JP3684692B2 - Freestanding container with excellent heat and pressure resistance - Google Patents

Description

【００４０】
本発明では、底部を高延伸配向状態とし、さらに加熱により結晶化度を向上させることにより、底谷部を高強度にすることができ、底谷部の７０℃での降伏荷重を２５ｋｇ／ｃｍ以上、特に３０ｋｇ／ｃｍ以上とすることができる。
上記の底谷部の７０℃での降伏荷重値を満足するには、底中央谷部５を含む底谷部の厚みは０．３ｍｍ以上とすることが好ましい。この際、底谷部、特に底中央部５の厚みが０．３ｍｍを下回り、その薄肉谷部位が比較的広範囲に存在する場合、７０℃での降伏荷重値が低下するため、充填殺菌後にその部位の変形が過大となり好ましくない。
【００４１】
一方、底部の厚みが１ｍｍを越えるときには、通常延伸加工に伴う配向結晶化度は１０％以下の数値となり、６０〜７０℃の温度域での好ましい降伏応力強度を得ることが難しくなる。また、底部に比較的大きな未配向の或いは低配向の厚肉部が存在すると、熱処理に際して熱結晶化（白化）が進行して、耐熱性は向上するとしても、耐衝撃性が低下する。さらに、低延伸配向厚肉部が底部の凹凸部に来る場合、その凹凸部分の境界に無理が生じて、ストレスクラック、クレーズ等の欠陥が発生しやすくなる。
これに対して、本発明では、前記底形状を採用することにより、足部の局部的な薄肉化を防止しながら、底部の高度の延伸配向が可能となり、これを高配向結晶化させることにより、７０℃の温度での降伏応力強度を十分高めて、６５〜７０℃程度温度で熱殺菌処理を行う耐熱耐圧容器として十分に使用できるのである。さらに、本発明容器の底部では高強度であるとともに柔軟性に富んでおり、底部の凹凸部位でのストレスクラック、クレーズ等の欠陥の発生は皆無となる。
【００４２】
上記したように、本発明容器では底部全体が高延伸状態にて１ｍｍ以下の肉厚に薄肉化されることが好ましいが、７０℃での降伏荷重が２５ｋｇ／ｃｍ以上である限りにおいて、比較的小さな領域にて１ｍｍを越える厚肉部が存在してもかまわない。特に、底中心部５ａ（ゲート部）が厚肉部として残存している場合には、その厚肉部の径が比較的小さく且つ底谷部の降伏荷重が本発明の範囲を満足する限りにおいて、比較的に好ましい耐熱耐圧性能を有することができる。
【００４３】
［底谷部及び底中央足付け根部の寸法関係］
本発明の容器では、底中央の谷部５が球面の一部からなっている。足先端部の肉厚を確保する成形上の観点から、図３において、底中央付近の谷部の曲率半径Ｒ₁ を胴部の半径Ｒ₀ （Ｄ₀ ／２）よりも大きくし、底部周縁の谷部の曲率半径Ｒ₂ を小さくして胴部と滑らかに接続することが好ましい。即ち、底中央谷部５は、底中心軸上に中心を有する曲率半径Ｒ₁ である球面上に位置しており、その球面の範囲は底中心部５ａを含み、球面の中心点と足先端部を結ぶ直線上にその球谷面が含まれることが好ましい。また、底中央谷部５の曲率半径Ｒ₁ は胴部半径 Ｒ₀ の１．３乃至２倍が好ましい。
【００４４】
底中央付近の谷部の曲率半径Ｒ₁ が１．３×Ｒ₀ を下回ると足部の成形性が劣り、足先端部の肉厚を確保することが難しくなる。一方、谷部の曲率半径Ｒ₁ が２×Ｒ₀ を上回ると、底部の耐熱耐圧強度が低下し、充填後の谷部の変形が大きくなりすぎる傾向にある。
【００４５】
曲率半径Ｒ₁ である谷部６の範囲は、その谷球面の中心と足接地部とを結ぶ直線と仮想谷球面とが交わる円の直径をＤ₁ としたとき、式
Ｄ₁ ／Ｄ₀ ＝０．５５〜０．７５
を満足する範囲となっていることが好適である。
【００４６】
谷部６は下に凸状で底中心部５ａが最下点であり、底中心部５ａより底中央５にて足部が始まる足付け根部８に至るまでは球面に沿って谷部は上昇すると共に、足付け根部よりも径方向外方では放射状に上昇し、足の付け根部より放射状に延びる足部は谷部とは逆に接地部に至るまで降下する曲線形状より成る。
【００４７】
［その他の底形状］
本発明の容器では、耐熱圧性の点で、成形性を損なわない範囲で谷部の表面積を増加させるように配慮している。
【００４８】
容器底部における諸寸法の説明をも兼ねる図２（要部拡大断面図）において、この容器の底部直上の胴部３はＤ₀ の胴径を有しており、底部４はＤ_F の底中央部直径を有している。底の中心から胴径Ｄ₀ の４０％の直径の円を描き、この円内に含まれる谷部４の表面積をＳとし、その胴径４０％の直径内に含まれる底部全体を谷部曲面にて覆った仮想曲面の表面積をＳ₀ とする。また、底の中心から胴径Ｄ₀ の８０％の直径の円を描き、この円内に含まれる谷部４の表面積をＳ’とし、その胴径８０％の直径内に含まれる底部全体を谷部曲面にて覆った仮想曲面の表面積をＳ₀ ’とする。
【００４９】
本発明では、谷部形状を、足部の成形性を損なわない範囲で谷部の面積を増やすように寸法を定める。即ち、底中央足付け根部の径Ｄ_F を適正値に保つこと、即ち、耐熱圧性の向上、成形性の確保を目的として、下記式
０．３５Ｄ₀ ≧Ｄ_F ≧０．２３Ｄ₀
を満足する範囲としている。
【００５０】
また、胴径Ｄ₀ の４０％の直径に含まれる谷部の表面積Ｓを
Ｓ／Ｓ₀ ＝０．６５〜０．９、好ましくは０．７〜０．８５
とし、胴径Ｄ₀ の８０％の直径に含まれる谷部の表面積Ｓ’
Ｓ’／Ｓ₀ ’＝０．２〜０．４５、好ましくは０．３〜０．４０
としている。
【００５１】
本発明では、図９に示すとおり、隣り合った足部間７，７を横切り且つ谷部６に垂直な面において、谷部６の一方の端とこれに対応する足部７の端とを結ぶ線ａと、谷部６の他方の端とこれに対応する足部７の端とを結ぶ線ａ’との間に、足部を挟む足部開き角度θを規定する。
【００５２】
本発明者らは、鋭意研究を行った結果、特に足部間を横切り且つ谷部に垂直な面において足先端部に至る谷部を挟む足部開き角度θに着目した。例えば上記足部開き角度θが５５°である容器に３ガスボリュームの内容物を充填すると、足部開き角度θは５８°に広がった。その充填品に７０℃の熱水シャワーを掛けて、底中心部が６５℃の温度で１５分間となる条件にて熱殺菌を行った場合、底部が変形して上記の足部開き角度θが９０°にまで広がってしまう観測結果が得られた。
【００５３】
本発明者らは熱殺菌時の上記足部開き角度θの著しい拡大が谷部の比較的大きな変形、すなわち谷部の膨張を生じさせると考えた。そこで、足先端部に至る足部位における谷部を挟む足部開き角度θを予めある程度以上に大きくしておけば、結果的に熱殺菌時の谷部の変形が抑制できることを思いつき、実験を行った。
実験の結果、上記足部開き角θを６５°以上とした容器では、熱殺菌処理時の谷部の変形が極めて小さくできることを見いだしたのである。
【００５４】
谷部を挟む足部開き角θを大きくすることは、例えば球面等の曲面の一部からなる谷部を足部が引っ張り上げるように作用する力の作用方向を球面の方向に近づけるものであり、そのため、球面状谷部に垂直に働く力成分、すなわち谷部を変形させる力成分を減じることになる。その結果、谷部の変形を減じることができるのである。
【００５５】
本発明では、足部間を横切り且つ谷部に垂直な面において足先端部に至る底谷部を挟む足部開き角度θを６５°以上、特に好ましくは７０°乃至９０°の範囲とする。足部開き角度θが６５°を下回った容器では、内容物の充填、熱殺菌処理後の足部開き角度θが大きく拡大し、それに伴って谷部の変形量も大きくなりすぎる。以上のように耐熱耐圧性能上は足部開き角度θを大きくすることが好ましいが、一方、足部開き角度θが大きくなりすぎると足先端接地部の幅が細くなる傾向にある。この足先端接地部が細くなりすぎると、特に充填前の空容器にて転倒しやすくなる傾向にあり、好ましくない。従って、足部開き角度θは９０°以下とすることが好ましい。
【００５６】
本発明では、さらに、底中心から足接地部までの高さである足高さＨ₀ （図３）は３ｍｍ乃至６ｍｍであることが好ましい。足高さＨ₀ が３ｍｍを下回ると、内容物の充填及び熱殺菌処理後の容器の自立性を有効に確保することが難しく、また、足高さＨ₀ が６ｍｍを上回ると、谷部から足部までの距離が長くなり、足部先端の厚みを確保することが難しくなる。
【００５７】
足部の本数は３乃至６本、特に４乃至５本であることが好ましい。足部の本数があまりにも少ない場合、足角度θを比較的大きく取るため、足接地部の幅を大きくすることが難しく、そのため空容器が転倒しやすくなる問題が生じる。一方、足部の本数を７本以上とすると、足角度θ及び谷部幅を好ましい範囲に収めることが難しくなり、さらに足部の幅が狭くなることにより、足部の成形性が劣ることになる。
【００５８】
［容器の製造法］
本発明の自立容器は、一度のブロー成形にて最終製品形状とする１段ブロー成形法或いは二度のブロー成形にて製品を得る２段ブロー成形法において、最終段のブロー成形型として、前述した容器底形状に対応した底形状の金型を用いることにより製造できる。
【００５９】
一般に２段ブロー成形法を用いることが好ましく、１次ブロー成形にてプリフォーム成形品から概ね底がフラットな２次成形品を作成し、その２次成形品の底部及び底部に連なる胴部の一部を加熱収縮させて３次成形品とし、さらにその３次成形体品を前記底形状の金型内で２次ブロー成形して最終形状とする工程を採用するのがよい。
【００６０】
［プリフォーム］
本発明において、プラスチック材料としては、延伸ブロー成形及び熱結晶化可能なプラスチック材料であれば、任意のものを使用し得るが、熱可塑性ポリエステル、特にエチレンテレフタレート系熱可塑性ポリエステルが有利に使用される。勿論、ポリカーボネートやアリレート樹脂等を用いることもできる。
【００６１】
本発明に用いるエチレンテレフタレート系熱可塑性ポリエステルは、エステル反復単位の大部分、一般に７０モル％以上、特に８０モル％以上をエチレンテレフタレート単位を占めるものであり、ガラス転移点（Ｔｇ）が５０乃至９０℃、特に５５乃至８０℃で、融点（Ｔｍ）が２００乃至２７５℃、特に２２０乃至２７０℃にある熱可塑性ポリエステルが好適である。
【００６２】
ホモポリエチレンテレフタレートが耐熱圧性の点で好適であるが、エチレンテレフタレート単位以外のエステル単位の少量を含む共重合ポリエステルも使用し得る。
【００６３】
テレフタル酸以外の二塩基酸としては、イソフタル酸、フタル酸、ナフタレンジカルボン酸等の芳香族ジカルボン酸；シクロヘキサンジカルボン酸等の脂環族ジカルボン酸；コハク酸、アジピン酸、セバチン酸、ドデカンジオン酸等の脂肪族ジカルボン酸；の１種又は２種以上の組合せが挙げられ、エチレングリコール以外のジオール成分としては、プロピレングリコール、１，４−ブタンジオール、ジエチレングリコール、１，６−ヘキシレングリコール、シクロヘキサンジメタノール、ビスフェノールＡのエチレンオキサイド付加物等の１種又は２種以上が挙げられる。
【００６４】
また、エチレンテレフタレート系熱可塑性ポリエステルにガラス転移点の比較的高い例えばポリエチレンナフタレート、ポリカーボネート或いはポリアリレート等を５％〜２５％程度をブレンドした複合材を用いることができ、それにより比較的高温時の材料強度を高めることができる。
さらに、ポリエチレンテレフタレートと上記のガラス転移点の比較的高い材料とを積層化して用いることができる。
【００６５】
用いるエチレンテレフタレート系熱可塑性ポリエステルは、少なくともフィルムを形成するに足る分子量を有するべきであり、用途に応じて、射出グレード或いは押出グレードのものが使用される。その固有粘度（Ｉ．Ｖ．）は一般的に０．６乃至１．４ｄｌ／ｇ、特に０．６３乃至１．３ｄｌ／ｇの範囲にあるものが望ましい。
【００６６】
本発明の容器の製造では、先ず有底筒状のプリフォームを成形し、このプリフォームの口頸部を加熱して、局部的に熱結晶化部を設ける。
【００６７】
本発明に用いるプリフォームの一例１次ブロー金型と共に示す図１０において、このプリフォーム２０は、口部２１、胴部２２及び閉塞底部２３から成っており、口部２１には、ネジ等の蓋締結機構２４及び容器保持のためのサポートリング２５等（図１参照）が設けられており、口部２１は熱結晶化すなわち球晶化されている。この球晶化された口部２１は、図１の容器口頸部１となるものである。
【００６８】
プラスチック材料のプリフォーム２０への成形には、射出成形を用いることができる。即ち、プラスチックを冷却された射出型中に溶融射出して、過冷却された非晶質のプラスチックプリフォームに成形する。
【００６９】
射出機としては、射出プランジャーまたはスクリューを備えたそれ自体公知のものが使用され、ノズル、スプルー、ゲートを通して前記ポリエステルを射出型中に射出する。これにより、ポリエステル等は射出型キャビティ内に流入し、固化されて延伸ブロー成形用のプリフォームとなる。
【００７０】
射出型としては、容器形状に対応するキャビティを有するものが使用されるが、ワンゲート型或いはマルチゲート型の射出型を用いるのがよい。
射出温度は２７０乃至３１０℃、圧力は２８乃至１１０ｋｇ／ｃｍ² 程度が好ましい。
【００７１】
プリフォーム２０の口部２１の球晶化は、これらの部分をそれ自体公知の手段で選択的に加熱することにより行うことができる。ポリエステル等の熱結晶化は、固有の結晶化温度で顕著に生じるので、一般にプリフォームの対応する部分を、結晶化温度に加熱すればよい。加熱は、赤外線加熱或いは誘電加熱等により行うことができ、一般に延伸すべき胴部を熱源から断熱材により遮断して、選択的加熱を行うのがよい。
【００７２】
上記の球晶化は、プリフォーム２０の延伸温度への予備加熱と同時に行っても或いは別個に行ってもよい。
【００７３】
プリフォームの延伸温度は、一般に８５乃至１３５℃、特に９０乃至１３０℃の温度が適当であり、その加熱は、赤外線加熱、熱風加熱炉、誘電加熱等のそれ自体公知の手段により行うことができる。また、口部球晶化は、プリフォーム口部を、他の部分と熱的に絶縁した状態で、一般に１４０乃至２２０℃、特に１６０乃至２１０℃の温度に加熱することにより行うことができる。プリフォーム口部の結晶化度は２５％以上であるのがよい。
【００７４】
尚、プリフォームからの延伸ブロー成形には、成形されるプリフォーム成形品に与えられた熱、即ち余熱を利用して、プリフォーム成形に続いて延伸ブロー成形を行う方法も使用できるが、一般には、一旦過冷却状態のプリフォーム成形品を製造し、このプリフォームを前述した延伸温度に加熱して延伸ブロー成形を行う方法が好ましい。
【００７５】
二段ブロー成形法によれば、このように口部球晶化及び延伸のための予備加熱を行ったプリフォームを１次ブロー金型内にて二軸延伸ブロー成形して、概ねフラットな底部を形成すると共に、プリフォームの口部球晶化及びその近傍以外の部分を高延伸倍率に延伸した２次成形品とし（図１１）；この２次成形品の底部及び底部に連なった胴部の少なくともその一部を加熱して、該底部及び一部胴部が収縮した３次成形品とし（図１２Ａ、Ｂ、Ｃ）；次いでこの３次成形品を２次ブロー金型内にてブロー成形して、複数の谷部及び足部から成り、高延伸により薄肉化された底部を有する最終製品とする（図１３及び図１４）。
【００７６】
［１次ブロー成形］
１次ブロー成形工程を示す図１０（成形前）及び図１１（成形後）において、プリフォーム２０は、コア金型３１によりその口部を支持されており、閉じた割金型３２内に保持される。コア金型の反対側には、２次成形品の底形状を規定する底金型３３も配置されている。プリフォーム２０内に延伸棒３４を挿入し、その先端をプリフォーム底部に押し当てて、プリフォーム２０を軸方向に引っ張り延伸すると共に、プリフォーム２０内に流体を吹き込んで、プリフォームを高さ及び周方向に膨張延伸させる。この際、延伸棒３４と同軸に、底金型３３の側にプレス棒３５を配置して、引っ張り延伸に際して、プリフォームの底部２３が延伸棒３４とプレス棒３５とにより狭持され、プリフォームの底部２３が形成される２次成形品３６の中心に位置するように位置規制する。底金型３３は、２次成形品３６の底形状を、続いて行う熱処理工程で底形状が以下に説明する好適な形に規制するためのものである。
【００７７】
即ち、図１０に示すとおり、底金型３３は概ねフラットな底形成部３７と、その中央において小径で突出した底凹部形成部３８とを備えている。これは、２次成形品３６の底部の収縮に際して、底部の中心側へのくぼみを抑制して、最終成形品の底形状に近い半球状面を形成するように作用するからである。
【００７８】
更に、図１１に示すとおり、１次ブロー成形に際して、２次成形品３６の底部の中央部外面に比較的小さな凹部３９を設けておくと、熱処理工程で、３次成形品の底肩部が径内方側に過度に引き込まれて底肩部径が小さくなり過ぎるのを防止する。これは、前記凹部３９が熱収縮時に底中央部を概ね平坦状に収縮させる作用をしているためと思われる。凹部３９の寸法は、径が最終容器の胴径Ｄ₀ の１５乃至６０％程度、深さが０．５乃至５ｍｍ程度が適当である。この凹部３９の形成は、底金型３３の中央部内面に内向きの突起３８を形成しておくことにより達成される。
【００７９】
延伸倍率は、軸方向延伸倍率を２乃至５倍、特に２．２乃至４倍、周方向延伸倍率を２．５乃至６．６倍、特に３乃至６倍とするのがよい。軸方向延伸倍率は、プリフォーム成形品の軸方向の長さと延伸棒のストローク長とによって決定されるが、周方向の延伸倍率は、プリフォームの径と金型キャビティの径とにより決定される。圧力流体としては、室温或いは加熱された空気や、その他のガス、例えば窒素、炭酸ガス或いは水蒸気等を使用することができ、その圧力は、通常１０乃至４０ｋｇ／ｃｍ² ゲージ、特に１５乃至３０ｋｇ／ｃｍ² ゲージの範囲にあるのがよい。
【００８０】
本発明では一次ブロー成形工程にて底部を比較的高延伸にて薄肉化することが好ましい。本発明では、延伸加工が終了する直前までの間でのプリフォーム底部の延伸棒とプレス棒とでの挟み込み部の温度低下を４０℃以内、より好ましくは２５℃以内とすることにより、その挟み込み部及びその周縁を比較的に高延伸状態にて薄肉化できる。
上記温度低下が２５℃以下の場合、底中心部５ａを含めた底全体が比較的高延伸状態にて、通常１ｍｍ以下の肉厚に薄肉化することができ、最終的に好ましい耐熱耐圧性能を有する容器を得ることができる。
また、上記温度低下が２５℃を越え４０℃以内の場合、通常延伸棒とプレス棒とでの挟み込み部、すなわち底中心部５ａの周辺は比較的高延伸状態にて薄肉化されるが、その挟み込み部はその周辺よりも比較的厚肉状にて残る。しかし、その挟み込み部の肉厚は通常１．５ｍｍ以下で、且つ比較的小径であるため、底中心部５ａが完全に高延伸状態に薄肉化された場合よりも多少性能が低下するが、最終的に比較的に好ましい耐熱耐圧性能を有することができる。
【００８１】
延伸加工が終了する直前までの間に、プリフォーム底部の挟み込み部の温度低下が４０℃を越えると、ブロー成形時のその挟み込み部周縁の延伸が困難となり、比較的低延伸状態で比較的厚肉のままで残ってしまう。すなわち、底中央以外の温度低下の少ない部分のみが比較的高延伸状態に延伸加工されることになる。
【００８２】
プリフォーム底部の挟み込み部の温度低下を低くするための手段として、延伸棒及びプレス棒からの過剰な熱伝導を防止することが有効である。具体的には、少なくとも延伸棒或いはプレス棒の先端部を断熱性能を有する耐熱性プラスチック材またはセラミック材とすることが好ましい。
また、プレス棒或いは延伸棒を加温し、比較的高温に温度制御する手段も有効である。プレス棒及び延伸棒の加温は、通常プリフォームの延伸温度に対応して６０℃乃至１３０℃とすることが好ましい。
その加温方式としては、電気ヒータ、高周波誘導加熱などによる電気的加熱方式、高温液体の循環による流体加熱方式、ヒートパイプなどの熱伝導方式等を採用することができる。
【００８３】
熱処理工程の詳細を示す図１２Ａにおいて、２次成形品３６はコア金型３１に支持させて自転しており、この２次成形品の底部３７及び底部に連なった胴部の少なくとも一部と対面するように第１の赤外線放射体４２が設けられている。第１の赤外線放射体４２は、２次成形品３６の底部４０の上方に位置し、胴部４１に概ね垂直に置かれており、この底部用赤外線放射体４２により、２次成形品の底部及び底部に連なる胴部の一部を最初に加熱収縮させる。
【００８４】
底部用赤外線放射体４２により先行して行われる２次成形品の加熱では、図１２のＢに示すとおり、主に２次成形品の底部及び胴部と底部の連結部が収縮するが、底部が中心部に向かって収縮し、且つ胴部と底部の連結部は底部用赤外線放射体４２に近い部位、即ち中心部に近い部位からその外側の部位に順次に収縮する。この段階では、胴部の円周方向への収縮は少ないため、底部の収縮形状は比較的径の大きな制御された底肩部４３を有するものとなる。
【００８５】
次に、少なくとも胴部の周囲に位置し、胴部に概ね平行に置かれた胴部用赤外線放射体４４により、２次成形品の底部に連なる胴部の一部を加熱収縮させる。１２図のＢ及びＣにおいて、胴部の他の部分を胴部用赤外線放射体４４から遮蔽するために熱遮蔽板４５が設けられている。
【００８６】
底部が収縮して得られた底肩部４３は、次の胴部用赤外線放射体４４による加熱において、さほど収縮することなく概ねその形状を確保することができる。
胴部用赤外線放射体４４による加熱は、底部が収縮して得られた底肩部４３より下方の胴部を加熱収縮させること及び底肩部４３近傍の温度を上昇させることに寄与する。
【００８７】
この様にして得られた３次成形品４６の加熱収縮部は、図１２のＣに示すとおり、底面が中心部より底肩部４３にかけて概ね平坦状乃至は凸状の比較的大きな曲率半径を有する曲面であり、底肩部４３より外側の部分４７は概ね円筒状乃至円錐台に近い形状にて急激に折れ曲がっている。
さらに、３次成形品４６の加熱された底肩部より内側の成分、底肩部近傍及び底肩部下方の円筒部は、２次ブロー成形に最適な温度レベルに保持される。
【００８８】
続いて行う２次ブロー成形において、３次成形品の底肩部４３及びその近傍が最終成形品の足先端部に来ることになる。従って、この底肩部４３を２次ブロー底型の谷部及び足先端部にできるだけ接近させること、及び底肩部を挟む底部及び円筒部の温度を上げて延び易くすることが重要であり、それにより２次ブロー成形時の好ましい成形性を確保することができる。
【００８９】
２次成形品３６の底部及び一部胴部の加熱は、１２０乃至２００℃の温度で行うのがよく、これにより、これらの部分の熱収縮と熱固定を有効に行うことができる。赤外線放射体からの加熱では、非接触式加熱であるので、底部及び一部胴部の収縮が、拘束なしに行われ、また、２次成形品の表面に照射された赤外線は、その一部が板厚分を通過し、照射部位に対向する反対側の内面側に至ってその一部がさらに吸収され内面側から器壁の赤外線による加熱が極めて効率良く短時間内に均一に行われる。
【００９０】
また、前記熱処理工程の赤外線放射体４２、４４を、２次成形品が移動する通路にそって、該通路の上部及び側面に配置し、該赤外線放射体で囲まれた空間内を２次成形品を軸方向に自転させて加熱しながら移動すれば、２次成形品の加熱収縮と工程間の移動が同時にできるので、ロスタイムなしで熱処理を行うことができると共に、生産性を向上させることができる。
【００９１】
赤外線放射体は４００〜１０００℃程度に加熱された比較的放射効率に優れた且つ比較的表面積の大きな面状の表面を有するものを組み合わせて使用するとよい。これにより、比較的高エネルギー密度の赤外線を２次成形品に照射することができ、短時間加熱が可能となる。特に、２次成形品の加熱部位は高延伸により薄肉化されているため、前記赤外線加熱体により例えば１０秒以下の短時間にて所定の温度とすることができる。その赤外線加熱体としては具体的には炭素鋼或いはステンレス鋼等の金属面、アルミナ、マグネシア或いはジルコニア等のセラミック面、セラミックとカーボン等の複合材面などの固体表面或いはガスを燃焼して得られる気体表面などが利用できる。固体からなる赤外線加熱体の表面は埋め込んだ電熱ヒータによる加熱或いは高周波誘導加熱などにより所定の温度とする。
【００９２】
一次ブロー成形にて高延伸により薄肉化された２次成形品の底部は比較的成形性に乏しく、２次ブロー成形を良好に行うためには成形部の温度を１２０〜２００℃とすることが必要である。また、３次成形品の加熱部位を１２０〜２００℃の温度に加熱して熱固定を行うことにより、最終的に容器の底谷部の結晶化度を前述した範囲にすることができる。底部高延伸配向による耐熱圧強度の向上を加えて、この底部結晶化によりさらに耐熱圧強度を高めることができる。
【００９３】
２次ブロー成形工程の詳細を示す図１３において、３次成形品４６は、コア金型３１によりその首部を支持されており、閉じた割金型５１内に保持される。コア金型の反対側には、最終容器の底形状を規定する底金型５２も配置されている。３次成形品４６内に流体を吹き込んで、３次成形品を２次ブロー成形し、所定の谷部及び足部を備えた最終容器（５本足）５０の底形状に形成する。成形された容器５０は、それ自体公知の取り出し機構（図示せず）により、開いた２次ブロー金型５１から外部に取り出される。
【００９４】
２次ブロー成形工程では、熱処理工程での成形品（３次成形品）を２次ブロー成形型中でブロー成形して、前記足部と谷部とが交互に配置された底部に成形する。この２次ブロー成形に際して、当然のことながら、用いる２次ブロー成形金型のキャビテイは３次成形品よりも大きく、自立性底形状を含めて、最終成形品の寸法及び形状に合致するものでなければならない。
【００９５】
また、３次成形品では、熱処理による結晶化で、弾性率が増加しているので、高い流体圧を用いて行うのがよく、一般に１５乃至４５ｋｇ／ｃｍ² の圧力を用いるのが好ましい。
【００９６】
２次ブロー成形に際して、金型の温度は、５乃至１３５℃の温度に維持して、成形後直ちに冷却が行われるようにしてもよいし、或いは、最終成形品中に冷風等を流して冷却が行われるようにしてもよい。
【００９７】
本発明の耐熱圧ポリエステルボトルは、自生圧力を有する内容物を充填し、加熱殺菌乃至滅菌する用途に有用であり、炭酸入り飲料や窒素充填飲料乃至調味料等を充填保存する容器として有用である。耐熱耐圧用容器として、ガス容量は３ＶＯＬ程度まで可能であり、加熱殺菌温度は、６０乃至８０℃が適当である。
【００９８】
【実施例】
本発明を次の具体例及び比較例により、更に説明する。
【００９９】
比較試験１
図１０乃至図１３に示されるような２段ブロー成形法の装置を用いて、最終成形品の最大胴径Ｄ₀ が９２．５ｍｍ、全高さが３０３ｍｍ、容量が１５００ｍｌで、底部が５本の足部及び谷部とから構成される図１に示されるようなポリエチレンテレフタレート（ＰＥＴ）製の容器を作成した。
【０１００】
有底状のプリフォームを用意し、図１０に示されるような、高さが３１８ｍｍで、底部に連なる胴部の直径が９２．５ｍｍであり、且つ中央部が内方に、径が３０ｍｍで深さが２ｍｍの凹状部を有する底型よりなるブロー金型を用いて、１次ブロー成形を行った。その１次ブロー成形では、最初にプリフォームを１００℃の延伸温度に加熱して金型内に導入し、次にプリフォームの底部を内部に設置された延伸棒と外部に設置されたプレス棒とで挟み込み、延伸棒でプリフォーム底部を突き上げながら同時に２０ｋｇｆ／ｃｍ² の圧縮空気をプリフォーム内に吹き込んでブロー成形し、２次成形品を得た。その際、延伸棒及びプレス棒の先端の材質を断熱性の良好なポリテトラフルオロエチレン製（ＴＦ製）とした。
得られた２次成形品の底部は中央に凹み（径が３０ｍｍ、深さが２ｍｍ）を有し、且つ底中心部を含んで０．３５〜０．６ｍｍの肉厚に高延伸配向されていた。その際の底部の結晶化度は２５〜３５％であった。
【０１０１】
次に、セラミック内に電熱ヒータを組み込んだ面状の赤外線加熱体を第１段階の底面に平行に配置した底部用赤外線放射体と、第２段階の底面に平行な底部用赤外線放射体と胴面に平行に配置した胴部用赤外線放射体とを組み合わせて成るトンネル状の熱処理装置中を２次成形品を自転させながら移動させることにより、２次成形品の底部及び底部に連なる胴部の一部を図１２に示すように加熱収縮させて、３次成形品を得た。赤外線加熱体の温度は底部用が９５０℃で、胴部用が９００℃であり、トータルの加熱時間は８秒間であった。得られた３次成形品の加熱部位は２次ブロー成形金型の底谷曲面に極く近接しており、且つ十分収まる形状であった。
【０１０２】
最後に、加熱状態にある３次成形品を所定の５足の底形状を有する２次ブロー金型を用いて、４０ｋｇｆ／ｃｍ² の圧縮空気にて２次ブロー成形して前記容器を得た。
その際、２次ブロー金型の５足底型として、図２に示されるように５本の足部中央に底幅が０．５〜１ｍｍで深さＨ₁ が１．６ｍｍの細溝を有しており、且つ底中央部が球面の一部である底形状の実施例１の底型と、図６に示されるように比較的大きな幅の足部付け根部を有し、且つ底中央部が平坦状である、すなわち底中心部と足付け根部が同一平面上にある底形状の比較例１の底型とを用意した。
また、いずれの底型においても底中心部から足接地部までの高さＨ₀ が４．５ｍｍ、足付け根部幅Ｗが１０ｍｍ、底中央を横切る谷部の曲率半径Ｒ₁ が８５ｍｍ、足部間を横切り且つ谷部に垂直な面において谷部を挟む足角度が７０°、胴径Ｄ₀ の４０％の直径内に含まれる底谷部の合計表面積Ｓと胴径Ｄ₀ の４０％の直径内に含まれる底部仮想曲面の表面積Ｓ₀ との比Ｓ／Ｓ₀ が０．８、胴径Ｄ₀ の８０％の直径内に含まれる底谷部の合計表面積Ｓ’と胴径Ｄ₀ の８０％の直径内に含まれる底部仮想曲面の表面積Ｓ₀ ’との比Ｓ’／Ｓ₀ ’が０．３４、及び足付け根部内側にある底中央谷部の直径を２８ｍｍとした。
【０１０３】
いずれの場合も得られた容器の底部の肉厚は０．２２〜０．６ｍｍの範囲であった。その内、底中央谷部の肉厚は０．４５〜０．５ｍｍであり、その部位の結晶化度は４０〜４５％であった。また、足先端部の肉厚は０．２２〜０．３ｍｍであり、過延伸に伴う白化は一切見られなかった。
【０１０４】
得られた容器の性能試験として、各例とも１０本の容器に２．８ガスボリューム（ＧＶ）及び２．３ガスボリューム（ＧＶ）の炭酸水を充填してキャッピングした後、７０℃の熱湯を容器上部から３０分間流すことにより内容物の加熱殺菌処理を行った。その加熱殺菌処理において底中心部は最大６９℃までの温度上昇が見られた。加熱殺菌処理の終了し冷却した容器底部の変形量を測定し、足高さ（Ｈ）がマイナスである、すなわち底中心部が足よりも下方に出ている自立性に欠ける容器の本数を調べた。結果を表１に示す。
また、実施例１の容器では、２．８ＧＶのガス圧にて加熱殺菌処理した容器底部の底足高さＨが０．５乃至０．７ｍｍであり、底中心部と足付け根部中央の細溝部の最上部との高さ方向の距離Ｈ₂ が１．２乃至１．５ｍｍであった。このように、実施例１の本発明容器では充填殺菌後も上記の細溝部の深さが余り変化することなく残されており、それが足付け根部及びそれに連なる底中心部の充填殺菌後の変形を抑制して、好ましい耐熱耐圧性が得られた。
一方、比較例１の容器では、２．８ＧＶのガス圧にて加熱殺菌処理した容器底部の底足高さＨは−０．３乃至−０．８ｍｍと、底中心部が足部よりも下方に突出しており、さらに底中心部の変形に同期して足付け根部も下方に大きな変形を生じていた。このように、比較例１の容器では充填殺菌に伴い底中央平坦部が概ね球面状に変形を行い、足付け根部にはその変形を抑制する能力が欠けていた。
【０１０５】
【表１】

【０１０６】
比較試験２
２段ブロー成形法により、最終成形品の最大胴径Ｄ₀ が９２．５ｍｍ、全高さが３０３ｍｍ、容量が１５００ｍｌで、底部が５本の足部及び谷部とから構成されポリエチレンテレフタレート（ＰＥＴ）製容器を作成した。
容器の作成は比較試験１に準じて行った。
その際、容器の底形状となる２次ブロー金型の底型として、実施例２、実施例３及び比較例２からなる３種類の底型を用意した。その内、実施例２及び実施例３では、図２に示されるような５本の足部中央に底幅が０．５〜１ｍｍで底中心部からの深さＨ₁ が約１．６ｍｍの細溝を設けた。一方、比較例２では、図１５に示されるように底中央の足付け根部が比較的小さな曲率半径の円弧からなるようにした。さらに、その３種類の底型にて、足部間を横切り且つ谷部に垂直な面において谷部を挟む足角度θ、底中央近傍における谷底部の曲率半径Ｒ₁ と胴部半径Ｒ₀ との比率Ｒ₁ ／Ｒ₀ 、足付け根部の径Ｄ_F （ｍｍ）、胴径Ｄ₀ の４０％の直径内に含まれる底谷部の合計表面積Ｓと胴径Ｄ₀ の４０％の直径内に含まれる底部仮想曲面の表面積Ｓ₀ との比Ｓ／Ｓ₀ 、及び胴径Ｄ₀ の８０％の直径内に含まれる底谷部の合計表面積Ｓ’と胴径Ｄ₀ の８０％の直径内に含まれる底部仮想曲面の表面積Ｓ₀ ’との比Ｓ’／Ｓ₀ ’の数値を適当に組み合わせた。
本比較試験に供した３つの２次ブロー金型の底形状の数値を表２に示す。なお、その３種類の底型では底中心部から足接地部までの高さＨ₀ を４．５ｍｍとした。
【０１０７】
何れの場合も得られた容器の底中心部を含めた半径３０ｍｍ内の底谷部の厚みは０．４〜０．６ｍｍであり、その部位の結晶化度は３０〜４７％であった。得られた容器の足先端部の厚みＴの測定値を表２に併せて示す。
【０１０８】
容器性能評価試験として、試作した各例とも１０本の容器に２．６ガスボリューム（ＧＶ）の炭酸水を充填してキャッピングした後、７０℃の熱湯を容器上部から３０分間流すことにより内容物の加熱殺菌処理を行った。その加熱殺菌処理において底中心部は最大６９℃までの温度上昇が見られた。加熱殺菌処理の終了し冷却した容器底部の変形量を測定し、足高さ（Ｈ）がマイナスである、すなわち底中央が足よりも下方に出ている自立性に欠ける容器の本数を調べた。その結果を表２に併せて示す。
【０１０９】
【表２】

【０１１０】
以上の比較試験１及び２の試験結果から本発明容器は耐熱耐圧性に優れていることが理解される。
【０１１１】
【発明の効果】
本発明によれば、樹脂の二軸延伸ブロー成形によって形成された口頚部、肩部、胴部及び複数の谷部及び足部とよりなる底部を備えた自立性容器において、前記足部を、底部中央にて谷部に接続する足部付け根部と、該足部付け根部の中央より放射状に延びている細溝部と、該細溝部を間に挟んで細溝部より外方に張り出した一対の凸状部とから構成し、且つ前記足部の一対の凸状部と谷部とを前記足部付け根部の位置で不連続な曲線となるように接続したことにより、底部全体が延伸により薄肉化されながら足部の過度の薄肉化が防止され、加熱殺菌時における底部の熱クリープ現象が完全に防止され、しかも優れた耐熱耐圧性、耐衝撃性及び自立性の組み合わせを有する二軸延伸樹脂容器を提供することができた。
【図面の簡単な説明】
【図１】本発明の自立容器の一部断面側面図である。
【図２】図１の自立容器の底面図である。
【図３】容器底部の図２におけるＡ−Ａ断面図である。
【図４】容器底部の図２におけるＢ−Ｂ断面図である。
【図５】内容物充填状態での容器底部の図３に対応する断面図である。
【図６】容器底部の足部と底中央谷部との接続幅を示す説明図である。
【図７】底中央谷部が平坦となった容器底部（比較例）の断面図である。
【図８】内容物充填状態での図７の容器底部の断面図である。
【図９】図１の自立容器の底部の斜視図である。
【図１０】１次ブロー成形工程を説明するための断面図であって、成形開始前の状態を示す。
【図１１】１次ブロー成形工程を説明するための断面図であって、成形開始後の状態を示す。
【図１２】熱処理工程を説明するための断面図であって、Ａは一段目の熱処理、Ｂは二段目の熱処理、Ｃは熱処理終了後の状態を示す。
【図１３】２次ブロー成形工程を説明するための断面図であって、成形終了後の状態を示す。
【図１４】最終成形品を示す側面図である。
【図１５】容器底部の足部と底中央谷部との接続幅（本発明範囲外）を示す説明図である。
【記号の説明】
１ 口頚部
２ 肩部
３ 胴部
４ 底部
５ 底中央谷部
５ａ 底中心部
６ 谷部
７ 足部
８ 付け根部
９ 接地部
１０ 細溝部
１１ａ、１１ｂ 凸状部
２０ プリフォーム２０
２１ 口部
２２ 胴部
２３ 閉塞底部
２４ 蓋締結機構
２５ サポートリング
３１ コア金型
３２ 割金型
３３ 底金型
３４ 延伸棒
３６ ２次成形品
３７ 底形成部
３８ 底凹部形成部
３９ 凹部
４０ 底部
４１ 胴部
４２ 底部用赤外線放射体
４３ 底肩部
４４ 赤外線放射体
４５ 熱遮蔽板４５
４６ ３次成形品
４７ 部分
５０ 容器
５１ 割金型
５２ 底金型[0001]
[Industrial application fields]
The present invention relates to a heat and pressure resistant self-supporting container that is formed by biaxial stretch blow molding of resin and has excellent heat and pressure resistance and self-supporting properties.
[0002]
[Prior art]
A biaxial stretch blow molded container of thermoplastic polyester such as polyethylene terephthalate (PET) has excellent transparency and surface gloss, as well as impact resistance, rigidity and gas barrier properties required for bottles. It is used as a bottled container for various liquids, that is, a bottle.
[0003]
In general, when producing a bottled product, it is necessary to heat sterilize or sterilize the contents after hot filling or filling the contents in order to improve the storage stability of the contents. However, polyester bottles have the disadvantage of inferior heat resistance and cause heat deformation and shrinkage deformation of the contents when hot filled, so heat setting after forming the biaxially stretched blow container (heat set) An operation is being performed.
[0004]
However, in applications where heat sterilization or sterilization is performed after filling and sealing the contents having an autogenous pressure (heat-resistant pressure bottle), pressure and heat simultaneously act on the bottom of the bottle, resulting in bulging deformation due to the thermal creep phenomenon. However, it is not sufficient to perform the heat fixing, and the bottom part of the bottle is rounded, and a separate hook part (base cup) is attached to the bottom (Japanese Utility Model Publication No. 55-142433 and Japanese Patent Publication No. Sho). 61-30982).
[0005]
Also, in such a two-piece heat-resistant pressure bottle, in order to minimize deformation due to heat and pressure at the bottom, Japanese Patent Publication No. 6-22862 discloses that the bottom center of unstretched or low stretch is heated by heating. It is described that crystallization is performed, and the entire container excluding the thermal crystallization portion is formed at a high stretch ratio by biaxially stretching blow-molding a preform formed by thermally crystallizing the bottom center portion and the mouth and neck portion. It is described that it can be stretched, and in particular, the hemispherical bottom can be thinned by stretching, except for the bottom center.
[0006]
A polyester bottle having a pressure resistance with a one-piece structure, that is, a petaloid type bottle has already been proposed. For example, in Japanese Patent Laid-Open No. 4-154535, a plurality of leg pieces are bulged at equal intervals and the leg pieces are provided. A biaxially stretched blow-molded bottle having a petaloid-type bottom portion with a valley wall formed between the center and an unstretched peripheral portion located around a central flat portion including the stretch center point of the bottom portion A biaxially stretched blow molded bottle is described in which the portion is crystallized in a form in which the density on the outer surface side is higher than the inner surface side of the wall of the central portion.
[0007]
Japanese Patent Laid-Open No. 5-147737 discloses a biaxially stretched bottle body, a curved bottom that bulges downward from the bottle body, and a curved bottom that protrudes downward integrally with the periphery of the curved bottom. A polyethylene comprising a biaxially stretched bottom having a plurality of hollow legs for allowing a bottle body provided in a self-supporting manner and an unstretched mouth having a screw forming portion provided on the outer periphery of the information of the bin body In the bottle body made of terephthalate resin, the bottom of the curved surface coincides with a virtual true curved surface having the same diameter as that of the bottle main body at the lowest portion, and has a shape that bulges downward from the virtual curved surface at the peripheral portion. A polyethylene terephthalate resin bottle is characterized.
[0008]
Further, in Japanese Patent Laid-Open No. 6-032340, in a pressure-resistant self-supporting container in which a plurality of legs that form a grounding part are integrally formed, the bottom of the container has a smooth curved surface that protrudes downward. And a plurality of legs formed at equal intervals in the circumferential direction around the center part of the bottom part, and the lower end surface of each leg part is wide and radially inward in the radially outer part. And has a trapezoidal outline that narrows the width of the leg portion, and a flat ground surface portion that is in contact with the container support surface when the container is not filled is formed on the radially outer portion in the lower end surface of the leg portion. In addition, a substantially flat inclined surface portion is formed on the inner side of the ground surface portion, and is continuous with the ground surface surface portion, and is inclined upward toward the inside of the container, and is formed between each leg portion and the bottom center portion. Has a smooth curved surface that is convex upward, and the center of the leg and the bottom Pressure-resistant self-supporting container, characterized by connecting the divided and smoothly are described.
[0009]
[Problems to be solved by the invention]
A container having a hemispherical bottom that has been thinned by stretching has excellent heat and pressure resistance, and is filled with contents to which an internal pressure such as carbonated beverages is applied, and heat sterilization treatment (flowing to 65 The base cup is manufactured separately from the container and must be fixed to the container by bonding or the like.
[0010]
A self-supporting container having a petaloid-type bottom, that is, a foot-integrated bottom has the advantage that it is not necessary to manufacture and attach a base cup, but its heat resistance, in particular, the heat and pressure resistance of the bottom is still insufficient. Has drawbacks. That is, in this type of container, there is always an unstretched or low-stretched thick part, and this part is subject to thermal creep deformation under the condition where heat and pressure act simultaneously, thereby impairing the self-supporting property of the container. is there.
[0011]
In other words, when forming a self-supporting container having a foot-integrated bottom, if the preform formed by thermally crystallizing the neck and neck is biaxially stretch blow molded at once, the bottom shape is complicated and the entire bottom is highly stretched. It is difficult to reduce the thickness below, and it is inevitable that a relatively thick low-stretched portion remains. This relatively thick, low-stretched portion is inferior in heat and pressure resistance, and if such a container is filled with contents and subjected to heat sterilization, it becomes difficult to ensure self-supporting properties.
In this way, at the bottom where the low-stretched thick-walled portion remains, as described in page 3 of the above-mentioned JP-A-6-0323340, in order to obtain the self-supporting property of the container, If an attempt is made to form irregularities, there will be a problem in that defects such as stress cracks and crazes are likely to occur due to unreasonableness at the boundaries between the irregularities.
[0012]
Furthermore, since the foot part that gives the container self-supporting properties is formed so as to protrude in the bottom direction from the valley part located on the hemispherical surface, the thickness of the foot part is inevitably thinned, and the foot part is formed at the time of blow molding. There is also a problem that it bursts or the pressure strength of the foot portion decreases.
[0013]
Therefore, the object of the present invention is to prevent the foot from being excessively thinned while the entire bottom is thinned by stretching, to completely prevent the thermal creep phenomenon of the bottom during heat sterilization, and The object is to provide a biaxially stretched resin container having no combination of defects, including a combination of excellent heat and pressure resistance, impact resistance, and self-supporting properties.
[0014]
[Means for Solving the Problems]
  According to the present invention, in the self-supporting container having a bottom portion formed of a mouth and neck portion, a shoulder portion, a trunk portion, and a plurality of valley portions and a foot portion formed by biaxial stretch blow molding of resin, the foot portion is The base of the foot connected to the valley at the center of the bottom, and extends radially from the center of the base of the footIn addition, it ends on the inner diameter side than the grounding part of the footIt is composed of a narrow groove portion and a pair of convex portions projecting outward from the narrow groove portion with the narrow groove portion in between, and the pair of convex portions and trough portions of the foot portion are the foot base portion A self-standing container excellent in heat and pressure resistance, characterized in that it is connected so as to form a discontinuous curve at the position.
[0015]
  In the self-supporting container of the present invention,
1. The narrow groove is, At the center of the base of the foot, the small radius of curvature (R _Three = 2 to 8 mm) and being smoothly connected to the troughs,
2.The foot base is separated into two foot bases by a narrow groove,
3.The pair of convex portions of the foot are formed substantially symmetrically with respect to the narrow groove,
4).The groove width at the bottom of the narrow groove portion is 5 mm or less, and the vertical distance H between the bottom center portion and the start end of the narrow groove portion located above the bottom center portion. ₁ Is in the range of 1 to 4 mm,
5. thisThe distance H in the vertical direction between the bottom center and the start end of the narrow groove located above the bottom center after filling the contents and heat sterilization₂Is 0.5 mm or more, particularly 1 mm or more,
Is preferred.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
[New bottom shape and action]
In FIG. 1 (partial cross-sectional side view) showing a heat-resistant pressure-resistant self-supporting container of the present invention, this container is made of a neck part 1, a shoulder part 2, a trunk part 3 and a bottom part 4 formed by biaxial stretch blow molding of resin. The bottom portion 4 includes a bottom central valley portion 5 that includes the bottom center portion 5a and extends in the vicinity thereof, and alternately has a plurality of valley portions 6 and a plurality of foot portions 7 on the periphery. The valley portion 6 is located on a virtual curved surface that is convex in the bottom direction, and the foot portion 7 located between the valley portions is provided so as to protrude in the bottom direction from the valley portion 6. The foot 7 has a grounding portion at a tip 9 extending radially and downward from the central base 8.
[0017]
In FIG. 2 (bottom view of the bottom) and FIG. 9 (perspective view of the bottom) for explaining the details of the arrangement of the bottom valley and the foot in this container, in the present invention, the foot 7 is placed at the bottom center. 5, a foot base portion 8 connected to the valley portion 6, a narrow groove portion 10 extending radially from the center of the foot base portion 8, and an outer side of the narrow groove portion with the narrow groove portion 10 interposed therebetween. It is composed of a pair of protruding convex portions 11a and 11b.
[0018]
By the presence of the narrow groove 10 at the center of the foot base 8, the foot base 8 is separated into two foot bases 8a and 8b, and a pair of foot parts. The convex portions 11 a and 11 b are formed substantially symmetrically with respect to the narrow groove portion 10. As shown in FIG. 2, the narrow groove portion 10 is preferably terminated on the radially inner side with respect to the ground contact portion 9 of the foot portion.
[0019]
As is clear from FIG. 4 showing the BB cross section of FIG. 2, the pair of convex portions 11a, 11b and the valley portion 6 (bottom center 5) of the foot portion are the foot root portion 8 (8a, 8b). It is also important that they are connected so as to form a discontinuous curve at the position. That is, the trough portion 6 has an outwardly convex curved surface (spherical surface), while the foot portion 7 also has a downwardly convex curved surface, but both are discontinuous curves, that is, the differential coefficients are discontinuous. Connected as a curve. It will be understood that the cross-sectional shape of the foot 7 has a vaginal shape (a vaginal shape).
[0020]
On the other hand, as is clear from FIG. 3 showing the AA cross section of FIG. 2, the narrow groove portion 10 has a small-diameter curvature portion (R_Three= 2 to 8 mm) It is preferable that the valley portion 6 is smoothly connected via 12.
[0021]
In the present invention, a biaxially stretched blow molded container excellent in heat and pressure resistance and self-supporting property can be provided by forming the above-mentioned specific petaloid-type bottom. That is, with this bottom shape, the entire bottom portion can be thinned into a highly stretched orientation state, whereby the yield strength per unit length at 70 ° C. of the bottom portion, that is, the heat and pressure resistant strength is remarkably improved. Can be used as
[0022]
In the petaloid type bottom portion having a conventionally known low-stretch orientation portion, the above-mentioned heat and pressure resistance is remarkably lowered, and is restricted by internal pressure or sterilization temperature during use. On the other hand, if the low stretch orientation part is heat-fixed to increase its crystallinity, the heat-resistant pressure resistance strength of the bottom part is improved, but whitening due to heat-fixing spherulization proceeds, and the whitened part has impact resistance. This causes a problem of significant reduction.
[0023]
As in the present invention, when it is attempted to make the bottom portion highly stretched and thin, particularly securing fall resistance and securing moldability are problematic. That is, when the container bottom is thinned, the center of gravity of the empty container shifts slightly upward as compared with the case where the bottom is thick, and falls easily. From the viewpoint of tipping resistance, it is necessary to slightly increase the diameter of the grounding portion or the width of the grounding portion at the bottom.
In addition, if too much emphasis is placed on the heat and pressure resistance of the bottom of the container, for example, if a petaloid-type bottom shape is employed such that the distance between the tip of the foot and the bottom valley is relatively large, the tip of the foot will be extremely stretched particularly Tend to be thinned or whitened, the pressure resistance at the tip of the foot may be insufficient, or aesthetically pleasing. Furthermore, it is necessary to make the grounding part diameter or the grounding part width somewhat larger than the conventional one in consideration of the fall resistance, but this promotes the whitening due to the thinning of the foot tip part or overstretching. And acts in the direction of lowering the formability of the bottom. On the other hand, when the petaloid bottom mold is determined with emphasis on the moldability of the tip of the foot, it is disadvantageous for normal heat and pressure resistance and tipping resistance.
[0024]
In the heat and pressure resistant self-standing container of the present invention, a petaloid-type bottom shape that satisfies the moldability, heat and pressure resistance, and tipping resistance of the foot tip is provided.
[0025]
The present inventors conducted analysis simulations of the heat and pressure resistance of various shapes of petaloid mold bottoms, prototyped several petaloid bottom molds based on the simulation, and evaluated the heat and pressure resistance.
As a result, as the stress applied to the bottom of the petaloid, a large force is acting on the valley and the boundary between the valley and the foot, and further, from the bottom central valley and the bottom to the foot root where the foot starts, It was found that a large force was concentrated and that the deformation at the center of the bottom valley part was greatly influenced by the shape of the bottom valley part and the shape of the foot root part where the stress concentration was large.
From the above,
A. Diameter D of the bottom central valley to the base of the foot at the bottom center_FTo make it as large as possible,
B. Making the bottom central valley a spherical shape with pressure resistance,
C. It has been found that reducing the connection width between the bottom base and the bottom central valley as much as possible is extremely effective for improving the heat and pressure resistance.
[0026]
As shown in FIG. 15, the tip of the foot root 8 at the center of the bottom is formed into an arc shape with a relatively small radius of curvature, the connection width with the bottom center valley 5 is reduced, and the diameter of the bottom center valley 5 is increased. As a result, the heat and pressure resistance can be improved. However, if the number of feet is relatively small, when the above bottom shape is adopted, the amount of resin to be stretched on the foot portion is reduced, and it becomes difficult to ensure the moldability of the foot tip portion 9.
[0027]
On the other hand, as shown in FIG. 6, it is a bottom shape in consideration of blow moldability, and when the connection width W between the bottom root portion 8 and the bottom central valley portion 5 is relatively large, after filling and sterilization of the contents The bulge at the center of the connecting portion is particularly large, and the bulge bulges further downward from the center of the bottom, resulting in a decrease in heat and pressure resistance.
Further, as shown in FIG. 7, when the bottom central valley portion 5 is flat, the bottom central valley portion 5 is deformed from a flat shape to a substantially spherical shape after filling and sterilization of the contents. As a result, the amount of deformation of the flat bottom central valley is relatively larger than that of the spherical bottom central valley from the beginning, and the heat and pressure resistance is reduced.
Therefore, in the bottom shape in which the bottom central valley portion is flat as shown in FIG. 7 and the bottom central portion and the foot root portion are connected with a relatively wide connection width W as shown in FIG. As described above, even if the entire bottom is highly stretched and oriented to increase the strength, it is difficult to obtain preferable heat and pressure resistance. In particular, in the case of relatively severe conditions in the content filling and sterilization process, for example, when the filling gas pressure is relatively high or the hot water shower temperature is relatively high, the bottom central valley portion 5 and the foot contact portion 9 are used in the empty container. Height H between₀(FIG. 7), as shown in FIG. 8, when the contents are filled and sterilized, the deformation of the bottom center part 5a becomes larger, and conversely, the center part 5a is illegally higher than the grounding part 9 by the height H. It comes to protrude and it becomes difficult to maintain independence.
[0028]
As a result of intensive studies, the inventors of the present invention have made the connection width W between the bottom root portion 8 and the bottom central valley portion 5 relatively large, and by providing a narrow groove portion 10 in the center of the connection portion. It was found that both the heat resistance and pressure resistance of the container and the moldability of the tip of the foot can be satisfied.
As shown in FIG. 2, the narrow groove portion 10 at the center of the foot 7 extends radially from the center of the foot base portion 8 (8 a, 8 b) toward the grounding portion 9, and preferably ends before the grounding portion 9. doing.
[0029]
The narrow groove portion 10 at the center of the foot greatly contributes to the improvement of heat and pressure resistance. When the container is filled with the contents and sterilized, the greatest force acts in the vicinity of the bottom central valley portion 5 and the foot root portion 8. At this time, the narrow groove portion 10 in the center of the foot is slightly deeper than the convex portions 11a and 11b on both sides, and is smoothly connected to the bottom central valley portion 5, and as a result, even in the foot base portion 8, The force concentrates in the vicinity of the pair of convex portions 8a and 8b having a small diameter. At that time, as shown in FIG. 2, the pair of convex portions 8a, 8b of the foot base portion 8 and the bottom central valley portion 5 are connected by a curve having a relatively small radius of curvature. Since the narrow groove portion 10 has the same strength as that of the trough portion 6, the amount of local deformation is relatively small, and as a result, the heat and pressure resistance is improved.
[0030]
Actually, the vertical distance H between the bottom center portion 5a and the start end (end portion in the radial direction) of the narrow groove portion 10 located above the bottom center portion.₁(FIG. 3) and the distance H in the vertical direction between the bottom center portion 5a after filling and sterilization and the start end of the narrow groove portion 10 when positioned above the bottom center portion.₂And (FIG. 5) is the vertical distance between the center of the bottom and the grounding portion 9 (in the case of an empty container, H in FIG. 3).₀After heating and filling, the amount of change is extremely smaller than the amount of change in H) of FIG. 5, and the deformation of the foot base 8 is suppressed by the narrow groove 10 at the center of the foot. By suppressing the deformation of the foot base 8 in this way, the amount of change in the vertical distance between the bottom center portion 5a and the grounding portion 9 is relatively small, and the narrow groove portion 10 at the center of the foot ensures heat and pressure resistance. It is understood that it works effectively against.
[0031]
Further, the portions 11a and 11b sandwiching the narrow groove portion 10 at the center of the foot are formed in a convex shape outward, and the bottom root valley portions 5a and 8b at the base portions 8a and 8b are connected by a discontinuous curve. It works extremely effectively in improving the formability of the foot 7 during stretch blow molding.
[0032]
That is, in the blow molding process of the petaloid mold bottom, first, the blow molded product comes into contact with the mold at the center of the bottom and the valley, and the contact position spreads radially in the direction of the foot tip. In the blow molding stage, the portion of the molded product that has once contacted the mold is restrained by the mold and cooled, so that subsequent stretching is limited. In the blow molding stage, when the mold and the product contact at the bottom foot part are made sequentially with a time difference from the center of the bottom to the peripheral part, the tip end part is excessively stretched locally. The degree of stretching becomes extremely thin, and preferable molding is not performed.
[0033]
On the other hand, if the foot bottom shape is convex outward and the foot and valley are connected by a discontinuous curve, the time for the molded product to reach the bottom of the foot at the blow molding stage is delayed. As a result, it is possible to prevent the tip of the foot from being in a locally overstretched state. Thus, according to the present invention, it is possible to obtain an effect of suppressing the overextension of the foot tip portion, increasing the thickness of the foot tip portion, and improving the moldability.
[0034]
In the case of the present invention, the narrow groove portion 10 exists in the center of the convex portions 11a and 11b, and in the blow molding stage, the molded product comes into contact with the mold portion corresponding to the narrow groove portion 10 at an early stage. Since the width of the bottom of the groove is narrow and the contact area is small, the degree of cooling is relatively small, and the convex portions 11a and 11b on both sides of the groove come into contact with the corresponding mold part due to the presence of the groove. Due to the delay of the time to perform, the presence of the narrow groove portion 10 at the center of the foot effectively works to improve the formability of the foot tip portion.
[0035]
Moreover, since the length of the bottom of the sole that is convex below the two peaks in the container of the present invention is longer than that of the straight shape, the relative deformation degree associated with the filling of the contents and the subsequent heat sterilization treatment And the foot height H, which is the distance between the bottom valley center portion 5 and the foot contact portion 9, increases. As a result, it has the effect of improving the heat and pressure resistance performance.
[0036]
The foot center narrow groove portion 10 of the present invention works effectively especially at the bottom center foot portion, and is preferably terminated before the ground contact portion 9. In particular, when the grounding portion 9 has a narrow groove extending to the outside of the grounding portion, a phenomenon in which the shapeability at the time of molding of the pair of grounding portions on both sides tends to be different between right and left. As a result, in an extreme case, only one of the pair of grounding portions is grounded, and the fall resistance of the empty container is lowered.
[0037]
In the container of the present invention, the groove width at the bottom of the narrow groove portion 10 is 5 mm or less, particularly 2 mm or less, and the vertical distance H between the bottom center portion 5a and the start end of the narrow groove portion located above the bottom center portion.₁Is preferably in the range of 1 to 4 mm, particularly 1 to 3 mm.
Further, in a container that has been sterilized after filling with the contents, the vertical distance H between the bottom center portion 5a and the start end of the narrow groove portion located above the bottom center portion.₂Is preferably in the range of 0.5 mm or more, particularly 1 mm or more.
Further, the two bases 8a and 8b separated by the narrow groove 10 have a radius of curvature of about 1 to 10 mm (R in FIG. 2)._Four) Is preferable.
[0038]
[Physical properties of petaloid type bottom]
In the container of the present invention, except for the bottom center portion 5a, the entire bottom portion is thinned in a highly stretched orientation state. That is, except for the bottom center portion 5a, highly oriented crystallization is performed so that the degree of crystallinity is 20% or more, particularly 25% or more, and the wall thickness is 0.15 to 1.0 mm, preferably 0.2 to 0.00. It is thinned by stretching so as to be 8 mm. The bottom center portion 5a (gate portion) is also preferably stretched and thinned so as to have the above-described orientation crystallinity and a thin-walled range.
[0039]
It is also important to further improve crystallization by heating the bottom in a blow molding process or subsequent heat treatment process. By heating the stretched portion, a transparent bottom substantially free of whitening can be formed.
At least trunk diameter D₀It is preferable from the viewpoint of heat and pressure resistance that the crystallinity of the valley included within 50% of the above is 30% or more.
In addition, crystallinity degree X of each part of the container_cIs measured by the density method, but the density ρ (g / cm of the measurement site)^Three) Measured with a density gradient tube, the crystal density ρ_c(1.455 g / cm^Three) And amorphous density ρ_am(1.335 g / cm^Three) And using the following formula to calculate.

[0040]
In the present invention, the bottom valley portion can be made to have high strength by bringing the bottom portion into a highly stretched orientation state and further improving the crystallinity by heating, and the yield load at 70 ° C. of the bottom valley portion is 25 kg / cm. In particular, it can be 30 kg / cm or more.
In order to satisfy the yield load value at 70 ° C. of the bottom valley, the thickness of the bottom valley including the bottom central valley 5 is preferably 0.3 mm or more. At this time, when the thickness of the bottom valley portion, particularly the bottom center portion 5 is less than 0.3 mm, and the thin valley portion is present in a relatively wide range, the yield load value at 70 ° C. decreases, The deformation of the part is excessive, which is not preferable.
[0041]
On the other hand, when the thickness of the bottom exceeds 1 mm, the orientation crystallinity usually associated with the stretching process is a numerical value of 10% or less, and it is difficult to obtain a preferable yield stress strength in a temperature range of 60 to 70 ° C. In addition, if there is a relatively large unoriented or low-oriented thick portion at the bottom, thermal crystallization (whitening) proceeds during heat treatment, and even though heat resistance is improved, impact resistance is reduced. Further, when the low-stretch oriented thick-walled portion comes to the concave and convex portion at the bottom, the boundary between the concave and convex portions is forced to cause defects such as stress cracks and crazes.
On the other hand, in the present invention, by adopting the bottom shape, it is possible to achieve a highly oriented orientation of the bottom portion while preventing local thinning of the foot portion, and by making this highly crystallized. The yield stress strength at a temperature of 70 ° C. can be sufficiently increased, and it can be sufficiently used as a heat-resistant and pressure-resistant container for performing a heat sterilization treatment at a temperature of about 65 to 70 ° C. Furthermore, the bottom of the container of the present invention is high in strength and rich in flexibility, and there is no occurrence of defects such as stress cracks and crazes in the uneven portion of the bottom.
[0042]
As described above, in the container of the present invention, the entire bottom is preferably thinned to a thickness of 1 mm or less in a highly stretched state, but as long as the yield load at 70 ° C. is 25 kg / cm or more, There may be a thick part exceeding 1 mm in a small area. In particular, when the bottom center portion 5a (gate portion) remains as a thick portion, as long as the diameter of the thick portion is relatively small and the yield load of the bottom valley portion satisfies the scope of the present invention. It can have a relatively preferable heat and pressure resistance performance.
[0043]
[Dimensional relationship between bottom valley and bottom center foot]
In the container according to the present invention, the valley portion 5 at the center of the bottom is a part of a spherical surface. From the viewpoint of molding to ensure the thickness of the foot tip, in FIG. 3, the radius of curvature R of the valley near the center of the bottom.₁Torso radius R₀(D₀/ 2), the radius of curvature R of the valley at the bottom periphery₂It is preferable to make the connection small and smooth with the body. That is, the bottom central valley 5 has a radius of curvature R having a center on the bottom central axis.₁It is preferable that the range of the spherical surface includes the bottom center portion 5a, and the spherical valley surface is included on a straight line connecting the center point of the spherical surface and the tip of the foot. Also, the radius of curvature R of the bottom central valley 5₁Is the trunk radius R₀Is preferably 1.3 to 2 times.
[0044]
The radius of curvature R of the valley near the bottom center₁1.3 × R₀If it is less than 1, the moldability of the foot is inferior, and it becomes difficult to ensure the thickness of the foot tip. On the other hand, the curvature radius R of the valley₁Is 2 × R₀If it exceeds 1, the heat-resistant pressure resistance strength of the bottom part is lowered, and the deformation of the valley part after filling tends to be too large.
[0045]
Radius of curvature R₁The range of the valley portion 6 is the diameter of a circle where the straight line connecting the center of the valley spherical surface and the foot contact portion intersects the virtual valley spherical surface D₁And the formula
D₁/ D₀= 0.55-0.75
It is preferable that the range satisfies the above.
[0046]
The valley portion 6 is convex downward, the bottom center portion 5a is the lowest point, and the valley portion rises along the spherical surface from the bottom center portion 5a to the foot root portion 8 where the foot portion starts at the bottom center 5. At the same time, the legs rise radially outwardly from the base of the foot, and the legs extending radially from the base of the foot have a curved shape that descends to the grounding portion as opposed to the valley.
[0047]
[Other bottom shapes]
In the container of the present invention, consideration is given to increasing the surface area of the valleys within the range where the moldability is not impaired in terms of heat and pressure resistance.
[0048]
In FIG. 2 (enlarged cross-sectional view of the main part), which also serves to explain various dimensions at the bottom of the container, the body 3 directly above the bottom of the container is D₀The bottom 4 is D_FThe bottom central part has a diameter. Body diameter D from bottom center₀The surface area of the virtual curved surface in which a circle having a diameter of 40% is drawn, and the surface area of the valley portion 4 included in the circle is S, and the entire bottom portion included in the diameter of the body diameter 40% is covered with the valley curved surface. S₀And Also, the diameter D from the center of the bottom₀ A virtual curved surface in which a circle having a diameter of 80% is drawn, the surface area of the valley 4 included in the circle is S ′, and the entire bottom included in the diameter of 80% of the trunk diameter is covered with a valley curved surface. Surface area is S₀'.
[0049]
In the present invention, the dimensions of the valley shape are determined so as to increase the area of the valley in a range that does not impair the formability of the foot. That is, the diameter D of the bottom center foot base_FFor the purpose of maintaining the proper value, that is, improving the heat and pressure resistance and ensuring the moldability.
0.35D₀≧ D_F≧ 0.23D₀
Is in a range that satisfies.
[0050]
Also, body diameter D₀The surface area S of the valley included in the diameter of 40% of
S / S₀= 0.65 to 0.9, preferably 0.7 to 0.85
And body diameter D₀Surface area S 'of the valley included in the diameter of 80% of
S '/ S₀'= 0.2 to 0.45, preferably 0.3 to 0.40
It is said.
[0051]
In the present invention, as shown in FIG. 9, one end of the valley portion 6 and the end of the foot portion 7 corresponding thereto are crossed between the adjacent foot portions 7 and 7 and perpendicular to the valley portion 6. A foot opening angle θ sandwiching the foot portion is defined between the connecting line a and a line a ′ connecting the other end of the valley portion 6 and the end of the foot portion 7 corresponding thereto.
[0052]
As a result of intensive studies, the present inventors have paid particular attention to the foot opening angle θ across the valley between the feet and across the valley reaching the tip of the foot in a plane perpendicular to the valley. For example, when a container having a foot opening angle θ of 55 ° is filled with the contents of 3 gas volumes, the foot opening angle θ spreads to 58 °. When the filled product is subjected to a hot water shower at 70 ° C. and subjected to heat sterilization at a temperature of 65 ° C. for 15 minutes at the center of the bottom, the bottom portion is deformed and the above foot opening angle θ is An observation result that spreads to 90 ° was obtained.
[0053]
The inventors of the present invention have considered that the significant increase in the foot opening angle θ during heat sterilization causes a relatively large deformation of the valley, that is, expansion of the valley. Therefore, it was conceived that if the foot opening angle θ sandwiching the valley at the foot portion leading to the tip of the foot is increased to a certain extent in advance, the deformation of the valley during heat sterilization can be suppressed as a result. It was.
As a result of the experiment, it has been found that in the container having the foot opening angle θ of 65 ° or more, the deformation of the valley during the heat sterilization treatment can be made extremely small.
[0054]
Increasing the foot opening angle θ across the valley is to make the direction of the force acting so that the foot pulls up the valley formed of a part of a curved surface such as a spherical surface close to the direction of the spherical surface. Therefore, the force component that works perpendicularly to the spherical valley, that is, the force component that deforms the valley is reduced. As a result, valley deformation can be reduced.
[0055]
In the present invention, the foot opening angle θ across the foot and sandwiching the bottom trough reaching the tip of the foot in a plane perpendicular to the trough is 65 ° or more, particularly preferably in the range of 70 ° to 90 °. In a container having a foot opening angle θ of less than 65 °, the foot opening angle θ after the filling of the contents and the heat sterilization treatment is greatly increased, and the deformation amount of the valley portion is excessively increased accordingly. As described above, it is preferable to increase the foot opening angle θ in terms of heat and pressure resistance, but when the foot opening angle θ is too large, the width of the foot tip grounding portion tends to be narrow. If the foot tip grounding portion is too thin, it tends to fall over in an empty container before filling, which is not preferable. Therefore, the foot opening angle θ is preferably 90 ° or less.
[0056]
In the present invention, the foot height H which is the height from the center of the bottom to the foot contact portion₀(FIG. 3) is preferably 3 mm to 6 mm. Foot height H₀Is less than 3 mm, it is difficult to effectively ensure the independence of the container after filling and heat sterilization, and the foot height H₀If it exceeds 6 mm, the distance from the valley to the foot becomes long, and it becomes difficult to ensure the thickness of the foot tip.
[0057]
The number of feet is preferably 3 to 6, particularly 4 to 5. When the number of feet is too small, the foot angle θ is relatively large, so that it is difficult to increase the width of the foot contact portion, which causes a problem that the empty container is likely to fall over. On the other hand, if the number of the foot portions is 7 or more, it becomes difficult to keep the foot angle θ and the valley width within a preferable range, and further, the foot width becomes narrow, so that the foot shape is inferior. Become.
[0058]
[Container manufacturing method]
The self-supporting container of the present invention is used as a final-stage blow molding die in a one-stage blow molding method for obtaining a final product shape by one blow molding or a two-stage blow molding method for obtaining a product by two blow moldings. It can be manufactured by using a bottom mold corresponding to the container bottom shape.
[0059]
In general, it is preferable to use a two-stage blow molding method. A secondary molded product having a substantially flat bottom is formed from a preform molded product by primary blow molding, and the bottom portion of the secondary molded product and the body portion connected to the bottom portion are formed. It is preferable to adopt a process in which a part is heated and shrunk to form a tertiary molded product, and the tertiary molded product is subjected to secondary blow molding in the bottom-shaped mold to obtain a final shape.
[0060]
[preform]
In the present invention, any plastic material can be used as long as it can be stretch blow molded and thermally crystallized, but thermoplastic polyester, particularly ethylene terephthalate thermoplastic polyester is advantageously used. . Of course, polycarbonate, arylate resin, etc. can also be used.
[0061]
The ethylene terephthalate thermoplastic polyester used in the present invention occupies most of the ester repeating units, generally 70 mol% or more, particularly 80 mol% or more of ethylene terephthalate units, and has a glass transition point (Tg) of 50 to 90. Thermoplastic polyesters having a melting point (Tm) of 200 to 275 ° C., particularly 220 to 270 ° C., at 55 ° C., in particular 55 to 80 ° C., are preferred.
[0062]
Homopolyethylene terephthalate is preferred in terms of heat and pressure resistance, but a copolyester containing a small amount of ester units other than ethylene terephthalate units can also be used.
[0063]
Dibasic acids other than terephthalic acid include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; succinic acid, adipic acid, sebacic acid, dodecanedioic acid, etc. Or a combination of two or more thereof. Examples of the diol component other than ethylene glycol include propylene glycol, 1,4-butanediol, diethylene glycol, 1,6-hexylene glycol, and cyclohexanedi. 1 type, or 2 or more types, such as methanol and the ethylene oxide adduct of bisphenol A, are mentioned.
[0064]
Also, it is possible to use a composite material obtained by blending ethylene terephthalate thermoplastic polyester having a relatively high glass transition point, for example, polyethylene naphthalate, polycarbonate or polyarylate in an amount of about 5% to 25%. The material strength can be increased.
Further, polyethylene terephthalate and a material having a relatively high glass transition point can be laminated and used.
[0065]
The ethylene terephthalate-based thermoplastic polyester to be used should have at least a molecular weight sufficient to form a film, and an injection grade or extrusion grade is used depending on the application. The intrinsic viscosity (IV) is generally in the range of 0.6 to 1.4 dl / g, particularly 0.63 to 1.3 dl / g.
[0066]
In the production of the container of the present invention, a bottomed cylindrical preform is first molded, and the neck of the preform is heated to locally provide a thermal crystallization portion.
[0067]
FIG. 10 showing an example of a preform used in the present invention together with a primary blow mold, this preform 20 is composed of a mouth part 21, a body part 22 and a closed bottom part 23, and the mouth part 21 has a screw or the like. A lid fastening mechanism 24, a support ring 25 for holding the container and the like (see FIG. 1) are provided, and the mouth portion 21 is thermally crystallized, that is, spheroidized. The spherulized mouth portion 21 is the container neck portion 1 of FIG.
[0068]
Injection molding can be used for molding the plastic material into the preform 20. That is, the plastic is melt-injected into a cooled injection mold to form a supercooled amorphous plastic preform.
[0069]
As the injection machine, a known one having an injection plunger or a screw is used, and the polyester is injected into an injection mold through a nozzle, a sprue and a gate. As a result, polyester or the like flows into the injection mold cavity and is solidified to form a stretch blow molding preform.
[0070]
As the injection mold, a mold having a cavity corresponding to the container shape is used, but a one-gate or multi-gate injection mold is preferably used.
Injection temperature is 270 to 310 ° C, pressure is 28 to 110 kg / cm²The degree is preferred.
[0071]
The spherulization of the mouth portion 21 of the preform 20 can be performed by selectively heating these portions by means known per se. Since thermal crystallization of polyester or the like occurs remarkably at a specific crystallization temperature, generally a corresponding portion of the preform may be heated to the crystallization temperature. Heating can be performed by infrared heating, dielectric heating, or the like. In general, it is preferable to perform selective heating by blocking a body portion to be stretched from a heat source with a heat insulating material.
[0072]
The above spherulization may be performed simultaneously with the preheating of the preform 20 to the stretching temperature or may be performed separately.
[0073]
The preform stretching temperature is generally 85 to 135 ° C., particularly 90 to 130 ° C., and the heating can be performed by means known per se such as infrared heating, hot air heating furnace, dielectric heating and the like. . In addition, the spheroidization of the mouth can be performed by heating the preform mouth part to a temperature of generally 140 to 220 ° C., particularly 160 to 210 ° C. while being thermally insulated from other parts. The crystallinity of the preform mouth is preferably 25% or more.
[0074]
In addition, for stretch blow molding from a preform, a method of performing stretch blow molding subsequent to preform molding using heat applied to the preform molded product to be molded, that is, residual heat, can be generally used. Is preferably a method in which a preform molded product once in a supercooled state is produced, and this preform is heated to the aforementioned stretching temperature and stretch blow molding is performed.
[0075]
According to the two-stage blow molding method, the preform which has been preheated for the spheroidizing and stretching of the mouth in this way is biaxially stretched and blown in a primary blow mold, so that a generally flat bottom And forming a secondary molded product in which the portion other than the mouth spherulite of the preform and the vicinity thereof is stretched at a high stretch ratio (FIG. 11); the bottom portion of the secondary molded product and the body portion connected to the bottom portion At least a part of the product is heated to form a third molded product in which the bottom part and part of the trunk part are contracted (FIGS. 12A, 12B, and 12C); this tertiary molded product is then blown in a secondary blow mold. The final product is formed from a plurality of valleys and legs, and has a bottom that is thinned by high stretching (FIGS. 13 and 14).
[0076]
[Primary blow molding]
In FIG. 10 (before molding) and FIG. 11 (after molding) showing the primary blow molding process, the preform 20 is supported by the core mold 31 and held in a closed split mold 32. Is done. A bottom mold 33 that defines the bottom shape of the secondary molded product is also arranged on the opposite side of the core mold. A stretching rod 34 is inserted into the preform 20, the tip is pressed against the bottom of the preform, the preform 20 is pulled and stretched in the axial direction, and a fluid is blown into the preform 20 to raise the height of the preform. And inflated and stretched in the circumferential direction. At this time, a press bar 35 is disposed coaxially with the stretching rod 34 on the side of the bottom mold 33, and at the time of tensile stretching, the bottom 23 of the preform is held between the stretching rod 34 and the pressing rod 35. The position is regulated so as to be positioned at the center of the secondary molded product 36 on which the bottom 23 of the product is formed. The bottom mold 33 is for restricting the bottom shape of the secondary molded product 36 to a suitable shape that will be described below in the subsequent heat treatment step.
[0077]
That is, as shown in FIG. 10, the bottom mold 33 includes a substantially flat bottom forming portion 37 and a bottom concave portion forming portion 38 that protrudes with a small diameter at the center thereof. This is because, when the bottom portion of the secondary molded product 36 is contracted, the depression toward the center of the bottom portion is suppressed, and the hemispherical surface close to the bottom shape of the final molded product is formed.
[0078]
Furthermore, as shown in FIG. 11, if a relatively small recess 39 is provided on the outer surface of the center of the bottom of the secondary molded product 36 during the primary blow molding, the bottom shoulder of the tertiary molded product can be removed in the heat treatment step. It is prevented that the diameter of the bottom shoulder becomes too small due to being excessively drawn inwardly in the diameter. This seems to be because the concave portion 39 has a function of contracting the central portion of the bottom in a substantially flat state when the heat shrinks. The size of the recess 39 is such that the diameter is the body diameter D of the final container.₀About 15 to 60% of the thickness and a depth of about 0.5 to 5 mm are appropriate. The formation of the recess 39 is achieved by forming an inward projection 38 on the inner surface of the center portion of the bottom mold 33.
[0079]
The stretching ratio is preferably 2 to 5 times, particularly 2.2 to 4 times in the axial direction, and 2.5 to 6.6 times, particularly 3 to 6 times in the circumferential direction. The axial stretch ratio is determined by the length of the preform in the axial direction and the stroke length of the stretch rod. The stretch ratio in the circumferential direction is determined by the diameter of the preform and the diameter of the mold cavity. . As the pressure fluid, room temperature or heated air, and other gases such as nitrogen, carbon dioxide or water vapor can be used, and the pressure is usually 10 to 40 kg / cm.²Gauge, especially 15-30kg / cm²It should be in the gauge range.
[0080]
In the present invention, it is preferable to make the bottom part thinner by relatively high stretching in the primary blow molding process. In the present invention, the temperature reduction of the sandwiched portion between the stretching rod and the press rod at the bottom of the preform until just before the stretching process is finished is within 40 ° C., more preferably within 25 ° C. The portion and the periphery thereof can be thinned in a relatively high stretched state.
When the temperature drop is 25 ° C. or less, the entire bottom including the bottom center portion 5a can be thinned to a thickness of usually 1 mm or less in a relatively high stretched state, and finally has a preferable heat and pressure resistance performance. A container having the same can be obtained.
In addition, when the temperature drop exceeds 25 ° C. and is within 40 ° C., the sandwiched portion between the normal stretching rod and the press rod, that is, the periphery of the bottom center portion 5a is thinned in a relatively high stretched state. The sandwiched portion remains relatively thicker than the surrounding area. However, since the thickness of the sandwiched portion is usually 1.5 mm or less and has a relatively small diameter, the performance is slightly lower than when the bottom center portion 5a is completely thinned to a highly stretched state. In particular, it can have a relatively preferable heat and pressure resistant performance.
[0081]
If the temperature drop of the sandwiched portion at the bottom of the preform exceeds 40 ° C. immediately before the end of the stretching process, it becomes difficult to stretch the periphery of the sandwiched portion during blow molding, and it is relatively thick in a relatively low stretched state. It will remain as meat. That is, only a portion with a small temperature decrease other than the bottom center is stretched into a relatively high stretched state.
[0082]
It is effective to prevent excessive heat conduction from the stretching bar and the press bar as a means for lowering the temperature drop at the sandwiched part at the bottom of the preform. Specifically, it is preferable to use at least the tip of the drawing rod or the press rod as a heat-resistant plastic material or ceramic material having heat insulation performance.
In addition, a means for heating the press bar or the stretching bar and controlling the temperature to a relatively high temperature is also effective. The heating of the press bar and the stretching bar is preferably 60 ° C. to 130 ° C. corresponding to the stretching temperature of the preform.
As the heating method, an electric heater, an electric heating method by high-frequency induction heating, a fluid heating method by circulating a high-temperature liquid, a heat conduction method such as a heat pipe, or the like can be adopted.
[0083]
In FIG. 12A showing the details of the heat treatment process, the secondary molded product 36 rotates while being supported by the core mold 31, and faces the bottom portion 37 of this secondary molded product and at least a part of the body portion connected to the bottom portion. Thus, a first infrared radiator 42 is provided. The first infrared radiator 42 is located above the bottom portion 40 of the secondary molded product 36 and is placed substantially perpendicular to the body portion 41. By the bottom infrared radiator 42, the bottom portion of the secondary molded product 36 is placed. And a part of trunk | drum connected to a bottom part is heat-shrinked first.
[0084]
In the heating of the secondary molded product performed in advance by the infrared radiator 42 for the bottom portion, as shown in FIG. 12B, the bottom portion of the secondary molded product and the connecting portion between the body portion and the bottom portion contract mainly. Contracts toward the center, and the connecting portion between the body and the bottom contracts sequentially from a portion close to the bottom infrared emitter 42, that is, from a portion close to the center to an outer portion thereof. At this stage, the shrinkage of the body portion in the circumferential direction is small, so that the shrinkage shape of the bottom portion has a controlled bottom shoulder portion 43 having a relatively large diameter.
[0085]
Next, a part of the body part connected to the bottom part of the secondary molded product is heated and shrunk by the body infrared radiation body 44 located at least around the body part and placed substantially parallel to the body part. In FIGS. 12B and 12C, a heat shielding plate 45 is provided to shield the other part of the trunk from the infrared radiator 44 for trunk.
[0086]
The bottom shoulder portion 43 obtained by shrinking the bottom portion can substantially secure its shape without being contracted so much in the subsequent heating by the body infrared radiation body 44.
Heating by the trunk infrared radiation body 44 contributes to heating and shrinking the trunk below the bottom shoulder 43 obtained by shrinking the bottom and raising the temperature in the vicinity of the bottom shoulder 43.
[0087]
The heat-shrinkable portion of the tertiary molded product 46 obtained in this way has a relatively large radius of curvature that is generally flat or convex from the bottom to the bottom shoulder 43 as shown in FIG. The portion 47 outside the bottom shoulder 43 is abruptly bent in a generally cylindrical shape or a shape close to a truncated cone.
Furthermore, the components inside the heated bottom shoulder of the tertiary molded product 46, the cylindrical portion near the bottom shoulder and below the bottom shoulder are maintained at a temperature level optimum for secondary blow molding.
[0088]
In the subsequent secondary blow molding, the bottom shoulder portion 43 of the tertiary molded product and its vicinity come to the foot tip of the final molded product. Therefore, it is important to make the bottom shoulder portion 43 as close as possible to the valley portion and foot tip portion of the secondary blow bottom mold, and to increase the temperature of the bottom portion and the cylindrical portion sandwiching the bottom shoulder portion so that the bottom shoulder portion 43 can easily extend. Thereby, preferable moldability at the time of secondary blow molding can be secured.
[0089]
Heating of the bottom part and a part of the body part of the secondary molded product 36 is preferably performed at a temperature of 120 to 200 ° C., so that heat contraction and heat fixation of these parts can be effectively performed. Since the heating from the infrared radiator is non-contact heating, the bottom part and part of the body part are contracted without restraint, and the infrared ray irradiated to the surface of the secondary molded product is a part thereof. Passes through the plate thickness and reaches the inner surface on the opposite side facing the irradiation site, and a part of it is further absorbed, and the heating of the vessel wall from the inner surface by infrared rays is performed extremely efficiently and uniformly within a short time.
[0090]
In addition, the infrared radiators 42 and 44 of the heat treatment step are arranged on the upper and side surfaces of the passage along the passage along which the secondary molded product moves, and the space surrounded by the infrared radiator is subjected to secondary molding. If the product is rotated while rotating in the axial direction and moved while being heated, the heat shrinkage of the secondary molded product and the movement between processes can be performed simultaneously, so heat treatment can be performed without loss time and productivity can be improved. it can.
[0091]
Infrared radiators may be used in combination with those heated to about 400 to 1000 ° C. and having a relatively high radiation efficiency and a surface with a relatively large surface area. Thereby, infrared rays with a relatively high energy density can be irradiated to the secondary molded product, and heating can be performed for a short time. In particular, since the heated portion of the secondary molded product is thinned by high stretching, the infrared heating body can be set to a predetermined temperature in a short time of 10 seconds or less, for example. Specifically, the infrared heating body is obtained by burning a solid surface such as a metal surface such as carbon steel or stainless steel, a ceramic surface such as alumina, magnesia or zirconia, or a composite material surface such as ceramic and carbon, or a gas. A gas surface can be used. The surface of the infrared heating body made of solid is set to a predetermined temperature by heating with an embedded electric heater or high-frequency induction heating.
[0092]
The bottom of the secondary molded product thinned by high stretch in the primary blow molding has relatively poor moldability, and the temperature of the molded part should be 120 to 200 ° C. in order to perform the secondary blow molding well. is necessary. In addition, by heating and fixing the heated part of the tertiary molded product to a temperature of 120 to 200 ° C., the crystallinity of the bottom valley portion of the container can be finally set to the above-described range. In addition to improving the heat-resistant pressure strength by the bottom high stretch orientation, the heat-resistant pressure strength can be further increased by this bottom crystallization.
[0093]
In FIG. 13 showing the details of the secondary blow molding process, the neck of the tertiary molded product 46 is supported by the core mold 31 and is held in the closed split mold 51. A bottom mold 52 that defines the bottom shape of the final container is also arranged on the opposite side of the core mold. A fluid is blown into the tertiary molded product 46, and the tertiary molded product is subjected to secondary blow molding to form a bottom shape of a final container (five legs) 50 having predetermined valleys and feet. The molded container 50 is taken out from the opened secondary blow mold 51 by a known take-out mechanism (not shown).
[0094]
In the secondary blow molding step, the molded product (tertiary molded product) in the heat treatment step is blow-molded in a secondary blow molding die and molded into the bottom portion where the foot portions and valley portions are alternately arranged. In this secondary blow molding, the cavity of the secondary blow mold to be used is naturally larger than that of the tertiary molded product and matches the size and shape of the final molded product including the self-supporting bottom shape. There must be.
[0095]
Further, since the elastic modulus of the tertiary molded product is increased by crystallization by heat treatment, it is preferable to use a high fluid pressure, and generally 15 to 45 kg / cm.² It is preferable to use a pressure of
[0096]
During secondary blow molding, the mold temperature may be maintained at a temperature of 5 to 135 ° C., and cooling may be performed immediately after molding, or cooling may be performed by flowing cool air or the like through the final molded product. May be performed.
[0097]
The heat-resistant polyester bottle of the present invention is useful for the purpose of filling and sterilizing or sterilizing contents having a self-generated pressure, and is useful as a container for filling and storing carbonated beverages, nitrogen-filled beverages, seasonings and the like. . As the heat and pressure resistant container, the gas capacity can be up to about 3 VOL, and the heat sterilization temperature is suitably 60 to 80 ° C.
[0098]
【Example】
The present invention will be further described by the following specific examples and comparative examples.
[0099]
Comparative test 1
Using the two-stage blow molding apparatus as shown in FIGS. 10 to 13, the maximum body diameter D of the final molded product₀Was made of polyethylene terephthalate (PET) as shown in FIG. 1 having a bottom of 52.5 mm, a total height of 303 mm, a capacity of 1500 ml, and a bottom consisting of five legs and valleys.
[0100]
A bottomed preform is prepared, and as shown in FIG. 10, the height is 318 mm, the diameter of the body part connected to the bottom part is 92.5 mm, the center part is inward, and the diameter is 30 mm. Primary blow molding was performed using a blow mold composed of a bottom mold having a concave portion with a depth of 2 mm. In the primary blow molding, the preform is first heated to a stretching temperature of 100 ° C. and introduced into a mold, and then the bottom of the preform is stretched inside and a press bar placed outside. 20kgf / cm at the same time while pushing up the bottom of the preform with a stretching rod²Was blown into the preform to obtain a secondary molded product. At that time, the material of the ends of the stretching rod and the press rod was made of polytetrafluoroethylene (made of TF) having good heat insulation.
The bottom part of the obtained secondary molded product has a recess (diameter: 30 mm, depth: 2 mm) at the center, and is highly stretched and oriented to a thickness of 0.35 to 0.6 mm including the bottom center part. It was. At that time, the bottom crystallinity was 25 to 35%.
[0101]
Next, a bottom infrared radiator in which a planar infrared heater incorporating an electric heater in a ceramic is arranged in parallel to the bottom surface of the first stage, and a bottom infrared radiator and a body parallel to the bottom surface of the second stage By moving the secondary molded product while rotating in a tunnel-shaped heat treatment apparatus combined with an infrared radiator for the trunk arranged in parallel to the surface, the bottom of the secondary molded product and the trunk connected to the bottom A part was heated and shrunk as shown in FIG. 12 to obtain a tertiary molded product. The temperature of the infrared heating body was 950 ° C. for the bottom portion and 900 ° C. for the body portion, and the total heating time was 8 seconds. The heating part of the obtained tertiary molded product was very close to the bottom valley curved surface of the secondary blow molding die, and had a shape that could be sufficiently accommodated.
[0102]
Finally, using a secondary blow mold having a predetermined five-leg bottom shape, the heated tertiary product is 40 kgf / cm.²The container was obtained by secondary blow molding with compressed air.
At this time, as shown in FIG. 2, the bottom width is 0.5 to 1 mm and the depth is H as the five-foot mold of the secondary blow mold.₁Has a bottom groove of Example 1 having a narrow groove of 1.6 mm and the bottom center part is a part of a spherical surface, and a foot base having a relatively large width as shown in FIG. And a bottom mold of Comparative Example 1 having a bottom shape in which the bottom center portion is flat, that is, the bottom center portion and the base of the foot are on the same plane.
Also, in any bottom mold, the height H from the bottom center to the foot contact portion₀Is 4.5mm, the foot root width W is 10mm, and the curvature radius R of the valley crossing the bottom center₁Is 85 mm, the foot angle across the valley between the legs and perpendicular to the valley is 70 °, the trunk diameter D₀The total surface area S and trunk diameter D of the bottom valley included in 40% of the diameter₀Surface area S of the bottom virtual curved surface contained within 40% of the diameter₀Ratio S / S₀0.8, body diameter D₀The total surface area S 'and the trunk diameter D of the bottom valley included in the diameter of 80%₀Surface area S of the bottom virtual curved surface contained within 80% of the diameter₀Ratio S '/ S₀'Was 0.34, and the diameter of the bottom central valley located inside the foot root was 28 mm.
[0103]
In any case, the thickness of the bottom of the obtained container was in the range of 0.22 to 0.6 mm. Among them, the thickness of the bottom central valley portion was 0.45 to 0.5 mm, and the crystallinity of the portion was 40 to 45%. Moreover, the thickness of the foot tip portion was 0.22 to 0.3 mm, and no whitening due to overstretching was observed.
[0104]
As a performance test of the obtained container, in each example, 10 containers were filled with 2.8 gas volume (GV) and 2.3 gas volume (GV) carbonated water and capped, and then hot water at 70 ° C. was added. The contents were heat sterilized by flowing from the top of the container for 30 minutes. In the heat sterilization treatment, a temperature increase up to 69 ° C. was observed at the center of the bottom. Measure the amount of deformation at the bottom of the cooled container after heat sterilization, and check the number of containers that have a negative foot height (H), that is, the bottom center part is below the foot It was. The results are shown in Table 1.
Further, in the container of Example 1, the bottom foot height H of the bottom of the container subjected to heat sterilization treatment at a gas pressure of 2.8 GV is 0.5 to 0.7 mm, and the bottom center and the center of the foot base are thin. Distance H in the height direction from the top of the groove₂Was 1.2 to 1.5 mm. As described above, in the container of the present invention of Example 1, the depth of the narrow groove portion remains even after filling and sterilization, and it remains after the filling and sterilization of the foot root portion and the bottom center portion connected thereto. Deformation was suppressed, and preferable heat and pressure resistance was obtained.
On the other hand, in the container of Comparative Example 1, the bottom foot height H of the bottom of the container heat-sterilized with a gas pressure of 2.8 GV is −0.3 to −0.8 mm, and the bottom center is below the foot. Further, the base of the foot portion was greatly deformed downward in synchronization with the deformation of the bottom center portion. As described above, in the container of Comparative Example 1, the bottom center flat portion deformed into a substantially spherical shape with filling sterilization, and the foot base portion lacked the ability to suppress the deformation.
[0105]
[Table 1]

[0106]
Comparative test 2
Maximum body diameter D of final molded product by two-stage blow molding method₀Was 92.5 mm, the total height was 303 mm, the capacity was 1500 ml, and the bottom part was composed of five legs and valleys to prepare a polyethylene terephthalate (PET) container.
The container was prepared according to Comparative Test 1.
At that time, three types of bottom molds consisting of Example 2, Example 3 and Comparative Example 2 were prepared as the bottom molds of the secondary blow mold that would be the bottom shape of the container. Among them, in Example 2 and Example 3, the bottom width is 0.5 to 1 mm at the center of the five feet as shown in FIG.₁Provided a narrow groove of about 1.6 mm. On the other hand, in Comparative Example 2, as shown in FIG. 15, the base of the foot at the center of the bottom is made of an arc having a relatively small radius of curvature. Furthermore, in the three types of bottom molds, a foot angle θ across the valley between the legs and perpendicular to the valley, a curvature radius R of the valley bottom near the bottom center₁And trunk radius R₀Ratio R₁/ R₀, Diameter D of the base of the foot_F(Mm), trunk diameter D₀The total surface area S and trunk diameter D of the bottom valley included in 40% of the diameter₀Surface area S of the bottom virtual curved surface contained within 40% of the diameter₀Ratio S / S₀, And trunk diameter D₀The total surface area S 'and the trunk diameter D of the bottom valley included in the diameter of 80%₀Surface area S of the bottom virtual curved surface contained within 80% of the diameter₀Ratio S '/ S₀The numerical values of ′ were appropriately combined.
Table 2 shows the numerical values of the bottom shapes of the three secondary blow molds subjected to this comparative test. In the three types of bottom molds, the height H from the center of the bottom to the foot contact part₀Was 4.5 mm.
[0107]
In any case, the thickness of the bottom valley portion within a radius of 30 mm including the bottom center portion of the obtained container was 0.4 to 0.6 mm, and the crystallinity of the portion was 30 to 47%. Table 2 also shows the measured values of the thickness T of the foot tip of the obtained container.
[0108]
As a container performance evaluation test, in each of the prototypes, 10 containers were filled with 2.6 gas volume (GV) of carbonated water, capped, and then heated by flowing hot water at 70 ° C for 30 minutes from the top of the container. Was subjected to heat sterilization treatment. In the heat sterilization treatment, a temperature increase up to 69 ° C. was observed at the center of the bottom. After the heat sterilization treatment, the amount of deformation at the bottom of the cooled container was measured, and the number of containers lacking independence in which the foot height (H) was negative, that is, the center of the bottom was below the foot was examined. . The results are also shown in Table 2.
[0109]
[Table 2]

[0110]
From the test results of the above comparative tests 1 and 2, it is understood that the container of the present invention is excellent in heat and pressure resistance.
[0111]
【The invention's effect】
According to the present invention, in the self-supporting container provided with a bottom portion composed of a mouth and neck portion, a shoulder portion, a trunk portion, and a plurality of valley portions and a foot portion formed by biaxial stretch blow molding of a resin, the foot portion, A pair of foot roots connected to the valley at the center of the bottom, a narrow groove extending radially from the center of the foot root, and a pair of protrusions extending outward from the narrow groove with the narrow groove interposed therebetween And a pair of convex parts and valleys of the foot part are connected so as to form a discontinuous curve at the position of the base part of the foot part. Biaxially stretched resin that has an excellent combination of heat and pressure resistance, impact resistance, and self-supporting properties, while preventing excessive thinning of the foot while completely preventing thermal creep of the bottom during heat sterilization A container could be provided.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional side view of a self-supporting container of the present invention.
FIG. 2 is a bottom view of the self-supporting container of FIG.
FIG. 3 is a cross-sectional view taken along line AA in FIG. 2 at the bottom of the container.
4 is a cross-sectional view taken along the line BB in FIG. 2 at the bottom of the container.
FIG. 5 is a cross-sectional view corresponding to FIG. 3 of the bottom of the container in the state of filling contents.
FIG. 6 is an explanatory diagram showing a connection width between a foot portion of a container bottom portion and a bottom central valley portion.
FIG. 7 is a cross-sectional view of a container bottom (comparative example) in which a bottom central valley is flat.
8 is a cross-sectional view of the bottom of the container of FIG. 7 in a state where the contents are filled.
9 is a perspective view of the bottom of the self-supporting container of FIG. 1. FIG.
FIG. 10 is a cross-sectional view for explaining a primary blow molding process, showing a state before starting molding.
FIG. 11 is a cross-sectional view for explaining a primary blow molding process, showing a state after the molding is started.
FIGS. 12A and 12B are cross-sectional views for explaining a heat treatment process, in which A is a first heat treatment, B is a second heat treatment, and C is a state after the heat treatment is completed;
FIG. 13 is a cross-sectional view for explaining a secondary blow molding process, showing a state after the molding is completed.
FIG. 14 is a side view showing a final molded product.
FIG. 15 is an explanatory view showing a connection width (outside the scope of the present invention) between a foot portion of a container bottom portion and a bottom central valley portion.
[Explanation of symbols]
1 mouth and neck
2 shoulder
3 trunk
4 Bottom
5 bottom central valley
5a Bottom center
6 Tanibe
7 feet
8 Roots
9 Grounding part
10 narrow groove
11a, 11b Convex part
20 Preform 20
21 mouth
22 Torso
23 Blocking bottom
24 Lid fastening mechanism
25 Support ring
31 Core mold
32 Split mold
33 Bottom mold
34 Stretching rod
36 Secondary molded products
37 Bottom forming part
38 Bottom recess formation
39 recess
40 Bottom
41 Torso
42 Infrared radiator for bottom
43 Bottom shoulder
44 Infrared emitter
45 Heat shielding plate 45
46 Tertiary molded products
47 pieces
50 containers
51 split mold
52 Bottom mold

Claims (7)

In a self-supporting container provided with a bottom part composed of a mouth and neck part, a shoulder part, a trunk part, a plurality of trough parts and a foot part formed by biaxial stretch blow molding of resin, the foot part is a trough part at the center of the bottom part. A foot base connected to the base, a narrow groove extending radially from the center of the foot base and ending radially inward of the grounding portion of the foot , and sandwiching the thin groove between And a pair of convex portions protruding outward from the narrow groove portion, and the pair of convex portions and trough portions of the foot portion become a discontinuous curve at the position of the base portion of the foot portion. A self-standing container with excellent heat and pressure resistance characterized by being connected. 2. The self-supporting container according to claim 1, wherein the narrow groove portion is smoothly connected to the valley portion through a small-diameter curvature portion (R ₃ = 2 to 8 mm) at a center position of the foot base portion. The self-supporting container according to claim 1 or 2, wherein the foot base portion is separated into two foot base portions by a narrow groove portion. The self-standing container according to any one of claims 1 to 3 , wherein the pair of convex portions of the foot portion are formed substantially symmetrically with respect to the narrow groove portion. The groove width at the bottom of the narrow groove is 5 mm or less, and the vertical distance H ₁ between the bottom center and the starting end of the narrow groove located above the bottom central is in the range of 1 to 4 mm. The self-supporting container in any one of thru | or 4. The distance H _{2 in} the vertical direction between the bottom center and the start end of the narrow groove located above the bottom center after filling the container with the contents and heat sterilization is 0.5 mm or more. The self-supporting container according to any one of 1 to 5 . Filling the contents into the container, after carrying out heat sterilization, according to claim 6, wherein the vertical distance of H ₂ and the starting end of the fine groove is located above the bottom center and bottom center portion is 1mm or more Self-supporting container.

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