JP2013019002A - Flat metal particle and manufacturing method thereof - Google Patents

Abstract

The present invention provides a metal particle that can be sintered at a low temperature when a coating film formed from a paste containing the metal particle is heat-treated.
The flat metal particles of the present invention are in the form of flakes, and have a plurality of curved portions recessed along the outer edge from the outer edge toward the inside of the particle when viewed in plan. It is preferable that L / (A × π) is larger than 1.2 when the particle diameter in plan view is A (μm) and the circumference is L (μm). It is also preferable that the average particle diameter D ₅₀ measured by the laser diffraction / scattering particle size distribution measurement method is 0.5 to ₅ μm.
[Selection] Figure 1

Description

  The present invention relates to flat metal particles and a method for producing the same.

  Conventionally, as a method of forming electrodes and circuits of electronic components, etc., after printing a conductive paste in which metal particles such as copper particles, which are conductive materials, are dispersed in a paste on a substrate, the paste is sintered or cured. A method of forming a circuit is known. For example, when using a conductive paste for conduction of the external electrode of the ceramic capacitor, the conductive paste is applied to the external electrode, and then the binder is removed by heating, after which the copper particles are sintered. In this case, the shape of the copper particles is preferably flat rather than spherical in order to maintain the appearance, improve the binder removal efficiency, and improve the conductivity. This is because flat particles have a large specific surface area and a large contact area between the particles, which is effective in reducing electrical resistance and increasing the accuracy of the conductor shape.

  Recently, for the purpose of further reducing the electric resistance, fine and thin flat copper particles that are particles that can be sintered at low temperature have been demanded. However, since flat copper particles are generally produced by mechanically deforming spherical copper particles with a ball mill using beads (see, for example, Patent Documents 1 and 2), they are fine and thin using this method. If it is going to manufacture flat copper particles, there will be a problem of separation of beads after manufacture and a problem of contamination. In addition, when the spherical copper particles as the raw material have a large particle size, it takes a long time to make the particles thin and flat, and it cannot be said that the production efficiency is good.

  In addition to flat copper particles, silver particles are generally produced by mechanically deforming spherical particles with a ball mill using beads or the like (see, for example, Patent Documents 3 and 4). Therefore, the silver flat particles have the same problem as the copper flat particles.

2007-84860 publication 2007-254845 2009-242914 2010-236039

  An object of the present invention is to provide flat metal particles having various performances further improved as compared with the flat metal particles of the prior art described above.

  The present invention provides a flat metal particle having a flake shape and having a plurality of curved portions recessed along the outer edge from the outer edge toward the inside of the particle when viewed in plan. .

  Further, the present invention is flaky, and when the particle diameter in plan view is A (μm) and the circumference is L (μm), L / (A × π) is greater than 1.2. The flat metal particle which is characterized is provided.

Furthermore, the present invention provides a suitable method for producing the flat metal particles as described above.
Including a step of thinning the metal particles dispersed in the liquid medium using a media mill,
As the metal particles, aggregated particles composed of substantially spherical primary particles having a primary particle diameter of 0.01 to 0.3 μm and having an average particle diameter D ₅₀ of 0.5 to ₅ μm are used. ,
The present invention provides a method for producing flat metal particles, characterized in that the media mill beads have a diameter of ₂₀ to 500 times the average particle diameter D50 of the aggregated particles.

  According to the flat metal particle of this invention, when heat-processing the coating film formed from the paste containing this particle | grain, particle | grains can be sintered at low temperature. Moreover, according to the manufacturing method of the present invention, such flat metal particles can be efficiently manufactured without requiring a long time.

1 is a scanning electron microscope image of flat metal particles obtained in Example 1. FIG. 2A and 2B are scanning electron microscope images of the flat metal particles obtained in Comparative Examples 1 and 2, respectively.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The flat metal particles of the present invention are characterized by their flat flaky shape. Specifically, the flat metal particles of the present invention are in the form of flakes and have a shape having a plurality of curved portions recessed from the outer edge toward the inside of the particles when viewed in plan. Conventional flaky metal particles were manufactured by crushing spherical particles with beads and plastically deforming them. Therefore, the outer edge (contour) in plan view is circular or similar, and the outer edge is compared. It had a smooth shape. In contrast to this, the flat metal particles of the present invention have a shape in which the outer edge in plan view is irregularly and intricately complicated toward the inside of the particle, as shown in FIG. 1 described later. This intricate shape is formed along the outer edge and around the entire circumference of the outer edge. As a result, the outer edge has a shape in which fine notches are continuous over the entire circumference.

  Since the outer edge in a plan view has a shape in which fine notches are continuous, the flat metal particles of the present invention have a very long circumference. Therefore, when the circumference is L (μm) and the particle diameter obtained from the area of the particle in plan view is A (μm), the value of L / (A × π) is a perfect circle of the same area. It becomes very large compared to. Specifically, in the flat metal particles of the present invention, the value of L / (A × π) is preferably greater than 1.2, more preferably 1.3 or more, and even more preferably 1.4 or more. It becomes a big value. According to the flat metal particles of the present invention having such a large value of L / (A × π), when the coating film formed from the paste containing the particles is heat-treated, the particles can be sintered at a low temperature. The advantageous effect of being able to be produced is produced. The larger the value of L / (A × π), the more advantageous from the viewpoint of low-temperature sinterability, but if it is as large as 2, a low-temperature sinterability that is industrially satisfactory can be obtained.

  When calculating the value of L / (A × π), the values of L and A can be measured by, for example, image analysis type particle size distribution measurement software Mac view. Arbitrary particles 50 or more are selected as measurement objects, and an average value thereof is calculated from the values of L and A measured for the particles. Then, a value of L / (A × π) is calculated from the calculated average value of L and A.

The flat metal particles of the present invention are preferably fine particles in addition to the outer edges having a complicated shape. Specifically, the flat metal particles of the present invention preferably have an average particle size D ₅₀ measured by a laser diffraction / scattering particle size distribution measuring method of 0.5 to 5 μm, preferably 0.5 to 3 μm. Is more preferable, and it is still more preferable that it is 0.5-2 micrometers. According to such a fine flat metal particle, when the outer edge of the particle has a complicated and fine notched shape, when a coating film formed from the paste containing the particle is heat-treated, The particles can be sintered at low temperatures.

  The flat metal particles of the present invention are flaky as described above. The thickness of the flaky metal particles is preferably 10 to 300 nm, and more preferably 10 to 200 nm. The thickness of the particles can be measured, for example, by the image analysis software Mac view as described above.

  As described above, the flat metal particle of the present invention has an intricate and complicated outer edge. As a whole, the outer shape in a plan view can take a circular shape, a polygonal shape, an indefinite shape, or the like. In particular, the amorphous shape as a whole is preferable because the particles can be sintered at a lower temperature when a coating film formed from the paste containing the particles of the present invention is heat-treated.

  There is no particular limitation on the type of metal constituting the flat metal particles of the present invention, and any of a single metal and its alloy can be used as long as it can be stably used in the environment where the particles of the present invention are used. it can. When the flat metal particles of the present invention are used, for example, as a raw material for conductive paste, the metal particles are preferably highly conductive. Examples of such metals include silver and copper, and alloys thereof.

  Next, the preferable manufacturing method of the flat metal particle of this invention is demonstrated. This production method includes a step of dispersing metal particles as a raw material in a liquid medium and flattening the metal particles using a media mill. And this manufacturing method has one of the characteristics in the point which uses a specific particle as a metal particle used as a raw material.

The raw material particles used in the present invention are agglomerated particles (secondary particles) made of an aggregate of fine primary particles. The fine primary particles constituting the aggregated particles preferably have a particle size (primary particle size) of 0.01 to 0.3 μm, more preferably 0.01 to 0.1 μm. Aggregates formed by agglomerating a plurality of such fine particles, that is, secondary particles have an average particle diameter D ₅₀ of preferably 0.5 to ₅ μm, more preferably 1 to 2 μm. By using the secondary particles having the above-mentioned size formed by agglomerating the primary particles having the above-mentioned size as raw materials, the flaky metal particles having the special outer diameter described above can be easily obtained. The use of such agglomerated particles is in sharp contrast to the conventional method for producing flaky particles in which individual primary particles are crushed by media mill beads into flaky shapes.

The particle size (primary particle size) of the primary particles in the aggregated particles used in this production method is measured from image analysis of a photograph observed with a scanning electron microscope (SEM). The average particle diameter D ₅₀ of the aggregated particles (secondary particles) that are aggregates of the primary particles is measured by a laser diffraction / scattering particle size distribution measurement method.

The aggregated particles used as the raw material particles have a primary particle size (nm) / average particle size D ₅₀ (nm) of 0 in addition to the primary particle size and average particle size D ₅₀ being within the above-mentioned ranges. 0.002-0.6, especially 0.005-0.1 are preferred. By setting the value of the primary particle diameter / average particle diameter D ₅₀ within this range, the desired flaky metal particles can be obtained more successfully.

  The agglomerated particles used as the raw material particles can be produced, for example, as in JP-A-2007-239077 when the agglomerated particles are made of silver. On the other hand, when the agglomerated particles are made of copper, for example, it can be produced as described in JP-A-2009-62598.

  Prior to being processed by the media mill, the raw material particles are dispersed in a liquid medium to form a slurry. As a liquid medium used for the preparation of the slurry, for example, water or an organic solvent can be used. A mixed solvent of water and an organic solvent can also be used. Examples of the organic solvent include lower monoalcohols having 1 to 4 carbon atoms such as methanol and ethanol; lower polyhydric alcohols having 1 to 4 carbon atoms such as ethylene glycol; lower carboxylic acids having 1 to 4 carbon atoms; These lower amines can be used alone or in combination of two or more. Of these liquid media, it is preferable to use an organic solvent because the dispersibility of the raw material particles in the slurry is increased and the stability of the quality when processing with a media mill is increased. In particular, it is preferable to use lower alcohols such as methanol because they are easily volatilized and are difficult to remain on the target flaky metal particles.

The concentration of the raw material particles in the slurry is preferably 10 to 60% by mass, and preferably 20 to 50% by mass from the viewpoint of productivity and the prevention of the generation of coarse particles.

  In order to prepare the slurry, it is only necessary to simply mix the raw material particles and the liquid medium. In some cases, the slurry may be prepared using a stirring and dispersing device. Examples of such an apparatus include a fluid mill and T.I. K. Examples include Fillmix (registered trademark).

When the slurry is prepared as described above, the slurry and media beads are placed in a bead mill and mixed and stirred. This production method is also characterized by the size of the beads used. In particular, the size of the beads used in the present production method is determined by the relationship between the average particle diameter D ₅₀ of the raw material particles. Specifically, the diameter D (μm) of the beads is preferably 20 to 500 times, more preferably 20 to 150 times the average particle diameter D ₅₀ (μm) of the aggregated particles used as the raw material particles. Is used. By using beads in this range, the desired flaky metal particles can be successfully obtained. When the diameter D of the beads is less than 20 times the average particle diameter D ₅₀ of the aggregated particles, the force to make the flakes is weak and the aggregated particles are only crushed. On the other hand, when the diameter D of the beads is more than 500 times the average particle diameter D ₅₀ of the aggregated particles, uniform flaking is not easy, and a plurality of particles are likely to flake together, and strong aggregation is required. It becomes a collection.

The diameter D of the beads, where that is a above relation with respect to the average particle diameter D ₅₀ of aggregated particles, the exact value of the diameter D of the beads, the ratio of the diameter D of the beads to the average particle diameter D ₅₀ of the aggregate particles Is within the above-mentioned range, it is preferably 20 to 100 μm, particularly preferably 20 to 50 μm.

  The material of the beads is determined by the relationship with the material of the aggregated particles that are the processing object. In general, satisfactory results are obtained by using beads of zirconia, alumina or glass. When glass beads are used, it is preferable that the components of the beads are unlikely to remain on the particle surface, and particles having a small amount of impurity components are easily obtained. However, when glass beads are used, it is necessary to adopt a condition that does not cause breakage of the glass beads during operation of the media mill. As in the case of glass beads, it is necessary for the alumina beads to adopt conditions that do not cause destruction of the alumina beads during the operation of the media mill. On the other hand, zirconia beads can be selected from a wide range of operating conditions because zirconia beads are not destroyed within the range of operating conditions of a media mill that can be normally considered.

  When the media mill is operated, it is preferable to contain 40 to 90% by volume of beads, more preferably 60 to 80% by volume of beads, based on the volume of the vessel vessel of the mill. Within this range, the raw material particles can be thinned efficiently, and the generation of coarse particles can be effectively prevented.

  What is necessary is just to adjust suitably the operation time of a media mill, a rotational speed, the frequency | count of a pass, etc. so that the target flaky metal particle may be obtained.

  According to this manufacturing method, the aggregated particles are thinned by plastic deformation due to collision with the beads. In this case, unlike the conventional thinning, the individual primary particles are not thinned, but the aggregated particles in which the primary particles are aggregated are thinned as a whole. As a result, the obtained metal particles have a complicated shape in which the outer edge in a plan view is obtained by randomly connecting the outer edges of individual thinned particles. Moreover, since each primary particle itself is very small, it becomes extremely thin by plastic deformation due to collision with the beads. Therefore, after the aggregated particles are exfoliated as a whole, the thickness thereof is extremely thin although the area of the particles in a plan view is relatively large. Therefore, the obtained flaky metal particles are easily sintered at a low temperature.

  In addition, according to this production method, since the raw material particles can be thinned without using fine beads and without requiring a long-time treatment, contamination from beads caused by a long-time treatment by a media mill is prevented. It is possible to avoid problems and problems of reduced production efficiency.

  When the target metal particles are obtained as described above, the slurry and the beads are separated. There are no particular limitations on the means for separation, and for example, the slurry can be easily separated by filtering the slurry containing beads in a mesh. Then, the slurry from which the beads have been removed is allowed to stand for a certain period of time to precipitate the metal particles, and then the supernatant is discarded and then filtered to collect the target metal particles. Further, when a device equipped with a bead separator is used as the media mill, ex-post bead separation is not necessary. Examples of such an apparatus include a super apex mill (trade name) manufactured by Kotobuki Kogyo Co., Ltd. and a dyno mill.

  The separated flaky metal particles are then washed and dried to remove impurities and moisture. For example, water and alcohols such as ethanol and methanol are used for washing. Preferably, the contaminant attached to the surface of the metal particles can be efficiently removed by washing with water and then repeatedly washing with alcohol twice or more and strengthening the washing. Drying after washing is generally performed at a temperature of about 50 ° C. to 80 ° C. for 3 hours to 8 hours.

  The flaky flat metal particles thus obtained are suitably used, for example, as a raw material for conductive paste by utilizing the low temperature sintering property. This conductive paste contains, for example, the flaky flat metal particles of the present invention, an organic vehicle, and glass frit. This organic vehicle includes a resin component and a solvent. Examples of the resin component include acrylic resin, epoxy resin, ethyl cellulose, carboxyethyl cellulose, and the like. Examples of the solvent include terpene solvents such as terpineol and dihydroterpineol, and ether solvents such as ethyl carbitol and butyl carbitol. Examples of the glass frit include borosilicate glass, borosilicate barium glass, and borosilicate zinc glass. The ratio of the metal particles in the conductive paste is preferably 36 to 97.5% by mass. The ratio of the glass frit is preferably 1.5 to 14% by mass. The proportion of the organic vehicle is preferably 1 to 50% by mass. As the metal particles in this conductive paste, only the flat metal particles of the present invention may be used, or the flat metal particles and copper particles having other shapes such as a spherical shape may be used in combination. By using a combination of the flat metal particles of the present invention and copper particles of other shapes such as spheres, it becomes easy to precisely adjust the viscosity of the paste.

  The conductive paste thus obtained is suitably used for, for example, circuit formation of printed wiring boards, ensuring electrical continuity of interconnectors of solar cell modules, external electrodes of ceramic capacitors, and EMI countermeasures. .

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

[Example 1]
(1) Production of Raw Material Particles Silver raw material particles were produced according to the method described in JP 2007-239077 A. 100 g of silver nitrate was used as a silver source. As a chelating agent, 150 g of ethylenediaminetetraacetic acid / tetrasodium salt was used. An additional 15 g of gelatin was used. These were stirred and dissolved in 2.0 liters of pure water to prepare a silver-containing solution having a liquid temperature of 50 ° C. On the other hand, potassium sulfite was used as a reducing agent, 150 g of which was stirred and dissolved in 2.0 liters of pure water to prepare a reducing agent-containing solution having a liquid temperature of 50 ° C. Next, the reducing agent-containing solution was added all at once to the silver-containing solution to obtain a mixed solution. And while maintaining the liquid temperature of this liquid mixture at 50 degreeC, it stirred for 1 hour, the reduction reaction was performed, and the raw material particle which consists of a fine silver particle was produced | generated in the liquid mixture. The primary particle diameter and the average particle diameter D ₅₀ of the obtained raw material particles was measured by the method described above, the primary particle diameter is 35 nm, the average particle diameter D ₅₀ was 1.0 .mu.m.

(2) Preparation of slurry and treatment with media mill 5 kg of the raw material particles obtained in the above (1) and 10 kg of methanol were mixed to prepare a methanol slurry having a raw material particle concentration of 33%. 15 kg of this slurry was placed in Star Mill (registered trademark) LMZ, which is a bead mill manufactured by Ashizawa Finetech Co., Ltd., and 4.85 kg of zirconia beads having a diameter of 0.1 mm were further placed, and the bead mill was operated for 20 minutes. Thereafter, the slurry and the beads were separated by filtration, and then the slurry was allowed to stand to precipitate the metal particles. The target metal particles were collected by removing the supernatant and filtering. Next, washing with water and subsequent washing with methanol were repeated twice to obtain the desired flaky flat metal particles.

(3) Evaluation FIG. 1 shows a scanning electron microscope (SEM) image of the obtained metal particles. As is clear from the figure, the obtained metal particles were flaky and flat, and had a plurality of curved portions whose outer edges in a plan view were recessed toward the inside of the particles. It can be seen that the overall shape in plan view is irregular. Moreover, about the obtained metal particle, L was measured for the particle diameter A and perimeter in planar view by the above-mentioned method. The results are shown in Table 1 below. Moreover, about the obtained metal particle, the electrical resistance value after baking at 150 degreeC was measured. The results are also shown in Table 1 below. The firing and measurement procedures are as follows. After removing the solvent at 80 ° C. for 10 minutes in an air atmosphere with a hot air dryer, the mixture was baked at 150 ° C. for 1 hour in an electric furnace. Thereafter, the specific resistance was measured with a resistivity meter manufactured by Mitsubishi Chemical.

[Comparative Example 1]
(1) Manufacture of raw material particles SPQ03R (trade name), which is silver powder manufactured by Mitsui Mining & Smelting, was used as raw material particles. The primary particle diameter and the average particle diameter D ₅₀ of the raw material particles was measured by the method described above, the primary particle size is 0.5 [mu] m, an average particle diameter D ₅₀ was 0.75 .mu.m.

(2) Preparation of slurry and treatment by media mill 1 kg of raw material particles and 4 kg of methanol were mixed to prepare a methanol slurry having a raw material particle concentration of 20%. 5 kg of this slurry was placed in Star Mill (registered trademark) LMZ, which is a bead mill manufactured by Ashizawa Finetech Co., Ltd., and 4.85 kg of zirconia beads having a diameter of 0.1 mm were further placed, and the bead mill was operated for 15 minutes. Thereafter, the slurry and the beads were separated by filtration, and then the slurry was allowed to stand to precipitate the metal particles. The target metal particles were collected by removing the supernatant and filtering. Next, washing with water and subsequent washing with methanol were repeated twice to obtain the desired flaky flat metal particles.

(3) Evaluation FIG. 2A shows a scanning electron microscope (SEM) image of the obtained metal particles. As is clear from the figure, although the obtained metal particles are flat, the outer edge in plan view is smooth and has a substantially circular shape. The particles were evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

[Comparative Example 2]
(1) Manufacture of raw material particles SPQ08S (trade name), which is silver powder manufactured by Mitsui Mining & Smelting, was used as raw material particles. The primary particle diameter and the average particle diameter D ₅₀ of the raw material particles was measured by the method described above, the primary particle size is 1.5 [mu] m, an average particle diameter D ₅₀ was 1.7 [mu] m.

(2) Preparation of slurry and treatment by media mill 2.3 kg of raw material particles and 4.7 kg of methanol were mixed to prepare a methanol slurry having a raw material particle concentration of 33%. 7 kg of this slurry was placed in Starmill (registered trademark) LMZ, which is a bead mill manufactured by Ashizawa Finetech Co., Ltd., and 4.85 kg of zirconia beads having a diameter of 0.1 mm were further placed, and the bead mill was operated for 10 minutes. Thereafter, the slurry and the beads were separated by filtration, and then the slurry was allowed to stand to precipitate the metal particles. The target metal particles were collected by removing the supernatant and filtering. Next, washing with water and subsequent washing with methanol were repeated twice to obtain the desired flaky flat metal particles.

(3) Evaluation FIG. 2B shows a scanning electron microscope (SEM) image of the obtained metal particles. As is clear from the figure, although the obtained metal particles are flat, the outer edge in plan view is smooth and has a substantially circular shape. The particles were evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

[Comparative Example 3]
Flat silver particles were obtained according to the method described in Example 1 of Patent Document 3 (2009-242914). A scanning electron microscope (SEM) image of the obtained particles is shown in FIG. As can be seen from the figure, the obtained metal particles are flat, but do not have a plurality of curved portions recessed from the outer edge toward the inside of the particles in plan view. The particles were evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

[Comparative Example 4]
Flat silver particles were obtained according to the method described in Example 1 of Patent Document 4 (2010-236039). A scanning electron microscope (SEM) image of the obtained particles is shown in FIG. As can be seen from the figure, the obtained metal particles are flat, but do not have a plurality of curved portions recessed from the outer edge toward the inside of the particles in plan view. The particles were evaluated in the same manner as in Example 1. The results are shown in Table 1 below.

  As is clear from the results shown in Table 1, the flat metal particles of the examples have lower electrical resistance during low-temperature sintering and excellent low-temperature sinterability than the particles of Comparative Examples 1 to 4. I understand that.

Claims (9)

  A flat metal particle having a plurality of curved portions which are in a flaky shape and are recessed from the outer edge toward the inside of the particle when viewed in plan, along the outer edge.   2. The flat metal particle according to claim 1, wherein L / (A × π) is larger than 1.2 when the particle diameter when viewed in plan is A (μm) and the circumference is L (μm).   A flat metal having a flaky shape, wherein L / (A × π) is larger than 1.2 when the particle diameter in a plan view is A (μm) and the circumference is L (μm) particle. The flat metal particle according to any one of claims 1 to 3, wherein an average particle diameter D50 measured by a laser diffraction / scattering particle size distribution measurement method is 0.5 to ₅ µm.   The flat metal particle according to any one of claims 1 to 4, wherein the metal is silver or copper. A method for producing flat metal particles in which metal particles dispersed in a liquid medium are thinned using a media mill,
As the metal particles, aggregated particles composed of substantially spherical primary particles having a primary particle diameter of 0.01 to 0.3 μm and having an average particle diameter D ₅₀ of 0.5 to ₅ μm are used. ,
A method for producing flat metal particles, wherein the media mill beads have a diameter of ₂₀ to 500 times the average particle diameter D50 of the aggregated particles. The method according to claim 6 the value of primary particle diameter / average particle diameter D ₅₀ is from .002 to .06.   The manufacturing method according to claim 6 or 7, wherein the metal particles are silver particles or copper particles.   A conductive paste comprising the flat metal particles according to any one of claims 1 to 5.