Copper powder

Abstract

The copper powder according to the present invention has a BET specific surface area of 1.0 m2 / g to 10.0 m2 / g, and contains an organic material having a molecular weight of 500 or less, and a polyether and / or a polyol.

Description

Technical Field

[0001] This specification discloses a technology related to copper powder. Background Art

[0002] For example, submicron-sized copper powder with a particle size of 1 μm or less is sometimes used as a material for internal and external electrodes of electronic components such as multilayer ceramic capacitors or inductors or for the manufacture of inkjet wiring in a state of being contained in a conductive paste.

[0003] The conductive paste containing copper powder is printed on a substrate for the purpose of forming a circuit or joining a semiconductor component and a substrate, etc., and is heated to sinter the copper powder. For the copper powder used in the conductive paste, low-temperature sinterability, that is, sintering at a low temperature, may be required. The reason is that copper powder sintered at a low temperature is more advantageous than copper powder sintered at a high temperature not only in terms of cost during heating but also can be applied to substrates with low heat resistance.

[0004] As a related technology, for example, there is that described in Patent Document 1. In Patent Document 1, under the theme of "providing copper powder having excellent low-temperature sinterability", there is proposed "a copper powder having a tap density of 1.30 g / cm 3 ~2.96 g / cm 3 , and D50 and the crystallite diameter D satisfy D / D50 ≧ 0.060, where the above D50 is the 50% particle size when the cumulative frequency reaches 50% in the particle size histogram based on the volume of copper particles, and the above crystallite diameter D is obtained from the diffraction peak of the Cu(111) plane in the X-ray diffraction curve obtained by powder X-ray diffraction method for this copper powder using the Scherrer equation".

[0005] Background Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 7122436 Gazette Summary of the Invention

[0008] [Problems to be Solved by the Invention]

[0009] Although the copper powder described in Patent Document 1 can be sintered at a relatively low temperature, there are sometimes requirements to effectively improve the low-temperature sinterability of the copper powder by different methods or viewpoints.

[0010] In this specification, there is provided copper powder having excellent low-temperature sinterability.

[0011] [Technical Means for Solving the Problems]

[0012] The copper powder disclosed in this specification has a BET specific surface area of 1.0 m 2 / g to 10.0 m 2 / g, and contains copper powder of an organic substance having a molecular weight of 500 or less, a polyether and / or a polyol.

[0013] [Effect of the Invention]

[0014] The above copper powder has excellent low-temperature sinterability. Description of the Drawings

[0015] Figure 1 is a SEM image of the copper powder obtained in Example 1.

[0016] Figure 2 is a SEM image of the copper powder obtained in Example 2.

[0017] Figure 3 is a SEM image of the copper powder obtained in Example 4.

[0018] Figure 4 is a SEM image of the copper powder obtained in Comparative Example 1.

[0019] Figure 5 is a SEM image of the copper powder obtained in Comparative Example 2. Detailed Description of the Invention

[0020] Hereinafter, embodiments of the above copper powder will be described in detail.

[0021] The copper powder of one embodiment has a BET specific surface area of 1.0 m 2 / g to 10.0 m 2 / g. To a certain extent, the specific surface area of the copper powder is relatively large, and the smaller the particle size, the more likely it is to sinter in the low-temperature region.

[0022] Furthermore, the copper powder contains an organic substance having a molecular weight of 500 or less (hereinafter, also referred to as "low-molecular organic substance"), a polyether and / or a polyol. When the polyether or polyol in the copper powder is thermally decomposed by heating, copper oxide on the surface of the copper powder is reduced and generated, and it is considered that the copper powder from which the surface oxide has been removed in this way promotes sintering at low temperatures. Furthermore, in fact, after analyzing the sintered body of the copper powder by X-ray diffraction method, it was confirmed that the copper oxide present in the copper powder was reduced. Also, through thermal analysis and the like, it was also confirmed that the decomposition temperature of the polyether or polyol was roughly the same as the sintering temperature of the copper powder.

[0023] ​​​​​Moreover, low-molecular-weight organic substances have the effect of suppressing the aggregation of copper powder. If such low-molecular-weight organic substances are added during the production of copper powder, it can be speculated that the above-mentioned polyethers or polyols are sufficiently attached to most of the copper particles dispersed by the low-molecular-weight organic substances. Thus, the low-temperature sintering effect brought by the polyethers or polyols can be significantly exerted. Therefore, from the perspective of improving low-temperature sinterability, the key lies in the copper powder containing both low-molecular-weight organic substances and polyethers and / or polyols. In addition, the molecular weight of the low-molecular-weight organic substance is 500 or less, and the residual amount of carbon that can hinder the sintering of copper powder during thermal decomposition is small.

[0024] As a result of these, it is considered that the low-temperature sinterability of the copper powder of this embodiment becomes excellent. However, it is not limited to the above theory.

[0025] (Specific surface area)

[0026] The BET specific surface area of the copper powder is 1.0 m 2 / g to 10.0 m 2 / g. For copper powder with a BET specific surface area that is relatively large to a certain extent, the particle size is small, and the sintering start temperature in an inert gas is relatively low. Furthermore, when the BET specific surface area is too large, it is difficult to ensure oxidation resistance, and there are concerns about problems with the paste properties of conductive pastes, etc. due to moisture absorption or aggregation. From this perspective, the BET specific surface area of the copper powder is more preferably 2.0 m 2 / g to 7.0 m 2 / g.

[0027] The measurement of the BET specific surface area of the copper powder can be carried out in accordance with JIS Z8830:2013. For example, it can be performed using BELSORP-mini II of MicrotracBEL Corporation. More specifically, after degassing 3 g of the copper powder sample in a vacuum at a temperature of 70 °C for 5 hours, the nitrogen adsorption isotherm is measured, and the results obtained are analyzed by the BET method to calculate the BET specific surface area.

[0028] (Composition)

[0029] Most of the copper powder is copper, and further contains low-molecular-weight organic substances and polyethers and / or polyols. Typically, the copper powder is copper powder in which at least a part of the surface of its copper particles is covered with low-molecular-weight organic substances and polyethers and / or polyols.

[0030] Copper powder contains low-molecular-weight organic substances. As described above, aggregation is suppressed and the dispersibility is increased. When performing surface treatment of polyether and / or polyol during the manufacture of copper powder, if low-molecular-weight organic substances are contained, copper powder effectively attached with polyether and / or polyol can be obtained. Polyether or polyol improves the low-temperature sinterability of copper powder. Therefore, copper powder containing not only polyether and / or polyol but also low-molecular-weight organic substances effectively achieves the low-temperature sintering by using polyether or polyol.

[0031] Moreover, when the low-molecular-weight organic substance has a molecular weight of 500 or less and an oxygen content of 50 mass% or more, it does not contain so much carbon. Therefore, when the copper powder is heated for sintering, the amount of carbon remaining after the thermal decomposition of the low-molecular-weight organic substance is relatively small, and it is not likely to hinder sintering.

[0032] Furthermore, for reference, the oxygen contents of specific examples of low-molecular-weight organic substances are shown below.

[0033] Glucose (C6H 12 O6): 53.29 mass%

[0034] Galactose (C6H 12 O6): 53.29 mass%

[0035] Mannose (C6H 12 O6): 53.29 mass%

[0036] Maltose (C 12 H 22 O 11 ): 51.42 mass%

[0037] Sucrose (C 12 H 22 O 11 ): 51.42 mass%

[0038] Lactose (C 12 H 22 O 11 ): 51.42 mass%

[0039] Citric acid (C6H8O7): 58.29 mass%

[0040] Acetic acid (C2H4O2): 53.29 mass%

[0041] Malic acid (C4H6O5): 59.66 mass%

[0042] Malonic acid (C3H4O4): 61.50 mass%

[0043] Succinic acid (C4H6O4): 54.19 mass%

[0044] Fumaric acid (C4H4O4): 55.14% by mass

[0045] Tartaric acid (C4H6O6): 63.96% by mass

[0046] Gluconic acid (C6H 12 O7): 57.10% by mass

[0047] Formic acid (CH2O2): 69.52% by mass

[0048] Oxalic acid (C2H2O4): 71.08% by mass

[0049] Aconitic acid (C6H6O6): 55.14% by mass

[0050] Pyruvic acid (C3H4O3): 54.50% by mass

[0051] Oxaloacetic acid (C4H4O5): 60.57% by mass

[0052] Lactic acid (C3H6O3): 53.29% by mass

[0053] Ascorbic acid (C6H8O6): 54.50% by mass

[0054] The low-molecular-weight organic substances preferably contained in the copper powder are at least one selected from the group consisting of carboxylic acids, carboxylates, glucose, maltose, sucrose, and lactose. Thus, copper powder that inhibits aggregation and does not impede sintering can be produced.

[0055] Among the above low-molecular-weight organic substances, if a carboxylic acid is added during the production of copper powder, it will coordinate with copper, reducing the reaction rate or the growth rate of copper particles. As a result, in addition to the particle shape of the copper powder approaching a spherical shape and the particle size distribution becoming narrower, aggregation also becomes less. Therefore, the copper powder preferably contains a carboxylic acid among the low-molecular-weight organic substances.

[0056] Specific examples of the carboxylic acid include: citric acid, acetic acid, malic acid, methyl dihydroxyvaleric acid, malonic acid, succinic acid, fumaric acid, tartaric acid, gluconic acid, formic acid, oxalic acid, aconitic acid, pyruvic acid, oxaloacetic acid, lactic acid, and their salts, etc. In particular, the copper powder more preferably contains citric acid and / or citrate as the low-molecular-weight organic substance. Citric acid or citrate has a high effect of inhibiting aggregation and not impeding sintering.

[0057] Furthermore, it is desirable that the copper powder does not contain high-molecular-weight organic substances such as gum arabic (organic substances with a molecular weight exceeding 500). The reason is that high-molecular-weight organic substances will cause a large amount of carbon residue during thermal decomposition upon heating, and there is a concern that it will impede the sintering of copper powder at a relatively low temperature.

[0058] In addition to the above-mentioned low-molecular-weight organic substances, the copper powder also contains polyethers and / or polyols. The polyethers or polyols in the copper powder act during heating to reduce the copper oxide that may naturally form on the surface of the copper powder to copper. Thereby, the sintering of the copper powder at low temperatures can be promoted. It is considered that the reducing power of the polyethers or polyols on the surface of the copper powder is stronger than that of the low-molecular-weight organic substances.

[0059] When the copper powder contains polyethers, the polyethers preferably include the general formula (1): RO(C2H4O) n nH (where R is H or a saturated or unsaturated hydrocarbon having 4 to 18 carbon atoms, and n is an integer from 2 to 30), and / or the general formula (2): RO(C3H6O) n nH (where R is H or a saturated or unsaturated hydrocarbon having 4 to 18 carbon atoms, and n is an integer from 2 to 30). When the copper powder contains the compound of the above general formula (1) or general formula (2), copper oxide can be reduced at a relatively low temperature. Examples of the compound of the general formula (1) include: polyethylene glycol HO(C2H4O) n nH, H 2m+1 mC m O(C2H4O) n nH (m: an integer from 4 to 18) such as polyoxyethylene alkyl ether, etc. Further, examples of the compound of the general formula (2) include: polypropylene glycol HO(C3H6O) n nH, H 2m+1 mC m O(C3H6O) n nH (m: an integer from 4 to 18) such as polyoxypropylene alkyl ether, etc. Further, examples also include H formed by combining a polyoxyethylene part and a polyoxypropylene part 2m+ 1C m O(C2H4O) n (C3H6O) l nH such as polyoxyethylene polyoxypropylene alkyl ether, etc.

[0060] The polyethers that can be contained in the copper powder preferably have an alkyl chain (i.e., a straight-chain or branched-chain alkyl group). If it has an alkyl chain, the dispersibility of the copper powder in the paste is improved. The reason is that since the alkyl chain is a hydrophobic functional group, it has good affinity with the hydrophobic organic solvent of the paste. Therefore, it is considered that when the copper powder having an alkyl chain is mixed with an organic solvent, the dispersed state of the copper powder can be maintained for a long time.

[0061] Furthermore, the copper powder may also contain polyols. Examples of the polyols include: glycerol, polyglycerol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, pentaerythritol, dipentaerythritol, etc.

[0062] Regarding the copper powder containing low-molecular organic substances, polyethers, or polyols, it can be confirmed by infrared spectroscopy, mass spectrometry, or the like.

[0063] In the identification using infrared spectroscopy, the diffuse reflection method can be used, and the device can be the FT / IR-6700 manufactured by JASCO Corporation. Regarding the sample holder of the diffuse reflection unit, it has multiple grooves for placing the sample, and the sample to be measured can be changed by rotating the holder. As the copper powder sample, without dilution with potassium bromide or the like, it is directly placed into the groove of the sample holder of the diffuse reflection unit and leveled with the flat part of a spatula to make the surface flat. The background measurement is carried out by the following procedure: For the part of the groove in the sample holder where no substance is placed, it is scanned at a resolution of 4 cm -1 in the wavelength range of 400 - 4000 cm -1 . Thereafter, the holder is rotated to align with the groove into which the copper powder is placed, and the measurement is carried out under the same conditions as above. Furthermore, the measurement is carried out at room temperature, and in order to obtain a sufficient spectrum, the number of accumulations is set to 256 times or more.

[0064] When the copper powder contains the polyether represented by the above general formula (1) or general formula (2), if the above infrared spectroscopy is used, a peak from saturated hydrocarbons (alkyl groups) is detected at 3000 - 2840 cm -1 , and a peak from ether bonds is detected at 1260 - 1000 cm -1 . Therefore, it can be judged from this that the copper powder contains polyether. Also, the peak from carboxylic acids or carboxylates in low-molecular organic substances is detected at 1500 - 1750 cm -1 , so it is also possible to confirm whether the copper powder contains carboxylic acids or carboxylates.

[0065] In addition, in the identification using mass spectrometry, a liquid chromatography-Orbitrap mass spectrometer (manufactured by Thermo Fisher Scientific, LC-Orbitrap MS, LC: Vanquish analytical purification LC system, Orbitrap MS: Orbitrap Exploris 240 mass spectrometer) can be used. Thereby, it is possible to confirm whether the copper powder contains polyols or low-molecular-weight organic substances. The measurement conditions are as follows. Copper powder (4 mL of the mixed solvent per 1 g of copper powder) is placed in a solution of 10 mmol / L ammonium acetate aqueous solution and acetonitrile (1:1 by volume ratio), and stirring operations are performed using a shaker and an ultrasonic cleaner. It is separated into copper powder and an extract by centrifugation, and the extract is collected by filtration through a syringe filter (manufactured by Merck Millipore, Millex (registered trademark)-LCR, material: hydrophilic PTFE, pore size: 0.45 μm). The extract is measured using the above liquid chromatography-Orbitrap mass spectrometer. A Hypersil GOLD (C18) column is used, and the mobile phase is introduced in such a way that it changes from a 10 mmol / L ammonium acetate aqueous solution to acetonitrile. The column temperature can be set to 40°C. In the negative ion detection mode, when a peak with an m / z value of 500 or less is detected, it can be said that the copper powder contains an organic substance with a molecular weight of 500 or less. In addition, as an example, in the positive ion detection mode, when a peak of an ion added to C3H8O3 is detected, it can be said that the copper powder contains glycerol, which is a kind of polyol.

[0066] The copper powder preferably has a carbon content of 0.15 mass% to 1.00 mass%. The carbon in the copper powder includes that from low-molecular-weight organic substances and from polyols and / or polyethers. When the carbon content in the copper powder is too small, the low-molecular-weight organic substances required for low-temperature sintering, and / or polyols or polyethers may be insufficient. On the other hand, if the carbon content is too large, after sintering of the copper powder, the amount of residual carbon becomes larger, and there is a concern that the sinterability may be reduced or it may be disadvantageous for low resistance. From this viewpoint, the carbon content of the copper powder is more preferably 0.15 mass% to 0.70 mass%.

[0067] The carbon content of the copper powder is measured by high-frequency induction furnace combustion-infrared absorption method. Specifically, a carbon-sulfur analyzer such as the CS844 type manufactured by LECO can be used. The sample collection amount is set to 0.2 g, adjusted to be within the intensity range of the calibration curve, the combustion aids are LECOCELII and Fe chips manufactured by LECO, and the measuring needle of the reference material is used as the calibration curve to measure the carbon content of the copper powder. Furthermore, after the sample is placed in an aluminum crucible for measurement, the aluminum crucible is used for measuring the carbon content of the copper powder after the following pretreatment. The above pretreatment is to first heat from room temperature to 1000°C at a certain heating rate in air for 2 hours, and then hold at 1000°C for 2 hours.

[0068] (Sintering start temperature)

[0069] When the copper powder as described above is heated in an inert gas, sintering sometimes occurs at a relatively low temperature. For example, the sintering start temperature is below 300°C. The sintering start temperature of the copper powder in an inert gas is preferably below 250°C.

[0070] The above-mentioned sintering start temperature is measured using thermomechanical analysis (TMA; Thermomechanical Analysis). Specifically, it is carried out as follows. That is, copper powder (about 0.3 g) is placed in a granulation mold with a hole of 5 mm in diameter, compressed with a force of 1 kN, and cylindrical copper powder particles (height: about 3 mm, diameter: about 5 mm) are produced. The height is measured using a micrometer (manufactured by Mitutoyo Corporation, coolant-proof micrometer MDC-25MX, maximum allowable error ±1 μm), and this is used as the initial particle height. The particle is set in a thermomechanical analysis device (manufactured by NETZSCH Corporation, TMA4000SE). After evacuating to below -0.1 MPa, N2 is introduced to form an inert environment. While flowing N2 at a flow rate of 500 mL / minute, a load of 10 g is applied, and at the same time, the temperature is raised from room temperature (25°C) to 700°C at a heating rate of 10°C / minute. At this time, during the heating period from room temperature to 700°C, the height of the particle is measured every 1 second, and the temperature when the particle height shrinks by 2% from the initial height is taken as the sintering start temperature.

[0071] (Manufacturing method)

[0072] To manufacture copper powder, various methods such as liquid phase methods like chemical reduction method or disproportionation method can be used. However, for example, in the case of the liquid phase method, it is important to add a specified organic substance, and preferably, after copper particles are generated by the reaction, the copper particles are brought into contact with a surface treatment agent. Hereinafter, a specific example of the case of using the chemical reduction method will be described in detail.

[0073] In the chemical reduction method, the following steps are carried out: Copper particles are generated by mixing and reacting a copper salt such as copper sulfate, a low molecular weight organic substance (organic substance with a molecular weight of 500 or less), a reducing agent, and a base in a liquid, and a copper slurry containing copper particles is obtained. The low molecular weight organic substance is as described above and includes, for example, citrates such as citric acid, sodium citrate, or potassium citrate. Examples of the reducing agent include hydrazine or sodium borohydride, and examples of the base include sodium hydroxide or ammonia.

[0074] As a more detailed example of this step, after heating an aqueous solution of copper sulfate to an appropriate reaction temperature, the pH value is adjusted with an aqueous solution of sodium hydroxide or an aqueous solution of ammonia, and then an aqueous solution of hydrazine is added all at once for reaction to reduce copper sulfate to cuprous oxide particles with a particle size of about 100 nm. After heating the cuprous oxide slurry containing cuprous oxide particles to the reaction temperature, an aqueous solution containing sodium hydroxide and hydrazine is added dropwise, and then, an aqueous solution of hydrazine is added dropwise thereafter, thereby reducing the cuprous oxide particles to copper particles.

[0075] Subsequently, a step of washing the above-mentioned copper slurry to obtain a washed copper slurry is carried out. The washing method is not particularly limited, and filtration press or decantation etc. can be adopted.

[0076] Subsequently, a surface treatment agent such as polyoxyethylene alkyl ether etc. is added to the above-mentioned washed copper slurry to carry out a surface treatment on the copper particles in the washed copper slurry. At this time, since the aggregation of copper particles is inhibited by the low-molecular organic substances contained in the washed copper slurry, most of the copper particles are effectively treated by polyoxyethylene alkyl ether etc. as a whole. When the copper particles aggregate, since the copper particles contact each other at the aggregated part, the surface treatment cannot be carried out sufficiently.

[0077] As described above, the surface treatment is preferably carried out after the reaction for generating copper particles. If polyoxyethylene alkyl ether is added during the reaction, there is a concern that the liquid may overflow from the reaction vessel due to foaming. When hydrazine is used as a reducing agent, from the viewpoint of safety, foaming is not desired. When an antifoaming agent is used, in addition to the increase in its cost, the components of the antifoaming agent may remain in the copper powder, which may affect the sintering characteristics or paste dispersibility.

[0078] Regarding the surface treatment agent, in order to uniformly contact with the copper particles in the slurry, a water-soluble polyoxyethylene alkyl ether is preferred. If it is water-insoluble, there is a concern that it may separate from the slurry and cannot be uniformly mixed, or the amount of adhesion cannot be controlled.

[0079] Subsequently, a step of drying the surface-treated copper slurry to obtain a dry powder is carried out. The drying method is not particularly limited, but from the viewpoint of controlling the amount of adhesion of the surface treatment agent, a method capable of carrying out total amount drying is preferred, such as drying with a spray dryer, FM stirrer, vacuum drying, vacuum heating drying, or heating drying in an inert gas atmosphere etc.

[0080] Subsequently, a step of crushing the dry powder using a jet mill, planetary ball mill or mortar etc. is carried out. Thereafter, a step of drying the crushed powder by vacuum drying, vacuum heating drying or heating drying in an inert gas atmosphere etc. is carried out. Thus, copper powder can be manufactured.

[0081] As described above, although the copper particles in the copper paste are made to contact the surface treatment agent before drying, the contact period between the copper particles and the surface treatment agent can also be after drying. For example, after the drying step of the crushed powder, the copper particles can be made to contact a polyoxyethylene alkyl ether or an aqueous solution of polyoxyethylene alkyl ether as the surface treatment agent. In this case, drying or crushing etc. can be performed as needed thereafter.

[0082] [Examples]

[0083] Next, since the copper powder as described above was trial-produced and its properties were confirmed, the description will be given below. However, the description here is only for illustration and is not intended to be limited thereto.

[0084] (Example 1)

[0085] A solution was prepared by mixing 2.7 g of citric acid in 1 kg of a 1 mol / L aqueous copper sulfate solution as Solution A. A solution was prepared by mixing 369 g of a 30 mass% aqueous sodium hydroxide solution and 37.5 g of an 80 mass% aqueous hydrazine solution in 1 L of pure water as Solution B. A solution was prepared by mixing 374 g of a 30 mass% aqueous sodium hydroxide solution and 31.4 g of an 80 mass% aqueous hydrazine solution in 1 L of pure water as Solution C. A solution was prepared by mixing 489 g of a 30 mass% aqueous sodium hydroxide solution in 1 L of pure water as Solution D. A solution was prepared by mixing 200 g of citric acid in 1 L of pure water as Solution E. A solution was prepared by mixing 76.7 g of an 80 mass% aqueous hydrazine solution in 1 L of pure water as Solution F.

[0086] Regarding the following addition ratios, unless otherwise specified, the ratios are described relative to 1 L of Solution A.

[0087] Solution A was placed in a reaction vessel, heated to 50°C, and Solution B was added at a ratio to reach 0.66 L. Subsequently, it was heated to 70°C, and Solution C was added at a ratio to reach 0.24 kg. Subsequently, Solution D was added to make the pH value 10.5, and Solution E as the citric acid component was added at a ratio to reach 1.5 g. Subsequently, Solution F was added at a ratio to reach 0.18 kg to obtain a copper paste. The washed copper paste was obtained by washing it with water.

[0088] The copper mass % in the washed copper paste was calculated by measuring the amount of water evaporation using an infrared moisture meter. An aqueous solution obtained by diluting polyoxyethylene alkyl ether (AE, EMULMIN NL-70 manufactured by Sanyo Chemical Industries, Ltd.) to 10% by mass was used as a surface treatment agent. The polyoxyethylene alkyl ether was added in an amount such that the mass of the polyoxyethylene alkyl ether relative to the copper in the washed copper paste was 1% by mass, and then stirred to obtain a surface-treated copper paste. The surface-treated copper paste was dried, jet milled, and vacuum dried to obtain copper powder.

[0089] (Example 2)

[0090] Solution B was added at a ratio to reach 0.65 L, solution D was replaced with a 30% by mass aqueous sodium hydroxide solution, and it was added such that the pH value became 10.3. The polyoxyethylene alkyl ether was added in an amount such that the mass of the polyoxyethylene alkyl ether relative to the copper in the washed copper paste was 0.65% by mass. Except for this, the same operations as in Example 1 were carried out to obtain copper powder.

[0091] (Example 3)

[0092] Except for adding the polyoxyethylene alkyl ether in an amount such that the mass of the polyoxyethylene alkyl ether relative to the copper in the washed copper paste was 0.14% by mass, the same operations as in Example 2 were carried out to obtain copper powder.

[0093] (Example 4)

[0094] Solution B was added at a ratio to reach 0.67 L, solution C was added at a ratio to reach 0.25 kg, and the polyoxyethylene alkyl ether was added in an amount such that the mass of the polyoxyethylene alkyl ether relative to the copper in the washed copper paste was 0.03% by mass. Except for this, the same operations as in Example 2 were carried out to obtain copper powder.

[0095] (Example 5)

[0096] Except for adding the polyoxyethylene alkyl ether in an amount such that the mass of the polyoxyethylene alkyl ether relative to the copper in the washed copper paste was 0.55% by mass, the same operations as in Example 4 were carried out to obtain copper powder.

[0097] (Example 6)

[0098] Before adding Solution D, 30 mass% aqueous sodium hydroxide solution was added so that the pH value became 8.0, and Solution D was added so that the pH value became 10.4. Polyoxyethylene alkyl ether was not added, and otherwise, the same operations as in Example 2 were carried out. Regarding the copper powder thus obtained, an aqueous solution of polyethylene glycol 200 (PEG 200, manufactured by FUJIFILM Wako Pure Chemical Corporation) was used as a surface treatment agent, and an amount such that polyethylene glycol 200 became 1 mass% relative to the mass of copper was added, followed by drying and pulverization to obtain copper powder.

[0099] (Example 7)

[0100] Except that the surface treatment agent was changed to polyethylene glycol 400 (PEG 400, manufactured by FUJIFILM Wako Pure Chemical Corporation), the same operations as in Example 6 were carried out to obtain copper powder.

[0101] (Example 8)

[0102] Except that the surface treatment agent was changed to polyethylene glycol 1000 (PEG 1000, manufactured by FUJIFILM Wako Pure Chemical Corporation), the same operations as in Example 6 were carried out to obtain copper powder.

[0103] (Example 9)

[0104] Except that the surface treatment agent was changed to polypropylene glycol 400 diol type (PPG 400 diol type, manufactured by FUJIFILM Wako Pure Chemical Corporation), the same operations as in Example 6 were carried out to obtain copper powder.

[0105] (Example 10)

[0106] Except that the surface treatment agent was changed to polypropylene glycol 700 diol type (PPG 700 diol type, manufactured by FUJIFILM Wako Pure Chemical Corporation), the same operations as in Example 6 were carried out to obtain copper powder.

[0107] (Example 11)

[0108] Except that the surface treatment agent was changed to polypropylene glycol 1000 diol type (PPG 1000 diol type, manufactured by FUJIFILM Wako Pure Chemical Corporation), the same operations as in Example 6 were carried out to obtain copper powder.

[0109] (Example 12)

[0110] The same operations as in Example 6 were carried out except that the surface treatment agent was changed to glycerin (manufactured by FUJIFILM Wako Pure Chemical Corporation), and copper powder was obtained.

[0111] (Comparative Example 1)

[0112] The same operations as in Example 1 were carried out except that polyoxyethylene alkyl ether was not added as a surface treatment agent, and copper powder was obtained.

[0113] (Comparative Example 2)

[0114] Regarding the addition ratio in Comparative Example 2, it is described as the addition ratio relative to 1 kg of cuprous oxide.

[0115] Cuprous oxide was mixed with pure water to prepare a 15.8 mass% cuprous oxide slurry, and a 0.016 mass% aqueous solution of gum arabic was added in such a ratio that the amount of gum arabic became 6 g. 32 mass% sulfuric acid was added thereto in such a ratio that the amount reached 1.8 kg. Thereafter, a 0.016 mass% aqueous solution of gum arabic was added in such a ratio that the amount of gum arabic became 4 g to obtain a copper slurry. The washed copper slurry was obtained by washing it with water. The washed copper slurry was dried, air pulverized, and vacuum dried to obtain copper powder.

[0116] (Comparative Example 3)

[0117] Copper powder synthesized under the production conditions of Comparative Example 2 was prepared, and an aqueous solution of polyoxyethylene alkyl ether (AE, EMULMIN NL-70 manufactured by Sanyo Chemical Industries, Ltd.) was used as a surface treatment agent. The above polyoxyethylene alkyl ether was added to the copper powder in an amount of 1 mass% relative to the copper mass, and it was dried and pulverized to obtain copper powder.

[0118] (Comparative Example 4)

[0119] The ratio of the raw materials in Comparative Example 1 was changed to obtain copper powder having a larger BET specific surface area than the copper powder of Comparative Example 1.

[0120] (Identification of organic substances)

[0121] As an example, the copper powder of Example 5 was analyzed by the above infrared spectroscopy method, and as a result, peaks were observed around 2900 cm -1 (from saturated hydrocarbons), around 1600 cm -1 (from carboxylic acids and carboxylates), and around 1100 cm -1 (from ether bonds). From this result, it was found that the copper powder of Example 5 contains polyether (hydrocarbon and ether bond derived therefrom) described in General Formula (1) or General Formula (2), and carboxylic acid or carboxylate.

[0122] Further, as an example, the copper powder of Example 5 was analyzed by the above-mentioned mass spectrometry. As a result, in the positive ion detection mode, the m / z values ranged from 275.2579 to 1040.7299, and the m / z values were detected at intervals of 44. The intensity was the highest at the m / z value of 556.4418, which was roughly consistent with the monoisotopic mass of 556.4425 of [C 28 H 58 O9+NH4] + obtained by adding an ammonium ion to the chemical formula with n = 8 corresponding to the general formula (1). Further, in the negative ion detection mode, the m / z value of 191.0196 was detected. This was roughly consistent with the monoisotopic mass of 191.0192 of [C6H8O7-H] - obtained by detaching a proton from the chemical formula corresponding to citric acid. From these results, it was found that the copper powder of Example 5 contained the compound represented by the general formula (1) and citric acid.

[0123] (Specific surface area)

[0124] The BET specific surface areas of the respective copper powders obtained in Examples 1 to 12 and Comparative Examples 1 to 4 were measured by the above method. The results are shown in Tables 1 and 2.

[0125] (SEM image)

[0126] The scanning electron microscope images (SEM images) of the respective copper powders obtained in Examples 1, 2, and 4 and Comparative Examples 1 and 2 are shown respectively in Figures 1 to 5 .

[0127] When comparing the BET specific surface areas shown in Table 1 of the respective copper powders of Examples 1, 2, and 4 and Comparative Examples 1 and 2 with Figures 1 to 5 , it was found that the BET specific surface area depends on the particle size. Although the BET specific surface areas of the copper powders of Examples 6 to 12 and Comparative Example 3 in Table 1 where the BET specific surface area was set to "1 to 10" were not measured, since the particle size was determined by the step of forming the copper particles, the BET specific surface areas of the copper powders of Examples 6 to 12 in which the copper particles were formed in the same manner as in Example 2 and the copper powder of Comparative Example 3 in which the copper particles were formed in the same manner as in Comparative Example 2 were likely to be in the range of 1 m 2 / g to 10 m 2 / g.

[0128] Further, when comparing Figure 1 and 4 with Figure 5 , it was found that each of the copper powders coated with citric acid in Examples 1 and Comparative Example 1 ( Figure 1 and 4 ) compared to the uncoated copper powder of Comparative Example 2 (Figure 5 ) The necking between particles is reduced, and each particle approaches a true sphere. Therefore, it is considered that the dispersibility of the copper powder coated with citric acid in the paste is improved.

[0129] (Carbon content)

[0130] By the above method, the carbon content of each copper powder obtained in Examples 1 to 12 and Comparative Examples 1 to 4 was measured. The results are shown in Tables 1 and 2.

[0131] (Low-temperature sinterability)

[0132] For each copper powder obtained in Examples 1 to 12 and Comparative Examples 1 to 4, after confirming the sintering start temperature in an inert gas by the above method, the results are shown in Table 1.

[0133] As can be seen from Table 1, the copper powders of Examples 1 to 12 contain low-molecular-weight organic substances, both polyethers and / or polyols. Therefore, compared with the copper powders of Comparative Examples 1 to 4, the sintering start temperature is lower.

[0134] (Preparation of copper powder paste)

[0135] For the copper powders of Example 3 and Comparative Example 4, copper powder pastes were prepared. Specifically, α-terpineol (80.5 g), oleic acid (6.5 g), and ethyl cellulose (49% ethoxylated) 10 (13.0 g) were mixed using a rotary mixer, and this was used as the medium liquid. Thereafter, copper powder (8.0 g) and the medium liquid (2.0 g) were mixed using a rotary mixer to obtain a copper powder paste.

[0136] (Viscosity of paste)

[0137] The viscosity of the prepared copper powder paste was measured by the following method. Regarding the viscosity of the copper powder paste, a rotary viscometer MCR102 manufactured by Anton Paar was used. The copper powder paste was placed on a thermostatic plate with the set temperature set to 25 ° C, and a cone plate with a cone angle of 2 ° (model: CP25-2) was used as the measurement jig. The gap setting at the measurement position was set to 1 mm, and the cone plate was pressed against the copper powder paste. Thereafter, the copper powder paste overflowing from the cone plate was removed. The measurement program took 392 seconds, and the shear rate was slowly increased from 0 to 1000 s -1 . Thus, the viscosity of the paste at each shear rate was measured. The viscosity of the copper powder paste at a shear rate of 1 s -1 is shown in Table 2.

[0138] As can be seen from Table 2, the difference between the copper powder of Example 3 and the copper powder of Comparative Example 4 lies in whether polyoxyethylene alkyl ether is added, and their BET specific surface areas are equal.

[0139] The viscosity of the copper powder paste obtained using the copper powder of Example 3 to which polyoxyethylene alkyl ether was added is lower than that of the copper powder paste obtained using the copper powder of Comparative Example 4 to which polyoxyethylene alkyl ether was not added.

[0140] The viscosity of the copper powder paste is lower the more dispersed the copper powder is in the paste. Therefore, it can be said that the dispersibility of the copper powder of Example 3 in the paste is higher than that of the copper powder of Comparative Example 4. As the reason, the inventor believes that by adding polyoxyethylene alkyl ether containing a hydrophobic alkyl chain to the copper powder, the compatibility between the hydrophobic medium liquid and the copper powder becomes higher, and the dispersibility of the copper powder in the paste is improved.

[0141] [Table 1]

[0142]

[0143]

[0144] [Table 2]

[0145]

[0146] Based on the above content, the possibility that the above copper powder has excellent low-temperature sinterability is suggested.

Claims

1. A copper powder having a BET specific surface area of 1.0 m 2 / g to 10.0 m 2 / g, containing an organic substance having a molecular weight of 500 or less, and a polyether and / or a polyol.

2. The copper powder according to claim 1 contains a compound represented by the following general formula (1) and / or a compound represented by the following general formula (2) as the polyether, RO(C2H4O) n H(1) (In general formula (1), R is H or a saturated or unsaturated hydrocarbon having 4 to 18 carbon atoms, and n is an integer of 2 to 30), RO(C3H6O) n H(2) (In general formula (2), R is H or a saturated or unsaturated hydrocarbon having 4 to 18 carbon atoms, and n is an integer of 2 to 30).

3. The copper powder according to claim 1 or 2, wherein The organic substance having a molecular weight of 500 or less includes at least one selected from the group consisting of carboxylic acids, carboxylates, glucose, maltose, sucrose, and lactose.

4. The copper powder according to claim 1 or 2, wherein, The organic substance having a molecular weight of 500 or less contains citric acid and / or citrate.

5. The copper powder according to claim 1 or 2 contains the polyether having an alkyl chain.

6. The copper powder according to claim 1 or 2 contains glycerol as the polyol.

7. The copper powder according to claim 1 or 2 has a carbon content of 0.15 mass% to 1.00 mass%.

8. The copper powder according to claim 1 or 2 has a sintering start temperature of 300 °C or less in an inert gas.

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