JP2008202125A - Method for manufacturing nanoparticle-containing solution, and conductive paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a nanoparticle-containing solution by which the progress status of metal nanoparticle synthesis can simply be comprehended. <P>SOLUTION: When reducing a metal precursor in a solution and synthesizing metal nanoparticles to manufacture a nanoparticle-containing solution, an ultraviolet-visible absorption spectrum of a reaction solution at the synthesis is measured over time and the status of synthesis of metal nanoparticles is grasped using the resulting measured results. It is preferable to confirm, from the measured results, one or more selected from the following (1), (2), (3) and (4): (1) absorbance due to absorption resulting from free electrons of metal nanoparticles is increased; (2) absorbance due to absorption resulting from metal ions is decreased; (3) the increase of absorbance in (1) and the decrease in absorbance in (2) are brought about while having an isosbestic point; and (4) no isosbestic point is observed and surface plasmon absorption of metal nanoparticles is observed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a nanoparticle-containing solution and a conductive paste.

  Nano-sized particles have characteristics that are not found in bulk-sized particles, and many studies have been conducted on methods for synthesizing nano-sized particles and their applications.

  Until now, nanoparticles such as Au, Ag, Pt, Pd, Cu, and Ni have been synthesized as metal nanoparticles, and can be used as conductive materials, catalyst materials, magnetic materials, nonlinear optical materials, coloring materials, and the like. Expected.

  Among these, copper nanoparticles can be applied as nano-sized wiring for electronic circuits and nonlinear optical materials. In particular, copper has attracted attention as a wiring material (conductive material) because it has higher resistance to ion migration than silver and is less expensive.

  However, copper has the property that when it becomes nano-sized, its surface activity becomes too high and it is easily oxidized even in a solvent. For this reason, it is generally considered that copper nanoparticles are difficult to synthesize compared to noble metal nanoparticles.

  Under such circumstances, conventionally, after synthesizing metal nanoparticles, the method for confirming the particle size of the metal nanoparticles is to isolate the metal nanoparticles from the synthesis solution and prepare a sample, and then use a transmission electron microscope ( The method of direct observation by TEM) was the mainstream.

  In addition, for example, Patent Document 1 discloses that the particle size distribution of the metal colloid liquid is defined by the measured value of the UV-visible absorbance because the metal colloid liquid itself cannot be observed by electron microscope observation.

  Specifically, in this document, a metal colloid solution was prepared by stirring an aqueous solution containing a silver salt such as silver nitrate and a reducing agent such as trisodium citrate or tannic acid for several hours to reduce the silver salt. Later, it is disclosed that the particle size distribution of this solution is measured by ultraviolet-visible absorbance analysis.

  If the particle size distribution is within a specific range, the particle size distribution can have a wide distribution width. Therefore, the metal colloid liquid contains not only metal colloid particles having a small particle size but also particles to some extent. It is described that metal colloidal particles having a large diameter can be mixed.

JP-A-2005-19028

  However, the former TEM observation takes time and effort for sample preparation, and the apparatus itself is very expensive.

  Therefore, TEM shows the synthesis status of metal nanoparticles in the actual production process, such as whether or not metal nanoparticles are synthesized, and if so, how much particle size metal nanoparticles are generated. It was virtually impossible to keep track of each observation.

  Moreover, the progress of the synthesis reaction cannot be known by TEM observation. Therefore, in order to know this, it was necessary to examine the raw material residue and the like using another analysis method.

  On the other hand, the technique described in the latter patent document 1 attempts to express high conductivity by defining the particle size distribution of the prepared metal colloid liquid by the measured value of ultraviolet-visible absorbance. Even if this technique is used, it is unclear how much metal nanoparticles have actually been generated. Therefore, it is difficult to grasp the synthesis state of metal nanoparticles by this technology.

  This invention is made | formed in view of the said problem, and provides the manufacturing method of the nanoparticle containing solution which can grasp | ascertain the synthetic | combination condition of a metal nanoparticle simply.

  In order to solve the above-mentioned problem, the method for producing a nanoparticle-containing solution according to the present invention is to reduce the metal precursor in the solution to synthesize metal nanoparticles and obtain a nanoparticle-containing solution. The gist is to include a procedure for measuring the ultraviolet-visible absorption spectrum of the solution over time and grasping the synthesis state of the metal nanoparticles using the obtained measurement results.

Here, the procedure preferably includes one or more confirmations selected from the following (1), (2), (3), and (4).
(1) Increase in absorbance due to absorption of metal nanoparticles from free electrons.
(2) Absorbance due to absorption derived from metal ions is reduced.
(3) An increase in absorbance in (1) and a decrease in absorbance in (2) occur while having an isosbestic point.
(4) It has no surface absorption, and has surface plasmon absorption of metal nanoparticles.

  Further, at the time of the synthesis, heating by an external heat source or microwave irradiation is preferably performed.

  Moreover, the said solution is good to contain the organic solvent which shows a reducibility with respect to the said metal precursor.

  In this case, the organic solvent is preferably a monohydric alcohol having 3 or more carbon atoms.

  Moreover, the said metal precursor is a copper precursor, and the said metal nanoparticle is good in it being a copper nanoparticle.

In this case, the copper precursor is represented by the following chemical formula 1, the copper nanoparticles are composed of a copper core derived from a copper component derived from the copper precursor represented by the chemical formula 1 below, and the chemical formula shown below. It is good to have the organic component which originates in the copper precursor represented by 1 and covers the circumference | surroundings of the said copper core.
(Chemical formula 1)
(R-A) _2- Cu
(Wherein, R represents a hydrocarbon group, A is COO, a _OSO 3, SO ₃ or OPO _3.)

  On the other hand, the gist of the conductive paste according to the present invention is that it contains metal nanoparticles collected from the nanoparticle-containing solution obtained by the method for producing a nanoparticle-containing solution.

  In the method for producing a nanoparticle-containing solution according to the present invention, when the metal precursor is reduced to synthesize metal nanoparticles, the ultraviolet-visible absorption spectrum of the reaction solution at the time of synthesis is measured over time. The procedure of grasping the synthesis status of metal nanoparticles using the measured results is included.

  The UV-visible absorption spectrum of the reaction solution measured over time at the time of synthesis shows information closely related to the presence or absence of synthesis of metal nanoparticles, the progress of the synthesis reaction, the approximate particle size of the generated metal nanoparticles, etc. Contains.

  Therefore, if this measurement result is used, the presence or absence of synthesis of the metal nanoparticles, the progress of the synthesis reaction, the approximate particle size of the generated metal nanoparticles, etc., without performing TEM observation or other analysis one by one It becomes possible to easily grasp the synthesis state of the particles.

  Therefore, according to the present invention, when the designed metal nanoparticles are synthesized or quality-controlled, or those that are out of design are synthesized, the synthesis conditions are promptly corrected to reject defective products. It can contribute to stable production of a solution containing nanoparticles, such as being able to reduce.

  Here, from the obtained measurement results, it can be seen that (1) the metal nanoparticles are synthesized if it is confirmed that the absorbance due to the absorption of free electrons from the metal nanoparticles increases.

  In addition, (2) if it is confirmed that the absorbance due to absorption derived from metal ions decreases, the progress of the synthesis reaction, such as how much the metal precursor as a raw material has been consumed and whether the synthesis reaction has been completed. I can grasp it.

  In addition, if it is confirmed that (3) an absorption point of (1) increases and a decrease in absorbance of (2) occurs while having an isosbestic point, metal nanoparticles having a particle size having no surface plasmon absorption can be obtained. You can see that it is obtained.

  In addition, (4) it is confirmed that metal nanoparticles having a particle diameter having surface plasmon absorption are obtained by confirming that the metal nanoparticles have surface plasmon absorption without having an absorption point.

  In the above production method, heating by an external heat source or microwave irradiation may be performed at the time of the synthesis, but heating by microwave irradiation is particularly preferable. This is because it is easy to synthesize monodisperse metal nanoparticles in a short time by generating the nuclei of metal nanoparticles uniformly by the rapid and uniform heating and ending the particle growth in a short time by heating for a short time. .

  Moreover, when the said solution contains the organic solvent which shows reducibility with respect to the said metal precursor, reduction | restoration of a metal precursor can be performed comparatively efficiently.

  In particular, if the organic solvent is a monohydric alcohol having 3 or more carbon atoms, the metal ions in the metal precursor can be reduced with a relatively weak reducing power.

  Moreover, when the said metal precursor is the said copper precursor, since a raw material is comparatively cheap, it becomes easy to suppress manufacturing cost. The copper nanoparticles have a copper core composed of a copper component derived from a specific copper salt and an organic component derived from the specific copper salt and covering the periphery of the copper core. It is difficult to oxidize even in a solvent exposed to. Moreover, it is hard to aggregate and its dispersibility is also good.

  On the other hand, the conductive paste according to the present invention contains metal nanoparticles collected from the nanoparticle-containing solution obtained by the above production method. Therefore, it has high quality, such as particle size control with higher accuracy than before.

  Therefore, when this is used, for example, as a wiring material, there is an advantage that the wiring width can be controlled with higher accuracy.

  Hereinafter, a method for producing a nanoparticle-containing solution according to the present embodiment (hereinafter sometimes referred to as “the present production method”) and a conductive paste according to the present embodiment (hereinafter also referred to as “the present paste”). This will be described in detail.

1. This production method is a method for producing a nanoparticle-containing solution by synthesizing metal nanoparticles by a solution reduction method. This production method includes a procedure for measuring the ultraviolet-visible absorption spectrum of the reaction solution at the time of the synthesis over time and grasping the synthesis state of the metal nanoparticles using the obtained measurement results.

(solution)
In the solution reduction method, metal nanoparticles are synthesized by reducing a metal precursor in a solution. The solution used for the synthesis includes at least a metal precursor capable of synthesizing the target metal nanoparticles and a solvent capable of dissolving or dispersing the metal precursor.

Specific examples of the metal precursor include, for example, general formula (RA) _n -M (where R is a hydrocarbon group, A is COO, OSO ₃ , SO ₃ or OPO ₃ , M is a metal, n is the same as the valence that the metal M can take and is an integer of 1 or more), metal alkoxide (metal isopropoxide, metal ethoxide, etc.), metal acetylacetone complex (metal acetylacetonate, etc.) ) And the like. These metal precursors may be contained in one or more kinds of solutions.

Among the metal precursors, those represented by the general formula (R-A) _n -M can be preferably used. This is because the metal precursor is relatively inexpensive, and thus has advantages such as a cost-effective nanoparticle-containing solution and a conductive paste. In addition, the organic component derived from the metal precursor is easily decomposed at a relatively low temperature, and therefore has an advantage that it is easy to obtain a conductive paste that can be easily reduced in resistance by low-temperature firing.

In the general formula (RA) _n -M, the hydrocarbon group R may be a saturated hydrocarbon group such as an alkyl group or an unsaturated hydrocarbon group such as an alkenyl group. The molecular structure may be linear or branched. Further, a part of hydrogen in the hydrocarbon group R may be substituted with another substituent such as a halogen element as long as it does not adversely affect the synthesis of metal nanoparticles.

  The number of carbon atoms of the hydrocarbon group R is not particularly limited. The carbon number of the hydrocarbon group R, that is, the hydrocarbon chain length, is closely related to the particle size and particle size distribution of the obtained metal nanoparticles, and by varying this, the particle size and particle size distribution of the metal nanoparticles are changed. Can be controlled.

  Moreover, when the carbon number of the hydrocarbon group R becomes excessively large, there is a tendency that the low-temperature sinterability of the obtained metal nanoparticles is lowered. On the other hand, when the carbon number of the hydrocarbon group R is excessively small, there is a tendency that the oxidation inhibiting effect is small when a metal that is easily oxidized such as copper is used. Therefore, the carbon number of the hydrocarbon group R is preferably selected in consideration of these.

  In the present production method, the upper limit value of the carbon number of the hydrocarbon group R is preferably 40 or less, more preferably 20 or less. On the other hand, the lower limit of the carbon number of the hydrocarbon group R is preferably 3 or more, more preferably 6 or more.

In the general formula (R-A) _n -M, CO can be particularly preferably used as A. This is because the bonding strength with the metal M is relatively weak and the synthesis time of the metal nanoparticles can be made relatively short, thereby contributing to an improvement in productivity.

In the general formula (RA) _n -M, any type of metal may be used for M, and can be appropriately selected depending on the use of the nanoparticle-containing solution.

  Specific examples of the metal M include, for example, copper, silver, gold, white metal (platinum, palladium, iridium, rhodium, ruthenium, osmium), nickel, zirconium, niobium, molybdenum, calcium, strontium, barium, and indium. , Cobalt, zinc, cadmium, aluminum, gallium, iron, chromium, manganese, yttrium, and the like.

  Among these, as the metal M, copper, silver, gold, white metal, nickel and the like can be exemplified as preferable ones from the viewpoint of low resistance, safety, reducibility, and the like.

  Specific examples of such metal precursors include fatty acid metal salts such as fatty acid copper salts, alkylsulfonic acid metal salts such as alkylsulfonic acid copper salts, and alkylphosphonic acid metal salts such as alkylphosphonic acid copper salts. Etc. can be illustrated as suitable.

  Specific examples of the solvent capable of dissolving or dispersing the metal precursor include alcohols such as diols, glycols and polyols, amines, hydrocarbons, ketones, ethers and esters. Examples of the organic solvent can be exemplified. These may be used alone or in combination.

  Of these organic solvents, preferably, a reducing organic solvent exhibiting reducibility with respect to the metal precursor can be suitably used. Further, the reducing organic solvent preferably has a relatively low solubility in water.

  Specific examples of such a reducing organic solvent include monohydric alcohols having 3 or more carbon atoms such as propanol, butanol, pentanol, hexanol, heptanol, and octanol. In particular, a monohydric alcohol having 3 to 30 carbon atoms, preferably 3 to 20 carbon atoms, more preferably 3 to 10 carbon atoms, and most preferably 4 to 8 carbon atoms, and the like can be exemplified as suitable ones. These may be contained alone or in combination of two or more.

  This is because when the carbon number is within the above range, the metal ion due to the metal precursor is not easily reduced rapidly, and the metal ion can be easily reduced with an appropriate reducing power.

  Whether the metal precursor is dissolved or dispersed in the organic solvent depends on the combination of the selected metal precursor and the organic solvent, the amount of the metal precursor relative to the organic solvent, and the like. Further, the amount of the metal precursor may be appropriately adjusted in consideration of the amount of metal nanoparticles to be synthesized.

One or more additives such as a catalyst, a reducing agent, and a nucleating agent such as PtCl ₄ are appropriately added to the above solution within a range that does not adversely affect the formation of metal nanoparticles. May be.

(Synthesis)
In this production method, the raw material solution is preferably heated from the viewpoint of promoting reduction of the metal precursor during the synthesis of the metal nanoparticles.

  In this case, the heating method is not particularly limited as long as it is given heat that can reduce the metal precursor. Specific examples of the heating method include, for example, electric heating using a heater, heated oil, a heat medium such as water, a method of heating a solution by an external heat source such as a burner flame, hot air, etc., microwave, etc. Examples thereof include a method of heating a solution by irradiating an electromagnetic wave, a high frequency, a laser beam, an electron beam or the like. These heating methods may be used alone or in combination of two or more methods.

  The heating temperature of the raw material solution varies depending on the type of metal precursor used. In addition, the heating is preferably performed in a state where the solution is present in an inert gas atmosphere such as nitrogen, helium, or argon in order not to oxidize the generated metal nanoparticles.

  Of the above heating methods, a method of heating the solution with an external heat source or a method of heating the solution by irradiating microwaves is preferably used. More preferably, the latter is used. This is because the raw material solution can be heated uniformly and metal nanoparticles can be synthesized in a relatively short time.

  In order to heat the raw material solution using these, more specifically, for example, the following may be performed.

  In the former case, the reaction vessel containing the raw material solution is brought into contact with or in proximity to a heat medium such as a liquid (for example, oil, water, etc.) heated to a temperature capable of reducing the metal precursor in the solution. The reaction vessel may be heated with a heater or a burner flame.

  On the other hand, in the latter case, the microwave used is not particularly limited. Specifically, for example, a microwave with a frequency of 2.45 GHz, which is usually used frequently in Japan, may be used. Hereinafter, the microwave irradiation conditions are based on the assumption that a microwave with a frequency of 2.45 GHz is selected. However, when other microwaves are selected, the irradiation conditions are appropriately set according to this. Change it.

  Microwave irradiation intensity varies depending on the type of metal precursor, organic solvent, etc., but it is easy to control the particle size distribution of the generated metal nanoparticles, and the following range is selected from the viewpoint of appropriate heating time. good.

The upper limit value of the microwave irradiation intensity is preferably 24 W / cm ³ or less, and more preferably 18 W / cm ³ or less.

On the other hand, the lower limit value of the microwave irradiation intensity is preferably 1 W / cm ³ or more, more preferably 2 W / cm ³ or more, and even more preferably 3 W / cm ³ or more. The irradiation intensity of these microwaves is a value represented by microwave output (W) / volume of reaction solution (cm ³ ).

  In addition, in any of the heating methods described above, the heating time varies depending on the metal precursor, the type of organic solvent, the heating temperature, etc., but the purity of the metal nanoparticles is sufficiently generated by the generation of side reactants that sufficiently generate metal nanoparticles. From the viewpoint of productivity and the like, it is preferable to select the following range.

  The upper limit of the heating time is preferably 2 hours or less, more preferably 1.5 hours or less, and even more preferably 1 hour or less.

  On the other hand, the lower limit of the heating time is preferably 30 seconds or longer, more preferably 1 minute or longer, and even more preferably 2 minutes or longer. However, in the case of microwave heating, the temperature raising time to the reaction temperature can be performed in a shorter time than external heating.

  In any of the heating methods described above, the heating temperature is preferably controlled to be substantially constant.

  The upper limit of the heating temperature is preferably 300 ° C. or less, more preferably 275 ° C. or less, and even more preferably 250 ° C. or less, from the viewpoints of productivity and ease of control of the synthesis reaction. good. On the other hand, the lower limit of the heating temperature is preferably 80 ° C. or higher, more preferably 100 ° C. or higher, and even more preferably 120 ° C. or higher, from the viewpoint of dispersibility of the metal precursor.

  In the case of performing microwave heating, the heating temperature is controlled by, for example, immersing a temperature sensor in the above solution and repeating on / off of microwave irradiation so that the temperature of the solution becomes constant. be able to. Further, microwave irradiation may be performed using a known microwave irradiation apparatus.

(Metal nanoparticles)
In this production method, the structure of the synthesized metal nanoparticles varies depending on the type of metal precursor used. For example, when the metal precursor represented by the general formula (RA) _n -M is used, metal nanoparticles whose surface is modified with an organic component such as a fatty acid group are synthesized.

That is, the metal nanoparticles include a metal core mainly composed of a metal component derived from the metal precursor, and an organic component (hereinafter referred to as “coating organic component”) that is derived from the metal precursor and covers the periphery of the metal core. It may be said.) For example, when a metal precursor represented by the general formula (RA) _n -M is used, the metal core is a metal M such as copper or silver, and the covering organic component is an RA such as a fatty acid group. -Group.

  The metal core may be composed of one or more metal components derived from one or more metal salts. Moreover, the said coating | coated organic component may be comprised from the 1 type, or 2 or more types of organic component originating in the 1 type, or 2 or more types of metal precursor.

  In addition, about the kind of metal core among the said metal nanoparticles, it can confirm by the X-ray diffraction method etc., for example. Moreover, about the kind of coating | coated organic component, it can confirm by NMR (nuclear magnetic resonance method), GC / MS (gas chromatography / mass spectrometry) etc., for example.

  The average particle diameter of the metal core is not particularly limited as long as it is nano-sized, and can be appropriately selected in consideration of its use. As an upper limit of the average particle diameter of the said metal core, 100 nm, 50 nm, 10 nm etc. can be illustrated, for example. On the other hand, examples of the lower limit of the average particle diameter of the metal core include 0.1 nm, 0.5 nm, and 1 nm.

  In addition, the average particle diameter is obtained by arbitrarily extracting 100 metal nanoparticles (although only a metal core can be observed with TEM) from a transmission electron microscope (TEM) photograph of the metal nanoparticles, and measuring the particle diameter. This is the value of the particle size (D50) when the number of particles is 50% when counted in order from the smallest diameter.

  In addition, the particle size distribution of the metal nanoparticles is not particularly limited, but is preferably relatively sharp. Specific examples of the particle size variation ε = (D90−D10) / D50 include, for example, 2, 1.5, 1.3 and the like as preferable upper limit values. On the other hand, the lower limit value of ε is not particularly illustrated because ε is preferably as close to 0 as possible.

  D90 and D10 are values calculated in the same manner as D50, and are the particle size at which the number of particles is 90% and the particle size at which the number of particles is 10%.

(Measurement of ultraviolet-visible absorption spectrum)
Here, in the above synthesis, for example, depending on factors such as the type of metal precursor to be used (chain length of the hydrocarbon group R in the compound represented by the general formula (RA) _n -M), the heating temperature, the heating time, and the like. The synthesis situation such as the particle size of the obtained metal nanoparticles is different.

  Until now, the method of observing a sample collected from the reaction solution by TEM and empirically determining the synthesis conditions for obtaining a desired particle size based on the result has been mainly used.

  On the other hand, this manufacturing method measures the ultraviolet-visible absorption spectrum of the reaction solution during the synthesis of metal nanoparticles over time and uses the obtained measurement results to determine the procedure for grasping the synthesis status of metal nanoparticles. Contains.

  The UV-visible absorption spectrum of the reaction solution measured over time at the time of synthesis shows information closely related to the presence or absence of synthesis of metal nanoparticles, the progress of the synthesis reaction, the approximate particle size of the generated metal nanoparticles, etc. Contains.

  Therefore, if this measurement result is used, the presence or absence of synthesis of the metal nanoparticles, the progress of the synthesis reaction, the approximate particle size of the generated metal nanoparticles, etc., without performing TEM observation or other analysis one by one The synthesis status of the particles can be easily grasped.

  In addition, this manufacturing method does not exclude grasping | ascertainment of the synthetic | combination condition by TEM observation at all, and you may use together with the said procedure as needed. However, this production method can significantly reduce the number of TEM observations as compared with the conventional method by measuring the change with time of the ultraviolet-visible absorption spectrum.

  The ultraviolet-visible absorption spectrum of the reaction solution may be measured using an ultraviolet-visible spectrophotometer using a sample taken from the reaction solution at an arbitrary time. When the sample has a high concentration, there are cases where sufficient absorption spectrum cannot be measured. At that time, the sample collected may be diluted to an appropriate concentration with an appropriate organic solvent such as toluene, and the absorption spectrum may be measured using this.

  FIG. 1 schematically shows an example of a measurement result when an ultraviolet-visible absorption spectrum of a reaction solution during the synthesis of metal nanoparticles is measured over time. The horizontal axis is the measurement wavelength, and the vertical axis is the absorbance. Moreover, in FIG. 1, the ultraviolet-visible absorption spectrum of the reaction solution in time t1-t4 (t1 <t2 <t3 <t4) is shown.

  In this production method, the synthesis status of the metal nanoparticles is grasped using the measurement results. Specifically, from the above measurement results, by confirming one or more selected from the following (1), (2), (3) and (4), the metal nanoparticles corresponding to the content It is preferable to grasp the synthesis state of

(1) Increase in absorbance due to absorption of metal nanoparticles from free electrons.
(2) Absorbance due to absorption derived from metal ions is reduced.
(3) An increase in absorbance in (1) and a decrease in absorbance in (2) occur while having an isosbestic point.
(4) It has no surface absorption, and has surface plasmon absorption of metal nanoparticles.

  Here, from the obtained measurement results, (1) an increase in absorbance (A in FIG. 1) due to free electron-derived absorption of metal nanoparticles (in FIG. 1, near absorption wavelength a) could be confirmed. In this case, it can be seen that metal nanoparticles are synthesized.

  In addition, (2) when the decrease in absorbance (B in FIG. 1) due to absorption derived from metal ions (absorption wavelength b in FIG. 1) can be confirmed, how much the metal precursor as a raw material is consumed. It is possible to grasp the progress of the synthesis reaction such as whether the synthesis reaction has been completed or not.

  Further, (3) having an isosbestic point (C in FIG. 1), an increase in absorbance in (1) (A in FIG. 1) and a decrease in absorbance in (2) (B in FIG. 1) It can be confirmed that metal nanoparticles having a particle size having no surface plasmon absorption are obtained.

  For example, it has been reported that copper nanoparticles do not have surface plasmon absorption unless they are 5 nm or more. Therefore, when using the copper precursor, if the above confirmation can be made, the copper nanoparticles produced by the synthesis should have a particle size of less than about 5 nm without performing TEM observations step by step. I understand.

  In addition, (4) when it is confirmed that the surface does not have an isosbestic point (C in FIG. 1) and has surface plasmon absorption of metal nanoparticles (D in FIG. 1, absorption wavelength d), surface plasmon It turns out that the metal nanoparticle of the particle size with absorption is obtained.

  For example, when the copper precursor is similarly used and the above confirmation can be made, it can be seen that the copper nanoparticles produced by the synthesis have a particle size of approximately 5 nm or more.

  In this way, according to the above, if the designed metal nanoparticles are synthesized or quality controlled, or if they are synthesized out of design, the synthesis conditions are corrected quickly and defective products are designed. It is possible to contribute to stable production of a solution containing nanoparticles, for example, by reducing the number of particles.

  As mentioned above, although this manufacturing method was demonstrated, the metal nanoparticle in the nanoparticle containing solution obtained by this manufacturing method can be applied to various uses.

  Specific applications include, for example, conductive paste materials used for fine wiring, interlayer bonding, bonding members (replacement of lead solder), anisotropic conductive film conductive materials (for example, dispersed in a resin film, Examples include a catalyst material, a coloring material, a pigment, and the like.

2. This paste contains the metal nanoparticles collect | recovered from the nanoparticle containing solution obtained by this manufacturing method.

  In order to recover the metal nanoparticles from the nanoparticle-containing solution, a general method may be used. Specifically, for example, various methods such as centrifugation, filtration, and solvent extraction can be exemplified. These may be used alone or in combination of two or more. These may be performed once or a plurality of times.

  As a more specific recovery method, for example, the supernatant of the synthesis solution is removed, and there is a cleaning property, and a poor solvent (for example, hexane or the like) is added to the metal nanoparticles, A method of recovering the metal nanoparticles can be exemplified by repeatedly performing the precipitation treatment by washing and centrifugation, and then drying the obtained precipitate under reduced pressure.

  In order to paste the collected metal nanoparticles into a paste, the collected metal nanoparticles may be dispersed in a solvent suitable for pasting using a dispersion means such as ultrasonic waves or bead mill.

  Specific examples of the organic solvent include hexane, toluene, xylene, octane, decane, undecane, tetradecane, terpineol, decanol, methyl ethyl ketone (MEK), acetone, tetrahydrofuran (THF), hexanol, dimethylformamide (DMF). N-methyl-2-pyrrolidone (NMP), dipropylene glycol monomethyl ether, methanol, ethanol, ethyl acetate, ethyl carbitol, ethyl carbitol acetate, butyl carbitol, butyl carbitol acetate and the like. These may be used alone or in combination.

  At this time, the concentration of the metal nanoparticles is not particularly limited, and can be appropriately adjusted in consideration of the application. Generally, for example, 90% by weight, 85% by weight, 80% by weight and the like can be exemplified as a preferable upper limit value of the concentration of metal nanoparticles. On the other hand, examples of preferable lower limit values that can be combined with these preferable upper limit values include 1% by weight, 2% by weight, and 5% by weight.

  In addition, one or more kinds of various additives such as a dispersant for improving the dispersion stability of the metal nanoparticles are added as long as the properties such as conductivity and sinterability are not adversely affected. Also good.

  Hereinafter, the present invention will be described in detail using examples. Here, the microwave long-alcohol reduction method is used to reduce the copper long-chain carboxylate dispersed in the solution to synthesize monodisperse copper nanoparticles, but this is not a limitation. .

  For example, in this example, a copper long-chain carboxylic acid salt was used as a copper precursor from the viewpoint of a weak binding force with copper and a quick synthesis reaction. Salts, copper long-chain phosphonates, and the like can be similarly applied.

1. Preparation of copper precursor First, a copper precursor used as a raw material was synthesized by the following procedure.

(Copper octoate)
51 mmol of sodium octoate (C ₇ H ₁₅ COONa) was dissolved at 80 ° C. in 400 ml of deionized water. Thereafter, a solution obtained by dissolving 25 mmol of copper (II) nitrate in 100 ml of deionized water was added to this solution to obtain a precipitate.

Next, the precipitate was repeatedly filtered and washed with deionized water. After further filtration and washing with methanol, the precipitate was dried under reduced pressure at 70 ° C. for 12 hours to obtain copper octoate ((C ₇ H ₁₅ COO) ₂ Cu).

(Copper myristate)
Copper myristate ((C ₁₃ H ₂₇ ) was prepared in the same manner as in the synthesis of copper octoate except that a solution obtained by dissolving 51 mmol of sodium myristate (C ₁₃ H ₂₇ COONa) in 200 ml of deionized water at 80 ° C. was used. COO) ₂ Cu) was obtained.

2. Preparation of Copper Precursor-Containing Solution Next, a solution containing the copper precursor synthesized above was prepared by the following procedure.

(Copper octoate containing solution)
The synthesized copper octanoate 0.5 mmol was mixed with 1-heptanol 50 mL, and copper octanoate was dispersed in 1-heptanol using ultrasonic waves to prepare a copper octoate-containing solution.

(Copper myristate containing solution)
A copper myristate-containing solution was prepared in the same manner as in the preparation of the copper octoate-containing solution except that 0.5 mmol of the synthesized copper myristate was used.

3. Time-lapse measurement of ultraviolet-visible absorption spectrum of reaction solution during synthesis of copper nanoparticles Next, using the microwave heating-alcohol reduction method, the copper precursor in the prepared copper precursor-containing solution was reduced to obtain copper. In synthesizing the nanoparticles, the ultraviolet-visible absorption spectrum of the reaction solution at the time of synthesis was measured over time.

That is, using a microwave heating apparatus for chemical synthesis (manufactured by Micro Electronics Co., Ltd., “MMG-213VP”) in a nitrogen atmosphere at 10 W / cm ³ (microwave frequency of 2.45 GHz), a copper octoate-containing solution Alternatively, the copper myristate-containing solution was heated. At this time, the heating temperature was 409K, 430K, or 449K, respectively. The heating temperature was obtained from an optical fiber thermometer (manufactured by Anritsu Keiki Co., Ltd., “AMOTH TM-5886”), and the temperature control was performed by repeatedly turning on / off the microwave irradiation.

  Moreover, the reaction solution in arbitrary time was fractionated, and the ultraviolet-visible absorption spectrum was measured using the ultraviolet visible spectrophotometer (the JASCO Corporation make, "V-570"). The measurement was performed at room temperature in a quartz cell (solution layer thickness L = 10 mm), and the measurement wavelength was in the range of 300-1200 nm.

4). Observation of Particle Shape and Particle Size Next, TEM observation was performed in order to support the relationship between the measurement results of the spectrum and the synthesis state of copper nanoparticles.

  That is, the particle shape and particle size of the copper nanoparticles contained in the reaction solution fractionated at an arbitrary time were measured using a transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, “Hitachi Transmission Electron Microscope H-9000”). ).

  In addition, the reaction solution was dropped onto a Cu grid with an elastic carbon support film and treated overnight at 50 ° C. under vacuum to use as an observation sample.

5. Results and Discussion Table 1 summarizes the relationship between the synthesis conditions and the experimental results described later when each copper precursor is reduced to synthesize copper nanoparticles.

5.1 Copper precursor: copper octoate, heating temperature: 409K, heating time: 0 minutes → 120 minutes (measurement points are 0, 5, 10, 20, 40, 60, 90, 120 minutes)
FIG. 2 shows the time-dependent change (0 minute → 120 minutes) of the ultraviolet-visible absorption spectrum of the copper octoate-containing solution heated at 409 K by microwave heating.

  According to FIG. 2, under this condition, an increase in absorbance near 400 nm was observed with an increase in heating time. The absorption near this is absorption derived from free electrons of the metal nanoparticles. From this, it can be seen that copper nanoparticles are synthesized if the increase in absorbance is confirmed.

In addition, a decrease in absorbance having a peak top at 696 nm was observed with the increase in absorbance near 400 nm. The peak are the absorption due to d-d transitions ^{Cu 2+,} it can be seen ^{that the Cu 2+} is reduced is reduced to Cu ^0. From this, it can be seen that if the decrease in absorbance is confirmed, it is possible to grasp the progress of the synthesis reaction, such as how much the raw copper octoate is consumed and whether the synthesis reaction is completed.

Further, these two changes in absorbance varied with an isosbestic point at 565 nm. This indicates that one chemical species has stoichiometrically changed to another. That is, it can be said that the series of ultraviolet-visible absorption spectrum changes in FIG. 2 represents a process in which Cu ²⁺ is reduced to Cu ⁰ and copper nanoparticles are generated.

  Here, it is reported that the copper nanoparticles do not have surface plasmon absorption unless they are 5 nm or more. According to FIG. 2, there is no place where the ultraviolet-visible absorption spectrum suddenly changes greatly, and no peak derived from the surface plasmon absorption of the copper nanoparticles is observed.

That is, if it is confirmed that an increase in absorbance due to absorption due to free electrons of copper nanoparticles and a decrease in absorbance due to absorption due to Cu ²⁺ occur while having an isosbestic point, TEM observation is not performed step by step. However, it turns out that the copper nanoparticle which has a particle size of less than 5 nm which does not have surface plasmon absorption is obtained.

  FIG. 3 is a TEM image of copper nanoparticles contained in the reaction solution after 90 minutes when the copper octoate-containing solution was microwave-heated at 409 K (spectrum in FIG. 2). FIG. 3B is an enlarged view of FIG. FIG. 4 is a histogram showing the particle size distribution of the copper nanoparticles calculated from FIG.

  The TEM image in FIG. 3 has a large number of particles, and a large number of fringes indicating the crystal existed on each particle. Further, the electron diffraction (ED) pattern obtained from this region showed that the copper had a face-centered cubic lattice (fcc) structure. Moreover, the average particle diameter of the copper nanoparticles estimated from the histogram of FIG. 4 was 3.2 nm.

  Thus, it was shown also from the TEM observation performed for support that the copper nanoparticle of less than 5 nm which does not have surface plasmon absorption exists mainly.

5.2 Copper precursor: copper myristate, heating temperature: 409K, heating time: 1 minute → 90 minutes (measurement points are 1, 5, 10, 20, 40, 60, 90 minutes)
FIG. 5 shows the time-dependent change (1 minute → 90 minutes) of the ultraviolet-visible absorption spectrum of the copper myristate-containing solution heated at 409 K by microwave heating.

  As shown in FIG. 5, even under this condition, as in “5.1”, there is an decrease in absorbance with a peak top at 696 nm as the absorbance near 400 nm increases while having an isosbestic point at 565 nm. Observed. Therefore, the same details as in 5.1 apply, such as copper nanoparticles having a particle size of less than 5 nm.

  FIG. 6 is a TEM image of copper nanoparticles contained in the reaction solution after 90 minutes when the copper myristic acid-containing solution was microwave-heated at 409 K (spectrum in FIG. 5). FIG. 6 (b) is an enlarged view of FIG. 6 (a). FIG. 7 is a histogram showing the particle size distribution of the copper nanoparticles calculated from FIG.

  According to this TEM observation, the average particle diameter of the copper nanoparticles was 2.1 nm, and it was confirmed that there were mainly copper nanoparticles of less than 5 nm having no surface plasmon absorption.

5.3 Copper precursor: copper octoate, heating temperature: 443 K, heating time: 0 minutes → 20 minutes (measurement points are 0, 1, 5, 10, 20 minutes)
FIG. 8 shows the time-dependent change (0 minute → 20 minutes) of the ultraviolet-visible absorption spectrum of the copper octoate-containing solution heated at 443 K by microwave heating.

  As shown in FIG. 8, in the case of this condition, for 0 minutes to 10 minutes, as in “5.1”, it has an isosbestic point at 565 nm and peaks at 696 nm with an increase in absorbance near 400 nm. A decrease in absorbance with a top was observed. Therefore, when heated for 0 to 10 minutes, copper nanoparticles having a particle size of less than 5 nm are obtained, and the same details as in 5.1 apply.

  However, when heated for 20 minutes, the ultraviolet-visible absorption spectrum changed greatly. That is, the isosbestic point that had existed so far suddenly disappeared, and a new absorption having a peak top at 596 nm was observed. This 596 nm peak is derived from surface plasmon absorption of copper nanoparticles.

That is, the series of changes in the ultraviolet-visible absorption spectrum represents a series of processes in which Cu ²⁺ is reduced to Cu ⁰ to produce copper nanoparticles and grow to a particle size of 5 nm or more.

From this, while having an isosbestic point, while the increase in the absorbance due to the absorption from the free electrons of the copper nanoparticles and the decrease in the absorbance due to the absorption from Cu ²⁺ occur, the particle size of less than 5 nm It can be seen that copper nanoparticles having a particle diameter of 5 nm or more are obtained when the isoabsorption point disappears and surface plasmon absorption of the copper nanoparticles occurs. Therefore, if this is utilized, it can be said that it becomes possible to selectively obtain copper nanoparticles having different particle sizes.

  FIG. 9 is a TEM image of copper nanoparticles contained in the reaction solution after 20 minutes when the copper octoate-containing solution was microwave-heated at 443 K (spectrum in FIG. 8). FIG. 9 (b) is an enlarged view of FIG. 9 (a). FIG. 10 is a histogram showing the particle size distribution of the copper nanoparticles calculated from FIG.

  According to this TEM observation, the average particle diameter of the copper nanoparticles was 6.0 nm, and it was confirmed that copper nanoparticles having a surface plasmon absorption of 5 nm or more are mainly present.

5.4 Copper precursor: copper myristate, heating temperature: 443K, heating time: 1 minute → 20 minutes (measurement points are 1, 10, 20 minutes)
FIG. 11 shows the time-dependent change (1 minute → 20 minutes) of the ultraviolet-visible absorption spectrum of the copper myristate-containing solution heated at 443 K by microwave heating.

  As shown in FIG. 11, even under this condition, as in “5.1”, there is a decrease in absorbance having a peak top at 696 nm with an increase in absorbance near 400 nm while having an isosbestic point at 565 nm. Observed. Therefore, the same details as in 5.1 apply, such as copper nanoparticles having a particle size of less than 5 nm. In addition, when FIG. 5 and FIG. 11 are compared, it can be seen that if heated at a higher temperature, copper nanoparticles having substantially the same particle diameter can be obtained in a shorter time.

  FIG. 12 is a TEM image of copper nanoparticles contained in the reaction solution after 20 minutes when the copper myristic acid-containing solution was microwave-heated at 443 K (spectrum in FIG. 11). FIG. 12B is an enlarged view of FIG. FIG. 13 is a histogram showing the particle size distribution of the copper nanoparticles calculated from FIG.

  According to this TEM observation, the average particle diameter of the copper nanoparticles was 2.6 nm, and it was confirmed that there were mainly copper nanoparticles of less than 5 nm having no surface plasmon absorption.

5.5 Copper precursor: copper myristate, heating temperature: 430 K, heating time: 1 minute → 70 minutes (measurement points are 1, 10, 20, 40, 60, 70 minutes)
FIG. 14 shows the time-dependent change (1 minute → 70 minutes) of the ultraviolet-visible absorption spectrum of the copper myristate-containing solution heated at 430 K by microwave heating.

  As shown in FIG. 14, in this condition, no peak derived from the surface plasmon absorption of the copper nanoparticles was observed for 1 minute to 60 minutes, and the isosbestic point was observed at 565 nm as in “5.1”. With the increase in absorbance near 400 nm, a decrease in absorbance with a peak top at 696 nm was observed. Therefore, when heated for 1 to 60 minutes, copper nanoparticles having a particle size of less than 5 nm are obtained, and the same details as described in “5.1” apply.

  However, as can be seen from the ultraviolet-visible absorption spectrum when heated for 70 minutes, the isoabsorption point suddenly disappeared and a peak (596 nm) derived from the surface plasmon absorption of the copper nanoparticles was generated.

  Therefore, it can be seen that when heated for 70 minutes, copper nanoparticles having a particle size of 5 nm or more are obtained.

  FIG. 15 is a TEM image of the copper nanoparticles contained in the reaction solution after 60 minutes when the copper myristic acid-containing solution was microwave-heated at 430K. FIG. 16 is a TEM image of copper nanoparticles contained in a reaction solution after 70 minutes when a copper myristic acid-containing solution is heated by microwave at 430K.

  According to this TEM observation, in this condition, if the heating is performed for 1 minute to 60 minutes, the average particle diameter of the copper nanoparticles remains at 2-3 nm without surface plasmon absorption, but is heated for 70 minutes. It was confirmed that many copper nanoparticles having a surface plasmon absorption and a particle diameter of 5 nm or more exist.

  As described above, according to the present invention, it is possible to easily grasp the synthesis state of metal nanoparticles by utilizing the change over time of the ultraviolet-visible absorption spectrum of the reaction solution during the synthesis of metal nanoparticles. It can be said.

  Although the embodiments and examples have been described above, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the above examples, copper nanoparticles were synthesized using a copper precursor, but in addition to the copper precursor, other metal precursors such as a silver precursor and a gold precursor were used, and the metal precursor was used. The present invention can also be applied to the synthesis of metal nanoparticles of the metal constituting the metal.

It is the figure which showed typically an example of the measurement result when the ultraviolet-visible absorption spectrum of the reaction solution at the time of the synthesis | combination of a metal nanoparticle was measured with time. It is the figure which showed the time-dependent change (0 minute-> 120 minutes) of the ultraviolet-visible absorption spectrum of the copper octoate containing solution heated at 409K by the microwave heating. It is a TEM image of the copper nanoparticle contained in the reaction solution after 90 minutes when a copper octoate containing solution is microwave-heated at 409K (spectrum in FIG. 2). It is a histogram which shows the particle size distribution of the copper nanoparticle computed from FIG.3 (b). It is the figure which showed the time-dependent change (1 minute-> 90 minutes) of the ultraviolet-visible absorption spectrum of the copper myristate containing solution heated at 409K by the microwave heating. It is a TEM image of the copper nanoparticle contained in the reaction solution after 90 minutes when the copper myristate containing solution is microwave-heated at 409K (spectrum in FIG. 5). It is a histogram which shows the particle size distribution of the copper nanoparticle computed from FIG.6 (b). It is the figure which showed the time-dependent change (0 minute-> 20 minutes) of the ultraviolet-visible absorption spectrum of the copper octoate containing solution heated at 443K by the microwave heating. It is a TEM image of the copper nanoparticle contained in the reaction solution after 20 minutes when the copper octoate containing solution is microwave-heated at 443 K (spectrum in FIG. 8). It is a histogram which shows the particle size distribution of the copper nanoparticle computed from FIG.9 (b). It is the figure which showed the time-dependent change (1 minute-> 20 minutes) of the ultraviolet-visible absorption spectrum of the copper myristate containing solution heated at 443K by the microwave heating. It is a TEM image of the copper nanoparticle contained in the reaction solution after 20 minutes when the copper myristate containing solution is microwave-heated at 443 K (spectrum in FIG. 11). It is a histogram which shows the particle size distribution of the copper nanoparticle computed from FIG.12 (b). It is the figure which showed the time-dependent change (1 minute-> 70 minutes) of the ultraviolet-visible absorption spectrum of the copper myristate containing solution heated at 430K by the microwave heating. It is a TEM image of the copper nanoparticle contained in the reaction solution after 60 minutes when a copper myristate containing solution is microwave-heated at 430K. It is a TEM image of the copper nanoparticle contained in the reaction solution after 70 minutes when a copper myristate containing solution is microwave-heated at 430K.

Claims (8)

In producing a nanoparticle-containing solution by synthesizing metal nanoparticles by reducing the metal precursor in the solution,
Nanoparticle-containing, characterized in that it includes a procedure for measuring the ultraviolet-visible absorption spectrum of the reaction solution during the synthesis over time, and using the obtained measurement results to grasp the synthesis status of the metal nanoparticles. A method for producing a solution. 2. The nanoparticle-containing solution according to claim 1, wherein the procedure includes one or more confirmations selected from the following (1), (2), (3), and (4): Production method.
(1) Increase in absorbance due to absorption of metal nanoparticles from free electrons.
(2) Absorbance due to absorption derived from metal ions is reduced.
(3) An increase in absorbance in (1) and a decrease in absorbance in (2) occur while having an isosbestic point.
(4) It has no surface absorption, and has surface plasmon absorption of metal nanoparticles.   The method for producing a nanoparticle-containing solution according to claim 1 or 2, wherein heating is performed by an external heat source or microwave irradiation during the synthesis.   The method for producing a nanoparticle-containing solution according to any one of claims 1 to 3, wherein the solution contains an organic solvent exhibiting reducibility with respect to the metal precursor.   The method for producing a nanoparticle-containing solution according to claim 4, wherein the organic solvent is a monohydric alcohol having 3 or more carbon atoms.   The said metal precursor is a copper precursor, The said metal nanoparticle is a copper nanoparticle, The manufacturing method of the nanoparticle containing solution in any one of Claim 1 to 5 characterized by the above-mentioned. The copper precursor is represented by the following chemical formula 1,
The copper nanoparticles are derived from a copper core composed of a copper component derived from a copper precursor represented by the following chemical formula 1 and a copper precursor represented by the chemical formula 1 below, and around the copper core The method for producing a nanoparticle-containing solution according to claim 6, further comprising an organic component covering the surface.
(Chemical formula 1)
(R-A) _2- Cu
(Wherein, R represents a hydrocarbon group, A is COO, a _OSO 3, SO ₃ or OPO _3.)   The electrically conductive paste containing the metal nanoparticle collect | recovered from the nanoparticle containing solution obtained by the manufacturing method of the nanoparticle containing solution in any one of Claim 1 to 7.