JP2009138136A - Ink set, inkjet recording method, ink cartridge, recording unit, inkjet recording apparatus and image-forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set which can obtain an image with inhibited bleeding without causing feathering in recording the image where the regions of colors different from each other are in close proximity with the use of a plurality of inks and further excels in reliability. <P>SOLUTION: In the ink set which records an image with the use of two or more inks comprising a black ink and a color ink, the black ink contains carbon black bonded to at least one hydrophilic group directly or through another atomic group, and the color ink contains a coloring material having a conductivity of a 0.05 mol/L coloring material aqueous solution of not less than 7 mS/cm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ink set composed of two or more kinds of inks, and more particularly to an ink jet recording method and an ink jet recording apparatus using an ink jet recording method, and further to an ink set suitable for an image forming method.

  In recent years, there is an increasing need for high-speed recording by an ink jet recording method. In order to increase the recording speed, there is a recording method in which an image for one line is formed in one scan. However, in this method, compared to a method of forming one line by two or more scans, color mixing (bleeding) at the boundary between images formed with different colors, particularly black ink containing pigment as a colorant and color ink, is conspicuous. There is a problem. This is because when the image for one line is formed in one scan, the time difference in which the adjacent ink droplets forming different colors are applied to the recording medium forms an image for one line in two or more scans. This is because the time difference is less than or equal to the case of That is, when one line is formed in one scan, ink droplets of different colors are more likely to be mixed on the recording medium.

  Conventionally, various techniques have been proposed for the purpose of more effectively suppressing bleeding at the boundary of each color region. For example, there is a proposal for suppressing bleeding at the boundary between images formed with black and color inks by using a black ink containing self-dispersing carbon black and a specific salt (see Patent Document 1). . In addition, there is a proposal for suppressing bleeding by using a self-dispersing carbon black and a black ink containing a poor solvent for the self-dispersing carbon black (see Patent Document 2). In this patent document 2, bleeding between the black ink and the color ink is carried out by including in the color ink a poor solvent for the self-dispersing pigment that destabilizes the dispersion stability of the self-dispersing pigment in the black ink. It is also described about suppressing the above. Further, there is a proposal for suppressing bleeding by combining a black ink containing self-dispersing carbon black and a color ink containing a color material having a polarity opposite to that of the carbon black (Patent Document 3). reference).

  As described above, in order to form a high-quality image in which bleeding is suppressed, conventionally, a measure of incorporating a salt or a poor solvent that promotes aggregation of the pigment into the black ink has been mainly taken. However, there is a problem that bleeding is still conspicuous in an ink jet recording method in which an image for one line is formed in one scan only by adding a polyvalent metal salt or the like to the ink.

On the other hand, by adding a polyvalent metal salt to the color ink to suppress bleeding, or by reversing the charge of the functional group of the self-dispersing carbon black and the charge of the functional group of the dye in the color ink Means for suppressing bleeding are proposed. However, if such an ink is used as an ink jet ink, the ink is hardened in the nozzles of the recording head and clogging may occur, which may make recording impossible. is there.
JP 2000-198955 A JP-A-2005-206615 Japanese Patent Laid-Open No. 10-140064

  Accordingly, an object of the present invention is to obtain an image in which bleeding is suppressed without causing feathering when recording an image in which different color areas are adjacent to each other with a plurality of inks. The object is to provide an ink set with higher reliability.

  Another object of the present invention is to provide an ink jet recording method capable of forming a high-quality image with suppressed bleeding by using the above excellent ink set.

  Another object of the present invention is to provide an ink cartridge, a recording unit, and an ink jet recording apparatus that can be suitably used in the above recording method.

  Furthermore, another object of the present invention is to provide an image forming method capable of effectively suppressing bleeding without causing feathering when performing image recording in which different color regions are adjacent to each other on a recording medium. Is to provide.

  The above object is achieved by the present invention described below. That is, the ink set of the present invention is an ink set for recording an image on a recording medium using two or more kinds of inks including a black ink and a color ink. The black ink has at least one hydrophilic group directly or It contains carbon black bonded through another atomic group, and the color ink contains a color material in which the conductivity of the 0.05 mol / L color material aqueous solution is 7 mS / cm or more. Features.

  The ink jet recording method according to another embodiment of the present invention is an ink jet recording method in which ink is ejected by an ink jet method to perform recording on a recording medium, wherein the ink is an ink constituting the ink set. It is characterized by.

  An ink cartridge according to another embodiment of the present invention is an ink cartridge including an ink storage portion that stores ink, and the ink stored in the ink storage portion is an ink constituting the ink set. It is characterized by that.

  According to another embodiment of the present invention, there is provided a recording unit including an ink storage portion for storing ink and a recording head for ejecting ink, wherein the ink stored in the ink storage portion is stored in the recording unit. And an ink constituting the ink set.

  An ink jet recording apparatus according to another embodiment of the present invention is an ink jet recording apparatus that includes an ink storage portion that stores ink and a recording head that discharges ink, and is stored in the ink storage portion. The ink is an ink constituting the above ink set.

  An image forming method according to another embodiment of the present invention is the image forming method in which black ink and at least one color ink are used for recording on a recording medium by an ink jet recording method. When forming an image in which the ink constituting the ink set is used as an ink and the image formed by the black ink and the image formed by the color ink are adjacent to each other, the black ink is used. After the scanning for applying, the scanning for applying the color ink is performed on the area where the image is formed.

  According to the present invention, when recording an image in which different color regions are adjacent to each other with a plurality of inks, an image with no bleeding can be obtained without causing feathering and more reliable. An ink set having excellent properties can be provided.

  In addition, according to another embodiment of the present invention, it is possible to provide an ink jet recording method capable of forming a high-quality image in which bleeding is suppressed by using the above excellent ink set.

  Further, according to another embodiment of the present invention, it is possible to provide an ink cartridge, a recording unit, and an ink jet recording apparatus that can be suitably used in the recording method.

  Furthermore, according to another embodiment of the present invention, bleeding can be effectively suppressed without causing feathering when recording an image in which different color areas are adjacent to each other on the recording medium. An image forming method can be provided.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

  By forming an image using the ink set of the present invention, it is possible to suppress the diffusion of the color material at the boundary portion of each color even on plain paper, which had various problems with the conventional ink, and feathering And high-quality images with reduced bleeding. Further, by using the ink set of the present invention, high-speed recording can be achieved, and further, the ink jet recording apparatus can be miniaturized, and a remarkable effect that feathering and bleeding are particularly effectively suppressed can be obtained. The present invention has been found.

[Mechanism for controlling bleeding]
Although the reason why the above-described effects can be obtained by the present invention is not clear, the present inventors presume the reason as follows. In general, when an image is formed with ink on a recording medium such as plain paper and an image recording in which different color areas are adjacent to each other is performed, feathering does not occur and the boundary between the areas of each color is detected. In order to obtain an image in which bleeding is suppressed, it is necessary to suppress the outflow of the color material to the adjacent region at the boundary. For this purpose, it is an important condition that the color material aggregates as soon as possible after the ink has landed on the recording medium.

  It is considered that the bleeding suppressing effect in the present invention is mainly caused by the color material in the color ink. The high color conductivity of the color material in an aqueous solution indicates that the ionic group of the color material itself and counter ions of the ionic group are abundant in the color ink. Carbon black in which at least one hydrophilic group is bonded directly or via another atomic group (hereinafter sometimes referred to as self-dispersing carbon black) tends to aggregate when the electrolyte concentration is high. In the ink set of the present invention, it is considered that the color material in the color ink serves as an aggregation trigger for self-dispersing carbon black. As a result of the study by the present inventors, it was found that when self-dispersing carbon black and a color material having high conductivity in an aqueous solution are mixed, the self-dispersing carbon black tends to aggregate and further the color material tends to become insoluble. It was. It is considered that the bleeding resistance has been dramatically improved due to these reasons.

  In addition, the absorbance of the filtrate obtained by adding a small amount of self-dispersing carbon black to the aqueous solution and filtering it was significantly lower than the absorbance of the aqueous solution of the colorant. This result also suggests that the aqueous solution of the colorant is insolubilized and associated by mixing with self-dispersing carbon black.

  From the above, on the recording medium, at the boundary portion of the image formed with the black ink containing self-dispersing carbon black and the color ink containing the color material showing high conductivity in the aqueous solution, It seems that this is happening. That is, on the recording medium, at the boundary portion of the image immediately after the black ink and the color ink have landed on the recording medium, the counter ions of the color material in the color ink are self-dispersing having the ionic functional group in the black ink. The concentration of the counter ions in the color ink is locally reduced by being attracted to the carbon black, and as a result, the color material existing near the boundary of the image becomes H-shaped and associates with it to cause bleeding. I think it will be suppressed.

<Ink set>
The ink set of the present invention is an ink set for recording an image on a recording medium using two or more kinds of ink including black ink and color ink.

  The ink set includes not only an ink cartridge in which a plurality of ink cartridges each containing two or more types of ink are integrated, but also a case where a plurality of single ink cartridges containing one type of ink are used in combination. In addition, the ink cartridge and the recording head are integrated.

  In addition, as an example of the ink set of the present invention, there is a case where the ink cartridges are used in combination as follows. For example, the ink cartridge may be used in combination with an ink cartridge that contains another black ink. Further, there is a case where the ink cartridge is used in combination with an ink cartridge in which an ink cartridge that further contains black ink, light cyan ink, and light magenta ink is integrated.

  Further, specific examples in the case where a plurality of individual ink cartridges are used in combination in the ink set include the following forms. There is a case where an independent ink cartridge that stores cyan ink, magenta ink, and yellow ink, respectively, and an ink cartridge that stores another black ink are used in combination. Further, there may be a case where ink cartridges that respectively contain black ink, light cyan ink, and light magenta ink are used in combination. In addition, there may be a case where a single ink cartridge that contains red ink, green ink, and blue ink is additionally used. In the present invention, it is particularly preferable that the ink set be in the form of a combination of a single ink cartridge and an ink cartridge containing another black ink.

  Hereinafter, with respect to the black ink and the color ink constituting the ink set of the present invention, components constituting each ink, characteristics of each ink, and the like will be described. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but is expressed as “contains a salt” for convenience.

(Black ink color material: carbon black)
The color material of the black ink used in the present invention is a carbon black (so-called self-dispersing type) in which at least one hydrophilic group is bonded to the surface of the carbon black particles directly or through another atomic group (—R—). Carbon black). Examples of the hydrophilic group include anionic groups such as — (COOM ₁ ) _n , —SO ₃ (M ₁ ), —PO ₃ H (M ₁ ), and —PO ₃ H (M ₁ ) _2. . In the formula, “M ₁ ” is a hydrogen atom, an alkali metal, ammonium, or organic ammonium, and n is 1 or more. Moreover, as said other atomic group (-R-), an alkylene group or an aromatic ring is mentioned. Examples of the alkylene group in the present invention include a methylene group, an ethylene group, and a propylene group. Examples of the aromatic ring include a benzene ring and a naphthalene ring. Of course, the present invention is not limited to this.

In the present invention, it is particularly preferable to use carbon black in which —R— (COOM ₁ ) _n group is bonded to the surface of the carbon black particles. In the above formula, R is an alkylene group or an aromatic ring, M ₁ is a hydrogen atom, an alkali metal, ammonium, or organic ammonium, and n is an integer of 2 or more. As the carbon black in which the —R— (COOM ₁ ) _n group is bonded to the surface of the carbon black particles, it is preferable to use a carbon black obtained by a diazo coupling method.

Further, as a more preferred embodiment, in the -R- bonded to the surface of the carbon black particles, - (COOM ₁₎ is a carbon atom adjacent to the carbon atom to which they are attached, - combining (COOM ₁₎ The effect of the present invention is more prominently exhibited when n is 2 or when R is C ₆ H ₃ . Note that in -R- bonded to the surface of the carbon black particles, - (COOM ₁₎ is a carbon atom adjacent to the carbon atom to which they are attached, - the fact that by combining (COOM ₁₎ As shown in the following structural formula (3), two or more adjacent carbon atoms in R each have a — (COOM ₁ ) group. In the present invention, it is particularly preferable to use carbon black in which a group represented by the following structural formula (3) is bonded to the surface of the carbon black particles. Of course, the present invention is not limited to this.

  Structural formula (3)

In the black ink used in the present invention, when the above-mentioned -R- (COOM ₁ ) _n groups are bonded to the surface of the carbon black particles at a higher density, for example, the ionic group density on the surface of the carbon black particles However, it is preferable that it is 2.00 micromol / m < ² > or more. This is because the aggregation of carbon black after the black ink is applied to the recording medium is further promoted, and the effects of the present invention can be obtained more remarkably. In the present invention, the ionic group density on the surface of the carbon black particles is greatly influenced by the specific surface area of the carbon black, the structure of the functional group bonded to the surface of the carbon black particles, etc. It is not limited to.

Furthermore, in the black ink used in the present invention, when M ₁ is ammonium, it is particularly preferable because more excellent water resistance of an image can be obtained. This is because, after the black ink is applied to the recording medium, ammonium is decomposed, the ammonia is evaporated, and the ionic group bonded to the carbon black surface becomes H type (acid type), and the hydrophilicity is lowered. It is thought to be due to. Here, carbon black in which M ₁ is ammonium can be obtained by the following method. For example, carbon black in which M ₁ is an alkali metal is used, and an ion exchange method is used to replace M ₁ with ammonium, or an acid is added to form H, and then ammonium hydroxide is added to add M _1. And the like.

  As the above-described carbon black, it is preferable to use carbon black such as furnace black, lamp black, acetylene black, and channel black for the black ink used in the present invention. Specifically, for example, the following commercially available products can be used. Carbon black can be used alone or in combination of two or more.

  Ray Van: 1170, 1190 ULTRA-II, 1200, 1250, 1255, 1500, 2000, 3500, 5000 ULTRA, 5250, 5750, 7000 (above, made in Colombia). Black Pearls L, Legal: 330R, 400R, 660R, Mogul L, Monak: 700, 800, 880, 900, 1000, 1100, 1300, 1400, 2000, Vulcan XC-72R (above, manufactured by Cabot). Color Black: FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex: 35, U, V, 140U, 140V, Special Black: 6, 5, 4A, 4 (above, manufactured by Degussa). No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (above, manufactured by Mitsubishi Chemical).

  Also, newly prepared carbon black can be used. Of course, the present invention is not limited to these, and any conventional carbon black can be used.

  The content (% by mass) of carbon black in the black ink used in the present invention is 0.1% by mass or more and 15.0% by mass or less, and further 1.0% by mass or more and 10.10% by mass based on the total mass of the ink. It is preferable that it is 0 mass% or less.

(Coloring material for color ink)
The color material of the color ink used in the present invention must be a color material having a conductivity of 7 mS / cm or more in a 0.05 mol / L aqueous solution. As long as this condition is satisfied, examples of the color material that can be used in the color ink include a compound represented by the following structural formula (1) and a compound represented by the structural formula (2). Of course, the present invention is not limited to these color materials.

  Structural formula (1)

(In Structural Formula (1), R ₁ is a hydrogen atom, an alkyl group, a hydroxyalkyl group, a cyclohexyl group, a mono- or dialkylaminoalkyl group, or a cyanoalkyl group, and R ₂ , R ₃ , R ₄ , R ₅ , And R ₆ are each independently a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a carboxyl group (provided that R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , and R ₁₃ are all hydrogen atoms. And each M is independently a hydrogen atom, an alkali metal, ammonium, or organic ammonium.)
Structural formula (2)

(In Structural Formula (2), each M is independently a hydrogen atom, an alkali metal, ammonium, or organic ammonium.)
M in Structural Formula (1) and Structural Formula (2) is each independently a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the organic ammonium include acetamide, benzamide, methylamino, butylamino, diethylamino, and phenylamino.

  The content (% by mass) of the color material in the color ink is preferably 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink. When the content of the color material is less than 0.1% by mass, sufficient image density may not be obtained. Further, when the content of the color material exceeds 10.0% by mass, the fixing recoverability (the performance of recovering by a recovery operation such as suction when the ink is solidified in the recording head without using the ink jet recording apparatus for a long time) ) There are cases where good ink jet characteristics cannot be obtained, for example, the ink cannot be obtained sufficiently. Furthermore, in the present invention, in order to obtain a higher image density, the content of the coloring material is preferably 3.0% by mass or more, and in order to obtain a particularly high image density, The colorant content is preferably 4.5% by mass or more.

  As the color material of the color ink used in the present invention, the compound represented by the structural formula (1) or the structural formula (2) may be used alone or in combination with other color materials for adjusting the color tone or the like. May be. However, when a color material other than a compound that satisfies the above-described conductivity condition is used in combination, the color material can be used in a range that does not impair the effects of the present invention.

(Verification of color materials)
For the verification of the color material used in the present invention, the following verification methods (1) to (3) using high performance liquid chromatography (HPLC) can be applied.
(1) Peak retention time (2) Maximum absorption wavelength at peak of (1) (3) M / Z of mass spectrum at peak of (1) (posi, negative)
The analysis conditions of high performance liquid chromatography are as follows. The ink diluted about 1,000 times with pure water is analyzed by high performance liquid chromatography under the following conditions, and the retention time of the peak and the maximum absorption wavelength of the peak are measured.
Column: Symmetry C18 2.1mm x 150mm
-Column temperature: 40 ° C
・ Flow rate: 0.2 ml / min
PDA: 210 nm to 700 nm
Mobile phase and gradient conditions: Table 1

The analysis conditions of the mass spectrum are as shown below. With respect to the obtained peak, a mass spectrum is measured under the following conditions, and the most strongly detected M / Z is measured for each of posi and negative.
・ Ionization method ・ ESI capillary voltage 3.5kV
Desolvent gas 300 ℃
Ion source temperature 120 ° C
・ Detector posi 40V 200-1500amu / 0.9sec
nega 40V 200-1500amu / 0.9sec
Table 2 below shows the retention time, maximum absorption wavelength, M / Z (posi), and M / Z (negative) values for the compounds A and B. When it corresponds to the value shown in Table 2, it can be judged that it corresponds to the compound used in the present invention.

(Salt used for black ink)
The black ink used in the present invention preferably contains a salt. The form of the salt in the black ink may be any form in which a part of the salt is dissociated or in a state in which the salt is completely dissociated.

Specific examples of the salt that can be used for the black ink include, for example, (M ₂ ) NO ₃ , CH ₃ COO (M ₂ ), C ₆ H ₅ COO (M ₂ ), C ₂ H ₄ (COO (M ₂ ) ) ₂ , C ₆ H ₄ (COO (M ₂ )) ₂ , (M ₂ ) ₂ SO ₄ (wherein M ₂ is an alkali metal, ammonium, or organic ammonium). Of course, it is not limited to these as long as the requirements of the present invention are satisfied.

  The salt content (% by mass) in the black ink is preferably 0.05% by mass or more and 10.0% by mass or less based on the total mass of the ink. When the content is less than 0.05% by mass, the effect of the present invention may not be sufficiently obtained. When the content is more than 10.0% by mass, the storage stability of the ink may not be obtained.

In addition, in the black ink, when M ₂ is ammonium, it is particularly preferable because more excellent water resistance of an image can be obtained. Among these, NH ₄ NO ₃ , C ₂ H ₄ (COONH ₄ ) ₂ , (NH ₄ ) ₂ SO _{4 and the} like are preferable because the water resistance of the image is developed in a relatively short time, and in particular, C ₆ H ₄ (COONH _{4 2} is preferred.

In the black ink, when the salt is C ₂ H ₄ (COO (M ₂ )) ₂ , C ₆ H ₄ (COO ( _M2 )) ₂ , (M ₂ ) ₂ SO ₄ , This is more preferable because the dispersion stability of carbon black is particularly excellent when water or the like evaporates.

In addition, it is particularly preferable that the valence of the functional group on the surface of the carbon black particle and the valence of the salt are the same because the effects of the present invention can be obtained more significantly. That is, in the carbon black in which —R— (COOM ₁ ) _n group is bonded to the surface of the carbon black particles, for example, when n is 2, a divalent salt is used as a salt used in combination with the carbon black. It is particularly preferred to use it. Specifically, carbon black having —R— (COOM ₁ ) ₂ groups bonded to the surface of the carbon black particles, C ₂ H ₄ (COO (M ₂ )) ₂ , C ₆ H ₄ (COO (M ₂ )) ₂ , (M ₂ ) ₂ SO _{4 and} the like. Of course, the present invention is not limited to this.

(Aqueous medium for each ink)
An aqueous medium that is a mixed solvent of water and a water-soluble organic solvent can be used for each of the black ink and the color ink constituting the ink set of the present invention. In the present invention, when selecting a water-soluble organic solvent, after determining the poor solvent for carbon black by the method described later, the water-soluble organic solvent is selected and appropriately mixed to prepare each ink. It is preferable to do.

  The content (% by mass) of the water-soluble organic solvent in each ink is 3.0% by mass or more and 50.0% based on the total mass of the ink including the water-soluble organic solvent that exhibits the behavior as a poor solvent described later. It is preferable that it is 3.0 mass% or less and also 40.0 mass% or less. Specifically, for example, the following water-soluble organic solvents can be used.

  Alkanols having 1 to 6 carbon atoms such as ethanol, isopropanol, n-butanol, isobutanol, sec-butanol and tert-butanol. Carboxylic acid amides such as N, N-dimethylformamide or N, N-dimethylacetamide. Ketones such as acetone, methyl ethyl ketone, 2-methyl-2-hydroxypentan-4-one; Cyclic ethers such as keto alcohol, tetrahydrofuran and dioxane. Glycerin. Glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2- or 1,3-propylene glycol, 1,2- or 1,4-butylene glycol, polyethylene glycol, and thiodiglycol; 1,3-butanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2-methyl-1,3-propanediol, 1,2,6-hexanetriol, etc. Alcoholic alcohols. Alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, and triethylene glycol monoethyl (or butyl) ether; Heterocycles such as 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methylmorpholine. Sulfur-containing compounds such as dimethyl sulfoxide;

  Moreover, it is preferable to use deionized water (ion exchange water) as the water. The water content (% by mass) in each ink is 10.0% by mass or more and 90.0% by mass or less, and further 30.0% by mass or more and 80.0% by mass or less based on the total mass of the ink. It is preferable that By setting the water content in such a range, it becomes easy to obtain an ink having an appropriate viscosity for stably discharging the ink and in which clogging at the nozzle tip is suppressed.

(Poor solvent for carbon black)
The poor solvent in the present invention refers to a solvent in which the dispersion state of carbon black cannot be stably maintained with respect to the water-soluble organic solvent. In the present invention, paying attention to the water-soluble organic solvent in the black ink and the color ink constituting the ink set, the carbon black in the black ink is particularly selected to exhibit the above behavior as a poor solvent. . Then, the poor solvent in the black ink and / or the color ink is used as an aggregation accelerator for carbon black.

  It is preferable that the poor solvent in the black ink has a content such that the dispersion state of the carbon black is stably maintained in the non-evaporated ink. In addition, when black ink is applied to the recording medium and the ink evaporates or when the amount of the poor solvent increases due to contact with the color ink containing the poor solvent, the carbon black may start to aggregate. It is preferable to make the content as possible. Further, it is preferable that the poor solvent in the color ink has such a content that the carbon black can start aggregation when it comes into contact with the black ink on the recording medium. By determining the content of the poor solvent in the black ink or the color ink as described above, the effect of the present invention can be obtained at a higher level.

  In the present invention, the water-soluble organic solvent that acts as a poor solvent for carbon black is used by determining the dispersion stability with respect to the target carbon black as follows. In the present invention, a water-soluble organic solvent that is not a poor solvent is referred to as a good solvent.

  More specifically, it can be determined by the following method whether the water-soluble organic solvent used with respect to a certain carbon black is a good solvent or a poor solvent. First, the following two types of dispersions are prepared: a carbon black dispersion A containing the water-soluble organic solvent to be determined, and an aqueous dispersion B of the carbon black.

  A: A carbon black dispersion having a composition in which the content of the water-soluble organic solvent to be determined is 50% by mass, the content of carbon black is 5% by mass, and the content of water is 45% by mass.

  B: An aqueous dispersion of carbon black having a composition in which the carbon black content is 5 mass% and the water content is 95 mass%.

  Next, the dispersion A was stored at 60 ° C. for 48 hours and then cooled to room temperature, and the average particle size of carbon black in the dispersion A was measured using a concentrated particle size analyzer (trade name: FPAR (registered trademark) -1000; Measured using Otsuka Electronics Co., Ltd.). The aqueous dispersion B is also stored at 60 ° C. for 48 hours in the same manner as described above, and then cooled to room temperature, and the average particle size of carbon black in the aqueous dispersion B is measured using a concentrated particle size analyzer or the like. . And let the value of the average particle diameter of each carbon black in the said dispersion A and the aqueous dispersion B be a particle size (A) and a particle size (B). At this time, when the particle size (A) is larger than the particle size (B), the water-soluble organic solvent is a poor solvent, and when the particle size (A) is equal to or less than the particle size (B), The organic solvent is determined as a good solvent.

  The content (mass%) of the poor solvent in each ink is 3.0 mass% or more and less than 50.0 mass%, further 10.0 mass% or more and 40.0 mass% or less based on the total mass of the ink. Preferably there is. When the content is less than 3.0% by mass, the effect of aggregating carbon black due to the poor solvent cannot be obtained, and there may be a case where more carbon black cannot be present on the surface of the recording medium. If the content is 50.0% by mass or more, the storage stability of the ink may not be obtained. The storage stability of the ink generally means storage stability in a state where water is not evaporated.

  Specific examples of the water-soluble organic solvent that can be used as the poor solvent include diols having hydroxyl groups at both ends of the main chain, such as isopropanol, 2-pyrrolidone, polyethylene glycol having an average molecular weight of 200 or more, and 1,5-pentanediol. And the like. Among them, it is particularly preferable to use isopropanol, 2-pyrrolidone, 1,5-pentanediol, polyethylene glycol 200 (average molecular weight 200), polyethylene glycol 600 (average molecular weight 600), or the like. Of course, the poor solvent which can be used by this invention is not restricted to these.

[Other ingredients]
In order to improve the moisture retention and the like, each of the black ink and the color ink used in the ink set of the present invention includes a moisture retention component such as urea, a urea derivative, trimethylolpropane, and trimethylolethane in addition to the above components. You may contain. The content (% by mass) of the moisturizing component in each ink is 0.1% by mass or more and 20.0% by mass or less, and further 3.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. It is preferable that

  Furthermore, each of the black ink and the color ink used in the ink set of the present invention includes a surfactant, a pH adjuster, a rust inhibitor, a preservative, an antifungal agent, and an antioxidant as necessary in addition to the above components. You may contain additives, such as an agent, a reduction inhibitor, an evaporation accelerator, and a chelating agent.

(Characteristics of each ink)
It is preferable that each of the black ink and the color ink used in the ink set of the present invention has such a characteristic that it can be favorably ejected from the recording head. Therefore, the viscosity of each of the black ink and the color ink is preferably 1 mPa · s to 15 mPa · s, and more preferably 1 mPa · s to 5 mPa · s. The surface tension of each of the black ink and the color ink is preferably 25 mN / m or more, more preferably 25 mN / m or more and 50 mN / m or less. Further, it is more preferable that the surface tension of the color ink is lower than the surface tension of the black ink. Specifically, it is particularly preferable that the surface tension of the black ink is 35 mN / m or more and 50 mN / m or less, and the surface tension of the color ink is 25 mN / m or more and 35 mN / m.

<Image forming method>
The image forming method of the present invention will be described below. In the image forming method of the present invention, an image is recorded on a recording medium using two or more inks including at least a black ink and a color ink having the configuration described above. In forming an adjacent image, after forming an image by performing scanning that applies an ink containing carbon black, a water solution that is a poor solvent for the carbon black is formed in the region where the image is formed. It is characterized in that scanning is performed by applying a different organic solvent and applying another ink.

  Hereinafter, an example in which an image containing carbon black is used as a black ink and an image is formed on a recording medium using an ink containing a water-soluble organic solvent that is a poor solvent for the carbon black as a color ink will be described. ,explain. FIG. 8 is an example of a recording head that can carry out the above-described image forming method of the present invention. As shown in FIG. 8, the recording head has an ejection port array (Bk) for ejecting black ink and three colors of cyan (C), magenta (M), and yellow (Y) as color inks. And an ejection port array for ejecting each of the inks.

  In the image forming method of the present invention, when an image is formed, a recording head in which a black ink discharge port array for discharging black ink and a color ink discharge port array are shifted in the sub-scanning direction is used. It is preferable. For this reason, for example, when forming an image in which black and color are mixed using the recording head shown in FIG. 8, the portion a in the drawing is used for black ink, and C, M, and Y are used. For the ink, it is preferable to form an image using the portion b in the figure. Hereinafter, the case of forming an image in which a black portion and a color portion are mixed will be described in more detail with reference to FIG.

  In FIG. 8, first, black image data is recorded on plain paper or the like by one-pass recording by scanning the print head in the horizontal direction (main scanning direction) in the drawing using the portion a of the discharge port array for black ink. Form on the medium. Next, the recording medium is conveyed by a distance a in the vertical direction (sub-scanning direction) in the drawing, and in the process of the forward direction of the main scanning of the next print head, using the portion of the color ink ejection port array b, The image is formed in one pass printing in the area where the image is formed with the a column of the black ink. At this time, the black ink ejection port array a simultaneously forms an image in the next area. By repeating this, black and color mixed image formation is performed.

  FIG. 9 shows another example of a recording head that can carry out the image forming method of the present invention. In FIG. 9, as in FIG. 8, for black ink, the portion a in the ejection port array is used, and for C, M, and Y inks, b in the diagram corresponding to the entire region of the ejection port array. Using this part, black and color mixed image formation is performed in the same manner as described above with reference to FIG.

  FIG. 10 shows another example of a recording head that can carry out the image forming method of the present invention. In FIG. 10, as in the case of FIG. 8, the portion a in the drawing of the ejection port array is used for black ink, and the C, M, and Y inks correspond to the entire region of the ejection port array for color ink. Using the portion b in the middle, image formation of mixed black and color is performed. In the recording head illustrated in FIG. 10, as shown in the drawing, a distance of one paper feed amount a ′ is placed between the portion a of the black ink ejection port array and the portion b of the color ink. ing. For this reason, the recording head having such a configuration causes an extra time difference for one print scan in a reciprocating period from the formation of a black image to the formation of a color image. Therefore, the recording head illustrated in FIG. 10 has a more advantageous configuration for preventing bleeding between black and color than the configuration illustrated in FIG.

  FIG. 11 shows another example of a recording head that can carry out the image forming method of the present invention. Even when such a recording head in which the ejection openings for black ink and color ink are arranged in a line in this order in the paper feeding direction is used, the image is formed after the black image is formed in accordance with the paper feeding. Will be.

  FIG. 12 shows another example of a recording head that can carry out the image forming method of the present invention. In the recording head shown in FIG. 12, the color ink ejection port arrays are arranged with cyan ink (C1, C2), magenta ink (magenta ink) so that the color ink ejection order is the same in forward scanning and backward scanning. M1, M2) and yellow ink (Y1, Y2) are provided in two rows, symmetrically in the main scanning direction. As a result, bidirectional recording is possible even in the formation of black and color mixed images. In this case, a black image is first formed in the portion a for black ink, then the recording medium is conveyed by a distance a, and the color ink is processed in the reverse direction of the main scanning of the next print head. By using the portion of the discharge port row b for forming an image, an image is formed in one-pass printing in the region where the image is formed in the above-described row a for black ink.

  Of course, in the bidirectional recording head as shown in FIG. 12, as described above, the nozzle arrangement of black ink and color ink is used, and an interval for one scanning is provided between the black and color image formation, and bleeding is performed. It is good also as a structure more advantageous with respect to prevention (refer FIG. 13). Although the image forming method of the present invention has been described above, the form of the recording head that can be used in the method of the present invention is not limited to FIGS.

<Recording method, recording unit, cartridge and recording apparatus>
Next, an example of the ink jet recording apparatus of the present invention will be described. The apparatus is characterized in that the ink set of the present invention described above is accommodated. First, an example of a head configuration which is a main part of an ink jet recording apparatus using thermal energy is shown in FIGS. FIG. 1 is a cross-sectional view of the head 13 along the ink flow path, and FIG. 2 is a cross-sectional view taken along line AB in FIG. The head 13 is obtained by bonding a heating element substrate 15 to a glass, ceramic, silicon or plastic plate having a flow path (nozzle) 14 through which ink passes.

The heating element substrate 15 includes a protective layer 16 formed of silicon oxide, silicon nitride, silicon carbide, etc., electrodes 17-1 and 17-2 formed of aluminum, gold, aluminum-copper alloy, etc., HfB ₂ , TaN, A heating resistor layer 18 formed of a high melting point material such as TaAl, a heat storage layer 19 formed of thermal silicon oxide, aluminum oxide or the like, and a substrate 20 formed of a material with good heat dissipation such as silicon, aluminum, or aluminum nitride. It has become more.

  When a pulsed electric signal is applied to the electrodes 17-1 and 17-2 of the head 13, the region indicated by n of the heating element substrate 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact with the surface. The pressure causes the meniscus 23 to protrude, and the ink 21 is ejected through the nozzles 14 of the head to form ink droplets 24 from the ejection orifices 22 and fly toward the recording medium 25. FIG. 3 shows an external view of an example of a multi-head in which a large number of heads shown in FIG. 1 are arranged. This multi-head is made by adhering a glass plate 27 having multi-nozzles 26 and a heating head 28 similar to that described in FIG.

  FIG. 4 shows an example of an ink jet recording apparatus incorporating this head. In FIG. 4, reference numeral 61 denotes a blade as a wiping member, one end of which is held and fixed by a blade holding member, and forms a cantilever. The blade 61 is disposed at a position adjacent to the recording area by the recording head 65, and in the illustrated example, is held in a form protruding in the moving path of the recording head 65.

  Reference numeral 62 denotes a cap on the projection port surface of the recording head 65, which is disposed at a home position adjacent to the blade 61, moves in a direction perpendicular to the moving direction of the recording head 65, contacts the ink ejection port surface, and performs capping. The structure to perform is provided. Further, reference numeral 63 denotes an ink absorber provided adjacent to the blade 61 and, like the blade 61, is held in a form protruding in the moving path of the recording head 65. The blade 61, the cap 62, and the ink absorber 63 constitute an ejection recovery unit 64, and the blade 61 and the ink absorber 63 remove moisture, dust, and the like from the ejection port surface.

  Reference numeral 65 denotes a recording head which has discharge energy generating means and performs recording by discharging ink onto a recording medium facing the discharge port surface on which the discharge port is arranged. Reference numeral 66 denotes a movement of the recording head 65 by mounting the recording head 65. It is a carriage for performing. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. As a result, the carriage 66 can move along the guide shaft 67, and the recording area and its adjacent area can be moved by the recording head 65.

  51 is a paper feed section for inserting a recording medium, and 52 is a paper feed roller driven by a motor (not shown). With these configurations, the recording medium is fed to a position facing the ejection port surface of the recording head 65, and discharged to a paper discharge unit provided with a paper discharge roller 53 as recording progresses. In the above configuration, when the recording head 65 finishes recording and returns to the home position, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the ejection port of the recording head 65 is wiped.

  When the cap 62 is in contact with the ejection surface of the recording head 65 to perform capping, the cap 62 moves so as to protrude into the moving path of the recording head. When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same position as the above-described wiping position. As a result, the ejection port surface of the recording head 65 is wiped even during this movement. The above-mentioned movement of the recording head to the home position is not only at the end of recording or at the time of ejection recovery, but also to the home position adjacent to the recording area at a predetermined interval while the recording head moves the recording area for recording. Then, the wiping is performed with this movement.

  FIG. 5 is a diagram illustrating an example of an ink cartridge that contains ink supplied to the recording head via an ink supply member, for example, a tube. Here, reference numeral 40 denotes an ink container, for example, an ink bag, in which supply ink is stored, and a rubber plug 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the ink bag 40 can be supplied to the head. An ink absorber 44 receives waste ink. The ink container preferably has a liquid contact surface made of polyolefin, particularly polyethylene.

  The ink jet recording apparatus used in the present invention is not limited to the one in which the head and the ink cartridge are separated as described above, but is preferably used in an apparatus in which they are integrated as shown in FIG. It is done. In FIG. 6, reference numeral 70 denotes a recording unit, in which an ink containing portion containing ink, for example, an ink absorber is housed, and the ink in the ink absorber has a head portion 71 color having a plurality of orifices. It is configured to be ejected as ink droplets. It is preferable for the present invention to use polyurethane as the material of the ink absorber. Alternatively, a structure in which the ink container is an ink bag with a spring or the like inside without using an ink absorber may be used. Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the cartridge with the atmosphere. The recording unit 70 is used in place of the recording head 65 shown in FIG. 4 and is detachable from the carriage 66.

  Next, a preferred example of an ink jet recording apparatus using mechanical energy will be described. As an ink jet recording apparatus using mechanical energy, a nozzle forming substrate having a plurality of nozzles, a pressure generating element made of a piezoelectric material and a conductive material arranged opposite to the nozzles, and the periphery of the pressure generating element are filled. An on-demand type recording head that includes ink, displaces a pressure generating element by an applied voltage, and discharges a small droplet of ink from a nozzle can be given. An example of the configuration of a recording head which is a main part of the recording apparatus is shown in FIG.

  The head includes an ink flow path 80 communicating with an ink chamber (not shown), an orifice plate 81 for ejecting ink droplets of a desired volume, a vibration plate 82 that directly applies pressure to ink, and the vibration plate 82. And a substrate 84 for indicating and fixing the orifice plate 81, the diaphragm 82 and the like.

  In FIG. 7, an ink flow path 80 is formed of a photosensitive resin or the like, an orifice plate 81 has a discharge port 85 formed by electroforming or punching a metal such as stainless steel or nickel, and the vibration plate 82 is The piezoelectric element 83 is formed of a dielectric material such as barium titanate or PZT. The piezoelectric element 83 is formed of a metal film such as stainless steel, nickel, or titanium and a highly elastic resin film. The recording head configured as described above applies a pulsed voltage to the piezoelectric element 83 to generate a distortion stress, and the energy deforms the vibration plate bonded to the piezoelectric element 83, so that the ink in the ink flow path 80 is obtained. Is pressed vertically and ink droplets (not shown) are ejected from the ejection ports 85 of the orifice plate 81 to perform recording. Such a recording head is used by being incorporated in an ink jet recording apparatus similar to that shown in FIG. The detailed operation of the ink jet recording apparatus can be performed in the same manner as described above.

  Next, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited by the following Example, unless the summary is exceeded. In the text, “parts” and “%” are based on mass unless otherwise specified.

<Preparation of pigment dispersion>
To a solution obtained by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water, 1.5 g of 4-amino-1,2-benzenedicarboxylic acid was added while being cooled to 5 ° C. Next, the container containing the solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 1.8 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. After stirring this solution for another 15 minutes, 6 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 ml / 100 g was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare self-dispersing carbon black. Furthermore, water was added to the self-dispersing carbon black obtained above to disperse the pigment so that the pigment content would be 10% by mass to prepare a dispersion. By the above method, a pigment dispersion was obtained in a state where self-dispersing carbon black having —C ₆ H ₃ — (COONa) ₂ groups introduced on the surface of carbon black particles was dispersed in water.

The ionic group density of the self-dispersing carbon black prepared above was measured and found to be 3.1 μmol / m ² . The ionic group density used here was measured by measuring the sodium ion concentration in the pigment dispersion prepared above using an ion meter (manufactured by Toa DKK), and determining the ion of self-dispersing carbon black from that value. Converted to sex group density.

<Determination of poor solvent and good solvent for each water-soluble organic solvent>
In order to select a water-soluble organic solvent that acts as a poor solvent or a good solvent for the carbon black in the pigment dispersion obtained above, the following experiment was conducted. First, using the pigment dispersion obtained above (pigment content: 10% by mass), a dispersion A and an aqueous dispersion B for determination of a poor solvent and a good solvent were prepared at the following blending ratio. did.

(Dispersion ratio)
[Dispersion A]
-Pigment dispersion (pigment content: 10% by mass) 50 parts-50 parts of each water-soluble organic solvent listed in Table 3 [Water dispersion B]
・ Pigment dispersion (pigment content: 10% by mass) 50 parts ・ Pure water 50 parts (judgment method and judgment result)
Next, 10 g of each of the dispersion A and the aqueous dispersion B prepared as described above was put into a transparent sample bottle with a glass lid, capped, and then sufficiently stirred, and this was stirred at 60 ° C. for 48 hours. Left to stand. Thereafter, using dispersion A cooled to room temperature as a measurement sample, the average particle size of carbon black in dispersion A was measured using a concentrated particle size analyzer (trade name: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.). . Further, the average particle size of carbon black in the aqueous dispersion B cooled to room temperature was also measured in the same manner as described above. A water-soluble organic solvent in which the average particle size of the carbon black in the dispersion A and the aqueous dispersion B after storage at 60 ° C. for 48 hours was larger than that of the aqueous dispersion B was determined as a poor solvent. Moreover, the water-soluble organic solvent in which the average particle diameter of the dispersion A after storage at 60 ° C. for 48 hours was equal to or less than that of the aqueous dispersion B was determined to be a poor solvent, that is, a good solvent.

  Table 3 shows the result of determining whether each water-soluble organic solvent corresponds to a poor solvent or a good solvent by measuring the average particle size of carbon black as described above. The results in Table 3 indicate that an increase in the average particle diameter of carbon black is recognized, and a case where it is determined as a poor solvent is ○, an increase in the average particle diameter of carbon black is not observed, and it is determined as a good solvent Is shown as x.

<Preparation of black ink>
Each component shown in Table 4 below was mixed and sufficiently stirred, and then pressure filtration was performed with a Fujifilm microfilter (registered trademark, manufactured by Fuji Film) having a pore size of 3.0 μm to prepare each black ink.

<Synthesis of coloring materials>
(Synthesis of Compound A)
In xylene, the compound represented by the following compound (1), sodium carbonate, and ethyl benzoyl acetate were reacted, and the reaction product was filtered and washed. This was reacted in N, N-dimethylformamide by sequentially adding metaaminoacetanilide, copper acetate, and sodium carbonate, and the reaction product was filtered and washed. Further, after sulfonation in fuming sulfuric acid, filtration and washing were performed, and this was subjected to a condensation reaction with cyanuric chloride in the presence of sodium hydroxide. Anthranilic acid was added to the reaction solution, and a condensation reaction was performed in the presence of sodium hydroxide. By filtering and washing this, the following compound A was obtained as a colorant corresponding to the compound represented by the structural formula (1).

  Compound (1)

  Compound A

(Synthesis of Compound B)
A known method for coupling diazotized 4-nitro-4′-aminostilbene-2,2-disulfonic acid with 3-aminonaphthalene-1-sulfonic acid, triazotizing it, and reducing the nitro group to an amino group The aminostilbene-triazole produced by the method was dissolved in water, and sodium nitrite and hydrochloric acid were added dropwise to carry out diazotization. This was dropped into an aqueous solution of a compound represented by the following compound (2), coupled, and then salted out with sodium chloride. This compound is diazotized with an aqueous sodium nitrite solution, and a 6-aminonaphthalene-2-sulfonic acid aqueous solution is added to the turbid solution, and the resulting triazole is salted out with sodium chloride to give a structure. The following compound B was obtained as a color material corresponding to the compound represented by the formula (2).

  Compound (2)

  Compound B

<Method of measuring conductivity of aqueous coloring material solution>
The electric conductivity of 0.05 mol / L aqueous solution of PRO-JET (registered trademark) Yellow 746 (manufactured by Avicia) used in the above-mentioned compound A, compound B, and comparative example was measured at 25 ° C. The results obtained are shown in Table 5.

<Preparation of color ink>
The components shown in Table 6 below were mixed and stirred sufficiently, and then pressure filtration was performed with a Fujifilm microfilter (manufactured by Fuji Film) having a pore size of 0.2 μm to prepare each color ink.

<Evaluation>
Each black ink and each color ink obtained above were combined as shown in Table 7 and used as an ink set. Each ink constituting the ink set was filled in an ink cartridge and mounted on a modified inkjet recording apparatus iP3100 (manufactured by Canon Inc.) that discharges ink from the recording head by the action of thermal energy. In the ink jet recording apparatus, the recording head was modified to have the configuration shown in FIG. 9 or FIG. Then, an image in which a solid image formed with black ink and a solid image formed with color ink were adjacent to each other was formed on a recording medium (trade name: Office Planner (registered trademark); manufactured by Canon Marketing Japan Inc.). In the obtained recorded matter, the degree of bleeding at the boundary between the image area formed with black ink and the image area formed with each of the above recording duties using the color ink is visually confirmed to prevent bleeding. Sexuality was evaluated. The evaluation criteria for bleeding resistance are as follows. Table 7 shows the evaluation results.

AAA: No bleeding AA: Bleeding carefully, but almost unnoticeable A: Bleeding is almost inconspicuous B: There is bleeding but no problem C: Bleeding is noticeable D: Bleeding so that the color boundary is not clear

  From Table 7, it was confirmed that bleeding was effectively suppressed by using a color ink containing a colorant having an electrical conductivity of 7 mS / cm or more in an aqueous solution of 0.05 mol / L. Further, it was confirmed that bleeding was further suppressed by adding a salt or a poor solvent to the black ink and a poor solvent to the color ink.

FIG. 2 is a longitudinal sectional view of a recording head. It is a vertical and horizontal view of a recording head. FIG. 2 is an external perspective view of a head in which the head shown in FIG. It is a perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view of an ink cartridge. It is a perspective view which shows an example of a recording unit. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. FIG. 3 is a diagram illustrating an example of a configuration of a recording head.

Explanation of symbols

13 Head 14 Ink Nozzle 15 Heating Element Substrate 16 Protective Layer 17-1, 17-2 Electrode 18 Heating Resistor Layer 19 Heat Storage Layer 20 Substrate 21 Ink 22 Discharge Orifice (Micropore)
23 Meniscus 24 Ink Drop 25 Recording Medium 26 Multi Nozzle 27 Glass Plate 28 Heating Head 40 Ink Bag 42 Plug 44 Ink Absorber 45 Ink Cartridge 51 Paper Feeder 52 Paper Feed Roller 53 Paper Discharge Roller 61 Blade 62 Cap 63 Ink Absorber 64 Ejection recovery unit 65 Recording head 66 Carriage 67 Guide shaft 68 Motor 69 Belt 70 Recording unit 71 Head unit 72 Atmospheric communication port 80 Ink flow path 81 Orifice plate 82 Vibration plate 83 Piezoelectric element 84 Substrate 85 Ejection port

Claims (15)

In an ink set for recording an image on a recording medium using two or more inks including black ink and color ink,
The black ink contains carbon black to which at least one hydrophilic group is bonded directly or through another atomic group,
The ink set according to claim 1, wherein the color ink contains a color material having an electrical conductivity of an aqueous color material solution of 0.05 mol / L of 7 mS / cm or more. The ink set according to claim 1, wherein the group bonded to the surface of the carbon black is a —R— (COOM ₁ ) _n group.
(In the above formula, R is an alkylene group or an aromatic ring, M ₁ is a hydrogen atom, an alkali metal, ammonium, or organic ammonium, and n is an integer of 2 or more.)   The ink set according to claim 1, wherein the black ink contains a poor solvent for the carbon black.   The ink set according to claim 1, wherein the color ink contains a salt. The ink set according to claim 1, wherein the color material contained in the color ink is a compound represented by the following structural formula (1).
Structural formula (1)

(In Structural Formula (1), R ₁ is a hydrogen atom, an alkyl group, a hydroxyalkyl group, a cyclohexyl group, a mono- or dialkylaminoalkyl group, or a cyanoalkyl group, and R ₂ , R ₃ , R ₄ , R ₅ , And R ₆ are each independently a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a carboxyl group (provided that R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , and R ₁₃ are all hydrogen atoms. And each M is independently a hydrogen atom, an alkali metal, ammonium, or organic ammonium.) The ink set according to any one of claims 1 to 4, wherein the color material contained in the color ink is a compound represented by the following structural formula (2).
Structural formula (2)

(In Structural Formula (2), each M is independently a hydrogen atom, an alkali metal, ammonium, or organic ammonium.)   The ink set according to claim 1, wherein the color ink contains a poor solvent for the carbon black.   The ink set according to claim 1, wherein the poor solvent is 2-pyrrolidone. In an inkjet recording method for recording on a recording medium by discharging ink by an inkjet method,
An ink jet recording method, wherein the ink is an ink constituting the ink set according to any one of claims 1 to 8. In an ink cartridge provided with an ink containing portion for containing ink,
An ink cartridge, wherein the ink stored in the ink storage portion is an ink constituting the ink set according to any one of claims 1 to 8. In a recording unit comprising an ink containing portion for containing ink and a recording head for ejecting ink,
The recording unit, wherein the ink stored in the ink storage unit is an ink constituting the ink set according to any one of claims 1 to 8. In an ink jet recording apparatus including an ink storage portion for storing ink and a recording head for discharging ink,
The ink accommodated in the said ink accommodating part is the ink which comprises the ink set in any one of Claims 1-8, The inkjet recording device characterized by the above-mentioned. In an image forming method of performing recording on a recording medium using a black ink and at least one color ink by an inkjet recording method,
An image formed by the black ink and an image formed by the color ink using the ink constituting the ink set according to any one of claims 1 to 8 as the black ink and the color ink. Forming an image formed by adhering the black ink to the region where the image is formed, and then performing the scanning to apply the color ink to the region where the image is formed. Method.   The image forming method according to claim 13, wherein after the scanning for applying the black ink is performed, the scanning for applying the color ink is performed after at least one scanning interval is left.   Ink application is performed using a recording head in which the ejection port array for ejecting the black ink and the ejection port array for ejecting the color ink are shifted in the sub-scanning direction. The image forming method according to claim 13 or 14.

Images