JP2007302798A - Cobalt-containing black pigment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cobalt-containing black pigment which essentially has a black degree and high electric resistance as black pigment powder for forming light-shielding layers and black electrodes for plasma displays, plasma address liquid crystals, and the like, has a small average primary particle diameter and a small coagulated particle diameter, and is excellent in initial dispersibility. <P>SOLUTION: This cobalt-containing black pigment is characterized in that an average primary particle diameter is 0.03 to 0.5 μm, and D<SB>50</SB>by the measurement of particle sizes based on the number of particles by a laser diffraction scattering method is 0.05 to 1.5 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a cobalt-containing black pigment, and more specifically, a primary particle size, a small aggregate particle size, and an excellent initial dispersibility, particularly a black matrix coloring composition, a plasma display, a plasma address liquid crystal, and the like The present invention relates to a cobalt-containing black pigment having excellent blackness and high electrical resistance used for forming a black electrode, a light shielding layer, and the like, and a method for producing the same.

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.

Typical examples of black pigments mainly composed of metal oxides include single-component metal oxide particles such as manganese oxide and copper oxide, and composite oxide particles of these metal elements.

  Furthermore, in the formation of black matrix on array type high light-shielding films such as plasma displays and plasma addressed liquid crystals, high electrical resistance is required to prevent conduction between electrodes, and black pigments that are inevitably used Needless to say, a high electrical resistance is preferable. However, a black pigment having both blackness and high electrical resistance has not been proposed yet. In addition, in the formation of a light-shielding film, a dense and thin film is required, and accordingly, black pigments are also required to have finer particle sizes, but the disadvantage is that aggregated particles are easily formed as the primary particles of the pigment are atomized. There is. On the other hand, some cobalt oxide particles have been conventionally proposed as battery materials and pigments (Patent Documents 1 and 2).

JP 2002-68750 A JP 2001-354428 A

Patent Document 1 proposes tricobalt tetroxide particles by wet synthesis. However, since it has not undergone the firing step, it may cause a color change under conditions where the crystal is unstable and heated at high temperatures. is there. In addition, since it is synthesized in a wet manner, impurities such as alkali metal salts derived from the reaction liquid are easily taken into the particles. Further, in Patent Document 2, the particle shape is almost spherical, the 50% particle size (D ₅₀ ) is 1.5 μm to 15 μm, D ₉₀ is less than twice D ₅₀ , and D ₁₀ is 1/5 or more of D ₅₀ . , and the and is the specific surface area of cobalt oxide powder, wherein has been proposed to be a 2m 2 ^/ g~15m 2 ^{/ g,} a large degree of aggregation of the particles, but advanced in miniaturization light-shielding film formed applications Even if it is used, it is difficult to obtain satisfactory characteristics.

  Accordingly, an object of the present invention is to provide a cobalt-containing black pigment that can eliminate the various disadvantages of the above-described conventional technology.

  That is, black dispersibility of black electrodes such as plasma displays and plasma addressed liquid crystals, and black pigment powder for forming a light shielding layer, which has both blackness and high electrical resistance, and initial dispersibility due to a small primary particle average diameter and agglomerated particle diameter It is to provide an excellent material.

The present invention is characterized in that the average primary particle diameter is 0.03 μm or more and 0.5 μm or less, and D ₅₀ in particle size measurement based on the number standard by the laser diffraction scattering method is 0.05 μm or more and less than 1.5 μm. The above object is achieved by providing a cobalt-containing black pigment.

  The cobalt-containing black pigment of the present invention has a proportion of divalent cobalt in the total cobalt of 40 to 70%, is excellent in blackness, has high electrical resistance, and has a small average primary particle size and agglomerated particle size. Therefore, it is suitable for applications such as black electrodes such as plasma displays and plasma address liquid crystals, and black pigment powder for forming a light shielding layer.

  Hereinafter, the present invention will be described based on preferred forms thereof.

  The cobalt-containing black pigment referred to in the present invention is a black particle having at least a main component of cobalt, and Si, Al, Mn, Ni, Zn, Cu, Mg, Ti, Zr, W, At least one or more of Mo, P and the like may be selected and contained.

The cobalt-containing black pigment of the present invention has an average primary particle diameter of 0.03 μm or more and 0.5 μm or less, and a D ₅₀ in a particle size measurement based on the number standard by the laser diffraction scattering method is 0.05 μm or more and less than 1.5 μm. It is important to be. When the average primary particle diameter is less than 0.03 μm, not only the color of the pigment becomes reddish but also a problem in dispersibility tends to occur, which is not preferable. On the other hand, when the thickness exceeds 0.5 μm, although the color tone when forming a film and forming a film is sufficient, problems such as insufficient hiding power and coloring power tend to occur. The primary particle average diameter is preferably 0.05 μm or more and 0.35 μm or less, more preferably 0.1 μm or more and 0.25 μm or less, and the hue, coloring power, and hiding power are not coarsened. Is easy to balance. This primary particle average diameter is measured by SEM observation.

Further, the D ₅₀ of the aggregated particles in the particle size measurement based on the number criterion by the laser diffraction scattering method is 0.05 μm or more and less than 1.5 μm. The D ₅₀ is a particle size distribution characteristic value that indicates the degree of aggregation of the particles, only a primary particle size of fine can not be said good pigment powder dispersibility. If this D ₅₀ is less than 0.05 .mu.m, since a level such that finer than the primary particle diameter be 0.03 .mu.m, not color pigments only exhibit redness, preferably it tends to occur a problem in dispersibility Absent. On the other hand, when the thickness exceeds 1.5 μm, the aggregation is too strong, which hinders dispersion at the time of coating, and tends to cause a hiding power and insufficient coloring power. The D ₅₀ is preferably 0.08 μm or more and 1.2 μm or less, more preferably 0.1 μm or more and 1 μm or less, and it is easy to balance the hue, coloring power and hiding power without impairing dispersibility.

In addition, the cobalt-containing black pigment of the present invention preferably has a D _MAX of 3 μm or less based on the number standard by a laser diffraction / scattering particle size distribution measurement method. This D _MAX is a particle size distribution characteristic value indicating the degree of coarse particles in the aggregated particles, and this numerical value affects the coating film characteristics when the pigment is used as a paint. When this D _MAX is more than 3 μm, an appearance defect or the like occurs in the coating film when the pigment is used as a paint due to the influence of coarse particles. When the D _MAX is preferably 2.5 μm or less, more preferably 2 μm or less, the coating film when used as a paint becomes more excellent in smoothness.

In addition, the cobalt-containing black pigment of the present invention preferably has a D ₉₀ of 0.5 μm or more and 2 μm or less based on the number standard by a laser diffraction / scattering particle size distribution measurement method. This D ₉₀ is a particle size distribution characteristic value indicating the degree of aggregation on the larger particle size side in the entire aggregated particle, and the degree of aggregation can be seen by comparing with the D ₅₀ or D ₁₀ value. When the D ₉₀ is less than 0.5 μm, the primary particle diameter becomes a level that becomes finer, so that not only the color of the pigment becomes reddish but also a problem in dispersibility tends to occur. On the other hand, when the thickness exceeds 2 μm, the aggregation is too strong, which may hinder dispersion at the time of forming a paint, and is liable to cause a hiding power or insufficient coloring power. The D ₉₀ is preferably 0.8 μm or more and 1.8 μm or less, more preferably 1 μm or more and 1.6 μm or less, and it is easy to balance the hue, coloring power and hiding power without impairing dispersibility.

The cobalt-containing black pigment of the present invention preferably has a D ₅₀ / primary particle average diameter ratio of 4 or less. The ratio of D ₅₀ / average primary particle diameter is a particle size distribution characteristic value indicating the degree of aggregation as viewed from the primary particle size. The larger this value, the more agglomeration is, and conversely, the theoretical value is less than 1. No (1 is monodisperse). When this numerical value exceeds 4, the aggregation is remarkable, which hinders dispersion at the time of coating, and tends to cause a hiding power and insufficient coloring power.

  Moreover, it is preferable that the shape of the particle | grains contained in the cobalt containing black pigment of this invention is granular. In addition to particles, particles having a shape such as a plate shape or needle shape are not only inferior in dispersibility and fluidity, but in the case of such particles, the particle size in the thickness direction is about several tens of nanometers, and light As a result, there is a bias in the absorption wavelength, and the hue as a black pigment deteriorates, which is insufficient for forming a black electrode such as a plasma display or a plasma addressed liquid crystal in which blackness is important, or a light shielding layer. The term “granular” as used herein means a spherical shape, a polyhedral shape, a spindle shape or the like, and excludes plate-like particles.

Moreover, it is preferable that the ratio of the bivalent cobalt with respect to the total cobalt in particle | grains of the cobalt containing black pigment of this invention is 40 to 70%. The ratio of divalent cobalt in the total cobalt content is a value obtained by multiplying 100 by the value obtained by dividing the divalent cobalt content contained in the entire particle by the total cobalt content contained in the entire particle. Common forms of cobalt oxide include tricobalt tetroxide (Co ₃ O ₄ ) and cobalt oxide (CoO and Co ₂ O ₃ ). Co ₃ O ₄ accounts for 33% of the total cobalt content of divalent cobalt. In addition, all the cobalt in CoO is divalent cobalt, and all the cobalt in Co ₂ O ₃ is trivalent. When the proportion of divalent cobalt in the total cobalt is large with respect to such cobalt oxide, the blackness and high electrical resistance, which are the effects of the present invention, can be further improved. When the proportion of divalent cobalt in the total cobalt is less than 40%, the blackness is insufficient, and when it exceeds 70%, there is a possibility that the pigment exhibits a blue-green color instead of a black pigment. The ratio of divalent cobalt in the total cobalt content is more preferably 40% to 60%.

  The cobalt-containing black pigment of the present invention preferably has a total cobalt content of 60 to 80% by mass relative to the entire particle. When the total cobalt content with respect to the whole particle is less than 60% by mass, the amount of components other than cobalt is excessive, which is not preferable because the effect of the present invention is lowered. On the other hand, if it exceeds 80% by mass, the charge balance between cobalt and oxygen is difficult to be obtained, and it becomes an unstable substance. The total cobalt content with respect to the entire particles is preferably 65% by mass to 75% by mass.

The cobalt-containing black pigment of the present invention preferably has a divalent cobalt content of 25 to 50% by mass with respect to the entire particle. When the divalent cobalt content with respect to the whole particle is less than 25% by mass, the blackness is insufficient, and when it exceeds 50% by mass, the blackness is similarly insufficient, which is not preferable. The divalent cobalt content with respect to the whole particle is more preferably 30% by mass to 45% by mass.

  The cobalt-containing black pigment of the present invention preferably has an alkali metal content in the particles of 100 ppm or less based on the entire particles. In this particle, especially the alkali metal on the particle surface is a high residual impurity in the prior art cobalt-containing black pigment obtained mainly by a wet reaction, but the content is suppressed to 100 ppm or less. When glass frit is used to form black electrodes such as plasma displays and plasma addressed liquid crystal, and light-shielding layers, the decrease in electrical resistance can be suppressed by the fact that few alkali metals behave ionically in glass. I can do it.

  In addition, the cobalt-containing black pigment of the present invention preferably has an L value of 38 or less and a b value of 0 or less when evaluating the coloring power. The coloring property is evaluated by adding 1.3 cc of castor oil to 0.5 g of black particles and 1.5 g of titanium oxide (R800 manufactured by Ishihara Sangyo Co., Ltd.), and kneading with a Hoover type Mahler. After adding 4.5 g of lacquer to 2.0 g of this kneaded sample and further kneading, this is applied onto a mirror-coated paper using a 4 mil applicator, dried, and then a color difference meter (Color by Tokyo Denshoku Co., Ltd.). It is obtained by measuring blackness (L value) and hue (a value, b value) with an analyzer TC-1800 type. When the L value is higher than 37, it cannot be said that sufficient colorability is obtained, and when the b value is higher than 0, the hue is yellow, which is not preferable. More preferably, the L value is 36 or less, and the b value is -0.5 or less.

  The cobalt-containing black pigment of the present invention has sufficient heat resistance during film formation. Specifically, the change in blackness (delta E) at around 600 ° C. for 1 hr is within 1.0. preferable.

  The cobalt-containing black pigment of the present invention preferably has a specular reflectance of 70% or more at a 20 ° incident angle when it is made into a paint. When the specular reflectance is less than 70%, the primary particles in the pigment are agglomerated so that the dispersion at the time of coating is hindered, and the formed film is uneven.

The cobalt-containing black pigment of the present invention has a high electric resistance. It is preferred in particular is the electrical resistance of 1 × 10 ⁵ Ωcm or more. When the electric resistance is lower than 1 × 10 ⁵ Ωcm, it is not preferable because the function cannot be sufficiently enhanced as a material for forming a black matrix on array type high light-shielding film such as a plasma display or a plasma addressed liquid crystal. More preferably, it is 5 × 10 ⁵ Ωcm or more, and still more preferably 1 × 10 ⁶ Ωcm.

The cobalt-containing black pigment of the present invention preferably has a particle surface coated with a hydrophobic agent. The cobalt-containing black pigment coated with a hydrophobic agent as described above has good compatibility with organic components when formed into a paint, improves dispersibility, and improves performance over time in a humid environment. Less prone to deterioration.

The hydrophobic agent used is an organic compound having a hydrophobic group, for example, titanate coupling agents, silane coupling agents, aluminate coupling agents, silicone compounds such as silicone oil, general purpose Surface active agents, higher fatty acids and salts thereof. Examples of titanate-based coupling agents include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, bis (dioctyl pyrophosphate) oxyacetate titanate, and bis (dioctyl pyrophosphate). Ethylene titanate and the like can be exemplified, and examples of the silane-based coupling agent include vinyltrichlorosilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane and the like. Examples of general-purpose surfactants include phosphate ester-based anionic surfactants, fatty acid ester-based nonionic surfactants, and natural oil and fat derivatives such as alkylamines. Examples of the higher fatty acid include oleic acid, stearic acid, isostearic acid, palmitic acid, isopalmitic acid and the like, and salts thereof can also be used.

Moreover, the coating amount of the hydrophobic drug <TXF LY = "0300"
LX = "1100" WI = "080" HE = "250"
FR = "0002"> is preferably 0.01% by mass to 2% by mass in terms of carbon. If the amount is less than 0.01% by mass, the effect is small, and if it exceeds 2% by mass, the effect corresponding to the amount added is not improved, which is uneconomical.

  Next, the preferable manufacturing method of the cobalt containing black pigment of this invention is demonstrated.

  The cobalt-containing black pigment of the present invention is obtained by neutralizing a cobalt (divalent) salt aqueous solution and an alkali solution at pH 10 to 13 and adjusting the temperature of the reaction slurry after the start of mixing neutralization or after the completion of mixing neutralization. While maintaining at 10 ° C. to 40 ° C., the cobalt hydroxide precursor obtained by continuously bubbling the oxygen-containing gas is filtered, washed, dried and crushed, and in a sealed atmosphere, 500 ° C. to 850 ° C. It can manufacture by performing a granulation process using the apparatus of a wet granulation after baking at 0 degreeC for 0.5 to 3 hours.

  In the production of the cobalt-containing black pigment of the present invention, it is necessary to obtain a cobalt hydroxide precursor using a wet neutralization method in order to obtain cobalt oxide particles having fine primary particles and high blackness.

Usually, a cobalt hydroxide precursor is obtained by neutralizing a water-soluble cobalt salt aqueous solution with a suitable alkali hydroxide, but in order to increase the blackness of the final cobalt-containing black pigment, It is necessary to control the pH at the time of summing within a specific range. Specifically, the pH at the time of mixing and neutralizing the cobalt (divalent) salt aqueous solution and the alkali solution is 10 to 13.

When the neutralization pH is lower than 10, trivalent cobalt hydroxide is likely to be produced during neutralization, which not only hinders the production of the cobalt hydroxide precursor, but also the particle size of the cobalt hydroxide precursor. This is not preferable because it becomes finer and the filterability is deteriorated, and problems such as easy sintering of particles occur when firing described later.
On the other hand, when the pH is higher than 13, cobalt (divalent) salt is liable to be excessively oxidized and may produce trivalent cobalt hydroxide, which is not preferable. When such a cobalt hydroxide precursor is used in the subsequent steps, it is difficult to control the shape and oxidation, and cobalt oxide particles having a high divalent cobalt content cannot be obtained. Considering more stable production of the cobalt hydroxide precursor, the pH during neutralization is more preferably 11 to 12.

  Moreover, in addition to controlling pH to 10-13 as mentioned above, it is good to maintain the temperature of a reaction slurry at 10 to 40 degreeC. When this temperature exceeds 40 ° C, the oxidation of cobalt hydroxide (divalent) proceeds due to continuous bubbling of the oxygen-containing gas, and trivalent cobalt oxyhydroxide (trivalent) precipitates. In addition, as disclosed in Patent Document 1, tricobalt tetroxide may be formed at this time, so that the content ratio of the divalent cobalt as intended by the present invention is high, and A stable cobalt hydroxide precursor for obtaining uniform cobalt oxide particles cannot be obtained. On the other hand, when the temperature is less than 10 ° C., it hinders the production of cobalt hydroxide, has no effect by lowering the liquid temperature, and is not practical.

  Also, a cobalt hydroxide precursor suitable for obtaining cobalt oxide with fine primary particles by continuously bubbling an oxygen-containing gas into the reaction slurry after the start of the mixed neutralization or after the completion of the mixed neutralization. Is obtained. If this operation is not performed, the resulting product, the cobalt hydroxide precursor, tends to aggregate, and the particles are not fine and uniform in size.

  The reason for this has not been fully investigated, but when a divalent cobalt hydroxide precursor is produced from a cobalt (divalent) salt in a reaction slurry by continuously bubbling an oxygen-containing gas at a low temperature range. The bubbling oxygen-containing gas enters between the precursor particles to be aggregated, and a thin oxide film is formed between the particles, which seems to play a role in preventing the aggregation of the particles. This effect cannot be obtained by simple mechanical stirring.

  Note that air may be used as the bubbling oxygen-containing gas, but the neutralization temperature is as low as 10 ° C. to 40 ° C., but in order to better control the adjustment of oxidation, the oxygen concentration is 5% by volume or more and less than 22% by volume. It is preferred to use an inert gas enriched air. In this case, the inert gas used is preferably nitrogen for practical use. By reducing oxygen in the air within this range, it becomes easy to produce the target cobalt hydroxide precursor without precise control of the amount of bubbling gas and bubbling time. When air is used as the bubbling oxygen-containing gas, it is preferable to bubble from 0.01 N liter / L · min to 0.3 N liter / L · min per reaction slurry for about 1 to 3 hours, and enrichment with inert gas When air is used, the bubbling gas speed and bubbling time may be adjusted according to the total amount of oxygen in the bubbling gas.

  The cobalt (divalent) salt used as a starting material is preferably a water-soluble salt such as cobalt sulfate (divalent), cobalt chloride (divalent), cobalt nitrate (divalent), or the like. In addition, alkali hydroxides such as sodium hydroxide and potassium hydroxide are industrially used as alkalis used for neutralization. The oxygen-containing gas used in the reaction is preferably air for practical use.

  Further, when the cobalt hydroxide precursor is generated, simply mixing an aqueous solution whose main component is a cobalt (divalent) salt and an alkaline solution provides sufficient stirring when the amount of the liquid mixture at the beginning of mixing is small. In some cases, it is difficult to obtain a uniform cobalt hydroxide precursor. In such a case, an alkaline solution prepared in a range of pH 10 to 13 sufficient for stirring is prepared, and a cobalt (divalent) salt aqueous solution is added to the alkaline solution to prepare a cobalt hydroxide precursor. It may be generated. Even in such a case, it is important to maintain the pH of the cobalt hydroxide precursor slurry at 10 to 13 while further adding an alkaline solution.

  The cobalt hydroxide precursor slurry thus obtained is subjected to conventional filtration and washing to evaporate the contained water.

  Filtration and washing are performed to remove by-products, unreacted materials, and excess alkali components. When by-products, unreacted substances, and excess alkali remain, the blackness and electrical resistance of the cobalt-containing black pigment that is finally produced may be affected.

  Moreover, it is preferable that the moisture content of the dry body which evaporated the water | moisture content is 1 mass% or less. The moisture content is controlled by appropriately adjusting the drying temperature and drying time. When the water content is more than 1% by mass, a large amount of water vapor is generated in the baking step described later, which is not preferable. More preferably, the water content is adjusted to 0.1 mass% to 0.6 mass%.

  Moreover, the dry body prepared so that the moisture content is 1% by mass or less is subjected to crushing operation. When the crushing operation is not performed, the dried product is supplied to a firing step described later in an aggregated state, which causes problems such as further aggregation being promoted by the firing. As the crushing device, a high-speed rotary hammer mill, impact mill, disk mill or the like is preferable.

The dried body thus obtained is fired in a sealed atmosphere at 500 ° C. to 850 ° C. for 0.5 to 3 hours. The atmosphere for firing may be air, but it is better not to introduce air from the outside in a sealed container. This is to suppress peroxidation caused by introducing excessive air. What is necessary is just to adjust the air capacity | capacitance in a baking apparatus to about 0.5 m < ³ > / kg or less with respect to dry body mass.

  On the other hand, the firing time and the firing temperature should be adjusted in order to promote the dehydration of cobalt hydroxide and improve the crystallinity of the divalent oxide while suppressing the sintering of the granular cobalt oxide black pigment to be produced. If the firing temperature is lower than 500 ° C., the shape change is not sufficient, and sufficient blackness and high electrical resistance cannot be obtained. On the other hand, when the temperature is higher than 850 ° C., the sintering of the particles proceeds, and there is a possibility that aggregation and solidification may not be released even in the subsequent process, which is not preferable. A more preferable temperature range of this firing temperature is 600 ° C to 800 ° C.

  Also, if the firing time is less than 0.5 hours, even if a high temperature range is selected within the above temperature range, the shape change may not be sufficient or unevenness may occur, resulting in sufficient blackness and high electrical properties. There is a possibility that resistance may not be obtained, and if it exceeds 3 hours, sintering proceeds even if a low temperature range is selected within the above temperature range, and aggregation and solidification can not be released even in a later process, Cobalt oxidation proceeds and the divalent cobalt content may be lowered, which is not preferable.

  The baked product obtained in this way, as it is or after the pulverization operation, is prone to agglomeration and solidification due to the calcination, so it is necessary to carry out a pulverization treatment. The pulverization treatment here is different from the pulverization operation performed on the above-described dried cobalt hydroxide. Since the crushing operation is merely to loosen the agglomerated particles, it does not release the agglomeration of the primary particles in the agglomerated particles after firing.

  On the other hand, the pulverization process refers to a process for forcibly releasing the aggregation of primary particles. For this pulverization treatment, a dry method using an air current collision type turbo classifier or the like may be employed. Preferably, for example, the fired product is once slurried with water, and the slurry is subjected to a bead mill using a medium or the like. It is preferable to employ a wet method in which treatment is performed with an attritor or an apparatus such as an optimizer that causes the aggregated particles to collide with each other. The pulverization treatment may be performed by selecting treatment conditions according to the functional capability of the apparatus and adjusting the treatment degree while checking the particle size distribution in the slurry. Moreover, although the removal of the alkali metal derived from the wet reaction intervening between the agglomerated particles also proceeds by this pulverization treatment, the degree of this may be checked by checking the conductivity of the water used as the dispersion medium.

Thus, the final cobalt-containing black pigment powder is obtained by subjecting the slurry after the pulverization treatment to normal filtration, washing, drying, and pulverization.

In addition, when the surface of the cobalt-containing black pigment powder particles is coated with a hydrophobizing agent, either a general wet method in which the agent is processed in a treatment solution diluted with an appropriate solvent or a dry method such as a masterbatch method is used. It may be used. Specifically, in the wet method, it may be added after completion of the reaction, or the cake after washing or the powder after dry pulverization may be added again as a slurry. Examples of the dry method include treatment with a Hensill mixer, a wheel-type kneader, or a rough machine.

  Hereinafter, the present invention will be specifically described with reference to examples and the like. However, the scope of the present invention is not limited to such examples.

[Example 1]
80 liters of pH 12 sodium hydroxide aqueous solution was put into a 200 liter reaction vessel. Subsequently, 60 liters of cobalt sulfate (divalent) aqueous solution containing 1.2 mol / liter of cobalt (divalent) was continuously charged into the reaction vessel at a rate of 1 liter / min. At the same time, using an aqueous sodium hydroxide solution, the pH of the reaction slurry was adjusted to 12 as appropriate. Meanwhile, the slurry temperature was maintained at 35 ° C., and air bubbling was always performed at a rate of 5 N liters / minute.
After mixing was completed, air bubbling was performed at a rate of 15 N liters / minute for 90 minutes while continuing stirring.

  The obtained cobalt hydroxide precursor slurry was filtered and washed, and the resulting cake was dried at 80 ° C. The dried body thus obtained had a water content of 0.5% by mass. The water content was measured according to the heating loss measurement method of JIS K 5101-1991. Furthermore, this dried product was crushed with a hammer mill.

  The crushed dried product thus obtained was calcined at 700 ° C. for 2 hours in a sealed atmosphere to obtain cobalt oxide particle powder.

  A solution obtained by adding 2 L of water to 400 g of this cobalt oxide particle powder and reslurrying the mixture is super-apex mill SAM-1 (manufactured by Sakai Kogyo Co., Ltd.) filled with 0.4 kg of zirconia beads having a diameter of 0.6 mm. After performing the pulverization treatment for a minute, filtration, washing, drying, and pulverization were performed in a conventional manner to obtain a cobalt-containing black pigment.

  The obtained cobalt-containing black pigment was evaluated by the method shown below. The evaluation results are shown in Table 1.

〔Evaluation methods〕
(A) Particle shape and particle shape were observed with a primary particle average diameter scanning microscope (magnification 40,000 times). At the same time, the ferret diameter of 200 particles was arbitrarily measured, and the number average value was taken as the primary particle average diameter.
(B) D ₅₀ , D ₉₀ , D _MAX by laser diffraction scattering type particle size distribution measurement method
0.1 g of a sample was added to 100 ml of a sodium hexametaphosphate aqueous solution adjusted to 0.1%, and dispersed in a BRANSON 2200 (trade name) ultrasonic bath for 3 minutes. The dispersion was measured with LS-230 (trade name) manufactured by Beckman Coulter.
(C) Total cobalt content with respect to the whole particle | grains The sample was melt | dissolved completely in the acid, and content of cobalt was calculated | required by ICP.
(D) The ratio of divalent cobalt to the total cobalt in the particles, and the divalent cobalt content relative to the entire particles. Add the sample to the ammonium iron sulfate (divalent) solution, dissolve completely with acid, and divalent in the solution. The iron ion concentration was determined by titration using potassium dichromate standard solution using sodium diphenylamine sulfonate as an indicator.
Next, the difference between the divalent iron ion concentration added in advance and the divalent iron ion concentration determined by titration was determined by calculation to determine the trivalent iron ion concentration.
Since trivalent iron ions are generated by the following chemical reaction, this concentration was defined as the trivalent cobalt ion concentration contained in the sample.
Co ³⁺ + Fe ²⁺ → Co ²⁺ + Fe ³⁺
The trivalent cobalt content with respect to the whole particle | grain was calculated | required from this, and the trivalent cobalt content with respect to the whole particle | grain was subtracted from the total cobalt content, and the bivalent cobalt content with respect to the whole particle | grain was calculated | required.
And the ratio of the bivalent cobalt with respect to the total cobalt in a particle | grain was calculated | required in (divalent cobalt content) / (total cobalt content) x100.
(E) The alkali metal amount sample in the particles was completely dissolved in acid, and the Na content was determined by ICP.
(F) 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.
(G) Coloring power (Evaluation of dispersibility and hue during coating)
Add 1.3 cc of castor oil to 0.5 g of black particles and 1.5 g of titanium oxide (R800 manufactured by Ishihara Sangyo Co., Ltd.), knead with Hoover-type Mahler, add 4.5 g of lacquer to 2.0 g of this kneaded sample, After further kneading, this was coated on a mirror-coated paper using a 4 mil applicator, dried, and then subjected to blackness (L value) and hue with a color difference meter (Tokyo Denshoku Color Analyzer TC-1800). (A value, b value) were measured.
(H) Electric resistance 10 g of a sample was put in a holder, and after applying a pressure of 58.9 MPa to form a 25 mmφ tablet, an electrode was attached and measurement was performed under a pressure of 14.7 MPa. The electrical resistance value was calculated from the thickness and cross-sectional area of the sample used for the measurement and the resistance value.
(I) Specular Reflectance Reflectance at 20 ° on the coated film surface obtained by spreading a kneaded product of a dispersion paste prepared in accordance with the Hoovermarler method of JIS K 5101 and nitrified cotton clear lacquer on a white paper using a 1 mil film applicator. The rate was measured.
(J) Specific surface area Measured with a 2200 type BET meter manufactured by Shimadzu Micromeritics.

[Example 2]
A cobalt-containing black pigment was obtained in the same manner as in Example 1 except that the zirconia beads used for the pulverization treatment were changed to φ0.3 m diameter products. What was obtained was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

Example 3
The pulverization treatment conditions were the same as in Example 1 except that the treatment was changed to treatment at 30 rpm for 30 minutes at 200 rpm with an attritor MA1SE (manufactured by Mitsui Mining Co., Ltd.) filled with 11 kg of φ5 mm diameter porcelain balls. A black pigment was obtained. What was obtained was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

Example 4
5 kg of the sample of Example 1 was prepared, and 0.5% by mass of decyltrimethoxysilane was added to the pigment to the sample. It was treated for a minute to obtain a hydrophobic pigment-coated cobalt-containing black pigment. What was obtained was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[Comparative Example 1]
A cobalt-containing black pigment was obtained in the same manner as in Example 1 except that the pulverization treatment was not performed. What was obtained was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[Comparative Example 2]
A cobalt-containing black pigment was obtained in the same manner as in Example 1 except that conventional hammer mill crushing was performed instead of the pulverization treatment. What was obtained was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

As is clear from Table 1, the cobalt-containing black pigments of the examples have a small average primary particle diameter, and D ₅₀ , D ₉₀ , and D _MAX showing the degree of aggregation are relatively small, and the specular reflectance after coating is made. It can be seen that it is high and has excellent dispersibility. Moreover, although the particles are fine, the blackness is excellent, the electric resistance is at a high level, and it has excellent characteristics as a black pigment.

In contrast, the cobalt-containing black pigment of the comparative example has an average primary particle size equivalent to that of the example, but D ₅₀ , D ₉₀ and D _MAX indicating the degree of aggregation are large, and it can be seen that the primary particles are largely aggregated. As a result, it can be seen that the specular reflectance after coating is low and the dispersibility is poor. Further, the blackness is inferior and the electric resistance is low.

Claims (8)

Cobalt-containing black, characterized in that the average primary particle diameter is 0.03 μm or more and 0.5 μm or less, and D ₅₀ in particle size measurement based on the number standard by the laser diffraction scattering method is 0.05 μm or more and less than 1.5 μm Pigments. 2. The cobalt-containing black pigment according to claim 1, wherein D _MAX based on a number criterion by a laser diffraction / scattering particle size distribution measurement method is 3 μm or less. 3. The cobalt-containing black pigment according to claim 1, wherein D ₉₀ based on a number criterion by a laser diffraction / scattering particle size distribution measurement method is 0.5 μm or more and 2 μm or less. The cobalt-containing black pigment according to any one of claims 1 to 3, wherein a ratio of divalent cobalt to total cobalt in the particles is 40 to 70%. The cobalt-containing black pigment according to any one of claims 1 to 4, wherein the total cobalt content with respect to the whole particle is 60 to 80% by mass. The cobalt-containing black pigment according to any one of claims 1 to 5, wherein the content of divalent cobalt with respect to the whole particle is 25% by mass to 50% by mass. The cobalt-containing black pigment according to claim 1, wherein the amount of alkali metal in the particles is 100 ppm or less. A cobalt-containing black pigment, wherein the surface of particles of the cobalt-containing black pigment according to claim 1 is coated with a hydrophobic agent.