JP2016195103A - Composite conductive particle and method for producing the same, and conductive resin - Google Patents
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本発明は、導電性核粒子をグラフェンで被覆してなる複合導電性粒子およびその製造方法、ならびに当該複合導電性粒子を含む導電性樹脂に関する。 The present invention relates to composite conductive particles obtained by coating conductive core particles with graphene, a method for producing the same, and a conductive resin including the composite conductive particles.
黒鉛は高導電性、耐熱性、軽量性、低熱膨張性、高熱伝導性、自己潤滑性などの多くの優れた特性を有する炭素材料として古くから知られており、数多くの用途において利用されている。近年、黒鉛に類する新たな炭素系材料として、樹脂材料を炭化焼成して得られるグラファイトシートやナノカーボン材料と言われるフラーレン、カーボンナノチューブ等が黒鉛同様の多くの優れた特性を有する材料として新たに見出され、幅広い用途への活用の取り組みがなされている。そしてごく最近では黒鉛の一部を形成する、ナノメートルオーダーの厚みを有するベンゼン環構造が面方向に多数敷き詰められた構造のグラフェンの作製方法が見出され、新材料として利用すべく研究開発が活発化している。 Graphite has long been known as a carbon material with many excellent properties such as high conductivity, heat resistance, light weight, low thermal expansion, high thermal conductivity, and self-lubricating properties, and is used in many applications. . In recent years, as a new carbon-based material similar to graphite, graphite sheets obtained by carbonizing and firing resin materials, fullerenes called nanocarbon materials, carbon nanotubes, etc. are newly developed as materials having many excellent characteristics similar to graphite. It has been discovered and is being used for a wide range of purposes. Most recently, a method for producing graphene with a structure in which a large number of benzene ring structures with a thickness of the order of nanometers, which form a part of graphite, are spread in the plane direction has been found, and research and development has been conducted to use it as a new material. It is becoming active.
グラフェンは黒鉛同様の高導電性・高伝熱性を持つことに加え、高強度／高弾性率、高い移動度、高ガスバリア性、高いフレキシブル性など多くの優れた物理特性を持つ材料であり、また化学的にも安定であることから、電池材料、エネルギー貯蔵材料、電子デバイス，複合材料などの領域で幅広い応用が期待されている。 Graphene is a material with many excellent physical properties such as high conductivity / high heat conductivity, high strength / elastic modulus, high mobility, high gas barrier property, high flexibility, etc. Since it is chemically stable, a wide range of applications are expected in the fields of battery materials, energy storage materials, electronic devices, and composite materials.
グラフェンの製造法としては、機械剥離法、ＣＶＤ（Ｃｈｅｍｉｃａｌ Ｖａｐｏｒ Ｄｅｐｏｓｉｔｉｏｎ）法、ＣＥＧ（Ｃｒｙｓｔａｌ Ｅｐｉｔａｘｉａｌ Ｇｒｏｗｔｈ）法、酸化還元法などが挙げられる。このうち、酸化還元法（天然黒鉛の酸化処理で酸化黒鉛または酸化グラファイトを得た後、還元反応によりグラフェンを作製する方法）はグラフェンの大量合成が可能であり、グラフェンを産業用途に応用する上で期待されている手法である。 Examples of the method for producing graphene include a mechanical peeling method, a CVD (Chemical Vapor Deposition) method, a CEG (Crystal Epitaxial Growth) method, and an oxidation-reduction method. Among these, the oxidation-reduction method (a method of producing graphene by a reduction reaction after obtaining graphite oxide or graphite oxide by oxidation treatment of natural graphite) is possible to synthesize graphene in large quantities. This is an expected method.
グラフェンは、高い導電性能を持つ上に薄片状の形状であるため、導電パスを多くすることができ、導電性樹脂用や電池電極用の導電材料として高いポテンシャルを持つ。特に薄片状でフレキシブルである点が、特に表面・界面における導電性を向上させるのに極めて適している。 Since graphene has a high conductive performance and a flaky shape, it can increase the number of conductive paths, and has a high potential as a conductive material for conductive resins and battery electrodes. In particular, the flaky and flexible point is extremely suitable for improving the conductivity at the surface and interface.
例えば、特許文献１には金属塩と酸化グラフェンを混合してから還元することで、金属ナノ粒子とグラフェンの複合体を作製する手法が開示されている。特許文献２にはナノカーボンと金属粒子の混合物を基板にコーティングする手法が開示されている。 For example, Patent Document 1 discloses a technique for preparing a composite of metal nanoparticles and graphene by mixing a metal salt and graphene oxide and then reducing the mixture. Patent Document 2 discloses a technique of coating a substrate with a mixture of nanocarbon and metal particles.
特許文献１では金属塩と酸化グラフェンを混合して還元することでグラフェン表面に金属ナノ粒子凝集体を付着させている。しかし、金属ナノ粒子は凝集しやすく、金属ナノ粒子の凝集体はナノ粒子間の接触抵抗が大きいため、グラフェンと金属ナノ粒子の複合物を樹脂などに混練しても十分な導電性が得られない。特許文献２では金属粒子とグラフェンを混合して塗布しているが、単に混合するだけでは金属粒子とグラフェンとの界面抵抗を下げることが出来ない。 In patent document 1, the metal nanoparticle aggregate is made to adhere to the graphene surface by mixing and reducing a metal salt and graphene oxide. However, metal nanoparticles tend to aggregate, and the aggregate of metal nanoparticles has a high contact resistance between the nanoparticles, so that sufficient conductivity can be obtained even when a composite of graphene and metal nanoparticles is kneaded into a resin or the like. Absent. In Patent Document 2, the metal particles and graphene are mixed and applied, but the interface resistance between the metal particles and graphene cannot be lowered simply by mixing.
以上のように、従来技術では導電性粒子の界面抵抗が大きく、樹脂や電極中における導電性を十分向上できている例はこれまで無かった。本発明は、界面抵抗が小さく、優れた導電性向上効果を有する導電性粒子を提供することを課題とする。 As described above, in the prior art, the interface resistance of conductive particles is large, and there has been no example in which the conductivity in a resin or an electrode can be sufficiently improved. An object of the present invention is to provide conductive particles having a low interface resistance and an excellent conductivity improving effect.
上記課題を解決するための本発明は、平均一次粒子径が１５μｍ以上５００μｍ以下の導電性核粒子がグラフェンに被覆されてなる複合導電性粒子である。 The present invention for solving the above problems is composite conductive particles obtained by coating graphene with conductive core particles having an average primary particle size of 15 μm or more and 500 μm or less.
従来の導電性粒子は粒子同士が点で接触していたために界面抵抗が大きかったが、本発明の複合導電性粒子によれば、フレキシブルなグラフェンにより導電性核粒子を被覆することで界面抵抗を下げることが可能である。また、本発明の複合導電性粒子を導電助剤として用いることにより、樹脂や電極中の導電性を向上することが出来る。 Conventional conductive particles have a large interfacial resistance because the particles are in contact with each other at points, but according to the composite conductive particles of the present invention, the interfacial resistance is reduced by covering the conductive core particles with flexible graphene. It is possible to lower. Moreover, the electroconductivity in resin or an electrode can be improved by using the composite electroconductive particle of this invention as a conductive support agent.
＜複合導電性粒子＞
本発明における導電性核粒子とは、体積固有抵抗率が１０−１Ω・ｃｍ以下の物質からなる粒子である。体積固有抵抗率が１０−１Ω・ｃｍ以下の物質としては、下記に制限されるものではないが、金、銀、銅、アルミニウム、白金、鉛、パラジウム、亜鉛、鉄、マンガン、ニッケル、モリブデン、タングステン、コバルト、チタン、ジルコニウム、クロムなどの金属、及び複数の金属が含まれる合金、或いは黒鉛が挙げられる。
<Composite conductive particles>
The conductive core particle in the present invention is a particle made of a substance having a volume resistivity of 10 −1 Ω · cm or less. The material having a volume resistivity of 10 −1 Ω · cm or less is not limited to the following, but gold, silver, copper, aluminum, platinum, lead, palladium, zinc, iron, manganese, nickel, molybdenum , Tungsten, cobalt, titanium, zirconium, chromium and the like, and alloys containing a plurality of metals, or graphite.
本発明において、導電性核粒子の平均一次粒子径は１５μｍ以上５００μｍ以下である。導電性核粒子の一次粒子径は大きいほど導電パスが大きくなり導電性能が向上するが、大きすぎると分散性能が低下する。導電性核粒子の平均一次粒子径は、好ましくは２０μｍ以上２００μｍ以下、さらに好ましくは２５μｍ以上１００μｍ以下、特に好ましくは３０μｍ以上６０μｍ以下である。 In the present invention, the average primary particle diameter of the conductive core particles is 15 μm or more and 500 μm or less. The larger the primary particle diameter of the conductive core particles is, the larger the conductive path is and the conductive performance is improved. The average primary particle diameter of the conductive core particles is preferably 20 μm to 200 μm, more preferably 25 μm to 100 μm, and particularly preferably 30 μm to 60 μm.
導電性核粒子の平均一次粒子径は電子顕微鏡により測定することが可能である。導電性核粒子の粉末を、カーボンテープに付着させて、観察しやすいように３００倍〜３０００倍の範囲で適宜調節して一次粒子の大きさを観察する。そして、各一次粒子の最も長い部分の長さ（長径）と最も短い部分の長さ（短径）を測定し、（長径＋短径）／２で求められる数値を一次粒子径とする。本発明においては、ランダムに導電性核粒子５０個について測定した平均値を導電性核粒子の平均一次粒子径とする。なお、グラフェンと複合した後の複合導電性粒子においては、グラフェンの厚みは導電性核粒子の一次粒子径と比較して非常に小さく、ほとんど無視できるため、本発明においては複合導電性粒子の粒子径を導電性核粒子の一次粒子径とみなすことができる。 The average primary particle diameter of the conductive core particles can be measured with an electron microscope. The size of the primary particles is observed by adhering the powder of the conductive core particles to the carbon tape and adjusting it appropriately within a range of 300 times to 3000 times so as to be easily observed. Then, the length of the longest part (major axis) and the length of the shortest part (minor axis) of each primary particle are measured, and the numerical value obtained by (major axis + minor axis) / 2 is defined as the primary particle diameter. In this invention, let the average value measured about 50 electroconductive nucleus particles at random be an average primary particle diameter of electroconductive nucleus particles. In the composite conductive particles after being combined with graphene, the thickness of the graphene is very small compared to the primary particle diameter of the conductive core particles and can be almost ignored. The diameter can be regarded as the primary particle diameter of the conductive core particles.
本発明における導電性核粒子の円形度は０．８０以上であることが好ましい。導電性核粒子が真球形に近いほど、本発明の複合導電性粒子が樹脂内等で配列しやすく、良好な導電パスを得ることが出来る。真球形に近いかどうかは下記の走査電子顕微鏡で測定したときの円形度、すなわち短径／長径の比から判断できる。本発明における円形度は、粒子径測定と同様、導電性核粒子５０個について円形度を測定した平均値であるものとする。なお、平均一次粒子径と同様、本発明においては複合導電性粒子の円形度を導電性核粒子の円形度とみなすことができる。 The circularity of the conductive core particles in the present invention is preferably 0.80 or more. The closer the conductive core particle is to a true sphere, the easier it is for the composite conductive particle of the present invention to be arranged in the resin or the like, and a better conductive path can be obtained. Whether it is close to a true sphere or not can be judged from the circularity when measured with the following scanning electron microscope, that is, the ratio of minor axis / major axis. The circularity in the present invention is an average value obtained by measuring the circularity of 50 conductive core particles as in the particle diameter measurement. As with the average primary particle diameter, in the present invention, the circularity of the composite conductive particles can be regarded as the circularity of the conductive core particles.
グラフェンとは、一般には１原子の厚みのｓｐ２結合炭素原子のシート（単層グラフェン）を指すが、本発明においては、単層グラフェンが積層した薄片上の形態を持つ物質もグラフェンに含めるものとする。 Graphene generally refers to a sheet of sp 2 bonded carbon atoms (single layer graphene) having a thickness of 1 atom, but in the present invention, a material having a form on a flake in which single layer graphene is laminated is also included in graphene And
本発明に用いられるグラフェンの厚み（グラフェン層に垂直な方向の大きさ）には特に制限は無いが、重量あたりの導電パスを最大化する観点から、薄いほうが好ましい。グラフェンの厚みは、好ましくは１００ｎｍ以下、より好ましくは５０ｎｍ以下、さらに好ましくは２０ｎｍ以下である。 The thickness of the graphene used in the present invention (the size in the direction perpendicular to the graphene layer) is not particularly limited, but is preferably thinner from the viewpoint of maximizing the conductive path per weight. The thickness of graphene is preferably 100 nm or less, more preferably 50 nm or less, and still more preferably 20 nm or less.
また、グラフェンの面方向の大きさ（グラフェン層に平行な方向の大きさ）にも特に制限は無いが、小さすぎるとグラフェン一個あたりの導電パスが短くなるため、グラフェン間の接触抵抗の影響で導電性が悪くなる傾向がある。そのため、本発明におけるグラフェンの面方向の大きさは、好ましくは０．５μｍ以上であり、より好ましくは０．７μｍ以上、さらに好ましくは１μｍ以上である。 In addition, there is no particular limitation on the size of the graphene in the plane direction (the size in the direction parallel to the graphene layer), but if it is too small, the conductive path per graphene will be shortened. There is a tendency for conductivity to deteriorate. Therefore, the size of the graphene in the present invention in the plane direction is preferably 0.5 μm or more, more preferably 0.7 μm or more, and further preferably 1 μm or more.
また、導電性核粒子に対してグラフェンが大きすぎると、一つのグラフェンに複数の導電性核粒子が付着するため、凝集の原因となる。そのため、本発明において、グラフェンの面方向の大きさは導電性核粒子の平均一次粒子径よりも小さいことが好ましい。より具体的には、グラフェンの面方向の大きさは、導電性核粒子の平均一次粒子径に対する比で０．０１以上１未満であることが好ましく０．０５以上０．７以下であることがより好ましく、０．１以上０．５以下であることがさらに好ましい。 Further, if the graphene is too large relative to the conductive core particles, a plurality of conductive core particles adhere to one graphene, which causes aggregation. Therefore, in the present invention, the size of the graphene in the plane direction is preferably smaller than the average primary particle diameter of the conductive core particles. More specifically, the size of the graphene in the plane direction is preferably 0.01 or more and less than 1 in terms of the ratio to the average primary particle diameter of the conductive core particles, and preferably 0.05 or more and 0.7 or less. More preferably, it is 0.1 or more and 0.5 or less.
なお、本発明の複合導電性粒子表面におけるグラフェンの面方向の大きさは、以下のように測定できる。導電性核粒子が金属である場合には、金属を酸などで溶解し、洗浄した後得られたグラフェンを、Ｎ−メチルピロリドン溶剤中で０．００１〜０．００５ｗｔ％にまで希釈・分散しグラフェン分散液を調整する。このグラフェン分散液をガラス基板などの平滑性の高い基板上に滴下・乾燥し、光学顕微鏡又はレーザー顕微鏡で観察する。一方、導電性核粒子が球状黒鉛である場合には、走査型電子顕微鏡で複合導電性粒子そのものの表面を観察する。このようにして観察したグラフェン小片の最も長い部分の長さ（長径）と最も短い部分の長さ（短径）を測定し、（長径＋短径）／２で求められる数値をグラフェンの面方向の大きさとする。本発明におけるグラフェンの面方向の大きさは、ランダムに５０個のグラフェン小片を測定した場合の平均値を指すものとする。 In addition, the magnitude | size of the surface direction of the graphene in the composite electroconductive particle surface of this invention can be measured as follows. When the conductive core particle is a metal, the graphene obtained after dissolving the metal with an acid or the like and washing it is diluted and dispersed to 0.001 to 0.005 wt% in an N-methylpyrrolidone solvent. Adjust the graphene dispersion. The graphene dispersion is dropped onto a highly smooth substrate such as a glass substrate, dried, and observed with an optical microscope or a laser microscope. On the other hand, when the conductive core particle is spherical graphite, the surface of the composite conductive particle itself is observed with a scanning electron microscope. The length of the longest part (major axis) and the length of the shortest part (minor axis) of the graphene pieces observed in this way are measured, and the numerical value obtained by (major axis + minor axis) / 2 is the surface direction of the graphene The size of The magnitude | size of the surface direction of the graphene in this invention shall point out the average value at the time of measuring 50 pieces of graphene pieces at random.
本発明に用いられるグラフェンの、Ｘ線光電子分光法で測定される官能基化率は、０．１５以上０．８０以下であることが好ましい。グラフェンの官能基化率は低いほど導電性は高くなるが、フレキシブル性や分散性は悪くなり、粒子に効率よく付着させることが難しくなる。逆に、官能基化率が高すぎると導電性が悪くなる。そのため、グラフェンの官能基化率は、０．１７以上であることが好ましく、０．２０以上であることがより好ましく、０．３０以上であることがさらに好ましい。また、０．６０以下であることが好ましく、０．４０以下で有ることがより好ましい。 The functionalization rate of the graphene used in the present invention, measured by X-ray photoelectron spectroscopy, is preferably 0.15 or more and 0.80 or less. The lower the functionalization rate of graphene, the higher the conductivity, but the flexibility and dispersibility deteriorate, making it difficult to adhere to the particles efficiently. On the other hand, when the functionalization rate is too high, the conductivity is deteriorated. Therefore, the functionalization rate of graphene is preferably 0.17 or more, more preferably 0.20 or more, and further preferably 0.30 or more. Moreover, it is preferable that it is 0.60 or less, and it is more preferable that it is 0.40 or less.
グラフェンの官能基化率は、Ｘ線光電子分光測定により求められる。Ｘ線光電子分光測定では、炭素を含有する試料を測定すると２８４ｅＶ付近に炭素に由来するピークが検出されるが、炭素が酸素に結合している場合は高エネルギー側にシフトすることが知られている。具体的には炭素が酸素に結合していないＣ−Ｃ結合、Ｃ＝Ｃ二重結合、Ｃ−Ｈ結合に基づくピークはシフトせずに２８４ｅＶ付近に検出され、Ｃ−Ｏ一重結合の場合２８６．５ｅＶ付近に、Ｃ＝Ｏ二重結合の場合２８７．５ｅＶ付近に、ＣＯＯ結合の場合２８８．５ｅＶ付近にシフトする。そのため、炭素に由来する信号は、２８４ｅＶ付近、２８６．５ｅＶ付近、２８７．５ｅＶ付近、２８８．５ｅＶ付近のそれぞれのピークを重ね合わせた形で検出される。この重ね合わせた形のピークをピークフィッティングにより各成分にピーク分離解析することにより、各々のピーク面積強度を算出することが可能である。グラファイト成分に基づき２８６ｅＶ付近と２９０．５ｅＶ付近にも信号が現われる。この信号はＣ−Ｃ、Ｃ＝Ｃ及びＣ−Ｈ結合に基づく成分としてフィッティングする。本発明における官能基化率は、
官能基化率＝［（Ｃ−Ｏ一重結合に基づくピーク面積）＋（Ｃ＝Ｏ二重結合に基づくピーク面積）＋（ＣＯＯ結合に基づくピーク面積）］／（Ｃ−Ｃ、Ｃ＝Ｃ及びＣ−Ｈ結合に基づくピーク面積）
で定義される数値である。
The functionalization rate of graphene is determined by X-ray photoelectron spectroscopy. In X-ray photoelectron spectroscopy, when a sample containing carbon is measured, a peak derived from carbon is detected in the vicinity of 284 eV, but it is known that when carbon is bonded to oxygen, it shifts to a higher energy side. Yes. Specifically, peaks based on C—C bonds, C═C double bonds, and C—H bonds in which carbon is not bonded to oxygen are detected in the vicinity of 284 eV without shifting, and in the case of C—O single bond 286 In the case of C = O double bond, it shifts to about 287.5 eV, and in the case of COO bond, it shifts to about 288.5 eV. Therefore, a signal derived from carbon is detected in a form in which respective peaks around 284 eV, 286.5 eV, 287.5 eV, and 288.5 eV are superimposed. It is possible to calculate the intensity of each peak area by performing peak separation analysis on each component by peak fitting of the superimposed peaks. Based on the graphite component, signals also appear in the vicinity of 286 eV and 290.5 eV. This signal is fitted as a component based on CC, C = C and CH bonds. The functionalization rate in the present invention is
Functionalization rate = [(peak area based on C—O single bond) + (C = peak area based on O double bond) + (peak area based on COO bond)] / (C—C, C = C and Peak area based on C—H bond)
It is a numerical value defined by.
導電性核粒子が金属粒子である場合は、グラフェン以外に炭素成分が存在しないため、複合導電性粒子を直接エックス線光電子分光測定することで容易にグラフェンの官能基化率を測定することが出来る。一方、導電性核粒子が球状黒鉛である場合は、複合導電性粒子のグラフェンと球状黒鉛を分離して測定する。分離するためには、複合導電性粒子をＮ−メチルピロリドン中に分散した後、強いせん断力を掛けてグラフェンの一部を導電性核粒子から剥離させた後、遠心分離機によって導電性核粒子を沈降させ、上澄みのグラフェンを乾燥する。そして、乾燥して得られたグラフェン粉末をエックス線光電子分光測定することで、グラフェンの官能基化率を測定することが出来る。 When the conductive core particle is a metal particle, there is no carbon component other than graphene. Therefore, the functional grouping ratio of graphene can be easily measured by directly measuring the composite conductive particle by X-ray photoelectron spectroscopy. On the other hand, when the conductive core particle is spherical graphite, the graphene and the spherical graphite of the composite conductive particle are separated and measured. To separate the composite conductive particles in N-methylpyrrolidone, a strong shear force is applied to separate a part of the graphene from the conductive core particles, and then the conductive core particles are separated by a centrifuge. And the supernatant graphene is dried. And the functionalization rate of graphene can be measured by measuring the graphene powder obtained by drying by X-ray photoelectron spectroscopy.
本発明において、グラフェンにより被覆される導電性粒子はグラフェンとの接着性を高めるために、表面に窒素原子を含む官能基を有することが好ましい。窒素原子を含む官能基はグラフェンとの親和性が高いため、窒素原子を含む官能基が存在することで導電性粒子とグラフェンとをより良好に接着することが可能になる。窒素原子を含む官能基の中でも、特にアミノ基がグラフェンとの親和性が高いため好ましい。 In the present invention, the conductive particles coated with graphene preferably have a functional group containing a nitrogen atom on the surface in order to enhance adhesion with graphene. Since the functional group containing a nitrogen atom has high affinity with graphene, the presence of the functional group containing a nitrogen atom makes it possible to bond the conductive particles and the graphene better. Among functional groups containing a nitrogen atom, an amino group is particularly preferable because of its high affinity with graphene.
導電性粒子の表面に窒素含有官能基を導入する方法は、特に限定されないが、例えば金属粒子の場合は、アミノ基とチオール基を持つ分子を金属−チオール間の結合を利用して金属粒子表面に結合させる手法が挙げられる。アミノ基とチオール基を持つ分子としては例として、２−アミノエタンチオール、３−アミノ−１プロパンチオール、４−アミノ−１−ブタンチオールなどが挙げられる。 The method for introducing a nitrogen-containing functional group into the surface of the conductive particle is not particularly limited. For example, in the case of a metal particle, a molecule having an amino group and a thiol group is bonded to the surface of the metal particle using a bond between metal and thiol. The method of combining with is mentioned. Examples of molecules having an amino group and a thiol group include 2-aminoethanethiol, 3-amino-1-propanethiol, 4-amino-1-butanethiol, and the like.
また、導電性粒子が黒鉛粒子の場合、黒鉛粒子の表面を強酸によりニトロ化して、その後還元によりニトロ基をアミノ基に変換する手法が挙げられる。強酸による黒鉛粒子のニトロ化の手法の例を挙げると、黒鉛粒子を、濃硝酸：濃硫酸＝１：３の体積比で混合した混酸により４０℃で３時間程度処理する手法が挙げられる。ニトロ基をアミノ基に変換するための還元剤に制限はないが、還元力の強い還元剤を用いることが有効で、例としては、無水ヒドラジン、亜ジチオン酸ナトリウムなどが挙げられる。 Further, in the case where the conductive particles are graphite particles, there is a method in which the surface of the graphite particles is nitrated with a strong acid, and then the nitro group is converted into an amino group by reduction. An example of a method for nitration of graphite particles with a strong acid is a method in which graphite particles are treated with a mixed acid mixed at a volume ratio of concentrated nitric acid: concentrated sulfuric acid = 1: 3 at 40 ° C. for about 3 hours. Although there is no restriction | limiting in the reducing agent for converting a nitro group into an amino group, It is effective to use a reducing agent with strong reducing power, for example, anhydrous hydrazine, sodium dithionite, etc. are mentioned.
グラフェンの被覆厚さに制限は無く、グラフェンが一層のみ被覆していても複数枚被覆していても良いが、グラフェン導電性よりも導電性核粒子の導電性が高い場合にはグラフェン被覆層は薄いほうが好ましい。被覆層の厚さは１０ｎｍ以下であることが好ましく、７ｎｍ以下であることがより好ましく、５ｎｍ以下であることがさらに好ましい。 There is no limitation on the thickness of the graphene coating, and the graphene coating may be a single layer or a plurality of layers, but if the conductivity of the conductive core particles is higher than the graphene conductivity, the graphene coating layer Thinner is preferable. The thickness of the coating layer is preferably 10 nm or less, more preferably 7 nm or less, and further preferably 5 nm or less.
導電性粒子の表面に窒素を含む官能基を有し、グラフェンが薄く（目安として、１０ｎｍ以下の厚みで）導電性粒子を被覆している場合、導電性粒子の表面の窒素原子を含む官能基はエックス線光電子分光法により検出することが可能である。この場合、複合導電性粒子のエックス線光電子分光測定による窒素比率は０．１％以上１％以下であることが好ましく、０．３％以上０．６％以下であることがさらに好ましい。 When the conductive particle has a functional group containing nitrogen on the surface of the conductive particle and the graphene is thin (with a thickness of 10 nm or less as a guide), the functional group containing a nitrogen atom on the surface of the conductive particle Can be detected by X-ray photoelectron spectroscopy. In this case, the nitrogen ratio of the composite conductive particles measured by X-ray photoelectron spectroscopy is preferably 0.1% or more and 1% or less, and more preferably 0.3% or more and 0.6% or less.
本発明の複合導電性粒子は、前述の導電性核粒子が前述のグラフェンに被覆されてなる粒子である。本発明において「被覆」とは、下記の手法で測定したグラフェン被覆率が０．３以上であることを意味する。 The composite conductive particle of the present invention is a particle obtained by coating the above-described conductive core particle with the above-mentioned graphene. In the present invention, “coating” means that the graphene coverage measured by the following method is 0.3 or more.
グラフェン被覆率は、複合導電性粒子表面の面積中における、グラフェンによって被覆されている面積の比率である。グラフェン被覆率は、導電性核粒子が金属粒子の場合は、走査型電子顕微鏡で複合導電性粒子表面を観察して得られた画像を解析することで求められる。金属粒子表面において、グラフェンが被覆している箇所と被覆していない箇所は、走査電子顕微鏡画像のコントラストから容易に判断することが出来るため、画像中の粒子表面の全面積のうち、グラフェンが被覆している部分の面積の割合から、被覆率を算出することが出来る。一方、導電性核粒子が球状黒鉛の場合は、ラマンマッピングにより測定することが可能である。炭素のラマン測定においては欠陥が多いほど結晶の乱れに起因するＤバンド（１３６０ｃｍ−１付近）のピークが大きくなり、欠陥が少ないほどＧバンド（１５８０ｃｍ−１付近）のピークが大きくなる。ここで、Ｄバンドのピーク強度をＩ１３６０とし、Ｇバンドのピーク強度をＩ１５８０とすると、黒鉛のＩ１３６０／Ｉ１５８０の値は０．５未満であり、酸化還元法で作製されるグラフェンの値は０．５以上であるため、複合導電性粒子表面の各箇所においてラマン測定を２次元的に行ってマッピングすることで、表面がどの程度グラフェンで覆われているかが分かる。本発明におけるグラフェン被覆率は、ランダムに５０個の複合導電性粒子についてグラフェン被覆率を測定した平均値を意味する。 The graphene coverage is the ratio of the area covered with graphene in the area of the composite conductive particle surface. When the conductive core particle is a metal particle, the graphene coverage is obtained by analyzing an image obtained by observing the surface of the composite conductive particle with a scanning electron microscope. On the metal particle surface, the graphene-coated part and the non-coated part can be easily judged from the contrast of the scanning electron microscope image, so the graphene covers the total area of the particle surface in the image. The coverage can be calculated from the ratio of the area of the portion that is being processed. On the other hand, when the conductive core particle is spherical graphite, it can be measured by Raman mapping. Peak increases of D band caused by the disorder of the crystal the more defects in Raman measurements of carbon (1360 cm around -1), a peak of G-band the smaller defects (1580 cm around -1) increases. Here, the peak intensity of D-band and I 1360, when the peak intensity of G-band and I 1580, the value of I 1360 / I 1580 of the graphite is less than 0.5, the graphene is prepared by oxidation-reduction method Since the value is 0.5 or more, it can be understood how much the surface is covered with graphene by performing two-dimensional Raman measurement and mapping at each location on the surface of the composite conductive particle. The graphene coverage in this invention means the average value which measured the graphene coverage about 50 composite electroconductive particles at random.
本発明の複合導電性粒子においては、グラフェン被覆率は０．５以上であることが好ましく、０．７以上であることがより好ましく、０．８以上であることがさらに好ましい。 In the composite conductive particles of the present invention, the graphene coverage is preferably 0.5 or more, more preferably 0.7 or more, and further preferably 0.8 or more.
本発明において、複合導電性粒子同士は凝集していないことが好ましい。凝集が少ないと、複合導電性粒子の凝集塊の径（凝集径）と複合導電性粒子の一次粒子径は近い値になり、凝集するほど凝集径は一次粒子径より大きくなる。すなわち、複合導電性粒子の凝集径は一次粒子径に近いほど好ましい。具体的には、凝集径に対する一次粒子径の比（凝集径／一次粒子径）は１．０以上１０．０以下であることが好ましく、１．０以上５．０以下であることがより好ましく、１．０以上３．０以下であることがさらに好ましく、１．０以上２．０以下であることが一層好ましい。凝集径はレーザー回折・散乱式粒径分布測定装置により測定することが可能である。レーザー回折・散乱式粒径分布測定装置としては、堀場製作所製ＬＡ−９２０などが例示される。本発明においては、湿式法で測定したときのＤ５０の値を複合導電性粒子の凝集径とする。なお、複合導電性粒子の一次粒子径は導電性核粒子の一次粒子径と同様の手法で電子顕微鏡により測定することが出来る。 In the present invention, the composite conductive particles are preferably not aggregated. When there is little aggregation, the diameter of the aggregate (aggregation diameter) of the composite conductive particles and the primary particle diameter of the composite conductive particles are close to each other. That is, the aggregated diameter of the composite conductive particles is preferably as close as possible to the primary particle diameter. Specifically, the ratio of the primary particle diameter to the aggregate diameter (aggregate diameter / primary particle diameter) is preferably 1.0 or more and 10.0 or less, and more preferably 1.0 or more and 5.0 or less. 1.0 or more and 3.0 or less is more preferable, and 1.0 or more and 2.0 or less is still more preferable. The agglomerated diameter can be measured by a laser diffraction / scattering type particle size distribution measuring apparatus. As a laser diffraction / scattering type particle size distribution measuring apparatus, LA-920 manufactured by Horiba, Ltd. is exemplified. In the present invention, the value of D50 when measured by a wet method is defined as the aggregate diameter of the composite conductive particles. The primary particle size of the composite conductive particles can be measured with an electron microscope in the same manner as the primary particle size of the conductive core particles.
複合導電性粒子の製造方法は特に限定されないが、溶剤中で導電性核粒子とグラフェンを混合してから乾燥する方法、導電性核粒子を酸化グラフェンで被覆した後、該酸化グラフェンを還元する方法が挙げられる。 The method for producing the composite conductive particles is not particularly limited, but is a method of drying after mixing the conductive core particles and graphene in a solvent, and a method of reducing the graphene oxide after coating the conductive core particles with graphene oxide Is mentioned.
導電性核粒子とグラフェンを溶剤中で混合する際に使用する溶剤としては、γブチロラクトン、ジメチルホルムアミド、ジメチルアセトアミド、Ｎ−メチルピロリドンなどが挙げられるが、中でもＮ−メチルピロリドンが適している。 Examples of the solvent used when mixing the conductive core particles and graphene in the solvent include γ-butyrolactone, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and the like. Among them, N-methylpyrrolidone is suitable.
導電性核粒子と酸化グラフェンを溶剤中で混合する際に使用する溶剤としては、酸化グラフェンと非常に親和性の良い水が適している。 As a solvent used when mixing the conductive core particles and graphene oxide in a solvent, water having a very good affinity with graphene oxide is suitable.
導電性核粒子と、グラフェン又は酸化グラフェンを溶剤中で混合する混合手法としては、マグネチックスターラー、メカニカルスターラー、遊星式ボールミル、ビーズミル、高速攪拌機、プラネタリーミキサー、フィルミックス（登録商標：プライミクス社）などが挙げられる。グラフェンを効率よく剥離させて導電性核粒子の表面に付着させるという点では高いせん断力が掛けられる攪拌機が適しており、特に周速５ｍ／ｓ以上で攪拌できる攪拌機がより適しているため、２０００ｒｐｍで攪拌が可能な高速攪拌機、あるいはフィルミックスが特に適している。 As a mixing method for mixing conductive core particles and graphene or graphene oxide in a solvent, a magnetic stirrer, mechanical stirrer, planetary ball mill, bead mill, high-speed stirrer, planetary mixer, Philmix (registered trademark: PRIMIX Corporation) Etc. A stirrer capable of applying a high shear force is suitable in terms of efficiently exfoliating the graphene and adhering to the surface of the conductive core particles, and particularly a stirrer capable of stirring at a peripheral speed of 5 m / s or more is more suitable. A high-speed stirrer or a fill mix that can be stirred at a high speed is particularly suitable.
攪拌により表面にグラフェンが十分付着した導電性核粒子分散液から溶剤を乾燥することにより、複合導電性粒子を得ることができる。また、同様に撹拌により表面に酸化グラフェンが十分付着した導電性核粒子分散液から溶剤を乾燥することにより、複合導電性粒子前駆体を得ることができる。乾燥する手法は限定されないが、ガラス基板などの平滑な基盤に塗布しホットプレートで乾燥する手法、ロータリーエバポレータにより乾燥する手法、スプレードライ、凍結乾燥などが挙げられるが、偏析が少ない状態で乾燥できる点で、スプレードライ、凍結乾燥が好ましい。 The composite conductive particles can be obtained by drying the solvent from the conductive core particle dispersion liquid in which graphene is sufficiently adhered to the surface by stirring. Similarly, a composite conductive particle precursor can be obtained by drying the solvent from the conductive core particle dispersion liquid in which graphene oxide is sufficiently adhered to the surface by stirring. Although the drying method is not limited, it can be applied to a smooth substrate such as a glass substrate and dried with a hot plate, dried with a rotary evaporator, spray dried, freeze dried, etc., but can be dried with little segregation. In this respect, spray drying and freeze drying are preferable.
酸化グラフェンと導電性核粒子を混合してから酸化グラフェンを還元する場合の還元手法は特に限定されないが、水素化ホウ素ナトリウム（ＮａＢＨ４）やヒドラジン（Ｎ２Ｈ４）などの還元剤による化学還元、レーザー光・フラッシュ光・紫外線・マイクロ波などの光源や電磁波を酸化グラフェンに吸収させた際に発生する熱により還元する光誘起熱還元、オーブンなどによる加熱還元などが挙げられる。熱による還元の場合、還元反応の際に酸化グラフェンから二酸化炭素が脱離するため、グラフェン構造から炭素が抜けて導電性が低くなる傾向がある。一方、化学還元による還元では熱による還元よりもグラフェン構造が壊れにくいため、還元手法としては化学還元の方が好ましい。 The reduction method for reducing graphene oxide after mixing graphene oxide and conductive core particles is not particularly limited, but chemical reduction with a reducing agent such as sodium borohydride (NaBH 4 ) or hydrazine (N 2 H 4 ) Examples of the light source include laser light, flash light, ultraviolet light, and microwaves, and light-induced thermal reduction that is reduced by heat generated when graphene oxide is absorbed by graphene oxide, and heat reduction using an oven. In the case of reduction by heat, carbon dioxide is desorbed from the graphene oxide during the reduction reaction, so that carbon tends to be released from the graphene structure and the conductivity tends to be low. On the other hand, in the reduction by chemical reduction, the graphene structure is less likely to be broken than in the reduction by heat. Therefore, the chemical reduction is preferable as the reduction method.
化学還元の還元剤としては、有機還元剤、無機還元剤が挙げられる。有機還元剤としてはアルデヒド系還元剤、ヒドラジン誘導体還元剤、アルコール系還元剤が挙げられ、中でもアルコール系還元剤は比較的穏やかに還元することができるため、特に好適である。アルコール系還元剤としては、メタノール、エタノール、プロパノール、イソプロピルアルコール、ブタノール、ベンジルアルコール、フェノール、エタノールアミン、エチレングリコール、プロピレングリコール、ジエチレングリコール、などが挙げられる。無機還元剤としては亜ジチオン酸ナトリウム、亜ジチオン酸カリウム、亜リン酸、水素化ホウ素ナトリウム、ヒドラジンなどが挙げられる。還元後の洗浄の容易さからは無機還元剤を用いる方が好ましく、中でも亜ジチオン酸ナトリウム、亜ジチオン酸カリウムは、官能基を比較的保持しながら還元できるので、好適である。 Examples of the chemical reducing agent include organic reducing agents and inorganic reducing agents. Examples of the organic reducing agent include aldehyde-based reducing agents, hydrazine derivative reducing agents, and alcohol-based reducing agents. Among them, alcohol-based reducing agents are particularly suitable because they can be reduced relatively gently. Examples of the alcohol-based reducing agent include methanol, ethanol, propanol, isopropyl alcohol, butanol, benzyl alcohol, phenol, ethanolamine, ethylene glycol, propylene glycol, diethylene glycol, and the like. Examples of the inorganic reducing agent include sodium dithionite, potassium dithionite, phosphorous acid, sodium borohydride, hydrazine and the like. In view of ease of washing after the reduction, it is preferable to use an inorganic reducing agent. Among them, sodium dithionite and potassium dithionite are preferable because they can be reduced while relatively retaining functional groups.
化学還元をする際には、被覆した酸化グラフェンが導電性核粒子から遊離する前に還元できることが好ましいため、予め溶剤中に還元剤を溶解し、還元反応に適した温度にした状態で、酸化グラフェンと導電性核粒子の複合体を投入することが好ましい。 When performing chemical reduction, it is preferable that the coated graphene oxide can be reduced before it is released from the conductive core particles. Therefore, the reducing agent is dissolved in a solvent in advance and the oxidation is performed at a temperature suitable for the reduction reaction. It is preferable to introduce a composite of graphene and conductive core particles.
還元が終わった後は、濾過・遠心分離を繰り返すことで洗浄し、乾燥することで、複合導電性粒子を得ることが出来る。 After the reduction, the composite conductive particles can be obtained by washing and drying by repeating filtration and centrifugation, and drying.
＜導電性樹脂＞
本発明の複合導電性粒子を含む樹脂は、導電性樹脂として有用である。複合導電性粒子を樹脂中に含ませる手法に制限は無いが、熱可塑性樹脂と複合導電性粒子を二軸混練器などで加熱しながら混練し冷却する方法、溶剤中に樹脂と複合導電性粒子を混合させた後に溶剤を除去する方法、エポキシ樹脂などの熱硬化性樹脂を硬化前に複合導電性粒子と混合してから硬化する方法、などが挙げられる。
<Conductive resin>
The resin containing the composite conductive particles of the present invention is useful as a conductive resin. There is no limitation on the method of including the composite conductive particles in the resin, but a method of kneading and cooling the thermoplastic resin and the composite conductive particles while heating with a biaxial kneader or the like, the resin and the composite conductive particles in a solvent And a method of removing the solvent after mixing, a method of curing a thermosetting resin such as an epoxy resin with the composite conductive particles before curing, and the like.
導電性樹脂に用いられる熱可塑性樹脂としては、ポリアミド系樹脂、ポリエチレン・ポリプロピレンなどのポリオレフィン系樹脂、ポリビニル系樹脂、ＡＢＳ樹脂、アクリル樹脂、メタクリル樹脂、ポリカーボネート、ポリスチレン、ポリエチレンテレフタレート、ポリブチレンテレフタレート、ポリフェニレンエーテル、ポリフェニレンスルフィド、ポリエーテルエーテルケトン、ポリアリルエーテルケトン、ウレタン樹脂、ポリビニルピロリドン、ポリビニルブチラール、ポリフッ化ビニリデンなどが挙げられる。 The thermoplastic resin used for the conductive resin includes polyamide resin, polyolefin resin such as polyethylene / polypropylene, polyvinyl resin, ABS resin, acrylic resin, methacrylic resin, polycarbonate, polystyrene, polyethylene terephthalate, polybutylene terephthalate, polyphenylene. Examples include ether, polyphenylene sulfide, polyether ether ketone, polyallyl ether ketone, urethane resin, polyvinyl pyrrolidone, polyvinyl butyral, and polyvinylidene fluoride.
また、熱硬化性樹脂としては、エポキシ樹脂、メラミン樹脂、ポリエステル樹脂、フェノール樹脂、天然ゴムや合成ゴムなどのエラストマーなどが挙げられる。 Examples of the thermosetting resin include epoxy resins, melamine resins, polyester resins, phenol resins, and elastomers such as natural rubber and synthetic rubber.
これらの中でも、エポキシ樹脂を用いることが好適である。エポキシ樹脂としては、ビスフェノールＡ型エポキシ樹脂、ビスフェノールＦ型エポキシ樹脂、ノボラック型エポキシ樹脂などが挙げられる。 Among these, it is preferable to use an epoxy resin. Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, and novolac type epoxy resin.
樹脂と複合導電性粒子の混合のために使用する溶剤としては、樹脂を溶解可能であり、真空乾燥などで容易に除去できれば特に制限されないが、グラフェンと親和性が良く、揮発しやすいＮ−メチルピロリドンが好適に用いられる。 The solvent used for mixing the resin and the composite conductive particles is not particularly limited as long as the resin can be dissolved and can be easily removed by vacuum drying or the like. However, N-methyl has good affinity with graphene and easily volatilizes. Pyrrolidone is preferably used.
〔測定例１：グラフェン（または酸化グラフェン）の面方向の大きさ〕
グラフェンの場合、溶剤としてＮ−メチルピロリドンを用いて０．００２ｗｔ％にまで希釈し、ガラス基板上に滴下・乾燥した。キーエンス社製レーザー顕微鏡ＶＫ−Ｘ２５０で基板上に付着したグラフェンを観察して、グラフェン小片の最も長い部分の長さ（長径）と最も短い部分の長さ（短径）をランダムに５０個測定し、（長径＋短径）／２で求められる数値の５０個分の平均値をグラフェン面方向の大きさとした。
[Measurement Example 1: Size of graphene (or graphene oxide) in the plane direction]
In the case of graphene, it was diluted to 0.002 wt% using N-methylpyrrolidone as a solvent, and dropped and dried on a glass substrate. The graphene adhering to the substrate is observed with a laser microscope VK-X250 manufactured by Keyence Corporation, and the length of the longest part (major axis) and the length of the shortest part (minor axis) of the graphene pieces are randomly measured. The average value of 50 numerical values obtained by (major axis + minor axis) / 2 was defined as the size in the graphene surface direction.
また、酸化グラフェンの場合は、溶剤としてＮ−メチルピロリドンに替えて水を用いる以外は同様にして、面方向の大きさを測定した。 In the case of graphene oxide, the size in the plane direction was measured in the same manner except that water was used instead of N-methylpyrrolidone as a solvent.
〔測定例２：グラフェン（または酸化グラフェン）の厚み〕
グラフェンの場合、溶剤としてＮ−メチルピロリドンを用いて、また、酸化グラフェンの場合、溶剤として水を用いて、０．００２ｗｔ％にまで希釈し、ガラス基板上に滴下・乾燥した。基板上のグラフェン又は酸化グラフェンを、原子間力顕微鏡（Ｄｉｍｅｎｓｉｏｎ Ｉｃｏｎ、Ｂｒｕｋｅｒ社）で観察して、グラフェン又は酸化グラフェンの厚みを測定した。一小片で厚みにバラつきがあった場合は面積平均を求めた。このように、ランダムに５０個のグラフェン小片または酸化グラフェン小片の厚みを測定し、平均値を求めた。
[Measurement Example 2: Graphene (or graphene oxide) thickness]
In the case of graphene, N-methylpyrrolidone was used as a solvent, and in the case of graphene oxide, water was used as a solvent, diluted to 0.002 wt%, and dropped onto a glass substrate and dried. Graphene or graphene oxide on the substrate was observed with an atomic force microscope (Dimension Icon, Bruker), and the thickness of graphene or graphene oxide was measured. When there was variation in the thickness of one small piece, the area average was determined. Thus, the thickness of 50 graphene pieces or graphene oxide pieces was measured randomly, and the average value was obtained.
〔測定例３：導電性核粒子および複合導電性粒子の平均一次粒子径および円形度〕
導電性核粒子および複合導電性粒子の平均一次粒子径は、走査型電子顕微鏡（日立ハイテク、Ｓ−５５００）を用いて測定した。導電性核粒子または複合導電性粒子の粉末を、カーボンテープに付着させて、粒子が観察しやすいように３００倍〜３０００倍の範囲で適宜調節して粒子の大きさを観察した。各粒子の最も長い部分の長さ（長径）と最も短い部分の長さ（短径）を測定し、（長径＋短径）／２で求められる数値を一次粒子径とした。このように、視野を変えながらランダムに５０個の粒子の一次粒子径を測定し、平均値を求めた。
[Measurement Example 3: Average primary particle diameter and circularity of conductive core particles and composite conductive particles]
The average primary particle diameter of the conductive core particles and the composite conductive particles was measured using a scanning electron microscope (Hitachi High-Tech, S-5500). The powder of the conductive core particles or composite conductive particles was adhered to the carbon tape, and the size of the particles was observed by adjusting appropriately within a range of 300 times to 3000 times so that the particles could be easily observed. The length (major axis) of the longest part and the length (minor axis) of the shortest part of each particle were measured, and the numerical value obtained by (major axis + minor axis) / 2 was defined as the primary particle diameter. Thus, the primary particle diameter of 50 particles was randomly measured while changing the field of view, and the average value was obtained.
円形度は、上記と同様に走査型電子顕微鏡で粒子を観察し、短径／長径の比を算出した。このように、ランダムに５０個の粒子の円形度を測定し、平均値を求めた。 As for the circularity, particles were observed with a scanning electron microscope in the same manner as described above, and the ratio of minor axis / major axis was calculated. Thus, the circularity of 50 particles was measured at random and the average value was obtained.
〔測定例４：複合導電性粒子のグラフェン被覆率〕
炭素の質量割合の測定は、炭素・硫黄同時定量分析装置（堀場製作所製 ＥＭＩＡ−９２０Ｖ）を用いて測定した。
[Measurement Example 4: Graphene coverage of composite conductive particles]
The mass ratio of carbon was measured using a carbon / sulfur simultaneous quantitative analyzer (EMIA-920V manufactured by Horiba, Ltd.).
〔測定例５：複合導電性粒子の凝集径〕
複合導電性粒子の凝集径は、レーザー回折・散乱測定装置（堀場製作所製ＬＡ−９２０）を用いて測定した。測定は湿式で水中に流通させながら測定し、Ｄ５０の値を凝集径とした。
[Measurement Example 5: Agglomerated diameter of composite conductive particles]
The aggregate diameter of the composite conductive particles was measured using a laser diffraction / scattering measuring device (LA-920 manufactured by Horiba, Ltd.). The measurement was performed while being wet-circulated in water, and the value of D50 was defined as the aggregate diameter.
〔測定例６：複合導電性粒子の炭素比率〕
複合導電性粒子の導電性核粒子が黒鉛以外の場合、炭素比率は、炭素・硫黄同時定量分析装置（堀場製作所製 ＥＭＩＡ−９２０Ｖ）を用いて測定した。
[Measurement Example 6: Carbon ratio of composite conductive particles]
When the conductive core particles of the composite conductive particles are other than graphite, the carbon ratio was measured using a carbon / sulfur simultaneous quantitative analyzer (EMIA-920V manufactured by Horiba, Ltd.).
〔測定例７：グラフェンの官能基化率〕
グラフェンのＸ線光電子測定には、Ｑｕａｎｔｅｒａ ＳＸＭ （登録商標：ＰＨＩ 社製）を使用した。励起Ｘ線は、ｍｏｎｏｃｈｒｏｍａｔｉｃ Ａｌ Ｋα１、２ 線（１４８６．６ ｅＶ）であり、Ｘ線径は２００μｍ、光電子脱出角度は４５°である。
[Measurement Example 7: Functionalization rate of graphene]
For the X-ray photoelectron measurement of graphene, Quantera SXM (registered trademark: manufactured by PHI) was used. Excited X-rays are monochromatic Al Kα1,2 rays (1486.6 eV), the X-ray diameter is 200 μm, and the photoemission angle is 45 °.
炭素原子に基づくピークを、Ｃ＝Ｃ結合、Ｃ−Ｈ結合に基づく２８４ｅＶ付近のピーク、Ｃ−Ｏ結合の場合に基づく２８６ｅＶ付近のピーク、Ｃ＝Ｏ結合に基づく２８７．５ｅＶ付近のピーク、ＣＯＯ結合に基づく２８８．５ｅＶ付近のピーク、の４つの成分にピーク分離し各ピークの面積比から官能基化率を求めた。 導電性核粒子が金属粒子である場合、複合導電性粒子を直接測定した。 Peaks based on carbon atoms are C = C bond, peak near 284 eV based on C—H bond, peak near 286 eV based on C—O bond, peak near 287.5 eV based on C═O bond, COO The peak was separated into four components of a peak near 288.5 eV based on the bond, and the functionalization rate was determined from the area ratio of each peak. When the conductive core particles were metal particles, the composite conductive particles were directly measured.
導電性核粒子が球状黒鉛である場合、複合導電性粒子をＮ−メチルピロリドン中に分散した後、フィルミックス（プライミクス社、３０−Ｌ型）を用いて周速３０ｍ／ｓで１分間処理し、グラフェンの一部を剥離させた後、遠心分離機で１００００ｇ５分間の条件で、導電性核粒子を沈降させ、上澄みのグラフェンを８０℃２時間真空乾燥することによりグラフェン粉末を得て、このグラフェン粉末を、エックス線光電子分光測定した。 When the conductive core particles are spherical graphite, the composite conductive particles are dispersed in N-methylpyrrolidone, and then treated for 1 minute at a peripheral speed of 30 m / s using a film mix (Primics Co., Ltd., 30-L type). The graphene powder was obtained by exfoliating a part of the graphene and then precipitating the conductive core particles in a centrifuge at 10,000 g for 5 minutes and vacuum drying the supernatant graphene for 2 hours at 80 ° C. The powder was measured by X-ray photoelectron spectroscopy.
〔測定例８：導電性樹脂の抵抗率測定〕
エポキシ樹脂Ｑｕｅｔｏｌ−８１２（日新ＥＭ社）１００ｍｌと、硬化剤ＭＮＡ（日新ＥＭ社）８９ｍｌと、促進剤ＤＭＰ−３０（日新ＥＭ社）３ｍｌとを混合した液を調製した。上記混合液と、本発明の複合導電性粒子（あるいは、一部の比較例ではグラフェン被覆前の導電性核粒子）を１ｇ：１ｇで混合したあと、４０℃で４８時間硬化させ、直径１３ｍｍ、高さ０．５ｍｍのペレットに成型し、ペレットの抵抗率を４端針型抵抗率計で抵抗率を測定した。
[Measurement Example 8: Measurement of resistivity of conductive resin]
A liquid was prepared by mixing 100 ml of epoxy resin Quetol-812 (Nisshin EM), 89 ml of curing agent MNA (Nisshin EM) and 3 ml of accelerator DMP-30 (Nisshin EM). The above mixed liquid and the composite conductive particles of the present invention (or conductive core particles before graphene coating in some comparative examples) were mixed at 1 g: 1 g, and then cured at 40 ° C. for 48 hours to obtain a diameter of 13 mm. The pellet was molded into a pellet having a height of 0.5 mm, and the resistivity of the pellet was measured with a four-end needle type resistivity meter.
〔測定例９：複合導電性粒子の表面窒素比率〕
複合導電性粒子の表面窒素比率は、エックス線光電子分光装置で測定した。エックス線光電子測定は、Ｑｕａｎｔｅｒａ ＳＸＭ （ＰＨＩ 社製）を使用して測定した。励起Ｘ線は、ｍｏｎｏｃｈｒｏｍａｔｉｃ Ａｌ Ｋα１，２ 線（１４８６．６ ｅＶ）であり、Ｘ線径は２００μｍ、光電子脱出角度は４５°であった。導電性被覆粒子の窒素原子割合は、ワイドスキャンの窒素原子のピーク面積と他元素のピーク面積から各元素の元素比率を求め、全体に対する窒素割合を求めた。
[Measurement Example 9: Surface Nitrogen Ratio of Composite Conductive Particles]
The surface nitrogen ratio of the composite conductive particles was measured with an X-ray photoelectron spectrometer. X-ray photoelectron measurement was performed using Quantera SXM (manufactured by PHI). Excited X-rays were monochromatic Al Kα1,2 rays (1486.6 eV), the X-ray diameter was 200 μm, and the photoelectron escape angle was 45 °. As for the nitrogen atom ratio of the conductive coated particles, the element ratio of each element was determined from the peak area of nitrogen atoms in a wide scan and the peak area of other elements, and the nitrogen ratio relative to the whole was determined.
〔合成例１：酸化グラフェンの合成〕
１５００メッシュの天然黒鉛粉末（上海一帆石墨有限会社）を原料として、氷浴中の黒鉛（石墨粉）１５ｇと硝酸ナトリウム７．５ｇを９８％濃硫酸３３０ｍｌ中に入れて攪拌しながら、過マンガン酸カリウム４５ｇを温度が１０℃以下になるように徐々に添加し、添加終了後１．５時間攪拌した後、３５℃で２．５時間攪拌する。その後イオン交換水を６９０ｍｌ加えて希釈して懸濁液とし、９０℃で１５分間反応する。最後に過酸化水素水５０ｍｌと脱イオン水１０２０ｍｌを加え３０分間反応して、酸化グラフェン分散液を得る。得られた酸化グラフェン分散液を、ｐＨ５になるまで濾過洗浄した。この酸化グラフェンの面方向の大きさは６．２μｍであり、厚みは９．８ｎｍであった。
[Synthesis Example 1: Synthesis of graphene oxide]
Using 1500-mesh natural graphite powder (Shanghai Isho Graphite Co., Ltd.) as a raw material, 15 g of graphite (graphite powder) and 7.5 g of sodium nitrate in an ice bath are placed in 330 ml of 98% concentrated sulfuric acid and stirred. 45 g of potassium acid is gradually added so that the temperature becomes 10 ° C. or less, and stirred for 1.5 hours after the addition is completed, and then stirred at 35 ° C. for 2.5 hours. Thereafter, 690 ml of ion-exchanged water is added to dilute to form a suspension and react at 90 ° C. for 15 minutes. Finally, 50 ml of hydrogen peroxide and 1020 ml of deionized water are added and reacted for 30 minutes to obtain a graphene oxide dispersion. The obtained graphene oxide dispersion was filtered and washed until pH 5 was reached. The size of the graphene oxide in the plane direction was 6.2 μm, and the thickness was 9.8 nm.
〔合成例２：酸化グラフェンの合成〕
合成例１で調製した酸化グラフェン分散液から０．５％酸化グラフェン分散液１００ｍｌを調整し、超音波ホモジェナイザーにより出力２００Ｗで１時間処理した。この酸化グラフェンの面方向の大きさは、１．４μｍであり、厚みは７．２ｎｍであった。
[Synthesis Example 2: Synthesis of graphene oxide]
From the graphene oxide dispersion prepared in Synthesis Example 1, 100 ml of 0.5% graphene oxide dispersion was prepared and treated with an ultrasonic homogenizer at an output of 200 W for 1 hour. The graphene oxide had a plane direction size of 1.4 μm and a thickness of 7.2 nm.
〔合成例３：球状黒鉛の調製〕
市販の黒鉛ＳＧ−ＢＬ４０（伊藤黒鉛社）を、造粒装置であるハイブリダイゼーションシステム（奈良機械製作所）で８０ｍ／ｓで３０分間処理した。黒鉛の平均粒径は４０ｕｍ、円形度は０．９１であった。
[Synthesis Example 3: Preparation of Spherical Graphite]
Commercially available graphite SG-BL40 (Ito Graphite Co., Ltd.) was treated at 80 m / s for 30 minutes with a hybridization system (Nara Machinery Co., Ltd.) which is a granulator. The average particle diameter of graphite was 40 um, and the circularity was 0.91.
［実施例１］
市販のニッケル粉末（Ａｌｆａ ａｅｓｅｒ社、４００メッシュ、球形粉末）を導電性核粒子として使用した。このニッケル粉末の平均一次粒子径は４５μｍ、円形度は０．８６であった。
[Example 1]
Commercially available nickel powder (Alfa aeser, 400 mesh, spherical powder) was used as the conductive core particles. This nickel powder had an average primary particle size of 45 μm and a circularity of 0.86.
合成例１で作製した酸化グラフェン水分散液を希釈して０．５％酸化グラフェン水分散液を調整した。酸化グラフェン水分散液とニッケル粉末の重量比を４．５：１００となるように、高速攪拌機（プライミクス社、ホモミクサーＭａｒｋ２．５）で攪拌した。高速攪拌機の攪拌羽の周長は９ｃｍで、８４００ｒｐｍで処理した。このときの攪拌羽の周速は１２．６ｍ／ｓである。得られた分散液を凍結乾燥により乾燥して酸化グラフェンで被覆された導電性核粒子を得た。亜ジチオン酸ナトリウムを４０℃の水に溶解させた直後に該粒子を投入し、３０分間攪拌して酸化グラフェンを還元した。得られた粒子を濾過した後、水中に再分散・濾過を３回繰り返して洗浄した後に真空乾燥し、ニッケルからなる核粒子がグラフェンに被覆されてなる複合導電性粒子を得た。 The graphene oxide aqueous dispersion prepared in Synthesis Example 1 was diluted to prepare a 0.5% graphene oxide aqueous dispersion. It stirred with the high-speed stirrer (Primics Co., homomixer Mark2.5) so that the weight ratio of a graphene oxide aqueous dispersion and nickel powder might be set to 4.5: 100. The circumference of the stirring blade of the high-speed stirrer was 9 cm, and the treatment was performed at 8400 rpm. The peripheral speed of the stirring blade at this time is 12.6 m / s. The obtained dispersion was dried by lyophilization to obtain conductive core particles coated with graphene oxide. Immediately after sodium dithionite was dissolved in water at 40 ° C., the particles were added and stirred for 30 minutes to reduce graphene oxide. The obtained particles were filtered, washed by repeating redispersion and filtration three times in water, and then vacuum-dried to obtain composite conductive particles in which core particles made of nickel were coated with graphene.
複合導電性粒子中に含まれる炭素比率を測定したところ、３．０％であった。複合導電性粒子表面のグラフェンの官能基化率を測定したところ、０．２５であった。複合導電性粒子中の導電性粒子の一次平均粒子径を測定したところ、４５μｍであった。グラフェン被覆率を測定したところ、０．７５であった。凝集径を測定したところ、６３μｍであった。また、測定例８に従って導電性樹脂とした場合の抵抗率を測定したところ、３．６Ω・ｃｍであった。 The ratio of carbon contained in the composite conductive particles was measured and found to be 3.0%. The functionalization rate of graphene on the surface of the composite conductive particle was measured and found to be 0.25. The primary average particle diameter of the conductive particles in the composite conductive particles was measured and found to be 45 μm. The graphene coverage was measured and found to be 0.75. The aggregation diameter was measured and found to be 63 μm. Moreover, when the resistivity in the case of using a conductive resin according to Measurement Example 8 was measured, it was 3.6 Ω · cm.
［実施例２］
市販のニッケル粉末（Ａｌｆａ ａｅｓｅｒ社、４００メッシュ、鱗片状粉末）を導電性核粒子として使用した。このニッケル粉末の平均一次径は４０μｍ、円形度は０．５９であった。このニッケル粉末を用いて実施例１と同様に複合導電性粒子を作製し、各種評価を行った。
[Example 2]
Commercially available nickel powder (Alfa aeser, 400 mesh, scaly powder) was used as the conductive core particles. This nickel powder had an average primary diameter of 40 μm and a circularity of 0.59. Using this nickel powder, composite conductive particles were produced in the same manner as in Example 1, and various evaluations were performed.
［実施例３］
複合導電性粒子作製時の酸化グラフェン水分散液とニッケル粉末の重量比を７．５：１００とした以外は実施例１と同様に複合導電性粒子を作製し、各種評価を行った。
[Example 3]
Composite conductive particles were prepared in the same manner as in Example 1 except that the weight ratio of the graphene oxide aqueous dispersion and the nickel powder at the time of preparing the composite conductive particles was 7.5: 100, and various evaluations were performed.
［実施例４］
市販のニッケル粉末（Ａｌｆａ ａｅｓｅｒ社、８００メッシュ、球形）を導電性粒子として使用した。このニッケル粉末の平均一次径は２０μｍ、円形度は０．８８であった。このニッケル粉末を用いて実施例１と同様に複合導電性粒子を作製し、各種評価を行った。
[Example 4]
Commercially available nickel powder (Alfa aeser, 800 mesh, spherical) was used as the conductive particles. This nickel powder had an average primary diameter of 20 μm and a circularity of 0.88. Using this nickel powder, composite conductive particles were produced in the same manner as in Example 1, and various evaluations were performed.
［実施例５］
グラフェンとして合成例２で作製したグラフェンを用いた以外は実施例４と同様にして複合導電性粒子を作製し、各種評価を行った。
[Example 5]
Composite conductive particles were prepared in the same manner as in Example 4 except that the graphene prepared in Synthesis Example 2 was used as graphene, and various evaluations were performed.
［実施例６］
導電性核粒子として合成例３で作製した球状黒鉛を用いた以外は実施例１と同様に複合導電性粒子を作製し、各種評価を行った。ただし導電性核粒子が黒鉛であるため、炭素比率は測定していない。
[Example 6]
Composite conductive particles were prepared in the same manner as in Example 1 except that the spherical graphite prepared in Synthesis Example 3 was used as the conductive core particles, and various evaluations were performed. However, since the conductive core particles are graphite, the carbon ratio is not measured.
［実施例７］
合成例３で作製した球状黒鉛３ｇを、濃硝酸と濃硫酸を体積比１：３で混合した混酸５０ｍｌ中、マグネチックスターラーで４０℃３時間攪拌した。ろ過洗浄後、水１００ｍｌに４０℃に加熱しながらマグネチックスターラーで攪拌分散し、３ｇの亜ジチオン酸ナトリウムを添加して、表面をアミノ化した球状黒鉛を得た。
[Example 7]
3 g of the spherical graphite produced in Synthesis Example 3 was stirred with a magnetic stirrer at 40 ° C. for 3 hours in 50 ml of mixed acid in which concentrated nitric acid and concentrated sulfuric acid were mixed at a volume ratio of 1: 3. After filtration and washing, the mixture was stirred and dispersed in 100 ml of water while heating at 40 ° C. with a magnetic stirrer, and 3 g of sodium dithionite was added to obtain spherical graphite having an aminated surface.
この表面をアミノ化した球状黒鉛導電性核粒子として用いた以外は、実施例１と同様に複合導電性粒子を作製し、各種評価を行った。ただし導電性核粒子が黒鉛であるため、炭素比率は測定していない。 Composite conductive particles were prepared in the same manner as in Example 1 except that this surface was used as spherical graphite conductive core particles aminated, and various evaluations were performed. However, since the conductive core particles are graphite, the carbon ratio is not measured.
［比較例１］
市販のニッケル粉末（高純度化学社、粒径３−５μｍ）を導電性粒子として使用した。このニッケル粉末の平均一次径は５．６μｍ、円形度は０．９１であった。このニッケル粉末を用いて実施例１と同様に複合導電性粒子を作製した。
[Comparative Example 1]
Commercially available nickel powder (high purity chemical company, particle size 3-5 μm) was used as the conductive particles. This nickel powder had an average primary diameter of 5.6 μm and a circularity of 0.91. Using this nickel powder, composite conductive particles were produced in the same manner as in Example 1.
［比較例２］
実施例１に用いたニッケル粉末をグラフェン被覆せずに樹脂混練し、測定例８に従って導電性樹脂の抵抗率を測定したところ、１５００Ω・ｃｍであった。
[Comparative Example 2]
The nickel powder used in Example 1 was kneaded with resin without being coated with graphene, and the resistivity of the conductive resin was measured according to Measurement Example 8. The result was 1500 Ω · cm.
［比較例３］
実施例４に用いたニッケル粉末をグラフェン被覆せずに樹脂混練し、測定例８に従って導電性樹脂の抵抗率を測定したところ、１７００Ω・ｃｍであった
［比較例４］
実施例６に用いた球状黒鉛をグラフェン被覆せずに樹脂混練し、測定例８に従って導電性樹脂の抵抗率を測定したところ、２４００Ω・ｃｍであった。
[Comparative Example 3]
The nickel powder used in Example 4 was kneaded with resin without being coated with graphene, and the resistivity of the conductive resin was measured according to Measurement Example 8. The result was 1700 Ω · cm [Comparative Example 4]
The spherical graphite used in Example 6 was kneaded with resin without being coated with graphene, and the resistivity of the conductive resin was measured according to Measurement Example 8. The result was 2400 Ω · cm.
各実施例、比較例における複合導電性粒子における炭素比率、平均粒子径（一次粒子径）、凝集径、凝集径／一次粒子径およびグラフェン被覆率、ならびに樹脂混練した際の樹脂の抵抗率を表１に示す。 The carbon ratio, average particle diameter (primary particle diameter), aggregate diameter, aggregate diameter / primary particle diameter and graphene coverage in the composite conductive particles in each example and comparative example, and the resistivity of the resin when the resin is kneaded are shown. It is shown in 1.
Claims (12)
The method for producing composite conductive particles according to claim 11, further comprising a step of introducing a nitrogen-containing functional group into the conductive core particles before coating the conductive core particles with graphene oxide.
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