JP3569989B2 - Method for producing biaxially oriented polyamide film - Google Patents
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Description
【０００１】
【産業上の利用分野】
本発明は、縦横逐次２軸延伸方法による２軸配向ポリアミドフィルムの製造法に関する。さらに詳しくは、幅方向に均一な物理的、化学的及び物理化学的性質を有する２軸配向ポリアミドフィルムの製造法に関するものである。
【０００２】
【従来の技術】
従来より２軸配向ポリアミドフィルムは、強靱性、高ガスバリヤー性、対ピンホール性、透明性、易印刷性などの諸特性が優れているため、スープ、こんにゃく、ハンバーグ、みそ、ハムなどを始めとする液状食品、水物食品、冷凍食品、レトルト食品、ペースト状食品、畜肉水産食品などの袋包装用材料として広く用いられている。
一般に、２軸配向フィルムの製造法として、縦横逐次２軸延伸法が知られており、ポリアミドフィルムに関してもこれが利用されている。
【０００３】
【発明が解決しようとする課題】
しかしながら、縦横逐次２軸延伸法は、フィルム幅方向の物性にバラツキが生じ易いことが知られている。この理由は、横延伸工程のテンター内で、横延伸による縦方向の応力と熱によって縦方向の収縮応力が生じる。ところで、フィルムの両端部はクリップに把持され拘束されているのに対し、フィルムの中央部は把持手段の影響力が弱く、拘束力が弱くなっている。従って、上記した応力の影響によってクリップで把持されている両端部に対してフィルム中央部分の走行速度が両端部に比べて遅れるため、幅方向に物性のバラツキが生じる。袋包装用材料に供されるポリアミドフィルムは、幅方向に物性、例えば沸水収縮率の斜め差等のバラツキが大きいと、製袋後の加熱処理等において、捻れ現象の原因となり、重大なトラブルとなる。
【０００４】
この問題を回避しようとすれば、縦延伸の倍率を下げ、上記した応力を低減することが有効であるが、縦方向の強度を損なうという別の問題が発生するのみならず、生産速度の低下につながり、工業生産上好ましくない。
【０００５】
本発明の目的は、逐次２軸延伸法における、横延伸工程で発生するフィルムの幅方向の物性のバラツキを低減する２軸配向ポリアミドフィルムの製造法を提供することにある。詳しくは、生産速度を下げることなくかつ縦延伸倍率を下げることなく、沸水収縮率の斜め差等の物性のフィルム幅方向のバラツキを低減する延伸方法を提供することにある。
【０００６】
【課題を解決するための手段】
上記課題に鑑み本発明者らが鋭意研究を行なった結果、ついに本発明に到達した。
すなわち本発明は、実質的に未配向のポリアミドシートを縦方向に延伸し、ついで横方向に延伸して得られるポリアミドフィルムの逐次２軸延伸方法において、縦延伸後のフィルムの中央部縦方向の熱収縮応力の最大値が０．６ｋｇ／ｍｍ2 以下になるように、縦延伸を〔ポリアミドのガラス転移温度（Ｔｇ）＋２０〕℃以上、〔ポリアミドの低温結晶化温度（Ｔｃ）＋２０〕℃以下の温度で、前段と後段の２段階に分けて行い、該前段（第１段目）の縦延伸での縦延伸倍率が１．１〜２．９倍であり、該後段（第２段目）の縦延伸において総合縦延伸倍率が３．０倍以上４．０倍以下となるよう調整され、かつ該後段の縦延伸はロールにフィルムを０．０１秒以上０．７０秒以下の間密着延伸させることを特徴とする２軸配向ポリアミドフィルムの製造法に関する。
【０００７】
本発明の方法は、ポリアミドフィルムの製造に適用され、特にナイロン６を主成分とするポリアミドから２軸配向フィルムを製造するのに好適である。該ポリアミドとして、例えばナイロン６、ナイロン６にナイロン塩などを少量共重合させた共重合体、ナイロン６とナイロン塩などとのブレンドなどが挙げられる。ナイロン塩としては、ヘキサメチレンジアミンとアジピン酸またはイソフタル酸とのナイロン塩、メタキシリレンジアミンとアジピン酸とのナイロン塩などが挙げられる。
上記ポリアミドにはその性質を損なわない範囲で、少量の各種耐ブロッキング剤、帯電防止剤、安定剤など公知の添加剤を含有させてもよい。
【０００８】
本発明によれば、実質的に未配向のポリアミドシートを縦に２段延伸し、続いて横延伸し、更に熱固定することによって２軸配向ポリアミドフィルムを得る。さらに詳しく言えば、実質的に未配向のポリアミドシートを縦延伸するにあたり、縦延伸を２段階で分け、縦延伸後のフィルムの中央部縦方向の熱収縮応力の最大値が０．６ｋｇ／ｍｍ２ 以下になるように、縦延伸の第１段と第２段の延伸倍率と延伸温度を調整しかつ第２段目の縦延伸の延伸ロールにフィルムを一定時間密着させて延伸する。ついで横延伸し、更に熱固定する。
【０００９】
以下、本発明による２軸配向ポリアミドフィルムの製造法を詳細に説明する。上記ポリアミド原料は、乾燥したのち、押出機により溶融押出し、口金より回転ドラム上にキャストして急冷固化し、ポリアミドシートを得る。このポリアミドシートは、実質的に未配向状態である。
【００１０】
このシートをまず〔原料ポリアミドのガラス転移温度（Ｔｇ）＋２０〕℃以上、〔原料ポリアミドの低温結晶化温度（Ｔｃ）＋２０〕℃以下の温度で、第１段目の縦延伸を行なう。ここで低温結晶化温度（Ｔｃ）とは、ガラス状態から加熱により起こる結晶化温度である。
該縦延伸を（原料ポリアミドのＴｇ＋２０）℃未満の温度で行なうと、ネッキングを生じ厚み斑が増大しやすくなる。一方、（原料ポリアミドのＴｃ＋２０）℃を越える温度で延伸を行なうと、熱結晶化が進行し、横延伸で破断しやすくなり好ましくない。より好ましい延伸温度は、（原料ポリアミドのＴｇ＋３０）℃〜（原料ポリアミドのＴｃ＋１０）℃である。
この第１段目の縦延伸での延伸倍率（延伸後のフィルムの走行速度／延伸前のフィルムの走行速度）が低すぎると延伸効果が得られず、逆に高すぎると配向結晶化が進行し厚み斑が増大しやすく、後述する第２段目延伸での延伸応力が高くなりすぎ破断したり、あるいは横延伸での破断につながることになる。さらに後述する縦延伸後のフィルムの中央部縦方向の熱収縮応力の最大値が、０．６ｋｇ／ｍｍ２ を越え、２軸配向フィルムの幅方向の物性のバラツキが大きくなる。この観点から、第１段目の縦延伸での延伸倍率は１．１〜２．９倍が好ましい。より好ましい延伸倍率は、１．５〜２．５倍である。
第１段目縦延伸には、熱ロール延伸、赤外線輻射延伸など公知の縦延伸方法を用いることができる。
【００１１】
この第１段目延伸後、引続き第２段目延伸を行なう。第２段目縦延伸には、熱ロール延伸を用いる。
第２段目の縦延伸でフィルムを延伸ロールに０．０１秒以上、０．７０秒以下、密着させて延伸させることが本発明の特徴の１つである。
該第２段目延伸において、延伸ロールにフィルムを密着させる時間を０．７０秒より長い時間密着させると、熱結晶化が進行し、横延伸応力が増大し、破断が頻発する。さらに、横方向の厚み斑も悪化し、かつ縦延伸後のフィルムの中央部縦方向の熱収縮応力の最大値が０．６ｋｇ／ｍｍ２ を越え、２軸配向フィルムの幅方向の物性のバラツキが大きくなる。一方密着時間が０．０１秒より短い場合、配向結晶化が進行し、横延伸応力が増大し、破断が頻発する。さらに延伸開始点が縦横両方向で不安定となり、縦横両方向の厚み斑も悪化し、かつ縦延伸後のフィルムの中央部縦方向の熱収縮応力の最大値が０．６ｋｇ／ｍｍ２ を越え、２軸配向フィルムの幅方向の物性のバラツキが大きくなる。好ましい密着時間は、０．１０秒以上０．３０秒以下である。
密着延伸させるには、幾何学的なロール配置、ロールの径、材質、粗さの各パラメータを考慮することで行う。
例えば、フィルムとの離型性の小さなロール材質でロール表面粗さを小さくし、ロール間距離を短くし、ロール径を大きくすることで、より密着延伸をしやすくする。
【００１２】
第２段目の縦延伸の延伸倍率は、総合縦延伸倍率が３．０倍以上、４．０倍以下となるように調整する。３．０倍未満であると２軸配向フィルムの幅方向の物性のバラツキは小さくなるものの、縦方向の強度が小さくなる。縦延伸倍率が４．０倍を超えると、２軸配向フィルムの幅方向の物性のバラツキを低減させる効果が発現しない場合もでてくる。さらに、縦延伸後のフィルムの中央部縦方向の熱収縮応力の最大値を０．６ｋｇ／ｍｍ２ を越え、２軸配向フィルムの幅方向の物性のバラツキが分布が大きくなる傾向がある。これを考慮すると、好ましい総合縦延伸倍率は、３．０〜３．８倍であり、より好ましくは、３．３〜３．６倍である。
【００１３】
第２段目縦延伸での延伸温度も、（原料ポリアミドのＴｇ＋２０）℃〜（原料ポリアミドのＴｃ＋２０）℃である。該延伸温度が（原料ポリアミドのＴｇ＋２０）℃未満では、延伸応力が高くなり横延伸で破断しやすくなる。一方（原料ポリアミドのＴｃ＋２０）℃を越えると、厚み斑が大きくなる。より好ましくは、（原料ポリアミドのＴｇ＋２５）℃〜（原料ポリアミドのＴｃ＋１０）℃である。
【００１４】
このようにして得られた１軸配向フィルムの中央部縦方向の熱収縮応力の最大値は、０．６ｋｇ／ｍｍ２ 以下である。熱収縮応力とは、加熱により発生する収縮時の単位断面積当たりの応力である。
該熱収縮応力の最大値が０．６ｋｇ／ｍｍ２ を越えると、２軸配向フィルムの幅方向の物性のバラツキが大きくなる。好ましくは、０．４０ｋｇ／ｍｍ２ 以下である。この場合のサンプリングは、１軸延伸後ステンター直前で巻き取り機を用いて行う。
【００１５】
得られた１軸配向フィルムは、次にステンターを用いて横方向に延伸する。ここで、横延伸温度が低すぎると、横延伸性が悪化（破断発生）する場合があり、一方高すぎると厚み斑が大きくなる傾向がある。このような点から、横延伸温度は１００℃〜融点未満の温度が好ましく、１００℃〜１８０℃がより好ましい。また、横方向の強度を確保する点から、横延伸倍率は３．０倍以上が好ましく、３．５倍以上がさらに好ましい。
このようにして得られた２軸配向フィルムは、熱固定され、巻取られる。
【００１６】
上記したように、本発明の方法によれば、縦延伸を２段階に分けて行い、かつ第２段目の延伸で、フィルムをロールに０．０１〜０．７０秒間、密着させて延伸させ、縦延伸後のフィルムの中央部縦方向の熱収縮応力の最大値を０．６ｋｇ／ｍｍ２ 以下とすることによって、幅方向の物性のバラツキの小さい２軸配向ポリアミドフィルムを得ることができる。その理由は、縦延伸を２段階に分割することによる延伸応力の削減効果のみならず、第２段目延伸でロール上に特定の時間密着させることで、第１段目延伸で発生した延伸応力を緩和させる効果があるからである。さらに、特定の条件下で縦延伸されたフィルムの中央部縦方向の熱収縮応力の最大値が０．６ｋｇ／ｍｍ２ 以下とすることにより、横延伸時に発生する縦方向の熱収縮応力を低減することが可能となり、横延伸時に横方向の配向形成が容易となり、かつ発現した横配向を熱固定時においても歪めることなく処理することができるためである。しかも横延伸応力低減により延伸性が向上するためと考えられる。
【００１７】
【実施例】
以下、実施例に基づき詳細に説明するが、本発明が下記実施例に限定されないことは言うまでもない。なお、実施例、比較例中に用いられるフィルム温度、物性値及び特性は、以下のように測定され、かつ定義される。
【００１８】
ガラス転移温度（Ｔｇ）及び低温結晶化温度（Ｔｃ）
未配向ポリアミドシートを液体窒素中で凍結し、減圧解凍後にセイコー電子製ＤＳＣを用い、昇温速度１０℃／分で測定した。
【００１９】
熱収縮応力
縦２段延伸後の１軸配向フィルムを、３０℃×１．０ｍｍＨｇ以下に調整された真空乾燥機内で６時間以上乾燥し、それを取り出し直ちにデシケーターを用いて、２０℃×３０％ＲＨの環境下で２４時間以上調整した後、セイコー電子工業（株）製ＴＭＡのＳＳＣ ５０２０を用い、昇温速度１０℃／分で測定した。
【００２０】
フィルム温度（延伸温度）
縦延伸における温度は、ミノルタ（株）製放射温度計ＩＲ−００４を用いフィルムの温度を測定した。
横延伸における温度は、レイテック・ジャパン（株）製の放射温度計ＲＨＰ３を用いフィルムの温度を測定した。
【００２１】
厚み斑
２軸配向ポリアミドフィルムを縦方向、横方向にそれぞれ１ｍ×５ｃｍの短冊状に切断し、安立電気（株）製厚さ計Ｋ３０６Ｃを用い厚み形状を測定する。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、平均値を厚み斑とした。
【００２２】
【数１】
沸水収縮率斜め差
２軸配向ポリアミドフィルムを全幅の中央から左右に全幅の４０％の位置（端部）から、それぞれ２１ｃｍ角に切り出しサンプルとする。各々のサンプルの中央を中心とする直径２０ｃｍの円を描き、縦方向を０°としたときの４５°及び１３５°方向に円の中心を通る直線を引き、各方向の直径を測定し、処理前の長さとする。
このサンプルを沸騰水中で３０分間加熱処理したのち取り出して、表面に付着した水分を除去、風乾する。
風乾後、各方向の直径を測定し、処理後の長さとする。下記式を用い沸水収縮率を算出する。
【００２４】
【数２】
縦方向を０°としたときの４５°と１３５°方向の沸水収縮率の差の絶対値を求め、両端部の平均値を沸水収縮率斜め差とした。
【００２６】
製膜状況
２時間、実施例１に記載した条件と同一条件でフィルムを逐次２軸延伸した。その間フィルムが破断するとすぐに製膜、延伸し、破断回数を調べた。
【００２７】
実施例１
ナイロン６ペレット〔相対粘度（ＲＶ）＝２．８〕を真空乾燥した後、これを押出し機に供給し２６０℃で溶融し、Ｔ型ダイよりシート状に押し出し、直流高電圧を印可して冷却ロール上に静電気的に密着させ、冷却固化せしめて厚さ２００μｍの未配向シートを得た。このシートのＴｇは４０℃、Ｔｃは６８℃であった。
このシートをまず５０℃の温度で予熱処理を行い、ついで、延伸温度７７℃で１．７倍に第１段目の縦延伸をした後、第２段目の延伸ロールに０．２０秒密着させ延伸温度７２℃で総合延伸倍率が３．４倍となるように第２段目の縦延伸を行い、引続きこのシートを連続的にステンターに導き、１３０℃で４倍に横延伸し、２１０℃で熱固定および５％の横弛緩処理を施した後に冷却し、両縁部を裁断除去して、２軸配向ポリアミドフィルムを得た。このときの製膜状況、フィルムの物性、特性を表１に示す。
【００２８】
実施例２
縦延伸の総合延伸倍率を３．１にする以外はすべて実施例１と同様にして２軸配向ポリアミドフィルムを得た。
【００２９】
実施例３
縦延伸の総合延伸倍率を３．７にする以外はすべて実施例１と同様にして２軸配向ポリアミドフィルムを得た。
【００３０】
実施例４
縦延伸の第２段目の延伸ロールとその後の冷却ロールの配置を変更し、第２段目の延伸ロールに０．０５秒密着させる以外はすべて実施例１と同様にして２軸配向ポリアミドフィルムを得た。
【００３１】
実施例５
縦延伸の第２段目の延伸ロールとその後の冷却ロールの配置を変更し、第２段目の延伸ロールに０．５０秒密着させる以外はすべて実施例１と同様にして２軸配向ポリアミドフィルムを得た。
【００３２】
比較例１
縦延伸の総合延伸倍率を４．１にする以外はすべて実施例１と同様にして２軸配向ポリアミドフィルムを得た。
【００３３】
比較例２
縦延伸の第１段目倍率を３．２にする以外はすべて実施例１と同様にして２軸配向ポリアミドフィルムを得た。
【００３４】
比較例３
縦延伸の第２段目でロールに密着させずに延伸する以外はすべて実施例１と同様にして２軸配向ポリアミドフィルムを得た。
【００３５】
比較例４
縦延伸の第２段目の延伸ロールとその後の冷却ロールの配置を変更し、第２段目の延伸ロールに０．８０秒密着させる以外はすべて実施例１と同様にして２軸配向ポリアミドフィルムを得た。
【００３６】
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。
【００３７】
【表１】
【発明の効果】
本発明の製造法によれば、破断なく、厚み斑が小さく、沸水収縮率の斜め差を小さくすることができ、縦横逐次延伸による２軸配向ポリアミドフィルムの製造法には、きわめて有効である。[0001]
[Industrial applications]
The present invention relates to a method for producing a biaxially oriented polyamide film by a longitudinal and lateral sequential biaxial stretching method. More specifically, the present invention relates to a method for producing a biaxially oriented polyamide film having uniform physical, chemical and physicochemical properties in the width direction.
[0002]
[Prior art]
Conventionally, biaxially oriented polyamide film has excellent properties such as toughness, high gas barrier property, anti-pinhole property, transparency, and easy printability, and has been used for soup, konjac, hamburger, miso, ham, etc. It is widely used as a bag packaging material for liquid foods, aquatic foods, frozen foods, retort foods, pasty foods, animal meat and fishery foods.
In general, a longitudinal and horizontal sequential biaxial stretching method is known as a method for producing a biaxially oriented film, and this is also used for a polyamide film.
[0003]
[Problems to be solved by the invention]
However, it is known that the longitudinal and horizontal sequential biaxial stretching method tends to cause variations in physical properties in the film width direction. The reason for this is that in the tenter in the transverse stretching step, longitudinal stress due to transverse stretching and heat in the longitudinal direction cause contraction stress in the longitudinal direction. By the way, while both ends of the film are gripped and restrained by the clip, the central portion of the film is weakly affected by the gripping means, and the restraining force is weak. Therefore, the running speed of the central portion of the film is slower than that of both ends gripped by the clip due to the influence of the above-described stress, and thus the physical properties vary in the width direction. Polyamide film used for bag packaging material has a large variation in physical properties in the width direction, for example, an oblique difference in boiling water shrinkage ratio, which causes a twisting phenomenon in a heat treatment after bag making, causing serious trouble. Become.
[0004]
In order to avoid this problem, it is effective to reduce the above-mentioned stress by reducing the stretching ratio in the longitudinal stretching, but another problem of impairing the strength in the longitudinal direction occurs, and the production speed decreases. It is not preferable for industrial production.
[0005]
An object of the present invention is to provide a method for producing a biaxially oriented polyamide film that reduces variations in physical properties in the width direction of a film generated in a transverse stretching step in a sequential biaxial stretching method. More specifically, it is an object of the present invention to provide a stretching method for reducing variations in physical properties such as oblique difference in boiling water shrinkage ratio in a film width direction without lowering a production rate and a longitudinal stretching ratio.
[0006]
[Means for Solving the Problems]
In view of the above problems, the present inventors have conducted intensive research and, as a result, have finally reached the present invention.
That is, the present invention relates to a method for sequentially biaxially stretching a polyamide film obtained by stretching a substantially unoriented polyamide sheet in the longitudinal direction and then stretching it in the transverse direction. The longitudinal stretching is performed so that the maximum value of the heat shrinkage stress is 0.6 kg / mm 2 or less [the glass transition temperature of the polyamide (Tg) +20] ° C. or more, and the low-temperature crystallization temperature of the polyamide (Tc) +20] ° C. or less. At a temperature of the first stage and the second stage , the longitudinal stretching ratio in the first stage (first stage) is 1.1 to 2.9 times, and the second stage (second stage) ) In the longitudinal stretching, the total longitudinal stretching ratio is adjusted to be 3.0 times or more and 4.0 times or less, and in the subsequent longitudinal stretching, the film is adhered to the roll for 0.01 seconds to 0.70 seconds. Biaxially oriented polyamide film characterized by being stretched Lum relates to a process for the preparation of.
[0007]
The method of the present invention is applied to the production of a polyamide film, and is particularly suitable for producing a biaxially oriented film from a polyamide containing nylon 6 as a main component. Examples of the polyamide include nylon 6, a copolymer obtained by copolymerizing a small amount of nylon 6 with nylon 6, a blend of nylon 6 with a nylon salt, and the like. Examples of the nylon salt include a nylon salt of hexamethylenediamine and adipic acid or isophthalic acid, and a nylon salt of metaxylylenediamine and adipic acid.
The polyamide may contain a small amount of various known additives, such as various antiblocking agents, antistatic agents and stabilizers, as long as the properties are not impaired.
[0008]
According to the present invention, a biaxially oriented polyamide film is obtained by vertically stretching a substantially unoriented polyamide sheet in two steps, subsequently stretching it in the horizontal direction, and further heat setting. More specifically, when the substantially unoriented polyamide sheet is longitudinally stretched, the longitudinal stretching is divided into two stages, and the maximum value of the heat shrinkage stress in the central longitudinal direction of the film after the longitudinal stretching is 0.6 kg / mm. The stretching ratio and stretching temperature of the first and second stages of longitudinal stretching are adjusted so as to be 2 or less, and the film is stretched by being in close contact with a stretching roll of the second stage of longitudinal stretching for a certain time. Then, it is stretched in the horizontal direction and further heat-set.
[0009]
Hereinafter, a method for producing a biaxially oriented polyamide film according to the present invention will be described in detail. After the polyamide raw material is dried, it is melt-extruded by an extruder, cast from a die on a rotating drum, quenched and solidified to obtain a polyamide sheet. This polyamide sheet is in a substantially unoriented state.
[0010]
The sheet is first subjected to the first-stage longitudinal stretching at a temperature of [glass transition temperature (Tg) of raw material polyamide (Tg) +20] ° C. and [low temperature crystallization temperature of raw material polyamide (Tc) +20] ° C. or less. Here, the low-temperature crystallization temperature (Tc) is a crystallization temperature caused by heating from a glassy state.
When the longitudinal stretching is performed at a temperature lower than (Tg of raw material polyamide + 20) ° C., necking is caused and unevenness in thickness tends to increase. On the other hand, if the stretching is performed at a temperature exceeding (Tc + 20 of the raw material polyamide) ° C., thermal crystallization proceeds, and it is easy to break in the transverse stretching, which is not preferable. A more preferred stretching temperature is (Tg of raw polyamide + 30) ° C. to (Tc of raw polyamide + 10) ° C.
If the stretching ratio (running speed of the film after stretching / running speed of the film before stretching) in the first-stage longitudinal stretching is too low, the stretching effect cannot be obtained, and if it is too high, the orientation crystallization proceeds. The thickness unevenness tends to increase, and the stretching stress in the second-stage stretching described later becomes too high, resulting in breakage or in transverse stretching. Furthermore, the maximum value of the heat shrinkage stress in the central longitudinal direction of the film after longitudinal stretching described later exceeds 0.6 kg / mm 2, and the variation in physical properties in the width direction of the biaxially oriented film becomes large. From this viewpoint, the stretching ratio in the first-stage longitudinal stretching is preferably 1.1 to 2.9 times. A more preferred stretching ratio is 1.5 to 2.5 times.
For the first-stage longitudinal stretching, a known longitudinal stretching method such as hot roll stretching or infrared radiation stretching can be used.
[0011]
After the first-stage stretching, the second-stage stretching is subsequently performed. For the second-stage longitudinal stretching, hot roll stretching is used.
One of the features of the present invention is that the film is brought into close contact with a stretching roll for 0.01 second or more and 0.70 second or less in the second-stage longitudinal stretching, and stretched.
In the second-stage stretching, if the time for bringing the film into close contact with the stretching roll is longer than 0.70 seconds, thermal crystallization proceeds, the transverse stretching stress increases, and breakage frequently occurs. In addition, the thickness unevenness in the horizontal direction is worsened, and the maximum value of the heat shrinkage stress in the central portion of the film after the longitudinal stretching exceeds 0.6 kg / mm 2, and the variation in the physical properties in the width direction of the biaxially oriented film. Becomes larger. On the other hand, if the adhesion time is shorter than 0.01 second, oriented crystallization proceeds, the transverse stretching stress increases, and breakage frequently occurs. Further, the stretching start point becomes unstable in both the vertical and horizontal directions, the thickness unevenness in both the vertical and horizontal directions worsens, and the maximum value of the heat shrinkage stress in the central longitudinal direction of the film after the longitudinal stretching exceeds 0.6 kg / mm 2 , Variations in physical properties in the width direction of the axially oriented film are increased. A preferred contact time is 0.10 seconds or more and 0.30 seconds or less.
The contact stretching is performed by taking into account the respective parameters of the geometric roll arrangement, the roll diameter, the material, and the roughness.
For example, by using a roll material having a small releasability from a film, the roll surface roughness is reduced, the distance between the rolls is reduced, and the roll diameter is increased, so that the contact stretching can be more easily performed.
[0012]
The stretching ratio of the second-stage longitudinal stretching is adjusted so that the total longitudinal stretching ratio is 3.0 times or more and 4.0 times or less. When the ratio is less than 3.0 times, the variation in physical properties in the width direction of the biaxially oriented film is reduced, but the strength in the vertical direction is reduced. If the longitudinal stretching ratio exceeds 4.0 times, the effect of reducing the variation in physical properties in the width direction of the biaxially oriented film may not be exhibited. Furthermore, the maximum value of the heat shrinkage stress in the longitudinal direction at the center of the film after longitudinal stretching exceeds 0.6 kg / mm 2, and the distribution of physical properties in the width direction of the biaxially oriented film tends to be large. In consideration of this, the preferable total longitudinal stretching ratio is 3.0 to 3.8 times, and more preferably 3.3 to 3.6 times.
[0013]
The stretching temperature in the second-stage longitudinal stretching is also (Tg of raw polyamide + 20) ° C. to (Tc of raw polyamide + 20) ° C. If the stretching temperature is lower than (Tg of the raw material polyamide + 20) ° C., the stretching stress is increased, and the film is easily broken by transverse stretching. On the other hand, if it exceeds (Tc + 20 of the raw material polyamide) ° C., thickness unevenness becomes large. More preferably, the temperature is (Tg of raw polyamide + 25) ° C. to (Tc of raw polyamide + 10) ° C.
[0014]
The maximum value of the heat shrinkage stress in the central longitudinal direction of the uniaxially oriented film thus obtained is 0.6 kg / mm 2 or less. The heat shrinkage stress is a stress generated by heating per unit sectional area during shrinkage.
When the maximum value of the heat shrinkage stress exceeds 0.6 kg / mm 2 , the variation in physical properties in the width direction of the biaxially oriented film becomes large. Preferably, it is 0.40 kg / mm 2 or less. In this case, sampling is performed using a winding machine immediately after the uniaxial stretching and immediately before the stenter.
[0015]
The obtained uniaxially oriented film is then stretched in the transverse direction using a stenter. Here, if the transverse stretching temperature is too low, the transverse stretchability may deteriorate (breakage may occur), while if too high, the thickness unevenness tends to increase. From such a point, the transverse stretching temperature is preferably from 100 ° C to less than the melting point, more preferably from 100 ° C to 180 ° C. In addition, from the viewpoint of securing the strength in the transverse direction, the transverse stretching ratio is preferably 3.0 times or more, and more preferably 3.5 times or more.
The biaxially oriented film thus obtained is heat-set and wound up.
[0016]
As described above, according to the method of the present invention, longitudinal stretching is performed in two stages, and in the second stage of stretching, the film is stretched in close contact with a roll for 0.01 to 0.70 seconds. By setting the maximum value of the heat shrinkage stress in the central portion in the longitudinal direction of the film after longitudinal stretching to 0.6 kg / mm 2 or less, a biaxially oriented polyamide film having small variations in physical properties in the width direction can be obtained. The reason is not only the effect of reducing the stretching stress by dividing the longitudinal stretching into two stages, but also the stretching stress generated in the first stage stretching by making it adhere to the roll for a specific time in the second stage stretching. This is because there is an effect of alleviating this. Furthermore, by setting the maximum value of the heat shrinkage stress in the longitudinal direction at the center of the film stretched under specific conditions to 0.6 kg / mm 2 or less, the heat shrinkage stress in the longitudinal direction generated during the transverse stretching is reduced. This makes it possible to easily form a lateral orientation at the time of lateral stretching, and to treat the developed lateral orientation without distortion even at the time of heat setting. Moreover, it is considered that the stretching property is improved by reducing the transverse stretching stress.
[0017]
【Example】
Hereinafter, the present invention will be described in detail with reference to Examples, but it goes without saying that the present invention is not limited to the following Examples. In addition, the film temperature, physical property values, and characteristics used in Examples and Comparative Examples are measured and defined as follows.
[0018]
Glass transition temperature (Tg) and low temperature crystallization temperature (Tc)
The unoriented polyamide sheet was frozen in liquid nitrogen, thawed under reduced pressure, and measured at a rate of temperature increase of 10 ° C./min using a DSC manufactured by Seiko Denshi.
[0019]
The uniaxially oriented film after the heat-shrinkage stress longitudinal two-step stretching is dried in a vacuum drier adjusted to 30 ° C. × 1.0 mmHg or less for 6 hours or more, and is taken out and immediately used at 20 ° C. × 30% using a desiccator. After adjusting for 24 hours or more in an environment of RH, the measurement was performed at a heating rate of 10 ° C./min using SSC 5020 of TMA manufactured by Seiko Electronic Industry Co., Ltd.
[0020]
Film temperature (stretching temperature)
The temperature in the longitudinal stretching was measured by using a radiation thermometer IR-004 manufactured by Minolta Co., Ltd.
For the temperature in the transverse stretching, the temperature of the film was measured using a radiation thermometer RHP3 manufactured by Raytec Japan Co., Ltd.
[0021]
The biaxially oriented polyamide film with uneven thickness is cut into strips of 1 m × 5 cm each in the vertical and horizontal directions, and the thickness shape is measured using a thickness gauge K306C manufactured by Anritsu Electric Co., Ltd. The thickness unevenness per meter was calculated by the following formula, and this was repeated five times, and the average value was regarded as the thickness unevenness.
[0022]
(Equation 1)
A biaxially oriented polyamide film having an oblique difference in boiling water shrinkage is cut into 21 cm square samples at positions (ends) of 40% of the entire width from the center of the entire width to the left and right. Draw a circle with a diameter of 20 cm centering on the center of each sample, draw straight lines passing through the center of the circle in 45 ° and 135 ° directions when the vertical direction is 0 °, measure the diameter in each direction, process It will be the previous length.
The sample is heat-treated in boiling water for 30 minutes, taken out, removed of water adhering to the surface, and air-dried.
After air-drying, the diameter in each direction is measured, and the measured length is used. The boiling water shrinkage is calculated using the following equation.
[0024]
(Equation 2)
The absolute value of the difference between the boiling water shrinkage in the 45 ° and 135 ° directions when the vertical direction was set to 0 ° was obtained, and the average value of both ends was defined as the oblique difference in the boiling water shrinkage.
[0026]
The film was successively biaxially stretched for 2 hours under the same conditions as described in Example 1 for 2 hours. As soon as the film was broken, the film was formed and stretched, and the number of breaks was examined.
[0027]
Example 1
Nylon 6 pellets [relative viscosity (RV) = 2.8] are vacuum-dried, then supplied to an extruder, melted at 260 ° C., extruded into a sheet from a T-die, and cooled by applying a high DC voltage. The non-oriented sheet having a thickness of 200 μm was obtained by electrostatically adhering it on a roll and solidifying it by cooling. The Tg of this sheet was 40 ° C. and the Tc was 68 ° C.
This sheet is first preheat-treated at a temperature of 50 ° C., then stretched at a stretching temperature of 77 ° C. 1.7 times in the first stage, and then adhered to a stretching roller of the second stage for 0.20 seconds. The second stage of longitudinal stretching was performed at a stretching temperature of 72 ° C. so that the total stretching ratio was 3.4 times. Subsequently, the sheet was continuously guided to a stenter, and laterally stretched 4 times at 130 ° C. After heat setting at 5 ° C. and 5% transverse relaxation treatment, the mixture was cooled, and both edges were cut off to obtain a biaxially oriented polyamide film. Table 1 shows the state of film formation, physical properties and characteristics of the film at this time.
[0028]
Example 2
A biaxially oriented polyamide film was obtained in the same manner as in Example 1 except that the total stretching ratio in longitudinal stretching was set to 3.1.
[0029]
Example 3
A biaxially oriented polyamide film was obtained in the same manner as in Example 1 except that the total stretching ratio in longitudinal stretching was changed to 3.7.
[0030]
Example 4
A biaxially oriented polyamide film was prepared in the same manner as in Example 1 except that the arrangement of the second-stage stretching roll and the subsequent cooling roll in longitudinal stretching was changed, and the two-stage stretching roll was adhered to the second-stage stretching roll for 0.05 seconds. Got.
[0031]
Example 5
A biaxially oriented polyamide film was prepared in the same manner as in Example 1 except that the arrangement of the second-stage stretching roll and the subsequent cooling roll in longitudinal stretching was changed, and the second-stage stretching roll was brought into close contact for 0.50 seconds. Got.
[0032]
Comparative Example 1
A biaxially oriented polyamide film was obtained in the same manner as in Example 1 except that the total stretching ratio in longitudinal stretching was set to 4.1.
[0033]
Comparative Example 2
A biaxially oriented polyamide film was obtained in the same manner as in Example 1 except that the first-stage magnification in longitudinal stretching was set to 3.2.
[0034]
Comparative Example 3
A biaxially oriented polyamide film was obtained in the same manner as in Example 1 except that in the second stage of longitudinal stretching, the film was stretched without adhering to a roll.
[0035]
Comparative Example 4
A biaxially oriented polyamide film was prepared in the same manner as in Example 1 except that the arrangement of the second-stage stretching roll and the subsequent cooling roll in longitudinal stretching was changed, and the roll was closely adhered to the second-stage stretching roll for 0.80 seconds. Got.
[0036]
Table 1 shows film forming conditions and film evaluation results in Examples and Comparative Examples.
[0037]
[Table 1]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the manufacturing method of this invention, a thickness unevenness is small without breaking, and the diagonal difference of boiling water shrinkage rate can be made small, and it is very effective for the manufacturing method of the biaxially oriented polyamide film by longitudinal and transverse sequential stretching.
Claims (1)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP928795A JP3569989B2 (en) | 1995-01-24 | 1995-01-24 | Method for producing biaxially oriented polyamide film |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP928795A JP3569989B2 (en) | 1995-01-24 | 1995-01-24 | Method for producing biaxially oriented polyamide film |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH08197620A JPH08197620A (en) | 1996-08-06 |
| JP3569989B2 true JP3569989B2 (en) | 2004-09-29 |
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| JP928795A Expired - Fee Related JP3569989B2 (en) | 1995-01-24 | 1995-01-24 | Method for producing biaxially oriented polyamide film |
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| JP (1) | JP3569989B2 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2001341198A (en) * | 2000-06-02 | 2001-12-11 | Unitika Ltd | Biaxially stretched polyamide film and method for manufacturing the same |
| JP4710126B2 (en) * | 2000-12-05 | 2011-06-29 | 東洋紡績株式会社 | Method for producing biaxially stretched polyamide film |
| JP4386001B2 (en) * | 2004-06-02 | 2009-12-16 | 東洋紡績株式会社 | Polyamide-based resin laminated film roll and method for producing the same |
| JP4386000B2 (en) * | 2004-06-02 | 2009-12-16 | 東洋紡績株式会社 | Polyamide-based resin laminated film roll and method for producing the same |
| JP3671978B1 (en) * | 2004-06-02 | 2005-07-13 | 東洋紡績株式会社 | Polyamide-based resin film roll and manufacturing method thereof |
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