JP7699524B2 - Nickel powder, conductive composition containing same, and conductive film - Google Patents

Description

The present invention relates to nickel powder. The present invention also relates to a conductive composition and a conductive film that contain the nickel powder.

Nickel powder is used, for example, to form internal electrodes of multilayer ceramic capacitors. Such nickel powder is required to be fine and have a sharp particle size distribution. For example, Patent Document 1 describes nickel powder in which the number of particles having a particle diameter of 1.2 times or more of the average particle diameter observed with a scanning electron microscope (hereinafter also referred to as "SEM") is 5% or less of the total number of particles, the number of particles having a particle diameter of 0.8 times or less of the average particle diameter is 5% or less of the total number of particles, and the tap density is 2.5 g/cm3 or ^more . This nickel powder is generally spherical or nearly spherical.

On the other hand, nickel powder consisting of dendrite-shaped particles is also known (see, for example, Patent Document 2). Dendrite nickel powder is used to manufacture a conductive film by kneading it into, for example, a resin. Dendrite nickel powder generally has a particle size of about 10-odd μm to several tens of μm.
Thus, most of the nickel powders known so far are on the submicron order or on the order of several tens of μm.

JP 2001-200301 A China Patent Publication No. 102392270

When using nickel powder to manufacture a conductive film, if the above-mentioned submicron-order nickel powder is used, the resistance of the film may increase due to the tendency for aggregation between particles to occur. On the other hand, if dendritic powder is used, it is not easy to make the conductive film thin, and the surface of the conductive film is prone to becoming uneven.

Therefore, the objective of the present invention is to provide nickel particles suitable for forming a conductive film that is easily thinned and has high conductivity.

The present invention relates to a magnet having a residual magnetization of 7.0 A·m ² /kg or more,
a volume cumulative particle size D ₅₀ (μm) at a cumulative volume of 50% by volume as measured by a laser diffraction/scattering particle size distribution measurement method is 1.0 μm or more and 5.0 μm or less;
The tap density TD (g/cm ³ ) measured in accordance with JIS Z2512 is 1.5 g/cm ³ or more and 3.5 g/cm ³ or less,
The present invention provides a nickel powder having a BET specific surface area of at least 0.5 as defined by SSA×TD/ _D50 , where SSA is m ² /g.

The present invention provides nickel particles suitable for forming conductive films that are easily thinned and have high electrical conductivity.

FIG. 1(a) is a schematic diagram showing the nickel powder that is the raw material for the nickel powder of the present invention, and FIG. 1(b) is a schematic diagram showing the process by which the nickel powder of the present invention is produced from the raw material nickel powder. FIG. 2 is a scanning electron microscope image of the nickel powder obtained in Example 1. FIG. 3 is a scanning electron microscope image of the nickel powder obtained in Example 2.

The present invention will be described below based on its preferred embodiments. The nickel powder of the present invention is composed of an aggregate of nickel particles. It is preferable that the nickel particles consist only of nickel, but it is acceptable for the nickel particles to contain trace amounts of unavoidable impurity elements as long as the effects of the present invention are not impaired.

The nickel powder of the present invention preferably has strong magnetic anisotropy. The inventors have found through their research that when the nickel powder of the present invention, which has strong magnetic anisotropy, is added to a resin or organic solvent to form a conductive composition, it can impart high conductivity to the conductive film formed from the conductive composition. In particular, when the tap density of the nickel powder of the present invention is within the range described below and the magnetic anisotropy is strong, this is preferable because the conductivity of the conductive film is further improved. To increase the magnetic anisotropy of the nickel powder, it is preferable to use nickel particles manufactured by, for example, the method described below.

Describing in more detail the magnetic properties of the nickel powder of the present invention, a residual magnetization of 7.0 A· ^m2 /kg or more is preferable in order to increase the conductivity of the conductive composition, and from the viewpoint of making this advantage even more pronounced, the residual magnetization is preferably 7 A· ^m2 /kg or more and 20 A· ^m2 /kg or less, more preferably 8 A· ^m2 /kg or more and 18 A· ^m2 /kg or less, and even more preferably 9 A· ^m2 /kg or more and 15 A· ^m2 /kg or less.
With regard to the saturation magnetization, a value of 10 A·m ² /kg or more is preferable in terms of increasing the conductivity of the conductive composition, and from the viewpoint of making this advantage even more pronounced, the saturation magnetization is preferably 10 A·m ² /kg or more and 100 A·m ² /kg or less, more preferably 20 A·m ² /kg or more and 90 A·m ² /kg or less, and even more preferably 30 A·m ² /kg or more and 80 A·m ² /kg or less.
On the other hand, the coercive force is preferably 10 kA/m or more and 30 kA/m or less in terms of increasing the electrical conductivity of the conductive composition. From the viewpoint of making this advantage more prominent, the coercive force is preferably 12 kA/m or more and 25 kA/m or less, more preferably 12 kA/m or more and 20 kA/m or less, and even more preferably 12 kA/m or more and 18 kA/m or less.
Details of the methods for measuring the various magnetic properties of the nickel powder of the present invention will be described in the examples below.

In addition to having high magnetic orientation, the nickel powder of the present invention preferably has a bulk density within a predetermined range. In other words, it is preferable that the nickel powder of the present invention has high particle packing. As a result, when the nickel powder of the present invention is added to a resin or an organic solvent to form a conductive composition, the conductive film formed from the conductive composition can be given high conductivity. From the viewpoint of making this advantage more prominent, the nickel powder of the present invention preferably has a tap density TD of 1.5 g/cm ³ or more and 3.5 g/cm ³ or less. Compared with nickel powder having a tap density TD of more than 3.5 g/cm ³ , nickel powder having such a tap density TD can give high conductivity to a resin or the like even when used in a relatively small amount. From this viewpoint, the tap density TD is more preferably 1.6 g/cm ³ or more and 3.0 g/cm ³ or less, and even more preferably 1.7 g/cm ³ or more and 2.5 g/cm ³ or less. Nickel powder having such a tap density TD is suitably manufactured by a manufacturing method described later.
In this specification, the tap density TD is a value measured in accordance with JIS Z2512.

In order to make the nickel powder of the present invention have the above-mentioned magnetic properties and tap density TD, it is advantageous to appropriately control the particle size of the nickel particles constituting the nickel powder. Also, from the viewpoint of making the conductive film thinner and smoothing the surface of the conductive film, it is advantageous to appropriately control the particle size of the nickel particles. From these viewpoints, the nickel particles preferably have a volume cumulative particle size _D50 at 50% cumulative volume measured by a laser diffraction scattering type particle size distribution measurement method of 1.0 μm or more and 5.0 μm or less, more preferably 1.5 μm or more and 5.0 μm or less, and even more preferably 2.0 μm or more and 4.5 μm or less.

In the nickel powder of the present invention, it is preferable that the nickel particles constituting the nickel powder have an anisotropic shape, in which the length L is large relative to the width W, rather than a spherical shape, in order to impart high conductivity to the conductive composition. For example, it is preferable that the nickel particles have a shape such as a rod, cigar, or spheroid that is long in one direction.
The degree of anisotropy of nickel particles can be evaluated by the aspect ratio, which is calculated by L/W, where L is the longest transverse length of the particle and W is the length of the perpendicular bisector of L across the particle.
Specifically, the aspect ratio is calculated by first photographing at least two fields of view with a SEM at a magnification that includes at least 50 particles to be measured. Next, at least 50 particles whose outlines can be confirmed are randomly selected from each image data, and the L/W value is calculated for each of the selected particles. The average value thus calculated is the aspect ratio in this specification.
In the nickel powder of the present invention, in order to impart high conductivity to the conductive composition, the aspect ratio measured by the above method is preferably 1.2 or more and 3.0 or less, more preferably 1.3 or more and 2.7 or less, and even more preferably 1.4 or more and 2.4 or less.

In the nickel powder of the present invention, the value of L itself is preferably 1.4 μm or more and 8.0 μm or less, more preferably 1.5 μm or more and 7.4 μm or less, and even more preferably 1.6 μm or more and 7.0 μm or less, provided that the aspect ratio satisfies the above-mentioned range.
The value of W itself is preferably 0.7 μm or more and 6.5 μm or less, more preferably 0.9 μm or more and 5.5 μm or less, and even more preferably 1.1 μm or more and 4.5 μm or less, provided that the aspect ratio satisfies the above-mentioned range.

In the present invention, when the nickel particles have an anisotropic shape, it is advantageous for the nickel particles to have a surface that is finely uneven rather than smooth, since this can impart high conductivity to the conductive composition.

In order to obtain a conductive film with high conductivity using the nickel powder of the present invention, it is advantageous for the nickel powder to have a large BET specific surface area SSA. Specifically, the SSA of the nickel powder of the present invention is preferably 1.0 m ² /g or more, more preferably 1.5 m ² /g or more, and even more preferably 1.8 m ² /g or more. The higher the SSA of the nickel powder, the more desirable it is. However, a high SSA value means that the particle diameter D ₅₀ of the nickel particles becomes small, and an excessively small particle diameter D ₅₀ is not desirable in the present invention. From this viewpoint, the SSA of the nickel powder of the present invention is preferably 3.0 m ² /g or less, more preferably 2.7 m ² /g or less, and even more preferably 2.5 m ² /g or less.
The method for measuring the BET specific surface area SSA will be described in detail in the Examples below.

In the nickel powder of the present invention, it is preferable that the above-mentioned SSA, tap density TD, and particle size _D50 satisfy a specific relationship, since this can impart higher electrical conductivity to the conductive film. Specifically, the value defined by SSA×TD/ _D50 is preferably 0.5 or more, more preferably 0.7 or more, and even more preferably 0.9 or more. Also, from the viewpoint of imparting higher electrical conductivity to the conductive film, the upper limit of SSA×TD/ _D50 is preferably 10.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less.

The technical meaning of the value of SSA×TD/ _D50 is as follows. In order to increase the conductivity of the conductive film obtained by using the nickel powder of the present invention, it is desirable that the SSA value is large as described above, and it is desirable that the TD value is within a predetermined range. From this viewpoint, it is desirable that the product of SSA and TD is also within a predetermined range. On the other hand, with regard to _D50 , there is a value within a range suitable for forming a desired conductive film. From this viewpoint, the present inventors considered that it would be advantageous to use the value obtained by dividing the product of SSA and TD by _D50 as an index in order to achieve the object of the present invention.

The nickel powder of the present invention preferably has a tap density TD in a predetermined range and also has an apparent density AD in a predetermined range. In particular, it is preferable that there is no large difference between the tap density TD value and the apparent density AD value, because even if the amount of nickel powder used is small, the conductivity between nickel particles can be sufficiently ensured. From this point of view, the value of AD/TD, which is the ratio of the apparent density AD to the tap density TD, is preferably 0.73 or more, more preferably 0.77 or more, and even more preferably 0.80 or more.
In this specification, the apparent density AD is a value measured in accordance with JIS Z2504.

In the nickel powder of the present invention, the value of the apparent density AD itself is preferably 1.0 g/cm3 or more and 2.5 g/cm3 or ^less , more preferably 1.2 g/ ^cm3 or more and 2.3 g/ ^cm3 or less, and even more preferably 1.3 g/ ^cm3 or more and 2.1 g/cm3 or less, provided that the value AD/ ^TD satisfies the ^above- mentioned range.

In the nickel powder of the present invention, it is preferable from the viewpoint of improving electrical conductivity that the crystallite size of the nickel in the nickel particles constituting the nickel powder satisfies a specific range. In particular, from the viewpoint of improving electrical conductivity, it is preferable that the crystallite size calculated from the half-width of the (111) peak among the diffraction peaks obtained by performing X-ray diffraction measurement on the nickel powder of the present invention is 10 nm or more and 100 nm or less, more preferably 20 nm or more and 70 nm or less, and even more preferably 30 nm or more and 50 nm or less. Nickel powder having such a crystallite size is suitably manufactured by the manufacturing method described below.

The nickel powder of the present invention is preferably low in oxygen concentration from the viewpoint of further increasing the electrical conductivity. From this viewpoint, the oxygen concentration of the nickel powder of the present invention is preferably 1.5 mass% or less, more preferably 1.0 mass% or less from the viewpoint of further increasing the electrical conductivity, and even more preferably 0.8 mass% or less. The lower the oxygen concentration, the better.
The measurement of the oxygen concentration will be explained in the Examples below.

The nickel particles of the present invention are also preferred in that the oxygen content per BET specific surface area is low, which can further increase the electrical conductivity. From this viewpoint, the oxygen content per BET specific surface area is preferably 0.5 mass%/( ^m2 /g) or less, more preferably 0.45 mass%/( ^m2 /g) or less, and even more preferably 0.4 mass%/( ^m2 /g) or less. The smaller the oxygen content per BET specific surface area, the more preferable it is. Such nickel powder is preferably produced by the production method described below.
The method for calculating the oxygen content per BET specific surface area will be explained in the examples described later.

Next, a preferred method for producing the nickel powder of the present invention will be described. The nickel powder of the present invention is preferably produced by pulverizing nickel powder, which is an aggregate of nickel particles having a dendritic shape (hereinafter, this nickel powder will also be referred to as "dendrite powder" for convenience).

The method for pulverizing the dendrite powder is not particularly limited as long as the desired nickel powder can be obtained, and either a dry method or a wet method may be adopted. Regardless of which method is adopted, it is preferable to adopt a pulverization method in which a dendrite particle 1 having a main axis 2 and branches 3 branching from the main axis 2 is cut as shown in Figures 1 (a) and 1 (b), and the cut pieces 4 generated by the cutting are not deformed as much as possible, from the viewpoint of easily obtaining nickel powder having a desired shape.
As such a crushing method, it is advantageous to use a method that does not use crushing media and is a dry method. One example of such a crushing method is a method of crushing dendritic powder in a dry manner using a rotating cutting blade. According to this crushing method, the dendritic particle 1 shown in FIG. 1(a) is cut by the rotating cutting blade to become the cut piece 4 shown in FIG. 1(b). In this case, by appropriately controlling the rotation speed of the cutting blade, the application of excessive external force to the cut piece 4 is suppressed, and deformation of the cut piece 4 is suppressed as much as possible.
In order to pulverize the dendrite powder in a dry manner using a rotating cutting blade, for example, a Force Mill (manufactured by Osaka Chemical Co., Ltd.) can be used, but is not limited to this.

When dendritic powder is crushed dry using rotating cutting blades, the various conditions such as the number, shape, size and rotation speed of the cutting blades should be such that the dendritic particles 1 are cut while causing minimal deformation of the cut pieces 4 produced by the cutting, as described above. Setting such conditions is within the ordinary skill of a person skilled in the art. Satisfactory results can be obtained by adopting at least the conditions described in the examples below.

The dendrite powder, which is the raw material for obtaining the nickel powder of the present invention, is an aggregate of nickel particles having a dendritic shape. As the dendrite powder, it is preferable to use one having a tap density TD of 0.2 g/cm ³ or more and 3.0 g/cm ³ or less, particularly 0.2 g/cm ^{3 or} more and 2.5 g/cm ³ or less, particularly 0.2 g/cm ³ or more and 1.7 g/cm 3 or less, and among them, 0.25 g/cm ³ or more and 0.8 g/cm ³ or less. By using the dendrite powder having such a tap density as the raw material, nickel powder having a desired tap density can be easily obtained.

In relation to the tap density, the dendritic powder preferably has an apparent density AD of 0.2 g/cm ³ or more and 2.0 g/cm ³ or less, more preferably 0.25 g/cm ³ or more and 1.5 g/cm ³ or less, and even more preferably 0.3 g/cm ³ or more and 1.5 g/cm ³ or less. By using a dendritic powder having such an apparent density as a raw material, nickel powder having a desired tap density and/or apparent density can be easily obtained.

In addition, the dendritic powder preferably has a ratio of apparent density AD to tap density TD, AD/TD, of 0.5 or more, more preferably 0.55 or more, and even more preferably 0.6 or more. The upper limit of AD/TD is preferably about 0.8.

The dendrite powder has a volume cumulative particle size _D50 at 50% cumulative volume as measured by a laser diffraction scattering particle size distribution measurement method of preferably 2.0 μm to 20.0 μm, more preferably 2.0 μm to 15.0 μm, and even more preferably 4.0 μm to 15.0 μm. By using a dendrite powder having such a particle size as a raw material, nickel powder having a desired particle size can be easily obtained.

The dendrite powder preferably has magnetic properties similar to those of the target nickel powder. As a result of the inventor's investigation, it was found that by adopting a crushing method in which the dendrite particles are cut and the cut pieces are not deformed as much as possible, the magnetic properties of the dendrite powder before crushing and the nickel powder after crushing do not change significantly. From this viewpoint, the residual magnetization of the dendrite powder is preferably 10 A·m ₂ /kg or more, more preferably 10 A·m ² /kg or more and 20 A·m ² /kg or less, even more preferably 10.5 A·m ² /kg or more and 18 A·m ² /kg or less, and even more preferably 10.5 A·m ² /kg or more and 16 A·m ² /kg or less.

The saturation magnetization is preferably 10 A·m ² /kg or more, more preferably 10 A·m ² /kg or more and 100 A·m ² /kg or less, even more preferably 20 A·m ² /kg or more and 90 A·m ² /kg or less, and even more preferably 30 A·m ² /kg or more and 80 A·m ² /kg or less.
The coercive force is preferably 10 kA/m or more and 30 kA/m or less, more preferably 12 kA/m or more and 25 kA/m or less, even more preferably 14 kA/m or more and 20 kA/m or less, and even more preferably 16 kA/m or more and 20 kA/m or less.

As described above, it is desirable for the nickel powder of the present invention to have a large BET specific surface area, and correspondingly, it is desirable for the dendritic powder to also have a large BET specific surface area. Specifically, the dendritic powder preferably has a BET specific surface area of 0.5 ^m2 /g or more and 5.0 ^m2 /g or less, more preferably 0.5 ^m2 /g or more and 4.5 ^m2 /g or less, and even more preferably 0.5 ^m2 /g or more and 4.0 ^m2 /g or less.

The dendritic powder having the above-mentioned specifications is preferably produced by an electrolytic method. In the process of producing the dendritic powder by the electrolytic method, an electrolytic solution containing nickel ions is used, an anode and a cathode are immersed in the electrolytic solution, and a direct current voltage is applied between the electrodes to perform electrolysis. Dendritic particles reduced by electrolysis are precipitated on the cathode.
The cathode may be made of any conductive material that does not affect electrolysis. The cathode is preferably made of, for example, stainless steel or titanium. As the stainless steel, austenitic stainless steel is preferable, and SUS304L and SUS316 are particularly preferable.
On the other hand, it is preferable that the anode is insoluble in electrolysis. The reason is as follows. For example, when nickel is used as the anode, the nickel dissolves into the electrolyte during electrolysis. The amount of nickel electrolytically deposited at the cathode is smaller than the amount of nickel dissolved at the anode due to gas generation. As a result, the concentration of nickel in the electrolyte increases over time, which hinders the generation of dendrite powder. This problem becomes more pronounced as the electrolysis time becomes longer.
As the insoluble anode, for example, DSE (registered trademark, manufactured by De Nora Permelec) can be used.

As the nickel ion source, a water-soluble nickel compound is preferably used. For example, nickel salts, which are compounds formed by neutralizing the electric charge of cations and anions, can be used. Examples of such nickel salts include nickel sulfate, nickel chloride, nickel acetate, nickel carbonate, and nickel nitrate. These nickel compounds may be used alone or in combination of two or more. In addition, by using metallic nickel for the anode electrode, it can be used as a nickel ion source. In particular, it is preferable to use nickel chloride or nickel sulfate as the nickel salt.

When nickel chloride is used as the nickel salt, in order to successfully precipitate the dendrite powder by electrolysis, it is advantageous to set the current density during electrolysis to preferably 500 A/m ² or more and 2800 A/m ² or less, more preferably 1000 A/m ² or more and 2500 A/m ² or less, and even more preferably 1200 A/m ² or more and 2000 A/m ² or less.
On the other hand, when nickel sulfate is used as the nickel salt, in order to successfully precipitate the dendrite powder by electrolysis, it is advantageous to set the current density during electrolysis to preferably 2200 A/m ² or more and 9000 A/m ² or less, more preferably 2500 A/m ² or more and 5000 A/m ² or less, and even more preferably 2500 A/m ² or more and 3500 A/m ² or less.

In order to successfully deposit the dendrite powder by electrolysis, in addition to using a relatively high current density during electrolysis, it is also advantageous to adjust the concentration of nickel ions in the electrolyte.
Specifically, when nickel chloride is used as the nickel salt, it is advantageous to set the concentration of nickel ions in the electrolytic solution to preferably 0.01 mol/L or more and 0.5 mol/L or less, more preferably 0.03 mol/L or more and 0.3 mol/L or less, and even more preferably 0.03 mol/L or more and 0.2 mol/L or less.
On the other hand, when nickel sulfate is used as the nickel salt, it is advantageous to set the concentration of nickel ions in the electrolytic solution to preferably 0.08 mol/L or more and 0.3 mol/L or less, more preferably 0.08 mol/L or more and 0.25 mol/L or less, and even more preferably 0.08 mol/L or more and 0.2 mol/L or less.
During electrolysis, it is preferable to maintain the nickel ion concentration in the electrolyte within the above range in order to stably generate dendrite powder. For this purpose, when the nickel ion concentration in the electrolyte is significantly reduced, it is preferable to add an appropriate amount of nickel chloride or nickel sulfate to the electrolyte.

The pH of the electrolyte during electrolysis is preferably set to a weakly acidic or neutral range from the viewpoint of successfully precipitating dendrite powder by electrolysis. If the pH is lowered, hydrogen gas is more likely to be generated than nickel ion reduction, making it difficult to obtain dendrite powder. From this viewpoint, when nickel chloride is used as the nickel salt, the pH of the electrolyte is preferably maintained between 3 and 10 during electrolysis, more preferably between 4 and 8, and even more preferably between 5 and 7. On the other hand, when nickel sulfate is used as the nickel salt, the pH of the electrolyte is preferably maintained between 5.5 and 10 during electrolysis, more preferably between 5.5 and 8, and even more preferably between 5.5 and 7. A basic substance such as ammonia can be used to adjust the pH. In addition, a supporting salt described below can also be used to adjust the pH.
It is preferable to maintain the pH of the electrolyte within the above range during electrolysis in order to stably produce dendrite powder. For this purpose, it is preferable to appropriately add a suitable amount of a pH adjuster to the electrolyte during electrolysis.

It is preferable to add a supporting salt to the electrolyte in order to successfully obtain nickel particles that have a dendritic shape and are fine particles. Examples of supporting salts include neutral chlorides such as sodium chloride, potassium chloride, lithium chloride, rubidium chloride, and cesium chloride, alkali metal salts of perchloric acid such as lithium perchlorate and sodium perchlorate, ammonium salts such as ammonium chloride, and alkali metal salts of sulfate such as sodium sulfate and potassium sulfate.

From the viewpoint of imparting sufficient conductivity to the electrolyte, the concentration of the supporting salt in the electrolyte is preferably set to 0.1 mol/L or more and 1.0 mol/L or less, more preferably set to 0.2 mol/L or more and 0.8 mol/L or less, and even more preferably set to 0.3 mol/L or more and 0.5 mol/L or less.

During electrolysis, it is preferable to heat the electrolyte and maintain the electrolyte at a predetermined temperature, from the viewpoint of accelerating the reduction of nickel ions and successfully obtaining nickel particles that are fine and have a dendritic shape. From this viewpoint, whether nickel chloride or nickel sulfate is used as the nickel salt, it is advantageous to maintain the temperature of the electrolyte during electrolysis preferably between more than 50°C and less than 90°C, more preferably between more than 50°C and less than 85°C, and even more preferably between 55°C and 85°C.

By carrying out electrolysis under the above conditions for a specified period of time, dendritic particles are precipitated on the cathode. The precipitated dendritic particles are collected by scraping them off the cathode, and dendritic powder, which is the raw material for nickel powder, is obtained.

The nickel powder of the present invention is preferably used for applications in which it is mixed with a non-conductive substance to impart conductivity to the non-conductive substance. For example, by mixing the nickel powder of the present invention with an organic solvent, a conductive composition such as a conductive ink or a conductive paste can be obtained. A coating film is formed from such a conductive composition, and the organic solvent is removed from the coating film to obtain a dried body, which can be used as a conductive film.
Moreover, a conductive composition can be obtained by kneading the nickel powder of the present invention into a resin. This conductive composition is suitably used, for example, as a conductive film or a conductive sheet.
When a conductive film is formed using the nickel powder of the present invention, it is easier to make the film thinner and the surface of the conductive film smoother than in the conventional technology in which a conductive film is formed using dendritic nickel powder. In addition, when making a conductive film thinner, it is generally necessary to mix a large amount of nickel powder into the conductive composition for forming the conductive film, but when the nickel powder of the present invention is used, sufficient conductivity is achieved even if the amount of nickel powder mixed into the conductive composition is reduced compared to the conventional technology.

The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

Example 1
(1) Production of dendritic powder In a 3 L beaker, a SUS316 cathode plate and an insoluble electrode plate DSE (registered trademark, manufactured by De Nora Permelec Co., Ltd.) were placed so that the distance between the electrode plates was 50 mm. The dimensions of the electrode plates were both 120 mm x 70 mm.
21.0 g of nickel chloride, 60.0 g of ammonium chloride, and 30.0 g of sodium chloride were dissolved in pure water to prepare an electrolyte solution with a total volume of 3 L. This electrolyte solution was filled into the beaker.
A DC voltage was applied between the electrodes to perform electrolysis for 3 minutes. During electrolysis, the electrolyte was heated to maintain the temperature at 60° C. The current density was maintained at 1500 A/m ^2. The pH of the electrolyte was maintained at 6.
The dendrite particles precipitated on the surface of the cathode plate by electrolysis were scraped off to recover the dendrite powder. The recovered dendrite powder was filtered through a Nutsche filter, washed with pure water and then with alcohol. It was then dried in the air at 80° C. for 8 hours.
The obtained dendritic powder had a tap density TD of 0.8 g/ ^cm3 , an apparent density AD of 0.6 g/ ^cm3 , a particle size _D50 of 8.0 μm, a residual magnetization of 11.0 A· ^m2 /kg, a saturation magnetization of 52.2 A· ^m2 /kg, and a coercive force of 17.2 kA/m.
(2) Pulverization of Dendrite Powder The dendritic powder was pulverized in a dry state for 10 minutes using a pulverizer having a rotating cutting blade (Force Mill, manufactured by Osaka Chemical Co., Ltd., rotation speed 22000 rpm) to obtain pulverized nickel powder. An SEM image of the obtained pulverized nickel powder is shown in FIG.

Example 2
In Example 1, the dendrite powder was pulverized for 5 minutes. Except for this, pulverized nickel powder was obtained in the same manner as in Example 1. An SEM image of the pulverized nickel powder obtained is shown in FIG.

Comparative Example 1
Nickel powder (manufactured by Strem Chemicals, USA) consisting of roughly spherical nickel particles was used as the nickel powder of this comparative example.

Comparative Example 2
In this comparative example, nickel powder was obtained as follows.
First, 445.28 g of ethylene glycol was put into the reaction vessel. Then, 31.31 g of nickel hydroxide, 2.15 g of polyvinylpyrrolidone, and 0.13 mL of 100 g/L palladium nitrate solution were put into the reaction vessel to prepare a mixed solution. This mixed solution was heated and stirred at 190° C. for 10 hours to synthesize nickel powder. The slurry containing this nickel powder was filtered through a Nutsche filter and then washed with pure water and alcohol in that order. Then, it was dried at 80° C. for 8 hours in a shelf vacuum dryer.

[Evaluation 1]
For the nickel powders obtained in the examples and comparative examples, the tap density TD and apparent density AD were measured by the above-mentioned method. The aspect ratio L/W was also measured by the above-mentioned method. Furthermore, the particle size _D50 and BET specific surface area SSA were measured by the method described below. Furthermore, the magnetic properties of the nickel powders were measured by the method described below. Furthermore, the value of SSA x TD/ _D50 was calculated by the method described below. Furthermore, the crystallite size of the nickel and the oxygen concentration of the nickel powder were measured by the method described below. Furthermore, the oxygen content per BET specific surface area was calculated by the method described below. The results are shown in Table 1 below.

[Particle size _D50 ]
A small amount of nickel powder was placed in a beaker, and a few drops of 3% Triton X solution (Kanto Chemical Co., Ltd.) were added and mixed with the powder, followed by adding 50 mL of 0.1% SN Dispersant 41 solution (San Nopco Co., Ltd.). The mixture was then dispersed for 2 minutes using an ultrasonic disperser TIPφ20 (Nihon Seiki Seisakusho Co., Ltd., OUTPUT: 8, TUNING: 5) to prepare a measurement sample. The particle size D ₅₀ of this measurement sample was measured using a laser diffraction scattering type particle size distribution measuring device MT3300 (Nikkiso Co., Ltd.).

[BET specific surface area SSA]
The measurement was performed by a BET single point method using a Monosorb manufactured by Yuasa Ionics Co., Ltd.

[Magnetic properties]
A vibrating sample magnetic measuring device (model: VSM-5, manufactured by Toei Kogyo Co., Ltd.) was used. The nickel powder obtained in the examples and comparative examples was packed into a cell with an inner diameter of 6 mm and a height of 2 mm, and set in the device. Measurements were performed while sweeping the magnetic field in the range of ±795.8 kA/m (=±10 kOe), and a hysteresis curve was created. The saturation magnetization, residual magnetization, and coercivity were determined based on this hysteresis curve.

[SSA×TD/D ₅₀ ]
The value of SSA×TD/D ₅₀ was calculated from the values of the BET specific surface area, the tap density TD, and the particle size D ₅₀ measured by the above-mentioned methods.

[Crystallite size]
The nickel powder obtained in the examples and comparative examples was subjected to X-ray diffraction measurement using a RINT2000 X-ray diffractometer manufactured by Rigaku Corporation. The obtained diffraction peaks were used to calculate the crystallite size by the Scherrer method. The X-ray diffraction conditions were 2θ/θ=5-80 deg, step width=0.01 deg, scan speed=0.2 deg/min, characteristic X-ray=Cu-Kα1 ray, and 1D detector. The crystallite size was calculated from the half-width of the Ni(111) peak using a Scherrer constant of 0.94.

[Oxygen Concentration]
The nickel powder obtained in the examples and comparative examples was placed in a graphite crucible and heated and melted in a He atmosphere using an EMGA-820ST manufactured by Horiba, Ltd. The carbon monoxide (carbon dioxide) generated by the crucible was measured by a non-dispersive infrared absorption method to measure the oxygen concentration (mass%).

[Oxygen content per BET specific surface area]
The oxygen content per BET specific surface area was calculated from the oxygen concentration measured by the above-mentioned method and the value of the BET specific surface area measured by the above-mentioned method.

[Evaluation 2]
The nickel powder obtained in the examples and comparative examples was mixed with a silicone sealant (manufactured by ThreeBond Co., Ltd., model number 5211) in a mixing ratio of 80% nickel powder to silicone sealant.
Further, toluene in an amount equal to the mass of the nickel powder was added, and the resulting mixture was thoroughly mixed using a mixer manufactured by Thinky Corporation (Awatori Rentaro (registered trademark), model number AR-100) to prepare a paste.
This paste was applied onto a glass plate and dried in air at 180°C for 3 hours to obtain a conductive film. The electrical resistance of this conductive film was measured by a four-probe method using a resistivity meter (MCP-T600, manufactured by Mitsubishi Chemical Corporation). The thickness of the conductive film was measured using a micrometer, and the resistivity of the conductive film was calculated from the formula: resistivity (Ω·cm) = width (cm) × thickness (μm) × electrical resistance (Ω) / (length (cm) × 10 ⁴ ). The results are shown in Table 1 below. The thickness of the conductive film is also shown in the table.

As shown in Table 1, the conductive films obtained in each example exhibit sufficient conductivity even when the amount of nickel powder mixed is a relatively small amount of 80%. In contrast, the conductive films obtained in Comparative Examples 1 and 2 did not exhibit sufficient conductivity due to the small amount of nickel powder mixed.

Claims (10)

The residual magnetization is 7.0 A·m ² /kg or more,
a volume cumulative particle size D ₅₀ (μm) at a cumulative volume of 50% by volume as measured by a laser diffraction/scattering particle size distribution measurement method is 1.0 μm or more and 5.0 μm or less;
The tap density TD (g/cm ³ ) measured in accordance with JIS Z2512 is 1.5 g/cm ³ or more and 3.5 g/cm ³ or less,
A nickel powder having a BET specific surface area of 0.5 or more as defined by SSA×TD/ _D50 , where SSA is m ² /g. The nickel powder according to claim 1, having a residual magnetization of 10 A·m ² /kg or more. The nickel powder according to claim 1 or 2, having a saturation magnetization of 10 A·m ² /kg or more. The nickel powder according to any one of claims 1 to 3, having a coercive force of 10 kA/m or more and 30 kA/m or less. The nickel powder according to any one of claims 1 to 4, wherein the _D50 is 1.5 µm or more and 5.0 µm or less. The nickel powder according to any one of claims 1 to 5, wherein the SSA is 1.0 m ² /g or more and 3.0 ^{m 2} /g or less. The nickel powder according to claim 1 , wherein the oxygen content per SSA is 0.5 mass%/(m ² /g) or less. The apparent density AD measured in accordance with JIS Z2504 is 1.0 g/cm ³ or more and 2.5 g/cm ³ or less,
The nickel powder according to any one of claims 1 to 7, wherein the ratio of the AD to the TD, that is, the value of AD/TD, is 0.73 or more and 0.93 or less. A conductive composition comprising the nickel powder according to any one of claims 1 to 8 and an organic solvent. A conductive film comprising a dried body of the conductive composition according to claim 9.

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