JP3724257B2 - Polymer composition and molded body thereof - Google Patents

Description

【０００８】
ただし、式中、Ｘはフッ素原子または塩素原子であり、Ｒ^fは２価のフッ素置換有機基であり、Ｙはヒドロキシアルキル基、カルボキシル基、または１価のカルボン酸誘導体基であり、Ｚは−Ｏ−Ｒ^fＹ以外の１価のフッ素置換有機基である。
【０００９】
また、本発明は、上記含フッ素重合体組成物を溶融成形してなる成形体を提供する。
【００１０】
含フッ素共重合体（Ｂ）は、含フッ素共重合体（Ａ）を熱処理することにより得られ、ＰＦＡ（Ｃ）の結晶核剤としての働きをする。
本発明の含フッ素重合体組成物は、過剰に溶融混練しても結晶核剤としての効果が低減しない。
【００１１】
【発明の実施の形態】
本発明は、含フッ素共重合体（Ｂ）とＰＦＡとを含む組成物である。含フッ素共重合体（Ａ）を熱処理することにより、得られる含フッ素共重合体（Ｂ）の溶融粘度が上昇する。これは、熱処理することにより、含フッ素共重合体（Ａ）の分子中の式２における官能基−Ｏ−Ｒ^fＹ部が、他の分子中の同官能基部と架橋反応することにより、架橋構造を有する含フッ素共重合体（Ｂ）が生成しているためと推定される。ただし、この説明は本発明の理解を助けるためのもので、何ら本発明を限定するものではない。
【００１２】
本発明の組成物中の含フッ素共重合体（Ｂ）はＰＦＡの結晶核剤となりうる。ＰＦＡに含フッ素共重合体（Ｂ）を少量添加し溶融混練して成形すると、その成形物に微細な球晶が生成する。また、過剰に溶融混練してもＰＴＦＥとは異なり結晶核剤としての効果が損なわれない。この効果は、おそらく含フッ素共重合体（Ｂ）が架橋していることによりＰＦＡと完全には混じり合わないためと推定される。
【００１３】
式１の単位において、Ｘはフッ素原子であるものが耐薬品性などの面からより好ましい。
式２の単位において、Ｒ^fすなわち２価のフッ素置換有機基は、置換フッ素原子の数が１個以上であればよく、完全フッ素化された２価のフッ素置換有機基がより好ましい。また、Ｒ^fは、炭素のみまたは炭素と酸素により鎖が形成された２価のフッ素置換有機基が好ましい。
【００１４】
その具体例としては、例えばパーフルオロアルキレン基またはエーテル結合を含有するパーフルオロアルキレン基が挙げられる。Ｒ^fの鎖を構成する炭素数は１〜１５、特に１〜１０の範囲が好ましい。Ｒ^fは直鎖の構造が好ましいが、分岐の構造であってもよい。分岐の構造である場合には、分岐部分の炭素数が１〜３程度の短鎖であるものが好ましい。特に好ましいＲ^fは−（ＣＦ₂）_m−（ｍは2〜６の整数）である。
【００１５】
Ｒ^fの具体例としては、例えば−（ＣＦ₂）₂−、−（ＣＦ₂）₃−、−（ＣＦ₂）₄−、−（ＣＦ₂）₅−、−（ＣＦ₂）₆−、−ＣＦ₂ＣＦ（ＣＦ₃）Ｏ（ＣＦ₂）₃−、−ＣＦ₂ＣＦ（ＣＦ₃）ＯＣＦ₂ＣＦ（ＣＦ₃）Ｏ（ＣＦ₂）₂−、−（ＣＦ₂ＣＦ₂Ｏ）₂−（ＣＦ₂）₃−，−ＣＦ₂ＣＦ（ＣＦ₃）ＣＦ₂ＣＦ₂ＣＦ（ＣＦ₃）ＣＦ₂−などが挙げられる。
【００１６】
式２におけるＹはヒドロキシアルキル基、カルボキシル基、または１価のカルボン酸誘導体基である。カルボン酸誘導体基としては−ＣＯＯＡ（Ａは炭素数１〜３程度のアルキル基、炭素数１〜３程度のフルオロアルキル基、アルカリ金属、アンモニウム塩基、または置換アンモニウム塩基）または−ＣＯＢ（Ｂはフッ素原子または塩素原子）が例示される。これらのうち、好ましいＹは、ヒドロキシアルキル基およびアルコキシカルボニル基であり、−ＣＨ₂ＯＨ、−ＣＨ₂ＣＨ₂ＯＨ、−ＣＯＯＣＨ₃が好ましい。
【００１７】
含フッ素共重合体（Ａ）中の式２で表される単位の含有量は、０．０１〜１モル％である。０．０１モル％未満では、含フッ素共重合体（Ｂ）の架橋密度が不充分でＰＦＡと過剰に溶融混練するとＰＦＡに混ざり合い結晶核剤としての効果が小さい。１モル％超では含フッ素共重合体（Ｂ）の溶融粘度が上昇しすぎ、ＰＦＡと混練しにくくなりフィッシュアイが発生する。
式２の単位は１種のみ含まれていてもよく２種以上含まれてもよい。
【００１８】
式３の単位において、Ｚすなわち１価のフッ素置換有機基は、式２の−Ｏ−Ｒ^fＹ以外の１価のフッ素置換有機基であり、耐熱性、耐薬品性などの点から炭素数１〜１０のパーフルオロアルコキシ基が好ましい。式３の含有量が３モル％超では含フッ素共重合体（Ｂ）の融点が低下しすぎ結晶核剤としての効果が低くなる。
【００１９】
含フッ素共重合体（Ｂ）は、含フッ素重合体（Ａ）を２００℃以上の温度で熱処理することにより得られる。２００℃未満では式２中の−Ｏ−Ｒ^fＹが架橋反応しにくい。融点以上では−Ｏ−Ｒ^fＹが架橋反応するが、含フッ素重合体（Ｂ）が融着するため、粉砕してＰＦＡに添加しないとフィッシュアイの原因になるおそれがあるので、好ましくは融点未満の熱処理温度を採用するのがよい。熱処理は、式２中のＹの５割以上、好ましくは９割以上が分解し、架橋反応するまでの時間行うことが好ましい。式２中のＹが架橋反応せず多量に残存すると、組成物の耐薬品性が低下するおそれがある。熱処理時間は、例えば３００℃では３時間以上が好ましい。本発明における熱処理は、酸素が存在する雰囲気で行うのが望ましい。
【００２０】
含フッ素共重合体（Ｂ）に架橋構造が生じていると推測される機構を以下に示す。含フッ素共重合体（Ａ）には、式２におけるＹがＩＲ分析により認められる。含フッ素共重合体（Ｂ）には、含フッ素共重合体（Ａ）に比べてＹの量が減少することが認められ、またはＹが認められない。また、含フッ素共重合体（Ｂ）の溶融粘度は含フッ素共重合体（Ａ）に比べて大きくなり、その上昇率は含フッ素共重合体（Ａ）中の式２におけるＹの含有割合が多いほど大きい。
【００２１】
例えば、式２中の−Ｒ^fＹが−（ＣＦ₂）₃ＣＯＯＣＨ₃であり、その式２で表される単位を０．２モル％、式１で表される単位を９９．８モル％含有し、溶融粘度が７．７×１０⁴ポアズの含フッ素共重合体（Ａ）を、３００℃で２０時間熱処理して得られる含フッ素共重合体（Ｂ）には、ＩＲ分析で−ＣＯＯＣＨ₃由来のピークが検出されず、その溶融粘度が１．６×１０⁶ポアズに上昇する。
【００２２】
架橋構造が生じる機構として、Ｙ、例えば−ＣＯＯＣＨ₃が熱と空気中の水分により加水分解反応、脱炭酸反応などを生起し、−ＣＦ₂ＣＦ₂・ラジカルが発生し、次いで共重合体鎖間の２個のラジカルがカップリングして架橋構造が生じると推定される。したがって、含フッ素共重合体（Ｂ）は、テトラフルオロエチレンの単独重合体（ＰＴＦＥ）、１重量％未満の微量のヘキサフルオロプロピレン、パーフルオロ（アルキルビニルエーテル）などに基づく重合単位を含有する変性ＰＴＦＥと異なる構造を有するものと推定される。
【００２３】
また、含フッ素共重合体（Ｂ）の結晶化熱は４０〜４９Ｊ／ｇであることが好ましい。熱処理により架橋構造が生成すると結晶性が低下して結晶化熱が下がる傾向にある。結晶化熱が４９Ｊ／ｇ超では含フッ素共重合体（Ｂ）の架橋密度が不充分で、ＰＦＡと過剰に溶融混練すると結晶核剤としての効果が低下する。また、４０Ｊ／ｇ未満では架橋密度が高くなりすぎＰＦＡと混合しにくくなりフィッシュアイの原因になる。
【００２４】
本発明組成物における含フッ素共重合体（Ｂ）の割合は、ＰＦＡと含フッ素共重合体（Ｂ）との合計１００重量部に対して０．０５〜２０重量部である。０．０５重量部未満では球晶の微細化の効果が少なく、２０重量部超では成形性を損ないやすい。
【００２５】
含フッ素共重合体（Ａ）およびその製造方法は公知である（特開平３−９１５１３、特開平３−２３４７５３）。
含フッ素共重合体（Ａ）は、式４で表される単量体、式５で表される単量体、および必要により式６で表される単量体を重合開始源の作用下に共重合することにより得られる。ただし式４におけるＸ、式５におけるＲ^fおよびＹ、式６におけるＺはいずれも前述と同じである。
【００２６】
【化３】

【００２７】
重合開始源としては、電離放射線や、有機パーオキシド系重合開始剤、酸化還元系重合開始剤などの重合開始剤などが採用できる。重合方法としては、懸濁重合、乳化重合、溶液重合、塊状重合など従来公知の重合方法が採用できる。
【００２８】
重合開始剤としては、ビス（フルオロアシル）パーオキシド類、ビス（クロロフルオロアシル）パーオキシド類、ジアルキルパーオキシジカーボネート類、ジアシルパーオキシド類、パーオキシエステル類、過硫酸塩類などが挙げられる。
【００２９】
重合媒体としては、溶液重合ではＣＣｌＦ₂ＣＦ₂ＣＣｌＦＨ（以下ＨＣＦＣ２２５ｃｂという）などのヒドロクロロフルオロカーボン類のほか、ｔ−ブタノールなどが挙げられ、懸濁重合、乳化重合では水または水と他の溶媒との混合溶媒が用いられる。重合温度は０℃〜１００℃、重合圧力は０．５〜３０ｋｇ／ｃｍ²の範囲から選択できる。
【００３０】
本発明におけるＰＦＡの原料単量体であるパーフルオロ（アルキルビニルエーテル）としては、ＰＦＡの高温における機械的強度の観点から、炭素数３〜１０のパーフルオロ（アルキルビニルエーテル）が好ましく、特に炭素数５のパーフルオロ（プロピルビニルエーテル）が好ましい。また、ＰＦＡ中のパーフルオロ（アルキルビニルエーテル）に基づく重合単位の含有割合は、ＰＦＡの成形性、高温における機械的強度の観点から１〜３モル％程度であることが好ましい。
【００３１】
また、ＰＦＡの溶融粘度は特に限定されないが、成形性の点から３７２℃における溶融粘度は５×１０³〜５×１０⁵ポアズであることが好ましい。
本発明の含フッ素重合体組成物は、ＰＦＡの優れた物性、成形性を損なうことなく、球晶サイズの小さい結晶化特性を有する。
【００３２】
含フッ素重合体組成物の溶融混練方法は特に限定されない。溶融したＰＦＡに含フッ素共重合体（Ｂ）を撹拌しながら混合する方法、単軸または２軸の混練押出機にＰＦＡと含フッ素共重合体（Ｂ）を同時に供給し混練する方法などが挙げられる。簡便さから、混練押出機により混練する方法が好ましい。混練時のＰＦＡおよび含フッ素共重合体（Ｂ）の形態も特に限定されず、ペレット、ビーズ、粉末等が用いられるが、含フッ素共重合体（Ｂ）の形態は粉末が好ましい。
【００３３】
本発明の含フッ素重合体組成物は、溶融成形できる。溶融成形とは、溶融した含フッ素重合体組成物を押出成形機、射出成形機または圧縮成形機を用いてフィルム、シート、チューブなどの成形体を成形すること、含フッ素重合体組成物を各種基材に被覆した成形体を成形することなどを含む。
【００３４】
本発明の含フッ素重合体組成物は、溶融成形により含フッ素重合体の球晶サイズが１０μｍ以下、好ましくは５μｍ以下の成形体を与え、また、内面粗度が０．３μｍ以下の押出成形チューブを与える。さらに、比較的遅い冷却速度でも微細な球晶を生成しやすい結晶化特性を有するので、押出成形法により厚肉チューブを成形する場合も、内面平滑性に優れたチューブを円滑有利に得ることができる。
【００３５】
本発明において、球晶サイズ、内面粗度、溶融粘度、融点、結晶化熱、結晶化温度、共重合体組成は以下の方法で測定される。
【００３６】
[球晶サイズ]
試料を３４０℃で厚さ２００μｍのフィルムに圧縮成形し、続いて冷却プレス機で約５分間で室温付近まで急冷して試験フィルムを作成する。試験フィルムの表面を偏光顕微鏡で観察することにより球晶サイズを測定した。
【００３７】
[内面粗度]
単軸押出機を用いて、試料を３８０℃で内径８ｍｍ、外径１０ｍｍのチューブに押出成形し、続いてチューブの外側から水冷して試験チューブを作成する。試験チューブの内面粗度（Ｒ_t）を粗さ計（サーフコーダＳＥ−３０Ｈ、小坂研究所製）にて測定した。
【００３８】
[溶融粘度]
島津製作所製フローテスターを用いてノズル長８ｍｍ、ノズル径２．１ｍｍのダイスを用いて荷重７ｋｇ、所定の温度で押出したときの流れ値Ｑ（ｃｍ³／秒）から、溶融粘度（ポアズ）＝４０９／Ｑなる式によって求めた。
【００３９】
[融点]
試料１０ｍｇをＤＴＡ（セイコー電子製）を用いて、昇温速度１０℃／分で測定し、吸熱ピークの先端の温度を融点とした。
【００４０】
[結晶化熱、結晶化温度]
試料１０ｍｇをＤＳＣ（セイコー電子製）を用いて、溶融状態から１０℃／分の速度で冷却し、結晶化させたときの結晶化熱とそのピーク温度を測定した。ピーク温度を結晶化温度とした。
【００４１】
[共重合体組成]
厚さ約３０μｍの成形フィルムをＩＲ分析し以下のように求めた。（ＣＦ₂＝ＣＦＯ（ＣＦ₂）₃ＣＯＯＣＨ₃に基づく重合単位）／（テトラフルオロエチレンに基づく重合単位）（モル比）は０．４２×（２３７０ｃｍ^-1における吸光度）／（１８００ｃｍ^-1における吸光度）として算出した。
【００４２】
【実施例】
［例１］
内容積１．１リットルのステンレス製反応容器を脱気し、水の４７０ｇ、ＨＣＦＣ２２５ｃｂの２９０ｇ、ＣＦ₂＝ＣＦＯ（ＣＦ₂）₃ＣＯＯＣＨ₃の１０．５ｇ、テトラフルオロエチレン（以下、ＴＦＥという）の８０ｇ、メタノールの４５ｇを仕込んだ。温度を５０℃に保持して、重合開始剤ビス（パーフルオロブチリル）パーオキシドの濃度が０．２５重量％のＨＣＦＣ２２５ｃｂ溶液を仕込み、反応を開始させた。反応中、系内にＴＦＥを導入し、反応圧力を１３．０ｋｇ／ｃｍ²に保持した。重合開始剤は重合速度がほぼ一定になるように断続的に仕込んだ。ＴＦＥの導入量が１００ｇになった時点で反応を終了させ、含フッ素共重合体Ａ１の白色粉末の１０６ｇを得た。ＮＭＲ分析の結果、含フッ素共重合体Ａ１はＣＦ₂＝ＣＦＯ（ＣＦ₂）₃ＣＯＯＣＨ₃に基づく重合単位の含有量が０．４モル％、融点が３１５℃、結晶化温度が２９５℃、結晶化熱が５１Ｊ／ｇ、３７２℃における溶融粘度が７．８×１０⁴ポアズであった。
【００４３】
続いて、含フッ素共重合体Ａ１を３００℃のオーブンで２４時間熱処理し、含フッ素共重合体Ｂ１を得た。ＩＲ分析の結果、含フッ素共重合体Ｂ１には−ＣＯＯＣＨ₃に由来するピークが検出されず、融点が３２０℃、結晶化温度が３０２℃、結晶化熱が４３Ｊ／ｇ、３７２℃における溶融粘度が５．３×１０⁶ポアズであった。
【００４４】
つぎに、ＴＦＥに基づく重合単位／ＣＦ₂＝ＣＦＯＣ₃Ｆ₇に基づく重合単位が９８．７／１．３（モル比）であり、３７２℃における溶融粘度が２．５×１０⁵ポアズ、結晶化温度が２８０℃であるＰＦＡ１を用い、このＰＦＡ１のビーズ状物の９５重量部と上記の含フッ素共重合体Ｂ１の粉末の５重量部を、２軸の混練押出機により溶融混練して、含フッ素重合体組成物１のペレットを得た。溶融混練条件は、シリンダ温度Ｃ１／Ｃ２／Ｃ３／Ｃ４／Ｃ５／Ｃ６／Ｈ＝２００℃／３５０℃／３８０℃／３８０℃／３８０℃／３８５℃／３８５℃、フィード量２０ｋｇ／ｈｒ、スクリュ回転数８０ｒｐｍであった。得られたペレットの３７２℃における溶融粘度は２．７×１０⁵ポアズであった。
【００４５】
この含フッ素重合体組成物１のペレットを圧縮成形して、厚さ２００μｍのフィルムを得た。このフィルムにおける球晶サイズは１〜３μｍであった。また、この含フッ素重合体組成物１から得られた押出成形チューブにおける内面粗度（Ｒ_t）は０．３μｍであった。
【００４６】
溶融混練条件として、シリンダ温度Ｃ１／Ｃ２／Ｃ３／Ｃ４／Ｃ５／Ｃ６／Ｈ＝２００℃／３９０℃／３９０℃／３９０℃／３９０℃／３９５℃／３９５℃、フィード量１０ｋｇ／ｈｒと過剰な条件に変更しても、球晶サイズ、押出成形チューブの内面粗度（Ｒ_t）は同じであった。
【００４７】
［例２］
ＣＦ₂＝ＣＦＯ（ＣＦ₂）₃ＣＯＯＣＨ₃の０．８ｇ、メタノールの５０ｇを用いる以外は例１と同様に重合を行い、含フッ素共重合体Ａ２の白色粉末の１０５ｇを得た。ＮＭＲ分析の結果、含フッ素共重合体Ａ２は、ＣＦ₂＝ＣＦＯ（ＣＦ₂）₃ＣＯＯＣＨ₃に基づく重合単位の含有量が０．０９モル％、融点が３２５℃、結晶化温度が３０９℃、結晶化熱が５３．７Ｊ／ｇ、３７２℃における溶融粘度が９．７×１０⁴ポアズであった。含フッ素共重合体Ａ２を３００℃で２４時間熱処理し、得られた含フッ素共重合体Ｂ２をＩＲ分析した結果、−ＣＯＯＣＨ₃に由来するピークは検出されず、融点が３２７℃、結晶化温度が３１５℃、結晶化熱が４７Ｊ／ｇ、３７２℃における溶融粘度が１．６×１０⁵ポアズであった。
【００４８】
含フッ素共重合体Ｂ２の５重量部と例１で用いたＰＦＡ１のビーズ状物の９５重量部を、２軸の混練押出機により溶融混練して、含フッ素重合体組成物２のペレットを得た。溶融混練条件は、シリンダ温度Ｃ１／Ｃ２／Ｃ３／Ｃ４／Ｃ５／Ｃ６／Ｈ＝２００℃／３５０℃／３８０℃／３８０℃／３８０℃／３８５℃／３８５℃、フィード量２０ｋｇ／ｈｒ、スクリュ回転数８０ｒｐｍであった。得られたペレットの３７２℃における溶融粘度は２．８×１０⁵ポアズであった。
【００４９】
この含フッ素重合体組成物２のペレットを圧縮成形して、厚さ２００μｍのフィルムを得た。このフィルムにおける球晶サイズは１〜３μｍであった。また、この含フッ素重合体組成物２から得られた押出成形チューブの内面粗度（Ｒ_t）は０．３μｍであった。
【００５０】
溶融混練条件として、シリンダ温度Ｃ１／Ｃ２／Ｃ３／Ｃ４／Ｃ５／Ｃ６／Ｈ＝２００℃／３９０℃／３９０℃／３９０℃／３９０℃／３９５℃／３９５℃、フィード量１０ｋｇ／ｈｒと過剰な条件に変更しても、球晶サイズ、押出成形チューブの内面粗度（Ｒ_t）は同じであった。
【００５１】
［例３（比較例）］
ＣＦ₂＝ＣＦＯ（ＣＦ₂）₃ＣＯＯＣＨ₃を用いず、メタノールの２０ｇを用いる以外は例１と同様にしてＴＦＥを重合し、白色ＰＴＦＥ粉末の１０５ｇを得た。このＰＴＦＥ粉末は、結晶化温度が３１５℃、結晶化熱が５５Ｊ／ｇ、３７２℃における溶融粘度が１．７×１０⁶ポアズであった。
【００５２】
このＰＴＦＥ粉末の５重量部と例１で用いたＰＦＡ１のビーズ状物の９５重量部を、２軸の混練押出機により溶融混練して、ペレット状の重合体組成物を得た。溶融混練条件は、シリンダ温度Ｃ１／Ｃ２／Ｃ３／Ｃ４／Ｃ５／Ｃ６／Ｈ＝２００℃／３５０℃／３８０℃／３８０℃／３８０℃／３８５℃／３８５℃、フィード量２０ｋｇ／ｈｒ、スクリュ回転数８０ｒｐｍであった。得られたペレットの３７２℃における溶融粘度は２．８×１０⁵ポアズであった。
【００５３】
この重合体組成物のペレットを圧縮成形して、厚さ２００μｍのフィルムを得た。このフィルムにおける球晶サイズは２〜５μｍであった。また、この重合体組成物から得られた押出成形チューブの内面粗度（Ｒ_t）は０．４μｍであった。
【００５４】
溶融混練条件として、シリンダ温度Ｃ１／Ｃ２／Ｃ３／Ｃ４／Ｃ５／Ｃ６／Ｈ＝２００℃／３９０℃／３９０℃／３９０℃／３９０℃／３９５℃／３９５℃、フィード量１０ｋｇ／ｈｒと過剰な条件に変更すると、球晶サイズは１０〜２０μｍ、押出成形チューブの内面粗度（Ｒ_t）は０．９μｍに増大した。
【００５５】
【発明の効果】
ＰＦＡの物性、加工性を損なうことなく、溶融成形において微細な球晶を生成するＰＦＡ組成物が容易に得られ、表面平滑性に優れた成形物を得ることができる。また、過剰な溶融混練条件においても、球晶を微細にする効果が低下しないし、表面平滑性の低下も認められない。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in crystallization characteristics of a tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (hereinafter referred to as PFA).
[0002]
[Prior art]
PFA is a polymer material having excellent heat resistance, chemical resistance, solvent resistance, and the like, and is used for various applications by taking advantage of its characteristics. However, PFA is a crystalline resin, and many crystal nuclei are generated in the melt during cooling and solidification after melt molding. Spherulite grows in the same direction around this crystal nucleus, and the growth of the spherulite stops after touching each other. It is known that the surface smoothness of a molded product in which spherulites are generated depends on the size of the spherulites, and if the spherulites are large, the surface smoothness is inferior. If the spherulites grow greatly and the surface smoothness of the molded product is inferior, impurities are likely to accumulate on the surface when used as a tube. When used as a pipe joint, stress cracks are likely to occur.
[0003]
It is known that the size of the spherulite depends on the cooling rate after melt molding. Finer spherulites are generated as the temperature is rapidly cooled, but depending on the molding method, there are cases where rapid cooling is impossible. For example, in the extrusion molding of thick-walled tubes, the inner surface of the pipe is not rapidly cooled when the extruded tube is cooled from the outer surface, so that a large spherulite is generated on the inner surface of the pipe and the smoothness of the inner surface is poor. There is a need for PFAs having crystallization characteristics that produce fine spherulites even at relatively slow cooling rates.
[0004]
As a method for making PFA spherulites fine, a method is known in which a small amount of specific polytetrafluoroethylene (hereinafter referred to as PTFE) is added to PFA as a crystal nucleating agent (JP-A-7-70397). However, fish eyes are likely to occur when PTFE and PFA are not sufficiently melt-kneaded. Moreover, when it melts and kneads excessively, PTFE mixes with PFA, and there is a problem that the effect of making spherulites fine as a crystal nucleating agent decreases.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to improve the crystallization characteristics so that small spherulites are formed without impairing the physical properties and moldability of PFA.
[0006]
[Means for Solving the Problems]
In the present invention, the unit represented by Formula 1 is 96 to 99.99 mol%, the unit represented by Formula 2 is 0.01 to 1 mol%, and the unit represented by Formula 3 is optionally 0 to A fluorine-containing copolymer (B) obtained by heat-treating a copolymer (A) (hereinafter referred to as a fluorine-containing copolymer (A)) containing 3 mol% at 200 ° C. or higher, and PFA (C) A fluorine-containing polymer composition containing 0.05 to 20 parts by weight of (B) with respect to a total of 100 parts by weight of (B) and (C).
[0007]
[Chemical formula 2]

[0008]
In the formula, X is a fluorine atom or a chlorine atom, R ^f is a divalent fluorine-substituted organic group, Y is a hydroxyalkyl group, a carboxyl group, or a monovalent carboxylic acid derivative group, and Z is It is a monovalent fluorine-substituted organic group other than —O—R ^f Y.
[0009]
Moreover, this invention provides the molded object formed by melt-molding the said fluoropolymer composition.
[0010]
The fluorine-containing copolymer (B) is obtained by heat-treating the fluorine-containing copolymer (A) and functions as a crystal nucleating agent for PFA (C).
Even if the fluoropolymer composition of the present invention is excessively melt-kneaded, the effect as a crystal nucleating agent is not reduced.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a composition comprising a fluorinated copolymer (B) and PFA. By heat-treating the fluorine-containing copolymer (A), the melt viscosity of the resulting fluorine-containing copolymer (B) increases. This is because the functional group —O—R ^f Y part in Formula 2 in the molecule of the fluorine-containing copolymer (A) undergoes a crosslinking reaction with the same functional group part in the other molecule by heat treatment. It is presumed that the fluorine-containing copolymer (B) having a structure is generated. However, this description is intended to help understanding of the present invention and does not limit the present invention.
[0012]
The fluorine-containing copolymer (B) in the composition of the present invention can be a crystal nucleating agent for PFA. When a small amount of the fluorinated copolymer (B) is added to PFA and melt-kneaded and molded, fine spherulites are generated in the molded product. Further, even if it is excessively melt-kneaded, the effect as a crystal nucleating agent is not impaired unlike PTFE. This effect is presumably because the fluorine-containing copolymer (B) is not completely mixed with PFA due to crosslinking.
[0013]
In the unit of Formula 1, X is more preferably a fluorine atom from the viewpoint of chemical resistance.
In the unit of Formula 2, R ^f, that is, the divalent fluorine-substituted organic group may have one or more substituted fluorine atoms, and a fully fluorinated divalent fluorine-substituted organic group is more preferable. R ^f is preferably a divalent fluorine-substituted organic group in which a chain is formed of only carbon or carbon and oxygen.
[0014]
Specific examples thereof include a perfluoroalkylene group or a perfluoroalkylene group containing an ether bond. The number of carbon atoms constituting the R ^f chain is preferably in the range of 1 to 15, particularly 1 to 10. R ^f preferably has a linear structure, but may have a branched structure. In the case of a branched structure, a short chain having about 1 to 3 carbon atoms in the branched portion is preferable. Particularly preferred R ^f is — (CF ₂ ) _m — (m is an integer of 2 to 6).
[0015]
Specific examples of R ^f include, for example, — (CF ₂ ) ₂ —, — (CF ₂ ) ₃ —, — (CF ₂ ) ₄ —, — (CF ₂ ) ₅ —, — (CF ₂ ) ₆ —, — CF ₂ CF (CF ₃ ) O (CF ₂ ) ₃ —, —CF ₂ CF (CF ₃ ) OCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ —, — (CF ₂ CF ₂ O) ₂ — (CF ₂ ) ₃₋ , —CF ₂ CF (CF ₃ ) CF ₂ CF ₂ CF (CF ₃ ) CF ₂ — and the like.
[0016]
Y in Formula 2 is a hydroxyalkyl group, a carboxyl group, or a monovalent carboxylic acid derivative group. As the carboxylic acid derivative group, -COOA (A is an alkyl group having about 1 to 3 carbon atoms, a fluoroalkyl group having about 1 to 3 carbon atoms, an alkali metal, an ammonium base, or a substituted ammonium base) or -COB (B is fluorine Atom or chlorine atom). Among these, preferable Y is a hydroxyalkyl group and an alkoxycarbonyl group, and —CH ₂ OH, —CH ₂ CH ₂ OH, and —COOCH ₃ are preferable.
[0017]
Content of the unit represented by Formula 2 in a fluorine-containing copolymer (A) is 0.01-1 mol%. If it is less than 0.01 mol%, the crosslinking density of the fluorine-containing copolymer (B) is insufficient, and if it is excessively melt-kneaded with PFA, it will be mixed with PFA and its effect as a crystal nucleating agent will be small. If it exceeds 1 mol%, the melt viscosity of the fluorinated copolymer (B) will increase too much, making it difficult to knead with PFA and causing fish eyes.
Only one type of unit of Formula 2 may be included, or two or more types may be included.
[0018]
In the unit of Formula 3, Z, that is, the monovalent fluorine-substituted organic group is a monovalent fluorine-substituted organic group other than —O—R ^f Y of Formula 2, and has a carbon number from the viewpoint of heat resistance and chemical resistance. 1-10 perfluoroalkoxy groups are preferred. If the content of Formula 3 exceeds 3 mol%, the melting point of the fluorine-containing copolymer (B) is too low, and the effect as a crystal nucleating agent is lowered.
[0019]
The fluorine-containing copolymer (B) can be obtained by heat-treating the fluorine-containing polymer (A) at a temperature of 200 ° C. or higher. If it is less than 200 ° C., —O—R ^f Y in Formula 2 is difficult to undergo a crosslinking reaction. Above the melting point, —O—R ^f Y undergoes a crosslinking reaction. However, since the fluoropolymer (B) is fused, if it is not pulverized and added to PFA, it may cause fish eyes. A heat treatment temperature of less than is good. The heat treatment is preferably performed for a period of time until 50% or more, preferably 90% or more, of Y in Formula 2 is decomposed and a crosslinking reaction occurs. If Y in Formula 2 does not undergo a crosslinking reaction and remains in a large amount, the chemical resistance of the composition may be reduced. The heat treatment time is preferably 3 hours or more at 300 ° C., for example. The heat treatment in the present invention is desirably performed in an atmosphere containing oxygen.
[0020]
A mechanism presumed that a cross-linked structure is generated in the fluorine-containing copolymer (B) is shown below. In the fluorine-containing copolymer (A), Y in Formula 2 is recognized by IR analysis. In the fluorine-containing copolymer (B), it is recognized that the amount of Y is reduced as compared with the fluorine-containing copolymer (A), or Y is not recognized. Further, the melt viscosity of the fluorinated copolymer (B) is larger than that of the fluorinated copolymer (A), and the rate of increase is determined by the content ratio of Y in Formula 2 in the fluorinated copolymer (A). The more it is, the bigger it is.
[0021]
For example, —R ^f Y in Formula 2 is — (CF ₂ ) ₃ COOCH ₃ , the unit represented by Formula 2 is 0.2 mol%, and the unit represented by Formula 1 is 99.8 mol%. The fluorine-containing copolymer (B) obtained by heat-treating the fluorine-containing copolymer (A) having a melt viscosity of 7.7 × 10 ⁴ poises at 300 ° C. for 20 hours has a —COOCH by IR analysis. _No peak derived from ₃ is detected and its melt viscosity rises to 1.6 × 10 ⁶ poise.
[0022]
As a mechanism for forming a cross-linked structure, Y, for example, —COOCH ₃ causes hydrolysis reaction, decarboxylation reaction, etc. by heat and moisture in the air to generate —CF ₂ CF ₂ .radical, and then between the copolymer chains. It is presumed that the two radicals are coupled to form a crosslinked structure. Therefore, the fluorine-containing copolymer (B) is a modified PTFE containing a polymer unit based on a tetrafluoroethylene homopolymer (PTFE), a trace amount of hexafluoropropylene of less than 1% by weight, perfluoro (alkyl vinyl ether) and the like. It is presumed to have a different structure.
[0023]
Moreover, it is preferable that the crystallization heat of a fluorine-containing copolymer (B) is 40-49 J / g. When a crosslinked structure is formed by heat treatment, the crystallinity is lowered and the crystallization heat tends to be lowered. If the heat of crystallization exceeds 49 J / g, the crosslinking density of the fluorinated copolymer (B) is insufficient, and if it is excessively melt-kneaded with PFA, the effect as a crystal nucleating agent is reduced. On the other hand, if it is less than 40 J / g, the crosslinking density becomes too high and it becomes difficult to mix with PFA, which causes fish eyes.
[0024]
The ratio of the fluorine-containing copolymer (B) in the composition of the present invention is 0.05 to 20 parts by weight with respect to a total of 100 parts by weight of the PFA and the fluorine-containing copolymer (B). If it is less than 0.05 part by weight, the effect of refining the spherulites is small, and if it exceeds 20 parts by weight, the moldability tends to be impaired.
[0025]
The fluorine-containing copolymer (A) and the production method thereof are known (Japanese Patent Laid-Open Nos. 3-91513 and 3-234533).
The fluorine-containing copolymer (A) comprises a monomer represented by formula 4, a monomer represented by formula 5, and, if necessary, a monomer represented by formula 6 under the action of a polymerization initiation source. Obtained by copolymerization. However, X in Formula 4, R ^f and Y in Formula 5, and Z in Formula 6 are all the same as described above.
[0026]
[Chemical 3]

[0027]
As the polymerization initiation source, ionizing radiation, a polymerization initiator such as an organic peroxide polymerization initiator, a redox polymerization initiator, or the like can be employed. As the polymerization method, conventionally known polymerization methods such as suspension polymerization, emulsion polymerization, solution polymerization and bulk polymerization can be employed.
[0028]
Examples of the polymerization initiator include bis (fluoroacyl) peroxides, bis (chlorofluoroacyl) peroxides, dialkyl peroxydicarbonates, diacyl peroxides, peroxyesters, persulfates and the like.
[0029]
Examples of the polymerization medium include hydrochlorofluorocarbons such as CClF ₂ CF ₂ CClFH (hereinafter referred to as HCFC225cb) in solution polymerization and t-butanol. In suspension polymerization and emulsion polymerization, water or water and other solvents are used. The mixed solvent is used. The polymerization temperature can be selected from the range of 0 to 100 ° C., and the polymerization pressure can be selected from the range of 0.5 to 30 kg / cm ² .
[0030]
The perfluoro (alkyl vinyl ether) which is a raw material monomer of PFA in the present invention is preferably a perfluoro (alkyl vinyl ether) having 3 to 10 carbon atoms, particularly 5 carbon atoms from the viewpoint of mechanical strength at high temperatures of PFA. Perfluoro (propyl vinyl ether) is preferred. Moreover, it is preferable that the content rate of the polymer unit based on the perfluoro (alkyl vinyl ether) in PFA is about 1-3 mol% from a viewpoint of the moldability of PFA and the mechanical strength in high temperature.
[0031]
The melt viscosity of PFA is not particularly limited, but the melt viscosity at 372 ° C. is preferably 5 × 10 ^{3 to} 5 × 10 ⁵ poise from the viewpoint of moldability.
The fluoropolymer composition of the present invention has crystallization characteristics with a small spherulite size without impairing the excellent physical properties and moldability of PFA.
[0032]
The method for melt-kneading the fluoropolymer composition is not particularly limited. A method of mixing the fluorine-containing copolymer (B) with molten PFA while stirring, a method of simultaneously feeding and kneading the PFA and the fluorine-containing copolymer (B) to a single-screw or biaxial kneader-extruder, and the like. It is done. In view of simplicity, a method of kneading with a kneading extruder is preferred. The form of PFA and fluorine-containing copolymer (B) at the time of kneading is not particularly limited, and pellets, beads, powders, and the like are used. The form of fluorine-containing copolymer (B) is preferably powder.
[0033]
The fluoropolymer composition of the present invention can be melt-molded. Melt molding refers to molding a molded product such as a film, a sheet, or a tube by using an extrusion molding machine, an injection molding machine or a compression molding machine, and various types of fluoropolymer compositions. Including forming a molded body coated on a substrate.
[0034]
The fluoropolymer composition of the present invention gives a molded product having a spherulite size of 10 μm or less, preferably 5 μm or less by melt molding, and an extruded tube having an inner surface roughness of 0.3 μm or less. give. Furthermore, since it has a crystallization characteristic that easily produces fine spherulites even at a relatively slow cooling rate, it is possible to smoothly and advantageously obtain a tube with excellent inner surface smoothness even when forming a thick tube by an extrusion method. it can.
[0035]
In the present invention, spherulite size, inner surface roughness, melt viscosity, melting point, heat of crystallization, crystallization temperature, and copolymer composition are measured by the following methods.
[0036]
[Spherulite size]
The sample is compression-molded into a film having a thickness of 200 μm at 340 ° C., and then rapidly cooled to around room temperature in a cooling press for about 5 minutes to prepare a test film. The spherulite size was measured by observing the surface of the test film with a polarizing microscope.
[0037]
[Inner surface roughness]
Using a single screw extruder, the sample is extruded into a tube having an inner diameter of 8 mm and an outer diameter of 10 mm at 380 ° C., and then water-cooled from the outside of the tube to prepare a test tube. The inner surface roughness (R _t ) of the test tube was measured with a roughness meter (Surfcoder SE-30H, manufactured by Kosaka Laboratory).
[0038]
[Melt viscosity]
From a flow value Q (cm ³ / sec) when extruded at a predetermined temperature using a Shimadzu flow tester with a nozzle length of 8 mm and a nozzle diameter of 2.1 mm, the melt viscosity (poise) = It calculated | required by the formula of 409 / Q.
[0039]
[Melting point]
10 mg of a sample was measured using a DTA (manufactured by Seiko Denshi) at a rate of temperature increase of 10 ° C./min, and the temperature at the end of the endothermic peak was taken as the melting point.
[0040]
[Heat of crystallization, crystallization temperature]
A 10 mg sample was cooled at a rate of 10 ° C./min from a molten state using DSC (manufactured by Seiko Denshi), and the heat of crystallization and its peak temperature were measured. The peak temperature was taken as the crystallization temperature.
[0041]
[Copolymer composition]
A molded film having a thickness of about 30 μm was subjected to IR analysis and determined as follows. (CF ₂ = polymer unit based on CFO (CF ₂ ) ₃ COOCH ₃ ) / (polymer unit based on tetrafluoroethylene) (molar ratio) is 0.42 × (absorbance at 2370 cm ⁻¹ ) / (absorbance at 1800 cm ⁻¹ ) ).
[0042]
【Example】
[Example 1]
A stainless steel reaction vessel having an internal volume of 1.1 liters was degassed, and 470 g of water, 290 g of HCFC225cb, 10.5 g of CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ , tetrafluoroethylene (hereinafter referred to as TFE) 80 g and 45 g of methanol were charged. While maintaining the temperature at 50 ° C., an HCFC225cb solution having a polymerization initiator bis (perfluorobutyryl) peroxide concentration of 0.25 wt% was charged to initiate the reaction. During the reaction, TFE was introduced into the system, and the reaction pressure was maintained at 13.0 kg / cm ² . The polymerization initiator was intermittently charged so that the polymerization rate was almost constant. The reaction was terminated when the amount of TFE introduced reached 100 g to obtain 106 g of a white powder of fluorine-containing copolymer A1. Results of NMR analysis, the fluorine-containing copolymer A1 is _{CF 2 = CFO (CF 2)} 3 content of the polymerized units based on COOCH ₃ 0.4 mol%, a melting point of 315 ° C., a crystallization temperature of 295 ° C., crystals The heat of formation was 51 J / g and the melt viscosity at 372 ° C. was 7.8 × 10 ⁴ poise.
[0043]
Subsequently, the fluorinated copolymer A1 was heat-treated in an oven at 300 ° C. for 24 hours to obtain a fluorinated copolymer B1. As a result of IR analysis, no peak derived from —COOCH ₃ was detected in the fluorinated copolymer B1, the melting point was 320 ° C., the crystallization temperature was 302 ° C., the crystallization heat was 43 J / g, and the melt viscosity at 372 ° C. Was 5.3 × 10 ⁶ poise.
[0044]
Next, the polymerized unit based on TFE / the polymerized unit based on CF ₂ = CFOC ₃ F ₇ is 98.7 / 1.3 (molar ratio), the melt viscosity at 372 ° C. is 2.5 × 10 ⁵ poise, crystals Using PFA1 having a conversion temperature of 280 ° C., 95 parts by weight of the PFA1 beads and 5 parts by weight of the powder of the fluorinated copolymer B1 were melt-kneaded by a twin-screw kneading extruder, A pellet of fluoropolymer composition 1 was obtained. Melting and kneading conditions are: cylinder temperature C1 / C2 / C3 / C4 / C5 / C6 / H = 200 ° C / 350 ° C / 380 ° C / 380 ° C / 380 ° C / 380 ° C / 385 ° C, feed amount 20 kg / hr, screw rotation It was several 80 rpm. The melt viscosity at 372 ° C. of the obtained pellet was 2.7 × 10 ⁵ poise.
[0045]
The pellet of this fluoropolymer composition 1 was compression molded to obtain a film having a thickness of 200 μm. The spherulite size in this film was 1-3 μm. Further, the inner surface roughness (R _t ) of the extruded tube obtained from this fluoropolymer composition 1 was 0.3 μm.
[0046]
As melt-kneading conditions, cylinder temperature C1 / C2 / C3 / C4 / C5 / C6 / H = 200 ° C / 390 ° C / 390 ° C / 390 ° C / 390 ° C / 395 ° C / 395 ° C, feed amount of 10 kg / hr is excessive. Even when the conditions were changed, the spherulite size and the inner surface roughness (R _t ) of the extruded tube were the same.
[0047]
[Example 2]
0.8g of _{CF 2 = CFO (CF 2)} 3 COOCH 3, except using 50g of methanol subjected to the same polymerization as in Example 1 to obtain 105g of a white powder of the fluorocopolymer A2. NMR analysis of the results, the fluorine-containing copolymer A2 _{is, CF 2 = CFO (CF 2} ) 3 content of the polymerized units based on COOCH ₃ 0.09 mol%, a melting point of 325 ° C., a crystallization temperature of 309 ° C., The heat of crystallization was 53.7 J / g, and the melt viscosity at 372 ° C. was 9.7 × 10 ⁴ poise. The fluorine-containing copolymer A2 was heat-treated at 300 ° C. for 24 hours, and as a result of IR analysis of the obtained fluorine-containing copolymer B2, no peak derived from —COOCH ₃ was detected, the melting point was 327 ° C., and the crystallization temperature. Was 315 ° C., the heat of crystallization was 47 J / g, and the melt viscosity at 372 ° C. was 1.6 × 10 ⁵ poise.
[0048]
5 parts by weight of the fluorocopolymer B2 and 95 parts by weight of the PFA1 beads used in Example 1 were melt-kneaded by a twin-screw kneading extruder to obtain a pellet of the fluoropolymer composition 2. It was. Melting and kneading conditions are: cylinder temperature C1 / C2 / C3 / C4 / C5 / C6 / H = 200 ° C / 350 ° C / 380 ° C / 380 ° C / 380 ° C / 380 ° C / 385 ° C, feed amount 20 kg / hr, screw rotation It was several 80 rpm. The melt viscosity at 372 ° C. of the obtained pellet was 2.8 × 10 ⁵ poise.
[0049]
The pellets of this fluoropolymer composition 2 were compression molded to obtain a film having a thickness of 200 μm. The spherulite size in this film was 1-3 μm. Further, the inner surface roughness (R _t ) of the extruded tube obtained from this fluoropolymer composition 2 was 0.3 μm.
[0050]
As melt-kneading conditions, cylinder temperature C1 / C2 / C3 / C4 / C5 / C6 / H = 200 ° C / 390 ° C / 390 ° C / 390 ° C / 390 ° C / 395 ° C / 395 ° C, feed amount 10 kg / hr Even when the conditions were changed, the spherulite size and the inner surface roughness (R _t ) of the extruded tube were the same.
[0051]
[Example 3 (comparative example)]
CF ₂ = without the _{CFO (CF 2) 3 COOCH 3} , except using 20g of methanol in the same manner as in Example 1 by polymerizing TFE, to obtain a 105g of white PTFE powder. This PTFE powder had a crystallization temperature of 315 ° C., a crystallization heat of 55 J / g, and a melt viscosity at 372 ° C. of 1.7 × 10 ⁶ poise.
[0052]
5 parts by weight of this PTFE powder and 95 parts by weight of the PFA1 beads used in Example 1 were melt-kneaded by a biaxial kneading extruder to obtain a pellet-shaped polymer composition. Melting and kneading conditions were as follows: cylinder temperature C1 / C2 / C3 / C4 / C5 / C6 / H = 200 ° C./350° C./380° C./380° C./380° C./385° C./385° C., feed amount 20 kg / hr, screw rotation It was several 80 rpm. The resulting pellet had a melt viscosity of 2.8 × 10 ⁵ poise at 372 ° C.
[0053]
The polymer composition pellets were compression molded to obtain a film having a thickness of 200 μm. The spherulite size in this film was 2-5 μm. Further, the inner surface roughness (R _t ) of the extruded tube obtained from this polymer composition was 0.4 μm.
[0054]
As melt-kneading conditions, cylinder temperature C1 / C2 / C3 / C4 / C5 / C6 / H = 200 ° C / 390 ° C / 390 ° C / 390 ° C / 390 ° C / 395 ° C / 395 ° C, feed amount 10 kg / hr When changed to the conditions, the spherulite size increased to 10-20 μm and the inner surface roughness (R _t ) of the extruded tube increased to 0.9 μm.
[0055]
【The invention's effect】
Without impairing the physical properties and processability of PFA, a PFA composition that produces fine spherulites in melt molding can be easily obtained, and a molded product having excellent surface smoothness can be obtained. Further, even under excessive melt-kneading conditions, the effect of making the spherulites fine is not lowered, and the surface smoothness is not lowered.

Claims (4)

96 to 99.99 mol% of the unit represented by Formula 1, 0.01 to 1 mol% of the unit represented by Formula 2, and 0 to 3 mol% of the unit represented by Formula 3 as an optional component. A composition comprising a fluorine-containing copolymer (B) obtained by heat-treating a copolymer (A) contained at a ratio of 200 ° C. or higher and a tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (C). The fluorine-containing polymer composition containing (B) at a ratio of 0.05 to 20 parts by weight with respect to 100 parts by weight as a total of (B) and (C).

In the formula, X is a fluorine atom or a chlorine atom, R ^f is a divalent fluorine-substituted organic group, Y is a hydroxyalkyl group, a carboxyl group, or a monovalent carboxylic acid derivative group, and Z is It is a monovalent fluorine-substituted organic group other than —O—R ^f Y. The fluoropolymer composition according to claim 1, wherein the perfluoro (alkyl vinyl ether) is perfluoro (propyl vinyl ether). A molded article obtained by melt-molding the fluoropolymer composition according to claim 1 or 2. 4. The molded article according to claim 3, wherein the spherulite size of the fluoropolymer constituting the molded article is 10 μm or less.