JP5522885B2 - Nickel powder, method for producing the same, and conductive paste - Google Patents

Description

  The present invention relates to nickel powder, a method for producing the same, and a conductive paste, and more specifically, for example, nickel powder used as a raw material for nickel paste used for forming an internal electrode of a multilayer ceramic capacitor, a method for producing the same, and the nickel The present invention relates to a conductive paste using powder.

  Nickel powder is used in various applications. For example, nickel powder is used in applications in which various electrodes and circuits are formed using a conductive paste containing the nickel powder. Specifically, nickel is generally used as an internal electrode of a multi-layer ceramic capacitor (MLCC), and the internal electrode uses a conductive paste containing nickel powder as a ceramic dielectric or the like. It is obtained by applying and baking.

  As a method for producing the nickel powder, for example, in Patent Document 1, a suspension obtained by suspending a solid compound such as a hydroxide such as nickel in a liquid polyol or a polyol mixture at a reaction temperature is at least 85 ° C. A reduction method is disclosed in which the solid compound is reduced with a polyol by heating to 1 and the resulting metal precipitate is isolated. According to this method, nickel powder can be obtained easily and economically.

JP 59-173206 A (first page)

  However, in recent years, due to the demand for smaller and larger capacity MLCC, there has been a demand for thinner internal electrodes and smoother electrode surfaces. For this reason, nickel powder is required to be atomized and sharp in particle size distribution. It has been. In addition, nickel powder having a low content of impurities such as carbon or a small amount of adhesion has been demanded from the demand for the conductivity of the internal electrode. On the other hand, the nickel powder obtained by the method described in Patent Document 1 is not sufficient in terms of atomization and sharpness of the particle size distribution, and a problem that a large amount of organic matter tends to adhere to the surface of the nickel powder. was there.

  Accordingly, an object of the present invention is to provide a nickel powder having a fine particle size, a sharp particle size distribution, and a low content or adhesion amount of impurities such as carbon, and a conductive paste using the nickel powder. There is.

  Under such circumstances, the present inventor has conducted extensive studies, and as a result, the reaction solution containing the nickel salt, polyol and noble metal catalyst is heated to the reduction temperature, and nickel ions in the reaction solution are reduced while maintaining the reduction temperature. In the manufacturing method of nickel powder, it discovered that the said objective could be achieved when the said reduction temperature was in a specific range, and came to complete this invention.

Method for producing nickel powder according to the present invention: The method for producing nickel powder according to the present invention comprises heating a reaction solution containing a nickel salt, a polyol and a noble metal catalyst to a reduction temperature, and maintaining the reduction temperature in the reaction solution. In the method for producing nickel powder for reducing the nickel ions, the reduction temperature is 150 ° C. to 210 ° C. and 37 ° C. to 30 ° C. lower than the boiling point of the polyol.

  And in the manufacturing method of the nickel powder which concerns on this invention, it is preferable that the said reaction liquid further contains a dispersing agent.

Nickel powder according to the present invention: nickel powder according to the present invention, which has been manufactured by the above manufacturing method, the image analysis average particle size Ri 0.02μm~0.2μm der, and, carbon content It is characterized by being 0.6% by weight or less .

Further, the nickel powder according to the present invention, the average particle diameter _{D 50} is characterized in that it is 0.1 .mu.m to 0.5 .mu.m.

Furthermore, the nickel powder according to the present invention is characterized in that the maximum particle size D _max is 0.7 μm or less.

Conductive paste according to the present invention: The conductive paste according to the present invention includes the nickel powder described in any of the above.

  The nickel powder according to the present invention or the nickel powder obtained by the production method according to the present invention is a fine particle, has a sharp particle size distribution, and has a small content or adhesion amount of impurities such as carbon. Further, since the conductive paste according to the present invention uses the nickel powder according to the present invention, the nickel thick film obtained by firing the conductive paste can be thinned, and the nickel thick film surface is smoothed. can do. Therefore, for example, if the conductive paste according to the present invention is used, the internal electrode of the MLCC can be thinned and the surface of the electrode can be smoothed, and the MLCC can be reduced in size and capacity. .

Form of nickel powder production method according to the present invention: The nickel powder production method according to the present invention comprises heating a reaction solution containing a nickel salt, a polyol and a noble metal catalyst within a specific temperature range, and adjusting the temperature within the specific temperature. While maintaining, the nickel salt in the reaction solution is reduced.

  The nickel salt used in the present invention is not particularly limited, and examples thereof include nickel hydroxide, nickel sulfate, nickel nitrate, nickel chloride, nickel bromide and nickel acetate. Among these, nickel hydroxide is preferable because it does not contain elements such as sulfur, carbon, and nitrogen that may adversely affect the operation of MLCC when contained in the MLCC internal electrode. In this invention, the said nickel salt can be used individually by 1 type or in combination of 2 or more types.

  The polyol used in the present invention refers to a substance having a hydrocarbon chain and a plurality of hydroxyl groups. Examples of the polyol include ethylene glycol (boiling point 197 ° C.), diethylene glycol (boiling point 245 ° C.), triethylene glycol (boiling point 278 ° C.), tetraethylene glycol (boiling point 327 ° C.), 1,2-propanediol (boiling point 188 ° C.). ), Dipropylene glycol (boiling point 232 ° C.), 1,2-butanediol (boiling point 193 ° C.), 1,3-butanediol (boiling point 208 ° C.), 1,4-butanediol (boiling point 235 ° C.), 2,3 -Butanediol (boiling point 177 ° C) 1,5-pentanediol (boiling point 239 ° C) and at least one selected from the group consisting of polyethylene glycol. Of these, ethylene glycol is preferred because it has a low boiling point, is liquid at room temperature, and is easy to handle. In the present invention, the polyol functions as a reducing agent for the nickel salt and also functions as a solvent.

  The noble metal catalyst used in the present invention promotes the reduction reaction of the nickel salt with polyol in the above reaction solution. For example, palladium compounds such as palladium chloride, palladium nitrate, palladium acetate, ammonium palladium chloride, silver nitrate, Silver compounds such as silver lactate, silver oxide, silver sulfate, silver cyclohexane acid and silver acetate, platinum compounds such as chloroplatinic acid, potassium chloroplatinate and sodium chloroplatinate, and gold such as chloroauric acid and sodium chloroaurate Compounds and the like. Among these, palladium nitrate, palladium acetate, silver nitrate, or silver acetate is preferable because the purity of the obtained nickel powder tends to be high and the manufacturing cost is low. The catalyst can be used in the form of the compound as it is or in the form of a solution of the compound.

  In the present invention, the reaction solution contains the above nickel salt, polyol and noble metal catalyst. The reaction solution can be prepared, for example, by adding a nickel salt, a polyol and a noble metal catalyst to water, stirring and mixing, and when the noble metal catalyst is present as an aqueous solution such as palladium nitrate, Without mixing the nickel salt, polyol and noble metal catalyst. When mixing the nickel salt, the polyol and the noble metal catalyst, the order of addition and the mixing method are not particularly limited. For example, a slurry may be prepared by premixing a nickel salt, a polyol, a noble metal catalyst, and, if necessary, a dispersant described later to prepare a slurry, and the slurry and the remainder of the polyol may be mixed to prepare a reaction solution.

  Moreover, it is preferable that the reaction liquid further contains a dispersant as necessary, because the obtained nickel powder becomes finer and the particle size distribution tends to be sharper. Examples of the dispersant used in the present invention include nitrogen-containing organic compounds such as polyvinylpyrrolidone, polyethyleneimine, polyacrylamide, poly (2-methyl-2-oxazoline), and polyvinyl alcohol. Among these, polyvinylpyrrolidone is preferable because the particle size distribution of the obtained nickel powder tends to be sharp. In this invention, the said dispersing agent can be used individually by 1 type or in combination of 2 or more types.

  In the present invention, the reaction solution is heated to a reduction temperature, and the nickel salt in the reaction solution is reduced while maintaining the reduction temperature to produce nickel powder. In the present invention, the reduction temperature is within a temperature range satisfying both of two temperature ranges defined from different viewpoints. Hereinafter, the temperature range defined from the first viewpoint is also referred to as a first temperature range, and the temperature range defined from the second viewpoint is also referred to as a second temperature range.

  As for the said reduction | restoration temperature, the 1st temperature range is 150 to 210 degreeC, Preferably it is 150 to 200 degreeC. When the reduction temperature is within this range, the reduction reaction is completed quickly, and the nickel powder obtained after the reaction does not easily contain impurities or adhere to the nickel powder.

  On the other hand, if the reduction temperature is less than 150 ° C., the reduction reaction tends to be very slow, which is not preferable. On the other hand, if the reduction temperature exceeds 210 ° C., it is not preferable because it is easy to coarsen and the product obtained by the reduction reaction tends to contain carbon and become nickel carbide powder.

  The reduction temperature is such that the second temperature range is 37 ° C. to 30 ° C. lower than the boiling point of the polyol. When the reduction temperature is within this range, the resulting nickel powder is difficult to become coarse particles or agglomerate, and the organic compound presumed to be a reaction byproduct of polyol adheres to the surface of the nickel powder. Can be suppressed, which is preferable.

  Note that if the reduction temperature is lower than 150 ° C. lower than the boiling point of the polyol, the reduction reaction may hardly proceed. On the other hand, when the reduction temperature exceeds 10 ° C. lower than the boiling point of the polyol, the organic compound presumed to be a reaction byproduct of the polyol tends to adhere to the surface of the nickel powder, which is not preferable.

  In the present invention, when the reduction temperature satisfies both the first temperature range and the second temperature range, the resulting nickel powder is fine, the particle size distribution is sharp, and the content or adhesion of impurities such as carbon The amount will be small.

  The time during which the reaction solution is maintained at the above-mentioned reduction temperature cannot be generally specified because an appropriate time varies depending on the composition of the reaction solution and the reduction temperature. When the time for maintaining the reaction solution at the above reduction temperature is within the above range, the growth of nickel powder nuclei is suppressed and the atmosphere in which a large number of nickel powder nuclei are likely to be generated is formed. Since the grain growth becomes substantially uniform, the resulting nickel powder can be prevented from becoming coarse particles or agglomerated. Therefore, in the present invention, the temperature of the reaction solution may be set to a temperature outside the range of the reduction temperature after that if the time is maintained at the reduction temperature for the time. For example, in order to improve the speed of the reduction reaction, the temperature of the reaction solution may be set to a temperature exceeding the reduction temperature. The nickel powder which concerns on this invention is obtained by performing the above process. Since the nickel powder according to the present invention is manufactured under the above conditions, it has the physical properties described below.

Nickel powder according to the present invention: The nickel powder according to the present invention is a powder substantially made of nickel and having a substantially spherical particle shape. The nickel powder according to the present invention has an image analysis average particle size of usually 0.02 μm to 0.2 μm, preferably 0.03 μm to 0.1 μm. An image analysis average particle size of less than 0.02 μm is not preferable because aggregation of primary particles tends to occur. In addition, if the average image analysis particle diameter exceeds 0.2 μm, the maximum value of the primary particle diameter becomes too large, and it becomes difficult to obtain a thin and smooth electrode film, which is not preferable. In the present invention, the image analysis average particle size is a magnification at which the number of primary particles in a screen is 100 or more using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). For example, the average particle diameter of 100 primary particles obtained by performing image analysis based on the image using a high-definition image analyzer IP-1000PC manufactured by Asahi Engineering Co., Ltd.

Nickel powder according to the present invention, the average particle diameter _{D 50,} typically 0.1 .mu.m to 0.5 .mu.m, preferably 0.2Myuemu～0.3Myuemu. Average particle diameter D _50, is less than 0.1 [mu] m, unfavorably easily oxidized nickel particles are particles too small. The average particle diameter D ₅₀ is more than 0.5 [mu] m, hard nickel thick film formed of a conductive paste containing the nickel powder sufficiently thin and smoothness of the surface of the nickel thick film is deteriorated It is not preferable because it is easy. In the present invention, D ₅₀ means a particle size (μm) at a time point when the cumulative volume determined by the laser diffraction scattering method using Microtrack HRA manufactured by Nikkiso Co., Ltd. is 50%.

The nickel powder according to the present invention has a maximum particle diameter _Dmax of usually 0.7 μm or less, preferably 0.5 μm or less. When the maximum particle size D _max exceeds 0.7 μm, it is difficult to sufficiently reduce the thickness of the nickel thick film formed with the conductive paste containing the nickel powder, and the smoothness of the surface of the nickel thick film tends to deteriorate. It is not preferable. In the present invention, D _max means the maximum particle size (μm) obtained by a laser diffraction scattering method using Microtrack HRA manufactured by Nikkiso Co., Ltd.

  The nickel powder according to the present invention has a standard deviation SD of the particle size of usually 0.05 to 0.2, preferably 0.05 to 0.1. It is preferable that the SD of the nickel powder is within this range because the nickel thick film formed from the conductive paste containing the nickel powder can be easily made sufficiently thin and the smoothness of the surface of the nickel thick film is difficult to deteriorate. In the present invention, SD means the standard deviation of the particle diameter required when measuring the particle size distribution by the laser diffraction scattering method using Microtrack HRA manufactured by Nikkiso Co., Ltd.

  The nickel powder according to the present invention has a carbon content of usually 0.6% by weight or less, preferably 0.3% by weight or less. It is preferable that the carbon content is within the above range because the nickel powder has high conductivity, which increases the MLCC capacitance and easily increases the electrode film density. When the nickel powder according to the present invention is produced by the method for producing a nickel powder according to the present invention, a nickel powder with a low content of impurities such as carbon or a small amount of adhesion is obtained, and the carbon content tends to be within the above range. .

Form of the conductive paste according to the present invention: The conductive paste according to the present invention includes the nickel powder according to the present invention, and includes a resin and a solvent in addition to the nickel powder. Examples of the resin used in the present invention include celluloses such as ethyl cellulose and nitrocellulose, and acrylic resins such as butyl methacrylate and methyl methacrylate. In this invention, the said resin can be used individually by 1 type or in mixture of 2 or more types. Examples of the solvent used in the present invention include terpenes such as terpineol and dihydroterpineol, alcohols such as octanol and decanol, and the like. In this invention, the said solvent can be used individually by 1 type or in mixture of 2 or more types.

  In the conductive paste according to the present invention, the content of the nickel powder according to the present invention is usually 40% by weight to 70% by weight, preferably 50% by weight to 60% by weight. It is preferable for the content of the nickel powder to fall within this range because the paste has good conductivity, high filling properties, and low heat shrinkage.

  The nickel powder according to the present invention is mixed with, for example, a known paste used for producing a conductive paste, thereby obtaining a conductive paste in which nickel powder is dispersed. The conductive paste can be used as, for example, a nickel paste used for forming an internal electrode of a multilayer ceramic capacitor.

  Examples are shown below, but the present invention is not construed as being limited thereto.

Premixing step: 50L (56 kg) of ethylene glycol (manufactured by Mitsui Chemicals), 12.47 kg of nickel hydroxide (manufactured by OM Group), and a palladium nitrate aqueous solution prepared at 100 g / l (manufactured by Tanaka Kikinzoku Co., Ltd.) 53 ml and polyvinyl pyrrolidone K30 (manufactured by Wako Pure Chemical Industries, Ltd.) 0.67 kg were mixed and stirred to prepare a solution (solution A).

Mixing step: On the other hand, 80 g (89 kg) of ethylene glycol (manufactured by Mitsui Chemicals Co., Ltd.) is placed in another tank, and with stirring, the entire amount of solution A is added and mixed to prepare a solution (solution B). did.

Reduction process: Solution B was sent to a reaction vessel, and ethylene glycol (manufactured by Mitsui Chemicals) 29L (32 kg) was added and mixed to prepare a reaction solution (reaction solution A). The reaction solution A was heated and maintained at 160 ° C. for 10 hours. By these operations, a slurry (slurry A) was obtained.

Washing step: Thereafter, 140 L of ethylene glycol in the upper part of the slurry A was discharged from the upper part of the reaction tank. Thereafter, the remaining slurry A was subjected to suction filtration for solid-liquid separation. After 200 L of water was added to the separated cake and decanted, water was removed. After decanting by adding 50 L of methanol to the powder obtained by removing water, methanol was removed. When the powder after removal of methanol was dried at 80 ° C. for 5 hours, nickel powder was obtained.

The obtained nickel powder was observed with a scanning electron microscope (SEM). A scanning electron micrograph of the nickel powder is shown in FIG. Then, the obtained nickel powder, by the following measuring method, the image analysis the average particle _{size, D 10, D 50, D} 90, D max, was measured SD and residual carbon amount. The results are shown in Table 1. A graph of the particle size distribution is shown in FIG.

Image analysis average particle diameter measurement method: Asahi Engineering Co., Ltd. observes the sample powder with a scanning electron microscope (SEM) at a magnification (50000 times) where the number of primary particles in the screen is 100 or more. Image analysis was performed based on the image using a high-definition image analyzer IP-1000PC, and the average particle diameter of 100 primary particles was measured.

Measuring method of particle diameters D ₁₀ , D ₅₀ , D ₉₀ , D _max , SD: About 0.1 g of a sample is put in a 200 cc sample container, and a dispersing agent of 0.1 g / l (SN Dispersant 5468 manufactured by Sannobuco Co., Ltd.) After adding and mixing 100 ml, a sample liquid was prepared by dispersing for 10 minutes with an ultrasonic disperser (US-300T manufactured by Nippon Seiki Co., Ltd.). With respect to the sample liquid, the particle diameters (μm) when the cumulative volume determined by the laser diffraction scattering method using Microtrac HRA manufactured by Nikkiso Co., Ltd. is 10%, 50%, and 90% are D ₁₀ , D ₅₀ and D ₉₀ and the maximum particle size was D _max . The standard deviation of the particle size distribution obtained during these measurements was taken as SD.

Method for measuring carbon residue: Using a carbon / sulfur simultaneous analyzer EMIA-320V manufactured by HORIBA, Ltd., a 0.5 g sample was heated and burned at an outlet setting of 175 mA, and the carbon content was measured by an infrared absorption method. .

[Comparative Example 1]
Premixing step and mixing step: The premixing step and the mixing step were performed in the same manner as in Example 1 to prepare Solution B.

Reduction process: Solution B was sent to a reaction vessel, and ethylene glycol (manufactured by Mitsui Chemicals) 29L (32 kg) was added and mixed to prepare a reaction solution (reaction solution A). When the reaction solution A was heated and held at 190 ° C. for 5 hours, a slurry (slurry B) was obtained.

Washing step: Thereafter, 140 L of the supernatant in the slurry B was discharged from the upper part of the reaction vessel. Thereafter, the remaining slurry B was subjected to suction filtration for solid-liquid separation. After 200 L of water was added to the separated cake and decanted, water was removed. Further, 50 L of methanol was added to the powder and decanted, and then methanol was removed. When the powder after removal of methanol was dried at 80 ° C. for 5 hours, nickel powder was obtained.

  The obtained nickel powder was observed with a scanning electron microscope (SEM). A scanning electron micrograph of the nickel powder is shown in FIG. And about the obtained nickel powder, it carried out similarly to Example 1, and measured various characteristics. The results are shown in Table 1. A graph of particle size distribution is shown in FIG.

From Table 1, it can be seen that the nickel powder of Example 1 has a smaller D _max and SD than the nickel powder of Comparative Example 1, and a smaller amount of residual carbon.

  The nickel powder and the conductive paste according to the present invention can be used, for example, as a nickel paste used for forming an internal electrode of a multilayer ceramic capacitor and a raw material thereof.

2 is a scanning electron micrograph of nickel powder of Example 1. FIG. 3 is a graph showing the particle size distribution of nickel powder of Example 1. 2 is a scanning electron micrograph of nickel powder of Comparative Example 1. 4 is a graph showing a particle size distribution of nickel powder of Comparative Example 1.

Claims (6)

In a method for producing nickel powder, a reaction solution containing a nickel salt, a polyol and a noble metal catalyst is heated to a reduction temperature, and nickel ions in the reaction solution are reduced while maintaining the reduction temperature.
The method for producing nickel powder, wherein the reduction temperature is 150 ° C. to 210 ° C. and 37 ° C. to 30 ° C. lower than the boiling point of the polyol.   The method for producing nickel powder according to claim 1, wherein the reaction liquid further contains a dispersant. A nickel powder produced by the method according to claim 1 or 2,
Image analysis The average particle diameter Ri 0.02μm~0.2μm der, and a nickel powder, wherein the carbon content is 0.6 wt% or less. The nickel powder according to claim 3, wherein the average particle diameter D ₅₀ is 0.1 μm to 0.5 μm. The nickel powder according to claim 3 or 4, wherein the maximum particle size D _max is 0.7 µm or less. The electroconductive paste characterized by including the nickel powder of any one of Claims 3-5 .