterocyclic thio group include 2-benzothiazolylthio and 1-phenyltetrazol-5-ylthio.

[0060] The sulfamoyl group includes a substituted or unsubstituted sulfamoyl group. As the substituted or unsubstituted sulfamoyl group, a sulfamoyl group having 0 to 30 carbon atoms is preferable. Examples of the sulfamoyl group include N-ethylsulfamoyl, N-(3-dodecyloxypropyl)sulfamoyl, N,N-dimethylsulfamoyl, N-acetylsulfamoyl, N-benzoylsulfamoyl, and N-(N'-phenylcarbamoyl)sulfamoyl.

[0061] The alkylsulfinyl group includes a substituted or unsubstituted alkylsulfinyl group. As the substituted or unsubstituted alkylsulfinyl group, an alkylsulfinyl group having 1 to 30 carbon atoms is preferable. Examples of the alkylsulfinyl group include methylsulfinyl and ethylsulfinyl.

[0062] The arylsulfinyl group includes a substituted or unsubstituted arylsulfinyl group. The substituted or unsubstituted arylsulfinyl group is preferably an arylsulfinyl group having 6 to 30 carbon atoms. Examples of the arylsulfinyl group include phenylsulfinyl and p-methylphenylsulfinyl.

[0063] The alkylsulfonyl group includes a substituted or unsubstituted alkylsulfonyl group. As the substituted or unsubstituted alkylsulfonyl group, an alkylsulfonyl group having 1 to 30 carbon atoms is preferable. Examples of the alkylsulfonyl group include methylsulfonyl and ethylsulfonyl.

[0064] The arylsulfonyl group includes a substituted or unsubstituted arylsulfonyl group. The substituted or unsubstituted arylsulfonyl group is preferably an arylsulfonyl group having 6 to 30 carbon atoms. Examples of the arylsulfonyl group include phenylsulfonyl and p-methylphenylsulfonyl.

[0065] The acyl group is preferably a formyl group, a substituted or unsubstituted alkylcarbonyl group having 2 to 30 carbon atoms, or a substituted or unsubstituted arylcarbonyl group having 7 to 30 carbon atoms. Furthermore, the acyl group is also preferably a substituted or unsubstituted heterocyclic carbonyl group having 4 to 30 carbon atoms and bonded to a carbonyl group via a carbon atom. Examples of the acyl group include acetyl, pivaloyl, 2-chloroacetyl, stearoyl, benzoyl, p-(n-octyloxy)phenylcarbonyl, 2-pyridylcarbonyl, and 2-furylcarbonyl.

[0066] The aryloxycarbonyl group includes a substituted or unsubstituted aryloxycarbonyl group. As the substituted or unsubstituted aryloxycarbonyl group, an aryloxycarbonyl group having 7 to 30 carbon atoms is preferable. Examples of the aryloxycarbonyl group include phenoxycarbonyl, o-chlorophenoxycarbonyl, m-nitrophenoxycarbonyl, p-(t-butyl)phenoxycarbonyl, etc.

[0067] The alkoxycarbonyl group includes a substituted or unsubstituted alkoxycarbonyl group. The substituted or unsubstituted alkoxycarbonyl group is preferably an alkoxycarbonyl group having 2 to 30 carbon atoms. Examples of the alkoxycarbonyl group include methoxycarbonyl, ethoxycarbonyl, t-butoxycarbonyl, and n-octadecyloxycarbonyl.

[0068] The carbamoyl group includes a substituted or unsubstituted carbamoyl group. As the substituted or unsubstituted carbamoyl group, a carbamoyl group having 1 to 30 carbon atoms is preferable. Examples of the carbamoyl group include carbamoyl, N-methylcarbamoyl, N,N-dimethylcarbamoyl, N,N-di-n-octylcarbamoyl, and N-(methylsulfonyl)carbamoyl.

[0069] The imido group includes a substituted or unsubstituted imido group. As the substituted or unsubstituted imido group, an imido group having 4 to 30 carbon atoms is preferable. Examples of the imido group include succinimide, phthalimide, glutarimide, and hexanimide.

[0070] The phosphino group includes a substituted or unsubstituted phosphino group. The substituted or unsubstituted phosphino group is preferably a phosphino group having 2 to 30 carbon atoms. Examples of the phosphino group include dimethylphosphino, diphenylphosphino, and methylphenoxyphosphino.

[0071] The phosphinyl group includes a substituted or unsubstituted phosphinyl group. As the substituted or unsubstituted phosphinyl group, a phosphinyl group having 2 to 30 carbon atoms is preferable. Examples of the phosphinyl group include phosphinyl, dioctyloxyphosphinyl, and diethoxyphosphinyl.

[0072] The phosphinyloxy group includes a substituted or unsubstituted phosphinyloxy group. As the substituted or unsubstituted phosphinyloxy group, a phosphinyloxy group having 2 to 30 carbon atoms is preferable. Examples of the phosphinyloxy group include diphenoxyphosphinyloxy and dioctyloxyphosphinyloxy.

[0073] The phosphinylamino group includes a substituted or unsubstituted phosphinylamino group. The substituted or unsubstituted phosphinylamino group is preferably a phosphinylamino group having 2 to 30 carbon atoms. Examples of the phosphinylamino group include dimethoxyphosphinylamino and dimethylaminophosphinylamino.

[0074] The silyl group includes a substituted or unsubstituted silyl group. As the substituted or unsubstituted silyl group, a silyl group having 3 to 30 carbon atoms is preferable. Examples of the silyl group include trimethylsilyl, t-butyldimethylsilyl, and phenyldimethylsilyl.

[0075] Among the above-mentioned monovalent groups, those having a hydrogen atom may have this hydrogen atom substituted with the above-mentioned monovalent group or a substituent described below. Examples of such a substituent include an alkylcarbonylaminosulfonyl group, an arylcarbonylaminosulfonyl group, an alkylsulfonylaminocarbonyl group, and an arylsulfonylaminocarbonyl group. Specific examples thereof include methylsulfonylaminocarbonyl, p-methylphenylsulfonylaminocarbonyl, acetylaminosulfonyl, and benzoylaminosulfonyl.

[0076] R1 is preferably the aforementioned alkyl group, aryl group or alkoxy group, more preferably an alkyl group, and even more preferably a t-butyl group.

[0077] In general formula (I), R2 represents -OR3 or -NHR4. R3 and R4 represent a hydrogen atom or a monovalent group. Examples of this monovalent group include the same groups as those exemplified for the monovalent group represented by R1, including preferred groups. R2 is preferably -OH or -NH2, and more preferably -NH2.

[0078] In general formula (I), R5 represents an alkyl group, an aryl group, or a monovalent triazine ring group having an ionic group as a substituent. It is more preferable that each group in R5 has one or two (more preferably two) ionic groups. The ionic group may be an acid type or a salt type. Examples of the ionic group include a carboxylic acid group, a sulfonic acid group, a phosphate group, and a phosphonic acid group. A preferred ionic group is a carboxylic acid group. Examples of counter ions when forming a salt include cations such as alkali metals, ammonia (NH3), and organic ammonium. Examples of alkali metals include lithium, sodium, and potassium. Examples of organic ammonium include alkylamines having 1 to 3 carbon atoms, such as methylamine and ethylamine; and organic ammoniums such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, and triisopropanolamine, each having 1 to 4 carbon atoms, such as mono-, di-, or trialkanolamines.

[0079] The alkyl group represented by R5 includes an alkyl group that may have a substituent other than the ionic group. Examples of the alkyl group represented by R5 include the same alkyl groups as those exemplified for the monovalent group represented by R1, including preferred examples. The aryl group represented by R5 includes an aryl group that may have a substituent other than the ionic group. Examples of the aryl group represented by R5 include the same aryl groups as those exemplified for the aryl group represented by R1, including preferred examples. The monovalent triazine ring group represented by R5 includes a triazine ring group that may have a substituent other than the ionic group. Note that when each group in R5 has a substituent other than the ionic group, examples of the substituent include the same aryl groups as those exemplified for the monovalent group represented by R1 (excluding the ionic group), including preferred examples. R5 is preferably an aryl group or a monovalent triazine ring group, more preferably an aryl group, and even more preferably a phenyl group.

[0080] In general formula (I), R6 represents an arylene group or a divalent heterocyclic group. The arylene group represented by R6 includes a substituted or unsubstituted arylene group. As the substituted or unsubstituted arylene group, an arylene group having 6 to 30 carbon atoms is preferable. Examples of the substituent include the same as those exemplified for the monovalent group represented by R1 above. Examples of the arylene group include phenylene and naphthylene.

[0081] The divalent heterocyclic group represented by R6 is preferably a 5- or 6-membered ring. These divalent heterocyclic rings may be further condensed and may be aromatic or non-aromatic heterocyclic rings. Heterocyclic groups can generally be classified into Type I and Type II. Type I heterocyclic groups are known as acidic nuclei. Examples of Type I heterocyclic groups include a 5-pyrazolone ring, a 5-aminopyrazole ring, an oxazolone ring, a barbituric acid ring, a pyridone ring, a rhodanine ring, a pyrazolidinedione ring, a pyrazolopyridone ring, and a Meldrum's acid ring. Of these, a 5-pyrazolone ring and a 5-aminopyrazole ring are preferred. Type II heterocyclic groups are known as basic nuclei. Examples of type II heterocyclic groups include pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, isoquinoline, quinazoline, cinnoline, phthalazine, quinoxaline, pyrrole, indole, furan, benzofuran, thiophene, benzothiophene, pyrazole, imidazole, benzimidazole, triazole, oxazole, benzoxazole, thiazole, benzothiazole, isothiazole, benzisothiazole, thiadiazole, isoxazole, benzisoxazole, pyrrolidine, piperidine, piperazine, imidazolidine, and thiazoline. Among these, aromatic heterocyclic groups are preferred, and pyridine, pyrazine, pyrimidine, pyridazine, triazine, pyrazole, imidazole, benzimidazole, triazole, thiazole, benzothiazole, isothiazole, benzisothiazole, and thiadiazole are more preferred, with thiadiazole being particularly preferred from the standpoint of light resistance. The divalent heterocyclic group may have a substituent. Examples of the substituent include the same groups as those exemplified for the monovalent group represented by R1.

[0082] In general formula (I), R7 represents a divalent linking group, and m represents 0 or 1. When m is 0, it means that two R6s are bonded to each other.

[0083] Examples of the divalent linking group represented by R7 include alkylene groups such as methylene, ethylene, propylene, butylene, and pentylene; alkenylene groups such as ethenylene and propenylene; alkynylene groups such as ethynylene and propynylene; arylene groups such as phenylene and naphthylene; divalent heterocyclic groups such as 6-chloro-1,3,5-triazine-2,4-diyl, pyrimidine-2,4-diyl, and quinoxaline-2,3-diyl; -O-; -CO-; -NR9- (R9 is a hydrogen atom, an alkyl group, or an aryl group); -S-; -SO2-; -SO-; and combinations thereof.

[0084] The alkylene group, alkenylene group, alkynylene group, arylene group, divalent heterocyclic group, alkyl group and aryl group represented by R9 may all have a substituent. Examples of the substituent include the same as those exemplified for the monovalent group represented by R1 above. Examples of the alkyl group and aryl group represented by R9 include the same as those exemplified for the alkyl group and aryl group among the monovalent groups represented by R1 above, including preferred ones.

[0085] R7 is more preferably an alkylene group having 10 or less carbon atoms, an alkenylene group having 10 or less carbon atoms, an alkynylene group having 10 or less carbon atoms, an arylene group having from 6 to 10 carbon atoms, a divalent heterocyclic group, -O-, -S-, or a combination thereof. Of these, a combination of -S- and an alkylene group is particularly preferred from the viewpoint of the stability of the compound represented by general formula (I).

[0086] The divalent linking group represented by R7 preferably has a total of 0 to 50 carbon atoms, more preferably 0 to 30 carbon atoms, and particularly preferably 0 to 10 carbon atoms.

[0087] Among the compounds represented by general formula (I), compounds represented by the following general formula (II) are preferred.

[0088] TIFF0007718833000003.tif44170

[0089] In general formula (II), R1 represents a monovalent group, R2 represents -OR3 or -NHR4 (R3 and R4 represent a hydrogen atom or a monovalent group), R6 represents an arylene group or a divalent heterocyclic group, R7 represents a divalent linking group, m represents 0 or 1, R8 represents an ionic group, and n represents 1 or 2.

[0090] R1 to R4, R6, and R7 in general formula (II) are the same as R1 to R4, R6, and R7 in general formula (I), and preferred groups and combinations thereof are also the same as R1 to R4, R6, and R7 in general formula (I). In general formula (II), the ionic group represented by R8 is the same as the ionic group described above for R5. Among these, a carboxylic acid group or a sulfonic acid group is preferred, with a carboxylic acid group being more preferred. Furthermore, the ionic group represented by R8 is preferably a salt type, and from the viewpoint of more easily enhancing the effect of inhibiting ink deposition, it preferably contains at least one of a sodium ion and a potassium ion as a counter ion forming the salt. Note that when the compound represented by general formula (I) has an ionic group as a monovalent group or substituent, it may be either an acid type or a salt type, as with R8. Examples of counter ions in the salt type include the same cations as those described above for R5.

[0091] In the present invention, it is particularly preferable that the compound represented by general formula (I) has the following structure: R2 is preferably an amino group; R6 is preferably a heterocyclic group, more preferably thiadiazole; and R7 is more preferably a combination of -S- and an alkylene group. The ionic group in the compound represented by general formula (I) is preferably an anionic group, more preferably a carboxylic acid group, and the total number of carboxylic acid groups is preferably 2 to 4, more preferably 4.

[0092] Preferred examples of the compound represented by general formula (I) in free acid form include the following exemplary compounds 1 to 39. Of course, the present invention is not limited to the following exemplary compounds as long as they are encompassed by the structure and definition of general formula (I). Among the following exemplary compounds, exemplary compounds 8 to 20, 25 to 29, 31, 32, and 39 are preferred, with exemplary compound 9 being more preferred.

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[0132] (Colorant verification method) To verify whether or not the coloring material (compound represented by general formula (I)) used in the present invention is contained in each ink, the following verification methods (1) to (3) using high performance liquid chromatography (HPLC) can be applied. (1) Peak retention time (2) Maximum absorption wavelength for peak (1) (3) M / Z (positive) and M / Z (negative) of the mass spectrum for the peak in (1)

[0133] The analytical conditions for high-performance liquid chromatography are as follows: A liquid (ink) diluted approximately 1,000 times with pure water is used as the measurement sample. Analysis is then performed by high-performance liquid chromatography under the conditions below, and the peak retention time and maximum absorption wavelength of the peak are measured. Column: SunFire C18 (Nihon Waters) 2.1mm x 150mm Column temperature: 40℃ ·Flow rate: 0.2mL / min PDA: 200nm~700nm Mobile phase and gradient conditions: Table 1

[0134] TIFF0007718833000043.tif35170

[0135] The mass spectrum analysis conditions are as follows: Mass spectrum is measured for the obtained peaks under the conditions below, and the most strongly detected MZ is measured for each of the positive and negative peaks. Ionization method: ESI Capillary voltage: 3.5kV Desolvation gas: 300℃ Ion source temperature: 120℃ Detector: posi;40V 200~1500amu / 0.9sec negative; 40V 200~1500amu / 0.9sec

[0136] Measurement was carried out using the method and conditions described above for Exemplary Compound 9, a specific example of the compound represented by General Formula (I). The resulting retention time, maximum absorption wavelength, M / Z (posi), and M / Z (negative) values are shown in Table 2. Measurement is carried out using the same method and conditions as above for an unknown ink, and if the measured values correspond to the values shown in Table 2, it can be determined that the ink contains the compound represented by General Formula (I) used in the ink of the present invention.

[0137] TIFF0007718833000044.tif26170

[0138] The content (mass %) of the colorant is preferably 0.10 mass % or more and 10.00 mass % or less, more preferably 0.50 mass % or more and 8.00 mass % or less, and even more preferably 0.80 mass % or more and 5.00 mass % or less, based on the total mass of the ink.

[0139] (sodium ions) The ink of the present invention contains sodium ions. The content (ppm) of sodium ions in the ink is 150 ppm or more and 1500 ppm or less based on the total mass of the ink.

[0140] To incorporate sodium ions into the ink, for example, a compound that generates sodium ions upon ionic dissociation may be added to the ink. Examples of such compounds include inorganic sodium salts and organic sodium salts. Examples of inorganic sodium salts include sodium halides such as sodium fluoride, sodium chloride, and sodium bromide; sodium salts of inorganic acids such as sodium carbonate, sodium sulfate, sodium phosphate, sodium nitrate, and sodium borate; and sodium hydroxide. Examples of organic sodium salts include sodium salts of organic acids such as sodium acetate and sodium benzoate. Similar effects can also be achieved by incorporating a compound represented by general formula (I) or other coloring materials containing sodium ions as counter ions into the ink.

[0141] (Water-soluble organic solvent) The ink contains a water-soluble organic solvent. The water-soluble organic solvent contained in the ink has a LogP of the water-soluble organic solvent calculated by the following formula (3): S LogP must be between -1.60 and -1.10. S is the sum of the LogP values of each water-soluble organic solvent in the ink weighted by its content (mass%). S means the LogP of the "total water-soluble organic solvent" in the ink. The type and content of the water-soluble organic solvent can be determined by gas chromatography (GC / MS) or high-performance liquid chromatography (LC / MS), etc. Note that while "water-soluble organic solvent" usually refers to a liquid, in the present invention, water-soluble organic solvents also include those that are solid at 25°C (room temperature). TIFF0007718833000045.tif25170 (Equation (3) shows the calculation formula for LogPs of n kinds of water-soluble organic solvents contained in the ink. In equation (3), LogP k represents the LogP of k types (k = 1 to n) of water-soluble organic solvents, and r k represents the content (mass %) of k-type (k=1 to n) water-soluble organic solvent in the ink.)

[0142] As mentioned above, we will now explain LogP (Log Pow), which is an index showing the polarity of water-soluble organic solvents. LogP refers to the partition coefficient between water and octanol (1-octanol). LogP is a physical property value related to the affinity of the target substance with water, and the larger this value, the lower the polarity and hydrophilicity. LogP is calculated as follows: LogP = Log 10 C o / C w (C o represents the concentration of the target substance in the octanol phase, and C wLogP is calculated using the relational expression (where LogP represents the concentration of the target substance in the aqueous phase). LogP can also be determined experimentally using the method described in JIS Z 7260-107. It can also be determined using commercially available calculation software such as "ACD / PhysChem Suite" (manufactured by ACD / Labs). In the examples described below, values determined using "ACD / PhysChem Suite Version 12.00" (manufactured by ACD / Labs) were used. LogP values for various water-soluble organic solvents are shown below.

[0143] Specific examples of water-soluble organic solvents include those shown below (numbers in parentheses are LogP values). Polyethylene glycol with a number average molecular weight of 1000 (-6.35), polyethylene glycol with a number average molecular weight of 400 (-2.82), polyethylene glycol with a number average molecular weight of 200 (-1.88), tetraethylene glycol (-1.88), bis(2-hydroxyethyl) sulfone (-1.86), glycerin (-1.85), urea (-1.66), triethylene glycol (-1.65), diethylene glycol (-1.41), 1,2,6-hexanetriol (-1.39), ethylene glycol (-1.36), ethyleneurea (-1.24), 1,3-propanediol (-1.09), 2-pyrrolidone (-1.09), 1,2-propanediol (-1.01), triethanolamine (-0.99), trimethylolpropane (-0.97), 1,4-butanediol (-0. 77), triethylene glycol monoethyl ether (-0.66), N-methyl-2-pyrrolidone (-0.64), γ-butyrolactone (-0.63), δ-valerolactam (-0.57), 1,5-pentanediol (-0.56), 3-methyl-1,5-pentanediol (-0.21), δ-valerolactone (-0.10), 1,6-hexanediol (-0.05), isopropanol (0.18), triethylene glycol monobutyl ether (0.36), 1,2-hexanediol (0.52), diethylene glycol monobutyl ether (0.60), ethylene glycol monobutyl ether (0.83), 1-pentanol (1.35), 1,2-octanediol (1.54), tripropylene glycol monobutyl ether (1.66), etc. The water-soluble organic solvent contained in the ink preferably has a vapor pressure lower than that of water, and a LogP of -10.00 or more and 2.00 or less.

[0144] Ink has LogP X The water-soluble organic solvent X having a LogP of -0.97 or more is contained. X Specific examples of water-soluble organic solvent X having a LogP of -0.97 or more are shown in parentheses. XThe results are as follows: trimethylolpropane (-0.97), 1,4-butanediol (-0.77), triethylene glycol monoethyl ether (-0.66), N-methyl 2-pyrrolidone (-0.64), γ-butyrolactone (-0.63), δ-valerolactam (-0.57), 1,5-pentanediol (-0.56), 3-methyl-1,5-pentanediol (-0.21), δ-valerolactone (-0.10), 1,6-hexanediol Examples of the ethanol include ethanol (-0.05), isopropanol (0.18), triethylene glycol monobutyl ether (0.36), 1,2-hexanediol (0.52), diethylene glycol monobutyl ether (0.60), ethylene glycol monobutyl ether (0.83), 1-pentanol (1.35), 1,2-octanediol (1.54), and tripropylene glycol monobutyl ether (1.66).

[0145] LogP in water-soluble organic solvent X X The water-soluble organic solvent X with the largest L LogP L and the LogP of the water-soluble organic solvent mentioned above S The difference between the LogP and the LogP of the water-soluble organic solvent X is preferably 2.00 or less. X The water-soluble organic solvent X with the largest L LogP L and LogP of water-soluble organic solvents S It is more preferable that the difference between LogP and is 1.00 or less, since the effect of suppressing ink deposition can be more effectively obtained. This is thought to be because the compound represented by general formula (I) does not rapidly aggregate in the waste ink absorber. When two or more types of water-soluble organic solvents X are present, the compound represented by general formula (I) is affected by the water-soluble organic solvent with the lower polarity, so that the difference between LogP and X The LogP of the water-soluble organic solvent X with the largest value L Consider the LogP in the water-soluble organic solvent X. X The water-soluble organic solvent X with the largest L LogP L and LogP of water-soluble organic solvents SThe difference between is preferably 0.50 or more, more preferably 0.80 or more, and even more preferably 0.90 or more.

[0146] Water-soluble organic solvent X is LogP X It is more preferable that the water-soluble organic solvent X1 has a value of -0.57 or more, since the lightfastness of the image is more likely to be improved. Furthermore, it is even more preferable that the water-soluble organic solvent X contains an alkanediol, since the lightfastness of the image is more likely to be improved. This is thought to be because the hydroxyl groups of the alkanediol form hydrogen bonds with the ionic groups in the compound represented by general formula (I), improving cohesion and lightfastness. An alkanediol refers to a compound in which two hydroxyl groups are bonded to at least one of the carbon atoms constituting a saturated hydrocarbon chain (which may be branched).

[0147] The content (mass%) of water-soluble organic solvent X in the ink is preferably 1.00% to 20.00% by mass, more preferably 2.00% to 15.00% by mass, and even more preferably 5.00% to 10.00% by mass, based on the total mass of the ink. The content (mass%) of water-soluble organic solvent Y in the ink is preferably 5.00% to 25.00% by mass, and even more preferably 10.00% to 20.00% by mass, based on the total mass of the ink. Furthermore, the content (mass%) of water-soluble organic solvent X, based on the total mass of the ink, is preferably 1.00 to 5.00 times the mass of the colorant content (mass%). A mass ratio of 1.00 or more can further enhance the effect of suppressing ink deposition. A mass ratio of 5.00 or less can further enhance the lightfastness of the image.

[0148] (aqueous medium) The ink of the present invention is an aqueous ink containing an aqueous medium, which is a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass %) in the ink is preferably 50.00% to 95.00% by mass, based on the total mass of the ink. Immediately after recording, the ink contains both water and a medium composed of a water-soluble organic solvent. It is believed that the presence of a large amount of highly polar water promotes the compound represented by formula (I) to gather in the water-soluble organic solvent layer immediately after the ink is applied to the recording medium and aggregate, thereby improving lightfastness. From this perspective, the water content (mass %) in the ink is more preferably 58.00% by mass or more.

[0149] (Other additives) In addition to the components described above, the ink of the present invention may contain various additives, as necessary, such as surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, antireducing agents, evaporation accelerators, chelating agents, and water-soluble resins. Note that these additives are not included in the "water-soluble organic solvent" of the present invention, because their content in the ink is usually small and they do not have a significant effect on the aggregation of the dye.

[0150] (Ink properties) The surface tension of the ink at 25°C is preferably 10 mN / m to 60 mN / m, more preferably 20 mN / m to 60 mN / m, and even more preferably 30 mN / m to 40 mN / m. By maintaining the surface tension of the ink within the above range, it is possible to effectively prevent irregular ejection (misalignment of the ink application location on the recording medium) due to wetting near the ejection orifice when applied to an inkjet system. The surface tension of the ink can be adjusted by appropriately setting the content of surfactants, water-soluble organic solvents, etc. in the ink. It is also preferable to adjust the viscosity of the ink to obtain good ejection characteristics when ejected from the ejection orifices of an inkjet recording head. The viscosity of the ink at 25°C is preferably 1.0 mPa·s to 5.0 mPa·s, and even more preferably 1.0 mPa·s to 3.0 mPa·s.

[0151] (Other inks) To record full-color images, the ink of the present invention can be used in combination with another ink having a hue different from that of the ink of the present invention. Examples of the other ink include at least one ink selected from the group consisting of black ink, cyan ink, magenta ink, yellow ink, red ink, green ink, and blue ink. Furthermore, these inks can also be used in combination with so-called light inks having substantially the same hue. The coloring materials used in the other inks and light inks can be known dyes or newly synthesized dyes.

[0152] <Ink cartridges> The ink cartridge of the present invention includes ink and an ink storage section that stores the ink. The ink stored in the ink storage section is the aqueous ink of the present invention described above. FIG. 1 is a cross-sectional view schematically illustrating one embodiment of the ink cartridge of the present invention. As shown in FIG. 1, the bottom of the ink cartridge is provided with an ink supply port 12 for supplying ink to the recording head. The interior of the ink cartridge serves as an ink storage section for storing the ink. The ink storage section is composed of an ink storage chamber 14 and an absorber storage chamber 16, which are connected to each other via a communication port 18. The absorber storage chamber 16 is also connected to the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 contains absorbers 22 and 24 that retain the ink in an impregnated state. The ink storage section may not have an ink storage chamber that stores liquid ink, but may instead use an absorber to hold all of the ink stored therein. Alternatively, the ink storage section may not have an absorber and may store all of the ink in a liquid state. Furthermore, the ink cartridge may be configured to have an ink storage section and a recording head.

[0153] <Inkjet recording method> The inkjet recording method of the present invention is a method of ejecting the above-described aqueous ink of the present invention from an inkjet recording head to record an image on a recording medium. Methods for ejecting the ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is particularly preferable to employ a method of ejecting the ink by applying thermal energy to the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be any known method.

[0154] FIG. 2 is a diagram schematically illustrating 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 components of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting a recording medium 32, and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 is equipped with recording heads 38 and 40, and is configured to accommodate an ink cartridge 42. While the head cartridge 36 is transported in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. An image is then recorded on the recording medium 32 by transporting the recording medium 32 in the sub-scanning direction by a transport means (not shown).

[0155] Although not shown, the inkjet recording device preferably includes a mechanism for forcibly discharging ink from the nozzles of the recording head to maintain a normal ink discharge state, and a waste ink container for accommodating the waste ink generated by the ink discharge. Furthermore, a waste ink container provided with a waste ink absorber for absorbing and retaining the waste ink is more preferable. The waste ink absorber can be selected without particular restrictions, as long as it can generate capillary force, such as a porous material or a fiber laminate. For example, urethane foam and fibrous polyester or pulp have high absorption properties and are suitable for the waste ink absorber. [Example]

[0156] The present invention will be described in more detail below with reference to Examples, Comparative Examples, and Reference Examples, but the present invention is not limited to the following Examples in any way as long as the gist of the present invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0157] <Synthesis of coloring materials> (Compound A) With reference to the descriptions in the above-mentioned Patent Documents 1 and 2, a potassium salt of a compound represented by the following formula (A) in free acid form (hereinafter referred to as "Compound A") was synthesized.

[0158] TIFF0007718833000046.tif45170

[0159] (Compound B) Using the same procedure as for compound A, a sodium salt of the compound represented by the above formula (A) in the free acid form (hereinafter referred to as "compound B") was synthesized.

[0160] (Compound C) Using the same procedure as for compound A, a lithium salt of the compound represented by the above formula (A) in the form of a free acid (hereinafter referred to as "compound C") was synthesized.

[0161] (Compound D) As Compound D, commercially available sodium salt type CI Direct Yellow 132 was prepared.

[0162] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in the upper row of Table 3 (Table 3-1 to Table 3-6), thoroughly stirring, and then filtering under pressure through a filter with a pore size of 0.20 μm. "Acetylenol E100" (manufactured by Kawaken Fine Chemicals) in Table 3 is the trade name of a nonionic surfactant. The lower row of Table 3 shows the ink properties. The parenthesized value for each water-soluble organic solvent in Table 3 indicates its LogP. The LogP of the water-soluble organic solvent was determined using the trade name "ACD / PhysChem Suite Version 12.00" (manufactured by ACD / Labs). For the inks of Comparative Examples 2 to 9 and Reference Example 1, which do not contain water-soluble organic solvent X, the LogP of the water-soluble organic solvent with the largest LogP among the water-soluble organic solvents in the ink is used for convenience. L The values were shown as

[0163] TIFF0007718833000047.tif166170

[0164] TIFF0007718833000048.tif167170

[0165] TIFF0007718833000049.tif169170

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[0168] TIFF0007718833000052.tif173170

[0169] <Evaluation> Each ink obtained above was filled into an ink cartridge, and the ink was then installed in an inkjet recording device (product name "PIXUS iP8600", manufactured by Canon) that ejects ink from a recording head using thermal energy. In this example, the recording duty of a solid image recorded by applying 22 ng of ink to a unit area of 1 / 600 inch x 1 / 600 inch was defined as 100%. In the present invention, the following evaluation criteria for each item were used, with "A" and "B" being acceptable levels and "C" being unacceptable levels. The evaluation results are shown in Table 4.

[0170] (Lightfastness) Using the inkjet recording device described above, a solid image was recorded at 100% recording duty on a recording medium (Canon Photo Paper Glossy Pro [Platinum Grade] PT101, manufactured by Canon) at 23°C and 55% relative humidity. The resulting image was dried for 24 hours at 23°C and 55% relative humidity. The optical density of the solid image was then measured (optical density before lightfastness testing). The image was placed in a Super Xenon Tester (SX-75, manufactured by Suga Test Instruments) and irradiated with xenon light at a chamber temperature of 24°C, 60% relative humidity, and an irradiation intensity of 100 klux for 168 hours. The optical density of the solid image was then measured (optical density after lightfastness testing). To evaluate lightfastness, the optical density was measured using a spectrophotometer (Spectrolino, manufactured by Gretag Macbeth) under conditions of a light source of D50 and a field of view of 2°. From the obtained optical density values before and after the light fastness test, the residual optical density rate = optical density after light fastness test / optical density before light fastness test × 100% was calculated, and the light fastness was evaluated according to the evaluation criteria shown below. A: The remaining optical density was 85% or more. B: The remaining optical density was 75% or more and less than 85%. C: The remaining optical density was less than 75%.

[0171] (Suppression of deposition) Using the inkjet recording device described above, a 2.5 cm x 2.5 cm solid image was recorded on a recording medium (product name "GF-600," manufactured by Canon) at 30°C and 10% relative humidity with a recording duty of 25%, followed by a two-minute pause and then another recording of the same solid image. When recording this solid image, 150 mg of ink was discharged into the waste ink absorber by the suction pump for each recording. This cycle was repeated for 8,000 sheets. After recording 8,000 sheets, the condition of the waste ink absorber was visually inspected and the ink deposition suppression performance was evaluated according to the following criteria. A: No deposits were found on the waste ink absorber. B: Deposits had formed on the surface of the waste ink absorber, but the waste ink was absorbed without overflowing. C: Deposits had formed on the waste ink absorber, and waste ink was overflowing and not being absorbed.

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Claims

1. A water-based inkjet ink containing a colorant and a water-soluble organic solvent, The colorant contains a compound represented by the following general formula (I): The water-soluble organic solvent has a LogP Ｘ a water-soluble organic solvent X having a value of -0.97 or more, the content (mass %) of the water-soluble organic solvent X is 0.20 times or more and 0.45 times or less in mass relative to the content (mass %) of the water-soluble organic solvent, based on the total mass of the ink; LogP of the water-soluble organic solvent at 25°C Ｓ is equal to or greater than -1.60 and equal to or less than -1.10, 1. A water-based ink, characterized in that the sodium ion content (ppm) based on the total mass of the ink is 150 ppm or more and 1500 ppm or less. (In the general formula (I), R １ represents a monovalent group, and R ２ Ha-OR ３ or -NHR ４ (R ３ and R ４ represents a hydrogen atom or a monovalent group; ５ represents an alkyl group, an aryl group, or a monovalent triazine ring group having an ionic group as a substituent, and R ６ represents an arylene group or a divalent heterocyclic group, R ７ represents a divalent linking group, and m represents 0 or 1.

2. In the water-soluble organic solvent X, the LogP Ｘ The water-soluble organic solvent X with the largest Ｌ LogP of Ｌ and the LogP Ｓ 2. The water-based ink according to claim 1, wherein the difference between

3. 3. The aqueous ink according to claim 1, wherein the content (% by mass) of the water-soluble organic solvent X is 1.00 to 5.00 times the content (% by mass) of the colorant, in terms of a mass ratio based on the total mass of the ink.

4. The water-soluble organic solvent X is Ｘ Water-soluble organic solvent X having a value of -0.57 or more １ The aqueous ink according to claim 1 , comprising:

5. The aqueous ink according to claim 1 , wherein the water-soluble organic solvent X comprises an alkanediol.

6. 6. The aqueous ink according to claim 5, wherein the alkanediol is at least one of 1,5-pentanediol and 3-methyl-1,5-pentanediol.

7. 7. The aqueous ink according to claim 1, wherein the compound represented by general formula (I) is a compound represented by the following general formula (II): (In the general formula (II), R １ represents a monovalent group, and R ２ Ha-OR ３ or -NHR ４ (R ３ and R ４ represents a hydrogen atom or a monovalent group; ６ represents an arylene group or a divalent heterocyclic group, R ７ represents a divalent linking group, m represents 0 or 1, R ８ represents an ionic group, and n represents 1 or 2.

8. The R ８ The aqueous ink according to claim 7 , wherein the ionic group represented by the formula (I) contains at least one of a sodium ion and a potassium ion as a counter ion that forms a salt.

9. 9. The aqueous ink according to claim 1, wherein the water-soluble organic solvent comprises a water-soluble organic solvent Y having a Log P at 25° C. of less than −0.

97.

10. 10. The aqueous ink according to claim 1, wherein the content (mass %) of the coloring material is 0.10 mass % or more and 10.00 mass % or less based on the total mass of the ink.

11. 11. The aqueous ink according to claim 1, wherein the content (mass %) of the water-soluble organic solvent X is 1.00 mass % or more and 20.00 mass % or less based on the total mass of the ink.

12. An ink cartridge comprising ink and an ink storage section for storing the ink, 12. An ink cartridge, wherein the ink is the aqueous ink according to claim 1.

13. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, comprising: An ink-jet recording method, wherein the ink is the aqueous ink according to any one of claims 1 to 11.

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