JP2009114281A - Pigment dispersion, pigment ink, ink cartridge, inkjet recording device, image-forming method and image-formed product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the quality of a monochrome image, and to achieve good jetting stability and image-forming speed in practical application. <P>SOLUTION: The pigment dispersion contains a black pigment, a cyan pigment, a dispersing agent and water, wherein the black pigment includes a first black pigment and a second black pigment having an average particle diameter larger than that of the first black pigment, and wherein the difference between the average particle diameter of the first black pigment and that of the cyan pigment is ≤50 nm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pigment dispersion, a pigment ink, an ink cartridge, an ink jet recording apparatus, an image forming method, and an image formed product.

The inkjet recording method has an advantage that a high-resolution full-color image can be obtained even with an apparatus having a simple configuration because the image forming process is simpler than other conventionally known recording methods.
As an ink applied to an ink jet recording system, a dye-based ink in which a water-soluble dye is dissolved in water or a mixed liquid of water and an organic solvent is conventionally known. Such dye-based inks are excellent in color tone clarity, but have the disadvantage of poor light resistance.
On the other hand, a pigment-based ink in which carbon black or various organic pigments are dispersed has an advantage that it has excellent light resistance as compared with a dye-based ink.

Since the pigment is insoluble in water, when the pigment is used in ink, it must be stably dispersed in water in the form of fine particles.
However, if the temperature conditions for the pigment dispersion system change, the pigment adsorption equilibrium of the dispersing agent breaks down, which affects the interaction between the pigment particles, causing changes in physical properties during long-term storage, and a large amount of aggregated foreign matter. The problem that occurs.
If physical properties change (especially viscosity change) occurs in the ink for an ink jet printer or aggregated foreign matter is generated, the quality is remarkably deteriorated and the head is clogged.

In addition, in order to improve the fineness of the image when using pigment ink, it is necessary to reduce the particle diameter of the pigment dispersed in the ink. However, depending on the method of the disperser, dispersion process conditions, etc. Then, when a small particle size pigment is used, liquid aggregation tends to occur, and there is a possibility that the discharge stability may be lowered.
Further, in order to improve nozzle clogging and color gamut, it is necessary to reduce the average particle diameter of the pigment, but conventionally known dispersants such as styrene-acrylic copolymers, styrene -Inks using polymer dispersants of maleic acid copolymer (Japanese Patent Laid-Open No. 56-147863), sodium naphthalene sulfonate formalin condensate (Japanese Patent Laid-Open No. 61-083267), and conventionally known surface activity Agents, for example, polyethylene glycol alkylphenyl ether (Japanese Patent Laid-Open No. 5-105837), polyethylene glycol alkylphenyl ether sulfate (Japanese Patent Laid-Open No. 10-168367), polyethylene glycol alkylphenyl ether phosphate (Japanese Patent Laid-Open No. 10-88050) In any of the inks using the surfactant of No. Hitoshitsubu diameter is relatively large, the discharge stability of sharpness and ink color, and the liquid for stability, and still left a problem to be solved.

On the other hand, the use of ink compositions of various colors and water-soluble auxiliary recording liquids equivalent thereto has been studied for the purpose of improving fixability, color developability, or optical density. There was an inconvenience of causing unevenness.
In particular, regarding an ink composition having a color material included in a resin, when a dye is used as the color material, the light resistance is insufficient, and when used in combination with a dye and a pigment, bleeding and color unevenness are caused. There was a problem that occurred. Further, when only the pigment is used, if the diameter of the pigment particles is large, there is a problem that the image has a graininess and glossiness and abrasion resistance are lowered.
In addition, when high-definition image formation is performed on plain paper using ink using small-sized pigment particles intended for use on predetermined dedicated paper, There was a problem that the pigment penetrated and the improvement of the optical density was hindered and a printed matter with a high optical density could not be obtained.

In view of the conventional problems described above, in Patent Document 1 described below, the image quality of both dedicated paper and plain paper is improved by using independent inks for the small particle size pigment and the large particle size pigment. However, there has been a problem that the discharge performance is deteriorated in the ink using the large particle size pigment particles (first problem).
Further, in Patent Document 2 below, for the purpose of improving the black reproducibility of a printed matter, a black is produced by combining a first black ink and a second black ink having a higher black density than the first black ink. A recording method for printing is proposed. However, when an achromatic image (especially a gray image) is printed in gradation, an image defect is observed in which a pale yellow image is seen at the boundary between the printed colors (second problem).
Further, in Patent Document 3 below, a technical proposal has been made to produce a pure black color by adding a cyan pigment and a magenta pigment to a black pigment. The inconvenience that a pure black image may not always be formed in the image after landing is recognized (third problem).
Furthermore, in Patent Documents 2 and 3 below, there are proposals for improving black reproducibility by using a plurality of black inks. However, a number of heads corresponding to a plurality of black inks are provided. Therefore, there is a practical problem that the image forming speed is inevitably reduced.

JP 2004-338297 A JP 2000-318293 A JP 2003-55592 A

  In the present invention, when the carbon black small particle size pigment particles are used, the pigment penetrates into the plain paper, and the second issue is the carbon black large particles. Dischargeability deteriorates when using diameter pigment particles, and the third problem is that, when using carbon black, pure black cannot be expressed, and furthermore, a practically good image forming speed is maintained. In order to solve the problem, the present invention proposes a pigment dispersion and pigment ink, and proposes an ink cartridge, an ink jet recording apparatus, an image forming method, and an image formed product using the pigment dispersion. did.

  The invention according to claim 1 is a pigment dispersion containing at least a black pigment, a cyan pigment, a dispersant, and water, wherein the black pigment comprises a first black pigment and the first black pigment. Also provided is a pigment dispersion comprising a second black having a large average particle size, wherein a difference between the average particle size of the first black pigment and the average particle size of the cyan pigment is 50 nm or less To do.

  In the invention of claim 2, the average particle size of the first black pigment is from 100 nm to 150 nm, the average particle size of the second black pigment is from 200 nm to 250 nm, and the first black pigment The pigment dispersion according to claim 1, wherein the second black pigment is contained in a mass ratio of 1: 0.01 or more and 0.1 or less.

  In the invention of claim 3, the total solid content concentration of the black pigment and the cyan pigment is 10% or more and 40% or less, and the black pigment and the cyan pigment are 1: 0. The pigment dispersion according to claim 1, wherein the pigment dispersion is contained in a ratio of 1 or more and 0.5 or less. However, the said solid content concentration shows solid content mass concentration.

  In the invention of claim 4, at least one of sodium naphthalene sulfonate formalin condensate and a compound represented by the following formula (1) is used as the dispersant. The pigment dispersion as described in any one of these is provided.

  According to a fifth aspect of the present invention, there is provided a pigment ink produced using the pigment dispersion according to any one of the first to fourth aspects.

  According to a sixth aspect of the invention, there is provided an ink cartridge characterized by containing the pigment ink according to the fifth aspect.

  According to a seventh aspect of the present invention, there is provided an ink jet recording apparatus wherein recording is performed by discharging the pigment ink according to the fifth aspect from a recording head.

  According to an eighth aspect of the present invention, there is provided an image forming method characterized in that recording is performed by ejecting pigment ink from a recording head using the ink jet recording apparatus according to the seventh aspect.

  According to a ninth aspect of the present invention, there is provided an image formed product produced by the image forming method according to the eighth aspect.

  According to the present invention, a high-quality image having high image density and excellent storage stability can be formed, occurrence of clogging of the ink discharge nozzles and the like can be prevented, and a practically sufficient image forming speed can be secured. I was able to.

Hereinafter, embodiments of the present invention will be described in detail.
The pigment dispersion of the present invention contains at least a black pigment, a cyan pigment, a dispersant, and water.
A black pigment is comprised from the 1st black pigment and the 2nd black pigment whose average particle diameter is larger than this. The difference between the particle size of the first black pigment and the particle size of the cyan pigment is 50 nm or less.

By using a black pigment and a cyan pigment in combination as described above, it is possible to avoid the slight coloring of the black pigment, thereby improving the image quality.
The slight coloring of the black is noticeable when the pigment concentration is low.
Since the black pigment is present in the ink composition as particles, if the concentration is high, nozzle clogging occurs in the ink jet recording method, so that the high concentration has a limit from a practical viewpoint. Therefore, it was necessary to devise measures to prevent the slight coloring caused by black.

The average particle diameter (D50) of the first black pigment particles is preferably 100 nm to 150 nm, more preferably 110 nm to 140 nm, and still more preferably 120 nm to 130 nm.
The average particle diameter (D50) of the second black pigment particles is preferably from 200 nm to 250 nm, more preferably from 210 nm to 240 nm, still more preferably from 220 nm to 230 nm.
When the average particle diameter (D50) of the first black pigment particles is smaller than 100 nm, the penetration of the pigment into the plain paper hinders the improvement of the optical density and a printed matter with a high optical density cannot be obtained. It was confirmed that the dischargeability deteriorated.
When the average particle diameter (D50) of the second black pigment particles exceeds 250 nm, the discharge performance deteriorates. When the average particle diameter is smaller than 200 nm, the effect of preventing the first black pigment particles from penetrating into the plain paper. It was confirmed that would not be able to be obtained sufficiently.
Further, the difference between the average particle diameter of the cyan pigment particles and the average particle diameter of the first black pigment is 50 nm or less, preferably 40 nm or less, and more preferably 30 nm or less. If the difference between these average particle diameters exceeds 50 nm, the first black pigment and the cyan pigment cause irregular reflection due to non-uniformity of each other's particles, resulting in inconvenience that pure black cannot be expressed. .
The average particle diameter (D50) of the pigment particles can be measured by a conventionally known method. For example, it can be measured by a particle size analyzer UPA150 (manufactured by Nikkiso).

The average particle diameter (D50) of the pigment can be controlled by the peripheral speed of the rotating part of the disperser, the dispersion time, the dispersion flow rate, and the dispersion temperature when dispersing using the disperser.
The disperser (media mill) is not particularly limited as long as it is a disperser that can use beads. Specific examples include “TORUSMILL” manufactured by Getzmann and “Star Mill manufactured by Ashizawa”. ”,“ Viscomil ”manufactured by Imex,“ Dynomill ”manufactured by Shinmaru Enterprises,“ Diamond Fine Mill ”manufactured by Mitsubishi Heavy Industries,“ Apex Mega ”manufactured by Kotobuki Giken Kogyo,“ Picomill ”manufactured by Asada Tekko, Eurotech "OB beads mill" manufactured by Mitsui Mining Co., Ltd.
When media amyl is used, the pigment particle size can be controlled by adjusting the size of the dispersion medium (beads).
For example, in order to make the average particle diameter (D50) 200 nm or less, it is preferable to make the beads about 0.01 mm to 1.0 mm, and more preferably 0.01 mm to 0.5 mm.
In addition, the particle size standard deviation can be made smaller than the average particle size (D50) by this method.

In addition, you may perform dispersion | distribution using a medialess mill as pre dispersion | distribution of the front process which performs media mill dispersion | distribution.
In particular, pre-dispersion treatment of coarse particles having a size of 1 μm or more is preferable because the dispersibility is improved and the particle size standard deviation in the particle size distribution of the pigment particles becomes smaller when the beads mill is dispersed in the subsequent step.
Furthermore, by using the above-mentioned medialess mill after the media mill dispersion, the rough pigment surface can be repaired and the dispersion stability can be improved.
The medialess mill is not particularly limited, but specific examples include “TK Philmix” manufactured by PRIMIX, “Artemizer” manufactured by Sugino Machine, “CLEAR SS5” manufactured by M Technique, “Claire mix W motion”, “Cabitron” manufactured by Eurotech, “IKA DR2000” manufactured by Shinmaru Enterprises, and the like.

The ratio of the first black pigment to the second black pigment is preferably 1: 0.01 or more and 0.1 or less in terms of mass ratio.
If the ratio of the second black pigment is less than 0.01, the penetration of the pigment into the plain paper of the first black pigment particles increases, which is not desirable.
On the other hand, when the ratio of the second black pigment exceeds 0.1, the dischargeability is inferior, which is not desirable.

The total solid content concentration (solid content mass concentration) of the black pigment and the cyan pigment is 10% or more and 40% or less, and the black pigment and the cyan pigment are in a mass ratio of 1: 0.1 or more and 0.5. It is preferable to include at the following ratios.
When the solid content concentration in the pigment is less than 10%, the viscosity becomes too low, and the pulverization due to collision with the beads is the main cause, resulting in inconvenience that the pigment surface becomes rough more than necessary and the dispersion stability is lowered. On the other hand, if it exceeds 40%, the viscosity becomes too high, and the kneading by friction between the beads and the pigment is mainly performed, and excessive power and heat generation are generated, which is not preferable from the viewpoint of production stability. Therefore, the total solid content concentration is 10% or more and 40% or less, and preferably 15% or more and 35% or less.
It was confirmed that a pure black image could not be formed when the content ratio of the black pigment and the cyan pigment was less than 1: 0.1 or more than 1: 0.5.

As the black pigment, carbon black produced by a furnace method or a channel method can be applied. Specifically, Pigment Black 7 (manufactured by Deguza Japan) is suitable.
The average primary particle size of the carbon black in 10.0nm~30.0nm, BET specific surface area is preferably those which are 100m ² / g~400m ² / g.
More preferably, the average primary particle size of the carbon black in 15.0Nm～20.0Nm, BET specific surface area is assumed to be 150m ² / g~300m ² / g.
The average primary particle diameter can be measured by photographing particles using an electron micrograph and calculating from the particle diameter and number in the photographed image. The BET specific surface area can be measured by the BET method by nitrogen adsorption.

  Specific examples of the cyan pigment applied in the present invention include Pigment Blue 1, Pigment Blue 2, Pigment Blue 3, Pigment Blue 15, Pigment Blue 15: 3, Pigment Blue 15: 4, Pigment Blue 16, Pigment Blue 22, and Pigment. Blue 60, bat blue 4, bat blue 60, etc. are mentioned, and in particular, pigment blue 15: 3 is mentioned. In particular, Pig. Blue 15: 3 is preferred.

As the dispersant, sodium naphthalene sulfonate formalin condensate can be applied. However, when the total content of dimers, trimers and tetramers of naphthalene sulfonic acid is less than 20% with respect to the total naphthalene sulfonate sodium formalin condensate, the dispersibility deteriorates and the pigment dispersion In addition, the storage stability of the ink is inferior, and as a result, the nozzles are likely to be clogged.
Further, when the total content of naphthalenesulfonic acid dimer, trimer and tetramer in the sodium naphthalenesulfonate formalin condensate exceeds 80% with respect to the total sodium naphthalenesulfonate formalin condensate, the viscosity becomes high. This causes the inconvenience that dispersion becomes difficult.
The sodium naphthalene sulfonate formalin condensate is a condensate of sodium naphthalene sulfonate and formaldehyde, and is not particularly limited as long as it consists of repetition of the above condensate.

Moreover, the compound shown to following formula (1) is also applicable as a dispersing agent.
By using this, it was confirmed that a pigment dispersion and a pigment ink having a small average particle size and a small standard deviation of the particle size distribution can be obtained.

In the above formula (1), n is preferably 20 or more and 100 or less, and more preferably 30 or more and 50 or less.
When n is less than 20, the dispersion stability tends to decrease, and the average particle size becomes large or the standard deviation in the particle size distribution becomes large. It was confirmed that the saturation at the time deteriorated.
On the other hand, if n is larger than 100, the viscosity of the produced ink becomes high, and there is a disadvantage that printing becomes difficult in the ink jet system.
In the compound of the above formula (1), polyoxyethylene (POE, n = 40) β naphthyl ether is particularly preferable.

In the pigment dispersion of the present invention, the content ratio of the dispersant is preferably 0.01 or more and 2 or less with respect to the black pigment and the cyan pigment 1 as a weight standard (mass ratio). More preferably, the ratio is 0.05 to 0.5 with respect to the black pigment and the cyan pigment 1.
When the content of the dispersant is less than 0.01, it has been confirmed that a sufficient dispersion effect cannot be obtained, and the storage stability of the pigment dispersion and the ink is inferior, resulting in nozzle clogging. It was confirmed that it was easy to do.
When the content of the dispersant is larger than 2, the viscosity of the pigment dispersion and the ink tends to be too high, and printing by the inkjet method tends to be difficult.

The pigment ink of the present invention is mainly composed of the above-described pigment dispersion, and in addition, preferably contains a wetting agent. The wetting agent preferably has a boiling point of 180 ° C. or higher.
By containing the wetting agent in the water-based pigment ink, it is possible to ensure the water retention and wettability of the ink composition, and as a result, there is no aggregation of the coloring material or increase in viscosity even if the water-based pigment ink is stored for a long period of time. Storage stability can be realized. Also, an ink for ink jet recording can be realized that maintains the fluidity of the dried material for a long time even when left in an open state at the nozzle tip of an ink jet printer. Furthermore, nozzle clogging does not occur during printing or when restarting after printing interruption, and high ejection stability can be obtained.

Specifically, the following can be applied as the wetting agent.
For example, ethylene glycol, diethylene glycol 1.3-butyl glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,5-pentanediol, 1,6-hexanediol, glycerin, 1,2,6-hexanetriol, 2 -Polyhydric alcohols such as ethyl-1,3-hexanediol, ethyl 1,2,4-butanetriol, 1,2,3-butanetriol, petriol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol Polyhydric alcohol alkyl ethers such as monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene Polyhydric alcohol aryl ethers such as glycol monophenyl ether and ethylene glycol monobenzyl ether; 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethylimidazolidinone, Nitrogen-containing heterocyclic compounds such as ε-caprolactam and γ-butyrolactone; amides such as formamide, N-methylformamide, N, N-dimethylformamide; monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, triethylamine, etc. Amines, sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, thiodiethanol, propylene carbonate, ethylene carbonate and the like. These wetting agents can be used alone or in admixture of two or more.
Among the above wetting agents, by containing 1.3-butyl glycol, diethylene glycol, triethylene glycol and / or glycerin, it is possible to effectively prevent clogging due to drying of ink, that is, prevention of poor jetting characteristics due to water evaporation, and a formed image An excellent effect can be obtained in improving the color saturation.

The pigment ink of the present invention preferably contains a penetrant.
Specific examples of penetrants include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene glycol ester, polyoxyethylene / polyoxypropylene decyl ether, acetylene surfactant, silicon surfactant And nonionic surfactants such as fluorinated surfactants and the like.

In the pigment ink of the present invention, a surfactant may be used in combination as long as the ink properties are not affected.
Specific examples of surfactants include nonionic surfactants such as BT series (Nikko Chemicals) Nonipol series (Sanyo Kasei), D-, P-series (Takemoto Yushi) Surfinol series (Air Products) Fin series (Nissin Chemical) EMALEX DAPE series (Nippon Emulsion), silicone surfactants (Toray Dow Corning, etc.), fluorine surfactants (Neos, Sumitomo 3M, Dupont, Daikin), etc.

  Further, in the present invention, when the aqueous pigment dispersion subjected to the heat treatment is used as the aqueous pigment ink, or the aqueous pigment obtained by performing the heat treatment on the aqueous pigment ink prepared using the unheated aqueous pigment dispersion. In any ink, after preparation of water-based pigment ink, perform vacuum / pressure filtration using a metal filter, membrane filter, etc. or centrifugal filtration with a centrifuge to remove coarse particles, foreign matter (dust / dust), etc. It is preferable to remove.

As described above, an ink cartridge can be produced by storing the pigment ink obtained from the pigment dispersion in a predetermined container.
By incorporating this ink cartridge into an ink jet apparatus, the ink jet recording apparatus of the present invention can be obtained, and an image formed product can be obtained by ejecting from an orifice in accordance with a predetermined recording signal and forming an image on a recording material.

Examples of the printing unit include a printing method using the above-described ink jet printer (ink jet printer) having a continuous jet type or on-demand type recording head.
Examples of the on-demand type include a piezo method, a thermal ink jet method, and an electrostatic method.
Conventionally known techniques can be applied to these ink cartridge formation, inkjet apparatus formation, and image formation method, and for example, the technique disclosed in Japanese Patent Application Laid-Open No. 2000-198958 can be used.

In addition, as a recording medium for forming an image using the pigment ink of the present invention, a recording medium having an absorptivity with respect to an ink composition such as paper and a substantially non-absorbing with respect to the ink composition are used. Either may be sufficient.
Specific examples of recording media include plastic sheets based on polyethylene terephthalate, polycarbonate, polypropylene, polyethylene, polysulfone, ABS resin, polyvinyl chloride, etc., metal surfaces such as brass, iron, aluminum, SUS, copper, or nonmetals Recording media that have been subjected to metal coating treatment by a technique such as vapor deposition on a base material, recording media that has been subjected to water repellency treatment using paper as a base material, recording media that are made of a so-called ceramic material obtained by firing an inorganic material at a high temperature, etc. Can be mentioned.

〔Example〕
EXAMPLES Hereinafter, although this invention is demonstrated in detail based on a specific Example, this invention is not limited to the following Example. In addition, the number of parts in an Example represents a weight part.
Table 1 below shows the composition of the sample pigment dispersion.

In Table 1, Bk represents black and C represents cyan.
The ratio of the Bk pigment (the first Bk pigment and the second Bk pigment) to the Bk dispersant is 4: 0.5. The ratio of C pigment to C dispersant is assumed to be 4: 1.5. Components other than the pigment and dispersant in Table 1 are water (ion exchange water).
The constitution and physical properties of dispersant types (a) to (e) in Table 1 are shown in Table 2 below.

  The mixed solution shown in Table 1 was premixed to obtain a mixed slurry. Using a disk-type media mill (UAM type Kotobuki Kogyo Co., Ltd.), circulating and dispersing for 3 minutes at a peripheral speed of 6 m / s and a liquid temperature of 10 ° C. using 0.03 mmφ zirconia beads and a filling rate of 60%, a centrifuge (Kubota) Coarse particles were centrifuged with Shoji Co., Ltd. Model-7700) to obtain a pigment dispersion.

Using this pigment dispersion, a pigment ink was prepared according to the following formulation, stirred for 30 minutes, filtered and vacuum deaerated with a membrane filter having a pore size of 0.8 μm to obtain the desired pigment ink. It was.
(Ink formulation)
Pigment dispersion (when the pigment concentration is 25%, total solid content is 8%) 40.0 parts Glycerol 7.5 parts Diethylene glycol 15.0 parts 2-Ethyl-1,3-hexanediol 3.0 parts 2-pyrrolidone 0 parts Polyoxyethylene (3) alkyl (C13) ether sodium acetate 0.5 parts Distilled water 31.0 parts

Next, printing was carried out on Xerox PPC paper XEROX4024 using an EPSON ink jet printer EM-930C, and the ejection stability was evaluated. The printed image was measured with an Xrite densitometer and evaluated.
Ink liquid storage stability was also evaluated by the following test method.
The measurement and evaluation methods are shown below, and the measurement and evaluation results are shown in Table 3.

(Evaluation 1: Discharge stability)
Regarding the ink ejection stability of the head, whether printing is performed and then the printer head is capped and the printer is left in an environment of 40 ° C. for one month, and then the ejection state is restored to the initial ejection state. This was evaluated in three stages according to the number of cleaning operations described below.
○: Recovered by one operation.
Δ: Recovered by 2 to 3 operations.
X: No recovery was observed even after three or more operations.

(Evaluation 2: Image evaluation)
Regarding the image density, a solid image of the image sample was obtained using an Xrite densitometer.
○: 1.30 or more Δ: 1.20 or more and less than 1.30 ×: less than 1.20

(Evaluation 3: Preservability of pigment dispersion and pigment ink)
Each ink was sealed in a polyethylene container, stored at 70 ° C. for 3 weeks, then measured for particle size, surface tension, and viscosity, and evaluated according to the following three levels according to the change rate from the initial physical properties.
○: Within 10% Δ: Within 30% ×: Over 50%

  As shown in Table 3 above, in Examples 1 to 11 using the pigment ink prepared from the pigment dispersion of the present invention, practically good images were obtained, and the ejection stability of the head nozzle was also good. The storage stability of the pigment dispersion and the pigment ink was also good.

Claims (9)

A pigment dispersion containing at least a black pigment, a cyan pigment, a dispersant, and water,
The black pigment comprises a first black pigment and a second black having an average particle size larger than that of the first black pigment,
A pigment dispersion, wherein a difference between an average particle diameter of the first black pigment and an average particle diameter of the cyan pigment is 50 nm or less. The average particle size of the first black pigment is 100 nm or more and 150 nm or less,
The average particle size of the second black pigment is 200 nm or more and 250 nm or less,
The pigment dispersion according to claim 1, wherein the first black pigment and the second black pigment are contained in a mass ratio of 1: 0.01 to 0.1. body. The total solid concentration of the black pigment and the cyan pigment is 10% or more and 40% or less,
The pigment dispersion according to claim 1 or 2, wherein the black pigment and the cyan pigment are contained in a mass ratio of 1: 0.1 or more and 0.5 or less. 4. The method according to claim 1, wherein at least one of sodium naphthalene sulfonate formalin condensate and a compound represented by the following formula (1) is used as the dispersant. 5. Pigment dispersion.

  A pigment ink produced using the pigment dispersion according to any one of claims 1 to 4.   An ink cartridge containing the pigment ink according to claim 5.   An ink jet recording apparatus, wherein recording is performed by discharging the pigment ink according to claim 5 from a recording head.   An image forming method comprising: performing recording by ejecting pigment ink from a recording head using the ink jet recording apparatus according to claim 7.   An image formed article produced by the image forming method according to claim 8.