KR20230002835A - silver particles - Google Patents

Abstract

Silver particles with excellent conductivity and dispersibility and a method for producing the same are provided. It has projections protruding radially from the center, the average particle diameter (D) is 0.1 to 10 μm, the specific surface area (S) is 0.1 to 10 m / g, and the true specific gravity (ρ) and average particle diameter ( The product of D) and the specific surface area (S) is 12 or more and 24 or less, silver particles.

Description

silver particles

The present invention relates to silver particles.

Regarding conductive ink or conductive paste, it is required to be capable of drawing wires with a narrower width and a smaller pitch. Moreover, even when it is applied thinly, it is desired to be able to form a smooth surface and to obtain highly reliable conductivity.

In response to such market demands, the use of silver nanoparticles, for example, has been examined. When silver nanoparticles are used, ultra-fine wires and thin films can be formed, but in order to obtain highly reliable conductivity, it is necessary to mix a high amount of silver nanoparticles, and deformation or cracking occurs due to volumetric shrinkage during firing. there is a risk of

In addition, the use of dendritic (dendritic) particles or flaky silver particles has been studied. When dendritic silver particles are used, since conductivity is expressed due to entanglement of the resin portion, conductivity can be maintained even if the compounding amount of the silver particles is reduced. Deformation and cracking can be suppressed by reducing the compounding amount, but since the resin part has a long protruding shape, it is not suitable for forming ultra-fine wires or thin films. In addition, when the resin portion is elongated, there are problems that bending of the resin portion affects conductivity and that a gap is easily generated between the resin portions when mixed with the resin component.

In addition, flaky silver particles easily cause adhesion between planes, and use of a large amount of surface treatment agent (lubricant) is required to improve dispersibility. However, when a large amount of the surface treatment agent is blended, there is a problem that the conductivity is lowered because the surface treatment agent inhibits the electrical connection between the flaky silver particles.

Japanese Unexamined Patent Publication No. 2011-168806 Japanese Unexamined Patent Publication No. 2011-26665 WO2012/063747 A1 Japanese Unexamined Patent Publication No. 2009-144196 Japanese Patent No. 4335968 Japanese Patent No. 4534098

This invention was made in view of the above problems, and aims at providing silver particles excellent in conductivity and dispersibility.

Patent Literatures 1 to 4 describe metal particles having protrusions protruding radially from the center, but as shown in FIG. 5, the silver particles of the present invention are a combination of shape, average particle diameter, and specific surface area. it is different

The silver particles according to the present invention have protrusions protruding radially from the center, have an average particle diameter (D) of 0.1 to 10 μm, a specific surface area (S) of 0.1 to 10 m / g, and a true specific gravity of the silver particles ( It is assumed that the product of true ratio weight (ρ), average particle diameter (D), and specific surface area (S) is 12 or more and 24 or less.

The silver particles can have a tap density of 2 to 4 g/cm 3 .

The manufacturing method of the silver particle which concerns on this invention is arrange|positioned facing each other so that approach/separation is possible, and the 1st processing with at least one side rotates with respect to the other side, and the 2nd processing with a processing part which has a surface, It is provided In the manufacturing method of silver particles in which silver particles are precipitated by reducing silver ions in a liquid phase reaction system using a forced thin film reactor, between the first processing with face and the second processing with face, The liquid to be treated is introduced, and a force is generated to move the second treated face away from the first treated face by the pressure of the treated fluid, and this force causes the first treated fluid to be treated. A minute distance is maintained between the face and the second handling face, and the fluid to be treated passing between the first handling face and the second handling face maintained at this minute distance forms a thin film fluid, Silver particles are obtained by the reaction of the metal ion and the reducing agent in the thin film fluid, the content ratio of silver nitrate and the reducing agent in the fluid to be treated is 0.3 to 0.9 in terms of molar ratio (silver nitrate/reducing agent), and the number of rotations of the processing part is 2000 It is -5000 rpm, and it is assumed that the back pressure in the processing part is 0.005 - 0.05 Mpa.

According to the silver particles of the present invention, excellent conductivity and dispersibility are obtained.

[Fig. 1] A schematic diagram showing the configuration of a forced thin film reactor.
[Fig. 2] A schematic diagram showing a processing section of a forced thin film reactor.
[Fig. 3] An electron micrograph of silver particles obtained in Examples (magnification: 20000 times).
[Fig. 4] An electron micrograph of silver particles obtained in Examples (magnification: 30000 times).
[Fig. 5] A scatter plot showing the relationship between average particle diameter and specific surface area.
[Fig. 6] A scatter plot showing the relationship between average particle diameter and tap density.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described more specifically.

As shown in Figs. 3 and 4 (electron micrographs of silver particles obtained in Examples described later), the silver particles according to one embodiment of the present invention have protrusions protruding radially from the center. In addition, the average particle diameter (D) is 0.1 to 10 μm, the specific surface area (S) is 0.1 to 10 m / g, and the true specific gravity (ρ) of the silver particles, the average particle diameter (D) and the specific surface area (S) It is assumed that the product of is 12 or more and 24 or less.

The average particle diameter of the silver particles according to this embodiment is not particularly limited as long as it is 0.1 to 10 μm, but, for example, when used for an electrically conductive paste, from the viewpoint of dispersibility and coatability, it is 1 μm to 5 μm It is desirable to be When it is 0.1 μm or more, good dispersibility is obtained and it is difficult to aggregate, and when it is 10 μm or less, it is easy to draw fine wiring. Here, the average particle diameter in this specification means the particle diameter (primary particle diameter) at 50% of the integrated value in the particle size distribution obtained by the laser diffraction scattering method.

The specific surface area of the silver particles according to the present embodiment is not particularly limited as long as it is 0.1 to 10 m 2 /g. For example, when used for a conductive paste, it is preferably 0.2 to 2 m 2 /g from the viewpoint of contact area and conductivity. Do. When it is 0.1 m 2 /g or more, compared with spherical silver particles, it is easy to obtain excellent conductivity, and when it is 10 m 2 /g or less, it is easy to improve the subject of dendrite-like silver particles. Here, the specific surface area in the present specification means that the measurement sample is placed in a vacuum dryer, treated at room temperature for 2 hours, and then filled with the sample so that the cell becomes dense, and then set in a BET specific surface area measuring device, Then, after performing a pretreatment for 60 minutes at a degassing temperature of 40°C, it is set as the measured value.

The shape of the silver particles according to the present embodiment can approximate a star polyhedron, and if a regular dodecahedron or a regular icosahedron is used as an approximate model, the specific surface area is expressed by the following equations (1) and (2) The theoretical value can be obtained by

<The forming polyhedron of the regular dodecahedron>

Specific surface area (S) ≈ 12 / (true specific gravity (ρ) × average particle diameter (D)) ... (One)

<The forming polyhedron of the regular icosahedron>

Specific surface area (S) ≈ 24 / (true specific gravity (ρ) × average particle diameter (D)) ... (2)

From the said Formula (1) and Formula (2), the product of the true specific gravity (rho) of the silver particle which concerns on this embodiment, the average particle diameter (D), and the specific surface area (S) is 12 or more and 24 or less. And, the true specific gravity (ρ) of silver is 10.49 g/cm 3 .

In addition, the theoretical value can be calculated|required for the specific surface area of silver particle of spherical shape and flake shape (when a planar shape is a perfect circle) by following Formula (3) and Formula (4).

<Jin Gu-sang>

Specific surface area (S) = 6 / (true specific gravity (ρ) × average particle diameter (D)) ... (3)

<Flakes>

Specific surface area (S) = 2 (aspect ratio + 2) / (true specific gravity (ρ) × average particle diameter (D)) ... (4)

From the above equation (3), the product of the true specific gravity (ρ) of the spherical silver particles, the average particle diameter (D), and the specific surface area (S) is 6. Since the silver particles according to the present embodiment have a product of true specific gravity (ρ), average particle diameter (D), and specific surface area (S) of 12 or more and 24 or less, compared to true spherical silver particles of the same volume, 2 to 4 times It can be seen that it has a specific surface area of about. The characteristic improved in proportion to a specific surface area can be improved by using the silver particle which concerns on this embodiment for a conductive composition etc. Specifically, compared to spherical silver particles, even with the same blending amount, the contact area between the particles increases, thereby improving conductivity, or increasing the bonding interface with the resin to be blended, so that the strength of the composition is improved compared to that of spherical silver particles. can

From the above formula (4), the product of the true specific gravity (ρ) of the flaky silver particles, the average particle diameter (D), and the specific surface area (S) is 24 to 204 when the aspect ratio of the flake silver particles is 10 to 100, , it can be seen that the specific surface area is about 4 to 35 times larger than that of spherical silver particles of the same volume. In addition, it was confirmed that the dendrite-like silver particles had a specific surface area about 10 to 30 times larger than that of spherical silver particles having the same volume, based on the measured values of commercially available products measured in Examples described later. Therefore, even for flaky or dendrite-like silver particles, by using them in a conductive composition or the like, the properties that are improved in proportion to the specific surface area can be improved over spherical silver particles, but as described above, flaky silver particles have dispersibility and conductivity As for compatibility, dendrite-like silver particles have problems such as being unsuitable for forming ultra-fine wires or thin films.

The specific surface area for the same volume of the silver particles according to the present embodiment is larger than that of the spherical shape and smaller than that of the flaky or dendrite phase, and the silver particles according to the present embodiment have a good balance of characteristics possessed by the spherical, flake, and dendrite phases. is to be provided with Specifically, since the silver particles according to the present embodiment have protrusions protruding radially from the central portion, adhesion between planes is difficult to occur, and even without a surface treatment agent (lubricant), it is difficult to aggregate, and excellent dispersibility is easily obtained. . In addition, since the silver particles according to the present embodiment have protrusions protruding radially from the center, excellent conductivity is easily obtained by entanglement of the protrusions, and when pressed to an electrical contact, a protective film or an oxide film on the surface of the electrical contact The so-called spike effect, which tears the insulating film of the back and improves connection reliability with the conductive circuit, is also obtained.

Here, the silver particle which concerns on this embodiment has a shape different from the conventionally known dendrite phase. Specifically, the silver particles related to this embodiment have protrusions protruding radially from the center, but in the case of the dendrite phase, the protrusions protruding from the surface of the particles diverge further from the main branch, resulting in a planar or three-dimensional shape. It is different from the silver particle concerning this embodiment in that it is dendritic grown by. Therefore, there is no problem that the bending of the resin part affects the conductivity, such as in the dendrite phase, or a problem that a gap is formed between the resin parts when mixed with the resin component. In addition, from the relationship between the average particle diameter and the specific surface area of the silver particles according to the present embodiment, the protruding portion can be adapted to the formation of ultra-fine lines or thin films, rather than a shape elongated like a dendrite.

Although the tap density of the silver particle concerning this embodiment is not specifically limited, It is preferable that it is 2-4 g/cm<3>, and it is more preferable that it is 2.5-3.5 g/cm<3>. When the tap density is within the above range, voids are less likely to occur when the conductive composition is produced, and volumetric shrinkage is less likely to occur during drying or firing.

As a method for producing silver particles according to the present embodiment, a method in which silver nitrate and a reducing agent are reacted in a thin film fluid using the forced thin film reactor 1 is exemplified.

As the forced thin film reaction device 1, as shown in FIGS. 1 and 2, for example, a liquid A tank 10 for storing an aqueous solution containing a reducing agent (hereinafter also referred to as liquid A), and a temperature of liquid A A liquid A heat exchanger 11 for adjusting the heat exchanger 11, a compressor not shown for sending air to the liquid A tank 10, a liquid B container 20 for storing an aqueous solution of silver nitrate (hereinafter also referred to as liquid B), A stirrer 21 for stirring the inside of the liquid B container 20, a pump 22 for liquid B for discharging liquid B from the liquid B container 20, and a heat exchanger for liquid B 23 for adjusting the temperature of liquid B ), and processing portion 3 that converts the fluids to be processed (liquid A and liquid B) into a thin film fluid, and the first processing portion 4 and the second processing portion 5 constituting the processing portion 3 ) and having a rotational drive device 2 that relatively rotates.

First, the flow of Liquid A will be described with reference to FIG. 1 . Air is sent into the liquid A tank 10 by a compressor (not shown) and the pressure in the liquid A tank 10 rises, so that the liquid A is transferred from the liquid A tank 10 to the heat exchanger 11 for liquid A. After being sent and temperature-adjusted, it is sent to the part 3 for a process.

The feeding speed of Liquid A is not particularly limited, but is preferably 200 to 1000 ml/min, and more preferably 500 to 700 ml/min. When the liquid feed rate is within the above range, silver particles having a desired average particle diameter and specific surface area are easily obtained.

Although the temperature of liquid A is not specifically limited, It is preferable that it is 10-40 degreeC, and it is more preferable that it is 20-30 degreeC. When the temperature of the liquid A is within the above range, it is easy to obtain silver particles having a desired average particle diameter and specific surface area.

Next, the flow of Liquid B will be described with reference to FIG. 1 . In the liquid B container 20, the stirrer 21 is rotating, so that silver nitrate is uniformly dispersed in the aqueous solution. And B liquid is sent to the processing part 3, after being sent to the B liquid heat exchanger 23 from the B liquid container 20 by the B liquid pump 22, and temperature-adjusted.

The feed rate of Liquid B is not particularly limited, but is preferably 10 to 200 ml/min, and more preferably 50 to 150 ml/min. When the liquid feed rate is within the above range, silver particles having a desired average particle diameter and specific surface area are easily obtained.

The temperature of Liquid B is not particularly limited, but is preferably 10 to 40°C, and more preferably 20 to 30°C. When the temperature of Liquid B is within the above range, it is easy to obtain silver particles having a desired average particle diameter and specific surface area.

As shown in FIG. 2, the processing portion 3 has a first processing portion 4 and a second processing portion 5 installed to be relatively approachable and separated from each other. The 1st handling with part 4 and the 2nd handling with part 5 each have the 1st handling with face (not shown) and the 2nd handling with face 5' facing each other. In the 1st handling part 4, for introducing liquid A sent to the part 3 for handling between the 1st handling with face and the 2nd handling with face 5', as shown by the arrow A As shown by the arrow B, the flow path 6 for liquid A and the liquid B sent to the part 3 for processing is for liquid B for introducing between the face 5' with the 1st handling and the 2nd handling with face 5' A flow path 7 is installed.

Through the flow passages 6 and 7, the first treatment with the face and the second treatment with the pressure of the fluid to be treated introduced between the face 5' (Liquid A and B) to be treated from the face with the first treatment A force is generated to move the two-handling face 5' in the direction of separation, and by this force, the first hand-handling face and the second hand-handling face 5' are held at a minute interval, and this The fluid to be processed that passes between the first processing face and the second processing face 5' held at a minute interval forms a thin film fluid. Then, the second processing portion 5 is relatively rotated with respect to the first processing portion 4 by the rotary driving device 2, so that the processing target fluid is uniformly mixed while the processing portion 3 ) is extruded outward in the radial direction of

In the mixed fluid to be treated, silver ions in the fluid to be treated are reduced and silver particles are precipitated by the reaction between silver nitrate and the reducing agent.

The content ratio of silver nitrate and reducing agent in the fluid to be treated is 0.3 to 0.9, preferably 0.5 to 0.7, in terms of molar ratio (silver nitrate/reducing agent). It is easy to obtain silver particles having a desired average particle diameter and specific surface area by making silver nitrate and a reducing agent react at the above content ratio.

The rotation speed of the part 3 for a process is 2000-5000 rpm, and it is preferable that it is 3000-4000 rpm. When the number of revolutions is 2000 rpm or more, the fluid to be treated in the processing portion 3 is sufficiently stirred, and uniform particles are easily generated. In addition, when the rotation speed is 5000 rpm or less, the target fluid does not become high temperature due to frictional heat, and desired particles are easily generated.

The back pressure in the processing part 3 is 0.005-0.05 MPa, and it is preferable that it is 0.01-0.03 MPa. When the back pressure is within the above range, it is easy to obtain silver particles having a desired average particle diameter and specific surface area. Here, the back pressure refers to the separation of the first processing portion 4 from the first processing surface 5' when the fluid to be processed passes between the first processing portion 4 and the second processing portion 5 It is the pressure which presses from the back surface of the 1st handling part 4 against the force which tries to spread in the direction to be made. When the back pressure is 0.005 MPa or more, the gap between the handling portion 3 is not too wide, and the desired stirring force is easily obtained.

The reducing agent is not particularly limited, but examples thereof include sodium borohydride, sodium hypophosphite, hydrazine, transition metal element ions (trivalent titanium ion, divalent cobalt ion, etc.), alcohol such as methanol, ethanol, 2-propanol, and glucose , reducing saccharides such as maltose, ascorbic acid, erythorbic acid, and the like.

As such a forced thin film reaction device 1, those described in Patent Documents 5 and 6 can be used, for example, and specifically, a forced thin film reaction device “ULREA SS-11” manufactured by M-technique, etc. can be used. can

<Example>

Examples of the present invention are shown below, but the present invention is not limited by the following examples. In the following, content and the like are based on mass unless otherwise specified.

[Example 1]

1 kg of L-ascorbic acid was dissolved in 10 L of water to prepare a 9.1 mass % L-ascorbic acid aqueous solution, which was used as reaction solution A. Furthermore, with respect to 2 L of water, 1 kg of silver nitrate was dissolved, and the 33 mass % silver nitrate aqueous solution was prepared, and it was set as the reaction liquid B.

The reaction was performed under the following conditions using a forced thin film reactor "ULREA SS-11" manufactured by M-technique. Specifically, the reaction solution A and the reaction solution B were mixed in a thin film fluid formed between the first processing face and the second processing face of the forced thin film reaction device, and the resulting mixed solution was allowed to stand still for 1 hour. After that, 550 g of silver particles were obtained by filter separation/washing using filter paper of No. 5 and drying within a vacuum desiccator for 24 hours (yield: about 85%).

<Device setting conditions>

Shape/Material of processing part: Silicon carbide (SiC) annular grooved disc and rotating disc

Rotational speed of processing unit: 3000 rpm

Back pressure of processing part: 0.02MPa

Temperature of reaction solution A: 25°C

Feeding rate of reaction solution A: 600 ml/min

Temperature of reaction solution B: 25°C

Feed rate of reaction solution B: 100 ml/min

About the obtained silver particle, the particle size distribution, specific surface area, and tap density were measured with the following measuring method.

- Average particle diameter (D50): integrated in the particle size distribution obtained by the laser diffraction scattering method using a laser diffraction type particle size distribution analyzer ("MT3300EX II" manufactured by Microtrac Bell Co., Ltd., measurement medium: water) The particle diameter at 50% of the value was taken as the average particle diameter.

Specific surface area: Put the measurement sample in a vacuum dryer, treat at room temperature for 2 hours, and then fill the sample so that the cell becomes dense, BET specific surface area measuring device (manufactured by Shimadzu Seisakusho, Inc. VII2390”), and then pre-processed at a degassing temperature of 40° C. for 60 minutes, and then measured.

・Tap density: After gently filling the cylinder of “Tap Denser KYT-5000” manufactured by Seishin Kikyo Co., Ltd. with the obtained silver particles, tapping (moving the cylinder upwards and then letting the cylinder fall freely) , the voids between the silver particles were destroyed, and the apparent bulk density when densely packed was measured.

The silver particles obtained in Example 1 had an average particle diameter of 4.97 μm, a specific surface area of 0.28 m 2 /g, and a tap density of 2.9 g/cm 3 , and the results were plotted on scatter plots in FIGS. 5 and 6 . From these results, the product of true specific gravity (ρ), average particle diameter (D), and specific surface area (S) was 14.6.

In addition, for a plurality of commercially available spherical silver particles, flaky silver particles, and dendrite-like silver particles, the average particle diameter, specific surface area, and tap density were extracted from the catalog, and those without description were measured according to the above method. The results are shown in Table 1 and plotted on the scatter plots in FIGS. 5 and 6 . In addition, the average particle diameter and specific surface area of silver particles were extracted from the descriptions of Patent Documents 1 to 4, and the regions 30 to 33 to which the silver particles described in these documents belong were shown in a scatter plot in FIG. 5 . In addition, the theoretical value of the specific surface area of the spherical silver particle and flaky silver particle calculated|required from said Formula (3) and Formula (4) was shown by the dotted line.

[Table 1]

5, flaky silver particle No. 13 belongs to the region 40. However, as described above, flaky silver particles are prone to flat surface adhesion, and a large amount of surface treatment agent (lubricant) is required to improve dispersibility, and since the surface treatment agent inhibits conductivity, dispersion There is a problem that it is difficult to balance performance and conductivity. Therefore, since the silver particle which concerns on this embodiment differs in shape from the flaky silver particle, it has a different characteristic.

5, in the region 40, spherical silver particles No. 2 belongs to However, since the spherical silver particles do not have protrusions, they have different characteristics at least regarding conductivity from the silver particles of the present embodiment.

From these results, it turns out that the silver particle which concerns on this embodiment differs from conventionally known spherical, flaky, and dendrite-shaped silver particle in shape, average particle diameter, and a combination of a specific surface area.

1: forced thin film reaction device
2: rotation drive mechanism
3: processing unit
4: first processing unit
5: second processing unit
5 ': 2nd processing surface
6: Euro for Liquid A
7: Euro for Liquid B
10: Liquid A tank
11: heat exchanger for liquid A
20: liquid B container
21 : Stirrer
22: pump for liquid B
23: B liquid heat exchanger
30: region to which the particles described in Patent Document 1 belong
31: region to which the particles described in Patent Document 2 belong
32: region to which the particles described in Patent Document 3 belong
33: region to which the particles described in Patent Document 4 belong
40: region to which silver particles according to the present invention belong

Claims (3)

With protrusions protruding radially from the center,
The average particle diameter (D) is 0.1 to 10 μm,
The specific surface area (S) is 0.1 to 10 m 2 / g,
The product of the true specific gravity (ρ) of the silver particles, the average particle diameter (D), and the specific surface area (S) is 12 or more and 24 or less,
silver particles. According to claim 1,
Silver particles having a tap density of 2 to 4 g/cm 3 . By using a forced thin-film reactor having a processing portion having a first processing surface and a second processing surface disposed opposite to each other so as to be approachable and spaced apart and having at least one side rotating with respect to the other side, the liquid phase A method for producing silver particles in which silver particles are precipitated by reducing silver ions in a reaction system of a liquid phase, the method comprising:
Between the 1st handling surface and the 2nd handling surface, the said fluid to be processed which becomes the liquid phase is introduced, and the pressure of this to-be-processed fluid moves in the direction which separates the 2nd handling surface from the 1st handling surface. By this force, the 1st processing with face and the 2nd processing with face are held at a minute interval, and the 1st processing with this minute interval is held between the face and the 2nd processing with face. The passing fluid forms a thin film fluid, and silver particles are obtained by reacting the metal ion with the reducing agent in the thin film fluid,
The content ratio of silver nitrate and reducing agent in the fluid to be treated is 0.3 to 0.9 in terms of molar ratio (silver nitrate/reducing agent);
The rotational speed of the processing portion is 2000 to 5000 rpm,
The back pressure in the processing part is 0.005 to 0.05 MPa,
A method for producing silver particles.

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