Nickel powder, conductive composition containing the same, and conductive film

Abstract

To provide a nickel particle suited for forming a conductive film easy to reduce a film thickness and having a high electric conductivity.SOLUTION: A nickel powder comprises a residual magnetization of 7.0 A m2 / kg or greater, a volume accumulation particle size D50 (μm) of 1.0 μm or greater and 5.0 μm or smaller in cumulative volume 50 vol.% based on a laser diffraction scattering particle-size distribution measuring method, a tap density TD (g / cm3) of 1.5 g / cm3 or higher and 3.5 g / cm3 or lower as measured conforming to JIS Z2512, and a value defined by SSA×TD / D50 of 0.5 or greater when a BET specific surface area is given as SSA(m2 / g).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to nickel powder. The present invention also relates to a conductive composition and a conductive film containing the nickel powder.

Background Art

[0002] Nickel powder is used, for example, in the formation of internal electrodes of multilayer ceramic capacitors. Such nickel powder is required to be fine and have a sharp particle size distribution. For example, in Patent Document 1, the number of particles having a particle size of 1.2 times or more the average particle diameter by observation with a scanning electron microscope (hereinafter also referred to as "SEM") is 5% or less of the total number of particles, and the number of particles having a particle size of 0.8 times or less the average particle diameter is 5% or less of the total number of particles, and the tap density is 2.5 g / cm 3 or more of nickel powder is described. This nickel powder is generally spherical or nearly spherical in shape.

[0003] On the other hand, nickel powder composed of dendritic particles is also known (see, for example, Patent Document 2). Dendritic nickel powder is used, for example, to knead it into a resin to produce a conductive film. The size of the dendritic nickel powder particles is generally often about ten-odd μm to several tens of μm. Thus, the nickel powder known so far is mostly on the submicron order or on the order of several tens of μm.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when manufacturing a conductive film using nickel powder, if the submicron-order nickel powder described above is used, the resistance of the film may increase due to easy aggregation between particles. On the other hand, when using dendritic powder, it is not easy to thin the conductive film, and unevenness is likely to occur on the surface of the conductive film.

[0006] Therefore, an object of the present invention is to provide nickel particles suitable for forming a conductive film that is easy to thin and has high conductivity.

Means for Solving the Problems

[0007] The present invention provides nickel powder 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 measured by the laser diffraction scattering method of particle size distribution is 1.0 μm or more and 5.0 μm or less, a 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, when the BET specific surface area is SSA (m 2 / g), the value defined by SSA×TD / D 50 is 0.5 or more.

Effects of the Invention

[0008] According to the present invention, nickel particles suitable for forming a conductive film that is easy to thin and has high conductivity are provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0010] 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 desirable that the nickel particles consist only of nickel, but the inclusion of a trace amount of inevitable impurity elements is allowed as long as the effects of the present invention are not impaired.

[0011] The nickel powder of the present invention preferably has strong magnetic anisotropy. As a result of the study by the present inventors, when the nickel powder of the present invention having strong magnetic anisotropy is added to a resin or an organic solvent to form a conductive composition, high conductivity can be imparted 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 later and the magnetic anisotropy is strong, the conductivity of the conductive film is further improved, which is preferable. To increase the magnetic anisotropy of the nickel powder, it is preferable to use, for example, nickel particles manufactured by the method described later.

[0012] When the magnetic properties of the nickel powder of the present invention are described in detail, the residual magnetization is 7.0 A·m 2 / kg or more, which is preferable from the viewpoint of increasing the conductivity of the conductive composition. From the viewpoint of making this advantage more remarkable, the residual magnetization is 7 A·m 2 / kg or more and 20 A·m 2 / kg or less, preferably 8 A·m 2 / kg or more and 18 A·m 2 / kg or less, more preferably 9 A·m 2 / kg or more and 15 A·m 2 / kg or less. Regarding the saturation magnetization, 10 A·m 2 / kg or more is preferable from the viewpoint of increasing the conductivity of the conductive composition. From the viewpoint of making this advantage more remarkable, the saturation magnetization is 10 A·m 2100 A·m / kg or more 2 It is preferably 20 A·m / kg or less 2 90 A·m / kg or more 2 It is more preferably 30 A·m / kg or less 2 80 A·m / kg or more 2 It is even more preferably 80 A·m / kg or less On the other hand, regarding the coercive force, it is preferably 10 kA / m or more and 30 kA / m or less from the viewpoint of enhancing the 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 method for measuring various magnetic properties of the nickel powder of the present invention will be described in the examples described later

[0013] In addition to having a high magnetic orientation, the nickel powder of the present invention preferably has a bulk density within a predetermined range. In other words, it is preferably one with high particle packing density. 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, high conductivity can be imparted to the conductive film formed from the conductive composition. From the viewpoint of making this advantage more prominent, the tap density TD of the nickel powder of the present invention is 1.5 g / cm 3 or more and 3.5 g / cm 3 or less. The nickel powder having such a tap density TD can impart high conductivity to a resin or the like even when used in a relatively small addition amount compared to nickel powder having a tap density TD greater than 3.5 g / cm 3 . 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. The nickel powder having such a tap density TD is preferably produced by the production method described later In this specification, the tap density TD is a value measured in accordance with JIS Z2512.

[0014] In order for the nickel powder of the present invention to have the above-described 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 thinning the conductive film 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 have a volume cumulative particle size D at 50% by volume in terms of cumulative volume measured by the laser diffraction scattering particle size distribution measurement method 50 of preferably 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.

[0015] Further, in the nickel powder of the present invention, it is preferable that the shape of the nickel particles constituting the nickel powder has anisotropy in which the length L is larger than the width W rather than being spherical, from the viewpoint that high conductivity can be imparted to the conductive composition. For example, the nickel particles preferably have a shape such as a rod shape long in one direction, a cigar shape, or a prolate ellipsoid shape. The degree of anisotropy of the nickel particles can be evaluated by the value of the aspect ratio. The aspect ratio is defined as L, the longest transverse length among the transverse lengths of the target particles, and W, the length across the particle by the perpendicular bisector of the transverse length L, and is calculated from L / W. Specifically, the method for calculating the aspect ratio is as follows: First, photograph at least two fields with SEM at a magnification that includes 50 or more particles to be measured. Next, randomly extract 50 or more particles whose contours can be confirmed from each image data, and obtain the value of L / W for each of the extracted particles. The average value calculated in this way is taken as the aspect ratio in this specification. In the nickel powder of the present invention, from the viewpoint that high conductivity can be imparted 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.

[0016] 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 still 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 still more preferably 1.1 μm or more and 4.5 μm or less, provided that the aspect ratio satisfies the above-mentioned range.

[0017] In the present invention, when the nickel particles have an anisotropic shape, it is also advantageous from the viewpoint that the nickel particles having finer irregularities on the surface rather than being smooth can impart high conductivity to the conductive composition.

[0018] In order to obtain a highly conductive conductive film using the nickel powder of the present invention, it is advantageous that the BET specific surface area SSA of the nickel powder is large. 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 still more preferably 1.8 m 2 / g or more. The higher the value of the SSA of the nickel powder, the more desirable. However, a high value of the SSA means that the particle size D 50 of the nickel particles becomes small, and an excessively small particle size 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 still 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 described later.

[0019] In the nickel powder of the present invention, the above-mentioned SSA, the tap density TD, and the particle size D50 When it satisfies a specific relationship, it is preferable because it can impart higher conductivity to the conductive film. Specifically, SSA × TD / D 50 The value defined by is preferably 0.5 or more, more preferably 0.7 or more, and even more preferably 0.9 or more. Also, SSA × TD / D 50 The upper limit of is preferably 10.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less from the viewpoint of imparting even higher conductivity to the conductive film.

[0020] SSA × TD / D 50 The technical meaning of the value of is as follows. In order to increase the conductivity of the conductive film obtained using the nickel powder of the present invention, as described above, it is desirable that the value of SSA is large, and it is desirable that the value of TD 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, for D 50 Regarding, there is a value within a range suitable for it from the viewpoint of forming a desired conductive film. From this viewpoint, the present inventors considered that it is advantageous for achieving the object of the present invention to use, as an index, the value obtained by dividing the product of SSA and TD by D 50 .

[0021] In addition to the tap density TD of the nickel powder of the present invention being within a predetermined range, it is preferable that the apparent density AD is also within a predetermined range. In particular, it is preferable that there is no large difference between the value of the tap density TD and the value of the apparent density AD because, even when the amount of nickel powder used is small, sufficient conductivity between nickel particles can be ensured. From this viewpoint, 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 refers to a value measured in accordance with JIS Z2504.

[0022] In the nickel powder of the present invention, the value of the apparent density AD itself is 1.0 g / cm on the condition that the value of AD / TD satisfies the above-described range3 Preferably, it is 2.5 g / cm or less, and 1.2 g / cm 3 or more, and preferably 2.3 g / cm or less, and 1.3 g / cm 3 or more, and more preferably 2.1 g / cm or less. 3 It is even more preferably 1.3 g / cm or more and 2.1 g / cm or less. 3 It is still more preferably 1.1 g / cm or more and 1.9 g / cm or less. 3 It is even more preferably 1.0 g / cm or more and 1.8 g / cm or less.

[0023] In the nickel powder of the present invention, it is preferable from the viewpoint of improving conductivity that the crystallite size of nickel in the nickel particles constituting the nickel powder satisfies a specific range. Specifically, among the diffraction peaks obtained by performing X-ray diffraction measurement on the nickel powder of the present invention, the crystallite size calculated from the half-value width of the (111) peak is preferably 10 nm or more and 100 nm or less from the viewpoint of improving conductivity, more preferably 20 nm or more and 70 nm or less, and even more preferably 30 nm or more and 50 nm or less. The nickel powder having such a crystallite size is preferably produced by the production method described below.

[0024] It is preferable that the nickel powder of the present invention has a low oxygen concentration from the viewpoint of further enhancing conductivity. From this viewpoint, the oxygen concentration of the nickel powder of the present invention is preferably 1.5% by mass or less, more preferably 1.0% by mass or less from the viewpoint of further enhancing conductivity, and even more preferably 0.8% by mass or less. The lower the oxygen concentration, the more preferable. The measurement of the oxygen concentration will be described in the examples below.

[0025] It is also preferable that the nickel particles of the present invention have a low oxygen content per BET specific surface area from the viewpoint of further enhancing conductivity. From this viewpoint, the oxygen content per BET specific surface area is preferably 0.5% by mass / (m 2 / g) or less, more preferably 0.45% by mass / (m 2 / g) or less, and even more preferably 0.4% by mass / (m 2 / g) or less. The lower the value of the oxygen content per BET specific surface area, the more preferable. 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 described in the examples described later.

[0026] 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 dendrite shape (hereinafter, this nickel powder is also conveniently referred to as "dendrite powder").

[0027] The pulverization of the dendrite powder is not particularly limited as long as the target nickel powder can be obtained, and either a dry method or a wet method may be employed. In any case, as shown in FIGS. 1(a) and 1(b), the dendrite particles 1 having the main axis 2 and the branch portions 3 branching from the main axis 2 are cut, and a pulverization method is adopted such that the cut pieces 4 generated by the cutting are not deformed as much as possible. This is preferable because it is easy to obtain nickel powder having a desired shape. As such a pulverization method, it is advantageous to use a method that does not use a pulverization medium and is a dry method. As an example of such a pulverization method, a method of dry-pulverizing dendrite powder with a rotating cutting blade can be mentioned. According to this pulverization method, the dendrite particles 1 shown in FIG. 1(a) are cut by the rotating cutting blade to become the cut pieces 4 shown in FIG. 1(b). In this case, by appropriately controlling the rotational speed of the cutting blade, excessive external force is prevented from being applied to the cut pieces 4, and deformation occurring in the cut pieces 4 is suppressed as much as possible. In order to dry-pulverize dendrite powder with a rotating cutting blade, for example, a force mill (manufactured by Osaka Chemical Co., Ltd.) can be used, but it is not limited thereto.

[0028] When dry-grinding dendritic powder with a rotating cutting blade, various conditions such as the number, shape, size, and rotational speed of the cutting blades should be such that, as described above, the dendritic particles 1 are cut and the cut pieces 4 generated by the cutting are not deformed as much as possible. Setting such conditions is within the scope of the ordinary ability of those skilled in the art. At least, by adopting the conditions described in the embodiments below, satisfactory results can be obtained.

[0029] The dendritic powder, which is a raw material for obtaining the nickel powder of the present invention, is an aggregate of nickel particles having a dendritic shape. As the dendritic powder, its tap density TD is 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, especially 0.2 g / cm 3 or more and 1.7 g / cm 3 or less, and among them, those having 0.25 g / cm 3 or more and 0.8 g / cm 3 or less are preferably used. By using dendritic powder having such a tap density as a raw material, nickel powder having a desired tap density can be easily obtained.

[0030] In relation to the tap density, the apparent density AD of the dendritic powder is preferably 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, still more preferably 0.3 g / cm 3 or more and 1.5 g / cm 3 or less. By using 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.

[0031] Moreover, for the dendritic powder, the ratio of the apparent density AD to the tap density TD, i.e., the value of AD / TD, is preferably 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.

[0032] The dendritic powder preferably has a volume cumulative particle size D at 50% by volume in the cumulative volume measured by the laser diffraction scattering particle size distribution measurement method 50 in the range of 2.0 μm or more and 20.0 μm or less, more preferably 2.0 μm or more and 15.0 μm or less, and even more preferably 4.0 μm or more and 15.0 μm or less. By using such dendritic powder as a raw material, nickel powder having a desired particle size can be easily obtained.

[0033] The magnetic properties of the dendritic powder are preferably the same as those of the target nickel powder. As a result of the study by the present inventors, it has been found that by adopting a pulverization method that cuts dendritic particles and causes as little deformation as possible to the cut pieces generated by the cutting, there is no significant change in the magnetic properties between the dendritic powder before pulverization and the nickel powder after pulverization. From this viewpoint, the residual magnetization of the dendritic powder is preferably 10 A·m2 / kg or more, 2 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 still more preferably 10.5 A·m 2 / kg or more and 16 A·m

[0034] Regarding the saturation magnetization, it 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 still more preferably 30 A·m2 80 A·m / kg or more 2 It is more preferably 80 A·m / kg or less. Regarding the coercive force, it 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, still 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.

[0035] As described above, it is desirable that the nickel powder of the present invention has a large BET specific surface area. Correspondingly, it is preferable that the dendritic powder also has a large BET specific surface area. Specifically, the BET specific surface area of the dendritic powder is preferably 0.5 m 2 / g or more and 5.0 m 2 / g or less, more preferably 0.5 m 2 / g or more and 4.5 m 2 / g or less, still more preferably 0.5 m 2 / g or more and 4.0 m 2 / g or less.

[0036] The dendritic powder having the above-described specifications is preferably produced by an electrolysis method. In the process of producing dendritic powder by the electrolysis method, an electrolytic solution containing nickel ions is used, an anode electrode and a cathode electrode are immersed in the electrolytic solution, and a DC voltage is applied between the two electrodes to perform electrolysis. The dendritic particles reduced by electrolysis are deposited on the cathode. The cathode may be composed of a conductive material that does not affect electrolysis. The cathode is preferably composed of, for example, stainless steel or titanium. As the stainless steel, austenitic stainless steel is preferable, and particularly SUS304L and SUS316 are preferable. On the one hand, the anode is preferably insoluble in electrolysis. The reason is as follows. When nickel is used as the anode, for example, nickel anodes will elute nickel into the electrolyte during electrolysis. The amount of nickel electrodeposited at the cathode is less than the amount of nickel eluted at the anode due to gas generation. As a result, the concentration of nickel in the electrolyte increases over time, which hinders the formation of dendrite powder. This inconvenience becomes more prominent as the electrolysis time lengthens. As the insoluble anode, for example, DSE (registered trademark, manufactured by Denora Permelec) can be used.

[0037] As the nickel ion source, water-soluble nickel compounds are preferably used. For example, nickel salts, which are compounds formed by the neutralization of cations and anions, can be mentioned. Such nickel salts include nickel sulfate, nickel chloride, nickel acetate, nickel carbonate, nickel nitrate, etc. These nickel compounds can be used alone or in combination of two or more. Also, by using metallic nickel for the anode electrode, it can be utilized as a nickel ion source. In particular, it is preferable to use nickel chloride or nickel sulfate as the nickel salt.

[0038] When using nickel chloride as the nickel salt, in order to successfully deposit dendrite powder by electrolysis, the current density during electrolysis is 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, even more preferably 1200 A / m 2 or more and 2000 A / m 2 or less, and it is advantageous to set it in this range. On the other hand, when using nickel sulfate as the nickel salt, in order to successfully deposit dendrite powder by electrolysis, the current density during electrolysis is preferably 2200 A / m 2 or more and 9000 A / m 2 or less, more preferably 2500 A / m 25000 A / m or more 2 preferably 2500 A / m or less 2 3500 A / m or more 2 It is advantageous to set it to 3500 A / m or less

[0039] In order to successfully deposit dendrite powder by electrolysis, in addition to making the current density during electrolysis relatively high, 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 electrolyte 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 electrolyte 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 keep the concentration of nickel ions in the electrolyte within the above-mentioned range from the viewpoint of stably generating dendrite powder. For this purpose, when the concentration of nickel ions in the electrolyte significantly decreases, it is preferable to add an appropriate amount of nickel chloride or nickel sulfate to the electrolyte

[0040] From the perspective of successfully depositing dendrite powder by electrolysis, it is preferable to set the pH of the electrolytic solution during electrolysis in the weakly acidic to neutral range. When the pH decreases, the generation of hydrogen gas becomes more likely than the reduction of nickel ions, making it difficult to obtain dendrite powder. From this perspective, when using nickel chloride as the nickel salt, it is preferably maintained at 3 or more and 10 or less, more preferably maintained at 4 or more and 8 or less, and even more preferably maintained at 5 or more and 7 or less during electrolysis. On the other hand, when using nickel sulfate as the nickel salt, it is preferably maintained at 5.5 or more and 10 or less, more preferably maintained at 5.5 or more and 8 or less, and even more preferably maintained at 5.5 or more and 7 or less during electrolysis. For pH adjustment, basic substances such as ammonia can be used, for example. Also, the supporting salts described below can be used for pH adjustment. During electrolysis, it is preferable to keep the pH of the electrolytic solution within the above-mentioned range from the point of stably generating dendrite powder. For this purpose, it is preferable to appropriately add an appropriate amount of pH adjuster to the electrolytic solution during electrolysis.

[0041] It is preferable to add a supporting salt to the electrolytic solution from the perspective of successfully obtaining nickel particles having a dendrite shape and being fine particles. Examples of the supporting salt 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 sulfuric acid such as sodium sulfate and potassium sulfate.

[0042] From the perspective of imparting sufficient conductivity to the electrolytic solution, the concentration of the supporting salt in the electrolytic solution is preferably set at 0.1 mol / L or more and 1.0 mol / L or less, more preferably set at 0.2 mol / L or more and 0.8 mol / L or less, and even more preferably set at 0.3 mol / L or more and 0.5 mol / L or less.

[0043] During electrolysis, heating the electrolyte to maintain it at a predetermined temperature is preferable from the viewpoint of promoting the reduction of nickel ions and successfully obtaining nickel particles that have a dendritic shape and are fine particles. From this viewpoint, regardless of 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 above 50°C and below 90°C, more preferably above 50°C and below 85°C, and even more preferably above 55°C and below 85°C.

[0044] By performing electrolysis for a predetermined time under the above conditions, dendritic particles are deposited on the cathode electrode. The deposited dendritic particles are recovered by scraping them off from the cathode electrode, and dendritic powder, which is a raw material for nickel powder, is obtained.

[0045] The nickel powder of the present invention is suitably 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. By forming a coating film from such a conductive composition and removing the organic solvent from the coating film to obtain a dried body, the dried body can be used as a conductive film. Also, 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 thin the film and easier to smooth the surface of the conductive film compared to the conventional technique of forming a conductive film using dendritic nickel powder. Further, when thinning the conductive film, generally, a large amount of nickel powder needs to be blended in the conductive composition for forming the conductive film. However, when using the nickel powder of the present invention, sufficient conductivity can be exhibited even if the amount of nickel powder blended in the conductive composition is reduced compared to the conventional amount.

Examples

[0046] Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass %”.

[0047] [Example 1] (1) Production of dendrite powder In a 3 L beaker, a SUS316 cathode plate and an insoluble electrode plate DSE (registered trademark, manufactured by Denora Permelec Co., Ltd.) were arranged such that the distance between the electrode plates was 50 mm. The dimensions of both electrode plates were 120 mm × 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 3 L of electrolyte in total. This electrolyte was filled into the above beaker. A DC voltage was applied between the above electrode plates and electrolysis was carried out for 3 minutes. During electrolysis, the electrolyte was heated to maintain the liquid temperature at 60°C. The current density was maintained at 1500 A / m 2 And the pH of the electrolyte was maintained at 6. The dendrite particles deposited on the surface of the cathode plate by electrolysis were scraped off to recover dendrite powder. The recovered dendrite powder was filtered with a Nutsche and then washed successively with pure water and alcohol. Then, it was dried at 80°C for 8 hours in an air atmosphere. The tap density TD of the obtained dendrite powder was 0.8 g / cm 3 And the apparent density AD was 0.6 g / cm 3 The particle size D 50 was 8.0 μm, the residual magnetization was 11.0 A·m 2 / kg, the saturation magnetization was 52.2 A·m 2 / kg, and the coercive force was 17.2 kA / m. (2) Grinding of dendrite powder The dendrite powder was ground dry for 10 minutes using a grinding device (Force Mill, manufactured by Osaka Chemical Co., Ltd., rotation speed 22000 rpm) having a rotating cutting blade to obtain ground nickel powder. The SEM image of the obtained ground nickel powder is shown in Fig. 2.

[0048] [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. The SEM image of the obtained pulverized nickel powder is shown in Figure 3.

[0049] 〔Comparative Example 1〕 Nickel powder composed of substantially spherical nickel particles (manufactured by Stream Chemicals, USA) was used as the nickel powder in this comparative example.

[0050] 〔Comparative Example 2〕 In this comparative example, nickel powder was obtained as follows. First, 445.28 g of ethylene glycol was put into a reaction vessel. Next, 31.31 g of nickel hydroxide, 2.15 g of polyvinylpyrrolidone, and 0.13 mL of a 100 g / L palladium nitrate solution were put into the above 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 with a Nutsche, and then washed successively with pure water and alcohol. Then, it was dried in a shelf vacuum dryer at 80 °C for 8 hours.

[0051] 〔Evaluation 1〕 Regarding the nickel powders obtained in the examples and comparative examples, the tap density TD and the apparent density AD were measured by the above method. Also, the aspect ratio L / W was measured by the above method. Furthermore, the particle size D 50 and the BET specific surface area SSA were measured by the methods described below. Furthermore, the magnetic properties of the nickel powder were measured by the methods described below. Furthermore, the value of SSA×TD / D 50 was calculated by the methods described below. Furthermore, the crystallite size of nickel and the oxygen concentration of the nickel powder were measured by the methods described below. Also, the oxygen content per BET specific surface area was calculated by the methods described below. The results are shown in Table 1 below.

[0052] 〔Particle size D 50 〕 Nickel powder was taken in a small beaker, 2 or 3 drops of 3% Triton X solution (manufactured by Kanto Chemical Co., Inc.) were added, and after allowing the powder to conform, 50 mL of 0.1% SN dispersant 41 solution (manufactured by San Nopco Ltd.) was added. Then, using an ultrasonic disperser TIPφ20 (manufactured by Nippon Seiki Co., Ltd., OUTPUT: 8, TUNING: 5), a dispersion treatment was performed for 2 minutes to prepare a measurement sample. This measurement sample was used with a laser diffraction scattering type particle size distribution measuring device MT3300 (manufactured by Nikkiso Co., Ltd.) to measure the particle size D 50 was measured.

[0053] 〔BET specific surface area SSA〕 Using Monosorb manufactured by Yuasa Ionics Co., Ltd., it was measured by the BET one-point method.

[0054] 〔Magnetic properties〕 A vibrating sample type magnetic measurement device (model: VSM-5, manufactured by Toyo Engineering 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 above device. Measurement was performed while sweeping the magnetic field in the range of ±795.8 kA / m (= ±10 kOe) to create a hysteresis curve. Based on this hysteresis curve, saturation magnetization, residual magnetization, and coercive force were determined.

[0055] 〔SSA×TD / D 50 〕 From the values of the BET specific surface area, tap density TD, and particle size D 50 measured by the above method, the values of SSA×TD / D 50 were calculated respectively.

[0056] 〔Crystallite size〕 Regarding the nickel powder obtained in the examples and comparative examples, X-ray diffraction measurement was performed using a RINT2000 X-ray diffractometer manufactured by Rigaku Corporation. Using the obtained diffraction peaks, the crystallite size was calculated by the Scherrer method. The X-ray diffraction conditions were 2θ / θ = 5 to 80 deg, step width = 0.01 deg, scan speed = 0.2 deg / min, characteristic X-ray = Cu-Kα1 line, and a 1D detector. The crystallite size was calculated from the half-width of the peak of Ni(111), adopting 0.94 as the Scherrer constant.

[0057] 〔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 thereby was measured by the non-dispersive infrared absorption method to measure the oxygen concentration (mass%).

[0058] 〔Oxygen Amount per BET Specific Surface Area〕 From the oxygen concentration measured by the above method and the value of the BET specific surface area measured by the above method, the oxygen content per BET specific surface area was calculated.

[0059] 〔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). The mixing ratio was such that the nickel powder was 80% with respect to the silicone sealant. Furthermore, toluene having the same mass as the mass of the nickel powder was added, and the obtained mixture was sufficiently mixed using a mixer (Avatotorentaro (registered trademark), model number AR-100) manufactured by Shin-Kee Co., Ltd. to prepare a paste. This paste was coated on a glass plate and dried at 180 °C for 3 hours in the air to obtain a conductive film. Regarding this conductive film, the electrical resistance was measured by the four-probe method using a resistivity measuring instrument (manufactured by Mitsubishi Chemical Corporation, MCP-T600). Also, the thickness of the conductive film was measured using a micrometer, and the specific resistance (Ω·cm) = width (cm) × thickness (μm) × electrical resistance (Ω) / (length (cm) × 10 4The resistivity of the conductive film was calculated from the formula in (0). The results are shown in Table 1 below. The thickness of the conductive film is also shown in the same table.

[0060]

Table 1

[0061] As shown in Table 1, it can be seen that the conductive films obtained in each example exhibit sufficient conductivity even when the blending amount of nickel powder is relatively small, i.e., 80%. In contrast, in the conductive films obtained in Comparative Examples 1 and 2, sufficient conductivity was not exhibited due to the small blending amount of nickel powder.

Claims

1. The residual magnetization is 7.0 A·m ２ / kg or more, and Volume cumulative particle size D at 50% volume in the cumulative volume by the laser diffraction scattering particle size distribution measurement method ５０ (μm) is 1.0 μm or more and 5.0 μm or less, 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, and When the BET specific surface area is SSA (m ２ / g), nickel powder in which the value defined by SSA × TD / D ５０ is 0.5 or more.

2. The residual magnetization is 10 A·m ２ / kg or more, the nickel powder according to claim 1.

3. The saturation magnetization is 10 A·m ２ / kg or more, the nickel powder according to claim 1 or 2.

4. 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.

5. The above-mentioned D ５０ is 1.5 μm or more and 5.0 μm or less, and the nickel powder according to any one of claims 1 to 4.

6. The SSA is 1.0 m ２ / g or more and 3.0 m ２ / g or less. The nickel powder according to any one of claims 1 to 5

7. The oxygen content per SSA is 0.5% by mass / (m ２ / g) or less, the nickel powder according to any one of claims 1 to 6.

8. 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, and The nickel powder according to any one of Claims 1 to 7, wherein the value of AD / TD, which is the ratio of AD to TD, is 0.73 or more and 0.93 or less.

9. A conductive composition comprising the nickel powder according to any one of Claims 1 to 8 and an organic solvent.

10. A conductive film comprising a dried product of the conductive composition according to Claim 9.

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