JPH11335602A - Recording ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a recording ink having properly dispersed carbon black and excellent storage stability of ink, capable of stably providing an excellent image, by using improved carbon black as a colorant. SOLUTION: This ink is obtained by dispersing carbon black containing a functional group which is generated by the decomposition of a free radical generator composed of an azo group-containing polymer and is linked to the surface by chemical bond into a water-based medium (preferably water or a water-soluble organic solvent such as methyl alcohol, ethyl alcohol or the like). The free radical generator is preferably an azo group-containing polymer having a structure of formula I (R1 and R2 are each an alkylene; A is a group containing NH groups or O atoms at both ends). The polymer is decomposed and functional groups of formula II and formula III are generated and bonded to the surface of carbon black. Consequently the mutual aggregation of the carbon black in the water-based medium can be prevented by the functional group bonded to the surface so that the clogging of a nozzle of a recording apparatus can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording ink in which a coloring material composed of carbon black is dispersed in an aqueous medium, and more particularly to a method for modifying carbon black to stabilize the dispersion of carbon black in the aqueous medium. To improve
The present invention is characterized in that storage stability and ejection stability of the recording ink are improved so that good recording can be stably performed by using the recording ink.

[0002]

2. Description of the Related Art Conventionally, as inks used in ink recording devices such as ink jet printers, water-based inks have been widely used in addition to oil-based inks in terms of easy handling and safety.

Here, as a water-based ink, a water-soluble dye is generally used as a coloring material, and a water-soluble dye dissolved in an aqueous medium has been widely used.

[0004] However, such water-based inks have poor water resistance, and when supplied to a recording medium such as plain paper to form an image, bleeding of the ink called bleeding or feathering occurs. There is a problem that ink flows.

Therefore, in recent years, it has been studied to use a pigment such as carbon black as a coloring material in an ink and to use an ink in which the pigment such as carbon black is dispersed in an aqueous medium. .

However, when carbon black is dispersed in an aqueous medium as described above, the dispersion stability of the carbon black in the aqueous medium is not sufficient, and when such an ink is used in an ink recording apparatus such as an ink jet printer. The carbon black in the ink gradually aggregates, thereby clogging the nozzles of the ink recording device, deteriorating the ejection stability of the ink, disturbing the formed image, and the density of the formed image. However, there is a problem that good recording cannot be stably performed due to variations in the recording quality.

For this reason, conventionally, an alkyl ether derivative of a polyhydric alcohol such as triethylene glycol monobutyl ether or an ester derivative of a polyhydric alcohol such as glyceryl monoacetate is conventionally contained in the ink in which carbon black is dispersed as described above. Attempts have been made to improve the dispersion stability of carbon black in the ink by adding a dispersant such as

However, when a large amount of the above dispersant is added to improve the dispersion stability of carbon black in the ink, the dispersant tends to cause clogging of the ink in the nozzles of the ink recording device, and the On the contrary, there is a problem that the ejection stability is deteriorated, and there is also a problem that the concentration of the coloring material in the ink is reduced due to the addition of the dispersant, thereby lowering the density of the formed image.

In recent years, Japanese Patent Application Laid-Open No. 5-230
As disclosed in JP-A-410, in order to improve the storage stability of an ink using carbon black, carbon black that has been surface-treated by graft polymerization of an acrylamide derivative, or that disclosed in Japanese Unexamined Patent Application Publication No.
As shown in JP-A-339516 and JP-A-6-25572, in order to improve the storage stability and dispersibility of an ink using carbon black, a monomer having a vinyl group is graft-polymerized to carbon black. It has been proposed to use

However, as shown in these publications,
Even when carbon black obtained by polymerizing an acrylamide derivative or a monomer having a vinyl group on the surface of carbon black is used, the ink tends to clog the nozzles of the ink recording device, and the ink cannot be stably ejected. There was.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems when carbon black is used as a coloring material in a recording ink used in an ink recording device such as an ink jet printer. Is what you do.

That is, in the present invention, carbon black is modified, and in a recording ink using this carbon black as a coloring material, the carbon black is maintained in an appropriately dispersed state, and the storage stability of the ink is improved. When such a recording ink is used for an ink recording device such as an ink jet printer, the ink is prevented from being clogged in a nozzle of the ink recording device, and the ink is stably ejected. Accordingly, it is an object of the present invention to stably obtain a good image with less disturbance of the image and uneven density.

[0013]

According to the recording ink of the present invention, in order to solve the above-mentioned problems, in a recording ink in which a coloring material made of carbon black is dispersed in an aqueous medium, As a coloring material, carbon black in which a functional group generated by decomposition of a radical generator composed of a polymer containing an azo group is chemically bonded to the surface is used.

Here, as the radical generator composed of the above-mentioned polymer containing an azo group, for example, a polymer containing an azo group of the structural formula (1) shown in the following Chemical Formula 2 is used. Can be.

[0015]

Embedded image

It should be noted that R ₁ and R ₂ in the structural formula (1)
Is selected from an alkylene group and a group having a substituent bonded thereto, and R ₁ and R ₂ may be the same or different groups, and A is a group having NH or O at both ends. is there.

Here, when the polymer containing an azo group represented by the above structural formula (1) is decomposed, functional groups represented by the following chemical formulas (2) and (3) are generated. Bonded to the surface of carbon black.

[0018]

Embedded image

Here, as in the case of the recording ink of the present invention, when carbon black having a functional group generated by the decomposition of the radical generator composed of the above-mentioned polymer containing an azo group bonded to the surface is used as a coloring material. The functional group suppresses the mutual aggregation of the carbon blacks in the aqueous medium, so that the carbon black is maintained in a state of being sufficiently dispersed in the recording ink, and the storage stability of the recording ink is improved. The performance is improved.

When the recording ink of the present invention is used in an ink recording device such as an ink jet printer, the recording ink is prevented from being clogged in the nozzles of the ink recording device, and the ink is stably ejected. As a result, it is possible to stably obtain a good image with less occurrence of image disturbance, density unevenness, and the like.

It is not clear why carbon black having a functional group bonded to its surface is suppressed from agglomerating in an aqueous medium when the carbon black is used as a coloring material. This is considered to be because the above functional group has hydrophilicity, and the carbon black is stably dispersed in the aqueous medium by this functional group.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a recording ink according to an embodiment of the present invention will be specifically described.

Here, in the recording ink of the present invention, known carbon blacks such as furnace black, acetylene black and channel black can be used as the carbon black used for the coloring material.
Furnace black includes, for example, Real250R, 415R, and 330R manufactured by Cabot, # 45L manufactured by Mitsubishi Chemical Corporation, and Print manufactured by Degussa.
ex-35 and the like, as acetylene black, for example, Denkenblack manufactured by Denki Kagaku Kogyo Co., Ltd.,
As the channel black, for example, Columbia
NeoSpectraII manufactured by nCarbon Co. can be used.

Examples of such radical generators comprising a polymer containing an azo group for bonding a functional group to the surface of carbon black include, for example, azo groups represented by the following structural formulas (4) to (8). A polymer containing a group can be used.

[0025]

Embedded image

In the recording ink of this embodiment, water or a water-soluble organic solvent is used as an aqueous medium for dispersing the coloring material composed of carbon black having the functional group bonded to the surface as described above, Examples of the water-soluble organic solvent include aliphatic alcohols having 1 to 5 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol.

Further, in this recording ink, in addition to the coloring material comprising carbon black in the aqueous medium, a viscosity adjuster, a surface tension adjuster, and a pH adjuster for improving the properties of the ink. It is preferable to add a humectant, a chelating agent, a penetrant, a fungicide, a quick-drying agent, a stabilizer, a fixing agent and the like.

Here, the viscosity adjusting agent is used for adjusting the viscosity of the ink to improve the ejection property of the ink and for adjusting the permeability of the ink into a recording medium such as plain paper. Polyalkylene glycols such as glycol and polypropylene glycol can be used, and polyethylene glycol is particularly preferable. When the viscosity modifier is added to the ink, the amount of the viscosity modifier is 0 to 10% by weight, preferably 0.1 to 8% by weight, more preferably 1 to 10% by weight.
It should be in the range of 5% by weight.

The surface tension adjusting agent is used for adjusting the surface tension of the ink to improve the ejection property of the ink and for adjusting the permeability of the ink to the recording medium. Agents, various surfactants such as silicon-based, fluorine-based, and acetylene-based surfactants, and anionic and cationic surfactants can be used. Preferably, nonionic surfactants are used.
When the surface tension adjuster is added to the ink, the amount of addition is in the range of 0.1 to 5% by weight, preferably 0.1 to 3% by weight, more preferably 0.2 to 1% by weight. To be.

The pH adjuster is used to keep the pH of the ink in an appropriate state and to suppress a decrease in the dispersion stability of carbon black due to a change in the pH. For example, NaHCO ₃ , Na ₂ B ₄ O ₇ , Na ₂ CO ₃ ,
KHCO ₃ , K ₂ CO ₃ , NaOH, CH ₃ COON
a, N (CH ₂ CH ₂ OH) ₃ or the like can be used;
In particular, it is preferable to use NaHCO ₃ . And
When such a pH adjuster is added to the ink, the amount of the pH adjuster is 0.1 to 1% by weight, preferably 0.1 to 1% by weight.
To 0.5% by weight, more preferably 0.2 to 0.5% by weight
Range.

The humectant is used to prevent the concentration, viscosity, etc. of the ink from changing due to the evaporation of water, which is the main component of the aqueous medium, and to prevent the ink ejection stability from deteriorating. 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, , 5-pentanediol, 1,7-heptanediol, 2-methyl-
2,4-pentanediol, 2-ethyl-1,3-hexanediol, glycerin, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol 200, dipropylene glycol, 2,2′-thiodiethanol, 1,2,2 Alkylene glycols such as 6-hexanetriol; 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-
Dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 2-methoxyethanol, 2-ethoxyethanol, 2- (methoxymethoxy) ethanol, 2-butoxyethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether , Triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, 1-
Use of lower alkyl ethers of polyhydric alcohols such as methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and tripropylene glycol monomethyl ether. In particular, it is preferable to use diethylene glycol, triethylene glycol, glycerin and the like. When such a humectant is added to the ink, the added amount is 1 to 10% by weight,
It is preferably in the range of 3 to 10% by weight, more preferably 5 to 8% by weight.

The chelating agent is used to trap metal ions present in the ink and to prevent the carbon ions from losing the dispersion stability of the carbon black. , Ethylenediaminetetraacetic acid, sodium nitrile triacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, sodium uramil diacetate, and the like. When such a chelating agent is added to the ink, the added amount is 0.1 to 1% by weight, preferably 0.1 to 0.5% by weight, more preferably 0.2 to 0.5% by weight.
% By weight.

The penetrant is used to enhance the permeability of the ink into the recording medium. For example, a penetrant may be a lower alkyl ether of a polyhydric alcohol such as diethylene glycol monobutyl ether or triethylene glycol monobutyl ether. Can be used. When such a penetrant is added to the ink, the amount added is 1 to 10% by weight, preferably 3 to 10% by weight.
%, More preferably in the range of 4 to 8% by weight.

The antifungal agent is used to prevent the occurrence of mold and the like in the ink. Or isothiazoline-based ones such as Proxel (manufactured by Zeneca) and Amorden (manufactured by Daiwa Chemical Industries), Preventol series (manufactured by Bayer), sodium omazine, dioxin, sodium dihydroacetate, water glass, etc. be able to. When the antifungal agent is added to the ink, the amount of the antifungal agent is 0.01 to 0.5% by weight, preferably 0.05 to 0.4% by weight, and more preferably 0.1 to 0% by weight. To be in the range of 4% by weight.

The quick-drying agent is used to prevent the ink from quickly drying or penetrating after the ink has adhered to the recording medium, thereby preventing the ink from adhering to another recording medium and becoming dirty. For example, lower alcohols such as methanol, ethanol, propanol, 2-propanol, 1-butanol, and 2-butanol are used.

The stabilizer is used to prevent the dispersion stability of carbon black from decreasing in an aqueous medium. Examples of the stabilizer include alcohol amines such as monoethanolamine, diethanolamine and triethanolamine. 2-pyrrolidone, N-methyl-2-
Pyrrolidone, 1,3-dimethylimidazolidinone, 1,
Cyclic amide compounds such as 3-dimethyl-2-imidazolidinone, sulfolane, dimethyl sulfoxide, and ε-caprolactam; imide compounds such as succinimide; formamide, sorbit, 1,3-bis (β-hydroxyethyl) urea, and the like Preferably, triethanolamine is used. When such a stabilizer is added to the ink, the amount of the stabilizer is 0.1 to 1% by weight, preferably 0.1 to 0.5% by weight.
More preferably, it is in the range of 0.2 to 0.5% by weight.

The fixing agent improves the fixability of the ink to the recording medium. Examples of the fixing agent include water-soluble polyesters, polyurethanes, polyamides, polyimides, polyacryls, and polyvinyl alcohols. Preferably, poly (meth) acrylates are used. When the fixing agent is added to the ink, the amount of the fixing agent is 0.1 to 1
It should be in the range of 5% by weight, preferably 1-10% by weight, more preferably 4-8% by weight.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, specific embodiments of the recording ink according to the present invention will be described, and in the recording ink according to the embodiment of the present invention, the color material composed of carbon black will be stable in an aqueous medium. It becomes clear that the storage stability of the ink, the ejection stability of the ink, and the like are improved, and that a good image without image disturbance or density unevenness is stably obtained. I do.

Example 1 In this example, furnace black having a particle size of 34 nm (manufactured by Cabot: Realgal 250R) was used as carbon black.
Was used.

On the other hand, as the radical generator, 4,4 ′
An azo group-containing polymer synthesized from -azobis-4-cyanopentanoyl chloride and polyethylene glycol (# 400, manufactured by Wako Pure Chemical Industries, Ltd.) was used.

Then, 3 g of the above carbon black was placed in a 200 ml three-necked flask equipped with a reflux condenser.
0.25 g (0.001 mol) of a radical generator composed of the above-mentioned polymer containing an azo group and 200 ml of distilled water as a solvent were used.
Then, the mixture was heated in a nitrogen atmosphere, stirred while gradually raising the liquid temperature and refluxing, and the aqueous solution of the above radical generator was added every 8 hours by a dropping funnel in an amount of 0.001 mol. After dropping twice, the reaction was allowed to proceed for another 24 hours. Thereafter, unreacted substances and by-products were removed by Soxhlet extraction using methanol as a solvent, and the functional groups generated by the decomposition of the radical generator described above were removed. A carbon black bonded to the surface was obtained.

Then, 5 parts by weight of the carbon black having the functional group bonded to the surface, 19 parts by weight of glycerin, 75 parts by weight of distilled water and 1 part by weight of triethanolamine were used.
These were mixed and stirred at room temperature for 3 hours in a ratio of parts by weight, then the particle size was adjusted with a homogenizer, and the mixture was filtered through a 10 μm membrane filter to prepare an ink.

Example 2 In this example, the same furnace black as that in Example 1 was used as carbon black.

On the other hand, in obtaining the radical generator, tetramethylene diamine (manufactured by Wako Pure Chemical Industries, Ltd.) was used in place of the polyethylene glycol used in Example 1 above. In the same manner as in Example 1, a polymer containing an azo group was obtained.

Using the radical generator composed of a polymer containing an azo group obtained in this manner, the functional group resulting from the decomposition of the radical generator is bonded to the surface in the same manner as in Example 1 above. Ink was prepared in the same manner as in Example 1 above, using the carbon black having the functional groups bonded to the surface thereof.

Example 3 In this example, the same furnace black as in Example 1 was used as carbon black.

On the other hand, in obtaining the radical generator, tetramethylene diamide was used in place of the polyethylene glycol used in Example 1 described above, and the other conditions were the same as in Example 1 described above. A polymer containing an azo group was obtained.

Using the radical generator made of the polymer containing an azo group thus obtained, the functional groups resulting from the decomposition of the radical generator are bonded to the surface in the same manner as in Example 1 described above. Ink was prepared in the same manner as in Example 1 above, using the carbon black having the functional groups bonded to the surface thereof.

Example 4 In this example, the same furnace black as in Example 1 was used as carbon black.

On the other hand, in obtaining the radical generator, pentaethylenehexamine (manufactured by Wako Pure Chemical Industries, Ltd.) was used in place of the polyethylene glycol used in Example 1 above. In the same manner as in Example 1, a polymer containing an azo group was obtained.

Using the radical generator composed of the polymer containing an azo group thus obtained, the functional group resulting from the decomposition of the radical generator is bonded to the surface in the same manner as in Example 1 described above. Ink was prepared in the same manner as in Example 1 above, using the carbon black having the functional groups bonded to the surface thereof.

Example 5 In this example, the same furnace black as in Example 1 was used as carbon black.

On the other hand, in obtaining the radical generator, pentaerythritol (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of the polyethylene glycol used in Example 1 above.
In the other cases, a polymer containing an azo group was obtained in the same manner as in Example 1 above.

Then, using the radical generator made of the polymer containing an azo group thus obtained, the functional groups resulting from the decomposition of the radical generator are bonded to the surface in the same manner as in Example 1 described above. Ink was prepared in the same manner as in Example 1 above, using the carbon black having the functional groups bonded to the surface thereof.

(Example 6) In this example, the functional groups resulting from the decomposition of the radical generator composed of the azo group-containing polymer were added to the surface of the carbon black in the same manner as in Example 1 described above. Was bound.

Thereafter, 4,4′-azobis-4-cyanopentanoic acid shown in the following chemical formula 5 was used as a radical generator, and the decomposition of the radical generator was carried out in the same manner as in Example 1 above. Was attached to the surface of the carbon black.

[0057]

Embedded image

Then, an ink was prepared in the same manner as in Example 1 above, using carbon black having a functional group of two kinds of radical generators bonded to the surface as described above.

(Comparative Example 1) In this comparative example, the same furnace black as that of the above-described Example 1 (Cagal, Realgal 250) was used as carbon black.
Using R), the carbon black was used as it was without bonding a functional group to the surface of the carbon black.

Then, 5 parts by weight of this carbon black, 19 parts by weight of glycerin, 75 parts by weight of distilled water, and 1 part by weight of triethanolamine were used, and ink was prepared in the same manner as in Example 1 above. Prepared.

(Comparative Example 2) In this comparative example, the same furnace black as that of the above-mentioned Example 1 was used as carbon black, and the carbon black was irradiated with ultraviolet rays to surface-treat the surface of the carbon black. After that, the carbon black thus surface-treated is
5 parts by weight, 8 parts by weight of acrylamide and 73 parts by weight of distilled water were mixed, and the mixture was stirred at 65 ° C. while blowing nitrogen gas into the solution to carry out polymerization for 1 hour.

Thereafter, the homopolymer was sufficiently removed by centrifugal separation, washed with hot water, and dried to obtain carbon black having acrylamide graft-polymerized on the surface.

Then, 3 parts by weight of the carbon black thus surface-treated, 10 parts by weight of glycerin, 1-
An ink was prepared in the same manner as in Example 1 above, using 4 parts by weight of propanol and 83 parts by weight of distilled water.

Next, the above Examples 1 to 6 and Comparative Examples 1 and 2
The dispersion stability, storage stability, temperature change stability, print quality, density unevenness, and ejection stability of each of the carbon black and recording ink prepared in 2 were evaluated. The results are shown in Table 1 below. Was.

Here, the dispersion stability was determined in Example 1.
10% by weight of each of the carbon blacks prepared in Comparative Examples 1 to 6 and Comparative Examples 1 and 2 was placed in a 10 ml centrifugal sedimentation tube, and a commercially available centrifuge (BE) was used.
CKMAN: Avanti J25)
After centrifugation at 000 rpm for 1 hour, the absorbance of the supernatant at 600 nm was measured, and the concentration of carbon black in the supernatant was determined based on a previously determined calibration curve. %, At least 0.05 wt.% And less than 0.01 wt.%, And at least 0.005 wt.%, X.

The storage stability was evaluated in Examples 1 to 5.
6 and each of the carbon blacks prepared in Comparative Examples 1 and 2 were dispersed in a 10% by weight aqueous solution.
0 ml of the centrifugal sedimentation tube, and the centrifugal sedimentation tube was allowed to stand at a temperature of 40 ° C. for 3 months.
and centrifuged in a centrifugal sedimentation tube to determine the concentration of carbon black in the supernatant. The concentration was 0.01% by weight or more. Is less than 0.005% by weight, and x is less than 0.005% by weight.

Regarding the temperature change stability, a 10% by weight aqueous dispersion of each of the carbon blacks prepared in Examples 1 to 6 and Comparative Examples 1 and 2 was placed in a 10 ml sample tube. -1 sample tube
After leaving for 1 hour at a temperature of 0 ° C., immediately leaving for 1 hour at a temperature of 50 ° C.
The cycle was repeated 5 times a day, and after such operation was continued for 3 days, the shear rate was compared before and after the test, and the presence or absence of the thixotropic property of the ink and the stability of the physical properties were confirmed. The sex was examined, and the case where there was no change even after the test was indicated by ○, and the case where there was a change was indicated by ×.

Regarding the print quality, Examples 1-6
And a width of 3 on plain paper using each ink of Comparative Examples 1 and 2.
A straight line of dots is printed, and TEP (Tentential Edge Prof) indicating the rattling degree in the straight line is displayed.
ile) was examined using a dot analyzer DA-5000S (manufactured by Oji Scientific Instruments), and the results were indicated by ○ when TEP was less than 60 μm, and by X when TEP was 60 μm or more.
Note that TEP indicates the backlash of a straight line as the amount of displacement from the originally expected straight line, and indicates the standard deviation value.

Further, regarding the density unevenness, Examples 1 to 6
Printing was performed on plain paper using the inks of Comparative Examples 1 and 2, and the image density (ID) of the solid printed portion was measured with a Sakura densitometer PDA65 (manufactured by Konica Corporation), and the image density of the printed portion was measured. Were determined, and the case where the density difference was less than 0.15 was indicated by ○, and the case where it was 0.15 or more was indicated by ×.

Regarding the ejection stability of the ink, the printing was performed continuously for 10 hours using each of the inks of Examples 1 to 6 and Comparative Examples 1 and 2, and then the power of the ink recording apparatus was turned off. After leaving it for 14 hours and setting this as one cycle, after repeating five cycles, a straight line having a line width of 150 μm was printed, and the image density on this straight line was measured using a microdensitometer (PDM5, manufactured by Konica Corporation). ,
A point where the image density is less than 0.3 is defined as a missing portion of the ink ejection, and the distance of the missing portion is checked.
When the distance is less than 10 μm, the result is indicated by x.

[0071]

[Table 1]

As is clear from the results, Examples 1 to
As shown in FIG. 6, when the functional group generated by the decomposition of the radical generator composed of an azo group-containing polymer is bonded to the surface of carbon black, the dispersion stability, storage stability, and temperature of this carbon black in an aqueous medium can be improved. The change stability was improved as compared with the carbon blacks in Comparative Examples 1 and 2 described above.

When each of the inks of Examples 1 to 6 using carbon black as described above was used in an ink recording apparatus, compared with the case of using the inks of Comparative Examples 1 and 2,
The clogging of the nozzles of the ink recording apparatus with the ink is suppressed, the ink is stably ejected, the printing quality is excellent, and good recording with little density unevenness can be performed.

[0074]

As described above in detail, in the recording ink of the present invention, a polymer containing an azo group is used as a radical generator, and the functional group generated by the decomposition of the polymer containing the azo group is chemically applied to the surface. Since the combined carbon black is used as a coloring material, when the coloring material is dispersed in an aqueous medium, the coloring material is stably dispersed in the aqueous medium, and the carbon blacks are mutually dispersed in the ink. Aggregation was suppressed, and the storage characteristics of the recording ink were improved.

Further, when the recording ink of the present invention is used in an ink recording device such as an ink jet printer, the recording ink is prevented from being clogged in the nozzles of the ink recording device, and the ink is stably ejected. As a result, a good image with less disturbance of the image, density unevenness and the like can be stably obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Miwa Saito, Inventor Minamita 2-chome, 3-chome, Azuchicho, Chuo-ku, Osaka (72) Inventor Takamasa Ueda 2-3-3, Azuchicho, Chuo-ku, Osaka-shi No. 13 Osaka International Building Minolta Co., Ltd.

Claims (2)

[Claims] In a recording ink in which a coloring material made of carbon black is dispersed in an aqueous medium, a functional group generated by decomposition of a radical generator made of a polymer containing an azo group is used as the coloring material. A recording ink characterized in that carbon black chemically bonded to the above is used. 2. The recording ink according to claim 1, wherein the radical generator comprises a polymer containing an azo group represented by the following structural formula (1). Embedded image R ₁ and R ₂ in the structural formula (1) are selected from an alkylene group and a group having a substituent bonded thereto.
R ₁ and R ₂ may be the same or different groups, and A is a group having NH or O at both ends.