JP4583147B2 - Conductive composite powder and method for producing the same - Google Patents

Description

  The present invention relates to a conductive composite powder and a method for producing the same, and more particularly to a conductive composite powder comprising silver-coated particles having a specific shape and powder characteristics and a method for producing the same.

Various known techniques have been disclosed for imparting conductivity to a base material by adding a conductive material to a non-conductive base material such as resin or rubber for the purpose of antistatic and electromagnetic wave shielding. .

Examples of the conductive material include various metal powders and metal-coated powders, and Patent Documents 1 and 2 are representative.

JP-A-1-197575 JP 2002-4057

  An important characteristic required for such a conductive material is that the specific resistance after being added to and processed in a non-conductive substrate is sufficiently low, but besides that, it is possible to suppress an increase in the weight and volume of the additive. Further, there is a demand for having oxidation resistance and small change with time, and having a function as a pigment that does not impair the texture of the processed molded article.

In response to the above requirements, when metal powder is used, since the metal powder has a high specific gravity, a large amount of addition is required in order to ensure conductivity. The weight of the electronic material for which low weight is desirable increases, which causes problems in terms of cost and performance.

Further, in the dissimilar metal-coated metal powder, for example, silver-coated copper powder can be used to reduce the cost, but a considerable amount of addition is also required, and the diffusion of the coated silver into copper In addition, the production of copper oxide causes a problem that the conductivity is deteriorated.

On the other hand, as for the metal-coated powder, the fact that various materials such as a metal oxide and a resin can be applied to the core material is also described in Patent Document 2 described above. Insufficient network formation increases the electrical resistance of the molded article, and lacks stability and reliability. Needle-like, rod-like, or whisker-like products are suitable for network formation, but when kneaded into a common resin, the core material breaks, and the expected conductivity may not be exhibited. Even if the property can be secured, problems such as inferior hue of the processed molded product obtained are caused.
That is, a conductive material that not only ensures conductivity but also satisfies the above technical problems in a well-balanced manner has not yet been found.

  As a result of intensive studies, the present inventors have found that the above problems can be solved if the conductive composite powder is made of silver-coated particles using a specific core material.

That is, the conductive composite powder of the present invention is a particle whose core material is a plate-like and nonmetallic inorganic compound particle, whose particle surface is coated with silver, and which has the following characteristics a) to c). It is characterized by comprising.
a) Average particle diameter: 2 to 15 μm
b) Aspect ratio A / B: 1 to 5 when the average major axis is A and the average minor axis is B
c) Average thickness C: 0.3 to 2.6 μm

  Further, the method for producing the conductive composite powder of the present invention comprises a catalyst activity treatment in which a slurry is contained in a water-dispersed plate-like nonmetallic inorganic compound particle, the surface of the inorganic compound particle is subjected to a catalyst activity treatment, and solid-liquid separation is performed. The subsequent particles are reslurried in an aqueous silver salt solution, a reducing agent is added to the slurry, and the surface of the particles after the catalyst activation treatment is coated with silver.

According to the conductive composite powder of the present invention, of course, low electrical resistance is ensured when added to a non-conductive substrate such as resin or rubber and processed for the purpose of antistatic, electromagnetic shielding, etc. It can suppress the increase in weight and volume of additives, has oxidation resistance and little change with time, and has a well-balanced function as a pigment that does not impair the texture of processed molded products. It is suitable for these members.
Moreover, according to the manufacturing method of the electroconductive composite powder of this invention, the said electroconductive composite powder can be produced efficiently and economically.

<Conductive composite powder>
The conductive composite powder of the present invention is a non-metallic inorganic compound particle having a plate-like core material. However, since the conductive composite powder is composed of particles having the following characteristics a) to c), naturally, the core particle used must also be of a very fine particle size and be a specific plate-like particle. .
a) Average particle diameter: 2 to 15 μm
b) Aspect ratio A / B: 1 to 5 when the average major axis is A and the average minor axis is B
c) Average thickness C: 0.3 to 2.6 μm

The characteristics required for the core material will be described in detail later. However, without selecting a core material, the object of the present invention is to increase the weight and volume of the additive while maintaining the conductivity. It is difficult to balance the function as a pigment that can suppress the above, has oxidation resistance, has little change with time, and does not impair the texture of the processed molded product.

  First, regarding the point that the core material is a non-metallic inorganic compound particle, if it is a metal, as described in the problem to be solved by the invention, a large amount of addition is required, which is unpleasant.

  Considering only the addition of conductivity by adding a small amount, it may be possible to select organic materials such as resins with low specific gravity. However, these materials are generally used as granular products, and network formation for conductivity is insufficient. It will be less effective.

  Therefore, the core material needs to be non-metallic inorganic compound particles. However, in order to solve the above problems, the particles constituting the conductive composite powder are considerably fine and have a specific aspect ratio and average thickness. It is important that the particles are particles.

  The conductive composite powder of the present invention has an average particle size of 2 to 15 μm and is a powder composed of considerably fine particles. When this average particle diameter is less than 2 μm, the particles are significantly aggregated, resulting in poor dispersibility in the resin and the like, which hinders the formation of a network for conduction. On the other hand, when the particle diameter exceeds 15 μm, the particle size of the particles is too large, and the amount of silver coated on the particles is relatively reduced, which also hinders the formation of a network for conduction. Further, since the particles are plate-like, the mechanical strength is remarkably lowered, and when processing into a paste or the like, breakage may occur, resulting in poor conductivity. This average particle diameter is preferably 3 to 14 μm, more preferably 5 to 12 μm.

  In the conductive composite powder of the present invention, the core material is plate-like, and the particles constituting the powder have an aspect ratio of A / B with an average major axis of A and an average minor axis of B. It has the characteristic of 1-5. It is important that the core particles have a plate shape. Otherwise, it is difficult to exhibit conductivity and pigment characteristics when forming a thin film conductive layer by coating or the like.

In the present invention, the form of the plate-like particles is further specified, and the difference from the rod-like or needle-like particles is clarified by the aspect ratio A / B. Incidentally, the average major axis A and the average minor axis B are average values of a specific number of particles measured at the plane part of the plate-like particle (a surface having a minor axis and a major axis and a relation of minor axis> thickness diameter). It is.

When the aspect ratio A / B is 1, it is substantially isotropic in the planar direction. Therefore, a numerical value less than 1 is never taken. When the aspect ratio A / B exceeds 5, the particles exhibit a needle shape, whisker shape, etc., and therefore, when kneaded into a common resin, the core material is damaged, and the expected conductivity is exhibited. Even if the electrical conductivity can be ensured, problems such as inferior hue of the processed molded product obtained may occur. This aspect ratio is preferably 1 to 4 and more preferably 1 to 3 in order to increase the network forming effect for electrical conduction.

Further, the conductive composite powder of the present invention has an average particle thickness (referred to as C) of 0.3 to 2.6 μm. The classification of the average thickness C and the average minor axis B is as described above. When the average thickness C is less than 0.3 μm, the mechanical strength of the particles is insufficient, and therefore the core material may be damaged when kneaded with a shared resin or the like. When it exceeds 2.6 μm, the particles are plate-like or rod-like, which affects the formation of a network for conduction.
This average thickness is preferably 0.5 to 2 [mu] m, more preferably 0.7 to 1.5 [mu] m, in order to increase the network forming effect for electrical conduction.

Further, the conductive composite powder of the present invention preferably has an aspect ratio A / C of 3 to 20 based on the average major axis A and the average thickness C. When this A / C is less than 3, the shape becomes close to a granular shape, which affects the formation of a network for conduction. In addition, when A / C exceeds 20, the mechanical strength of the particles is insufficient, and therefore the core material may be damaged when kneaded with a shared resin or the like. The aspect ratio A / C is preferably 4 to 15 and more preferably 5 to 10 in order to increase the network forming effect for conductivity.

In the present invention, the separation between the plate-like particles and the flaky particles is only specified by the aspect ratio, and particles generally regarded as flaky particles having the above-mentioned aspect ratio fall within the scope of the present invention. (Applicable to both particles constituting the conductive composite powder and particles constituting the core powder).

Moreover, it is important that the conductive composite powder of the present invention has a particle surface coated with silver. Silver is used because it is excellent not only in conductivity but also in oxidation resistance.

In addition, as for the particle | grain surface being coat | covered with silver, the state (for example, layer shape) in which the background of a core material is not exposed is ideal, However, Fine silver particles are distributed on the particle | grain surface without extreme bias. Things are also included.

In the conductive composite powder of the present invention, the core material is preferably any one selected from barium sulfate, calcium carbonate, zinc oxide, and boron nitride. These particles can produce a fine plate-like powder without particularly machining, and exhibit a particle size form required by the present invention. In particular, barium sulfate is preferable because it has an excellent ability to shield even X-rays and the like having a very small wavelength, so that the function of an application member using the barium sulfate can be enhanced.

Moreover, it is preferable that the conductive composite powder of this invention is 30-60 mass% of covering silver quantity with respect to the whole particle | grain. As the amount of the coated silver increases, a conductive effect is expected. However, if the amount is too large, the cost is not good. The smaller the number, the more advantageous in terms of cost, but conversely, it is inferior in conductivity, and affects reliability and stability. The amount of the coated silver is preferably 35 to 55% by mass, and more preferably 40 to 50% by mass.

The conductive composite powder of the present invention preferably has a reduced silver coating thickness of 0.1 to 0.8 μm. In consideration of reacting a certain weight of silver to a certain weight of core material, in order to obtain a high conductivity of the conductive composite powder, a silver coating that draws out conductivity relative to the total specific surface area of the core material The thickness must be a certain amount or more. In the present invention, the silver coating thickness is converted as an average value from the specific surface area and the coating silver amount obtained by the laser diffraction / scattering particle size distribution measuring apparatus.

When the converted silver coating thickness is less than 0.1 μm, there is a risk of hindering the formation of a network for conduction. On the other hand, when the thickness exceeds 0.8 μm, the mechanical strength of the silver coating is lowered, peeling is likely to occur, conductivity is deteriorated, and the cost is uneconomical. The converted silver coating thickness is preferably 0.15 to 0.6 μm, and more preferably 0.2 to 0.4 μm.

In the conductive composite powder of the present invention, the outermost surface of the particles may be coated with a fatty acid. By having this fatty acid coating, the fluidity of the powder increases and the dispersibility when kneaded into the resin is improved. The fatty acid coating amount may be about 0.1 to 1% with respect to the conductive composite powder. When the fatty acid coating amount is less than 0.1%, the above effect cannot be obtained, and when it exceeds 1%, the conductivity is impaired. Examples of fatty acids to be coated include saturated fatty acids such as stearic acid, lauric acid, capric acid, and palmitic acid, and unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, and sorbic acid.

<Method for producing conductive composite powder>
The conductive composite powder of the present invention can be produced by subjecting the surface of the plate-like nonmetallic inorganic compound particles, which are the core material, to catalytic activity treatment under specific conditions, followed by silver coating.

  As described above, non-metallic inorganic compound particles are preferable as the core material to be used. However, in order to solve the above problems, the particles should not be plate-like particles having a very fine particle and a specific aspect ratio. Don't be. Suitable materials having such characteristics include barium sulfate, calcium carbonate, zinc oxide, boron nitride and the like.

  Examples of the shape close to the plate-like particle include particles having a laminated structure such as mica, but even if the particle surface is coated with silver, it may be peeled off when kneaded with a resin or the like, resulting in particles lacking the silver coating. Is not preferable.

  In addition, the form of the conductive composite powder of the present invention is specified by being composed of plate-like particles having an average particle diameter and an aspect ratio, but the core material used is naturally in accordance with the characteristics. is there.

Since the amount of silver coated on the core particles only needs to ensure the effects of the present invention, the average particle diameter of the core material may be about 1 to 13 μm. Similarly, the aspect ratio A / B of the core particles is 1 to 1 μm. About 5 and the aspect ratio A / C of the core particles may be about 3-20.

In the method for producing a conductive composite powder of the present invention, first, a treatment liquid for performing catalytic activity treatment on the surface of the core powder particles is prepared. This treatment liquid is prepared by adding a water-soluble palladium salt or the like as a catalyst to water obtained by adding an acid or alkali for pH adjustment as necessary. At this time, the palladium salt used is preferably stabilized with hydrogen chloride, but is not limited thereto. The amount of the catalyst material may be about 0.01 to 2 mmol with respect to 100 g of the core material. In addition to the palladium salt, it is preferable to add and use a tin salt, a reducing agent, etc. in addition to the palladium salt in order to carry out the catalytic activity treatment smoothly.

Next, an appropriately selected core powder is added to the treatment liquid and stirred to disperse and form a slurry, and at the same time, a catalytic activity treatment is performed.

The slurry concentration at this time is preferably about 100 to 500 g / L because the catalyst activation treatment can be efficiently performed. When this slurry concentration is outside the above range, the catalyst concentration is excessive or insufficient with respect to the core material concentration, and the active treatment state on the surface of the core particle becomes non-uniform, resulting in unevenness in the silver coating state. Prone to occur.

The treatment temperature during the catalyst activation treatment varies depending on the type of catalyst used, but when it is carried out at about 15 to 45 ° C., the treatment can be carried out uniformly and efficiently on the particle surface. When the treatment temperature is less than 15 ° C., the activation treatment is difficult to proceed, and when it exceeds 45 ° C., the colloidal particles of the catalyst substance become large, and the activation of the surface of the core material particles may be uneven.
After completion of the catalyst activation treatment, the post-reaction slurry is made into a catalyst-activated cake by conventional filtration and water washing.

Next, preparation for carrying out the silver coating process is performed.
In the method for producing a conductive composite powder of the present invention, an aqueous silver salt solution is used as the silver coating treatment liquid, silver ions are reduced with an appropriate reducing agent, and the surface of the core material particles is coated with silver.

The silver salt aqueous solution can be used in various ways as long as it is a water-soluble salt such as silver nitrate or silver acetate, but preferably a silver ammine complex aqueous solution used in combination with ammonia can stabilize the silver concentration contributing to the reaction and is suitable. is there. Moreover, it is preferable to add an ammonium salt as a buffering agent to the silver ammine complex aqueous solution because the complex in the aqueous solution becomes more stable.

Typical examples of the ammonium salt include ammonium sulfate and ammonium nitrate, but are not limited thereto. However, chloride-based ammonium salts cannot be used because they form silver chloride.

As an example of the preparation of a specific silver salt aqueous solution, ammonia is added to the silver nitrate aqueous solution. In this case, a silver ion concentration of about 0.25 to 0.8 mol / L is preferable because it can stably and uniformly coat the core particles.

When this silver ion concentration is less than 0.25 mol / L, the silver ion concentration at the time of the silver coating reaction is dilute, so that silver is reduced and precipitated alone in the reaction slurry, There is a possibility that unevenness occurs in the coating, resulting in poor conductivity. On the other hand, when it exceeds 0.8 mol / L, the reaction proceeds rapidly due to the high concentration of silver ions at the time of the silver coating reaction, and the reducing agent component is easily incorporated into the silver coating. May become defective.

The catalyst-activated cake is added to the silver ammine complex aqueous solution and sufficiently stirred and dispersed to prepare a silver coating slurry. The slurry concentration of about 30 to 150 g / L is suitable because it can stably and uniformly coat the core particles with silver.

If this slurry concentration is out of the above range, the silver ion concentration is excessive or insufficient with respect to the core material concentration, and as a result, silver particles are precipitated alone, or the silver coating state is uneven. It's easy to do.

The silver coating amount is more preferably adjusted according to the total surface area of the core particles to be processed. Specifically, adjusting the amount of silver in the silver salt aqueous solution so that the amount of silver coated on the conductive composite powder particles is 1 to 10 g / m ² is preferable in terms of conductivity improvement and cost.

Next, a reducing agent is added to the silver coating slurry to perform silver coating treatment.
The reducing agent used in this case can be variously used such as hydrazine, hydroquinone, Rochelle salt, formalin, glucose, potassium sulfite, etc., but preferably using hydroquinone, hydrazine, Rochelle salt, independent core particles of precipitated silver are generated. It is difficult and can efficiently coat the core particles with silver, which is preferable.

  The time to the appropriate reaction end point in the silver coating treatment varies depending on the reducing agent, but it is 60 to 120 minutes for hydrazine and potassium sulfite, 30 to 60 minutes for Rochelle salt, formalin and glucose, and about 1 to 10 minutes for hydroquinone. Is preferred. The reaction time may be adjusted by appropriately selecting means such as adjusting the reducing agent concentration, adjusting the addition time, or adjusting the reaction slurry temperature.

In order to adjust the end point of the reaction, in a preliminary experiment, an analytical sample is collected from the reaction slurry over time, and the concentration of silver ions in the slurry is analyzed using ICP or the like. The time point at which this occurs is confirmed as the reaction end point. In an actual reaction, when 5 minutes are added to the above end point time, the silver ion concentration is confirmed to be 0 and set as the reaction time. During this reaction time, stirring may be continued at a constant temperature.

When the reaction time is less than the appropriate range for each reducing agent, the reaction is too early, and independent precipitated silver core particles are likely to be generated, which may hinder the silver coating on the core material particles. When exceeding, there exists a possibility that a part of reducing agent component may be taken in inside a core particle and remain | survived.

Moreover, about the slurry pH before reaction, it is good to adjust so that it may become 8-11. When this pH is less than 8, the reaction proceeds fast, the surface of the silver coating becomes rough, and the hue tends to be poor. Moreover, when pH exceeds 11, there exists a possibility that a reducing agent component may be taken in in silver coating and electroconductivity may become bad.

The resulting slurry after completion of the silver coating treatment is subjected to conventional filtration and water washing to obtain a conductive composite powder cake. It is preferable to use warm water for washing because the washing effect is improved. Further, when an organic reducing agent is used in the silver coating treatment, it is preferable to use hot water containing sodium carbonate as a degreasing agent because the residual carbon on the particle surface can be reduced. If necessary, a dispersant may be used in combination.
The conductive composite powder cake is made into a conductive composite powder by ordinary drying.

In order to coat the outermost surface of the particles of the conductive composite powder with the fatty acid, a method of filtering and drying the conductive composite powder cake in a solvent containing the fatty acid may be employed. What is necessary is just to adjust a fatty acid amount so that it may become 0.1 to 1% with respect to electroconductive composite powder, after processing. Since the fatty acid which can be used was mentioned above, it is omitted. Solvents that can be used include acetone, alcohols and the like. The concentration of fatty acid contained in the solvent for coating treatment is preferably adjusted to be about 1 to 10 g / L.

According to the method for producing a conductive composite powder of the present invention, an optimal silver coating can be performed on a fine plate-like nonmetallic inorganic compound particle having various functions required for a conductive material in a well-balanced manner, and Efficient production is possible.

  Hereinafter, the present invention will be specifically described with reference to examples and the like.

[Example 1]
To 2.8 L of pure water, 350 mL of hydrochloric acid and 300 mL of OPC-80 catalyst (Okuno Pharmaceutical Co., Ltd.) having a Pd concentration of 3.8 g / L and a Sn salt content of 35% were added, and the liquid temperature was kept at 40 ° C. Then, plate-like barium sulfate A (made by Sakai Chemical) having an average particle diameter of 8.1 μm, an aspect ratio A / B of 2.7, and an aspect ratio A / C of 9.1 is obtained by pulverizing with a hammer mill. Furthermore, 700 g of plate-like barium sulfate powder having an average particle diameter of 5.2 μm, an aspect ratio A / B of 2.4, and an aspect ratio A / C of 4.8 is added to form a slurry, and stirred for 15 minutes to treat the catalyst. Went. The treated slurry was filtered with a Buchner funnel, washed with 8 L of pure water, and again subjected to catalyst activity treatment by filtration.

Next, 910 g of silver nitrate was dissolved in 7.7 L of pure water, 1.19 L of 25% ammonia water was added, and 500 g of ammonium sulfate was further added to prepare a silver ammine complex aqueous solution adjusted to pH 9.4. The catalyst active-treated cake was added to the silver ammine complex aqueous solution, and the mixture was stirred and dispersed at 40 ° C. for 5 minutes to obtain a reaction slurry. Then, a reducing agent solution in which 80 mL of hydrazine monohydrate was dissolved in 6.3 L of pure water was quantitatively added to this reaction slurry in 100 minutes, and after complete addition, the mixture was stirred for 7 minutes. Then, the silver coating reaction on the core material was terminated.

Next, the slurry was filtered with a Buchner funnel, and washed with pure water at 70 ° C. Further, after washing with 10 L of 3.4% sodium carbonate aqueous solution, washing with pure water was performed again. The cake after filtration was dried in the air at 70 ° C. for 12 hours.

Various characteristics were evaluated by the following evaluation methods. The results are shown in Tables 1 and 2.
<Evaluation method>
(A) Average particle size and specific surface area: Take a small amount of sample in a beaker, add a few drops of 3% Triton X solution (manufactured by Kanto Chemical Co., Ltd.) After adding about 50 mL of 41 solution (manufactured by San Nopco), it was dispersed for 2 minutes using an ultrasonic disperser TIPΦ20 (manufactured by Nippon Seiki Seisakusho, OUTPUT: 8, TUNING: 5). The average particle diameter (MV) and specific surface area of this measurement sample were measured using a laser diffraction / scattering particle size distribution analyzer MT3300 (manufactured by Nikkiso).
(B) Average major axis A, average minor axis B, average thickness C: A 1,200-fold photograph was taken with a transmission electron microscope, and the average major axis A and average minor axis B of 100 particles were measured. Further, the sample was filled with an epoxy resin, and the cross section of the powder filled with the resin using a 20% slurry of water-resistant sandpaper P400, P800, P1500 and pure alumina powder was polished, A 000 × photograph was taken, and the average thickness C of 100 particles was measured.
(C) Aspect ratio: Aspect ratios A / B and A / C were determined from A, B, and C determined in (b).
(D) Covered silver content with respect to the whole particle: The sample was dissolved in nitric acid, the amount of silver was determined by ICP analysis, divided by the sample weight, multiplied by 100, and the silver content was determined.
(E) Silver coating thickness on the particle surface (converted value): Using the specific surface area of the core material measured in (a) and the silver content obtained by ICP analysis in (d),
Silver coating thickness (μm) = {silver content / (10.49 × 100)} / {(core material specific surface area × (1−silver content / 100))
(F) Powder volume resistance: Four-probe resistance measuring instrument Loresta GP (Mitsubishi) in a state in which 3 g of a sample was pressurized with a Loresta PD-41 type (manufactured by Mitsubishi Chemical) at a press pressure of 10 kN into a cylindrical pellet having a diameter of 20 mm (Made by Chemical).
(G) Specific resistance of the kneaded composition with rubber:
3 g of a sample, 1.3 g of rubber raw material KE45 (manufactured by Shin-Etsu Chemical Co., Ltd.), and 2 mL of toluene were mixed and kneaded to form a paste. This rubber paste was molded on an OHP sheet using an applicator to a thickness of 60 μm, and then cured in a dryer at 70 ° C. for 30 minutes. This molded body is cut to a size of 10 mm × 50 mm square, and the electric resistance is changed to a digital voltmeter (YOKOGAWA
It was measured by ELECTRIC WORKS. The specific resistance is: specific resistance (Ω · cm) = width (cm) × film thickness (μm) × resistance (Ω) / length (cm) × 0.0001
It was calculated by the following formula.
(H) Conductive oxidation resistance: After holding the sample at 150 ° C. and RH 30% for 24 hours, measure the dust resistance by the same method as in (f), and the value after heat treatment / heat treatment Calculated with the previous value.
(I) Hiding power (functional evaluation as a pigment)
The hiding power was measured in accordance with the hiding rate test paper method described in JIS K 5101-1991. Since the evaluation method was a relative method, 8 coating films of Example 1 to Comparative Example 3 were compared at the same time, and the one with the largest hiding power was indicated as 1, and the one with the smallest hiding power was indicated as 8.

[Example 2]
Produced in the same manner as in Example 1, the cake after washing was reslurried in 2 L acetone solution in which 0.9 g of stearic acid was dissolved, and stirred and dispersed for 10 minutes, followed by solid-liquid separation, and an atmospheric atmosphere at 70 ° C. Dry in a dryer for 12 hours.
Similar to Example 1, various characteristics were evaluated. The results are shown in Tables 1 and 2.

Example 3
To 2.8 L of pure water, 350 mL of hydrochloric acid and 300 mL of OPC-80 catalyst (Okuno Pharmaceutical Co., Ltd.) with a Pd concentration of 3.8 g / L and a Sn salt content of 35% were added, and the liquid temperature was kept at 40 ° C. Then, 700 g of plate-like barium sulfate / A (manufactured by Sakai Chemical) having an average particle diameter of 8.1 μm, an aspect ratio A / B of 2.7, and an aspect ratio A / C of 9.1 was added to make a slurry. The catalyst activity treatment was performed with stirring for a minute. The treated slurry was filtered with a Buchner funnel, washed with 8 L of pure water, and again subjected to catalyst activity treatment by filtration.

Next, 910 g of silver nitrate was dissolved in 7.7 L of pure water, 1.19 L of 25% ammonia water was added, and 680 g of ammonium sulfate was further added to prepare a silver ammine complex aqueous solution adjusted to pH 9.1. The catalyst active-treated cake was added to the silver ammine complex aqueous solution, and the mixture was stirred and dispersed at 40 ° C. for 5 minutes to obtain a reaction slurry. Then, a reducing agent solution in which 294 g of hydroquinone was dissolved in 6.3 L of pure water was added to the slurry for reaction at a stroke, and the reaction vessel was cooled and stirred for 8 minutes to complete the silver coating reaction on the core material. I let you.

The following processing was performed in the same manner as in Example 1, and various characteristics were evaluated. The results are shown in Tables 1 and 2.
On the other hand, as a result of measuring the X-ray transmittance of this powder by the following evaluation method, it was 30.5%.

<X-ray transmittance evaluation method>
3 g of a sample and rubber raw material KE45 (manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed so that the volume became 0.325 cm ^2, and further 2 mL of toluene was added and kneaded to form a paste. This paste was applied onto a polyethylene sheet at a thickness of 60 μm using an applicator, dried and cured at 70 ° C. for 30 minutes. This sheet is set in an X-ray diffractometer M21X (Bruker AXS), the input count is 10800 counts with a source Cu, a wavelength of 1.54184 mm, a counting time of 1.0 sec, the output count is measured, and the output count / input X-ray transmittance (%) was determined by counting 100.

Example 4
Produced in the same manner as in Example 3, the cake after washing was reslurried in 2 L of acetone solution in which 0.9 g of stearic acid was dissolved. After stirring and dispersing for 10 minutes, solid-liquid separation was performed, and an atmospheric atmosphere at 70 ° C. Dry in a dryer for 12 hours.
Similar to Example 1, various characteristics were evaluated. The results are shown in Tables 1 and 2.

Example 5
To 2.8 L of pure water, 350 ml of hydrochloric acid and 300 ml of OPC-80 catalyst (Okuno Pharmaceutical Co., Ltd.) with a Pd concentration of 3.8 g / L and a Sn salt content of 35% were added, and the liquid temperature was kept at 40 ° C. After that, 600 g of plate-like calcium carbonate powder having an average particle size of 3.1 μm, an aspect ratio A / B of 2.8, and an aspect ratio A / C of 4.3 is added to make a slurry, and stirred for 15 minutes to obtain catalytic activity. Processed. The treated slurry was filtered with a Buchner funnel, washed with 8 L of pure water, and again subjected to catalyst activity treatment by filtration.

Next, 910 g of silver nitrate was dissolved in 7.7 L of pure water, 1.19 L of 25% ammonia water was added, and further 820 g of ammonium sulfate was added to prepare a silver ammine complex aqueous solution adjusted to pH 8.9. The catalyst active-treated cake was added to the silver ammine complex aqueous solution and stirred and dispersed at 60 ° C. for 5 minutes to obtain a reaction slurry. Then, a reducing agent solution in which 420 g of Rochelle salt was dissolved in 6.3 L of pure water was poured into the slurry for reaction at a stretch and stirred for 57 minutes to complete the silver coating reaction on the core material.

The washed cake was reslurried in 2 L acetone solution in which 0.9 g of stearic acid was dissolved, stirred and dispersed for 10 minutes, solid-liquid separation, and further dried in an air atmosphere dryer at 70 ° C. for 12 hours. .
Similar to Example 1, various characteristics were evaluated. The results are shown in Tables 1 and 2.

[Comparative Example 1]
100 g of plate (flake) copper powder obtained by pulverizing electrolytic copper powder having an average particle size of 8.2 μm, aspect ratio A / B of 1.5, and aspect ratio A / C of 6.9 is After slurried in water and kept at 50 ° C., 9.2 g of hydrazine monohydrate was added and held for 30 minutes (to improve surface oxidation and facilitate silver coating). Next, this slurry was filtered with a Buchner funnel and washed with 600 mL of pure water, and then 300 mL of methanol was poured into the powder and similarly sucked to remove moisture.

The copper powder cake was slurried again with 1 L of pure water, and then 8.5 g of EDTA was added to prepare a stirred and dissolved copper powder-containing slurry. Further, 35 g of silver nitrate was dissolved in 480 mL of pure water, and the aqueous silver nitrate solution was quantitatively added to the copper powder slurry over 2 hours. The silver-coated copper powder-containing slurry thus obtained was washed and filtered, and dried in an air dryer at 70 ° C. for 5 hours. The obtained conductive powder was evaluated for various characteristics in the same manner as in Example 1. The results are shown in Tables 1 and 2. Further, the X-ray transmittance of this powder was measured in the same manner as in Example 3. As a result, it was 46.3%.

[Comparative Example 2]
After adding 30 mL of hydrochloric acid and 30 mL of OPC-80 catalyst (Okuno Pharmaceutical Co., Ltd.) having a Pd concentration of 3.8 g / L and a Sn salt content of 35% to 280 mL of pure water and keeping the liquid temperature at 40 ° C. Then, 60 g of true spherical silica powder having an average particle size of 13.1 μm was slurried, and stirred for 15 minutes for catalyst activation treatment. The treated slurry was filtered with a Buchner funnel, washed with 1 L of pure water, and again a catalyst-activated cake was obtained by filtration.

Next, 195.2 g of silver nitrate was dissolved in 7.2 L of pure water, 261 mL of 25% ammonia water was added to form an ammine complex, and the temperature was maintained at 60 ° C. The catalyst active-treated cake was added thereto and stirred and dispersed at 60 ° C. for 5 minutes to obtain a reaction slurry. Then, a reducing agent solution in which 90.1 g of Rochelle salt was dissolved in 1.8 L of pure water was poured into the reaction slurry at once, and stirred for 52 minutes to complete the silver coating reaction on the core material.

Next, the slurry was filtered with a Buchner funnel, and washed with pure water at 70 ° C. Further, after washing with 10 L of 3.4% sodium carbonate aqueous solution, washing with pure water was performed again. The cake after filtration was dried in the air at 70 ° C. for 12 hours.
Similar to Example 1, various characteristics were evaluated. The results are shown in Tables 1 and 2.

[Comparative Example 3]
A plate-like silver powder having an average particle size of 5.7 μm, an aspect ratio A / B of 1.4, and an aspect ratio A / C of 4.4 was evaluated for various characteristics in the same manner as in Example 1. The results are shown in Tables 1 and 2.

As can be seen from Tables 1 and 2, the conductive composite powders of the examples not only exhibit excellent conductivity by having a silver coating in an appropriate core material, but also have oxidation resistance with respect to their conductive performance. Therefore, it has a function as a pigment that does not impair the texture of the processed molded product.
Furthermore, when barium sulfate was used as a core material as in Example 3, it was found that the X-ray shielding rate was also excellent.

On the other hand, the powders of Comparative Example 1 and Comparative Example 3 are composed only of metal components, and not only the powder volume resistance but also the specific resistance of the molded product is large due to the low specific gravity. all right.
Moreover, as for the powder of the comparative example 1, the copper particle was a core material and was inferior also in oxidation resistance.

  Moreover, since the powder of the comparative example 2 is a silica particle in which the core material has a spherical shape, the formation of a network for electrical conduction is insufficient, and the specific resistance of the molded product is large. Furthermore, due to the spherical shape, it was inferior in hiding power when viewed as a pigment.

The conductive composite powder of the present invention can ensure sufficient conductivity when used for a non-conductive substrate such as resin or rubber for the purpose of antistatic, electromagnetic wave shielding, etc. It has a function as a pigment that can suppress the increase, has oxidation resistance, has little change with time, and does not impair the texture of the processed molded product.

SEM observation photograph (magnification: 5000 times) of the conductive composite powder of Example 3 centered on the flat part. SEM observation photograph (magnification: 2000 times) of the conductive composite powder of Example 3 with a focus on the thickness portion.

Claims (11)

A conductive composite powder comprising core particles of plate-like and non-metallic inorganic compound particles, the particle surfaces of which are coated with silver, and particles having the following characteristics (a) to (e):
(a) The volume average particle diameter (MV) measured using a laser diffraction / scattering particle size distribution analyzer is 2 to 15 μm.
(b) A is the average major axis, which is the average value of the major axis of the particles measured in a photograph (1,200 times) taken with a transmission electron microscope, and is the average value of the minor axis of the particles measured in the same manner. When the average minor axis is B, the aspect ratio A / B of the average major axis A to the average minor axis B is 1 to 5.
(C) the run 査型electron microscope average thickness is an average value of the thickness of the particles is measured in pictures taken (1000-fold) at (SEM) upon C, the average minor diameter B> The average thickness C .
(D) The aspect ratio A / C of the average major axis A to the average thickness C is 3 to 20.
(E) Average thickness C is 0.3 to 2.6 μm. 2. The conductive composite powder according to claim 1, wherein the nonmetallic inorganic compound particles as the core material are any one selected from barium sulfate, calcium carbonate, zinc oxide, and boron nitride. 3. The conductive composite powder according to claim 1, wherein in the particles coated with silver, the amount of coated silver with respect to the entire particles is 30 to 60% by mass. In particles coated with the silver, conductive composite powder according to any one of claims 1 to 3 basis silver coating thickness of 0.1 to 0.8 [mu] m. In particles coated with the silver, conductive composite powder according to any one of claims 1 to 4, which is subjected to further fatty acid coating.   In a slurry containing non-metallic inorganic compound particles dispersed in water, the surface of the inorganic compound particles is subjected to catalytic activity treatment, and the solid-liquid separated particles after catalytic activity treatment are reslurried in an aqueous silver salt solution. A method for producing a conductive composite powder, wherein a reducing agent is added to a slurry, and the surface of the particles after the catalytic activity treatment is coated with silver. The manufacturing method of the electroconductive composite powder of Claim 6 whose said silver salt aqueous solution is a silver ammine complex. Wherein the aqueous silver salt solution, method for producing a conductive composite powder according to claim 7 Symbol mounting adding an ammonium salt as a buffering agent. The method for producing a conductive composite powder according to any one of claims 6 to 8, wherein a slurry pH before the reaction when silver coating is performed on the particle surfaces after the catalytic activity treatment is 8 to 11. Reducing agent used in making the silver coated on the particle surface after the catalyst activation treatment is either hydrazine, hydroquinone, Rochelle salt, selected formalin, glucose, from among potassium sulfite, any claim 6-9 A method for producing the conductive composite powder according to claim 1. The electroconductive composition containing the electroconductive composite powder in any one of Claims 1-5 .