WO2018163619A1 - Method for producing silver nano-particles - Google Patents

Method for producing silver nano-particles Download PDF

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Publication number
WO2018163619A1
WO2018163619A1 PCT/JP2018/001793 JP2018001793W WO2018163619A1 WO 2018163619 A1 WO2018163619 A1 WO 2018163619A1 JP 2018001793 W JP2018001793 W JP 2018001793W WO 2018163619 A1 WO2018163619 A1 WO 2018163619A1
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silver
amine
oxalate
silver oxalate
heating
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PCT/JP2018/001793
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French (fr)
Japanese (ja)
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祐樹 新谷
外村　卓也
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バンドー化学株式会社
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Priority to JP2018504302A priority Critical patent/JP6404523B1/en
Publication of WO2018163619A1 publication Critical patent/WO2018163619A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
    • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
    • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables

Definitions

  • the present invention relates to a method for producing silver nanoparticles.
  • the fine metal particles used in the conductive ink are nanometer-sized particles that are much smaller than the conductive fillers in the conventional conductive paste, so they can be sintered at low temperatures due to the melting point drop unique to nanoparticles.
  • high conductivity close to that of a metal foil can be realized. Examples of the type of metal used in such a conductive ink include silver, gold, and copper.
  • Patent Document 1 relates to a method for producing nanometer-sized silver ultrafine particles, and reacts silver oxalate with oleylamine to produce a complex compound containing at least silver, oleylamine, and oxalate ions, and the resulting complex compound Discloses a method for producing silver ultrafine particles by thermally decomposing the above.
  • Patent Document 2 relates to a method for producing metal nanoparticles, wherein a complexing reaction liquid is obtained by heating a mixture containing nickel carboxylate and primary amine to a temperature in the range of 100 to 165 ° C.
  • a method of obtaining a slurry of nickel nanoparticles coated with a primary amine by heating the crystallization reaction liquid to a temperature of 170 ° C. or higher by microwave irradiation to reduce nickel ions in the complexation reaction liquid is disclosed. .
  • Patent Documents 3 and 4 disclose a method for producing fine metal particles by irradiating and heating a microwave to an organic solvent in which a metal oxide or a metal hydroxide is dispersed.
  • Patent Document 5 in a method for producing metal nanoparticles in which metal nanoparticles are formed in a solution by a chemical reaction, a step of dispersing a powder of an inorganic compound that is a metal source in the solution, and a step of adding a dispersant
  • a method for producing metal nanoparticles which includes a step of irradiating at least one of heat and cavitation to reduce an inorganic compound, and microwaves are mentioned as a heat irradiation method.
  • a method of producing silver nanoparticles by producing a silver reduction reaction by heating using a mixture of amine and silver oxalate as a starting material is silver carbonate.
  • silver nanoparticles can be produced at a low temperature and silver nanoparticles with few impurities can be easily obtained.
  • the silver oxalate-amine complex has a high viscosity, and when heated and reduced by an ordinary method such as an oil bath, it takes time to synthesize silver nanoparticles, and thus the productivity is low.
  • Patent Document 1 describes that by using oleylamine, silver ultrafine particles having a narrow particle size distribution and excellent storage stability can be obtained.
  • a small amount of silver oxalate of 150 mmol or less is used.
  • There was room for improvement in terms of productivity because it was reduced by heating at 0 ° C. for 1 hour.
  • countermeasures against the difficulty in synthesizing particles with an increase in the charged amount have been demanded.
  • Patent Document 2 not only two-stage heating is performed for the formation of a complexing reaction solution and heat reduction, but also heat reduction is performed at a very high temperature, and a silver oxalate-amine complex is prepared. Unlike the method for producing silver nanoparticles at a low temperature, silver nanoparticles having excellent conductivity and low-temperature sintering properties for printed electronics are not produced.
  • heat reduction at a high temperature as in Patent Document 2 is performed, the volatilization of the amine proceeds excessively, and the amine coordinated to the particles is removed.
  • Patent Document 5 discloses a method of heating a solution by irradiating microwaves, but it does not heat a highly viscous silver oxalate-amine complex.
  • the present invention has been made in view of the above situation, and a silver nanoparticle production method capable of producing a large amount of silver nanoparticles having a narrow particle size distribution in a short time from a highly viscous silver oxalate-amine complex.
  • the purpose is to provide.
  • the inventors of the present invention have studied various methods for producing silver nanoparticles, and have focused on a method for obtaining silver nanoparticles from a silver oxalate-amine complex.
  • a method for obtaining silver nanoparticles from a silver oxalate-amine complex due to the high viscosity of the silver oxalate-amine complex, it has been difficult to produce silver nanoparticles with a narrow particle size distribution in a short time with an increase in the charged amount by a normal method such as an oil bath.
  • the present inventors have found that microwave absorption of alkylamine and alkoxyamine is good, and combined at least one of alkylamine and alkoxyamine with heating by microwave irradiation. As a result of the reduction, it was found that silver nanoparticles could be synthesized in just a few minutes, and the present invention was completed.
  • the method for producing silver nanoparticles of the present invention comprises a mixing step of mixing an amine and silver oxalate to obtain a silver oxalate-amine complex in which the amine is coordinated to silver oxalate, and the above silver oxalate-amine complex. Heating with microwave irradiation and reducing the silver oxalate-amine complex, wherein the amine contains at least one compound selected from at least one of alkylamines and alkoxyamines. It is characterized by.
  • the method for producing silver nanoparticles of the present invention may include a step of adding a solvent to the silver oxalate-amine complex between the mixing step and the heating step.
  • the amine preferably includes at least one compound selected from at least one of an alkylamine having 5 or less carbon atoms and an alkoxyamine having 5 or less carbon atoms.
  • a large amount of silver nanoparticles having a narrow particle size distribution can be produced from a highly viscous silver oxalate-amine complex in a short time.
  • the method for producing silver nanoparticles of the present invention comprises a mixing step of mixing an amine and silver oxalate to obtain a silver oxalate-amine complex in which the amine is coordinated to silver oxalate, and the above silver oxalate-amine complex. Heating with microwave irradiation and reducing the silver oxalate-amine complex, wherein the amine contains at least one compound selected from at least one of alkylamines and alkoxyamines. It is characterized by.
  • the method for producing silver nanoparticles of the present invention includes a mixing step of mixing an amine and silver oxalate to obtain a silver oxalate-amine complex in which the amine is coordinated with silver oxalate.
  • the amine includes at least one compound selected from at least one of alkylamine and alkoxyamine. Specifically, only one type of compound classified as an alkylamine may be used, two or more types of compounds classified as an alkylamine may be used, or 1 classified as an alkoxyamine. Only one type of compound may be used, two or more types of compounds classified as alkoxyamines may be used, or one or more types of compounds classified as alkylamines and 1 classified as alkoxyamines Two or more kinds of compounds may be used in combination.
  • the amine mixed with silver oxalate is preferably at least one of alkylamine and alkoxyamine, but other than alkylamine and alkoxyamine as long as it does not cause a reduction reaction before the heating step.
  • An amine may be added.
  • an amine having a hydroxyl group such as an alkanolamine is highly polar for use as a ligand, and if the amount is large, it may cause a reduction reaction before the heating step.
  • an amine other than alkylamine and alkoxyamine it is preferably 5 equivalents or less based on the number of moles of silver oxalate used.
  • the alkylamine may be any one having an alkyl group and an amine functional group in the molecule, and may be a diamine having two amine functional groups in the molecule. Further, the alkylamine may be any of primary amine, secondary amine, and tertiary amine, but is preferably a primary amine from the viewpoint of promoting the formation of a complex.
  • the alkyl group may be linear or branched, and may partially contain a saturated carbocycle, but a linear alkylamine is preferably used.
  • alkylamine examples include ethylamine, propylamine, butylamine, pentylamine, hexylamine, 1,2-ethanediamine, 1,4-butanediamine, 1,5-pentanediamine and the like.
  • alkylamines having 5 or less carbon atoms are preferably used from the viewpoint of promoting the formation of a complex and enhancing the dispersibility in a highly polar solvent.
  • any alkoxyamine may be used as long as it has an alkoxy group and an amine functional group in the molecule.
  • the alkoxyamine may be any of primary amine, secondary amine, and tertiary amine, but is preferably a primary amine from the viewpoint of promoting the formation of a complex.
  • the alkoxy group may be linear or branched, and may partially contain a saturated carbocyclic ring or an unsaturated carbocyclic ring, but a linear alkoxyamine is preferably used.
  • Specific examples of the alkoxyamine include N- (3-methoxypropyl) propane-1,3-diamine, 2-methoxyethylamine, 3-methoxypropylamine, 3-ethoxypropylamine and the like.
  • an alkoxyamine having 5 or less carbon atoms is preferably used.
  • the silver oxalate is the simplest silver dicarboxylate, and the silver oxalate-amine complex synthesized using silver oxalate is reduced at a low temperature in a short time. This is suitable for the synthesis of silver fine particles. Further, when silver oxalate is used, no by-product is generated at the time of synthesis, and only carbon dioxide derived from oxalate ions is produced outside the system.
  • a mixing ratio of the amine and the silver oxalate it is preferable to increase the number of moles of the amine rather than the number of moles of silver atoms, and it is more preferable to add 2 moles or more of the amine to 1 mole of silver atoms. .
  • an appropriate amount of amine can be attached to the surface of the silver nanoparticles produced by the reduction, and the silver nanoparticles can be provided with excellent dispersibility and low-temperature sinterability with respect to various dispersion media.
  • the mixing method of the amine and the silver oxalate is not particularly limited. However, since the viscosity increases due to the complex formation of the amine and silver oxalate, for example, a mixed solution of an amine and silver oxalate is used as a magnetic stirrer. A method of stirring using a rotating body such as is used. Stirring is preferably performed at room temperature (10 to 30 ° C.). The appearance of a silver oxalate-amine complex can be visually confirmed by the formation of a viscous white substance.
  • substances other than amine and silver oxalate may be added as long as they do not interfere with the formation of the silver oxalate-amine complex.
  • a polymer dispersant may be used.
  • a commercially available polymer dispersant can be used as the polymer dispersant.
  • polymer dispersants examples include, for example, Solsperse 11200, Solsperse 13940, Solsperse 16000, Solsperse 17000, Solsperse 18000, Solsperse 20000, Solsperse 24000, Solsperse 26000, Solsperse 27000, Solsperse 28000 (above, Nippon Lubrizol Corporation) DISPERBYK-102, 110, 111, 170, 190.194N, 2015, 2090, 2096 (above, manufactured by Big Chemie Japan); EFKA-46, EFKA-47, EFKA-48, EFKA-49 (above, EFKA Chemical Co.); polymer 100, polymer 120, polymer 150, polymer 400, polymer 401, polymer 402, polymer 4 3, polymer 450, polymer 451, polymer 452, polymer 453 (manufactured by EFKA Chemical Co., Ltd.); Ajisper PB711, Ajisper PA111, Ajisper PB
  • the method for producing silver nanoparticles of the present invention may include a step of adding a solvent to the silver oxalate-amine complex between the mixing step and the heating step. Since the silver oxalate-amine complex is a paste-like thickener, the particle size of the silver nanoparticles obtained after the heating step can be reduced by adding a solvent before heating to lower the viscosity. It is possible to improve the dispersibility of the silver nanoparticles.
  • the solvent is not particularly limited as long as it can disperse the silver oxalate-amine complex obtained in the mixing step and reduce the viscosity.
  • the solvent is compatible with the dispersion medium in producing the conductive ink.
  • a solvent that can be a good solvent for the silver nanoparticles to be produced for example, an organic solvent is used.
  • the solvent acts as a reducing agent for the silver oxalate-amine complex. It is desirable not to.
  • organic solvent examples include good solvents such as N-methylpyrrolidone, terpene, terpineol (terpineol), dihydroterpinyl acetate, isophorone, tripropylene glycol dimethyl ether, toluene, and tridecane.
  • good solvents such as N-methylpyrrolidone, terpene, terpineol (terpineol), dihydroterpinyl acetate, isophorone, tripropylene glycol dimethyl ether, toluene, and tridecane.
  • the said solvent only 1 type may be used and a mixed solvent may be used.
  • a solvent may be added to the silver oxalate-amine complex in the heating step.
  • the silver oxalate-amine complex itself can be directly heated, the silver oxalate can be used even in a thickened state containing almost no solvent.
  • -It is easy to reduce the amine complex on a scale of 100 mmol or more based on silver oxalate, and is excellent in that it can be carried out on a large scale of 1 mol or more.
  • the method for producing silver nanoparticles of the present invention includes a heating step in which the silver oxalate-amine complex is heated by irradiation with microwaves to reduce the silver oxalate-amine complex.
  • the amine complex silver is decomposed by a reduction reaction by heating by microwave irradiation without using a reducing agent, whereby silver is decomposed. Can be generated.
  • microwave irradiation can be performed in a short time.
  • the maximum heating temperature in the heating step is preferably in the range of 80 to 160 ° C, more preferably 100 to 130 ° C.
  • the microwave irradiation time in the heating step depends on the synthesis scale and the irradiation amount per unit time, but is preferably within 30 minutes, more preferably within 5 minutes, and even more preferably within 3 minutes. When the irradiation time exceeds 30 minutes, short-chain ligands are particularly likely to be detached, so that generated particles are likely to aggregate and dispersion stability may be lowered. In addition, the longer the irradiation time, the lower the productivity.
  • the microwave irradiation time is preferably short from the viewpoint of productivity, and irradiation may be terminated immediately after the reduction reaction is completed, but it is usually performed for 1 minute or longer.
  • amine complex silver composed of silver oxalate and amine has very high viscosity at room temperature. For this reason, stirring is particularly difficult when synthesizing a large volume of 100 mmol or more, and when heat transfer heating such as an oil bath or a heater is used, the viscosity decreases due to the temperature rise and sufficient stirring is performed. In the initial stage of heating (until the system temperature is close to 90 ° C.) until it becomes possible, the heating unevenness becomes particularly large. Therefore, a reduction reaction occurs in the vicinity of the wall surface of the reaction vessel, but the central part of the reaction vessel is difficult to warm, so that nucleation of particles becomes uneven in the system, and coarse particles are likely to be generated.
  • the microwave irradiation enables the heating of the vicinity of the wall and the central part at the same time without using heat transfer from the wall surface of the reaction vessel. Also, the inside of the system can be heated uniformly. That is, the combination of silver oxalate and alkylamine and / or alkoxyamine is optimal in that silver nanoparticles having a narrow particle size distribution can be produced in a short time using a simple method of microwave irradiation.
  • the generated silver atoms aggregate to form silver nanoparticles, but since amine molecules are coordinated to the silver atoms generated by the above thermal decomposition method, the amine molecules coordinated to the silver atoms It is presumed that the movement of silver atoms when aggregation occurs due to the action is controlled. As a result, it is possible to produce silver nanoparticles that are very fine and have a narrow particle size distribution.
  • silver nanoparticles having an average particle diameter of 1 ⁇ m or less can be obtained by performing the heating step.
  • the particle diameter of the silver nanoparticles is nanometer size, a melting point drop occurs and the silver nanoparticles can be fired at a low temperature.
  • a fine conductive pattern having a line width of, for example, 5 ⁇ m or less can be formed by using a printing method.
  • the average particle diameter of the obtained silver nanoparticles is preferably 1 to 200 nm. If the average particle diameter of the silver nanoparticles is 200 nm or less, the dispersibility of the silver nanoparticles is unlikely to change over time.
  • the obtained silver nanoparticles may contain particles having an average particle diameter of more than 200 nm and 1 ⁇ m or less. Further, the obtained silver nanoparticles may contain nano-sized particles having an average particle diameter of 1 to 200 nm and submicron-sized particles having an average particle diameter of more than 200 nm and 1 ⁇ m or less. By using nano-sized particles and sub-micron-sized particles together, the nano-sized particles have a lower melting point around the sub-micron-sized particles, thereby forming a better conductive path than when using only sub-micron-sized particles. Can be made. Furthermore, the silver nanoparticles obtained in the heating step may contain micron-sized particles having an average particle diameter of more than 1 ⁇ m, and are removed after the heating step, if necessary.
  • the average particle diameter of the silver nanoparticles can be measured by a dynamic light scattering method, a small angle X-ray scattering method, or a wide angle X-ray diffraction method.
  • the “average particle diameter” refers to a dispersion median diameter.
  • the dispersed median diameter is calculated by obtaining a dispersed particle diameter with a dynamic light scattering method (Dynamic Light Scattering) using the particle diameter standard as a volume standard.
  • alkylamine and / or alkoxyamine molecules adhere to the surface of the silver nanoparticles obtained in the heating step by a relatively weak bond, and a protective film is formed on the surface of the silver nanoparticles.
  • the protective coating prevents aggregation of silver nanoparticles and is excellent in storage stability because the silver nanoparticles coated with the protective coating constitute inorganic colloidal particles.
  • the alkylamine and / or alkoxyamine forming the protective film can be easily removed by heating or the like, silver nanoparticles that can be sintered at a low temperature can be produced.
  • the dispersion containing silver nanoparticles obtained as described above contains a metal salt counterion, a residue of a dispersant, etc. Concentration tends to be high. The liquid in such a state is likely to precipitate due to aggregation of silver nanoparticles due to high electrical conductivity. Or, even if it does not precipitate, if the counter ion of the metal salt, excessive dispersant or the like more than the amount necessary for dispersion remains, there is a possibility that the conductivity is deteriorated. Therefore, after the heating step, it is preferable to carry out a washing step of washing the dispersion containing silver nanoparticles to remove excess residues.
  • a cleaning method in the above-described cleaning step for example, a dispersion containing silver nanoparticles having at least a part of the surface coated with an organic component is allowed to stand for a certain period of time, and after removing the supernatant liquid, silver nanoparticles are precipitated.
  • a solvent for example, water, methanol, methanol / water mixed solvent, etc.
  • washing methods include a method of performing centrifugation instead of the above standing, a method of desalting with an ultrafiltration device, an ion exchange device, and the like.
  • the weight ratio of silver atoms to the entire nonvolatile content of the silver nanoparticles is preferably 90% by weight or more.
  • the non-volatile content refers to components other than the solvent, and includes, in addition to silver nanoparticles, organic components that coat silver nanoparticles, polymer dispersants, and the like. When the weight ratio of silver atoms is 90% by weight or more, a conductive pattern having a high silver content can be formed.
  • the obtained silver nanoparticles are mixed with optional components such as water, organic solvents, dispersants, oligomer components, surfactants, thickeners, surface tension modifiers, etc., and have appropriate viscosity and adhesion depending on the purpose of use.
  • a silver nanoparticle dispersion provided with functions such as drying, surface tension, and printability can be obtained, and, for example, a conductive ink used in printed electronics technology can be obtained.
  • Such a silver nanoparticle dispersion is applied onto a substrate using a printing method such as an inkjet method, a flexo method, screen printing, gravure offset printing, or a dispenser, and further baked to form a conductive pattern. can do.
  • the conductive pattern for example, wiring constituting an electronic circuit formed on the electronic circuit board can be cited.
  • the method for performing the firing is not particularly limited, and for example, a conventionally known gear oven or the like can be used.
  • the firing temperature is preferably less than 140 ° C, and more preferably 120 ° C or less.
  • the volume resistance value of the conductive pattern can be controlled by the firing temperature and time, the silver nanoparticles obtained in the present invention sinter (neck) the silver nanoparticles even when fired at a temperature of less than 140 ° C.
  • a conductive pattern having excellent conductivity can be formed, it can be formed on a substrate that is relatively weak against heat.
  • the lower limit of the firing temperature is not necessarily limited, and is preferably a temperature at which a conductive pattern can be formed on a substrate and an organic component or the like can be removed by evaporation or decomposition. Further, the firing time is not particularly limited, and can be appropriately adjusted according to the firing temperature.
  • the volume resistance value of the conductive pattern obtained by the present invention is preferably 110 ⁇ ⁇ cm or less, more preferably 100 ⁇ ⁇ cm or less, and further preferably 50 ⁇ ⁇ cm or less.
  • the volume resistance value is calculated based on the following formula (1).
  • the film thickness of the conductive pattern after the firing step is, for example, 0.1 to 5 ⁇ m, preferably 0.1 to 1 ⁇ m.
  • Example 1 9.0 g of 3-methoxypropylamine (manufactured by Wako Pure Chemical Industries, Ltd., first grade reagent, carbon number: 4) and 0.2 g of a polymer dispersant (manufactured by Big Chemie Japan, “DISPERBYK-102”) are mixed. Then, the mixture was thoroughly stirred with a magnetic stirrer to prepare an amine mixture. Next, 3.0 g (10 mmol) of silver oxalate was added while stirring. After the addition of silver oxalate, stirring was continued at room temperature to change the silver oxalate to a viscous white substance, and stirring was terminated when the change was found to be apparently finished (mixing step) .
  • the obtained mixed solution was transferred to a microwave heating device (“ ⁇ Reactor EX” manufactured by Shikoku Keiki Kogyo Co., Ltd.), the peak temperature in the system was set to 120 ° C. in the output automatic control mode, and the temperature was raised by 30 ° C./min.
  • the mixture was heated to a profile.
  • the synthesis state of the silver nanoparticles was confirmed by blowing carbon dioxide gas, and the heating of the mixed solution was finished in 3 minutes to obtain a suspension of silver nanoparticles (heating process).
  • Example 2 A conductive ink containing silver nanoparticles was obtained in the same manner as in Example 1 except that the amount of raw material used was scaled 10 times. Specifically, 90.0 g of 3-methoxypropylamine, 2.0 g of the polymer dispersant, 30.4 g of silver oxalate, and 100 mL of the solvent during washing were used.
  • Example 3 A conductive ink containing silver nanoparticles was obtained in the same manner as in Example 1 except that the amount of the raw material used was scaled 100 times and the mixture was heated for 5 minutes. Specifically, 900.0 g of 3-methoxypropylamine, 20.0 g of the polymer dispersant, 304.0 g of silver oxalate, and 1000 mL of the solvent during washing were used.
  • Example 4 In the same manner as in Example 3, 304.0 g of silver oxalate was added and stirring was continued at room temperature to finish changing the silver oxalate to a viscous white substance. Then, N-methylpyrrolidone (Wako Pure Chemical Industries, Ltd.) A conductive ink containing silver nanoparticles was obtained in the same manner as in Example 3 except that 580.0 g of Reagent Grade 1 manufactured by KK were added.
  • Example 5 The same procedure as in Example 1 was conducted except that 9.0 g of 3-methoxypropylamine used for preparation of the amine mixture was changed to 9.0 g of pentylamine (manufactured by Wako Pure Chemical Industries, reagent grade 1, carbon number: 5). A conductive ink containing silver nanoparticles was obtained.
  • Example 1 A conductive ink containing silver nanoparticles was obtained in the same manner as in Example 1 except that the heating method of the mixed solution was changed from microwave heating to an oil bath and heated in an oil bath at 120 ° C. for 15 minutes.
  • Example 2 A conductive ink containing silver nanoparticles was obtained in the same manner as in Example 2 except that the heating method of the mixed solution was changed from microwave heating to an oil bath and heated in an oil bath at 120 ° C. for 15 minutes.
  • a conductive ink is applied on a slide glass having a volume resistance value of 25 mm ⁇ 25 mm by spin coating under the condition of 2000 rpm ⁇ 15 seconds, and then heated and baked in a gear oven at 120 ° C. for 30 minutes.
  • the surface resistance value of this film was measured with a resistivity meter ("Loresta", manufactured by Mitsubishi Chemical Analytech Co., Ltd., four deep needle method) to obtain a surface resistance value.
  • the thickness was measured with a laser microscope (manufactured by Keyence Corporation). And based on the following formula
  • Formula: Volume resistance value ( ⁇ ⁇ cm) surface resistance value ( ⁇ / ⁇ ) ⁇ film thickness ( ⁇ m) / 10000
  • Example 1 to 5 rapid heating was possible by using microwaves, and the synthesis time could be greatly shortened.
  • the vicinity of the wall and the center of the reaction vessel were heated at the same time, and the viscous mixed liquid could be heated evenly, so that silver nanoparticles having a small dispersed median diameter were produced. I was able to.
  • the silver nanoparticles obtained in Examples 1 to 5 had good dispersibility and dilutability, and had a low volume resistance when fired at a low temperature (120 ° C.).
  • Example 4 the solvent was added during the synthesis of the complex, so that the viscosity of the mixed solution was reduced and the mixture could be heated more uniformly. Therefore, the dispersion median diameter was smaller than in Example 3 and the dilution was excellent. Silver nanoparticles could be produced.
  • the method for producing silver nanoparticles of the present invention is characterized in that microwaves are irradiated to uniformly heat a highly viscous silver oxalate-amine complex without heating unevenness.
  • the viscosity of the silver oxalate-amine complex can also be reduced by adding a solvent to the silver oxalate-amine complex.
  • the method for producing nanoparticles (hereinafter also referred to as “the method for producing the second silver nanoparticles of the present invention”) can also effectively prevent uneven heating in the heating step, and is highly viscous silver oxalate— It is useful as a method for producing a large amount of silver nanoparticles having a narrow particle size distribution in a short time from an amine complex. Moreover, the coarsening of a particle
  • a heating process may serve as the solvent addition process. That is, the silver oxalate-amine complex may be heated in parallel with the addition of the solvent.
  • a mixing process may serve as the solvent addition process. That is, the amine and silver oxalate may be mixed in parallel with the addition of the solvent.
  • the mixing step also serves as a solvent addition step, it is preferable to use a non-alcohol solvent or an organic solvent compatible with the resulting silver nanoparticles.
  • the heating method is not particularly limited, and heating by an oil bath or the like can also be applied.

Abstract

The present invention provides a method for producing silver nano-particles that can produce silver nano-particles with a narrow particle size distribution in large amounts in a short time from a highly viscous silver oxalate-amine complex. This method for producing silver nano-particles comprises: a mixing step for mixing an amine with silver oxalate to obtain a silver oxalate-amine complex in which the amine is coordinated with the silver oxalate; and a heating step for heating the silver oxalate-amine complex by irradiating the same with microwaves to reduce the silver oxalate-amine complex. The amine comprises at least one kind of compound selected from alkylamines and/or alkoxyamines.

Description

銀ナノ粒子の製造方法Method for producing silver nanoparticles
本発明は、銀ナノ粒子の製造方法に関する。 The present invention relates to a method for producing silver nanoparticles.
近年、金属微粒子を含有する導電性インクを基材上に印刷して焼成することにより、極めて微細な電子回路やデバイスを形成するプリンテッドエレクトロニクス技術が注目されている。導電性インクに用いられる金属微粒子は、従来から知られた導電ペースト中の導電フィラーよりもはるかに小さいナノメートルサイズの粒子であるため、ナノ粒子特有の融点降下によって低温で焼結させることができ、かつ金属箔に近い高い導電性を実現できるという特徴がある。このような導電性インクに用いられる金属の種類としては、銀、金、銅等が挙げられる。 In recent years, printed electronics technology that forms extremely fine electronic circuits and devices by printing and firing conductive ink containing metal fine particles on a substrate has attracted attention. The fine metal particles used in the conductive ink are nanometer-sized particles that are much smaller than the conductive fillers in the conventional conductive paste, so they can be sintered at low temperatures due to the melting point drop unique to nanoparticles. In addition, there is a feature that high conductivity close to that of a metal foil can be realized. Examples of the type of metal used in such a conductive ink include silver, gold, and copper.
特許文献１には、ナノメートルサイズの銀超微粒子の製造方法に関し、シュウ酸銀と、オレイルアミンとを反応させて少なくとも銀とオレイルアミンとシュウ酸イオンとを含む錯化合物を生成し、生成した錯化合物を加熱分解して銀超微粒子を生成する方法が開示されている。 Patent Document 1 relates to a method for producing nanometer-sized silver ultrafine particles, and reacts silver oxalate with oleylamine to produce a complex compound containing at least silver, oleylamine, and oxalate ions, and the resulting complex compound Discloses a method for producing silver ultrafine particles by thermally decomposing the above.
また、特許文献２には、金属ナノ粒子の製造方法に関し、カルボン酸ニッケル及び１級アミンを含む混合物を１００～１６５℃の範囲内の温度に加熱して錯化反応液を得た後、錯化反応液をマイクロ波照射によって１７０℃以上の温度に加熱して錯化反応液中のニッケルイオンを還元し、１級アミンで被覆されたニッケルナノ粒子のスラリーを得る方法等が開示されている。 Patent Document 2 relates to a method for producing metal nanoparticles, wherein a complexing reaction liquid is obtained by heating a mixture containing nickel carboxylate and primary amine to a temperature in the range of 100 to 165 ° C. A method of obtaining a slurry of nickel nanoparticles coated with a primary amine by heating the crystallization reaction liquid to a temperature of 170 ° C. or higher by microwave irradiation to reduce nickel ions in the complexation reaction liquid is disclosed. .
また、特許文献３及び４には、金属酸化物又は金属水酸化物を分散した有機溶媒にマイクロ波を照射して加熱することにより金属微粒子を製造する方法が開示されている。 Patent Documents 3 and 4 disclose a method for producing fine metal particles by irradiating and heating a microwave to an organic solvent in which a metal oxide or a metal hydroxide is dispersed.
また、特許文献５には、金属ナノ粒子を溶液中で化学反応によって形成する金属ナノ粒子の作製方法において、溶液に金属源である無機化合物の粉末を分散させる工程と、分散剤を添加する工程と、熱及びキャビテーションの少なくとも一方を照射し、無機化合物を還元する工程を含むことを特徴とする金属ナノ粒子の作製方法が開示されており、熱の照射方法としてマイクロ波が挙げられている。 In addition, in Patent Document 5, in a method for producing metal nanoparticles in which metal nanoparticles are formed in a solution by a chemical reaction, a step of dispersing a powder of an inorganic compound that is a metal source in the solution, and a step of adding a dispersant And a method for producing metal nanoparticles, which includes a step of irradiating at least one of heat and cavitation to reduce an inorganic compound, and microwaves are mentioned as a heat irradiation method.
特開２００９－２７０１４６号公報JP 2009-270146 A 特開２０１３－８７３０８号公報JP 2013-87308 A 特開２０１１－１２２９０号公報JP 2011-12290 A 特開２０１３－２３６９９号公報JP 2013-23699 A 特開２０１０－６５２６５号公報JP 2010-65265 A
導電性インクに用いられる金属微粒子を製造する方法のなかでも、出発原料としてアミンとシュウ酸銀の混合物を用い、加熱により銀の還元反応を生じさせて銀ナノ粒子を製造する方法は、炭酸銀を用いる場合等に比べて低温で銀ナノ粒子を製造でき、かつ、不純物の少ない銀ナノ粒子を容易に得られるという利点がある。しかしながら、シュウ酸銀－アミン錯体は粘性が高く、オイルバス等の通常の方法で加熱還元した場合には、銀ナノ粒子の合成に時間がかかるため、生産性が低かった。また、合成スケールを大きくすると、粘性が高いために反応系内の加熱ムラが起こりやすく、それによって粗大粒子が出来やすくなり、粒度分布の狭い銀ナノ粒子を短時間で製造することは困難であった。 Among the methods for producing fine metal particles used in conductive inks, a method of producing silver nanoparticles by producing a silver reduction reaction by heating using a mixture of amine and silver oxalate as a starting material is silver carbonate. As compared with the case of using silver, there are advantages that silver nanoparticles can be produced at a low temperature and silver nanoparticles with few impurities can be easily obtained. However, the silver oxalate-amine complex has a high viscosity, and when heated and reduced by an ordinary method such as an oil bath, it takes time to synthesize silver nanoparticles, and thus the productivity is low. In addition, when the synthetic scale is increased, the viscosity is high, so heating unevenness in the reaction system is likely to occur, thereby making it easy to produce coarse particles, and it is difficult to produce silver nanoparticles with a narrow particle size distribution in a short time. It was.
特許文献１では、オレイルアミンを用いることにより、粒度分布が狭く、保存安定性に優れた銀超微粒子が得られると記載されているが、実施例はいずれも１０ｍｍｏｌ以下の少量のシュウ酸銀を１５０℃で１時間加熱して還元しており、生産性の点で改善の余地があった。特に銀ナノ粒子の製造を量産レベルで行うためには、仕込み量の増加に伴い粒子合成が難しくなることに対する対策が求められていた。 Patent Document 1 describes that by using oleylamine, silver ultrafine particles having a narrow particle size distribution and excellent storage stability can be obtained. However, in all of the examples, a small amount of silver oxalate of 150 mmol or less is used. There was room for improvement in terms of productivity because it was reduced by heating at 0 ° C. for 1 hour. In particular, in order to produce silver nanoparticles at a mass production level, countermeasures against the difficulty in synthesizing particles with an increase in the charged amount have been demanded.
また、特許文献２では、錯化反応液の生成と加熱還元のために２段階の加熱を行っているだけでなく、加熱還元を非常に高温で実施しており、シュウ酸銀－アミン錯体を用いて低温で銀ナノ粒子を製造する方法とは異なり、プリンテッドエレクトロニクス用の導電性及び低温焼結性に優れた銀ナノ粒子を製造するものではない。特許文献２のような高温での加熱還元が行われると、アミンの揮発が進み過ぎるとともに、粒子に配位したアミンが外れてしまう。 In Patent Document 2, not only two-stage heating is performed for the formation of a complexing reaction solution and heat reduction, but also heat reduction is performed at a very high temperature, and a silver oxalate-amine complex is prepared. Unlike the method for producing silver nanoparticles at a low temperature, silver nanoparticles having excellent conductivity and low-temperature sintering properties for printed electronics are not produced. When heat reduction at a high temperature as in Patent Document 2 is performed, the volatilization of the amine proceeds excessively, and the amine coordinated to the particles is removed.
また、特許文献３及び４では、マイクロ波の吸収性（加熱性）の良い有機溶媒中に金属酸化物又は金属水酸化物を分散させた液に対してマイクロ波を照射して加熱しているが、粘性の高いシュウ酸銀－アミン錯体を加熱するものではなかった。特許文献５においても、溶液に対してマイクロ波を照射して加熱する方法が開示されているが、粘性の高いシュウ酸銀－アミン錯体を加熱するものではなかった。 Moreover, in patent document 3 and 4, the microwave is irradiated and heated with respect to the liquid which disperse | distributed the metal oxide or the metal hydroxide in the organic solvent with the high microwave absorption (heating property). However, it did not heat the highly viscous silver oxalate-amine complex. Patent Document 5 discloses a method of heating a solution by irradiating microwaves, but it does not heat a highly viscous silver oxalate-amine complex.
本発明は、上記現状に鑑みてなされたものであり、粘性の高いシュウ酸銀－アミン錯体から粒度分布の狭い銀ナノ粒子を短時間で大量に製造することができる銀ナノ粒子の製造方法を提供することを目的とする。 The present invention has been made in view of the above situation, and a silver nanoparticle production method capable of producing a large amount of silver nanoparticles having a narrow particle size distribution in a short time from a highly viscous silver oxalate-amine complex. The purpose is to provide.
本発明者らは、銀ナノ粒子の製造方法について種々検討したところ、シュウ酸銀－アミン錯体から銀ナノ粒子を得る方法に着目した。しかしながら、シュウ酸銀－アミン錯体の粘性が高いために、オイルバス等の通常の方法では、仕込み量が増えるほど粒度分布の狭い銀ナノ粒子を短時間で製造することは困難であった。これに対して、本発明者らは、鋭意検討した結果、アルキルアミン及びアルコキシアミンのマイクロ波吸収性が良いことを見出し、アルキルアミン及びアルコキシアミンの少なくとも一方とマイクロ波照射による加熱とを組み合わせて還元を行なえば、僅か数分で銀ナノ粒子を合成できることを見出し、本発明を完成した。 The inventors of the present invention have studied various methods for producing silver nanoparticles, and have focused on a method for obtaining silver nanoparticles from a silver oxalate-amine complex. However, due to the high viscosity of the silver oxalate-amine complex, it has been difficult to produce silver nanoparticles with a narrow particle size distribution in a short time with an increase in the charged amount by a normal method such as an oil bath. On the other hand, as a result of intensive studies, the present inventors have found that microwave absorption of alkylamine and alkoxyamine is good, and combined at least one of alkylamine and alkoxyamine with heating by microwave irradiation. As a result of the reduction, it was found that silver nanoparticles could be synthesized in just a few minutes, and the present invention was completed.
本発明の銀ナノ粒子の製造方法は、アミンとシュウ酸銀とを混合し、シュウ酸銀にアミンが配位したシュウ酸銀－アミン錯体を得る混合工程と、上記シュウ酸銀－アミン錯体にマイクロ波を照射して加熱し、上記シュウ酸銀－アミン錯体の還元を行う加熱工程とを含み、上記アミンは、アルキルアミン及びアルコキシアミンの少なくとも一方から選択される少なくとも１種の化合物を含むことを特徴とする。 The method for producing silver nanoparticles of the present invention comprises a mixing step of mixing an amine and silver oxalate to obtain a silver oxalate-amine complex in which the amine is coordinated to silver oxalate, and the above silver oxalate-amine complex. Heating with microwave irradiation and reducing the silver oxalate-amine complex, wherein the amine contains at least one compound selected from at least one of alkylamines and alkoxyamines. It is characterized by.
本発明の銀ナノ粒子の製造方法は、上記混合工程と上記加熱工程との間に、上記シュウ酸銀－アミン錯体に溶媒を添加する工程を有してもよい。 The method for producing silver nanoparticles of the present invention may include a step of adding a solvent to the silver oxalate-amine complex between the mixing step and the heating step.
上記アミンは、炭素数５以下のアルキルアミン、及び、炭素数５以下のアルコキシアミンの少なくとも一方から選択される少なくとも１種の化合物を含むことが好ましい。 The amine preferably includes at least one compound selected from at least one of an alkylamine having 5 or less carbon atoms and an alkoxyamine having 5 or less carbon atoms.
本発明によれば、粘性の高いシュウ酸銀－アミン錯体から粒度分布の狭い銀ナノ粒子を短時間で大量に製造することができる。 According to the present invention, a large amount of silver nanoparticles having a narrow particle size distribution can be produced from a highly viscous silver oxalate-amine complex in a short time.
本発明の銀ナノ粒子の製造方法は、アミンとシュウ酸銀とを混合し、シュウ酸銀にアミンが配位したシュウ酸銀－アミン錯体を得る混合工程と、上記シュウ酸銀－アミン錯体にマイクロ波を照射して加熱し、上記シュウ酸銀－アミン錯体の還元を行う加熱工程とを含み、上記アミンは、アルキルアミン及びアルコキシアミンの少なくとも一方から選択される少なくとも１種の化合物を含むことを特徴とする。 The method for producing silver nanoparticles of the present invention comprises a mixing step of mixing an amine and silver oxalate to obtain a silver oxalate-amine complex in which the amine is coordinated to silver oxalate, and the above silver oxalate-amine complex. Heating with microwave irradiation and reducing the silver oxalate-amine complex, wherein the amine contains at least one compound selected from at least one of alkylamines and alkoxyamines. It is characterized by.
（混合工程）
本発明の銀ナノ粒子の製造方法は、アミンとシュウ酸銀とを混合し、シュウ酸銀にアミンが配位したシュウ酸銀－アミン錯体を得る混合工程を含む。 (Mixing process)
The method for producing silver nanoparticles of the present invention includes a mixing step of mixing an amine and silver oxalate to obtain a silver oxalate-amine complex in which the amine is coordinated with silver oxalate.
上記アミンは、アルキルアミン及びアルコキシアミンの少なくとも一方から選択される少なくとも１種の化合物を含む。具体的には、アルキルアミンに分類される１種類の化合物のみが用いられてもよいし、アルキルアミンに分類される２種類以上の化合物が用いられてもよいし、アルコキシアミンに分類される１種類の化合物のみが用いられてもよいし、アルコキシアミンに分類される２種類以上の化合物が用いられてもよいし、アルキルアミンに分類される１種類以上の化合物とアルコキシアミンに分類される１種類以上の化合物が併用されてもよい。 The amine includes at least one compound selected from at least one of alkylamine and alkoxyamine. Specifically, only one type of compound classified as an alkylamine may be used, two or more types of compounds classified as an alkylamine may be used, or 1 classified as an alkoxyamine. Only one type of compound may be used, two or more types of compounds classified as alkoxyamines may be used, or one or more types of compounds classified as alkylamines and 1 classified as alkoxyamines Two or more kinds of compounds may be used in combination.
また、シュウ酸銀と混合されるアミンは、アルキルアミン及びアルコキシアミンの少なくとも一方のみであることが好ましいが、加熱工程の前に還元反応を引き起こさないものであれば、アルキルアミン及びアルコキシアミン以外のアミンが添加されてもよい。例えば、アルカノールアミンのような水酸基を有するアミンは、配位子として用いるには極性が高く、配合量が多い場合は加熱工程の前に還元反応を引き起こしてしまう可能性がある。アルキルアミン及びアルコキシアミン以外のアミンが添加される場合には、使用するシュウ酸銀のｍｏｌ数に対して５当量以下にすることが好ましい。 Further, the amine mixed with silver oxalate is preferably at least one of alkylamine and alkoxyamine, but other than alkylamine and alkoxyamine as long as it does not cause a reduction reaction before the heating step. An amine may be added. For example, an amine having a hydroxyl group such as an alkanolamine is highly polar for use as a ligand, and if the amount is large, it may cause a reduction reaction before the heating step. When an amine other than alkylamine and alkoxyamine is added, it is preferably 5 equivalents or less based on the number of moles of silver oxalate used.
アルキルアミンは、分子内にアルキル基及びアミン官能基を有するものであればよく、分子内にアミン官能基を２つ有するジアミンであってもよい。また、アルキルアミンは、１級アミン、２級アミン及び３級アミンのいずれであってもよいが、錯体の形成を促進する観点から、１級アミンであることが好ましい。アルキル基は、直鎖状であっても分岐鎖状であってもよく、一部に飽和炭素環を含んでもよいが、直鎖状アルキルアミンが好適に用いられる。アルキルアミンの具体例としては、エチルアミン、プロピルアミン、ブチルアミン、ペンチルアミン、ヘキシルアミン、１，２－エタンジアミン、１，４－ブタンジアミン、１，５－ペンタンジアミン等が挙げられる。なかでも、錯体の形成を促進する観点及び極性の高い溶媒への分散性を高める観点からは、炭素数５以下のアルキルアミンが好適に用いられる。 The alkylamine may be any one having an alkyl group and an amine functional group in the molecule, and may be a diamine having two amine functional groups in the molecule. Further, the alkylamine may be any of primary amine, secondary amine, and tertiary amine, but is preferably a primary amine from the viewpoint of promoting the formation of a complex. The alkyl group may be linear or branched, and may partially contain a saturated carbocycle, but a linear alkylamine is preferably used. Specific examples of the alkylamine include ethylamine, propylamine, butylamine, pentylamine, hexylamine, 1,2-ethanediamine, 1,4-butanediamine, 1,5-pentanediamine and the like. Among these, alkylamines having 5 or less carbon atoms are preferably used from the viewpoint of promoting the formation of a complex and enhancing the dispersibility in a highly polar solvent.
アルコキシアミンは、分子内にアルコキシ基及びアミン官能基を有するものであればよい。また、アルコキシアミンは、１級アミン、２級アミン及び３級アミンのいずれであってもよいが、錯体の形成を促進する観点から、１級アミンであることが好ましい。アルコキシ基は、直鎖状であっても分岐鎖状であってもよく、一部に飽和炭素環又は不飽和炭素環を含んでもよいが、直鎖状アルコキシアミンが好適に用いられる。アルコキシアミンの具体例としては、例えば、Ｎ－（３－メトキシプロピル）プロパン－１，３－ジアミン、２－メトキシエチルアミン、３－メトキシプロピルアミン、３－エトキシプロピルアミン等が挙げられる。なかでも、錯体の形成を促進する観点及び極性の高い溶媒への分散性を高める観点からは、炭素数５以下のアルコキシアミンが好適に用いられる。 Any alkoxyamine may be used as long as it has an alkoxy group and an amine functional group in the molecule. Further, the alkoxyamine may be any of primary amine, secondary amine, and tertiary amine, but is preferably a primary amine from the viewpoint of promoting the formation of a complex. The alkoxy group may be linear or branched, and may partially contain a saturated carbocyclic ring or an unsaturated carbocyclic ring, but a linear alkoxyamine is preferably used. Specific examples of the alkoxyamine include N- (3-methoxypropyl) propane-1,3-diamine, 2-methoxyethylamine, 3-methoxypropylamine, 3-ethoxypropylamine and the like. Among these, from the viewpoint of promoting the formation of a complex and enhancing the dispersibility in a highly polar solvent, an alkoxyamine having 5 or less carbon atoms is preferably used.
上記シュウ酸銀は、最も単純なジカルボン酸銀であり、シュウ酸銀を用いて合成されるシュウ酸銀－アミン錯体は、低温かつ短時間で還元が進むことから、銀ナノ粒子（ナノメートルサイズの銀微粒子）の合成に好適である。更に、シュウ酸銀を用いると、合成時には副生成物が発生せず、系外にシュウ酸イオン由来の二酸化炭素が出るのみであるため、合成後に精製の手間が少ないという利点もある。 The silver oxalate is the simplest silver dicarboxylate, and the silver oxalate-amine complex synthesized using silver oxalate is reduced at a low temperature in a short time. This is suitable for the synthesis of silver fine particles. Further, when silver oxalate is used, no by-product is generated at the time of synthesis, and only carbon dioxide derived from oxalate ions is produced outside the system.
上記アミンと上記シュウ酸銀との混合比率としては、銀原子のモル数よりも上記アミンのモル数を多くすることが好ましく、銀原子１ｍｏｌに対して上記アミンを２ｍｏｌ以上添加することがより好ましい。これにより、還元によって生成される銀ナノ粒子の表面にアミンを適量付着させることができ、銀ナノ粒子に種々の分散媒に対する優れた分散性と低温焼結性とを付与することができる。 As a mixing ratio of the amine and the silver oxalate, it is preferable to increase the number of moles of the amine rather than the number of moles of silver atoms, and it is more preferable to add 2 moles or more of the amine to 1 mole of silver atoms. . As a result, an appropriate amount of amine can be attached to the surface of the silver nanoparticles produced by the reduction, and the silver nanoparticles can be provided with excellent dispersibility and low-temperature sinterability with respect to various dispersion media.
上記アミンと上記シュウ酸銀との混合方法は特に限定されないが、アミンとシュウ酸銀とが錯形成することで粘度が上昇することから、例えば、アミンとシュウ酸銀の混合液を、マグネティックスターラー等の回転体を用いて攪拌する方法が用いられる。攪拌は、室温（１０～３０℃）で行うことが好ましい。シュウ酸銀－アミン錯体が得られたことは、粘性のある白色の物質の生成により外見的に確認できる。 The mixing method of the amine and the silver oxalate is not particularly limited. However, since the viscosity increases due to the complex formation of the amine and silver oxalate, for example, a mixed solution of an amine and silver oxalate is used as a magnetic stirrer. A method of stirring using a rotating body such as is used. Stirring is preferably performed at room temperature (10 to 30 ° C.). The appearance of a silver oxalate-amine complex can be visually confirmed by the formation of a viscous white substance.
上記混合工程では、シュウ酸銀－アミン錯体の形成を妨げない範囲で、アミン及びシュウ酸銀以外の物質を添加してもよく、例えば、高分子分散剤を用いてもよい。高分子分散剤としては、市販されている高分子分散剤を使用することができる。市販の高分子分散剤としては、例えば、ソルスパース（ＳＯＬＳＰＥＲＳＥ）１１２００、ソルスパース１３９４０、ソルスパース１６０００、ソルスパース１７０００、ソルスパース１８０００、ソルスパース２００００、ソルスパース２４０００、ソルスパース２６０００、ソルスパース２７０００、ソルスパース２８０００（以上、日本ルーブリゾール社製）；ＤＩＳＰＥＲＢＹＫ－１０２、１１０、１１１、１７０、１９０．１９４Ｎ、２０１５、２０９０、２０９６（以上、ビックケミー・ジャパン社製）；ＥＦＫＡ－４６、ＥＦＫＡ－４７、ＥＦＫＡ－４８、ＥＦＫＡ－４９（以上、ＥＦＫＡケミカル社製）；ポリマー１００、ポリマー１２０、ポリマー１５０、ポリマー４００、ポリマー４０１、ポリマー４０２、ポリマー４０３、ポリマー４５０、ポリマー４５１、ポリマー４５２、ポリマー４５３（以上、ＥＦＫＡケミカル社製）；アジスパーＰＢ７１１、アジスパーＰＡ１１１、アジスパーＰＢ８１１、アジスパーＰＷ９１１（以上、味の素社製）；フローレンＤＯＰＡ－１５Ｂ、フローレンＤＯＰＡ－２２、フローレンＤＯＰＡ－１７、フローレンＴＧ－７３０Ｗ、フローレンＧ－７００、フローレンＴＧ－７２０Ｗ（以上、共栄社化学工業社製）；ＴＥＧＯ　Ｄｉｓｐｅｒｓシリーズの６１０、６１０Ｓ、６３０、６５１、６５５、７５０Ｗ、７５５Ｗ（エボニック社製）、ディスパロンシリーズのＤＡ－３７５、ＤＡ－１２００（楠本化成社製）等が挙げられる。 In the mixing step, substances other than amine and silver oxalate may be added as long as they do not interfere with the formation of the silver oxalate-amine complex. For example, a polymer dispersant may be used. A commercially available polymer dispersant can be used as the polymer dispersant. Examples of commercially available polymer dispersants include, for example, Solsperse 11200, Solsperse 13940, Solsperse 16000, Solsperse 17000, Solsperse 18000, Solsperse 20000, Solsperse 24000, Solsperse 26000, Solsperse 27000, Solsperse 28000 (above, Nippon Lubrizol Corporation) DISPERBYK-102, 110, 111, 170, 190.194N, 2015, 2090, 2096 (above, manufactured by Big Chemie Japan); EFKA-46, EFKA-47, EFKA-48, EFKA-49 (above, EFKA Chemical Co.); polymer 100, polymer 120, polymer 150, polymer 400, polymer 401, polymer 402, polymer 4 3, polymer 450, polymer 451, polymer 452, polymer 453 (manufactured by EFKA Chemical Co., Ltd.); Ajisper PB711, Ajisper PA111, Ajisper PB811, Ajisper PW911 (manufactured by Ajinomoto Co., Inc.); Florene DOPA-15B, Floren DOPA-22 , FLOREN DOPA-17, FLOREN TG-730W, FLOREN G-700, FLOREN TG-720W (above, manufactured by Kyoeisha Chemical Co., Ltd.); TEGO Dispers series 610, 610S, 630, 651, 655, 750W, 755W (Evonik) And Disparon series DA-375 and DA-1200 (Enomoto Kasei Co., Ltd.).
（溶媒添加工程）
本発明の銀ナノ粒子の製造方法は、混合工程と加熱工程との間に、シュウ酸銀－アミン錯体に溶媒を添加する工程を含んでもよい。シュウ酸銀－アミン錯体はペースト状の増粘物であることから、加熱前に溶媒を添加して粘度を下げておくことで、加熱工程後に得られる銀ナノ粒子の粒径をより小さなものとすることや、銀ナノ粒子の分散性の向上を図ることができる。 (Solvent addition process)
The method for producing silver nanoparticles of the present invention may include a step of adding a solvent to the silver oxalate-amine complex between the mixing step and the heating step. Since the silver oxalate-amine complex is a paste-like thickener, the particle size of the silver nanoparticles obtained after the heating step can be reduced by adding a solvent before heating to lower the viscosity. It is possible to improve the dispersibility of the silver nanoparticles.
上記溶媒としては、混合工程で得られたシュウ酸銀－アミン錯体を分散させ、粘度を低下させることができるものであれば特に限定されないが、導電性インクを作製する際の分散媒と相溶するもの（極性が近いもの）や、製造される銀ナノ粒子の良溶媒となり得る溶媒が好ましく、例えば、有機溶媒が用いられる。また、加熱工程の前にシュウ酸銀－アミン錯体の還元が生じると、加熱による均一な銀ナノ粒子の合成が妨げられるため、上記溶媒は、シュウ酸銀－アミン錯体に対して還元剤として作用しないものであることが望ましい。上記有機溶媒としては、例えば、Ｎ－メチルピロリドン、テルペン、ターピネオール（テルピネオール）、ジヒドロターピニルアセテート、イソホロン、トリプロピレングリコールジメチルエーテル、トルエン、トリデカン等の良溶媒が挙げられる。上記溶媒は、１種類のみが用いられてもよく、混合溶媒が用いられてもよい。 The solvent is not particularly limited as long as it can disperse the silver oxalate-amine complex obtained in the mixing step and reduce the viscosity. However, the solvent is compatible with the dispersion medium in producing the conductive ink. And a solvent that can be a good solvent for the silver nanoparticles to be produced, for example, an organic solvent is used. In addition, if the reduction of the silver oxalate-amine complex occurs before the heating step, the synthesis of uniform silver nanoparticles by heating is hindered, so that the solvent acts as a reducing agent for the silver oxalate-amine complex. It is desirable not to. Examples of the organic solvent include good solvents such as N-methylpyrrolidone, terpene, terpineol (terpineol), dihydroterpinyl acetate, isophorone, tripropylene glycol dimethyl ether, toluene, and tridecane. As for the said solvent, only 1 type may be used and a mixed solvent may be used.
なお、本発明の銀ナノ粒子の製造方法では、加熱工程においてシュウ酸銀－アミン錯体に溶媒を添加してもよい。 In the method for producing silver nanoparticles of the present invention, a solvent may be added to the silver oxalate-amine complex in the heating step.
なお、本発明の銀ナノ粒子の製造方法によれば、シュウ酸銀－アミン錯体自体を直接加熱することができることから、溶媒がほとんど含まれない増粘物の状態であっても、シュウ酸銀－アミン錯体の還元をシュウ酸銀基準で１００ｍｍｏｌ以上のスケールで行うことが容易であり、特に１ｍｏｌ以上の大スケールで行うことができる点において優れている。 According to the method for producing silver nanoparticles of the present invention, since the silver oxalate-amine complex itself can be directly heated, the silver oxalate can be used even in a thickened state containing almost no solvent. -It is easy to reduce the amine complex on a scale of 100 mmol or more based on silver oxalate, and is excellent in that it can be carried out on a large scale of 1 mol or more.
（加熱工程）
本発明の銀ナノ粒子の製造方法は、シュウ酸銀－アミン錯体にマイクロ波を照射して加熱し、シュウ酸銀－アミン錯体の還元を行う加熱工程を含む。本発明においては、マイクロ波の吸収性能の高いアルキルアミン及び／又はアルコキシアミンを用いることにより、還元剤を用いずに、マイクロ波の照射による加熱によってアミン錯体銀を還元反応により分解して銀を生成させることができる。また、シュウ酸銀は、炭酸銀やカルボキシル基を１つだけ有するカルボン酸に比べて、低温で還元反応を生じさせることができるので、マイクロ波の照射は短時間でよい。加熱工程における加熱の最高温度は、８０～１６０℃の範囲内であることが好ましく、より好ましくは１００～１３０℃である。加熱工程におけるマイクロ波照射時間は、合成スケールや単位時間当たりの照射量に依るが、３０分以内であることが好ましく、より好ましくは５分以内であり、更に好ましくは３分以内である。照射時間が３０分を超えると、特に短鎖の配位子が外れやすくなるため、生成する粒子が凝集し易くなり、分散安定性が低下するおそれがある。また、照射時間が長いほど、生産性が低下することになる。マイクロ波照射時間は、生産性の観点からは短い方がよく、還元反応が終われば直ちに照射を終了してよいが、通常は、１分以上行う。 (Heating process)
The method for producing silver nanoparticles of the present invention includes a heating step in which the silver oxalate-amine complex is heated by irradiation with microwaves to reduce the silver oxalate-amine complex. In the present invention, by using an alkylamine and / or alkoxyamine having a high microwave absorption performance, the amine complex silver is decomposed by a reduction reaction by heating by microwave irradiation without using a reducing agent, whereby silver is decomposed. Can be generated. Further, since silver oxalate can cause a reduction reaction at a lower temperature than silver carbonate or a carboxylic acid having only one carboxyl group, microwave irradiation can be performed in a short time. The maximum heating temperature in the heating step is preferably in the range of 80 to 160 ° C, more preferably 100 to 130 ° C. The microwave irradiation time in the heating step depends on the synthesis scale and the irradiation amount per unit time, but is preferably within 30 minutes, more preferably within 5 minutes, and even more preferably within 3 minutes. When the irradiation time exceeds 30 minutes, short-chain ligands are particularly likely to be detached, so that generated particles are likely to aggregate and dispersion stability may be lowered. In addition, the longer the irradiation time, the lower the productivity. The microwave irradiation time is preferably short from the viewpoint of productivity, and irradiation may be terminated immediately after the reduction reaction is completed, but it is usually performed for 1 minute or longer.
ところで、シュウ酸銀とアミンからなるアミン錯体銀は、常温での粘性が非常に高い。このため、特に１００ｍｍｏｌ以上の大容量の合成を行う場合には、攪拌が困難であり、オイルバスやヒーター等の伝熱加熱を用いた場合には、温度上昇により粘性が低下して充分に攪拌できるようになるまでの加熱初期の段階（系内温度が９０℃近くまで）で、加熱ムラが特に大きくなってしまう。したがって、反応容器の壁面近傍では還元反応が生じるが、反応容器の中心部は温まりにくいため、粒子の核生成が系内で不均一になり、粗大粒子が発生しやすくなる。また、シュウ酸銀とアミンからなるアミン錯体銀は増粘性であるため、液系の出発原料を用いたとしても、系内の温度ムラを抑制することは困難である。更に、超音波のような他の方法では、温度上昇がさせ難くシュウ酸銀－アミン錯体を還元させることはできない。これに対して、マイクロ波の照射によれば、反応容器の壁面側からの伝熱を利用せず、壁面近傍と中心部を同時に加熱できることから、粘性の高いシュウ酸銀－アミン錯体であっても系内を均一に加熱することができる。すなわち、シュウ酸銀とアルキルアミン及び／又はアルコキシアミンとの組み合わせは、マイクロ波照射という簡便な方法を用いて粒度分布の狭い銀ナノ粒子を短時間で製造できる点において、最適なものである。 By the way, amine complex silver composed of silver oxalate and amine has very high viscosity at room temperature. For this reason, stirring is particularly difficult when synthesizing a large volume of 100 mmol or more, and when heat transfer heating such as an oil bath or a heater is used, the viscosity decreases due to the temperature rise and sufficient stirring is performed. In the initial stage of heating (until the system temperature is close to 90 ° C.) until it becomes possible, the heating unevenness becomes particularly large. Therefore, a reduction reaction occurs in the vicinity of the wall surface of the reaction vessel, but the central part of the reaction vessel is difficult to warm, so that nucleation of particles becomes uneven in the system, and coarse particles are likely to be generated. Further, since amine complex silver composed of silver oxalate and amine is thickened, it is difficult to suppress temperature unevenness in the system even if a liquid starting material is used. Furthermore, it is difficult to raise the temperature by other methods such as ultrasonic waves, and the silver oxalate-amine complex cannot be reduced. On the other hand, the microwave irradiation enables the heating of the vicinity of the wall and the central part at the same time without using heat transfer from the wall surface of the reaction vessel. Also, the inside of the system can be heated uniformly. That is, the combination of silver oxalate and alkylamine and / or alkoxyamine is optimal in that silver nanoparticles having a narrow particle size distribution can be produced in a short time using a simple method of microwave irradiation.
また、シュウ酸銀－アミン錯体をアミンの存在下で熱分解することで、アミンにより被覆された銀ナノ粒子を製造する熱分解法においては、単一種の分子である銀アミン錯体の分解反応により銀原子が生成するため、反応系内に均一に銀原子を生成することが可能であり、複数の成分間の反応により銀原子を生成する場合に比較して、反応を構成する成分の組成揺らぎに起因する反応の不均一が抑制され、特に工業的規模で多量の銀ナノ粒子を製造する際に有利である。 In the thermal decomposition method for producing silver nanoparticles coated with amine by thermally decomposing silver oxalate-amine complex in the presence of amine, a decomposition reaction of silver amine complex, which is a single kind of molecule, is performed. Since silver atoms are generated, it is possible to generate silver atoms uniformly in the reaction system. Compared to the case where silver atoms are generated by the reaction between multiple components, the composition fluctuation of the components constituting the reaction The heterogeneity of the reaction due to the is suppressed, and this is particularly advantageous when producing a large amount of silver nanoparticles on an industrial scale.
また、生成した銀原子は凝集して銀ナノ粒子を形成するが、上記熱分解法により生成した銀原子にはアミン分子が配位結合していることから、銀原子に配位したアミン分子の働きにより凝集を生じる際の銀原子の運動がコントロールされるものと推察される。この結果として、非常に微細で、粒度分布が狭い銀ナノ粒子を製造することが可能となる。 In addition, the generated silver atoms aggregate to form silver nanoparticles, but since amine molecules are coordinated to the silver atoms generated by the above thermal decomposition method, the amine molecules coordinated to the silver atoms It is presumed that the movement of silver atoms when aggregation occurs due to the action is controlled. As a result, it is possible to produce silver nanoparticles that are very fine and have a narrow particle size distribution.
本発明の銀ナノ粒子の製造方法によれば、上記加熱工程を行うことにより、平均粒子径が１μｍ以下の銀ナノ粒子が得られる。銀ナノ粒子の粒子径がナノメートルサイズであると、融点降下が生じ、低温で焼成できる。また、印刷法を用いて、例えば線幅が５μｍ以下の微細な導電性パターンを形成することができる。得られる銀ナノ粒子の平均粒子径は、１～２００ｎｍであることが好ましい。銀ナノ粒子の平均粒子径が２００ｎｍ以下であれば、銀ナノ粒子の分散性が経時的に変化しにくい。 According to the method for producing silver nanoparticles of the present invention, silver nanoparticles having an average particle diameter of 1 μm or less can be obtained by performing the heating step. When the particle diameter of the silver nanoparticles is nanometer size, a melting point drop occurs and the silver nanoparticles can be fired at a low temperature. In addition, a fine conductive pattern having a line width of, for example, 5 μm or less can be formed by using a printing method. The average particle diameter of the obtained silver nanoparticles is preferably 1 to 200 nm. If the average particle diameter of the silver nanoparticles is 200 nm or less, the dispersibility of the silver nanoparticles is unlikely to change over time.
得られる銀ナノ粒子は、平均粒子径が２００ｎｍを超え、１μｍ以下の粒子を含有してもよい。また、得られる銀ナノ粒子は、平均粒子径が１～２００ｎｍであるナノサイズ粒子と、平均粒子径が２００ｎｍを超え、１μｍ以下のサブミクロンサイズ粒子とを含有してもよい。ナノサイズ粒子とサブミクロンサイズ粒子とを併用することで、ナノサイズ粒子がサブミクロンサイズ粒子の周囲で融点降下することにより、サブミクロンサイズ粒子のみを用いた場合よりも、良好な導電パスを形成させることができる。更に、上記加熱工程で得られる銀ナノ粒子は、平均粒子径が１μｍを超えるミクロンサイズ粒子を含んでいてもよく、必要に応じて、加熱工程後に除去される。 The obtained silver nanoparticles may contain particles having an average particle diameter of more than 200 nm and 1 μm or less. Further, the obtained silver nanoparticles may contain nano-sized particles having an average particle diameter of 1 to 200 nm and submicron-sized particles having an average particle diameter of more than 200 nm and 1 μm or less. By using nano-sized particles and sub-micron-sized particles together, the nano-sized particles have a lower melting point around the sub-micron-sized particles, thereby forming a better conductive path than when using only sub-micron-sized particles. Can be made. Furthermore, the silver nanoparticles obtained in the heating step may contain micron-sized particles having an average particle diameter of more than 1 μm, and are removed after the heating step, if necessary.
銀ナノ粒子の平均粒子径は、動的光散乱法、小角Ｘ線散乱法、広角Ｘ線回折法で測定することができる。本明細書中、「平均粒子径」とは、分散メジアン径をいう。分散メジアン径は、動的光散乱法（Ｄｙｎａｍｉｃ　Ｌｉｇｈｔ　Ｓｃａｔｔｅｒｉｎｇ）にて、粒子径基準を体積基準として、分散粒径を得ることで算出される。 The average particle diameter of the silver nanoparticles can be measured by a dynamic light scattering method, a small angle X-ray scattering method, or a wide angle X-ray diffraction method. In the present specification, the “average particle diameter” refers to a dispersion median diameter. The dispersed median diameter is calculated by obtaining a dispersed particle diameter with a dynamic light scattering method (Dynamic Light Scattering) using the particle diameter standard as a volume standard.
また、上記加熱工程で得られる銀ナノ粒子の表面には、アルキルアミン及び／又はアルコキシアミンの分子が比較的弱い結合により付着し、銀ナノ粒子の表面に保護被膜が形成される。保護被膜は、銀ナノ粒子同士の凝集を防止するとともに、保護被膜で被覆された銀ナノ粒子が無機コロイド粒子を構成することから、保存安定性に優れる。また、上記保護被膜を形成するアルキルアミン及び／又はアルコキシアミンは、加熱等により容易に脱離可能であるため、低温で焼結可能な銀ナノ粒子を製造することが可能となる。 In addition, alkylamine and / or alkoxyamine molecules adhere to the surface of the silver nanoparticles obtained in the heating step by a relatively weak bond, and a protective film is formed on the surface of the silver nanoparticles. The protective coating prevents aggregation of silver nanoparticles and is excellent in storage stability because the silver nanoparticles coated with the protective coating constitute inorganic colloidal particles. Moreover, since the alkylamine and / or alkoxyamine forming the protective film can be easily removed by heating or the like, silver nanoparticles that can be sintered at a low temperature can be produced.
上記のようにして得られた銀ナノ粒子を含む分散液には、銀ナノ粒子の他に、金属塩の対イオン、分散剤の残留物等が存在しており、液全体の電解質濃度や有機物濃度が高い傾向にある。このような状態の液は、電導度が高い等の理由で銀ナノ粒子の凝析が起こり、沈殿し易い。または、沈殿しなくても、金属塩の対イオン、分散に必要な量以上の過剰な分散剤等が残留していると、導電性を悪化させるおそれがある。そこで、上記加熱工程の後に、銀ナノ粒子を含む分散液を洗浄して余分な残留物を取り除く洗浄工程を実施することが好ましい。 In addition to silver nanoparticles, the dispersion containing silver nanoparticles obtained as described above contains a metal salt counterion, a residue of a dispersant, etc. Concentration tends to be high. The liquid in such a state is likely to precipitate due to aggregation of silver nanoparticles due to high electrical conductivity. Or, even if it does not precipitate, if the counter ion of the metal salt, excessive dispersant or the like more than the amount necessary for dispersion remains, there is a possibility that the conductivity is deteriorated. Therefore, after the heating step, it is preferable to carry out a washing step of washing the dispersion containing silver nanoparticles to remove excess residues.
上記洗浄工程における洗浄方法としては、例えば、表面の少なくとも一部を有機成分で被覆された銀ナノ粒子を含む分散液を一定時間静置し、上澄み液を取り除いた後、銀ナノ粒子を沈殿させる溶媒（例えば、水、メタノール、メタノール／水混合溶媒等）を加えて撹枠し、再度一定期間静置して上澄み液を取り除く処理を幾度か繰り返すものが挙げられる。他の洗浄方法としては、上記の静置の代わりに遠心分離を行う方法、限外濾過装置やイオン交換装置等により脱塩する方法等が挙げられる。 As a cleaning method in the above-described cleaning step, for example, a dispersion containing silver nanoparticles having at least a part of the surface coated with an organic component is allowed to stand for a certain period of time, and after removing the supernatant liquid, silver nanoparticles are precipitated. A solvent (for example, water, methanol, methanol / water mixed solvent, etc.) is added, and the mixture is stirred and left standing again for a certain period to remove the supernatant liquid several times. Examples of other washing methods include a method of performing centrifugation instead of the above standing, a method of desalting with an ultrafiltration device, an ion exchange device, and the like.
銀ナノ粒子の不揮発分全体に対する銀原子の重量比率は、９０重量％以上であることが好ましい。上記不揮発分とは、溶媒以外の成分をいい、銀ナノ粒子の他に、銀ナノ粒子を被覆する有機成分、高分子分散剤等が含まれる。銀原子の重量比率が９０重量％以上であることで、銀含有率の高い導電性パターンを形成することができる。 The weight ratio of silver atoms to the entire nonvolatile content of the silver nanoparticles is preferably 90% by weight or more. The non-volatile content refers to components other than the solvent, and includes, in addition to silver nanoparticles, organic components that coat silver nanoparticles, polymer dispersants, and the like. When the weight ratio of silver atoms is 90% by weight or more, a conductive pattern having a high silver content can be formed.
得られた銀ナノ粒子は、水、有機溶媒、分散剤、オリゴマー成分、界面活性剤、増粘剤、表面張力調整剤等の任意成分と混合され、使用目的に応じた適度な粘性、密着性、乾燥性、表面張力、印刷性等の機能が付与された銀ナノ粒子分散体とされ、例えば、プリンテッドエレクトロニクス技術で利用される導電インクを得ることができる。このような銀ナノ粒子分散体は、インクジェット法、フレキソ法、スクリーン印刷、グラビアオフセット印刷等の印刷法やディスペンサーを用いて、基材上に塗布し、更に焼成することで、導電性パターンを形成することができる。導電性パターンとしては、例えば、電子回路基板上に形成される電子回路を構成する配線が挙げられる。 The obtained silver nanoparticles are mixed with optional components such as water, organic solvents, dispersants, oligomer components, surfactants, thickeners, surface tension modifiers, etc., and have appropriate viscosity and adhesion depending on the purpose of use. In addition, a silver nanoparticle dispersion provided with functions such as drying, surface tension, and printability can be obtained, and, for example, a conductive ink used in printed electronics technology can be obtained. Such a silver nanoparticle dispersion is applied onto a substrate using a printing method such as an inkjet method, a flexo method, screen printing, gravure offset printing, or a dispenser, and further baked to form a conductive pattern. can do. As the conductive pattern, for example, wiring constituting an electronic circuit formed on the electronic circuit board can be cited.
上記焼成を行う方法は特に限定されるものではなく、例えば従来公知のギヤオーブン等を用いることができる。上記焼成の温度は、１４０℃未満であることが好ましく、１２０℃以下であることがより好ましい。導電性パターンの体積抵抗値は、焼成の温度と時間によって制御できるが、本発明で得られる銀ナノ粒子は、１４０℃未満の温度で焼成しても銀ナノ粒子同士を焼結（ネッキング）させることができ、優れた導電性を有する導電性パターンを形成できることから、比較的熱に弱い基材上にも形成できる。上記焼成の温度の下限は必ずしも限定されず、基材上に導電性パターンを形成できる温度であって、かつ、有機成分等を蒸発又は分解により除去できる温度であることが好ましい。また、焼成時間は特に限定されず、焼成温度に応じて適宜調整することができる。 The method for performing the firing is not particularly limited, and for example, a conventionally known gear oven or the like can be used. The firing temperature is preferably less than 140 ° C, and more preferably 120 ° C or less. Although the volume resistance value of the conductive pattern can be controlled by the firing temperature and time, the silver nanoparticles obtained in the present invention sinter (neck) the silver nanoparticles even when fired at a temperature of less than 140 ° C. In addition, since a conductive pattern having excellent conductivity can be formed, it can be formed on a substrate that is relatively weak against heat. The lower limit of the firing temperature is not necessarily limited, and is preferably a temperature at which a conductive pattern can be formed on a substrate and an organic component or the like can be removed by evaporation or decomposition. Further, the firing time is not particularly limited, and can be appropriately adjusted according to the firing temperature.
本発明により得られる導電性パターンの体積抵抗値は、１１０μΩ・ｃｍ以下であることが好ましく、１００μΩ・ｃｍ以下であることがより好ましく、５０μΩ・ｃｍ以下であることが更に好ましい。上記体積抵抗値は、下記式（１）に基づき算出される。
式（１）：（体積抵抗値）＝（抵抗値）×（被膜幅）×（被膜厚さ）／（端子間距離）＝（表面抵抗値）×（被膜厚さ） The volume resistance value of the conductive pattern obtained by the present invention is preferably 110 μΩ · cm or less, more preferably 100 μΩ · cm or less, and further preferably 50 μΩ · cm or less. The volume resistance value is calculated based on the following formula (1).
Formula (1): (Volume resistance value) = (resistance value) × (film width) × (film thickness) / (distance between terminals) = (surface resistance value) × (film thickness)
上記焼成工程後の導電性パターンの被膜厚さは、例えば、０．１～５μｍであり、好ましくは０．１～１μｍである。 The film thickness of the conductive pattern after the firing step is, for example, 0.1 to 5 μm, preferably 0.1 to 1 μm.
以下、本発明について実施例を掲げて更に詳しく説明するが、本発明はこれらの実施例のみに限定されるものではない。 EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail about this invention, this invention is not limited only to these Examples.
＜実施例１＞
３－メトキシプロピルアミン（和光純薬工業社製、試薬一級、炭素数：４）９．０ｇと、高分子分散剤（ビックケミー・ジャパン社製、「ＤＩＳＰＥＲＢＹＫ－１０２」）０．２ｇとを混合し、マグネティックスターラーにてよく撹拌してアミン混合液を作製した。次いで、撹拌を行いながら、シュウ酸銀３．０ｇ（１０ｍｍｏｌ）を添加した。シュウ酸銀の添加後、室温で攪拌を続けることでシュウ酸銀を粘性のある白色の物質へと変化させ、当該変化が外見的に終了したと認められる時点で撹拌を終了した（混合工程）。 <Example 1>
9.0 g of 3-methoxypropylamine (manufactured by Wako Pure Chemical Industries, Ltd., first grade reagent, carbon number: 4) and 0.2 g of a polymer dispersant (manufactured by Big Chemie Japan, “DISPERBYK-102”) are mixed. Then, the mixture was thoroughly stirred with a magnetic stirrer to prepare an amine mixture. Next, 3.0 g (10 mmol) of silver oxalate was added while stirring. After the addition of silver oxalate, stirring was continued at room temperature to change the silver oxalate to a viscous white substance, and stirring was terminated when the change was found to be apparently finished (mixing step) .
得られた混合液をマイクロ波加熱装置（四国計測工業株式会社製、「μＲｅａｃｔｏｒＥＸ」）に移し、出力自動制御モードにて系内のピーク温度を１２０℃に設定し、３０℃／ｍｉｎの昇温プロファイルにして混合液の加熱を行った。炭酸ガスの吹き出しにより銀ナノ粒子の合成状況を確認し、混合液の加熱を３分間で終了し、銀ナノ粒子の懸濁液を得た（加熱工程）。 The obtained mixed solution was transferred to a microwave heating device (“μReactor EX” manufactured by Shikoku Keiki Kogyo Co., Ltd.), the peak temperature in the system was set to 120 ° C. in the output automatic control mode, and the temperature was raised by 30 ° C./min. The mixture was heated to a profile. The synthesis state of the silver nanoparticles was confirmed by blowing carbon dioxide gas, and the heating of the mixed solution was finished in 3 minutes to obtain a suspension of silver nanoparticles (heating process).
次に、懸濁液の分散媒を置換するため、メタノールと水の混合溶媒１０ｍＬを加えて撹拌後、遠心分離により銀ナノ粒子を沈殿させて分離し、分離した銀ナノ粒子に対してメタノールと水の混合溶媒１０ｍＬを加え、撹拌、遠心分離を行うことで銀ナノ粒子を沈殿させて精製分離し、分離したものを室温で２０分間乾燥してスラリーを得た。得られたスラリー５０重量部に対して、同重量部のエタノール（和光純薬工業社製試薬）を添加しマグネティックスターラー上で撹拌しエタノール中に分散させた。その後、遠心分離を行い、粗大分の除去を行った後、上澄みを回収し、銀ナノ粒子を含む導電性インクを得た。 Next, in order to replace the dispersion medium of the suspension, 10 mL of a mixed solvent of methanol and water is added and stirred, and then silver nanoparticles are precipitated and separated by centrifugation. 10 mL of a mixed solvent of water was added, silver nanoparticles were precipitated and purified by stirring and centrifuging, and the separated was dried at room temperature for 20 minutes to obtain a slurry. To 50 parts by weight of the obtained slurry, the same part by weight of ethanol (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) was added, stirred on a magnetic stirrer, and dispersed in ethanol. Then, after centrifugal separation and removal of coarse components, the supernatant was recovered to obtain a conductive ink containing silver nanoparticles.
＜実施例２＞
使用する原料の量を１０倍スケールにしたこと以外は実施例１と同様にして、銀ナノ粒子を含む導電性インクを得た。具体的には、３－メトキシプロピルアミンを９０．０ｇ、高分子分散剤を２．０ｇ、シュウ酸銀を３０．４ｇ、洗浄時の溶媒を１００ｍＬにした。 <Example 2>
A conductive ink containing silver nanoparticles was obtained in the same manner as in Example 1 except that the amount of raw material used was scaled 10 times. Specifically, 90.0 g of 3-methoxypropylamine, 2.0 g of the polymer dispersant, 30.4 g of silver oxalate, and 100 mL of the solvent during washing were used.
＜実施例３＞
使用する原料の量を１００倍スケールにし、混合液の加熱を５分間行ったこと以外は実施例１と同様にして、銀ナノ粒子を含む導電性インクを得た。具体的には、３－メトキシプロピルアミンを９００．０ｇ、高分子分散剤を２０．０ｇ、シュウ酸銀を３０４．０ｇ、洗浄時の溶媒を１０００ｍＬにした。 <Example 3>
A conductive ink containing silver nanoparticles was obtained in the same manner as in Example 1 except that the amount of the raw material used was scaled 100 times and the mixture was heated for 5 minutes. Specifically, 900.0 g of 3-methoxypropylamine, 20.0 g of the polymer dispersant, 304.0 g of silver oxalate, and 1000 mL of the solvent during washing were used.
＜実施例４＞
実施例３と同様にしてシュウ酸銀を３０４．０ｇ加え、室温で攪拌を続けることでシュウ酸銀を粘性のある白色の物質へと変化させ終わった後、Ｎ－メチルピロリドン（和光純薬工業社製、試薬一級）を５８０．０ｇ加えたこと以外は実施例３と同様にして、銀ナノ粒子を含む導電性インクを得た。 <Example 4>
In the same manner as in Example 3, 304.0 g of silver oxalate was added and stirring was continued at room temperature to finish changing the silver oxalate to a viscous white substance. Then, N-methylpyrrolidone (Wako Pure Chemical Industries, Ltd.) A conductive ink containing silver nanoparticles was obtained in the same manner as in Example 3 except that 580.0 g of Reagent Grade 1 manufactured by KK were added.
＜実施例５＞
アミン混合液の作製に用いる３－メトキシプロピルアミン９．０ｇをペンチルアミン９．０ｇ（和光純薬工業社製、試薬一級、炭素数：５）に変更したこと以外は実施例１と同様にして、銀ナノ粒子を含む導電性インクを得た。 <Example 5>
The same procedure as in Example 1 was conducted except that 9.0 g of 3-methoxypropylamine used for preparation of the amine mixture was changed to 9.0 g of pentylamine (manufactured by Wako Pure Chemical Industries, reagent grade 1, carbon number: 5). A conductive ink containing silver nanoparticles was obtained.
＜比較例１＞
混合液の加熱方法をマイクロ波加熱からオイルバスに変更し、１２０℃で１５分間オイルバスにより加熱したこと以外は実施例１と同様にして、銀ナノ粒子を含む導電性インクを得た。 <Comparative Example 1>
A conductive ink containing silver nanoparticles was obtained in the same manner as in Example 1 except that the heating method of the mixed solution was changed from microwave heating to an oil bath and heated in an oil bath at 120 ° C. for 15 minutes.
＜比較例２＞
混合液の加熱方法をマイクロ波加熱からオイルバスに変更し、１２０℃で１５分間オイルバスにより加熱したこと以外は実施例２と同様にして、銀ナノ粒子を含む導電性インクを得た。 <Comparative example 2>
A conductive ink containing silver nanoparticles was obtained in the same manner as in Example 2 except that the heating method of the mixed solution was changed from microwave heating to an oil bath and heated in an oil bath at 120 ° C. for 15 minutes.
＜評価試験＞
実施例及び比較例で作製した導電性インクについて、下記の方法により評価した。その結果を下記表１に示した。 <Evaluation test>
The conductive inks produced in the examples and comparative examples were evaluated by the following methods. The results are shown in Table 1 below.
（１） 分散メジアン径
導電性インクをエタノールで１００倍に希釈した試料を堀場製作所社製の動的光散乱式粒径分布測定装置（型番：ＬＢ－５５０）を用い、動的光散乱法（Ｄｙｎａｍｉｃ　Ｌｉｇｈｔ　Ｓｃａｔｔｅｒｉｎｇ）にて測定し、分散粒径を得た。測定時の溶媒屈折率は１．３６１とした。
（判定基準）
○：メジアン径４０ｎｍ以下
△：メジアン径４０ｎｍ超～５０ｎｍ以下
×：メジアン径５０ｎｍ超 (1) Using a dynamic light scattering type particle size distribution measuring apparatus (model number: LB-550) manufactured by HORIBA, Ltd., a sample obtained by diluting a dispersion median diameter conductive ink 100 times with ethanol is used. Measured by Dynamic Light Scattering) to obtain a dispersed particle size. The solvent refractive index at the time of measurement was 1.361.
(Criteria)
○: Median diameter 40 nm or less Δ: Median diameter 40 nm to 50 nm or less ×: Median diameter 50 nm or more
（２）分散性
導電性インクを分散媒で２倍希釈してから容器中に静置し、室温で１日放置後、沈殿の有無及び上澄みの状態を目視で観察することにより、分散性を評価した。
（判定基準）
○：容器下に沈降物がほとんど認められなかった
×：容器上下で明らかに濃度差があり、沈降物がはっきり認められた (2) The dispersible conductive ink is diluted twice with a dispersion medium, and then left in a container. After standing at room temperature for 1 day, the presence or absence of precipitation and the state of the supernatant are visually observed, thereby improving dispersibility. evaluated.
(Criteria)
○: Almost no sediment was observed under the container ×: There was a clear difference in concentration between the top and bottom of the container, and the sediment was clearly recognized
（３）希釈性
導電性インクを分散媒に１００倍希釈したときの分散性を目視で評価した。評価は、希釈直後と希釈後１週間の時点で行った。
（判定基準）
○：分散した
△：一部凝集や銀の析出が見られた
×：凝集・沈殿が生じた (3) Dispersibility The dispersibility when the conductive ink was diluted 100 times in a dispersion medium was visually evaluated. Evaluation was performed immediately after dilution and at one week after dilution.
(Criteria)
○: Dispersed △: Partial aggregation or silver precipitation was observed ×: Aggregation / precipitation occurred
（４）体積抵抗値
２５ｍｍ×２５ｍｍのスライドガラス上に、スピンコート法により２０００ｒｐｍ×１５秒の条件で導電性インクを塗布し、その後ギヤオーブン中で１２０℃、３０分間の条件で加熱・焼成することにより焼結させ、導電性被膜を形成した。この被膜の表面抵抗値を抵抗率計（三菱化学アナリテック社製、「ロレスタ」、四深針方式）で測定し表面抵抗値を得た。次いで、厚みをレーザー顕微鏡（キーエンス社製）で測定した。そして、以下の式に基づき、表面抵抗値と導電性被膜の厚みから体積抵抗値を換算した。
式：体積抵抗値（Ω・ｃｍ）＝表面抵抗値（Ω／□）×被膜厚さ（μｍ）／１００００ (4) A conductive ink is applied on a slide glass having a volume resistance value of 25 mm × 25 mm by spin coating under the condition of 2000 rpm × 15 seconds, and then heated and baked in a gear oven at 120 ° C. for 30 minutes. To form a conductive film. The surface resistance value of this film was measured with a resistivity meter ("Loresta", manufactured by Mitsubishi Chemical Analytech Co., Ltd., four deep needle method) to obtain a surface resistance value. Subsequently, the thickness was measured with a laser microscope (manufactured by Keyence Corporation). And based on the following formula | equation, the volume resistance value was converted from the surface resistance value and the thickness of the conductive film.
Formula: Volume resistance value (Ω · cm) = surface resistance value (Ω / □) × film thickness (μm) / 10000
（５）合成時間
加熱工程における加熱に要した時間を生産性の観点から以下のように評価した。
（判定基準）
○：５分以内
△：５分超～１５分以内 (5) Synthesis time The time required for heating in the heating step was evaluated as follows from the viewpoint of productivity.
(Criteria)
○: Within 5 minutes △: Over 5 minutes to 15 minutes
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
表１から分かるように、実施例１～５では、マイクロ波を用いることで急速加熱することができ、合成時間を大幅に短縮することができた。また、マイクロ波加熱によれば、反応容器の壁面近傍と中心部を同時に加熱し、粘性のある混合液をムラなく加熱することができたので、分散メジアン径の小さい銀ナノ粒子を製造することができた。更に、実施例１～５において得られた銀ナノ粒子は、分散性及び希釈性が良好であり、低温（１２０℃）で焼成したときの体積抵抗値が低いものであった。 As can be seen from Table 1, in Examples 1 to 5, rapid heating was possible by using microwaves, and the synthesis time could be greatly shortened. In addition, according to microwave heating, the vicinity of the wall and the center of the reaction vessel were heated at the same time, and the viscous mixed liquid could be heated evenly, so that silver nanoparticles having a small dispersed median diameter were produced. I was able to. Furthermore, the silver nanoparticles obtained in Examples 1 to 5 had good dispersibility and dilutability, and had a low volume resistance when fired at a low temperature (120 ° C.).
また、実施例３及び４の結果から、マイクロ波を用いる場合には、シュウ酸銀基準で１ｍｏｌ以上に合成スケールを大きくしても、短時間で小粒径の銀ナノ粒子を製造できることが分かった。実施例４では、錯体合成時に溶媒を添加したことにより、混合液の粘性を低下させ、より均一に加熱することができたので、実施例３よりも分散メジアン径が小さく、希釈性に優れた銀ナノ粒子を製造することができた。 Further, from the results of Examples 3 and 4, it is understood that when microwaves are used, even if the synthesis scale is increased to 1 mol or more based on silver oxalate, small-sized silver nanoparticles can be produced in a short time. It was. In Example 4, the solvent was added during the synthesis of the complex, so that the viscosity of the mixed solution was reduced and the mixture could be heated more uniformly. Therefore, the dispersion median diameter was smaller than in Example 3 and the dilution was excellent. Silver nanoparticles could be produced.
一方、比較例１及び２では、オイルバスを用いたため、合成時間が長くなった。また、オイルバスでは合成スケールが大きくなると、反応容器の壁面近傍と中心部との加熱ムラが発生するため、比較例２では、得られた銀ナノ粒子の分散メジアン径が大きく、分散性及び希釈性が悪化した。 On the other hand, in Comparative Examples 1 and 2, since the oil bath was used, the synthesis time was long. In addition, in the oil bath, when the synthetic scale becomes large, uneven heating occurs in the vicinity of the wall surface and the central portion of the reaction vessel. Therefore, in Comparative Example 2, the dispersion median diameter of the obtained silver nanoparticles is large, dispersibility and dilution. Sex deteriorated.
（付記）
本発明の銀ナノ粒子の製造方法は、粘性の高いシュウ酸銀－アミン錯体を加熱ムラなく均一に加熱するためにマイクロ波を照射する点に特徴があるが、上記溶媒添加工程のように、シュウ酸銀－アミン錯体に溶媒を添加することによっても、シュウ酸銀－アミン錯体の粘度を下げることが可能である。アミンとシュウ酸銀とを混合し、シュウ酸銀にアミンが配位したシュウ酸銀－アミン錯体を得る混合工程と、上記シュウ酸銀－アミン錯体に溶媒を添加する溶媒添加工程と、上記シュウ酸銀－アミン錯体を加熱し、上記シュウ酸銀－アミン錯体の還元を行う加熱工程とを含み、上記アミンは、アルキルアミン及びアルコキシアミンの少なくとも一方から選択される少なくとも１種の化合物を含む銀ナノ粒子の製造方法（以下、「本発明の第二の銀ナノ粒子の製造方法」ともいう）もまた、加熱工程における加熱ムラを効果的に防止することができ、粘性の高いシュウ酸銀－アミン錯体から粒度分布の狭い銀ナノ粒子を短時間で大量に製造する方法として有用である。また、製造される銀ナノ粒子の良溶媒となり得る溶媒を加熱前又は加熱中に予め添加しておくことで粒子の粗大化を防止できる。 (Appendix)
The method for producing silver nanoparticles of the present invention is characterized in that microwaves are irradiated to uniformly heat a highly viscous silver oxalate-amine complex without heating unevenness. The viscosity of the silver oxalate-amine complex can also be reduced by adding a solvent to the silver oxalate-amine complex. A mixing step of mixing an amine and silver oxalate to obtain a silver oxalate-amine complex in which the amine is coordinated to silver oxalate; a solvent addition step of adding a solvent to the silver oxalate-amine complex; A heating step of heating an acid silver-amine complex and reducing the silver oxalate-amine complex, wherein the amine contains at least one compound selected from at least one of alkylamine and alkoxyamine. The method for producing nanoparticles (hereinafter also referred to as “the method for producing the second silver nanoparticles of the present invention”) can also effectively prevent uneven heating in the heating step, and is highly viscous silver oxalate— It is useful as a method for producing a large amount of silver nanoparticles having a narrow particle size distribution in a short time from an amine complex. Moreover, the coarsening of a particle | grain can be prevented by adding in advance the solvent which can become a good solvent of the silver nanoparticle manufactured before or during a heating.
なお、本発明の第二の銀ナノ粒子の製造方法では、加熱工程が溶媒添加工程を兼ねてもよい。すなわち、シュウ酸銀－アミン錯体の加熱を溶媒の添加と並行して行ってもよい。また、本発明の第二の銀ナノ粒子の製造方法では、混合工程が溶媒添加工程を兼ねてもよい。すなわち、アミンとシュウ酸銀との混合を溶媒の添加と並行して行ってもよい。混合工程が溶媒添加工程を兼ねる場合には、非アルコール溶媒や出来上がる銀ナノ粒子と相溶性のある有機溶媒が用いられることが好ましい。 In addition, in the manufacturing method of the 2nd silver nanoparticle of this invention, a heating process may serve as the solvent addition process. That is, the silver oxalate-amine complex may be heated in parallel with the addition of the solvent. Moreover, in the manufacturing method of the 2nd silver nanoparticle of this invention, a mixing process may serve as the solvent addition process. That is, the amine and silver oxalate may be mixed in parallel with the addition of the solvent. When the mixing step also serves as a solvent addition step, it is preferable to use a non-alcohol solvent or an organic solvent compatible with the resulting silver nanoparticles.
本発明の第二の銀ナノ粒子の製造方法では、加熱方法は特に限定されず、オイルバス等による加熱を適用することも可能である。 In the second method for producing silver nanoparticles of the present invention, the heating method is not particularly limited, and heating by an oil bath or the like can also be applied.

Claims (3)

  1. アミンとシュウ酸銀とを混合し、シュウ酸銀にアミンが配位したシュウ酸銀－アミン錯体を得る混合工程と、
    前記シュウ酸銀－アミン錯体にマイクロ波を照射して加熱し、前記シュウ酸銀－アミン錯体の還元を行う加熱工程とを含み、
    前記アミンは、アルキルアミン及びアルコキシアミンの少なくとも一方から選択される少なくとも１種の化合物を含むことを特徴とする銀ナノ粒子の製造方法。     A mixing step of mixing an amine and silver oxalate to obtain a silver oxalate-amine complex in which an amine is coordinated with silver oxalate;
    Heating the silver oxalate-amine complex by irradiating it with microwaves, and reducing the silver oxalate-amine complex.
    The method for producing silver nanoparticles, wherein the amine contains at least one compound selected from at least one of alkylamine and alkoxyamine.
  2. 前記混合工程と前記加熱工程との間に、前記シュウ酸銀－アミン錯体に溶媒を添加する工程を有することを特徴とする請求項１に記載の銀ナノ粒子の製造方法。 The method for producing silver nanoparticles according to claim 1, further comprising a step of adding a solvent to the silver oxalate-amine complex between the mixing step and the heating step.
  3. 前記アミンは、炭素数５以下のアルキルアミン、及び、炭素数５以下のアルコキシアミンの少なくとも一方から選択される少なくとも１種の化合物を含むことを特徴とする請求項１又は２に記載の銀ナノ粒子の製造方法。
          3. The silver nanoparticle according to claim 1, wherein the amine contains at least one compound selected from at least one of an alkylamine having 5 or less carbon atoms and an alkoxyamine having 5 or less carbon atoms. 4. Particle production method.
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