JP3606782B2 - Conductive paint - Google Patents
Conductive paint Download PDFInfo
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- JP3606782B2 JP3606782B2 JP2000017834A JP2000017834A JP3606782B2 JP 3606782 B2 JP3606782 B2 JP 3606782B2 JP 2000017834 A JP2000017834 A JP 2000017834A JP 2000017834 A JP2000017834 A JP 2000017834A JP 3606782 B2 JP3606782 B2 JP 3606782B2
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- boron
- fiber
- carbon fiber
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- mass
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 239000003973 paint Substances 0.000 title claims description 41
- 229920000049 Carbon (fiber) Polymers 0.000 claims description 74
- 239000004917 carbon fiber Substances 0.000 claims description 74
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 53
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 52
- 229910052796 boron Inorganic materials 0.000 claims description 52
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 23
- 239000000843 powder Substances 0.000 claims description 19
- 239000013078 crystal Substances 0.000 claims description 16
- 229920005989 resin Polymers 0.000 claims description 16
- 239000011347 resin Substances 0.000 claims description 16
- 229910052799 carbon Inorganic materials 0.000 claims description 12
- 229910052751 metal Inorganic materials 0.000 claims description 9
- 239000002184 metal Substances 0.000 claims description 9
- 239000000463 material Substances 0.000 claims description 7
- 229920001187 thermosetting polymer Polymers 0.000 claims description 5
- 229920005992 thermoplastic resin Polymers 0.000 claims description 4
- 238000001035 drying Methods 0.000 claims description 3
- 239000004567 concrete Substances 0.000 claims description 2
- 239000004033 plastic Substances 0.000 claims description 2
- 229920003023 plastic Polymers 0.000 claims description 2
- 239000002023 wood Substances 0.000 claims description 2
- 239000010419 fine particle Substances 0.000 claims 1
- 239000000835 fiber Substances 0.000 description 51
- 239000000945 filler Substances 0.000 description 22
- 238000010438 heat treatment Methods 0.000 description 22
- 238000000034 method Methods 0.000 description 19
- 239000011248 coating agent Substances 0.000 description 11
- 238000000576 coating method Methods 0.000 description 11
- 150000001639 boron compounds Chemical class 0.000 description 10
- 238000002425 crystallisation Methods 0.000 description 9
- 230000008025 crystallization Effects 0.000 description 9
- 238000002156 mixing Methods 0.000 description 9
- 239000000203 mixture Substances 0.000 description 8
- 238000010298 pulverizing process Methods 0.000 description 7
- ZWEHNKRNPOVVGH-UHFFFAOYSA-N 2-Butanone Chemical compound CCC(C)=O ZWEHNKRNPOVVGH-UHFFFAOYSA-N 0.000 description 6
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 6
- 238000005087 graphitization Methods 0.000 description 6
- 239000002245 particle Substances 0.000 description 6
- 239000003054 catalyst Substances 0.000 description 5
- 239000003795 chemical substances by application Substances 0.000 description 5
- 230000000052 comparative effect Effects 0.000 description 5
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- 239000002657 fibrous material Substances 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 239000002134 carbon nanofiber Substances 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- 229910002804 graphite Inorganic materials 0.000 description 4
- 239000010439 graphite Substances 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- LCGLNKUTAGEVQW-UHFFFAOYSA-N Dimethyl ether Chemical compound COC LCGLNKUTAGEVQW-UHFFFAOYSA-N 0.000 description 3
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 description 3
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 3
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 3
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 239000012298 atmosphere Substances 0.000 description 3
- MTHSVFCYNBDYFN-UHFFFAOYSA-N diethylene glycol Chemical compound OCCOCCO MTHSVFCYNBDYFN-UHFFFAOYSA-N 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 229910052709 silver Inorganic materials 0.000 description 3
- 239000004332 silver Substances 0.000 description 3
- 239000007858 starting material Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 241000287828 Gallus gallus Species 0.000 description 2
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- CTQNGGLPUBDAKN-UHFFFAOYSA-N O-Xylene Chemical compound CC1=CC=CC=C1C CTQNGGLPUBDAKN-UHFFFAOYSA-N 0.000 description 2
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 239000006230 acetylene black Substances 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 229910021393 carbon nanotube Inorganic materials 0.000 description 2
- 239000002041 carbon nanotube Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000005611 electricity Effects 0.000 description 2
- 238000009503 electrostatic coating Methods 0.000 description 2
- 239000003822 epoxy resin Substances 0.000 description 2
- 244000144992 flock Species 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 230000005484 gravity Effects 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- 239000005011 phenolic resin Substances 0.000 description 2
- 229920000647 polyepoxide Polymers 0.000 description 2
- 230000003068 static effect Effects 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 239000008096 xylene Substances 0.000 description 2
- UOCLXMDMGBRAIB-UHFFFAOYSA-N 1,1,1-trichloroethane Chemical compound CC(Cl)(Cl)Cl UOCLXMDMGBRAIB-UHFFFAOYSA-N 0.000 description 1
- SCYULBFZEHDVBN-UHFFFAOYSA-N 1,1-Dichloroethane Chemical compound CC(Cl)Cl SCYULBFZEHDVBN-UHFFFAOYSA-N 0.000 description 1
- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical compound [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 description 1
- 239000004925 Acrylic resin Substances 0.000 description 1
- 229920000178 Acrylic resin Polymers 0.000 description 1
- 241000234282 Allium Species 0.000 description 1
- 235000002732 Allium cepa var. cepa Nutrition 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 239000004640 Melamine resin Substances 0.000 description 1
- 229920000877 Melamine resin Polymers 0.000 description 1
- LSDPWZHWYPCBBB-UHFFFAOYSA-N Methanethiol Chemical compound SC LSDPWZHWYPCBBB-UHFFFAOYSA-N 0.000 description 1
- NTIZESTWPVYFNL-UHFFFAOYSA-N Methyl isobutyl ketone Chemical compound CC(C)CC(C)=O NTIZESTWPVYFNL-UHFFFAOYSA-N 0.000 description 1
- UIHCLUNTQKBZGK-UHFFFAOYSA-N Methyl isobutyl ketone Natural products CCC(C)C(C)=O UIHCLUNTQKBZGK-UHFFFAOYSA-N 0.000 description 1
- 238000001069 Raman spectroscopy Methods 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 229920001807 Urea-formaldehyde Polymers 0.000 description 1
- BZHJMEDXRYGGRV-UHFFFAOYSA-N Vinyl chloride Chemical compound ClC=C BZHJMEDXRYGGRV-UHFFFAOYSA-N 0.000 description 1
- 238000000862 absorption spectrum Methods 0.000 description 1
- 150000008065 acid anhydrides Chemical class 0.000 description 1
- 239000012190 activator Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 150000001412 amines Chemical class 0.000 description 1
- 238000001241 arc-discharge method Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000005885 boration reaction Methods 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 239000012461 cellulose resin Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000000748 compression moulding Methods 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 239000007822 coupling agent Substances 0.000 description 1
- 239000003431 cross linking reagent Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 239000002270 dispersing agent Substances 0.000 description 1
- 238000000635 electron micrograph Methods 0.000 description 1
- 239000000839 emulsion Substances 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- 150000002170 ethers Chemical class 0.000 description 1
- 125000001495 ethyl group Chemical group [H]C([H])([H])C([H])([H])* 0.000 description 1
- 239000005038 ethylene vinyl acetate Substances 0.000 description 1
- 239000007849 furan resin Substances 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 238000005469 granulation Methods 0.000 description 1
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- 150000008282 halocarbons Chemical class 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
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- 229910010272 inorganic material Inorganic materials 0.000 description 1
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- 150000002576 ketones Chemical class 0.000 description 1
- 239000004816 latex Substances 0.000 description 1
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- 230000007774 longterm Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 150000002902 organometallic compounds Chemical class 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 229920001568 phenolic resin Polymers 0.000 description 1
- 239000000049 pigment Substances 0.000 description 1
- 239000004014 plasticizer Substances 0.000 description 1
- 229920001200 poly(ethylene-vinyl acetate) Polymers 0.000 description 1
- 229920002037 poly(vinyl butyral) polymer Polymers 0.000 description 1
- 229920006122 polyamide resin Polymers 0.000 description 1
- 229920005749 polyurethane resin Polymers 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
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- 230000003014 reinforcing effect Effects 0.000 description 1
- 238000007761 roller coating Methods 0.000 description 1
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- 239000010703 silicon Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
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- 238000007711 solidification Methods 0.000 description 1
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- 238000005507 spraying Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- -1 storage stability Substances 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 239000002562 thickening agent Substances 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
- 229920006337 unsaturated polyester resin Polymers 0.000 description 1
- 238000007740 vapor deposition Methods 0.000 description 1
- 239000012808 vapor phase Substances 0.000 description 1
- 238000001947 vapour-phase growth Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Paints Or Removers (AREA)
Description
【0001】
【発明の属する技術分野】
本発明は、電気抵抗が低く、長期間の使用に耐える導電性塗料に関するものであり、特に静電塗装、静電気防止や電磁波シールドを目的に、または抵抗体、回路やコピー機ロール用の導電性インク等に好適に使用される導電性塗料に関する。
【0002】
【従来の技術】
最近、電子機器などの電磁波シールド性、制電性、静電気防止性が要求される分野において、導電性の塗料が使用されるようになっている。これらの塗料においては、フィラーとして銀、アルミニウム、銅などの金属粉、カーボン粉などが使用されている。また、静電塗装用の下地塗料にも導電性の良好な塗料が要求されている。
【0003】
【発明が解決しようとする課題】
しかしながら、銀は高価で高比重であり、また他の金属粉は酸化、腐食等により導電性が低下するという欠点がある。一方、カーボン粉は安価で金属粉のような問題は少ないが、導電性が不十分であるなどの欠点があった。これはカーボン粉自身の導電性が金属粉に比べて低いことと、アスペクト比(長さ/径)が小さいことに起因する。このためこの分野では、導電性が高く、低比重で、アスペクト比が大きく、安価なフィラーが望まれている。
【0004】
そこで、特公平6−39576号公報における繊維径が小さくアスペクト比が大きい特異な構造を有する易黒鉛化性の炭素質繊維や、特開平7−102197号公報における微細糸状の炭素フィブリルが互いに絡み合った凝集体からなる炭素フィブリル材料など、前記の欠点を改良するフィラーが提案されている。
しかし、これらフィラーでは、十分な導電性を得ようとすると数十質量%という多量を添加する必要があり、少なからずコストアップにつながるだけでなく、樹脂との混合時に取り扱いが煩雑になったり、混合後の塗料の流動性が低下して塗布が難しくなるといった問題が起こってくる。
【0005】
従って、本発明は導電性が高く、化学的に安定であり、かつ低コストの導電性塗料を提供することを目的とする。
【0006】
【課題を解決するための手段】
本発明者らは、先に、特願平11−81260号明細書において、従来得られなかった高い結晶性を持つ微細な炭素繊維とその製造法、及びその繊維をフィラーとしてより性能の高い電池用電極を開示した。その炭素繊維は、直径が0.01〜5μm、アスペクト比が10以上で、繊維中にホウ素を0.1〜3質量%含有する微細な炭素繊維で、X線回折法で求めた炭素の面間隔d002 が3.385Å以下、結晶のc軸方向の厚さLcが400Å以下である微細な炭素繊維である。
【0007】
この微細な炭素繊維は高い結晶性を持つため導電性に優れる。そこで、本発明者らは前記の従来の導電性塗料の欠点を改良するため、この微細な炭素繊維について検討を進めた結果、少量の添加で高い導電性を有する導電性塗料が得られることを見い出した。さらに、同じ添加量であれば抵抗値を従来の値の2分の1以下にできることも見い出した。
【0008】
こうして、本発明は、熱可塑性樹脂または熱硬化性樹脂70〜99.8質量部と、直径が0.01〜5μm、アスペクト比が10以上で、繊維中にホウ素を0.1〜3質量%含有する微細な炭素繊維30〜0.2質量部を含有してなることを特徴とする導電性塗料を提供する。
微細な炭素繊維の、X線回折法で求めた炭素の面間隔d002 は3.385Å以下で、結晶のc軸方向の厚さLcが400Å以下であることができる。
【0009】
また、微細な炭素繊維の粉体抵抗が嵩密度0.8g/cm3 のとき0.01Ω・cm以下であり、得られる乾燥塗料の抵抗値は0.01Ω・cm以下であることができる。
【0010】
【発明の実施の形態】
(微細な炭素繊維)
本発明の導電性塗料に添加する炭素繊維は直径が0.01〜5μm、アスペクト比が10以上の微細な炭素繊維である。
繊維径が0.01μm未満であると繊維の強度が弱く、フィラーとして使用した場合に繊維の切断が多くなり、繊維としての機能が損なわれやすい。一方、繊維は、フィラーとしての添加率(質量%)を一定とした場合、径が太くなるとそれだけ繊維の本数が減ることになり、フィラーとしての繊維の機能が十分発揮されない。また、径が5μmより太くなると繊維自体の生産性が著しく低下するので、工業的にコストが高くなる。これらの理由から繊維径は0.01〜5μmである。1μm以下の繊維径のものが好ましい。
【0011】
また、繊維のアスペクト比が10未満では炭素繊維を塗料に添加した場合の塗料の導電性が十分ではない。好ましくはアスペクト比が50以上である。
微細な炭素繊維の長さは特に制限はなく、その下限はアスペクト比の下限から定まる長さが好ましい。繊維の長さは、長すぎると繊維の絡み合い等によりフィラーとしての分散性に問題が生じる、あるいは塗膜表面に凹凸を生じやすいので、上限は400μmが好ましく、さらに好ましくは100μmである。したがって、例えばアスペクト比が50以上の場合、繊維径が0.01μmでは繊維長さは0.5μm以上、径が1μmでは長さは50μm以上が好ましい。その上限はいずれも好ましくは400μm、さらに好ましくは100μmである。
【0012】
本発明に用いる微細な炭素繊維はその結晶内にホウ素を含有することを特徴とする。本発明者らは、微細な炭素繊維の結晶内にホウ素を含ませることにより、所望の導電性などの特性を得ることに成功したものである。その製法については後述するが、ホウ素含有量0.1〜3質量%で効果的に高結晶化、即ち、高導電性が達成される。好ましくは0.2〜3質量%のホウ素を含む。しかし、ホウ素は熱処理における繊維の結晶化の際に存在すればよく、高結晶化した後さらに高温で処理する等によりホウ素が揮散し、含有量が0.1質量%を下回らない範囲で添加量よりも濃度が低くなっても構わない。
【0013】
また、本発明に用いるホウ素を結晶内に含有する微細な炭素繊維は、結晶性が高く、X線回折法で求めた面間隔d002 が3.385Å以下であり、結晶のc軸方向の厚さLcが400Å以下の範囲のものであることができる。微細な炭素繊維において面間隔d002 を3.385Å以下にすることは従来可能ではなかった。さらに、この微細な炭素繊維はd002 が小さいにもかかわらず、結晶のc軸方向の厚さLcが400Å以下であることができることも従来にない特徴である。また、この微細な炭素繊維は、ホウ素を含有し、d002 及びLcの値が上記の範囲内にあり、かつラマン吸収スペクトルのR値(1580cm−1の吸収強度IG と1360cm−1の吸収強度ID の比R=ID /IG )が0.5以上となる特徴を有する。
【0014】
さらに、この微細な炭素繊維の粉体抵抗は、嵩密度が0.8g/cm3 のとき、0.01Ω以下であることができる。微細な炭素繊維がこのように高い導電性を有することにより、それを含有する塗料の導電性も向上する。
(微細な炭素繊維の製法)
本発明で使用する上記の微細な炭素繊維はホウ素を繊維の結晶構造の中に取り込み、その触媒的な作用により製造することができる。高結晶化に効果的なホウ素の含有量は、上記の如く、一般的には0.1〜3質量%、好ましくは0.2〜3質量%である。
【0015】
出発原料とする炭素繊維は、ベンゼン等の有機化合物の熱分解により気相で成長させた微細な炭素繊維を用いることができる。この炭素繊維は、例えば特開平7−150419号公報、特開平5−321039号公報、特開昭60−215816号公報、特開昭61−70014号公報、特公平5−36521号公報、特公平3−61768号公報等に示される方法で製造することができる。また、繊維径が0.01μm以上であれば、同じ年輪構造をもつカーボンナノチューブやカーボンナノファイバーと呼ばれる微細な繊維状物質も使用できる。従って、アーク放電法やレーザー法等によって製造される多重構造のカーボンナノチューブ、カーボンナノファイバー等についても使用できる。
【0016】
本発明者らの検討によって、このような微細な炭素繊維は、熱処理で結晶性を上げることはできるが、熱処理だけではd002 は3.385Åが限界であり、それより結晶性の向上が望めないことがわかった。そこでさらに、高結晶化するために黒鉛化の触媒について検討した結果、ホウ素が特に有効であった。
通常の炭素材料については、ホウ素を添加して熱処理し結晶性を高めることは種々検討されている。(「炭素」1996、No. 172、89〜94頁、特開平3−245458号公報、特開平5−251080号公報、特開平5−266880号公報、特開平7−73898号公報、特開平8−31422号公報、特開平8−306359号公報、特開平9−63584号公報、特開平9−63585号公報)しかし、径が5μm以下の微細な気相法炭素繊維に対して、ホウ素を導入して特性を改善した例は今までにない。その理由は下記▲1▼〜▲5▼のように、形状の特徴からなかなかホウ素を用いた黒鉛化が行いにくいことと、繊維が特殊な構造を持つためにホウ素の触媒効果が期待できないためであった。
【0017】
▲1▼ 気相法炭素繊維は、繊維の切断面の結晶構造が同心円状に発達した長ねぎ状の繊維である。
▲2▼ 繊維の長さは製造条件によって異なるが、例えば0.01〜0.5μm程度の径の繊維では単繊維だけでなく枝分かれした繊維も多く存在するので明確には規定しがたいが、直線部分を走査型電子顕微鏡で測定した限りでは、平均が少なくとも5μm以上あるものがほとんどである。
【0018】
▲3▼ また、この繊維は長繊維に加えて枝分かれした微細な繊維も含むために、長い繊維はもちろんのこと、5μm程度の短い繊維であっても、少なくとも大きさが10μm以上、場合によっては100μm以上の大きなフロック状になりやすい。
▲4▼ したがって、集合体としての嵩密度は小さく、0.05g/cm3 以下、通常は0.01g/cm3 以下である。しかもフロック状の立体構造を持っているので、黒鉛化触媒との接触が難しく、均一にホウ素化しがたい。
【0019】
▲5▼ また、微細な炭素繊維は表面がしっかりしたベーサルプレーン(六角網目構造の平面)で覆われているので、ホウ素を用いて黒鉛化してもポリゴニゼーション時に立体障害のため結晶性の向上が阻害される。
本発明者らは、微細な炭素繊維にホウ素をドーピングすることにより高結晶化できることを見い出した。
【0020】
ホウ素をドーピングするためには、原料の微細な炭素繊維として、ドーピングしやすいあまり結晶の発達していない低温処理品、好ましくは1500℃以下で熱処理された炭素繊維を用いることが好ましい。低温処理の炭素繊維であっても、ホウ素を触媒として用いた処理(ホウ素化処理)の時に最終的には黒鉛化温度まで加熱処理されるので、結晶の未発達の未熱処理品でも十分使用できる。2000℃以上、好ましくは2300℃以上の温度で黒鉛化処理された炭素繊維を用いることもできなくはないが、エネルギーの削減の面から考えれば何ら前もって黒鉛化処理しておく必要はなく、むしろ低温処理品を用いて黒鉛化と同時に触媒作用を働かせるほうが好ましい。
【0021】
また、炭素中のホウ素の含有量が最も多くかつドープしやすい温度は2000〜2300℃との報告もあり、これより高い温度で処理されて結晶化した材料では触媒効果が小さい。
原料の微細な炭素繊維として、取扱容易のためあらかじめ解砕、粉砕したものを用いることができるが、解砕、粉砕はホウ素またはホウ素化合物との混合ができる程度で十分である。すなわち、ホウ素化処理した後でも最終的には解砕、粉砕、分級等のフィラー化処理を行うので、ホウ素化処理の前にフィラーとしての適正な長さにする必要はない。気相成長法で一般的に得られる太さ(径)0.01〜5μm程度、長さ0.5〜400μm程度の炭素繊維をそのまま用いることができる。これらはフロック状になっていてもよい。また原料繊維は熱処理したものでもよいが、熱処理温度は1500℃以下とすることが好ましい。
【0022】
ホウ素をドーピングするために用いるホウ素源としては、ホウ素化処理は2000℃以上の温度で行われるので、少なくとも2000℃に達する前に分解等によっても蒸発しない物質、例えば、元素状ホウ素、B2 O3 、ホウ素、B4 C,BN、その他のホウ素化合物を使用することが好ましい。
炭素にホウ素をドーピングできる量は一般的には3質量%以下である。ホウ素含有量0.1〜3質量%で効果的に高結晶化、即ち、高導電性が達成される。好ましくは0.2〜3質量%のホウ素を含む。しかし、ホウ素は熱処理における繊維の結晶化の際に存在すればよく、高結晶化した後さらに高温で処理する等によりホウ素が揮散し、含有量が0.1質量%を下回らない範囲で添加量よりも濃度が低くなっても構わない。
【0023】
したがって、配合時のホウ素またはホウ素化合物の添加量は反応率を考慮して炭素量に対してホウ素原子換算で10質量%以下で十分である。ホウ素の使用量が多いと処理コストが高くなるだけでなく、熱処理の段階で溶融焼結しやすく、固まったり繊維表面を被覆して電気抵抗を上昇させるなど、フィラー特性が失われることがある。
【0024】
ホウ素の導入反応を効率よく行うには、炭素繊維とホウ素またはホウ素化合物とをよく混合しできるだけ均一に接触させる必要がある。微細な炭素繊維は三次元の立体構造を持ち、フロック状を形成しやすいだけでなく、嵩密度がきわめて小さく空隙率が非常に大きい。しかも添加するホウ素量は10質量%以下、好ましくは5質量%以下と少ないので、単に両者を混合しただけでは均一に接触させることは難しい。そこで、ホウ素またはホウ素化合物の粒子はできるだけ粒径の小さいものを使用して炭素繊維とホウ素化合物をできるだけ均一に接触させる必要がある。また、粒子が大きいと部分的に高濃度領域が発生することになり、固結化の原因になりかねない。具体的には、粒度は平均粒径で100μm以下、好ましくは50μm以下、より好ましくは20μm以下である。
【0025】
炭素繊維とホウ素またはホウ素化合物とを均一に混合しそのまま熱処理することもできるが、気相法による微細な炭素繊維は嵩密度が非常に小さいため、好ましくは高密度化し、かつその状態をできるだけ維持(固定化)して熱処理する。その好ましい方法として、両者を混合した後、混合物に圧力を加えて圧縮し高密度化して固定化する方法が挙げられる。
【0026】
炭素繊維とホウ素またはホウ素化合物との混合は、均一性が保持できればいずれの方法でもよい。混合機としては市販の混合機のいずれでもよいが、微細な炭素繊維はフロック状になりやすいので、これを解砕するためにチョッパー付きのヘンシェルミキサータイプのものであればより好ましい。使用する原料炭素繊維は先に述べたように製造されたままのものでも、その1500℃以下の温度での処理品でもよい。ただし、経済的には製造されたままのものが好ましい。
【0027】
炭素繊維とホウ素またはホウ素化合物との混合物を高密度化し、両者が分離しないように固定化する方法としては、成形法、造粒法、あるいは混合物をるつぼに入れて一定の形状に圧縮して詰め込む方法等、いずれの方法でもよい。また成形法の場合、成形体の形状は円柱状、板状、直方体等、いずれの形状でもよい。このようにしてホウ素またはホウ素化合物を添加し、嵩密度を高めた炭素繊維は次に熱処理する。
【0028】
ホウ素を炭素の結晶内に導入するために必要な処理温度は一般的に2000℃以上、好ましくは2300℃以上である。処理温度が2000℃に満たないとホウ素と炭素との反応性が悪く、ホウ素の導入が難しい。ホウ素の導入を一層促進し、かつ炭素の結晶性を向上させ、特にd002 を3.385Å以下にするには2300℃以上に保つことが好ましい。熱処理温度の上限は特にないが、装置等の制約から3200℃程度である。
【0029】
使用する熱処理炉は2000℃以上、好ましくは2300℃以上の目標とする温度が保持できる炉であればよく、通常のアチソン炉、抵抗炉、高周波炉等の何れの装置でもよい。また、場合によっては、粉体または成形体に直接通電して加熱する方法も使用できる。
熱処理の雰囲気は、非酸化性の雰囲気、好ましくはアルゴン等の希ガス雰囲気である。熱処理の時間は、生産性の面からはできるだけ短いほうが好ましい。特に長時間加熱していると、焼結が進行するので収率も悪化する。したがって、成形体等の中心部の温度が目標温度に達した後、1時間以下の保持時間で十分である。
【0030】
圧縮成形等で高密度化した炭素繊維は熱処理すると一部が焼結し、ブロック状になるので、フィラーとして適する形態とするために、成形体を解砕することが望ましい。そのため、このブロックを解砕、粉砕、分級してフィラーとして適するように処理すると同時に、非繊維物を分離する。その際に粉砕しすぎるとフィラー性能が低下し、また粉砕が不十分だと塗料主剤との混合がうまくいかず、添加効果が出ないおそれがある。
【0031】
フィラーとして望ましい形態にするためには、熱処理後のブロック状物をまず2mm以下の大きさに解砕し、さらに粉砕機で粉砕する。解砕機としては通常使用されるアイスクラッシャーやロートプレックス等の装置が使用できる。粉砕機としては衝撃式粉砕機のパルベライザーや自由粉砕機、またミクロジェット等の粉砕機が使用できる。非繊維物を分離する分級は気流式分級機等で行うことができる。粉砕分級条件は粉砕機の種類や操作条件によって異なるが、フィラー特性を発揮させるためには、繊維の長さが5〜400μmにするのが好ましい。アスペクト比は好ましくは10以上、さらに好ましくは50以上である。
【0032】
また、粉砕分級後の嵩密度は、0.001〜0.2g/cm3 、好ましくは0.005〜0.15g/cm3 、さらに好ましくは0.01〜0.1g/cm3 である。嵩密度が0.2g/cm3 以上になると、径によっては繊維の長さが5μm以下のように短くなりフィラー効果が低下する。また、0.001g/cm3 より小さいと径によっては400μmを超えるような長いものとなり、フィラーとしての詰まりが悪くなる。嵩密度とは、容器に繊維を充填し振動させ、体積がほぼ一定に達したときの体積と質量から求めたタッピング嵩密度である。
【0033】
上記のような方法で製造した繊維中にホウ素を含有する微細な炭素繊維は、嵩密度0.8g/cm3 のときの粉体抵抗が、0.01Ω・cm以下になることができる。一方、これと同形状で繊維中にホウ素を含まない気相成長法による微細な炭素繊維は、嵩密度0.8g/cm3 のときの粉体抵抗が0.01〜0.03Ω・cm程度である。これは、黒鉛化時にホウ素を触媒として添加すると結晶性が向上し、その結果、導電性が向上したことによる。このように、従来より導電性がほぼ1桁向上した微細な炭素繊維を用いることにより、電気抵抗が低く、静電気防止や電磁波シールド等の目的に好適に使用される本発明の導電性塗料を提供することができる。
【0034】
(樹脂)
本発明の導電性塗料に用いることができる熱可塑性樹脂または熱硬化性樹脂を例示すると、熱可塑性樹脂としては、ポリアミド樹脂、ポリウレタン樹脂、塩化ビニル樹脂、エチレン−酢酸ビニル共重合体、アクリル樹脂、セルロース樹脂、ブチラール樹脂など、熱硬化性樹脂としては、フェノール樹脂、エポキシ樹脂、尿素樹脂、メラミン樹脂、キシレン樹脂、フラン樹脂、不飽和ポリエステル樹脂、ケイ素樹脂などが挙げられ、またこれらの前駆体も使用できる。
【0035】
これら樹脂に対して、必要であれば、公知の硬化剤や硬化助剤、硬化用触媒や活性剤を使用することができる。例えば、エポキシ樹脂に対し、硬化剤としてアミン系やメルカプタン系化合物、あるいは酸無水物などが使用できる。
上記の樹脂はエマルジョンまたはラテックスとして用いることもできるが、溶媒に溶かして、溶液として使用するのが好ましい。
【0036】
溶媒は、前記樹脂を溶解または分散するものであれば特に制限はない。例えば、トルエン、キシレンなどの炭化水素、ジクロロエタン、トリクロロエタンなどのハロゲン化炭化水素、イソプロピルアルコール、ブタノールなどのアルコール類、メチルエチルケトン、メチルイソブチルケトンなどのケトン類、酢酸エチル、プロピル酸エチルなどのエステル類、エチレングリコールのメチルエーテル、ジエチレングリコールのジメチルエーテルなどのエーテル類、水などが使用できる。
【0037】
(導電性塗料の組成)
本発明において熱可塑性樹脂あるいは熱硬化性樹脂に対する微細な炭素繊維の含有量は、内割りで、30〜0.2質量%、好ましくは10〜0.5質量%である。樹脂に対して炭素繊維が30質量%を超えると流動性が低下し、均一な塗布が困難になる、塗膜強度、基質の接着性が低下するなどの問題が起こる。また、0.2質量%に達しないと炭素繊維による効果が乏しく、塗料に用いたときの導電性が十分でない。
【0038】
溶媒の量は特に限定されず、塗料の種類、保存性、塗工性、乾燥性などを考慮して決めればよい。
本発明の導電性塗料には、必要に応じて塗料特性を向上させるための添加剤を使用することができる。例えば、フィラーである炭素繊維の分散性を上げるための分散剤、他の繊維状物や無機物、金属などの粉体や薄片物、印刷適性を上げるためのレベリング剤、熱や酸化、光に対する安定剤、カップリング剤、増粘剤、顔料、可塑剤、架橋剤、充填剤などを混ぜることができる。
【0039】
また、さらに導電性を向上させるためには、他の導電性粉体と混合して使用することもできる。他の導電性粉体としては、アセチレンブラック、ケッチェンブラック等のカーボンブラック、グラファイト粉、各種炭素繊維、金、銀、ニッケル、アルミニウム等の粉末または繊維、金属コートガラス繊維、などが挙げられる。
【0040】
(塗料の製造)
本発明の導電性塗料は、通常、前記樹脂の溶液と微細な炭素繊維を混合することによって製造することができる。混合装置としては、3本ロール、ボールミルなどの通常の装置を用いることができる。また本発明の導電性塗料は、刷毛塗り、ローラーコート、スプレーなどの通常の方法で塗布することができる。
【0041】
このようにして製造された本発明の導電性塗料は、塗工し乾燥後、0.01Ω・cm以下の抵抗値を有することができる。
【0042】
【発明の効果】
本発明の導電性塗料は、高い導電性を有する微細な炭素繊維が多くの接触点で接触しながら樹脂中に均一に分散しているので、極めて導電性の高い塗料である。また、炭素繊維の補強効果により塗膜強度に優れ、金属フィラーのように長期間の使用で酸化、腐食等による導電性の低下することもない。したがって、コンクリート、金属、木材、プラスチックなど、各種基材に塗布し、静電気防止や電磁波シールドの目的に好適に使用できる。
【0043】
【実施例】
以下、実施例により本発明を具体的に説明する。
(実施例1〜4、および比較例1〜2)
出発原料である微細な炭素繊維は、遷移金属を含有する有機金属化合物の存在のもとにベンゼンを熱分解する公知の方法(例えば特開平7−150419号公報)で得た炭素繊維をさらに1200℃で熱処理して得た。得られた炭素繊維はフロック状に集合していたがこれを解砕し、嵩密度を0.02g/cm3 、繊維の長さを10〜100μmとした。繊維径は大部分が0.5μm以下(電子顕微鏡写真で観察した平均的な繊維径は0.2μm)であった。この炭素繊維のX線回折による炭素の面間隔d002 は3.407Åで、結晶のc軸方向の厚さLcは56Åであった。
【0044】
この繊維2.88kgに平均粒径15μmのB4 C粉末を120g添加し、ヘンシェルミキサーで十分に混合した。この混合物を容量50リットルの円筒状の黒鉛ルツボに詰め込み圧縮して、嵩密度を0.075g/cm3 とした。黒鉛製の加圧板で圧縮したまま蓋をし、アチソン炉に入れて加熱処理した。このときの温度は2900℃、2900℃になってからの加熱時間は60分間であった。
【0045】
加熱処理後冷却し、ルツボから炭素繊維を取り出し、バンタムミルで粉砕し、その後、非繊維状物を気流分級機で分離した。
得られた繊維の径は2900℃熱処理前と変わらず大部分が0.5μm以下、長さは5〜30μm、嵩密度は0.04g/cm3 であった。また、この繊維のホウ素含有量は1.03質量%、d002 は3.380Å、Lcは290Åであった。また、嵩密度0.8g/cm3 のときの粉体抵抗は0.003Ω・cmであった。
【0046】
次にこの微細な炭素繊維を用いて以下のように導電性塗料を作製した。フェノール樹脂の20質量%メチルエチルケトン溶液に、表1に示す質量比で前記微細な炭素繊維を3本ロールで混合して、各導電性塗料を得た。
これをガラス板上に塗布し、溶剤を乾燥後、ガラスから塗膜をはがして、体積固有抵抗および引張強度を測定した。その結果を表1に示す。
(比較例3〜4)
実施例で示した出発原料である微細な炭素繊維3.0kgを容量50リットルの円筒状の黒鉛ルツボに詰め込み圧縮して、嵩密度を0.075g/cm3 とした。黒鉛製の加圧板で圧縮したまま蓋をし、アチソン炉に入れて加熱処理した。このときの温度は2900℃、2900℃になってからの加熱時間は60分間であった。加熱処理後冷却し、ルツボから炭素繊維を取り出し、バンタムミルで粉砕し、その後、非繊維状物を気流分級機で分離した。
【0047】
得られた繊維の径は2900℃熱処理前と変わらず大部分が0.5μm以下、長さは5〜30μm、嵩密度は0.04g/cm3 であった。また、この繊維のd002 は3.388Å、Lcは280Åであった。また、嵩密度0.8g/cm3 のときの粉体抵抗は0.013Ω・cmであった。
この微細な炭素繊維を用いて実施例と同様の方法で表1に示す質量比で塗料を作製し、体積固有抵抗および引張強度を測定した。その結果を表1に示す。
(比較例5)
微細な炭素繊維の代わりにアセチレンブラックを使用したほかは実施例と同様の方法で塗料を作製し、体積固有抵抗および引張強度を測定した。その結果を表1に示す。
【0048】
【表1】
【0049】
表1から明らかなように、実施例1〜4の導電性塗料は、優れた導電性を示し、塗料の強度低下も見られなかった。また、実施例3と比較例3、実施例4と比較例4を比べて明らかなように、微細な炭素繊維の添加量が同じ場合、本発明の導電性塗料の抵抗値は従来のものの1/2以下とすることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conductive paint having a low electrical resistance and capable of withstanding long-term use, and particularly for the purpose of electrostatic coating, antistatic and electromagnetic wave shielding, or a conductive material for resistors, circuits and copier rolls. The present invention relates to a conductive paint suitably used for ink or the like.
[0002]
[Prior art]
Recently, conductive paints have been used in fields where electromagnetic shielding properties, antistatic properties, and antistatic properties are required, such as electronic devices. In these paints, metal powders such as silver, aluminum, and copper, and carbon powders are used as fillers. In addition, a paint having good conductivity is also required for a base paint for electrostatic coating.
[0003]
[Problems to be solved by the invention]
However, silver is expensive and has a high specific gravity, and other metal powders have the disadvantage that their conductivity is reduced due to oxidation, corrosion and the like. On the other hand, carbon powder is inexpensive and has few problems like metal powder, but has disadvantages such as insufficient conductivity. This is due to the fact that the conductivity of the carbon powder itself is lower than that of the metal powder and the aspect ratio (length / diameter) is small. For this reason, in this field, an inexpensive filler with high conductivity, low specific gravity, large aspect ratio, and the like is desired.
[0004]
Therefore, graphitizable carbonaceous fibers having a unique structure with a small fiber diameter and a large aspect ratio in Japanese Patent Publication No. 6-39576 and the fine filamentous carbon fibrils in Japanese Patent Application Laid-Open No. 7-102197 are entangled with each other. Fillers that improve the above-mentioned drawbacks, such as carbon fibril materials made of aggregates, have been proposed.
However, with these fillers, it is necessary to add a large amount of several tens of mass% in order to obtain sufficient conductivity, which not only leads to a cost increase, but also handling becomes complicated when mixing with the resin, There arises a problem that the fluidity of the paint after mixing is lowered and application becomes difficult.
[0005]
Accordingly, an object of the present invention is to provide a conductive paint having high conductivity, chemical stability, and low cost.
[0006]
[Means for Solving the Problems]
In the specification of Japanese Patent Application No. 11-81260, the present inventors previously described a fine carbon fiber having high crystallinity, which has not been obtained in the past, a method for producing the same, and a battery having higher performance using the fiber as a filler. An electrode is disclosed. The carbon fiber is a fine carbon fiber having a diameter of 0.01 to 5 μm, an aspect ratio of 10 or more, and containing 0.1 to 3% by mass of boron in the fiber. Interval d 002 Is a fine carbon fiber in which the thickness Lc in the c-axis direction of the crystal is 400 mm or less.
[0007]
This fine carbon fiber has high crystallinity and is therefore excellent in conductivity. Therefore, the present inventors have studied the fine carbon fiber in order to improve the drawbacks of the conventional conductive paint, and as a result, a conductive paint having high conductivity can be obtained with a small amount of addition. I found it. Furthermore, it has been found that the resistance value can be reduced to half or less of the conventional value if the added amount is the same.
[0008]
Thus, the present invention provides a thermoplastic resin or thermosetting resin of 70 to 99.8 parts by mass, a diameter of 0.01 to 5 μm, an aspect ratio of 10 or more, and 0.1 to 3% by mass of boron in the fiber. Provided is a conductive paint characterized by containing 30 to 0.2 parts by mass of fine carbon fibers.
Interplanar spacing d of fine carbon fibers determined by X-ray diffraction method 002 Is 3.385 mm or less, and the thickness Lc in the c-axis direction of the crystal is 400 mm or less.
[0009]
In addition, the powder resistance of fine carbon fibers has a bulk density of 0.8 g / cm 3 In this case, the resistance value of the obtained dry paint can be 0.01 Ω · cm or less.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
(Fine carbon fiber)
The carbon fibers added to the conductive paint of the present invention are fine carbon fibers having a diameter of 0.01 to 5 μm and an aspect ratio of 10 or more.
When the fiber diameter is less than 0.01 μm, the strength of the fiber is weak, and when it is used as a filler, the fiber is frequently cut and the function as the fiber is easily impaired. On the other hand, when the addition rate (mass%) as a filler is constant, the number of fibers decreases as the diameter increases, and the function of the fiber as a filler is not sufficiently exhibited. Further, when the diameter is larger than 5 μm, the productivity of the fiber itself is remarkably lowered, so that the cost is industrially increased. For these reasons, the fiber diameter is 0.01 to 5 μm. Those having a fiber diameter of 1 μm or less are preferred.
[0011]
Further, when the fiber aspect ratio is less than 10, the conductivity of the paint when carbon fiber is added to the paint is not sufficient. The aspect ratio is preferably 50 or more.
The length of the fine carbon fiber is not particularly limited, and the lower limit is preferably a length determined from the lower limit of the aspect ratio. If the length of the fiber is too long, there is a problem in dispersibility as a filler due to entanglement of the fiber or the like, and unevenness is likely to occur on the surface of the coating film. Therefore, the upper limit is preferably 400 μm, and more preferably 100 μm. Therefore, for example, when the aspect ratio is 50 or more, the fiber length is preferably 0.5 μm or more when the fiber diameter is 0.01 μm, and the length is preferably 50 μm or more when the diameter is 1 μm. The upper limit is preferably 400 μm, and more preferably 100 μm.
[0012]
The fine carbon fiber used in the present invention is characterized by containing boron in the crystal. The inventors of the present invention have succeeded in obtaining desired characteristics such as conductivity by including boron in fine carbon fiber crystals. Although the manufacturing method will be described later, high crystallization, that is, high conductivity is achieved effectively when the boron content is 0.1 to 3% by mass. Preferably 0.2-3 mass% boron is included. However, boron may be present at the time of crystallization of the fiber in the heat treatment, and boron is volatilized by, for example, processing at a higher temperature after high crystallization, and the addition amount is within a range where the content does not fall below 0.1% by mass. The concentration may be lower than that.
[0013]
Further, the fine carbon fiber containing boron in the crystal used in the present invention has high crystallinity, and the interplanar spacing d determined by the X-ray diffraction method. 002 Is 3.385 mm or less and the thickness Lc in the c-axis direction of the crystal is 400 mm or less. Face spacing d in fine carbon fiber 002 In the past, it was not possible to reduce the value to 3.385 mm or less. Furthermore, this fine carbon fiber is d 002 Although the thickness of the crystal is small, the thickness Lc in the c-axis direction of the crystal can be 400 mm or less. The fine carbon fiber contains boron, and d 002 And Lc are within the above range, and the R value (1580 cm) of the Raman absorption spectrum. -1 Absorption intensity I G And 1360cm -1 Absorption intensity I D Ratio R = I D / I G ) Is 0.5 or more.
[0014]
Furthermore, the powder resistance of this fine carbon fiber has a bulk density of 0.8 g / cm. 3 In this case, it can be 0.01Ω or less. Since the fine carbon fiber has such high conductivity, the conductivity of the coating material containing it is also improved.
(Production method of fine carbon fiber)
The fine carbon fiber used in the present invention can be produced by incorporating boron into the crystal structure of the fiber and its catalytic action. As described above, the boron content effective for high crystallization is generally 0.1 to 3% by mass, preferably 0.2 to 3% by mass.
[0015]
As the carbon fiber used as a starting material, fine carbon fiber grown in a gas phase by thermal decomposition of an organic compound such as benzene can be used. This carbon fiber is disclosed in, for example, JP-A-7-150419, JP-A-5-321039, JP-A-60-215816, JP-A61-70014, JP 5-36521, JP It can be produced by the method disclosed in JP-A-3-61768. Moreover, if the fiber diameter is 0.01 μm or more, a fine fibrous substance called carbon nanotube or carbon nanofiber having the same annual ring structure can be used. Therefore, it can also be used for multi-structure carbon nanotubes, carbon nanofibers and the like produced by an arc discharge method, a laser method, or the like.
[0016]
According to the study by the present inventors, such fine carbon fibers can be improved in crystallinity by heat treatment, but d by heat treatment alone. 002 It was found that the limit of 3.385 mm is the limit, and improvement in crystallinity cannot be expected. Therefore, as a result of examining a graphitization catalyst for high crystallization, boron was particularly effective.
For ordinary carbon materials, various studies have been made to increase the crystallinity by adding boron to heat treatment. ("Carbon" 1996, No. 172, pages 89-94, JP-A-3-245458, JP-A-5-251080, JP-A-5-266880, JP-A-7-73898, JP-A-8 -31422, JP-A-8-306359, JP-A-9-63584, JP-A-9-63585) However, boron is introduced into fine vapor grown carbon fiber having a diameter of 5 μm or less. Thus, there has never been an example of improved characteristics. The reasons are as follows (1) to (5) because it is difficult to graphitize with boron due to the characteristics of the shape and the catalytic effect of boron cannot be expected because the fiber has a special structure. there were.
[0017]
{Circle around (1)} Vapor grown carbon fiber is a long onion fiber in which the crystal structure of the cut surface of the fiber has developed concentrically.
(2) The length of the fiber varies depending on the production conditions. For example, in the case of a fiber having a diameter of about 0.01 to 0.5 μm, there are many branched fibers as well as single fibers. As long as the linear portion is measured with a scanning electron microscope, most of them have an average of at least 5 μm or more.
[0018]
(3) Since this fiber includes fine fibers branched in addition to long fibers, not only long fibers but also short fibers of about 5 μm are at least 10 μm in size. It tends to be a large flock of 100 μm or more.
(4) Therefore, the bulk density as an aggregate is small, 0.05 g / cm. 3 Hereinafter, usually 0.01 g / cm 3 It is as follows. Moreover, since it has a flock-like three-dimensional structure, it is difficult to contact with the graphitization catalyst, and it is difficult to form a uniform boron.
[0019]
(5) In addition, fine carbon fiber is covered with a solid basal plane (plane of hexagonal mesh structure), so even if graphitized with boron, crystallinity is improved due to steric hindrance during polygonization. Is inhibited.
The present inventors have found that high crystallization can be achieved by doping fine carbon fibers with boron.
[0020]
In order to dope boron, it is preferable to use a low-temperature treated product that is easy to be doped and does not develop a crystal, preferably carbon fiber that has been heat-treated at 1500 ° C. or less, as the fine carbon fiber of the raw material. Even low-temperature treated carbon fibers are finally heat-treated up to the graphitization temperature during treatment using boron as a catalyst (boration treatment), so even unheated products with undeveloped crystals can be used sufficiently. . Carbon fiber graphitized at a temperature of 2000 ° C. or higher, preferably 2300 ° C. or higher cannot be used, but it is not necessary to perform graphitization in advance from the viewpoint of energy reduction. It is preferable to use a low-temperature treated product to cause a catalytic action simultaneously with graphitization.
[0021]
Further, there is a report that the temperature at which boron content in carbon is the highest and which is easily doped is 2000 to 2300 ° C., and a material crystallized by processing at a temperature higher than this has a small catalytic effect.
The fine carbon fibers of the raw material can be pulverized and pulverized in advance for easy handling, but pulverization and pulverization are sufficient to be mixed with boron or a boron compound. That is, even after the boronation treatment, the filler formation treatment such as pulverization, pulverization, and classification is finally performed. Therefore, it is not necessary to set the filler to an appropriate length before the boronation treatment. Carbon fibers having a thickness (diameter) of about 0.01 to 5 μm and a length of about 0.5 to 400 μm, which are generally obtained by vapor deposition, can be used as they are. These may be flocked. The raw fiber may be heat-treated, but the heat treatment temperature is preferably 1500 ° C. or lower.
[0022]
As a boron source used for doping boron, the boronation treatment is performed at a temperature of 2000 ° C. or higher. Therefore, a substance that does not evaporate even by decomposition before reaching at least 2000 ° C., for example, elemental boron, B 2 O 3 , Boron, B 4 C, BN and other boron compounds are preferably used.
The amount of boron that can be doped with carbon is generally 3% by mass or less. High crystallization, that is, high conductivity is achieved effectively with a boron content of 0.1 to 3 mass%. Preferably 0.2-3 mass% boron is included. However, boron may be present at the time of crystallization of the fiber in the heat treatment, and boron is volatilized by, for example, processing at a higher temperature after high crystallization, and the addition amount is within a range where the content does not fall below 0.1% by mass. The concentration may be lower than that.
[0023]
Therefore, it is sufficient that the amount of boron or boron compound added at the time of blending is 10% by mass or less in terms of boron atom with respect to the carbon amount in consideration of the reaction rate. When the amount of boron used is large, not only does the processing cost increase, but the filler characteristics may be lost, such as being easily melt-sintered at the stage of heat treatment, and solidifying or covering the fiber surface to increase the electrical resistance.
[0024]
In order to carry out the boron introduction reaction efficiently, it is necessary to mix carbon fibers and boron or a boron compound well and make them contact as uniformly as possible. Fine carbon fibers not only have a three-dimensional structure and are easy to form a flock, but also have a very low bulk density and a very high porosity. In addition, since the amount of boron added is as small as 10% by mass or less, preferably 5% by mass or less, it is difficult to bring them into uniform contact simply by mixing the two. Therefore, it is necessary to use boron or boron compound particles having a particle size as small as possible to bring the carbon fiber and boron compound into contact as uniformly as possible. Further, if the particles are large, a high concentration region is partially generated, which may cause solidification. Specifically, the particle size is 100 μm or less, preferably 50 μm or less, more preferably 20 μm or less in terms of average particle size.
[0025]
Carbon fiber and boron or boron compound can be mixed uniformly and heat treated as it is, but fine carbon fiber by vapor phase method has very low bulk density, so it is preferably densified and maintained as much as possible (Immobilize) and heat treatment. As a preferable method, there is a method in which both are mixed and then compressed by applying pressure to the mixture to increase the density and fix the mixture.
[0026]
Mixing of carbon fiber and boron or boron compound may be performed by any method as long as uniformity can be maintained. Although any commercially available mixer may be used as the mixer, fine carbon fibers are likely to be in the form of flocs, and therefore, a Henschel mixer type with a chopper is more preferable in order to crush this. The raw material carbon fiber to be used may be as produced as described above or may be processed at a temperature of 1500 ° C. or lower. However, those that are produced economically are preferred.
[0027]
As a method of densifying a mixture of carbon fiber and boron or boron compound so that they do not separate, a molding method, a granulation method, or a mixture is put into a crucible and compressed into a certain shape and packed. Any method such as a method may be used. In the case of a molding method, the shape of the molded body may be any shape such as a columnar shape, a plate shape, and a rectangular parallelepiped. The carbon fiber to which boron or a boron compound is added in this way to increase the bulk density is then heat treated.
[0028]
The processing temperature required to introduce boron into the carbon crystal is generally 2000 ° C. or higher, preferably 2300 ° C. or higher. If the treatment temperature is less than 2000 ° C., the reactivity between boron and carbon is poor and it is difficult to introduce boron. Further promote the introduction of boron and improve the crystallinity of carbon, especially d 002 It is preferable to keep the temperature at 2300 ° C. or higher in order to make the temperature below 3.385 mm. The upper limit of the heat treatment temperature is not particularly limited, but is about 3200 ° C. due to restrictions such as equipment.
[0029]
The heat treatment furnace used may be a furnace capable of maintaining a target temperature of 2000 ° C. or higher, preferably 2300 ° C. or higher, and may be any apparatus such as a normal Atchison furnace, resistance furnace, high-frequency furnace, or the like. Moreover, depending on the case, the method of heating by energizing powder or a molded object directly can also be used.
The atmosphere for the heat treatment is a non-oxidizing atmosphere, preferably a rare gas atmosphere such as argon. The heat treatment time is preferably as short as possible from the viewpoint of productivity. In particular, when the heating is performed for a long time, the yield is also deteriorated because the sintering proceeds. Therefore, a holding time of 1 hour or less is sufficient after the temperature of the central part of the molded body or the like reaches the target temperature.
[0030]
Since the carbon fibers densified by compression molding or the like are partially heat-treated to form a block shape when heat-treated, it is desirable to crush the molded body in order to obtain a form suitable as a filler. Therefore, this block is crushed, pulverized and classified so as to be suitable as a filler, and at the same time, the non-fibrous material is separated. At that time, if the powder is pulverized too much, the filler performance is deteriorated, and if the pulverization is insufficient, the mixing with the paint main agent may not be successful and the effect of addition may not be obtained.
[0031]
In order to obtain a desirable form as the filler, the block-like product after the heat treatment is first pulverized to a size of 2 mm or less and further pulverized by a pulverizer. As the crusher, a commonly used device such as an ice crusher or a rotoplex can be used. As the pulverizer, a pulverizer such as an impact pulverizer, a free pulverizer, or a pulverizer such as a microjet can be used. The classification for separating the non-fiber material can be performed by an airflow classifier or the like. Although the pulverization classification conditions vary depending on the type of the pulverizer and the operation conditions, the fiber length is preferably 5 to 400 μm in order to exhibit the filler characteristics. The aspect ratio is preferably 10 or more, more preferably 50 or more.
[0032]
The bulk density after pulverization classification is 0.001 to 0.2 g / cm. 3 , Preferably 0.005 to 0.15 g / cm 3 More preferably, 0.01 to 0.1 g / cm 3 It is. Bulk density is 0.2g / cm 3 If it becomes above, depending on a diameter, the length of a fiber will become short like 5 micrometers or less, and a filler effect will fall. 0.001 g / cm 3 If it is smaller, the length becomes longer than 400 μm depending on the diameter, and clogging as a filler is worsened. The bulk density is a tapping bulk density obtained from a volume and a mass when the container is filled with fibers and vibrated to reach a substantially constant volume.
[0033]
The fine carbon fiber containing boron in the fiber produced by the above method has a bulk density of 0.8 g / cm. 3 In this case, the powder resistance can be 0.01 Ω · cm or less. On the other hand, a fine carbon fiber by the vapor phase growth method having the same shape and containing no boron in the fiber has a bulk density of 0.8 g / cm. 3 In this case, the powder resistance is about 0.01 to 0.03 Ω · cm. This is because crystallinity is improved when boron is added as a catalyst during graphitization, and as a result, conductivity is improved. As described above, the use of fine carbon fibers whose conductivity is improved by an order of magnitude compared to the prior art provides a conductive paint of the present invention that has a low electrical resistance and is preferably used for purposes such as static electricity prevention and electromagnetic wave shielding. can do.
[0034]
(resin)
Examples of the thermoplastic resin or thermosetting resin that can be used in the conductive paint of the present invention include polyamide resin, polyurethane resin, vinyl chloride resin, ethylene-vinyl acetate copolymer, acrylic resin, Examples of thermosetting resins such as cellulose resin and butyral resin include phenolic resin, epoxy resin, urea resin, melamine resin, xylene resin, furan resin, unsaturated polyester resin, silicon resin, etc. Can be used.
[0035]
For these resins, known curing agents, curing aids, curing catalysts and activators can be used if necessary. For example, an amine-based or mercaptan-based compound or an acid anhydride can be used as a curing agent for the epoxy resin.
The above resin can be used as an emulsion or a latex, but it is preferably used as a solution by dissolving in a solvent.
[0036]
The solvent is not particularly limited as long as it dissolves or disperses the resin. For example, hydrocarbons such as toluene and xylene, halogenated hydrocarbons such as dichloroethane and trichloroethane, alcohols such as isopropyl alcohol and butanol, ketones such as methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate and ethyl propylate, Ethers such as methyl ether of ethylene glycol and dimethyl ether of diethylene glycol, water and the like can be used.
[0037]
(Composition of conductive paint)
In this invention, content of the fine carbon fiber with respect to a thermoplastic resin or a thermosetting resin is 30-0.2 mass% in an internal division, Preferably it is 10-0.5 mass%. When the amount of carbon fiber exceeds 30% by mass with respect to the resin, the fluidity is lowered, causing problems such as difficulty in uniform coating, reduced coating strength, and adhesion of the substrate. Moreover, if it does not reach 0.2 mass%, the effect by carbon fiber will be scarce, and the electroconductivity when used for a paint will not be sufficient.
[0038]
The amount of the solvent is not particularly limited, and may be determined in consideration of the type of paint, storage stability, coating property, drying property, and the like.
In the conductive paint of the present invention, an additive for improving paint properties can be used as necessary. For example, dispersants to increase the dispersibility of carbon fibers as fillers, other fibrous and inorganic materials, powders and flakes such as metals, leveling agents to increase printability, stability to heat, oxidation, and light Agents, coupling agents, thickeners, pigments, plasticizers, crosslinking agents, fillers, and the like can be mixed.
[0039]
Moreover, in order to improve electroconductivity further, it can also be used by mixing with other electroconductive powder. Examples of other conductive powders include carbon black such as acetylene black and ketjen black, graphite powder, various carbon fibers, powder or fiber such as gold, silver, nickel, and aluminum, and metal-coated glass fiber.
[0040]
(Manufacture of paint)
The conductive paint of the present invention can be usually produced by mixing the resin solution and fine carbon fibers. As the mixing device, a normal device such as a three-roll or ball mill can be used. The conductive paint of the present invention can be applied by a usual method such as brush coating, roller coating, spraying or the like.
[0041]
The conductive paint of the present invention thus produced can have a resistance value of 0.01 Ω · cm or less after coating and drying.
[0042]
【The invention's effect】
The conductive paint of the present invention is a highly conductive paint because fine carbon fibers having high conductivity are uniformly dispersed in the resin while contacting at many contact points. In addition, the coating effect is excellent due to the reinforcing effect of the carbon fiber, and there is no deterioration in conductivity due to oxidation, corrosion or the like after a long period of use unlike a metal filler. Therefore, it can be applied to various substrates such as concrete, metal, wood, plastic, etc., and can be suitably used for the purpose of preventing static electricity and shielding electromagnetic waves.
[0043]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
(Examples 1-4 and Comparative Examples 1-2)
The fine carbon fiber as a starting material is further obtained by further adding 1200 carbon fibers obtained by a known method (for example, JP-A-7-150419) in which benzene is thermally decomposed in the presence of an organometallic compound containing a transition metal. Obtained by heat treatment at ℃. The obtained carbon fiber was aggregated in a floc form, but this was crushed and the bulk density was 0.02 g / cm. 3 The fiber length was 10 to 100 μm. Most of the fiber diameter was 0.5 μm or less (average fiber diameter observed by electron micrograph was 0.2 μm). Interplanar spacing d of carbon by X-ray diffraction of this carbon fiber 002 Was 3.407 mm and the thickness Lc in the c-axis direction of the crystal was 56 mm.
[0044]
B of 2.88 kg of this fiber with an average particle size of 15 μm 4 120 g of C powder was added and mixed thoroughly with a Henschel mixer. This mixture is packed into a cylindrical graphite crucible with a capacity of 50 liters and compressed to a bulk density of 0.075 g / cm. 3 It was. The lid was covered while being compressed with a graphite pressure plate, and was heated in an Atchison furnace. At this time, the heating time after the temperature reached 2900 ° C. and 2900 ° C. was 60 minutes.
[0045]
After the heat treatment, the mixture was cooled, the carbon fiber was taken out from the crucible, pulverized with a bantam mill, and then the non-fibrous material was separated with an air classifier.
The diameter of the obtained fiber is the same as before heat treatment at 2900 ° C., most of which is 0.5 μm or less, the length is 5 to 30 μm, and the bulk density is 0.04 g / cm. 3 Met. Moreover, the boron content of this fiber is 1.03% by mass, d 002 Was 3.380cm and Lc was 290cm. Moreover, bulk density 0.8g / cm 3 The powder resistance at this time was 0.003 Ω · cm.
[0046]
Next, using this fine carbon fiber, a conductive paint was prepared as follows. The fine carbon fibers were mixed with a 20 mass% methyl ethyl ketone solution of a phenol resin at a mass ratio shown in Table 1 with three rolls to obtain each conductive paint.
This was coated on a glass plate, the solvent was dried, the coating film was peeled off from the glass, and the volume resistivity and tensile strength were measured. The results are shown in Table 1.
(Comparative Examples 3-4)
The starting material shown in the examples, 3.0 kg of fine carbon fiber, was packed into a cylindrical graphite crucible with a capacity of 50 liters and compressed to a bulk density of 0.075 g / cm. 3 It was. The lid was covered while being compressed with a graphite pressure plate, placed in an Atchison furnace, and heat-treated. At this time, the heating time after the temperature reached 2900 ° C. and 2900 ° C. was 60 minutes. After the heat treatment, the mixture was cooled, the carbon fiber was taken out from the crucible, pulverized with a bantam mill, and then the non-fibrous material was separated with an air classifier.
[0047]
The diameter of the obtained fiber is the same as before heat treatment at 2900 ° C., most of which is 0.5 μm or less, the length is 5 to 30 μm, and the bulk density is 0.04 g / cm. 3 Met. This fiber d 002 Was 3.388 Å and Lc was 280 Å. Moreover, bulk density 0.8g / cm 3 The powder resistance at this time was 0.013 Ω · cm.
Using this fine carbon fiber, a coating material was produced at a mass ratio shown in Table 1 in the same manner as in the Examples, and the volume resistivity and tensile strength were measured. The results are shown in Table 1.
(Comparative Example 5)
A coating material was prepared in the same manner as in Example except that acetylene black was used instead of fine carbon fiber, and volume resistivity and tensile strength were measured. The results are shown in Table 1.
[0048]
[Table 1]
[0049]
As is clear from Table 1, the conductive paints of Examples 1 to 4 showed excellent conductivity, and the strength of the paint was not reduced. Further, as is clear from comparison between Example 3 and Comparative Example 3 and Example 4 and Comparative Example 4, when the addition amount of fine carbon fibers is the same, the resistance value of the conductive paint of the present invention is 1 of the conventional one. / 2 or less.
Claims (5)
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WO2003040445A1 (en) | 2001-11-07 | 2003-05-15 | Showa Denko K.K. | Fine carbon fiber, method for producing the same and use thereof |
JP4462891B2 (en) * | 2002-10-22 | 2010-05-12 | 大阪瓦斯株式会社 | Electromagnetic wave absorbing coating composition, electromagnetic wave absorbing housing, and electromagnetic wave absorbing film or sheet |
KR101156012B1 (en) | 2002-12-26 | 2012-06-18 | 쇼와 덴코 가부시키가이샤 | Carbonaceous material for electrically conductive material and use thereof |
JP4342929B2 (en) * | 2002-12-26 | 2009-10-14 | 昭和電工株式会社 | Carbonaceous material for conductive composition and use thereof |
CN100584881C (en) * | 2003-04-24 | 2010-01-27 | 昭和电工株式会社 | Carbon fiber-containing resin dispersion solution and resin composite material |
JP2004339485A (en) * | 2003-04-24 | 2004-12-02 | Showa Denko Kk | Carbon fiber-containing resin dispersion, and resin composite material |
JP4454353B2 (en) | 2003-05-09 | 2010-04-21 | 昭和電工株式会社 | Linear fine carbon fiber and resin composite using the same |
JP2005133149A (en) * | 2003-10-30 | 2005-05-26 | Nippon Steel Corp | Surface treated metallic material having excellent conductivity |
JP5496470B2 (en) * | 2008-05-01 | 2014-05-21 | 保土谷化学工業株式会社 | Ink containing fine carbon fiber for static electricity suppression |
KR101099830B1 (en) * | 2009-06-03 | 2011-12-27 | 장관식 | Antistatic composition for inside addition and products comprising thereof |
JP2017048333A (en) * | 2015-09-03 | 2017-03-09 | 大阪ガスケミカル株式会社 | Antistatic coating material and coated floor using the same |
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