JP2012184506A - Metal nanoparticle, and manufacturing method of metal nanoparticle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal nanoparticle superior in low-temperature sinterability, and a method for manufacturing the same.SOLUTION: The metal nanoparticle includes a core, comprising a noble metal particle or a noble metal alloy particle, and a copper layer coating it. The metal nanoparticle has average particle diameter of 20-60 nm and standard deviation of 10% or less, and further, is comprised by combining with an organic amine compound as a protective agent. The metal nanoparticle is manufactured by adding a copper compound and a noble metal compound, insoluble in a solvent, to the solvent, and adding the protective agent, comprising the organic amine compound, and a reducing agent, and further, applying ultrasonic waves.

Description

  The present invention relates to a metal nanoparticle constituting a conductive ink / conductive paste and a method for producing the same. In detail, it is related with the metal nanoparticle excellent in low temperature sintering property.

  As a method for forming a wiring circuit of an electric / electronic device, a method using a conductive ink / conductive paste is known. This method is to form a wiring circuit by applying conductive ink with a wiring pattern of a desired shape with a printer or the like and baking it, and it is a method by which a complicated and fine wiring pattern can be easily formed. is there. The conductive ink / conductive paste used here is formed by dispersing metal nanoparticles of conductive metal such as copper in an appropriate solvent.

  In the production of metal nanoparticles, a gas phase reaction method in which the raw metal is evaporated and released into the gas phase to recover the metal nanoparticles has been known for a long time, but is suitable for industrial production from the viewpoint of production efficiency. Absent. Therefore, a liquid phase reaction method such as a polyol method has been effective from recent years as a production method for efficiently producing metal nanoparticles. In the method for producing metal nanoparticles based on this polyol method, a metal salt such as copper oxide or copper sulfate is dissolved in a polyol which is a solvent, and a reducing agent and a polymer compound such as polyvinylpyrrolidone or polyethyleneimine are used as a protective agent. It is added to reduce metal ions and simultaneously bond and protect the protective agent to metal atoms to form metal nanoparticles.

Japanese Patent No. 4428138 Japanese Patent No. 4449676

  By the way, in the formation of the wiring circuit using the conductive ink or the like, as described above, the conductive ink is applied to the substrate and baked. In the firing process, the metal nanoparticles in the ink are sintered to obtain a density that can function as a conductive material. The firing temperature at this time is preferably as low as possible. However, the conductive ink using the conventional metal nanoparticles cannot be said to have a sufficiently low sintering temperature, and heating at about 250 to 300 ° C. is necessary.

  Then, an object of this invention is to provide the metal nanoparticle excellent in low temperature sintering property, and its manufacturing method.

  The inventors of the present invention have studied the above-mentioned problems, and optimized the particle size and particle size distribution, and further optimized the protective agent as the configuration of the metal nanoparticles that solves the above problem. That is, the present invention is a metal nanoparticle composed of a core composed of noble metal particles or noble metal alloy particles and a copper layer covering the core, and has an average particle size of 20 to 60 nm and a standard deviation of 10% or less. These are metal nanoparticles formed by bonding organic amine compounds of the following formulae.

(R is an alkyl group. When n is 2 or more, it may be a different alkyl group.)

  According to the present inventors, the sintering of metal nanoparticles in a conductive ink tends to proceed at a low temperature when the particle size is reduced and the particle size is uniform. Therefore, in the present invention, the average particle size is 20 to 60 nm and the standard deviation is 10% or less. About a particle size, More preferably, it is 30-50 nm.

  Moreover, this invention prescribes | regulates the kind of protective agent in addition to particle | grain properties. In the conventional metal nanoparticles by the polyol method, a polymer organic compound such as PVP has been used as a protective agent. Such a high molecular organic compound becomes an obstacle to the sintering of the metal nanoparticles, and may increase the sintering temperature. In view of this point, the present invention uses an organic amine compound that does not easily generate carbon that inhibits sintering and vaporizes and decomposes at 300 ° C. or lower.

  The metal nanoparticles according to the present invention have a structure in which particles made of a noble metal or an alloy thereof are used as a core and a copper layer covering the core is combined. The reason why such a composite structure is adopted is that, by compositing appropriate core particles, this acts as a nucleus for forming metal nanoparticles and contributes to the formation of particles having a uniform particle diameter. Here, the reason why the outer layer exposed on the surface is made of copper is because the usefulness as a conductive material such as conductive ink is emphasized. The core particles are composed of a noble metal or an alloy thereof because the catalytic action of the noble metal is suitable as a nucleus for forming metal nanoparticles, and the noble metal is a chemically stable metal, and is used as a copper conductive material. This is because it is difficult to inhibit the action.

  The inclusion of the noble metal alloy as the core particle takes into consideration the case where the noble metal is alloyed with copper in the process of forming the metal nanoparticles. However, this alloying is not limited to an alloy having a so-called stoichiometric composition, but includes alloying in a state in which noble metal atoms are partially dissolved in copper. In addition, this noble metal or noble metal alloy is in a non-oxidized state and does not contain an oxide. This is because the oxide may adversely affect the sinterability of the metal nanoparticles, and is not preferable for the electrical characteristics after sintering. Furthermore, the metal nanoparticles according to the present invention are preferably in a state where the noble metal particles or the noble metal alloy particles as the core are completely covered with copper. Even if it is a noble metal, exposure to the nanoparticle surface affects the sinterability.

  The noble metal content in the metal nanoparticles is preferably 1/100 to 5/100 in terms of molar ratio. If it is less than 1/100, metal nanoparticles having an appropriate particle size cannot be formed. On the other hand, if it exceeds 5/100, it becomes difficult to maintain a state in which the precious metal is completely covered.

  Next, the manufacturing method of the metal nanoparticle which concerns on this invention is demonstrated. The method according to the present invention is basically similar to the polyol method described in the prior art. That is, a copper raw material and a noble metal raw material serving as a nucleus for nanoparticle formation are added to the solvent, and a reducing agent and a protective agent are added. In the present invention, a metal compound insoluble in a solvent is applied as a copper raw material and a noble metal raw material, and ultrasonic waves are further applied.

  The reason why the metal compound insoluble in the solvent is used as the metal raw material is to make the manufactured metal nanoparticles finer and uniform in particle size. In the conventional polyol method, a raw material soluble in a solvent is added, metal ions (noble metal ions, copper ions) are present in the solvent from the start of the reaction, and nucleation and grain growth proceed with the addition of the reducing agent. . At this time, when the raw material concentration is increased to ensure production efficiency, the reduction reaction proceeds too quickly, and the particle size tends to be coarse. Further, in the conventional method, in consideration of the speed of such a reduction reaction, a polymer organic compound such as PVP having a high protection performance is used to enclose the particles at the same time as the formation of the particles and suppress the generation of coarse particles. However, as described above, the use of a high molecular organic compound such as PVP is not preferable for the subsequent characteristics as a conductive ink.

  Therefore, in the present invention, for the purpose of controlling a reduction reaction for forming fine metal nanoparticles, a metal compound insoluble in a solvent is applied as a metal raw material, and ultrasonic waves are applied. That is, a copper compound and a noble metal compound that are insoluble in the solvent are added to the solvent, a protective agent composed of an organic amine compound represented by the following formula, and a reducing agent are added. A method for producing metal nanoparticles comprising a step of eluting copper ions and noble metal ions from a compound and the noble metal compound and reducing them.

(R is an alkyl group. When n is 2 or more, it may be a different alkyl group.)

  Here, the raw metal compound does not generate metal ions as it is, but cavitation bubbles due to ultrasonic dense waves are generated on the surface of the metal compound. The gas phase in the cavitation bubble is in a high-temperature and high-pressure environment, and even a metal compound insoluble in the solvent dissolves and releases metal ions in that region. And metal nanoparticles are produced | generated by the reduction | restoration of a noble metal ion and the reduction | restoration of a copper ion. Based on the solid-liquid reaction that occurs uniformly in such a reaction system, the metal nanoparticles produced by the method according to the present invention are fine and uniform in particle size.

  The above-mentioned solid-liquid reaction proceeds sequentially by repeating cavitation bubble generation → metal compound dissolution → metal ion reduction → new compound surface exposure. Therefore, since the metal ion in the reaction system is always adjusted to an appropriate amount, the amount of the protective agent can be reduced, and a protective agent having a low protective action can also be used. Furthermore, since the cavitation bubble generated by ultrasonic waves generates reducing radicals, the amount of reducing agent can also be reduced. And even if the density | concentration of a metal raw material is made into a high density | concentration by these effects | actions, the production | generation of a coarse metal particle can be suppressed and efficient manufacture is attained.

  Hereinafter, the method according to the present invention will be described in more detail. As the solvent, a solvent conventionally used in metal nanoparticle formation can be applied. For example, polar solvents such as water, alcohol, polyol, aldehyde, and ketones, and nonpolar solvents include toluene, hexane, cyclohexane, and xylene.

  About the copper compound and noble metal compound which are the metal raw materials added to a solvent, these need to be insoluble in a solvent. Insoluble in a solvent means that it does not dissolve in a solvent in a steady state at room temperature (solubility of 0.01 mol / L or less at 25 ° C.). The noble metal compound is a noble metal compound of any of Pd, Pt, Ru, Ir, and Rh. A plurality of noble metal compounds may be added in combination (for example, a Pd compound and an Rh compound may be added in combination).

  Specifically, as the copper compound and the noble metal compound, an acetylacetonate complex, a formic acid complex, an acetic acid complex, an ammine complex, or a chelate complex can be applied. Regarding the copper raw material, in addition to the complex, organometallic compounds such as ethylenediamine copper (II), cyclohexane butyrate copper (II), stearic acid copper (II), and copper carbonate can also be applied. The precious metal compound is preferably added in a molar ratio of 1/100 to 5/100 with respect to the copper compound. In addition, about a copper compound, it is preferable to add 1/10-10/10 by molar ratio with respect to a solvent. The present invention enables efficient production by relatively increasing the concentration of the copper raw material.

  As the protective agent, an organic amine compound is added as described above. Preferred organic amine compounds are dodecylamine, butylamine, trimethylamine and oleylamine. The addition amount of the protective agent is preferably 3 times or less in terms of molar ratio with respect to the copper compound.

  As the reducing agent, application of ascorbic acid, citric acid, oxalic acid, and acetic acid is preferable. Moreover, it is preferable that the addition amount of a reducing agent shall be 1 to 2 times by molar ratio with respect to a copper compound, and 1/10 to 4/10 by molar ratio with respect to a solvent. As described above, in the present invention using cavitation bubbles by ultrasonic waves, the amount of reducing agent added is reduced.

  The application conditions of the ultrasonic waves are preferably a frequency of 15 kHz to 200 kHz and an output of 20 W to 200 W. Moreover, the temperature of the reaction system when the reaction is advanced by applying ultrasonic waves is preferably in the range of 10 ° C. to 60 ° C., and the reaction time is preferably 10 minutes to 5 hours.

  As described above, the metal nanoparticles according to the present invention can be sintered at a low temperature, and can form a copper film suitable as a wiring material.

  Moreover, the manufacturing method of the metal nanoparticle which concerns on this invention can reduce the usage-amount of a protective agent and a reducing agent by the effect | action of an ultrasonic wave. Therefore, the reaction liquid used in the copper fine particle manufacturing process can be used as it is as a raw material for conductive ink and paste. In particular, reduction of the amount of the protective agent used is effective, and the content of the amine compound as the protective agent is 3 times or less in molar ratio to the copper compound and 1/10 or less in molar ratio to the solvent By using a nanoparticle solution, it can be used as a conductive ink and paste material for forming a high-quality copper film.

The SEM photograph of the copper fine particle manufactured in 2nd Embodiment. The X-ray-diffraction analysis result of the copper fine particle manufactured in 2nd Embodiment. The TG-DTA analysis result of the copper fine particle (sample No. 1, 2) manufactured by 2nd Embodiment. XANES of copper fine particles (sample Nos. 3 and 4) measured in the third embodiment. The radial distribution function obtained from EXAFS of the copper fine particles (sample Nos. 3 and 4) measured in the third embodiment. The X-ray-diffraction analysis result of the copper film (Pd complex use) manufactured in 4th Embodiment. The X-ray-diffraction analysis result of the copper film (Rh complex use) manufactured in 4th Embodiment.

First embodiment : 100 mL of ethanol as a solvent, 0.05 M of copper acetylacetonate complex (Cu (acac) ₂ ) as a copper raw material, 1.5 μl of palladium acetylacetonato complex (Pd (acac) ₂ ) as a noble metal raw material × 10 ⁻³ M was added (copper raw material: Pd raw material was set to 100: 3). To this, 0.1 M dodecylamine as a protective agent and 0.2 M L-ascorbic acid as a reducing agent were further added, and ultrasonic waves were applied. The ultrasonic application conditions were a frequency of 97.0 kHz and an output of 100 W. The reaction was carried out for 3 hours while maintaining the liquid temperature at 40 ° C.

  The copper fine particles obtained by the above treatment were filtered, and SEM observation was performed to examine the particle size and distribution. As a result, the average particle size was 43.5 nm, and the standard deviation was 8.86%.

Second Embodiment : Here, as in the first embodiment, while using a copper acetylacetonate complex (Cu (acac) ₂ ) as a copper raw material and a palladium acetylacetonate complex (Pd (acac) ₂ ) as a noble metal raw material, Copper fine particles were produced by changing the addition amount of the palladium acetylacetonate complex. The addition amount of the palladium acetylacetonato complex is 5.0 × 10 ⁻⁴ M (copper raw material: Pd raw material = 100: 1), 2.5 × 10 ⁻³ M (copper raw material: Pd raw material = 100: no addition). 5). Other production conditions (copper acetylacetonate complex concentration, ultrasonic conditions, etc.) were the same as in the first embodiment. And the particle size and distribution were examined about the obtained copper fine particle. The results are shown in Table 1.

  From the above results, it can be seen that when noble metal raw material (palladium complex) is not added, copper particles having a large particle size and a large variation (standard deviation) can be obtained. This indicates that the presence of a noble metal raw material serving as a nucleus is indispensable even with the characteristics of the present invention of solvent-insoluble metal raw material and application of ultrasonic waves. On the other hand, it was confirmed that the addition of the noble metal raw material produced copper fine particles having a fine particle size.

  1 and 2 show SEM photographs and X-ray diffraction analysis results of the produced copper fine particles. The produced copper fine particles have a spherical shape. Further, only the copper diffraction pattern is detected in the result of X-ray diffraction. This indicates that the possibility that Pd is exposed on the surface of the copper fine particles is very low and has a composite structure having Pd as a core.

  3 shows NO. 1 and NO. The result when performing a TG-DTA analysis about the copper fine particle of 2 is shown. From this figure, the mass of the copper fine particles produced using the palladium complex is reduced in the vicinity of 210 ° C. On the other hand, the copper fine particles to which the palladium complex is not added are reduced in mass at 300 ° C. or higher. The temperature showing mass loss in TG-DTA analysis is not the sintering temperature of the fine particles, but is strongly related to this. That is, the copper fine particles refined using the palladium complex can be expected to reduce the sintering temperature.

Third Embodiment : Here, structural analysis was performed on the copper fine particles ( No. 3 to No. 4) manufactured in the second embodiment. The structural analysis was performed by X-ray absorption fine structure (XAFS) measurement. XAFS measurement was performed at the beam line BL-15 owned by the Saga Prefectural Kyushu Synchrotron Light Research Center using a Si (311) double crystal monochromator, and the X range from the PdK absorption edge to the wide X-ray absorption fine structure (EXAFS) region. A linear absorption spectrum was measured. The measurement was performed at room temperature.

  FIG. 4 shows an X-ray absorption near edge structure (XANES) by XAFS measurement. Each spectrum is normalized by its peak top intensity. From FIG. 3 (Cu: Pd = 100: 3), No. 3 4 (Cu: Pd = 100: 5), the spectra of copper fine particles show almost the same shape, and peaks are observed in the vicinity of 24360 eV and 24381 eV. Show. However, the spectrum of these samples is broader than the spectrum of Pd metal, and it is presumed that Pd may be partially or wholly dissolved in the Cu phase. Moreover, it is suggested that Pd in these copper fine particles is not oxidized when compared with the spectrum of PdO powder as a standard sample.

  FIG. 5 shows a radial distribution function obtained by Fourier transform based on a wide area X-ray absorption fine structure (EXAFS) by XAFS measurement. From FIG. 3 (Cu: Pd = 100: 3), No. 3 The copper fine particles of 4 (Cu: Pd = 100: 5) show almost similar distribution functions. And it turns out that any copper fine particle shows the distribution function different from Pd metal powder and PdO powder. That is, these samples have a peak at a position smaller than the Pd—Pd bond distance of the Pd metal powder and larger than the Pd—O bond distance of PdO. It is inferred that the shift of the main peak in these samples indicates a Pd—Cu bond. From the above results, it is considered that in the copper fine particles in the present embodiment, non-oxidized Pd exists inside, and at least partially alloyed with Cu.

Fourth Embodiment : Here, the NO. 2 and NO. It was decided to check the sinterability using the copper fine particles of No. 3. In this test, copper fine particles were produced in the same manner as in the second embodiment, the reaction liquid precipitate (copper fine particles) was collected and applied on a glass substrate, and heated and baked in a nitrogen atmosphere in an electric furnace. The film is observed for external appearance and XRD analysis is performed to confirm the presence or absence of oxidation of the film. The firing conditions were a nitrogen atmosphere, a temperature of 150 ° C., and a heating time of 10 minutes.

  FIG. 6 shows the results of XRD analysis. From this figure, it is considered that the film obtained by firing each sample is made of copper, and since no peak of copper oxide was observed, the film was not oxidized. As for the appearance of the film, no abnormal grain growth of copper particles was observed, and the film was a very clean film with a uniform particle diameter. From the above, it was confirmed that the copper fine particles according to this embodiment can be fired even at a relatively low temperature of 150 ° C.

In the present embodiment, further, rhodium was applied as a noble metal raw material to produce copper fine particles, and the sinterability was also confirmed. As the rhodium complex, a rhodium acetylacetonate complex (Rh (acac) ₃ ) was used, and its addition amount was set to 1/100 with respect to the copper raw material. Other manufacturing conditions were the same as those in the first embodiment.

  FIG. 7 shows the results of XRD analysis after the produced fine particles were sintered in the same manner as described above. From this figure, no peak of copper oxide was observed for the sample using rhodium. Therefore, when an XRD analysis was performed on the copper fine particles with respect to a film having a baking time of 60 minutes, no copper oxide peak was observed here. The copper fine particles produced by applying rhodium are considered to have high resistance to oxidation.

As described above, the metal nanoparticles according to the present invention are excellent in low-temperature sinterability and can form a copper coating at a relatively low temperature. The metal nanoparticle production method according to the present invention uses a metal raw material insoluble in a solvent and utilizes the action of ultrasonic waves, thereby efficiently producing fine and uniform metal nanoparticle particles. be able to.

Claims (10)

In metal nanoparticles composed of a core composed of noble metal particles or noble metal alloy particles and a copper layer covering the core,
The average particle size is 20 to 60 nm, the standard deviation is 10% or less,
Furthermore, the metal nanoparticle which the organic amine compound of a following formula couple | bonds as a protective agent.
(R is an alkyl group. When n is 2 or more, it may be a different alkyl group.)   The metal nanoparticle according to claim 1, wherein the noble metal is at least one of Pd, Pt, Ru, Ir, and Rh.   3. The metal nanoparticles according to claim 1, wherein the metal nanoparticles have a noble metal content in a molar ratio of 1/100 to 5/100. A method for producing metal nanoparticles according to any one of claims 1 to 3,
In addition to adding a copper compound and a noble metal compound insoluble in the solvent to the solvent, a protective agent composed of an organic amine compound of the following formula, and a reducing agent are added,
Furthermore, by applying ultrasonic waves,
The manufacturing method of the metal nanoparticle including the process of eluting a copper ion and a noble metal ion from the said copper compound and the said noble metal compound, and reducing these.
(R is an alkyl group. When n is 2 or more, it may be a different alkyl group.)   The method according to claim 4, wherein the noble metal compound is a compound of at least one of Pd, Pt, Ru, Ir, and Rh.   The method according to claim 4 or 5, wherein the copper compound and / or the noble metal compound is an acetylacetonate complex, a formic acid complex, an acetic acid complex, an ammine complex, or a chelate complex.   The method according to any one of claims 4 to 6, wherein the noble metal compound is added in a molar ratio of 1/100 to 5/100 with respect to the copper compound.   The method according to any one of claims 4 to 7, wherein the reducing agent is any one of ascorbic acid, citric acid, oxalic acid, and acetic acid.   The method according to any one of claims 4 to 8, wherein the ultrasonic wave is applied with a frequency of 15 kHz to 200 kHz and an output of 20 W to 200 W. A solution containing the metal nanoparticles according to any one of claims 1 to 3,
The metal nanoparticle solution whose content of the organic amine compound which is a protective agent is 1/10 or less in molar ratio with respect to the solvent.