JP5044801B2 - Method for modifying fluoropolymer and method for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for modifying a fluoropolymer, wherein the unstable group of a melt processable fluoropolymer having an unstable group can be quickly and efficiently stabilized and wherein the molecular weight of the fluoropolymer can be adjusted at the same time. SOLUTION: The process for modifying a fluoropolymer comprises a step (A) of melting and kneading a melt processable fluoropolymer having an unstable group in the presence of an oxygen-containing gas and a step (B) of melting and kneading the fluoropolymer treated with an oxygen-containing gas, in the presence of oxygen and water.

Description

【００４７】
この反応は加熱、通常２７０〜４５０℃、好ましくは３００〜４００℃において行なわれる。
【００４８】
また、この反応を促進するためには、アルカリ金属、アルカリ土類金属、アンモニウム塩を含む化合物、またはアンモニア、アルコール類、アミンまたはその塩などの反応促進剤を添加することが有効である。具体的には、水酸化カリウム、水酸化ナトリウムなどの水酸化物、炭酸カリウム、炭酸カルシウムなどの炭酸塩、硫酸カリウムなどの硫酸塩、硝酸カリウムなどの硝酸塩、水酸化アンモニウムなどのアンモニウム塩、アンモニア、メタノール、エタノールなどのアルコール、アミンまたはその塩などがあげられる。アルカリ金属またはアルカリ土類金属化合物の場合は−ＣＦ₂Ｈ末端となり、アンモニウム塩やアンモニア、アミンの場合は酸アミド末端基（−ＣＯＮＨ₂)となり（高温では一部−ＣＦ₂Ｈ末端となる）、アルコールの場合はアルキルエステル末端基（−ＣＯＯＲ）となる。
【００４９】
反応促進剤の添加は、予め含フッ素重合体に配合していても、また工程（Ａ）で添加してもよいが、工程（Ｂ）で水といっしょに添加する方が重合体に均一に分散できる点から好ましい。添加量は処理すべき含フッ素重合体の種類にもよるが、アルカリ金属およびアルカリ土類金属化合物の場合はアルカリ金属およびアルカリ土類金属の原子数に換算して、アンモニアの場合はアンモニアの分子数に換算して、アンモニウム塩化合物の場合はアンモニウム塩の数に換算して、含フッ素重合体中の不安定基（カルボン酸末端基）総数の１０％以下、好ましくは０．１〜１０％、特に好ましくは０．２〜５％とする。添加量が多すぎると、不安定末端基の安定化速度は増大するが、重合体の着色を完全に排除できず、また重合体自体が劣化してメルトフローレートが低下する傾向がある。
【００５０】
なお、カルボン酸末端基の安定化方法としては、フッ素ガスなどによるフッ素化処理があるが、本発明における工程（Ｂ）ではフッ素化処理は行なわない。もちろん、本発明の安定化処理工程後に、必要であればさらにフッ素化処理を施してもよい。
【００５１】
ビニル末端基
カルボン酸末端基および不安定な主鎖の結合から熱または剪断力が加わることにより生ずると推定されている。
【００５２】

【００５３】
このビニル末端基はフッ素化処理してトリフルオロメチル基に変換されるか、次の反応式にしたがって酸フルオライドを介してカルボン酸基に変換される。
【００５４】
−ＣＦ＝ＣＦ₂ ＋ Ｏ₂ → −ＣＯＦ ＋ ＣＯＦ₂ （IV）
−ＣＯＦ ＋ Ｈ₂Ｏ → −ＣＯＯＨ ＋ ＨＦ （Ｖ）
【００５５】
生成したカルボン酸末端基は前記の方法で処理される。ただし、前記の米国特許第４，６７５，３８０号明細書では処理が複雑になる酸フルオライドに変化させないように、酸素を実質的に存在させずにビニル末端基で停止させている。
【００５６】
しかし、ビニル末端基は加熱されると次式に示すように解重合を起こし炭素を発生するので、前記米国特許第４，６７５，３８０号明細書では暗色の溶融混練物が得られている。
【００５７】

【００５８】
酸フルオライド末端基
前記式(V)にしたがってカルボン酸基に一旦戻したのち安定化処理されている 。
【００５９】
このように、含フッ素重合体の安定化処理は多くの場合、最終的にはカルボン酸末端基を水と熱により安定化する反応が律速反応となり、また、できるだけビニル末端基の解重合が生じない方法がとられている。たとえば前記ＷＯ９８／０９７８４号パンフレット記載の方法では、カルボン酸末端基の安定化反応を優先させ、解重合により着色の原因となる炭素が発生しないようにビニル末端基の発生がマイルドに生ずる条件、すなわち安定化処理をほぼ大気圧下（ＷＯ９８／０９７８４号パンフレット記載の実施例１および２ではいずれも絶対圧力約０．１ＭＰａ）で行ない、さらに混練を動力係数Ｋが８０００未満、好ましくは７０００以下という緩やかな条件で行なうことを特徴としているため、安定化処理に要する時間が長くなっている。
【００６０】
本発明では、逆に酸素、ついで水を積極的に反応系に存在させることによってビニル末端基を迅速に酸フルオライドに変換し（反応（IV））、解重合を低減して炭素の発生を抑制し、着色を防止すると共に、カルボン酸末端基の安定化反応（Ｉ）を加圧状態とすることにより促進するものである。そのためには、水の存在が必須である。
【００６１】
水はカルボン酸末端基を安定化する反応(I)および酸フルオライドをカルボン 酸に変換する反応（Ｖ）で使用する。
【００６２】
水の添加量は、前記反応に必要な理論量よりも過剰量である必要があるが、その量は添加する圧力、押出機内の状態に大きく左右され、実機で確認しつつ決定する。
【００６３】
前記のとおりカルボン酸末端基を安定化させる反応（Ｉ）はアルカリ金属化合物などの反応促進剤を添加することにより、大きく促進されるので、水は促進剤を溶解させた水溶液の形で添加することが好ましい。水溶液の濃度は前記の促進剤の必要量を基準に適宜選定すればよい。
【００６４】
この安定化処理工程（Ｂ）はたとえば混練機として、混練機内の反応圧力を高めることができるスクリュー型押出機、特に２軸スクリュー型押出機などを用いて行なうことが好ましい。
【００６５】
供給する水分量は、たとえば混練機（押出機）中で発生する不安定末端基の数と同じ分子数であれば理論的には安定化できるが、実際には過剰の、特に不安定末端基数の１０倍以上の分子数の水を供給することが好ましい。上限は特に限定されない。
【００６６】
なお前記のように、特段の手立てをしないと混練機に供給される重合体には大気と同様の空気と共に水分が含まれているが、この程度の酸素量および水分量では本発明が達成できる分子量調整効果と安定化効果は奏されない。その理由は、おそらく処理の間に低分子量物や重合体中の各種添加剤（たとえば重合開始剤など）が分解してガスを発生させるため、処理工程における酸素や水分の分圧を下げてしまい、重合体と酸素や水分との接触が不充分となってしまうためであると考えられる。
【００６７】
工程（Ｂ）での圧力は、好ましくは絶対圧力を０．２ＭＰａ以上、好ましくは０．３ＭＰａ以上の加圧状態とする。加圧することにより、たとえば供給する水の侵入が促進され、迅速な安定化処理が可能になる。混練機を使用する場合、圧力は混練機に取り付けられた圧力計により測定できる。上限はメルトシール部の状態や押出機の型式などによって異なるが、１０ＭＰａ以下、好ましくは５ＭＰａ以下である。
【００６８】
また、この工程（Ｂ）での混練には、前記のとおり、酸素の存在が欠かせない。すなわち工程（Ｂ）でも溶融混練時に着色の原因物質が生じるため、そうした物質を酸化除去するために酸素が必要となる。工程（Ｂ）に存在させる酸素は、連続法において工程（Ａ）で比較的多量に供給されている場合は積極的に追加する必要はないが、着色が生じるようであれば適宜追加する。工程（Ａ）と工程（Ｂ）を分けて行なう場合は工程（Ａ）で導入された酸素が少なくなっているため、積極的に酸素を含むガスを供給することが望ましい。
【００６９】
工程（Ａ）および（Ｂ）での加圧は、たとえば後述する酸素を含むガスおよび／または水を圧入することにより、あるいは酸素を含むガスおよび／または水を加熱してその自圧下に供給することにより行なうことができる。
【００７０】
工程（Ａ）で処理された含フッ素重合体を以上の条件下に溶融混練することにより、不安定基は末端基と主鎖中の不安定結合を問わず、短時間でかつ効率よく安定化でき、しかも着色の原因となる炭素の発生も抑制できる。
【００７１】
本発明においては、分子量調整工程（Ａ）と安定化処理工程（Ｂ）とを別々の装置（押出機または混練機）で行なってもよく、また１台の混練機（押出機）で連続して行なってもよい。
【００７２】
別の混練機で行なう場合、工程（Ａ）と（Ｂ）の条件を独立に設定変更できる点で有利である。一方、１台の混練機で行なう場合は、コスト面で有利である。
【００７３】
本発明を連続して実施する場合に使用できる混練機としては多軸型混練機、たとえば二軸スクリュー型押出機、有効容積率が極めて小さいニーダーなどがあげられる。これらのうち滞留時間分布が狭く連続操作が可能でメルトシールにより反応部の圧力を高めることができる点から二軸スクリュー型押出機が好ましい。
【００７４】
本発明を二軸スクリュー型押出機を混練機として用い工程（Ａ）と（Ｂ）を連続して行なう場合の押出機を図１にしたがって簡単に説明する。
【００７５】
図１において、１は混練機として用いる二軸スクリュー型押出機であり、モーター２に連結された２本のスクリュー３が内挿されている。含フッ素重合体４はホッパー５から溶融工程（Ｄ）に供給され、加熱溶融されながら分子量調整工程（Ａ）に送られる。分子量調整工程（Ａ）は酸素含有ガス（空気）供給口６近傍から始まり、水供給口７近傍で終わる。この水供給口７近傍からは安定化処理工程（Ｂ）が始まり、排気口８近傍まで続く。排気口８からは脱気工程（Ｃ）が始まり、押出口９まで続く。
【００７６】
本発明における特徴は、分子量調整工程（Ａ）が始まる地点に酸素含有ガス供給口６を設け、工程（Ａ）において酸素の存在下で含フッ素重合体に分子量を調整し得る量のセン断力と温度を供給したのち、水を水供給口７から供給し不安定基を安定化する点にある。したがって、酸素含有ガス供給口６と水供給口７とは含フッ素重合体の分子量を調整し得るのに充分な時間を与える間隔をあけて設けられる。また、図示していないが、工程（Ｂ）の開始部分に酸素含有ガスの供給口を設けてもよい。
【００７７】
分子量調整工程（Ａ）における処理時間すなわち滞留時間（スクリューの回転数に対応）は、混練機（押出機）の構造、空気の供給量、処理（加熱）温度、内部圧力などによって異なるが、好ましくは０．２〜５分間である。
【００７８】
分子量調整工程（Ａ）の温度は、通常２７０〜４５０℃、好ましくは３００〜４００℃である。
【００７９】
酸素含有ガスの供給量は、たとえば空気（酸素含有割合２１容量％）を重合体供給量１ｋｇ／分当たり０．１〜２リットル／分、好ましくは０．２〜１．５リットル／分であるが、この範囲に限定されない。
【００８０】
このように分子量調整工程（Ａ）の制御には多数のファクターが絡んでいるが、実際的には、後述するとおり、安定化処理工程（Ｂ）あるいは脱気工程（Ｃ）の終端部に設けられたオンライン自動溶融粘度測定器１０によって処理後の含フッ素重合体のメルトフローレートを常時監視しておき、目的とするメルトフローレートの範囲内に維持されるように、温度、スクリュー回転数（滞留時間）、酸素供給量の少なくとも１つを制御すればよい。
【００８１】
メルトフローレートの監視は常時行なうが、オンライン自動溶融粘度測定器の能力により、測定に要する時間（５〜１０分間）間隔で監視し測定する場合も、結果的には断続的ではあるが、本発明でいう常時の範囲内である。また、品質管理に支障がない限り、多少時間を空けて行なってもよい。
【００８２】
通常は、酸素の存在により溶融重合体は劣化し分子量が小さくなると考えられているが、本発明のように積極的に酸素含有ガスを単独で供給するときには分子量が増大する。ただ、この傾向は後述する制御方法により制御できる。必要があれば、逆に分子量の小さい重合体に調整することもできる。
【００８３】
工程（Ａ）で分子量が調整（通常は増大）された含フッ素重合体に水供給口７から水が供給され、工程（Ｂ）にて不安定基が安定化される。安定化機構は前述のとおりである。この安定化処理工程（Ｂ）では、水の存在により、工程（Ａ）で増加した分子量が低下する。この分子量の低下分を考慮して、工程（Ａ）での分子量を増大させておくことが望ましい。
【００８４】
供給する水は液状でも気体状（スチーム）でもよいが、混練機内の温度を低下させない点からスチームの形で供給することが好ましい。
【００８５】
安定化処理工程（Ｂ）における処理時間すなわち滞留時間（スクリューの回転数に対応）は、押出機の構造、水の供給量、処理（加熱）温度などによって異なるが、好ましくは０．２〜５分間である。滞留時間が長くなりすぎると分子量が低下する傾向にある。
【００８６】
安定化処理工程（Ｂ）の温度は、通常２７０〜４５０℃、好ましくは３００〜４００℃である。
【００８７】
水の供給量は、たとえば重合体供給量１ｋｇ／分当たり５〜５０ｇ／分、好ましくは１５〜３５ｇ／分であるが、この範囲に限定されない。ただし、水の供給量を増やしていくと分子量が大きくなっていく傾向がある。これは、潜熱により処理温度が低下したり、水蒸気が発生することにより重合体が発泡することによる見掛けの粘度が小さくなり、重合体に加えられるせん断力が小さくなるためと考えられる。
【００８８】
この工程（Ｂ）において酸素含有ガスを供給する場合、供給量は重合体供給量１ｋｇ／分当たり１００リットル／分以下（酸素濃度２１容量％）、好ましくは７５リットル／分以下である。
【００８９】
本発明において、安定化処理工程（Ｂ）ではガス状物質、たとえばフッ化水素、炭酸ガス、分解により発生する少量のモノマーなどが発生することがあるが、これらのガスを安定化処理済みの含フッ素重合体内部から取り出し混練機１の外部に排出するため、絶対圧力が０．１ＭＰａ以下の状態に保持された脱気工程（Ｃ）を安定化処理工程（Ｂ）に引き続き混練機１内に設けることが好ましい。この脱気工程（Ｃ）での絶対圧力は重合体の溶融状態や押出機のスクリューの回転数などの運転条件により異なるが、排気口８に重合体が侵入しない程度の減圧が好ましい。
【００９０】
本発明の方法で得られ混練機から排出された含フッ素重合体は通常ペレットの形をしており、かかるペレットを溶融成形に供しても得られる成形品に気泡や空隙は生じず、着色も生じない。
【００９１】
なお、要すれば混練機から取り出した混練物（ペレット）に前記フッ素化処理を施してもよい。
【００９２】
本発明の改質法は単に不安定基を安定化するだけでなく分子量の調整をも行うため、押出機の運転の制御も重要である。
【００９３】
かかる制御は、混練機の出口部分（安定化処理工程（Ｂ）または脱気工程（Ｃ）の終端部分）の重合体のメルトフローレートを常時測定し、得られるメルトフローレート値に基づいて、
（１）混練機のスクリュー回転数、
（２）酸素を含むガス供給量、
（３）水の供給量、または
（４）混練機の内部温度
の少なくとも１つを自動制御することにより、実施できる。本発明はかかる自動制御法にも関する。
【００９４】
以下、図２に示すブロックダイヤグラムにしたがって、本発明の自動制御法を説明する。
【００９５】
まず、混練機１の出口部分の重合体のメルトフローレートの測定は、オンライン溶融粘度測定装置１０（図１にも示してある）により行なう。得られたメルトフローレート測定値はオンライン自動制御中央処理装置１１に送られ、目的とする所定のメルトフローレート範囲と比較される。その結果、所定のメルトフローレート範囲であれば混練機１の運転条件をそのまま維持する。このオンライン自動制御中央処理装置としては、通常のコンピューターを使用することができる。
【００９６】
メルトフローレート値が所定のメルトフローレート範囲から高い方に外れた場合、スクリュー用モーター１２、酸素含有ガス供給装置１３、水供給装置１４および混練機温度調節装置１５に、つぎの制御命令の少なくとも１つを送る。
【００９７】
（１）モーターの回転数を低くし混練機のスクリュー回転数を下げる。
この制御により、重合体に与えるセン断力を小さくし、重合体分子の切断を少なくする。
（２）酸素含有ガス供給量を増やす。
この制御により、重合体中の不安定基、特に末端不安定基の化学的分解とラジカル発生量を増やし、重合体同士のカップリング（結合）を促進する。
（３）水の供給量を増やす。
この制御により、重合体温度を下げ、また重合体の見掛け粘度を下げて押出機から加えられるせん断力を小さくし、分子量の低下を抑制する。
（４）混練機の内部温度を下げる。
この制御により、重合体中の不安定基、特に末端不安定基の熱分解とラジカル発生量を増やし、重合体同士のカップリング（結合）を促進する。
【００９８】
一方、逆にメルトフローレート値が所定のメルトフローレート範囲から低い方に外れた場合、スクリュー用モーター１２、酸素含有ガス供給装置１３、水供給装置１４および混練機温度調節装置１５に、つぎの制御命令の少なくとも１つを送る。
【００９９】
（１）混練機のスクリュー回転数を上げる。
（２）酸素を含むガス供給量を減らす。
（３）水の供給量を減らす。
（４）混練機の内部温度を上げる。
【０１００】
これらの制御の作用および効果は前記の高い方に外れた場合の逆である。
【０１０１】
（１）ないし（４）の制御は１つでもよく、また２つ以上同時にまたは順次に行なってもよい。特に短時間に制御できるため制御後のメルトフローレートを比較的早く判別できる点から、スクリューの回転数の制御を優先することが好ましい。
【０１０２】
目的とする所定のメルトフローレート範囲は、使用する含フッ素重合体の種類、目的とする分子量、重合体組成などによって、さらには実験的に適宜設定すればよい。
【０１０３】
【実施例】
つぎに本発明を実施例に基づいて説明するが、本発明はかかる実施例のみに限定されるものではない。
【０１０４】
（メルトフローレート：ＭＦＲ）
ＡＳＴＭ Ｄ−２１１６にしたがって、３７２℃、負荷５ｋｇにて測定する。
単位はｇ／１０分である。
【０１０５】
使用したオンライン溶融粘度測定器はＡＳＴＭ Ｄ−２１１６に準じたメルトフローレートの値を表示できるものある。
【０１０６】
（末端基の定量）
米国特許第３，０８５，０８３号、米国特許第４，６７５，３８０号各明細書、特開平４−２０５０７号公報などに記載の赤外分光分析法により、末端基ごとに定量する。評価は、各末端基の個数を炭素原子１０⁶個あたりの個数で行なう。
【０１０７】
実施例１
過硫酸アンモニウム（ＡＰＳ）を重合開始剤としてテトラフルオロエチレン（ＴＦＥ）とヘキサフルオロプロピレン（ＨＦＰ）とパーフルオロ（プロピルビニルエーテル）（ＰＰＶＥ）を８７／１２／１（モル比）で乳化重合して得られたＰＰＶＥ変性ＦＥＰ（３７２℃におけるメルトフローレート：２５ｇ／１０分、カリウム濃度：１５ｐｐｍ）を用いた。
【０１０８】
混練機としては、１５個の混練ブロック（バレル）からなり、軸径４７ｍｍ、Ｌ／Ｄ５２．５の二軸スクリュー型押出機を使用した。このうち、原料供給部に第１バレルを、溶融工程（Ｄ）には第２〜第６バレルを、分子量調整工程（Ａ）には第７〜第９バレルを、安定化処理工程（Ｂ）には第１０〜第１２バレルを、そして脱気工程（Ｃ）には第１３〜第１５バレルを当てた。なお、ホッパーは第１バレルに、酸素含有ガス供給口は第７バレルの先端部分に、水供給口は第１０バレルの先端部分に、排気口は第１３バレルの先端部分に設け、オンライン溶融粘度測定器を第１５バレルに配設した。
【０１０９】
目的とするメルトフローレートを２２．５〜２８．０ｇ／１０分とし、運転条件をつぎのとおりに設定し、前記変性ＦＥＰを溶融押出しした。
原料供給速度：５０ｋｇ／ｈｒ
溶融工程（Ｄ）の温度：３５０℃
空気の供給量：４０リットル／分
分子量調整工程（Ａ）の温度：３００℃
分子量調整工程（Ａ）の内圧：２．５ＭＰａ
水の供給量：１．５ｋｇ／ｈｒ
安定化処理工程（Ｂ）の温度：４１０℃
安定化処理工程（Ｂ）の内圧：２．４ＭＰａ
脱気工程（Ｃ）の温度：３２５℃
脱気工程（Ｃ）の内圧：０．０６ＭＰａ
スクリュー回転数：２００ｒｐｍ
【０１１０】
運転開始３０分後に第１０バレルの水供給口の直前でサンプリングしたＦＥＰのメルトフローレートは２０．０ｇ／１０分と高くなっており、分子量が増大していた。このときのオンライン溶融粘度測定器（第１５バレルに配設されている）でのメルトフローレートは２０．９ｇ／１０分であった。
【０１１１】
そこで、スクリュー回転数を２５０ｒｐｍに上げたところ、メルトフローレートは第１０バレル地点で２３．７ｇ／１０分となり、オンライン溶融粘度測定器では２４．３ｇ／１０分と目標範囲内になった。
【０１１２】
なお、スクリュー回転数２００ｒｐｍおよび２５０ｒｐｍのいずれの運転条件においても、得られたＦＥＰの不安定基の個数はゼロであった。
【０１１３】
この実施例の結果から、押出機の最終端でのメルトフローレートの測定値によりスクリュー回転数を変化させることによって、処理された含フッ素重合体のメルトフローレートを制御できることがわかる。さらに、オンラインメルトフローレート測定器の測定データをフィードバック方式でオンライン処理することにより、運転を中断することなく直ちに分子量の調整を行なうことができることがわかる。
【０１１４】
比較例１
実施例１の変性ＦＥＰを用い、空気と水を第７バレルの供給口から同時に供給した（工程（Ａ）と工程（Ｂ）を区分けしなかった）ほかはつぎに示す条件で押出機を運転した。
原料供給速度：５０ｋｇ／ｈｒ
溶融工程（Ｄ）の温度：３５０℃
空気の供給量：４０リットル／分
分子量調整工程（Ａ）の温度：３５０℃
分子量調整工程（Ａ）の内圧：２．２ＭＰａ
水の供給量：１．５ｋｇ／ｈｒ
安定化処理工程（Ｂ）の温度：３５０℃
安定化処理工程（Ｂ）の内圧：２．２ＭＰａ
脱気工程（Ｃ）の温度：３２５℃
脱気工程（Ｃ）の内圧：０．０６ＭＰａ
スクリュー回転数：２００ｒｐｍ
【０１１５】
その結果、オンライン溶融粘度測定器でのメルトフローレート測定値は２４．３ｇ／１０分であったが、不安定基の個数は炭素数１０⁶個あたり２５個であった。
【０１１６】
そこで、第７〜１２バレルの温度を３７５℃、ついで３９０℃、さらに４２０℃に上げたところ、表１に示すとおり、不安定基は減少していくが、メルトフローレートは順次低下（分子量が小さくなる）した。
【０１１７】
【表１】

【０１１８】
このように空気と水を同時に供給すると分子量調整と安定化処理とを同時に適切に制御することは困難である。
【０１１９】
【発明の効果】
本発明の改質法によれば、迅速にかつ効率的に不安定基を有する溶融加工可能な含フッ素重合体の不安定基を安定化でき、しかも分子量の調整も同時に行なうことができる。
【０１２０】
また、本発明の制御方法によれば、押出機の出口部分のメルトフローレートの測定値の変化をオンライン自動制御処理し、直ちに目的メルトフローレートに戻すことができる。
【図面の簡単な説明】
【図１】本発明の改質法の実施に好適な押出機の概略断面図である。
【図２】本発明の制御方法を説明するためのブロックダイヤグラムである。
【符号の説明】
１ 混練機
２ モーター
３ スクリュー
４ 含フッ素重合体
５ ホッパー
６ 酸素含有ガス供給口
７ 水供給口
８ 排気口
９ 押出口
１０ オンライン溶融粘度測定器
１１ オンライン制御中央処理装置
１２ スクリュー用モーター
１３ 酸素含有ガス供給装置
１４ 水供給装置
１５ 混練機温度調節装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a modification method for stabilizing a melt-processable fluoropolymer having an unstable group and making the molecular weight uniform. More specifically, the present invention relates to a method for modifying a fluorine-containing polymer that adjusts the molecular weight using unstable terminal groups and / or unstable bonds existing in the main chain, and further stabilizes efficiently in a short time. The present invention also relates to an automatic control method suitable for the reforming method.
[0002]
[Prior art]
The melt-processable fluorine-containing polymer is, for example, a copolymer (FEP) of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) or a copolymer of TFE and perfluoro (alkyl vinyl ether) (PAVE) ( PFA) and a copolymer of TFE and ethylene (ETFE) are well known. Among such fluoropolymers that can be melt-processed, there are those in which bubbles and voids are produced in a molded product produced by melt-processing. It is considered that this is caused by a volatile substance generated by the unstable terminal group of the fluoropolymer being decomposed by heat (US Pat. No. 3,085,083).
[0003]
The unstable end groups present in the melt-processable fluoropolymer depend on the type of polymerization method, polymerization initiator, chain transfer agent and the like. For example, when a persulfate (such as ammonium persulfate or potassium persulfate) often used in emulsion polymerization is used as a polymerization initiator, a carboxylic acid end group is generated. Although this carboxylic acid end group depends on the melting conditions, a vinyl end group (—CF═CF₂) And acid fluoride end groups (—COF). These end groups are thermally unstable and produce volatile substances that cause bubbles and voids in the final product.
[0004]
U.S. Pat. No. 3,085,083 describes the stable -CF by treating these unstable end groups in the presence of water and heat.₂In the method described in Japanese Examined Patent Publication No. 46-23245, it is reacted with a fluorinating agent such as fluorine gas, and converted to -CF._ThreeIt is converted into a stable end group.
[0005]
In addition, unstable bonds may occur in the main chain of the fluoropolymer depending on how the repeating units are bonded. For example, in the case of FEP, which is a TFE-HFP copolymer, it is said that the bonds between HFPs are unstable and are broken by mechanical force (shearing force) applied during melt-kneading to produce unstable vinyl end groups. (US Pat. No. 4,675,380).
[0006]
In U.S. Pat. No. 4,675,380, an unstable end group is formed by cutting a HFP-HFP bond by applying a large shearing force by a twin screw extruder during melt kneading. However, this method uses a twin-screw type extruder that can apply a large shear force in a short time. It is not planned to process unstable end groups in a twin screw extruder. On the other hand, since vinyl end groups change to acid fluoride end groups in the presence of oxygen, treatment is performed in an atmosphere substantially free of oxygen from the fluorine-containing polymer and the extruder, and the vinyl end groups are removed and stabilized. Is performed outside the twin screw extruder. In order to exhaust volatile substances generated during melt-kneading in the twin-screw extruder to the outside of the extruder, the inside of the extruder is depressurized (absolute pressure is less than 0.1 MPa). Coloring due to carbon generated by polymerization occurs.
[0007]
In order to eliminate the disadvantages of such a twin screw type extruder, in the method described in the pamphlet of WO 98/09784, a so-called surface renewal type kneader in which the effective volume ratio (effective space in the container / space in the container) is larger than 0.3. And the formula: K = Pv / μ / n²(Where Pv is the required power per unit volume (W / m^Three), Μ is the melt viscosity at 372 ° C. of the polymer (Pa · s), and n is the number of revolutions (rps)). The stabilization process of the unstable group is performed by taking a long time of 10 minutes or more.
[0008]
However, long-term melt-kneading using a surface renewal type kneader solves the problem of coloring, but not only the processing efficiency is unavoidable, but also the vinyl terminal group depolymerization proceeds and the resin progresses. Degradation is likely to occur. In addition, there is a problem that the processing apparatus becomes large and it takes time to replace the residue when the processing resin is switched.
[0009]
Furthermore, WO00 / 26260 pamphlet describes that an unstable group can be stabilized in a short time by actively supplying a gas containing oxygen and water to a twin-screw extrusion kneader. However, nothing is said about the supply sequence of oxygen-containing gas and water and the molecular weight of the polymer obtained.
[0010]
[Problems to be solved by the invention]
However, in the various stabilization methods described above, since the melt-kneading conditions are harsh, the polymer is deteriorated and the molecular weight is reduced.
[0011]
The object of the present invention is to stabilize the unstable group of the melt-processable fluoropolymer in a short time and prevent the molecular weight from being lowered, and further to make the molecular weight uniform to improve the workability, to prevent bubbles and coloring. It is an object of the present invention to provide a method for modifying a fluorine-containing polymer which can easily produce a molded product having no problem, and a control method particularly suitable for the modification method.
[0012]
[Means for Solving the Problems]
That is, the present invention relates to a step (A) of melt-kneading a melt-processable fluorine-containing polymer having an unstable group in the presence of a gas containing oxygen, for example, air, and a fluorine-containing heavy treated with a gas containing oxygen. The present invention relates to a method for modifying a fluoropolymer comprising a step (B) of melt-kneading a coalescence in the presence of oxygen and water.
[0013]
These steps (A) and (B) may be carried out separately, but are preferably carried out continuously in one kneader.
[0014]
When continuously carried out in the kneader, it is preferable to supply a gas containing oxygen upstream in the extrusion direction of the fluoropolymer and to supply water downstream thereof. Further, the gas containing oxygen supplied in the process A is brought into the process B without being removed. This is because substances that can cause coloration are generated even in the process B, and thus the presence of oxygen is necessary to oxidize these substances. Note that a gas containing oxygen may be positively supplied in the process B for the purpose of supplementing the gas containing oxygen supplied in the process A. For the same reason, when the process A and the process B are performed separately, the gas containing oxygen is positively supplied also in the process B.
[0015]
The treatment temperature in these steps (A) and (B) is suitably 270 to 450 ° C. When the step (A) and / or the step (B) is in a pressurized state, the absolute pressure is 0.2 MPa or more, preferably 0.3 MPa or more.
[0016]
The labile group of the fluorinated polymer may be present at the terminal of the polymer chain, or may be an unstable bond part of the main chain.
[0017]
In step (A) and / or step (B), a compound containing an alkali metal, alkaline earth metal, or ammonium salt that promotes stabilization of an unstable terminal group of carboxylic acid type, an alcohol, an amine or a salt thereof, or Preferably ammonia is present. These additives may be mixed in the polymer in advance or may be added in each step.
[0018]
The kneading machine used for melt kneading may be a kneading machine that gives a relatively large shearing force such as a screw type extruder, and a multi-screw type kneading machine, particularly a twin-screw type extruder is preferred.
[0019]
The modification method of the present invention can be applied to any melt-processable fluorine-containing polymer having an unstable group. In particular, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and perfluoro (alkyl vinyl ether) (PAVE). It is effective for stabilizing the unstable group of the copolymer composed of at least two monomers selected from the group consisting of
[0020]
Such a fluoropolymer includes, for example, a copolymer comprising 0.5 to 13% by weight of perfluoro (methyl vinyl ether) (PMVE), 0.05 to 3% by weight of PAVE other than PMVE, and the balance of TFE, or TFE-HFP. And a TFE-HFP copolymer containing an unstable group produced by an emulsion polymerization method.
[0021]
Further, in order to discharge various gaseous substances generated by the treatment in the steps (A) and (B) to the outside of the kneader, a deaeration treatment step (with an absolute pressure of 0.1 MPa or less downstream of the step (B) ( C) may be provided.
[0022]
The present invention also provides a melt flow rate of the polymer at the outlet portion of the kneader when the fluorine-containing polymer having an unstable group is stabilized by melting and kneading with a kneader using an oxygen-containing gas and water. (MFR) is constantly measured and based on the resulting melt flow rate value,
(1) Screw rotation speed of kneader,
(2) supply amount of gas containing oxygen,
(3) Water supply amount, or
(4) Internal temperature of kneader
And a method for controlling the melt flow rate in which at least one of the above is automatically controlled to maintain the melt flow rate of the polymer at the outlet portion within the intended melt flow rate range.
[0023]
Measurement of the melt flow rate of the polymer at the outlet portion is performed by an on-line melt viscosity measuring device, and automatic control is performed by on-line automatic control, so that a stabilized fluoropolymer having a constant melt flow rate is always obtained. It can be provided more easily.
[0024]
For example, when the melt flow rate value of the polymer at the outlet portion is increased,
(1) Decreasing the screw speed of the kneader,
(2) Increasing the supply amount of gas containing oxygen,
(3) Increase water supply, or
(4) Lower the internal temperature of the kneader
At least one of these controls may be performed automatically,
When the melt flow rate value of the polymer at the outlet portion is reduced,
(1) Increase the screw speed of the kneader,
(2) reduce the amount of gas containing oxygen,
(3) reduce water supply, or
(4) Raise the internal temperature of the kneader
It is sufficient to automatically perform at least one of the controls.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
First, the melt-processable fluoropolymer having an unstable group to be modified by the present invention will be described.
[0026]
Known fluorine-containing polymers that can be melt-processed include copolymers obtained by copolymerizing two or more monomers such as TFE, HFP, and PAVE as described above. Specific examples of the copolymer include FEP-based polymers such as TFE-HFP copolymer (FEP) and TFE-HFP-PAVE copolymer; TFE-PAVE copolymer (PFA) and TFE-PMVE-PAVE. PFA polymers such as copolymers (other than PMVE) are included.
[0027]
As PAVE, the formula:
CF₂= CFO (CF₂)_mF
(Wherein m is an integer of 1 to 6) represented by vinyl ether (where m is 1 is PMVE), and the formula:
CF₂= CF (O-CF₂CF (CF_Three))_nOC_ThreeF₇
(Wherein n is an integer of 1 to 4).
[0028]
These melt-processable fluoropolymers have more or less unstable groups. In particular, typical examples of fluorine-containing polymers for which stabilization of unstable groups is desired include FEP polymers, which are also produced by an emulsion polymerization method using a persulfate that causes unstable groups as an initiator. In addition, a fluorine-containing polymer produced by a polymerization method in which the polymer terminal is not saturated with a fluorine atom or a hydrogen atom is also a polymer for which stabilization treatment is strongly demanded. Among them, polymers with few unstable groups can be obtained depending on the polymerization method and initiator used, or by using alkanes such as methane as chain transfer agents. However, these polymers are also made more stable by the modification treatment of the present invention.
[0029]
For the treatment only for stabilizing the unstable group of the fluoropolymer, it is sufficient to positively add a gas containing oxygen and water as described in the pamphlet of WO00 / 26260. . The mechanism of stabilization of the labile group is described in detail in WO 00/26260 pamphlet.
[0030]
The object of the present invention is not only to stabilize unstable groups but also to adjust the molecular weight so as to obtain a polymer having a molecular weight as uniform as possible. For this reason, in the present invention, the fluoropolymer is first melt-kneaded in the presence of a gas containing oxygen, for example, air (step (A)). This oxygen-containing gas is not sufficient in terms of the amount of oxygen present in the raw fluoropolymer or the amount of oxygen in the atmosphere originally present in the surroundings, and is actively injected. An important point is that water does not coexist in the treatment step (A) with the oxygen-containing gas.
[0031]
In the processing step (A), although estimated, it is considered that the following reaction occurs.
[0032]
First, by melt-kneading, a polymer with an excessively large molecular weight is cut by heat and shearing force during kneading, resulting in a decrease in molecular weight. On the other hand, the presence of oxygen causes coupling between polymer ends to increase the molecular weight. Reaction occurs. At this time, if the kneading ability is too strong, the average molecular weight tends to decrease, and if the kneading ability is weak, the average molecular weight tends to increase.
[0033]
For this step (A), it is preferable to use, for example, a screw type extruder (kneading machine), particularly a twin screw type extruder, to which an appropriate shear force is applied.
[0034]
Oxygen (O₂) Is present depending on the temperature at the time of the reaction, the processing time in the processing step (A), the type of the extruder, the type and amount of the unstable terminal group, etc., but the unstable group (for example, —CF═CF₂) And at least the same molar amount and the amount exhausted without contributing to diffusion loss or reaction, it is preferable to use an excess amount, for example, a 10-fold molar amount or more, particularly a 50-500 molar amount.
[0035]
The oxygen-containing gas may be supplied by diluting the oxygen gas to an appropriate concentration (for example, 10 to 30% by volume) with an inert gas such as nitrogen gas or argon gas, but it is economical to use air as it is. To preferred.
[0036]
Oxygen may be always present in the steps (A) and (B), may be contained before the fluoropolymer is added to the step (A), or may be supplied in the step (A). Of course, you may use both together.
[0037]
The treatment temperature varies depending on the fluoropolymer to be treated, the target molecular weight, the polymer composition, and the like, but is usually selected within the range of 270 to 450 ° C.
[0038]
Further, the shearing force to be applied varies depending on the type of the melt-kneading apparatus to be used, the type of the fluoropolymer to be treated, the target molecular weight, the polymer composition and the like. For example, when using a screw type extruder, it is preferable to select from the range of 200 to 6000 / sec.
[0039]
The pressure in the processing step (A) is usually a pressurized state. Preferably, it is performed at 0.2 MPa or more, further 0.3 MPa or more.
[0040]
In this way, the molecular weight of the fluoropolymer is adjusted using oxygen, shearing force and heat. The adjustment of the molecular weight can be confirmed by the fact that the melt flow rate at the end of the step (A) is stable.
[0041]
Since the fluorinated polymer cannot stabilize the unstable group only by the presence of oxygen, in the present invention, it is then melt-kneaded in the presence of oxygen while actively introducing water to stabilize the unstable group and coloring. The material is removed by oxidation (step (B)). However, when water is introduced at the same time or close to the oxygen-containing gas in the step (A), the unstable group is stabilized in a state where the molecular weight is not sufficiently adjusted, and the molecular weight can no longer be adjusted.
[0042]
In this step (B), the fluoropolymer is sent with the unstable group partially changed in step (A).
[0043]
Specifically, it is a stabilization reaction described in WO00 / 26260 pamphlet.
[0044]
That is, as described above, the unstable group includes a carboxylic acid group (—COOH) caused by a polymerization initiator, a chain transfer agent, and the like, and a vinyl group (—CF═CF₂) And acid fluoride groups (—COF 3) derived from this vinyl group are known, and these unstable groups are usually located at the end of the polymer chain (main chain or side chain). In addition, depending on the type of polymer and the production method, unstable bonds may occur in the bonding portion in the main chain of the polymer. For example, in a TFE-HFP polymer, TFE and HFP are randomly polymerized, but HFP-HFP bonds may be repeated in the polymer chain, and this HFP-HFP bond is mechanical force (shearing force). It is expected that an unstable vinyl group and an acid fluoride group are generated.
[0045]
The reaction for stabilizing these unstable groups is considered as follows.
[0046]

[0047]
This reaction is carried out with heating, usually 270 to 450 ° C, preferably 300 to 400 ° C.
[0048]
In order to promote this reaction, it is effective to add a reaction accelerator such as a compound containing an alkali metal, an alkaline earth metal or an ammonium salt, or ammonia, alcohols, amine or a salt thereof. Specifically, hydroxides such as potassium hydroxide and sodium hydroxide, carbonates such as potassium carbonate and calcium carbonate, sulfates such as potassium sulfate, nitrates such as potassium nitrate, ammonium salts such as ammonium hydroxide, ammonia, Examples thereof include alcohols such as methanol and ethanol, amines or salts thereof. -CF for alkali metal or alkaline earth metal compounds₂In the case of ammonium salt, ammonia, or amine, the acid amide end group (-CONH₂(Partly at high temperatures -CF₂In the case of alcohol, it becomes an alkyl ester end group (—COOR).
[0049]
The reaction accelerator may be added to the fluoropolymer in advance, or may be added in the step (A), but it is more uniform in the polymer when added together with water in the step (B). This is preferable because it can be dispersed. The amount added depends on the type of fluoropolymer to be treated, but in the case of alkali metal and alkaline earth metal compounds, it is converted to the number of atoms of alkali metal and alkaline earth metal. In the case of an ammonium salt compound, in terms of the number, the number of unstable groups (carboxylic acid end groups) in the fluoropolymer is not more than 10%, preferably 0.1 to 10% in terms of the number of ammonium salts. Particularly preferably, the content is 0.2 to 5%. If the amount added is too large, the stabilization rate of the unstable end groups increases, but the coloration of the polymer cannot be completely eliminated, and the polymer itself tends to deteriorate and the melt flow rate tends to decrease.
[0050]
In addition, as a method for stabilizing the carboxylic acid end group, there is a fluorination treatment with fluorine gas or the like, but the fluorination treatment is not performed in the step (B) in the present invention. Of course, after the stabilization treatment step of the present invention, if necessary, further fluorination treatment may be performed.
[0051]
Vinyl end group
It is presumed to be caused by the application of heat or shearing force from the carboxylic acid end group and the unstable main chain bond.
[0052]

[0053]
This vinyl end group is fluorinated and converted to a trifluoromethyl group, or converted to a carboxylic acid group via an acid fluoride according to the following reaction formula.
[0054]
-CF = CF₂  + O₂      → -COF + COF₂    (IV)
-COF + H₂O → -COOH + HF (V)
[0055]
The resulting carboxylic acid end groups are treated as described above. However, in the above-mentioned US Pat. No. 4,675,380, oxygen is terminated at a vinyl end group without substantially existing oxygen so as not to change into acid fluoride which complicates processing.
[0056]
However, when the vinyl end group is heated, it undergoes depolymerization as shown in the following formula to generate carbon, so in US Pat. No. 4,675,380, a dark-colored melt-kneaded product is obtained.
[0057]

[0058]
Acid fluoride end group
According to the formula (V), the carboxylic acid group is once returned to the stabilization treatment.
[0059]
As described above, in many cases, the stabilization treatment of the fluorine-containing polymer finally results in a rate-limiting reaction that stabilizes the carboxylic acid end groups with water and heat, and the vinyl end groups are depolymerized as much as possible. No way is taken. For example, in the method described in the pamphlet of WO98 / 09784, the stabilization reaction of the carboxylic acid end group is prioritized, and the vinyl end group is generated mildly so that the carbon causing the coloring is not generated by depolymerization, that is, Stabilization is carried out under almost atmospheric pressure (both in Example 1 and 2 described in WO 98/09784, the absolute pressure is about 0.1 MPa), and further kneading is performed at a moderate power coefficient K of less than 8000, preferably 7000 or less. Since the process is performed under various conditions, the time required for the stabilization process is increased.
[0060]
In the present invention, on the contrary, by actively allowing oxygen and then water to be present in the reaction system, the vinyl end group is rapidly converted to acid fluoride (reaction (IV)) to reduce depolymerization and suppress carbon generation. In addition to preventing coloration, the stabilization reaction (I) of the carboxylic acid end group is promoted by bringing it into a pressurized state. For that, the presence of water is essential.
[0061]
Water is used in reactions (I) that stabilize carboxylic acid end groups and reactions (V) that convert acid fluoride to carboxylic acid.
[0062]
The amount of water added needs to be an excess amount than the theoretical amount necessary for the reaction, but the amount depends largely on the pressure to be added and the state in the extruder, and is determined while confirming with the actual device.
[0063]
As described above, the reaction (I) for stabilizing the carboxylic acid end group is greatly promoted by adding a reaction accelerator such as an alkali metal compound, so water is added in the form of an aqueous solution in which the accelerator is dissolved. It is preferable. What is necessary is just to select the density | concentration of aqueous solution suitably on the basis of the required amount of the said promoter.
[0064]
This stabilization treatment step (B) is preferably carried out using, for example, a screw type extruder, particularly a twin screw type extruder, which can increase the reaction pressure in the kneading machine, as a kneading machine.
[0065]
The amount of water to be supplied can be stabilized theoretically if the number of molecules is the same as the number of unstable terminal groups generated in, for example, a kneader (extruder), but in reality, the number of excessive, particularly unstable terminal groups is excessive. It is preferable to supply water having a molecular number of 10 times or more. The upper limit is not particularly limited.
[0066]
As described above, the polymer supplied to the kneader contains moisture together with air similar to the atmosphere unless special measures are taken. However, the present invention can be achieved with this amount of oxygen and moisture. The molecular weight adjusting effect and stabilizing effect are not achieved. The reason is probably that low molecular weight substances and various additives in the polymer (for example, polymerization initiators) are decomposed during the process to generate gas, thereby reducing the partial pressure of oxygen and moisture in the process. This is considered to be because the contact between the polymer and oxygen or moisture becomes insufficient.
[0067]
The pressure in the step (B) is preferably a pressurized state in which the absolute pressure is 0.2 MPa or more, preferably 0.3 MPa or more. By pressurizing, for example, intrusion of supplied water is promoted, and a rapid stabilization process becomes possible. When a kneader is used, the pressure can be measured with a pressure gauge attached to the kneader. The upper limit varies depending on the state of the melt seal part and the type of the extruder, but is 10 MPa or less, preferably 5 MPa or less.
[0068]
In addition, the presence of oxygen is indispensable for the kneading in this step (B) as described above. That is, in step (B), a substance causing coloring is generated during melt-kneading, so oxygen is required to oxidize and remove the substance. The oxygen present in the step (B) does not need to be positively added when a relatively large amount is supplied in the step (A) in the continuous method, but is added as appropriate if coloring occurs. In the case where the step (A) and the step (B) are performed separately, the amount of oxygen introduced in the step (A) is small, so it is desirable to actively supply a gas containing oxygen.
[0069]
The pressurization in the steps (A) and (B) is performed, for example, by press-fitting oxygen-containing gas and / or water, which will be described later, or by heating oxygen-containing gas and / or water and supplying it under its own pressure. Can be done.
[0070]
By melt-kneading the fluoropolymer treated in the step (A) under the above conditions, the unstable group can be stabilized in a short time and efficiently regardless of the unstable bond in the terminal group and main chain. In addition, the generation of carbon that causes coloring can also be suppressed.
[0071]
In the present invention, the molecular weight adjustment step (A) and the stabilization treatment step (B) may be performed by separate apparatuses (extruder or kneader), or continuously by one kneader (extruder). You may do it.
[0072]
When using another kneader, it is advantageous in that the conditions of steps (A) and (B) can be set and changed independently. On the other hand, using a single kneader is advantageous in terms of cost.
[0073]
Examples of the kneader that can be used when the present invention is continuously carried out include a multi-screw kneader, such as a twin screw extruder, a kneader with an extremely small effective volume ratio, and the like. Among these, a twin screw type extruder is preferred because the residence time distribution is narrow and continuous operation is possible and the pressure in the reaction section can be increased by melt sealing.
[0074]
An extruder in the case where the present invention is used to continuously perform steps (A) and (B) using a twin screw extruder as a kneader will be briefly described with reference to FIG.
[0075]
In FIG. 1, 1 is a twin screw type extruder used as a kneading machine, and two screws 3 connected to a motor 2 are inserted therein. The fluoropolymer 4 is supplied from the hopper 5 to the melting step (D) and sent to the molecular weight adjusting step (A) while being heated and melted. The molecular weight adjustment step (A) starts near the oxygen-containing gas (air) supply port 6 and ends near the water supply port 7. The stabilization process (B) starts from the vicinity of the water supply port 7 and continues to the vicinity of the exhaust port 8. A degassing step (C) starts from the exhaust port 8 and continues to the extrusion port 9.
[0076]
A feature of the present invention is that an oxygen-containing gas supply port 6 is provided at a point where the molecular weight adjusting step (A) starts, and an amount of shearing force that can adjust the molecular weight of the fluoropolymer in the presence of oxygen in the step (A). After the temperature is supplied, water is supplied from the water supply port 7 to stabilize unstable groups. Therefore, the oxygen-containing gas supply port 6 and the water supply port 7 are provided with an interval that gives a sufficient time to adjust the molecular weight of the fluoropolymer. Although not shown, an oxygen-containing gas supply port may be provided at the start of the step (B).
[0077]
The treatment time in the molecular weight adjustment step (A), that is, the residence time (corresponding to the number of rotations of the screw) varies depending on the structure of the kneader (extruder), the supply amount of air, the treatment (heating) temperature, the internal pressure, etc. Is 0.2 to 5 minutes.
[0078]
The temperature in the molecular weight adjusting step (A) is usually 270 to 450 ° C, preferably 300 to 400 ° C.
[0079]
The supply amount of the oxygen-containing gas is, for example, 0.1 to 2 liters / minute, preferably 0.2 to 1.5 liters / minute of air (21% by volume of oxygen content) per 1 kg / minute of polymer supply amount. However, it is not limited to this range.
[0080]
As described above, a number of factors are involved in the control of the molecular weight adjustment step (A). In practice, however, as described later, it is provided at the end of the stabilization treatment step (B) or the deaeration step (C). The melt flow rate of the fluorinated polymer after treatment is constantly monitored by the online automatic melt viscosity measuring device 10 and the temperature, screw rotation speed ( Residence time) and at least one of oxygen supply amount may be controlled.
[0081]
Although the melt flow rate is constantly monitored, the on-line automatic melt viscosity measuring instrument is capable of monitoring and measuring at intervals required for the measurement (5 to 10 minutes) due to the ability of the on-line automatic melt viscosity measuring instrument. It is within the normal range in the invention. Moreover, as long as there is no problem in quality control, it may be performed after some time.
[0082]
Usually, it is considered that the polymer melt deteriorates due to the presence of oxygen and the molecular weight decreases, but the molecular weight increases when the oxygen-containing gas is positively supplied alone as in the present invention. However, this tendency can be controlled by a control method described later. If necessary, it can be adjusted to a polymer having a low molecular weight.
[0083]
Water is supplied from the water supply port 7 to the fluoropolymer whose molecular weight has been adjusted (usually increased) in step (A), and unstable groups are stabilized in step (B). The stabilization mechanism is as described above. In this stabilization treatment step (B), the molecular weight increased in step (A) decreases due to the presence of water. It is desirable to increase the molecular weight in the step (A) in consideration of the decrease in the molecular weight.
[0084]
The supplied water may be liquid or gaseous (steam), but is preferably supplied in the form of steam from the viewpoint of not lowering the temperature in the kneader.
[0085]
The treatment time in the stabilization treatment step (B), that is, the residence time (corresponding to the rotation speed of the screw) varies depending on the structure of the extruder, the amount of water supplied, the treatment (heating) temperature, etc., but preferably 0.2 to 5 For minutes. If the residence time is too long, the molecular weight tends to decrease.
[0086]
The temperature in the stabilization treatment step (B) is usually 270 to 450 ° C, preferably 300 to 400 ° C.
[0087]
The amount of water supplied is, for example, 5 to 50 g / min, preferably 15 to 35 g / min per 1 kg / min of polymer supply, but is not limited to this range. However, the molecular weight tends to increase with increasing water supply. This is presumably because the treatment temperature is lowered by latent heat or the apparent viscosity due to foaming of the polymer due to the generation of water vapor is reduced, and the shearing force applied to the polymer is reduced.
[0088]
When supplying the oxygen-containing gas in this step (B), the supply amount is 100 liter / minute or less (oxygen concentration 21 vol%) per 1 kg / minute of the polymer supply amount, preferably 75 liter / minute or less.
[0089]
In the present invention, in the stabilization treatment step (B), gaseous substances such as hydrogen fluoride, carbon dioxide gas, and a small amount of monomer generated by decomposition may be generated. The degassing step (C) in which the absolute pressure is maintained at 0.1 MPa or less is taken into the kneader 1 following the stabilization treatment step (B) in order to take out from the fluoropolymer and discharge to the outside of the kneader 1. It is preferable to provide it. The absolute pressure in the degassing step (C) varies depending on the operating conditions such as the melted state of the polymer and the number of rotations of the screw of the extruder, but is preferably reduced so that the polymer does not enter the exhaust port 8.
[0090]
The fluoropolymer obtained by the method of the present invention and discharged from the kneader is usually in the form of pellets, and no bubbles or voids are produced in the molded product obtained by subjecting such pellets to melt molding. Does not occur.
[0091]
If necessary, the fluorination treatment may be performed on the kneaded product (pellet) taken out from the kneader.
[0092]
Since the reforming method of the present invention not only stabilizes unstable groups but also adjusts the molecular weight, control of the operation of the extruder is also important.
[0093]
Such control is performed by constantly measuring the melt flow rate of the polymer at the outlet portion of the kneader (the end portion of the stabilization treatment step (B) or the degassing step (C)), and based on the obtained melt flow rate value.
(1) Screw rotation speed of kneader,
(2) supply amount of gas containing oxygen,
(3) Water supply amount, or
(4) Internal temperature of kneader
This can be implemented by automatically controlling at least one of the above. The invention also relates to such an automatic control method.
[0094]
Hereinafter, the automatic control method of the present invention will be described with reference to the block diagram shown in FIG.
[0095]
First, the measurement of the melt flow rate of the polymer at the outlet portion of the kneader 1 is performed by an on-line melt viscosity measuring apparatus 10 (also shown in FIG. 1). The obtained melt flow rate measurement value is sent to the on-line automatic control central processing unit 11 and compared with a predetermined melt flow rate range of interest. As a result, the operating conditions of the kneader 1 are maintained as they are within a predetermined melt flow rate range. A normal computer can be used as the online automatic control central processing unit.
[0096]
When the melt flow rate value deviates from a predetermined melt flow rate range, the screw motor 12, the oxygen-containing gas supply device 13, the water supply device 14 and the kneading machine temperature control device 15 are informed of at least the following control command. Send one.
[0097]
(1) Lower the number of revolutions of the motor and reduce the number of revolutions of the screw of the kneader.
By this control, the shearing force applied to the polymer is reduced, and the polymer molecules are cut less.
(2) Increase the supply amount of oxygen-containing gas.
This control increases the chemical decomposition and radical generation amount of unstable groups in the polymer, particularly terminal unstable groups, and promotes coupling (bonding) between polymers.
(3) Increase water supply.
By this control, the polymer temperature is lowered, the apparent viscosity of the polymer is lowered, the shearing force applied from the extruder is reduced, and the decrease in molecular weight is suppressed.
(4) Lower the internal temperature of the kneader.
This control increases the thermal decomposition and radical generation amount of unstable groups in the polymer, particularly terminal unstable groups, and promotes coupling (bonding) between polymers.
[0098]
On the other hand, if the melt flow rate value deviates from the predetermined melt flow rate range, the screw motor 12, the oxygen-containing gas supply device 13, the water supply device 14 and the kneader temperature control device 15 are Send at least one of the control instructions.
[0099]
(1) Increase the screw speed of the kneader.
(2) Reduce the amount of gas containing oxygen.
(3) Reduce water supply.
(4) Raise the internal temperature of the kneader.
[0100]
The actions and effects of these controls are the reverse of the above-mentioned cases where they deviate from the higher one.
[0101]
The control of (1) to (4) may be one, or two or more may be performed simultaneously or sequentially. In particular, since the melt flow rate after control can be determined relatively quickly because it can be controlled in a short time, priority is given to control of the rotational speed of the screw.
[0102]
The target predetermined melt flow rate range may be appropriately set experimentally depending on the type of the fluoropolymer used, the target molecular weight, the polymer composition, and the like.
[0103]
【Example】
Next, the present invention will be described based on examples, but the present invention is not limited to such examples.
[0104]
(Melt flow rate: MFR)
Measured according to ASTM D-2116 at 372 ° C. and a load of 5 kg.
The unit is g / 10 minutes.
[0105]
The on-line melt viscosity measuring instrument used can display the value of the melt flow rate according to ASTM D-2116.
[0106]
(Quantification of end groups)
Each terminal group is quantified by infrared spectroscopic analysis described in US Pat. No. 3,085,083, US Pat. No. 4,675,380, JP-A-4-20507, and the like. The evaluation is based on the number of each end group being 10 carbon atoms.⁶Do this in pieces per piece.
[0107]
Example 1
Obtained by emulsion polymerization of tetrafluoroethylene (TFE), hexafluoropropylene (HFP) and perfluoro (propyl vinyl ether) (PPVE) at 87/12/1 (molar ratio) using ammonium persulfate (APS) as a polymerization initiator. PPVE-modified FEP (melt flow rate at 372 ° C .: 25 g / 10 min, potassium concentration: 15 ppm) was used.
[0108]
As a kneading machine, a twin screw type extruder having 15 kneading blocks (barrels) and having a shaft diameter of 47 mm and L / D 52.5 was used. Of these, the first barrel is in the raw material supply section, the second to sixth barrels are in the melting step (D), the seventh to ninth barrels are in the molecular weight adjustment step (A), and the stabilization treatment step (B). The 10th to 12th barrels were applied, and the 13th to 15th barrels were applied to the degassing step (C). The hopper is provided at the first barrel, the oxygen-containing gas supply port is provided at the tip of the seventh barrel, the water supply port is provided at the tip of the tenth barrel, and the exhaust port is provided at the tip of the thirteenth barrel. A measuring instrument was placed in the 15th barrel.
[0109]
The target melt flow rate was 22.5 to 28.0 g / 10 min, the operating conditions were set as follows, and the modified FEP was melt extruded.
Raw material supply rate: 50 kg / hr
Melting step (D) temperature: 350 ° C.
Air supply rate: 40 liters / minute
Temperature of molecular weight adjustment step (A): 300 ° C
Internal pressure in the molecular weight adjustment step (A): 2.5 MPa
Water supply rate: 1.5 kg / hr
Temperature of stabilization treatment step (B): 410 ° C
Internal pressure in stabilization process (B): 2.4 MPa
Temperature of degassing step (C): 325 ° C
Internal pressure in degassing step (C): 0.06 MPa
Screw rotation speed: 200rpm
[0110]
The melt flow rate of FEP sampled immediately before the water supply port of the 10th barrel 30 minutes after the start of operation was as high as 20.0 g / 10 minutes, and the molecular weight was increased. At this time, the melt flow rate in the on-line melt viscosity measuring device (disposed in the 15th barrel) was 20.9 g / 10 min.
[0111]
Therefore, when the screw rotation speed was increased to 250 rpm, the melt flow rate was 23.7 g / 10 minutes at the 10th barrel point, and the on-line melt viscosity measuring device was within the target range of 24.3 g / 10 minutes.
[0112]
Note that the number of unstable groups in the obtained FEP was zero under both operating conditions of screw rotation speeds of 200 rpm and 250 rpm.
[0113]
From the results of this example, it can be seen that the melt flow rate of the treated fluoropolymer can be controlled by changing the screw rotation speed according to the measured value of the melt flow rate at the final end of the extruder. Furthermore, it is understood that the molecular weight can be adjusted immediately without interrupting the operation by processing the measurement data of the online melt flow rate measuring device online by the feedback method.
[0114]
Comparative Example 1
Using the modified FEP of Example 1, the extruder was operated under the following conditions except that air and water were simultaneously supplied from the supply port of the seventh barrel (step (A) and step (B) were not separated). .
Raw material supply rate: 50 kg / hr
Melting step (D) temperature: 350 ° C.
Air supply rate: 40 liters / minute
Temperature of molecular weight adjustment step (A): 350 ° C
Internal pressure in the molecular weight adjustment step (A): 2.2 MPa
Water supply rate: 1.5 kg / hr
Stabilization process step (B) temperature: 350 ° C.
Internal pressure in stabilization process (B): 2.2 MPa
Temperature of degassing step (C): 325 ° C
Internal pressure in degassing step (C): 0.06 MPa
Screw rotation speed: 200rpm
[0115]
As a result, the melt flow rate measured with an on-line melt viscometer was 24.3 g / 10 min, but the number of unstable groups was 10 carbon atoms.⁶There were 25 pieces per piece.
[0116]
Therefore, when the temperature of the seventh to twelfth barrels was increased to 375 ° C., then 390 ° C., and further to 420 ° C., as shown in Table 1, the unstable groups decreased, but the melt flow rate decreased gradually (molecular weight decreased). It became small).
[0117]
[Table 1]

[0118]
Thus, when air and water are supplied simultaneously, it is difficult to appropriately control the molecular weight adjustment and the stabilization treatment at the same time.
[0119]
【The invention's effect】
According to the modification method of the present invention, the unstable group of the melt-processable fluoropolymer having an unstable group can be stabilized quickly and efficiently, and the molecular weight can be adjusted simultaneously.
[0120]
Further, according to the control method of the present invention, it is possible to perform online automatic control processing for the change in the measured value of the melt flow rate at the exit portion of the extruder and immediately return it to the target melt flow rate.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an extruder suitable for carrying out the reforming method of the present invention.
FIG. 2 is a block diagram for explaining a control method of the present invention.
[Explanation of symbols]
1 Kneading machine
2 Motor
3 Screw
4 Fluoropolymer
5 Hopper
6 Oxygen-containing gas supply port
7 Water supply port
8 Exhaust vent
9 Extrusion port
10 Online melt viscosity meter
11 Online control central processing unit
12 Screw motor
13 Oxygen-containing gas supply device
14 Water supply device
15 Kneader temperature control device

Claims (18)

The melt-processable fluoropolymer having unstable end groups to generate a thermally unstable and volatile substances non-presence of water, and melt-kneaded under the supply of the inert gas or air containing oxygen molecular weight Molecular weight adjusting step (A) for homogenizing , and stabilizing treatment step for stabilizing the unstable terminal group by melt-kneading the fluoropolymer obtained in the step (A) in the presence of oxygen and water A method for modifying a fluoropolymer comprising (B).   The reforming method according to claim 1, wherein the steps (A) and (B) are continuously carried out in one kneader.   The reforming method according to claim 2, wherein in the kneader, a gas containing oxygen is supplied upstream of the fluoropolymer in the extrusion direction and water is supplied downstream thereof.   The reforming method according to any one of claims 1 to 3, wherein the melt kneading in the steps (A) and (B) is performed at 270 to 450 ° C.   The reforming method according to claim 1, wherein the kneader is a screw type extruder.   The reforming method according to claim 5, wherein the screw type extruder is a twin screw type extruder.   The reforming method according to claim 1, wherein the gas containing oxygen is air.   In the step (A) and / or the step (B), a compound containing an alkali metal, an alkaline earth metal or an ammonium salt, an alcohol, an amine or a salt thereof, or ammonia is present in any one of claims 1 to 7. The described modification method. The reforming method according to any one of claims 1 to 8 , wherein an absolute pressure in the step (A) and / or the step (B) is 0.2 MPa or more. Said fluoropolymer is tetrafluoroethylene, according to any one of claims 1 to 9, which is a copolymer comprising at least two monomers selected from the group consisting of hexafluoropropylene and perfluoro (alkyl vinyl ether) Reforming method. The fluoropolymer is composed of 0.5 to 13% by weight of perfluoro (methyl vinyl ether), 0.05 to 3% by weight of perfluoro (alkyl vinyl ether) other than perfluoro (methyl vinyl ether) and the remainder of tetrafluoroethylene. The modification method according to claim 10, which is a copolymer. The modification method according to claim 10 , wherein the fluoropolymer is a copolymer containing tetrafluoroethylene and hexafluoropropylene. The modification method according to any one of claims 10 to 12 , wherein the fluorine-containing copolymer is a copolymer containing an unstable terminal group produced by an emulsion polymerization method. The reforming method according to any one of claims 2 to 13 , wherein the kneader includes a degassing treatment step (C) having an absolute pressure of 0.1 MPa or less downstream of the step (B). Homogenizing the molecular weight of the fluoropolymer non presence of water, and melt-kneaded under the supply of the inert gas or air containing oxygen with unstable end groups to generate thermally unstable and volatile substances the fluoropolymer having the unstable terminal groups obtained by melt-kneaded by a kneader at a molecular weight adjusting step (a), the unstable terminal groups by melt-kneading in the presence of gas and water containing oxygen In the stabilization treatment step (B) for stabilizing the melt, the melt flow rate of the polymer at the outlet portion of the kneader is constantly measured when the mixture is stabilized by the kneader, and based on the obtained melt flow rate value. (1) the screw rotation speed of the kneader in step (A) and / or step (B),
(2) supply amount of gas containing oxygen,
(3) Melt flow rate in which at least one of the water supply amount or (4) the internal temperature of the kneader is automatically controlled to maintain the melt flow rate of the polymer at the outlet portion within the intended melt flow rate range. Control method. The control method according to claim 15, wherein the melt flow rate of the polymer at the outlet portion is measured by an on-line melt viscosity measuring device, and the automatic control is performed by on-line automatic control. When the melt flow rate value of the polymer at the outlet portion increases,
(1) Decreasing the screw speed of the kneader,
(2) Increasing the supply amount of gas containing oxygen,
The control method according to claim 15 or 16 , wherein at least one of (3) increasing the supply amount of water or (4) lowering the internal temperature of the kneader is automatically performed. When the melt flow rate value of the polymer at the outlet portion is reduced,
(1) Increase the screw speed of the kneader,
(2) reduce the amount of gas containing oxygen,
The control method according to claim 15 or 16 , wherein at least one of (3) reducing the amount of water supplied or (4) increasing the internal temperature of the kneader is automatically performed.

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