JP2019002054A - Copper particle - Google Patents

Abstract

To provide a copper particle more excellent in low-temperature sinterability than the conventional.SOLUTION: A copper particle satisfies the following conditions (a) and (b). At a plurality of temperatures upon a temperature rise of a copper particle from 30°C to 350°C in an inert atmosphere, an XRD measurement is made on the copper particle in a state the temperatures are once held. In the relationship of a crystallite size ratio that is a ratio of the crystallite size at each temperature to a copper crystallite size at 30°C and the temperature, obtained from the measurement result, (a) the temperature at which the crystallite size becomes 1.2 is 250°C or lower and (b) the amount of change in the crystallite size ratio per unit temperature in a temperature range of 250°C or higher and 350°C or lower is 2.0×10or greater.SELECTED DRAWING: None

Description

  The present invention relates to copper particles.

  As a conventional technique related to copper particles, for example, one described in Patent Document 1 is known. In this document, the average particle diameter by SEM observation is 0.05 to 0.35 μm, the BET specific surface area value and the carbon content have a specific relationship, and the BET specific surface area value and the oxygen content have a specific relationship. The copper powder is described.

  In Patent Document 2, in the presence of a complexing agent selected from amines, nitrogen-containing heterocyclic compounds, nitriles and cyanates, ketones, amino acids, alkanolamines or salts thereof, and protective colloids, A method is described in which divalent copper oxide and a reducing agent are mixed in a liquid medium to produce metallic copper fine particles.

  Patent Document 3 describes that metal copper fine particles are produced by mixing a divalent copper oxide and a reducing agent in a medium in the presence of a complexing agent and a protein-based protective agent. . As the complexing agent, a compound having nitrogen, oxygen and sulfur as donor atoms is used. Specific examples thereof include aminopolycarboxylic acids.

  Patent Document 4 describes that polyethylene imine is added as a dispersant and copper oxide, hydroxide or salt is heated and reduced in a polyethylene glycol or ethylene glycol solution to produce copper fine particles. .

International Publication No. 2012/157704 Pamphlet JP 2012-052240 A JP 2012-162807 A JP 2005-330552 A

  In conventional wet copper particle production methods, copper particles are often synthesized in the presence of an organic polymer compound called a protective colloid or a protective agent. This is because as the particle size of the particles becomes smaller, the surface energy becomes larger, and as a result, aggregation tends to occur. In addition, an oxide film is easily formed on the particle surface due to an increase in surface area.

  However, when copper particles having an organic polymer compound on the particle surface are used for forming an electric circuit or joining electronic parts, there is a disadvantage that the sintering temperature of the copper particles increases.

  Accordingly, an object of the present invention is to provide copper particles having low-temperature sinterability that is superior to conventional ones.

The present invention provides copper particles that satisfy the following conditions (a) and (b).
In a plurality of temperatures during which the copper particles were heated from 30 ° C. to 350 ° C. in an inert atmosphere, XRD measurement was performed on the copper particles in a state where the temperature was once maintained, and obtained from the measurement results. In the relationship between the crystallite size ratio, which is the ratio of the crystallite size at each temperature to the crystallite size of copper at 30 ° C., and the temperature,
(A) the temperature at which the crystallite size ratio is 1.2 is 250 ° C. or less,
(B) The amount of change in the crystallite size ratio per unit temperature in the temperature range of 250 ° C. or higher and 350 ° C. or lower is 2.0 × 10 ⁻³ or higher.

  According to the present invention, copper particles having low-temperature sinterability superior to conventional ones are provided.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. In the following description, the term “particle” may refer to a powder that is an aggregate of particles and may refer to individual particles constituting the powder, depending on the context. The copper particles of the present invention are characterized by the relationship between the crystallite size of copper measured by the high temperature XRD method and the temperature.

  The high temperature XRD method is a method in which a sample is placed on a heatable stage and XRD (powder X-ray diffraction) measurement of the sample is performed while gradually heating the sample by heating the stage. XRD measurement is performed in a state where the temperature is once maintained at a plurality of temperatures while the copper particles are heated from 30 ° C. to 350 ° C. in an inert atmosphere with copper particles as a measurement target. The “plurality of temperatures” refers to temperatures determined at predetermined temperature intervals appropriately selected from a range of 10 ° C. to 100 ° C., for example. For example, when the temperature interval is 10 ° C., it is a temperature obtained by dividing the range from 30 ° C. to 350 ° C. in increments of 10 ° C. The rate of temperature increase from 30 ° C. to 350 ° C. does not essentially affect the measurement result of the crystallite size ratio described later, and generally can be appropriately selected from the range of 1 ° C./min to 10 ° C./min. Good. The time for maintaining the temperature is sufficient for the XRD measurement to be completed, and may be a time that does not cause the crystallite size to be excessively large. In general, it is preferably 1 minute or less, and 30 seconds or less. It is more preferable that it is 15 seconds or less. The atmosphere during measurement is an inert atmosphere such as nitrogen gas.

An X-ray diffraction chart at each temperature during temperature rise is obtained by the high temperature XRD method. Based on this chart, the crystallite size at each temperature is calculated. And the relationship between the crystallite size ratio (C / C1) which is the ratio of the crystallite size C at each temperature to the crystallite size C1 at 30 ° C. and the temperature is obtained from the calculation result. Based on this relationship, it is determined whether or not the following conditions (a) and (b) are satisfied. The copper particles of the present invention satisfy both the conditions (a) and (b).
(A) The temperature at which the crystallite size ratio is 1.2 is 250 ° C. or less,
(B) The amount of change in the crystallite size ratio per unit temperature in the temperature range of 250 ° C. to 350 ° C. is 2.0 × 10 ⁻³ or more.

  The condition (a) is that the crystallite size ratio C / C1, which is the ratio of the crystallite size C at each temperature to the crystallite size C1 at 30 ° C., is 1.2 in the relationship between the crystallite size ratio and the temperature. The temperature is specified to be 250 ° C. or lower. This regulation means that the copper particles grow at a relatively low temperature, that is, the low-temperature sinterability is high. From this viewpoint, the temperature at which C / C1 = 1.2 is preferably 200 ° C. or lower. The temperature at which C / C1 = 1.2 can also be taken as the sintering start temperature of the copper particles.

  In addition to having the low temperature sinterability which is the condition of (a), the condition of (b) is a crystallite size ratio per unit temperature (C in a temperature range of 250 ° C. to 350 ° C. which is a relatively high temperature) / C1) means that the amount of change is large. Specifically, the copper particles of the present invention start to be sintered at a low temperature, and the size of the crystallites increases with the start of sintering, that is, the sintering proceeds rapidly. In contrast to this, the conventional copper particles have a high sintering start temperature, and even if the sintering starts, the degree of progress is moderate. The rapid progress of sintering is advantageous in that, when copper particles are used as a bonding material, members to be bonded (for example, metal members) can be bonded at a low temperature in a short time.

The change amount of the crystallite size ratio per unit temperature in the copper particles of the present invention is 2.0 × 10 ⁻³ or more as described above in the temperature range of 250 ° C. or more and 350 ° C. or less, more preferably 3.0. × 10 ⁻³ or more, more preferably 4.0 × 10 ⁻³ or more. When the amount of change in the crystallite size ratio per unit temperature is within this range, the sintering of the copper particles that have started sintering proceeds rapidly. The reason why the sintering of the copper particles proceeds quickly is that the copper particles of the present invention have no organic polymer on the surface of the particles, and when heated due to the small crystallites. This is thought to be because crystallite diffusion is likely to occur at the interface where the particles contact each other.

  The amount of change in the crystallite size ratio (C / C1) per unit temperature is based on the relationship between the crystallite size ratio (C / C1) calculated in the temperature range of 250 ° C. to 350 ° C. and the temperature. It is the value of the slope obtained by performing the regression calculation, and the amount of change in the crystallite size ratio (C / C1) per 1 ° C. rise in temperature.

  The relationship between the crystallite size ratio and the temperature is as described above, and the copper crystallite size itself in the copper particles is preferably 10 nm or more and 30 nm or less at 30 ° C., and more preferably 10 nm or more and 25 nm or less. Preferably, it is 10 nm or more and 20 nm or less. When the copper crystallite size in the copper particles is within this range, when the copper particles are used as a bonding material, they are bonded at a relatively low temperature (for example, 200 ° C. or less) even in an inert atmosphere such as nitrogen gas. It is preferable because members (for example, metal members) can be joined to each other.

The crystallite size is calculated from the diffraction peak obtained by powder X-ray diffraction according to the Scherrer equation. In the present invention, the X-ray diffraction intensity of the copper particles was measured in a measurement range 2θ = 38 ° to 48 ° using a CuKα ray using a fully automatic horizontal multipurpose X-ray diffractometer manufactured by Rigaku Corporation. From the peak width (half width) of the X-ray diffraction peak on the crystal plane (111) at that time, the crystallite size was calculated by the following Scherrer equation.
Scherrer's formula: D = Kλ / βcosθ
D: Crystallite size K: Scherrer constant (0.94)
λ: X-ray wavelength β: Half width [rad]
θ: Diffraction angle

  The copper particles of the present invention that satisfy the above conditions (a) and (b) are suitably used as a circuit forming material for a flexible substrate made of, for example, polyimide or a liquid crystal polymer. This is because when the copper particles of the present invention are used as a circuit forming material, the heat treatment temperature during circuit formation can be made lower than the heat resistance temperature of the flexible substrate.

  In order to obtain the copper particles of the present invention having low temperature sinterability, for example, the copper particles may be produced by the method described later. The present inventor considers the reason why the copper particles of the present invention have low-temperature sinterability as follows. When the copper particles of the present invention are produced by the production method described later, the copper particles do not have an organic polymer on the surface. In addition to this, the copper particles have a smaller crystallite size than conventional copper particles, so that the diffusion of crystallites proceeds at the interface where the particles contact each other even at low temperatures. For these reasons, it is considered that the copper particles of the present invention are sintered at a low temperature. In order to facilitate the diffusion of crystallites at the interface where the particles contact each other, it is advantageous to produce copper particles by, for example, a method described later.

  It is preferable that the copper particle of this invention does not have the layer which consists of an agent for suppressing the aggregation between particle | grains and / or the oxidation of particle | grains on the particle surface as much as possible. In the present specification, the agent for suppressing aggregation between particles and / or the oxidation of particles is a function of adhering to the surface of copper particles and suppressing aggregation between the copper particles, and / or the copper particles. A wide range of compounds having the function of inhibiting the oxidation of In that sense, in the following description, this agent will be referred to as a “protecting agent” for convenience.

  Examples of the protective agent include organic polymer compounds such as natural polymers and synthetic polymers. Examples of natural polymers include proteins such as gelatin, gum arabic, casein, sodium caseinate, ammonium caseinate, starch, dextrin, agar, and sodium alginate. Synthetic polymers include cellulose compounds such as hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose and ethyl cellulose, polyvinyl compounds such as polyvinyl alcohol and polyvinyl pyrrolidone, polyacrylic acid compounds such as sodium polyacrylate and ammonium polyacrylate, polyethylene And glycols. In addition, examples of the protective agent include phosphates such as sodium pyrophosphate, chain fatty acids such as stearic acid, lauric acid, and oleic acid. In addition, various coupling agents containing metalloids or metals such as silicon, titanium, zirconium and aluminum are also included.

  Even when the copper particles of the present invention do not have a large amount of a protective agent layer on the particle surface, the copper particles of the present invention have good low-temperature sinterability. From the viewpoint of further improving the low-temperature sinterability, it is preferable that the copper particles have as little content of an element that forms a protective agent layer.

  The copper particles of the present invention are preferably fine particles. Specifically, the average particle diameter D of the primary particles is preferably 0.01 μm or more and 0.3 μm or less, and 0.02 μm or more and 0.21 μm or less. Is more preferably 0.05 μm or more and 0.10 μm or less. By setting the average particle diameter D of the copper particles to 0.3 μm or less, the copper particles are easily sintered at a low temperature when a film is formed using the copper particles. Moreover, it is hard to produce a space | gap between particle | grains and can reduce the specific resistance of a film | membrane. On the other hand, by setting the average particle diameter D of the copper particles to 0.01 μm or more, the particles can be prevented from shrinking when the copper particles are fired. In the present invention, the average particle diameter D of the primary particles of the copper particles is an arithmetic average particle diameter of the Heywood diameters of a plurality of particles measured using an image observed with a scanning electron microscope or a transmission electron microscope. The particle shape of the copper particles of the present invention is preferably spherical from the viewpoint of improving the dispersibility of the copper particles.

  When the copper particles are fine particles, the specific surface area increases, so the surface is easily oxidized. In order to prevent oxidation, a protective agent may be applied to the surface of the particles, but in that case, the low-temperature sinterability of the copper particles is impaired. Therefore, in the present invention, it is advantageous that an organic substance having a —COO— group and containing nitrogen is present instead of the conventional protective agent. As a result of the study by the present inventor, it was found that this organic matter can effectively prevent the oxidation of copper particles with a small amount of adhesion.

The adhesion amount of the organic substance containing nitrogen can be expressed by the contents of carbon and nitrogen contained in the copper particles when the specific surface area of the copper particles is used as a reference. When the carbon content in the copper particles is PC (mass%), the nitrogen content in the copper particles is PN (mass%), and the specific surface area of the copper particles is SSA (m ² / g), the PC and SSA The ratio of PC / SSA as a ratio is preferably in the range of 0.01 to 0.1, more preferably in the range of 0.01 to 0.8, and still more preferably 0.01 to 0.6. The range is as follows. The value of PN / SSA, which is the ratio of PN to SSA, is preferably 0.001 or more and 0.05 or less, more preferably 0.01 or more and 0.03 or less, and still more preferably 0.00. The range is from 01 to 0.015. Copper particles containing carbon and nitrogen within this range are those in which oxidation of the particle surface is effectively prevented by the action of organic substances containing nitrogen.

  The copper particles of the present invention can be used in the form of a composition comprising the copper particles. For example, the copper particles of the present invention can be used in the form of a composition comprising at least the copper particles and an organic solvent. As an organic solvent, the thing similar to what was used until now in the technical field of the 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.

  The composition 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. Furthermore, in addition to the copper particles obtained by the production method of the present invention, other copper particles are appropriately added to the above composition as necessary for the purpose of further improving various performances of the composition. You may mix | blend.

  The compounding amount of the copper particles and the organic solvent in the composition can be adjusted in a wide range depending on the specific application of the composition and the coating method of the 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 composition can be used as a conductive material. Specifically, a film can be formed by applying the above composition on a substrate to form a coating film and firing the coating film. This film is suitably used, for example, as a conductor film for forming a circuit of a printed wiring board and ensuring electrical continuity of an external electrode of a ceramic capacitor. 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, a liquid crystal polymer, etc. according to the kind of electronic circuit in which a copper particle is used is mentioned. The composition can also be used as a bonding material for die bonding for bonding a die of a semiconductor device and a support (for example, a wiring body). Alternatively, it can also be used as a bonding material for bonding a heat dissipation metal member such as a heat spreader installed on a semiconductor and the semiconductor. In these cases, the film obtained from the composition functions as a heat conductor. Moreover, it can also be made to function as a heat conductor by heating, after filling the said composition in a via | veer.

  Next, the suitable manufacturing method of the copper particle of this invention is demonstrated. In this production method, it is preferable to obtain copper particles in a wet manner, that is, in an aqueous liquid. In the present invention, a copper complex is preferably used as the copper source of the copper particles. This copper complex has a structure in which a ligand is coordinated to a copper ion as a central metal element. As this copper ion, one having a positive divalent charge is generally used.

  In the present invention, it is preferable to use a nitrogen-containing compound having a plurality of — (C═O) O— sites as a ligand used for coordination with a copper ion to form a copper complex. As such a nitrogen-containing compound, aminopolycarboxylic acids are preferably used. Examples of aminopolycarboxylic acids include ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), ethylenediaminediacetic acid (EDDA), and ethylene glycol diethyl etherdiaminetetraacetic acid (GEDA). Among these aminopolycarboxylic acids, a nitrogen-containing compound having three or four — (C═O) O— moieties is coordinated from the viewpoint of easily obtaining fine and low sintering temperature copper particles. It is preferable to use it as a child, in particular ethylenediaminetetraacetic acid (EDTA) or nitrilotriacetic acid (NTA) is preferable, and nitrilotriacetic acid (NTA) is particularly preferable. That is, it is preferable to use a copper-nitrilotriacetic acid complex as the copper complex. In this copper complex, one nitrilotriacetic acid is generally coordinated to one positive divalent copper ion. The state of nitrilotriacetic acid coordinated to the copper ion depends on the pH of the aqueous solution in which the copper complex is dissolved.

  When a copper-nitrilotriacetic acid complex is used as the copper complex, the copper complex can be preferably prepared by the procedure described below. That is, a water-soluble nitrilotriacetic acid salt, for example, disodium nitrilotriacetate, is prepared and dissolved in water to prepare an aqueous solution of nitrilotriacetic acid. A copper source compound is added to this aqueous solution. As the copper source compound, for example, a divalent copper compound can be used. Specific examples thereof include copper hydroxide (II), copper acetate (II), copper nitrate (II), copper sulfate (II) and the like. When the copper source compound is water-soluble, a copper-nitrilotriacetic acid complex is generated in the aqueous solution by adding the copper source compound to the aqueous solution. When the copper source compound is insoluble in water, the pH of the aqueous solution is adjusted to dissolve the copper source compound in water. For example, when using copper (II) hydroxide which is a water-insoluble compound as a copper source compound, after adding copper (II) hydroxide to an aqueous solution of nitrilotriacetic acid, an appropriate amount of a basic compound is added to the aqueous solution. As the basic compound, for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is preferably used. The basic compound is added in such an amount that the pH of copper (II) hydroxide is dissolved in water. Thereby, a copper-nitrilotriacetic acid complex is formed in the aqueous solution. When an unreacted solid content remains in the aqueous solution after the copper-nitrilotriacetic acid complex is formed, the solid content is removed using a separation means such as filtration. The concentration of the copper complex in the aqueous solution is preferably 0.001 mol / L or more and 1 mol / L or less, more preferably 0.1 mol / L or more and 0.5 mol / L or less based on copper ions.

  A reducing agent is added to the aqueous solution of the copper complex thus obtained so that the reducing agent acts on the copper complex, and the copper ions in the copper complex are reduced to metallic copper. In this production method, the method for adding the reducing agent is not particularly limited, and the whole amount of the reducing agent may be added all at once, or may be continuously dropped over a predetermined time. Among these methods, there is an advantage that foaming due to a reduction reaction can be suppressed by adopting continuous dripping. When the reducing agent is allowed to act, it is preferable that no protective agent other than the ligand component of the copper complex be present in the aqueous solution of the copper complex. When the copper ion in the copper complex is reduced in a state where the protective agent is present in the aqueous solution of the copper complex, the agent adheres to the surface of the copper particles generated by the reduction. Since the copper particles having the protective agent attached to the surface are less likely to be sintered due to the presence of the protective agent, the copper particles have the disadvantage that the sintering start temperature tends to increase. .

  The present inventor believes that ligand decomposition occurs when copper particles are generated by reduction of the copper complex. A decomposition product generated by the decomposition of the ligand may have a — (C═O) O— site and a nitrogen-containing site that the ligand originally had. The decomposition product having such a site is likely to adhere to the surface of the copper particles generated by the reduction. As a result, when the copper particles obtained by this production method are subjected to XPS measurement, a —COO— group and N are detected.

  In the present invention, when the reducing agent is allowed to act on the copper complex, it is most preferable that no protective agent other than the ligand component of the copper complex is present in the system, but as long as the effect of the present invention is not impaired. Inevitably, a small amount of a protective agent other than the ligand component of the copper complex is allowed to be mixed.

  When the reducing agent is allowed to act on the copper complex, the pH in the system is preferably set to 8.0 or more and 14.0 or less, more preferably 8.6 or more and 13.0 or less, and 8.9 More preferably, it is set to 12.9 or less. In particular, when hydrazine is used as the reducing agent, the pH in the system is particularly preferably set to 12.4 or more from the viewpoint of effectively preventing particle aggregation. By adding a reducing agent to an aqueous solution within this pH range, copper particles that are fine and have a low sintering temperature can be easily obtained. Various acids and basic substances can be used to adjust the pH. For example, sodium hydroxide or ammonia can be used.

  As the reducing agent that acts on the copper complex, a compound having a reducing ability capable of reducing the copper ion in the copper complex to metallic copper can be used without any particular limitation. Examples of such a reducing agent include hydrazine compounds such as hydrazine, hydrazine hydrochloride, hydrazine sulfate and hydrazine hydrate, sodium borohydride, sodium sulfite, sodium hydrogen sulfite, sodium thiosulfate, sodium nitrite, sodium hyponitrite. , Phosphorous acid, sodium phosphite, hypophosphorous acid, sodium hypophosphite and the like. These reducing agents can be used individually by 1 type or in combination of 2 or more types. In particular, hydrazine-based compounds such as hydrazine are preferably used because they have a strong reducing power, and hydrazine is particularly preferably used because it generates less impurities after reduction. The amount of the reducing agent used is not particularly limited as long as it is an amount capable of generating copper particles from a copper complex, and can be appropriately set. Generally, it is preferable to use a reducing agent in the range of 0.5 mol or more and 50 mol or less with respect to 1 mol of copper. By using a reducing agent within this range, fine copper particles can be sufficiently generated without excessive reduction. From this viewpoint, the more preferable amount of the reducing agent used is in the range of 1 mol to 5 mol with respect to 1 mol of copper.

  When the reducing agent is added to the aqueous solution containing the copper complex, the liquid is stirred for a predetermined time to perform aging. The temperature of the aqueous solution at the time of adding the reducing agent and the temperature of the aqueous solution at the time of aging are not critical in this production method, and can be generally performed at a room temperature of 20 ° C. or more and 25 ° C. or less. In this way, target copper particles can be obtained. The copper particles thus obtained do not have a layer on the particle surface, which is composed of an agent (a substance other than an organic compound derived from a ligand of a copper complex) for suppressing aggregation between particles. It becomes. The copper particles obtained in this way are generally spherical. Spherical copper particles are preferable from the viewpoint of easily increasing the dispersibility. The present invention does not exclude that the obtained copper particles inevitably contain other elements or that the surface of the copper particles is oxidized as long as the significance of the present invention is not impaired.

  In this manufacturing method, the particle size of the obtained copper particles can be adjusted by appropriately setting the pH when the reducing agent in the above-described step is allowed to act. For example, fine copper particles having an average primary particle size D of 0.01 μm or more and 0.3 μm or less can be obtained.

  The copper particles obtained in this way may be dispersed in an organic solvent such as water or alcohol after being washed by pure water repulp washing or decantation method, etc. to obtain slurry, ink, paste, or the like. Alternatively, the copper particles may be dried to obtain a dry powder. Furthermore, it is good also as compositions, such as a slurry, an ink, and a paste, adding a solvent, resin, etc. so that the obtained copper particle may mention later. This composition can be suitably used as a conductive or thermally conductive composition.

  Conventionally, fine copper particles that do not have a protective agent layer and aggregate when dried are difficult to take out as a dry powder. For this reason, conventionally, when storing and transporting such copper particles, water, an organic solvent, a resin, or the like is added to the copper particles to form an aqueous slurry or paste. On the other hand, the copper particles obtained by this production method can be stored and transported as a dry powder because they do not have a protective agent layer and hardly aggregate when dried. This is advantageous in that the storage space for the copper particles can be reduced and it can be easily transported.

  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]
(1) Preparation of aqueous copper complex solution 244 g of nitrilotriacetic acid disodium was dissolved in 1202 g of water to obtain an aqueous solution. To this aqueous solution, 51 g of copper (II) hydroxide was added and dispersed in the liquid. Under this dispersion state, 203 g of 10% aqueous sodium hydroxide solution was added and stirred. Next, an aqueous solution containing a copper-nitrilotriacetic acid complex was obtained by removing water-insoluble matter by filtration. The concentration of the copper-nitrilotriacetic acid complex in this aqueous solution was 0.3 mol / L based on copper. The pH of the aqueous solution was 12.9.

(2) Preparation of reducing agent aqueous solution 31 g of hydrazine monohydrate was dissolved in 469 g of water to obtain a hydrazine aqueous solution. The concentration of hydrazine in this aqueous solution was 1.2 mol / L.

(3) Synthesis of copper particles 1600 g of the aqueous copper complex solution obtained in (1) above was used, and 400 g of the reducing agent aqueous solution obtained in (2) was added at room temperature with stirring. The amount of reducing agent was about 1 mole per mole of copper. The mixture was stirred for 1 hour for aging. Subsequently, centrifugal washing with pure water was performed, and further solvent substitution with ethanol was performed. Then, it concentrated by centrifugation and performed the vacuum drying of the solid content in this order, and obtained the target copper particle.

[Examples 2 to 6]
Copper particles were obtained in the same manner as in Example 1 except that the conditions shown in Table 1 below were adopted.

[Comparative Example 1]
(1) Preparation of organic polymer protective agent aqueous solution 6 g of gelatin was dissolved in 78 g of water and allowed to stand at room temperature for 1 hour to swell the gelatin. Next, the mixture was heated to 40 ° C. with stirring, and stirring was continued while maintaining the temperature for 1 hour. Next, 8 g of 5% aqueous sodium hydroxide solution was added and stirring was continued to obtain an aqueous gelatin solution. The gelatin concentration in this aqueous solution was 6.5%.

(2) Synthesis of cupric oxide 1000 g of an aqueous sodium hydroxide solution (2 mol / L) and 1000 g of an aqueous copper nitrate solution (1 mol / L) are mixed, heated to 40 ° C. with stirring, and the temperature is maintained for 6 hours. Stirring was continued while maintaining. This aqueous solution was filled in an autoclave and hydrothermal synthesis was performed at 100 ° C. for 96 hours. The obtained product was washed with pure water and subsequently freeze-dried to obtain cupric oxide.

(3) Preparation of reducing agent aqueous solution 5 g of hydrazine monohydrate was dissolved in 90 g of water. Next, 5 g of pyrocatechol was added to obtain a target aqueous solution. The concentration of hydrazine in this aqueous solution was 1 mol / L. The concentration of pyrocatechol was 0.2 mol / L.

(4) Synthesis of Copper Particles 92 g of the organic polymer protective agent aqueous solution obtained in (1) above was used, and 8 g of cupric oxide obtained in (2) above was added thereto at room temperature. While stirring the solution, 100 g of the reducing agent aqueous solution obtained in (3) above was added. Stirring was continued and aging was performed for 5 hours. Next, 0.02 g of proteolytic enzyme (actinase E) was added to the solution, and the enzyme was washed under an environment of 35 ° C. for 24 hours. Thereafter, centrifugal washing was performed, followed by lyophilization to obtain copper particles.

[Evaluation]
For the copper particles obtained in Examples and Comparative Examples, the crystallite size, the crystallite size ratio, the temperature at which the crystallite size ratio is 1.2 or more (° C.), and 250 ° C. or more and 350 ° C. or less by the above-described methods. The amount of change in the crystallite size ratio per unit temperature in the temperature range was measured. Moreover, the average particle diameter D of primary particles, the specific surface area SSA, the content rate of carbon and nitrogen were measured. Moreover, XPS measurement was performed and the presence or absence of the detection of -COO-group and N was measured. The measurement results of the temperature dependence of the crystallite size ratio are shown in Table 2 below. The other results are shown in Table 3 below. XRD measurement was performed in a nitrogen atmosphere using a fully automatic horizontal multi-purpose X-ray diffractometer manufactured by Rigaku Corporation and a high-speed two-dimensional X-ray detector PILATUS3 R 100K manufactured by the company as a detector. Measured in a range of 2θ = 38 to 48 ° with a temperature increase rate of ˜400 ° C. and a rate of temperature increase of 10 ° C./min. Further, the time required for one XRD measurement was 15 seconds, and the temperature of the measurement atmosphere was maintained without increasing the temperature during the XRD measurement. Measurement temperature was 30 degreeC, 50 degreeC, 100 degreeC, 150 degreeC, 200 degreeC, 250 degreeC, 300 degreeC, 350 degreeC, and 400 degreeC.

[Average particle diameter D of primary particles]
A scanning electron microscope (SEM) image was taken using a scanning electron microscope (XL30SFEG, manufactured by Japan FI Eye Co., Ltd.). The magnification was determined according to the particle size of the particles, and photographing was performed in the range of 5000 to 150,000 times. The SEM image was analyzed using image analysis software Mac-View (manufactured by Mountec), and the Heywood diameter was determined for 100 or more particles per sample. The arithmetic average value of the Heywood diameter was defined as the average particle diameter D of the primary particles.

[Specific surface area (SSA)]
The specific surface area (SSA) was calculated from the following formula using the average particle diameter D of the primary particles.
SSA = 6 / (ρ * D)
In the formula, SSA represents a specific surface area [m ² / g], ρ represents a copper density [g / m ³ ], and D represents an average particle diameter [m] of primary particles.

[Carbon content ratio PC]
Measurement was performed using a gas analyzer (EMIA-920V manufactured by Horiba, Ltd.).
[Nitrogen content PN]
Measurements were made using an oxygen / nitrogen / hydrogen analyzer (ONH836 from Leco).

[XPS measurement]
An XPS apparatus (VersaProbe II manufactured by ULVAC-PHI Co., Ltd.) was used. The copper particles were compression molded with a hand press in a nitrogen atmosphere and then removed with a blower to obtain a measurement sample. Thereafter, the sample was placed in a transfer vessel manufactured by the same company in a nitrogen atmosphere and introduced into the apparatus. As the X-ray source, a monochrome Al—Kα ray (hν = 1486.7 eV, 100 W) was used. Measurement was performed with a pass energy of 26 eV, an energy step of 0.1 eV, and an angle between the detector and the sample stage of 45 °. For charging neutralization, low-speed ions and electrons were used. MultiPak 9.0 manufactured by ULVAC-PHI was used for data analysis. The obtained spectrum was subjected to charge correction with a C1s binding energy of 284.8 eV. After correction, smoothing was performed by the Savitzky-Golay method, and the background was removed by the Shirley method. With respect to the obtained spectrum, the presence or absence of detection of -COO-group and N was confirmed. The —COO— group is a peak appearing at a binding energy of 288.0 eV or more and 289.2 eV or less, and N is a peak appearing at a binding energy of 390 eV or more and 410 eV or less.

  As is clear from the results shown in Table 3, it can be seen that the copper particles of each Example are excellent in low-temperature sintering properties.

Claims (6)

Copper particles satisfying the following conditions (a) and (b).
XRD measurement was performed on the copper particles at a plurality of temperatures while the copper particles were heated from 30 ° C. to 350 ° C. in an inert atmosphere, and obtained from the measurement results. In the relationship between the crystallite size ratio, which is the ratio of the crystallite size at each temperature to the crystallite size of copper at 30 ° C., and the temperature,
(A) the temperature at which the crystallite size ratio is 1.2 is 250 ° C. or less,
(B) The amount of change in the crystallite size ratio per unit temperature in the temperature range of 250 ° C. or higher and 350 ° C. or lower is 2.0 × 10 ⁻³ or higher.   The copper particle according to claim 1, wherein —COO— group and N are detected by XPS measurement. The value of PC / SSA, which is the ratio of the carbon content ratio PC (mass%) and the specific surface area SSA (m ² / g), is 0.01 or more and 0.1 or less, and the nitrogen content ratio PN (mass%) The copper particle according to claim 1 or 2, wherein a value of PN / SSA, which is a ratio to the specific surface area SSA (m ² / g), is 0.001 or more and 0.05 or less.   The composition containing the copper particle as described in any one of Claim 1 thru | or 3.   The composition according to claim 4, which is used as a conductive material.   The composition according to claim 4, which is used as a bonding material for die bonding.