阅读说明：本技术 铜纳米油墨的制造方法和铜纳米油墨 (Method for producing copper nano ink and copper nano ink ) 是由 冈田一诚 杉浦元彦 觉道浩树 于 2018-10-04 设计创作，主要内容包括：一种铜纳米油墨的制造方法,其包含：制备包含铜纳米粒子和阴离子的铜纳米粒子水分散液的制备步骤；和在所述制备步骤之后将所述铜纳米粒子水分散液在5℃以下储存的储存步骤,其中在所述储存步骤中,将所述铜纳米粒子水分散液的铜离子浓度控制为0.1g/L以上且1.0g/L以下,并且将阴离子浓度控制为0.5g/L以上且8.0g/L以下。(A method of making a copper nanoink, comprising: a preparation step of preparing an aqueous dispersion of copper nanoparticles containing copper nanoparticles and anions; and a storage step of storing the aqueous copper nanoparticle dispersion at 5 ℃ or lower after the preparation step, wherein in the storage step, the copper ion concentration of the aqueous copper nanoparticle dispersion is controlled to 0.1g/L or more and 1.0g/L or less, and the anion concentration is controlled to 0.5g/L or more and 8.0g/L or less.)

1. A method of making a copper nanoink, comprising:

a preparation step of preparing an aqueous dispersion of copper nanoparticles containing copper nanoparticles and anions; and

a storage step of storing the aqueous copper nanoparticle dispersion at 5 ℃ or lower after the preparation step,

wherein in the storage step, the copper ion concentration of the aqueous copper nanoparticle dispersion is controlled to be 0.1g/L or more and 1.0g/L or less, and the anion concentration is controlled to be 0.5g/L or more and 8.0g/L or less.

2. The method for producing a copper nanoink according to claim 1, wherein the anion is a chloride ion.

3. The method for producing a copper nanoink according to claim 1 or 2, wherein control is performed in the production step so that 50 ≦ CxD ≦ 150 with the anion concentration set to C [ g/L ] and the average particle size of the copper nanoparticles set to D [ nm ].

4. The method for manufacturing a copper nanoink according to claim 1, 2, or 3, wherein the storing step is performed immediately after the preparing step.

5. A copper nano ink in which copper nanoparticles and anions are dispersed in water,

wherein the copper ion concentration is 0.1g/L or more and 1.0g/L or less and the anion concentration is 0.5g/L or more and 8.0g/L or less, and

wherein the change rate of the copper ion concentration is set to R [%/h]And the storage temperature of the copper nano ink is set to be T DEG C]In the case of (1.0 × 10), 1.0 ×^-2×T≤R≤9.0×10^-2×T。

Technical Field

The present invention relates to a method for producing copper nano ink and copper nano ink. This application is based on and claims priority from japanese patent application No. 2018-000859, filed on 5.1.2018, the entire contents of which are hereby incorporated by reference.

Background

In recent years, copper nano-ink in which copper nanoparticles are dispersed in a solvent such as water is used to form a metal layer of a printed wiring board or the like.

The above-mentioned metal layer comprises a sintered body of copper nanoparticles and is formed by sintering a coating layer formed on the surface of a base film by applying a copper nano ink (see japanese patent laid-open No. 2016-152405).

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent laid-open No. 2016-152405

Disclosure of Invention

A method of manufacturing a copper nano ink according to one aspect of the present disclosure includes: a preparation step of preparing an aqueous dispersion of copper nanoparticles containing copper nanoparticles and anions; and a storage step of storing the aqueous copper nanoparticle dispersion at 5 ℃ or lower after the preparation step, wherein in the storage step, the copper ion concentration of the aqueous copper nanoparticle dispersion is controlled to 0.1g/L or more and 1.0g/L or less, and the anion concentration is controlled to 0.5g/L or more and 8.0g/L or less.

The copper nano ink according to another aspect of the present disclosure is a copper nano ink in which copper nanoparticles and anions are dispersed in water, wherein a copper ion concentration is 0.1g/L or more and 1.0g/L or less and an anion concentration is 0.5g/L or more and 8.0g/L or less, and wherein the rate of change in the copper ion concentration is set to R [%/h]And the storage temperature of the copper nano ink is set to be T DEG C]In the case of (1.0 × 10), 1.0 ×^-2×T≤R≤9.0×10^-2×T。

Drawings

Fig. 1 is a flowchart illustrating a method of manufacturing a copper nano ink according to one embodiment of the present disclosure.

Fig. 2 is a flowchart showing details of a preparation step in the method of manufacturing the copper nano ink of fig. 1.

Detailed Description

[ problem to be solved by the present disclosure ]

The copper nanoparticles contained in the conventional copper nano ink are easily oxidized by contacting with air or dissolved oxygen in the ink. In addition, the copper nanoparticles become copper ions by oxidation. Therefore, the copper ion concentration of the copper nano ink becomes high, and the dispersibility of the copper nanoparticles in the ink deteriorates. Therefore, when the copper nano ink is coated on the surface of the base film, it is difficult to uniformly disperse the copper nano particles on the surface of the base film, and it is difficult to form a sufficiently dense metal layer.

In view of the above, an object of the present disclosure is to provide a method for producing a copper nano ink capable of improving the dispersibility of copper nanoparticles, and to provide a copper nano ink in which the dispersibility of copper nanoparticles is high.

[ Effect of the present disclosure ]

The method for manufacturing the copper nano ink according to the present disclosure can improve the dispersibility of the copper nanoparticles. In addition, in the copper nano-ink according to the present disclosure, the dispersibility of the copper nanoparticles is high.

[ problem to be solved by the present disclosure ]

First, aspects of the present disclosure are listed and described below.

A method of manufacturing a copper nano ink according to one aspect of the present disclosure includes: a preparation step of preparing an aqueous dispersion of copper nanoparticles containing copper nanoparticles and anions; and a storage step of storing the aqueous copper nanoparticle dispersion at 5 ℃ or lower after the preparation step, wherein in the storage step, the copper ion concentration of the aqueous copper nanoparticle dispersion is controlled to 0.1g/L or more and 1.0g/L or less, and the anion concentration is controlled to 0.5g/L or more and 8.0g/L or less.

According to the method for producing a copper nano-ink, the dispersibility of copper nanoparticles in the obtained copper nano-ink can be improved by preparing the aqueous copper nanoparticle dispersion containing copper nanoparticles and anions in the preparation step and by controlling the copper ion concentration and the anion concentration of the aqueous copper nanoparticle dispersion in the storage step to be within the above-mentioned ranges.

Preferably, the anion is chloride. In this manner, by making the anion a chloride ion, the copper ion concentration of the aqueous copper nanoparticle dispersion can be easily and reliably controlled within the above range in the storage step.

Preferably, control is performed in the preparation step so that 50. ltoreq. CxD. ltoreq.150 with the anion concentration set to C [ g/L ] and the average particle size of the copper nanoparticles set to D [ nm ]. In this way, by controlling the value of C × D in the preparation step to be within the above range, the copper ion concentration of the aqueous copper nanoparticle dispersion can be easily and reliably controlled to be within the above range in the storage step.

Preferably, the storing step is performed immediately after the preparing step. In this way, by performing the storage step immediately after the preparation step, the copper ion concentration of the obtained copper nano ink can be kept sufficiently low.

A copper nano ink according to an aspect of the present disclosure is a copper nano ink in which copper nanoparticles and anions are dispersed in water, wherein a copper ion concentration is 0.1g/L or more and 1.0g/L or less and an anion concentration is 0.5g/L or more and 8.0g/L or less, and wherein a rate of change in the copper ion concentration is set to R [%/h]And the storage temperature of the copper nano ink is set to be T DEG C]In the case of (1.0 × 10), 1.0 ×^-2×T≤R≤9.0×10^-2×T。

The copper nano ink can keep low copper ion concentration, so that the dispersibility of copper nano particles is high.

It should be noted that in the present disclosure, the "average particle size" of the copper nanoparticles refers to a median diameter calculated from a volume-based cumulative distribution measured by a laser diffraction method. The "rate of change in copper ion concentration [%/h ] in the copper nanoink refers to a value obtained by dividing the rate of increase in copper ion concentration [% ] of the copper nanoink by the storage time [ h ] of the copper nanoink, with the copper ion concentration obtained immediately after storage calculated as 100%.

[ details of embodiments of the present disclosure ]

Hereinafter, a method of manufacturing a copper nano ink and a copper nano ink according to one embodiment of the present disclosure will be described with reference to the accompanying drawings.

[ method for producing copper nano ink ]

As shown in fig. 1, the method for manufacturing the copper nano ink includes: a preparation step (S01) (hereinafter, referred to as "preparation step") of preparing an aqueous dispersion of copper nanoparticles containing copper nanoparticles and anions; and a storage step (S02) (hereinafter, referred to as "storage step") of storing the aqueous copper nanoparticle dispersion at 5 ℃ or less after the preparation step (S01). In the method for producing a copper nanoink, the copper ion concentration of the aqueous copper nanoparticle dispersion is controlled to be 0.1g/L or more and 1.0g/L or less and the anion concentration is controlled to be 0.5g/L or more and 8.0g/L or less in the storage step (S02). It should be noted that "copper nanoparticles" refer to copper particles having a particle size of 1nm or more and less than 1 μm.

According to the method of manufacturing the copper nano-ink, the copper ion concentration of the obtained copper nano-ink can be kept low by preparing the copper nanoparticle aqueous dispersion containing copper nanoparticles and anions in the preparation step (S01) and by controlling the copper ion concentration and the anion concentration of the copper nanoparticle aqueous dispersion within the above-mentioned ranges in the storage step (S02). More specifically, according to the method for producing a copper nano-ink, in the storing step (S02), by controlling the anion concentration of the copper nanoparticle aqueous dispersion within the above range and by controlling the copper nanoparticle aqueous dispersion at 5 ℃ or lower, it is possible to suppress an increase in the copper ion concentration of the copper nanoparticle aqueous dispersion. Therefore, in the storing step (S02), the copper ion concentration of the aqueous copper nanoparticle dispersion can be controlled to be within the above range. Therefore, the method for manufacturing the copper nano ink can keep the concentration of copper ions of the obtained copper nano ink low. Therefore, the method for manufacturing the copper nano ink can improve the dispersibility of the copper nanoparticles in the copper nano ink. The reason why the dispersibility of the copper nanoparticles can be improved by keeping the copper ion concentration of the copper nano ink low is considered to be because by keeping the copper ion concentration of the copper nano ink low, the decrease in the potential on the surfaces of the copper nanoparticles is suppressed and the electrostatic repulsion between the copper nanoparticles is easily obtained.

(preparation step)

As shown in fig. 2, the preparing step (S01) includes a copper nanoparticle precipitation step (S11), a copper nanoparticle washing step (S12), and a copper nanoparticle aqueous dispersion preparing step (S13).

< copper nanoparticle precipitation step >

S11 is performed, for example, by a liquid phase reduction method. In the liquid-phase reduction method, copper ions are reduced by a reducing agent in a solution containing a complexing agent and a dispersing agent to precipitate copper nanoparticles in the solution.

In S11, for example, a water-soluble copper compound as a source of copper ions forming copper nanoparticles, a dispersant, and a complexing agent are dissolved in water, and a reducing agent is added to reduce the copper ions for a certain period of time. The copper nanoparticles produced by the liquid phase reduction method are uniform spherical or granular in shape. The copper nanoparticles produced by the liquid phase reduction method may be fine particles having an average particle size of 50nm or less, for example. As the water-soluble copper compound to be the source of copper ions, for example, copper (II) nitrate trihydrate (Cu (NO)₃)₂·3H₂O), copper (II) sulfate pentahydrate (CuSO)₄·5H₂O), and the like.

As the reducing agent, various reducing agents capable of reducing copper ions and precipitating copper ions in a reaction system of a liquid phase (aqueous solution) can be used. Examples of reducing agents include sodium borohydride; sodium hypophosphite; hydrazine; transition metal ions such as trivalent titanium ions and divalent cobalt ions; ascorbic acid; reducing sugars such as glucose and fructose; polyols such as ethylene glycol and glycerol, and the like. Among them, trivalent titanium ions are preferable as the reducing agent. It should be noted that the liquid-phase reduction method using trivalent titanium ions as a reducing agent is called a titanium redox method. In the titanium redox method, when trivalent titanium ions are oxidized into tetravalent titanium ions, copper ions are reduced by redox so that copper nanoparticles are precipitated. By this titanium redox method, copper nanoparticles having a fine and uniform particle size are easily formed.

From the viewpoint of preventing deterioration of peripheral parts, it is preferable that the dispersant is free from sulfur, phosphorus, boron, halogen, and alkali.

Preferred examples of the dispersant include: nitrogen-containing polymeric dispersants such as polyethyleneimine and polyvinylpyrrolidone; hydrocarbon polymer dispersants having carboxylic acid groups in the molecule, such as polyacrylic acid and carboxymethyl cellulose; a polymer dispersant having a polar group such as a polval (polyvinyl alcohol), a styrene-maleic acid copolymer, an olefin-maleic acid copolymer, and a copolymer having a polyethyleneimine moiety and a polyethylene oxide moiety in one molecule.

As the complexing agent, one or more of sodium citrate, sodium tartrate, sodium acetate, gluconic acid, sodium thiosulfate, ammonia, ethylenediaminetetraacetic acid, and the like can be used. Among them, sodium citrate is preferable as the complexing agent.

In order to adjust the particle size of the copper particles, the types and mixing ratios of the metal compound, the dispersant, and the reducing agent may be adjusted, and the stirring speed, temperature, time, pH, and the like at the time of subjecting the copper compound to the reduction reaction may be adjusted. The lower limit of the pH value of the reaction system is preferably 7, and the upper limit of the pH value 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 size can be obtained. In this case, the pH of the reaction system can be easily adjusted within the above range by using a pH adjuster. Examples of pH adjusters that can be used include common acids and bases such as hydrochloric acid, sulfuric acid, nitric acid, sodium hydroxide, sodium carbonate, and ammonia. In particular, nitric acid and sodium carbonate which do not contain impurity elements such as alkali metals, alkaline earth metals, halogen elements, sulfur, phosphorus, and boron are preferable in order to prevent deterioration of peripheral members.

For example, the content percentage of the copper nanoparticles in the copper nanoparticle dispersion liquid is preferably 0.1 mass% or more and 5.0 mass% or less.

The lower limit of the average particle size of the copper nanoparticles in the copper nanoparticle dispersion liquid is preferably 5nm and more preferably 10 nm. On the other hand, the upper limit of the average particle size is preferably 200nm, more preferably 100nm, and further more preferably 50 nm. Since the specific surface area increases as the particle size of the copper nanoparticles decreases, in the method for manufacturing the copper nano-ink, the anion concentration required to prevent the oxidation of the copper nanoparticles increases as the particle size of the copper nanoparticles decreases. On the other hand, when the anion concentration is too high, in the case of forming a metal layer using the copper nano-ink obtained by the method for producing a copper nano-ink, anions tend to remain in the metal layer, which may adversely affect the subsequent etching step. In this regard, when the average particle size is less than the lower limit, the required anion concentration may be high and subsequent etching may not be easy. In contrast, when the average particle size exceeds the upper limit, it may be difficult to form a sufficiently dense metal layer.

Preferably, the particle size of the copper nanoparticles in the copper nanoparticle dispersion is relatively uniform. For example, the upper limit of the coefficient of variation of the particle size distribution of the copper nanoparticles is preferably 45%, and more preferably 35%. When the coefficient of variation exceeds the above upper limit, it may not be easy to appropriately adjust the anion concentration required to prevent oxidation of the copper nanoparticles.

In S11, an anion is added to produce a copper nanoparticle dispersion. In the method of manufacturing the copper nano-ink, after anions are added in S11 to manufacture a copper nanoparticle dispersion liquid and the copper nanoparticles are washed in S12, the anion concentration of the copper nanoparticle aqueous dispersion liquid may be appropriately adjusted by mixing the copper nanoparticles with water while adjusting the concentration of the copper nanoparticles in S13. In S11, an ionic compound containing an anion may be added to produce a copper nanoparticle dispersion liquid, and a molecular compound dissociated into anions in the copper nanoparticle dispersion liquid may be added. Further, the anion may be derived from an additive such as a reducing agent or a pH adjuster added in the step of performing the liquid phase reduction method. Examples of the anion include chloride ion, sulfate ion, nitrate ion, carbonate ion, and the like.

< copper nanoparticle washing step >

In S12, the copper nanoparticles precipitated in S11 are washed. In S12, the amount of anions attached to the surface of the copper nanoparticles is adjusted.

S12 includes, for example, a centrifugation step of centrifuging the copper nanoparticle dispersion liquid obtained in S11 and a water washing step of washing with water the copper nanoparticle concentrate containing copper nanoparticles separated from the liquid phase in the centrifugation step. In S12, the centrifugation step and the water washing step may each be performed only once, or the centrifugation step and the water washing step may be alternately repeated a plurality of times.

The lower limit of the centrifugal acceleration in the centrifugation step is preferably 10000G and more preferably 20000G. On the other hand, the upper limit of the centrifugal acceleration is preferably 100000G and more preferably 70000G. When the centrifugal acceleration is less than the lower limit, the copper nanoparticles may not be sufficiently centrifuged. In contrast, when the centrifugal acceleration exceeds the upper limit, the concentration of the copper nanoparticle concentrate after centrifugation may be excessively high, causing the copper nanoparticle concentrate to adhere to a container or the like and the yield to be lowered. On the other hand, when the centrifugal acceleration is within the above range, the copper nanoparticles can be appropriately washed while adjusting the amount of anions attached to the surfaces of the copper nanoparticles.

< preparation step of aqueous Dispersion of copper nanoparticles >

In S13, a copper nanoparticle aqueous dispersion is prepared by adding water, preferably pure water, to the copper nanoparticles washed in S12. In S13, the copper ion concentration and the anion concentration in the aqueous copper nanoparticle dispersion are adjusted by adjusting the concentration of copper nanoparticles. It should be noted that in S13, an organic solvent may be added in a predetermined ratio together with the above-mentioned water as needed.

As described above, the aqueous dispersion of copper nanoparticles prepared in S13 contained the anion added in S11. Examples of the anion contained in the aqueous dispersion of copper nanoparticles include chloride ion, sulfate ion, nitrate ion, carbonate ion and the like, and among them, chloride ion is preferable. By making the anion a chloride ion, the copper ion concentration of the aqueous copper nanoparticle dispersion can be easily and reliably controlled within an appropriate range in the storage step (S02).

The coefficient of variation of the average particle size and the particle size distribution of the copper nanoparticles contained in the aqueous copper nanoparticle dispersion prepared in S13 may be similar to the coefficient of variation of the average particle size and the particle size distribution of the copper nanoparticles precipitated in S11.

The lower limit of the concentration of copper nanoparticles in the aqueous copper nanoparticle dispersion prepared in S13 is preferably 10 mass% and more preferably 20 mass%. On the other hand, the upper limit of the concentration of the copper nanoparticles is preferably 50 mass% and more preferably 40 mass%. When the concentration of the copper nanoparticles is less than the lower limit, the copper ion concentration and the anion concentration of the aqueous copper nanoparticle dispersion may be insufficient. In contrast, when the concentration of the copper nanoparticles exceeds the upper limit, the copper ion concentration and the anion concentration of the aqueous dispersion of copper nanoparticles may be excessively high.

The lower limit of the anion concentration of the aqueous dispersion of copper nanoparticles prepared in S13 is preferably 0.5g/L and more preferably 1.0 g/L. On the other hand, the upper limit of the anion concentration is preferably 8.0g/L, more preferably 6.5g/L, and further more preferably 5.0 g/L. The anion concentration of the aqueous copper nanoparticle dispersion is usually not substantially changed in the storage step (S02) described later. Therefore, when the anion concentration is less than the lower limit, the dispersibility of the copper nanoparticles may be insufficient due to the insufficient anion concentration in the storage step (S02). In contrast, when the anion concentration exceeds the upper limit, in the case of forming a metal layer using the copper nano-ink obtained by the method for producing a copper nano-ink, anions tend to remain in the metal layer, which may adversely affect the subsequent etching step.

In S13, it is preferable that the control is performed so that 50. ltoreq. CxD. ltoreq.150 where the anion concentration of the aqueous copper nanoparticle dispersion is C [ g/L ] and the average particle size of the copper nanoparticles is D [ nm ]. Further, the lower limit of C × D is more preferably 60 and further more preferably 70. On the other hand, the upper limit of C × D is more preferably 100 and further more preferably 80. Since the specific surface area increases as the particle size of the copper nanoparticles decreases, in the method for manufacturing the copper nano-ink, the anion concentration required to prevent the oxidation of the copper nanoparticles increases as the particle size of the copper nanoparticles decreases. In this regard, by controlling the particle size and anion concentration of the copper nanoparticles within the above ranges, the copper ion concentration of the aqueous copper nanoparticle dispersion can be easily and reliably controlled within an appropriate range in the storage step (S02).

(storage step)

In S02, the aqueous copper nanoparticle dispersion prepared in S01 was stored. In the method for producing the copper nanoink, the copper ion concentration of the aqueous dispersion of copper nanoparticles tends to increase immediately after the preparation of the aqueous dispersion of copper nanoparticles. Therefore, in order to appropriately control the copper ion concentration of the aqueous copper nanoparticle dispersion, it is preferable to perform S02 immediately after S01. That is, in the method for producing a copper nano ink, it is preferable that the aqueous dispersion of copper nanoparticles prepared in S01 is stored for the following time period in S02: from immediately after S01 to when the aqueous dispersion of copper nanoparticles was used. Therefore, the copper ion concentration in the obtained copper nano ink can be kept sufficiently low. The upper limit of the interval between the preparation of the aqueous dispersion of copper nanoparticles by S01 and the start of S02 is preferably 5 hours, more preferably 2 hours, and further more preferably 1 hour. When the interval exceeds the upper limit, the copper ion concentration of the aqueous dispersion of copper nanoparticles may become excessively high between S01 and S02.

It should be noted that the shorter the interval, the better and the lower limit may be 0 hour. It should be noted that, in the method for producing a copper nanoink, the aqueous dispersion of copper nanoparticles stored in S02 is referred to as a "copper nanoink".

In S02, the copper ion concentration of the aqueous copper nanoparticle dispersion prepared in S01 is controlled to be 0.1g/L or more and 1.0g/L or less, and the anion concentration is controlled to be 0.5g/L or more and 8.0g/L or less.

As described above, the copper ion concentration of the aqueous copper nanoparticle dispersion prepared in S01 tends to increase immediately after the aqueous copper nanoparticle dispersion is prepared. Therefore, in S02, the anion concentration of the aqueous copper nanoparticle dispersion is controlled to be within the above range in order to suppress an increase in the copper ion concentration of the aqueous copper nanoparticle dispersion. As described above, in S02, the anion concentration of the aqueous copper nanoparticle dispersion does not substantially change. Therefore, the anion concentration in the aqueous copper nanoparticle dispersion in S02 was approximately equal to the anion concentration in the aqueous copper nanoparticle dispersion prepared in S13. The lower limit of the anion concentration in the aqueous dispersion of copper nanoparticles in S02 is preferably 1.0 g/L. On the other hand, the upper limit of the anion concentration is preferably 6.5g/L and more preferably 5.0 g/L. When the anion concentration is less than the lower limit, the copper ion concentration of the aqueous copper nanoparticle dispersion tends to increase, and the dispersibility of copper nanoparticles may decrease. In contrast, when the anion concentration exceeds the upper limit, in the case of forming a metal layer using the copper nano-ink obtained by the method for producing a copper nano-ink, anions tend to remain in the metal layer, which may adversely affect the subsequent etching step.

Further, in S02, the storage environment of the aqueous dispersion of copper nanoparticles prepared in S01 was controlled to 5 ℃ or lower. Further, the upper limit of the storage temperature of the aqueous dispersion of copper nanoparticles in S02 is preferably 3 ℃ and more preferably 2 ℃. In S02, the aqueous dispersion of copper nanoparticles prepared in S01 is stored in a storage container such as a refrigerator for control. By controlling the storage environment of the aqueous copper nanoparticle dispersion to 5 ℃ or lower, the increase in the copper ion concentration of the aqueous copper nanoparticle dispersion can be suppressed.

The storage time of the aqueous dispersion of copper nanoparticles in S02 is not particularly limited. The storage time of the copper nanoparticle aqueous dispersion in S02 may be, for example, 20 days or longer, 30 days or longer, or 100 days or longer. According to the method for producing a copper nanoink, a copper nanoink having high dispersibility of copper nanoparticles can be produced even when the storage time in S02 is within the above range.

[ copper Nano ink ]

The copper nano ink is a copper nano ink in which copper nanoparticles and anions are dispersed in water, wherein a copper ion concentration is 0.1g/L or more and 1.0g/L or less and an anion concentration is 0.5g/L or more and 8.0g/L or less, and a rate of change in the copper ion concentration is set to R [%/h]And the storage temperature of the copper nano ink is set to be T DEG C]In the case of (1.0 × 10), 1.0 ×^-2×T≤R≤9.0×10^-2× t. the copper nano-ink may be composed of, for example, the aqueous copper nanoparticle dispersion prepared in the above-mentioned preparation step (S01), or may be composed of the aqueous copper nanoparticle dispersion after storage in the storage step (S02).

Since the copper nanoink has a rate of change in copper ion concentration within the above range, the copper ion concentration can be kept low within the above range even in the case of relatively long-term storage. Therefore, the copper nano ink has high dispersibility of the copper nanoparticles when in use.

The upper limit of the rate of change R of the copper ion concentration is preferably 4.0 × 10^-2× T, more preferably 3.0 × 10T^-2× T, and even more preferably 2.0 × 10^-2× T when the rate of change R of the copper ion concentration exceeds the upper limitThe storage time of the copper nano ink cannot be sufficiently prolonged, and the use time may be limited.

The variation coefficient of the average particle size and the particle size distribution of the copper nanoparticles of the copper nano ink may be similar to the variation coefficient of the average particle size and the particle size distribution of the copper nanoparticles of the aqueous copper nanoparticle dispersion. In addition, the copper ion concentration and the anion concentration of the copper nano-ink may be similar to those of the copper nanoparticle aqueous dispersion. Further, in the case where the anion concentration of the copper nano ink is set to C '[ g/L ] and the average particle size of the copper nanoparticles is set to D' [ nm ], the value of C '× D' may be similar to that in S13.

[ other embodiments ]

The embodiments disclosed above are to be considered in all respects as illustrative and not restrictive. The scope of the invention is not limited to the configurations of the above-described embodiments but is indicated by the claims, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

For example, in the method for producing a copper nano ink, it is preferable that the anion is added to the copper nanoparticle dispersion in the copper nanoparticle precipitation step (S11), but the anion may be added in another step such as the copper nanoparticle aqueous dispersion preparation step (S13), for example.

The washing procedure in the copper nanoparticle washing step (S12) is not limited to the procedure in the above embodiment. In S12, the copper nanoparticles may be washed, for example, by a filtration treatment, an electrodialysis treatment, or the like.