【発明の詳細な説明】[Detailed description of the invention]
本発明は、低温収縮率は小さくて印刷、製袋等
の加工適性に優れ、しかも高温収縮率は大きくて
実用価値も高い積層収縮フイルムを得るための熱
処理方法に関するものである。
ポリアミド系樹脂シートとポリオレフイン系シ
ートとの積層延伸フイルムの製造法は、例えば特
公昭45−279号、特開昭51−92882号の各公報等に
記載されていて公知であるが、これらはいずれも
ポリアミド系樹脂シートの強度とポリオレフイン
系シートのシール性を共に生かしたフイルムを一
挙に製造しようとするものである。従来公知のか
かる方法によつて得られたポリアミド系樹脂シー
トとポリオレフイン系シートとの積層延伸フイル
ムは、従来のポリアミド系樹脂延伸フイルムに未
延伸のポリオレフイン系フイルムをラミネートし
たものに比べ、高温収縮率が大きくなつてハム等
の物品充填後加温時の緊縛力を強くし実用上好ま
しい半面、低温収縮率、例えば35℃即ち室温レベ
ルでの１日の収縮率も大きくなるため、保存時に
自然収縮してフイルム面にタワミが生じシワが入
つて印刷、製袋等の加工適性が悪化し商品価値を
損ねるという欠点を有する。
本発明は、上記の従来の欠点を解消し、上記の
如き実用上好ましい高温収縮率を保持した状態で
室温レベルでの低温収縮率を好ましい程度まで低
下させたポリアミド系樹脂シートとポリオレフイ
ン系シートとの積層収縮フイルムを得るための積
層延伸フイルムの熱処理方法を提供せんとするも
ので、その要旨とするところは、ポリアミド系樹
脂シートとポリオレフイン系シートとの積層二軸
延伸フイルムを熱処理温度50〜90℃でたて、よこ
おのおの２〜15％弛緩熱処理することを特徴とす
る積層延伸フイルムの熱処理方法に存する。
本発明に用いられる積層延伸フイルムにおい
て、ポリアミド系樹脂（以下「PA」という。）シ
ートとポリオレフイン系（以下「PO」という。）
シートとの積層構成としては、PA／PO、PO／
PA／PO等があげられるが、４層以上でもよい
し、積層の順序も限定されない。積層する方法と
しては、共押出法、押出ラミネート法、加熱圧着
ロール法、ドライラミネート法等があげられ、こ
れらを適宜組合せてもよい。これらの場合、PA
層は、その優れたガス遮断性や、強靭性を利用す
るものであり、その具体例としては、６，66，
10，11，12の各ナイロン、又はこれら２種以上の
コーポリマー及び混合物があげられる。なお、厚
さは10〜100μのものが使用可能であるが、生産
性、コスト等から10〜60μのものが適当である。
また、PO層は、本発明の方法で得られる積層収
縮フイルムを包装袋等に成形加工する際その優れ
たシール性を利用するものであり、その具体例と
しては、低密度ポリエチレン（以下「LDPE」と
いう。）、中密度ポリエチレン（以下「MDPE」と
いう。）、エチレン−酢酸ビニルコーポリマー（以
下「EVA」という。）アイオノマー樹脂、ポリプ
ロピレン等があげられる。その厚さは10〜100μ
で使用可能であるが、包装袋等の成形加工時必要
となるシール性熱接着適性等の実用的見地からす
れば10〜70μが好ましい。本発明で用いられる積
層延伸フイルムは、上記のようにして得られた積
層シートを、POシートの延伸可能な温度（一般
に90〜165℃の範囲にあり、使用するPOシートに
より適宜選択する。）で逐次二軸もしくは同時二
軸にて延伸することによつて得られる。この場
合、延伸倍率は、たて延伸倍率及びよこ延伸倍率
が各々２倍以上必要である。
本発明の方法では、以上のようにして得られた
PAシートとPOシートとの積層延伸フイルムを熱
処理温度50〜90℃でたて、よこおのおの２〜15％
弛緩熱処理する。かかる弛緩熱処理の効果は、処
理時間の影響をほとんど受けず、熱処理温度と弛
緩率によつて決定される。すなわち、熱処理温度
を50℃以下と低くしたり弛緩率を２％よりも小さ
くすると、得られた積層収縮フイルムは、室温レ
ベルで自然収縮が発生しフイルムにタワミが生じ
て印刷適性を悪化させ製袋時シワ等が入り商品価
値を損ね、一方、熱処理温度を90℃以上に上げる
とか弛緩率を15％よりも大きくすると、得られた
積層収縮フイルムは、室温レベルでの自然収縮は
なくなるが、ハム等の物品充填後加温時の緊縛力
が弱くいわゆる加温時の収縮不足による商品の外
観不良が発生する。これに対して本発明の方法に
よれば、積層延伸フイルムをかかる範囲に入らな
い熱処理温度と弛緩率で弛緩熱処理することによ
り、35℃のオーブン中に１日放置した時の低温収
縮率が２％以下であり、かつ90℃の温水中に５分
間放置した時の高温収縮率が15％以上である積層
収縮フイルムを得ることができる。
以上詳記したように、本発明の方法により熱処
理された積層延伸フイルムは、室温レベルでの低
温収縮率が極めて小さいためロールフイルムの状
態で自然収縮による中タルミ、渕タルミ、シワ等
の発生がないから長期間保存の後でも印刷、製袋
等の加工適性に優れ、しかも高温収縮率は大きい
ためハム等を充填後加温時の収縮による緊縛力が
強いから商品の外観を良好にして実用価値を高め
るほか、PAのガス遮断性、強靭性とPOの優れた
シール性を兼ね備えた積層収縮フイルムの包装材
として格別な効果を奏するものである。
次に本発明を実施例及び比較例により更に具体
的に説明する。
実施例 １〜12
市販の６−ナイロン（以下「６−PA」とい
う。）シートの両側に市販のEVAもしくはLDPE
の各シートをオゾンを用いる共押出法もしくはド
ライラミネート法により、また６−PAシートの
一方の側にEVAシートを他方の側にLDPEシート
をドライラミネート法により、それぞれ積層し
た。得られた各三層シートを下記表−１に示す
「たて×よこ」の延伸倍率で逐次又は同時二軸延
伸して表−１に示す厚さ構成の積層延伸フイルム
を得た。得られた積層延伸フイルムを、下記表−
１に示す熱処理温度と弛緩率で弛緩熱処理した。
かくして得られた12種類の本発明の積層フイル
ムにつき、低温（自然）収縮率及び高温収縮率を
測定し、印刷・製袋した後の外観を判定し、印刷
された積層フイルムにて折幅235mm、長さ500mmの
チユーブを作成し、この中に直径130mm、長さ320
mm、重さ1.5Kgのハムを挿入して両端をシールし
た後90℃の温水中で５分間煮沸した後の外観を下
記表−１に示す。なお、低温または高温収縮率と
は、フイルムの流れ方向をたて方向、それと直角
な方向をよこ方向とし、たて、よこ各100mmの正
方形の試料を積層延伸フイルムから採取し、各試
料を低温収縮率の場合は35℃×１日、高温収縮率
の場合は90℃×５分の状態に放置した後の各辺の
長さｌを測定し、１００−ｌ／１００×100（％）で表
わした
値である。
The present invention relates to a heat treatment method for obtaining a laminated shrink film that has a small low-temperature shrinkage rate and is excellent in processing suitability for printing, bag making, etc., and has a high high-temperature shrinkage rate and is of high practical value. A method for producing a laminated stretched film of a polyamide resin sheet and a polyolefin sheet is known, for example, as described in Japanese Patent Publication No. 45-279 and Japanese Patent Application Laid-Open No. 51-92882. The aim is to simultaneously produce a film that takes advantage of both the strength of polyamide resin sheets and the sealing properties of polyolefin sheets. A laminated stretched film of a polyamide resin sheet and a polyolefin sheet obtained by such a conventionally known method has a higher high-temperature shrinkage rate than a conventional stretched polyamide resin film laminated with an unstretched polyolefin film. This increases the binding force during heating after filling the product such as ham, which is preferable for practical purposes. However, the low-temperature shrinkage rate, for example, the shrinkage rate at 35°C (1 day at room temperature) also increases, so natural shrinkage during storage is reduced. This has the disadvantage that the film surface is sagging and wrinkled, which deteriorates its suitability for processing such as printing and bag making, and reduces its commercial value. The present invention solves the above-mentioned conventional drawbacks, and provides a polyamide resin sheet and a polyolefin sheet that have a low-temperature shrinkage rate at a room temperature level reduced to a preferable level while maintaining a practically preferable high-temperature shrinkage rate as described above. The purpose of the present invention is to provide a method for heat treating a laminated stretched film to obtain a laminated shrink film.The gist thereof is to heat-treat a laminated biaxially stretched film of a polyamide resin sheet and a polyolefin sheet at a temperature of 50 to 90°C. The present invention relates to a method for heat treating a laminated stretched film, which comprises heating the laminated stretched film at 2 to 15% in each direction. In the laminated stretched film used in the present invention, a polyamide-based resin (hereinafter referred to as "PA") sheet and a polyolefin-based (hereinafter referred to as "PO") sheet
The laminated configuration with the sheet is PA/PO, PO/
Examples include PA/PO, but four or more layers may be used, and the order of lamination is not limited. Examples of the laminating method include a coextrusion method, an extrusion lamination method, a hot press roll method, and a dry lamination method, and these may be appropriately combined. In these cases, P.A.
The layer utilizes its excellent gas barrier properties and toughness, and specific examples include 6, 66,
Examples include nylon 10, 11, and 12, or copolymers and mixtures of two or more of these nylons. Note that a thickness of 10 to 100 μm can be used, but a thickness of 10 to 60 μm is appropriate from the viewpoint of productivity, cost, etc.
In addition, the PO layer utilizes its excellent sealing properties when the laminated shrink film obtained by the method of the present invention is molded into packaging bags, etc. A specific example thereof is low density polyethylene (hereinafter referred to as "LDPE"). ), medium density polyethylene (hereinafter referred to as ``MDPE''), ethylene-vinyl acetate copolymer (hereinafter referred to as ``EVA'') ionomer resin, polypropylene, etc. Its thickness is 10~100μ
However, it is preferably 10 to 70 μm from a practical standpoint, such as sealability and thermal adhesion suitability, which are required when forming packaging bags and the like. The laminated stretched film used in the present invention is prepared by heating the laminated sheet obtained as described above at a temperature at which the PO sheet can be stretched (generally within the range of 90 to 165°C, which is appropriately selected depending on the PO sheet used). It can be obtained by sequential biaxial or simultaneous biaxial stretching. In this case, as for the stretching ratio, the longitudinal stretching ratio and the horizontal stretching ratio must each be 2 times or more. In the method of the present invention, the above-obtained
A laminated stretched film of PA sheet and PO sheet is heat-treated at a temperature of 50 to 90℃, each horizontally 2 to 15%
Relaxation heat treatment. The effect of such relaxation heat treatment is hardly affected by the treatment time and is determined by the heat treatment temperature and relaxation rate. In other words, if the heat treatment temperature is lowered to 50°C or less or the relaxation rate is lower than 2%, the obtained laminated shrink film will undergo natural shrinkage at room temperature level, causing the film to sag, impairing its printability and making it difficult to manufacture. On the other hand, if the heat treatment temperature is raised to 90°C or higher or the relaxation rate is increased to more than 15%, the resulting laminated shrink film will not shrink naturally at room temperature, but The binding force during heating after filling the product such as ham is weak, and the appearance of the product is poor due to so-called insufficient shrinkage during heating. On the other hand, according to the method of the present invention, by subjecting the laminated stretched film to relaxation heat treatment at a heat treatment temperature and relaxation rate that do not fall within this range, the low-temperature shrinkage rate when left in an oven at 35°C for one day is 2. % or less, and which has a high-temperature shrinkage rate of 15% or more when left in hot water at 90°C for 5 minutes. As detailed above, the laminated stretched film heat-treated by the method of the present invention has an extremely low low-temperature shrinkage rate at room temperature, so it does not suffer from the occurrence of center sagging, fuchi sagging, wrinkles, etc. due to natural shrinkage in the rolled film state. Because of this, it has excellent suitability for processing such as printing and bag making even after long-term storage.Moreover, the high temperature shrinkage rate is high, so the binding force due to shrinkage when heated after filling with ham etc. is strong, so the appearance of the product is good and it can be put to practical use. In addition to increasing its value, it is extremely effective as a packaging material for laminated shrink film, which combines the gas barrier properties and toughness of PA with the excellent sealing properties of PO. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Examples 1 to 12 Commercially available EVA or LDPE on both sides of a commercially available 6-nylon (hereinafter referred to as "6-PA") sheet
Each sheet was laminated by a coextrusion method using ozone or a dry lamination method, and an EVA sheet was laminated on one side of the 6-PA sheet, and an LDPE sheet was laminated on the other side by a dry lamination method. Each of the obtained three-layer sheets was sequentially or simultaneously biaxially stretched at the "vertical x horizontal" stretching ratio shown in Table 1 below to obtain a laminated stretched film having the thickness shown in Table 1. The obtained laminated stretched film is shown in the table below.
Relaxation heat treatment was performed at the heat treatment temperature and relaxation rate shown in 1. The low-temperature (natural) shrinkage rate and high-temperature shrinkage rate of the 12 types of laminated films of the present invention thus obtained were measured, and the appearance after printing and bag making was determined. , create a tube with a length of 500 mm, and in this tube have a diameter of 130 mm and a length of 320 mm.
After inserting a ham measuring 1.5 kg in weight and sealing both ends, the appearance after boiling in 90°C hot water for 5 minutes is shown in Table 1 below. Low-temperature or high-temperature shrinkage refers to the film's flow direction as the vertical direction, and the direction perpendicular to that as the horizontal direction. Square samples of 100 mm in length and width are taken from the laminated stretched film, and each sample is For shrinkage rate, measure the length l of each side after leaving it at 35℃ x 1 day, and for high temperature shrinkage rate at 90℃ x 5 minutes, and calculate it as 100-l/100 x 100 (%). This is the expressed value.
【表】
比較例 １〜８
比較のため、実施例１における積層延伸フイル
ムを熱処理温度及び弛緩率（たて×よこ）はそれ
ぞれ50℃及び１％、100℃、90℃及び18％、40℃
及び15％で弛緩熱処理した場合、並びに、実施例
１〜７、同８、同９、同10〜12のそれぞれにおけ
る積層延伸フイルムを弛緩熱処理しなかつた場合
につき、低温（自然）収縮率及び高温収縮率と印
刷、製袋の外観及びハム充填後の外観とを下記表
−２に表示する。[Table] Comparative Examples 1 to 8 For comparison, the heat treatment temperature and relaxation rate (vertical x horizontal) of the laminated stretched film in Example 1 were 50°C, 1%, 100°C, 90°C, 18%, and 40°C, respectively.
and 15%, and when the laminated stretched films in Examples 1 to 7, 8, 9, and 10 to 12 were not subjected to relaxation heat treatment, the low-temperature (natural) shrinkage rate and high temperature The shrinkage rate, printing, appearance of bag making, and appearance after filling with ham are shown in Table 2 below.
【表】
上記実施例、比較例から明らかな通り、本発明
方法により熱処理された積層延伸フイルムは、低
温収縮率が小さくかつ高温収縮率が大きいので包
装用フイルムとして優れた積層収縮フイルムであ
ることが判る。[Table] As is clear from the above examples and comparative examples, the laminated stretched film heat-treated by the method of the present invention has a small low-temperature shrinkage rate and a large high-temperature shrinkage rate, so it is an excellent laminated shrink film as a packaging film. I understand.