JP3828566B2 - Cobalt-containing granular black pigment - Google Patents

Description

  The present invention relates to a cobalt-containing granular black pigment, and more specifically, characterized in that cobalt (divalent) in the total cobalt contained is contained in a specific proportion, particularly a black matrix coloring composition, The present invention relates to a cobalt-containing granular black pigment having excellent blackness and high electrical resistance, which is used for forming a black electrode such as a plasma display or a plasma addressed liquid crystal or a light shielding layer.

  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.

  Further, in forming a black matrix on array type high light-shielding film such as a plasma display or a plasma address liquid crystal, as disclosed in Patent Document 1, it is required to have a high electric resistance to prevent conduction between electrodes. Needless to say, it is preferable that the black pigment inevitably used also has a high electric resistance. However, a black pigment having both blackness and high electrical resistance has not been proposed yet.

  Some cobalt oxide particles have been proposed as battery materials (Patent Documents 2 and 3). Patent Document 2 describes tricobalt tetroxide particles by wet synthesis or a mixture of tricobalt tetroxide particles and cobalt oxyhydroxide particles. Patent Document 3 describes plate-like tricobalt tetraoxide particles. However, these cobalt oxides are produced for the purpose of battery materials, and are insufficient in terms of blackness and high electrical resistance.

JP 2000-162643 A JP 10-324523 A Japanese Patent Laid-Open No. 9-22692

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

  That is, the object is to provide a material having both blackness and high electrical resistance that should be provided as a black pigment powder for forming a black electrode such as a plasma display or a plasma address liquid crystal or a light shielding layer.

  The present invention achieves the above object by providing a black pigment which is an oxide containing at least cobalt and the proportion of divalent cobalt in the total cobalt is 40% to 70%. .

  Since the cobalt-containing granular black pigment of the present invention is excellent in blackness and has high electric resistance, it is suitable for uses such as black electrodes for plasma displays and plasma addressed 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 granular black pigment referred to in the present invention is black particles having at least a main component of cobalt, and Si, Al, Mn, Ni, Zn, Cu, Mg, Ti, Zr, and W depending on required characteristics. , Mo, P or the like may be selected and contained.

In the cobalt-containing granular black pigment of the present invention, it is important that the ratio of the divalent cobalt content to the total cobalt content is 40% to 70%. The ratio of the divalent cobalt content (% by mass) to the total cobalt content (% by mass) is a value obtained by dividing the divalent cobalt content contained in the entire particle by the total cobalt content contained in the entire particle. (%) Multiplied by 100. 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 divalent cobalt in the total cobalt. In addition, all the cobalt in CoO is divalent cobalt, and all the cobalt in Co ₂ O ₃ is trivalent. The cobalt-containing granular black pigment of the present invention is different from the cobalt oxide in the proportion of divalent cobalt in the total cobalt, and both the blackness and the high electrical resistance, which are the effects of the present invention, can be achieved depending on the element configuration. Achieved. When the proportion of divalent cobalt in the total cobalt is less than 40%, the blackness is insufficient, and when it exceeds 70%, the pigment exhibits a blue-green color instead of a black pigment. Can not demonstrate. The proportion of the divalent cobalt is more preferably 40% to 60%.

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

The cobalt-containing granular black pigment of the present invention has a total cobalt content of 60% by mass to 80% by mass with respect to the entire particle, and a divalent cobalt content with respect to the entire particle of 20 % by mass to 50% by mass. It is preferable. The total cobalt content with respect to the entire particle is not theoretically less than 60% by mass, and when a large amount of other elements than cobalt is included, there is a concern about adverse effects on blackness and resistance, which is not preferable. On the other hand, if it exceeds 80% by mass, it is difficult to balance the charge of cobalt and oxygen, and the stability of the product is lacking. Further, when the divalent cobalt content with respect to the whole particle is less than 20 % by mass, the blackness is insufficient, and when it is more than 50% by mass, the blackness is similarly insufficient, which is not preferable. Regarding the total cobalt content and the divalent cobalt content, the total cobalt content is 65 to 75% by mass, and the divalent cobalt content with respect to the entire particle is 25% to 45% by mass. Further preferred.

  The cobalt-containing granular black pigment of the present invention preferably has a primary particle size of 0.02 μm to 0.6 μm. When the primary particle diameter is less than 0.02 μm, the color becomes reddish or a problem occurs in dispersibility, which is not preferable. On the other hand, when it exceeds 0.6 μm, although the color is sufficient, problems such as insufficient coloring power tend to occur. The primary particle diameter is more preferably 0.05 μm to 0.3 μm because it is easy to balance the hue and coloring power.

  In addition, the cobalt-containing granular 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 colorability. 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 was 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. The blackness and hue are more preferably an L value of 36 or less and a b value of -0.5 or less.

The cobalt-containing granular black pigment of the present invention is characterized by high electrical resistance. Specifically, the electric resistance value is preferably 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.

Next, the preferable manufacturing method of the cobalt containing granular black pigment of this invention is demonstrated.
When the cobalt-containing granular black pigment of the present invention neutralizes a cobalt (divalent) salt with an alkali hydroxide containing an alkali metal salt at a liquid temperature of 40 ° C. or lower to produce cobalt hydroxide (divalent). In addition, an inert gas is continuously bubbled into the slurry, and the obtained cobalt hydroxide (divalent) is filtered, washed, dried and crushed, and then fired at 400 ° C. to 800 ° C. Can be manufactured.

  This production method is inert when neutralizing and mixing cobalt hydroxide (divalent) with an aqueous solution whose main component is a cobalt (divalent) salt and an alkali hydroxide aqueous solution containing an alkali metal salt. It is important to continuously bubble the gas. When the inert gas is not bubbled, a part of cobalt hydroxide (divalent) in the slurry is oxidized by dissolved oxygen in the slurry and oxygen absorbed from the liquid surface to form cobalt hydroxide (trivalent). In this case, the divalent cobalt content ratio in the finally obtained cobalt-containing granular black pigment is lowered. That is, it is necessary to maintain a condition in which trivalent cobalt hydroxide is not generated as much as possible in the slurry. Examples of the inert gas include nitrogen gas, helium gas, and argon gas.

  Here, cobalt (divalent) is preferably a water-soluble salt such as cobalt sulfate (divalent), cobalt chloride (divalent), cobalt nitrate (divalent), and the like. As the alkali, an aqueous alkali hydroxide solution containing an alkali metal salt such as sodium hydroxide or potassium hydroxide is used.

  Moreover, in order to produce | generate reliably the cobalt containing granular black pigment of this invention, although pH will produce | generate if the hydroxide at the time of producing | generating cobalt hydroxide (divalent) is 9 or more, 11 to 13 and It is preferable to do this. When the pH is lower than 11, the generated cobalt hydroxide (divalent) particles become very fine, resulting in problems such as poor filterability and easy sintering between particles when firing described below. Therefore, it is not preferable. On the other hand, when the pH is higher than 13, cobalt hydroxide (divalent) is liable to be oxidized even when bubbling with an inert gas is not preferable.

  In addition, when producing cobalt hydroxide (divalent), it is preferable that an aqueous solution containing a cobalt (divalent) salt as a main component and an alkali hydroxide aqueous solution containing an alkali metal salt are uniformly mixed and contacted with each other. However, since uniform mixing contact by simple free fall is difficult, it is better to make contact by using a Y-shaped mixing tube. Further simple contact methods include the following methods. In advance, an aqueous alkali hydroxide solution containing a small amount of alkali metal salt that can be stirred at least is put into the reaction vessel. This aqueous alkali hydroxide solution is prepared to have a pH of 11 to 13 in order to suppress fluctuations in pH during the reaction. A cobalt (divalent) salt aqueous solution and an alkali hydroxide are added to the reaction vessel at an appropriate rate. In this way, it is possible to make almost uniform mixing contact while suppressing fluctuations in pH during the reaction.

  Moreover, the slurry temperature at the time of producing | generating cobalt hydroxide (divalent) shall be 40 degrees C or less. When the slurry temperature is higher than 40 ° C., cobalt hydroxide (divalent) is liable to be oxidized even when bubbling with an inert gas is not preferable. Although there is no restriction | limiting in particular as a preferable minimum temperature of slurry temperature, The temperature higher than 0 degreeC is preferable from cooling too much more than necessary because it is uneconomical.

  The cobalt hydroxide (divalent) thus obtained is filtered and washed to evaporate the contained water and further subjected to crushing operation.

  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 granular black pigment to be 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. The water content is more preferably adjusted to 0.1% by mass to 0.6% by mass.

  In addition, it is important to perform a crushing operation on a dried product prepared with a moisture content of 1% by mass or less. When the crushing operation is not performed, the agglomerated cobalt hydroxide (divalent) is supplied to the firing step described later, and problems such as further promotion of aggregation are caused by the firing. As the crushing device, a high-speed rotary hammer mill, impact mill, disk mill or the like is preferable.

  The cobalt hydroxide (divalent) thus obtained is fired at 400 ° C. to 800 ° C. in the atmosphere. This is because it does not change to a cobalt-containing granular black pigment unless firing is performed in the atmosphere. When the firing temperature is less than 400 ° C., the shape change is not sufficient, and sufficient blackness and high electrical resistance cannot be obtained. On the other hand, when the temperature exceeds 800 ° C., the sintering of the particles proceeds and the particle diameter increases, and the oxidation of cobalt proceeds in the firing step, which may reduce the divalent cobalt content. . The firing temperature is more preferably 500 ° C to 700 ° C.

  In addition, the cobalt-containing granular black pigment obtained in this way can be further increased in electrical resistance by treating with a wheel-type kneader having an action of compression, shearing and spatula. Examples of the wheel-type kneader that works by compression, shearing, and spatula include Yodomill manufactured by Yodocasting. As preferable processing conditions, it is good to perform the processing for 10 minutes to 90 minutes at a linear pressure of 30 kgf / cm to 160 kgf / cm. Thereby, the electrical resistance value of the cobalt-containing granular black pigment is improved by about the first power. The linear pressure is more preferably 30 kgf / cm to 120 kgf / cm.

  The cobalt-containing granular black pigment thus obtained can be further processed by blending and mixing other materials to obtain a black pigment composition in a paste or slurry state.

  As other materials, additives such as a resin, a solvent, and, if necessary, an inorganic powder such as glass powder, a paste, a surfactant, a curing accelerator, and an auxiliary agent can be used.

  Resins include acrylic resin, polyester resin, polyurethane resin, epoxy resin, phenol resin, melamine resin, amino resin, vinyl chloride resin, silicone resin, rosin resin such as gum rosin, lime rosin, maleic acid resin, polyamide resin, nitrocellulose , Rosin-modified resins such as ethylene-vinyl acetate copolymer resin, rosin-modified phenol resin, rosin-modified maleic resin, petroleum resin, water-soluble acrylic resin, water-soluble styrene-maleic acid resin, water-soluble alkyd resin, water-soluble melamine resin Water-soluble urethane emulsion resins, water-soluble epoxy resins, water-soluble polyester resins and the like can be used.

  As the solvent, toluene, xylene, thinner, butyl acetate, methyl acetate, methyl isobutyl ketone, methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, glycol ether solvents such as propylene glycol monomethyl ether, ethyl acetate, butyl acetate, Ester solvents such as amyl acetate, aliphatic hydrocarbon solvents such as hexane, heptane, and octane, alicyclic hydrocarbon solvents such as cyclohexane, petroleum solvents such as mineral spirits, and ketone solvents such as acetone and methyl ethyl ketone. Other compatible alcohols such as methanol, ethanol and propanol, glycols such as ethylene glycol and propylene glycol, propylene glycol monomethyl ether, Glycol ethers such as glycol monoethyl ether, 2-pyrrolidone, N- methylpyrrolidone, dimethylformamide, it may be used a polar solvent such as dimethyl sulfoxide and the like.

  The ratio of the blending components of the composition can be adjusted to a form to be used to make a paste or a slurry, and is not particularly limited. 1 mass%-70 mass% may be sufficient, Preferably about 10 mass%-60 mass% are good.

  Since the black pigment composition is excellent in blackness and contains a cobalt-containing granular black pigment having high electrical resistance, it can be suitably used as a black matrix coloring composition.

  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. Next, 60 liters of a 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. Added continuously. The flow rate of sodium hydroxide was adjusted appropriately so that the slurry pH in the reaction vessel was constantly measured and the pH of the slurry was 12. Meanwhile, the slurry temperature was maintained at 35 ° C., and nitrogen gas was continuously blown at a rate of 5 liters / minute. 12 liters of 12 mol / liter sodium hydroxide aqueous solution was used.
After mixing, nitrogen gas bubbling and stirring were continued for another 30 minutes.

  The obtained cobalt hydroxide (divalent) slurry was filtered and washed, and the obtained hydrous cobalt hydroxide (divalent) was dried at 80 ° C. The cobalt hydroxide (divalent) dried product thus obtained had a water content of 0.5% by mass. The water content was measured according to the heat loss measurement method of JIS K 5101-1991. Further, the dried cobalt hydroxide (divalent) was pulverized with a hammer mill to obtain cobalt hydroxide (divalent) powder.

  The cobalt hydroxide (divalent) powder thus obtained was baked at 600 ° C. for 120 minutes in the air to obtain a cobalt-containing granular black pigment.

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

〔Evaluation methods〕
(A) Total cobalt content with respect to the whole particle The cobalt-containing granular black pigment was completely dissolved in acid, and the content of cobalt was determined by ICP.
(B) Divalent cobalt content and Co ²⁺ / total Co ratio with respect to the whole particles Add 0.1 g of sample to 5.0 ml of 0.5N ammonium iron sulfate (divalent) solution, and (1 + 1) completely dissolve in 20 ml of hydrochloric acid did. Concentrated sulfuric acid: phosphoric acid = 1: 1 (weight ratio) 10 ml of mixed acid and water were added to dilute to a total volume of 200 ml. The divalent amine ion concentration in the solution was determined by titration using an N / 10 potassium dichromate standard solution using sodium diphenylamine sulfonate as an indicator.
Next, the divalent iron ion mol in the sample solution obtained from the divalent iron ion mol amount in the initial 0.5N ammonium iron sulfate (divalent) solution and the divalent iron ion concentration and liquid volume by titration. The difference in amount was defined as the trivalent iron ion molar amount.
Since trivalent iron ions are generated by the following chemical reaction, the trivalent iron ion molar amount was considered to indicate the trivalent cobalt ion molar amount.
Co ³⁺ + Fe ²⁺ → Co ²⁺ + Fe ³⁺
The trivalent cobalt content (mass%) in the sample was determined by the trivalent cobalt ion molar amount (mol) × 58.93 ÷ 0.1 × 100.
From the above results, (divalent cobalt content) = (total cobalt content) − (trivalent cobalt content) was determined. Further, the Co ²⁺ / total Co ratio was determined by (divalent cobalt content) ÷ (total cobalt content) × 100.
(C) Particle shape and particle diameter The particle shape was observed with a scanning microscope (magnification 40,000 times). At the same time, the ferret diameter of 200 particles was arbitrarily measured, and the number average value thereof was taken as the primary particle diameter.
(D) Electric resistance value 10 g of a sample was put in a holder, and a pressure of 600 kgf / cm ² was applied to form a 25 mmφ tablet mold. Then, an electrode was attached and measurement was performed in a pressurized state of 150 kgf / cm ² . The electrical resistance value was calculated from the thickness and cross-sectional area of the sample used for the measurement and the resistance value.
(E) Blackness and hue The blackness and hue of the powder were 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) Coloring power (color developability when dispersed during coating)
1.3 cc of castor oil was added to 0.5 g of black particles and 1.5 g of titanium oxide (R800 manufactured by Ishihara Sangyo Co., Ltd.), and kneaded 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.). The coloring power (L value, a value, b value) was measured with an analyzer TC-1800 type.
(G) Specific surface area Measured with a 2200 type BET meter manufactured by Shimadzu-Micromeritics.
(H) Oil absorption amount Measured according to JIS K 5101-1991.

[Example 2]
Particles were obtained in the same manner as in Example 1 except that the firing temperature was 750 ° C. The obtained particles were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

Example 3
Particles were obtained in the same manner as in Example 1 except that the pH at which cobalt hydroxide was generated was 11.2. The obtained particles were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

Example 4
What was obtained in Example 1 was treated for 30 minutes at a linear pressure of 40 kgf / cm using a Yodomill manufactured by Yodocasting. The obtained particles were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[Comparative Example 1]
Particles were obtained in the same manner as in Example 1 except that the firing temperature was 300 ° C. The obtained particles were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[Comparative Example 2]
When cobalt hydroxide (divalent) was produced, particles were obtained in the same manner as in Example 1 except that the neutralization solution temperature was 50 ° C. The obtained particles were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[Comparative Example 3]
When cobalt hydroxide (divalent) was produced, particles were obtained in the same manner as in Example 1 except that the alkali used was 9.0 liters of 28% ammonia. The obtained particles were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

As is apparent from Table 1, the cobalt-containing granular black pigments of Examples 1 to 4 have excellent blackness and high electrical resistance, and are black electrodes such as black matrix coloring compositions, plasma displays, and plasma address liquid crystals. It is excellent as a material for forming a light shielding layer.
Moreover, the SEM photograph of the cobalt-containing black granular pigment of Example 1 is shown in FIG. The particles obtained by Example 1 were granular.

  In contrast, the particles of Comparative Example 1 had a high divalent cobalt content ratio of 72.4% in the total cobalt, and the particles had a plate shape. For this reason, the hue was bad, and the b value was particularly high. And the particle | grains of the comparative example 1 were a thing with low electrical resistance. The particles of Comparative Example 2 had a low trivalent cobalt content ratio of 33.0% in the total cobalt, and had a composition of tricobalt tetroxide. Although the particles are granular, the blackness is inferior because of the low divalent cobalt content compared to the particles of the present invention. The particles of Comparative Example 3 were plate-like and had a large particle size and excellent blackness and hue, but low coloring power and poor pigment performance.

1 is a scanning electron micrograph of the cobalt-containing granular black pigment obtained in Example 1. FIG.

Claims (4)

A cobalt-containing granular black pigment characterized in that it is an oxide containing at least cobalt and the proportion of divalent cobalt in the total cobalt is 40% to 70%. The total cobalt content with respect to the whole particle is 60% by mass to 80% by mass, and the divalent cobalt content with respect to the whole particle is 25 % by mass to 50% by mass. Cobalt-containing granular black pigment. The cobalt-containing granular black pigment according to claim 1 or 2, wherein the primary particle diameter is 0.02 to 0.6 µm. The black pigment composition containing the cobalt containing granular black pigment in any one of Claims 1-3.