JP4810747B2 - Method for producing biaxially stretched polyester film - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は均一な二軸延伸熱可塑性フィルムな製造方法に係わる。さらに詳しくは、横延伸装置によって幅方向延伸、熱固定される際に生じるボーイング現象を抑制し、幅方向に均一な性質を有する二軸延伸ポリエステルフィルムの製造方法に関する。
【０００２】
【従来の技術】
ポリエステルフィルム、特に二軸延伸されたポリエステルフィルムは、機械的強度や熱寸法安定性などが優れていることから磁気記録用の基材、電子・電気材料、各種包装材料などに広く使用されており、フィルムの幅方向のどの部分でも同じ物性値である事が望ましい。
【０００３】
しかし、従来の製造方法では製品フィルムの幅方向の物性を均一にすることは極めて困難であった。この理由は、延伸工程の横延伸装置内においてフィルムの両端はクリップに把持されていて、幅方向延伸によって生じる長手方向の延伸応力と熱によって生じる収縮応力、そして、熱固定工程によって発生する収縮応力は、フィルムの端部においては把持手段であるクリップによって拘束されているに対し、フィルムの中央部は把持手段の影響が低く拘束力が弱くなり、上記の応力の影響によってクリップで把持されている端部に対してフィルムの中央部分は遅れが生じるためである。
【０００４】
そして、幅方向延伸と熱固定を連続に同一の横延伸装置で行う場合において、横延伸装置に入る前のフィルムの面上に幅方向に沿って直線を描いておくと、この直線は横延伸装置内で変形してフイルムの進行方向に対して延伸工程の始めの領域で凸型に変形し、延伸工程の終わり直前の領域で直線に戻り、延伸工程終了後には凹型に変形する。さらに熱固定工程の領域で凹形の変形は最大値に達し、このまま曲線は変化しないでその後の横延伸装置を通過し、横延伸装置を出たフィルムには凹形の変形が残る。この現象はボーイング現象と称されているものであるが、このボーイング現象はフィルムの物性値を幅方向に不均一にする原因となっている。ボーイング現象によって、幅方向両端部のフィルムには長手方向に対して傾斜した配向主軸が生じ、その配向主軸の角度は幅方向で異なる傾向がある。
【０００５】
この結果、例えば熱収縮率の縦方向から±４５°方向の物性値の差がフィルムの幅方向で異なってくる。このボーイング現象は、包装用途を一例とすると、印刷ラミネート加工、製袋工程等において印刷ピッチずれ、斑の発生、カーリング、蛇行などのトラブルの原因になっている。さらに詳しく述べると、幅方向延伸と熱固定間に冷却工程を設ける従来技術としては、特公昭３５−１１７７４号公報には幅方向延伸と熱固定工程の間に２０℃〜１５０℃の弛緩工程を介在させ、実質冷却工程を設けた製造方法が提案されている。しかし、この冷却工程の長さについては全く記載されていないばかりか、ボーイング現象の抑制の効果も全く不明である。
【０００６】
さらに、ボーイング現象を抑制ないし解消する技術として、特開昭５０−７３９７８号公報には延伸工程と熱固定工程との間にニップロール群を設置するフィルムの製造方法が提案されている。しかし、この技術ではニップロールを設置する中間帯の温度がガラス転移点以上なので、ニップ点でのフイルムの剛性が低いため改良効果が少ない。
【０００７】
また、特公昭６３−２４４５９号公報には横延伸完了後のフイルムの両端部を把持しながら中央付近の狭い範囲のみをニップロールによって強制的な前進をもたらす工程が提案されている。しかし、この技術ではニップロールを横延伸装置内の高温領域に設置する必要があり、ロール及びその周辺装置を冷却する必要があり、またフィルムが高温であるためロールによる傷が発生するおそれあり、実用面で制約される。
【０００８】
また、特公昭６２−４３８５６号公報には、横延伸直後のフイルムをガラス転移点以下に冷却した後、多段に熱固定を行ない熱固定と同時に幅方向に伸張する技術が提案されている。しかし、この技術では冷却工程でボーイング現象の抑制が少ないためか、又は熱固定でボーイング現象が再発生しやすいためか冷却工程に加えて多段に熱固定する工程と再延伸との複雑な工程となっている。そのため横延伸装置内の雰囲気湿度やフィルム温度を長時間にわたり安定して制御することが困難ではないかと懸念される。また、この技術も特公昭３５−１１７７４号公報と同様に冷却工程の長さなどは記載されていない。
【０００９】
また、特開平１−１６５４２３号公報には幅方向延伸後のフィルムを幅方向延伸温度以下に冷却した後、多段に昇温しながら幅方向に再度伸張する技術が提案されている。しかし、この技術では、特公昭６２−４３８５６号公報の場合と同様に冷却工程でのボーイング現象の抑制効果が少ないためか、また、熱固定工程でボーイングが発生しやすいためか、冷却工程に加えて多段に熱固定する工程と再延伸する工程との複雑な工程となっている。そのため横延伸装置内の雰囲気温度やフィルム温度を長時間にわたり安定して制御することが困難ではないかと懸念される。また、冷却温度はガラス転移点以上延伸温度以下が好ましいとの記載がある。しかし、この程度の冷却工程の長さや冷却工程の温度がガラス転移点以上では、ボーイング現象の抑制効果が少ないことが危惧され、上記のような複雑な工程を採用せざるを得なかったと推測される。
【００１０】
また、特公平１−２５６９４号公報、特公平１−２５６９６号公報には、フィルムの走行方向を逆転させて横延伸、熱固定をする技術が提案されている。しかし、この技術ではフィルムの走行方向を逆転させるのにフィルムを一旦巻き取る必要があり、オンラインでの製造方法であるため生産性の面で制約を受けるなどの問題点がある。
【００１１】
さらに、特開昭３２−１８３３２７号公報には縦延伸後、横延伸装置で横延伸、熱固定する際に、横延伸工程と熱固定工程との間に側端部分のみガラス転移点以上熱固定温度以下の温度の予熱工程を設置する技術が提案されている。しかし、この技術では、予熱工程の温度を幅方向に温度勾配を持たせながら制御しなければならないため、フィルム温度を長時間にわたり制御することが困難ではないかと懸念される。なお、この技術の実施例ではこの予熱工程の長さがフイルム幅の半分と短いことからボーイング現象の抑制の効果が少ないと推測される。
【００１２】
また、特公平２−４５９７６号公報には、熱固定工程を２段階に分けて、第２段階目でフイルム幅方向に温度分布を付与する熱処理方法が提案されている。しかし、この技術では熱処理工程で発現するボーイング現象の抑制に効果があるものの、延伸工程で発現するボーイング現象の抑制効果がなく、最終的に得られるボーイング現象の抑制効果が少ないことが推測される。
【００１３】
【発明が解決しようとする課題】
かかる課題に対し、ボーイング現象を抑制せしめて幅方向に物性の均一なポリエステルフイルムを得ることができる効果的な幅方向延伸にかかわる製造方法を提供することにある。
【００１４】
本発明者らは、横延伸装置内におけるボーイング線の変化を観察し、種々の研究からボーイング現象の発生過程を解明し、このボーイング現象を抑制する手段を検討して本発明に到達した。すなわち本発明の二軸延伸ポリエステルフィルムの製造方法は、実質的に無配向のポリエステルフィルムを長手方向に延伸し、ついで幅方向に延伸する二軸延伸ポリエステルフィルムを製造する方法であって、熱風を出す装置の中央部に遮蔽板を設置してフィルムにかかる熱風の風量を幅方向端部で増加させることによって、フィルム幅方向端部のフィルム温度を中央部のフィルム温度より高くして幅方向に延伸することを特徴とする。この場合において、中央より端部の方のスリット幅が１．１倍〜５．０倍大きい、スリット状の熱風を出す装置を用いて加熱することが好適である。さらにまた、この場合において、フィルム幅方向に全幅加熱することができ、かつ、中央より端部の方が熱風を出す穴の総面積が１．１倍〜５．０倍大きい、多孔穴状の熱風を出す装置を用いて加熱することが好適である。
【００１５】
【発明の実施の形態】
以下、本発明を詳細に説明する。
【００１６】
本発明に使用されるポリエステルとは、ポリエチレンテレフタレート、ポリブチレンテレフタレート、ポリエチレンナフタレートなどのポリエステル類であり、これらの混合物あるいは共重合ポリエステルでも構わない。該ポリエステルは、上記ポリエステル以外に本発明の効果を損なわない範囲で、有機もしくは無機の滑剤、酸化防止剤、熱安定剤、紫外線吸収剤、帯電防止剤などの添加物を含むポリエステル組成物を用いることができる。
【００１７】
本発明におけるポリエステルを押出機に代表される周知の溶融押出装置に供給し、該ポリエステルの軟化点以上の温度で加熱溶融する。溶融した該組成物は、Ｔダイなどのスリット状ダイから押し出し、冷却ロール上に密着せしめ冷却固化し、実質的に無配向のポリエステルフイルムを得る。
【００１８】
前記実質的に無配向のポリエステルフイルムを複数のロール間に供給することにより、連続的に長手方向に延伸した一軸延伸フイルムを得る。すなわち 低周速回転に設定した複数のロール（以下、ロール群という）と高周速回転に設定したロール群を通過させることにより、各ロール群の速度差によってフィルムに張力を与えて長手方向に延伸する。
長手方向に延伸して得られた一軸延伸フィルムを予熱、延伸、熱固定、冷却工程からなる横延伸装置を用いて幅方向に延伸し，フィルムワインダー等でによって巻き取られることは公知である。
【００１９】
本発明では、製膜・延伸条件として、このような樹脂の溶融・押出し条件、キャスティング条件、長手方向延伸条件、幅方向延伸条件、熱固定条件、巻き条件等を適宣選択できる。また本発明では、幅方向延伸、冷却、熱固定工程が連接している場合や、上記工程間に長手方向あるいは幅方向あるいは長手／幅両方向の再延伸工程 及び弛緩 または定長熱処理工程が含まれる場合は当然含まれる。さらに、長手方向へ延伸後幅方向に延伸する製造方法以外の延伸方式も本発明に含まれる。例えば、長手方向に延伸後 幅方向に延伸してフイルムを更に再長手方向に延伸する方式、長手方向の多段延伸方式、などその要旨を越えない限り上記に限定されるものではない。
【００２０】
本発明の特徴である二軸延伸ポリエステルフィルムの幅方向延伸方法を詳細に説明する。
【００２１】
本願発明では、長手方向に延伸された一軸延伸ポリエステルフィルムを横延伸装置を用いて幅方向に延伸する際、フィルムを熱風で加熱し、さらにフィルムにかかる熱風の風量を幅方向で変化させることが必要である。
【００２２】
このとき、幅方向延伸工程でフィルムの幅方向に温度分布を付与するのが好ましい。
【００２３】
長手方向に延伸された一軸延伸ポリエステルフィルムを横延伸装置を用いて幅方向に延伸する際、横延伸装置のフイルム温度は、フィルムの幅方向中央部でガラス転移温度〜融点未満の温度、好ましくは１１０℃〜１８０℃であり、さらに好ましくは、１４０℃〜１６０℃である。さらに、フィルムの幅方向両端部は、中央部に比べ１℃以上３０℃以下の温度差分熱風の風量が多くなるようにするのが好ましい。
【００２４】
フィルム温度を中央部より高温にするフィルム両端部割合は、フィルム全幅に対して５％以上３０％以下が好ましい。フィルムの幅方向中央部の温度がガラス転移温度未満の低温では、幅方向延伸性が悪く破断が多発し、かつ、幅方向延伸に起因する幅方向の厚み斑が増大し好ましくなく、また、フィルムの幅方向中央部の温度が融点近傍以上の高温では、厚み斑が増加し好ましくない。また、フィルムの幅方向両端部の温度差を中央部に比べ１℃未満にすると、本発明によるフィルム幅方向の物性差を均一化する効果が低減し好ましくなく、フィルムの幅方向両端部の温度差が中央部に比べ３０℃を越えるとフィルム幅方向両端部の熱結晶化が進行し破断が多発し、かつ、横方向の厚み斑が増大し好ましくない。また、フィルム温度を中央部より高温にするフィルム両端部のフィルム全幅に対する割合が５％未満では、本発明による、フィルム幅方向の物性差を均一化する効果が低減し、かつ 幅方向延伸による変化がクリップの極近傍に極度に集中するため破断が多発し好ましくなく、フィルム温度を中央部より高温にするフィルム両端部のフィルム全幅に対する割合が３０％を越えると、フィルム幅方向の物性差が均一化される幅方向の割合が低減し好ましくない。
【００２５】
フィルムを熱風で加熱し、さらにフィルムにかかる熱風の風量を幅方向で変化させる方法としては、フィルム幅方向に全幅加熱することができるスリット状の熱風を出す装置の中央より端部のスリット幅を１．１倍〜２．５倍に広げる方法、フィルム幅方向に全幅加熱する事ができる多孔穴状の熱風を出す装置の中央より端部の熱風を出す穴の総面積が１．１倍〜２．５倍になるよう穴をあける方法、フィルム幅方向に全幅加熱する事ができるスリット状または多孔穴状の熱風を出す装置の中央部に遮蔽板を設置する方法が好ましい。
【００２６】
幅方向延伸倍率は、２．５倍以上である。幅方向延伸倍率が２．５倍未満では、横方向の強度が低くなり、かつ、幅方向延伸に起因する横方向の厚み斑が増大し好ましくない。より好ましくは３．０倍以上である。
【００２７】
また、上記加熱方法によるフイルム幅方向の温度の制御は、テンター内にフィルム幅方向またはフィルム流れ方向に対し仕切り板を設けることでより精度の高い制御が可能となる。また、上記加熱方法によって加熱されたフィルムを計測するには、赤外線放射温度計を用いて測定する方法、熱電対を横延伸装置内でフィルムに接触させながら測定する方法等を選択することで行うことが出来る。
【００２８】
【作用】
本発明によれば、ポリエステルフィルムを幅方向に延伸する際、横方向延伸装置内で幅方向フィルム端部の温度を中央部より高温にすることで、フィルム端部の幅方向延伸応力を強制的に減少させる事により、本来 長手方向一軸延伸後の長手方向一軸延伸フィルムで生じていた幅方向の中央部と端部の物性差を小さくし 均一に幅方向に延伸することによって、幅方向延伸過程に発生するボーイングを抑制することが出来る。
【００２９】
【実施例】
次に 本発明を実施例によって具体的に説明する。なお、実施例及び比較例の評価に用いた測定方法は次の通りである。
【００３０】
１．ボーイング
本発明の効果確認のためボーイングを評価した。ボーイングは、横延伸装置に入る前の長手方向一軸延伸フィルムの表面に幅方向に直線を描き、最終的に得られた弓形の状況を、
Ｂ＝ｂ／Ｗ×１００ （％）
ここで、Ｂ＝ボーイング（％）
Ｗ＝フィルム幅（ｍｍ）
ｂ＝ボーイング線の最大凹量（ｍｍ）
によって算出した。
【００３１】
２．厚みムラ
本発明の効果確認のため厚み斑を評価した。厚み斑は、二軸延伸ポリエステルフィルムを長手方向、幅方向にそれぞれ２ｍ×５ｃｍの短冊状に切断し、安立電機（株）製厚さ計Ｋ３０６Ｃを用い厚み形状を測定し、下記式により１ｍ当たりの厚み斑を算出し、これを５回繰り返して平均値を厚み斑とした。
厚み斑（％）＝（最大厚み−最小厚み）／平均厚み×１００
【００３２】
３．熱収縮率
フィルムの中央部、及び 中央から両側にそれぞれ幅方向に４５％(フィルムの全幅を１００％として) 離れた位置のフィルムを，２３℃×６５％ＲＨの雰囲気中で、幅方向に１５mm、長さ方向に２００mmの寸法にカットし、標線間の寸法（Ｌ0）を読取顕微鏡によって正確に測定した後、１５０℃のオーブン内３０分間入れ、オーブンからフィルムを出した後、２３℃×６５％ＲＨの雰囲気中に１５分以上 放置して平衡に達してから前期標線間の寸法（Ｌ1）を測定し、次式より求めた。
熱収縮率（％）＝ [（Ｌ0−Ｌ1）／Ｌ0] × １００
【００３３】
４．熱収縮率の斜め差
フィルムの中央部、及び端部すなわち中央から両側にそれぞれ幅方向に４５％(フィルムの全幅を１００％として) 離れた位置のフイルムについてフィルム幅方向に対して斜め４５°と１３５°方向の熱収縮率を測定し、その差を求めた。
測定サンプルは上記斜め方向に沿って幅１５mm×長さ２００mmの寸法にカットし、１５０℃のオーブン内に３０分間入れ、オーブンからフィルムを出した後、２３℃×６５％ＲＨの雰囲気中に15分以上放置してから寸法を測定し、処理前の寸法に対する収縮率を求めた。各斜め方向の収縮率の差の絶対値を熱収縮率の斜め差とした。
熱収縮率の斜め差が大きいフィルムほど高温に晒された時にカールしやすいなどの不具合が生じる。
【００３４】
５．熱収縮応力
フィルムの中央部、及び端部すなわち中央から両側にそれぞれ幅方向に45%(フィルムの全幅を100%として) 離れた位置の幅方向延伸直後フィルムを、23℃×65%RHの雰囲気中で，幅方向に4mm，長手方向に10mmの寸法にカットし、厚みＴ(mm)を測定した。それをセイコー電子工業(株) SSC-5200型を用いて長さを固定したまま 5℃／分で昇温して熱収縮力 Ｇ(N)を測定し、次式より熱収縮応力を求めた。
熱収縮応力（Ｎ/mm2）＝ Ｇ／(４×Ｔ)
【００３５】
製膜状況は、２時間、同一条件で二軸延伸し、破断回数を調べた。
【００３６】
（実施例１）
十分に乾燥した無機滑剤を０．１重量%含むポリエチレンテレフタレートペレット(極限粘度０．６２)を押し出し機に供給し、２８５℃で溶融し、Ｔダイよりフィルム状に押し出し、直流高電圧を印加した電極を用いて冷却ロールに静電密着させ冷却固化せしめて厚さ２００μmの無配向フィルムを得た。横延伸工程でフィルムをクリップに把持しやすいようにするため、この無配向フィルムの端部の厚さは中央部の厚さの１．５倍にした。
無配向フィルムを長手方向に７５℃で３．８倍に延伸し、その後 横延伸装置によって幅方向に４．０倍延伸し、熱固定および５％の幅方向弛緩処理を施した後に冷却し二軸延伸ポリエステルフィルムとした。横延伸装置内における温度は、予熱温度を熱風吹き付けによりフイルム全幅で１００℃、延伸温度を熱風吹き付けによりフイルム中央部で１４０℃、また幅方向にスリット状から熱風を吹き出す装置の中央に遮蔽率８０％の遮蔽板を設置。フィルム幅方向中央部と端部で５℃の温度差がつくようにした。幅方向延伸後のフィルム幅方向温度は横延伸工程後、赤外線放射温度計を用いて測定した。熱固定温度は、熱風吹き付けによりフイルム全幅で２３５℃とした。
また この横延伸装置は幅方向延伸と熱固定の間に中間ゾーンが設置されている。そこにフィルムを巻き取るロールが設置されてあり、そこで幅方向延伸直後のフィルムを採取することができる。またここでの幅方向フィルム端部とは、全幅に対して２０％の幅を左右両クリップより中央部に均等に分割した幅を示す。つまりフィルム幅方向中央位置に６０％遮蔽した事になる。その後、通常のようにしてフィルムを巻き取った。
【００３７】
（実施例２）
横延伸装置内で幅方向延伸温度を１５０℃とする以外は実施例１と同様にして二軸延伸ポリエステルフィルムを得た。
【００３８】
（実施例３）
横延伸装置内で幅方向延伸温度を１５０℃とし、幅方向にスリット状から熱風を吹き出す装置の中央に遮蔽率１００％の遮蔽板を設置。フィルム幅方向中央部と端部で７℃の温度差がつくようにした以外は実施例１と同様にして二軸延伸ポリエステルフィルムを得た。
【００３９】
（実施例４）
横延伸装置内で幅方向に遮蔽する位置を、フィルム幅方向全幅の中央位置２０％とする以外は実施例１と同様にして二軸延伸ポリエステルフィルムを得た。
【００４０】
（比較例１）
横延伸装置内の幅方向にフィルムを延伸する際、中央に遮蔽板を使用せずに幅方向で温度差を設けない以外は実施例１と同様にして2軸配向ポリエステルフィルムを得た。
【００４１】
実施例と比較例における製膜条件とフィルム評価結果を表１に示す。
【００４２】
【表１】
【発明の効果】
本発明によれば、幅方向延伸でのボーイング現象が抑制し、熱収縮率の斜め差が小さく、厚み斑も小さな二軸延伸ポリエステルフィルムを破断の少ない状態で製造できることがわかる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a uniform biaxially stretched thermoplastic film. More specifically, the present invention relates to a method for producing a biaxially stretched polyester film having a uniform property in the width direction by suppressing the bowing phenomenon that occurs when the film is stretched in the width direction and heat-set by a transverse stretching apparatus.
[0002]
[Prior art]
Polyester films, especially biaxially stretched polyester films, are widely used for base materials for magnetic recording, electronic / electrical materials, and various packaging materials because of their excellent mechanical strength and thermal dimensional stability. It is desirable that the same physical property value be obtained in any part in the width direction of the film.
[0003]
However, it has been extremely difficult to make the physical properties in the width direction of the product film uniform by the conventional manufacturing method. The reason for this is that both ends of the film are held by clips in the transverse stretching apparatus in the stretching process, and the longitudinal stretching stress generated by the width direction stretching and the shrinkage stress generated by the heat, and the shrinkage stress generated by the heat setting process. Is restrained by the clip as the gripping means at the end of the film, whereas the central part of the film has a low influence of the gripping means and the restraining force becomes weak, and is gripped by the clip due to the above stress. This is because the central portion of the film is delayed with respect to the end portion.
[0004]
And in the case where the width direction stretching and heat setting are continuously performed with the same transverse stretching apparatus, if a straight line is drawn along the width direction on the surface of the film before entering the transverse stretching apparatus, this straight line is transversely stretched. It is deformed in the apparatus and deformed into a convex shape in the region at the beginning of the stretching process with respect to the film traveling direction, returns to a straight line in the region immediately before the end of the stretching step, and deformed into a concave shape after the stretching step. Further, the concave deformation reaches a maximum value in the region of the heat setting process, and the curve does not change as it is and passes through the subsequent horizontal stretching apparatus, and the concave deformation remains in the film exiting the horizontal stretching apparatus. This phenomenon is called a bowing phenomenon. This bowing phenomenon causes the physical properties of the film to be uneven in the width direction. Due to the bowing phenomenon, an orientation main axis inclined with respect to the longitudinal direction is generated in the film at both ends in the width direction, and the angle of the orientation main axis tends to be different in the width direction.
[0005]
As a result, for example, the difference in physical property value in the direction of ± 45 ° from the longitudinal direction of the heat shrinkage rate differs in the width direction of the film. Taking the packaging application as an example, this bowing phenomenon causes troubles such as printing pitch shift, occurrence of spots, curling, and meandering in the printing lamination process and the bag making process. More specifically, as a conventional technique for providing a cooling step between width direction stretching and heat setting, Japanese Patent Publication No. 35-11774 discloses a relaxation step of 20 ° C. to 150 ° C. between width direction stretching and heat setting step. A manufacturing method in which a substantial cooling step is provided is proposed. However, the length of the cooling process is not described at all, and the effect of suppressing the bowing phenomenon is not known at all.
[0006]
Furthermore, as a technique for suppressing or eliminating the bowing phenomenon, Japanese Patent Application Laid-Open No. 50-73978 proposes a film manufacturing method in which a nip roll group is installed between a stretching process and a heat setting process. However, in this technique, since the temperature of the intermediate zone in which the nip roll is installed is higher than the glass transition point, the improvement effect is small because the rigidity of the film at the nip point is low.
[0007]
Japanese Patent Publication No. 63-24459 proposes a process of forcibly advancing only a narrow range near the center by nip roll while gripping both end portions of the film after completion of transverse stretching. However, in this technology, it is necessary to install the nip roll in a high temperature region in the transverse stretching apparatus, the roll and its peripheral devices need to be cooled, and the film is hot, so there is a risk of scratches caused by the roll. Limited in terms.
[0008]
Japanese Patent Publication No. 62-43856 proposes a technique in which a film immediately after transverse stretching is cooled to a glass transition point or less, and then heat-fixed in multiple stages and simultaneously stretched in the width direction. However, in this technology, because the suppression of the bowing phenomenon is small in the cooling process, or because the bowing phenomenon is likely to occur again by heat setting, in addition to the cooling process, the process of heat setting in multiple stages and the complicated process of redrawing It has become. Therefore, there is a concern that it may be difficult to stably control the atmospheric humidity and film temperature in the transverse stretching apparatus over a long period of time. In this technique, the length of the cooling process is not described as in Japanese Patent Publication No. 35-11774.
[0009]
Japanese Patent Application Laid-Open No. 1-165423 proposes a technique in which a film after stretching in the width direction is cooled to a temperature equal to or lower than the stretching temperature in the width direction and then stretched again in the width direction while raising the temperature in multiple stages. However, in this technique, as in the case of Japanese Examined Patent Publication No. 62-43856, it is because the effect of suppressing the bowing phenomenon in the cooling process is small, or because the bowing is likely to occur in the heat setting process, in addition to the cooling process. Thus, it is a complicated process of heat fixing in multiple stages and re-stretching. Therefore, there is concern that it may be difficult to stably control the atmospheric temperature and the film temperature in the transverse stretching apparatus over a long period of time. Further, there is a description that the cooling temperature is preferably from the glass transition point to the drawing temperature. However, when the length of the cooling process and the temperature of the cooling process are above the glass transition point, it is feared that the effect of suppressing the bowing phenomenon is small, and it is assumed that the complicated process as described above must be adopted. The
[0010]
Japanese Patent Publication Nos. 1-256694 and 1-256696 propose a technique of reversing the running direction of the film to perform transverse stretching and heat fixing. However, in this technique, it is necessary to take up the film once in order to reverse the traveling direction of the film, and there is a problem that it is restricted in terms of productivity because it is an online manufacturing method.
[0011]
Furthermore, in Japanese Patent Application Laid-Open No. 32-183327, after longitudinal stretching, when transverse stretching and heat setting with a transverse stretching apparatus, only the side end portion is heat fixed above the glass transition point between the transverse stretching step and the heat fixing step. A technique for installing a preheating process at a temperature lower than the temperature has been proposed. However, with this technique, since the temperature of the preheating process must be controlled with a temperature gradient in the width direction, there is a concern that it may be difficult to control the film temperature over a long period of time. In the embodiment of this technique, it is estimated that the effect of suppressing the bowing phenomenon is small because the length of the preheating step is as short as half the film width.
[0012]
Japanese Patent Publication No. 2-45976 proposes a heat treatment method in which the heat setting process is divided into two stages and a temperature distribution is imparted in the film width direction in the second stage. However, although this technique is effective in suppressing the bowing phenomenon that occurs in the heat treatment process, it is presumed that the bowing phenomenon that occurs in the drawing process is not effective, and the effect of suppressing the bowing phenomenon that is finally obtained is small. .
[0013]
[Problems to be solved by the invention]
In order to solve this problem, an object of the present invention is to provide a production method for effective stretching in the width direction that can suppress the bowing phenomenon and obtain a polyester film having uniform physical properties in the width direction.
[0014]
The present inventors have observed the change of the bowing line in the transverse stretching apparatus, elucidated the generation process of the bowing phenomenon from various studies, and studied the means for suppressing this bowing phenomenon, and reached the present invention. That method of manufacturing a biaxially oriented polyester film of the present invention is a substantially stretched polyester film having no orientation in the longitudinal direction, then a method of producing a biaxially oriented polyester film stretched in the width direction, the hot air By installing a shielding plate at the center of the device to increase the amount of hot air applied to the film at the end in the width direction , the film temperature at the end in the film width direction is made higher than the film temperature at the center and in the width direction. It is characterized by stretching . In this case, the slit width towards the end portions than Hisashi Naka is 1.1 times to 5.0 times greater, it is preferable to heat using a device issuing a slit-shaped hot air. Furthermore, in this case, it is possible to heat the film in the width direction of the film, and the total area of the holes from which the hot air is blown out from the center is 1.1 to 5.0 times larger than the center. Ru preferably der be heated using a device issuing the hot air.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0016]
The polyester used in the present invention is a polyester such as polyethylene terephthalate, polybutylene terephthalate, or polyethylene naphthalate, and may be a mixture or copolymer polyester thereof. As the polyester, a polyester composition containing additives such as an organic or inorganic lubricant, an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent and the like is used as long as the effects of the present invention are not impaired. be able to.
[0017]
The polyester in the present invention is supplied to a known melt-extrusion apparatus represented by an extruder, and is heated and melted at a temperature above the softening point of the polyester. The melted composition is extruded from a slit-shaped die such as a T-die, closely adhered onto a cooling roll, and cooled and solidified to obtain a substantially non-oriented polyester film.
[0018]
By supplying the substantially non-oriented polyester film between a plurality of rolls, a uniaxially stretched film continuously stretched in the longitudinal direction is obtained. That is, by passing a plurality of rolls set to low peripheral speed rotation (hereinafter referred to as roll groups) and a roll group set to high peripheral speed rotation, the film is tensioned by the speed difference of each roll group in the longitudinal direction. Stretch.
It is known that a uniaxially stretched film obtained by stretching in the longitudinal direction is stretched in the width direction using a transverse stretching apparatus comprising preheating, stretching, heat setting, and cooling steps, and wound by a film winder or the like.
[0019]
In the present invention, as the film forming / stretching conditions, such resin melting / extrusion conditions, casting conditions, longitudinal direction stretching conditions, width direction stretching conditions, heat setting conditions, winding conditions, and the like can be appropriately selected. Further, in the present invention, when the stretching in the width direction, cooling, and heat setting are connected, the redrawing step in the longitudinal direction or the width direction or both the longitudinal / width directions and the relaxation or constant length heat treatment step are included between the above steps. The case is of course included. Furthermore, a stretching method other than the manufacturing method of stretching in the width direction after stretching in the longitudinal direction is also included in the present invention. For example, a method of stretching in the longitudinal direction and then stretching in the width direction to further stretch the film in the re-longitudinal direction, a multistage stretching method in the longitudinal direction, and the like are not limited to the above as long as they do not exceed the gist.
[0020]
The width direction stretching method of the biaxially stretched polyester film, which is a feature of the present invention, will be described in detail.
[0021]
In the present invention, when a uniaxially stretched polyester film stretched in the longitudinal direction is stretched in the width direction using a transverse stretching apparatus, the film is heated with hot air, and the amount of hot air applied to the film can be changed in the width direction. is necessary.
[0022]
At this time, it is preferable to provide a temperature distribution in the width direction of the film in the width direction stretching step.
[0023]
When the uniaxially stretched polyester film stretched in the longitudinal direction is stretched in the width direction using a transverse stretching apparatus, the film temperature of the transverse stretching apparatus is a temperature lower than the glass transition temperature to the melting point at the center in the width direction of the film, preferably It is 110 degreeC-180 degreeC, More preferably, it is 140 degreeC-160 degreeC. Furthermore, it is preferable that both ends in the width direction of the film have a larger amount of temperature difference hot air of 1 ° C. or more and 30 ° C. or less than the center portion.
[0024]
The ratio of both ends of the film that makes the film temperature higher than the center is preferably 5% or more and 30% or less with respect to the entire width of the film. At a low temperature where the temperature in the center of the film in the width direction is lower than the glass transition temperature, the width direction stretchability is poor and breakage frequently occurs, and the uneven thickness in the width direction due to the width direction stretching increases, which is not preferable. When the temperature in the center in the width direction is higher than the melting point, the thickness unevenness increases, which is not preferable. Further, if the temperature difference at both ends in the width direction of the film is less than 1 ° C. compared to the central portion, the effect of uniformizing the physical property difference in the film width direction according to the present invention is reduced, which is not preferable. If the difference exceeds 30 ° C. compared to the central portion, thermal crystallization at both ends in the film width direction proceeds, breakage occurs frequently, and lateral thickness unevenness increases, which is not preferable. In addition, when the ratio of the film both ends at which the film temperature is higher than the central portion to the total film width is less than 5%, the effect of uniforming the physical property difference in the film width direction according to the present invention is reduced, and the change by stretching in the width direction Are concentrated in the very vicinity of the clip, causing many breaks, which is undesirable, and when the ratio of the film end to the total width of the film exceeds 30%, the physical property difference in the film width direction is uniform. The ratio in the width direction is reduced, which is not preferable.
[0025]
As a method of heating the film with hot air and changing the air volume of the hot air applied to the film in the width direction, the slit width at the end from the center of the device that emits slit-like hot air that can be heated in the film width direction is used. 1.1 times to 2.5 times widening method, the total area of the hole that emits hot air at the end from the center of the device that emits hot air in the form of a porous hole that can be heated in the full width direction in the film width direction is 1.1 times The method of making a hole so that it may become 2.5 times, and the method of installing a shielding plate in the center part of the apparatus which emits a slit-like or perforated hole-like hot air that can be heated in the film width direction are preferable.
[0026]
The draw ratio in the width direction is 2.5 times or more. If the stretching ratio in the width direction is less than 2.5 times, the strength in the lateral direction is lowered, and uneven thickness in the lateral direction due to stretching in the width direction increases, which is not preferable. More preferably, it is 3.0 times or more.
[0027]
Further, the temperature in the film width direction by the heating method can be controlled with higher accuracy by providing a partition plate in the film width direction or the film flow direction in the tenter. Moreover, in order to measure the film heated by the said heating method, it performs by selecting the method of measuring using an infrared radiation thermometer, the method of measuring while contacting a thermocouple with a film within a transverse stretching apparatus, etc. I can do it.
[0028]
[Action]
According to the present invention, when the polyester film is stretched in the width direction, the width direction stretching stress of the film end is forced by setting the temperature of the width direction film end to a temperature higher than the center in the transverse direction stretching apparatus. By reducing the physical property difference between the central part and the end part in the width direction, which originally occurred in the uniaxially stretched film in the longitudinal direction after the uniaxial stretching in the longitudinal direction. Boeing that occurs in can be suppressed.
[0029]
【Example】
Next, the present invention will be specifically described with reference to examples. In addition, the measuring method used for evaluation of an Example and a comparative example is as follows.
[0030]
1. Boeing was evaluated to confirm the effect of the present invention. Boeing draws a straight line in the width direction on the surface of the uniaxially stretched film in the longitudinal direction before entering the transverse stretching apparatus, and finally the arcuate situation obtained,
B = b / W × 100 (%)
Where B = Boeing (%)
W = film width (mm)
b = Maximum concave amount of the Boeing line (mm)
Calculated by
[0031]
2. Thickness unevenness Thickness spots were evaluated to confirm the effect of the present invention. Thickness unevenness is obtained by cutting a biaxially stretched polyester film into 2 mx 5 cm strips each in the longitudinal direction and width direction, measuring the thickness shape using an Anritsu Electric Co., Ltd. thickness gauge K306C, The thickness unevenness was calculated, and this was repeated 5 times to obtain the average value as the thickness unevenness.
Thickness unevenness (%) = (maximum thickness−minimum thickness) / average thickness × 100
[0032]
3. The film at the center of the heat shrinkage film and 45% in the width direction on both sides from the center (with the total width of the film as 100%) is 15 mm in the width direction in an atmosphere of 23 ° C. × 65% RH. After cutting to 200 mm in the length direction and measuring the dimension between the marked lines (L 0 ) accurately with a reading microscope, it was placed in an oven at 150 ° C. for 30 minutes, and the film was taken out of the oven, then 23 ° C. The size (L 1 ) between the previous marked lines was measured after standing for 15 minutes or more in an atmosphere of × 65% RH and reaching equilibrium, and was calculated from the following equation.
Thermal contraction rate (%) = [(L 0 −L 1 ) / L 0 ] × 100
[0033]
4). 45% diagonally with respect to the film width direction with respect to the film width direction of 45% in the width direction (with the total width of the film as 100%) at the center and the edge, that is, both sides from the center. The thermal contraction rate in the 135 ° direction was measured, and the difference was obtained.
The measurement sample was cut into a dimension of width 15 mm × length 200 mm along the above oblique direction, placed in an oven at 150 ° C. for 30 minutes, and the film was removed from the oven, and then placed in an atmosphere of 23 ° C. × 65% RH. The dimensions were measured after being allowed to stand for at least minutes, and the shrinkage ratio relative to the dimensions before the treatment was determined. The absolute value of the difference in shrinkage rate in each oblique direction was defined as the oblique difference in heat shrinkage rate.
A film having a larger oblique difference in thermal shrinkage causes problems such as easier curling when exposed to high temperatures.
[0034]
5. The film immediately after stretching in the width direction at 45% in the width direction (with the total width of the film as 100%) at the center and edges, i.e. both sides from the center, of the heat shrinkage stress film, at 23 ° C x 65% RH Inside, it was cut into a dimension of 4 mm in the width direction and 10 mm in the longitudinal direction, and the thickness T (mm) was measured. The heat shrinkage force G (N) was measured by raising the temperature at 5 ° C / min with the length fixed using Seiko Electronics Co., Ltd. SSC-5200 type, and the heat shrinkage stress was calculated from the following equation. .
Thermal shrinkage stress (N / mm 2 ) = G / (4 × T)
[0035]
The state of film formation was biaxially stretched under the same conditions for 2 hours, and the number of breaks was examined.
[0036]
(Example 1)
Polyethylene terephthalate pellets (intrinsic viscosity 0.62) containing 0.1% by weight of a sufficiently dried inorganic lubricant were supplied to an extruder, melted at 285 ° C., extruded into a film form from a T die, and a DC high voltage was applied. The electrode was electrostatically adhered to a cooling roll and solidified by cooling to obtain a non-oriented film having a thickness of 200 μm. In order to make it easy to grip the film with the clip in the transverse stretching step, the thickness of the end portion of the non-oriented film was 1.5 times the thickness of the central portion.
The non-oriented film was stretched 3.8 times in the longitudinal direction at 75 ° C., then stretched 4.0 times in the width direction by a transverse stretching apparatus, subjected to heat setting and 5% width direction relaxation treatment, and then cooled and cooled. An axially stretched polyester film was obtained. The temperature in the transverse stretching apparatus is a preheating temperature of 100.degree. C. for the entire film width by blowing hot air, a stretching temperature of 140.degree. % Shielding plate installed. A temperature difference of 5 ° C. was made between the central part and the end part in the film width direction. The film width direction temperature after stretching in the width direction was measured using an infrared radiation thermometer after the transverse stretching step. The heat fixing temperature was set to 235 ° C. in the whole film width by blowing hot air.
In this transverse stretching apparatus, an intermediate zone is installed between stretching in the width direction and heat setting. The roll which winds up a film there is installed, and the film immediately after width direction extending | stretching can be extract | collected there. Moreover, the width direction film edge part here shows the width | variety which divided | segmented 20% of width | variety equally into the center part from both right and left clips. In other words, 60% is shielded at the central position in the film width direction. Thereafter, the film was wound up as usual.
[0037]
(Example 2)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the widthwise stretching temperature was 150 ° C. in the transverse stretching apparatus.
[0038]
(Example 3)
In the transverse stretching device, the stretching temperature in the width direction is set to 150 ° C., and a shielding plate having a shielding rate of 100% is installed at the center of the device that blows hot air from the slit shape in the width direction. A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that a temperature difference of 7 ° C. was applied between the central part and the end part in the film width direction.
[0039]
Example 4
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the position shielded in the width direction in the transverse stretching apparatus was set to 20% of the center position of the entire width in the film width direction.
[0040]
(Comparative Example 1)
When the film was stretched in the width direction in the transverse stretching apparatus, a biaxially oriented polyester film was obtained in the same manner as in Example 1 except that a central plate was not used and no temperature difference was provided in the width direction.
[0041]
Table 1 shows film forming conditions and film evaluation results in Examples and Comparative Examples.
[0042]
[Table 1]
【The invention's effect】
According to this invention, it turns out that the bowing phenomenon by width direction extending | stretching is suppressed, the diagonal difference of a thermal contraction rate is small, and a biaxially stretched polyester film with a small thickness spot can be manufactured in a state with few fractures.
Claims (4)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001107269A JP4810747B2 (en) | 2001-04-05 | 2001-04-05 | Method for producing biaxially stretched polyester film |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001107269A JP4810747B2 (en) | 2001-04-05 | 2001-04-05 | Method for producing biaxially stretched polyester film |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2002301763A JP2002301763A (en) | 2002-10-15 |
| JP4810747B2 true JP4810747B2 (en) | 2011-11-09 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2001107269A Expired - Fee Related JP4810747B2 (en) | 2001-04-05 | 2001-04-05 | Method for producing biaxially stretched polyester film |
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| JP (1) | JP4810747B2 (en) |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5247070A (en) * | 1975-10-13 | 1977-04-14 | Mitsubishi Plastics Ind | Method for elongation of linear polyester films |
| JPS6079916A (en) * | 1983-10-11 | 1985-05-07 | Mitsubishi Monsanto Chem Co | Heating method of thermoplastic resin film |
| JPS61143115A (en) * | 1984-12-17 | 1986-06-30 | Oji Yuka Gouseishi Kk | Method for cooling thermoplastic resin film |
| JPH0596619A (en) * | 1991-10-08 | 1993-04-20 | Mitsubishi Heavy Ind Ltd | Film stretching machine |
| JPH07253638A (en) * | 1994-01-31 | 1995-10-03 | Fuji Photo Film Co Ltd | Photographic polyester substrate and its film forming method |
| JP3828950B2 (en) * | 1995-12-15 | 2006-10-04 | 東芝機械株式会社 | Method for calculating position corresponding to die bolt on biaxially stretched film and method for controlling thickness of biaxially stretched film using the same calculation method |
| JPH10142735A (en) * | 1996-11-15 | 1998-05-29 | Fuji Photo Film Co Ltd | Polyester supporter and silver halide photographic sensitive material using it |
| JP2000062019A (en) * | 1998-08-17 | 2000-02-29 | Toray Ind Inc | Method and apparatus for preparing stretched film |
-
2001
- 2001-04-05 JP JP2001107269A patent/JP4810747B2/en not_active Expired - Fee Related
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| Publication number | Publication date |
|---|---|
| JP2002301763A (en) | 2002-10-15 |
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