JP2005163141A - Copper powder, its production method, flowable composition with the same blended, and electrode obtained by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide copper powder which has more excellent oxidation resistance, and has excellent conductivity as well. <P>SOLUTION: The surface of copper grains are coated with a sulfur compound such as acid thiols, e.g., mercaptopropionic acid, mercaptoacetic acid, thiodipropionic acid, mercaptosuccinic acid and thioacetic acid, and a silicon oxide. The copper powder is produced by reacting a copper compound and a reducing agent in the presence of a sulfur compound to obtain copper grains coated with the sulfur compound, and next subjecting a silicon compound such as alkoxysilane to hydrolysis in the presence of the obtained copper grains. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a copper powder excellent in oxidation resistance, a method for producing the same, a fluid composition containing the copper powder, and an electrode formed using the copper powder.

  Copper powder is an inexpensive material with good electrical conductivity, and as a material to ensure electrical continuity such as external electrodes such as capacitors, electrode members such as printed wiring board circuits, and various electrical contact members. Widely used. In recent years, it has begun to be used for internal electrodes of multilayer ceramic capacitors. Multilayer ceramic capacitors are rapidly spreading because they are easy to obtain a large capacity compared to other types of capacitors such as electrolytic capacitors and film capacitors, are excellent in mountability, and have high safety and stability. With the recent miniaturization of electronic equipment, multilayer ceramic capacitors are also in the direction of miniaturization, but in order to maintain a large capacity, it is necessary to miniaturize without reducing the number of laminated ceramic sheets. However, since there is a limit to thinning the sheet, the miniaturization of the multilayer ceramic capacitor is realized by thinning the internal electrode using fine metal particles such as palladium, nickel and copper.

  In such fields, generally, metal particles are mixed with a binder such as an epoxy resin or a phenol resin to form a paste or paint, and the metal paste / paint is, for example, a printed wiring board on a substrate. In the case of a multilayer ceramic capacitor after printing, it is applied onto a thin ceramic sheet, the sheets are laminated, and then heated and fired to form an electric circuit, an electrode, and the like. In order to ensure electrical continuity, the metal particles used should not contain metal oxides as much as possible. However, copper powder is very easy to oxidize, and heat firing is performed using an inert gas such as nitrogen gas. Even if it is performed in an oxidizing atmosphere, the oxidation of the surface of the copper particles cannot be sufficiently prevented, and an electrode having a desired performance cannot be obtained.

For this reason, copper powder excellent in oxidation resistance is required, for example, by reacting copper powder, alkoxysilane, and water in a water-soluble organic solvent to produce a hydrolysis product of alkoxysilane. A technique has been proposed in which a gelling agent is added to the resulting suspension to deposit a SiO ₂ gel coating film on the surface of the copper powder particles (see Patent Document 1). On the other hand, a metal derived from the water-soluble salt by adding an aqueous solution containing an alkali metal salt of silicic acid to a slurry in which metal copper fine particles are dispersed in the liquid, and then adjusting the pH with an acid or alkali. There has been proposed a technique for improving heat shrinkage specification by fixing an oxide or a composite oxide on the surface of a copper fine particle (see Patent Document 2). Furthermore, the technique which processes a copper particle with a silicone oil and a sulfur compound is also proposed (patent document 3).

JP 2003-16832 A JP 2000-345201 A Japanese Patent Application No. 2003-292861

By covering the surface of the copper particles with silicon oxide or the like, contact between the copper particles and oxygen in the atmosphere is avoided to some extent, and the oxidation resistance of the copper particles is improved, but the effect is not sufficient and further There is a need for improvement. That is, in the technique described in Patent Document 1, a SiO ₂ gel coating film is formed on the surface of the copper particles. Although the oxidation resistance of relatively large copper particles having an average particle diameter of about 1 to 10 μm is improved, the fine electrode For fine particles having an average particle size of 1 μm or less used in the above, a sufficient film cannot be formed, so that the effect is not sufficient. On the other hand, in the technique described in Patent Document 2, although heat shrinkage characteristics are improved and delamination and cracks generated during the production of the multilayer ceramic capacitor are suppressed, the effect of oxidation resistance is insufficient. Although the surface is oxidized, the desired oxidation resistance is still not obtained. The technique described in Patent Document 3 shows excellent oxidation resistance at a high temperature of about 500 ° C., but the oxidation starts from a relatively low temperature of less than 200 ° C., so it is not appropriate depending on the type of electrode and the manufacturing method. There wasn't. Therefore, the present invention provides a copper powder that is further excellent in oxidation resistance and excellent in conductivity.

  The present inventor considered that it is necessary to form a dense silicon oxide coating layer uniformly on the entire surface of the copper particles in order to further improve the oxidation resistance of the copper particles. The present inventors completed the present invention by discovering that when a sulfur compound is present in the object coating step, a coating of silicon oxide is easily formed on the surface of the copper particles, and the oxidation resistance can be improved.

That is, the present invention
(1) Copper powder characterized by covering the surface of copper particles with a sulfur compound and silicon oxide, (2) Copper particles by hydrolyzing a hydrolyzable silicon compound in the presence of the sulfur compound and copper particles The copper powder is coated with a sulfur compound and silicon oxide.
Moreover, this invention is a fluid composition formed by mix | blending the said copper powder, Furthermore, it is an electrode formed using the said copper powder.

  The present invention is a copper powder excellent in oxidation resistance, and by covering the surface of the copper particles in combination with a sulfur compound and silicon oxide, the silicon oxide coating tends to be dense, It is considered that a uniform coating layer is easily formed on the entire surface of the copper particles, and the oxidation resistance of the copper particles can be further improved. For this reason, it is highly effective for fine copper particles with a large specific surface area, ensuring electrical continuity such as external electrodes and internal electrodes such as capacitors, electrode members such as circuits of printed wiring boards, and various electrical contact members. It can be widely used as a material for this purpose. In particular, when applied to an electrode member such as an external electrode such as a capacitor, an internal electrode, or a circuit of a printed wiring board, a thin film and a high-density electrode can be obtained. In addition, when an alkoxysilane hydrolysis product is used as a silicon oxide, there is an effect of improving the affinity with a binder resin or a solvent, and it is easy to disperse and can be made into a paste or paint with a small amount of a binder resin or a solvent. Easy to do.

  The present invention is a copper powder in which the surface of copper particles is coated with a sulfur compound and silicon oxide. In general, it is said that silicon oxide is difficult to coat on the surface of copper particles. For this reason, it is considered that a dense coating layer cannot be obtained with silicon oxide, and sufficient oxidation resistance cannot be obtained. One sulfur compound is easily coated on copper particles, and in the present invention, a dense silicon oxide coating layer is probably formed via the sulfur compound present on the surface of the copper particles. Guessed. When metallic copper is oxidized, it becomes CuO and the weight increases. Therefore, the temperature at which the rate of weight increase is 0.5% with respect to the weight after heating for 10 hours at a temperature of 60 ° C. in a non-oxidizing atmosphere. When used as an index, this temperature is 250 ° C. or higher and lower than 300 ° C. in the copper powder of the present invention, and hardly oxidizes when heated and fired at a relatively low temperature.

  In the present invention, coating means a state in which sulfur compound or silicon oxide is attached to the surface of copper particles in some form, specifically, sulfur compound or silicon oxide reacts chemically with the surface of copper particles. In a state of being bonded to each other, in a state of being physically adsorbed on the surface of the copper particles, a state in which these are combined, or a sulfur compound is adhered to the surface of the copper particles, and the sulfur compound and silicon oxide are chemically bonded. Include physically adsorbed state. In a preferred coating form, a sulfur compound adsorption layer is formed on the surface of the copper particles, and a silicon oxide coating layer is formed thereon, so that the silicon oxide coating layer becomes denser. The covering state can be inferred by, for example, XPS or Auger spectroscopy in addition to observation with an electron microscope. There is no restriction | limiting in particular in the thickness of a coating layer, Usually, about 1-100 nm grade, Preferably it is 1-50 nm, More preferably, it is 1-25 nm, More preferably, it is 2-15 nm.

In the present invention, the silicon oxide is a compound including silicon oxide, silicon hydrated oxide, silicon hydroxide, hydrolyzed products of silicon compounds such as alkoxysilane and chlorosilane, water glass, etc. And silicate neutralized hydrolysis products, and silicone oil is not included. In particular, a hydrolysis product of alkoxysilane is preferable because a denser film can be formed. The silicon oxide coating layer may contain an unreacted hydrolyzable silicon compound monomer or oligomer, an alkali component of water glass, or the like as long as the effects of the present invention are not impaired. The coating amount of silicon oxide is preferably in the range of 5 to 20% by weight in terms of SiO ₂ with respect to the copper particles because excellent oxidation resistance is obtained, and more preferably in the range of 6 to 15% by weight.

  Sulfur compounds include thiols, thioglycols, thioamides, dithiols, thiolic acids (thionic acids), which are organic compounds RSH (R is a hydrocarbon group such as an alkyl group) having a mercapto group (—SH), and In addition to the derivatives, sulfur compounds such as thiones, polythiols, thiocarbonates, thioureas, hydrogen sulfide, and derivatives thereof can be used, and one or more of these may be used. . Specifically, examples of the thiols include acid thiols such as mercaptopropionic acid, mercaptoacetic acid, thiodipropionic acid, mercaptosuccinic acid, and thioacetic acid, methyl mercaptan, ethyl mercaptan, propyl mercaptan, isopropyl mercaptan, n- Aliphatic thiols such as butyl mercaptan, dodecanethiol, hexanethiol, allyl mercaptan, dimethyl mercaptan, mercaptoethanol, aminoethyl mercaptan, thiodiethylamine, cysteine, alicyclic thiols such as cyclohexylthiol, and aromatic thiols such as thiophenol Examples of thioglycols include, for example, thiodiethylene glycol, thiodiglycolic acid, methyl thioglycolate, ethylenethioglycol, Te is, for example, thioformamide and the like. Among them, a sulfur compound having a hydroxyl group at the terminal, such as acid thiols such as mercaptopropionic acid, mercaptoacetic acid, thiodipropionic acid, mercaptosuccinic acid, and thioacetic acid is preferable because the oxidation resistance is further improved. The content of the sulfur compound can be appropriately set, and at least, it is preferable to set it in the range of 0.5 to 50 parts by weight with respect to 1000 parts by weight of copper because the effect is easily obtained, and the range of 1 to 20 parts by weight is preferable. Further preferred.

  The shape of the copper particles may be any shape such as a spherical shape, a plate shape, a flake shape, and a square shape, and is preferably a substantially spherical particle having excellent filling properties. Moreover, what kind of thing may be sufficient as the magnitude | size of a copper particle, and if it is 10 micrometers or less as an average particle diameter, it will be easy to use for a paste, ink, and a coating material. In particular, the range of 0.005 to 1 μm is preferable because a high-density electrode having almost no defects can be easily obtained and the dispersibility in a paint or the like is excellent. A more preferable range is 0.05 to 1.0 μm, a further preferable range is 0.1 to 1.0 μm, and a most preferable range is 0.2 to 1.0 μm. The average particle diameter is expressed as a cumulative 50% diameter measured by electron microscopy. The particle shape of copper is observed with an electron microscope.

  Next, the present invention is a method for producing a copper powder in which the surface of a copper particle is coated with a sulfur compound and silicon oxide, wherein the hydrolyzable silicon compound is hydrolyzed in the presence of the sulfur compound and the copper particle, The surface of the copper particles is covered with a sulfur compound and silicon oxide. Here, the hydrolysis refers to a reaction including neutralization hydrolysis and heat hydrolysis in addition to normal hydrolysis in which a hydrolyzable compound and water are reacted. Specifically, it is in a suspension state in which copper particles are dispersed in an aqueous medium solution or an organic medium solution such as alcohol, the suspension and the silicon compound are mixed, and the silicon compound is hydrolyzed by a conventional method. Or when neutralizing and coat | covering the silicon oxide on the surface of a copper particle, a sulfur compound is made to exist. The sulfur compound may be present in advance in the suspension of copper particles, and may be added to the solution containing the silicon compound, or may be added separately during the hydrolysis or neutralization of the silicon compound. Can exist. In a preferred embodiment, when the surface of the copper particles is preliminarily coated with a sulfur compound, the silicon oxide coating layer becomes denser. Since sulfur compounds easily adsorb to copper particles, adding sulfur compounds in the process of producing copper particles, or adding them to the suspension in advance before mixing with silicon compounds, the sulfur compounds on the surface of the copper particles. An adsorption layer is formed.

  As the sulfur compound, the above-described sulfur compounds can be used. For example, thiols, thioglycols, and thioamides, which are organic compounds RSH (R is a hydrocarbon group such as an alkyl group) having a mercapto group (-SH). In addition to dithiols, thiolic acids (thionic acids) and derivatives thereof, sulfur compounds such as thiones, polythiols, thiocarbonates, thioureas, hydrogen sulfide, and derivatives thereof can be used. You may use 1 type (s) or 2 or more types. In particular, when a sulfur compound having a hydroxyl group at the terminal, such as acid thiols such as mercaptopropionic acid, mercaptoacetic acid, thiodipropionic acid, mercaptosuccinic acid, and thioacetic acid, a dense silicon oxide coating layer is easily obtained. Therefore, it is preferable.

As the hydrolyzable silicon compound, a silicon compound having a hydrolyzable group such as an alkoxy group or a halogen group, or a silicate such as water glass can be used. Of these, alkoxysilane is preferable because it easily controls the hydrolysis reaction. Alkoxysilane is a compound represented by the chemical formula: R ′ _4-n Si (OR) _n (wherein R and R ′ are the same or different alkyl groups, and n is an integer of 1 to 4) or a part thereof. It is a compound that includes a condensed oligomer. The alkoxysilane represented by the above chemical formula is preferably a tetraalkoxysilane having a large number of reactive alkoxy groups, for example, n = 4, and the smaller the R molecular weight, the easier the hydrolysis proceeds. Silane, tetraethoxysilane and the like are more preferable. In addition, when an oligomer is used, it is preferable because the rate control and handling of hydrolysis / condensation polymerization are easier than those of the monomer, and those having an average degree of polymerization of about 3 to 10 are more preferable. The silicon compound can be used as it is, or can be used by appropriately dissolving in a liquid such as water or alcohol. Mixing of the silicon compound and the suspension of copper particles can be performed by an ordinary method such as adding and mixing the silicon compound to the suspension, and may be aged for an arbitrary time after mixing.

  When hydrolyzing a hydrolyzable silicon compound in the presence of the sulfur compound and copper particles, if the hydrolysis is carried out in the presence of a protective colloid, the protective colloid suppresses aggregation of copper particles. Since the silicon oxide can be coated in a state in which the copper particles are dispersed, the individual copper particles are uniformly coated, which is preferable because a denser coating layer can be easily obtained. As the protective colloid, known ones can be used. For example, protein systems such as gelatin, gum arabic, casein, sodium caseinate, ammonium caseinate, natural polymers such as starch, dextrin, agar, sodium alginate, hydroxy Synthesis of celluloses such as ethyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, vinyls such as polyvinyl alcohol and polyvinyl pyrrolidone, acrylic acids such as sodium polyacrylate and ammonium polyacrylate, higher fatty acids such as stearic acid, polyethylene glycol, etc. Examples thereof include polymers, polyvalent carboxylic acids such as citric acid, aniline or derivatives thereof, and these may be used alone or in combination. The protective colloid acts as a dispersion stabilizer for the copper particles. When the amount used is in the range of 1 to 100 parts by weight with respect to 100 parts by weight of copper, the copper particles are preferably dispersed and stabilized. The range of 50 parts by weight is more preferred.

  If copper particles previously coated with a sulfur compound are used, it is preferable to hydrolyze the hydrolyzable silicon compound by mixing an alkaline aqueous suspension containing the copper particles and a hydrolyzable silicon compound. . The alkaline aqueous suspension in which the copper particles coated with the sulfur compound are suspended uses water or a mixture of water and a hydrophilic organic medium such as alcohol as the medium, and the pH of the aqueous suspension is preferably 8 to The range is 13, and more preferably 9-12. It is preferable that the aqueous suspension is alkaline because condensation polymerization of the hydrolysis product proceeds and a coating layer is easily formed. Various basic substances can be used for pH adjustment. Particularly, when ammonium compounds and amines are used, they are easily removed by washing, and even if they remain in the copper particles after washing, they are easily decomposed. In the case of using an electrode, it is preferable because the conductivity is hardly hindered. Examples of the ammonium compound include ammonia, ammonium carbonate, and ammonium hydrogen carbonate. Examples of the amine include primary amines such as ethylamine, propylamine, and butylamine, and primary amines such as diethylamine, dipropylamine, and dibutylamine. Tertiary amines such as secondary amines, triethylamine, tripropylamine, tributylamine, 2- (dimethylamino) ethanol, 2- (diethylamino) ethanol, 2-aminoethanol, diethanolamine, N-butyldiethanolamine, Examples thereof include alkanolamines such as ethanolamine, and these may be used singly or in combination of two or more. When such a hydrolyzable silicon compound is mixed with such an alkaline aqueous suspension, it reacts with water and hydrolyzes to form a silicon oxide coating.

  As the copper particles used in the present invention, those obtained by a known method can be used. For example, (a) a method of reducing a copper compound in a gas phase such as an atomizing method, and (b) a liquid of a wet reduction method. And a method of reducing the copper compound in the phase. Among these, the method (b) that does not require special equipment is industrially advantageous.

  When applying the wet method, it is preferable to perform the reduction reaction in the presence of a sulfur compound because copper particles are formed and at the same time the surface of the copper particles can be coated with the sulfur compound. In the present invention, a first step of obtaining copper particles coated with a sulfur compound by reacting a copper compound with a reducing agent in the presence of a sulfur compound, a hydrolyzable silicon compound in the presence of the obtained copper particles It is possible to apply a method comprising a second step of hydrolysis. Specifically, the copper compound is dissolved in an organic medium such as water or alcohols, and then mixed with a reducing agent to cause the sulfur compound to exist when the reduction reaction is performed. The sulfur compound may be added to the copper compound solution or the reducing agent, or the sulfur compound may be added separately during the reduction reaction. The amount of the sulfur compound used can be set as appropriate, and is preferably at least 0.5 to 50 parts by weight with respect to 1000 parts by weight of the copper compound because the effect is easily obtained, preferably 1 to 20 parts by weight. Is more preferable.

  As the sulfur compound used in the first step, the above-described sulfur compound can be used. For example, thiols that are organic compounds RSH (R is a hydrocarbon group such as an alkyl group) having a mercapto group (-SH), In addition to thioglycols, thioamides, dithiols, thiolic acid (thionic acid) and derivatives thereof, thiones, polythiols, thiocarbonates, thioureas, hydrogen sulfide and other sulfur compounds and their derivatives, etc. These may be used, and one or more of these may be used. In particular, when a sulfur compound having a hydroxyl group at the end, such as an acid thiol such as mercaptopropionic acid, mercaptoacetic acid, thiodipropionic acid, mercaptosuccinic acid, thioacetic acid, etc. is used, a dense silicon oxide coating is formed in the second step. Since a layer is easy to be obtained, it is preferable. The mixing amount of the sulfur compound can be appropriately set. At least, it is preferable to set the amount in the range of 0.5 to 50 parts by weight with respect to 1000 parts by weight of copper because the effect is easily obtained, and the range of 1 to 20 parts by weight is preferable. Further preferred.

  Copper compounds include copper oxide, copper chloride, copper chlorate, copper bromide, copper iodide, copper sulfate, copper nitrate, copper carbonate, copper carbonate hydroxide, tetraammine copper sulfate, potassium tetracyanocuprate, etc. Inorganic copper compounds of hydrates, copper formate, copper acetate, copper oxalate and the like, and organic copper compounds of these hydrates can be used, among which copper oxide is preferred. In the present invention, a copper oxide is used in the sense of including a copper hydrated oxide and a copper hydroxide in addition to a normal copper oxide. As the copper oxide, cuprous oxide ( Alternatively, cuprous oxide), copper oxide (or cupric oxide), or the like can be used.

  Moreover, a well-known thing can be used as a reducing agent, For example, hydrazine type reducing agents, such as hydrazine, hydrazine hydrochloride, hydrazine sulfate, hydrazine compounds, such as hydrazine hydrate, sodium borohydride, sodium sulfite, hydrogen sulfite Sodium, sodium thiosulfate, sodium nitrite, sodium hyponitrite, phosphorous acid and its metal salts such as sodium phosphite, hypophosphorous acid and its metal salts such as sodium hypophosphite, aldehydes, alcohols , Amines, saccharides and the like, and one or more of these may be used. In particular, hydrazine-based reducing agents are preferred because of their strong reducing power. The amount of the reducing agent used can be appropriately set as long as it is an amount capable of generating copper particles from the copper compound, and is preferably in the range of 0.2 to 5 mol with respect to 1 mol of copper contained in the copper compound. . The reduction reaction temperature is preferably in the range of 10 ° C. to the boiling point of the liquid medium used, since the reaction is easy to proceed, and more preferably in the range of 40 to 95 ° C.

  In the reduction reaction of the first step, a basic substance may be added, and the reduction reaction may be performed after preferably adjusting the pH to a range of 8 to 13, more preferably 9 to 12. It is preferable to adjust the pH in advance, because it is easy to obtain copper particles having a uniform particle shape and a uniform particle size distribution. Various basic substances can be used for adjusting the pH. Particularly, when the above-mentioned ammonium compound or amines such as primary amine, secondary amine, tertiary amine, alkanolamine are used. It is preferable because it is easily pyrolyzed. These basic substances may be used alone or in combination of two or more.

  Further, in the reduction reaction in the first step, it is more preferable to make a protective colloid present because aggregation of the produced copper particles is suppressed. As the protective colloid, known ones can be used. For example, the above-mentioned natural polymer, synthetic polymer, polyvalent carboxylic acid, aniline or derivatives thereof can be used, and these can be used alone or in combination. May be. The amount used is preferably in the range of 1 to 100 parts by weight with respect to 100 parts by weight of the copper compound, since the produced copper particles are easily dispersed and stabilized, and more preferably in the range of 2 to 50 parts by weight. After the first step, filtration, washing, and drying may be appropriately performed as necessary, and the second step may be directly performed after the first step.

  Next, in the second step, a suspension obtained by dispersing copper particles coated with a sulfur compound in an aqueous medium or an organic medium such as alcohol is mixed with the hydrolyzable silicon compound, This compound is hydrolyzed, and the surface of the copper particles is further coated with silicon oxide. A preferred form of the second step is that the hydrolyzable silicon compound is hydrolyzed in the presence of the protective colloid, and the aggregation of the copper particles is suppressed. The protective colloid used in the second step may be the same as or different from that used in the first step, without removing the one used in the first step by washing or the like. It can be subsequently used in the second step.

  A preferred form of the second step is to hydrolyze the hydrolyzable silicon compound using an alkaline aqueous suspension in which copper particles coated with a sulfur compound are dispersed in an alkaline medium. As the polycondensation proceeds, a coating layer is easily formed. This alkaline aqueous suspension uses water or a mixture of water and a hydrophilic organic medium such as alcohol as a medium, and the pH of the aqueous suspension is preferably in the range of 8 to 13, more preferably 9 to 12. The range. Various basic substances can be used for adjusting the pH. Particularly, when the above-mentioned ammonium compound or amines such as primary amine, secondary amine, tertiary amine, alkanolamine are used. It is preferable because it is easily pyrolyzed. These basic substances may be used alone or in combination of two or more. When such a hydrolyzable silicon compound is mixed with such an alkaline aqueous suspension, it reacts with water and hydrolyzes to form a silicon oxide coating.

  In addition, when the protective colloid is present in an alkaline aqueous suspension containing copper particles coated with a sulfur compound, hydrolysis / condensation polymerization of the hydrolyzable silicon compound can be controlled, and a denser coating layer is formed. Since it is easy, it is more preferable. Hydrolyzable silicon compounds such as alkoxysilanes are easily hydrolyzed in an alkaline region, and the resulting hydrolysis product and polycondensation of hydroxyl groups on the copper particles proceed to bond firmly to the copper particles. However, under the alkalinity, the polycondensation of the hydrolysis products also proceeds, and polysiloxane is formed in a phase different from the particle surface. Therefore, it is estimated that the coating layer is difficult to be bulky and dense. Therefore, when a protective colloid is present, it functions to control the condensation polymerization of the hydrolysis product and polymerizes after the hydrolysis product is bonded to the surface of the copper particles, so a dense polysiloxane coating layer. It is considered that the oxidation resistance is improved. In addition, the protective colloid is considered to have an effect of suppressing aggregation of copper particles, and since the surface of the hydrolyzable silicon compound can be coated with the hydrolyzable silicon compound in a state where the copper particles are dispersed, Since the condensation polymerization product is uniformly coated, it is considered that a denser coating layer is easily obtained.

  After obtaining copper particles as described above, filtration, washing, and drying are performed as appropriate, and pulverized as necessary. Drying is preferably performed in an atmosphere of a non-oxidizing gas (inert gas) such as nitrogen gas, helium gas, or argon gas so that the copper particles are not easily oxidized.

  The copper powder of the present invention is used as a composition having fluidity such as copper paste, copper ink or copper paint (copper ink) by mixing with a solvent or a binder resin as necessary. The solvent can be appropriately selected depending on the application, for example, a relatively high boiling nonpolar solvent or low polarity solvent, specifically, terpineol, mineral spirit, xylene, toluene, ethylbenzene, mesitylene, hexane, heptane, Octane, decane, dodecane, cyclohexane, cyclooctane and the like can be used. Further, the binder resin can also be appropriately selected according to the application, for example, phenol resin, epoxy resin, unsaturated polyester resin, vinyl ester resin, diallyl phthalate resin, oligoester acrylate resin, xylene resin, bismaleimide triazine resin, Examples include thermosetting resins such as furan resin, urea resin, polyurethane resin, melamine resin, and silicon resin. Phenol resin and epoxy resin are more preferable as resin components because they have good adhesion to the substrate. It is. The blending amount of the solvent and the binder resin can be appropriately set according to the use. For example, the solvent is about 1 to 500 parts by weight and the binder resin is about 1 to 50 parts by weight with respect to 100 parts by weight of the copper powder. be able to. Such a fluid composition may be blended with a fluidity modifier such as a viscosity modifier and various additives such as glass.

  Such a flowable composition can be used to produce an internal electrode of a multilayer ceramic capacitor, a circuit of a printed wiring board, and other electrodes after being applied to a substrate by a normal method and then heated and fired. . Since the copper powder of the present invention is excellent in oxidation resistance, the electrode manufactured using the copper powder has excellent electrical characteristics.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1
Industrial copper oxide (N-120: manufactured by NTC) as a copper compound, 0.5 g of 3-mercaptopropionic acid as a sulfur compound, 3 g of polyvinyl alcohol (average polymerization degree 1000 to 1500) as a protective colloid, hydrazine as a reducing agent After adding 15.65 g of monohydrate (80%) to 400 ml of pure water at room temperature, the pH was adjusted to 10 with 2- (dimethylamino) ethanol. Thereafter, the temperature was raised to 80 ° C. over 40 minutes, and a reduction reaction was carried out at 80 ° C. for 2 hours to form copper particles coated with 3-mercaptopropionic acid in the liquid medium. Next, while maintaining the temperature of the medium at 80 ° C., a treatment solution in which 8.9 g of tetraethoxysilane (corresponding to 10% by weight as SiO _{2 with} respect to the copper particles) was dissolved in 100 ml of ethanol was added over 30 minutes. Aged for 2 hours. After aging, the filtrate is washed with water until the electric conductivity of the filtrate becomes 100 μS / cm or less, and then the copper particles are filtered off and dried at 60 ° C. for 10 hours in an atmosphere of dry nitrogen gas. Sample A) was obtained.

Example 2
Implemented except that 6.4 g of tetraethoxysilane oligomer (ethyl silicate 40: Colcoat, average polymerization degree = 5) (equivalent to 10% by weight as SiO _{2 with} respect to copper particles) was used instead of tetraethoxysilane. The copper powder (sample B) of the present invention was obtained in the same manner as in Example 1.

Example 3
A copper powder (sample C) of the present invention was obtained in the same manner as in Example 1 except that the amount of tetraethoxysilane used was changed to 13.4 g (corresponding to 15% by weight as SiO ₂ with respect to the copper particles).

Example 4
A copper powder (sample D) of the present invention was obtained in the same manner as in Example 2 except that the amount of ethyl silicate 40 used was changed to 9.6 g (corresponding to 15% by weight as SiO ₂ with respect to the copper particles).

Example 5
Other than using mercaptoacetic acid instead of 3-mercaptopropionic acid, changing the amount of polyvinyl alcohol used to 2 g and the amount of tetraethoxysilane to 5.3 g (corresponding to 6% by weight as SiO ₂ with respect to copper particles) Obtained the copper powder (sample E) of this invention like Example 1. FIG.

Example 6
Implemented except using 3.8 g of tetraethoxysilane oligomer (ethyl silicate 40: Colcoat, average polymerization degree = 5) (equivalent to 6 wt% as SiO _{2 with} respect to copper particles) instead of tetraethoxysilane In the same manner as in Example 5, a copper powder (sample F) of the present invention was obtained.

Comparative Example 1
A copper powder (sample G) was obtained in the same manner as in Example 1 except that tetraethoxysilane was not used.

Comparative Example 2
A copper powder (sample H) was obtained in the same manner as in Example 5 except that tetraethoxysilane was not used.

Comparative Example 3
Industrial copper oxide (N-120: manufactured by NC Tech Co.) 32 g as a copper compound, polyvinyl alcohol (average polymerization degree 1000 to 1500) 3 g as a protective colloid, hydrazine monohydrate (80%) 15.65 g as a reducing agent After adding to 400 ml of pure water at room temperature, the pH was adjusted to 10 with 2- (dimethylamino) ethanol. Then, it heated up to the temperature of 80 degreeC over 40 minutes, and it was made to reduce-react at 80 degreeC for 2 hours, and the copper particle which the sulfur compound was not substantially processed on the particle | grain surface was produced | generated in the liquid medium. Next, the filtrate was washed with water until the electrical conductivity reached 100 μS / cm or less, and after removing the protective colloid and other salts, the copper particles were filtered off to obtain a wet cake of copper particles. When this wet cake was dispersed in 400 ml of pure water, a suspension of copper particles having a pH of 6.4 was obtained. While maintaining the temperature of this suspension at 80 ° C., a treatment solution in which 8.9 g of tetraethoxysilane (corresponding to 10% by weight as SiO _{2 with} respect to copper particles) was dissolved in 100 ml of ethanol was added over 30 minutes, Aged for 2 hours. Thereafter, in the same manner as in Example 1, it was washed with water, filtered and dried to obtain a copper powder (Sample I).

Evaluation 1: Measurement of average particle diameter The 50% cumulative average particle diameter of the copper particles contained in Samples A to I obtained in Examples 1 to 6 and Comparative Examples 1 to 3 was measured by electron microscopy. The results are shown in Table 1.

Evaluation 2: Evaluation of oxidation resistance Samples A to I obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were heated at a temperature of 60 ° C. for 10 hours in a nitrogen gas atmosphere, and then a TAS-200 type thermobalance. The temperature at which the rate of weight increase was 0.5% was measured using (Rigaku Corporation, temperature rising rate 5 ° C./min), and this was used as the oxidation start temperature. In addition, 10 g of the heated sample was further heated and fired at 150 ° C., 200 ° C., 300 ° C., and 400 ° C. in an oxidizing air atmosphere for 20 minutes, and the weight increase rate was calculated. did. The results are shown in Table 1. The higher the oxidation start temperature and the smaller the weight increase, the better the oxidation resistance, and it can be seen that the copper powder of the present invention is excellent in oxidation resistance. In particular, the copper powder of the present invention has a favorable oxidation start temperature of 250 ° C. or higher and lower than 300 ° C.

  Using the copper powder obtained in the examples of the present invention, a fluid composition of copper paste, copper ink or copper paint (copper ink) is prepared by mixing with a solvent and a binder resin, and the substrate is prepared by a usual method. After application, the electrode was baked by heating to obtain an electrode. It was confirmed that the obtained electrode had excellent electrical characteristics.

INDUSTRIAL APPLICABILITY The present invention is useful as a material for ensuring electrical continuity, such as external electrodes such as capacitors, internal electrodes, electrode members such as printed wiring board circuits, and various electrical contact members. In particular, the copper powder of the present invention is made into a fluid composition such as copper paste, copper ink, copper paint (copper ink), etc., for example, for internal electrodes of multilayer ceramic capacitors, circuits of printed wiring boards, and other electrodes. If used, it is expected that an excellent electrical property can be obtained.

Claims (14)

A copper powder comprising a surface of copper particles coated with a sulfur compound and silicon oxide. The copper powder according to claim 1, wherein the silicon oxide is a hydrolysis product of alkoxysilane. A method for producing a copper powder, comprising hydrolyzing a hydrolyzable silicon compound in the presence of a sulfur compound and copper particles, and coating the surfaces of the copper particles with a sulfur compound and silicon oxide. 4. The method for producing copper powder according to claim 3, wherein alkoxysilane is used as the hydrolyzable silicon compound. The method for producing copper powder according to claim 3, wherein the hydrolyzable silicon compound is hydrolyzed in the presence of a protective colloid. The method for producing a copper powder according to claim 3, wherein copper particles whose surfaces are previously coated with a sulfur compound are used. The production of copper powder according to claim 6, wherein the hydrolyzable silicon compound is hydrolyzed by mixing an alkaline aqueous suspension containing copper particles coated with a sulfur compound and a hydrolyzable silicon compound. Method. A first step of obtaining a copper particle coated with a sulfur compound by reacting a copper compound with a reducing agent in the presence of a sulfur compound, hydrolyzing a hydrolyzable silicon compound in the presence of the obtained copper particle A method for producing a copper powder comprising the second step of coating the surfaces of copper particles with a sulfur compound and silicon oxide. The method for producing a copper powder according to claim 8, wherein the first step is further performed in the presence of a protective colloid. The method for producing a copper powder according to claim 8, wherein the second step is performed in the presence of a protective colloid. 9. The hydrolyzable silicon compound is hydrolyzed by mixing an alkaline aqueous suspension containing copper particles coated with a sulfur compound and a hydrolyzable silicon compound in the second step. The manufacturing method of the copper powder of description. The method for producing a copper powder according to claim 11, wherein alkoxysilane is used as the hydrolyzable silicon compound. A fluid composition comprising the copper powder according to claim 1. An electrode formed using the copper powder according to claim 1.