JP2004083890A - Polylactic acid foamed particle and molded product of the polylactic acid foamed particle - Google Patents
Polylactic acid foamed particle and molded product of the polylactic acid foamed particle Download PDFInfo
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- JP2004083890A JP2004083890A JP2003185453A JP2003185453A JP2004083890A JP 2004083890 A JP2004083890 A JP 2004083890A JP 2003185453 A JP2003185453 A JP 2003185453A JP 2003185453 A JP2003185453 A JP 2003185453A JP 2004083890 A JP2004083890 A JP 2004083890A
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- Prior art keywords
- bead
- polylactic acid
- particles
- foamed
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Links
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- 238000001864 heat-flux differential scanning calorimetry Methods 0.000 claims abstract description 21
- 239000004310 lactic acid Substances 0.000 claims abstract description 20
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は微生物分解性を有するポリ乳酸発泡粒子及び該発泡粒子成形体に関する、更に詳しくは、発泡粒子同士の融着性及び寸法安定性に優れ、密度ばらつきの小さい、均一な機械的物性を有するポリ乳酸発泡粒子成形体の製造に好適に供されるポリ乳酸発泡粒子及びポリ乳酸発泡粒子成形体に関する。
【０００２】
【従来の技術】
ポリスチレン、ポリエチレン、ポリプロピレン等の樹脂からなる発泡粒子成形体は包装用緩衝材、農産箱、魚箱、自動車部材、建築材料、土木材料等として幅広く使用されている。しかしながら、これらの発泡粒子成形体は使用後、自然環境下に放置された場合に、微生物により殆ど分解されないためごみ散乱による環境破壊の問題を引き起こす虞がある。
【０００３】
一方、微生物により分解される樹脂の研究もなされており、これまでに例えば外科用の縫合糸としてポリ乳酸からなる微生物分解性樹脂等が実用化され長年の実績をおさめている。また、近年、ポリ乳酸の原料である乳酸がとうもろこし等を原材料として発酵法によって大量且つ安価に製造できるようになってきている。
そこで、実用性、人体安全性、微生物分解性において実績をおさめているポリ乳酸からなる発泡体が望まれてきている。
【０００４】
ポリ乳酸からなる発泡体に関する先行技術としては、特表平５−５０８６６９号公報、特開平４−３０４２４４号公報、特開平５−１３９４３５号公報、特開平５−１４０３６１号公報、特開平９−２６３６５１号公報等の押出発泡体に関するもの、特開平５−１７０９６５号公報（特許文献１）、特開平５−１７０９６６号公報（特許文献２）、特開２０００−１３６２６１号公報（特許文献３）等の発泡粒子に関するものが挙げられる。
【０００５】
上記ポリ乳酸発泡体に関する先行技術において特に発泡粒子に関するものは、形状的な制約を比較的受けずに所望の形状の発泡体を得ることができ、軽量性、緩衝性、断熱性などの目的に応じた物性設計も容易であるため実用性のあるものとして特に有望である。
【０００６】
しかし、従来のポリ乳酸からなる発泡粒子成形体は発泡性の非発泡樹脂粒子を金型内に充填し熱風により該樹脂粒子を発泡させると同時に粒子同士を相互に融着したものであるため発泡粒子成形体の部分部分の密度ばらつきが大きく、発泡粒子同士の融着性、寸法安定性が不充分なものであり機械的物性に劣るものであった。
【０００７】
【特許文献１】
特開平５−１７０９６５号公報
【特許文献２】
特開平５−１７０９６６号公報
【特許文献３】
特開２０００−１３６２６１号公報
【０００８】
【発明が解決しようとする課題】
本発明は、発泡粒子の型内成形に好適なポリ乳酸発泡粒子及び発泡粒子同士の融着性、寸法安定性、外観、機械的物性に優れたポリ乳酸発泡粒子成形体を提供することをその課題とする。
【０００９】
【課題を解決するための手段】
上記課題を解決するために本発明者らは鋭意検討した結果、本発明を完成するに至った。
すなわち、本発明によれば、以下に示すポリ乳酸発泡粒子及び発泡粒子成形体が提供される。
（１）乳酸成分単位を５０モル％以上含むポリ乳酸からなる発泡粒子であって、該発泡粒子の熱流束示差走査熱量測定における吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）と発熱量（ΔＨｅｘｏ：Ｂｅａｄ）との差（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）が０Ｊ／ｇ以上３０Ｊ／ｇ未満であり、且つ該吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）が１５Ｊ／ｇ以上であることを特徴とするポリ乳酸発泡粒子。
（２）発泡粒子の熱流束示差走査熱量測定における吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）と発熱量（ΔＨｅｘｏ：Ｂｅａｄ）との差（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）が５Ｊ／ｇ以上１５Ｊ／ｇ未満であることを特徴とする前記（１）に記載のポリ乳酸発泡粒子。
（３）ポリ乳酸が結晶性ポリ乳酸と非結晶性ポリ乳酸との混合物であることを特徴とする前記（１）または（２）に記載のポリ乳酸発泡粒子。
（４）発泡粒子の見かけ密度が、０．０１５〜０．３ｇ／ｃｍ３であることを特徴とする前記（１）〜（３）のいずれかに記載のポリ乳酸発泡粒子。
（５）前記（１）〜（４）のいずれかに記載の発泡粒子を型内成形して得られる発泡粒子成形体であって、該発泡粒子成形体の曲げ強さ（Ａ：Ｎ／ｃｍ２）と該発泡粒子成形体の密度（Ｂ：ｇ／ｃｍ３）との比（Ａ／Ｂ）が２９４（Ｎ・ｃｍ／ｇ）以上であることを特徴とするポリ乳酸発泡粒子成形体。
（６）乳酸成分単位を５０モル％以上含むポリ乳酸からなる発泡粒子を型内成形して得られる発泡粒子成形体であって、該発泡粒子成形体の曲げ強さ（Ａ：Ｎ／ｃｍ２）と該発泡粒子成形体の密度（Ｂ：ｇ／ｃｍ３）との比（Ａ／Ｂ）が２９４（Ｎ・ｃｍ／ｇ）以上であることを特徴とするポリ乳酸発泡粒子成形体。
【００１０】
【発明の実施の形態】
本発明において、乳酸成分単位を５０モル％以上含むポリ乳酸からなる発泡粒子（以下、単に発泡粒子ともいう）は、前記ポリ乳酸から作製されている樹脂粒子を架橋させることなく発泡させることにより製造される無架橋のものである。前記ポリ乳酸には、例えば、（１）乳酸の重合体、（２）乳酸と他の脂肪族ヒドロキシカルボン酸とのコポリマー、（３）乳酸と脂肪族多価アルコールと脂肪族多価カルボン酸とのコポリマー、（４）乳酸と脂肪族多価カルボン酸とのコポリマー、（５）乳酸と脂肪族多価アルコールとのコポリマー、（６）前記（１）〜（５）の何れかの組み合わせによる混合物が包含される。尚、上記乳酸の具体例としては、Ｌ−乳酸、Ｄ−乳酸、ＤＬ−乳酸又はそれらの環状２量体であるＬ−ラクチド、Ｄ−ラクチド、ＤＬ−ラクチド又はそれらの混合物を挙げることができる。また、前記他の脂肪族ヒドロキシカルボン酸としては、グリコール酸、ヒドロキシ酪酸、ヒドロキシ吉草酸、ヒドロキシカプロン酸、ヒドロキシへプタン酸等が挙げられる。また、前記脂肪族多価アルコールとしては、エチレングリコール、１，４−ブタンジオール、１，６−ヘキサンジオール、１，４−シクロヘキサンジメタノール、ネオペンチルグリコール、デカメチレングリコール、グリセリン、トリメチロールプロパン、ペンタエリトリット等が挙げられる。また、前記脂肪族多価カルボン酸としては、コハク酸、アジピン酸、スベリン酸、セバシン酸、ドデカンジカルボン酸、無水コハク酸、無水アジピン酸、トリメシン酸、プロパントリカルボン酸、ピロメリット酸、無水ピロメリット酸等が挙げられる。
本発明にて用いるポリ乳酸は、上述したポリ乳酸の中で、下記熱流束示差走査熱量測定によって求められる吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）が１５Ｊ／ｇ以上、好ましくは２０Ｊ／ｇ以上、更に好ましくは２５Ｊ／ｇ以上のものである。尚、本発明にて用いるポリ乳酸の該吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）の上限は、特に限定されるものではないが概ね６０Ｊ／ｇである。そして、本発明にて用いる該吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）が１５Ｊ／ｇ以上のポリ乳酸としては、結晶性ポリ乳酸、或いは、結晶性ポリ乳酸と非結晶性ポリ乳酸との混合物が挙げられる。
【００１１】
上記ポリ乳酸の吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）は、ＪＩＳ Ｋ７１２２−１９８７に記載される熱流束示差走査熱量測定によって求められる値とする。但し、ポリ乳酸１〜４ｍｇを試験片とし、試験片の状態調節およびＤＳＣ曲線の測定は以下の手順にて行う。試験片をＤＳＣ装置の容器に入れ、２００℃まで加熱溶融させ、その温度に１０分間保った後、１１０℃まで２℃／分の冷却速度にて冷却し、その温度に１２０分間保った後、４０℃まで２℃／分の冷却速度にて冷却する熱処理後、再度、２℃／分の加熱速度にて吸熱ピーク終了時より約３０℃高い温度まで加熱溶融させる際にＤＳＣ曲線を得る。尚、ポリ乳酸の吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）は、図１に示すように、該ＤＳＣ曲線の吸熱ピークの低温側のベースラインから吸熱ピークが離れる点を点ａとし、吸熱ピークが高温側のベースラインへ戻る点を点ｂとして、点ａと点ｂとを結ぶ直線と、ＤＳＣ曲線に囲まれる部分の面積から求められる値とする。また、ベースラインはできるだけ直線になるように装置を調節することとし、どうしても図２に示すようにベースラインが湾曲してしまう場合は、吸熱ピークの低温側の湾曲したベースラインをその曲線の湾曲状態を維持して高温側へ延長する作図により明らかになる、該湾曲した低温側のベースラインから吸熱ピークが離れる点を点ａ、吸熱ピークの高温側の湾曲したベースラインをその曲線の湾曲状態を維持して低温側へ延長する作図により明らかになる、該湾曲した高温側ベースラインへ吸熱ピークが戻る点を点ｂとする。
なお、上記吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）の測定において、試験片の前記熱処理条件を採用する理由は、ポリ乳酸試験片の結晶化を極力進ませて、完全に結晶化した状態、或いは、それに近い状態に調整されたものとするためである。更に、ＤＳＣ曲線の測定条件として２℃／分の加熱速度を採用する理由は、上記吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）の測定において発熱ピークが現れる場合、発熱ピークと吸熱ピークとをなるべく分離し、正確な吸熱量（ΔＨｅｎｄｏ： Ｍａｔｅｒｉａｌ）を熱流束示差走査熱量測定にて求める際に、２℃／分の加熱速度が好適であるという発明者の知見に基づくものである。
【００１２】
また、本発明において上記ポリ乳酸には、本発明の目的、効果を阻害しない範囲において他の樹脂を混合することができる。ポリ乳酸と他の樹脂との混合樹脂中にはポリ乳酸が５０重量％以上、好ましくは７０重量％以上、更に好ましくは９０重量％以上含まれる。
尚、ポリ乳酸と混合できる他の樹脂としては、ポリエチレン系樹脂、ポリプロピレン系樹脂、ポリスチレン系樹脂、ポリエステル系樹脂等が挙げられ、中でも脂肪族エステル成分単位を少なくとも３５モル％含む生分解性脂肪族ポリエステル系樹脂が好ましい。この場合の脂肪族ポリエステル系樹脂には、上記ポリ乳酸以外のヒドロキシ酸重縮合物、ポリカプロラクトン等のラクトンの開環重合物、及びポリブチレンサクシネート，ポリブチレンアジペート，ポリブチレンサクシネートアジペート，ポリ（ブチレンアジペート／テレフタレート）等の脂肪族多価アルコールと脂肪族多価カルボン酸との重縮合物等が挙げられる。
【００１３】
上記ポリ乳酸の製造方法の具体例としては、例えば、乳酸又は乳酸と脂肪族ヒドロキシカルボン酸の混合物を原料として、直接脱水重縮合する方法（例えば、米国特許第５３１０８６５号に示されている製造方法）、乳酸の環状二量体（ラクチド）を重合する開環重合法（例えば、米国特許２７５８９８７号に開示されている製造方法）、乳酸と脂肪族ヒドロキシカルボン酸の環状２量体、例えば、ラクチドやグリコリドとε−カプロラクトンを、触媒の存在下、重合する開環重合法（例えば、米国特許４０５７５３７号に開示されている製造方法）、乳酸と脂肪族二価アルコールと脂肪族二塩基酸の混合物を、直接脱水重縮合する方法（例えば、米国特許第５４２８１２６号に開示されている製造方法）、脂肪族二価アルコールと脂肪族二塩基酸とのポリマーと乳酸重合体とを有機溶媒存在下に縮合する方法（例えば、欧州特許公報第０７１２８８０ Ａ２号に開示されている製造方法）、乳酸を触媒の存在下、脱水重縮合反応を行うことによりポリエステル重合体を製造するに際し、少なくとも一部の工程で、固相重合を行う方法、等を挙げることができるが、ポリ乳酸の製造方法は、特に限定されない。また、少量のグリセリンのような脂肪族多価アルコール、ブタンテトラカルボン酸のような脂肪族多塩基酸、多糖類等のような多価アルコール類を共存させて共重合体としても良い。
【００１４】
本発明の発泡粒子は、発泡粒子の熱流束示差走査熱量測定により求められる発熱量（ΔＨｅｘｏ：Ｂｅａｄ）と吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）との関係において、（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）が０Ｊ／ｇ以上３０Ｊ／ｇ未満であり、且つ吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）が１５Ｊ／ｇ以上のものである。即ち、本発明の発泡粒子は、発泡粒子の熱流束示差走査熱量測定により得られるＤＳＣ曲線において、吸熱ピークが存在し、そのピーク面積は１５Ｊ／ｇ以上の吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）に対応するものである。一方、発熱ピークは存在してもしなくても良い。発熱ピークが存在しない場合、ΔＨｅｘｏ：Ｂｅａｄは０Ｊ／ｇであり、発熱ピークが存在する場合、ΔＨｅｘｏ：Ｂｅａｄはその発熱ピーク面積から求められる値である。そして本発明では、（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）が０Ｊ／ｇ以上３０Ｊ／ｇ未満であることが重要である。
ここで、発熱量（ΔＨｅｘｏ：Ｂｅａｄ）とは、加熱速度２℃／分における熱流束示差走査熱量測定により試験片の結晶化が促進され、それに伴って放出される熱量を指し、発熱量（ΔＨｅｘｏ：Ｂｅａｄ）が大きいほど発泡粒子の結晶化が進んでいないことを意味する。また、吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）とは、加熱速度２℃／分における熱流束示差走査熱量測定により試験片の結晶が溶融する際の融解熱量を指し、吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）が大きい発泡粒子ほど、結晶化が進むことにより、該発泡粒子から得られる発泡粒子成形体の耐熱性が優れたものとなることを意味する。該吸熱量と該発熱量との差（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）は、熱流束示差走査熱量測定に使用する発泡粒子が既に有している結晶が溶融する際の融解熱量に相当し、該値が小さいほど発泡粒子の結晶化が進んでいないことを意味する。
（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）は、型内成形性がより良好なものとなる点から、好ましくは３〜２５Ｊ／ｇ、更に好ましくは５Ｊ／ｇ以上、１５Ｊ／ｇ未満である。（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）が３０Ｊ／ｇ以上の場合、発泡粒子を型内に充填して加熱し型内成形を行っても、発泡粒子相互の融着性が良好な成形体が得られないか、型内成形にて得られる発泡粒子成形体の収縮が大きなものとなり外観が悪いものとなる。なお、（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）は０Ｊ／ｇであってもかまわない。（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）の値が小さいほど発泡粒子の型内成形時の加熱温度を低くできるが、あまり低すぎると型内成形時の温度調整が難しく得られる発泡粒子成形体の収縮率が不均一となる虞がある。
本発明においては、（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）を前記範囲とすることで、発泡粒子は型内成形性に優れたものとなり、得られる発泡粒子成形体は、発泡粒子同士の融着性、寸法安定性、外観、機械的物性に優れたものとなる。
【００１５】
更に本発明では、発泡粒子の吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）が１５Ｊ／ｇ以上であることが耐熱性に優れる発泡粒子成形体を得るために少なくとも必要である。本発明の場合、吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）は、１５Ｊ／ｇ以上４０Ｊ／ｇ以下であることが好ましく、１５Ｊ／ｇ以上３０Ｊ／ｇ未満であることが更に好ましい。特に２０Ｊ／ｇ以上３０Ｊ／ｇ未満であることが発泡粒子の型内成形性の観点から好ましい。
該吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）が小さすぎると、発泡粒子の型内成形により得られる発泡粒子成形体の収縮率が大きくなり寸法安定性に劣ってしまい、該吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）が大きすぎると、発泡粒子相互の融着性が良好な成形体が得られない虞や、得られる発泡粒子成形体の収縮が大きなものとなる虞がある。
また、発泡粒子の示差走査熱量測定における発熱量（ΔＨｅｘｏ：Ｂｅａｄ）が３〜２５Ｊ／ｇ、更に８〜２３Ｊ／ｇ、特に１０〜２０Ｊ／ｇのものとなっていることが得られる発泡粒子の成形時における発泡粒子相互の融着性や最終的に得られる発泡粒子成形体の表面平滑性の点で特に優れたものとなるため好ましい。
【００１６】
尚、本明細書において発泡粒子の発熱量（ΔＨｅｘｏ：Ｂｅａｄ）および吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）は、ＪＩＳ Ｋ７１２２−１９８７に記載される熱流束示差走査熱量測定によって求められる値とする。但し、発泡粒子或いは発泡粒子から切出した発泡体片１〜４ｍｇを試験片とし、該試験片の状態調節およびＤＳＣ曲線の測定は以下の手順にて行う。試験片をＤＳＣ装置の容器に入れ、熱処理を行わず、２℃／分の加熱速度にて４０℃から２００℃まで昇温する際のＤＳＣ曲線を得る。尚、発泡粒子の発熱量（ΔＨｅｘｏ：Ｂｅａｄ）は該ＤＳＣ曲線の発熱ピークの低温側のベースラインから発熱ピークが離れる点を点ｃとし、発熱ピークが高温側のベースラインへ戻る点を点ｄとして、点ｃと点ｄとを結ぶ直線と、ＤＳＣ曲線に囲まれる部分の面積から求められる値とする。また、発泡粒子の吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）は、該ＤＳＣ曲線の吸熱ピークの低温側のベースラインから吸熱ピークが離れる点を点ｅとし、吸熱ピークが高温側のベースラインへ戻る点を点ｆとして、点ｅと点ｆとを結ぶ直線と、ＤＳＣ曲線に囲まれる部分の面積から求められる値とする。尚、該ＤＳＣ曲線におけるベースラインはできるだけ直線になるように装置を調節することとする。また、どうしてもベースラインが湾曲してしまう場合は、発熱ピークの低温側の湾曲したベースラインをその曲線の湾曲状態を維持して高温側へ延長する作図により明らかになる、該湾曲した低温側のベースラインから発熱ピークが離れる点を点ｃ、発熱ピークの高温側の湾曲したベースラインをその曲線の湾曲状態を維持して低温側へ延長する作図により明らかになる、該湾曲した高温側ベースラインへ発熱ピークが戻る点を点ｄとし、吸熱ピークの低温側の湾曲したベースラインをその曲線の湾曲状態を維持して高温側へ延長する作図により明らかになる、該湾曲した低温側のベースラインから吸熱ピークが離れる点を点ｅ、吸熱ピークの高温側の湾曲したベースラインをその曲線の湾曲状態を維持して低温側へ延長する作図により明らかになる、該湾曲した高温側ベースラインへ吸熱ピークが戻る点を点ｆとする。
【００１７】
例えば、図３に示すような場合には、上記の通り定められる点ｃと点ｄとを結ぶ直線とＤＳＣ曲線に囲まれる部分の面積から発泡粒子の発熱量（ΔＨｅｘｏ：Ｂｅａｄ）を求め、上記の通り定められる点ｅと点ｆとを結ぶ直線とＤＳＣ曲線に囲まれる部分の面積から発泡粒子の吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）を求める。また、発泡粒子の発熱ピークと吸熱ピークとが図４に示すように重なる場合には、上記のように点ｄと点ｅを定めることが困難である為、上記の通り定められる点ｃと点ｆとを結ぶ直線とＤＳＣ曲線との交点を点ｄ（点ｅ）と定めることにより、発泡粒子の発熱量（ΔＨｅｘｏ：Ｂｅａｄ）及び吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）を求める。また、発泡粒子の発熱ピーク及び／又は吸熱ピークが２つ以上現れる場合には、複数のピークの面積の合計から発泡粒子の発熱量（ΔＨｅｘｏ：Ｂｅａｄ）及び／又は吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）を求める。即ち、例えば図５に示すように、吸熱ピークの低温側に小さな発熱ピークが発生するような場合には、発泡粒子の発熱量（ΔＨｅｘｏ：Ｂｅａｄ）は、図５中の第１の発熱ピークの面積Ａと第２の発熱ピークの面積Ｂとの和から求められる。即ち、該面積Ａは第１の発熱ピークの低温側のベースラインから第１の発熱ピークが離れる点を点ｃとし、第１の発熱ピークが高温側のベースラインへ戻る点を点ｄとして、点ｃと点ｄとを結ぶ直線とＤＳＣ曲線に囲まれる部分の面積とする。そして、該面積Ｂは第２の発熱ピークの低温側のベースラインから第２の発熱ピークが離れる点を点ｇとし、吸熱ピークが高温側のベースラインへ戻る点を点ｆとして、点ｇと点ｆとを結ぶ直線とＤＳＣ曲線との交点を点ｅと定め、点ｇと点ｅとを結ぶ直線とＤＳＣ曲線に囲まれる部分の面積とする。一方、図５において、発泡粒子の吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）は点ｅと点ｆとを結ぶ直線とＤＳＣ曲線に囲まれる部分の面積から求められる値とする。
【００１８】
なお、上記発熱量（ΔＨｅｘｏ：Ｂｅａｄ）および吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）の測定において、ＤＳＣ曲線の測定条件として、２℃／分の加熱速度を採用する理由は、発熱ピークと吸熱ピークとをなるべく分離し、正確な吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）および（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）を熱流束示差走査熱量測定にて求める際に、２℃／分の加熱速度が好適であるという発明者の知見に基づくものである。
【００１９】
本発明において上記発泡粒子の吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）は、基本的には基材樹脂の結晶性および結晶化速度に依存する。したがって、本発明ではポリ乳酸として結晶性ポリ乳酸を含むものが使用される。即ち、（ｉ）結晶性のポリ乳酸のみからなるもの、（ｉｉ）結晶性ポリ乳酸と非結晶性ポリ乳酸とのポリ乳酸混合物からなるものが挙げられる。そして、（ΔＨｅｎｄｏ：Ｂｅａｄ）および（ΔＨｅｘｏ：Ｂｅａｄ）の調整の容易さの点で（ｉｉ）のポリ乳酸混合物を該ポリ乳酸として使用することが好ましい。また、（ｉｉ）のポリ乳酸混合物からなるものの中でも、該ポリ乳酸混合物に対して結晶性ポリ乳酸の割合が３５重量％以上、更に４５〜８０重量％となるように混合されていることが好ましい。結晶性ポリ乳酸の割合が少ない場合は得られる発泡粒子成形体の耐熱性が不十分となる虞があり、結晶性ポリ乳酸の割合が多い場合は、ポリ乳酸発泡粒子の結晶化が進んでいると発泡粒子成形時の発泡粒子相互の融着性が不十分となる虞がある。よって、該吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）の調整方法としては、▲１▼本発明にて特定される吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）となる結晶性ポリ乳酸を選択する方法、▲２▼結晶性の異なる２種以上の結晶性ポリ乳酸同士をブレンドして本発明にて特定される吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）とする方法、▲３▼１種又は２種以上の結晶性ポリ乳酸と、１種又は２種以上の非結晶性ポリ乳酸をブレンドして本発明にて特定される吸熱量（ΔＨｅｎｄｏ：Ｂｅａｄ）とする方法等が挙げられ、特に上記▲３▼の方法が好ましい。
【００２０】
尚、本明細書において結晶性ポリ乳酸とは、前述のポリ乳酸の吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）の測定手順により得られるＤＳＣ曲線において２Ｊ／ｇを超える吸熱ピークが現れるものとする。尚、該結晶性ポリ乳酸の吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）は通常２０〜６５Ｊ／ｇである。また、本明細書において非結晶性ポリ乳酸とは、前述のポリ乳酸の吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）の測定手順により得られるＤＳＣ曲線において２Ｊ／ｇ以下の吸熱ピークが現れるもの或いは吸熱ピークが現れないものである。
【００２１】
また、上記発泡粒子の発熱量（ΔＨｅｘｏ：Ｂｅａｄ）は発泡粒子を得るまでの熱履歴によって異なってくる。発熱量（ΔＨｅｘｏ：Ｂｅａｄ）は、発泡粒子を得るために使用される樹脂粒子作製時の冷却条件、該樹脂粒子の発泡剤の含浸条件、該樹脂粒子の発泡条件等により異なってくることから、各条件の制御で発熱量（ΔＨｅｘｏ：Ｂｅａｄ）を調整することができる。詳しくは、該樹脂粒子を急冷することにより発熱量（ΔＨｅｘｏ：Ｂｅａｄ）は大きくなり、該樹脂粒子へ発泡剤を含浸させる際の雰囲気温度を高くすること、該発泡粒子を加熱発泡させる際の加熱時間を長くすることにより発熱量（ΔＨｅｘｏ：Ｂｅａｄ）は小さくなる。これらの方法、更に必要に応じてその他の方法を組み合わせることにより発熱量（ΔＨｅｘｏ：Ｂｅａｄ）を調整できる。したがって、上記（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）は、用いるポリ乳酸の結晶性、結晶化速度及び樹脂粒子作製条件、該樹脂粒子への発泡剤含浸条件、該樹脂粒子の発泡条件により調整することができる。
【００２２】
本発明の発泡粒子を製造するには、以下に示す製造方法が好適に採用される。本発明の発泡粒子を得るには、先ず上記の通り、主成分が、結晶性ポリ乳酸を含むポリ乳酸から構成されている基材樹脂から樹脂粒子を作る。この樹脂粒子は、例えば、基材樹脂を押出機で該樹脂が十分溶融する温度以上に加熱して溶融混練した後、ストランド状に押出し、該ストランド状の押出物を水没させることにより急冷した後、適宜の長さに切断するか又はストランドを適宜長さに切断後または切断と同時に、急冷することによって得ることができる。その他、基材樹脂から樹脂粒子を製造する方法としては、基材樹脂を押出機で該樹脂が十分溶融する温度以上に加熱して溶融混練した後、板状または塊状に押出し、該押出物を冷却プレスにより冷却、或いは、該押出物を水没させることにより冷却した後、該冷却樹脂を破砕したり、格子状に破断すること等によっても得ることができる。尚、上記の樹脂粒子を作る際の冷却は、以降の工程にて得られる発泡粒子の（ΔＨｅｘｏ：Ｂｅａｄ）及び（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）の調整の容易さの点から水没させる方法等による急冷が好ましい。
【００２３】
基材樹脂から得られた樹脂粒子の１個当りの重量は、０．０５〜１０ｍｇ、好ましくは０．１〜４ｍｇにするのがよい。該粒子重量が前記範囲より小さくなると、その樹脂粒子の製造が困難になる。一方、該粒子重量が前記範囲より大きくなると、発泡剤の均一な含浸が難しくなり得られる発泡粒子の中心部の密度が大きなものとなる虞がある。また該樹脂粒子の形状は特に制約されず、円柱状の他、球状、角柱状等の各種の形状とすることができる。
基材樹脂を上記の通り押出機で溶融混練しストランド状等に押出して樹脂粒子を得る工程において、基材樹脂を予め乾燥させておくことが基材樹脂の加水分解による劣化を抑制するうえで好ましい。また、樹脂粒子を得る工程において、樹脂の加水分解による劣化を抑制するために、ベント口付き押出機を使用して、真空吸引して基材樹脂から水分を除去する方法も採用できる。
【００２４】
前記基材樹脂は、例えば、黒、灰色、茶色、青色、緑色等の着色顔料又は染料を添加して着色したものであってもよい。着色した基材樹脂より得られた着色樹脂粒子を用いれば、着色された発泡粒子及び発泡粒子成形体を得ることができる。
着色剤としては、有機系、無機系の顔料、染料などが挙げられる。このような、顔料及び染料としては、従来公知の各種のものを用いることができる。
【００２５】
また、基材樹脂には、気泡調整剤として、例えばタルク、炭酸カルシウム、ホウ砂、ほう酸亜鉛、水酸化アルミニウム等の無機物をあらかじめ添加することができる。基材樹脂に着色顔料、染料又は無機物等の添加剤を添加する場合は、添加剤をそのまま基材樹脂に練り込むこともできるが、通常は分散性等を考慮して添加剤のマスターバッチを作り、それと基材樹脂とを混練することが好ましい。
【００２６】
着色顔料又は染料の添加量は着色の色によっても異なるが、通常、基材樹脂１００重量部に対して０．００１〜５重量部とするのが好ましい。また、無機物の添加量は、基材樹脂１００重量部に対して０．００１〜５重量部、更に０．０２〜１重量部とすることが好ましい。無機物を基材樹脂に添加することにより、得られる発泡粒子の発泡倍率の向上効果を得ることができる。
【００２７】
また、本発明では、難燃剤、帯電防止剤、耐候剤等の添加剤の基材樹脂への混合も可能である。尚、製品が使用後に廃棄されることを想定すると、顔料及び気泡調整剤等の添加剤の高濃度添加は好ましくない。
【００２８】
また、得られた樹脂粒子は高温、高湿条件下を避けて加水分解が進行しないような環境下で保存することが好ましい。
【００２９】
次に、樹脂粒子に発泡剤を含浸させる。本発明では、上記発泡粒子を得るに際して用いられる発泡剤としては、従来公知のもの、例えば、プロパン、ブタン、ペンタン、ヘキサン、１，１，１，２−テトラフロロエタン、１−クロロ−１，１−ジフロロエタン、１，１−ジフロロエタン等の有機系物理発泡剤や、窒素、二酸化炭素、アルゴン、空気等の無機系物理発泡剤が挙げられるが、なかでもオゾン層の破壊がなく且つ安価な無機ガス系発泡剤が好ましく、特に窒素、空気、二酸化炭素が好ましい。本発明においては、ポリ乳酸に対する含浸性に優れ少ない発泡剤の使用量で低い見かけ密度の発泡粒子が得られる点から二酸化炭素が最も好ましい。
【００３０】
なお、本発明において上記の物理発泡剤の使用が好ましいが、樹脂粒子を押出機を使用して造粒する際に化学発泡剤を添加することにより、化学発泡剤を使用して発泡性樹脂粒子を形成することもできる。
【００３１】
発泡剤として二酸化炭素を使用して、該発泡剤を樹脂粒子に含浸させて発泡性粒子とする方法について詳述する。
この場合の樹脂粒子に二酸化炭素を含浸させる方法としては、密閉容器内に樹脂粒子を入れ、更に該容器内に二酸化炭素を圧入して、温度調整された該容器内にて樹脂粒子内に二酸化炭素を含浸させて発泡性粒子を得る方法が採用できる。また、他の方法として、密閉容器内に水などの分散媒と共に樹脂粒子を入れ、更に該容器内に二酸化炭素を圧入して、その内容物を温度調整しつつ攪拌して、樹脂粒子内に二酸化炭素を含浸させる方法等を採用することもできる。
【００３２】
これらの方法において樹脂粒子に対する二酸化炭素の含浸は、樹脂粒子が入れられている密閉容器内に二酸化炭素を容器内が通常、０．５〜１０ＭＰａ（Ｇ）の圧力範囲になるように圧入することにより実施される。また、発泡剤の含浸温度は、好ましくは５〜６０℃、更に好ましくは５〜４０℃である。尚、該含浸温度は密閉容器内に分散媒を使用せず樹脂粒子を入れて二酸化炭素を含浸させる場合は、樹脂粒子雰囲気の気体の温度であり、密閉容器内に分散媒と共に樹脂粒子を入れて二酸化炭素を含浸させる場合は、該分散媒の温度である。また、発泡剤の含浸時間は、好ましくは１０分間〜２４時間、更に好ましくは２０分間〜１２時間である。
【００３３】
特に、発泡剤に二酸化炭素を使用する場合においては、その二酸化炭素の樹脂粒子中への含浸量は、通常、２．５〜３０重量％、好ましくは３〜２０重量％となるように実施することが好ましい。含浸量が少なすぎる場合は、十分に樹脂粒子を発泡させられない虞があり、一方、含浸量が多すぎる場合は、二酸化炭素の含浸により樹脂粒子の結晶化が進行し易くなるため、得られた発泡粒子の結晶化が進み過ぎていると該発泡粒子の型内成形時の膨張性や融着性が不十分となる虞がある。
【００３４】
目標とする二酸化炭素含浸量がＸ（重量％）の場合の発泡剤の含浸温度は、（−２．５Ｘ＋５５）（℃）以下の温度とすることが更に好ましい。（−２．５Ｘ＋５５）（℃）を超えると、特に結晶性の高いポリ乳酸では極度な結晶化の進行により樹脂粒子の発泡性が低下する可能性や、得られた発泡粒子を型内にて加熱成形する際に発泡粒子の膨張性、発泡粒子相互の融着性が低下する虞がある。
【００３５】
本明細書において樹脂粒子中への物理発泡剤の含浸量（重量％）は次式によって求められる。
【数１】
物理発泡剤の含浸量（重量％）＝｛樹脂粒子に含浸した物理発泡剤の重量
（ｇ）×１００｝／｛物理発泡剤含浸前の樹脂粒子の重量（ｇ）＋樹脂粒子に
含浸した物理発泡剤の重量（ｇ）｝
上式における樹脂粒子に含浸した物理発泡剤の重量は物理発泡剤含浸前後の樹脂粒子の重量差から求められ、樹脂粒子の重量測定は０．０００１ｇの位まで計測することとする。
【００３６】
上記の通り得られた発泡性粒子は、発泡粒子成形体用原料として用いられる。発泡性粒子を用いて発泡粒子成形体とするには、該発泡性粒子を加熱して発泡粒子とした後、この発泡粒子を型内に充填し、加熱し、融着させればよい。
【００３７】
発泡性粒子を発泡させる方法としては、その樹脂粒子を加熱軟化させて発泡させる方法が採用できる。即ち、二酸化炭素等の発泡剤が含浸している発泡性粒子を加熱し、これを発泡させる。発泡させるための加熱媒体としては、水蒸気、加熱温度調整した空気や窒素等が挙げられるが、好ましくは空気と水蒸気との混合ガスが用いられる。発泡性粒子を加熱し発泡させる方法としては、密閉容器内に発泡性粒子を充填し加熱媒体を導入して発泡させる従来公知の方法が採用できる。尚、密閉容器にはわずかに内部の加熱媒体を排気させる開孔弁が備わっていることが、密閉容器内の雰囲気温度を容易に一定に保つことができることから好ましい。
【００３８】
発泡剤が含浸している樹脂粒子を加熱する際の雰囲気温度、すなわち発泡温度は、通常、（ガラス転移温度−３０℃）〜（ガラス転移温度＋６０℃）、好ましくは（ガラス転移温度−１０℃）〜（ガラス転移温度＋４０℃）である。尚、上記ガラス転移温度は樹脂粒子を構成しているポリ乳酸のガラス転移温度である。発泡温度が前記範囲より低いと、十分な発泡が起こり難く、また前記範囲より高いと発泡粒子の独立気泡率が低下してしまい良好な成形性を示す発泡粒子が得られ難い。
【００３９】
尚、本明細書においてガラス転移温度の測定はＪＩＳ Ｋ７１２１−１９８７により熱流束示差走査熱量測定にて加熱速度１０℃／分の条件で得られるＤＳＣ曲線の中間点ガラス転移温度として求められる値である。尚、ガラス転移温度を求めるための試験片はＪＩＳ Ｋ７１２１−１９８７の３．試験片の状態調節（３）記載の『一定の熱処理を行った後、ガラス転移温度を測定する場合』に基づいて状態調整を行ったものを試験片とする。
【００４０】
尚、得られた発泡粒子は高温、高湿条件下を避けて加水分解しないような条件下で保存することが好ましい。
【００４１】
本発明の発泡粒子において、その見かけ密度は、０．０１５〜０．３ｇ／ｃｍ３、更に０．０１５〜０．２ｇ／ｃｍ３、特に０．０１５〜０．０８ｇ／ｃｍ３であることが好ましい。
見かけ密度が前記範囲より大きい場合は、発泡粒子の密度のばらつきが大きくなり易く、型内にて加熱成形の際の発泡粒子の膨張性、融着性のばらつきに繋がり、得られる発泡粒子成形体の物性低下の虞がある。一方、見かけ密度が前記範囲より小さい場合、発泡倍率が高いために、収縮率が大きな発泡粒子成形体となる虞れがある。
【００４２】
本明細書において発泡粒子の見かけ密度は、２３℃の水の入ったメスシリンダーを用意し、該メスシリンダーに相対湿度５０％、２３℃、１ａｔｍの条件にて２日放置した５００個以上の発泡粒子（発泡粒子群の重量Ｗ１）を金網などを使用して沈めて、水位上昇分より読みとられる発泡粒子群の容積Ｖ１（ｃｍ３）にてメスシリンダーに入れた発泡粒子群の重量Ｗ１（ｇ）を割り算することにより求める（Ｗ１／Ｖ１）。
【００４３】
本発明の発泡粒子の平均気泡径は、１０〜８００μｍであり、好ましくは３０〜５００μｍである。該気泡径が前記範囲より小さいと、型内成形時において発泡粒子を構成する気泡の膜強度が弱すぎるために破泡等が生じ、養生回復性の悪い発泡粒子成形体となる虞がある。また、該気泡径が前記範囲より大きいと型内成形時において該膜強度が強すぎるために、十分な膨張が生じず、表面平滑性の劣った発泡粒子成形体となってしまう虞がある。
【００４４】
本明細書において、発泡粒子の平均気泡径は、発泡粒子を略二分割し、その発泡粒子断面に存在する全ての気泡の最大径を求め、この操作を１０個以上の発泡粒子について行ない、求められた該最大径の算術平均値をもって平均気泡径とする。
【００４５】
本発明の発泡粒子成形体は、該発泡粒子成形体の曲げ強さ（Ａ：Ｎ／ｃｍ２）と該発泡粒子成形体の密度（Ｂ：ｇ／ｃｍ３）との比（Ａ／Ｂ）が２９４（Ｎ・ｃｍ／ｇ）以上のものであり、好ましくは４９０（Ｎ・ｃｍ／ｇ）以上、更に好ましくは６８６（Ｎ・ｃｍ／ｇ）以上のものである。該発泡粒子成形体は、上記発泡粒子を型内成形することにより得ることができる。
【００４６】
上記（Ａ／Ｂ）の値を満足する本発明の発泡粒子成形体は、発泡粒子相互の融着性が良好なものであり、（Ａ／Ｂ）の値が大きいほど発泡粒子相互の融着力が高いものとなる。尚、上記（Ａ／Ｂ）の値の上限は発泡粒子成形体の密度にもよるが概ね１４７０（Ｎ・ｃｍ／ｇ）である。そして、上記（Ａ／Ｂ）の値を満足する発泡粒子成形体を得るための方法としては、本発明の前記発泡粒子を型内に充填して加熱成形する方法が例示される。
【００４７】
本明細書において、発泡粒子成形体の曲げ強さＡは、試験片の寸法が長さ１５０ｍｍ、幅２５ｍｍ、高さ１０ｍｍのもので、試験片の幅２５ｍｍ、長さ１５０ｍｍの片面側を気泡断面が露出したカット面とし、他方の面には成形スキンを有する試験片を用意して、該試験片の成形スキンを有する面を下面としてＪＩＳ Ｋ７２２１−１９８４に準拠して測定される最大の曲げ強さである。
【００４８】
また、該発泡粒子成形体の熱流束示差走査熱量測定における吸熱量（ΔＨｅｎｄｏ：Ｍｏｌｄ）と発熱量（ΔＨｅｘｏ：Ｍｏｌｄ）との差（ΔＨｅｎｄｏ：Ｍｏｌｄ−ΔＨｅｘｏ：Ｍｏｌｄ）が１５Ｊ／ｇ以上、更に２０Ｊ／ｇ以上、特に２５Ｊ／ｇ以上であることが耐熱性の点から好ましい。尚、（ΔＨｅｎｄｏ：Ｍｏｌｄ−ΔＨｅｘｏ：Ｍｏｌｄ）の上限は概ね６０Ｊ／ｇである。
【００４９】
上記発泡粒子成形体の（ΔＨｅｎｄｏ：Ｍｏｌｄ−ΔＨｅｘｏ：Ｍｏｌｄ）の調整方法としては、型内成形後、該成形体を構成するポリ乳酸のガラス転移温度を基準として、ガラス転移温度以上で、且つ発泡粒子成形体が変形しない温度以下、好ましくは（ガラス転移温度＋５℃）〜（ガラス転移温度＋６０℃）、更に好ましくは（ガラス転移温度＋５℃）〜（ガラス転移温度＋３０℃）の温度で保持することにより（ΔＨｅｎｄｏ：Ｍｏｌｄ−ΔＨｅｘｏ：Ｍｏｌｄ）を大きくすることができる。尚、上記ガラス転移温度は発泡粒子成形体を構成しているポリ乳酸のガラス転移温度である。また、上記温度範囲にて発泡粒子成形体を保持する際の保持時間は、好ましくは５〜１５００分、更に好ましくは、６０〜１０００分である。尚、上記発泡粒子成形体の上記保持工程は、発泡粒子の型内成形に連続して金型内にて行なわれても、型内成形後、金型から取り出して発泡粒子成形体の養生室中にて行われても良い。
【００５０】
本明細書において発泡粒子成形体の熱流束示差走査熱量測定における発熱量（ΔＨｅｘｏ：Ｍｏｌｄ）と吸熱量（ΔＨｅｎｄｏ：Ｍｏｌｄ）は、ＪＩＳ Ｋ７１２２−１９８７に準拠して測定され、発泡粒子成形体から切り出した１〜４ｍｇの試験片を使用する以外は、前述した発泡粒子の（ΔＨｅｘｏ：Ｂｅａｄ）と（ΔＨｅｎｄｏ：Ｂｅａｄ）の測定方法と同様にして求められる。
【００５１】
発泡粒子成形体を製造するための発泡粒子を型内に充填して加熱する型内成形方法において、発泡粒子を型内に充填した後に、スチーム、熱風等の加熱媒体により該発泡粒子を加熱して成形を行うことが好ましい。尚、加熱媒体の温度は発泡粒子の表面が溶融する温度であればよい。この加熱成形により発泡粒子は相互に融着し、一体となった発泡成形体を与える。この場合の成形型としては慣用の金型や特開２０００−１５７０８号公報に記載の連続成形装置に使用されているスチールベルトが用いられる。
【００５２】
発泡粒子成形体を製造する場合、空気、窒素、二酸化炭素等の無機ガス、または、ブタン等の有機ガスが圧入された加圧状態の容器内にて発泡粒子を保持することにより、型内に充填する発泡粒子の内部圧力を予め高めておくことが好ましい。内部圧力が高められた発泡粒子を成形用発泡粒子として用いることにより、発泡粒子の成形時の発泡性、融着性や発泡粒子成形体の回復性が向上する。内部圧力が高められた発泡粒子内の気体量は、好ましくは０．３〜４ｍｏｌ／（１０００ｇ発泡粒子）、更に好ましくは０．７〜４ｍｏｌ／（１０００ｇ発泡粒子）の範囲内で調整されることが好ましい。
尚、本明細書において、１０００ｇの発泡粒子内の気体量（ｍｏｌ／１０００ｇ発泡粒子）は以下のように求められる。
【００５３】
【数２】
発泡粒子内の気体量（ｍｏｌ／１０００ｇ発泡粒子）
＝ ｛気体増加量（ｇ）×１０００｝／｛気体の分子量（ｇ／ｍｏｌ）
×発泡粒子重量（ｇ）｝
【００５４】
前記式中の気体増加量（ｇ）は次のように求める。
成形型に充填される、内部圧力が高められた発泡粒子を５００個以上取り出して６０秒以内に相対湿度５０％、２３℃の大気圧下の恒温恒湿室に移動し、その恒温恒湿室内の秤に乗せ、該発泡粒子を取り出して１２０秒後の重量を読み取る。このときの重量をＱ（ｇ）とする。次に、該発泡粒子を相対湿度５０％、２３℃の大気圧下の同恒温恒湿室内にて２４０時間放置する。発泡粒子内の高い圧力の気体は時間の経過とともに気泡膜を透過して外部に抜け出すため発泡粒子の重量はそれに伴って減少し、２４０時間後では平衡に達しているため実質的にその重量は安定している。上記２４０時間後の該発泡粒子の重量を同恒温恒湿室内にて測定し、このときの重量をＳ（ｇ）とする。上記のいずれの重量も０．０００１ｇまで読み取るものとする。この測定で得られたＱ（ｇ）とＳ（ｇ）の差を前記式中の気体増加量（ｇ）とする。また、前記式中の発泡粒子重量は２４０時間後の該発泡粒子の重量Ｓ（ｇ）とする。
【００５５】
本発明の発泡粒子及び発泡粒子成形体は、以下の方法により測定されるゲル分率が、２％以下（０％も含む）であり、好ましくは０％である。このことは、発泡粒子及び発泡粒子成形体が無架橋のものであることを意味する。
ゲル分率の測定は、次のように測定される。１５０ｍｌのフラスコに、発泡粒子又は発泡粒子成形体片約１ｇを精秤した重量Ｗ２の試験片と１００ｍｌのクロロホルムを入れ、約６１℃の沸騰クロロホルムを１０時間加熱還流させることにより試験片を加熱処理する。得られた加熱処理物を２００メッシュの金網を有する吸引濾過装置を用いて濾過処理する。得られた金網上の濾過処理物を８０℃のオーブン中で３０〜４０トールの条件下にて８時間乾燥する。この際に得られた乾燥物重量Ｗ３を測定する。この重量Ｗ３の試験片重量Ｗ２に対する重量百分率［（Ｗ３／Ｗ２）×１００］（％）をゲル分率とする。
【００５６】
発泡粒子成形体の形状は特に制約されず、その形状は、容器状、板状、筒状、柱状、シート状、ブロック状等の各種の形状が例示される。また、寸法安定性、表面平滑性において優れたものである。
発泡粒子成形体の密度（ｇ／ｃｍ３）は、好ましくは０．０１〜０．２ｇ／ｃｍ３、更に好ましくは０．０１５〜０．１ｇ／ｃｍ３のものであり、発泡粒子成形体の外形寸法から求められる体積ＶＭ（ｃｍ３）にて発泡粒子成形体重量ＷＭ（ｇ）を割り算する（ＷＭ／ＶＭ）ことにより求められる。
【００５７】
【発明の効果】
本発明の発泡粒子は、発泡粒子の（ΔＨｅｎｄｏ：Ｂｅａｄ−ΔＨｅｘｏ：Ｂｅａｄ）及び（ΔＨｅｎｄｏ：Ｂｅａｄ）が特定の値を有するものであることによって、型内成形する際の発泡粒子相互の融着性、二次発泡性に優れ、型寸法に対する寸法変化の小さい良好な発泡粒子成形体を得ることができるものである。
また、本発明の発泡粒子成形体は、密度ばらつきが小さく、寸法安定性、緩衝性、表面平滑性及び機械的強度に優れ、緩衝材、包装資材等として好適に使用されると共に、生分解性を有しているためその後の廃棄処分が容易となるなどその産業的意義は多大である。
【００５８】
【実施例】
次に、本発明を実施例により更に詳しく説明する。
【００５９】
実施例１〜６、比較例１〜４
吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）が３７Ｊ／ｇである結晶性ポリ乳酸（島津製作所（株）製、ラクティ９０３０）と吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）が０Ｊ／ｇである非結晶性ポリ乳酸（島津製作所（株）製、ラクティ９８００）とを表１に示したブレンド比（重量比）でブレンドし、このブレンド物とタルクとを押出機にて溶融混練した後、ストランド状に押出し、次いでこのストランドを約２５℃の水中で急冷固化させた後に切断して、直径約１．３ｍｍ、長さ約１．９ｍｍ、１個当たり約３ｍｇの円柱状の樹脂粒子を得た。なお、タルクは樹脂粒子中への添加量が２０００ｐｐｍとなるように添加した。
【００６０】
次に、５Ｌの内容積を有する密閉容器内を表１に示す含浸温度に調整して上記の樹脂粒子１０００ｇを該容器中へ投入した。二酸化炭素（ＣＯ２）を圧力調整弁を介して密閉容器内に圧入し、密閉容器内のＣＯ２圧力が表１に示す含浸圧力になるように調整し、表１に示す含浸条件にて保持した。次に、密閉容器内の圧力を大気圧とした後、二酸化炭素が含浸した発泡性樹脂粒子を取出した。得られた発泡性樹脂粒子の二酸化炭素含浸量を表１に示す。
【００６１】
この二酸化炭素が含浸した樹脂粒子を、圧力調整弁の付いた密閉容器内に充填した後、表１に示す発泡温度の水蒸気を５秒間導入して加熱し、樹脂粒子を発泡させて無架橋の発泡粒子を得た。この発泡粒子の性状を表１に示す。
【００６２】
得られた発泡粒子を密閉容器内に充填し、二酸化炭素にて加圧して発泡粒子の内部圧力を高める操作を行い、発泡粒子１０００ｇ当りの発泡粒子内のＣＯ２量を表２に示す値とした後、成形空間部の形状が縦２００ｍｍ、横２５０ｍｍ、厚み１２ｍｍの金型に表２に示す圧縮率［（圧縮前の発泡粒子の嵩体積（ｃｍ３）−型締後の金型成形空間部の内容積（ｃｍ３））×１００／型締後の金型成形空間部の内容積（ｃｍ３）］［％］にて発泡粒子を充填し、表２に示す成形温度の水蒸気で加熱成形した。得られた成形体を温度３０℃、相対湿度１０％の条件で２４時間養生した。養生後の発泡粒子成形体の寸法安定性、融着性等を評価してその結果を表２に示す。
【００６３】
尚、上記した圧縮前の発泡粒子の嵩体積は、空のメスシリンダーに発泡粒子群を入れた際にメスシリンダーの目盛りが示す発泡粒子群の体積Ｖ２（ｃｍ３）と該粒子群の重量Ｗ４（ｇ）とから求められる発泡粒子の嵩密度（Ｗ４／Ｖ２）にて、金型内に充填された発泡粒子群の重量（ｇ）を割り算することにより求められる。
【００６４】
【表１】
【表２】
実施例７
吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）が４９Ｊ／ｇである結晶性ポリ乳酸（三井化学（株）製、レイシアＨ−１００、）と吸熱量（ΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌ）が０Ｊ／ｇである非結晶性ポリ乳酸（三井化学（株）製、レイシアＨ−２８０）とを表３に示したブレンド比（重量％）でブレンドし、このブレンド物にタルク配合量が２０００ｐｐｍとなるように添加し、これらを押出機にて溶融混練した後、ストランド状に押出した。次いでこのストランドを約２５℃の水中で急冷固化させた後に切断して、樹脂粒子の長さ（Ｌ）と直径（Ｄ）との比（Ｌ／Ｄ）が１．５、１個当たり約３ｍｇの円柱状の樹脂粒子を得た。
【００６７】
得られた樹脂粒子から、ＣＯ２含浸条件を表３に示す通りとした以外は、実施例１と同様の操作にて発泡性樹脂粒子を得た。
次に、発泡性樹脂粒子を、圧力調整弁の付いた密閉容器内に充填した後、０．０５ＭＰａ（Ｇ）（６５℃）の水蒸気を５秒間導入して加熱し、樹脂粒子を発泡させて無架橋の発泡粒子を得た。この発泡粒子の性状を表３に示す。
次に、得られた発泡粒子を密閉容器内に充填し、二酸化炭素にて加圧して発泡粒子の内部圧力を高める操作を行い、発泡粒子１０００ｇ当りの発泡粒子内のＣＯ２量を１．３ｍｏｌ／１０００ｇとした後、成形空間部の形状が縦２００ｍｍ、横２５０ｍｍ、厚み１０ｍｍの金型に圧縮率５０％にて発泡粒子を充填し、１２５℃（０．１２７ＭＰａ（Ｇ））の水蒸気で加熱成形した。得られた発泡粒子成形体を金型から取り出して温度３０℃、相対湿度１０％の条件で１２時間養生した。養生後の発泡粒子成形体の寸法安定性、融着性等を評価してその結果を表４に示す。
【００６８】
実施例８
容量５Ｌの密閉容器内に、実施例７と同様の方法で得られた樹脂粒子１０００ｇと、分散媒としての水３Ｌとを入れ、次に二酸化炭素（ＣＯ２）を圧力調整弁を介して密閉容器内に圧入し、密閉容器内のＣＯ２圧力が表３に示す圧力になるように調整し分散媒を攪拌しながら、表３に示す含浸条件にて保持した。次に、密閉容器内の圧力を大気圧とした後、分散媒と共に二酸化炭素が含浸した発泡性樹脂粒子を取出した。
次に、発泡性樹脂粒子を、圧力調整弁の付いた密閉容器内に充填した後、０．０５ＭＰａ（Ｇ）（６５℃）の水蒸気を５秒間導入して加熱し、樹脂粒子を発泡させて無架橋の発泡粒子を得た。この発泡粒子の性状を表３に示す。
次に、得られた発泡粒子を実施例７と同様の条件にて発泡粒子の内部圧力を高める操作を行った後に、実施例７と同様の条件にて型内成形して発泡粒子成形体を得た。得られた発泡粒子成形体を金型から取り出して温度３０℃、相対湿度１０％の条件で１２時間養生した。養生後の発泡粒子成形体の寸法安定性、融着性等を評価してその結果を表４に示す。
【００６９】
【表３】
【表４】
尚、表１〜４に示した物性等の測定方法または評価方法は以下の通りである。
（独立気泡率）
発泡粒子の独立気泡率は、ＡＳＴＭ−Ｄ２８５６−７０の手順Ｃに従って、東芝ベックマン株式会社の空気比較式比重計９３０型を使用して測定された発泡粒子サンプルの真の体積Ｖｘを用い、次式により独立気泡率Ｓ（％）を計算した。尚、上記発泡粒子サンプルの真の体積Ｖｘの測定は、発泡粒子を空のメスシリンダーに入れた際にメスシリンダーの目盛りが示す容積が１２．５ｃｍ３の容量の発泡粒子をサンプルとしてサンプルカップ内に収容して測定する。
【００７２】
【数３】
Ｓ（％）＝（Ｖｘ−Ｗ／ρ）×１００／（Ｖａ−Ｗ／ρ）
Ｖｘ：上記方法で測定された発泡粒子サンプルの真の体積（ｃｍ３）であり、発泡粒子サンプルを構成する樹脂の容積と、発泡粒子サンプル内の独立気泡部分の気泡全容積との和に相当する。
Ｖａ：測定に使用された発泡粒子サンプルを水の入ったメスシリンダーに沈めた際の水位上昇分から求められる見かけ上の発泡粒子サンプルの体積（ｃｍ３）。
Ｗ：測定に使用された発泡粒子サンプルの全重量（ｇ）。
ρ：発泡粒子サンプルを構成する樹脂の密度（ｇ／ｃｍ３）。
【００７３】
（融着性）
成形体から縦１００ｍｍ、横３０ｍｍ、厚さ１０ｍｍの試験片を切り出し、該試験片の縦方向両端部を持ち曲げ破断させて、破断面において材料破壊した発泡粒子の個数（ｂ）と破断面に存在する発泡粒子の個数（ｎ）との比（ｂ／ｎ）を求め以下の基準にて評価した。
◎：ｂ／ｎの値が０．５以上
○：ｂ／ｎの値が０．２以上から０．５未満
△：ｂ／ｎの値が０を超え０．２未満
×：ｂ／ｎの値が０
【００７４】
（寸法安定性）
横の長さ２５０ｍｍの金型寸法と金型成形後３０℃で２４時間養生した該金型寸法に対応する発泡粒子成形体の長さ（Ｘ）とを基に下記式により収縮率を算出し、以下の基準にて評価した。
【００７５】
【数４】
収縮率（％）＝［（２５０−Ｘ）／２５０］×１００
但し、Ｘは平面視、縦約２００ｍｍ、横約２５０ｍｍの成形体における縦方向の長さを２等分する横方向の成形体の長さ（ｍｍ）である。
○：収縮率が５％以下
×：収縮率が５％超
【００７６】
（外観）
発泡粒子成形体の外観を目視により下記の基準にて評価した。
○：表面平滑性、金型形状再現性共に優れる。
×：成形体表面の発泡粒子間に多数の凹凸（ボイド）が存在している。
【００７７】
（耐熱性）
実施例及び比較例で得られた発泡粒子成形体から試験片（縦１５０ｍｍ、横１５０ｍｍ、厚み１０ｍｍ）を切り取り、ＪＩＳ Ｋ６７６７−１９７６の５．７加熱寸法変化に準拠し、試験片を下記試験温度のオーブン中で２２時間加熱して寸法変化率を下記式により算出し、以下の基準にて評価した。
【００７８】
【数５】
寸法変化率（％）＝［（Ｙ−１５０）／１５０］×１００
但し、Ｙは、試験片の中央に縦方向および横方向にそれぞれ互いに平行に３本、合計６本の長さ１００ｍｍの直線を５０ｍｍ間隔になるように記入した（この操作により、試験片には一辺が１００ｍｍの正方形が４分割された図が描かれる）試験片を使用し、上記の加熱試験を行った後の該６本の線の長さの平均値（ｍｍ）である。
◎：試験温度８０℃における寸法変化率が±２％未満
○：試験温度６０℃における寸法変化率が±２％未満
△：試験温度６０℃における寸法変化率が±２％以上、±５％未満
×：試験温度６０℃における寸法変化率が±５％以上
【００７９】
（ポリ乳酸、ポリ乳酸発泡粒子およびポリ乳酸発泡粒子成形体の吸熱量、発熱量の測定）
測定装置は株式会社島津製作所製商品名「ＤＳＣ―５０」を用い、解析ソフトは「島津熱分析ワークステーションＴＡ−６０ＷＳ用部分面積解析プログラムｖｅｒｓｉｏｎ１．５２」を用いた。
【図面の簡単な説明】
【図１】熱流束示差走査熱量測定により求められるポリ乳酸のΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌを示すＤＳＣ曲線の説明図。
【図２】熱流束示差走査熱量測定により求められるポリ乳酸のΔＨｅｎｄｏ：Ｍａｔｅｒｉａｌを示すＤＳＣ曲線の他の説明図。
【図３】熱流束示差走査熱量測定により求められる発泡粒子のΔＨｅｘｏ：Ｂｅａｄ及びΔＨｅｎｄｏ：Ｂｅａｄを示すＤＳＣ曲線の説明図。
【図４】熱流束示差走査熱量測定により求められる発泡粒子のΔＨｅｘｏ：Ｂｅａｄ及びΔＨｅｎｄｏ：Ｂｅａｄを示すＤＳＣ曲線の他の説明図。
【図５】熱流束示差走査熱量測定により求められる発泡粒子のΔＨｅｘｏ：Ｂｅａｄ及びΔＨｅｎｄｏ：Ｂｅａｄを示すＤＳＣ曲線の更に他の説明図。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to polylactic acid foamed particles having microbial degradability and molded articles of the foamed particles, and more particularly, has excellent mechanical properties and fusion properties between foamed particles, small variance in density, and uniform mechanical properties. The present invention relates to a polylactic acid foamed particle suitably used for producing a polylactic acid foamed particle molded article and a polylactic acid foamed particle molded article.
[0002]
[Prior art]
Expanded particle molded articles made of resins such as polystyrene, polyethylene, and polypropylene are widely used as cushioning materials for packaging, agricultural boxes, fish boxes, automobile members, building materials, civil engineering materials, and the like. However, when these foamed particle molded bodies are left in a natural environment after use, they are hardly decomposed by microorganisms, and may cause a problem of environmental destruction due to dust scattering.
[0003]
On the other hand, research has also been conducted on resins that can be decomposed by microorganisms. For example, biodegradable resins made of polylactic acid and the like as surgical sutures have been put to practical use and have achieved many years of experience. In recent years, lactic acid, which is a raw material of polylactic acid, can be produced in large quantities at low cost by fermentation using corn or the like as a raw material.
Therefore, a foam made of polylactic acid, which has a proven track record in practicality, human safety, and microbial degradability, has been desired.
[0004]
As prior art relating to a foam made of polylactic acid, JP-A-5-508669, JP-A-4-304244, JP-A-5-139435, JP-A-5-140361, and JP-A-9-263661. JP-A-5-170965 (Patent Document 1), JP-A-5-170966 (Patent Document 2), JP-A-2000-136261 (Patent Document 3), etc. And those relating to expanded particles.
[0005]
In the prior art relating to the above-mentioned polylactic acid foam, particularly those relating to expanded particles, it is possible to obtain a foam of a desired shape without comparatively being restricted in shape, and for the purpose of lightness, cushioning, heat insulation and the like. It is particularly promising as a practical one because it is easy to design physical properties according to it.
[0006]
However, the conventional foamed molded article made of polylactic acid is formed by filling expandable non-foamed resin particles in a mold, foaming the resin particles by hot air, and simultaneously fusing the particles to each other. The density variation of the part of the particle molded product was large, the fusion property between the expanded particles and the dimensional stability were insufficient, and the mechanical properties were poor.
[0007]
[Patent Document 1]
JP-A-5-170965
[Patent Document 2]
JP-A-5-170966
[Patent Document 3]
JP 2000-136261 A
[0008]
[Problems to be solved by the invention]
The present invention provides polylactic acid expanded particles suitable for in-mold molding of expanded particles and a molded article of expanded polylactic acid particles having excellent fusion property between the expanded particles, dimensional stability, appearance, and mechanical properties. Make it an issue.
[0009]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, completed the present invention.
That is, according to the present invention, the following polylactic acid foamed particles and foamed molded article are provided.
(1) Expanded particles made of polylactic acid containing 50 mol% or more of a lactic acid component unit, the endothermic amount (ΔH) of the expanded particles measured by a heat flux differential scanning calorimeter. endo: Bead ) And calorific value (ΔH exo: Bead ) (ΔH endo: Bead −ΔH exo: Bead ) Is 0 J / g or more and less than 30 J / g, and the endothermic amount (ΔH endo: Bead ) Is 15 J / g or more.
(2) Endotherm (ΔH) in the heat flux differential scanning calorimetry of the expanded particles endo: Bead ) And calorific value (ΔH exo: Bead ) (ΔH endo: Bead −ΔH exo: Bead ) Is 5 J / g or more and less than 15 J / g. The expanded polylactic acid particles according to the above (1), wherein
(3) The polylactic acid expanded particles according to (1) or (2), wherein the polylactic acid is a mixture of crystalline polylactic acid and non-crystalline polylactic acid.
(4) The apparent density of the expanded particles is 0.015 to 0.3 g / cm. 3 The expanded polylactic acid particles according to any one of the above (1) to (3), wherein
(5) A foamed particle molded article obtained by in-mold molding the foamed particle according to any one of the above (1) to (4), wherein the flexural strength (A: N / cm) of the foamed particle molded article 2 ) And the density of the foamed particle molded product (B: g / cm 3 ) (N / cm / g) or more.
(6) A foamed particle molded article obtained by molding in-mold foamed particles made of polylactic acid containing 50 mol% or more of a lactic acid component unit, and the flexural strength (A: N / cm) of the foamed particle molded article 2 ) And the density of the foamed particle molded product (B: g / cm 3 ) (N / cm / g) or more.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, expanded particles of polylactic acid containing 50 mol% or more of a lactic acid component unit (hereinafter, also simply referred to as expanded particles) are produced by expanding resin particles made of the polylactic acid without crosslinking. Non-crosslinked. Examples of the polylactic acid include (1) a polymer of lactic acid, (2) a copolymer of lactic acid and another aliphatic hydroxycarboxylic acid, and (3) lactic acid, an aliphatic polyhydric alcohol and an aliphatic polycarboxylic acid. (4) a copolymer of lactic acid and an aliphatic polyhydric carboxylic acid, (5) a copolymer of lactic acid and an aliphatic polyhydric alcohol, (6) a mixture of any of the above (1) to (5) Is included. Specific examples of the lactic acid include L-lactic acid, D-lactic acid, DL-lactic acid, and L-lactide, D-lactide, DL-lactide, or a mixture thereof, which is a cyclic dimer thereof. . Examples of the other aliphatic hydroxycarboxylic acids include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, and hydroxyheptanoic acid. Further, as the aliphatic polyhydric alcohol, ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, decamethylene glycol, glycerin, trimethylolpropane, Pentaerythritol and the like. Examples of the aliphatic polycarboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedicarboxylic acid, succinic anhydride, adipic anhydride, trimesic acid, propanetricarboxylic acid, pyromellitic acid, and pyromellitic anhydride. Acids and the like.
The polylactic acid used in the present invention is, among the above-mentioned polylactic acids, an endothermic amount (ΔH) determined by the following heat flux differential scanning calorimetry. endo: Material ) Is 15 J / g or more, preferably 20 J / g or more, more preferably 25 J / g or more. The endothermic amount (ΔH) of the polylactic acid used in the present invention. endo: Material Although the upper limit of () is not particularly limited, it is approximately 60 J / g. Then, the endothermic amount (ΔH) used in the present invention. endo: Material ) Of 15 J / g or more include crystalline polylactic acid, or a mixture of crystalline polylactic acid and non-crystalline polylactic acid.
[0011]
Endothermic amount of the polylactic acid (ΔH endo: Material ) Is a value determined by heat flux differential scanning calorimetry described in JIS K7122-1987. However, 1 to 4 mg of polylactic acid was used as a test piece, and the condition adjustment of the test piece and the measurement of the DSC curve were performed in the following procedure. The test piece was placed in a container of a DSC apparatus, heated and melted to 200 ° C., kept at that temperature for 10 minutes, cooled to 110 ° C. at a cooling rate of 2 ° C./min, kept at that temperature for 120 minutes, After the heat treatment of cooling to 40 ° C. at a cooling rate of 2 ° C./min, a DSC curve is obtained again when heating and melting at a heating rate of 2 ° C./min to a temperature about 30 ° C. higher than the end of the endothermic peak. The endothermic amount of polylactic acid (ΔH endo: Material ) Is, as shown in FIG. 1, a point at which the endothermic peak departs from the low-temperature base line of the endothermic peak of the DSC curve is point a, and a point at which the endothermic peak returns to the high-temperature side baseline is point b. The value is determined from the straight line connecting a and the point b and the area of the portion surrounded by the DSC curve. In addition, the apparatus should be adjusted so that the baseline is as straight as possible. If the baseline is inevitably curved as shown in FIG. 2, the curved base line on the low temperature side of the endothermic peak should be curved. The point where the endothermic peak separates from the curved low-temperature base line, which is clarified by the drawing that extends to the high-temperature side while maintaining the state, is point a, and the high-temperature end-curved base line of the endothermic peak is the curved state of the curve. The point at which the endothermic peak returns to the curved high-temperature-side baseline, which is evident from the drawing extending to the low-temperature side while maintaining the above, is defined as point b.
The heat absorption (ΔH endo: Material In the measurement of), the reason why the heat treatment condition of the test piece is adopted is that the crystallization of the polylactic acid test piece is advanced as much as possible, and that the test piece is adjusted to a completely crystallized state or a state close to it. It is. Further, the reason why the heating rate of 2 ° C./min is adopted as the measurement condition of the DSC curve is that the above-mentioned endothermic amount (ΔH endo: Material )), When an exothermic peak appears, the exothermic peak and the endothermic peak are separated as much as possible, and an accurate endothermic amount (ΔH endo: Material ) Is determined based on the heat flux differential scanning calorimetry based on the knowledge of the inventor that a heating rate of 2 ° C./min is suitable.
[0012]
Further, in the present invention, other resins can be mixed with the above-mentioned polylactic acid as long as the objects and effects of the present invention are not impaired. A mixed resin of polylactic acid and another resin contains 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more of polylactic acid.
Other resins that can be mixed with polylactic acid include polyethylene resins, polypropylene resins, polystyrene resins, polyester resins, and the like. Among them, biodegradable aliphatic containing at least 35 mol% of an aliphatic ester component unit Polyester resins are preferred. Examples of the aliphatic polyester-based resin in this case include hydroxy acid polycondensates other than the above-mentioned polylactic acid, ring-opening polymers of lactones such as polycaprolactone, and polybutylene succinate, polybutylene adipate, polybutylene succinate adipate, and polybutylene succinate adipate. And polycondensates of aliphatic polyhydric alcohols such as (butylene adipate / terephthalate) and aliphatic polycarboxylic acids.
[0013]
Specific examples of the method for producing polylactic acid include, for example, a method of directly dehydrating and polycondensing lactic acid or a mixture of lactic acid and an aliphatic hydroxycarboxylic acid as a raw material (for example, a production method described in US Pat. No. 5,310,865). ), A ring-opening polymerization method for polymerizing a cyclic dimer of lactic acid (lactide) (for example, the production method disclosed in US Pat. No. 2,589,877), a cyclic dimer of lactic acid and an aliphatic hydroxycarboxylic acid, for example, lactide -Opening polymerization in which glyceride and ε-caprolactone are polymerized in the presence of a catalyst (for example, the production method disclosed in US Pat. No. 4,057,537), a mixture of lactic acid, an aliphatic dihydric alcohol and an aliphatic dibasic acid (For example, the production method disclosed in US Pat. No. 5,428,126), an aliphatic dihydric alcohol and an aliphatic dihydric alcohol. A method of condensing a polymer with a base acid and a lactic acid polymer in the presence of an organic solvent (for example, a production method disclosed in European Patent Publication No. 0712880 A2), a method of subjecting lactic acid to a dehydration polycondensation reaction in the presence of a catalyst. In producing the polyester polymer by performing the method, a method of performing solid phase polymerization in at least a part of the steps can be exemplified, but the method of producing polylactic acid is not particularly limited. In addition, a small amount of an aliphatic polyhydric alcohol such as glycerin, an aliphatic polybasic acid such as butanetetracarboxylic acid, and a polyhydric alcohol such as a polysaccharide may coexist to form a copolymer.
[0014]
The expanded particles of the present invention have a calorific value (ΔH) determined by heat flux differential scanning calorimetry of the expanded particles. exo: Bead ) And the amount of heat absorbed (ΔH endo: Bead ), (ΔH endo: Bead −ΔH exo: Bead ) Is 0 J / g or more and less than 30 J / g, and the endothermic amount (ΔH endo: Bead ) Is 15 J / g or more. That is, the expanded particles of the present invention have an endothermic peak in the DSC curve obtained by the heat flux differential scanning calorimetry of the expanded particles, and the peak area has an endothermic amount (ΔH) of 15 J / g or more. endo: Bead ). On the other hand, the exothermic peak may or may not be present. When no exothermic peak is present, ΔH exo: Bead Is 0 J / g, and when an exothermic peak exists, ΔH exo: Bead Is a value obtained from the heat generation peak area. In the present invention, (ΔH endo: Bead −ΔH exo: Bead ) Is more than 0 J / g and less than 30 J / g.
Here, the calorific value (ΔH exo: Bead ) Means the amount of heat released by the crystallization of the test piece by heat flux differential scanning calorimetry at a heating rate of 2 ° C./min. exo: Bead The larger () means that the crystallization of the expanded particles has not progressed. In addition, the heat absorption (ΔH endo: Bead ) Indicates the heat of fusion when the crystal of the test piece is melted by the heat flux differential scanning calorimetry at a heating rate of 2 ° C./min, and the heat absorption (ΔH endo: Bead The larger the expanded particles, the more the crystallization proceeds, which means that the expanded particles obtained from the expanded particles have higher heat resistance. The difference between the heat absorption and the heat generation (ΔH endo: Bead −ΔH exo: Bead ) Is equivalent to the heat of fusion when the crystals already possessed by the foamed particles used for the heat flux differential scanning calorimetry are melted. The smaller the value is, the less the crystallization of the foamed particles is progressed. .
(ΔH endo: Bead −ΔH exo: Bead ) Is preferably 3 to 25 J / g, more preferably 5 J / g or more and less than 15 J / g, since in-mold moldability becomes better. (ΔH endo: Bead −ΔH exo: Bead ) Is 30 J / g or more, even if the foamed particles are filled into a mold and heated to perform in-mold molding, a molded body having good fusion property between the foamed particles cannot be obtained. The foamed particle molded product obtained by the above method has a large shrinkage and a poor appearance. Note that (ΔH endo: Bead −ΔH exo: Bead ) May be 0 J / g. (ΔH endo: Bead −ΔH exo: Bead The smaller the value of ()), the lower the heating temperature during the in-mold molding of the foamed particles can be. is there.
In the present invention, (ΔH endo: Bead −ΔH exo: Bead ) Is in the above range, the foamed particles have excellent in-mold moldability, and the obtained foamed particle molded article has excellent fusion property between foamed particles, dimensional stability, appearance, and mechanical properties. It will be.
[0015]
Further, in the present invention, the endothermic amount (ΔH endo: Bead ) Is at least 15 J / g in order to obtain a foamed molded article having excellent heat resistance. In the case of the present invention, the endothermic amount (ΔH endo: Bead ) Is preferably from 15 J / g to 40 J / g, and more preferably from 15 J / g to less than 30 J / g. In particular, it is preferably from 20 J / g to less than 30 J / g from the viewpoint of the in-mold moldability of the expanded particles.
The heat absorption (ΔH endo: Bead ) Is too small, the shrinkage of the expanded bead obtained by in-mold molding of the expanded bead becomes large, resulting in poor dimensional stability. endo: Bead If) is too large, there is a possibility that a molded article having good fusion property between the expanded particles may not be obtained, and that the obtained expanded particle molded article may have a large shrinkage.
Further, the calorific value (ΔH) in the differential scanning calorimetry of the expanded particles is used. exo: Bead ) Is 3 to 25 J / g, more preferably 8 to 23 J / g, particularly 10 to 20 J / g. It is particularly preferable in terms of the surface smoothness of the foamed particle molded product, which is preferable.
[0016]
In this specification, the calorific value of the expanded particles (ΔH exo: Bead ) And the amount of heat absorbed (ΔH endo: Bead ) Is a value determined by heat flux differential scanning calorimetry described in JIS K7122-1987. However, the foamed particles or 1 to 4 mg of foam pieces cut out from the foamed particles are used as test pieces, and the condition adjustment of the test pieces and the measurement of the DSC curve are performed in the following procedure. The test piece is placed in a container of a DSC device, and a DSC curve is obtained when the temperature is raised from 40 ° C. to 200 ° C. at a heating rate of 2 ° C./min without heat treatment. Note that the calorific value of the expanded particles (ΔH exo: Bead ) Is a straight line connecting point c and point d, with the point at which the exothermic peak departs from the low-temperature base line of the exothermic peak of the DSC curve as point c and the point at which the exothermic peak returns to the high-temperature base line as point d. And a value obtained from the area of the portion surrounded by the DSC curve. Further, the endothermic amount of the expanded particles (ΔH endo: Bead ) Is a point e where the endothermic peak departs from the low-temperature base line of the endothermic peak of the DSC curve, and a point f where the endothermic peak returns to the high-temperature base line is point f. It is a value obtained from the area of the portion surrounded by the straight line and the DSC curve. The apparatus is adjusted so that the baseline in the DSC curve is as straight as possible. Also, if the baseline is inevitably curved, it becomes clear from the drawing that the curved base line on the low temperature side of the heat generation peak is extended to the high temperature side while maintaining the curved state of the curve. The point at which the exothermic peak departs from the baseline is point c, and the curved high-temperature-side base line, which is clarified by drawing the curved base line on the high-temperature side of the exothermic peak to the low-temperature side while maintaining the curved state of the curve, becomes apparent. The point at which the exothermic peak returns to point d is defined as the point d, and the curved low-temperature side baseline of the endothermic peak is clarified by drawing the curved low-temperature side baseline while maintaining the curved state of the curve to the high-temperature side. The point at which the endothermic peak separates from the point e is clarified by drawing a curve that extends the curved base line on the high-temperature side of the endothermic peak to the low-temperature side while maintaining the curved state of the curve. To become, to a point f a point where endothermic peak returns to the high temperature side base line and the curved.
[0017]
For example, in the case as shown in FIG. 3, the calorific value (ΔH) of the expanded particles is determined from the area of the portion surrounded by the straight line connecting the points c and d determined as described above and the DSC curve. exo: Bead ) Is determined, and the endothermic amount (ΔH) of the expanded particles is determined from the area of the portion surrounded by the straight line connecting the points e and f determined as described above and the DSC curve. endo: Bead ). Further, when the exothermic peak and the endothermic peak of the expanded particles overlap as shown in FIG. 4, it is difficult to determine the points d and e as described above. f is determined as a point d (point e) by the DSC curve, the calorific value (ΔH exo: Bead ) And the amount of heat absorbed (ΔH endo: Bead ). When two or more exothermic peaks and / or endothermic peaks of the expanded particles appear, the calorific value of the expanded particles (ΔH exo: Bead ) And / or heat absorption (ΔH endo: Bead ). That is, for example, as shown in FIG. 5, when a small exothermic peak is generated on the lower temperature side of the endothermic peak, the calorific value (ΔH exo: Bead ) Is obtained from the sum of the area A of the first heat generation peak and the area B of the second heat generation peak in FIG. That is, the area A is defined as a point c where the first exothermic peak departs from the low-temperature base line of the first exothermic peak and a point d where the first exothermic peak returns to the high-temperature base line. The area defined by a straight line connecting the point c and the point d and a portion surrounded by the DSC curve. The area B is defined as a point g where the point at which the second exothermic peak separates from the low-temperature base line of the second exothermic peak is point g, and a point f where the endothermic peak returns to the high-temperature side baseline as point g. The intersection of the straight line connecting the point f and the DSC curve is defined as a point e, and the area between the straight line connecting the points g and e and the DSC curve is defined as the area. On the other hand, in FIG. 5, the endothermic amount (ΔH endo: Bead ) Is a value obtained from the area of the portion surrounded by the straight line connecting the points e and f and the DSC curve.
[0018]
The heat value (ΔH exo: Bead ) And the amount of heat absorbed (ΔH endo: Bead The reason why the heating rate of 2 ° C./min is adopted as the measurement condition of the DSC curve in the measurement of (2) is that the exothermic peak and the endothermic peak are separated as much as possible, and the accurate endothermic amount (ΔH endo: Bead ) And (ΔH endo: Bead −ΔH exo: Bead ) Is determined based on the heat flux differential scanning calorimetry based on the knowledge of the inventor that a heating rate of 2 ° C./min is suitable.
[0019]
In the present invention, the endothermic amount (ΔH endo: Bead ) Basically depends on the crystallinity and crystallization rate of the base resin. Therefore, in the present invention, polylactic acid containing crystalline polylactic acid is used. That is, (i) one composed only of crystalline polylactic acid, and (ii) one composed of a polylactic acid mixture of crystalline polylactic acid and non-crystalline polylactic acid. And (ΔH endo: Bead ) And (ΔH exo: Bead It is preferable to use the polylactic acid mixture of (ii) as the polylactic acid in view of the ease of adjustment in ()). In addition, among those made of the polylactic acid mixture of (ii), it is preferable that the ratio of the crystalline polylactic acid to the polylactic acid mixture is 35% by weight or more, more preferably 45 to 80% by weight. . When the proportion of crystalline polylactic acid is small, the heat resistance of the obtained expanded bead molded article may be insufficient, and when the proportion of crystalline polylactic acid is large, crystallization of the expanded polylactic acid particles is progressing. There is a possibility that the fusion property between the expanded particles and the expanded particles during the molding of the expanded particles may be insufficient. Therefore, the heat absorption (ΔH endo: Bead The adjustment method of (1) is as follows: (1) The endothermic amount (ΔH) specified in the present invention. endo: Bead )), And (2) an endothermic amount (ΔH) specified in the present invention by blending two or more crystalline polylactic acids having different crystallinities. endo: Bead (3) One or two or more types of crystalline polylactic acid and one or more types of non-crystalline polylactic acid are blended to determine the endothermic amount (ΔH) specified in the present invention. endo: Bead ), And the above method (3) is particularly preferable.
[0020]
In this specification, crystalline polylactic acid refers to the above-mentioned endothermic amount of polylactic acid (ΔH endo: Material ), An endothermic peak exceeding 2 J / g appears in the DSC curve obtained by the measurement procedure. The endothermic amount (ΔH) of the crystalline polylactic acid endo: Material ) Is usually from 20 to 65 J / g. In the present specification, the non-crystalline polylactic acid refers to the above-mentioned endothermic amount of polylactic acid (ΔH endo: Material In the DSC curve obtained by the measurement procedure of (1), an endothermic peak of 2 J / g or less appears or an endothermic peak does not appear.
[0021]
Further, the calorific value of the expanded particles (ΔH exo: Bead ) Depends on the heat history until the foamed particles are obtained. Heat value (ΔH exo: Bead ) Varies depending on the cooling conditions during the production of the resin particles used to obtain the foamed particles, the impregnation conditions of the resin particles with the foaming agent, the foaming conditions of the resin particles, and the like. Quantity (ΔH exo: Bead ) Can be adjusted. Specifically, the heat value (ΔH exo: Bead ) Is increased, and the amount of heat generation (ΔH) is increased by increasing the ambient temperature when impregnating the resin particles with a foaming agent and increasing the heating time when foaming the foamed particles by heating. exo: Bead ) Becomes smaller. By combining these methods and, if necessary, other methods, the calorific value (ΔH exo: Bead ) Can be adjusted. Therefore, the above (ΔH endo: Bead −ΔH exo: Bead ) Can be adjusted by the crystallinity of the polylactic acid to be used, the crystallization rate, the conditions for preparing the resin particles, the conditions for impregnating the resin particles with the blowing agent, and the conditions for expanding the resin particles.
[0022]
In order to produce the expanded beads of the present invention, the following production method is suitably employed. In order to obtain the foamed particles of the present invention, first, as described above, resin particles are made from a base resin composed mainly of polylactic acid containing crystalline polylactic acid. The resin particles, for example, after the base resin is melted and kneaded by heating the resin to a temperature or higher enough to melt the resin in an extruder, extruded into strands, and quenched by submerging the extruded strands. It can be obtained by cutting to an appropriate length or by quenching the strand after or simultaneously with the cutting to an appropriate length. In addition, as a method for producing resin particles from a base resin, the base resin is heated to a temperature at which the resin is sufficiently melted by an extruder, melted and kneaded, and then extruded into a plate or lump, and the extrudate is formed. After being cooled by a cooling press or by cooling the extrudate by submerging the extrudate, the resin can be obtained by crushing the cooling resin or breaking it into a lattice. In addition, the cooling at the time of producing the above resin particles is performed by (ΔH exo: Bead ) And (ΔH endo: Bead −ΔH exo: Bead Rapid cooling by a method of submersion in water or the like is preferred from the viewpoint of ease of adjustment in (3).
[0023]
The weight per resin particle obtained from the base resin is preferably 0.05 to 10 mg, and more preferably 0.1 to 4 mg. If the particle weight is smaller than the above range, it becomes difficult to produce the resin particles. On the other hand, if the particle weight is larger than the above range, uniform impregnation of the foaming agent becomes difficult, and the density of the obtained foamed particles at the center may become large. The shape of the resin particles is not particularly limited, and may be various shapes such as a sphere, a prism, and the like in addition to a column.
In the step of obtaining resin particles by extruding the base resin into a strand or the like by melt-kneading with an extruder as described above, it is necessary to dry the base resin in advance in order to suppress deterioration of the base resin due to hydrolysis. preferable. Further, in the step of obtaining the resin particles, a method of removing water from the base resin by vacuum suction using an extruder with a vent port can be employed in order to suppress the deterioration due to hydrolysis of the resin.
[0024]
The base resin may be colored by adding a coloring pigment or dye such as black, gray, brown, blue, and green. If colored resin particles obtained from a colored base resin are used, colored foamed particles and foamed particle molded articles can be obtained.
Examples of the coloring agent include organic and inorganic pigments and dyes. As such pigments and dyes, various conventionally known pigments and dyes can be used.
[0025]
In addition, an inorganic substance such as talc, calcium carbonate, borax, zinc borate, and aluminum hydroxide can be added to the base resin in advance as a cell regulator. When adding an additive such as a coloring pigment, a dye or an inorganic substance to the base resin, the additive can be kneaded into the base resin as it is, but usually, a master batch of the additive is used in consideration of dispersibility and the like. It is preferable to make it and knead it with the base resin.
[0026]
The amount of the coloring pigment or dye varies depending on the coloring color, but is usually preferably 0.001 to 5 parts by weight based on 100 parts by weight of the base resin. The amount of the inorganic substance to be added is preferably 0.001 to 5 parts by weight, more preferably 0.02 to 1 part by weight, based on 100 parts by weight of the base resin. By adding an inorganic substance to the base resin, the effect of improving the expansion ratio of the obtained expanded particles can be obtained.
[0027]
In the present invention, additives such as a flame retardant, an antistatic agent, and a weathering agent can be mixed with the base resin. In addition, assuming that the product is discarded after use, it is not preferable to add a high concentration of an additive such as a pigment and a cell regulator.
[0028]
Further, the obtained resin particles are preferably stored in an environment in which hydrolysis does not proceed while avoiding high temperature and high humidity conditions.
[0029]
Next, the resin particles are impregnated with a foaming agent. In the present invention, as the blowing agent used for obtaining the expanded particles, conventionally known blowing agents, for example, propane, butane, pentane, hexane, 1,1,1,2-tetrafluoroethane, 1-chloro-1, Organic physical foaming agents such as 1-difluoroethane and 1,1-difluoroethane, and inorganic physical foaming agents such as nitrogen, carbon dioxide, argon, and air are exemplified. Gas-based blowing agents are preferred, and nitrogen, air and carbon dioxide are particularly preferred. In the present invention, carbon dioxide is most preferable because expanded particles having a low apparent density can be obtained by using a small amount of a foaming agent which is excellent in impregnation with polylactic acid.
[0030]
In the present invention, the use of the above-mentioned physical foaming agent is preferable, but by adding the chemical foaming agent when granulating the resin particles using an extruder, the foamable resin particles using the chemical foaming agent are added. Can also be formed.
[0031]
A method of using carbon dioxide as a foaming agent and impregnating the resin particles with the foaming agent to form foamable particles will be described in detail.
As a method of impregnating the resin particles with carbon dioxide in this case, the resin particles are put in a closed container, carbon dioxide is further injected into the container, and the carbon dioxide is put into the resin particles in the temperature-controlled container. A method of impregnating carbon to obtain expandable particles can be employed. Further, as another method, resin particles are put together with a dispersion medium such as water in a closed container, carbon dioxide is further injected into the container, and the content is stirred while the temperature is adjusted, and the resin particles are introduced into the resin particles. A method of impregnating with carbon dioxide or the like can also be adopted.
[0032]
In these methods, the impregnation of the resin particles with carbon dioxide is performed by injecting carbon dioxide into the closed container containing the resin particles so that the pressure in the container is usually in the range of 0.5 to 10 MPa (G). It is implemented by. Further, the impregnation temperature of the foaming agent is preferably 5 to 60C, more preferably 5 to 40C. In addition, when impregnating carbon dioxide by putting resin particles into a closed container without using a dispersion medium, the impregnation temperature is the temperature of the gas in the resin particle atmosphere. When the carbon dioxide is impregnated with carbon dioxide, the temperature is the temperature of the dispersion medium. The impregnation time of the blowing agent is preferably 10 minutes to 24 hours, more preferably 20 minutes to 12 hours.
[0033]
In particular, when carbon dioxide is used as the blowing agent, the amount of carbon dioxide impregnated into the resin particles is usually 2.5 to 30% by weight, preferably 3 to 20% by weight. Is preferred. If the impregnation amount is too small, there is a risk that the resin particles may not be sufficiently foamed.On the other hand, if the impregnation amount is too large, the crystallization of the resin particles due to impregnation with carbon dioxide is likely to proceed, so that the resin particles are obtained. If the crystallization of the expanded particles is excessively advanced, the expandability and the fusibility of the expanded particles during in-mold molding may be insufficient.
[0034]
When the target carbon dioxide impregnation amount is X (% by weight), the impregnating temperature of the blowing agent is more preferably (-2.5X + 55) (° C.) or lower. If the temperature exceeds (−2.5X + 55) (° C.), particularly in the case of polylactic acid having high crystallinity, the foamability of the resin particles may decrease due to extreme crystallization, and the obtained foamed particles may be placed in a mold. During the heat molding, the expandability of the expanded particles and the fusion property between the expanded particles may be reduced.
[0035]
In the present specification, the impregnation amount (% by weight) of the physical blowing agent in the resin particles is determined by the following equation.
(Equation 1)
Impregnation amount of physical foaming agent (% by weight) = ｛weight of physical foaming agent impregnated in resin particles
(G) × 100｝ / ｛weight (g) of resin particles before impregnation with a physical foaming agent + resin particles
Weight of impregnated physical blowing agent (g)｝
In the above formula, the weight of the physical foaming agent impregnated in the resin particles is obtained from the weight difference between the resin particles before and after the impregnation with the physical foaming agent, and the weight of the resin particles is measured to the order of 0.0001 g.
[0036]
The expandable particles obtained as described above are used as a raw material for a foamed molded article. In order to form a foamed particle molded article using the foamable particles, the foamable particles may be heated to form foamed particles, and then the foamed particles may be filled in a mold, heated, and fused.
[0037]
As a method of expanding the expandable particles, a method of heating and softening the resin particles to expand the resin particles can be adopted. That is, the expandable particles impregnated with a blowing agent such as carbon dioxide are heated to foam them. Examples of the heating medium for foaming include water vapor, air and nitrogen whose heating temperature is adjusted, and a mixed gas of air and water vapor is preferably used. As a method of heating and expanding the expandable particles, a conventionally known method of filling the expandable particles in a closed container and introducing a heating medium to expand the expandable particles can be adopted. In addition, it is preferable that the closed container is provided with an opening valve for slightly exhausting the internal heating medium, because the atmospheric temperature in the closed container can be easily maintained constant.
[0038]
The ambient temperature when heating the resin particles impregnated with the foaming agent, that is, the foaming temperature, is usually (glass transition temperature−30 ° C.) to (glass transition temperature + 60 ° C.), preferably (glass transition temperature−10 ° C.). ) To (glass transition temperature + 40 ° C.). The above glass transition temperature is the glass transition temperature of the polylactic acid constituting the resin particles. If the foaming temperature is lower than the above range, sufficient foaming is unlikely to occur. If the foaming temperature is higher than the above range, the closed cell ratio of the foamed particles is reduced, and it is difficult to obtain foamed particles having good moldability.
[0039]
In the present specification, the measurement of the glass transition temperature is a value obtained as a midpoint glass transition temperature of a DSC curve obtained at a heating rate of 10 ° C./min by heat flux differential scanning calorimetry according to JIS K7121-1987. . The test piece for determining the glass transition temperature is based on JIS K7121-1987, Section 3. Conditioning of Test Specimen The condition of the specimen is adjusted based on “When measuring the glass transition temperature after performing a constant heat treatment” described in (3), and the specimen is used as the test specimen.
[0040]
In addition, it is preferable to store the obtained expanded particles under conditions that avoid hydrolysis under high temperature and high humidity conditions.
[0041]
In the expanded particles of the present invention, the apparent density is 0.015 to 0.3 g / cm. 3 , And 0.015 to 0.2 g / cm 3 , Especially 0.015 to 0.08 g / cm 3 It is preferable that
If the apparent density is larger than the above range, the variation in the density of the foamed particles is likely to be large, which leads to the variation in the expandability and the fusion property of the foamed particles at the time of heat molding in a mold, and the obtained foamed particle molded article There is a possibility that the physical properties of the material may decrease. On the other hand, when the apparent density is smaller than the above range, since the expansion ratio is high, there is a possibility that a foamed particle molded article having a large shrinkage ratio may be obtained.
[0042]
In this specification, the apparent density of the foamed particles is as follows: a graduated cylinder containing water at 23 ° C. is prepared, and the graduated cylinder is left in the graduated cylinder under conditions of 50% relative humidity, 23 ° C. and 1 atm for 2 days or more. The particles (weight W1 of the expanded particle group) are submerged using a wire mesh or the like, and the volume V1 (cm) of the expanded particle group read from the rise in water level 3 ) Is obtained by dividing the weight W1 (g) of the group of expanded particles put in the measuring cylinder (W1 / V1).
[0043]
The average cell diameter of the expanded particles of the present invention is from 10 to 800 μm, preferably from 30 to 500 μm. If the cell diameter is smaller than the above-mentioned range, the film strength of the cells constituting the foamed particles during the in-mold molding is too weak, so that foam breakage or the like occurs, and there is a possibility that a foamed particle molded article having poor curing recovery properties may be obtained. On the other hand, if the cell diameter is larger than the above range, the film strength is too strong at the time of molding in the mold, so that sufficient expansion does not occur, and there is a possibility that a foamed particle molded article having poor surface smoothness may be obtained.
[0044]
In this specification, the average cell diameter of the expanded particles is determined by dividing the expanded particles into approximately two parts, obtaining the maximum diameter of all the cells present in the cross section of the expanded particles, performing this operation on 10 or more expanded particles, The arithmetic mean value of the obtained maximum diameter is defined as an average bubble diameter.
[0045]
The expanded particle molded article of the present invention has a flexural strength (A: N / cm) of the expanded particle molded article. 2 ) And the density of the foamed particle molded product (B: g / cm 3 ) (A / B) is 294 (N · cm / g) or more, preferably 490 (N · cm / g) or more, more preferably 686 (N · cm / g) or more. It is. The foamed particle molded body can be obtained by molding the foamed particles in a mold.
[0046]
The foamed particle molded article of the present invention that satisfies the value of (A / B) has a good fusion property between the foamed particles, and the larger the value of (A / B), the greater the fusion force between the foamed particles. Will be higher. The upper limit of the value of (A / B) is generally 1470 (N · cm / g) although it depends on the density of the foamed particle molded product. As a method for obtaining a foamed particle molded article satisfying the value of (A / B), a method of filling the foamed particle of the present invention in a mold and performing heat molding is exemplified.
[0047]
In the present specification, the bending strength A of the foamed particle molded product is such that the dimensions of the test piece are 150 mm in length, 25 mm in width, and 10 mm in height. A test piece having a molded skin was prepared on the other face, and the maximum bending strength measured according to JIS K7221-1984 with the face having the molded skin of the test piece as the lower face. That's it.
[0048]
In addition, the endothermic amount (ΔH endo: Mold ) And calorific value (ΔH exo: Mold ) (ΔH endo: Mold −ΔH exo: Mold ) Is preferably 15 J / g or more, more preferably 20 J / g or more, particularly preferably 25 J / g or more from the viewpoint of heat resistance. Note that (ΔH endo: Mold −ΔH exo: Mold ) Is approximately 60 J / g.
[0049]
(ΔH) endo: Mold −ΔH exo: Mold The adjustment method of the above) is, after the in-mold molding, the glass transition temperature of the polylactic acid constituting the molded body as a reference, and the glass transition temperature or higher and the temperature at which the foamed particle molded body is not deformed, preferably (glass transition temperature). (ΔT) by maintaining at a temperature of (temperature + 5 ° C.) to (glass transition temperature + 60 ° C.), more preferably (glass transition temperature + 5 ° C.) to (glass transition temperature + 30 ° C.) endo: Mold −ΔH exo: Mold ) Can be increased. The above glass transition temperature is the glass transition temperature of the polylactic acid constituting the foamed molded article. The holding time for holding the foamed particle molded product in the above temperature range is preferably 5 to 1500 minutes, and more preferably 60 to 1000 minutes. In addition, even if the above-mentioned holding step of the above-mentioned foamed particle molded article is performed in the mold following the in-mold molding of the foamed particle, after the in-mold molding, the molded article is taken out of the mold and cured in the curing room of the foamed particle molded article. It may be done inside.
[0050]
In the present specification, the calorific value (ΔH) in the heat flux differential scanning calorimetry of the foamed particle molded product exo: Mold ) And the amount of heat absorbed (ΔH endo: Mold ) Is measured in accordance with JIS K7122-1987, and (ΔH) of the above-mentioned expanded particles is used except that a test piece of 1 to 4 mg cut out from the expanded particle molded article is used. exo: Bead ) And (ΔH endo: Bead ) Can be determined in the same manner as in the measurement method of (2).
[0051]
In an in-mold molding method of filling and heating foamed particles in a mold for producing a foamed particle molded article, after filling the foamed particles in the mold, the foamed particles are heated by a heating medium such as steam or hot air. It is preferable to carry out molding. The temperature of the heating medium may be a temperature at which the surface of the foamed particles melts. By this heat molding, the foamed particles fuse with each other to give an integral foamed molded article. In this case, a conventional mold or a steel belt used in a continuous molding apparatus described in JP-A-2000-15708 is used as a molding die in this case.
[0052]
When manufacturing a foamed particle molded body, air, nitrogen, an inorganic gas such as carbon dioxide, or an organic gas such as butane, by holding the foamed particles in a pressurized container that has been press-fitted, into the mold It is preferable to increase the internal pressure of the expanded beads to be filled in advance. By using the foamed particles having an increased internal pressure as the foamed particles for molding, the foaming property and the fusion property at the time of molding the foamed particles and the recoverability of the foamed particle molded article are improved. The amount of gas in the expanded particles with the increased internal pressure is preferably adjusted within a range of 0.3 to 4 mol / (1000 g expanded particles), more preferably 0.7 to 4 mol / (1000 g expanded particles). Is preferred.
In addition, in this specification, the gas amount (mol / 1000g expanded particles) in 1000 g of expanded particles is obtained as follows.
[0053]
(Equation 2)
Amount of gas in expanded particles (mol / 1000g expanded particles)
= {Gas increase (g) x 1000} / {Gas molecular weight (g / mol)
× foamed particle weight (g)｝
[0054]
The gas increase (g) in the above equation is determined as follows.
500 or more foamed particles with an increased internal pressure to be filled in a mold are taken out and moved within 60 seconds to a constant temperature / humidity room at 50% relative humidity and 23 ° C. under atmospheric pressure. And take out the foamed particles and read the weight after 120 seconds. The weight at this time is defined as Q (g). Next, the foamed particles are allowed to stand for 240 hours in the same constant temperature and humidity room at a relative humidity of 50% and an atmospheric pressure of 23 ° C. The gas of high pressure inside the foamed particles permeates through the cell membrane and escapes to the outside with the passage of time, and the weight of the foamed particles decreases accordingly. stable. The weight of the foamed particles after 240 hours is measured in the same constant temperature and humidity chamber, and the weight at this time is defined as S (g). Any of the above weights shall be read up to 0.0001 g. The difference between Q (g) and S (g) obtained in this measurement is defined as the gas increase (g) in the above equation. The weight of the expanded particles in the above formula is defined as the weight S (g) of the expanded particles after 240 hours.
[0055]
The gel fraction of the foamed particles and foamed molded article of the present invention is 2% or less (including 0%), preferably 0%, as measured by the following method. This means that the expanded particles and the expanded particle molded article are non-crosslinked.
The gel fraction is measured as follows. A test piece having a weight W2 obtained by precisely weighing about 1 g of a foamed particle or a foamed particle molded article and 100 ml of chloroform in a 150 ml flask and heating and refluxing boiling chloroform at about 61 ° C for 10 hours are heated to heat the test piece. I do. The obtained heat-treated product is subjected to filtration using a suction filtration device having a 200-mesh wire net. The obtained filtered product on the wire mesh is dried in an oven at 80 ° C. under the conditions of 30 to 40 torr for 8 hours. The dry matter weight W3 obtained at this time is measured. The weight percentage [(W3 / W2) × 100] (%) of the weight W3 with respect to the test piece weight W2 is defined as a gel fraction.
[0056]
The shape of the foamed particle molded body is not particularly limited, and examples of the shape include various shapes such as a container shape, a plate shape, a tubular shape, a column shape, a sheet shape, and a block shape. Further, it is excellent in dimensional stability and surface smoothness.
Density of foamed molded article (g / cm 3 ) Is preferably 0.01 to 0.2 g / cm 3 , More preferably 0.015 to 0.1 g / cm 3 And the volume VM (cm) determined from the external dimensions of the foamed particle molded article 3 ) Is obtained by dividing (WM / VM) the weight WM (g) of the foamed particle molded product.
[0057]
【The invention's effect】
The expanded particles of the present invention have a (ΔH endo: Bead −ΔH exo: Bead ) And (ΔH endo: Bead ) Has a specific value, thereby obtaining a good foamed particle molded article having excellent fusion property between foamed particles and secondary foamability during in-mold molding, and having a small dimensional change with respect to the mold dimension. Can be done.
Further, the foamed particle molded article of the present invention has small density variation, excellent dimensional stability, cushioning property, surface smoothness and mechanical strength, and is suitably used as a cushioning material, a packaging material, etc. Therefore, its industrial significance is enormous, for example, since subsequent disposal is easy.
[0058]
【Example】
Next, the present invention will be described in more detail with reference to examples.
[0059]
Examples 1 to 6, Comparative Examples 1 to 4
Heat absorption (ΔH endo: Material ) Of 37 J / g (Lacty 9030, manufactured by Shimadzu Corporation) and an endothermic amount (ΔH endo: Material ) Is 0 J / g and non-crystalline polylactic acid (Lacti 9800, manufactured by Shimadzu Corporation) is blended at a blend ratio (weight ratio) shown in Table 1, and this blend and talc are mixed in an extruder. After extruding into a strand, the strand is quenched and solidified in water at about 25 ° C., and then cut into a circle having a diameter of about 1.3 mm, a length of about 1.9 mm, and a circle of about 3 mg per piece. Columnar resin particles were obtained. In addition, talc was added so that the addition amount to resin particles might be 2000 ppm.
[0060]
Next, the inside of a closed container having an inner volume of 5 L was adjusted to the impregnation temperature shown in Table 1, and 1,000 g of the above resin particles were charged into the container. Carbon dioxide (CO 2 ) Is press-fitted into a closed vessel via a pressure regulating valve, and CO 2 The pressure was adjusted to the impregnation pressure shown in Table 1 and maintained under the impregnation conditions shown in Table 1. Next, after the pressure in the sealed container was set to the atmospheric pressure, expandable resin particles impregnated with carbon dioxide were taken out. Table 1 shows the carbon dioxide impregnation amounts of the obtained expandable resin particles.
[0061]
After filling the resin particles impregnated with carbon dioxide into a closed container equipped with a pressure regulating valve, steam having a foaming temperature shown in Table 1 is introduced for 5 seconds and heated to expand the resin particles and to form a non-crosslinked resin. Expanded particles were obtained. Table 1 shows the properties of the expanded particles.
[0062]
The obtained foamed particles are filled in a closed container, and the internal pressure of the foamed particles is increased by pressurizing with carbon dioxide. 2 After setting the amount to the value shown in Table 2, the compression space [(bulk volume (cm) of the expanded particles before compression) shown in Table 2 was applied to a mold having a molding space having a shape of 200 mm in length, 250 mm in width and 12 mm in thickness. 3 ) -Internal volume of mold space after mold clamping (cm 3 )) × 100 / internal volume of mold space after mold clamping (cm 3 )] [%] To fill the foamed particles, and heat-molded with steam having a molding temperature shown in Table 2. The obtained molded body was cured at a temperature of 30 ° C. and a relative humidity of 10% for 24 hours. The dimensional stability, fusion property, and the like of the molded foamed particles after curing were evaluated, and the results are shown in Table 2.
[0063]
The bulk volume of the expanded particles before compression is determined by measuring the volume V2 (cm) of the expanded particles indicated by the scale of the graduated cylinder when the expanded particles are placed in an empty measuring cylinder. 3 ) And the weight W4 (g) of the particle group, and the weight (g) of the expanded particle group filled in the mold is divided by the bulk density (W4 / V2) of the expanded particle. .
[0064]
[Table 1]
[Table 2]
Example 7
Heat absorption (ΔH endo: Material ) Of 49 J / g (Laissia H-100, manufactured by Mitsui Chemicals, Inc.) and an endothermic amount (ΔH endo: Material ) Is 0 J / g and non-crystalline polylactic acid (Laissia H-280, manufactured by Mitsui Chemicals, Inc.) is blended at a blend ratio (% by weight) shown in Table 3, and the talc content of the blend is They were added so as to have a concentration of 2000 ppm, and were melt-kneaded with an extruder, and then extruded in a strand shape. Next, the strand is quenched and solidified in water at about 25 ° C., and then cut, so that the ratio (L / D) of the length (L) to the diameter (D) of the resin particles is 1.5, and about 3 mg per piece. Was obtained.
[0067]
From the obtained resin particles, CO 2 Except that the impregnation conditions were as shown in Table 3, foamable resin particles were obtained in the same manner as in Example 1.
Next, after filling the expandable resin particles into a sealed container equipped with a pressure regulating valve, steam of 0.05 MPa (G) (65 ° C.) is introduced for 5 seconds and heated to expand the resin particles. Non-crosslinked foamed particles were obtained. Table 3 shows the properties of the expanded particles.
Next, the obtained foamed particles are filled in a closed container, and an operation of increasing the internal pressure of the foamed particles by pressurizing with carbon dioxide is performed. 2 After adjusting the amount to 1.3 mol / 1000 g, a mold having a molding space of 200 mm in length, 250 mm in width, and 10 mm in thickness was filled with foamed particles at a compression ratio of 50%, and the temperature was 125 ° C. (0.127 MPa (G)). ) With water vapor. The obtained foamed particle molded product was taken out of the mold and cured at a temperature of 30 ° C. and a relative humidity of 10% for 12 hours. The dimensional stability, fusing property and the like of the molded foamed particles after curing were evaluated, and the results are shown in Table 4.
[0068]
Example 8
1000 g of resin particles obtained in the same manner as in Example 7 and 3 L of water as a dispersion medium were placed in a closed container having a capacity of 5 L, and then carbon dioxide (CO 2) was added. 2 ) Is press-fitted into a closed vessel via a pressure regulating valve, and CO 2 The pressure was adjusted to the pressure shown in Table 3, and the dispersion medium was stirred and maintained under the impregnation conditions shown in Table 3. Next, after the pressure in the closed container was set to the atmospheric pressure, the expandable resin particles impregnated with carbon dioxide together with the dispersion medium were taken out.
Next, after filling the expandable resin particles into a sealed container equipped with a pressure regulating valve, steam of 0.05 MPa (G) (65 ° C.) is introduced for 5 seconds and heated to expand the resin particles. Non-crosslinked foamed particles were obtained. Table 3 shows the properties of the expanded particles.
Next, the obtained foamed particles were subjected to an operation of increasing the internal pressure of the foamed particles under the same conditions as in Example 7, and then molded in a mold under the same conditions as in Example 7 to obtain a foamed particle molded body. Obtained. The obtained foamed particle molded product was taken out of the mold and cured at a temperature of 30 ° C. and a relative humidity of 10% for 12 hours. The dimensional stability, fusing property and the like of the molded foamed particles after curing were evaluated, and the results are shown in Table 4.
[0069]
[Table 3]
[Table 4]
The methods for measuring or evaluating the properties and the like shown in Tables 1 to 4 are as follows.
(Closed cell rate)
The closed cell ratio of the foamed particles is calculated by the following equation using the true volume Vx of the foamed particle sample measured using an air-comparison hydrometer 930 of Toshiba Beckman Co., Ltd. in accordance with Procedure C of ASTM-D2856-70. To calculate the closed cell ratio S (%). In addition, the measurement of the true volume Vx of the foamed particle sample was performed by measuring the volume indicated by the scale of the measuring cylinder when the foamed particles were placed in an empty measuring cylinder to 12.5 cm. 3 The expanded particles having a volume of are stored in a sample cup as a sample and measured.
[0072]
[Equation 3]
S (%) = (Vx−W / ρ) × 100 / (Va−W / ρ)
Vx: true volume (cm) of the expanded particle sample measured by the above method 3 ), Which corresponds to the sum of the volume of the resin constituting the expanded particle sample and the total volume of the cells in the closed cell portion in the expanded particle sample.
Va: apparent foam particle sample volume (cm) determined from the rise in water level when the foam particle sample used for measurement was submerged in a graduated cylinder filled with water. 3 ).
W: Total weight (g) of the foamed particle sample used for the measurement.
ρ: Density of resin constituting the expanded particle sample (g / cm) 3 ).
[0073]
(Fusibility)
A test piece having a length of 100 mm, a width of 30 mm, and a thickness of 10 mm is cut out from the molded body, and the test piece is bent at both ends in the vertical direction and subjected to bending fracture. The ratio (b / n) to the number (n) of the existing expanded particles was determined and evaluated according to the following criteria.
◎: b / n value is 0.5 or more
：: b / n value is 0.2 or more and less than 0.5
Δ: The value of b / n is more than 0 and less than 0.2
×: The value of b / n is 0
[0074]
(Dimensional stability)
The shrinkage ratio was calculated from the following equation based on the dimensions of the mold having a width of 250 mm and the length (X) of the foamed particle molded article corresponding to the dimensions of the mold aged at 30 ° C. for 24 hours after molding. Was evaluated according to the following criteria.
[0075]
(Equation 4)
Shrinkage (%) = [(250−X) / 250] × 100
Here, X is the length (mm) of the molded body in the horizontal direction that divides the length in the vertical direction of the molded body of about 200 mm in length and about 250 mm in width in plan view into two equal parts.
○: Shrinkage rate is 5% or less
×: Shrinkage rate of more than 5%
[0076]
(appearance)
The appearance of the foamed particle molded article was visually evaluated according to the following criteria.
：: Both surface smoothness and mold shape reproducibility are excellent.
×: Many irregularities (voids) exist between the foamed particles on the surface of the molded product.
[0077]
(Heat-resistant)
A test piece (length: 150 mm, width: 150 mm, thickness: 10 mm) was cut out from the foamed molded article obtained in each of Examples and Comparative Examples, and the test piece was subjected to the following test temperature in accordance with 5.7 heating dimensional change of JIS K6767-1976. Was heated in an oven for 22 hours, the dimensional change was calculated by the following equation, and evaluated according to the following criteria.
[0078]
(Equation 5)
Dimensional change rate (%) = [(Y−150) / 150] × 100
However, Y was written in the center of the test piece in three lines parallel to each other in the vertical and horizontal directions, a total of six straight lines having a length of 100 mm at intervals of 50 mm. (A diagram in which a square having a side of 100 mm is divided into four squares is drawn.) The average value (mm) of the lengths of the six lines after performing the above-described heating test using a test piece.
：: dimensional change rate at test temperature of 80 ° C is less than ± 2%
：: The dimensional change at a test temperature of 60 ° C. is less than ± 2%
Δ: The dimensional change rate at a test temperature of 60 ° C. is ± 2% or more and less than ± 5%.
×: The dimensional change rate at a test temperature of 60 ° C. is ± 5% or more.
[0079]
(Measurement of heat absorption and calorific value of polylactic acid, polylactic acid expanded particles and polylactic acid expanded particle molded body)
The measuring device used was "DSC-50" (trade name, manufactured by Shimadzu Corporation), and the analysis software used was "partial area analysis program version 1.52 for Shimadzu Thermal Analysis Workstation TA-60WS".
[Brief description of the drawings]
FIG. 1. ΔH of polylactic acid determined by heat flux differential scanning calorimetry endo: Material Explanatory drawing of a DSC curve showing.
FIG. 2: ΔH of polylactic acid determined by heat flux differential scanning calorimetry endo: Material FIG. 5 is another explanatory diagram of the DSC curve showing the graph.
FIG. 3 shows ΔH of foamed particles obtained by heat flux differential scanning calorimetry. exo: Bead And ΔH endo: Bead Explanatory drawing of a DSC curve showing.
FIG. 4 shows ΔH of expanded particles determined by heat flux differential scanning calorimetry. exo: Bead And ΔH endo: Bead FIG. 5 is another explanatory diagram of the DSC curve showing the graph.
FIG. 5: ΔH of expanded particles determined by heat flux differential scanning calorimetry exo: Bead And ΔH endo: Bead Still another explanatory view of a DSC curve showing a curve.
Claims (6)
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