JP3552685B2 - Tetrafluoroethylene polymer with excellent strength - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、強度に優れたテトラフルオロエチレン重合体（以下、ＰＴＦＥという）に関する。詳しくは、ペースト押出成形後の延伸操作に好適に使用できる強度に優れたＰＴＦＥに関する。
【０００２】
【従来の技術】
従来、ＰＴＦＥは、テトラフルオロエチレン（以下、ＴＦＥという）を単独で重合することにより、または必要に応じて改質モノマーと共に重合することにより得られ、種々の用途に使用されている。
ＰＴＦＥは、水性分散重合により製造することができ、重合体粒子が分散した水性分散液の状態で得ることもできるし、水性分散重合液を凝固、乾燥させてファインパウダーとして得ることもできる。
従来のＰＴＦＥファインパウダーは、高い溶融粘度を有しており、溶融温度では容易に流動しないため、非溶融二次加工性を有する。そのため、ＰＴＦＥファインパウダーは、一般的には、ＰＴＦＥファインパウダーを潤滑剤とブレンドし、潤滑化ＰＴＦＥを押出し法により造形し、次いで潤滑剤を除去して得られる押出し物を、通常はＰＴＦＥの融点より高い温度で融合（燒結）させて、最終製品形状にするペースト押出し成形が行われている。
【０００３】
一方、ＰＴＦＥファインパウダーから得られる重要な他の製品としては、衣服、テント、分離膜等の製品用の通気性布材料が挙げられる。これらの製品は、ＰＴＦＥファインパウダーをペースト押出し成形して得られる押出し物を、未燒結状態において急速に延伸させ、水蒸気は透過できるが、凝縮水は透過できない性質を付与することにより得ることができる。
米国特許第４，６５４，４０６号明細書および米国特許４，５７６，８６９号明細書には、延伸性ＰＴＦＥファインパウダーの技術を改善し、１７質量％の潤滑剤を添加して得られた押出し物を、１０％／秒〜１００％／秒の速度で少なくとも１０００％延伸することにより、少なくとも７５％の延伸均一性が達成されることが記載されている。
しかしながら、ＰＴＦＥを延伸して得た延伸製品に対する要求物性は年々高くなっており、この改良ＰＴＦＥから得た延伸製品でも、強度が充分でないという問題点を有している。
【０００４】
【発明が解決しようとする課題】
本発明は、上記従来技術の状況に鑑みてなされたものであり、延伸性、フィブリル化性および非溶融二次加工性を有するＰＴＦＥであって、破断強度が高く、標準比重が小さいＰＴＦＥを提供することを目的とする。
【０００５】
【課題を解決するための手段】
本発明は、延伸性、フィブリル化性および非溶融二次加工性を有するＰＴＦＥであって、該重合体が２．１６０以下の標準比重、３２．０Ｎ（３．２６ｋｇｆ）〜４９．０Ｎ（５．０ｋｇｆ）の破断強度を有することを特徴とするＰＴＦＥを提供する。
ここで、標準比重とは、ＪＩＳ Ｋ６９３５−２に従って測定した値をいう。
また、本発明は、上記ＰＴＦＥにおいて、標準比重が２．１５７以下であるＰＴＦＥを提供する。
また、本発明は、上記ＰＴＦＥにおいて、応力緩和時間が、少なくとも６５０秒であるＰＴＦＥを提供する。
【０００６】
また、本発明は、上記ＰＴＦＥにおいて、破断強度が、３４．３Ｎ（３．５ｋｇｆ）〜４９．０Ｎ（５．０ｋｇｆ）であるＰＴＦＥを提供する。
また、本発明は、上記ＰＴＦＥにおいて、押出し圧力が、９．８ＭＰａ（１００ｋｇｆ／ｃｍ２）〜１９．６ＭＰａ（２００ｋｇｆ／ｃｍ２）であるＰＴＦＥを提供する。
また、本発明は、上記ＰＴＦＥにおいて、ＰＴＦＥがファインパウダーであるＰＴＦＥを提供する。
また、本発明は、上記ＰＴＦＥにおいて、ＰＴＦＥが水性分散液の分散固体成分であるＰＴＦＥを提供する。
さらに、本発明は、 上記の特性を有するＰＴＦＥからなる多孔体およびその物品を提供する。
【０００７】
【発明の実施の形態】
本発明のＰＴＦＥは、ＴＦＥの単独重合体であってもよいし、ＴＦＥ以外のエチレン性不飽和基を有する含フッ素モノマーなどの改質モノマーとの共重合体であってもよい。エチレン性不飽和基を有する含フッ素モノマーとしては、例えば、ヘキサフルオロプロピレン、パーフルオロブテン−１、パーフルオロへキセン−１、パーフルオロノネン−１、パーフルオロ（メチルビニルエーテル）、パーフルオロ（エチルビニルエーテル）、パーフルオロ（プロピルビニルエーテル）、パーフルオロ（ヘプチルビニルエーテル）、（パーフルオロメチル）エチレン、（パーフルオロブチル）エチレン、クロロトリフルオロエチレン等が挙げられる。これらの含フッ素モノマーは単独で用いてもよいし、２種以上を併用してもよい。改質モノマーは、通常１質量％以下であることが好ましく、より好ましくは０．５質量％以下である。
本発明のＰＴＦＥは、延伸性、フィブリル化性、非溶融二次加工性を有する。これらの性質は、ペースト押出し成形に通常要求される性質である。
【０００８】
また、本発明のＰＴＦＥは、標準比重、破断強度が特定の範囲にあるものであり、これにより特徴付けられる。
本発明のＰＴＦＥの標準比重（以下、ＳＳＧという）は、２．１６０以下であり、好ましくは２．１５７以下である。ＳＳＧは、平均分子量の指標であり、本発明のＰＴＦＥのＳＳＧは非常に小さい値、すなわち、平均分子量が高いといえる。ＳＳＧは、平均分子量の増大に伴い、減少する傾向がある。すなわち、本発明のＰＴＦＥは、ＳＳＧ値が小さいので、その平均分子量がかなり高いものであることが予測できる。ＳＳＧ値が２．１６０以下のＰＴＦＥは、押出し物の延伸倍率が３０００％を超え、延伸均一性にも優れる。
本発明のＰＴＦＥの延伸物の破断強度は、３２．０Ｎ（３．２６ｋｇｆ）〜４９．０Ｎ（５．０ｋｇｆ）の範囲であり、好ましくは３４．３Ｎ（３．５ｋｇｆ）〜４９．０Ｎ（５．０ｋｇｆ）の範囲である。これは、驚くべきことに、特開２０００−１４３７２７公報記載のＰＴＦＥより高い破断強度を有している。高い破断強度ほど、耐久性等に優れるので好ましい。一方、破断強度が５．０ｋｇｆを超えるＰＴＦＥは、実質上、製造が非常に困難となる傾向がある。
また、本発明のＰＴＦＥは、押出し圧力が、９．８ＭＰａ（１００ｋｇｆ／ｃｍ２）〜１９．６ＭＰａ（２００ｋｇｆ／ｃｍ２）であるものが好ましく、９．８ＭＰａ（１００ｋｇｆ／ｃｍ２）〜１６．７ＭＰａ（１７０ｋｇｆ／ｃｍ２）であるものがより好ましく、９．８ＭＰａ（１００ｋｇｆ／ｃｍ２）〜１５．２ＭＰａ（１５５ｋｇｆ／ｃｍ２）であるものが特に好ましい。
【０００９】
本発明のＰＴＦＥは、応力緩和時間が、少なくとも６５０秒であるものが好ましく、少なくとも７００秒であるものがより好ましく、少なくとも７３０秒であるものが特に好ましい。
本発明のＰＴＦＥは、水性分散重合により製造することができる。
水性分散重合は、ＴＦＥ単独、またはＴＦＥと改質モノマーとを用い、分散剤および重合開始剤を含有する水系媒体中で、行うことができる。重合温度は、通常５０〜１２０℃の範囲であり、好ましくは６０〜１００℃の範囲である。重合圧力は、適宜選定すればよいが、０．５〜４．０ＭＰａの範囲になるようにすればよく、好ましくは１．０〜２．５ＭＰａの範囲である。
【００１０】
分散剤としては、連鎖移動性の少ないアニオン系界面活性剤がより好ましく、フルオロカーボン系の界面活性剤が特に好ましい。具体例としては、ＸＣｎＦ２ｎＣＯＯＭ（ここで、Ｘは水素、塩素、フッ素、（ＣＦ３）２ＣＦを、Ｍは水素、ＮＨ４、アルカリ金属を、ｎは６〜１２の整数を示す。）、ＣｍＦ２ｍ＋１Ｏ（ＣＦ（ＣＦ３）ＣＦ２Ｏ）ｐＣＦ（ＣＦ３）ＣＯＯＭ（ここで、Ｍは水素、ＮＨ４、アルカリ金属を、ｍは１〜１２の整数を、ｐは０〜５の整数を示す。）、ＣｎＦ２ｎ＋１ＳＯ３Ｍ、ＣｎＦ２ｎ＋１ＣＨ２ＣＨ２ＳＯ３Ｍ等が挙げられる。パーフルオロカーボン系の界面活性剤がより好ましく、Ｃ７Ｆ１５ＣＯＯＮＨ４、Ｃ８Ｆ１７ＣＯＯＮＨ４、Ｃ９Ｆ１９ＣＯＯＮＨ４、Ｃ１０Ｆ２１ＣＯＯＮＨ４、Ｃ７Ｆ１５ＣＯＯＮａ、Ｃ８Ｆ１７ＣＯＯＮａ、Ｃ９Ｆ１９ＣＯＯＮａ、Ｃ７Ｆ１５ＣＯＯＫ、Ｃ８Ｆ１７ＣＯＯＫ、Ｃ９Ｆ１９ＣＯＯＫ、Ｃ３Ｆ７Ｏ（ＣＦ（ＣＦ３）ＣＦ２Ｏ）２ＣＦ（ＣＦ３）ＣＯＯＮＨ４等が挙げられる。これらは、単独で又は２種以上を組み合わせて用いてもよい。分散剤の量は、使用される水の質量基準で、２５０〜５０００ｐｐｍの範囲にすることが好ましい。この範囲にすることで水性分散液の安定性が向上し、得られるＰＴＦＥの破断強度が高くなる。また、水性分散液の安定性をさらに向上するために重合中に分散剤を追加添加することも好ましい。
【００１１】
重合開始剤としては、特定のレドックス系重合開始剤を用いるとＳＳＧが低く、押出し圧力が低く、破断強度が大きい本発明のＰＴＦＥが得られる。特定のレドックス系重合開始剤としては、過硫酸塩、臭素酸塩等の水溶性酸化剤と亜硫酸塩やジイミン等の還元剤の組合せが挙げられる。特に、特定のレドックス系重合開始剤として、臭素酸塩と亜硫酸塩の組み合わせがより好ましく、臭素酸カリウムと亜硫酸アンモニウムの組合せが最も好ましい。臭素酸塩と亜硫酸塩を用いる場合には、どちらかをあらかじめ重合槽に仕込み、ついでもう一方を連続的または断続的に加えて重合を開始させることが好ましく、臭素酸塩をあらかじめ重合槽に仕込み、ついで亜硫酸塩を連続的または断続的に加えることがより好ましい。重合開始剤の量は、適宜選定すればよいが、水の質量基準で２〜６００ｐｐｍが好ましく、臭素酸塩と亜硫酸塩の組合せの場合にはそれぞれ５〜３００ｐｐｍが好ましい。また、あらかじめ臭素酸塩を重合槽に仕込む場合は、臭素酸塩濃度を高くすることにより水性分散液の安定性がさらに向上する。重合開始剤の量は、少ないほど吸熱比が小さいＰＴＦＥが得られる傾向となるので好ましい。また、重合開始剤の量は、あまりに少ないと重合速度が遅くなりすぎる傾向となり、あまりに多いと生成するＰＴＦＥのＳＳＧが高くなる傾向となる。
【００１２】
水性分散重合は、安定化助剤の存在下に実施することが好ましい。安定化助剤としては、パラフィンワックス、フッ素系オイル、フッ素系溶剤、シリコーンオイル等が好ましい。これらは、単独で又は２種以上を組み合わせて用いてもよい。特に、パラフィンワックスの存在下に行うことが好ましい。パラフィンワックスとしては、室温で液体でも、半固体でも、固体であってもよいが、炭素数１２以上の飽和炭化水素が好ましい。パラフィンワックスの融点は、通常４０〜６５℃が好ましく、５０〜６５℃がより好ましい。パラフィンワックスの量は、使用される水の質量基準で０．１〜１２質量％が好ましく、０．１〜８質量％がより好ましい。
水性分散重合は、通常、水系重合混合物を穏やかに撹拌することにより行われる。生成した水性分散液中のＰＴＦＥ微粒子が凝集しないように撹拌条件が制御される。水性分散重合は、通常、水性分散液中のＰＴＦＥ微粒子の濃度が１５〜４０質量％になるまで行われる。
水性分散重合は、酸を添加して酸性状態で行うことが水性分散液の安定化のために好ましい。酸としては、硫酸、塩酸、硝酸等の酸が好ましく、硝酸がより好ましい。硝酸を加えることにより水性分散液の安定性がさらに向上する。
水性分散重合によりＰＴＦＥ微粒子が分散した水性分散液が得られるが、水性分散液中のＰＴＦＥ微粒子の粒径は、通常０．０２〜１．０μｍと広い分布を有し、平均粒子径は０．１〜０．４μｍ程度である。
得られた水性分散重合液からＰＴＦＥ微粒子を凝集し、乾燥させてＰＴＦＥファインパウダーを得る。凝集方法としては、水性分散液を高速撹拌することによってＰＴＦＥ微粒子を凝集させることが好ましい。このとき、凝析剤を添加することが好ましい。凝析剤としては、炭酸アンモニウムや多価無機塩類、鉱酸類、陽イオン界面活性剤、アルコール等が好ましく、炭酸アンモニウムがより好ましい。
【００１３】
凝集により湿潤状態で得られるＰＴＦＥの乾燥は、任意の温度で行うことができるが、１００〜２５０℃の範囲で行うことが好ましく、１３０〜２００℃の範囲で行うことが特に好ましい。乾燥によって、本発明のＰＴＦＥァインパウダーを得ることができる。このＰＴＦＥファインパウダーは、その平均粒径が１００〜８００μｍの範囲のものが好ましく、４００〜６００μｍの範囲のものが特に好ましい。
また、本発明は、上記の特性を有するＰＴＦＥからなる多孔体およびその物品を提供する。多孔体は、種々の方法により製造したものが挙げられるが、例えば、ペースト押出し成形後に延伸を施すことにより得られる多孔体および多孔体からなるフィルム、チューブなどが挙げられる。
ペースト押出し成形とは、ＰＴＦＥファインパウダーを潤滑剤と混合して、ＰＴＦＥファインパウダーに流動性を持たせてシート、チューブ等の成形物を成形するものである。潤滑剤の混合割合は、ＰＴＦＥファインパウダーに流動性を持たせるように、適宜選定すればよく、通常１０〜３０質量％にすればよい。潤滑剤としては、ナフサ、沸点が２００℃以上の石油系炭化水素が好ましく用いられる。また、延伸は、適当な速度、例えば５％／秒〜１０００％／秒の速度で、適当な延伸倍率、例えば５００％以上の延伸倍率になるように施せばよい。
多孔体の空孔率は特に制限ないが、通常空孔率が５０〜９７％の範囲が好ましく、７０〜９５％の範囲が特に好ましい。
多孔体で構成される物品の形状は、シート状、フィルム状、繊維状など種々の形状にすることができる。
【００１４】
【実施例】
以下、実施例により本発明を具体的に説明するが、本願発明はこれらに限定されない。以下において、部は質量部を示す。例１〜４が実施例であり、例５が比較例である。
なお、実施例において、延伸性の評価、破断強度、応力緩和時間の測定は、以下に示す方法により行った。
【００１５】
（１）押出し圧および延伸性の評価
室温で２時間以上放置されたＰＴＦＥのファインパウダー１００ｇを内容量９００ｃｃのガラス瓶に入れ、アイソパーＨ（登録商標、エクソン社製）潤滑剤２１．７ｇを添加し、３分間混合してＰＴＦＥ混合物を得る。得られたＰＴＦＥ混合物を２５℃恒温槽に２時間放置した後に、リダクションレシオ（ダイスの入り口の断面積と出口の断面積の比）１００、押出し速度５１ｃｍ／分の条件で、２５℃にて、直径２．５ｃｍ、ランド長１．１ｃｍ、導入角３０°のオリフィスを通して、ペースト押出ししビードを得る。このときの押出しに要する圧力を測定し、押出し圧とする。得られたビードを２３０℃で３０分間乾燥し、潤滑剤を除去する。次いで、ビードの長さを適当な長さに切断し、クランプ間が３．８ｃｍまたは５．１ｃｍのいずれかの間隔となるよう、各末端を固定し、空気循環炉中で３００℃に加熱する。次いで、クランプが所定の間隔になるまで所定の速度で延伸する。この延伸方法は、押出しスピード（５１ｃｍ／分）が異なることを除いて、本質的に米国特許第４，５７６，８６９号明細書に開示された方法に従っている。「延伸」とは、長さの増加であり、通常元の長さと関連して表わされる。
【００１６】
（２）破断強度の測定
破断強度試験測定用のサンプルは、クランプ間隔５．１ｃｍ、延伸速度１００％／秒、総延伸２４００％を用い、延伸性の評価と同様にして、ビードを延伸することにより、作製する。破断強度は、延伸ビードから得られる３つのサンプル、延伸ビードの各末端から１つ（クランプの範囲においてネックダウンがあればそれを除く）、およびその中心から１つ、の最小引張り破断負荷（力）として、測定される。５．０ｃｍのゲージ長である、ジョーにおいてサンプルを挟んで固定し、可動ジョー３００ｍｍ／分のスピードで駆動させ、引張り試験機（エイアンドディ社製）を用いて、室温で測定する。
【００１７】
（３）応力緩和時間の測定
応力緩和時間の測定用のサンプルは、クランプ間隔３．８ｃｍ、延伸速度１０００％／秒、総延伸２４００％を用い、延伸性の評価のように、ビードを延伸することにより、作製する。この延伸ビードのサンプルの両方の末端は、固定具につなげることにより、ぴんと張られた全長２５ｃｍの延伸ビードである。応力緩和時間とは、このサンプルが３９０℃、すなわち、米国特許第５，４７０，６５５号明細書に開示されている延長鎖形状の溶ける３８０℃より高い温度でオーブン中に放置した後に破断するのに要する時間である。固定具におけるサンプルは、オーブンの側部にある（覆われた）スロットを通してオーブンに挿入されるので、サンプルを配置する間に温度は下降することがなく、それゆえに米国特許第４，５７６，８６９号明細書に開示されたように回復にしばしの時間を必要としない。
【００１８】
［例１］
１００Ｌの重合槽に、パラフィンワックスの９２８ｇ、超純水の５５Ｌ、パーフルオロオクタン酸アンモニウムの３６ｇ、コハク酸の１ｇ、１Ｎの硝酸水溶液の８ｍｌ、臭素酸カリウムの０．４ｇを仕込んだ。窒素パージ、脱気を行った後に、６５℃に昇温した。温度が安定した後にＴＦＥを導入し、１．９ＭＰａの圧力とした。内容物を撹拌下に、亜硫酸アンモニウム１４０ｐｐｍ水溶液１Ｌを６０分連続添加して重合を開始した。重合が進行すると共にＴＦＥが消費されて重合槽内の圧力が低下したので、圧力を一定に保つようにＴＦＥを連続的に供給した。亜硫酸アンモニウムの添加終了後にパーフルオロオクタン酸アンモニウムの１１．１質量％水溶液１Ｌを添加した。重合開始から２７０分経過した時点で、撹拌およびＴＦＥの供給を停止し、重合槽内のＴＦＥをパージし、ついで気相を窒素で置換した。得られた固形分２８．９質量％のＰＴＦＥ水性分散液を炭酸アンモニウム存在下で凝集し、湿潤状態のＰＴＦＥを分離した。得られた湿潤状態のＰＴＦＥを１６０℃で乾燥して、ＰＴＦＥファインパウダーを得た。そして、得られたＰＴＦＥファインパウダーのＳＳＧおよび平均粒径を測定した。また、得られたＰＴＦＥファインパウダーを前述の方法でペースト押出ししてビードを得た。この時の押出し圧力を測定した。ついでビードを延伸して得た延伸ビードの破断強度、応力緩和時間を測定した。
ついで、ＰＴＦＥファインパウダー６００ｇをガラス製のボトルに２０重量％の割合で潤滑剤であるアイソパーＧ（Ｅｘｘｏｎ社製）を加え、１００ｒｐｍで３０分間回転させることにより混合した。ブレンドした樹脂を室温で２４時間熟成させた。この樹脂を０．２ＭＰａの圧力を１２０秒間プレスして直径６８ｍｍのプレフォームを得た。このプレフォームを直径１１ｍｍのオリフィスを通して押出しを行い、押出し物を厚さ０．１ｍｍまで圧延した。該圧延シートを長さ５ｃｍ、幅２ｃｍの短冊状とし、３００℃の温度下、１００％／秒の速度で１０倍に延伸した。得られたフィルムの空孔率は、９０％であった。
【００１９】
［例２］
１００Ｌの重合槽に、パラフィンワックスの９２８ｇ、超純水の５５Ｌ、パーフルオロオクタン酸アンモニウムの３６ｇ、コハク酸の１ｇ、１Ｎの硝酸水溶液の８ｍｌ、臭素酸カリウムの０．４ｇを仕込んだ。窒素パージ、脱気を行った後に、８５℃に昇温した。温度が安定した後にＴＦＥを導入し、１．９ＭＰａの圧力とした。内容物を撹拌下に、亜硫酸アンモニウム１４０ｐｐｍ水溶液１Ｌを６０分連続添加して重合を開始した。重合が進行すると共にＴＦＥが消費されて重合槽内の圧力が低下したので、圧力を一定に保つようにＴＦＥを連続的に供給した。亜硫酸アンモニウムの添加終了後にパーフルオロオクタン酸アンモニウムの１１．１質量％水溶液１Ｌを添加した。重合開始から２７０分経過した時点で、撹拌およびＴＦＥの供給を停止し、重合槽内のＴＦＥをパージし、ついで気相を窒素で置換した。得られた固形分２９．６質量％のＰＴＦＥ水性分散液を炭酸アンモニウム存在下で凝集し、湿潤状態のＰＴＦＥを分離した。得られた湿潤状態のＰＴＦＥを２５０℃で乾燥して、ＰＴＦＥファインパウダーを得た。例１と同様にして、ＰＴＦＥファインパウダーのＳＳＧおよび平均粒径、ペースト押出し時の押出し圧力、延伸ビードの破断強度、応力緩和時間を測定した。
【００２０】
［例３］
１００Ｌの重合槽に、パラフィンワックスの９２８ｇ、超純水の５５Ｌ、パーフルオロオクタン酸アンモニウムの２５ｇ、コハク酸の１ｇ、１Ｎの硝酸水溶液の８ｍｌ、臭素酸カリウムの０．４ｇを仕込んだ。窒素パージ、脱気を行った後に、８５℃に昇温した。温度が安定した後にＴＦＥを導入し、１．９ＭＰａの圧力とした。内容物を撹拌下に、亜硫酸アンモニウム１４０ｐｐｍ水溶液１Ｌを６０分連続添加して重合を開始した。重合が進行すると共にＴＦＥが消費されて重合槽内の圧力が低下したので、圧力を一定に保つようにＴＦＥを連続的に供給した。亜硫酸アンモニウムの添加終了後にパーフルオロオクタン酸アンモニウムの１１．１質量％水溶液１Ｌを添加した。重合開始から２５０分経過した時点で、撹拌およびＴＦＥの供給を停止し、重合槽内のＴＦＥをパージし、ついで気相を窒素で置換した。得られた固形分２４．１質量％のＰＴＦＥ水性分散液を炭酸アンモニウム存在下で凝集し、湿潤状態のＰＴＦＥを分離した。得られた湿潤状態のＰＴＦＥを１４０℃で乾燥して、ＰＴＦＥファインパウダーを得た。例１と同様にして、ＰＴＦＥファインパウダーのＳＳＧおよび平均粒径、ペースト押出し時の押出し圧力、延伸ビードの破断強度、応力緩和時間を測定した。
【００２１】
［例４］
１００Ｌの重合槽に、パラフィンワックスの９２８ｇ、超純水の５５Ｌ、パーフルオロオクタン酸アンモニウムの２５ｇ、コハク酸の１ｇ、１Ｎの硝酸水溶液の８ｍｌ、臭素酸カリウムの６ｇを仕込んだ。窒素パージ、脱気を行った後に、８５℃に昇温した。温度が安定した後にＴＦＥを導入し、１．２ＭＰａの圧力とした。内容物を撹拌下に、亜硫酸アンモニウム３００ｐｐｍ水溶液０．４Ｌを８０分連続添加して重合を開始した。重合が進行すると共にＴＦＥが消費されて重合槽内の圧力が低下したので、圧力を一定に保つようにＴＦＥを連続的に供給した。重合開始後６０分後にパーフルオロオクタン酸アンモニウムの３．６質量％水溶液１Ｌを添加した。また、亜硫酸アンモニウムの添加終了後に再びパーフルオロオクタン酸アンモニウムの８．１質量％水溶液１Ｌを添加した。重合開始から２２０分経過した時点で、撹拌およびＴＦＥの供給を停止し、重合槽内のＴＦＥをパージし、ついで気相を窒素で置換した。得られた固形分２６．０質量％のＰＴＦＥ水性分散液を炭酸アンモニウム存在下で凝集し、湿潤状態のＰＴＦＥを分離した。得られた湿潤状態のＰＴＦＥを２００℃で乾燥して、ＰＴＦＥファインパウダーを得た。例１と同様にして、ＰＴＦＥファインパウダーのＳＳＧおよび平均粒径、ペースト押出し時の押出し圧力、延伸ビードの破断強度、応力緩和時間を測定した。
【００２２】
［例５（比較例）］
１００Ｌの重合槽に、パラフィンワックスの７３６ｇ、超純水の５９Ｌ、パーフルオロオクタン酸アンモニウムの３３ｇを仕込んだ。７０℃に昇温し、窒素パージ、脱気を行った後、ＴＦＥを導入し、１．９ＭＰａの圧力とした。撹拌下に、ジコハク酸パーオキサイドの０．５質量％水溶液１Ｌを圧入して重合を開始した。重合の進行に伴いＴＦＥが消費されて重合槽内の圧力が低下したので、圧力を一定に保つように重合中はＴＦＥを連続的に供給した。重合開始から４５分後から６℃／時で９０℃まで昇温した。また、ＴＦＥの供給量が６．６ｋｇとなった時点で、パーフルオロオクタン酸アンモニウムの５．６質量％水溶液１Ｌを添加した。重合開始から１６０分経過した時点で、撹拌およびＴＦＥの供給を停止し、重合槽内のＴＦＥをパージして重合を停止した。得られた固形分２４．３質量％のＰＴＦＥ水性分散液を凝集し、湿潤状態のＰＴＦＥを分離した。得られた湿潤状態のＰＴＦＥを２０５℃で乾燥して、ＰＴＦＥファインパウダーを得た。例１と同様にして、ＰＴＦＥファインパウダーのＳＳＧおよび平均粒径、ペースト押出し時の押出し圧力、延伸ビードの破断強度、応力緩和時間を測定した。
【００２３】
【表１】
【発明の効果】
本発明のＰＴＦＥは、標準比重が低く、破断強度が優れ、ペースト押出成形後の延伸操作に好適に使用できる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a tetrafluoroethylene polymer (hereinafter referred to as PTFE) having excellent strength. More specifically, the present invention relates to PTFE having excellent strength that can be suitably used for a stretching operation after paste extrusion.
[0002]
[Prior art]
Conventionally, PTFE is obtained by polymerizing tetrafluoroethylene (hereinafter, referred to as TFE) alone or, if necessary, by polymerizing with a modifying monomer, and has been used for various purposes.
PTFE can be produced by aqueous dispersion polymerization, and can be obtained in the form of an aqueous dispersion in which polymer particles are dispersed, or can be obtained as a fine powder by coagulating and drying the aqueous dispersion polymerization solution.
Conventional PTFE fine powder has high melt viscosity and does not flow easily at the melting temperature, and therefore has non-melt secondary workability. Therefore, PTFE fine powder is generally obtained by blending PTFE fine powder with a lubricant, molding the lubricated PTFE by an extrusion method, and then removing the lubricant to obtain an extruded product usually having a melting point of PTFE. Paste extrusion has been performed which fuses (sinters) at higher temperatures into the final product shape.
[0003]
On the other hand, other important products obtained from PTFE fine powder include breathable cloth materials for products such as clothes, tents and separation membranes. These products can be obtained by rapidly stretching an extruded product obtained by paste extrusion of PTFE fine powder in an unsintered state, and imparting a property that allows water vapor to pass through but not condensed water. .
U.S. Pat. Nos. 4,654,406 and 4,576,869 describe an extruded PTFE fine powder technique which is improved and obtained by adding 17% by weight of a lubricant. It is stated that stretching the article at a rate of 10% / sec to 100% / sec by at least 1000% achieves a stretch uniformity of at least 75%.
However, the required physical properties of a stretched product obtained by stretching PTFE are increasing year by year, and the stretched product obtained from the improved PTFE has a problem that the strength is not sufficient.
[0004]
[Problems to be solved by the invention]
The present invention has been made in view of the state of the prior art described above, and provides PTFE having stretchability, fibrillation property and non-melt secondary workability, which has a high breaking strength and a small standard specific gravity. The purpose is to do.
[0005]
[Means for Solving the Problems]
The present invention relates to PTFE having stretchability, fibrillation property and non-melt fabrication property, wherein the polymer has a standard specific gravity of 2.160 or less, 32.0 N (3.26 kgf) to 49.0 N (5. A PTFE having a breaking strength of 0.0 kgf).
Here, the standard specific gravity refers to a value measured according to JIS K6935-2.
The present invention also provides the PTFE having a standard specific gravity of 2.157 or less.
Further, the present invention provides the PTFE, wherein the stress relaxation time is at least 650 seconds.
[0006]
The present invention also provides the PTFE having a breaking strength of 34.3 N (3.5 kgf) to 49.0 N (5.0 kgf).
Further, in the above PTFE, extrusion pressure, to provide a PTFE is 9.8MPa (100kgf / cm 2) ~19.6MPa (200kgf / cm 2).
Further, the present invention provides the PTFE, wherein the PTFE is a fine powder.
Further, the present invention provides the above PTFE, wherein the PTFE is a solid component dispersed in an aqueous dispersion.
Further, the present invention provides a porous body made of PTFE having the above-mentioned properties and an article thereof.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
The PTFE of the present invention may be a homopolymer of TFE or a copolymer with a modified monomer other than TFE, such as a fluorine-containing monomer having an ethylenically unsaturated group. Examples of the fluorine-containing monomer having an ethylenically unsaturated group include hexafluoropropylene, perfluorobutene-1, perfluorohexene-1, perfluorononene-1, perfluoro (methyl vinyl ether), and perfluoro (ethyl vinyl ether) ), Perfluoro (propyl vinyl ether), perfluoro (heptyl vinyl ether), (perfluoromethyl) ethylene, (perfluorobutyl) ethylene, chlorotrifluoroethylene, and the like. These fluorinated monomers may be used alone or in combination of two or more. The amount of the modifying monomer is usually preferably 1% by mass or less, more preferably 0.5% by mass or less.
The PTFE of the present invention has stretchability, fibrillation, and non-melt secondary workability. These properties are those normally required for paste extrusion.
[0008]
The PTFE of the present invention has a standard specific gravity and a breaking strength in specific ranges, and is characterized by this.
The standard specific gravity (hereinafter, referred to as SSG) of the PTFE of the present invention is 2.160 or less, preferably 2.157 or less. SSG is an index of the average molecular weight, and the SSG of the PTFE of the present invention can be said to have a very small value, that is, a high average molecular weight. SSG tends to decrease with increasing average molecular weight. That is, since the PTFE of the present invention has a small SSG value, it can be predicted that the average molecular weight is considerably high. PTFE having an SSG value of 2.160 or less has a stretch ratio of the extruded product exceeding 3000% and is excellent in stretch uniformity.
The breaking strength of the expanded product of the PTFE of the present invention is in the range of 32.0 N (3.26 kgf) to 49.0 N (5.0 kgf), and preferably 34.3 N (3.5 kgf) to 49.0 N (5 kg). 0.0kgf). It surprisingly has a higher breaking strength than PTFE described in JP 2000-143727. Higher breaking strength is preferable because of excellent durability and the like. On the other hand, PTFE having a breaking strength exceeding 5.0 kgf tends to be extremely difficult to manufacture substantially.
Further, PTFE of the present invention, the extrusion pressure is preferably has a 9.8MPa (100kgf / cm 2) ~19.6MPa (200kgf / cm 2), 9.8MPa (100kgf / cm 2) ~16.7MPa more preferably those which are (170kgf / cm 2), those particularly preferably 9.8MPa (100kgf / cm 2) ~15.2MPa (155kgf / cm 2).
[0009]
The PTFE of the present invention preferably has a stress relaxation time of at least 650 seconds, more preferably at least 700 seconds, and particularly preferably at least 730 seconds.
The PTFE of the present invention can be produced by aqueous dispersion polymerization.
The aqueous dispersion polymerization can be carried out using TFE alone or TFE and a modifying monomer in an aqueous medium containing a dispersant and a polymerization initiator. The polymerization temperature is usually in the range of 50 to 120 ° C, preferably in the range of 60 to 100 ° C. The polymerization pressure may be appropriately selected, but may be in the range of 0.5 to 4.0 MPa, preferably in the range of 1.0 to 2.5 MPa.
[0010]
As the dispersant, an anionic surfactant having a low chain transfer property is more preferable, and a fluorocarbon surfactant is particularly preferable. As a specific example, XC n F 2n COOM (here, X represents hydrogen, chlorine, fluorine, (CF 3 ) 2 CF, M represents hydrogen, NH 4 , an alkali metal, and n represents an integer of 6 to 12. .), C m F 2m + 1 O (CF (CF 3) CF 2 O) p CF (CF 3) COOM ( wherein, M is hydrogen, NH 4, an alkali metal, m is 1 to 12 integer, p is an integer of 0~5.), C n F 2n + 1 SO 3 M, C n F 2n + 1 CH 2 CH 2 SO 3 M , and the like. Perfluorocarbon surfactants are more preferable, and C 7 F 15 COONH 4, C 8 F 17 COONH 4 , C 9 F 19 COONH 4 , C 10 F 21 COONH 4 , C 7 F 15 COONa 4 , C 8 F 17 COONa. , C 9 F 19 COONa, C 7 F 15 COOK , C 8 F 17 COOK, C 9 F 19 COOK, C 3 F 7 O (CF (CF 3 ) CF 2 O) 2 CF (CF 3 ) COONH 4 and the like. No. These may be used alone or in combination of two or more. The amount of the dispersant is preferably in the range of 250 to 5000 ppm based on the mass of water used. When the content is in this range, the stability of the aqueous dispersion is improved, and the breaking strength of the obtained PTFE is increased. It is also preferable to add a dispersant during polymerization in order to further improve the stability of the aqueous dispersion.
[0011]
As the polymerization initiator, the use of a specific redox polymerization initiator SSG is low, low extrusion pressure, PTFE of the present invention the breaking strength is large is obtained. Specific redox polymerization initiators, persulfates, and combinations of a water-soluble oxidizing agent and a sulfite or diimine such a reducing agent such as bromate. In particular, as a specific redox polymerization initiator, a combination of bromate and sulfite is more preferable, and a combination of potassium bromate and ammonium sulfite is most preferable. When using a bromate and a sulfite, it is preferable to charge one of them in a polymerization tank in advance, and then add the other continuously or intermittently to start polymerization. More preferably, the sulfite is added continuously or intermittently. The amount of the polymerization initiator may be appropriately selected, but is preferably 2 to 600 ppm based on the mass of water, and preferably 5 to 300 ppm in the case of a combination of bromate and sulfite. When the bromate is previously charged into the polymerization tank, the stability of the aqueous dispersion is further improved by increasing the bromate concentration. The smaller the amount of the polymerization initiator, the more preferable it is because PTFE having a small endothermic ratio tends to be obtained. On the other hand, if the amount of the polymerization initiator is too small, the polymerization rate tends to be too slow. If the amount is too large, the SSG of PTFE formed tends to be high.
[0012]
The aqueous dispersion polymerization is preferably carried out in the presence of a stabilizing aid. As the stabilizing aid, paraffin wax, fluorinated oil, fluorinated solvent, silicone oil and the like are preferable. These may be used alone or in combination of two or more. In particular, it is preferable to carry out in the presence of paraffin wax. The paraffin wax may be liquid, semi-solid or solid at room temperature, but is preferably a saturated hydrocarbon having 12 or more carbon atoms. Usually, the melting point of paraffin wax is preferably from 40 to 65 ° C, more preferably from 50 to 65 ° C. The amount of paraffin wax is preferably from 0.1 to 12% by mass, more preferably from 0.1 to 8% by mass, based on the mass of water used.
The aqueous dispersion polymerization is usually performed by gently stirring the aqueous polymerization mixture. The stirring conditions are controlled so that the PTFE fine particles in the generated aqueous dispersion do not aggregate. The aqueous dispersion polymerization is usually performed until the concentration of the PTFE fine particles in the aqueous dispersion becomes 15 to 40% by mass.
The aqueous dispersion polymerization is preferably performed in an acidic state by adding an acid for stabilizing the aqueous dispersion. As the acid, acids such as sulfuric acid, hydrochloric acid, and nitric acid are preferable, and nitric acid is more preferable. The addition of nitric acid further improves the stability of the aqueous dispersion.
An aqueous dispersion in which PTFE fine particles are dispersed is obtained by aqueous dispersion polymerization. The particle size of the PTFE fine particles in the aqueous dispersion has a wide distribution of usually 0.02 to 1.0 μm, and the average particle size is 0.1 to 1.0 μm. It is about 1 to 0.4 μm.
PTFE fine particles are aggregated from the obtained aqueous dispersion polymerization solution and dried to obtain a PTFE fine powder. As the aggregating method, it is preferable that the PTFE fine particles are agglomerated by stirring the aqueous dispersion at a high speed. At this time, it is preferable to add a coagulant. As the coagulant, ammonium carbonate, polyvalent inorganic salts, mineral acids, cationic surfactants, alcohols and the like are preferable, and ammonium carbonate is more preferable.
[0013]
Drying of PTFE obtained in a wet state by agglomeration can be performed at any temperature, but is preferably performed in the range of 100 to 250 ° C, particularly preferably in the range of 130 to 200 ° C. By drying, the PTFE fine powder of the present invention can be obtained. The PTFE fine powder preferably has an average particle size in the range of 100 to 800 μm, particularly preferably 400 to 600 μm.
Further, the present invention provides a porous body made of PTFE having the above-mentioned characteristics and an article thereof. Examples of the porous body include those manufactured by various methods. Examples of the porous body include a porous body obtained by performing stretching after paste extrusion molding, and a film or tube made of the porous body.
Paste extrusion molding refers to mixing PTFE fine powder with a lubricant to give PTFE fine powder fluidity to form molded articles such as sheets and tubes. The mixing ratio of the lubricant may be appropriately selected so that the PTFE fine powder has fluidity, and may be usually 10 to 30% by mass. As the lubricant, naphtha or a petroleum hydrocarbon having a boiling point of 200 ° C. or more is preferably used. The stretching may be performed at an appropriate speed, for example, at a speed of 5% / sec to 1000% / sec, so that an appropriate stretching ratio, for example, a stretching ratio of 500% or more is obtained.
The porosity of the porous body is not particularly limited, but usually the porosity is preferably in the range of 50 to 97%, and particularly preferably in the range of 70 to 95%.
The shape of the article made of the porous body can be various shapes such as a sheet shape, a film shape, and a fiber shape.
[0014]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. In the following, “part” indicates “part by mass”. Examples 1 to 4 are Examples, and Example 5 is a Comparative Example.
In the examples, evaluation of stretchability, measurement of rupture strength, and measurement of stress relaxation time were performed by the following methods.
[0015]
(1) Evaluation of Extrusion Pressure and Stretchability 100 g of PTFE fine powder left at room temperature for 2 hours or more was placed in a 900 cc glass bottle, and 21.7 g of Isopar H (registered trademark, exxon) lubricant was added. Mix for 3 minutes to obtain PTFE mixture. After leaving the obtained PTFE mixture in a 25 ° C. constant temperature bath for 2 hours, at 25 ° C. under the conditions of a reduction ratio (ratio of the cross-sectional area of the entrance of the die to the cross-sectional area of the exit) of 100 and an extrusion speed of 51 cm / min. A paste extruded bead is obtained through an orifice having a diameter of 2.5 cm, a land length of 1.1 cm, and an introduction angle of 30 °. The pressure required for the extrusion at this time is measured, and is defined as the extrusion pressure. The obtained beads are dried at 230 ° C. for 30 minutes to remove the lubricant. The bead length is then cut to a suitable length, each end is fixed so that the gap between the clamps is either 3.8 cm or 5.1 cm, and heated to 300 ° C. in an air circulation furnace. . Next, the clamp is stretched at a predetermined speed until a predetermined interval is reached. This stretching method essentially follows the method disclosed in U.S. Pat. No. 4,576,869, except that the extrusion speed (51 cm / min) is different. "Stretch" is an increase in length, usually expressed in relation to the original length.
[0016]
(2) Measurement of breaking strength The sample for the breaking strength test measurement is to stretch the bead in the same manner as in the evaluation of stretchability, using a clamp interval of 5.1 cm, a stretching speed of 100% / sec, and a total stretching of 2400%. To produce. The breaking strength was the minimum tensile breaking load (force) of the three samples obtained from the stretched bead, one from each end of the stretched bead (excluding any neckdown in the range of the clamp), and one from its center. ) Is measured. A sample having a gauge length of 5.0 cm is sandwiched between jaws and fixed. The movable jaw is driven at a speed of 300 mm / min, and measured at room temperature using a tensile tester (manufactured by A & D).
[0017]
(3) Measurement of Stress Relaxation Time The sample for measuring the stress relaxation time stretches the beads as in the evaluation of stretchability using a clamp interval of 3.8 cm, a stretching speed of 1000% / sec, and a total stretching of 2400%. In this way, it is produced. Both ends of the stretch bead sample are stretch beads of 25 cm overall length that are taut by connecting to a fixture. The stress relaxation time is defined as the sample breaking after standing in an oven at 390 ° C., ie, above 380 ° C., the melting temperature of the extended chain configuration disclosed in US Pat. No. 5,470,655. It is the time required. Since the sample in the fixture is inserted into the oven through a slot (covered) on the side of the oven, the temperature does not drop during sample placement, and therefore, US Pat. No. 4,576,869. Recovery does not require much time as disclosed in the specification.
[0018]
[Example 1]
Into a 100 L polymerization tank were charged 928 g of paraffin wax, 55 L of ultrapure water, 36 g of ammonium perfluorooctanoate, 1 g of succinic acid, 8 ml of 1N aqueous nitric acid, and 0.4 g of potassium bromate. After nitrogen purging and degassing, the temperature was raised to 65 ° C. After the temperature was stabilized, TFE was introduced to a pressure of 1.9 MPa. While stirring the contents, 1 L of a 140 ppm aqueous solution of ammonium sulfite was continuously added for 60 minutes to initiate polymerization. As the polymerization proceeded, TFE was consumed and the pressure in the polymerization tank decreased, so TFE was continuously supplied to keep the pressure constant. After the completion of the addition of ammonium sulfite, 1 L of an aqueous solution of 11.1% by mass of ammonium perfluorooctanoate was added. When 270 minutes had elapsed from the start of the polymerization, the stirring and the supply of TFE were stopped, TFE in the polymerization tank was purged, and the gas phase was replaced with nitrogen. The obtained PTFE aqueous dispersion having a solid content of 28.9% by mass was aggregated in the presence of ammonium carbonate to separate wet PTFE. The obtained wet PTFE was dried at 160 ° C. to obtain a PTFE fine powder. Then, the SSG and average particle size of the obtained PTFE fine powder were measured. Also, the obtained PTFE fine powder was paste-extruded by the method described above to obtain a bead. The extrusion pressure at this time was measured. Then, the breaking strength and the stress relaxation time of the stretched bead obtained by stretching the bead were measured.
Then, 600 g of PTFE fine powder was added to a glass bottle at a ratio of 20% by weight with Isopar G (manufactured by Exxon), which was a lubricant, and mixed by rotating at 100 rpm for 30 minutes. The blended resin was aged at room temperature for 24 hours. This resin was pressed at a pressure of 0.2 MPa for 120 seconds to obtain a preform having a diameter of 68 mm. The preform was extruded through an orifice having a diameter of 11 mm, and the extruded product was rolled to a thickness of 0.1 mm. The rolled sheet was formed into a strip having a length of 5 cm and a width of 2 cm, and stretched 10 times at a temperature of 300 ° C. at a rate of 100% / sec. The porosity of the obtained film was 90%.
[0019]
[Example 2]
Into a 100 L polymerization tank were charged 928 g of paraffin wax, 55 L of ultrapure water, 36 g of ammonium perfluorooctanoate, 1 g of succinic acid, 8 ml of 1N aqueous nitric acid, and 0.4 g of potassium bromate. After nitrogen purging and degassing, the temperature was raised to 85 ° C. After the temperature was stabilized, TFE was introduced to a pressure of 1.9 MPa. While stirring the contents, 1 L of a 140 ppm aqueous solution of ammonium sulfite was continuously added for 60 minutes to initiate polymerization. As the polymerization proceeded, TFE was consumed and the pressure in the polymerization tank decreased, so TFE was continuously supplied to keep the pressure constant. After the completion of the addition of ammonium sulfite, 1 L of an aqueous solution of 11.1% by mass of ammonium perfluorooctanoate was added. When 270 minutes had elapsed from the start of the polymerization, the stirring and the supply of TFE were stopped, TFE in the polymerization tank was purged, and the gas phase was replaced with nitrogen. The obtained PTFE aqueous dispersion having a solid content of 29.6% by mass was aggregated in the presence of ammonium carbonate to separate wet PTFE. The obtained wet PTFE was dried at 250 ° C. to obtain a PTFE fine powder. In the same manner as in Example 1, the SSG and the average particle size of the PTFE fine powder, the extrusion pressure during paste extrusion, the breaking strength of the stretched bead, and the stress relaxation time were measured.
[0020]
[Example 3]
A 100 L polymerization tank was charged with 928 g of paraffin wax, 55 L of ultrapure water, 25 g of ammonium perfluorooctanoate, 1 g of succinic acid, 8 ml of 1N nitric acid aqueous solution, and 0.4 g of potassium bromate. After nitrogen purging and degassing, the temperature was raised to 85 ° C. After the temperature was stabilized, TFE was introduced to a pressure of 1.9 MPa. While stirring the contents, 1 L of a 140 ppm aqueous solution of ammonium sulfite was continuously added for 60 minutes to initiate polymerization. As the polymerization proceeded, TFE was consumed and the pressure in the polymerization tank decreased, so TFE was continuously supplied to keep the pressure constant. After the completion of the addition of ammonium sulfite, 1 L of an aqueous solution of 11.1% by mass of ammonium perfluorooctanoate was added. When 250 minutes had elapsed from the start of the polymerization, stirring and supply of TFE were stopped, TFE in the polymerization tank was purged, and then the gas phase was replaced with nitrogen. The obtained PTFE aqueous dispersion having a solid content of 24.1% by mass was aggregated in the presence of ammonium carbonate to separate wet PTFE. The obtained wet PTFE was dried at 140 ° C. to obtain a PTFE fine powder. In the same manner as in Example 1, the SSG and the average particle size of the PTFE fine powder, the extrusion pressure during paste extrusion, the breaking strength of the stretched bead, and the stress relaxation time were measured.
[0021]
[Example 4]
Into a 100 L polymerization tank were charged 928 g of paraffin wax, 55 L of ultrapure water, 25 g of ammonium perfluorooctanoate, 1 g of succinic acid, 8 ml of 1N nitric acid aqueous solution, and 6 g of potassium bromate. After nitrogen purging and degassing, the temperature was raised to 85 ° C. After the temperature was stabilized, TFE was introduced to a pressure of 1.2 MPa. While stirring the contents, 0.4 L of a 300 ppm aqueous solution of ammonium sulfite was continuously added for 80 minutes to initiate polymerization. As the polymerization proceeded, TFE was consumed and the pressure in the polymerization tank decreased, so TFE was continuously supplied to keep the pressure constant. 60 minutes after the start of the polymerization, 1 L of a 3.6% by mass aqueous solution of ammonium perfluorooctanoate was added. After the completion of the addition of ammonium sulfite, 1 L of an 8.1% by mass aqueous solution of ammonium perfluorooctanoate was added again. At 220 minutes after the start of the polymerization, the stirring and the supply of TFE were stopped, the TFE in the polymerization tank was purged, and then the gas phase was replaced with nitrogen. The obtained PTFE aqueous dispersion having a solid content of 26.0% by mass was aggregated in the presence of ammonium carbonate to separate wet PTFE. The obtained wet PTFE was dried at 200 ° C. to obtain a PTFE fine powder. In the same manner as in Example 1, the SSG and the average particle size of the PTFE fine powder, the extrusion pressure during paste extrusion, the breaking strength of the stretched bead, and the stress relaxation time were measured.
[0022]
[Example 5 (Comparative Example)]
A 100 L polymerization tank was charged with 736 g of paraffin wax, 59 L of ultrapure water, and 33 g of ammonium perfluorooctanoate. After the temperature was raised to 70 ° C., nitrogen purge and degassing were performed, TFE was introduced to a pressure of 1.9 MPa. Under stirring, 1 L of a 0.5% by mass aqueous solution of disuccinic acid peroxide was injected to initiate polymerization. Since TFE was consumed as the polymerization progressed and the pressure in the polymerization tank decreased, TFE was continuously supplied during the polymerization so as to keep the pressure constant. After 45 minutes from the start of the polymerization, the temperature was raised to 90 ° C. at 6 ° C./hour. When the supply amount of TFE reached 6.6 kg, 1 L of a 5.6% by mass aqueous solution of ammonium perfluorooctanoate was added. When 160 minutes had elapsed from the start of the polymerization, the stirring and the supply of TFE were stopped, and TFE in the polymerization tank was purged to stop the polymerization. The obtained PTFE aqueous dispersion having a solid content of 24.3% by mass was aggregated to separate wet PTFE. The obtained wet PTFE was dried at 205 ° C. to obtain a PTFE fine powder. In the same manner as in Example 1, the SSG and the average particle size of the PTFE fine powder, the extrusion pressure during paste extrusion, the breaking strength of the stretched bead, and the stress relaxation time were measured.
[0023]
[Table 1]
【The invention's effect】
The PTFE of the present invention has a low standard specific gravity and excellent breaking strength, and can be suitably used for a stretching operation after paste extrusion.
Claims (8)
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
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| JP2001226171A JP3552685B2 (en) | 2000-10-30 | 2001-07-26 | Tetrafluoroethylene polymer with excellent strength |
| EP20010123224 EP1201689B1 (en) | 2000-10-30 | 2001-10-02 | Tetrafluoroethylene polymer for stretching |
| DE60135894T DE60135894D1 (en) | 2000-10-30 | 2001-10-02 | Tetrafluoroethylene polymer for elongation |
| US09/970,674 US6518381B2 (en) | 2000-10-30 | 2001-10-05 | Tetrafluoroethylene polymer for stretching |
| CNB011377550A CN100478367C (en) | 2000-10-30 | 2001-10-30 | Tetrafluoroethylene polymer for expansion |
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| JP2000331277 | 2000-10-30 | ||
| JP2000-331277 | 2000-10-30 | ||
| JP2001226171A JP3552685B2 (en) | 2000-10-30 | 2001-07-26 | Tetrafluoroethylene polymer with excellent strength |
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