JP5213592B2 - Copper fine powder, dispersion thereof and method for producing copper fine powder - Google Patents

Description

  The present invention is a copper fine powder composed of fine copper particles, and has a particularly high uniformity in particle diameter, and a copper fine powder suitable as a filler for conductive ink for forming fine circuit patterns and electrodes, and dispersion thereof The present invention relates to a liquid and a method for producing the copper fine powder.

  Conventionally, a screen printing method with good productivity has been widely used as a method for printing circuit patterns and electrodes. However, as electronic devices have become lighter and thinner in recent years, further miniaturization of electronic wiring and electrodes has been required. In order to meet such a need for thinning, a conductive filler applicable to a new printing method such as an ink jet method is required.

  Most of the fillers for conductive pastes that have been widely used so far have a particle size on the order of μm. However, in order to apply to a new printing technique such as an ink jet method, it is desired to use extremely fine particles (nanoparticles) having a particle diameter of 50 nm or less as a filler. In addition, it is extremely advantageous in industrial production of electronic circuits to perform firing after drawing a circuit pattern at as low a temperature as possible. The use of nanoparticles is also effective for significantly reducing the firing temperature.

  Among metal nanoparticles, silver nanoparticles are already in practical use. Since silver is relatively difficult to oxidize and has excellent weather resistance, it is considered that industrial production of nanoparticles is relatively easy to implement. However, silver has the disadvantage that it is prone to electromigration. It is also expensive. For this reason, in applications where electromigration is avoided or where lower cost members are required, application of copper nanoparticles instead of silver nanoparticles is desired. Various studies have also been made on copper nanoparticle production techniques (for example, Patent Documents 1 to 3).

JP 2002-121606 A JP 2005-330552 A JP 2007-56321 A

  Copper has the advantage of being cheaper and less susceptible to electromigration than silver, but has the disadvantage of being easily oxidized. In particular, in the case of nanoparticles having a large specific surface area, the susceptibility to oxidation is significantly increased. For this reason, it is unexpectedly difficult to manufacture copper nanoparticles industrially stably. As a result of various studies, the inventors have developed a method for synthesizing copper nanoparticles covered with an organic polymer by a wet process as a method for synthesizing copper nanoparticles that are extremely unlikely to undergo surface oxidation, and in Japanese Patent Application No. 2007-313366. Proposed.

  Copper nanoparticles that are covered with such an organic polymer are excellent in oxidation resistance and hardly corrode. However, since individual copper particles are covered with a polymer, in order to impart conductivity to a circuit pattern drawn using these copper particles, for example, firing at a temperature of about 500 ° C. is required. . In this case, the “reduction in sintering temperature”, which is a merit of nanoparticles, cannot be fully utilized.

  On the other hand, in order to draw fine circuit patterns and the like efficiently industrially, not only the particle diameter is small, but also the uniformity of the particle diameter is high, that is, the particle size distribution as copper fine powder is sharp. It is extremely effective. Use of nanoparticles with high uniformity in particle diameter as the filler facilitates optimization of ink jet conditions (nozzle shape, discharge pressure, etc.), and is advantageous in preventing nozzle clogging and uneven drawing. Further, the coarse particles are not settled and separated in the liquid medium, which is advantageous in keeping the dispersion state uniform. Furthermore, the fluctuation of the sintering temperature between lots can be suppressed to be small, and the firing temperature can be easily controlled. However, it is not easy to obtain copper fine particles with a sharp particle size distribution that are not protected by organic polymers for copper nanoparticles that are inherently susceptible to oxidation. It is more difficult to recover the copper fine powder in a state where it has a property of dispersing particles when mixed in an appropriate solvent.

  In view of the present situation, the present invention provides a fine powder of copper nanoparticles having high particle size uniformity and good dispersibility in a solvent without using a polymer as a protective material, and An object is to provide a dispersion of the fine powder.

The above object is composed of copper particles having a surfactant molecule composed of an organic compound having a molecular weight of 200 to 400 attached to the surface, an average particle diameter D _TEM determined by TEM observation is 50 nm or less, and the following formula (1) The CV value defined by the above is achieved by a copper fine powder having excellent uniformity in particle diameter, which is 50% or less, preferably 25% or less. The copper particles reduce, for example, a copper compound dissolved in a solvent in which an alcohol and an organic compound having a molecular weight of 200 to 400 as a surfactant are dissolved into metallic copper by using the reducing power of the alcohol. At the same time, it is synthesized by a synthesis method in which the deposited copper metal is coated with the surfactant molecules in the solvent.
CV value = σ _D / D _TEM × 100 (1)
Here, σ _D is a standard deviation with respect to the particle size of each particle to be measured by _DTEM .

The average particle diameter D _TEM is an observation image of copper fine powder observed by a TEM (transmission electron microscope), and randomly selects 100 or more particles (for example, 300 particles) that can grasp the overall shape of the particles. It can be determined by measuring the particle diameter of the particles and calculating their average value. As the particle diameter of each particle, the length (major diameter) of the largest diameter portion grasped on the image is adopted.

The present invention also provides a copper particle dispersion in which the copper fine powder is monodispersed in a polar solvent.
Monodispersed means that individual particles can move independently in the liquid.

Such a copper fine powder is composed of R-OH, where R is a linear alkyl group having 7 to 8 carbon atoms, and an organic compound having a molecular weight of 200 to 400 which is a surfactant. In a solvent in which the copper compound is dissolved in the solvent in the following (a) molar ratio, with the hydroxide mixed in the following (b) molar ratio, the temperature range of (c) below production of copper fine powder having a by holding, step of average particle diameter D _TEM molecules of the surface active agent which is obtained by adhering to and TEM observation on the surface to synthesize the following copper particles 50 nm (copper particle synthesis process) to It can be obtained by the method.
(A) [Surfactant molecule] / [copper ion] molar ratio: 1 to 20
(B) Molar ratio of [hydroxide ion in hydroxide] / [alcohol A]: 0.008 to 0.5
(C) When the boiling point of the alcohol having the lowest boiling point constituting alcohol A is A _BP (° C.), the temperature range is (A _BP −50 ° C.) or more and A _BP or less.

In addition, after the above synthesis step,
A step (solid-liquid separation step) of solid-liquid separation of the slurry containing the synthesized copper particles and recovering the solid content;
A step of washing the organic compound of impurities mixed in the solid content with an organic solvent, and a step of washing the inorganic salt of impurities with a mixture of the organic solvent and water (washing step);
A method for producing a copper fine powder having the following is provided.

In the above production method, for example, copper (II) chloride or copper (II) acetate can be used as the copper compound, and sodium hydroxide or potassium hydroxide can be used as the hydroxide. Examples of the surfactant include oleylamine (C ₉ H ₁₈ = C ₉ H ₁₇ —NH ₂ , molecular weight of about 267).

  ADVANTAGE OF THE INVENTION According to this invention, the copper fine powder comprised by the copper nanoparticle with a high uniformity of a particle diameter can be provided now. The individual particles are not surrounded by the organic polymer, but are protected by the adhesion of surfactant molecules having a molecular weight of 200 to 400, and can be monodispersed in a liquid medium. ing. Such copper fine powder is suitable for the fine line printing technique by the inkjet method or the like. It is also expected to replace silver fine powder that is prone to migration.

Copper fine powder of the present invention has an average particle diameter D _TEM which is obtained by TEM observation is constituted by the following "copper nanoparticles" 50nm. Moreover, the CV value defined by the following formula (1) is 50% or less.
CV value = σ _D / D _TEM × 100 (1)
The CV value is an index representing the uniformity of the particle diameter of the particles constituting the fine powder. According to the study by the inventors, in consideration of dispersibility in a liquid medium, applicability to fine line printing technology such as an ink jet method, stability of sintering temperature, etc., copper fine powder having a CV value of 50% or less It is very convenient to be. It is more preferably 25% or less, and further preferably 15% or less. In the ink jet method, if there are a large number of fine particles having a particle size significantly smaller than the average particle size, it causes troubles such as nozzle clogging, and industrial implementation is difficult. As can be seen from the equation (1), in order to realize the same CV value, the restriction on the standard deviation σ becomes more severe as the average particle diameter D _TEM becomes smaller.

Even if the CV value is sufficiently small, if the average particle diameter D _TEM exceeds 50 nm, the effect of reducing the sintering temperature is diminished, and the applicability to the ink jet method is diminished. D _TEM is more preferably 40 nm or less, and further preferably 25 nm or less, or even 20 nm or less. On the other hand, it is not always easy to industrially manufacture a copper fine powder having a very small D _{TEM and} having a highly uniform particle diameter. As a result of various investigations, D _TEM is practical in the range of more than 4 nm, it may be managed to 5nm or more or more 7 nm.

  In addition to a small CV value, it is desirable that each copper particle has a square shape as few as possible and has a shape close to a sphere. For example, when the ratio of the diameter of the longest part (major axis) of a particle on the TEM image to the diameter (minor axis) of the longest part perpendicular to the major axis is defined as the aspect ratio, the aspect ratio of each particle The average value (average aspect ratio) is preferably 1 to 1.5, and more preferably 1 to 1.2. Such a copper fine powder having a small CV value and an aspect ratio close to 1 is extremely effective for preventing nozzle clogging of ink jet, stabilizing discharge conditions, and stabilizing sintering temperature.

  Another major feature of the copper fine powder of the present invention is that surfactant molecules comprising an organic compound having a molecular weight of 200 to 400 are attached to the surface of each particle. For surfactants with a molecular weight of over 400, when firing a coating of copper fine powder, if the firing temperature is lowered, desorption and volatilization hardly occur, and the low-temperature sinterability unique to metal nanoparticles may not be fully utilized. is there. On the other hand, the surfactant also functions as a “buoy ring” that gives buoyancy to the copper particles in the liquid medium. In order to sufficiently secure the dispersibility of copper nanoparticles having an average particle size of 50 nm or less in liquid (particularly the property of maintaining a monodispersed state for a long period of time), surfactant molecules having a molecular weight of 200 or more are attached. Is extremely advantageous. In addition, since copper particles are more easily oxidized than silver particles, it is desirable that the organic compound of the surfactant has a molecular weight of 200 or more in order to ensure the storage stability of the copper fine powder.

As a result of investigations by the inventors, a primary amine having an unsaturated bond is particularly suitable as the surfactant. Among organic compounds having a relatively large molecular weight of 200 to 400, primary amines having an unsaturated bond are easily desorbed from the copper particles by heating at the time of firing, and are easy to volatilize and remove. Depending on the application, it may be necessary to replace the surfactant with another type, but the primary amine having an unsaturated bond has a property of being easily desorbed from the copper particles, and the surface activity. It is also advantageous for changing the agent. Such amines can be exemplified oleylamine _{(C 9 H 18 = C 9} H 17 -NH 2, molecular weight of about 267).

  The copper fine powder of the present invention reduces a copper compound dissolved in a solvent in which an alcohol and an organic compound having a molecular weight of 200 to 400 as a surfactant are dissolved into metallic copper by using the reducing power of the alcohol. In addition, it can be produced by a wet synthesis method in which the deposited copper metal is coated with the surfactant molecules in the solvent. Such a method for synthesizing metal nanoparticles using the reducing power of alcohol has already been put into practical use as a method for producing silver fine powder. However, it was found that the reduction precipitation reaction with copper alcohol does not occur as easily as with silver. That is, in wet synthesis of copper nanoparticles, it is difficult to control the particle size and particle size distribution, and a device for advancing the reaction is required.

As a result of detailed studies, the inventors have found that when a hydroxide ion is present in a certain concentration or more in an alcohol solvent, a copper precipitation reaction utilizing the reducing power of the alcohol proceeds smoothly. It was. The hydroxide ion (OH ⁻ ) can be supplied by an alkali metal hydroxide (for example, NaOH) dissolved in an alcohol solvent. This hydroxide ion is considered to have a function of promoting modification of the alcohol solvent and formation of a metal complex that can be more easily reduced. In the wet reaction using the alcohol solvent applied in the present invention, the deposition reaction rate can be controlled by the hydroxide ion concentration. Experimentally, a hydroxide ion concentration range suitable for the synthesis of copper nanoparticles having a small particle diameter exists.

Hereinafter, the manufacturing method of the copper fine powder of this invention is demonstrated more concretely.
[Copper particle synthesis process]
As a copper atom supply substance, a copper compound that can be completely dissolved in a solvent described later is used. It is relatively desirable to select a copper salt that forms a neutral salt with the hydroxide described below. For example, copper (II) chloride; CuCl ₂ , copper acetate (II); Cu ₂ (CH ₃ COO) _{4 and the} like may be mentioned as suitable objects.
As alcohol A used as a reducing agent, R-OH, where R is a linear alkyl group having 7 to 8 carbon atoms, can be used. Specifically, 1-heptanol; CH ₃ (CH ₂ ) ₆ OH, boiling point 176.8 ° C., and 1-octanol; CH ₃ (CH ₂ ) ₇ OH, boiling point 194.5 ° C. correspond to this.
As the surfactant, an organic compound having a molecular weight of 200 to 400 is used as described above. For example, a primary amine having an unsaturated bond such as oleylamine is preferred.
As the hydroxide, sodium hydroxide that dissolves well in the alcohol A and the surfactant; NaOH, potassium hydroxide; KOH and the like are suitable.

  In order to cause a copper precipitation reaction, it is important to create a state in which the above-mentioned raw material materials are uniformly and well dissolved. As described above, since the precipitation reaction of copper by the reducing power of alcohol A proceeds due to the presence of hydroxide, first, a solution in which a copper compound is dissolved in a solvent in which alcohol A and a surfactant are dissolved It is efficient to prepare a (reaction source solution), raise the temperature, and mix the hydroxide after reaching a predetermined temperature.

The reaction temperature is preferably (A _BP −50 ° C.) or more and A _BP or less when the boiling point of the alcohol A is A _BP (° C.). The reaction hardly proceeds at a temperature lower than (A _BP- 50 ° C.). On the other hand, in the temperature range exceeding A _BP without the reaction environment be stabilized by boiling phenomenon, it becomes a negative factor even on synthesizing the small particles of CV value. When alcohol A is a mixture of two or more alcohols (1-heptanol and 1-octanol mixed solution), the boiling point of the alcohol having the lowest boiling point among the alcohols constituting alcohol A is A _BP (° C.). It may be adopted as. However, the amount of the alcohol having the lowest boiling point is small, and after the alcohol is volatilized and removed during the reaction to increase the boiling point, the boiling point A _BP (° C.) is determined again by the remaining alcohol, and (A _BP − The reaction may be allowed to proceed in a temperature range of 50 ° C. or more and _ABP or less. The reaction temperature is more preferably (A _BP −30 ° C.) or higher and A _BP or lower.

  The molar ratio [alcohol A] / [copper ion] is preferably 20 or more. However, if the amount of the solvent increases too much, the amount of hydroxide used increases, which is uneconomical, so the molar ratio of [alcohol A] / [copper ion] may be approximately 300 or less.

  The molar ratio of [surfactant molecule] / [copper ion] is preferably in the range of 1-20. When this molar ratio is too small, it becomes difficult to quickly surround the deposited copper with surfactant molecules, and the particles are likely to become coarse. In addition, the amount of the surfactant that adheres to the surface of the copper particles is insufficient, and the copper particles tend to aggregate. As a result of various studies, the molar ratio of [surfactant molecule] / [copper ion] is preferably 1 or more, more preferably 2.5 or more, and even more preferably 5 or more. On the other hand, an excessive molar ratio of [surfactant molecule] / [copper ion] is wasteful and uneconomical. Therefore, it is efficient that the [surfactant molecule] / [copper ion] molar ratio is in the range of 20 or less, and it may be controlled to 15 or less, or 10 or less.

  When the reaction source liquid is heated to the above reaction temperature and then mixed with a hydroxide, a copper reduction reaction with alcohol A proceeds, and metallic copper precipitates in the liquid. At that time, the deposited copper particles are quickly surrounded by the surfactant molecules present in the surrounding area, and growth to coarse particles is suppressed, and copper nanoparticles are synthesized. By stabilizing the temperature condition and the stirring condition, it is possible to obtain copper nanoparticles having a uniform particle diameter.

  The molar ratio of [hydroxide ion in hydroxide] / [alcohol A] is preferably in the range of 0.008 to 0.5. If the concentration of hydroxide ions present in the liquid is too low, an environment in which the reduction and precipitation reaction of copper by alcohol proceeds cannot be realized. According to the study by the inventors, it has been found that it is difficult to specify a suitable amount of hydroxide even if the amount of hydroxide mixed is arranged in a molar ratio with respect to copper. This is thought to be because the hydroxide does not directly participate in the copper precipitation reaction itself. Rather, the amount of hydroxide required could be defined by the molar ratio to alcohol A, the main solvent. In the examination so far, copper nanoparticles can be synthesized satisfactorily by setting the molar ratio of [hydroxide ion in hydroxide] / [alcohol A] to 0.008 or more. The molar ratio [hydroxide ion in hydroxide] / [alcohol A] is more preferably 0.01 or more, and still more preferably 0.015 or more. However, when an excessive amount of hydroxide is added, a gel-like product is generated in the reaction solution, and it may be difficult to recover the particles. It is desirable to adjust the molar ratio of [hydroxide ion in hydroxide] / [alcohol A] within a range of 0.5 or less, and usually 0.2 or less is sufficient, for example 0.1 or less or It may be controlled to 0.075 or less.

  The reaction time from the start of mixing the hydroxide can be adjusted within a range of about 1 to 12 hours. After completion of the reaction, the mixture is cooled to a temperature at which solid-liquid separation can be performed, but an organic solvent may be added to the liquid during the cooling process. As a result, the liquid is diluted and the increase in the viscosity of the slurry accompanying the temperature drop is suppressed, and the solid-liquid separation operation in the subsequent process is facilitated. However, if the surfactant used is easily soluble in the organic solvent for dilution (high solubility), a large amount of dilution may cause desorption of surfactant molecules attached to the copper particles. . In order to prevent this, it is effective to previously dissolve the surfactant in an organic solvent for dilution. For example, when oleylamine is used as the surfactant and methanol is used as the solvent for dilution, it is effective to dissolve some oleylamine in the methanol in advance and add it. This dilution operation is not necessarily required, and may be performed according to the workability of solid-liquid separation.

[Solid-liquid separation process]
Next, the slurry containing the copper nanoparticles synthesized as described above is subjected to solid-liquid separation to recover the solid content. Centrifugation is suitable for the solid-liquid separation method.

[Washing process]
The recovered solid content contains copper nanoparticles having a surface-active agent attached thereto, and various reaction products and remaining raw material are mixed in the copper nanoparticles. It is important to eliminate these mixed substances (impurities) as much as possible in order to obtain copper fine powder with good dispersibility. In the known method of synthesizing silver nanoparticles in a mixed solvent of alcohol and surfactant, the impurities mixed in the synthesized silver nanoparticles are mainly organic substances, and methanol or other organic solvent is used as a cleaning liquid. For example, it is possible to obtain silver fine powder having excellent dispersibility by performing the operation of “ultrasonic cleaning → solid-liquid separation” once or a plurality of times. However, in the above synthesis method according to the present invention, a hydroxide is allowed to coexist in order to advance the reaction. For this reason, an inorganic compound having a considerably higher solubility in water rather than an organic solvent may be generated as a reaction product of a hydroxide and a copper compound. Efficient removal of this inorganic substance becomes a major issue in the cleaning process.

  Of course, it is possible to remove inorganic substances by a washing operation using an organic solvent as a washing liquid as in the conventional case. However, the inventors further studied, and in order to finish the cleaning process more efficiently, organic impurities out of impurities mixed in the solid content were washed and removed with an organic solvent, and inorganic type impurities were removed. It has been found that it is effective to employ a multi-step cleaning process in which impurities are cleaned and removed with a mixture of an organic solvent and water. Specifically, an operation of “ultrasonic cleaning using an organic solvent as a cleaning liquid → ultrasonic cleaning using a mixed liquid of an organic solvent and water as a cleaning liquid → solid-liquid separation” may be performed. Alternatively, an operation of “ultrasonic cleaning using an organic solvent as a cleaning liquid → solid-liquid separation” and an operation of “ultrasonic cleaning using a mixed liquid of an organic solvent and water as a cleaning liquid → solid-liquid separation” may be sequentially performed.

  For example, when copper (II) chloride is used as the copper compound and sodium hydroxide is used as the hydroxide, sodium chloride is mixed as an impurity in the solid content recovered from the slurry after the reaction. May produce coarse sodium chloride crystals that can be observed with the naked eye. When an alkali metal such as Na is mixed as an impurity in the copper fine powder, there is a concern that the copper fine powder may adversely affect an electronic component using the electronic circuit. The alkali metal salt can be efficiently removed by using a mixed liquid of an organic solvent and water as a cleaning liquid. This is considered to be due to the fact that alkali metal salts have the property of being very soluble in water. However, since copper fine powder is easily oxidized, it is difficult to wash with water. That is, it is important to use a cleaning liquid in which water is added to and mixed with an organic solvent. The proportion of water in the mixture of the organic solvent and water is preferably 20 to 80% by mass. In addition, it is desirable to perform a cleaning operation using a mixed liquid of an organic solvent and water in a short time. For example, it is desirable that ultrasonic cleaning using a mixed liquid of an organic solvent and water as a cleaning liquid is completed in 5 to 20 seconds.

  The copper fine powder washed in this way has surfactant molecules attached to the surface and exhibits good dispersibility in various polar solvents. For example, copper fine powder using oleylamine as a surfactant was confirmed to be monodispersed in a hydrocarbon liquid medium such as toluene, decane, tetradecane, and isoparaffin solvents. Moreover, it is possible to obtain copper fine powder suitable for various media by performing an operation in which the surfactant adhering to the particles of the copper fine powder is replaced with another type of surfactant in an organic solvent. . In particular, oleylamine, a surfactant, has the property of adhering to copper particles, but it is very easy to dissolve in alcohol solvents, etc., so copper fine powder with oleylamine attached and other desired surface activity By adding a large amount of an alcohol solvent in which oleylamine is easily dissolved in an organic solvent in which the agent is dissolved, it is possible to replace the surfactant relatively easily.

Example 1
1-heptanol (special grade made by Wako Pure Chemical Industries, Ltd.) as alcohol A which is a reducing agent, anhydrous copper chloride (II) (made by Wako Pure Chemical Industries, Ltd.) as a copper compound, and oleylamine (Wako Pure Chemical, Ltd.) as a surfactant Kogyo Kogyo Co., Ltd.) and sodium hydroxide granules (manufactured by Wako Pure Chemical Industries, Ltd.) were prepared as hydroxides.

[Copper particle synthesis process]
After mixing 2.5 g of anhydrous copper chloride (II) and 10 g of methanol (manufactured by Wako Pure Chemical Industries, Ltd.) and completely dissolving copper chloride in methanol using an ultrasonic disperser, 28.0 g of oleylamine was added. Then, the mixture was again completely dissolved with an ultrasonic disperser, and 70 mL of 1-heptanol was added to this solution. This mixed solution was transferred to a separable flask equipped with a refluxer and set in a mantle heater.

  Separately, 1.4 g of sodium hydroxide granules was added to 50 mL of 1-heptanol, and heated at 160 ° C. for 40 minutes while stirring at 300 rpm with a magnetic stirrer to prepare a solution in which sodium hydroxide was completely dissolved.

  While nitrogen gas was blown into the liquid in the separable flask set in the mantle heater at a flow rate of 500 mL / min, the liquid was stirred with a propeller at a rotation speed of 200 rpm. The temperature of the liquid was increased to 160 ° C. at a rate of temperature increase of 3.2 ° C./min while maintaining nitrogen gas blowing and stirring, and maintained at 160 ° C. for 30 minutes, and then sodium hydroxide was added to the 1-heptanol. The total amount of 160 ° C. solution in which was dissolved was charged. Thereafter, stirring was maintained at 200 rpm, and nitrogen gas was switched to be introduced into the gas phase portion in the flask, and reflux was performed for 1 hour while maintaining the liquid in the separable flask at 160 ° C. That is, by maintaining the reaction temperature at 160 ° C. for 1 hour, an attempt was made to proceed the copper reduction precipitation reaction. The total amount of 1-heptanol present in the liquid at the start of the reaction is 98.628 g corresponding to a volume of 70 + 50 = 120 mL.

Then, while maintaining stirring at 200 rpm, it was cooled to 90 ° C. over about 40 minutes, at which point a total amount of a mixed solution of 3.0 g of oleylamine and 50 mL of methanol was added, and then stirring was continued for 10 minutes while lowering the temperature. did.
In addition, the preparation amount and reaction temperature of each raw material are shown in Table 1 (the same applies in the following examples).

[Solid-liquid separation process]
After the liquid temperature became 50 ° C. or lower, the slurry after the reaction was distributed to four centrifuge tubes in a nitrogen atmosphere, and 10 minutes at 3000 rpm using a centrifuge (Hitachi Koki Co., Ltd .; CF7D2). Solid-liquid separation was performed by centrifugation, the supernatant was discarded, and the solid content was recovered.

[Washing process]
The obtained solid content was washed in a nitrogen atmosphere by the following procedure.
1. Four centrifuge tubes containing a solid solution containing 1.0 g of maleic anhydride (manufactured by Wako Pure Chemical Industries, Ltd.) dissolved in 100 mL of ethanol (manufactured by Wako Pure Chemical Industries, Ltd.). 10 ml each of this washing solution was added to each and ultrasonic washing was performed for 5 minutes.
2. 10 mL each of a solution obtained by dissolving 1.0 g of maleic anhydride (manufactured by Wako Pure Chemical Industries, Ltd.) in 100 mL of pure water is added to each of the four centrifuge tubes after the ultrasonic cleaning, and ultrasonic cleaning is performed for 10 seconds. It was.
3. Then, solid-liquid separation was performed by centrifuging at 2400 rpm for 10 minutes using the above-mentioned centrifuge, and the supernatant was discarded and the solid content was recovered.
4. Add 5 mL of toluene and 0.25 mL of oleylamine to each of the 4 centrifuge tubes from which the solids were collected, and ultrasonically wash for 5 minutes. Then add 10 mL of methanol to each of the centrifuge tubes, and then ultrasonically wash for 5 minutes. did.
5. Then, solid-liquid separation was carried out by centrifuging at 2400 rpm for 10 minutes using the above-mentioned centrifuge, and the supernatant was discarded and the solid content was recovered.

  In this way, a washed paste-like solid was obtained. This solid content was dispersed in toluene to obtain a dispersion.

[TEM observation]
About said dispersion liquid, particle | grains were observed with TEM (transmission electron microscope). An example of the TEM photograph is shown in FIG. It can be seen that the particles are monodispersed.
In a TEM image with a magnification of 600,000 times, 300 independent copper particles that do not overlap were randomly selected to measure the diameter (major axis), and the average value of the measured diameters of all the particles was defined as the average particle diameter _DTEM . .
Further, the standard deviation σ _D was calculated for the measured diameters of all the particles, and the CV value was obtained by the following (1).
CV value = σ _D / D _TEM × 100 (1)
The standard deviation σ _D of the particle size was calculated by using the STDEV function incorporated in Microsoft spreadsheet software “Excel”.

In this example, the average particle diameter D _TEM is 10.5 nm, CV value was 13.0%. The average aspect ratio is in the range of 1 to 1.2.
As a result of X-ray diffraction of the particles, it was confirmed that metallic copper was synthesized.

(Production of fired film)
After the dispersion (copper particle dispersion) was applied to a glass plate, the glass plate was heated to 300 ° C. at a rate of temperature increase of 10 ° C./min in a 4% by volume hydrogen-nitrogen mixed gas atmosphere. Was fired for 60 minutes to prepare a fired film. As a result of step measurement using a surface roughness / contour shape measuring machine (manufactured by Tokyo Seimitsu Co., Ltd .; SURFCOM 1500DX), the thickness of the fired film was 2.52 μm.

  When the volume resistivity of this fired film was measured by a four-terminal four-probe method using a low resistivity meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd .; Loresta GP MCP-T610), it was 208 μΩ · cm. That is, it was confirmed that a copper conductive film was obtained at a firing temperature of 300 ° C.

Example 2
The same experiment as in Example 1 was performed with the amounts of anhydrous copper chloride, 1-heptanol, oleylamine and sodium hydroxide as shown in Table 1.
The average particle diameter D of the particles obtained _TEM is 6.7 nm, CV value was 24.28%. The average aspect ratio is in the range of 1 to 1.2. An example of a TEM photograph of the particles is shown in FIG.
As a result of X-ray diffraction, it was confirmed that the particles were metallic copper.

Example 3
The same experiment as in Example 1 was performed with the amounts of anhydrous copper chloride, 1-heptanol, oleylamine and sodium hydroxide as shown in Table 1.
The average particle diameter D of the particles obtained _TEM is 9.0 nm, CV value was 18.20%. The average aspect ratio is in the range of 1 to 1.2. An example of a TEM photograph of the particles is shown in FIG.
As a result of X-ray diffraction, it was confirmed that the particles were metallic copper.

Example 4
The same experiment as in Example 1 was performed except that the amounts of anhydrous copper chloride, 1-heptanol, oleylamine and sodium hydroxide were as shown in Table 1 and the holding time at the reaction temperature was changed from 1 hour to 12 hours. It was.
The average particle diameter D of the particles obtained _TEM is 9.4 nm, CV value was 14.50%. The average aspect ratio is in the range of 1 to 1.2. An example of a TEM photograph of the particles is shown in FIG.
As a result of X-ray diffraction, it was confirmed that the particles were metallic copper.

<< Comparative Example 1 >>
In addition to anhydrous copper chloride (II) and sodium hydroxide granules, isoheptanol (special grade manufactured by Wako Pure Chemical Industries, Ltd.) is used as alcohol A as a reducing agent, and 1-vinyl-2-pyrrolidone polymer is used as a protective material. (PVP polymer; manufactured by Wako Pure Chemical Industries, Ltd., PVP K30 or K15, number average molecular weight of about 40000) was prepared.

  To 200 mL of isoheptanol, 1.0 g of anhydrous copper chloride (II) and 8.48 g of PVP polymer were added and stirred at a room temperature with a magnetic stirrer. Next, 1.75 g of sodium hydroxide granules were added and dissolved with a magnetic stirrer. The container was transferred to a container equipped with a reflux condenser and placed on an oil bath, and the liquid was stirred with a magnetic stirrer at a rotation speed of 200 rpm while nitrogen gas was blown into the solution at a flow rate of 400 mL / min. With the nitrogen gas blowing and stirring maintained, the liquid temperature was increased to 176 ° C. at a heating rate of 10 ° C./min, and held for 1 hour while refluxing at 176 ° C. to reduce and precipitate copper. .

After the slurry after the reaction became 50 ° C. or lower, the slurry was treated according to the following procedure.
1. To 5 mL of the slurry after the reaction, 25 mL of acetone (manufactured by Wako Pure Chemical Industries, Ltd.) was added and dispersed in an ultrasonic disperser for 10 minutes.
2. This dispersion was subjected to solid-liquid separation by centrifuging at 3000 rpm for 10 minutes using a centrifuge (manufactured by Hitachi Koki Co., Ltd .; CF7D2), and the supernatant was discarded to recover the solid content.
3. The steps 1 and 2 were repeated.
4. To the obtained slurry, 8 mL of water and 32 mL of acetone were added and dispersed in an ultrasonic disperser over 10 minutes.
5. This dispersion was subjected to solid-liquid separation by centrifuging at 3000 rpm for 20 minutes using the above centrifuge, and the supernatant was discarded to recover the solid content.
6. Methanol was added to the recovered pasty solids to obtain a dispersion, and the dispersion was subjected to the above centrifugal separator to obtain a dispersion in which coarse particles and aggregated particles were separated and removed.
In addition, as a result of performing X-ray diffraction about solid content of said 6, it was confirmed that metallic copper is synthesize | combined.

Using the obtained dispersion, a fired film was produced at a firing temperature of 300 ° C. in the same manner as in Example 1 and measurement of the volume resistivity was attempted, but the resistance value was not measurable. Even in the case of a fired film (film thickness: 0.492 μm) fired at 500 ° C. in a hydrogen atmosphere, the volume resistivity was very high at 4.48 × 10 ⁴ μΩ · cm. From this, it was confirmed that copper nanoparticles coated with an organic polymer are difficult to sinter.

Example 5
The same experiment as in Example 2 was performed with alcohol A as 1-octanol.
An example of a TEM photograph of the obtained particles is shown in FIG. As a result of X-ray diffraction, it was confirmed that the particles were metallic copper. A copper fine powder having an average particle diameter _DTEM of 20 nm or less and a CV value of 50% or less was obtained.

<< Comparative Example 2 >>
The same experiment as in Example 2 was performed by setting the alcohol A to 1-butanol and the reaction temperature to 120 ° C.
An example of a TEM photograph of the obtained particles is shown in FIG. The particles are coarsened.

<< Comparative Example 3 >>
The same experiment as in Example 2 was performed using alcohol A as 2-octanol.
An example of a TEM photograph of the obtained particles is shown in FIG. Coarse particles and fine particles are mixed and particle size distribution is poor.

<< Comparative Example 4 >>
The same experiment as in Example 2 was performed with alcohol A as ethylene glycol and a reaction temperature of 120 ° C.
An example of a TEM photograph of the obtained particles is shown in FIG. The particles are coarsened.

Example 6
The same experiment as in Example 2 was performed with the reaction temperature lowered to 140 ° C.
An example of a TEM photograph of the obtained particles is shown in FIG. As a result of X-ray diffraction, it was confirmed that the particles were metallic copper. Copper fine powder having an average particle diameter _DTEM of 20 nm or less was obtained.

<< Comparative Example 5 >>
The same experiment as in Example 2 was performed at a reaction temperature of 100 ° C.
An example of a TEM photograph of the obtained particles is shown in FIG. As a result of X-ray diffraction, almost no metallic copper was produced.

<< Comparative Example 6 >>
The same experiment as in Example 2 was performed at a reaction temperature of 120 ° C.
An example of a TEM photograph of the obtained particles is shown in FIG. Coarse copper particles were produced.

<< Comparative Example 7 >>
The same experiment as in Example 2 was performed at a reaction temperature of 180 ° C. higher than the boiling point of alcohol A.
An example of a TEM photograph of the obtained particles is shown in FIG. Irregular coarse particles were generated.

Example 7
The same experiment as in Example 2 was performed with the amount of oleylamine charged to 2.8 g.
An example of a TEM photograph of the obtained particles is shown in FIG. As a result of X-ray diffraction, it was confirmed that the particles were metallic copper. A copper fine powder having an average particle diameter _DTEM of 20 nm or less and a CV value of 50% or less was obtained.

<< Comparative Example 8 >>
The amount of oleylamine charged was reduced to 0.7 g, and the same experiment as in Example 2 was performed.
An example of a TEM photograph of the obtained particles is shown in FIG. Particle coarsening and agglomeration occurred.

<< Comparative Example 9 >>
The same experiment as in Example 2 was performed with the amount of oleylamine charged to 0.0 g (no addition).
An example of a TEM photograph of the obtained particles is shown in FIG. The reaction product became an amorphous coarse mass.

Example 8
The amount of sodium hydroxide input was reduced to 0.45 g, and the same experiment as in Example 2 was performed.
An example of a TEM photograph of the obtained particles is shown in FIG. As a result of X-ray diffraction, it was confirmed that the particles were metallic copper. A copper fine powder having an average particle diameter _DTEM of 20 nm or less and a CV value of 50% or less was obtained.

<< Comparative Example 10 >>
The amount of sodium hydroxide input was reduced to 0.15 g, and the same experiment as in Example 2 was performed.
An example of a TEM photograph of the obtained particles is shown in FIG. As a result of X-ray diffraction, formation of metallic copper was not observed.

Example 9
The same experiment as in Example 6 was performed, except that 0.74 g of copper (II) acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was used as the copper compound, and the amount of sodium hydroxide added was 0.30 g. .
An example of a TEM photograph of the obtained particles is shown in FIG. As a result of X-ray diffraction, it was confirmed that the particles were metallic copper. A copper fine powder having an average particle diameter _DTEM of 50 nm or less and a CV value of 50% or less was obtained.

4 is a TEM photograph of particles obtained in Example 1. FIG. 4 is a TEM photograph of particles obtained in Example 2. 4 is a TEM photograph of particles obtained in Example 3. FIG. 4 is a TEM photograph of particles obtained in Example 4. FIG. 4 is a TEM photograph of particles obtained in Example 5. FIG. 4 is a TEM photograph of particles obtained in Comparative Example 2. 4 is a TEM photograph of particles obtained in Comparative Example 3. 4 is a TEM photograph of particles obtained in Comparative Example 4. 4 is a TEM photograph of particles obtained in Example 6. 10 is a TEM photograph of particles obtained in Comparative Example 5. 10 is a TEM photograph of particles obtained in Comparative Example 6. 10 is a TEM photograph of particles obtained in Comparative Example 7. 4 is a TEM photograph of particles obtained in Example 7. FIG. 10 is a TEM photograph of particles obtained in Comparative Example 8. 10 is a TEM photograph of particles obtained in Comparative Example 9. 4 is a TEM photograph of particles obtained in Example 8. 10 is a TEM photograph of particles obtained in Comparative Example 10. 10 is a TEM photograph of particles obtained in Example 9.

Claims (7)

R-OH, where R is a linear alkyl group having 7 to 8 carbon atoms, and is dissolved in a solvent in which one or more alcohols represented by a surfactant and an organic compound having a molecular weight of 200 to 400 as a surfactant are dissolved. The molecular weight 200 synthesized by a synthesis method in which the copper compound is reduced to metallic copper using the reducing power of the alcohol and the deposited metallic copper is coated with the surfactant molecules in the solvent. consists of copper particles molecule of the surfactant comprising an organic compound of 400 is adhered to the surface, the mean particle diameter D _TEM which is obtained by TEM observation 50nm or less, and the following (1) being defined CV value formula Copper fine powder whose 50% or less.
CV value = σ _D / D _TEM × 100 (1)
Here, σ _D is a standard deviation with respect to the particle size of each particle to be measured by _DTEM . The copper fine powder according to claim 1, wherein the CV value is 25% or less. A copper particle dispersion in which the copper fine powder according to claim 1 or 2 is monodispersed in a polar solvent. In a solvent in which one or more alcohols A represented by R—OH, where R is a linear alkyl group having 7 to 8 carbon atoms, and an organic compound having a molecular weight of 200 to 400 as a surfactant are dissolved together, By maintaining the liquid in which the copper compound is dissolved at the molar ratio of the following (a) in the temperature range of the following (c) while the hydroxide is mixed at the molar ratio of the following (b), method for producing a copper fine powder having an average particle diameter D _TEM molecules of the surfactant which is obtained by observing TEM is attached to the surface to synthesize the following copper particles 50nm.
(A) [Surfactant molecule] / [copper ion] molar ratio: 1 to 20
(B) Molar ratio of [hydroxide ion in hydroxide] / [alcohol A]: 0.008 to 0.5
(C) When the boiling point of the alcohol having the lowest boiling point constituting alcohol A is A _BP (° C.), the temperature range is (A _BP −50 ° C.) or more and A _BP or less. In a solvent in which one or more alcohols A represented by R—OH, where R is a linear alkyl group having 7 to 8 carbon atoms, and an organic compound having a molecular weight of 200 to 400 as a surfactant are dissolved together, By maintaining the liquid in which the copper compound is dissolved at the molar ratio of the following (a) in the temperature range of the following (c) while the hydroxide is mixed at the molar ratio of the following (b), A step of synthesizing copper particles having an average particle diameter D _TEM of 50 nm or less as determined by TEM observation, where the surfactant molecules are attached to the surface;
Solid-liquid separation of the slurry containing the synthesized copper particles, and recovering the solid content,
Washing the organic compound of impurities mixed in the solid content with an organic solvent, washing the inorganic salt of impurities with a mixture of the organic solvent and water,
The manufacturing method of the copper fine powder which has this.
(A) [Surfactant molecule] / [copper ion] molar ratio: 1 to 20
(B) Molar ratio of [hydroxide ion in hydroxide] / [alcohol A]: 0.008 to 0.5
(C) When the boiling point of the alcohol having the lowest boiling point constituting alcohol A is A _BP (° C.), the temperature range is (A _BP −50 ° C.) or more and A _BP or less. The method for producing copper fine powder according to claim 4 or 5 , wherein the copper compound is copper (II) chloride or copper (II) acetate, and the hydroxide is sodium hydroxide or potassium hydroxide. The method for producing a copper fine powder according to any one of claims 4 to 6 , wherein the surfactant is oleylamine.