JPH0557207B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing conductive fine powder, and more specifically, it is capable of imparting conductivity to plastics used in electronic devices and construction materials when mixed therewith. The present invention relates to a method for producing a conductive fine powder that can be mixed into a paint to form a conductive coating film without impairing the transparency of plastics or the coating film. [Prior Art] Metal oxides, such as indium oxide and tin oxide doped with different elements, are known as fine powders that can be mixed into plastics and paints to impart electrical conductivity to them. This type of conductive fine powder is generally produced by chemical means using a suitable metal halide or alkoxide as a starting material.
The publication describes that a specific solution in which specific amounts of tin chloride and antimony chloride are dissolved is poured into heated water to hydrolyze the chloride, and the precipitate that is precipitated is filtered and washed, followed by heat treatment. A method for producing antimony-containing tin oxide fine powder is described. [Problems to be Solved by the Invention] Conventional methods for producing conductive fine powder by chemical means, whether starting from halides or alkoxides, produce conductive fine powder by hydrolysis. A powder precursor is precipitated in a liquid, and this precipitate is in a state of agglomeration of extremely fine primary particles. Therefore, the fine powder obtained by filtering and washing the precipitate and then heating it becomes a strong sintered product because the primary particles are fine, and its particle size distribution is generally broad. Therefore, when mixing and dispersing conductive fine powder into plastics or paints, it is necessary to crush the fine powder in order to make the mixing and dispersion uniform. However, in conventional conductive fine powder produced through a precipitate generation process, the primary particles have an extremely small particle size and high surface activity, resulting in strong bonding between particles and progressing sintering. Moreover, the above-mentioned pulverization is not always easy. In addition, even if the agglomerated particles are pulverized by pulverization and the average particle size is reduced, the particle size distribution cannot be sharpened, and since particles inherently have a strong cohesive force, they are not likely to reagglomerate. In order to prevent this, a relatively large amount of surfactant must be used, which is disadvantageous. [Means for Solving the Problems] The inventors of the present invention have developed a method for solving the problems in view of the fact that the above-mentioned problems can hardly be solved when conductive fine powder is manufactured through a precipitate generation process as in the past. Instead of precipitating a conductive fine powder precursor in a liquid, we dispersed it in the form of colloidal particles, thereby developing a method for producing conductive fine powder that does not have the above-mentioned drawbacks. That is, the method for producing a conductive fine powder according to the present invention involves holding an aqueous solution containing a tin compound or an indium compound under a pH condition of 8 to 12 to gradually hydrolyze the tin or indium compound. The method is characterized in that a sol containing colloidal particles of a metal oxide and/or a hydrous oxide is produced, and then this sol is dried and fired. Alternatively, a sol containing colloidal particles of tin oxide and/or hydrous oxide can be prepared by holding an aqueous solution of a tin compound under a pH condition of 8 to 12 and gradually hydrolyzing the tin compound in the solution. After generating and collecting colloidal particles from the sol, the colloidal particles are impregnated with an aqueous solution of at least one of an antimony compound, a phosphorus compound, and a fluorine compound, and then the particles are dried and calcined, or Aqueous solution of indium compound at pH 8-12
By gradually hydrolyzing the indium compound in the liquid while maintaining the conditions, a sol containing colloidal particles of indium oxide and/or hydrated oxide is generated, and the colloidal particles are recovered from this sol. The colloidal particles are impregnated with an aqueous solution of a tin compound and/or a fluorine compound, and then the particles are dried and fired. [Function] In the method of the present invention, a water-soluble tin compound or an indium compound that is hydrolyzable in the pH range of 8 to 12 is used as a starting material, and specifically, potassium stannate, sodium stannate, etc. and indium compounds such as indium nitrate and indium sulfate can be used. When the metal species contained in the aqueous solution containing a tin compound or an indium compound (hereinafter referred to as the raw material liquid) is either tin or indium, the fine powder produced in the present invention is a tin oxide or an indium oxide. However, by dissolving a small amount of a compound of a different element in the raw material liquid, a conductive fine powder doped with a different element can be manufactured.
By the way, by dissolving a small amount of tartarite or ammonium fluoride in a raw material liquid containing a tin compound, it is possible to obtain a conductive fine powder in which tin oxide is doped with antimony or fluorine, and an indium compound can be obtained. By dissolving a small amount of a tin compound in a raw material liquid containing indium oxide, it is possible to obtain a conductive fine powder in which indium oxide is doped with tin. The concentration of the tin compound or indium compound contained in the raw material liquid can be arbitrarily selected, but is generally preferably in the range of 0.5 to 30 wt%. In the method of the present invention, the tin compound or indium compound contained in the above-mentioned raw material liquid is hydrolyzed under conditions of pH 8 to 12 together with a compound of a different element serving as a dopant when the compound is coexisting with the different element. , while the hydrolysis reaction is occurring, the reaction system is
The PH must always be kept at any constant value in the range of 8-12. If the pH is less than 8, even if it is close to PH8,
When the particle size distribution becomes broad and the pH value further decreases, metal oxides or hydrous oxides generated by hydrolysis precipitate, making it impossible to disperse them in the liquid as colloidal particles, thus making it difficult to prepare a sol. This is because it cannot be done. Also, the PH of the reaction system is
If it exceeds 12, it is not impossible to prepare a sol, but when washing the colloid particles filtered from the sol, the alkaline content cannot be sufficiently removed, resulting in a deterioration in the conductivity of the final fine powder. Because it does. Therefore, when carrying out the hydrolysis reaction of the present invention, a reactor containing water adjusted to a constant pH in the range of 8 to 12 is prepared, and if the raw material liquid is alkaline, it is reacted with an acid aqueous solution. It is preferable to add it to the reactor at a feed rate that does not cause the PH inside the container to deviate from the specified range.If the raw material liquid is acidic, add it and the alkaline aqueous solution to the reactor in the same manner as above. is recommended. There are no particular restrictions on the solid content concentration of the sol produced in the reactor, but generally speaking, as the concentration increases, the particle size distribution of the colloid particles produced tends to become broader. The reaction temperature for hydrolysis can be arbitrarily selected usually within the range of 30 to 90°C. By hydrolyzing the raw material liquid preferably gradually under the above PH conditions, colloidal particles consisting of tin or indium oxide or hydrous oxide are produced, and a sol containing these particles as a dispersoid is prepared. be done. In this case, if the dopant coexists in the raw material liquid, it goes without saying that colloidal particles containing the dopant can be obtained. The average particle size of the colloidal particles obtained by hydrolysis is in the range of 0.05 to 0.3 μm, preferably 0.07 to 0.2 μm, and the particle size distribution is such that 80% or more of all particles are 0.5 to 1.5 times the average particle size. within the range of The average particle size and particle size distribution of the colloidal particles can be controlled by the concentration and supply rate of the raw material liquid supplied to the hydrolysis reaction system, and the lower the concentration of the raw material liquid, the sharper the particle size distribution. Further, the slower the feed rate of the raw material liquid, the larger the colloid particles can grow. After the sol is prepared, the sol is filtered to collect colloidal particles, washed to remove by-product salts and other substances adhering to the particles, dried, and further calcined to obtain the object of the present invention. Conductive fine powder can be obtained. The electrically conductive fine powder doped with a different element can also be produced by the following method. That is, an aqueous solution of a tin compound is used as a raw material solution, a sol is generated by gradually hydrolyzing the tin compound in the solution under the above reaction conditions, colloidal particles are collected from this sol, and then an antimony compound, A conductive fine powder in which a tin compound is doped with antimony, phosphorus, fluorine, etc. is obtained by impregnating the colloidal particles with an aqueous solution of at least one of a phosphorus compound and a fluorine compound, and then drying and firing the particles. can be manufactured. Alternatively, an aqueous solution of an indium compound is used as the raw material liquid, a sol is generated in the same manner as above, and after collecting colloidal particles from this sol, the colloidal particles are impregnated with an aqueous solution of a tin compound and/or a fluorine compound, and then By drying and firing these particles, it is possible to produce a conductive fine powder in which an indium compound is doped with tin and/or fluorine. Even when the raw material solution is an aqueous solution of a tin compound or an aqueous solution of an indium compound, if by-product salts are generated during the sol generation process, not only will the colloid particles be more likely to aggregate, but the final The specific resistance of the conductive fine powder obtained in the process increases due to the contamination of accessory salts, so if the formation of accessory salts is expected, the colloidal particles recovered from the sol should be added to the compound of the doping element. It is recommended that by-product salts be washed away from colloidal particles prior to impregnation with an aqueous solution. The colloidal particles obtained by the above method are slightly sintered during the firing process, so the average particle size of the powder is 20
~50μm, but the specific surface area of this powder is 50
m ² /g or less, which is smaller than the specific surface area of 70 to 100 m 2 /g of conventional powder produced through a precipitation process, which means that the fine powder produced by the method of the present invention has a specific surface area of 70 to 100 m ² /g. This indicates that it is composed of primary particles that are larger than conventional fine powders. The fine powder produced by the method of the present invention can also be easily released from its sintered state by pulverization, and a conductive fine powder of about 0.05 to 0.4 μm can be obtained by ordinary pulverization means. The fine powder thus obtained contains only a small amount of coarse particles of, for example, 0.8 μm or more. [Example] Example 1 316.0 g of potassium stannate and 38.4 g of tartarite were added to water.
A raw material solution was prepared by dissolving 686 g of the raw material. The above raw material solution was added together with nitric acid over 12 hours to 1000g of water heated to 50℃ and under stirring, and the pH in the system was adjusted.
Hydrolysis was performed while maintaining the temperature at 8.5 to obtain a sol. Colloidal particles were filtered from this sol, washed to remove by-product salts, dried, and calcined in air at 350°C for 3 hours, and further calcined in air at 650°C for 2 hours to obtain a fine powder. Ta. Example 2 A fine powder was obtained in exactly the same manner as in Example 1, except that the pH of the hydrolysis reaction system was maintained at 11. Example 3 A fine powder was obtained in exactly the same manner as in Example 1, except that the time required for adding the raw material liquid was 6 hours, and the pH of the hydrolysis reaction system was maintained at 9.0. Example 4 A fine powder was obtained in exactly the same manner as in Example 3, except that the time required for adding the raw material liquid was 20 hours. Example 5 A fine powder was obtained in exactly the same manner as in Example 3, except that a solution in which 316.0 g of potassium stannate and 38.4 g of tartarite were dissolved in 3183 g of water was used as the raw material liquid. Example 6 A fine powder was obtained in exactly the same manner as in Example 3, except that a solution in which 316.0 g of potassium stannate and 38.4 g of tartarite were dissolved in 353 g of water was used as the raw material liquid. Example 7 A fine powder was obtained in exactly the same manner as in Example 1, except that a solution in which 331.8 g of potassium stannate and 17.1 g of ammonium fluoride were dissolved in 686 g of water was used as the raw material liquid. Example 8 686g of 371.6g of potassium stannate as raw material liquid
A fine powder was obtained in exactly the same manner as in Example 1, except that a solution dissolved in water was used. Example 9 316.0 g of potassium stannate and 38.4 g of tartarite were
A raw material solution was prepared by dissolving it in 328 g of water heated to 50 °C, and the procedure was exactly the same as in Example 1, except that this raw material solution and nitric acid were added to 50 g of water heated to 50 °C and under stirring. A fine powder was obtained. Example 10 A solution of 79.9 g of indium nitrate dissolved in 686 g of water and a solution of 12.7 g of potassium stannate dissolved in a 10 wt % potassium hydroxide solution were prepared. The above indium nitrate solution and potassium stannate solution were added over 2 hours to 1000 g of water heated to 50°C and stirred, and the PH in the system was maintained at 11 to perform hydrolysis and form a sol. Obtained. Colloidal particles are filtered from this sol, washed to remove by-product salts, and then dried.
Fired at 350℃ in air for 3 hours, then further heated at 600℃ in air.
The mixture was fired for 2 hours to obtain a fine powder. Example 11 A fine powder was obtained in the same manner as in Example 10, except that the time required for adding the indium nitrate solution and the potassium stannate solution was extended to 7 hours. Example 12 A fine powder was obtained in exactly the same manner as in Example 10, except that the pH of the hydrolysis reaction system was maintained at 12. Example 13 A raw material solution was prepared by dissolving 371.6 g of potassium stannate in 686 g of water. heated to 50℃ and under stirring
The above raw material solution was added to 1000 g of water over 12 hours together with nitric acid, and the pH in the system was maintained at 8.5 to carry out hydrolysis to obtain a sol. Colloidal particles were filtered from this sol, washed to remove by-product salts, and then dried. 10wt of antimony fluoride to the resulting particles
% aqueous solution was impregnated. Then, the particles were calcined in air at 350°C for 3 hours, and then heated at 650°C in air.
A fine powder was obtained by firing at ℃ for 2 hours. Example 14 Example 13 except that after filtering the colloidal particles from the sol and removing by-product salts, 13 g of 20% phosphoric acid was impregnated instead of the antimony fluoride aqueous solution without drying. A fine powder was obtained in exactly the same manner as above. Example 15 A raw material solution was prepared by dissolving 79.9 g of indium nitrate in 686 g of water. heated to 50℃ and under stirring
The above raw material solution was added to 1000g of water over 2 hours together with a 10wt% potassium hydroxide solution, and the pH in the system was adjusted.
was maintained at 11.0 and hydrolysis was carried out to obtain a sol.
Colloidal particles were filtered from this sol, washed to remove by-product salts, and the particles were dried, calcined in air at 650°C for 2 hours, and further calcined in air at 600°C for 2 hours to obtain a fine powder. . Example 16 Colloidal particles were filtered from the sol obtained in Example 15, washed to remove by-product salts, and then impregnated with 66.5 g of a 10 wt% aqueous solution of tin fluoride whose pH was adjusted to 1 with hydrochloric acid. . Then dry this particle in air for 350 min.
℃ for 3 hours, and then in air at 650℃ for 2 hours to obtain a fine powder. Comparative Examples 1-2 Fine powder was obtained in exactly the same manner as in Example 1, except that the pH of the hydrolysis reaction system was changed to 7 and 13, respectively. Comparative Examples 3-4 Fine powder was obtained in exactly the same manner as in Example 10, except that the pH of the hydrolysis reaction system was changed to 7 and 13, respectively. Comparative Example 5 A solution is prepared by dissolving 173 g of tin chloride and 20.9 g of antimony chloride in 300 c.c. of methanol. The above solution was added to 3000 g of water heated to 90°C and stirred over 4 hours to cause hydrolysis, and the precipitate formed was filtered and washed, dried and then heated in air for 500 g.
A fine powder was obtained by firing at ℃ for 2 hours. Regarding the sols obtained in each of the above examples and comparative examples, the average particle size of the colloidal particles dispersed therein was measured to determine the particle size distribution, and for the fine powder, the average particle size, specific surface area, and specific resistance were measured. did. The results are shown in Table-1. The measurement method is as follows. Average particle size Ultracentrifugal particle size analyzer (manufactured by Horiba, product name:
CAPA-500), adjust the solid content concentration of the measurement sample solution to 0.5wt%, and in the case of colloidal particles,
Measurement was performed by centrifugal sedimentation at 5000 rpm, and in the case of fine powder, natural sedimentation. Specific surface area The specific surface area of the fine powder was measured by the BET method. Specific resistance A certain amount (0.5 g) of fine powder was pressurized to 100 Kg/cm ² and the specific resistance was measured.

【table】

[Table] [Effects of the Invention] The method of the present invention allows metal oxides or their hydrated oxides, which are precursors of conductive fine powder, to be produced in the range of an average particle size of 0.05 to 0.3 μm without precipitating the metal oxides or their hydrous oxides. The conductive fine powder produced by the present invention is obtained by generating colloidal particles with a sharp particle size distribution, and drying and baking a sol in which the colloidal particles are dispersed. The primary particles constituting the powder are larger than conventional conductive fine powder produced through a precipitate generation process, and therefore its sintering force is weak. Therefore, the conductive fine powder of the present invention can be easily released from its sintered state by ordinary pulverization means, and the conductive fine powder of the present invention can be easily released from its sintered state with a particle size of 0.05 to 0.4 μm.
It is possible to obtain a powder with a particle size of approximately Therefore,
The electrically conductive fine powder of the present invention can be mixed into plastics and the like to impart electrical conductivity to them without impairing their transparency.

Claims (1)

[Claims] 1. By holding an aqueous solution containing a tin compound or an indium compound under PH conditions of 8 to 12 and gradually hydrolyzing the tin or indium compound, metal oxides and/or water-containing 1. A method for producing conductive fine powder, which comprises producing a sol containing colloidal particles of an oxide, and then drying and firing the sol. 2. A sol containing colloidal particles of tin oxide and/or hydrated oxide is produced by holding an aqueous solution of a tin compound under PH conditions of 8 to 12 and gradually hydrolyzing the tin compound in the solution. After collecting colloidal particles from this sol, at least one of an antimony compound, a phosphorus compound, and a fluorine compound is added.
1. A method for producing conductive fine powder, which comprises impregnating the colloidal particles with an aqueous solution of seeds, and then drying and calcining the particles. 3 By holding an aqueous solution of an indium compound under a pH condition of 8 to 12 and gradually hydrolyzing the indium compound in the solution, a sol containing colloidal particles of indium oxide and/or hydrous oxide is produced. After collecting the colloidal particles from the sol, the colloidal particles are impregnated with an aqueous solution of a tin compound and/or a fluorine compound, and then the particles are dried and fired. Manufacturing method.