Cuprous oxide powder and production method for cuprous oxide powder

Abstract

To provide cuprous oxide powder with a relatively high packed bulk density and a production method for the cuprous oxide powder.SOLUTION: The cuprous oxide powder contains sulfur (S) with a content of less than 140 mass ppm and chlorine (Cl) with a content of less than 1000 mass ppm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This specification discloses techniques relating to cuprous oxide powder and a method for producing cuprous oxide powder. [Background technology]

[0002] Conductive pastes containing copper powder can be used for forming copper wiring, etc. In such applications, the conductive paste is applied to a predetermined location and then heated to remove organic matter contained in the conductive paste and sinter the copper powder into a conductive film-like sintered body, which then functions as copper wiring. Among several metals considered as potential wiring materials, copper is preferred because it is cheaper than silver and platinum and has low migration.

[0003] When forming copper wiring with a fine pattern, it is desirable that the copper powder in the conductive paste used for the formation be fine. However, fine copper powder is prone to agglomeration. The agglomerated copper powder can impair the smoothness of the conductive paste when it is applied, which can cause breaks in the copper wiring.

[0004] To address this issue, it is effective to use cuprous oxide powder, which is less prone to aggregation than copper powder, in the conductive paste. In this case, when forming copper wiring, the conductive paste containing cuprous oxide powder is heated in a reducing atmosphere, whereby the cuprous oxide is reduced to copper, resulting in a copper sintered body.

[0005] As an example of this type of technology, Patent Document 1 describes, under the objective of "providing a metal thin film precursor dispersion that can form a metal thin film having electrical conductivity equivalent to that of a bulk metal thin film and few pinholes," "a metal thin film precursor dispersion containing a metal thin film precursor, characterized in that the surface tension of the dispersion is 40 mN / m or less, and that the boiling point of a compound other than the metal thin film precursor that is contained in the dispersion at 5 wt % or more is 150°C or more and 400°C or less, or the burn-out temperature of the compound is 150°C or more and 400°C or less."

[0006] Furthermore, Patent Document 2 proposes "cuprous oxide particles characterized by being surface-treated with at least one organic acid or organic amine having 6 to 20 carbon atoms," with the objective of "providing cuprous oxide particles with excellent oxidation resistance and storage stability." [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-257935 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-144615 Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, cuprous oxide powder is required to have a high packed bulk density, because in many cases, cuprous oxide powder with a high packed bulk density becomes a high-density sintered body after heating and can exhibit excellent electrical conductivity.

[0009] This specification provides cuprous oxide powder having a relatively high packed bulk density and a method for producing the cuprous oxide powder. [Means for solving the problem]

[0010] The cuprous oxide powder disclosed in this specification has a sulfur (S) content of less than 140 ppm by mass and a chlorine (Cl) content of less than 1000 ppm by mass.

[0011] The method for producing cuprous oxide powder disclosed in this specification includes the steps of adding a reducing agent to a solution containing copper sulfate, and maintaining the temperature of the solution at 80°C to 90°C and the pH at 4 to 5.5 to produce cuprous oxide particles. [Effects of the Invention]

[0012] The above-mentioned cuprous oxide powder has a relatively high compacted bulk density. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the above-mentioned cuprous oxide powder will be described in detail. In one embodiment, the cuprous oxide powder has a sulfur (S) content of less than 140 ppm by mass and a chlorine (Cl) content of less than 1000 ppm by mass.

[0014] The sulfur content of the cuprous oxide powder is set to less than 140 ppm by mass. This results in the cuprous oxide powder having a high packed bulk density. This is based on the new finding that there is a relationship between sulfur content and packed bulk density, which was previously unknown, and more specifically, that there is a correlation between the two such that the lower the sulfur content, the higher the packed bulk density. As a result, when the cuprous oxide powder is heated, it is expected to become a copper sintered body having relatively high density and electrical conductivity.

[0015] In a production method using copper sulfate as described below, the sulfur content of the cuprous oxide powder tends to be high. However, by employing a specific production method, the sulfur content can be effectively reduced, as will be described in detail later. Furthermore, this production method produces cuprous oxide powder with a low chlorine content of less than 1000 ppm by mass.

[0016] (cuprous oxide powder) The cuprous oxide powder may be any powder containing cuprous oxide (copper oxide (I), CuO), and typically is mostly composed of cuprous oxide, with the remainder other than the components described below being cuprous oxide. The presence of cuprous oxide in the cuprous oxide powder can be confirmed by X-ray diffraction (XRD).

[0017] The cuprous oxide powder is substantially free of sulfur, or if it contains sulfur, the sulfur content is less than 140 ppm by mass. Such cuprous oxide powder with a low sulfur content has a high packed bulk density. Cuprous oxide powder with a sulfur content of 140 ppm by mass or more tends to have a low packed bulk density. From this viewpoint, the sulfur content of the cuprous oxide powder is preferably 130 ppm by mass or less, and more preferably 100 ppm by mass or less.

[0018] On the other hand, although there is no particular problem with an excessively low sulfur content, when a sulfur compound such as copper sulfate is used as the raw material for the cuprous oxide powder, the cuprous oxide powder may contain about 10 ppm by mass of sulfur even after careful washing. For this reason, the preferred range of the sulfur content of the cuprous oxide powder is 10 ppm by mass to 140 ppm by mass.

[0019] The sulfur content is measured using a high-frequency induction furnace combustion-infrared absorption method. Specifically, using a carbon-sulfur analyzer such as the LECO Japan CS844, a 0.5g sample is adjusted to fall within the calibration curve intensity range, 1.40g of copper chips are added as a combustion improver, and the copper is used as a certified reference material for the calibration curve to measure the sulfur content of the copper powder. Oxygen with a purity of 99.5% or higher is used as the carrier gas, and the maximum integration time is 65 seconds. The furnace output is set to 70%.

[0020] Cuprous oxide powder may have a chlorine content of less than 1000 ppm by mass, or even 200 ppm by mass or less, particularly 50 ppm by mass or less, due to being produced using, for example, chlorine-free copper sulfate as a raw material, and may even be substantially free of chlorine. Since chlorine is a corrosive element, a low chlorine content is required when cuprous oxide powder is used as an electronic material. Cuprous oxide powder produced from waste liquid after using an etching solution containing iron (III) chloride tends to contain a fairly large amount of chlorine (for example, several thousand ppm by mass or more).

[0021] Chlorine content can be measured by combustion-ion chromatography. In this method, a cuprous oxide powder sample is combusted and decomposed, and the desorbed hydrogen chloride or chlorine gas is collected in an absorbent solution and measured by ion chromatography. A Metrohm 930 Combustion IC can be used. The combustion temperature is set to 1100°C, and the absorbent solution in the absorption section is 0.1% H2O2. The ion chromatography in the analytical section uses a Metrosep A Supp 5-250 / 4.0 separation column, 3.2 mM Na2CO3 + 1.0 mM NaHCO3 as the eluent, and an electrical conductivity detector. The sample volume is 250 μL, the column temperature is 35°C, and no gradient is used. A suppressor is used to reduce background, and the suppressor regeneration solution is 100 mM H2SO4. Before measuring the sample, the components to be used (combustion boat, combustion capsule, and quartz wool) are thoroughly washed with ultrapure water and then dried. A blank measurement is also performed using the cleaned components, and measurements are performed after confirming that the blank value is 0.01 μg / mL or less. The standard solution used is 1000 mg / L of chloride ions for ion chromatography manufactured by Kanto Chemical Co., Inc., diluted to 1 mg / L with ultrapure water, and solutions diluted 5, 10, and 50 times inside the device are used as calibration curve solutions.

[0022] The carbon (C) content of the cuprous oxide powder is 0.5% by mass or less, more preferably 0.2% by mass or less, and even more preferably 0.1% by mass or less. If the carbon content is too high, the amount of impurities may be high, which may result in poor electrical conductivity of the sintered body obtained after heating the paste. On the other hand, a low carbon content may mean that the cuprous oxide powder is coated with a trace amount of organic matter such as glycerin. In this case, the oxidation prevention effect of the coating may not be fully achieved, and the cuprous oxide powder may be oxidized to copper (II) oxide (CuO), resulting in a decrease in purity. From this perspective, it is more preferable that the carbon (C) content of the cuprous oxide powder be 0.01% by mass to 0.5% by mass. However, if the cuprous oxide powder is handled in a manner that suppresses oxidation, oxidation can be prevented even with a low carbon content.

[0023] Carbon content is measured using a high-frequency induction furnace combustion-infrared absorption method. Specifically, a carbon-sulfur analyzer such as the LECO Japan CS844 is used to measure the carbon content of copper powder. A 0.2 g sample is adjusted to fall within the calibration curve intensity range, and the combustion improver is a LECO Japan LECOCEL II and Fe chips. A standard steel pin is used for the calibration curve. The sample is placed in an alumina crucible for measurement. The alumina crucible is pretreated by heating from room temperature to 1000°C in air at a constant rate over two hours and then holding at 1000°C for two hours before being used to measure the carbon content of the copper powder.

[0024] The nitrogen (N) content of cuprous oxide powder can range from 10 ppm by mass to 300 ppm by mass, typically from 10 ppm by mass to 200 ppm by mass. Although a low nitrogen content is not particularly harmful, when a nitrogen compound such as hydrazine is used as a raw material for cuprous oxide powder, the cuprous oxide powder may contain approximately 10 ppm by mass of nitrogen even after careful cleaning. Furthermore, excessive nitrogen content can generate toxic gases (NOx) during firing. In theory, cuprous oxide powder can be produced using copper nitrate (Cu(NO3)2) as a raw material, but this likely results in cuprous oxide powder containing a relatively high amount of nitrogen (N) (e.g., several thousand ppm by mass or more). On the other hand, when cuprous oxide powder is produced using a raw material that does not contain nitrogen (N), such as copper sulfate, the nitrogen content is relatively low. Even when nitrogen-containing hydrazine is used to reduce copper sulfate during production, the nitrogen content of the cuprous oxide powder may be low as described above.

[0025] The nitrogen content is measured using the inert gas fusion-thermal conductivity method. Specifically, a LECO Japan TC600 oxygen and nitrogen analyzer is used, with the sample amount adjusted to 0.05 g so that it falls within the strength range of the calibration curve. The sample is enclosed in a Ni capsule in the flux, and a standard steel pin is used on the calibration curve to measure the nitrogen content of the copper powder. The graphite crucible used is LECO Japan P / N776-247.

[0026] The sodium (Na) content of the cuprous oxide powder may be 10 ppm by mass to 300 ppm by mass, typically 10 ppm by mass to 100 ppm by mass. Although there is no particular problem with a sodium content that is too low, when a sodium compound such as sodium hydroxide is used as a raw material for the cuprous oxide powder, the cuprous oxide powder may contain about 10 ppm by mass of sodium even after careful washing. Furthermore, if the sodium content is too high, it may cause a short circuit when attempting to form thin wiring using the cuprous oxide powder.

[0027] The sodium content can be measured using an atomic absorption spectrophotometer (Z2310) manufactured by Hitachi High-Tech Science Corporation. Specifically, the sodium content is measured by acid decomposition-atomic absorption spectrometry. A 1g sample is taken, and after acid decomposition with hydrochloric acid and nitric acid, the volume is adjusted to a constant volume in a 100mL measuring flask. The sodium content of copper powder can be measured using a calibration curve prepared by adjusting the acid concentration to the same as the sample solution and diluting the atomic absorption standard solution (preparing at least three points of the Na standard solution concentration between 0 and 1μg / mL). The calibration curve is a quadratic curve. The measurement conditions for the instrument are a wavelength of 589nm and an air-C2H2 flame type.

[0028] The particle size (BET diameter) of the cuprous oxide powder is preferably less than 10.0 μm, more preferably less than 6.0 μm, and even more preferably less than 3.0 μm. Because the cuprous oxide powder has a relatively small particle size, it can be suitably used for predetermined applications such as the formation of fine copper wiring. However, if the particle size of the cuprous oxide powder is too small, the cuprous oxide powder may aggregate in the paste. The cuprous oxide powder may have a particle size (BET diameter) of, for example, 0.05 μm to 10.0 μm.

[0029] The BET specific surface area of ​​cuprous oxide powder can be measured in accordance with JIS Z8830:2013 using, for example, a BELSORP-mini II from Microtrac-Bell Co., Ltd. More specifically, a 3 g sample of cuprous oxide powder is degassed for 5 hours at a temperature of 50°C in a vacuum of an absolute pressure of 10 Pa or less, and then the nitrogen adsorption isotherm is measured, and the results obtained are analyzed by the BET method to calculate the BET specific surface area of ​​the cuprous oxide powder. From the BET specific surface area of ​​this cuprous oxide powder, the BET diameter of the cuprous oxide powder can be calculated using the following formula. BET diameter = 6 / (ρ × S) where ρ is the density of cuprous oxide (g / cm 3 ), S is the BET specific surface area (m 2 / g). The density of cuprous oxide is 6.0 g / cm 3 Let's say.

[0030] The cuprous oxide powder may be used by being contained in a conductive paste or other paste used for forming copper wiring in solar cells, etc. The cuprous oxide powder described above can be particularly suitably used for such applications.

[0031] (Manufacturing method) The cuprous oxide powder described above can be produced by a chemical reduction method. In the chemical reduction method, a copper salt such as copper sulfate, a reducing agent such as hydrazine, and an alkali such as sodium hydroxide are mixed in a liquid and reacted. This reduces the copper salt to cuprous oxide, producing cuprous oxide particles. In a more specific example, an aqueous copper sulfate solution is heated to an appropriate reaction temperature, the pH is adjusted with an aqueous sodium hydroxide solution or an aqueous ammonia solution, and then an aqueous hydrazine solution is added to carry out the reaction, reducing the copper sulfate to cuprous oxide particles. This results in an unwashed powder of cuprous oxide particles.

[0032] In one embodiment of the production method, a reducing agent is added to a solution containing copper sulfate, and the temperature of the solution is maintained at 80°C to 90°C, while the pH of the solution is maintained at 4 to 5.5 to generate cuprous oxide particles. Thereafter, while maintaining the temperature of the solution at 80°C to 90°C, it is preferable to increase the pH of the solution to 10 to 11 by adding an alkali and maintain it within that range.

[0033] Generally, in an aqueous reaction, if the reaction temperature is close to the boiling point (100°C), it becomes difficult to control the temperature and concentration due to evaporation of the liquid, and there is a risk that the reaction may occur excessively, making it impossible to ensure safety. Despite these risks, the present inventors have discovered that by deliberately controlling the reaction temperature in the cuprous oxide particle production step and the subsequent holding step to around 85°C, which is much higher than the general reaction temperature, it is possible to reduce the sulfur content of the produced cuprous oxide particles.

[0034] The powder obtained in the above step (unwashed powder) can be washed. In the step of washing the unwashed powder, the unwashed powder is filtered, for example, using a filter press to form a cake, which is then washed by passing a washing liquid such as pure water through it. It is desirable to repeat such washing and filtration.

[0035] After washing and filtering, drying and crushing are carried out as necessary to produce cuprous oxide powder with a low sulfur content. [Example]

[0036] Next, the cuprous oxide powder described above was experimentally produced and its effects were confirmed, which will be described below. However, the description here is merely for illustrative purposes and is not intended to be limiting.

[0037] (Examples 1 and 2) 45.4 kg of caustic soda (NaOH) was dissolved in approximately 220 L of water in a 300 L reactor, and the temperature was allowed to drop below 35°C. 8.7 kg of 80% hydrazine hydrate (N2H4·H2O) was then added and stirred until no residue remained, yielding Solution A. 3 In a reaction vessel, 140 kg of copper sulfate pentahydrate (CuSO4·5H2O) was dissolved in 600 L of water with stirring to obtain solution B. Solution A was added dropwise to the above solution B at a rate of 2.4 to 2.9 L / min to generate cuprous oxide particles (unwashed powder). 3 The reaction vessel was stirred at 330 rpm, and the temperature (reaction temperature) was maintained at 85 to 90°C and the pH at 4 to 5.5. After the dropwise addition of solution A, the temperature (reaction temperature) was kept at 85 to 90°C, and the pH was maintained at 10 to 11 using caustic soda for 60 minutes. 3 The reaction vessel was cooled to below 55°C. The cuprous oxide particles (unwashed powder) were then filtered and washed using a filter press until the conductivity of the filtrate fell below 20 μS / cm, producing a dehydrated cake. Air was then pumped in to dry the cake. The dehydrated cake was then dried in a vacuum dryer (-0.1 MPa, 60°C) for 120 hours. It was then crushed in a pulverizer (crusher) until it passed through a filter with 1 mm openings. This yielded cuprous oxide powder.

[0038] Example 3 Cuprous oxide powder was obtained in the same manner as in Example 1, except that the amount of 80% hydrazine hydrate added was 8.75 kg.

[0039] (Comparative Example 1) The same procedure as in Example 1 was carried out except that the amount of 80% hydrazine hydrate added was 8.8 kg and the reaction temperature was 40 to 55°C, to obtain cuprous oxide powder.

[0040] (Comparative Example 2) The same procedure as in Example 1 was carried out except that the amount of 80% hydrazine hydrate added was 8.7 kg and the reaction temperature was 40 to 55°C, to obtain cuprous oxide powder.

[0041] (evaluation) The cuprous oxide powders obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were measured for particle size (BET diameter), sulfur content (S), chlorine content (Cl), carbon content (C), and sodium content (Na) according to the methods described above. The results are shown in Table 1.

[0042] Three lots of cuprous oxide powder were produced using the same production method as in Examples 1 and 2, and the nitrogen contents were measured using an ON736 oxygen / nitrogen analyzer manufactured by LECO Japan, and were found to be 150 ppm by mass, 150 ppm by mass, and 130 ppm by mass, respectively. Example 3 contains approximately the same amount of nitrogen-containing hydrazine as Examples 1 and 2. Therefore, it is highly likely that the nitrogen content of the cuprous oxide powder in Example 3 is at most 300 ppm by mass, and even less than 200 ppm by mass.

[0043] As described above, NaOH, N2H4·H2O, and CuSO4·5H2O were used as raw materials to produce cuprous oxide powder. Therefore, cuprous oxide powder produced from these raw materials contains almost no elements other than those contained in the raw materials. Therefore, it is highly likely that the content of elements other than those contained in the raw materials is less than 10 ppm by mass.

[0044] The packed bulk density of each cuprous oxide powder in Examples 1 to 3 and Comparative Examples 1 and 2 was measured by the following method. The measurement was performed using a Powder Tester (registered trademark) PT-X manufactured by Hosokawa Micron Corporation, and the measurement environment was a temperature range of 23 to 25°C and a relative humidity range of 19 to 36%. A cylindrical 10 cc cup (outer diameter: 24 mm, height: 28 mm, volume: 10 cm3) was used. 3A guide was attached to the 10cc cup and set in the Powder Tester PT-X. The guide was used to spread excess particles on the top surface of the cup to completely fill the entire 10cc cup, and it covered a height of 25 mm from the opening of the 10cc cup. A sieve (diameter: 75 mm, height: 18 mm, mesh size: 710 μm, wire diameter: 450 μm) was attached to the vibrator above the 10cc cup, and a chute was installed between the 10cc cup and the sieve so that particles that passed through the sieve would fall into the 10cc cup. Approximately 200 g of cuprous oxide powder was then placed on the sieve, and the sieve vibration (amplitude: 1.5 mm, frequency: 50 Hz) was initiated. The vibration was stopped when the particles overflowed from the 10cc cup with the guide attached. The 10cc cup was then tapped up and down (number of times: 1000, stroke: 18 mm, tapping frequency: 1 time / second) to fill the particles. After tapping, the guide was removed, and the excess part protruding from the top of the 10cc cup was leveled off, and the weight of the cuprous oxide powder in the cup was measured. The packed bulk density was calculated from this weight, and the results are also shown in Table 1.

[0045] [Table 1]

[0046] The packed bulk density tends to increase as the particle size increases. Therefore, it is appropriate to compare the packed bulk densities of particles with similar particle sizes. Comparing the packed bulk densities of Comparative Examples 1 and 2, which have a particle size (BET diameter) of 0.18 μm, it can be seen that the lower the sulfur content, the higher the packed bulk density. Furthermore, in the cuprous oxide powders of Examples 1 to 3, which have particle sizes (BET diameters) of 0.38 μm to 0.48 μm, the lower the sulfur content, the higher the packed bulk density.

[0047] (Reference example 1) 600 mL of water was placed in a 1 L beaker, and 136 g of caustic soda (NaOH) was added and dissolved, then cooled to 25-30°C. 26 g of 80% hydrazine hydrate (N2H4·H2O) was added to obtain Solution C. 1800 mL of ion-exchanged water was placed in a 5 L beaker, and 420 g of copper sulfate pentahydrate (CuSO4·5H2O) was added and dissolved, then heated to 55°C (the temperature before the reaction) to obtain Solution D. Solution C was added dropwise to solution D over 80 minutes to produce cuprous oxide particles (unwashed powder). During this process, stirring was continued at 140 rpm, and the temperature was controlled so that the liquid temperature during the reaction was 53-57°C (approximately 55°C). After adding solution C, the pH was maintained at 10-11 using caustic soda for 30 minutes. The cuprous oxide particles (unwashed powder) were then filtered and washed using filter paper until the conductivity of the filtrate fell below 20 μS / cm, producing a filter cake. The filter cake was then spread on a stainless steel pad, vacuum-dried at 60°C, and crushed. This yielded cuprous oxide powder.

[0048] (Reference example 2) The same operation as in Reference Example 1 was carried out, except that the amount of 80% hydrazine hydrate was changed to 25 g, the temperature of Solution D before the reaction was set to 70°C, and the liquid temperature during the reaction was controlled to 68 to 72°C (approximately 70°C), to obtain cuprous oxide powder.

[0049] (Reference example 3) The same operation as in Reference Example 1 was carried out, except that the temperature of Solution D before the reaction was set to 85°C and the liquid temperature during the reaction was controlled to 83 to 87°C (approximately 85°C), to obtain cuprous oxide powder.

[0050] (evaluation) The sulfur content (S) and sodium content (Na) of the cuprous oxide powders obtained in Reference Examples 1 to 3 were measured according to the methods described above. The results are shown in Table 2. The particle size was measured using a laser diffraction / scattering particle size distribution analyzer LA960 / V2 manufactured by Horiba, Ltd. More specifically, 180 ml of ion-exchanged water was placed in the sample tank of the analyzer, and the ion-exchanged water was circulated between the sample tank and the flow cell using a centrifugal pump attached to the analyzer. 30 mg of sodium hexametaphosphate was added to the sample tank to form a dispersion solvent. The cuprous oxide powder was then added to the analyzer after adjusting its concentration so that the transmittance (R) and transmittance (B) were 80-90%. After ultrasonic dispersion treatment for 5 minutes using an ultrasonic probe inside the analyzer with a 30 W output, the particle size distribution was measured. The refractive index (n) of the cuprous oxide was 2.710, and the refractive index (n) of the solvent (water) was 1.333.

[0051] [Table 2]

[0052] As shown in Table 2, it was found that the sulfur content (S) of the resulting cuprous oxide powder decreased as the reaction temperature increased. It was also found that the sodium content (Na) decreased as the reaction temperature increased.

[0053] From the above, it is believed that cuprous oxide powder with a sulfur (S) content of less than 0.014 mass % has a relatively high packed bulk density compared to cuprous oxide powder of a similar particle size.

Claims

1. A cuprous oxide powder having a sulfur (S) content of less than 140 ppm by mass and a chlorine (Cl) content of less than 1000 ppm by mass.

2. 2. The cuprous oxide powder according to claim 1, wherein the carbon (C) content is 0.5% by mass or less.

3. The cuprous oxide powder according to claim 1 or 2, wherein the nitrogen (N) content is 10 ppm by mass to 300 ppm by mass.

4. The cuprous oxide powder according to claim 1 or 2, wherein the sodium (Na) content is 10 ppm by mass to 300 ppm by mass.

5. A method for producing cuprous oxide powder, comprising the steps of adding a reducing agent to a solution containing copper sulfate, and maintaining the temperature of the solution at 80°C to 90°C and the pH at 4 to 5.5 to generate cuprous oxide particles.

6. 6. The method for producing cuprous oxide powder according to claim 5, further comprising, after the step of producing the cuprous oxide particles, a step of maintaining the temperature of the solution at 80°C to 90°C and the pH at 10 to 11.

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