KR101356377B1 - Nickel powder, method for producing same, and polymer ptc device using such nickel powder - Google Patents

Abstract

The present invention is inexpensive, has a low electrical resistance in a state kneaded with a resin, has excellent weather resistance, and can stably use nickel powder which can be used as conductive particles for conductive paste and conductive particles for conductive resin stably over a long period of time. to provide. Containing 1 to 20 mass% of cobalt, the remainder being made of secondary particles in which nickel and inevitable impurities are formed, and primary particles are aggregated, and the average primary particle diameter is 1.0 to 3.0 µm, and the standard deviation of the primary particle diameter ( σ) and the average primary particle diameter (d) is a nickel powder having a ratio of σ / d of 0.4 or less, an average secondary particle diameter of 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. do.

Nickel powder, cobalt, tap density, specific surface area, standard deviation, average primary particle diameter

Description

Nickel powder, its manufacturing method, and polymer PCC using the said nickel powder {NICKEL POWDER, METHOD FOR PRODUCING SAME, AND POLYMER PTC DEVICE USING SUCH NICKEL POWDER}

The present invention relates to a nickel powder, a method for producing the same, and a polymer PTC device using the nickel powder. The said nickel powder can be used suitably as electroconductive particle for electrically conductive paste and electrically conductive resin, and can be especially suitably used as an electrically conductive filler for a polymer PTC element.

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

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

Among the metal powders, the precious metal powder has high conductivity and low electric resistance, but has a problem of being expensive. In addition, nonmetallic powders such as nickel (Ni) and copper (Cu) are inexpensive and have high conductivity. However, since they have poor weather resistance, they can be kneaded with a resin and used for a long time as a conductive paste or conductive resin. There is a problem that the electrical resistance rises.

In addition, although carbon powder is inexpensive and has high weather resistance, there is 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 Application Laid-Open No. 2002-025345) and Patent Document 2 (Japanese Patent Application Laid-Open No. 2002-075057), silver is coated on the surface of Ni particles or Cu particles. Powders coated with precious metals such as (Ag) have been proposed. Since these powders cover Ni particles or Cu particles with a noble metal, the characteristics thereof are generally improved, but there is a problem with respect to migration resistance. Particularly, the powder coated with Ag is not suitable for use in a use environment where migration resistance is required. In addition, coating Ni particles or Cu particles with a noble metal is expensive.

In addition, Patent Document 3 (Japanese Patent Application Laid-Open No. 2001-043734) discloses that by changing the surface shape of Ni particles or the like, for example, by forming a hemispherical small bump on the surface, Attempts have been made to lower the electrical resistance when kneaded. However, since the weather resistance of the particles is intact, it cannot be said that the stability in long-term use is improved.

Moreover, although this inventor has proposed Ni powder which has a specific shape and improved electroconductivity and weather resistance by adding cobalt (Co) (refer patent document 4), further improvement is anticipated. From such a situation, the provision of the electroconductive particle which is inexpensive, excellent in weather resistance, has low electrical resistance in the state kneaded with resin, and can be used stably for a long time is expected.

Patent Document 1: Japanese Patent Application Laid-Open No. 2002-25345

Patent Document 2: Japanese Patent Application Laid-Open No. 2002-75057

Patent Document 3: Japanese Patent Application Laid-Open No. 2001-43734

Patent Document 4: International Publication No. 2005/023461 Pamphlet

SUMMARY OF THE INVENTION The present invention has been made in view of these problems, and is inexpensive, has low electrical resistance in a state of being kneaded with a resin, has excellent weather resistance, and can stably conduct conductive pastes, conductive resins, and conductive fillers for PTC devices over a long period of time. It aims at providing the nickel powder which can be used as electroconductive particle used for etc., and its manufacturing method.

The nickel powder which concerns on this invention contains 1-20 mass% of cobalt, remainder consists of nickel and the unavoidable impurity, and also consists of the secondary particle which the primary particle aggregated, and the average primary particle diameter is 1.0-3.0 micrometers, The ratio of the ratio σ / d ₁ of the standard deviation (σ) of the primary particle diameter to 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, It is characterized by the specific surface area of 2.0 m <2> / g or less.

That the average primary particle diameter (d ₁₎ and the average secondary particle diameter (d ₂₎ ratio d ₂ / d ₁ value is within the range of 5 to 60 is preferred.

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 mass of the said surface layer part.

The manufacturing method of the nickel powder which concerns on this invention adds a divalent nickel salt to the aqueous solution containing a reducing agent, and adds a divalent nickel salt to the aqueous solution after a 1st reduction precipitation process which precipitates nickel, and the aqueous solution after a 1st reduction precipitation process. And a second reduction precipitation step of further depositing 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 the reduction precipitation step, divalent cobalt salt is added to an aqueous solution in which nickel is precipitated to precipitate nickel to obtain nickel powder, and the obtained nickel powder is dried at 80 to 230 ° C. in an inert atmosphere or vacuum, or in air. After drying at 80 to 150 ℃ characterized in that the heat treatment of 200 to 400 ℃ in a reducing atmosphere.

Content of cobalt ion in the aqueous solution which added the bivalent cobalt salt in the said 2nd reduction precipitation process is 1-40 mass% with respect to the total amount of the nickel ion and cobalt ion in the said aqueous solution, and the cobalt ion concentration in the said aqueous solution is It is preferable that the nickel powder which is higher than the cobalt ion concentration in the aqueous solution in the said 1st reduction precipitation process, and is obtained through the said 1st and 2nd reduction precipitation processes contains 1-20 mass% of cobalt.

In addition, a divalent cobalt salt is added to the aqueous solution in the said 1st reduction precipitation process so that cobalt ion content in the said aqueous solution may be 1-20 mass% with respect to the total amount of the nickel ion and cobalt ion in the said aqueous solution, You may add a bivalent cobalt salt to the aqueous solution in a 2nd reduction precipitation process so that cobalt ion content in the said aqueous solution may be 1-20 mass% with respect to the total amount of the nickel ion and cobalt ion in the said aqueous solution.

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 mass of the said surface layer part, and content of cobalt as whole nickel powder is 4 thru | or. It is preferable that it is 10 mass%, and it is preferable that content of cobalt in the inside of nickel powder is 3-6 mass% per said total mass inside. In addition, it is preferable that the tap density of 2.3 to 3.0 g / mL is preferred, and d ₂ / d ₁ is from 8 to 16. Moreover, it is more preferable that the polymer PTC element has one or more of these characteristics, and it is especially preferable to have all.

The polymer PTC element which concerns on this invention is a polymer PTC element which consists of a polymer PTC element which consists of a conductive filler and a polymer material, and the metal electrode arrange | positioned on at least 1 surface of a polymer PTC element, The said nickel powder and the said method It is characterized by using any one of nickel powder manufactured by the above as a conductive filler.

When the nickel powder which concerns on this invention is knead | mixed with resin and a resin molded object is produced, the resin molded object with remarkably low electric resistance can be obtained. In addition, the obtained resin molded article has excellent weather resistance and can be used stably for a long time. Therefore, the nickel powder which concerns on this invention can be used suitably as electroconductive particle used for an electrically conductive paste, an electrically conductive resin, etc. In addition, as mentioned later, the nickel powder of this invention can be used suitably also as a conductive filler of a polymer PTC element.

In addition, since the nickel powder which concerns on this invention can be obtained without using an expensive material and does not require a complicated process, it is inexpensive.

In addition, although the nickel powder which concerns on patent document 4 is excellent in weatherability, the average primary particle diameter of the nickel powder which concerns on this invention is 1.0-3.0, whereas the average primary particle diameter of nickel powder which concerns on patent document 4 is 0.2-2.0 micrometers. The tap density of the nickel powder according to the present invention is 1.0 to 3.5 g / mL, whereas the tap density of the nickel powder according to Patent Document 4 is 0.5 to 2.0 g / mL. In addition, nickel minutes according to the present invention, the ratio σ / d ₁ of the standard deviation of primary particle diameter (σ) and average primary particle diameter (d ₁₎ 0.4 or less, and specifies the specific surface area of less than 2.0 ㎡ / g . For this reason, the nickel powder which concerns on this invention becomes favorable weather resistance more than the nickel powder which concerns on patent document 4. As shown in FIG.

In addition, since the nickel powder which concerns on this invention can be used suitably for a polymer PTC element, and the increase of resistivity is small also in severe environments, such as high temperature and dry conditions (for example, in-vehicle environment of a summer), compared with the conventional PTC element Is useful.

Fig. 1 is a photograph by a scanning electron microscope (SEM) of nickel powder obtained in the first embodiment. The magnification of (b) is larger than that of (a).

FIG. 2 is a photograph taken by a scanning electron microscope (SEM) of nickel powder obtained in Comparative Example 2. FIG. The magnification of (b) is larger than that of (a).

Fig. 3 is a graph showing the resistance-temperature curves of the PTC devices of Examples and Comparative Examples.

4 is a graph showing changes over time of the resistance value under the high temperature and dry conditions of the PTC devices of Examples and Comparative Examples.

Fig. 5 is a graph showing the change over time of the rate of change of the resistance value after tripping under the high temperature and dry conditions of the PTC elements of the Examples and Comparative Examples.

Fig. 6 is a graph showing changes over time of the resistance values of the PTC devices of Examples and Comparative Examples under room temperature and normal humidity conditions.

Fig. 7 is a graph showing the change over time of the rate of change of the resistance value after tripping at room temperature and normal humidity conditions of the PTC elements of the Examples and Comparative Examples.

8 is a graph showing a change over time of the resistance value under oxidation acceleration conditions of the PTC devices of Examples and Comparative Examples.

9 is a graph showing the change over time of the rate of change of the resistance value after tripping under oxidation acceleration conditions of the PTC devices of Examples and Comparative Examples.

10 is a graph showing the rate of change of the resistance value by the trip cycle test.

The present inventors have conducted studies on the electrical resistance of nickel powder-kneaded resins. As a result, the particle diameter and tap density of nickel powder have a large effect on the electrical resistance of a molded article using a resin kneaded with nickel powder. It has been found that the electrical resistance of the molded body can be significantly lowered by controlling the tap density in a specific range.

In addition, it was found that the weather resistance of the nickel powder is improved by including a small amount of cobalt in the nickel powder, and in particular by adding cobalt in the surface layer portion of the nickel powder. It has also been found that weather resistance is further improved by suppressing fluctuations in primary particle diameter and by setting the specific surface area to a specific value.

The present invention has been completed based on these findings. Hereinafter, the nickel powder which concerns on this invention is demonstrated in detail, and the manufacturing method of the nickel powder which concerns on this invention is demonstrated.

The nickel powder which concerns on this invention contains 1-20 mass% of cobalt, remainder consists of nickel and the unavoidable impurity, and also consists of the secondary particle which the primary particle aggregated, and the average primary particle diameter is 1.0-3.0 micrometers, The ratio of the ratio σ / d ₁ of the standard deviation (σ) of the primary particle diameter to 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 specific surface area is 2.0 m 2 / g or less.

`` Average primary particle diameter, standard deviation of primary particle diameter ''

The primary particle diameter is the particle diameter of the individual particle | grains which are aggregated, and it measures by SEM observation. Specifically, the nickel powder is fixed to the sample holder with a conductive double-sided tape, and observed at an acceleration voltage of 20 kW and a magnification of 2500 times by JSM-6360LA manufactured by Nippon Denshi Corporation. The particle diameters were obtained for 200 or more primary particles, except that the image processing software (SmileView) attached to the apparatus was applied to the obtained SEM image, and the particles were not overlapped to determine the particle diameter. By measuring, 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 making an average primary particle diameter into the range of 1.0-3.0 micrometers, nickel powder aggregates suitably and it becomes a secondary particle of complex shape, such as a chain shape. By using such secondary particles, in the resin molded article obtained by kneading with the resin, the nickel powder is entangled with each other to form a network, and the resin molded article exhibits a remarkably low electrical resistance and excellent weather resistance.

On the other hand, the average primary particle diameter of the nickel powder concerning patent document 4 (international application publication 2005/023461 pamphlet) is 0.2-2.0 micrometers. Even if the average primary particle diameter of nickel powder is 0.2 micrometer or more and less than 1.0 micrometer, if the cobalt contains 1-20 mass% as a whole, the weather resistance of nickel powder is favorable. However, when the average primary particle diameter of nickel powder is 0.2 micrometer or more and less than 1.0 micrometer, the influence of the oxidation of the surface of nickel powder becomes larger than the case where the average primary particle diameter of nickel powder is 1.0-3.0 micrometers, and it mixes with resin The weather resistance of the molded article obtained by this is worse than when the average primary particle diameter is 1.0-3.0 micrometers. Therefore, it is preferable that the average primary particle diameter of nickel powder is 1.0 micrometer or more.

On the other hand, when the average primary particle diameter of nickel powder exceeds 3.0 micrometers, in the molded object obtained by kneading | mixing with resin, the contact between nickel powder will decrease and the resistance of a molded object will rise. If the average primary particle diameter is larger, the aggregation of the nickel powder itself becomes smaller, the state of monodispersion becomes closer, the contact between the nickel powder decreases further, and the resistance of the molded body further rises.

The ratio σ / d ₁ of the standard deviation σ of the primary particle diameter and the average primary particle diameter d ₁ represents the degree of variation of the primary particle diameter. By setting sigma / d ₁ to 0.4 or less, the particles having a small primary particle diameter are greatly reduced, and the average primary particle diameter is increased even if the number of particles whose primary particle diameter is about the average value or more does not change. Thereby, aggregation is possible even for the nickel powder which has a larger average primary particle diameter than before. Moreover, when an average primary particle diameter becomes large, it becomes possible to knead | mix a large amount of nickel powder with resin conventionally, and weather resistance improves. In addition, even when the fine primary particles which are easy to oxidize decrease, oxidation of nickel powder is suppressed and weather resistance improves significantly.

`` Average secondary particle diameter ''

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, the nickel powder was poured into a 0.2 mass% aqueous solution of sodium hexamethaphosphate using MICROTRAC HRA MODEL 9320-X100 manufactured by Nikki Sobu Co., Ltd., and ultrasonic stirring was performed at 300 W for 10 minutes, followed by FRA mode. The average particle size (D50) is measured at, and the average secondary particle diameter (d ₂ ) is obtained.

By setting the average secondary particle diameter in the range of 5 to 60 µm, the sites where the nickel powder (in particular, the particles constituting the powder) come into contact with each other after kneading with the resin are increased, and the electrical resistance of the resin molded article is significantly reduced. However, when an average secondary particle diameter is less than 5 micrometers, since there is little aggregation, the site | parts which become entangled with each other decrease and the resistance value after kneading with resin becomes high. Moreover, when average secondary particle diameter exceeds 60 micrometers, since the dispersion | distribution of the nickel powder in resin may become uneven, it is unpreferable.

`` Tap density ''

The tap density of the nickel powder affects the dispersion degree of the nickel powder in the resin. The measurement of the tap density was carried out using a shake specific gravity measuring instrument KRS-409 manufactured by Seishakusho Co., Ltd. 15 g of nickel powder is weighed into a 20 mL measuring cylinder, and the tap speed is 120 times / minute, and 500 taps are performed at a tap height of 20 mm. Thereafter, the volume of nickel powder is read from the scale of the measuring cylinder, and the mass (g) of nickel powder is divided by the read volume and calculated.

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

In contrast, 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 not less than 0.5 g / mL and less than 1.0 g / mL, the weather resistance of the nickel powder is good as long as 1 to 20 mass% of the cobalt is contained as a whole. However, in order to improve the weather resistance of the resin molding, 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 becomes difficult to increase the nickel powder kneaded into the resin, and thus the weather resistance is lower than that of the tap density of 1.0 g / mL. Therefore, it is preferable that the tap density of nickel powder is 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, and the mutual contact (in detail, the particles constituting the powder) decreases, and the electrical resistance of the resin molded article increases.

`` Specific surface area ''

The specific surface area greatly influences the weather resistance of nickel powder. In order to measure the specific surface area, Multi Sove 16 manufactured by Yuasa Ionics Co., Ltd. is used. After degassing with nitrogen gas at a degassing temperature of 200 deg.

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

`` Cobalt content ''

The nickel powder which concerns on this invention contains 1-20 mass% of cobalt based on the total mass of the whole nickel powder, and this weather resistance of a nickel powder improves remarkably. This is because cobalt is slightly more ionized than nickel, and in addition to cobalt being preferentially corroded, corroded cobalt is conductive. However, when the content of cobalt is less than 1% by mass of the entire nickel powder, there is no effect of improving weather resistance, and even if it is added in excess of 20% by mass, it becomes expensive in terms of cost and is not preferable.

"Cobalt content of the primary particle which exists in the surface layer part of a secondary particle"

In order to ensure sufficient weather resistance while keeping the cobalt content as low 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 part of the secondary particle | grains of nickel powder is a site | part which precipitated by the 2nd reduction precipitation process, when producing nickel powder by a 2 step reduction precipitation process.

It is preferable to make cobalt content in the said surface layer part into the range of 1-40 mass% per mass of the said surface layer part. In order to obtain required weather resistance, it is necessary to contain 1 mass% or more of cobalt in the said surface layer part. However, even if it adds exceeding 40 mass% to the said surface layer part, it is difficult to further improve weather resistance. Moreover, when it adds exceeding 40 mass% to the said surface layer part, nickel powder becomes ferromagnetic and it is unpreferable when using for electronic components etc. In addition, as apparent from the above description, the present invention does not exclude the form in which cobalt is contained in the nickel powder. That is, in addition to the surface layer part of nickel powder, cobalt may be included inside, and such a case may be preferable. For example, this is the case where nickel powder is used for the polymer PTC element mentioned later.

`` Value of Average Secondary Particle Diameter (d ₂ ) / Average Primary Particle Diameter (d ₁ ) ''

Further, in the nickel minutes according to the present invention, the value of the average secondary particle diameter (d ₂₎ / average primary particle diameter (d ₁₎ is preferably in the range of 5 to 60. When the value of the average secondary particle diameter (d ₂ ) / average primary particle diameter (d ₁ ) is in the range of 5 to 60, contact between the nickel powders (in particular, the particles constituting the powder) kneaded with the resin It becomes easy to occur and the electrical resistance of the resin molding obtained is small. However, when this ratio is less than 5, contact between nickel powder becomes difficult to occur and it is unpreferable. In addition, since the aggregation becomes larger when it exceeds 60, dispersion in resin becomes uneven and it is unpreferable.

`` Production method of nickel powder ''

Next, the manufacturing method of the nickel powder which concerns on this invention is demonstrated. The nickel powder which concerns on this invention is manufactured by a two-step reduction precipitation process and a drying and heating process.

First, in the first reduction precipitation step, almost all nickel is precipitated by adding an aqueous solution containing a divalent nickel salt to an aqueous solution containing a reducing agent (usually containing an reducing agent in excess). Subsequently, in the second reduction precipitation step, a reducing agent is added to the aqueous solution containing the nickel powder precipitated by the first reduction precipitation step, if necessary, and a divalent nickel salt aqueous solution is also added to further precipitate nickel. .

In the production, a low hydrophilic surfactant is added in at least the first reduction precipitation step. For example, if it is a modified silicone oil type surfactant, the thing whose HLB value represented by following formula (1) is 10 or less is added. By adding a low hydrophilic surfactant, the concentration of nickel ions in the reaction can be suppressed to prevent excessive nucleation, and the generation of fine nickel primary particles can be suppressed to grow into primary particles of appropriate size.

[Equation 1]

HLB value = (inorganic value / organic value) × 10

If no surfactant is added, excessive nucleation occurs and fine nickel primary particles are generated. In addition, since the particles do not grow into primary particles of a suitable size, the variation of the primary particle diameter also increases.

Even if the surfactant is added, when the HLB value of the surfactant to be added exceeds 10, fluctuations in the primary particle diameter are suppressed, but fine nickel primary particles are generated and the average primary particle diameter becomes small.

Moreover, complexing agents normally used, such as polyhydric carboxylic acid, such as tartaric acid, and ethylenediamine, sodium hydroxide for pH adjustment, etc. can be added to the aqueous solution containing a reducing agent. 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 above production method, the nickel particles precipitated by the first reduction precipitation process become secondary particles in which primary particles are appropriately aggregated to constitute the interior of the nickel powder, but the cohesive force is weak, and the separation operation with the finished solution is performed. Or it mixes easily at the time of kneading with resin, and becomes a single particle. By continuing the second reduction precipitation step, however, the precipitated nickel makes the coagulation solid, so that it is possible to maintain proper coagulation without being separated even in subsequent operations. The nickel precipitated in the second reduction precipitation process is agglomerated on the outside of the nickel secondary particles precipitated in the first reduction precipitation process to form a surface layer portion of the nickel powder, and is thought to form a nickel powder having high strength by structurally connecting a network. do. Thus, the electrical resistance of the molded object by kneading | mixing of the nickel powder obtained and resin is remarkably low.

The above-described two-stage reduction precipitation step is carried out, and the production is performed by adjusting the concentration of the nickel salt or the reducing agent, the temperature and other conditions of the aqueous solution. Average primary particle diameter is 1.0 to 3.0 μm, ratio σ / d ₁ of standard deviation (σ) of primary particle diameter to average primary particle diameter (d ₁ ) is 0.4 or less, average secondary particle diameter is 5 to 60 μm, tap density Is 1.0 to 3.5 g / mL, and the specific surface area is 2.0 m 2 / g or less].

In order to contain cobalt in this nickel powder, a bivalent cobalt salt is contained in aqueous solution in only the 2nd reduction precipitation process, or both the 1st reduction precipitation process and the 2nd reduction precipitation process among the two steps of reduction precipitation processes mentioned above. It is good to precipitate nickel in the state which added. When cobalt is contained in the whole nickel powder including the inside, nickel may be precipitated in the state which added bivalent cobalt salt to aqueous solution in each of the 1st and 2nd reduction precipitation processes, and content of the cobalt ion in aqueous solution is What is necessary is just to be 1-20 mass% with respect to the total amount of the nickel ion and cobalt ion in aqueous solution in any process. When cobalt is contained in the surface layer portion more than the inside of the nickel powder, more divalent cobalt salt is added to the aqueous solution in the second reduction precipitation step than the first reduction precipitation step, and finally the cobalt content of the entire nickel powder is 1 to 1 It is good to adjust so that it may become 20 mass%.

When the nickel powder is not contained inside the cobalt and only cobalt is contained in the surface layer portion, the cobalt salt is not added to the aqueous solution in the first reduction precipitation step, and the divalent cobalt is added to the aqueous solution only in the second reduction precipitation step. Salt may be added. The amount of cobalt salt added at that time may be 1 to 40% by mass relative to the total amount of nickel ions and cobalt ions in the aqueous solution, whereby the cobalt content in the surface layer portion of the nickel powder is 1 to 40. It can be set as the mass%.

As described above, the nickel powder obtained in the two-stage reduction step is heated and dried in an inert atmosphere or in a vacuum at 80 to 230 ° C, whereby nickel atoms on the surface are diffused to further dissipate micropores, thereby reducing the specific surface area. If 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 it exceeds 230 degreeC, the nickel hydroxide which passivates the surface will decompose | disassemble, oxidation will advance after drying, and resistance at the time of resin kneading will become high. The drying temperature is more preferably 120 to 230 ° C in that the micropores are sufficiently extinguished.

In addition, after drying the nickel powder obtained in the reduction step of the two steps at 80 to 150 ℃ in the air, and then heated at 200 to 400 ℃ in a reducing atmosphere it can be sufficiently eliminated micropores. When dried in the atmosphere, a large amount of hydroxide is formed on the surface to increase the specific surface area, and the resistance value after the resin kneading is greatly increased, but it can be decomposed except that a small amount of nickel hydroxide remains by heating in a reducing atmosphere after drying. Can be made small. When heating in a reducing atmosphere is less than 200 ° C, decomposition of nickel hydroxide is insufficient, the specific surface area is large, and the resistance value after resin kneading also increases. When it exceeds 400 degreeC, nickel hydroxide will not only decompose excessively but nickel powder will sinter.

Thus, in the manufacturing method of the nickel powder which concerns on this invention, expensive materials, such as a noble metal, are not used, and a complicated process is not needed. Therefore, the nickel powder which concerns on this invention can be obtained in low cost.

`` Polymer PTC Device ''

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 this invention mentioned above or later as a conductive filler. Hereinafter, although the said polymer PTC element is demonstrated, the polymer PTC element itself is well-known and the description regarding the polymer PTC element itself is abbreviate | omitted.

Specifically, the PTC device according to the present invention includes a polymer PTC element including (A) (a1) a conductive filler and (a2) a polymer material, and (B) a metal electrode disposed on at least one surface of the polymer PTC element. And the nickel powder according to the present invention is used as the conductive filler. In addition, the consideration about the physical properties of the nickel powder in the above-mentioned molded article, in particular, the influence on the weather resistance, the conductivity, and the like, is similarly suitable for the nickel powder as the conductive filler in the polymer PTC element.

The polymer material used in the polymer PTC device according to the present invention may be a known polymer material used for a normal polymer PTC device that brings about PTC properties. Such polymer materials are thermoplastic crystalline polymers, and examples thereof include polyethylene, ethylene copolymers, fluorine-containing polymers, polyamides, and polyesters, and these may be used alone or in combination.

More specifically, as polyethylene, high density polyethylene, low density polyethylene and the like can be used, and as the ethylene copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-butyl acrylate copolymer, an ethylene-vinylacetate copolymer, and an ethylene-polyoxymethylene A copolymer etc. can be used, As a fluorine-containing polymer, a polyvinylidene fluoride, a ethylene tetrafluoride- ethylene-6 fluorine propylene copolymer, etc. can be used, As a polyamide, 6- nylon, 6, 6- nylon, 12 -Nylon etc. can be used and polybutylene terephthalate (PBT), polyethylene terephthalate (PET), etc. can be used as polyester.

The metal electrode used for the polymer PTC element which concerns on this invention may be comprised from any well-known metal material used for the normal polymer PTC element. The metal electrode may be in the form of a plate or foil, for example. As long as the PTC element aimed at by this invention can be obtained, a metal electrode is not specifically limited. Specifically, a roughened metal plate, roughened metal foil, etc. can be illustrated. When using the roughened metal electrode, a roughening surface contacts a PTC element. For example, a commercially available electrodeposited copper foil and a nickel plated electrodeposited copper foil can be used.

Such &quot; metal electrode &quot; is disposed on at least one of the main surfaces of the PTC element, preferably on two opposite main surfaces of the PTC element. You may arrange | position a metal electrode similarly to the normal manufacturing method of a PTC element. For example, you may arrange | position by carrying out thermocompression bonding of a metal electrode to the plate-shaped or sheet-like PTC element obtained by extrusion molding. In another embodiment, the mixture of the polymer material and the conductive filler may be extruded on the metal electrode. After that, cutting may be carried out as necessary to obtain a smaller PTC element.

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 PTC element of the present invention described above, and such a PTC device is electrically connected to a wiring or an electronic component. It also provides an electrical device (such as a mobile phone).

The nickel powder of this invention which is especially preferable to use in the PTC element of this invention is as follows, for example.

(Content of cobalt)

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, in particular 5 To 7 mass% (for example, 6 mass%).

In addition, in the surface layer part of nickel powder, based on the total mass of the said surface layer part, 3-40 mass% of cobalt, Preferably it is 8-30 mass%, More preferably, it is 8-20 mass%, for example 9 15 mass%, especially 10 mass%.

In addition, the nickel powder which is preferably used for a PTC element may contain cobalt also in the inner part in addition to the surface layer part, and although it is preferable, it does not necessarily need to contain cobalt inside. When cobalt is contained inside, it is preferable that the quantity of cobalt inside is 2-7 mass% (especially 3-6 mass%) based on the total mass inside.

As a specific example of the nickel powder which concerns on this invention especially preferable for use in the PTC element which concerns on this invention, it is any one of the various combinations comprised in the range of 3 types of cobalt content mentioned above, For example, the following is illustrated. The amount of cobalt as a whole is 5 to 7% by mass, the amount of cobalt at 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.

(Average primary particle diameter)

For example 1.5 to 2.5 μm, preferably 1.7 to 2.2 μm.

(Standard deviation / mean primary particle diameter of primary particle diameter)

For example 0.3 or less, preferably 0.25 or less.

(Average secondary particle diameter)

For example from 10 to 40 μm, preferably from 15 to 30 μm.

(Average secondary particle diameter / average primary particle diameter)

For example 5 to 20, preferably 8 to 16, more preferably 10 to 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 it functions as a predetermined PTC element. For example, the conductive filler is 65 to 90 mass%, preferably 70 to 85 mass% on a mass basis.

In the PTC device according to the present invention containing the nickel powder according to the present invention as described above, even when used for a long time in an environment that may be exposed to high temperature and dry conditions, the resistance value of the PTC device in comparison with the conventional PTC device The increase is greatly suppressed.

Hereinafter, this invention is further demonstrated by an Example and a comparative example. Examples and comparative examples regarding the nickel powder are the first to twelfth embodiments and the first to sixth comparative examples, and the examples and the comparative examples regarding the polymer PTC element are Examples A to D and Comparative Examples A and B. .

"Examples and Comparative Examples (First to Twelfth Examples and First to Sixth Comparative Examples) Regarding Nickel Powder"

(Embodiment 1)

37.8 L of 25% aqueous sodium hydroxide solution and 1209 g of tartaric acid were added to 138 L of pure water, and it heated to 70 degreeC, stirring. An aqueous solution obtained by adding a modified silicone oil-based surfactant having a number of hydrazine of 28.8 L and an HLB value of 9 to 60% in an aqueous solution, and further mixing an aqueous solution of cobalt chloride and an aqueous solution of nickel chloride (Co content is 5% by mass relative to the amount of Ni + Co). 3.7 kg) was added in a Ni + Co equivalent mass to precipitate nickel powder by the first reduction precipitation step. Next, an aqueous solution in which 60% water was mixed with 4.8 L of hydrazine, an aqueous solution of cobalt chloride and an aqueous nickel chloride solution in an aqueous solution after the completion of the precipitation of the nickel powder by the first reduction precipitation step (Co content is 10% by mass relative to the amount of Ni + Co). 3.7 kg was added to the Ni + Co equivalent mass (mass of the sum of Ni and Co in which the salts contained in the aqueous solution were converted into metals), and the nickel powder was further precipitated by the second reduction precipitation step. . Then, after filtration and water washing, it dried at 80 degreeC in vacuum and obtained nickel powder.

Co content of the obtained nickel powder was 6.6 mass%. The powder properties are shown in Table 1 below. However, Co content in the whole nickel powder is an analysis value, but Co content of the surface layer part is computed from the value which converted Ni and Co in the salt in the aqueous solution in a 2nd reduction precipitation process. Specifically, it calculated as the ratio of the said Co converted value with respect to the sum value of the said Ni converted value and the said Co converted value.

D ₁ of Table 1 represents an average primary particle diameter was measured by SEM observation. Specifically, the nickel powder was fixed to the sample holder with a conductive double-sided tape, and observed at an acceleration voltage of 20 kPa and a magnification of 2500 times by JSM-6360LA manufactured by Nippon Denshi Corporation. Then, on the obtained SEM, by applying the image processing software (SmileView) attached to the apparatus, the particle diameter was measured for 200 or more primary particles, except that the particles could not be superimposed and the particle diameter could not be determined. The average particle diameter (d ₁ ) of the primary particles was obtained. Moreover, the standard deviation of the primary particle diameter was also calculated from the obtained data.

Table 1 of d ₂ indicates the average secondary particle diameter and the particle diameter of the secondary particles was measured by a laser particle size distribution measurement. Specifically, the nickel powder was poured into a 0.2 mass% aqueous solution of sodium hexamethaphosphate using MICROTRAC HRA MODEL 9320-X100 manufactured by Nikki Sobu Co., Ltd., and ultrasonic stirring was performed at 300 W for 10 minutes, followed by FRA mode. The average particle size (D50) was measured at, and this was taken as the average secondary particle diameter (d ₂ ).

Σ in Table 1 represents the standard deviation of the average primary particle diameter d ₁ , and σ / d ₁ represents the ratio of the standard deviation σ of the primary particle diameter to the average primary particle diameter d ₁ .

The measurement of the tap density in Table 1 was carried out using a shaking specific gravity measuring instrument KRS-409 manufactured by Seishakusho Co., Ltd. 15 g of nickel powder was weighed into a 20 mL measuring cylinder, and 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 measuring cylinder, and the mass (g) of the nickel powder was divided by the read volume and calculated.

In order to measure the specific surface area of Table 1, multi-sorb 16 made by Yuasa Ionics was used. After degassing with nitrogen gas at a degassing temperature of 200 deg.

Next, the nickel powder and the polyethylene resin were mixed so that the nickel powder content was 35% by volume and 43% by volume relative to the nickel powder + polyethylene resin, and kneaded at a temperature equal to or higher than the melting point of the polyethylene resin to form a sheet.

The molded sheet-shaped sample was taken out at 25 (mm) W x 60 (mm) L, and the surface resistivity was measured in accordance with JISK 7194. As a result, the initial surface resistivity of the 35 volume% kneaded product was 0.209? In the% kneaded product, it was 0.036 Ω / square. In addition, the low-resistance meter (Lorestar GP, the product made by DIA Instruments) was used for this measurement.

In addition, in order to evaluate weather resistance, after performing the moisture resistance test which hold | maintains a sheet-like sample for 168 hours in the constant temperature and humidity tank set to 85 degreeC-85% RH, surface resistivity was measured similarly to the above. In the 35 volume% kneaded product, it showed 0.217 ohms / square, and in the 43 volume% kneaded product, it showed 0.033 ohms / square. These results are shown in Table 2.

(Second Embodiment)

As in the first embodiment, two steps of reduced precipitation of nickel were carried out by a two steps of reduced precipitation processes. 25.2 L of 25% aqueous sodium hydroxide solution and 806 g of tartaric acid were added to 138 L of pure water, and it heated to 70 degreeC, stirring. A modified silicone oil-based surfactant having 19.2 L of hydrazine and a HLB value of 9 was added to this aqueous solution. Without adding a cobalt chloride aqueous solution to this aqueous solution, only 2.5 kg of nickel chloride aqueous solution was added in terms of Ni to give a first reduction precipitation step. Next, the aqueous solution which mixed the cobalt chloride aqueous solution and the nickel chloride aqueous solution in the aqueous solution after completion | finish of precipitation of the nickel powder by this 1st reduction precipitation process (Aqueous solution mixed so that Co content might be 10 mass% with respect to Ni + Co amount). ) Was added at a weight of Ni + Co in terms of 2.5 kg, and the nickel powder was further precipitated by the second reduction precipitation step.

Then, after filtration and water washing, it dried at 80 degreeC in vacuum and obtained nickel powder.

The obtained nickel powder contained Co only in the surface layer part, and Co content as a whole was 5.0 mass%. The powder characteristics are shown in Table 1. In addition, as a result of evaluating this nickel powder in the same manner as in the first embodiment, the initial surface resistivity of the 35 volume% kneaded product (that is, the mixture of 35 volume% as described above) was 0.711 Ω / square, In the 43 volume% kneaded product (that is, the 43 volume% mixed as mentioned above), it was 0.194 (ohm) / square. Moreover, as a result of measuring the surface resistivity after a moisture proof test, it showed 0.706 (ohm) / square in 35 volume% kneaded goods, and 0.160 (ohm) / square was shown in 43 volume% kneaded goods. These results are shown in Table 2.

(Third Embodiment)

94.8 g of sodium hydroxide and 12.6 g of tartaric acid were added to 2280 mL of pure water, and the mixture was warmed to 65 ° C while stirring. 180 mL of hydrazine and a modified silicone oil-based surfactant having an HLB value of 9 were added to this aqueous solution, and an aqueous solution containing an aqueous cobalt chloride solution and an aqueous nickel chloride solution (mixed so that the Co content was 1 mass% based on the amount of Ni + Co). 39 g was added to Ni + Co equivalent mass to precipitate nickel powder by the first reduction precipitation process. Next, an aqueous solution obtained by mixing 45 mL of hydrazine and an aqueous solution of cobalt chloride and an aqueous nickel chloride solution (aqueous solution such that the Co content is 1.5% by mass based on the amount of Ni + Co) is added to the aqueous solution after the completion of the first reduction precipitation step. 39g was added by mass conversion + Co, and nickel powder was further precipitated by the 2nd reduction precipitation process. Then, after filtration and water washing, it dried at 80 degreeC in vacuum and obtained nickel powder.

Co content as the whole of the obtained nickel powder was 1.2 mass%. The powder characteristics are shown in Table 1. Moreover, as a result of evaluating this nickel powder similarly to Example 1, the initial surface resistivity of the 35 volume% kneaded product was 0.725 ohms / square, and it was 0.203 ohm / square in the 43 volume% kneaded product. Moreover, as a result of measuring the surface resistivity after a moisture proof test, 0.720 (ohm) / square was shown with 35 volume% kneaded goods, and 0.173 (ohm) / square was shown with 43 volume% kneaded goods. These results are shown in Table 2.

(Fourth Embodiment)

In the same manner as in the third embodiment, two steps of reduced precipitation of nickel were carried out by a two steps of reduced precipitation processes. In the third embodiment, heating up to 65 ° C, and in the fourth embodiment, heating up to 60 ° C, and the cobalt chloride aqueous solution and the nickel chloride aqueous solution are mixed in both the first reduction precipitation step and the second reduction precipitation step. Aqueous solution [Aqueous solution mixed so that the Co content is 20% by mass with respect to the amount of Ni + Co (in the third embodiment, in the first reduction precipitation step, the Co content is 1% by mass with respect to the amount of Ni + Co and the second reduction precipitation In the step, Co content is 1.5% by mass relative to the amount of Ni + Co), and 39 g of Ni + Co equivalent mass was added to precipitate nickel powder. Then, after filtration and water washing, it dried at 80 degreeC in vacuum and obtained nickel powder.

Co content as a whole of the obtained nickel powder was 19.4 mass%. The powder characteristics are shown in Table 1. Moreover, as a result of evaluating this nickel powder similarly to Example 1, the initial surface resistivity of the 35 volume% kneaded product was 0.097 ohms / square, and it was 0.033 ohm / square in the 43 volume% kneaded product. Moreover, as a result of measuring the surface resistivity after a moisture proof test, it showed 0.115 (ohm) / square in 35 volume% kneaded goods, and 0.035Ω / square in 43 volume% kneaded goods. These results are shown in Table 2.

(Fifth Embodiment)

In the same manner as in the third embodiment, two steps of reduced precipitation of nickel were carried out by a two steps of reduced precipitation processes. The cobalt chloride aqueous solution was not added to the aqueous solution added in the first reduction precipitation step, but only 39 g of the nickel chloride aqueous solution was added at a Ni equivalent mass 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 [aqueous solution mixed so that the Co content is 40% by mass relative to the amount of Ni + Co (in the third embodiment, the Co content is Ni + Co 1.5 mass% to the amount] was added in a Ni + Co equivalent mass to 39 g to precipitate a nickel powder. Then, after filtration and water washing, it dried at 80 degreeC in vacuum and obtained nickel powder.

The obtained nickel powder contained Co only in the surface layer part, and Co content as a whole of the obtained nickel powder was 18.7 mass%. The powder characteristics are shown in Table 1. In addition, as a result of evaluating this nickel powder in the same manner as in the first example, the initial surface resistivity of the 35 volume% kneaded product was 0.539 Ω / □, and the 43 volume% kneaded product was 0.178 Ω / □. Moreover, as a result of measuring the surface resistivity after a moisture proof test, it showed 0.609 (ohm) / square in the 35 volume% kneaded product, and showed 0.176 (ohm) / square in the 43 volume% kneaded product. These results are shown in Table 2.

(Sixth Embodiment)

In the same manner as in the first example, the nickel powder was precipitated by reducing the nickel in two steps by the two-step reduction precipitation step. Then, after filtration and water washing, it dried in vacuum at 150 degreeC and obtained nickel powder. The sixth embodiment differs from the first embodiment only in that the drying temperature in the vacuum is 150 ° C (in the first embodiment, 80 ° C).

Co content as a whole of the obtained nickel powder was 6.5 mass%, and the specific surface area was 0.94 m <2> / g. The powder characteristics are shown in Table 1.

Next, as a result of measuring the surface resistivity in the same manner as in the first example, the initial surface resistivity was 0.147 Ω / □, and the surface resistivity after the moisture resistance test was 0.112 Ω / □. These results are shown in Table 2.

(Seventh Embodiment)

As in the first embodiment, two steps of reduced precipitation of nickel were carried out by a two steps of reduced precipitation processes. In the first reduction precipitation process, an aqueous solution in which a cobalt chloride aqueous solution and a nickel chloride aqueous solution are mixed [aqueous solution mixed so that the Co content becomes mass% relative to the Ni + Co amount (in the first embodiment, the Co content is equal to the Ni + Co amount). 5 mass%)] was added in a Ni + Co equivalent mass to precipitate the nickel powder. Next, in the second reduction precipitation step, an aqueous solution in which 60% water is mixed with an aqueous hydrazine, a cobalt chloride solution, and an aqueous nickel chloride solution after 35 minutes has elapsed after the 60% water has started adding hydrazine in the first reduction precipitation process. (Aqueous solution mixed so that Co content became 10 mass% with respect to Ni + Co amount) was added, and nickel powder was deposited. Then, after filtration and water washing, it dried in vacuum at 200 degreeC and obtained nickel powder.

Co content as a whole of the obtained nickel powder was 6.2 mass%, and the specific surface area was 0.65 m <2> / g. The powder properties are shown in Table 1 below. Moreover, as a result of evaluating this nickel powder similarly to Example 1, the initial surface resistivity was 0.151 ohms / square, and the surface resistivity after a moisture resistance test was 0.122 ohms / square. These results are shown in Table 2.

(Example 8)

As in the first embodiment, two steps of reduced precipitation of nickel were carried out by a two steps of reduced precipitation processes. 25.2 L of 25% aqueous sodium hydroxide solution and 806 g of tartaric acid were added to 138 L of pure water, and it heated to 75 degreeC, stirring. 19.2 L of hydrazine was added to this aqueous solution, and in the 1st reduction precipitation process, the cobalt chloride aqueous solution was not added but only 2.5 kg of nickel chloride aqueous solution was added by Ni conversion mass, and nickel powder was precipitated. Next, in the second reduction precipitation step, an aqueous solution in which 60% water is mixed with an aqueous hydrazine, a cobalt chloride aqueous solution, and a nickel chloride aqueous solution after 50 minutes has elapsed after the 60% water has started adding hydrazine in the first reduction precipitation process. (Aqueous solution mixed so that Co content became 10 mass% with respect to Ni + Co amount) 2.5 kg of Ni + Co conversion mass was added, and nickel powder was deposited. Then, after filtration and water washing, it dried in vacuum at 220 degreeC and obtained nickel powder.

The obtained nickel powder contained Co only in the surface layer part, Co content as a whole was 4.6 mass%, and the specific surface area was 0.97 m <2> / g. The powder characteristics are shown in Table 1. Moreover, as a result of evaluating this nickel powder similarly to Example 1, the initial surface resistivity was 0.209 Ω / square, and the surface resistivity after the moisture resistance test was 0.190 Ω / square. These results are shown in Table 2.

(Example 9)

As in the first embodiment, two steps of reduced precipitation of nickel were carried out by a two steps of reduced precipitation processes. In the 1st reduction precipitation process, 25.2 L of 25% sodium hydroxide aqueous solution and 806 g of tartaric acid were added to 138 L of pure waters, and it heated to 70 degreeC, stirring. 19.2 L of hydrazine 60% was added to this aqueous solution, and in the 1st reduction precipitation process, the aqueous solution which mixed the cobalt chloride aqueous solution and the nickel chloride aqueous solution (the aqueous solution which mixed so that Co content might be 1.5 mass% with respect to Ni + Co amount). ) Was added 2.5 kg of Ni + Co equivalent mass to precipitate nickel powder. Next, in the second reduction precipitation step, an aqueous solution in which 60% water is mixed with an aqueous hydrazine, a cobalt chloride aqueous solution, and a nickel chloride aqueous solution after 40 minutes has elapsed after 60% water has started adding hydrazine in the first reduction precipitation process. (Aqueous solution mixed so that Co content became 1.5 mass% with respect to Ni + Co quantity) 2.5 kg of Ni + Co conversion mass was added, and nickel powder was deposited. Then, after filtration and water washing, it dried at 120 degreeC in vacuum and obtained nickel powder.

Co content as a whole of the obtained nickel powder was 1.3 mass%, and the specific surface area was 0.85 m <2> / g. The powder characteristics are shown in Table 1. Moreover, as a result of evaluating this nickel powder similarly to Example 1, the initial surface resistivity was 0.361 Ω / square, and the surface resistivity after the moisture resistance test was 0.318 Ω / square. These results are shown in Table 2.

(Example 10)

94.8 g of sodium hydroxide and 12.6 g of tartaric acid were added to 2280 mL of pure water, and the mixture was warmed to 55 ° C while stirring. 180 mL of hydrazine and a modified silicone oil-based surfactant having an HLB value of 9 were added to this aqueous solution, and an aqueous solution containing a cobalt chloride solution and a nickel chloride solution (mixed so that the Co content was 20% by mass with respect to the amount of Ni + Co). One aqueous solution) was added with 39 g of nickel chloride solution in terms of Ni + Co mass to precipitate nickel powder by the first reduction precipitation process. Next, in the second reduction precipitation step, 30 minutes after the addition of the hydrazine in the first reduction precipitation step, 45 mL of hydrazine and an aqueous solution in which a cobalt chloride aqueous solution and a nickel chloride aqueous solution are mixed (co content is 39 g of the aqueous solution mixed so that the amount of Ni + Co became 20 mass%) was added in a Ni + Co equivalent mass to further precipitate the nickel powder. Then, after filtration and water washing, it dried in vacuum at 200 degreeC and obtained nickel powder.

Co content as a whole of the obtained nickel powder was 18.8 mass%, and the specific surface area was 1.09 m <2> / g. The powder properties are shown in Table 1 below. Moreover, as a result of evaluating this nickel powder similarly to Example 1, the initial surface resistivity was 0.085 ohms / square, and the surface resistivity after a moisture resistance test showed 0.081 ohms / square. These results are shown in Table 2.

(Example 11)

In the same manner as in the tenth example, the reduction precipitation of nickel in two steps was performed by a two-step reduction precipitation step, but the heating was performed to 70 ° C. In the first reduction precipitation step, the cobalt chloride aqueous solution was not added, but only 39 g of the nickel chloride aqueous solution was added to the Ni equivalent mass to precipitate the nickel powder. Next, in the second reduction precipitation process, 45 minutes after the addition of hydrazine in the first reduction precipitation process, 45 mL of hydrazine and an aqueous solution in which a cobalt chloride aqueous solution and a nickel chloride aqueous solution are mixed (co content is 39 g of the aqueous solution mixed so as to be 40 mass% with respect to the amount of Ni + Co was added at a Ni + Co equivalent mass to further precipitate the nickel powder. Then, after filtration and water washing, it dried in vacuum at 220 degreeC and obtained nickel powder.

The obtained nickel powder contained Co only in the surface layer part, Co content as a whole was 19.1 mass%, and the specific surface area was 1.15 m <2> / g. The powder characteristics are shown in Table 1. Moreover, as a result of evaluating this nickel powder similarly to Example 1, the initial surface resistivity was 0.406 ohms / square, and the surface resistivity after a moisture resistance test showed 0.369 ohms / square. These results are shown in Table 2 below.

(Example 12)

As in the seventh example, two steps of reduced precipitation of nickel were carried out by a two steps of reduced precipitation processes. Then, after filtration and water washing, it dried at 110 degreeC in air | atmosphere, and heated at 350 degreeC in nitrogen-10% hydrogen for 2 hours. Co content as a whole of the obtained nickel powder was 5.9 mass%, and the specific surface area was small as 0.35 m <2> / g. The powder characteristics are shown in Table 1. In addition, as a result of evaluating this nickel powder in the same manner as in the first example, 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 the second embodiment, two steps of reduced precipitation of nickel were carried out by a two-step reduction precipitation process, but in the first reduction precipitation process, a nickel powder was added by adding a modified silicone oil-based surfactant having an HLB value of 11. Got.

The obtained nickel powder contained Co only in the surface layer part, and Co content was 4.8 mass%. The powder properties are shown in Table 1 below. The average primary particle diameter (d ₁₎ has been reduced because of having an HLB value of 11, the modified silicone oil-based surface active agent was used to. Moreover, as a result of evaluation similar to Example 1 about this nickel powder, the initial surface resistivity of the 35 volume% kneaded product was 0.043 ohm / square, However, when the nickel powder was kneaded by 43 volume%, between nickel powders The resin was absorbed (in detail, between the particles constituting the powder), and kneading was impossible. Moreover, as a result of measuring the surface resistivity after a moisture proof test, the 35 volume% kneaded product showed 0.059 (ohm) / square. These results are shown in Table 2.

(Comparative Example 2)

The nickel powder was obtained in the same manner as in Example 2 except that the nickel powder was obtained by two steps of reduction precipitation of nickel by a two-step reduction precipitation step, except that the powder was subjected to grinding after vacuum drying to obtain a nickel powder. Since the grinding treatment was performed, the tap density was increased to 3.61 g / mL.

The obtained nickel powder contained Co only in the surface layer part, and Co content was 4.6 mass%. The powder characteristics are shown in Table 1. Moreover, as a result of evaluation similar to Example 1 about this nickel powder, the initial surface resistivity of 35 volume% kneaded goods was 356 ohms / square, and it was 129 ohm / square in 43 volume% kneaded products. Since the initial surface resistivity was high, the moisture resistance test was not performed about these samples. These results are shown in Table 2.

(Third comparative example)

164 g of sodium hydroxide and 21 g of ethylenediamine were added to 3800 mL of pure water, and the mixture was warmed to 85 ° C while stirring. To this aqueous solution, 130 g of nickel chloride aqueous solution was added (300 cobalt chloride aqueous solution was not added) in 300 mL of hydrazine and the mass equivalent to Ni, and nickel powder was precipitated by the reduction precipitation process of only one step. Then, after filtration and water washing, it dried at 80 degreeC in vacuum and obtained nickel powder.

The obtained nickel powder does not contain Co. The powder characteristics are shown in Table 1. In addition, as a result of kneading with the polyethylene resin in the same manner as in the first example, the nickel powder was not absorbed between the nickel powders even when the nickel powder was kneaded by 35% by volume.

(Comparative Example 4)

Table 1 shows the powder properties of a typical filler nickel powder (manufactured by INCO Corporation) which is commercially available as conductive particles for the conductive paste and the conductive resin. This nickel powder does not contain Co.

As a result of evaluating this nickel powder in the same manner as in the first example, the initial surface resistivity of the 35 volume% kneaded product was 0.124 Ω / □, and the 43 volume% kneaded product was 0.043 Ω / □. Moreover, as a result of measuring the surface resistivity after a moisture proof test, it was 0.406 (ohm) / square in 35 volume% kneaded goods, and 0.068 (ohm) / square in 43 volume% kneaded goods. These results are shown in Table 2.

(Comparative Example 5)

In the same manner as in the second example, the reduction precipitation of nickel in two steps was performed by a two-step reduction precipitation step, but the heating was performed to 70 ° C. In the first reduction precipitation step, a nickel powder was obtained by adding a modified silicone oil-based surfactant having an HLB value of 11. Next, in the second reduction precipitation step, after 25 minutes have elapsed since the 60% number started the addition of the hydrazine in the first reduction precipitation step, an aqueous solution in which the 60% number mixed the aqueous solution of hydrazine, cobalt chloride, and nickel chloride solution (Aqueous solution mixed so that Co content became 10 mass% with respect to Ni + Co amount) 2.5 kg of Ni + Co conversion mass was added, and nickel powder was deposited. Then, after filtration and water washing, it dried at 80 degreeC in vacuum and obtained nickel powder.

The obtained nickel powder contained Co only in the surface layer part, Co content was 5.0 mass%, and the specific surface area was 2.26 m <2> / g. The powder characteristics are shown in Table 1. Moreover, as a result of evaluating this nickel powder similarly to Example 1, the initial surface resistivity was 0.039 Ω / square, and the surface resistivity after the moisture resistance test was 0.051 Ω / square. These results are shown in Table 2.

(Comparative Example 6)

As in the second embodiment, two steps of reduced precipitation of nickel were carried out by a two steps of reduced precipitation processes. 32.9 L of 25% aqueous sodium hydroxide solution and 1617 g of tartaric acid were added to 160 L of pure water, and it heated to 60 degreeC, stirring. 38.5 L of hydrazine was added to this aqueous solution, and in the 1st reduction precipitation process, the cobalt chloride aqueous solution was not added, but only nickel chloride aqueous solution was added 4.8 kg by mass conversion in Ni, and nickel powder was precipitated. Next, in the second reduction precipitation step, after 30 minutes have elapsed since 60% of the first reduction precipitation step started the addition of hydrazine, an aqueous solution in which a cobalt chloride aqueous solution and a nickel chloride aqueous solution were mixed (Co content is Ni 4.8 kg) was added in a Ni + Co equivalent mass to further precipitate nickel. Then, after filtration and water washing, it dried at 100 degreeC in air | atmosphere, and further heat-processed at 350 degreeC in nitrogen-10% hydrogen for 2 hours, and obtained nickel powder.

The obtained nickel powder contained Co only in the surface layer part, Co content was 5.0 mass%, and the specific surface area was 1.13 m <2> / g. The powder characteristics are shown in Table 1. Moreover, as a result of evaluating this nickel powder similarly to Example 1, the initial surface resistivity was 0.046 ohms / square, and the surface resistivity after a moisture resistance test showed 0.066 ohms / square. These results are shown in Table 2.

Table 1

[Table 2]

In the first to fifth embodiments within the scope of the present invention, even if the kneading ratio of Ni powder is 35% by volume or 43% by volume, kneading with polyethylene resin is possible, and the sixth to twelfth embodiments are kneading ratio of Ni powder. Kneading with a polyethylene resin was possible at this 35% by volume. In addition, in the 1st-12th Example within the range of this invention, the surface resistivity of the sheet-like sample shape | molded after resin kneading was small as 0.8 ohm / square or less before and after a moisture proof test. In addition, the rate of increase of the surface resistivity before and after the moisture test (surface resistivity after the moisture test / surface resistivity before the moisture test) is at most 1.19, and the first to twelfth embodiments within the scope of the present invention are excellent in weather resistance and also for a long time. I think it can be used stably throughout.

In contrast, in the first comparative example, 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 less than 1.0 µm which is the lower limit of the present invention. In the case of this 43 volume%, kneading with a polyethylene resin was impossible. When the kneading ratio of Ni powder was 35% by volume, kneading with polyethylene resin could be carried out, but the specific surface area of Ni powder was 2.03 m 2 / g, which is higher than 2.0 m 2 / g, which is the upper limit of the present invention. The increase rate (surface resistivity after moisture resistance test / surface resistivity before moisture resistance test) of surface resistivity before and after was 1.36 (kneading ratio of Ni powder is 35 volume%), and weatherability is inferior.

Since the 2nd comparative example has a tap density of 3.61 g / mL and it exceeds 3.5 g / mL which is an upper limit of this invention, it is thought that the nickel powder is uneven in resin and mutual contact of the particle | grains which comprise powder is reduced, Ni When the kneading ratio of powder is 35% by volume, the initial value of the surface resistivity is 356 Ω / square, and when the kneading ratio of Ni powder is 43% by volume, the initial value of the surface resistivity is 129 Ω / □. Even in the case, the surface resistivity of the sheet-shaped sample molded after the resin kneading was very large.

In the third comparative example, since the tap density was less than 1.0 g / mL, which is the lower limit of the present invention, at 0.61 g / mL, it became difficult to increase the amount of nickel to be kneaded with the resin, and the kneading ratio of the Ni powder was 35% by volume. Even kneading with polyethylene resin was impossible.

Since the 4th comparative example is Ni powder which does not contain Co, the increase rate (surface resistivity after a moisture proof test / surface resistivity before a moisture proof test) before and after a moisture proof test is 3.28 (the kneading ratio of Ni powder is 35 volume%) And 1.59 (Ni-kneading ratio is 43% by volume), which results in poor weather resistance.

In the fifth comparative example, the average primary particle diameter is less than the present invention, the standard deviation of the primary particle diameter is large, and the specific surface area is large, so that the increase rate of the surface resistivity is 1.31, which is inferior in weatherability.

In the sixth comparative example, the specific surface area is within the scope of the present invention, but since the average primary particle diameter is less than the present invention and the standard deviation of the primary particle diameter is also large, the increase rate of the surface resistivity is 1.43, which is inferior in weatherability.

1 (a) and 1 (b) show photographs of a scanning electron microscope (SEM) of nickel powder obtained in the first embodiment, and FIGS. 2 (a) and 2 (b) b) The photograph by a scanning electron microscope (SEM) of the nickel powder obtained by the 2nd comparative example is shown.

As can be seen from FIG. 1 (a) and FIG. 1 (b), the nickel powder obtained in the first embodiment has a uniform primary particle diameter of about 1.8 mu m. On the other hand, as can be seen from Figs. 2A and 2B, the nickel powder obtained in the second comparative example contains particles in which the primary particle size is not uniform in size, which deteriorates weather resistance. There are many fine primary particles which are considered to be the cause of this.

"Examples and Comparative Examples (Examples A to D and Comparative Examples A and B) Regarding Polymer PTC Devices ''

Next, the Example which manufactured the PTC element which concerns on this invention using the nickel powder which concerns on this invention is demonstrated. Moreover, the comparative example for a comparison is also demonstrated.

(1) conductive filler

Nickel-cobalt alloy filler (i.e., nickel powder of the present invention or nickel powder for comparison) as a conductive filler, high-density polyethylene as a polymer material, and roughened nickel foil as a metal electrode (Fukuda Kinzoku Kogyo Co., Ltd.) First, a thickness of about 25 μm) was used to manufacture the PTC device.

The used nickel powder was manufactured in the said 1st Example, 6th Example, 7th Example, and 12th Example, and the PTC element was manufactured using these. These PTC elements are called PTC elements of Example A, Example B, Example C, and Example D, respectively. In addition, the nickel powder of the said 6th comparative example and the 5th comparative example was used as a conductive filler for comparison. These PTC elements are called PTC elements of Comparative Example A and Comparative Example B, respectively.

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

[Table 3]

In addition, Co content was computed as what precipitated substantially all the nickel salt and cobalt salt of the aqueous solution used for manufacture.

(2) polymer materials

As the polymer material, commercially available high density polyethylene (PETROTHENE LB832, manufactured by EQUISTAR, density: 0.957 to 0.964 g / ml, melt index: 0.23 to 0.30 g / 10 minutes, melting point: 135 ± 3 ° C) was used.

(3) metal electrodes

As the metal electrode, a nickel metal foil (Kuko Kogyo Kogyo Co., Ltd., electrolytic nickel foil, thickness: about 25 µm) was used.

(4) Manufacture of PTC Element

(4-1) Preparation of PTC Composition

2 mass% of coupling agents (made by KENRICH PETROCHEMICALS, Inc., NZ-33) are added to a powder-like polymer material, and they are mixed for 30 seconds with a kitchen blender (manufactured by Sunburst Co., Ltd., MILL MIXER MODEL FM-50). To obtain a polymer mixture. Nickel powder and Mg (OH) ₂ (manufactured by Albermal, H10) were added thereto in the amounts shown in Table 4 below, and mixed with a kitchen blender for 30 seconds to obtain a conductive polymer composition.

[Table 4]

45 mL of the obtained conductive polymer composition was put into a mill (Toyo Seiki Co., Ltd. make, Labo Plastomil type 50C150, blade R60B), and it knead | mixed for 15 minutes by the preset temperature of 160 degreeC, and blade rotation speed 60 RPM, and obtained the PTC composition.

(4-2) Preparation of PTC Element Disc

The PTC composition obtained in (4-1) was made into a sandwich structure such as iron plate / teflon (registered trademark) sheet / thickness adjusting spacer (manufactured by SUS with a thickness of 0.5 mm) + PTC composition / teflon (registered trademark) sheet / iron plate, They were preliminarily pressed for 3 minutes at a temperature of 180 to 200 ° C and a pressure of 0.5 MPa by a thermal pressure press machine (manufactured by Toho Press Co., Ltd., Hydraulic Molding Machine: Type T-1), and then press-bonded at a pressure of 5 MPa for 4 minutes. Thereafter, the resultant was pressurized at 0.5 MPa for 4 minutes using a cooling press machine (manufactured by Toho Press Co., Ltd., hydraulic molding machine: Type T-1) in which water having a set temperature of 22 ° C. was circulated by a cooler to form a sheet-like polymer PTC element. (PTC element disc) was produced.

(4-3) Fabrication of Polymer PTC Device Flock Discs

Next, using the PTC element disc and the metal electrode produced in (4-2), iron plate / Teflon (registered trademark) sheet / silicon rubber / Teflon (registered trademark) sheet / metal electrode / thickness adjusting spacer (thickness 0.5 mm) Made of SUS) + PTC element disc / metal electrode / Teflon (registered trademark) sheet / silicone rubber / Teflon (registered trademark) sheet / iron sheet, etc. The press was carried out for 4 minutes at a press pressure of 9 MPa. Thereafter, a cold press was performed at 9 MPa for 4 minutes using the above-mentioned cold press machine circulated with water having a set temperature of 22 ° C. by a cooler, and the metal electrodes were thermocompression-bonded to the main surfaces of both sides of the polymer PTC element (PTC element disc). A polymer PTC element floc disk (assembly of PCT elements before cutting) was produced.

(4-4) Manufacturing of PTC Element

An electron beam of 1000 kGy was irradiated to the polymer PTC element floc disc prepared in (4-3), and it punched by the manual punch machine at 3x4 mm after that, and obtained the test piece of a polymer PTC element.

(4-5) Manufacturing of PTC Device

A pure Ni lead piece of thickness 0.125 mm, hardness 1 / 4H, and 4 mm x 5.2 mm was soldered on both sides of the 3 x 4 mm test piece punched in (4-4) to test the strap-shaped PTC device as a whole. Obtained as. For soldering, about 2.0 mg of paste solder (M705-728C, manufactured by Senju Kinzoku Kogyo Co., Ltd.) is used for one side, and is a reflow furnace (made by Nippon Avionics, model TCW-118N) under a nitrogen atmosphere. , Auxiliary heater temperature control 360 ° C., preheat temperature control 250 ° C., reflow temperature control (1) 240 ° C., reflow temperature control (2) 370 ° C., belt speed 370 mm / min) were used.

(5) Measurement of initial resistance

About the obtained test sample, resistance value (resistance value between two leads) was measured two days after manufacture. 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 that of the PTC element. In addition, a milliohm meter (4263A by HEWLETT PACKARD company) was used for the measurement of the initial resistance value and the resistance value of a PTC element under various conditions as mentioned later. Table 5 shows the measurement results (unit: Ω) of the initial resistance.

[Table 5]

From this result, although the resistance value of the test sample of an Example was a little low, it turns out that any test sample also has a low resistance value normally, including the sample of a comparative example.

(6) PTC characteristic check

Next, the R (resistance) -T (temperature) test was performed by measuring resistance-temperature characteristics about each of five test samples of an Example and a comparative example. The test temperature range was 20 to 150 degreeC, and the ambient humidity of the test sample was 60% or less. The ambient temperature of the test sample was increased by 5 DEG C, held for 10 minutes in the temperature atmosphere, and then the PTC element resistance value was measured. 3 shows the ratio (ie, the ratio of resistance change) to the resistance value at the initial temperature (21 ° C) of the resistance value measured at each temperature.

From the results of FIG. 3, for the devices of Examples and Comparative Examples, the threshold temperature (the temperature of the PTC device rises from room temperature in the range of about 120 ° C to 130 ° C, and the resistance of the PTC device, also called the trip temperature, increases rapidly. Temperature], and for any device, the resistance value after such a range is at least about 10 ¹⁵ times greater than the previous resistance value, and therefore it is clear that any test sample has a switching function as a PTC device. In general, when the resistance value is at least about 10 ³ times or more, it may be considered to have a function as a PTC element.

(7) Measurement of change over time of resistance value under high temperature and dry conditions

The test samples of Examples and Comparative Examples were stored in a constant temperature oven (Yamato constant temperature oven DK600) managed under high temperature and dry conditions of 85 ° C ± 3 ° C and a relative humidity of 10% or less, and stored for 24 hours, 165 hours, 502 hours, and After the elapse of 1336 hours of storage time, five test samples of each of Examples and Comparative Examples were taken out of the constant temperature oven and allowed to stand at room temperature for 1 hour, and then the resistance value (resistance value before tripping) was measured by milliohmmeter. After the resistance measurement, a voltage was applied for 5 minutes at a setting of 6 V / 50 A using a DC stabilized power supply (Kikusui Denshi Kogyo Co., PAD35-60L) to trip the device. Then, after leaving at room temperature for 1 hour similarly, the resistance value (post-trip resistance value) of the element was measured by the milliohmmeter. The measurement results are shown in Tables 6 and 7 below. The results are also shown in Figs. 4 (85 ° C storage resistance value) and 5 (85 ° C storage trip jump) with respect to the storage time. In addition, the numerical value of Table 6 is a resistance value before a trip, and a unit is m (ohm). Table 7 shows the ratio of the resistance value after tripping after the passage of time with respect to the resistance value before tripping, that is, the retention time at 85 ° C, that is, the resistance change rate.

[Table 6]

[Table 7]

Under high temperature and dry conditions, with respect to the resistance value before the trip, the change over time is not so large for any of the samples of the Examples and Comparative Examples, but for the resistance value after the trip, the sample of the Comparative Example clearly shows the increase rate of the resistance value. This is big.

(8) Measurement of change over time of resistance value under normal temperature and normal humidity conditions

(7) and (6) for the PTC device stored in the room temperature of the test sample of the Example and the comparative example managed by 23 +/- 5 degreeC and 20-60% of relative humidity (equivalent to the general humidity without humidity control). The same test was conducted. However, the number of samples used was 20 pieces, and after 1002 hours, each 5 pieces were taken out after the elapse of 1863 hours of storage time, and the resistance value (resistance value before tripping) was measured. In addition, the resistance value after tripping was similarly measured. The measurement results are shown in Tables 8 and 9 below. The results are shown in Fig. 6 (normal storage resistance value) and Fig. 7 (normal storage trip jump) with respect to the storage time. In addition, the numerical value of Table 8 is a resistance value before a trip, and a unit is m (ohm). Table 9 shows the ratio of the resistance value after the trip after the passage of time to the resistance value before the trip, that is, the retention time at room temperature is 0 hours, that is, the resistance change rate.

[Table 8]

[Table 9]

Under normal temperature and normal humidity conditions, the time-dependent effects on the resistance value before the trip and the resistance value after the trip are small, but the samples of the comparative example are relatively tripped. The rate of increase of the subsequent resistance value is large.

(9) Acceleration test under pressure

The test sample was put into a pressure vessel, compressed air was supplied to it, it was set as the pressurized atmosphere of 40 atmospheres, and the conditions which can accelerate the oxidation of the electrically conductive filler of a PTC element were set. After 14 days and 28 days of test samples were stored in this pressurized atmosphere, the test samples were held for 1 hour in an air and room temperature atmosphere, and then the resistance values were measured as described above (these measured values are shown in FIG. And “4 weeks.” In addition, before storage, it is indicated as “initial stage”. Moreover, the PTC element was tripped similarly to the above after that, and it was left to stand at room temperature similarly after that for 1 hour, and the resistance value was measured. The measurement results are shown in Tables 10 and 11 below. The results are shown in FIG. 8 (resistance value after 40 atmosphere pressure test) and FIG. 9 (trip jump after 40 atmosphere pressure test) with respect to the storage time. In addition, the numerical value of Table 10 is a resistance value before a trip, and a unit is m (ohm). Table 11 shows the retention time at 40 atmospheres as 0 hours, and the ratio of the resistance value after tripping to the resistance value before the trip, i.e., the resistance change rate.

[Table 10]

[Table 11]

From these results, under the pressurization condition, the influence over time is not so large with respect to the resistance value before a trip in any of the sample of an Example and a comparative example. However, about the resistance value after a trip, it turns out that the sample of a comparative example becomes remarkable when time passes. In particular, for the samples of Examples A and B, particularly good results are obtained regarding the increase in the resistance value after the trip.

(10) Trip cycle test

For the samples of the Examples and Comparative Examples, the resistance value before the test was measured using a milliohmmeter at room temperature. Thereafter, these samples were set in a trip cycle tester. In this tester, MODEL PAD 35-60L made from KISUNI DENIS was used as a power supply, and it set to the voltage of 6 Vdc and 50 A of test currents.

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

When the application time for 6 seconds had ended, the application of current and voltage was canceled, leaving the driver unattended for 54 seconds. The on / off of this current and voltage application is controlled by the sequencer, and this was defined as one cycle, and 200 cycles were performed for each sample.

After the predetermined number of cycles are finished, the sample is detached from the tester once, and after 1 hour has elapsed after the end of the predetermined number of cycles, the resistance value of the sample is measured. Then, the sample is set again in the tester and tripped. The cycle test was continued. In addition, 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. In addition, the numerical value of a table | surface and a figure is shown by the ratio of the resistance value after completion | finish of each cycle with respect to the resistance value in initial value (0 cycle), ie, a resistance change rate.

[Table 12]

The resistance value increased considerably after the end of 200 cycles for the sample of Comparative Example A, but the increase in the resistance value was not that much for the sample of the Example.

From the results of the examples and comparative examples relating to the PTC device described above, the samples of the examples, in particular the samples of Examples A and B, have a high temperature, dry storage condition, normal temperature, normal humidity storage condition, and accelerated atmosphere compared to the samples of the comparative example. It was confirmed that good performance was maintained in all of the storage conditions and trip cycle tests under the following conditions. Therefore, when the nickel powder of this invention used for manufacturing such a sample is used as a conductive filler, a preferable PTC element can be manufactured. This is presumably because the nickel powder of the present invention is selected as having specific characteristics from the nickel powder containing cobalt. That is, in addition to the characteristics of the nickel powder containing Co itself, it is considered that it originates in selecting a specific range from a more controlled primary particle diameter distribution and the morphological (morphological) viewpoint of a secondary particle.

It should be noted that, in particular, when the PTC element is subjected to high temperature and 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 element was performed on normal temperature and normal humidity conditions. In this evaluation, as can be seen from the results of FIGS. 6 and 7, the increase in the resistance value of the device is not remarkable. However, in the evaluation under high temperature and dry conditions, the difference in increase in the resistance value of the PTC element becomes apparent. The environment in which PTC elements are used varies widely, and it may be used in high temperature and dry conditions (for example, in-car environment in summer). Since the PTC element of the present invention has a small increase in resistivity even in such a harsh environment, it is useful in comparison with the conventional PTC element.

The nickel powder which concerns on this invention can be used suitably as electroconductive particle for electrically conductive paste and electrically conductive resin, and also as an electrically conductive filler of a polymer PTC element.

In addition, the PTC device according to the present invention has a switching performance equivalent to that of a PTC device using nickel powder containing only nickel as the conductive filler, and further shows improved performance with respect to changes over time. Likewise, it can be used over a wider and longer period in electrical devices and the like.

Claims (12)

Containing 1 to 20 mass% of cobalt, the remainder being made of secondary particles in which nickel and inevitable impurities are formed, and primary particles are aggregated, and the average primary particle diameter is 1.0 to 3.0 µm, and the standard deviation of the primary particle diameter ( (sigma)) and the ratio of the ratio of the average primary particle diameter (d ₁ ) sigma / d ₁ is 0.4 or less, the average secondary particle diameter is 5 to 60 ㎛, tap density 1.0 to 3.5 g / mL, specific surface area 2.0 m 2 / g Nickel powder which is characterized by the following. The nickel powder according to claim 1, wherein the value of the ratio d ₂ / d ₁ of the average primary particle diameter (d ₁ ) and the average secondary particle diameter (d ₂ ) is in a range of 5 to 60. The cobalt content of the primary particles present in the surface layer portion of the secondary particles is 1 to 40 mass%, based on the total mass of the surface layer portion, The nickel powder is characterized in that the secondary particles of the nickel powder is precipitated in the second step of the reduction precipitation process. A first reduction precipitation step of precipitating nickel by adding a divalent nickel salt to an aqueous solution containing a reducing agent; and a second reduction precipitation step of further depositing nickel by adding at least a divalent nickel salt to the aqueous solution after the first reduction precipitation step. An aqueous solution which comprises a low hydrophilic surfactant having a HLB value of 10 or less in at least a first reduction precipitation step among the first and second reduction precipitation steps, and precipitates nickel in at least a second reduction precipitation step. Divalent cobalt salt was added to precipitate nickel to obtain nickel powder, and the obtained nickel powder was dried at 80 to 230 ° C. in an inert atmosphere or vacuum, or at 80 to 150 ° C. in air, and then in a reducing atmosphere. A method for producing nickel powder, which is subjected to a heat treatment at 200 to 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 based on the total amount of nickel ions and cobalt ions in the aqueous solution. 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. The manufacturing method of the nickel powder characterized by the above-mentioned. The divalent cobalt salt is added to the aqueous solution in the said 1st reduction precipitation process so that cobalt ion content in the said aqueous solution may be 1-20 mass% with respect to the total amount of the nickel ion and cobalt ion in the said aqueous solution. At the same time, a divalent cobalt salt 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 relative to the total amount of nickel ions and cobalt ions in the aqueous solution. The manufacturing method of the nickel powder to be used. The nickel powder of Claim 3 whose cobalt content of the primary particle which exists in the surface layer part of a said secondary particle is 8-20 mass% per mass of the said surface layer part. The nickel powder according to claim 1 or 2, wherein the content of cobalt as the whole nickel powder is 4 to 10 mass%. The nickel powder according to claim 1 or 2, wherein the content of cobalt in the interior of the nickel powder is 3 to 6 mass% per total mass of the interior. The nickel powder according to claim 1 or 2, wherein the tap density is 2.3 to 3.0 g / mL. The nickel powder according to claim 2, wherein the value of the ratio d ₂ / d ₁ is in the range of 8 to 16. (A) (a1) conductive filler and     (a2) a polymer PTC element comprising a polymer material, (B) It is a polymer PTC element which has a metal electrode arrange | positioned on at least 1 surface of a polymer PTC element, The nickel powder of Claim 1 or 2, or any one of Claims 4-6. The nickel powder manufactured by the method is used as a conductive filler, The polymer PTC element characterized by the above-mentioned.

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