DESCRIPTION Title of Invention

YELLOW PIGMENT MIXTURE DISPERSION FOR INKJET RECORDING

Technical Field

The present invention relates to a yellow pigment dispersion, an ink for inkjet recording, an inkjet recording cartridge, an inkjet recording method, an inkjet recording apparatus and an inkjet recorded matter.

Background Art

Recently, in particular, a material for forming a color image has been the mainstream of an image recording material, and concretely, an inkjet recording material, a thermal transfer recording material, an electrophotographic recording material, a transfer silver halide photosensitive material, a printing ink, a recording pen and the like have become much used. In imaging devices such as CCD or the like of photographing appliances, and in displays such as LCD and PDP, a color filter is used for recording and reproducing color images. In these color image recording materials and color filters, used are colorants (dyes and pigments) of three primary colors in a so-called additive color mixing method or subtractive color-mixing method for the purpose of exhibiting or recording a full-color image. At present, however, there is known no colorant having absorption characteristics capable of realizing a favorable color reproduction region and having good fastness enough to be resistant to various service conditions and environmental conditions, and it is i earnestly desired to improve colorants.

Dyes and pigments for the above applications are required to satisfy the following properties common to them. Specifically, they have absorption characteristics favorable for color reproduction, and they have good fastness under environmental conditions under which they are used, for example, having good light- fastness, heat resistance and fastness to oxidizing gas such as ozone, etc. In addition, pigments serving as colorant are additionally required to satisfy the properties that they are substantially insoluble in water and organic solvent, that they have good fastness to chemicals, and that, when they are used as particles, they do not lose good absorption characteristics in the molecular dispersion state thereof. These necessary properties may be controlled by regulating the intensity of the intermolecular interaction; however, the two are in a trade-off relationship, and therefore, it is difficult to satisfy both the two.

When used, in addition, pigments are further required to satisfy the following requirements. They must have a necessary particle size and a particle form for expressing the desired transparency; they must have good fastness under environmental conditions under which they are used, for example, having good light- fastness, heat resistance, fastness to oxidizing gas such as ozone and the like, and good chemical fastness to organic solvent, sulfurous gas, etc.; and they may be dispersed as fine particles in the medium to be used and their dispersion state therein is stable. In particular, pigments that have a good color hue and a high tinctorial strength even under light or in wet heat or in an active gas in the environment and have good fastness to light are earnestly desired.

Specifically, the necessary properties of pigments cover a broader range as compared with dyes that are required to satisfy the properties as colorant molecules, or that is, pigments are required to satisfy not only the properties as colorant molecules but also all the above-mentioned necessary properties for solid aggregates of colorant molecules (dispersion of fine particles). As a result, the compound group usable as pigments is extremely limited as compared with that of dyes; and even when high-performance dyes could be derived into pigments, there may be only a few pigments capable of satisfying the necessary requirements as fine particle dispersions, and it is not easy to develop satisfactory pigments. This is confirmed from the fact that the number of the pigments registered in the color index is less than 1/10 of the number of the dyes registered therein.

Azo pigments have excellent color characteristics of color hue and tinctorial strength, and are therefore widely used as a printing ink, an inkjet ink, an electrophotographic material etc. Above all, azo pigments that are most typically used are yellow diarylide pigments and red naphthol azo pigments. The diarylide pigments include, for example, C.I. Pigment Yellow 12, 13, 17, etc. The naphthol azo pigments include C.I. Pigment Red 208, 242, etc. However, these pigments have poor fastness, and in particular, their light-fastness is extremely bad; and therefore, when the printed matter with the pigment is exposed to light, the pigment is decomposed and faded, and the printed matter is not suitable to long-term storage.

To overcome the drawbacks, some azo pigments have been disclosed, of which the fastness was enhanced by increasing the molecular weight thereof or by introducing thereinto a group having a strong intermolecular reaction effect (for example, see JP-A 56-38354, USP 2936306 and JP-A 11-100519). However, even the improved pigments are still unsatisfactory. For example, though the light- fastness of the pigment described in JP-A 56-38354 was enhanced in some degree, but is still not enough; and for example, the pigments described in USP 2936306 and JP-A 11-100519 are defective in that their color characteristics are not good as their color hue is greenish and their tinctorial strength is low.

JP-A 2005-213357 and JP-A 2003-246942 disclose dyes having good color characteristics of excellent color reproducibility and having sufficient fastness. However, concrete compounds described in the patent publications are all soluble in water or organic solvent, and therefore their fastness to chemicals is still insufficient.

In full color expression according to a subtractive color-mixing method with three colors of yellow, magenta and cyan, or four colors of the three and black, when a pigment of poor fastness is used for one color, the printed matter may lose the gray balance with the lapse of time; and when a pigment having poor color properties is used, the color reproducibility in printing lowers. Accordingly, for obtaining printed matters capable of securing good color reproducibility for a long period of time, a pigment and a pigment dispersion satisfying both good color properties and good fastness are desired.

Summary of Invention

An object of the invention is to provide a yellow pigment dispersion, an ink for inkjet recording, an inkjet recording cartridge, an inkjet recording method and an inkjet recording apparatus capable of giving a recorded matter having excellent color hue, tinctorial strength, light-fastness and ozone gas-fastness.

Another object of the invention is to provide an in inkjet recorded matter having excellent color hue, tinctorial strength, light-fastness and ozone gas-fastness.

The present inventors have assiduously studied in consideration of the above- mentioned current situation in the art, and have found that a pigment dispersion of a bisazo pigment, in which the pigment mother nucleus is composed of a pyrazole ring having a specific substituent and another pyrazole ring differing from the former in the substituent and in which the two pigment mother nuclei bond to each other via a nitrogen-containing hetero ring therebetween, or its tautomer satisfies both excellent color properties and excellent fastness.

Specifically, the invention is as follows:

(I) A yellow pigment dispersion, including: a coloring agent that contains at least one of an azo pigment represented by following formula (1) and a tautomer of the azo pigment, and at least one pigment selected from the group consisting of C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 138, 139, 150, 151, 154, 155, 180, 185 and 213: Formula (1):

(2) The yellow pigment dispersion as described in (1), wherein the azo pigment or the tautomer of the azo pigment shows characteristic X-ray diffraction peaks at Bragg angles (2Θ + 0.2°) of 7.2°and 25.9° in CuKa characteristic X-ray diffractometry.

(3) The yellow pigment dispersion as described in (1) or (2), wherein the azo pigment or the tautomer of the azo pigment is contained in an amount of 10% by mass or more with respect to a total pigment solid content in the yellow pigment dispersion.

(4) The yellow pigment dispersion as described in any of (1) to (3), further including: a dispersant in an amount of from 10 to 140% by mass with respect to the coloring agent.

(5) An ink composition, including: the yellow pigment dispersion as described in any of (1) to (4).

(6) The ink composition as described in (5), further including: a high-boiling-point organic solvent in an amount of from 0.1 to 30% by mass with respect to a total amount of the ink composition.

(7) The ink composition as described in (5) or (6), further including: a penetration promoter in an amount of from 1 to 20% by mass with respect to the total amount of the ink composition.

(8) An ink for inkjet recording, including: the yellow pigment dispersion as described in any of (1) to (4) or the ink composition as described in any of (5) to (7).

(9) An inkjet recording cartridge, including: the ink for inkjet recording as described in (8).

(10) An inkjet recording method of forming an image with the ink for inkjet recording as described in (8).

(11) An inkjet recording apparatus for forming an image using the ink for inkjet recording as described in (8).

(12) An inkjet recorded matter having an image formed with the ink for inkjet recording as described in (8). Brief Description of Drawings

Fig. 1 is an X-ray diffraction pattern of the azo pigment (1) produced according to Production Example 1.

Description of Embodiments

The invention is described in detail hereinunder.

The yellow pigment dispersion of the invention contains at least one of an azo pigment of the following formula (1) and a tautomer of the azo pigment (hereinafter this may be simply referred to as "azo dye of formula (I)"), and at least one pigment selected from the group consisting of C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 138, 139, 150, 151, 154, 155, 180, 185 and 213 (hereinafter this may be simply referred to as "yellow pigment of group (A)" or "yellow pigment (A)").

( 1 ) :

Preferably, the yellow pigment dispersion contains the azo pigment of formula (1) in an amount of at least 10% by mass with respect to the total pigment solid content in the yellow pigment dispersion, more preferably in an amount of from 30% by mass to 100% by mass, even more preferably from 55% by mass to 95% by mass, still more preferably from 70% by mass to 85% by mass.

The other ingredient than the azo pigment represented by formula (1) that may be in the yellow pigment dispersion of the invention includes tautomers, crystalline polymorphisms, salts, hydrates and the like of the azo pigment represented by formula (1).

The content of the yellow pigment of group (A) in the yellow pigment dispersion of the invention is preferably from 0.1% by mass to less than 99% by mass with respect to the total pigment solid content in the dispersion, more preferably from 1% by mass to less than 70% by mass, even more preferably from 5% by mass to less than 45% by mass, most preferably from 15% by mass to less than 30% by mass.

The yellow pigment dispersion of the invention contains the azo pigment of formula (1) (azo pigment (I)) and the yellow pigment of group (A) (yellow pigment (A)), therefore having excellent color hue, tinctorial strength, light-fastness and ozone gas-fastness.

Regarding the proportion of the content of the azo pigment (1) and the yellow pigment (A) in the yellow pigment dispersion, the ratio of azo pigment (l)/yellow pigment (A) preferably falls within a range of from 5/95 (mas.%/mas.%) to 95/5 (mas.%/mas.%), more preferably from 20/80 (mas.%/mas.%) to 80/20 (mas.%/mas.%), even more preferably from 40/60 (mas.%/mas.%) to 60/40 (mas.%/mas.%).

When the yellow pigment dispersion of the invention contains the azo pigment (1) and the yellow pigment (A) in the range mentioned above and when the yellow pigment dispersion is used in an ink for inkjet recording or the like, it exhibits more excellent color hue, tinctorial strength, light-fastness and ozone gas-fastness.

The azo pigment (1) includes an azo pigment of formula (1) showing characteristic X-ray diffraction peaks at Bragg angles (2Θ ± 0.2°) of 7.2° and 25.9° in CuKa characteristic X-ray diffractometry (hereinafter this may be referred to as "α- crystalline form azo pigment") and an azo pigment of formula (1) showing characteristic X-ray diffraction peaks at Bragg angles (2Θ ± 0.2°) of 6.6°, 8.9°, 11.7°, 18.4°, 25.7° and 26.7° in CuKa characteristic X-ray diffractometry (hereinafter this may be referred to as "β-crystalline form azo pigment").

Preferably, the azo pigment of formula (1) is the α-crystalline form azo pigment showing characteristic X-ray diffraction peaks at Bragg angles (2Θ ± 0.2°) of 7.2° and 25.9° in CuKa characteristic X-ray diffractometry, as exhibiting more excellent color hue, tinctorial strength, light-fastness and ozone gas-fastness.

In the invention, the azo pigment may be analyzed for X-ray diffractiometry according to the Japanese Industrial Standards JIS K0131 (general rule of X-ray diffractiometry), using a powdery X-ray diffractiometer RINT 2500 (by Rigaku).

For preparing the azo pigment of formula (1) in the invention, employable is a method of azocoupling a diazonium salt derived from a heterocyclic amine (diazo component) of the following formula (2) and a compound (coupling component) of the following formula (3) in which the reaction condition (solvent, pH, reaction temperature, reaction time, etc.) is controlled. ( 2 ) :

( 3 ) :

Molecules each having a single crystalline morphology may gather densely and therefore their intermolecular cross-interaction is high. As a result, their solvent resistance, heat stability, light-fastness, vapor resistance and printing density increase, and further they broaden a color reproduction range.

Accordingly, the azo pigment of formula (1) preferably has a crystal morphology showing characteristic X-ray diffraction peaks at Bragg angles (2Θ ± 0.2°) of 7.2° and 25.9° in CuKa characteristic X-ray diffractometry, more preferably a crystal morphology showing characteristic X-ray diffraction peaks at Bragg angles (2Θ ± 0.2°) of 7.2°, 15.0°, 19.8° and 25.9° in CuKa characteristic X-ray diffractometry. Of those, most preferred is a crystal morphology having a characteristic X-ray diffraction peak at 7.2°, 8.2°, 10.0°, 13.4°, 15.0°, 19.8° and 25.9°.

When observed with a transmission microscope, the length in the long axis direction of the primary particles of the azo pigment of formula (1) described in the above is preferably from 0.01 μm to 30 μm, more preferably from 0.02 μm to 30 μm, even more preferably from 0.03 μm to 2 μm.

The azo pigment whose primary particles, as observed with a transmission microscope, have a length in the long axis direction of at least 0.01 μm can more surely exhibit good fastness to light and ozone and, when formed into a pigment dispersion, the pigment secures better dispersibility. On the other hand, the azo pigment whose primary particles have a length of at most 30 μm are advantageous in that, when the pigment particles are dispersed to have a desired volume-average particle diameter, they are hardly in an over-dispersed state (in a state where the primary particles are broken), and the active surface of the pigment particles is hardly exposed out, and therefore the particles hardly aggregate, and for these reasons, the pigment dispersion can secure more the storage stability thereof.

The pigment whose primary particles have a size falling within the above range can be pigment particles that form a strong and stable three-dimensional network having a strong intramolecular/intermolecular interaction, and therefore exhibits high fastness to light, heat, moisture and oxidizing gas, and the colored matter with the pigment dispersion is favorable as excellent in the storage stability.

For measuring the volume-average particle size of the pigment dispersion of the invention, used is Nanotrack UPA particle sizer (UPA-EXl 50, by Nikkiso). Briefly, for example, 3 ml of a pigment dispersion is put into a sample cell, and analyzed according to a predetermined measurement method. Regarding the parameters to be inputted in the device, the ink viscosity is inputted for the viscosity, and the pigment density is for the density of the dispersed particles.

Preferably, the volume-average particle size (Mv) of the azo pigment dispersion of formula (1) is from 0.01 μm to 30 μnx, more preferably from 0.02 μm to 30 μm, even more preferably from 0.03 μm to 20 μm; and above all, most preferably from 30 nm to 150 nm.

The above range is preferred in that the printing density of the printed matter is high, the stability of the dispersion increases, the color reproducibility in the color mixed part with red, green and the like is enhanced, and when the dispersion is used in inkjet printing, it hardly clogs the nozzle. In addition, the other advantages are that the pigment dispersion hardly aggregates and the temporal stability of the dispersion is high.

In order to make the volume-average particle size of the pigment dispersion of the invention fall within the above range, the pigment dispersion conditions to be mentioned hereinunder may be suitably combined whereby the size of the pigment particles may be controlled with ease.

A method for producing the azo pigment composition containing at least one of the azo pigment of the following formula (1) or its tautomer, which shows characteristic X-ray diffraction peaks at Bragg angles (2Θ ± 0.2°) of 7.2° and 25.9° in CuKa characteristic X-ray diffractometry, is described in detail hereinunder.

The method for producing the azo pigment of the following formula (1) includes a step azocoupling a diazonium salt derived from a heterocyclic amine (diazo component) of the following formula (2) and a compound (coupling component) of the following formula (3): ( 2 )

( 3 ) :

( 1 )

Preparation Step of Diazonium Salt of Heterocyclic Amine

Preparation of a diazonium salt of the heterocyclic amine represented by formula (2) (diazo component) and coupling reaction of the diazonium salt with the compound represented by formula (3) (coupling component) can be performed by a conventional method.

As for the preparation of a diazonium salt of the heterocyclic amine represented by formula (2), there may be applied, for example, a conventional method of preparing a diazonium salt by using a nitrosonium ion source such as nitrous acid, nitrite or nitrosyl sulfuric acid, in a reaction medium containing an acid (e.g., hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, propionic acid, methanesulfonic acid, trifluoromethanesulfonic acid).

Preferred examples of the acid include acetic acid, propionic acid, methanesulfonic acid, phosphoric acid and sulfuric acid which are used individually or in combination. Among these, a combination system of phosphoric acid or acetic acid with sulfuric acid, a combination system of acetic acid with propionic acid, and a combination system of acetic acid with propionic acid and sulfuric acid are more preferred, and a combination system of acetic acid with propionic acid, and a combination system of acetic acid with propionic acid and sulfuric acid are still more preferred.

Preferred examples of the reaction medium (solvent) include an organic acid and an inorganic acid. Among these, phosphoric acid, sulfuric acid, acetic acid, propionic acid and methanesulfonic acid are preferred, and acetic acid and/or propionic acid are more preferred.

Preferred examples of the nitrosonium ion source include nitrous acid esters, nitrites and nitrosyl sulfuric acid. Among these, sodium nitrite, potassium nitrite, isoamyl nitrite, nitrosyl sulfuric acid (for example, an ONHSO ₄ sulfuric acid solution) are preferred, and isoamyl nitride and nitrosyl sulfuric acid (for example, a sulfuric acid solution containing from 40 to 50 mass% of ONHSO ₄ ) are more preferred. Above all, when nitrosyl sulfuric acid is used in the above-described preferred acid-containing reaction medium, a diazonium salt can be stably and effectively prepared.

The amount of the solvent used is preferably from 0.5 to 50 times by mass, more preferably from 1 to 20 times by mass, still more preferably from 3 to 15 times by mass, based on the diazo component of formula (2).

In the present invention, the diazo component of formula (2) may be in state of being dispersed in a solvent or depending on the kind of the diazo component, may be in a solution state.

The amount of the nitrosonium ion source used is preferably from 0.95 to 5.0 equivalent, more preferably from 1.00 to 3.00 equivalent, still more preferably from 1.00 to 1.10 equivalent, based on the diazo component.

The reaction temperature is preferably from -15°C to 4O ⁰ C, more preferably from -5°C to 35°C, still more preferably from -0°C to 30°C. If the reaction temperature is less than -10°C, the reaction proceeds at an extremely slow rate and the synthesis uneconomically takes so much time, whereas if the synthesis is performed at a high temperature exceeding 40 ⁰ C, the amount of a by-product produced increases and this is not preferred.

The reaction time is preferably from 30 to 300 minutes, more preferably from 30 to 200 minutes, still more preferably from 30 to 150 minutes. Coupling Reaction Step

The coupling reaction may be performed in from an acidic reaction medium to a basic reaction medium but in the case of the azo pigment of the present invention, the coupling reaction is preferably performed in from an acidic reaction medium to a neutral reaction medium. In particular, when the coupling reaction is performed in an acidic reaction medium, an azo pigment can be effectively derived by suppressing the decomposition of the diazonium salt.

Preferred examples of the reaction medium (solvent) which can be used include an organic acid, an inorganic acid and an organic solvent, with an organic solvent being preferred. A solvent causing no liquid separation phenomenon during the reaction and providing a uniform solution with the solvent is preferred. Examples thereof include an alcoholic organic solvent such as methanol, ethanol, propanol, isopropanol, butanol, tert-butyl alcohol and amyl alcohol, a ketone-based organic solvent such as acetone and methyl ethyl ketone, a diol-based organic solvent such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol and 1,3-propanediol, an ether-based organic solvent such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and ethylene glycol diethyl ether, a tetrahydrofuran, a dioxane and an acetonitrile. The solvent may be a mixed solution of two or more kinds of these solvents.

An organic solvent having a polarity parameter (ET) value of 40 or more is preferred. Above all, the solvent is preferably a glycol-based solvent having two or more hydroxyl groups in the solvent molecule, an alcoholic solvent having a carbon number of 3 or less, or a ketone-based solvent having a total carbon number of 5 or less, more preferably an alcohol solvent having a carbon number of 2 or less (e.g., methanol, ethylene glycol), or a ketone-based solvent having a total carbon number of 4 or less (e.g., acetone, methyl ethyl ketone). A mixed solvent thereof may also be used.

The amount of the solvent used is preferably from 1 to 100 times by mass, more preferably from 1 to 50 times by mass, still more preferably from 2 to 30 times by mass, based on the coupling component represented by formula (3). In the present invention, the coupling component represented by formula (3) may be in a state of being dispersed in a solvent or depending on the kind of the coupling component, may be in a solution state.

The amount of the coupling component used is, in terms of the diazo component, preferably from 0.95 to 5.0 equivalent, more preferably from 1.00 to 3.00 equivalent, still more preferably from 1.00 to 1.50 equivalent, based on the azo coupling site.

The reaction temperature is preferably from -30 ⁰ C to 30°C, more preferably from -15°C to 10 ⁰ C, still more preferably from -10 ⁰ C to 5°C. If the reaction temperature is less than -30 ⁰ C, the reaction proceeds at an extremely slow rate and the synthesis uneconomically takes so much time, whereas if the synthesis is performed at a high temperature exceeding 30 ⁰ C, the amount of a by-product produced increases and this is not preferred.

The reaction time is preferably from 30 to 300 minutes, more preferably from 30 to 200 minutes, still more preferably from 30 to 150 minutes.

In the production method of the azo pigment composition for use in the present invention, the product (crude azo pigment) obtained through these reactions is usually treated according to a post-treatment method in the normal organic synthesis reaction and used after being or not being purified.

That is, for example, the reaction product isolated from the reaction system can be used without purification or can be used after performing purification operations such as recrystallization and salt formation, individually or in combination.

Also, after the completion of reaction, the reaction solvent is or is not removed by distillation, the reaction product is poured in water or ice, then is or is not neutralized, further is isolated or extracted with an organic solvent/an aqueous solution, and thereafter can be used without purification or can be used after performing purification operations such as recrystallization and salt formation, individually or in combination.

The production method of the azo pigment composition for use in the present invention is described in more detail below.

The production method of the azo pigment composition for use in the present invention is characterized in that in a coupling reaction between a diazonium compound obtained by converting a heterocyclic amine represented by formula (2) into a diazonium form and a compound represented by formula (3), the coupling reaction is performed after dissolving the compound represented by formula (3) in an organic solvent.

The reaction for preparing a diazonium salt of the heterocyclic amine represented by formula (2) may be performed, for example, by reacting the heterocyclic amine with a reagent such as sodium nitrite and nitrosyl sulfuric acid in an acidic solvent such as sulfuric acid, phosphoric acid and acetic acid at a temperature of 15°C or less for approximately from 10 minutes to 6 hours. The coupling reaction is preferably performed by reacting the diazonium salt obtained by the method above with a compound represented by formula (3) at 40°C or less, preferably 15°C or less, for approximately from 10 minutes to 12 hours.

The above-described tautomer and/or polymorphic crystalline form can be controlled by the production conditions at the coupling reaction. As to the method for producing a pigment composition containing as the main component a crystal in a more preferred embodiment of the present invention, that is, a crystal of formula (1) having characteristic X-ray diffraction peaks at 7.2° and 25.9° (α-crystalline form azo pigment), it is preferred to use, for example, the method of the present invention of once dissolving the compound represented by formula (3) in an organic solvent and then performing a coupling reaction. Examples of the organic solvent which can be used here include an alcohol solvent and a ketone-based solvent. Preferred examples of the alcohol solvent include methanol, ethanol, isopropanol, ethylene glycol and diethylene glycol, with methanol being more preferred. Preferred examples of the ketone-based solvent include acetone, methyl ethyl ketone and cyclohexanone, with acetone being more preferred.

Another production method of the azo pigment composition of the present invention is characterized in that in a coupling reaction between a diazonium compound obtained by converting a heterocyclic amine represented by formula (2) into a diazonium form and a compound represented by formula (3), the coupling reaction is performed in the presence of a polar aprotic solvent.

A pigment composition containing as the main component a crystal of formula (1) having characteristic X-ray diffraction peaks at 7.2° and 25.9° (α- crystalline form azo pigment) can be efficiently produced also by the method of performing the coupling reaction in the presence of a polar aprotic solvent. Examples of the polar aprotic solvent include N,N-dimethylformamide, N ,N- dimethylacetamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, tetramethylurea, acetone, methyl ethyl ketone, acetonitrile, and a mixed solvent thereof. Among these solvents, acetone, methyl ethyl ketone, N,N-diniethylacetamide and acetonitrile are preferred. In the case of using such a solvent, the compound represented by formula (2) may or may not be completely dissolved in the solvent.

According to the usage of the compound obtained by the production method above, the pH may or may not be adjusted by adding a base as a purification step. In the case of adjusting the pH, the pH is preferably from 4 to 10, more preferably from 5 to 8, still more preferably from 5.5 to 7.5.

When the pH is 10 or less, in view of hue, neither discoloration/color fading nor increase of reddish tint are caused, which is preferred from the standpoint of ensuring a hue of constant quality. When the pH is 4 or more, this is preferred because, for example, in use as an ink for inkjet recording, a problem such as corrosion of a nozzle hardly arises.

The compound represented by formula (1) is obtained as a crude azo pigment (crude) by the production method above.

The present invention also relates to an azo pigment composition produced by the above-described production method. Post-Treatment Step

The production method of the present invention preferably contains a step of performing a post-treatment. Examples of the post-treatment step include a step of controlling a pigment particle by a milling treatment (e.g., solvent salt milling, salt milling, dry milling, solvent milling, acid pasting) or a solvent heating treatment, and a step of surface treatment with a resin, a surfactant, a dispersant or the like.

The compound represented by formula (1) of the present invention is preferably subjected to a solvent heating treatment and/or a solvent salt milling as the post-treatment step. For example, an azo pigment in desired crystalline morphology can be produced by performing reflux in an organic solvent excluding water.

Examples of the solvent used in the solvent heating treatment include water, an aromatic hydrocarbon-based solvent such as toluene and xylene, a halogenated hydrocarbon-based solvent such as chlorobenzene and o-dichlorobenzene, an alcohol- based solvent such as isopropanol and isobutanol, a polar aprotic organic solvent such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, acetone, methyl ethyl ketone and acetonitrile, glacial acetic acid, pyridine, and a mixture thereof. In such a solvent, an inorganic or organic acid or base may be further added.

The temperature at the solvent heating treatment varies depending on the primary particle diameter of the desired pigment but is preferably from 40 to 150 ⁰ C, more preferably from 60 to 100°C, and the treatment time is preferably from 30 minutes to 24 hours.

Examples of the solvent salt milling include a method of performing kneading and milling in a kneader after charging thereinto the crude azo pigment, an inorganic salt and an organic solvent incapable of dissolving them. The inorganic salt which can be suitably used is a water-soluble inorganic salt, and, for example, an inorganic salt such as sodium chloride, potassium chloride and sodium sulfate is preferably used. It is more preferred to use an inorganic salt having an average particle diameter of 0.5 to 50 μm. The amount of the inorganic salt used is preferably from 3 to 20 times by mass, more preferably from 5 to 15 times by mass, based on the crude azo pigment. The organic solvent which can be suitably used is a water-soluble organic solvent and in view of safety, a high boiling point solvent is preferred, because the solvent enters a readily evaporatable state by the rise of temperature during kneading. Examples of such an organic solvent include diethylene glycol, glycerin, ethylene glycol, propylene glycol, liquid polyethylene glycol, liquid polypropylene glycol, 2- (methoxymethoxy)ethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol, 2- (hexyloxy)ethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, l-methoxy-2-propanol, l-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol and a mixture thereof. The amount of the water-soluble organic solvent used is preferably from 0.1 to 5 times by mass based on the crude azo pigment. The kneading temperature is preferably from 20 to 13O ⁰ C, more preferably from 40 to 110°C. Examples of the kneading machine which can be used include a kneader and a mix-muller.

In the invention, for producing the azo pigment composition containing the β- crystalline form azo pigment, employable is a method of controlling the reaction condition (solvent used, pH value, reaction temperature, reaction time, etc.) in the step of azocoupling a diazonium salt derived from the heterocyclic amine of formula (2) and the compound of formula (3) in which the reaction condition (solvent used, pH value, reaction temperature, reaction time, etc.) is controlled. The condition (solvent used, pH value, reaction temperature, reaction time, etc.) in post-treating the azo pigment prepared as in the above, in the subsequent step may be controlled to give the intended crystalline form azo pigment with ease.

As described above, the yellow pigment dispersion of the present invention contains yellow pigment of group (A) in addition to azo pigment of formula (1).

The Yellow pigment of group (A) is preferably at least one pigment selected from the group consisting of C.I. Pigment Yellow 74, 110, 120, 128, 138, 139, 150, 155, 185 and 213 from the standpoint of color hue, image fastness and pigment dispersibility, more preferably at least one pigment selected from the group consisting of C.I. Pigment Yellow 74, 128, 155, 138, 139, 185 and 213, and most preferably at least one pigment selected from the group consisting of C.I. Pigment Yellow 74, 128, 155, 185 and 213.

The yellow pigment dispersion of the invention may be an aqueous system or a non-aqueous system, but a pigment dispersion of aqueous system is preferred. In the aqueous pigment dispersion, as for the aqueous liquid in which the pigment is dispersed, a mixture containing water as the main component and having added thereto, if desired, a hydrophilic organic solvent may be used. Examples of the hydrophilic organic solvent include alcohols (e.g., methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, tert-butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol), polyhydric alcohols (e.g., ethylene glycol, diethylene glycol, Methylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol), glycol derivatives (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, ethylene glycol diacetate, ethylene glycol monomethyl ether acetate, triethylene glycol monoethyl ether, ethylene glycol monophenyl ether), amines (e.g., ethanolamine, diethanolamine, triethanolamine, N- methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenetriamine, triethylenetetramine, polyethyleneimine, tetramethylpropylenediamine), formamide, N,N-dimethylformamide, N ₃ N- dimethylacetamide, dimethylsulfoxide, sulfolane, 2-pyrrolidone, N-methyl-2- pyrrolidone, N-vinyl-2-pyrrolidone, 2-oxazolidone, 1,3 -dim ethyl -2-imidazolidinone, acetonitrile, and acetone.

Furthermore, the aqueous pigment dispersion of the present invention may contain an aqueous resin. The aqueous resin includes a water-dissolvable resin capable of dissolving in water, a water-dispersible resin capable of dispersing in water, a colloidal dispersion resin, and a mixture thereof. Specific examples of the aqueous resin include acryl-based, styrene-acryl-based, polyester-based, polyamide- based, polyurethane-based and fluorine-based resins.

For enhancing the dispersion of the pigment and the quality of the image, a surfactant and a dispersant may be used. The surfactant includes anionic, nonionic, cationic and amphoteric surfactants, and any surfactant may be used, but an anionic or nonionic surfactant is preferably used. Examples of the anionic surfactant include a fatty acid salt, an alkylsulfuric acid ester salt, an alkylbenzenesulfonate, an alkylnaphthalenesulfonate, a dialkylsulfosuccinate, an alkyldiaryl ether disulfonate, an alkylphosphate, a polyoxyethylene alkyl ether sulfate, a polyoxyethylene alkylaryl ether sulfate, a naphthalenesulfonic acid-formalin condensate, a polyoxyethylene alkylphosphoric acid ester salt, a glycerol borate fatty acid ester and a polyoxyethylene glycerol fatty acid ester.

Examples of the nonionic surfactant include a polyoxyethylene alkyl ether, a polyoxyethylene alkylaryl ether, a polyoxyethylene oxypropylene block copolymer, a sorbitan fatty acid ester, a polyoxyethylene sorbitan fatty acid ester, a polyoxyethylene sorbitol fatty acid ester, a glycerin fatty acid ester, a polyoxyethylene fatty acid ester, a polyoxyethylene alkylamine and a fluorine- or silicon-containing surfactant.

As the dispersant, also usable are polymers or base-containing commercial dispersants such as vinyl polymers, modified polyurethanes, salts of polyaminoamide and acid ester, modified polyethyleneimines, modified polyallylamines, etc.

Only one type or two or more different types of dispersants may be in the yellow pigment dispersion. The dispersant content in the yellow pigment dispersion is preferably from 10% by mass to 150% by mass with respect to the total pigment solid content in the dispersion, more preferably from 10 to 100% by mass, and above all, most preferably from 30 to 80% by mass.

Further, the dispersant content in the yellow pigment dispersion is preferably from 10 to 140% by mass with respect to the coloring agent, from the view point of temporal stability of the dispersion, jettability of the ink for inkjet ink, printing density, color reproduction of the recorded matter or the like, more preferably from 20 to 80% by mass, most preferably from 30 to 55% by mass. The non-aqueous pigment dispersion is obtained by dispersing the pigment of formula (1) and the yellow pigment of group (A) in a non-aqueous vehicle. Examples of the resin used for the non-aqueous vehicle include petroleum resin, casein, shellac, rosin-modified maleic acid resin, rosin-modified phenol resin, nitrocellulose, cellulose acetate butyrate, cyclized rubber, chlorinated rubber, oxidized rubber, hydrochlorinated rubber, phenol resin, alkyd resin, polyester resin, unsaturated polyester resin, amino resin, epoxy resin, vinyl resin, vinyl chloride, vinyl chloride-vinyl acetate copolymer, acrylic resin, methacrylic resin, polyurethane resin, silicon resin, fluororesin, drying oil, synthesized drying oil, styrene/maleic acid resin, styrene/acryl resin, polyamide resin, polyimide resin, benzoguanamine resin, melamine resin, urea resin chlorinated polypropylene, butyral resin and vinylidene chloride resin. A photo-curable resin may also be used as the non-aqueous vehicle.

Examples of the solvent used for the non-aqueous vehicle include an aromatic solvent such as toluene, xylene and methoxybenzene, an acetic acid ester-based solvent such as ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate, a propionate-based solvent such as ethoxyethyl propionate, an alcohol-based solvent such as methanol and ethanol, an ether-based solvent such as butyl cellosolve, propylene glycol monomethyl ether, diethylene glycol ethyl ether and diethylene glycol dimethyl ether, a ketone-based solvent such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, an aliphatic hydrocarbon-based solvent such as hexane, a nitrogen compound-based solvent such as N,N-dimethylformamide, γ-butyrolactam, N- methyl-2-pyrrolidone, aniline and pyridine, a lactone-based solvent such as γ- butyrolactone, and a carbamic acid ester such as a 48:52 mixture of methyl carbamate and ethyl carbamate.

Preferably, the yellow pigment dispersion of the invention further contains a high-boiling-point organic solvent in an amount of from 0.1 to 30% by mass of the total amount of the ink composition, more preferably from 0.5 to 20% by mass, even more preferably from 1.0 to 20% by mass.

The high-boiling-point organic solvent is an organic solvent having a boiling point of not lower than 150°C, preferably not lower than 170°C. For example, there are mentioned high-boiling-point organic solvents described in JP-A 2001-262018, JP-A 2001-240763, JP-A 2001-335734, JP-A 2002-80772. Above all, preferred are polyalcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, propylene glycol, butylene glycol, 1,2,6- hexanetriol, thioglycol, 1,2-hexanediol, glycerin, trimethylolethane, trimethylolpropane, etc.; polyalcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, etc.; urea, 2-pyrrolidone, N-methyl-2-pyrrolidone, l,3-dimethyl-2- imidazolidinone; and more preferred are propylene glycol, 1,2-hexanediol, glycerin, trimethylolpropane, triethylene glycol monobutyl ether, 2-pyrrolidone. The yellow pigment dispersion of the invention is produced by dispersing the above-mentioned azo pigment and a water-based or nonaqueous medium, using a dispersing apparatus. As the dispersing apparatus, herein usable is any of a simple stirrer, an impeller stirring system, an in-line stirring system, a milling system (e.g., colloid mill, ball mill, sand mill, bead mill, attritor, roll mill, jet mill, paint shaker, agitator mill, etc.), an ultrasonic system, a high-pressure emulsion dispersion system (high-pressure homogenizer; concretely, commercially-available Gaulin homogenizer, microfluidizer, DeBEE 2000).

In the invention, preferably, the volume-average particle size of the pigment dispersion is from 0.01 μm to 0.2 μm. The volume-average particle size of the pigment dispersion means the particle size of the pigment dispersion composed of a pigment and a pigment dispersant, or in case where an additive such as synergist (pigment derivative) or the like adheres to the pigment or the pigment dispersion, it means the particle size of the additive-adhering dispersion. For measuring the volume-average particle size of the pigment in the invention, used is Nanotrack UPA particle sizer (UPA-EXl 50, by Nikkiso). Briefly, 3 ml of a pigment dispersion is put into a sample cell, and analyzed according to a predetermined measurement method. Regarding the parameters to be inputted in the device, the ink viscosity is inputted for the viscosity, and the pigment density is for the density of the dispersed particles.

More preferably, the volume-average particle size is from 20 nm to 200 nm, even more preferably from 30 nm to 180 nm, and above all, most preferably from 30 nm to 150 nm. When the volume-average particle size of the particles in the pigment dispersion is less than 20 nm, then the dispersion could not secure storage stability; but on the other hand, when more than 250 nm, then the optical density of the composition may be low. Preferably, the concentration of all the pigment to be in the yellow pigment dispersion of the invention is within a range of from 1 to 35% by mass, more preferably from 2 to 25% by mass, even more preferably from 2 to 20% by mass, and above all, still more preferably from 5 to 20% by mass. When the concentration is less than 1% by mass, and when the pigment dispersion alone is used as an ink by itself, it could not give a sufficient image density. When the concentration of more than 35% by mass, then the storage stability may lower.

Regarding the application of the yellow pigment dispersion of the invention, the dispersion is usable in an image-recording material for forming images, especially for forming color images. Concretely, the dispersion is usable typically for an inkjet recording material to be mentioned in detail hereinunder, and also for a thermal transfer recording material, a pressure-sensitive recording material, an electrophotographic recording material, a transfer silver halide photosensitive material, a printing ink, a recording pen, etc., preferably it is for an inkjet recording material, a thermal recording material and an electrophotographic recording material, more preferably for an inkjet recording material.

The pigment dispersion is also applicable to color filters for recording and reproducing color images in solid-state imaging devices such as CCD or the like and in displays such as LCD, PDP, etc.; and to dyeing liquids for dyeing various fibers.

The yellow pigment dispersion of the invention may be in any form of an emulsion dispersion or a solid dispersion, depending on the type of the system to which is it applied.

The yellow pigment dispersion of the invention contains, as the coloring agent to be therein, the azo pigment of formula (1) and the yellow pigment of the above group (A). The yellow pigment dispersion of the invention may contain a medium; and when a solvent is used for the medium, the dispersion is favorable for an ink for inkjet recording. The color composition of the invention may be produced by dispersing the coloring agent in an oleophilic medium or an aqueous medium. Preferably, the agent is dispersed in an aqueous medium. The yellow pigment dispersion of the invention may contain, if desired, any other additive not detracting from the effect of the invention. The other additive includes known additives, for example, a drying inhibitor (wetting agent), an antifading agent, an emulsion stabilizer, a penetration promoter, a UV absorbent, a preservative, a antifungal agent, a pH controlling agent, a surface tension controlling agent, a defoaming agent, a viscosity controlling agent, a dispersant, a dispersion stabilizer, an rust inhibitor, a chelating agent, etc. (described in JP-A 2003-306623). For a water-based ink, these various additives may be added directly thereto. For an oily ink, in general, they are added to the azo pigment dispersion after its preparation, but as the case may be, they may be added to an oily phase or an aqueous phase during the preparation of the dispersion.

The penetration promoter is used for the purpose of more smoothly penetrating the inkjet ink into paper. As the penetration promoter, usable are alcohols such as ethanol, isopropanol, butanol, di(tri)ethylene glycol monobutyl ether, 1,2-hexanediol, etc.; sodium laurylsulfate, sodium oleate, nonionic surfactants, etc. These may be in the ink generally in an amount of from 1 to 30% by mass to be sufficiently effective therein; and preferably, the amount thereof to be added is within a range within which they are effective for preventing print bleeding and print through.

Preferably, the yellow pigment dispersion of the invention contains the penetration promoter in an amount of from 1 to 20% by mass with respect to the total amount of the ink composition, more preferably from 1 to 15% by mass, even more preferably from 3 to 10% by mass. Ink for InkJet Recording

The ink for inkjet recording (hereinafter this may be referred to simply as "ink") of the invention comprises the yellow pigment dispersion mentioned in the above. Preferably, it may be prepared as mixed with a water-soluble solvent, water or the like. However, when nonproblematic, the pigment dispersion of the invention may be used directly as it is.

The content of the pigment dispersion in the ink is preferably from 1 to 100% by mass in consideration of the color hue, the color density, the saturation and the transparency of the image formed on a recording medium, more preferably from 3 to 20% by mass, even more preferably from 3 to 10% by mass.

Preferably, the ink contains the pigment of the invention (that is, the azo pigment of formula (1) and the yellow pigment of group (A)) in an amount of from 0.1 parts by mass to 20 parts by mass relative to 100 parts by mass of the ink, more preferably from 0.2 parts by mass to 10 parts by mass, even more preferably from 1 to 10 parts by mass, and above all, most preferably from 3.0 to 8.0 parts by mass. The ink of the invention may contain any other pigment along with the pigment of the invention. In case where the ink contains the additional pigment, preferably, the total content of the pigments falls within the above range.

The ink may be used not only for single color image formation but also for full color image formation. For full color image formation, used are a magenta color ink, a cyan color ink and a yellow color ink; and for controlling the color tone, a black color ink may be additionally used.

The water-soluble solvent usable in the invention includes polyalcohols, polyalcohol derivatives, nitrogen-containing solvents, alcohols, sulfur-containing solvents, etc.

Specific examples of the solvent are described. The polyalcohols include ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, Methylene glycol, 1 ,2-hexanediol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerin, etc.

The polyalcohol derivatives include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, Methylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, diglycerin ethyleneoxide adduct, etc.

The nitrogen-containing solvents include pyrrolidone, N-methyl-2- pyrrolidone, cyclohexylpyrrolidone, triethanolamine, etc.; the alcohols include ethanol, isopropyl alcohol, butyl alcohol, benzyl alcohol, etc.; the sulfur-containing solvents include thiodiethanol, thiodiglycerol, sulfolane, dimethyl sulfoxide, etc. In addition, propylene carbonate, ethylene carbonate and the like are also usable.

One or more water-soluble solvents may be used in the invention either singly or as combined. Preferably, the content of the water-soluble solvent is from 1% by mass to 60% by mass of the entire ink, preferably from 5% by mass to 40% by mass. When the amount of the water-soluble solvent in the ink is less than 1% by mass, the ink could not produce a sufficient optical density; but on the contrary, when more than 60% by mass, the liquid viscosity may increase and the ink liquid jetting state may be unstable.

The preferred physical properties of the ink of the invention are mentioned below. The ink surface tension is preferably from 20 mN/m to 60 mN/m, more preferably from 20 mN/m to 45 mN/m, even more preferably from 25 mN/m to 35 mN/m. When the surface tension is lower than 20 mN/m, the liquid may overflow on the nozzle face of the recording head, therefore interfering with correct printing. On the other hand, when higher than 60 mN/m, the penetration of the ink into the recording medium after printing thereon may be delayed and the drying time may be long. The surface tension is measured in an environment at 23°C and 55% RH, using a Wilhelmy surface tensiometer, similarly to the above.

The ink viscosity is preferably from 1.2 mPa-s to 8.0 mPa-s, more preferably from 1.5 mPa-s to less than 6.0 mPa-s, even more preferably from 1.8 mPa-s to less than 4.5 mPa-s. When the viscosity is more than 8.0 mPa-s, then the ink jettability may worsen. On the other hand, when less than 1.2 mPa-s, then the long-term jettability may worsen.

The above viscosity (including that to be mentioned below) is measured at 23 ⁰ C and at a shearing speed of 1400 s ^"1 , using a rotary viscometer Rheomat 115 (by Contraves).

In addition to the above-mentioned ingredients, water is added to the ink within a range within which the ink can have the above-mentioned preferred surface tension and viscosity. Not specifically defined, the amount of water to be added may be from 10% by mass to 99% by mass of the total ink, more preferably from 30% by mass to 80% by mass.

Further if desired, for the purpose of controlling the properties of the ink, for example, for the purpose of enhancing the jettability of the ink, polyethyleneimine, polyamines, polyvinylpyrrolidone, polyethylene glycol, cellulose derivatives (e.g., ethyl cellulose, carboxymethyl cellulose), polysaccharides and their derivatives, other water-soluble polymers, polymer emulsions (e.g., acrylic polymer emulsions, polyurethane emulsions, hydrophilic latex), hydrophilic polymer gel, cyclodextrin, macrocyclic amines, dendrimer, crown ethers, urea and its derivatives, acetamide, silicone surfactants, fluorine-containing surfactants and the like may be added to the ink.

For controlling the electroconductivity and the pH of the ink, alkali metal compounds such as potassium hydroxide, sodium hydroxide, lithium hydroxide, etc.; nitrogen-containing compounds such as ammonium hydroxide, triethanolamine, diethanolamine, ethanolamine, 2-amino-2-methyl-l-propanol, etc.; alkaline earth metal compounds such as calcium hydroxide, etc.; acids such as sulfuric acid, hydrochloric acid, nitric acid, etc.; salts of strong acid and weak alkali such as ammonium sulfate, etc. may be added to the ink.

In addition, if desired, a pH buffer, an antioxidant, an antifungal agent, a viscosity controlling agent, an electroconductive agent, a UV absorbent and the like may be added to the ink.

InkJet Recording Method, InkJet Recording Cartridge, InkJet Recording Apparatus, InkJet Recorded Matter

The inkjet recording method is a method for forming an image on the surface of a recording medium by using an ink for inkjet recording and by jetting out the ink onto the surface of a recording medium through a recording head of an inkjet recording apparatus in accordance with the recording signal given to the apparatus.

The inkjet recording apparatus is an apparatus for forming an image using an ink for inkjet recording, which comprises a recording head for jetting out an ink (and optionally a processing liquid) onto the surface of a recording medium and in which the ink is jetted out onto the surface of the recording medium through the recording head. The inkjet recording apparatus may comprise an inkjet recording cartridge (this may be hereinafter referred to as "ink cartridge") detachable from the body of the inkjet recording apparatus body. In this case, ink is put into the ink for inkjet recording cartridge.

As the inkjet recording apparatus, herein usable is an ordinary inkjet recording apparatus equipped with a printing system where an ink for inkjet recording is usable, and apart from it, the apparatus may further comprise, if desired, a heater or the like for controlling the drying of ink, or a intermediate transfer mechanism in which ink and processing liquid are first jetted out (printed) on an intermediate, and then transferred onto the recording medium such as paper or the like.

For the inkjet recording ink cartridge, herein usable is any conventional known ink cartridge which can be detachable from an inkjet recording apparatus equipped with a recording head, and which, while fitted to the inkjet recording apparatus, may feed ink to the recording head.

In the inkjet recording method (apparatus), preferably employed is a thermal inkjet recording system or a piezo inkjet recording system from the viewpoint of evading troubles of bleeding and intercolor bleeding. In the thermal inkjet recording system, the ink is heated to have a lowered viscosity during jetting, but the ink temperature lowers on the recording medium, the ink viscosity rapidly increases. Accordingly, the ink of the invention is effective for solving the problems of bleeding and intercolor bleeding. On the other hand, the piezo inkjet system, a high- viscosity liquid may be jetted out, and the high- viscosity liquid hardly spreads in the plane direction on the recording medium; and therefore in the system, the ink of the invention is effective for solving the problems of bleeding and intercolor bleeding.

In the inkjet recording method (apparatus), preferably, an ink cartridge filled with an ink liquid (and optionally a processing liquid tank) is used for supplying (feeding) an ink to the apparatus. Preferably, the ink cartridge is detachable from the body of the apparatus, and by changing the detachable ink cartridge of the type, ink supply may be continued with ease.

In the inkjet recorded matter of the invention, an image is formed with the ink for inkjet recording of the invention mentioned in the above. The image formation is favorably attained using the above-mentioned inkjet recording apparatus and according to the above-mentioned inkjet recording method.

The invention is described in more detail with reference to the following Examples, to which, however, the invention should not be limited. "Part" in Examples is by mass.

Examples

The pigment composition of the invention was analyzed for X-ray diffractiometry according to the Japanese Industrial Standards JIS KO 131 (general rule of X-ray diffractiometry), using a powdery X-ray diffractiometer RINT 2500 (by Rigaku) with CuKa ray under the condition mentioned below. Measuring instrument used: an automatic X-ray diffraction apparatus, RINT 2500, manufactured by Rigaku Corporation X-Ray tube: Cu Tube voltage: 55 kV Tube current: 28O mA Scan method: 2Θ/Θ scan Scan speed: 6 deg./min Sampling interval: 0.100 deg. Start angle (2Θ): 5 deg. Stop angle (2Θ): 55 deg.

Divergence slit: 2 deg.

Scattering slit: 2 deg.

Receiving slit: 0.6 mm

A vertical goniometer was used.

[Production Example 1] Production of Azo Pigment Composition (1)

A production scheme for the azo pigment (1) is shown below.

(a) (b)

(C) (d)

(β)

(1) Production of Intermediate (a)

To 29.7 g (0.3 mol) of methyl cyanoacetate, 42.4 g (0.4 mol) of trimethyl orthoformate, 20.4 g (0.2 mol) of acetic acid anhydride and 0.5 g of p-toluenesulfonic acid were added. The resulting mixture was heated at 110 ⁰ C (outer temperature) and stirred for 20 hours while distilling off low-boiling-point components produced from the reaction system. The obtained reaction solution was concentrated under reduced pressure and then subjected to silica gel column purification to obtain 14.1 g of Intermediate (a) (yellow powder, yield: 30%). The NMR measurement results of Intermediate (a) obtained are as follows. 1H-NMR (300 MHz, CDCl ₃ ) 7.96 (s, IH), 4.15 (s, 3H), 3.81 (s, 3H).

(2) Production of Intermediate (b)

To 7.4 mL (141 mmol) of methylhydrazine, 150 mL of isopropanol was added. The resulting mixture was cooled to 15°C (inner temperature) and after gradually adding thereto 7.0 g (49.6 mmol) of Intermediate (a), the mixed solution was heated at 50°C and stirred for 1 hour and 40 minutes. The obtained reaction solution was concentrated under reduced pressure and then subjected to silica gel column purification to obtain 10.5 g of Intermediate (b) (white powder, yield: 50%). The NMR measurement results of Intermediate (b) obtained are as follows. 1H-NMR (300 MHz, CDCl ₃ ) 7.60 (s, IH), 4.95 (brs, 2H), 3.80 (s, 3H), 3.60 (s, 3H).

(3) Production of Intermediate (c):

136 mL of water was added to 1.1 L of methanol, then 182 g (2.17 mols) of sodium hydrogencarbonate was added thereto and stirred at room temperature. At the temperature, 200 g (1.08 mols) of cyanuric chloride was portion wise added thereto. After the addition, the inside temperature was elevated up to 30°C. At the temperature, this was stirred for 30 minutes, then 500 mL of water was added thereto, and the precipitated solid was taken out through filtration, washed with 500 mL of water and 300 mL of methanol poured thereto, and dried to give 168 g of the above- mentioned intermediate (c) (white powder, yield 86.2%). The NMR data of the obtained intermediate (c) are as follows: 1H-NMR (300 MHz ₅ CDCl ₃ ): 4.14 (s, 3H)

(4) Production of Intermediate (d):

673 mL of water was added to 363 mL (7.46 mols) of hydrazine monohydrate, cooled at 1O ⁰ C (inside temperature), and 168 g (934 mmols) of the intermediate (c) was gradually added to the mixture liquid (at inside temperature of not higher than 20°C), then the ice bath was removed, and this was restored to room temperature and stirred at the temperature for 30 minutes. The crystal precipitated out from the reaction liquid was taken out through filtration, washed with 700 mL of water and 1 L of acetonitrile poured thereto, and dried to give a crude product (white powder) of the above-mentioned intermediate (d).

(5) Production of Intermediate (e):

480 mL of ethylene glycol was added to the crude product of the intermediate (d), and stirred at room temperature. 257 g (2.06 mols) of pivaloylacetonitrile was added to the suspension, and heated so that the inside temperature could reach 50°C. At the temperature, 12 M hydrochloric acid was dropwise added thereto so that the mixture could have a pH of 3, and then this was heated up to 80°C (inside temperature), and stirred for 3 hours. After the reaction, this was cooled with ice until the inside temperature could reach 8 ⁰ C, and the crystal thus precipitated out was taken out through filtration, washed with water poured thereto, and purified through a silica gel column to give 105 g of the above-mentioned intermediate (e) (white powder, yield in the two steps, 29.2 %). The NMR data of the obtained intermediate (e) are as follows:

¹ H-NMR (300 MHz, d-DMSO): 7.00 (s, 4H), 5.35 (s, 2H), 4.05 (s, 3H), 1.22 (s,

18)

(6) Production of Azo Pigment (1):

A mixture liquid of 125 mL of acetic acid and 24 mL of sulfuric acid was cooled with ice to 3°C (inside temperature). At the temperature, 26.4 g of nitrosyl sulfuric acid was added to it, and then at the temperature, 11.6 g of the intermediate (b) was portionwise added thereto and dissolved. At the temperature, this was stirred for 1 hour, then at the temperature, 1.2 g of urea was portionwise added thereto, and stirred for 15 minutes at the temperature to give a diazonium salt solution. Apart from this, 11.6 g of the intermediate (e) was completely dissolved in 405 mL of methanol at room temperature, and cooled with ice to -3°C (inside temperature). At the temperature, the above-mentioned diazonium salt solution was portionwise added thereto so that the inside temperature could be not higher than 3°C, and after the addition, this was stirred for 2 hours. The ice bath was removed, then the mixture was stirred at room temperature for 10 minutes, and the precipitated crystal was taken out through filtration, washed with 150 mL of methanol poured thereto, and further with 100 mL of water poured thereto. Not dried, the obtained crystal was suspended in 750 mL of water, then aqueous 8 N potassium hydroxide solution was added thereto to make it have a pH of 5.7. This was stirred at room temperature for 20 minutes, then the formed crystal was collected through filtration, fully washed with water poured thereto, and then with 80 mL of methanol poured thereto. The obtained crystal was dried at room temperature for 12 hours.

The obtained crystal was suspended in a mixed solution of 180 mL of dimethylacetamide and 180 mL of water, then heated up to 85 ⁰ C (inside temperature), and stirred at the temperature for 2 hours. Subsequently, the formed crystal was collected through filtration while hot, then suspended in 300 mL of methanol, and stirred at room temperature for 30 minutes. The formed crystal was collected through filtration, and dried at room temperature for 5 hours to give 19.5 g of the azo pigment (1). Yield, 90.3%.

The obtained azo pigment (1) was visually observed with a transmission microscope (JEOL's electronic microscope, JEM-1010), and the length in the long axis direction of the primary particles was about 150 nm.

The azo pigment (1) was analyzed for X-ray diffractiometry under the condition mentioned in the above, and this gave characteristic X-ray diffraction peaks at Bragg angles (2Θ + 0.2°) of 7.2° and 25.9°. Fig. 1 shows the CuKa characteristic X-ray diffraction pattern of the azo pigment (1). [Production Example 2]

Preparation of Vinyl Polymer Solution (1)

The following monomer ingredients were mixed to make 100 parts by mass in total, and further 1 part by mass of a polymerization initiator, 2,2'-azobis(2,4- dimethylvaleronitrile) was added thereto. This was fully purged with nitrogen gas to give a monomer mixture.

Phenoxyethyl methacrylate 54.9 parts by mass

Methyl methacrylate 35 parts by mass

Methacrylic acid 10 parts by mass

2-Mercaptoethanol 0.1 parts by mass

Next, 100 parts by mass of methyl ethyl ketone was added to it and heated up to 75°C with stirring in a nitrogen atmosphere. With still stirring at 75°C, the above monomer mixture was drop wise added to it, taking 3 hours. Further, this was reacted for 5 hours with stirring. Next, the reaction product was spontaneously cooled to 25°C, then methyl ethyl ketone was added thereto to dilute it to have a solid content of 50%, thereby preparing a vinyl polymer solution (1) having a mean molecular weight of 41,000. [Example 1] Preparation of Pigment Dispersion 1

2.25 parts by mass of the azo pigment (1) produced in Production Example 1, 0.25 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 1 (volume-average particle size, Mv: about 73 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EX150)). [Example 2] Preparation of Pigment Dispersion 2

2.0 parts by mass of the azo pigment (1) produced in Production Example 1, 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 2 (volume-average particle size, Mv: about 78 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Example 3] Preparation of Pigment Dispersion 3

1.5 parts by mass of the azo pigment (1) produced in Production Example 1, 1.0 part by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 3 (volume-average particle size, Mv: about 82 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Example 4] Preparation of Pigment Dispersion 4

1.25 parts by mass of the azo pigment (1) produced in Production Example 1, 1.25 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 4 (volume-average particle size, Mv: about 83 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EX150)). [Example 5] Preparation of Pigment Dispersion 5

2.25 parts by mass of the azo pigment (1) produced in Production Example 1, 0.25 parts by mass of C.I. Pigment Yellow 155 (Clarient's INKJET YELLOW 4G VP2532), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 2 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 5 (volume-average particle size, Mv: about 75 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Example 6] Preparation of Pigment Dispersion 6

2.0 parts by mass of the azo pigment (1) produced in Production Example 1, 0.5 parts by mass of C.I. Pigment Yellow 155 (Clarient's INKJET YELLOW 4G VP2532), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 2 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 6 (volume-average particle size, Mv: about 80 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Example 7] Preparation of Pigment Dispersion 7

1.5 parts by mass of the azo pigment (1) produced in Production Example 1, 1.0 part by mass of C.I. Pigment Yellow 155 (Clarient's INKJET YELLOW 4G VP2532), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 2 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 7 (volume-average particle size, Mv: about 84 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Example 8] Preparation of Pigment Dispersion 8

1.25 parts by mass of the azo pigment (1) produced in Production Example 1, 1.25 parts by mass of C.I. Pigment Yellow 155 (Clarient's INKJET YELLOW 4G VP2532), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 2 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 8 (volume-average particle size, Mv: about 83 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXlSO)). [Example 9] Preparation of Pigment Dispersion 9

2.25 parts by mass of the azo pigment (1) produced in Production Example 1, 0.25 parts by mass of C.I. Pigment Yellow 110 (Ciba Specialty's IRGAZIN YELLOW 2RLT), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 9 (volume-average particle size, Mv: about 81 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Example 10] Preparation of Pigment Dispersion 10

2.25 parts by mass of the azo pigment (1) produced in Production Example 1, 0.25 parts by mass of C.I. Pigment Yellow 128 (Ciba Specialty's CROMOPHT AL YELLOW 8GN), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 10 (volume-average particle size, Mv: about 84 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Example 11] Preparation of Pigment Dispersion 11

2.25 parts by mass of the azo pigment (1) produced in Production Example 1, 0.25 parts by mass of C.I. Pigment Yellow 138 (BASF's PALIOTOL L YELLOW 0960 HD), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 11 (volume-average particle size, Mv: about 81 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EX150)). [Example 12] Preparation of Pigment Dispersion 12

2.25 parts by mass of the azo pigment (1) produced in Production Example 1, 0.25 parts by mass of C.I. Pigment Yellow 139 (BASF's PALIOTOL D YELLOW 1891), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 12 (volume-average particle size, Mv: about 83 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Example 13] Preparation of Pigment Dispersion 13

2.25 parts by mass of the azo pigment (1) produced in Production Example 1, 0.25 parts by mass of C.I. Pigment Yellow 150 (Ciba Specialty's CROMOPHT AL YELLOW LA2), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 13 (volume-average particle size, Mv: about 70 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Example 14] Preparation of Pigment Dispersion 14

2.25 parts by mass of the azo pigment (1) produced in Production Example 1, 0.25 parts by mass of C.I. Pigment Yellow 185 (BASF's PALIOTOL L YELLOW Dl 155), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 14 (volume-average particle size, Mv: about 76 nm, as measured withNikkiso's Nanotrac 150 (UPA-EXl 50)). [Example 15] Preparation of Pigment Dispersion 15

2.25 parts by mass of the azo pigment (1) produced in Production Example 1, 0.25 parts by mass of C.I. Pigment Yellow 213 (Clarient's Hostperm Yellow H5G), 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. After the dispersion, the zirconia beads were separated to give a yellow pigment dispersion 15 (volume-average particle size, Mv: about 70 nm, as measured with

Nikkiso's Nanotrac 150 (UPA-EX150)).

[Comparative Example 1] Preparation of Comparative Pigment Dispersion 1

A yellow comparative pigment dispersion 1 was produced in the same manner as in Example 1, for which, however, 2.25 parts by mass of the azo pigment (1) and 0.25 parts by mass of C.I. Pigment Yellow 74, totaling 2.5 parts by mass, used in Example 1 were replaced with 2.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) and the mixture was dispersed until the volume- average particle size (Mv) of the resulting pigment dispersion could be at most 100 nm (volume- average particle size, Mv: about 68 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EX150)). [Comparative Example 2] Preparation of Comparative Pigment Dispersion 2

A yellow comparative pigment dispersion 2 was produced in the same manner as in Example 5, for which, however, 2.25 parts by mass of the azo pigment (1) and 0.25 parts by mass of C.I. Pigment Yellow 155, totaling 2.5 parts by mass, used in Example 5 were replaced with 2.5 parts by mass of CL Pigment Yellow 155 (Clarient's INKJET YELLOW 4G VP2532) and the mixture was dispersed until the volume-average particle size (Mv) of the resulting pigment dispersion could be at most 100 nm (volume-average particle size, Mv: about 38 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EX150)). [Comparative Example 3] Preparation of Comparative Pigment Dispersion 3

A yellow comparative pigment dispersion 3 was produced in the same manner as in Example 9, for which, however, 2.25 parts by mass of the azo pigment (1) and 0.25 parts by mass of CL Pigment Yellow 110, totaling 2.5 parts by mass, used in Example 9 were replaced with 2.5 parts by mass of CI. Pigment Yellow 110 (Ciba Specialty's IRGAZIN YELLOW 2RLT) and the mixture was dispersed until the volume-average particle size (Mv) of the resulting pigment dispersion could be at most 100 nm (volume-average particle size, Mv: about 55 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EX150)). [Comparative Example 4] Preparation of Comparative Pigment Dispersion 4

A yellow comparative pigment dispersion 4 was produced in the same manner as in Example 10, for which, however, 2.25 parts by mass of the azo pigment (1) and 0.25 parts by mass of C.I. Pigment Yellow 128, totaling 2.5 parts by mass, used in Example 10 were replaced with 2.5 parts by mass of C.I. Pigment Yellow 128 (Ciba Specialty's CROMOPHT AL YELLOW 8GN) and the mixture was dispersed until the volume-average particle size (Mv) of the resulting pigment dispersion could be at most 100 nm (volume- average particle size, Mv: about 50 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Comparative Example 5] Preparation of Comparative Pigment Dispersion 5

A yellow comparative pigment dispersion 5 was produced in the same manner as in Example 11, for which, however, 2.25 parts by mass of the azo pigment (1) and 0.25 parts by mass of C.I. Pigment Yellow 138, totaling 2.5 parts by mass, used in Example 11 were replaced with 2.5 parts by mass of C.I. Pigment Yellow 138 (BASF's PALIOTOL L YELLOW 0960 HD) and the mixture was dispersed until the volume-average particle size (Mv) of the resulting pigment dispersion could be at most 100 nm (volume-average particle size, Mv: about 78 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EXl 50)). [Comparative Example 6] Preparation of Comparative Pigment Dispersion 6

A yellow comparative pigment dispersion 6 was produced in the same manner as in Example 12, for which, however, 2.25 parts by mass of the azo pigment (1) and 0.25 parts by mass of C.I. Pigment Yellow 139, totaling 2.5 parts by mass, used in Example 12 were replaced with 2.5 parts by mass of C.I. Pigment Yellow 139 (BASF's PALIOTOL D YELLOW 1891) and the mixture was dispersed until the volume-average particle size (Mv) of the resulting pigment dispersion could be at most 100 nm (volume-average particle size, Mv: about 51 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EX150)). [Comparative Example 7] Preparation of Comparative Pigment Dispersion 7

A yellow comparative pigment dispersion 7 was produced in the same manner as in Example 13, for which, however, 2.25 parts by mass of the azo pigment (1) and 0.25 parts by mass of C.I. Pigment Yellow 150, totaling 2.5 parts by mass, used in Example 13 were replaced with 2.5 parts by mass of C.I. Pigment Yellow 150 (Ciba Specialty's CROMOPHTAL YELLOW LA2) and the mixture was dispersed until the volume-average particle size (Mv) of the resulting pigment dispersion could be at most 100 nm (volume-average particle size, Mv: about 67 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EX150)). [Comparative Example 8] Preparation of Comparative Pigment Dispersion 8

A yellow comparative pigment dispersion 8 was produced in the same manner as in Example 14, for which, however, 2.25 parts by mass of the azo pigment (1) and 0.25 parts by mass of C.I. Pigment Yellow 185, totaling 2.5 parts by mass, used in Example 14 were replaced with 2.5 parts by mass of C.I. Pigment Yellow 185 (BASF's PALIOTOL YELLOW Dl 155) and the mixture was dispersed until the volume-average particle size (Mv) of the resulting pigment dispersion could be at most 100 nm (volume-average particle size, Mv: about 70 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EX150)). [Comparative Example 9] Preparation of Comparative Pigment Dispersion 9 A yellow comparative pigment dispersion 9 was produced in the same manner as in Example 15, for which, however, 2.25 parts by mass of the azo pigment (1) and 0.25 parts by mass of C.I. Pigment Yellow 213, totaling 2.5 parts by mass, used in Example 15 were replaced with 2.5 parts by mass of C.I. Pigment Yellow 213 (Clarient's Hostperm Yellow H5G) and the mixture was dispersed until the volume- average particle size (Mv) of the resulting pigment dispersion could be at most 100 nm (volume-average particle size, Mv: about 44 nm, as measured with Nikkiso's Nanotrac 150 (UPA-EX150)). [Comparative Example 10] Preparation of Comparative Pigment Dispersion 10

When 2.25 parts by mass of the azo pigment (1) and 0.25 parts by mass of C.I. Pigment Yellow 74, totaling 2.5 parts by mass, used in Example 1 were replaced with 2.5 parts by mass of a compound of the following formula (DYE-A), and this was processed in the same manner as in Example 1. However, this was dissolved and could not be dispersed.

( D Y E - A )

<Dispersibility>

2.5 parts by mass of pigment, 0.5 parts by mass of sodium oleate, 5 parts by mass of glycerin and 42 parts by mass of water were mixed and dispersed, using a planetary ball mill with 100 parts by mass of zirconia beads having a diameter of 0.1 mm therein, at 300 rpm for 3 hours. The particle size of the resulting dispersion was measured. The sample containing coarse particles of 100 nm or more was ranked as "B"; the sample that could not be dispersed was ranked as "C"; and the sample with few coarse particles was ranked as "A". The pigment dispersions 1 to 15 of the invention, the comparative pigment dispersions 1 to 10 were evaluated and the results are shown in Table 1. <Storage Stability >

The pigment dispersions obtained in Examples 1 to 15 and Comparative Examples 1 to 9 was kept at room temperature for 4 weeks. As a result, those containing visible precipitates therein were ranked as "B"; and those not containing visible precipitates therein were ranked as "A". The results are shown in Table 1. <Tinctorial Strength Evaluation>

The pigment dispersions obtained in Examples 1 to 15 and Comparative Examples 1 to 9 were individually applied onto Epson's photomat paper, using a No. 3 bar coater. The image density of the coated paper was measured with a reflection densitometer (X-Rite's X-Rite 983). The tinctorial strength (OD: optical density) of the tested samples was evaluated based on the following criteria. The sample having OD of at least 1.4 was ranked as "A"; the sample having OD of from 1.2 to less than 1.4 was ranked as "B"; and the sample having OD of less than 1.2 was ranked as "C". The results are shown in Table 1. <Color Hue Evaluation>

Regarding the color hue thereof, the coated paper was visually checked for the cbromaticity thereof. The sample satisfying both little greenish appearance and great sharpness was ranked as "A" (excellent); the sample satisfying either one of the two was ranked as "B" (good), and the sample not satisfying both the two was ranked as "C" (weak). The results are shown in Table 1. <Light-Fastness Evaluation>

The coated paper having an image density of 1.0, which was used for color hue evaluation, was kept exposed to xenon light from a fade meter (99000 lux, with TAC filter) for 14 days, and the image density before and after exposure to xenon was measured with a reflection densitometer. The sample having a color retention ([density after exposure/density before exposure) x 100%] of at least 90 % was ranked as "A"; the sample having a color retention of 80% or more and less than 90% was ranked as "B"; the sample having a color retention of 60% or more and less than 80% was ranked as "C"; and the sample having a color retention of less than 60% was ranked as "D". The pigment dispersions 1 to 15 and the comparative pigment dispersions 1 to 9 were thus evaluated. The results are shown in Table 1. <Ozone Gas-Fastness Evaluation>

The coated paper having an image density of 1.0, which was used for color hue evaluation, was kept exposed to an environment having an ozone concentration of 5.0 ppm at 25°C and at a relative humidity of 50% for 28 days, and the image density before and after exposure to ozone gas was measured with a reflection densitometer. The sample having a color retention ([density after exposure/density before exposure) x 100%] of at least 90 % was ranked as "A"; the sample having a color retention of at least 80% or more and less than 90% was ranked as "B"; the sample having a color retention of 70% or more and less than 80% was ranked as "C"; and the sample having a color retention of less than 70% was ranked as "D". The pigment dispersions 1 to 15 and the comparative pigment dispersions 1 to 9 were thus evaluated. The results are shown in Table 1.

In the following Table, for example, "(l)/PY-74 = 9/1" means that the azo pigment (1) and the C.I. Pigment Yellow 74 were used in a ratio by mass of 9/1.

Table 1

Table 1 (cont.)

Ln

Table 1 (cont.)

[Example 16] Preparation of Yellow Pigment Ink 1

5% by mass, as the solid content thereof, of the yellow pigment dispersion 1 produced in Example 1, 10% by mass of glycerin, 5% by mass of 2-pyrrolidone, 2% by mass of 1,2-hexanediol, 2% by mass of triethylene glycol monobutyl ether, 0.5% by mass of propylene glycol, 1% by mass of Surfinol 465 (Air Products' nonionic surfactant) and 74.5% by mass of ion-exchanged water were mixed, and the resulting mixture was filtered through a 20-ml syringe equipped with a 1.2-μm filter (acetyl cellulose film, outer diameter 25 mm, by FUJIFILM) to remove coarse particles thereby producing a yellow pigment ink 1. [Example 17] Preparation of Yellow Pigment Ink 2

Yellow pigment ink 2 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 2 produced in Example 2 was sued in place of the yellow pigment dispersion 1. [Example 18] Preparation of Yellow Pigment Ink 3

Yellow pigment ink 3 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 3 produced in Example 3 was sued in place of the yellow pigment dispersion 1. [Example 19] Preparation of Yellow Pigment Ink 4

Yellow pigment ink 4 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 4 produced in Example 4 was sued in place of the yellow pigment dispersion 1. [Example 20] Preparation of Yellow Pigment Ink 5

Yellow pigment ink 5 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 5 produced in Example 5 was sued in place of the yellow pigment dispersion 1. [Example 21] Preparation of Yellow Pigment Ink 6

Yellow pigment ink 6 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 6 produced in Example 6 was sued in place of the yellow pigment dispersion 1. [Example 22] Preparation of Yellow Pigment Ink 7

Yellow pigment ink 7 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 7 produced in Example 7 was sued in place of the yellow pigment dispersion 1. [Example 23] Preparation of Yellow Pigment Ink 8

Yellow pigment ink 8 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 8 produced in Example 8 was sued in place of the yellow pigment dispersion 1. [Example 24] Preparation of Yellow Pigment Ink 9

Yellow pigment ink 9 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 9 produced in Example 9 was sued in place of the yellow pigment dispersion 1. [Example 25] Preparation of Yellow Pigment Ink 10

Yellow pigment ink 10 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 10 produced in Example 10 was sued in place of the yellow pigment dispersion 1. [Example 26] Preparation of Yellow Pigment Ink 11

Yellow pigment ink 11 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 11 produced in Example 11 was sued in place of the yellow pigment dispersion 1. [Example 27] Preparation of Yellow Pigment Ink 12 Yellow pigment ink 12 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 12 produced in Example 12 was sued in place of the yellow pigment dispersion 1. [Example 28] Preparation of Yellow Pigment Ink 13

Yellow pigment ink 13 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 13 produced in Example 13 was sued in place of the yellow pigment dispersion 1. [Example 29] Preparation of Yellow Pigment Ink 14

Yellow pigment ink 14 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 14 produced in Example 14 was sued in place of the yellow pigment dispersion 1. [Example 30] Preparation of Yellow Pigment Ink 15

Yellow pigment ink 15 was produced in the same manner as in Example 16, for which, however, the pigment dispersion 15 produced in Example 15 was sued in place of the yellow pigment dispersion 1. [Comparative Example 11] Preparation of Comparative Yellow Pigment Ink 1

Comparative yellow pigment Ink 1 was produced in the same manner as in Example 16, for which, however, the comparative pigment dispersion 1 produced in Comparative Example 1 was sued in place of the yellow pigment dispersion 1. [Comparative Example 12] Preparation of Comparative Yellow Pigment Ink 2

Comparative yellow pigment Ink 2 was produced in the same manner as in Example 16, for which, however, the comparative pigment dispersion 2 produced in Comparative Example 2 was sued in place of the yellow pigment dispersion 1. [Comparative Example 13] Preparation of Comparative Yellow Pigment Ink 3

Comparative yellow pigment Ink 3 was produced in the same manner as in Example 16, for which, however, the comparative pigment dispersion 4 produced in Comparative Example 4 was sued in place of the yellow pigment dispersion 1. [Example 31]

The yellow pigment ink of Examples 16 to 30 and Comparative Examples 11 to 13 was charged into the yellow ink cartridge of Seiko Epson's InkJet Printer PX- V630. As an image-receiving sheet, Seiko Epson's Photo Cryspia <high gloss> was used. A yellow monochromatic image pattern to give a stepwise changing yellow OD density of from 0.7 to 1.8 was printed on the sheet with the ink to obtain recorded matters. For the color setup, no color correction was made and the printing quality was on a photo level. Thus obtained recorded matters were evaluated in point of the color hue, the print characteristic, the image fastness (light-fastness, ozone gas- fastness) and the image quality. [Color Hue Test Method]

The reflection density of each recorded matter of Example 31 on which yellow monochromatic image pattern having a stepwise changing density was recorded with inkjet printer was measured with a spectral photometer GRETAG SPM-50 (by GRETAG).

The measurement condition was as follows: The light source was D50 with no filter; the white standard was absolute white; the viewing angle was 2°; and L*, a* and b* by CIE were measured. Based on the following criteria, the samples were evaluated. [Criteria for Judgment]

Rating A: When a*=0, b*>95 and when b*=95, a*<-5; and when -5<a*<0, b*<30 and when 60<b*<95, a*<-10.

Rating B: Either one out of the conditions in rating A is not satisfied. Rating C: Both of the conditions in rating A are not satisfied. [Evaluation of Tinctorial Strength]

The yellow pigment ink solution prepared above was charged into the cartridge for yellow ink solution of an inkjet printer, PX-V630, manufactured by Seiko Epson Corporation, and a yellow solid print pattern was produced using an image-receiving sheet, CRISPIA, produced by Seiko Epson Corporation under the conditions of color setting: no color correction and printing quality: photo. The tinctorial strength was rated A when 2.0≤ODmax in terms of single color density, rated B when 1.8<ODmax<2.0, and rated C when 1.5<ODmax<1.8. [Test Method for Light Fastness]

Xenon light (99,000 lux) was irradiated on an image for 14 days by using a weather meter (manufactured by Atlas). The OD value of single color (yellow) recorded in each recorded matter of Example 31 was measured using a reflection densitometer (X-Rite 31 OTR) every time a fixed period passed from the initiation of irradiation. As for the reflection density, 3 points of 0.7, 1.0 and 1.8 were measured.

The residual ratio of optical density (ROD) was determined from the obtained results according to the formula: ROD (%) = (D/D ₀ )xl00.

(In the formula, D indicates the OD value after the exposure test, and Do indicates the OD value before the exposure test.)

Based on the test results above, the light fatness of the images recorded in the recorded matter was ranked based on the following criteria. [Criteria for Judgment]

Rating A: ROD after 14 days from the initiation of test is 85% or more at all points of density.

Rating B: ROD after 14 days from the initiation of test is less than 85% at any one point of density.

Rating C: ROD after 14 days from the initiation of test is less than 85% at any two points of density.

Rating D: ROD after 14 days from the initiation of test is less than 85% at all points of density.

In this test, a recorded matter undergoing little reduction in ROD even when exposed to light for a long period time is excellent. The results obtained are shown as "Light Fastness" in Table 2-1. [Test Method for Ozone Gas Fastness]

The recorded matter was exposed to an ozone gas for 28 days under the conditions of an ozone gas concentration being set to 5 ppm (25°C, 50% RH). The ozone gas concentration was set using an ozone gas monitor (Model: OZG-EM-Ol) manufactured by APPLICS. The OD value of single color (yellow) recorded in image-receiving sheet, CRISPIA, produced by Seiko Epson Corporation was measured using a reflection densitometer (X-Rite 31 OTR) every time a fixed period passed from the initiation of irradiation. As for the reflection density, 3 points of 0.7, 1.0 and 1.8 were measured.

The residual ratio of optical density (ROD) was determined from the obtained results according to the formula: ROD (%) = (D/D ₀ )xl00.

(In the formula, D indicates the OD value after the exposure test, and D ₀ indicates the OD value before the exposure test.)

Based on the test results above, the ozone gas fastness of image recorded in the recorded matter was ranked based on the following criteria. [Criteria for Judgment]

Rating A: ROD after 28 days from the initiation of test is 85% or more at all points of density.

Rating B: ROD after 28 days from the initiation of test is less than 85% at any one point of density.

Rating C: ROD after 28 days from the initiation of test is less than 85% at any two points of density.

Rating D: ROD after 28 days from the initiation of test is less than 85% at all points of density.

In this test, a recorded matter undergoing little reduction in ROD even when exposed to light for a long period time is excellent. The results obtained are shown as "Ozone Gas Fastness" in Table 2-1.

Table 2-1

[Example 32]

The yellow pigment ink of Examples 16 to 30 and Comparative Examples 11 to 13 were charged into the yellow ink cartridge of Seiko Epson's InkJet Printer PX-V630. As an image-receiving sheet, Xerox's plain paper (4024) was used. A yellow monochromatic image pattern to give a stepwise changing yellow OD density of from 0.3 to 1.0 was printed on the sheet with the ink to obtain recorded matters. For the color setup, no color correction was made and the printing quality was on a photo level. Thus obtained recorded matters were evaluated in point of the image fastness (light-fastness, ozone gas-fastness). [Test Method for Light Fastness]

Xenon light (99,000 lux) was irradiated on an image for 7 days by using a weather meter (manufactured by Atlas). The OD value of single color (yellow) recorded in each recorded matter of Example 32 was measured using a reflection densitometer (X-Rite 31 OTR) every time a fixed period passed from the initiation of irradiation. As for the reflection density, 3 points of 0.5, 0.8 and 1.0 were measured.

The residual ratio of optical density (ROD) was determined from the obtained results according to the formula: ROD (%) = (D/D ₀ )xl00.

(In the formula, D indicates the OD value after the exposure test, and D ₀ indicates the OD value before the exposure test.)

Based on the test results above, the light fatness of the images recorded in the recorded matter was ranked based on the following criteria. [Criteria for Judgment]

Rating A: ROD after 7 days from the initiation of test is 85% or more at all points of density.

Rating B: ROD after 7 days from the initiation of test is less than 85% at any one point of density.

Rating C: ROD after 7 days from the initiation of test is less than 85% at any two points of density.

Rating D: ROD after 7 days from the initiation of test is less than 85% at all points of density.

In this test, a recorded matter undergoing little reduction in ROD even when exposed to light for a long period time is excellent. The results obtained are shown as "Light Fastness" in Table 2-2. [Test Method for Ozone Gas Fastness]

The recorded matter was exposed to an ozone gas for 14 days under the conditions of an ozone gas concentration being set to 5 ppm (25°C, 50% RH). The ozone gas concentration was set using an ozone gas monitor (Model: OZG-EM-01) manufactured by APPLICS. The OD value of single color (yellow) recorded in image- receiving sheet, Xerox's plain paper (4024), was measured using a reflection densitometer (X-Rite 31 OTR) every time a fixed period passed from the initiation of irradiation. As for the reflection density, 3 points of 0.5, 0.8 and 1.0 were measured.

The residual ratio of optical density (ROD) was determined from the obtained results according to the formula: ROD (%) = (D/D ₀ )xl00.

Li the formula, D indicates the OD value after the exposure test, and D ₀ indicates the OD value before the exposure test.

Based on the test results above, the ozone gas fastness of image recorded in the recorded matter was ranked based on the following criteria. [Criteria for Judgment]

Rating A: ROD after 14 days from the initiation of test is 85% or more at all points of density. Rating B: ROD after 14 days from the initiation of test is less than 85% at any one point of density.

Rating C: ROD after 14 days from the initiation of test is less than 85% at any two points of density.

Rating D: ROD after 14 days from the initiation of test is less than 85% at all points of density.

In this test, a recorded matter undergoing little reduction in ROD even when exposed to light for a long period time is excellent. The results obtained are shown as "Ozone Gas Fastness" in Table 2-2.

Table 2-2

[Example 41]

(Preparation of Aqueous Dispersion of Pigment-Containing High-Molecular Vinyl

Polymer Particles)

10 parts by mass of the high-molecular vinyl polymer solution (1) having a solid content of 50% prepared in Production Example 2 was neutralized with aqueous solution of 5 mol/L sodium hydroxide added thereto. In this, the alkali amount necessary for completely neutralizing the methacrylic acid or acrylic acid in the high- molecular vinyl polymer was added. 9.5 parts by mass of the azo pigment (1) produced in Production Example 1 and 0.5 parts by mass of Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) were added to it, and optionally kneaded with a roll mill for 4 hours. The mixture was dispersed in 100 parts by mass of ion-exchanged water. The organic solvent was completely evaporated away from the resulting dispersion under reduced pressure at 55°C, and the residue was concentrated by removing water, thereby giving an aqueous dispersion having solid content of 15 mas.% of pigment-containing vinyl polymer particles. (Preparation of Self-Dispersible Polymer Fine Particles)

350.0 g of methyl ethyl ketone was put into a 2-liter three-neck flask equipped with a stirrer, a thermometer, a reflux condenser tube and a nitrogen gas introducing duct, and heated up to 75°C. While the inside of the reactor was kept at 75 ⁰ C, a mixture solution of 162.0 g of phenoxyethyl acrylate, 180.0 g of methyl methacrylate, 18.0 g of acrylic acid, 70 g of methyl ethyl ketone and 1.44 g of polymerization initiator "V-601" (by Wako Pure Chemicals) was dropwise added thereto at a constant speed so that the addition could finish in 2 hours. After the addition, a solution of 0.72 g of "V-601" and 36.0 g of methyl ethyl ketone was added thereto and stirred at 75 ⁰ C for 2 hours, and then a solution of 0.72 g of "V- 601" and 36.0 g of isopropanol was added thereto and stirred at 75°C for 2 hours, and thereafter this was heated up to 85°C and kept stirred for further 2 hours. The mass- average molecular weight (Mw) of the obtained copolymer was 64000 (as polystyrene-equivalent one in gel permeation chromatography (GPC) in which the columns were TSKgel Super HZM-H, TSKgel Super HZ4000, TSKgel Super HZ2000 (all by Tosoh)); and the acid value thereof was 38.9 (mg-KOH/g).

Next, 668.3 g of the above mixed solution in room temperature was taken, and 388.3 g of isopropanol and 145.7 ml of aqueous solution of 1 mol/L NaOH were added thereto, and heated up to 80°C (reactor inside temperature). Next, 720.1 g of distilled water was dropwise added thereto at a speed of 20 ml/min to prepare an aqueous dispersion. Next, under the atmospheric pressure, the reactor inside temperature was kept at 80°C for 2 hours, then at 85°C for 2 hours, and at 90°C for 2 hours; and thereafter the pressure inside the reactor was reduced to evaporate away isopropanol, methyl ethyl ketone and distilled water totaling 913.7 g, thereby giving an aqueous dispersion (emulsion) of self-dispersible polymer fine particles (B-Ol) having a solid concentration of 28.0%.

The following ingredients were mixed to prepare a yellow pigment ink composition 21.

Using a pH meter, Toa DKK's WM-50EG, the pH of the ink composition was measured and was 8.5.

Aqueous dispersion of pigment-containing vinyl polymer particles mentioned above 25 parts by mass

Glycerin 5 parts by mass

Diethylene glycol 5 parts by mass

Triethylene glycol monobutyl ether 5 parts by mass Polyoxypropylene glyceryl ether 10 parts by mass

Dipropylene glycol 5 parts by mass

Triethanolamine 1 part by mass

Olfm ElOlO (by Nisshin Chemical Industry)

1 part by mass

Aqueous dispersion of self-dispersible polymer fine particles (B-Ol)

15 parts by mass

Ion-exchanged water 28 parts by mass

[Example 42]

In the same manner as in Example 41, a yellow pigment ink composition 22 was produced, for which, however, 9 parts by mass of the azo pigment (1) and 1 part by mass of CL Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) were used in place of 9.5 parts by mass of the azo pigment (1) and 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41. [Example 43]

In the same manner as in Example 41, a yellow pigment ink composition 23 was produced, for which, however, 0.5 parts by mass of C.I. Pigment Yellow 155 (Clarient's INKJET YELLOW 4G VP2532) were used in place of 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41. [Example 44]

In the same manner as in Example 41, a yellow pigment ink composition 24 was produced, for which, however, 0.5 parts by mass of C.I. Pigment Yellow 110 (Ciba Specialty's IRGAZIN YELLOW 2RLT) were used in place of 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41. [Example 45]

In the same manner as in Example 41, a yellow pigment ink composition 25 was produced, for which, however, 0.5 parts by mass of C.I. Pigment Yellow 128 (Ciba Specialty's CROMOPHTAL YELLOW 8GN) were used in place of 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41. [Example 46]

In the same manner as in Example 41, a yellow pigment ink composition 26 was produced, for which, however, 0.5 parts by mass of C.I. Pigment Yellow 138 (BASF's PALIOTOL L YELLOW 0960 HD) were used in place of 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41. [Example 47]

In the same manner as in Example 41, a yellow pigment ink composition 27 was produced, for which, however, 0.5 parts by mass of C.I. Pigment Yellow 139 (BASF's PALIOTOL D YELLOW 1891) were used in place of 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41. [Example 48]

In the same manner as in Example 41, a yellow pigment ink composition 28 was produced, for which, however, 0.5 parts by mass of C.I. Pigment Yellow 150 (Ciba Specialty's CROMOPHTAL YELLOW LA2) were used in place of 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41. [Example 49] In the same manner as in Example 41, a yellow pigment ink composition 29 was produced, for which, however, 0.5 parts by mass of C.I. Pigment Yellow 185 (BASF's PALIOTOL L YELLOW Dl 155) were used in place of 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41. [Example 50]

In the same manner as in Example 41, a yellow pigment ink composition 30 was produced, for which, however, 0.5 parts by mass of C.I. Pigment Yellow 213 (Clarient's Hostperm Yellow H5G) were used in place of 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41. [Comparative Example 21]

In the same manner as in Example 41, a comparative yellow ink composition

21 was produced, for which, however, 10 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) were used in place of 9.5 parts by mass of the azo pigment (1) and 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41.

[Comparative Example 22]

In the same manner as in Example 41, a comparative yellow ink composition

22 was produced, for which, however, 10 parts by mass of C.I. Pigment Yellow 155 (Clarient's INKJET YELLOW 4G VP2532) were used in place of 9.5 parts by mass of the azo pigment (1) and 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41.

[Comparative Example 23]

In the same manner as in Example 41, a comparative yellow ink composition

23 was produced, for which, however, 10 parts by mass of C.I. Pigment Yellow 128 (Ciba Specialty's CROMOPHT AL YELLOW 8GN) were used in place of 9.5 parts by mass of the azo pigment (1) and 0.5 parts by mass of C.I. Pigment Yellow 74 (Ciba Specialty's Iralite YELLOW GO) used in Example 41. [Example 51]

The yellow ink compositions of Examples 41 to 50 and Comparative Examples 21 to 23 were charged into the yellow ink cartridge of Seiko Epson's InkJet Printer PX-V630. As an image-receiving sheet, used were Seiko Epson's Photo Cryspia <high gloss>. A yellow monochromatic image pattern to give a stepwise changing yellow density of from 0.7 to 1.8 was printed on the sheet with the ink to obtain each recorded matter. Thus obtained recorded matters were evaluated in point of the color hue, the print characteristic and the image fastness (light-fastness, ozone gas-fastness). [Color Hue Test Method]

The reflection density of each recorded matter of Example 51 on which yellow monochromatic image pattern having a stepwise changing density was recorded was measured with a spectral photometer GRETAG SPM-50 (by GRETAG).

The measurement condition was as follows: The light source was D50 with no filter; the white standard was absolute white; the viewing angle was 2°; and L*, a* and b* by CIE were measured. Based on the following criteria, the samples were evaluated. The results obtained are shown in Table 3. [Criteria for Judgment]

Rating A: When a*=0, b*>95 and when b*=95, a*<-5; and when -5<a*<0, b*<30 and when 60<b*<95, a*<-10.

Rating B: Either one out of the conditions in rating A is not satisfied.

Rating C: Both of the conditions in rating A are not satisfied. [Evaluation of Tinctorial Strength]

The yellow ink compositions of Example 41 to 50 and Comparative Example 21 to 23 were charged into the cartridge for yellow ink solution of an inkjet printer, PX-V630, manufactured by Seiko Epson Corporation, and a yellow solid print pattern was produced using an image-receiving sheet, CRISPIA, produced by Seiko Epson Corporation under the conditions of color setting: no color correction and printing quality: photo. The tinctorial strength was rated A when 2.0<ODmax in terms of single color density, rated B when 1.8<ODmax<2.0, rated C when 1.5<ODmax<1.8, and rated D 0Dmax<1.5. The results obtained are shown in Table 3 as "Tinctorial Strength." [Test Method for Light Fastness]

Xenon light (100,000 lux) was irradiated on an image of each recorded matter of Example 51 for 42 days by using a weather meter (manufactured by Atlas). The OD value of single color (yellow) recorded in each recorded matter was measured using a reflection densitometer (X-Rite 31 OTR) every time a fixed period passed from the initiation of irradiation. As for the reflection density, 3 points of 0.7, 1.0 and 1.8 were measured.

The residual ratio of optical density (ROD) was determined from the obtained results according to the formula: ROD (%) = (D/D ₀ )xl00.

In the formula, D indicates the OD value after the exposure test, and D ₀ indicates the OD value before the exposure test.

Based on the test results above, the light fatness of the color (yellow) recorded in the recorded matter was ranked based on the following criteria. [Criteria for Judgment]

Rating A: ROD after 42 days from the initiation of test is 85% or more at all points of density.

Rating B: ROD after 42 days from the initiation of test is less than 85% at any one point of density.

Rating C: ROD after 42 days from the initiation of test is less than 85% at any two points of density.

Rating D: ROD after 42 days from the initiation of test is less than 85% at all points of density.

In this test, a recorded matter undergoing little reduction in ROD even when exposed to light for a long period time is excellent. The results obtained are shown as "Light Fastness" in Table 3. [Test Method for Ozone Gas Fastness]

Each recorded matter of Example 51 was exposed to an ozone gas for 28 days under the conditions of an ozone gas concentration being set to 5 ppm (25°C, 50% RH). The ozone gas concentration was set using an ozone gas monitor (Model: OZG-EM-01) manufactured by APPLICS. The OD value of color (yellow) recorded in each printed material was measured using a reflection densitometer (X-Rite 31 OTR) every time a fixed period passed from the initiation of irradiation. As for the reflection density, 3 points of 0.7, 1.0 and 1.8 were measured.

The residual ratio of optical density (ROD) was determined from the obtained results according to the formula: ROD (%) = (D/D ₀ )χl00.

(In the formula, D indicates the OD value after the exposure test, and D ₀ indicates the OD value before the exposure test.)

Based on the test results above, the ozone gas fastness of color (yellow) recorded in the recorded matter was ranked based on the following criteria. [Criteria for Judgment]

Rating A: ROD after 28 days from the initiation of test is 85% or more at all points of density.

Rating B: ROD after 28 days from the initiation of test is less than 85% at any one point of density.

Rating C: ROD after 28 days from the initiation of test is less than 85% at any two points of density.

Rating D: ROD after 28 days from the initiation of test is less than 85% at all points of density.

In this test, a recorded matter undergoing little reduction in ROD even when exposed to light for a long period time is excellent. The results obtained are shown as "Ozone Gas Fastness" in Table 3.

Table 3

OO

From these results, it is known that the yellow pigment dispersion of the invention is readily dispersible and stable, and has excellent yellow color hue, high tinctorial strength and excellent light- fastness and ozone gas-fastness.

Accordingly, the yellow pigment dispersion of the invention is usable, for example, in inkjet and the like printing inks, color toners for electrophotography, color filters for use in displays such as LCD or PDP or in imaging devices such as CCD, and in coating materials, colored plastics, etc.

Industrial Applicability

The yellow pigment dispersion, the ink for inkjet recording, the inkjet recording cartridge, the inkjet recording method and the inkjet recording apparatus of the invention make it possible to produce a recorded matter having excellent color hue, tinctorial strength, light-fastness and ozone gas-fastness.

The inkjet recorded matter of the invention has excellent tinctorial strength, light-fastness and ozone-gas-fastness.

The yellow pigment dispersion of the invention is a coloring matter excellent in light-fastness and is therefore usable, for example, in inkjet and the like printing inks, color toners for electrophotography, color filters for use in displays such as LCD or PDP or in imaging devices such as CCD, and in coating materials, colored plastics, etc.

This application is based on Japanese patent application JP 2009-058713, filed on March 11, 2009, and JP 2010-053666, filed on March 10, 2010 the entire content of which is hereby incorporated by reference, the same as if set forth at length.