Copper powder and method for manufacturing the same

Abstract

The copper powder of this invention is composed of multiple copper particles having different aspect ratios. The tap density is 4.0 g / cm³. 3 Above and 7.0 g / cm 3 The following is a table showing the standard deviation SD of particle size distribution determined using laser diffraction scattering particle size distribution method, relative to the volumetric cumulative particle size D at 50% of the cumulative volume. 50 The ratio is the dispersion D P The value is 0.55 or higher and 0.90 or lower. Preferably, the average aspect ratio of the copper particles is 1.05 or higher and 3.00 or lower. Preferably, the average roundness is 0.60 or higher and 0.95 or lower. Preferably, the percentage of copper particles with a roundness exceeding 0.95 is 5.0% or lower. Preferably, the proportion of copper particles with a roundness exceeding 0.70 but below 0.95 is greater than the proportion of copper particles with a roundness below 0.70.

Description

Technical Field

[0001] This invention relates to copper powder and its manufacturing method. Background Technology

[0002] Copper is a highly conductive metal and a versatile material, making it widely used in industry as a conductive material. For example, copper powder, as an aggregate of copper particles, is widely used as a raw material for various electronic components, such as external electrodes in multilayer ceramic capacitors (MLCCs) and wiring on various substrates.

[0003] For example, the applicant previously proposed a flattened copper powder by plastic deformation of the copper powder particles (see Patent Document 1). The standard deviation SD and cumulative weight particle size D of this flattened copper powder were measured by a laser diffraction scattering particle size distribution method. 50 SD / D representation 50 The value is below 0.55, and the particle size D is accumulated by weight. 90 / cumulative particle size D 10 The value is 4.5 or less, and the aspect ratio is 3 to 200. This flat copper powder is manufactured as follows: copper powder in an aggregated state is degranulated, and copper powder particles with an aggregation degree of 1.6 or less after degranulation are used. Media beads with a particle size of 0.5 mm or less are used to compress the copper powder particles in a high-energy ball mill to plastically deform them, thereby forming a flat shape.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: US2006 / 0137488 A1 Summary of the Invention

[0007] Flat copper powder has lower filling capacity compared to spherical copper powder, which is easier to fill densely. Therefore, the sintered film formed by sintering flat copper powder is less dense than that formed by sintering spherical copper powder. In addition, flat copper powder obtained by mechanical processing has lower crystallinity than spherical copper powder and tends to be easier to sinter.

[0008] For example, in the case of sintering with a binder, such as in MLCCs, sintering copper powder can lead to gas leakage, resulting in cracks and voids. Therefore, it is desirable to avoid interparticle sintering during the binder removal process. Furthermore, at high sintering temperatures, it is difficult to obtain a dense sintered film. For these reasons, copper powder that can be sintered within a suitable temperature range is ideal.

[0009] Therefore, the objective of this invention is to provide copper powder and a method for manufacturing the same, wherein the copper powder does not sinter in the binder removal process and can form a dense sintered film by, for example, low-temperature sintering at about 800°C.

[0010] This invention provides a copper powder composed of multiple copper particles having different aspect ratios.

[0011] The tap density of the copper powder is 4.0 g / cm³. 3 Above and 7.0 g / cm 3 the following,

[0012] The standard deviation SD of the particle size distribution of the copper powder determined by laser diffraction scattering particle size distribution method is relative to the volumetric cumulative particle size D at 50% of the cumulative volume. 50 The ratio is the dispersion D. P The value is above 0.55 and below 0.90.

[0013] In addition, the present invention provides a method for manufacturing copper powder, which includes the following steps: using a media stirring mill to plastically deform raw material powder composed of copper particles into a flat shape.

[0014] The material to be processed, which is composed of a slurry containing the aforementioned raw material powder, passes through the aforementioned media stirred mill apparatus of the material-passing type only once. Attached Figure Description

[0015] Figure 1 (a) to Figure 1 (d) is a schematic diagram illustrating the method for determining the aspect ratio of copper particles in copper powder according to the present invention.

[0016] Figure 2 (a) is a cross-sectional image of the coating obtained using the copper powder obtained in Example 1. Figure 2 (b) is a cross-sectional image of the coating obtained using the copper powder obtained in Comparative Example 2.

[0017] Figure 3 (a) is a distribution diagram made by taking the minor axis of the copper particles in the copper powder obtained in Example 1 on the horizontal axis and the roundness of the copper particles on the vertical axis. Figure 3 (b) is a distribution diagram of Example 2. Figure 3 (c) is the distribution diagram of Example 3. Figure 3 (d) is the distribution diagram of Example 4. Figure 3 (e) is the distribution of Comparison Example 1. Figure 3 (f) is the distribution diagram of Comparative Example 2.

[0018] Figure 4(a) is a distribution diagram made by taking the minor axis of the copper particles in the copper powder obtained in Example 1 on the horizontal axis and the aspect ratio of the copper particles on the vertical axis. Figure 4 (b) is a distribution diagram of Example 2. Figure 4 (c) is the distribution diagram of Example 3. Figure 4 (d) is the distribution diagram of Example 4. Figure 4 (e) is the distribution of Comparison Example 1. Figure 4 (f) is the distribution diagram of Comparative Example 2. Detailed Implementation

[0019] The present invention will now be described based on its preferred embodiments. The copper powder of the present invention is composed of a plurality of copper particles. The copper particles are preferably particles substantially composed of copper element, or copper-based alloy particles. The copper powder is preferably composed of an aggregate of such particles.

[0020] The former refers to particles that are essentially composed of copper, with the remainder containing unavoidable elements. In this case, the copper particles are ideally composed solely of copper, but trace amounts of unavoidable elements are permissible. When unavoidable elements are present in the copper particles, it is preferable that the content of these unavoidable elements be 1% by mass or less, from the perspective of not easily impairing the original properties of the copper particles and imparting suitable properties to the copper powder composed of these particles. Unavoidable elements include, for example, O (oxygen) and C (carbon) elements derived from atmospheric oxygen and carbon dioxide, and N (nitrogen) elements that may sometimes be introduced during the manufacturing process of copper particles. The presence and content of unavoidable elements can be determined, for example, through gas analysis.

[0021] In the case of the latter type of particles, the proportion of copper in the particles is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0022] One of the characteristics of the copper powder of the present invention is its high density.

[0023] In the past, when sintering copper powder to produce sintered films, it was desirable for the copper particles constituting the copper powder to have a uniform shape in order to obtain a sintered film that suppressed quality fluctuations. However, there are limits to the degree to which conventional copper powder can improve density, making it difficult to achieve the density required in recent years.

[0024] Regarding this improvement, the inventors conducted in-depth research and discovered that by ensuring a predetermined distribution of the shape and size of the copper particles constituting the copper powder, the copper particles can be densely packed, minimizing the gaps between them, thus improving the density of the copper powder and consequently enhancing the density of the sintered film manufactured by sintering the copper powder. Furthermore, it was found that copper powder with a predetermined distribution of the shape and size of the copper particles, compared to conventional flat copper powder, suppresses particle shape deformation and crystal strain caused by processing. This suppresses the formation of active sites that are prone to sintering (i.e., sintering active sites), resulting in sinterability to the point that sintering does not occur during the binder removal process. Therefore, for example, in the case of manufacturing the external electrode of an MLCC using copper powder, the dry film containing copper powder and resin is difficult to sinter during the binder removal process, thus reducing the likelihood of cracks and voids forming. In the subsequent sintering process, a highly dense sintered film can be obtained.

[0025] Specifically, the copper particles preferably have a flat shape. In this specification, "flat" has the same meaning as "flake-like" or "scaly," referring to particles with a plate-like shape. Spherical copper particles are permissible in the copper powder.

[0026] The flatness of copper particles is determined by their aspect ratio and roundness. In the copper powder of this invention, when the flatness of copper particles exhibits a distribution, this distribution can be defined by the distribution of roundness. Details regarding the distribution of the flatness of copper particles will be described later.

[0027] like Figure 1 (a) to Figure 1 As shown in (d), the aspect ratio refers to the rectangle S with the smallest area among all rectangles S circumscribed around particle P in a cross-section of particle P (see reference). Figure 1 When the long side of rectangle S is set as the major axis W1 and the short side of rectangle S is set as the minor axis W2, the value is defined by the ratio of major axis W1 to minor axis W2 (major axis W1 / minor axis W2). As described below, when the raw material powder is preferably spherical, in the case of manufacturing the copper powder of the present invention using the raw material powder, an aspect ratio close to 1 means that the shape of the copper particles is close to a sphere. From the viewpoint that a dense sintered film can be formed by improving the density of the copper powder, for example by low-temperature firing at about 800°C, the average aspect ratio of the copper particles (hereinafter also referred to as "average aspect ratio") is preferably 1.05 or more, more preferably 1.20 or more, and even more preferably 1.40 or more. From the same viewpoint, the average aspect ratio of the copper particles is preferably 3.00 or less, more preferably 2.70 or less, and even more preferably 2.40 or less. In the following description, firing at about 800°C is also referred to as "low-temperature firing".

[0028] The major diameter W1 and minor diameter W2 of the copper particles can be appropriately set in a manner that has the above-mentioned average aspect ratio.

[0029] The average aspect ratio can be determined using the following method. Specifically, first, at least three fields of view are captured using a scanning electron microscope (SEM) at magnification, showing the cross-sections of at least 50 copper particles as the measurement targets. Next, at least 300 copper particles whose outlines can be clearly identified are randomly selected from each image data, and the major axis W1 and minor axis W2 values ​​are measured for each selected copper particle. The ratio of major axis W1 to minor axis W2 is calculated based on these values. This calculated value is used as the average aspect ratio in this specification.

[0030] The detailed method for measuring the average aspect ratio is also described in the examples described later.

[0031] When the copper powder of the present invention preferably contains copper particles with an aspect ratio within a specified range, it is preferable that one or more copper particles have different aspect ratios from each other. From the viewpoint that a dense sintered film can be formed by low-temperature sintering by improving the density of the copper powder, it is particularly preferable that the aspect ratio of the multiple copper particles in the copper powder varies continuously.

[0032] In the copper powder of the present invention, the shape distribution of copper particles is also characterized by the sphericity distribution of the copper particles. The term "sphericity" here refers to a value calculated based on equation (1) described later. As will be described later, when the raw material powder is preferably spherical, in the case of manufacturing the copper powder of the present invention using the raw material powder, a sphericity close to 1 means that the shape of the copper particles is close to that of a sphere. Based on this sphericity, it is possible to specify what shape of copper particles is distributed to what extent.

[0033] From the viewpoint that a dense sintered film can be formed by low-temperature sintering by improving the density of copper powder, the average sphericity of the copper powder (hereinafter also referred to as "average sphericity") is preferably 0.95 or less, more preferably 0.90 or less, and even more preferably 0.85 or less. From the same viewpoint, the average sphericity of the copper powder is preferably 0.60 or more, more preferably 0.65 or more, and even more preferably 0.70 or more.

[0034] In the copper powder of the present invention, the shape distribution of copper particles is also characterized by the distribution of the number frequency of copper particles relative to their roundness. Preferably, the distribution map of the copper powder of the present invention, with the roundness of the copper particles on the horizontal axis and the number frequency of the copper particles on the vertical axis, is depicted as convex upwards in a predetermined shape. In other words, in the copper powder, it is particularly preferred that copper particles with a predetermined roundness are distributed according to a predetermined number frequency.

[0035] Specifically, from the viewpoint of suppressing the formation of sintering active sites, preventing sintering during the binder removal process, and enabling the formation of a dense sintered film through low-temperature sintering, the proportion of copper particles with a sphericity exceeding 0.95 in the copper powder is preferably 5.0% or less, more preferably 4.0% or less, and even more preferably 3.0% or less. A sphericity exceeding 0.95 means that the copper particles are extremely close to spheres. From the viewpoint of making the above effect more significant, the lower the proportion of copper particles with a sphericity exceeding 0.95, the better, but it can also be 0.1% or more.

[0036] Furthermore, from the viewpoint that a dense sintered film can be formed by low-temperature sintering by improving the density of copper powder, it is preferable that the copper powder contains more copper particles with larger sphericity than copper particles with smaller sphericity. This is because by distributing the copper powder in this way, the copper particles can be densely packed, the gaps between the copper particles can be minimized as much as possible, the density of the copper powder can be improved, and thus the density of the sintered film manufactured by sintering the copper powder can be improved.

[0037] From the viewpoint that a dense sintered film can be formed by low-temperature firing by improving the density of copper powder, it is preferable that the proportion of copper particles with a sphericity greater than 0.70 and less than 0.95 is greater than the proportion of copper particles with a sphericity less than 0.70 in the copper powder.

[0038] Furthermore, in the copper powder, the ratio of the number of copper particles with a sphericity greater than 0.70 and less than 0.95 to the number of copper particles with a sphericity of less than 0.70 (hereinafter also referred to as "ratio A") is preferably a predetermined value or higher. Specifically, from the viewpoint that a dense sintered film can be formed by low-temperature sintering by improving the density of the copper powder, ratio A is preferably 1.10 or higher, more preferably 1.30 or higher, and even more preferably 1.50 or higher. From the viewpoint that the above effect is more significant, a larger ratio A is more preferred, but it can also be 8.00 or lower.

[0039] As described above, it is preferable to include more copper particles with larger sphericity than copper particles with smaller sphericity. However, from the viewpoint of imparting high filling properties to the copper powder of the present invention, it is preferable that the proportion of copper particles with a sphericity greater than 0.70 and less than 0.95 is within a specified range. From the viewpoint of making this advantage more significant, with the value of ratio A within the above-described range, the proportion of copper particles with a sphericity greater than 0.70 and less than 0.95 is preferably 50.0% or more, more preferably 55.0% or more, and even more preferably 60.0% or more. From the same viewpoint, with the value of ratio A within the above-described range, the proportion of copper particles with a sphericity greater than 0.70 and less than 0.95 is preferably 95.0% or less, more preferably 90.0% or less, and even more preferably 85.0% or less.

[0040] Furthermore, from the viewpoint of imparting high filling properties to the copper powder of the present invention, it is also preferable that the proportion of copper particles with a sphericity of 0.70 or less is within a specified range. From the viewpoint of making this advantage more significant, provided that the ratio A is within the above-mentioned range, the proportion of copper particles with a sphericity of 0.70 or less is preferably 1.0% or more, more preferably 5.0% or more, and even more preferably 10.0% or more. Similarly, provided that the ratio A is within the above-mentioned range, the proportion of copper particles with a sphericity of 0.70 or less is preferably 45.0% or less, more preferably 40.0% or less, and even more preferably 35.0% or less.

[0041] The roundness of the copper particles was calculated using the following method. First, at least three fields of view were captured using SEM at a magnification of at least 50 cross-sections of copper particles as the measurement targets. Next, 300 non-overlapping copper particles were randomly selected from each image data. With the area of ​​the two-dimensional projection image of the copper particle cross-section set as S and the perimeter set as L, the roundness of the copper particle cross-section was calculated based on the following formula (1). The arithmetic mean of the roundness of each copper particle cross-section was taken as the roundness. When the two-dimensional projection image of the copper particle was a perfect circle, the roundness of the copper particle was 1.

[0042] 4πS / L 2 …(1)

[0043] Detailed methods for measuring roundness are also described in the examples described later.

[0044] In order to make the sphericity and distribution of the copper powder within the above-mentioned range, it is preferable, for example, to flatten the raw material powder by the manufacturing method described later.

[0045] The copper powder of the present invention preferably has a bulk density within a specified range. In other words, the copper particles in the copper powder preferably have few gaps between each other, i.e., high density. By using such copper powder, a dense sintered film can be formed by low-temperature sintering.

[0046] Specifically, from the viewpoint that a dense sintered film can be formed through low-temperature firing, the tap density of copper powder is preferably 4.0 g / cm³. 3 The above is further optimized to 4.2 g / cm³. 3 The above, and more preferably 4.4 g / cm³ 3 That's all. Furthermore, from the same perspective, the preferred tap density of the copper powder is 7.0 g / cm³. 3 The following is a further preferred value: 6.5 g / cm³ 3 The preferred value is 6.0 g / cm³. 3 the following.

[0047] Copper powder with such tap density can be suitably manufactured by the manufacturing method described later.

[0048] In this specification, "tap density" refers to the value measured according to JIS Z2512. Detailed methods for determining tap density are described in the examples described later.

[0049] The copper powder of the present invention is preferably composed of copper particles having different particle sizes. In other words, the copper particles in the copper powder preferably have a wide particle size distribution. This allows the copper particles to be densely packed, minimizing the gaps between the copper particles and improving the density of the copper powder. As a result, a dense sintered film can be formed by low-temperature sintering.

[0050] In copper powder, copper particles exhibit a wide particle size distribution, which can be determined by the standard deviation SD (μm) of the particle size distribution relative to the volumetric cumulative particle size D at 50% of the cumulative volume, using a laser diffraction scattering particle size distribution method. 50 (μm) (hereinafter also referred to as "particle size D") 50 The ratio of ) to the dispersion D P To define. Specifically, from the viewpoint that a dense sintered film can be formed by low-temperature sintering by improving the density of copper powder, the dispersion D P The value of is preferably 0.55 or higher, more preferably 0.60 or higher, and even more preferably 0.65 or higher. From the same perspective, the dispersion D P The value is preferably 0.90 or less, more preferably 0.89 or less, and even more preferably 0.88 or less.

[0051] Particle size D 50 The determination method is described in the examples described later.

[0052] As described above, copper particles preferably have a wide particle size distribution, but from the perspective of suppressing the formation of sintering active sites and imparting sinterability to the copper powder of the present invention to a degree that prevents sintering during the binder removal process, a particle size D is preferred. 50 Within the specified range. From the perspective of making this advantage more significant, the dispersion D... P Given that the value is within the above range, the particle size D of the copper powder 50 Preferably, the micrometer size is 2.00 μm or larger, more preferably 2.50 μm or larger, and even more preferably 3.00 μm or larger. Furthermore, the dispersion D... P Given that the value is within the above range, the particle size D 50 Preferably, it is 8.00 μm or less, more preferably 7.00 μm or less, and even more preferably 6.00 μm or less.

[0053] In the copper powder of the present invention, the dispersion D P Given that the value is within the above-mentioned range, the standard deviation SD of the particle size distribution is preferably 1.00 μm or more, more preferably 1.50 μm or more, and even more preferably 2.00 μm or more. Furthermore, the dispersion D... P Given that the value is within the above range, the standard deviation SD of the particle size distribution is preferably 6.00 μm or less, more preferably 5.00 μm or less, and even more preferably 4.00 μm or less.

[0054] By keeping the standard deviation of particle size distribution (SD) within the above range, the formation of sintering active sites can be suppressed. As a result, a dense sintered film can be formed without sintering during the binder removal process and by low-temperature firing.

[0055] The method for determining the standard deviation (SD) of particle size distribution is described in the examples described later.

[0056] In the copper powder of the present invention, the distribution of copper particles with a specified sphericity at a specified frequency and the wide particle size distribution of the copper particles can also be specified by the product of the number ratio of the sphericity of the copper particles and the particle size. Specifically, it is preferable that the number ratio of copper particles with a sphericity of 0.70 or less and the cumulative particle size D at 90% of the cumulative volume using the laser diffraction scattering particle size distribution measurement method are... 90 (μm) (hereinafter also referred to as "particle size D") 90 The product of P) 90 The value of (number % μm) is within the specified range.

[0057] From the perspective of suppressing the formation of sintering active sites, avoiding sintering during the binder removal process, and forming a dense sintered film through low-temperature firing, the accumulated P 90Preferably, it is 500%·μm or less, more preferably 450%·μm or less, and even more preferably 400%·μm or less. Product P 90 A small value for P indicates that the particle flattening is not significant. 90 A larger value for P indicates a greater degree of particle flattening. From the perspective of making the above effect more significant, the product P... 90 The smaller the value, the better, but it can also be above 100%·μm.

[0058] Particle size D 90 The determination method is described in the examples described later.

[0059] In the copper powder of the present invention, the distribution of copper particles with a specified sphericity at a specified number frequency, and the wide particle size distribution of the copper particles, can also be specified by the product of sphericity and particle size, which is different from the above-mentioned sphericity and particle size. Specifically, it is preferable that the ratio of the number of copper particles with a sphericity greater than 0.70 and less than 0.95 is equal to the particle size D. 50 Product of (μm) P 50 The value of (number % μm) is within the specified range.

[0060] From the perspective of suppressing the formation of sintering active sites, avoiding sintering during the binder removal process, and forming a dense sintered film through low-temperature firing, the accumulated P 50 Preferably, it is 180%·μm or more, more preferably 200%·μm or more, and even more preferably 220%·μm or more. From the same point of view, the product P... 50 Preferably, it is 400%·μm or less, more preferably 350%·μm or less, and even more preferably 300%·μm or less. Product P 50 A value within the above range means that although the particle shape is deformed (e.g., flattened), the degree is not significant.

[0061] In the copper powder of the present invention, the distribution of copper particles with a specified sphericity at a specified number frequency, and the wide particle size distribution of the copper particles, can also be specified by the product of sphericity and particle size, which are further different from the aforementioned sphericity and particle size. Specifically, it is preferable that the proportion of copper particles with a sphericity exceeding 0.95 is equal to the cumulative particle size D at 10% of the cumulative volume using a laser diffraction scattering particle size distribution determination method. 10 (μm) (hereinafter also referred to as "particle size D") 10 The product of P) 10 The value of (number % μm) is within the specified range.

[0062] From the perspective of suppressing the formation of sintering active sites, avoiding sintering during the binder removal process, and forming a dense sintered film through low-temperature firing, the accumulated P 10 Preferably, it is 0.1%·μm or more, more preferably 0.2%·μm or more, and even more preferably 0.3%·μm or more. Product P 10 A value above the aforementioned value indicates that the degree of particle flattening is not significant. From the perspective of making the above effect more pronounced, the product P... 10 The larger the value, the better, but it can also be below 3.5%·μm.

[0063] Particle size D 10 The determination method is described in the examples described later.

[0064] In the copper powder of this invention, the particle size D 10 and particle size D 90 Preferably, the particle sizes are within a specified range. By giving the copper particles a wide particle size distribution and keeping these particle sizes within a specified range, the formation of sintering active sites can be suppressed, thus imparting to the copper powder of the present invention a degree of sinterability that prevents sintering during the binder removal process.

[0065] From the perspective of making the above advantages more significant, with the product P 10 Given that the value is within the above range, the particle size D of the copper powder 10 Preferably, it is 0.4 μm or more, more preferably 0.7 μm or more, and even more preferably 1.0 μm or more. From the same point of view, with the product P... 10 Given that the value is within the above range, the particle size D of the copper powder 10 Preferably, it is 4.0 μm or less, more preferably 3.0 μm or less, and even more preferably 2.0 μm or less.

[0066] From the perspective of making the above advantages more significant, with the product P 90 Given that the value is within the above range, the particle size D of the copper powder 90 Preferably, it is 4.0 μm or more, more preferably 5.0 μm or more, and even more preferably 6.0 μm or more. From the same point of view, with the accumulation P... 90 Given that the value is within the above range, the particle size D of the copper powder 90 Preferably, it is 16.0 μm or less, more preferably 14.0 μm or less, and even more preferably 12.0 μm or less.

[0067] To improve the particle size and dispersion D of copper powder P The value, and the product P 90 , P 50 Sum of products P 10 The value is within the above range, for example, the raw material powder is preferably flattened by the manufacturing method described later.

[0068] From the viewpoint that a dense sintered film can be formed by low-temperature sintering by improving the density of the copper powder, it is preferable that there is a predetermined relationship between the minor axis of the copper particles constituting the copper powder and the roundness of the copper particles. Specifically, it is preferable that the roundness of the copper particles has a small dependence on the minor axis of the copper particles.

[0069] Figure 3 (a) to Figure 3 (f) is a distribution diagram of the copper powder obtained in Examples 1 to 4 and Comparative Examples 1 and 2 described later, with the horizontal axis representing the minor axis of the copper particles and the vertical axis representing the roundness of the copper particles. Figure 3 (a) to Figure 3 As shown in (d), in the copper powder of the embodiment, regardless of the distribution of the minor axis of the copper particles, the roundness of the copper particles is generally concentrated within a certain value or a range with a certain width. In contrast, in the copper powder of the comparative example, although the roundness of the copper particles takes various values, the minor axis of the copper particles is generally concentrated within a certain value or a range with a certain width. Therefore, it can be understood that the copper powder of the present invention takes various roundness values ​​regardless of the value of the minor axis of the copper particles.

[0070] In order to give the copper powder of the present invention such a relationship, it is preferable, for example, to flatten the raw material powder by the manufacturing method described later.

[0071] Furthermore, from the viewpoint that a dense sintered film can be formed by low-temperature sintering by improving the density of copper powder, the copper powder of the present invention preferably has a predetermined relationship between the minor axis of the copper particles constituting the copper powder and the aspect ratio of the copper particles. Specifically, it is preferable that the aspect ratio of the copper particles has a small dependence on the minor axis of the copper particles.

[0072] Figure 4 (a) to Figure 4 (f) is a distribution diagram of the copper powder obtained in Examples 1 to 4 and Comparative Examples 1 and 2 described later, with the horizontal axis representing the minor axis of the copper particles and the vertical axis representing the aspect ratio of the copper particles. Figure 4 (a) ~ Figure 4 As shown in (d), in the copper powder of the embodiment, regardless of the distribution of the minor axis of the copper particles, the aspect ratio of the copper particles is generally concentrated in a certain value or within a certain width range. In contrast, in the copper powder of the comparative example, although the aspect ratio of the copper particles takes various values, the minor axis of the copper particles is generally concentrated in a certain value or within a certain width range. Therefore, it can be understood that the copper powder of the present invention takes various aspect ratios regardless of the value of the minor axis of the copper particles.

[0073] In order to give the copper powder of the present invention such a relationship, it is preferable, for example, to flatten the raw material powder by the manufacturing method described later.

[0074] Furthermore, regarding the copper powder of the present invention, from the viewpoint that a dense sintered film can be formed by low-temperature sintering by improving the density of the copper powder, it is also preferable that the aspect ratio and particle size of the copper particles constituting the copper powder have a predetermined relationship. Specifically, in a distribution map prepared with the image resolution particle size of the copper particles on the horizontal axis and the aspect ratio of the copper particles on the vertical axis, it is preferable that there is a positive correlation between the aspect ratio and the image resolution particle size of the copper particles. In other words, it is preferable that the larger the particle size of the copper particles, the larger the aspect ratio. By making the copper powder have this relationship, the gaps between copper particles with both small aspect ratios and large image resolution particle sizes can be filled with copper particles with small aspect ratios and small image resolution particle sizes, thus further improving the density of the copper powder.

[0075] In this specification, "image resolution particle size" refers to the major diameter W1 of the copper particle as measured by the aspect ratio determination method described above.

[0076] As described above, the copper powder of the present invention has high density and sinterability to the extent that sintering does not occur during the binder removal process. The degree of such sinterability can be evaluated by thermomechanical analysis of the copper powder. Here, when performing thermomechanical analysis under a nitrogen atmosphere and a heating rate of 10°C / min, the temperature at which the copper powder shrinks by 10% relative to its maximum shrinkage rate is defined as the shrinkage initiation temperature. From the viewpoint of imparting sinterability to the copper powder to the extent that sintering does not occur during the binder removal process, the shrinkage initiation temperature of the copper powder is preferably 500°C or higher, more preferably 515°C or higher, and even more preferably 530°C or higher. From the viewpoint of making the above effects more significant, a higher shrinkage initiation temperature is more preferred; however, in the case of using it as an external electrode for MLCCs, it is preferable to have a temperature close to that of the glass powder used with the copper powder of the present invention for manufacturing the external electrode.

[0077] The method for determining the shrinkage initiation temperature is described in the examples described later.

[0078] Next, a preferred method for manufacturing the copper powder of the present invention will be described. The manufacturing method of the present invention includes a step of plastically deforming the raw material powder into a flat shape.

[0079] First, prepare the raw material powder. The raw material powder consists of copper particles. The shape of the raw material powder can be spherical, polyhedral, spindle-shaped, or amorphous. From the viewpoint that copper powder with an aspect ratio and roundness within the above-mentioned range can be obtained smoothly through the flattening operation described later, it is preferable to use raw material powder composed of spherical copper particles.

[0080] Using raw material powder whose physical properties are within the specified range can readily produce copper powder with physical properties such as aspect ratio, roundness, and particle size that are within the aforementioned range, and is therefore preferred.

[0081] Regarding the particle size D of the raw material powder 50 From the above perspective, it is preferable to use raw material powder with a particle size of 1.0 μm or larger. Similarly, it is preferable to use a particle size D. 50 It is a raw material powder with a particle size of less than 10.0 μm.

[0082] Regarding the standard deviation (SD) of the particle size distribution of the raw material powder, from the above perspective, it is preferable to use raw material powder with a particle size distribution of 0.5 μm or larger. Similarly, it is preferable to use raw material powder with a particle size distribution standard deviation (SD) of 10.0 μm or smaller.

[0083] Raw material powders with these physical properties can be obtained, for example, by atomization methods such as gas atomization and water atomization, as well as plasma methods. Alternatively, they can be readily obtained by a wet reduction method, in which an aqueous solution of copper salt reacts with an alkaline agent to precipitate copper hydroxide, which is then reduced to cuprous oxide in a liquid in a single step, and the cuprous oxide is further reduced to metallic copper in a liquid in a second step. From the viewpoint of readily obtaining copper powder with aspect ratio, sphericity, and particle size within the aforementioned ranges, it is preferable to use raw material powder containing a large number of spherical copper particles, i.e., raw material powder obtained by a wet reduction method.

[0084] After preparing the raw material powder, prepare the workpiece containing the raw material powder. The workpiece consists of a slurry containing the raw material powder and a liquid medium. Examples of liquid media include water and organic solvents. A mixture of water and organic solvents may also be used. Examples of organic solvents include aliphatic alcohols with 1 to 22 carbon atoms. These organic solvents may be used alone or in combination of two or more. From the viewpoint of improving the dispersibility of the raw material powder in the workpiece and improving the stability of the quality during the flattening operation, organic solvents are preferred. From the viewpoint of easy volatilization of the medium and that the medium is less likely to remain on the target copper powder, monoalkyl alcohols with 1 to 4 carbon atoms are preferred. Examples of such alcohols include methanol, ethanol, n-propanol, sec-propanol, n-butanol, sec-butanol, and tert-butanol.

[0085] Depending on the requirements, the processed material may also contain additives such as lubricants. Lubricants have the properties of inhibiting particle aggregation, reducing friction between particles, and facilitating sliding. Examples of lubricants include carboxylic acids such as citric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, oleic acid, and stearic acid. These additives can be used alone or in combination of two or more. From the viewpoint of effectively flattening relatively monodisperse particles and effectively reducing the proportion of copper particles that are extremely close to spherical in shape, such as copper particles with a sphericity exceeding 0.95, it is preferable to use lubricants, and stearic acid is particularly preferred.

[0086] To prepare the material to be processed, the raw material powder and liquid medium are simply mixed with the desired additives. Depending on the circumstances, a stirring and dispersing device can also be used to prepare the dispersion. Examples of such devices include fluid mills and TKFILMIX (registered trademark) manufactured by PRIMIX Corporation.

[0087] From the viewpoint of facilitating the plastic deformation of the raw material powder, the concentration of the raw material powder in the processed material is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. Similarly, from the same viewpoint, the concentration of the raw material powder in the processed material is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0088] When the workpiece contains a lubricant, from the viewpoint of smoothly obtaining copper powder with aspect ratio, roundness, and particle size within the aforementioned ranges, the lubricant content in the workpiece is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.08% by mass or more, relative to the copper particle content in the raw material powder. From the viewpoint of suppressing sintering defects caused by lubricant residue, the lubricant content in the workpiece is preferably 1.0% by mass or less, more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less, relative to the copper particle content in the raw material powder.

[0089] After the preparation of the workpiece is completed, the raw material powder composed of copper particles in the workpiece is plastically deformed into a flat shape. Flattening of the raw material powder can be performed, for example, by a media stirring mill such as a bead mill, ball mill, or grinding mill. From the viewpoint of successfully obtaining copper powder with aspect ratio, roundness, and particle size within the aforementioned ranges, it is preferable to use a device that applies relatively low stress to the raw material powder in the workpiece. By performing this treatment, the raw material powder can be flattened without excessively changing the aspect ratio, roundness, and particle size originally possessed by the raw material powder composed of copper particles. Therefore, the original properties of the copper particles are not easily damaged, and copper powder with high density can be successfully obtained. In particular, copper particles with various roundness and aspect ratios and copper powder composed of such copper particles can be successfully obtained without excessively deforming the original shape (e.g., spherical) of the raw material powder. Furthermore, the formation of active sites that serve as the starting point for sintering can be suppressed, imparting sinterability to the extent that sintering does not occur during the binder removal process.

[0090] Media stirred mills, which apply relatively low stress to the raw material powder in the processed material, include, for example, processed material pass-through type (so-called through-type) devices. Media stirred mills generally employ processed material pass-through type, processed material multi-pass type, and circulating type operation methods. The circulating type is a device that flattens the processed material while circulating it within the device, making it difficult to adjust the stress applied to the raw material powder. In contrast, the processed material pass-through type and processed material multi-pass type are devices that flatten the processed material by setting the number of times it passes through the device, making it easy to adjust the stress applied to the raw material powder. From the viewpoint of flattening the raw material powder with relatively low stress, processed material pass-through type devices are particularly preferred. As such a device, the Star Mill (registered trademark) LMZ10 bead mill manufactured by Ashizawa Finetech Ltd. can be used, for example.

[0091] From the perspective of not easily damaging the original properties of copper particles, smoothly obtaining copper powder with high density, and suppressing the formation of sintering active sites, and imparting sinterability to the extent that sintering does not occur in the binder removal process, it is most preferable to flatten the workpiece by passing it only once in a workpiece-through type media stirring mill.

[0092] In this case, from the viewpoints of not easily damaging the original properties of copper particles, smoothly obtaining copper powder with high density, and suppressing the formation of sintering active sites to impart sinterability to the extent that sintering does not occur during the binder removal process, the circumferential speed of the mill is preferably 4 m / s or more, more preferably 6 m / s or more, and even more preferably 8 m / s or more. From the same viewpoint, the circumferential speed of the mill is preferably 20 m / s or less, more preferably 17 m / s or less, and even more preferably 14 m / s or less.

[0093] From the perspective of preserving the original properties of copper particles, smoothly obtaining highly dense copper powder, and suppressing the formation of sintering active sites to impart sinterability to the extent that sintering does not occur during the binder removal process, the diameter of the pulverizing medium is preferably 0.050 mm or more and 0.5 mm or less, more preferably 0.075 mm or more and 0.3 mm or less. The material of the pulverizing medium is usually zirconium oxide or alumina.

[0094] After the raw material powder is flattened, solid-liquid separation is performed using methods such as vacuum dehydration, pressure filtration, centrifugation, and ultrafiltration to remove copper powder from the processed material. Then, the copper powder is washed with solvents and dried.

[0095] Thus, the copper powder of the present invention is obtained. Without impairing the effects of the present invention, a metal can be deposited on the surface of the copper powder. This allows the utilization of various properties possessed by the metal. There are no particular limitations on the metal used, as long as it is a metal other than copper and silver.

[0096] The copper powder of the present invention can be dispersed in organic solvents and resins, and used in the form of conductive resin compositions such as paste compositions.

[0097] The conductive resin composition is constituted by comprising at least the copper powder of the present invention and an organic solvent. As the organic solvent, the same organic solvents used to date in the field of conductive resin compositions comprising metal powder can be used without particular limitation. Examples of such organic solvents include monohydric alcohols such as terpineol; polyols; polyol alkyl ethers such as ethyl carbitol; polyol aryl ethers; polyethers; esters such as carbitol acetate, butyl cellosolve acetate, and butyl carbitol acetate; nitrogen-containing heterocyclic compounds; amides; amines; and saturated hydrocarbons. One of these organic solvents can be used alone or in combination of two or more. From the viewpoint of having high reducing power and suppressing accidental oxidation of the copper powder during sintering, polyethers such as polyethylene glycol and polypropylene glycol are preferred. Similarly, when polyethylene glycol is used as the organic solvent, its number average molecular weight is preferably 120 or more and 400 or less, more preferably 180 or more and 400 or less.

[0098] In addition to copper powder, the conductive resin composition may contain at least one of a dispersant, an organic carrier, and glass powder. Examples of dispersants include, for example, nonionic surfactants that do not contain sodium, calcium, phosphorus, sulfur, or chlorine. Examples of organic carriers include mixtures comprising resin components such as acrylic resins, epoxy resins, ethyl cellulose, and carboxyethyl cellulose, and solvents such as terpene solvents such as terpineol and dihydroterpene solvents, or ether solvents such as ethyl carbitol and butyl carbitol. Examples of glass powders include, for example, borosilicate glass, barium borosilicate glass, and zinc borosilicate glass. These can be used individually or in combination of two or more.

[0099] The aforementioned conductive resin composition is coated onto a substrate to form a coating film, which is then sintered to form a sintered body of copper powder. This sintered body is suitable for applications such as circuit formation in printed circuit boards and ensuring electrical conductivity of the external electrodes of multilayer ceramic capacitors. Depending on the type of electronic circuit using copper powder, examples of printed circuit boards include those formed from glass epoxy resin or flexible printed circuit boards formed from polyimide.

[0100] The content of copper powder and organic solvent in the conductive resin composition can be appropriately set according to the specific use and coating method of the conductive resin composition, preferably 5% by mass or more and 95% by mass or less, and more preferably 80% by mass or more and 90% by mass or less.

[0101] The coating of conductive resin compositions can be carried out by methods such as inkjet printing, dispensing machine, micro dispensing machine, gravure printing, screen printing, dip coating, spin coating, spray coating, bar coating, and roller coating.

[0102] The sintering temperature of the coating only needs to be above the sintering start temperature of the copper powder, for example, it can be set to 500°C or higher and 900°C or lower. Sintering can be carried out, for example, in an oxidizing atmosphere or a non-oxidizing atmosphere. Examples of oxidizing atmospheres include atmospheres containing oxygen. Examples of non-oxidizing atmospheres include reducing atmospheres such as hydrogen and carbon monoxide, weakly reducing atmospheres such as hydrogen-nitrogen mixtures, and inactive atmospheres such as argon, neon, helium, and nitrogen. Regardless of the atmosphere, under the condition of being within the above-mentioned temperature range, the sintering time is preferably 0.1 hours or more and 5 hours or less, more preferably 0.2 hours or more and 3 hours or less.

[0103] During the sintering process of the coating, the resin components in the coating are thermally decomposed (binder removal process). The heating temperature for the thermal decomposition of the resin components varies depending on the type of resin component, but is typically above 300°C and below 500°C under a nitrogen atmosphere. When the heating temperature of the coating containing the copper powder of the present invention reaches this range, the sintering of the copper powder has not yet begun, so the decomposed resin components effectively escape to the outside of the coating through the gaps between the copper particles. As a result, bubbles caused by the decomposition products of the resin components are less likely to form in the obtained sintered body, thus increasing its density. In the binder removal process, a certain temperature can be maintained for a specified time, or the temperature can be increased over time.

[0104] The resulting sintered body is obtained by sintering the copper powder of the present invention, and is therefore dense.

[0105] The present invention has been described above based on its preferred embodiments, but the present invention is not limited to the foregoing embodiments.

[0106] Regarding the aforementioned embodiments, copper powder and its manufacturing method are further disclosed.

[0107] [1] A copper powder, which is composed of multiple copper particles having different aspect ratios to each other.

[0108] The tap density of the copper powder is 4.0 g / cm³. 3 Above and 7.0 g / cm 3 the following,

[0109] The standard deviation SD of the particle size distribution of the copper powder determined by laser diffraction scattering particle size distribution method is relative to the volumetric cumulative particle size D at 50% of the cumulative volume. 50 The ratio is the dispersion D. P The value is above 0.55 and below 0.90.

[0110] [2] According to the copper powder described in [1], wherein the average aspect ratio of the aforementioned copper particles is 1.05 or more and 3.00 or less.

[0111] [3] The copper powder according to [1] or [2] has an average sphericity of 0.60 or more and 0.95 or less.

[0112] [4] The copper powder according to any one of [1] to [3], wherein,

[0113] The number of copper particles with a roundness exceeding 0.95 is less than 5.0%.

[0114] The proportion of the aforementioned copper particles with a roundness greater than 0.70 and less than 0.95 is greater than the proportion of the aforementioned copper particles with a roundness of less than 0.70.

[0115] [5] The copper powder according to any one of [1] to [4], wherein the ratio of the number of the aforementioned copper particles with a sphericity of 0.70 or less to the cumulative particle size D at 90% of the cumulative volume using the laser diffraction scattering particle size distribution determination method. 90 The product of (μm) is less than 500 (number % μm).

[0116] [6] The copper powder according to any one of [1] to [5], wherein the ratio of the number of the aforementioned copper particles with a sphericity of more than 0.70 and less than 0.95 is proportional to the aforementioned particle size D. 50 The product of (μm) is 180 (number % μm) or more and 400 (number % μm) or less.

[0117] [7] The copper powder according to any one of [1] to [6], wherein the proportion of the number of the aforementioned copper particles with a sphericity exceeding 0.95 is equal to the cumulative particle size D at 10% of the cumulative volume using the laser diffraction scattering particle size distribution determination method. 10 The product of (μm) is 0.1 (number % μm) or more.

[0118] [8] The copper powder according to any one of [1] to [7], wherein the aforementioned particle size D 50 It is above 2.0μm and below 8.0μm.

[0119] [9] The copper powder according to any one of [1] to [8], wherein when thermomechanical analysis is performed under a nitrogen atmosphere and a heating rate of 10°C / min, the temperature at which the powder shrinks by 10% relative to the maximum shrinkage rate is 500°C or higher.

[0120]

[10] A method for manufacturing copper powder, comprising the following steps: using a media stirring mill device to plastically deform raw material powder composed of copper particles into a flat shape,

[0121] The material to be processed, which is composed of a slurry containing the aforementioned raw material powder, passes through the aforementioned media stirred mill apparatus of the material-passing type only once.

[0122]

[11] A sintered body of copper powder as described in any one of [1] to [9].

[0123]

[12] A multilayer ceramic capacitor having an external electrode made of a sintered body as described in

[11] .

[0124]

[13] A paste composition comprising any one of [1] to [9] copper powder.

[0125] Example

[0126] The present invention will now be described in more detail through examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" refers to "mass %".

[0127] [Example 1]

[0128] As raw material powder, wet copper granules 1110 manufactured by Mitsui Metals Mining Co., Ltd. were prepared. Details of the wet copper granules are shown in Table 1 below. 1 kg of wet copper granules were mixed with 1 kg of methanol to prepare a slurry.

[0129] Next, the raw material powder was flattened using a Star Mill (registered trademark) LMZ10 bead mill manufactured by Ashizawa Finetech Ltd. Specifically, zirconia beads with a diameter of 0.2 mm were used, and the circumferential speed of the mill was set to 12 m / s, so that the material was flattened in one pass.

[0130] Then, the copper powder is subjected to solid-liquid separation, washed and dried to obtain the target copper powder.

[0131] [Example 2]

[0132] In the preparation of the treated material in Example 1, 1 g of stearic acid was used as a lubricant. Otherwise, the target copper powder was obtained in the same manner as in Example 1.

[0133] [Example 3]

[0134] In Example 1, the diameter of the zirconia beads was changed to 0.1 mm. Otherwise, the target copper powder was obtained in the same manner as in Example 1.

[0135] [Example 4]

[0136] In Example 2, the diameter of the zirconia beads was changed to 0.1 mm. Otherwise, the target copper powder was obtained in the same manner as in Example 2.

[0137] [Comparative Example 1]

[0138] In Example 1, the number of times the workpiece passes through the device is changed to three. The device is cleaned after each pass, ensuring no workpiece residue remains inside. Otherwise, the target copper powder is obtained in the same manner as in Example 1.

[0139] [Comparative Example 2]

[0140] In Comparative Example 1, the number of times the material to be processed passed through the apparatus was changed to 4. Otherwise, the target copper powder was obtained in the same manner as in Comparative Example 1.

[0141] [evaluate]

[0142] For the copper powder obtained in the examples and comparative examples, the average aspect ratio and average roundness, tap density, standard deviation (SD) of particle size distribution, and particle size were measured according to the method described later. The cross-sectional image of the particles from Example 1 obtained from the determination of the average aspect ratio and average roundness was used as... Figure 2 (a) uses the particle cross-sectional image of Comparative Example 2 as... Figure 2 (b)

[0143] Based on the values ​​obtained from the measurements of average aspect ratio and average roundness, a distribution map was created with the minor axis of the copper particle on the horizontal axis and the roundness of the copper particle on the vertical axis. The distribution map of Example 1 was used as... Figure 3 (a) The distribution map of Example 2 is used as Figure 3 (b) uses the distribution map of Example 3 as... Figure 3 (c) The distribution map of Example 4 is used as Figure 3 (d) The distribution plot of Comparative Example 1 is used as Figure 3 (e) uses the distribution plot of Comparative Example 2 as... Figure 3 (f).

[0144] Furthermore, based on the values ​​obtained from the measurements of average aspect ratio and average roundness, a distribution map was created with the minor axis of the copper particle as the horizontal axis and the aspect ratio of the copper particle as the vertical axis. The distribution map from Example 1 was used as... Figure 4 (a) The distribution map of Example 2 is used as Figure 4(b) uses the distribution map of Example 3 as... Figure 4 (c) The distribution map of Example 4 is used as Figure 4 (d) The distribution plot of Comparative Example 1 is used as Figure 4 (e) uses the distribution plot of Comparative Example 2 as... Figure 4 (f).

[0145] Furthermore, for the copper powder obtained in the examples and comparative examples, the shrinkage initiation temperature was determined according to the method described later, and the sintering density was evaluated.

[0146] These results are shown in Table 1.

[0147] [Average aspect ratio and average roundness]

[0148] 10g of copper powder obtained in the examples and comparative examples was mixed with 10g of butylcarbidol (manufactured by Daishin Chemical Co., Ltd.) containing 35% of 1256 (bisphenol A type solid epoxy resin, manufactured by Mitsubishi Chemical Co., Ltd.). The mixture was then stirred at 2000 rpm for 1 minute using a rotary mixer manufactured by THINKY CORPORATION, followed by degassing at 2200 rpm for 30 seconds to obtain a paste. The resulting paste was then subjected to a three-roll mill at 20 μm and in three passes to break up any agglomerates, yielding the final paste.

[0149] The final paste was printed onto copper foil using a scraper with a width of 2 cm x 1 cm x a thickness of approximately 55 μm. The coating was then heated at 150°C for 10 minutes in atmospheric conditions to obtain a dried coating. The dried coating was then cross-sectionally processed using a NEC (Japan Electronics) cross-section polishing machine (SM-09010) at 6 kV and 40–50 mA. Cross-sectional images of the particles were obtained using a NEC scanning electron microscope (JSM-7100F). The aspect ratio and roundness of more than 300 copper particles in the obtained cross-sectional images were measured using Mac-View image resolution particle size distribution software (Mountiech Co., Ltd.). The average aspect ratio and the average roundness were taken as the average roundness.

[0150] [Tap density]

[0151] The tapped density was determined using a tapping machine (model: KSR-406, manufactured by Kuramachi Co., Ltd.). Specifically, the tapped density was measured in a volume of 150 cm³. 3 120g of copper powder was placed in a graduated cylinder. The striking stroke was set to 4cm and the number of strikes was set to 300 for measurement.

[0152] Particle size D 50 Particle size D 10 Particle size D90 and standard deviation SD]

[0153] Using an automated sample feeder (Microtrac SDC, manufactured by MicrotracBEL Corp.) with a laser diffraction particle size distribution measuring apparatus, two drops of pure water containing 0.1% polyoxyethylene octylphenyl ether were used to wet copper powder. This pure water was then added to a 0.1% aqueous solution of SN Dispersant 5468 (manufactured by San Nopco Limited). After irradiating the aqueous solution with 40W ultrasound for 5 minutes, the particle size distribution was measured using a MicrotracBEL Corp. laser diffraction particle size distribution measuring machine (MT3300EX II). The particle size D was determined from the obtained volume-based particle size distribution chart. 50 Particle size D 10 Particle size D 90 and standard deviation (SD).

[0154] The particle size D will be measured. 50 Particle size D 10 Particle size D 90 Set the flow rate to 65% at standard deviation (SD), set the solvent refractive index to 1.33, set the particle permeability condition to "reflection", set the measurement range to above 0.122 μm and below 704.0 μm, and set the measurement time to 30 seconds.

[0155] [Shrinkage start temperature]

[0156] The TMA / EXSTAR 6000 manufactured by Seiko Instruments Inc. was used as the measuring apparatus. 0.2 g of copper powder was placed into an aluminum mold container with a diameter of 4.0 mm, and granules were formed by applying a pressure of 1.0 MPa to the copper powder. The length of the resulting granules was measured and used as a sample. The sample was mounted on the measuring apparatus, and the temperature was increased at 10 °C / min under a nitrogen atmosphere and a load of 49 mN. Measurements were started from room temperature (25 °C), and a graph showing the relationship between temperature and shrinkage rate (%) was obtained. The shrinkage onset temperature was determined from the graph standardized based on the maximum shrinkage rate.

[0157] [Sintering density]

[0158] 10g of copper powder obtained in the examples and comparative examples was mixed with 1.5g of terpineol, which contained 10% of Techpolymer (registered trademark) IBM-2 (an acrylic resin manufactured by Sekisui Chemicals Co., Ltd.). The mixture was then stirred at 2000 rpm for 1 minute using a rotary mixer manufactured by THINKYCORPORATION, followed by degassing at 2200 rpm for 30 seconds to obtain a paste. The resulting paste was then subjected to a three-roll mill at 20 μm in three passes to break up any agglomerates, yielding the final paste.

[0159] Using a squeegee, the final paste was printed onto a 5cm x 5cm alumina substrate at a depth of 2cm x 1cm x approximately 55μm. The coating was then heated at 150°C for 10 minutes in atmospheric conditions to obtain a dried coating.

[0160] Using a KTF773N1 sintering furnace manufactured by JTEKT Thermo Systems Corporation, the temperature was increased to 800°C at a rate of 30°C / min under a nitrogen atmosphere, and the dried coating was sintered at 800°C for 10 minutes to obtain a sintered film.

[0161] Next, the mass of the sintered film, including the mass of the alumina substrate, was weighed using a 5-position balance (AUW220D) manufactured by Shimadzu Corporation. The mass of the sintered film was calculated by subtracting the previously weighed mass of the alumina substrate from this value. Additionally, the thickness of the sintered film was measured at three arbitrary points using a MICROGRANITE prepared by Precision Lapping. The average of the obtained values ​​was taken as the thickness of the sintered film. The volume of the sintered film was calculated by multiplying this thickness by the longitudinal and transverse lengths obtained from the measurement. Based on the mass and volume of the sintered film, its density was calculated. A higher density of the sintered film indicates higher sintering compactness.

[0162] [Table 1]

[0163]

[0164] Depend on Figure 2 As can be clearly seen from the cross-sectional images of the particles shown, the copper powder obtained in Example 1 is composed of copper particles with various aspect ratios and roundness. In contrast, the copper powder obtained in Comparative Example 2 has more copper particles that are excessively flattened.

[0165] Depend on Figure 3 As can be clearly seen from the distribution diagram, in the copper powder of the embodiment, regardless of the distribution of the minor diameter of the copper particles, the roundness of the copper particles is generally concentrated in a range with a certain width. In contrast, in the copper powder of the comparative example, although the roundness of the copper particles takes various values, the minor diameter of the copper particles is generally concentrated in a range with a certain width.

[0166] Depend on Figure 4 As can be clearly seen from the distribution diagram, in the copper powder of the embodiment, regardless of the distribution of the minor axis of the copper particles, the aspect ratio of the copper particles is generally concentrated in a range with a certain width. In contrast, in the copper powder of the comparative example, although the aspect ratio of the copper particles takes various values, the minor axis of the copper particles is generally concentrated in a range with a certain width.

[0167] As can be clearly seen from the results shown in Table 1, the copper powder obtained in the examples has higher shrinkage initiation temperature and sintering density compared to the copper powder obtained in the comparative examples.

[0168] Industrial availability

[0169] According to the present invention, copper powder and a method for manufacturing the same are provided, wherein the copper powder does not sinter in the binder removal process and can form a dense sintered film by, for example, low-temperature sintering at about 800°C.

Claims

1. A copper powder comprising a plurality of copper particles having different aspect ratios. The tap density of the copper powder is 4.0 g / cm³. 3 Above and 7.0 g / cm 3 the following, The standard deviation SD of the particle size distribution of the copper powder determined by laser diffraction scattering particle size distribution method is relative to the volumetric cumulative particle size D at 50% of the cumulative volume. 50 The ratio is the dispersion D. P The value is above 0.55 and below 0.

90.

2. The copper powder according to claim 1, wherein, The average aspect ratio of the copper particles is greater than 1.05 and less than 3.

00.

3. The copper powder according to claim 1 or 2, wherein the average sphericity is 0.60 or higher and 0.95 or lower.

4. The copper powder according to claim 1 or 2, wherein, The number of copper particles with a roundness exceeding 0.95 is less than 5.0%. The proportion of copper particles with a roundness greater than 0.70 and less than 0.95 is greater than the proportion of copper particles with a roundness of less than 0.

70.

5. The copper powder according to claim 1 or 2, wherein, The proportion of copper particles with a sphericity of 0.70 or less and the cumulative volumetric particle size D at 90% of the cumulative volume determined by laser diffraction scattering particle size distribution method. 90 The product of (μm) is less than 500 (number % μm).

6. The copper powder according to claim 1 or 2, wherein, The ratio of the number of copper particles with a roundness greater than 0.70 and less than 0.95 to the particle size D 50 The product of (μm) is 180 (number % μm) or more and 400 (number % μm) or less.

7. The copper powder according to claim 1 or 2, wherein, The proportion of copper particles with a roundness exceeding 0.95 and the cumulative volumetric particle size D at 10% of the cumulative volume determined by laser diffraction scattering particle size distribution method. 10 The product of (μm) is 0.1 (number % μm) or more.

8. The copper powder according to claim 1 or 2, wherein, The particle size D 50 It is above 2.0μm and below 8.0μm.

9. The copper powder according to claim 1 or 2, wherein, When thermomechanical analysis was performed under a nitrogen atmosphere and a heating rate of 10°C / min, the temperature at which the shrinkage was 10% relative to the maximum shrinkage rate was above 500°C.

10. A method for manufacturing copper powder, comprising the following steps: using a media stirring mill to plastically deform raw material powder composed of copper particles into a flat shape, The workpiece consisting of a slurry containing the raw material powder is passed through the media stirred mill apparatus of the workpiece passage type only once.

11. A sintered body of copper powder as described in claim 1 or 2.

12. A multilayer ceramic capacitor having an external electrode formed of a sintered body as described in claim 11.

13. A paste composition comprising the copper powder of claim 1 or 2.

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