JP2019178404A - Core shell particle and application thereof - Google Patents

Abstract

Provided is a technique capable of appropriately suppressing formation of secondary particles due to sticking without lowering the yield of core-shell particles. A core-shell particle disclosed herein is composed of an Ag core particle containing silver as a main component and a Pd shell containing palladium as a main component and covering at least a part of the surface of the Ag core particle. I have. In such core-shell particles, polyvinylpyrrolidone is selectively attached to the surface of the Pd shell. Therefore, it is possible to prevent PVP from hindering the precipitation of the Pd shell on the surface of the Ag core particles, and to appropriately suppress a decrease in the yield of the core shell particles. Since PVP is attached to the surface of the Pd shell, the occurrence of sticking via the Pd shell can be suitably suppressed, and the particle size can be suitably controlled in the submicron region. [Selection diagram] None

Description

  The present invention relates to core-shell particles. Specifically, the present invention relates to a core-shell particle in which a Pd shell mainly containing palladium (Pd) is formed on the surface of an Ag core particle mainly containing silver (Ag).

  In recent years, core-shell particles have been used in various industrial fields from the viewpoint of imparting functionality and reducing costs. For example, in the field of conductive pastes and catalysts, development of core-shell particles in which a Pd shell mainly composed of palladium (Pd) is formed on the surface of an Ag core particle mainly composed of (Ag) is being promoted. Yes. Patent Documents 1 and 2 disclose an example of a method for producing core-shell particles. For example, in Patent Document 1, after adding a reducing agent to an aqueous silver chloride silver solution to form silver particles (Ag core particles), palladium (Pd shell) is coated on the silver particles and palladium-coated silver powder (core-shell particles) is applied. A method of manufacturing is described.

By the way, with recent demands for downsizing electronic components and thinning of electrodes, the particle size of the metal particles in the powder material is smaller and sharper than the powder material for the conductive paste. It is required to have a distribution. For this reason, when core-shell particles are used as a powder material for conductive paste, it is important to control the particle diameter of the core-shell particles in the submicron region.
However, when core-shell particles are produced by a conventional method, the core-shell particles (primary particles) after production are aggregated and connected (necked), and secondary particles such as large aggregates and connected (necked) agglomerates are formed. A large amount may be formed. Since the secondary particles are fixed to each other by a shell and are so strong that they cannot be crushed, the particle size of the powder material containing the core-shell particles is significantly larger than the particle size of the core, In addition, the variation in particle size becomes a cause.

  For example, Patent Document 1 discloses a technique for preventing aggregation of Ag core particles (silver powder). However, since it is difficult to suppress the connection itself by the Pd shell with such a technique, the secondary particles are still huge. Could be formed. For example, Patent Document 1 describes that palladium-coated silver powder (core-shell particles) having an average particle diameter of about 0.4 μm is formed. However, since the average particle size described in Patent Document 1 is evaluated by a scanning electron microscope (SEM), it is considered that the particle size of primary particles is measured, and a powder containing core-shell particles. When the material is actually manufactured, there is a problem that a large amount of secondary particles to which a plurality of primary particles are fixed are formed.

On the other hand, Non-Patent Document 1 proposes a technique for reducing the particle diameter of metal particles contained in a powder material. Such Non-Patent Document 1 discloses a technique for generating metal ultrafine particles whose surfaces are protected by PVP by depositing metal particles (Rh, Pd, etc.) in the presence of polyvinylpyrrolidone (PVP). ing. Thus, Non-Patent Document 1 shows that PVP has an action of precipitating metal as fine particles.
Non-Patent Documents 2 and 3 disclose techniques for using the above-described PVP for manufacturing core-shell particles. For example, in Non-Patent Document 2, first, a solution in which silver nitrate and PVP are dissolved is prepared, and Ag is precipitated from the solution to produce Ag core particles. Then, palladium nitrate is dissolved in the dispersion containing the Ag core particles, and then Pd is deposited to form a Pd shell on the surface of the Ag core particles. This Non-Patent Document 2 describes that the average particle diameter of Ag @ Pd fine particles (core-shell particles) obtained by such a procedure is about 5.0 nm.

JP-A-8-176605 Patent No. 5535507

Tsuji, Naoki Toshima, Polymer Papers, Vol. 46 (1989) no. 9, pp. 551 9th Molecular Science Symposium Abstract 2P077 Nature nanotechnology, 6, 302 (2011) Supplementary information

However, when the techniques described in Non-Patent Documents 2 and 3 described above are actually used, there may be a problem that a large amount of fine Pd single particles are easily formed. Specifically, in Non-Patent Documents 2 and 3, when the distribution state of Ag element and Pd element by FE-SEM and EDX element mapping is confirmed, a large amount of Pd single particles are formed. Since it is extremely difficult to extract only the core-shell particles from such a powder material containing a large amount of single Pd particles, when the methods of Non-Patent Documents 2 and 3 described above are applied to the actual manufacturing process, Since the ratio of the core-shell particles contained in the material (yield of the core-shell particles) is greatly reduced, the characteristics peculiar to the core-shell particles cannot be sufficiently exhibited, and the production efficiency may be reduced.
As described above, as one of the causes that a large amount of fine Pd single particles are produced, as shown in Non-Patent Document 1, PVP has an action of precipitating metal particles as fine particles. Therefore, when it is required to deposit a film-like metal (shell) as in core-shell particles, the technique using PVP as in Non-Patent Documents 2 and 3 has been considered inappropriate.

  The present invention has been made in view of such a point, and the main object of the present invention is to appropriately suppress the formation of secondary particles due to fixation without reducing the yield of the core-shell particles, thereby reducing the core-shell particles. Provided is a technique capable of efficiently obtaining a powder material having a particle diameter controlled in a submicron region.

  In order to achieve the above-described object, the core-shell particles disclosed herein are provided.

  The core-shell particles disclosed here are composed of Ag core particles mainly composed of silver and Pd shells mainly composed of palladium covering at least a part of the surface of the Ag core particles. In such core-shell particles, polyvinylpyrrolidone is selectively attached to the surface of the Pd shell.

As described above, when a powder material containing core-shell particles is actually produced, the technique using PVP as in Non-Patent Documents 2 and 3 produces many fine Pd single particles, and the yield of core-shell particles Was thought to be inappropriate because of a significant drop. One of the causes of this phenomenon is that PVP has an action of precipitating metal particles as fine particles (see Non-Patent Document 1).
However, the present inventor used PVP for the production of core-shell particles in order to appropriately suppress the formation of secondary particles due to fixation of primary particles, and then reduced the yield of the core-shell particles due to the use of the PVP. I thought about creating a technology to prevent this.
And as a result of repeating further original examination based on this idea, when this inventor precipitated Ag core particle in presence of PVP, PVP adheres to the surface of the said Ag core particle, Ag It has been found that the difficulty in precipitating Pd shells on the surface of the core particles is one cause of the above-described decrease in the yield of the core-shell particles.

The core-shell particle disclosed here is based on such knowledge, and unlike the conventional technique in which PVP is attached to the surface of the Ag core particle, Pd is hardly attached to the surface of the Ag core particle. PVP is selectively attached to the surface of the Pd shell at the time of shell generation. As a result, the Pd shell can be suitably deposited on the surface of the Ag core particles, so that the formation of fine Pd single particles is prevented despite the presence of PVP and the decrease in the yield of the core shell particles is suppressed. be able to.
In the core-shell particles disclosed here, PVP is attached to the surface of the Pd shell, and the outer surface of the core-shell particles is protected by the PVP. For this reason, it can suppress suitably that several core shell particle | grains (primary particle) adhere through a Pd shell, and it can suppress appropriately that a huge secondary particle is formed.
In this specification, “polyvinylpyrrolidone selectively adheres to the surface of the Pd shell” means that PVP adheres preferentially to the surface of the Pd shell compared to the surface of the Ag core particles. It typically includes substantially no PVP attached to the surface of the Ag core particles.

Moreover, the powder material of the following structures is provided as another aspect of the present invention.
The powder material disclosed herein includes core-shell particles composed of Ag core particles mainly composed of silver and Pd shells mainly composed of palladium covering at least a part of the surface of the Ag core particles. It is a powder material containing at least.
In such a powder material, the Z average particle diameter (D _DLS ) measured by performing analysis by the cumulant method in the dynamic light scattering method is 0.1 μm to 1.5 μm, and the polydispersity index ( PDI) is 0.4 or less.

As described above, the core-shell particles generated without substantially attaching PVP to the surface of the Ag core particles and selectively attaching PVP to the surface of the Pd shell are caused by adhesion through the Pd shell. The formation of secondary particles is appropriately suppressed. For this reason, the powder material containing such core-shell particles has a small particle size and a sharp particle size distribution. Specifically, the above-described powder material including the core-shell particles has a Z average particle diameter (D _DLS ) of 0 measured by performing analysis by a cumulant method in a dynamic light scattering method (DLS: Dynamic light scattering). 0.1 μm to 1.5 μm, and the polydispersity index (PDI) is 0.4 or less. Since the particle diameter of the core-shell particles is suitably controlled in the submicron region, such a powder material can greatly contribute to downsizing of electronic parts and thinning of electrodes.
In the present specification, when measuring an index relating to particle diameter (for example, the above-mentioned “Z average particle diameter (D _DLS )” and “polydispersity index (PDI)”) using _DLS , the dispersion medium for measurement includes A predetermined dispersion medium such as water, N, N-dimethylformamide (DMF), ethylene glycol (EG), isobornyl acetate (IBA) or the like is used. In addition, when measuring with such DLS, various means (for example, selection of an appropriate dispersion medium, addition of a dispersant, a thickener, etc.) are used to suppress aggregation and sedimentation of core-shell particles in the powder material. Use of an agent, surface modification of core-shell particles, use of a dispersing device, etc.) may be used. In addition, when using a dispersing device, it is preferable to use an ultrasonic dispersing device from a viewpoint of preventing a deformation | transformation and destruction of a primary particle.

Moreover, the powder material obtained by this invention also has the following characteristics.
The powder material disclosed herein includes core-shell particles composed of Ag core particles mainly composed of silver and Pd shells mainly composed of palladium covering at least a part of the surface of the Ag core particles. It is a powder material containing at least.
In such a powder material, the peak particle size measured by performing the analysis by the NNLS method in the dynamic light scattering method is in the range of 0.1 μm to 1.5 μm, and the peak intensity of the peak particle size is Is 90% or more.

As described above, in the powder material in which the core-shell particles are generated so that the PVP is selectively attached to the surface of the Pd shell without substantially attaching the PVP to the surface of the Ag core particles, the contained core-shell particles Have a small particle size and a sharp particle size distribution. As described above, when the dynamic light scattering method is performed on the powder material and analyzed by the cumulant method, the Z average particle diameter (D _DLS ) becomes 0.1 μm to 1.5 μm, and the polydispersity index (PDI) becomes 0.4 or less. However, the analysis method for specifying such a powder material is not limited to the cumulant method, and an NNLS method (Nonnegative Last Squares Method) can also be used in DLS. When analysis by the NNLS method is performed, the peak particle size is in the range of 0.1 μm to 1.5 μm, and the peak intensity of the peak particle size is 90% or more. Such a powder material can greatly contribute to miniaturization of electronic components and thinning of electrodes because the particle diameter of the core-shell particles is suitably controlled in the submicron region.
The “peak particle diameter” and “peak intensity of the peak particle diameter” in the present specification are, as described above, the powder material without agglomeration or sedimentation in a predetermined solvent such as water, DMF, EG, IBA. This is a value obtained by performing measurement in a state where is dispersed.

In a preferred embodiment of the powder material disclosed herein, the content of core-shell particles is 90% or more.
As described in Non-Patent Documents 2 and 3, when PVP is attached to the surface of the Ag core particles, a large amount of fine single particles are formed, and the yield of the core-shell particles is reduced. On the other hand, in this invention, since Pd shell can be deposited suitably on the surface of Ag core particle, formation of a fine single particle can be prevented and the fall of the yield of core-shell particle can be suppressed. Therefore, the powder material disclosed here contains core-shell particles at a high content. Specifically, in the powder material disclosed here, the content of core-shell particles is 90% or more (typically 95% or more, for example, 99%) with respect to the entire powder material including single particles of Pd and Ag. Above).
In addition, this "core-shell particle content" refers to the particle diameter (equivalent circle diameter) for each particle using FE-SEM, energy dispersive X-ray spectroscopy (EDX). After the measurement, core-shell determination by element mapping was performed, and the calculation was performed assuming that all the particles were spheres having a diameter equivalent to a circle. The ratio of the core-shell particles to the total volume of the particles is shown. Here, “all particles” refers to all particles mainly composed of a core component and / or a shell component. The measurement of the “content ratio of core-shell particles” is based on observation of a plurality of visual fields and evaluation of a total of 200 or more particles.

In a preferred embodiment of the powder material disclosed herein, polyvinylpyrrolidone is selectively attached to the surface of the core-shell particles.
As in the embodiment described above, by generating core shell particles in which PVP is selectively attached to the surface of the Pd shell, a powder material containing core shell particles with a controlled particle size in a submicron region in a high yield is obtained. However, the PVP may be removed from the surface of the Pd shell after the formation of the core shell particles. However, as in this embodiment, the powder material in which PVP is left attached to the surface of the Pd shell can be suitably dispersed in a dispersion medium when preparing a conductive paste. It can be used more suitably as a material.

In a preferred embodiment of the powder material disclosed herein, the BET particle diameter (D _BET ) converted from the BET specific surface area and the Z average particle diameter (D _DLS ) have the relationship represented by the following formula (1): Satisfies.
D _DLS / D _BET ≦ 10.0 (1)
Among various indexes for evaluating the particle size of particles contained in the powder material, the Z average particle size (D _DLS ) measured by the DLS method increases when huge secondary particles are formed by sticking. have. On the other hand, the BET particle diameter (D _BET ) converted from the BET specific surface area has a characteristic that it is less susceptible to the above-mentioned fixation than the Z average particle diameter (D _DLS ). Therefore, it is possible to evaluate as the ratio of Z-average particle diameter to BET particle diameter _{(D BET) (D DLS)} (D DLS / D BET) is reduced, the secondary particles contained in the powder material is small.
And the powder material of this aspect whose _DDLS / _DBET is 10.0 or less like said Formula (1) has very little content of the secondary particle by fixation through Pd shell, The particle diameter of the core-shell particles is suitably controlled in the submicron region.
As described above, “D _DLS / D _BET ” in this specification is measured in a state in which the powder material is dispersed in a predetermined solvent such as water, DMF, EG, IBA without being aggregated or settled. It is a value obtained by doing.

In addition, as another aspect of the present invention, the following conductive paste is provided.
The conductive paste disclosed here is a conductive paste in which the powder material according to each aspect described above is dispersed in a dispersion medium.
As described above, a conductive paste in which a powder material containing core-shell particles is dispersed in a dispersion medium is suitably used for forming electronic parts and electrodes. At this time, since the conductive paste disclosed here uses a powder material containing core-shell particles whose particle diameter is controlled in the submicron region, a sufficiently thin electrode is preferably formed. Can do.

As another aspect of the present invention, the following powder material manufacturing method is provided.
The method for producing a powder material disclosed herein is composed of Ag core particles mainly composed of silver, and a Pd shell mainly composed of palladium covering at least a part of the surface of the Ag core particles. This is a method for producing a powder material containing at least core-shell particles.
Then, such a production method includes a mixed solution preparation step of preparing an Ag dispersion mixed solution in which Ag core particles are dispersed in a solution in which a palladium complex and polyvinyl pyrrolidone are dissolved, and an Ag dispersion containing polyvinyl pyrrolidone and Ag core particles. A Pd shell precipitation step of adding a reducing agent to the mixed solution and precipitating a Pd shell on the surface of the Ag core particles.

As described above, the present invention is characterized in that the core-shell particles are generated so that PVP selectively adheres to the surface of the Pd shell.
Here, in the method for producing a powder material disclosed herein, an Ag-dispersed mixed solution in which powdered Ag (Ag core particles) is dispersed in a mixed solution in which a Pd complex and PVP are dissolved is prepared, and the Ag dispersion is performed. A reducing agent is added to the mixed solution to precipitate a Pd shell.
In this way, when powdered Ag core particles are dispersed in a mixed solution containing PVP and Pd, PVP adheres to the surface of Ag core particles, unlike the conventional technique in which Ag core particles are precipitated in the presence of PVP. No longer. This utilizes the characteristic of PVP that it easily adheres to the particle surface in the process of precipitation of metal particles. Therefore, in the production method disclosed herein, PVP is suppressed from adhering to the surface of the Ag core particle, and the formation of the Pd shell can be prevented from being inhibited by the PVP. High powder material can be manufactured. And in a Pd shell precipitation process, since PVP selectively adheres to the surface of the Pd shell, it is possible to appropriately suppress the formation of huge secondary particles due to fixation via the Pd shell.
Thus, according to the manufacturing method disclosed herein, it is possible to efficiently manufacture a powder material containing core-shell particles whose particle diameter is suitably controlled in the submicron region.

In a preferred embodiment of the method for producing a powder material disclosed herein, the reducing agent is hydrazine carbonate, hydrazine, hydrazine hydrate, phenyl hydrazine, hydrazine sulfate, hydrazine dihydrochloride, alkyl hydrazine, tartaric acid, tartrate, Citric acid, citrate, ascorbic acid, ascorbate, sodium borohydride.
The reducing agent used in the production method disclosed herein is not particularly limited, and various materials described above can be used. Among these, hydrazine carbonate, tartrate (for example, sodium tartrate), citrate (for example, sodium citrate) from the viewpoint that it is not a poisonous substance and can easily form a uniform and smooth Pd shell. ) Can be preferably used.

Moreover, in the preferable one aspect | mode of the manufacturing method of the powder material disclosed here, the density | concentration of the polyvinyl pyrrolidone in Ag dispersion liquid mixture is 0.1g / L-200g / L.
If the amount of PVP contained in the Ag-dispersed mixed solution is too large, when Pd is precipitated from the mixed solution, fine Pd single particles may be precipitated, and the yield of the core-shell particles may be reduced. On the other hand, if the amount of PVP is too small, PVP cannot be properly attached to the surface of the Pd shell, and there is a high possibility that primary particles will stick together by necking through the Pd shell. Considering these points, the PVP concentration in the Ag dispersion liquid mixture is preferably in the range of 0.1 g / L to 200 g / L, and more preferably in the range of 1 g / L to 6 g / L.

Moreover, in one preferable aspect of the method for producing a powder material disclosed herein, when the total content of the Ag element and the Pd element in the Ag dispersion mixed solution is 100%, the content of the Ag element is expressed by weight. The addition amounts of the palladium complex and the Ag core particles are adjusted so as to be 70% to 99%.
When the content of Ag element (Ag / Pd ratio) becomes too large, there is a high possibility that core-shell particles in which the Pd shell is not properly formed are generated. On the other hand, if the Ag / Pd ratio becomes too small, Pd that could not be precipitated on the surface of the Ag core particles may be precipitated as Pd single particles, or a lot of secondary particles may be generated via the Pd shell. is there. Considering these points, the addition amount of the palladium complex and Ag core particles so that the content of Ag element is 70% to 99% (preferably 80% to 98%, more preferably 80% to 95%). Is preferably adjusted. As a result, a powder material having a high yield of core-shell particles and a small amount of secondary particles due to fixation can be produced. The contents of Ag element and Pd element can be measured using ICP-AES (high frequency inductively coupled plasma emission spectroscopy), XRF (fluorescence X-ray analysis), or the like.

3 is an FE-SEM photograph of sample 1 Ag powder. 3 is an FE-SEM photograph of a powder material of Sample 5. 4 is an FE-SEM photograph of a powder material of Sample 9. 3 is an FE-SEM photograph of a powder material of Sample 10. 3 is an FE-SEM photograph of a powder material of Sample 11. 3 is an FE-SEM photograph of a powder material of Sample 12. It is a FE-SEM photograph of Ag powder of sample 13. 4 is an FE-SEM photograph of a powder material of Sample 14. 3 is an FE-SEM photograph of a powder material of Sample 15. 4 is an FE-SEM photograph of a powder material of Sample 16. 4 is an FE-SEM photograph of a powder material of Sample 17. It is the photograph which shows the FE-SEM photograph of the powder material of sample 9, the photograph which shows the distribution state of Ag element by EDX mapping, and the distribution state of Pd element. It is the photograph which shows the FE-SEM photograph of the powder material of the sample 15, the photograph which shows the distribution state of Ag element by EDX mapping, and the distribution state of Pd element. It is the FE-SEM photograph of the powder material of the sample 16, the photograph which shows the distribution state of Ag element by EDX mapping, and the photograph which shows the distribution state of Pd element. It is the FE-SEM photograph of the powder material of the sample 17, the photograph which shows the distribution state of Ag element by EDX mapping, and the photograph which shows the distribution state of Pd element. It is a figure which shows the particle size distribution by DLS method of Ag powder of the sample 1. FIG. It is a figure which shows the particle size distribution by DLS method of the powder material of the sample 9. It is a figure which shows the particle size distribution by DLS method of the powder material of the sample 10. FIG. It is a figure which shows the particle size distribution by DLS method of the powder material of the sample 11. It is a figure which shows the particle size distribution by DLS method of Ag powder of the sample 13. FIG. It is a figure which shows the particle size distribution by DLS method of the powder material of the sample 14. FIG. It is a figure which shows the particle size distribution by DLS method at the time of redispersing the dry powder of the powder material of the sample 14 in water (sample 14A). It is a figure which shows the particle size distribution by the DLS method at the time of redispersing the dry powder of the powder material of the sample 14 in DMF (sample 14B). It is a figure which shows the particle size distribution by the DLS method at the time of re-dispersing the dry powder of the powder material of the sample 14 to EG (sample 14C). It is a figure which shows the particle size distribution by the DLS method at the time of redispersing the dry powder of the powder material of the sample 14 to IBA (sample 14D). It is a figure which shows the particle size distribution by DLS method of the powder material of the sample 15. FIG. It is a figure which shows the particle size distribution by the DLS method at the time of redispersing the dry powder of the powder material of the sample 15 in water (sample 15A). It is a figure which shows the result of the XRD measurement in a test example. It is a TG-DTA result of the powder material of Sample 1. It is a TG-DTA result of the powder material of Sample 9. It is a TG-DTA result of the powder material of Sample 13. It is a TG-DTA result of the powder material of Sample 14.

  Hereinafter, an embodiment of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In the present specification, when the numerical range is indicated as “A to B”, it means “A or more and B or less”.

1. Core-shell particle The core-shell particle according to the present embodiment includes an Ag core particle mainly composed of silver (Ag), and a Pd shell mainly composed of palladium (Pd) covering at least a part of the surface of the Ag core particle. It is composed of In such core-shell particles, polyvinylpyrrolidone (PVP) is selectively attached to the surface of the Pd shell. Hereinafter, each element of the core-shell particle according to the present embodiment will be specifically described.

(1) Ag core particle Ag core particle is a metal particle which contains silver (Ag) as a main component.
Such Ag core particles may contain various metal elements in addition to the main component Ag. For example, when the amount of all metal elements contained in the Ag core particles is 100 mol%, the amount of Ag element is preferably 90 to 100 mol%, and preferably 95 to 100 mol%. At this time, in addition to the Ag element, the metal elements that can be contained in the Ag core particles include nickel (Ni), copper (Cu), aluminum (Al), palladium (Pd), iron (Fe), cobalt (Co), gold (Au), platinum (Pt), ruthenium (Ru), iridium (Ir), indium (In), zinc (Zn), tin (Sn), bismuth (Bi), antimony (Sb), and the like. Among these, considering ease of familiarity with the Pd shell and the like, it is preferable that Pd, Pt, and the like are contained as metal elements other than Ag. Moreover, the various metal elements described above may be contained in the Ag core particles in the state of a compound such as an oxide or a sulfide.
Further, although the present invention is not particularly limited, the shape of the Ag core particle is preferably a substantially spherical shape, and the particle diameter is suitably 0.01 μm to 1 μm, for example, 0.05 μm to 0.8 μm. And preferably 0.1 μm to 0.4 μm. In addition, the particle diameter here is a peak particle diameter measured by analyzing by NNLS method in a dynamic light scattering method (DLS).

(2) Pd Shell On the other hand, the Pd shell is a metal film mainly composed of palladium (Pd).
Similar to the Ag core particles described above, the Pd shell may contain various metal elements in addition to Pd. For example, when the amount of all metal elements contained in the Pd shell is 100 mol%, the amount of the Pd element is preferably 90 to 100 mol%, and preferably 95 to 100 mol%. In addition to Pd, metal elements that can be contained in the Pd shell include nickel (Ni), copper (Cu), aluminum (Al), palladium (Pd), iron (Fe), cobalt (Co), and gold (Au). Platinum (Pt), ruthenium (Ru), iridium (Ir), indium (In), zinc (Zn), tin (Sn), bismuth (Bi), antimony (Sb), and the like. Also, considering the improvement of chemical and thermal stability on the surface of the core-shell particles and the familiarity with Ag core particles, among these metal elements, Au, Pt, Ag, etc. are included as metal elements other than Pd. It is preferable. The various metal elements described above may be contained in the Pd shell in the state of a compound such as an oxide, phosphide, or nitride. Moreover, although this invention is not specifically limited, 0.2 nm-100 nm are suitable for the thickness of Pd shell, 1 nm-50 nm are preferable, for example, it sets to about 5 nm.

(3) Polyvinylpyrrolidone And in the core-shell particle which concerns on this embodiment, as mentioned above, polyvinylpyrrolidone (PVP) has adhered selectively to the surface of Pd shell. This polyvinylpyrrolidone is a polymer of N-vinyl-2-pyrrolidone (CH ₂ CHNC ₃ H ₃ CO), and can be used as a surface protective agent that protects the particle surface and inhibits the coarsening of other particles.

As described above, in the core-shell particles to which PVP is not attached, the particles are fixed to each other and huge secondary particles are easily formed, so that it is difficult to control the particle diameter in the submicron region. On the other hand, if PVP adheres to the surface of the Ag core particle in the process of generating the core-shell particle, it becomes difficult for the Pd shell to precipitate on the surface of the Ag core particle. May decrease.
On the other hand, in the core-shell particles according to this embodiment, polyvinylpyrrolidone (PVP) is selectively attached to the surface of the Pd shell. That is, in this embodiment, PVP is not substantially attached to the surface of the Ag core particles, and PVP is attached to the surface of the Pd shell when the Pd shell is generated. In this manner, in the process of generating the core-shell particles, by selectively attaching PVP to the surface of the Pd shell, it is possible to suitably suppress the adhesion between the primary particles without reducing the yield of the core-shell particles. . Note that PVP may be attached to the surface of the Ag core particles as long as it does not inhibit the formation of the Pd shell.

2. Powder Material As another aspect of the present invention, a powder material containing core-shell particles is provided. Hereinafter, a powder material containing core-shell particles will be described as another embodiment of the present invention.

  The powder material according to the present embodiment includes at least core-shell particles. However, in addition to the core-shell particles, the powder material may include materials (Ag particles, single Pd particles, etc.) that can be generated in the process of generating the core-shell particles. Moreover, various additives (ceramic fillers, resin beads, surface modifiers, etc.) may be added to the powder material according to the present embodiment as necessary.

And the core-shell particle contained in the powder material which concerns on this embodiment is a core-shell particle which concerns on above-described embodiment. That is, the powder material according to the present embodiment includes core-shell particles in which PVP is selectively attached to the surface of the Pd shell. As described above, since the core shell particles are suitably prevented from fixing via the Pd shell by the PVP adhering to the surface of the Pd shell, the particle diameter is controlled in the submicron region.
For this reason, in the powder material according to the present embodiment, the Z average particle diameter (D _DLS ) measured by DLS (cumulant method) is 0.1 μm to 1.5 μm (typically 0.1 μm to 1 μm), The polydispersity index (PDI) is 0.4 or less (typically 0.3 or less, preferably 0.2 or less). Thus, the use of a powder material having a small core-shell particle size and a sharp particle size distribution can greatly contribute to the miniaturization of electronic components and the thinning of electrodes.

  In addition, in the core-shell particle which concerns on said embodiment, generation | occurrence | production of the adhesion | attachment via Pd shell is suppressed by making PVP adhere to the surface of Pd shell. However, since the adhesion suppressing effect by the PVP only needs to be exhibited when the Pd shell is precipitated, the PVP may be removed from the surface of the Pd shell of the core-shell particles after the powder material is manufactured. As a means for removing such PVP, a cleaning process using a centrifugal separation, a heating process, or the like can be given. However, from the viewpoint of ensuring the dispersibility of the core-shell particles when preparing a conductive paste in which a powder material is dispersed in a dispersion medium, PVP does not need to be removed and remains attached to the surface of the Pd shell. Is preferred.

Moreover, in this embodiment, since PVP is prevented from adhering to the surface of the Ag core particle, the core-shell particle can be obtained with a high yield. Therefore, in the powder material according to the present embodiment, the core-shell particles at a content rate of 90% or more (typically 95% or more, for example, 99% or more) with respect to the entire powder material including single particles of Pd and Ag. It is included.
In addition, the content rate of the core-shell particles in the powder material is determined by measuring the particle diameter (equivalent circle diameter) for each particle using FE-SEM and EDX, and then performing core-shell determination by element mapping. This is the volume-based existence ratio of the core-shell particles with respect to all the particles calculated on the assumption that all the particles are spheres having an equivalent circle diameter.

In the powder material according to the present embodiment, the BET particle diameter (D _BET ) converted from the BET specific surface area and the Z average particle diameter (D _DLS ) measured by the DLS method are expressed by the following formula (1). It is preferable that the relationship shown is satisfied.
D _DLS / D _BET ≦ 10.0 (1)
Z-average particle diameter in the above equation ₍₁₎ (D _DLS) is a value that increases significantly the secondary particles due to sticking occurs. On the other hand, the BET particle diameter (D _BET ) is a value that is less susceptible to sticking than the Z average particle diameter. Therefore, by calculating the value of the Z average particle diameter (D _DLS ) with respect to the BET particle diameter (D _BET ), the degree to which the core-shell particles of the powder material are fixed can be evaluated. Here, when such D _DLS / D _BET is 10.0 or less, the content of secondary particles due to fixation through the Pd shell is very small, and the particle diameter of the core-shell particles is suitably controlled in the submicron region. It can be evaluated that the powder material is made. In addition, a powder material having a smaller content of secondary particles due to fixation (a powder material having a D _DLS / D _BET of 2.0 or less) is more preferably used for thinning the electrode. it can.

Moreover, the powder material according to the present embodiment may be provided in the state of a conductive paste dispersed in a dispersion medium such as water or an organic solvent. Such a conductive paste contains core-shell particles whose particle diameter is controlled in the submicron region, and therefore a sufficiently thin electrode can be suitably formed. In addition, the dispersion medium which disperse | distributes powder material should just be what can disperse | distribute electroconductive powder favorably, and what is used for the conventional conductor paste can be especially used without a restriction | limiting. Examples of the organic solvent for the dispersion medium include petroleum hydrocarbons (particularly aliphatic hydrocarbons) such as mineral spirits, cellulose polymers such as ethyl cellulose, ethylene glycol and diethylene glycol derivatives, toluene, xylene, butyl carbitol ( BC), terpineol and other high boiling organic solvents may be used alone or in combination.
Furthermore, the conductive paste at this time includes a dispersant, a resin material (for example, an acrylic resin, an epoxy resin, a phenol resin, an alkyd resin, a cellulosic polymer, polyvinyl alcohol, rosin, in addition to a powder material containing core-shell particles. Resin, etc.), vehicle, filler, glass frit, surfactant, antifoaming agent, plasticizer (eg, phthalic acid ester such as dioctyl phthalate (DOP)), thickener, antioxidant, dispersant, polymerization inhibitor Additives such as may be included.

The powder material according to this embodiment is controlled so that most of the core-shell particles have a particle size in the submicron region. As described above, such a powder material when analyzed by the cumulant method at DLS is, Z-average particle diameter _{(D DLS)} is 0.1μm~1.5μm next, and polydispersity index (PDI) is 0. 4 or less. However, the analysis method for specifying the powder material is not limited to the cumulant method, and the NNLS method can also be used. As described above, when the powder material according to the present embodiment is analyzed using the NNLS method, the peak particle size is in the range of 0.1 μm to 1.5 μm (typically 0.1 μm to 1 μm). And the peak intensity of the peak particle size is 90% or more.

3. Next, as another aspect of the present invention, a method for manufacturing the powder material according to the above embodiment will be described.
The manufacturing method of the powder material which concerns on this embodiment is equipped with (1) liquid mixture preparation process and (2) Pd shell precipitation process. Hereinafter, each step will be specifically described.

(1) Mixed liquid preparation process In the manufacturing method according to this embodiment, an Ag-dispersed mixed liquid in which Ag core particles are dispersed in a solution in which Pd and PVP are dissolved is prepared. Specifically, after a palladium complex is dissolved in a predetermined solvent, a mixed solution containing Pd and PVP is prepared by dissolving PVP in the Pd solution. Then, Ag powder mixture is added and dispersed while stirring the liquid mixture to prepare an Ag dispersion liquid mixture.

  As described above, in the manufacturing method according to the present embodiment, unlike the prior art in which Ag core particles are generated in the presence of PVP, Ag core particles in a powder state are separately prepared, and the powder is added to a mixed solution in which Pd and PVP are dissolved. Ag core particles in a state are dispersed. As will be described in detail later, this suppresses the PVP from adhering to the surface of the Ag core particle and suppresses the inhibition of the formation of the Pd shell by the PVP adhering to the surface of the Ag core particle.

In the present embodiment, the palladium complex serving as the Pd source is not particularly limited as long as it contains Pd element and can be easily dissolved in a desired solvent. For example, diamminedichloropalladium (II), tetraamminedichloropalladium. In addition, chloropalladic acid or a salt thereof can be preferably used.
Moreover, the solvent should just be able to melt | dissolve the palladium complex mentioned above and PVP suitably, and can disperse Ag core particle | grains, and can select various liquids suitably. As an example of such a solvent, aqueous ammonia, water, alcohol, a mixture thereof, and the like can be given. Among these, considering the solubility of diamminedichloropalladium, ammonia water can be particularly preferably used.

  Moreover, when there is too much amount of PVP contained in Ag dispersion liquid mixture, when depositing Pd from the said liquid mixture, there exists a possibility that a fine Pd single particle may precipitate and the yield of a core-shell particle may fall. On the other hand, if the amount of PVP is too small, PVP cannot be properly attached to the surface of the Pd shell, and there is a high possibility that sticking through the Pd shell will occur. Considering these points, the PVP concentration in the Ag dispersion liquid mixture is preferably in the range of 0.1 g / L to 200 g / L, more preferably in the range of 0.5 g / L to 50 g / L. For example, it may be set within a range of 1 g / L to 6 g / L.

(2) Pd shell precipitation step Next, in the manufacturing method according to the present embodiment, a Pd shell precipitation step is performed in which a reducing agent is added to the Ag dispersion liquid mixture to precipitate a Pd shell on the surface of the Ag core particles. Thereby, core-shell particles in which the surface of the Ag core particles is covered with the Pd shell are formed.

In addition, as the reducing agent used in this step, for example, hydrazine compounds such as hydrazine carbonate, hydrazine, hydrazine hydrate, phenyl hydrazine, hydrazine sulfate, hydrazine dihydrochloride, and alkyl hydrazine can be used. Other examples of the reducing agent include organic acids such as tartaric acid, citric acid and ascorbic acid and salts thereof (tartrate, citrate and ascorbate), sodium borohydride and the like. Among these, hydrazine carbonate, tartrate (for example, sodium tartrate), citrate (for example, citrate) from the viewpoint that it is not a poisonous substance and can easily form a uniform and smooth Pd shell. Acid sodium) and the like can be used particularly preferably.
In this step, it is preferable to advance the reduction reaction while dispersing (stirring) the Ag-dispersed mixed solution after adding the reducing agent in order to suitably precipitate Pd to form a Pd shell. The means for dispersion (stirring) at this time is not particularly limited. For example, ultrasonic dispersion or dispersion by shearing force can be employed.

Hereinafter, the state in the Ag dispersion liquid mixture in the Pd shell precipitation step of the manufacturing method according to the present embodiment will be described in comparison with the state of the liquid mixture in the conventional manufacturing method.
In the conventional method for producing core-shell particles, first, Ag core particles are generated by precipitating Ag from a mixed solution in which Ag and PVP are dissolved. At this time, since PVP has a property of easily adhering to the particle surface in the process of precipitation of the metal particles, PVP adheres to the surface of the Ag core particle before forming the Pd shell. Therefore, in the conventional manufacturing method, precipitation of Pd shell on the Ag core particle surface is inhibited by PVP, so that fine Pd single particles are easily formed, and the yield of the core-shell particles is lowered.

On the other hand, in the manufacturing method according to this embodiment, Ag core particles in a powder state are dispersed in a mixed solution in which Pd and PVP are dissolved. Therefore, it is possible to suppress the PVP from adhering to the surface of the Ag core particles. . In this embodiment, PVP adheres to the surface of the Pd shell in the Pd shell deposition step. For this reason, according to this embodiment, PVP is not substantially attached to the surface of the Ag core particle, and core shell particles in which PVP is selectively attached to the surface of the Pd shell are generated. The yield can be improved.
And since the surface of the Pd shell is protected by PVP in this core-shell particle, the formation of huge secondary particles by adhesion through the Pd shell is preferably suppressed, and the particle diameter is submicron. Controlled by the region.
As described above, according to the manufacturing method according to the present embodiment, it is possible to suitably manufacture a powder material containing core-shell particles whose particle diameter is controlled in a submicron region with a high yield.

In the mixed liquid preparation step of the above embodiment, Ag core particles in a powder state are suspended in a mixed liquid in which Pd and PVP are dissolved. The term “suspension” as used herein does not necessarily refer to a dispersion-stabilized state, and may be a state where Ag core particles are aggregated or a state where the core particles settle when left standing. .
Moreover, the order of each process in a liquid mixture preparation process is not specifically limited. For example, Ag core particles may be added to the Pd solution before dissolving PVP, and PVP may be dissolved in the slurry. Moreover, PVP and Pd complex may be dissolved in the slurry of Ag core particles, and any other mixing order can be employed. Even in this case, the adhesion between the particles can be suitably suppressed without reducing the yield of the core-shell particles.

Further, from the viewpoint of further improving the yield of the core-shell particles and suppressing the generation of secondary particles due to fixation, when the mixed solution preparation step is performed, the addition amounts of the palladium complex and the Ag core particles are appropriately adjusted. preferable.
Specifically, if the content of Ag element (Ag / Pd ratio) becomes too large, there is a high possibility that core-shell particles in which the Pd shell is not properly formed are generated, while the Ag / Pd ratio is If it is too small, Pd that could not be precipitated on the surface of the Ag core particles may be precipitated as a single Pd particle, or a lot of secondary particles may be generated by fixing via the Pd shell. Considering this point, when the total content of Ag element and Pd element in the Ag dispersion mixture is 100%, the content of Ag element in the Ag dispersion mixture is 70% to 99% by weight. (Preferably 80% to 95%, for example 90%). Thereby, the yield of the core-shell particles can be improved, and the generation of secondary particles due to fixation can be suppressed.

[Test example]
Hereinafter, although the test example regarding this invention is demonstrated, this test example is not intending limiting this invention.

A. First Test In this test, as a preliminary test for confirming the knowledge described in the above embodiment, Ag powder in a powder state is dispersed in a mixed solution in which PVP is dissolved, and the Ag powder is dispersed in the Ag powder. It was confirmed whether PVP adhered or not.

1. Test conditions By dissolving 2.62 g of palladium complex (diamminedichloropalladium (II)) and 0.80 g of polyvinylpyrrolidone K-90 (manufactured by Wako Pure Chemical Industries, Ltd.) in 400 ml of 0.17% aqueous ammonia. Solution A was prepared.
Next, 360 ml of the above-mentioned solution A was collected, 10.8 g of Ag powder (SPQ02X manufactured by Mitsui Kinzoku Kogyo Co., Ltd.) was added to the mixture, and the mixture was stirred with a magnetic stirrer and then subjected to ultrasonic dispersion for 10 minutes. Thus, a slurry-like Ag dispersion liquid mixture was prepared. And 40 ml of Ag dispersion liquid mixture was collected, Ag powder was precipitated by performing centrifugation of 6000 rpm for 10 minutes, and supernatant liquid (solution B) was collected.

2. Evaluation test The above-mentioned solution A and solution B were subjected to TOC (Total Organic Carbon) analysis to evaluate whether PVP was adhered to the Ag powder.
Here, first, TOC was performed using a total organic carbon meter (TOC-VCPH manufactured by Shimadzu Corporation). Specifically, the total carbon (TC: Total Carbon) of each of Solution A and Solution B was measured by a 680 ° C. combustion oxidation method based on JIS-K-0102 22.1 (2016). Then, phosphoric acid was added to each solution, and inorganic carbon (IC: Inorganic Carbon) such as carbon dioxide was measured. And the total organic carbon (TOC) of a supernatant liquid and Ag dispersion | distribution liquid mixture was computed by subtracting inorganic carbon (IC) from the measured total carbon (TC).

  As a result of the above-described evaluation test, the total organic carbon (TOC) of each of the supernatant and the Ag dispersion mixture was substantially the same value (about 1.22 g / L). From this result, it was found that PVP did not adhere to the Ag powder precipitated by centrifugation, and almost all of the PVP added to the Ag dispersion mixture remained dissolved in the supernatant. From this, even if Ag powder was dispersed in a solution containing PVP, it was confirmed that PVP was not adsorbed on the Ag powder.

B. Second Test Next, in this test, in order to compare the conventional technique with the present invention, 17 types of powder material samples were prepared, and various evaluation tests were performed on each sample.

1. Each sample Hereinafter, the powder material of each sample will be described.

(1) Sample 1
In this test example, first, a powder material made of Ag powder (SPQ02X manufactured by Mitsui Kinzoku Kogyo Co., Ltd.) not coated with a Pd shell was prepared as a sample 1 for comparison. In Samples 2 to 12 described later, the same Ag powder as Sample 1 is used as Ag core particles of core-shell particles.

(2) Sample 2
In this sample, first, a slurry-like mixed solution was prepared so that the weight ratio of Ag to Pd was 90:10. Specifically, in 100 ml of 0.17% aqueous ammonia, 0.655 g of palladium complex (diamminedichloropalladium (II)) and 0.30 g of a dispersant (polyethylene glycol # 200 (manufactured by Kanto Chemical Co., Inc.)) Was dissolved. Then, 3.0 g of Ag powder (SPQ02X manufactured by Mitsui Kinzoku Kogyo Co., Ltd.) similar to Sample 1 above was added, stirred with a magnetic stirrer, and then subjected to ultrasonic dispersion for 10 minutes to prepare a slurry Ag dispersion liquid mixture. .
Next, 0.85 ml of a reducing agent (hydrazine carbonate, manufactured by Otsuka Chemical Co., Ltd.) is added while stirring the above Ag dispersion liquid mixture with a magnetic stirrer, and the palladium complex in the Ag dispersion liquid mixture is all reduced, and Pd Stirring was continued for 30 minutes so as to precipitate the core-shell particles. Then, XRF (X-Ray Fluorescence) analysis of the supernatant was performed to confirm that the palladium complex in the Ag dispersion mixture was all reduced and precipitated as Pd.

(3) Sample 3
Preparation of core-shell particles under the same conditions as in Sample 2, except that 0.15 g of a wet dispersant (BYK, ANTI-TERRA250) was dissolved in the Ag dispersion mixture instead of 0.30 g of polyethylene glycol. Tried.

(4) Sample 4
An attempt was made to produce core-shell particles under the same conditions as Sample 3, except that the amount of the wetting dispersant added was increased from 0.15 g to 2.00 g.

(5) Sample 5
Preparation of core-shell particles was attempted under the same conditions as Sample 3, except that the wetting and dispersing agent was changed from BYK's ANTI-TERRA250 to BYK's BYK-LP C22136.

(6) Sample 6
Preparation of core-shell particles was attempted under the same conditions as Sample 3, except that the wetting and dispersing agent was changed from BYK's ANTI-TERRA250 to BYK's BYK-LP C22139.

(7) Sample 7
Preparation of core-shell particles was attempted under the same conditions as Sample 3, except that the wetting and dispersing agent was changed from BYK's ANTI-TERRA250 to BYK's BYK-LP C22141.

(8) Sample 8
Preparation of core-shell particles was attempted under the same conditions as Sample 3, except that the wetting and dispersing agent was changed from BYK's ANTI-TERRA250 to BYK's DISPERBYK102.

(9) Sample 9
In Sample 9, unlike Samples 2 to 8 described above, no dispersant was added to the Ag dispersion mixture, and instead, polyvinyl pyrrolidone (PVP) was dissolved to try to produce core-shell particles.
Specifically, 2.62 g of diamminedichloropalladium (II) and 0.80 g of polyvinylpyrrolidone K90 (manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 400 ml of 0.17% aqueous ammonia. Then, 12.0 g of Ag powder similar to Samples 1 to 8 was added, and after stirring with a magnetic stirrer, ultrasonic dispersion was performed for 10 minutes to prepare a slurry Ag dispersion mixture.
Next, 40 ml of the above Ag dispersion mixture was collected, and this Ag dispersion mixture was designated as Solution C. Then, 3.06 ml of hydrazine carbonate was added while stirring the remaining Ag dispersion mixture with a magnetic stirrer, and stirring was continued for 30 minutes. At this time, blackening and foaming of the slurry showing Pd precipitation due to reduction of the Pd complex were observed about 130 s to 160 s after the addition of hydrazine carbonate. As a result of XRF analysis of the supernatant, it was confirmed that all the Pd complex was reduced and deposited.
Then, about 40 ml of the AgPd slurry thus obtained was collected, and the supernatant obtained by centrifugation (6000 rpm, 10 min.) Was used as Solution D. Then, after most of the remaining AgPd slurry is sedimented by centrifugation (6000 rpm, 10 min.), Re-dispersion in 40 ml of pure water and sedimentation by centrifugation (6000 rpm, 10 min.) Are repeated three times to obtain AgPd. The powder was washed to obtain undried AgPd wet powder. Next, a portion of the wet powder of AgPd was redispersed in 40 ml of acetone and settled by centrifugation (6000 rpm, 10 min.) Three times to replace the water contained in AgPd with acetone, and then at room temperature. Vacuum dried for 1 hour and crushed in a mortar to obtain dried AgPd powder.

(10) Sample 10
Preparation of core-shell particles was attempted under the same conditions as in Sample 9, except that the treatment after adding Ag powder and stirring with a magnetic stirrer was changed from ultrasonic dispersion to precision dispersion by shearing force. For precision dispersion by shearing force, dispersion was carried out for 10 minutes using a precision dispersion apparatus (CLEAMIX CLM-0.8S) manufactured by M Technique Co., Ltd. with the rotor rotation speed set to 18000 rpm.

(11) Sample 11
Preparation of core-shell particles was attempted under the same conditions as Sample 10, except that the amount of PVP added was reduced from 0.80 g to 0.40 g.

(12) Sample 12
In this sample, an attempt was made to produce core-shell particles without adding PVP or a dispersant. The other conditions were set to the same conditions as Sample 9.

(13) Sample 13
In sample 13, as a comparison object with samples 14 and 15 to be described later, a powder material made only of Ag powder used in these samples was prepared. In addition, the Ag powder of this sample is produced | generated by the liquid phase synthesis which adds a reducing agent to Ag ammine complex solution.

(14) Sample 14
In sample 14, core shell particles were prepared under the same conditions as in sample 9, except that Ag powder produced by liquid phase synthesis in the same procedure as in sample 13 was used and the amount of each raw material added was changed. Tried.
Specifically, 0.655 g of diamminedichloropalladium (II) and 0.20 g of polyvinylpyrrolidone K90 were dissolved in 100 ml of 0.17% aqueous ammonia. Then, 3.0 g of Ag powder obtained by liquid phase synthesis was added, stirred with a magnetic stirrer, and then subjected to ultrasonic dispersion for 10 minutes to prepare a slurry Ag dispersion mixed solution.
Next, while stirring the above Ag dispersion liquid mixture with a magnetic stirrer, 0.85 ml of hydrazine carbonate is added, and stirring is performed so that the palladium complex in the Ag dispersion liquid mixture is all reduced and Pd is precipitated. Continued for a minute and tried to produce core-shell particles. At this time, blackening and foaming of the slurry showing Pd precipitation due to reduction of the Pd complex were observed about 80 s to 90 s after the addition of hydrazine carbonate. And it was confirmed by XRF analysis of the supernatant that all the Pd complexes were reduced and precipitated.
The AgPd slurry thus obtained is precipitated by centrifugation (6000 rpm, 10 min.), And then redispersed in 40 ml of pure water and sedimentation by centrifugation (6000 rpm, 10 min.) Is repeated three times to obtain AgPd. The powder was washed to obtain undried AgPd wet powder. Next, a part of the AgPd wet powder was collected, and after redispersion in 40 ml of acetone and sedimentation by centrifugation (6000 rpm, 10 min.) Were repeated three times, the water contained in AgPd was replaced with acetone. Was dried in a vacuum for 1 hour and crushed in a mortar to obtain a dried AgPd powder.

(15) Sample 15
Preparation of core-shell particles under the same conditions as Sample 14 except that the solvent for dissolving the palladium complex and PVP was changed from 100 ml of 0.17% aqueous ammonia to 33.3 ml of 0.51% aqueous ammonia. It was. In addition, about 130 to 150 seconds after the addition of hydrazine carbonate, blackening and foaming of the slurry showing Pd precipitation due to reduction of the Pd complex were observed.

(16) Sample 16
In Sample 16, Ag powder was formed by liquid phase synthesis without using PVP or a dispersant, and then the surface of the Ag powder (Ag core particles) was covered with a Pd shell to produce core shell particles. In addition, this sample reproduces the manufacturing method described in Example 7 of Patent Document 1 (Japanese Patent Laid-Open No. 8-176605) described above on a scale of 1/10, and the weight ratio of Ag and Pd is The amount of each raw material added is adjusted to be 30:70.
Specifically, first, silver chloride corresponding to 1.8 g of silver (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 22 ml of 25% aqueous ammonia and kept at a liquid temperature of 40 ° C. did. Next, 1.13 g of L-ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) and a reducing agent (hydrazine hydrate ((NH ₂ ) ₂ H ₂ O 98 manufactured by Wako Pure Chemical Industries, Ltd.)) were added to 5 ml of pure water. %)) Was dissolved and kept at a liquid temperature of 40 ° C. This solution was designated as solution B. And while stirring above-mentioned A liquid, the B liquid was added over 0.5 minute using the syringe pump, silver in the solution was deposited, and Ag powder was produced | generated.
Then, 3.0 g of hydrazine hydrate was added again to the obtained suspension of Ag powder, and 84 ml of tetraamminedichloropalladium (Pd (NH ₃ ) ₄ Cl ₂ ) solution corresponding to a palladium amount of 50 g / l was instantaneously added. In addition, preparation of core-shell particles was attempted.

(17) Sample 17
Preparation of core-shell particles was attempted under the same conditions as in Sample 16, except that the weight ratio of Ag and Pd was adjusted to 90:10 by changing the amount of tetraamminedicropalladium solution added to 4 ml.

2. Evaluation Test Next, an evaluation test performed on each sample described above will be described.

(1) Visual evaluation The liquid mixture under stirring in the transparent container after adding the reducing agent was visually observed to evaluate the precipitation state of each sample. And the case where the remarkable sedimentation of powder material was not confirmed while stirring the liquid mixture and the aggregation of powder material was not confirmed was set as "Evaluation A". Moreover, the case where aggregation was confirmed while conspicuous sedimentation of the powder material was not confirmed during the stirring of the mixed liquid was set as “Evaluation B”. And the case where sedimentation and aggregation were confirmed even if the liquid mixture was stirred was designated as “Evaluation C”. The evaluation results are shown in Table 1 described later.
As a result of this visual evaluation, a part of the sample in which sedimentation and aggregation occurred remarkably and a sample in which so-called mirror-like precipitation in which the deposited metal adheres to the wall surface of the transparent container were subjected to each test described later. It was judged that there was no point in doing the evaluation test.

(2) Microscopic observation of powder material Microscopic observation of the powder material was performed on each of the above samples. In such microscopic observation, a field emission scanning electron microscope (FE-SEM: Field Emission Microscope, model number S-4700) manufactured by Hitachi High-Technologies Corporation was used. FE-SEM photographs of Samples 1, 5, 9-17 photographed at this time are shown in FIGS.

  Further, for Samples 9 and 15 to 17, elemental mapping by energy dispersive X-ray spectroscopy (EDX) was performed to analyze the distribution states of the Ag element and the Pd element. The analysis results are shown in FIGS. In addition, the above-mentioned FE-SEM and energy dispersive X-ray analysis (model number: X-max) made by HORIBA were used for elemental mapping by EDX in this test.

(3) BET measurement In this test, BET measurement of Ag powder of Samples 1 and 9 to 15 and AdPd dry powder was performed. Specifically, the test dispersion in which each sample was dispersed was subjected to a specific surface area measuring device (model number: BELSORP-max) manufactured by Microtrack Bell, and the N ₂ adsorption isotherm at −196 ° C. was measured. The BET specific surface area was determined based on the BET multipoint method. Based on the following formula (2), the BET particle diameter (D _BET ) was calculated from the BET specific surface area. Table 2 shows the calculation results.

D _BET = 6 / (ρ · s) (2)
D _BET : BET particle diameter ρ: Density s: BET specific surface area

The “density ρ” in the above formula (2) was set to “Ag density = 10.49 g / cm ³ ” in the samples 1 and 13 which are powder materials made only of Ag powder. On the other hand, in Samples 9 to 12, 14, and 15, which are powder materials containing core-shell particles, “density of core-shell particles (Pd ratio 10 wt%) = 10.64 g / cm ³ ” was set.

(4) DLS measurement In this test, the slurry by which the Ag powder and AdPd powder of sample 1 and 9-17 were ultrasonically dispersed in the pure water was measured by the dynamic light scattering method (DLS). Specifically, the DLS measurement of the test dispersion liquid of each sample was performed in a temperature environment of 20 ° C. using a dynamic light scattering measurement device (Zetasizer Nano ZS) manufactured by Malvern. The cumulant method and the NNLS method were used for the analysis.
Samples 14 and 15 were also subjected to DLS measurement of slurries (samples 14A to 14D and sample 15A) in which dried powder of AdPd was redispersed in various dispersion media shown in Table 2. Here, “DMF” in Table 2 represents N, N-dimethylformamide, “EG” represents ethylene glycol, and “IBA” represents isobornyl acetate.
The results of the above DLS analysis are shown in Table 2 and FIGS.

(5) TOC measurement In this test, the TOC of samples 9 to 11 was measured. Specifically, for each of solution C and solution D, total carbon (TC) was measured by a 680 ° C. combustion oxidation method. Then, phosphoric acid was added to each solution, and inorganic carbon (IC) such as carbon dioxide was measured. Further, total organic carbon (TOC) was calculated by subtracting inorganic carbon (IC) from the measured total carbon (TC).
In this test, the value of the difference between the TOC of the solution C and the TOC of the solution D is regarded as the amount of carbon derived from PVP adsorbed on the Pd shell, and the PVP weight derived from this amount of carbon is used as the unwashed AgPd-containing PVP. The amount. Table 3 shows the calculation results.

(6) TG-DTA measurement In this test, the amount of organic matter contained in the dried AgPd powder was measured by performing differential thermal-thermogravimetric simultaneous measurement (TG-DTA: Thermogravimetry-Differential Thermal Analysis).
Specifically, using a differential thermal balance apparatus (Thermo plus TG8120) manufactured by Rigaku Corporation, the mixture was heated from room temperature to 600 ° C. at a temperature rising rate of 20 ° C./min, and held for 10 minutes. The weight reduced to approximately 150 ° C. is regarded as “the weight of the desorbed adsorbed water”, and the weight reduced with the exothermic peak after 150 ° C. is determined as “the weight of PVP removed by organic combustion (after washing AgPd-containing PVP). Amount) ”. Table 3 shows the measurement results.
Furthermore, in this test, the value of the difference between the “unwashed AgPd-containing PVP amount” obtained by TOC analysis and the “after-washing AgPd-containing PVP amount” obtained by TG-DTA was calculated, and this calculation result was calculated. It was regarded as “the amount of PVP removed by the washing treatment (AgPd weakly adsorbed PVP amount)”. The calculation results are also shown in Table 3.

(7) XRD analysis Powder X-ray diffraction (XRD: X-ray diffraction) was performed on the AgPd dry powders of Samples 9 to 12, 14, and 15. Here, the XRD analysis apparatus (model number: RINT-TTR III) manufactured by Rigaku Corporation is used, the X-ray is set to CuKα line (tube voltage 10 kV, tube current 50 mA), the sampling width is set to 0.01 °, and scanning is performed. The speed was set at 2 ° / min.

3. Evaluation Results (1) Observation Results Table 1 below shows the results of the above-described visual evaluation and element mapping by FE-SEM and EDX. Moreover, the FE-SEM photograph of sample 1, 4, 9-17 is shown in FIGS. 1-11, and the elemental mapping result of sample 9, 15-17 is shown in FIGS.

  First, in Samples 2 to 8, aggregation and sedimentation were visually observed, and it was clear that a large amount of large secondary particles were formed. In Sample 4, as shown in FIG. 2, adhesion through the Pd shell was generated, and Pd deposited in the form of particles was confirmed. In Samples 3 and 5 to 8, Pd was deposited in a mirror shape on the container wall surface, not on Ag. For this reason, even if a dispersant is added to the mixed solution, it is difficult to suppress adhesion between the core-shell particles, and the Pd shell becomes Ag by adsorbing the dispersant onto the surface of the Ag powder (Ag core particles). It was found that it was difficult to deposit uniformly on the top. Further, in Sample 12 to which no dispersant or the like was added, aggregation and sedimentation were visually observed, and it was clear that a large amount of large secondary particles were formed. Similarly, Samples 16 and 17 reproducing the method described in Patent Document 1 also formed core-shell particles (primary particles) having a submicron region particle size (about 0.4 μm). Many secondary particles in which the particles were fixed to each other were formed (see FIGS. 10 and 11).

  On the other hand, as shown in FIGS. 3 to 5 and FIGS. 8 and 9, in the samples 9 to 11 and the samples 14 and 15, necking of each particle was appropriately suppressed. Considering the result of this test and the result of the first test described above, when the Pd shell is precipitated from an Ag suspension mixed liquid in which Ag core particles of a separately produced powder are dispersed, it is precipitated in the presence of PVP. It was found that since PVP selectively adheres to the surface of the Pd shell, the adhesion through the Pd shell can be appropriately suppressed.

Further, as shown in FIGS. 12 and 13, as a result of element mapping for Sample 9 and Sample 15, Pd element is present in these samples so as to cover the surface of the Ag core particle almost uniformly, and Pd alone Particles were not confirmed. From this, when the Ag core particles of the powder are dispersed in the mixed solution in which PVP and Pd are dissolved and the Pd shell is precipitated in the presence of PVP, the generation of Pd single particles is suppressed by the PVP. It was found that formation can be prevented from being inhibited.
As shown in FIGS. 14 and 15, as a result of element mapping for samples 16 and 17, it was confirmed that Pd element was present in these samples so as to cover a plurality of Ag core particles. From this, in the powder materials of Samples 16 and 17, it was confirmed that the Ag core particles were fixed to each other via the Pd shell. In Sample 17, it was also confirmed that Pd was segregated.

(2) BET and DLS measurement results The analysis results of the BET measurement and the DLS measurement described above are shown in Table 2, and the DLS measurement results of Samples 1, 9 to 11 and 13 to 15 are shown in FIGS. Show. 22 to 25 show the results of DLS measurement when the AgPd dry powder of sample 14 is redispersed in a predetermined dispersion medium (samples 14A to 14D), and FIG. 27 shows the AgPd dry powder of sample 15. The result of the DLS measurement when redispersed in water (sample 15A) is shown.
In addition, as mentioned above, in this test, DLS measurement was tried also about sample 12, 16, and 17, but sedimentation was quick and DLS measurement was not able to be performed. Moreover, the pattern obtained by the XRD analysis is shown in FIG.

As shown in Table 2 and FIGS. 16 to 21 and 28, in Samples 9 to 11 and Samples 14 and 15, the Z average particle diameter (D _DLS ) by DLS analysis is 0.1 μm to 1.5 μm (100 nm to 1500 nm). ) And the polydispersity index (PDI) was 0.4 or less. On the other hand, Sample 12 to which no PVP or a dispersant was added could not be measured because of rapid precipitation and difficulty in dispersion. Also, comparing sample 1,9～11, Sample 1 (Ag powder) to it can be seen _{that D DLS} samples 9-11 forming the Pd shell is not remarkably increased. This tendency is the same in the comparison of Samples 13 and 14-15.
Moreover, when comparing the BET specific surface areas of Samples 1 and 9 to 12, the Ag powder (Sample 1) before forming the Pd shell is 1.88, and the samples 9 to 12 having the Pd shell are decreased from 1.88. Was. Among these samples, the decrease in the BET specific surface area of Samples 9 to 11 was suppressed to within 0.2, but the decrease in the BET specific surface area of Sample 12 to which PVP was not added was the largest at 0.3. became. Further, in Samples 9 to 11 and Samples 14 and 15, the DLS / BET value was suppressed to 2.0 or less.
Considering these results, as in Samples 9 to 11 and Samples 14 and 15, PVP is selectively adhered to the surface of the Pd shell, thereby increasing the particle size from Ag particles (aggregation / connection (necking)). ) Was suppressed, and it was confirmed that a powder material in which the particle diameter of the core-shell particles was controlled in the submicron region could be produced.

Further, from the results of the dry powders shown in Samples 14A and 15A, the core-shell particles in which PVP is selectively attached to the Pd shells, even when they are dried and dispersed again in water, the Z average particle diameter (D _DLS ) and PDI did not change significantly, and the results showed that dispersion after drying was easy.
Further, from the results shown in Table 2 and FIGS. 21 to 27, even when the dry powder of the core-shell particles in which PVP is selectively attached to the Pd shell is redispersed in DMF, EG, IBA, In the same manner as in the case of being dispersed, the Z average particle diameter was in the range of 0.1 μm to 1.5 μm, and the PDI was in the range of 0.4 or less. Therefore, even if the dispersion medium at the time of measurement is changed, if the powder material is uniformly dispersed in the dispersion medium, the Z average particle diameter of the powder material disclosed here is 0.1 μm to 1 μm. It was confirmed that the PDI was 0.4 or less.
In addition, as a result of the XRD analysis shown in FIG. 28, Pd and Ag peaks were confirmed in all of Samples 9 to 12 and Samples 14 and 15. In addition, no clear peak shift was observed in each sample.

(3) Evaluation results regarding the state of PVP Table 3 shows the results of an evaluation test (TOC measurement, TG-DTA) for analyzing the state of PVP adhering to the surface of the PD shell.

As shown in Table 3, in any of Samples 9 to 11, the TOC (PVP amount) of the solution D was greatly reduced from the TOC (PVP amount) of the solution C. Furthermore, in any of the samples, a large amount of “unwashed AgPd-containing PVP” indicating the amount of PVP adhering to the Pd surface was confirmed.
From these results, PVP is not attached to the Ag core particles in the state of the Ag dispersion liquid mixture, but since the amount of PVP in the supernatant liquid after Pd precipitation is reduced, a lot of PVP is attached to the Pd shell, It is understood that it settled with the core-shell particles. Therefore, when core-shell particles were produced by the procedures of Samples 9 to 11, it was found that PVP did not substantially adhere to the Ag core particles and PVP selectively adhered to the Pd shell.

  Moreover, in any of Samples 9 to 11, a certain amount of organic matter was confirmed in the TG-DTA measurement of the dry powder material. From this, it was confirmed that PVP was adhered to the surface of the core-shell particles even after performing a plurality of washings. On the other hand, a certain amount of “AgPd weakly adsorbed PVP amount” indicating the amount of PVP removed during the cleaning treatment was also confirmed. From this, it was also confirmed that the PVP adhering to the surface of the core-shell particles can be removed as necessary by repeating the washing treatment using centrifugation.

(4) Additional test on TG-DTA Moreover, in order to analyze the organic substance contained in each sample in more detail, Sample 1 and Sample 13 consisting only of Ag powder, and Sample using Ag powder of Sample 13 14 was also subjected to TG-DTA measurement. And about the sample 1, 9, 13, 14, the chart regarding the temperature rise and weight change during TG-DTA measurement was created. The results are shown in FIGS.

  As shown in FIG. 29 and FIG. 30, when Sample 1 and Sample 9 were compared, one sample showed one exothermic peak, but the temperature at which the exothermic peak occurred was different. And it is estimated that the exothermic peak confirmed by the sample 9 is based on combustion of PVP. From this, in Sample 9, almost all of the organic substances mixed in the raw material of the Ag core particles are removed or modified in the process of generating the core-shell particles, and almost all of the organic substances existing after the generation of the core-shell particles are obtained. It is understood that it has been replaced with one derived from organic matter mixed in PVP or Ag raw material.

  On the other hand, as shown in FIG. 31, in sample 13, a plurality of gentle exothermic peaks were confirmed within the range of 137.6 ° C. to 210.4 ° C. From this, it is understood that the Ag core particles produced by the liquid phase synthesis contain trace amounts of various kinds of organic substances. On the other hand, in the sample 14 using the Ag core particle of such liquid phase synthesis, as shown in FIG. 32, the exothermic peak in the low temperature region confirmed in the sample 13 has almost disappeared and is derived from PVP. And a sharp exothermic peak (245.1 ° C.) expected. From this, even when Ag core particles obtained by liquid phase synthesis are used, most of the organic substances are removed during the production process of the core-shell particles and replaced with those derived from organic substances mixed in PVP and Ag raw materials. It is guessed.

  As shown in FIG. 32, in sample 14, a slight exothermic peak occurred in the vicinity of 190.degree. This is considered to be because some of the various organic substances contained in the Ag core particles produced by the liquid phase synthesis remained after the core-shell particles were produced. Considering this result and the results of the various evaluation tests described above, even if a part of the organic matter contained in the Ag core particle is not completely removed during the generation process of the core-shell particle, a suitable core-shell particle is selected. It is speculated that it can be generated. Further, from these results, it is understood that the “unwashed AgPd-containing PVP amount” in Table 3 mentioned above may contain organic substances other than PVP, and does not necessarily indicate the amount of PVP alone. Is done.

  As mentioned above, although the specific example of this invention was demonstrated in detail based on the test example, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

Claims (11)

A core-shell particle composed of an Ag core particle mainly composed of silver and a Pd shell mainly composed of palladium covering at least a part of the surface of the Ag core particle,
Core-shell particles in which polyvinylpyrrolidone is selectively attached to the surface of the Pd shell. A powder material comprising at least core-shell particles composed of Ag core particles mainly composed of silver and Pd shells mainly composed of palladium covering at least a part of the surface of the Ag core particles,
Z average particle diameter (D _DLS ) measured by performing analysis by cumulant method in dynamic light scattering method is 0.1 μm to 1.5 μm, and polydispersity index (PDI) is 0.4 or less There is a powder material. A powder material comprising at least core-shell particles composed of Ag core particles mainly composed of silver and Pd shells mainly composed of palladium covering at least a part of the surface of the Ag core particles,
Powder having a peak particle size measured by performing analysis by the NNLS method in the dynamic light scattering method is in the range of 0.1 μm to 1.5 μm, and the peak intensity of the peak particle size is 90% or more. Body material.   The powder material according to claim 2 or 3, wherein the content of the core-shell particles is 90% or more.   The powder material according to any one of claims 2 to 4, wherein polyvinylpyrrolidone is selectively attached to the surface of the core-shell particles. A BET specific BET particle diameter converted from the surface area _{(D BET),} the Z average particle diameter _{(D DLS),} but satisfy the relationship shown in the following equation (1), one of the claims 2 to 5 one The powder material according to item.
D _DLS / D _BET ≦ 10.0 (1)   The electrically conductive paste which disperse | distributed the powder material as described in any one of Claims 2-6 to the dispersion medium. In a method for producing a powder material comprising at least core-shell particles composed of Ag core particles mainly composed of silver and Pd shells mainly composed of palladium covering at least a part of the surface of the Ag core particles. There,
A mixed solution preparation step of preparing an Ag dispersion mixed solution in which the Ag core particles are dispersed in a solution in which a palladium complex and polyvinylpyrrolidone are dissolved;
A method for producing a powder material, comprising: a Pd shell precipitation step of adding a reducing agent to the Ag dispersion mixed liquid containing the polyvinyl pyrrolidone and Ag core particles to precipitate a Pd shell on the surface of the Ag core particles.   The reducing agent is hydrazine carbonate, hydrazine, hydrazine hydrate, phenyl hydrazine, hydrazine sulfate, hydrazine dihydrochloride, alkyl hydrazine, tartaric acid, tartrate, citric acid, citrate, ascorbic acid, ascorbate, sodium borohydride The method for producing a powder material according to claim 8, wherein   The manufacturing method of the powder material of Claim 8 or Claim 9 whose density | concentration of the polyvinyl pyrrolidone in the said Ag dispersion liquid mixture is 0.1g / L-200g / L. When the total content of Ag element and Pd element in the Ag dispersion mixture is 100%, the palladium complex and the Ag core are adjusted so that the Ag element content is 70% to 99% by weight. The manufacturing method of the powder material as described in any one of Claims 8-10 which adjusts the addition amount of particle | grains.