JP7280665B2 - Copper nanopowder, copper nanoink, and method for forming conductive film - Google Patents

Description

TECHNICAL FIELD The present application relates to a copper nanopowder, a copper nanoink, and a method for forming a conductive film.

A method of forming a conductive film such as a metal wiring by a printing method such as inkjet printing or screen printing using an ink containing copper nanopowder is desired. For example, a technique is disclosed in which a pattern is formed by printing using ink containing fine copper particles, and a conductive film is formed by photobaking (see, for example, Patent Documents 1 and 2).

JP 2013-105605 A JP 2013-104089 A

By using the above technique, a conductive film can be formed at low cost. However, the above technique requires a large amount of light firing sintering energy. In this case, the substrate may be damaged. Therefore, it is desirable to lower the photofiring sintering energy.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a copper nanopowder, a copper nanoink, and a method for forming a conductive film that can reduce the photofiring sintering energy.

The copper nanopowder according to the present invention has an average particle size of 10 nm or more and less than 100 nm, contains 0.15 mass% or more of phosphorus, and has an oxygen concentration of 0.54 mass% or more. .1 mass% or less.

In the copper nanopowder, the average particle size of the copper nanopowder may be 29 nm or more and 44 nm or less. The copper nanopowder may contain 0.15 mass% or more and 0.175 mass% or less of phosphorus.

A copper nanoink according to the present invention comprises any one of the copper nanopowder described above, a solvent, and a dispersing agent that disperses the copper nanopowder in the solvent.

A method for forming a conductive film according to the present invention is characterized by forming a film of the copper nano-ink on the surface of an object, drying the film, and forming a conductive film by light firing in which the dried film is irradiated with light. do.

According to the copper nanopowder, the copper nanoink, and the method for forming a conductive film according to the present invention, it is possible to reduce the light firing sintering energy.

(a) to (d) are diagrams illustrating the conductive film forming method according to the embodiment.

(Phosphorus-containing copper nanopowder)
The phosphorous-containing copper nanopowder according to this embodiment has an average particle size of 10 nm or more and less than 100 nm. When the phosphorous-containing copper nanopowder has an average particle size within this range, it can be sintered by photofiring. The phosphorous-containing copper nanopowder contains phosphorus (P). At least part of phosphorus is dissolved in the phosphorus-containing copper nanopowder. In this embodiment, the phosphorous-containing copper nanopowder contains 0.15 mass % or more of phosphorus (P). Phosphorus-containing copper nanopowder containing 0.15 mass% or more of phosphorus can reduce the light firing sintering energy compared to copper nanopowder containing no phosphorus. Thereby, it becomes possible to form a conductive film with low damage on a low heat-resistant substrate such as PET (polyethylene terephthalate). This is probably because the phosphorous-containing copper nanopowder contains phosphorus, thereby lowering the sintering initiation temperature. In addition, it is considered that oxygen, which inhibits sintering, is less likely to adhere to the surface of the phosphorous-containing copper nanopowder because phosphorus has a property of surface activity and gathers on the surface of the phosphorous-containing copper nanopowder.

When oxygen becomes less likely to adhere to the surface of the phosphorous-containing copper nanopowder, the oxidation resistance of the phosphorous-containing copper nanopowder is improved. As a result, changes in physical properties due to oxidation can be suppressed compared to copper nanopowder that does not contain phosphorus. For example, even if a copper nano ink containing a phosphorous-containing copper nanopowder is printed and then photo-fired after a predetermined time (for example, 24 hours) has passed, a low resistance equivalent to that obtained by photo-firing immediately after printing can be obtained.

When phosphorus gathers on the surface of the phosphorous-containing copper nanopowder, the wettability of the surface of the phosphorous-containing copper nanopowder to the dispersant or dispersion medium is improved compared to the surface of the copper nanopowder that does not contain phosphorus. As a result, when the copper nanoink containing the phosphorous-containing copper nanopowder is inkjet-printed, the coffee ring phenomenon may be suppressed. Further, when a copper nano ink containing phosphorous copper nano powder is subjected to gravure offset printing, edges may become sharp.

If the oxygen concentration in the phosphorous-containing copper nanopowder according to the present embodiment is too low, the cohesive force is strong, which may cause problems such as difficulty in dispersion. Therefore, in the present embodiment, a lower limit is set for the oxygen concentration of the phosphorous-containing copper nanopowder. Specifically, the phosphorous-containing copper nanopowder has an oxygen concentration of 0.54 mass% or more. On the other hand, if the oxygen concentration in the phosphorous-containing copper powder powder according to the present embodiment is too high, the oxygen on the surface of the copper nanopowder inhibits sintering. There may be problems such as being unable to Therefore, in the present embodiment, an upper limit is set for the oxygen concentration of the phosphorous-containing copper nanopowder. Specifically, the phosphorous-containing copper nanopowder has an oxygen concentration of 1.1 mass% or less.

From the viewpoint of lowering the light firing sintering energy, the phosphorus concentration in the phosphorous-containing copper nanopowder is preferably higher. For example, the phosphorus concentration in the phosphorous-containing copper nanopowder is preferably 0.26 mass% or more.

On the other hand, if the phosphorus concentration in the phosphorous-containing copper nanopowder is too high, there is a risk that the volume resistivity will increase. Therefore, it is preferable to set an upper limit for the phosphorus concentration of the phosphorous-containing copper nanopowder. For example, the phosphorus concentration of the phosphorous-containing copper nanopowder is preferably 1 mass% or less, more preferably 0.35 mass% or less.

From the viewpoint of sufficiently obtaining the effect of lowering the photofiring sintering energy due to the inclusion of phosphorus, the oxygen concentration of the phosphorous-containing copper nanopowder is preferably 0.80 mass% or less.

If the average particle size of the phosphorous-containing copper nanopowder is too small, the attractive force acting between the particles is strong and the particles tend to agglomerate, which may cause problems such as difficulty in dispersion. Therefore, it is preferable to set a lower limit for the average particle size of the phosphorous-containing copper nanopowder. For example, when the BET specific surface area is converted into an average particle size, the average particle size is preferably 29 nm or more. On the other hand, if the average particle size of the phosphorous-containing copper nanopowder is too large, the sintering temperature will be high, which may cause a problem that the effect of lowering the photofiring sintering energy due to the inclusion of phosphorus cannot be obtained. Therefore, it is preferable to set an upper limit for the average particle size of the phosphorous-containing copper nanopowder. For example, when the BET specific surface area is converted into an average particle size, the average particle size is preferably 44 nm or less.

(copper nano ink)
The copper nanoink according to this embodiment contains the phosphorous-containing copper nanopowder described above, a solvent, and a dispersant.

The solvent (dispersion medium) is not particularly limited. As a solvent, for example, a polar dispersion medium can be used. A protic dispersion medium or an aprotic dispersion medium can be used as the polar dispersion medium. The protic dispersion medium is a linear or branched alkyl compound or alkenyl compound having 5 to 30 carbon atoms and one hydroxyl group. This protic dispersion medium may have 1 to 10 ether bonds and may have 1 to 5 carbonyl groups. By setting the number of carbon atoms to 5 or more, elution (corrosion) of the fine copper particles into the dispersion medium is suppressed, and good dispersion stability is obtained. By setting the number of carbon atoms to 30 or less, the decrease in polarity of the dispersion medium is suppressed, and the dispersant is easily dissolved.

Examples of such protic dispersion media include 3-methoxy-3-methylbutanol, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl. Ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-tert-butyl ether, 2-octanol, etc., but not limited thereto. do not have.

The protic dispersion medium may be a linear or branched alkyl compound or alkenyl compound having 2 to 30 carbon atoms and having 2 to 6 hydroxyl groups. This protic dispersion medium may have 1 to 10 ether bonds and may have 1 to 5 carbonyl groups.

Examples of such protic dispersion media include 2-methylpentane-2,4-diol, ethylene glycol, propylene glycol, 1,5-pentanediol, diethylene glycol, triethylene glycol, glycerin, and sorbitol. , but not limited to these.

Examples of the aprotic polar dispersion medium having a dielectric constant of 30 or more include propylene carbonate, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphoramide, N-methylpyrrolidone, N-ethylpyrrolidone, and nitrobenzene. , N,N-diethylformamide, N,N-dimethylacetamide, furfural, γ-butyrolactone, ethylene sulfite, sulfolane, dimethyl sulfoxide, succinonitrile, ethylene carbonate and the like, but are not limited thereto. .

These polar dispersion media may be used singly or in combination of two or more.

Dispersants are not particularly limited. As a dispersant, for example, a compound having a molecular weight of 200 or more and 100000 or less or a salt thereof having at least one or more acidic functional groups can be used. The acidic functional group of the dispersant is acidic, that is, a functional group having proton-donating properties, such as a phosphoric acid group, a phosphonic acid group, a sulfonic acid group, a sulfate group, and a carboxyl group.

When these dispersing agents are used, one type may be used alone, or two or more types may be mixed and used as appropriate. The concentration of the dispersant is, for example, 0.5 mass % or more and 50 mass % or less with respect to the copper fine particle dispersion. A sufficient dispersing effect can be obtained by setting the concentration of the dispersing agent to 0.5 mass % or more. By setting the concentration of the dispersant to 50 mass % or less, good printing characteristics can be obtained when the copper fine particle dispersion is used in a printing method.

Leveling agents, surface conditioners, antifoaming agents, anticorrosive agents, photobaking modifiers, and the like can be appropriately added to these copper fine particle dispersions in accordance with the application within a range that does not impair the dispersion stability.

In the copper fine particle dispersion mixed as described above, if the dispersant has an acidic functional group and the dispersion medium is a polar dispersion medium, the dispersant has compatibility with the dispersion medium. Furthermore, when the dispersion medium is a protic dispersion medium, it has proton-donating properties, so that hydrogen bonds are formed between the dispersion medium molecules and interact with the acidic functional groups of the dispersant. When the dispersion medium is an aprotic polar dispersion medium, it does not have proton-donating properties, but has a high dielectric constant of 30 or more, so the acidic functional group of the dispersant can dissociate protons (H ⁺ ).

Since the surfaces of the fine copper particles are covered with dispersant molecules, the fine copper particles are dispersed in the dispersion medium by electrostatic interaction between the dispersant and the dispersion medium. Since the fine copper particles have a small particle diameter, if the electrostatic interaction between the dispersant and the dispersion medium is large, aggregation is prevented. .

When the protic dispersion medium has an ether bond or a carbonyl group, the polarity increases, so the compatibility with the dispersant increases, and the dispersion stability of the copper fine particle dispersion increases.

Copper nano ink may have resin further. For example, by adding a resin to the fine copper particle dispersion, each line width can be printed at once (batch printing) in the gravure offset printing method. That is, good printing characteristics can be obtained. In order to obtain good printing properties, the higher the resin concentration, the better. This is because the amount of the copper fine particle dispersion absorbed by the blanket can be suppressed by controlling the rheological properties of the copper fine particle dispersion with the resin. Furthermore, by using a resin that does not easily wet the blanket, the copper fine particle dispersion is less likely to remain on the blanket.

Resins are not particularly limited, but thermoplastic resins, thermosetting resins, thermally decomposable resins, and the like can be used. Examples of thermoplastic resins include vinyl-based polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, vinyl chloride/vinyl acetate copolymer, polystyrene-based polystyrene, styrene/acrylonitrile copolymer, and styrene/butadiene/acrylonitrile copolymer. coalescence, polyethylene, ethylene-vinyl acetate copolymer, polyphenol, polypropylene, polyacetal, polyester, terpene resin, cyclized rubber, alkyd resin, acrylic polymethyl acrylate, polymethyl methacrylate, modified acrylic, Methacryl-styrene copolymer, cellulose acetate, polycarbonate, polyethylene terephthalate, polyamide polyamide, polyimide, polyamideimide, nylon, polyurethane, fluorine resin, etc., but not limited to these. . Examples of thermosetting resins include, but are not limited to, phenol resins, melamine resins, epoxy resins, unsaturated polyesters, and silicones. Moreover, these may be cured by photoreaction with ultraviolet rays instead of heat. Examples of decomposable resins include, but are not limited to, polyperoxides. These resins may be used alone or in combination of two or more.

As the resin, it is preferable to use polyvinylpyrrolidone, polyester resin, epoxy resin, polyvinyl alcohol, terpene phenol resin, acrylic resin, urea-modified medium-polarity polyamide, modified urea, and the like. Since these resins have relatively high polarity, they are compatible with fine copper particles and a polar dispersion medium, but are less compatible with a non-polar blanket. Since the resin is easily compatible with the copper fine particles and the polar dispersion medium, the rheological properties of the copper fine particle dispersion can be changed, and by controlling the rheological properties, the amount of the copper fine particle dispersion absorbed by the blanket can be suppressed. . In addition, since the resin is difficult to adapt to the blanket, the copper fine particle dispersion is less likely to remain on the blanket. For the above reasons, it is believed that these resins exhibit good printing properties.

(Conductive film forming method)
1(a) to 1(d) are diagrams illustrating the conductive film forming method according to the embodiment. As illustrated in FIG. 1A, a copper nanoink liquid film 20a is formed on a substrate 10 by a printing method or the like.

The substrate 10 is not particularly limited. As the base material 10, an inorganic base material, an organic base material, an organic/inorganic base material, or the like can be used. Examples of inorganic substrates that can be used include glass, ceramics, silicon wafers, and aluminum. As the organic/inorganic substrate, for example, an organic/inorganic composite material such as glass epoxy can be used. For example, a thermoplastic resin can be used as the organic base material. Examples of thermoplastic resins include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, polyethylene, styrene. Vinyl acetate copolymer, polypropylene, polyacetal, polymethyl methacrylate, methacrylic/styrene copolymer, cellulose acetate, polycarbonate, polyamide, thermoplastic polyurethane, polytetrafluoroethylene, polyimide and the like can be used.

Next, a drying process is performed on the liquid film 20a. By drying the film, the resin, solvent, and dispersing agent in the copper fine particle dispersion are evaporated, leaving the copper fine particles. Drying time of the film is completed in about 30 minutes in an air atmosphere at 100° C., for example. A stream of air or nitrogen may be applied to the coating to reduce the drying time of the coating. By the drying treatment, as illustrated in FIG. 1B, the copper fine particles 30 remain on the base material 10, and the coating 20b of the copper fine particles 30 is formed on the base material 10 as a conductive film.

Next, as illustrated in FIG. 1(c), the film 20b is irradiated with light. Thereby, the film 20b is photobaked. In the photobaking, reduction of the surface oxide film of the copper fine particles 30 in the coating 20b and sintering of the copper fine particles 30 occur. As illustrated in FIG. 1( d ), the copper fine particles 30 melt together during sintering and adhere to the substrate 10 . The photobaking may be performed at room temperature in the atmosphere. A light source used for photobaking is, for example, a xenon lamp. A laser device may be used as the light source. The irradiation energy of light emitted from the light source is, for example, 0.1 J/cm ² or more and 100 J/cm ² or less. The irradiation time is, for example, 0.1 ms or more and 100 ms or less. The number of times of irradiation may be one time or multiple times of multi-stage irradiation. In the case of multistage irradiation, the irradiation time is the total time not including intervals. The conductive film 20c that has been light-baked by light irradiation becomes bulky and conductive, and adheres to the substrate 10. As shown in FIG.

In the present embodiment, since the phosphorous-containing copper nanopowder described above is used, the conductive film 20c with low resistance can be formed with low light firing and sintering energy. For example, the low-resistance conductive film 20c can be formed with irradiation energy of 1.7 J/cm ² or less. Also, the low-resistance conductive film 20c can be formed with irradiation energy of 1.4 J/cm ² or less.

(Method for producing phosphorous-containing copper nanopowder)
Phosphorus-containing copper nanopowder can be produced, for example, from a copper-phosphorus alloy raw material. In the production of the copper-phosphorus alloy raw material, high-purity copper such as JIS standard C1020 oxygen-free copper, C1011 oxygen-free copper for electron tubes, C1100 tough pitch copper, etc. is used as the copper raw material, and is used to produce strips, wires, plates, tubes, lumps, and the like. Various shapes such as spheres and grains, and copper phosphide (I) and phosphorus-containing copper as phosphorus raw materials with a known phosphorus concentration, such as strips, wires, plates, tubes, lumps, spheres, grains, etc. of each shape can be mixed and used. For example, in order to achieve the desired phosphorus concentration, raw materials in various shapes such as strips, wires, plates, tubes, lumps, spheres, and grains are further cut, thinned, and pulverized to a convenient weight. They are processed, added or subtracted as appropriate, weighed to the appropriate weight, and mixed.

For example, the above mixed raw material is mixed with ceramic crucibles, saggers, boats, quartz crucibles, boats, carbon crucibles, boats, tungsten, molybdenum, tantalum, niobium, etc. It is charged into a refractory vessel such as a high-melting-point metal crucible, boat, filament, etc., which is not corroded by copper even at a temperature sufficiently higher than the melting point of copper, and heated and melted. When the mixed raw material is heated and melted, it is preferably carried out in a vacuum or an atmosphere of an inert gas such as argon or helium in order to prevent oxidation of the raw material, achieve high purity, and achieve uniform melting and mixing. For heating, high-frequency induction heating and various heater-type resistance heating are performed by inserting the raw material into the refractory vessel mentioned above, and a resistor such as a metal or compound is energized to heat it and placed on the resistor. A method such as direct resistance heating that melts the raw material, or a heating method that charges the raw material in a water-cooled copper hearth and irradiates the raw material with an electron beam, arc, plasma, or the like can be used.

The copper-phosphorus alloy raw material having a predetermined phosphorus concentration melted by these methods may be used as it is for powder production, or it may be cooled or cast and then processed into an appropriate shape and size for use as a raw material.

The production of phosphorous-containing copper nanopowder using this copper-phosphorus alloy raw material can be carried out in any of the above-described ways in a vacuum or in an inert gas atmosphere such as argon or helium under reduced pressure, for example, if a dry gas phase production method is used. A method in which the raw material is melted by the above heating method to form it, or a raw material is processed into a wire or rod shape, and the raw material is sandwiched between suitable electrodes in a vacuum or in an inert gas atmosphere such as argon or helium under reduced pressure. It can be carried out by a method of heating and evaporating by connecting with a wire and passing a large current through it.

Equipment requirements for producing phosphorus-containing copper nanopowder by a dry vapor phase production method have been disclosed in many existing literatures, but a vessel that can withstand reduced pressure and a heating method and the dissolution amount of raw materials differ. However, it is preferable to use water-cooling or air-cooling, or use a heat shielding plate made of metal or refractory, etc., in order to suppress deterioration in the strength of the decompression vessel due to radiant heat or heat conduction. A vacuum pump is connected to such a decompression vessel, the internal pressure of the decompression vessel can be monitored by a suitable pressure gauge, and a vessel connected to a suitable inert gas supply facility such as argon or helium is used. can be done. Using these facilities, a vacuum vessel equipped with a heat source corresponding to one of the heating methods described above is decompressed with a vacuum pump, and an inert gas such as argon or helium is introduced to set the pressure to a predetermined level. , the raw material adjusted to a predetermined phosphorus concentration is dissolved. Vapors of the dissolved raw materials are generated in the decompressed container, and collide and coalesce with the residual gas in the decompressed container to form powder.

(Example)
Phosphorus-containing copper nanopowder according to the above embodiment was produced below. In Example 1, the phosphorus concentration was 0.155 mass %, the oxygen concentration was 0.67 mass %, and the average particle diameter converted from the BET specific surface area was 38 nm. In Example 2, the phosphorus concentration was set to 0.175 mass%, the oxygen concentration was set to 1.10 mass%, and the average particle diameter converted from the BET specific surface area was set to 40 nm. In Example 3, the phosphorus concentration was 0.283 mass %, the oxygen concentration was 0.54 mass %, and the average particle diameter converted from the BET specific surface area was 29 nm. In Example 4, the phosphorus concentration was 0.297 mass %, the oxygen concentration was 0.80 mass %, and the average particle diameter converted from the BET specific surface area was 43 nm. In Example 5, the phosphorus concentration was set to 0.262 mass %, the oxygen concentration was set to 0.71 mass %, and the average particle diameter converted from the BET specific surface area was set to 44 nm. In Comparative Example 1, the phosphorus concentration was set to 0 mass%, the oxygen concentration was set to 0.56 mass%, and the average particle diameter converted from the BET specific surface area was set to 39 nm. In Comparative Example 2, the phosphorus concentration was set to 0.158 mass%, the oxygen concentration was set to 1.20 mass%, and the average particle diameter converted from the BET specific surface area was set to 38 nm. In Comparative Example 3, the phosphorus concentration was 0.231 mass%, the oxygen concentration was 3.00 mass%, and the average particle diameter converted from the BET specific surface area was 43 nm.

Copper nano-inks were prepared using the phosphorous-containing copper nanopowder of Examples 1-5. In addition, copper nano-ink was produced using the copper nano-powder of Comparative Examples 1-3. Using each copper nanoink, a conductive film having a thickness of 0.5 μm was formed on a PET substrate by photobaking. The irradiation energy, as shown in Table 2, was 1.2 J/cm ² , 1.4 J/cm ² and 1.7 J/cm ² . The sheet resistance of the conductive film was measured.

First, in any of Examples 1 to 5, the phosphorous-containing copper nanopowder could be sintered by light firing. This is probably because the phosphorous-containing copper nanopowder had an average particle size of 10 nm or more and less than 100 nm, and the oxygen concentration of the phosphorous-containing copper nanopowder was 0.54 mass% or more. In addition, in any of Examples 1 to 5, a low-resistance conductive film could be formed with a low photofiring sintering energy of 1.7 J/cm ² or less. This is probably because the melting point of the copper nanopowder was lowered by setting the phosphorus concentration to 0.15 mass% or more, and oxygen, which inhibits sintering, became less likely to adhere to the surface of the phosphorous-containing copper nanopowder. . In addition, it is considered that the oxygen concentration of the phosphorous-containing copper nanopowder was 1.1 mass % or less, so that the effect of reducing the photofiring sintering energy due to the inclusion of phosphorus was sufficiently obtained.

In addition, in Example 1, a conductive film having a lower resistance than in Example 2 could be formed. It is considered that this is because the oxygen concentration of 0.80 mass % or less was able to sufficiently obtain the effect of lowering the photofiring and sintering energy. Next, in Examples 3 to 5, a conductive film having a resistance lower than that in Examples 1 and 2 could be formed. It is believed that this is because the required light firing and sintering energy could be sufficiently reduced by setting the phosphorus concentration to 0.26 mass % or more.

On the other hand, in Comparative Example 1, the copper nanopowder was not sintered. It is considered that this is because the copper nanopowder did not contain phosphorus, and the required light firing and sintering energy could not be sufficiently reduced, resulting in insufficient irradiation energy. Also in Comparative Example 2, the copper nanopowder was not sintered at irradiation energies of 1.2 J/cm ² and 1.4 J/cm ² . Although sintered at an irradiation energy of 1.7 J/cm ² , cracks appeared in the conductive film. This is because the phosphorus concentration in the copper nanopowder was 0.15 mass% or more, but the oxygen concentration exceeded 1.1 mass%, so the required light firing sintering energy could not be sufficiently reduced. This is probably because the irradiation energy was insufficient. Also in Comparative Example 3, the copper nanopowder was not sintered. As in Comparative Example 2, the phosphorus concentration in the copper nanopowder was 0.15 mass% or more, but the oxygen concentration exceeded 1.1 mass%, so that the required light firing sintering energy was sufficiently reduced. It is considered that this is because the irradiation energy was insufficient.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention described in the scope of claims. Change is possible.

Claims (5)

A copper nanopowder having an average particle size of 10 nm or more and less than 100 nm,
containing 0.15 mass% or more of phosphorus,
The copper nanopowder, wherein the oxygen concentration of the copper nanopowder is 0.54 mass% or more and 1.1 mass% or less. The copper nanopowder according to claim 1, wherein the copper nanopowder has an average particle size of 29 nm or more and 44 nm or less. The copper nanopowder according to claim 1 or 2, containing 0.15 mass% or more and 0.175 mass% or less of phosphorus. The copper nanopowder according to any one of claims 1 to 3 ,
a solvent;
and a dispersing agent that disperses the copper nanopowder in the solvent. Forming a film of the copper nanoink according to claim 4 on the surface of an object,
drying the film;
A method for forming a conductive film, wherein the conductive film is formed by photobaking in which the dried film is irradiated with light.

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