JP2008081772A - Method and device for producing metal particulate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for stably producing metal particulate where, in reaction using a reducing agent having decomposability, e.g., using a reducing agent decomposed with the lapse of time, to generate by-produced gas, heterogenization of a mixing field caused by the by-produced gas is suppressed by suppressing the decomposition of the reducing agent itself, and metal particulate of a fine size having excellent monodispersibility can be stably produced. <P>SOLUTION: In the method for producing metal particulate provided with a mixing stage where a first solution L1 at least comprising the decomposable reducing agent and a precipitating substance, and a second solution L2 comprising metal atoms or metal ions producing metal particulate are brought into mixing reaction by a liquid phase process so as to form metal particulate, two step cooling is carried out through a first cooling step for preparing the first liquid L1, and preliminarily cooling the prepared first liquid L1 to a first temperature higher than the precipitation temperature of the precipitating substance and lower than the decomposition temperature of the reducing agent, and a second cooling stage for cooling the first liquid L1 to a second temperature lower than the first temperature, immediately before the mixing stage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method and apparatus for producing metal fine particles, and more particularly to production of metal fine particles for producing a multi-component alloy, wherein the reducing agent decomposes with time before and after the initial reaction of forming the metal fine particles. The present invention relates to a method and apparatus for producing fine metal particles accompanied with raw gas.

  As magnetic particles capable of increasing the coercive force of a magnetic layer constituting a magnetic recording medium, metal particles of a multi-component alloy are attracting attention. In the production of such metal fine particles, by-product gas may be generated in the process of forming the metal fine particles. As this by-product gas, for example, there are a gas generated by the decomposition of the reducing agent used in the initial reaction over time and a gas generated as a by-product of the reaction.

  As described above, it is known that the reaction involving the by-product gas is generally difficult to continuously process. The reason for this is that if the by-product gas cannot be removed efficiently in the continuous processing flow, the continuous processing flow becomes unstable and the mixing field and reaction field become non-uniform. When performing liquid temperature control, since gas has a low thermal conductivity, the reaction temperature may not be accurately controlled.

As a countermeasure, for example, in an apparatus for continuously producing metal fine particles of a multi-component alloy, a first mixing apparatus that mixes a plurality of types of solutions for performing an initial reaction, and a metal generated by the initial reaction. A gas-liquid separation device is provided between the second mixing device that mixes another solution with the reaction solution containing the fine particles and introduces different metal atoms into the metal fine particles, thereby stabilizing the by-product gas generated in the initial reaction. It has been proposed to stabilize the flow of the reaction solution to make the reaction uniform (for example, Patent Document 1).
JP-A-2005-133135

  However, even if the by-product gas generated as a by-product of the reaction can be removed, Patent Document 1 does not suppress the decomposition of the reducing agent itself. For this reason, there are many reducing agents that are not used in the reaction, and there is a problem that a large excess of reducing agent must be supplied to the reaction field.

  Further, in the mixing field where the liquid phase reaction is performed, if the reducing agent decomposes with time and bubbles are generated, there is a problem that the mixing field becomes non-uniform and the mixing performance is deteriorated.

  In addition, as a method of suppressing the decomposition of the reducing agent itself, there is a method of cooling the reducing agent. However, depending on the cooling temperature, the solubility of the substance contained in the reducing agent solution may be reduced and precipitation may occur.

  As a result of such adverse effects, the metal fine particles produced have a large particle size and often have poor dispersibility.

  The present invention has been made in view of such circumstances. In a reaction using a reducing agent having decomposability, for example, a reducing agent that decomposes with time to generate a by-product gas, the reducing agent itself is decomposed. Providing a method and apparatus for producing metal fine particles that can suppress non-uniformity of the mixing field due to by-product gas by suppressing the fine particles and can stably produce fine metal fine particles having excellent monodispersibility. Objective.

  In order to achieve the above object, the first aspect of the present invention provides a first solution containing at least a decomposable reducing agent and a depositing substance, and a second solution containing a metal atom or a metal ion for producing metal fine particles. A metal fine particle production method comprising a mixing step of forming a metal fine particle by mixing and reacting with a solution of the above by a liquid phase method, wherein the first solution is prepared, and the prepared first solution is added to the first solution. A first cooling step of pre-cooling to a first temperature higher than the precipitation temperature of the precipitating substance and lower than the decomposition temperature of the reducing agent; and immediately before the mixing step, the first solution is added to the first solution. Provided is a method for producing fine metal particles, characterized by performing two-stage cooling including a second cooling step of cooling to a second temperature lower than the first temperature.

  According to the first aspect of the present invention, when the first solution containing the reducing agent is prepared, the solution is gently cooled in a range that does not cause precipitation in the solution, and immediately cooled to a lower temperature immediately before mixing and reaction. The reducing agent can be sufficiently cooled and mixed and reacted without causing precipitation. Thereby, even if there is exotherm such as heat of mixing or heat of reaction in the mixing step, it is possible to suppress decomposition of the reducing agent. Therefore, for example, when using a reducing agent that decomposes over time to generate by-product gas, decomposition of the reducing agent itself can be suppressed before and after mixing and reaction, so that mixing of by-product gas in the mixing field is suppressed. In addition, metal fine particles having a small size and excellent monodispersibility can be stably produced. Here, the decomposable reducing agent includes both a reducing agent that decomposes with time to generate by-product gas and a reducing agent that does not generate by-product gas. Here, the precipitating substance means a substance that easily precipitates when the temperature of the solution is lowered, and examples thereof include a surfactant. The decomposition temperature is a temperature measured by JISK7210.

  A second aspect of the present invention is characterized in that, in the first aspect, the mixing step is instantaneous mixing in which the first solution and the second solution are instantaneously mixed and reacted.

  Because of the instantaneous mixing, the reaction field can be made uniform before the reaction between the first and second solutions starts, and the particle size of the fine particles can be easily controlled.

  A third aspect of the present invention is the method according to the first or second aspect, wherein the liquid phase method is a reverse micelle method, and the first solution includes a water-insoluble organic solvent containing a surfactant as the precipitation substance and the reduction A reverse micelle solution (solution L1) mixed with a reducing agent aqueous solution containing an agent, and the second solution contains a water-insoluble organic solvent containing a surfactant and the metal atom or metal ion. It is a reverse micelle solution (solution L2) mixed with an aqueous metal salt solution.

  According to the third aspect, it is easy to control the particle diameter of the metal fine particles produced by performing the liquid phase method by the reverse micelle method.

  A fourth aspect of the present invention is the method according to any one of the first to third aspects, wherein the residence time of the first solution in the second cooling step is set after the first solution is set to the second temperature. It is characterized in that it is shorter than the time until the depositing substance in 1 solution starts to precipitate.

  A fifth aspect of the present invention according to the fourth aspect is characterized in that the residence time is 1 minute or less.

  According to claims 4 and 5, the first solution containing the reducing agent can be sufficiently cooled without causing precipitation before the mixing step. Here, since the time until the depositing substance starts to precipitate varies depending on the composition of the solution, it can be obtained by measuring the deposition temperature according to the composition of the solution in advance.

  A sixth aspect of the present invention is characterized in that, in any one of the first to fifth aspects, a pH adjusting step for adjusting a pH of the first solution is provided before the mixing step.

  According to the sixth aspect, by adjusting to a pH range where the reducing agent does not decompose before mixing and reaction, decomposition of the reducing agent can be suppressed even in the mixing field.

  According to a seventh aspect of the present invention, in order to achieve the above object, a first solution containing at least a decomposable reducing agent and a second solution containing metal atoms or metal ions for producing metal fine particles are used. A method for producing metal fine particles comprising a mixing step of forming a metal fine particle by mixing and reacting by a phase method, wherein before the mixing step, the pH of the first solution is brought to a pH region where the reducing agent is not decomposed. Provided is a method for producing metal fine particles, which comprises a pH adjusting step for adjusting.

  According to the seventh aspect, since the pH is adjusted to a pH range in which the reducing agent does not decompose before mixing and reaction, it is possible to suppress decomposition of the reducing agent even in the mixing field.

  An eighth aspect of the present invention is the method according to any one of the first to seventh aspects, wherein in the mixing step, one or more of the first solution and the second solution are mixed in a high-pressure jet flow of 1 MPa or more. Features.

  According to claim 8, one or more of the first solution and the second solution are caused to collide as a high-pressure jet flow of 1 MPa or more, and the first and second solutions are brought into contact with each other by the energy of the collision. Can be mixed and reacted instantaneously and efficiently.

  A ninth aspect is characterized in that, in any one of the first to eighth aspects, the metal fine particles are alloy particles.

10. In any one of the preceding claims, wherein the alloy particles are characterized by an alloy particle capable of forming a CuAu type or Cu ₃ Au type hard magnetic ordered alloy phase.

  According to an eleventh aspect of the present invention, in order to achieve the above object, a first solution containing at least a decomposable reducing agent and a precipitating substance, and a second atom containing a metal atom or metal ion for producing metal fine particles. An apparatus for producing fine metal particles comprising a mixing unit for forming a fine metal particle by mixing and reacting with a solution of the above by a liquid phase method, and preparing the first solution and cooling the prepared first solution in advance A first-stage first cooling section to be provided; a second-stage second cooling section that is provided immediately before the mixing section and cools the cooled first solution in the first cooling section; There is provided a metal fine particle manufacturing apparatus comprising a control means for controlling a cooling temperature in the first cooling section and the second cooling section.

  Claim 11 constitutes the present invention as an apparatus.

  A twelfth aspect of the present invention is the control device according to the eleventh aspect, wherein the control unit is configured such that the first solution prepared in the first cooling unit is higher than a precipitation temperature of the precipitating substance and lower than a decomposition temperature at which the reducing agent decomposes. The first temperature is controlled to be a first temperature, and the second solution is controlled to a second temperature lower than the first temperature in the second cooling unit.

  A thirteenth aspect of the present invention is characterized in that, in the eleventh or twelfth aspect, the mixing unit is an instantaneous mixing unit that instantaneously mixes and reacts the first solution and the second solution.

  According to a fourteenth aspect of the present invention, in order to achieve the above object, a first solution containing at least a decomposable reducing agent and a second solution containing metal atoms or metal ions for producing metal fine particles are used. An apparatus for producing metal fine particles comprising a mixing unit for forming a metal fine particle by mixing and reacting by a phase method, the pH adjusting unit being provided immediately before the mixing unit and adjusting the pH of the first solution; And a control unit that controls the pH adjusting unit so that the first solution is in a pH range in which the reducing agent is not decomposed.

  According to the present invention, in a reaction using a reducing agent having decomposability, for example, a reducing agent that decomposes with time to generate a by-product gas, mixing with the by-product gas is suppressed by inhibiting the decomposition of the reducing agent itself. It is possible to stably produce metal fine particles that are excellent in monodispersity with a small size while suppressing field non-uniformity.

  Preferred embodiments of a method and apparatus for producing metal fine particles according to the present invention will be described below with reference to the accompanying drawings. The metal fine particle production method and apparatus according to the present invention is a metal fine particle production method by a liquid phase reaction method (liquid-liquid reaction), and any metal can be used as long as a reducing agent that decomposes with time is used. It can also be applied to the production of fine particles.

  Metal fine particles such as alloy particles can be produced by a gas phase method other than the liquid phase method, but the liquid phase method is preferable in view of excellent mass productivity. Various conventionally known methods can be applied as the liquid phase method, but it is preferable to apply a reduction method to which these are improved, and the reverse micelle method in which the particle size of alloy particles can be easily controlled among the reduction methods. Is particularly preferred.

  As the first solution L1, a reducing agent solution can be preferably used. In addition, as the second solution L2, a solution containing two or more kinds of metal ions selected from groups 8, 9, and 10 of the periodic table can be suitably used, and Fe, Pt, Co, Ni , Pd metal ions are preferred. As the third solution L3, a solution containing one or more metal ions selected from the groups 11, 12, 13, 14, and 15 of the periodic rate table can be suitably used. Cu, Ag, Au , Al, Zn, and Sn are preferred.

Of the liquid phase reaction methods, the reverse micelle method is preferred in which the particle size of the metal fine particles can be easily controlled, and the first and second solutions L1 and L2 are reversed using a water-insoluble organic solvent containing a surfactant. It is preferable to prepare it as a micelle solution. An oil-soluble surfactant is used as the surfactant to be used. Specifically, sulfonate type (for example, aerosol OT (manufactured by Wako Pure Chemical Industries), quaternary ammonium salt type (for example, cetyltrimethylammonium bromide), ether type (for example, pentaethylene glycol dodecyl ether) and the like can be mentioned. Further, preferable examples of the water-insoluble organic solvent for dissolving the surfactant include alkanes, ethers, alcohols, etc. The alkanes are preferably alkanes having 7 to 12 carbon atoms. Is preferably heptane, octane, isooctane, nonane, decane, undecane, dodecane, etc. The ether is preferably diethyl ether, dipropyl ether, dibutyl ether, etc. The alcohol is preferably ethoxyethanol, ethoxypropanol, or the like. , Reducing agent solution The reducing agent, alcohols, _{polyalcohols; H 2; HCHO, S 2} O 6 2-, H 2 PO 2 -, BH 4 -, N 2 H 5 +, H 2 PO 3 - and the like compounds comprising However, it is preferable to use two or more in combination.

  A preferred embodiment of a method and apparatus for producing metal fine particles using the various solutions will be described below.

  First, a first embodiment according to the present invention will be described. The present embodiment is a method for suppressing decomposition of a reducing agent before the initial reaction by cooling the solution containing the reducing agent and the surfactant in two stages before performing the initial reaction for producing metal fine particles. It is.

  FIG. 1 is a schematic configuration diagram of a continuous production apparatus 10 for metal fine particles according to the present invention. Hereinafter, an example in which a solution for producing metal fine particles of a multicomponent alloy to be contained in a magnetic layer of a magnetic recording medium is used will be described.

  As shown in FIG. 1, the apparatus for continuously producing metal fine particles 10 mainly includes a first mixing device 12 that continuously supplies and mixes first and second solutions for performing an initial reaction, and an initial reaction. And a second mixing device 14 for continuously supplying and mixing the third solution to the reaction liquid containing the metal fine particles generated in step 1 to introduce different metal atoms into the crystal lattice of the metal fine particles.

  On the upstream side of the first mixing device 12, a first preparation tank 16 (corresponding to a first cooling unit together with a temperature control jacket 24 described later) prepared while cooling the first solution, and the first A static mixer 18 for cooling the first solution between one preparation tank 16 and the first mixing device 12 (corresponding to a second cooling unit together with a temperature control jacket 25 described later), One preparation tank 16 and control means 20 (control means) for controlling the cooling temperature of the static mixer 18 are provided. In the vicinity of the first mixing device 12, a second preparation tank 22 for preparing a second solution is provided. Further, a third preparation tank 23 for preparing a third solution is provided in the vicinity of the second mixing device 14.

  In the first preparation tank 16, a water-insoluble organic solvent containing a surfactant and a reducing agent aqueous solution are mixed with a stirrer 16a to prepare a reverse micelle solution of the first solution L1.

  In the second preparation tank 22, a water-insoluble organic solvent containing a surfactant and a metal salt aqueous solution containing two or more kinds of metal ions selected from Groups 8, 9, and 10 of the periodic table are mixed with a stirrer 22a. A reverse micelle solution of the second solution L2 is prepared by mixing. A temperature adjustment jacket 24 is provided on the outer periphery of the first preparation tank 16. Further, the temperature control jacket 24 is provided with a temperature measurement unit 27 for measuring the temperature of the temperature control jacket 24 so that the measurement result can be output to the control means 20. As a result, the first solution in the first preparation tank 16 is cooled to the first temperature. Further, a temperature adjustment jacket 26 is provided on the outer periphery of the second preparation tank 22 and is adjusted to a temperature suitable for the initial reaction.

  In the third preparation tank 23, a water-insoluble organic solvent containing a surfactant and a metal aqueous solution containing one or more metal ions selected from Groups 11, 12, 13, 14, and 15 of the periodic table; Are mixed with a stirrer 23a to prepare a reverse micelle solution of the third solution L3. In addition, a temperature adjustment jacket 28 is provided on the outer periphery of the third preparation tank 23 and is adjusted to a temperature suitable for the reaction in the second mixing device 14.

  The static mixer 18 is provided immediately before the first mixing device 12, and a temperature control jacket 25 is wound around the outer periphery. The temperature control jacket 25 is provided with a temperature measurement unit 29 for measuring the temperature of the temperature control jacket 25, and the measurement result from the temperature measurement unit 29 is output to the control means 20. .

  The control means 20 adjusts the cooling temperature of the temperature adjustment jacket 25 formed on the outer periphery of the static mixer 18 based on the measurement result in the temperature measurement unit 29. Further, the control means 20 adjusts the cooling temperature of the temperature adjustment jacket 24 formed on the outer periphery of the first preparation tank 16 based on the measurement result in the temperature measurement unit 27. As such a control means, a publicly known thing can be used, for example, an integrated constant temperature water circulation device (registered trademark name: COOLNICS) can be used. As a result, the first solution prepared in the first preparation tank 16 is cooled stepwise just before it is supplied to the first mixing device 12.

  As the static mixer 18, a publicly known one can be used. In the present embodiment, the example in which the temperature control in the first preparation tank 16 and the static mixer 18 is performed by one control means 20 is shown, but the present invention is not limited to this, and the control means may be provided separately. Good.

  In the present embodiment, the temperature of the first solution (first temperature) in the first preparation tank 16 is higher than the precipitation temperature of the depositing substance (surfactant in the present embodiment) and the reducing agent. The temperature is set lower than the decomposition temperature. Since the deposition temperature of the surfactant varies depending on the composition and type of the solution, it can be determined by measuring the relationship between the liquid temperature and the solubility in advance. Here, the decomposition temperature of the reducing agent refers to a value measured according to JISK7210.

  The temperature of the first solution in the static mixer 18 (second temperature) is cooled so as to be lower than the temperature in the first preparation tank 16 (first temperature). Specifically, the second temperature is set to a temperature at which the reducing agent is not decomposed even in a mixing field where heat of mixing or reaction is likely to occur, such as a mixing field that is mixed by a high-pressure jet stream. This temperature is determined by mixing field conditions, liquid composition, liquid viscosity, and the like. For this reason, the second temperature is determined by obtaining in advance experiments or simulations a temperature at which decomposition of the reducing agent does not occur under stirring conditions assuming the same stirring force and frictional heat as the mixing field. Is done. In addition, the presence or absence of decomposition | disassembly of a reducing agent can be judged by the particle size collect | recovered, a particle size distribution, etc. Moreover, if it is a reducing agent which generate | occur | produces a bubble by decomposition | disassembly, it can carry out by judging the presence or absence of the generation | occurrence | production of the bubble visually.

In this case, if the second temperature is lower than the first temperature, the surfactant may start to precipitate after a predetermined time has elapsed. For this reason, the residence time of the first solution in the static mixer 18 is set to be shorter than the time until the surfactant starts to precipitate. For example, in the case of the reducing agent (NaBH ₄ ) used in the examples to be described later, it takes about 1 minute to start precipitation at a liquid temperature of 8 ° C., so the residence time is set to 1 minute or less. As described above, the residence time of the first solution in the static mixer 18 is set by adjusting the length of the static mixer 18 and the supply flow rate of the first solution.

  In the present embodiment, an example in which the static mixer 12 is provided immediately before the first mixing device 12 has been described. However, the piping immediately before the first mixing device 12 is cooled without providing the static mixer 12. It is good also as a structure. Moreover, in FIG. 1, although shown about the example which cools only the part immediately before the 1st mixing apparatus 12 among the piping which connects the 1st preparation tank 16 and the 1st mixing apparatus 12, it is limited to this. Alternatively, the entire piping connecting the first preparation tank 16 and the first mixing device 12 may be further cooled than the first preparation tank 16 within a range where precipitation does not occur. In addition, the pipe 36 communicating with the first and second mixing devices 12 and 14 may be further cooled than the first preparation tank 16 to suppress decomposition of the reducing agent flowing through the pipe 36. Further, in the present embodiment, an example in which the cooling temperature is adjusted in two stages before being supplied to the first mixing device 12 is shown, but the present invention is not limited to this, and the cooling temperature may be adjusted in three or more stages.

  Next, with reference to FIG. 1, the operation of the apparatus for continuously producing metal fine particles 10 according to the present invention will be described.

  The first and second solutions L1 and L2 prepared in the first and second preparation tanks 16 and 22 are supplied to the first mixing device 12 via the supply pipes 30 and 32 by the supply pumps 34 and 34, respectively. Supplied. At this time, the temperature of the first solution containing the reducing agent in the first preparation tank 16 is higher than the precipitation temperature of the surfactant and lower than the decomposition temperature of the reducing agent (first (First cooling step). That is, since the upper limit temperature at which the reducing agent is not decomposed is set, the solubility of the first solution does not extremely decrease and precipitation does not occur.

  Thereafter, the first solution is cooled to a lower temperature (second temperature) by the static mixer 18 around which the temperature control jacket 25 is wound (second cooling step). The residence time of the first solution in the static mixer 18 is set to be shorter than the time until the surface active agent or the like in the first solution starts to precipitate, so that the first solution is not precipitated. To the first mixing device 12.

  As described above, the first solution containing the reducing agent is sufficiently cooled without causing precipitation during the period from the preparation of the first solution to immediately before the first solution is supplied to the first mixing device 12.

  On the other hand, the second solution containing the metal salt is heated to a temperature suitable for the initial reaction performed in the first mixing device 12 by the temperature control jacket 26.

  In the first mixing device 12, the two solutions L1 and L2 are instantaneously mixed and reacted. Thus, in the case of a flow system reaction, the by-product gas generated by the decomposition of the reducing agent that proceeds continuously from before the reaction is prevented from being mixed into the mixing device 12, thereby allowing the inside of the mixing device 12. It is very important to improve the mixing performance of the two liquids and to stabilize and homogenize the reaction. In the present invention, before the two liquids are mixed and reacted, the reducing agent is sufficiently cooled without generating precipitates, so that the decomposition of the reducing agent can be suppressed even in the mixing field 52 that is mixed by a high-pressure jet stream. Can do. Thereby, non-uniform reaction can be prevented, and fine metal particles with excellent monodispersity can be formed.

  The length of the pipe 36 is set to a length sufficient to complete the initial reaction started by mixing in the first mixing device 12 until it reaches the second mixing device 14. In the second mixing device 14, the third solution L3 prepared in the third preparation tank 23 is continuously supplied to the reaction liquid LM via the supply pipe 38, and the metal fine particles formed in the initial reaction are mixed. Different metal atoms are continuously introduced (doping) into the crystal lattice. Thereby, metal fine particles of a multi-component alloy are produced.

  In this case, in the subsequent stage of the second mixing device 14, the mixed solution mixed in the second mixing device 14 is recovered, and the fourth solution L4 obtained by mixing the chelating agent solution and the reducing agent solution is added and mixed. A tank 40 is preferably provided.

  The mixed liquid mixed in the second mixing device 14 is collected in the mixing tank 40, and about 40 ° C. while gently stirring with the stirrer 40a about 5 minutes after adding the third solution from the addition tank 42. Then, the fourth solution L4 is added and aged for 120 minutes. Thereby, the doping in the second mixing device 14 is terminated. A heating jacket 44 is provided on the outer periphery of the mixing tank 40 and is heated to an appropriate temperature.

  As described above, since the first solution containing the reducing agent is cooled to a temperature that does not decompose even in the mixing field, decomposition of the reducing agent itself (generation of bubbles) can be suppressed before and after the reaction. Thereby, the reaction in the mixing field can be made uniform, and fine metal fine particles having excellent monodispersity can be produced. Moreover, not only the utilization factor of a reducing agent can be improved, but also the yield of metal fine particles can be improved. Further, when the first solution is cooled, precipitation of the surfactant and the like is not accompanied, so that problems such as clogging of the orifice and non-uniform size of the reverse micelle can be eliminated.

  Next, a second embodiment according to the present invention will be described. This embodiment is a method for suppressing decomposition of the reducing agent in the initial reaction by adjusting the pH of the solution containing the reducing agent and the surfactant before performing the initial reaction for producing the metal fine particles.

  FIG. 2 is a schematic configuration diagram of a continuous production apparatus 10 'for metal fine particles according to the present invention.

  The continuous production apparatus 10 ′ shown in FIG. 2 is different from the temperature control mechanism (temperature measuring units 27, 29, etc.) in the first preparation tank 16 and the static mixer 18 in FIG. 46, except that the pH measurement unit 47 and the control means 48) are provided.

  The pH adjusting unit 46 can be added to the first solution from an acid or alkaline solution storage unit via an addition pipe with a valve and a pump (both not shown). The pH adjusting unit 46 is provided with a pH measuring unit 47, and the measurement result of the pH measuring unit 47 is output to the control means 48. The control means 48 can control the pH adjusting unit 46 based on the measurement result.

  Thus, the first solution is adjusted to a pH region where the reducing agent is not decomposed, and then supplied to the first mixing device 12.

  Any acid or alkali solution for adjusting the pH used in the pH adjusting unit 46 can be used as long as it does not significantly inhibit the intended reaction of the first and second solutions. In the embodiment of FIG. 2, the example of adjusting the pH after adjusting the first solution has been described. However, the embodiment is not limited thereto, and the first solution is prepared in the first preparation tank 16. The pH can be adjusted from the beginning. Further, in FIG. 2, the static mixer 18 of FIG. 1 having a cooling function may be further provided immediately before the first mixing device 12, and the pH adjustment step of the first solution and the cooling step may be combined.

  Next, with reference to FIG. 2, an operation of the continuous metal particle production apparatus 10 according to the present invention will be described.

  The first and second solutions L1 and L2 prepared in the first and second preparation tanks 16 and 22 are supplied to the first mixing device 12 via the supply pipes 30 and 32 by the supply pumps 34 and 34, respectively. Supplied. Since the first solution containing the reducing agent has already started to be decomposed from the time of preparation in the first preparation tank 16, the pH adjusting unit 46 is adjusted to a pH region where the reducing agent is not decomposed.

  In this manner, the reducing agent is sufficiently cooled without causing precipitation between the time when the first solution is prepared and the time immediately before being supplied to the first mixing device 12.

  On the other hand, the second solution containing the metal salt is heated to a temperature suitable for the initial reaction performed in the first mixing device 12 by the temperature control jacket 26.

  In the first mixing device 12, the two solutions L1 and L2 are instantaneously mixed and reacted. In the present invention, before mixing the two liquids, the first solution containing the reducing agent is adjusted to a pH region where the reducing agent is not decomposed, so that the decomposition of the reducing agent in the mixing field 52 can be suppressed. Thereby, non-uniform reaction can be prevented, and fine metal particles with excellent monodispersity can be formed. Moreover, not only the utilization factor of a reducing agent can be improved, but also the yield of metal fine particles can be improved.

  Next, in each of the above embodiments, an apparatus configuration suitable as the first mixing apparatus 12 used in the continuous production apparatus 10 and 10 ′ for metal fine particles will be described. In addition, the 1st mixing apparatus 12 demonstrated below shall be applicable also to the 2nd mixing apparatus 14. FIG.

  As a mixing apparatus used in the present invention, a finely divided metal fine particle having good monodispersibility, which can be instantaneously mixed in a mixing field and can quickly discharge without reacting the reaction liquid LM reacting by mixing in the mixing field. Is preferable in forming. As such a mixing device, a high-pressure mixing method, a high-speed stirring mixing method, or a microgap mixing method can be preferably used. In the present embodiment, a particularly preferred high-pressure mixing type mixing apparatus will be described.

(1) High-pressure mixing method The types of the high-pressure mixing method can be suitably used as a one-jet type, a T-shaped / Y-shaped type, or a two-jet facing type, and examples of applying these methods to the mixing device 12 I will explain it.

a) One-Jet Type FIG. 3 is a cross-sectional view showing the concept of the one-jet type first mixing device 12.

  As shown in FIG. 3, the first mixing device 12 has an opening on one end side of a mixer 54 in which a cylindrical mixing field 52 for mixing and reacting the first and second solutions L1 and L2 is formed. In addition, a first conduit 56 for introducing the first solution L1 into the mixing field 52 is connected, and a discharge pipe 58 for a reaction solution mixed and reacted in the mixing field 52 is connected to the other end side opening. A second conduit 60 for introducing the second solution L2 into the mixing field 52 is connected to the side of the mixer 54 near the outlet of the first conduit 56. A first orifice 62 and a second orifice 64 are formed in the distal ends of the first conduit 56 and the second conduit 60, respectively, thereby disturbing the first conduit 56 and the second conduit 60. A first nozzle 66 and a second nozzle 68 are formed for ejecting a stream of liquid. In FIG. 3, the first solution L1 is introduced from the first conduit 56 and the second solution L2 is introduced from the second conduit 60. However, both solutions can be reversed. Further, if the connection position of the discharge pipe 58 is in the vicinity of the other end side of the mixer 54, the discharge pipe 58 may be connected to the side surface portion of the mixer 54.

  A jacket 70 in which a heat medium having a relatively large heat capacity such as water and oil flows is wound around the outer periphery of the mixer 54, and a heat medium inlet 70A and a heat medium outlet 70B of the jacket are not shown. Connected to the supply device. The mixing reaction temperature is preferably set appropriately to a predetermined temperature suitable for the initial reaction depending on the types of the first and second solutions L1 and L2.

  As a method of drilling the first and second orifice materials 72 and 74 in the block-shaped orifice material 72, a processing method of precisely opening an ejection hole of about 100 μm in the orifice material 72 made of metal, ceramics, glass or the like. Known micro cutting processing, micro grinding processing, injection processing, micro electric discharge processing, LIGA method, laser processing, SPM processing and the like can be suitably used.

  The material of the orifice material 72 is preferably a material having good workability and a hardness close to diamond. Therefore, as materials other than diamond, those obtained by hardening various metals and metal alloys such as quenching, nitriding, and sintering can be preferably used. Ceramics can also be suitably used because of its high hardness and superior workability than diamond. In the present embodiment, an example of an orifice will be described as the throttle structure of the first nozzle 66 and the second nozzle 68. However, the present invention is not limited to the orifice as long as it has a function of ejecting turbulent liquid. Other methods can be used.

  The first conduit 56 and the second conduit 60 are provided with pressurizing means (not shown), and the first solution L1 and the second solution L2 are applied to the first and second nozzles 66 and 68, respectively. Pressure supplied. However, the pressure ejected from the second nozzle 68 to the mixing field 52 is made smaller than the pressure of the high-pressure jet stream ejected from the first nozzle 66 to the mixing field 52. Various means are known as pressurizing means for applying a high pressure to the liquid, and any means can be used. However, relatively easy and inexpensive means such as a plunger pump and a booster pump are available. It is preferable to use a reciprocating pump. In addition, although a high pressure cannot be generated as much as a reciprocating pump, some rotary pumps can generate a high pressure, and such a pump can be used.

  The first solution L1 is ejected from the first nozzle 66 to the mixing field 52 as a turbulent flow having a Reynolds number of 10,000 or more as a high-pressure jet flow of 1 MPa or more and flowing into the mixing field 52. From 68, the second solution L2 having a pressure lower than that of the first solution L1 is jetted into the mixing field 52 as a cross flow substantially orthogonal to the first solution L1. In this case, even if the second solution L2 is not completely orthogonal to the first solution L1 at an angle of 90 °, the second solution L2 only needs to have an orthogonal velocity vector component as a main component. Thus, the first solution L1 and the second solution L2 are instantaneously and efficiently mixed under an appropriate mixing reaction temperature condition, and the reaction solution LM that reacts by mixing is immediately discharged from the discharge pipe 58 to the pipe 36. Is done. As a result, fine metal particles having a fine size and good monodispersibility are formed.

  As schematically shown in FIG. 4, the mixing reaction is a second solution that is ejected from a substantially orthogonal direction to the first solution L <b> 1 into the first solution L <b> 1 having a high-speed turbulent high-pressure jet flow. By entraining so as to entrain L2, the high-efficiency mixing efficiency is obtained by utilizing the large eddy viscosity generated by mixing the first solution L1 and the second solution L2. The mixing field 52, the first and second nozzles 66 and 68, and the discharge pipe 58 of the mixing device 12 are formed to have the following relationship.

  That is, it is necessary to form eddy viscosity in the mixing field 52, and as shown in FIG. 3, the cylinder diameter D1 of the mixing field 52 is the orifice diameter D2 of the first nozzle 66 and the orifice diameter of the second nozzle 68. It is formed with a larger diameter than D3. In particular, the eddy viscosity produced by the first solution L1 which is a straight flow A is important for improving the mixing efficiency, and the dimensional ratio of the cylinder diameter D1 of the mixing field 52 to the orifice diameter D2 of the first nozzle 66 is 1 The range of 1 to 50 times is preferable, and the range of 1.1 to 20 times is more preferable. Further, in order to make the second solution L2 that is a cross flow B orthogonal to the straight flow A easy to be caught in the solution L1 of the straight flow A, the pressure of the cross flow B is lower than the pressure of the straight flow A. Thus, it is preferable that the jet flow velocity be equal to or less than the jet flow velocity of the straight flow A. Specifically, the flow rate ratio of the jet flow velocity of the cross flow B to the jet flow velocity of the straight flow A is 0.05 to 0.4 times, more preferably 0.1 to 0.3 times.

  Further, the cross flow B is mixed with the cross flow B at a position before the eddy viscosity C formed by the straight flow A being ejected from the first nozzle 66 having a small diameter to the mixing field 52 having a larger diameter is maximized. It is necessary that the second nozzle 68 is disposed between the first nozzle 66 and the maximum position of the eddy viscosity C. Therefore, it is necessary to know the position where the eddy viscosity C is maximized, but the position of the mixing field 52 where the eddy viscosity C is maximized is known as the flow analysis software that is already commercially available in Japan as the flow analysis software. This can be grasped by performing a simulation in advance using the R-Flow numerical analysis software manufactured by R-Flow. In this case, as can be seen from FIG. 4, the position where the eddy viscosity C is maximum has a region instead of a pin point, and therefore the maximum position of the eddy viscosity C may be set to a point P that is substantially the center of the eddy viscosity C. . Therefore, the second nozzle 68 may be positioned before the point P, but more preferably the second nozzle 68 is positioned so that the cross flow B can be ejected at an early stage of formation of the eddy viscosity C.

  Further, when analyzed by the above numerical analysis software, the center point P in the region where the eddy viscosity C appears is related to the flow velocity of the straight flow A, and the maximum flow velocity of the straight flow A (usually the flow velocity at the first nozzle position). ) Substantially corresponds to a position where it is reduced to 1/10. Therefore, if the position where the maximum flow velocity of the straight flow A is reduced to 1/10 is calculated and the second nozzle 68 is positioned so that the orthogonal flow B can be ejected before that point, it is also necessary to calculate the point P. Absent.

  Further, it is necessary to ensure the length L (see FIG. 3) of the mixing field 52 necessary for forming the maximum eddy viscosity C in the mixing field 52. However, if it is too long, the reaction liquid LM is mixed in the mixing field 52. Stagnation and backflow are likely to occur, which adversely affects the fine particle size and monodispersity of the metal fine particles. Therefore, the length L of the mixing field 52 is preferably 2 to 5 times, more preferably 2 to 3 times the distance from the first nozzle 66 to the point P which is the maximum position of the eddy viscosity C.

  Further, when liquid is ejected from the first nozzle 66 or the second nozzle 68 having a small diameter to the mixing field 52 having a larger diameter than the first nozzle 66 or the second nozzle 68, cavitation is likely to occur. An interface is formed, reducing the mixing efficiency. Therefore, in order to increase the mixing efficiency using the eddy viscosity C, it is necessary to prevent the gas-liquid interface from being formed in the mixing field 52. Therefore, as shown in FIG. 3, it is necessary to reduce the diameter D4 of the discharge pipe 58 with the third orifice 74 so as to be smaller than the cylinder diameter D1 of the mixing field 52, and to mix while increasing the pressure of the mixing field 52. It is. Thereby, since cavitation can be eliminated, mixing efficiency is further improved. In order to shorten the residence time in the portion not contributing to the mixing in the discharge pipe 58 as much as possible, the outlet in the mixing field 52 is narrowed, and at least the discharge pipe 58 having an inner diameter smaller than the cylinder diameter D1 of the mixing field 52 is set as much as possible. It is preferable to shorten the length and connect to the pipe 36.

  The shape of the jet flow ejected from the first nozzle 66 to the mixing field 52 is restricted by the first orifice 62 provided in the first nozzle 66, and this jet flow shape affects the mixing performance. Therefore, it is preferable to appropriately use the first orifice 62 that forms a jet flow shape such as a filament shape, a conical shape, a slit shape, or a fan shape in accordance with the purpose of the mixing reaction. For example, in the case of a reaction with a very fast reaction speed on the order of milliseconds, it is necessary to eject the straight flow A and the cross flow B so that the eddy viscosity C is instantaneously maximized in the narrowest possible range. A first orifice 62 that forms a linear jet shape is preferred. Also, when the reaction rate is relatively slow, it is better to increase the entrained interface area created by the straight flow A by jetting the straight flow A and the cross flow B so that the eddy viscosity C is maximized in the widest possible range. In this case, the first orifice 62 that forms a thin jet flow shape is preferable. In the case of an intermediate reaction rate between a very low reaction rate on the order of milliseconds and a relatively low reaction rate, the first orifice 62 that forms a conical jet flow shape is preferable.

  5 to 8 illustrate the first orifice 62 for forming the shape of each of the squirrel, conical, slit, and fan-like jets, and (a) in each figure shows the orifice at the tip. FIG. 2B is a longitudinal sectional view of the orifice, and FIG. 3C is a transverse sectional view of the orifice.

  FIG. 5 shows a first orifice 62 for ejecting a straight linear flow A in the mixing field 52, and is formed in a linear shape. FIG. 6 shows a first orifice 62 for ejecting the conical straight flow A to the mixing field 52, and is formed in a trumpet shape having an open front end. FIG. 7 shows a first orifice 62 for ejecting a straight flow A of a thin film to the mixing field 52, which is formed in a rectangular slit shape. FIG. 8 shows a first orifice 62 for ejecting the straight flow A of a fan-shaped thin film to the mixing field 52, and the tip portion is formed with a fan-shaped diameter.

  The first mixing device 12 of the one-jet mixing method is not limited to the above-described FIG. 3, and the first solution L1 and the second solution L2 are larger in diameter than the nozzle diameter from each nozzle. A static mixing device for discharging the mixed reaction liquid from a discharge port having a diameter smaller than the diameter of the mixing field and discharging at least one of the solution L1 and the solution L2 to 1 MPa or more. At a position before the eddy viscosity formed by the high-pressure jet flow with respect to the flow direction is maximized as a turbulent flow having a Reynolds number of 10,000 or more when flowing into the mixing field. Any remaining solution may be used as long as it can be added at a pressure lower than that of the high-pressure jet stream.

b) T-shaped / Y-shaped FIGS. 9 and 10 are cross-sectional views of the first mixing device 12 of T-shaped / Y-shaped, FIG. 9 is a T-shaped tube, and FIG. 10 is a Y-shaped tube. Is the case.

  As shown in FIG. 9 and FIG. 10, a high-pressure jet of 1 MPa or more is applied to the first solution L1 and the second solution L2 at the intersection (mixing field) of very thin pipes such as T-shaped tubes and Y-shaped tubes. Both liquids are instantaneously mixed by colliding with a flow, and the reacted reaction liquid is discharged from the discharge pipe in a short time. That is, the first solution L1 is ejected from the first addition pipe 76 to the mixing field 78 with a high-pressure jet flow of 1 MPa or more, and the second solution L2 is ejected from the second addition pipe 80 with a high-pressure jet flow of 1 MPa or more. Both solutions are caused to collide by being ejected to the mixing field 78. The reaction liquid LM that is mixed by the energy of the collision and reacts by mixing is discharged from the discharge pipe 82 in a short time. The pressures of the first solution L1 and the second solution L2 may be the same or different as long as the pressure is 1 MPa or more. A jacket 84 is wound around the outer periphery of the first addition pipe 76, the second addition pipe 80, and the discharge pipe 82, and the mixing reaction temperature with the first and second solutions L 1 and L 2 in the mixing field 78. Is controlled.

  9 and 10, reference numeral 84 </ b> A is a heat medium inlet of the jacket 84, and reference numeral 84 </ b> B is a heat medium outlet.

  As a result, the first solution L1 and the second solution L2 are instantaneously and efficiently mixed and reacted under an appropriate mixing reaction temperature condition, and the reaction solution is immediately discharged from the discharge pipe 82. Metal fine particles having a good monodispersity in size can be formed.

c) Two-jet opposed type FIG. 11 shows a mixing method in which the concept of eddy viscosity is added to a T-shape, and the same members as those in FIG. In this mixing method, the first solution L1 and the second solution L2 are jetted from the opposing direction by a high-pressure jet flow of 1 MPa or more, and the mixing field 52 is ejected larger than the nozzle diameter for ejecting the L1 solution and the L2 solution. Are mixed using the eddy viscosity generated in both solutions, and the reaction liquid LM is discharged from the discharge pipe 58 having a diameter smaller than the diameter of the mixing field 52.

  The first mixing device 12 of FIG. 11 has a first opening at one end of a mixer 54 in which a cylindrical mixing field 52 is formed in which a first solution L1 and a second solution L2 are mixed and reacted. A first conduit 56 for introducing the second solution L1 into the mixing field 52 is connected, and a second conduit 60 for introducing the second solution L2 into the mixing field 52 is connected to the other end side opening. Further, a discharge pipe 58 that discharges the reaction liquid LM mixed and reacted in the mixing field 52 from the mixing field 52 is connected to the central opening of the mixer 54.

  A first orifice 62 and a second orifice 64 are provided inside the distal ends of the first conduit 56 and the second conduit 60, respectively, so that the first conduit 56 and the second conduit 60 are not disturbed. A first nozzle 66 and a second nozzle 68 that inject a straight flow A1, A2 of the flow are formed. In the present embodiment, an example in which the first solution L1 is ejected from the first nozzle 66 and the second solution L2 is ejected from the second nozzle 68 will be described.

  A jacket 70 is wound around the outer periphery of the mixer 54, and the mixing reaction temperature with the first and second solutions L1 and L2 in the mixer 54 is controlled in the same manner as described with reference to FIG.

  The cylinder diameter D1 of the mixing field 52, the orifice diameter D2 of the first nozzle 66, the orifice diameter D3 of the second nozzle 68, and the dimensional relationship thereof are the same as those of the one-jet type. Further, the method of forming the first and second orifices 62 and 64, the material of the orifice material 72, and the pressurizing means are the same as described in the one-jet type. Moreover, the shape of the straight flow A1, A2 can also be formed in the shape of each of the yarn-line shape, the conical shape, the slit shape and the fan-like shape described in the one-jet type.

  Then, as shown in FIG. 12, the first and second nozzles 66 and 68 are used to cause the first solution L1 and the second solution L2 to flow at one end and the other end of the mixing field 52 with a high-pressure jet flow of 1 MPa or more. And collide in the mixing field 52 as turbulent straight flow A1 and A2 facing each other. A reaction in which the two eddy viscosities C and D formed by the two straight flow streams A1 and A2 are overlapped so that the solution L1 and the solution L2 are instantaneously mixed under an appropriate mixing reaction temperature condition and reacted by mixing. The liquid LM is immediately discharged from the discharge pipe 58 to the pipe 36. Thereby, fine metal particles having a fine size and good monodispersibility can be formed.

  In such a mixing reaction, when the respective eddy viscosities C and D formed in the mixing field 52 by the two high-speed, straight flow streams A1 and A2 of the opposing turbulent flow become maximum, the overlapping portion E becomes as large as possible. In this way, high-performance mixing efficiency is obtained. Therefore, the straight flow A1, A2 does not collide with the mixing field 52 immediately after being jetted, and the portion E where the two eddy viscosities C, D formed in the mixing field 52 by the straight flow A1, A2 overlap each other as much as possible. It is preferable to enlarge it. For this purpose, it is preferable to appropriately set the separation distance L (see FIG. 11) between the first nozzle 66 and the second nozzle 68 facing each other, in other words, the length of the mixing field. Thus, by appropriately setting the separation distance L between the first nozzle 66 and the second nozzle 68, it is possible to reliably increase the overlapping portion E between the eddy viscosities C and D that are maximized. In addition, the two eddy viscosities C and D can be substantially completely overlapped. Therefore, it is necessary to know the position where the eddy viscosities C and D are maximized, but the position of the mixing field 52 where the eddy viscosities C and D are maximized is already commercially available in Japan as flow analysis software and is good as flow analysis software. By performing a simulation in advance using the known numerical analysis software R-Flow manufactured by R-Flow, the distance from the first nozzle 66 to the eddy viscosity C and the distance from the second nozzle 68 to the eddy viscosity D The distance can be grasped. In this case, as can be seen from FIG. 12, the position where the eddy viscosities C and D are maximum has a region instead of a pinpoint. Accordingly, the separation distance L between the first nozzle 66 and the second nozzle 68 is such that the maximum position of the eddy viscosities C and D is the points P1 and P2 that are substantially central portions of the eddy viscosities C and D, and the points P1 and P2 And the total value from the first nozzle 66 to the point P11 and the second nozzle 68 to the point P2. As another method for grasping the points P1 and P2, the points P1 and P2 at which the eddy viscosities C and D caused by the straight flow A1 and A2 become maximum are analyzed by the above numerical analysis software. It has a relationship with the flow velocity, and substantially corresponds to a position where the maximum flow velocity of the straight flow A1, A2 (usually, the flow velocity at the first or second nozzle position) is reduced to 1/10. Therefore, the points P1 and P2 may be grasped by calculating the position where the maximum flow velocity of the straight flow A1 and A2 decreases to 1/10. In this way, by making the eddy viscosities C and D overlap at the position where the eddy viscosities C and D are maximized, the contact efficiency at the liquid-liquid interface between the straight flow A1 and the straight flow A2 is increased and the mixing reaction is performed. In addition to the effect of improving the performance, there is also an effect of suppressing heat generation due to liquid-liquid friction caused by the collision between the straight flow A1 and the straight flow A2.

  The following operation was performed in high purity nitrogen gas. In this example, an experiment was carried out until metal fine particles were generated in the initial reaction (reaction between the first and second solutions in the first mixing device 12 in FIG. 1), in which the reducing agent is particularly likely to decompose. Then, the particle size and particle size distribution of the obtained metal fine particles were evaluated.

(Example A)
(1) Preliminary experiment 1
To an aqueous reducing agent solution in which 5.7 g of NaBH ₄ (manufactured by Wako Pure Chemical Industries) was dissolved in 270 mL of H ₂ O (deoxygenated), an alkane solution in which 278 g of aerosol OT was dissolved in 2700 mL of decane (manufactured by Wako Pure Chemical Industries) was added and mixed Thus, a reverse micelle solution of the first solution L1 was prepared. The concentration of the reducing agent NaBH ₄ in the first solution L1 was 26 mmol / L.

Triammonium iron oxalate (Fe (NH ₄ ) ₃ (C ₂ O ₄ ) ₃ ) (manufactured by Wako Pure Chemical Industries, Ltd.) 5.3 g and potassium chloroplatinate (K ₂ PtCl ₄ ) (manufactured by Wako Pure Chemical Industries, Ltd.) 4.8 g And an alkane solution in which 148 g of aerosol OT (manufactured by Wako Pure Chemical Industries) is dissolved in 1440 mL of decane (manufactured by Wako Pure Chemical Industries) is added to and mixed with an aqueous solution of metal salt dissolved in 144 mL of H ₂ O (deoxygenated). A reverse micelle solution of the second solution L2 was prepared. The metal ion concentration of the second solution L2 was 8 mmol / L.

When the first solution L1 was prepared, bubbles were constantly generated. Thus, the bubbles were collected and analyzed by gas chromatography. As a result, it was found to be H ₂ . Since it is known that NaBH ₄ is hydrolyzed to generate H ₂ , it was inferred that the hydrolysis of NaBH _{4 has} already progressed since the preparation of the first solution L1.

Therefore, the cooling temperature of the first solution L1 containing NaBH ₄ was changed, and the region where the hydrolysis of NaBH ₄ did not occur was examined. NaBH ₄ was hydrolyzed by visually observing whether bubbles were generated. That is, the first solution L1 was put into a 100 mL beaker, and slowly stirred with a magnetic stirrer at a constant rotational speed (a rotational speed at which bubbles were not entrained and no liquid layer separation occurred), and the cooling temperature was changed. . As a result, it was confirmed that bubbles were not generated when the first solution L1 was cooled to 11.5 ° C. or lower.

  Next, based on the above results, 2 L of the first solution L1 and 1 L of the second solution L2 are put into the tank, mixed at a low speed for 10 minutes (initial reaction), and measured. Metal nanoparticles for use were prepared. At this time, the liquid temperature of the solution in the tank was cooled to 11.5 ° C. (Example 1). And the yield, volume average particle diameter, and particle size distribution of the obtained metal nanoparticles were measured.

  The yield was the amount of fine metal particles actually produced relative to the theoretical production amount. The amount of metal fine particles actually produced was measured by ICP spectroscopic analysis (inductively coupled high-frequency plasma spectroscopic analysis).

  The volume average particle size and particle size distribution were determined by a dynamic light scattering method (manufactured by Nikkiso Co., Ltd., UPA-EX).

  Comparative Example 1 is the same as Example 1 except that the solution in the tank was not cooled.

Further, in Examples 2, 3 and 4, the concentration of NaBH ₄ in the first solution L1 was changed from 5.7 g (26 mmol / L) to 2.9 g (14 mmol / L) and 1.4 g (7 mmol / L), respectively. , Except that the amount was changed to 0.7 g (3 mmol / L). The results are shown in Table 1.

表１に示すように、混合前に冷却した実施例１では、混合前に冷却しなかった比較例１よりも、粒子サイズが小さく、単分散の優れた金属ナノ粒子が得られた。

As shown in Table 1, in Example 1 cooled before mixing, metal nanoparticles having a smaller particle size and excellent monodispersion were obtained than Comparative Example 1 that was not cooled before mixing.

Furthermore, when cooling the first solution L1 to 11.5 ° C. prior to mixing, NaBH ₄ concentration yields even 7 mmol / L was found to be almost not reduced (Examples 1-4).

Also, according to theoretical values calculated as being from NaBH ₄ 8 electron emission, in Comparative Example 1 does not perform the cooling of NaBH _4, whereas it is necessary to supply NaBH ₄ equal to 10 times the theoretical value In Examples 1 to _{4 where} the cooling of NaBH ₄ was performed, it was found that it was sufficient to supply NaBH ₄ corresponding to about 2.5 times the theoretical value.

From the above, by cooling before mixing and reacting the first solution containing NaBH ₄ , it is confirmed that the decomposition of NaBH _{4 in} the mixing field can be suppressed and the yield and monodispersity of the metal nanoparticles can be improved. did.

(2) This experiment 1
Next, based on the result of the preliminary experiment 1, in the first mixing device 12 of FIG. 1 excluding the static mixer 18, the first and second solutions L1 and L2 are mixed and subjected to an initial reaction, Metal nanoparticles were prepared.

  The temperature control jacket 24 was adjusted to cool the first solution L1 in the first preparation tank 16 to 11.5 ° C. and then supplied to the first mixing device 12 (Example 5).

  The first mixing device 12 is a one-jet type mixer in which the first orifice 62 has a diameter of 0.2 mm, the diameter D1 of the mixing field 52 is 4 mm, and the length L of the mixing field 52 is 90 mm. Was used. Then, the first solution L1 (26 mmol / L) was supplied into the mixing field 52 by a high-pressure jet flow, and the second solution L2 was supplied into the mixing field 52 at a flow rate of 0.05 m / second.

表２に示すように、第１の溶液Ｌ１を混合前に冷却した実施例５では、混合前に冷却しなかった（室温の）比較例２よりも、粒度分布が狭くなり単分散性が向上した。しかし、２液をタンク内でゆっくりと混合した場合（実施例１では収率２５％）よりも収率が低下した。これは、高圧ジェット流で混合させる場合は、タンク内でゆっくりと混合する場合と違って、摩擦熱等によってＮａＢＨ_４の分解が進み易くなっているためであることが推察される。 Comparative Example 2 is a case similar to Example 5 except that the first solution L1 was not cooled before the reaction. The results are shown in Table 2.

As shown in Table 2, in Example 5 in which the first solution L1 was cooled before mixing, the particle size distribution was narrower and monodispersity was improved than in Comparative Example 2 (at room temperature) that was not cooled before mixing. did. However, the yield was lower than when the two liquids were slowly mixed in the tank (yield 25% in Example 1). This is presumably because, when mixing with a high-pressure jet flow, decomposition of NaBH ₄ is likely to proceed due to frictional heat, etc., unlike when mixing slowly in the tank.

(3) Preliminary experiment 2
For the measurement, the first and second solutions L1 and L2 are initially reacted in a stirring tank using a high-speed rotating blade (30 mm diameter, 2000 rpm), simulating the mixing field of the first mixing device 12 in FIG. Metal nanoparticles were prepared. At this time, it was verified, whether the decomposition of NaBH ₄ in the mixing field when varying the cooling temperature of the first solution containing NaBH _4. At the same time, the presence or absence of precipitation of the surfactant (aerosol OT) accompanying the cooling of the first solution was also observed.

First, prior to the experiment, it was confirmed that only water was stirred in a stirring tank and no bubbles were generated. Further, it was confirmed that bubbles were generated when the first solution containing NaBH ₄ was stirred at room temperature. And the cooling temperature of the 1st solution L1 in a stirring tank was changed as Table 4 (Examples 6-9). The results are shown in Table 3.

表３に示すように、本実施例の条件下では、第１の調製タンク１６での冷却温度を８．０℃以下にすると、気泡の発生はなくＮａＢＨ_４の分解は起こらなかったが、９．０℃以上にすると気泡が発生した。これは、表１の実施例１において１１．５℃に冷却すると気泡が発生しなかったこととは異なり、高速攪拌下では摩擦熱が生じたり、反応表面積が増加したりすることで、ＮａＢＨ_４の分解し易くなるためと推察される。したがって、表３のように２液を高圧ジェット流で混合させるような高流速場では（特に摩擦熱で発熱しているワンジェット混合器内では）、ＮａＢＨ_４の分解が起こり易くなり、これにより収率が低下したものと考えられる。

As shown in Table 3, under the conditions of this example, when the cooling temperature in the first preparation tank 16 was 8.0 ° C. or lower, no bubbles were generated and NaBH ₄ was not decomposed. When the temperature was higher than 0 ° C., bubbles were generated. This is different from the fact that bubbles were not generated when cooled to 11.5 ° C. in Example 1 of Table 1, and frictional heat was generated or the reaction surface area was increased under high-speed stirring, so that NaBH ₄ This is presumed to be easy to decompose. Therefore, in a high flow velocity field in which two liquids are mixed with a high-pressure jet flow as shown in Table 3 (particularly in a one-jet mixer that generates heat due to frictional heat), NaBH ₄ is likely to be decomposed. It is thought that the yield was lowered.

  On the other hand, when the cooling temperature in the first preparation tank 16 was set to 9.0 ° C. or less, the surfactant (aerosol OT) in the first solution L1 started to precipitate after about 1 minute had passed (Example 6). 7). Even if the reaction is performed in the mixing field 52 with such precipitation occurring, the precipitate may clog the first orifice 62 or make the size of the reverse micelle in the reverse micelle method non-uniform.

Thus, in order to suppress the precipitation of the surfactant and to suppress the decomposition of NaBH ₄ , 1) In the step of preparing the first solution, the surface activity is within a range that minimizes the decomposition of NaBH _4. 2) Cooling to a temperature lower than the decomposition temperature of NaBH ₄ in the mixing field 52 immediately before supplying to the mixing field 52 (second cooling process) It was found that it is important to take two cooling steps. In the second cooling step, there is a time lag between when the temperature is lowered and when the surfactant starts to precipitate. Therefore, the residence time of the first solution in the second cooling step is shorter than the time lag. Must be set.

Thus, at the time of preparation it is possible uniformly stirred without causing precipitation, can be reliably suppress the decomposition of NaBH ₄ in the mixing field.

(4) This experiment 2
Next, based on the above knowledge, the first and second solutions L1 and L2 were mixed together in the first mixing device 12 of FIG. 1 to cause an initial reaction, thereby producing metal nanoparticles.

  In Example 12, the liquid temperature (first temperature) of the first solution L1 in the first preparation tank 16 is cooled to 11.5 ° C., which is a critical temperature at which no bubbles are generated (first cooling). Step), just before supplying to the first mixing device 12, the static mixer 18 cools the liquid temperature (second temperature) lower than the first temperature (second cooling step). At this time, the second temperature was set to a temperature at which bubbles were not generated in the preliminary experiment 2 (8.0 ° C.).

  As in the first experiment (2), the first mixing device 12 has the orifice 62 having a diameter of 0.2 mm, the mixing field 52 having a diameter D1 of 4 mm, and the mixing field 52 having a length L of 90 mm. A one-jet type mixer was used. Then, the first solution L1 (26 mmol / L) was supplied into the mixing field 52 by a high-pressure jet flow, and the second solution L2 was supplied into the mixing field 52 at a flow rate of 0.05 m / second.

  Further, the residence time of the first solution L1 in the static mixer 18 was 18 seconds, and the liquid temperature of the first solution L1 could be measured by a K thermocouple at the outlet of the static mixer 18.

  Comparative Example 3 is the same as Example 12 except that the second cooling step for cooling to 8.0 ° C. is not provided immediately before the first mixing device 12 in Example 12.

Further, in Examples 11, 12, and 13, the concentration of NaBH ₄ in the first solution L1 was changed from 5.7 g (26 mmol / L) to 2.9 g (14 mmol / L) and 1.4 g (7 mmol / L), respectively. This is the same as in Example 10 except that the amount was changed to 0.7 g (3 mmol / L). The results are shown in Table 4.

表４に示されるように、第１の冷却工程で第１の溶液を１１．５℃に冷却し、更に第２の冷却工程で８．０℃に冷却した実施例１０では、収率が高く、粒子サイズが小さく単分散性の優れた金属ナノ粒子が得られた。一方、第２の冷却工程を設けなかった比較例３では、収率は６７％と低いだけでなく、金属ナノ粒子の単分散性も低かった。これより、第２の冷却工程を設けることで、混合場５２におけるＮａＢＨ_４の分解を効果的に抑制できたことを確認した。

As shown in Table 4, in Example 10 in which the first solution was cooled to 11.5 ° C. in the first cooling step and further cooled to 8.0 ° C. in the second cooling step, the yield was high. As a result, metal nanoparticles having a small particle size and excellent monodispersibility were obtained. On the other hand, in Comparative Example 3 in which the second cooling step was not provided, the yield was not only as low as 67%, but the monodispersity of the metal nanoparticles was also low. From this, it was confirmed that the decomposition of NaBH ₄ in the mixing field 52 could be effectively suppressed by providing the second cooling step.

Furthermore, when the first solution is cooled to 11.5 ° C. in the first cooling step and further cooled to 8.0 ° C. in the second cooling step, the yield is almost reduced even when the NaBH ₄ concentration is 7 mmol / L. (Examples 10 to 13).

Thus, by cooling in two steps prior to mixing and reacting the first solution containing NaBH _4, while suppressing the precipitation such as a surfactant occurs, the decomposition of NaBH ₄ in the mixing field It was confirmed that it could be reliably suppressed and the yield and monodispersity of the metal nanoparticles could be improved.

(Example B)
(1) Preliminary experiment Alkane dissolved in 2700 mL of decane (manufactured by Wako Pure Chemical Industries) in a reducing agent aqueous solution prepared by dissolving 5.7 g of NaBH ₄ (manufactured by Wako Pure Chemical Industries) in 270 mL of H ₂ O (deoxygenated). The solution was added and mixed to prepare a reverse micelle solution of the first solution L1. The concentration of the reducing agent NaBH ₄ in the first solution L1 was 26 mmol / L.

Triammonium iron oxalate (Fe (NH ₄ ) ₃ (C ₂ O ₄ ) ₃ ) (manufactured by Wako Pure Chemical Industries, Ltd.) 5.3 g and potassium chloroplatinate (K ₂ PtCl ₄ ) (manufactured by Wako Pure Chemical Industries, Ltd.) 4.8 g And an alkane solution in which 148 g of aerosol OT (manufactured by Wako Pure Chemical Industries) is dissolved in 1440 mL of decane (manufactured by Wako Pure Chemical Industries) is added to and mixed with an aqueous solution of metal salt dissolved in 144 mL of H ₂ O (deoxygenated). A reverse micelle solution of the second solution L2 was prepared. The metal ion concentration of the second solution L2 was 8 mmol / L.

It is known that the hydrolysis rate of NaBH ₄ depends on the pH, and the hydrolysis rate increases particularly when the pH is 7 or less. Therefore, the presence or absence of hydrolysis (generation of bubbles) of NaBH ₄ when the pH of the first solution L1 was changed was observed. As a result, when 0.6 mL of NaOH (1N) was added to 200 mL of the first solution L1 (pH unadjusted, pH: 11.3) to adjust the pH to 12, bubbles due to hydrolysis of NaBH ₄ were Did not occur.

(2) This experiment Next, based on said result, in the 1st mixing apparatus 12 of FIG. 2, 1st, 2nd solution L1, L2 is mixed and it is made to react initially, and a metal nanoparticle is produced. did.

  In the pH adjusting unit 46 of FIG. 2, the pH of the first solution L1 was adjusted to 12 (Example 14).

  As the first mixing device 12, the orifice 62 has a diameter of 0.2 mm, the mixing field 52 has a diameter D1 of 4 mm, and the mixing field 52 has a length L of 90 mm, as in Example A described above. A one-jet type mixer was used. Then, the first solution L1 (26 mmol / L) was supplied into the mixing field 52 by a high-pressure jet flow, and the second solution L2 was supplied into the mixing field 52 at a flow rate of 0.05 m / second.

  Examples 15 and 16 are the same as Example 14 except that the pH of the first solution L1 before mixing was adjusted to 13 and 14, respectively.

  Comparative Example 4 is the same as Example 14 except that the pH was not adjusted before mixing. The results are shown in Table 5.

表５に示されるように、ｐＨを調整した実施例１４、１５は、ｐＨを調整しなかった比較例４よりも収率が高く、特にｐＨが１２のとき最も収率が高かった。一方、ｐＨを１３を超えるように調整すると、収率は低下する傾向がみられた。これは、ｐＨが１３を超えると水酸化物が生成し易くなり、還元反応効率が低下するためであると推測される。

As shown in Table 5, in Examples 14 and 15 in which the pH was adjusted, the yield was higher than that in Comparative Example 4 in which the pH was not adjusted. In particular, when the pH was 12, the yield was the highest. On the other hand, when the pH was adjusted to exceed 13, the yield tended to decrease. This is presumed to be because when the pH exceeds 13, hydroxides are easily generated, and the reduction reaction efficiency is lowered.

From the above, by adjusting the pH of the first solution L1 before mixing and reacting the first and second solutions in the mixing field, the hydrolysis rate of NaBH ₄ can be reduced and the yield is improved. I knew it was possible.

It is a conceptual diagram which shows the structure of the continuous manufacturing apparatus of the metal microparticle which concerns on this invention. It is a conceptual diagram which shows the structure of the continuous manufacturing apparatus of the metal fine particle of another aspect which concerns on this invention. It is sectional drawing which shows the mixing apparatus of a one jet type high pressure mixing system. It is explanatory drawing explaining the mixing theory of a one jet type high pressure mixing system. It is explanatory drawing explaining the shape of the 1st nozzle of the mixing apparatus of a one jet type high pressure mixing system. It is explanatory drawing explaining another shape of a 1st nozzle. It is explanatory drawing explaining another shape of a 1st nozzle. It is explanatory drawing explaining the other shape of a 1st nozzle. It is sectional drawing which shows the mixing apparatus of a T-shaped high pressure mixing system. It is sectional drawing which shows the mixing apparatus of a Y-shaped high pressure mixing system. It is sectional drawing which shows the mixing apparatus of a two jet opposing type high pressure mixing system. It is explanatory drawing explaining the mixing theory of the two jet opposing type high pressure mixing system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10, 10 '... Continuous manufacturing apparatus, 12 ... 1st mixing apparatus, 14 ... 2nd mixing apparatus, 16 ... 1st preparation tank, 18 ... Static mixer, 20 ... Control means (temperature), 22 ... 1st 2 preparation tanks, 23... 3rd preparation tank, 24, 25... Temperature control jacket, 27, 29... Temperature measurement section, 46... PH adjustment section, 47. ... mixing field

Claims (14)

A first solution containing at least a decomposable reducing agent and a depositing substance and a second solution containing metal atoms or metal ions for producing metal fine particles are mixed and reacted by a liquid phase method to produce metal fine particles. A method for producing metal fine particles comprising a mixing step to form,
First preparing the first solution and precooling the prepared first solution to a first temperature higher than the precipitation temperature of the precipitating substance and lower than the decomposition temperature of the reducing agent. A cooling process;
Immediately before the mixing step, two-stage cooling is performed, wherein the first solution is cooled to a second temperature lower than the first temperature. .   2. The method for producing metal fine particles according to claim 1, wherein the mixing step is instantaneous mixing in which the first solution and the second solution are instantaneously mixed and reacted. The liquid phase method is a reverse micelle method,
The first solution is a reverse micelle solution (solution L1) obtained by mixing a water-insoluble organic solvent containing a surfactant as the depositing substance and a reducing agent aqueous solution containing the reducing agent. 2. The solution 2 is a reverse micelle solution (solution L2) obtained by mixing a water-insoluble organic solvent containing a surfactant and a metal salt aqueous solution containing the metal atom or metal ion. Or the manufacturing method of the metal microparticle of 2.   The residence time of the first solution in the second cooling step is the time from when the first solution is set to the second temperature until the precipitation substance in the first solution starts to precipitate. The method for producing metal fine particles according to any one of claims 1 to 3, wherein the length is also shortened.   The method for producing fine metal particles according to claim 4, wherein the residence time is 1 minute or less.   The method for producing metal fine particles according to any one of claims 1 to 5, further comprising a pH adjusting step for adjusting the pH of the first solution before the mixing step. A mixing step in which a first solution containing at least a decomposable reducing agent and a second solution containing metal atoms or metal ions for producing metal fine particles are mixed and reacted by a liquid phase method to form metal fine particles. A method for producing fine metal particles comprising:
A method for producing metal fine particles, comprising a pH adjusting step of adjusting the pH of the first solution to a pH region in which the reducing agent is not decomposed before the mixing step.   8. The mixing process according to claim 1, wherein in the mixing step, one or more of the first solution and the second solution are mixed by a high-pressure jet flow of 1 MPa or more. A method for producing fine metal particles.   The method for producing fine metal particles according to claim 1, wherein the fine metal particles are alloy particles. The alloy particles, CuAu type or Cu ₃ Au type hard manufacturing method of metal fine particles according to any one of claims 1 to 9, wherein the magnetic ordered an alloy particle capable of forming an alloy phase. A first solution containing at least a decomposable reducing agent and a depositing substance and a second solution containing metal atoms or metal ions for producing metal fine particles are mixed and reacted by a liquid phase method to produce metal fine particles. An apparatus for producing metal fine particles having a mixing part to be formed,
A first cooling unit for preparing the first solution and precooling the prepared first solution;
A second cooling unit in a second stage that is provided immediately before the mixing unit and cools the cooled first solution in the first cooling unit;
An apparatus for producing fine metal particles, comprising: a control unit that controls a cooling temperature in the first cooling unit and the second cooling unit.   The control means controls the first solution prepared in the first cooling unit to have a first temperature that is higher than a precipitation temperature of the precipitating substance and lower than a decomposition temperature at which the reducing agent decomposes. The apparatus for producing fine metal particles according to claim 11, wherein the second cooling unit controls the first solution to a second temperature lower than the first temperature.   The apparatus for producing fine metal particles according to claim 11 or 12, wherein the mixing unit is an instantaneous mixing unit that instantaneously mixes and reacts the first solution and the second solution. A mixing section for forming metal fine particles by mixing and reacting a first solution containing at least a decomposable reducing agent and a second solution containing metal atoms or metal ions for producing metal fine particles by a liquid phase method; An apparatus for producing fine metal particles comprising:
A pH adjusting unit that is provided immediately before the mixing unit and adjusts the pH of the first solution;
Control means for controlling the pH adjuster so that the first solution is in a pH region where the reducing agent is not decomposed;
An apparatus for producing metal fine particles, comprising:

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