JP2001023435A - Conductive silica and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high conductivity and high heat resistance by sequentially forming a silicon polymer compound layer, a nickel layer, and a gold layer on a silica surface. SOLUTION: After silica powder is treated with a silicon polymer compound having a reducing property and its surface is treated with a solution containing metal salt with a standard oxidation-reduction potential of 0.54 V or more for depositing metal colloid, electroless nickel-plating and gold-plating is applied, and consequently, conductive silica having lamination of a silicon polymer compound layer, a nickel layer, and a gold layer layered sequentially on the silica surface is provided. The conductive silica has high conductivity and high heat resistance hardly causing peeling of the plated layer in a heating process at 200 deg.C or more. If silicone rubber and the like is blended, a conductive rubber molding with high reliability can be provided. In this way, powder exhibiting high conductivity is provided. Especially, when silica is dispersed in a reducing agent-containing aqueous solution and non-electrolytic plating is carried out in the nickel plating process during the manufacture, coagulation-free conductive silica with a four-layer structure consisting of silica, a silicon polymer compound, nickel and gold is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a conductive silica suitable as a conductive filler in various conductive compositions such as a conductive silicone rubber composition and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Powders,
In particular, a metal-coated powder produced by coating a non-conductive powder with various metals has a large degree of freedom in selecting a material serving as a base filler, and as a conductive filler, a paint, a filler,
Because application can be expected in a wide field such as coating agent,
Various manufacturing methods have been studied and put to practical use by an electroless plating method or the like. Among them, it has been already practiced to obtain a metal-coated powder by plating an insulating inorganic powder such as alumina, alumina silicate, glass, and mica, or a resin powder of polystyrene or polyphenolic carbon (Japanese Patent Publication No. JP-A-2-25431, JP-B-6-9677
No. 1).

[0003] However, the electroless plating method has a problem in adhesion between a plating metal and a powder, and a silane coupling agent (for example, γ) is required to produce a powder having a metal film having better adhesion. -Aminopropyltriethoxysilane) using a silane monomer (Japanese Unexamined Patent Publication No. Sho 61)
-257479 and JP Sho 62-297471), a method of using a palladium colloid sol using a reducing agent such as NaBH ₄ (JP 63-79975
And a method of etching the surface of a powder is proposed. However, at present, good metal-coated powders have not always been obtained by these methods. In particular, a conductive powder having high heat resistance such that peeling between a metal and a resin does not occur even at a temperature of 200 ° C. has not been obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a conductive silica having high conductivity and high heat resistance and a method for producing the same.

[0005]

Means for Solving the Problems and Embodiments of the Invention The present inventors have made intensive studies to achieve the above object, and as a result, treated silica powder with a silicon-based polymer compound having a reducing property, Then, the surface is exposed to a standard redox potential of 0.54.
After treatment with a solution containing a metal salt of V or more to precipitate a colloid of the metal, electroless nickel plating and then gold plating are performed, so that a silicon-based polymer compound layer, a nickel layer, and a gold layer are formed on the silica surface. Is obtained by sequentially forming conductive silica, this conductive silica has high conductivity,
Having a high heat resistance that the plating layer is hard to be peeled off even when heat-treated at 200 ° C. or more. By blending this conductive silica with silicone rubber or the like, for example, a highly reliable conductive rubber molded body can be obtained. Was found.

That is, silicon-based polymer compounds are very interesting polymers because of their metallic properties, electron delocalization, high heat resistance and flexibility, and good thin-film formation characteristics, as compared with carbon. Silicon-based polymer compounds having a Si-Si bond or Si-H bond, particularly polysiloxane or polysiloxane having a hydrogen atom directly bonded to a silicon atom, are known as polymer compounds having a reducing property and are used for various purposes. ing. Further, it is well known that polysilane is a precursor of a silicon carbide ceramic material, and polysiloxane is a precursor of a silicon oxide ceramic material, and becomes an insulating material having extremely excellent heat resistance by post-treatment such as heat treatment.

The applicant of the present invention has proposed that when a powder whose surface has been treated with a silicon-based polymer compound having such a reducing action is brought into contact with a solution containing metal ions, a metal colloid is generated and retained on the powder surface. And a method for producing a metal-coated powder with good adhesion utilizing the same is disclosed in Japanese Patent Application No. 10-1.
As proposed in Japanese Patent No. 21836, this method, when performing electroless plating on a powder surface-treated with a silicon-based polymer compound, plating proceeds between adjacent powders, and the produced metal-coated powder There was a problem that the particle size was large. In addition, when compounded with a rubber having high heat resistance such as silicone rubber and used under conditions of high temperature and high humidity, there has been a problem in that the conductivity is reduced due to oxidation of metal or separation between powder and metal.

As a result of studying to solve such a problem, silica was used as a powder to be treated with a silicon-based polymer compound, nickel was used as a powder coating metal, and gold was plated on the surface of the nickel, thereby reducing the cost. It has been found that a powder which is not oxidized even at high temperature and high humidity and can exhibit high conductivity can be obtained. In particular, when producing the metal-coated powder, silica is dispersed in an aqueous solution containing a reducing agent as a nickel plating step, and an aqueous solution of a nickel salt is added to the aqueous solution together with a gas, and electroless plating is performed. -Silicon polymer compound -Nickel-Gold 4
Conductive silica having a layer structure is obtained, and this silica is found to have higher conductivity and higher heat resistance,
The present invention has been made.

Accordingly, the present invention provides an electroconductive silica, characterized in that a silicon-based polymer compound layer, a nickel layer and a gold layer are sequentially formed on a silica surface;
Conductive silica, characterized in that a silicon-based polymer compound is partially or entirely ceramicized on a silica surface, a nickel layer and a gold layer are sequentially formed, [III]
(1) a first step of treating a silica powder with a silicon-based polymer compound having a reducing property to form a layer of the silicon-based polymer compound on the surface of silica; (2) a powder obtained in the first step A second step of treating the body with a solution containing a metal salt composed of a metal having a standard oxidation-reduction potential of 0.54 V or more to precipitate the metal colloid on the silicon-based polymer compound layer on the silica surface.
(3) a third step of performing electroless nickel plating using the metal colloid as a catalyst to form a metal nickel layer on the surface of the silicon-based polymer compound layer, and (4) further performing gold plating to form gold on the metal nickel layer. A method for producing conductive silica, comprising a fourth step of forming a layer; [I
V] In the third step, the powder obtained in the second step is dispersed in an aqueous solution containing a reducing agent, and an aqueous nickel salt solution is added to the aqueous solution together with a gas, whereby electroless nickel plating is performed. Production method, [V] The above production method, wherein the powder obtained in the fourth step is heat-treated at a temperature of 200 ° C. or more in a reducing gas atmosphere to ceramicize a part or all of the silicon-based polymer compound. I will provide a.

Hereinafter, the present invention will be described in more detail.
In the method for producing conductive silica of the present invention, the raw material silica is a powder composed of silicon dioxide and has high heat resistance. The shape is not particularly limited, such as powder, fiber, flake, etc., but the metal to be plated (nickel,
In order to minimize the amount of gold) and highly fill silicone rubber or the like, it is desirable that the spherical particles have the smallest specific surface area with the same particle diameter. Such silica can be easily obtained by burning chlorosilane, hydrolyzing alkoxysilane, oxidizing gasified metallic silicon, or melting quartz powder. In order to reduce the specific surface area, it is desirable that the inside does not have a cavity connected to the surface, and fused quartz is suitably used. The average particle size of the silica powder is 0.01 to 1000 μm, more preferably 0.1 to 1000 μm.
100 μm. If the thickness is less than 0.01 μm, the specific surface area is increased, so that the amount of the plated metal is increased, which is expensive and is not economically desirable. On the other hand, if it is larger than 1000 μm, it may be difficult to mix with silicone rubber or the like.

In the first step of the method for producing conductive silica according to the present invention, the silica powder is treated with a reducing silicon-based polymer compound to form a layer of the silicon-based polymer compound on the silica surface. This is the step of performing

Here, as the silicon-based polymer compound having a reducing action, polysilane, polycarbosilane, polysiloxane and polysilazane having a Si—Si bond or a Si—H bond can be used. A polysiloxane having a hydrogen atom directly bonded to an atom is preferably used.

Among them, polysilane has S in its main chain.
Examples include a polymer compound having an i-Si bond and represented by the following general formula (1).

[0014] ^{_{(R 1 m R 2 n X}} p Si) q (1) the above formula ^{(1), R 1, R} 2 are each hydrogen atom, a substituted or unsubstituted monovalent hydrocarbon group, R ¹ And R ² may be the same or different from each other, and as the monovalent hydrocarbon group, an aliphatic, alicyclic or aromatic monovalent hydrocarbon group is used. As the aliphatic or alicyclic monovalent hydrocarbon group, those having 1 to 12 carbon atoms, particularly 1 to 6 carbon atoms, are preferable, and examples thereof include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group, and hexyl group. And cycloalkyl groups such as a cyclopentyl group and a cyclohexyl group. Further, as the aromatic monovalent hydrocarbon group,
Those having 6 to 14 carbon atoms, particularly those having 6 to 10 carbon atoms are suitable, for example, phenyl group, tolyl group, xylyl group, naphthyl group,
And a benzyl group. In addition, as the substituted monovalent hydrocarbon group, part or all of the hydrogen atoms of the unsubstituted monovalent hydrocarbon group exemplified above may be a halogen atom, an alkoxy group,
Those substituted with an amino group, an aminoalkyl group and the like, for example, a monofluoromethyl group, a trifluoromethyl group, m-
And a dimethylaminophenyl group.

X is the same group as R ¹ , an alkoxy group, a halogen atom, an oxygen atom or a nitrogen atom. As the alkoxy group, a methoxy group, an ethoxy group, an isopropoxy group, etc. Examples of the compound (4) and the halogen atom include a fluorine atom, a chlorine atom, and a bromine atom. X is a methoxy group among these;
Ethoxy groups are preferably used.

M is 0.1 ≦ m ≦ 1, preferably 0.5 ≦ m
m ≦ 1, n is 0.1 ≦ n ≦ 1, preferably 0.5 ≦ n ≦
1, p is 0 ≦ p ≦ 0.5, preferably 0 ≦ p ≦ 0.2, and 1 ≦ m + n + p ≦ 2.5, preferably 1.5
≦ m + n + p ≦ 2, and q is 2 ≦ q ≦ 1
00,000, preferably an integer in the range of 10 ≦ q ≦ 10,000.

Further, a silicon-based polymer compound having a hydrogen atom (Si-H group) directly bonded to a silicon atom has the following general formula having a Si-H group in a side chain and a Si-O-Si bond in a main chain. The polysiloxane represented by (2) is preferably used.

[0018] In ^{_{(R 3 a R 4 b H}} c SiO d) e (2) the above formulas, R ^3, R ⁴ are each a hydrogen atom, a substituted or unsubstituted monovalent hydrocarbon group, an alkoxy group or a halogen atom And R ³ and R ⁴ may be the same or different from each other, but as the monovalent hydrocarbon group, aliphatic,
An alicyclic or aromatic monovalent hydrocarbon group is used. As the aliphatic or alicyclic monovalent hydrocarbon group, C1 to C12,
Particularly, those having 1 to 6 are preferable, and examples thereof include an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group and a hexyl group, and a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group. The aromatic monovalent hydrocarbon group preferably has 6 to 14 carbon atoms, particularly 6 to 10 carbon atoms, and examples thereof include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a benzyl group. As the substituted aliphatic, alicyclic or aromatic monovalent hydrocarbon group, a part or all of the hydrogen atoms of the unsubstituted monovalent hydrocarbon group exemplified above may be a halogen atom, an alkoxy group, an amino group. And those substituted with an aminoalkyl group, such as a monofluoromethyl group, a trifluoromethyl group, and an m-dimethylaminophenyl group. As the alkoxy group, those having 1 to 4 carbon atoms such as a methoxy group, an ethoxy group, and an isopropoxy group are preferable, and examples of the halogen atom include a fluorine atom, a chlorine atom, and a bromine atom. And ethoxy groups are preferably used.

A is 0.1 ≦ a ≦ 1, preferably 0.5 ≦ a
a ≦ 1, b is 0.1 ≦ b ≦ 1, preferably 0.5 ≦ b ≦
1, c is 0.01 ≦ c ≦ 1, preferably 0.1 ≦ c ≦ 1
And 1 ≦ a + b + c ≦ 2.5, preferably 1 ≦
This is a number that satisfies a + b + c ≦ 2.2. d is 1 ≦ d ≦
1.5. e is an integer in the range of 2 ≦ e ≦ 100,000, preferably 10 ≦ e ≦ 10,000.

In the first step, specifically, a silicon-based polymer having a reducing property is dissolved in an organic solvent, silica powder is added and mixed therein, and then the organic solvent is removed.
It can be performed by forming a layer of a silicon-based polymer compound on the surface of silica.

In this step, examples of the organic solvent in which the silicon-based polymer compound is dissolved include aromatic hydrocarbon solvents such as benzene, toluene, and xylene; hexane;
Octane, aliphatic hydrocarbon solvents such as cyclohexane,
Ether solvents such as tetrahydrofuran and dibutyl ether, esters such as ethyl acetate, aprotic polar solvents such as dimethylformamide, dimethylsulfoxide and hexamethylphosphoric triamide, nitromethane, acetonitrile and the like are preferably used.

The concentration of the solution containing the silicon-based polymer compound is as follows:
0.01 to 50% (% by weight, the same applies hereinafter), preferably 0.01 to 30%, more preferably 1 to 20%, and if the concentration is less than 0.01%, a large amount of solvent is used. When the concentration exceeds 50%, the silicon-based polymer compound may not be sufficiently formed on the entire surface of the powder.

As a method for treating a powder with a silicon-based polymer compound dissolved in an organic solvent, the polymer is dissolved in a solvent and mixed with the powder in a diluted state, and the slurry is rotated in a vessel by stirring blades in a vessel. A stirring method in which the slurry is dispersed and contacted, and a spray method in which the slurry is dispersed in an air stream and dried instantaneously, etc., can be suitably used.

In the above treatment step, the organic solvent is distilled off by raising the temperature or reducing the pressure. Usually, the temperature is higher than the boiling point of the solvent, specifically 40 to 200 ° C. under a reduced pressure of 1 to 100 mmHg. It is effective to dry while stirring at about the temperature.

After the treatment, the solvent is effectively distilled off by leaving it to stand at a temperature of about 40 to 200 ° C. for a while in a dry atmosphere or under reduced pressure, whereby the treated powder is dried and the silicon-based polymer is dried. A compound-treated powder can be manufactured.

The thickness of the silicon-based polymer compound layer is 0.00
It is 1 to 1 μm, preferably 0.01 to 0.1 μm.
If the thickness is less than 0.001 μm, the silica cannot be completely covered, and there is a possibility that a portion where plating does not occur may be formed. On the other hand, if the thickness is too large, the amount of the silicon-based polymer compound may increase and the cost may increase.

The silica powder becomes hydrophobic by the treatment with a silicon-based polymer compound. For this reason, the affinity for the solvent in which the metal salt is dissolved decreases, and the metal salt does not disperse in the liquid, so that the efficiency of the metal salt reduction reaction may decrease. The reduction in the efficiency of the metal salt reduction reaction caused by this can be improved by adding a surfactant. As the surfactant, those which lower only the surface tension without causing foaming are desirable. Surfynol 104, 420, 504
(Nissin Chemical Industry Co., Ltd.) and other nonionic surfactants can be suitably used.

Next, in the second step, the powder obtained by forming the silicon-based polymer compound layer on the silica surface obtained in the first step is mixed with a metal salt comprising a metal having a standard oxidation-reduction potential of 0.54 V or more. This is a step of precipitating the metal colloid on the silicon-based polymer compound layer by treating with a solution containing the metal colloid. In this treatment, the surface of the silicon-based polymer compound-treated powder is brought into contact with a solution containing a metal salt. And a metal film is formed.

Here, as a metal salt having a standard oxidation-reduction potential of 0.54 V or more, more specifically, gold (standard oxidation-reduction potential 1.50 V), palladium (standard oxidation-reduction potential 0.1 V).
99V), silver (standard oxidation-reduction potential 0.80V) and the like are preferably used. The standard oxidation-reduction potential is 0.54
Salts such as copper (standard oxidation-reduction potential 0.34 V) and nickel (standard oxidation-reduction potential 0.25 V) lower than V are not easily reduced by the silicon-based polymer compound.

As the gold salt, Au⁺Or Au³⁺Including
Specifically, NaAuCl_Four, NaAu
(CN)_Two, NaAu (CN)_FourEtc. are exemplified. Paraj
Pum²⁺And usually comprises Pd
-Z_TwoCan be expressed in the form Z is Cl, Br, I
Such as halogen, acetate, trifluoroacetate,
Acetylacetonate, carbonate, perchlore
, Nitrate, sulfate, and oxide salts
is there. Specifically, PdCl_Two, PdBr_Two, PdI _Two,
Pd (OCOCH_Three)_Two, Pd (OCOCF_Three)_Two, PdS
O_Four, Pd (NO_Three)_Two, PdO, and the like. With silver salt
Then, dissolved in a solvent, Ag⁺Can be generated,
Usually Ag-Z (Z is perchlorate, borate, phosphine
Salts such as sulfates and sulfonates)
It can be represented by a shape. Specifically, AgBF_Four, Ag
ClO_Four, AgPF₆, AgBPh_Four, Ag (CF_ThreeS
O_Three), AgNO_ThreeEtc. are exemplified.

As the solvent for dissolving the silicon-based polymer, water, ketones such as acetone and methyl ethyl ketone, alcohols such as methanol and ethanol,
Examples include aprotic polar solvents such as dimethylformamide, dimethylsulfoxide, and hexamethylphosphoric triamide. Among them, water is preferably used.

The concentration of the metal salt varies depending on the solvent in which the salt is dissolved, but is preferably from 0.01% to a saturated solution of the salt. If the concentration is less than 0.01%, the effect of the plating catalyst may not be sufficient, and if the concentration exceeds the saturated solution, solid salts may precipitate, which is not preferable. When the solvent is water, the concentration of the metal salt is 0.01 to 20%, especially 0.1 to 20%.
It is preferably in the range of 5% to 5%. The silicon-based polymer compound-treated powder is treated at a temperature of room temperature to 70 ° C. for 0.1 to 12 hours.
It may be immersed in the metal salt solution for 0 minute, more preferably for about 1 to 15 minutes. Thereby, a metal colloid-treated powder can be manufactured.

In the second step, it is preferable that the powder treated with the silicon-based polymer compound is first brought into contact with a surfactant diluted with water, and then with a solution containing the metal salt. Since the surface becomes hydrophobic by the treatment with the silicon-based polymer compound in the first step, the affinity with the solvent for dissolving the metal salt is reduced, and it is difficult to disperse in the liquid, and the efficiency of the metal salt reduction reaction is reduced. And the silicon-based polymer compound-treated powder can be easily dispersed in a solution containing a metal salt in a short time.

Here, the surfactant includes an anionic surfactant, a cationic surfactant, a zwitterionic surfactant,
Nonionic surfactants can be used.

As the anionic surfactant, a sulfonate type, a sulfate type, a carboxylate type and a phosphate type can be used. As the cationic surfactant, an ammonium salt, an alkylamine salt, and a pyridinium salt can be used. As amphoteric surfactants, betaine-based, aminocarboxylic acid-based, amine oxide-based, and nonionic surfactants include:
Ether type, ester type and silicone type can be used.

More specifically, as the anionic surfactant, an alkylbenzene sulfonate, a sulfosuccinate, an alkyl polyoxyethylene sulfate, an alkyl phosphate, a long-chain fatty acid soap and the like can be used. Further, as the cationic surfactant, an alkyltrimethylammonium chloride salt, a dialkyldimethylammonium chloride salt, an alkylpyridinium chloride salt or the like can be used. As the amphoteric surfactant, betaine-based sulfonic acid salts and betaine-based aminocarboxylic acid amine salts can be used. As the nonionic surfactant, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyalkylene-modified polysiloxane and the like can be used. Further, a commercially available aqueous solution obtained by mixing such a surfactant, for example, Mama Lemon (trade name, manufactured by Lion Corporation) can also be used.

If necessary, the above surfactant may be added in an amount of 0.000 to 100 parts by weight of the metal salt solution.
It can be used in the range of 1 to 10 parts by weight, particularly 0.001 to 1 part by weight, especially 0.01 to 0.5 part by weight.

After the metal salt treatment, the powder is treated with the same solvent containing no metal salt as described above to remove the unnecessary metal salt not supported on the powder, and finally remove the unnecessary solvent from the powder. It can be dried and removed. Drying is usually 0-150
It is preferably carried out at a normal pressure or a reduced pressure at a temperature of ° C.

The third step is a step of performing electroless nickel plating on the powder having the metal colloid adhered to the surface thereof using the metal colloid as a catalyst to form a metal nickel layer on the surface of the silicon-based polymer compound layer. is there.

This electroless nickel plating solution is usually a water-soluble nickel metal salt such as nickel sulfate and nickel chloride,
Commercial products can be used, including reducing agents such as sodium hypophosphite, hydrazine and sodium borohydride, complexing agents such as sodium acetate, phenylenediamine and sodium potassium tartrate.

As the electroless nickel plating method, according to a conventional method, a batch method in which powder is charged into an electroless plating solution and plating is performed, or a dropping method in which a plating solution is dropped on powder dispersed in water, is used. Possible (Development and application of conductive filler, p
182, Technical Information Association, 1994). In any method, by controlling the plating rate, there is no change in trying to prevent agglomeration and obtain a uniform film with good adhesion, but it is sometimes difficult to obtain such nickel-coated silica. . This is because powders with a high specific surface area are inherently very active in the plating reaction and begin to suddenly become uncontrollable, whereas the start of plating is often delayed by the effect of oxygen in the atmosphere, so nickel plating takes time. This is because it is difficult to obtain uniformly plated powder.

For this reason, it is preferable to perform nickel plating of silica by the following method. That is, the nickel plating solution is separated into an aqueous solution containing a reducing agent, a pH adjusting agent, a complexing agent, and the like and a nickel salt aqueous solution. Silica is a reducing agent, pH
Disperse in an aqueous solution containing an adjusting agent, a complexing agent, etc., and keep the temperature at the optimal temperature for nickel plating. It has been found that adding an aqueous nickel salt solution to a gas and adding it to an aqueous solution containing a reducing agent in which silica is dispersed is very effective for obtaining a nickel-coated silica without aggregation. The nickel salt aqueous solution is converted into a reducing agent by gas, p
It is quickly and uniformly dispersed in an aqueous solution containing an H adjuster, a complexing agent, and the like, and the powder surface is nickel-plated.

The introduction of gas often results in reduced plating efficiency due to foaming, which can be prevented by adding antifoaming surfactants. As the surfactant, one having an antifoaming action and lowering the surface tension is desirable, and a polyether-modified silicone-based surfactant such as KS-538 (manufactured by Shin-Etsu Chemical Co., Ltd.) can be suitably used.

In electroless nickel plating, the oxygen concentration in the plating solution affects nickel deposition. When the amount of dissolved oxygen is large, colloidal palladium, which is the nucleus of the plating catalyst, is oxidized to palladium cation and elutes in the solution, or the nickel surface once deposited is oxidized, thereby suppressing nickel deposition. . Conversely, if the amount of dissolved oxygen is small, the stability of the plating solution is reduced, nickel is easily deposited in places other than silica, and the formation of fine nickel powder and the formation of bumpy precipitates occur. . For this reason, it is preferable to control the amount of dissolved oxygen in the plating solution between 1 and 20 ppm. If it exceeds 20 ppm, a reduction in plating rate and generation of unplated portions may be recognized, and if it is less than 1 ppm, generation of bump-like precipitates may be recognized.

For this purpose, it is preferable to use a mixture of an oxygen-containing gas such as air and an inert gas such as argon or nitrogen. In the case of powder plating, the start of plating is often slow, but once plating is started, the reaction may run away. It is also effective to switch to air after confirming that the plating reaction has started. Plating temperature is 35-12
A temperature of 0 ° C. and a contact time of 1 minute to 16 hours are suitably used.
More desirably, the treatment is performed at 40 to 85 ° C. for 10 to 60 minutes.

The fourth step is a step of forming a gold plating layer on the nickel layer by performing gold plating after the electroless nickel plating.

In this case, an electroplating solution or an electroless plating solution may be used as the gold plating solution, and a known composition or a commercially available product can be used, but an electroless gold plating solution is preferable. The gold plating method can be performed according to the above-described ordinary method. At this time, it is effective to remove the oxidized and passivated surface of nickel with dilute acid and perform gold plating. The plating temperature and contact time are the same as in the case of nickel plating.

At the end of plating, it is preferable to wash with water in order to remove unnecessary surfactants.

The silica thus obtained is a conductive silica having a four-layer structure of silica-silicon polymer compound-nickel-gold.

The thickness of the nickel layer is 0.01 to 10 μm,
Desirably, the thickness is 0.1 to 2 μm. If the thickness is less than 0.01 μm, the silica may be completely covered, and it may be difficult to obtain sufficient hardness and strength. On the other hand, when the thickness is more than 10 μm, the amount of nickel increases and the specific gravity increases, so that the cost becomes high at the time of compounding.

The thickness of the gold layer is 0.001 to 1 μm, preferably 0.01 to 0.1 μm. If it is less than 0.001 μm, the resistivity becomes high, so that sufficient conductivity may not be obtained at the time of compounding. If it exceeds 1 μm, the amount of gold increases and the cost becomes high.

Finally, it is desirable to heat-treat the conductive silica at a temperature of 200 ° C. or higher in the presence of a reducing gas. The processing conditions are usually 200 to 900 ° C, and the processing time is 1
Minutes to 24 hours are preferably used. More preferably 25
The treatment is preferably performed at 0 to 500 ° C. for 30 minutes to 4 hours. As a result, the silicon-based polymer compound between the powder and the metal is changed into a ceramic, and has higher heat resistance, insulation and adhesion. The atmosphere at this time is reduced with a reducing system such as hydrogen to reduce the oxides in the metal and change the silicon-based polymer compound into a stable structure, whereby the silica and the metal are firmly bonded to each other and have a high conductivity. A powder exhibiting properties can be obtained.

When the heat treatment is performed in the hydrogen-reducing atmosphere as described above, the silicon-based polymer compound can mainly obtain a silicon carbide ceramic.

That is, due to the high-temperature treatment, the silicon-based polymer between the powder and the metal is partially or entirely changed to ceramic, and has higher heat resistance, insulation and adhesion.

The conductive silica of the present invention is suitably used as a conductive filler or the like. For example, by being mixed with a rubber composition such as a silicone rubber composition or a resin composition,
High conductivity can be provided.

[0056]

According to the present invention, conductive silica having a four-layer structure of silica-silicon-based polymer compound-nickel-gold having no aggregation can be obtained by an inexpensive and simple process. This conductive silica has excellent conductivity and heat resistance, and has wide application as a material for producing a conductive rubber molded article or the like.

[0057]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.

[Synthesis Example] Production of phenylpolysilane (hereinafter abbreviated as PPHS)
Bis (cyclopentadienyl) dimethylzirconocene was prepared as a catalyst in the system by adding a diethyl ether solution of methyllithium to bis (cyclopentadienyl) dichlorozirconocene in a flask purged with argon. To this was added 50 times the molar amount of phenylsilane as a catalyst, and the mixture was heated and stirred at 150 ° C. for 24 hours. After this,
When the catalyst was removed by adding molecular sieves and filtering, the weight average molecular weight was 2,6 almost quantitatively.
A PPHS solid of 00 was obtained.

[Example] Spherical silica US-10 (manufactured by Mitsubishi Rayon Co., Ltd .; average particle size: 10 μm) was used as a powder for producing PPHS-treated spherical silica . PPHS5g
Was dissolved in 65 g of toluene.
100 g, and stirred for 1 hour to form a slurry. Using a rotary evaporator, at a temperature of 80 ° C., 45 mmH
When 65 g of toluene was distilled off at a pressure of g and dried, PPHS-treated spherical silica was obtained. This PPHS
The treated spherical silica was finally crushed by a roller or the like.

Production of Palladium Colloidal Precipitated Silica PPHS-treated spherical silica is hydrophobized and, when poured into water, floats on the water surface. Surfynol 504 (surfactant manufactured by Nissin Chemical Industry Co., Ltd.) as surfactant.
100 g of the PPHS-treated spherical silica obtained in the synthesis example was added to 50 g of a 5% aqueous solution, and the mixture was dispersed in a short time of about 5 minutes when stirred. The palladium treatment is performed using the silica-
1% PdCl ₂ aqueous solution was added to 70 g of the aqueous dispersion at 70 g.
g (0.7 g as palladium chloride, 0.4 g as palladium), stirred for 30 minutes, filtered, and washed with water. As a result of these treatments, palladium colloid-precipitated silica was obtained, which was colored black-gray and had the silica surface adhered with palladium colloid. The silica is isolated by filtration,
Immediately after washing, plating was performed.

Nickel in silica deposited with palladium colloid
As a nickel-plating reducing solution, 2.0 M sodium hypophosphite and sodium acetate diluted with ion-exchanged water were used.
100 g of a mixed solution of 0 M and glycine 0.5 M was used.
The palladium colloid precipitated silica was dispersed in a nickel plating reducing solution together with 0.5 g of KS-538 (antifoaming agent manufactured by Shin-Etsu Chemical Co., Ltd.). The liquid temperature was raised from room temperature to 65 ° C. with vigorous stirring. 2.0 M of sodium hydroxide diluted with ion-exchanged water was added dropwise while being accompanied by air gas, and at the same time, nickel sulfate 1.0 M diluted with ion-exchanged water was added.
M was added dropwise to the reducing solution while being accompanied by nitrogen gas. As a result, the silica became black with fine foaming, and metallic nickel precipitated on the silica surface. In this silica, metallic nickel was precipitated on the entire surface, and neither aggregation nor formation of bumps was observed.

[0062] Kojundo Chemical Laboratory Ltd. gold plating solution K-2 as a gold reduction gold plating solution of nickel plated silica
100 g of 4N was used without dilution. Silica in which metallic nickel was precipitated on the entire surface was dispersed in a gold plating solution. When the liquid temperature was raised from room temperature to 95 ° C. with vigorous stirring, the silica became golden with fine bubbles, and gold precipitated on the silica surface.

The silica precipitated on the bottom of the plating water was filtered, washed with water, dried (30 minutes at 50 ° C.), and then fired at 300 ° C. for 1 hour in an electric furnace replaced with hydrogen. Observation with a stereomicroscope revealed that silica in which the entire surface of the silica was covered with gold was obtained. In this silica, palladium, nickel and gold were detected by IPC analysis.

Silica-silicon polymer compound-nickel
-Identification of conductive silica having a gold structure Gold-plated silica is an epoxy resin (Araldite A /
After mixing in B), the mixture was cured, and the section was observed with an electron microscope. As a result, a two-layer structure of a silica portion and a multi-phase plating portion was confirmed.

When the gold-plated silica was analyzed by Auger electron spectroscopy for the constituent elements existing in the depth direction while ion-etching the surface, a gold layer, a nickel layer, and a silicon-based polymer compound were measured in the depth direction. It became clear that a four-layer structure of a layer (a layer containing carbon and silicon) and a silica layer was formed. The appearance observed under a microscope was yellow, the specific gravity was 3.5, and the thickness of each layer was 0.03 μm of a gold layer.
m, the nickel layer was 0.25 μm, and the silicon-based polymer compound layer was 0.1 μm.

Silica-silicon polymer compound-nickel
-Characteristics of conductive silica having a gold structure The resistivity of gold-plated silica is such that a cylindrical cell having four terminals is filled with gold-plated silica, and the area of both ends is 0.2 cm ^2.
A current of 1 to 10 mA flows from an SMU-257 (a current source manufactured by Keithle Co.) from the terminal of
The voltage was measured by measuring the voltage drop from a terminal that was set apart and using a nanovolt meter manufactured by Keithley Model 2000. The resistivity was 2.2 mΩ · cm. This silica was put in a mortar, crushed for 1 minute, and examined for changes after heat treatment (200 ° C., 4 hours). As a result, there was no change in appearance and resistivity.

When the reaction was carried out without using any nitrogen gas or air gas in the nickel plating step of the palladium colloid-precipitated silica, aggregation and formation of bumps were observed. Initially, the resistivity was 3.2 mΩ · cm. This silica was put in a mortar, crushed for 1 minute, and the change after heat treatment (200 ° C., 4 hours) was examined. Metal peeling occurred, the appearance became brown, and the resistivity was 75 mΩ ·
cm.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01B 1/24 H01B 1/24 Z F term (Reference) 4G072 AA25 AA38 AA41 BB05 BB07 DD02 DD03 DD04 DD05 GG01 GG03 HH14 HH28 LL11 LL13 LL14 LL15 MM02 MM31 QQ06 QQ09 UU07 UU08 4G075 AA24 AA27 AA30 BA06 CA02 CA51 CA54 CA65 4K018 BA01 BA04 BA20 BC22 BC26 BC30 4K022 AA05 AA41 BA14 CA06 CA09 CA20 CA21 CA22 DA01 DA03 DA03 DA05 DA03 DA03

Claims (9)

[Claims] 1. A conductive silica comprising a silica-based polymer compound layer, a nickel layer and a gold layer sequentially formed on a silica surface. 2. A conductive silica comprising a silica surface, and a layer in which a silicon-based polymer compound is partially or entirely ceramicized, a nickel layer and a gold layer are sequentially formed on the silica surface. 3. A first step of (1) treating silica powder with a silicon-based polymer compound having a reducing property to form a layer of the silicon-based polymer compound on the surface of silica; and (2) a first step. A second step of treating the powder obtained in the above with a solution containing a metal salt composed of a metal having a standard oxidation-reduction potential of 0.54 V or more to precipitate the metal colloid on the silicon-based polymer compound layer on the silica surface. (3) a third step of performing electroless nickel plating using the metal colloid as a catalyst to form a metal nickel layer on the surface of the silicon-based polymer compound layer, and (4) further performing gold plating to form gold on the metal nickel layer. A method for producing conductive silica, comprising a fourth step of forming a layer. 4. The production method according to claim 3, wherein the silicon-based polymer compound having a reducing property is polysilane, polycarbosilane, polysiloxane or polysilazane having a Si—Si bond and / or a Si—H bond. 5. The method according to claim 4, wherein the polysilane is represented by the following general formula (1). (R ¹ _m R ² _n X _p Si) _q (1) (wherein, R ¹ and R ² are each a hydrogen atom, a substituted or unsubstituted monovalent hydrocarbon group, X is the same group as R ¹ , alkoxy) Group, halogen atom, oxygen atom or nitrogen atom.
Is 0.1 ≦ m ≦ 1, n is 0.1 ≦ n ≦ 1, and p is 0 ≦ p ≦
Q is a number satisfying 1 ≦ m + n + p ≦ 2.5, and q is an integer of 2 ≦ q ≦ 100,000. ) 6. The method according to claim 4, wherein the polysiloxane is represented by the following general formula (2). _{^{(R 3 a R 4 b H}} c SiO d) e (2) ( wherein, R ^3, R ⁴ are each hydrogen atom, a substituted or unsubstituted monovalent hydrocarbon group, an alkoxy group or a halogen atom .a Is 0.1 ≦ a ≦ 1, b is 0.1 ≦ b ≦ 1, c
Is 0.01 ≦ c ≦ 1 and 1 ≦ a + b + c ≦ 2.
5, d is a number satisfying 1 ≦ d ≦ 1.5. e is 2 ≦
e is an integer of 100,000 or less. ) 7. The production method according to claim 3, wherein the metal having a standard oxidation-reduction potential of 0.54 V or more is palladium, silver or gold. 8. In a third step, electroless nickel plating is performed by dispersing the powder obtained in the second step in an aqueous solution containing a reducing agent and adding an aqueous nickel salt solution to the aqueous solution together with a gas. The method according to any one of claims 3 to 7, wherein: 9. The powder obtained in the fourth step is heat-treated at a temperature of 200 ° C. or more in a reducing gas atmosphere to convert part or all of the silicon-based polymer compound into a ceramic. 9. The method according to any one of items 8 to 8.