Silver microparticles and method for producing silver microparticles

Abstract

This invention provides silver microparticles with small particle size and uniform granular shape, as well as a method for manufacturing silver microparticles. The BET specific surface area of ​​the silver microparticles is 10 m². 2 The reflectance value is above 10, and the temperature is above 10 / g. Additionally, the heating peak temperature in differential thermal analysis is below 250℃, and the weight reduction per unit area equivalent is 0.5 × 10⁻⁶. ‑3 g / m 2 above.

Description

Technical Field

[0001] This invention relates to silver microparticles and methods for manufacturing silver microparticles, which can be used in various devices such as electrodes for electronic components such as conductive paste and multilayer ceramic capacitors, wiring for printed circuit boards, wiring for touch panels, flexible electronic paper, and solar cells and light-emitting components. In particular, it relates to silver microparticles formed using conductive wiring and methods for manufacturing silver microparticles. Background Technology

[0002] Currently, various microparticles, including metal microparticles, oxide microparticles, nitride microparticles, and carbide microparticles, are used for a wide range of applications. Among these microparticles, silver microparticles can be used as electrodes in electronic components such as conductive paste and multilayer ceramic capacitors, as well as in wiring on printed circuit boards, wiring in touch panels, flexible electronic paper, and various devices such as solar cells and light-emitting components. Silver electrodes and silver wiring can be obtained by sintering silver microparticles. Silver microparticles and their manufacturing methods are described, for example, in Patent Document 1.

[0003] Patent document 1 describes silver microparticles having a surface coating, wherein the surface coating contains at least a carboxyl group.

[0004] In addition, Patent Document 1 describes a method for manufacturing silver microparticles using silver powder via a gas-phase method; it is a method for manufacturing silver microparticles that includes a step of supplying an organic acid to the silver microparticles.

[0005] Existing technical documents Patent documents Patent Document 1: International Publication No. 2019 / 146412 Summary of the Invention

[0006] The technical problem that the invention aims to solve As described above, Patent Document 1 discloses silver microparticles and a method for manufacturing silver microparticles. However, current technology requires small particle size and granular shape with uniform particle size.

[0007] The purpose of this invention is to solve the aforementioned problems based on known technologies, and to provide silver microparticles with small particle size and uniform particle shape, as well as a method for manufacturing silver microparticles.

[0008] Means for solving technical problems The above objectives can be achieved through the following configuration.

[0009] The invention [1] is a silver microparticle with a BET specific surface area of ​​10 m². 2 / g or higher, with a positive reflectance value of 10 or higher.

[0010] The invention [2] is silver microparticles as described in the invention [1], wherein the heating peak temperature in differential thermal analysis is below 250°C.

[0011] Invention [3] refers to silver microparticles as described in invention [1] or [2], wherein the weight reduction per unit area equivalent is 0.5 × 10⁻⁶. -3 g / m 2 above.

[0012] Invention [4] is a method for manufacturing silver microparticles, which uses silver powder to manufacture silver microparticles by thermal plasma method; it has the steps of supplying silver powder to thermal plasma flame and supplying cooling gas to thermal plasma flame; the cooling gas contains methane gas and oxygen, and the ratio of oxygen to methane gas, i.e. oxygen / methane gas, is 1 to 50 by volume.

[0013] The effects of the invention According to the present invention, silver microparticles with small particle size and uniform particle shape and particle size can be provided, as well as a method for manufacturing silver microparticles. Attached Figure Description

[0014] Figure 1 This is a schematic diagram illustrating an example of a microparticle manufacturing apparatus used in the method for manufacturing silver microparticles according to an embodiment of the present invention.

[0015] Figure 2 A schematic diagram illustrating silver microparticles in an embodiment of the present invention.

[0016] Figure 3 A schematic diagram illustrating the value of positively reflected light.

[0017] Figure 4 A schematic diagram illustrating the value of positively reflected light.

[0018] Figure 5 A schematic diagram showing the SEM image of silver microparticles in Example 5.

[0019] Figure 6 A schematic diagram showing the SEM image of silver microparticles in Comparative Example 3.

[0020] Figure Labels 10 Microparticle manufacturing apparatus (manufacturing device); 12 Plasma torch; 12a Quartz tube; 12b High-frequency oscillation coil; 12c Plasma gas supply port; 14 Material supply device; 14a Supply pipe; 15 Primary microparticles; 16 Chamber; 16a Inner wall; 18 Secondary microparticles; 19 Cyclone separator; 19a Inlet pipe; 19b Outer cylinder; 19c Frustum conical section; 19d Coarse particle recovery chamber; 19e Inner pipe; 20 Recovery section; 20a Recovery chamber; 20b Filter; 22 Plasma gas supply section; 22c Piping; 24 Plasma generation section; 26 Gas supply section; 26c Piping; 28 Thermal plasma flame; 28b Tail end; 30 Vacuum pump; 40 Silver microparticles; 40a, 51a Surface; 41 Surface coating; 50, 51 Membrane; 52 Substrate; 100 coarse particles; Ld diffused reflected light; Li incident light; Lr positive reflected light; Ls internal scattered light. Detailed Implementation

[0021] Hereinafter, based on the preferred embodiments shown in the accompanying drawings, the silver microparticles and the method for manufacturing silver microparticles of the present invention will be described in detail.

[0022] Furthermore, the figures described below are illustrative and used to illustrate the present invention, and the present invention is not limited to the figures shown below.

[0023] Furthermore, the "~" in the following numerical ranges includes the values ​​listed on both sides. For example, ε is the numerical value ε α ~numerical value ε β This means that the range of ε includes the numerical value ε. α With the numerical value ε β The range of ε is represented by mathematical notation. α ≤ε≤ε β .

[0024] In addition, unless otherwise specified, all numerical values ​​include the generally permissible error range in the corresponding technical field.

[0025] [Methods for manufacturing silver microparticles] The following describes an example of a method for manufacturing silver microparticles according to the present invention.

[0026] Figure 1 This is a schematic diagram illustrating an example of a microparticle manufacturing apparatus used in the method for manufacturing silver microparticles according to an embodiment of the present invention.

[0027] Figure 1 The microparticle manufacturing apparatus 10 shown (hereinafter simply referred to as manufacturing apparatus 10) is used for the manufacture of silver microparticles. The manufacturing apparatus 10 is used in a manufacturing method for manufacturing silver microparticles by thermal plasma method.

[0028] The manufacturing apparatus 10 includes a plasma torch 12 that generates a thermal plasma flame, a material supply device 14 that supplies raw material powder for silver microparticles into the plasma torch 12, a chamber 16 that functions as a cooling tank for generating primary silver microparticles 15, a cyclone separator 19 that removes coarse silver particles with a particle size greater than a predetermined particle size from the primary silver microparticles 15, and a recovery unit 20 that recovers secondary silver microparticles 18 with a desired particle size that have been classified by the cyclone separator 19.

[0029] Furthermore, the manufacturing apparatus 10 includes a plasma gas supply unit 22, a plasma generation unit 24, and a gas supply unit 26.

[0030] Both primary silver microparticles 15 and secondary silver microparticles 18 are equivalent to the silver microparticles of the present invention. The secondary silver microparticles are the product obtained by fractionation of primary silver microparticles 15.

[0031] Regarding the material supply device 14, chamber 16, cyclone separator 19, and recovery unit 20, various devices disclosed in Japanese Patent Application Publication No. 2007-138287 can be used, for example. Furthermore, the primary silver particles 15 are simply referred to as primary particles 15.

[0032] In this embodiment, silver microparticles are manufactured using silver powder. The average particle size of the silver powder is appropriately set to facilitate evaporation in a thermal plasma flame, for example, being 100 μm or less, preferably 10 μm or less, and more preferably 5 μm or less.

[0033] The plasma torch 12 is, for example, composed of a quartz tube 12a and a high-frequency oscillating coil 12b surrounding its outer side. At the upper part of the plasma torch 12, a supply tube 14a (described later) is provided in its central portion for supplying raw material powder, silver microparticles, into the plasma torch 12. A plasma gas supply port 12c is formed on the periphery (on the same circumference) of the supply tube 14a, and the plasma gas supply port 12c is annular.

[0034] The plasma gas supply unit 22 supplies plasma gas into the plasma torch 12 and is connected to the plasma gas supply port 12c via the pipe 22c. The plasma gas is supplied from the plasma gas supply unit 22 through the annular plasma gas supply port 12c, for example, from the direction indicated by arrow P and the direction indicated by arrow S into the plasma torch 12.

[0035] The plasma gas supply unit 22 has a gas supply unit corresponding to the type of gas constituting the plasma. For example, if the plasma gas is a mixture of hydrogen and argon, hydrogen is stored in the first gas supply unit (not shown), and argon is stored in the second gas supply unit (not shown). Although the first and second gas supply units are not shown, they are each equipped with a regulator (pressure regulator) and an adjustment valve for controlling the gas supply amount.

[0036] Hydrogen is supplied from the first gas supply unit of the plasma gas supply unit 22, and argon is supplied from the second gas supply unit. These gases are then supplied to the plasma torch 12 via pipe 22c and plasma gas supply port 12c, in the directions indicated by arrows P and S. Alternatively, only argon may be supplied in the direction indicated by arrow P.

[0037] The plasma generating unit 24 has a high-frequency power supply (not shown), which is connected to the high-frequency oscillation coil 12b. The plasma generating unit 24 has the function of supplying a high-frequency voltage to the high-frequency oscillation coil 12b. When a high-frequency voltage is applied to the high-frequency oscillation coil 12b from the plasma generating unit 24, a thermal plasma flame 28 is generated inside the plasma torch 12.

[0038] The temperature of the thermal plasma flame 28 needs to be higher than the boiling point of the raw material powder. On the other hand, the higher the temperature of the thermal plasma flame 28, the easier it is for the raw material powder to become a gaseous state, which is preferable, but there is no particular limitation on the temperature. For example, the temperature of the thermal plasma flame 28 can also be 6000℃, and theoretically it is considered to be around 10000℃.

[0039] In addition, the pressure atmosphere inside the plasma torch 12 is preferably below atmospheric pressure. Here, there is no particular limitation on the atmosphere below atmospheric pressure, for example, it is 0.5 kPa to 100 kPa.

[0040] Furthermore, the outer side of the quartz tube 12a is surrounded by a concentrically formed tube (not shown), and cooling water is circulated between the tube and the quartz tube 12a to water-cool the quartz tube 12a, preventing the quartz tube 12a from becoming excessively hot due to the hot plasma flame 28 generated inside the plasma torch 12.

[0041] The material supply device 14 is connected to the upper part of the plasma torch 12 via a supply pipe 14a. The material supply device 14 supplies raw material powder to the thermal plasma flame 28 inside the plasma torch 12, for example, in powder form.

[0042] As a material supply device 14 for supplying silver powder in powder form, the device disclosed in, for example, Japanese Patent Application Publication No. 2007-138287 can be used as described above. In this case, the material supply device 14 includes, for example, a storage tank (not shown) for storing silver powder, a screw feeder (not shown) for quantitatively conveying silver powder, a dispersion section (not shown) for dispersing the silver powder conveyed by the screw feeder into a primary particle state before final dispersion, and a carrier gas supply source (not shown).

[0043] Silver powder, together with a carrier gas subjected to extrusion pressure from a carrier gas supply source, is supplied via supply pipe 14a to the hot plasma flame 28 within the plasma torch 12.

[0044] The material supply device 14 is not particularly limited in its configuration, as long as it can prevent the silver powder from agglomerating and maintain a dispersed state in distributing the silver powder into the plasma torch 12. An inert gas, such as argon, is used as the carrier gas. The flow rate of the carrier gas can be controlled using a flow meter, such as a float-type flow meter. Furthermore, the flow rate value of the carrier gas refers to the scale value of the flow meter.

[0045] The chamber 16 is located below and adjacent to the plasma torch 12, and is connected to a gas supply unit 26. Primary silver particles 15 are generated within the chamber 16. Additionally, the chamber 16 functions as a cooling tank.

[0046] The gas supply unit 26 supplies cooling gas into the chamber 16. The gas supply unit 26 includes piping 26c. Furthermore, the gas supply unit 26 includes a gas supply source (not shown) for storing gas, and a pressure-applying unit (not shown) such as a compressor or blower that applies extrusion pressure to the quenching gas supplied to the chamber 16. Additionally, an adjusting valve (not shown) is provided to control the amount of gas supplied from the gas supply source. The gas supply source uses a composition corresponding to the cooling gas, which is a mixture of argon, methane, and oxygen.

[0047] In the gas supply section 26, for example, argon is stored in the first gas supply source (not shown), methane gas (CH4 gas) is stored in the second gas supply source (not shown), and oxygen gas (O2 gas) is stored in the third gas supply source (not shown).

[0048] The gas supply section 26 faces the tail 28b of the thermal plasma flame 28, that is, one end of the thermal plasma flame 28 opposite to the plasma gas supply port 12c, i.e., the terminal part (tail 28b) of the thermal plasma flame 28, at an angle of, for example, 45°, in the direction of arrow Q, as a cooling gas supply of a mixture of argon, methane, and oxygen, and flows along the inner wall 16a of the chamber 16 from top to bottom, i.e., in... Figure 1 The direction of arrow R shown indicates that the cooling gas is supplied.

[0049] By supplying cooling gas from the gas supply unit 26 into the chamber 16, the silver powder, which is in a gaseous state in the thermal plasma flame 28, is rapidly cooled to obtain primary silver particles 15. In addition, the aforementioned cooling gas has the additional effect of aiding in the classification of the primary particles 15 in the cyclone separator 19. The cooling gas is, for example, a mixture of argon, methane, and oxygen.

[0050] The cooling gas contains methane and oxygen, with the oxygen to methane ratio (volume ratio) being 1 to 50% by volume, preferably 10 to 40% by volume.

[0051] When the oxygen / methane gas ratio is 1~50% by volume, a BET specific surface area of ​​10 m² is obtained. 2 Silver microparticles with a g / g or higher and a positive reflectance value of 10 or higher.

[0052] In addition, when the oxygen / methane gas content is 10~40% by volume, the positive reflection value of the produced silver microparticles becomes higher, that is, the particle size of the silver microparticles becomes higher, the particle size is more uniform, and the particle size deviation becomes smaller, which is better.

[0053] When the oxygen / methane gas ratio exceeds 50% by volume, it does not form particles but rather a foil-like structure, making it impossible to obtain silver microparticles. This is because the increased oxygen content causes the methane gas to burn rather than thermally decompose. The amount of hydrocarbons on the surface of the silver microparticles produced by the thermal decomposition of methane gas decreases, resulting in insufficient coating of the silver microparticles and hindering the bonding process.

[0054] The cooling gas is a mixture of argon, methane, and oxygen, but it can also be composed of only two gases: methane and oxygen.

[0055] The oxygen to methane gas ratio (volume ratio) mentioned above is the oxygen / methane gas ratio, measured using the flow rates of oxygen and methane under standard conditions (0°C, 1 atm). The flow rates of both oxygen and methane are measured using flow meters, such as float-type flow meters.

[0056] When newly generated silver primary microparticles 15 collide with each other, forming aggregates and causing uneven particle size, this becomes a factor in mass reduction. However, the mixed gas supplied as cooling gas in the direction of arrow Q towards the tail 28b (terminal part) of the hot plasma flame 28 dilutes the primary microparticles 15, preventing the silver microparticles from colliding and agglomerating.

[0057] In addition, by supplying a mixed gas as cooling gas in the direction of arrow R, the primary microparticles 15 are prevented from adhering to the inner wall 16a of the chamber 16 during the recovery process, thereby increasing the yield of the generated primary microparticles 15.

[0058] like Figure 1 As shown, chamber 16 is connected to a cyclone separator 19 for classifying primary silver particles 15 to the desired particle size. The cyclone separator 19 includes an inlet pipe 19a that supplies primary particles 15 from chamber 16, a cylindrical outer cylinder 19b connected to the inlet pipe 19a and located at the upper part of the cyclone separator 19, a truncated cone portion 19c that extends continuously downward from the lower part of the outer cylinder 19b and has a gradually decreasing inner diameter, a coarse particle recovery chamber 19d connected to the lower side of the truncated cone portion 19c and recovering coarse particles with a particle size greater than or equal to the desired particle size, and an inner pipe 19e that is connected to the recovery section 20 described in detail later and protrudes from the outer cylinder 19b.

[0059] An airflow containing primary microparticles 15 is blown into the inner circumferential wall of the outer cylinder 19b from the inlet pipe 19a of the cyclone separator 19, thereby causing the airflow to... Figure 1 As indicated by arrow T, the flow originates from the inner circumferential wall of the outer cylinder 19b and flows toward the truncated cone portion 19c, forming a descending swirling flow.

[0060] Then, when the aforementioned descending vortex flow reverses and becomes an upward flow, the coarse particles cannot ride the upward flow due to the balance between centrifugal force and resistance. They descend along the side of the truncated cone 19c and are recovered in the coarse particle recovery chamber 19d. In addition, the microparticles, which are more affected by resistance than centrifugal force, are discharged from the inner tube 19e to the outside of the system along with the upward flow from the inner wall of the truncated cone 19c.

[0061] Additionally, a negative pressure (attraction force) is generated from the recovery unit 20 (described in detail later) through the inner tube 19e. Then, the silver microparticles separated from the aforementioned swirling airflow are attracted by this negative pressure (attraction force) as indicated by the symbol U and sent to the recovery unit 20 through the inner tube 19e.

[0062] An extension of the inner tube 19e, which serves as the outlet for the airflow within the cyclone separator 19, is provided with a recovery section 20 for recovering secondary microparticles (silver microparticles) 18 with the desired nanometer-scale particle size. The recovery section 20 includes a recovery chamber 20a, a filter 20b disposed within the recovery chamber 20a, and a vacuum pump 30 connected via a pipe disposed below the recovery chamber 20a. Microparticles from the cyclone separator 19 are drawn into the recovery chamber 20a by the vacuum pump 30 and recovered while remaining on the surface of the filter 20b.

[0063] Furthermore, in the aforementioned manufacturing apparatus 10, the number of cyclone separators used is not limited to one, but may be two or more.

[0064] Next, an example of a method for manufacturing silver microparticles using the manufacturing apparatus 10 described above will be explained.

[0065] The method for manufacturing silver microparticles uses silver powder and produces silver microparticles through a thermal plasma method.

[0066] In the method for manufacturing silver microparticles, firstly, silver powder with an average particle size of 5 μm or less, as the raw material powder for silver microparticles, is fed into a material supply device 14. The material supply device 14 supplies the silver powder to a thermal plasma flame 28, as described later.

[0067] A high-frequency voltage is applied to the high-frequency oscillation coil 12b from the plasma generation unit 24, generating a thermal plasma flame 28 within the plasma torch 12. The plasma gas used is, for example, argon and hydrogen.

[0068] Additionally, from the gas supply section 26 toward the tail 28b of the thermal plasma flame 28, i.e., the terminal part of the thermal plasma flame 28, a mixture of argon, methane, and oxygen is supplied as a cooling gas in the direction of arrow Q (the cooling gas supply step). In the cooling gas, the oxygen / methane ratio is 1 to 50% by volume. At this time, a mixture of argon, methane, and oxygen is also supplied as a cooling gas in the direction of arrow R.

[0069] Next, in the material supply device 14, silver powder is transported as a carrier gas using, for example, argon gas, and supplied to the thermal plasma flame 28 within the plasma torch 12 via the supply pipe 14a. The supplied silver powder evaporates into a gaseous state in the thermal plasma flame 28 and is rapidly cooled by a cooling gas to generate primary silver particles 15 (silver microparticles). Thus, the method for manufacturing silver microparticles includes the steps of supplying silver powder to the thermal plasma flame and supplying a cooling gas to the thermal plasma flame.

[0070] Then, the primary silver particles 15 obtained in chamber 16 are blown in from the inlet pipe 19a of the cyclone separator 19 along with the airflow along the inner circumferential wall of the outer cylinder 19b, thereby causing the airflow to... Figure 1 As indicated by arrow T, the particles flow along the inner circumferential wall of the outer cylinder 19b, forming a swirling flow and descending. Then, when this descending swirling flow reverses and becomes an upward flow, the balance between centrifugal force and drag prevents coarse particles from riding the upward flow. They descend along the side of the truncated cone portion 19c and are recovered in the coarse particle recovery chamber 19d. Additionally, microparticles, which are more affected by drag than centrifugal force, are discharged from the inner wall of the truncated cone portion 19c along with the upward flow from the inner wall and exit the system.

[0071] The discharged secondary microparticles (silver microparticles) 18 are drawn back by the negative pressure (attraction) from the recovery section 20 of the vacuum pump 30. Figure 1The particles are attracted to the direction indicated by the symbol U and sent to the recovery section 20 through the inner tube 19e, where they are recovered by the filter 20b. The internal pressure within the cyclone separator 19 is preferably below atmospheric pressure at this time. Furthermore, the particle size of the secondary microparticles (silver microparticles) 18 is arbitrarily nanometer-sized according to the intended purpose.

[0072] Secondly, let's explain silver microparticles.

[0073] The silver microparticles of the present invention are manufactured, for example, by the manufacturing method described above, and obtained in a particle state. Thus, the silver microparticles of the present invention are not uniformly dispersed within the solvent, but rather exist individually. Therefore, there are no particular limitations on their combination with the solvent, and the choice of solvent offers a high degree of freedom.

[0074] Here, Figure 2 This is a schematic diagram showing silver microparticles in an embodiment of the present invention.

[0075] like Figure 2 As shown, silver microparticles 40 have a surface coating 41 on their surface 40a. The surface state of the silver microparticles 40, including the surface coating 41 on surface 40a, was investigated, due to hydrocarbons (C... n H m ) exists on the surface, and the surface coating 41 is composed of hydrocarbons (C n H m It is composed of ).

[0076] Hydrocarbons (C n H m It is a substance generated by the thermal decomposition of methane gas contained in the cooling gas through a thermal plasma flame.

[0077] Furthermore, the surface state of the silver microparticles 40 can be investigated using, for example, FT-IR (Fourier Transform Infrared Spectrophotometer).

[0078] The silver microparticles of this invention have a BET specific surface area of ​​10 m². 2 / g or higher, with a positive reflectance value of 10 or higher. BET specific surface area is 10m². 2 When the positive reflection value is above 10 / g, the silver microparticles have small and uniform particle size.

[0079] BET specific surface area is a value measured using the BET method. The BET specific surface area is 10 m². 2 At concentrations above a certain level (g), silver microparticles have small particle sizes. The optimal BET specific surface area is 10 m². 2 / g~25m 2 / g.

[0080] The silver microparticles of this invention are referred to as nanoparticles, with a particle size of 1 nm to 57 nm. The particle size is a value converted from the BET specific surface area, representing the average particle size.

[0081] The positive reflectance value is an indicator of the particle size or deviation in particle shape, with an upper limit of 100. A higher positive reflectance value indicates granular particle shape and uniform particle size. When the positive reflectance value is above 10, the silver microparticles exhibit granular shape with minimal deviation in particle size and uniform particle size. The optimal positive reflectance value for silver microparticles is 15–40.

[0082] As mentioned above, the positive reflectance value of silver microparticles is 10 or higher, preferably 15 to 40.

[0083] The normal reflectance value can be used to evaluate whether the silver microparticles are granular or have a uniform particle size. This is based on the fact that the normal reflectance value can evaluate the uniformity of the film. Specifically, when the silver microparticles are granular and have a uniform particle size, the film uniformity is high, resulting in increased normal reflectance. On the other hand, when the silver microparticles are non-granular and have an irregular particle size, the film uniformity is low, resulting in increased diffuse reflectance. This is used to evaluate whether the silver microparticles are granular or have a uniform particle size.

[0084] Here, Figure 3 and Figure 4 This is a schematic diagram illustrating the value of reflected light. The incident light incident on the object is shown below.

[0085] Incident light = Normally reflected light + Diffused reflected light + Internally scattered light + Transmitted light + Absorbed light When the silver microparticles 40 have a granular shape and uniform particle size, the film is uniform and dense, becomes smooth, and has a higher positive reflectance value. Therefore, the positive reflectance value becomes an indicator of the granular shape and uniform particle size of the silver microparticles, as well as the uniformity, density, and smoothness of the film.

[0086] Figure 3 The film 50 shown is formed on the substrate 52 and contains a plurality of silver microparticles 40. The plurality of silver microparticles 40 are granular in shape with uniform particle size and good dispersion. Figure 4 The film 51 shown is formed on the substrate 52 and contains a plurality of silver microparticles 40. However, the shape of the plurality of silver microparticles 40 is non-granular and the particle size is irregular. The dispersion state of the silver microparticles 40 in the film 51 is also poor.

[0087] incident to Figure 3 Incident light Li on surface 50a of the film 50, as shown, produces positively reflected light Lr. Figure 4 The film 51 shown generates positively reflected light Lr from incident light Li incident on surface 51a.

[0088] Figure 3 The membrane 50 shown is a uniform membrane because the silver microparticles 40 have a granular shape, uniform particle size, good dispersion, and few voids. This results in less internal scattered light (Ls) and diffused reflected light (Ld), while increasing the amount of positively reflected light (Lr). In other words, the positively reflected light value is high when the silver microparticles 40 have a granular shape and uniform particle size.

[0089] Figure 4 The membrane 51 shown is non-particulate and irregular in size due to the non-particulate shape and poor dispersion of the silver microparticles 40, resulting in numerous voids and an uneven membrane. This leads to an increase in internal scattered light Ls and diffused reflected light Ld, while the amount of positively reflected light Lr decreases. In other words, the positively reflected light value is small when the silver microparticles 40 are non-particulate and irregular in size.

[0090] The positive reflectance value can be used to evaluate the particle size or deviation of silver microparticles. The positive reflectance value can be measured using, for example, a spectrophotometer.

[0091] The optimal temperature for the pyrolysis peak in differential thermal analysis of silver microparticles is below 250℃, and more preferably between 170℃ and 200℃.

[0092] In differential thermal analysis, when the heating peak temperature is below 250℃, the heating peak temperature generated below 250℃ causes silver microparticles to sinter together, which can exhibit electrical conductivity.

[0093] When the silver microparticles of the present invention are heated in atmosphere, the hydrocarbons (C) constituting the surface coating of the coated silver microparticles... n H m The carbon dioxide reacts with oxygen in the atmosphere, burning and decomposing while generating heat. The pyrolysis peak temperature (°C) in differential thermal analysis is measured using a TG-DTA (differential thermal and thermogravimetric analysis device) to determine the degree of this heat generation, displaying the temperature at which the heat is at its peak. That is, the lower the pyrolysis peak temperature, the easier it is for the hydrocarbons in the thin film on the coated surface to decompose. Since the silver microparticles that have lost their film can easily come into contact with each other, it indicates that the silver microparticles can be sintered at a lower temperature.

[0094] The calorimetric peak temperature in differential thermal analysis is measured in the atmosphere using a TG-DTA (Differential Thermal and Thermogravimetric Analysis) device. The TG-DTA device used is, for example, the STA7200 (trade name) from Hitachi Advanced Technology & Science Co., Ltd.

[0095] The preferred weight reduction per unit area equivalent of silver microparticles is 0.5 × 10⁻⁶. -3 g / m 2 The above is preferred to be 0.9 g / m³. 2 ~2×10 -3g / m 2 .

[0096] The weight reduction amount per unit area equivalent (g / m 2 ) is calculated by measuring the weight reduction ratio (mass%) in the atmosphere using TG-DTA (simultaneous differential thermal and thermogravimetric analyzer), and dividing the weight reduction ratio (mass%) by the BET specific surface area (m 2 / g). That is, the weight reduction amount per unit area equivalent (g / m 2 ) = (weight reduction ratio (mass%)) / (BET specific surface area (m 2 / g).

[0097] When the weight reduction amount per unit area equivalent is 0.5×10 -3 g / m 2 or more, the obtained silver fine particles have high granularity and small variation in particle diameter.

[0098] The present invention is basically configured as described above. Although the silver fine particles and the method for producing the same of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various improvements or modifications can of course be made without departing from the gist of the present invention.

[0099] [Examples] Hereinafter, the features of the present invention will be described more specifically with reference to Examples. The processing content, processing sequence, etc. shown in the following Examples can be appropriately modified without departing from the gist of the present invention. Therefore, the scope of the present invention should not be restrictively interpreted by the specific examples shown below.

[0100] In the present Examples, the production conditions for the silver fine particles of Examples 1 to 6 and Comparative Examples 1 to 8 are shown in Table 1 below. In addition, for the silver fine particles of Examples 1 to 6 and Comparative Examples 1 to 3, the BET specific surface area, regular reflection light value, exothermic peak temperature, and weight reduction amount per unit area equivalent were measured. The results are shown in Table 2 below. In Comparative Examples 4 to 8, for the items not measured among the regular reflection light value, exothermic peak temperature, weight reduction ratio and weight reduction amount per unit area equivalent, the corresponding columns for the regular reflection light value, exothermic peak temperature, weight reduction ratio and weight reduction amount per unit area equivalent in the following Table 2 are marked with "-".

[0101] In addition, as the production conditions, Table 1 below shows the plasma gas flow rate and the cooling gas flow rate when producing the silver fine particles of Examples 1 to 6 and Comparative Examples 1 to 8.

[0102] Hereinafter, the BET specific surface area, regular reflection light value, exothermic peak temperature in differential thermal analysis, and weight reduction amount per unit area equivalent will be described.

[0103] <BET Specific Surface Area> Regarding the silver microparticles produced, the BET specific surface area (m²) was measured using a Macsorb HM-1208 instrument manufactured by Mountech, Inc. 2 / g).

[0104] Furthermore, the BET diameter shown in Table 2 below is derived from the measured BET specific surface area (m²). 2 The particle size of silver microparticles converted to g).

[0105] <Reflected light value> The positive reflected light value was measured as described below.

[0106] First, silver microparticles are dispersed in a solution composed of a solvent and a dispersant. Then, this dispersion is coated onto a glass slide to form a film, and the normal reflectance of the film is measured using a spectrophotometer. The normal reflectance of the film is taken as the normal reflectance of the silver microparticles.

[0107] Furthermore, the dispersant used is BYK-112 (manufactured by BYK Chemical Japan Co., Ltd.).

[0108] <Energy Peak Temperature in Differential Thermal Analysis> The temperature of the pyroelectric peak in differential thermal analysis was measured using Hitachi Advanced Technology & Science Co., Ltd. (STA7200, trade name).

[0109] <Weight reduction per unit area> The weight reduction percentage (mass%) was measured using Hitachi Advanced Technology & Science Co., Ltd.'s STA7200 (trade name).

[0110] Using the BET specific surface area and weight reduction ratio measured as described above, the weight reduction per unit area equivalent (g / m²) is calculated using the following formula. 2 ).

[0111] Weight reduction per unit area equivalent (g / m²) 2 = (weight reduction percentage (mass%)) / (BET specific surface area (m²)) 2 / g) ) The following describes the silver microparticles of Examples 1-6 and Comparative Examples 1-8.

[0112] The silver microparticles of Examples 1-6 and Comparative Examples 1-8 were produced using the microparticle manufacturing apparatus 10 described above.

[0113] In the preparation of silver microparticles in Examples 1-6 and Comparative Examples 1-8, silver powder with an average particle size of 15 μm was used as the raw material powder. In addition, as the manufacturing conditions for the silver microparticles in Examples 1-6 and Comparative Examples 1-8, the power input to the plasma was fixed at 15 kW, and the pressure inside the plasma torch (internal pressure of the device) was 40 kPa.

[0114] Argon was used as the carrier gas, and a mixture of argon and hydrogen was used as the plasma gas. Examples 1-6 used a mixture of argon, methane, and oxygen as the cooling gas. Comparative Examples 1-4 used a mixture of argon and methane as the cooling gas. Comparative Examples 5 and 6 used a mixture of argon, methane, and hydrogen as the cooling gas. Comparative Examples 7 and 8 used a mixture of argon, methane, and oxygen as the cooling gas.

[0115] In Examples 1-6 and Comparative Examples 1-8, the flow rate of the plasma gas, as well as the composition and flow rate of the cooling gas, were varied. The flow rate of the cooling gas was the flow rate under standard conditions (temperature 0°C, 1 atmosphere). The flow rate of the cooling gas was measured using a float-type flow meter for each gas component constituting the cooling gas, such as argon.

[0116] (Examples 1-6) In Example 1, regarding the plasma gas, the flow rate of argon was 170 L / min, and the flow rate of hydrogen was 5 L / min.

[0117] Regarding the cooling gases, the flow rate of argon was 50 L / min, the flow rate of methane was 15 L / min, and the flow rate of oxygen was 0.15 L / min. In Example 1, the oxygen / methane ratio was 1 volume.

[0118] In Example 2, compared to Example 1, the flow rates of argon (100 L / min), methane (15 L / min), and oxygen (1.5 L / min) were the same as in Example 1. The oxygen / methane ratio in Example 2 was 10% by volume.

[0119] In Example 3, compared to Example 1, the flow rates of argon (450 L / min), methane (15 L / min), and oxygen (1.5 L / min) were the same as in Example 1. The oxygen / methane ratio in Example 3 was 10% by volume.

[0120] Compared to Example 1, Example 4 differs from Example 1 in that the flow rate of argon is 200 L / min and the flow rate of hydrogen is 5 L / min for the plasma gas. Additionally, the flow rates of argon, methane, and oxygen are the same as in Example 1, except that the flow rates of argon, methane, and oxygen are 900 L / min, 10 L / min, and 5 L / min for the cooling gas. The oxygen / methane ratio in Example 4 is 50% by volume.

[0121] Compared to Example 1, Example 5 differs from Example 1 in that the flow rate of argon is 200 L / min and the flow rate of hydrogen is 5 L / min for the plasma gas. Furthermore, the flow rate of cooling gases is the same as in Example 1, except that the flow rate of argon is 900 L / min, the flow rate of methane is 15 L / min, and the flow rate of oxygen is 5 L / min. The oxygen / methane ratio in Example 5 is 33.3% by volume.

[0122] Compared to Example 1, Example 6 differs from Example 1 in that the flow rate of argon is 200 L / min and the flow rate of hydrogen is 5 L / min for the plasma gas. Furthermore, the flow rate of cooling gases is the same as in Example 1, except that the flow rate of argon is 900 L / min, the flow rate of methane is 25 L / min, and the flow rate of oxygen is 5 L / min. The oxygen / methane ratio in Example 6 is 20% by volume.

[0123] (Comparative Examples 1-8) Compared to Example 1, in Comparative Example 1, the flow rate of argon was 200 L / min and the flow rate of hydrogen was 5 L / min for the plasma gas. The cooling gas was a mixture of argon and methane, with an argon flow rate of 150 L / min and a methane flow rate of 15 L / min, except that it was the same as in Example 1.

[0124] In Comparative Example 2, compared to Example 1, the plasma gas flow rate was 200 L / min for argon and 5 L / min for hydrogen. The cooling gas was a mixture of argon and methane, with an argon flow rate of 450 L / min and a methane flow rate of 15 L / min, otherwise identical to Example 1.

[0125] In Comparative Example 3, compared to Example 1, the flow rate of argon was 160 L / min and the flow rate of hydrogen was 5 L / min for the plasma gas. The cooling gas was a mixture of argon and methane, with an argon flow rate of 900 L / min and a methane flow rate of 6 L / min, otherwise identical to Example 1.

[0126] In Comparative Example 4, compared to Example 1, the flow rate of argon was 200 L / min and the flow rate of hydrogen was 5 L / min for the plasma gas. The cooling gas was a mixture of argon and methane, with an argon flow rate of 900 L / min and a methane flow rate of 10 L / min, otherwise identical to Example 1.

[0127] In Comparative Example 5, compared to Example 1, the plasma gas flow rate was 210 L / min for argon and 5 L / min for hydrogen. The cooling gas was a mixture of argon, methane, and hydrogen, with an argon flow rate of 600 L / min, a methane flow rate of 10 L / min, and a hydrogen flow rate of 5 L / min, all other than being the same as in Example 1.

[0128] In Comparative Example 6, compared to Example 1, the flow rate of argon was 210 L / min and the flow rate of hydrogen was 5 L / min for the plasma gas. The cooling gas was a mixture of argon, methane, and hydrogen, with a flow rate of 600 L / min for argon, 10 L / min for methane, and 10 L / min for hydrogen, except that it was the same as in Example 1.

[0129] Compared to Example 1, Comparative Example 7 differed from Example 1 in that the flow rate of argon was 200 L / min and the flow rate of hydrogen was 5 L / min for the plasma gas. Furthermore, the flow rate of argon was 900 L / min, the flow rate of methane was 1 L / min, and the flow rate of oxygen was 5 L / min for the cooling gas, except that in Example 1. The oxygen / methane ratio in Comparative Example 7 was 500% by volume.

[0130] Compared to Example 1, Comparative Example 8 differs from Example 1 in that the flow rate of argon gas is 200 L / min and the flow rate of hydrogen gas is 5 L / min. Furthermore, the flow rates of cooling gases are the same as in Example 1, except that the flow rates of argon gas and methane gas are 900 L / min, 1 L / min, and 1 L / min. The oxygen / methane gas ratio in Comparative Example 8 is 100% by volume.

[0131] Furthermore, since Comparative Examples 7 and 8 were in foil form instead of particle form, the BET specific surface area and BET diameter could not be measured. Therefore, the BET specific surface area and BET diameter columns in Table 2 below are marked with "-". Because Comparative Examples 7 and 8 were in foil form, the positive reflection value, heating peak temperature, weight reduction percentage, and weight reduction per unit area equivalent were not measured. Therefore, the positive reflection value, heating peak temperature, weight reduction percentage, and weight reduction per unit area equivalent columns in Table 2 below are marked with "-".

[0132] [Table 1]

[0133] [Table 2]

[0134] As shown in Table 2, Examples 1-6, compared to Comparative Examples 1-8, can produce BET specific surface areas of 10 m². 2 Silver microparticles with a g / g or higher and a positive reflectance value of 10 or higher.

[0135] Examples 1-6 have a BET specific surface area of ​​10m². 2 The particle size is small and the particle size is above 10 g. In addition, in Examples 1 to 6, the positive reflection value is above 10, the particle shape is granular and the particle size is uniform.

[0136] On the other hand, in Comparative Examples 1-6, none of the particles achieved a BET specific surface area of ​​10 m². 2Particles with a g / g or higher and a positive reflectance value of 10 or higher are considered to be produced. This is believed to be because when the cooling gas does not contain oxygen, the thermal decomposition of methane gas does not produce sufficient hydrocarbons to reach the surface of the coated silver microparticles. As a result, the growth of silver microparticles cannot be suppressed, leading to the formation of non-granular particles or coarse particles.

[0137] Furthermore, neither Comparative Examples 7 nor 8 were formed into particles but rather into foils. This is because, in Comparative Examples 7 and 8, the high oxygen content resulted in the non-thermal decomposition and combustion of methane gas. Consequently, the amount of hydrocarbons on the surface of the coated silver microparticles produced by the thermal decomposition of methane gas was reduced, leading to insufficient surface coating of the silver microparticles and accelerated adhesion. Because Comparative Examples 7 and 8 were in foil form, the BET specific surface area and BET diameter could not be measured.

[0138] Here, Figure 5 This is a schematic diagram showing the SEM (Scanning Electron Microscope) image of silver microparticles in Example 5. Figure 6 This is a schematic diagram showing the SEM image of silver microparticles in Comparative Example 3. The SEM images were obtained using a JSM-6700F manufactured by Nippon Electronics Co., Ltd.

[0139] like Figure 5 As shown, the silver microparticles in Example 5 are granular in shape, with small particle size and uniform particle size, without any coarse particles. On the other hand, as... Figure 6 As shown, the silver microparticles in Comparative Example 3 are non-granular, with coarse particles (100) and irregular particle size.

[0140] In addition, from Examples 1 to 6, when the oxygen / methane gas (volume ratio) was 10 to 40 vol%, the positive reflection value increased.

Claims

1. A type of silver microparticle, characterized in that, BET has a specific surface area of ​​10m² 2 / g or higher, with a positive reflection value of 10 or higher.

2. The silver microparticles as described in claim 1, characterized in that, The pyrolysis peak temperature in differential thermal analysis is below 250℃.

3. The silver microparticles as described in claim 1 or 2, characterized in that, The weight reduction per unit area equivalent is 0.5 × 10⁻⁶. -3 g / m 2 above.

4. A method for manufacturing silver microparticles, using silver powder and manufacturing silver microparticles via thermal plasma method, characterized in that, The method includes the steps of supplying the silver powder to a thermal plasma flame and supplying a cooling gas to the thermal plasma flame; the cooling gas contains methane gas and oxygen, and the ratio of oxygen to methane gas, i.e., oxygen / methane gas, is 1 to 50 by volume.

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