JP2018127712A - Method for producing copper nanoink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a copper nanoink, capable of easily producing a minute copper nanoink with high-concentration.SOLUTION: A method for producing a copper nanoink uses a copper nanoparticle dispersion with an average particle diameter of 50 nm or less, obtained by a liquid phase reduction method. The method for producing the copper nanoink includes: a film concentration step of separating a liquid phase by an ultrafilter membrane from the copper nanoparticle dispersion; and a centrifugal concentration step of centrifugal separation of the liquid phase from the copper nanoparticle dispersion.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a copper nano ink.

  A liquid phase reduction method in which metal nanoparticles are precipitated in a solution is known. In this liquid phase reduction method, metal ions are precipitated in a solution by reducing metal ions with a reducing agent in the solution. In addition to the metal nanoparticles, the metal nanoparticle dispersion obtained by the liquid phase reduction method contains impurities such as a reducing agent, metal ions derived from the solution raw material, and a dispersant. When the metal nanoparticles are used as a conductive material, the above components other than the metal nanoparticles may adversely affect the durability, sinterability, and the like.

  Therefore, a method for removing components other than metal nanoparticles from the metal nanoparticle dispersion is being studied today. As a method for removing components other than such metal nanoparticles, for example, a method of centrifuging metal nanoparticles using a centrifuge has been proposed (see Japanese Patent Application Laid-Open No. 2009-62570).

  The manufacturing method of the high concentration metal nanoparticle dispersion described in the above publication is said to be able to increase the concentration of metal nanoparticles by removing a part of the dispersion medium from the metal nanoparticle dispersion by centrifugation. Yes. In the production method described above, it is said that fine metal nanoparticles can be centrifuged in a short centrifugal force and in a short time by adding a dispersibility reducing agent to the metal nanoparticle dispersion before centrifugation.

JP 2009-62570 A

  However, in the production method described in the above publication, the concentration of metal nanoparticles in the dispersion is lowered due to the dispersibility reducing agent. Therefore, depending on this manufacturing method, it is difficult to sufficiently increase the concentration of the metal nanoparticles after centrifugation. Further, according to this method, since it takes time to replace the dispersion during centrifugation, the workability is low and the cost is high.

  This invention is made | formed based on such a situation, and makes it a subject to provide the manufacturing method of the copper nano ink which can manufacture a high concentration and fine copper nano ink easily.

  The method for producing a copper nano ink according to one aspect of the present invention made to solve the above problems is a method for producing a copper nano ink using a copper nano particle dispersion having an average particle diameter of 50 nm or less obtained by a liquid phase reduction method. And a membrane concentration step of separating the liquid phase from the copper nanoparticle dispersion with an ultrafiltration membrane, and a centrifugal concentration step of centrifuging the liquid phase from the copper nanoparticle dispersion.

  The method for producing a copper nano ink of the present invention can easily produce a high concentration and fine copper nano ink.

It is a flowchart which shows the manufacturing method of the copper nano ink which concerns on one Embodiment of this invention. It is a schematic diagram which shows the manufacturing apparatus of the copper nano ink used for the manufacturing method of the copper nano ink of FIG. It is a typical flowchart which shows the manufacturing method of the copper nano ink which concerns on the form different from the manufacturing method of the copper nano ink of FIG.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

  A method for producing a copper nano ink according to an aspect of the present invention is a method for producing a copper nano ink using a copper nano particle dispersion having an average particle diameter of 50 nm or less obtained by a liquid phase reduction method, wherein the copper nano particle dispersion A membrane concentration step of separating the liquid phase from the liquid with an ultrafiltration membrane, and a centrifugal concentration step of centrifuging the liquid phase from the copper nanoparticle dispersion.

  When copper nano ink is produced only by membrane concentration using an ultrafiltration membrane, the copper nanoparticles are exposed to a large amount of water for a long time during concentration, so the copper nanoparticles are likely to oxidize and aggregate, making it difficult to produce fine copper nano inks. . On the other hand, when manufacturing copper nano ink only by centrifugal concentration, workability | operativity is bad and cost tends to increase. On the other hand, the manufacturing method of the copper nano ink includes both the membrane concentration step and the centrifugal concentration step, thereby suppressing the decrease in workability and the increase in cost while suppressing the oxidative aggregation of the copper nanoparticles. . Therefore, the manufacturing method of the copper nano ink can easily manufacture a high concentration and fine copper nano ink.

  The centrifugal concentration step may be performed after the membrane concentration step. As described above, by performing the centrifugal concentration step after the membrane concentration step, a high concentration and fine copper nano ink can be more reliably manufactured.

  The molecular weight cutoff of the ultrafiltration membrane is preferably 3000 or more and 50000 or less. Thus, permeation | transmission of the ultrafiltration membrane of a copper nanoparticle can fully be prevented because the molecular weight cut off of the said ultrafiltration membrane is in the said range. Thereby, high concentration of the copper nanoparticles by the film concentration step can be promoted.

  The centrifugal acceleration in the centrifugal concentration step is preferably 20000 G or more. Thus, when the centrifugal acceleration in the centrifugal concentration step is equal to or higher than the lower limit, the copper nanoparticles can be sufficiently centrifugally concentrated. “G” means gravitational acceleration. The centrifugal acceleration means a maximum acceleration.

  The copper nano-ink manufacturing method includes a water addition step of adding water to the copper nanoparticle dispersion to be treated after the centrifugal concentration step, and a centrifugal separation of the liquid phase from the copper nanoparticle dispersion after the water addition step. And a centrifugal concentration step. Moreover, as an addition amount of the water with respect to 100 mass parts of copper nanoparticles in the said water addition process, 150 mass parts or more and 1000 mass parts or less are preferable. According to this configuration, it is possible to further promote the increase in the concentration of the copper nanoparticles while suppressing the oxidative aggregation of the copper nanoparticles caused by the addition of water.

  An inert gas may be supplied to the flow path of the copper nanoparticle dispersion in the membrane concentration step. Thus, by supplying an inert gas to the flow path of the copper nanoparticle dispersion liquid in the membrane concentration step, the oxidative aggregation of the copper nanoparticles can be more reliably suppressed.

  In the present invention, the “average particle diameter” of the copper nanoparticles in the copper nanoparticle dispersion means a median diameter calculated from a volume-based cumulative distribution measured by a laser diffraction method. The “fraction molecular weight” refers to a molecular weight having a specific solute permeation inhibition rate of 90% on the fraction curve.

[Details of the embodiment of the present invention]
Hereinafter, embodiments of the method for producing a copper nano ink according to the present invention will be described in detail with reference to the drawings.

[First embodiment]
The method for producing a copper nano ink is a method for producing a copper nano ink using a copper nano particle dispersion liquid having an average particle diameter of 50 nm or less obtained by a liquid phase reduction method. As shown in FIG. 1, the manufacturing method of the copper nano ink includes a membrane concentration step of separating the liquid phase from the copper nanoparticle dispersion with an ultrafiltration membrane, and the liquid phase is centrifuged from the copper nanoparticle dispersion. A centrifugal concentration step. The copper nano ink obtained by the method for producing copper nano ink is used to form a sintered layer of copper nanoparticles on the base film, for example, by applying and baking the base film constituting the printed wiring board. .

  When copper nano ink is produced only by membrane concentration using an ultrafiltration membrane, the copper nanoparticles are exposed to a large amount of water for a long time during concentration, so the copper nanoparticles are likely to oxidize and aggregate, making it difficult to produce fine copper nano inks. . On the other hand, when manufacturing copper nano ink only by centrifugal concentration, workability | operativity is bad and cost tends to increase. On the other hand, the manufacturing method of the copper nano ink includes both the membrane concentration step and the centrifugal concentration step, thereby suppressing the decrease in workability and the increase in cost while suppressing the oxidative aggregation of the copper nanoparticles. . Therefore, the manufacturing method of the copper nano ink can easily manufacture a high concentration and fine copper nano ink.

  First, the copper nanoparticle dispersion obtained by the liquid phase reduction method used in the method for producing copper nanoink will be described.

(Copper nanoparticle dispersion)
The above copper nanoparticle dispersion solution, for example, dissolves a water-soluble copper compound that forms the copper ion in water and a dispersant, and reduces the copper ion for a certain time by adding a reducing agent. Can be obtained. Copper nanoparticles produced by the liquid phase reduction method are spherical or granular in shape, and can be made into fine particles having an average particle diameter of 50 nm or less. Examples of the water-soluble copper compound that is the source of the copper ions include copper nitrate (II) (Cu (NO ₃ ) ₂ ), copper sulfate (II) pentahydrate (CuSO ₄ .5H ₂ O), and the like. It is done.

  As the reducing agent, various reducing agents capable of reducing and precipitating copper ions in a liquid phase (aqueous solution) reaction system can be used. Examples of the reducing agent include sodium borohydride, sodium hypophosphite, hydrazine, transition metal ions such as trivalent titanium ions and divalent cobalt ions, reducing sugars such as ascorbic acid, glucose and fructose, Examples include polyhydric alcohols such as ethylene glycol and glycerin. Among these, a trivalent titanium ion is preferable as the reducing agent. The liquid phase reduction method using trivalent titanium ions as a reducing agent is referred to as a titanium redox method. In the titanium redox method, copper ions are reduced by the redox action when trivalent titanium ions are oxidized to tetravalent, and copper nanoparticles are deposited. According to this titanium redox method, it is easy to form copper nanoparticles having a fine and uniform particle size.

  To adjust the particle size of the copper nanoparticles, adjust the type and mixing ratio of the copper compound, dispersant and reducing agent, and adjust the stirring speed, temperature, time, pH, etc. when the copper compound is reduced. do it. The lower limit of the pH of the reaction system is preferably 7, and the upper limit of the pH of the reaction system is preferably 13. By setting the pH of the reaction system within the above range, copper nanoparticles having a minute particle diameter can be obtained. At this time, the pH of the reaction system can be easily adjusted to the above range by using a pH adjuster. As this pH adjuster, common acids or alkalis such as hydrochloric acid, sulfuric acid, nitric acid, sodium hydroxide, sodium carbonate, ammonia and the like can be used. In particular, alkali metals, alkaline earths are used to prevent deterioration of peripheral members. Nitric acid and ammonia which do not contain impurities such as metals, halogen elements, sulfur, phosphorus and boron are preferred.

  As a content rate of the copper nanoparticle in a copper nanoparticle dispersion liquid, 0.1 to 5.0 mass% is preferable, for example.

(manufacturing device)
The manufacturing method of the copper nano ink can be performed using, for example, the manufacturing apparatus 1 of FIG. The production apparatus 1 includes a membrane concentration unit 2 that separates a liquid phase from the copper nanoparticle dispersion with an ultrafiltration membrane, and a centrifugal concentration unit 3 that centrifuges the liquid phase from the copper nanoparticle dispersion. In the manufacturing apparatus 1, a centrifugal concentration unit 3 is connected downstream of the membrane concentration unit 2. Thereby, the manufacturing apparatus 1 is configured to centrifugally concentrate the copper nanoparticle dispersion liquid after the membrane concentration by the membrane concentration unit 2 using the centrifugal concentration unit 3.

[Membrane concentration section]
The membrane concentration unit 2 includes a dispersion liquid storage tank 11 that stores a copper nanoparticle dispersion liquid A having an average particle diameter of 50 nm or less obtained by a liquid phase reduction method, and the copper nanoparticle dispersion liquid A is sent from the dispersion liquid storage tank 11. The membrane concentration tank 12 is provided, and an ultrafiltration membrane 12 a is disposed in the membrane concentration tank 12. The ultrafiltration membrane 12a membrane-separates the liquid phase from the copper nanoparticle dispersion A by the crossflow method.

  The dispersion liquid storage tank 11 is formed airtight. The dispersion liquid storage tank 11 constitutes a part of the flow path of the copper nanoparticle dispersion liquid A. Connected to the upper part of the dispersion liquid storage tank 11 are a dispersion liquid supply pipe 21a to which the copper nanoparticle dispersion liquid A is supplied and an inert gas supply pipe 21b to which the inert gas B is supplied. Further, a dispersion liquid discharge pipe 21 c for discharging the copper nanoparticle dispersion liquid A is connected to the lower part of the dispersion liquid storage tank 11. The dispersion discharge pipe 21c is provided with a pump 22 that pumps the copper nanoparticle dispersion A to the ultrafiltration membrane 12a side. Further, a reflux pipe 21 d for introducing the copper nanoparticle dispersion liquid A refluxed from the ultrafiltration membrane 12 a into the dispersion liquid storage tank 11 is connected to the upper part of the dispersion liquid storage tank 11.

  The membrane concentration tank 12 is a container capable of storing a liquid in a pressurized state in which the internal pressure is higher than the atmospheric pressure. The membrane concentration tank 12 is formed airtight. Inside the membrane concentration tank 12, a plurality of ultrafiltration membranes 12a are arranged to extend in the vertical direction. One end of the dispersion discharge pipe 21 c is connected to the lower part of the membrane concentration tank 12. One end of the reflux pipe 21 d is connected to the upper part of the membrane concentration tank 12. The dispersion liquid storage tank 11, the membrane concentration tank 12, and the dispersion liquid discharge pipe 21c and the reflux pipe 21d that connect them form a closed space in which the copper nanoparticle dispersion liquid A circulates. The membrane concentration tank 12 is connected to a discharge pipe 21e that discharges the liquid phase that has passed through the ultrafiltration membrane 12a to the outside of the system. Further, a switching valve 23 is provided in the dispersion liquid discharge pipe 21c. Connected to the switching valve 23 is a concentrate supply pipe 21f for supplying the copper nanoparticle dispersion liquid concentrated by liquid phase separation by the ultrafiltration membrane 12a to the centrifugal concentrator 3 (hereinafter, the concentrate is referred to as a concentrate). The copper nanoparticle dispersion liquid supplied from the supply pipe 21f to the centrifugal concentration unit 3 is also referred to as “copper nanoparticle concentrated liquid C”).

  The ultrafiltration membrane 12a is a hollow fiber membrane, for example, and has a flow path formed therein. The ultrafiltration membrane 12a has a large number of micropores. The lower end of the flow path communicates with the dispersion liquid discharge pipe 21c, and the upper end of the flow path communicates with the reflux pipe 21d. When the copper nanoparticle dispersion liquid A is supplied into the ultrafiltration membrane 12a from the dispersion liquid discharge pipe 21c, the ultrafiltration membrane 12a sends the copper nanoparticles to the reflux pipe 21d side while allowing the liquid phase to permeate through the micropores to the outside. Thereby, the ultrafiltration membrane 12a membrane-separates a liquid phase from the copper nanoparticle dispersion liquid A. The material of the ultrafiltration membrane 12a is not particularly limited, and for example, synthetic resin is used.

  The lower limit of the molecular weight cut off of the ultrafiltration membrane 12a is preferably 3000, and more preferably 6000. On the other hand, the upper limit of the molecular weight cut off of the ultrafiltration membrane 12a is preferably 50000, more preferably 20000. If the molecular weight cut-off is less than the lower limit, it may be difficult to produce the ultrafiltration membrane 12a. Moreover, when the said molecular weight cut off is less than the said minimum, there exists a possibility that a copper nanoparticle may become easy to oxidatively aggregate by requiring time for membrane separation of a liquid phase. On the contrary, when the molecular weight cut off exceeds the upper limit, the copper nanoparticles may permeate to the outside through the fine pores.

  In the manufacturing apparatus 1, the copper nanoparticle dispersion liquid A is continuously or intermittently supplied to the dispersion liquid storage tank 11. Further, the copper nanoparticle dispersion liquid A circulates in a circulation path formed by the dispersion liquid storage tank 11, the dispersion liquid discharge pipe 21c, the membrane concentration tank 12, and the reflux pipe 21d. Thereby, the density | concentration of the copper nanoparticle in the copper nanoparticle dispersion liquid A which circulates through this circulation path | route can be maintained constant. The concentration of the copper nanoparticles in the copper nanoparticle dispersion A can be adjusted, for example, by adjusting the flow rate of the liquid using a valve (not shown) and a switching valve 23 provided in the discharge pipe 21e.

(Centrifuge concentration part)
The centrifugal concentration unit 3 includes a centrifuge 13. As the centrifuge 13, a known configuration can be used. The centrifuge 13 is connected to the concentrated liquid supply pipe 21f described above. The centrifuge 13 is a copper nanoparticle dispersion (hereinafter referred to as “copper nanoparticle concentrate E”) obtained by concentrating the copper nanoparticle concentrate C supplied from the concentrate supply pipe 21f by the separation of the liquid phase D and the liquid phase D. Centrifuge). In addition, the copper nanoparticle concentrate E is formed as copper nanoink by mixing with water, for example.

  The centrifuge 13 is configured to be able to take out the copper nanoparticle concentrate E after centrifugation. Moreover, the centrifuge 13 may have, for example, a centrifuge that performs centrifuge and a relay container that is disposed so as to surround the centrifuge. In this case, the centrifuge 13 is configured so that the copper nanoparticle concentrate E after centrifugation is housed in a relay container, and water such as pure water is added to the relay container to dilute the copper nanoparticle concentrate E. May be. According to this configuration, the centrifuge 13 can discharge the copper nano ink formed by dilution of the copper nanoparticle concentrate E.

<Membrane concentration process>
The membrane concentration step is performed by the membrane concentration unit 2. Specifically, in the membrane concentration step, a copper nanoparticle dispersion liquid A having an average particle diameter of 50 nm or less obtained by a liquid phase reduction method is supplied to the dispersion liquid storage tank 11 and is contained in the copper nanoparticle dispersion liquid A. The concentration of copper nanoparticles is increased by subjecting the liquid phase to be separated by the ultrafiltration membrane 12a.

  The lower limit of the concentration ratio of the copper nanoparticle dispersion liquid A in the membrane concentration step is preferably 7 times and more preferably 10 times. On the other hand, the upper limit of the concentration ratio of the copper nanoparticle dispersion A is preferably 30 times, and more preferably 25 times. If the concentration rate is less than the lower limit, it is necessary to increase the concentration rate in the centrifugal concentration step, which may increase the production cost of the copper nano ink. On the other hand, when the concentration ratio exceeds the upper limit, the viscosity of the copper nanoparticle dispersion A becomes too high, and the filtration rate by the ultrafiltration membrane 12a may decrease. Moreover, when the said concentration rate exceeds the said upper limit, the adhesiveness of the copper nanoparticle dispersion liquid A will become high because the viscosity of the copper nanoparticle dispersion liquid A will become high too much, and the recovery rate of the copper nanoparticle dispersion liquid A will fall. There is a risk.

  As a minimum of solid content concentration of copper nanoparticle dispersion liquid A concentrated by the above-mentioned membrane concentration process, 2 mass% is preferred and 5 mass% is more preferred. On the other hand, the upper limit of the solid content concentration is preferably 20% by mass, and more preferably 10% by mass. If the solid content concentration is less than the lower limit, it is necessary to increase the concentration rate in the centrifugal concentration step, which may increase the production cost of the copper nano ink. On the contrary, when the solid content concentration exceeds the upper limit, the copper nanoparticles may be oxidized and aggregated.

  In the membrane concentration step, it is preferable to supply the inert gas B to the flow path of the copper nanoparticle dispersion A. In the method for producing copper nano ink, the copper nanoparticle dispersion liquid A circulates in a closed space formed by the dispersion liquid storage tank 11, the membrane concentration tank 12, and the dispersion liquid discharge pipe 21c and the reflux pipe 21d connecting them. . Therefore, it is easy to exclude gaseous oxygen from this circulation path by supplying the inert gas B to the flow path of the copper nanoparticle dispersion A in the membrane concentration step. As a result, the copper nanoink manufacturing method can more reliably suppress the oxidative aggregation of the copper nanoparticles. The “inert gas” is a gas that does not corrode copper nanoparticles and has a low oxygen concentration, specifically, a gas having a volume content of oxygen of 10% or less, preferably 1% or less. . Examples of the inert gas include nitrogen gas and argon gas. Of these, inexpensive nitrogen is preferred.

<Centrifuge concentration process>
The centrifugal concentration step is performed by the centrifugal concentration unit 3. In the present embodiment, the centrifugal concentration step is performed after the membrane concentration step. Specifically, in the centrifugal concentration step, the copper nanoparticle concentrate C concentrated after the membrane concentration step is centrifuged into a copper nanoparticle concentrate E and a liquid phase D. The said copper nanoink manufacturing method can manufacture a high concentration and fine copper nanoink more reliably by performing the said centrifugal concentration process after the said film | membrane concentration process.

  As a minimum of centrifugal acceleration in the above-mentioned centrifugal concentration process, 20000G is preferred and 50000G is more preferred. If the centrifugal acceleration is less than the lower limit, the copper nanoparticles may not be sufficiently concentrated by centrifugation. In addition, although it does not specifically limit as an upper limit of the said centrifugal acceleration, For example, it can be set to 120,000G. If the centrifugal acceleration exceeds the upper limit, the concentration of the copper nanoparticle concentrate E after centrifugal concentration becomes too high, and the copper nanoparticle dispersion E may adhere to a container or the like and the yield may decrease.

  As a minimum of solid content concentration of copper nanoparticle concentrate E after centrifugation in the above-mentioned centrifugal concentration process, 50 mass% is preferred and 70 mass% is more preferred. If the solid content concentration is less than the lower limit, impurities in the copper nano ink may not be sufficiently removed. On the other hand, the upper limit of the solid content concentration is not particularly limited, but may be 95% by mass, for example.

[Second Embodiment]
The method for producing a copper nano ink is a method for producing a copper nano ink using a copper nano particle dispersion liquid having an average particle diameter of 50 nm or less obtained by a liquid phase reduction method. As shown in FIG. 3, the manufacturing method of the copper nano ink includes a membrane concentration step of separating the liquid phase from the copper nanoparticle dispersion with an ultrafiltration membrane, and the liquid phase is centrifuged from the copper nanoparticle dispersion. Centrifugal concentration step, water addition step of adding water to the copper nanoparticle dispersion to be treated after the centrifugal concentration step, and re-centrifugal concentration step of centrifuging the liquid phase from the copper nanoparticle dispersion after the water addition step With. Moreover, it is preferable that the manufacturing method of the said copper nano ink is further equipped with the granulation process of granulating a copper nanoparticle dispersion liquid between the said water addition process and a recentrifugation concentration process. The manufacturing method of the copper nano ink is performed using, for example, the manufacturing apparatus 1 of FIG. The method for producing the copper nano ink can be performed in the same procedure as the method for producing the copper nano ink of FIG. 1 except that the method includes the water addition step, the re-centrifugation concentration step, and the granulation step. Therefore, below, only a water addition process, a re-centrifugal concentration process, and a granulation process are demonstrated.

<Water addition process>
The water addition step is performed when the conductivity of the liquid phase D discharged in the centrifugal concentration step exceeds a specified value. Specifically, the water addition step is performed, for example, when the conductivity of the liquid phase D is more than 100 μS / cm. When the conductivity of the liquid phase D exceeds the specified value, the copper nano-ink manufacturing method performs the water addition step and the re-centrifugal concentration step, and the conductivity of the liquid phase D discharged in the re-centrifugal concentration step. When the value exceeds the specified value, the water addition step and the re-centrifugal concentration step are repeated again. The manufacturing method of the said copper nano ink can suppress the content rate of the impurity in the copper nano ink obtained by having the said water addition process and the re-centrifugal concentration process lower.

  The water addition step is performed by adding water to the copper nanoparticle concentrate E that has been centrifuged by the centrifuge 13. As a minimum of the addition amount of the water with respect to 100 mass parts of copper nanoparticles in the above-mentioned water addition process, 150 mass parts is preferred and 300 mass parts is more preferred. On the other hand, the upper limit of the addition amount is preferably 1000 parts by mass, and more preferably 800 parts by mass. If the addition amount is less than the lower limit, the number of the water addition step and the re-centrifugal concentration step increases, and the production efficiency of the copper nanoink may not be sufficiently improved. On the contrary, when the addition amount exceeds the upper limit, the copper nanoparticles may be oxidized and aggregated due to the addition of water.

<Granulation process>
In the pulverization step, the copper nanoparticle concentrate E after the addition of water is irradiated with ultrasonic waves, or the copper nanoparticle concentrate is processed by a known apparatus such as a high-pressure homogenizer or a mixer. Disperse in the liquid. The said pulverization process can be performed after discharging | emitting the copper nanoparticle concentrate E centrifuged by the said centrifugal concentration process out of the centrifuge 13 before water addition or after water addition, for example.

<Recentrifugal concentration step>
The re-centrifugal concentration step is performed by centrifuging the copper nanoparticle concentrate E to which water has been added in the water addition step with the centrifuge 13. In the re-centrifugation concentration step, it is preferable that the copper nanoparticle concentrate E is centrifuged after the copper nanoparticles are dispersed in the liquid by the pulverization step.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  For example, in the above-described embodiment, the method of performing the centrifugal concentration step after the membrane concentration step has been described. However, in the method for producing the copper nano ink, the centrifugal concentration step may be performed before the membrane concentration step. Moreover, the manufacturing method of the said copper nano ink does not necessarily need to be performed using the manufacturing apparatus 1 of FIG.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

[No. 1]
(Preparation of copper nanoparticle dispersion)
A copper nanoparticle dispersion was prepared by a liquid phase reduction method. Specifically, 800 g (0.1 M) of a titanium trichloride solution as a reducing agent, 500 g of sodium carbonate as a pH adjusting agent, 900 g of sodium citrate as a complexing agent, and polyvinylpyrrolidone as a dispersing agent (molecular weight 30000) 10 g was dissolved in 10 L of pure water in a beaker, and the aqueous solution was kept at 35 ° C. Moreover, 25 g of copper nanoparticles were deposited by adding an aqueous solution of 100 g (0.04 M) of copper nitrate trihydrate kept at the same temperature (35 ° C.) as this aqueous solution in 2 seconds while stirring. The average particle diameter of the copper nanoparticles was 15 nm.

(Membrane concentration process)
The copper nanoparticle dispersion was subjected to cross flow filtration using an ultrafiltration membrane with a molecular weight cut off of 10,000, and concentrated 20 times until the concentration of copper nanoparticles reached 4% by mass while desalting. Further, when performing cross flow filtration, nitrogen gas was continuously supplied to the flow path of the copper nanoparticle dispersion at 100 ml / min.

(Centrifugal concentration process)
Using the rotor “P70AT” manufactured by Hitachi Koki Co., Ltd., the copper nanoparticle concentrate concentrated by the membrane concentration step is ultracentrifugated at 50000 rpm for 1 hour at a maximum centrifugal acceleration of 70000G, and the copper nanoparticle concentrate and liquid phase Was centrifuged.

(Water addition process and re-centrifugal concentration process)
The procedure for adding 80 g of pure water (addition amount 320 parts by mass with respect to 100 parts by mass of copper nanoparticles) to the copper nanoparticle dispersion liquid centrifuged in the centrifugal concentration process and performing the centrifugal concentration process again under the same conditions as above is 2 Repeated times. Pure water was added to the copper nanoparticle concentrate after the re-centrifugal concentration step to produce a copper nanoink having a copper nanoparticle concentration of 30% by mass.

[No. 2-No. 5, no. 7-No. 12]
No. 1 except that the molecular weight cut off of the ultrafiltration membrane, the number of rotations in the centrifugal concentration step, the maximum centrifugal acceleration, the number of times of the water addition step and the re-centrifugal concentration step, and the amount of pure water added were as shown in Table 1. In the same manner as in Example 1, a copper nano ink was produced.

[No. 6]
The molecular weight cutoff of the ultrafiltration membrane, the number of rotations in the centrifugal concentration step, the maximum centrifugal acceleration, the number of water addition steps and the re-centrifugation concentration step, and the amount of pure water added are as shown in Table 1, and in the membrane concentration step No. except that nitrogen gas was not supplied. In the same manner as in Example 1, a copper nano ink was produced.

[No. 13]
Table 1 shows the rotational speed, maximum centrifugal acceleration, the number of times of the water addition step and the re-centrifugation concentration step, and the amount of pure water added in the centrifugal concentration step. In the same manner as in Example 1, a copper nano ink was produced. In addition, No. In No. 13, since the membrane concentration step was not performed, the amount of the copper nanoparticle dispersion in the centrifugal concentration step was increased, and it was necessary to perform 34 cycles of ultracentrifugation once per hour.

[No. 14]
The number of rotations in the centrifugal concentration step, the maximum centrifugal acceleration, the number of water addition steps and the re-centrifugal concentration step, and the amount of pure water added are as shown in Table 1, the centrifugation time in the centrifugal concentration step is 3 minutes, and the above No. except that the membrane concentration step was not performed. In the same manner as in Example 1, a copper nano ink was produced. In addition, No. 14 does not carry out the membrane concentration step, the processing amount of the copper nanoparticle dispersion liquid in the centrifugal concentration step is increased, and it is necessary to carry out 34 cycles of ultracentrifugation once for 3 minutes.

[No. 15]
(Membrane concentration process)
No. The copper nanoparticle dispersion similar to 1 was subjected to cross flow filtration using an ultrafiltration membrane having a fractional molecular weight of 10,000, and concentrated 20 times until the concentration of copper nanoparticles reached 4% by mass while desalting. Further, when performing cross flow filtration, nitrogen gas was continuously supplied to the flow path of the copper nanoparticle dispersion at 100 ml / min.

(Water addition process and re-membrane concentration process)
The procedure for adding 80 g of pure water (addition amount 320 parts by mass with respect to 100 parts by mass of copper nanoparticles) to the copper nanoparticle concentrate concentrated by the membrane concentration step and performing the membrane concentration step again under the same conditions as above is 2 Repeated times. Pure water was added to the copper nanoparticle concentrate after the remembrane concentration step to produce a copper nanoink having a copper nanoparticle concentration of 4 mass%.

[No. 16]
Except that the amount of pure water added in the water addition step and the number of times of the water addition step and the re-membrane concentration step are as shown in Table 2, In the same manner as in Example 15, a copper nano ink was produced.

<SEM diameter>
No. 1-No. As for the copper nano ink produced in No. 16, 100 copper nanoparticles contained in the copper nano ink were arbitrarily extracted, and the surfaces of these copper nanoparticles were observed with a scanning electron microscope (SEM). The particle diameter at which the cumulative volume upon integration was 50% was determined. Table 3 shows the particle diameter (SEM diameter). In addition, No. For No. 15, the copper nanoparticles were buried in impurities and the SEM diameter could not be measured. For No. 16, the copper nanoparticles were excessively oxidized and aggregated, and the SEM diameter could not be measured.

<Particle size distribution diameter>
No. 1-No. For copper nano ink produced in 16, using a particle size distribution based made Microtrac Bell Inc. "Nanotrac Wave-EX150", to obtain an average particle diameter _{D 50} which is calculated from the cumulative volume distribution as a size distribution diameter. The particle size distribution diameter is shown in Table 3.

<Presence / absence of precipitation>
No. 1-No. About the copper nano ink manufactured by No. 16, the presence or absence of precipitation after leaving still for one week after manufacture was confirmed visually, and the following criteria evaluated. The evaluation results are shown in Table 3.
A: No precipitate is observed B: Slight precipitate is observed C: A large amount of precipitate is observed

[Evaluation results]
As shown in Table 3, no. In No. 15, since the centrifugal concentration step was not performed, desalting was not sufficiently performed, and there were many impurities, and the SEM diameter could not be measured. No. In No. 16, the addition of a large amount of pure water enabled a certain level of concentration without performing the centrifugal concentration step. However, the use of a large amount of pure water causes the copper nanoparticles to oxidize and aggregate, resulting in SEM. The diameter could not be measured, and the particle size distribution diameter was as large as 5000 nm. Furthermore, no. In No. 13, since the membrane concentration step was not performed, it was necessary to process a 10 L copper nanoparticle dispersion in the centrifugal concentration step, and the processing time of the centrifugal concentration step was very long. Specifically, 34 cycles were required for treatment of 10 L of the copper nanoparticle dispersion, and it took about 35 hours including the replacement time of the copper nanoparticle dispersion, and the productivity was extremely low. No. 14, no. Although the total production time could be shortened by shortening the centrifugation time to 3 minutes with respect to 13, small particles could not be sufficiently separated in the centrifugal concentration step, and the copper nanoparticles were replaced when the copper nanoparticle dispersion was replaced. As a result of contact with the atmosphere, the copper nanoparticles were oxidized and aggregated, the resulting copper nanoparticles were increased in size, and both the SEM diameter and the particle size distribution diameter were increased.

  On the other hand, No. which performed both the said membrane concentration process and the centrifugal concentration process. 1-No. No. 12 has an SEM diameter of 80 nm or less, a particle size distribution diameter of 200 nm or less, and almost no precipitate is observed. Among them, when supplying nitrogen gas to the flow path of the copper nanoparticle dispersion in the membrane concentration step, when the molecular weight cut off of the ultrafiltration membrane is 6000 or more and 10,000 or less, and the rotation speed in the centrifugal concentration step is 50000 rpm. When the centrifugal acceleration is 70,000 G or more, the SEM diameter and the particle size distribution diameter are small. In particular, no. 1, no. 2, no. 9-No. No. 12 has a low SEM diameter and particle size distribution diameter.

  No. 1, no. 9-No. As can be seen from FIG. 12, when the amount of pure water added is 80 g or less (320 parts by mass or less with respect to 100 parts by mass of copper nanoparticles), oxidative aggregation of copper nanoparticles due to the addition of pure water The SEM diameter and the particle size distribution diameter are both reduced. Further, when the amount of pure water added per time is sufficiently small, the SEM diameter and the particle size distribution diameter of the copper nanoparticles are kept small even if the number of times pure water is added is increased. However, no. In No. 11, the loss due to adhesion to the centrifuge increased, and the yield could not be sufficiently improved.

  As described above, the method for producing a copper nano ink of the present invention can easily produce a high concentration and fine copper nano ink, and is therefore suitable as a method for producing a copper nano ink for forming a sintered layer of a printed wiring board. .

DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus 2 Membrane concentration part 3 Centrifugal concentration part 11 Dispersion liquid storage tank 12 Membrane concentration tank 12a Ultrafiltration membrane 13 Centrifuge 21a Dispersion liquid supply pipe 21b Inert gas supply pipe 21c Dispersion liquid discharge pipe 21d Reflux pipe 21e Discharge Pipe 21f Concentrated liquid supply pipe 22 Pump 23 Switching valve A Copper nanoparticle dispersion B Inert gas C Copper nanoparticle concentrate D Liquid phase E Copper nanoparticle concentrate

Claims (6)

A method for producing a copper nano ink using a copper nanoparticle dispersion liquid having an average particle diameter of 50 nm or less obtained by a liquid phase reduction method,
A membrane concentration step of separating the liquid phase from the copper nanoparticle dispersion with an ultrafiltration membrane;
A method for producing a copper nano ink, comprising: a centrifugal concentration step of centrifuging a liquid phase from the copper nanoparticle dispersion.   The method for producing a copper nano ink according to claim 1, wherein the centrifugal concentration step is performed after the membrane concentration step.   The method for producing a copper nano ink according to claim 1 or 2, wherein the ultrafiltration membrane has a molecular weight cut-off of 3,000 to 50,000.   The method for producing a copper nano ink according to claim 1, wherein the centrifugal acceleration in the centrifugal concentration step is 20000 G or more. After the centrifugal concentration step, a water addition step of adding water to the copper nanoparticle dispersion to be treated,
A re-centrifugation concentration step of centrifuging the liquid phase from the copper nanoparticle dispersion after the water addition step,
5. The method for producing a copper nano ink according to claim 1, wherein an amount of water added to 100 parts by mass of the copper nanoparticles in the water addition step is 150 parts by mass or more and 1000 parts by mass or less.   The method for producing a copper nano ink according to any one of claims 1 to 5, wherein an inert gas is supplied to the flow path of the copper nanoparticle dispersion in the film concentration step.

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