JP5941082B2 - Copper powder - Google Patents

Description

  The present invention relates to copper powder.

  As a conventional technique relating to a wet copper powder production method for reducing copper ions in a liquid using a reducing agent, for example, a method using hydrazine as a reducing agent is known (see Patent Documents 1 to 3). Patent Document 1 describes a method in which hydrazine or a hydrazine compound is added to a copper hydroxide slurry to produce copper oxide, and this copper oxide is reduced to copper by a hydrazine or hydrazine compound. Patent Document 2 describes that after the pH of a copper salt aqueous solution is adjusted to 12 or more before addition of a hydrazine-based reducing agent, a reducing sugar is added and then a hydrazine-based reducing agent is added. Patent Document 3 discloses a method in which a copper hydroxide slurry is reduced with a first reducing agent to form a cuprous oxide slurry, and the cuprous oxide slurry is reduced with a second reducing agent to obtain copper powder. As hydrazine, an aqueous ammonia solution is used in combination as a pH adjuster.

  As another method for producing copper powder, the present applicant firstly mixed an oil phase in which a copper compound is dissolved in an organic solvent and an aqueous phase in which a reducing agent is dissolved in water. A method of reducing copper at the interface with the phase has been proposed (see Patent Document 4).

  As yet another method for producing copper powder, Patent Document 5 describes a method for producing copper fine particles by adding a reducing agent and reducing and precipitating a metal from a copper compound solution. A nucleus in an independent monodispersed state composed of copper ultrafine particles is generated by adding a reducing agent, and then (ii) metallic copper is reduced and precipitated from a copper salt solution in the presence of the copper ultrafine particles and the reducing agent. Is described.

  Patent Document 6 discloses a method in which cupric sulfate, ethylene glycol, and sodium hydroxide are mixed to produce copper hydroxide, and then sucrose is added and then the liquid is heated to produce copper particles. Is described.

JP-A-62-99406 JP-A-4-116109 JP 2007-254846 A JP 2009-62598 A Japanese Patent Laid-Open No. 10-317022 Japanese Patent Laid-Open No. 2004-225087

  According to the methods described in Patent Documents 1 to 3, it is easy to obtain a primary particle having a submicron order particle size. On the other hand, according to the methods described in Patent Documents 4 to 6, copper particles having a particle diameter in a range called nanoparticles are easily obtained. By the way, when a conductor film is formed using copper particles having a particle size of submicron order, the sintering start temperature tends to increase due to the size of the particle size, and the conductor film is formed on a substrate having low heat resistance. It is difficult to form. On the other hand, when a conductor film is formed using copper nanoparticles, the sintering start temperature tends to be low, but the particles tend to shrink significantly due to the heat applied in the firing step during film formation.

  Therefore, the subject of this invention is providing the copper powder which can eliminate the various fault which the prior art mentioned above has.

  As a result of intensive studies by the inventor to solve the above-mentioned problems, a copper powder having a specific particle size is applied with a larger amount of an organic surface treatment agent than in the past, and unexpectedly high-temperature sinterable copper powder. It was found that can be obtained.

The present invention has been made on the basis of the above knowledge, the average particle diameter D of the primary particles is 0.10 μm or more and 0.6 μm or less, and an organic surface treatment agent is applied to the particle surface. the proportion of the organic surface treatment agent occupying in the grains in the applied state is state, and are 0.25 mass% or more 5.50 mass% or less in terms of carbon atoms,
The organic surface treatment agent in which the organic surface treatment agent is directly bonded to the surface of the copper particles, and the organic surface treatment agent that is located outside the organic surface treatment agent and is not bonded to the surface of the copper particles. And consist of
Those wherein occupying the organic surface treatment agent, the proportion of the organic surface treatment agent not bound to the surface of the copper particles provide a copper powder Ru der less 80.0 wt% to 15.0 wt% in terms of carbon atoms is there.

  Furthermore, this invention provides the electroconductive composition containing the said copper powder and an organic solvent.

  According to the present invention, copper powder having good low-temperature sinterability is provided. Moreover, according to this invention, the copper powder which can form a conductor film with low specific resistance and high adhesiveness with a base material easily is provided.

  Hereinafter, the copper powder of this invention is demonstrated based on the preferable embodiment. Hereinafter, when referred to as copper powder, it may refer to copper powder that is an aggregate of a plurality of copper particles, or may refer to individual copper particles that constitute copper powder, depending on the context.

  One feature of the copper powder of the present invention is that the average particle size D of the primary particles has a particle size in a submicron order range of 0.10 to 0.6 μm. In the prior art in this technical field, the study mainly focused on nano-order copper particles having a particle size smaller than the above range, particularly smaller than 0.1 μm, and sub-micron order copper particles having a particle size larger than the above range. There are few studies on copper particles having a particle size in the above range. When the present inventors synthesize copper particles having a particle size in the above range by adopting the production method described later, and apply a specific amount of organic surface treatment agent on the surface, surprisingly, the low temperature of the copper powder. The inventors have found that the sinterability is improved and that the conductor film formed from the copper particles is dense and has high conductivity, thereby completing the present invention.

  By setting the average particle diameter D of the copper powder of the present invention to 0.6 μm or less, the copper powder is easily sintered at a low temperature when the conductor film is formed using the copper powder. Moreover, it is hard to produce a space | gap between particle | grains and the specific resistance of a conductor film can be reduced. On the other hand, by setting the average particle diameter D of the copper powder to 0.10 μm or more, the shrinkage of the particles when the copper powder is fired can be prevented. From these viewpoints, the average particle diameter D is more preferably 0.15 to 0.4 μm. In the present invention, the average particle diameter D of the primary particles of the copper powder is a volume average particle diameter obtained by converting a ferret diameter of a plurality of particles measured using an observation image by a scanning electron microscope into a sphere, specifically Can be measured by the measuring method described in the examples described later. The particle shape of the copper powder of the present invention is preferably spherical from the viewpoint of enhancing the dispersibility of the copper powder.

  In the copper powder of the present invention, an organic surface treatment agent is applied to the surface of the particles, whereby a surface treatment layer is formed. An organic surface treating agent is an agent for suppressing aggregation between copper particles. Until now, in the technical field, when an organic surface treatment agent is applied to the surface of copper particles, the sintering start temperature tends to increase due to that, so the amount of the organic surface treatment agent used is It has been considered to be as small as possible within a range in which aggregation during the period can be suppressed. Contrary to such conventional technical common sense, surprisingly, for copper particles having a particle size in a predetermined range, the sintering start temperature is lower when a larger amount of organic surface treatment agent is applied than before. As a result of the inventor's investigation, it has been found that the low temperature sinterability is improved.

  What is suitably used in the present invention as an agent for suppressing aggregation between copper particles is, for example, various fatty acids or aliphatic amines. In particular, it is preferable to use a saturated or unsaturated fatty acid or an aliphatic amine having 6 to 18 carbon atoms, particularly 10 to 18 carbon atoms, from the viewpoint of improving low-temperature sinterability. Specific examples of such fatty acids or aliphatic amines include benzoic acid, pentanoic acid, hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, palmitic acid, oleic acid, stearic acid, pentylamine, hexylamine, Examples include octylamine, decylamine, laurylamine, oleylamine, stearylamine and the like. These fatty acids or aliphatic amines can be used singly or in combination of two or more.

  The organic surface treatment agent can be applied to the particle surface by, for example, mixing copper powder and the organic surface treatment agent in a subsequent step of copper powder production. The amount of the organic surface treatment agent applied is such that the proportion P1 of the organic surface treatment agent in the powder with the organic surface treatment agent applied is 0.25% by mass or more and 5.50% by mass in terms of carbon atoms. The following is preferable. This range is larger than the conventionally used amount of organic surface treatment agent. By setting the ratio P1 of the organic surface treatment agent to 0.25% by mass or more in terms of carbon atoms, the low-temperature sinterability of the copper powder can be significantly improved. Moreover, by setting it as 5.50 mass% or less, low temperature sintering property can be improved significantly, avoiding extreme shrinkage. From the viewpoint of making these effects more prominent, the ratio P1 of the organic surface treatment agent is more preferably 0.25% by mass or more and 5.50% by mass or less in terms of carbon atoms, and 0.30% by mass. It is more preferable to set it as 5.00 mass% or less, and it is still more preferable that it is 0.35 mass% or more and 4.50 mass% or less.

The ratio P1 of the organic surface treatment agent applied to the surface of the copper particles can be measured as follows. Heating 0.5 g of copper powder in an oxygen stream with a carbon / sulfur analyzer (Horiba, EMIA-320V) to decompose the carbon content of the powder into CO or CO ₂ and quantify the amount. Can be measured.

As described above, the amount of the organic surface treating agent employed in the present invention is larger than that in the past. Therefore, the surface treatment layer formed on the surface of the copper particles is relatively thick. Therefore, the organic surface treatment agent constituting this surface treatment layer is composed of an organic surface treatment agent that is directly bonded to the surface of the copper particles (hereinafter referred to as “binding surface treatment agent”) and the binding surface treatment agent. And an organic surface treatment agent (hereinafter referred to as “free surface treatment agent”) which is located on the outside and is not bonded to the surface of the copper particles. Even if the conventional copper powder treated with the organic surface treatment agent is composed only of the binding surface treatment agent or contains the free surface treatment agent in addition to the binding surface treatment agent, The ratio of the surface treatment agent was low. In contrast, the copper powder of the present invention contains both a binding surface treatment agent and a free surface treatment agent, and has a high ratio of the free surface treatment agent. Specifically, the ratio P2 of the free surface treatment agent in the whole organic surface treatment agent is preferably 15.0% by mass or more and 80.0% by mass or less in terms of carbon atoms, and 20.0% by mass. The content is more preferably 79.0% by mass or less, and further preferably 22.0% by mass or more and 78.0% by mass or less. By being in such a range, it becomes possible to lower the melting temperature of the copper particles due to the removal of the oxide film on the surface of the copper particles by the free surface treating agent and the co-melting effect.

  The ratio P2 of the free surface treatment agent in the entire organic surface treatment agent can be measured by the following method. 10 g of copper powder is added to 50 mL of a solvent (for example, isobutanol) in which the organic surface treatment agent is dissolved, and dispersion treatment is performed for 5 minutes with an ultrasonic homogenizer (output 300 W, frequency 19.5 kHz). Thereafter, the powder is recovered, and the surface treatment amount adsorbed thereon is measured by the method described above. P2 can be obtained by subtracting this value from P1.

In the copper powder of the present invention, the surface of the particles is treated with an organic surface treatment agent, so that the primary particles are less aggregated. The degree of primary particle agglomeration can be evaluated using the value of D / D _BET , which is the ratio of the average particle size D _{BET in} terms of spheres based on the BET specific surface area and the average particle size D of the primary particles, as a scale. . The copper powder of the present invention has a D / D _BET value of 0.5 or more and 1.0 or less. The value of D / D _BET is a measure showing how wide the particle size distribution is compared with the ideal monodispersed state in which the copper powder has a uniform particle size and no aggregation, and can be used to estimate the degree of aggregation. .

The evaluation of the D / D _BET value is basically based on the premise that the copper powder has a continuous distribution (one mountain distribution) in addition to being uniform with few pores on the particle surface. When the value of D / D _BET is 1 under this precondition, the copper powder can be interpreted as the ideal monodispersed state described above. On the other hand, it can be inferred that the larger the value of D / D _BET is, the wider the particle size distribution of the copper powder is, and the particle size is uneven or there is much aggregation. It is rare that the value of D / D _BET is less than 1, which is often observed when the copper powder is in a state deviating from the preconditions mentioned above. Examples of the state deviating from the above preconditions include a state where pores are present on the particle surface, a state where the particle surface is non-uniform, a state where agglomeration exists locally, and the like.

From the viewpoint of making the copper powder of the present invention less aggregated of primary particles, the value of D / D _BET is more preferably 0.5 or more and 1.0 or less. The value of D _BET can be determined by measuring the BET specific surface area of the copper powder by a gas adsorption method. Specifically, the BET specific surface area and the value of D _BET can be determined by the method described in the examples described later.

The D / D _BET value in the copper powder of the present invention is as described above, and the D _BET value itself is preferably 0.08 μm to 0.6 μm, and more preferably 0.1 μm to 0.4 μm. It is still more preferably 0.12 μm or more and 0.4 μm or less. Moreover, the value of the BET specific surface area in the copper powder of the present invention (that is, the copper particles with the organic surface treatment agent applied) is preferably 1.7 m ² / g or more and 8.5 m ² / g or less. More preferably, it is 2.5 m ² / g or more and 4 m ² / g or less.

  The copper powder of the present invention preferably has a copper crystallite diameter of 60 nm or less, more preferably 50 nm or less, and still more preferably 40 nm or less. The lower limit is preferably 10 nm. By setting the size of the crystallite diameter within this range, the low sinterability of the copper powder is further improved. The crystallite diameter of the copper powder can be measured by the method described in Examples described later.

  The copper powder of the present invention having the above-described features can be sintered at a low temperature. Specifically, the sintering start temperature is preferably 150 ° C. or higher and 300 ° C. or lower, more preferably 150 ° C. or higher and 295 ° C. or lower, and still more preferably 150 ° C. or higher and 290 ° C. In particular, when the sintering start temperature is within the above range, the copper powder of the present invention can be suitably used as a wiring material for a flexible substrate made of polyimide. This is because the glass transition point of polyimide generally used for a flexible substrate exceeds 300 ° C.

  Next, the suitable manufacturing method of the copper powder of this invention is demonstrated. This production method is characterized in that, in the reduction of copper ions in a wet manner using hydrazine as a reducing agent, an organic solvent having compatibility with water and capable of reducing the surface tension of water is used as a solvent. I will. This manufacturing method can manufacture the copper powder of this invention easily and simply by using this organic solvent.

  In this production method, water and the organic solvent are used as a liquid medium, and a reaction solution containing a monovalent or divalent copper source is mixed with hydrazine, and the copper source is reduced to produce copper particles.

  Examples of the organic solvent include monohydric alcohols, polyhydric alcohols, polyhydric alcohol esters, ketones, ethers, and the like. As the monohydric alcohol, those having 1 to 5 carbon atoms, particularly 1 to 4 carbon atoms are preferable. Specific examples include methanol, ethanol, n-propanol, isopropanol, t-butanol and the like.

  Examples of the polyhydric alcohol include diols such as ethylene glycol, 1,2-propylene glycol and 1,3-propylene glycol, and triols such as glycerin.

  Examples of the ester of the polyhydric alcohol include the fatty acid ester of the polyhydric alcohol described above. As the fatty acid, for example, a monovalent fatty acid having 1 to 8 carbon atoms, particularly 1 to 5 carbon atoms is preferable. The ester of the polyhydric alcohol preferably has at least one hydroxyl group.

  As the ketone, an alkyl group bonded to a carbonyl group having 1 to 6 carbon atoms, particularly 1 to 4 carbon atoms is preferable. Specific examples of the ketone include methyl ethyl ketone and acetone.

  Examples of the ether include dimethyl ether, ethyl methyl ether, diethyl ether, cyclic compounds such as octacene, tetrahydrofuran, and tetrahydropyran, and polyethers such as polyethylene glycol and polypropylene glycol.

  Of the various organic solvents described above, it is preferable to use a monohydric alcohol from the viewpoints of economy and safety.

In the liquid medium, the ratio of the mass of the organic solvent to the mass of water (the mass of the organic solvent / the mass of water) is preferably 1/99 to 90/10, and more preferably 1.5 / 98.5. To 90/10. If the ratio of water and organic solvent is within this range, the surface tension of water during wet reduction can be reduced moderately, and copper powder having D and D / D _BET values within the above range can be easily obtained. Can get to. The liquid medium preferably consists only of the organic solvent and water.

  In this production method, a reaction liquid is prepared by dissolving or dispersing a copper source in the liquid medium. Examples of the method for preparing the reaction liquid include a method in which a liquid medium and a copper source are mixed and stirred. In the reaction solution, the ratio of the copper source to the liquid medium is such that the mass of the liquid medium is preferably 2 g or more and 2000 g or less, more preferably 4 g or more and 1000 g or less with respect to 1 g of the copper source. It is preferable for the ratio of the copper source to the liquid medium to be within this range since the productivity of copper powder synthesis is high.

As the copper source, various monovalent or divalent copper compounds can be used. In particular, it is preferable to use copper chloride, copper acetate, copper hydroxide, copper sulfate, copper oxide, or cuprous oxide. When these copper compounds are used as the copper source, copper powder having D and D / D _BET values within the above ranges can be easily obtained. Moreover, copper powder with few impurities can be obtained.

Next, the reaction solution and hydrazine are mixed. The amount of hydrazine added is preferably 0.5 to 50 mol, more preferably 1 to 20 mol with respect to 1 mol of copper. When the amount of hydrazine added is within this range, a copper powder having a D / D _BET value within the above range can be easily obtained. For the same reason, the temperature of the reaction solution is preferably maintained at 30 ° C. or higher and 90 ° C. or lower, particularly 40 ° C. or higher and 70 ° C. or lower, from the mixing start point to the end point. For the same reason, it is preferable to continue stirring of the reaction solution from the start of mixing to the end of reaction.

The reaction solution and hydrazine are preferably mixed as in any of the following (a) and (b). By doing so, it is possible to effectively prevent inconvenience caused by a rapid reaction.
(A) Hydrazine is added to the reaction solution a plurality of times at intervals.
(B) Hydrazine is continuously added to the reaction solution over a predetermined time.
In the case of (a), the plurality of times is preferably about 2 times or more and 9 times or less. The interval between the additions of hydrazine is preferably about 5 minutes to 90 minutes.
In the case of (b), the predetermined time is preferably about 1 minute to 180 minutes. The reaction solution is preferably aged by continuing stirring even after mixing with hydrazine is completed. This is because it is easy to obtain a copper powder having a D / D _BET value within the above range.

  In this production method, it is preferable to use only hydrazine as the reducing agent because copper powder with less impurities can be obtained.

  The copper powder thus obtained (that is, the copper powder before the surface treatment) is subjected to a surface treatment with an organic surface treatment agent after washing by a decantation method or the like. The surface treatment can be performed as follows, for example. That is, an organic solvent compatible with water in a 5.0 to 50.0 mass% copper powder water slurry having a conductivity of 2.0 mS or less, heated to the melting point of the organic surface treatment agent or higher (for example, 25 to 70 ° C). Surface treatment can be performed by instantly adding the surface treatment agent dissolved in and then stirring for 1 hour. By setting the slurry conductivity to 2.0 mS or less, the surface treatment can be performed while the copper powder in the slurry is uniformly dispersed without agglomeration. In addition, by increasing the temperature during the treatment above the melting point of the surface treatment agent and adding the organic surface treatment agent instantly, it becomes possible to uniformly treat the surface while preventing the organic surface treatment agent from solidifying. . By passing through the above process, the adsorption amount to the copper powder can be controlled.

  The copper powder of the present invention obtained by the surface treatment in this manner can be dispersed in water or an organic solvent and used in a slurry state. Moreover, the copper powder of this invention can also be dried and used in the state of dry powder. Furthermore, the copper powder of the present invention can be used in the form of a conductive composition such as a conductive ink or a conductive paste by adding a solvent, a resin or the like, as will be described later.

  The conductive composition containing the copper powder of the present invention comprises at least the copper powder and an organic solvent. As an organic solvent, the thing similar to what was used until now in the technical field of the electroconductive composition containing a metal powder can be especially used without a restriction | limiting. Examples of such organic solvents include monoalcohols, polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, esters, nitrogen-containing heterocyclic compounds, amides, amines, and saturated hydrocarbons. . These organic solvents can be used alone or in combination of two or more.

  Examples of monoalcohol include 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, cyclohexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, glycidol, benzyl alcohol, and methylcyclohexanol. 2-methyl 1-butanol, 3-methyl-2-butanol, 4-methyl-2-pentanol, isopropyl alcohol, 2-ethylbutanol, 2-ethylhexanol, 2-octanol, 2-methoxyethanol, 2-ethoxy Ethanol, 2-n-butoxyethanol, 2-phenoxyethanol and the like can be used.

  As the polyhydric alcohol, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tetraethylene glycol, etc. should be used. Can do.

  Examples of the polyhydric alcohol alkyl ether include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, Propylene glycol monobutyl ether or the like can be used.

  As the polyhydric alcohol aryl ether, ethylene glycol monophenyl ether or the like can be used. As the esters, ethyl cellosolve acetate, butyl cellosolve acetate, γ-butyrolactone and the like can be used. As the nitrogen-containing heterocyclic compound, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like can be used. As amides, formamide, N-methylformamide, N, N-dimethylformamide and the like can be used. As the amines, monoethanolamine, diethanolamine, triethanolamine, tripropylamine, tributylamine and the like can be used.

   As the saturated hydrocarbon, for example, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane and the like can be used.

  You may add a dispersing agent to the electrically conductive composition of this invention as needed. As the dispersant, nonionic surfactants that do not contain sodium, calcium, phosphorus, sulfur, chlorine and the like are suitable. Examples of the nonionic surfactant include polyhydric alcohol fatty acid esters, propylene glycol fatty acid esters, Glycerin fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene polyoxypropylene alkyl ether, polyoxyalkylene alkyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxy Ethylene sorbite fatty acid ester, polyoxyethylene hydrogenated castor oil, polyoxyethylene alkylamine, polyoxyalkylene alkylamine, alkyl amine Kanoruamido, polyoxyethylene alkyl phenyl ether or the like can be used.

  The conductive composition of the present invention may further contain an organic vehicle or glass frit. The organic vehicle includes a resin component and a solvent. Examples of the resin component include acrylic resin, epoxy resin, ethyl cellulose, carboxyethyl cellulose, and the like. Examples of the solvent include terpene solvents such as terpineol and dihydroterpineol, and ether solvents such as ethyl carbitol and butyl carbitol. Examples of the glass frit include borosilicate glass, borosilicate barium glass, and borosilicate zinc glass.

  In addition to the copper powder of the present invention, other copper powders may be appropriately blended with the conductive composition of the present invention as needed for the purpose of further improving various performances of the conductive composition. Good.

  The compounding quantity of the copper powder and the organic solvent in the electrically conductive composition of this invention can be adjusted in a wide range according to the specific use of this electrically conductive composition, and the coating method of this electrically conductive composition. As the coating method, for example, an inkjet method, a dispenser method, a micro dispenser method, a gravure printing method, a screen printing method, a dip coating method, a spin coating method, a spray coating method, a bar coating method, a roll coating method, or the like can be used.

  The conductive composition of the present invention has different viscosities depending on the content ratio of the copper powder, and is referred to by various names such as ink, slurry, and paste depending on the difference in viscosity. The content rate of the copper powder in the electrically conductive composition of this invention can be set in the wide range of 5 mass% or more and 95 mass% or less, for example. In this range, when using an inkjet printing method as a coating method, it is preferable to set the content rate of copper powder to 10 mass% or more and 50 mass% or less, for example. When the screen printing method is used, it is preferably set to, for example, 60% by mass or more and 95% by mass or less. When using an applicator, it is preferable to set to 5 mass% or more and 90 mass% or less, for example. When the content ratio of the copper powder is high, for example, around 90% by mass, it is preferable to use a dispenser method as a coating method.

  The conductive composition of the present invention can be applied to a substrate to form a coating film, and a conductive film can be formed by firing the coating film. The conductor film is suitably used for forming a circuit of a printed wiring board and ensuring electrical continuity of an external electrode of a ceramic capacitor, for example. As a board | substrate, the flexible printed circuit board which consists of a printed circuit board which consists of glass epoxy resin etc., a polyimide, etc. is mentioned according to the kind of electronic circuit in which copper powder is used.

  The baking temperature of the formed coating film should just be more than the baking start temperature of the copper powder mentioned above. The baking temperature of a coating film can be 170-300 degreeC, for example. The firing atmosphere can be performed, for example, in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include a reducing atmosphere such as hydrogen and carbon monoxide, a weak reducing atmosphere such as a hydrogen-nitrogen mixed atmosphere, and an inert atmosphere such as argon, neon, helium, and nitrogen. In any case of a reducing atmosphere, a weak reducing atmosphere, and an inert atmosphere, it is preferable that the respective atmospheres are formed after the inside of the heating furnace is once vacuumed to remove oxygen before heating. When calcination is performed in a hydrogen-nitrogen mixed atmosphere, the hydrogen concentration is preferably set to a concentration lower than the explosion limit concentration. Specifically, the hydrogen concentration is preferably about 1% by volume to 4% by volume. Whichever atmosphere is used, the firing time is preferably 10 minutes to 3 hours, particularly preferably 30 minutes to 2 hours.

  The conductive film thus obtained has high conductivity due to the copper powder of the present invention blended as a constituent component of the conductive composition. Moreover, adhesiveness with the application target object of an electroconductive composition will become high. The present inventor believes that the reason for this is that the copper powder of the present invention has good low-temperature sinterability. Specifically, it is considered that the copper powder of the present invention having good low-temperature sinterability is easily melted in the firing process of the coating film containing the copper powder and the particles are face-to-face-associated, so that the conductivity is increased. On the other hand, when the low temperature sinterability is not good, the particles are only in point contact even when the coating film is baked, so it is not easy to increase the conductivity. Regarding adhesion, the contact area between the melted particles and the surface of the base material is increased by melting of the particles in the firing step, and an anchor effect is generated between the melted particles and the surface of the base material, resulting in adhesion. It is thought to be higher.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
In a 36 liter stainless steel tank, 5.0 liters of warm pure water and 5.0 liters of methanol were placed, and 2.5 kg of copper acetate was placed therein. The cuprous oxide was dissolved by stirring at a liquid temperature of 40.0 ° C. for 30 minutes. Next, 150.0 g of hydrazine was added all at once in the liquid, and then stirring was continued for 30 minutes to produce cuprous oxide fine particles in the liquid. After 30 minutes, 1400.0 g of hydrazine was added all at once to the liquid, and stirring was continued for 60 minutes to reduce the cuprous oxide fine particles to copper fine particles. The aqueous copper fine particle slurry thus obtained was washed with a rotary filter until the conductivity reached 1.0 mS. The obtained copper powder 20% by mass aqueous slurry was heated to 50 ° C., and a methanol solution in which 32 g of lauric acid was dissolved was added instantaneously and stirred for 1 hour. Thereafter, solid-liquid separation was performed by filtration. The obtained copper powder was vacuum dried to obtain an organic surface-treated copper powder.

[Examples 2 to 5 and Comparative Examples 1 and 2]
Except for changing the type of organic solvent, the amount of water and organic solvent used, the type of copper source, or the type and amount of the organic surface treatment agent as described in Table 1 below, the same as in Example 1, The intended copper powder was obtained.

[Measurement / Evaluation]
About the copper powder obtained in Examples 1 to 5 and the copper powder of Comparative Examples 1 and 2, the average particle diameter in terms of spheres based on the average particle diameter D (nm) of the primary particles and the BET specific surface area by the following method The diameter D _BET (nm) was determined. Furthermore, D / D _BET was calculated from the obtained D and D _BET values. Further, the amount of carbon in the powder was measured by the following method, and based on this, the proportion P1 of the organic surface treatment agent and the proportion P2 of the free surface treatment agent were determined. Moreover, the crystallite diameter (nm) of copper was calculated | required with the following method. Further, the sintering start temperature (° C.) was determined by the following method. These results are shown in Table 2.

[Average particle diameter D of primary particles]
Using a scanning electron microscope (JSM-6330F manufactured by JEOL Ltd.), the copper powder was observed at a magnification of 10,000 times or 30,000 times, and the horizontal ferret diameter was measured for 200 particles in the field of view. . From the measured value, the volume average particle diameter converted to a sphere was calculated and used as the average particle diameter D (μm) of the primary particles.

[BET specific surface area]
Using Yuasa Ionics Co., Ltd. Monosorb, the measurement was performed by the one-point method. The amount of the measured powder was 1.0 g, and the preliminary degassing condition was 150 ° C. for 15 minutes.

[Average particle diameter D _{BET in} terms of sphere based on BET specific surface area]
It calculated | required by the following formula from the value of the BET specific surface area (SSA) obtained above and the density (8.94 g / cm < ³ >) of copper near room temperature.
D _BET (μm) = 6 / (SSA (m ² /g)×8.94 (g / cm ³ ))

(Crystallite diameter)
X-ray diffraction measurement of copper powder was performed using Ultimate IV made by Rigaku Corporation. Using the obtained (111) peak, the crystallite diameter (nm) was calculated by the Scherrer method.

[Sintering start temperature]
Sintering start temperature was measured using Seiko Instruments Inc. EXSTAR 6000. Pellets were produced by putting 500 mg of powder in an aluminum cup having a diameter of 4.0 mm and press-molding it at 1.0 MPa. The powder pellets were heated at 10 ° C./min in a 1 vol% hydrogen-99 vol% atmosphere. In this way, measurement is started from room temperature (25 ° C.), and a graph showing the relationship between temperature and displacement (%) is obtained. The relationship between the two is that the amount of displacement does not change in the low temperature region and becomes a flat graph, and the amount of displacement becomes negative (shrinks) as the temperature reaches the high temperature region. Or, depending on the case, due to variations in the production of pellets, after the displacement amount once rises to the plus (expansion) side in the low temperature range, the displacement amount finally decreases as the high temperature range is reached. Becomes minus (shrinkage). Therefore, in the present invention, when the displacement graph changes from a flat state to a negative value as the temperature rises, the heat shrinkage start temperature is the temperature at which the displacement amount is reduced by 1.0% from the flat state. Defined as starting temperature. In addition, when the displacement amount graph changes so as to rise once in the positive direction and then decrease in the negative direction as the temperature rises, the displacement amount decreases by 1.0% from the time when the amount changes from rising to falling. This temperature is defined as the heat shrinkage start temperature.

  As is apparent from the results shown in Table 2, it can be seen that the copper powder of each example has a lower sintering start temperature and good low-temperature sinterability than the copper powder of Comparative Example 1.

Claims (6)

The average particle diameter D of the primary particles is 0.10 μm or more and 0.6 μm or less, and the organic surface treatment agent is applied to the particle surface, and the organic surface occupies the particles in the state where the organic surface treatment agent is applied ratio of treatment agent state, and are 0.25 mass% or more 5.50 mass% or less in terms of carbon atoms,
The organic surface treatment agent in which the organic surface treatment agent is directly bonded to the surface of the copper particles, and the organic surface treatment agent that is located outside the organic surface treatment agent and is not bonded to the surface of the copper particles. And consist of
The organic occupying the surface treatment agent, copper powder proportion of the organic surface treatment agent that is not bound Ru der less 80.0 wt% to 15.0 wt% in terms of carbon atoms on the surface of the copper particles.   The copper powder according to claim 1, wherein the organic surface treatment agent is a fatty acid or aliphatic amine having 6 to 18 carbon atoms. Claim 1 or 2 the value of the average particle diameter D D / D _BET which is the ratio of the _BET in true sphere-equivalent based on the average particle diameter D and the BET specific surface area of the primary particles is 0.5 to 1.0 The copper powder as described in. The copper powder according to any one of claims 1 to 3 , wherein the crystallite diameter of copper is 60 nm or less. The copper powder according to any one of claims 1 to 4, wherein a sintering start temperature is 150 ° C or higher and 300 ° C or lower. The electroconductive composition containing the copper powder and organic solvent as described in any one of Claims 1 thru | or 5 .