JP2004292627A - Metal nanorod, metal nanorod-containing composition, its manufacturing process and its application - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal nanorod having a sharp selective light absorption to specific wavelengths in the visual light to near infrared region and an excellent electromagnetic wave shielding property. <P>SOLUTION: The metal nanorod is a rod-shaped metal particle. The coefficients of variation in the long axis and the short axis are each not more than 20%. Preferably, the metal nanorod is a rod-shaped metal particle obtained by reduction of metal ions, the length of the long axis is less than 400 nm, the aspect ratio of the long axis to the short axis is not more than 100, and the coefficients of variation in the long axis and the short axis are each not more than 20%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００１３】
本発明の金属ナノロッドは長軸と短軸の各長さについて、何れもその変動係数Ｃｖが２０％以下であり、均一な形状を有する。従って、光吸収波長域が狭く、特定の波長域においてシャープな光吸収性能を有する。例えば、長軸が４００ｎｍ未満であって、長軸／短軸のアスペクト比が約５．０の金属ナノロッドを含むものは８５０ｎｍ波長の光を吸収するが、本発明に係る金属ナノロッドのこの波長域の透過率は概ね１０％台であって高い光吸収性能を有する一方、周辺の波長域では高い透過率を示し、特定の波長域においてシャープな光吸収性能を有する。
【００１４】
金属ナノロッドは、例えば電解還元によって製造することができる。電解液中に差し入れた金属電極に電圧を加えると、陽極から金属イオンが溶出して陰極で還元される。還元された金属イオンは適度な大きさのクラスターを形成して陰極を離れ、このクラスターが液中で次第に成長してロッド状の金属粒子が形成される。具体的には、長軸が４００ｎｍ未満であり、長軸／短軸のアスペクト比が１００以下の金属ナノロッドを得ることができる。この電解還元において、クラスターの成長を促すために界面活性剤を添加した電解液を用いるが、アルキル鎖を含み、該アルキル鎖長を限定した界面活性剤を用いることによって金属ナノロッドの長軸および短軸の変動係数を制御することができる。具体的には、好ましくは４級アンモニウム塩型のアルキル鎖を含む界面活性剤であってアルキル鎖長が異なる２種の界面活性剤を含む液中で金属イオンを還元することによって、金属ナノロッドの長軸および短軸について、各軸長の変動係数を２０％以下に抑制することができる。
【００１５】
アルキル鎖長が異なる２種の界面活性剤としては、例えば、以下の化学式（イ）（ロ）で表される、（ＣＨ_２）基の数ｎが１〜１５の整数（アルキル鎖の炭素数２〜１６）の界面活性剤を用いることができる。
（イ） ＣＨ_３（ＣＨ_２）_ｎＮ^＋（ＣＨ_３）_３Ｂｒ⁻：
ＣＨ_３（ＣＨ_２）_１５Ｎ^＋（ＣＨ_３）_３Ｂｒ⁻〔ＣＴＡＢ：ｎ＝１５〕
（ロ） （ＣＨ_３（ＣＨ_２）_ｎ）_４Ｎ^＋Ｂｒ⁻：
（ＣＨ_３（ＣＨ_２）_１１）_４Ｎ^＋Ｂｒ⁻〔ＴＣ１２ＡＢ：ｎ＝１１〕
（ＣＨ_３（ＣＨ_２）_５）_４Ｎ^＋Ｂｒ⁻ 〔ＴＣ６ＡＢ：ｎ＝５〕
【００１６】
長軸および短軸の各軸長の変動係数を２０％以下に抑制した金属ナノロッドを分散剤、分散媒、およびバインダー（樹脂）と混合することによって金属ナノロッド含有組成物を得ることができる。この組成物の金属ナノロッドの含有量は組成物中の固形分換算量で０．１ｗｔ％〜９５ｗｔ％、好ましくは２０〜９０ｗｔ％が適当である。金属ナノロッドの含有量がこれより少ないとその効果が不十分になり、これより金属ナノロッドの含有量が多いと相対的にバインダー（樹脂）成分が少なくなるので適当ではない。
【００１７】
分散剤は窒素原子および／またはイオウ原子を含有するものが好ましい。例えば窒素原子やイオウ原子を吸着部位に含むシランカップリング剤などが用いられる。金属ナノロッドはこの窒素原子やイオウ原子と吸着してバインダー中に分散する。分散媒は水性溶または非水性の何れでもよく、両方を用いてもよい。バインダーは水分散系、非水系、水溶性樹脂の何れか１種類もしくはその混合物を用いることができる。上記金属ナノロッドを分散剤の存在下で分散媒に分散させ、この分散液をバインダーと混合することによって長軸および短軸の変動係数を２０％以下に抑制した金属ナノロッドを含有するコーティング組成物を得ることができる。
【００１８】
上記コーティング組成物を基材表面に塗布することによって長軸および短軸の変動係数を２０％以下に抑制した金属ナノロッドが表面に分散した基材を得ることができる。また、本発明の上記金属ナノロッドまたは上記コーティング組成物を樹脂やガラスに練り込むことによって長軸および短軸の変動係数を２０％以下に抑制した金属ナノロッドが内部に分散した基材を得ることができる。これらの基材は樹脂やガラスなどの透明材料で形成されたものは、上記金属ナノロッドによって特定波長の光を吸収するので、ＰＤＰ用光学フィルター、カラーフィルター、熱線カットフィルターなどに利用することができる。
【００１９】
【実施例および比較例】
以下に本発明の実施例および比較例を示す。
〔実施例１〕
電解液として、界面活性剤〔ＣＨ_３（ＣＨ_２）_１５Ｎ^＋（ＣＨ_３）_３Ｂｒ⁻：ＣＴＡＢ（アルキル鎖の炭素数１６）〕を０．０８ｍｏｌ／ｌ、界面活性剤〔（ＣＨ_３（ＣＨ_２）_１１）_４Ｎ^＋Ｂｒ⁻：ＴＣ１２ＡＢ（アルキル鎖の炭素数１２）〕０．００５４ｍｏｌ／ｌを含む１００ｍｌの水を用い、金板を陽極とし、白金板を陰極とし、さらに白金板の側方に電圧を加えない銀板を設けた電解装置によって、２０ｍＡの定電流を電極に加え、超音波振動を与えながら電解を２時間行って金ナノロッドを得た。この金ナノロッドの長軸と短軸の変動係数はおのおの１０％であり、長軸の平均長さ５０ｎｍ、長軸／短軸のアスペクト比は約５．０であった。
この金ナノロッドを含有する電解水溶液から遠心分離によって過剰の界面活性剤を除去した後、金ナノロッド含有量が８５重量％になるようにアクリル樹脂エマルジョン（固形分４０重量％）を混合して塗料とした。この塗料をガラス基板に塗布して乾燥することによって、金ナノロッドが表面に分散した塗膜（膜厚２μｍ）を有するガラス基板を得た。このガラス基板の分光特性および表面抵抗値をそれぞれ測定した。この結果を表１に示した。なお、分光特性の測定は日本分光社製装置（Ｖ−５７０）を用い、表面抵抗値の測定は三菱化学社製装置（ロレスタ・ＧＰ、４端針法）を用いた。
【００２０】
〔実施例２〕
実施例１のＴＣ１２ＡＢに代えて界面活性剤として〔（ＣＨ_３（ＣＨ_２）_５）_４Ｎ^＋Ｂｒ⁻：ＴＣ６ＡＢ（アルキル鎖の炭素数６）〕を０．００８１ｍｏｌ／ｌ用いた以外は実施例１と同様にして金ナノロッドを得た。この金ナノロッドの長軸と短軸の変動係数はおのおの１５％であり、長軸の平均長さ４０ｎｍ、長軸／短軸のアスペクト比は約５．０であった。さらに実施例１と同様にしてこの金ナノロッドを８５重量％含有する塗料を調製した。この塗料をガラス基板に塗布して乾燥することによって、金ナノロッドが表面に分散した塗膜（膜厚２μｍ）を有するガラス基板を得た。このガラス基板の分光特性および表面抵抗値をそれぞれ実施例１と同様にして測定した。この結果を表１に示した。
【００２１】
〔比較例１〕
実施例１のＴＣ１２ＡＢに代えて界面活性剤として〔（ＣＨ_３）_４Ｎ^＋Ｂｒ⁻：ＴＣ１ＡＢ（アルキル鎖の炭素数１）〕を０．００８１ｍｏｌ／ｌ用いた以外は実施例１と同様にして金ナノロッドを得た。この金ナノロッドの長軸と短軸の変動係数は４０％であり、長軸の平均長さ３０ｎｍ、長軸／短軸のアスペクト比は約５．０であった。さらに、実施例１と同様にしてこの金ナノロッドを８５重量％含有する塗料を調製した。この塗料をガラス基板に塗布して乾燥することによって、金ナノロッドが表面に分散した塗膜（膜厚２μｍ）を有するガラス基板を得た。このガラス基板の分光特性および表面抵抗値を実施例１と同様にして測定した。この結果を表１に示した。
【００２２】
〔比較例２〕
実施例１のＴＣ１２ＡＢに代えて界面活性剤としてＴＣ１ＡＢとＴＣ６ＡＢの混合液（混合比ＴＣ１ＡＢ：ＴＣ６ＡＢ＝９：１）を０．００８１ｍｏｌ／ｌ用いた以外は実施例１と同様にして金ナノロッドを得た。この金ナノロッドの長軸の変動係数は２０％、短軸の変動係数は４０％であり、長軸の平均長さ３０ｎｍ、長軸／短軸のアスペクト比は約５．０であった。さらに、実施例１と同様にしてこの金ナノロッドを８５重量％含有する塗料を調製した。この塗料をガラス基板に塗布して乾燥することによって、金ナノロッドが表面に分散した塗膜（膜厚２μｍ）を有するガラス基板を得た。このガラス基板の分光特性および表面抵抗値をそれぞれ実施例１と同様にして測定した。この結果を表１に示した。
【００２３】
〔比較例３〕
実施例１のＴＣ１２ＡＢに代えて界面活性剤としてＴＣ１ＡＢとＴＣ１２ＡＢの混合液（混合比ＴＣ１ＡＢ：ＴＣ１２ＡＢ＝９：１）を０．００８１ｍｏｌ／ｌ用いた以外は実施例１と同様にして金ナノロッドを得た。この金ナノロッドの長軸の変動係数は４０％、短軸の変動係数は２０％であり、長軸の平均長さ３０ｎｍ、長軸／短軸のアスペクト比は約５．０であった。さらに、実施例１と同様にしてこの金ナノロッドを８５重量％含有する塗料を調製した。この塗料をガラス基板に塗布して乾燥することによって、金ナノロッドが表面に分散した塗膜（膜厚２μｍ）を有するガラス基板を得た。このガラス基板の分光特性および表面抵抗値をそれぞれ実施例１と同様にして測定した。この結果を表１に示した。
【００２４】
表１に示すように、長軸および短軸の変動係数が２０％以下である本発明の金属ナノロッドが分散した塗膜を有するガラス基板は、何れも７００ｎｍにおける透過率は８０〜８５％であるが、８５０ｎｍにおける透過率は１０％であり、この波長に対して優れた選択的な光吸収性能を有する（実施例１、２）。一方、比較例１〜３は７００ｎｍおよび８５０ｎｍにおける透過率は何れも４０〜６０％であり、選択的な光吸収能力は大幅に低く、７００ｎｍにおいても光吸収作用を有している。さらに、本発明の実施例１、２の基板表面抵抗は比較例１〜３よりも小さく、導電性に優れている。
【００２５】
【表１】

【００２６】
【発明の効果】
本発明の金属ナノロッドは長軸と短軸の変動係数が小さいので、ロッド形状が均一であり、特定波長に対してシャープな光吸収性能を有し、周辺の波長に対して大きな影響を与えずに特定波長に対して高い光吸収効果を発揮する。本発明の金属ナノロッドを用いることにより、可視光域〜近赤外線光域の特定波長に対してシャープな選択的光吸収性能を有し、かつ電磁波遮蔽性能に優れた光学フィルムを得ることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a metal nanorod having a function of absorbing visible light and near infrared light and a function of shielding electromagnetic waves, a metal nanorod having a uniform long axis and a short axis, a coating composition containing the same, and a coating composition in which the metal nanorod is dispersed. The present invention relates to a substrate having a film or a substrate into which the metal nanorods are kneaded.
[0002]
[Prior art]
When light is applied to metal fine particles, a resonance absorption phenomenon called plasmon absorption occurs. This absorption phenomenon varies in the absorption wavelength range depending on the type and shape of the metal. For example, a gold colloid in which spherical gold fine particles are dispersed in water has an absorption region around 530 nm. However, when the shape of the fine particles is a rod shape with a short axis of 10 nm, in addition to the absorption around 530 nm caused by the short axis of the rod, It is known to have absorption on the long wavelength side caused by the long axis of the rod (for example, SS Chang et al, Langmuir, 1999, 15. p701-709).
[0003]
Conventionally, it has been known that metal fine particles exhibit such plasmon absorption, but a composition utilizing this phenomenon or a substrate coated or kneaded with this composition has not been known so far. For example, JP-A-11-80647 and JP-A-11-319538 describe a colloid solution containing colloidal particles of a noble metal or copper and a polymer pigment dispersant. The purpose of the present invention is to increase the stability of the metal particles, but is not to specify the shape of the metal fine particles so as to obtain an absorption effect against visible light / near infrared light or an electromagnetic wave shielding effect. Japanese Patent Publication No. Hei 9-506210 describes metal carbide nanoparticles and a method for producing the same. However, it is necessary to specify the ratio of the short axis to the long axis of the metal fine particles to enhance the absorption function for near-infrared light. Is not recognized and is not shown to embody this in paints.
[0004]
Furthermore, the metal nanorods described in the conventional literature (S. S. Chang et al, Langmuir, 1999, 15. p701-709) are not uniform in shape, so the absorption wavelength range is widened and sharp light is narrow in the wavelength range. There is a problem that the absorption effect cannot be obtained.
[0005]
[Means for Solving the Problems]
The present invention has solved the above-mentioned conventional problems. In a method for producing a metal nanorod by reduction of metal ions, a method of producing a metal nanorod in which the length of the major axis and the minor axis is small and each length is uniform. And a composition and a substrate containing the metal nanorod.
[0006]
That is, the present invention relates to (1) metal nanorods, which are rod-shaped metal particles, each of which has a variation coefficient of the length of the major axis and the minor axis of 20% or less. The metal nanorods of the present invention are (2) rod-shaped metal particles obtained by reduction of metal ions, having a major axis of less than 400 nm, a major axis / minor axis aspect ratio of 100 or less, and a major axis and a minor axis. Includes each having a coefficient of variation of length of 20% or less.
[0007]
The present invention also relates to (3) a metal nanorod-containing composition comprising the metal nanorod described in (1) or (2) above, a dispersant, a dispersion medium, and a binder (resin). The metal nanorod-containing composition of the present invention comprises (4) a metal nanorod content (solid content equivalent in the composition) of 0.1 wt% to 95 wt%, and (5) a dispersant comprising nitrogen atoms and / or Or those containing sulfur atoms.
[0008]
Furthermore, the present invention relates to (6) a metal nanorod-containing base material having a coating film on the surface of which a metal nanorod formed by the composition according to any one of (3) to (5) is dispersed. . The metal nanorod-containing substrate of the present invention is kneaded with (7) the metal nanorod described in (1) or (2) or the metal nanorod-containing composition described in any of (3) to (5). And (8) those in which the substrate is transparent glass or plastic.
[0009]
Further, the present invention provides (9) a method for producing metal nanorods by reducing metal ions in a liquid containing a surfactant, wherein CH ₃ (CH ₂ ) _n N ⁺ (CH ₃ ) ₃ Br ⁻ (n is A surfactant represented by a chemical formula of (CH ₃ (CH ₂ ) _n ) ₄ N ⁺ Br ⁻ (n is an integer of 1 to 15); The present invention relates to a method for producing a metal nanorod, wherein the variation coefficient of the major axis and the minor axis of the metal nanorod is controlled to 20% or less by using the mixed surfactant. Further, the present invention is characterized in that (10) the metal nanorods described in the above (1) or (2) are dispersed in a dispersion medium in the presence of a dispersant, and this dispersion is mixed with a binder (resin). The present invention relates to a method for producing a metal nanorod-containing composition.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be specifically described based on embodiments.
The present invention relates to a metal nanorod having a uniform long axis and short axis. Specifically, for example, rod-shaped metal particles obtained by reduction of metal ions, the major axis is less than 400 nm, preferably 5 to 200 nm, and the major axis / minor axis aspect ratio is 100 or less, preferably In 2 to 10 metal nanorods, the variation coefficients of the major axis and the minor axis are each 20% or less, preferably 15% or less.
[0011]
In general, the variation coefficient Cv is determined by the following equation [1] when the unbiased variance U and the arithmetic mean value X are used. The unbiased variance U is determined by the following equation [2]. When this is applied to the lengths of the major axis and the minor axis of the metal nanorods, the variation coefficient Cv of the major axis length and the variation coefficient Cv of the minor axis length become the unbiased variance U of each length and the arithmetic mean value. X is given by the following equation [1], and this unbiased variance U is given by the following equation [2]. Specifically, when the measured number n of the metal nanorods and each measured value of the measured number n are Xi (i = 1, 2,..., N), the difference between each measured value Xi and the arithmetic average value X (Xi− The value obtained by summing the squares of X) for 1 to n and dividing the sum by (n-1) is the unbiased variance U. In this way, for each of the major axis and minor axis lengths, the unbiased variance U is obtained based on the actual measured value Xi and its arithmetic mean X, and based on the unbiased variance U, the major axis length and the minor axis length are determined. Is determined in each case.
[0012]
【formula】

[0013]
The metal nanorod of the present invention has a uniform shape with a variation coefficient Cv of 20% or less for each of the major axis and the minor axis. Therefore, the light absorption wavelength range is narrow, and the light absorption performance is sharp in a specific wavelength range. For example, a metal nanorod having a major axis of less than 400 nm and a major axis / minor axis aspect ratio of about 5.0 absorbs light having a wavelength of 850 nm. Has a high light absorption performance in the order of 10%, and has a high transmittance in a peripheral wavelength range, and has a sharp light absorption performance in a specific wavelength range.
[0014]
Metal nanorods can be produced, for example, by electrolytic reduction. When a voltage is applied to the metal electrode inserted in the electrolyte, metal ions elute from the anode and are reduced at the cathode. The reduced metal ions form clusters of an appropriate size and leave the cathode, and the clusters gradually grow in the liquid to form rod-shaped metal particles. Specifically, a metal nanorod having a major axis of less than 400 nm and an aspect ratio of major axis / minor axis of 100 or less can be obtained. In this electrolytic reduction, an electrolytic solution to which a surfactant is added is used to promote the growth of clusters. However, by using a surfactant containing an alkyl chain and having a limited alkyl chain length, the long axis and the short axis of the metal nanorod can be reduced. The coefficient of variation of the axis can be controlled. Specifically, a metal ion is reduced in a liquid containing a surfactant, preferably a surfactant containing an alkyl chain of a quaternary ammonium salt type, having two different alkyl chain lengths. With respect to the major axis and the minor axis, the variation coefficient of each axis length can be suppressed to 20% or less.
[0015]
As the two kinds of surfactants having different alkyl chain lengths, for example, the number n of (CH ₂ ) groups represented by the following chemical formulas (a) and (b) is an integer of 1 to 15 (the carbon number of the alkyl chain). Surfactants 2) to 16) can be used.
(A) CH ₃ (CH ₂ ) _n N ⁺ (CH ₃ ) ₃ Br ⁻ :
^{_{CH 3 (CH 2) 15 N}} + (CH 3) 3 Br - [CTAB: n = 15]
_{(Ii) (CH 3 (CH 2)} n) 4 N + Br -:
_{(CH 3 (CH 2) 11} ) 4 N + Br - [TC12AB: n = 11]
_{(CH 3 (CH 2) 5} ) 4 N + Br - [TC6AB: n = 5]
[0016]
A metal nanorod-containing composition can be obtained by mixing a metal nanorod in which the variation coefficient of each of the major axis and the minor axis is suppressed to 20% or less with a dispersant, a dispersion medium, and a binder (resin). The content of the metal nanorods in this composition is from 0.1 wt% to 95 wt%, preferably from 20 to 90 wt%, in terms of the solid content in the composition. If the content of the metal nanorods is less than this, the effect becomes insufficient, and if the content of the metal nanorods is greater than this, the binder (resin) component relatively decreases, which is not suitable.
[0017]
The dispersant preferably contains a nitrogen atom and / or a sulfur atom. For example, a silane coupling agent containing a nitrogen atom or a sulfur atom in an adsorption site is used. The metal nanorods adsorb to the nitrogen and sulfur atoms and disperse in the binder. The dispersion medium may be either aqueous or non-aqueous, or both may be used. As the binder, any one of an aqueous dispersion type, a non-aqueous type, and a water-soluble resin or a mixture thereof can be used. The metal nanorods are dispersed in a dispersion medium in the presence of a dispersing agent, and a coating composition containing the metal nanorods in which the variation coefficient of the long axis and the short axis is suppressed to 20% or less by mixing the dispersion with a binder. Obtainable.
[0018]
By applying the above coating composition to the surface of the substrate, a substrate in which metal nanorods having a variation coefficient of the major axis and the minor axis of 20% or less are dispersed on the surface can be obtained. Further, by kneading the metal nanorods or the coating composition of the present invention into a resin or glass, it is possible to obtain a substrate in which the metal nanorods in which the variation coefficient of the major axis and the minor axis is suppressed to 20% or less are dispersed. it can. These substrates formed of a transparent material such as resin or glass absorb light of a specific wavelength by the metal nanorods, and thus can be used as an optical filter for PDP, a color filter, a heat ray cut filter, and the like. .
[0019]
[Examples and Comparative Examples]
Hereinafter, examples and comparative examples of the present invention will be described.
[Example 1]
As an electrolytic solution, a surfactant [CH ₃ (CH ₂ ) ₁₅ N ⁺ (CH ₃ ) ₃ Br ⁻ : CTAB (alkyl chain having 16 carbon atoms)] 0.08 mol / l and a surfactant [(CH ₃ ( ^{_{CH 2) 11) 4 N +}} Br -: TC12AB ( with 100ml water containing several 12)] 0.0054 mol / l of carbon atoms in the alkyl chain, a gold plate as an anode, the platinum plate as a cathode, and further the platinum plate Electrolysis was performed for 2 hours while applying a constant current of 20 mA to the electrodes and applying ultrasonic vibration using an electrolysis apparatus provided with a silver plate to which no voltage was applied on the side, to obtain gold nanorods. The variation coefficient of the major axis and minor axis of this gold nanorod was 10% each, the average major axis length was 50 nm, and the aspect ratio of major axis / minor axis was about 5.0.
After removing excess surfactant by centrifugation from the electrolytic aqueous solution containing the gold nanorods, an acrylic resin emulsion (solid content: 40% by weight) was mixed so that the gold nanorods content became 85% by weight, and the paint and did. This paint was applied to a glass substrate and dried to obtain a glass substrate having a coating film (film thickness: 2 μm) in which gold nanorods were dispersed on the surface. The spectral characteristics and surface resistance of the glass substrate were measured. The results are shown in Table 1. The spectral characteristics were measured using a device manufactured by JASCO Corporation (V-570), and the surface resistance was measured using a device manufactured by Mitsubishi Chemical Corporation (Loresta GP, four-point needle method).
[0020]
[Example 2]
Example 2 Example 2 was repeated except that [(CH ₃ (CH ₂ ) ₅ ) ₄ N ⁺ Br ⁻ : TC6AB (the number of carbon atoms in the alkyl chain was 6)] was used as a surfactant instead of TC12AB of Example 1. A gold nanorod was obtained in the same manner as in 1. The coefficient of variation of the major axis and minor axis of this gold nanorod was 15%, the average major axis length was 40 nm, and the aspect ratio of major axis / minor axis was about 5.0. Further, in the same manner as in Example 1, a paint containing 85% by weight of the gold nanorod was prepared. This paint was applied to a glass substrate and dried to obtain a glass substrate having a coating film (film thickness: 2 μm) in which gold nanorods were dispersed on the surface. The spectral characteristics and surface resistance of this glass substrate were measured in the same manner as in Example 1. The results are shown in Table 1.
[0021]
[Comparative Example 1]
In the same manner as in Example 1 except that 0.0081 mol / l of [(CH ₃ ) ₄ N ⁺ Br ⁻ : TC1AB (the number of carbon atoms in the alkyl chain)] was used as a surfactant instead of TC12AB of Example 1 A gold nanorod was obtained. The variation coefficient of the major axis and minor axis of this gold nanorod was 40%, the average major axis length was 30 nm, and the aspect ratio of major axis / minor axis was about 5.0. Further, a coating material containing 85% by weight of the gold nanorod was prepared in the same manner as in Example 1. This paint was applied to a glass substrate and dried to obtain a glass substrate having a coating film (film thickness: 2 μm) in which gold nanorods were dispersed on the surface. The spectral characteristics and surface resistance of this glass substrate were measured in the same manner as in Example 1. The results are shown in Table 1.
[0022]
[Comparative Example 2]
Gold nanorods were obtained in the same manner as in Example 1 except that 0.0081 mol / l of a mixed solution of TC1AB and TC6AB (mixing ratio TC1AB: TC6AB = 9: 1) was used as a surfactant instead of TC12AB of Example 1. Was. The variation coefficient of the major axis of the gold nanorod was 20%, the variation coefficient of the minor axis was 40%, the average length of the major axis was 30 nm, and the aspect ratio of the major axis / minor axis was about 5.0. Further, a coating material containing 85% by weight of the gold nanorod was prepared in the same manner as in Example 1. This paint was applied to a glass substrate and dried to obtain a glass substrate having a coating film (film thickness: 2 μm) in which gold nanorods were dispersed on the surface. The spectral characteristics and surface resistance of this glass substrate were measured in the same manner as in Example 1. The results are shown in Table 1.
[0023]
[Comparative Example 3]
Gold nanorods were obtained in the same manner as in Example 1 except that 0.0081 mol / l of a mixed solution of TC1AB and TC12AB (mixing ratio TC1AB: TC12AB = 9: 1) was used as a surfactant instead of TC12AB of Example 1. Was. The variation coefficient of the major axis of this gold nanorod was 40%, the variation coefficient of the minor axis was 20%, the average length of the major axis was 30 nm, and the aspect ratio of the major axis / minor axis was about 5.0. Further, a coating material containing 85% by weight of the gold nanorod was prepared in the same manner as in Example 1. This paint was applied to a glass substrate and dried to obtain a glass substrate having a coating film (film thickness: 2 μm) in which gold nanorods were dispersed on the surface. The spectral characteristics and surface resistance of this glass substrate were measured in the same manner as in Example 1. The results are shown in Table 1.
[0024]
As shown in Table 1, each of the glass substrates having a coating film in which the metal nanorods of the present invention have a variation coefficient of the major axis and the minor axis of 20% or less has a transmittance at 700 nm of 80 to 85%. However, the transmittance at 850 nm is 10%, and has excellent selective light absorption performance for this wavelength (Examples 1 and 2). On the other hand, in Comparative Examples 1 to 3, the transmittances at 700 nm and 850 nm are all 40 to 60%, and the selective light absorbing ability is significantly low, and has a light absorbing effect even at 700 nm. Furthermore, the substrate surface resistances of Examples 1 and 2 of the present invention are smaller than Comparative Examples 1 to 3, and are excellent in conductivity.
[0025]
[Table 1]

[0026]
【The invention's effect】
Since the metal nanorods of the present invention have a small variation coefficient between the long axis and the short axis, the rod shape is uniform, has a sharp light absorption performance for a specific wavelength, and does not greatly affect peripheral wavelengths. It exhibits a high light absorption effect for a specific wavelength. By using the metal nanorods of the present invention, it is possible to obtain an optical film having sharp selective light absorption performance for a specific wavelength in the visible light region to near infrared light region and excellent electromagnetic wave shielding performance.

Claims (10)

Metal nanorods, which are rod-shaped metal particles, wherein the coefficient of variation of the length of the major axis and the minor axis is not more than 20% each. Rod-shaped metal particles obtained by reduction of metal ions, having a major axis of less than 400 nm, a major axis / minor axis aspect ratio of 100 or less, and a variation coefficient of major and minor axis lengths of 20% or less, respectively. The metal nanorod according to claim 1, which is: A metal nanorod-containing composition comprising the metal nanorod according to claim 1, a dispersant, a dispersion medium, and a binder (resin). 4. The metal nanorod-containing composition according to claim 3, wherein the content of the metal nanorod (in terms of solid content in the composition) is 0.1 wt% to 95 wt%. 5. 5. The metal nanorod-containing composition according to claim 3, wherein the dispersant contains a nitrogen atom and / or a sulfur atom. A metal nanorod-containing base material, comprising a coating film on the surface of which the metal nanorods formed by the composition according to claim 3 are dispersed. A metal nanorod-containing base material, into which the metal nanorod according to claim 1 or 2 or the metal nanorod-containing composition according to any one of claims 3 to 5 is kneaded. 8. The substrate according to claim 6, wherein the substrate is transparent glass or plastic. In a method for producing metal nanorods by reducing metal ions in a liquid containing a surfactant, a chemical formula of CH ₃ (CH ₂ ) _n N ⁺ (CH ₃ ) ₃ Br ⁻ (n is an integer of 1 to 15) is used. By using a mixed surfactant of a surfactant represented by the following formula and a surfactant represented by a chemical formula of (CH ₃ (CH ₂ ) _n ) ₄ N ⁺ Br ⁻ (n is an integer of 1 to 15) A method for producing a metal nanorod, wherein a coefficient of variation of a long axis and a short axis of the metal nanorod is controlled to 20% or less. A method for producing a metal nanorod-containing composition, comprising dispersing the metal nanorod according to claim 1 or 2 in a dispersion medium in the presence of a dispersant, and mixing the dispersion with a binder (resin).