JP2005239511A - Composite black oxide particle, its manufacturing method, black paint, and black matrix - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite black oxide particle excellent not only in the thermal degradation suppression for blackness and hue but also in the surface smoothness when the coating film is formed, its manufacturing method, a black paint, and a black matrix. <P>SOLUTION: The composite black oxide particle is composed of oxides of cobalt, copper, manganese, and silicon, where the copper/cobalt molar ratio is 0.1-0.5, the manganese/cobalt molar ratio is 0.2-1.0, and the silicon content to the total oxide particles is 0.1-3 mass%. In the method of manufacturing the composite black oxide particle, an aqueous solution of metal salts prepared from water-soluble salts of cobalt, copper, and manganese and an alkali hydroxide are mixed and neutralized and the obtained metal hydroxide slurry is oxidized while keeping its pH at 10-13. The obtained precursor slurry is subjected to solid-liquid separation and heat-treated at 400-700°C, where an aqueous solution of a water-soluble silicon salt is added to the water-soluble salt of cobalt, copper, and manganese or an aqueous solution of a water-soluble silicon salt is added before the solid-liquid separation and its pH is controlled at 6-10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to composite black oxide particles, a production method thereof, a black pigment, and a black matrix, and more specifically, composite black oxide particles composed of oxides of cobalt, copper, manganese, and silicon, for paints, for inks, Suitable for black pigments for toners, rubbers and plastics, especially for black matrix coloring compositions, plasma displays, black electrodes on front plates of plasma addressed liquid crystals, etc. The present invention relates to composite black oxide particles excellent in, a method for producing the same, a black pigment, and a black matrix.

  Black pigments used in paints, inks, toners, rubbers and plastics, etc. are required to be excellent in properties such as blackness, hue, coloring power, hiding power, etc. and inexpensive. Carbon black Iron oxide pigments such as magnetite and other complex oxide pigments are used depending on the application.

  In recent years, in addition to the demand for higher performance and higher quality in any of the above fields, for example, black pigments mainly composed of metal oxides are not only excellent in blackness but also black matrix. Suppression of heat resistance deterioration of hue required at the time of firing at the time of formation, dispersibility in a vehicle required when making a paint using a resin, a solvent, etc., a coating film when the paint is made into a coating film What is excellent in surface smoothness etc. is calculated | required.

  Representative examples of such black pigments mainly composed of metal oxides include single-component metal oxide particles such as cobalt oxide, manganese oxide, and copper oxide, Cu—Cr, Cu—Mn, and Cu—Cr. -Mn-based, Cu-Fe-Mn-based, Co-Mn-Fe-based, Co-Fe-Cr-based composite oxide particles, and the like.

JP-A-9-237570 Japanese Patent Laid-Open No. 10-231441

  In the metal oxide particles having a single composition, those having a large particle diameter have high blackness, but when they become submicron level particles, they are brown, or such particles are difficult to produce. To do.

Moreover, composite oxide particles also have advantages and disadvantages in terms of performance required for black pigments.
First, in the case of containing chromium as a component, such as Cu—Cr and Cu—Cr—Mn, it is difficult to produce particles of submicron level in addition to the problem of toxicity of chromium.

  In addition, in the case of the Cu—Mn system as disclosed in Patent Document 1, it is easy to make particles fine, but the shape is likely to be indefinite, the particles are likely to aggregate, and the dispersibility and coating when formed into a paint are also easily observed. The smoothness of the film is poor.

Also, in the case of the Cu—Fe—Mn system as disclosed in Patent Document 1, the blackness is high, the shape is uniform, and the dispersibility is excellent, or Co as disclosed in Patent Document 2 is used. In the case of the -Mn-Fe system, the shape is uniform and the dispersibility is excellent. However, due to the fact that both contain iron (the blackness depends on Fe ²⁺ but easily deteriorates with time), the weather resistance is inferior, and the heat resistance deterioration of the hue is also inferior. It is said.

  As described above, as a black pigment mainly composed of a metal oxide, not only is it excellent in terms of suppressing blackness and heat resistance deterioration of hue, but also a material excellent in surface smoothness of a coating film especially when it is made into a paint. In fact, no satisfactory material has yet been found.

  Therefore, the object of the present invention is mainly suitable for black pigments for paints, inks, toners, rubbers and plastics, and particularly for black matrix coloring compositions, plasma displays, plasma address liquid crystal and other front plates. Black oxide, suitable for forming a light shielding layer, not only excellent in terms of suppressing heat resistance deterioration of blackness and hue, but also composite black oxide particles excellent in surface smoothness of the coating film when made into a paint, and It is in providing the manufacturing method.

  As a result of intensive studies on materials mainly composed of various metal oxides, the present inventors have found that specific Co—Cu—Mn—Si based composite oxide particles can solve the above problems, and have completed the present invention. It was.

  That is, the composite black oxide particles of the present invention are made of oxides of cobalt, copper, manganese and silicon, the copper / cobalt molar ratio is 0.1 to 0.5, and the manganese / cobalt molar ratio is 0. 0.2 to 1.0, and silicon is contained in an amount of 0.1 to 3% by mass based on the whole oxide particles.

  In addition, the method for producing composite black oxide particles of the present invention is obtained by neutralizing and mixing a metal salt mixed aqueous solution prepared using a water-soluble salt of cobalt, copper, and manganese, and an alkali hydroxide. The hydroxide slurry was oxidized while maintaining the pH at 10 to 13, and an aqueous solution of water-soluble silicate was added to the obtained precursor slurry to adjust to pH 6 to 10, and after solid-liquid separation, the temperature was 400 to 700 ° C. It is characterized by heat-treating.

  Furthermore, the method for producing composite black oxide particles of the present invention comprises neutralizing a metal salt mixed aqueous solution prepared using an aqueous solution of cobalt, copper, manganese water-soluble salt and water-soluble silicate, and alkali hydroxide. The mixture is oxidized while maintaining the obtained metal hydroxide slurry at pH 10 to 13, and the obtained precursor slurry is subjected to heat treatment at a temperature of 400 to 700 ° C. after solid-liquid separation.

  The black composite oxide particles according to the present invention are not only excellent in terms of blackness and hue heat resistance deterioration suppression, but also particularly excellent in surface smoothness of the coating film when formed into a coating material. It is suitable as a black pigment for inks, inks, toners, rubbers and plastics. Particularly, it is suitable for forming a black matrix coloring composition, a plasma display, a black electrode on a front plate such as a plasma address liquid crystal, and a light shielding layer. In addition, the black matrix, plasma display, and plasma addressed liquid crystal formed with black paint using such black composite oxide particles have excellent blackness, hue and heat resistance, and uniformity and gloss of the fired coating. It is.

Embodiments of the present invention will be described below.
The composite black oxide particles of the present invention comprise oxides of cobalt, copper, manganese and silicon, the copper / cobalt molar ratio is 0.1 to 0.5, and the manganese / cobalt molar ratio is 0.2. ˜1.0, and 0.1 to 3% by mass of silicon with respect to the whole oxide particles.

In examining the composite black oxide particles of the present invention, according to the present inventors producing composite black oxide particles of various systems (compositions), many of them exhibit a plate-like or irregular shape. We know that things can be obtained. For example, plate-like particles can be easily obtained in Co-Mn, Co-Cu, Co-Mn-Fe, etc., and in Mn-Cu, Mn-Cu-Ni, Co-Fe-Cr, etc. Is easy to obtain irregularly shaped particles. When the shape of the particles is plate-like, the shape may be uniform to some extent, but the dispersibility when made into a paint is granular, especially compared to Co-Cu-Mn-based particles exhibiting a spherical or pseudo-spherical shape, It was much inferior.
In addition, it has been found that the particles having an irregular shape are inferior in the surface smoothness of the coating film when the coating is formed, as well as the dispersibility when the coating is formed. .

  Therefore, the present inventors first proceeded with studies on the shape of the composite black oxide particles that are granular, particularly spherical or pseudo-spherical, and this has been achieved in the Cu—Fe—Mn system and the Co—Cu—Mn system. I found out. However, in the Cu-Fe-Mn system, not only the dispersibility when made into a paint and the surface smoothness of the paint film when the paint is made into a coating film, but also the blackness is excellent, It is inferior in terms of heat resistance, and is subject to discoloration and fading.

  For this reason, it has been found that a Co—Cu—Mn-based material is preferable. However, even this composition does not satisfy all the problems required by the present invention. Here, the present inventors have paid attention to the ratios of these components, and have found that the surface smoothness of the coating film when made into a paint is improved by further containing silicon.

  First, it is important that the copper / cobalt molar ratio in the present invention is 0.1 to 0.5. When this molar ratio is less than 0.1, the resulting particles are easily coarsened and have poor colorability when formed into a paint. When this molar ratio exceeds 0.5, amorphous particles are likely to be generated, and the dispersibility and blackness when formed into a paint are inferior.

  In the present invention, it is important that the manganese / cobalt molar ratio is 0.2 to 1.0. When this molar ratio is less than 0.2, the resulting particles are likely to be indeterminate such as a plate shape, the dispersibility when formed into a paint is poor, and the colorability of the coating film is also poor. In addition, even when the molar ratio exceeds 1.0, the obtained particles tend to be indeterminate such as a plate shape. Moreover, it tends to be finer and the redness of the particles becomes stronger.

Moreover, silicon should just exist in either the inside of a particle | grain, or a particle | grain surface, and it is important that content of silicon is 0.1-3.0 mass% with respect to an oxide particle. If the amount is less than 0.1% by mass, the effect of improving the surface smoothness when the coating film is formed is poor. If the amount exceeds 3.0% by mass, the specific surface area is increased, and the coating film has been converted into a paint. The surface smoothness is lowered, and the blackness and hue are also deteriorated.
Incidentally, the composite black oxide particles of the present invention often take a spinel type or an inverse spinel type as a crystal structure, and are preferable in terms of blackness and hue as compared with other forms.

  The composite black oxide particles of the present invention preferably have an average particle size of 0.05 to 0.15 μm. Such fine composite black oxide particles are excellent in the surface smoothness of the coating film when made into a paint, and the glossiness of the coating film becomes high.

  Further, the composite black oxide particles of the present invention have a variation coefficient of 40% or less obtained by (standard deviation of ferret diameter by SEM photograph) / (average particle diameter of ferret diameter by SEM photograph) × 100 (%). It is preferable. When this coefficient of variation exceeds 40%, the particle size distribution of the particles is too wide, and there are too many aggregated particles or too many coarse particles, resulting in poor dispersibility and smoothness of the coating film. .

The composite black oxide particles of the present invention preferably have a specific surface area by BET of 10 to 40 m ² / g. Here, when the specific surface area by BET is less than 10 m ² / g, the particles themselves are too large, and there is a possibility that the colorability when formed into a paint may be poor, and when it exceeds 40 m ² / g, it is converted into a paint. In addition to being inferior in surface smoothness of the coating film when made into a paint, the particles may be too fine and the blackness may be lowered.

  Further, the composite black oxide particles of the present invention preferably have a reflectance (20 degrees) measured by a color difference meter of 40% or more, and more preferably 60% or more. When this reflectance is less than 40%, the glossiness of the coating film when in paint is inferior.

  Further, the composite black oxide particles of the present invention have an L value of 20 or less, an a value of 0.1 or less, and a b value of 0 in a color difference meter according to JIS K5101-1991. .1 or less is preferable. When these numerical values do not satisfy the above conditions, the blackness is low, the hue is strong reddish or yellowish, which is a problem as a black pigment.

Further, the composite black oxide particles of the present invention can be obtained by (ΔL ² + Δa ² + Δb ² ) ^1/2 from the blackness and hue values of samples before and after heat treatment at 180 ° C. for 2 hours in air. The ΔE value is preferably 0.5 or less. When this ΔE exceeds 0.5, the blackness and the heat resistance deterioration property of the hue are inferior.

Next, a preferred method for producing the composite black oxide particles of the present invention will be described.
The method for producing black composite oxide particles according to the present invention is obtained by neutralizing and mixing a metal salt mixed aqueous solution prepared using a water-soluble salt of cobalt, copper, and manganese, and an alkali hydroxide, and the resulting metal hydroxide The product slurry was oxidized while maintaining the pH at 10 to 13, and an aqueous solution of water-soluble silicate was added to the obtained precursor slurry to adjust to pH 6 to 10, and after solid-liquid separation, the temperature was 400 to 700 ° C., 1 Metal salt mixed aqueous solution prepared with water-soluble salt of cobalt, copper and manganese containing aqueous solution of water-soluble silicate for more than 3 hours or less and neutralized with alkali hydroxide The mixture is oxidized while maintaining the obtained metal hydroxide slurry at a pH of 10 to 13, and the precursor slurry obtained is subjected to heat treatment at a temperature of 400 to 700 ° C. after solid-liquid separation. .

  In the present invention, the composition ratio of cobalt, copper, and manganese is important when preparing a mixed aqueous solution using water-soluble salts of cobalt, copper, and manganese. In order to dissolve the metal salt used in the aqueous solution, the temperature of the aqueous solution is preferably 30 to 60 ° C.

  If this temperature is less than 30 ° C., there is a high possibility that undissolved metal salt remains in the aqueous solution, and when mixed with alkali hydroxide to form a composite hydroxide, a hydroxide having a non-uniform composition May be formed. Further, when the temperature exceeds 60 ° C., the size of the nuclei tends to be non-uniform, and the size of the finally obtained composite oxide particles is assumed to vary.

  The metal salts of cobalt, copper, and manganese used for the preparation of the aqueous solution are not particularly limited as long as they are water-soluble, such as sulfates, nitrates, carbonates, chlorides, etc. Use the right one. The metal ion concentration in the aqueous solution may be adjusted to about 0.5 to 2.0 mol / L in terms of total ion concentration in consideration of productivity and the like.

  An aqueous solution composed of water-soluble salts of cobalt, copper and manganese thus obtained and an alkali hydroxide are mixed to produce a hydroxide slurry of a mixture of cobalt, copper and manganese.

  The alkali hydroxide used for this neutralization is preferably a caustic alkali such as sodium hydroxide or potassium hydroxide. Moreover, about the neutralization mixing, any mixing mode may be used, but it is preferable to add alkali hydroxide to the water-soluble salt aqueous solution of cobalt, copper, and manganese, and if the addition is performed during 60 to 120 minutes, This is more preferable because hydroxide core particles having a uniform composition can be obtained. If the addition time is shorter than 60 minutes, a non-uniform composition of hydroxide is formed or amorphous particles are likely to be generated, and if it exceeds 120 minutes, a uniform composition of hydroxide is formed. The growth of nuclei also proceeds, and irregularly shaped particles tend to be generated.

The obtained hydroxide slurry is adjusted in a pH range of 10 to 13, and an appropriate oxidizing agent (hydrogen peroxide or the like) is added and an oxygen-containing gas, preferably air is blown into the black composite oxide particles in the slurry. Is generated.
When the pH during the reaction is less than 10, the particle growth is difficult to proceed and the particles are easily atomized. Moreover, when pH exceeds 13, a particle | grain tends to become an indefinite shape.
In this case, the reaction temperature is preferably more than 40 ° C. and 60 ° C. or less. If this temperature is 40 ° C. or lower, the particles may be atomized and the blackness may be lowered. When the temperature exceeds 60 ° C., irregularly shaped particles are likely to be generated frequently.

  The oxidation reaction is continued until the redox potential in the slurry reaches equilibrium. An aqueous solution of a water-soluble silicate may be added to the obtained precursor slurry, but before that, the precursor slurry is heated to 80 to 150 ° C. and then stirred at 80 to 100 ° C. for 1 to 6 hours. Alternatively, the black composite oxide particles in the slurry may be aged by treating at 100 to 150 ° C. using an autoclave or the like.

  This aging is preferable because the reaction can proceed to form granular particles. If the treatment temperature at this time is less than 80 ° C. (100 ° C. when using an autoclave), the reaction does not proceed so easily that granular particles cannot be formed, and amorphous particles tend to be generated. When the temperature exceeds 100 ° C. (150 ° C. when using an autoclave), the particle size distribution of the particles obtained due to the high reaction rate becomes wide, which is not preferable.

The precursor slurry obtained above is stirred and mixed while adjusting the pH to 6 to 10 by adding an aqueous solution of water-soluble silicate. When the pH during this addition is less than 6 or exceeds pH 10, film formation is unlikely to proceed on the particle surface.
Moreover, in this addition, it is preferable to add over 30 to 120 minutes and to stir and mix over 30 to 120 minutes after the addition.

  The precursor slurry thus obtained is subjected to conventional filtration (solid-liquid separation), washing, dehydration, drying at 50 to 120 ° C., and then pulverized. Heat treatment at 700 ° C. to stabilize the morphology. The treatment time for this heat treatment is preferably more than 1 hour and 3 hours or less. If the heat treatment time is 1 hour or less, the form of the oxide is not stable, and the hue may be deteriorated. On the other hand, if it exceeds 3 hours, the coloring power may be reduced due to the effect of inter-particle sintering. Since the black composite iron oxide particles after the heat treatment may be partially aggregated, a conventional crushing treatment may be added.

  If the temperature during the heat treatment is less than 400 ° C., the form of the oxide is not stable, and the stability of various properties may be lacking. Moreover, when it exceeds 700 degreeC, there exists a possibility that blackness and a hue may become bad by an excessive heat load. Note that the atmosphere during the heat treatment may be in the air or in an inert gas atmosphere.

  By the way, in the above method for producing composite black oxide particles, instead of adding an aqueous solution of a water-soluble silicon salt before solid-liquid separation of the precursor slurry, it is added to the original water-soluble salt of cobalt, copper, and manganese. By doing so, the composite black oxide particles of the present invention can be produced.

  If the composite black oxide particles of the present invention are used as a black pigment, and the black matrix, plasma display, or plasma address liquid crystal obtained by using the black pigment, the surface of heat resistance deterioration of blackness and hue is suppressed. In addition, it is excellent in surface smoothness of the coating film when it is made into a paint.

  Hereinafter, the present invention will be specifically described with reference to examples and the like.

[Example 1]
830 g of cobalt sulfate heptahydrate, 224 g of copper sulfate pentahydrate and 324 g of manganese sulfate pentahydrate are introduced into 6 liters of water at a temperature of 45 ° C. and dissolved by stirring. Next, 1 mol / L aqueous solution of caustic soda is added to this mixed aqueous solution. 7.1 liters was added over about 90 minutes, and the resulting hydroxide slurry was adjusted to a pH of 12. The liquid temperature after completion of the addition was 50 ° C.
30 minutes after the adjustment was completed, air was blown in at a rate of 3 liters / minute for about 2 hours while maintaining the liquid temperature at 50 ° C.
Thereafter, stirring of the reaction solution was continued, the temperature was raised to 85 ° C. in about 60 minutes, and then held for 1 hour.
After holding for 1 hour, 1.6 liters of a 0.1 mol / L sodium silicate aqueous solution was added to the resulting composite iron oxide particle slurry over 60 minutes, adjusted to pH 7 using dilute sulfuric acid, and stirred and mixed for 60 minutes. . Then, it filtered and wash | cleaned, and dried the washing | cleaning cake at 80 degreeC for 10 hours. The dried product is pulverized and fired in the air at 600 ° C. for 2 hours to obtain a particle size of 0.07 μm,
Composite iron oxide particles having a BET of 27 m ² / g were obtained.
About the obtained complex oxide particle, various characteristics were evaluated with the evaluation method shown below. The results are shown in Tables 2 and 3.

<Evaluation method>
(A) Co, Cu, Mn, and Si contents: Samples were dissolved and measured by ICP.
(B) Average particle diameter, (c) A 100,000 times photograph was taken with an SEM (scanning electron microscope), and the ferret diameter of 200 particles was measured. (d) Specific surface area: Measured with a 2200 type BET meter manufactured by Shimadzu-Micromeritics. (e) Blackness and hue: The blackness of the powder was measured according to JIS K5101-1991. Add 1.4 cc of castor oil to 2.0 g of sample and knead with Hoover type Mahler. 7.5 g of lacquer is added to 2.0 g of this kneaded sample, and after further kneading, this is applied onto a mirror coated paper using a 4 mil applicator, dried, and then a color difference meter (manufactured by Tokyo Denshoku Co., Ltd., Color Analyzer). Blackness (L value) and hue (a value, b value) were measured with TC-1800 type. (F) Heat resistance test; put the sample in a watch glass, and dry it at 180 ° C. for 2 hours in a ventilated dryer (Oven PH-201 made by Tabai Espec), in the same manner as (e), Blackness and hue were measured. (G) Specular reflectance (glossiness associated with surface smoothness of coating film); 60 g of a solution obtained by dissolving styrene acrylic resin (TB-1000F) in (resin: toluene = 1: 2), sample after heat treatment 10 g of glass beads having a diameter of 1 mm and 90 g were placed in a bottle having an internal volume of 140 ml, capped, and then mixed for 30 minutes with a paint shaker (manufactured by Toyo Seiki Co., Ltd.). This was applied onto a glass plate using a 4 mil applicator, dried, and then measured for blackness with a color difference meter and a reflectance of 20 degrees with a murasumi-type GLOSS METER (GM-3M).

[Example 2]
830 g of cobalt sulfate heptahydrate, 224 g of copper sulfate pentahydrate and 324 g of manganese sulfate pentahydrate are poured into 6 liters of water at a temperature of 45 ° C. and dissolved by stirring. Next, 0.1 mol / L sodium silicate 1 .6 liters was added. To this mixed aqueous solution, 7.1 liters of a 1 mol / L aqueous solution of caustic soda was added over about 90 minutes, and the pH of the resulting hydroxide slurry was adjusted to 12. The liquid temperature after completion of the addition was 50 ° C.
30 minutes after the adjustment was completed, air was blown in at a rate of 3 L / min for about 2 hours while maintaining the liquid temperature at 50 ° C.
Thereafter, stirring of the reaction solution was continued, the temperature was raised to 85 ° C. in about 60 minutes, and then held for 1 hour.
After holding for 1 hour, the produced composite iron oxide particle slurry was filtered and washed, and the washed cake was dried at 80 ° C. for 10 hours. The dried product was pulverized and calcined at 600 ° C. for 2 hours in the air to obtain composite iron oxide particles having a particle size of 0.07 μm and BET of 26 m ² / g.
Various characteristics of the obtained composite oxide particles were evaluated in the same manner as in Example 1. The results are shown in Tables 2 and 3.

[Comparative Examples 1-3]
As shown in Table 1, composite oxide particles were obtained in the same manner as in Example 1 except that each production condition was changed.
Various characteristics of the obtained composite oxide particles were evaluated in the same manner as in Example 1. The results are shown in Tables 2 and 3.

  As is clear from Table 3, the black composite oxide particles of the examples are excellent in blackness and hue (including heat resistance), and particularly excellent in surface smoothness when a paint is formed into a coating film.

  Compared to this, the composite iron oxide particles of Comparative Example 1 do not contain silicon, so the blackness and hue (including heat resistance) are the same as in the Examples, but when the paint was turned into a coating film The surface smoothness of is poor.

  Further, the composite iron oxide particles of Comparative Example 2 contained excessive silicon, resulting in an increase in specific surface area and a decrease in blackness and hue. Further, the surface smoothness when the paint is formed into a coating film is also inferior.

Further, the composite iron oxide particles of Comparative Example 3 are not so much improved in surface smoothness when the paint is formed into a coating film due to the lack of silicon.

Claims (8)

It consists of oxides of cobalt, copper, manganese and silicon, the copper / cobalt molar ratio is 0.1-0.5, the manganese / cobalt molar ratio is 0.2-1.0, and silicon Composite black oxide particles characterized by containing 0.1 to 3% by mass with respect to the whole oxide particles. 2. The composite black pigment according to claim 1, wherein the primary average particle diameter is 0.05 to 0.15 μm, and the coefficient of variation CV of the following formula (1) in the particle size distribution by SEM observation is 40% or less. particle.
CV value (%) = (standard deviation of particle diameter by SEM observation (μm)) / (number average particle diameter by SEM observation (μm)) × 100 (1) The composite black oxide particles according to claim 1 or 2, wherein the specific surface area by BET is 10 to 40 m ² / g. The composite black oxide particles according to claim 1, wherein a reflectance (20 degrees) by a color difference meter is 40% or more. The black coating material containing the composite black oxide particle in any one of Claims 1-4. A black matrix formed by the black paint according to claim 5. A metal salt mixed aqueous solution prepared using water-soluble salts of cobalt, copper and manganese and an alkali hydroxide are neutralized and mixed, and the obtained metal hydroxide slurry is oxidized while maintaining the pH at 10 to 13, Production of composite black oxide particles characterized in that an aqueous solution of water-soluble silicate is added to the obtained precursor slurry to adjust to pH 6 to 10, and after solid-liquid separation, heat treatment is performed at a temperature of 400 to 700 ° C. Method. A metal salt mixed aqueous solution prepared using an aqueous solution of a water-soluble salt of cobalt, copper, manganese and a water-soluble silicate and an alkali hydroxide were neutralized and mixed, and the resulting metal hydroxide slurry was adjusted to pH 10-13. A method for producing composite black oxide particles, wherein the precursor slurry obtained is oxidized while being maintained at a temperature and subjected to heat treatment at a temperature of 400 to 700 ° C. after solid-liquid separation.