JP7608105B2 - Water-based ink, ink cartridge, and ink-jet recording method - Google Patents

Description

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

In recent years, inkjet recording methods have achieved higher quality images than ever before, due to miniaturization of ink droplets and improved color gamuts with the introduction of multi-color inks. However, on the other hand, the demands on color materials and inks have become greater, and stricter characteristics are being required in terms of improved spectral characteristics such as color development and hue, and ink reliability such as light resistance. In light of this situation, inks containing specific compounds (dyes) as color materials have been proposed in order to improve these various characteristics (see Patent Documents 1 and 2).

JP 2004-83903 A JP 2007-63520 A

The dyes used in inkjet inks are currently unable to meet requirements such as simultaneously satisfying high levels of spectral reflectance characteristics (hue) and lightfastness.

Therefore, the object of the present invention is to provide a water-based ink that has a good hue as a yellow ink and is capable of recording images that are excellent in both color development and light resistance. Another object of the present invention is to provide an ink cartridge and an ink-jet recording method that use this water-based ink.

The above object can be achieved by the present invention as described below. That is, according to the present invention, there is provided an aqueous ink for inkjet recording containing a first coloring material and a second coloring material, wherein the first coloring material is a compound represented by the following general formula (1) , the second coloring material is a compound represented by the following general formula (2), and the proportion (mass %) of the content of the second coloring material in the total content (mass %) of the first coloring material and the second coloring material in the aqueous ink is 0.20 mass % or more and 2.00 mass % or less .

（前記一般式（１）中、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 (1), each M independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.)

（前記一般式（２）中、Ｒ_１及びＲ_２はそれぞれ独立に、水素原子、－ＣＯＯＭ、又は－ＳＯ_３Ｍを表し、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 (2), R ₁ and R ₂ each independently represent a hydrogen atom, -COOM, or -SO ₃ M, and each M independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.)

According to the present invention, it is possible to provide an aqueous ink that has a good hue as a yellow ink and is capable of recording images that are excellent in both color development and light resistance. In addition, according to the present invention, it is possible to provide an ink cartridge and an inkjet recording method that use this aqueous ink.

FIG. 1 is a cross-sectional view illustrating an embodiment of an ink cartridge of the present invention. 1A and 1B are diagrams 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 a main portion of the inkjet recording apparatus, and FIG. 1B is a perspective view of a head cartridge.

The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociated ions, but for convenience, it will be expressed as "containing a salt." In addition, water-based ink for inkjet printing may be simply referred to as "ink." Physical property values are values at room temperature (25°C) unless otherwise specified.

After investigation, the inventors discovered that by using a first coloring material and a second coloring material in combination, it is possible to obtain an ink that exhibits good spectral reflectance characteristics in the yellow region and can record images with excellent light resistance, and thus arrived at the present invention. The first coloring material (a compound represented by the following general formula (1)) has excellent light resistance, but has a reddish hue. On the other hand, the second coloring material (a compound represented by the following general formula (2)) has high coloring power, so it has excellent color development and a greenish hue. In addition, since the first coloring material and the second coloring material have similar structures, it is presumed that the excellent properties of each of the above-mentioned coloring materials are not impaired even when they are used in combination, and the above-mentioned effects can be obtained.

<Ink>
The aqueous ink of the present invention contains a first coloring material and a second coloring material. The first coloring material is a compound represented by the following general formula (1). The second coloring material is a compound represented by the following general formula (2). The ink of the present invention does not need to be of an active energy ray curable type, and therefore does not need to contain a monomer having a polymerizable group. The components constituting the ink of the present invention and the physical properties of the ink will be described in detail below.

(Coloring material)
The ink of the present invention contains a compound represented by the following general formula (1) as a first coloring material, and a compound represented by the following general formula (2) as a second coloring material. These coloring materials are water-soluble dyes. For purposes of color matching, dyes having structures different from those of the first coloring material and the second coloring material may be used in combination.

In general formula (1), each M independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

In formula (2), R ₁ and R ₂ each independently represent a hydrogen atom, -COOM, or -SO ₃ M, and each M independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

Examples of the alkali metal represented by M in the compound represented by general formula (1) and the compound represented by general formula (2) include lithium, sodium, and potassium. Similarly, examples of the organic ammonium represented by M include alkyl ammoniums such as methyl ammonium, dimethyl ammonium, trimethyl ammonium, tetramethyl ammonium, ethyl ammonium, n-propyl ammonium, and n-butyl ammonium; and mono-, di-, or trialkanol ammoniums such as monoethanol ammonium, diethanol ammonium, and triethanol ammonium. From the viewpoint of increasing water solubility, lithium, sodium, potassium, and ammonium are preferred as the above M.

The compound (first coloring material) represented by general formula (1) is C.I. Direct Yellow 132. From the viewpoints of high water solubility and ease of availability, C.I. Direct Yellow 132, which is a compound in which M in general formula (1) represents sodium, is more preferable.

As the compound (second color material) represented by general formula (2), a compound in which either one of R ₁ and R ₂ in general formula (2) represents a hydrogen atom, and the other represents -SO ₃ M, is more preferred. Among the compounds (second color materials) represented by general formula (2), a compound represented by the following general formula (2.1) is more preferred because it has high water solubility and is likely to give an image with even more excellent light resistance.

In general formula (2.1), M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. M in this general formula (2.1) has the same meaning as M in general formula (2), including the preferred ones.

Preferred examples of the compound represented by general formula (2) as the second coloring material, expressed in free acid form, include compounds II-1 to II-5 shown in the following chemical formulas (II-1) to (II-5), respectively. Of course, in the present invention, the compound represented by general formula (2) is not limited to the compounds shown below, so long as it is included in the structure and definition of general formula (2). In the present invention, of the free acid compounds shown below, compound II-1, which is included in the compound represented by the above-mentioned general formula (2.1), is preferred.

The compound represented by general formula (2) which is the second coloring material can be synthesized, for example, by the method described below. _R3 and _R4 in general formulas (a) and (c) described in the description of the synthesis method below correspond to _R1 and _R2 in general formula (2), respectively, and each independently represents a hydrogen atom, -COOH, or _-SO3H .

A compound represented by the following general formula (a) is diazotized in a conventional manner to obtain a diazo compound, which is then subjected to a coupling reaction in a conventional manner with a compound represented by the following chemical formula (b) (2-methoxyaniline) to obtain a compound represented by the following general formula (c) (intermediate).

The diazotization of the compound represented by the general formula (a) can be carried out, for example, by adding a diazotizing agent to a solution of the compound in the presence of an inorganic acid such as hydrochloric acid or sulfuric acid at a liquid temperature of about -50 to 100°C (preferably -10 to 10°C). Examples of the diazotizing agent that can be used include nitrosylsulfuric acid; and alkali metal nitrites such as sodium nitrite and potassium nitrite. The coupling reaction between the diazo compound represented by the general formula (a) and the compound represented by the chemical formula (b) can be carried out, for example, in a liquid medium at a temperature of about -50 to 100°C (preferably -10 to 10°C) and at an acidic to neutral pH value. Examples of the liquid medium that can be used include water, organic solvents, and mixtures thereof. The pH value is preferably 2 to 7, and the pH value can be adjusted by adding a base. Examples of bases that can be used 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; and organic amines. The compound represented by general formula (a) and the compound represented by chemical formula (b) may be used in approximately stoichiometric amounts.

Next, the compound represented by chemical formula (b) is diazotized in a conventional manner to obtain a diazo compound, which is then subjected to a coupling reaction in a conventional manner with the compound (intermediate) represented by general formula (c) obtained as described above. This makes it possible to obtain a compound (second coloring material) represented by free acid type general formula (2) (wherein M represents a hydrogen atom).

The diazotization of the compound represented by chemical formula (b) can be carried out, for example, by adding the above-mentioned diazotizing agent to a solution of the compound in the presence of an inorganic acid such as hydrochloric acid or sulfuric acid at a liquid temperature of about -50 to 100°C (preferably -10 to 10°C). The coupling reaction between the diazo compound represented by chemical formula (b) and the compound (intermediate) represented by general formula (c) can be carried out, for example, in a liquid medium at a temperature of about -50 to 100°C (preferably -10 to 10°C) and at a neutral to alkaline pH value. As the liquid medium, water, an organic solvent, or a mixture thereof can be used. The pH value is preferably 7 to 9, and the pH value can be adjusted by adding the above-mentioned base. The compound represented by chemical formula (b) and the compound represented by general formula (c) may be used in approximately stoichiometric amounts.

After synthesis of the above-mentioned free acid type compound represented by general formula (2), the following treatment can be carried out as necessary to obtain a salt type compound represented by general formula (2) (second coloring material). One example is a method in which a desired salt is added to the reaction system to salt out. Another example is a method in which a mineral acid such as hydrochloric acid is added to the reaction system to separate the free acid type compound, the resulting compound is washed, and the desired salt is added to the free acid again in a liquid medium (preferably water) to obtain a salt type compound.

(Method of verifying color materials)
In order to verify whether or not the coloring material used in the present invention is contained in the ink, the following verification methods (1) to (3) using high performance liquid chromatography (HPLC) can be applied.
(1) Retention time of the peak; (2) Maximum absorption wavelength of the peak in (1); (3) Mass spectrum m/z (positive) and m/z (negative) of the peak in (1);

The analysis conditions for the high performance liquid chromatography are as follows: A liquid (ink) diluted approximately 1,000 times with pure water is used as a measurement sample. Then, analysis by high performance liquid chromatography is performed under the following conditions to measure the retention time of the peak and the maximum absorption wavelength of the peak.
Column: SunFire _C18 (manufactured by Nippon Waters) 2.1 mm x 150 mm
Column temperature: 40°C
・Flow rate: 0.2mL/min
・PDA: 200nm to 700nm
Mobile phase and gradient conditions: Table 1

The mass spectrum analysis conditions are as follows: Mass spectrum is measured for the obtained peak under the conditions below, and the most strongly detected m/z is measured for each of the positivity and negativity.
Ionization method: ESI
Capillary voltage: 3.5 kV
Desolvation gas: 300°C
Ion source temperature: 120° C.
Detector:
posi; 40V 200-1500amu/0.9sec
nega; 40V 200-1500amu/0.9sec

The results of the measurements made under the above-mentioned method and conditions are shown below.
- Sodium salt of the compound represented by the chemical formula (I) described below (hereinafter referred to as "Compound 1-1")
HPLC purity at 254 nm = 98.1%
m/z=319.2 ([M-2Na] ^2- ), 639.2 ([M-2Na+H] ^- )
Sodium salt of the above compound II-1 (hereinafter referred to as "compound 2-1A")
HPLC purity at 254 nm = 97.3%
m/z=441.2 ([M-Na] ^- )

(Colorant Content)
The content ratio (mass%) of the second coloring material in the total content of the first coloring material and the second coloring material in the aqueous ink is preferably 0.20% by mass or more and 2.00% by mass or less. The content ratio (mass%) of the second coloring material can be calculated by the formula: _C2 /( _C1 + _C2 )×100 (mass%), where _C1 (mass%) is the content of the first coloring material in the ink, and _C2 (mass%) is the content of the second coloring material. The content ratio (mass%) of the second coloring material is more preferably 0.50% by mass or more and 1.00% by mass or less. Specifically, from the viewpoint of easily obtaining an image having a hue more preferable as a yellow ink, it is preferably 0.50% by mass or more. In addition, from the viewpoint of easily obtaining an image having even more excellent color development and light resistance, it is preferably 1.00% by mass or less.

The total content of the first coloring material and the second coloring material in the aqueous ink ( _C1 + _C2 ; %) is preferably 2.500% by mass or more and 6.500% by mass or less, based on the total mass of the ink. The total content (%) of these coloring materials is more preferably 3.000% by mass or more and 6.000% by mass or less. Specifically, when the total content of the coloring materials is relatively high, an image with even better color development and light resistance is easily obtained, so the total content is preferably 3.000% by mass or more. Furthermore, if the total content of the coloring materials is appropriate, an image with even better color development is easily obtained within a suitable hue range, so the total content is preferably 6.000% by mass or less.

The content (mass%) of the first coloring material in the aqueous ink is preferably 0.100% by mass or more and 10.000% by mass or less, and more preferably 0.500% by mass or more and 6.500% by mass or less, based on the total mass of the ink. The content (mass%) of the second coloring material in the aqueous ink is preferably 0.010% by mass or more and 5.000% by mass or less, and more preferably 0.010% by mass or more and 1.000% by mass or less, based on the total mass of the ink. The ratio of the total content (mass%) of the first coloring material and the second coloring material to the total content (mass%) of all coloring materials in the aqueous ink is preferably 10.0% by mass or more. The ratio is more preferably 20.0% by mass or more, particularly preferably 50.0% by mass or more, and may be 100.0% by mass.

In the present invention, an image having a hue that is preferable for yellow ink means the following two things. That is, it means that an image recorded using only yellow ink does not have a reddish or greenish tinge. In addition to this, it means that when recording a secondary color image recorded using yellow ink, that is, an image in the red or green region, the hue of either the red or green region is not significantly lost.

More specifically, a* and b* in the L ^* a*b* color system defined by the CIE (Commission Internationale de Illumination) are measured for a solid image recorded on a white recording medium using only yellow ink at an ink application amount of about ^0.06 g/inch2. Then, an ^{image having a hue angle (H°) calculated based on the following formula (A) from the obtained a* and b * values} and having a hue angle of 85° or more and ⁹² ° or less is considered to be an image having a good hue as a yellow ink. In addition, an ink capable of recording an image having such a hue angle (H°) is considered to have a preferred hue as a yellow ink. From the viewpoint of a better hue as a yellow ink, it is more preferable that the hue angle (H°) is 88° or more and 90° or less. The values of ^a* and b ^* can be measured, for example, using a spectrophotometer (trade name: Spectrolino; manufactured by Gretag Macbeth). Of course, the present invention is not limited to this. The "white recording medium" used in color measurement may be a recording medium having an ISO whiteness index (JIS P 8148) of about 80% or more, which utilizes diffuse blue light reflectance.

Formula (A)
For a ^* ≧0, b ^* ≧0 (first quadrant), H°=tan ⁻¹ (b ^* /a ^* )
In the case where a ^* ≦0, b ^* ≧0 (second quadrant), H°=180+tan ⁻¹ (b ^* /a ^* )
In the third quadrant, ^H °= ¹⁸⁰ +tan ⁻¹ (b ^* /a ^* ),
In the fourth quadrant, ^H °=360 ⁺ tan ⁻¹ (b ^* /a ^* ),

(Aqueous medium)
The ink of the present invention is an aqueous ink containing at least water as an aqueous medium. As the water, deionized water (ion-exchanged water) is preferably used. The content (mass %) of water in the ink is preferably 10.000 mass % or more and 90.000 mass % or less, more preferably 50.000 mass % or more and 90.000 mass % or less, based on the total mass of the ink.

The aqueous medium may further contain a water-soluble organic solvent. There are no particular limitations on the water-soluble organic solvent as long as it is water-soluble, and monohydric alcohols, polyhydric alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing polar solvents, sulfur-containing polar solvents, etc. can be used. It is preferable to use a water-soluble organic solvent with a lower vapor pressure than water. The content (mass %) of the water-soluble organic solvent in the ink is preferably 3.000 mass % or more and 50.000 mass % or less based on the total mass of the ink.

(Other additives)
In addition to the above-mentioned components, the ink of the present invention may contain, if necessary, water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea. Furthermore, the ink of the present invention may contain, if necessary, various additives such as surfactants, pH adjusters, preservatives, antifungal agents, antioxidants, reduction inhibitors, evaporation promoters, chelating agents, and water-soluble resins. Among these, it is preferable to include a surfactant in the ink. The content (mass %) of the surfactant in the aqueous ink is preferably 0.100 mass % or more and 1.500 mass % or less, and more preferably 0.200 mass % or more and 1.200 mass % or less, based on the total mass of the ink.

<Ink cartridge>
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 water-based ink of the present invention described above. FIG. 1 is a cross-sectional view that shows a schematic diagram of an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to a recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section is composed of an ink storage chamber 14 and an absorber storage chamber 16, which are communicated with each other via a communication port 18. The absorber storage chamber 16 is also communicated 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 section may not have an ink storage chamber that stores liquid ink, and may be in a form in which the entire amount of ink stored is held by the absorber. The ink storage section may also be in a form in which the entire amount of ink stored is stored in a liquid state, without having an absorber. Furthermore, the ink cartridge may be configured to have an ink container and a recording head.

<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 imparting mechanical energy to the ink and a method of imparting thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of ejecting the ink by imparting thermal energy to the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be known.

2 is a diagram showing an example of an inkjet recording device used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording device, and (b) is a perspective view of the head cartridge. The inkjet recording device is provided with a conveying means (not shown) for conveying the recording medium 32, and a carriage shaft 34. The carriage shaft 34 is capable of mounting a head cartridge 36. The head cartridge 36 is equipped with recording heads 38 and 40, and is configured so that an ink cartridge 42 is set thereon. While the head cartridge 36 is conveyed 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. Then, an image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by a conveying means (not shown). There are no particular limitations on the recording medium 32, but it is preferable to use a recording medium based on paper, such as a recording medium without a coating layer such as plain paper, or a recording medium with a coating layer such as glossy paper or matte paper.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to the following examples as long as it does not deviate from the gist of the invention. The terms "parts" and "%" used to describe the amounts of components are by weight unless otherwise specified.

<Synthesis of coloring materials>
(Synthesis of Compound 1-1)
10.0 parts of a compound represented by the following chemical formula (a1) was dispersed in 30.0 parts of water. 17.0 parts of concentrated hydrochloric acid was added to this to prepare a solution, which was then cooled in an ice bath. A solution of 4.2 parts of sodium nitrite dissolved in 10.0 parts of water was added dropwise to this solution at a liquid temperature of 0 to 5°C, and the mixture was stirred at the same temperature for 30 minutes. Next, 0.8 parts of amidosulfuric acid was added to obtain a diazotized liquid.

A solution was prepared by dissolving 6.8 parts of 2-methoxyaniline (see chemical formula (b) above) in 25.0 parts of methanol. This solution was added dropwise to the diazotization liquid while maintaining the above temperature. After the addition was complete, a saturated sodium acetate solution was added to adjust the pH to 3.0-3.5, and the mixture was stirred for an additional 2 hours to allow the reaction to proceed.

Thereafter, 25% aqueous sodium hydroxide solution was added dropwise to neutralize the mixture, and the pH was adjusted to about 7.0. Then, 12.0 parts of sodium chloride was added, and the mixture was stirred at 60° C. for 30 minutes. The mixture was cooled to room temperature, and the precipitate was separated by filtration to obtain a crude product of the compound (intermediate) represented by the following chemical formula (c1) (yield: 89%). The analysis results of the compound (intermediate) represented by the following chemical formula (c1) were HPLC purity (254 nm) 99.7%, m/z=306.0 ([M-Na] ⁻ ), and purity: 76.8% (including salt).

13.0 parts of the crude compound (intermediate) represented by the above chemical formula (c1) and 1.96 parts of sodium hydrogen carbonate were dissolved in 250 parts of water, and 2.42 parts of triphosgene were added and stirred at a liquid temperature of 30°C for 4 hours. 1.96 parts of sodium hydrogen carbonate was further added to this solution and stirred for 2 hours to cause a reaction. Then, 250 parts of water was added to dissolve the intermediate, and the insoluble matter was removed by filtration. 10.0 parts of sodium chloride was added to the filtrate to salt out, and the mixture was dissolved in N,N-dimethylformamide to remove the salt, and the solvent was distilled off under reduced pressure. In this way, 9.7 parts of the sodium salt of the compound represented by the following chemical formula (I) in free acid form (hereinafter referred to as "compound 1-1") was obtained (yield 93%).

(Compounds 1-2 and 1-3)
A potassium salt of the compound represented by the above chemical formula (I) (hereinafter referred to as "compound 1-2") was obtained in the same manner as above, except that the compound used for salting out in the synthesis flow of compound 1-1 was changed. In addition, an ammonium salt of the compound represented by the above chemical formula (I) (hereinafter referred to as "compound 1-3") was obtained in the same manner.

(Compound 2-1A)
23.7 parts of concentrated hydrochloric acid was added to a solution obtained by dissolving 10.0 parts of 2-methoxyaniline (see the above-mentioned chemical formula (b)) in 15.8 parts of methanol, and the solution was cooled in an ice bath. A solution obtained by dissolving 5.8 parts of sodium nitrite in 10.0 parts of water was added dropwise to this solution at a liquid temperature of 0 to 5°C, and the solution was stirred at the same temperature for 30 minutes. Then, 1.1 parts of amidosulfuric acid was added to prepare liquid 1. Separately from this, 32.6 parts of the crude compound (intermediate) represented by the chemical formula (c1) obtained above and 31.6 parts of sodium carbonate were dissolved in 300 parts of water, cooled in an ice bath, and the liquid temperature was kept at 0 to 5°C. This solution was added dropwise to the previously prepared liquid 1 while maintaining the temperature. After the dropwise addition, the solution was stirred overnight and reacted. Thereafter, concentrated hydrochloric acid was added dropwise to neutralize the solution, and the pH was adjusted to about 7.0. Next, 56.0 parts of sodium chloride was added to salt out, and the salt was removed by dissolving in N,N-dimethylformamide, and the solvent was distilled off under reduced pressure. In this way, the sodium salt of compound II-1 represented by the above-mentioned chemical formula (II-1) (hereinafter referred to as "compound 2-1A") was obtained (yield 67%).

(Compounds 2-1B and 2-1C)
A potassium salt of compound II-1 represented by the above-mentioned chemical formula (II-1) (hereinafter referred to as "compound 2-1B") was obtained in the same manner as in the synthesis of compound 2-1A, except that the compound used in the salting out step in the synthesis flow of compound 2-1A was changed. Similarly, an ammonium salt of compound II-1 represented by the above-mentioned chemical formula (II-1) (hereinafter referred to as "compound 2-1C") was obtained.

(Compounds 2-2 to 2-5)
Compounds II-2-1A, each represented by the above-mentioned chemical formulas (II-2) to (II-5), were synthesized in the same manner as in the synthesis of compound 2-1A, except that the starting material in the synthesis flow of compound 2-1A was changed. These are referred to as "Compound 2-2", "Compound 2-3", "Compound 2-4", and "Compound 2-5", respectively. In the synthesis of compounds 2-2 to 2-5, the compound represented by the above chemical formula (a1) used in the synthesis of compound 2-1A was changed to compounds represented by the following chemical formulas (a2) to (a5), respectively. It was used as such.

(Comparative Compound 1)
Comparative compound 1 represented by the following chemical formula (3-1) was synthesized in the same manner as in "Synthesis Example 2" described in Patent Document 1 (JP 2004-83903 A), except that the 1,3-dibromopropane used in this synthesis example was changed to 1,2-dibromoethane. In the following chemical formula, "t-Bu" represents a tert-butyl group.

(Comparative Compound 2)
Comparative compound 2 represented by the following chemical formula (3-2) was synthesized according to the synthesis example of "DYE-11" described in Patent Document 2 (JP-A-2007-63520). "t-Bu" in the following chemical formula represents a tert-butyl group.

<Ink Preparation>
Each ink was prepared by mixing the components (unit: %) shown in the upper part of Table 2 (Table 2-1 to Table 2-3), 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 2 is the trade name of a nonionic surfactant. The lower part of Table 2 shows the ink properties, including the content C ₁ (%) of the first coloring material in the ink, the content C ₂ (%) of the second coloring material, and their total content (C ₁ +C ₂ ) (%), as well as the value of C ₂ /(C ₁ +C ₂ )×100 (%).

<Evaluation>
Each ink obtained above was filled into an ink cartridge, and the ink cartridge was mounted on an inkjet recording device (product name "PIXUS iP8600", manufactured by Canon) that ejects ink from a recording head by the action of thermal energy. In this embodiment, a solid image recorded by applying eight ink droplets of 2.6 ng to a unit area of 1/2400 inch x 1/1200 inch is defined as having a "recording duty of 100%". In the present invention, in the evaluation criteria for each of the following items, "A" and "B" were set as acceptable levels, and "C" was set as an unacceptable level. The evaluation results are shown in Table 3.

(Color development)
Using the above inkjet recording device, an image was recorded on a recording medium (product name "Canon Photo Paper Glossy Pro [Platinum Grade] PT201", manufactured by Canon) with the recording duty changed from 0% to 100% in 10% increments. The obtained recorded matter was dried for 24 hours in an environment with a temperature of 23°C and a relative humidity of 55%. The optical density of the image part with a recording duty of 100% in the recorded matter was measured using a spectrophotometer (product name "Spectrolino", manufactured by Gretag Macbeth), and the color development of the image was evaluated according to the following evaluation criteria.
A: The optical density was 2.2 or more.
B: The optical density was 2.0 or more and less than 2.2.
C: The optical density was less than 2.0.

(Hue)
Using the above inkjet recording device, an image was recorded on a recording medium (product name "Canon Photo Paper Glossy Pro [Platinum Grade] PT201", manufactured by Canon) with the recording duty changed from 0% to 100% in 10% increments. The obtained recorded matter was dried for 24 hours in an environment with a temperature of 23°C and a relative humidity of 55%. For the part of the image in the recorded matter with a recording duty of 100%, a ^* and b ^* in the L ^* a ^* b ^* color system defined by the CIE (International Commission on Illumination) were measured. The values of a ^* and b ^* were measured using a spectrophotometer (product name "Spectrolino", manufactured by Gretag Macbeth) under the conditions of light source: D50 and field of view: 2°. From the obtained values of a ^* and b ^* , the hue angle (H°) was calculated based on the following formula (A).
Formula (A)
For a ^* ≧0, b ^* ≧0 (first quadrant), H°=tan ⁻¹ (b ^* /a ^* )
In the case where a ^* ≦0, b ^* ≧0 (second quadrant), H°=180+tan ⁻¹ (b ^* /a ^* )
In the third quadrant, ^H °= ¹⁸⁰ +tan ⁻¹ (b ^* /a ^* ),
In the fourth quadrant, ^H °=360 ⁺ tan ⁻¹ (b ^* /a ^* ),

From the obtained H° value, the hue of the image was evaluated according to the following evaluation criteria.
A: H° was 88° or more and 90° or less.
B: H° was 85° or more and less than 88°, or more than 90° and 92° or less.
C: H° was less than 85° or more than 92°.

(Light resistance)
Using the inkjet recording device, a solid image with a recording duty of 25% was recorded on a recording medium (product name "Canon Photo Paper Glossy Pro [Platinum Grade] PT201", manufactured by Canon). The obtained recorded matter was dried for 24 hours in an environment with a temperature of 23°C and a relative humidity of 55%. The optical density of the solid image in the recorded matter was measured (optical density before lightfastness test). The recorded matter was placed in a Super Xenon Tester (product name "SX-75", manufactured by Suga Testing Instruments) and irradiated with xenon light for 100 hours at an internal temperature of 24°C, a relative humidity of 60%, and an irradiation intensity of 100 klux. Thereafter, the optical density of the solid image in the recorded matter was measured (optical density after lightfastness test). From the obtained values of the optical density before the lightfastness test and the optical density after the lightfastness test, the residual optical density rate = optical density after lightfastness test / optical density before lightfastness test x 100 (%) was calculated, and the lightfastness of the image was evaluated according to the evaluation criteria shown below.
A: The remaining optical density was 80% or more.
B: The remaining optical density was 70% or more and less than 80%.
C: The remaining optical density was less than 70%.

Claims (14)

A water-based inkjet ink containing a first color material and a second color material,
The first coloring material is a compound represented by the following general formula (1),
The second coloring material is a compound represented by the following general formula (2),
An aqueous ink characterized in that the ratio (mass %) of the content of the second coloring material to the total content (mass %) of the first coloring material and the second coloring material in the aqueous ink is 0.20 mass % or more and 2.00 mass % or less .

(In the general formula (1), each M independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.)

(In the general formula (2), R ₁ and R ₂ each independently represent a hydrogen atom, -COOM, or -SO ₃ M, and each M independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.) 2. The aqueous ink according to claim 1, wherein the proportion (mass %) of the content of the second coloring material in the total content (mass %) of the first coloring material and the second coloring material in the aqueous ink is 0.50 mass % or more and 1.00 mass % or less. 3. The aqueous ink according to claim 1, wherein the total content (mass %) of the first coloring material and the second coloring material in the aqueous ink is 2.500 mass % or more and 6.500 mass % or less, based on the total mass of the ink. 4. The aqueous ink according to claim 1, wherein the total content (mass %) of the first coloring material and the second coloring material in the aqueous ink is 3.000 mass % or more and 6.000 mass % or less, based on the total mass of the ink. 5. The water-based ink according to claim 1 , wherein the content (mass %) of the first coloring material in the water-based ink is 0.100 mass % or more and 10.000 mass % or less based on the total mass of the ink. 6. The water-based ink according to claim 1 , wherein the content (mass %) of the first coloring material in the water-based ink is 0.500 mass % or more and 6.500 mass % or less based on the total mass of the ink. 7. The water-based ink according to claim 1 , wherein the content (mass %) of the second coloring material in the water-based ink is 0.010 mass % or more and 5.000 mass % or less based on the total mass of the ink. 8. The water-based ink according to claim 1 , wherein the content (mass %) of the second coloring material in the water-based ink is 0.010 mass % or more and 1.000 mass % or less based on the total mass of the ink. 9. The aqueous ink according to claim 1, wherein a ratio (mass %) of a total content of the first coloring material and the second coloring material to a total content (mass %) of all coloring materials in the aqueous ink is 10.0 mass % or more . 10. The aqueous ink according to claim 1, wherein a ratio (mass %) of a total content of the first coloring material and the second coloring material to a total content (mass %) of all coloring materials in the aqueous ink is 20.0 mass % or more . 11. The aqueous ink according to claim 1, wherein a ratio (mass %) of a total content of the first coloring material and the second coloring material to a total content (mass %) of all coloring materials in the aqueous ink is 100.0 mass % or less . The aqueous ink according to claim 1 , wherein the second coloring material is a compound represented by the following general formula (2.1):

(In the general formula (2.1), M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.) An ink cartridge including an ink and an ink storage section for storing the ink,
13. An ink cartridge, wherein the ink is a water-based ink as claimed in claim 1. 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 a water-based ink according to claim 1 .

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