JP4686797B2 - Cavity-containing polyester film - Google Patents

Description

つまり各周波数のMTF が求まればこのkpは求まることになる。しかし、通常MTF は例えば線の幅と間隔（空間周波数）が異なるスクリーンを用紙や被記録フィルム上に置いたものや直接印字をしたものの反射光の濃度から求めたり、空間周波数が連続的に変化する正弦関数分布の光から同様に反射濃度を用いて求める。だがこの方法は比較的周波数の低いところしか求められない。特に用紙や被記録用フィルムでkpを求めようとした場合は誤差が非常に大きくなるため、後述する実施例の方法から求めたkpと用紙や被記録用フィルムに印刷したものの鮮明さとが比較的よく一致する一つの方法と考える。
【００２０】
均一な２軸配向フィルムであって、前記ダイナミック硬度、光沢および平均光移動距離を得るための達成手段を例示しながら詳細に説明する。まず、平均粒径が０．１〜５μｍの微粒子に由来する微細空洞を含有するポリエステル層（スキン層）をフィルム表面に接合することによって、前記ダイナミック硬度と光沢度を達成することが出来る。かかるスキン層中の空洞含有率についても何ら制限されるものではないが、２０体積％以上の空洞を形成することが好ましい。なお、微粒子に由来する微細空洞とは微粒子のまわりの少なくとも一部に空洞が存在することを言い、例えばフィルムの電子顕微鏡による断面写真などで確認することができる。
【００２１】
そして、スキン層中に添加される粒子の平均径が０．１μｍに満たない場合には、後述するフィルム延伸工程での空洞形成能が著しく低下し、フィルム表面のダイナミック硬度を５．０以下とすることが困難となり、所期の熱転写感度特性の向上効果が得られない。逆に平均径が５μｍを超える粒子を用いた場合には、空洞形成能は優れるものの、フィルム表面の平滑性が著しく低下して光沢度を20％以上とすることが困難となり、熱転写感度特性をかえって低下させてしまう。好ましくは０．１〜３μｍ、より好ましくは０．１〜２μｍで最も好ましくは０．１〜１μｍである。
【００２２】
かかるスキン層に添加可能な粒子としては、無機粒子であっても有機粒子であってもよく、何ら制限されるものではないが、例えば二酸化チタンや炭酸カルシウム、硫酸バリウム、硫化亜鉛、二酸化珪素、酸化アルミニウム、タルク、カオリンなどが挙げられる。またこれらの粒子は必要に応じて表面処理をしても構わない。その処理剤としては酸化アルミニウム、二酸化珪素、酸化亜鉛、シリコン系樹脂、シロキサン系樹脂、フッ素系樹脂、シランカップリング剤やチタネートカップリング剤、ポリオールやポリビニルピリジンなどが挙げられるが、これらに限定されるものではない。
【００２３】
その中でも特に好ましい粒子としては、酸化チタン微粒子および硫化亜鉛微粒子が挙げられる。更に、フィルムにより効果的に隠蔽性を付与出来る観点から、酸化チタン微粒子が最も好んで用いられる。酸化チタン微粒子はアナターゼ型、ルチル型の何れでもよい。また、粒子表面にアルミナやシリカ等の無機処理を施してもよいし、シリコン系あるいはアルコール系等の有機処理を施してもよい。
【００２４】
また、スキン層中に添加される微粒子の濃度は、２０〜５０重量％とする。そして、添加量が２０％に満たない場合には空洞の形成能が不十分となって、フィルム表面のダイナミック硬度を５．０以下とすることが困難となる。逆に５０％を超える場合には、フィルム表面の平滑性が急激に損なわれ、フィルム表面の光沢度を２０％以上とすることが困難となる。
【００２５】
また、スキン層には、必要に応じて着色剤、耐光剤、蛍光剤、帯電防止剤などを添加することも可能である。
【００２６】
また、スキン層の厚みは１〜20μｍかつフィルム全体厚みの30％未満であることが好ましい。そして、スキン層の厚みが１μｍに満たない場合には、フィルム表面積あたりの微粒子濃度のバラツキが大きくなるため、画像濃度にムラが生じ、印刷物がザラついた印象を与える傾向にある。一方、20μｍを超える厚みでスキン層を形成しても、画像濃度の向上効果は得られず無意味である。更に、スキン層厚みがフィルム全体厚みの30％を超える場合には、フィルム全体の延伸性が著しく低下する傾向にあり、安定した工業生産性を確保する上で好ましくない。
【００２７】
なお平均光移動距離はスキン層およびコア層の粒子の添加量や種類、空洞の量および厚み比などにより制御できる。他のパラメータや生産性などを考慮すると、その一例としてはスキン層に酸化チタンを用いた場合、その添加量は２０〜４０重量％、スキン層の厚みは全体の厚みの５〜２５％、見かけ比重は０．７５〜１．０５程度が良いようである。しかし、本発明においてはこの方法に限定されるものでない。
【００２８】
本発明の空洞含有ポリエステル系フィルムの製造方法は逐次２軸延伸方法により製造することが出来る。まず、スキン層をフィルム表面に接合する方法としては、Ａ層とＢ層の樹脂を別々の押出機に供給した後、溶融状態で積層して同一のダイから押し出す共押出法を採用することが最も好ましい。
【００２９】
こうして得られた未延伸シートは、更に速度差をもったロール間での延伸（ロール延伸）やクリップに把持して拡げていくことによる延伸（テンター延伸）や空気圧によって拡げることによる延伸（インフレーション延伸）などによって２軸配向処理される。配向処理することにより、ポリエステル／非相溶性樹脂間およびポリエステル／微粒子間で界面剥離を生じ、微細空洞が多数発現する。
従って、未延伸シートを延伸・配向処理する条件は、空洞の生成と密接に関係する。以下では、最も好んで用いられる逐次２軸延伸方法、特に未延伸シートを長手方向次いで幅方向に延伸する方法を例にとり、延伸・配向条件を説明する。
【００３０】
まず、第１段の縦延伸工程は、フィルム内部に微細な空洞を多数形成するために最も重要なプロセスである。縦延伸は、周速が異なる２本あるいは多数本のロール間で延伸する。このときの加熱手段としては、加熱ロールを用いる方法でも非接触の加熱方法を用いる方法でもよく、それらを併用してもよい。この中で最も好ましい延伸方法としては、ロール加熱と非接触加熱を併用する方法があげられる。この場合、まず加熱ロールを用いてフィルムを50℃〜ポリエステルのガラス転移点以下の温度に予備加熱した後、フィルムの表裏について独立した制御系の赤外線ヒータで加熱する。このとき、スキン層面がより低温となるように加熱し、不足する熱量は反対面からの赤外線加熱で補う。このように、フィルム表裏を異なる温度に加熱して延伸することが極めて重要である。そして、非接触の加熱装置で温度差を設ける方法は一つの好ましい例に過ぎず、他の方法、例えば異なる温度のロール間にフィルムを挟んで加熱する方法等によっても同様の効果が得られる。何れにしろ、フィルム全体の加熱を反スキン層側から主体的に行ってフィルムを均一に延伸するに足りる十分な熱量を供給し、スキン層面をより低い温度で延伸することが、スキン層中に無機微粒子由来の空洞を多数形成させるために重要なポイントである。
【００３１】
次いで、このようにして得られた１軸延伸フィルムをテンターに導入し、幅方向に 2.5〜５倍に延伸する。このときの好ましい延伸温度は、１００℃〜２００℃である。
このようにして得られた２軸延伸フィルムに対し、必要に応じて熱処理を施す。熱処理はテンター中で行うのが好ましく、ポリエステルの融点Ｔｍ−50℃〜Ｔｍの範囲で行うのが好ましい。
【００３２】
上記の製造方法で得られた本発明の空洞含有フィルムは、スキン層中に十分な微細空洞を含有するとともに、その製造安定性も優れている。
また、本発明の空洞含有ポリエステル系フィルムは、少なくともそのいずれか一方の表面に塗布層を有していても構わない。そして、塗布層を設けることにより、インキやコーティング剤などの塗れ性や接着性を改良することができる。塗布層を構成する化合物としては、ポリエステル系樹脂が好ましいが、この他にも、ポリウレタン樹脂、ポリエステルウレタン樹脂、アクリル系樹脂など、通常のポリエステルフィルムの接着性を向上させる手段として開示されている化合物等が適用可能である。
【００３３】
また塗布層を設ける方法としては、グラビアコート方式、キスコート方式、ディップ方式、スプレイコート方式、カーテンコート方式、エアナイフコート方式、ブレードコート方式、リバースロールコート方式など通常用いられている方法が適用できる。塗布する段階としては、フィルムの延伸前に塗布する方法、縦延伸後に塗布する方法、配向処理の終了したフィルム表面に塗布する方法などのいずれの方法も可能である。
【００３４】
このようにして得られた空洞含有ポリエステル系フィルムは、従来の空洞含有フィルムに対し、優れた耐折れシワ性と表面の平滑性を有しつつ、飛躍的な画像濃度の向上効果が得られる。
本発明の空洞含有ポリエステル系フィルムを用い、熱転写受像シートを作成するためには、フィルム表面に熱転写インクシートから移行してくるインクや拡散性（昇華性）染料を受容するための記録層を形成すればよい。この場合、フィルム上に直接記録層を形成してもよいし、易接着層や白色度向上層あるいは帯電防止層等の下塗り層を介して形成してもよい。
【００３５】
また、本発明の空洞含有ポリエステル系フィルムを単独で基材として用いてもよいし、他の基材と複合して用いてもよい。複合可能な他の基材としては、天然紙、各種合成樹脂フィルム、織布、不織布等が挙げられるが、これらに制限されるものではない。
また、受容層を形成する面とは反対側の面に粘着加工を施し、熱転写印刷可能な粘着ラベルとして用いてもよい。
【００３６】
かくして得られた空洞含有ポリエステルフィルムは従来提案されていたものに比べ、表面平滑性に優れ、十分な画像濃度、解像度が得られ、かつ耐折れシワ性に優れたものであるため、ラベル、カード、包装材料、地図、白板、建材、壁紙、化粧板、配送伝票、磁気カード、電気絶縁材料、ディスプレイ反射板、好ましくは、熱転写、昇華転写、レーザービームプリンタ、インクジェットプリンタなどの受像シート、印画紙などに最適な基材となる。
【００３７】
実施例
次に本発明の実施例および比較例を示す。
本発明に用いる測定・評価方法を以下に示す。
１）見かけ比重
フィルムを１０ｃｍ×１０ｃｍの正方形に正確に切り出し、その厚みを５０点測定して平均厚みｔ（単位μｍ）を求める。次にサンプルの重量を０．１ｍｇまで測定し、ｗ（単位ｇ）とする。そして、下式によって見かけ比重を計算した。
見かけ比重（−）＝（ｗ／ｔ）×１００００
【００３８】
２）ダイナミック硬度
島津製作所製ダイナミック超微小硬度計（ＤＵＨ−２０１）を用い、１１５゜の三角すい圧子に０．２ｇｆの荷重を与え荷重と圧子の押し込み深さからダイナミック硬度を次式により求めた。

【００３９】
３）表面光沢度
日本電色工業社製 ＶＧＳ−１００１ＤＰを用いて、６０度での反射率を求めた。
【００４０】
４）熱転写感度特性（相対画像濃度）
下記組成の塗工液
水分散性共重合ポリエステル樹脂 ： ２ 部
水分散性アクリル・スチレン共重合樹脂： ５ 部
水分散性イソシアネート系架橋剤 ： ０．５部
水 ： ６７．４部
イソプロピルアルコール ： ２５ 部
界面活性剤 ： ０．１部
を乾燥後重量が４ｇ／ｍ² となるようにフィルム表面に塗工し、寸法固定して１６０℃で３０秒間熱処理して記録層を形成し、熱転写受像シートを作成する。
このようにして得た熱転写受像シートをＡ６サイズにカットしたサンプルについて、市販のインクリボン（株式会社キャラベルデータシステム製昇華転写プリンター用プリントセットＰ−ＰＳ１００）と市販熱転写プリンタ（ボン電気株式会社製熱転写型ラベルプリンターＢＬＰ−３２３）を用いて、印字スピード１００ｍｍ／秒、ヘッド電圧１８Ｖで印字する。印字パターンには、Ｃ（シアン）、Ｍ（マジェンタ）、Ｙ（イエロー）、およびそれらを重ね印字したＫ（ブラック）の４色について、各色９ｍｍ×９ｍｍの正方形のベタ文字を７個ずつ（計２８個）Ａ６シート内に配置したパターンを用いる。
印字後、マクベス濃度計（ＴＲ−９２７）を用いて、ＣＭＹＫ各色の反射濃度を計測し、４色（計２８カ所）の平均濃度を求める。
同様に、市販の受像紙（株式会社キャラベルデータシステム製昇華転写プリンター用プリントセットＰ−ＰＳ１００：天然紙の両面に発泡ポリプロピレンフィルムをラミネートし、記録層を形成したもの）についても同様の方法で平均濃度を求め、市販受像紙の濃度に対するサンプルの濃度の比率（％）で熱転写感度特性を評価する。
【００４１】
５）耐折れシワ性
上記の方法で作成した熱転写受像シートを長さ５ｃｍ、幅１ｃｍの短冊状に切り取り、直径５ｍｍのガラス棒に巻き付け、しごく。その後サンプルを再度伸ばし、実体顕微鏡を用いて表面に発生した折れシワの状態を観察した。
ランクＡ：折れシワなし
ランクＢ：全面に細い折れシワあり
ランクＣ：全面に太い折れシワあり
【００４２】
６）スキン層の厚み
フィルムの切断面を電子顕微鏡で観察して実測した。
【００４３】
７）スキン層中の空洞含有率
未延伸フィルムのスキン層厚みをＴ１ 、２軸延伸フィルムのスキン層厚みをＴ２ 、フィルムの総合延伸倍率＝縦延伸倍率×横延伸倍率（未延伸フィルムに倍率マーカーを記入して実測）をＤとし、次式によって算出した。
空洞含有率（％）＝１００−１００×Ｔ１ ／（Ｔ２ ×Ｄ）
なお、スキン層中の空洞含有率は上記の方法によって計測出来る他、ヒートプレス前後のスキン層厚み変化率や電子顕微鏡を用いた断面観察等からも算出可能である。ヒートプレス法で空洞含有率を評価する場合には、ヒートプレス機でフィルム中の空洞を完全に押しつぶし、ヒートプレス前後でのＢ層厚み（電子顕微鏡観察）変化率をＦ＝（ヒートプレス後のＢ層厚み）／（ヒートプレス前のＢ層厚み）、ヒートプレス前後でのフィルム単位面積当たりの重量変化率をＧ＝（ヒートプレス後の単位面積当たり重量）／（ヒートプレス前の単位面積当たり重量）とした場合、次式によって算出出来る。
空洞含有率（％）＝１００−（Ｆ／Ｇ）×１００
【００４４】
８）フィルム内部の平均光移動距離kp
測定フィルム上にドットスクリーンを置き各ドット面積比でのフィルム部分の反射率を測定する。その面積比に対する反射率をプロットし、式２と最小二乗法にて最小値になるようにkpの値を決定する。その時のkpの値を平均光移動距離とする。なお、測定機、条件などは以下のとおりとする。
スクリーン：透明ポリエステルの上に写真用乳剤にてＡＭハーフトーンを６５ｄｐｉで作成したもの。ドット面積率は０〜１００％までで少なくとも１０％おきと９５％を使用する。
測定装置：Edmund Scientific 社製Infiviver ビデオマイクロスコープからＣＣＤカメラ（ソニー（株）製XC-78 ）にて画像を取り込む。このとき拡大率は１４インチテレビモニタにて横幅が２ｍｍとなるようする。画像は５１２×３８４ピクセルに分解し、各点での反射率（酸化アルミニウム白板を基準とする）を求めると反射率の分布が得られる。その最も点の多い反射率をこのサンプルの反射率Rpとし、各ドット面積比F に対してプロットする。なお画像解析ソフトはIMAGELAB（Werner Frei Associates製）を用いたが、機能を満たせば他のソフトでも構わない。
【００４５】
【数２】

なお、このＡの値は、Imaging Science（著者J.C.Dainty他、出版Academic Press）のpp244 に報告している紙のMTF の求め方で、酸化チタン（TA-300富士チタン株式会社製）を５％含有した厚さ100 μm のポリエステルフィルムにてMTF を求め、それが最小二乗法にて式１にもっとも近似するときのkpを求める。このkpを用いて上記のスクリーンを用いた方法で最小となるＡの値が0.810 でありそれを採用した。
サンプルはRpが台座の影響を実質的に受けない枚数重ねて行う。
【００４６】
９）画像の鮮明度
プリンター（オリンパス光学製 CAMEDIA P-300）にてPhotoCD （コダック製）からの画像を打ち出し、鮮明な画像なら◎、実質的に問題がなければ○、ぼやけて見えるなら×とした。
【００４７】
実施例１
（空洞形成剤の調整）
原料として、メルトフローレート1.7 のポリスチレン樹脂（三井東圧株式会社製トーポレックス570-57U ）２０重量％とメルトフローレート1.7 のポリプロピレン樹脂（三井東圧株式会社製ノーブレンFO-50F）２０重量％およびメルトフローレート８のポリメチルペンテン樹脂（三井石油化学株式会社製ＴＰＸ，ＤＸ−８４５）６０重量％をペレット混合し、２軸押し出し機に供給して十分に混練りし、空洞形成剤を調整した。
【００４８】
（微粒子含有マスターペレットの作成）
原料として極限粘度0.64のポリエチレンテレフタレート樹脂５０重量％に平均粒径 0.3μｍ（電顕法）のアナタース型二酸化チタン（富士チタン株式会社製TA-300）５０重量％を混合したものをベント式２軸押し出し機に供給して予備混練りした後、溶融ポリマーを連続的にベント式単軸混練り機に供給して混練りして微粒子（酸化チタン）含有マスターペレットを調整した。
次いで、上記の方法で得られた空洞形成剤１０重量％と微粒子（酸化チタン）含有マスターペレット５重量％および固有粘度0.62のポリエチレンテレフタレート樹脂８５重量％をペレット混合して真空乾燥を施し、Ａ層を構成するフィルムの原料とした。
一方、極限粘度0.62のポリエチレンテレフタレート樹脂３０重量％と前記の微粒子（酸化チタン）含有マスターペレット７０重量％をペレット混合して真空乾燥を施し、Ｂ層を構成するフィルムの原料とした。
【００４９】
（未延伸フィルムの作製）
次いで上記の各層を構成するフィルムの原料をそれぞれ別個の押出し機に供給し、フィードブロックを用い、Ａ層の片面にＢ層を溶融状態で接合した。このとき、Ａ層とＢ層の吐出量比率は、ギアポンプを用いて93対７体積比に制御した。次いでＴダイを用いて30℃に調節された冷却ドラム上に押し出し、厚み約６００μｍの未延伸シートを作成した。このとき、Ｂ層側が非ドラム面、Ａ層側がドラム面となるように押し出した。
【００５０】
（２軸延伸フィルムの作製）
得られた未延伸シートを、加熱ロールを用いて６５℃に均一加熱し、６５℃に温度制御したメタルロールと温度非制御のゴムロールとでフィルムを挟んで速度規制（２ｍ／分）し、同様に速度規制（６．８ｍ／分）した高速ロール（メタルロールは３０℃に温度制御、ゴムロールは温度制御せず）との間で３．４倍に延伸した。このとき、速度規制した２組のロールは、速度規制点の間隔が２５ｃｍとなるように平行に設置し、Ｂ面（非ドラム面）側がゴムロール面に接触するように配置した。また、ニップロール中央部に金反射膜を備えた赤外線加熱ヒータ（定格２０Ｗ／ｃｍ）をフィルムの両面に対向して設置（フィルム表面から１ｃｍの距離）し、Ａ層面を定格の１００％の電流で加熱し、Ｂ層面を定格の６０％で加熱した。このようにして得られた１軸延伸フィルムをテンターに導き、１４０℃に加熱して 3.7倍に横延伸し、幅固定して 220℃で５秒間の熱処理を施し、更に 220℃で幅方向に４％緩和させることにより、厚み75μｍの空洞含有ポリエステル系フィルム（実施例１）を得た。
【００５１】
比較例１
フィルムの縦延伸に際し、フィルムの両面を定格の９５％の電流値で赤外線加熱することを除いては、実施例１と全く同様の方法で空洞含有ポリエステル系フィルム（比較例１）を得た。
【００５２】
比較例２
Ｂ層の原料として、極限粘度0.62のポリエチレンテレフタレート樹脂８４重量％と微粒子（酸化チタン）含有マスターペレット１６重量％をペレット混合して真空乾燥したものを用いること以外は、実施例１と同様の方法で空洞含有ポリエステル系フィルム（比較例２）を得た。
【００５３】
比較例３
Ａ層を構成するフィルムの原料として、真空乾燥を施した微粒子（酸化チタン）含有マスターペレット１０重量％と真空乾燥を施した固有粘度0.62のポリエチレンテレフタレート樹脂８３重量％およびメルトフローレート1.7 のポリスチレン樹脂（三井東圧株式会社製トーポレックス570-57U ）７重量％をペレット混合したものを用いること以外は、実施例１と同様の方法で空洞含有ポリエステル系フィルム（比較例３）を得た。
【００５４】
実施例２
Ｂ層に用いる微粒子含有マスターペレットとして、酸化チタン粒子に代えて平均粒子径 0.3μｍ（電顕法）の硫化亜鉛微粒子を用いること以外は、実施例１と同様の方法で空洞含有ポリエステル系フィルム（実施例２）を得た。なお、Ａ層の原料は実施例１と全く同一のものを用いた。
【００５５】
実施例３
Ａ層とＢ層の吐出量比率を８５対１５体積比に変更し、Ｂ層吐出量を均等に二分割してＡ層の両面にＢ層を形成すること以外は実施例１と同様の方法により、Ｂ１層（非ドラム面）／Ａ層／Ｂ２層（ドラム面）構成の未延伸シートを作成した。その後の延伸・熱処理工程は実施例１と全く同様の方法で空洞含有ポリエステル系フィルム（実施例３）を得た。
【００５６】
実施例４
Ｂ層の原料として、固有粘度０．６２のポリエチレンテレフタレート樹脂４０重量％と実施例１で用いた微粒子（酸化チタン）含有マスターペレット５０重量％、蛍光増白剤含有マスターペレット（固有粘度０．６２のポリエチレンテレフタレート樹脂中にイーストマン社製ＯＢ−１を２重量％含有）１０重量％をペレット混合して真空乾燥したものを用いた。これ以外は実施例１と全く同じ方法で未延伸フィルムを作成した。
得られた未延伸シートを、加熱ロールを用いて８３℃に均一加熱し、９３℃に温度制御したメタルロールと非加熱のゴムロールとでフィルムを挟んで速度規制（２ｍ／分）し、同様に速度規制（６．８ｍ／分）した高速ロール（メタルロールは３０℃に制御、ゴムロール温度は制御せず）との間で 3.4倍に延伸した。このとき、速度規制した２組のロールは、速度規制点の間隔が２５ｃｍとなるように平行に設置し、Ｂ面（非ドラム面）側がゴムロール面に接触するように配置した。なお、本実施例では補助加熱装置を用いず、ロール加熱のみによってフィルムを加熱した。
このようにして得られた１軸延伸フィルムをテンターに導き、１３０℃に加熱して 3.5倍に横延伸し、幅固定して 220℃で５秒間の熱処理を施し、更に 220℃で幅方向に４％緩和して空洞含有ポリエステル系フィルム（実施例４）を得た。
【００５７】
比較例４
真空乾燥を施した固有粘度0.62のポリエチレンテレフタレートチップ８８重量％に分子量４０００のポリエチレングリコールフレーク２重量％およびメルトフローレート１８０のポリメチルペンテンペレット（三井石油化学株式会社製ＴＰＸ，ＤＸ−８２０）１０重量％を加えて混合し、Ａ層を構成するフィルムの原料とした。
一方、実施例１と同様の方法で、平均粒子径０．８μｍ（電顕法）の炭酸カルシウム粒子（備北粉化株式会社製、ソフトン３２００）を３０重量％含む微粒子（炭酸カルシウム）含有マスターペレットを作成し、このマスターペレット４５重量％と極限粘度0.62のポリエチレンテレフタレート樹脂５５重量％を混合して真空乾燥を施し、Ｂ層を構成するフィルムの原料とした。
上記の各層を構成するフィルムの原料をそれぞれ別個の押出し機に供給し、フィードブロックを用い、Ａ層の両面にＢ層を接合した。その後の工程は、常法により、98℃で 3.5倍に縦延伸し、 125℃で 3.2倍に横延伸、次いで 220℃で熱処理し、空洞含有ポリエステル系フィルム（比較例４）を得た。
【００５８】
比較例５
Ａ層を構成するフィルムの原料組成比率を、空洞形成剤／微粒子（酸化チタン）含有マスターペレット／固有粘度０．６２のポリエチレンテレフタレート樹脂＝７／５／８８とすること以外は、実施例１と全く同様の方法で空洞含有ポリエステル系フィルム（比較例５）を得た。
【００５９】
【発明の効果】
本願発明は表面平滑性に優れ、十分な画像濃度、解像度が得られ、かつ耐折れシワ性に優れた空洞含有ポリエステルフィルムである。
【００６０】
【表１】

【００６１】
【表２】

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a void-containing polyester film. More preferably, the present invention relates to a void-containing polyester film suitable as a substrate for an image receiving sheet such as thermal transfer, sublimation transfer, and ink jet printer.
[0002]
[Prior art]
As a conventional thermal transfer image receiving sheet, natural paper or a sheet having a recording layer formed on the surface of natural paper is known. However, with this method, only those with insufficient surface smoothness can be obtained. On the other hand, in order to improve the smoothness of the image receiving sheet, a thin polypropylene synthetic paper and natural paper laminated together or a thick polypropylene synthetic paper is used as a base material, and a recording layer is formed on these surfaces. The provided one is widely used. This is because polypropylene-based synthetic paper has surface smoothness that cannot be obtained with natural paper and also has appropriate cushioning properties. And, by having an appropriate cushioning property, it becomes possible to make uniform and sufficient contact between the heating head / transfer ribbon / image receiving sheet at the time of thermal transfer, and a uniform and high density printed matter can be obtained. . However, when polypropylene synthetic paper is used as the base material, the polypropylene synthetic paper is extremely plastically deformed and is not flexible enough. There was a serious drawback that the quality of the printed matter was significantly impaired.
On the other hand, a method using a polyester-based void-containing film instead of polypropylene-based synthetic paper has also been proposed. However, the polyester-based void-containing film is generally more rigid than polypropylene-based synthetic paper and has insufficient cushioning properties. Therefore, in order to obtain the same image density as when using polypropylene-based synthetic paper using a polyester-based void-containing film, the void content is higher than that of polypropylene-based synthetic paper in order to ensure cushioning properties. There must be. As a result, the size of the cavities becomes remarkably large, and the smoothness of the surface is impaired, or the surface is easily folded and wrinkles are likely to occur, resulting in the end-to-end fall. Further, when the void content is increased, the production stability becomes extremely poor, and it is extremely difficult to produce it stably on an industrial scale.
[0003]
[Problems to be solved by the invention]
The present invention is intended to solve the above-mentioned drawbacks of the prior art, that is, the problem that an image receiving sheet excellent in surface smoothness, sufficient image density and sharpness, and excellent in crease resistance cannot be obtained. It is.
[0004]
[Means for Solving the Problems]
  The present invention has an average particle size of 0.1 to 1 μm20 to 50% by weight of the fine particlesA polyester layer (skin layer) containing a large number of cavities derived from the resin and a film (core layer) containing cavities derived from a thermoplastic resin incompatible with the polyester are oriented in at least one axis. A void-containing polyester-based film containing a large number of voids inside,The film is obtained by heating and stretching the front and back of the film at different temperatures in the longitudinal stretching step by a sequential biaxial stretching method, and a thermoplastic resin that is incompatible with the polyester is a polystyrene resin, a polyolefin resin, It is selected from acrylic resin, polycarbonate resin, polysulfone resin, cellulose resin,The void content in the skin layer is 20% by volume or more, the apparent specific gravity is 1.1 or less, the dynamic hardness of at least one surface thereof is 5.0 or less, and the surface of the film A void-containing polyester-based film having a glossiness of 20% or more and an average light movement distance of 0.10 mm or less.
[0005]
The polyester in the present invention is a polycondensation of an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid or an ester thereof with a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol or neopentyl glycol. Polyester produced. In addition to the method of directly reacting aromatic dicarboxylic acid and glycol, these polyesters can be polycondensed by transesterification of alkyl ester of aromatic dicarboxylic acid and glycol, or diglycol ester of aromatic dicarboxylic acid. Can be produced by a method such as polycondensation. Typical examples of such polyester include polyethylene terephthalate, polyethylene butylene terephthalate, polyethylene-2, 6-naphthalate and the like. This polyester may be a homopolymer or a copolymer of a third component. In any case, in the present invention, a polyester having an ethylene terephthalate unit, a butylene terephthalate unit or an ethylene-2,6-naphthalate unit of 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more is preferable. .
[0006]
The thermoplastic resin incompatible with the polyester used in the present invention is arbitrary, and is not particularly limited as long as it is incompatible with the polyester. The term “cavity derived from a thermoplastic resin incompatible with polyester” means that a cavity exists around the thermoplastic resin, and can be confirmed by, for example, a cross-sectional photograph of the film taken with an electron microscope. Specific examples include polystyrene resins, polyolefin resins, polyacrylic resins, polycarbonate resins, polysulfone resins, and cellulose resins. In particular, polystyrene resins or polyolefin resins such as polymethylpentene and polypropylene are preferably used.
[0007]
However, more preferable examples of the thermoplastic resin incompatible with polyester include the following. That is, as a thermoplastic resin incompatible with polyester, it contains at least a polystyrene resin, a polymethylpentene resin, and a polypropylene resin. The content (a wt%) of the polystyrene resin and the content of the polymethylpentene resin The amount (b wt%) and the content of the polypropylene resin (c wt%) satisfy the following relationship: 0.01 ≦ a / (b + c) ≦ 1, c / b ≦ 1, 3 ≦ a + b + c ≦ 20 Is most preferable, and is suitable for increasing the void ratio and improving the crease resistance.
[0008]
Here, the polystyrene-based resin refers to a thermoplastic resin having a polystyrene structure as a basic constituent element. In addition to homopolymers such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene, other components are grafted or blocked. A copolymerized modified resin, such as an impact-resistant polystyrene resin or a modified polyphenylene ether resin, or a mixture of a thermoplastic resin compatible with these polystyrene resins, such as polyphenylene ether, is included.
[0009]
The polymethylpentene-based resin is a polymer having units derived from 4-methylpentene-1 at 80 mol% or more, preferably 90 mol% or more, and other components include ethylene units, propylene units, Examples include units derived from butene-1 units, 3-methylbutene-1, and the like.
The melt flow rate of such polymethylpentene is preferably 200 g / 10 min or less, more preferably 30 g / 10 min or less. This is because when the melt flow rate exceeds 200 g / 10 min, it is difficult to obtain the effect of reducing the weight of the film.
[0010]
The polypropylene resin in the present invention also includes modified resins obtained by grafting or block copolymerizing other components in addition to homopolymers such as isotactic polypropylene and syndiotactic polypropylene.
In addition, as the presence state of the polypropylene resin in the present invention, the above polypropylene resin may be used separately from the polymethylpentene, or a propylene unit may be used as a copolymerization component in the polymethylpentene resin. You may use what was introduced.
[0011]
The mixing amount of these void forming agents, that is, thermoplastic resins incompatible with the polyester, with respect to the polyester varies depending on the amount of the target void, but may be in the range of 3 to 20% by weight with respect to the entire film. More preferably, it is 5 to 18% by weight. And if it is less than 3 weight%, there exists a limit in increasing the production amount of a cavity. On the other hand, if it is 20% by weight or more, the stretchability of the film is remarkably impaired, and the heat resistance, strength, and waist strength are impaired.
[0012]
In addition, in the film, inorganic or organic particles may be added to the polyester or incompatible resin as necessary in order to improve the concealability and the like. Examples of the particles that can be added include silica, kaolinite, talc, calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, titanium oxide, zinc sulfide, and organic white pigments. is not.
[0013]
The void-containing polyester film of the present invention needs to have an apparent specific gravity of 1.3 or less, preferably 1.2 or less, more preferably 1.1 or less. If the apparent specific gravity is greater than 1.3, the amount of voids in the film is too small, and a sufficient image density cannot be obtained during thermal transfer printing. On the other hand, although the lower limit of the apparent specific gravity is not restricted, it is preferably 0.7 or more, and more preferably 0.8 or more, in order to ensure folding resistance.
[0014]
The void-containing polyester film of the present invention needs to have a dynamic hardness of 5.0 or less, more preferably 4.0 or less, and most preferably 3.0 or less. This requirement is the most important component of the present invention. By satisfying this requirement, the image density during thermal transfer printing can be dramatically improved. On the contrary, when the dynamic hardness of the film surface exceeds 5.0, only an image density equivalent to the conventionally known void-containing polyester film can be obtained.
[0015]
The void-containing polyester film of the present invention is required to have a surface dynamic hardness of 5.0 or less and a glossiness of the surface of 20% or more, more preferably 30% or more. This means that when the glossiness of the surface is less than 20%, the smoothness of the film surface and thus the thermal smoothness of the thermal transfer image-receiving sheet is impaired, and uniform adhesion between the ink ribbon and the image-receiving paper is obtained during thermal transfer printing. This is because the image density becomes extremely low. Also, the thermal transfer image is rough and the print quality is greatly reduced.
[0016]
The method for obtaining the dynamic hardness and glossiness is arbitrary and is not limited at all. For example, more fine cavities can be formed in the vicinity of the film surface.
[0017]
Furthermore, the void-containing film of the present invention should have an average light moving distance inside the film of 0.15 mm or less, preferably 0.13 mm or less, more preferably 0.10 mm or less. If the average light moving distance exceeds 0.15 mm, the printed image is inferior in sharpness and the image looks blurred.
[0018]
This average light travel distance can usually be obtained from MTF, which is an index representing the high resolution of the photographic material. A Probability Description of the Yule-Nielsen Effect II: The Impact of Halftone Geometry (Journal of Imaging Science and Technology pp637, volume 41, 1997) Yes.
[0019]
[Expression 1]

In other words, if the MTF for each frequency is obtained, this kp can be obtained. However, MTF is usually obtained from the density of reflected light of screens with different line widths and spacing (spatial frequency) placed on paper or recording film or printed directly, or the spatial frequency changes continuously. Similarly, it is obtained from the light having a sinusoidal distribution using the reflection density. However, this method is only required for relatively low frequencies. In particular, when trying to obtain kp for paper or recording film, the error becomes very large, so the kp obtained from the method of the example described later and the sharpness of the printed material on the paper or recording film are relatively Think of it as a way to match well.
[0020]
  A uniform biaxially oriented film, which will be described in detail by exemplifying means for obtaining the dynamic hardness, gloss, and average light travel distance. First, the average particle size is 0.15The dynamic hardness and glossiness can be achieved by bonding a polyester layer (skin layer) containing fine cavities derived from fine particles of μm to the film surface. The void content in the skin layer is not limited at all, but it is preferable to form a void of 20% by volume or more. Note that the fine cavities derived from the fine particles mean that there are cavities in at least a part of the periphery of the fine particles, and can be confirmed by, for example, a cross-sectional photograph of the film using an electron microscope.
[0021]
And when the average diameter of the particle | grains added in a skin layer is less than 0.1 micrometer, the cavity formation ability in the film extending process mentioned later falls remarkably, and the dynamic hardness of a film surface is 5.0 or less. This makes it difficult to achieve the desired effect of improving the thermal transfer sensitivity characteristics. Conversely, when particles with an average diameter exceeding 5 μm are used, the ability to form cavities is excellent, but the smoothness of the film surface is significantly reduced, making it difficult to achieve a glossiness of 20% or more. On the contrary, it will decrease. Preferably it is 0.1-3 micrometers, More preferably, it is 0.1-2 micrometers, Most preferably, it is 0.1-1 micrometers.
[0022]
The particles that can be added to the skin layer may be inorganic particles or organic particles, and are not limited at all. For example, titanium dioxide, calcium carbonate, barium sulfate, zinc sulfide, silicon dioxide, Examples include aluminum oxide, talc, and kaolin. These particles may be surface-treated as necessary. Examples of the treatment agent include aluminum oxide, silicon dioxide, zinc oxide, silicon-based resin, siloxane-based resin, fluorine-based resin, silane coupling agent and titanate coupling agent, polyol and polyvinylpyridine, but are not limited thereto. It is not something.
[0023]
Among these, particularly preferred particles include titanium oxide fine particles and zinc sulfide fine particles. Furthermore, titanium oxide fine particles are most preferably used from the viewpoint of effectively imparting concealability by the film. The titanium oxide fine particles may be either anatase type or rutile type. The particle surface may be subjected to inorganic treatment such as alumina or silica, or may be subjected to organic treatment such as silicon or alcohol.
[0024]
  The concentration of fine particles added to the skin layer is,20-50% by weight.When the amount added is less than 20%, the ability to form cavities becomes insufficient, and it becomes difficult to make the dynamic hardness of the film surface 5.0 or less. On the other hand, when it exceeds 50%, the smoothness of the film surface is abruptly lost, and it becomes difficult to make the glossiness of the film surface 20% or more.
[0025]
In addition, a coloring agent, a light fastness agent, a fluorescent agent, an antistatic agent, and the like can be added to the skin layer as necessary.
[0026]
The thickness of the skin layer is preferably 1 to 20 μm and less than 30% of the total film thickness. When the thickness of the skin layer is less than 1 μm, the variation in the fine particle concentration per film surface area increases, so that the image density is uneven and the printed material tends to give a rough impression. On the other hand, even if the skin layer is formed with a thickness exceeding 20 μm, the effect of improving the image density is not obtained and is meaningless. Furthermore, when the thickness of the skin layer exceeds 30% of the total film thickness, the stretchability of the entire film tends to be remarkably lowered, which is not preferable for ensuring stable industrial productivity.
[0027]
The average light moving distance can be controlled by the amount and type of particles in the skin layer and the core layer, the amount of cavities, and the thickness ratio. In consideration of other parameters and productivity, as an example, when titanium oxide is used for the skin layer, the addition amount is 20 to 40% by weight, and the thickness of the skin layer is 5 to 25% of the total thickness. The specific gravity seems to be about 0.75 to 1.05. However, the present invention is not limited to this method.
[0028]
  The method for producing the void-containing polyester film of the present invention is as follows:By sequential biaxial stretching methodCan be manufactured. First, as a method of joining the skin layer to the film surface, it is possible to adopt a co-extrusion method in which the resins of the A layer and the B layer are supplied to separate extruders, then laminated in a molten state and extruded from the same die. Most preferred.
[0029]
The unstretched sheet thus obtained can be further stretched between rolls with different speeds (roll stretching), stretched by gripping and expanding by a clip (tenter stretching), or stretched by air pressure (inflation stretching). ) Or the like. By performing the orientation treatment, interfacial peeling occurs between the polyester / incompatible resin and between the polyester / fine particles, and many fine cavities appear.
Therefore, the conditions for stretching / orienting the unstretched sheet are closely related to the formation of cavities. In the following, the stretching / orientation conditions will be described by taking as an example a sequential biaxial stretching method that is most preferably used, particularly a method of stretching an unstretched sheet in the longitudinal direction and then in the width direction.
[0030]
First, the first-stage longitudinal stretching process is the most important process for forming many fine cavities in the film. In the longitudinal stretching, stretching is performed between two or many rolls having different peripheral speeds. As a heating means at this time, a method using a heating roll or a method using a non-contact heating method may be used, or they may be used in combination. Among these, the most preferable stretching method is a method using both roll heating and non-contact heating. In this case, first, the film is preheated to a temperature of 50 ° C. to a glass transition point of polyester or less using a heating roll, and then heated on the front and back of the film by an independent infrared heater of a control system. At this time, the skin layer surface is heated so as to have a lower temperature, and the insufficient amount of heat is compensated by infrared heating from the opposite surface. Thus, it is very important to heat and stretch the film at different temperatures. And the method of providing a temperature difference with a non-contact heating device is only one preferable example, and the same effect can be obtained by other methods, for example, a method of heating a film between rolls of different temperatures. In any case, it is possible to heat the entire film mainly from the anti-skin layer side to supply a sufficient amount of heat sufficient to stretch the film uniformly and to stretch the skin layer surface at a lower temperature. This is an important point for forming many cavities derived from inorganic fine particles.
[0031]
Next, the uniaxially stretched film thus obtained is introduced into a tenter and stretched 2.5 to 5 times in the width direction. A preferable stretching temperature at this time is 100 ° C to 200 ° C.
The biaxially stretched film thus obtained is subjected to heat treatment as necessary. The heat treatment is preferably performed in a tenter, and is preferably performed in the range of the melting point Tm-50 ° C. to Tm of the polyester.
[0032]
The void-containing film of the present invention obtained by the above production method contains sufficient fine cavities in the skin layer and has excellent production stability.
Moreover, the void-containing polyester film of the present invention may have a coating layer on at least one surface thereof. By providing the coating layer, it is possible to improve the paintability and adhesion of ink and coating agent. The compound constituting the coating layer is preferably a polyester resin, but in addition to this, a compound disclosed as a means for improving the adhesion of a normal polyester film, such as a polyurethane resin, a polyester urethane resin, or an acrylic resin. Etc. are applicable.
[0033]
In addition, as a method for providing the coating layer, conventionally used methods such as a gravure coating method, a kiss coating method, a dip method, a spray coating method, a curtain coating method, an air knife coating method, a blade coating method, and a reverse roll coating method can be applied. As a step of applying, any method such as a method of applying before stretching of the film, a method of applying after longitudinal stretching, and a method of applying to the film surface after the orientation treatment is possible.
[0034]
The void-containing polyester film thus obtained has a remarkable effect of improving the image density while having excellent crease resistance and surface smoothness as compared with the conventional void-containing film.
In order to produce a thermal transfer image-receiving sheet using the void-containing polyester film of the present invention, a recording layer is formed on the film surface to receive ink or diffusible (sublimation) dye transferred from the thermal transfer ink sheet. do it. In this case, the recording layer may be formed directly on the film, or may be formed through an undercoat layer such as an easy adhesion layer, a whiteness improving layer, or an antistatic layer.
[0035]
Further, the void-containing polyester film of the present invention may be used alone as a base material, or may be used in combination with another base material. Examples of other base materials that can be combined include natural paper, various synthetic resin films, woven fabrics, and non-woven fabrics, but are not limited thereto.
Alternatively, the surface opposite to the surface on which the receiving layer is formed may be subjected to adhesive processing and used as an adhesive label capable of thermal transfer printing.
[0036]
The void-containing polyester film thus obtained has superior surface smoothness, sufficient image density and resolution, and is excellent in folding and wrinkle resistance as compared with those conventionally proposed. , Packaging materials, maps, white boards, building materials, wallpaper, decorative boards, delivery slips, magnetic cards, electrical insulating materials, display reflectors, preferably thermal transfer, sublimation transfer, image-receiving sheets such as laser beam printers and inkjet printers, photographic paper It is an optimal base material for such as.
[0037]
Example
Next, examples and comparative examples of the present invention will be shown.
The measurement / evaluation method used in the present invention is shown below.
1) Apparent specific gravity
The film is accurately cut into a 10 cm × 10 cm square, and its thickness is measured at 50 points to obtain an average thickness t (unit: μm). Next, the weight of the sample is measured to 0.1 mg and set to w (unit: g). And the apparent specific gravity was calculated by the following formula.
Apparent specific gravity (−) = (w / t) × 10000
[0038]
2) Dynamic hardness
Using a dynamic ultra-micro hardness meter (DUH-201) manufactured by Shimadzu Corporation, a load of 0.2 gf was applied to a 115 ° triangular pyramid indenter, and the dynamic hardness was determined from the load and the indentation depth of the indenter by the following equation.

[0039]
3) Surface glossiness
The reflectance at 60 degrees was determined using VGS-1001DP manufactured by Nippon Denshoku Industries Co., Ltd.
[0040]
4) Thermal transfer sensitivity characteristics (relative image density)
Coating liquid with the following composition
Water dispersible copolyester resin: 2 parts
Water-dispersible acrylic / styrene copolymer resin: 5 parts
Water-dispersible isocyanate crosslinking agent: 0.5 part
Water: 67.4 parts
Isopropyl alcohol: 25 parts
Surfactant: 0.1 part
After drying, the weight is 4g / m²Then, the film surface is coated, the dimensions are fixed, and heat treatment is performed at 160 ° C. for 30 seconds to form a recording layer, thereby producing a thermal transfer image receiving sheet.
About the sample which cut the thermal transfer image-receiving sheet thus obtained into A6 size, a commercially available ink ribbon (print set P-PS100 for sublimation transfer printer manufactured by Caravel Data Systems Co., Ltd.) and a commercially available thermal transfer printer (manufactured by Bon Electric Co., Ltd.) Printing is performed at a printing speed of 100 mm / second and a head voltage of 18 V using a thermal transfer type label printer BLP-323). The print pattern includes 7 solid solid letters of 9 mm x 9 mm each for 4 colors of C (cyan), M (magenta), Y (yellow), and K (black) on which these are overprinted. 28) A pattern arranged in an A6 sheet is used.
After printing, the Macbeth densitometer (TR-927) is used to measure the reflection density of each color of CMYK, and the average density of the four colors (28 places in total) is obtained.
Similarly, commercially available image-receiving paper (print set P-PS100 for sublimation transfer printer manufactured by Caravel Data Systems Co., Ltd .: a foamed polypropylene film laminated on both sides of natural paper to form a recording layer) in the same manner. The average density is obtained, and the thermal transfer sensitivity characteristic is evaluated by the ratio (%) of the density of the sample to the density of the commercially available image receiving paper.
[0041]
5) Folding resistance
The thermal transfer image-receiving sheet prepared by the above method is cut into a strip shape having a length of 5 cm and a width of 1 cm, wound around a glass rod having a diameter of 5 mm, and then ironed. Thereafter, the sample was stretched again, and the state of wrinkles generated on the surface was observed using a stereomicroscope.
Rank A: No wrinkles
Rank B: There are thin creases on the entire surface.
Rank C: There are thick creases on the entire surface.
[0042]
6) Skin layer thickness
The cut surface of the film was measured with an electron microscope.
[0043]
7) Cavity content in skin layer
The skin layer thickness of the unstretched film is T1, the skin layer thickness of the biaxially stretched film is T2, and the total stretch ratio of the film = longitudinal stretch ratio × lateral stretch ratio (measured by entering a magnification marker on the unstretched film) is D. Calculated by the following equation.
Cavity content (%) = 100-100 × T1 / (T2 × D)
The void content in the skin layer can be measured by the above method, and can also be calculated from the rate of change in skin layer thickness before and after heat pressing, cross-sectional observation using an electron microscope, and the like. When the void content is evaluated by the heat press method, the voids in the film are completely crushed with a heat press machine, and the change rate of the B layer thickness (observed with an electron microscope) before and after the heat press is F = (after the heat press). B layer thickness) / (B layer thickness before heat press), weight change rate per unit area of film before and after heat press G = (weight per unit area after heat press) / (per unit area before heat press) Weight), it can be calculated by the following formula.
Cavity content (%) = 100− (F / G) × 100
[0044]
8) Average light travel distance kp inside the film
A dot screen is placed on the measurement film, and the reflectance of the film portion at each dot area ratio is measured. The reflectance with respect to the area ratio is plotted, and the value of kp is determined so as to be the minimum value using Equation 2 and the least square method. The value of kp at that time is defined as the average light movement distance. The measuring equipment and conditions are as follows.
Screen: An AM halftone made of photographic emulsion on a transparent polyester at 65 dpi. The dot area ratio is 0 to 100%, and at least every 10% and 95% are used.
Measuring device: An image is captured from an Infiviver video microscope manufactured by Edmund Scientific with a CCD camera (XC-78 manufactured by Sony Corporation). At this time, the magnification is set to be 2 mm on a 14-inch TV monitor. The image is decomposed into 512 × 384 pixels, and when the reflectance at each point (based on the white plate of aluminum oxide) is obtained, the reflectance distribution is obtained. The reflectance with the most points is defined as the reflectance Rp of this sample and plotted against each dot area ratio F 1. Note that IMAGELAB (manufactured by Werner Frei Associates) was used as the image analysis software, but other software may be used as long as the function is satisfied.
[0045]
[Expression 2]

The value of A is 5% of titanium oxide (TA-300 manufactured by Fuji Titanium Co., Ltd.), which is the paper MTF calculation method reported in pp244 of Imaging Science (author JCDainty et al., Publishing Academic Press). The MTF is obtained from the polyester film having a thickness of 100 μm and the kp when it is most approximated to Equation 1 is obtained by the least square method. Using this kp, the minimum A value in the method using the above screen was 0.810, which was adopted.
Samples are piled up so that Rp is not substantially affected by the pedestal.
[0046]
9) Image sharpness
An image from PhotoCD (manufactured by Kodak) was launched with a printer (OLYMPUS Optical CAMEDIA P-300). A clear image was marked with ◎.
[0047]
Example 1
(Adjustment of cavity forming agent)
As raw materials, 20% by weight of a polystyrene resin having a melt flow rate of 1.7 (Topolex 570-57U manufactured by Mitsui Toatsu Co., Ltd.) and 20% by weight of a polypropylene resin having a melt flow rate of 1.7 (Noblen FO-50F manufactured by Mitsui Toatsu Co., Ltd.) 60% by weight of polymethylpentene resin (TPI, DX-845 manufactured by Mitsui Petrochemical Co., Ltd.) having a melt flow rate of 8 was mixed with pellets, supplied to a biaxial extruder, and kneaded sufficiently to prepare a cavity forming agent. .
[0048]
(Preparation of fine particle-containing master pellets)
Bent-type biaxial extrusion of 50% by weight of polyethylene terephthalate resin with an intrinsic viscosity of 0.64 as a raw material and 50% by weight of anatase-type titanium dioxide (TA-300 manufactured by Fuji Titanium Co., Ltd.) with an average particle size of 0.3μm After being supplied to the machine and pre-kneaded, the molten polymer was continuously supplied to the vent type single-screw kneader and kneaded to prepare fine particle (titanium oxide) -containing master pellets.
Next, 10% by weight of the cavity forming agent obtained by the above method, 5% by weight of fine pellets (titanium oxide) -containing master pellets and 85% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 are mixed in pellets and vacuum-dried. Was used as a raw material for the film.
On the other hand, 30% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 70% by weight of the above-mentioned fine pellets (titanium oxide) containing master pellets were mixed in a vacuum and vacuum-dried to obtain a film material constituting the B layer.
[0049]
(Preparation of unstretched film)
Subsequently, the raw material of the film which comprises said each layer was each supplied to the separate extruder, and B layer was joined to the single side | surface of A layer in the molten state using the feed block. At this time, the discharge amount ratio of the A layer and the B layer was controlled to 93 to 7 volume ratio using a gear pump. Next, the sheet was extruded onto a cooling drum adjusted to 30 ° C. using a T die to prepare an unstretched sheet having a thickness of about 600 μm. At this time, extrusion was performed so that the B layer side was a non-drum surface and the A layer side was a drum surface.
[0050]
(Production of biaxially stretched film)
The obtained unstretched sheet is uniformly heated to 65 ° C. using a heating roll, and the speed is regulated (2 m / min) by sandwiching a film between a metal roll whose temperature is controlled to 65 ° C. and a rubber roll whose temperature is not controlled. The film was stretched 3.4 times with a high-speed roll that was speed-controlled (6.8 m / min) (the temperature of the metal roll was controlled at 30 ° C., and the temperature of the rubber roll was not controlled). At this time, the two sets of rolls whose speed was restricted were arranged in parallel so that the distance between the speed restriction points was 25 cm, and the B surface (non-drum surface) side was placed in contact with the rubber roll surface. In addition, an infrared heater (rated 20 W / cm) equipped with a gold reflective film at the center of the nip roll was placed opposite to both sides of the film (a distance of 1 cm from the film surface), and the A layer surface was at 100% of the rated current. The layer B surface was heated to 60% of the rating. The uniaxially stretched film thus obtained is guided to a tenter, heated to 140 ° C., stretched by a factor of 3.7, fixed in width, subjected to heat treatment at 220 ° C. for 5 seconds, and further in the width direction at 220 ° C. By relaxing 4%, a void-containing polyester film (Example 1) having a thickness of 75 μm was obtained.
[0051]
Comparative Example 1
In the longitudinal stretching of the film, a void-containing polyester film (Comparative Example 1) was obtained in the same manner as in Example 1 except that both surfaces of the film were heated by infrared radiation at a current value of 95% of the rating.
[0052]
Comparative Example 2
The same method as in Example 1 except that 84% by weight of polyethylene terephthalate resin with an intrinsic viscosity of 0.62 and 16% by weight of master pellets containing fine particles (titanium oxide) were mixed and dried in vacuum as the raw material for layer B A void-containing polyester film (Comparative Example 2) was obtained.
[0053]
Comparative Example 3
As raw materials for the film constituting the layer A, 10% by weight of fine pellets (titanium oxide) containing master pellets subjected to vacuum drying, 83% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 subjected to vacuum drying, and a polystyrene resin having a melt flow rate of 1.7 (Mitsui Toatsu Co., Ltd. Topolex 570-57U) A void-containing polyester film (Comparative Example 3) was obtained in the same manner as in Example 1 except that 7% by weight of the mixture was used.
[0054]
Example 2
A void-containing polyester film (implemented in the same manner as in Example 1), except that zinc sulfide fine particles having an average particle size of 0.3 μm (electron microscopic method) are used in place of titanium oxide particles as fine particle-containing master pellets for layer B. Example 2) was obtained. The raw material for layer A was exactly the same as in Example 1.
[0055]
Example 3
The same method as in Example 1 except that the ratio of the discharge amount of the A layer and the B layer is changed to 85:15 volume ratio, the B layer discharge amount is equally divided into two and the B layer is formed on both sides of the A layer. Thus, an unstretched sheet having a B1 layer (non-drum surface) / A layer / B2 layer (drum surface) configuration was prepared. Subsequent stretching and heat treatment steps were carried out in the same manner as in Example 1 to obtain a void-containing polyester film (Example 3).
[0056]
Example 4
As raw materials for the B layer, 40% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62, 50% by weight of fine pellet (titanium oxide) -containing master pellets used in Example 1, and an optical brightener-containing master pellet (inherent viscosity of 0.62) (2% by weight of OB-1 manufactured by Eastman Co., Ltd. in polyethylene terephthalate resin) was mixed with pellets and vacuum-dried. Except for this, an unstretched film was prepared in exactly the same manner as in Example 1.
The obtained unstretched sheet was uniformly heated to 83 ° C. using a heating roll, and the speed was regulated (2 m / min) by sandwiching the film between a metal roll controlled to 93 ° C. and a non-heated rubber roll. The film was stretched 3.4 times with a high-speed roll (metal roll was controlled at 30 ° C., rubber roll temperature was not controlled) regulated at speed (6.8 m / min). At this time, the two sets of rolls whose speed was restricted were arranged in parallel so that the distance between the speed restriction points was 25 cm, and the B surface (non-drum surface) side was placed in contact with the rubber roll surface. In this example, the auxiliary heating device was not used, and the film was heated only by roll heating.
The uniaxially stretched film thus obtained is guided to a tenter, heated to 130 ° C. and stretched 3.5 times, fixed in width, subjected to heat treatment at 220 ° C. for 5 seconds, and further in the width direction at 220 ° C. By relaxing 4%, a void-containing polyester film (Example 4) was obtained.
[0057]
Comparative Example 4
10 weights of polymethylpentene pellets (TPI, DX-820, Mitsui Petrochemical Co., Ltd.) of 88 weight% of polyethylene terephthalate chips having an intrinsic viscosity of 0.62 after vacuum drying, 2 weight% of polyethylene glycol flakes having a molecular weight of 4000 and a melt flow rate of 180 % Were mixed and used as the raw material for the film constituting the A layer.
On the other hand, a master pellet containing fine particles (calcium carbonate) containing 30% by weight of calcium carbonate particles having an average particle diameter of 0.8 μm (electron microscopy) (Softon 3200, manufactured by Bihoku Flourishing Co., Ltd.) was obtained in the same manner as in Example 1. The master pellet 45% by weight and a polyethylene terephthalate resin 55% by weight with an intrinsic viscosity of 0.62 were mixed and vacuum-dried to obtain a film material constituting the B layer.
The raw material of the film which comprises each said layer was supplied to the respectively separate extruder, and B layer was joined to both surfaces of A layer using the feed block. Subsequent steps were longitudinally stretched 3.5 times at 98 ° C., transversely stretched 3.2 times at 125 ° C., and then heat treated at 220 ° C. to obtain a void-containing polyester film (Comparative Example 4).
[0058]
Comparative Example 5
Example 1 except that the raw material composition ratio of the film constituting the A layer is cavity forming agent / fine particle (titanium oxide) -containing master pellet / polyethylene terephthalate resin having an intrinsic viscosity of 0.62 = 7/5/88 A void-containing polyester film (exactly the same method)Comparative Example 5)
[0059]
【The invention's effect】
The present invention is a void-containing polyester film having excellent surface smoothness, sufficient image density and resolution, and excellent crease resistance.
[0060]
[Table 1]

[0061]
[Table 2]

Claims (5)

  A polyester layer (skin layer) containing 20 to 50% by weight of fine particles having an average particle diameter of 0.1 to 1 μm and containing many cavities derived from the fine particles, and cavities derived from a thermoplastic resin incompatible with the polyester Is a void-containing polyester film containing a large number of cavities inside by being oriented at least uniaxially by laminating a film (core layer) containing the film in a longitudinal direction by a sequential biaxial stretching method. The film is obtained by heating and stretching the front and back of the film at different temperatures. The thermoplastic resin incompatible with the polyester is a polystyrene resin, a polyolefin resin, a polyacrylic resin, a polycarbonate resin, or a polysulfone resin. Resin and cellulosic resin, the void content in the skin layer is 20% by volume or more, and the apparent ratio 1.1 or less, the dynamic hardness of at least one of the surfaces thereof is 5.0 or less, the glossiness of the surface of the film is 20% or more, and the average light movement distance is 0.10 mm or less. A void-containing polyester film characterized by that.   The void-containing polyester film according to claim 1, wherein the thickness of the skin layer is 1 to 20 µm and less than 30% of the total film thickness.   2. The void-containing polyester film according to claim 1, wherein the fine particles added to the skin layer are titanium oxide.   2. The void-containing polyester film according to claim 1, wherein the fine particles added to the skin layer are zinc sulfide. As a thermoplastic resin incompatible with polyester, it contains at least a polystyrene resin, a polymethylpentene resin, and a polypropylene resin. 5. The void-containing polyester film according to claim 1, wherein the content (b wt%) and the content (c wt%) of the polypropylene resin satisfy the following relationship.
0.01 ≦ a / (b + c) ≦ 1 , c / b ≦ 1 , 3 ≦ a + b + c ≦ 20