JP2003059342A - Conductive powder and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide conductive powder usable as an industrially useful filler, not causing performance degradation when using it by kneading it with resin or the like, having a friction static charge quantity nearly equal to zero, light- colored and having a small specific gravity. SOLUTION: This conductive powder comprises conductive particles and/or aggregates thereof obtained by making silicon atom concentration in a coating layer of each conductive particle continuously or gradually reduce toward the outside from the center side of the particle in the radial direction of the particle when the coating layer formed of a conductive oxide containing silicon atoms such as a tin-based composite oxide containing a silica constituent is formed on the surface of each inorganic oxide particle containing silica as a main constituent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive powder composed of conductive particles obtained by coating inorganic oxide particles containing silica as a main component with a conductive oxide, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, conductive fillers have been used in various fields. For example, in order to prevent dust from adhering to various plastic products due to static electricity or dust explosion of flammable powder contained in a plastic container, powdered or fibrous conductive filler is added to the raw material plastic. Then, various plastic products have been given conductivity to have antistatic ability. Further, also in black toner and color toner used in the electrophotographic field such as dry printers and copiers, in order to control surface physical properties such as volume resistivity and triboelectric charge amount of the toner particles themselves, a conductive filler is used. It is used. Further, in addition to the toner, a similar conductive filler is required in order to control the volume resistivity of the member used for the electrophotographic photosensitive drum and the charging member.

As described above, conductive fillers are used in various industrial fields and their applications are expanding and diversifying, but the degree of conductivity (value of volume resistivity) required for each application is different, Further, various performances are required in addition to conductivity. One of the demands is to reduce the color. For example, in a tray for transporting electronic parts used in the manufacture of ICs, LSIs, etc., and in a packaging bag for flammable powders such as wheat flour, transparency is required to identify the contents, and thus such applications are required. It is desired that the conductive filler used in the above is a light color system. Also, for toners, the use for color electrophotography has been rapidly increasing in recent years, and therefore, a light-colored conductive filler is required in order to increase the degree of freedom in coloring the toner.

Carbon black and metal powders have been used as the conductive fillers generally used in the past, but when these are used, it is difficult to freely color them and it is difficult to meet the above requirements. . In particular, when a metal powder is used, there is a problem that its conductivity decreases over time because it is gradually oxidized by moisture in the air, and when it is used as a conductive filler for toner, the image quality becomes uneven. May be.

As such a light-colorable conductive substance, oxide-based fillers such as indium oxide-based, zinc oxide-based, and tin dioxide-based fillers are considered. Among them, tin dioxide-based fillers are relatively inexpensive. , Because it has low toxicity, it is promising.
However, since tin dioxide is generally low in conductivity and has a small controllable width, it is possible to control the volume resistivity of antimony, fluorine, phosphorus, arsenic, bismuth, selenium, tellurium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, etc. Dopant having an action of decreasing (improving conductivity) (hereinafter, also referred to as conductivity improving dopant).
Need to be added to enhance conductivity. However, when a large amount of these conductivity-improving dopants are added, not only can the coloring be reduced and the above-described lightening cannot be achieved, but the conductivity-improving dopant is generally harmful. Due to the large number of them, their uses are limited, and caution is required during production, use, or disposal.
Therefore, it is necessary to reduce the amount of the conductivity improving dopant added as much as possible, or to use a dopant having low toxicity depending on the application.

In order to satisfy the above requirements, for example, Japanese Patent Publication No. 62-1572, Japanese Patent Publication No. 62-1573,
Japanese Examined Patent Publication No. 62-1574 and Japanese Patent Laid-Open No. 3221
Japanese Patent Laid-Open Publication No. 2004-242242 discloses that tin dioxide powder containing no dopant for improving conductivity has a volume resistivity of 10 ⁴ to 10 ⁷ Ωc.
m is described. In addition, JP-A-6-34
No. 5429 discloses that a solution containing a stannic salt is neutralized to deposit a precipitate, and then the precipitate is fired in an inert or weakly reducing atmosphere to obtain 2.0 × 10 ^8.
It is described that a tin dioxide powder having a volume resistivity of 10 ⁻¹ to 10 ⁴ Ωcm when measured by a powder compacting method with a very high pressing pressure of Pa is obtained.

However, with these tin dioxide powders,
Regarding the one having a low volume resistivity, the above-mentioned JP-A-6-345 is used.
As described in Japanese Patent No. 429, the surface of tin dioxide powder is locally reduced to metallic tin, so that the resulting tin dioxide powder contains metallic tin and is colored, or the metallic tin is oxidized. The volume resistivity greatly increases with time,
It is expected that it will be difficult to control the volume resistivity in various plastic and toner addition applications. Further, since tin dioxide powder which does not contain a dopant for improving conductivity has a high volume resistivity, it is necessary to add a large amount to various plastics in order to use it as a conductive filler, which causes a problem of impairing the properties of the plastic. Therefore, in consideration of the above-mentioned harmfulness, tin dioxide powder in which the addition amount of the conductivity improving dopant is reduced as much as possible, the conductivity is high (the volume resistivity is low), and the conductivity is less likely to change over time is sought. Has been.

In addition, in a plastic product for electronic parts, which is averse to static electricity, it is also important to add a conductive filler to efficiently dissipate static electricity generated by friction between plastic products or other substances. However, since the amount of the conductive filler added may be limited depending on the application, it is preferable not to generate static electricity if possible. Static electricity is generated when two or more substances come into contact with each other and rub against each other, whereby electric charges are transferred between these substances and a positive or negative charge is applied. For example, when the same substance contacts and rubs like a plastic film wound in a roll, the triboelectrification characteristics are close to neutral, that is, measured using a Faraday cage in order to prevent the generation of static electricity as much as possible. A plastic film having a triboelectrification amount close to zero is preferable, and for that purpose, a conductive filler for controlling the triboelectrification amount and efficiently dissipating the static electricity even if static electricity should occur is desired. For example, plastic products used in trays for transporting electronic parts and packaging bags for flammable powders are thought to be due to the addition of other additives such as plasticizers and silica. It is difficult to suppress the generation of static electricity because the measured triboelectric charge amount is −several hundred μC / g or less, that is, the absolute value often takes a very large negative value. Therefore, as the conductive filler, one having an absolute value as small as possible, that is, one having a value close to zero (specifically, about −100 to 0 μC)
/ G) or a conductive filler having a polarity opposite to the triboelectric charge amount of the tray or the packaging bag described above is preferably added to bring the triboelectric charge amount close to zero as a whole.

Further, in the electrophotographic apparatus, it is necessary to strictly control the triboelectric charge amount of the toner itself in order to obtain a high quality printed matter. However, the toner contains additives for controlling other characteristics, such as coloring materials and external additives. However, addition of various additives affects the triboelectric charge amount of the toner. Is added to control the triboelectric charge amount of the toner. In recent years, for the purpose of downsizing an electrophotographic apparatus and eliminating waste toner, a so-called cleanerless system type electrophotographic apparatus (for example, Japanese Patent Laid-Open No. 11-2
12337, JP 2000-162849 A, JP 2
No. 000-267337) has been proposed, but in this method, it is necessary to strictly control the triboelectric charge amount of the toner.

In the cleanerless system, after the toner image is transferred onto the transfer material, the transfer residual toner left untransferred on the photosensitive drum is scraped off by the charging member (magnetic particles etc.) of the charging section, and once transferred to the charging section. After storing it, return it to the photosensitive drum again, and then collect it in the developing unit containing toner.
It is a reuse system. Since this system does not need to newly provide a cleaner part, it has an advantage that the apparatus can be downsized, and since it does not generate waste toner, it is a preferable system from the viewpoint of environmental protection. In the cleanerless system, in order to prevent a phenomenon in which the transfer residual toner once stored in the charging unit is unnecessarily charged by sliding friction with the charging member, that is, charge-up, the toner is approximately (10 ² to 10 ⁹ Ωcm). Fine powder (hereinafter, also referred to as conductivity control powder) having a volume resistivity of
Although it is necessary to have a function of releasing the electric charge, the frictional charge amount control of the toner is complicated because a conductive control powder is newly added to the toner. There are several developing methods. If you adopt the method of developing with the toner charged positively on the photosensitive drum side and negatively charged,
Even if the conductive control powder is added to the toner, it is necessary that the conductive control powder also has the property of being charged from zero to minus so that the toner can be charged negatively. However, in order to minimize the influence on the triboelectric charge amount of the toner, a toner whose triboelectric charge amount has a small absolute value (specifically,
(About 100 to 0 μC / g) is preferable, and it has been attempted to add tin dioxide powder to the toner by a toner maker (for example, JP-A-11-212337,
JP-A-2000-162849, JP-A-2000-267
337). However, the triboelectric charge amount of tin dioxide powder is usually about −120 μC / g (Small.Surface.320.vol23.No.6 [1985]). Therefore, when tin dioxide powder is added to the toner, the triboelectric charge amount of the toner is reduced. It will have a big impact. Further, tin dioxide powder has a specific gravity of about 7 and is very heavy, so that a lighter conductive filler to be added to plastic products and toners is required. Furthermore, in order to facilitate the handling of the powder or to improve the fluidity of the toner, a spherical shape or a substantially spherical shape is preferable.

In response to such a request, for example, Japanese Patent Laid-Open No.
6-114215, JP-A-56-114216, JP-A-56-114217, and JP-A-56-114218.
JP-A No. 1994-242 discloses a method for producing a metal oxide powder coated with tin dioxide. However, although the powder produced by this method has a high degree of lightness and a low specific gravity, the coating layer is very easily peeled off, so that the conductivity is reduced when kneaded with various plastics and toners. Or
There is a problem in that a metal oxide such as silica having a triboelectric charge amount of −100 μC / g is exposed on the surface, so that the triboelectric charge amount is significantly reduced.

[0012]

As described above, although it is considered that the tin-based oxide containing tin dioxide as a main component can be an industrially useful conductive filler, it is highly safe and is a light-colored type. , The volume resistivity is lower, the volume resistivity does not change, the triboelectric charge amount has a negative value close to zero, the specific gravity is light, and the spherical or substantially spherical shape is So far unknown. An object of the present invention is to provide such conductive particles or conductive powder and a method for producing the same.

[0013]

Means for Solving the Problems The inventors of the present invention have made extensive studies to achieve the above object. As a result, when a coating layer made of a conductive oxide is formed on the surface of inorganic oxide particles containing silica as a main component, the coating layer contains silicon atoms and the concentration of silicon atoms in the coating layer is increased. It was found that a conductive powder satisfying the above-mentioned requirements can be obtained when the number of particles is decreased from the center side to the outside, and the present invention has been completed.

That is, the present invention relates to a conductive powder comprising conductive particles and / or aggregates thereof, in which a coating layer made of a conductive oxide is formed on the surface of inorganic oxide particles containing silica as a main component. The conductive powder is characterized in that the coating layer of the conductive particles contains silicon atoms and the concentration of silicon atoms in the coating layer decreases from the center side of the particles toward the outside.

The conductive particles constituting the conductive powder of the present invention are inorganic oxide particles containing silica as a main component (hereinafter,
Also called core particles. ) Has a specific coating layer formed of a conductive oxide containing a silicon atom,
Since the silicon atom concentration in the coating layer decreases continuously or stepwise from the surface of the core particle to the surface of the coating layer, there is no clear boundary between the core particle and the coating layer, and the adhesion Is very high. Further, the conductive powder of the present invention, although the reason is unknown, has a triboelectric charge amount closer to zero as compared with the conventional tin dioxide powder, so that dust adhesion to various plastic products and plastic It can be used for various purposes, such as conductive filler added for the purpose of preventing dust explosion of flammable powder contained in a container, or conductivity control powder for toner of electrophotographic devices. . Furthermore, when the conductive powder of the present invention is kneaded into various plastics, the coating layer is peeled off from each conductive particle, and the triboelectric charge amount is −several hundred μC.
The core particles exhibiting / g are not exposed, and it is difficult for the conductivity to decrease and the triboelectric charge amount to significantly decrease. Further, among the above-mentioned conductive powder of the present invention, the conductive particles forming the spherical particles or spherical particles have a characteristic that particles have less aggregation and have good fluidity and are easy to handle. It is particularly suitable for applications such as conductivity control powder for toner.

Another aspect of the present invention is that a silicon-containing compound capable of forming a polysiloxane bond by a hydrolysis / polycondensation reaction and a hydrolysis / polycondensation in a suspension of inorganic oxide particles containing silica as a main component. A metal atom or a metalloid atom-containing compound capable of forming a -MOMM bond (where M means a metal atom or metalloid atom whose oxide exhibits conductivity) by a reaction, At the same time continuously or intermittently,
Further, it is added such that the ratio of the weight of the silicon-containing compound at the time of addition to the weight of the metal atom- or metalloid atom-containing compound is continuously or stepwise reduced from the start of the addition to the end of the addition, and the silica is the main component. Production of a conductive powder of the present invention, which comprises depositing a polycondensate of a hydrolyzate of these compounds on the surface of inorganic oxide particles, and then heat-treating the particles on which the polycondensate is deposited. Is the way. According to this method, the conductive powder of the present invention can be efficiently produced.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive powder of the present invention comprises conductive particles in which a specific coating layer made of a conductive oxide containing silicon atoms is formed on the surface of core particles, and / or aggregates thereof. The core particle is not particularly limited as long as it is an inorganic oxide particle containing silica as a main component, and may be made of only silica or may contain an inorganic oxide other than silica.
In addition, here, having silica as a main component means that a silica component is a component with the largest content in a core particle. By using silica as the main component of the core particles, it is possible not only to increase the dichroism of the conductive powder finally obtained or to reduce the specific gravity, but also to reduce the manufacturing cost, Further, there is an advantage that spherical or substantially spherical conductive particles can be easily produced. From the viewpoint that such a merit is large, the content of the silica component in the core particles is 50 to 100% by weight,
It is particularly preferably 80 to 100% by weight, and 90 to
Most preferably 100% by weight.

The inorganic oxide component other than silica which may be contained in the core particles is not particularly limited as long as it does not reduce the lightness. Specific examples of suitable inorganic oxide components include tin oxide such as tin dioxide and tin monoxide, zinc oxide, antimony oxide, indium oxide, alumina, zirconia, titania, boron oxide, phosphorus oxide, magnesia, Examples thereof include calcium oxide and rare earth oxides. Plural kinds of these inorganic oxide components may be contained. When the core particles contain these inorganic oxide components, especially the same kind of inorganic oxide component as the conductive inorganic oxide contained in the coating layer, the coating layer tends to be easily formed. Among these, tin oxide, zinc oxide, conductive oxides such as indium oxide, or alumina, zirconia, because of the ease of forming the coating layer,
It is particularly preferable to use titania or the like. When the core particles contain an inorganic oxide component other than silica, these inorganic oxide components may be solid-dissolved in silica or may be phase-separated and dispersed in the silica matrix as fine crystals.

The size of the core particles is not particularly limited,
It may be appropriately determined depending on the application, but if it is too large, it becomes difficult to coat the core particles uniformly,
The average particle diameter of the core particles is preferably 30 μm or less. The lower limit of the particle diameter is not particularly limited, and may be any small value as long as it can be discriminated by observation with a transmission electron microscope (TEM). The shape of the core particles is not particularly limited, but it is preferably spherical or substantially spherical. The spherical or substantially spherical shape as used herein means that the conductive particles have a spherical shape or a shape close thereto, and the average degree of uniformity is 0.66 to 1.
It is 00. When conductive particles are produced using such spherical or substantially spherical core particles, similarly spherical or substantially spherical conductive particles can be easily obtained. Such conductive particles are particularly useful because they have high fluidity, are easy to handle, and can be easily filled into various plastics. The above-mentioned average uniformity is the maximum width (major axis: L) and the maximum width (minor axis: minor axis: n) of each of n (n> 30) conductive particles.
It is the average of the values of B / L calculated in B). These major axis and minor axis are, for example, electron microscope (SE
It can be determined by taking a photograph with M or TEM) and measuring the major axis and the minor axis of particles observed in the unit visual field of the photograph.

In the conductive particles constituting the conductive powder of the present invention, the coating layer formed on the core particles is made of a conductive oxide containing silicon atoms, and the concentration of silicon atoms in the coating layer is It must decrease from the center of the particle toward the outside. That is, although silicon atoms usually exist as oxides in the coating layer, the silicon atoms in the coating layer do not disperse at a uniform concentration, but move from the core particle surface toward the surface of the coating layer. Therefore, it is important that the silicon atom concentration (or silicon oxide concentration) is continuously or stepwise reduced, in other words, that there is a concentration gradient.
When the coating layer has such a structure, the adhesive force between the core particle and the coating layer can be increased, and the coating layer is very unlikely to come off. On the outer surface of the coating layer, the concentration of silicon atoms may be zero or may remain slightly. However, from the viewpoint of reducing the volume resistivity of the conductive particles of the present invention and making the triboelectric charge amount closer to zero, the silicon atom concentration of the outer surface portion of the coating layer is set to the value of another oxide constituting the coating layer. 20 mol% or less, especially 1 with respect to the total number of moles of the metal atom or metalloid atom and silicon atom of the component
It is preferably 0 mol% or less. Further, the silicon atom concentration in the vicinity of the interface with the core particle in the coating layer is preferably in the range of 99 to 80% of the silicon atom concentration in the core particle from the viewpoint of high adhesion to the core particle.

The concentration of silicon atoms in the core particles and the coating layer is obtained by pre-treating the conductive particles as they are, or by cutting the conductive particles, or gradually removing the surface by chemical etching or physical etching. Can be measured using a technique such as a transmission electron microscope (TEM) capable of elemental analysis, a scanning electron microscope, fluorescent X-ray analysis, or ICP emission spectroscopic analysis. When the composition of the core particles and the coating layer are close to each other in the vicinity of the interface, the boundary between the two becomes unclear, but when conducting elemental analysis from the particle center toward the outside of the conductive particles, the concentration of silicon atoms Can be confirmed as the point where the number starts to decrease.

Further, regarding whether the coating layer is easily peeled off, the conductive particles after kneading with a resin or the like are observed with a SEM to observe the change of the surface, or the friction after crushing the conductive particles in a mortar or the like. It can be clarified by measuring the charge amount. In the latter method of measuring the triboelectric charge amount, after grinding, a large amount of silica is exposed on the surface when the coating layer is peeled off, and the triboelectric charge amount largely shifts to the negative side. Recognize.

The conductive oxide forming the coating layer is not particularly limited as long as it is a composite oxide containing at least a part of silicon atoms and has conductivity as a whole. Examples of oxide components other than the silicon oxide component forming the coating layer include tin oxide, zinc oxide, antimony oxide,
Examples thereof include conductive oxides such as indium oxide, those obtained by adding a conductivity improving dopant to these oxides, and composite oxides thereof. Among these, tin oxide, indium oxide, zinc oxide, those obtained by adding a conductivity improving dopant to these oxides, or composite oxides of these are preferably used. In particular, it is preferable to use tin oxide and / or zinc oxide because they are relatively inexpensive and have high adhesiveness to the core particles of the coating layer. Furthermore, tin oxide is preferable because of its low toxicity. It is preferably used. When the conductivity improving dopant is added to these oxides (or composite oxides), the type and amount thereof may be determined in consideration of safety and powder color tone. A general amount of the dopant added is 5% by weight or less based on the total amount of the conductive oxide. The conductivity improving dopant may be pentavalent or hexavalent such as antimony, niobium, tantalum, molybdenum, tungsten, phosphorus, vanadium.
Elements that can be valence ions can be used. However, in consideration of safety, it is preferable that the amount of highly toxic elements such as antimony and vanadium is small in quantity.

The thickness of the coating layer in the conductive particles constituting the conductive powder of the present invention is not particularly limited,
If it is too thin, high conductivity cannot be obtained, and if it is extremely thick, it is difficult to stably manufacture it. Therefore, it is preferably 1/300 to 1/2 of the average particle diameter of the core particles. The thickness of the coating layer can be determined from the difference between the particle diameters of the core particles before coating and the conductive particles obtained after coating, which are measured by TEM or SEM during production. For the same reason as in the case of the core particles, the average particle diameter of the conductive particles is 40 μm or less, particularly 0.01 to
It is preferably 30 μm, and its shape is preferably spherical or substantially spherical.

The conductive powder of the present invention comprises the above-mentioned conductive particles and / or aggregates thereof. Generally, it is difficult to obtain a powder consisting of only independent particles having a very small particle size, and it is often agglomerated due to a drying step or the like during production, and it is difficult to return such aggregated particles to complete independent particles. is there. Also in the conductive powder of the present invention, when the particle size of the conductive particles is large, it is possible to obtain a powder in which the conductive particles exist in an independent state, but when the particle size of the conductive particles is small It is common to include agglomerated particles as described above. Depending on the application, the particles may contain agglomerated particles, but in the case of applications such as conductive control powders for toner, the average particle size in the case of containing agglomerated particles is 0. The thickness is preferably 01 to 5 μm, more preferably 0.01 to 2 μm. In addition, in the film addition application, the average particle size in the case of containing agglomerated particles is 0.0 so that a smooth surface is easily obtained, though it depends on the thickness of the film.
The thickness is preferably 1 to 20 μm, more preferably 0.01 to 10 μm.

The method for producing the conductive powder of the present invention is not particularly limited, but it can be suitably produced by the following method. That is, in a suspension containing inorganic oxide particles containing silica as a main component, a silicon-containing compound capable of forming a polysiloxane bond by a hydrolysis / polycondensation reaction and -MOM-M- by a hydrolysis / polycondensation reaction. Bond (However, M means a metal atom or a metalloid atom whose oxide exhibits conductivity. The bond is focused on the oxo group, and M
The valence of is not particularly limited as long as it is 2 or more, for example, M (-
O) _n − (where n is an integer of 2 or more) is also included. } The metal atom- or metalloid atom-containing compound capable of forming the above-mentioned compound is added substantially simultaneously, continuously or intermittently, and the ratio of the weight of the silicon-containing compound to the weight of the metal atom- or metalloid atom-containing compound at the start of addition is large. From the addition at such a time as to be continuously or stepwise reduced over the end of the addition, to deposit a polycondensate of a hydrolyzate of these compounds on the surface of the inorganic oxide particles containing silica as a main component, and then on the surface. It can be suitably produced by heat-treating the particles on which the polycondensate is deposited.

Here, the suspension containing inorganic oxide particles (core particles) containing silica as a main component is obtained by hydrolyzing a silicon-containing compound capable of forming a polysiloxane bond by a hydrolysis / polycondensation reaction in a solvent. It is preferable to use a suspension of spherical or substantially spherical silica particles obtained by a polycondensation reaction. As described above, the silica particles are inorganic oxides other than silica, that is, tin oxide, zinc oxide, antimony oxide, indium oxide, alumina, zirconia, titania, boron oxide, phosphorus oxide, magnesia, calcium oxide, rare earth oxides, etc. You may include the ingredient of.

The silica particles obtained by the above method may be used as they are in a state of being dispersed in a solvent as a suspension, or may be taken out once by filtration, washed with water, calcined and the like, and then described later again. It may be a suspension obtained by suspending in the solvent of. For example, JP-A-58-110414
As described in No. 3, a method of adding a silicon alkoxide or other metal alkoxide, or a solution of these alkoxides dissolved in a solvent in a mixed solvent of a basic aqueous solution such as aqueous ammonia and an alcohol, or sodium silicate. A method of dropping or mixing in an acidic solvent is preferably used.

Usually, the shape of the core particles produced by the method of dropping in the solvent as described above is spherical or substantially spherical, and when the core particles having such a shape are used, the core particles in the suspension are It is preferable because the amount of agglomeration is small and a uniform coating layer can be obtained, and the coating layer is less likely to peel off and the fluidity of the conductive particles coated with the coating layer is improved. In some cases, silica alone as the component in the core particles is preferable because spherical or substantially spherical particles can be easily obtained.

Further, a suspension obtained by suspending core particles produced by another method such as a melting method or a spray pyrolysis method from a precursor of an inorganic oxide containing silica as a raw material in a solvent described later. However, in this case, it is preferable that the shape of the core particles is spherical or substantially spherical for the above reason.

As the solvent of the above suspension, a silicon-containing compound described below and a compound containing a metal atom or a metalloid atom undergo a hydrolysis / polycondensation reaction to form a polycondensate of a hydrolyzate of these compounds on the core particle surface. There is no particular limitation as long as it precipitates. Specifically, water or alcohols such as methanol, ethanol, propanol and butanol, diethyl ketone, methyl n-butyl ketone, di-n-propyl ketone, methyl isobutyl ketone, diisobutyl ketone and other ketones, isopropyl ether, n-butyl ether, etc. Such as ether. Of these, alcohol is preferable because it is easy to obtain, and methanol, ethanol, and isopropyl alcohol are particularly preferable because they are relatively inexpensive and easy to handle. When using an organic solvent, it is necessary to add water in an amount sufficient to cause a hydrolysis reaction. Further, if a basic aqueous solution of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, or an acidic aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, or the like is mixed in the solvent,
It is particularly preferable because the hydrolysis / polycondensation reaction proceeds efficiently and in a short time.

The ratio of the core particles to the solvent in the above suspension is not particularly limited, but if the amount of the core particles is too large, the viscosity of the suspension becomes high, the coating layer is not uniformly formed, and the solvent is If it is too large, the efficiency will be poor and the productivity will be reduced. The preferable ratio of the core particles to the solvent cannot be generally stated because it varies depending on the composition and thickness of the target coating layer, but the weight ratio of the core particles to the total weight of the core particles and the solvent is from 0.1 to 10. % Is often good, more preferably 0.5 to 8%, and further 0.8 to 5%.

As the silicon-containing compound used in the present invention, known compounds can be used without limitation as long as they can form a polysiloxane bond by a hydrolysis / polycondensation reaction. As a specific example of such a silicon-containing compound, silicon alkoxide monomers such as Si (OCH ₃ ) ₄ and Si (OCH ₂ CH ₃ ) ₄ and these monomers are 2 to
6 molecules condensed oligomer or CH ₃ Si (OC
_{H 3) 3, CH 3 Si} (OCH 2 CH 3) 3, CH 3 C
Examples thereof include alkylalkoxysilane compounds such as H ₂ Si (OCH ₂ CH ₃ ) ₃ . Further, silicates such as sodium silicate, potassium silicate, and ammonium silicate, or chlorosilanes such as tetrachlorosilane and trichlorosilane can also be used.

In the present invention, the metal atom or metalloid atom-containing compound used is not particularly limited as long as it can form a -MOMM bond through a hydrolysis / polycondensation reaction. Soluble in water or water-soluble organic solvent because it is often used by dissolving it in water or water-soluble organic solvent for the purpose of easy addition to suspension or controlling the rate of hydrolysis / polycondensation reaction. What is preferable. For example, tin chlorides such as stannous chloride, stannic chloride, tin oxychloride, stannous bromide, tin-containing compounds such as hydrates thereof, zinc-containing compounds such as zinc chloride and zinc acetate, pentachloride Antimony, antimony chloride such as antimony trichloride, antimony-containing compounds such as antimony tribromide, indium trichloride (hereinafter also referred to as indium chloride), indium-containing compounds such as indium sulfate and indium nitrate, tin methoxide, zinc isopropoxide And metal alkoxides such as indium ethoxide.
Among the above, chloride is preferable because it is easily dissolved in water or a water-soluble organic solvent, easy to handle, and inexpensive. However, from the viewpoint of safety, it is preferable to use the toxic antimony-containing compound in an amount as small as possible.

Usually, a silicon-containing compound and a compound containing a metal atom or a metalloid atom are preferably used so that they do not form a precipitate even when mixed in the same solvent. Therefore, any of these compounds has a basic property. In the case of containing, the solution of the above suspension preferably has an acidic property in order to efficiently proceed the hydrolysis / polycondensation reaction. On the contrary, when any of these compounds has an acidic property, the solution of the above suspension preferably has a basic property. For example,
A silicon alkoxide such as tetramethoxysilane or tetraethoxysilane is used as the silicon-containing compound, and a metal chloride such as zinc chloride, tin chloride, antimony chloride or indium chloride is used as the compound containing a metal atom or a semimetal atom, and the solution is acidic. In the case where it has properties, it is preferable to use an alcohol / water mixed solution in which a basic compound such as sodium hydroxide or ammonia is dissolved, as the solution of the suspension. In the above example, the silicon alkoxide may precipitate a hydrolyzed / polycondensate in either an acidic aqueous solution or a basic aqueous solution, but zinc chloride, tin chloride, antimony chloride, which is a compound containing a metal atom or a metalloid atom, In the present example, a solvent containing a basic compound such as ammonia water or an ammonia-containing alcohol / water mixed solution is preferable because the hydrolysis / polycondensation reaction of metal chloride such as indium chloride easily proceeds in the presence of a base.

The silicon-containing compound and the compound containing a metal atom or a metalloid atom may be added to the suspension as they are, but a solution prepared by dissolving in a suitable solvent such as water or a water-soluble organic solvent may be added. Addition to the suspension is preferable because the rate of hydrolysis / polycondensation reaction is controlled and a coating layer having a uniform thickness is formed. The concentration of the metal atom- or metalloid atom-containing compound in the solvent of the solution is not particularly limited as long as it is within the range of dissolution, but if the concentration is too low, the productivity decreases, and if it is too high, the coating with a non-uniform thickness. Since it may form a layer, the concentration is 0.01 to 1 liter of solution.
It is preferably 10 moles, particularly preferably 0.1 to 5 moles.

In the production method of the present invention, the silicon-containing compound and the compound containing a metal atom or a metalloid atom are continuously or intermittently substantially simultaneously, and at the time of addition, the weight of the metal-containing compound or the metalloid is equal to that of the metal-containing compound. A method is used in which the ratio with respect to the weight of the atom-containing compound is added to the suspension so that it decreases continuously or stepwise from the start of addition to the end of addition. As such an addition method, for example, a solution in which a silicon-containing compound is dissolved (referred to as a solution A) and a solution in which a metal atom or metalloid atom-containing compound is dissolved (referred to as a solution B) are prepared and suspended in a suspension. Solution A is added continuously or stepwise, and at the same time or after a predetermined time, solution B is added into Solution A, and the mixed solution is added to the suspension. A method of depositing a polycondensate of a hydrolyzate of these compounds on the surface of the core particles can be adopted.
When the ratio of the solution A to be added to the solution B is changed so as to decrease with time, the ratio of the silicon-containing compound decreases with the passage of time, and instead the ratio of the metal atom or metalloid atom-containing compound increases. To go. Therefore, it is possible to form a coating layer made of a conductive oxide in which the concentration of silicon atoms is continuously or intermittently reduced toward the outer side in the radial direction around the core particles. In the above method, in order to prevent the concentration of the solution A or the solution B from locally increasing when added to the suspension, the solution B is added to the solution A in advance to obtain a mixed solution, which is suspended. Although the mode of adding to the liquid is shown,
If the solution is sufficiently stirred, both solutions may be added separately.

The core particles having the above-mentioned polycondensate deposited on the surface thereof are usually the solvent in the suspension after the addition of the silicon-containing compound or the like by filtration or the like (hereinafter also referred to as the suspension after addition). After separation, it is heat treated, but if a reaction product that is difficult to sublime during heat treatment is generated by the neutralization reaction,
In order to control the volume resistivity and the triboelectric charge amount, chlorine ions, acetate ions, nitrate ions, sulfate ions, ammonium ions, sodium ions, potassium ions and the like, which are present in the neutralization liquid and are derived from the starting tin compound, etc. You may heat-process after removing the reaction product etc. of. The method for removing chlorine ions, acetate ions, nitrate ions, sulfate ions, ammonium ions, sodium ions, potassium ions and reaction products thereof is not particularly limited. To give a specific example, the suspension after addition is filtered once,
There is a method of repeating a washing step of re-dispersing the filtered cake-like precipitate in a water-based solution or an organic solvent-based solution, followed by washing, or decantation. It is preferable to remove the ions by the washing step or decantation because conductive particles having a uniform coating layer thickness can be obtained even after the heat treatment described below.

The cake-like precipitate recovered by the above method is
After drying, it is heat-treated for the purpose of improving conductivity and controlling the triboelectric charge amount. The heat treatment method is not particularly limited, and the gel powder or the precipitate is placed in a container having low reactivity with the precipitate at a high temperature such as alumina or quartz glass, and heat treated using a commercially available electric furnace, or A heat treatment device such as a spray pyrolysis device or spray dry may be used. The heat treatment conditions such as heat treatment temperature and time and heat treatment atmosphere are not particularly limited, but the heat treatment conditions may greatly affect the volume resistivity, the triboelectric charge amount, and the like. Preferably from 300 ° C to 1500 ° C, further from 400 ° C to 12
A temperature of 00 ° C is preferred. When the heat treatment temperature is lower than 300 ° C, a large amount of hydroxyl groups remain, and the volume resistivity may change with time. Further, if it exceeds 1500 ° C., coarse particles may be generated by sintering, which is not preferable. The heat treatment time varies depending on the type of heat treatment apparatus and the heat treatment temperature, but is 0. 0 from the viewpoint of volume resistivity control and energy saving.
It is preferably 1 second to 100 hours or less. The heat treatment atmosphere is not particularly limited, but an atmosphere containing oxygen is desirable from the viewpoint of preventing metal deposition in the coating layer due to reduction as much as possible. It is particularly preferable to carry out the treatment in an air atmosphere from the viewpoint that a large-scale device is not required. However, when conductive particles having a lower volume resistivity are required, it may be preferable to perform firing in an inert atmosphere such as nitrogen or argon as long as metal precipitation does not occur. The presence or absence of metal precipitation can be analyzed by a method such as powder color tone, X-ray diffraction analysis, or electron beam diffraction analysis.

[0040]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these contents. In addition, each evaluation of the electroconductive particle or electroconductive powder in an Example and a comparative example was performed as follows.

That is, the volume resistivity was measured by compacting powder (using a sample after crushing for 3 minutes in a mortar) using a jig consisting of a die and a punch. That is, a hollow (hole diameter φ15 mm) cylindrical die (insulator, φ50 mm ×) attached with a copper lower punch (φ15 mm × height 10 mm)
The sample is placed in a height of 50 mm, and an upper punch made of copper (φ15 mm × height 50 mm) is placed at the upper end of the sample to be 5.6.
The sample was pressure-molded at a pressure of × 10 ⁷ Pa (load of 1 ton) to produce a pellet-shaped test piece. Then, while the test piece is being pressed, the resistance value between the upper punch and the lower punch is measured by Hewlett Packard (HEWLETT PACKAR).
D) The volume resistivity was calculated from the cross-sectional area and height of the test piece by measurement with a 3478A multimeter manufactured by the company by the four-terminal method. The upper limit of measurement in this measurement method was 10 ⁸ Ωcm, and a sample exceeding this value was determined to be unmeasurable. In addition, the change in volume resistivity with time is 200 at 120 ° C in air.
After standing for a period of time, it was cooled to room temperature, pulverized again in a mortar for 3 minutes, and then the volume resistivity was measured by the above method. The value obtained by dividing the volume resistivity after leaving at high temperature by the volume resistivity before leaving at high temperature was used as an index of the change in volume resistivity with time.

As for the triboelectric charge amount, a blow-off charge amount measuring device TB-200 manufactured by Toshiba Chemical Co., Ltd. is used as a device, and a carrier iron powder T manufactured by Powder Tech Co. is used as a carrier.
It was measured using EFV-200 / 300. The sample was mixed with a carrier in advance, and the mixture was conditioned at 35 ° C. and 85% humidity, and then subjected to the standard toner charge amount measurement method (blow-off method) of the Japan Imaging Society.

The color tone of the sample was visually observed.

Further, the specific gravity was measured by the liquid immersion method. That is, the total mass (W ₁ ) when the pycnometer was filled with pure water was weighed, and then the sample (mass M) was put into the pycnometer and filled with pure water to heat it to sufficiently remove air bubbles, and then cooled. rear weighed _{(W 2),} and the specific gravity d of powder d = M
It was calculated from / (W ₁ + M−W ₂ ).

The average degree of uniformity was determined as an index showing whether the conductive particles are spherical or substantially spherical. As described above, the average degree of uniformity is obtained by taking a SEM photograph of conductive particles and determining the maximum width (major axis; L) for any 50 of them.
And the maximum width (minor axis; B) in the direction orthogonal thereto was measured, and B / L was averaged.

Further, it was confirmed by the following method whether or not the silicon atom concentration in the coating layer of the conductive particles decreased from the center side to the outside. That is, first, put the conductive particles in a 30% hydrochloric acid solution containing 2% hydrofluoric acid, and
Minutes, 10 minutes, 60 minutes under pressure acid decomposition, the coating layer is gradually dissolved and removed from the outside, and then silicon atoms and tin atoms contained in the filtrate of each solution are analyzed by ICP emission spectroscopy.
And, analysis of other added metal atoms or metalloid atoms was performed. From the analysis, silicon atom (mol) / [silicon atom (mol)
+ Tin atom (mol) + other metal atom or metalloid atom (mol)] (unit:%) was calculated, and the change in silicon atom concentration from the outside to the center of the conductive particle was observed.

Example 1 Tetraethoxysilane 83.3 in 120 ml of methanol
After adding g, 7.2 ml of 0.1N hydrochloric acid was added, and the mixture was stirred at room temperature for 30 minutes to prepare a silicon-containing compound solution (referred to as solution A). Further, 36.7 g of anhydrous stannous chloride (SnCl ₂ ) and 0.22 g of antimony trichloride (SbCl ₃ ) were added to 600 ml of methanol, and then dry oxygen was introduced into the liquid and stirred to contain tin and antimony. A compound solution (referred to as solution B) was prepared. Separately methanol 120
0 ml and ammonia water (28 wt% product) mixed solution (C
Liquid), and gradually add C to the above liquid A while stirring.
Core particles were prepared by adding to the liquid. Liquid A 150
When ml was added, solution B was gradually added to solution A being added and mixed. After the addition of the liquids A and B was completed, the produced precipitate was separated by filtration, and the obtained cake-like precipitate was dried using a vacuum dryer to obtain a dry gel powder. Using a commercially available electric furnace, the dry gel powder was heated to 500 ° C in air.
Was fired to obtain a conductive powder. As a result of SEM observation of the powder, spherical particles and aggregated particles thereof were observed, and the average particle diameter of the primary particles (spherical particles) was 0.3 μm. As a result of measuring the silicon atom concentration in the radial direction of the spherical particles by the above-mentioned method, the silicon atom concentration was increased from the outside of the spherical particles toward the center in the order of 3%, 20% and 34%. It was found that in the coating layer, the silicon concentration continuously decreased from the center to the outside. Other evaluation results are shown in Table 1.

[0048]

[Table 1]

Example 2 In Example 1, antimony trichloride (SbCl ₃ ) was used.
Conductive powder was obtained in the same manner as in Example 1 except that 2.32 g was used. As a result of SEM observation of the powder, spherical particles and aggregated particles thereof were observed, and the average particle diameter of the spherical particles was 0.3 μm. As a result of measuring the silicon atom concentration in the radial direction of the spherical particles by the method described above, the silicon atom concentration was 3% in order from the outside of the spherical particles toward the center,
Since it increased to 20% and 34%, it was found that the silicon concentration in the coating layer continuously decreased from the center to the outside. Other evaluation results are shown in Table 1.

Example 3 A conductive powder was obtained in the same manner as in Example 1, except that 0.71 g of tantalum pentachloride (TaCl ₅ ) was used instead of antimony trichloride. SE of the powder
As a result of M observation, spherical particles and aggregated particles thereof were observed, and the average particle diameter of the spherical particles was 0.3 μm. As a result of measuring the silicon atom concentration in the radial direction of the spherical particles by the above-mentioned method, the silicon atom concentration was increased from the outside of the spherical particles toward the center in the order of 3%, 20% and 34%. From the results, it was found that in the coating layer, the silicon concentration continuously decreased from the center to the outside. Other evaluation results are shown in Table 1.

Example 4 In Example 3, the solution B was further mixed with magnesium chloride (M
Conductive powder was obtained in the same manner as in Example 3 except that 0.34 g of gCl ₂ ) was added. As a result of SEM observation of the powder, spherical particles and aggregated particles thereof were observed, and the average particle diameter of the spherical particles was 0.3 μm. As a result of measuring the silicon atom concentration in the radial direction of the spherical particles by the method described above, the silicon atom concentration was measured from the outside of the spherical particles toward the center,
Since it increased in order of 3%, 20%, and 34%, it was found that the silicon concentration in the coating layer continuously decreased from the center to the outside. Other evaluation results are shown in Table 1.

Example 5 In Example 1, the solution A was further supplemented with aluminum trichloride 6
A conductive powder was obtained in the same manner as in Example 1 except that 0.98 g of a hydrate (AlCl ₃ .6H ₂ O) was added.
As a result of SEM observation of the powder, spherical particles and aggregated particles thereof were observed, and the average particle diameter of the spherical particles was 0.3 μm.
Met. As a result of measuring the silicon atom concentration in the radial direction of the spherical particles by the above-mentioned method, the silicon atom concentration was increased from the outside of the spherical particles toward the center in the order of 3%, 20% and 34%. From the results, it was found that in the coating layer, the silicon concentration continuously decreased from the center to the outside. Other evaluation results are shown in Table 1.

Example 6 In Example 1, 13 ml of methanol was added with 0.77 g of anhydrous stannous chloride (SnCl ₂ ), dry oxygen was introduced into the solution, and the mixture was stirred. Conductive powder was obtained in the same manner as in Example 1 except that the above was further added. As a result of SEM observation of the powder, spherical particles and aggregated particles thereof were observed, and the average particle diameter of the spherical particles was 0.3 μm. The concentration of silicon atoms in the radial direction of the spherical particles was measured by the above-mentioned method. As a result, the concentration of silicon atoms was 3%, 20% in order from the outside of the spherical particles toward the center.
%, 34%, so in the coating layer,
It was found that the silicon concentration continuously decreased from the center to the outside. Other evaluation results are shown in Table 1.

Example 7 62.5 g of tetraethoxysilane in 54 ml of methanol
Was added, 10.8 ml of 0.1N hydrochloric acid was added, and the mixture was stirred, hydrolyzed, and kept at 70 ° C. After one day and night,
A wet gel solidified in agar was obtained. Put in the dryer 2
After drying at 00 ℃, crush with a mortar and jet mill,
It was baked at 00 ° C. Then, classification was performed to obtain an amorphous silica powder having an average particle diameter of 1 μm. The amorphous silica powder was put into the liquid C described in Example 1 and dispersed. 30m methanol
After adding 20.8 g of tetraethoxysilane to 1
A silicon-containing compound solution (referred to as solution D) prepared by adding 1.8 ml of 0.1N hydrochloric acid and stirring at room temperature for 30 minutes, and solution B described in Example 1 were prepared. Liquid D was gradually added to the amorphous silica dispersion, and liquid B was gradually added to and mixed with liquid D at the same time. After the addition of all the solutions was completed, the resulting precipitate was treated in the same manner as in Example 1 to obtain a conductive powder. As a result of SEM observation of the powder, there was no smooth silica surface of the amorphous particles before coating, and amorphous particles slightly larger than the amorphous particles before coating and aggregated particles thereof were observed. It is considered that the entire surface of the amorphous particles is covered with the coating layer. The concentration of silicon atoms in the radial direction of the particles was measured by the above-mentioned method.
Since it increased to 0% and 34%, it was found that the silicon concentration in the coating layer continuously decreased from the center to the outside. Other evaluation results are shown in Table 1.

Further, 50 parts by weight of the obtained conductive powder was added to 50 parts by weight of polypropylene resin and kneaded at 230 ° C. by using a twin-screw extruder to obtain pellets. As a result of SEM observation, no smooth surface, which was considered to be the silica surface of the amorphous particles before coating, was not observed at all, and therefore it is considered that the coating layer of the conductive particles existing on the fracture surface was not peeled off.

Example 8 A conductive powder was obtained in the same manner as in Example 1 except that the atmosphere during firing was nitrogen. As a result of SEM observation of the powder, spherical particles and aggregated particles thereof were observed, and the average particle diameter of the spherical particles was 0.3 μm. As a result of measuring the silicon atom concentration in the radial direction of the spherical particles by the above-mentioned method, the silicon atom concentration was increased from the outside of the spherical particles toward the center in the order of 3%, 20% and 34%. From the results, it was found that in the coating layer, the silicon concentration continuously decreased from the center to the outside. Other evaluation results are shown in Table 1.

Comparative Example 1 Liquid A, liquid B and liquid C were prepared in the same manner as in Example 1. First, liquid A and liquid B were mixed and stirred to obtain a silicon-containing compound, a tin-containing compound and an antimony-containing compound. A dissolved solution (referred to as solution E) was prepared. The liquid D was gradually added to the liquid C to obtain a precipitate. The obtained precipitate was treated in the same manner as in Example 1 to obtain a conductive powder. As a result of SEM observation of the powder, substantially spherical particles were aggregated, and the particles had an average particle diameter of 8 μm.
As a result of measuring the silicon atom concentration in the radial direction of the particles by the above-mentioned method, the silicon atom concentrations were 33%, 33% and 34%, and there was almost no change. Other evaluation results are shown in Table 2.
Shown in.

[0058]

[Table 2]

Comparative Example 2 Liquid A and liquid C were prepared in the same manner as in Example 1, and liquid A 150
The addition was terminated when ml was added to the liquid C. The obtained precipitate was filtered, dried and calcined in the same manner as in Example 1 to obtain spherical silica powder. As a result of SEM observation of the powder, only spherical particles were observed and the average particle diameter was 0.27 μm. The concentration of silicon atoms in the radial direction of the spherical silica particles was measured by the above-mentioned method. As a result, the concentration of silicon atoms was 10 in order from the outside of the spherical particles toward the center.
It was 0%, 100%, 100%, and there was no change. ICP emission spectroscopic analysis was performed on tin atoms and antimony atoms, but the results were below the detection limit. Other evaluation results are shown in Table 2.

Comparative Example 3 A conductive powder was obtained in the same manner as in Example 7, except that the liquid D was not used. As a result of SEM observation of the powder, irregular particles of about 1 μm in which fine particles of about 0.01 to 0.05 μm adhered in an island shape on a part of the surface, 0.0
Coarse particles in which fine particles of about 1 to 0.05 μm were aggregated were observed. Judging from the size, it is considered that the irregular particles are silica particles and the fine particles on the surface are tin oxide-antimony composite oxides. As a result of elemental analysis of the agglomerated coarse particles, silicon atoms were not detected, and tin atoms and antimony atoms were detected, so that the coating layer was formed only on a part of the surface of the amorphous silica particles. It is considered that the tin oxide-antimony composite oxide was independently deposited as fine particles. Other evaluation results are shown in Table 2.

Further, 50 parts by weight of the obtained conductive powder was added to 50 parts by weight of polypropylene resin and kneaded at 230 ° C. using a twin-screw extruder to obtain pellets. As a result of SEM observation, many smooth silica surfaces were observed in which the coating layer did not exist on the surface of the conductive particles present on the fracture surface. Therefore, most of the coating layer once formed on the amorphous silica particles was observed. Is considered to have peeled off.

[0062]

EFFECT OF THE INVENTION Since the conductive particles of the present invention have a concentration of silicon atoms in the coating layer formed on the surface of the core particle decreasing from the center side to the outside of the particle, that is, they have a graded composition structure. The characteristic is that the coating layer does not easily peel off even if it is rubbed between particles or with external materials. Therefore, for example, even when it is kneaded into a resin or the like and used, the volume resistivity does not change and stable conductivity can be exhibited. Further, since the powder has a light color tone, a low specific gravity, and a triboelectric charge amount of zero to a small negative value, it is suitable as a conductive filler for various plastics and toners.

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Claims (4)

[Claims] 1. A conductive powder comprising conductive particles and / or an agglomerate thereof, wherein a coating layer made of a conductive oxide is formed on the surface of inorganic oxide particles containing silica as a main component, said conductive powder comprising: A conductive powder, wherein the coating layer of the conductive particles contains silicon atoms, and the concentration of silicon atoms in the coating layer decreases from the center side of the particles toward the outside. 2. The conductive powder according to claim 1, wherein the conductive particles are spherical or substantially spherical. 3. A silicon-containing compound capable of forming a polysiloxane bond by a hydrolysis / polycondensation reaction in a suspension of inorganic oxide particles containing silica as a main component, and -MO by a hydrolysis / polycondensation reaction. -M- bond (however, M means a metal atom or a metalloid atom whose oxide shows conductivity)
The metal atom- or metalloid atom-containing compound capable of forming a compound is continuously or intermittently substantially simultaneously, and the ratio of the silicon-containing compound weight to the metal atom- or metalloid atom-containing compound weight at the time of addition is from the start of addition. It is added so as to decrease continuously or stepwise at the end of the addition, to deposit a polycondensate of a hydrolyzate of these compounds on the surface of the inorganic oxide particles containing silica as a main component, and then to add the polycondensate to the surface. The method for producing a conductive powder according to claim 1 or 2, wherein the particles in which the polycondensate is deposited are heat-treated. 4. A suspension containing silica-based inorganic particles, which is obtained by subjecting a silicon-containing compound capable of forming a polysiloxane bond by a hydrolysis / polycondensation reaction to a hydrolysis / polycondensation reaction in a solvent. The method according to claim 3, wherein a suspension in which the spherical or substantially spherical silica particles are suspended is used.