Precious metal nanoparticles and their uses

Abstract

The noble metal particulates disclosed herein contain a noble metal element as the main constitutional metal element, retain an imine compound on the surfaces, and have an amine / imine ratio (A / I ratio), which is the area ratio between the peak area of an amine compound and the peak area of the imine compound as determined through a thermal decomposition GCMS analysis at a thermal decomposition temperature of 300°C, not more than 1.

Description

[Technical Field]

[0001] This invention relates to precious metal nanoparticles composed of precious metals such as gold, platinum, and palladium. Furthermore, this invention relates to a powder material containing such precious metal nanoparticles and a paste-like (slurry-like) dispersion in which the precious metal nanoparticles are dispersed in a medium. This application claims priority under Japanese Patent Application No. 2020-018028, filed on February 5, 2020, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, precious metal nanoparticles and materials prepared in paste (slurry) form containing such precious metal nanoparticles have been developed for various applications. For example, conventionally, so-called "solder" and "brazing materials" were used as bonding materials for joining semiconductor devices. However, bonding using these materials involves harsh conditions such as high temperatures of 300°C or higher and high pressure, which can cause damage to the components and devices being joined. For this reason, instead of using "solder" and "brazing materials," development is underway to create low-temperature sintering paste materials that utilize surface activation through the micronization of metal particles, and paste materials in which conductive materials are dispersed in a resin matrix (for example, Patent Document 1).

[0003] As low-temperature sinterable materials, many paste materials mainly composed of nano-sized and submicron-sized silver nanoparticles have been developed. Furthermore, in recent years, there has been a growing demand for paste materials mainly composed of gold nanoparticles that can be used in environments requiring higher reliability. These nanoparticles made of precious metals have high surface energy and tend to aggregate easily. Therefore, methods are being considered to prevent aggregation of these precious metal nanoparticles by using some kind of compound (also called a protective agent here) on the surface of these nanoparticles. As an example, a technique employing alkylamines is known. Specifically, it has been found that the strong coordination of the amino group of alkylamines to the metal allows for the stable dispersion of noble metal nanoparticles, and dispersions of noble metal nanoparticles using alkylamines as a protective agent have been reported (for example, Non-Patent Document 1, Patent Document 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5613253 [Patent Document 2] Japanese Patent Publication No. 2018-154806 [Patent Document 3] Japanese Patent Publication No. 2013-1954 [Non-patent literature]

[0005] [Non-Patent Document 1] Chem.Mater., Vol.16(No.13), 2004, pp.2509 [Overview of the project]

[0006] However, the protective power of alkylamines is proportional to the length and amount of alkyl chain attached. Therefore, increasing the stability (dispersibility) of alkylamines necessitates a relatively higher sintering temperature to completely burn off the protective agent, which is counterproductive to the development of low-temperature sinterable fine particle materials. Furthermore, gold fine particles, in particular, are more prone to aggregation and sedimentation than silver fine particles, making it difficult to obtain a stable dispersion at high concentrations even when using long-chain alkylamines. For example, in the precious metal fine particles such as Au and Ag disclosed in Patent Document 3, a mixed protective film of carboxylic acid and amine is applied to the surface of the fine particles to avoid aggregation, but removing this protective film requires sintering at relatively high temperatures for a long time. Also, perhaps due to the aggregation problem, high concentrations are not mentioned, limiting their applications.

[0007] Therefore, the present invention was created to solve the problems related to noble metal fine particles as described above, and an object thereof is to provide noble metal fine particles having a protective component that can achieve high dispersion stability and low-temperature sinterability that can be sintered at a relatively low temperature. Another object is to provide a powder material and a paste-like (slurry-like) dispersion containing the noble metal fine particles. Furthermore, a method for manufacturing a noble metal sintered body using the noble metal fine particles disclosed herein is provided.

[0008] In order to achieve the above object, the present invention provides noble metal fine particles whose main constituent metal element is a noble metal element. An imine compound is held on the surface of the noble metal fine particles disclosed herein. And the amine / imine ratio (A / I ratio), which is the area ratio of the peak area of the imine compound determined in a pyrolysis GCMS analysis with a pyrolysis temperature of 300 °C and the peak area of the amine compound (including the case where it is substantially 0), is 1 or less. In the present specification and claims, the term "noble metal fine particles" means a population of a large number of fine particles (i.e., particles), unless otherwise specifically indicating a single particle unit. For example, the noble metal fine particles in the "powder material or dispersion containing noble metal fine particles" described later refer to noble metal fine particles as particles, not a single particle. In Japanese, since the singular or plural is ambiguous, it is defined as above to clarify the meaning of "noble metal fine particles".

[0009] The inventor has found that an imine compound formed by the dehydration condensation of a carbonyl compound (e.g., a carbonyl compound such as an aldehyde formed by the oxidation of alcohol as a solvent) and a primary amine is held on the surface of noble metal fine particles such as gold fine particles so that the A / I ratio is 1 or less (more preferably, the A / I ratio is 0.6 or less). As a result, the noble metal fine particles have high dispersibility in various organic solvents, and a dense noble metal sintered body can be obtained by firing the noble metal fine particles at a low firing temperature of 300 °C or lower (e.g., about 250 to 300 °C), thus completing the present invention.

[0010] A preferred embodiment of precious metal nanoparticles is characterized by having a ratio of DDLS / DSEM of 2 or less, which is the ratio of the Z-mean particle size (DDLS) based on dynamic light scattering (DLS) measured while dispersed in a predetermined medium to the mean particle size (DSEM) based on a field emission scanning electron microscope (FE-SEM) image. DDLS / DSEM is a suitable indicator of the degree of adhesion, or in other words, the dispersibility, of precious metal nanoparticles. Precious metal nanoparticles characterized by a DDLS / DSEM of 2 or less exhibit particularly good dispersibility and can be well used for applications such as forming conductors like fine electrodes, or as a raw material for precious metal catalysts. A DDLS / DSEM of 1.7 or less is more preferable, and 1.5 or less is particularly preferable.

[0011] A preferred embodiment of the noble metal nanoparticles is characterized by having a Z-average particle size (DDLS) of 200 nm or less. Such small-particle-sized precious metal nanoparticles can be particularly suitable for applications such as forming conductors, especially fine electrodes, or as raw materials for precious metal catalysts. DDLS is more preferably 150 nm or less, and is particularly preferably 50 nm to 150 nm.

[0012] A preferred embodiment of the noble metal nanoparticles is one in which the above imine compound has the following structural formula: R 0 R 1 C=N-(CH2)-R 2 It is a compound represented by, where R 0 is hydrogen, R 1 and R 2 Each of these is characterized by being a hydrocarbon group with 3 to 7 carbon atoms. Since noble metal nanoparticles having relatively low molecular weight and short hydrocarbon groups (e.g., alkylimines) on their surface can be easily detached by low-temperature firing below 300°C, dense sintered bodies can be easily manufactured.

[0013] Furthermore, one embodiment of the precious metal nanoparticles disclosed herein is gold nanoparticles whose main constituent metal element is gold (Au). Gold nanoparticles, in particular, are prone to aggregation and sedimentation among precious metal nanoparticles, making them a suitable target for the technology disclosed herein.

[0014] The precious metal nanoparticles disclosed herein can be suitably used in various industrial fields, but are particularly suitable for use in conductive pastes, bonding materials (power devices, semiconductor packaging, die bonding, etc.), solder substitutes, plating substitutes, decorative applications, reflective materials, antibacterial agents, catalysts, etc. A particularly suitable application is the formation of electrodes (conductors) for fine electronic components. Accordingly, the present invention can provide a powder material comprising any of the precious metal fine particles disclosed herein, and a dispersion of the precious metal fine particles comprising the precious metal fine particles and a medium for dispersing the precious metal fine particles, such as a conductive paste (paste-like or slurry-like composition). Furthermore, the present invention provides a method for manufacturing a precious metal sintered body using any of the precious metal nanoparticles disclosed herein. By using the precious metal nanoparticles disclosed herein as a material, a precious metal sintered body of a desired form can be manufactured by heat treatment (sintering) at 300°C or below.

[0015] In one preferred embodiment of the dispersion, the dispersion medium is characterized by containing a cyclic alcohol having a hydroxyl group on a cyclic chain. By using a cyclic alcohol as the dispersion medium, particularly high dispersion stability can be achieved. This makes it easier to prepare higher concentration dispersions (e.g., conductive pastes). [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a graph showing the TG-DTA measurement results for several examples and comparative examples. [Figure 2] Figure 2 shows the pyrolysis GCMS spectrum obtained for Example 1. [Figure 3]Figure 3 shows the pyrolysis GCMS spectrum obtained for Example 2. [Figure 4] Figure 4 shows the pyrolysis GCMS spectrum obtained for Example 3. [Figure 5] Figure 5 shows the pyrolysis GCMS spectrum obtained for Example 4. [Figure 6] Figure 6 shows the pyrolysis GCMS spectrum obtained for Example 5. [Figure 7] Figure 7 shows the pyrolysis GCMS spectrum obtained for Example 6. [Figure 8] Figure 8 shows the pyrolysis GCMS spectrum obtained for Comparative Example 1. [Figure 9] Figure 9 shows the pyrolysis GCMS spectrum obtained for Comparative Example 3. [Figure 10] Figure 10 shows the pyrolysis GCMS spectrum obtained for Comparative Example 4 (the powder in the dispersion of Comparative Example 4-1 that has been dried). [Figure 11] Figure 11 shows the pyrolysis GCMS spectrum obtained for Comparative Example 5. [Figure 12] Figure 12 shows the MS spectra of the peak (■) of imine compound A detected in Examples 1-4 and Comparative Example 1. [Figure 13] Figure 13 shows the MS spectrum of peak (■) of imine compound B detected in Example 5. [Figure 14] Figure 14 shows the MS spectrum of peak (■) of imine compound C detected in Example 6. [Figure 15] Figure 15 shows the MS spectrum (library data) of imine compound B obtained by library search. [Figure 16] Figure 16 shows an FESEM image (50,000x magnification) of the precious metal nanoparticles according to Example 1. [Figure 17] Figure 17 shows an FESEM image (50,000x magnification) of the precious metal nanoparticles according to Example 2. [Figure 18] Figure 18 shows an FESEM image (50,000x magnification) of the precious metal nanoparticles according to Example 3. [Figure 19] Figure 19 shows an FESEM image (50,000x magnification) of the precious metal nanoparticles according to Example 4. [Figure 20] Figure 20 shows an FESEM image (50,000x magnification) of the precious metal nanoparticles according to Example 5. [Figure 21] Figure 21 shows an FESEM observation image (50,000x magnification) of the precious metal nanoparticles according to Example 6. [Figure 22] Figure 22 shows an FESEM image (50,000x magnification) of precious metal nanoparticles related to Comparative Example 1. [Figure 23] Figure 23 shows an FESEM image (50,000x magnification) of precious metal nanoparticles related to Comparative Example 3. [Figure 24] Figure 24 shows the FESEM observation image (50,000x magnification) of the precious metal nanoparticles related to Comparative Example 4. [Figure 25] Figure 25 shows an FESEM image (50,000x magnification) of precious metal nanoparticles related to Comparative Example 5. [Modes for carrying out the invention]

[0017] Preferred embodiments of the present invention will be described below. Matters other than those specifically mentioned herein that are necessary for carrying out the present invention can be understood as design matters for those skilled in the art based on the prior art. The present invention can be carried out based on the contents disclosed herein and common technical knowledge in the art. In this specification and in the claims, when a specified numerical range is written as A to B (where A and B are arbitrary numbers), it means A or greater and B or less. Therefore, it includes the case where the value is greater than A and less than B.

[0018] The precious metal nanoparticles disclosed herein are precious metal nanoparticles whose main constituent metal element is a precious metal element, and the type of precious metal is not limited. Typical examples include gold (Au), silver (Ag), palladium (Pd), platinum (Pt), rhodium (Rh), etc., or alloys thereof. Here, the main constituent metal element refers to the metal element that constitutes the precious metal nanoparticles. Ideally, the precious metal nanoparticles disclosed herein consist only of precious metal elements, but they may also contain various metal elements and nonmetal elements as impurities. The organic content in the total weight (100 wt%) of the precious metal nanoparticles (referring to the aggregate before calcination), as measured based on TG-DTA, is preferably about 2 wt% or less, more preferably 1.5 wt% or less, and particularly preferably 1 wt% or less.

[0019] The surface of the precious metal nanoparticles disclosed herein is protected by an imine compound. Specifically, as in the reaction system described in the examples below, a mixture is prepared of a precious metal salt or precious metal complex (for example, chloroauric acid (HAuCl4) when the precious metal is gold) that is soluble in a predetermined alcohol-based solvent that will serve as the raw material for precious metal nanoparticles, an alkylamine in a sufficient amount (for example, 3 molar equivalents or more) relative to the precious metal, and an alcohol-based solvent capable of dissolving the raw material, such as an alkyl alcohol, and this mixture is heated to, for example, 80°C or higher. As a result, precious metal ions are reduced from the precious metal salt or complex, and precious metal nanoparticles are produced. The reduction treatment time for precious metal ions can be set as appropriate. There are no particular restrictions, but for example, 0.5 to 5 hours is preferable. Recovery of the noble metal fine particles generated by the reduction treatment as described above may be the same as the recovery of conventional metal particles, and there is no particular limitation. Preferably, the noble metal fine particles generated in the liquid are sedimented, centrifuged, and the supernatant is removed. Preferably, washing and centrifugation are repeated a plurality of times with a suitable dispersion medium, and the noble metal fine particles are dispersed in a suitable dispersion medium, whereby a dispersion of the desired noble metal fine particles can be obtained. Further, by adding components such as a binder, a paste (slurry) composition (for example, a conductor paste for forming an electrode film or the like) can be prepared.

[0020] In the technique disclosed herein, in the process of generating noble metal fine particles by the above reduction treatment, an imine compound (typically an alkylimine) is generated by dehydration condensation of a carbonyl compound derived from alcohol and an alkylamine (primary amine), and is retained on the surface of the noble metal fine particles. Therefore, on the surface of the noble metal fine particles generated in the reaction system as described above, in addition to the imine compound, there may be present an organic substance which can also be said to be a residue such as an alkylamine that did not participate in the formation of the imine by the above dehydration condensation. Preferably, the amine / imine ratio (A / I ratio), which is the area ratio of the peak area of the imine compound determined in the pyrolysis GCMS analysis with a pyrolysis temperature of 300 °C and the peak area of the amine compound (including the level where the amine compound cannot be detected, that is, the case where the peak area is 0), is preferably such that the abundance ratio of the imine compound is 1 or less. It is particularly preferable that the imine compound production rate is high such that the A / I ratio is 0.6 or less (for example, it can be 0.01 to 0.2).

[0021] Preferably, the imine compound generated in the above reaction system (several examples described later will be helpful for reference) and retained on the surface of the noble metal fine particles is one having a relatively small molecular weight, specifically, an alkylimine having a hydrocarbon group with about 10 or less carbon atoms, for example, 4 to 10 carbon atoms. For example, the structural formula: R 0 R 1 C=N-(CH2)-R 2 is a compound represented by. R 0 [[ID=1 and R 2 These are alkyl groups or hydrogen atoms that are partially substituted or unsubstituted, independently of each other. A preferred example is R 0 is hydrogen, R 1 and R 2 Examples include hydrocarbon groups having 3 to 9 (more preferably 3 to 7) carbon atoms. For example, an imine compound with the above structural formula, R 0 is hydrogen, R 1 and R 2 Specific preferred examples include CH3(CH2)6, CH3(CH2)4, or CH3(CH2)2, respectively.

[0022] These types of imine compounds, which have relatively small molecular weights and short chain lengths, can be selectively (preferentially) produced in the above reaction system by selecting the appropriate alcohol solvent and primary amine. For example, if octanol (CH3(CH2)7OH) is used as the alcohol solvent and octylamine (CH3(CH2)7NH2) is used as the primary amine, the resulting imine compound will have R in the above structural formula. 0 is hydrogen, R 1 and R 2 Each of these can be CH3(CH2)6. Alternatively, if the primary amine is replaced with butylamine (CH3(CH2)3NH2) in this reaction system, the resulting imine compound will have R in the above structural formula. 0 is hydrogen, R 1 and R 2 At least one of them may be CH3(CH2)2. Alternatively, if the primary amine is replaced with hexylamine (CH3(CH2)5NH2) in this reaction system, the resulting imine compound will have R in the above structural formula. 0 is hydrogen, R 1 and R 2 At least one of them can be CH3(CH2)4. Thus, in the above reaction system, the molecular weight of the imine compound produced (in other words, R) can be determined by the appropriate selection of the alcohol solvent and the amine compound used.0 , R 1 , R 2 The composition of the material can be varied as appropriate. Furthermore, the structure of the resulting imine compound can be identified by measuring the pyrolysis GC-MS spectrum, as will be evident from the examples described later.

[0023] Regarding the particle size distribution of the precious metal nanoparticles disclosed herein, it is preferable that the ratio of the Z-mean particle size (DDLS) based on dynamic light scattering (DLS) to the average particle size (DSEM) based on field emission scanning electron microscope (FE-SEM) images, i.e., DDLS / DSEM, is 2 or less. Precious metal nanoparticles having such characteristics have particularly excellent dispersibility and can contribute to the miniaturization of electronic components and the thinning of electrodes in the field of electronic materials. Furthermore, precious metal nanoparticles with a relatively small average particle size, such as a Z-mean particle size (DDLS) of 200 nm or less, can further suitably advance the thinning of electrodes and the improvement of reliability.

[0024] By dispersing the precious metal nanoparticles disclosed herein in a dispersion medium consisting of a suitable aqueous or organic solvent, dispersions for various applications can be obtained. For example, a composition (conductor paste) can be prepared in paste form by dispersing noble metal nanoparticles in a predetermined organic solvent and further adding components such as a binder, conductive material, and viscosity modifier as needed. As described above, such a conductor paste contains noble metal nanoparticles whose Z-average particle size is controlled to be in the submicron region, so that sufficiently thin electrodes can be suitably formed. The dispersion medium for the conductive paste can be any medium that can effectively disperse the conductive powder material, as in the conventional method, and can be any medium used in conventional conductive paste preparation without any particular limitations. For example, as an organic solvent, one or more types of high-boiling point organic solvents such as petroleum hydrocarbons (especially aliphatic hydrocarbons) like mineral spirits, cellulosic polymers like ethylcellulose, ethylene glycol and diethylene glycol derivatives, toluene, xylene, butyl carbitol (BC), and terpineol can be used.

[0025] Suitable dispersion media for preparing the dispersions disclosed herein include cyclic alcohols having hydroxyl groups on a cyclic chain. The inclusion of cyclic alcohols as a dispersion medium enables high dispersion stability. Preferred examples include cyclic alcohols having 5-membered to 8-membered rings. Examples include terpineol, menthonol (dihydroterpineol), menthol (2-isopropyl-5-methylcyclohexanol), cyclopentanol, cyclohexanol, cycloheptanol, etc. These cyclic alcohols may be used individually or in mixtures of two or more. There are no particular restrictions on the content of cyclic alcohols, but 10 to 100% by mass of the total dispersion medium is appropriate, and 70 to 100% by mass is preferred.

[0026] The following describes an example of the precious metal nanoparticles disclosed herein, relating to gold (Au) nanoparticles with an imine compound retained on their surface; however, such examples are not intended to limit the present invention.

[0027] <1. Examples of gold nanoparticle manufacturing> Example 1: 20.5 g of tetrahydrate chlorauric acid (product of Inui Shoki Kinzoku Kako Co., Ltd.) was mixed with 50 mL of octanol (product of Fujifilm Wako Pure Chemical Industries, Ltd.), and the resulting solution was cooled and stirred in an ice bath. Next, n-octylamine (a product of Fujifilm Wako Pure Chemical Industries, Ltd.) in an amount equivalent to 5 molars relative to the gold content was gradually added to the above solution while suppressing the generation of heat, in order to prepare a chlorauroic acid-octylamine complex-forming solution. This complex-forming solution was subjected to a reduction treatment by heating it in an oil bath at 140°C in an air atmosphere while stirring for 3 hours to reduce the gold ions and synthesize the gold nanoparticles according to this example. Subsequently, the reaction solution was allowed to cool naturally, industrial alcohol (Amakasu Chemical Industry product) was added to settle the gold nanoparticles, and the supernatant was removed by decantation. After repeating this operation three times, industrial alcohol was added, and centrifugation was performed at 3000 rpm for 3 minutes at least two times (three times in this case), and the supernatant was removed. Then, the mixture was dried at room temperature for 12 hours to obtain a dried powder material consisting of precious metal nanoparticles according to Example 1.

[0028] Example 2: Except for using the same materials and procedures as in Example 1, a dried powder material consisting of noble metal fine particles according to Example 2 was obtained. Example 3: Except for the amount of n-octylamine being 25 molar equivalents relative to the gold content, a dried powder material consisting of noble metal fine particles according to Example 3 was obtained using the same materials and procedures as in Example 1.

[0029] Example 4: A dried powder material consisting of noble metal fine particles according to Example 4 was obtained using the same materials and procedures as in Example 1, except that 50 molar equivalents of pure water relative to the gold content were added to the chlorauric acid-octylamine complex-forming solution of Example 1 and the reaction was carried out by heating. Example 5: A dried powder material consisting of noble metal nanoparticles according to Example 5 was obtained using the same materials and procedures as in Example 2, except that n-butylamine was used instead of n-octylamine. Example 6: A dried powder material consisting of noble metal nanoparticles according to Example 5 was obtained using the same materials and procedures as in Example 2, except that n-hexylamine was used instead of n-octylamine.

[0030] Comparative Example 1: 20.5 g of tetrahydrate chloroauric acid (product of Inui Sho Kikinzoku Kako Co., Ltd.) was sealed in a Schlenk tube and dehydrated by heating at 130°C for 4 hours under reduced pressure. Next, the inside of the Schlenk tube was replaced with a nitrogen atmosphere, and then n-octylamine was added in an amount equivalent to 10 molar equivalents relative to the gold content. Then, a reduction treatment was performed by heating at 100°C for 3 hours while flowing nitrogen at a flow rate of 0.2 L / min to reduce the gold ions and synthesize gold nanoparticles related to this comparative example. Subsequently, the reaction solution was allowed to cool naturally, industrial alcohol (Amakasu Chemical Industry product) was added to settle the gold nanoparticles, and the supernatant was removed by decantation. After repeating this operation three times, industrial alcohol was added, and centrifugation was performed at 3000 rpm for 3 minutes, and the supernatant was removed. Then, the dried powder material according to Comparative Example 1 was obtained by drying at room temperature for 12 hours.

[0031] Comparative Example 2: A dried powder material according to Comparative Example 2 was obtained using the same materials and procedures as in Example 1, except that the amount of n-octylamine was 2 molar equivalents relative to the gold content. Comparative Example 3: A dried powder material according to Comparative Example 3 was obtained using the same materials and procedures as in Example 2, except that n-dodecylamine was used instead of n-octylamine. Comparative Example 4: A dried powder material according to Comparative Example 4 was obtained using the same materials and procedures as in Example 2, except that oleylamine was used instead of n-octylamine. Comparative Example 5: A dried powder material according to Comparative Example 5 was obtained using the same materials and procedures as in Example 2, except that the centrifugation described above was performed only once.

[0032] <2. Example of manufacturing a gold nanoparticle dispersion> Example 1-1: Menthonol, a cyclic alcohol, was added to the powder material according to Example 1 as a dispersion medium, and the mixture was allowed to stand for at least 3 hours. Afterward, the solvent was replaced by centrifugation. The obtained wet powder was mixed and dispersed with menthol in such a way that the weight of gold nanoparticles was 80-90 wt% of the total amount, using a rotary-orbit mixer to prepare the dispersion according to Example 1-1.

[0033] Example 2-1: The dispersion according to Example 2-1 was prepared using the same materials and procedures as in Example 1-1, except that the powder material according to Example 2 was used. Example 2-2: The dispersion according to Example 2-2 was prepared using the same materials and procedures as in Example 2-1, except that a mixed alcohol of menthonol / menthol (mass ratio 80 / 20) was used as the dispersion medium. Examples 2-3: The dispersion according to Example 2-3 was prepared using the same materials and procedures as in Example 2-1, except that a mixed alcohol of menthonol / menthol (mass ratio 50 / 50) was used as the dispersion medium. Examples 2-4: The dispersion according to Example 2-4 was prepared using the same materials and procedures as in Example 2-1, except that a mixed alcohol of menthonol / cyclopentanol (mass ratio 80 / 20) was used as the dispersion medium. Examples 2-5: The dispersion according to Example 2-5 was prepared using the same materials and procedures as in Example 2-1, except that a mixed alcohol of menthonol / cycloheptanol (mass ratio 80 / 20) was used as the dispersion medium.

[0034] Example 3-1: The dispersion according to Example 3-1 was prepared using the same materials and procedures as in Example 1-1, except that the powder material according to Example 3 was used. Example 4-1: The dispersion according to Example 4-1 was prepared using the same materials and procedures as in Example 1-1, except that the powder material according to Example 4 was used. Example 5-1: The dispersion according to Example 5-1 was prepared using the same materials and procedures as in Example 1-1, except that the powder material according to Example 5 was used. Example 6-1: The dispersion according to Example 6-1 was prepared using the same materials and procedures as in Example 1-1, except that the powder material according to Example 6 was used.

[0035] Comparative Example 1-1: A dispersion according to Comparative Example 1-1 was prepared using the same materials and procedures as in Example 2-2, except that the powder material according to Comparative Example 1 was used. Comparative Example 3-1: A dispersion according to Comparative Example 3-1 was prepared using the same materials and procedures as in Example 2-2, except that the powder material according to Comparative Example 3 was used. Comparative Example 4-1: A dispersion according to Comparative Example 4-1 was prepared using the same materials and procedures as in Example 2-2, except that the powder material according to Comparative Example 4 was used. Comparative Example 5-1: A dispersion according to Comparative Example 5-1 was prepared using the same materials and procedures as in Example 1-1, except that the powder material according to Comparative Example 5 was used.

[0036] <3. Evaluation Test> (1) Physical characteristics of gold nanoparticles Using a field emission scanning electron microscope (FE-SEM: Hitachi High-Technologies Corporation, S-4700), gold nanoparticles in the powder materials of each example and comparative example were observed (see Figures 16-25). Specifically, five images were randomly selected from a 100,000x or 50,000x field of view, and the particle size of 40 independent particles was measured. The average particle size (DSEM) was then calculated from a total of 200 particle sizes. The results are shown in the corresponding column of Table 1.

[0037] Furthermore, for each example and comparative example, samples of appropriate concentrations were prepared by ultrasonic dispersion using a Zetasizer Nano ZS (Malvern Panalytical product) with N,N-dimethylformamide (DMF) as the dispersion medium. DLS measurements were performed at 20°C, and the Z-mean particle size (DDLS) was calculated based on the general cumulant method. Samples with a DDLS / DSEM ratio greater than 2 were judged to be aggregated. The results are shown in the corresponding columns of Table 1.

[0038] Furthermore, thermal analysis of the gold nanoparticles (dried powder material) was performed on the powder materials related to each example and comparative example using a thermogravimetric analyzer (Rigaku Corporation product, TG-DTA / H). Specifically, approximately 20 mg of each powder material related to each example and comparative example was heated from room temperature to 400°C at a rate of 10°C / min, and the thermal behavior was observed when held at 400°C for 50 minutes. The weight loss rate at this time was defined as the organic matter content relative to the total weight (100 wt%) of the precious metal nanoparticles (dried powder). The results are shown in the corresponding columns of Table 1. In addition, the TG-DTA measurement results (graphs) for Examples 1 and 5 and Comparative Examples 3 and 4 are shown in Figure 1.

[0039] [Table 1]

[0040] As shown in Table 1, the gold nanoparticles in the powder materials of each example all had a DDLS / DSEM of 2 or less, confirming that they possessed good dispersibility. Furthermore, in each example, the Z-mean particle size (DDLS) was 150 nm or less, confirming that these are good powder materials that contribute to the miniaturization of electronic components and the thinning of electrodes. Furthermore, as shown in the relevant column of Table 1 and Figure 1, in the powder materials related to each example, no large exothermic peaks (derived from oxidation) above 200°C, which are observed in alkylamine particles, were detected in TG-DTA. This indicates that the organic molecules present on the surface of the gold nanoparticles in each example were converted from alkylamines to imine compounds (alkylimines: see the structural formula above) in the reaction system in which the gold nanoparticles were synthesized, and that almost no amine added to the reaction system remained. On the other hand, in the powder materials related to each comparative example, a large exothermic peak was detected at temperatures above 200°C in TG-DTA, indicating that the conversion from alkylamine to imine compound was not successfully achieved in the above reaction system. Consequently, the dispersibility was also poor, and the DDLS / DSEM score was significantly higher than 2.

[0041] (2) Detection of imine compounds The dried gold nanoparticle powder materials for each example and comparative example were analyzed using a pyrolysis GCMS system (GCMS-QP2010 Ultra, manufactured by Shimadzu Corporation). Specifically, approximately 20 mg of dried gold nanoparticles were heated at 300°C for 18 seconds to induce thermal decomposition, and the gaseous components generated from the sample were measured by GC-MS. A Frontier Labs Ultra ALLOY±5 (UA5-30M-0.25F) column was used, and the column oven temperature was increased from 40°C to 320°C at a rate of 10°C / min, and held at 320°C for 32 minutes. The ionization method used in the mass spectrometer was the electron shock method (EI method). The pyrolysis GCMS spectra obtained for Examples 1, 2, 3, 4, 5, and 6 are shown in Figures 2, 3, 4, 5, 6, and 7, respectively. The pyrolysis GCMS spectra obtained for Comparative Examples 1, 3, 4 (except for the powder in the dispersion of Comparative Example 4-1, which was dried) and 5 are shown in Figures 8, 9, 10, and 11, respectively. Furthermore, Figure 12 shows the MS spectra of the peak (■ in the corresponding pyrolysis GCMS spectrum) of imine compound A detected in Examples 1-4 and Comparative Example 1. Figure 13 shows the MS spectrum of the peak (■ in the corresponding pyrolysis GCMS spectrum) of imine compound B detected in Example 5. Figure 14 shows the MS spectrum of the peak (■ in the corresponding pyrolysis GCMS spectrum) of imine compound C detected in Example 6. The MS spectrum shown in Figure 15 is the library data referenced when assigning the peak (■) of imine compound B obtained through a library search.

[0042] The identified imine compounds A, B, and C were as follows: Imine compound A Structural formula: R 0 R 1 C=N-(CH2)-R 2 An imine compound represented by R 0 is hydrogen, R 1 and R 2 These are each CH3(CH2)6. Imine compound B Structural formula: R 0 R 1 C=N-(CH2)-R 2 An imine compound represented by R 0 is hydrogen, R 1 and R 2 These are each CH3(CH2)2. ·Imine compound C Structural formula: R 0 R 1 C=N-(CH2)-R 2 An imine compound represented by R 0 is hydrogen, R 1 and R 2 These are CH3(CH2)4, respectively.

[0043] The imine compounds A, B, and C were identified as described above through the following analytical steps. Specifically, the amine peaks (○) observed in each spectrum and the peak of imine compound B (■) observed in the spectrum of Example 5 were assigned by performing a GCMS library search (see Figure 15). On the other hand, since there was no data for imine compounds A and C in the library, they were assigned to the following categories based on the following considerations. In the MS spectra of imine compounds A, B, and C (see Figures 12-14), the values ​​of 56(57), 70, 84, 98(99), and 112, which are thought to originate from fragments on the low molecular weight side, are almost identical, suggesting that they have a similar skeleton. Therefore, it is highly probable that A and C, like imine compound B, also possess an imine skeleton. Furthermore, since a molecular weight of 84 was most frequently detected in the MS spectrum of imine compound B, it is considered that cleavage (fragmentation) mainly occurs at the position shown in the following structural formula. The numbers attached to the structural formula correspond to the molecular weight of the fragment ions after cleavage.

[0044] [ka]

[0045] Therefore, it is presumed that compounds A and C, which are thought to have similar skeletons, primarily undergo cleavage at similar positions. In addition, in the MS spectrum of compound B, molecular weights 57, 70, and 99 are determined to originate from fragment peaks resulting from cleavage at positions other than those mentioned above, while 126 is determined to originate from a molecular ion peak. Based on the above considerations and the components present during synthesis, the structures of compounds A and C were inferred. First, regarding compound A, as shown in the structural formula below, the most frequently detected molecular weight was 140, which is thought to be derived from cleavage at the same position as compound B. In addition, molecular weights of 168 and 196, which are thought to be the molecular weights of fragment peaks derived from cleavage at other positions, were detected, and 238, which is thought to be the molecular weight of the molecular ion peak, was detected.

[0046] [ka]

[0047] Next, regarding compound C, its structure was determined from the fact that the most detected molecular weight was 112, which is thought to be derived from cleavage at the same position as compound B, as shown in the structural formula below, and that 140, 168, etc., which are thought to be the molecular weights of fragment peaks derived from cleavage at other positions, were detected, as well as 184, which is thought to be the molecular weight of the molecular ion peak.

[0048] [ka]

[0049] As shown in the corresponding column of Table 1, it was confirmed that the desired imine compound (in this case, alkylimine) was formed on the surface of the gold nanoparticles in each example. Furthermore, as is clear from the thermal decomposition GCMS spectra of each example, the amount of imine compound formed was greater than the amount of residual amine compound (see A / I ratio described later). On the other hand, in each comparative example, there were many miscellaneous peaks originating from oxidative decomposition, and the formation of imine compounds was at a level that could be described as extremely low or nonexistent. Furthermore, in the case of Comparative Example 2, the synthesis of gold nanoparticles itself was unsuccessful.

[0050] Next, the area values ​​of each peak were calculated from the pyrolysis GC-MS spectra using analysis software. Then, the amine / imine ratio (A / I ratio) was determined from the area values ​​of each imine compound and amine compound (or the sum of the peak areas if there were multiple peaks). The results are shown in Table 2.

[0051] [Table 2]

[0052] As shown in Table 2, the A / I ratio for the gold nanoparticles (powder) in each example was 1 or less (specifically 0.6 or less), indicating that the conversion from amine compounds to imine compounds was carried out with high efficiency. On the other hand, in each comparative example, there were many miscellaneous decomposition products derived from oxidative decomposition, and the A / I ratio was above 1 in all cases.

[0053] (3) Performance evaluation of gold nanoparticle dispersion First, the paste-like dispersions used in each example and comparative example were evaluated as follows: those with a rough, matte appearance and those where the liquid and particles separated, making film formation impossible, were marked with ×, and those with a smooth, metallic luster were marked with ○. The corresponding columns in Table 3 show ○ and ×. In other words, all the paste-like dispersions in each example were marked with ○, and all the paste-like dispersions in each comparative example were marked with ×.

[0054] A calcined film was formed using the dispersions from each example and comparative example as materials, and its performance was evaluated. As described above, paste-like dispersions of each example and comparative example, prepared so that the weight of gold nanoparticles was 80-90 wt% of the total weight, were applied to a glass substrate. Specifically, the dispersion applied to a 1 cm × 1 cm × 100 μm metal mask was squeezed with a rubber squeegee to coat each dispersion into a predetermined shape. After drying at 60°C for 1 hour, a firing treatment was performed at 250°C or 300°C for 30 minutes to form a fired film (gold film) of the predetermined shape. The sheet resistance of the obtained fired film was measured using a commercially available resistivity meter, the Loresta GP (MCP-T610, manufactured by Mitsubishi Chemical Analytec Co., Ltd.). Film thickness was measured using a thickness gauge (TH-102, manufactured by Tester Sangyo Co., Ltd.). Volume resistivity was calculated as the product of the obtained sheet resistance and film thickness. The results are shown in Table 3. Furthermore, the ion milling polished surface was observed using FESEM. Specifically, a 10,000x FESEM image was obtained. Is it a statue?The area of ​​the black voids was determined using "Image Pro," image analysis software from Media Cybernetics, and the density (%) was calculated as 1 - (area of ​​voids / total area)%. The results are shown in the corresponding column of Table 3.

[0055] [Table 3]

[0056] As is clear from the results shown in Table 3, the sintered films (film-like noble metal sintered bodies) made of gold nanoparticles from each example, which have an imine compound on their surface at a suitable A / I ratio (see Table 2), exhibit high density. As a result, it was confirmed that conductive films with low volume resistivity and good conductivity can be formed. It was also confirmed that good sintered films can be obtained at low heat treatment temperatures of 250-300°C. Thus, the precious metal nanoparticles disclosed herein provide a powder material that achieves high dispersion stability and low-temperature sinterability, allowing for sintering at relatively low temperatures. Furthermore, since a highly conductive precious metal sintered body (a fired film in this example) can be obtained, a paste-like (slurry-like) dispersion mainly composed of the precious metal nanoparticles disclosed herein can be used for various applications.

Claims

1. Precious metal nanoparticles containing precious metal elements, wherein the organic matter content relative to the total particle weight based on TG-DTA is 0.58 wt% or more and 2 wt% or less, The surface holds an imine compound, In pyrolysis GCMS analysis at a pyrolysis temperature of 300°C, the amine / imine ratio (A / I ratio), which is the area ratio of the peak area of ​​the imine compound to the peak area of ​​the amine compound, is 0 or more and 1 or less. The imine compound has the following structural formula: R ０ R １ C=N-(CH ２ )-R ２ It is a compound represented by, where R ０ is hydrogen, R １ and R ２ These are hydrocarbon groups with 3 to 9 carbon atoms, The organic matter content relative to the total particle weight, based on the aforementioned TG-DTA, was measured when the particles were heated to 400°C at a rate of 10°C / min and then held for 50 minutes. These are precious metal nanoparticles.

2. The noble metal fine particles according to claim 1, wherein the A / I ratio is 0.6 or less.

3. The noble metal nanoparticles according to claim 1 or 2, wherein the ratio of the Z-mean particle size (DDLS) based on dynamic light scattering (DLS) measurement while dispersed in a predetermined medium to the mean particle size (DSEM) based on field emission scanning electron microscope (FE-SEM) images, i.e., DDLS / DSEM, is 2 or less.

4. The noble metal nanoparticles according to any one of claims 1 to 3, wherein the Z-mean particle size (DDLS) based on the dynamic light scattering (DLS) method measured while dispersed in a predetermined medium is 200 nm or less.

5. R of the imine compound １ and R ２ are each a hydrocarbon group having 3 to 7 carbon atoms, and the noble metal fine particles according to any one of claims 1 to 4.

6. The precious metal fine particles according to any one of claims 1 to 5, wherein the aforementioned precious metal element includes gold (Au).

7. A powder material comprising noble metal fine particles as described in any one of claims 1 to 6.

8. Precious metal microparticles and A dispersion medium for dispersing the noble metal fine particles, It is equipped with, The aforementioned precious metal nanoparticles are It contains precious metal elements, and the organic content relative to the total particle weight based on TG-DTA is 0.58 wt% or more and 2 wt% or less. The surface holds an imine compound, In pyrolysis GCMS analysis at a pyrolysis temperature of 300°C, the amine / imine ratio (A / I ratio), which is the area ratio of the peak area of ​​the imine compound to the peak area of ​​the amine compound, is 0 or more and 1 or less. The molecular weight of the imine compound is 56 or more and 238 or less. The dispersion medium includes a cyclic alcohol having a hydroxyl group on a cyclic chain, The organic matter content relative to the total particle weight, based on the aforementioned TG-DTA, was measured when the temperature was raised to 400°C at a rate of 10°C / min and then held for 50 minutes in a dispersion of noble metal nanoparticles.

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