JP3626592B2 - Polyester film for metal plate lamination molding - Google Patents

Description

【００４１】
本発明では、基準長を２．５ｍｍとして５個測定し、値の大きい方から１個を除いた４個の平均値としてＲａを表わす。
【００４２】
本発明の積層フィルムは、層（Ａ）と層（Ｂ）を積層した構造であり、かかる積層構造のフィルムは、例えば、それぞれの層を構成する共重合ポリエステルを別々に溶融して、共押出しし、固化前に積層融着させた後、二軸延伸、熱固定する方法、それぞれの層を構成する共重合ポリエステルを別々に溶融して、押出ししてフィルムを製造し、未延伸状態または延伸後、両者を積層する方法などにより製造することができる。
【００４３】
この場合、層（Ａ）の厚さ方向の屈折率は、１．５００〜１．５４０であることが好ましく、１．５０５〜１．５３０であることがさらに好ましい。屈折率が１．５００未満であると成形加工性が不十分になることがあり、他方１．５４０を超えると非晶に近い構造となるため、耐熱性が低下することがある。
【００４４】
ここで、厚さ方向の屈折率は、アッベの屈折計の接眼側に偏光板アナライザーを取り付け、単色光ＮａＤ線で測定する。マウント液はヨウ化メチレンを用い、測定温度は２５℃である。
【００４５】
本発明の積層フィルムは、好ましくは厚みが６〜７５μｍである。更に１０〜７５μｍ、特に１５〜５０μｍであることが好ましい。厚みが６μｍ未満では加工時に破れなどが生じやすくなり、一方７５μｍを超えるものは過剰品質であって不経済である。
【００４６】
また、層（Ａ）の厚みＴ_Ａと層（Ｂ）の厚みＴ_Ｂの比（Ｔ_Ａ／Ｔ_Ｂ）は、０．０２〜１．５、さらに０．０４〜０．６７、特に０．０４〜０．２５が好ましい。具体的には、例えば厚みが２０μｍの積層フィルムの場合、層（Ａ）の厚みを０．５〜１５μｍ、好ましくは１〜１０μｍ、さらに好ましくは１〜４μｍとする。
【００４７】
本発明のポリエステルフィルムは、特に食品缶または飲料缶に用いられるものであるから、該フィルムより溶出あるいは飛散する物質が少ないほど良いが、それらの物質を全くなくすことは実質的に不可能である。そこで、食品缶または飲料缶用途に使用するためには、例えばイオン交換水で１２１℃、２時間抽出したときのフィルム１平方インチ当りの抽出量が０．５ｍｇ以下であることが好ましく、０．１ｍｇ以下であることが更に好ましい。
【００４８】
上記抽出量を少なくするには、フィルムのガラス転移温度を高くすればよい。フィルムのガラス転移温度は該フィルムを構成するポリマーのガラス転移温度と配向度によって決まるが、配向度を上げると成形加工性が悪化するので、ポリマー（共重合ポリエステル）のガラス転移温度をできるだけ高くするのが好ましい。
【００４９】
本発明の積層フィルムが貼合せられる金属板、特に製缶用金属板としては、ブリキ、ティンフリースチール、アルミニウム等の板が適切である。金属板へのポリエステルフィルムの貼合せは、例えば下記▲１▼、▲２▼の方法で行うことができる。
▲１▼ 金属板をフィルムの融点以上に加熱しておいてフィルムを貼合せた後冷却し、金属板に接するフィルムの表層部（薄層部）を非晶化して密着させる。
▲２▼ フィルムに予め接着剤層をプライマーコートしておき、この面と金属板を貼合せる。接着剤層としては公知の樹脂接着剤、例えばエポキシ系接着剤、エポキシ−エステル系接着剤、アルキッド系接着剤等を用いることができる。
【００５０】
なお、本発明の積層フィルムを金属板に貼り合わせる際には、層（Ｂ）の側を金属板に貼り合わせるようにする。
【００５１】
さらに、本発明の積層フィルムにおいては、必要に応じて層（Ａ）と層（Ｂ）の間に他の追加の層を積層してもよい。
【００５２】
【実施例】
以下、実施例により本発明を更に説明する。なお、フィルムの特性は下記の方法で測定した。
（１）共重合ポリエステルの固有粘度
オルトクロロフェノール中、３５℃で測定する。
【００５３】
（２）共重合ポリエステルの融点
Ｄｕ Ｐｏｎｔ Ｉｎｓｔｒｕｍｅｎｔｓ ９１０ ＤＳＣを用い、昇温速度２０℃／分で融解ピークを求める方法による。なおサンプル量は２０ｍｇとする。
【００５４】
（３）共重合ポリエステルのガラス転移温度（Ｔｇ）
ＤＳＣ測定用パンに２０ｍｇのフィルムサンプルを入れ、２９０℃加熱ステージ上で５分間加熱溶融後、すばやく試料パンを氷の上に敷いたアルミ箔上で急冷固化し、Ｄｕ Ｐｏｎｔ Ｉｎｓｔｒｕｍｅｎｔｓ ９１０ ＤＳＣを用い、昇温速度２０℃／分でガラス転移点を求める方法による。
【００５５】
（４）フィルムの損失弾性率の最高温ピーク温度（Ｔｅ）
動的粘弾性測定装置を用いて測定周波数１０Ｈｚ、動的変位±２５×１０^−４ｃｍにて損失弾性率を求め、このときの最高温ピーク温度をもって示す。
【００５６】
（５）表面粗さ（Ｒａ）
（株）小坂研究所製、触針式表面粗さ計（ＳＵＲＦＣＯＲＤＥＲ ＳＥ−３０Ｃ）を用いて、触針半径２μｍ、測定圧０．０３ｇ、カットオフ値０．２５ｍｍの条件で測定する。
【００５７】
（６）巻取り性
フィルム製造工程で、フィルムをロール状に巻き取る際、滑り不良によって発生するロール表面の小突起を観察し、下記の基準で評価した。
◎：小突起は全く認められない。
○：多少小突起が認められるが、取扱い上特に問題はない。
×：小突起が多数発生し、取扱い性が悪化する。
【００５８】
（７）深絞り加工性
フィルムをポリエステルの融点以上に加熱した板圧０．２５ｍｍのティンフリースチールの両面に貼合せ、水冷した後１５０ｍｍ径の円板状に切り取り、絞りダイスとポンチを用いて４段階で深絞り加工し、５５ｍｍ径の側面無継目容器（以下、缶と略す）を作成した。この缶について以下の観察および試験を行い、各々下記の基準で評価した。
【００５９】
▲１▼深絞り加工性−１
○：フィルムに異常なく加工されたフィルムに白化や破断が認められない。
△：フィルムの缶上部に白化が認められる。
×：フィルムの一部にフィルム破断が認められる。
▲２▼深絞り加工性−２
○：異常なく加工され、缶内フィルム面の防錆性試験（１％ＮａＣｌ水溶液を缶内に入れ、電極を挿入し、缶体を陽極にして６Ｖの電圧をかけた時の電流値を測定する。以下、ＥＲＶ試験と略す）において０．２ｍＡ以下を示す。
×：フィルムに異常はないが、ＥＲＶ試験では電流値が０．２ｍＡを超えており、通電箇所を拡大観察するとフィルムの粗大滑剤を起点としたピンホール状の割れが認められる。
【００６０】
（８）耐衝撃性
深絞り成形が良好な缶について、水を満注し、０℃に冷却した後、各テストにつき１０個ずつを高さ３０ｃｍから塩ビタイル床面に落とした後、缶内のＥＲＶ試験を行った結果、
○：全１０個について０．２ｍＡ以下であった。
△：１〜５個について０．２ｍＡを超えていた。
×：６個以上について０．２ｍＡを超えているか、あるいは落下後既にフィルムのひび割れが認められた。
【００６１】
（９）耐熱脆化性
深絞りが良好であった缶を２００℃×５分間加熱保持した後、前述の耐衝撃性評価を行った結果、
○：全１０個について０．２ｍＡ以下であった。
△：１〜５個について０．２ｍＡを超えていた。
×：６個以上について０．２ｍＡを超えているか、あるいは２００℃×５分間加熱後既にフィルムのひび割れが認められた。
【００６２】
（１０）耐レトルト性
深絞り成形が良好な缶について、水を満注し、蒸気滅菌器で１２０℃、１時間レトルト処理を行い、しかる後、５０℃で３０日間保存した。得られた缶を各テストにつき１０個ずつ高さ５０ｃｍから塩ビタイル床面に落とした後、缶内のＥＲＶ試験を行った。
○：全１０個について０．２ｍＡ以下であった。
△：１〜５個について０．２ｍＡを超えていた。
×：６個以上について０．２ｍＡを超えているか、あるいは落下後既にフィルムのひび割れが認められた。
【００６３】
（１１）保味保香性−１
深絞り成形が良好な缶について、イオン交換水を充填し、常温下（２０℃）３０日間保管する。その浸漬液を用いて３０人のパネラーにて試飲テストを行い、比較用のイオン交換水と比較し、下記基準で評価した。
◎：３０人中３人以下が比較液と比べて味、香りの変化を感じた。
〇：３０人中４人〜６人が比較液と比べて味、香りの変化を感じた。
△：３０人中７人〜９人が比較液と比べて味、香りの変化を感じた。
×：３０人中１０人以上が比較液と比べて味、香りの変化を感じた。
【００６４】
（１２）保味保香性−２
深絞り成形が良好な缶について、イオン交換水を充填し、蒸気滅菌器で１２０℃、１時間レトルト処理を行い、しかる後、常温下（２０℃）３０日間保管する。その浸漬液を用いて３０人のパネラーにて試飲テストを行い、比較用のイオン交換水と比較し、下記基準で評価した。
◎：３０人中３人以下が比較液と比べて味、香りの変化を感じた。
〇：３０人中４人〜６人が比較液と比べて味、香りの変化を感じた。
△：３０人中７人〜９人が比較液と比べて味、香りの変化を感じた。
×：３０人中１０人以上が比較液と比べて味、香りの変化を感じた。
【００６５】
［実施例１〜８および比較例１〜５］
表１に示す共重合成分を共重合した共重合ポリエチレンテレフタレート（固有粘度０．６４、粒径比１．１、平均粒径０．３μｍの真球状シリカを０．１重量％含有）が層（Ａ）、同じく表１に示す成分を共重合した共重合ポリエチレンテレフタレート（固有粘度０．６４、粒径比１．１、平均粒径１．５μｍの真球状シリカを０．１重量％含有）が層（Ｂ）となるように、それぞれ別々に乾燥した後、２８０℃で溶融し、互いに隣接したダイから共押出しし、積層・融着させた後、急冷固化して未延伸フィルムを得た。次いで、この未延伸フィルムを表１に示す温度および倍率で縦延伸した後、表１に示す温度および倍率で横延伸し、更に１７０℃で熱固定して二軸延伸積層フィルムを得た。
【００６６】
なお、比較例５では層（Ｂ）を設けずに層（Ａ）のみからなる二軸延伸フィルム（厚み２０μｍ）を作成した。
【００６７】
得られたフィルムの厚みは２０μｍ、層（Ａ）、層（Ｂ）の厚みはそれぞれ４μｍ、１６μｍ、層（Ａ）、層（Ｂ）の表面粗さはそれぞれ５ｎｍ、２３ｎｍであった。また、層（Ａ）の共重合ポリエステルのガラス転移温度（Ｔｇ）、屈折率、積層フィルムの損失弾性率の最高ピーク温度（Ｔｅ）およびイオン交換水抽出量を表２に、評価結果を表３に示す。
【００６８】
【表１】

【００６９】
【表２】

【００７０】
【表３】

【００７１】
表３の評価結果から明らかなように、層（Ａ）、層（Ｂ）の共重合ポリエステルの融点がいずれも２１０〜２４５℃である本発明の場合（実施例１〜８）は、良好な結果が得られたが、どちらかの融点が２１０℃未満の場合（比較例１、３）は、耐熱性が劣り、レトルト処理後の保味保香性が悪く、２４５℃を超える場合（比較例２、４）は、成形加工性が不良であった。また、層（Ｂ）を設けない単層フィルム（比較例５）は巻取り性が劣っていた。
【００７２】
［実施例９〜１０および比較例６〜７］
実施例２において、それぞれ表４に示すように共重合比を変更した層（Ａ）の共重合ポリエステルを溶融押出しし、急冷固化して得た未延伸フィルムを、それぞれ表４に示す条件で延伸、熱固定して二軸延伸積層フィルムを得た。
【００７３】
得られたフィルムの厚みは２０μｍ、層（Ａ）、層（Ｂ）の厚みはそれぞれ４μｍ、１６μｍであった。また、層（Ａ）の共重合ポリエステルのガラス転移温度（Ｔｇ）、屈折率、積層フィルムの損失弾性率の最高ピーク温度（Ｔｅ）およびイオン交換水抽出量を表５に、評価結果を表６に示す。
【００７４】
【表４】

【００７５】
【表５】

【００７６】
【表６】

【００７７】
表６の評価結果から明らかなように、Ｔｇが７８℃以上、かつＴｅ−Ｔｇが３０℃以下の本発明の場合（実施例９〜１０）は、良好な結果が得られたが、Ｔｇが７８℃未満の場合（比較例６）は、耐熱性が劣り、レトルト後の保味保香性が悪く、Ｔｅ−Ｔｇが３０℃を超える場合（比較例７）は、成形加工性が低下した。
【００７８】
［実施例１１〜１２および比較例８〜９］
実施例２において、層（Ａ）および層（Ｂ）に含まれる真球状シリカの平均粒径および含有量を表７に示すようにそれぞれ変更した二軸延伸フィルムを得た。
【００７９】
得られたフィルムの厚みは２０μｍ、層（Ａ）、層（Ｂ）の厚みはそれぞれ４μｍ、１６μｍであった。また、層（Ａ）の共重合ポリエステルのガラス転移温度（Ｔｇ）、屈折率、積層フィルムの損失弾性率の最高ピーク温度（Ｔｅ）およびイオン交換水抽出量は実施例２と同じ値を示した。得られたフィルムの表面粗さ（Ｒａ）を表７、評価結果を表８に示す。
【００８０】
【表７】

【００８１】
【表８】

【００８２】
層（Ａ）の表面粗さが１５ｎｍ以下で層（Ｂ）の表面粗さが１５ｎｍ以上である本発明の場合（実施例１１〜１２）は、良好な結果が得られたが、層（Ａ）の表面粗さが１５ｎｍを超える場合（比較例８）は、保味保香性があまり向上せず、層（Ｂ）の表面粗さが１５ｎｍ未満の場合（比較例９）は、巻取り性が不十分であった。
【００８３】
【発明の効果】
本発明の金属板貼合せ成形加工用ポリエステルフィルムは、金属板と貼合わせた後製缶加工、例えば深絞り加工して金属缶を成形するにあたり、共重合ポリエステルが持っている優れた成形加工性、耐熱性、耐衝撃性、耐レトルト性を保持しながら、保味保香性、特にレトルト後の保味保香性が改善され、しかも巻取り性が向上したものであり、金属容器用フィルムとして極めて有用である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyester film for metal plate laminating processing, and more specifically, it exhibits excellent molding processability when it is bonded to a metal plate to make cans such as drawing, and has heat resistance, retort resistance, and retention. The present invention relates to a polyester film for laminating and processing metal plates, which can produce metal cans excellent in taste-retaining properties, impact resistance, etc., such as beverage cans and food cans.
[0002]
[Prior art]
Metal cans are generally painted to prevent corrosion on the inside and outside surfaces. Recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, there is a method of obtaining rust prevention without using organic solvents. Development is progressing, and one of them is coating with a thermoplastic film.
[0003]
That is, a method for making a can by drawing or the like after laminating a thermoplastic resin film on a metal plate such as tinplate, tin-free steel, or aluminum has been studied.
[0004]
As this thermoplastic resin film, it is gradually becoming clear that a copolymerized polyester film is suitable in terms of molding processability, heat resistance, impact resistance, and flavor retention. However, this polyester film does not always have sufficient flavor retention, when it contains beverages that have an extremely delicate taste, such as green tea, and mineral water that requires tasteless and odorless. Changes to are sensed.
[0005]
In contrast, Japanese Patent Laid-Open No. 6-116376 proposes a metal film forming polyester film having improved flavor properties, which is made of a copolyester containing a specific amount of an alkali metal element and a germanium element. However, when this film is used, it shows excellent flavor retention in a process where heat is not applied at the stage where the contents such as the cold pack system are filled, but at the stage where the contents such as retort treatment are filled. In the process in which heat treatment is performed, sufficient flavor retention properties are not always obtained.
[0006]
[Problems to be solved by the invention]
The object of the present invention is to eliminate the problems of the prior art and maintain the excellent processability, impact resistance, heat resistance, and retort resistance of the copolyester film while maintaining the flavor retention. In particular, an object of the present invention is to provide a polyester film for metal plate laminating molding processing which improves the flavor retention and fragrance properties after retort treatment and further improves the winding property.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors made ethylene terephthalate as a main repeating unit among copolyesters, and used a copolyester having a specific melting point, a specific glass transition temperature, By making a laminated film having a two-layer structure in which a layer having dynamic viscoelasticity and a layer made of a copolyester having a specific melting point are laminated, the taste-retaining property, in particular, the taste-retaining property after retorting. It has been found that the properties are remarkably improved and the winding property is improved, and the present invention has been achieved.
[0008]
That is, the present invention comprises a layer (A) composed of a copolyester having a melting point of 210 to 245 ° C. and a layer (B) composed of a copolyester having a melting point of 210 to 245 ° C., whose main repeating unit is ethylene terephthalate. A laminated film formed by laminating a glass transition temperature (Tg) in DSC measurement of the copolymer polyester constituting the layer (A) and a maximum temperature peak temperature (Te) of a loss elastic modulus of the laminated film (1) ) And (2), the surface roughness (Ra) of the layer (A) side surface of the laminated film is 15 nm or less, and the surface roughness (Ra) of the layer (B) side surface of the laminated film is 15 nm or more. It is a polyester film for metal plate lamination molding processing characterized by being.
[0009]
[Expression 2]
Tg ≧ 78 (1)
Te−Tg ≦ 30 (2)
(Here, Tg is the glass transition temperature (° C.) in DSC measurement after 290 ° C. heat melting and quenching, and Te is the maximum temperature peak temperature (° C.) of the loss elastic modulus of the film.)
[0010]
The copolymerization component of the copolymerized polyester is preferably 2,6-naphthalenedicarboxylic acid, and the extraction amount when the film is extracted with ion exchange water at 121 ° C. for 2 hours is 0.5 mg. / Inch ² The following is preferable.
[0011]
In the present invention, as the copolyester used in the layer (A), while maintaining excellent heat resistance, impact resistance, and retort resistance, it has a taste-retaining property, in particular, a taste-retaining property after retorting. Therefore, a copolymerized polyester having ethylene terephthalate as a main repeating unit, that is, a copolymerized polyethylene terephthalate is used.
[0012]
The copolyester in the present invention is a copolyester that is substantially linear and comprises terephthalic acid as the main dicarboxylic acid component and ethylene glycol as the main glycol component.
[0013]
In the present invention, the copolymerization component of the copolymerized polyester may be a dicarboxylic acid component or a diol component.
[0014]
Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid, and cyclohexanedicarboxylic acid. Examples of the diol component include aliphatic diols such as 1,4-butanediol, 1,6-hexanediol and diethylene glycol, and alicyclic rings such as 1,4-cyclohexanedimethanol. Aromatic diols such as aromatic diols and bisphenol A. These can be used alone or in combination of two or more.
[0015]
The proportion of the copolymerization component is a proportion that results in a polymer melting point of 210 to 245 ° C., preferably 215 to 240 ° C., depending on the type. When the melting point is less than 210 ° C., the heat resistance is poor. On the other hand, if the melting point exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.
[0016]
Here, the melting point of the copolyester is measured by a method of obtaining a melting peak at a heating rate of 20 ° C./min using Du Pont Instruments 910 DSC. The sample amount is 20 mg.
[0017]
The intrinsic viscosity (orthochlorophenol, 35 ° C.) of the copolyester used in the present invention is preferably 0.52 to 1.50, more preferably 0.57 to 1.00, and particularly preferably 0.00. 60-0.80. When this intrinsic viscosity is less than 0.52, impact resistance may be insufficient, which is not preferable. On the other hand, when the intrinsic viscosity exceeds 1.50, molding processability may be impaired.
[0018]
In the laminated film of the present invention, the glass transition temperature (Tg) in the DSC measurement of the copolyester constituting the layer (A) and the maximum temperature peak temperature (Te) of the loss elastic modulus of the laminated film are the following formulas (1) and ( It is necessary to satisfy 2).
[0019]
[Equation 3]
Tg ≧ 78 (1)
Te−Tg ≦ 30 (2)
(Here, Tg is the glass transition temperature (° C.) in DSC measurement after 290 ° C. heat melting and quenching, and Te is the maximum temperature peak temperature (° C.) of the loss elastic modulus of the film.)
[0020]
When the Tg of the film is less than 78 ° C., the heat resistance becomes inferior, and the flavor retention after retort deteriorates. For this reason, as the copolymerization component of the copolymerized polyester, it is preferable to use at least one component that does not change or increases the glass transition temperature when the ratio of the copolymerization component is increased. Examples of components that increase the glass transition temperature when the proportion of the copolymer component is increased include 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component and 1,4-cyclohexanedimethanol as the diol component. it can.
[0021]
Here, Tg of polyester puts a 20 mg film sample in a pan for DSC measurement, heats and melts on a 290 ° C. heating stage for 5 minutes, and then quickly solidifies rapidly on an aluminum foil in which the sample pan is laid on ice, By using a Du Pont Instruments 910 DSC, the glass transition point is determined at a heating rate of 20 ° C./min.
[0022]
Furthermore, when the value of Te-Tg exceeds 30, the molecular orientation and crystallinity of the film become too high, so that the moldability is remarkably lowered. Although the value of Te depends on the copolymerization component and the amount of copolymerization, a method of adjusting the biaxial stretching ratio, stretching temperature, and heat setting temperature is particularly preferred depending on the film forming conditions.
[0023]
Here, Te is a measurement frequency of 10 Hz using a dynamic viscoelasticity measuring apparatus, and dynamic displacement ± 25 × 10. ^-4 It is calculated in cm.
[0024]
In the present invention, a typical example of the copolyester constituting the layer (B) is a copolyester having ethylene terephthalate as a main repeating unit.
[0025]
The copolymerization component of the copolymerized polyester constituting the layer (B) may be a dicarboxylic acid component or a diol component.
[0026]
Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid, and cyclohexanedicarboxylic acid. Examples of the diol component include aliphatic diols such as 1,4-butanediol, 1,6-hexanediol, diethylene glycol and neopentyl glycol, and 1,4-cyclohexanedimethanol. And an aromatic diol such as bisphenol A. These can be used alone or in combination of two or more. Of these, 2,6-naphthalene dicarboxylic is preferable.
[0027]
The proportion of the copolymerization component is a proportion that results in a polymer melting point of 210 to 245 ° C., preferably 215 to 240 ° C., depending on the type. When the melting point is less than 210 ° C., the heat resistance is poor. On the other hand, if the melting point exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.
[0028]
Here, the melting point of the copolyester constituting the layer (B) is measured by a method of obtaining a melting peak at a heating rate of 20 ° C./min using Du Pont Instruments 910 DSC. The sample amount is 20 mg.
[0029]
The intrinsic viscosity (orthochlorophenol, 35 ° C.) of the copolyester constituting the layer (B) is preferably 0.52 to 0.80, more preferably 0.54 to 0.70, particularly preferably. Is 0.57 to 0.65. When this intrinsic viscosity is less than 0.52, impact resistance may be insufficient, which is not preferable. On the other hand, when the intrinsic viscosity exceeds 0.80, molding processability may be impaired.
[0030]
The copolymer polyester constituting the layer (A) and the copolymer polyester constituting the layer (B) in the present invention are not limited by the production method, but esterification reaction of terephthalic acid, ethylene glycol and copolymer components Then, the reaction product obtained is subjected to a polycondensation reaction until a desired degree of polymerization is obtained to obtain a copolymer polyester, or terephthalic acid dimethyl ester, ethylene glycol and a copolymer component are transesterified, and then obtained. A preferred example is a method in which the obtained reaction product is subjected to a polycondensation reaction until a desired degree of polymerization is obtained to obtain a copolymer polyester. Moreover, the copolymer polyester obtained by said method (melt polymerization) can be made into a polymer with a higher polymerization degree by the polymerization method (solid phase polymerization) in a solid-phase state as needed.
[0031]
If necessary, additives such as an antioxidant, a heat stabilizer, a viscosity modifier, a plasticizer, a hue improver, a lubricant, a nucleating agent, and an ultraviolet absorber can be added to the copolymer polyester.
[0032]
Furthermore, the surface on the layer (A) side of the laminated film in the present invention needs to have a surface roughness (Ra) of 15 nm or less, preferably 1 to 15 nm, more preferably 2 to 10 nm. The layer (A) is a layer located on the side in contact with the contents of the can when pasted on a metal can. Can be improved. In addition, when the surface roughness (Ra) is less than 1 nm, the film surface is likely to be damaged.
[0033]
In order to make the surface roughness (Ra) of the layer (A) 15 nm or less, the average particle diameter and the amount of the lubricant added to the copolymer polyester constituting the layer (A) may be appropriately selected.
[0034]
The lubricant is not limited to inorganic or organic, but is preferably inorganic. Examples of the inorganic lubricant include silica, alumina, titanium dioxide, calcium carbonate, and barium sulfate. Examples of the organic lubricant include silicone resin particles and crosslinked polystyrene particles. In particular, a preferable lubricant from the viewpoint of pinhole resistance is a monodispersed lubricant having a particle size ratio (major axis / minor axis) of 1.0 to 1.2. Examples of such a lubricant include true spherical silica, true spherical silicone resin particles, true spherical crosslinked polystyrene particles, and the like.
[0035]
For example, when silica is used as a lubricant, 0.04% by weight or less may be added for silica having an average particle diameter of 1.5 μm, and 0.25% by weight or less for silica having an average particle diameter of 0.8 μm. . When the addition amount is 0.2% by weight, the average particle size of silica is 0.70 μm or less, and when the addition amount is 0.05% by weight, the average particle size of silica is 1.3 μm or less. That's fine.
[0036]
On the other hand, the layer (B) needs to have a surface roughness (Ra) of 15 nm or more. When the surface roughness (Ra) is less than 15 nm, the handleability (winding property) of the laminated film is deteriorated, which is inappropriate.
[0037]
When layer (B) is laminated to a metal can, the layer (B) is a layer that is bonded to the metal can and does not directly contact the contents of the can, so the surface roughness (Ra) is 15 nm or more. Even so, it doesn't make the contents taste bad.
[0038]
In the case of the layer (B), a desired surface roughness (Ra) can be obtained by appropriately selecting the average particle diameter and the addition amount of the filler added to the copolyester within the above range. .
[0039]
The surface roughness (Ra) of the film is the centerline average roughness determined according to JIS-B0601, and a portion of the measurement length L is extracted from the film surface roughness curve in the direction of the centerline. When the center line of the extracted part is the X axis, the direction of the vertical magnification is the Y axis, and the roughness curve is represented by Y = f (x), the value (Ra: nm) given by the following formula is the film surface roughness. Define as
[0040]
[Expression 4]

[0041]
In the present invention, five are measured with a reference length of 2.5 mm, and Ra is expressed as an average value of four obtained by removing one from the larger value.
[0042]
The laminated film of the present invention has a structure in which the layer (A) and the layer (B) are laminated. For example, a film having such a laminated structure is obtained by separately melting the copolyester constituting each layer and coextruding. Then, after solidifying and fusing before solidification, biaxial stretching, heat setting method, copolyester constituting each layer is melted separately and extruded to produce a film, unstretched or stretched Then, it can manufacture by the method of laminating | stacking both.
[0043]
In this case, the refractive index in the thickness direction of the layer (A) is preferably 1.500 to 1.540, and more preferably 1.505 to 1.530. If the refractive index is less than 1.500, the molding processability may be insufficient, while if it exceeds 1.540, the structure is close to amorphous, and the heat resistance may be reduced.
[0044]
Here, the refractive index in the thickness direction is measured with a monochromatic light NaD line by attaching a polarizing plate analyzer to the eyepiece side of Abbe's refractometer. The mounting solution uses methylene iodide, and the measurement temperature is 25 ° C.
[0045]
The laminated film of the present invention preferably has a thickness of 6 to 75 μm. Furthermore, it is preferable that it is 10-75 micrometers, especially 15-50 micrometers. If the thickness is less than 6 μm, tearing or the like is likely to occur during processing, while those exceeding 75 μm are excessive quality and uneconomical.
[0046]
Further, the thickness T of the layer (A) _A And thickness T of layer (B) _B Ratio (T _A / T _B ) Is preferably 0.02 to 1.5, more preferably 0.04 to 0.67, and particularly preferably 0.04 to 0.25. Specifically, for example, in the case of a laminated film having a thickness of 20 μm, the thickness of the layer (A) is 0.5 to 15 μm, preferably 1 to 10 μm, and more preferably 1 to 4 μm.
[0047]
Since the polyester film of the present invention is particularly used for food cans or beverage cans, it is better that there are less substances to be eluted or scattered from the film, but it is substantially impossible to eliminate these substances at all. . Therefore, for use in food cans or beverage can applications, for example, the extraction amount per square inch of film when extracted with ion-exchanged water at 121 ° C. for 2 hours is preferably 0.5 mg or less. More preferably, it is 1 mg or less.
[0048]
In order to reduce the extraction amount, the glass transition temperature of the film may be increased. The glass transition temperature of the film is determined by the glass transition temperature and the degree of orientation of the polymer constituting the film, but if the degree of orientation is increased, the moldability deteriorates, so the glass transition temperature of the polymer (copolyester) is made as high as possible. Is preferred.
[0049]
As a metal plate to which the laminated film of the present invention is bonded, particularly a metal plate for can making, a plate made of tin, tin-free steel, aluminum or the like is suitable. The polyester film can be bonded to the metal plate by the following methods (1) and (2), for example.
(1) The metal plate is heated to the melting point of the film or higher, and the film is bonded and then cooled, and the surface layer portion (thin layer portion) of the film in contact with the metal plate is amorphized and adhered.
{Circle around (2)} An adhesive layer is preliminarily coated on the film, and this surface is bonded to a metal plate. As the adhesive layer, known resin adhesives such as epoxy adhesives, epoxy-ester adhesives, alkyd adhesives, and the like can be used.
[0050]
When the laminated film of the present invention is bonded to a metal plate, the layer (B) side is bonded to the metal plate.
[0051]
Furthermore, in the laminated film of this invention, you may laminate | stack another additional layer between a layer (A) and a layer (B) as needed.
[0052]
【Example】
The following examples further illustrate the present invention. The film characteristics were measured by the following method.
(1) Intrinsic viscosity of copolyester
Measure in orthochlorophenol at 35 ° C.
[0053]
(2) Melting point of copolyester
By using a Du Pont Instruments 910 DSC, the melting peak is determined at a heating rate of 20 ° C./min. The sample amount is 20 mg.
[0054]
(3) Glass transition temperature (Tg) of copolymerized polyester
A 20 mg film sample was placed in a DSC measurement pan, heated and melted on a 290 ° C. heating stage for 5 minutes, and then quickly solidified on an aluminum foil laid on ice, using a Du Pont Instruments 910 DSC, According to a method for obtaining a glass transition point at a temperature rising rate of 20 ° C./min.
[0055]
(4) Maximum temperature peak temperature (Te) of loss elastic modulus of the film
Using a dynamic viscoelasticity measuring device, measurement frequency 10 Hz, dynamic displacement ± 25 × 10 ^-4 The loss elastic modulus is obtained in cm, and the maximum temperature peak temperature at this time is indicated.
[0056]
(5) Surface roughness (Ra)
Using a stylus type surface roughness meter (SURFCORDER SE-30C) manufactured by Kosaka Laboratory Ltd., measurement is performed under the conditions of a stylus radius of 2 μm, a measurement pressure of 0.03 g, and a cutoff value of 0.25 mm.
[0057]
(6) Windability
In the film manufacturing process, when the film was wound into a roll, small protrusions on the roll surface generated due to slip failure were observed and evaluated according to the following criteria.
A: No small protrusion is observed.
○: Some small protrusions are recognized, but there is no particular problem in handling.
X: Many small protrusions are generated, and handleability deteriorates.
[0058]
(7) Deep drawability
The film is laminated on both sides of tin-free steel with a plate pressure of 0.25mm heated to the melting point of polyester, cooled with water, cut into a 150mm diameter disk, and deep-drawn in four stages using a drawing die and punch. , 55 mm diameter side surface seamless container (hereinafter abbreviated as can). The cans were observed and tested as follows and evaluated according to the following criteria.
[0059]
(1) Deep drawability-1
A: No whitening or breakage is observed in a film processed without abnormality in the film.
(Triangle | delta): Whitening is recognized by the can upper part of a film.
X: Film breakage is observed in a part of the film.
(2) Deep drawability-2
○: Processed without abnormality, rust prevention test for film surface in can (1% NaCl aqueous solution is put in can, electrode is inserted, current value when voltage of 6V is applied with can body as anode is measured. Hereinafter, 0.2 mA or less is shown in the ERV test.
X: Although there was no abnormality in the film, the current value exceeded 0.2 mA in the ERV test, and pinhole-like cracks starting from the coarse lubricant of the film were observed when the energized part was enlarged and observed.
[0060]
(8) Impact resistance
For cans with good deep drawing, water was fully poured, cooled to 0 ° C., and 10 pieces were dropped from a height of 30 cm onto a PVC tile floor for each test, and then an ERV test in the can was performed. result,
○: It was 0.2 mA or less for all 10 pieces.
(Triangle | delta): It exceeded 0.2 mA about 1-5 pieces.
X: It exceeded 0.2 mA about 6 or more, or the crack of the film was already recognized after dropping.
[0061]
(9) Heat embrittlement
As a result of conducting the above-mentioned impact resistance evaluation after heating and holding the can with good deep drawing at 200 ° C. for 5 minutes,
○: It was 0.2 mA or less for all 10 pieces.
(Triangle | delta): It exceeded 0.2 mA about 1-5 pieces.
X: It exceeded 0.2mA about 6 or more pieces, or the crack of the film was already recognized after heating at 200 degreeC x 5 minutes.
[0062]
(10) Retort resistance
About a can with good deep drawing, water was fully poured and subjected to a retort treatment at 120 ° C. for 1 hour in a steam sterilizer, and then stored at 50 ° C. for 30 days. Ten cans obtained were dropped from a height of 50 cm onto a PVC tile floor surface for each test, and then an ERV test in the cans was performed.
○: It was 0.2 mA or less for all 10 pieces.
(Triangle | delta): It exceeded 0.2 mA about 1-5 pieces.
X: It exceeded 0.2 mA about 6 or more, or the crack of the film was already recognized after dropping.
[0063]
(11) Flavor retention -1
A can with good deep drawing is filled with ion exchange water and stored at room temperature (20 ° C.) for 30 days. Using the immersion liquid, a tasting test was conducted with 30 panelists, and compared with comparative ion-exchanged water, and evaluated according to the following criteria.
A: Less than 3 out of 30 felt changes in taste and aroma compared to the comparative solution.
◯: 4 to 6 out of 30 felt changes in taste and aroma compared to the comparison solution.
(Triangle | delta): 7-9 people among 30 felt the change of taste and fragrance compared with the comparison liquid.
X: 10 or more people out of 30 felt changes in taste and aroma compared with the comparative solution.
[0064]
(12) Aroma-retaining property-2
A can with good deep drawing is filled with ion exchange water, subjected to a retort treatment at 120 ° C. for 1 hour in a steam sterilizer, and then stored at room temperature (20 ° C.) for 30 days. Using the immersion liquid, a tasting test was conducted with 30 panelists, and compared with comparative ion-exchanged water, and evaluated according to the following criteria.
A: Less than 3 out of 30 felt changes in taste and aroma compared to the comparative solution.
◯: 4 to 6 out of 30 felt changes in taste and aroma compared to the comparison solution.
(Triangle | delta): 7-9 people among 30 felt the change of taste and fragrance compared with the comparison liquid.
X: 10 or more people out of 30 felt changes in taste and aroma compared with the comparative solution.
[0065]
[Examples 1-8 and Comparative Examples 1-5]
Copolymerized polyethylene terephthalate (containing intrinsic viscosity of 0.64, particle size ratio of 1.1, average particle size of 0.1 μm containing 0.1% by weight of true spherical silica) obtained by copolymerizing the copolymer components shown in Table 1 is a layer ( A), a copolymerized polyethylene terephthalate copolymerized with the components shown in Table 1 (containing 0.1% by weight of true spherical silica having an intrinsic viscosity of 0.64, a particle size ratio of 1.1, and an average particle size of 1.5 μm) Each layer was dried separately so as to form a layer (B), melted at 280 ° C., coextruded from adjacent dies, laminated and fused, and then rapidly cooled and solidified to obtain an unstretched film. Next, this unstretched film was longitudinally stretched at the temperature and magnification shown in Table 1, and then horizontally stretched at the temperature and magnification shown in Table 1, and further heat-set at 170 ° C. to obtain a biaxially stretched laminated film.
[0066]
In Comparative Example 5, a biaxially stretched film (thickness 20 μm) composed only of the layer (A) was prepared without providing the layer (B).
[0067]
The thickness of the obtained film was 20 μm, the thicknesses of the layers (A) and (B) were 4 μm and 16 μm, and the surface roughnesses of the layers (A) and (B) were 5 nm and 23 nm, respectively. Table 2 shows the glass transition temperature (Tg), refractive index, maximum peak temperature (Te) of loss elastic modulus of the laminated film, and ion-exchanged water extraction amount of the copolyester of layer (A), and Table 3 shows the evaluation results. Shown in
[0068]
[Table 1]

[0069]
[Table 2]

[0070]
[Table 3]

[0071]
As is clear from the evaluation results in Table 3, in the case of the present invention in which the melting points of the copolymer polyesters of the layer (A) and the layer (B) are 210 to 245 ° C. (Examples 1 to 8), they are good. Although the results were obtained, when either melting point was less than 210 ° C. (Comparative Examples 1 and 3), the heat resistance was inferior, the flavor retention after retort treatment was poor, and the temperature exceeded 245 ° C. (Comparison Examples 2 and 4) had poor moldability. Moreover, the winding property was inferior in the single layer film (comparative example 5) which does not provide a layer (B).
[0072]
[Examples 9 to 10 and Comparative Examples 6 to 7]
In Example 2, unstretched films obtained by melt-extrusion of the copolyester of the layer (A) with the copolymerization ratio changed as shown in Table 4 and rapid solidification were stretched under the conditions shown in Table 4, respectively. And heat setting to obtain a biaxially stretched laminated film.
[0073]
The thickness of the obtained film was 20 μm, and the thicknesses of the layer (A) and the layer (B) were 4 μm and 16 μm, respectively. Table 5 shows the glass transition temperature (Tg), refractive index, maximum peak temperature (Te) of loss elastic modulus of the laminated film, and ion-exchanged water extraction amount of the copolyester of layer (A), and Table 6 shows the evaluation results. Shown in
[0074]
[Table 4]

[0075]
[Table 5]

[0076]
[Table 6]

[0077]
As is clear from the evaluation results in Table 6, in the case of the present invention (Examples 9 to 10) with Tg of 78 ° C. or higher and Te-Tg of 30 ° C. or lower, good results were obtained. When the temperature is less than 78 ° C. (Comparative Example 6), the heat resistance is inferior, the flavor retention after retort is poor, and when Te-Tg exceeds 30 ° C. (Comparative Example 7), the molding processability is lowered. .
[0078]
[Examples 11 to 12 and Comparative Examples 8 to 9]
In Example 2, biaxially stretched films were obtained in which the average particle diameter and content of the spherical silica contained in the layer (A) and the layer (B) were changed as shown in Table 7.
[0079]
The thickness of the obtained film was 20 μm, and the thicknesses of the layers (A) and (B) were 4 μm and 16 μm, respectively. Further, the glass transition temperature (Tg), refractive index, maximum peak temperature (Te) of loss elastic modulus of the laminated film, and ion-exchanged water extraction amount of the copolyester of the layer (A) showed the same values as in Example 2. . Table 7 shows the surface roughness (Ra) of the obtained film, and Table 8 shows the evaluation results.
[0080]
[Table 7]

[0081]
[Table 8]

[0082]
In the case of the present invention in which the surface roughness of the layer (A) was 15 nm or less and the surface roughness of the layer (B) was 15 nm or more (Examples 11 to 12), good results were obtained, but the layer (A ) Exceeds 15 nm (Comparative Example 8), the taste-retaining property is not improved so much. When the surface roughness of the layer (B) is less than 15 nm (Comparative Example 9), winding is performed. Sex was insufficient.
[0083]
【The invention's effect】
The polyester film for metal plate laminating and forming process of the present invention has excellent molding processability possessed by the copolyester when forming a metal can by forming a metal can by laminating with a metal plate. , While maintaining heat resistance, impact resistance, and retort resistance, it has improved flavor retention, especially after retort, and improved winding properties. As extremely useful.

Claims (4)

Laminated film formed by laminating a layer (A) made of a copolyester having a melting point of 210 to 245 ° C. having ethylene terephthalate as a main repeating unit and a layer (B) made of a copolyester having a melting point of 210 to 245 ° C. The glass transition temperature (Tg) in DSC measurement of the copolyester constituting the layer (A) and the maximum temperature peak temperature (Te) of the loss elastic modulus of the laminated film are expressed by the following formulas (1) and (2). Satisfied, the surface roughness (Ra) of the layer (A) side surface of the laminated film is 15 nm or less, and the surface roughness (Ra) of the layer (B) side surface of the laminated film is 15 nm or more. Polyester film for metal plate lamination molding.

(Here, Tg is the glass transition temperature (° C.) in DSC measurement after 290 ° C. heat melting and quenching, and Te is the maximum temperature peak temperature (° C.) of the loss elastic modulus of the film.) The polyester film for metal plate lamination molding processing according to claim 1, wherein the copolymerization component of the copolymer polyester constituting the layer (A) is 2,6-naphthalenedicarboxylic acid. The polyester film for metal plate lamination molding processing according to claim 1, wherein the copolymerization component of the copolymer polyester constituting the layer (B) is 2,6-naphthalenedicarboxylic acid. The polyester film for metal plate lamination molding processing according to any one of claims 1 to 3, wherein an extraction amount when the film is extracted with ion-exchanged water at 121 ° C for 2 hours is 0.5 mg / inch ² or less.