Copper powder and method for producing same

Abstract

A copper powder according to the present invention comprises a plurality of copper particles having different aspect ratios. The tap density is 4.0 g / cm3 to 7.0 g / cm3. The value of the dispersity DP, which is the ratio of the standard deviation SD of the particle size distribution to the volume cumulative particle diameter D50 at a cumulative volume of 50 vol% according to measurement of the particle size distribution by laser diffraction scattering, is 0.55-0.90. The average aspect ratio of the copper particles is preferably 1.05-3.00. The average circularity is preferably 0.60-0.95. Preferably not more than 5.0% by number of the copper particles have a circularity greater than 0.95. The percentage by number of copper particles having a circularity of more than 0.70 but not more than 0.95 is preferably larger than the percentage by number of the copper particles having a circularity of 0.70 or less.

Description

Copper powder and its manufacturing method

[0001] The present invention relates to copper powder and a method for producing the same.

[0002] Copper is a highly conductive metal and a versatile material, and is therefore widely used industrially as a conductive material. For example, copper powder, an aggregate of copper particles, is widely used as a raw material for manufacturing various electronic components, such as external electrodes of multilayer ceramic capacitors (hereinafter also referred to as "MLCCs") and wiring to various substrates.

[0003] For example, the present applicant has previously proposed a flat copper powder in which copper powder particles are flattened by plastic deformation (see Patent Document 1). This flat copper powder has a standard deviation SD of particle size distribution and a weight cumulative particle size D measured by a laser diffraction scattering particle size distribution measurement method. ５０ SD / D expressed using ５０ The value of the weight cumulative particle size D is 0.55 or less. ９０ / weight cumulative particle size D １０ The value represented by the formula (2) is 4.5 or less, and the aspect ratio is 3 to 200. This flat copper powder is produced by subjecting copper powder in an agglomerated state to a deagglomeration treatment, and using copper powder particles having an agglomeration degree of 1.6 or less after the deagglomeration treatment, the copper powder particles are compressed and plastically deformed in a high-energy ball mill using media beads having a particle size of 0.5 mm or less, to form a flattened shape.

[0004] US2006 / 0137488 A1

[0005] Because flat copper powder has lower packing properties than spherical copper powder, which tends to pack more closely, sintered films formed by sintering flat copper powder tend to be less dense than those formed by sintering spherical copper powder. Furthermore, flat copper powder obtained by mechanical processing has lower crystallinity than spherical copper powder and tends to sinter more easily. For example, when sintering copper powder in the presence of a binder, as in MLCC, gas escape becomes difficult as sintering progresses, leading to cracks and voids. Therefore, it is desirable to avoid interparticle sintering during the binder removal process as much as possible. Furthermore, high sintering temperatures make it difficult to obtain dense sintered films. For these reasons, copper powder that can be sintered within an appropriate temperature range is ideal. Therefore, the present invention aims to provide a copper powder and a method for producing the same that does not sinter during the binder removal process and that can form dense sintered films by low-temperature sintering, for example, at approximately 800°C.

[0006] The present invention provides a copper powder comprising a plurality of copper particles having different aspect ratios, the copper powder having a tap density of 4.0 g / cm ３ 7.0g / cm or more ３ or less, and the volume cumulative particle size D at 50% cumulative volume by a laser diffraction scattering particle size distribution measurement method is ５０ The dispersity D is the ratio of the standard deviation SD of the particle size distribution to Ｐ The present invention provides copper powder having a value of 0.55 or more and 0.90 or less.

[0007] The present invention also provides a method for producing copper powder, which includes a step of plastically deforming a raw material powder consisting of copper particles into a flat shape using a media agitation mill, and in which a workpiece consisting of a slurry containing the raw material powder is passed through the workpiece passing type media agitation mill only once.

[0008] Figures 1(a) to 1(d) are schematic diagrams showing a method for measuring the aspect ratio of copper particles in the copper powder of the present invention. Figure 2(a) is a cross-sectional image of a coating film obtained using the copper powder obtained in Example 1, and Figure 2(b) is a cross-sectional image of a coating film obtained using the copper powder obtained in Comparative Example 2. Figure 3(a) is a distribution diagram created by plotting the minor axis of the copper particles in the copper powder obtained in Example 1 against the circularity of the copper particles on the vertical axis. Figure 3(b) is a distribution diagram for Example 2, Figure 3(c) is a distribution diagram for Example 3, Figure 3(d) is a distribution diagram for Example 4, Figure 3(e) is a distribution diagram for Comparative Example 1, and Figure 3(f) is a distribution diagram for Comparative Example 2. FIG. 4( a) is a distribution diagram created by taking the minor axis of the copper particles in the copper powder obtained in Example 1 on the vertical axis and the aspect ratio of the copper particles on the vertical axis; FIG. 4( b) is a distribution diagram for Example 2; FIG. 4( c) is a distribution diagram for Example 3; FIG. 4( d) is a distribution diagram for Example 4; FIG. 4( e) is a distribution diagram for Comparative Example 1; and FIG. 4( f) is a distribution diagram for Comparative Example 2.

[0009] The present invention will be described below based on preferred embodiments. The copper powder of the present invention is composed of a plurality of copper particles. The copper particles are preferably particles composed essentially of elemental copper or copper-based alloy particles. The copper powder is preferably composed of an aggregate of such particles. The former particles are particles composed essentially of elemental copper with the remainder containing unavoidable elements. In this case, the copper particles are preferably composed only of elemental copper, but trace amounts of unavoidable elements are acceptable. When the copper particles contain unavoidable elements, the content of the unavoidable elements is preferably 1% by mass or less, since this prevents the inherent properties of the copper particles from being impaired and allows the copper powder made of the copper particles to have suitable properties. Examples of unavoidable elements include oxygen (O) and carbon (C) derived from oxygen and carbon dioxide in the atmosphere, as well as nitrogen (N), which may be mixed in during the copper particle manufacturing process. The presence and content of unavoidable elements can be measured, for example, by gas analysis. In the latter case, the content of copper elements in the particles is preferably 80% by mass or more, more preferably 90% by mass or more.

[0010] One of the characteristics of the copper powder of the present invention is its high density. Conventionally, when sintering copper powder to produce a sintered film, uniform shape of the copper particles constituting the copper powder is desirable in order to obtain a sintered film with reduced quality variation. However, conventional copper powders have limitations in the degree of density that can be increased, making it difficult to achieve the density currently required. The present inventors conducted extensive research to address this issue and found that by providing 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 voids between the copper particles, thereby increasing the density of the copper powder and, ultimately, the density of the sintered film produced by sintering the copper powder. Furthermore, copper powder having a predetermined distribution of the shape and size of the copper particles exhibits less deformation of particle shape and crystal distortion due to processing than conventional flat copper powder, thereby suppressing the formation of active sites (i.e., sintering active sites) that facilitate sintering. Therefore, the copper powder has a sinterability to a degree that does not sinter during the binder removal process. As a result, for example, when an external electrode of an MLCC is manufactured using copper powder, the dry film containing copper powder and resin is less likely to sinter during the binder removal process, making it less likely for cracks and voids to form, and a highly dense sintered film can be obtained in the subsequent sintering process.

[0011] Specifically, the copper particles preferably have a flattened shape. In this specification, "flattened" is synonymous with "thin plate-like" or "flake-like" and means that the particles have a thin plate-like shape. The copper powder is allowed to contain spherical copper particles. The degree of flattening of the copper particles is specified by the aspect ratio and circularity. In the copper powder of the present invention, there is a distribution in the degree of flattening of the copper particles, and this distribution can be defined by the distribution of circularity. Details of the distribution of the degree of flattening of the copper particles will be described later.

[0012] As shown in FIGS. 1( a) to 1(d), the aspect ratio is a value defined as the ratio of the major axis W1 to the minor axis W2 (major axis W1 / minor axis W2), where W1 is the long side of the rectangle S (see FIG. 1(d)) that has the smallest area among all rectangles S circumscribing the particle P in a cross-sectional view of the particle P and W2 is the short side of the rectangle S. As will be described later, the raw material powder is preferably spherical. When the copper powder of the present invention is produced using the raw material powder, an aspect ratio close to 1 means that the shape of the copper particles is close to a perfect sphere. From the viewpoint of increasing the density of the copper powder and enabling the formation of a dense sintered film by low-temperature firing at, for example, about 800°C, the copper particles preferably have an average aspect ratio (hereinafter also referred to as the "average aspect ratio") of 1.05 or more, more preferably 1.20 or more, and even more preferably 1.40 or more. From the same viewpoint, the copper particles preferably have an average aspect ratio of 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." The major axis W1 and minor axis W2 of the copper particles may be appropriately set so as to have the above-mentioned average aspect ratio.

[0013] The average aspect ratio can be measured by the following method. Specifically, first, three or more fields of view are photographed using a scanning electron microscope (hereinafter also referred to as "SEM") at a magnification that includes at least 50 cross sections of the copper particles to be measured. Next, 300 or more copper particles whose outlines can be confirmed are randomly selected from each image data, and the values ​​of the major axis W1 and minor axis W2 are measured for each of the selected copper particles. Based on these values, the value of major axis W1 / minor axis W2 is calculated. The value calculated in this manner is referred to as the average aspect ratio in this specification. A detailed method for measuring the average aspect ratio will also be described in the Examples below.

[0014] The copper powder of the present invention preferably contains copper particles having an aspect ratio within a predetermined range, and it is preferable that one or more copper particles have different aspect ratios from one another. In particular, from the viewpoint of increasing the density of the copper powder and enabling the formation of a dense sintered film by low-temperature sintering, it is preferable that the aspect ratios of the copper particles in the copper powder change continuously.

[0015] In the copper powder of the present invention, the shape distribution of copper particles is also characterized by the circularity distribution of the copper particles. The "circularity" here refers to a value calculated based on Equation (1) described below. As described below, the raw material powder is preferably spherical. When the copper powder of the present invention is produced using the raw material powder, a circularity close to 1 means that the copper particles are nearly spherical. Based on this circularity, it is possible to determine the shape and extent of the distribution of copper particles. From the viewpoint of increasing the density of the copper powder and enabling the formation of a dense sintered film by low-temperature sintering, the copper powder preferably has an average circularity (hereinafter also referred to as "average circularity") of 0.95 or less, more preferably 0.90 or less, and even more preferably 0.85 or less. From the same viewpoint, the average circularity of the copper powder is preferably 0.60 or more, more preferably 0.65 or more, and even more preferably 0.70 or more.

[0016] 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 the circularity. The copper powder of the present invention preferably has a distribution diagram, where the horizontal axis represents the circularity of copper particles and the vertical axis represents the number frequency of copper particles, that is convex upward with a predetermined shape. In other words, it is particularly preferable that copper particles having a predetermined circularity are distributed with a predetermined number frequency in the copper powder. Specifically, from the viewpoints of suppressing the formation of sintering active sites, preventing sintering in the binder removal step, and enabling the formation of a dense sintered film by low-temperature firing, the number ratio of copper particles having a circularity of more than 0.95 in the copper powder is preferably 5.0 number% or less, more preferably 4.0 number% or less, and even more preferably 3.0 number% or less. A circularity of more than 0.95 means that the copper particles are extremely close to being spherical. In order to make the above-mentioned effect more pronounced, the smaller the proportion of copper particles having a circularity of more than 0.95, the better, but it may be 0.1% by number or more.

[0017] In addition, from the viewpoint of enabling the formation of a dense sintered film by low-temperature firing by increasing the density of the copper powder, it is preferable that the copper powder contains more copper particles with a relatively high circularity than copper particles with a relatively low circularity. Having such a distribution in the copper powder allows the copper particles to be densely packed, minimizing the gaps between the copper particles as much as possible, thereby increasing the density of the copper powder and, ultimately, the density of the sintered film produced by sintering the copper powder. In order to enable the formation of a dense sintered film by low-temperature firing by increasing the density of the copper powder, it is preferable that the number proportion of copper particles having a circularity of more than 0.70 and not more than 0.95 in the copper powder is greater than the number proportion of copper particles having a circularity of 0.70 or less. In addition, it is preferable that the ratio of the number proportion of copper particles having a circularity of more than 0.70 and not more than 0.95 in the copper powder to the number proportion of copper particles having a circularity of 0.70 or less (hereinafter also referred to as "ratio A") is a predetermined value or greater. Specifically, from the viewpoint of increasing the density of the copper powder and enabling the formation of a dense sintered film by low-temperature firing, the ratio A is preferably 1.10 or more, more preferably 1.30 or more, and even more preferably 1.50 or more. From the viewpoint of making the above-mentioned effect more pronounced, the larger the ratio A, the better, but it may be 8.00 or less.

[0018] As described above, it is preferable to include more copper particles with a relatively high circularity than copper particles with a relatively low circularity, but it is preferable that the number proportion of copper particles with a circularity of more than 0.70 and not more than 0.95 be within a predetermined range in order to impart high packing properties to the copper powder of the present invention. From the viewpoint of making this advantage more pronounced, the number proportion of copper particles with a circularity of more than 0.70 and not more than 0.95 is preferably 50.0 number% or more, more preferably 55.0 number% or more, and even more preferably 60.0 number% or more, provided that the value of ratio A is within the above-mentioned range. From the same viewpoint, the number proportion of copper particles with a circularity of more than 0.70 and not more than 0.95 is preferably 95.0 number% or less, more preferably 90.0 number% or less, and even more preferably 85.0 number% or less, provided that the value of ratio A is within the above-mentioned range.

[0019] In addition, it is also preferable that the number proportion of copper particles having a circularity of 0.70 or less is within a predetermined range, from the viewpoint of imparting high packing properties to the copper powder of the present invention. From the viewpoint of making this advantage more pronounced, the number proportion of copper particles having a circularity of 0.70 or less is preferably 1.0 number% or more, more preferably 5.0 number% or more, and even more preferably 10.0 number% or more, provided that the value of ratio A is within the above-mentioned range. From the same viewpoint, the number proportion of copper particles having a circularity of 0.70 or less is preferably 45.0 number% or less, more preferably 40.0 number% or less, and even more preferably 35.0 number% or less, provided that the value of ratio A is within the above-mentioned range.

[0020] The circularity of copper particles is calculated by the following method. First, three or more fields of view of the cross-sections of the copper particles to be measured are photographed using an SEM at a magnification that includes 50 or more particles. Next, 300 copper particles that do not overlap are randomly selected from each image data. When the area of ​​the two-dimensional projection image of the copper particle cross-section is S and the perimeter is L, the circularity of the copper particle cross-section is calculated based on the following formula (1). The arithmetic mean value of the circularity of each copper particle cross-section is taken as the circularity mentioned above. When the two-dimensional projection image of the copper particle is a perfect circle, the circularity of the copper particle is 1. 4πS / L ２ ...(1) A detailed method for measuring the circularity will be explained in the examples below.

[0021] In order to set the circularity and circularity distribution of the copper powder within the above ranges, it is preferable to flatten the raw material powder by, for example, the manufacturing method described below.

[0022] The copper powder of the present invention preferably has a bulk density within a predetermined range. In other words, it is preferable that there are few voids between the copper particles in the copper powder, that is, that the copper powder has high density. By using such copper powder, it becomes possible to form a dense sintered film by low-temperature firing. Specifically, from the viewpoint of enabling the formation of a dense sintered film by low-temperature firing, it is preferable that the tap density of the copper powder is 4.0 g / cm. ３ It is preferable that the density is 4.2 g / cm or more. ３ More preferably, it is 4.4 g / cm or more. ３From the same viewpoint, it is more preferable that the tap density of the copper powder is 7.0 g / cm or more. ３ Preferably, it is 6.5 g / cm or less. ３ More preferably, it is 6.0 g / cm or less. ３ It is more preferable that the tap density is less than 0.05. Copper powder having such a tap density is preferably produced by the production method described below. In this specification, the "tap density" refers to a value measured in accordance with JIS Z2512. The detailed method for measuring the tap density will be described in the examples described below.

[0023] The copper powder of the present invention is preferably composed of copper particles having different particle sizes. In other words, it is preferable that the copper particles in the copper powder have a wide particle size distribution. This also makes it possible to pack the copper particles densely, making the gaps between the copper particles as small as possible, and increasing the density of the copper powder. As a result, a dense sintered film can be formed by low-temperature sintering. The copper powder having a wide particle size distribution can be determined by the volume cumulative particle size D at 50% cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method. ５０ (μm) (hereinafter simply referred to as “particle size D ５０ The dispersity D is the ratio of the standard deviation SD (μm) of the particle size distribution to the Ｐ Specifically, from the viewpoint of making it possible to form a dense sintered film by low-temperature firing by increasing the density of the copper powder, the degree of dispersion D Ｐ The value of the dispersity D is preferably 0.55 or more, more preferably 0.60 or more, and even more preferably 0.65 or more. Ｐ The value of particle diameter D is preferably 0.90 or less, more preferably 0.89 or less, and even more preferably 0.88 or less. ５０ The method for measuring this will be explained in the Examples below.

[0024] As mentioned above, it is preferable that the copper particles have a wide particle size distribution. ５０It is preferable that the particle diameter D of the copper powder of the present invention is in the predetermined range in order to suppress the formation of sintering active sites and to impart to the copper powder of the present invention a degree of sinterability that prevents sintering in the binder removal step. ５０ is the dispersity D Ｐ Provided that the value of is within the above range, it is preferably 2.00 μm or more, more preferably 2.50 μm or more, and even more preferably 3.00 μm or more. ５０ is the dispersity D Ｐ Provided that the value of is within the above range, it is preferably 8.00 μm or less, more preferably 7.00 μm or less, and even more preferably 6.00 μm or less.

[0025] In the copper powder of the present invention, the standard deviation SD of the particle size distribution is Ｐ Provided that the value of is within the above range, it is preferably 1.00 μm or more, more preferably 1.50 μm or more, and even more preferably 2.00 μm or more. The standard deviation SD of the particle size distribution is Ｐ Provided that the value of is within the above-mentioned range, it is preferably 6.00 μm or less, more preferably 5.00 μm or less, and even more preferably 4.00 μm or less. When the standard deviation SD of the particle size distribution is within the above-mentioned range, the formation of sintering active sites can be suppressed, and as a result, sintering does not occur in the binder removal step, and a dense sintered film can be formed by low-temperature firing. The method for measuring the standard deviation SD of the particle size distribution will be explained in the Examples below.

[0026] In the copper powder of the present invention, the copper particles having a predetermined circularity are distributed at a predetermined number frequency, and the copper particles have a wide particle size distribution, which can be defined by the product of the number ratio of the circularity of the copper particles and the particle size. Specifically, the product of the number ratio of copper particles having a circularity of 0.70 or less and the volume cumulative particle size D at 90% of the cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method can be defined by the product of the number ratio of copper particles having a circularity of 0.70 or less and the volume cumulative particle size D at 90% of the cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method. ９０ (μm) (hereinafter simply referred to as “particle size D ９０ ") and the product P ９０It is preferable that the value of (number %·μm) is within a predetermined range. From the viewpoint of suppressing the formation of sintering active points, preventing sintering in the binder removal step, and enabling the formation of a dense sintered film by low-temperature firing, ９０ is preferably 500 number %·μm or less, more preferably 450 number %·μm or less, and even more preferably 400 number %·μm or less. ９０ A small value of means that the degree of flattening of the particles is not large, and the product P ９０ A larger value of P means that the particles are flattened to a greater extent. ９０ The smaller the value of is, the more preferable it is, but it may be 100 number % μm or more. ９０ The method for measuring this will be explained in the Examples below.

[0027] In the copper powder of the present invention, the copper particles having a predetermined circularity are distributed at a predetermined number frequency, and the copper particles have a wide particle size distribution, which can also be defined by a product of the circularity and the particle size, which is different from the above-mentioned circularity and particle size. Specifically, the product of the number ratio of copper particles having a circularity of more than 0.70 and 0.95 or less and the particle size D ５０ (μm) and product P ５０ It is preferable that the value of (number %·μm) is within a predetermined range. From the viewpoint of suppressing the formation of sintering active points, preventing sintering in the binder removal step, and enabling the formation of a dense sintered film by low-temperature firing, ５０ is preferably 180 number % μm or more, more preferably 200 number % μm or more, and even more preferably 220 number % μm or more. ５０ is preferably 400 number %·μm or less, more preferably 350 number %·μm or less, and even more preferably 300 number %·μm or less. ５０ The value of being in the above range means that the particle shape is deformed (for example, flattened), but the degree of deformation is not large.

[0028] In the copper powder of the present invention, the copper particles having a predetermined circularity are distributed at a predetermined number frequency, and the copper particles have a wide particle size distribution, which can be defined by a product of the circularity and the particle size, which is different from the above-mentioned circularity and particle size. Specifically, the product of the number ratio of copper particles having a circularity of more than 0.95 and the volume cumulative particle size D at 10% by volume of the cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method can be defined by the product of the number ratio of copper particles having a circularity of more than 0.95 and the volume cumulative particle size D at 10% by volume of the cumulative volume. １０ (μm) (hereinafter simply referred to as “particle size D １０ ") and the product P １０ It is preferable that the value of (number %·μm) is within a predetermined range. From the viewpoint of suppressing the formation of sintering active points, preventing sintering in the binder removal step, and enabling the formation of a dense sintered film by low-temperature firing, １０ is preferably 0.1 number %·μm or more, more preferably 0.2 number %·μm or more, and even more preferably 0.3 number %·μm or more. １０ The value of P is equal to or greater than the above value, which means that the degree of flattening of the particles is not large. １０ The larger the value, the better, but it may be 3.5 number % μm or less. １０ The method for measuring this will be explained in the Examples below.

[0029] In the copper powder of the present invention, the particle diameter D １０ and particle size D ９０ It is preferable that the particle diameters of the copper particles are within a predetermined range. Although the copper particles have a wide particle size distribution, by having the particle diameters within a predetermined range, it is possible to suppress the formation of sintering active sites and to impart to the copper powder of the present invention a degree of sinterability that prevents sintering in the binder removal step. From the viewpoint of making the above-mentioned advantages more pronounced, it is preferable that the particle diameter D of the copper powder is within a predetermined range. １０ is the product P １０ Provided that the value of is within the above range, it is preferably 0.4 μm or more, more preferably 0.7 μm or more, and even more preferably 1.0 μm or more. １０ is the product P １０In order to make the above-mentioned advantages more remarkable, the particle diameter D of the copper powder is preferably 4.0 μm or less, more preferably 3.0 μm or less, and even more preferably 2.0 μm or less, provided that the value of D is within the above-mentioned range. ９０ is the product P ９０ Provided that the value of is within the above range, it is preferably 4.0 μm or more, more preferably 5.0 μm or more, and even more preferably 6.0 μm or more. ９０ is the product P ９０ Provided that the value of is within the above range, it is preferably 16.0 μm or less, more preferably 14.0 μm or less, and even more preferably 12.0 μm or less.

[0030] Copper powder particle size and dispersion D Ｐ and the value of the product P ９０ , product P ５０ and product P １０ In order to set the value of in the above range, it is preferable to flatten the raw material powder by, for example, the manufacturing method described below.

[0031] 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 circularity of the copper particles, from the viewpoint of increasing the density of the copper powder and enabling the formation of a dense sintered film by low-temperature sintering. Specifically, it is preferable that the circularity of the copper particles is less dependent on the minor axis of the copper particles. Figures 3(a) to 3(f) are distribution diagrams plotted with the minor axis of the copper particles on the horizontal axis and the circularity of the copper particles on the vertical axis for the copper powders obtained in Examples 1 to 4 and Comparative Examples 1 and 2 described below. As is clear from the results shown in Figures 3(a) to 3(d), in the copper powders of the Examples, the circularity of the copper particles is generally concentrated at a constant value or within a range having a certain width, regardless of the distribution of the minor axis of the copper particles. In contrast, in the copper powders of the Comparative Examples, the circularity of the copper particles varies, but the minor axis of the copper particles is generally concentrated at a constant value or within a range having a certain width. Therefore, it can be understood that the copper powder of the present invention has various degrees of circularity, regardless of the value of the minor axis of the copper particles. In order for the copper powder of the present invention to have such a relationship, it is preferable to flatten the raw material powder, for example, by the production method described below.

[0032] Furthermore, from the viewpoint of enabling the formation of a dense sintered film by low-temperature sintering by increasing the density of the copper powder, it is also preferable that the copper powder of the present invention 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 dependence of the aspect ratio of the copper particles on the minor axis of the copper particles is small. Figures 4(a) to 4(f) are distribution diagrams created by plotting the minor axis of the copper particles on the horizontal axis and the aspect ratio of the copper particles on the vertical axis for the copper powders obtained in Examples 1 to 4 and Comparative Examples 1 and 2 described below. As is clear from the results shown in Figures 4(a) to 4(d), in the copper powders of the Examples, the aspect ratios of the copper particles are generally concentrated at a constant value or within a range having a certain width, regardless of the distribution of the minor axis of the copper particles. In contrast, in the copper powders of the Comparative Examples, although the aspect ratios of the copper particles vary, the minor axis of the copper particles is generally concentrated at a constant value or within a range having a certain width. Therefore, it can be understood that the copper powder of the present invention can have various aspect ratios regardless of the value of the minor axis of the copper particles. In order for the copper powder of the present invention to have such a relationship, it is preferable to flatten the raw material powder, for example, by the production method described below.

[0033] Furthermore, the copper powder of the present invention preferably has a predetermined relationship between the aspect ratio and particle size of the copper particles constituting the copper powder, from the viewpoint of increasing the density of the copper powder and enabling the formation of a dense sintered film by low-temperature sintering. Specifically, in a distribution diagram created by plotting the image analysis particle size of copper particles on the horizontal axis and the aspect ratio of the copper particles on the vertical axis, it is preferable that there be a positive correlation between the aspect ratio and the image analysis particle size of copper particles. In other words, it is preferable that the larger the particle size of copper particles, the larger the aspect ratio. When copper powder has this relationship, copper particles with both a large aspect ratio and a small image analysis particle size can fill the gaps between copper particles with both a large aspect ratio and a small image analysis particle size, thereby further increasing the density of the copper powder. In this specification, the "image analysis particle size" refers to the major axis W1 of the copper particles measured using the above-mentioned aspect ratio measurement method.

[0034] As described above, the copper powder of the present invention is highly dense and has a degree of sinterability that prevents sintering during the binder removal process. The degree of sinterability can be evaluated by thermomechanical analysis of the copper powder. Here, the temperature at which the copper powder shrinks by 10% relative to the maximum shrinkage rate when subjected to thermomechanical analysis under conditions of a nitrogen atmosphere and a heating rate of 10°C / min is defined as the shrinkage onset temperature. To impart a degree of sinterability that prevents sintering during the binder removal process to the copper powder, the shrinkage onset 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. To further enhance the above-mentioned effects, the higher the shrinkage onset temperature, the better. However, when used as an external electrode for an MLCC, the shrinkage onset temperature is preferably close to the sintering temperature of the glass frit used together with the copper powder of the present invention to manufacture the external electrode. The method for measuring the shrinkage onset temperature will be described in the Examples below.

[0035] Next, a preferred method for producing the copper powder of the present invention will be described. The production method of the present invention includes a step of plastically deforming raw material powder into a flattened shape.

[0036] First, raw material powder is prepared. The raw material powder is composed of copper particles. The shape of the raw material powder may be spherical, polygonal, spindle-shaped, or irregular. From the viewpoint of successfully obtaining copper powder having an aspect ratio and circularity within the above-mentioned ranges by the flattening operation described below, it is preferable to use raw material powder composed of spherical copper particles.

[0037] It is preferable to use raw material powder whose physical property values ​​are within a predetermined range, because this makes it possible to successfully obtain copper powder whose physical property values ​​of the object to be manufactured, such as aspect ratio, circularity, and particle size, are within the above-mentioned ranges.

[0038] Particle size D of raw material powder ５０ From the above viewpoint, it is preferable to use raw material powder having a particle size D of 1.0 μm or more. ５０ It is preferable to use raw material powder having a particle size of 10.0 μm or less.

[0039] From the above viewpoint, it is preferable to use raw material powder having a standard deviation SD of particle size distribution of 0.5 μm or more. From the same viewpoint, it is preferable to use raw material powder having a standard deviation SD of particle size distribution of 10.0 μm or less.

[0040] A raw material powder having such physical properties can be obtained, for example, by atomization methods such as gas atomization and water atomization, and by a plasma method. Alternatively, it can also be easily obtained by a wet reduction method in which an aqueous copper salt solution is reacted with an alkaline agent to precipitate copper hydroxide, this copper hydroxide is primarily reduced to cuprous oxide in the liquid, and the cuprous oxide is secondarily reduced to metallic copper in the liquid. From the viewpoint of successfully obtaining copper powder having an aspect ratio, circularity, and particle size within the above-mentioned ranges, it is preferable to use a raw material powder obtained by a wet reduction method, which is a raw material powder containing a large number of spherical copper particles.

[0041] Once the raw material powder is prepared, a workpiece containing the raw material powder is prepared. The workpiece consists of a slurry containing the raw material powder and a liquid medium. Examples of the liquid medium include water and organic solvents. A mixed solvent of water and an organic solvent can also be used. Examples of the organic solvent include aliphatic alcohols having 1 to 22 carbon atoms. These organic solvents can be used alone or in combination of two or more. Of these liquid media, the use of organic solvents is preferred because it improves the dispersibility of the raw material powder in the workpiece and improves the stability of quality during the flattening operation. It is preferable to use a monohydric alkyl alcohol having 1 to 4 carbon atoms because the medium is easily volatilized and is less likely to remain in the target copper powder. Examples of such alcohols include methanol, ethanol, n-propanol, sec-propanol, n-butanol, sec-butanol, and tert-butanol.

[0042] If necessary, additives such as lubricants may be added to the material to be treated. Lubricants have the property of suppressing particle aggregation and reducing friction between particles, making them more slippery. 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 particles that are relatively close to monodispersion and effectively reducing the proportion of copper particles that are extremely close to spherical, such as copper particles with a circularity of more than 0.95, it is preferable to use a lubricant, and stearic acid is particularly preferable.

[0043] To prepare the material to be treated, the raw material powder, the liquid medium, and, if necessary, additives are simply mixed together. In some cases, the dispersion may be prepared using a stirring and dispersing device. Examples of such devices include a fluid mill and T. K. Filmix (registered trademark) manufactured by Primix Corporation.

[0044] From the viewpoint of successfully plastically deforming the raw material powder, the concentration of the raw material powder in the workpiece is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. From the same viewpoint, the concentration of the raw material powder in the workpiece is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0045] When the workpiece contains a lubricant, the content of the lubricant 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 content of copper particles in the raw material powder, from the viewpoint of successfully obtaining copper powder having an aspect ratio, circularity, and particle size within the above-mentioned ranges. From the viewpoint of suppressing sintering defects due to residual lubricant, the content of the lubricant 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 content of copper particles in the raw material powder.

[0046] Once the workpiece is prepared, the raw material powder consisting of copper particles contained in the workpiece is plastically deformed into a flattened shape. The flattening of the raw material powder can be performed using a media-agitating mill such as a bead mill, ball mill, or attritor. To successfully obtain copper powder with aspect ratios, circularity, and particle sizes within the above-mentioned ranges, it is preferable to use a device capable of applying relatively small stress to the raw material powder contained in the workpiece. By performing such a process, the raw material powder can be flattened without excessively changing the aspect ratio, circularity, and particle size of the raw material powder consisting of copper particles. This makes it possible to successfully obtain highly dense copper powder while minimizing the loss of the inherent properties of the copper particles. In particular, copper particles with various circularities 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, which are the starting points for sintering, can be suppressed, imparting a degree of sinterability that prevents sintering during the binder removal process.

[0047] Examples of media agitation mills that can apply relatively small stresses to the raw material powder in the workpiece include workpiece-passing (so-called pass-type) devices. Media agitation mills generally employ three operating methods: workpiece-passing, workpiece-multiple-passing, and circulation. The circulation type flattens the workpiece while circulating it through the device, making it difficult to adjust the magnitude of the stress applied to the raw material powder. In contrast, the workpiece-passing and workpiece-multiple-passing types flatten the workpiece by setting the number of times the workpiece passes through the device, making it easier to adjust the magnitude of the stress applied to the raw material powder. From the perspective of flattening the raw material powder with relatively small stresses, it is particularly preferable to use a workpiece-passing device. An example of such a device is the Star Mill (registered trademark) LMZ10, a bead mill manufactured by Ashizawa Finetech Co., Ltd.

[0048] From the viewpoint of preventing the inherent properties of the copper particles from being impaired, successfully obtaining a highly dense copper powder, and suppressing the formation of sintering active sites and imparting a degree of sinterability that prevents sintering in the binder removal step, it is most preferable to flatten the material by passing it through a material-passing medium-agitation mill only once. In this case, the peripheral speed of the mill is preferably 4 m / sec or more, more preferably 6 m / sec or more, and even more preferably 8 m / sec or more, from the viewpoint of preventing the inherent properties of the copper particles from being impaired, successfully obtaining a highly dense copper powder, and suppressing the formation of sintering active sites and imparting a degree of sinterability that prevents sintering in the binder removal step. From the same viewpoint, the peripheral speed of the mill is preferably 20 m / sec or less, more preferably 17 m / sec or less, and even more preferably 14 m / sec or less.

[0049] The diameter of the grinding media is preferably 0.050 mm or more and 0.5 mm or less, and more preferably 0.075 mm or more and 0.3 mm or less, from the viewpoints of preventing the inherent properties of the copper particles from being impaired, successfully obtaining a highly dense copper powder, and of suppressing the formation of sintering active sites and imparting a degree of sintering that prevents sintering in the binder removal step. The material of the grinding media is generally zirconia, alumina, or the like.

[0050] After flattening the raw material powder, the copper powder is separated and removed from the material to be treated by a solid-liquid separation method such as vacuum dehydration, filter press, centrifugation, or ultrafiltration, and then washed with a solvent or the like and dried.

[0051] The copper powder of the present invention is obtained in this manner. A metal may be disposed on the surface of the copper powder as long as the effects of the present invention are not impaired. This allows the various properties of the metal to be utilized. The metal is not particularly limited as long as it is a metal other than copper or silver.

[0052] The copper powder of the present invention can be dispersed in an organic solvent and a resin, etc., and used in the form of a conductive resin composition such as a paste composition. The conductive resin composition contains at least the copper powder of the present invention and an organic solvent. The organic solvent can be any of those previously used in the technical field of conductive resin compositions containing metal powder, without any particular limitation. Examples of such organic solvents include monohydric alcohols such as terpineol; polyhydric alcohols; polyhydric alcohol alkyl ethers such as ethyl carbitol; polyhydric alcohol aryl ethers; polyethers; esters such as carbitol acetate, butyl cellosolve acetate, and butyl carbitol acetate; nitrogen-containing heterocyclic compounds; amides; amines; and saturated hydrocarbons. These organic solvents can be used alone or in combination. Polyethers such as polyethylene glycol and polypropylene glycol are preferred because of their high reducing activity and the ability to suppress unintended oxidation of the copper powder during sintering. From the same perspective, when polyethylene glycol is used as the organic solvent, its number-average molecular weight is preferably 120 to 400, and more preferably 180 to 400.

[0053] In addition to copper powder, the conductive resin composition may contain at least one of a dispersant, an organic vehicle, and a glass frit. Examples of dispersants include nonionic surfactants that do not contain sodium, calcium, phosphorus, sulfur, or chlorine. Examples of organic vehicles include mixtures containing resin components such as acrylic resins, epoxy resins, ethyl cellulose, and carboxyethyl cellulose, and solvents such as terpene-based solvents such as terpineol and dihydroterpineol, or ether-based solvents such as ethyl carbitol and butyl carbitol. Examples of glass frits include borosilicate glass, barium borosilicate glass, and zinc borosilicate glass. These may be used alone or in combination.

[0054] The conductive resin composition described above can be applied to a substrate to form a coating film, which can then be sintered to form a sintered body of copper powder. The sintered body is suitable for use, for example, in forming circuits on printed wiring boards or for ensuring electrical continuity between external electrodes of multilayer ceramic capacitors. Examples of printed wiring boards include printed wiring boards made of glass epoxy resins and flexible printed wiring boards made of polyimide, depending on the type of electronic circuit in which the copper powder is used.

[0055] The contents of copper powder and organic solvent in the conductive resin composition can be appropriately set depending on the specific use of the conductive resin composition and the application method, but are 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.

[0056] The conductive resin composition can be applied by, for example, an inkjet method, a dispenser method, a microdispenser method, a gravure printing method, a screen printing method, a dip coating method, a spin coating method, a spray coating method, a bar coating method, a roll coating method, or the like.

[0057] The sintering temperature of the coating film may be any temperature equal to or higher than the sintering initiation temperature of the copper powder, and may be, for example, 500°C to 900°C. Sintering can be carried out, for example, in an oxidizing atmosphere or a non-oxidizing atmosphere. Examples of oxidizing atmospheres include oxygen-containing atmospheres. Examples of non-oxidizing atmospheres include reducing atmospheres such as hydrogen and carbon monoxide, weakly reducing atmospheres such as hydrogen-nitrogen mixed atmospheres, and inert atmospheres such as argon, neon, helium, and nitrogen. Regardless of the atmosphere, the sintering time is preferably 0.1 to 5 hours, more preferably 0.2 to 3 hours, provided that the temperature is within the above-mentioned range. During the sintering process of the coating film, the resin component in the coating film is thermally decomposed (the binder removal process). The heating temperature at which the resin component is thermally decomposed varies depending on the type of resin component, but is generally 300°C to 500°C in a nitrogen atmosphere. When the heating temperature of the coating containing the copper powder of the present invention reaches this range, sintering of the copper powder has not yet begun, and the decomposed resin components effectively escape to the outside of the coating through the gaps between the copper particles. As a result, the resulting sintered body is highly dense because bubbles caused by decomposition of the resin components are less likely to form. In the binder removal process, a constant temperature may be maintained for a predetermined time, or the temperature may be increased over time.

[0058] The sintered body thus obtained is dense because it is obtained by sintering the copper powder of the present invention.

[0059] Although the present invention has been described above based on the preferred embodiments, the present invention is not limited to the above embodiments.

[0060]

[0013] In relation to the above embodiment, a copper powder and a method for producing the same are further disclosed. [1] A copper powder comprising a plurality of copper particles having different aspect ratios, and having a tap density of 4.0 g / cm ３ 7.0g / cm or more ３ or less, and the volume cumulative particle size D at 50% cumulative volume by a laser diffraction scattering particle size distribution measurement method is ５０ The dispersity D is the ratio of the standard deviation SD of the particle size distribution to Ｐ The copper powder has a value of 0.55 or more and 0.90 or less.

[0061] [2] The copper powder according to [1], wherein the copper particles have an average aspect ratio of 1.05 or more and 3.00 or less. [3] The copper powder according to [1] or [2], wherein the copper particles have an average circularity of 0.60 or more and 0.95 or less. [4] The copper powder according to any one of [1] to [3], wherein the copper particles having a circularity of more than 0.95 account for 5.0% by number or less, and the number proportion of the copper particles having a circularity of more than 0.70 and 0.95 or less is greater than the number proportion of the copper particles having a circularity of 0.70 or less. [5] The copper powder according to [1], wherein the number proportion of the copper particles having a circularity of 0.70 or less and the volume cumulative particle size D at 90% by volume of the cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method are 5.0% by number or less. ９０ [6] The copper powder according to any one of [1] to [4], wherein the product of the number percentage of the copper particles having a circularity of more than 0.70 and 0.95 or less and the particle diameter D ５０ The copper powder according to any one of [1] to [5], wherein the product of (μm) and (μm) is 180 (number % μm) or more and 400 (number % μm) or less.

[0062] [7] The ratio of the number of copper particles having a circularity of more than 0.95 to the volume cumulative particle diameter D at 10% by volume of the cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method １０ [8] The copper powder according to any one of [1] to [6], wherein the product of the particle diameter D and the particle size (μm) is 0.1 (number % μm) or more. ５０

[10] A copper powder according to any one of [1] to [7], having a diameter of 2.0 μm or more and 8.0 μm or less. [9] The copper powder according to any one of [1] to [8], having a temperature of 500°C or more at which it shrinks by 10% relative to the maximum shrinkage when subjected to thermomechanical analysis in a nitrogen atmosphere at a heating rate of 10°C / min.

[10] A method for producing copper powder, comprising a step of plastically deforming a raw material powder made of copper particles into a flat shape using a media agitation mill, wherein a workpiece made of a slurry containing the raw material powder is passed through the media agitation mill of a workpiece passing type only once.

[11] A sintered body of the copper powder according to any one of [1] to [9].

[0063]

[12] A multilayer ceramic capacitor having external electrodes made of the sintered body according to

[11] .

[13] A paste composition containing the copper powder according to any one of [1] to [9].

[0064] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0065] Example 1 Wet copper particles 1110 manufactured by Mitsui Mining & Smelting Co., Ltd. were prepared as raw material powder. Details of the wet copper particles are shown in Table 1 below. 1 kg of the wet copper particles was mixed with 1 kg of methanol to prepare a material to be treated as a slurry. The raw material powder was then flattened using a Star Mill (registered trademark) LMZ10 bead mill manufactured by Ashizawa Finetech Co., Ltd. Specifically, zirconia beads with a diameter of 0.2 mm were used, and the peripheral speed of the mill was set to 12 m / sec, and the material to be treated was passed through the mill once to flatten it. The copper powder was then subjected to solid-liquid separation, washed, and dried to obtain the desired copper powder.

[0066] Example 2 The target copper powder was obtained in the same manner as in Example 1, except that 1 g of stearic acid was used as a lubricant in the preparation of the treated material in Example 1.

[0067] Example 3 The target copper powder was obtained in the same manner as in Example 1, except that the diameter of the zirconia beads was changed to 0.1 mm.

[0068] Example 4 The target copper powder was obtained in the same manner as in Example 2, except that the diameter of the zirconia beads was changed to 0.1 mm.

[0069] Comparative Example 1 In Example 1, the number of times the workpiece was passed through the apparatus was changed to three. The apparatus was cleaned after each pass of the workpiece, and the workpiece was passed through the apparatus without remaining in the apparatus. Otherwise, the target copper powder was obtained in the same manner as in Example 1.

[0070] Comparative Example 2 In Comparative Example 1, the number of times the material to be treated was passed through the apparatus was changed to 4. Otherwise, the same procedure as in Comparative Example 1 was carried out to obtain the target copper powder.

[0071] [Evaluation] The copper powders obtained in the Examples and Comparative Examples were measured for average aspect ratio, average circularity, tap density, standard deviation of particle size distribution (SD), and particle size according to the methods described below. The particle cross-sectional images of Example 1 and Comparative Example 2 obtained in the measurements of average aspect ratio and average circularity are shown in Figure 2(a) and Figure 2(b), respectively. Based on the values ​​obtained in the measurements of average aspect ratio and average circularity, distribution diagrams were created by plotting the minor axis of the copper particles along the minor axis and the circularity of the copper particles along the vertical axis. The distribution diagram of Example 1 is shown in Figure 3(a), the distribution diagram of Example 2 is shown in Figure 3(b), the distribution diagram of Example 3 is shown in Figure 3(c), the distribution diagram of Example 4 is shown in Figure 3(d), the distribution diagram of Comparative Example 1 is shown in Figure 3(e), and the distribution diagram of Comparative Example 2 is shown in Figure 3(f). Based on the values ​​obtained in the measurements of the average aspect ratio and average circularity, a distribution diagram was prepared by plotting the minor axis of the copper particles along the minor axis and the aspect ratio of the copper particles along the vertical axis. The distribution diagram for Example 1 is shown in Figure 4(a), the distribution diagram for Example 2 is shown in Figure 4(b), the distribution diagram for Example 3 is shown in Figure 4(c), the distribution diagram for Example 4 is shown in Figure 4(d), the distribution diagram for Comparative Example 1 is shown in Figure 4(e), and the distribution diagram for Comparative Example 2 is shown in Figure 4(f). Furthermore, the shrinkage onset temperature of the copper powders obtained in the examples and comparative examples was measured according to the method described below, and the sintering density was evaluated. The results are shown in Table 1.

[0072] [Average Aspect Ratio and Average Circularity] 10 g of butyl carbitol (manufactured by Taishin Chemical Co., Ltd.) containing 35% 1256 (bisphenol A-type solid epoxy resin, manufactured by Mitsubishi Chemical Corporation) was added to 10 g of the copper powder obtained in the Examples and Comparative Examples. This mixture was mixed at 2000 rpm for 1 minute using a planetary centrifugal mixer manufactured by Thinky Corporation, and then degassed at 2200 rpm for 30 seconds to obtain a paste. The resulting paste was subjected to a three-roll process under three passes at 20 μm to break down agglomerates and obtain the final paste. The final paste was printed onto copper foil measuring 2 cm long x 1 cm wide x approximately 55 μm thick using a squeegee. This coating was then heated at 150°C for 10 minutes in an atmospheric atmosphere to obtain a dried coating. The dried coating film obtained was subjected to cross-section processing using a JEOL cross-section polisher (SM-09010) under conditions of 6 kV and 40 to 50 mA, and a particle cross-section image was obtained using a JEOL scanning electron microscope (JSM-7100F). More than 300 copper particles in the obtained particle cross-section image were measured using image analysis particle size distribution measurement software (Mac-View) manufactured by Mountec Co., Ltd., to obtain the aspect ratio and circularity. The average value of the obtained aspect ratios was taken as the average aspect ratio, and the average value of the circularities was taken as the average circularity.

[0073] [Tap Density] The tap density was measured using a tapping machine (model: KSR-406, manufactured by Kuramochi Scientific Machinery Manufacturing Co., Ltd.). ３ 120 g of copper powder was placed in a measuring cylinder. The tap stroke was set to 4 cm, and the number of tappings was set to 300 times for measurement.

[0074] [Particle size D ５０ , particle size D １０ , particle size D ９０Using an automatic sample feeder for a laser diffraction particle size distribution analyzer ("Microtrac SDC" manufactured by Microtrac Bell Co., Ltd.), copper powder was soaked in two drops of pure water containing 0.1% polyoxyethylene octylphenyl ether, and the pure water was added to a 0.1% aqueous solution of SN Dispersant 5468 manufactured by San Nopco Ltd. 40 W ultrasonic waves were irradiated to this aqueous solution for 5 minutes, and the particle size distribution was measured using a laser diffraction particle size distribution analyzer "MT3300EX II" manufactured by Microtrac Bell Co., Ltd., and the particle size D was calculated from the obtained volume-based particle size distribution chart. ５０ , particle size D １０ , particle size D ９０ and standard deviation SD were measured. ５０ , particle size D １０ , particle size D ９０ The flow rate when measuring the standard deviation SD was 65%, the "solvent refractive index" was 1.33, the particle permeability condition was "reflection", the measurement range was 0.122 μm or more and 704.0 μm or less, and the measurement time was 30 seconds.

[0075] [Shrinkage Start Temperature] A TMA / EXSTAR 6000 manufactured by Seiko Instruments Inc. was used as the TMA measuring device. 0.2 g of copper powder was placed in a 4.0 mm diameter aluminum mold container and press-molded to produce a pellet under a pressure of 1.0 MPa. The pellet length of the resulting pellet was measured and used as a sample. The sample was placed in the measuring device and heated at a rate of 10°C / min under a load of 49 mN in a nitrogen atmosphere. Measurement was started from room temperature (25°C), and a graph showing the relationship between temperature and shrinkage rate (%) was obtained. The shrinkage start temperature was determined from the graph normalized based on the maximum shrinkage rate.

[0076] [Sintering Density] 1.5 g of terpineol containing 10% Techpolymer (registered trademark) IBM-2 (acrylic resin, manufactured by Sekisui Plastics Co., Ltd.) dissolved therein was added to 10 g of the copper powder obtained in the Examples and Comparative Examples. This mixture was mixed at 2000 rpm for 1 minute using a planetary centrifugal mixer manufactured by Thinky Corporation, and then degassed at 2200 rpm for 30 seconds to obtain a paste. The resulting paste was subjected to a three-roll process under three passes at 20 μm to break down agglomerates and obtain a final paste. The final paste was printed onto a 5 cm x 5 cm alumina substrate, measuring 2 cm long x 1 cm wide x approximately 55 μm thick, using a squeegee. This coating was heated at 150°C for 10 minutes in an atmospheric atmosphere to obtain a dried coating. Using a KTF773N1 firing furnace manufactured by JTEKT Thermosystems Corporation, the temperature was raised to 800 ° C. at a heating rate of 30 ° C. / min under a nitrogen atmosphere, and the dried coating film was fired at 800 ° C. for 10 minutes to obtain a sintered film. Then, using a 5-digit balance manufactured by Shimadzu Corporation, AUW220D, the mass of the sintered film, including the mass of the alumina substrate, was weighed. The mass of the sintered film was calculated by subtracting the mass of the alumina substrate weighed in advance from this value. Furthermore, using a MICROGRANITE manufactured by PRECISION LAPPING, the thickness of the sintered film was measured at any three locations. The average value of the obtained values ​​was used as the thickness of the sintered film. The volume of the sintered film was calculated by multiplying this thickness by the vertical length and horizontal length obtained by measuring the sintered film. The density of the sintered film was calculated based on the mass and volume of the sintered film. The higher the density of the sintered film, the higher the sintering density.

[0077]

[0078] As is clear from the particle cross-sectional image shown in Figure 2, the copper powder obtained in Example 1 is composed of copper particles having various aspect ratios and circularities, while the copper powder obtained in Comparative Example 2 contains many excessively flattened copper particles. As is clear from the distribution diagram shown in Figure 3, in the copper powders of the Examples, the circularity of the copper particles is generally concentrated within a certain range regardless of the distribution of the minor diameter of the copper particles, while in the copper powders of the Comparative Examples, the minor diameter of the copper particles is generally concentrated within a certain range, although the circularity of the copper particles varies. As is clear from the distribution diagram shown in Figure 4, in the copper powders of the Examples, the aspect ratio of the copper particles is generally concentrated within a certain range regardless of the distribution of the minor diameter of the copper particles, while in the copper powders of the Comparative Examples, the aspect ratio of the copper particles is generally concentrated within a certain range, although the aspect ratio of the copper particles varies. As is clear from the results shown in Table 1, the copper powders obtained in the examples have higher shrinkage starting temperatures and sintering densities than the copper powders obtained in the comparative examples.

[0079] According to the present invention, there are provided copper powder that does not undergo sintering in the binder removal step and that allows the formation of a dense sintered film by low-temperature firing at, for example, about 800° C., and a method for producing the same.

Claims

1. Copper powder consisting of multiple copper particles having different aspect ratios, and having a tap density of 4.0 g / cm ３ 7.0g / cm or more ３ or less, and the volume cumulative particle size D at 50% cumulative volume by a laser diffraction scattering particle size distribution measurement method is ５０ The dispersity D is the ratio of the standard deviation SD of the particle size distribution to Ｐ The copper powder has a value of 0.55 or more and 0.90 or less.

2. The copper powder according to claim 1, wherein the copper particles have an average aspect ratio of 1.05 or more and 3.00 or less.

3. The copper powder according to claim 1 or 2, having an average circularity of 0.60 or more and 0.95 or less.

4. The copper powder according to claim 1 or 2, wherein the copper particles having a circularity of more than 0.95 account for 5.0% by number or less, and the number proportion of the copper particles having a circularity of more than 0.70 but not more than 0.95 is greater than the number proportion of the copper particles having a circularity of 0.70 or less.

5. The ratio of the number of copper particles having a circularity of 0.70 or less and the volume cumulative particle size D at 90% by volume of the cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method ９０ The copper powder according to claim 1 or 2, wherein the product of (μm) and (number % μm) is 500 (number % μm) or less.

6. The ratio of the number of copper particles having a circularity of more than 0.70 and not more than 0.95 and the particle diameter D ５０ The copper powder according to claim 1 or 2, wherein the product of (μm) and (μm) is 180 (number % μm) or more and 400 (number % μm) or less.

7. The ratio of the number of copper particles having a circularity of more than 0.95 and the volume cumulative particle size D at 10% by volume of the cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method １０ The copper powder according to claim 1 or 2, wherein the product of (μm) and (number % μm) is 0.1 (number % μm) or more.

8. The particle size D ５０ The copper powder according to claim 1 or 2, wherein the particle size is 2.0 μm or more and 8.0 μm or less.

9. The copper powder according to claim 1 or 2, wherein when thermomechanical analysis is carried out in a nitrogen atmosphere at a temperature increase rate of 10°C / min, the temperature at which the powder shrinks by 10% relative to the maximum shrinkage is 500°C or higher.

10. A method for producing copper powder, comprising a step of plastically deforming raw material powder consisting of copper particles into a flattened shape using a media agitation mill, wherein a workpiece consisting of a slurry containing the raw material powder is passed through the workpiece passing type media agitation mill only once.

11. A sintered body of the copper powder according to claim 1 or 2.

12. A multilayer ceramic capacitor having external electrodes made of the sintered body according to claim 11.

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

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