JP4688708B2 - Black composite oxide particles, production method thereof, black paste and black matrix - Google Patents

Description

  The present invention relates to black complex oxide particles and a method for producing the same. The present invention also relates to a black paste containing the black composite oxide particles. The present invention further relates to a black matrix formed from the black paste.

  Black pigments used for paints, inks, toners, rubbers / plastics, etc. are required to be excellent in properties such as blackness, hue, coloring power, hiding power and the like and inexpensive. As such a black pigment, metal oxide pigments such as iron oxide pigments such as carbon black and magnetite, and other complex oxide pigments are used depending on applications.

  In recent years, high performance and high quality are demanded in any of the above fields. For example, a black pigment containing a metal oxide as a main component is not only excellent in blackness but also has oxidation resistance, resin, and the like required at the time of firing when forming a black matrix used in a flat panel display. What is required is excellent in dispersibility in a vehicle required for forming a paint using a solvent or the like, and surface smoothness of a coating film when the coating is formed into a coating film. Typical examples of black pigments mainly composed of metal oxides include metal oxide particles having a single composition such as cobalt oxide, manganese oxide, and copper oxide, Cu-Cr, Cu-Mn, and Cu-Cr-Mn. , Cu—Fe—Mn, Co—Mn—Fe, Co—Fe—Cr, and the like (see Patent Documents 1 to 3).

JP-A-9-237570 Japanese Patent Laid-Open No. 10-231441 JP-A-9-124972

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

  Moreover, composite oxide particles also have advantages and disadvantages in terms of performance required for black pigments. For example, in the case of composite oxide particles containing chromium, such as Cu-Cr-based composite oxide particles and Cu-Cr-Mn-based composite oxide particles, there is a problem in toxicity of chromium. Also, it is difficult to produce submicron level particles.

  The Cu—Mn-based composite oxide particles as disclosed in Patent Document 1 are easy to be atomized, but the shape is likely to be indefinite. In addition, the particles tend to aggregate and are inferior in dispersibility and smoothness of the coating film when formed into a paint. Furthermore, the particles cannot be made black without undergoing a firing step. Firing causes sintering between particles.

Similarly, Cu—Fe—Mn composite oxide particles as disclosed in Patent Document 1 have high blackness, a uniform shape and excellent dispersibility. The -Mn-Fe composite oxide particles have a uniform shape and excellent dispersibility. However, all are said to be inferior in weather resistance and inferior in acid resistance due to containing iron. This is because the blackness depends on Fe ²⁺ , which tends to deteriorate over time.

  As described above, as a black pigment mainly composed of a metal oxide, a material satisfying with respect to blackness, oxidation resistance, dispersibility at the time of coating, and surface smoothness of the coating when the coating is coated The reality is that it has not been found yet. An object of the present invention is to provide a material that can meet these requirements.

  As a result of intensive studies on various metal oxides exhibiting black color, the present inventors have found that specific Co—Mn-based composite oxide particles can achieve the above object, and have completed the present invention.

  That is, the present invention contains 35 to 70% by weight of cobalt and 5 to 40% by weight of manganese, the molar ratio Co / Mn of cobalt to manganese is 0.5 to 14, and primary particles based on observation by a scanning electron microscope The above object is achieved by providing black composite oxide particles characterized in that the number-based average particle diameter of the particles is 0.05 to 0.3 μm and is octahedral. The present invention also provides a black paste containing the black composite oxide particles and a black matrix formed from the black paste.

  Further, according to the present invention, as a preferred method for producing the black composite oxide particles, a metal salt mixed aqueous solution in which a water-soluble salt of cobalt and manganese is dissolved and an alkali are neutralized and mixed, and the resulting metal hydroxide slurry is 60 The present invention provides a method for producing black composite oxide particles characterized by oxidation with an oxidizing gas under conditions maintained at -95 ° C and pH 10-13.

  The black complex oxide particles according to the present invention have high blackness and heat resistance, and the particles are less likely to be detached from the coating film containing the particles due to the octahedral shape. Accordingly, the black composite oxide particles are suitable as black pigments for paints, inks, toners, rubbers and plastics. In particular, it is suitable for forming a black composition for forming a black matrix of a flat panel display, a black electrode of a front plate such as a plasma display or a plasma address liquid crystal, and a light shielding layer. In addition, a black matrix, a plasma display, and a plasma addressed liquid crystal formed from a black paste using such black composite oxide particles are excellent in blackness, heat resistance, uniformity of the fired film, and glossiness.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The black complex oxide particles of the present invention are black and contain cobalt and manganese. The black composite oxide particles of the present invention are characterized by high blackness and high heat resistance despite being manufactured without a firing step, as is apparent from the manufacturing method described later. It is done. Further, it is characterized by an octahedral shape.

  In order to obtain composite oxide particles having high blackness and heat resistance, the black composite oxide particles of the present invention have an octahedral shape. As a result of the study by the present inventors, it has been found that when the composite oxide particles containing cobalt and manganese have an octahedral shape, the crystallinity of the particles is increased, and the blackness and heat resistance are increased. Furthermore, it has also been found that, when a coating film is formed from a paste containing particles due to the octahedral shape, the particles are less likely to be detached from the coating film. The octahedral complex oxide particles can be preferably manufactured according to the manufacturing method described later.

  Although related to the shape of the particles, it is important that the black composite oxide particles of the present invention are fine particles. Specifically, the number-based average particle diameter of primary particles based on observation with a scanning electron microscope (hereinafter referred to as SEM) is 0.05 to 0.3 μm, preferably 0.10 to 0.2 μm. Thus, the coating film formed from the coating material containing fine black complex oxide particles has good surface smoothness, and the glossiness of the coating film becomes high. As will be described later, since the black composite oxide particles of the present invention are produced without undergoing a firing step, the degree of aggregation between the particles is low, and fine particles are easily obtained.

  Next, the composition of the black composite oxide particles of the present invention will be described. The cobalt content in the black composite oxide particles is 35 to 70% by weight, preferably 40 to 70% by weight. If the cobalt content is less than 35% by weight, the heat resistance and electrical resistance will be reduced. If the cobalt content is more than 70% by weight, the blackness is lowered.

  On the other hand, the manganese content in the black composite oxide particles of the present invention is 5 to 40% by weight, preferably 10 to 35% by weight. If the manganese content is less than 5% by weight, the blackness will be lowered. If the manganese content is more than 40% by weight, the color will be poor and the heat resistance and electrical resistance will be reduced.

  In the black composite oxide particles of the present invention, the ratio of cobalt and manganese, which are essential metal components, is also important. When the cobalt / manganese molar ratio Co / Mn is 0.5 to 14, preferably 1 to 6, octahedral black composite oxide particles can be successfully obtained, and the balance of blackness and electrical resistance is balanced. An advantageous effect is obtained. Specifically, when the molar ratio of cobalt / manganese is less than 0.5, the blackness may be lowered, and when the molar ratio exceeds 14, the color becomes worse and the heat resistance is reduced. In some cases, the electrical resistance is lowered.

  The black composite oxide particles of the present invention preferably have a sharp primary particle number-based particle size distribution based on SEM observation. In general, the width of the particle size distribution of the granules is represented by a coefficient of variation. The coefficient of variation (%) is calculated by (standard deviation / number-based average particle diameter of primary particles based on SEM observation) × 100. A large coefficient of variation indicates that the particle size distribution has a width, and conversely a small coefficient of variation indicates that the particle size distribution is sharp. In the present invention, the coefficient of variation (CV value) of the primary particle diameter in the primary particle number-based particle size distribution based on SEM observation is preferably a small value of 40% or less, more preferably 30% or less. The coefficient of variation is calculated from the number-based average particle diameter and standard deviation of a specific number of primary particles (for example, 200 in the examples described later) by SEM observation.

Further, in the black composite oxide particles of the present invention, in addition to the average particle size of the primary particles being within the above-mentioned range, the maximum particle size D _{max of the} aggregated particles based on the number criterion is preferably small. . Thereby, the detachment of particles from the coating film can be more effectively prevented. From this viewpoint, the maximum particle diameter D _max of the aggregated particles based on the number standard is preferably 4 μm or less, particularly 3 μm or less. The lower limit value of the maximum particle size D _max is not particularly limited and is preferably as small as possible. However, if the value is about 0.2 μm, the detachment of particles from the coating film can be effectively prevented. The maximum particle diameter D _max of the aggregated particles is measured by a particle size distribution measuring apparatus using a laser diffraction scattering method.

In the black composite oxide particles of the present invention, the D ₅₀ value of the aggregated particles in the number-based particle size distribution is preferably 0.1 to 1.5 μm. It is difficult to make the D ₅₀ value less than 0.1 μm from the viewpoint of the primary particle size. On the other hand, when the D ₅₀ value exceeds 1.5 μm, the aggregation is too strong and the dispersibility becomes poor in any of various applications. The D ₅₀ value of the aggregated particles is measured by a particle size distribution measuring apparatus using a laser diffraction scattering method.

  Although it is related to the shape and particle size of the particles, the black composite oxide particles of the present invention have high particle dispersibility. When specular reflectance is adopted as a measure of dispersibility, the black composite oxide particles of the present invention have a high value of 70 or more, particularly 85 or more.

  Although related to the specular reflectance, the black composite oxide particles of the present invention have a low oil absorption of preferably 10 to 40 ml / 100 g, more preferably 15 to 30 ml / 100 g. The black composite oxide particles of the present invention having a low oil absorption amount have few aggregated particles, and as a result, the dispersibility when formed into a paint is improved.

The black complex oxide particles of the present invention are also characterized by low magnetism. The low magnetism means that the particles are hardly aggregated and the dispersibility is improved. From this point of view, black complex oxide particles, saturation magnetization of at 796 kA / m conditions 3am ² / kg or less, and particularly preferably 2Am ² / kg or less. The lower limit of the saturation magnetization is not particularly limited and is preferably as small as possible. However, if the value is about 0.1 Am ² / kg, aggregation of particles can be effectively prevented.

  It is preferable that the black complex oxide particles of the present invention contain only the above-described cobalt and manganese as metal components, and do not substantially contain other heavy metal elements having a large environmental load. When a metal element is contained, it is preferable to contain a light metal element having an atomic number of 20 or less. When the black complex oxide particles contain the light metal element other than cobalt and manganese, the content is preferably 0.05 to 5% by weight, particularly preferably 0.1 to 3% by weight.

The black complex oxide particles of the present invention are also characterized by a small specific surface area by BET. The reason why the specific surface area is small is not clear, but it has been found that the BET specific surface area obtained can be reduced by producing black composite oxide particles according to the production method described later. BET specific surface area of the black complex oxide particles is preferably a low level of 5 to 30 m ² / g, more preferably 10 to 25 ² / g. A low specific surface area is advantageous in that it is not easily affected by the surrounding environment. In particular, it is less susceptible to humidity. That is, the black complex oxide particles of the present invention have low hygroscopicity.

In connection with the low hygroscopicity, the black composite oxide particles of the present invention have a high volume electric resistance value. Specifically, the volume electric resistance value measured under conditions of 25 ° C. and 55% RH is preferably 1 × 10 ⁴ Ω · cm or more, more preferably 1 × 10 ⁴ to 1 × 10 ⁸ Ω · cm. More preferably, it is 1 × 10 ⁵ to 1 × 10 ⁸ Ω · cm. The high volume electric resistance value has an advantageous effect that when the black composite oxide particles are used for a black matrix, the electrodes can be reliably insulated.

  The black complex oxide particles of the present invention are also characterized by high blackness. It should be noted that particles having high blackness can be obtained without going through the firing step. In general, the composite oxide particles containing no iron are improved in blackness through a firing step, but in the present invention, by adopting the manufacturing method described later, black that should be satisfied without going through the firing step. Particles having a degree can be obtained. The blackness of the particles is measured according to JIS K5101-1991. The L value of particles measured using a color difference meter is a low value of 20 or less. The a value is 0.1 or less, and the b value is 0.1 or less.

In addition to high blackness, the black composite oxide particles of the present invention are also characterized by high heat resistance. The heat resistance as used herein means that the blackness does not decrease even when subjected to heat. As a measure of heat resistance, the value of ΔE defined by the following formula is adopted in the present invention.
ΔE = (ΔL ² + Δa ² + Δb ² ) ^1/2
In the formula, ΔL, Δa, and Δb respectively represent differences in L value, a value, and b value before and after heating in air at 600 ° C. for 1 hour.

  The black complex oxide particles of the present invention have a small ΔE value of 0.5 or less, particularly 0.3 or less. As is clear from the results of Comparative Example 1 described later, the Co—Mn—Fe-based composite oxide particles described in Patent Document 2 described above have a ΔE even though the composite oxide particles are manufactured through a firing step. The value becomes a large value of 4.01. That is, it is inferior in heat resistance. The reason why the black composite oxide particles of the present invention have high heat resistance is not clear, but a binary component material of cobalt and manganese is used, and a wet oxidation method described later is used as a method for producing the black composite oxide particles. I guess that is due.

  Next, a preferred method for producing the black composite oxide particles of the present invention will be described. This manufacturing method is roughly divided into two steps: (a) a metal hydroxide slurry preparation step and (b) a wet oxidation step. Further, the firing is not performed after wet oxidation. Each process will be described below.

  First, the step (a) will be described. A metal hydroxide slurry is obtained by neutralizing and mixing a metal salt mixed aqueous solution in which a water-soluble salt of cobalt and manganese is dissolved and an alkali. Specifically, an alkali is gradually added to the metal salt mixed aqueous solution to obtain a metal hydroxide slurry. Although there is no restriction | limiting in particular in the addition time of an alkali, it is preferable that it is 60 to 120 minutes from the point from which a uniform metal hydroxide nucleus is obtained. If the alkali addition time is too short, metal hydroxides having a non-uniform composition are formed, and irregular particles tend to be generated. If the addition time of the alkali is too long, a hydroxide having a uniform composition is formed, but the growth of nuclei also proceeds, and irregularly shaped particles tend to be generated.

  Control of temperature is also important in the preparation of metal hydroxide slurries. If the temperature at the time of preparation is too low, a large amount of metal hydroxide nuclei are generated in relation to solubility, and the particle size distribution of the finally obtained composite oxide particles becomes broad. From this viewpoint, it is preferable to mix the metal salt mixed aqueous solution and the alkali at 60 to 90 ° C, particularly 70 to 90 ° C.

  Examples of the water-soluble metal salts of cobalt and manganese include sulfates, nitrates, carbonates, and chlorides. The concentration of metal ions in the metal salt mixed aqueous solution may be adjusted to a total ion concentration of about 0.5 to 2.0 mol / L in consideration of productivity and the like. The molar ratio of cobalt ions and manganese ions in the metal salt mixed aqueous solution affects the composition of the resulting composite oxide particles. The molar ratio of cobalt ions / manganese ions is preferably 0.5 to 14, particularly 1 to 6.

  As the alkali, it is preferable to use a caustic alkali such as sodium hydroxide or potassium hydroxide. The concentration of the alkali hydroxide is preferably about 0.5 to 2.0 mol / L. The amount of alkali hydroxide added is preferably adjusted so that the resulting metal hydroxide slurry has a pH of about 10 to 13.

  Next, step (b) will be described. When a metal hydroxide slurry is obtained, an oxidizing gas is blown into the slurry and wet oxidation is performed to obtain composite oxide particles. As the oxidizing gas, air is typically used, but other oxygen-containing gas may be used. In wet oxidation, it is important to adjust the liquid temperature. Specifically, wet oxidation is performed in a state where the metal hydroxide slurry is maintained at 60 to 95 ° C, particularly 70 to 95 ° C. When wet oxidation is performed at a temperature outside this range, the resulting composite oxide particles tend to be atomized. In addition, amorphous particles tend to be generated.

  In wet oxidation, it is also important to adjust the pH of the liquid. In this production method, wet oxidation is carried out in a state where the pH of the liquid is maintained at a relatively high pH range of 10 to 13, particularly pH 11 to 13.

  Wet oxidation continues until the redox potential in the slurry reaches equilibrium.

  The slurry containing the composite oxide particles that have been wet-oxidized is subjected to conventional filtration, washing, and dehydration. Next, it is pulverized after drying at 50 to 120 ° C. In the production of composite oxide particles not containing iron, generally, the particles are blackened by firing thereafter. In contrast, in this production method, black particles are obtained only by wet oxidation without firing. This is a feature of the present manufacturing method. Not firing is advantageous in terms of production efficiency and energy loss. It is also advantageous in that no interparticle sintering occurs.

  The black composite oxide particles obtained in this way are suitably used as black pigments for paints, inks, toners, rubbers and plastics because of their high blackness. For example, black complex oxide particles are mixed with various organic solvents to form a black slurry. The black composite oxide particles are mixed with a known coating film forming component containing a resin and glass frit (glass powder) to form a black paste. Such a black paste is suitably used for forming a black matrix of a flat display panel. Moreover, such a black paste is suitably used for forming a black electrode and a light shielding layer on a front plate such as a plasma display or a plasma address liquid crystal.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
The amounts of cobalt sulfate heptahydrate and manganese sulfate pentahydrate shown in Table 1 were put into 6 liters of water and dissolved by stirring. To this mixed metal salt aqueous solution, 10 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 slurry temperature was maintained at 65 ° C. during the addition of caustic soda. A metal hydroxide slurry was thus obtained.

  While maintaining the liquid temperature of the obtained metal hydroxide slurry at 65 ° C., air was blown in at a rate of 3 L / min for 2 hours. As a result, a slurry of black complex oxide particles was obtained. After stopping the blowing of air, stirring of the reaction solution was continued, the temperature was raised to 85 ° C. in about 60 minutes, and then kept for 1 hour for aging. Then, the produced | generated complex oxide particle slurry was filtered and wash | cleaned, the washing | cleaning cake was dried at 80 degreeC for 10 hours, and the dried product was grind | pulverized.

[Performance evaluation]
The obtained composite oxide particles were evaluated as follows (however, (7) was excluded) . The results are shown in Tables 2 and 3.
(1) Co and Mn contents The sample was dissolved and measured by ICP.
(2) Average primary particle size, particle shape and coefficient of variation, and maximum particle size _Dmax and D50 of aggregated particles
The average particle size and particle shape of the primary particles were taken with a SEM at a magnification of 100,000 times, 200 particles were randomly selected, observed and measured. The variation coefficient was calculated by (standard deviation / average particle diameter of primary particles) × 100 by obtaining a standard deviation from the measured primary particle diameter. On the other hand, the maximum particle diameters _Dmax and D50 of the aggregated particles were measured using LS230 (trade name) manufactured by Beckman Coulter. As a pretreatment for the measurement, the sample was put in an aqueous solution to which sodium hexametaphosphate as a dispersant was added, and the suspension was irradiated with ultrasonic waves for 5 minutes to obtain a measurement sample. The concentration of sodium hexametaphosphate in the suspension was 1% by weight.
(3) BET specific surface area Measured with a 2200 type BET meter made by Shimadzu Micromeritics.
(4) Oil absorption amount It carried out based on JISK5101.
(5) Volume electric resistance The sample was exposed in an environment room for 24 hours in an environment of 25 ° C. and 55% RH. Next, 10 g of the exposed sample was placed in a holder, and a pressure of 600 kg / cm 2 was applied to form a 25 mmφ tablet. An electrode was attached to the compact, and the electrical resistance was measured under a pressure of 150 kg / cm ² . The volume resistance value was determined from the thickness and cross-sectional area of the sample used for the measurement and the resistance value.
(6) Blackness and hue This was carried out in accordance with JIS K-1991. To 2.0 g of the sample, 1.4 cc of castor oil was added and kneaded with a Hoover type Mahler. 7.5 g of lacquer was added to 2.0 g of this kneaded sample, and after further kneading, this was applied onto mirror-coated paper using a 4 mil applicator. After drying, the blackness (L value) and the hue (a value, b value) were measured with a color difference meter (manufactured by Tokyo Denshoku Co., Ltd., color analyzer TC-1800 type). The heat treatment of the sample (600 ° C., 1 hour) was performed in an air atmosphere by placing the sample in an alumina dish into an electric muffle furnace FUW230A (trade name) manufactured by Advantech.
(7) Heat resistance ΔE
ΔE was calculated from the following equation. In the formula, ΔL, Δa, and Δb respectively represent differences in L value, a value, and b value before and after heat treatment in an air atmosphere at 600 ° C. for 1 hour. The heat treatment method is the same as (6) above.
ΔE = (ΔL ² + Δa ² + Δb ² ) ^1/2
(8) Specular Reflectance 60 g of a solution prepared by dissolving styrene acrylic resin (TB-1000F) in (resin: toluene = 1: 2), 10 g of a sample after heat treatment, 90 g of glass beads having a diameter of 1 mm, having an inner volume of 140 ml After putting in a bottle and capping, it was mixed for 30 minutes with a paint shaker (manufactured by Toyo Seiki Co., Ltd.). This was applied to a glass plate using a 4 mil applicator, and after drying, the reflectivity at 60 degrees was measured with an uneven GLOSS METER (GM-3M).
(9) Aggregation degree Using “Powder Tester Type PT-R” (trade name) manufactured by HOSOKAWA MICRON, measurement was performed at a vibration time of 65 seconds.
(10) Saturation magnetization Using a vibrating sample magnetometer VSM-P7 manufactured by Toei Industry Co., Ltd., measurement was performed with a load magnetic field of 796 kA / m.

[Examples 2 and 3 and Comparative Examples 1 to 4]
Composite oxide particles were obtained in the same manner as in Example 1 except that each production condition was changed as shown in Table 1. 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 example 1 corresponds to the example in Patent Document 2 described above.

As is clear from the results shown in Tables 2 and 3, it can be seen that the black composite oxide particles of the examples have a small specific surface area. Further, it can be seen that the volume electric resistance value is high and the dispersibility is good (the specular reflectance is high, the oil absorption is low, and the saturation magnetization is low).

Claims (12)

  Number average average particle size of primary particles based on observation with a scanning electron microscope, comprising 35 to 70% by weight of cobalt and 5 to 40% by weight of manganese, and having a molar ratio Co / Mn of cobalt to manganese of 0.5 to 14. A black composite oxide particle having a diameter of 0.05 to 0.3 μm and an octahedral shape.   2. The black composite oxide particles according to claim 1, wherein the coefficient of variation of the primary particle diameter in the number-based particle size distribution of the primary particles based on observation with a scanning electron microscope is 40% or less. The black composite oxide particles according to claim 1 or 2, wherein the maximum particle diameter _Dmax of the aggregated particles in the particle size distribution based on the number criterion using a laser diffraction scattering method is 4 µm or less. The black composite oxide particles according to any one of claims 1 to 3, having a volume electric resistance value of 1 x 10 ⁴ Ω · cm or more.   The black complex oxide particles according to any one of claims 1 to 4, wherein the black complex oxide particles are produced without undergoing a firing step. Black complex oxide particles according to any one of the metal elements other than cobalt and manganese claims 1 that contains no 5. The black complex oxide particles according to any one of claims 1 to 6, wherein the saturation magnetization is 3 Am ² / kg or less. The black complex oxide particles according to any one of claims 1 to 7, wherein the specific surface area by BET is 5 to 30 m ² / g.   A black slurry containing the black complex oxide particles according to claim 1 and an organic solvent.   A black paste comprising the black complex oxide particles according to claim 1, a coating film-forming component containing a resin, and glass frit.   A black matrix formed of the black paste according to claim 10.   2. The method for producing black composite oxide particles according to claim 1, wherein a metal salt mixed aqueous solution in which water-soluble salts of cobalt and manganese are dissolved and an alkali are neutralized and mixed. A method for producing black composite oxide particles, characterized by oxidizing with oxidizing gas under conditions maintained at -95 ° C and pH 10-13.