JP2004195773A - Biaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film which has good dimensional stability at the time of processing of the film and is excellent in the coating processing properties of a magnetic layer in particular at the time of processing of a magnetic tape, traveling durability when adapted to the production of the magnetic tape, storage stability and electromagnetic conversion characteristics. <P>SOLUTION: The biaxially oriented polyester film is characterized in that the heat-shrinkage factor in the width direction thereof under a 100°C/30 min condition is -0.4-0%, a crystal size χc in the thickness direction thereof is 50-80 Å, the modulus of elasticity Ym in the longitudinal direction of the film is 6-15 GPa, and the ratio Ym/Yt of the modulus of elasticity Ym in the longitudinal direction and the modulus of elasticity Yt in the width direction is 1.2-2.5. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

２ｃｍ×２ｃｍに切り出して、方向をそろえて重ね合わせ、コロジオン・エタノール溶液で固めた試料をセットして、広角Ｘ線回折測定で得られた２θ／θ強度データのうち、各方向の面の半価幅から、下記のＳｃｈｅｒｒｅｒの式を用いて計算した。ここで厚み方向の結晶サイズは、配向主方向に垂直な方向（１００面）を測定した。
【００５９】
結晶サイズχｃ（Å）＝Ｋλ／β_Oｃｏｓθ_B
Ｋ ：定数（＝１．０）
λ ：Ｘ線の波長（＝１．５４１８Å）
θ_B ：ブラック角
β_O ＝（β_E ²−β_I ²）^1/2
β_E ：みかけの半価幅（実測値）
β_I ：装置定数（＝１．０４６×１０^-2）
（３）弾性率
ＡＳＴＭ−Ｄ８８２に規定された方法に従って、オリエンテック（株）製フイルム強伸度自動測定装置“テンシロンＡＭＦ／ＲＴＡ−１００”を用いて、幅１０ｍｍ、試長１００ｍｍのサンプルを、温度２３℃、湿度６５％ＲＨ、引張り速度１０ｍｍ／分の条件で、５回測定を行い、その平均値をとった。
【００６０】
（４）厚みむら
アンリツ（株）製フィルムシックネステスタ「ＫＧ６０１Ａ」及び電子マイクロメーター「Ｋ３０６Ｃ」を用いて、長手方向に、３０ｍｍ幅、１０ｍ長でサンプリングした支持体サンプルについて、厚みを搬送速度３ｍ／分で連続的に測定する。この測定結果から、１０ｍ長における厚みの最大値をＴｍａｘ、最小値をＴｍｉｎ、厚み平均値をＴａｖｅとし、Ｒ＝Ｔｍａｘ−Ｔｍｉｎを求め、ＲとＴａｖｅから下記式により厚みむら（％）を求めた。
【００６１】
厚みむら（％）＝（Ｒ／Ｔａｖｅ）×１００
（５）ｘ／Ｌ
白色光を光源として偏光顕微鏡を用い、その消光値から配向主軸とフィルム幅方向との狭角を求め、これを配向角（°）とする。この配向角をフィルム幅方向の全幅について測定し、フィルム幅方向における配向角の最大値と最小値の差ｘ（°）を求める。この配向角の差ｘ（°）のフィルム幅Ｌ（ｍ）に対する比の値ｘ／Ｌ（°／ｍ）を求める。なお、配向主軸は幅方向を０°、幅方向と垂直な方向（長手方向）を９０°とした。
【００６２】
（６）表面粗さＲａ
小坂研究所製の高精度薄膜段差測定器ＥＴ−１０を用いて、触針先端半径０．５ｍ、触針荷重５ｍｇ、測定長１ｍｍ、カットオフ値０．０８ｍｍでの中心線平均粗さＲａを、フィルム幅方向に走査して、２０回測定を行ない、その平均値をとる。
【００６３】
（７）幅寸法変化率
２３℃、６５％ＲＨの雰囲気下において、試料長（フィルム長手方向）：１４３ｍｍ、幅：３１ｍｍの支持体サンプルを、２４時間調湿調温した後、大日本印刷（株）製クロムマスク上の中央に、サンプルを貼り付け、光学顕微鏡を用いて、幅方向の寸法（Ａｍｍ）を測定する。その後、サンプルを、４９℃、９０％ＲＨの雰囲気中に、長手方向に３２ＭＰａの荷重をかけた状態で、７２時間放置する。７２時間放置後、荷重を解放し、２３℃、６５％ＲＨの条件下にて２４時間調湿調温後、サンプル幅方向の寸法（Ｂｍｍ）を測定する。幅方向の寸法変化率は下記式により求める。なお、該測定は５回行い、５回の平均値を採用した。
【００６４】
幅寸法変化率（％）＝（（Ａ−Ｂ）／Ａ）×１００
（８）クリープコンプライアンス
二軸配向フィルムを、幅４ｍｍ、試長１５ｍｍにサンプリングし、真空理工（株）製ＴＭＡ ＴＭ−３０００および加熱制御部ＴＡ−１５００にセットし、５０℃、６５％ＲＨの条件下に調湿調温し、その時の試料フィルムの長さをＬ₀（μｍ）とした。その後２８ＭＰａの荷重を試料フィルムにかけて、３０分間保持した後の試料フィルムの長さをＬ₁（μｍ）とした。このときの試料フィルムの伸縮量から、次式より、クリープコンプライアンスを算出した。
クリープコンプライアンス（ＧＰａ^-1）＝｛（Ｌ₁−Ｌ₀）／Ｌ₀｝／０．０２８なお、測定は５回行い、５回の平均値を採用した。また、ここでいうクリープとは一定応力のもとで歪みが時間と共に増大する現象のことであり、クリープコンプライアンスとはこの歪みと一定応力の比であり、「高分子化学序論（第２版）」（（株）化学同人発行）ｐ１５０に記載されたものである。
【００６５】
（９）フィルム全厚み、及び積層厚み
透過型電子顕微鏡（日立（株）製Ｈ−６００型）を用いて、加速電圧１００ｋＶで、支持体の断面を、超薄切片（ＲｕＯ₄染色）で観察する。その界面の観察結果から、全厚み、及び積層厚みを求める。倍率は判定したい支持体の全厚み、積層厚みによって適宜倍率に設定すればよいが、一般的には全厚み測定には１千倍、積層厚み測定には１万〜１０万倍が適当である。
【００６６】
また、２次イオン質量分析装置（ＳＩＭＳ）を用いて積層厚みを測定することもできる。表層から深さ３，０００ｎｍの範囲のフィルム中の不活性粒子の内もっとも高濃度の粒子に起因する元素（Ｍ⁺）と、ポリエステルの炭素元素との濃度比（Ｍ⁺／Ｃ⁺）を、表面から深さ３，０００ｎｍまで厚さ方向にＳＩＭＳで分析する。表層では不活性粒子に起因する元素濃度は低く、表面から遠ざかるにつれて不活性粒子に起因する元素濃度は高くなる。本発明のフィルムの場合は、一旦極大値となった不活性粒子に起因する元素濃度がまた減少し始める。この濃度分布曲線において、不活性粒子に起因する元素濃度が極大値の１／２まで減少した深さを積層厚みとする。測定条件は次の通りである。
【００６７】
１）測定装置
２次元イオン質量分析装置（ＳＩＭＳ）
西独、ＡＴＯＭＩＫＡ社製 Ａ−ＤＩＤＡ３０００
２）測定条件
１次イオン種 ：O₂ ⁺
１次イオン加速電圧：１２ＫＶ
１次イオン電流 ：２００ｎＡ
ラスター領域 ：４００μｍ□
分析領域 ：ゲート３０％
測定真空度 ：５．０×１０^-9Ｔｏｒｒ
Ｅ−ＧＵＮ ：０．５ＫＶ−３．０Ａ
なお、表層から深さ３，０００ｎｍの範囲に最も多く含有する不活性粒子が有機高分子粒子の場合はＳＩＭＳでは測定し難いので、表面からエッチングしながらＸＰＳ（Ｘ線光電子分光法）、ＩＲ（赤外分光法）などで上記同様のデプスプロファイルを測定し積層厚みを求めることもできる。
【００６８】
（１０）ポリマの熱特性（ガラス転移温度、融点）
示差走査熱量計として、セイコー電子工業（株）社製のロボットＤＳＣ「ＲＤＣ２２０」を用いて、データ解析装置として、同社製ディスクステーション「ＳＳＣ／５２００」を用いて、下記条件で比熱測定を行い、ＪＩＳ Ｋ７１２１に従って融点（Ｔｍ）等を決定した。
【００６９】
測定条件
加熱温度：２７０〜５４０Ｋ（ＲＣＳ冷却法）
温度校正：高純度インジウム及びスズの融点
温度変調振幅：±１Ｋ
温度変調周期：６０秒
平均昇温速度：約１０ｍｇ
試料重量：アルミニウム製開放型容器（３３ｍｇ）
なお、ガラス転移温度（Ｔｇ）は、次式により算出した。
【００７０】
ガラス転移温度＝（補外ガラス転移開始温度＋補外ガラス転移終了温度）／２
（１１）磁気テープの走行耐久性および保存安定性
本発明の二軸配向ポリエステルフィルムの表面Ａ（原料（Ａ１）の層の表面）側に、下記組成の磁性塗料と非磁性下層塗料とをエクストルージョンコーターにより重層塗布（上層は磁性塗料で塗布厚０．２μｍ、非磁性下層の厚みは１．５μｍとした。）し、磁気配向させ、乾燥させる。次いで反対面（表面Ｂ側）に、下記組成のバックコート層を形成した後、小型テストカレンダー装置（スチール／ナイロンロール、５段）で、温度８５℃、線圧２００ｋｇ／ｃｍでカレンダー処理した後、６０℃で４８時間のキュアリングを施し、磁気記録媒体とした。
【００７１】
（磁性塗料の組成）
・強磁性金属粉末 ：１００重量部
・変成塩化ビニル共重合体 ： １０重量部
・変成ポリウレタン ： １０重量部
・ポリイソシアネート ： ５重量部
・ステアリン酸 ： １．５重量部
・オレイン酸 ： １重量部
・カーボンブラック ： １重量部
・アルミナ ： １０重量部
・メチルエチルケトン ： ７５重量部
・シクロヘキサノン ： ７５重量部
・トルエン ： ７５重量部
（バックコートの組成）
・カーボンブラック（平均粒径２０ｎｍ） ： ９５重量部
・カーボンブラック（平均粒径２８０ｎｍ）： １０重量部
・αアルミナ ： ０．１重量部
・変成ポリウレタン ： ２０重量部
・変成塩化ビニル共重合体 ： ３０重量部
・シクロヘキサノン ：２００重量部
・メチルエチルケトン ：３００重量部
・トルエン ：１００重量部
この磁気記録媒体を１／２インチ幅にスリットし、磁気テープとして、長さ６７０ｍ分を、カセットに組み込んでカセットテープとした。該カセットテープを、Ｑｕａｎｔｕｍ社製ＤＬＴ（ＩＶ）Ｄｒｉｖｅを用い、１５０時間走行させ、次の基準でテープの走行耐久性を評価した。
【００７２】
◎：テープ端面の伸び、折れ曲がりがなく、削れ跡が見られないもの。
【００７３】
○：テープ端面の伸び、折れ曲がりがないが、若干削れ跡がもられるもの。
【００７４】
△：テープ端面の伸びはないが、一部折れ曲がり、削れ跡が見られるもの。
【００７５】
×：テープ端面の一部が伸び、ワカメ状の変形が見られ、削れ跡が見られるもの。
【００７６】
また、上記作製したカセットテープをＱｕａｎｔｕｍ社製ＤＬＴ（ＩＶ）Ｄｒｉｖｅを用い、データを読み込んだ後、カセットテープを６０℃、８０％ＲＨの雰囲気中に１００時間保存した後、データを再生して次の基準で、テープの保存安定性を評価した。
【００７７】
◎：テープ幅の変化が２μｍ以下であり、トラックずれがなく、正常に再生したもの。
【００７８】
○：テープ幅の変化が２μｍを超え、４μｍ以下であり、トラックずれが無く、正常に再生したもの。
【００７９】
△：テープ幅の変化が４μｍを超え、６μｍ以下であり、トラックずれが無く、正常に再生したもの。
【００８０】
×：テープ幅の変化が４μｍを超え、読みとり不可が見られるもの。
【００８１】
（１２）磁気テープの磁性層塗布むら
磁気記録媒体を樹脂埋めし、それをダイヤモンドカッターで切り出し、その断面を透過型電子顕微鏡で観察して、磁性塗料と非磁性下層塗料の総厚みを測定し、該厚みの最大値をＭｍａｘ、最小値をＭｍｉｎ、該厚み平均値をＭａｖｅとし、Ｒ＝Ｍｍａｘ−Ｍｍｉｎを求め、ＲとＭａｖｅから下記式により磁性層むら（％）を求め、
磁性層むら（％）＝（Ｒ／Ｍａｖｅ）×１００
次の基準で磁性層塗布むらを評価した。
【００８２】
◎：磁性層むらが８％以下であるもの。
【００８３】
○：磁性層むらが８％を超え、１２％以下の範囲であるもの。
【００８４】
△：磁性層むらが１２％を超え、１５％以下の範囲であるもの。
【００８５】
×：磁性層むらが１５％を超えるもの。
【００８６】
（１３）磁気テープの電磁変換特性（Ｃ／Ｎ）
磁気記録媒体を８ｍｍ幅にスリットし、パンケーキを作製した。次いで、このパンケーキから長さ２００ｍ分の磁気テープをカセットに組み込んで、カセットテープとした。
【００８７】
該磁気テープを市販のＨｉ８用ＶＴＲ（ＳＯＮＹ社製ＥＶ−ＢＳ３０００）を用いて、７ＭＨｚ±１ＭＨｚのＣ／Ｎの測定を行った。このＣ／Ｎを市販されているＨｉ８用ＭＰビデオテープと比較して、次の通りランク付けした。
【００８８】
○：＋３ｄＢ以上のもの
△：＋１ｄＢ以上、＋３ｄＢ未満のもの
×：＋１ｄＢ未満のもの
【００８９】
【実施例】
実施例１
ＤＭＴ法による重合を行った。即ち、テレフタル酸ジメチル１９４重量部とエチレングリコール１２４重量部に、酢酸マグネシウム４水塩０．１重量部を加え、１４０〜２３０℃でメタノールを留出しつつエステル交換反応を行った。次いで、リン酸トリメチル０．０５重量部のエチレングリコール溶液、および三酸化アンチモン０．０５重量部を加えて５分間撹拌した後、生成した低重合体を３０ｒｐｍで攪拌しながら、反応系を２３０℃から２９０℃まで徐々に昇温するとともに、圧力を０．１ｋＰａまで下げた。最終温度、最終圧力到達までの時間はともに６０分とした。３時間重合反応させ所定の攪拌トルクとなった時点で反応系を窒素パージし常圧に戻して重縮合反応を停止し、重合生成物を冷水中にストランド状に吐出し、直ちにカッティングして固有粘度０．６５のポリエチレンテレフタレートのペレットとした。
【００９０】
上記方法により得られた固有粘度０．６５のポリエチレンテレフタレート（ＰＥＴ）について、ＤＳＣを用いて熱特性を測定したところ、Ｔｇ：８２℃、Ｔｍ：２５６℃であった。
【００９１】
このＰＥＴを用い、押出機２台（Ａ、Ｂ）を用いて、次の方法で製膜を行った。
【００９２】
２８５℃に加熱された押出機Ａには、実質的に不活性粒子を含有しない固有粘度０．６５のＰＥＴに平均粒径０．０７μｍのシリカ粒子を０．１重量％含有させた原料（Ａ１）を、１８０℃で３時間減圧乾燥した後に供給した。また、２８５℃に加熱した押出機Ｂには、上記した実質的に不活性粒子を含有しない固有粘度０．６５のＰＥＴに平均粒径０．３μｍの架橋ポリスチレン粒子を０．５重量％含有させた原料（Ｂ１）を、１８０℃で３時間真空乾燥した後に供給した。
【００９３】
続いて、原料（Ａ１）をサンドフィルター、１．２μｍカットの繊維焼結ステンレス金属フィルターおよび０．８μｍカットの繊維焼結ステンレス金属フィルターの順に３段階に濾過し、また、原料（Ｂ１）をサンドフィルター、３μｍカットの繊維焼結ステンレス金属フィルターの順に２段階で濾過した後、ポリマーの温度が２８５℃となるようにしてＴダイで合流させ口金からシート状に押出した。この時、ドラフト比（＝口金リップ間隙／押し出されたシート厚み）は５、ＬＤ間（口金リップと冷却ドラムとの距離）は２０ｍｍとした。さらに、このシート状押出ポリマを表面温度２５℃のキャストドラム上に、テープ状（厚み０．０４ｍｍ、幅７．２ｍｍ）の電極を用いた静電印加法により密着させて冷却固化させ、２層積層した未延伸フィルム（積層厚み比Ａ１／Ｂ１＝５／１）を作製した。
【００９４】
この得られた未延伸フィルムをロール式延伸機にて、まず、ロールの周速差を利用して長手方向に１２０℃、１．７倍に予備延伸した後、さらに長手方向に１１５℃、２．１倍に延伸し、続いて、ステンターにより幅方向に９５℃、３．３倍に延伸し、さらにロール縦延伸機を用いて１５０℃、１．９倍に再縦延伸を行った後、テンターにおいて２００℃で１．３倍に再横延伸を行った。その後、一旦、７０℃までフィルムを冷却し、引き続き、フィルムの中央部が２２０℃でフィルム端部は中央部より１０℃高くなるように温度勾配をつけて、１２秒間の熱処理を行った後、２２０℃のゾーンで幅方向に４％の弛緩率で１段目の弛緩処理を行い、次いで、１７５℃のゾーンで幅方向に３％の弛緩率で２段目の弛緩処理を行い、さらに、１００℃のゾーンで幅方向に１．５％の弛緩率で３段目の弛緩処理を行い、フィルムを室温まで徐冷して巻き取り、厚み４μｍの二軸延伸ポリエステルフィルムを作製した。なお、フィルム厚みは、押出量の調節により所望水準とした。
【００９５】
表１、２に得られた二軸配向ポリエステルフィルムの製膜条件を示す。また、表３、４に、二軸配向ポリエステルフィルムと該フィルムを支持体としたものから得られた磁気記録媒体の特性として、磁気テープの、磁性層塗布むら、走行耐久性、保存安定性、磁気変換特性を示す。
【００９６】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性に優れており、磁性層塗布むらがなく、走行耐久性、保存安定性等に優れた磁気テープとすることができた。
【００９７】
実施例２
延伸条件、熱処理条件、弛緩処理条件を表１に示す条件に変更することにした以外は実施例１と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【００９８】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性に優れており、磁性層塗布むらが少なく、走行耐久性、保存安定性等、電磁変換特性に優れた磁気テープとすることができた。
【００９９】
実施例３
弛緩処理条件を表１に示す条件に変更することにした以外は実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１００】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性に優れており、磁性層塗布むらが少なく、走行耐久性、保存安定性、電磁変換特性に優れた磁気テープとすることができた。
【０１０１】
実施例４
熱処理条件を表１に示す条件に変更することにした以外は実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１０２】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは比較的寸法安定性に優れており、走行耐久性、保存安定性、電磁変換特性に優れた磁気テープとすることができた。
【０１０３】
実施例５
熱処理条件を表１に示す条件に変更することにした以外は実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１０４】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性に優れており、磁性層塗布むらがなく、走行耐久性、保存安定性、電磁変換特性に優れた磁気テープとすることができた。
【０１０５】
実施例６
延伸条件を表１に示す条件に変更することにした以外は実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１０６】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性に優れており、磁性層塗布むらが少なく、走行耐久性、保存安定性、電磁変換特性に優れた磁気テープとすることができた。
【０１０７】
実施例７
実施例１と同様な方法で固有粘度０．８５のポリエチレンテレフタレート（ＰＥＴ）のペレット（Ｔｇ８０℃）を製造した。このＰＥＴのペレット５０重量％と、Ｇｅｎｅｒａｌ Ｅｌｅｃｔｒｉｃ（ＧＥ）社製の固有粘度０．６８のポリエーテルイミド（ＰＥＩ）”ウルテム”１０１０（Ｔｇ２１６℃）５０重量％とを、２９０℃に加熱された同方向回転タイプのベント式２軸混練押出機に供給して、ＰＥＩを５０重量％含有したブレンドチップ（Ｉ）を作製した。このブレンドチップ（Ｉ）について、ＤＳＣを用いて熱特性を測定したところ、Ｔｇ：８９℃、Ｔｍ：２５４℃であった。
【０１０８】
次いで、押出機２台（Ａ、Ｂ）を用いて、次の方法で製膜を行った。
【０１０９】
２９５℃に加熱された押出機Ａには、実施例１と同様にして得た実質的に不活性粒子を含有しない固有粘度０．６５のポリエチレンテレフタレート（ＰＥＴ）に平均粒径０．０９μｍのシリカ粒子を０．０５重量％含有させたペレット（ＩＩ）と、上記方法で得たＰＥＩを含有したブレンドチップ（Ｉ）とを８：２の比でドライブレンドした混合原料（Ａ１）を、１８０℃で３時間減圧乾燥した後に供給した。また、２９５℃に加熱した押出機Ｂには、実施例１と同様にして得た実質的に不活性粒子を含有しない固有粘度０．６５のポリエチレンテレフタレート（ＰＥＴ）に平均粒径０．３μｍの炭酸カルシウム粒子を０．５重量％含有させたペレット（ＩＩＩ）と、上記方法で得たＰＥＩを含有したブレンドチップ（Ｉ）とを８：２の比でドライブレンドした混合原料（Ｂ１）を、１８０℃で３時間減圧乾燥した後に供給した。
【０１１０】
続いて、混合原料（Ａ１）をサンドフィルター、１．２μｍカットの繊維焼結ステンレス金属フィルターおよび０．８μｍカットの繊維焼結ステンレス金属フィルターの順に３段階に濾過し、また、混合原料（Ｂ１）をサンドフィルター、３μｍカットの繊維焼結ステンレス金属フィルターの順に２段階で濾過した後、ポリマーの温度が２９５℃となるようにしてＴダイで合流させ口金からシート状に押出した。この時、ドラフト比（＝口金リップ間隙／押し出されたシート厚み）は５、ＬＤ間（口金リップと冷却ドラムとの距離）は２０ｍｍとした。さらに、このシート状押出ポリマを表面温度２５℃のキャストドラム上に、テープ状（厚み０．０４ｍｍ、幅７．２ｍｍ）の電極を用いた静電印加法により密着させて冷却固化させ、２層積層した未延伸フィルム（積層厚み比Ａ１／Ｂ１＝５／１）を作製した。
【０１１１】
この得られた未延伸フィルムをロール式延伸機にて、まず、ロールの周速差を利用して長手方向に１１８℃、１．６倍に延伸した後、さらに長手方向に１１０℃、２倍延伸し、続いて、ステンターにより幅方向に１００℃、３．３倍に延伸し、さらにロール縦延伸機を用いて１５０℃、１．７倍に再縦延伸を行った後、テンターにおいて２０５℃で１．３倍に再横延伸を行った。その後、一旦、７０℃までフィルムを冷却し、引き続き、フィルムの中央部が２２０℃でフィルム端部は中央部より１０℃高くなるように温度勾配をつけて７秒間の熱処理を行った後、２１０℃のゾーンで幅方向に４％の弛緩率で１段目の弛緩処理を行い、次いで、１６０℃のゾーンで幅方向に２％の弛緩率で２段目の弛緩処理を行い、さらに、１００℃のゾーンで幅方向に１％の弛緩率で３段目の弛緩処理を行い、フィルムを室温まで徐冷して巻き取り、厚み４μｍの二軸延伸ポリエステルフィルムを作製した。なお、フィルム厚みは、押出量の調節により所望水準とした。
【０１１２】
表１、３が示すように、得られた二軸配向ポリエステルフィルムは寸法安定性に優れており、磁性層むらが少なく、走行耐久性、保存安定性、電磁変換特性に優れた磁気テープとすることができた。
【０１１３】
実施例８
ナフタレン−２，６ジカルボン酸ジメチル１００部およびエチレングリコール６０部を、エステル交換触媒として酢酸マンガン四水塩０．０３部を使用し、１５０℃から２３８℃に徐々に昇温しながら１２０分間エステル交換反応を行った。途中、反応温度が１７０℃に達した時点で、三酸化アンチモン０．０２４部を添加し、エステル交換反応終了後、リン酸トリメチルをエチレングリコール中で１３５℃、５時間、１．１〜１．６ｋｇ／ｃｍ²の加圧下で加熱処理した溶液（燐酸トリメチル換算量で０．０２３部）を添加した。その後、反応生成物を重合反応器に移し、２９０℃まで昇温し、０．２ｍｍＨｇ以下の高減圧下にて重縮合反応を行って、２５℃のｏ−クロロフェノール溶融で測定した固有粘度が０．６１ｄｌ／ｇ、ＤＥＧ共重合量１．０ｍｏｌ％のポリエチレン２，６−ナフタレンジカルボキシレートのペレットを得た。
【０１１４】
上記方法により得られた固有粘度が０．６１ｄｌ／ｇのポリエチレン−２，６−ナフタレンジカルボキシレート（ＰＥＮ）について、ＤＳＣを用いて熱特性を測定したところ、Ｔｇ：１１９℃、Ｔｍ：２６１℃であった。
【０１１５】
このＰＥＮを用いて、押出機２台（Ａ、Ｂ）を用いて、次の方法で製膜を行った。３００℃に加熱された押出機Ａには、上記方法で得た実質的に不活性粒子を含有しない固有粘度０．６１のＰＥＮに平均粒径０．０９μｍのシリカ粒子を０．０５重量％含有させた原料（Ａ１）を、１８０℃で３時間減圧乾燥した後に供給した。また、３００℃に加熱した押出機Ｂには、上記方法で得た実質的に不活性粒子を含有しない固有粘度０．６１のＰＥＮに平均粒径０．３μｍの炭酸カルシウム粒子を０．５重量％含有させた原料（Ｂ１）を、１８０℃で３時間減圧乾燥した後に供給した。
【０１１６】
続いて、原料（Ａ１）をサンドフィルター、１．２μｍカットの繊維焼結ステンレス金属フィルターおよび０．８μｍカットの繊維焼結ステンレス金属フィルターの順に３段階に濾過し、また、原料（Ｂ１）をサンドフィルター、３μｍカットの繊維焼結ステンレス金属フィルターの順に２段階で濾過した後、ポリマーの温度が２５５℃となるようにしてＴダイで合流させ口金からシート状に押出した。この時、ドラフト比（＝口金リップ間隙／押し出されたシート厚み）は５、ＬＤ間（口金リップと冷却ドラムとの距離）は２０ｍｍとした。さらに、このシート状押出ポリマを表面温度２５℃のキャストドラム上に、テープ状（厚み０．０４ｍｍ、幅７．２ｍｍ）の電極を用いた静電印加法により密着させて冷却固化させ、２層積層した未延伸フィルム（積層厚み比Ａ１／Ｂ１＝５／１）を作製した。
【０１１７】
この得られた未延伸フィルムをロール式延伸機にて、まず、ロールの周速差を利用して長手方向に１３５℃、５．５倍に延伸し、続いて、ステンターにより幅方向に１３５℃、３．５倍に延伸し、さらにロール縦延伸機を用いて１７０℃、１．６倍に再縦延伸を行った後、テンターにおいて１８０℃で１．４倍に再横延伸を行った。その後、一旦、７０℃までフィルムを冷却し、引き続き、フィルムの中央部が２１５℃でフィルム端部は中央部より１０℃高くなるように温度勾配をつけて７秒間の熱処理を行った後、２１０℃のゾーンで幅方向に４％の弛緩率で１段目の弛緩処理を行い、次いで、１６０℃のゾーンで幅方向に２％の弛緩率で２段目の弛緩処理を行い、さらに、１００℃のゾーンで幅方向に１％の弛緩率で３段目の弛緩処理を行い、フィルムを室温まで徐冷して巻き取り、厚み４μｍの二軸延伸ポリエステルフィルムを作製した。なお、フィルム厚みは、押出量の調節により所望水準とした。
【０１１８】
表１、３が示すように、得られたフィルムの寸法安定性は比較的優れており、磁性層塗布むらも少なく、走行耐久性にも比較的優れ、保存安定性、電磁変換特性が優れた磁気テープとすることができた。
【０１１９】
比較例１
熱処理時間を５秒にし、弛緩処理を施さないことにした以外は実施例８と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１２０】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性が劣っており、保存安定性、電磁変換特性も劣った磁気テープとなった。
【０１２１】
比較例２
弛緩処理を表１に示す条件で一段のみで施すことにした以外は、実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１２２】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性が劣っており、電磁変換特性も劣った磁気テープとなった。
【０１２３】
比較例３
弛緩率を表１に示す条件で施すことにした以外は、実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１２４】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性が劣っており、保存安定性、電磁変換特性も劣った磁気テープとなった。
【０１２５】
比較例４
弛緩率を表１に示条件で二段で施すことにした以外は、実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１２６】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性が劣っており、保存安定性、電磁変換特性も劣った磁気テープとなった。
【０１２７】
比較例５
弛緩率を表１に示条件で二段で施すことにした以外は、実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。得られたフィルムは皺のあるものとなった。
【０１２８】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性が劣っており、保存安定性、電磁変換特性も劣った磁気テープとなった。
【０１２９】
比較例６
弛緩処理温度を表１に示す条件で施すことにした以外は、実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成し、これからなる支持体から実施例１と同様の方法で磁気記録媒体を作成した。
【０１３０】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性が劣っており、電磁変換特性が劣った磁気テープとなった。
【０１３１】
比較例７
熱処理条件と弛緩処理条件を表１に示す条件に変更するこにした以外は、実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成し、これからなる支持体から実施例１と同様の方法で磁気記録媒体を作成した。
【０１３２】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは結晶サイズχｃが小さく、磁性層むらがあり、電磁変換特性が劣った磁気テープとなった。
【０１３３】
比較例８
延伸条件を表１に示す条件に変更することにした以外は、実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１３４】
表１、３に示したとおり、得られた二軸配向ポリエステルフィルムは寸法安定性が劣っており、走行耐久性、電磁変換特性が劣った磁気テープとなった。
【０１３５】
実施例９
延伸条件を表１に示す条件に変更することにした以外は、実施例２と同様にして、厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１３６】
表１、３が示すように、得られたフィルムの寸法安定性は比較的優れており、磁性層塗布むらも比較的少なく、走行耐久性、保存安定性にも比較的優れ、電磁変換特性が優れた磁気テープとすることができた。
【０１３７】
実施例１０
実施例１での原料（Ａ１）と原料（Ｂ１）を口金から押出す際のドラフト比を２０に変更し、静電印加法で冷却ドラムにシートを密着させる際のテープ状の電極を、ワイヤー電極（直径：０．１５ｍｍφ）に変更した以外は実施例１と同様にして２層積層した未延伸フィルムを作成した。該未延伸フィルムを実施例２と同様にして厚み４μｍのフィルムの二軸配向ポリエステルフィルムを作成した。
【０１３８】
表２、４が示すように、得られたフィルムの寸法安定性は実施例２と比較すると若干悪いが、磁性層むらも比較的少なく、走行耐久性、保存安定性、電磁変換特性も比較的良好な磁気テープとなった。
【０１３９】
実施例１１
実施例２でのフィルムを再横延伸した後の熱処理を、フィルムの端部から中央部にかけて温度勾配をかけずに、２１５℃で熱処理することにした以外は実施例２と同様にして厚み４μｍの二軸配向ポリエステルフィルムを作成した。
【０１４０】
表２、４が示すように、得られたフィルムの寸法安定性は実施例２と比較すると若干悪いが、磁性層むらも比較的少なく、走行耐久性、保存安定性、電磁変換特性も比較的良好な磁気テープとなった。
【０１４１】
実施例１２
実施例１での原料（Ｂ１）中に配合した粒子を、平均粒径０．０４μｍのシリカ粒子を０．０５重量％含有と変更した以外は実施例１と同様にして２層積層した未延伸フィルムを作成した。該未延伸フィルムを実施例２と同様にして、厚み４μｍの二軸延伸ポリエステルフィルムを作製した。
【０１４２】
表２、４が示すように、得られたフィルムは寸法安定性は優れており、磁性層むらも少なく、走行耐久性、保存安定性、電磁変換特性に優れた磁気テープとすることができた。
【０１４３】
実施例１３
実施例１での原料（Ａ１）中に配合した粒子を、平均粒径０．０３μｍのシリカ粒子を０．３重量％含有と変更した以外は実施例１と同様にして２層積層した未延伸フィルムを作成した。該未延伸フィルムを実施例２と同様にして、厚み４μｍの二軸延伸ポリエステルフィルムを作製した。
【０１４４】
表２、４が示すように、得られたフィルムは寸法安定性に優れており、磁性層むらも少なく、保存安定性に優れた磁気テープとすることができた。
【０１４５】
実施例１４
実施例１での原料（Ａ１）中に配合した粒子を、粒子径０．０３μｍのアルミナ粒子を０．３重量％と粒子径０．４μｍの架橋ポリスチレン粒子を０．５重量％とを含有と変更した以外は実施例１と同様にして２層積層した未延伸フィルムを作成した。該未延伸フィルムを実施例２と同様にして、厚み４μｍの二軸延伸ポリエステルフィルムを作製した。
【０１４６】
表２、４が示すように、得られたフィルムは寸法安定性に優れており、走行耐久性、保存安定性に優れた磁気テープとすることができた。
【０１４７】
実施例１５
実施例１での原料（Ｂ１）中に配合した粒子を、平均粒径１．２μｍの炭酸カルシウム粒子を０．５重量％含有と変更した以外は実施例１と同様にして２層積層した未延伸フィルムを作成した。該未延伸フィルムを実施例２と同様にして、厚み４μｍの二軸延伸ポリエステルフィルムを作製した。
【０１４８】
表２、４が示すように、得られた支持体は寸法安定性に優れており、磁性層むらも少なく、保存安定性、電磁変換特性に優れた磁気テープとすることができた。
【０１４９】
【表１】

【０１５０】
【表２】

【０１５１】
【表３】

【０１５２】
【表４】

【０１５３】
【発明の効果】
二軸配向ポリエステルフィルムにおいて、幅方向の熱収縮率、厚み方向の結晶サイズχｃ、フィルム長手方向の弾性率Ｙｍ、長手方向の弾性率Ｙｍと幅方向の弾性率Ｙｔの比Ｙｍ／Ｙｔを本発明の範囲内とすることにより、特に高密度記録媒体のベースフィルムに適した特性を具備することができ、フィルム加工時の寸法安定性が良好で、磁気テープ加工時の磁性層塗布加工適性にも優れ、磁気テープとした時の記録トラックずれが起こりにくく、走行耐久性、保存安定性、電磁変換特性に優れたものとなり、その興行的価値は極めて高い。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is excellent in dimensional stability, rigidity, thickness uniformity, width dimensional uniformity, excellent in suitability for applying a magnetic layer at the time of processing to a magnetic tape, and has little track deviation even when stored for a long time under high temperature and high humidity. The present invention relates to a biaxially oriented polyester film that can be used as a magnetic tape having excellent running durability, dimensional stability, and electromagnetic conversion characteristics.
[0002]
[Prior art]
Biaxially oriented polyester films are used in various applications because of their excellent thermal properties, dimensional stability, mechanical properties, and ease of control of surface morphology, and are particularly useful as supports for magnetic recording media. well known. In recent years, magnetic tapes have been required to have higher densities in order to reduce the weight, size, and long-term recording of equipment. For high-density recording, it is useful to shorten the recording wavelength and reduce the recording area. However, when the recording area is reduced, there is a problem in that the recording track is likely to be displaced due to heat during the running of the magnetic tape and thermal deformation during storage of the tape. Accordingly, there is an increasing demand for improvements in properties such as thermal dimensional stability and storage stability in a tape usage environment. Further, in order to reduce the recording area, it is necessary to further reduce the thickness of the magnetic layer.However, the mechanical strength becomes insufficient, so that the rigidity of the magnetic tape using the film becomes weak. It becomes easy to be stretched, and for example, a problem that a tape is easily damaged or a head touch is deteriorated and electromagnetic conversion characteristics are deteriorated easily occurs.
[0003]
Therefore, in the case of a thinned tape, it is desired to meet the above-mentioned requirement of dimensional stability and obtain compatibility (such as head contact and running property) with a conventional thick tape. An aromatic polyamide having high rigidity is used for the support in view of strength and dimensional stability. However, the amount of this aromatic polyamide film on the market at present is significantly smaller than that of a conventional polyester film, and there are many restrictions on the quantitative expansion of a metal thin film type magnetic recording medium using an aromatic polyamide film.
[0004]
On the other hand, polyethylene terephthalate (hereinafter, referred to as PET) and polyethylene naphthalate (hereinafter, referred to as PEN) have low rigidity as they are, and as a technique for increasing the strength of a biaxially oriented polyester film, there are two techniques, longitudinal and lateral. There is known a method of stretching a stretched film vertically and horizontally again to increase the strength (for example, Patent Documents 1 and 2). However, the dimensions change depending on the environmental conditions in the processing steps in various applications. In particular, in the processing steps for a magnetic recording medium, the magnetic layer tends to be uneven, or the dimensions change due to the use environment conditions, and the recording track is displaced. Problems such as errors occurring during recording / reproducing, difficulty in handling thin films due to insufficient strength, and inability to obtain desired electromagnetic conversion characteristics were likely to occur.
[0005]
Further, a method of improving dimensional stability by combining two-stage fine stretching in the width direction and aging treatment is also known (for example, Patent Document 3). Properties, such as dimensional stability and strength of the support, resulting in non-uniformity, resulting in uneven application of the magnetic layer in the processing step of the magnetic recording medium, and use as a magnetic recording medium. The dimensional stability under the environment is not sufficient. Further, a method of increasing the strength of a biaxially stretched polyester film by forming a metal-based reinforcing film on the film surface (for example, Patent Documents 4 and 5) is known. However, there is a problem that curling occurs and processing is difficult. Further, a method of improving dimensional stability by setting the crystal size to a specified range (for example, Patent Document 6) is known. However, in this method, coating unevenness of a magnetic layer is easily generated, and a usage environment as a magnetic tape is used. The dimensional stability underneath was insufficient.
[0006]
As described above, in the case of the conventional biaxially oriented polyester film, those satisfying all the important characteristics as a magnetic recording medium such as dimensional stability, rigidity, uniform thickness, uniformity of physical properties in the width direction have not been obtained, Many problems remain when applied to high-capacity, high-density recording media.
[0007]
[Patent Document 1]
JP-A-10-329209
[0008]
[Patent Document 2]
JP-A-10-128845
[0009]
[Patent Document 3]
JP 2002-11786 A
[0010]
[Patent Document 4]
JP 2000-11376 A
[0011]
[Patent Document 5]
JP-A-11-33925
[0012]
[Patent Document 6]
JP 2001-30350 A
[0013]
[Problems to be solved by the invention]
The object of the present invention is to solve the above-mentioned problems, and in particular, to excel in dimensional stability, rigidity, uniformity in thickness, uniformity in width dimension, excellent suitability for coating a magnetic layer at the time of processing on a magnetic tape, and high temperature and high humidity. An object of the present invention is to provide a biaxially oriented polyester film which can be used as a magnetic tape with less track deviation even after long-term storage and excellent in running durability, dimensional stability and electromagnetic conversion characteristics.
[0014]
[Means for Solving the Problems]
In recent magnetic recording material applications, further thinning and higher density of the base film for long-time recording are required. In the present invention, in addition to the dimensional stability of the magnetic tape in the drive in the longitudinal and width directions due to temperature, humidity, tension, and the like, the most important characteristics for satisfying the demand are a magnetic layer coating process. In this study, attention was paid to the suppression of unevenness of the magnetic layer. As a result of diligent studies, the heat shrinkage, crystal size in the thickness direction χc, and elastic modulus as the index of the dimensional stability are set to the following ranges, so that the length of the tape processing process and the magnetic tape use environment with respect to the temperature, humidity, and tension can be measured. It was found that a highly rigid biaxially oriented polyester film having little dimensional change in the width direction and the width direction and having excellent running durability and storage stability was obtained.
[0015]
That is, in the present invention for achieving the above object, the heat shrinkage at −100 ° C. for 30 minutes in the width direction is −0.4% or more and less than 0%, the crystal size {c} in the thickness direction is 50 to 80 °, and the lengthwise direction. It is characterized by a biaxially oriented polyester film having an elastic modulus Ym of 6 to 15 GPa and a ratio Ym / Yt of the elastic modulus Ym in the longitudinal direction and the elastic modulus Yt in the width direction of 1.2 to 2.5.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
As the polyester used in the present invention, for example, an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid, or a polyester mainly containing an aliphatic dicarboxylic acid and a diol can be used. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-diphenyldicarboxylic acid , 4,4'-diphenyletherdicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, etc., of which terephthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid can be preferably used. As the alicyclic dicarboxylic acid, for example, cyclohexanedicarboxylic acid or the like can be used. As the aliphatic dicarboxylic acid, for example, adipic acid, suberic acid, sebacic acid, dodecandioic acid and the like can be used. These acid components may be used alone or in combination of two or more. Further, an oxyacid such as hydroxyethoxybenzoic acid may be partially copolymerized.
[0017]
Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentanediol. , 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2'-bis (4 '-Β-hydroxyethoxyphenyl) propane and the like can be used. Among them, ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol and the like are particularly preferable, and ethylene glycol is particularly preferable. thing It can be. These diol components may be used alone or in combination of two or more. Among them, polyethylene terephthalate containing an ethylene terephthalate unit as a main component is preferable.
[0018]
In addition, other compounds such as polyfunctional compounds such as trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, 2,4-dioxybenzoic acid, lauryl alcohol, and phenyl isocyanate may be used as the polyester. You may copolymerize within the range which is linear.
[0019]
As the polyester used in the present invention, polyethylene terephthalate, polyethylene-2,6-naphthalate, or a copolymer or modified product containing these as a main component is also preferably used from the viewpoint of achieving the effects of the present invention.
[0020]
Here, a small amount of an acid component other than terephthalic acid may be copolymerized as the acid component. Further, a glycol component other than ethylene glycol may be added as a copolymer component.
[0021]
The polyester used in the present invention may contain polyetherimide in a range of 5 to 30% by weight. The polyetherimide used is a polymer containing an aliphatic, alicyclic or aromatic ether unit and a cyclic imide group as a repeating unit, and is not particularly limited as long as it is a polymer having melt moldability. For example, US Pat. Nos. 4,141,927, 2,622,678, 2,606,912, 2,606,914, 2,596,565, 2,596,566, 2,598,478, polyetherimides, 2,598,536, and 2,599,171. Japanese Patent Application Laid-Open No. 9-48852, Japanese Patent No. 2565556, Japanese Patent No. 2564636, Japanese Patent No. 25664637, Japanese Patent No. 25656348, Japanese Patent No. 25663547, Japanese Patent No. 2558341, Japanese Patent No. 2558339, and Japanese Patent No. 2834580. It is a polymer of description. As long as the effects of the present invention are not impaired, the main chain of the polyetherimide contains cyclic imides, structural units other than ether units, for example, aromatic, aliphatic, alicyclic ester units, oxycarbonyl units and the like. May be. In the present invention, polyetherimide having a glass transition temperature of 350 ° C. or lower, more preferably 250 ° C. or lower is preferable, and 2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propane dianhydride and m -Condensates with phenylenediamine or p-phenylenediamine are most preferred from the viewpoint of compatibility with polyester, cost, melt moldability and the like. This polyetherimide is available from General Electric under the trademark "Ultem" (registered trademark).
[0022]
The biaxially oriented polyester film in the present invention preferably contains inert particles. Examples of the inert particles include clay, mica, titanium oxide, calcium carbonate, kaolin, talc, wet or dry silica, colloidal silica, inorganic particles such as calcium phosphate, barium sulfate, aluminum silicate, alumina and zirconia, and acrylic acid. And organic particles containing styrene or the like as a component, and so-called internal particles that are precipitated by a catalyst or the like added during the polyester polymerization reaction. Among these, crosslinked polymer particles, alumina, spherical silica, and aluminum silicate are particularly preferred.
[0023]
The biaxially oriented polyester film in the present invention is within a range that does not impair the effects of the present invention, and various other additives such as a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a pigment, and a dye. And organic lubricants such as fatty acid esters and waxes.
[0024]
In addition, the biaxially oriented polyester film of the present invention has a heat shrinkage of −0.4% or more and less than 0% at 100 ° C. and 30 minutes in the width direction, but −0.35% to −0.05%. It is preferably in the range, more preferably in the range of -0.25 to -0.15%. When the heat shrinkage is 0% or more, friction between the magnetic tape and the magnetic recording head, shrinkage in the width direction due to heat history in the tape processing step, storage stability of data, and the like are deteriorated. On the other hand, if the heat shrinkage is less than -0.4%, wrinkles are likely to occur due to the heat history in the tape processing step.
[0025]
The crystal size {c} in the thickness direction is in the range of 50 to 80%. By setting the crystal size Δc to the above range, the frequency of tape breakage is low, the application unevenness and wrinkling of the magnetic layer in the tape processing step can be suppressed, and the dimensional change of the tape under the magnetic tape use environment can be reduced. Also, the occurrence of edge damage can be suppressed. Here, the thickness direction is a direction perpendicular to the normal direction of the crystal plane closest to the polyester main chain direction, and is the direction of the (100) plane in polyethylene terephthalate and polyethylene-2,6-naphthalate. The crystal size Δc in the thickness direction varies depending on the polyester used, but in the case of polyethylene terephthalate, it is preferably 55 to 75 °, and more preferably 58 to 70 °. When the polyester used is polyethylene-2,6-naphthalate, the range is preferably 50 to 65 °.
[0026]
Furthermore, in the present invention, the elastic modulus Ym in the longitudinal direction of the biaxially oriented polyester film is in the range of 6 to 15 GPa. If the elastic modulus Ym in the longitudinal direction is less than 6 GPa, there is a problem that the recording track is easily shifted in the width direction due to the tension in the longitudinal direction in the tape drive, and contracts in the width direction due to the deformation of the extension. Easy to do. Further, due to frequent occurrence of dropouts, storage stability of data is deteriorated, and electromagnetic conversion characteristics are easily deteriorated. On the other hand, when the elastic modulus Ym in the longitudinal direction exceeds 15 GPa, the tape is likely to break, or the Young's modulus in the width direction is insufficient, which causes edge damage.
[0027]
The ratio Ym / Yt of the elastic modulus Ym in the longitudinal direction and the elastic modulus Yt in the width direction is in the range of 1.2 to 2.5. When Ym / Yt is in this range, the longitudinal tension in the data tape and the dimensional changes in the longitudinal and width directions due to the heat and tension applied in the tape processing step can be suppressed, and the storage stability of data is also improved. be able to.
[0028]
The above-mentioned elastic modulus Ym in the longitudinal direction is preferably in the range of 7-14.5 GPa, more preferably 8-14 GPa, and Ym / Yt is preferably 1.4-2.2, more preferably 1.5. ２．０2.0.
[0029]
Further, the biaxially oriented polyester film of the present invention preferably has an elastic modulus Yt in the film width direction of 4.5 to 9 GPa, more preferably 5 to 8.5 GPa, and still more preferably 5.5. ８8 GPa. If the elastic modulus Yt in the width direction is less than 4.5 GPa, it may cause edge damage. On the other hand, when the elastic modulus Yt in the width direction exceeds 9 GPa, the Young's modulus in the longitudinal direction may be reduced, or the slit property may be deteriorated. Further, setting the Young's modulus Yt in the width direction to the above range is effective in suppressing a dimensional change in the width direction with respect to the temperature, humidity, and tension of the magnetic tape use environment.
[0030]
The biaxially oriented polyester film of the present invention preferably has a thickness unevenness in the film longitudinal direction of 1 to 5%, more preferably 1 to 4%, and still more preferably 1 to 3%. It is. If the thickness non-uniformity exceeds the above range, coating non-uniformity of the magnetic layer is liable to occur. In particular, in the case of a multi-head of a linear tape, the contact with the head at the end is weakened, which causes PES noise.
[0031]
In the biaxially oriented polyester film of the present invention, the ratio x / L of the difference x (゜) between the maximum value and the maximum value of the orientation angle in the film width direction to the film width L (m) is 0 to 15 (゜ / m). ), More preferably 0 to 10 (０〜 / m), and still more preferably 0 to 5 (゜ / m).
[0032]
If the thickness unevenness and x / L exceed the above ranges, the unevenness in physical properties causes unevenness in the dimensional change rate, and as a result, the size in the longitudinal direction and the width direction with respect to the temperature, humidity, and tension of the environment in which the magnetic tape is used. This may cause deterioration in stability, uneven application of the magnetic layer in the tape processing step, and an increase in the number of places that cannot be commercialized, resulting in a decrease in yield.
[0033]
The surface roughness Ra of the surface A of the biaxially oriented polyester film of the present invention is preferably 1.5 to 20 nm, more preferably 2 to 15 nm, and still more preferably 3 to 8 nm. Here, the surface A indicates a surface on a side on which a magnetic layer is applied when a magnetic tape is formed. If the Ra of the surface A is less than the lower limit of the above range, the magnetic layer formed on the film surface A is too smooth, and the digital linear tape (DLT), the linear tape open (LTO), the quarter inch cassette (QIC), During magnetic recording / reproduction in a data recording device such as a digital video cassette (DVC), the magnetic layer is easily worn by the magnetic head. On the other hand, when Ra of the surface A exceeds the upper limit of the above range, the magnetic layer is too rough, and the electromagnetic conversion characteristics of the magnetic tape tend to be reduced. In other words, by setting the Ra of the surface A within the above range, it is possible to minimize the wear of the magnetic layer by the magnetic head during recording / reproducing and to keep the electromagnetic conversion characteristics of the magnetic recording tape favorable.
[0034]
The surface roughness Ra of the surface B opposite to the surface A of the support of the present invention is preferably from 5 to 50 nm, more preferably from 6 to 30 nm, and even more preferably from 7 to 10 nm. Here, the surface B is a surface on the running surface side of the magnetic tape. By setting the Ra of the surface B within the above range, when the film is formed and then slit into a predetermined width, it is easy to collect a product having a good winding shape, and the magnetic layer is formed on the film surface A of the support. In the state where the film is wound up in a roll shape after the formation of the support, the roughness of the film surface B of the support is transferred to the surface A side, thereby making it possible to minimize the occurrence of undulating deformation in the magnetic layer.
[0035]
When the biaxially stretched polyester film used in the present invention contains inert particles, the average particle size is preferably 0.001 to 2 μm, more preferably 0.005 to 1 μm, and still more preferably 0.01 to 0.5 μm. It is. If the average particle size of the inert particles is less than the lower limit of the above range, the particles may not function as film surface projections. In addition, when the value exceeds the upper limit of the above range, the protrusion may become coarse and easily fall off.
[0036]
Further, the content of the inert particles contained in the biaxially stretched polyester film used in the present invention is preferably 0.01 to 3% by weight, more preferably 0.02 to 1% by weight, and further preferably 0.1 to 1% by weight. 0.5 to 0.5% by weight. If the content of the inert particles is less than the lower limit of the above range, there is a tendency that the film does not work effectively on running characteristics and the like. On the other hand, if the ratio exceeds the upper limit of the above range, the particles are aggregated into coarse projections and easily fall off.
[0037]
Further, in the present invention, it is particularly preferable to adopt a two-layer structure in which a film layer having a role of improving the running property and the handling property of the film is laminated on one side of the base layer portion of the film. Note that the base layer portion is a layer having the largest thickness in the layer thickness, and the other portion is a laminated portion. Physical properties such as elastic modulus and dimensional stability, which are important for magnetic material applications, are determined mainly by the physical properties of the base layer. When the relationship between the average particle size d (nm) of the inactive particles and the thickness t (nm) of the two-layer structure film is 0.2d ≦ t ≦ 10d, the laminated portion is uniform. This is preferable because a projection having a height can be obtained.
[0038]
Further, the biaxially oriented polyester film of the present invention is not particularly limited, but has a width (A) before being treated for 72 hours under a condition of 49 ° C. and 90% RH under a load of 32 MPa applied in the longitudinal direction. The width dimension change rate (%) obtained from the width dimension (B) after the treatment by the following formula is preferably in the range of 0 to 0.3%, more preferably 0 to 0.25%, More preferably, it is 0 to 0.2%.
[0039]
Width change rate (%) = {(AB) / A} × 100
If the width dimension change rate exceeds the upper limit of the above range, wrinkles are likely to be generated during tape processing. Further, when the value is less than the lower limit of the above range, width shrinkage easily occurs during tape processing, dimensional stability is deteriorated, running durability of the tape is deteriorated, and data retention such as frequent occurrence of dropout is liable to deteriorate. .
[0040]
Although the biaxially oriented polyester film of the present invention is not particularly limited, the creep compliance after 30 minutes of aging at a temperature of 50 ° C. and a load of 28 MPa is 0.11 to 0.4 GPa.^-1It is preferable that If the creep compliance exceeds the upper limit of the above range, elongation deformation of the magnetic tape caused by tension during running or storage of the magnetic tape, and track deviation at the time of recording / reproduction tend to occur. In addition, when it is less than the lower limit of the above range, the magnetic tape may be broken. The creep compliance is more preferably 0.13 to 0.35 GPa.^-1, Most preferably 0.15 to 0.30 GPa^-1Range.
[0041]
The biaxially oriented polyester film of the present invention is preferably used for magnetic recording tapes, capacitors, heat-sensitive transfer ribbons, heat-sensitive stencil sheets, and the like. A particularly preferred application is a high-density magnetic recording medium for data storage or the like that requires a uniform and fine surface morphology. The recording capacity is preferably 30 GB (gigabyte) or more, more preferably 70 GB or more, and still more preferably 100 GB or more. The thickness of the base film for a high-density magnetic recording medium is preferably from 2 to 8 μm. More preferably, it is 3.5 to 6.5 μm, further preferably 4 to 6 μm.
[0042]
By providing a magnetic layer on the surface A side of the biaxially oriented polyester film of the present invention, a magnetic recording medium can be manufactured.
[0043]
Preferable examples of the magnetic layer include a magnetic layer in which a ferromagnetic metal thin film or a ferromagnetic metal fine powder is dispersed in a binder. As the ferromagnetic metal thin film, iron, cobalt, nickel and other alloys are preferable. Further, as the ferromagnetic metal fine powder, ferromagnetic hexagonal ferrite fine powder, iron, cobalt, nickel and other alloys are preferable. As the binder, for example, a thermoplastic resin, a thermosetting resin, a reactive resin, or a mixture thereof is used. Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, and vinyl ether. There are a polymer or a copolymer, a polyurethane resin, and various rubber-based resins which are contained as a simple substance. In addition, as a thermoplastic resin or a reactive resin, a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin, an epoxy-polyamide resin, and a polyester resin. A mixture of an isocyanate prepolymer, a mixture of a polyurethane and a polyisocyanate, and the like can be given. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use an electron beam curing type resin.
[0044]
The magnetic layer is formed by kneading the magnetic powder with a polymer (binder) such as thermoplastic, thermosetting, or radiation curable, applying, drying, and calendering, and depositing a metal or alloy. Any of dry methods in which a magnetic metal thin film layer is directly formed on a substrate film by a method, a sputtering method, an ion pre-coating method, or the like can be adopted.
[0045]
In the magnetic recording medium of the present invention, a protective film may be provided on the ferromagnetic metal film. With this protective film, running durability and corrosion resistance can be further improved. Examples of the protective film include oxide protective films such as silica, alumina, titania, zirconia, cobalt oxide, and nickel oxide; nitride protective films such as titanium nitride, silicon nitride, and boron nitride; silicon carbide, chromium carbide, and boron carbide. Examples of the protective film include a carbon protective film made of carbon such as a carbide protective film, graphite, and amorphous carbon. The carbon protective film is a carbon film formed of an amorphous structure, a graphite structure, a diamond structure, or a mixture thereof formed by a plasma CVD method, a sputtering method, or the like, and is particularly preferably a hard carbon film generally called diamond-like carbon. . The surface of the hard carbon protective film may be subjected to a surface treatment with an oxidizing or inert gas plasma for the purpose of further improving the adhesion with the lubricant provided on the hard carbon protective film.
[0046]
In the present invention, in order to improve the running durability and corrosion resistance of the magnetic recording medium, it is preferable to add a lubricant or a rust inhibitor to the magnetic film or the protective film.
[0047]
Next, the method for producing the support (biaxially oriented polyester film) of the present invention will be specifically described, but is not limited thereto.
[0048]
The biaxially oriented polyester film of the present invention is a film in which a sheet obtained by melt-molding a polyester resin is stretched and oriented by sequentially and / or simultaneously biaxially stretching in a longitudinal direction and a width direction. Can be obtained by successively stretching at a multi-step temperature and highly oriented.
[0049]
Hereinafter, an example in which a film made of polyethylene terephthalate (PET) is manufactured by a sequential biaxial stretching method will be described as a preferable manufacturing method.
[0050]
First, the high molecular weight polyethylene terephthalate used in the present invention is produced by a usual method, that is, any one of the following processes. That is, (1) a low molecular weight polyethylene terephthalate or oligomer is obtained by a direct esterification reaction using terephthalic acid and ethylene glycol as raw materials, and a high molecular weight polymer is obtained by a subsequent polycondensation reaction using antimony trioxide or a titanium compound as a catalyst. (2) Process of obtaining low molecular weight product by transesterification using dimethyl terephthalate and ethylene glycol as raw materials, and obtaining high molecular weight polymer by subsequent polycondensation reaction using antimony trioxide or titanium compound as catalyst (DMT method). Here, the esterification proceeds without a catalyst, but the transesterification reaction usually proceeds using a compound such as manganese, calcium, magnesium, zinc, lithium, or titanium as a catalyst. After substantial completion, a phosphorus compound may be added for the purpose of inactivating the catalyst used in the reaction.
[0051]
The PET pellets obtained by the above method were dried under reduced pressure at 180 ° C. for 3 hours or more, heated to a temperature equal to or higher than the melting point of the polymer, discharged quantitatively from a T-die die, and applied to a cooling drum while applying a high voltage. It is closely contacted and cooled to obtain an unstretched film. Here, in the present invention, in order to make the thickness unevenness of the finally obtained biaxially oriented polyester film 1 to 5%, for example, the draft ratio of the die (= die lip gap / extruded sheet thickness) Is preferably 1 to 15, more preferably 2 to 10, and more preferably 2 to 8. Further, in the electrostatic application method, a wire electrode having a diameter of 0.15 mm is generally used, but from the viewpoint of reducing thickness unevenness, a wire electrode having a diameter of preferably 0.05 to 0.3 mm, more preferably 0.1 to 0. It is preferable to use a .2 mm wire electrode. It is more preferable to use a tape-shaped electrode having a rectangular cross section and a uniform shape in the longitudinal direction.
[0052]
Subsequently, the unstretched film is heated by a group of heating rolls in the range of Tg (glass transition temperature of polyester) to (Tg + 55 ° C.) and stretched 3 to 8 times in one step or multiple steps in the longitudinal direction, and 20 to 20 times. It cools with a 50 degreeC cooling roll group. At this time, in order to satisfy the elastic modulus of the present invention, the stretching speed in the longitudinal direction is set at 50,000 to 200,000% / min, and the first-stage stretching condition is set to a temperature range of (Tg + 10) to (Tg + 40) ° C. Then, the film is stretched 1.5 to 4.5 times in a temperature range of (first stage stretching temperature −40) ° C. to (first stage stretching temperature −10) ° C. Is preferred. Subsequently, stretching in the lateral direction is performed. As a stretching method in the width direction, for example, a method using a stenter is generally used. The stretching temperature in the width direction is in the range of Tg to (Tm (melting point of polyester) -40) ° C, and the magnification is 3 to 8 times (when performing vertical stretching again, the first stage stretching is 3 to 4.5 times). The stretching speed is preferably in the range of 2,000 to 10,000% / min. Further, after the transverse stretching, re-longitudinal stretching and / or re-lateral stretching is performed. Regarding the conditions for re-longitudinal stretching, it is preferable that stretching in the longitudinal direction is performed by a group of heating rolls at a temperature of Tg to (Tg + 70) ° C., and that stretching is performed in a range of 1.2 to 2.2 times. As a method of re-transverse stretching, a method using a tenter is preferable, and the temperature is preferably in the range of (Tm-140) ° C to (Tm-40) ° C, and the stretching ratio is preferably in the range of 1.2 to 2.0 times. Subsequently, the stretched film is heat-treated under tension and while relaxing in the width direction. At this time, the heat setting temperature is preferably (Tm-50) ° C to (Tm-20) ° C, and more preferably, in order to obtain the crystal size (χc) in the thickness direction of the obtained film of 50 to 80 °. (Tm−45) ° C. to (Tm−25) ° C., more preferably (Tm−35) ° C. to (Tm−30) ° C., and the heat fixing time is preferably 3 to 20 seconds, more preferably It is preferable to carry out in a range of 5 to 15 seconds. Further, in order to make the heat shrinkage of the obtained film not less than -0.4% and less than 0%, it is preferable to perform the relaxation treatment in at least two stages after the heat treatment. After the relaxation treatment of (Heat setting temperature -10) ° C to the heat setting temperature and the relaxation rate in the range of 1 to 5%, the relaxation treatment of the second and subsequent stages is (Heat setting temperature-150) ° C to (Heat It is carried out at a fixing temperature of -10) ° C, and the total relaxation rate is preferably 3 to 15%, more preferably 5 to 13%, and still more preferably 7 to 10%. In the relaxation treatment of the second and subsequent stages, the relaxation treatment of the second stage is (heat setting temperature −50) ° C. to (heat fixing temperature −10) ° C., and the relaxation treatment of the third stage is (heat fixing temperature −150). C. to (heat setting temperature -135) .degree. C., so that the relaxation treatment temperature is more than the first stage> the second stage> the third stage, and the relaxation rate is more than the first stage> the second stage> the third stage. preferable. Further, at this time, in order to set the x / L of the obtained biaxially oriented polyester film to 0 to 15 (゜ / m), the film is once again transversely stretched and then cooled once to a glass transition temperature or lower. Alternatively, a temperature gradient is applied so that the edge of the film is higher than the center, and after preheating with maintaining the temperature of the center at 90 ° C. or lower, a method of heat treatment, or after biaxially stretching the film, It is preferable to use a method of performing heat treatment so that the temperature at the edge of the film is higher than the temperature at the center by 10 ° C. or more.
[0053]
Thereafter, the film edge is removed and the film is wound up on a roll. If necessary, the film may be heated in a hot-air oven in a state where the film is wound around a core (roll-shaped film). The preferred treatment temperature is in the range of (Tg-10) ° C to (Tg-60) ° C, more preferably in the range of (Tg-15) ° C to (Tg-55) ° C, and still more preferably (Tg-20) to (Tg-20). Tg-50). A preferred treatment time is in the range of 10 to 360 hours, more preferably in the range of 24 to 240 hours, and even more preferably 72 to 168 hours. Further, the heat treatment with the roll film can be performed in two or more stages by changing the temperature and the time within the above-mentioned temperature and time. Performing this roll-shaped heat treatment is preferable because the dimensional stability of the creep characteristics is improved.
[0054]
According to the above-described method, a biaxially oriented polyester film having excellent dimensional stability, thickness uniformity, uniformity of physical properties in the width direction, and rigidity can be obtained, and a problem or the like generated during the manufacture of a magnetic recording medium can be solved.
[0055]
[Method of measuring physical properties and method of evaluating effects]
The method for measuring characteristic values and the method for evaluating effects are as follows. Note that the longitudinal direction (MD) and the width direction (TD) when measuring a sheet-shaped magnetic recording medium before being slit (before it becomes a tape shape) are two axes constituting a support in the recording medium. It is the same as the longitudinal direction and the width direction of the oriented polyester film.
[0056]
(1) Heat shrinkage
According to the method specified in JIS-C2318, a sample having a width of 10 mm and a gap of about 100 mm was heat-treated at a temperature of 100 ° C. and a load of 0.5 g for 30 minutes. The gap between the marked lines before and after the heat treatment was measured by using a thermal shrinkage rate measuring device manufactured by Technonis Co., Ltd., and the heat shrinkage rate was calculated from the following equation.
[0057]
Heat shrinkage (%) = {(L0−L) / L0} × 100
L0: Mark line gap before heat treatment
L: Mark line gap after heat treatment
(2) Crystal size (χc)
Diffraction intensity was measured by a reflection method using an X-ray diffractometer. Using a sample laminated so that the film thickness was 50 μm as a sample, measurement was performed under the following conditions while changing the X-ray irradiation angle in a plane (100 planes) perpendicular to the longitudinal direction of the film.
[0058]

A sample cut into 2 cm x 2 cm, aligned in the same direction, superimposed, set a sample solidified with a collodion-ethanol solution, and set the half of the plane in each direction out of 2θ / θ intensity data obtained by wide-angle X-ray diffraction measurement From the price range, it was calculated using the following Scherrer equation. Here, the crystal size in the thickness direction was measured in a direction (100 planes) perpendicular to the main orientation direction.
[0059]
Crystal size χc (Å) = Kλ / β_Ocos θ_B
K: constant (= 1.0)
λ: wavelength of X-ray (= 1.5418 °)
θ_B: Black horn
β_O= (Β_E ^Two−β_I ^Two)^1/2
β_E: Apparent half width (measured value)
β_I: Device constant (= 1.046 × 10^-2)
(3) Elastic modulus
According to the method specified in ASTM-D882, a sample having a width of 10 mm and a test length of 100 mm was sampled at a temperature of 23 ° C. and a humidity using an automatic film strength and elongation measuring device “Tensilon AMF / RTA-100” manufactured by Orientec Co., Ltd. The measurement was performed five times under the conditions of 65% RH and a tensile speed of 10 mm / min, and the average value was taken.
[0060]
(4) Uneven thickness
Using a film thickness nest tester “KG601A” manufactured by Anritsu Corporation and an electronic micrometer “K306C”, the thickness of a support sample sampled at a length of 30 mm and a length of 10 m continuously in the longitudinal direction at a transport speed of 3 m / min. Measure. From this measurement result, the maximum value of the thickness at a length of 10 m was Tmax, the minimum value was Tmin, the average value of the thickness was Tave, R = Tmax−Tmin was determined, and the thickness unevenness (%) was determined from R and Tave by the following equation. .
[0061]
Uneven thickness (%) = (R / Tave) × 100
(5) x / L
Using a polarizing microscope with white light as a light source, the narrow angle between the main alignment axis and the film width direction is determined from the extinction value, and this is defined as the alignment angle (°). This orientation angle is measured for the entire width in the film width direction, and the difference x (°) between the maximum value and the minimum value of the orientation angle in the film width direction is determined. The value x / L (° / m) of the ratio of the orientation angle difference x (°) to the film width L (m) is determined. The main orientation axis was 0 ° in the width direction and 90 ° in the direction (longitudinal direction) perpendicular to the width direction.
[0062]
(6) Surface roughness Ra
The center line average roughness Ra at a stylus tip radius of 0.5 m, a stylus load of 5 mg, a measurement length of 1 mm, and a cutoff value of 0.08 mm was measured using a high-precision thin film step measuring device ET-10 manufactured by Kosaka Laboratory. The measurement is performed 20 times by scanning in the film width direction, and the average value is taken.
[0063]
(7) Width change rate
In an atmosphere of 23 ° C. and 65% RH, a support sample having a sample length (film longitudinal direction) of 143 mm and a width of 31 mm was humidified and conditioned for 24 hours, and then placed on a chrome mask manufactured by Dai Nippon Printing Co., Ltd. A sample is attached to the center, and the dimension (Amm) in the width direction is measured using an optical microscope. Thereafter, the sample is left for 72 hours in a 49 ° C., 90% RH atmosphere with a load of 32 MPa applied in the longitudinal direction. After standing for 72 hours, the load is released, and the humidity and temperature are controlled at 23 ° C. and 65% RH for 24 hours, and then the dimension (Bmm) in the sample width direction is measured. The dimensional change rate in the width direction is obtained by the following equation. The measurement was performed five times, and an average value of the five measurements was adopted.
[0064]
Width change rate (%) = ((A−B) / A) × 100
(8) Creep compliance
A biaxially oriented film was sampled to a width of 4 mm and a test length of 15 mm, and was set on TMA TM-3000 manufactured by Vacuum Riko Co., Ltd. and a heating control unit TA-1500, and was conditioned at 50 ° C. and 65% RH. And the length of the sample film at that time is L₀(Μm). Thereafter, a load of 28 MPa is applied to the sample film, and the length of the sample film after holding for 30 minutes is L₁(Μm). From the amount of expansion and contraction of the sample film at this time, creep compliance was calculated from the following equation.
Creep compliance (GPa^-1) = ｛(L₁-L₀) / L₀｝ /0.028 The measurement was performed five times, and the average value of the five measurements was adopted. In addition, creep here is a phenomenon in which strain increases with time under a constant stress, and creep compliance is a ratio of this strain to a constant stress, and is described in "Introduction to Polymer Chemistry (Second Edition)". (Issued by Kagaku Doujin Co., Ltd.) p150.
[0065]
(9) Total film thickness and laminated thickness
Using a transmission electron microscope (H-600 manufactured by Hitachi, Ltd.), the cross section of the support was ultrathin section (RuO) at an acceleration voltage of 100 kV._Four(Staining). From the observation result of the interface, the total thickness and the lamination thickness are obtained. The magnification may be appropriately set according to the total thickness of the support to be determined and the lamination thickness, but generally, 1,000 times for the total thickness measurement and 10,000 to 100,000 times for the lamination thickness measurement are appropriate. .
[0066]
Further, the thickness of the laminate can be measured using a secondary ion mass spectrometer (SIMS). The element (M) originating from the highest concentration of the particles among the inert particles in the film having a depth of 3,000 nm from the surface layer⁺) And the concentration ratio of the carbon element of the polyester (M⁺/ C⁺) Is analyzed by SIMS in the thickness direction from the surface to a depth of 3,000 nm. In the surface layer, the element concentration due to the inert particles is low, and the element concentration due to the inert particles increases as the distance from the surface increases. In the case of the film of the present invention, the element concentration caused by the inert particles that have once reached a maximum value starts to decrease again. In this concentration distribution curve, the depth at which the element concentration caused by the inert particles is reduced to half of the maximum value is defined as the lamination thickness. The measurement conditions are as follows.
[0067]
1) Measuring device
Two-dimensional ion mass spectrometer (SIMS)
A-DIDA3000 manufactured by Atomika, West Germany
2) Measurement conditions
Primary ion species: O_Two ⁺
Primary ion acceleration voltage: 12 KV
Primary ion current: 200 nA
Raster area: 400 μm □
Analysis area: Gate 30%
Measurement vacuum degree: 5.0 × 10^-9Torr
E-GUN: 0.5KV-3.0A
In the case where the inert particles most contained in the range of 3,000 nm in depth from the surface layer are organic polymer particles, it is difficult to measure by SIMS. Therefore, XPS (X-ray photoelectron spectroscopy), IR ( Infrared spectroscopy) or the like may be used to measure the same depth profile as above to determine the lamination thickness.
[0068]
(10) Thermal properties of polymer (glass transition temperature, melting point)
Specific heat measurement was performed under the following conditions using a differential scanning calorimeter using a robot DSC “RDC220” manufactured by Seiko Denshi Kogyo KK and a data analysis device using a disk station “SSC / 5200” manufactured by the company. The melting point (Tm) and the like were determined according to JIS K7121.
[0069]
Measurement condition
Heating temperature: 270-540K (RCS cooling method)
Temperature calibration: melting point of high purity indium and tin
Temperature modulation amplitude: ± 1K
Temperature modulation cycle: 60 seconds
Average heating rate: about 10mg
Sample weight: open aluminum container (33mg)
The glass transition temperature (Tg) was calculated by the following equation.
[0070]
Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2
(11) Running durability and storage stability of magnetic tape
On the surface A (surface of the layer of the raw material (A1)) of the biaxially oriented polyester film of the present invention, a magnetic paint having the following composition and a non-magnetic lower layer paint are applied in multiple layers by an extrusion coater (the upper layer is coated with a magnetic paint. 0.2 μm, and the thickness of the non-magnetic lower layer was 1.5 μm.), Magnetically oriented, and dried. Next, a back coat layer having the following composition was formed on the opposite surface (surface B side), and calendered at a temperature of 85 ° C. and a linear pressure of 200 kg / cm with a small test calender (steel / nylon roll, 5 steps). At 60 ° C. for 48 hours, a magnetic recording medium was obtained.
[0071]
(Composition of magnetic paint)
-Ferromagnetic metal powder: 100 parts by weight
-Modified vinyl chloride copolymer: 10 parts by weight
-Modified polyurethane: 10 parts by weight
・ Polyisocyanate: 5 parts by weight
-Stearic acid: 1.5 parts by weight
・ Oleic acid: 1 part by weight
・ Carbon black: 1 part by weight
・ Alumina: 10 parts by weight
・ Methyl ethyl ketone: 75 parts by weight
・ Cyclohexanone: 75 parts by weight
・ Toluene: 75 parts by weight
(Composition of back coat)
・ Carbon black (average particle size: 20 nm): 95 parts by weight
・ Carbon black (average particle size: 280 nm): 10 parts by weight
・ Α-alumina: 0.1 parts by weight
-Modified polyurethane: 20 parts by weight
・ Modified vinyl chloride copolymer: 30 parts by weight
・ Cyclohexanone: 200 parts by weight
・ Methyl ethyl ketone: 300 parts by weight
・ Toluene: 100 parts by weight
This magnetic recording medium was slit into a 1/2 inch width, and a 670 m long magnetic tape was assembled into a cassette to form a cassette tape. The cassette tape was run for 150 hours using DLT (IV) Drive manufactured by Quantum, and the running durability of the tape was evaluated according to the following criteria.
[0072]
：: No tape end surface elongation, no bend, and no trace of scraping.
[0073]
：: No tape end surface elongation or bending, but slight scraping marks.
[0074]
Δ: The tape end face was not stretched, but was partially bent and scraping marks were observed.
[0075]
×: A part of the tape end face is elongated, wakame-like deformation is observed, and scraping marks are observed.
[0076]
Further, after reading the data of the cassette tape prepared above using a DLT (IV) Drive manufactured by Quantum, the cassette tape was stored in an atmosphere of 60 ° C. and 80% RH for 100 hours. The storage stability of the tape was evaluated according to the following criteria.
[0077]
A: The tape was reproduced normally without a change in the tape width of 2 μm or less, without track deviation.
[0078]
：: The tape width was changed more than 2 μm and was 4 μm or less, there was no track shift and the tape was reproduced normally.
[0079]
Δ: The change in the tape width was more than 4 μm and 6 μm or less, there was no track deviation, and the tape was reproduced normally.
[0080]
X: The change in the tape width exceeds 4 μm, and reading is impossible.
[0081]
(12) Uneven coating of magnetic layer on magnetic tape
The magnetic recording medium is filled with a resin, cut out with a diamond cutter, the cross section is observed with a transmission electron microscope, the total thickness of the magnetic paint and the non-magnetic lower paint is measured, and the maximum value of the thickness is set to Mmax and the minimum value. The value is Mmin, the thickness average value is Mave, R = Mmax−Mmin is obtained, and the magnetic layer unevenness (%) is obtained from R and Mave by the following equation.
Unevenness of magnetic layer (%) = (R / Mave) × 100
The coating unevenness of the magnetic layer was evaluated according to the following criteria.
[0082]
A: Magnetic layer unevenness is 8% or less.
[0083]
：: The unevenness of the magnetic layer is more than 8% and 12% or less.
[0084]
Δ: Magnetic layer unevenness is more than 12% and 15% or less.
[0085]
X: Magnetic layer unevenness exceeding 15%.
[0086]
(13) Electromagnetic conversion characteristics of magnetic tape (C / N)
The magnetic recording medium was slit into a width of 8 mm to prepare a pancake. Next, a 200 m-long magnetic tape was assembled from the pancake into a cassette to form a cassette tape.
[0087]
The magnetic tape was measured for C / N at 7 MHz ± 1 MHz using a commercially available VTR for Hi8 (EV-BS3000 manufactured by Sony Corporation). This C / N was compared with a commercially available MP video tape for Hi8 and ranked as follows.
[0088]
：: +3 dB or more
Δ: +1 dB or more and less than +3 dB
×: less than +1 dB
[0089]
【Example】
Example 1
Polymerization by the DMT method was performed. That is, 0.1 part by weight of magnesium acetate tetrahydrate was added to 194 parts by weight of dimethyl terephthalate and 124 parts by weight of ethylene glycol, and a transesterification reaction was performed at 140 to 230 ° C. while distilling off methanol. Next, an ethylene glycol solution of 0.05 parts by weight of trimethyl phosphate and 0.05 parts by weight of antimony trioxide were added, and the mixture was stirred for 5 minutes. The resulting low polymer was stirred at 30 rpm, and the reaction system was heated to 230 ° C. The temperature was gradually raised to 290 ° C., and the pressure was lowered to 0.1 kPa. The time required to reach the final temperature and the final pressure was 60 minutes. When the polymerization reaction was carried out for 3 hours and the specified stirring torque was reached, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction. A pellet of polyethylene terephthalate having a viscosity of 0.65 was obtained.
[0090]
The thermal characteristics of the polyethylene terephthalate (PET) having an intrinsic viscosity of 0.65 obtained by the above method were measured by DSC, and were found to be Tg: 82 ° C and Tm: 256 ° C.
[0091]
Using this PET, a film was formed by the following method using two extruders (A, B).
[0092]
The extruder A heated to 285 ° C. contains a raw material (A1) containing 0.1% by weight of silica particles having an average particle size of 0.07 μm in PET having an intrinsic viscosity of 0.65 and containing substantially no inert particles. ) Was supplied after drying under reduced pressure at 180 ° C. for 3 hours. The extruder B heated to 285 ° C. was made to contain 0.5% by weight of crosslinked polystyrene particles having an average particle size of 0.3 μm in PET having an intrinsic viscosity of 0.65 and containing substantially no inert particles. The raw material (B1) was supplied after being vacuum-dried at 180 ° C. for 3 hours.
[0093]
Subsequently, the raw material (A1) was filtered in three stages in the order of a sand filter, a 1.2 μm cut fiber-sintered stainless steel metal filter, and a 0.8 μm cut fiber-sintered stainless steel metal filter. After filtering in two steps in the order of a filter and a fiber-sintered stainless steel metal filter cut at 3 μm, the polymer was joined with a T-die so that the temperature of the polymer became 285 ° C., and extruded from a die into a sheet. At this time, the draft ratio (= base lip gap / extruded sheet thickness) was 5, and the distance between the LDs (the distance between the base lip and the cooling drum) was 20 mm. Further, the sheet-shaped extruded polymer is adhered to a cast drum having a surface temperature of 25 ° C. by an electrostatic application method using a tape-shaped (0.04 mm in thickness, 7.2 mm in width) electrode, and cooled and solidified to form two layers. A laminated unstretched film (lamination thickness ratio A1 / B1 = 5/1) was produced.
[0094]
The obtained unstretched film is first preliminarily stretched at 120 ° C. and 1.7 times in the longitudinal direction using a difference in peripheral speed of a roll by a roll-type stretching machine. After stretching the film by a factor of 1, then stretching the film in the width direction to 95 ° C. and 3.3 times by a stenter, and further performing longitudinal stretching again to 1.9 times at 150 ° C. using a roll longitudinal stretching machine. Re-horizontal stretching was performed 1.3 times at 200 ° C. in a tenter. Thereafter, the film is once cooled to 70 ° C., and subsequently, a temperature gradient is applied so that the center of the film is 220 ° C. and the end of the film is 10 ° C. higher than the center, and after performing a heat treatment for 12 seconds, In the zone of 220 ° C., the first-stage relaxation process is performed at a relaxation rate of 4% in the width direction, and then, in the zone of 175 ° C., the second-stage relaxation process is performed at a relaxation ratio of 3% in the width direction. A third-stage relaxation treatment was performed at a relaxation rate of 1.5% in the width direction in a zone at 100 ° C., and the film was gradually cooled to room temperature and wound up to produce a biaxially stretched polyester film having a thickness of 4 μm. In addition, the film thickness was set to a desired level by adjusting the extrusion amount.
[0095]
Tables 1 and 2 show film forming conditions of the obtained biaxially oriented polyester film. Tables 3 and 4 show the properties of the biaxially oriented polyester film and the magnetic recording medium obtained from the film using the film as a support. It shows the magnetic conversion characteristics.
[0096]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film has excellent dimensional stability, has no unevenness in coating of the magnetic layer, and can be used as a magnetic tape having excellent running durability and storage stability. did it.
[0097]
Example 2
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 1 except that the stretching conditions, heat treatment conditions, and relaxation treatment conditions were changed to the conditions shown in Table 1.
[0098]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film has excellent dimensional stability, has less unevenness in coating of the magnetic layer, and has excellent electromagnetic conversion characteristics such as running durability and storage stability. And could be.
[0099]
Example 3
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2 except that the relaxation treatment conditions were changed to the conditions shown in Table 1.
[0100]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film has excellent dimensional stability, has less uneven coating of the magnetic layer, and has excellent running durability, storage stability, and electromagnetic conversion characteristics. We were able to.
[0101]
Example 4
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2 except that the heat treatment conditions were changed to the conditions shown in Table 1.
[0102]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film was relatively excellent in dimensional stability, and could be used as a magnetic tape having excellent running durability, storage stability, and electromagnetic characteristics. .
[0103]
Example 5
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2 except that the heat treatment conditions were changed to the conditions shown in Table 1.
[0104]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film has excellent dimensional stability, has no unevenness in coating of the magnetic layer, and has excellent running durability, storage stability, and electromagnetic conversion characteristics. We were able to.
[0105]
Example 6
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2 except that the stretching conditions were changed to the conditions shown in Table 1.
[0106]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film has excellent dimensional stability, has less uneven coating of the magnetic layer, and has excellent running durability, storage stability, and electromagnetic conversion characteristics. We were able to.
[0107]
Example 7
In the same manner as in Example 1, pellets of polyethylene terephthalate (PET) having an intrinsic viscosity of 0.85 (Tg of 80 ° C.) were produced. 50% by weight of the PET pellets and 50% by weight of a polyetherimide (PEI) "Ultem" 1010 (Tg at 216 ° C.) having an intrinsic viscosity of 0.68 manufactured by General Electric (GE) were heated to 290 ° C. The mixture was fed to a directional rotation type vent-type twin-screw kneading extruder to produce a blend chip (I) containing 50% by weight of PEI. The thermal characteristics of this blend chip (I) were measured using DSC, and it was Tg: 89 ° C and Tm: 254 ° C.
[0108]
Next, using two extruders (A, B), a film was formed by the following method.
[0109]
The extruder A heated to 295 ° C. was made of polyethylene terephthalate (PET) having an intrinsic viscosity of 0.65 and containing substantially no inert particles, obtained in the same manner as in Example 1, and silica having an average particle size of 0.09 μm. The mixed raw material (A1) obtained by dry-blending the pellet (II) containing 0.05% by weight of the particles and the blend chip (I) containing PEI obtained by the above method at a ratio of 8: 2 was heated at 180 ° C. And dried under reduced pressure for 3 hours. The extruder B heated to 295 ° C. was mixed with polyethylene terephthalate (PET) having an intrinsic viscosity of 0.65 and containing substantially no inert particles and having an average particle size of 0.3 μm. A mixed raw material (B1) obtained by dry-blending a pellet (III) containing 0.5% by weight of calcium carbonate particles and a blend chip (I) containing PEI obtained by the above method at a ratio of 8: 2, It was supplied after drying under reduced pressure at 180 ° C. for 3 hours.
[0110]
Subsequently, the mixed raw material (A1) was filtered in three stages in the order of a sand filter, a 1.2 μm cut fiber-sintered stainless steel metal filter, and a 0.8 μm cut fiber-sintered stainless steel metal filter. Was filtered in two stages in the order of a sand filter and a fiber-sintered stainless steel metal filter having a cut of 3 μm, and then joined by a T-die so that the temperature of the polymer became 295 ° C., and extruded from a die into a sheet. At this time, the draft ratio (= base lip gap / extruded sheet thickness) was 5, and the distance between the LDs (the distance between the base lip and the cooling drum) was 20 mm. Further, the sheet-shaped extruded polymer is adhered to a cast drum having a surface temperature of 25 ° C. by an electrostatic application method using a tape-shaped (0.04 mm in thickness, 7.2 mm in width) electrode, and cooled and solidified to form two layers. A laminated unstretched film (lamination thickness ratio A1 / B1 = 5/1) was produced.
[0111]
The obtained unstretched film is stretched at 118 ° C. in the longitudinal direction by 1.6 times using a difference in peripheral speed of the roll by a roll stretching machine, and then further stretched at 110 ° C. in the longitudinal direction by 2 times. The film is stretched in the width direction at 100 ° C. and 3.3 times by a stenter, and further stretched again at 150 ° C. and 1.7 times by a roll longitudinal stretching machine. The film was stretched transversely 1.3 times. Thereafter, the film was once cooled to 70 ° C., and then subjected to a heat treatment for 7 seconds with a temperature gradient such that the central portion of the film was 220 ° C. and the edge of the film was 10 ° C. higher than the central portion, followed by heating at 210 ° C. The first-stage relaxation process is performed in the zone at 4 ° C. at a relaxation rate of 4% in the width direction, and the second-stage relaxation process is performed in the zone at 160 ° C. at a relaxation ratio of 2% in the width direction. A third-stage relaxation treatment was performed at a relaxation rate of 1% in the width direction in a zone of ° C, and the film was gradually cooled to room temperature and wound up to produce a biaxially stretched polyester film having a thickness of 4 µm. In addition, the film thickness was set to a desired level by adjusting the extrusion amount.
[0112]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film is excellent in dimensional stability, has less unevenness in the magnetic layer, and is a magnetic tape excellent in running durability, storage stability, and electromagnetic conversion characteristics. I was able to.
[0113]
Example 8
Transesterification of 100 parts of dimethyl naphthalene-2,6-dicarboxylate and 60 parts of ethylene glycol for 120 minutes while gradually increasing the temperature from 150 ° C. to 238 ° C. using 0.03 part of manganese acetate tetrahydrate as a transesterification catalyst. The reaction was performed. On the way, when the reaction temperature reaches 170 ° C., 0.024 parts of antimony trioxide is added, and after the transesterification reaction is completed, trimethyl phosphate is added to ethylene glycol at 135 ° C. for 5 hours at 1.1 to 1.1. 6kg / cm^Two(0.023 part in terms of trimethyl phosphate) was added under heat. Thereafter, the reaction product was transferred to a polymerization reactor, the temperature was raised to 290 ° C., the polycondensation reaction was performed under a high vacuum of 0.2 mmHg or less, and the intrinsic viscosity measured by melting o-chlorophenol at 25 ° C. A pellet of polyethylene 2,6-naphthalenedicarboxylate having a copolymerization amount of DEG of 0.61 dl / g and 1.0 mol% was obtained.
[0114]
The thermal properties of the polyethylene-2,6-naphthalenedicarboxylate (PEN) having an intrinsic viscosity of 0.61 dl / g obtained by the above method were measured by using DSC. Tg: 119 ° C., Tm: 261 ° C. Met.
[0115]
Using this PEN, a film was formed by the following method using two extruders (A, B). Extruder A heated to 300 ° C. contains 0.05% by weight of silica particles having an average particle size of 0.09 μm in PEN having an intrinsic viscosity of 0.61 and containing substantially no inert particles obtained by the above method. The raw material (A1) was supplied after drying under reduced pressure at 180 ° C. for 3 hours. Further, in extruder B heated to 300 ° C., 0.5 wt% of calcium carbonate particles having an average particle diameter of 0.3 μm were added to PEN having an intrinsic viscosity of 0.61 containing substantially no inert particles and obtained by the above method. % Of the raw material (B1) was dried at 180 ° C. for 3 hours under reduced pressure and supplied.
[0116]
Subsequently, the raw material (A1) was filtered in three stages in the order of a sand filter, a 1.2 μm cut fiber-sintered stainless steel metal filter, and a 0.8 μm cut fiber-sintered stainless steel metal filter. After filtering at two stages in the order of a filter and a 3 μm-cut fiber sintered stainless metal filter, the polymers were joined by a T-die so that the temperature of the polymer became 255 ° C., and extruded from a die into a sheet. At this time, the draft ratio (= base lip gap / extruded sheet thickness) was 5, and the distance between the LDs (the distance between the base lip and the cooling drum) was 20 mm. Further, the sheet-shaped extruded polymer is adhered to a cast drum having a surface temperature of 25 ° C. by an electrostatic application method using a tape-shaped (0.04 mm in thickness, 7.2 mm in width) electrode, and cooled and solidified to form two layers. A laminated unstretched film (laminated thickness ratio A1 / B1 = 5/1) was produced.
[0117]
The obtained unstretched film is first stretched at 135 ° C. 5.5 times in the longitudinal direction using a difference in peripheral speed of the roll by a roll stretching machine, and subsequently, 135 ° C. in the width direction by a stenter. The film was stretched 3.5 times, and further longitudinally stretched 1.6 times at 170 ° C. using a roll longitudinal stretching machine, and then transversely stretched 1.4 times at 180 ° C. in a tenter. Thereafter, the film is once cooled to 70 ° C., and then subjected to a heat treatment for 7 seconds with a temperature gradient such that the central portion of the film is 215 ° C. and the edge of the film is higher than the central portion by 10 ° C. The first-stage relaxation process is performed in the zone at 4 ° C. at a relaxation rate of 4% in the width direction, and the second-stage relaxation process is performed in the zone at 160 ° C. at a relaxation ratio of 2% in the width direction. A third-stage relaxation treatment was performed at a relaxation rate of 1% in the width direction in a zone of ° C, and the film was gradually cooled to room temperature and wound up to produce a biaxially stretched polyester film having a thickness of 4 µm. The film thickness was set to a desired level by adjusting the extrusion amount.
[0118]
As shown in Tables 1 and 3, the obtained film has relatively excellent dimensional stability, less unevenness in coating of the magnetic layer, relatively excellent running durability, excellent storage stability and excellent electromagnetic conversion characteristics. It could be a magnetic tape.
[0119]
Comparative Example 1
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 8, except that the heat treatment time was set to 5 seconds and the relaxation treatment was not performed.
[0120]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film was inferior in dimensional stability, and was a magnetic tape having inferior storage stability and electromagnetic conversion characteristics.
[0121]
Comparative Example 2
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2, except that the relaxation treatment was performed only in one stage under the conditions shown in Table 1.
[0122]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film was inferior in dimensional stability and magnetic tape with inferior electromagnetic conversion characteristics.
[0123]
Comparative Example 3
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2 except that the relaxation rate was determined under the conditions shown in Table 1.
[0124]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film was inferior in dimensional stability, and was a magnetic tape having inferior storage stability and electromagnetic conversion characteristics.
[0125]
Comparative Example 4
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2 except that the relaxation rate was determined in two steps under the conditions shown in Table 1.
[0126]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film was inferior in dimensional stability, and was a magnetic tape having inferior storage stability and electromagnetic conversion characteristics.
[0127]
Comparative Example 5
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2 except that the relaxation rate was determined in two steps under the conditions shown in Table 1. The resulting film was wrinkled.
[0128]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film was inferior in dimensional stability, and was a magnetic tape having inferior storage stability and electromagnetic conversion characteristics.
[0129]
Comparative Example 6
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2 except that the relaxation treatment was performed under the conditions shown in Table 1. A magnetic recording medium was created.
[0130]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film was inferior in dimensional stability and was a magnetic tape having inferior electromagnetic conversion characteristics.
[0131]
Comparative Example 7
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2 except that the heat treatment conditions and the relaxation treatment conditions were changed to the conditions shown in Table 1. A magnetic recording medium was prepared in the same manner.
[0132]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film was a magnetic tape having a small crystal size Δc, uneven magnetic layers, and poor electromagnetic conversion characteristics.
[0133]
Comparative Example 8
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2, except that the stretching conditions were changed to the conditions shown in Table 1.
[0134]
As shown in Tables 1 and 3, the obtained biaxially oriented polyester film was inferior in dimensional stability, resulting in a magnetic tape having inferior running durability and electromagnetic conversion characteristics.
[0135]
Example 9
A biaxially oriented polyester film having a thickness of 4 μm was prepared in the same manner as in Example 2, except that the stretching conditions were changed to the conditions shown in Table 1.
[0136]
As shown in Tables 1 and 3, the dimensional stability of the obtained film is relatively excellent, the coating unevenness of the magnetic layer is relatively small, the running durability and the storage stability are relatively excellent, and the electromagnetic conversion characteristics are excellent. Excellent magnetic tape was obtained.
[0137]
Example 10
The draft ratio at the time of extruding the raw material (A1) and the raw material (B1) from the die in Example 1 was changed to 20, and the tape-shaped electrode when the sheet was brought into close contact with the cooling drum by the electrostatic application method was replaced with a wire An unstretched film in which two layers were laminated was prepared in the same manner as in Example 1 except that the electrode (diameter: 0.15 mmφ) was changed. A biaxially oriented polyester film having a thickness of 4 μm was prepared from the unstretched film in the same manner as in Example 2.
[0138]
As shown in Tables 2 and 4, the dimensional stability of the obtained film was slightly worse than that of Example 2, but the unevenness of the magnetic layer was relatively small, and the running durability, storage stability and electromagnetic conversion characteristics were also relatively low. It became a good magnetic tape.
[0139]
Example 11
The thickness of the film was 4 μm in the same manner as in Example 2 except that the heat treatment after re-laterally stretching the film in Example 2 was performed at 215 ° C. without applying a temperature gradient from the edge to the center of the film. Was prepared.
[0140]
As shown in Tables 2 and 4, the dimensional stability of the obtained film was slightly worse than that of Example 2, but the unevenness of the magnetic layer was relatively small, and the running durability, storage stability and electromagnetic conversion characteristics were also relatively low. It became a good magnetic tape.
[0141]
Example 12
Unstretched two-layer laminate in the same manner as in Example 1 except that the particles blended in the raw material (B1) in Example 1 were changed to contain 0.05% by weight of silica particles having an average particle size of 0.04 μm. A film was made. In the same manner as in Example 2, a biaxially stretched polyester film having a thickness of 4 μm was prepared from the unstretched film.
[0142]
As shown in Tables 2 and 4, the obtained films had excellent dimensional stability, little unevenness in the magnetic layer, and could be used as magnetic tapes having excellent running durability, storage stability, and electromagnetic conversion characteristics. .
[0143]
Example 13
Unstretched two-layer laminate in the same manner as in Example 1 except that the particles mixed in the raw material (A1) in Example 1 were changed to contain 0.3% by weight of silica particles having an average particle diameter of 0.03 μm. A film was made. In the same manner as in Example 2, a biaxially stretched polyester film having a thickness of 4 μm was prepared from the unstretched film.
[0144]
As shown in Tables 2 and 4, the obtained films were excellent in dimensional stability, there was little unevenness in the magnetic layer, and a magnetic tape excellent in storage stability could be obtained.
[0145]
Example 14
The particles blended in the raw material (A1) in Example 1 contain 0.3% by weight of alumina particles having a particle diameter of 0.03 μm and 0.5% by weight of crosslinked polystyrene particles having a particle diameter of 0.4 μm. An unstretched film in which two layers were laminated was prepared in the same manner as in Example 1 except for the change. In the same manner as in Example 2, a biaxially stretched polyester film having a thickness of 4 μm was prepared from the unstretched film.
[0146]
As shown in Tables 2 and 4, the obtained films were excellent in dimensional stability, and could be used as magnetic tapes excellent in running durability and storage stability.
[0147]
Example 15
Two layers were laminated in the same manner as in Example 1 except that the particles blended in the raw material (B1) in Example 1 were changed to contain 0.5% by weight of calcium carbonate particles having an average particle diameter of 1.2 μm. A stretched film was made. In the same manner as in Example 2, a biaxially stretched polyester film having a thickness of 4 μm was prepared from the unstretched film.
[0148]
As shown in Tables 2 and 4, the obtained support was excellent in dimensional stability, there was little unevenness in the magnetic layer, and a magnetic tape excellent in storage stability and electromagnetic conversion characteristics could be obtained.
[0149]
[Table 1]

[0150]
[Table 2]

[0151]
[Table 3]

[0152]
[Table 4]

[0153]
【The invention's effect】
In the biaxially oriented polyester film, the heat shrinkage in the width direction, the crystal size Δc in the thickness direction, the elastic modulus Ym in the longitudinal direction of the film, and the ratio Ym / Yt of the elastic modulus Ym in the longitudinal direction to the elastic modulus Yt in the width direction are defined by the present invention. By setting it within the range, characteristics suitable for a base film of a high-density recording medium can be provided, and dimensional stability at the time of film processing is good. It is excellent, hardly causes a recording track shift when used as a magnetic tape, and has excellent running durability, storage stability, and electromagnetic conversion characteristics, and is extremely high in box office value.

Claims (7)

The heat shrinkage at −100 ° C. for 30 minutes in the width direction is −0.4% or more and less than 0%, the crystal size in the thickness direction {c} is 50 to 80 °, the elastic modulus Ym in the longitudinal direction is 6 to 15 GPa, and A biaxially oriented polyester film having a ratio Ym / Yt of the elastic modulus Ym to the elastic modulus Yt in the width direction of 1.2 to 2.5. The biaxially oriented polyester film according to claim 1, wherein the elastic modulus Yt in the width direction is 4.5 to 9 GPa. The biaxially oriented polyester film according to claim 1 or 2, wherein the thickness unevenness in the longitudinal direction is 1 to 5%. The ratio x / L of the difference x (゜) between the maximum value of the orientation angle in the width direction and the maximum value to the width L (m) is 0 to 15 (゜ / m). Biaxially oriented polyester film. The biaxial orientation according to any one of claims 1 to 4, wherein the surface roughness Ra of one surface A is 1.5 to 20 nm, and the surface roughness Ra of the other surface B is 5 to 50 nm. Polyester film. The polymer according to any one of claims 1 to 5, comprising at least one polymer selected from the group consisting of polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, a copolymer thereof, and a modified product thereof. 2. The biaxially oriented polyester film according to 1. A magnetic recording medium using the biaxially oriented polyester film according to claim 1.