Method of producing gold powder

Abstract

To provide a method of producing a gold powder excellent in dispersibility in a gold paste and having great tap density.SOLUTION: A method of producing a gold powder comprises a reduction step that precipitates a gold particle by subjecting a chloroauric acid solution to reduction treatment using a reducer solution containing a reducer consisting preferably of potassium sulfite or sodium sulfite. Preferably, by adding ferric chloride to the chloroauric acid solution to adjust the content of the ferric chloride, iron is contained in a range of 0.001 pt.mass or more and less than 0.67 pt.mass, preferably 0.01 pt.mass or more and 0.50 pt.mass or less, with respect to 100 pts.mass of gold contained in the chloroauric acid solution.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing gold powder, and more particularly to a method for producing gold powder, which is the main component of gold paste used as a raw material for producing conductive films such as wiring layers and electrodes of electronic devices. [Background technology]

[0002] Gold (Au) is chemically stable, has excellent corrosion resistance, and has excellent electrical and thermal conductivity, making it an industrially useful metal used in a variety of fields. For example, in the field of electronic devices, gold is used in the form of gold paste as a raw material for producing conductive films such as wiring layers and electrodes. This gold paste consists of components such as gold powder, resin, hardener, and solvent, and is generally prepared by kneading these components using a three-roll mill.

[0003] For example, Patent Document 1 discloses a technique for producing gold paste by weighing out gold powder as a conductive metal powder, a binder resin such as epoxy resin, a curing agent such as a phenolic compound, and a diluent such as alkylacetalized polyvinyl alcohol or ethylene glycol in a predetermined mixing ratio and kneading them in a three-roll mill. The gold paste produced in this way is printed in a predetermined pattern and then heated and baked to form a conductive film having the predetermined pattern. The gold powder particles in the formed conductive film are connected to form electrically connected current paths, allowing the film to function as a wiring layer, electrode, or the like. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-111525 Summary of the Invention [Problem to be solved by the invention]

[0005] The gold paste is required to have an appropriate paste composition from the viewpoints of printability when producing a conductive film and the properties of the conductive film obtained by firing. Furthermore, the gold powder, which is a major component, is sometimes evaluated for its desired properties in terms of the properties of the conductive film. In evaluating the properties of such gold powder, powder properties such as particle size, specific surface area, purity, dispersibility, and tap density are often inspected. Among these powder properties, the preferred ranges for particle size and specific surface area are determined appropriately based on the composition of the gold paste and the viscosity required for the gold paste.

[0006] Among the powder characteristics described above, a high purity of gold powder is preferable. This is because if the impurity concentration inside the gold particles making up the gold powder is high or if impurities are concentrated on the surface of the gold particles, the resistance value of the conductive film may increase, potentially reducing reliability. Furthermore, impurities may be concentrated on the surface of gold particles due to heat, for example. This can change the surface properties, potentially altering compatibility with paste components and adversely affecting kneadability and viscosity. Furthermore, if the impurity concentration varies depending on the gold powder lot, the gold paste manufacturing process itself may become unstable. Thus, it is desirable for gold powder to have a consistently low impurity concentration, i.e., a high purity.

[0007] Among the powder properties, the dispersibility of gold powder in the gold paste is often important. This is because uniform dispersion of gold powder in the gold paste allows for the formation of wiring layers of uniform thickness and electrodes of uniform thickness after firing the gold paste. Conversely, poor dispersibility of gold powder in the gold paste makes the gold powder more likely to aggregate and form agglomerates. These agglomerates may be crushed between rolls and become flakes during a paste kneading process, for example, using a three-roll mill. Furthermore, if agglomerates or flakes larger than the thickness of the conductive film are formed, they may cause protrusions in the conductive film or cause the distribution of gold particles constituting the conductive film to become uneven, resulting in problems such as locally increasing or decreasing the resistance value of the conductive film or increasing its variability, or weakening the mechanical strength of the conductive film.

[0008] The dispersibility of gold powder in the gold paste can be evaluated based on whether the gold particles constituting the gold powder are individually dispersed in the gold paste, with almost no agglomerates present, and whether the surfaces of the gold particles are compatible with the other components of the gold paste. The former can be evaluated by dropping a container containing the powder sample to be measured onto a table and tapping it. This is the bulk density measured when the surface height of the powder sample no longer changes. A high tap density is desirable. The latter can be evaluated by a surface texture evaluation method, typically the solubility parameter (SP). However, the SP value varies depending on the components constituting the gold paste, making it difficult to identify a single preferred range.

[0009] In addition, since gold powder is the main component of gold paste and accounts for a large proportion of the price of gold paste, low manufacturing costs are also required for gold powder for gold paste. In order to reduce the manufacturing costs of gold powder, it is necessary not only to reduce the unit prices of the raw materials and ingredients used, but also to stably manufacture gold powder that has the properties required for gold paste.

[0010] A known method for producing gold powder for use in gold paste involves adding an aqueous solution of a reducing agent such as a sulfite (sodium sulfite or potassium sulfite) to a chloroauric acid (HAuCl4) solution to reduce the gold ions, causing the gold to precipitate. The resulting gold powder slurry containing fine gold particles is then subjected to solid-liquid separation, washed, and dried by heating to produce gold powder of relatively high purity.

[0011] However, the gold powder produced by the above method generally has a relatively small average particle size of up to about 1 μm, and a tap density of 5 g / cm 3Because the gold pastes that can be used are limited in this regard, the gold particles can only be precipitated to a certain extent. When using the reduction reaction described above to precipitate gold particles, a technique for adjusting particle size is known: changing the amount of reducing agent added or the solution temperature during the reduction reaction. In the reduction process described above, where sulfite is added to a chloroauric acid solution, it is possible to increase the particle size of gold particles to approximately 3 μm by increasing the amount of sulfite added. However, if the amount of reducing agent added is excessively large, the reduction reaction becomes faster, and the generated nuclei grow larger while retaining a highly cohesive surface. This likely leads to the resulting gold powder containing a large amount of aggregates, resulting in a lower tap density and poor dispersibility. Furthermore, increasing the amount of reducing agent added is undesirable because it increases costs.

[0012] On the other hand, the particle size of gold particles can also be increased by lowering the liquid temperature during the reduction reaction. However, even if the liquid temperature is lowered to 10°C, the average particle size only increases to about 1.5 μm. Therefore, providing a separate cooling system such as a chiller to cool the liquid temperature is undesirable from the viewpoint of production costs. Thus, when producing gold powder by precipitating gold particles through reduction treatment of a chloroauric acid solution, there are limitations to increasing both the average particle size and tap density. The present invention was made in consideration of these problems of the prior art, and aims to provide a method for producing gold powder with excellent dispersibility in gold paste and a high tap density. [Means for solving the problem]

[0013] The method for producing gold powder according to the present invention includes a reduction step in which a chloroauric acid solution is reduced using a reducing agent solution to precipitate gold particles, and is characterized in that the chloroauric acid solution contains iron in an amount ranging from 0.001 to less than 0.67 parts by mass per 100 parts by mass of gold. [Effects of the Invention]

[0014] According to the present invention, gold powder with excellent dispersibility in gold paste and high tap density can be stably produced. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flowchart of a method for producing gold powder according to an embodiment of the present invention. [Figure 2] 1 is a graph showing the relationship between the average particle size of gold powder produced in an example of the present invention and the iron content relative to 100 parts by mass of gold in the chloroauric acid solution used as the raw material. [Figure 3] 1 is a graph showing the relationship between the tap density of gold powder produced in an example of the present invention and the iron content relative to 100 parts by mass of gold in the chloroauric acid solution used as the raw material. [Figure 4] 1 is a graph showing the relationship between the average particle size and tap density of gold powder produced in an example of the present invention. [Figure 5] This is an SEM image of gold powder obtained when the iron content ratio per 100 parts by mass of gold in the chloroauric acid solution used as the raw material in an example of the present invention was set to 0.667 parts by mass, and it can be seen that particles with uneven surfaces have been formed. DETAILED DESCRIPTION OF THE INVENTION

[0016] Specific embodiments of the gold powder manufacturing method according to the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments and can include various modifications and alternatives without departing from the spirit of the present invention. In other words, the rights of the present invention extend to the scope of the claims and their equivalents.

[0017] The following embodiments of the present invention are based on the fact that the particle size of gold particles can be adjusted by the amount of iron ions added to a chloroauric acid solution, thereby controlling the tap density, which affects dispersibility. Specifically, as shown in Figure 1, the gold powder manufacturing method of this embodiment includes the following steps: (1) adding ferric chloride to a chloroauric acid solution of a predetermined concentration to adjust the iron-to-gold ratio within a predetermined range; (2) adding a reducing agent solution to the chloroauric acid solution with the adjusted iron content to precipitate gold particles; (3) separating the slurry containing gold particles obtained in the reduction step S2 using a solid-liquid separation device such as a filter (filter paper); (4) washing the wet gold powder obtained in the solid-liquid separation step S3; and (5) drying the washed gold powder.

[0018] In the gold powder manufacturing method according to the embodiment of the present invention, in the adjusting step S1, the chloroauric acid solution contains iron in an amount ranging from 0.001 to 0.67 parts by weight, preferably from 0.01 to 0.50 parts by weight, and more preferably from 0.02 to 0.33 parts by weight, per 100 parts by weight of gold. This allows the average particle size of the gold powder to be adjusted over a wider range without requiring expensive capital investment or increasing the amount of additives used, and also enables the stable production of gold powder with a high tap density. The resulting gold powder can be used as the main component of gold paste, which is used as a raw material for producing conductive films such as wiring layers and electrodes in electronic devices, thereby improving the performance of the electronic devices.

[0019] As described above, as long as the iron content of the chloroauric acid solution used as the raw material is within the range of 0.001 parts by weight to less than 0.67 parts by weight per 100 parts by weight of gold, the particle size and tap density can be increased with increasing iron content. In other words, by adjusting the amount of ferric chloride added so that the iron content is within the upper limit of 0.67 parts by weight per 100 parts by weight of gold in the chloroauric acid solution, the average particle size and tap density of the gold powder can be simultaneously adjusted. However, if the iron content increases to 0.67 parts by weight, the linear relationship between the average particle size and tap density of the gold powder remains unchanged, but there is a risk of an increase in particles with uneven surfaces. If this is a problem, it is preferable to set the upper limit of the iron content per 100 parts by weight of gold to 0.50 parts by weight or less.

[0020] On the other hand, if the lower limit of the iron content per 100 parts by mass of gold is lower than 0.001 parts by mass, the effect is almost impossible to obtain, resulting in a result equivalent to no addition. To obtain a stable effect, it is preferable to set the lower limit of the iron content per 100 parts by mass of gold to 0.01 parts by mass or more, and it is even more preferable to set this lower limit to 0.02 parts by mass or more to allow for some leeway.

[0021] The ferric chloride added to the chloroauric acid solution can be commercially available industrially produced ferric chloride. The ferric chloride is not contained in the gold powder. In other words, the iron remains in the treatment solution after the reduction treatment and is discharged to the waste liquid side in the solid-liquid separation step S3. This is because the iron in the ferric chloride added to the chloroauric acid solution is dissolved in Fe in the chloroauric acid solution. 3+ Therefore, in the presence of excess sulfite, this Fe 3+This is thought to be due to the fact that the iron dissolved in the form of a complex and was discharged as is along with the waste liquid. Furthermore, by analyzing the iron concentration of the waste liquid and calculating the iron content in the waste liquid, it was possible to confirm that most of the iron from the ferric chloride added to the chloroauric acid solution was present in the waste liquid. Meanwhile, analysis of the gold powder produced showed that the iron concentration was less than 10 ppm. Since the iron added to the chloroauric acid solution was hardly distributed in the gold powder, high-purity gold powder could be produced. However, even higher-quality gold powder could be produced by using ferric chloride with a higher purity.

[0022] Potassium sulfite or sodium sulfite can be used as a reducing agent for reducing the chloroauric acid solution. These sulfites are commercially available and industrially produced, but when it is desired to produce higher quality gold powder, high purity sulfites are preferred.

[0023] By using the gold powder manufacturing method according to the embodiment of the present invention, the average particle size of the obtained gold powder, as determined from SEM images, can be controlled to within the range of 1.0 μm to 2.0 μm, and the tap density can be varied linearly in proportion to the average particle size. Within the above average particle size range, the tap density of the gold powder can be controlled to 5.0 g / cm. 3 The above can be ensured, and therefore, gold powder with excellent dispersibility can be provided. Next, the method for producing gold powder of the present invention will be explained in more detail by giving examples and comparative examples, but the present invention is not limited in any way to the following examples and comparative examples. [Example]

[0024] Example 1 A 2.4 L volume of chloroauric acid solution, diluted with pure water to a gold content of 80 g and a gold concentration of 33.3 g / L, was placed in a 5 L beaker equipped with a stirrer equipped with a 60 mm diameter flat paddle blade and adjusted to a liquid temperature of 18 ± 1 °C. 0.171 g of ferric chloride (manufactured by Toa Gosei Co., Ltd.) was added to this chloroauric acid solution, resulting in an iron content of 0.028 parts by mass per 100 parts by mass of gold in the chloroauric acid solution. The above amounts and content were calculated using the analytical results of an iron concentration of 13.0% for the ferric chloride used. Separately, 200 g of potassium sulfite (manufactured by Daito Chemical Co., Ltd.: Lot. No. 11002-1) was dissolved in pure water to prepare a reducing agent solution with a concentration of 250 g / L and a liquid volume of 0.8 L. This solution was placed in a 2 L beaker and adjusted to a liquid temperature of 18 ± 1 °C.

[0025] The 5-L beaker containing the chloroauric acid solution had four 15-mm-wide, rectangular baffles mounted at equal intervals (i.e., every 90°) around the periphery. A turbulent flow was maintained by rotating the agitator at 530 rpm, and the reducing agent solution was supplied to the beaker. The reducing agent solution was supplied through a funnel with a fixed outlet at a random position on the circumference, approximately half the radius of the 5-L beaker containing the chloroauric acid solution, as viewed from above. The funnel had a capacity of approximately 1 L and was equipped with a valve and a 21-mm inner diameter hose at its bottom. The temperature-adjusted reducing agent solution was temporarily stored in the funnel, and the valve at its bottom was suddenly opened to supply the solution to a fixed location at a fixed time each time. The supply time for 0.8 L of reducing agent solution was 2.6 seconds.

[0026] After adding the reducing agent solution as described above, stirring was continued for 5 minutes. During this time, the liquid temperature rose by several degrees and the pH dropped due to the reduction reaction. However, this increase in liquid temperature stopped after about 1 minute, and the decrease in pH stopped after about 5 minutes. Five minutes after adding the reducing agent solution, the gold powder-containing slurry was filtered through filter paper to separate the solid and liquid, and the gold powder was recovered. The recovered gold powder was placed in 1 L of pure water at approximately 50 °C, repulped, and washed by stirring for 20 minutes. The washed gold powder-containing slurry was again filtered through filter paper to separate the solid and liquid, and the gold powder was recovered. The recovered gold powder was placed in 1 L of pure water at room temperature, repulped, and washed again by stirring for 20 minutes. The washed gold powder-containing slurry was again filtered through filter paper to separate the solid and liquid, and the gold powder was recovered. The recovered gold powder was then dried by heating in an atmospheric oven at an ambient temperature of 105 °C. The dried gold powder weighed approximately 79 g.

[0027] The gold powder obtained after the drying treatment was observed under an SEM, and the particle size was measured on a 5000x magnification photograph of the SEM image. The particle sizes of 200 or more gold particles selected at random within 1 to 3 fields of view were measured, and the average particle size was calculated by arithmetically averaging the measured values. 3 The tap density was measured by tapping the sample 50 times with a 10 mm stroke. The obtained gold powder had an average particle size of 1.10 μm and a tap density of 5.04 g / cm. 3 It was.

[0028] Example 2 Gold powder was produced in the same manner as in Example 1, except that 0.342 g of ferric chloride was added to the chloroauric acid solution, and the iron content was 0.056 parts by mass per 100 parts by mass of gold in the chloroauric acid solution. The gold powder obtained had an average particle size of 1.16 μm and a tap density of 5.50 g / cm. 3 It was.

[0029] Example 3 Gold powder was produced in the same manner as in Example 1, except that 1.196 g of ferric chloride was added to the chloroauric acid solution, and the iron content was 0.194 parts by mass per 100 parts by mass of gold in the chloroauric acid solution. The gold powder obtained had an average particle size of 1.47 μm and a tap density of 7.54 g / cm. 3 It was.

[0030] Example 4 Gold powder was produced in the same manner as in Example 1, except that 2.051 g of ferric chloride was added to the chloroauric acid solution, and the iron content was 0.333 parts by mass per 100 parts by mass of gold in the chloroauric acid solution. The gold powder obtained had an average particle size of 1.81 μm and a tap density of 8.46 g / cm. 3 It was.

[0031] Example 5 Gold powder was produced in the same manner as in Example 1, except that 3.077 g of ferric chloride was added to the chloroauric acid solution, and the iron content was 0.500 parts by mass per 100 parts by mass of gold in the chloroauric acid solution. The gold powder obtained had an average particle size of 2.03 μm and a tap density of 9.01 g / cm. 3 It was.

[0032] (Comparative Example) Gold powder was produced in the same manner as in Example 1, except that ferric chloride was not added to the chloroauric acid solution. The obtained gold powder had an average particle size of 0.87 μm and a tap density of 4.84 g / cm. 3 It was.

[0033] (Reference example) Gold powder was produced in the same manner as in Example 1, except that 4.102 g of ferric chloride was added to the chloroauric acid solution, and the iron content was 0.667 parts by mass per 100 parts by mass of gold in the chloroauric acid solution. The gold powder obtained had an average particle size of 2.13 μm and a tap density of 9.49 g / cm. 3 It was.

[0034] (evaluation) Figure 2 shows a graph illustrating the relationship between the average particle size of the gold powders produced in the Examples, Comparative Examples, and Reference Examples and the iron content per 100 parts by mass of gold in the chloroauric acid solution used as a raw material in their production. Similarly, Figure 3 shows a graph illustrating the relationship between the tap density of the gold powders produced in the Examples, Comparative Examples, and Reference Examples and the iron content per 100 parts by mass of gold in the chloroauric acid solution used as a raw material in their production. Furthermore, Figure 4 shows the correlation between the average particle size and tap density of these gold powders. As shown in Figures 2 to 4, both the average particle size and tap density increased linearly with the addition of ferric chloride up to a ratio of 0.333 parts by mass of iron per 100 parts by mass of gold in the chloroauric acid solution. Above 0.333 parts by mass, the average particle size and tap density increased, although the rate of change became smaller. This trend remained almost constant up to an iron content of 0.667 parts by mass.

[0035] Quantitative analysis of the wastewater separated from solids after reduction treatment during the production of gold powder in Examples 1 to 5 and the Reference Example revealed iron concentrations equivalent to the amount of iron added by the addition of ferric chloride. Quantitative analysis of the iron concentrations in the gold powders produced in Examples 1 to 5 and the Reference Example revealed iron concentrations less than 10 wtppm in all cases. These results confirmed that the iron content of the ferric chloride added to the chloroauric acid solution was not incorporated into the gold powder and was discharged along with the wastewater after reduction treatment. Furthermore, by adding ferric chloride to the chloroauric acid solution at an iron content of 0.667 parts by mass or less per 100 parts by mass of gold, the average particle size of the gold powder could be increased up to approximately 2 μm, and the tap density could be increased accordingly. However, when the iron content reached 0.667 parts by mass, an increase in gold particles with uneven surfaces was observed, as shown in the SEM image in Figure 5. These results demonstrate that the gold powders produced using the manufacturing method of the present invention all possessed excellent dispersibility suitable for use in gold pastes.

Claims

1. A method for producing gold powder, which includes a reduction step in which a chloroauric acid solution is reduced using a reducing agent solution to precipitate gold particles, characterized in that the chloroauric acid solution contains iron in an amount ranging from 0.001 parts by mass to less than 0.67 parts by mass per 100 parts by mass of gold.

2. 2. The method for producing gold powder according to claim 1, wherein the chloroauric acid solution contains iron in an amount ranging from 0.01 to 0.50 parts by mass per 100 parts by mass of gold.

3. 2. The method for producing gold powder according to claim 1, wherein the iron content is adjusted by adding ferric chloride to the chloroauric acid solution.

4. 2. The method for producing gold powder according to claim 1, wherein the reducing agent used in the reducing agent solution is potassium sulfite or sodium sulfite.

5. The gold powder has an average particle size of 1.0 μm or more and 2.0 μm or less, and a tap density of 5.0 g / cm, as determined from an SEM image. ３ The method for producing gold powder according to any one of claims 1 to 4, characterized in that:

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