JP2007146251A - Nickel powder, its production method and polymer-ptc element using the nickel powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nickel powder which is inexpensive, has low electric resistance in a state kneaded with a resin, also has excellent weatherability, and usable as electrically conductive particles for electrically conductive paste and electrically conductive particles for an electrically conductive resin over a long period. <P>SOLUTION: The nickel powder has a composition comprising 1 to 20 mass% cobalt, and the balance nickel with inevitable impurities, and is composed of secondary particles in which primary particles are flocculated. Further, the average primary particle diameter is 1.0 to 3.0 μm; the ratio between the standard deviation σ of the primary particle diameter and the average primary particle diameter d, σ/d is ≤0.4; the average secondary particle diameter is 5 to 60 μm; the tap density is 1.0 to 3.5 g/mL, and the specific surface area is ≤2.0 m<SP>2</SP>/g. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to nickel powder, a method for producing the same, and a polymer PTC element using the nickel powder. The nickel powder can be suitably used as conductive particles for conductive paste and conductive resin, and can be particularly preferably used as a conductive filler for polymer PTC elements.

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

  The conductive paste is a paste obtained by kneading conductive particles and various resins, and the conductive resin is a molded body obtained by curing this. The properties required for the conductive particles include high electrical conductivity of the particles themselves, low electrical resistance even when kneaded with a resin, high migration resistance, and excellent weather resistance. Currently, metal powder or carbon powder is used as the conductive particles.

  Among metal powders, noble metal powders have high conductivity and low electrical resistance, but are expensive. In addition, base metal powders typified by nickel (Ni) or copper (Cu) are inexpensive in cost and have high conductivity, but are inferior in weather resistance. When used as a conductive paste or conductive resin for a long period of time, there is a problem that the electrical resistance increases.

  In addition, carbon powder is inexpensive and has high weather resistance, but has a problem of low electrical conductivity and high electrical resistance when kneaded with a resin.

  In order to solve these problems, in Patent Document 1 (Japanese Patent Laid-Open No. 2002-025345) and Patent Document 2 (Japanese Patent Laid-Open No. 2002-0755057), the surface of Ni particles or Cu particles such as silver (Ag) is used. A powder coated with a noble metal has been proposed. Since these powders are coated with Ni particles or Cu particles with a noble metal, the characteristic aspects are generally improved, but there is a problem with migration resistance. In particular, the powder coated with Ag is not suitable for use in a use environment where migration resistance is required. Moreover, coating Ni particles and Cu particles with a noble metal is costly.

  Moreover, in patent document 3 (Unexamined-Japanese-Patent No. 2001-043734), by changing the surface shape of Ni particles etc., for example, forming a hemispherical nodule on the surface, the electrical resistance when kneaded with resin is increased. There are also attempts to lower it. However, since the point that the weather resistance of the particles is inferior remains, it cannot be said that the stability in long-term use is improved.

  Furthermore, although this inventor has proposed Ni powder which has specific shape and improved electroconductivity and weather resistance by adding cobalt (Co) (refer patent document 4), further improvement is anticipated. Has been. Under such circumstances, it is desired to provide conductive particles that are inexpensive, have excellent weather resistance, have low electrical resistance when kneaded with a resin, and can be used stably over a long period of time.

JP 2002-25345 A JP 2002-75057 A JP 2001-43734 A International Publication No. 2005/023461 Pamphlet

  The present invention has been made in view of such problems, is inexpensive, has low electrical resistance in a state of being kneaded with a resin, has excellent weather resistance, is stable over a long period of time, a conductive paste, An object of the present invention is to provide nickel powder that can be used as conductive particles used for conductive resins, conductive fillers for PTC elements, and the like, and a method for producing the same.

The nickel powder according to the present invention contains 1 to 20% by mass of cobalt, the remainder is composed of nickel and inevitable impurities, and is composed of secondary particles in which primary particles are aggregated, and the average primary particle diameter is 1. 0 to 3.0 μm, the ratio of the standard deviation σ of the primary particle diameter to the average primary particle diameter d ₁ σ / d ₁ is 0.4 or less, the average secondary particle diameter is 5 to 60 μm, and the tap density is 1.0. -3.5 g / mL, and a specific surface area is 2.0 m < ² > / g or less, It is characterized by the above-mentioned.

The ratio d ₂ / d ₁ between the average primary particle diameter d ₁ and the average secondary particle diameter d ₂ is preferably in the range of 5-60.

  Moreover, it is preferable that cobalt content of the primary particle which exists in the surface layer part of the said secondary particle is 1-40 mass% per the total mass of this surface layer part.

  The method for producing nickel powder according to the present invention includes a first reduction precipitation step of depositing nickel by adding a divalent nickel salt to an aqueous solution containing a reducing agent, and at least an aqueous solution after the first reduction precipitation step. A second reduction precipitation step in which a divalent nickel salt is added and nickel is further precipitated. Among the first reduction precipitation steps, the HLB value is 10 in at least the first reduction precipitation step. In addition to adding the following low hydrophilic surfactant, at least in the second reduction precipitation step, a divalent cobalt salt is added to an aqueous solution for depositing nickel to precipitate nickel to obtain nickel powder. The obtained nickel powder is dried at 80 to 230 ° C. in an inert atmosphere or vacuum, or is dried in air at 80 to 150 ° C. and then reduced to 200 in a reducing atmosphere. Characterized by a heat treatment at 400 ° C..

  The content of cobalt ions in the aqueous solution to which the divalent cobalt salt is added in the second reduction precipitation step is 1 to 40% by mass with respect to the total amount of nickel ions and cobalt ions in the aqueous solution, and The cobalt ion concentration in the aqueous solution is higher than the cobalt ion concentration in the aqueous solution in the first reduction precipitation step, and the nickel powder obtained through the first and second reduction precipitation steps contains 1 to 20 mass of cobalt. % Content is preferable.

  Further, the divalent cobalt salt is added to the aqueous solution in the first reduction precipitation step so that the cobalt ion content in the aqueous solution is 1 to 20% by mass with respect to the total amount of nickel ions and cobalt ions in the aqueous solution. Is added to the aqueous solution in the second reduction precipitation step so that the cobalt ion content in the aqueous solution is 1 to 20% by mass with respect to the total amount of nickel ions and cobalt ions in the aqueous solution. The cobalt salt may be added.

When using the said nickel powder for a polymer PTC element, it is preferable that content of cobalt in the surface layer part of the said secondary particle is 8-20 mass% per the total mass of this surface layer part, The content of cobalt is preferably 4 to 10% by mass, and the content of cobalt in the nickel powder is preferably 3 to 6% by mass with respect to the total mass of the inside. Furthermore, the tap density is preferably 2.3 to 3.0 g / mL, and d ₂ / d ₁ is preferably 8 to 16.

  A polymer PTC element according to the present invention is a polymer PTC element comprising a polymer PTC element comprising a conductive filler and a polymer material, and a metal electrode disposed on at least one surface of the polymer PTC element, Either the nickel powder or the nickel powder produced by the method is used as a conductive filler.

  When the nickel powder according to the present invention is kneaded with a resin to produce a resin molded body, a resin molded body with extremely low electrical resistance can be obtained. Moreover, the obtained resin molding has excellent weather resistance and can be used stably for a long period of time. Therefore, the nickel powder according to the present invention can be used very suitably as conductive particles used in conductive pastes, conductive resins, and the like. Moreover, as will be described later, the nickel powder of the present invention can also be suitably used as a conductive filler of a polymer PTC element.

  Furthermore, the nickel powder according to the present invention is inexpensive because it does not use an expensive material and can be obtained without requiring a complicated process.

In addition, although the nickel powder according to Patent Document 4 is also excellent in weather resistance, the average primary particle diameter of the nickel powder according to the present invention is 0.2 to 2.0 μm with respect to the average primary particle diameter of the nickel powder according to Patent Document 4. Is 1.0 to 3.0 μm, and the tap density of the nickel powder according to Patent Document 4 is 0.5 to 2.0 g / mL, whereas the tap density of the nickel powder according to the present invention is 1.0. ~ 3.5 g / mL. Furthermore, in the nickel powder according to the present invention, the ratio σ / d ₁ between the standard deviation σ of the primary particle diameter and the average primary particle diameter d ₁ is set to 0.4 or less, and the specific surface area is set to 2.0 m ² / g or less. Yes. For this reason, the nickel powder according to the present invention has better weather resistance than the nickel powder according to Patent Document 4.

  Further, the nickel powder according to the present invention can be suitably used for a polymer PTC element, and since the increase in resistivity is small even in a severe environment such as a high temperature and a dry condition (for example, an environment in a car on a summer day). It is useful compared with the conventional PTC element.

  As a result of advancing research on the electrical resistance of a resin in which nickel powder is kneaded, the present inventors give the particle size and tap density of the nickel powder to the electrical resistance of a molded body using the resin in which nickel powder is kneaded. It has been found that the electrical resistance of the molded body can be greatly reduced by controlling the particle size and tap density of the nickel powder within a specific range.

  Moreover, it discovered that the weather resistance of nickel powder was improved by making a nickel powder contain a small amount of cobalt, especially by making a surface layer part of nickel powder contain cobalt. Furthermore, it has also been found that the weather resistance is further improved by suppressing the fluctuation of the primary particle diameter and setting the specific surface area to a specific value.

  The present invention has been completed based on such findings. Hereinafter, the nickel powder according to the present invention will be described in detail, and the method for producing the nickel powder according to the present invention will also be described.

The nickel powder according to the present invention contains 1 to 20% by mass of cobalt, the remainder is composed of nickel and inevitable impurities, and is composed of secondary particles in which primary particles are aggregated, and the average primary particle diameter is 1. 0 to 3.0 μm, the ratio of the standard deviation σ of the primary particle diameter to the average primary particle diameter d ₁ σ / d ₁ is 0.4 or less, the average secondary particle diameter is 5 to 60 μm, and the tap density is 1.0. -3.5 g / mL, and a specific surface area is 2.0 m < ² > / g or less.

"Average primary particle size, standard deviation of primary particle size"
The primary particle size is the particle size of each aggregated particle, and is measured by SEM observation. Specifically, nickel powder is fixed to a sample holder with a conductive double-sided tape, and observed with JSM-6360LA manufactured by JEOL Ltd. at an acceleration voltage of 20 kV and a magnification of 2500 times. Then, the image processing software (SmileView) attached to the apparatus is applied to the obtained SEM image, and the particle diameters of 200 or more primary particles are measured except for particles that overlap and the particle diameter cannot be determined. Thus, the average particle diameter d ₁ of the primary particles is obtained. In addition, the standard deviation of the primary particle diameter is also calculated from the obtained data.

  By setting the average primary particle diameter in the range of 1.0 to 3.0 μm, the nickel powder is appropriately aggregated to form secondary particles having a complicated shape such as a chain. By forming such secondary particles, in the resin molded body obtained by kneading with the resin, the nickel powders are entangled with each other to form a network, and the resin molded body exhibits extremely low electrical resistance and excellent weather resistance. Will show gender.

  On the other hand, the average primary particle diameter of the nickel powder according to Patent Document 4 (International Publication No. 2005/023461 pamphlet) is 0.2 to 2.0 μm. Even if the average primary particle diameter of the nickel powder is 0.2 μm or more and less than 1.0 μm, the weather resistance of the nickel powder is good if 1 to 20 mass% of cobalt is contained as a whole. However, when the average primary particle diameter of the nickel powder is 0.2 μm or more and less than 1.0 μm, the influence of oxidation on the surface of the nickel powder is more than the case where the average primary particle diameter of the nickel powder is 1.0 to 3.0 μm. The weather resistance of the molded product obtained by kneading with the resin becomes worse than when the average primary particle size is 1.0 to 3.0 μm. Therefore, it is preferable that the average primary particle diameter of nickel powder is 1.0 μm or more.

  On the other hand, when the average primary particle diameter of the nickel powder exceeds 3.0 μm, in the molded body obtained by kneading with the resin, the contacts between the nickel powders decrease and the resistance of the molded body increases. When the average primary particle size is further increased, the aggregation of the nickel powder itself is reduced, becoming close to a monodispersed state, the number of contacts between the nickel powders is further decreased, and the resistance of the molded body is further increased.

The ratio σ / d ₁ between the standard deviation σ of the primary particle diameter and the average primary particle diameter d ₁ indicates the degree of fluctuation of the primary particle diameter. By setting σ / d ₁ to 0.4 or less, particles having a small primary particle size are greatly reduced, and even if the number of particles having a primary particle size of about the average value or more is not changed, the average primary particle size is not changed. Becomes larger. Thereby, even if it is nickel powder which has a larger average primary particle diameter than before, aggregation is attained. Further, since the average primary particle size is increased, a larger amount of nickel powder can be kneaded with the resin than before, and weather resistance is improved. Furthermore, the reduction of fine primary particles that are easily oxidized also suppresses the oxidation of the nickel powder and greatly improves the weather resistance.

"Average secondary particle size"
When the nickel powder aggregates, secondary particles are formed. The particle size of the secondary particles is measured by laser particle size distribution measurement. Specifically, using MICROTRAC HRA MODEL 9320-X100 manufactured by Nikkiso Co., Ltd., nickel powder was put into a 0.2% by mass aqueous solution of sodium hexametaphosphate, and after ultrasonic stirring at 300 W for 10 minutes, FRA the average particle size (D50) measured by mode, to do this the average secondary particle diameter d _2.

  By setting the average secondary particle diameter in the range of 5 to 60 μm, the number of locations where the nickel powders come into contact with each other after kneading with the resin increases, and the electrical resistance of the resin molded product is significantly reduced. However, when the average secondary particle size is less than 5 μm, the number of entangled portions decreases because of less aggregation, and the resistance value after kneading with the resin increases. Moreover, when the average secondary particle diameter exceeds 60 μm, the dispersion of the nickel powder in the resin may be non-uniform, which is not preferable.

"Tap density"
The tap density of the nickel powder affects the degree of dispersion of the nickel powder in the resin. For the measurement of the tap density, a shaking specific gravity measuring device KRS-409 manufactured by Kuramochi Scientific Instruments Co., Ltd. is used. 15 g of nickel powder is weighed and placed in a 20 mL graduated cylinder, the tap speed is 120 times / minute, and the tap is carried out 500 times at a tap height of 20 mm. Thereafter, the volume of the nickel powder is read from the scale of the graduated cylinder, and the mass (g) of the nickel powder is divided by the read volume.

  By setting the tap density in the range of 1.0 to 3.5 g / mL, nickel powder is uniformly dispersed in the resin, and the electric resistance of the resin molded product is significantly reduced.

  On the other hand, the tap density of the nickel powder according to Patent Document 4 is 0.5 to 2.0 g / mL. Even if the tap density of the nickel powder is 0.5 g / mL or more and less than 1.0 g / mL, the weather resistance of the nickel powder is good as long as 1 to 20% by mass of cobalt is contained. However, in order to improve the weather resistance of the resin molded body, it is effective to increase the amount of nickel powder to be kneaded. When the tap density is 0.5 g / mL or more and less than 1.0 g / mL, it is difficult to increase the amount of nickel powder kneaded into the resin, so that the weather resistance is lower than that when the tap density is 1.0 g / mL. End up. Therefore, the tap density of the nickel powder is preferably 1.0 g / mL or more.

  On the other hand, when the tap density of the nickel powder exceeds 3.5 g / mL, the nickel powder is unevenly distributed in the resin, the mutual contact is reduced, and the electric resistance of the resin molded body is increased.

"Specific surface area"
The specific surface area greatly affects the weather resistance of the nickel powder. For the measurement of the specific surface area, a multisorb 16 manufactured by Yuasa Ionics is used. After degassing with nitrogen gas at a degassing temperature of 200 ° C. and a degassing time of 15 minutes, measurement is performed by the BET one-point method using nitrogen 30% -argon mixed gas adsorption.

When the specific surface area is 2.0 m ² / g or less, the surface micropores are reduced, the surface oxidation is suppressed, and the weather resistance is greatly improved. When the specific surface area is 1.2 m ² / g or less, the effect of improving weather resistance is further increased, which is preferable.

"Cobalt content"
The nickel powder according to the present invention contains 1 to 20 mass% of cobalt based on the total mass of the nickel powder, and the weather resistance of the nickel powder is remarkably improved by this cobalt. This is because cobalt is slightly less basic than nickel and in addition to preferential corrosion of cobalt, the corroded cobalt is conductive. However, if the cobalt content is less than 1% by mass of the entire nickel powder, there is no effect of improving weather resistance, and even if it exceeds 20% by mass, it is not preferred because it is expensive in cost.

"Cobalt content of primary particles present in the surface layer of secondary particles"
In order to ensure sufficient weather resistance while reducing the cobalt content as much as possible, it is preferable to contain a large amount of cobalt in the surface layer portion of the secondary particles of nickel powder. Here, the surface layer portion of the secondary particles of nickel powder refers to a portion deposited by the second stage reduction deposition process when the nickel powder is produced by a two stage reduction deposition process.

  The cobalt content in the surface layer part is preferably in the range of 1 to 40% by mass with respect to the total mass of the surface layer part. In order to obtain the required weather resistance, it is necessary for the surface layer portion to contain 1% by mass or more of cobalt. However, it is difficult to further improve the weather resistance even if it is added to the surface layer in excess of 40% by mass. Moreover, when it adds exceeding 40 mass% to this surface layer part, nickel powder will become ferromagnetism and it is not preferable when using it for an electronic component etc. As is apparent from the above description, the present invention does not exclude an aspect in which cobalt is also contained in the nickel powder. That is, in addition to the surface layer portion of the nickel powder, cobalt may be contained inside, and such a case may be preferable. For example, this is the case when nickel powder is used for the polymer PTC element described below.

“Average secondary particle diameter d ₂ / average primary particle diameter d ₁ ”
Furthermore, in the nickel powder according to the present invention, the average secondary particle diameter d ₂ / average primary particle diameter d ₁ is preferably in the range of 5-60. When the value of average secondary particle diameter d ₂ / average primary particle diameter d ₁ is in the range of 5 to 60, contact between the resin and the kneaded nickel powder is likely to occur, and the resulting resin molded body has a small electric resistance. Become. However, when this ratio is less than 5, it is difficult to cause contact between nickel powders. Moreover, since aggregation will become large when it exceeds 60, dispersion | distribution in resin becomes non-uniform and is not preferable.

"Production method of nickel powder"
Next, the nickel powder manufacturing method according to the present invention will be described. The nickel powder according to the present invention is produced by a two-stage reduction precipitation process and a drying / heating process.

First, in the first reduction precipitation step, an aqueous solution containing a divalent nickel salt is added to an aqueous solution containing a reducing agent (generally containing an excessive reducing agent) to add almost all of the nickel. Precipitate. Then, in the second reduction precipitation step, a reducing agent is added to the aqueous solution containing the nickel powder precipitated in the first reduction precipitation step as needed, and a divalent nickel salt aqueous solution is also added to add nickel. Precipitate further.

  In the production, a low hydrophilic surfactant is added at least in the first reduction precipitation step. For example, in the case of a modified silicone oil-based surfactant, one having an HLB value represented by the following formula 1 of 10 or less is added. By adding a low-hydrophilic surfactant, the nickel ion concentration during the reaction is suppressed to prevent excessive nucleation, and the generation of fine nickel primary particles is suppressed to grow into primary particles of an appropriate size. Can be made.

  When no surfactant is added, excessive nucleation occurs and fine primary nickel particles are generated. Further, since the primary particles do not grow to an appropriate size, the primary particle size varies greatly.

  Even if a surfactant is added, if the HLB value of the surfactant to be added exceeds 10, the dispersion of the primary particle diameter can be suppressed, but fine nickel primary particles are generated, and the average primary particle diameter becomes small. End up.

  The aqueous solution containing the reducing agent may be added with a polyvalent carboxylic acid such as tartaric acid, a commonly used complexing agent such as ethylenediamine, sodium hydroxide for pH adjustment, or the like. The reducing agent is not particularly limited as long as it can reduce and precipitate nickel, but a hydrazine-based reducing agent is suitable.

  In the production method, the nickel particles precipitated by the first reduction precipitation step become secondary particles in which primary particles are appropriately aggregated and constitute the inside of the nickel powder, but the aggregation force is weak, In the separation operation or kneading with the resin, it is easily separated and becomes a single particle. However, by continuing the second reduction precipitation step, the agglomeration is further strengthened by the deposited nickel, and an appropriate agglomeration can be maintained without separation even in subsequent operations. The nickel deposited in the second reduction deposition step aggregates outside the nickel secondary particles deposited in the first reduction deposition step to form a surface layer portion of the nickel powder, structurally connects the networks, and has high strength. It is thought to form nickel powder. The electric resistance of the molded body obtained by kneading the nickel powder and resin thus obtained is extremely low.

By passing through the above-described two-stage reduction precipitation process and adjusting the concentration of nickel salt and reducing agent, the temperature of the aqueous solution, and other conditions, the above-mentioned powder characteristics (secondary particles aggregated) It consists of the following particles, average primary particle diameter of 1.0 to 3.0 m, the ratio sigma / d ₁ of the standard deviation sigma of the primary particle diameter average primary particle diameter d ₁ is 0.4 or less, an average secondary particle diameter 5 to 60 μm, a tap density of 1.0 to 3.5 g / mL, and a specific surface area of 2.0 m ² / g or less) can be obtained.

  In order to contain cobalt in the nickel powder, the aqueous solution is added to the aqueous solution only in the second reduction precipitation step or in both the first reduction precipitation step and the second reduction precipitation step. What is necessary is just to precipitate nickel in the state which added the bivalent cobalt salt. In the case where cobalt is contained in the entire nickel powder including the inside, nickel may be precipitated in a state where a divalent cobalt salt is added to the aqueous solution in each of the first and second reduction precipitation steps. What is necessary is just to make content of cobalt ion in 1-20 mass% with respect to the total amount of nickel ion and cobalt ion in aqueous solution in any process. When more cobalt is contained in the surface layer portion than inside the nickel powder, more divalent cobalt salt is added to the aqueous solution in the second reduction precipitation step than in the first reduction precipitation step. What is necessary is just to adjust so that the cobalt content of the whole nickel powder may be 1-20 mass%.

  Further, when cobalt is not contained in the nickel powder and cobalt is contained only in the surface layer portion, the cobalt salt is not added to the aqueous solution in the first reduction precipitation step, and only in the second reduction precipitation step. A divalent cobalt salt may be added to the aqueous solution. In this case, the cobalt salt may be added so that the content of cobalt ions in the aqueous solution is 1 to 40% by mass with respect to the total amount of nickel ions and cobalt ions in the aqueous solution. The cobalt content in the surface layer of can be 1 to 40% by mass.

The nickel powder obtained by the two-step reduction process as described above is heated at 80 to 230 ° C. in an inert atmosphere or vacuum and dried, so that nickel atoms on the surface diffuse and micropores are further formed. It disappears and the specific surface area becomes smaller. When the drying temperature is less than 80 ° C., the disappearance of the micropores is not sufficient, and the specific surface area exceeds 2.0 m ² / g. On the other hand, when the temperature exceeds 230 ° C., nickel hydroxide passivating the surface is decomposed, oxidation proceeds after drying, and resistance during resin kneading increases. The drying temperature is more preferably 120 to 230 ° C. from the viewpoint of sufficiently eliminating the micropores.

  In addition, after the nickel powder obtained in the two-stage reduction process is dried at 80 to 150 ° C. in the air, the micropores are sufficiently extinguished by heating at 200 to 400 ° C. in a reducing atmosphere. Can do. When dried in the air, a large amount of hydroxide is generated on the surface and the specific surface area increases, and the resistance value after kneading the resin increases significantly. It can be decomposed except that a small amount of nickel hydroxide remains, and the specific surface area can be reduced. When heating in a reducing atmosphere is less than 200 ° C., the decomposition of nickel hydroxide is insufficient, the specific surface area is large, and the resistance value after resin kneading becomes high. When it exceeds 400 ° C., nickel hydroxide is not only decomposed too much but also nickel powders are sintered.

  Thus, the nickel powder manufacturing method according to the present invention does not use an expensive material such as a noble metal and does not require a complicated process. Therefore, the nickel powder according to the present invention can be obtained at low cost.

"Polymer PTC element"
As mentioned above, although the nickel powder which concerns on this invention, and its manufacturing method were demonstrated, this invention also provides the polymer PTC element which used the nickel powder of the above-mentioned or below-mentioned this invention as an electroconductive filler. Hereinafter, the polymer PTC element will be described, but the polymer PTC element itself is well known, and the description of the polymer PTC element itself is omitted.

  Specifically, the PTC element according to the present invention includes (A) (a1) a conductive filler, and (a2) a polymer PTC element comprising a polymer material, and (B) at least one surface of the polymer PTC element. The nickel powder according to the present invention is used as a conductive filler. In addition, the consideration about the physical property of nickel powder in the above-mentioned molded object, especially the consideration about the influence which it has on a weather resistance, electroconductivity, etc. are similarly applied to the nickel powder as the electroconductive filler in a polymer PTC element.

  The polymeric material used in the polymeric PTC device according to the present invention may be a known polymeric material used in conventional polymeric PTC devices that provides PTC properties. Such polymeric materials are thermoplastic crystalline polymers, which can include, for example, polyethylene, ethylene copolymers, fluorine-containing polymers, polyamides and polyesters, which may be used alone or in combination.

  More specifically, high-density polyethylene, low-density polyethylene, etc. can be used as polyethylene; ethylene copolymers include ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate copolymer, ethylene-vinyl acetate copolymer. Polymers, ethylene-polyoxymethylene copolymers, etc. can be used; as fluorine-containing polymers, polyvinylidene fluoride, difluoroethylene-4 fluoroethylene-6 fluoropropylene copolymers, etc. can be used; 6-nylon, 6,6-nylon, 12-nylon and the like can be used; and as the polyester, polybutylene terephthalate (PBT), polyethylene terephthalate (PET) and the like can be used.

  The metal electrode used in the polymer PTC element according to the present invention may be composed of any known metal material used in conventional polymer PTC elements. The metal electrode may be in the form of a plate or foil, for example. The metal electrode is not particularly limited as long as the target PTC element of the present invention can be obtained. Specifically, a roughened metal plate, a roughened metal foil, etc. can be illustrated. When using a roughened metal electrode, the roughened surface contacts the PTC element. For example, a commercially available electrodeposited copper foil or nickel-plated electrodeposited copper foil can be used.

  Such a “metal electrode” is disposed on at least one of the major surfaces of the PTC element, and preferably on two opposing major surfaces of the PTC element. The metal electrode may be arranged in the same manner as a conventional method for manufacturing a PTC element. For example, you may arrange | position by thermocompression-bonding a metal electrode to the plate-shaped or sheet-shaped PTC element obtained by extrusion molding. In another embodiment, a mixture of polymeric material and conductive filler may be extruded onto a metal electrode. Then, it is good also as a PTC element of a smaller form by cut | disconnecting as needed.

  In addition, the present invention provides a PTC device in which a metal lead is electrically connected to at least one metal electrode of the above-described PTC element of the present invention, and further, such a PTC device is used as a wiring or an electronic component. An electrically connected electrical device (eg, a mobile phone) is also provided.

The nickel powder of the present invention particularly preferred for use in the PTC element of the present invention is, for example, as follows:
(Cobalt content)
Based on the total mass of the nickel powder, cobalt is 2 to 20% by mass, preferably 3 to 18% by mass, more preferably 3 to 15% by mass, for example 4 to 10% by mass, especially 5 to 7% by mass ( For example, 6% by mass).

  Moreover, in the surface layer part of nickel powder, cobalt is 3-40 mass% on the basis of the total mass of this surface layer part, Preferably it is 8-30 mass%, More preferably, 8-20 mass%, For example, 9-15 mass %, Especially 10% by mass.

  Further, the nickel powder preferably used for the PTC element may contain cobalt in the inside which is in addition to the surface layer portion, and it is preferable, but it is not always necessary to contain cobalt in the inside. When cobalt is contained inside, the amount of cobalt inside is preferably 2 to 7% by mass (particularly 3 to 6% by mass) based on the total mass of the inside.

  A specific example of the nickel powder according to the present invention that is particularly preferable for use in the PTC element according to the present invention is any one of various combinations constituted by the above-described three types of cobalt content. The amount of cobalt as a whole is 5 to 7% by mass, the amount of cobalt in the surface layer is 9 to 12% by mass, and the amount of cobalt inside is 4 to 5% by mass.

(Tap density)
For example, 2.0 to 3.5 g / mL, preferably 2.3 to 3.0 g / mL.

(Primary particle size)
For example, 1.5 to 2.5 μm, preferably 1.7 to 2.2 μm.

(Standard deviation of primary particle size / Primary particle size)
For example, 0.3 or less, preferably 0.25 or less.

(Secondary particle size)
For example, 10 to 40 μm, preferably 15 to 30 μm.

(Secondary particle size / primary particle size)
For example, 5-20, preferably 8-16, more preferably 10-15.

(Specific surface area)
For example, 2 or less, preferably 1.7 or less.

  In the polymer PTC element of the polymer PTC element of the present invention, the ratio between the polymer material and the conductive filler may be any suitable ratio as long as the function as a predetermined PTC element is exhibited. For example, the conductive filler is 65 to 90% by mass, preferably 70 to 85% by mass on a mass basis.

  The PTC element according to the present invention including the nickel powder according to the present invention as described above is compared with the conventional PTC element even when used over a long period of time in an environment where it can be exposed to a high temperature and a dry state. In this case, the increase in resistance value is greatly suppressed.

  The present invention will be further described below with reference to examples and comparative examples. Examples and comparative examples relating to nickel powder are Examples 1 to 12 and Comparative Examples 1 to 6, and Examples and comparative examples relating to polymer PTC elements are Examples A to D and Comparative Examples A and B. .

"Examples and comparative examples relating to nickel powder (Examples 1 to 12 and Comparative Examples 1 to 6)"
Example 1
To 138 L of pure water, 37.8 L of 25% aqueous sodium hydroxide solution and 1209 g of tartaric acid were added, and the mixture was heated to 70 ° C. with stirring. To this aqueous solution was added 60% hydrogenated hydrazine 28.8L and a modified silicone oil surfactant having an HLB value of 9, and further mixed with a cobalt chloride aqueous solution and a nickel chloride aqueous solution (Co content was 5% relative to the Ni + Co amount). 3.7 kg of Ni + Co equivalent mass) was added, and nickel powder was precipitated by the first reduction precipitation step. Next, 4.8 L of 60% hydrated hydrazine and an aqueous solution in which a cobalt chloride aqueous solution and a nickel chloride aqueous solution are mixed with the aqueous solution after the completion of the nickel powder precipitation by the first reduction precipitation step (the Co content is reduced to the Ni + Co amount). 3.7 kg of Ni + Co equivalent mass (total mass of Ni and Co in which the salt contained in the aqueous solution is converted to metal) is added to the second reduction precipitation step. Further, nickel powder was precipitated. Then, after filtering and washing with water, it was made to dry at 80 degreeC in the vacuum, and nickel powder was obtained.

  The resulting nickel powder had a Co content of 6.6% by mass. The powder characteristics are shown in Table 1 below. However, although the Co content in the entire nickel powder is an analytical value, the Co content in the surface layer portion is calculated from the Ni-converted and Co-converted values of the salt in the aqueous solution in the second reduction precipitation step. Specifically, it was calculated as a ratio of the Co-converted value to the total value of the Ni-converted value and the Co-converted value.

D _{1 in} Table 1 means an average primary particle diameter, and was measured by SEM observation. Specifically, nickel powder was fixed to a sample holder with a conductive double-sided tape, and observed with JSM-6360LA manufactured by JEOL Ltd. at an acceleration voltage of 20 kV and a magnification of 2500 times. Then, the image processing software (SmileView) attached to the apparatus is applied to the obtained SEM image, and the particle diameters of 200 or more primary particles are measured except for particles that overlap and the particle diameter cannot be determined. Thus, the average particle diameter d ₁ of the primary particles was obtained. Further, the standard deviation of the primary particle size was also calculated from the obtained data.

Table d ₂ in 1 means average secondary particle diameter, the particle size of secondary particles measured by a laser particle size distribution measurement. Specifically, using MICROTRAC HRA MODEL 9320-X100 manufactured by Nikkiso Co., Ltd., nickel powder was put into a 0.2% by mass aqueous solution of sodium hexametaphosphate, and after ultrasonic stirring at 300 W for 10 minutes, FRA the average particle size (D50) is measured in the mode, which was used as a mean secondary particle diameter d _2.

In Table 1, σ represents the standard deviation of the average primary particle diameter d ₁ , and σ / d ₁ represents the ratio between the standard deviation σ of the primary particle diameter and the average primary particle diameter d ₁ .

  For the measurement of the tap density in Table 1, a shaking specific gravity measuring device KRS-409 manufactured by Kuramochi Scientific Instruments Ltd. was used. 15 g of nickel powder was weighed and placed in a 20 mL graduated cylinder, the tap speed was 120 times / minute, and 500 taps were performed at a tap height of 20 mm. Thereafter, the volume of the nickel powder was read from the scale of the graduated cylinder, and the mass (g) of the nickel powder was divided by the read volume.

  For the measurement of the specific surface area in Table 1, a multisorb 16 manufactured by Yuasa Ionics was used. After degassing with nitrogen gas at a degassing temperature of 200 ° C. and a degassing time of 15 minutes, measurement was performed by a BET one-point method using nitrogen 30% -argon mixed gas adsorption.

  Next, the nickel powder and the polyethylene resin are mixed so that the nickel powder content is 35% by volume and 43% by volume with respect to the nickel powder + polyethylene resin, and kneaded at a temperature equal to or higher than the melting point of the polyethylene resin. The sheet was formed into a sheet shape.

  The molded sheet-like sample was cut out to 25W × 60L, and the surface resistivity was measured according to JIS K 7194. The initial surface resistivity of the 35% by volume kneaded product was 0.209Ω / □, and 43% by volume kneaded. The product was 0.036Ω / □. For this measurement, a low resistivity meter (Loresta-GP, manufactured by Dia Instruments Co., Ltd.) was used.

  Furthermore, in order to evaluate the weather resistance, after performing a moisture resistance test in which the sheet-like sample was held in a constant temperature and humidity chamber set at 85 ° C. to 85% RH for 168 hours, the surface resistivity was measured in the same manner as described above. . The 35% by volume kneaded product showed 0.217Ω / □, and the 43% by volume kneaded product showed 0.033Ω / □. These results are shown in Table 2.

(Example 2)
Similarly to Example 1, two-step reduction precipitation of nickel was performed by a two-step reduction precipitation step. To 138 L of pure water, 25.2 L of 25% aqueous sodium hydroxide solution and 806 g of tartaric acid were added and heated to 70 ° C. with stirring. To this aqueous solution, 19.2 L of 60% hydrazine hydrate and a modified silicone oil surfactant having an HLB value of 9 were added. To this aqueous solution, no cobalt chloride aqueous solution was added, and only 2.5 kg of nickel chloride aqueous solution was added in terms of Ni to perform the first reduction precipitation step. Next, an aqueous solution obtained by mixing an aqueous solution of cobalt chloride and an aqueous solution of nickel chloride with the aqueous solution after completion of the precipitation of nickel powder in the first reduction precipitation step (mixed so that the Co content is 10% by mass with respect to the Ni + Co amount). The aqueous solution was added in an amount of 2.5 kg in terms of Ni + Co, and nickel powder was further precipitated by the second reduction precipitation step. Then, after filtering and washing with water, it was made to dry at 80 degreeC in the vacuum, and nickel powder was obtained.

  The obtained nickel powder contained Co only in the surface layer portion, and the overall Co content was 5.0% 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 surface resistivity of the 35% by volume kneaded product was 0.711Ω / □, and that of the 43% by volume kneaded product was 0.194Ω / □. there were. Furthermore, when the surface resistivity after the moisture resistance test was measured, it was 0.706Ω / □ for the 35% by volume kneaded product and 0.160Ω / □ for the 43% by volume kneaded product. These results are shown in Table 2.

(Example 3)
To 2280 mL of pure water, 94.8 g of sodium hydroxide and 12.6 g of tartaric acid were added and heated to 65 ° C. with stirring. To this aqueous solution, 180 mL of hydrazine and a modified silicone oil surfactant having an HLB value of 9 were added, and an aqueous solution in which a cobalt chloride aqueous solution and a nickel chloride aqueous solution were mixed (mixed so that the Co content was 1% by mass with respect to the Ni + Co amount). 39 g of Ni + Co equivalent mass was added, and nickel powder was precipitated by the first reduction precipitation step. Next, an aqueous solution obtained by mixing 45 mL of hydrazine and an aqueous cobalt chloride solution and an aqueous nickel chloride solution (mixed so that the Co content is 1.5% by mass with respect to the Ni + Co content) is added to the aqueous solution after the completion of the first reduction precipitation step. 39 g of Ni + Co equivalent mass was added, and nickel powder was further precipitated by the second reduction precipitation step. Then, after filtering and washing with water, it was made to dry at 80 degreeC in the vacuum, and nickel powder was obtained.

  The total nickel content of the obtained nickel powder was 1.2% 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 surface resistivity of the 35% by volume kneaded product was 0.725Ω / □, and that of the 43% by volume kneaded product was 0.203Ω / □. there were. Furthermore, when the surface resistivity after the moisture resistance test was measured, it was 0.720Ω / □ for the 35% by volume kneaded product and 0.173Ω / □ for the 43% by volume kneaded product. These results are shown in Table 2.

Example 4
In the same manner as in Example 3, two-stage reduction precipitation of nickel was performed by a two-stage reduction precipitation process. In Example 3, the heating is up to 65 ° C., but in Example 4, the heating is up to 60 ° C., and both the cobalt chloride aqueous solution and the nickel chloride aqueous solution are used in both the first reduction precipitation step and the second reduction precipitation step. (In Example 3, in the first reduction precipitation step, the Co content is 1% by mass with respect to the Ni + Co content, and the second aqueous solution in which the Co content is 20% by mass with respect to the Ni + Co content. In the reductive precipitation step, Co content was 1.5% by mass with respect to the Ni + Co amount.)) 39) was added in terms of Ni + Co equivalent mass to precipitate nickel powder. Then, after filtering and washing with water, it dried at 80 degreeC in the vacuum, and obtained nickel powder.

  The overall nickel content of the obtained nickel powder was 19.4% by mass. The powder characteristics are shown in Table 1. Further, when this nickel powder was evaluated in the same manner as in Example 1, the initial surface resistivity of the 35% by volume kneaded product was 0.097Ω / □, and that of the 43% by volume kneaded product was 0.033Ω / □. there were. Furthermore, when the surface resistivity after the moisture resistance test was measured, it was 0.115Ω / □ for the 35% by volume kneaded product and 0.035Ω / □ for the 43% by volume kneaded product. These results are shown in Table 2.

(Example 5)
In the same manner as in Example 3, two-stage reduction precipitation of nickel was performed by a two-stage reduction precipitation process. The aqueous solution to be added in the first reduction precipitation step was not added with the cobalt chloride aqueous solution, but only 39 g of the nickel chloride aqueous solution was added in terms of Ni to perform the first reduction precipitation step. In the second reduction precipitation step, an aqueous solution in which a cobalt chloride aqueous solution and a nickel chloride aqueous solution are mixed (an aqueous solution in which the Co content is 40% by mass with respect to the Ni + Co amount (in Example 3, the Co content is Ni + Co 1.5 mass% with respect to the quantity.)) 39g was added by Ni + Co conversion mass, and nickel powder was deposited. Then, after filtering and washing with water, it dried at 80 degreeC in the vacuum, and obtained nickel powder.

  The obtained nickel powder contained Co only in the surface layer portion, and the Co content as a whole of the obtained nickel powder was 18.7% 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 surface resistivity of the 35% by volume kneaded product was 0.539Ω / □, and that of the 43% by volume kneaded product was 0.178Ω / □. there were. Furthermore, when the surface resistivity after the moisture resistance test was measured, it was 0.609Ω / □ for the 35% by volume kneaded product and 0.176Ω / □ for the 43% by volume kneaded product. These results are shown in Table 2.

(Example 6)
In the same manner as in Example 1, two-step reduction precipitation of nickel was performed by a two-step reduction precipitation step to deposit nickel powder. Then, after filtering and washing with water, it was made to dry at 150 degreeC in vacuum, and nickel powder was obtained. Example 6 is different from Example 1 only in that the drying temperature in vacuum is 150 ° C. (Example 1 is 80 ° C.).

The total nickel content of the obtained nickel powder was 6.5% by mass, and the specific surface area was 0.94 m ² / g. The powder characteristics are shown in Table 1.

  Next, when the surface resistivity was measured in the same manner as in Example 1, the initial surface resistivity was 0.147Ω / □, and the surface resistivity after the moisture resistance test was 0.112Ω / □. These results are shown in Table 2.

(Example 7)
Similarly to Example 1, two-step reduction precipitation of nickel was performed by a two-step reduction precipitation step. In the first reduction precipitation step, an aqueous solution in which an aqueous cobalt chloride solution and an aqueous nickel chloride solution are mixed (an aqueous solution in which the Co content is 4% by mass with respect to the Ni + Co content (in Example 1, the Co content is Ni + Co content). 5% by mass with respect to Ni. Co.) in terms of Ni + Co was added to precipitate nickel powder. Next, in the second reduction precipitation step, 35 minutes after the start of the addition of 60% hydrazine in the first reduction precipitation step, a further 60% hydrazine, cobalt chloride aqueous solution and nickel chloride aqueous solution are added. An aqueous solution in which (Co content was mixed so that the Co content was 10% by mass with respect to the Ni + Co amount) was added to precipitate nickel powder. Then, after filtering and washing with water, it was made to dry at 200 degreeC in vacuum, and nickel powder was obtained.

The total nickel content of the obtained nickel powder was 6.2% by mass, and the specific surface area was 0.65 m ² / g. The powder characteristics are shown in Table 1 below. Further, when this nickel powder was evaluated in the same manner as in Example 1, the initial surface resistivity was 0.151 Ω / □, and the surface resistivity after the moisture resistance test was 0.122 Ω / □. These results are shown in Table 2.

(Example 8)
Similarly to Example 1, two-step reduction precipitation of nickel was performed by a two-step reduction precipitation step. To 138 L of pure water, 25.2 L of 25% aqueous sodium hydroxide and 806 g of tartaric acid were added and heated to 75 ° C. with stirring. To this aqueous solution, 19.2 L of 60% hydrazine hydrate was added, and in the first reduction precipitation process, no cobalt chloride aqueous solution was added, and only 2.5 kg of nickel chloride aqueous solution in terms of Ni was added to obtain nickel powder. Precipitated. Next, in the second reduction precipitation step, 50 minutes after the start of the addition of 60% hydrazine in the first reduction precipitation step, 60% hydrazine, cobalt chloride aqueous solution and nickel chloride aqueous solution are further added. An aqueous solution (mixed so that the Co content was 10% by mass with respect to the Ni + Co content) was added in an amount of 2.5 kg in terms of Ni + Co to precipitate nickel powder. Then, after filtering and washing with water, it was made to dry at 220 degreeC in vacuum, and nickel powder was obtained.

The obtained nickel powder contained Co only in the surface layer portion, the Co content as a whole was 4.6% by mass, and the specific surface area was 0.97 m ² / g. 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 surface resistivity was 0.209 Ω / □, and the surface resistivity after the moisture resistance test was 0.190 Ω / □. These results are shown in Table 2.

Example 9
Similarly to Example 1, two-step reduction precipitation of nickel was performed by a two-step reduction precipitation step. In the first reduction precipitation step, 25.2 L of 25% aqueous sodium hydroxide and 806 g of tartaric acid were added to 138 L of pure water and heated to 70 ° C. with stirring. To this aqueous solution, 19.2 L of 60% hydrazine hydrate was added, and in the first reduction precipitation step, an aqueous solution in which a cobalt chloride aqueous solution and a nickel chloride aqueous solution were mixed (the Co content was 1.5% by mass with respect to the Ni + Co amount). 2.5 kg of Ni + Co equivalent mass was added to precipitate nickel powder. Next, in the second reduction precipitation step, 40 minutes after the start of the addition of 60% hydrazine in the first reduction precipitation step, 60% hydrazine, cobalt chloride aqueous solution and nickel chloride aqueous solution are further added. An aqueous solution (mixed so that the Co content is 1.5% by mass with respect to the Ni + Co content) was added in an amount of 2.5 kg in terms of Ni + Co, thereby precipitating nickel powder. Then, after filtering and washing with water, it was made to dry at 120 degreeC in vacuum, and nickel powder was obtained.

The total nickel content of the obtained nickel powder was 1.3% by mass, and the specific surface area was 0.85 m ² / g. 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 surface resistivity was 0.361Ω / □, and the surface resistivity after the moisture resistance test was 0.318Ω / □. These results are shown in Table 2.

(Example 10)
Sodium hydroxide 94.8g and tartaric acid 12.6g were added to pure water 2280mL, and it heated to 55 degreeC, stirring. To this aqueous solution, 180 mL of hydrazine and a modified silicone oil surfactant having an HLB value of 9 were added, and an aqueous solution in which an aqueous cobalt chloride solution and an aqueous nickel chloride solution were mixed (mixed so that the Co content was 20% by mass with respect to the Ni + Co content). In addition, 39 g of nickel chloride aqueous solution in terms of Ni + Co equivalent mass was added, and nickel powder was precipitated by the first reduction precipitation step. Next, in the second reduction precipitation step, 30 minutes after the start of the addition of hydrazine in the first reduction precipitation step, 45 mL of hydrazine, a cobalt chloride aqueous solution and a nickel chloride aqueous solution are further mixed (Co-containing solution). 39 g of an aqueous solution mixed so that the amount becomes 20% by mass with respect to the Ni + Co amount) was added in terms of Ni + Co equivalent mass, and nickel powder was further precipitated. Then, after filtering and washing with water, it was made to dry at 200 degreeC in vacuum, and nickel powder was obtained.

The total nickel content of the obtained nickel powder was 18.8% by mass, and the specific surface area was 1.09 m ² / g. The powder characteristics are shown in Table 1 below. The nickel powder was evaluated in the same manner as in Example 1. As a result, the initial surface resistivity was 0.085Ω / □, and the surface resistivity after the moisture resistance test was 0.081Ω / □. These results are shown in Table 2.

(Example 11)
In the same manner as in Example 10, two-stage reduction and precipitation of nickel was performed by a two-stage reduction and precipitation process, but the heating was performed up to 70 ° C. In the first reduction precipitation process, no cobalt chloride aqueous solution was added, and 39 g of nickel chloride aqueous solution alone was added in terms of Ni to precipitate nickel powder. Next, in the second reduction precipitation step, 45 minutes after the start of the addition of hydrazine in the first reduction precipitation step, 45 mL of hydrazine, a cobalt chloride aqueous solution and a nickel chloride aqueous solution are further mixed (Co-containing solution). 39 g of an aqueous solution mixed in an amount of 40% by mass with respect to the amount of Ni + Co) was added in terms of Ni + Co equivalent to further precipitate nickel powder. Then, after filtering and washing with water, it dried at 220 degreeC in the vacuum, and obtained nickel powder.

The obtained nickel powder contained Co only in the surface layer portion, the Co content as a whole was 19.1% by mass, and the specific surface area was 1.15 m ² / g. 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 surface resistivity was 0.406 Ω / □, and the surface resistivity after the moisture resistance test was 0.369 Ω / □. These results are shown in Table 2 below.

(Example 12)
Similarly to Example 7, two-step reduction precipitation of nickel was performed by a two-step reduction precipitation step. Then, after filtering and washing with water, it dried at 110 degreeC in air | atmosphere, and also heated at the temperature of 350 degreeC in nitrogen -10% hydrogen for 2 hours. The total nickel content of the obtained nickel powder was 5.9% by mass, and the specific surface area was as small as 0.35 m ² / g. 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 surface resistivity was 0.205 Ω / □, and the surface resistivity after the moisture resistance test was 0.196 Ω / □. These results are shown in Table 2.

(Comparative Example 1)
As in Example 2, two-stage reduction and precipitation of nickel was performed by a two-stage reduction and precipitation process. In the first reduction and precipitation process, a modified silicone oil surfactant having an HLB value of 11 was added. Nickel powder was obtained.

The obtained nickel powder contained Co only in the surface layer portion, and the Co content was 4.8% by mass. The powder characteristics are shown in Table 1 below. Since a modified silicone oil-based surfactant having an HLB value of 11 was used, the average primary particle diameter d ₁ was reduced. The nickel powder was evaluated in the same manner as in Example 1. As a result, the initial surface resistivity of the 35% by volume kneaded product was 0.043Ω / □, but when the nickel powder was kneaded by 43% by volume. Kneading was impossible because the resin was absorbed between the nickel powders. Furthermore, when the surface resistivity after the moisture resistance test was measured, the 35% by volume kneaded product showed 0.059Ω / □. These results are shown in Table 2.

(Comparative Example 2)
Except that the nickel powder was obtained by pulverizing after vacuum drying, the nickel powder was obtained by performing the two-stage reduction precipitation of nickel by the two-stage reduction precipitation process in the same manner as in Example 2. Since the pulverization process was performed, the tap density increased to 3.61 g / mL.

  The obtained nickel powder contained Co only in the surface layer portion, and the Co content was 4.6% 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 surface resistivity of the 35% by volume kneaded product was 356Ω / □, and that of the 43% by volume kneaded product was 129Ω / □. Due to the high initial surface resistivity, these samples were not subjected to a moisture resistance test. These results are shown in Table 2.

(Comparative Example 3)
To 3800 mL of pure water, 164 g of sodium hydroxide and 21 g of ethylenediamine were added and heated to 85 ° C. with stirring. To this aqueous solution, 300 mL of hydrazine and 130 g of nickel chloride aqueous solution in terms of Ni were added (no cobalt chloride aqueous solution was added), and nickel powder was precipitated by a single-step reduction precipitation process. Then, after filtering and washing with water, it dried at 80 degreeC in the vacuum, and obtained nickel powder.

  The obtained nickel powder does not contain Co. The powder characteristics are shown in Table 1. Further, when this nickel powder was kneaded with a polyethylene resin in the same manner as in Example 1, even when the nickel powder was kneaded at 35% by volume, the resin was absorbed between the nickel powders, which was impossible.

(Comparative Example 4)
Table 1 shows the powder characteristics of typical filler-like nickel powder (manufactured by INCO) commercially available as conductive particles for conductive paste and conductive resin. This nickel powder does not contain Co.

  When this nickel powder was evaluated in the same manner as in Example 1, the initial surface resistivity of the 35% by volume kneaded product was 0.124Ω / □, and that of the 43% by volume kneaded product was 0.043Ω / □. . Furthermore, when the surface resistivity after the moisture resistance test was measured, it was 0.406Ω / □ for the 35% by volume kneaded product and 0.068Ω / □ for the 43% by volume kneaded product. These results are shown in Table 2.

(Comparative Example 5)
In the same manner as in Example 2, two-stage reduction and precipitation of nickel was performed by a two-stage reduction and precipitation process, but the heating was performed up to 70 ° C. In the first reduction deposition step, a modified silicone oil surfactant having an HLB value of 11 was added to obtain nickel powder. Next, in the second reduction precipitation step, 60 minutes of hydrazine, cobalt chloride aqueous solution and nickel chloride aqueous solution are further added after 25 minutes from the start of the addition of 60% hydrazine in the first reduction precipitation step. An aqueous solution (mixed so that the Co content was 10% by mass with respect to the Ni + Co content) was added in an amount of 2.5 kg in terms of Ni + Co to precipitate nickel powder. Then, after filtering and washing with water, it was made to dry at 80 degreeC in the vacuum, and nickel powder was obtained.

The obtained nickel powder contained Co only in the surface layer portion, the Co content was 5.0% by mass, and the specific surface area was 2.26 m ² / g. 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 surface resistivity was 0.039Ω / □, and the surface resistivity after the moisture resistance test was 0.051Ω / □. These results are shown in Table 2.

(Comparative Example 6)
In the same manner as in Example 2, two-stage reduction precipitation of nickel was performed by a two-stage reduction precipitation process. To 160 L of pure water, 32.9 L of 25% aqueous sodium hydroxide and 1617 g of tartaric acid were added, and the mixture was heated to 60 ° C. with stirring. To this aqueous solution, 38.5 L of 60% hydrazine hydrate was added, and in the first reduction precipitation process, no cobalt chloride aqueous solution was added, and only 4.8 kg of nickel chloride aqueous solution was added in terms of Ni to obtain nickel powder. Precipitated. Next, in the second reduction precipitation step, 30 minutes after the start of the addition of 60% hydrazine in the first reduction precipitation step, an aqueous solution in which a cobalt chloride aqueous solution and a nickel chloride aqueous solution are further mixed (Co 4.8 kg of Ni + Co equivalent mass was added so that the content was 10% by mass with respect to the Ni + Co content, and nickel was further precipitated. Then, after filtering and washing with water, it was dried at 100 ° C. in the atmosphere, and further heat-treated at 350 ° C. in nitrogen-10% hydrogen for 2 hours to obtain nickel powder.

The obtained nickel powder contained Co only in the surface layer portion, the Co content was 5.0% by mass, and the specific surface area was 1.13 m ² / g. 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 surface resistivity was 0.046Ω / □, and the surface resistivity after the moisture resistance test was 0.066Ω / □. These results are shown in Table 2.

  In Examples 1 to 5 within the scope of the present invention, kneading with a polyethylene resin is possible regardless of whether the Ni powder kneading ratio is 35% by volume or 43% by volume. The powder kneading ratio was 35% by volume and kneading with polyethylene resin was possible. Moreover, in Examples 1-12 within the scope of the present invention, the surface resistivity of the sheet-like sample molded after resin kneading was as small as 0.8Ω / □ or less before and after the moisture resistance test. Furthermore, the rate of increase of the surface resistivity before and after the moisture resistance test (surface resistivity after the moisture resistance test / surface resistivity before the moisture resistance test) is 1.19 at the maximum, and Example 1 within the scope of the present invention. -12 is also excellent in weather resistance, and can be used stably over a long period of time.

On the other hand, in Comparative Example 1, since the modified silicone oil-based surfactant having an HLB value of 11 was added, the average primary particle diameter was 0.9 μm, which is lower than the lower limit of 1.0 μm of the present invention. When the Ni powder kneading ratio was 43% by volume, kneading with polyethylene resin was impossible. When the Ni powder kneading ratio was 35% by volume, kneading with polyethylene resin could be carried out, but the Ni powder specific surface area was 2.03 m ² / g, which is the upper limit of 2.0 m of the present invention. ² / g, the rate of increase in surface resistivity before and after the moisture resistance test (surface resistivity after the moisture resistance test / surface resistivity before the moisture resistance test) is 1.36 (the mixing ratio of Ni powder is 35% by volume) and the weather resistance is poor.

  Since Comparative Example 2 has a tap density of 3.61 g / mL, which exceeds the upper limit of 3.5 g / mL of the present invention, it is considered that nickel powder is unevenly distributed in the resin and mutual contact is reduced. When the Ni powder kneading ratio is 35% by volume, the initial value of the surface resistivity is 356Ω / □, and when the Ni powder kneading ratio is 43% by volume, the initial value of the surface resistivity is 129Ω / □, In any case, the surface resistivity of the sheet-like sample molded after the resin kneading became extremely large.

  Since Comparative Example 3 has a tap density of 0.61 g / mL, which is lower than the lower limit of 1.0 g / mL of the present invention, it is difficult to increase the amount of nickel powder kneaded into the resin, and the Ni powder kneading ratio However, kneading with a polyethylene resin was impossible even when the content was 35% by volume.

  Since Comparative Example 4 is Ni powder containing no Co, the rate of increase in surface resistivity before and after the moisture resistance test (surface resistivity after the moisture resistance test / surface resistivity before the moisture resistance test) is 3.28 ( Ni powder kneading ratio is 35% by volume) and 1.59 (Ni powder kneading ratio is 43% by volume), and the weather resistance is inferior.

  In Comparative Example 5, the average primary particle diameter is lower than that of the present invention, the standard deviation of the primary particle diameter is large, and the specific surface area is large. Therefore, the increase rate of the surface resistivity is as large as 1.31, and the weather resistance is poor. .

  In Comparative Example 6, the specific surface area is in the range of the present invention, but the average primary particle diameter is lower than that of the present invention, and the standard deviation of the primary particle diameter is large. Inferior.

  Moreover, the photograph by the scanning electron microscope (SEM) of the nickel powder obtained in Example 1 is shown to FIG. 1 (a), (b), FIG. 2 (a), (b) is obtained by the comparative example 2. FIG. The photograph by the scanning electron microscope (SEM) of the nickel powder was shown.

  As can be seen from FIGS. 1 (a) and 1 (b), the nickel powder obtained in Example 1 has a primary particle diameter of about 1.8 μm. On the other hand, as can be seen from FIGS. 2 (a) and 2 (b), the nickel powder obtained in Comparative Example 2 contains particles having irregular primary particle sizes, which deteriorates the weather resistance. There are many fine primary particles that are considered to be the cause.

“Examples and Comparative Examples of Polymer PTC Devices (Examples A to D and Comparative Examples A and B)”
Next, the Example which manufactured the PTC element which concerns on this invention using the nickel powder which concerns on this invention is described. A comparative example for comparison will also be described.

(1) Conductive filler Nickel-cobalt alloy filler (that is, nickel powder of the present invention or nickel powder for comparison) is used as the conductive filler, high-density polyethylene is used as the polymer material, and rough metal is used as the metal electrode. A PTC element was manufactured using surface nickel foil (made by Fukuda Metal Foil Industry Co., Ltd., thickness: about 25 μm).

  The nickel powder used was manufactured in Example 1, Example 6, Example 7 and Example 12, and a PTC element was manufactured using these. These PTC elements are called PTC elements of Example A, Example B, Example C, and Example D, respectively. For comparison, the nickel powders of Comparative Examples 6 and 5 were used as conductive fillers. These PTC elements are called PTC elements of Comparative Example A and Comparative Example B, respectively.

  The Co content inside the used nickel powder is as shown in Table 3 below.

  The Co content was calculated on the assumption that substantially all of the nickel salt and cobalt salt of the aqueous solution used for the production were precipitated.

(2) Polymer material As the polymer material, commercially available high-density polyethylene (Equistar, PETROTHENE LB832, density: 0.957-0.964 g / ml, melt index: 0.23-0.30 g / 10 min, melting point 135 ± 3 ° C.) was used.

(3) Metal electrode As a metal electrode, nickel metal foil (the Fukuda metal foil powder industry make, electrolytic nickel foil, thickness: about 25 micrometers) was used.

(4) Manufacture of a PTC element (4-1) Manufacture of a PTC composition 2% by mass of a coupling agent (KENRICH PETROCHEMICALS, NZ-33) is added to a polymer material in powder form with respect to the mass of polyethylene. A polymer blend was obtained by mixing for 30 seconds in a kitchen blender (Sun Corporation, MILL MIXER MODEL FM-50). To this, nickel powder and Mg (OH) 2 (manufactured by Albemarle, H10) were added in the amounts shown in Table 4 below, and mixed with a kitchen blender for 30 seconds to obtain a conductive polymer composition.

  45 mL of the obtained conductive polymer composition was put into a mill (manufactured by Toyo Seiki Seisakusho, Lab Plast Mill Model 50C150, Blade R60B), and kneaded at a preset temperature of 160 ° C. and a blade rotation speed of 60 RPM for 15 minutes to obtain a PTC composition. Obtained.

(4-2) Preparation of PTC Element Master Plate The PTC composition obtained in (4-1) was prepared by using an iron plate / Teflon (registered trademark) sheet / thickness adjusting spacer (made of SUS having a thickness of 0.5 mm) + PTC composition. / Teflon (registered trademark) sheet / steel plate in a sandwich structure, and these are stacked. Using a hot-pressure press (manufactured by Toho Press, hydraulic molding machine: model T-1), the temperature is 180 to 200 ° C., the pressure is 0.5 MPa. Was pre-pressed for 3 minutes, and then this press was performed for 4 minutes at a pressure of 5 MPa. Then, using a cooling press machine (manufactured by Toho Press Mfg. Co., Ltd., hydraulic molding machine: model T-1) in which water at a set temperature of 22 ° C. was circulated with a chiller, the sheet was pressed at 0.5 MPa for 4 minutes. The polymer PTC element (PTC element original plate) was prepared.

(4-3) Production of polymer PTC element plaque original plate Next, using the PTC element original plate and metal electrode prepared in (4-2), iron plate / Teflon (registered trademark) sheet / silicon rubber / Teflon (registered trademark) ) Sheet / metal electrode / thickness adjusting spacer (made of SUS having a thickness of 0.5 mm) + PTC element original plate / metal electrode / Teflon (registered trademark) sheet / silicon rubber / Teflon (registered trademark) sheet / iron plate The main press was performed for 4 minutes at a temperature of 220 to 230 ° C. and a press pressure of 9 MPa with the above-mentioned hot-pressing machine. Then, using the above cooling press machine in which water at a set temperature of 22 ° C. was circulated with a chiller, a cooling press was performed at 9 MPa for 4 minutes, and metal electrodes were placed on the main surfaces on both sides of the polymer PTC element (PTC element original plate). A polymer PTC element plaque original plate (an assembly of PCT elements before cutting) subjected to thermocompression bonding was produced.

(4-4) Manufacture of PTC Element The polymer PTC element plaque original plate prepared in (4-3) is irradiated with an electron beam of 1000 kGy, and then punched into a 3 × 4 mm by a manual punch device to form a polymer PTC. A test piece of the device was obtained.

(4-5) Manufacture of PTC device Pure Ni lead pieces having a thickness of 0.125 mm, a hardness of 1/4 H, and a 4 mm x 5.2 mm are formed on both sides of the 3 x 4 mm test piece punched in (4-4). By soldering, an overall strap-shaped PTC device was obtained as a test sample. For soldering, paste solder (M705-728C, manufactured by Senju Metal Industry Co., Ltd.) is used in an amount of about 2.0 mg per side, and a reflow furnace (manufactured by Nippon Avionics Co., Ltd., model TCW-118N, auxiliary heater) is used in a nitrogen atmosphere. A temperature control of 360 ° C., preheat temperature control of 250 ° C., reflow temperature control (1) 240 ° C., reflow temperature control (2) 370 ° C., belt speed of 370 mm / min) were used.

(5) Measurement of initial resistance value About the obtained test sample, the resistance value (resistance value between two leads) was measured two days after production. This resistance value can be called the initial resistance value of the PTC element because the resistance value of the lead is much smaller than the resistance value of the PTC element. Note that a milliohm meter (4263A manufactured by HEWLETT PACKARD) was used to measure the initial resistance value and the resistance value of the PTC element under various conditions as described later. Table 5 shows the measurement results (unit: Ω) of the initial resistance value.

  From this result, it can be seen that although the resistance value of the test sample of the example is slightly lower, all the test samples including the sample of the comparative example have a low resistance value as usual.

(6) Confirmation of PTC characteristics Next, an R (resistance) -T (temperature) test was performed by measuring resistance-temperature characteristics for each of five test samples of Examples and Comparative Examples. The test temperature range was 20 ° C. to 150 ° C., and the ambient humidity of the test sample was 60% or less. After the ambient temperature of the test sample was raised by 5 ° C. and held in that temperature atmosphere for 10 minutes, the PTC element resistance value was measured. FIG. 3 shows the ratio of the resistance value measured at each temperature to the resistance value at the initial temperature (21 ° C.) (that is, the ratio of resistance change).

From the results of FIG. 3, the resistance of the PTC element, also called the trip temperature (trip temperature) when the temperature of the PTC element rises from room temperature, is about 120 ° C. to 130 ° C. For any element, the resistance value after such a range is at least about 10 ¹⁵ times greater than the previous resistance value, so any test sample It is clear that it has a switching function as a PTC element. In general, when the resistance value is increased by at least about 10 ³ times or more, it may be considered to have a function as a PTC element.

(7) Measurement of time-dependent change in resistance value under high temperature / dry conditions The test samples of the examples and comparative examples were controlled at a high temperature / dry condition of 85 ° C. ± 3 ° C. and a relative humidity of 10% or less. In a constant temperature oven DK600 manufactured by Yamato), and after the storage time of 24 hours, 165 hours, 502 hours and 1336 hours, five test samples of each example and comparative example were taken out of the constant temperature oven and brought to room temperature. After standing for 1 hour, the resistance value (resistance value before trip) was measured with a milliohm meter. After measuring the resistance value, a DC stabilized power supply (PAD35-60L, manufactured by Kikusui Electronics Co., Ltd.) was used, voltage was applied for 5 minutes at a setting of 6 V / 50 A, and the device was tripped. Thereafter, the device was allowed to stand at room temperature for 1 hour, and then the resistance value of the element (resistance value after trip) was measured with a milliohm meter. The measurement results are shown in Table 6 and Table 7 below. The results are shown in FIG. 4 (85 ° C. storage resistance value) and FIG. 5 (85 ° C. storage trip jump) with respect to the storage time. The numerical values in Table 6 are resistance values before tripping, and the unit is mΩ. Table 7 shows the ratio of the resistance value after trip after each time to the resistance value before trip when the storage time at 85 ° C. is 0 hour, that is, the resistance change rate.

  Under high-temperature and dry conditions, the resistance value before tripping does not change much over time in both the example and comparative example samples, but the resistance value after tripping is evident in the comparative example sample. The increasing rate of the resistance value is large.

(8) Measurement of resistance change with time under normal temperature and normal humidity conditions The test samples of the examples and comparative examples were measured at 23 ± 5 ° C. and a relative humidity of 20 to 60% (general humidity when the humidity was not controlled). The same test as in the above (7) was carried out on the PTC element stored at room temperature controlled to correspond to However, the number of samples used was 20 each, and after 1002 hours and after the storage time of 1863 hours, 5 samples were taken out and resistance values (resistance values before tripping) were measured. Moreover, the resistance value after a trip was measured similarly. The measurement results are shown in Table 8 and Table 9 below. The results are shown in FIG. 6 (room temperature storage resistance value) and FIG. 7 (room temperature storage trip jump) with respect to the storage time. The numerical values in Table 8 are resistance values before tripping, and the unit is mΩ. Table 9 shows the ratio of the resistance value after the trip after each elapsed time, that is, the resistance change rate, to the resistance value before the trip when the storage time at room temperature is 0 hour.

  Under normal temperature and normal humidity conditions, both the resistance value before tripping and the resistance value after tripping, both in the example and the comparative sample, are not so affected over time. The rate of increase in resistance after tripping is relatively large for the sample.

(9) Oxidation accelerated test under pressure A test sample is placed in a pressure vessel, and compressed air is supplied to the pressurized atmosphere at 40 atm to accelerate the oxidation of the conductive filler of the PTC element. Set. After storing the test samples for 14 days and 28 days in this pressurized atmosphere, after holding them in the atmosphere at room temperature for 1 hour, resistance values were measured in the same manner as above (these measured values are shown in FIG. These are illustrated as “2week” and “4week”, respectively, and are illustrated as “initial” before storage.) Thereafter, the PTC element was tripped in the same manner as described above, and then left at room temperature for 1 hour to measure the resistance value. The measurement results are shown in Table 10 and Table 11 below. The results are shown in FIG. 8 (resistance value after 40 atm pressurization test) and FIG. 9 (trip jump after 40 atm pressurization test) with respect to the storage time. In addition, the numerical value in Table 10 is the resistance value before the trip, and the unit is mΩ. Table 11 shows the ratio of the resistance value after the trip after each lapse of time to the resistance value before the trip when the storage time at 40 atmospheres is 0 hour, that is, the resistance change rate.

  From these results, under pressure conditions, the resistance value before tripping has little influence over time for both the example and comparative sample. However, with respect to the resistance value after the trip, it can be seen that the increase in the resistance value becomes more remarkable with the passage of time in the sample of the comparative example. Especially for the samples of Example A and Example B, particularly good results have been obtained with respect to the increase in resistance value after tripping.

(10) Trip cycle test About the sample of an Example and a comparative example, the resistance value before a test was measured using the milliohm meter at room temperature. Thereafter, these samples were set in a trip cycle tester. In this testing machine, MODEL PAD 35-60L manufactured by Kikusui Electronics was used as the power supply, and the voltage was set to 6 Vdc and the test current was limited to 50 A.

  A 50 A current was applied to each sample for 6 seconds. The sample tripped within this application time, and a voltage of 6 V was applied to the sample for the remaining time.

  When the application time of 6 seconds was finished, the current / voltage application was canceled and no application was applied for 54 seconds. On / OFF of the current / voltage application is controlled by a sequencer, which is defined as one cycle, and tripping was performed for each sample for 200 cycles.

  After the predetermined number of cycles, the sample is once removed from the testing machine, and after the predetermined number of cycles, after 1 hour, the resistance value of the sample is measured, and then the sample is returned to the testing machine. The trip cycle test was continued after setting. The predetermined number of cycles was 50 cycles, 100 cycles, and 200 cycles. The measurement results of this resistance value are shown in Table 12 and FIG. The numerical values in the tables and figures are shown as the ratio of the resistance value after the end of each cycle to the resistance value at the initial value (0 cycle), that is, the resistance change rate.

  For the sample of Comparative Example A, the resistance value increased considerably after the end of 200 cycles, whereas for the sample of the Example, the resistance value did not increase much.

  From the results of the examples and comparative examples relating to the PTC element described above, the samples of the examples, particularly the samples of Example A and Example B, were compared with the samples of the comparative examples at high temperature / dry storage conditions, normal temperature / normal humidity storage conditions. It was confirmed that good performance was maintained both in the storage conditions under the accelerated atmosphere and in the trip cycle test. Therefore, when the nickel powder of the present invention used for producing such a sample is used as a conductive filler, a preferable PTC element can be produced. This is presumed to be because the nickel powder of the present invention is selected from nickel powder containing cobalt as having specific characteristics. That is, in addition to the characteristics of the nickel powder itself containing Co, it is caused by selecting a specific range from the viewpoint of a more controlled primary particle size distribution and secondary particle size morphology. It is considered a thing.

  Of particular note is that when the PTC element is exposed to high temperature / dry conditions for a long time, the resistance value after the trip increases, but in the case of the PTC element of the present invention, the increasing rate is relatively small. Conventionally, evaluation of PTC elements has been performed under normal temperature and normal humidity conditions. In such an evaluation, as can be seen from the results of FIGS. 6 and 7, the increase in the resistance value of the element is not remarkable. However, in the evaluation under the high temperature / dry conditions, the difference in the increase in the resistance value of the PTC element becomes clear. The environment in which the PTC element is used varies, and may be used at high temperatures and in dry conditions (for example, the environment in a car on a summer day). The PTC element of the present invention is more useful than the conventional PTC element because the increase in resistivity is small even in such a severe environment.

  The nickel powder according to the present invention can be suitably used as conductive particles for conductive paste and conductive resin, and as a conductive filler for polymer PTC elements.

  In addition, the PTC element according to the present invention has a switching performance equivalent to that of a PTC element using nickel powder containing only nickel as a conductive filler, and further shows improved performance against long-term changes over time. Like a conventional PTC element, it can be used for a longer period of time in an electric device or the like.

2 is a photograph of the nickel powder obtained in Example 1 taken with a scanning electron microscope (SEM). The enlargement rate of (b) is larger than the enlargement rate of (a). It is the photograph by the scanning electron microscope (SEM) of the nickel powder obtained by the comparative example 2. The enlargement rate of (b) is larger than the enlargement rate of (a). It is a graph which shows the resistance-temperature curve of the PTC element of an Example and a comparative example. It is a graph which shows a time-dependent change of the resistance value on the high temperature and dry conditions of the PTC element of an Example and a comparative example. It is a graph which shows a time-dependent change of the change rate of the resistance value after the trip under high temperature and dry conditions of the PTC element of an Example and a comparative example. It is a graph which shows the time-dependent change of the resistance value on room temperature and normal humidity conditions of the PTC element of an Example and a comparative example. It is a graph which shows a time-dependent change of the change rate of the resistance value after the trip on the room temperature and normal humidity conditions of the PTC element of an Example and a comparative example. It is a graph which shows the time-dependent change of the resistance value on the oxidation acceleration conditions of the PTC element of an Example and a comparative example. It is a graph which shows a time-dependent change of the resistance value change rate after the trip under the oxidation acceleration conditions of the PTC element of an Example and a comparative example. It is a graph which shows the change rate of the resistance value by a trip cycle test.

Claims (12)

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 composed of secondary particles. The primary particles have an average primary particle size of 1.0 to 3.0 μm. The ratio σ / d ₁ of the standard deviation σ of the diameter and the average primary particle diameter d ₁ is 0.4 or less, the average secondary particle diameter is 5 to 60 μm, the tap density is 1.0 to 3.5 g / mL, the ratio Nickel powder having a surface area of 2.0 m ² / g or less. _2. The nickel powder according to claim ₁ , wherein the value of the ratio d ₂ / d ₁ between the average primary particle diameter d ₁ and the average secondary particle diameter d ₂ is in the range of 5-60.   The nickel powder according to claim 1 or 2, wherein the cobalt content of the primary particles present in the surface layer portion of the secondary particles is 1 to 40 mass% per total mass of the surface layer portion.   Adding a divalent nickel salt to an aqueous solution containing a reducing agent to precipitate nickel; adding at least a divalent nickel salt to the aqueous solution after the first reducing precipitation step; and A second reduction precipitation step for precipitating nickel, and adding a low hydrophilic surfactant having an HLB value of 10 or less in at least the first reduction precipitation step among the first and second reduction precipitation steps In addition, at least in the second reduction precipitation step, a divalent cobalt salt is added to an aqueous solution for depositing nickel to precipitate nickel to obtain nickel powder, and the obtained nickel powder is further subjected to inert atmosphere or vacuum. It is characterized by drying at 80 to 230 ° C. in the atmosphere, or drying at 80 to 150 ° C. in the air and then heat treatment at 200 to 400 ° C. in a reducing atmosphere. Method of manufacturing that nickel powder.   The content of cobalt ions in the aqueous solution to which the divalent cobalt salt is added in the second reduction precipitation step is 1 to 40% by mass with respect to the total amount of nickel ions and cobalt ions in the aqueous solution, and The cobalt ion concentration in the aqueous solution is higher than the cobalt ion concentration in the aqueous solution in the first reduction precipitation step, and the nickel powder obtained through the first and second reduction precipitation steps contains 1 to 20 mass of cobalt. % Nickel content, The manufacturing method of the nickel powder of Claim 4 characterized by the above-mentioned.   A divalent cobalt salt is added to the aqueous solution in the first reduction precipitation step so that the cobalt ion content in the aqueous solution is 1 to 20% by mass with respect to the total amount of nickel ions and cobalt ions in the aqueous solution. In addition, the divalent cobalt is added to the aqueous solution in the second reduction precipitation step so that the cobalt ion content in the aqueous solution is 1 to 20% by mass with respect to the total amount of nickel ions and cobalt ions in the aqueous solution. The method for producing nickel powder according to claim 4, wherein a salt is added.   The nickel powder according to claim 3, wherein the content of cobalt in the surface layer portion of the secondary particles is 8 to 20 mass% with respect to the total mass of the surface layer portion.   The nickel powder according to any one of claims 1 to 3 and claim 7, wherein the content of cobalt as a whole of the nickel powder is 4 to 10% by mass.   The nickel powder according to any one of claims 1 to 3 and claims 7 and 8, wherein the content of cobalt in the nickel powder is 3 to 6% by mass based on the total mass of the nickel powder.   The nickel powder according to any one of claims 1 to 3 and claims 7 to 9, wherein a tap density is 2.3 to 3.0 g / mL. Nickel powder according to any one of claims 1 to 3 and claims 7 to 10 values of the ratio d ₂ / d ₁ is equal to or is in the range of 8-16. (A) (a1) a conductive filler, and (a2) a polymer PTC element comprising a polymer material, and (B) a polymer PTC element comprising a metal electrode disposed on at least one surface of the polymer PTC element The nickel powder according to any one of claims 1 to 3 and claims 7 to 11 and the nickel powder produced by the method according to claims 4 to 6 are used as a conductive filler. Polymer PTC element.