JP2010236007A - Spherical silver particles, method for producing silver particles, and production apparatus - Google Patents

Abstract

Disclosed are a spherical silver particle having an appropriate particle diameter excellent in dispersibility and having a low shrinkage rate during heat treatment, a method for producing the spherical silver particle, and a production apparatus.
A central part 11 is a spherical crystallite aggregate, and an outer peripheral part 12 in which rod-like crystallites are radially formed on the outer periphery of the central part 11. The average particle diameter of the spherical silver particles 10 is 0.08 μm to 1.0 μm, and the diameter of the central portion 11 in the cross-sectional structure observation is preferably 0.75 to 0.99 times the diameter of the spherical silver particles 10.
[Selection] Figure 1

Description

  The present invention relates to silver particles having an appropriate particle diameter excellent in dispersibility and having good shrinkage resistance against heating, and a method for producing the silver particles. More specifically, spherical silver particles having a particle size and dispersibility suitable as a paste component to be used as a wiring material or an electrode material of an electronic device and having a low shrinkage rate during heat treatment, a method for producing the silver particles, and a production apparatus It is about.

  In recent years, there has been a demand for miniaturization and high density of electronic devices in order to improve the functionality of electronic devices. In order to achieve finer wiring and electrodes, silver used as a paste material for forming them As for the particles, finer and highly dispersible fine particles are required. On the other hand, when the fine particles are heat-treated, there is a problem that the shrinkage rate of the powder is large, the wiring becomes thin and becomes high resistance, or is disconnected. The reason is as follows. Usually, the fine wiring formed by the conductive paste containing silver particles is volatilized or burned away by the solvent or resin that is a conductive inhibitor in the paste by drying or heat treatment in the manufacturing process, and the silver on the surface of the fine particles is Conductivity is improved by diffusion bonding. However, when fine particles having a large shrinkage rate are used, adjacent fine particles are joined and attracted when the fine particles shrink by drying or heat treatment. Thereby, the location where microparticles | fine-particles gathered locally in the wiring after formation arises. On the other hand, in the portion where the attracted fine particles existed, the wiring becomes thin and constriction occurs. When such a wiring is energized, the current concentrates in the constricted portion, resulting in a high resistance, and in the case of severe contraction, the wire is disconnected and completely loses conduction.

  Conventionally, as a method for producing silver particles used in electronic equipment materials, there is a method of obtaining silver particles having an average particle diameter of about several μm by reducing silver salt ammine complex to precipitate silver particles, washing and drying the silver particles. It is known (for example, refer to Patent Document 1). Further, a method is known in which silver particles having an average particle size of 1 μm or less are obtained by adding ammonium sulfite and the like to hydroquinone as a reducing agent (see, for example, Patent Document 2). In addition, hydroquinone is used as a reducing agent, and an alkali such as NaOH is added thereto to control the oxidation-reduction potential. Further, the silver solution and the reducing agent solution are discharged into the air and collided to mix, thereby obtaining an average particle size of 1 μm or less. There is known a method for producing silver particles which do not contain coarse particles of 5 μm or more (see, for example, Patent Document 3).

JP 2001-107101 A (claims 4 and 5 and paragraph [0023]) JP-A-8-92612 (Claim 1) JP 2008-050697 A (paragraph [0006] and paragraph [0013])

  However, in the production method disclosed in Patent Document 1, it is difficult to stably obtain fine particles having an average particle size of 1 μm or less, and since the particle size distribution is wide and the particles are likely to aggregate, the particle size is small. There is a problem that it is difficult to produce uniform fine silver particles of 1 μm or less. Moreover, when the silver particle manufactured by the method shown by the said patent document 2 is used as a paste raw material, there exist problems, such as a poor dispersibility. Furthermore, when the silver particles produced by the method disclosed in Patent Document 3 are used as a paste raw material, the shrinkage rate during firing of the silver particles is high, and problems such as high resistance and disconnection are likely to occur.

  An object of the present invention is to provide spherical silver particles having an appropriate particle diameter excellent in dispersibility and having a low shrinkage rate during heat treatment.

  Another object of the present invention is a method and apparatus for producing spherical silver particles, which can stably obtain spherical silver particles having an appropriate particle size with excellent dispersibility and a low shrinkage ratio during heat treatment. Is to provide.

  A first aspect of the present invention is a spherical silver particle having a central portion that is a spherical crystallite aggregate and an outer peripheral portion in which rod-like crystallites are radially formed on the outer periphery of the central portion.

  A second aspect of the present invention is an invention based on the first aspect, wherein the average particle diameter of the spherical silver particles is 0.08 μm to 1.0 μm, and the diameter of the central part in the cross-sectional structure observation is the spherical silver It is characterized by being 0.75 to 0.99 times the diameter of the particles.

  A third aspect of the present invention is an invention based on the first or second aspect, and is characterized in that the shrinkage rate when heated at a temperature of 550 ° C. for 10 minutes is 2 to 5%.

  A fourth aspect of the present invention is a method for producing spherical silver particles according to the first to third aspects, wherein the first solution containing silver and the second solution containing hydroquinone are converted into silver in the first solution. Injecting and colliding the first solution and the second solution separately in the air so that the hydroquinone in the second solution with respect to 1 mol falls within the range of 0.25 to 0.45 mol, and the first solution and And a step of dropping the liquid mixture of the second solution into a liquid cooled to 10 ° C. or lower.

  According to a fifth aspect of the present invention, the first and second solutions are separately jetted and collided and mixed in the air to form a mixed solution, and the mixed solution falling in the air is received. In a spherical silver particle manufacturing apparatus including a receiving tank, the receiving tank includes a cooling mechanism that keeps the synthetic liquid in the receiving tank at 10 ° C. or less, and a discharge port that extracts the synthetic liquid in the receiving tank from the bottom of the receiving tank. And

  The spherical silver particles of the first aspect of the present invention have a structure having a central portion that is a spherical crystallite aggregate and an outer peripheral portion in which rod-like crystallites are radially formed on the outer periphery of the central portion. Since a highly crystalline structure is disposed on the outer peripheral portion, the shrinkage rate due to heating can be reduced.

  In the spherical silver particles of the third aspect of the present invention, the shrinkage rate when heated at 550 ° C. for 10 minutes is as low as 2 to 5%, so that fine wirings, electrodes, etc. are formed from the conductive paste produced using this. If it does so, the disconnection and high resistance at the time of the heat processing in manufacturing processes, such as wiring and an electrode, can be suppressed.

  In the production method of the fourth aspect of the present invention, when the silver ammine complex aqueous solution and the reducing agent solution are discharged and mixed in the air, the reducing agent is only hydroquinone 0.25 to 0.45 mol per 1 mol of silver. Since no auxiliary reducing agent or the like is used, the amount of reducing agent used can be suppressed and the manufacturing cost can be reduced.

  In the manufacturing method of the 5th viewpoint of this invention, the 1st solution and the 2nd solution which are jetted separately, respectively, the 1st nozzle and the 2nd nozzle which are made to collide and mix in the air to make a liquid mixture, and the mixing which falls in the air In a spherical silver particle manufacturing apparatus including a receiving tank for receiving a liquid, the receiving tank includes a cooling mechanism for keeping the synthetic liquid in the receiving tank at 10 ° C. or less, and a discharge port for extracting the synthetic liquid in the receiving tank from the bottom of the receiving tank. As a result, the spherical silver particles of the first to third aspects of the present invention can be efficiently produced.

FIG. 3 is a photograph of a cross-sectional structure of spherical silver particles of Example 2 observed with a TEM. 6 is a schematic diagram showing a cross-sectional structure of spherical silver particles of Example 3. FIG. It is a schematic diagram which shows the principal part in the manufacturing apparatus of this invention. It is the schematic which shows an example of the manufacturing apparatus of this invention.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings. As shown in FIGS. 1 and 2, the spherical silver particles 10 of the present invention include a central portion 11 that is a spherical crystallite aggregate, and an outer peripheral portion in which rod-like crystallites are radially formed on the outer periphery of the central portion 11. 12. Although ordinary spherical silver particles are not shown in the figure, when the cross section thereof is observed with a transmission electron microscope (hereinafter referred to as TEM), it is common to have a structure like an aggregate of spherical crystallites in the entire region. is there. On the other hand, in the spherical silver particle 10 of the present invention, a central part 11 made of a spherical crystallite aggregate and a rod-like crystallite larger than the crystallite constituting the central part are radially arranged on the outer periphery of the central part 11. It has a structured. The spherical silver particles 10 of the present invention have a structure with high crystallinity on the outer periphery by having a structure in which the rod-like crystallites are radially arranged so as to cover the central portion 11 formed of the spherical crystallite aggregate. Is placed. Thereby, the shrinkage rate by heating can be reduced compared with the conventional one.

  The shrinkage rate of general spherical silver particles is, for example, 6 to 15% when heated at 550 ° C. for 10 minutes. On the other hand, in the case of the spherical silver particles of the present invention, the shrinkage rate when heated under the same conditions is about 2 to 5%. Therefore, if a fine wiring, an electrode, etc. are formed with the electrically conductive paste manufactured using the spherical silver particle of this invention, the disconnection and high resistance at the time of heat processing in manufacturing processes, such as a wiring and an electrode, can be suppressed.

  The average particle diameter of the spherical silver particles 10 of the present invention is preferably 0.08 μm to 1.0 μm, and more preferably 0.1 to 0.6 μm. In addition, the diameter of the central portion 11 in the cross-sectional structure observation is preferably 0.75 to 0.99 times, more preferably 0.80 to 0.95 times the diameter of the spherical silver particles 10. When the diameter of the central portion 11 in the cross-sectional structure observation is less than 0.75 times, there is no particular problem in terms of performance as silver particles used in the conductive paste, but when the silver particles are generated, the reducing agent is insufficient and the entire amount of silver is recovered. This is not preferable because the manufacturing cost increases. On the other hand, when the ratio exceeds 0.99 times, most of the spherical silver particles 10 are constituted by the central portion 11, and it is difficult to obtain the above effect. In the present specification, the average particle diameter is observed with a scanning electron microscope (hereinafter referred to as SEM), and when the particle diameters of 50 particles selected arbitrarily are measured in an image of the obtained micrograph. The average value of The diameter of the central portion 11 of the spherical silver particles 10 is a diameter obtained by cutting the spherical silver particles 10 with a focused ion beam apparatus (hereinafter referred to as FIB apparatus) or the like and measuring the cross-sectional diameter by TEM observation. Further, the heat shrinkage rate refers to the shrinkage rate of the particle diameter calculated by observing with a SEM equipped with a heating stage and comparing the particle diameter before and after heating in the obtained microscope image.

  Next, the manufacturing method and manufacturing apparatus of the spherical silver particles of the present invention will be described. First, the manufacturing apparatus used in order to manufacture the spherical silver particle of this invention is demonstrated. As shown in FIG. 4, the manufacturing apparatus 20 of the present invention includes a first nozzle 21 and a second nozzle 22 that face each other obliquely downward. Storage tanks 23 and 24; pipes 25 and 26 for supplying a solution from the storage tanks 23 and 24 to the first nozzle 21 or the second nozzle 22; and liquid feed pumps 27 and 28 provided in the pipes 25 and 26; Adjustment units 29 and 30 provided between the liquid feed pumps 27 and 28 and the first nozzle 21 or the second nozzle 22, and a receiving tank 50 installed below the first nozzle 21 and the second nozzle 22.

  Then, as shown in FIG. 3, after the first solution 41 and the second solution 42 are separately jetted from the first nozzle 21 and the second nozzle 22, respectively, they are collided and mixed in the air to become a mixed solution 43. The mixed solution 43 falls and is stored in the receiving tank 50. The first nozzle 21 and the second nozzle 22 are arranged so that the nozzle angle θ and the inter-nozzle distance h can be freely adjusted. The receiving tank 50 includes a cooling mechanism that keeps the mixed solution 43 in the receiving tank 50 at 10 ° C. or lower. Although the cooling mechanism is not particularly limited, for example, it has a jacket structure in which a cooling pipe 52 is disposed inside the wall of the receiving tank 50, and an inlet 51 that introduces the refrigerant into the wall of the receiving tank 50 through the cooling pipe 52; And an outlet 53 for deriving this. Moreover, the discharge port 54 which can take out the synthetic | combination liquid stored in the receiving tank 50 from the receiving tank 50 rapidly is provided.

  Then, the method to manufacture the spherical silver particle of this invention using this manufacturing apparatus 20 is demonstrated. The spherical silver particles of the present invention can be obtained by reducing the silver ammine complex to precipitate silver particles. That is, a silver solution is precipitated by mixing a first solution containing silver and a second solution containing hydroquinone as a reducing agent under predetermined conditions.

  A solution suitable as the first solution containing silver includes a silver ammine complex aqueous solution prepared by mixing a silver nitrate solution with an aqueous ammonia solution. The silver concentration of this silver ammine complex aqueous solution is preferably in the range of 20 to 180 g / L, and can be prepared, for example, by mixing an aqueous ammonia solution with a silver nitrate solution having a silver concentration of 34 to 200 g / L. On the other hand, the 2nd solution used as a reducing agent solution is adjusted by dissolving hydroquinone which is a reducing agent with ion-exchange water.

  The first solution and the second solution are stored in the storage tanks 23 and 24 of the manufacturing apparatus 20 shown in FIG. 4, and the first nozzle 21 and the second solution are passed through the pipelines 25 and 26 by the liquid feed pumps 27 and 28, respectively. 2 nozzles 22 are sent out. The flow rates of the first solution 41 and the second solution 42 ejected from the first nozzle 21 and the second nozzle 22 can be appropriately adjusted by the adjusting units 29 and 30. The first solution 41 and the second solution 42 sprayed separately from the first nozzle 21 and the second nozzle 22 are collision-mixed in the air. In the production method of the present invention, the amount of hydroquinone used as the reducing agent is 0.25 to 0.45 mol with respect to 1 mol of silver to be reduced. Usually, the amount of hydroquinone considered to be necessary for reducing 1 mol of silver is 0.5 mol, but in the production method of the present invention, the amount of hydroquinone is less than 0.5 mol. The reaction can be carried out without adding a reducing agent or the like. This is because benzoquinone, which is an oxidized form of hydroquinone, that is, hydroquinone reduces the silver ammine complex, and benzoquinone generated by oxidation of itself reduces silver further. Although the reducing power of benzoquinone is not so strong, since silver is a metal having a precious redox potential and is easily reduced to metallic silver, the silver ammine complex can be easily reduced to silver by benzoquinone. Thereby, in the manufacturing method of this invention, the usage-amount of hydroquinone can be reduced and manufacturing cost can be reduced. In the production method of the present invention, the reducing agent is set to 0.25 to 0.45 mol with respect to 1 mol of silver. If the amount is less than 0.25 mol, the reducing agent is insufficient and the total amount of silver cannot be reduced, and the recovery rate. This is because when the amount exceeds 0.45 mol, the particles do not have a two-layer structure of the central portion 11 and the outer peripheral portion 12, and the heat shrinkage rate increases.

  The flow rates of the first solution 41 and the second solution 42 from the first nozzle 21 and the second nozzle 22 consider the particle size distribution of the silver particles to be produced, and the amount of hydroquinone used per 1 mol of silver is within the above-mentioned range. Can be adjusted as appropriate. Specifically, when the first solution containing silver and the second solution that is a reducing agent solution are jetted from each nozzle at the same flow rate and mixed, for example, the silver concentration in the first solution is 20 g / L. At this time, the concentration of hydroquinone in the second solution may be 5.1 to 9.2 g / L. When the silver concentration in the first solution is 180 g / L, the concentration of hydroquinone in the second solution is 45.9 to 82.7 g / L. In addition, the first solution and the second solution do not have to be jetted and mixed at the same flow rate. When the second solution is jetted and mixed at a flow rate three times that of the first solution, for example, the first solution When the silver concentration in the solution is 180 g / L, the concentration of hydroquinone in the second solution may be 15.3 to 27.6 g / L.

  In FIG. 3, by decreasing the nozzle angle θ to increase the inter-nozzle distance h and adjusting the flow pressure to decrease the flow rate, the particle size increases and the particle size distribution tends to widen. On the other hand, when the nozzle angle θ is increased to decrease the inter-nozzle distance h and the flow rate is increased, the particle size tends to decrease and the particle size distribution tends to become narrower. Therefore, it is preferable that the nozzle angle θ is 45 to 150 degrees and the inter-nozzle distance h is in the range of 0.5 to 20 mm. The flow pressures of the first solution 41 and the second solution 42 are preferably in the range of 0.5 to 20 kPa and 0.5 to 60 kPa, respectively. The flow rates of the first solution 41 and the second solution 42 are preferably 0.5 to 15 L / min and 0.5 to 45 L / min, respectively.

  Under such conditions, the mixed solution 43 of the first solution 41 and the second solution 42 sprayed from the first nozzle 21 and the second nozzle 22 and collided and mixed in the air is stored in advance in the receiving tank 50 and is 10 ° C. Drop into the cooled liquid below. By setting the temperature to 10 ° C. or lower, unlike the spherical crystallites constituting the crystallite aggregate of the central portion 11 as shown in FIG. 1 or FIG. 2, a rod-like crystallite larger than this crystallite is obtained. Spherical silver particles 10 having a structure that grows radially from the center of the sphere can be obtained on the outer periphery of the central portion 11. The technical reason is that the reduction rate of silver ions by benzoquinone is strongly influenced by temperature, and when the liquid temperature exceeds 10 ° C, it becomes the same as the reduction rate of silver ions by hydroquinone and is the same in the entire region of silver particles. Crystallites grow. However, when the temperature is 10 ° C. or lower, the reduction rate by benzoquinone is extremely reduced, and crystallites grow slowly, and this crystallite with high crystallinity grows on the outer periphery of the central portion. For this reason, the liquid temperature of the liquid which drops the liquid mixture 43 shall be 10 degrees C or less. When the liquid temperature exceeds 10 ° C., the produced silver particles do not have the above two-layer structure, and the effect of the present invention cannot be obtained. On the other hand, the lower limit value of the liquid temperature is not particularly limited. However, considering the problem of cooling cost and the discharge of the synthetic liquid from the bottom of the receiving tank 50 by a pump, it is reasonable to reach about 0 ° C. As the liquid stored in the receiving tank 50 in advance, water, a mixture of water and methanol or ethanol, drainage liquid generated by solid-liquid separation described later, and the like can be used. The reason why the mixed solution 43 is dropped directly into the liquid stored in the receiving tank 50 without being dropped directly into the receiving tank 50 is that the reduction reaction is not completed in the falling mixed liquid 43 and is directly in the receiving tank 50. This is because, when dropped, the silver deposits on the wall surface of the receiving tank 50, and when it is peeled off, there is a problem that coarse flat silver is mixed.

  The synthetic liquid in which silver is deposited in the receiving tank 50 is easily taken out from the discharge port 54 provided at the bottom of the receiving tank 50 shown in FIG. 3, and the silver particles can be recovered by solid-liquid separation. The collected silver particles are then subjected to a cleaning process such as alkali cleaning, amide solvent cleaning or strong reducing agent aqueous solution cleaning, whereby organic substances on the particle surface are removed. The spherical silver particle of this invention is obtained by the above process. In the production method of the present invention, since the oxidation product of benzoquine or benzoquinone produced by the reduction reaction adheres to the surface of the spherical silver particles and prevents aggregation of the spherical silver particles, a dispersant is used in any step. There is no need.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
First, an aqueous silver nitrate solution having a concentration of 25 g / L is added to and mixed with an aqueous silver nitrate solution having a silver concentration of 200 g / L so that the amount of ammonia relative to 1 mol of silver is 3.0 mol. An aqueous silver ammine complex solution having a concentration of 100 g / L was prepared, and this was used as the first solution. On the other hand, hydroquinone was dissolved in ion-exchanged water to prepare a hydroquinone aqueous solution having a concentration of 25.5 g / L, which was used as the second solution.

  Next, the prepared first solution and second solution are respectively stored in the storage tanks 23 and 24 of the manufacturing apparatus 20 shown in FIG. 4, and the first nozzle is passed through the pipelines 25 and 26 by the liquid feed pumps 27 and 28. 21 to the second nozzle 22. And the 1st solution 41 and the 2nd solution 42 were each injected separately from the 1st nozzle 21 and the 2nd nozzle 22, and it carried out collision mixing in the air, and was set as the liquid mixture 43. At this time, the flow rates of the first solution 41 and the second solution 42 from the first nozzle 21 and the second nozzle 22 were both 7.5 L / min. That is, the amount of hydroquinone used relative to 1 mol of silver was 0.25 mol. The flow pressures of the first solution 41 and the second solution 42 were both 5 kPa. Further, the nozzle angle θ of the first nozzle 21 and the second nozzle 22 in FIG. 3 was 90 degrees, and the inter-nozzle distance h was 2 mm. The mixed solution 43 subjected to the collision mixing was dropped into water that was previously adjusted to a temperature of 5 ° C. in a receiving tank 50 having a cooling mechanism shown in FIG.

  Next, the synthesis solution in which the silver in the receiving tank 50 was deposited was taken out from the discharge port 54 provided at the bottom of the receiving tank 50, and the solid was recovered by solid-liquid separation. The collected silver is mixed and washed with 1 g of silver hydroxide so that the amount of sodium hydroxide at a concentration of 4 g / L is 4 mL, organic substances adhering to the surface of the silver particles are removed, and this is further solidified by a centrifuge. The liquid was separated. The process from this washing to solid-liquid separation was defined as 1 cycle, and this was repeated 3 cycles. Finally, the solid after washing was dried with hot air at 50 ° C. to obtain a silver powder.

<Example 2>
A silver powder was obtained in the same manner as in Example 1, except that the hydroquinone concentration in the second solution was 30.6 g / L, that is, the amount of hydroquinone used was 0.30 mol with respect to 1 mol of silver.

<Example 3>
A silver powder was obtained in the same manner as in Example 1 except that the hydroquinone concentration in the second solution was 37.5 g / L, that is, the amount of hydroquinone used relative to 1 mol of silver was 0.35 mol.

<Example 4>
A silver powder was obtained in the same manner as in Example 1 except that the hydroquinone concentration in the second solution was 40.8 g / L, that is, the amount of hydroquinone used relative to 1 mol of silver was 0.40 mol.

<Example 5>
A silver powder was obtained in the same manner as in Example 1 except that the hydroquinone concentration in the second solution was 45.9 g / L, that is, the amount of hydroquinone used relative to 1 mol of silver was 0.45 mol.

<Example 6>
Silver powder was obtained in the same manner as in Example 3 except that the temperature of the water in the receiving tank 50 was set to 1 ° C. in advance.

<Example 7>
Silver powder was obtained in the same manner as in Example 3 except that the temperature of the water in the receiving tank 50 was set to 10 ° C. in advance.

<Comparative Example 1>
A silver powder was obtained in the same manner as in Example 1, except that the hydroquinone concentration in the second solution was 15.3 g / L, that is, the amount of hydroquinone used relative to 1 mol of silver was 0.15 mol.

<Comparative example 2>
A silver powder was obtained in the same manner as in Example 1 except that the hydroquinone concentration in the second solution was 20.4 g / L, that is, the amount of hydroquinone used relative to 1 mol of silver was 0.20 mol.

<Comparative Example 3>
A silver powder was obtained in the same manner as in Example 1, except that the hydroquinone concentration in the second solution was 51.0 g / L, that is, the amount of hydroquinone used relative to 1 mol of silver was 0.50 mol.

<Comparative example 4>
A silver powder was obtained in the same manner as in Example 1, except that the hydroquinone concentration in the second solution was 56.1 g / L, that is, the amount of hydroquinone used was 0.55 mol with respect to 1 mol of silver.

<Comparative Example 5>
A silver powder was obtained in the same manner as in Example 3 except that the temperature of the water in the receiving tank 50 was previously set to 15 ° C.

<Comparison test and evaluation>
The average particle diameter of the spherical silver particles in the silver powders obtained in Examples 1 to 7 and Comparative Examples 1 to 5, the diameter of the central portion with respect to the average particle diameter, and the heat shrinkage ratio of the spherical silver particles were determined. Moreover, the disconnection in the wiring produced using these silver powder was evaluated. These results are shown in Table 1 below.

  (1) Average particle diameter of spherical silver particles: The obtained silver powder was observed by SEM, and the particle diameters of 50 arbitrarily selected particles were measured in the image of the obtained micrograph, and the average value of these particles was measured. Was calculated. In addition, in the image of the micrograph, the particle was overlapped and the diameter was calculated by complementing from the curvature of the visible part.

  (2) Average particle diameter of spherical silver particles: The obtained silver particles were cut with a focused ion beam apparatus (FIB apparatus), and the cross-sectional diameter was measured by TEM observation. The image of the micrograph which observed the cross section of the spherical silver particle obtained in Example 2 by TEM is shown in FIG. Moreover, the schematic diagram showing the cross section of the spherical silver particle obtained in Example 3 is shown in FIG. In addition, the boundary between the central portion and the outer peripheral portion was determined by visual observation from the obtained micrograph image.

  (3) Heat shrinkage rate: Using a SEM having a heating stage, independent single particles that were not in contact with surrounding particles were discovered. And the diameter of the single particle | grains before and behind the heat processing hold | maintained for 10 minutes at the temperature of 550 degreeC with the heating stage was measured from the image of each micrograph, and it computed by comparing this.

  (4) Existence of disconnection: First, 70 g of silver powder obtained in Examples 1 to 7 and Comparative Examples 1 to 5 and 25 g of a solution in which α-terpineol was dissolved so that ethylcellulose having an average molecular weight of 100,000 was 10 wt%; Then, 5 g of glass frit was roll mill mixed to obtain each conductive paste.

  Using these conductive pastes, paste-like lines having a line width of 50 μm and a length of 100 mm were printed on a glass substrate by screen printing. Subsequently, after drying this for 30 minutes at the temperature of 100 degreeC, the wiring was formed by baking for 10 minutes at the temperature of 550 degreeC. Wiring was formed at 10 points for each conductive paste.

  With respect to these wirings, a tester was applied to both ends of the formed wirings, and a case where continuity was not obtained was judged as a disconnection.

  Of the wirings formed at 10 points for each conductive paste, there is a wiring that is judged to be broken even at one point, “Yes”, and the case where it is judged that there is no breaking in all 10 wirings. “No”.

As is clear from Table 1, in Examples 1 to 7 according to the production method of the present invention, it was confirmed that the spherical silver particles of the present invention having a central portion and an outer peripheral portion were obtained. On the other hand, in Comparative Examples 3 and 4 in which the amount of hydroquinone used relative to 1 mol of silver exceeds 0.45 mol, and in Comparative Example 5 where the temperature of water in the receiving tank exceeds 10 ° C., silver particles having no outer peripheral portion were produced. . In Comparative Examples 1 and 2 in which the amount of hydroquinone used relative to 1 mol of silver is less than 0.25 mol, the spherical silver particles of the present invention having a central portion and an outer peripheral portion can be obtained, but silver cannot be reduced and the recovery rate is poor. It became.

  Further, the spherical silver particles of the present invention have a low heat shrinkage rate of 2 to 5%, and no disconnection was confirmed in the wiring formed using this. From this, it was confirmed that the spherical silver particles of the present invention are effective for forming fine wiring.

  The spherical silver particles of the present invention can be suitably used as a paste material for forming electronic equipment, electronic device wiring, electrodes, and the like that are required to be miniaturized and densified.

10 spherical silver particles 11 central part 12 outer peripheral part

Claims (5)

  A spherical silver particle having a central part which is a spherical crystallite aggregate and an outer peripheral part in which rod-like crystallites are radially formed on the outer periphery of the central part.   2. The spherical shape according to claim 1, wherein the spherical silver particles have an average particle diameter of 0.08 μm to 1.0 μm, and the diameter of the central portion in cross-sectional structure observation is 0.75 to 0.99 times the diameter of the spherical silver particles. Silver particles.   The spherical silver particles according to claim 1 or 2, which have a shrinkage ratio of 2 to 5% when heated at a temperature of 550 ° C for 10 minutes. A method for producing the spherical silver particles according to any one of claims 1 to 3,
The first solution containing silver and the second solution containing hydroquinone are prepared so that the hydroquinone in the second solution with respect to 1 mol of silver in the first solution falls within the range of 0.25 to 0.45 mol. Injecting each of the first solution and the second solution separately and colliding them in the air;
Dropping the mixed solution of the first solution and the second solution into a liquid cooled to 10 ° C. or lower. A method for producing spherical silver particles, comprising: A spherical silver particle comprising: a first nozzle and a second nozzle that separately jet a first solution and a second solution, collide and mix in the air to form a mixed solution; and a receiving tank that receives the mixed solution that falls in the air In manufacturing equipment,
The receiving tank is a cooling mechanism for keeping the synthesis solution in the receiving tank at 10 ° C. or lower;
An apparatus for producing spherical silver particles, comprising: a discharge port for extracting the synthesis solution in the receiving tank from the bottom of the receiving tank.