JP4097501B2 - Biaxially stretched multilayer laminated film and method for producing the same - Google Patents
Biaxially stretched multilayer laminated film and method for producing the same Download PDFInfo
- Publication number
- JP4097501B2 JP4097501B2 JP2002301439A JP2002301439A JP4097501B2 JP 4097501 B2 JP4097501 B2 JP 4097501B2 JP 2002301439 A JP2002301439 A JP 2002301439A JP 2002301439 A JP2002301439 A JP 2002301439A JP 4097501 B2 JP4097501 B2 JP 4097501B2
- Authority
- JP
- Japan
- Prior art keywords
- layer
- film
- polyester
- multilayer laminated
- laminated film
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- 239000000203 mixture Substances 0.000 claims description 29
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- QYQADNCHXSEGJT-UHFFFAOYSA-N cyclohexane-1,1-dicarboxylate;hydron Chemical compound OC(=O)C1(C(O)=O)CCCCC1 QYQADNCHXSEGJT-UHFFFAOYSA-N 0.000 description 2
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Description
【０００１】
【発明の属する技術分野】
本発明は屈折率の低い層と屈折率の高い層とを交互に規則的に配置させた、層間の屈折率差および各層の厚みによって任意の波長帯の光を選択的に反射する多層積層フィルムに関する。
【０００２】
【従来の技術】
多層積層フィルムは、屈折率の低い層と高い層とを交互に多数積層したものであり、層間の構造的な光干渉によって、特定波長の光を選択的に反射または透過する光学干渉フィルムとすることができる。このような多層積層フィルムは、選択的に反射または透過する光の波長を可視光領域とすれば、構造的な発色により意匠性に優れた、例えば、玉虫色に見える真珠光沢フィルムとできる。しかも、ここで得られる意匠性は、多層積層フィルムの構造的な発色によることから、染料などによる発色と異なり退色の問題もない。また、このような多層積層フィルムは、膜厚を徐々に変化させたり、異なる反射ピークを有するフィルムを貼り合せたりすることで金属を使用したフィルムと同等の高い反射率を得ることができ、金属光沢フィルムや反射ミラーとして使用することもできる。
【０００３】
これらの多層積層フィルムは、特開昭５６−９９３０７号公報などでポリエチレンテレフタレートとポリメチルメタクリレートなどの異なる素材の熱可塑性樹脂を用いた多層積層フィルムが提案されている。また、特表平９−５０６８３７号公報やＷＯ０１／４７７１１号公報などで、例えば屈折率の高い層として、ポリエチレン２，６−ナフタレンジカルボキシレートからなる層を用い多層延伸フィルムも提案されている。
【０００４】
【特許文献１】
特開昭５６−９９３０７号公報
【特許文献２】
特表平９−５０６８３７号公報
【特許文献３】
ＷＯ０１／４７７１１号公報
【０００５】
【発明が解決しようとする課題】
しかしながら、このような多層積層フィルムは、層間の屈折率差を大きくするために、組成の異なる樹脂を組み合わせるため、各層間の密着が弱く層間剥離現象が発生しがちであった。また、組成の異なる樹脂を組み合わせるため、どうしても延伸を均一に行うのが難しく、強度の不十分な裂けやすいフィルムになり易かった。
【０００６】
すなわち、従来からの多層延伸フィルムの各層の屈折率差は、各層を構成する樹脂の有する屈折率差に由来していた。例えば、特開昭５６−９９３０７号公報に記載されているように、屈折率の高い層には、ポリエチレンテレフタレートを使用し、屈折率の低い層には、ポリメタクリレートのような屈折率の低い樹脂を用いてきていた。しかし、樹脂の有する屈折率に頼って層間の屈折率差を設ける従来の考え方では、各層を構成する樹脂は、どうしても組成の大きく異なる樹脂を選択する必要があり、層間の密着性の劣るものしか得られなかった。例えば、特表平９−５０６８３７号公報やＷＯ０１／４７７１１号公報では、屈折率の高い層に屈折率の高いポリエチレン２，６−ナフタレンジカルボキシレート（以下、ＰＥＮと称することがある。）を使用し、屈折率の低い層に熱可塑性エラストマーを使用した２軸延伸フィルムや屈折率の高い層に屈折率の高いＰＥＮを使用し、屈折率の低い層にイソフタル酸を３０モル％共重合したＰＥＮを使用した１軸延伸多層延伸フィルムが例示されている。これらの多層積層フィルムは屈折率の低い層を実質的に非晶質にしており、このような多層積層フィルムに延伸処理を施しても、層間密着性が十分に得られなかったり、２軸延伸処理が面方向に均一に行えず、膜質が不均一化したりして、実用上課題が潜在していた。
【０００７】
本発明は、従来の多層積層フィルムが有する上述の課題を解消し、層間の密着性が高く、しかも裂けにくい多層積層フィルムを提供することにある。
【０００８】
【課題を解決するための手段】
本発明の二軸延伸多層積層フィルムは、厚みが０．０５〜０．５μｍの範囲にある第１の層と、第１の層を構成するポリエステル組成物とは組成を異にするポリエステル組成物からなる厚みが０．０５〜０．５μｍの範囲にある第２の層とを１１層以上交互に積層した、波長３５０〜２０００ｎｍの光に対する反射率曲線に、最大反射率が反射率のベースラインよりも２０％以上高い反射ピークを有する積層フィルムであって、示差走査熱量測定法により測定される結晶化ピークが、１００〜１９０℃の範囲にあり、フィルム中のエチレンテレフタレート成分の割合が、ポリエステルの全繰返し単位を基準として、８０モル％以上であり、第１の層を構成するポリエステルが結晶性ポリエステルであり全繰返し単位の９０モル％以上がエチレンテレフタレート成分であり、第２の層を構成するポリエステルが結晶性ポリエステルであり全繰返し単位の７５〜９７モル％がエチレンテレフタレート成分であることを特徴とする。
【０００９】
すなわち、屈折率の高い層と屈折率の低い層を構成する樹脂組成を極限まで近くしても、屈折率の低い層を構成する樹脂の融点を屈折率の高い層を構成する樹脂より低くして、かつ２軸延伸処理後に該融点の低い樹脂からなる層の分子配向を緩和させることにより、層間の屈折率差を発現させつつ、２軸延伸加工性もすぐれ、層間密着性も優れた多層延伸フィルムが得られる。こうした本発明は、各層を構成する樹脂の組合せとして、従来から層間の屈折率差を発現させ難いとされていた極めて組成の近い樹脂の組合せを採用して、多層積層フィルムに十分な強度と層間の密着性を具備させながら、驚くべきことに層間の屈折率差も十分に具備させたものである。
【００１０】
また、本発明の好ましい態様として、示差走査熱量測定法により測定される融点が２つ以上存在し、そのそれぞれが少なくとも５℃以上異なること、また示差走査熱量測定法により測定される結晶化ピークが１００℃〜１９０℃の範囲に存在すること、フィルム中の全繰返し単位の１．５〜２０モル％がテレフタル酸またはイソフタル酸成分であること、第１の層を構成するポリエステルが、結晶性ポリエステルであり、全繰返し単位の９５モル％以上をエチレンテレフタレート成分で占められていること、第２の層を構成するポリエステルが、結晶性ポリエステルであり、全繰返し単位の７５〜９７モル％をエチレンテレフタレート成分で占められていること、フィルムの製膜方向および幅方向の破断強度が、いずれも５０ＭＰａ以上であることのいずれかを具備する二軸延伸多層積層フィルムも提供される。
【００１１】
さらにまた、本発明によれば、エチレンテレフタレートを主たる成分とする融点が２５０〜２６０℃の第１の層用ポリエステルと該第１の層用ポリエステルよりも融点が１５℃以上低い第２の層用ポリエステルとを１１層以上交互に積層したシート状物とする工程、得られたシート状物を製膜方向および幅方向にそれぞれ２〜５０倍延伸する工程、および第２の層用ポリエステルの融点よりも１０℃低い温度から第１の層用ポリエステルの融点よりも１５℃低い温度で熱固定する工程からなる二軸延伸多層積層フィルムの製造方法も提供される。
【００１２】
【発明の実施の形態】
本発明の二軸延伸多層積層フィルムは、ポリエステル組成物からなる厚みが０．０５〜０．５μｍの第１の層と、同じくポリエステル組成物からなる厚みが０．０５〜０．５μｍの第２の層とを交互に少なくとも１１層積層されたものである。なお、第１の層と第２の層とを構成するポリエステル組成物は、組成は非常に近いものであるが組成を異にすることが必要である。積層数が１１層未満だと、多重干渉による選択反射が小さく、十分な反射率が得られない。積層数の上限は、生産性などの観点から高々５０１層であることが好ましい。また、第１の層および第２の層は、層間の光干渉によって選択的に光を反射するために、それぞれ１層の厚みが０．０５〜０．５μｍである。本発明の多層積層フィルムが示す選択反射は、紫外光、可視光、近赤外光の範囲において、適宜、その層厚を調整することで実現できる。それぞれの１層厚みが０．０５μｍ未満であると、その反射光はポリエステル組成分の吸収によって反射性能が得られなくなる。一方、０．５μｍを超えると、層間の光干渉によって選択的に反射する光が赤外光の領域に達し、光学的特性としての有用性がえられなくなる。なお、説明の便宜上、屈折率の高い層を第１の層、屈折率の低い層を第２の層と、以下、称する。
【００１３】
また、本発明の二軸延伸多層積層フィルムは、波長３５０〜２０００ｎｍの光に対する反射率曲線に、最大反射率が反射率のベースラインよりも２０％以上高い、好ましくは３０％以上高い、さらに好ましくは５０％以上高い反射ピークを有する。図１は、本発明の二軸延伸多層積層フィルムの反射率曲線の一例を示す。該図１中の、１は最大反射率と反射率のベースラインの差、２は反射率のベースラインを示す。二軸延伸多層積層フィルムに、最大反射率が反射率のベースラインよりも２０％以上高い反射ピークが存在しないと、特定波長の光を選択的に反射または透過する光学干渉フィルムとしては使用できず、例えば真珠光沢フィルムとして使用できない。
【００１４】
ところで、本発明の最大の特徴は、上述の厚み構成で、二軸延伸多層積層フィルムを構成する第１の層と第２の層に、従来の樹脂の屈折率差に頼らず、十分な屈折率差を付与したことにある。樹脂の屈折率差に頼らずに二軸延伸多層積層フィルムを構成する第１の層と第２の層に十分な屈折率差を付与するには、例えば延伸後の熱処理によって屈折率差を付与する方法が挙げられる。そして、本発明の二軸延伸多層積層フィルムは、極めて組成の類似した樹脂を第１の層および第２の層を構成する樹脂として選択でき、そのような組成の類似した樹脂の選択によって層間の密着性が飛躍的に向上されたものである。したがって、本発明の二軸延伸多層積層フィルムは、全繰返し単位の８０モル％以上がエチレンテレフタレート成分のポリエステルからなる。エチレンテレフタレート成分が全繰返し単位の８０モル％未満だと、層間の密着性が低下する。なお、エチレンテレフタレート成分以外の共重合成分としては、融点を低下させやすいことから、２，６−ナフタレンジカルボン酸またはイソフタル酸成分が好ましい。２，６−ナフタレンジカルボン酸またはイソフタル酸成分の共重合割合は、繰返し単位を基準として、１．５〜２０モル％の範囲である。２，６−ナフタレンジカルボン酸またはイソフタル酸成分のモル数が、下限よりも少ないと、第１の層と第２の層に十分な屈折率差を付与しがたく、他方、２，６−ナフタレンジカルボン酸またはイソフタル酸成分のモル数が上限よりも多いと、第１の層と第２の層を構成するポリエステルの組成が大きく異なり、層間の密着性が低下しやすい。
【００１５】
［第１の層］
本発明において、第１の層を構成する樹脂は、主たる繰返し単位がエチレンテレフタレート成分からなるポリエステルである。好ましくは、後述の第２の層を構成するポリエステルよりも融点を高度に維持できることから、ホモポリエチレンテレフタレートまたは繰返し単位の９０モル％以上がエチレンテレフタレート成分からなる共重合ポリエチレンテレフタレートである。エチレンテレフタレート成分のモル数が繰返し単位の９０モル％未満だと、融点が低下し、後述の第２の層を構成するポリエステルとの融点差が得られがたく、結果として、多層延伸フィルムに十分な屈折率差を付与しがたい。これらの中でも、融点を高度に維持できることから、ホモポリエチレンテレフタレートが好ましい。エチレンテレフタレート成分以外の共重合成分としては、イソフタル酸、２，６−ナフタレンジカルボン酸、２，７−ナフタレンジカルボン酸のような他の芳香族カルボン酸；アジピン酸、アゼライン酸、セバシン酸、デカンジカルボン酸等の如き脂肪族ジカルボン酸；シクロヘキサンジカルボン酸の如き脂環族ジカルボン酸等の酸成分や、ブタンジオール、ヘキサンジオール等の如き脂肪族ジオール；シクロヘキサンジメタノールの如き脂環族ジオール等、グリコール成分を好ましく挙げることができる。
【００１６】
ところで、第１の層を構成する樹脂の融点は、２５０〜２６０℃の範囲であることが、後述の第２の層を構成する樹脂との融点差を比較的大きくできることから好ましい。第１の層を構成する樹脂の融点が下限よりも低いと、第２の層を構成する樹脂との融点差が小さくなり、結果として、得られる多層延伸フィルムに十分な屈折率差を付与することが困難になる。なお、共重合していないポリエチレンテレフタレートの融点は、通常２５６℃近傍である。
【００１７】
［第２の層］
本発明において、第２の層を構成する樹脂は、主たる繰返し単位がエチレンテレフタレート成分からなるポリエステルである。特に２軸延伸における製膜性の観点から、結晶性ポリエステルであることが好ましい。また、前述の第１の層を構成するポリエステルよりも融点を低くできることから、繰返し単位の７５〜９７モル％がエチレンテレフタレート成分からなり、３〜２５モル％がそれ以外の共重合成分からなる共重合ポリエチレンテレフタレートである。エチレンテレフタレート成分のモル数が繰返し単位の７５モル％未満であるか共重合成分のモル数が２５モル％を超えると、実質的にポリマーが非晶性を示し、２軸延伸での製膜性が低下し、かつ前述の第１の層を構成するポリエステルとの組成が大きく異なり、層間の密着性が低下しやすい。他方、エチレンテレフタレート成分のモル数が繰返し単位の９７モル％を超えるか共重合成分のモル数が３モル％未満だと、前述の第１の層を構成するポリエステルとの融点差が小さくなり、結果として、多層延伸フィルムに十分な反射率を付与することが困難となる。エチレンテレフタレート成分以外の共重合成分としては、イソフタル酸、２，６−ナフタレンジカルボン酸、２，７−ナフタレンジカルボン酸のような他の芳香族カルボン酸；アジピン酸、アゼライン酸、セバシン酸、デカンジカルボン酸等の如き脂肪族ジカルボン酸；シクロヘキサンジカルボン酸の如き脂環族ジカルボン酸等の酸成分や、ブタンジオール、ヘキサンジオール等の如き脂肪族ジオール；シクロヘキサンジメタノールの如き脂環族ジオール等、グリコール成分を好ましく挙げることができる。これらの中でも、比較的、延伸性を維持しながら融点を低下させやすいことから２，６−ナフタレンジカルボン酸またはイソフタル酸が好ましい。
【００１８】
ところで、第２の層を構成する樹脂の融点は、２００〜２４５℃の範囲であることが、前述の第１の層を構成する樹脂との融点差を比較的大きくできることから好ましい。第２の層を構成する樹脂の融点が上限よりも高いと、第１の層を構成する樹脂との融点差が小さくなり、結果として、得られる多層延伸フィルムに十分な屈折率差を付与することが困難になる。一方、第２の層を構成する樹脂の融点が下限よりも低くするには、第１の層を構成する樹脂との組成が大きく変更することになり、得られる二軸延伸多層積層フィルムに十分な層間の密着性を付与することが困難になる。なお、第２の層を構成する樹脂の融点は、フィルムにする前の段階から低い必要はなく、延伸処理後に低くなっていれば良い。例えば、ホモポリエチレンテレフタレートとそれ以外の他のポリエステルとを用意し、これらを溶融混練時にエステル交換させたものであってもよいことは容易に理解されるであろう。
【００１９】
［二軸延伸多層積層フィルム］
本発明の二軸延伸多層積層フィルムは、上述の第１の層および第２の層を、交互に少なくとも１１層積層したものである。なお、本発明の二軸延伸多層積層フィルムは、前述のとおり、十分な機械的強度を具備する観点から、２軸方向に延伸されていることが必要である。
【００２０】
特に、本発明の二軸延伸多層積層フィルムは、層間の密着性及び２軸延伸加工の製膜性を確保する観点から、第１の層、第２の層ともに、結晶性を示し、かつ第２の層の樹脂は、延伸後には、少なくとも部分的に溶融されていることが好ましい。このようにして得られた二軸延伸多層積層フィルムは、示差走査熱量測定法（ＤＳＣ）装置で測定される融点が２つ以上存在し、かつそれらの融点か５℃以上異なることが好ましい。ここで、測定される融点は、高融点側が高屈折率を示す第１の層であり、低融点側は、低屈折率を示す第２の層であることは容易に想像がつくであろう。また、さらに好ましくは、延伸後に第２の層は少なくとも部分的に溶融されているために、ＤＳＣ装置で測定される結晶化ピークが１００℃〜１９０℃の範囲に存在することが好ましい。結晶化ピークが１００℃未満であると、フィルムの延伸時に一方の層が急激に結晶化し、製膜時の製膜性が低下しやすく、かつ、膜質の均質性が低下しやすく、結果として、色の斑などが発生することがある。一方で結晶化ピークが１９０℃を越えると、熱固定処理で第二の層を融解するときに、結晶化が同時に起こり、十分な屈折率差を発現させ難くなる。
【００２１】
このように、本発明の二軸延伸多層積層フィルムは、ともに結晶性を示す第一の層の樹脂と第二の層の樹脂を延伸することによって、均質な膜質のフィルムが得られ、かつ延伸工程の後に第二の層を融解することで、層間密着性を向上させることと同時に反射性能を向上させることができる。従って、本発明の二軸延伸多層積層フィルムでは、ＤＳＣ装置による結晶ピークが１００℃〜１９０℃に存在し、融点差が５℃以上異なる２つ以上の融解ピークが観測される二軸延伸多層積層フィルムが好ましい。
【００２２】
また、本発明の二軸延伸多層積層フィルムは、延伸処理された方向の破断強度は、それぞれ５０ＭＰａ以上であることが好ましい。破断強度が５０ＭＰａ未満だと、多層延伸フィルムの加工時における取り扱い性が低下したり、製品にしたときの耐久性が低下したりする。また、破断強度が５０ＭＰａ以上であると、フィルムの腰が強くなり、巻取り性が向上するという利点もある。好ましい破断強度は、縦方向が８０ＭＰａ以上、特に１００ＭＰａ以上で、横方向が８０ＭＰａ以上、特に１００ＭＰａ以上である。また、縦方向と横方向の強度比は、３以下であることが耐引裂き性を十分に具備できることから好ましい。特に縦方向と横方向の強度比が２以下であると、さらに耐引裂き性を向上できることから好ましい。破断強度の上限は、特に限定はされないが、延伸工程の安定性を維持する観点から、高々５００ＭＰａであることが好ましい。
【００２３】
また、本発明の二軸延伸多層積層フィルムは、熱寸法安定性が高いことが特徴であり、延伸処理された方向（製膜方向および幅方向）の１５０℃で３０分間処理したときの熱収縮率が、それぞれ３．０％以下が好ましい。より好ましくは、２．５％以下、更に好ましくは、２．０％以下である。また、本発明の二軸延伸多層積層フィルムの２００℃で１０分間処理したときの製膜方向および幅方向の熱収縮率は、それぞれ５．０％以下が好ましい。より好ましい熱収縮率はそれぞれ４．０％以下、更に好ましい熱収縮率はそれぞれ３．０％以下である。熱寸法安定性が高いことから、本発明の二軸延伸多層積層フィルムは、ＰＶＣシートとの貼り合せや、エンボス加工などの工程適性に優れているといえる。
【００２４】
また、本発明の二軸延伸多層積層フィルムは、第１の層および第２の層を構成する樹脂が、ともに結晶性樹脂であることが好ましい。第１の層および第２の層を構成する樹脂がともに結晶性樹脂であると、延伸などの処理が不均一になりがたく、結果としてフィルムの厚み斑を小さくすることができる。この厚み斑の範囲は、光学的影響を及ぼすことが可能な面積を考慮した範囲内におけるフィルム厚みの最大値と最小値の差が、５μｍ未満であることが好ましい。これはより好ましくは３μｍ未満であり、さらにより好ましくは１．５μｍ未満である。フィルム厚みの変動率が５μｍ以上になると、反射する光の色が変化してしまい、色の斑となって現れる。
【００２５】
本発明の二軸延伸多層積層フィルムは、フィルムの巻取り性を向上させるため、第１の層または第２の層の少なくとも１方に、平均粒径が０．０１μｍ〜２μｍの不活性粒子を、多層延伸フィルムの重量を基準として、０．００１重量％〜０．５重量％含有することが好ましい。不活性粒子の平均粒径が下限よりも小さいか、含有量が下限よりも少ないと、多層延伸フィルムの巻取り性を向上させる効果が不十分になりやすく、他方、不活性粒子の含有量が上限を超えるか、平均粒径が上限を超えると、粒子による多層延伸フィルムの光学特性の悪化が顕著になる。好ましい不活性粒子の平均粒径は、０．０５〜１μｍ、特に０．１〜０．３μｍの範囲である。また、好ましい不活性粒子の含有量は、０．００５〜０．２重量％の範囲である。
【００２６】
二軸延伸多層積層フィルムに含有させる不活性粒子としては、例えばシリカ、アルミナ、炭酸カルシウム、燐酸カルシウム、カオリン、タルクのような無機不活性粒子、シリコーン、架橋ポリスチレン、スチレン−ジビニルベンゼン共重合体のような有機不活性粒子を挙げることができる。これらの不活性粒子は、その長径と短径の比が１．２以下、さらには１．１以下である球状粒子（以下、真球状粒子ということがある）であることが、フィルムの滑り性と光学特性を高度に維持できることから好ましい。また、これらの不活性粒子は、粒度分布がシャープであることが好ましく、例えば相対標準偏差が０．３未満、さらには０．２未満のものが好ましい。相対標準偏差が大きい粒子を使用すると、粗大粒子の頻度が多くなり、光学的な欠陥を生ずる場合がある。ここで、不活性粒子の平均粒径、粒径比及び相対標準偏差は、まず粒子表面に導電性付与のための金属を極く薄くスパッターし、電子顕微鏡にて、１万〜３万倍に拡大した像から、長径、短径および面積円相当径を求め、次いでこれらを次式に当てはめることで算出される。
平均粒径＝測定粒子の面積円相当径の総和／測定粒子数
粒径比＝粒子の平均長径／該粒子の平均短径
【００２７】
［塗布層］
ところで、本発明の二軸延伸多層フィルムに不活性粒子を含有させない場合などには、二軸延伸フィルムの加工工程において、易滑性塗布層を少なくとも片面に設けることが好ましい。塗布層を構成する組成物は、ポリエステル樹脂組成物やアクリル樹脂組成物に易滑性を付与させるために滑剤（フィラー、ワックス）を添加することが好ましい。滑剤を添加することで滑性、耐ブロッキング性が更に良化することができる。
【００２８】
塗布層のポリエステル樹脂は、ガラス転移点（Ｔｇ）が５０〜１００℃、更に好ましくは６０〜９０℃のものである。該ポリエステル樹脂は、水に可溶性または分散性のポリエステルが好ましいが、多少の有機溶剤を含有しても良い。
【００２９】
かかる塗布層のポリエステル樹脂としては、以下のような多塩基酸またはそのエステル形成誘導体とポリオールまたはそのエステル形成誘導体からなるものを好ましく挙げることができる。すなわち、多塩基酸成分としてはテレフタル酸、イソフタル酸、フタル酸、無水フタル酸、２，６−ナフタレンジカルボン酸、１、４−シクロヘキサンジカルボン酸、アジピン酸、セバシン酸、トリメリット酸、ピロメリット酸、ダイマー酸、５−ナトリウムスルホイソフタル酸等が挙げられる。これら酸成分を２種以上用いて共重合ポリエステル樹脂を合成する。また、若干量ながら不飽和多塩基酸成分のマレイン酸、イタコン酸等及びｐ−ヒドロキシ安息香酸等の如きヒドロキシカルボン酸を用いることができる。また、ポリオール成分としては、エチレングリコール、１，４−ブタンジオール、ジエチレングリコール、ジプロピレングリコール、１，６−ヘキサンジオール、１，４−シクロヘキサンジメタノール、キシレングリコール、ジメチロールプロパン、ポリ（エチレンオキシド）グリコール、ポリ（テトラメチレンオキシド）グリコール等が挙げられる。また、これらモノマーが挙げられるがこれらに限定されるものではない。
【００３０】
また、塗布層のアクリル樹脂としては、ガラス転移点（Ｔｇ）が−５０〜５０℃、更に好ましくは−５０〜２５℃のものを好ましく挙げることができる。該アクリル樹脂は、水に可溶性または分散性のアクリル樹脂が好ましいが、多少の有機溶剤を含有しても良い。かかるアクリル樹脂としては以下のようなアクリルモノマーから共重合できる。このアクリルモノマーとしては、アルキルアクリレート、アルキルメタクリレート（アルキル基としては、メチル基、エチル基、ｎ−プロピル基、イソプロピル基、ｎ−ブチル基、イソブチル基、ｔ−ブチル基、２−エチルヘキシル基、シクロヘキシル基等）；２−ヒドロキシエチルアクリレート、２−ヒドロキシエチルメタクリレート、２−ヒドロキシプロピルアクリレート、２−ヒドロキシプロピルメタクリレート等のヒドロキシ含有モノマー；グリシジルアクリレート、グリシジルメタクリレート、アリルグリシジルエーテル等のエポキシ基含有モノマー；アクリル酸、メタクリル酸、イタコン酸、マレイン酸、フマール酸、クロトン酸、スチレンスルホン酸及びその塩（ナトリウム塩、カリウム塩、アンモニウム塩、第三級アミン塩等）等のカルボキシ基またはその塩を含有するモノマー；アクリルアミド、メタクリルアミド、Ｎ−アルキルアクリルアミド、Ｎ−アルキルメタクリルアミド、Ｎ，Ｎ−ジアルキルアクリルアミド、Ｎ，Ｎ−ジアルキルメタクリレート（アルキル基としては、メチル基、エチル基、ｎ−プロピル基、イソプロピル基、ｎ−ブチル基、イソブチル基、ｔ−ブチル基、２−エチルヘキシル基、シクロヘキシル基等）、Ｎーアルコキシアクリルアミド、Ｎ−アルコキシメタクリルアミド、Ｎ，Ｎ−ジアルコキシアクリルアミド、Ｎ，Ｎ−ジアルコキシメタクリルアミド（アルコキシ基としては、メトキシ基、エトキシ基、ブトキシ基、イソブトキシ基等）、アクリロイルモルホリン、Ｎ−メチロールアクリルアミド、Ｎ−メチロールメタクリルアミド、Ｎ−フェニルアクリルアミド、Ｎ−フェニルメタクリルアミド等のアミド基を含有するモノマー；無水マレイン酸、無水イタコン酸等の酸無水物のモノマー；ビニルイソシアネート、アリルイソシアネート、スチレン、α−メチルスチレン、ビニルメチルエーテル、ビニルエチルエーテル、ビニルトリアルコキシシラン、アルキルマレイン酸モノエステル、アルキルフマール酸モノエステル、アルキルイタコン酸モノエステル、アクリロニトリル、メタクリロニトリル、塩化ビニリデン、エチレン、プロピレン、塩化ビニル、酢酸ビニル、ブタジエン等のモノマーが挙げられる。また、これらモノマーを挙げられるがこれらに限定されるものではない。
【００３１】
塗膜層に含有させる滑剤としては、従来からポリエステルフィルムの滑り性付与剤として知られているものを好適に用いることができる。例えば、炭酸カルシウム粒子、酸化カルシウム粒子、酸化アルミニウム粒子、カオリン粒子、酸化珪素粒子、酸化亜鉛粒子、カーボンブラック粒子、炭化珪素粒子、酸化錫粒子、架橋アクリル樹脂粒子、架橋ポリスチレン樹脂粒子、メラミン樹脂粒子、架橋シリコーン樹脂粒子等が挙げられる。特に、酸化珪素粒子、架橋アクリル樹脂粒子、架橋ポリスチレン樹脂粒子などが塗布層への分散性などの観点から特に好ましい。
【００３２】
塗膜を形成するための塗液は、水溶液、水分散液或いは乳化液等の水性塗液の形態で使用されるのが好ましい。塗膜を形成するために、必要に応じて、前記組成物以外の他の樹脂、例えばオキサゾリン基を有する重合体、メラミン、エポキシ、アジリジン等の架橋剤、帯電防止剤、着色剤、界面活性剤、紫外線吸収剤、滑剤（フィラー、ワックス）などを添加することができる。塗液が水性塗液である場合の固形分濃度は、通常２０重量％以下であり、更には１〜１０重量％であることが好ましい。この割合が１重量％未満であると、ポリエステルフィルムへの塗れ性が不足し、一方、２０重量％を越えると塗剤の安定性や塗布外観が悪化することがある。
【００３３】
水性塗液のフィルムへの塗布は、任意の段階で実施することができるが、二軸延伸多層積層フィルムの製造過程で実施するのが好ましく、さらには配向結晶化が完了する前のフィルムに塗布するのが好ましい。ここで、結晶配向が完了する前のフィルムとは、未延伸フィルム、未延伸フィルムを縦方向または横方向の何れか一方に配向せしめた一軸配向フィルム、さらには縦方向および横方向の二方向に低倍率延伸配向せしめたもの（最終的に縦方向また横方向に再延伸せしめて配向結晶化を完了せしめる前の二軸延伸フィルム）等を含むものである。なかでも、未延伸フィルムまたは一方向に配向せしめた一軸延伸フィルムに、上記組成物の水性塗液を塗布し、そのまま縦延伸および／または横延伸と熱固定とを施すのが好ましい。
【００３４】
水性塗液をフィルムに塗布する際には、塗布性を向上させるための予備処理としてフィルム表面にコロナ表面処理、火炎処理、プラズマ処理等の物理処理を施すか、あるいは組成物と共にこれと化学的に不活性な界面活性剤を併用することが好ましい。かかる界面活性剤は、ポリエステルフィルムへの水性塗液の濡れを促進するものであり、例えば、ポリオキシエチレンアルキルフェニルエーテル、ポリオキシエチレン−脂肪酸エステル、ソルビタン脂肪酸エステル、グリセリン脂肪酸エステル、脂肪酸金属石鹸、アルキル硫酸塩、アルキルスルホン酸塩、アルキルスルホコハク酸塩等のアニオン型、ノニオン型界面活性剤を挙げることができる。界面活性剤は、塗膜を形成する組成物中に、１〜１０重量％含まれていることが好ましい。
【００３５】
塗液の塗布量は、塗膜の厚さが０．０２〜０．３μｍ、好ましくは０．０７〜０．２５μｍの範囲となるような量であるのが好ましい。塗膜の厚さが薄過ぎると、接着力が不足し、逆に厚過ぎると、ブロッキングを起こしたり、ヘーズ値が高くなったりする可能性がある。
【００３６】
塗布方法としては、公知の任意の塗工法が適用できる。例えばロールコート法、グラビアコート法、ロールブラッシュ法、スプレーコート法、エアーナイフコート法、含浸法、カーテンコート法などを単独または組合せて用いることができる。なお、塗膜は、必要に応じ、フィルムの片面のみに形成してもよいし、両面に形成してもよい。
【００３７】
本発明の二軸延伸多層積層フィルムは、その厚み分布が均一であると、特定の波長帯の光を選択的に反射できることから好ましい。なお、厚み分布は、第１の層だけの厚み分布と第２の層だけの厚み分布が均一であればよく、第１の層と第２の層の厚みは、異なっていても良い。また、使用する用途が、例えば反射ミラーや金属光沢フィルムなどの場合、特定の波長帯だけでなく、可視光線の波長帯全体を反射することが好ましい。このような場合、反射する光の波長帯が異なる本発明の二軸延伸多層積層フィルムを複数枚貼合わせたり、第１の層と第２の層の厚みを徐々に変化させた二軸延伸多層積層フィルムを用いることが好ましく、これらも本発明の二軸延伸多層積層フィルムに含まれることは、容易に理解されるであろう。
【００３８】
本発明の二軸延伸多層積層フィルムは、ヘーズが１０％以下であることが好ましい。不活性粒子による光の散乱などでヘーズが１０％以下になると、フィルム自体が白っぽくなり、光沢が失われる。
【００３９】
［二軸延伸多層積層フィルムの製造方法］
本発明の二軸延伸多層積層フィルムは、融点が２５０〜２６０℃のエチレンテレフタレート成分を主たる繰返し単位とするポリエステル（第１の層用）と、該第１の層を構成するポリエステルよりも、延伸処理後の融点が少なくとも１０℃以上低い、エチレンテレフタレート成分を主たる繰返し単位とするポリエステル（第２の層用）とを、溶融状態で交互に少なくとも１１層以上重ね合わせた状態で、押出し、多層未延伸フィルム（シート状物とする工程）とする。なお、第１の層および第２の層を構成するポリエステルは、前述の第１の層および第２の層で説明したのと、同様である。第１の層用ポリエステルの融点が２５０℃未満だと、第２の層用ポリエステルとの融点差が十分につかず、結果として、得られる多層延伸フィルムの層間に十分な屈折率差が付与できない。一方、ホモポリエチレンテレフタレートの融点が２５６℃近傍であることから、第１の層用ポリエステルの融点の上限は高々２６０℃程度である。また、第２の層用ポリエステルの融点が、第１の層用ポリエステルよりも１５℃以上低くないときは、第２の層用ポリエステルとの融点差が十分につかず、結果として、得られる多層延伸フィルムの層間に十分な屈折率差が付与できない。第１の層用ポリエステルの融点と第２の層用ポリエステルの融点差の上限は、両者の密着性を維持する観点から、高々５０℃であることが好ましい。
【００４０】
このようにして得られた多層未延伸フィルムは、製膜方向とそれに直交する幅方向の２軸方向（フィルム面に沿った方向）に延伸される。延伸温度は、第１の層のポリエステルのガラス転移点の温度（Ｔｇ）〜Ｔｇ＋５０℃の範囲が好ましい。このときの面積倍率は５〜５０倍であることが好ましい。延伸倍率が大きい程、第１の層および第２の層の個々の層における面方向のバラツキが、延伸による薄層化により小さくなる、すなわち、多層延伸フィルムの光干渉が面方向に均一になるので好ましい。２方向に延伸する際の延伸方法は、逐次２軸延伸でも同時２軸延伸であってもよい。
【００４１】
本発明の最大の特徴は、このようにして延伸された多層フィルムを、第２の層用ポリエステルの融点よりも１０℃低い温度から、第１の層用ポリエステルの融点よりも１５℃低い温度の範囲で熱処理して、第２の層内の分子鎖の配向を緩和させ、第２の層の屈折率を低下させることにある。熱処理の温度が、第２の層用ポリエステルの融点よりも１０℃を超えて低いと、第２の層内の分子鎖の配向を緩和させて屈折率を低下させる効果が不十分となり、得られる多層延伸フィルムに十分な屈折率差を付与できない。一方、熱処理の温度が、第１の層用ポリエステルの融点よりも１０℃以上低い温度でないと、第１の層内の分子鎖の配向も緩和されて屈折率が低下し、得られる多層延伸フィルムに十分な屈折率差を付与できない。好ましい熱処理の温度は、第２の層用ポリエステルの融点よりも６℃低い温度から、第１の層用ポリエステルの融点よりも１６℃低い温度、さらには第２の層用ポリエステルの融点よりも２℃低い温度から、第１の層用ポリエステルの融点よりも１８℃低い温度である。なお、熱処理の時間は、１〜６０秒が好ましい。
【００４２】
また、この熱処理の温度や時間を変化させることにより、樹脂の組成を変化させることなく、第２の層の屈折率を調整することができる、すなわち樹脂の組成を変化させることなく、多層延伸フィルムの反射特性を変化させることができる。
【００４３】
【実施例】
実施例をもって、本発明をさらに説明する。なお、実施例中の物性や特性は、下記の方法にて測定または評価した。
【００４４】
（１）ポリエステル樹脂の融点およびガラス転移点（Ｔｇ）
ポリエステル樹脂試料を１０ｍｇサンプリングし、ＤＳＣ装置（ＴＡインスツルメンツ社製、商品名：ＤＳＣ２９２０）を用い、２０℃／ｍｉｎ．の昇温速度で、融点を測定する。
【００４５】
（２）各層の厚み
サンプルを三角形に切り出し、包埋カプセルに固定後、エポキシ樹脂にて包埋する。そして、包埋されたサンプルをミクロトーム（ＵＬＴＲＡＣＵＴ−Ｓ、製造元：ライヘルト社）で製膜方向と厚み方向に沿って切断し、厚さ５０ｎｍの薄膜切片にした。得られた薄膜切片を、透過型電子顕微鏡（製造元：日本電子（株）、商品名：ＪＥＭ２０１０）を用いて、加速電圧１００ｋＶにて観察・撮影し、写真から各層の厚みを測定した。
【００４６】
（３）フィルムのＤＳＣによる融点、結晶化ピークの測定
サンプルフィルムを１０ｍｇサンプリングし、ＤＳＣ装置（ＴＡインスツルメンツ社製、商品名：ＤＳＣ２９２０）にて、２０℃／ｍｉｎ．の昇温速度で、結晶化温度および融点を測定する。
【００４７】
（４）反射率、反射波長
分光光度計（島津製作所製、ＭＰＣ−３１００）を用い、各波長でのアルミ蒸着したミラーとの相対鏡面反射率を波長３５０ｎｍから２０００ｎｍの範囲で測定する。その測定された反射率の中で最大のものを、最大反射率としその波長を反射波長とする。
【００４８】
（５）全光線透過率及びヘーズ
ＪＩＳ Ｋ７１０５に準じて、ヘーズ測定機（日本電色工業（株）製、ＮＤＨ−２０）を使用して全光線透過率Ｔt（％）と散乱光透過率Ｔd（％）とを測定し、以下の式からヘーズ（％）を算出する。
ヘーズ（％）＝（Ｔd／Ｔt）×１００
【００４９】
（６）破断強度
製膜方向の破断強度は、サンプルフィルムを試料幅（幅方向）１０ｍｍ、長さ（製膜方向）１５０ｍｍに切り出し、チャック間１００ｍｍ、引っ張り速度１００ｍｍ／ｍｉｎで、チャート速度５００ｍ／ｍｉｎの条件でインストロンタイプの万能引っ張り試験装置にてサンプルを引っ張る。そして得られた荷重−伸び曲線から破断強度を測定した。
【００５０】
また、幅方向の破断強度は、サンプルフィルムを試料幅（製膜方向）１０ｍｍ、長さ（幅方向）１５０ｍｍに切り出す以外は、製膜方向の破断強度の測定と同様に行った。
【００５１】
（７）熱収縮率
１５０℃で３０分間処理したときの熱収縮率は、１５０℃に温度設定されたオーブンの中に無緊張状態で３０分間フィルムを保持し、加熱処理前後での寸法変化を熱収縮率として下記式により算出する。
熱収縮率％＝（（Ｌ０−Ｌ）／Ｌ０）×１００
Ｌ０：熱処理前の標点間距離。
Ｌ ：熱処理後の漂点間距離。
【００５２】
また、２００℃で１０分間処理したときの熱収縮率は、２００℃に温度設定されたオーブンの中に無緊張状態で１０分間フィルムを保持し、加熱処理前後での寸法変化を熱収縮率として上記式により算出する。
【００５３】
（８）厚み変動幅
製膜方向および幅方向にそれぞれ１ｍ×１ｍとなるように切り出したフィルムサンプルを縦方向及び幅方向に沿ってそれぞれ２ｃｍ幅で２５本に切り出し、各サンプルの厚みを電子マイクロメータ及びレコーダー（Ｋ−３１２Ａ，Ｋ３１０Ｂ、安立電気（株）製）を使用して連続的に測定する。さらに測定点を２００ｍｍごとに細分化し、その中での厚みの最大値と最小値を読み取り、その差を厚み変動幅とする。
【００５４】
（９）層間の密着性
サンプルフィルム（１０ｍｍ×５０ｍｍ）の両面に２４ｍｍ幅の粘着テープ（ニチバン社製、商品名：セロテープ）を１００ｍｍ貼り付け、１８０度の剥離角度で剥がした後、剥離面を観察する。これを各１０サンプルについて行い、層間剥離の生じた回数を算出した。
【００５５】
（１０）色の斑
Ａ４サイズのサンプルフィルムを１０枚用意し、それぞれのサンプルフィルムを白色の普通紙に重ね、３０ルクスの照明の下、目視にてサンプルフィルム内の透過色の色の斑を評価した。また、Ａ４サイズのサンプルフィルムを１０枚用意し、それぞれのサンプルフィルムの裏面を黒色のスプレーにて着色した後、３０ルクスの照明の下、目視にてサンプルフィルム内の反射色の色の斑を評価した。
【００５６】
そして、透過色および反射色の色の斑を総合して、以下の評価基準で判断した。
○：サンプル内に視認できる色の斑がない。
△：サンプル内に一部、色の異なる部分が見られる。
×：明らかに斑や筋となって見える色斑が確認できる。
【００５７】
【実施例１】
固有粘度（オルトクロロフェノール、３５℃）０．６３のポリエチレンテレフタレート（表１中で「ＰＥＴ」と表記）を第１の層用ポリエステルとし、第２の層用ポリエステルとしてイソフタル酸を１２モル％共重合した固有粘度（オルトクロロフェノール、３５℃）０．６１の共重合ポリエチレンテレフタレート（表１中で「ＩＡ１２ＰＥＴ」と表記）に、不活性粒子として真球状シリカ粒子（平均粒径：１．５μｍ、長径と短径の比：１．０２、粒径の平均偏差：０．１。表１中では種類「ア」と表記）を０．１０重量％添加したものを準備した。そして、第１の層用ポリエステルおよび第２の層用ポリエステルを、それぞれ１７０℃で３時間乾燥後、押出し機に供給し、２８０℃まで加熱して溶融状態とし、第１の層用ポリエステルを１０１層、第２の層用ポリエステルを１００層に分岐させた後、第１の層と第２の層が交互に積層するような多層フィードブロック装置を使用して、その積層状態を保持したままダイへと導き、キャスティングドラム上にキャストして各層の厚みが等しくなるように第１の層と第２の層が交互に積層された総数２０１層の未延伸多層積層フィルムを作成した。このとき第１の層と第２の層の押出し量が１：１になるように調整し、かつ、両端層が第１の層になるように積層した。この多層未延伸フィルムを９０℃の温度で製膜方向に３．６倍延伸し、更に９５℃の温度で幅方向に３．９倍に延伸し、２３０℃で３秒間熱固定処理を行った。
【００５８】
得られた二軸延伸多層積層フィルムの物性を表２に示す。
【００５９】
【実施例２、３、および５〜７】
第２の層用ポリエステルおよび製造条件を表１に示すように変更する以外は、実施例１と同様な操作を繰り返した。なお表１で各層の樹脂の種類として記した記号は、「ＩＡ８ＰＥＴ」がイソフタル酸を８モル％共重合した固有粘度（オルトクロロフェノール、３５℃）０．６５のポリエチレンテレフタレートであり、「ＩＡ２０ＰＥＴ」がイソフタル酸を２０モル％共重合した固有粘度（オルトクロロフェノール、３５℃）０．５８のポリエチレンテレフタレートである。また不活性粒子の種類として記した記号は、「イ」が塊状炭酸カルシウム（平均粒径：１．５μｍ、長径と短径の比：１．３０、粒径の平均偏差：０．３）であり、「ウ」が真球状シリコーン粒子（平均粒径：０．１μｍ、長径と短径の比：１．１０、粒径の平均偏差：０．２）である。
【００６０】
得られた多層延伸フィルムの物性を表２に示す。
【００６１】
【実施例４】
固有粘度（オルトクロロフェノール、３５℃）０．６３のポリエチレンテレフタレート（ＰＥＴ）を第１の層用ポリエステルとし、第２の層用ポリエステルとして２，６−ナフタレンジカルボン酸を１０モル％共重合した固有粘度（オルトクロロフェノール、３５℃）０．７０の共重合ポリエチレンテレフタレート（表１中で「ＮＤＣ１０ＰＥＴ」と表記）を準備した。そして、第１の層用ポリエステルおよび第２の層用ポリエステルを、それぞれ１７０℃で３時間乾燥後、押出し機に供給し、２８０℃まで加熱して溶融状態とし、第１の層用ポリエステルを１０１層、第２の層用ポリエステルを１００層に分岐させた後、第１の層と第２の層が交互に積層するような多層フィードブロック装置を使用して、その積層状態を保持したままダイへと導き、キャスティングドラム上にキャストして各層の厚みが等しくなるように第１の層と第２の層が交互に積層された総数２０１層の未延伸多層積層フィルムを作成した。このとき両端層が第１の層になるように積層した。この多層未延伸フィルムを９０℃の温度で製膜方向に３．６倍延伸し、その片面に下記塗膜用組成物の濃度１．６％の水性塗液をロールコーターで、乾燥後の厚みが０．１μｍになるように均一に塗布した。
【００６２】
［塗膜用組成物］
・酸成分がテレフタル酸８５モル％／イソフタル酸１３モル％／５−ナトリウムスルホイソフタル酸１２モル％、グリコール成分がブチレングリコール８０モル％／ビスフェノールＡのエチレンオキシド２モル付加物２０モル％である共重合ポリエステル樹脂：４５重量％
・メチルメタクリレート８０モル％／エチルアクリレート１０モル％／Ｎ−メチロールアクリルアミド５モル％／２−ヒドロキシエチルメタクリレート５モル％からなるアクリル樹脂：３５重量％
・メチルメタクリレート・ジビニルベンゼン共重合体からなる４０ｎｍの平均粒子径を有する滑剤：１５重量％
・ポリオキシエチレン（ｎ＝７）ラウリルエーテルからなる界面活性剤：５重量％
こうした組成からなる塗液を塗布後、８０℃で乾燥し、９５℃の温度でフィルムを幅方向に３．９倍に延伸し、２３０℃で３秒間熱固定処理を行った。
【００６３】
得られた二軸延伸多層積層フィルムの物性を表２に示す。
【００６４】
【比較例１】
固有粘度（オルトクロロフェノール、３５℃）０．６５のポリエチレン２，６−ナフタレンジカルボキシレート（表１中で「ＰＥＮ」と表記）に、不活性粒子として真球状シリカ粒子（平均粒径：０．２０μｍ、長径と短径の比：１．０２、粒径の平均偏差：０．１。表１中では種類「エ」と表記）を０．１０重量％添加したものを第１の層用ポリエステルとし、イソフタル酸を１２モル％共重合した固有粘度（オルトクロロフェノール、３５℃）０．６１の共重合ポリエチレンテレフタレート（ＩＡ１２ＰＥＴ）を第２の層用ポリエステルとして準備した。そして、第１の層用ポリエステルおよび第２の層用ポリエステルを、それぞれ１７０℃で５時間乾燥後、押出し機に供給し、３００℃まで加熱して溶融状態とし、第１の層用ポリエステルを１０１層、第２の層用ポリエステルを１００層に分岐させた後、第１の層と第２の層が交互に積層するような多層フィードブロック装置を使用して、その積層状態を保持したままダイへと導き、キャスティングドラム上にキャストして各層の厚みが等しくなるように第１の層と第２の層が交互に積層された総数２０１層の未延伸多層積層フィルムを作成した。このとき第１の層と第２の層の押出し量が１：１になるように調整し、かつ、両端層が第２の層になるように積層した。この多層未延伸フィルムを１１０℃の温度で製膜方向に３．６倍延伸し、更に１１５℃の温度で幅方向に３．９倍に延伸し、２００℃で３秒間熱固定処理を行った。
【００６５】
得られた多層延伸フィルムは、色斑がひどく、層間の剥離特性の劣るフィルムであった。その物性を表２に示す。
【００６６】
【比較例２〜４】
製造条件を表１に示すように変更した以外は、比較例１と同様な操作を繰り返した。なおなお表１で各層の樹脂の種類として記した記号において、「ＩＡ３ＰＥＴ」はイソフタル酸を３モル％共重合した固有粘度（オルトクロロフェノール、３５℃）０．６５のポリエチレンテレフタレートである。比較例２と３で得られたフィルムは、反射性能に劣るフィルムであった。比較例４で得られたフィルムは比較例１同様、色斑がひどく、層間の剥離特性の劣るフィルムであった。その物性を表２に示す。
【００６７】
【表１】
【表２】
【発明の効果】
本発明の２軸延伸多層積層フィルムは、構造的な発色により玉虫色に見えるなど優れた意匠性を有するだけでなく、優れた層間の密着性および高度の破断強度を有することから、その工業的価値は高い。特に本発明の二軸延伸多層積層ポリエステルフィルムは、外来光にさらされ、装飾性だけでなく、取り扱い性や内容物を保護しうる高度の機械特性が求められる包装用フィルムをはじめ、極狭幅にスリットされた装飾性繊維や、その選択波長反射性能からホログラムシールの代替用偽造防止フィルムなどに極めて好適である。
【図面の簡単な説明】
【図１】フィルムの反射率特性例。
【符号の説明】
１ 最大反射率と反射率のベースラインの差
２ 反射率のベースライン[0001]
BACKGROUND OF THE INVENTION
The present invention is a multilayer laminated film that selectively reflects light in an arbitrary wavelength band according to the difference in refractive index between layers and the thickness of each layer, in which layers having a low refractive index and layers having a high refractive index are alternately and regularly arranged. About.
[0002]
[Prior art]
The multilayer laminated film is obtained by alternately laminating a plurality of layers having a low refractive index and a layer having a high refractive index, and is an optical interference film that selectively reflects or transmits light of a specific wavelength by structural optical interference between the layers. be able to. Such a multilayer laminated film can be made into a pearly luster film that is excellent in design, for example, looks like iridescent, due to structural color development, if the wavelength of light that is selectively reflected or transmitted is in the visible light region. In addition, the design property obtained here is due to the structural coloration of the multilayer laminated film, so that there is no problem of fading unlike the coloration due to dyes. In addition, such a multilayer laminated film can obtain a high reflectivity equivalent to a film using metal by gradually changing the film thickness or by laminating films having different reflection peaks. It can also be used as a glossy film or a reflection mirror.
[0003]
As these multilayer laminated films, multilayer multilayer films using thermoplastic resins of different materials such as polyethylene terephthalate and polymethyl methacrylate have been proposed in JP-A-56-99307. Further, in Japanese Patent Laid-Open No. 9-506837 and WO01 / 47711, a multilayer stretched film using a layer made of
[0004]
[Patent Document 1]
JP-A-56-99307 [Patent Document 2]
Japanese Patent Publication No. 9-506837 [Patent Document 3]
WO01 / 47711 gazette [0005]
[Problems to be solved by the invention]
However, since such multilayer laminated films combine resins having different compositions in order to increase the difference in refractive index between layers, adhesion between the layers is weak and the delamination phenomenon tends to occur. In addition, since resins having different compositions are combined, it is difficult to uniformly stretch the film, and it is easy to form a film with insufficient strength and easy to tear.
[0006]
That is, the refractive index difference of each layer of the conventional multilayer stretched film is derived from the refractive index difference of the resin constituting each layer. For example, as described in JP-A-56-99307, polyethylene terephthalate is used for a layer having a high refractive index, and a resin having a low refractive index such as polymethacrylate is used for a layer having a low refractive index. Has been used. However, according to the conventional concept of providing a difference in refractive index between layers depending on the refractive index of the resin, it is necessary to select resins having different compositions for each layer, and the adhesion between the layers is inferior. It was not obtained. For example, in Japanese Patent Publication No. 9-506837 and WO 01/47711,
[0007]
An object of the present invention is to provide a multilayer laminated film that solves the above-mentioned problems of conventional multilayer laminated films, has high interlayer adhesion, and is difficult to tear.
[0008]
[Means for Solving the Problems]
The biaxially stretched multilayer laminated film of the present invention is a polyester composition having a composition different from that of the first layer having a thickness in the range of 0.05 to 0.5 μm and the polyester composition constituting the first layer. A reflectance curve for light with a wavelength of 350 to 2000 nm, in which 11 or more second layers having a thickness of 0.05 to 0.5 μm are alternately stacked, and the maximum reflectance is the baseline of the reflectance A crystallization peak measured by a differential scanning calorimetry method in the range of 100 to 190 ° C., and the proportion of the ethylene terephthalate component in the film is a polyester film. of, based on the total repeating units state, and are more than 80 mol%, the polyester constituting the first layer is more than 90 mol% of the total repeating units be crystalline polyester ethylene It is a terephthalate component, and the polyester constituting the second layer is a crystalline polyester, and 75 to 97 mol% of all repeating units is an ethylene terephthalate component .
[0009]
That is, even if the resin composition constituting the high refractive index layer and the low refractive index layer is close to the limit, the melting point of the resin constituting the low refractive index layer is made lower than that of the resin constituting the high refractive index layer. In addition, by relaxing the molecular orientation of the layer made of the resin having a low melting point after the biaxial stretching treatment, a multi-layer having excellent biaxial stretching workability and excellent interlayer adhesion while expressing the refractive index difference between the layers. A stretched film is obtained. The present invention employs a combination of resins having a very close composition, which has conventionally been difficult to express a difference in refractive index between layers, as a combination of resins constituting each layer, so that the multilayer laminated film has sufficient strength and interlayer. Surprisingly, the difference in refractive index between the layers is sufficiently provided.
[0010]
Further, as a preferred embodiment of the present invention, there are two or more melting points measured by differential scanning calorimetry, each of which differs by at least 5 ° C., and a crystallization peak measured by differential scanning calorimetry It exists in the range of 100 ° C. to 190 ° C., 1.5 to 20 mol% of all repeating units in the film is a terephthalic acid or isophthalic acid component, and the polyester constituting the first layer is a crystalline polyester 95% by mole or more of all repeating units are occupied by ethylene terephthalate component, the polyester constituting the second layer is a crystalline polyester, and 75 to 97% by mole of all repeating units is ethylene terephthalate. Occupied by the components, the breaking strength in the film forming direction and the width direction of the film are both 50 MPa or more Biaxially oriented multi-layer laminate film comprising any of the possible is also provided.
[0011]
Furthermore, according to the present invention, the first layer polyester having a melting point of 250 to 260 ° C. mainly comprising ethylene terephthalate and the second layer having a melting point of 15 ° C. or more lower than that of the first layer polyester. From the melting point of the second layer polyester, the step of forming a sheet-like product in which 11 or more layers of polyester are alternately laminated, the step of stretching the obtained sheet-like product in the film forming direction and the width direction, respectively, 2 to 50 times There is also provided a method for producing a biaxially stretched multilayer laminated film comprising a step of heat setting from a temperature lower by 10 ° C. to a temperature lower by 15 ° C. than the melting point of the first layer polyester.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The biaxially stretched multilayer laminated film of the present invention includes a first layer having a thickness of 0.05 to 0.5 μm made of a polyester composition and a second layer having a thickness of 0.05 to 0.5 μm also made of a polyester composition. 11 layers are alternately stacked. The polyester composition constituting the first layer and the second layer has a very close composition but needs to have a different composition. If the number of layers is less than 11, selective reflection due to multiple interference is small, and sufficient reflectance cannot be obtained. The upper limit of the number of stacked layers is preferably at most 501 from the viewpoint of productivity. The first layer and the second layer each have a thickness of 0.05 to 0.5 μm in order to selectively reflect light by optical interference between layers. The selective reflection exhibited by the multilayer laminated film of the present invention can be realized by appropriately adjusting the layer thickness in the range of ultraviolet light, visible light, and near infrared light. When the thickness of each layer is less than 0.05 μm, the reflected light cannot be reflected due to absorption of the polyester composition. On the other hand, if it exceeds 0.5 μm, the light selectively reflected by the light interference between layers reaches the infrared light region, and the usefulness as an optical characteristic cannot be obtained. For convenience of explanation, a layer having a high refractive index is hereinafter referred to as a first layer, and a layer having a low refractive index is hereinafter referred to as a second layer.
[0013]
Further, the biaxially stretched multilayer laminated film of the present invention has a reflectance curve with respect to light having a wavelength of 350 to 2000 nm, the maximum reflectance is 20% or more higher than the reflectance baseline, preferably 30% or more, more preferably Has a reflection peak higher by 50% or more. FIG. 1 shows an example of the reflectance curve of the biaxially stretched multilayer laminated film of the present invention. In FIG. 1, 1 is the difference between the maximum reflectance and the baseline of reflectance, and 2 is the baseline of reflectance. If the biaxially stretched multilayer laminate film does not have a reflection peak whose maximum reflectance is 20% or more higher than the baseline of reflectance, it cannot be used as an optical interference film that selectively reflects or transmits light of a specific wavelength. For example, it cannot be used as a pearlescent film.
[0014]
By the way, the greatest feature of the present invention is that the first layer and the second layer constituting the biaxially stretched multilayer laminated film have the above-described thickness configuration, and do not rely on the refractive index difference of the conventional resin, and are sufficiently refracted. It is in giving a rate difference. In order to give a sufficient refractive index difference to the first layer and the second layer constituting the biaxially stretched multilayer laminated film without depending on the refractive index difference of the resin, for example, the refractive index difference is given by heat treatment after stretching. The method of doing is mentioned. In the biaxially stretched multilayer laminated film of the present invention, a resin having a very similar composition can be selected as a resin constituting the first layer and the second layer. Adhesiveness has been dramatically improved. Therefore, in the biaxially stretched multilayer laminated film of the present invention, 80 mol% or more of all repeating units are made of polyester having an ethylene terephthalate component. When the ethylene terephthalate component is less than 80 mol% of all repeating units, the adhesion between the layers is lowered. The copolymer component other than the ethylene terephthalate component is preferably a 2,6-naphthalenedicarboxylic acid or isophthalic acid component because the melting point is likely to be lowered. The copolymerization ratio of the 2,6-naphthalenedicarboxylic acid or isophthalic acid component is in the range of 1.5 to 20 mol% based on the repeating unit. If the number of moles of the 2,6-naphthalenedicarboxylic acid or isophthalic acid component is less than the lower limit, it is difficult to give a sufficient refractive index difference between the first layer and the second layer, while 2,6-naphthalene When the number of moles of the dicarboxylic acid or isophthalic acid component is larger than the upper limit, the composition of the polyester constituting the first layer and the second layer is greatly different, and the adhesion between the layers tends to be lowered.
[0015]
[First layer]
In the present invention, the resin constituting the first layer is a polyester whose main repeating unit is an ethylene terephthalate component. Preferably, homopolyethylene terephthalate or copolymer polyethylene terephthalate in which 90 mol% or more of repeating units are composed of an ethylene terephthalate component can be maintained at a higher melting point than the polyester constituting the second layer described later. When the number of moles of the ethylene terephthalate component is less than 90 mol% of the repeating unit, the melting point is lowered, and it is difficult to obtain a difference in melting point from the polyester constituting the second layer described later. It is difficult to give a large difference in refractive index. Among these, homopolyethylene terephthalate is preferable because the melting point can be maintained at a high level. Examples of copolymer components other than the ethylene terephthalate component include other aromatic carboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid; adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid Aliphatic dicarboxylic acids such as acids; acid components such as alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; aliphatic diols such as butanediol and hexanediol; glycol components such as alicyclic diols such as cyclohexanedimethanol Can be preferably mentioned.
[0016]
By the way, the melting point of the resin constituting the first layer is preferably in the range of 250 to 260 ° C., since the difference in melting point from the resin constituting the second layer described later can be relatively large. When the melting point of the resin constituting the first layer is lower than the lower limit, the melting point difference from the resin constituting the second layer is reduced, and as a result, a sufficient refractive index difference is imparted to the resulting multilayer stretched film. It becomes difficult. In addition, the melting point of non-copolymerized polyethylene terephthalate is usually around 256 ° C.
[0017]
[Second layer]
In the present invention, the resin constituting the second layer is a polyester whose main repeating unit is an ethylene terephthalate component. In particular, from the viewpoint of film forming property in biaxial stretching, a crystalline polyester is preferable. Further, since the melting point can be made lower than that of the polyester constituting the first layer, 75 to 97 mol% of the repeating units are composed of an ethylene terephthalate component, and 3 to 25 mol% is a copolymer composed of other copolymer components. Polymerized polyethylene terephthalate. When the number of moles of the ethylene terephthalate component is less than 75 mol% of the repeating unit or the number of moles of the copolymer component exceeds 25 mol%, the polymer is substantially amorphous and film-forming properties by biaxial stretching And the composition of the polyester constituting the first layer is greatly different, and the adhesion between the layers tends to decrease. On the other hand, if the number of moles of the ethylene terephthalate component exceeds 97 mol% of the repeating unit or the number of moles of the copolymer component is less than 3 mol%, the melting point difference from the polyester constituting the first layer is reduced, As a result, it becomes difficult to give sufficient reflectivity to the multilayer stretched film. Examples of copolymer components other than the ethylene terephthalate component include other aromatic carboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid; adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid Aliphatic dicarboxylic acids such as acids; acid components such as alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; aliphatic diols such as butanediol and hexanediol; glycol components such as alicyclic diols such as cyclohexanedimethanol Can be preferably mentioned. Among these, 2,6-naphthalenedicarboxylic acid or isophthalic acid is preferable because it is relatively easy to lower the melting point while maintaining stretchability.
[0018]
By the way, the melting point of the resin constituting the second layer is preferably in the range of 200 to 245 ° C., since the difference in melting point from the resin constituting the first layer can be relatively large. When the melting point of the resin constituting the second layer is higher than the upper limit, the melting point difference from the resin constituting the first layer is reduced, and as a result, a sufficient refractive index difference is imparted to the resulting multilayer stretched film. It becomes difficult. On the other hand, in order for the melting point of the resin constituting the second layer to be lower than the lower limit, the composition with the resin constituting the first layer will be greatly changed, which is sufficient for the obtained biaxially stretched multilayer laminated film. It becomes difficult to provide adhesion between layers. Note that the melting point of the resin constituting the second layer does not need to be low from the stage before forming the film, and may be low after the stretching treatment. For example, it will be easily understood that homopolyethylene terephthalate and other polyesters other than that may be prepared and transesterified at the time of melt kneading.
[0019]
[Biaxially stretched multilayer laminated film]
The biaxially stretched multilayer laminated film of the present invention is obtained by alternately laminating at least 11 layers of the above-mentioned first layer and second layer. In addition, as mentioned above, the biaxially stretched multilayer laminate film of the present invention needs to be stretched in the biaxial direction from the viewpoint of having sufficient mechanical strength.
[0020]
In particular, the biaxially stretched multilayer laminated film of the present invention exhibits crystallinity in both the first layer and the second layer from the viewpoint of ensuring adhesion between layers and film forming properties of biaxial stretching. The resin of the second layer is preferably at least partially melted after stretching. The biaxially stretched multilayer laminated film thus obtained preferably has two or more melting points measured by a differential scanning calorimetry (DSC) apparatus, and their melting points are preferably different by 5 ° C. or more. Here, it can be easily imagined that the measured melting point is the first layer exhibiting a high refractive index on the high melting point side, and the second layer exhibiting the low refractive index on the low melting point side. . Further, more preferably, since the second layer is at least partially melted after stretching, it is preferable that the crystallization peak measured by the DSC apparatus exists in the range of 100 ° C to 190 ° C. When the crystallization peak is less than 100 ° C., one layer is rapidly crystallized when the film is stretched, the film-forming property at the time of film formation tends to be lowered, and the homogeneity of the film quality is likely to be lowered. Color spots may occur. On the other hand, if the crystallization peak exceeds 190 ° C., when the second layer is melted by heat setting, crystallization occurs at the same time, making it difficult to express a sufficient refractive index difference.
[0021]
As described above, the biaxially stretched multilayer laminated film of the present invention is obtained by stretching the resin of the first layer and the resin of the second layer, both of which exhibit crystallinity, to obtain a film having a uniform film quality and stretching. By melting the second layer after the process, the interlayer adhesion can be improved and simultaneously the reflection performance can be improved. Therefore, in the biaxially stretched multilayer laminate film of the present invention, a biaxially stretched multilayer laminate in which a crystal peak by a DSC apparatus exists at 100 ° C. to 190 ° C., and two or more melting peaks different in melting point difference by 5 ° C. or more are observed. A film is preferred.
[0022]
The biaxially stretched multilayer laminated film of the present invention preferably has a breaking strength in the stretched direction of 50 MPa or more. When the breaking strength is less than 50 MPa, the handleability during processing of the multilayer stretched film is lowered, and the durability when it is made into a product is lowered. In addition, when the breaking strength is 50 MPa or more, there is an advantage that the film becomes firm and the winding property is improved. The preferred breaking strength is 80 MPa or more in the longitudinal direction, particularly 100 MPa or more, and 80 MPa or more, particularly 100 MPa or more in the transverse direction. In addition, the strength ratio in the longitudinal direction and the transverse direction is preferably 3 or less because tear resistance can be sufficiently obtained. In particular, the strength ratio in the longitudinal direction and the transverse direction is preferably 2 or less because tear resistance can be further improved. The upper limit of the breaking strength is not particularly limited, but is preferably at most 500 MPa from the viewpoint of maintaining the stability of the stretching process.
[0023]
Further, the biaxially stretched multilayer laminated film of the present invention is characterized by high thermal dimensional stability, and heat shrinkage when treated at 150 ° C. for 30 minutes in the stretched direction (film forming direction and width direction). Each rate is preferably 3.0% or less. More preferably, it is 2.5% or less, and further preferably 2.0% or less. Moreover, when the biaxially stretched multilayer laminated film of the present invention is treated at 200 ° C. for 10 minutes, the thermal shrinkage in the film forming direction and the width direction is preferably 5.0% or less, respectively. A more preferable heat shrinkage rate is 4.0% or less, and a still more preferable heat shrinkage rate is 3.0% or less. Since the thermal dimensional stability is high, it can be said that the biaxially stretched multilayer laminated film of the present invention is excellent in process suitability such as bonding with a PVC sheet and embossing.
[0024]
In the biaxially stretched multilayer laminated film of the present invention, it is preferable that the resins constituting the first layer and the second layer are both crystalline resins. If both the resin constituting the first layer and the second layer are crystalline resins, the treatment such as stretching is unlikely to be uneven, and as a result, the thickness unevenness of the film can be reduced. The thickness unevenness range is preferably such that the difference between the maximum value and the minimum value of the film thickness within a range in consideration of the area capable of optical influence is less than 5 μm. This is more preferably less than 3 μm and even more preferably less than 1.5 μm. When the variation rate of the film thickness is 5 μm or more, the color of the reflected light changes and appears as a color spot.
[0025]
In order to improve the rollability of the film, the biaxially stretched multilayer laminated film of the present invention has inert particles having an average particle diameter of 0.01 μm to 2 μm in at least one of the first layer and the second layer. The content is preferably 0.001 to 0.5% by weight based on the weight of the multilayer stretched film. If the average particle size of the inert particles is smaller than the lower limit or the content is less than the lower limit, the effect of improving the winding property of the multilayer stretched film tends to be insufficient, while the content of the inert particles is When the upper limit is exceeded or the average particle diameter exceeds the upper limit, the deterioration of the optical properties of the multilayer stretched film due to the particles becomes remarkable. Preferred average particle diameter of the inert particles is in the range of 0.05 to 1 μm, particularly 0.1 to 0.3 μm. Moreover, content of a preferable inert particle is the range of 0.005-0.2 weight%.
[0026]
Examples of the inert particles contained in the biaxially stretched multilayer laminated film include inorganic inert particles such as silica, alumina, calcium carbonate, calcium phosphate, kaolin, and talc, silicone, crosslinked polystyrene, and styrene-divinylbenzene copolymer. Such organic inert particles can be mentioned. These inert particles are spherical particles whose ratio of major axis to minor axis is 1.2 or less, and further 1.1 or less (hereinafter sometimes referred to as true spherical particles). And optical properties can be maintained at a high level. Further, these inert particles preferably have a sharp particle size distribution. For example, those having a relative standard deviation of less than 0.3, more preferably less than 0.2 are preferable. When particles having a large relative standard deviation are used, the frequency of coarse particles increases, which may cause optical defects. Here, the average particle size, the particle size ratio, and the relative standard deviation of the inert particles are first sputtered with a metal for imparting conductivity to the particle surface very thinly, and 10,000 to 30,000 times by an electron microscope. From the enlarged image, the major axis, the minor axis, and the equivalent area circle diameter are obtained, and then these are applied to the following equation.
Average particle size = total area equivalent circle diameter of measured particle / measured particle number particle size ratio = average long diameter of particle / average short diameter of the particle
[Coating layer]
By the way, when an inert particle is not included in the biaxially stretched multilayer film of the present invention, it is preferable to provide an easy-to-slip coating layer on at least one surface in the processing step of the biaxially stretched film. It is preferable to add a lubricant (filler, wax) to the composition constituting the coating layer in order to impart easy lubricity to the polyester resin composition or the acrylic resin composition. By adding a lubricant, the lubricity and blocking resistance can be further improved.
[0028]
The polyester resin of the coating layer has a glass transition point (Tg) of 50 to 100 ° C, more preferably 60 to 90 ° C. The polyester resin is preferably water-soluble or dispersible polyester, but may contain some organic solvent.
[0029]
Preferred examples of the polyester resin for the coating layer include those composed of the following polybasic acids or ester-forming derivatives thereof and polyols or ester-forming derivatives thereof. That is, as the polybasic acid component, terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid , Dimer acid, 5-sodium sulfoisophthalic acid and the like. A copolymer polyester resin is synthesized using two or more of these acid components. In addition, an unsaturated polybasic acid component such as maleic acid, itaconic acid or the like, or a hydroxycarboxylic acid such as p-hydroxybenzoic acid may be used in a slight amount. The polyol component includes ethylene glycol, 1,4-butanediol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, xylene glycol, dimethylolpropane, and poly (ethylene oxide) glycol. , Poly (tetramethylene oxide) glycol and the like. Moreover, although these monomers are mentioned, it is not limited to these.
[0030]
Moreover, as an acrylic resin of an application layer, a thing with a glass transition point (Tg) of -50-50 degreeC, More preferably, -50-25 degreeC can be mentioned preferably. The acrylic resin is preferably an acrylic resin that is soluble or dispersible in water, but may contain some organic solvent. Such an acrylic resin can be copolymerized from the following acrylic monomers. Examples of the acrylic monomer include alkyl acrylate and alkyl methacrylate (the alkyl group includes methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group). Groups); hydroxy-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate; epoxy group-containing monomers such as glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether; acrylic Acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid and its salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt) ) Or other carboxy group or a salt thereof; acrylamide, methacrylamide, N-alkyl acrylamide, N-alkyl methacrylamide, N, N-dialkyl acrylamide, N, N-dialkyl methacrylate (the alkyl group is a methyl group) , Ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group, etc.), N-alkoxyacrylamide, N-alkoxymethacrylamide, N, N- Dialkoxyacrylamide, N, N-dialkoxymethacrylamide (alkoxy groups include methoxy group, ethoxy group, butoxy group, isobutoxy group, etc.), acryloylmorpholine, N-methylolacrylamide, N-methylolmethacrylamide Monomers containing amide groups such as N-phenylacrylamide and N-phenylmethacrylamide; monomers of acid anhydrides such as maleic anhydride and itaconic anhydride; vinyl isocyanate, allyl isocyanate, styrene, α-methylstyrene, vinylmethyl Ether, vinyl ethyl ether, vinyl trialkoxysilane, alkylmaleic acid monoester, alkyl fumaric acid monoester, alkylitaconic acid monoester, acrylonitrile, methacrylonitrile, vinylidene chloride, ethylene, propylene, vinyl chloride, vinyl acetate, butadiene, etc. These monomers are mentioned. Moreover, although these monomers are mentioned, it is not limited to these.
[0031]
As the lubricant contained in the coating layer, those conventionally known as slipperiness imparting agents for polyester films can be suitably used. For example, calcium carbonate particles, calcium oxide particles, aluminum oxide particles, kaolin particles, silicon oxide particles, zinc oxide particles, carbon black particles, silicon carbide particles, tin oxide particles, crosslinked acrylic resin particles, crosslinked polystyrene resin particles, melamine resin particles And crosslinked silicone resin particles. In particular, silicon oxide particles, crosslinked acrylic resin particles, crosslinked polystyrene resin particles and the like are particularly preferable from the viewpoint of dispersibility in the coating layer.
[0032]
The coating liquid for forming the coating film is preferably used in the form of an aqueous coating liquid such as an aqueous solution, an aqueous dispersion or an emulsion. In order to form a coating film, if necessary, other resins than the above composition, for example, a polymer having an oxazoline group, a cross-linking agent such as melamine, epoxy, aziridine, an antistatic agent, a colorant, a surfactant. UV absorbers, lubricants (fillers, waxes) and the like can be added. When the coating liquid is an aqueous coating liquid, the solid content concentration is usually 20% by weight or less, and preferably 1 to 10% by weight. When this ratio is less than 1% by weight, the coatability to the polyester film is insufficient. On the other hand, when it exceeds 20% by weight, the stability of the coating and the appearance of the coating may be deteriorated.
[0033]
Application of the aqueous coating liquid to the film can be carried out at any stage, but it is preferably carried out during the production process of the biaxially stretched multilayer laminated film, and further applied to the film before the completion of oriented crystallization. It is preferable to do this. Here, the film before the crystal orientation is completed is an unstretched film, a uniaxially oriented film in which the unstretched film is oriented in either the longitudinal direction or the transverse direction, and further in two directions, the longitudinal direction and the transverse direction. It includes those that have been stretched and oriented at a low magnification (biaxially stretched film before being finally re-stretched in the machine direction or the transverse direction to complete orientation crystallization). In particular, it is preferable to apply the aqueous coating liquid of the above composition to an unstretched film or a uniaxially stretched film oriented in one direction, and perform longitudinal stretching and / or lateral stretching and heat setting as it is.
[0034]
When applying an aqueous coating liquid to a film, as a pretreatment for improving the coating property, the film surface is subjected to physical treatment such as corona surface treatment, flame treatment, plasma treatment, etc., or chemically combined with the composition. It is preferable to use an inert surfactant in combination. Such a surfactant promotes the wetting of the aqueous coating liquid onto the polyester film. For example, polyoxyethylene alkylphenyl ether, polyoxyethylene-fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester, fatty acid metal soap, Examples include anionic and nonionic surfactants such as alkyl sulfates, alkyl sulfonates, and alkyl sulfosuccinates. The surfactant is preferably contained in an amount of 1 to 10% by weight in the composition forming the coating film.
[0035]
The coating amount of the coating liquid is preferably such an amount that the thickness of the coating film is in the range of 0.02 to 0.3 μm, preferably 0.07 to 0.25 μm. If the thickness of the coating film is too thin, the adhesive strength is insufficient, and conversely if it is too thick, blocking may occur or the haze value may increase.
[0036]
As a coating method, any known coating method can be applied. For example, a roll coating method, a gravure coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, a curtain coating method and the like can be used alone or in combination. In addition, a coating film may be formed only in the single side | surface of a film as needed, and may be formed in both surfaces.
[0037]
The biaxially stretched multilayer laminated film of the present invention is preferable because the thickness distribution is uniform because it can selectively reflect light in a specific wavelength band. Note that the thickness distributions of the first layer and the second layer need only be uniform, and the thicknesses of the first layer and the second layer may be different. In addition, when the application to be used is, for example, a reflection mirror or a metallic gloss film, it is preferable to reflect not only a specific wavelength band but also the entire visible wavelength band. In such a case, a plurality of biaxially stretched multilayer laminated films of the present invention having different wavelength bands of reflected light are laminated, or a biaxially stretched multilayer in which the thicknesses of the first layer and the second layer are gradually changed. It will be readily understood that laminate films are preferably used and are also included in the biaxially oriented multilayer laminate film of the present invention.
[0038]
The biaxially stretched multilayer laminated film of the present invention preferably has a haze of 10% or less. If the haze is 10% or less due to light scattering by inert particles, the film itself becomes whitish and loses gloss.
[0039]
[Method for producing biaxially stretched multilayer laminated film]
The biaxially stretched multilayer laminated film of the present invention is stretched more than polyester (for the first layer) having an ethylene terephthalate component having a melting point of 250 to 260 ° C. as a main repeating unit and the polyester constituting the first layer. A polyester (second layer) having a melting point of at least 10 ° C. lower than that of the ethylene terephthalate component as a main repeating unit is extruded in a molten state and alternately laminated in at least 11 layers. It is set as a stretched film (process made into a sheet-like material). The polyester constituting the first layer and the second layer is the same as that described for the first layer and the second layer. When the melting point of the first layer polyester is less than 250 ° C., the difference in melting point from the second layer polyester is not sufficiently applied, and as a result, a sufficient refractive index difference cannot be imparted between the layers of the resulting multilayer stretched film. On the other hand, since the melting point of homopolyethylene terephthalate is around 256 ° C., the upper limit of the melting point of the first layer polyester is about 260 ° C. at most. In addition, when the melting point of the second layer polyester is not lower by 15 ° C. or more than the first layer polyester, the difference in melting point from the second layer polyester is not sufficient, and as a result, the resulting multilayer stretch A sufficient refractive index difference cannot be imparted between the layers of the film. The upper limit of the melting point difference between the first layer polyester and the second layer polyester is preferably at most 50 ° C. from the viewpoint of maintaining the adhesion between the two layers.
[0040]
The multilayer unstretched film thus obtained is stretched in the biaxial direction (the direction along the film surface) in the film forming direction and the width direction perpendicular thereto. The stretching temperature is preferably in the range of the glass transition temperature (Tg) to Tg + 50 ° C. of the polyester of the first layer. The area magnification at this time is preferably 5 to 50 times. The larger the draw ratio, the smaller the variation in the plane direction in the individual layers of the first layer and the second layer is reduced by thinning by stretching, that is, the optical interference of the multilayer stretched film becomes uniform in the plane direction. Therefore, it is preferable. The stretching method for stretching in two directions may be sequential biaxial stretching or simultaneous biaxial stretching.
[0041]
The most important feature of the present invention is that the multilayer film thus stretched has a temperature lower by 10 ° C. than the melting point of the polyester for the second layer, and 15 ° C. lower than the melting point of the polyester for the first layer. Heat treatment in a range is to relax the orientation of molecular chains in the second layer and lower the refractive index of the second layer. When the temperature of the heat treatment is lower than the melting point of the polyester for the second layer by more than 10 ° C., the effect of reducing the refractive index by relaxing the molecular chain orientation in the second layer is obtained and obtained. A sufficient refractive index difference cannot be imparted to the multilayer stretched film. On the other hand, if the temperature of the heat treatment is not lower by 10 ° C. or more than the melting point of the polyester for the first layer, the orientation of molecular chains in the first layer is relaxed and the refractive index is lowered, and the resulting multilayer stretched film Cannot provide a sufficient difference in refractive index. A preferable heat treatment temperature is 6 ° C. lower than the melting point of the second layer polyester, 16 ° C. lower than the melting point of the first layer polyester, and 2 more than the melting point of the second layer polyester. The temperature is lower by 18 ° C. than the melting point of the first layer polyester. The heat treatment time is preferably 1 to 60 seconds.
[0042]
Further, by changing the temperature and time of this heat treatment, the refractive index of the second layer can be adjusted without changing the resin composition, that is, the multilayer stretched film without changing the resin composition. The reflection characteristics can be changed.
[0043]
【Example】
The invention is further described by way of examples. In addition, the physical property and characteristic in an Example were measured or evaluated by the following method.
[0044]
(1) Melting point and glass transition point (Tg) of polyester resin
10 mg of a polyester resin sample was sampled, and a DSC apparatus (trade name: DSC2920, manufactured by TA Instruments) was used at 20 ° C./min. The melting point is measured at a temperature increase rate of.
[0045]
(2) A thickness sample of each layer is cut into a triangle, fixed in an embedded capsule, and then embedded in an epoxy resin. And the embedded sample was cut | disconnected along the film forming direction and thickness direction with the microtome (ULTRACUT-S, manufacturer: Reichert), and it was set as the thin film slice | slice of thickness 50nm. The obtained thin film slices were observed and photographed at an accelerating voltage of 100 kV using a transmission electron microscope (manufacturer: JEOL Ltd., trade name: JEM2010), and the thickness of each layer was measured from the photograph.
[0046]
(3) Measurement of melting point and crystallization peak of film by DSC 10 mg of sample film was sampled, and 20 ° C./min. With a DSC apparatus (trade name: DSC2920, manufactured by TA Instruments). The crystallization temperature and the melting point are measured at a temperature rising rate of.
[0047]
(4) Reflectance and reflection wavelength Using a spectrophotometer (manufactured by Shimadzu Corp., MPC-3100), the relative specular reflectance with the aluminum-deposited mirror at each wavelength is measured in the wavelength range of 350 nm to 2000 nm. The maximum reflectance among the measured reflectances is defined as the maximum reflectance, and the wavelength thereof is defined as the reflection wavelength.
[0048]
(5) Total light transmittance and haze According to JIS K7105, total light transmittance T t (%) and scattered light transmittance using a haze measuring machine (NDH-20, manufactured by Nippon Denshoku Industries Co., Ltd.) T d (%) is measured, and haze (%) is calculated from the following equation.
Haze (%) = (T d / T t ) × 100
[0049]
(6) Breaking strength The breaking strength in the film forming direction is that the sample film is cut into a sample width (width direction) of 10 mm and length (film forming direction) of 150 mm, the chuck is 100 mm, the pulling speed is 100 mm / min, and the chart speed is 500 m / min. The sample is pulled with an Instron type universal tensile testing device under the condition of min. And the breaking strength was measured from the obtained load-elongation curve.
[0050]
The breaking strength in the width direction was the same as the measurement of breaking strength in the film forming direction, except that the sample film was cut into a sample width (film forming direction) of 10 mm and a length (width direction) of 150 mm.
[0051]
(7) Heat shrinkage rate The heat shrinkage rate when treated at 150 ° C. for 30 minutes is such that the film is held in an unstrained state for 30 minutes in an oven set at 150 ° C., and the dimensional change before and after the heat treatment is observed. The heat shrinkage is calculated by the following formula.
Thermal shrinkage% = ((L0−L) / L0) × 100
L0: Distance between gauge points before heat treatment.
L: Distance between floating points after heat treatment.
[0052]
In addition, the heat shrinkage rate when treated at 200 ° C. for 10 minutes is that the film is held in an unstrained state for 10 minutes in an oven set at 200 ° C., and the dimensional change before and after the heat treatment is defined as the heat shrinkage rate. Calculated by the above formula.
[0053]
(8) Thickness variation width Film samples cut to be 1 m × 1 m in the film forming direction and the width direction are cut into 25 pieces each having a width of 2 cm along the vertical direction and the width direction, and the thickness of each sample is measured with an electronic micro Measurement is performed continuously using a meter and a recorder (K-312A, K310B, manufactured by Anritsu Electric Co., Ltd.). Further, the measurement points are subdivided every 200 mm, the maximum value and the minimum value of the thickness are read, and the difference is defined as the thickness fluctuation range.
[0054]
(9) Adhesion between
[0055]
(10) Color spots 10 A4 size sample films are prepared, and each sample film is layered on white plain paper. Under the illumination of 30 lux, the transparent color spots in the sample film are visually observed. evaluated. In addition, 10 A4-size sample films were prepared, and the back surface of each sample film was colored with a black spray. Then, under the illumination of 30 lux, the reflected color spots in the sample film were visually observed. evaluated.
[0056]
Then, the color spots of the transmitted color and the reflected color were synthesized and judged according to the following evaluation criteria.
○: There is no visible color spot in the sample.
Δ: Part of the sample with a different color is observed.
X: Color spots that clearly appear as spots or streaks can be confirmed.
[0057]
[Example 1]
Polyethylene terephthalate (indicated as “PET” in Table 1) having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.63 is used as the first layer polyester, and 12 mol% of isophthalic acid is used as the second layer polyester. Copolymerized polyethylene terephthalate (indicated as “IA12PET” in Table 1) having a polymerized intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.61 and spherical silica particles (average particle size: 1.5 μm, as inert particles) The ratio of the major axis to the minor axis: 1.02, the average deviation of the particle size: 0.1. The first layer polyester and the second layer polyester are each dried at 170 ° C. for 3 hours and then supplied to an extruder, heated to 280 ° C. to be in a molten state, and the first layer polyester is 101. After the polyester for the second layer and the second layer are branched into 100 layers, a multilayer feedblock device in which the first layer and the second layer are alternately stacked is used, and the die is maintained while maintaining the stacked state. Then, the film was cast on a casting drum to produce a total of 201 unstretched multilayer laminated films in which the first layer and the second layer were alternately laminated so that the thickness of each layer was equal. At this time, the extrusion amount of the first layer and the second layer was adjusted to be 1: 1, and the both end layers were laminated so as to be the first layer. This multilayer unstretched film was stretched 3.6 times in the film forming direction at a temperature of 90 ° C., further stretched 3.9 times in the width direction at a temperature of 95 ° C., and heat-fixed at 230 ° C. for 3 seconds. .
[0058]
Table 2 shows the physical properties of the obtained biaxially stretched multilayer laminated film.
[0059]
Examples 2, 3, and 5-7
The same operation as in Example 1 was repeated except that the polyester for the second layer and the production conditions were changed as shown in Table 1. In addition, the symbol described as the kind of resin of each layer in Table 1 is polyethylene terephthalate having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.65 obtained by copolymerizing “IA8PET” with 8 mol% of isophthalic acid, and “IA20PET”. Is polyethylene terephthalate having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.58 obtained by copolymerization of 20 mol% of isophthalic acid. In addition, the symbol described as the kind of the inert particle is “I” is massive calcium carbonate (average particle diameter: 1.5 μm, ratio of major axis to minor axis: 1.30, average deviation of particle diameter: 0.3) “U” is a true spherical silicone particle (average particle diameter: 0.1 μm, ratio of major axis to minor axis: 1.10, average deviation of particle diameter: 0.2).
[0060]
Table 2 shows the physical properties of the obtained multilayer stretched film.
[0061]
[Example 4]
Intrinsic viscosity (orthochlorophenol, 35 ° C.) 0.63 polyethylene terephthalate (PET) is used as the first layer polyester, and 2,6-naphthalenedicarboxylic acid is copolymerized at 10 mol% as the second layer polyester. Copolymerized polyethylene terephthalate (indicated as “NDC10PET” in Table 1) having a viscosity (orthochlorophenol, 35 ° C.) of 0.70 was prepared. The first layer polyester and the second layer polyester are each dried at 170 ° C. for 3 hours and then supplied to an extruder, heated to 280 ° C. to be in a molten state, and the first layer polyester is 101. After the polyester for the second layer and the second layer are branched into 100 layers, a multilayer feedblock device in which the first layer and the second layer are alternately stacked is used, and the die is maintained while maintaining the stacked state. Then, the film was cast on a casting drum to produce a total of 201 unstretched multilayer laminated films in which the first layer and the second layer were alternately laminated so that the thickness of each layer was equal. At this time, the both end layers were laminated so as to be the first layer. This multilayer unstretched film is stretched 3.6 times in the film-forming direction at a temperature of 90 ° C., and an aqueous coating liquid having a concentration of 1.6% of the coating film composition described below is applied on one side thereof with a roll coater and the thickness after drying. Was uniformly applied to a thickness of 0.1 μm.
[0062]
[Coating composition]
Copolymerization in which the acid component is 85 mol% terephthalic acid / 13 mol% isophthalic acid / 5 mol 12-sodium sulfoisophthalic acid, the glycol component is 80 mol% butylene glycol / 20 mol
Acrylic resin composed of 80% by mole of methyl methacrylate / 10% by mole of ethyl acrylate / 5% by mole of N-methylolacrylamide / 2% by mole of 2-hydroxyethyl methacrylate: 35% by weight
-Lubricant having an average particle diameter of 40 nm made of a methyl methacrylate-divinylbenzene copolymer: 15% by weight
-Surfactant comprising polyoxyethylene (n = 7) lauryl ether: 5% by weight
After applying a coating liquid having such a composition, it was dried at 80 ° C., stretched 3.9 times in the width direction at a temperature of 95 ° C., and heat-set at 230 ° C. for 3 seconds.
[0063]
Table 2 shows the physical properties of the obtained biaxially stretched multilayer laminated film.
[0064]
[Comparative Example 1]
[0065]
The obtained multilayer stretched film was a film with severe color spots and inferior peeling properties between layers. The physical properties are shown in Table 2.
[0066]
[Comparative Examples 2 to 4]
The same operation as in Comparative Example 1 was repeated except that the production conditions were changed as shown in Table 1. In Table 1, “IA3PET” is polyethylene terephthalate having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.65 obtained by copolymerization of 3 mol% of isophthalic acid. The films obtained in Comparative Examples 2 and 3 were inferior in reflection performance. Similar to Comparative Example 1, the film obtained in Comparative Example 4 was a film with severe color spots and inferior peeling properties between layers. The physical properties are shown in Table 2.
[0067]
[Table 1]
[Table 2]
【The invention's effect】
The biaxially stretched multilayer laminated film of the present invention has not only excellent design properties such as an iridescent color due to structural color development, but also has excellent interlayer adhesion and high breaking strength, so that its industrial value. Is expensive. In particular, the biaxially stretched multilayer laminated polyester film of the present invention is exposed to extraneous light and has a very narrow width, including packaging films that require not only decorativeness but also high mechanical properties that can protect handling and contents. Therefore, it is extremely suitable for decorative fibers slitted in a thin film or for anti-counterfeiting films for substituting hologram seals because of its selective wavelength reflection performance.
[Brief description of the drawings]
FIG. 1 shows an example of reflectance characteristics of a film.
[Explanation of symbols]
1 Difference between maximum reflectance and
Claims (4)
Priority Applications (11)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2002301439A JP4097501B2 (en) | 2002-03-01 | 2002-10-16 | Biaxially stretched multilayer laminated film and method for producing the same |
| TW92103797A TWI281891B (en) | 2002-03-01 | 2003-02-24 | Biaxially oriented multi-layered laminated film and method for manufacture thereof |
| US10/476,572 US20050014011A1 (en) | 2002-03-01 | 2003-02-25 | Biaxially oriented multi-layer laminated film and method for manufacture thereof |
| CNB038005972A CN100457446C (en) | 2002-03-01 | 2003-02-25 | Biaxially stretched multilayered laminated film and manufacturing method therefor |
| KR1020047001139A KR100954710B1 (en) | 2002-03-01 | 2003-02-25 | Biaxially Stretched Multilayer Laminated Films and Manufacturing Method Thereof |
| EP14168613.9A EP2803482B1 (en) | 2002-03-01 | 2003-02-25 | Biaxially drawn multilayer laminated film and method for producing the same |
| KR1020097027330A KR100994662B1 (en) | 2002-03-01 | 2003-02-25 | Biaxially oriented multi-layer laminated film and method for manufacture thereof |
| EP20030707066 EP1481798B1 (en) | 2002-03-01 | 2003-02-25 | Biaxially oriented multi-layer laminated film and method for manufacture thereof |
| PCT/JP2003/002073 WO2003074272A1 (en) | 2002-03-01 | 2003-02-25 | Biaxially oriented multi-layer laminated film and method for manufacture thereof |
| US11/549,018 US20070090557A1 (en) | 2002-03-01 | 2006-10-12 | Biaxially drawn multilayer laminated film and method for producing the same |
| US12/709,069 US8053062B2 (en) | 2002-03-01 | 2010-02-19 | Biaxially drawn multilayer laminated film and method for producing the same |
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| JP2002-55488 | 2002-03-01 | ||
| JP2002055488 | 2002-03-01 | ||
| JP2002301439A JP4097501B2 (en) | 2002-03-01 | 2002-10-16 | Biaxially stretched multilayer laminated film and method for producing the same |
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| JP2003320632A JP2003320632A (en) | 2003-11-11 |
| JP4097501B2 true JP4097501B2 (en) | 2008-06-11 |
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Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP4527952B2 (en) * | 2003-08-11 | 2010-08-18 | 帝人株式会社 | Biaxially stretched multilayer laminated film |
| JP4310312B2 (en) | 2003-10-27 | 2009-08-05 | 帝人デュポンフィルム株式会社 | Near-infrared shielding film |
| JP4665421B2 (en) * | 2004-03-31 | 2011-04-06 | 東レ株式会社 | Laminated film |
| JP4691910B2 (en) * | 2004-06-11 | 2011-06-01 | 東レ株式会社 | Screen reflector and screen |
| JP4804193B2 (en) * | 2006-03-30 | 2011-11-02 | 帝人デュポンフィルム株式会社 | Biaxially stretched multilayer laminated film |
| JP4773930B2 (en) * | 2006-11-27 | 2011-09-14 | 帝人デュポンフィルム株式会社 | Biaxially stretched multilayer laminated film and identification medium |
| JP4944726B2 (en) * | 2007-10-18 | 2012-06-06 | 帝人デュポンフィルム株式会社 | Biaxially oriented multilayer laminated film for acoustic diaphragm and method for producing the same |
| JP2009184284A (en) * | 2008-02-08 | 2009-08-20 | Toray Ind Inc | Laminated film |
| TWI744982B (en) * | 2020-07-15 | 2021-11-01 | 南亞塑膠工業股份有限公司 | Polyester film for laser embossing and method for manufacturing the same |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0962807B1 (en) * | 1993-12-21 | 2008-12-03 | Minnesota Mining And Manufacturing Company | Multilayered optical film |
| JPH09300518A (en) * | 1996-05-16 | 1997-11-25 | Toray Ind Inc | Laminated film and its production |
| JPH10278157A (en) * | 1997-04-10 | 1998-10-20 | Toray Ind Inc | Laminated film, glass-flying preventive film, and agricultural film |
| JP4274696B2 (en) * | 1998-01-13 | 2009-06-10 | スリーエム カンパニー | Modified copolyester and improved multilayer reflective film |
| JP3752410B2 (en) * | 1999-12-24 | 2006-03-08 | 帝人株式会社 | Multilayer laminated stretched film |
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