JP7526543B2 - Surface-modified conductive metal particles, surface-modified conductive metal particle dispersion, and surface-modified conductive metal particle-dispersed resin composition - Google Patents

Description

The present invention relates to surface-modified conductive metal particles, a surface-modified conductive metal particle dispersion, and a surface-modified conductive metal particle-dispersed resin composition.

A resin composition in which conductive metal particles are dispersed in a resin is known as a highly refractive material. For example, Patent Document 1 describes a high-refractive-index metal ultrafine particle-dispersed polymer in which ultrafine metal particles with a particle diameter of 0.001 to 0.1 μm are dispersed in a polymer. Patent Document 2 describes a high-refractive-index film having a high-refractive-index layer containing a binder and flat metal particles. Patent Document 2 describes that the flat metal particles exhibit localized surface plasmon resonance, which causes absorption of visible light (light with a wavelength of 400 nm or more and less than 780 nm), making it possible to reduce the transmittance of visible light.

JP 2000-327836 A International Publication No. 2018/180211

Surface plasmon resonance of conductive metal particles is a phenomenon in which light incident on the surface of the conductive metal particles affects the free electrons on the surface of the conductive metal particles, causing collective vibrational motion (plasma vibration). As described in Patent Document 2, this surface plasmon resonance has the effect of reducing the transmittance of visible light. However, in conductive metal particles used as optical elements that refract and disperse or focus visible light, the occurrence of surface plasmon resonance is undesirable because it reduces the transmittance of visible light.

The present invention aims to provide conductive metal particles that exhibit high visible light transmittance when dispersed in a solvent or resin, and a dispersion liquid and resin composition in which such conductive metal particles are dispersed.

To solve the above problems, the present invention provides the following means.

[1] Surface-modified conductive metal particles comprising: conductive metal particles; and a sulfur-containing organic material bonded to a surface of the conductive metal particles, the sulfur-containing organic material including an oligothiophene and an alkanethiol.
[2] The surface-modified conductive metal particles according to [1], wherein the conductive metal particles have an average particle size of 1.5 nm or more and 50 nm or less.
[3] The surface-modified conductive metal particles according to [1] or [2], wherein the conductive metal particles are at least one type selected from the group consisting of gold particles, silver particles, and copper particles.
[4] The surface-modified conductive metal particle according to any one of [1] to [3], wherein the amount of the sulfur-containing organic material bound per ¹ nm2 of the surface area of the conductive metal particle is in the range of 0.2 molecules to 10 molecules.
[5] The surface-modified conductive metal particles according to any one of [1] to [4], wherein the number of thiophene rings in one molecule of the oligothiophene is within the range of 3 to 15.
[6] The surface-modified conductive metal particles according to any one of [1] to [5], wherein the oligothiophene is a compound represented by the following formula (1):
X-L-D (1)
In formula (1), X represents a bonding group connecting to the conductive metal particle, L represents a linking group, and D represents a dendron.
[7] The surface-modified conductive metal particles according to any one of [1] to [6], wherein the alkanethiol has 3 or more and 20 or less carbon atoms.
[8] The surface-modified conductive metal particles according to any one of [1] to [7], wherein the content of the alkanethiol per 1 mole of the oligothiophene is in the range of 0.1 moles or more and 9.0 moles or less.
[9] The surface-modified conductive metal particles according to any one of [1] to [8], wherein a dispersion liquid in which the surface-modified conductive metal particles are dispersed in chloroform and the concentration of the surface-modified conductive metal particles is 0.29 mg/mL has an absorbance of 0.50 or less at a wavelength of 650 nm as measured using a cell having an optical path length of 1 cm.

[10] A surface-modified conductive metal particle dispersion liquid in which surface-modified conductive metal particles described in any one of [1] to [9] are dispersed in a solvent.

[11] A surface-modified conductive metal particle-dispersed resin composition in which surface-modified conductive metal particles described in any one of [1] to [9] are dispersed in a resin.

According to the present invention, it is possible to provide conductive metal particles that exhibit high visible light transmittance when dispersed in a solvent or resin, as well as a dispersion liquid and a resin composition in which such conductive metal particles are dispersed.

FIG. 1 is a schematic diagram showing a surface-modified conductive metal particle according to one embodiment of the present invention. FIG. 2 is a TEM photograph of the surface-modified gold particles obtained in Example 1. FIG. 3 is a TEM photograph of the surface-modified gold particles obtained in Comparative Example 1. FIG. 4 is a TEM photograph of the surface-modified gold particles obtained in Comparative Example 2. FIG. 5 is a graph showing the absorbance of the dispersions of the surface-modified gold particles obtained in Example 1 and Comparative Examples 1 and 2.

An example of an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the drawings used in the following description may show enlarged characteristic parts for the sake of convenience in order to make the features of the present invention easier to understand. For this reason, the dimensional ratios of each component may differ from the actual ones.

[Surface modified conductive metal particles]
FIG. 1 is a schematic diagram showing a surface-modified conductive metal particle according to one embodiment of the present invention.
As shown in FIG. 1, the surface-modified conductive metal particle 1 includes a conductive metal particle 2 and a sulfur-containing organic substance 3 bonded to the surface of the conductive metal particle 2. The sulfur-containing organic substance 3 is an oligothiophene 3a and alkanethiol 3b.

The shape of the conductive metal particles 2 is not particularly limited, and may be, for example, a sphere, an oval sphere, a polygonal column, a polygonal pyramid, a flat shape, or an irregular shape. The average particle diameter of the conductive metal particles 2 is not particularly limited, and may be, for example, in the range of 1.0 nm to 100 nm. The average particle diameter of the conductive metal particles 2 may be in the range of 1.5 nm to 50 nm, or in the range of 3.0 nm to 10 nm. The average particle diameter of the conductive metal particles 2 is the average value of the particle diameters of 50 conductive metal particles 2 measured using a TEM (transmission electron microscope).

The conductive metal particles 2 are not particularly limited, but may be, for example, at least one type selected from the group consisting of gold particles, silver particles, and copper particles. These metal particles may be used alone or in combination of two or more types.

The amount of sulfur-containing organic material 3 (total of oligothiophene 3a and alkanethiol 3b) bonded to the surface of conductive metal particle 2 is not particularly limited, but is, for example, in the range of 0.2 molecules to 10 molecules per nm2 of the surface area of conductive metal particle ^2. The amount of sulfur-containing organic material 3 bonded may be in the range of 2 molecules to 11 molecules, or in the range of 3 molecules to 10 molecules.

Oligothiophene 3a is a compound having a thiophene ring. The number of thiophene rings in one molecule of oligothiophene 3a is not particularly limited, but is, for example, in the range of 3 to 15. The number of thiophene rings may be in the range of 5 to 10.

The oligothiophene 3a may be, for example, a compound represented by the following formula (1):
X-L-D (1)
In formula (1), X represents a bonding group that connects to the conductive metal particle 2, L represents a linking group, and D represents a dendron.

The bonding group represented by X is a group having affinity for the conductive metal particle 2. An example of the bonding group is S derived from a ^-SR1 group ( ^R1 is a hydrogen atom or a heterocyclic group).

The linking group represented by L is a divalent group having one or more atoms. Examples of the linking group include a divalent hydrocarbon group, an oxygen atom, a carbonyl group, an imino group, and a group combining these. The divalent hydrocarbon group includes a chain hydrocarbon group and a cyclic hydrocarbon group. The chain hydrocarbon group may be branched. The number of carbon atoms of the chain hydrocarbon group may be, for example, in the range of 1 to 12. The number of carbon atoms of the cyclic hydrocarbon group may be, for example, in the range of 6 to 12. The divalent hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group. The linking group may be, for example, * ¹ -alkylene group-oxygen atom-phenylene group-(* ¹ represents a bond to X (bonding group)).

The dendron represented by D may be represented by the following formula (2):

In formula (2), * ² represents a bond to L (linking group), and R ²¹ , R ²² , R ²³¹ , and R ²⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, and a thiophene ring. The thiophene ring may have a substituent. Examples of the substituent include an alkyl group having 1 to 12 carbon atoms, and a thiophene ring. Furthermore, the substituted thiophene ring may have an alkyl group having 1 to 12 carbon atoms or a thiophene ring as a substituent.

The number of carbon atoms in alkanethiol 3b is not particularly limited, but is, for example, in the range of 3 to 20. The number of carbon atoms in alkanethiol 3b may be in the range of 5 to 20, or in the range of 7 to 15. The hydrocarbon group in alkanethiol 3b may be linear or branched. An example of alkanethiol 3b is 1-dodecanethiol.

There is no particular restriction on the content of oligothiophene 3a and alkanethiol 3b in sulfur-containing organic matter 3. For example, the content of alkanethiol 3b per mole of oligothiophene 3a may be in the range of 0.1 moles to 9.0 moles. The content of alkanethiol 3b per mole of oligothiophene 3a may be in the range of 0.2 moles to 7.0 moles, or in the range of 0.3 moles to 4.0 moles.

The surface-modified conductive metal particles 1 of this embodiment can be produced, for example, by mixing conductive metal ions, oligothiophene, and alkanethiol in a polar organic solvent, adding a reducing agent to the resulting mixture, and precipitating the conductive metal particles. As the polar organic solvent, chloroform or tetrahydrofuran can be used. As the reducing agent, a borane-tert-butylamine complex can be used. After the reducing agent is added to the mixture, the mixture may be stirred while being heated at a temperature of 40° C. or higher and lower than the boiling point of the polar organic solvent.

The surface-modified conductive metal particles 1 produced in the polar organic solvent can be recovered by centrifugation, filtration, decantation, etc. The recovered surface-modified conductive metal particles 1 may be washed and dried.

The surface-modified conductive metal particle 1 of this embodiment configured as described above contains the conductive metal particle 2, and the oligothiophene 3a and alkanethiol 3b bonded to the surface of the conductive metal particle 2, so that surface plasmon resonance is unlikely to occur. This is due to the interaction between the metal nanoparticles and the sulfur-containing organic matter.

Since the surface-modified conductive metal particles 1 of this embodiment are unlikely to cause surface plasmon resonance, the dispersion liquid and resin composition in which they are dispersed have improved visible light transmittance.
Although not limited thereto, for example, a dispersion liquid in which surface-modified conductive metal particles 1 are dispersed in chloroform and the concentration of surface-modified conductive metal particles 1 is 0.29 mg/mL may have an absorbance of light with a wavelength of 650 nm measured using a cell with an optical path length of 1 cm of 0.50 or less, 0.40 or less, or 0.38 or less.

It is known that metal particles have the effect of improving the refractive index of resins when dispersed in the resin. For this reason, surface-modified conductive metal particles 1 can be used as a raw material for high refractive index materials. Surface-modified conductive metal particles 1 can be advantageously used as a raw material for high refractive index materials used in optical elements that refract and diverge or focus visible light, such as eyeglass lenses, camera lenses, visible light reflective films, and visible light filters.

[Surface-modified conductive metal particle dispersion]
A surface-modified conductive metal particle dispersion liquid according to one embodiment of the present invention is a liquid in which the surface-modified conductive metal particles according to the present embodiment are dispersed in a solvent.

The solvent is not particularly limited and may be either a polar organic solvent or a non-polar organic solvent. Examples of the solvent that can be used include alcohols, ketones, halogenated aliphatic hydrocarbons, aromatic hydrocarbons, halogenated aromatic hydrocarbons, ether solvents, ester solvents, and amides. Examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 1-pentanol, and 1-hexanol. Examples of ketones include acetone and methyl ethyl ketone. Examples of halogenated aliphatic hydrocarbons include chloroform and dichloromethane. Examples of aromatic hydrocarbons include benzene, toluene, and xylene. Examples of halogenated aromatic hydrocarbons include chlorobenzene. Examples of ether solvents include diethyl ether and tetrahydrofuran. Examples of ester solvents include propyl formate, methyl acetate, ethyl acetate, and butyl acetate. Examples of amides include dimethylformamide and dimethylacetamide.

The concentration of the surface-modified conductive metal particles in the dispersion is not particularly limited, but is, for example, in the range of 0.1 mg/mL or more and 1.0 mg/mL or less.

The surface-modified conductive metal particle dispersion liquid of this embodiment configured as described above has high visible light transmittance because the surface-modified conductive metal particles of this embodiment are dispersed therein.

[Surface modified conductive metal particle dispersed resin composition]
The surface-modified conductive metal particle-dispersed resin composition according to one embodiment of the present invention is a resin in which the surface-modified conductive metal particles according to the present embodiment are dispersed.

The resin may be a thermoplastic resin or a thermosetting resin. Examples of the resin include polyolefin resin, acrylic resin, epoxy resin, phenolic resin, urethane resin, polyester resin, and styrene resin.

The concentration of the surface-modified conductive metal particles in the resin composition is not particularly limited, but is, for example, in the range of 0.1% by mass or more and 60% by mass or less.

The surface-modified conductive metal particle-dispersed resin composition of this embodiment configured as described above has high visible light transmittance because the surface-modified conductive metal particles of this embodiment are dispersed therein.

[Example 1]
0.0625 mmol of a thiophene dendron (7T) compound represented by the following formula and 0.0625 mmol of tetrachloroauric (III) acid tetrahydrate were added to 8 mL of THF (tetrahydrofuran) and dissolved by stirring for 5 minutes.

0.0625 mmol of 1-dodecanethiol was added to THF in which thiophene dendron (7T) compound and tetrachloroauric acid (III) tetrahydrate were dissolved, and the mixture was stirred at room temperature for 3 hours. After stirring, the liquid temperature was heated to 55°C. Next, a solution in which 0.125 mmol of borane-tert-butylamine was dissolved in 2 mL of THF was added, and the liquid temperature was maintained at 55°C while stirring for 5 minutes. After stirring, the mixture was allowed to cool to room temperature, a mixed solution of chloroform and methanol was added, and the mixture was centrifuged to separate and remove the solids, and the supernatant was collected, and the collected supernatant was dried. The solid obtained by drying was again centrifuged and washed with THF and methanol, and the precipitate was dried to obtain surface-modified gold particles surface-modified with thiophene dendron (7T) compound and 1-dodecanethiol.

[Comparative Example 1]
Surface-modified gold particles surface-modified with a thiophene dendron (7T) compound were obtained in the same manner as in Example 1, except that the amount of the thiophene dendron (7T) compound added was 0.1250 mmol and 1-dodecanethiol was not added.

[Comparative Example 2]
A mixed solvent containing ethanol and chloroform in a volume ratio of 1:3 was prepared. 0.0625 mmol of tetrachloroauric (III) acid tetrahydrate was added to 8 mL of this mixed solvent and stirred for 5 minutes to prepare a tetrachloroauric (III) acid solution. Next, 0.1250 mmol of 1-dodecanethiol was added to the tetrachloroauric (III) acid solution and stirred at room temperature for 3 hours. After stirring, the liquid temperature was heated to 55°C. Next, a solution in which 0.125 mmol of borane-tert-butylamine was dissolved in 2 mL of a mixed solvent containing ethanol and chloroform in a volume ratio of 1:3 was added, and the liquid temperature was kept at 55°C and stirred for 5 minutes. After stirring, the mixture was allowed to cool to room temperature, and then the solid content was collected using a centrifugation method, washed with chloroform and methanol, and then dried to obtain surface-modified gold particles surface-modified with 1-dodecanethiol.

[evaluation]
(1) Amount of sulfur-containing organic matter bonded to the surface-modified gold particles The amount of sulfur-containing organic matter bonded to the surface-modified gold particles per ¹ nm2 of surface area was evaluated by thermogravimetric differential thermal analysis and nuclear magnetic resonance analysis. The results are shown in Table 1 below.

(2) Average particle size The surface-modified gold particles were observed using a TEM, and the particle sizes of 50 surface-modified gold particles were measured to calculate the average particle size. Figure 2 shows a TEM photograph of the surface-modified gold particles produced in Example 1, Figure 3 shows a TEM photograph of the surface-modified gold particles produced in Comparative Example 1, and Figure 42 shows a TEM photograph of the surface-modified gold particles produced in Comparative Example 2. Table 1 shows the average particle size.

(3) Visible Light Absorbance 0.29 mg of surface-modified gold particles were added to 1.0 mL of chloroform and mixed by stirring to prepare a surface-modified gold particle dispersion.
The resulting surface-modified gold particle dispersion was placed in a cell (light path length: 1 cm), and the absorbance of light with wavelengths of 250 nm to 900 nm was measured using a spectrophotometer. The absorbance curve is shown in FIG. 5, and the absorbance of light with a wavelength of 650 nm is shown in Table 1.

From the results of Table 1 and Figure 5, it was confirmed that the surface-modified gold particles of Example 1, whose surfaces were modified with oligothiophene and alkanethiol, had a lower visible light absorbance and a higher visible light transmittance when made into a dispersion liquid, compared to the surface-modified gold particles of Comparative Example 1, whose surfaces were modified with oligothiophene alone, and the surface-modified gold particles of Comparative Example 2, whose surfaces were modified with alkanethiol alone. Therefore, the surface-modified gold particles of Example 1 can be advantageously used as a raw material for a highly refractive material of an optical element that refracts visible light to diverge or focus it.

The dispersion containing the surface-modified conductive metal particles of the present invention can be advantageously used for producing a highly refractive material film. Also, the resin composition containing the surface-modified conductive metal particles of the present invention can be advantageously used as a highly refractive material.

1 Surface-modified conductive metal particles 2 Conductive metal particles 3 Sulfur-containing organic substances 3a Oligothiophenes 3b Alkanethiols

Claims (11)

The conductive metal particles include a sulfur-containing organic material bonded to the surface of the conductive metal particles,
The sulfur-containing organic material comprises an oligothiophene and an alkanethiol. The surface-modified conductive metal particles described in claim 1, wherein the average particle diameter of the conductive metal particles is 1.5 nm or more and 50 nm or less. The surface-modified conductive metal particles according to claim 1, wherein the conductive metal particles are at least one type selected from the group consisting of gold particles, silver particles and copper particles. 2. The surface-modified conductive metal particle according to claim 1, wherein the amount of the sulfur-containing organic material bound per ¹ nm2 of the surface area of the conductive metal particle is in the range of 0.2 molecules to 10 molecules. The surface-modified conductive metal particles according to claim 1, wherein the number of thiophene rings in one molecule of the oligothiophene is in the range of 3 to 15. 2. The surface-modified conductive metal particle according to claim 1, wherein the oligothiophene is a compound represented by the following formula (1):
X-L-D (1)
In formula (1), X represents a bonding group connecting to the conductive metal particle, L represents a linking group, and D represents a dendron. The surface-modified conductive metal particles according to claim 1, wherein the number of carbon atoms in the alkanethiol is in the range of 3 to 20. The surface-modified conductive metal particles described in claim 1, wherein the content of the alkanethiol per 1 mole of the oligothiophene is in the range of 0.1 moles or more and 9.0 moles or less. The surface-modified conductive metal particles according to claim 1, wherein a dispersion liquid in which the surface-modified conductive metal particles are dispersed in chloroform and the concentration of the surface-modified conductive metal particles is 0.29 mg/mL has an absorbance of 0.50 or less at a wavelength of 650 nm measured using a cell with an optical path length of 1 cm. A surface-modified conductive metal particle dispersion in which the surface-modified conductive metal particles described in claim 1 are dispersed in a solvent. A surface-modified conductive metal particle-dispersed resin composition in which the surface-modified conductive metal particles according to claim 1 are dispersed in a resin.

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