JP5554656B2 - Method for producing ultrafine carbon fiber cotton - Google Patents
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- JP5554656B2 JP5554656B2 JP2010176199A JP2010176199A JP5554656B2 JP 5554656 B2 JP5554656 B2 JP 5554656B2 JP 2010176199 A JP2010176199 A JP 2010176199A JP 2010176199 A JP2010176199 A JP 2010176199A JP 5554656 B2 JP5554656 B2 JP 5554656B2
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- 229920000049 Carbon (fiber) Polymers 0.000 title claims description 71
- 239000004917 carbon fiber Substances 0.000 title claims description 71
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims description 55
- 238000004519 manufacturing process Methods 0.000 title claims description 27
- 229920000742 Cotton Polymers 0.000 title description 5
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Description
本発明は極細炭素繊維綿状体の製造方法に関する。更に詳しくは、電池電極材料、電池電極添加材、および樹脂添加材などとして有用な極細炭素繊維綿状体の製造方法に関する。 The present invention relates to a method for producing an ultrafine carbon fiber cotton-like body. More specifically, the present invention relates to a method for producing an ultrafine carbon fiber cotton useful as a battery electrode material, a battery electrode additive, a resin additive and the like.
極細炭素繊維は高強度、高弾性率、高導電性、高熱伝導性、軽量等の優れた特性を有している事から、高性能複合材料のフィラーとして使用されている。その用途は、従来からの機械的強度向上を目的とした補強用フィラーに留まらず、炭素材料に備わった高導電性を生かし、電磁波シールド材、静電防止材用の導電性樹脂フィラーとして、あるいは樹脂への静電塗料のためのフィラーとしての用途が期待されている。また炭素材料としての化学的安定性、熱的安定性と微細構造との特徴を生かし、フラットディスプレー等の電界電子放出材料としての用途も期待されている。また高熱伝導性を有していることから、蓄熱放射材としての用途も期待されている。
このような、高性能複合材料用としての極細炭素繊維の製造法として、気相法、および樹脂組成物の溶融紡糸から製造する方法の２つが報告されている。
Extra fine carbon fiber has excellent properties such as high strength, high elastic modulus, high conductivity, high thermal conductivity, and light weight, and is therefore used as a filler for high performance composite materials. Its application is not limited to conventional fillers for the purpose of improving mechanical strength, but by taking advantage of the high conductivity of carbon materials, as an electromagnetic shielding material, a conductive resin filler for antistatic materials, or Use as a filler for electrostatic coatings on resins is expected. In addition, it is expected to be used as a field electron emission material such as a flat display by utilizing the characteristics of chemical stability, thermal stability and fine structure as a carbon material. Moreover, since it has high heat conductivity, the use as a heat storage radiation material is also anticipated.
Two methods for producing such ultrafine carbon fibers for use in high-performance composite materials have been reported: a gas phase method and a method of producing a resin composition from melt spinning.
気相法を用いた製造法としては、例えばベンゼン等の有機化合物を原料とし、触媒としてフェロセン等の有機遷移金属化合物をキャリアーガスとともに高温の反応炉に導入し、基盤上に生成させる方法（例えば、特許文献１を参照。）、浮遊状態で気相法により炭素繊維を生成させる方法（例えば、特許文献２を参照。）、あるいは反応炉壁に成長させる方法（例えば、特許文献３を参照。）等が開示されている。しかし、これらの方法で得られる極細炭素繊維は高強度、高弾性率を有するものの、繊維の分岐が多く、補強用フィラーとしては性能が非常に低いといった問題があった。また、極細炭素繊維に触媒金属が含まれるので、これを除去するためにもコスト高になるといった問題もあった。 As a production method using a gas phase method, for example, an organic compound such as benzene is used as a raw material, and an organic transition metal compound such as ferrocene is introduced into a high-temperature reactor together with a carrier gas as a catalyst, and generated on a substrate (for example, , See Patent Document 1), a method of generating carbon fibers by a vapor phase method in a floating state (see, for example, Patent Document 2), or a method of growing on a reaction furnace wall (see, for example, Patent Document 3). ) Etc. are disclosed. However, although the ultrafine carbon fibers obtained by these methods have high strength and high elastic modulus, there are many problems of fiber branching and the performance as a reinforcing filler is very low. Further, since the ultrafine carbon fiber contains a catalyst metal, there is a problem that the cost is high in order to remove the catalyst metal.
一方、樹脂組成物の溶融紡糸から炭素繊維を製造する方法としては、熱可塑性樹脂と熱可塑性炭素前駆体からなる混合物から前駆体繊維を形成した後、溶剤を用いて熱可塑性樹脂を除去して繊維状炭素前駆体を形成し、これを炭素化して製造する方法（例えば、特許文献４を参照）が開示されている。
該方法の場合、分岐構造の少ない極細炭素繊維が得られるが、極細炭素繊維の集合体内に極細炭素繊維が二次元に密に集積した構造が多く含まれるため、フィラーとして用いた場合に分散性に劣るといった問題があった。
On the other hand, as a method for producing carbon fiber from melt spinning of a resin composition, after forming a precursor fiber from a mixture of a thermoplastic resin and a thermoplastic carbon precursor, the thermoplastic resin is removed using a solvent. A method of forming a fibrous carbon precursor and carbonizing it is disclosed (for example, see Patent Document 4).
In the case of this method, an ultrafine carbon fiber with few branched structures can be obtained. However, since the aggregate of ultrafine carbon fibers contains many structures in which the ultrafine carbon fibers are densely integrated in two dimensions, it is dispersible when used as a filler. There was a problem of being inferior.
本発明の目的は、上記従来技術が有していた問題を解決し、中間体である熱可塑性炭素前駆体繊維の段階で折損による繊維長の減少を極力抑えて３次元的な繊維の絡みを持たせることで、電池電極材料、電池電極添加材、および樹脂添加材などとして有用な極細炭素繊維綿状体の製造方法を提供することにある。 The object of the present invention is to solve the above-mentioned problems of the prior art and suppress the reduction of the fiber length due to breakage as much as possible at the stage of the thermoplastic carbon precursor fiber which is an intermediate, and to prevent the entanglement of the three-dimensional fiber. It is in providing the manufacturing method of an ultrafine carbon fiber cotton-like body useful as a battery electrode material, a battery electrode additive, a resin additive, etc. by having.
本発明者らは、上記従来技術に鑑み鋭意検討を重ねた結果、本発明を完成するに至った。すなわち、本発明は、以下の構成を要旨とするものである。 As a result of intensive studies in view of the above prior art, the present inventors have completed the present invention. That is, the gist of the present invention is as follows.
１． 以下（１）〜（５）の工程よりなる極細炭素繊維綿状体の製造方法。
（１） 熱可塑性樹脂１００質量部と、レーヨン、ピッチ、ポリアクリロニトリル、ポリα−クロロアクリロニトリル、ポリカルボジイミド、ポリイミド、ポリエーテルイミド、ポリベンゾアゾール、リグニンおよびアラミドよりなる群から選ばれる少なくとも１種の熱可塑性炭素前駆体１〜１５０質量部からなる混合物から前駆体繊維を形成する工程。
（２） 溶剤により前駆体繊維中の熱可塑性樹脂を溶解除去して熱可塑性炭素前駆体繊維とし、その分散液を作製する工程。
（３） 前記熱可塑性炭素前駆体繊維分散液を冷媒中に滴下させ、該分散液の凍結体を作製する工程。
（４） 前記凍結体を凍結乾燥させることにより、熱可塑性炭素前駆体繊維から成る低密度構造体を形成させる工程。
（５） 前記低密度構造体を不融化処理した後、炭素化または黒鉛化する工程。
２． 下記式（Ｉ）で表される熱可塑性樹脂を用いることを特徴とする上記１．項記載の極細炭素繊維綿状体の製造方法。
４． ピッチがメソフェーズピッチである上記１．項記載の極細炭素繊維綿状体の製造方法。
５． 前記熱可塑性樹脂を溶解する溶剤が、シクロヘキサンである、上記１．項記載の極細炭素繊維綿状体の製造方法。
1. A method for producing an ultrafine carbon fiber flocculent comprising the steps (1) to (5) below.
(1) 100 parts by mass of a thermoplastic resin and at least one selected from the group consisting of rayon, pitch, polyacrylonitrile, poly α-chloroacrylonitrile, polycarbodiimide, polyimide, polyetherimide, polybenzoazole, lignin and aramid The process of forming precursor fiber from the mixture which consists of 1-150 mass parts of thermoplastic carbon precursors.
(2) A step of dissolving and removing the thermoplastic resin in the precursor fiber with a solvent to obtain a thermoplastic carbon precursor fiber, and producing a dispersion thereof.
(3) A step of dripping the thermoplastic carbon precursor fiber dispersion into a refrigerant to produce a frozen body of the dispersion.
(4) A step of forming a low-density structure composed of thermoplastic carbon precursor fibers by freeze-drying the frozen body.
(5) A process of carbonizing or graphitizing the low-density structure after infusibility treatment.
2. 1. A thermoplastic resin represented by the following formula (I) is used. The manufacturing method of the ultrafine carbon fiber cotton-like body of description.
4). The above 1. in which the pitch is a mesophase pitch. The manufacturing method of the ultrafine carbon fiber cotton-like body of description.
5. 1. The solvent according to 1. above, wherein the solvent for dissolving the thermoplastic resin is cyclohexane. The manufacturing method of the ultrafine carbon fiber cotton-like body of description.
本発明の製造方法によって得られた極細炭素繊維綿状体は、極細炭素繊維による３次元のネットワーク構造が形成されているなどの特徴により、電池電極材料、電池電極添加材、および樹脂添加材などに使用するとき、優れた導電特性を付与することができる。 The ultrafine carbon fiber cotton obtained by the production method of the present invention has a battery electrode material, a battery electrode additive, a resin additive, etc. due to the feature that a three-dimensional network structure is formed by the ultrafine carbon fiber. When used in the present invention, excellent conductive properties can be imparted.
以下、本発明の極細炭素繊維綿状体の製造方法について詳細に説明する。
（１） 熱可塑性樹脂１００質量部と、レーヨン、ピッチ、ポリアクリロニトリル、ポリα−クロロアクリロニトリル、ポリカルボジイミド、ポリイミド、ポリエーテルイミド、ポリベンゾアゾール、リグニンおよびアラミドよりなる群から選ばれる少なくとも１種の熱可塑性炭素前駆体１〜１５０質量部からなる混合物から前駆体繊維を形成する工程
Hereinafter, the manufacturing method of the ultrafine carbon fiber cotton-like body of this invention is demonstrated in detail.
(1) 100 parts by mass of a thermoplastic resin and at least one selected from the group consisting of rayon, pitch, polyacrylonitrile, poly α-chloroacrylonitrile, polycarbodiimide, polyimide, polyetherimide, polybenzoazole, lignin and aramid Forming precursor fibers from a mixture of 1 to 150 parts by weight of a thermoplastic carbon precursor
＜ａ． 熱可塑性樹脂＞
本発明の製造方法において使用する熱可塑性樹脂は、前駆体繊維の形成した後に、熱可塑性樹脂を溶解する溶剤により除去される必要がある。このような熱可塑性樹脂として、ポリオレフィン、ポリメタクリレート、ポリメチルメタクリレート等のポリアクリレート系ポリマー、ポリスチレン、ポリカーボネート、ポリアリレート、ポリエステルカーボネート、ポリサルホン等からなる群より選ばれる１種類以上が好ましく使用される。これらの中でも繊維形成性に優れ、溶剤による溶解除去に好適な熱可塑性樹脂として、例えば下記式（Ｉ）で表されるポリオレフィン系の熱可塑性樹脂が好ましく使用される。
<A. Thermoplastic resin>
The thermoplastic resin used in the production method of the present invention needs to be removed with a solvent that dissolves the thermoplastic resin after the precursor fibers are formed. As such a thermoplastic resin, at least one selected from the group consisting of polyacrylate polymers such as polyolefin, polymethacrylate, polymethylmethacrylate, polystyrene, polycarbonate, polyarylate, polyester carbonate, polysulfone and the like is preferably used. Among these, for example, a polyolefin-based thermoplastic resin represented by the following formula (I) is preferably used as a thermoplastic resin that is excellent in fiber forming properties and suitable for dissolution and removal with a solvent.
上記式（Ｉ）で表される化合物としては、ポリ−４−メチルペンテン−１やポリ−４−メチルペンテン−１の共重合体、例えばポリ−４−メチルペンテン−１にビニル系モノマーが共重合したポリマーなどや、ポリエチレンを例示することができ、ポリエチレンとしては、低密度ポリエチレン、中密度ポリエチレン、高密度ポリエチレン、直鎖状低密度ポリエチレンなどのエチレンの単独重合体またはエチレンとα−オレフィンとの共重合体；エチレン・酢酸ビニル共重合体などのエチレンと他のビニル系単量体との共重合体等が挙げられる。 Examples of the compound represented by the above formula (I) include poly-4-methylpentene-1 and a copolymer of poly-4-methylpentene-1, for example, poly-4-methylpentene-1 and a vinyl monomer. Polymerized polymers and the like, and polyethylene can be exemplified. As the polyethylene, a homopolymer of ethylene such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene or ethylene and α-olefin A copolymer of ethylene and another vinyl monomer such as an ethylene / vinyl acetate copolymer.
エチレンと共重合されるα−オレフィンとしては、例えば、プロピレン、１−ブテン、１−ヘキセン、１−オクテンなどが挙げられる。他のビニル系単量体としては、例えば、酢酸ビニル等のビニルエステル、アクリル酸およびメタクリル酸、並びにこれら不飽和カルボン酸と炭素数１〜４の脂肪族アルコール類とのエステル化物が挙げられる。 Examples of the α-olefin copolymerized with ethylene include propylene, 1-butene, 1-hexene, 1-octene and the like. Examples of the other vinyl monomers include vinyl esters such as vinyl acetate, acrylic acid and methacrylic acid, and esterified products of these unsaturated carboxylic acids and aliphatic alcohols having 1 to 4 carbon atoms.
また、本発明の熱可塑性樹脂は熱可塑性炭素前駆体との溶融混練の容易さから、非晶性の場合、ガラス転移温度が２５０℃以下、結晶性の場合、結晶融点が３００℃以下であるものが好ましい。 In addition, the thermoplastic resin of the present invention has a glass transition temperature of 250 ° C. or lower in the case of amorphous, and a crystal melting point of 300 ° C. or lower in the case of crystallinity because of ease of melt kneading with the thermoplastic carbon precursor. Those are preferred.
＜ｂ． 熱可塑性炭素前駆体＞
本発明の製造方法に用いられる熱可塑性炭素前駆体は、レーヨン、ピッチ、ポリアクリロニトリル、ポリα−クロロアクリロニトリル、ポリカルボジイミド、ポリイミド、ポリエーテルイミド、ポリベンゾアゾール、リグニンおよびアラミドよりなる群から選ばれる少なくとも１種である。
<B. Thermoplastic carbon precursor>
The thermoplastic carbon precursor used in the production method of the present invention is selected from the group consisting of rayon, pitch, polyacrylonitrile, poly α-chloroacrylonitrile, polycarbodiimide, polyimide, polyetherimide, polybenzoazole, lignin and aramid. At least one.
これらの熱可塑性炭素前駆体の中でも、酸素ガス雰囲気下またはハロゲンガス雰囲気下、２００℃以上３５０℃未満で２〜３０時間保持した後、次いで不活性ガス雰囲気下で３５０℃以上５００℃未満の温度で５時間保持することで、初期質量の８０質量％以上が残存する熱可塑性炭素前駆体を用いるのが好ましい。上記条件で、残存量が初期質量の８０質量％未満であると、熱可塑性炭素前駆体の繊維からなる低密度構造体から充分な炭化率で極細炭素繊維綿状体を得ることができず、好ましくない。 Among these thermoplastic carbon precursors, after being held at 200 ° C. or higher and lower than 350 ° C. for 2 to 30 hours in an oxygen gas atmosphere or a halogen gas atmosphere, then at a temperature of 350 ° C. or higher and lower than 500 ° C. in an inert gas atmosphere. It is preferable to use a thermoplastic carbon precursor in which 80% by mass or more of the initial mass remains by holding for 5 hours. Under the above conditions, if the residual amount is less than 80% by mass of the initial mass, it is not possible to obtain an ultrafine carbon fiber flocculent with a sufficient carbonization rate from a low-density structure composed of fibers of a thermoplastic carbon precursor, It is not preferable.
上記のような熱可塑性炭素前駆体の中でも、ピッチ、ポリアクリロニトリル、ポリカルボジイミド、リグニンが好ましく、ピッチが更に好ましく、ピッチのうち一般的に高強度、高弾性率の期待されるメソフェーズピッチが特に好ましい。 Among the thermoplastic carbon precursors as described above, pitch, polyacrylonitrile, polycarbodiimide, and lignin are preferable, pitch is more preferable, and mesophase pitch that is generally expected to have high strength and high elastic modulus is particularly preferable. .
メソフェーズピッチとは溶融状態において光学的異方性相（液晶相）を形成しうるピッチである。メソフェーズピッチの原料としては石炭や石油の蒸留残渣を使用してもよく、有機化合物を使用しても良いが、不融化や炭素化または黒鉛化のしやすさから、ナフタレン等の芳香族炭化水素を原料としたメソフェーズピッチを用いるのが好ましい。 The mesophase pitch is a pitch that can form an optically anisotropic phase (liquid crystal phase) in a molten state. As a raw material for mesophase pitch, a distillation residue of coal or petroleum may be used, or an organic compound may be used. However, aromatic hydrocarbons such as naphthalene are used because they are easily infusible, carbonized, or graphitized. It is preferable to use a mesophase pitch using as a raw material.
＜ｃ． 熱可塑性樹脂と熱可塑性炭素前駆体とからなる混合物の製造＞
本発明の製造方法において用いられる熱可塑性樹脂と熱可塑性炭素前駆体とからなる混合物は、該熱可塑性樹脂１００質量部と該熱可塑性炭素前駆体１〜１５０質量部とを含むものであり、該熱可塑性炭素前駆体が５〜１００質量部であると好ましい。該熱可塑性炭素前駆体の量が１５０質量部を超えると所望の分散径を有する熱可塑性炭素前駆体が得られず、１質量部未満であると目的とする極細炭素繊維綿状体を安価に製造する事ができない等の問題が生じるため好ましくない。
<C. Production of a mixture comprising a thermoplastic resin and a thermoplastic carbon precursor>
A mixture comprising a thermoplastic resin and a thermoplastic carbon precursor used in the production method of the present invention includes 100 parts by mass of the thermoplastic resin and 1 to 150 parts by mass of the thermoplastic carbon precursor, It is preferable that the thermoplastic carbon precursor is 5 to 100 parts by mass. If the amount of the thermoplastic carbon precursor exceeds 150 parts by mass, a thermoplastic carbon precursor having a desired dispersion diameter cannot be obtained, and if it is less than 1 part by mass, the intended ultrafine carbon fiber flocculent can be obtained at low cost. This is not preferable because problems such as inability to manufacture can occur.
本発明で使用する混合物から、繊維径が２μｍ未満である炭素繊維を製造するためには、熱可塑性炭素前駆体の熱可塑性樹脂中への分散径が０．０１〜５０μｍとなるのが好ましい。 In order to produce carbon fibers having a fiber diameter of less than 2 μm from the mixture used in the present invention, the dispersion diameter of the thermoplastic carbon precursor in the thermoplastic resin is preferably 0.01 to 50 μm.
熱可塑性炭素前駆体の熱可塑性樹脂中への分散径が０．０１〜５０μｍの範囲を逸脱すると、高性能複合材料用としての炭素繊維を製造することが困難となることがある。熱可塑性炭素前駆体の分散径のより好ましい範囲は０．０１〜３０μｍである。また、熱可塑性樹脂と熱可塑性炭素前駆体からなる混合物を、３００℃で３分間保持した後、熱可塑性炭素前駆体の熱可塑性樹脂中への分散径が０．０１〜５０μｍであることが好ましい。 When the dispersion diameter of the thermoplastic carbon precursor in the thermoplastic resin deviates from the range of 0.01 to 50 μm, it may be difficult to produce carbon fibers for high performance composite materials. A more preferable range of the dispersion diameter of the thermoplastic carbon precursor is 0.01 to 30 μm. Moreover, it is preferable that the dispersion diameter in the thermoplastic resin of a thermoplastic carbon precursor is 0.01-50 micrometers after hold | maintaining the mixture which consists of a thermoplastic resin and a thermoplastic carbon precursor at 300 degreeC for 3 minute (s). .
一般に、熱可塑性樹脂と熱可塑性炭素前駆体との溶融混練で得た混合物を、溶融状態で保持しておくと時間と共に熱可塑性炭素前駆体が凝集するが、熱可塑性炭素前駆体の凝集により、分散径が５０μｍを超えると、高性能複合材料用としての炭素繊維を製造することが困難となることがある。 Generally, when a mixture obtained by melt-kneading a thermoplastic resin and a thermoplastic carbon precursor is kept in a molten state, the thermoplastic carbon precursor aggregates with time, but due to the aggregation of the thermoplastic carbon precursor, If the dispersion diameter exceeds 50 μm, it may be difficult to produce carbon fibers for high performance composite materials.
熱可塑性炭素前駆体の凝集速度の程度は、使用する熱可塑性樹脂と熱可塑性炭素前駆体との種類により変動するが、より好ましくは３００℃で５分以上、更に好ましくは３００℃で１０分以上、０．０１〜５０μｍの分散径を維持していることが好ましい。なお、混合物中で熱可塑性炭素前駆体は島相を形成し、球状あるいは楕円状となるが、本発明で言う分散径とは混合物中で熱可塑性炭素前駆体の球形の直径または楕円体の長軸径を意味する。 The degree of the aggregation rate of the thermoplastic carbon precursor varies depending on the types of the thermoplastic resin and the thermoplastic carbon precursor used, but is more preferably 5 minutes or more at 300 ° C., more preferably 10 minutes or more at 300 ° C. It is preferable to maintain a dispersion diameter of 0.01 to 50 μm. The thermoplastic carbon precursor in the mixture forms an island phase and is spherical or elliptical. The dispersion diameter referred to in the present invention is the spherical diameter of the thermoplastic carbon precursor or the length of the ellipsoid in the mixture. It means the shaft diameter.
熱可塑性樹脂と熱可塑性炭素前駆体とから混合物を製造する方法は、溶融状態における混練が好ましい。熱可塑性樹脂と熱可塑性炭素前駆体の溶融混練は公知の方法を必要に応じて用いる事ができ、例えば一軸式混練機、二軸式混練機、ミキシングロール、バンバリーミキサー等からなる群より選ばれる１種類以上が挙げられる。これらの中で上記熱可塑性炭素前駆体を熱可塑性樹脂に良好にミクロ分散させるという目的から、二軸式混練機が好ましく使用され、二軸式混練機（同方向）であるとより好ましい。 As a method for producing a mixture from a thermoplastic resin and a thermoplastic carbon precursor, kneading in a molten state is preferable. The melt kneading of the thermoplastic resin and the thermoplastic carbon precursor can be performed using a known method as required, and is selected from the group consisting of, for example, a uniaxial kneader, a biaxial kneader, a mixing roll, and a Banbury mixer. One or more types may be mentioned. Among these, a biaxial kneader is preferably used and a biaxial kneader (same direction) is more preferable for the purpose of favorably microdispersing the thermoplastic carbon precursor in the thermoplastic resin.
上記の溶融混練温度としては１００℃〜４００℃で行うのが好ましい。溶融混練温度が１００℃未満であると、熱可塑性炭素前駆体が溶融状態にならず、熱可塑性樹脂とのミクロ分散が困難であるため好ましくない。一方、４００℃を超える場合、熱可塑性樹脂と熱可塑性炭素前駆体の分解が進行するためいずれも好ましくない。溶融混練温度のより好ましい範囲は１５０℃〜３５０℃である。また、溶融混練の時間としては０．５〜２０分間、好ましくは１〜１５分間である。溶融混練の時間が０．５分間未満の場合、熱可塑性炭素前駆体のミクロ分散が困難であるため好ましくない。一方、２０分間を超える場合、炭素繊維の生産性が著しく低下し好ましくない。 The melt kneading temperature is preferably 100 ° C to 400 ° C. When the melt kneading temperature is less than 100 ° C., the thermoplastic carbon precursor is not in a molten state, and micro-dispersion with the thermoplastic resin is difficult, which is not preferable. On the other hand, when the temperature exceeds 400 ° C., the decomposition of the thermoplastic resin and the thermoplastic carbon precursor proceeds, which is not preferable. A more preferable range of the melt kneading temperature is 150 ° C to 350 ° C. The melt kneading time is 0.5 to 20 minutes, preferably 1 to 15 minutes. When the melt kneading time is less than 0.5 minutes, it is not preferable because micro dispersion of the thermoplastic carbon precursor is difficult. On the other hand, when it exceeds 20 minutes, the productivity of carbon fibers is remarkably lowered, which is not preferable.
上記の溶融混練により混合物を製造する際は、酸素ガス含有量１０体積％未満のガス雰囲気下で行うことが好ましい。本発明で使用する熱可塑性炭素前駆体は酸素と反応することで溶融混練時に変性不融化してしまい、熱可塑性樹脂中へのミクロ分散を阻害することがある。このため、不活性ガスを流通させながら溶融混練を行い、できるだけ酸素ガス含有量を低下させることが好ましい。より好ましい溶融混練時の酸素ガス含有量は５体積％未満、更には１％体積未満である。 When producing a mixture by said melt-kneading, it is preferable to carry out in gas atmosphere with oxygen gas content of less than 10 volume%. The thermoplastic carbon precursor used in the present invention reacts with oxygen to be modified and infusible at the time of melt kneading, which may inhibit micro-dispersion in the thermoplastic resin. For this reason, it is preferable to perform melt kneading while circulating an inert gas to reduce the oxygen gas content as much as possible. The oxygen gas content during melt kneading is more preferably less than 5% by volume, and further less than 1% by volume.
＜ｄ． 前駆体繊維の形成＞
上記の熱可塑性樹脂と熱可塑性炭素前駆体との混合物から前駆体繊維を製造する方法としては、混合物を紡糸口金より溶融紡糸することにより得る方法などを例示することができる。
溶融紡糸する際の紡糸温度としては１５０℃〜４００℃、好ましくは１８０℃〜３５０℃である。紡糸引取り速度としては１ｍ／分〜２０００ｍ／分である事が好ましい。
<D. Formation of precursor fiber>
Examples of the method for producing the precursor fiber from the mixture of the thermoplastic resin and the thermoplastic carbon precursor include a method obtained by melt spinning the mixture from a spinneret.
The spinning temperature for melt spinning is 150 ° C to 400 ° C, preferably 180 ° C to 350 ° C. The spinning take-up speed is preferably 1 m / min to 2000 m / min.
また、別法として熱可塑性樹脂と熱可塑性炭素前駆体の溶融混練で得た混合物から、メルトブロー法により前駆体繊維を形成する方法も例示することができる。メルトブローの条件としては、吐出ダイ温度が１５０〜４００℃、ガス温度が１５０〜４００℃の範囲が好適に用いられる。メルトブローの気体噴出速度は、前駆体繊維の繊維径に影響するが、通常２０００〜１００ｍ／ｓであり、より好ましくは１０００〜２００ｍ／ｓである。メルトブロー法により前駆体繊維を形成する場合、不織布とすることもできる。
該混合物を溶融混練し、その後ダイより吐出する際、溶融混練した後溶融状態のままで配管内を送液し吐出ダイまで連続的に送液するのが好ましく、溶融混練から紡糸口金吐出までの移送時間は１０分間以内である事が好ましい。
Moreover, the method of forming precursor fiber by the melt blow method from the mixture obtained by melt-kneading a thermoplastic resin and a thermoplastic carbon precursor as another method can also be illustrated. As the conditions for the melt blow, a discharge die temperature of 150 to 400 ° C. and a gas temperature of 150 to 400 ° C. are preferably used. Although the gas blowing speed of the melt blow affects the fiber diameter of the precursor fiber, it is usually 2000 to 100 m / s, more preferably 1000 to 200 m / s. When the precursor fiber is formed by the melt blow method, it may be a non-woven fabric.
When the mixture is melt-kneaded and then discharged from the die, it is preferable to send the inside of the pipe in the molten state after melt-kneading and continuously feed it to the discharge die, from melt-kneading to spinneret discharge. The transfer time is preferably within 10 minutes.
（２） 溶剤により前駆体繊維中の熱可塑性樹脂を溶解除去して熱可塑性炭素前駆体繊維とし、その分散液を作製する工程
本工程においては、前記の工程にて得られた熱可塑性樹脂と熱可塑性炭素前駆体との混合物の前駆体繊維と溶剤とを接触させて前駆体繊維中の熱可塑性樹脂を除去して、熱可塑性炭素前駆体繊維とし、その分散液を作成する。
(2) A step of dissolving and removing the thermoplastic resin in the precursor fiber with a solvent to obtain a thermoplastic carbon precursor fiber, and producing a dispersion thereof In this step, the thermoplastic resin obtained in the above step and The precursor fiber of the mixture with the thermoplastic carbon precursor is brought into contact with a solvent to remove the thermoplastic resin in the precursor fiber to obtain a thermoplastic carbon precursor fiber, and a dispersion thereof is prepared.
本工程において、前駆体繊維と溶剤とを接触させて前駆体繊維中の熱可塑性樹脂を除去する方法としては、前駆体繊維と溶剤とを混合して前駆体繊維中の熱可塑性樹脂を溶剤（液相）に溶出させた後、デカンテーションや濾過などにより固液分離するなどの公知の方法を用いることができ、このデカンテーションや濾過の際に、完全に固液分離せず、熱可塑性樹脂が溶出した液の一部を分離し、新たに溶剤を添加して更にデカンテーションまたは濾過を繰り返すことにより、液成分を熱可塑性樹脂が含まれない溶剤に置換し、熱可塑性炭素前駆体繊維が溶剤に分散した液を得る方法（以下、「溶剤置換法」と称することがある）も好ましい。また、ソックスレー抽出装置、バッテリー抽出機、ボールマン抽出機、ロトセル抽出機、ルルギ抽出機、ケネディ抽出機、バチューカタンク抽出機、ボノトー抽出機などの固液抽出装置を用いて上記と同様に前駆体繊維中の熱可塑性樹脂を溶剤により除去する方法も好ましい。 In this step, as a method for removing the thermoplastic resin in the precursor fiber by bringing the precursor fiber into contact with the solvent, the precursor fiber and the solvent are mixed to remove the thermoplastic resin in the precursor fiber from the solvent ( After elution into the liquid phase), a known method such as solid-liquid separation by decantation or filtration can be used. During this decantation or filtration, the thermoplastic resin does not completely separate into solid and liquid. After separating a part of the liquid eluted, the solvent was replaced with a solvent not containing a thermoplastic resin by adding a new solvent and repeating decantation or filtration. A method of obtaining a liquid dispersed in a solvent (hereinafter sometimes referred to as “solvent replacement method”) is also preferable. In addition, a precursor similar to the above using a solid-liquid extraction device such as a Soxhlet extraction device, a battery extraction device, a Ballman extraction device, a Rotocell extraction device, a Lurgi extraction device, a Kennedy extraction device, a bachuca tank extraction device or a Bonoto extraction device A method of removing the thermoplastic resin in the body fibers with a solvent is also preferable.
本工程において用いる溶剤としては、選択した熱可塑性樹脂の溶解度が高く、熱可塑性炭素前駆体の溶解度が低いもの、例えば、ベンゼン、ヘキサン、エタノール、メタノール、ジエチルエーテル、アセトン、四塩化炭素、クロロホルム、酢酸、二硫化炭素、ペンタン、シクロヘキサン、ヘプタン、リグロイン、石油エーテル、ベンゼン、トルエン、キシレン、グリセリン、ピリジン、デカリンなど種々の有機溶媒よりなる群から、用いる熱可塑性樹脂の溶解性、取り扱い容易性などを考慮して、１種類以上を適宜選択することができる。熱可塑性樹脂として、ポリエチレン等のポリオレフィン樹脂類を採用する際は、それらの溶解性が優れているという点で、シクロヘキサン、ヘキサン、トルエン、キシレン、デカリンからなる群から選ばれる１種類以上が好ましく、ポリオレフィン樹脂類除去後の操作容易性から、シクロヘキサン、ヘキサン、トルエンからなる群から選ばれる１種類以上が特に好ましい。 As the solvent used in this step, the selected thermoplastic resin has high solubility, and the thermoplastic carbon precursor has low solubility, for example, benzene, hexane, ethanol, methanol, diethyl ether, acetone, carbon tetrachloride, chloroform, From the group consisting of various organic solvents such as acetic acid, carbon disulfide, pentane, cyclohexane, heptane, ligroin, petroleum ether, benzene, toluene, xylene, glycerin, pyridine, decalin, solubility of thermoplastic resin used, ease of handling, etc. In consideration of the above, one or more types can be appropriately selected. When adopting polyolefin resins such as polyethylene as the thermoplastic resin, at least one kind selected from the group consisting of cyclohexane, hexane, toluene, xylene, decalin is preferable in that their solubility is excellent. One or more types selected from the group consisting of cyclohexane, hexane, and toluene are particularly preferable from the viewpoint of ease of operation after removing the polyolefin resins.
熱可塑性樹脂の除去における上記溶剤の使用量は、前駆体繊維１００質量部に対し、１０００〜１００，０００質量部が好ましい。１０００質量部以下のときは、熱可塑性樹脂の除去が困難となり、好ましくない。また、１００，０００質量部より多いときは生産性が低下して好ましくない。より好ましい使用量は、１０，０００〜５０，０００質量部である。また、使用した溶剤は、蒸留等の方法により精製し、再利用することも可能である。 As for the usage-amount of the said solvent in the removal of a thermoplastic resin, 1000-100,000 mass parts is preferable with respect to 100 mass parts of precursor fibers. When it is 1000 parts by mass or less, it is difficult to remove the thermoplastic resin, which is not preferable. Moreover, when more than 100,000 mass parts, productivity falls and it is not preferable. A more preferable usage amount is 10,000 to 50,000 parts by mass. The used solvent can be purified and reused by a method such as distillation.
該溶剤で熱可塑性樹脂の除去処理を行う温度は、５０℃から２５０℃であると好ましい。当該温度が５０℃より低いと熱可塑性樹脂の除去に長時間を要するため好ましく、また、２５０℃より高いと得られるピッチ繊維が短くなり好ましくない。該除去処理温度としては６０〜２１０℃であるとより好ましい。 The temperature at which the thermoplastic resin is removed with the solvent is preferably 50 ° C to 250 ° C. When the temperature is lower than 50 ° C., it is preferable because it takes a long time to remove the thermoplastic resin. When the temperature is higher than 250 ° C., the resulting pitch fiber is not preferable. The removal treatment temperature is more preferably 60 to 210 ° C.
また、本工程において用いる上記溶剤には、ヨウ素を添加してもよい。ヨウ素を添加することにより、熱可塑性炭素前駆体（特に、ピッチ）の溶解を抑制することができることから好ましい。用いるヨウ素としては、市販されているヨウ素単体（Ｉ２）の粉末、フレーク、粒状体、結晶品を使用できる。また、ヨウ化物塩を、先述したような溶剤に加え、そこに酸性物質や酸化剤を加えることにより、ヨウ素単体を遊離させて熱可塑性樹脂の除去に用いること等もできるが、副反応や分解物が少ないことや、安価で操作が簡便なことから、前記のようなヨウ素単体を、先述したような溶剤に溶解して用いる態様が好ましい。 なお、添加するヨウ素の濃度としては、溶剤に対して０．１〜３０質量％であることが、ピッチの溶解を抑制しながら熱可塑性樹脂だけを除去することが出来ることから好ましい。ヨウ素の含有量が０．１質量％以下では、ピッチの溶解抑制効果が不十分でピッチ繊維の折損が起こり、繊維長が長いピッチ繊維を得ることができず、好ましくない。また３０質量％以上のときは、それ以上ヨウ素含有量が大きくても効果に影響はなく、製造コストが高くなるため好ましくない。好ましいヨウ素の含有量は０．１〜２質量％である。 Further, iodine may be added to the solvent used in this step. Addition of iodine is preferable because dissolution of the thermoplastic carbon precursor (particularly pitch) can be suppressed. As iodine to be used, commercially available iodine simple substance (I 2 ) powder, flakes, granules, and crystalline products can be used. In addition, by adding an iodide salt to the solvent as described above and adding an acidic substance or an oxidant thereto, iodine itself can be liberated and used for removing the thermoplastic resin. Since there are few things and it is cheap and operation is easy, the aspect which uses the above iodine simple substance in a solvent as mentioned above is preferable. In addition, as a density | concentration of the iodine to add, it is preferable from 0.1-30 mass% with respect to a solvent from being able to remove only a thermoplastic resin, suppressing melt | dissolution of a pitch. When the content of iodine is 0.1% by mass or less, the effect of inhibiting the dissolution of pitch is insufficient, the pitch fiber breaks, and pitch fibers having a long fiber length cannot be obtained, which is not preferable. Further, when it is 30% by mass or more, even if the iodine content is larger than that, the effect is not affected, and the production cost is increased, which is not preferable. A preferable iodine content is 0.1 to 2% by mass.
本発明においては、上記のとおり、溶剤により前駆体繊維中の熱可塑性樹脂を溶解・除去して得られた熱可塑性炭素前駆体繊維を更に溶媒に分散させて分散液（熱可塑性炭素前駆体繊維分散液）とする。この場合の溶媒は、上記の熱可塑性樹脂に除去に用いた溶剤と同じでも良く、異なったものでも良く、または、熱可塑性樹脂に除去に用いた溶剤と、それとは別の種類の溶媒との混合液でも良い。 In the present invention, as described above, the thermoplastic carbon precursor fiber obtained by dissolving and removing the thermoplastic resin in the precursor fiber with a solvent is further dispersed in a solvent to obtain a dispersion (thermoplastic carbon precursor fiber). Dispersion). In this case, the solvent may be the same as or different from the solvent used for the removal of the thermoplastic resin, or the solvent used for the removal of the thermoplastic resin and another type of solvent. A mixed solution may be used.
該分散液を得る方法としては、前記の固液抽出等の方法により前駆体繊維中の熱可塑性樹脂を溶解・除去する際に固液分離して熱可塑性炭素前駆体繊維を単離してから、溶媒に分散させても良いが、前記のとおり、前駆体繊維から熱可塑性樹脂を除去する際に、溶剤置換法により、該溶剤に熱可塑性炭素前駆体繊維が分散した液を得る方法が、操作の簡便さの点で好ましい。 As a method for obtaining the dispersion liquid, the thermoplastic carbon precursor fiber is isolated by solid-liquid separation when the thermoplastic resin in the precursor fiber is dissolved and removed by the above-described method such as solid-liquid extraction. Although it may be dispersed in a solvent, as described above, when removing the thermoplastic resin from the precursor fiber, a method of obtaining a liquid in which the thermoplastic carbon precursor fiber is dispersed in the solvent by a solvent replacement method is It is preferable in terms of simplicity.
（３） 前記熱可塑性炭素前駆体繊維分散液を冷媒中に滴下させ、該分散液の凍結体を作製する工程
本工程では、前工程で得られた熱可塑性炭素前駆体繊維分散液を冷媒中に滴下させ、該分散液の凍結体を作製する。該分散液を冷媒中に滴下することなく、そのまま冷却するなどすると、凍結が徐々に進行させると、溶媒の結晶成長が大きくなり、その結晶成長により熱可塑性炭素前駆体繊維からなる繊維が排除され、熱可塑性炭素前駆体繊維からなる繊維が局所的に集合した粗密構造が形成されてしまい、結果的に極細炭素繊維綿状体を作製することができない。
該熱可塑性炭素前駆体繊維分散液を冷媒中に滴下させる方法としては特に制限されず、例えば、連続的な滴下方法や、間欠的な滴下方法などのいずれの滴下方法であってもよい。
(3) A step of dripping the thermoplastic carbon precursor fiber dispersion into the refrigerant to produce a frozen body of the dispersion. In this step, the thermoplastic carbon precursor fiber dispersion obtained in the previous step is added to the refrigerant. To prepare a frozen body of the dispersion. If the dispersion is cooled as it is without being dropped into the refrigerant, the crystal growth of the solvent increases as the freezing progresses gradually, and the fibers consisting of the thermoplastic carbon precursor fibers are eliminated by the crystal growth. As a result, a coarse / dense structure in which fibers composed of thermoplastic carbon precursor fibers are locally gathered is formed, and as a result, an ultrafine carbon fiber flocculant cannot be produced.
The method for dropping the thermoplastic carbon precursor fiber dispersion into the refrigerant is not particularly limited, and may be any dropping method such as a continuous dropping method or an intermittent dropping method.
冷媒としては、分散液の溶媒の融点よりも低融点で、冷却および凍結を速やかに実施できるものであれば特に限定されないが、液体窒素や水が好ましい一例として挙げられる。。この場合の水は氷水でもよく、また塩化カルシウムのような無機塩やメタノールなどの水溶性有機化合物を含むものであってもよい。
なお、上記のとおり熱可塑性炭素前駆体繊維分散液を冷媒中に滴下させて得られた凍結体を更に、冷凍機などで冷凍してより低温の凍結体としても良い。
The refrigerant is not particularly limited as long as it has a melting point lower than the melting point of the solvent of the dispersion and can be quickly cooled and frozen, but preferred examples include liquid nitrogen and water. . The water in this case may be ice water or may contain an inorganic salt such as calcium chloride or a water-soluble organic compound such as methanol.
Note that the frozen body obtained by dripping the thermoplastic carbon precursor fiber dispersion in the refrigerant as described above may be further frozen in a refrigerator or the like to form a lower temperature frozen body.
（４） 前記凍結体を凍結乾燥させることにより、熱可塑性炭素前駆体繊維から成る低密度構造体を形成させる工程
前記熱可塑性炭素前駆体繊維が分散した凍結体を、凍結乾燥させることにより、熱可塑性炭素前駆体繊維から成る低密度構造体を形成させる。この凍結乾燥により、凍結体中の溶媒などの易揮発成分が昇華し、得られる熱可塑性炭素前駆体繊維からなる繊維を嵩高くすることができることから、極細炭素繊維綿状体を作製するために必要である。この凍結乾燥を行う温度、圧力は、使用する溶媒によって異なるが、通常は−３０〜０℃、３０〜１００Ｐａであると好ましい。凍結乾燥の時間は特に制限されないが、好ましくは１〜２４０時間であり、より好ましくは３〜１２０時間であり、更に好ましくは８〜７２時間であり、特に好ましくは１２〜６０時間である。
(4) A step of forming a low-density structure composed of thermoplastic carbon precursor fibers by freeze-drying the frozen body, and by freeze-drying the frozen body in which the thermoplastic carbon precursor fibers are dispersed, A low density structure consisting of plastic carbon precursor fibers is formed. This lyophilization sublimates easily volatile components such as a solvent in the frozen body, and the resulting fiber made of the thermoplastic carbon precursor fiber can be made bulky. is necessary. The temperature and pressure at which this lyophilization is carried out vary depending on the solvent used, but usually it is preferably −30 to 0 ° C. and 30 to 100 Pa. The time for lyophilization is not particularly limited, but is preferably 1 to 240 hours, more preferably 3 to 120 hours, still more preferably 8 to 72 hours, and particularly preferably 12 to 60 hours.
（５） 前記低密度構造体を不融化処理した後、炭素化または黒鉛化する工程
本工程では、まず、前記工程で得られた低密度構造体について不融化処理を行う。
不融化の方法としては空気、酸素、オゾン、二酸化窒素、ハロゲンなどのガス気流処理、酸性水溶液などの溶液処理など公知の方法で行うことができるが、生産性の面からガス気流下での不融化が好ましい。使用するガス成分としては取り扱いの容易性から空気、酸素それぞれ単独か、あるいはこれらを含む混合ガスであることが好ましく、特にコストの関係から空気を用いるのが特に好ましい。使用する酸素ガス濃度としては、全ガス組成の１０〜１００体積％の範囲にあることが好ましい。酸素ガス濃度が全ガス組成の１０体積％未満であると、熱可塑性炭素前駆体繊維から成る低密度構造体の不融化に多大の時間を要してしまうので好ましくない。
(5) Step of carbonizing or graphitizing the low-density structure after infusibilizing the low-density structure In this step, first, the low-density structure obtained in the step is infusibilized.
As an infusibilization method, it can be performed by a known method such as a gas stream treatment with air, oxygen, ozone, nitrogen dioxide, halogen, etc., or a solution treatment with an acidic aqueous solution. Fusing is preferred. The gas component to be used is preferably air, oxygen alone or a mixed gas containing these from the viewpoint of ease of handling, and particularly preferably air from the viewpoint of cost. The oxygen gas concentration used is preferably in the range of 10 to 100% by volume of the total gas composition. If the oxygen gas concentration is less than 10% by volume of the total gas composition, it is not preferable because it takes a long time to infusibilize the low-density structure composed of thermoplastic carbon precursor fibers.
上記のガス気流下での不融化処理について、処理温度は５０〜３５０℃が好ましく、６０〜３００℃であるとより好ましく、１００〜３００℃であると更に好ましく、２００〜３００℃であると極めて好ましい。不融化処理時間は１０〜１２００分が好ましく、１０〜６００分であるとより好ましく、３０〜３００分であると更に好ましく、６０〜２１０分であると極めて好ましい。 As for the infusibilization treatment under the gas stream, the treatment temperature is preferably 50 to 350 ° C, more preferably 60 to 300 ° C, still more preferably 100 to 300 ° C, and extremely preferably 200 to 300 ° C. preferable. The infusible treatment time is preferably 10 to 1200 minutes, more preferably 10 to 600 minutes, still more preferably 30 to 300 minutes, and most preferably 60 to 210 minutes.
上記不融化により熱可塑性炭素前駆体繊維から成る低密度構造体の軟化点は著しく上昇するが、所望の極細の炭素繊維を得るという目的から軟化点が４００℃以上となる事が好ましく、５００℃以上である事が更に好ましい。 Although the softening point of the low density structure composed of the thermoplastic carbon precursor fiber is remarkably increased by the infusibilization, the softening point is preferably 400 ° C. or higher for the purpose of obtaining a desired ultrafine carbon fiber, and 500 ° C. It is more preferable that it is the above.
上記のとおり不融化処理を受けた低密度構造体を不活性ガス雰囲気下での高温処理により炭素化または黒鉛化し、所望の極細炭素繊維綿状体とする。該綿状体を構成する極細炭素繊維の繊維径としては、最小値及び最大値が０．００１μｍ（１ｎｍ）〜２μｍの範囲にあることが好ましく、平均繊維径で０．０１μｍ〜０．５μｍ（１０ｎｍ〜５００ｎｍ）であるとより好ましく、０．０１μｍ〜０．３μｍ（１０ｎｍ〜３００ｎｍ）であると更に好ましい。 The low-density structure subjected to the infusibilization treatment as described above is carbonized or graphitized by high-temperature treatment under an inert gas atmosphere to obtain a desired ultrafine carbon fiber flocculent body. As the fiber diameter of the ultrafine carbon fiber constituting the cotton-like body, the minimum value and the maximum value are preferably in the range of 0.001 μm (1 nm) to 2 μm, and the average fiber diameter is 0.01 μm to 0.5 μm ( 10 nm to 500 nm), more preferably 0.01 μm to 0.3 μm (10 nm to 300 nm).
本工程における炭素化または黒鉛化の処理（熱処理）は公知の方法で行うことができる。使用される不活性ガスとしては窒素、アルゴン等があげられ、処理温度は５００℃〜３５００℃が好ましく、８００℃〜３０００℃であるとより好ましい。特に、黒鉛化処理温度としては２０００℃〜３５００℃が好ましく、２６００℃〜３０００℃であるとより好ましく、５００℃〜１８００℃で炭素化処理した後、上記の黒鉛化処理温度で黒鉛化処理するなど、複数の温度設定で炭素化または黒鉛化処理を行うことも好ましい。また、炭素化または黒鉛化の処理時間は、０．１〜２４時間であると好ましく、０．２〜１０時間であるとより好ましく、０．５〜８時間であると更に好ましい。なお、炭素化または黒鉛化する際の、酸素濃度は２０体積ｐｐｍ以下、更には１０体積ｐｐｍ以下であることが好ましい。
上記の方法を実施することで、所望の極細炭素繊維綿状体を得ることができる。
The carbonization or graphitization treatment (heat treatment) in this step can be performed by a known method. Nitrogen, argon, etc. are mention | raise | lifted as an inert gas used, 500 to 3500 degreeC of process temperature is preferable, and it is more preferable in it being 800 to 3000 degreeC. In particular, the graphitizing temperature is preferably 2000 ° C. to 3500 ° C., more preferably 2600 ° C. to 3000 ° C., and after carbonizing at 500 ° C. to 1800 ° C., the graphitizing is performed at the graphitizing temperature. It is also preferable to perform carbonization or graphitization at a plurality of temperature settings. The treatment time for carbonization or graphitization is preferably 0.1 to 24 hours, more preferably 0.2 to 10 hours, and further preferably 0.5 to 8 hours. It should be noted that the oxygen concentration at the time of carbonization or graphitization is preferably 20 ppm by volume or less, more preferably 10 ppm by volume or less.
By carrying out the above method, a desired ultrafine carbon fiber flocculent body can be obtained.
以下、本発明を実施例により更に具体的に説明するが、本発明はこれにより何等限定を受けるものでは無い。
（ｉ） 極細炭素繊維よりなる綿状体の形態確認、および極細炭素繊維の繊維径の測定
電界放出形走査電子顕微鏡（株式会社日立ハイテクノロジーズ社製、型式Ｓ−４８００）を用いて観察および写真撮影を行った。極細炭素繊維の平均繊維径は、得られた電子顕微鏡写真（１０，０００倍または３０，０００倍）から無作為に２５０箇所を選択して繊維径を測定し、それらのすべての測定結果（ｎ＝２５０）の平均値を平均繊維径とした。
（ｉｉ） 黒鉛結晶性の評価方法
Ｘ線回折測定はリガク社製ＲＩＮＴ−２１００を用いてＪＩＳ Ｒ７６５１法に準拠し、格子面間隔(ｄ００２)および結晶子大きさ(Ｌｃ００２)を測定した。
（ｉｉｉ） 体積抵抗率の測定方法
体積抵抗率の測定はダイヤインスツルメンツ社製の粉体抵抗システム(ＭＣＰ−ＰＤ５１)を用いて０．２５〜２．５０ｋＮの荷重下で四探針方式の電極ユニットを用いて測定した。体積抵抗率は充填密度の変化に伴う体積抵抗率の関係図から充填密度が０．８ｇ/ｃｍ３時の体積抵抗率の値をもって試料の体積抵抗率とした。
EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention does not receive any limitation by this.
(I) Confirmation of form of cotton-like body made of ultrafine carbon fiber and measurement of fiber diameter of ultrafine carbon fiber Observation and photograph using field emission scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, model S-4800) I took a picture. The average fiber diameter of the ultrafine carbon fiber was determined by randomly selecting 250 locations from the obtained electron micrograph (10,000 times or 30,000 times), and measuring all the measurement results (n = 250) was the average fiber diameter.
(Ii) Evaluation Method of Graphite Crystallinity X-ray diffraction measurement was performed using RINT-2100 manufactured by Rigaku Corporation in accordance with JIS R7651 method, and the lattice spacing (d 002 ) and crystallite size (Lc 002 ) were measured.
(Iii) Volume resistivity measurement method Volume resistivity is measured using a four-probe type electrode unit under a load of 0.25 to 2.50 kN using a powder resistance system (MCP-PD51) manufactured by Dia Instruments. It measured using. The volume resistivity was defined as the volume resistivity of the sample with the value of the volume resistivity at a packing density of 0.8 g / cm 3 based on the relationship diagram of the volume resistivity accompanying the change in the packing density.
［実施例１］
熱可塑性樹脂としてポリ−４−メチルペンテン−１（ＴＰＸ：グレードＲＴ−１８［三井化学株式会社製、結晶融点：２３７℃］１００質量部と、熱可塑性炭素前駆体としてメソフェーズピッチＡＲ−ＭＰＨ（三菱ガス化学株式会社製）１１．１質量部を二軸混練機（同方向）（東芝機械株式会社製ＴＥＭ−２６ＳＳ、バレル温度３１０℃、窒素気流下）で溶融混練して混合物を作製した。次いで、上記混合物をメルトブロー溶融紡糸機により、吐出ダイ温度が３９０℃、ガス温度が３９０℃、気体噴出速度が１０００ｍ／ｓの条件により、平均繊維径２３μｍの短繊維形状の前駆体繊維を作製した。次に、シクロヘキサン４００ｍＬ（３１２ｇ）中に上記前駆体繊維４ｇを投入し、この液を油浴中に浸して搖動させながら加熱することで１５分かけて７５℃へ昇温して、該前駆体繊維中のポリ−４−メチルペンテン−１を溶出させた。直ちにこの溶液を熱濾過し、濾液が出にくくなったらフレッシュなシクロヘキサンを追加する操作を繰り返すことにより（２００ｍｌ、８０℃、４回）、ポリ−４−メチルペンテン−１が除去された、メソフェーズピッチ繊維分散液（固形物濃度：０．２９質量％）を調製し室温まで冷却した。次に、該分散液を氷水中に滴下することにより、メソフェーズピッチ繊維分散液の凍結体を作製した。この凍結体を回収し、−２０℃の冷凍室に入れ試料を凍結させた後、６０Ｐａの減圧下にて４８時間凍結乾燥を行い該凍結体中のシクロヘキサンを昇華させ、メソフェーズピッチ繊維からなる低密度構造体を得た。次に、この低密度構造体を空気中で２１５℃、３時間不融化処理を行った後、窒素（酸素含有量１０体積ｐｐｍ未満）雰囲気下で１０００℃処理後、アルゴン（酸素含有量１０体積ｐｐｍ未満）雰囲気下で３０００℃処理を行うことにより、黒鉛化された極細炭素繊維綿状体を作製した。
この極細炭素繊維綿状体を走査電子顕微鏡により観察し、平均繊維径が１１０ｎｍの極細炭素繊維が綿花状に３次元に絡まった構造であることを確認した。該極細炭素繊維綿状体の走査電子顕微鏡の観察像を図１および図２に示す。また、該極細炭素繊維綿状体の格子面間隔(ｄ００２)は０．３３７５ｎｍ、結晶子大きさ（Ｌｃ００２）は４０ｎｍ、体積抵抗率は０．０１２Ω・ｃｍであった。
[Example 1]
100 parts by mass of poly-4-methylpentene-1 (TPX: grade RT-18 [manufactured by Mitsui Chemicals, Inc., crystal melting point: 237 ° C.] as a thermoplastic resin, and mesophase pitch AR-MPH (Mitsubishi, as a thermoplastic carbon precursor) 11.1 parts by mass of Gas Chemical Co., Ltd. was melt-kneaded with a twin-screw kneader (same direction) (TEM-26SS manufactured by Toshiba Machine Co., Ltd., barrel temperature 310 ° C., under nitrogen stream) to prepare a mixture. A short fiber-shaped precursor fiber having an average fiber diameter of 23 μm was produced from the above mixture by a melt blow melt spinning machine under the conditions of a discharge die temperature of 390 ° C., a gas temperature of 390 ° C., and a gas ejection speed of 1000 m / s. Next, 4 g of the above precursor fiber is put into 400 mL (312 g) of cyclohexane, and this solution is immersed in an oil bath and heated while being shaken. The temperature was raised to 75 ° C. over a period of time to elute poly-4-methylpentene-1 in the precursor fiber, and the solution was immediately filtered hot, and fresh cyclohexane was added when the filtrate was difficult to come out. By repeating the operation (200 ml, 80 ° C., 4 times), a mesophase pitch fiber dispersion (solid concentration: 0.29 mass%) from which poly-4-methylpentene-1 was removed was prepared and cooled to room temperature Next, a frozen body of the mesophase pitch fiber dispersion liquid was prepared by dropping the dispersion liquid into ice water, and the frozen body was collected and placed in a freezer at −20 ° C. to freeze the sample. The cyclohexane in the frozen body was sublimated for 48 hours under a reduced pressure of 60 Pa to obtain a low-density structure composed of mesophase pitch fibers. After infusible treatment at 15 ° C. for 3 hours, after treatment at 1000 ° C. in an atmosphere of nitrogen (oxygen content less than 10 ppm by volume), and at 3000 ° C. in an atmosphere of argon (oxygen content less than 10 ppm by volume). Thus, a graphitized ultrafine carbon fiber cotton-like body was produced.
This ultrafine carbon fiber flocculent was observed with a scanning electron microscope, and it was confirmed that the ultrafine carbon fiber having an average fiber diameter of 110 nm was entangled three-dimensionally in the form of cotton. The observation image of the ultrafine carbon fiber flocculent with a scanning electron microscope is shown in FIG. 1 and FIG. Further, the lattice spacing (d 002 ) of the ultrafine carbon fiber flocculent body was 0.3375 nm, the crystallite size (Lc 002 ) was 40 nm, and the volume resistivity was 0.012 Ω · cm.
［実施例２］
実施例１と同様に、ポリ−４−メチルペンテン−１（ＴＰＸ：グレードＲＴ−１８［三井化学株式会社製、結晶融点：２３７℃］１００質量部と、メソフェーズピッチＡＲ−ＭＰＨ（三菱ガス化学株式会社製）１１．１質量部との混合物を調製し、該混合物をマルチホ−ル溶融紡糸機(株式会社ムサシノキカイ社製ＭＭＳ−２０)により、紡糸温度３４６℃の条件により、平均繊維径１００μｍの長繊維形状の前駆体繊維を作製した。次に、８０℃に加熱したシクロヘキサン１００ｍＬ（７８ｇ）に、ヨウ素０．４ｇ（溶剤であるシクロヘキサンに対して０．５１質量％）を溶解させた液中に、上記前駆体繊維２ｇを投入し、該前駆体繊維中のポリ−４−メチルペンテン−１を溶出させた。直ちにこの溶液を熱濾過し、濾液が出にくくなったらフレッシュなシクロヘキサンを追加する操作を繰り返すことにより（２００ｍｌ、８０℃、４回）、ポリ−４−メチルペンテン−１が除去された、メソフェーズピッチ繊維分散液（固形物濃度：０．２８質量％）を調製し、更に室温まで冷却した。該分散液を用いて、以下、実施例１と同様に操作を行い、黒鉛化された極細炭素繊維綿状体を得た。
該極細炭素繊維綿状体を走査電子顕微鏡により観察し、平均繊維径が２００ｎｍの極細炭素繊維が綿花状に３次元に絡まった構造であることを確認した。該極細炭素繊維綿状体の走査電子顕微鏡の観察像を図３および図４に示す。また、該極細炭素繊維綿状体の格子面間隔(ｄ００２)は０．３３７５ｎｍ、結晶子大きさ（Ｌｃ００２）は４６ｎｍ、体積抵抗率は０．０１４Ω・ｃｍであった。
[Example 2]
In the same manner as in Example 1, 100 parts by mass of poly-4-methylpentene-1 (TPX: grade RT-18 [manufactured by Mitsui Chemicals, Inc., crystal melting point: 237 ° C.] and mesophase pitch AR-MPH (Mitsubishi Gas Chemical Co., Ltd.) (Manufactured by the company) 11.1 parts by weight of the mixture was prepared, and the mixture was measured with a multi-hole melt spinning machine (MMS-20 manufactured by Musashino Kikai Co., Ltd.) under conditions of a spinning temperature of 346 ° C. and an average fiber diameter of 100 μm. A fiber-shaped precursor fiber was prepared, and then, in 100 mL (78 g) of cyclohexane heated to 80 ° C., 0.4 g of iodine (0.51% by mass with respect to cyclohexane as a solvent) was dissolved. Then, 2 g of the precursor fiber was added to elute poly-4-methylpentene-1 in the precursor fiber. By repeating the operation of adding fresh cyclohexane (200 ml, 80 ° C., 4 times), poly-4-methylpentene-1 was removed, and mesophase pitch fiber dispersion (solids concentration: 0.28 mass%) Then, using the dispersion, the same procedure as in Example 1 was followed to obtain a graphitized ultrafine carbon fiber flocculent body.
The ultrafine carbon fiber flocculent body was observed with a scanning electron microscope, and it was confirmed that the ultrafine carbon fiber having an average fiber diameter of 200 nm was entangled three-dimensionally in the form of cotton. The observation image of the ultrafine carbon fiber flocculent with a scanning electron microscope is shown in FIG. 3 and FIG. Further, the lattice spacing (d 002 ) of the ultrafine carbon fiber flocculent body was 0.3375 nm, the crystallite size (Lc 002 ) was 46 nm, and the volume resistivity was 0.014 Ω · cm.
［比較例１］
メソフェーズピッチ繊維分散液の凍結体を作製する方法を、メソフェーズピッチ繊維分散液（固形物濃度：０．２９質量％）を、１００ｍＬビーカーに、９０ｍＬずつ小分けにし、−２０℃の冷凍室に入れる方法で行った以外は、実施例１と同様に操作を行い黒鉛化された極細炭素繊維の集合体を得た。
該極細炭素繊維集合体を走査電子顕微鏡により観察し、平均繊維径が１１０ｎｍの極細炭素繊維が、綿花状に３次元に絡まった構造では無く２次元に絡まり層状に集合した、極細炭素繊維の分散性の低い構造であることを確認した。該極細炭素繊維集合体の走査電子顕微鏡の観察像を図５および図６に示す。また、該極細炭素繊維集合体の格子面間隔(ｄ００２)は０．３３７５ｎｍ、結晶子大きさ（Ｌｃ００２）は４０ｎｍ、体積抵抗率は０．０１２Ω・ｃｍであった。
[Comparative Example 1]
A method for preparing a frozen mesophase pitch fiber dispersion is a method in which a mesophase pitch fiber dispersion (solids concentration: 0.29% by mass) is divided into 90 mL portions in a 100 mL beaker and placed in a −20 ° C. freezer. A graphitized ultrafine carbon fiber aggregate was obtained in the same manner as in Example 1 except that the procedure was performed in the same manner as in Example 1.
Dispersion of ultrafine carbon fibers in which the ultrafine carbon fiber aggregates are observed with a scanning electron microscope and the ultrafine carbon fibers having an average fiber diameter of 110 nm are gathered in a two-dimensional entanglement rather than a cotton-like three-dimensional structure. It was confirmed that the structure was low. Scanning electron microscope images of the ultrafine carbon fiber aggregate are shown in FIGS. The ultrafine carbon fiber aggregate had a lattice spacing (d 002 ) of 0.3375 nm, a crystallite size (Lc 002 ) of 40 nm, and a volume resistivity of 0.012 Ω · cm.
［比較例２］
メソフェーズピッチ繊維分散液の凍結体を作製する方法を、メソフェーズピッチ繊維分散液（固形物濃度：０．２８質量％）を、１００ｍＬビーカーに、９０ｍＬずつ小分けにし、−２０℃の冷凍室に入れる方法で行った点以外は、実施例２と同様に操作を行い黒鉛化された極細炭素繊維よりなる集合体を作製した。
該極細炭素繊維集合体を走査電子顕微鏡により観察し、平均繊維径が２００ｎｍの極細炭素繊維が、綿花状に３次元に絡まった構造では無く２次元に絡まり層状に集合した、極細炭素繊維の分散性の低い構造であることを確認した。該極細炭素繊維集合体の走査電子顕微鏡の観察像を図７および図８に示す。また、該極細炭素繊維集合体の格子面間隔(ｄ００２)は０．３３７５ｎｍ、結晶子大きさ（Ｌｃ００２）は４５ｎｍ、体積抵抗率は０．０１１Ω・ｃｍであった。
[Comparative Example 2]
A method for preparing a frozen mesophase pitch fiber dispersion is a method in which a mesophase pitch fiber dispersion (solid concentration: 0.28% by mass) is divided into 90 mL portions in a 100 mL beaker and placed in a −20 ° C. freezer. Except for the points performed in step 1, the same operation as in Example 2 was performed to produce an aggregate made of graphitized ultrafine carbon fibers.
Dispersion of ultrafine carbon fibers in which the ultrafine carbon fiber aggregates are observed with a scanning electron microscope, and the ultrafine carbon fibers having an average fiber diameter of 200 nm are gathered in a two-dimensional entanglement rather than a cotton-like three-dimensional structure. It was confirmed that the structure was low. FIGS. 7 and 8 show images of the ultrafine carbon fiber aggregate observed with a scanning electron microscope. Moreover, the lattice spacing (d 002 ) of the ultrafine carbon fiber aggregate was 0.3375 nm, the crystallite size (Lc 002 ) was 45 nm, and the volume resistivity was 0.011 Ω · cm.
本発明の製造方法によって得られる極細炭素繊維綿状体は電池電極材料、電池電極添加材、および樹脂添加材など種々の用途に好適である。 The ultrafine carbon fiber flocculent obtained by the production method of the present invention is suitable for various uses such as battery electrode materials, battery electrode additives, and resin additives.
Claims (5)
（１） 熱可塑性樹脂１００質量部と、レーヨン、ピッチ、ポリアクリロニトリル、ポリα−クロロアクリロニトリル、ポリカルボジイミド、ポリイミド、ポリエーテルイミド、ポリベンゾアゾール、リグニンおよびアラミドよりなる群から選ばれる少なくとも１種の熱可塑性炭素前駆体１〜１５０質量部からなる混合物から前駆体繊維を形成する工程。
（２） 溶剤により前駆体繊維中の熱可塑性樹脂を溶解除去して熱可塑性炭素前駆体繊維とし、その分散液を作製する工程。
（３） 前記熱可塑性炭素前駆体繊維分散液を冷媒中に滴下させ、該分散液の凍結体を作製する工程。
（４） 前記凍結体を凍結乾燥させることにより、熱可塑性炭素前駆体繊維から成る低密度構造体を形成させる工程。
（５） 前記低密度構造体を不融化処理した後、炭素化または黒鉛化する工程。 A method for producing an ultrafine carbon fiber flocculent comprising the steps (1) to (5) below.
(1) 100 parts by mass of a thermoplastic resin and at least one selected from the group consisting of rayon, pitch, polyacrylonitrile, poly α-chloroacrylonitrile, polycarbodiimide, polyimide, polyetherimide, polybenzoazole, lignin and aramid The process of forming precursor fiber from the mixture which consists of 1-150 mass parts of thermoplastic carbon precursors.
(2) A step of dissolving and removing the thermoplastic resin in the precursor fiber with a solvent to obtain a thermoplastic carbon precursor fiber, and producing a dispersion thereof.
(3) A step of dripping the thermoplastic carbon precursor fiber dispersion into a refrigerant to produce a frozen body of the dispersion.
(4) A step of forming a low-density structure composed of thermoplastic carbon precursor fibers by freeze-drying the frozen body.
(5) A process of carbonizing or graphitizing the low-density structure after infusibility treatment.
Priority Applications (1)
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