JP2004338208A - Method for manufacturing modified polytetrafluoroethylene film - Google Patents

Method for manufacturing modified polytetrafluoroethylene film Download PDF

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Publication number
JP2004338208A
JP2004338208A JP2003137141A JP2003137141A JP2004338208A JP 2004338208 A JP2004338208 A JP 2004338208A JP 2003137141 A JP2003137141 A JP 2003137141A JP 2003137141 A JP2003137141 A JP 2003137141A JP 2004338208 A JP2004338208 A JP 2004338208A
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Japan
Prior art keywords
ptfe
film
radiation
powder
modified
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JP2003137141A
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Japanese (ja)
Inventor
Tomoyuki Murakami
知之 村上
Soji Nishiyama
総治 西山
Takashi Wano
隆司 和野
Takeshi Suwa
武 諏訪
Yosuke Morita
洋右 森田
Masaru Yoshida
勝 吉田
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Nitto Denko Corp
Japan Atomic Energy Agency
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Japan Atomic Energy Research Institute
Nitto Denko Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a modified PTFE film good in radiation resistance without accompanying the lowering of the mechanical physical properties thereof and requiring much equipment cost. <P>SOLUTION: This modified polytetrafluoroethylene film is manufactured by irradiating a porous lumpy molded article, which is obtained by molding a polytetrafluoroethylene powder into a lumpy shape, with radiation at a temperature higher than the melting point of polytetrafluoroethylene substantially in the absence of oxygen to modify the same and cutting the modified lumpy molded article to form a long film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【0001】
【発明の属する技術分野】
本発明は、改質ポリテトラフルオロエチレン(以下、ポリテトラフルオロエチレンをPTFEという)フィルムの製造方法に関する。さらに詳述するなら、本発明は、燃料電池などの電解質膜基材に使用される耐放射線性を有するPTFEフィルムの製造方法に関するものであり、本発明の製造方法による基材を使用すれば、従来は耐放射線性が乏しい故に困難であった、電解質膜の製造における放射線グラフト重合の適用が可能となる。また、本発明の製造方法による基材は耐磨耗性が優れるていることから、各種摺動材への適用も期待される。
【0002】
【従来の技術】
PTFEは耐薬品性、耐熱性に優れており、産業用、民生用樹脂として広く利用されている。しかし、PTFEはγ線、電子線などの放射線に対する感受性が極めて大きく、放射線により分子切断が生じて機械的特性が低下する。そのためPTFEは放射線照射下において使用し難い。
【0003】
上記PTFEの耐放射線性に関する問題に対して、特許文献1には、短尺のPTFEフィルムに、PTFEの結晶融点以上の温度で酸素不在下において、1×10Gy以上の電離性放射線を照射して、当該PTFEフィルムを改質する方法が開示されている。かかる方法によれば、耐放射線性の改質されたPTFEフィルムが得られている。
【0004】
上記方法を、長尺PTFEフィルムに適用する場合には、当該フィルムを連続するライン上でPTFEの融点以上の高温に保持しつつ、しかも酸素不在下で連続的に放射線を照射しなければならず、腰のないフィルムを走行させるために複雑な設備となり、多大な設備投資を必要とするため、実用的な製造方法とはいえなかった。そこで、本発明者等はこの問題点を解決すべく検討を重ねた結果、PTFE粉末を塊状に圧縮成形した後、焼成して得られる成形物に、酸素不在下、PTFEの融点以上の温度にて、放射線を照射して前記塊状成形物を改質した後、これを切削して長尺フィルムとすることを特徴とする改質PTFEフィルムの製造方法を開発した(特許文献2を参照のこと)。
【0005】
しかしながら、特許文献2に記載される方法をスケールアップしたところ、得られるフィルムのフィルム強度や破断伸びは、塊状成形物の厚さ方向の外部表面から切削して約3mmまでは良好であったが、さらに、厚さ方向の外部表面から5mm以上になると、それらの機械的物性が低下することが判明した。
【0006】
【特許文献1】特開平6−116423号公報
【特許文献2】特開2002−36376号公報
【0007】
【発明が解決しようとする課題】
本発明は、上記従来技術の問題点を解決するため、耐放射線性の良好な改質PTFEフィルムを、その機械的物性の低下を伴わず、多大な設備投資を必要とすることなく、製造しうる方法を提供することを目的とする。
【0008】
【課題を解決するための手段】
本発明者らは、上記課題を解決すべく鋭意検討を重ねた結果、以下に示す方法により上記目的を達成できることを見出し、本発明を完成するに至った。
【0009】
すなわち、本発明は、PTFE粉末を多孔質の塊状に成形した後、酸素不在下、PTFEの融点以上の温度にて、放射線を照射して前記塊状成形物を改質した後、これを切削して長尺フィルムとすることを特徴とする改質PTFEフィルムの製造方法である。
【0010】
多孔質のPTFE成形体に放射線照射することにより、PTFE粉末に吸着している酸素の除去が容易となり、また、放射線照射によって生成されるPTFEからの分解ガスが円滑に除去されるものと考えられる。
【0011】
肉厚の塊状成形物を成形した場合、塊状成形物の内部に吸着している酸素は雰囲気を真空引きしても除去されにくいことは自明であり、また、酸素存在下では改質が進行しないことは特許文献1にも記載されている。
【0012】
本発明の改質は、放射線照射によってPTFE分子鎖からF原子が離脱した主鎖の2ケのC同士が化学結合して架橋する、PTFEの架橋によって達成されると思料されるところ、このとき、離脱したF原子が元の主鎖Cに再結合しては架橋構造とならず、耐放射線性の改質効果は不充分なものとなる。従って、離脱したF原子がFガス等となってPTFEの架橋を阻害しないよう、フッ素系分解ガスを系外へ拡散させる工夫が必要となる。
【0013】
本発明者等は、PTFE粉末を多孔質または繊密な状態で圧縮成形した各々体積27cmの円柱体を成形し、酸素不在下で340℃にてγ線を100kGy照射した。これら成形体の照射前後の重量変化を測定したところ、多孔質の成形体は重量減少が3.7%であるのに対して、繊密な成形体の重量減少は0.9%であった。このことは、多孔質の成形体では、照射による分解生成物が系外へ飛散して架橋反応が円滑に進行したものと考えられる。
【0014】
本発明の製造方法により得られるPTFEフィルムは、若干の通気性があるが、燃料電池用電解質膜の基材として採用する際、グラフト重合することで多孔質の孔内がグラフトモノマーで充填されガス透過性が消失されるので、燃料電池において、ガスのクロスオーバー現象は認められなかった。
【0015】
上記本発明の製造方法によれば、PTFEの改質が、PTFEの塊状成形物に対して施されるため、特許文献1に開示されているPTFEフィルムに改質を施す方法に比べて非常に簡易な方法であり、多大な設備投資を必要としない。また、上記本発明の製造方法により得られる改質PTFEフィルムは、特許文献1に開示されているPTFEフィルムに改質を施したものと同様、PTFEに架橋構造等が付与されるため、優れた耐放射線性を有する。
【0016】
上記本発明の製造方法に従えば、長尺フィルムの厚さ調整は通常の切削と同様の方法によりに容易に行うことができる。ここで、本発明でいう長尺とは通常10m以上をいう。
【0017】
本発明における放射線の線質は、透過力を有する線質が有用であり放射線のなかでもγ線またはX線もしくは電子線が本発明に適している。放射線として電子線を用いる場合には、透過力がよく、PTFEの塊状成形物の内部まで改質できる5×10電子ボルト以上、さらには7×10電子ボルト以上のものが好ましい。上記のように放射線の線質を選択することにより、効果的にPTFEフィルムの改質を行うことができる。
【0018】
【発明の実施の形態】
本発明の製造方法では、予めPTFE粉末を多孔質状に成形した後、焼成して塊状の成形物を作成する。成形物の焼成は、圧縮成形後にPTFEの融点以上に加熱して焼成してもよく、あるいは、放射線改質する際に融点以上の温度ですることにより焼成してもよい。
【0019】
本発明において多孔質状とは、見掛けの比重が通常の繊密成形物の2.14〜2.22より低くければよく、具体的には、2.20以下であればよい。好ましくは、多孔質状成形体の見掛けの比重は2.15〜1.50である。見掛けの比重が1.5以下になると、切削フィルムの外観上に0.2mm程度の穴が存在し、引張り強度も低下するので、用途によっては不具合をきたす。PTFEフィルムを燃料電池の電解質膜用基材として用いる場合には、成形体の見掛けの比重は2.00以上が好ましい。
【0020】
PTFE粉末を多孔質状に圧縮成形する方法には、以下の2つの方法がある。
【0021】
一の方法は、予め焼成したPTFE粉末、または焼成したPTFE粉末と未焼成粉末とを混合して、圧縮成形する方法である。焼成粉末の混合比率は5%〜100%の範囲がこのましい。混合比率が5%以下だと、多孔質構造が得られないので改質しにくい。また95%以上だと、PTFE粉末の結着が不充分で見かけの比重が小さく引張り強度が低いが、用途によっては使用に耐える。焼成粉末は結着しにくいため、これを混合することにより粒子間に隙間を生じ多孔質成形物が得られる。焼成PTFE粉末の粒子径が大きいと、得られる多孔質成形物の孔径も大きくなるので、通常、焼成PTFE粉末の粒子径は300μ以下が好ましい。
【0022】
別の方法は、未焼成PTFE粉末を圧縮成形する際の圧力を低くすることにより多孔質成形物が得る方法である。通常の繊密な成形品を製造する際の圧力は200〜400kgf/cmであるが、多孔質成形物を得る場合の成形圧力は150kgf/cm以下、好ましくは50kgf/cm以下である。PTFE粉末の粒子径は特に制限されないが、通常、0.1〜500μm程度とするのが好ましい。
【0023】
圧縮成形は、所望形状の金型に前記原料粉末を均一に充填し、通常、常温でプレスで挟んで100〜1000kgf/cm程度で圧縮を行う。
【0024】
所望形状の金型は特に制限されず、得られる成形物が塊状となるようなものであれば、板状、円柱状、円筒状等のいずれでもよいが、塊状成形物を切削することによりフィルム化の容易な円筒状のものが好ましい。また、放射線として電子線を採用する場合には、塊状成形物(PTFE)内部に電子がチャージアップするおそれがあるので、チャージした電子を逃す細工、たとえば、塊状成形物を中空状とし、内面側にもアースを取ることは有効である。
【0025】
圧縮成形による予備成形の後には、この予備成形物を金型から取り出し、炉に入れ、340〜380℃程度に昇温し、その温度で焼結が全体に均一に完了するまで保持する。これによりPTFEの焼結体である塊状の成形物が得られる。予備成形物の焼成は、圧縮成形後に行ってもよく、あるいは、放射線改質する際に行ってもよい。
【0026】
なお、上記は、塊状PTFE成形物の圧縮成形法として、フリーベイキング法を代表させて説明したが、適宜、ホットコイニング法、自動圧縮成形法、等圧圧縮成形法等を適宜に応用することもできる。ただし、ホットコイニング法を採用するときは、融点以上の温度での樹脂膨張により多孔質の状態が消滅することがあるので注意を要する。
【0027】
次いで、上記の塊状成形物を、酸素不在下、340℃近辺の温度にて、放射線を照射して改質する。
【0028】
放射線の照射環境である「酸素不在下」とは、実質的な真空中(1Pa以下)ないしは窒素、ヘリウム、アルゴン等の不活性ガス雰囲気下をいう。PTFEの分解ガスを成形物から除去するという観点からは、照射雰囲気を真空とし、更に容器を真空ポンプで引き続けることが最も好ましい方法である。
【0029】
照射温度はPTFEの結晶融点(327℃)以上であり、327℃以下では改質(架橋反応)が進行しない。一方、照射温度が高くなりすぎるとPTFEの分解が進み強度低下するため、照射温度の上限は360℃である。従って、照射温度は、好ましくは327℃〜360℃であり、更に好ましくは335〜345℃である。
【0030】
放射線量は、通常1×10Gy〜1×10Gy程度とする。PTFEの改質(架橋物性)を有効に発現させるためには、放射線量は1×10Gy以上とするのが好ましい。一方、放射線量を多くしすぎるとPTFEの分解が進むため、放射線量は1×10Gy以下とするのが好ましい。
【0031】
放射線照射により改質されたPTFEの塊状成形物は、切削して長尺フィルムとする。切削方法は特に制限されず、一般的なPTFEの切削工具を使用できる。また長尺フィルムの厚さに応じて、切削工具の種類、使用条件等が適宜に選択される。
【0032】
【実施例】
以下、実施例にて本発明を詳述するが、本発明はこれら実施例に限定されるものではない。
【0033】
実施例1
PTFEの焼成粉末は以下のように作成した。PTFEモールディングパウダー(ダイキン工業(株)製,品番ポリフロンTFEM−12)をステンレス板に広げ、そのまま360℃の炉に30分投入し、焼成粉末を作成した。
【0034】
この焼成粉末と未焼成粉末を重量で50%ずつ混合し、内径200mmφ、肉厚30mm、高さ800mmφの金型に入れ、280kg/cmの圧力で1時間圧縮して予備成形した。この予備成形品を金型に入れたまま、360℃の炉に48時間入れ、粉末同士を結着させ、外径約200mmφ、高さ500mmの円柱状ブロックを得た。このブロックの見掛け比重は2.09であった。
【0035】
次いで、この円柱状ブロックを内径300mmφ、高さ700mmのステンレス製の容器に入れ、容器内部の空気を窒素に置換し、更に容器の外周にバンドヒータを巻き内部温度を340℃±10℃に設定した後、20時間そのまま維持することで、円柱状ブロック全体を340℃±5℃にした。温度を340℃±5℃に維持しつつ、放射線を均一に照射するため容器を毎分1回転させながら、毎時2×10Gyのコバルト60γ線を50時間照射して(放射線量1×10Gy)、改質PTFEの円柱状ブロックを得た。
【0036】
この改質PTFEの円柱状ブロックを切削旋盤にて切削し、厚さ0.1mm、幅460mm、長さ150mの長尺PTFEフィルムを得た。
【0037】
実施例2
内径200mmφ、肉厚30mm、高さ800mmφの金型にPTFEモールディングパウダー(ダイキン工業(株)製,品番ポリフロンTFEM−12)を入れ、35kgf/cmの圧力で1時間圧縮して予備成形した。この予備成形品を金型に入れたまま、360℃の炉に48時間入れ焼成し、外径約200mmφ、高さ500mmの円柱状ブロックを得た。このブロックの見掛け比重は2.11であった。
【0038】
以下は実施例1と同様に操作して、改質PTFEの円柱状ブロックを得た。そして、実施例1と同様に切削し、厚さ0.1mm、幅460mm、長さ150mの長尺PTFEフィルムを得た。
【0039】
(評価)
実施例で得られた改質PTFEフィルムについて、空気中、室温で、電子線を1×10Gy照射した前後の降伏点強度、破断伸びを万能引張り試験機にて、20℃で、200mm/分の引張り速度で測定した。また、比較例1として、未改質の切削PTFEシート(実施例1で焼成後、照射せずに切削した0.1mm厚)についても同様の測定を行った。評価結果を表1に示す。
【0040】
【表1】

Figure 2004338208
【0041】
表1に示したように、改質PTFEフィルムでは、空気中で放射線を照射しても降伏点強度、破断伸びの低下が殆どなく耐放射線性に優れていることが認められる。
【0042】
【発明の効果】
本発明の製造方法によれば、耐放射線性の良好な改質PTFEフィルムを、多大な設備投資をすることなく製造することができる。特に、PTFEフィルムの厚さが1mm未満のものを製造する場合に有用である。
【0043】
得られた改質PTFEフィルムは、未改質のPTFEフィルムに比べて耐放射線性に優れている。本発明により得られた改質PTFEフィルムは、これまで使用が不可能であった放射線環境下での工業材料として使用できる。
【0044】
また、PTFEは耐放射線性に乏しいことから、放射線グラフト共重合では強度低下を来たすことから不向きであったが、本発明により得られた改質PTFEフィルムは耐放射線性を有するので、前照射法や同時照射法で放射線グラフト共重合してイオン交換膜や電池隔膜の基材として採用しうる物性とすることもできる。
【0045】
また改質PTFEフィルムは、未改質のPTFEフィルムによりも降状点強度が向上している。また、未改質のPTFEフィルムと同等の破断伸びを有し、低磨耗量といった物性にも優れる。このように改質PTFEフィルムはゴム特性を備えているので、シール材料やパッキン材料として耐熱、耐薬品性、耐クリープ性を具備した特性が要求させる各種用途へも利用できる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a modified polytetrafluoroethylene (hereinafter, polytetrafluoroethylene is referred to as PTFE) film. More specifically, the present invention relates to a method for producing a radiation-resistant PTFE film used for an electrolyte membrane substrate such as a fuel cell. Conventionally, radiation graft polymerization can be applied in the production of an electrolyte membrane, which has been difficult because of poor radiation resistance. Further, since the substrate produced by the production method of the present invention has excellent wear resistance, application to various sliding materials is also expected.
[0002]
[Prior art]
PTFE has excellent chemical resistance and heat resistance, and is widely used as an industrial or consumer resin. However, PTFE has extremely high sensitivity to radiation such as γ-rays and electron beams, and molecular breaks occur due to the radiation, thereby deteriorating mechanical properties. Therefore, PTFE is difficult to use under irradiation of radiation.
[0003]
Regarding the above-mentioned problem concerning the radiation resistance of PTFE, Patent Document 1 discloses that a short PTFE film is irradiated with ionizing radiation of 1 × 10 3 Gy or more in the absence of oxygen at a temperature higher than the crystal melting point of PTFE. Thus, a method for modifying the PTFE film is disclosed. According to such a method, a radiation-resistant modified PTFE film is obtained.
[0004]
When the above method is applied to a long PTFE film, the film must be continuously irradiated in the absence of oxygen while keeping the film at a high temperature equal to or higher than the melting point of PTFE on a continuous line. However, since complicated equipment is required for running a film having no rigidity and a large capital investment is required, it cannot be said that this is a practical manufacturing method. The inventors of the present invention have conducted various studies to solve this problem, and as a result, after compression-molding PTFE powder into a lump, a molded product obtained by firing is heated to a temperature higher than the melting point of PTFE in the absence of oxygen. Thus, a method for producing a modified PTFE film characterized by irradiating radiation to modify the mass-formed product and cutting the mass into a long film was developed (see Patent Document 2). ).
[0005]
However, when the method described in Patent Document 2 was scaled up, the film strength and elongation at break of the obtained film were good up to about 3 mm when cut from the external surface in the thickness direction of the massive molded product. Further, it has been found that when the distance from the outer surface in the thickness direction is 5 mm or more, their mechanical properties deteriorate.
[0006]
[Patent Document 1] JP-A-6-116423 [Patent Document 2] JP-A-2002-36376
[Problems to be solved by the invention]
In order to solve the above-mentioned problems of the prior art, the present invention is to produce a modified PTFE film having good radiation resistance without reducing mechanical properties and without requiring a large capital investment. The purpose of the present invention is to provide a method that can
[0008]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that the above object can be achieved by the following method, and have completed the present invention.
[0009]
That is, the present invention, after forming the PTFE powder into a porous mass, in the absence of oxygen, at a temperature equal to or higher than the melting point of PTFE, irradiating radiation to modify the mass, and then cutting the mass. And producing a modified PTFE film.
[0010]
By irradiating the porous PTFE molded body with radiation, it is considered that oxygen adsorbed on the PTFE powder can be easily removed, and the decomposition gas from PTFE generated by the radiation irradiation is smoothly removed. .
[0011]
It is obvious that, when a thick mass is molded, oxygen adsorbed inside the mass is difficult to be removed even if the atmosphere is evacuated, and the reforming does not proceed in the presence of oxygen. This is also described in Patent Document 1.
[0012]
The modification of the present invention is considered to be achieved by the crosslinking of PTFE, in which two Cs of the main chain from which the F atom has been removed from the PTFE molecular chain by irradiation are chemically bonded and crosslinked. When the separated F atom is recombined with the original main chain C, the F atom does not form a crosslinked structure, and the effect of modifying the radiation resistance becomes insufficient. Therefore, leaving the F atoms are not to inhibit the crosslinking of PTFE becomes F 2 gas or the like, it is necessary to devise to diffuse the fluorine-based decomposition gas to the outside of the system.
[0013]
The present inventors formed a columnar body having a volume of 27 cm 3 by compression-molding PTFE powder in a porous or dense state, and irradiated 100 kGy of γ-ray at 340 ° C. in the absence of oxygen. When the weight change of these molded articles before and after irradiation was measured, the weight loss of the porous molded article was 3.7%, while the weight loss of the dense molded article was 0.9%. . This is considered to be due to the fact that in the porous molded body, the decomposition product by irradiation scattered outside the system and the crosslinking reaction proceeded smoothly.
[0014]
Although the PTFE film obtained by the production method of the present invention has some air permeability, when it is used as a base material for an electrolyte membrane for a fuel cell, the porous pores are filled with a graft monomer by graft polymerization to obtain a gas. Since the permeability was lost, no gas crossover phenomenon was observed in the fuel cell.
[0015]
According to the production method of the present invention, since the PTFE is modified on the PTFE bulk molded product, the PTFE modification is very much compared to the method of modifying the PTFE film disclosed in Patent Document 1. This is a simple method and does not require a large capital investment. Further, the modified PTFE film obtained by the production method of the present invention is excellent in that a cross-linked structure or the like is imparted to PTFE as in the case of modifying the PTFE film disclosed in Patent Document 1. Has radiation resistance.
[0016]
According to the manufacturing method of the present invention, the adjustment of the thickness of the long film can be easily performed by the same method as in ordinary cutting. Here, the long length in the present invention usually means 10 m or more.
[0017]
As the radiation quality in the present invention, a radiation quality having a transmitting power is useful, and among the radiations, γ-rays, X-rays, or electron beams are suitable for the present invention. When an electron beam is used as the radiation, it is preferable that the electron beam has a good penetrating power and is 5 × 10 6 electron volts or more, and more preferably 7 × 10 6 electron volts or more, which can modify the inside of the PTFE bulk molding. By selecting the radiation quality as described above, the PTFE film can be effectively modified.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
In the production method of the present invention, a PTFE powder is previously formed into a porous shape, and then fired to form a lump-shaped molded product. The firing of the molded article may be performed by heating to a temperature equal to or higher than the melting point of PTFE after the compression molding, or may be performed by heating at a temperature equal to or higher than the melting point during radiation modification.
[0019]
In the present invention, the term "porous" means that the apparent specific gravity may be lower than 2.14 to 2.22 of an ordinary fine molded product, and specifically, may be 2.20 or less. Preferably, the apparent specific gravity of the porous molded body is 2.15 to 1.50. When the apparent specific gravity is 1.5 or less, a hole of about 0.2 mm is present on the appearance of the cut film, and the tensile strength is reduced. When the PTFE film is used as a substrate for an electrolyte membrane of a fuel cell, the apparent specific gravity of the molded body is preferably 2.00 or more.
[0020]
There are the following two methods for compression molding PTFE powder into a porous shape.
[0021]
One method is a method in which PTFE powder fired in advance or a mixture of fired PTFE powder and unfired powder is compression-molded. The mixing ratio of the calcined powder is preferably in the range of 5% to 100%. If the mixing ratio is 5% or less, a porous structure cannot be obtained, so that it is difficult to modify. If it is 95% or more, the binding of the PTFE powder is insufficient, the apparent specific gravity is small, and the tensile strength is low. Since the calcined powder is difficult to bind, a gap is formed between the particles by mixing the calcined powder to obtain a porous molded product. If the particle size of the calcined PTFE powder is large, the pore size of the obtained porous molded product is also large. Therefore, usually, the particle size of the calcined PTFE powder is preferably 300 µm or less.
[0022]
Another method is a method of obtaining a porous molded product by lowering the pressure at the time of compression molding of unfired PTFE powder. The pressure at the time of producing a normal fine molded product is 200 to 400 kgf / cm 2 , but the molding pressure at the time of obtaining a porous molded product is 150 kgf / cm 2 or less, preferably 50 kgf / cm 2 or less. . Although the particle diameter of the PTFE powder is not particularly limited, it is usually preferable to be about 0.1 to 500 μm.
[0023]
In the compression molding, the raw material powder is uniformly filled in a mold having a desired shape, and is usually compressed at about 100 to 1000 kgf / cm 2 at room temperature by pressing with a press.
[0024]
The mold having the desired shape is not particularly limited, and may be any of a plate shape, a columnar shape, a cylindrical shape, and the like, as long as the obtained molded product has a lump shape. It is preferable to use a cylindrical material which can be easily formed. When an electron beam is used as the radiation, there is a possibility that the electrons may be charged up inside the massive molded product (PTFE). It is effective to take the ground as well.
[0025]
After the preforming by compression molding, the preformed product is taken out of the mold, placed in a furnace, heated to about 340 to 380 ° C., and held at that temperature until the sintering is completed uniformly. As a result, a massive molded product that is a sintered body of PTFE is obtained. The firing of the preform may be performed after compression molding, or may be performed during radiation modification.
[0026]
In the above description, the free baking method has been described as a representative example of the compression molding method of the massive PTFE molded product. However, a hot coining method, an automatic compression molding method, an equal pressure compression molding method, or the like may be appropriately applied. it can. However, when the hot coining method is employed, care must be taken because the porous state may disappear due to resin expansion at a temperature higher than the melting point.
[0027]
Next, the above-mentioned bulk molded article is irradiated with radiation at a temperature of around 340 ° C. in the absence of oxygen to modify it.
[0028]
The term "in the absence of oxygen", which is a radiation irradiation environment, refers to a substantially vacuum (1 Pa or less) or an atmosphere of an inert gas such as nitrogen, helium, or argon. From the viewpoint of removing the decomposition gas of PTFE from the molded product, it is most preferable to set the irradiation atmosphere to a vacuum and further continue to pull the container with a vacuum pump.
[0029]
The irradiation temperature is equal to or higher than the crystal melting point of PTFE (327 ° C.), and if it is lower than 327 ° C., the reforming (crosslinking reaction) does not proceed. On the other hand, if the irradiation temperature is too high, the decomposition of PTFE proceeds and the strength decreases, so the upper limit of the irradiation temperature is 360 ° C. Therefore, the irradiation temperature is preferably from 327C to 360C, and more preferably from 335C to 345C.
[0030]
The radiation dose is usually about 1 × 10 3 Gy to 1 × 10 7 Gy. The radiation dose is preferably 1 × 10 4 Gy or more in order to effectively express PTFE modification (crosslinking properties). On the other hand, if the radiation dose is too high, the decomposition of PTFE proceeds, so that the radiation dose is preferably 1 × 10 6 Gy or less.
[0031]
The block-shaped PTFE mass modified by irradiation is cut into a long film. The cutting method is not particularly limited, and a general PTFE cutting tool can be used. In addition, the type of the cutting tool, the use conditions, and the like are appropriately selected according to the thickness of the long film.
[0032]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.
[0033]
Example 1
The fired powder of PTFE was prepared as follows. PTFE molding powder (manufactured by Daikin Industries, Ltd., product number: Polyflon TFEM-12) was spread on a stainless steel plate, and was directly charged into a furnace at 360 ° C. for 30 minutes to prepare a fired powder.
[0034]
The fired powder and the unfired powder were mixed by 50% by weight, placed in a mold having an inner diameter of 200 mmφ, a wall thickness of 30 mm, and a height of 800 mmφ, and compressed for 1 hour at a pressure of 280 kg / cm 2 for preforming. The preform was placed in a mold at a temperature of 360 ° C. for 48 hours in a mold, and the powders were bonded together to obtain a cylindrical block having an outer diameter of about 200 mmφ and a height of 500 mm. The apparent specific gravity of this block was 2.09.
[0035]
Next, the cylindrical block is placed in a stainless steel container having an inner diameter of 300 mm and a height of 700 mm, the air inside the container is replaced with nitrogen, and a band heater is further wrapped around the outer periphery of the container to set the internal temperature to 340 ° C. ± 10 ° C. After that, the entire columnar block was kept at 340 ° C. ± 5 ° C. by keeping the same for 20 hours. While maintaining the temperature at 340 ° C. ± 5 ° C., the container is irradiated with 2 × 10 3 Gy / hour of cobalt 60γ ray for 50 hours while rotating the container once per minute for uniform irradiation with radiation (radiation dose 1 × 10 5 Gy) to obtain a columnar block of modified PTFE.
[0036]
The columnar block of the modified PTFE was cut by a cutting lathe to obtain a long PTFE film having a thickness of 0.1 mm, a width of 460 mm, and a length of 150 m.
[0037]
Example 2
A PTFE molding powder (manufactured by Daikin Industries, Ltd., polyflon TFEM-12) was placed in a mold having an inner diameter of 200 mmφ, a wall thickness of 30 mm, and a height of 800 mmφ, and was compressed and preformed at 35 kgf / cm 2 for 1 hour. With the preform kept in the mold, it was placed in a furnace at 360 ° C. for 48 hours and fired to obtain a cylindrical block having an outer diameter of about 200 mmφ and a height of 500 mm. The apparent specific gravity of this block was 2.11.
[0038]
The following operations were performed in the same manner as in Example 1 to obtain a columnar block of modified PTFE. Then, cutting was performed in the same manner as in Example 1 to obtain a long PTFE film having a thickness of 0.1 mm, a width of 460 mm, and a length of 150 m.
[0039]
(Evaluation)
Regarding the modified PTFE film obtained in the examples, the yield point strength and elongation at break before and after irradiation of an electron beam at 1 × 10 4 Gy in air at room temperature were measured at 20 ° C. at 200 ° C. It was measured at a pull rate of min. Further, as Comparative Example 1, the same measurement was performed on an unmodified cut PTFE sheet (0.1 mm thick cut without irradiation after firing in Example 1). Table 1 shows the evaluation results.
[0040]
[Table 1]
Figure 2004338208
[0041]
As shown in Table 1, it is recognized that the modified PTFE film has almost no decrease in yield point strength and elongation at break even when irradiated with radiation in the air, and has excellent radiation resistance.
[0042]
【The invention's effect】
According to the production method of the present invention, a modified PTFE film having good radiation resistance can be produced without significant investment in equipment. In particular, it is useful when manufacturing a PTFE film having a thickness of less than 1 mm.
[0043]
The resulting modified PTFE film has better radiation resistance than the unmodified PTFE film. The modified PTFE film obtained according to the present invention can be used as an industrial material under a radiation environment, which has heretofore been impossible to use.
[0044]
Further, PTFE is poor in radiation resistance, and thus is not suitable because radiation graft graft copolymerization causes a reduction in strength. However, since the modified PTFE film obtained by the present invention has radiation resistance, the pre-irradiation method Alternatively, radiation graft copolymerization may be performed by a simultaneous irradiation method to obtain physical properties that can be used as a base material for an ion exchange membrane or a battery membrane.
[0045]
In addition, the modified PTFE film has an improved yield point strength over the unmodified PTFE film. Further, it has an elongation at break equivalent to that of an unmodified PTFE film, and is excellent in physical properties such as low abrasion. Since the modified PTFE film has rubber properties as described above, it can be used for various applications that require properties having heat resistance, chemical resistance, and creep resistance as seal materials and packing materials.

Claims (3)

ポリテトラフルオロエチレン粉末を塊状に成形した成形物が多孔質であり、その後実質的に酸素不在下でポリテトラフルオロエチレンの融点以上の温度にて、放射線を照射して前記塊状成形物を改質した後、これを切削して長尺フィルムとすることを特徴とする改質ポリテトラフルオロエチレンフィルムの製造方法。The molded product obtained by molding the polytetrafluoroethylene powder into a lump is porous, and thereafter, the radiation is irradiated at a temperature equal to or higher than the melting point of the polytetrafluoroethylene in the absence of oxygen to modify the lump-shaped molded article. And producing a long film by cutting the modified polytetrafluoroethylene film. 成形して得られた成形物の見掛けの比重が2.20以下の多孔質である、請求項1記載の改質ポリテトラフルオロエチレンフィルムの製造方法。The method for producing a modified polytetrafluoroethylene film according to claim 1, wherein the molded product obtained by molding is porous with an apparent specific gravity of 2.20 or less. 原料のポリテトラフルオロエチレン粉末が、予め焼成したポリテトラフルオロエチレン粉末、または焼成したポリテトラフルオロエチレン粉末と未焼成粉末とを混合したものである、請求項1又は2に記載の改質ポリテトラフルオロエチレンフィルムの製造方法。The modified polytetrafluoroethylene according to claim 1 or 2, wherein the raw material polytetrafluoroethylene powder is pre-fired polytetrafluoroethylene powder, or a mixture of fired polytetrafluoroethylene powder and unfired powder. A method for producing a fluoroethylene film.
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WO2012077636A1 (en) 2010-12-06 2012-06-14 日東電工株式会社 Method for producing porous epoxy resin sheet
JP2014005314A (en) * 2011-06-13 2014-01-16 Nitto Denko Corp Method and apparatus for producing thermosetting resin porous sheet, thermosetting resin porous sheet and sheet roll
US9186633B2 (en) 2008-10-23 2015-11-17 Nitto Denko Corporation Method for producing porous thermosetting resin sheet, porous thermosetting resin sheet and composite semipermeable membrane using same
US9504966B2 (en) 2008-09-26 2016-11-29 Nitto Denko Corporation Composite semi-permeable membrane and method for producing same

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Publication number Priority date Publication date Assignee Title
US9504966B2 (en) 2008-09-26 2016-11-29 Nitto Denko Corporation Composite semi-permeable membrane and method for producing same
US9186633B2 (en) 2008-10-23 2015-11-17 Nitto Denko Corporation Method for producing porous thermosetting resin sheet, porous thermosetting resin sheet and composite semipermeable membrane using same
WO2012077636A1 (en) 2010-12-06 2012-06-14 日東電工株式会社 Method for producing porous epoxy resin sheet
JP2014005314A (en) * 2011-06-13 2014-01-16 Nitto Denko Corp Method and apparatus for producing thermosetting resin porous sheet, thermosetting resin porous sheet and sheet roll

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