JP3644947B2 - Heat-resistant electret material, heat-resistant electret using the same, method for producing the same, and electrostatic acoustic sensor - Google Patents
Heat-resistant electret material, heat-resistant electret using the same, method for producing the same, and electrostatic acoustic sensor Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、イヤホン、ヘッドホンまたはマイクロホン等に使用されるエレクトレット用材料、それを用いたエレクトレットおよびその製造方法、並びに静電型音響センサーに関する。
【０００２】
【従来の技術】
従来よりイヤホン、ヘッドホンまたはマイクロホン等に使用されるエレクトレットとしては、金属シートにエレクトレットを構成しうる熱可塑性樹脂フィルムをラミネートし、この樹脂をエレクトレット化する方法が提案されている（特許文献１参照。）。
【０００３】
また、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体（ＦＥＰ）の微粒子が分散された有機溶媒を金属板に塗布して薄膜を形成し、その薄膜をエレクトレット化する方法（特許文献２参照。）、また金属板にＦＥＰの微粒子が分散されたスプレー液を噴霧した後、焼成してエレクトレット化する方法（特許文献３参照。）等も提案されている。
【０００４】
【特許文献１】
特開昭６４−４４０１０号公報
【０００５】
【特許文献２】
特開平１１−１５０７９５号公報
【０００６】
【特許文献３】
特開２０００−１１５８９５号公報
【０００７】
【発明が解決しようとする課題】
しかし、従来のエレクトレットを用いてマイクロホン等を製造する際にフロー装置やリフロー装置による半田付けを行うと、半田付けの際の高温によりエレクトレットの機能が低下するという問題があった。特に最近では鉛フリー半田が多用されるにともない、半田付け時の温度がさらに高温の２６０℃程度となり、エレクトレットの機能自体が喪失するという大きな問題が生じるおそれがある。
【０００８】
本発明は、耐熱性が高いエレクトレット用材料、それを用いた耐熱性エレクトレットおよびその製造方法、並びに静電型音響センサーを提供する。
【０００９】
【課題を解決するための手段】
本発明は、フッ素樹脂を含む多孔性シートであって、前記多孔性シートの多孔度が１５〜８０％であることを特徴とする耐熱性エレクトレット用材料を提供する。
【００１０】
また、本発明は、金属板の表面に、上記耐熱性エレクトレット用材料を配置したことを特徴とする耐熱性エレクトレットを提供する。
【００１１】
また、本発明は、金属板の表面に、上記耐熱性エレクトレット用材料を貼り合わせることを特徴とする耐熱性エレクトレットの製造方法を提供する。
【００１２】
また、本発明は、金属板の表面にフッ素樹脂を含む樹脂組成物をコーティングした後、前記樹脂組成物を発泡させることにより、前記金属板の表面にフッ素樹脂を含む多孔性樹脂層を形成することを特徴とする耐熱性エレクトレットの製造方法を提供する。
【００１３】
また、本発明は、金属板の表面にフッ素樹脂と、フッ素樹脂より低い温度で分解する添加樹脂とを含む樹脂組成物をコーティングした後、前記樹脂組成物を焼成することにより前記添加樹脂を分解・除去し、前記金属板の表面にフッ素樹脂を含む多孔性樹脂層を形成することを特徴とする耐熱性エレクトレットの製造方法を提供する。
【００１４】
また、本発明は、金属板の表面に粉体状のフッ素樹脂を含む樹脂組成物をコーティングして空隙を形成した後、前記樹脂組成物を焼成することにより、前記金属板の表面にフッ素樹脂を含む多孔性樹脂層を形成することを特徴とする耐熱性エレクトレットの製造方法を提供する。
【００１５】
また、本発明は、上記耐熱性エレクトレットを備えたことを特徴とする静電型音響センサーを提供する。
【００１６】
【発明の実施の形態】
本発明の耐熱性エレクトレット用材料は、フッ素樹脂を含む多孔性シートからなり、その多孔性シートの多孔度が１５〜８０％、より好ましくは５０〜８０％であることを特徴とする。
【００１７】
一般にフッ素樹脂は耐熱性が高い樹脂であり、さらに多孔度が１５〜８０％の多孔性フッ素樹脂シートをエレクトレット用材料に用いることにより、高温時におけるエレクトレットの表面電位の低下を抑制して、エレクトレットの耐熱特性を向上できる。ここで、多孔度が１５％を下回ると高温でのエレクトレットの表面電位の低下が大きくなるおそれがあり、多孔度が８０％を超えるとエレクトレット用材料としてのシートの作成が困難になる。なお、代表的なフッ素樹脂であるポリテトラフルオロエチレン（ＰＴＦＥ）の融点は約３２７℃である。これにより、加工温度が３００℃程度になるＭＥＭＳ（Ｍｉｃｒｏ Ｅｌｅｃｔｒｏ Ｍｅｃｈａｎｉｃａｌ Ｓｙｓｔｅｍｓ）技術を用いてマイクロホン等を製造できる。
【００１８】
また、本発明の耐熱性エレクトレット用材料は、上記多孔性シートに、フッ素樹脂を含むフィルムをさらに貼り付けることもできる。これにより、エレクトレットの表面を平滑にすることができ、エレクトレットをマイクロホン等に使用した場合に振動板の動作を妨げない。
【００１９】
また、本発明の耐熱性エレクトレット用材料は、上記フッ素樹脂が、ポリテトラフルオロエチレン（ＰＴＦＥ）、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル共重合体（ＰＦＡ）、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体（ＦＥＰ）およびテトラフルオロエチレン−パーフルオロメチルビニルエーテル（ＭＦＡ）からなる群から選択された少なくとも１つであることが好ましい。
【００２０】
これらを用いることにより、製品表面に防汚性、耐薬品性、撥水性、耐候性等の優れた機能を付与できる。また、エレクトレットのフレキシビリティが損なわれない。さらに、エレクトレットのエンボス加工なども比較的容易に出来る。
【００２１】
また、上記多孔性シートの誘電率および体積抵抗率は、それぞれ２．１以下、１．０×１０16Ωｃｍ以上である。なお、誘電率の下限値は、空気の誘電率＝１に近いほど好ましい。また、多孔性シートとすることにより、フッ素樹脂そのものの誘電率より、見かけ上の誘電率は低くなる。
【００２２】
また、本発明の耐熱性エレクトレットは、金属板の表面に、上記耐熱性エレクトレット用材料を配置したことを特徴とする。これにより、耐熱性に優れたエレクトレットを提供できる。
【００２３】
上記多孔性シートの厚さは特に限定されないが、通常５〜４００μｍ、好ましくは１０〜５０μｍである。この範囲内であれば、エレクトレットの特性を維持しつつ、エレクトレットの薄型化、小型化が図れるからである。また、上記多孔性シートの形態としては、不織布、織布、ペーパー、延伸膜、未焼成テープ等を使用できる。
【００２４】
また、本発明の耐熱性エレクトレットは、上記金属板が、黄銅、アルミニウム、ステンレス鋼、銅、チタン、洋白、リン青銅、それらの合金、それらがメッキされた金属およびそれらが蒸着された金属からなる群から選択された少なくとも１つから形成されていることが好ましい。これらの金属は耐蝕性、電気伝導性、加工性の点で優れているからである。
【００２５】
なお、上記金属板の使用にあたっては、先ず油脂等の付着のないものを用い、さらには上記多孔性シートとの接着性を良くするために下地処理を行うことが好ましい。下地処理は、例えば、陽極酸化、化成処理による皮膜の形成或いはカップリング剤の利用、その他接着性を改善する方法等が挙げられる。
【００２６】
また、本発明の耐熱性エレクトレットの製造方法は、金属板の表面に、上記耐熱性エレクトレット用材料を貼り合わせることを特徴とする。即ち、例えば、多孔度が１５〜８０％のフッ素樹脂を含む多孔性シートを準備し、加熱ロールおよび加熱源を有さないロールの一対からなる圧着ロールのうち、加熱ロール側に金属板を供給し、加熱源を有さないロール側に上記多孔性シートを供給しつつ、上記圧着ロールの間に上記金属板および上記多孔性シートを挿入し、上記金属板と上記多孔性シートとの接触時間を１〜３秒、接触帯幅を１〜２０ｍｍに制御し、上記金属板と上記多孔性シートとを熱圧着することができる。
【００２７】
この方法により得られたエレクトレット用積層板は、所定の大きさに切断され、次にコロナ放電等により分極帯電された後、エージング処理が行われ、イヤホン、ヘッドホンまたはマイクロホン等に利用される。
【００２８】
また、本発明の耐熱性エレクトレットの他の製造方法は、金属板の表面にフッ素樹脂を含む樹脂組成物をコーティングした後、この樹脂組成物を発泡させることにより、この金属板の表面にフッ素樹脂を含む多孔性樹脂層を形成することを特徴とする。即ち、例えば、フッ素樹脂と溶剤とを含む樹脂組成物をスプレー等を用いて金属板にコーティングし、その樹脂組成物を焼成する際に発泡させることにより、金属板の表面にフッ素樹脂を含む多孔性樹脂層を形成することができる。発泡させる手段としては、発泡剤を用いる方法、または減圧下で焼成する方法などを用いることができる。
【００２９】
また、本発明の耐熱性エレクトレットのさらに他の製造方法は、金属板の表面にフッ素樹脂と、フッ素樹脂より低い温度で分解する添加樹脂とを含む樹脂組成物をコーティングした後、上記樹脂組成物を焼成することにより上記添加樹脂を分解・除去し、上記金属板の表面にフッ素樹脂を含む多孔性樹脂層を形成することを特徴とする。
【００３０】
上記添加樹脂の大きさ、形を変えることにより、多孔性樹脂層の形態を任意に制御できる。上記添加樹脂としては、ポリエチレン、シリコーンなどを用いることができる。通常、フッ素樹脂は４００℃近い温度で焼成するため、焼成時に上記添加樹脂が分解・消失して空隙が形成される。
【００３１】
また、本発明の耐熱性エレクトレットのさらに他の製造方法は、金属板の表面に粉体状のフッ素樹脂を含む樹脂組成物をコーティングして空隙を形成した後、この樹脂組成物を焼成することにより、この金属板の表面にフッ素樹脂を含む多孔性樹脂層を形成することを特徴とする。この方法では、発泡剤や添加樹脂を用いなくても、粉体の大きさ、形、コーティング層の厚さなどを変えることにより、多孔性樹脂層の形態を任意に制御できる。
【００３２】
また、本発明の静電型音響センサーは、上記耐熱性エレクトレットを備えたことを特徴とする。静電型音響センサーとしては、例えば、マイクロホン、イヤホン、ヘッドホン、補聴器、超音波センサー、加速度センサーなどが含まれる。
【００３３】
【実施例】
以下、実施例と比較例を用いて本発明をさらに詳細に説明する。
【００３４】
（実施例１）
ダイキン工業社製の目付量５０ｇ／ｍ2のＰＴＦＥ不織布をカレンダーロールで押し固め、このＰＴＦＥ不織布をエレクトレット用材料として準備した。このＰＴＦＥ不織布と、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、縦５０ｃｍ、横２０ｃｍの大きさに切断して実施例１のエレクトレットを得た。熱圧着は、温度３３０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００３５】
図１は、本実施例で作製したエレクトレットの断面図である。本実施例のエレクトレット１は、ＰＴＦＥ不織布２とステンレス鋼板３とが熱圧着されて形成されている。
【００３６】
（実施例２）
ダイキン工業社製の目付量１５０ｇ／ｍ2のＰＴＦＥ不織布をエレクトレット用材料として準備した。このＰＴＦＥ不織布と、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して実施例２のエレクトレットを得た。熱圧着は、温度３６０℃、圧力６ｋｇｆ／ｃｍ2で行った。
【００３７】
（実施例３）
ダイキン工業社製の目付量１５０ｇ／ｍ2のＰＴＦＥ不織布をエレクトレット用材料として準備した。このＰＴＦＥ不織布と、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して実施例３のエレクトレットを得た。熱圧着は、温度３６０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００３８】
（実施例４）
ダイキン工業社製の目付量２５０ｇ／ｍ2のＰＴＦＥ不織布をエレクトレット用材料として準備した。このＰＴＦＥ不織布と、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して実施例４のエレクトレットを得た。熱圧着は、温度３６０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００３９】
（実施例５）
ダイキン工業社製のＰＴＦＥペーパー“ＰＡ−５Ｌ”をエレクトレット用材料として準備した。このＰＴＦＥペーパーと、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して実施例５のエレクトレットを得た。熱圧着は、温度３６０℃、圧力６ｋｇｆ／ｃｍ2で行った。
【００４０】
（実施例６）
ダイキン工業社製のＰＴＦＥペーパー“ＰＡ−５Ｌ”をエレクトレット用材料として準備した。このＰＴＦＥペーパーと、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して実施例６のエレクトレットを得た。熱圧着は、温度３６０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００４１】
（実施例７）
ダイキン工業社製の目付量１５０ｇ／ｍ2のＰＴＦＥ不織布と、ダイキン工業社製の厚さ２５μｍのＰＦＡフィルム“ＡＦ−００２５”とを貼り合わせたシートをエレクトレット用材料として準備した。このシートのＰＴＦＥ不織布側と、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して実施例７のエレクトレットを得た。熱圧着は、温度３４０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００４２】
（実施例８）
ダイキン工業社製の目付量２５０ｇ／ｍ2のＰＴＦＥ不織布と、ダイキン工業社製の厚さ２５μｍのＰＦＡフィルム“ＡＦ−００２５”とを貼り合わせたシートをエレクトレット用材料として準備した。このシートのＰＴＦＥ不織布側と、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して実施例８のエレクトレットを得た。熱圧着は、温度３４０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００４３】
（比較例１）
ダイキン工業社製の厚さ５０μｍのＰＦＡフィルムを３枚重ねたフィルム“ＡＦ−００５０”をエレクトレット用材料として準備した。このフィルムと、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して比較例１のエレクトレットを得た。熱圧着は、温度３６０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００４４】
（比較例２）
ダイキン工業社製の厚さ５０μｍのＦＥＰフィルムを３枚重ねたフィルム“ＮＦ−００５０”をエレクトレット用材料として準備した。このフィルムと、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して比較例２のエレクトレットを得た。熱圧着は、温度３６０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００４５】
（比較例３）
日東電工社製の厚さ２５μｍのＰＴＦＥフィルムを６枚重ねたフィルム“９２０−ＵＬ”をエレクトレット用材料として準備した。このフィルムと、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して比較例３のエレクトレットを得た。熱圧着は、温度３６０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００４６】
（比較例４）
ダイキン工業社製の厚さ２５μｍのＰＦＡフィルム“ＡＦ−００２５”をエレクトレット用材料として準備した。このフィルムと、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して比較例４のエレクトレットを得た。熱圧着は、温度３６０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００４７】
（比較例５）
ダイキン工業社製の厚さ２５μｍのＦＥＰフィルム“ＮＦ−００２５”をエレクトレット用材料として準備した。このフィルムと、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して比較例５のエレクトレットを得た。熱圧着は、温度３３０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００４８】
（比較例６）
日東電工社製の厚さ２５μｍのＰＴＦＥフィルム“９２０−ＵＬ”をエレクトレット用材料として準備した。このフィルムと、厚さ０．２ｍｍのステンレス鋼板とを加熱ロールを用いて熱圧着し、実施例１と同様の大きさに切断して比較例６のエレクトレットを得た。熱圧着は、温度３４０℃、圧力３ｋｇｆ／ｃｍ2で行った。
【００４９】
次に、これらの実施例１〜８、比較例１〜６のエレクトレットを用いて、熱圧着したエレクトレット用材料の厚さ、その表面粗さ、その多孔度、およびエレクトレットの表面電位残存率を測定した。
【００５０】
エレクトレット用材料の厚さは、マイクロメーターを用いてエレクトレットのステンレス鋼板以外の層厚さを測定して求めた。エレクトレット用材料の表面粗さは、ミツトヨ社製の表面粗さ計“Ｓｕｆｅｔｅｓｔ−２０１”を用いて測定した。エレクトレット用材料の多孔度は、日立製の電子顕微鏡“Ｓ−２３８０Ｎ／ＥＭＡＸ−７０００”を用いた電子顕微鏡写真から測定した。
【００５１】
また、エレクトレットの表面電位残存率は、次のようにして測定した。まず、マイナスのコロナ放電にて温度２５℃で試料を分極処理し、その直後の表面電位をＴｒｅｋ社製の表面電位計“ｍｏｄｅｌ ３４４”にて測定した。続いて、２７０℃または３００℃にて１０分間保持した後、その表面電位を同様にして測定した。そして、エレクトレットを分極処理した直後の表面電位を基準（１００％）として、２７０℃または３００℃で１０分間保持した後の表面電位をその相対値（％）として求めた。
【００５２】
以上の測定の結果を表１に示す。また、図２には、実施例３および比較例４〜６の表面電位残存率と温度との関係を示した。
【００５３】
【表１】
表１から明らかなように、実施例１〜６の表面電位残存率は、比較例１〜６の全てに比べて優れていることが分かる。また、実施例７および実施例８の３００℃における表面電位残存率は、比較例１〜６の全てに比べて優れていることが分かる。
【００５５】
また、実施例１〜６からエレクトレット用材料の多孔度が高くなるほど表面電位の残存率は向上することが分かる。特に、多孔度が５０％以上が好ましい。
【００５６】
また、実施例７および実施例８は、比較例１〜６と同程度の表面粗さであるが、その内部に多孔部を備えているので、表面電位の低下が抑えられている。
【００５７】
また、エレクトレット用材料の厚さは、表面電位残存率にはあまり影響しなかった。
【００５８】
【発明の効果】
以上のように本発明は、金属板の表面に、フッ素樹脂を含む多孔性シートであって、上記多孔性シートの多孔度が１５〜８０％である耐熱性エレクトレット用材料を貼り合わせることにより、耐熱性に優れたエレクトレットおよびそれを用いた各種の静電型音響センサーを提供でき、その工業的価値は大である。
【図面の簡単な説明】
【図１】実施例１で作製したエレクトレットの断面図である。
【図２】エレクトレットの表面電位残存率と温度との関係を示す図である。
【符号の説明】
１ エレクトレット
２ ＰＴＦＥ不織布
３ ステンレス鋼板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electret material used for an earphone, a headphone, a microphone, or the like, an electret using the material, a manufacturing method thereof, and an electrostatic acoustic sensor.
[0002]
[Prior art]
Conventionally, as an electret used for an earphone, a headphone, a microphone, or the like, a method has been proposed in which a thermoplastic resin film that can constitute an electret is laminated on a metal sheet and the resin is converted into an electret (see Patent Document 1). ).
[0003]
Further, a method of forming a thin film by applying an organic solvent in which fine particles of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are dispersed to a metal plate, and electretizing the thin film (see Patent Document 2), In addition, a method of spraying a spray liquid in which fine particles of FEP are dispersed on a metal plate and then firing it to make an electret (see Patent Document 3) has been proposed.
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 64-44010
[Patent Document 2]
JP-A-11-150795 [0006]
[Patent Document 3]
Japanese Patent Laid-Open No. 2000-115895
[Problems to be solved by the invention]
However, when soldering is performed using a flow device or a reflow device when a microphone or the like is manufactured using a conventional electret, there is a problem that the function of the electret deteriorates due to a high temperature during soldering. In particular, as lead-free solder is frequently used recently, the temperature at the time of soldering becomes about 260 ° C., which is a higher temperature, and there is a possibility that a big problem that the function of the electret itself is lost may occur.
[0008]
The present invention provides an electret material having high heat resistance, a heat-resistant electret using the material, a method for producing the same, and an electrostatic acoustic sensor.
[0009]
[Means for Solving the Problems]
The present invention provides a heat-resistant electret material, which is a porous sheet containing a fluororesin, wherein the porosity of the porous sheet is 15 to 80%.
[0010]
Moreover, this invention provides the heat resistant electret characterized by arrange | positioning the said heat resistant electret material on the surface of a metal plate.
[0011]
Moreover, this invention provides the manufacturing method of the heat resistant electret characterized by bonding the said heat resistant electret material on the surface of a metal plate.
[0012]
In the present invention, a porous resin layer containing a fluororesin is formed on the surface of the metal plate by coating the resin composition containing a fluororesin on the surface of the metal plate and then foaming the resin composition. The manufacturing method of the heat-resistant electret characterized by this is provided.
[0013]
In addition, the present invention provides a resin composition containing a fluororesin and an additive resin that decomposes at a lower temperature than the fluororesin on the surface of the metal plate, and then decomposes the additive resin by firing the resin composition. -A heat-resistant electret manufacturing method characterized by removing and forming a porous resin layer containing a fluororesin on the surface of the metal plate.
[0014]
In addition, the present invention provides a resin composition containing a powdery fluororesin on the surface of a metal plate to form voids, and then firing the resin composition to obtain a fluororesin on the surface of the metal plate. The manufacturing method of the heat resistant electret characterized by forming the porous resin layer containing this is provided.
[0015]
The present invention also provides an electrostatic acoustic sensor comprising the above heat-resistant electret.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The heat-resistant electret material of the present invention comprises a porous sheet containing a fluororesin, and the porosity of the porous sheet is 15 to 80%, more preferably 50 to 80%.
[0017]
In general, a fluororesin is a resin having high heat resistance, and furthermore, by using a porous fluororesin sheet having a porosity of 15 to 80% as a material for electrets, it is possible to suppress a decrease in the surface potential of the electret at a high temperature. Can improve the heat resistance. Here, if the porosity is less than 15%, the surface potential of the electret may be greatly lowered at a high temperature. If the porosity exceeds 80%, it is difficult to produce a sheet as an electret material. Note that polytetrafluoroethylene (PTFE), which is a typical fluororesin, has a melting point of about 327 ° C. Thereby, a microphone etc. can be manufactured using the MEMS (Micro Electro Mechanical Systems) technology in which processing temperature becomes about 300 ° C.
[0018]
Moreover, the heat-resistant electret material of this invention can further affix the film containing a fluororesin on the said porous sheet. Thereby, the surface of the electret can be smoothed, and the operation of the diaphragm is not hindered when the electret is used for a microphone or the like.
[0019]
In the heat-resistant electret material of the present invention, the fluororesin may be polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer. Preferably, it is at least one selected from the group consisting of (FEP) and tetrafluoroethylene-perfluoromethyl vinyl ether (MFA).
[0020]
By using these, excellent functions such as antifouling property, chemical resistance, water repellency and weather resistance can be imparted to the product surface. Moreover, the flexibility of the electret is not impaired. Furthermore, the electret can be embossed relatively easily.
[0021]
The porous sheet has a dielectric constant and a volume resistivity of 2.1 or less and 1.0 × 10 16 Ωcm or more, respectively. The lower limit of the dielectric constant is preferably as close as possible to the dielectric constant of air = 1. Moreover, by using a porous sheet, the apparent dielectric constant is lower than the dielectric constant of the fluororesin itself.
[0022]
The heat-resistant electret according to the present invention is characterized in that the heat-resistant electret material is disposed on the surface of a metal plate. Thereby, the electret excellent in heat resistance can be provided.
[0023]
Although the thickness of the said porous sheet is not specifically limited, Usually, 5-400 micrometers, Preferably it is 10-50 micrometers. This is because within this range, the electret can be made thinner and smaller while maintaining the characteristics of the electret. Moreover, as a form of the said porous sheet, a nonwoven fabric, a woven fabric, paper, a stretched film, an unbaked tape, etc. can be used.
[0024]
In the heat-resistant electret of the present invention, the metal plate is made of brass, aluminum, stainless steel, copper, titanium, white, phosphor bronze, alloys thereof, metal plated with them, and metal deposited with them. It is preferably formed from at least one selected from the group consisting of: This is because these metals are excellent in terms of corrosion resistance, electrical conductivity, and workability.
[0025]
In addition, when using the said metal plate, it is preferable to first use what does not adhere fats and oils, and also to perform a ground treatment in order to improve adhesiveness with the said porous sheet. Examples of the base treatment include anodization, formation of a film by chemical conversion treatment, use of a coupling agent, and other methods for improving adhesiveness.
[0026]
Moreover, the manufacturing method of the heat resistant electret of this invention sticks the said material for heat resistant electrets on the surface of a metal plate. That is, for example, a porous sheet containing a fluororesin having a porosity of 15 to 80% is prepared, and a metal plate is supplied to the heating roll side of the pressure roll made of a pair of a heating roll and a roll having no heating source. The metal plate and the porous sheet are inserted between the pressure-bonding rolls while supplying the porous sheet to the roll side having no heating source, and the contact time between the metal plate and the porous sheet 1 to 3 seconds and the contact band width to 1 to 20 mm, and the metal plate and the porous sheet can be thermocompression bonded.
[0027]
The electret laminate obtained by this method is cut to a predetermined size, and then polarized and charged by corona discharge or the like, and then subjected to an aging treatment and used for an earphone, a headphone, a microphone, or the like.
[0028]
Another method for producing the heat-resistant electret according to the present invention is to coat a resin composition containing a fluororesin on the surface of the metal plate, and then foam the resin composition to form a fluororesin on the surface of the metal plate. A porous resin layer containing is formed. That is, for example, a resin composition containing a fluororesin and a solvent is coated on a metal plate using a spray or the like, and foamed when the resin composition is baked, so that the surface of the metal plate contains a fluororesin. A functional resin layer can be formed. As a means for foaming, a method using a foaming agent, a method of firing under reduced pressure, or the like can be used.
[0029]
Further, another method for producing the heat-resistant electret of the present invention is the method in which the surface of the metal plate is coated with a resin composition containing a fluororesin and an additive resin that decomposes at a temperature lower than that of the fluororesin. The additive resin is decomposed and removed by firing and a porous resin layer containing a fluororesin is formed on the surface of the metal plate.
[0030]
By changing the size and shape of the additive resin, the form of the porous resin layer can be arbitrarily controlled. As the additive resin, polyethylene, silicone, or the like can be used. Usually, since a fluororesin is baked at a temperature close to 400 ° C., the additive resin is decomposed / disappeared at the time of baking to form voids.
[0031]
Still another method for producing the heat-resistant electret according to the present invention is to form a void by coating a resin composition containing a powdery fluororesin on the surface of a metal plate, and then firing the resin composition. Thus, a porous resin layer containing a fluororesin is formed on the surface of the metal plate. In this method, the form of the porous resin layer can be arbitrarily controlled by changing the size and shape of the powder, the thickness of the coating layer, and the like without using a foaming agent or an additive resin.
[0032]
Moreover, the electrostatic acoustic sensor of the present invention includes the above heat-resistant electret. Examples of the electrostatic acoustic sensor include a microphone, an earphone, a headphone, a hearing aid, an ultrasonic sensor, an acceleration sensor, and the like.
[0033]
【Example】
Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples.
[0034]
(Example 1)
A PTFE nonwoven fabric having a basis weight of 50 g / m 2 manufactured by Daikin Industries, Ltd. was pressed with a calender roll, and this PTFE nonwoven fabric was prepared as an electret material. This PTFE nonwoven fabric and a stainless steel plate having a thickness of 0.2 mm were thermocompression bonded using a heating roll, and cut into a size of 50 cm in length and 20 cm in width to obtain the electret of Example 1. Thermocompression bonding was performed at a temperature of 330 ° C. and a pressure of 3 kgf / cm 2 .
[0035]
FIG. 1 is a cross-sectional view of an electret produced in this example. The electret 1 of the present embodiment is formed by thermocompression bonding of a PTFE
[0036]
(Example 2)
A PTFE nonwoven fabric with a basis weight of 150 g / m 2 manufactured by Daikin Industries, Ltd. was prepared as an electret material. This PTFE nonwoven fabric and a stainless steel plate having a thickness of 0.2 mm were subjected to thermocompression bonding using a heating roll, and cut into the same size as in Example 1 to obtain the electret of Example 2. Thermocompression bonding was performed at a temperature of 360 ° C. and a pressure of 6 kgf / cm 2 .
[0037]
(Example 3)
A PTFE nonwoven fabric with a basis weight of 150 g / m 2 manufactured by Daikin Industries, Ltd. was prepared as an electret material. The PTFE nonwoven fabric and a stainless steel plate having a thickness of 0.2 mm were thermocompression bonded using a heating roll, and cut into the same size as in Example 1 to obtain the electret of Example 3. Thermocompression bonding was performed at a temperature of 360 ° C. and a pressure of 3 kgf / cm 2 .
[0038]
(Example 4)
A PTFE nonwoven fabric having a basis weight of 250 g / m 2 manufactured by Daikin Industries, Ltd. was prepared as an electret material. The PTFE nonwoven fabric and a stainless steel plate having a thickness of 0.2 mm were thermocompression bonded using a heating roll and cut into the same size as in Example 1 to obtain the electret of Example 4. Thermocompression bonding was performed at a temperature of 360 ° C. and a pressure of 3 kgf / cm 2 .
[0039]
(Example 5)
A PTFE paper “PA-5L” manufactured by Daikin Industries, Ltd. was prepared as an electret material. The PTFE paper and a stainless steel plate having a thickness of 0.2 mm were thermocompression bonded using a heating roll and cut into the same size as in Example 1 to obtain the electret of Example 5. Thermocompression bonding was performed at a temperature of 360 ° C. and a pressure of 6 kgf / cm 2 .
[0040]
(Example 6)
A PTFE paper “PA-5L” manufactured by Daikin Industries, Ltd. was prepared as an electret material. The PTFE paper and a stainless steel plate having a thickness of 0.2 mm were subjected to thermocompression bonding using a heating roll and cut into the same size as in Example 1 to obtain the electret of Example 6. Thermocompression bonding was performed at a temperature of 360 ° C. and a pressure of 3 kgf / cm 2 .
[0041]
(Example 7)
A sheet in which a PTFE nonwoven fabric having a basis weight of 150 g / m 2 manufactured by Daikin Industries, Ltd. and a PFA film “AF-0025” having a thickness of 25 μm manufactured by Daikin Industries, Ltd. was prepared was prepared as an electret material. The PTFE nonwoven fabric side of this sheet and a stainless steel plate having a thickness of 0.2 mm were thermocompression bonded using a heating roll and cut into the same size as in Example 1 to obtain the electret of Example 7. Thermocompression bonding was performed at a temperature of 340 ° C. and a pressure of 3 kgf / cm 2 .
[0042]
(Example 8)
A sheet in which a PTFE nonwoven fabric having a basis weight of 250 g / m 2 manufactured by Daikin Industries, Ltd. and a PFA film “AF-0025” having a thickness of 25 μm manufactured by Daikin Industries, Ltd. was prepared as an electret material. The PTFE nonwoven fabric side of this sheet and a stainless steel plate having a thickness of 0.2 mm were thermocompression bonded using a heating roll and cut into the same size as in Example 1 to obtain the electret of Example 8. Thermocompression bonding was performed at a temperature of 340 ° C. and a pressure of 3 kgf / cm 2 .
[0043]
(Comparative Example 1)
A film “AF-0050” obtained by stacking three 50 μm thick PFA films manufactured by Daikin Industries, Ltd. was prepared as an electret material. This film and a stainless steel plate having a thickness of 0.2 mm were thermocompression bonded using a heating roll, and cut into the same size as in Example 1 to obtain the electret of Comparative Example 1. Thermocompression bonding was performed at a temperature of 360 ° C. and a pressure of 3 kgf / cm 2 .
[0044]
(Comparative Example 2)
A film “NF-0050” obtained by stacking three FEP films with a thickness of 50 μm manufactured by Daikin Industries, Ltd. was prepared as an electret material. This film and a stainless steel plate having a thickness of 0.2 mm were thermocompression bonded using a heating roll, and cut into the same size as in Example 1 to obtain an electret of Comparative Example 2. Thermocompression bonding was performed at a temperature of 360 ° C. and a pressure of 3 kgf / cm 2 .
[0045]
(Comparative Example 3)
A film “920-UL” obtained by stacking six PTFE films having a thickness of 25 μm manufactured by Nitto Denko Corporation was prepared as an electret material. This film and a stainless steel plate having a thickness of 0.2 mm were subjected to thermocompression bonding using a heating roll and cut into the same size as in Example 1 to obtain an electret of Comparative Example 3. Thermocompression bonding was performed at a temperature of 360 ° C. and a pressure of 3 kgf / cm 2 .
[0046]
(Comparative Example 4)
A 25-μm thick PFA film “AF-0025” manufactured by Daikin Industries, Ltd. was prepared as an electret material. This film and a stainless steel plate having a thickness of 0.2 mm were thermocompression bonded using a heating roll, and cut into the same size as in Example 1 to obtain an electret of Comparative Example 4. Thermocompression bonding was performed at a temperature of 360 ° C. and a pressure of 3 kgf / cm 2 .
[0047]
(Comparative Example 5)
A 25 μm thick FEP film “NF-0025” manufactured by Daikin Industries, Ltd. was prepared as an electret material. This film and a stainless steel plate having a thickness of 0.2 mm were subjected to thermocompression bonding using a heating roll and cut into the same size as in Example 1 to obtain an electret of Comparative Example 5. Thermocompression bonding was performed at a temperature of 330 ° C. and a pressure of 3 kgf / cm 2 .
[0048]
(Comparative Example 6)
A 25-μm thick PTFE film “920-UL” manufactured by Nitto Denko Corporation was prepared as an electret material. This film and a stainless steel plate having a thickness of 0.2 mm were subjected to thermocompression bonding using a heating roll and cut into the same size as in Example 1 to obtain an electret of Comparative Example 6. Thermocompression bonding was performed at a temperature of 340 ° C. and a pressure of 3 kgf / cm 2 .
[0049]
Next, using the electrets of Examples 1 to 8 and Comparative Examples 1 to 6, the thickness, surface roughness, porosity and electret surface potential residual rate of the electret material subjected to thermocompression bonding were measured. did.
[0050]
The thickness of the electret material was determined by measuring the layer thickness of the electret other than the stainless steel plate using a micrometer. The surface roughness of the electret material was measured using a surface roughness meter “Suffestest-201” manufactured by Mitutoyo Corporation. The porosity of the electret material was measured from an electron micrograph using an electron microscope “S-2380N / EMAX-7000” manufactured by Hitachi.
[0051]
Moreover, the surface potential residual ratio of the electret was measured as follows. First, the sample was polarized at a temperature of 25 ° C. with a negative corona discharge, and the surface potential immediately after that was measured with a surface potential meter “model 344” manufactured by Trek. Subsequently, after holding at 270 ° C. or 300 ° C. for 10 minutes, the surface potential was measured in the same manner. Then, using the surface potential immediately after the electret was polarized as a reference (100%), the surface potential after being held at 270 ° C. or 300 ° C. for 10 minutes was obtained as a relative value (%).
[0052]
The results of the above measurement are shown in Table 1. FIG. 2 shows the relationship between the surface potential remaining rate and the temperature in Example 3 and Comparative Examples 4 to 6.
[0053]
[Table 1]
As can be seen from Table 1, the surface potential residual ratios of Examples 1 to 6 are superior to all of Comparative Examples 1 to 6. Moreover, it turns out that the surface potential residual rate in 300 degreeC of Example 7 and Example 8 is excellent compared with all of Comparative Examples 1-6.
[0055]
Moreover, it turns out that the residual rate of surface potential improves, so that the porosity of the material for electrets becomes high from Examples 1-6. In particular, the porosity is preferably 50% or more.
[0056]
Moreover, although Example 7 and Example 8 are surface roughness comparable as Comparative Examples 1-6, since the porous part is provided in the inside, the fall of surface potential is suppressed.
[0057]
Further, the thickness of the electret material did not significantly affect the surface potential remaining rate.
[0058]
【The invention's effect】
As described above, the present invention is a porous sheet containing a fluororesin on the surface of the metal plate, and by bonding the heat-resistant electret material having a porosity of 15 to 80%, An electret excellent in heat resistance and various electrostatic acoustic sensors using the same can be provided, and its industrial value is great.
[Brief description of the drawings]
1 is a cross-sectional view of an electret produced in Example 1. FIG.
FIG. 2 is a diagram showing the relationship between the surface potential remaining rate of the electret and the temperature.
[Explanation of symbols]
1
Claims (17)
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| US7449811B2 (en) * | 2004-11-26 | 2008-11-11 | The University Of Tokyo | Electrostatic induction conversion device |
| JP4670050B2 (en) * | 2004-11-26 | 2011-04-13 | 国立大学法人 東京大学 | Electret and electrostatic induction type conversion element |
| JP2006165724A (en) * | 2004-12-03 | 2006-06-22 | Audio Technica Corp | Manufacturing method of electret condenser microphone |
| JP4627676B2 (en) * | 2005-03-31 | 2011-02-09 | シチズン電子株式会社 | An electret condenser microphone using a heat-resistant charged resin body and a manufacturing method thereof. |
| JP2007129543A (en) * | 2005-11-04 | 2007-05-24 | Hosiden Corp | Electret condenser microphone |
| JP2007145960A (en) * | 2005-11-25 | 2007-06-14 | Oji Paper Co Ltd | Polymer foam for electret and method for producing the same and electret |
| JP2007295308A (en) * | 2006-04-25 | 2007-11-08 | Citizen Electronics Co Ltd | Method of manufacturing electret capaciter microphone |
| KR100774303B1 (en) | 2006-06-05 | 2007-11-08 | (주)상아프론테크 | Electret for high temperature, process for preparing the same, and microphone comprising the electret |
| JP4862700B2 (en) * | 2007-03-12 | 2012-01-25 | ヤマハ株式会社 | Electrostatic speaker |
| JP2012164735A (en) * | 2011-02-04 | 2012-08-30 | Sumitomo Electric Ind Ltd | Fluororesin film piezoelectric element |
| JP2013162051A (en) * | 2012-02-07 | 2013-08-19 | Sumitomo Electric Ind Ltd | Piezoelectric element made of fluororesin film and manufacturing method therefor |
| JP6417557B2 (en) * | 2014-09-29 | 2018-11-07 | 東邦化成株式会社 | Method for manufacturing piezoelectric element |
| CN115589761B (en) * | 2022-12-12 | 2023-03-10 | 杭州兆华电子股份有限公司 | Preparation method of porous piezoelectric electret |
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| JP2000153122A (en) * | 1998-11-17 | 2000-06-06 | Tonen Tapirusu Kk | Filter unit |
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