JP2018162442A - Ink, ink cartridge, and ink jet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink having excellent ozone resistance and capable of recording an image having excellent bronze resistance as well as inhibiting color tone change even under an environment where various water-soluble organic solvents are present.SOLUTION: An ink for ink jet contains a first coloring material and a second coloring material, where the first coloring material and the second coloring material are compounds represented by the general formula (II) in the figure or derivative compounds.SELECTED DRAWING: None

Description

  The present invention relates to an ink, an ink cartridge, and an ink jet recording method.

  The ink jet recording method is a recording method for recording an image by applying ink droplets to a recording medium, and is rapidly spreading due to its low cost and an improved recording speed. In general, the recorded matter obtained by the ink jet recording method has low image fastness as compared with a silver salt photograph. In particular, when the recorded material is exposed to environmental gases such as light, humidity, heat, or ozone gas present in the air for a long time, the color material of the recorded material deteriorates, and the color tone of the image or fading easily occurs. There are problems such as.

  The discoloration of an image recorded using an ink containing a black color material (black ink) is often accompanied by a change in color tone due to deterioration of the color material. Various proposals have been made regarding techniques for improving the ozone resistance of black color materials. Patent Document 1 proposes a technique for improving ozone resistance by using a compound having a specific tetrakisazo structure as a coloring material.

  Another problem with the ink jet recording method is the occurrence of a so-called bronze phenomenon in which an image reflects light and emits a metallic luster in a high-density image. The bronze phenomenon is a phenomenon that is likely to occur when the solubility of the color material in water is reduced or the crystallinity of the color material is increased in order to improve fastness. When the bronze phenomenon occurs, not only the optical density is lowered, but also the image quality is significantly lowered. In particular, in black ink, in recent years, a technique for improving fastness by crystallizing a color material when an image is recorded on a recording medium is often used. There is also a problem that the bronze phenomenon becomes remarkable due to the aggregation of the materials. Therefore, there is a strong demand for both bronze resistance and robustness.

  Furthermore, as another problem of the ink jet recording method, when a plurality of inks are applied to the recording medium in a superimposed manner, the color tone recorded in a single color may change, and a desired color tone may not be obtained. It is done. In particular, in black ink, the color tone is likely to change due to the influence of a water-soluble organic solvent contained in another ink applied in a superimposed manner. Therefore, as a technique for suppressing a change in color tone, Patent Document 2 discloses a technique for containing an additive. Patent Document 3 discloses a technique of mixing color materials having different amounts of change in the maximum absorption wavelength of the UV-Vis absorption spectrum in a high polarity solvent and a low polarity solvent.

International Publication No. 2012/081640 Special table 2007-510760 gazette JP 2014-065895 A

  However, as a result of the study by the present inventors, it was found that an image recorded with an ink containing a tetrakisazo compound described in Patent Document 1 has insufficient ozone resistance. It was also found that the bronze resistance and the suppression of color change were at an insufficient level. Furthermore, the present inventors added the additive described in Patent Document 2 and the compound having a different amount of change in the maximum absorption wavelength described in Patent Document 3 to the tetrakisazo compound described in Patent Document 1. And examined. As a result, it was found that although the improvement in the suppression of the color tone was recognized, the ozone resistance and the bronze resistance were not improved. That is, it has been found that no technology has been proposed so far that satisfies all of ozone resistance, bronze resistance, and suppression of color change.

  Accordingly, an object of the present invention is an ink capable of recording an image having excellent ozone resistance and not only suppressing color change even in an environment where various water-soluble organic solvents exist, but also having excellent bronze resistance. Is to provide. Another object of the present invention is to provide an ink cartridge and an ink jet recording method using the ink.

  The above object is achieved by the present invention described below. That is, according to the present invention, there is provided an inkjet ink containing a first color material and a second color material, wherein the first color material is a compound represented by the following general formula (I): There is provided an ink characterized in that the second colorant is a compound represented by the following general formula (II).

（前記一般式（Ｉ）中、Ｒ₁は炭素数１乃至４のアルキル基を表す。Ｍはそれぞれ独立に、水素原子、アルカリ金属、アンモニウム、又は有機アンモニウムを表す。ｐはそれぞれ独立に１以上４以下の整数を表し、ｑは１又は２を表す。）

(In the general formula (I), R ₁ represents an alkyl group having 1 to 4 carbon atoms. M independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. P represents each independently 1 or more. Represents an integer of 4 or less, q represents 1 or 2)

（前記一般式（ＩＩ）中、Ｒ₂は炭素数１乃至４のアルキル基を表す。Ｍはそれぞれ独立に、水素原子、アルカリ金属、アンモニウム、又は有機アンモニウムを表す。ｒはそれぞれ独立に１以上４以下の整数を表し、ｓは１又は２を表す。）

(In the general formula (II), R ₂ represents an alkyl group having 1 to 4 carbon atoms. M independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. R each independently represents 1 or more. Represents an integer of 4 or less, and s represents 1 or 2.)

  According to the present invention, there is provided an ink that is excellent in ozone resistance and not only suppresses a change in color tone even in an environment where various water-soluble organic solvents exist, but also can record an image excellent in bronze resistance. can do. In addition, according to the present invention, it is possible to provide an ink cartridge and an ink jet recording method using this ink.

It is sectional drawing which shows typically one Embodiment of the ink cartridge of this invention. FIG. 2 is a diagram schematically illustrating an example of an ink jet recording apparatus used in the ink jet recording method of the present invention, in which (a) is a perspective view of a main part of the ink jet recording apparatus, and (b) is a perspective view of a head cartridge. It is a conceptual diagram which illustrates typically the energy level of the color material in a low polarity environment and a high polarity environment.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but it is expressed as “contains a salt” for convenience. Ink jet ink may be simply referred to as “ink”. Physical property values are values at normal temperature (25 ° C.) unless otherwise specified.

  The present inventors first studied a tetrakisazo compound having high ozone resistance. As a result, it was found that although the ozone resistance of the first color material (the compound represented by the general formula (I)) was improved, there were problems in the bronze resistance and the suppression of color tone change.

  The first color material is a color material that has improved ozone resistance by facilitating the association of molecules. Molecular association is generally caused by intermolecular forces such as ionic bonds, dipole-dipole interactions and van der Waals forces. When used as a coloring material to be contained in the ink, it is most preferable to associate molecules by utilizing a dipole-dipole interaction from the viewpoint of the balance of associating force in the ink and suppression of aggregation. Dipole-dipole interaction is when a plurality of atoms with different electronegativity are bonded to each other, a charge bias (polarization) occurs between these atoms. A phenomenon that is attracted.

  The ground state (HOMO) of a molecule causing polarization may be affected by the dielectric constant of a substance present in the surroundings. As shown in FIG. 3, for example, in a highly polar environment (when a substance having a high dielectric constant is present), the polarization of molecules is stabilized. For this reason, the energy level of the ground state (HOMO) in a highly polar environment is significantly higher than the energy level of the ground state (HOMO) in a low polarity environment (when a substance having a low dielectric constant is present). May decrease.

  On the other hand, the excited state (LUMO) of a molecule causing such polarization is a state in which the polarization is small because electrons flow in the opposite direction to the polarization, that is, the direction of weakening the polarization. For this reason, the energy level of the excited state (LUMO) is less affected by the dielectric constant of the surrounding material, compared to the energy level of the ground state (HOMO), and can be used in high and low polar environments. Not much different from below. Therefore, the color material polarized in this manner in the molecule causes a difference in the band gap of HOMO-LUMO between a high polarity environment and a low polarity environment, resulting in a change in color tone. This phenomenon is called solvatochromism. When such a first color material is used for ink, the maximum absorption wavelength of the color material shifts due to the difference in the environment in which the color material is placed (difference in the dielectric constant of the surrounding materials), and the color tone changes. Will occur.

  When a plurality of inks are applied in a superimposed manner on the recording medium, the type and content of the water-soluble organic solvent present in each ink are often not uniform. Therefore, the color material is placed in an environment where various water-soluble organic solvents are present. When the first color material is used as an ink and a plurality of inks are applied in layers, the maximum absorption wavelength of the color material is determined. Shifts to a color change.

  As a result of studies to solve the above-mentioned problems, the present inventors have found an ink configuration capable of recording an image in which a change in color tone is suppressed even in an environment where various water-soluble organic solvents exist. The ink contains a second color material (a compound represented by the general formula (II)) together with a first color material in which molecules easily associate. As a result, even in an environment where various water-soluble organic solvents are present, it is possible to obtain an ink capable of recording an image in which a uniform color tone is maintained with a small shift in the maximum absorption wavelength.

  Further, molecules of the first color material are likely to associate with each other, and the color material aggregates on the recording medium, resulting in a bronze phenomenon. However, it has been clarified that the bronzing phenomenon can be suppressed in the ink of the present invention.

  The present inventors presume the reason why the shift of the maximum absorption wavelength is reduced by including the second color material together with the first color material in the ink as follows. In the first color material, molecules are electrostatically attracted and associated with each other by polarization, but the polarization of the first color material is stabilized in a highly polar environment. For this reason, the energy level of the ground state (HOMO) in a highly polar environment is significantly higher than the energy level of the ground state (HOMO) in a low polarity environment (when a substance having a low dielectric constant is present). It is falling. On the other hand, when the ink contains the first color material and the second color material having a structure similar to that of the first color material, an association occurs between the first color material and the second color material. .

  The general formula (I) representing the first colorant has a substituent containing a heterocycle substituted with a cyano group, in addition to the structure of the general formula (II) representing the second colorant, The degree of polarization in the molecule is large. Therefore, the apparent degree of polarization in the molecule is smaller when the association occurs between the first color material and the second color material than when the association occurs only with the first color material. It will be.

  Therefore, the energy level of the ground state when the association occurs between the first color material and the second color material in a highly polar environment is compared to that when the association occurs only with the first color material. The degree of decrease is smaller than the energy level of the ground state in a low-polarity environment. As a result, it is presumed that the color tone change is suppressed.

  The reason why the bronzing phenomenon is suppressed by including the second color material together with the first color material in the ink is presumed as follows. As described above, the apparent degree of polarization in the molecule is greater when the association occurs between the first color material and the second color material than when the association occurs only with the first color material. Therefore, it is presumed that the color material hardly aggregates on the recording medium and the bronze phenomenon is suppressed.

<Ink>
The inkjet ink of the present invention contains two kinds of color materials. Hereinafter, the components constituting the ink of the present invention and the physical properties of the ink will be described in detail.

(Coloring material)
The ink of the present invention contains a compound represented by the following general formula (I) as the first color material and a compound represented by the following general formula (II) as the second color material.

（前記一般式（Ｉ）中、Ｒ₁は炭素数１乃至４のアルキル基を表す。Ｍはそれぞれ独立に、水素原子、アルカリ金属、アンモニウム、又は有機アンモニウムを表す。ｐはそれぞれ独立に１以上４以下の整数を表し、ｑは１又は２を表す。）

(In the general formula (I), R ₁ represents an alkyl group having 1 to 4 carbon atoms. M independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. P represents each independently 1 or more. Represents an integer of 4 or less, q represents 1 or 2)

（前記一般式（ＩＩ）中、Ｒ₂は炭素数１乃至４のアルキル基を表す。Ｍはそれぞれ独立に、水素原子、アルカリ金属、アンモニウム、又は有機アンモニウムを表す。ｒはそれぞれ独立に１以上４以下の整数を表し、ｓは１又は２を表す。）

(In the general formula (II), R ₂ represents an alkyl group having 1 to 4 carbon atoms. M independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. R each independently represents 1 or more. Represents an integer of 4 or less, and s represents 1 or 2.)

  From the viewpoint of ozone resistance, the first coloring material is preferably a compound represented by the following general formula (I ′).

（前記一般式（Ｉ’）中、Ｒ₁は炭素数１乃至４のアルキル基を表す。Ｍはそれぞれ独立に、水素原子、アルカリ金属、アンモニウム、又は有機アンモニウムを表す。）

(In the general formula (I ′), R ₁ represents an alkyl group having 1 to 4 carbon atoms. M independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium.)

In general formulas (I), (II), and (I ′), R ₁ and R ₂ each independently represents an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group having 1 to 4 carbon atoms include linear or branched alkyl groups. Examples of the alkyl group include straight chain alkyl groups such as methyl group, ethyl group, n-propyl group, and n-butyl group; branched chain groups such as isopropyl group, isobutyl group, sec-butyl group, and tert-butyl group. An alkyl group etc. can be mentioned. Of these, a linear alkyl group is preferable, and a methyl group is more preferable.

  In general formulas (I), (II), and (I ′), M independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the organic ammonium include alkylamines having 1 to 3 carbon atoms such as methylamine and ethylamine; 1 to 3 carbon atoms such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, and triisopropanolamine. 4 mono-, di- or trialkanolamines. In the present invention, it is preferable that M in the general formulas (I), (II), and (I ′) is at least one of sodium and lithium.

  When a specific example of the compound represented by the general formula (I) is represented in a free acid form, for example, exemplified compounds 1-1 and 1-2 shown below can be exemplified. Of course, in the present invention, the compound represented by the general formula (I) is not limited to the exemplified compounds shown below as long as it is included in the structure of the general formula (I) and the definition thereof.

  Moreover, when the specific example of a compound represented by general formula (II) is represented with a free acid type, the example compound 2-1 shown below etc. can be mentioned, for example. Of course, in the present invention, the compound represented by the general formula (II) is not limited to the exemplified compounds shown below as long as it is included in the structure of the general formula (II) and its definition.

The compound represented by the general formula (I) can be synthesized based on a known method. An example of the synthesis method will be described below. In the general formula listed in the description of synthesis methods below (1) ~ (8), R 1, M, p, and q are, respectively, R _1, M in the general formula (I), p, and q and interchangeably is there.

  A diazo compound obtained by diazotizing a compound represented by the following general formula (1) by a conventional method and a compound represented by the following general formula (2) are subjected to a coupling reaction by a conventional method, and the following general formula ( The compound represented by 3) is obtained.

  A diazo compound obtained by diazotizing a compound represented by the general formula (3) by a conventional method and a compound represented by the following general formula (4) are subjected to a coupling reaction by a conventional method, and the following general formula (5 ) Is obtained.

  A diazo compound obtained by diazotizing a compound represented by the general formula (5) by a conventional method and a compound represented by the following general formula (6) are subjected to a coupling reaction, and represented by the following general formula (7). To obtain the compound. The compound represented by the general formula (6) can be synthesized according to the method described in JP-A No. 2004-083492.

  A diazo compound obtained by diazotizing a compound represented by the general formula (7) by a conventional method and a compound represented by the following general formula (8) are subjected to a coupling reaction by a conventional method, whereby the general formula ( A compound represented by I) can be obtained. The compound represented by the general formula (8) can be synthesized according to the method described in International Publication No. 2007/077931.

The compound represented by the general formula (II) can also be synthesized based on a known method. For example, according to the synthesis method up to the step of obtaining the compound represented by the general formula (7) in the synthesis example of the compound represented by the general formula (I), the compound represented by the general formula (II) Can be synthesized. In this case, the method of synthesizing the compound represented by the general formula (II) is the same as that in the general formula (II) for R ₁ , M, p, and q in the general formulas (1) to (7). It can be described by replacing with R ₂ , M, r, and s.

  Each step in the method for synthesizing the compound represented by formula (I) will be further described below. First, diazotization of the compound represented by the above general formula (1) can be performed according to a known method. For example, diazotization can be performed with nitrite in an aqueous liquid medium at a temperature of -5 to 30 ° C, preferably 0 to 15 ° C. As the nitrite, for example, an alkali metal nitrite such as sodium nitrite can be used. A coupling reaction between the diazotized compound of the compound represented by the general formula (1) and the compound represented by the general formula (2) can also be performed according to a known method. For example, it is advantageous to perform the coupling reaction in an aqueous liquid medium at a temperature of −5 to 30 ° C., preferably 0 to 25 ° C., and at an acidic to neutral pH value, for example, pH 1 to 6. Since the diazotization reaction liquid is acidic and the reaction system is further acidified by the progress of the coupling reaction, the pH of the reaction liquid is adjusted to a preferred value by adding a base. Examples of the base include alkali metal hydroxides such as lithium hydroxide and sodium hydroxide; alkali metal carbonates such as lithium carbonate, sodium carbonate and potassium carbonate; alkali metal acetates such as sodium acetate; ammonia; organic An amine or the like can be used. The compound represented by the general formula (1) and the compound represented by the general formula (2) may be used in a substantially stoichiometric amount.

  The diazotization of the compound represented by the general formula (3) can be performed according to a known method. For example, diazotization can be performed with nitrite in an aqueous liquid medium at a temperature of -5 to 40 ° C, preferably 5 to 30 ° C. A coupling reaction between the diazotized compound of the compound represented by the general formula (3) and the compound represented by the general formula (4) can also be performed according to a known method. For example, it is advantageous to carry out the coupling reaction in an aqueous liquid medium at a temperature of −5 to 40 ° C., preferably 10 to 30 ° C., and at an acidic to neutral pH value, for example, pH 2 to 7. Since the diazotization reaction liquid is acidic and the reaction system is further acidified by the progress of the coupling reaction, the pH of the reaction liquid is adjusted to a preferred value by adding a base. The same base as described above can be used. Moreover, what is necessary is just to use the compound represented by General formula (3) and the compound represented by General formula (4) in a substantially stoichiometric amount.

  The diazotization of the compound represented by the general formula (5) can be performed according to a known method. For example, diazotization can be performed using nitrite in an aqueous liquid medium at a temperature of -5 to 50 ° C, preferably 5 to 40 ° C. A coupling reaction between the diazotized compound of the compound represented by the general formula (5) and the compound represented by the general formula (6) can also be performed according to a known method. For example, it is advantageous to perform the coupling reaction in an aqueous liquid medium at a temperature of −5 to 50 ° C., preferably 10 to 40 ° C., and at an acidic to neutral pH value, for example, pH 2 to 7. Since the diazotization reaction liquid is acidic and the reaction system is further acidified by the progress of the coupling reaction, the pH of the reaction liquid is adjusted to a preferred value by adding a base. The same base as described above can be used. Moreover, what is necessary is just to use the compound represented by General formula (5), and the compound represented by General formula (6) in a substantially stoichiometric amount.

  The diazotization of the compound represented by the general formula (7) can also be performed according to a known method. For example, diazotization can be performed using nitrite in an aqueous liquid medium at a temperature of −5 to 50 ° C., preferably 10 to 40 ° C. A coupling reaction between the diazotized compound of the compound represented by the general formula (7) and the compound represented by the general formula (8) can also be performed according to a known method. For example, it is advantageous to perform the coupling reaction in an aqueous liquid medium at a temperature of −5 to 50 ° C., preferably 10 to 40 ° C., and at a weakly acidic to alkaline pH value. The coupling reaction is preferably carried out at a weakly acidic to weakly alkaline pH value, for example, pH 5 to 10, and the pH value is adjusted by adding a base. The same base as described above can be used. The compound represented by the general formula (7) and the compound represented by the general formula (8) may be used in a substantially stoichiometric amount.

  A compound represented by the general formula (I) in a salt form can be obtained by performing the following treatment after the synthesis flow. A method of salting out by adding a desired salt to the reaction system can be mentioned. Further, a mineral acid such as hydrochloric acid is added to the reaction system to separate a free acid type compound, and then the resulting compound is washed and again free acid in an aqueous liquid medium (preferably water). And a method of adding a desired salt to obtain a salt-type compound.

(Color material verification method)
For verification of whether or not the color material used in the present invention is contained in the ink, the following verification methods (1) and (2) using high performance liquid chromatography (HPLC) can be applied.
(1) Retention time of peak (2) M / Z (posi), M / Z (negative) of mass spectrum for peak of (1)

The analysis conditions of high performance liquid chromatography are as follows. A liquid (ink) diluted about 1,000 times with pure water is used as a measurement sample. Analysis by high performance liquid chromatography is performed under the following conditions, and the retention time of the peak is measured.
Column: SunFire C18 (Nippon Waters) 2.1mm x 150mm
-Column temperature: 40 ° C
・ Flow rate: 0.2 mL / min
PDA: 200 nm to 700 nm
Mobile phase and gradient conditions: Table 1

The analysis conditions of the mass spectrum are as shown below. About the obtained peak, a mass spectrum is measured on condition of the following, M / Z detected most strongly is measured with respect to each of posi and nega.
・ Ionization method: ESI
・ Capillary voltage: 3.5kV
-Desolvent gas: 300 ° C
-Ion source temperature: 120 ° C
·Detector:
posi; 40V 200-1500amu / 0.9sec
nega; 40V 200-1500amu / 0.9sec

  Under the above-described method and conditions, measurement was performed on exemplary compounds 1-1 and 1-2, which are specific examples of the first color material, and exemplary compound 2-1, which is a specific example of the second color material. As a result, the retention time, M / Z (posi), and M / Z (negative) values obtained are shown in Table 2. When the unknown ink is measured under the same method and conditions as described above and corresponds to the values shown in Table 2, it can be determined that the ink corresponds to the compound used in the ink of the present invention. The lower part of Table 2 also shows the analysis results for the comparative compounds used in the comparative examples described later.

(Coloring material content)
The content Y (% by mass) of the second color material based on the total mass of the ink is 0.01 times the mass ratio (Y / X) to the content X (% by mass) of the first color material. It is preferable that it is above, and it is more preferable that it is 0.08 times or more. When the above-mentioned mass ratio (Y / X) is less than 0.01 times, the color tone change may not be sufficiently suppressed. On the other hand, if the mass ratio (Y / X) is less than 0.08 times, the bronze resistance may not be sufficiently improved. The content Y (mass%) of the second color material is a mass ratio (Y / X) to the content X (mass%) of the first color material, and is preferably 0.35 times or less. If the mass ratio (Y / X) is more than 0.35 times, ozone resistance may not be sufficiently improved.

  From the viewpoint of image performance and ink reliability, the total content (% by mass) of the first color material and the second color material in the ink is preferably 0.200 mass based on the total mass of the ink. % Or more and 10.000% by mass or less is preferable. Especially, it is more preferable that it is 0.500 mass% or more and 7.000 mass% or less. The content (% by mass) of the first color material in the ink is preferably 0.100% by mass or more and 5.000% by mass or less based on the total mass of the ink. The content (% by mass) of the second coloring material in the ink is preferably 0.100% by mass or more and 5.000% by mass or less based on the total mass of the ink.

  The ink may further contain a coloring material other than the compound represented by the general formula (I) and the compound represented by the general formula (II) as long as the object of the present invention is not impaired. .

(Aqueous medium)
In the ink of the present invention, water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent can be used. In the present invention, it is preferable to use an aqueous ink containing at least water as an aqueous medium. It is preferable to use deionized water (ion exchange water) as the water. The content (% by mass) of water in the ink is preferably 10.000% by mass or more and 90.000% by mass or less based on the total mass of the ink.

  The water-soluble organic solvent is not particularly limited as long as it is water-soluble, and alcohol, polyhydric alcohol, polyglycol, glycol ether, nitrogen-containing polar solvent, sulfur-containing polar solvent and the like can be used. The content (% by mass) of the water-soluble organic solvent in the ink is preferably 5.000% by mass or more and 90.000% by mass or less based on the total mass of the ink. The content (% by mass) of the water-soluble organic solvent is more preferably 5.000% by mass to 50000% by mass, and further preferably 10.000% by mass to 50.000% by mass. preferable. If the content of the water-soluble organic solvent is out of the above range, a high level of ink ejection stability may not be obtained sufficiently.

(Other additives)
In addition to the above-described components, the ink of the present invention includes a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an antioxidant, an evaporation accelerator, Various additives such as a chelating agent and a water-soluble resin may be contained.

(Ink physical properties)
In the present invention, the viscosity of the ink at 25 ° C. is preferably 1.0 mPa · s or more and 5.0 mPa · s or less, and more preferably 1.0 mPa · s or more and 3.5 mPa · s or less. The static surface tension of the ink at 25 ° C. is preferably 28 mN / m or more and 45 mN / m or less. Furthermore, the pH of the ink at 25 ° C. is preferably 5 or more and 9 or less.

<Ink cartridge>
The ink cartridge of the present invention includes ink and an ink storage unit that stores the ink. And the ink accommodated in this ink accommodating part is the ink of this invention demonstrated above. FIG. 1 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage portion for storing ink. The ink storage portion is composed of an ink storage chamber 14 and an absorber storage chamber 16, which communicate with each other via a communication port 18. The absorber housing chamber 16 communicates with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage unit may have a form in which the entire amount of ink stored is held by an absorber without having an ink storage chamber for storing liquid ink. Further, the ink storage portion may have a form that does not have an absorber and stores the entire amount of ink in a liquid state. Further, the ink cartridge may be configured to have an ink storage portion and a recording head.

<Inkjet recording method>
The ink jet recording method of the present invention is a method of recording an image on a recording medium by discharging the ink of the present invention described above from an ink jet recording head. Examples of the method for ejecting ink include a method for imparting mechanical energy to the ink and a method for imparting thermal energy to the ink. In the present invention, it is particularly preferable to employ a method in which thermal energy is applied to the ink and the ink is ejected. Other than using the ink of the present invention, the steps of the ink jet recording method may be known.

  2A and 2B are diagrams schematically showing an example of an ink jet recording apparatus used in the ink jet recording method of the present invention. FIG. 2A is a perspective view of a main part of the ink jet recording apparatus, and FIG. 2B is a perspective view of a head cartridge. It is. The ink jet recording apparatus is provided with a conveying means (not shown) for conveying 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 includes recording heads 38 and 40, and is configured such that an ink cartridge 42 is set. While the head cartridge 36 is conveyed 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 conveyed in the sub-scanning direction by a conveying unit (not shown), whereby an image is recorded on the recording medium 32.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited at all by the following Example, unless the summary is exceeded. What is described as “parts” and “%” with respect to the component amounts is based on mass unless otherwise specified. For simplicity, each compound in the synthesis examples is shown as a free acid type in principle.

<Synthesis of first color material>
(Compound A)
[Step 1]
After adding 12.2 parts of 2-amino-5-nitrobenzenesulfonic acid represented by the following formula (1.1) to 50.0 parts of water, pH 4.0 to 5.0 is obtained by adding a 25% aqueous sodium hydroxide solution. As an aqueous solution was obtained. After adding 18.3 parts of 35% hydrochloric acid, 10.5 parts of 40% aqueous sodium nitrite solution was added and allowed to react for about 30 minutes. To this, 1.5 parts of sulfamic acid was added and stirred for 5 minutes to obtain a diazo reaction liquid.

  On the other hand, 11.0 parts of the compound of the following formula (2.1) was added to 100.0 parts of water, and an aqueous solution was obtained at pH 4.0 to 5.0 by adding a 25% aqueous sodium hydroxide solution. This aqueous solution was added dropwise to the diazo reaction solution obtained above over about 5 minutes. After the dropwise addition, the mixture was reacted for 3 hours while maintaining the pH at 4.0 to 6.0 by adding a 15% aqueous sodium carbonate solution, and then sodium chloride was added. The precipitated solid was collected by filtration to obtain 103.8 parts of a wet cake containing a compound represented by the following formula (3.1).

[Step 2]
After adding the total amount of the wet cake of the compound represented by the formula (3.1) obtained in Step 1 to 80.0 parts of water, the aqueous solution was adjusted to pH 6.0 to 7.0 by adding 25% aqueous sodium hydroxide solution. Got. After adding 16.5 parts of 35% hydrochloric acid, 10.6 parts of 40% aqueous sodium nitrite solution was added and allowed to react for about 30 minutes. 7.5 parts of sulfamic acid was added here, and it stirred for 5 minutes, and obtained the diazo reaction liquid.

  On the other hand, after adding 64.7 parts of a wet cake of a compound represented by the following formula (4.1) to 100.0 parts of water, the aqueous solution was adjusted to pH 4.0 to 5.0 by adding a 25% aqueous sodium hydroxide solution. Obtained. This aqueous solution was added dropwise to the diazo reaction solution obtained above over about 5 minutes. After the dropwise addition, the mixture was reacted for 3 hours while maintaining the pH at 3.0 to 3.5 by adding a 15% aqueous sodium carbonate solution. Sodium chloride was added to this liquid, and the precipitated solid was collected by filtration to obtain 104.0 parts of a wet cake containing a compound represented by the following formula (5.1).

[Step 3]
52.0 parts of a wet cake of the compound represented by the formula (5.1) obtained in Step 2 was added to 100.0 parts of water, and dissolved by stirring. After adding 7.8 parts of 35% hydrochloric acid, 2.8 parts of 40% aqueous sodium nitrite solution was added and stirred for about 30 minutes. The sulfamic acid 0.8 part was added here, and it stirred for 5 minutes, and obtained the diazo reaction liquid.

  On the other hand, 3.7 parts of a compound represented by the following formula (6.1) was added to 80.0 parts of water, and an aqueous solution was obtained at pH 6.0 to 7.0 by adding a 25% aqueous sodium hydroxide solution. This aqueous solution was added dropwise to the diazo reaction solution obtained above over about 5 minutes. After the dropwise addition, the mixture was reacted for 3 hours while maintaining the pH at 3.0 to 4.5 by adding a 15% aqueous sodium carbonate solution. After the pH was adjusted to 7.0 to 7.5 by adding a 25% aqueous sodium hydroxide solution, sodium chloride was added. The precipitated solid was collected by filtration to obtain 29.5 parts of a wet cake containing a compound represented by the following formula (7.1).

[Step 4]
29.5 parts of a wet cake of the compound represented by the formula (7.1) obtained in Step 3 was added to 80.0 parts of water and dissolved by stirring. After adding 6.3 parts of 35% hydrochloric acid, 2.3 parts of 40% aqueous sodium nitrite solution was added and stirred for about 30 minutes. 0.5 parts of sulfamic acid was added here, and it stirred for 5 minutes, and obtained the diazo reaction liquid.

  On the other hand, 4.4 parts of a compound represented by the following formula (8.1) was added to 80.0 parts of water, and an aqueous solution was obtained at pH 6.0 to 7.0 by adding a 5% aqueous sodium hydroxide solution. . The diazo reaction liquid obtained above was dropped into this aqueous solution at 15 to 30 ° C. over about 30 minutes. At this time, a 15% aqueous sodium carbonate solution was added to maintain the pH of the reaction solution at 6.5 to 7.5, and the reaction was further continued for 2 hours while maintaining the same temperature and pH adjustment. Sodium chloride was added to the reaction solution for salting out, and the precipitated solid was collected by filtration to obtain 21.5 parts of a wet cake. The obtained wet cake was dissolved in 40.0 parts of water, the pH was adjusted to 7.0 to 7.5 with 35% hydrochloric acid, 400.0 parts of methanol was added, and the precipitated solid was collected by filtration. . The obtained wet cake was again dissolved in 40.0 parts of water, and then 300.0 parts of methanol was added. The precipitated solid was collected by filtration and dried to obtain 12.1 parts of Compound A which is a sodium salt of a compound represented by the following formula (A) as a free acid form as a black powder.

(Compound B)
According to the synthesis method of Compound A, except that the compound represented by Formula (4.1) used in “Step 2” in the synthesis of Compound A was changed to the compound represented by Formula (4.2) below. Thus, Compound B which is a sodium salt of a compound represented by the following formula (B) as a free acid type was obtained.

<Synthesis of second color material>
(Compound C)
The process up to “Step 2” in the synthesis of Compound A was performed to synthesize the compound represented by the above formula (5.1). 52.0 parts of a wet cake of the compound represented by the formula (5.1) obtained in Step 2 was added to 100.0 parts of water, and dissolved by stirring. After adding 7.8 parts of 35% hydrochloric acid, 2.8 parts of 40% aqueous sodium nitrite solution was added and stirred for about 30 minutes. The sulfamic acid 0.8 part was added here, and it stirred for 5 minutes, and obtained the diazo reaction liquid.

  On the other hand, 3.7 parts of the compound represented by the above formula (6.1) was added to 80.0 parts of water, and an aqueous solution was obtained by adding a 25% aqueous sodium hydroxide solution to pH 7.5 to 8.0. This aqueous solution was added dropwise to the diazo reaction solution obtained above at 15 to 30 ° C. over about 30 minutes. At this time, a 15% aqueous sodium carbonate solution was added to maintain the pH of the reaction solution at 7.5 to 8.5, and the reaction was further continued for 2 hours while maintaining the same temperature and pH adjustment. After the reaction, sodium chloride was added for salting out, and the precipitated solid was collected by filtration and dried to obtain 20.0 g of a wet cake. The obtained wet cake was dissolved in 100.0 parts of water, the pH was adjusted to 7.0 to 7.5 with 35% hydrochloric acid, 80.0 parts of methanol was added, and the precipitated solid was collected by filtration. . The obtained wet cake was again dissolved in 60.0 parts of water, and 90.0 parts of methanol was added. The precipitated solid was collected by filtration and dried to obtain 5.0 g of Compound C which is a sodium salt of a compound represented by the following formula (C) as a free acid form.

(Compound D)
According to the synthesis method of Compound C, the free acid was used except that the compound represented by Formula (4.1) used in the synthesis of Compound C was changed to the compound represented by Formula (4.2). Compound D which is a sodium salt of a compound represented by the following formula (D) as a type was obtained.

(Comparative Compound E)
With reference to the description in Patent Document 1, Comparative Compound E, which is a sodium salt of a compound represented by the following formula (E) as a free acid form, was obtained.

(Comparative Compound F)
In the synthesis example of “[Example 1]” described in Patent Document 1, synthesis up to “(Step 5)” was performed, and a compound represented by the following formula (F1) as a free acid form (in Patent Document 1) A compound represented by the formula (19) described) was obtained as a wet cake. 45.0 parts of wet cake was added to 250.0 parts of water and dissolved by stirring. After 16.5 parts of 35% hydrochloric acid was salified, 4.7 parts of a 40% aqueous sodium nitrite solution were added and stirred for about 30 minutes. 2.0 parts of sulfamic acid was added here, and it stirred for 5 minutes, and obtained the diazo reaction liquid.

  On the other hand, 5.5 parts of the compound represented by the above formula (6.1) was added to 60.0 parts of water, and an aqueous solution was obtained at pH 7.5 to 8.5 by adding 25% aqueous sodium hydroxide solution. . This aqueous solution was added dropwise to the diazo reaction solution obtained above at 15 to 30 ° C. over about 30 minutes. At this time, an aqueous sodium carbonate solution was added to maintain the pH of the reaction solution at 7.5 to 8.5, and the reaction was further continued for 2 hours while maintaining the same temperature and pH adjustment. Sodium chloride was added to the reaction solution for salting out, and the precipitated solid was collected by filtration to obtain 36.5 parts of a wet cake. The obtained wet cake was dissolved in 150.0 parts of water, the pH was adjusted to 7.0 to 7.5 with 35% hydrochloric acid, 110.0 parts of methanol was added, and the precipitated solid was collected by filtration. . The obtained wet cake was again dissolved in 80.0 parts of water, and then 120.0 parts of methanol was added. The precipitated solid was collected by filtration and dried to obtain comparative compound F which is a sodium salt of a compound represented by the following formula (F) as a free acid form.

(Comparative Compound G)
With reference to the description in WO 2006/001274, a comparative compound G, which is a sodium salt of a compound represented by the following formula (G) as a free acid form, was synthesized.

<Preparation of ink>
Each component (unit:%) shown in the upper part of Tables 3-1 to 3-5 was mixed and stirred sufficiently, and each ink was prepared by pressure filtration with a filter having a pore size of 0.20 μm. “Acetylenol E100” (manufactured by Kawaken Fine Chemical Co., Ltd.) in Tables 3-1 to 3-5 is a trade name of a nonionic surfactant. The lower part of Tables 3-1 to 3-5 shows the values of the content X (%) of the first color material, the content Y (%) of the second color material, and the Y / X value in the ink. It was. The Examples and Comparative Examples shown in Tables 3-1 to 3-5 are composed of two types of ink compositions having different polarities. The polarity of the ink was varied by properly using glycerin, which is a water-soluble organic solvent having a high dielectric constant, and 1,2-hexanediol, which is a water-soluble organic solvent having a low dielectric constant. Specifically, the polarity of the ink is relatively increased by using a composition (H) that uses glycerin, and the polarity of the ink is relatively set by using a composition (L) that uses 1,2-hexanediol. Was lowered.

<Evaluation>
Each ink obtained above was filled in an ink cartridge and mounted on an ink jet recording apparatus (trade name “PIXUS iP8600”, manufactured by Canon Inc.) that discharges ink from the recording head by the action of thermal energy. In this embodiment, a solid image recorded by applying 2.5 pL of ink to a unit area of 1/2400 inch × 1/1200 inch is defined as “recording duty is 100%”. Using this inkjet recording apparatus, each image was recorded on a recording medium (trade name “Canon Photo Paper / Glossy Pro [Platinum Grade] PT201”, manufactured by Canon) in an environment of a temperature of 23 ° C. and a relative humidity of 55%. The hue and optical density were measured using a spectrophotometer (trade name “Spectrolino”, manufactured by Gretag Macbeth) under the conditions of light source: D50 and field of view: 2 °. “A” and “b” in the following description of the evaluation method of the color change are a ^* and b ^* in the L ^* a ^* b ^* color system defined by the CIE (International Lighting Commission). The evaluation results are shown in Table 4. In the present invention, “AA”, “A” and “B” are acceptable levels and “C” is unacceptable levels in the evaluation criteria for the following items.

(Color change)
Solid images having a recording duty of 50% were recorded using inks having compositions H and L shown in Tables 3-1 to 3-5. The recorded matter was placed in a room at 25 ° C. for 24 hours and dried. Thereafter, the hue (a and b) of the solid image was measured. Each value at the composition H was a ₁ and b ₁ , and each value at the composition L was a ₂ and b ₂ . From each obtained value, ΔC ^* = [(a ₁ −a ₂ ) ² + (b ₁ −b ₂ ) ² ] ^1/2 was calculated, and the change in color tone was evaluated according to the following evaluation criteria. In this evaluation, assuming that an image superimposed with another ink is recorded, ΔC ^* is obtained from each image recorded with each ink of composition H and composition L. When ΔC ^* is small, it means that even if the polarity of the ink is different, the difference in color tone of the image is small and the change in color tone is suppressed.
A: ΔC ^* was less than 5.
B: ΔC ^* was 5 or more and less than 8.
C: ΔC ^* was 8 or more.

(Ozone resistance)
A solid image having a recording duty of 40% was recorded using ink of composition L. The recorded matter was placed in a room at 25 ° C. for 24 hours and dried, and then the optical density of the solid image was measured (optical density before the ozone resistance test). This recorded material was placed in an ozone test apparatus (trade name “OMS-H”, manufactured by Suga Test Instruments Co., Ltd.) and exposed to ozone for 24 hours under the conditions of a bath temperature of 23 ° C., a relative humidity of 50%, and an ozone gas concentration of 10 ppm. It was. The recorded matter was further placed in a room at 25 ° C. for 24 hours. Thereafter, the optical density of the solid image in the recorded material was measured (optical density after the ozone resistance test). From the obtained optical density before the ozone resistance test and the optical density value after the ozone resistance test, the residual ratio of optical density (%) = (optical density after the ozone resistance test / optical before the ozone resistance test) Concentration) × 100 was calculated, and ozone resistance was evaluated according to the evaluation criteria shown below.
AA: The residual ratio of the optical density was 82% or more.
A: The residual ratio of the optical density was 80% or more and less than 82%.
B: The residual ratio of the optical density was 75% or more and less than 80%.
C: The residual ratio of the optical density was less than 75%.

(Bronze resistance)
A solid image having a recording duty of 100% was recorded using ink of composition L. After the recorded matter was placed in a room at 25 ° C. for 24 hours and dried, a solid image was visually confirmed, and bronze resistance was evaluated according to the following evaluation criteria.
A: The bronze phenomenon did not occur.
B: The bronzing phenomenon was confirmed when the angle at which the image was viewed was changed.
C: The bronze phenomenon was confirmed without changing the viewing angle of the image.

Claims (7)

An ink-jet ink containing a first color material and a second color material,
The ink, wherein the first color material is a compound represented by the following general formula (I), and the second color material is a compound represented by the following general formula (II).

(In the general formula (I), R ₁ represents an alkyl group having 1 to 4 carbon atoms. M independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. P represents each independently 1 or more. Represents an integer of 4 or less, q represents 1 or 2)

(In the general formula (II), R ₂ represents an alkyl group having 1 to 4 carbon atoms. M independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. R each independently represents 1 or more. Represents an integer of 4 or less, and s represents 1 or 2.) The ink according to claim 1, wherein the first color material is a compound represented by the following general formula (I ′).

(In the general formula (I ′), R ₁ represents an alkyl group having 1 to 4 carbon atoms. M independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium.)   3. The ink according to claim 1, wherein the content (% by mass) of the second color material is 0.01 times or more in terms of a mass ratio with respect to the content (% by mass) of the first color material.   The content (mass%) of the second color material is 0.08 times or more in terms of a mass ratio with respect to the content (mass%) of the first color material. The ink described in 1.   5. The content (mass%) of the second color material is a mass ratio with respect to the content (mass%) of the first color material, and is 0.35 times or less. The ink described in 1. An ink cartridge comprising ink and an ink containing portion for containing the ink,
The ink cartridge according to claim 1, wherein the ink is an ink according to claim 1. An inkjet recording method for recording an image on a recording medium by discharging ink from an inkjet recording head,
An ink jet recording method, wherein the ink is the ink according to any one of claims 1 to 5.

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