Black ink composition, ink set containing the same, and ink jet recording method Number:7,520,928 from the United States Patent and Trademark Office (PTO) owispatent

Title: Black ink composition, ink set containing the same, and ink jet recording method

Abstract: Black ink compositions are provided. First embodiment contains a water-soluble long-wavelength dye L and a water-soluble short-wavelength dye S, in which the water-soluble short-wavelength dye S has 3 or more azo groups per molecule and a naphthalene skeleton. Second embodiment contains a water-soluble short-wavelength dye S whose absorption spectrum in aqueous solvent has a maximum between 440 nm and 540 nm and a half-band width of 90 to 200 nm and a water-soluble long-wavelength dye L whose absorption spectrum in aqueous solvent has a maximum between 550 nm and 700 nm and a half-band width of 100 nm or more. Third embodiment contains water, a water-miscible organic solvent, and a coloring material, in which C. I. Direct Red 84 is contained as a water-soluble short-wavelength dye S.

Patent Number: 7,520,928 Issued on 04/21/2009 to Ikeda,   et al.

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Inventors:	Ikeda; Kenji (Saitama, JP), Tanaka; Toshiharu (Kanagawa, JP)
Assignee:	FUJIFILM Corporation (Tokyo, JP)
Appl. No.:	11/632,653
Filed:	July 12, 2005
PCT Filed:	July 12, 2005
PCT No.:	PCT/JP2005/013225
371(c)(1),(2),(4) Date:	January 16, 2007
PCT Pub. No.:	WO2006/006726
PCT Pub. Date:	January 19, 2006

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Foreign Application Priority Data

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Jul 13, 2004 [JP]			2004-206329
Jul 13, 2004 [JP]			2004-206330
Jul 13, 2004 [JP]			2004-206331

Current U.S. Class:	106/31.52 ; 106/31.49; 106/31.58; 106/31.59; 347/100
Current International Class:	C09D 11/00 (20060101); B41J 2/01 (20060101); C09D 11/02 (20060101)
Field of Search:	106/31.27,31.52,31.58,31.49,31.59 347/100

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References Cited [Referenced By]

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U.S. Patent Documents

5256194	October 1993	Nishiwaki et al.
7029523	April 2006	Taguchi et al.
7037365	May 2006	Taguchi et al.
7048790	May 2006	Taguchi et al.
7211133	May 2007	Taguchi
7267715	September 2007	Taguchi et al.
7303272	December 2007	Taguchi et al.
2002/0121219	September 2002	Stramel et al.
2004/0154496	August 2004	Taguchi
2004/0187232	September 2004	Chino et al.
2007/0101899	May 2007	Taguchi et al.
2007/0139499	June 2007	Yabuki et al.
2007/0240608	October 2007	Ogawa
2007/0266890	November 2007	Taguchi et al.
2008/0043078	February 2008	Wachi

Foreign Patent Documents

	1403338		Mar., 2004		EP
	1403339		Mar., 2004		EP
	1420051		May., 2004		EP
	1420051		May., 2005		EP
	7-173422		Jul., 1995		JP
	2002-332426		Nov., 2002		JP
	2003-238863		Aug., 2003		JP
	WO 97/16496		May., 1997		WO
	WO 2004/029166		Apr., 2004		WO
	2005/044936		May., 2005		WO
	WO 2005/040292		May., 2005		WO
	WO 2005/042652		May., 2005		WO
	2005/121261		Dec., 2005		WO
	WO 2005/121261		Dec., 2005		WO
	WO 2006/006703		Jan., 2006		WO

Other References

Extended European Search Report dated Jul. 31, 2008. cited by other.

Primary Examiner: Klemanski; Helene
Attorney, Agent or Firm: Sughrue Mion, PLLC

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Claims

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The invention claimed is:

1. A black ink composition comprising: a water-soluble short-wavelength dye S whose absorption spectrum in aqueous solvent has a maximum between 440 nm and 540 nm and a half-band width of 90 to 200 nm; and a water-soluble long-wavelength dye L whose absorption spectrum in aqueous solvent has a maximum between 550 nm and 700 nm and a half-band width of 100 nm or more; wherein, the water-soluble short-wavelength dye S has a structure having 3 to 6 azo groups per molecule; and the water-soluble long-wavelength dye L has a hydroxyl group at a conjugate position of an azo group.

2. The black ink composition of claim 1, wherein the water-soluble short-wavelength dye S does not have a phenolic hydroxyl group.

3. A black ink composition comprising: a water-soluble long-wavelength dye L; and a water-soluble shod-wavelength dye S, wherein the water-soluble short-wavelength dye S has 3 or more azo groups per molecule and a naphthalene skeleton.

4. The black ink composition of claim 3, wherein the water-soluble short-wavelength dye S is a complementary color dye for the water-soluble long-wavelength dye L.

5. The black ink composition of claim 1, wherein the water-soluble short-wavelength dye S is contained in an amount of 0.1 to 4% by weight.

6. The black ink composition of claim 1, wherein the water-soluble long-wavelength dye L is an azo dye having a naphthalene skeleton.

7. The black ink composition of claim 1, wherein the water-soluble long-wavelength dye L has 2 to 4 azo groups per molecule and the azo groups are conjugated with each other.

8. The black ink composition of claim 1, wherein the water-soluble long-wavelength dye L has one or less heterocycle in a chromophore.

9. The black ink composition of claim 1, wherein the water-soluble long-wavelength dye L has an associating ability.

10. The black ink composition of claim 1, comprising a water-miscible organic solvent.

11. The black ink composition of claim 10, wherein the water-miscible organic solvent has a vapor pressure of 2,000 Pa or less.

12. The black ink composition of claim 10, wherein the water-miscible organic solvent is one or more selected from the group consisting of alcohol compounds, heterocycle-containing organic solvents, and alkyl ethers of polyhydric alcohols.

13. The black ink composition of claim 10, the water-miscible organic solvent is one or more selected from the group consisting of diethylene glycol, triethylene glycol, glycerin, triethylene glycol monobutyl ether, 1,5-pentanediol, 1,2-hexanediol, isopropanol, triethanolamine, and 2-pyrrolidone.

14. The black ink composition of claim 1, comprising a surfactant.

15. The black ink composition of claim 1, comprising a preservative.

16. The black ink composition of claim 1, having a viscosity of 1 to 20 mPasec.

17. The black ink composition of claim 1, having a surface tension of 20 to 50 mN/m.

18. The black ink composition of claim 1, having a pH of 7 to 9.

19. The black ink composition of claim 1, containing C. I. Direct Red 84 as the water-soluble shod-wavelength dye S.

20. A black ink composition comprising: water; a water-miscible organic solvent; and a coloring material containing a water-soluble short-wavelength dye S, wherein C. I. Direct Red 84 is contained as the water-soluble short-wavelength dye S.

21. An ink set comprising a black ink composition of claim 1.

22. An inkjet recording method, wherein a black ink composition of claim 1 is used to form an image on an image receiving material comprising: a support; and an ink receiving layer containing a white inorganic pigment particle.

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Description

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TECHNICAL FIELD

The present invention relates to a black ink composition comprising an azo dye having a particular structure and property (preferably, an image forming black ink composition (preferably, an inkjet ink composition)), an ink set comprising the same, and an inkjet recording method employing the black ink composition or the ink set.

BACKGROUND ART

An inkjet recording method has been spreading rapidly and is still being improved because of inexpensive material cost, high-speed recording, less noise during recording, and easy implementation of color recording.

The inkjet recording method includes: a continuous method which causes a droplet to continuously travel by air; and an on-demand method which causes a droplet to travel by air, depending on an image information signal. The droplet is ejected by using a pressure using a piezo element; by generation of bubbles in ink by heating; by using ultrasonic wave; or by suctioning with electrostatic force.

Examples of inkjet recording inks include water inks, oil inks, and solid (fusible) inks.

A coloring agent for use in the inkjet recording ink needs to have good solubility and dispersibility with respect to a solvent; excellent color developing ability which allows high-density recording; good hue; excellent fastness to light, heat, and active gas in the environment (NO.sub.x, acidic gas (ozone, etc.), SO.sub.x, etc.); excellent fastness to water and chemicals; good fixing ability and bleeding resistance with respect to an image receiving material; excellent preservability as ink; no toxicity; high purity; and inexpensive availability. However, it is considerably difficult to find a coloring agent meeting these criteria to a high extent. Particularly, there is a strong desire for a coloring agent for black ink which has good black tonality, allows high-density printing, and has fastness to light, humidity and heat.

Disazo dyes and trisazo dyes have been used as black dyes. When only these dyes are used, blue to green light are insufficiently absorbed, so that it is often that satisfactory black tonality is not obtained. Therefore, a color correcting dye which absorbs blue to green light is generally used in combination with the above-described dyes. Such a color correcting dye has been proposed in, for example, Japanese Unexamined Patent Publication No. H09-255906 and Japanese Patent No. 3178200 so as to make an attempt to improve black tonality adjusting ability, color developing ability, fastness, ink preservation stability, water resistance, and prevention of nozzle clogging.

However, the color correcting dye proposed in the related art has problems with the color tonality adjusting ability. Specifically, for example, it absorbs a very short wavelength, so that a large amount thereof needs to be added. Further, another color correcting dye is required.

Dyes capable of absorbing blue to green light are generally known, however, most of them have poor fastness, so that their hue may be significantly altered by exposure to light, heat, or active gas in the environment; and insufficient fixing ability, so that yellow bleeding appears at a contour portion under high temperature and high humidity conditions, for example. Therefore, a further improvement is required.

In consideration of these drawbacks, Japanese Unexamined Patent Publication No. 2002-332426 describes a black ink composition in which a triazine dye which has a maximum absorption of visible spectra in aqueous solvent at 435 nm (color correcting dye) is blended with a black dye.

However, a general black dye has a maximum absorption between 570 nm and 620 nm. Therefore, even when the color correcting dye is used, it is clear that a preferable black tonality is not obtained, taking into account a complementary color relationship which is important for adjustment of black tonality ("Shikisai Kagaku Handobukku (Handbook of Color Science) (Second Edition)", University of Tokyo Press, 1998, pp. 560-562).

Japanese Unexamined Patent Publication No. H08-302255 describes CI Direct Red 84. However, the publication does not disclose a black ink composition in which CI Direct Red 84 is used as a short-wavelength dye in combination with a long-wavelength dye.

Japanese Unexamined Patent Publication No. 2000-265099 describes CI Direct Red 84, which is used to obtain magenta (column 8). Similarly, however, the publication does not disclose a black ink composition in which CI Direct Red 84 is used as a short-wavelength dye in combination with a long-wavelength dye.

DISCLOSURE OF THE INVENTION

An object of an illustrative, non-limiting embodiment of the present invention is provided to solve the above-described conventional problems. The following object is achieved by the present invention.

An object of an illustrative, non-limiting embodiment of the present invention is to provide a black ink composition containing a water-soluble short-wavelength dye S and a water-soluble long-wavelength dye L, which does not require a large amount to be added and other color correcting dyes, can achieve excellent black tonality and high-density printing, has excellent weather resistance, heat resistance, water resistance (no bleeding), hue, and solution stability; an ink set comprising the same; and an inkjet recording method using the same.

First Embodiment

A-1) A black ink composition containing: a water-soluble long-wavelength dye L; and a water-soluble short-wavelength dye S, wherein the water-soluble short-wavelength dye S has 3 or more azo groups per molecule and a naphthalene skeleton.

A-2) The black ink composition of A-1), in which the water-soluble short-wavelength dye S is used as a complementary color dye (or a color correcting dye) for the water-soluble long-wavelength dye L.

A-3) The black ink composition of A-1) or A-2), in which the water-soluble short-wavelength dye S is contained in an amount of 0.1 to 4% by weight.

A-4) The black ink composition of any of A-1) to A-3), in which the water-soluble long-wavelength dye L is an azo dye having a naphthalene skeleton.

A-5) The black ink composition of any of A-1) to A-4), in which the water-soluble short-wavelength dye S has a structure having 3 to 6 azo groups per molecule.

A-6) The black ink composition of any of A-1) to A-5), in which the water-soluble long-wavelength dye L has 2 to 4 azo groups per molecule and the azo groups are conjugated with each other.

A-7) The black ink composition of any of A-1) to A-6), in which the water-soluble long-wavelength dye L has a hydroxyl group at a conjugate position of an azo group.

A-8) The black ink composition of any of A-1) to A-7), in which the water-soluble long-wavelength dye L has one or less heterocycle in a chromophore.

A-9) The black ink composition of any of 1) to 8), in which the water-soluble long-wavelength dye L has an associating ability.

A-10) The black ink composition of any of A-1) to A-9), containing a water-miscible organic solvent.

A-11) The black ink composition of A-10), in which the water-miscible organic solvent has a vapor pressure of 2,000 Pa or less.

A-12) The black ink composition of A-10) or A-11), in which the water-miscible organic solvent is one or more selected from the group consisting of alcohol compounds, heterocycle-containing organic solvents, and alkyl ethers of polyhydric alcohols.

A-13) The black ink composition of any of A-10) to A-12), containing one or more water-miscible organic solvents selected from the group consisting of diethylene glycol, triethylene glycol, glycerin, triethylene glycol monobutyl ether, 1,5-pentanediol, 1,2-hexanediol, isopropanol, triethanolamine, and 2-pyrrolidone.

A-14) The black ink composition of any of A-1) to A-13), containing a surfactant.

A-15) The black ink composition of any of A-1) to A-14), containing a preservative.

A-16) The black ink composition of any of A-1) to A-15), having a viscosity of 1 to 20 mPasec.

A-17) The black ink composition of any of A-1) to A-16), having a surface tension of 20 to 50 mN/m.

A-18) The black ink composition of any of A-1) to A-17), having a pH of 7 to 9.

A-19) An ink set comprising the black ink composition of any of A-1) to A-18).

A-20) An inkjet recording method, in which the black ink composition of any of A-1) to A-18) or the ink set of A-19) is used to form an image on an image receiving material including a support and an ink receiving layer containing a white inorganic pigment particle.

Second Embodiment

B-1) A black ink composition containing a water-soluble short-wavelength dye S whose absorption spectrum in aqueous solvent has a maximum between 440 nm and 540 nm and a half-band width of 90 to 200 nm and a water-soluble long-wavelength dye L whose absorption spectrum in aqueous solvent has a maximum between 550 nm and 700 nm and a half-band width of 100 nm or more.

B-2) The black ink composition of B-1), in which the water-soluble short-wavelength dye S has 2 to 6 azo groups per molecule and does not have a phenolic hydroxyl group.

B-3) The black ink composition of B-1) or B-2), in which the water-soluble short-wavelength dye S is contained in an amount of 0.1 to 4% by weight.

B-4) The black ink composition of any of B-1) to B-3), in which the water-soluble long-wavelength dye L has 2 to 4 azo groups per molecule and the azo groups are conjugated with each other.

B-5) The black ink composition of any of B-1) to B-4), in which the water-soluble long-wavelength dye L has a hydroxyl group at a conjugate position of an azo group.

B-6) The black ink composition of any of B-1) to B-5), in which the water-soluble long-wavelength dye L has one or less heterocycle in a chromophore.

B-7) The black ink composition of any of B-1) to B-6), in which the water-soluble long-wavelength dye L has an associating ability.

B-8) The black ink composition of any of B-1) to B-7), containing a water-miscible organic solvent.

B-9) The black ink composition of B-8), in which the water-miscible organic solvent has a vapor pressure of 2,000 Pa or less.

B-10) The black ink composition of B-8) or B-9), in which the water-miscible organic solvent is one or more selected from the group consisting of alcohol compounds, heterocycle-containing organic solvents, and alkyl ethers of polyhydric alcohols.

B-11) The black ink composition of any of B-8) to B-10), containing one or more water-miscible organic solvents selected from the group consisting of diethylene glycol, triethylene glycol, glycerin, triethylene glycol monobutyl ether, 1,5-pentanediol, 1,2-hexanediol, isopropanol, triethanolamine, and 2-pyrrolidone.

B-12) The black ink composition of any of B-1) to B-11), containing a surfactant.

B-13) The black ink composition of any of B-1) to B-12), containing a preservative.

B-14) The black ink composition of any of B-1) to B-13), having a viscosity of 1 to 20 mPasec.

B-15) The black ink composition of any of B-1) to B-14), having a surface tension of 20 to 50 mN/m.

B-16) The black ink composition of any of B-1) to B-15), having a pH of 7 to 9.

B-17) An ink set comprising the black ink composition of any of B-1) to B-16).

B-18) An inkjet recording method, in which the black ink composition of any of B-1) to B-16) or the ink set of B-17) is used to form an image on an image receiving material including a support and an ink receiving layer containing a white inorganic pigment particle.

Third Embodiment

C-1) A black ink composition containing water, a water-miscible organic solvent, and a coloring material containing a water-soluble short-wavelength dye S, wherein C. I. Direct Red 84 is contained as the water-soluble short-wavelength dye S.

C-2) The black ink composition of C-1), in which the coloring material contains a water-soluble long-wavelength dye L.

C-3) The black ink composition of C-1) or C-2), in which the water-soluble short-wavelength dye S is used as a complementary color dye (or a color correcting dye) for the water-soluble long-wavelength dye L.

C-4) The black ink composition of any of C-1) to C-3), in which the water-soluble short-wavelength dye S is contained in an amount of 0.1 to 4% by weight.

C-5) The black ink composition of any of C-2) to C-4), in which the water-soluble long-wavelength dye L is an azo dye having a naphthalene skeleton.

C-6) The black ink composition of any of 2) to 5), in which the water-soluble long-wavelength dye L has 2 to 4 azo groups per molecule and the azo groups are conjugated with each other.

C-7) The black ink composition of any of C-2) to C-6), in which the water-soluble long-wavelength dye L has a hydroxyl group at a conjugate position of an azo group.

C-8) The black ink composition of any of C-2) to C-7), in which the water-soluble long-wavelength dye L has one or less heterocycle in a chromophore.

C-9) The black ink composition of any of C-2) to C-8), in which the water-soluble long-wavelength dye L has an associating ability.

C-10) The black ink composition of any of C-1) to C-9), in which the water-miscible organic solvent has a vapor pressure of 2,000 Pa or less.

C-11) The black ink composition of any of C-1) to C-10), in which the water-miscible organic solvent is one or more selected from the group consisting of alcohol compounds, heterocycle-containing organic solvents, and alkyl ethers of polyhydric alcohols.

C-12) The black ink composition of any of C-1) to C-11), containing one or more water-miscible organic solvents selected from the group consisting of diethylene glycol, triethylene glycol, glycerin, triethylene glycol monobutyl ether, 1,5-pentanediol, 1,2-hexanediol, isopropanol, triethanolamine, and 2-pyrrolidone.

C-13) The black ink composition of any of C-1) to C-12), containing a surfactant.

C-14) The black ink composition of any of C-1) to C-13), containing a preservative.

C-15) The black ink composition of any of C-1) to C-14), having a viscosity of 1 to 20 mPasec.

C-16) The black ink composition of any of C-1) to C-15), having a surface tension of 20 to 50 mN/m.

C-17) The black ink composition of any of C-1) to C-16), having a pH of 7 to 9.

C-18) An ink set comprising the black ink composition of any of C-1) to C-17).

C-19) An inkjet recording method, in which the black ink composition of any of C-1) to C-17) or the ink set of C-18) is used to form an image on an image receiving material including a support and an ink receiving layer containing a white inorganic pigment particle.

By using the black ink composition of the present invention in inkjet recording, it is possible to form an image which has good black tonality, high printing density, and high fastness to light and active gas in the environment. In addition, bleeding in an image during preservation under high temperature and high humidity can be significantly reduced.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, exemplary embodiments of the present invention will be described in more detail.

(Dyes)

(Water-Soluble Short-Wavelength Dye S)

A water-soluble short-wavelength dye S (hereinafter also referred to a short-wavelength dye S) according to a first embodiment of the present invention has 3 or more azo groups per molecule and a naphthalene skeleton.

Due to this structure, the short-wavelength dye S has an enhanced level of color developing ability, and a broader coloring matter plane (a broader dye plane), thereby making it possible to provide an image having good fixing ability.

The number of azo groups is preferably 3 to 6 per molecule, more preferably 4 to 6 per molecule, in terms of color developing ability and fixing ability.

As used herein, the naphthalene skeleton means a structure including a naphthalene ring. The short-wavelength dye S preferably has 2 to 4 naphthalene rings per molecule.

It is also preferable that the short-wavelength dye S of the present invention does not have a dissociative phenolic hydroxyl group which is present in general coloring matters (or dyes). Due to this feature, the short-wavelength dye S has the following preferable performance: a small change in tonality depending on an image receiving material used; low reactivity to acidic gas (ozone in the air, etc.), i.e., excellent gas resistance; and the like.

As used herein, the dissociative phenolic hydroxyl group means a dissociative hydroxyl group substituted with an aryl group. This aryl group may be substituted with other substituents.

In the present invention, C. I. Direct Red 84 (its structure will be described below) may be used as the short-wavelength dye S, singly or in combination with other short-wavelength dyes S.

Note that C. I. Direct Red 84 has 4 azo groups per molecule and a naphthalene skeleton, and does not have a phenolic hydroxyl group.

It is also preferable that the short-wavelength dye S is a dye whose absorption spectrum in aqueous solvent has a maximum between 440 nm and 540 nm (absorption maximum: .lamda.max) and a half-band width of 90 to 200 nm, i.e., achieves broad absorption. As used herein, the aqueous solvent means a solvent which contains water as a major ingredient and in which a dye which may contain an appropriate amount of a water-miscible organic solvent is dissolved or dispersed. The absorption spectrum means a spectrum which is measured using a spectrophotometer which employs a commonly used 1-cm cell. The same is true of a water-soluble long-wavelength dye L described below.

The absorption spectrum of the water-soluble short-wavelength dye S is one that is measured using a single compound. In other words, when the absorption spectrum in aqueous solvent of the short-wavelength dye S is measured, the properties, such as a desired absorption maximum and half-band width, are obtained from a single compound, but not from a combination of a plurality of compounds. Note that it is clear that, in the present invention, compounds having absorption spectra different from each other may be used in combination as long as the above-described features of the short-wavelength dye S are satisfied. Further, in the present invention, short-wavelength dyes having other structures may be used in combination with the short-wavelength dye S having the above-described molecular structure.

The short-wavelength dye S has the above-described absorption characteristics, thereby making it possible to absorb a wide range of light, from blue to green, which tends to be insufficiently absorbed by the water-soluble long-wavelength dye L (e.g., a disazo dye, a trisazo dye, etc.). Thus, the short-wavelength dye S has an absorption property which is preferable as a complementary color dye.

The absorption maximum of the short-wavelength dye S is preferably between 450 nm and 520 nm, particularly preferably between 460 nm and 500 nm.

The half-band width of the absorption maximum of the short-wavelength dye S is preferably between 100 nm and 180 nm, particularly preferably between 110 nm to 160 nm.

A water-soluble short-wavelength dye S according to a second embodiment of the present invention is the above-described dye whose absorption spectrum in aqueous solvent has a maximum between 440 nm and 540 nm (absorption maximum: .lamda.max) and a half-band width of 90 to 200 nm, i.e., achieves broad absorption.

Further, the short-wavelength dye S of the second embodiment of the present invention preferably has 2 to 6 azo groups per molecule. Due to this structure, the short-wavelength dye S has an enhanced level of color developing ability, and a broader coloring matter plane, thereby making it possible to provide an image having good fixing ability.

The number of azo groups is preferably 4 to 6 per molecule in terms of color developing ability and fixing ability.

An example of the short-wavelength dye S of the present invention is a polyazo dye represented by a formula below. However, the short-wavelength dye S of the present invention is not particularly limited as long as it has the structure and/or physical properties defined herein to solve the above-described problems. (D).sub.n-Y

In the above-described formula, D represents a coloring matter residue comprising 1 to 3 azo groups conjugated with each other and a chromophore containing 3 to 4 aromatic rings having a total of 20 or more .pi. electrons; n represents 1 or 2; and Y represents a hydrogen atom when n is 1, or a divalent linking group when n is 2. Note that the aromatic ring contained in the chromophore may be either a heterocycle or a hydrocarbon ring, preferably a hydrocarbon ring. When the aromatic rings constituting the chromophore are condensed rings, the number of .pi. electrons on the aromatic rings is assumed to be the number of .pi. electrons on the entire condensed rings. For example, a naphthalene ring has 10 .pi. electrons. Examples of the divalent linking group represented by Y include an alkylene group, an arylene group, a heterocyclic residue, --CO--, --SO.sub.n-- (n: 0, 1, 2), --NR-- (R: a hydrogen atom, an alkyl group, an aryl group), --O--, and a divalent group composed of a combination thereof. These groups may have a substituent group, such as an alkyl group, an aryl group, an alkoxy group, an amino group, an acyl group, an acylamino group, a halogen atom, a hydroxyl group, a carboxyl group, a sulfamoyl group, a carbamoyl group, a sulfonamide group, or the like. Particularly preferable examples of the linking group include --NH--CO--NH--, --NH--CS--NH--, and a group represented by formula below.

As used herein, the alkyl group means a monovalent saturated hydrocarbon group which has a linear, branched or cyclic (either monocyclic or polyeyclic (either bridged or spiro polycyclic)) structure or a combination thereof. The alkyl group encompasses cycloalkyl groups, cycloalkylalkyl groups, and the like. When the alkyl group may be substituted with a substituent, substituted alkyl groups are encompassed by the alkyl group.

As used herein, an alkenyl group means a monovalent unsaturated hydrocarbon group which has a linear, branched or cyclic (monocyclic or polycyclic (either bridged or spiro polycyclic)) structure or a combination thereof and has one or more carbon-carbon double bonds, except for aromatic groups. When the alkenyl group may be substituted with a substituent, substituted alkenyl groups are encompassed by the alkenyl group.

As used herein, for example, the substituted alkyl group means an alkyl group whose hydrogen atom is substituted with other substituents. The alkyl group may be substituted at one or more positions with each of one or more substituents. The same is true of other substituted groups, such as substituted aryl groups and the like.

##STR00001##

In the above-described formula, X represents a hydroxyl group, a sulfo group, an alkoxy group, an aryloxy group, an amino group (including an alkylamino group, an arylamino group), or an alkyl- or arylsulphenyl group. In addition, each group may have a substituent.

As the short-wavelength dye S, for example, C. I. Direct Red 84, C. I. Direct Brown 106, and C. I. Direct Brown 202, which are commercially available, are useful. Among these dyes, C. I. Direct Red 84 is particularly useful because it can be used to adjust the tonality of a number of black dyes and it has excellent color developing ability, fastness and fixing ability.

Examples of the short-wavelength dye S preferably used in the present invention will be illustrated below in the form of a free acid, though may be used in the form of any salt.

Examples of a preferable counter cation include alkali metals (e.g., lithium, sodium, potassium), ammonium, and organic cations (e.g., pyridinium, tetramethylammonium, guanidium).

TABLE-US-00001 ##STR00002## A 1 ##STR00003## 2 ##STR00004## 3 ##STR00005## 4 ##STR00006## 5 ##STR00007## 6 ##STR00008##

TABLE-US-00002 ##STR00009## A X 7 ##STR00010## --NHC.sub.2H.sub.4OH 8 ##STR00011## --NHC.sub.2H.sub.4OH 9 ##STR00012## --NHC.sub.2H.sub.4OH 10 ##STR00013## --N(C.sub.2H.sub.4OH).sub.2 11 ##STR00014## --N(C.sub.2H.sub.4OH).sub.2 12 ##STR00015## --NHC.sub.2H.sub.4OH

TABLE-US-00003 ##STR00016## A 13 ##STR00017## 14 ##STR00018## 15 ##STR00019##

Among these dyes, C. I. Direct Red 84 (a Na salt of the above-described compound example 2) and C. I. Direct Brown 106 (a Na salt of the above-described compound example 14) are particularly useful because they are commercially available. Among them, C. I. Direct Red 84 is particularly useful because it can be used to adjust the tonality of a number of black dyes and they have excellent color developing ability, fastness and fixing ability.

Note that, the above-described short-wavelength dyes S other than commercially available dyes can be easily synthesized from commercially available starting materials in accordance with the synthesis route of C. I. Direct Red 84 or C. I. Direct Brown 106 described in "The Colour Index Fourth Edition" (published by The Society of Dyers and Colourists).

The black ink composition of the present invention contains the short-wavelength dye S in an amount of 0.1 to 4% by weight, preferably 0.5 to 3.0% by weight, and particularly preferably 1.0 to 2.5% by weight. The amount can be changed as appropriate and as required.

(Water-Soluble Long-Wavelength Dye L)

According to an embodiment of the black ink composition of the present invention, a water-soluble long-wavelength dye L (hereinafter also referred to as a long-wavelength dye L) preferably has a naphthalene skeleton. More preferably, the long-wavelength dye L has a structure represented by formulas 1 to 3 described below.

The long-wavelength dye L preferably has 2 to 4 azo groups per molecule which are conjugated with each other.

It is also preferable that the long-wavelength dye L has a hydroxyl group at a conjugate position of the azo group or one or less heterocycle in a chromophore, because of securing high color developing ability; absorption characteristics having a broad half-band width, which are appropriate for black tonality; and ink stability, though the reason is uncertain. As used herein, the conjugate position means a substitution position which has a conjugate relationship with the azo group. The hydroxyl group is preferably introduced at an ortho- or para-position into the azo group.

Generally, a dye having a hydroxyl group at a conjugate position of an azo group may have less fastness to light and active gas in the air, depending on the type of an image receiving material or preservation conditions for a printed material. Therefore, it is more preferable that the long-wavelength dye L has associating ability so that a reaction can be physically suppressed.

It can be determined whether or not a dye is in an associated state, as follows. A visible absorption spectrum is measured while changing the dye concentration, to examine an absorption maximum wavelength, a molar absorption constant and a change in waveform of the dye, thereby determining whether or not the dye has associating ability. These physical properties of the solution are compared with the absorption spectrum of the dye on an image receiving material, thereby easily determining whether or not a dye is in an associated state.

Specifically, a dye is preferable which has a relationship represented by: .epsilon.1/.epsilon.2>1.2 where .epsilon.1 is a molar absorption constant at a absorption maximum wavelength in a visible region when 0.1 mmol/1 dye aqueous solution is measured using a cell having an optical path length of 1 cm, and .epsilon.2 is a molar absorption constant when 0.2 mol/1 aqueous solution is measured using a liquid crystal cell having an optical path length of 5 .mu.m, as defined in Japanese Patent Application No. 2004-65569.

It is also preferable that the absorption spectrum in aqueous solvent of the long-wavelength dye L has a maximum (absorption maximum) between 550 nm and 700 nm and a half-band width of 100 nm or more (preferably, 120 to 500 nm, more preferably 120 to 350 nm).

The absorption spectrum of the long-wavelength dye L is one that is measured using a single compound. In other words, when the absorption spectrum in aqueous solvent of the long-wavelength dye L is measured, the properties, such as a desired absorption maximum and half-band width and the like, are obtained from a single compound, but not from a combination of a plurality of compounds. Note that it is clear that, in the present invention, compounds having absorption spectra different from each other may be used in combination as long as the above-described features of the long-wavelength dye L are satisfied. Further, in the present invention, other long-wavelength dyes may be used in combination with the long-wavelength dye L having the above-described molecular structure.

A black ink composition according to another embodiment of the present invention contains a water-soluble long-wavelength dye L whose absorption spectrum in aqueous solvent has a maximum (absorption maximum) between 550 nm and 700 nm and a half-band width of 100 nm or more (preferably, 120 to 500 nm, more preferably 120 to 350 nm). By using the water-soluble long-wavelength dye L in combination with the above-described short-wavelength dye S (particularly, the short-wavelength dye S of the second embodiment), good black tonality can be obtained.

Among the long-wavelength dyes L preferably used in the present invention, those represented by formulas below are particularly preferable.

In the formulae below, the dye is represented in the form of a free acid, though may be used for actual use in the form of any salt.

##STR00020##

In formulae (1) to (3), when there are a plurality of substituents which are represented by the same symbol in the same molecule, they may be either the same or different from each other. X represents an amino group, a hydroxyl group or a hydrogen atom. Y represents a hydrogen atom or an amino group. R represents a hydrogen atom, or an alkyl group, aralkyl group, an alkenyl group, an aryl group, a heterocyclic group, acyl group or a sulfonyl group which may have a substituent. Representative examples of the substituent which may be possessed by these groups include halogen atoms, ionic hydrophilic groups (a sulfo group, a carboxyl group, etc.), alkoxy groups, a hydroxy group, acylamino groups, acyl groups, a carbamoyl group, a sulfamoyl group, and the like. n represents an integer of 0 to 3. A sulfo group may be substituted at any position on a benzene ring or a naphthalene ring. A.sub.1 and A.sub.2 each represent a monovalent aromatic group or heterocyclic group. B represents a divalent aromatic group or heterocyclic group. A.sub.1 and A.sub.2 may be substituted with an azo group. A.sub.1, A.sub.2 and B may have a substituent. The number of heterocycles contained in a chromophore of the dye is preferably one or less. The dye may be in the form of a chelate dye in which a portion of the dye represented by the above-described formulas may be dissociated and a transition metal is coordinated to the dye.

Among the above-described formulas, dyes represented by formula (1) or (2) are preferable. Among them, the dyes represented by formula (1) are particularly preferable. Among the dyes represented by formula (1), dyes in which X is an amino group or a hydroxyl group are preferable. The dyes in which X is a hydroxyl group are particularly preferable. In terms of fastness, dyes which are substituted with an electron-withdrawing group or in which any of A.sub.1, A.sub.2 and B is a heterocycle are preferable.

Examples of a preferable electron-withdrawing group include a nitro group, a cyano group, a halogen group, a sulfamoyl group, a carbamoyl group, an ester group, and the like.

Examples of a preferable heterocycle include pyrazole, thiazole, isothiazole, oxazole, isoxazole and pyridine which may have a condensed ring.

Among those represented by formula (1), compounds represented by formula (4) below are particularly preferable.

##STR00021##

In formula (4), A.sub.3 and A.sub.4 each independently represent a heterocyclic group or an aryl group represented by formula 5 below. n represents an integer of 0 to 3.

##STR00022##

In formula (5), EWG (Electron Withdrawing Group) represents an electron withdrawing group selected from the group consisting of a nitro group, a cyano group, an azo group, a sulfamoyl group, a carbamoyl group, and an ester group. Preferably, EWG represents a nitro group or an azo group. Z represents a substituent selected from an alkyl group, an alkoxy group, a sulfo group, a carboxyl group, an amino group, and an acylamino group. A substituent represented by EWG or Z may further have a substituent. p represents an integer of 0 to 4. q represents an integer of 0 to 3, preferably 1 or 2.

Hereinafter, examples of the long-wavelength dye L will be illustrated in the form of a free acid, though may be used in the form of any salt.

Examples of a preferable counter cation, include alkali metals (e.g., lithium, sodium, potassium), ammonium, and organic cations (e.g., pyridinium, tetramethylammonium, guanidium).

TABLE-US-00004 ##STR00023## A.sub.1 A.sub.2 1-1 ##STR00024## ##STR00025## 1-2 ##STR00026## ##STR00027## 1-3 ##STR00028## ##STR00029## 1-4 ##STR00030## ##STR00031## 1-5 ##STR00032## ##STR00033## 1-6 ##STR00034## ##STR00035## 1-7 ##STR00036## ##STR00037##

TABLE-US-00005 ##STR00038## A.sub.1 A.sub.2 1-8 ##STR00039## ##STR00040## 1-9 ##STR00041## ##STR00042## 1-10 ##STR00043## ##STR00044## 1-11 ##STR00045## ##STR00046## 1-12 ##STR00047## ##STR00048## 1-13 ##STR00049## ##STR00050##

TABLE-US-00006 ##STR00051## A.sub.1 A.sub.2 1-14 ##STR00052## ##STR00053## 1-15 ##STR00054## ##STR00055## 1-16 ##STR00056## ##STR00057## 1-17 ##STR00058## ##STR00059## 1-18 ##STR00060## ##STR00061## 1-19 ##STR00062## ##STR00063##

TABLE-US-00007 A B R ##STR00064## 2-1 ##STR00065## ##STR00066## H 2-2 ##STR00067## ##STR00068## H 2-3 ##STR00069## ##STR00070## H 2-4 ##STR00071## ##STR00072## H 2-5 ##STR00073## ##STR00074## H 2-6 ##STR00075## ##STR00076## --CH.sub.2CO.sub.2H 2-7 ##STR00077## ##STR00078## ##STR00079## ##STR00080## A B R 2-8 ##STR00081## ##STR00082## H 2-9 ##STR00083## ##STR00084## H 2-10 ##STR00085## ##STR00086## H 2-11 ##STR00087## ##STR00088## H 2-12 ##STR00089## ##STR00090## ##STR00091## 2-13 ##STR00092## ##STR00093## --COCH.sub.3

TABLE-US-00008 3-1 ##STR00094## 3-2 ##STR00095## 3-3 ##STR00096## 4-1 ##STR00097## 4-2 ##STR00098##

In addition to the dyes represented by the above-described formulas, a dye described in each of Japanese Unexamined Patent Publication Nos. H10-130557, H09-255906, H07-97541 and H06-234944, European Patent No. 982371 A1, Japanese Unexamined Patent Publication Nos. 2002-302619, 2002-327131 and 2002-265809, International Publication Nos. 2000-43450, 2000-43451, 2000-43452, 2000-43453, 2003-106572 and 2003-104332, and Japanese Unexamined Patent Publication Nos. 2003-238862 and 2004-83609, can be preferably used as the long-wavelength dye L.

The black ink composition of the present invention contains the above-described long-wavelength dye L in an amount of preferably 0.2 to 30% by weight, particularly preferably 0.5 to 15% by weight, and most preferably 1 to 10% by weight.

Regarding a ratio of the short-wavelength dye S to the long-wavelength dye L, the amount of the short-wavelength dye S is preferably 1 to 50% by weight with respect to the long-wavelength dye L, more preferably 5 to 40% by weight, and most preferably 10 to 30% by weight.

(Black Ink Composition)

The black ink composition of the present invention means an ink composition containing at least a short-wavelength dye S and a long-wavelength dye L. The black ink composition of the present invention can contain a medium. When a solvent is used as the medium, the black ink composition of the present invention is particularly preferable as an inkjet recording ink.

The black ink composition of the present invention can be produced by using an oil medium or a water medium as the medium and dissolving and/or dispersing the dye of the present invention into the medium. Preferably, a water medium is used. The water medium contains water as a major ingredient, and may also be blended with a water-miscible organic solvent as required. An example of the water-miscible organic solvent is disclosed in Japanese Unexamined Patent Publication No. 2003-306623. Note that two or more water-miscible organic solvents may be used in combination. The black ink composition of the present invention includes an ink composition which does not contain a medium, and may be an ink composition containing water, a water-miscible organic solvent and a short-wavelength dye S.

Hereinafter, ingredients of the black ink composition of the present invention will be described in detail. When an ink set comprises the black ink composition of the present invention and other color ink compositions, information about the black ink composition of the present invention can be applied to the other color ink compositions.

(Water)

Although water is not particularly limited, it is preferable that water contains less impurities. Ultrapure water having a resistance value of 18 M.OMEGA. or more is more preferable.

(Water-Miscible Organic Solvent)

The water-miscible organic solvent preferably has a vapor pressure of 2000 Pa or less. The vapor pressure is a value measured at 20.degree. C. The water-miscible organic solvent having such a vapor pressure has a dry protecting function for preventing nozzle clogging due to dried ink and a penetration promoting function for causing ink to penetrate into paper better.

In the present invention, water-miscible organic solvents having a vapor pressure at 20.degree. C. of 2,000 Pa or less may be used singly or in combination of two or more. When a plurality of water-miscible organic solvents are used, it is preferable that at least one of the water-miscible organic solvents has a vapor pressure at 20.degree. C. of 2,000 Pa or less.

Specific examples of a water-miscible organic solvent having the dry protecting function include polyhydric alcohols (e.g., representatively, ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, thiodiglycol, dithiodiglycol, 2-methyl-1,3-propanediol, 1,2,6-hexanetriol, an acetylene glycol derivative, glycerin, trimethyrolpropane, etc.), lower alkyl ethers of polyhydric alcohols (e.g., ethylene glycol monomethyl (or monoethyl) ether, diethylene glycol monomethyl (or monoethyl) ether, triethylene glycol monomethyl (or monobutyl) ether, etc.), heterocycles (e.g., 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-ethylmorpholine, etc.), sulfur-containing compounds (e.g., sulfolane, dimethyl sulfoxide, 3-sulfolene, etc.), polyfunctional compounds (e.g., diacetone alcohol, diethanol amine, etc.), and urea derivatives. Among them, polyhydric alcohols, such as glycerin, diethylene glycol, and the like, are more preferable.

Examples of a water-miscible organic solvent having the penetration promoting function include lower monoalkyl ethers of polyhydric alcohols (e.g., monomethyl ether, monoethyl ether, mono-n-butyl ether, mono-iso-butyl ether, mono-n-hexyl ether and the like of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol and diproplylene glycol), lower dialkyl ethers of polyhydric alcohols (e.g., dimethyl ether, diethyl ether and the like of ethylene glycol, diethylene glycol, triethylene glycol and propylene glycol), and the like.

In addition to the above-described functions, the water-miscible organic solvent for use in the present invention may also have other functions, such as a viscosity adjusting function and the like.

It is preferable that the water-miscible organic solvent contains at least one selected from the group consisting of alcohol compounds, heterocycle-containing organic solvents, and alkyl ethers of polyhydric alcohols.

Examples of the alcohol compound include monovalent alcohols having 1 to 4 carbon atoms, alkanediols, and the like.

As the monovalent alcohol having 1 to 4 carbon atoms, methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol, 2-methyl-1-propanol (isobutanol), tert-butanol, and the like are preferable.

Examples of the alkanediol include 1,2-alkanediol (e:g., 1,2-pentanediol, 1,2-hexanediol), terminal diols (e.g., 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, etc.), branched diols (e.g., 2,2-dimethyl-1,3-propanediol, 2-methyl-1,4-butanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 3-methyl-1,3-butanediol, 2-methyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol); and the like. These are used singly or in combination.

An example of the heterocycle-containing organic solvent is represented by formula (A) below.

##STR00099##

In formula (A), X.sub.1 represents a carbonyl group or a group containing a heteroatom, and Z.sub.1 represents a group of atoms which can constitute a heterocycle.

Examples of X.sub.1 include a carbonyl group, an oxycarbonyl group, a carbonate group, an amide group, an urethane group, an ureido group, an amino group, an imino group, an ether group, an thioether group, a phosphoric acid derivative group, a phosphonic acid derivative group, a sulfonyl group, a sulfonamide group, a sulfonyl urea group, and the like. Among them, the amide group is preferable.

Z.sub.1 represents a group of atoms which can constitute a heterocycle. Z.sub.1 may be a ring composed of only carbon atoms. Alternatively, Z.sub.1 may contain a heteroatom in the carbon atom chain. The ring may or may not have an aromatic property. Z.sub.1 may also be a compound in which a plurality of rings are condensed.

The compound represented by formula (A) can have various substituents in its structure. Examples of the substituent include aryl groups (e.g., preferably having 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, and particularly preferably 1 to 8 carbon atoms (e.g., methyl, ethyl, iso-propyl, tert-butyl, n-octyl, n-decyl, n-hexadecyl, cyclopropyl, cyclopentyl, cyclohexyl, etc.)), alkenyl groups (e.g., preferably having 2 to 20 carbon atoms, more preferably 2 to 12 carbon atoms, and particularly preferably 2 to 8 carbon atoms (e.g., vinyl, allyl, 2-butenyl, 3-pentenyl, etc.)), alkynyl groups (e.g., preferably having 2 to 20 carbon atoms, more preferably 2 to 12 carbon atoms, and particularly preferably 2 to 8 carbon atoms (e.g., propargyl, 3-pentynyl, etc.)), aryl groups (e.g., preferably having 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, and particularly preferably 6 to 12 carbon atoms (e.g., phenyl, p-methylphenyl, naphthyl, etc.)), amino groups (e.g., preferably having 0 to 20 carbon atoms, more preferably 0 to 12 carbon atoms, and particularly preferably 0 to 6 carbon atoms (e.g., amino, methylamino, dimetylamino, diethylamino, diphenylamino, dibenzylamino, etc.)), alkoxy groups (e.g., preferably having 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, and particularly preferably 1 to 8 carbon atoms (e.g., methoxy, ethoxy, butoxy, etc.)), aryloxy groups (e.g., preferably having 6 to 20 carbon atoms, more preferably 6 to 16 carbon atoms, and particularly preferably 6 to 12 carbon atoms (e.g., phenyloxy, 2-naphthyloxy, etc.)), acyl groups (e.g., preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms (e.g., acetyl, benzoyl, formyl, pivaloyl, etc.)), alkoxycarbonyl groups (e.g., preferably having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, and particularly preferably 2 to 12 carbon atoms (e.g., methoxycarbonyl, ethoxycarbonyl, etc.)), aryloxycarbonyl groups (e.g., preferably having 7 to 20 carbon atoms, more preferably 7 to 16 carbon atoms, and particularly preferably 7 to 10 carbon atoms (e.g., phenyloxycarbonyl, etc.)), acyloxy groups (e.g., preferably having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, and particularly preferably 2 to 10 carbon atoms (e.g., acetoxy, benzoyloxy, etc.)), acylamino groups (e.g., preferably having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, and particularly preferably 2 to 10 carbon atoms (e.g., acetylamino, benzoylamino, etc.)), alkoxycarbonylamino groups (e.g., preferably having 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, and particularly preferably 2 to 12 carbon atoms (e.g., methoxycarbonylamino, etc.)), aryloxycarbonylamino groups (e.g., preferably having 7 to 20 carbon atoms, more preferably 7 to 16 carbon atoms, and particularly preferably 7 to 12 carbon atoms (e.g., phenyloxycarbonylamino, etc.)), sulfonylamino groups (e.g., preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms (e.g., methylsulfonylamino, phenylsulfonylamino, etc.)), sulfamoyl groups (e.g., preferably having 0 to 20 carbon atoms, more preferably 0 to 16 carbon atoms, and particularly preferably 0 to 12 carbon atoms (e.g., sulfamoyl, methylsulfamoyl, dimethylsulfamoyl, phenylsulfamoyl, etc.)), carbamoyl groups (e.g., preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms (e.g., carbamoyl, methylcarbamoyl, diethylcarbamoyl, phenylcarbamoyl, etc.)), alkylthio groups (e.g., preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms (e.g., methylthio, ethylthio, etc.)), arylthio groups (e.g., preferably having 6 to 20 carbon atoms, more preferably 6 to 16 carbon atoms, and particularly preferably 6 to 12 carbon atoms (e.g., phenylthio, etc.)), sulfonyl groups (e.g., preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms (e.g., mesyl, tosyl, etc.)), sulfinyl groups (e.g., preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms (e.g., methlsulfinyl, phenylsulfinyl, etc.)), ureido groups (e.g., preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms (e.g., ureide, methylureide, phenylureide, etc.)), phosphoric acid amide groups (e.g., preferably having 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, and particularly preferably 1 to 12 carbon atoms (e.g., diethyl phosphoric acid amide, phenyl phosphoric acid amide, etc.)), a hydroxy group, a mercapto group, halogen atoms (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom), a cyano group, a sulfo group, a carboxyl group, a nitro group, a hydroxamic acid group, a sulfino group, a hydrazino group, an imino group, heterocyclic groups (e.g., preferably having 1 to 30 carbon atoms, and more preferably 1 to 12 carbon atoms, and having a heteroatom, such as a nitrogen atom, an oxygen atom or a sulfur atom, (e.g., specifically, imidazolyl, pyridyl, quinolyl, furyl, thienyl, piperidyl, morpholino, benzoxazolyl, benzoimidazolyl, benzothiazolyl, carbazolyl, azepinyl, etc.)), silyl groups (e.g., preferably having 3 to 40 carbon atoms, more preferably 3 to 30 carbon atoms, and particularly preferably 3 to 24 carbon atoms (e.g., trimethylsilyl, triphenylsilyl, etc.)), and the like. These substituents may be further substituted. When there are two or more substituents, these substituents may be the same or different. If possible, the substituents may be linked to form a ring(s).

The compound represented by formula (A) is preferably a monocyclic compound and is preferably liquid under room temperature and atmospheric pressure. As the compound represented by formula (A), various compounds, such as those having an oil- or water-soluble structure or the like, can be used, preferably a water-soluble compound.

Examples of a compound which is preferably used as the compound represented by formula (A) include 2-pyrrolidone, .epsilon.-caprolactam, tetrahydrofuran, 1,4-dioxane, 1,3-dimethylimidazolidinone (e.g., 1,3-dimethylimidazolidinone-2-on), N-methylpyrrolidone, ethylene urea, sulfolane, pyridine, pyrazine, morpholine, 1-methyl-2-pyridone, 2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, 2,4,4-trimethyl-2-oxazoline, and the like. These are used singly or in combination. The present invention is not limited by this.

Examples of alkyl ethers of polyhydric alcohols include lower monoalkyl ethers of polyhydric alcohols (e.g., monomethyl ether, monoethyl ether, mono-n-butyl ether, mono-iso-butyl ether, mono-n-hexyl ether and the like of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, diproplylene glycol, and tripropylene glycol), lower dialkyl ethers of polyhydric alcohols (e.g., dimethyl ether, diethyl ether, di-n-butyl ether, di-iso-butyl ether, di-n-hexyl ether and the like of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, diproplylene glycol, and tripropylene glycol), and the like. These are used singly or in combination.

The black ink composition of the present invention preferably contains, as a water-miscible organic solvent, one or more selected, from diethylene glycol, triethylene glycol,