JP2005240164A - Nickel powder and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nickel powder which is inexpensive, has superior weatherability, has low electric resistance in a state of having been kneaded with a resin, has reduced electrical resistance at the beginning of and during use, can be stably used for a long period, and is suitable as a conductive particle used in a conductive paste and a conductive resin, and to provide a manufacturing method therefor. <P>SOLUTION: The nickel powder comprises 1-20 mass% cobalt and the balance nickel with unavoidable impurities; is composed of secondary particles made of aggregated primary particles; and includes 0.8 mass% or less oxygen. The nickel powder preferably contains cobalt only on the surface layer part of the secondary particles, and the cobalt content in the surface layer part is preferably 1 to 40 mass%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to nickel powder suitable as conductive particles for conductive paste and conductive resin, and a method for producing the same.

  Conventionally, Sn—Pb-based solder has been used for connecting electronic devices, but in recent years, the use of conductive paste has been studied in response to the Pb-free. In recent years, devices using conductive resins have been widely used.

  The conductive paste used for these applications is obtained by kneading conductive particles and various resins, and the conductive resin is a molded body obtained by curing the conductive paste.

  The properties required of the conductive particles include high conductivity of the particles themselves, low electrical resistance of a paste obtained by kneading with the various resins and a molded product obtained by curing the paste, high migration resistance, It is excellent in weather resistance.

  Currently, metal powder or carbon powder is used as the conductive particles. However, among the metal powders, noble metal powders have high conductivity and low electrical resistance, but there is a problem that they are expensive. In addition, base metal powders typified by nickel or copper are inexpensive and have high conductivity, but they have poor weather resistance. There is a problem that resistance increases. On the other hand, carbon powder is inexpensive and has high weather resistance, but has low conductivity, and there is a problem that the electrical resistance of a conductive paste or conductive resin using carbon powder is high.

  As a method for solving these problems, a powder in which the surface of nickel particles or copper particles is coated with a noble metal such as Ag has been proposed (Japanese Patent Laid-Open Nos. 2002-025345 and 2002-077507). These powders are improved in cost by coating nickel particles or copper particles with a noble metal, but are expensive in cost. In particular, Ag-coated powder is not suitable for use in a use environment in which migration resistance is required for a conductive paste or a conductive resin.

  In addition, attempts have been made to lower the electrical resistance of conductive paste and conductive resin by changing the surface shape of nickel particles or the like, for example, by forming a hemispherical nodule on the surface (Japanese Patent Laid-Open No. 2001-043734). JP, 7-507655, A). However, since the point that the weather resistance of the conductive particles is inferior is not improved, it cannot be said that the stability in long-term use is improved.

  Under such circumstances, it is desired to provide conductive particles that are inexpensive, have excellent weather resistance, have a low electrical resistance in a state of being made into a conductive paste or conductive resin, and can be used stably over a long period of time.

JP 2002-025345 A

JP 2002-075057 A

JP 2001-043734 A

JP 7-507655 Gazette

  In view of the above-described conventional circumstances, the present invention is inexpensive and excellent in weather resistance, has a low electrical resistance in a state of being made into a conductive paste or a conductive resin, particularly reduces initial electrical resistance, and is in use An object of the present invention is to provide nickel powder that can be used stably over a long period of time while suppressing an increase in resistance, and that is suitable as conductive particles for conductive paste and conductive resin, and a method for producing the same.

  The nickel powder according to the present invention is a nickel powder mainly containing secondary particles in which cobalt is contained in an amount of 1 to 20 mass%, the balance is nickel and inevitable impurities, and primary particles are aggregated, and the oxygen content is 0. .8% by mass or less.

  Nickel powder is composed of secondary particles in which primary particles are aggregated. Further, nickel containing cobalt is further precipitated and crystal is grown on the primary particles in the surface layer portion of the secondary particles, and this portion is the surface layer portion of the nickel powder. Form. In addition, although it may contain cobalt also in the inside of nickel powder, ie, the part inside a surface layer part, it is preferable to exist only in a surface layer part.

  That is, the nickel powder according to another embodiment contains 1 to 20% by mass of cobalt, the remainder consists of nickel and inevitable impurities, and consists of secondary particles in which primary particles are aggregated, and the oxygen content is 0.8% by mass or less. The primary particles existing on the surface of the secondary particles further have a surface layer part in which crystals are grown, and the cobalt content of the surface layer part is 40% by mass or less, and the cobalt content is present inside the nickel powder. Try to be more.

  More preferably, the nickel powder contains 1 to 20% by mass of cobalt, the remainder consists of nickel and inevitable impurities, and consists of secondary particles in which primary particles are aggregated, and the oxygen content is 0.8% by mass or less. The primary particles present on the surface of the secondary particles further have a surface layer part in which crystals are grown, cobalt is contained only in the surface layer part, and the cobalt content in the surface layer part is 1 to 40% by mass. Like that.

  These nickel powders according to the present invention have an average primary particle diameter of 0.2 to 2.0 [mu] m by observation with a scanning electron microscope (SEM), and an average secondary particle diameter (D50) of 8 to 50 [mu] m by laser flow distribution measurement. The tap density is preferably 0.5 to 2.0 g / ml.

  The method for producing nickel powder according to the present invention includes a first reduction precipitation step in which a reducing agent is added to an aqueous solution containing a divalent nickel salt to precipitate nickel, and at least a divalent nickel salt solution is added to the aqueous solution. And a second-stage reduction precipitation step for further depositing nickel, and at least in the second-stage reduction precipitation step, a divalent cobalt salt is added to the aqueous solution. A nickel powder manufacturing method for depositing nickel powder in a state, wherein the obtained nickel powder is heat-treated at a temperature of 100 to 500 ° C. in a reducing atmosphere.

  In the first-stage reduction and precipitation step, primary particles that are crystal grains grown and secondary particles aggregated therewith are formed. In the second-stage reduction and precipitation step, the primary particles mainly on the surface of the secondary particles are formed. Cobalt nickel is deposited on the particles, and the primary particles are crystal-grown. Thereby, the surface layer part of nickel powder is formed.

  Therefore, cobalt can be present only in the surface layer portion of the nickel powder by adding cobalt only in the second reduction deposition step.

  When a divalent cobalt salt is added to the aqueous solution in the first and second reduction precipitation processes, the amount of the divalent cobalt salt is 1 to 20% by mass of cobalt with respect to the total of nickel and cobalt. It is preferable that

  It is preferable that the amount of the divalent cobalt salt added to the aqueous solution in the second stage reduction precipitation step is larger than the amount of the divalent cobalt salt added to the aqueous solution in the first stage reduction precipitation step.

  Further, the divalent cobalt salt is added only in the second reduction precipitation step, and the amount of the divalent cobalt salt added to the aqueous solution is 1 to 40% by mass of cobalt with respect to the total of nickel and cobalt. It is preferable that

  The nickel powder of the present invention is inexpensive, and the conductive paste or conductive resin obtained by kneading with the resin has an extremely low electrical resistance, can suppress the rise from the initial use to the in-use, and has excellent weather resistance It can be used stably for a long time. Therefore, the nickel powder of the present invention is inexpensive and extremely suitable as conductive particles for conductive paste and conductive resin.

  As a result of advancing research on the electrical resistance of conductive paste obtained by kneading nickel powder with resin and conductive resin, the inventors have made the oxygen content of nickel powder containing cobalt below a specific value. As a result, the electrical resistance of the conductive paste and the conductive resin is greatly reduced and the weather resistance is improved. In particular, the cobalt content in the surface layer of nickel powder is important in improving the electrical resistance and weather resistance. I found out.

  In addition, the present inventors reduced the oxygen content in a state in which the particle size and tap density of nickel powder having a large influence on the electrical resistance of the conductive paste and conductive resin were controlled within a specific range, so that the conductive paste It has been found that the electrical resistance of the conductive resin and the conductive resin is greatly reduced and has excellent weather resistance.

  That is, in one aspect, the nickel powder of the present invention contains 1 to 20% by mass of cobalt, and is composed of secondary particles in which primary particles are aggregated in nickel powder composed of inevitable impurities and nickel, and has an oxygen content of 0. 0.8 mass% or less.

In another embodiment, consists of secondary particles formed by aggregation of primary particles, has a surface layer portion of the primary particles present on the surface of the secondary particles are further grown, the cobalt content of the surface layer portion 40 It is preferable that the content is less than or equal to mass% and is greater than the cobalt content in the nickel powder, that is, in the portion inside the surface layer portion.

  Specifically, nickel containing cobalt is further deposited on primary particles mainly existing on the surface of the nickel powder, and crystal growth is performed, whereby a surface layer portion of the nickel powder is formed.

  Moreover, in another aspect, the nickel powder of the present invention has a cobalt content of 0% by mass inside the nickel powder, and the surface layer portion is coated with nickel containing 1 to 40% by mass of cobalt. The oxygen content is preferably 0.8% by mass or less.

  Further, the nickel powder has an average primary particle size of 0.2 to 2.0 μm by observation with a scanning electron microscope (SEM), an average secondary particle size (D50) of 8 to 50 μm by laser particle size distribution measurement, It is desirable that the tap density is 0.5 to 2.0 g / ml. Here, the average secondary particle diameter (D50) is a particle diameter at which the cumulative volume is 50% by laser particle size distribution measurement.

  Moreover, the manufacturing method of the nickel powder of this invention manufactures from the aqueous solution containing a bivalent nickel salt by a two-step reduction precipitation process. That is, in the first stage of the reduction precipitation step, a reducing agent is added to an aqueous solution containing a divalent nickel salt (generally excessively added) to precipitate almost all of the nickel, and the primary grains which are crystal grown Particles and their aggregated secondary particles are formed, and subsequently, in the second reduction precipitation step, the first reduction reduction step is completed, and a divalent nickel salt solution is added to the aqueous solution containing the precipitated nickel powder, If necessary, a reducing agent is further added, so that nickel is further precipitated and crystal-grown on the primary particles existing on the surface of the secondary particles, thereby covering the surfaces of the secondary particles. Heat treatment is performed at a temperature of 100 to 500 ° C., preferably 200 to 450 ° C., more preferably 300 to 400 ° C. in a reducing atmosphere, using nickel powder produced by the above method as a raw material.

  The nickel powder of the present invention is composed of secondary particles in a form in which primary particles are strongly agglomerated, and by adding 1 to 20% by mass of cobalt, the weather resistance of the nickel powder is significantly improved and further improved. By reducing the oxygen content to 0.8% by mass or less, the surface electrical resistance value at the initial stage of use is lowered, and the increase in the surface electrical resistance value during use is suppressed, and is reduced to 0.8% by mass or less. By reducing the oxygen content, the oxide film on the surface of the nickel powder that becomes resistance becomes thin, and the surface electrical resistance value at the initial stage of use decreases.

  It is considered that cobalt is preferentially oxidized because cobalt (Co) has a slightly lower potential than nickel (Ni) by using a conductive paste or conductive resin. When the oxygen content is low, that is, when the surface layer in the initial stage of use has a small amount of nickel oxide, the cobalt oxidation product produced during use is relative to the nickel oxidation product compared to the case where the oxygen content is high. The amount is thought to increase. In this sense, the primary layer on the surface of the secondary particles of nickel powder is further crystal-grown with nickel containing cobalt, thereby forming a surface layer portion covering the surface of the secondary particles as a dual structure, the surface layer. It is preferable to increase the cobalt content of the part.

  The oxidation products of cobalt include oxides and hydroxides, but these are more conductive than nickel oxides, and are considered to suppress an increase in surface electrical resistance during use. In addition, cobalt is considered to have an effect of improving the weather resistance of nickel itself by oxidizing preferentially over nickel.

  However, when the oxygen content exceeds 0.8% by mass, these effects cannot be obtained, and when the cobalt content is less than 1% by mass of the entire nickel powder, there is no effect of improving weather resistance. On the other hand, even if the total cobalt content exceeds 20% by mass, it is not preferable because it is expensive in cost.

  Therefore, it is preferable to increase the cobalt in the surface layer part to 40% by mass and lower the internal cobalt content accordingly. Furthermore, in order to ensure sufficient weather resistance with a small cobalt content, it is preferable to contain cobalt only in the surface layer portion of the nickel powder. In these cases, the surface layer part of the nickel powder is a part formed in the second reduction precipitation process in the nickel powder production method by the two-stage reduction precipitation process, and is present on the surface of the secondary particles. Further, it is composed of nickel with cobalt deposited thereon. In the second stage, since the energy required for crystal growth of the primary particles on the surface of the secondary particles is lower, new primary particles are hardly generated.

  The cobalt content in the surface layer is preferably in the range of 40% by mass or less. Even if it exceeds 40 mass%, it is difficult to obtain further improvement in weather resistance, and nickel powder becomes ferromagnetism, which is not preferable when used for electronic parts and the like.

  Furthermore, in the nickel powder of the present invention, the average primary particle diameter by scanning electron microscope observation is 0.2 to 2.0 μm, the average secondary particle diameter (D50) by laser particle size distribution measurement is 8 to 50 μm, and the tap density is 0.00. A range of 5 to 2.0 g / ml is desirable. Thereby, oxygen content can be controlled reliably. Here, regarding the meaning of D50, the average secondary particle diameter (D50) is a particle diameter at which the cumulative volume is 50% by laser particle size distribution measurement. Moreover, the average primary particle diameter by SEM observation shows the particle diameter of the aggregated individual particle | grains, and measures 100 particle diameters in the visual field of a scanning electron microscope (SEM) 5000 time photograph, and calculates | requires the average. Further, the tap density is obtained by measuring the volume after tapping 10 g of Ni powder with a stroke length of 20 mm for 500 times.

  By setting the average primary particle diameter in the range of 0.2 to 2.0 μm by SEM observation, the nickel powder primary particles are appropriately aggregated to form secondary particles having a complicated shape such as a chain, and after kneading with the resin In the conductive paste or conductive resin, the secondary particles are entangled with each other to form a network, and thus the electrical resistance is remarkably low. However, when the average primary particle diameter is less than 0.2 μm, the primary particles are too agglomerated and the secondary particle shape after aggregation becomes extremely large lump or sphere, which is not preferable. On the other hand, when the average primary particle diameter exceeds 2.0 μm, the aggregation of the primary particles is small, and the primary particles remain close to the dispersed state, and the electric resistance becomes high, which is not preferable.

  The secondary particle size by laser particle size distribution measurement indicates the particle size of secondary particles in which primary particles are aggregated. By setting the average secondary particle diameter (D50) by laser particle size distribution measurement to be in the range of 8 to 50 μm, the number of locations where nickel powders come into contact with each other after kneading with the resin increases, and the surface electrical resistance of the resulting molded body is It drops significantly. However, when the average secondary particle diameter (D50) is less than 8 μm, the number of entangled portions decreases because of less aggregation, and the surface electrical resistance value of the conductive paste or conductive resin increases. Moreover, when the average secondary particle diameter (D50) exceeds 50 μm, the dispersion of nickel powder in the conductive paste or conductive resin becomes non-uniform, and the surface electrical resistance value of the conductive paste or conductive resin becomes high, which is not preferable.

  Further, the tap density of the nickel powder affects the degree of dispersion in the resin. By setting the tap density in the range of 0.5 to 2.0 g / ml, nickel powder is uniformly dispersed in the conductive paste or conductive resin, and the surface electrical resistance value is remarkably low. However, if the tap density exceeds 2.0 g / ml, nickel powder is unevenly distributed in the conductive paste or conductive resin, reducing mutual contact. Conversely, if the tap density is less than 0.5 g / ml, kneading with the resin is not possible. It becomes difficult and a molded body cannot be obtained.

  Next, the manufacturing method of the nickel powder of this invention is demonstrated. The nickel powder of the present invention is produced from an aqueous solution containing a divalent nickel salt by a two-step reduction precipitation process. That is, in the first reduction precipitation step, a reducing agent is added to an aqueous solution containing a divalent nickel salt (generally in excess) to precipitate almost all of the nickel, and primary particles and their aggregated secondary In the second stage of the reduction and precipitation process, the divalent nickel salt solution is added to the aqueous solution containing the nickel powder that has been deposited after the first stage of the reduction and precipitation process. Is further deposited on the primary particles existing on the surface of the secondary particles, the primary particles are crystal-grown, and the surface of the secondary particles is coated. In order to make this nickel powder contain cobalt, the divalent cobalt salt is added to the aqueous solution only in the second stage or in both the first stage and the second stage in the two-stage reduction and precipitation process described above. And nickel may be deposited. At that time, a polyvalent carboxylic acid such as tartaric acid, a commonly used complexing agent such as ethylenediamine, sodium hydroxide for adjusting pH, and the like can be added to the aqueous solution containing the divalent nickel salt. The reducing agent is not particularly limited as long as nickel can be deposited by reduction, but a hydrazine-based reducing agent can be preferably used.

  In the above production method, first, the nickel particles precipitated in the first reduction precipitation step become secondary particles in which the primary particles are appropriately aggregated, but the cohesive force is weak, and the separation operation from the reacted solution or When kneading with the resin, it is easily separated into individual particles. However, by subsequently performing the second stage reduction deposition step, it was further coated with the deposited nickel, and the agglomeration became strong, and an appropriate agglomerated state could be maintained without separation even in the subsequent operation, thus obtained. The electrical resistance of the molded body by kneading nickel powder and resin is also extremely low. The nickel deposited in the second reduction deposition step is deposited on the primary particles present on the surface of the aggregated nickel secondary particles deposited in the first reduction deposition step, and the primary particles are crystal-grown. The surface layer is formed, and the newly deposited nickel connects the surface layer portions of the secondary particles in a network structure to form a high strength nickel powder.

  The nickel powder produced through the two-step reduction precipitation process is adjusted by adjusting the concentration of nickel salt and reducing agent, the temperature of the aqueous solution, and other conditions, so that the above-mentioned powder characteristics, that is, the average by observation with a scanning electron microscope The primary particle diameter can be in the range of 0.2 to 2.0 μm, the average secondary particle diameter by laser particle size distribution measurement is 8 to 50 μm, and the tap density is in the range of 0.5 to 2.0 g / ml.

  In order to make this nickel powder contain cobalt, the divalent cobalt salt is added to the aqueous solution only in the second stage or in both the first stage and the second stage in the two-stage reduction and precipitation process described above. And nickel may be deposited. In particular, when nickel is not contained in the nickel powder and cobalt is contained only in the surface layer portion, cobalt is not added in the first reduction deposition process, and the aqueous solution is added in the second reduction deposition process. Add divalent cobalt salt. In this case, the addition amount of the cobalt salt is 1 to 40% by weight with respect to the total amount of nickel and cobalt in the aqueous solution, whereby the cobalt content in the surface portion of the nickel powder can be 1 to 40% by weight.

  In addition, when cobalt is contained not only in the surface layer but also in the entire nickel powder including the inside, a divalent cobalt salt is added to each aqueous solution in the first and second reduction and precipitation processes. . In this case, the addition amount of the cobalt salt is set to 1 to 20% by weight with respect to the total amount of nickel and cobalt in the aqueous solution in each of the first and second reduction precipitation processes, or the second stage What is necessary is just to adjust so that the addition amount of the cobalt salt of a reduction | restoration precipitation process may be increased from the 1st stage, and the cobalt content of the whole nickel powder may finally become 1 to 20 weight%.

  The nickel of the present invention is obtained by drying the nickel powder obtained by the above-described production method in the atmosphere at 80 to 100 ° C. or in vacuum. Furthermore, the obtained nickel powder is heat-treated in a reducing atmosphere at a temperature of 100 to 500 ° C., preferably 200 to 450 ° C., more preferably 300 to 400 ° C. That is, by performing heat treatment in a reducing atmosphere, oxides or hydroxides on the surface of the nickel powder are reduced and organic substances are decomposed to obtain nickel powder having an oxygen content of 0.8% by mass or less. The reducing atmosphere is not particularly limited, and a hydrogen gas atmosphere in which nickel and cobalt can be reduced, a hydrogen-nitrogen mixed gas atmosphere, and other reducing atmospheres can be used. The method for producing nickel powder of the present invention is particularly suitable for nickel powder produced by a wet method having a high oxygen content.

  In the said manufacturing method, the heat processing temperature is 100 to 500 degreeC. Below 100 ° C., not only the reduction is not sufficiently performed, but also the evaporation or decomposition of organic substances is small, the oxygen content is not sufficiently reduced, and the desired oxygen content nickel powder cannot be obtained. When the temperature exceeds 500 ° C., the oxygen content can be reduced, but the nickel powder is sintered, making it difficult to use as conductive particles.

(Example 1)
Sodium hydroxide and tartaric acid were added to 306 liters of pure water and heated to 65 ° C. with stirring. To this aqueous solution, 39 liters of 60% hydrazine hydrate and 5 kg of nickel chloride aqueous solution with a nickel equivalent amount were added, and nickel was precipitated by the first reduction reaction. Next, an aqueous solution obtained by mixing a cobalt chloride aqueous solution and a nickel chloride aqueous solution so that the cobalt content is 10% by mass with respect to the Ni + Co amount is added to the aqueous solution after completion of the reduction precipitation in the first stage by adding 5 kg in terms of Ni + Co equivalent. Further, nickel was precipitated by the second-stage reduction reaction. Then, after filtering and washing with water, it dried at 100 degreeC in air | atmosphere, and obtained nickel powder. Furthermore, the obtained nickel powder was heat-treated at 350 ° C. for 1 hour in a 4% hydrogen-nitrogen mixed gas.

The nickel powder after the heat treatment contained cobalt only in the surface layer portion, and the oxygen content was 0.4% by mass. The powder characteristics are shown in Table 1. However, although the total cobalt content is an analytical value, the cobalt content in the surface layer portion is a value calculated from the cobalt content relative to the Ni + Co content in the aqueous solution in the second stage reduction precipitation step. Moreover, the SEM diameter in Table 1 means the average primary particle diameter by SEM observation, and D50 means the average secondary particle diameter by laser particle size distribution measurement.

Next, 2.4 g of the nickel powder obtained under the above conditions was kneaded with 3 g of a thermosetting resin (phenol resin), and formed into a sheet and cured. When the volume resistivity of the cured sheet sample was measured with a low resistivity meter (manufactured by Dia Instruments, Loresta GP), the initial volume resistivity was 0.051 Ω · cm. Furthermore, in order to evaluate the weather resistance, after performing a moisture resistance test in which the same nickel powder was held in a constant temperature and humidity chamber set at 85 ° C. to 85% RH for 40 hours, a thermosetting resin (phenolic resin) was used in the same manner as described above. ) And the volume resistivity of the sheet obtained by kneading were measured to show 0.120 Ω · cm. These results are summarized in Table 2. In addition, Ω · cm means a resistance per unit volume, that is, a volume resistivity (JIS K 6911).

(Example 2)
In the same manner as in Example 1, two-stage nickel reduction precipitation was performed, followed by washing with water and filtration, followed by air drying at 100 ° C. to obtain nickel powder. Furthermore, only the heat treatment temperature was changed, and heat treatment was performed at 210 ° C. for 1 hour in a 4% hydrogen-nitrogen mixed gas.

  The nickel powder after the heat treatment contained cobalt only in the surface layer portion, and the oxygen content was 0.5% by mass. The powder characteristics are shown in Table 1. Further, when the obtained nickel powder was evaluated in the same manner as in Example 1, the initial volume resistivity was 0.049 Ω · cm, and the volume resistivity after the moisture resistance test was 0.510 Ω · cm. These results are summarized in Table 2.

(Example 3)
In the same manner as in Example 1, two-stage nickel reduction precipitation was performed, followed by washing with water and filtration, followed by air drying at 100 ° C. to obtain nickel powder. Furthermore, only the heat treatment temperature was changed, and heat treatment was performed at 450 ° C. for 1 hour in a 4% hydrogen-nitrogen mixed gas.

  The nickel powder after the heat treatment contained cobalt only in the surface layer portion, and the oxygen content was 0.2% by mass. The powder characteristics are shown in Table 1. Further, when the obtained nickel powder was evaluated in the same manner as in Example 1, the initial volume resistivity was 0.036 Ω · cm, and the volume resistivity after the moisture resistance test was 0.414 Ω · cm. These results are summarized in Table 2.

Example 4
In the same manner as in Example 1, two-stage nickel reduction precipitation was performed, followed by washing with water and filtration, followed by air drying at 100 ° C. to obtain nickel powder. Furthermore, heat treatment conditions were changed, and heat treatment was performed at 350 ° C. for 2 hours in a 2% hydrogen-nitrogen mixed gas.

  The nickel powder after the heat treatment contained cobalt only in the surface layer portion, and the oxygen content was 0.6% by mass. The powder characteristics are shown in Table 1. Moreover, when this nickel powder was evaluated in the same manner as in Example 1, the initial volume resistivity was 0.029 Ω · cm, and the volume resistivity after the moisture resistance test was 0.111 Ω · cm. These results are summarized in Table 2.

(Example 5)
Sodium hydroxide and tartaric acid were added to 3800 ml of pure water and heated to 80 ° C. with stirring. To this aqueous solution, an aqueous solution obtained by mixing 300 ml of hydrazine, an aqueous solution of cobalt chloride and an aqueous solution of nickel chloride so that the cobalt content is 2% by mass with respect to the amount of Ni + Co is added in an amount of Ni + Co equivalent of 65 g. Was precipitated. Next, 65 g of a mixed solution of cobalt chloride and nickel chloride, which is the same as the addition in the first stage, is added to the aqueous solution after the completion of the reduction precipitation in the first stage in an equivalent amount of Ni + Co. Was precipitated. Then, after filtering and washing with water, it dried at 100 degreeC in air | atmosphere, and obtained nickel powder. Further, heat treatment was performed for 1 hour at 300 ° C. in a 4% hydrogen-nitrogen mixed gas.

  The nickel powder after the heat treatment contained cobalt in the whole (inside and on the surface layer portion), and the oxygen content was 0.4% by mass. The powder characteristics are shown in Table 1. Moreover, when this nickel powder was evaluated in the same manner as in Example 1, the initial volume resistivity was 0.069 Ω · cm, and the volume resistivity after the moisture resistance test was 1.41 Ω · cm. These results are summarized in Table 2.

(Example 6)
Sodium hydroxide and tartaric acid were added to 3800 ml of pure water and heated to 80 ° C. with stirring. At the first stage of reduction precipitation, 300 ml of hydrazine and nickel chloride aqueous solution are added to the aqueous solution in an equivalent amount of 65 g. Only at the time of reduction precipitation at the second stage, the cobalt chloride aqueous solution and the nickel chloride aqueous solution have a cobalt content of Ni + Co. On the other hand, 65 g of an aqueous solution mixed so as to be 35% by mass was added at a Ni + Co equivalent, and nickel powder was precipitated by a reduction reaction. Then, after filtering and washing with water, it dried at 100 degreeC in air | atmosphere, and obtained nickel powder. Further, heat treatment was performed for 1 hour at 250 ° C. in a 4% hydrogen-nitrogen mixed gas.

  The nickel powder after the heat treatment contained cobalt only in the surface layer portion, and the oxygen content was 0.8% by mass. The powder characteristics are shown in Table 1. The nickel powder was evaluated in the same manner as in Example 1. As a result, the initial volume resistivity was 0.095 Ω · cm, and the low volume efficiency after the moisture resistance test was 1.04 Ω · cm. These results are summarized in Table 2.

(Example 7)
In the same manner as in Example 1, two-stage nickel reduction precipitation was performed, followed by washing with water and filtration, followed by vacuum drying to obtain nickel powder. Furthermore, heat treatment conditions were changed, and heat treatment was performed at 150 ° C. for 2 hours in a 10% hydrogen-nitrogen mixed gas.

  The nickel powder after the heat treatment contained cobalt only in the surface layer portion, and the oxygen content was 0.6% by mass. The powder characteristics are shown in Table 1. The nickel powder was evaluated in the same manner as in Example 1. As a result, the initial volume resistivity was 0.047 Ω · cm, and the volume resistivity after the moisture resistance test was 1.61 Ω · cm. These results are summarized in Table 2.

(Example 8)
In the same manner as in Example 1, two-stage nickel reduction precipitation was performed, followed by washing with water and filtration, followed by air drying at 100 ° C. to obtain nickel powder. Furthermore, only the heat treatment temperature was changed, and heat treatment was performed at 300 ° C. for 1 hour in a 4% hydrogen-nitrogen mixed gas.

The nickel powder after the heat treatment contained cobalt only in the surface layer portion, and the oxygen content was 0.6% by mass. The powder characteristics are shown in Table 1. Moreover, when this nickel powder was evaluated in the same manner as in Example 1, the initial volume resistivity was 0.045 Ω · cm, and the volume resistivity after the moisture resistance test was 0.161 Ω · cm. These results are summarized in Table 2.
Example 9
In the same manner as in Example 1, two-stage nickel reduction precipitation was performed, followed by washing with water and filtration, followed by air drying at 100 ° C. to obtain nickel powder. Furthermore, only the heat treatment temperature was changed, and heat treatment was performed at 400 ° C. for 1 hour in a 4% hydrogen-nitrogen mixed gas.

  The nickel powder after the heat treatment contained cobalt only in the surface layer portion, and the oxygen content was 0.5% by mass. The powder characteristics are shown in Table 1. Moreover, when this nickel powder was evaluated in the same manner as in Example 1, the initial volume resistivity was 0.050 Ω · cm, and the volume resistivity after the moisture resistance test was 0.254 Ω · cm. These results are summarized in Table 2.

(Comparative Example 1)
In the same manner as in Example 5, two-stage nickel reduction precipitation was performed, but no cobalt chloride aqueous solution was added during the first-stage and second-stage reduction precipitation. After filtration and washing with water, air drying was performed at 100 ° C. to obtain nickel powder. However, no heat treatment was performed. The nickel chloride aqueous solution was added in an amount of 13 g with a nickel equivalent at the first stage of reduction precipitation, and 5 g with a nickel equivalent at the second stage of reduction precipitation.

  The nickel powder did not contain cobalt, and the oxygen content was 0.8% by mass. The powder characteristics are shown in Table 1. Moreover, when this nickel powder was evaluated in the same manner as in Example 1, the initial volume resistivity was 0.073 Ω · cm, and the volume resistivity after the moisture resistance test was 9.56 Ω · cm. These results are summarized in Table 2.

(Comparative Example 2)
Table 1 shows the powder characteristics of typical filler-like nickel powder commercially available as conductive particles for conductive paste and conductive resin. The oxygen content was 0.2% by mass. Moreover, when this nickel powder was evaluated in the same manner as in Example 1, the initial volume resistivity was 0.073 Ω · cm, and the volume resistivity after the moisture resistance test was 5.31 Ω · cm. These results are summarized in Table 2.

(Comparative Example 3)
In the same manner as in Example 1, two-stage nickel reduction precipitation was performed, followed by washing with water and filtration, followed by air drying at 100 ° C. to obtain nickel powder. However, no heat treatment was performed. The obtained nickel powder contained cobalt only in the surface layer portion, and the oxygen content was 1.0% by mass. The powder characteristics are shown in Table 1. The nickel powder was evaluated in the same manner as in Example 1. As a result, the initial volume resistivity was 0.237 Ω · cm, and the volume resistivity after the moisture resistance test was 5.31 Ω · cm. These results are summarized in Table 2.

(Comparative Example 4)
In the same manner as in Example 1, two-stage nickel reduction precipitation was performed, followed by washing with water and filtration, followed by air drying at 100 ° C. to obtain nickel powder. Furthermore, only the heat treatment temperature was changed, and heat treatment was performed at 550 ° C. for 1 hour in a 4% hydrogen-nitrogen mixed gas.

Although the oxygen content of the nickel powder after the heat treatment was 0.2% by mass, sintering was progressing, and it was impossible to use as conductive particles, and volume resistivity was not measured.

Claims (8)

  Cobalt is contained in 1 to 20% by mass, the remainder is nickel and inevitable impurities, nickel powder mainly composed of secondary particles in which primary particles are aggregated, and the oxygen content is 0.8% by mass or less Nickel powder characterized by that.   Cobalt is contained in an amount of 1 to 20% by mass, the balance is made of nickel and inevitable impurities, and the primary particles are agglomerated secondary particles. The oxygen content is 0.8% by mass or less and exists on the surface of the secondary particles. A nickel powder, wherein the primary particles further have a surface layer part in which crystals are grown, and the cobalt content of the surface layer part is 40% by mass or less and is higher than the cobalt content present inside the nickel powder.   Cobalt is contained in an amount of 1 to 20% by mass, the balance is made of nickel and inevitable impurities, and the primary particles are agglomerated secondary particles. The oxygen content is 0.8% by mass or less and exists on the surface of the secondary particles. A nickel powder characterized in that the primary particles further have a surface layer part in which crystals are grown, cobalt is contained only in the surface layer part, and the cobalt content in the surface layer part is 1 to 40% by mass.   The average primary particle diameter by scanning electron microscope (SEM) observation is 0.2 to 2.0 μm, the average secondary particle diameter (D50) by laser flow distribution measurement is 8 to 50 μm, and the tap density is 0.5 to The nickel powder according to claim 1, wherein the nickel powder is 2.0 g / ml.   A first-stage reduction-precipitation step of depositing nickel by adding a reducing agent to an aqueous solution containing a divalent nickel salt, and adding at least a divalent nickel salt solution to the aqueous solution to further precipitate nickel A nickel powder for depositing nickel powder in a state in which a divalent cobalt salt is added to an aqueous solution in at least the second stage of the first and second stage reduction deposition processes. It is a manufacturing method, Comprising: The nickel powder obtained is heat-processed at the temperature of 100-500 degreeC in reducing environment, The manufacturing method of the nickel powder characterized by the above-mentioned.   The amount of the divalent cobalt salt added to the aqueous solution in the first and second reduction and precipitation steps is such that cobalt is 1 to 20% by mass with respect to the total of nickel and cobalt. The manufacturing method of the nickel powder of Claim 4.   The amount of the divalent cobalt salt added to the aqueous solution in the second stage reduction precipitation step is larger than the amount of the divalent cobalt salt added to the aqueous solution in the first stage reduction precipitation step. The manufacturing method of the nickel powder as described in 2. The divalent cobalt salt is added only in the second reduction precipitation step, and the amount of the divalent cobalt salt added to the aqueous solution is 1 to 40% by mass of cobalt with respect to the total of nickel and cobalt. The method for producing nickel powder according to claim 4, wherein: