JP2004292489A

JP2004292489A - Styrenic resin expandable particle, method for producing the same, expanded particle and expansion molded product

Info

Publication number: JP2004292489A
Application number: JP2003083089A
Authority: JP
Inventors: Nobuyuki Komatsuzaki; 信之小松崎; Toshiro Kobayashi; 敏朗小林; Hideki Kobayashi; 秀樹小林; Naoya Morishima; 直也森島
Original assignee: Sekisui Plastics Co Ltd
Current assignee: Sekisui Kasei Co Ltd
Priority date: 2003-03-25
Filing date: 2003-03-25
Publication date: 2004-10-21

Abstract

<P>PROBLEM TO BE SOLVED: To provide a styrenic resin expandable particle affording an expansion molded product having good mechanical strengths and heat insulating performances by an in-mold molding method and using a recycled resin, and to provide a method for producing the same, an expanded particle and the expansion molded product. <P>SOLUTION: The styrenic resin particle is characterized in that microcells having ≤0.2 mm cell diameter and coarse cells having ≥0.35 mm cell diameter randomly exist together in the particle cross section of the expanded particle expanded to 20 kg/m<SP>3</SP>bulk density. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、スチレン系樹脂発泡性粒子とその製造方法、発泡粒子及び発泡成形体に関する。本発明のスチレン系樹脂発泡性粒子は、発泡させた粒子中に微小気泡と粗大気泡とがランダムに混在しており、熱伝導率が低く、機械強度が高い特性を有する。本発明のスチレン系樹脂発泡性粒子は、包装緩衝材、魚箱、断熱材等に用いられる発泡成形体の製造に有用である。
【０００２】
【従来の技術】
スチレン系樹脂発泡成形体は、比較的安価で、低圧の蒸気加熱により比較的簡単に発泡成形でき、高い緩衝性、断熱性を有する有用な材料である。
一般にスチレン系樹脂発泡成形体は、（ｉ）スチレン系樹脂粒子にブタンなどの揮発性有機化合物発泡剤を含浸させたスチレン系樹脂発泡性粒子（ビーズ）を発泡させて得られる発泡粒子を、所望形状のキャビティを有する成形型に充填し、蒸気加熱して発泡粒子同士を融着せしめて発泡成形体を製造する型内成形法、（ｉｉ）押出機内でスチレン系樹脂と発泡剤とを溶融混練し、押出機吐出口に取り付けたダイから押出発泡させてボード状などの発泡成形体を製造する押出発泡成形法などの方法によって製造される。
また、上記（ｉ）型内成形法において用いられるスチレン系樹脂発泡性粒子を製造する方法としては、（ａ）懸濁重合含浸法、（ｂ）押出機内でスチレン系樹脂と発泡剤とを溶融混練し、押出機吐出口に取り付けたダイから押し出し、粒子状にカットする押出法などが用いられている。
【０００３】
上記（ｉ）型内成形法において用いられるスチレン系樹脂発泡性粒子は、所定密度まで発泡させて得られた発泡性粒子中の気泡の大きさが、その製造方法によって異なり、上記（ａ）懸濁重合含浸法で製造した発泡性粒子を用いると気泡径の小さい発泡粒子となり、（ｂ）押出法で製造した発泡性粒子を用いると気泡径の大きい発泡粒子となる。また、発泡粒子中の気泡径の大きさは、得られる発泡成形体の断熱性、機械強度などに影響を及ぼし、気泡径が大きいと断熱性が良好となり、気泡径が小さいと機械強度が良好となる。
【０００４】
従来、スチレン系樹脂発泡成形体の機械強度を向上させるため、或いは成形時の冷却時間を短縮するために、発泡粒子中の気泡構造に着目した技術が提案されている。例えば、（ａ）懸濁重合含浸法によってスチレン系樹脂発泡性粒子を製造する際に、特定のポリプロピレンオキシド−エチレンオキシド共重合体を含浸工程での界面活性剤として用いることにより、予備発泡後の発泡粒子が外側周辺に向かって気泡径が小さくなり、中心に向かって大きくなる気泡構造を示す発泡性粒子を得るビーズ製造法が提案されている（例えば、特許文献１参照。）。
また、（ａ）懸濁重合含浸法によってスチレン系樹脂発泡性粒子を製造する際に、モノマーの重合転化率が３０％以上の時点で、水性媒体に対する濃度が０．０２〜５．０ｍｏｌ／Ｌとなるように、塩化ナトリウム、塩化カリウムなどの電解質を添加することによって、発泡時に中心部の気泡が細かく、その外周部の気泡が粗い気泡構造を有し、表面が綺麗で機械強度に優れる発泡成形体を与え得る発泡性粒子が提案されている（例えば、特許文献２参照。）。
また、（ｂ）押出法によってスチレン系樹脂発泡性粒子を製造する際に、発泡剤添加溶融樹脂をダイヘッドより加熱加圧液で満たされたカッター室内に押し出し、即時切断して粒子状とした後に、圧力容器に移して徐冷し、次いで圧力容器を開放系にして、４０℃以上でＤＳＣ測定による高温側ピークより１５℃高い温度以下の温度条件で熟成することによって、セル径が大きく、均一化された発泡粒子が得られることが開示されている（例えば、特許文献３参照。）。
また、上記（ｉｉ）押出発泡成形法により製造され、発泡成形体を構成する気泡が、主として気泡径０．２５ｍｍ以下の微小気泡と、気泡径０．３〜１ｍｍの気泡よりなるスチレン系樹脂押出発泡体が提案されている（例えば、特許文献４，５参照。）。
【０００５】
【特許文献１】
特開昭５７−１１１３３１号公報
【特許文献２】
特開平７−２９２１５０号公報
【特許文献３】
特開平７−３１４４３８号公報
【特許文献４】
特公平５−４９７０１号公報
【特許文献５】
特開２００２−１９４１２９号公報
【０００６】
【発明が解決しようとする課題】
しかしながら、上述した従来技術にあっては、次のような問題があった。
特許文献１に開示される従来技術は、発泡粒子の気泡が外側周辺に向かって気泡径が小さくなる気泡構造を有しているので、これを成形型内に充填後、加熱発泡成形する際に、発泡成形体の表面が溶融しやすくなり、外観が損なわれるという問題がある。また、得られる発泡成形体において発泡粒子同士が融着した部分に微小気泡が連続して存在することになり、発泡成形体の断熱性能が低下する問題がある。
特許文献２に開示される従来技術は、発泡粒子の中心部に微小気泡が存在し、その外周部に大きめの気泡が存在する構造であるが、懸濁重合含浸法で製造した発泡性粒子は、発泡後の気泡径が全体的に小さいため、得られる発泡成形体は断熱性能が充分に得られない問題がある。
特許文献３に開示された従来技術は、気泡径が均一に粗大な気泡構造を有する発泡粒子が得られることから、これを用いて製造される発泡成形体の機械強度が充分でないという問題がある。
特許文献４，５に開示された従来技術では、微小気泡と粗大気泡とが混在した発泡成形体を得ることができるが、しかしながら、これらは（ｉｉ）押出発泡成形法により製造されものであり、形状が板状に限定され、種々の形状の発泡成形体を製造できる型内成形法に比べ、形状選択の自由度が狭いという問題がある。
【０００７】
また、別な課題として、上述した各従来技術では、スチレン系樹脂として新規に製造したスチレン系樹脂を対象としており、リサイクル用スチレン系樹脂の使用は考えられておらず、リサイクル用スチレン系樹脂の使用による環境負荷低減効果が得られない。特に（ａ）懸濁重合含浸法ではリサイクル用スチレン樹脂の使用は困難である。
リサイクル用スチレン系樹脂は、梱包緩衝材や魚箱などの発泡成形体を、例えばリモネンに溶解し、スチレン系樹脂ペレットを再生するリモネン再生法などによって得られ、このリサイクル用スチレン系樹脂を原料とし、又は新規に製造した樹脂に混合して利用する試みが進められている。しかし、リサイクル用スチレン系樹脂は成分が均一でないために、これを用いて発泡性粒子を製造し、予備発泡後に型内成形して得られた発泡成形体は、新規製造樹脂を用いて製造したものと比べて機械強度が劣り、その結果リサイクル用スチレン系樹脂の使用が控えられるという問題がある。
【０００８】
本発明は上記事情に鑑みてなされ、型内成形法により機械強度と断熱性能が良好な発泡成形体が得られるとともに、リサイクル用スチレン系樹脂を使用しても従来品と遜色ない性能を有する発泡成形体を製造し得るスチレン系樹脂発泡性粒子とその製造方法、発泡粒子及び発泡成形体の提供を目的とする。
【０００９】
【課題を解決するための手段】
上記目的を達成するため、本発明は、嵩密度２０ｋｇ／ｍ^３に発泡させた発泡粒子の粒子切断面に、気泡径０．２ｍｍ以下の微小気泡と、気泡径０．３５ｍｍ以上の粗大気泡とがランダムに混在することを特徴とするスチレン系樹脂発泡性粒子を提供する。
本発明のスチレン系樹脂発泡性粒子において、上記発泡粒子の粒子切断面にある全気泡面積に対し、上記微小気泡の合計面積が２０〜８０％を占め、上記粗大気泡が１０〜７０％を占めることが好ましい。
また、スチレン系樹脂と、該スチレン系樹脂１００質量部に対して、発泡剤２〜１５質量部と、次式（１）
Ｒ−ＣＯＮＨ_２・・・（１）
［式中、Ｒは１１〜２１個の炭素原子を持ったアルキル基又はアルケニル基を表す。］で示される脂肪酸アミド及び次式（２）
Ｒ^１−ＣＯＮＨ−Ｒ^２−ＮＨＣＯ−Ｒ^３・・・（２）
［式中、Ｒ^１とＲ^３は、同一又は異なってよい、１１〜２１個の炭素原子を持ったアルキル基又はアルケニル基を表し、Ｒ^２はメチレン基またはエチレン基を表す。］で表される脂肪酸ビスアミドからなる群から選択される１種又は２種以上の気泡調整剤０．０５〜１．９質量部とを含むことが好ましい。気泡調整剤として、特にステアリン酸エチレンビスアミドが好ましい。
また本発明は、押出機内で、スチレン系樹脂と、発泡剤と、次式（１）
Ｒ−ＣＯＮＨ_２・・・（１）
［式中、Ｒは１１〜２１個の炭素原子を持ったアルキル基又はアルケニル基を表す。］で示される脂肪酸アミド及び次式（２）
Ｒ^１−ＣＯＮＨ−Ｒ^２−ＮＨＣＯ−Ｒ^３・・・（２）
［式中、Ｒ^１とＲ^３は、同一又は異なってよい、１１〜２１個の炭素原子を持ったアルキル基又はアルケニル基を表し、Ｒ^２はメチレン基またはエチレン基を表す。］で表される脂肪酸ビスアミドからなる群から選択される１種又は２種以上の気泡調整剤０．０５〜１．９質量部とを溶融混練し、発泡剤含有溶融樹脂を多孔ダイから液体中に押出し、押出しと同時に液体中で樹脂を切断し、嵩密度２０ｋｇ／ｍ^３に発泡させた発泡粒子の粒子切断面に、気泡径０．２ｍｍ以下の微小気泡と、気泡径０．３５ｍｍ以上の粗大気泡とがランダムに混在する発泡性粒子を得ることを特徴とするスチレン系樹脂発泡性粒子の製造方法を提供する。気泡調整剤として、特にステアリン酸エチレンビスアミドが好ましい。
本発明の方法において、上記発泡粒子の粒子切断面にある全気泡面積に対し、上記微小気泡の合計面積が２０〜８０％を占め、上記粗大気泡が１０〜７０％を占めることが好ましい。
また、上記スチレン系樹脂発泡性粒子は、スチレン系樹脂１００質量部に対して、上記発泡剤２〜１５質量部と、上記含窒素化合物０．０５〜１．９質量部とを含むことが好ましい。
さらに本発明は、上記スチレン系樹脂発泡性粒子を加熱発泡して形成されたスチレン系樹脂発泡粒子を提供する。
また本発明は、発泡粒子を、目的成形体形状に合致するキャビティを有する成形型のキャビティ内に充填し、型内成形して形成されたスチレン系樹脂発泡成形体を提供する。
【００１０】
【発明の実施の形態】
以下、図面を参照して本発明の実施の形態を説明する。
図１は、本発明のスチレン系樹脂発泡性粒子（以下、発泡性粒子と記す。）の製造方法を実施するのに用いる製造装置の一例を示す図である。この製造装置は、ホッパー２から供給されるスチレン系樹脂、気泡調整剤などの原料を溶融混練し、これに発泡剤供給部１０から発泡剤を圧入し、混練して発泡剤添加溶融樹脂とする押出機１と、押出機１の吐出口に取り付けられ、発泡剤添加溶融樹脂が押し出される多数のノズルが樹脂吐出面に設けられたダイ３と、ダイ３の樹脂吐出面に隣接配置されたカッター５を回転可能に収容するとともに、循環水の出入り口を有するカッター室４と、カッター室４を介して設けられた循環水の流路６と、流路６の途中に設けられた固液分離・乾燥機７及び循環用ポンプ８と、固液分離・乾燥機７から分離、乾燥された発泡性粒子９を入れる容器１１とを備えて構成されている。
【００１１】
本発明で用いられるスチレン系樹脂は、特に限定されるものではなく、新規に製造されたスチレン系樹脂、リサイクル用スチレン系樹脂、それらの混合物が挙げられる。
【００１２】
新規に製造されたスチレン系樹脂としては、スチレン単量体のみから得られるポリスチレンホモポリマー、スチレン単量体とスチレンと共重合可能な他のモノマーあるいはその誘導体から得られるランダム、ブロックあるいはグラフト共重合体、後臭素化ポリスチレン、ゴム強化ポリスチレンなどの変成ポリスチレンなどが挙げられる。スチレンと共重合可能なモノマーとしては、メチルスチレン、ジメチルスチレン、エチルスチレン、ジエチルスチレン、イソプロピルスチレンなどのスチレン誘導体、ビニルトルエン、ビニルキシレン、ジビニルベンゼンなどのビニル化合物、アクリル酸、メタクリル酸、アクリル酸メチル、メタクリル酸メチル、ブタジエン、アクリロニトリルなどの不飽和化合物あるいはその誘導体、無水マレイン酸、無水イタコン酸などが挙げられ、これらを単独で又は２種以上混合して使用することができる。
【００１３】
また上記リサイクル用スチレン系樹脂は、種々の分野において用いられた発泡ポリスチレンを、再利用のために回収した材料からなるものである。
近年、環境負荷低減、エコロジーの観点から、再利用材料の積極的な使用が望まれている。発泡ポリスチレンにあっては、家電製品の梱包材、魚箱等を回収し、再利用することが進められている。しかし、これまでリサイクル用スチレン系樹脂は、発泡成形体の原料として用いた場合、得られる発泡成形体の機械強度などの性能が新規製造樹脂のみを用いて製造した発泡成形体よりも劣るために、使用し難い問題があった。本発明では、発泡性粒子を発泡させて得られるスチレン系樹脂発泡粒子（以下、発泡粒子と記す。）の気泡構造を、微小気泡と粗大気泡とがランダムに混在する構造とし、その発泡粒子を型内成形して得られる発泡性粒子において、機械強度と断熱性能を共に向上し得ることにより、リサイクル用スチレン系樹脂を原料として使用しても従来品と遜色ない性能を有する発泡成形体を製造し得る。なお、リサイクル用スチレン系樹脂の製造方法は、特に限定されず、従来周知の製造方法（再生方法）、例えば、梱包材、魚箱などの発泡成形体回収品をリモネンに溶解せしめ、この溶液を真空加熱してリモネンを留去するとともに、溶融スチレン系樹脂を取り出してペレット化するリモネン再生法などが用いられる。
【００１４】
本発明に用いられる発泡剤としては、塩化メチル、塩化メチレン、塩化エチル等の塩素化炭化水素、プロパン、ｎ−ブタン、イソブタン、ｎ−ペンタン、イソペンタン、ネオペンタン等の脂肪族炭化水素、１，１−ジクロロ−１−フルオロエタン（ＨＣＦＣ−１４１ｂ）、１，１−ジクロロ−２，２，２−トリフルオロエタン（ＨＣＦＣ−１２３）、クロロジフルオロメタン（ＨＣＦＣ−２２）、１−クロロ−１，２，２，２−テトラフルオロエタン（ＨＣＦＣ−１２４）等のクロロフルオロカーボン、１，１−ジフルオロエタン（ＨＦＣ−１５２ａ）、１，１，１−トリフルオロエタン（ＨＦＣ−１４３ａ）、１，１，１，２−テトラフルオロエタン（ＨＦＣ−１３４ａ）、ジフルオロメタン（ＨＦＣ−３２）等のフルオロカーボン、各種アルコール、二酸化炭素、水、及び窒素などの物理発泡剤が挙げられ、これらの中の１種又は２種以上を併用して使用することができる。この内特に好ましい発泡剤は、ガス保持性と高発泡性に優れるｎ−ペンタンとイソペンタンである。発泡剤の添加量は、スチレン系樹脂１００質量部に対して２〜１５質量部の範囲とされ、より好ましくは４〜１２質量部の範囲とされる。
【００１５】
本発明に用いられる気泡調整剤としては、次式（１）
Ｒ−ＣＯＮＨ_２・・・（１）
［式中、Ｒは１１〜２１個の炭素原子を持ったアルキル基又はアルケニル基を表す。］で示される脂肪酸アミド及び次式（２）
Ｒ^１−ＣＯＮＨ−Ｒ^２−ＮＨＣＯ−Ｒ^３・・・（２）
［式中、Ｒ^１とＲ^３は、同一又は異なってよい、１１〜２１個の炭素原子を持ったアルキル基又はアルケニル基を表し、Ｒ^２はメチレン基またはエチレン基を表す。］で表される脂肪酸ビスアミドからなる群から選択される１種又は２種以上が挙げられる。上記脂肪酸アミドの具体例としては、ステアリン酸アミド、オレイン酸アミド、エルカ酸アミド、ベヘニン酸アミド、パルミチン酸アミド、ミリスチン酸アミド、ラウリン酸アミドなどが挙げられる。また上記脂肪酸ビスアミドの具体例としては、ステアリン酸エチレンビスアミド、オレイン酸エチレンビスアミド、エルカ酸エチレンビスアミド、ベヘニン酸エチレンビスアミド、パルミチン酸エチレンビスアミド、ミリスチン酸エチレンビスアミド、ラウリン酸エチレンビスアミドなどが挙げられる。この内特に好ましい気泡調整剤は、微小気泡と粗大気泡とが特に顕著にあらわれるステアリン酸ビスアミドである。
【００１６】
上記脂肪酸アミド及び脂肪酸ビスアミドからなる群から選択使用される気泡調整剤の添加量は、スチレン系樹脂１００質量部に対し、０．０５〜１．９質量部の範囲が好ましく、０．１〜１．５質量部の範囲がより好ましい。この気泡調整剤の添加量が上記範囲未満であると、発泡粒子において微小気泡と粗大気泡とがランダムに混在する気泡構造が得られなくなる。一方、気泡調整剤の添加量が上記範囲を超えると、ダイから溶融樹脂を押し出す際、その押し出し状態が不安定となり、良品が得られなくなる。
【００１７】
なお、本発明の発泡性樹脂には、上記気泡調整剤以外に、スチレン系樹脂の押出成形の分野で従来周知の各種添加剤を、本発明の効果を損なわない範囲で必要により添加することができる。そのような添加剤としては、例えば、難燃剤、帯電防止剤、色素（顔料）、充填剤、滑剤、光沢剤などが挙げられるが、これらに限定されない。
【００１８】
上記スチレン系樹脂、気泡調整剤及び必要において添加される添加剤は、ホッパー２から押出機１内に供給され、この押出機１内で溶融混練される。なお、ここで用いられる押出機１の型式は特に限定されず、熱可塑性樹脂の成形に従来から使用されている各種型式の押出機、例えば、単軸押出機、二軸押出機、タンデム押出機などの中から選択して使用することができる。
【００１９】
押出機１内で溶融混練された樹脂は、吐出口に向けスクリューで移送される途中、発泡剤供給部１０において発泡剤が圧入される。発泡剤添加溶融樹脂は、押出機１の吐出口からダイ３に入り、カッター室４に連通し循環水と接している樹脂吐出面に設けられた多数の円孔状のノズルから押し出される。ノズルから押し出された発泡剤添加溶融樹脂は、カッター室４内に循環供給されている循環水と接触し、急速に冷却されると共に、押し出し直後にカッター５によって粒子状に切断される。
【００２０】
カッター５によって切断され、循環水と接触して冷却された樹脂は、ほぼ球状の発泡性粒子となり、循環水流により運ばれて、カッター室４から固液分離・乾燥機７に運ばれる。固液分離・乾燥装置７に入った発泡性粒子９は、ここで循環水と分離され、さらに乾燥後、取り出されて容器１１に収容される。一方、発泡性粒子９と分離した循環水は、循環用ポンプ８、流路６を経て再びカッター室４の入口に送られる。
【００２１】
このように製造された本発明の発泡性粒子は、嵩密度２０ｋｇ／ｍ^３に発泡させた発泡粒子の粒子切断面に、気泡径０．２ｍｍ以下の微小気泡と、気泡径０．３５ｍｍ以上の粗大気泡とがランダムに混在する特徴を有している。図２は、後述する実施例において、本発明に係る発泡性粒子（実施例１）を発泡させた発泡粒子切断面の電子顕微鏡観察像を示している。この図２に示したように、この発泡粒子の切断面には、粗大気泡と微小気泡とがランダムに混在している。
【００２２】
この発泡粒子の切断面において、気泡は、主に０．２ｍｍ以下の微小気泡と、０．３５ｍｍ以上の粗大気泡とから構成されている。一方、それらの中間の気泡径、すなわち気泡径が０．２ｍｍを超え０．３５ｍｍ未満の気泡は小数である。本発明において、上記発泡粒子の粒子切断面にある全気泡面積に対し、上記微小気泡の合計面積が２０〜８０％を占め、上記粗大気泡が１０〜７０％を占めることが好ましい。微小気泡の面積割合及び粗大気泡の面積割合が上記範囲を外れると、発泡粒子を型内成形して得られるスチレン系樹脂発泡成形体（以下、発泡成形体と記す。）の機械強度及び断熱性能を向上させるという本発明の効果が少なくなり、又は充分に得られなくなる。
【００２３】
本発明の発泡性粒子は、従来周知の型内成形法を用いて発泡成形体に成形することができる。すなわち、まず発泡性粒子を自由に膨張可能な条件下で蒸気加熱し、所望の発泡倍率まで予備発泡させて発泡粒子を作製し、次いで成形する目的形状と合致するキャビティを有する成形型のキャビティ内に発泡粒子を充填し、蒸気加熱して発泡粒子同士を融着せしめ、その後冷却して離型し、発泡成形体を得る。
【００２４】
このように製造された本発明の発泡成形体は、上述した本発明の発泡粒子と同様、粗大気泡と微小気泡とがランダムに混在している気泡構造を有しており、良好な機械強度を有すると同時に、良好な断熱性能を有している。
【００２５】
上述した通り、本発明の発泡粒子及び発泡成形体は、粗大気泡と微小気泡とがランダムに混在している気泡構造を有している。後述する実施例において実証されている通り、殆ど微小気泡のみからなる気泡構造を有する発泡粒子を成形して得られた発泡成形体は、機械強度は充分であるが、熱伝導率が高く断熱性に劣る。一方、殆ど粗大気泡のみからなる気泡構造を有する発泡粒子を成形して得られた発泡成形体は、機械強度が低い。本発明の発泡成形体は、粗大気泡と微小気泡とがランダムに混在していることで、充分な機械強度が得られると同時に、熱伝導率が低く良好な断熱性を有している。
また、リサイクル用スチレン系樹脂を用いて発泡成形体を製造する場合、新規製造樹脂に比べて発泡成形体の機械強度が低くなるが、本発明にあっては、リサイクル用スチレン系樹脂を原料として用いて従来品と遜色ない機械強度を有する発泡成形体が得られる。
【００２６】
本発明の発泡成形体は、本発明の発泡性粒子を原料として型内成形法で製造されたものなので、箱形、突起や凹部を有する厚板状、収納品の形状に合わせた複雑形状などの所望の形状に成形することができ、例えば、家電製品や精密機器及びそれらの部品の梱包用緩衝材、断熱材、建材、畳芯材、魚箱等の食品保存用容器、車両内装材などの種々の用途に使用することができる。
【００２７】
【実施例】
以下、実施例により本発明の効果を実証する。
なお、以下の実施例及び比較例において、気泡面積占有率、熱伝導率、曲げ強度及び落球高さの測定は、以下の通り行った。
【００２８】
（気泡面積占有率）
発泡粒子の粒子切断面の気泡径は下記の要領で測定されたものをいう。まず、発泡粒子の中央部を切断する。そして、発泡粒子の切断面を走査型電子顕微鏡を用いて５０倍に拡大し、撮影し、拡大写真を得る。次に、拡大写真上に表れた気泡のうち測定しようとする気泡を特定し、この特定した気泡の長径距離と短径距離を測定しこれらの平均値から気泡径距離を算出する、気泡径距離を写真の拡大倍率で除したものを特定した気泡の気泡径とする。
次に、発泡粒子の粒子切断面において、全気泡面積に対する測定対象となる気泡の合計面積の比率（気泡面積占有率）は下記の要領で測定されたものをいう。前記拡大写真上に表れた気泡において、測定対象となる気泡を黒く塗りつぶした面積の合計、即ち、測定対象となる気泡の占める合計面積を求める。ここで黒く塗りつぶした面積の合計は、例えば、タマヤ計測システム社から商品名「ＰＬＡＮＩＸ５０００」にて市販されている測定機器を用いて算出することができる。
そして、全気泡面積に対する、気泡径０．２ｍｍ以下の微小気泡の合計面積が占める比率（気泡占有率）は、下記式により算出される。
（全気泡面積に対する微小気泡の合計面積が占める比率〔％〕）
＝１００×微小気泡の合計面積／全気泡面積
同様に、全気泡面積に対する、気泡径０．３５ｍｍ以上の粗大気泡の合計面積が占める比率（気泡占有率）は、下記式により算出される。
（全気泡面積に対する粗大気泡の合計面積が占める比率〔％〕）
＝１００×粗大気泡の合計面積／全気泡面積
【００２９】
（熱伝導率）
ＪＩＳＡ１４１２−２：１９９９「熱絶縁材の熱抵抗及び熱伝導率の測定方法−第２部：熱流計法（ＨＦＭ）法」に記載の方法に従って実施した。試験体は長さ２００ｍｍ×幅２００ｍｍ×厚み１０〜２５ｍｍの大きさとし、試験体平均温度は、０℃、２０℃及び３０℃の３点とした。測定装置は英弘精機産業社製、ＨＣ−０７１Ｈを用い、装置の低温板は試験体平均温度より１０℃低くし、また高温板は試験体平均温度よりも１０℃高く設定して測定した。測定結果から回帰直線を算出し、２０℃での熱伝導率測定値を求めた。
合わせて米国標準規格技術研究所の押出法ポリスチレン標準板（ＮＩＳＴ−ＳＲＭ１４５３）を同様にして測定し、２０℃での熱伝導率λを算出し、標準板の公称値から装置の補正係数を求めた。試験体の熱伝導率λは、次式により算出した。
熱伝導率λ（Ｗ／ｍ・Ｋ）＝試験体の２０℃での熱伝導率測定結果×標準板（ＮＩＳＴ）の公称値／標準板（ＮＩＳＴ）の２０での熱伝導率測定結果
【００３０】
（曲げ強度）
ＪＩＳＡ９５１１に規定された試験法に準じて測定した（単位：ＭＰａ）。
【００３１】
（落球衝撃強度高さ）
ＪＩＳＫ７２１１に規定された試験法に準じて測定した（表１中では「落球高さ」と略記する。）。発泡成形体に重量２５５ｇの剛球を垂直に落下させ、発泡成形体の５０％が破壊したところの落下高さとした（単位：ｃｍ）。
【００３２】
［実施例１］
ポリスチレン（東洋スチレン社製、ＨＲＭ１０Ｎ）１００質量部、気泡調整剤としてステアリン酸エチレンビスアミド０．５質量部を混合し、押出機に投入して加熱溶融し、混練後、発泡剤としてイソペンタン５．５質量部を押出機途中より圧入した。発泡剤添加溶融樹脂を、押出機吐出口に取り付けた０．５ｍｍの円孔が３００個配置された多孔ダイよりカッター室内の加圧水中に押し出し、ダイの樹脂吐出面に密接して設置されたカッターの回転刃にて押出物を切断し、冷却、乾燥して発泡性粒子を得た。この発泡性粒子にステアリン酸亜鉛、ステアリン酸トリグリセライド、ステアリン酸モノグリセライドをコーティングした後、蒸気加熱して嵩倍率５０倍の予備発泡粒子を得た。この予備発泡粒子を成形型のキャビティに充填し型内成形を行い、発泡成形体を得た。得られた発泡成形体の密度は２０ｋｇ／ｍ^３であった。発泡粒子の気泡面積占有率、発泡成形体の熱伝導率、曲げ強度及び落球高さを測定し、結果を表１に示す。また、予備発泡粒子の切断面の電子顕微鏡観察像を図２に示し、発泡成形体の切断面の電子顕微鏡観察像を図５に示す。
【００３３】
［実施例２］
ポリスチレンとしてリサイクル用スチレン系樹脂（大塚産業社製、リモネン再生原料、以下リモネン再生原料と記す）とした以外は、実施例１と同様に行った。結果を表１に示す。
【００３４】
［実施例３］
気泡調整剤（ステアリン酸エチレンビスアミド）の添加量を０．１質量部とした以外は、実施例１と同様に行った。結果を表１に示す。
【００３５】
［実施例４］
気泡調整剤（ステアリン酸エチレンビスアミド）の添加量を１．０質量部とした以外は、実施例１と同様に行った。結果を表１に示す。
【００３６】
［比較例１］
気泡調整剤としてタルクを０．８質量部添加した以外は、実施例１と同様に行った。結果を表１に示す。また、予備発泡粒子の切断面の電子顕微鏡観察像を図４に示し、発泡成形体の切断面の電子顕微鏡観察像を図７に示す。
【００３７】
［比較例２］
ポリスチレンとしてリモネン再生原料を使用した以外は、比較例１と同様に行った。結果を表１に示す。
【００３８】
［比較例３］
気泡調整剤（ステアリン酸エチレンビスアミド）の添加量を２．０質量部とした以外は、実施例１と同様に行った。結果を表１に示す。本例では、発泡剤添加溶融樹脂の押出状態が不安定となり、発泡性粒子の良品が得られなかった。
【００３９】
［比較例４］
撹拌機付き５０リットルオートクレーブに、イオン交換水２０リットル、第３リン酸カルシウム５０ｇ、ドデシルベンゼンスルホン酸ナトリウム０．６ｇ、ポリエチレンワックス（ペトロライト社製、ＰＷ−１０００）３．６ｇを投入した。次いで撹拌下、ｔ−ブチルパーオキシ２−エチルヘキサノエート４５ｇ、１，１−ビス（ｔ−ブチルパーオキシ）３，３，５−トリメチルシクロヘキサン２７ｇ、可塑剤としてシクロヘキサン２７０ｇをスチレンモノマー１８ｋｇに溶解させたものを投入した。撹拌下、３０分間室温のまま放置した後、１時間かけて９０℃まで昇温した。次いで９０℃から１００℃まで５時間半かけて昇温させ、ここで２５％の塩化ナトリウム水溶液７００ｇ（イオン交換水に対する濃度は０．１５ｍｏｌ／Ｌに相当）を５分間かけてオートクレーブ内に投入した後、イソブタン１．７ｋｇをオートクレーブ内に圧入した。更に１００℃から１１０℃まで１時間半かけて昇温し、２時間保持した。室温まで冷却した後、遠心分離器にて発泡性粒子を取り出した。この発泡性粒子にステアリン酸亜鉛、ステアリン酸トリグリセライド、ステアリン酸モノグリセライドをコーティングした後、蒸気加熱して嵩倍率５０倍の予備発泡粒子を得た。この予備発泡粒子を成形型のキャビティに充填し型内成形を行い、発泡成形体を得た。得られた発泡成形体の密度は２０ｋｇ／ｍ^３であった。発泡粒子の気泡面積占有率、発泡成形体の熱伝導率、曲げ強度及び落球高さを測定し、結果を表１に示す。また、予備発泡粒子の切断面の電子顕微鏡観察像を図３に示し、発泡成形体の切断面の電子顕微鏡観察像を図６に示す。
【００４０】
［比較例５］
２５％の塩化ナトリウム水溶液７００ｇ（イオン交換水に対する濃度は０．１５ｍｏｌ／Ｌに相当）の代わりにポリプロピレンオキシドエチレンオキシドコポリマー（日本油脂社製、プロノン２０１）３．６ｇをオートクレーブ内に投入した以外は、比較例４と同様に行った。結果を表１に示す。
【００４１】
【表１】

【００４２】
表１及び図２及び５に示した結果から、本発明に係る実施例１〜４の発泡粒子は、気泡径０．２ｍｍ以下の微小気泡と、気泡径０．３５ｍｍ以上の粗大気泡とがランダムに混在する気泡構造を有していた。本発明に係る実施例１〜４のうち、新規製造樹脂を用いて製造された実施例１の発泡成形体は、従来の押出法で得られた発泡性粒子を用いた比較例１の発泡成形体と比べて、良好な機械強度を有していた。また、実施例１の発泡成形体は、懸濁重合含浸法で得られた発泡性樹脂を用いた比較例４，５の発泡成形体に比べ、熱伝導率が低く、優れた断熱性を有していた。従って、本発明の発泡性粒子を用いて得られた発泡成形体は、良好な機械強度を有すると同時に、良好な断熱性能を併せ持つ、優れた特性を有することが実証された。
また、リモネン再生原料を用いた実施例２で得られた発泡成形体は、比較例１、４，５に匹敵する機械強度と断熱性能を示した。従って、本発明によれば、リサイクル用スチレン系樹脂を原料として、充分実用性のある発泡成形体が得られることが実証された。
【００４３】
一方、押出法で製造した発泡性粒子に係る比較例１〜３の発泡粒子は、図４及び７に示した通り、粗大気泡が多く、外周部に微小気泡が少し存在する気泡構造を有していた。この比較例１〜３の発泡成形体は機械強度が低かった。
また、懸濁重合含浸法で製造した発泡性粒子に係る比較例４，５の発泡粒子は、図３及び６に示した通り、全てが微小気泡からなる気泡構造を有していた。この比較例４，５の発泡成形体は熱伝導率が高く、断熱性能が悪かった。
【００４４】
【発明の効果】
本発明によれば、良好な機械強度を有すると同時に、良好な断熱性能を併せ持つ、優れた特性を有する発泡成形体を製造し得る発泡性粒子、該発泡性粒子を発泡させた発泡粒子及び該発泡粒子を型内成形して得られる発泡成形体を提供することができる。
また、本発明によれば、リサイクル用スチレン系樹脂を原料として、充分実用性のある発泡成形体を得ることができ、スチレン系樹脂の再利用を図る上で極めて有用である。
【図面の簡単な説明】
【図１】本発明の発泡性粒子の製造方法に用いられる製造装置を示す概略構成図である。
【図２】実施例１で製造した発泡粒子の切断面の電子顕微鏡観察像である。
【図３】比較例１で製造した発泡粒子の切断面の電子顕微鏡観察像である。
【図４】比較例４で製造した発泡粒子の切断面の電子顕微鏡観察像である。
【図５】実施例１で製造した発泡成形体の切断面の電子顕微鏡観察像である。
【図６】比較例１で製造した発泡成形体の切断面の電子顕微鏡観察像である。
【図７】比較例４で製造した発泡成形体の切断面の電子顕微鏡観察像である。
【符号の説明】
１…押出機、２…ホッパー、３…ダイ、４…カッター室、５…カッター、６…流路、７…固液分離・乾燥機、８…循環用ポンプ、９…発泡性粒子、１０…発泡剤供給部、１１…容器。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to expandable styrene resin particles, a method for producing the same, expanded particles, and expanded molded articles. The styrenic resin expandable particles of the present invention have characteristics in which microbubbles and coarse bubbles are randomly mixed in the expanded particles, and have low thermal conductivity and high mechanical strength. The styrene resin foamable particles of the present invention are useful for producing foamed molded articles used for packaging cushioning materials, fish boxes, heat insulating materials and the like.
[0002]
[Prior art]
Styrene resin foam molded articles are useful materials that are relatively inexpensive, can be foam molded relatively easily by low-pressure steam heating, and have high buffering properties and heat insulation properties.
In general, a styrene-based resin foam molded article is obtained by expanding (i) styrene-based resin foamable particles (beads) obtained by impregnating a styrene-based resin particle with a volatile organic compound foaming agent such as butane, by using foamed particles. An in-mold molding method in which a molding die having a cavity having a shape is filled, and steam heating is performed to fuse the foamed particles together to produce a foamed molded product. (Ii) A styrene resin and a foaming agent are melt-kneaded in an extruder. Then, it is produced by a method such as an extrusion foam molding method of producing a molded foam such as a board by extruding and foaming from a die attached to a discharge port of an extruder.
Further, (i) a method for producing the styrene-based resin expandable particles used in the in-mold molding method includes (a) a suspension polymerization impregnation method, and (b) a method in which a styrene-based resin and a foaming agent are melted in an extruder. An extrusion method of kneading, extruding from a die attached to a discharge port of an extruder, and cutting into particles is used.
[0003]
In the styrene-based resin expandable particles used in the (i) in-mold molding method, the size of the bubbles in the expandable particles obtained by expanding the particles to a predetermined density differs depending on the manufacturing method. When the expandable particles produced by the turbid polymerization impregnation method are used, the foamed particles have a small cell diameter, and when the expandable particles produced by the extrusion method (b) are used, the foamed particles have a large cell diameter. In addition, the size of the cell diameter in the foamed particles affects the heat insulating property and mechanical strength of the obtained foamed molded article. The larger the cell diameter, the better the heat insulating property, and the smaller the cell diameter, the better the mechanical strength. It becomes.
[0004]
Conventionally, in order to improve the mechanical strength of a styrene-based resin foam molded article, or to shorten the cooling time during molding, a technique that focuses on the cell structure in foamed particles has been proposed. For example, (a) when producing styrene-based resin expandable particles by a suspension polymerization impregnation method, by using a specific polypropylene oxide-ethylene oxide copolymer as a surfactant in the impregnation step, foaming after pre-expansion is performed. There has been proposed a bead manufacturing method for obtaining expandable particles having a cell structure in which the cell diameter decreases toward the outer periphery and increases toward the center (for example, see Patent Document 1).
(A) When producing styrene-based resin expandable particles by the suspension polymerization impregnation method, when the polymerization conversion of the monomer is 30% or more, the concentration in the aqueous medium is 0.02 to 5.0 mol / L. By adding an electrolyte such as sodium chloride, potassium chloride, etc., the foam at the center is fine at the time of foaming, and the foam at the outer periphery has a coarse bubble structure, the foaming with a clean surface and excellent mechanical strength There has been proposed an expandable particle capable of providing a molded article (for example, see Patent Document 2).
(B) When producing the styrene-based resin expandable particles by the extrusion method, the blowing agent-added molten resin is extruded from a die head into a cutter chamber filled with a heated and pressurized liquid, and immediately cut into particles. The cell diameter is large and uniform by transferring to a pressure vessel and slowly cooling, then opening the pressure vessel and aging it at a temperature not higher than 40 ° C. and 15 ° C. or higher than the high-temperature peak by DSC measurement. It has been disclosed that the foamed particles can be obtained (for example, see Patent Document 3).
Further, (ii) a styrene resin extruded by the extrusion foam molding method, wherein the foam constituting the foam molded article is mainly composed of microbubbles having a bubble diameter of 0.25 mm or less and bubbles having a bubble diameter of 0.3 to 1 mm. Foams have been proposed (for example, see Patent Documents 4 and 5).
[0005]
[Patent Document 1]
JP-A-57-111331
[Patent Document 2]
JP-A-7-292150
[Patent Document 3]
JP-A-7-314438
[Patent Document 4]
Japanese Patent Publication No. 5-49701
[Patent Document 5]
JP 2002-194129 A
[0006]
[Problems to be solved by the invention]
However, the above-described related art has the following problems.
The prior art disclosed in Patent Document 1 has a cell structure in which cells of expanded particles have a cell structure in which the cell diameter decreases toward the outer periphery. In addition, there is a problem that the surface of the foamed molded product is easily melted and the appearance is impaired. In addition, microbubbles are continuously present in a portion where the foamed particles are fused in the obtained foamed molded article, and there is a problem that the heat insulating performance of the foamed molded article is reduced.
The prior art disclosed in Patent Literature 2 has a structure in which microbubbles are present at the center of the foamed particles and large bubbles are present at the outer periphery thereof. In addition, since the cell diameter after foaming is small as a whole, there is a problem that the obtained foamed molded article cannot have sufficient heat insulating performance.
The prior art disclosed in Patent Literature 3 has a problem in that since foamed particles having a uniform and coarse cell structure and a cell structure are obtained, the mechanical strength of a foamed molded article manufactured using the same is not sufficient. .
In the prior arts disclosed in Patent Documents 4 and 5, foamed molded articles in which fine cells and coarse cells are mixed can be obtained. However, these are produced by (ii) an extrusion foaming method, The shape is limited to a plate shape, and there is a problem that the degree of freedom in shape selection is narrower than in-mold molding methods capable of producing foamed molded articles of various shapes.
[0007]
Also, as another problem, in each of the above-mentioned conventional technologies, a styrene resin newly manufactured as a styrene resin is targeted, and the use of a styrene resin for recycling is not considered. The effect of reducing the environmental load due to use cannot be obtained. In particular, it is difficult to use a styrene resin for recycling in the suspension polymerization impregnation method (a).
The styrene-based resin for recycling is obtained by dissolving a foamed molded article such as a packing cushion or a fish box in limonene, for example, and regenerating styrene-based resin pellets by a limonene recycling method. Attempts have been made to mix and use it with newly produced resins. However, since the styrene-based resin for recycling has non-uniform components, expandable particles are manufactured using the same, and the expanded molded body obtained by in-mold molding after preliminary expansion is manufactured using a newly manufactured resin. There is a problem that the mechanical strength is inferior to that of the styrene resin, and as a result, the use of the styrene resin for recycling is refrained.
[0008]
The present invention has been made in view of the above circumstances, and a foamed molded article having excellent mechanical strength and heat insulation performance is obtained by an in-mold molding method, and a foamed foam having a performance comparable to a conventional product even when a styrene-based resin for recycling is used. It is an object of the present invention to provide a styrene-based resin expandable particle capable of producing a molded article, a method for producing the same, a foamed particle, and an expanded molded article.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a bulk density of 20 kg / m ³ The styrene-based resin foamable particles, characterized in that microbubbles having a bubble diameter of 0.2 mm or less and coarse bubbles having a bubble diameter of 0.35 mm or more are randomly mixed on the cut surface of the foamed particles that have been foamed into provide.
In the styrene-based resin expandable particles of the present invention, the total area of the microbubbles occupies 20 to 80% and the coarse cells occupy 10 to 70% of the total cell area on the particle cut surface of the expanded particles. Is preferred.
Further, a styrene-based resin and 2 to 15 parts by mass of a foaming agent with respect to 100 parts by mass of the styrene-based resin, the following formula (1)
R-CONH ₂ ... (1)
[In the formula, R represents an alkyl group or an alkenyl group having 11 to 21 carbon atoms. A fatty acid amide represented by the following formula (2):
R ¹ -CONH-R ² -NHCO-R ³ ... (2)
[Wherein, R ¹ And R ³ Represents an alkyl group or an alkenyl group having 11 to 21 carbon atoms, which may be the same or different; ² Represents a methylene group or an ethylene group. ] It is preferable to contain 0.05 to 1.9 parts by mass of one or two or more types of cell regulators selected from the group consisting of fatty acid bisamides represented by the formula: Ethylene bisamide stearate is particularly preferred as the cell regulator.
In addition, the present invention provides a method in which a styrene-based resin, a foaming agent, and the following formula (1) are used in an extruder.
R-CONH ₂ ... (1)
[In the formula, R represents an alkyl group or an alkenyl group having 11 to 21 carbon atoms. A fatty acid amide represented by the following formula (2):
R ¹ -CONH-R ² -NHCO-R ³ ... (2)
[Wherein, R ¹ And R ³ Represents an alkyl group or an alkenyl group having 11 to 21 carbon atoms, which may be the same or different; ² Represents a methylene group or an ethylene group. Is melt-kneaded with 0.05 to 1.9 parts by mass of one or more types of cell regulators selected from the group consisting of fatty acid bisamides represented by Extruded, and simultaneously cut the resin in the liquid at the same time as the extrusion, bulk density 20 kg / m ³ Styrene-based foamed particles obtained by randomly mixing microbubbles having a cell diameter of 0.2 mm or less and coarse cells having a cell diameter of 0.35 mm or more on the cut surface of the expanded foamed particles. Provided is a method for producing resin expandable particles. Ethylene bisamide stearate is particularly preferred as the cell regulator.
In the method of the present invention, it is preferable that the total area of the microbubbles occupies 20 to 80% and the coarse cells occupy 10 to 70% of the total cell area on the cut surface of the expanded particles.
In addition, the styrene-based resin expandable particles preferably include 2 to 15 parts by mass of the blowing agent and 0.05 to 1.9 parts by mass of the nitrogen-containing compound based on 100 parts by mass of the styrene-based resin. .
Further, the present invention provides expanded styrene-based resin particles formed by heating and expanding the above-mentioned styrene-based resin expandable particles.
The present invention also provides a foamed styrene-based resin article formed by filling foam particles into a cavity of a molding die having a cavity conforming to the shape of a target molded article, and molding in-mold.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an example of a production apparatus used to carry out a method for producing styrene-based resin expandable particles (hereinafter referred to as expandable particles) of the present invention. This manufacturing apparatus melts and kneads raw materials such as a styrene-based resin and a cell regulator supplied from a hopper 2, presses a blowing agent from a blowing agent supply unit 10 into the melt, and kneads to obtain a blowing agent-added molten resin. An extruder 1, a die 3 attached to a discharge port of the extruder 1, and provided with a number of nozzles on a resin discharge surface for extruding a blowing agent-added molten resin, and a cutter arranged adjacent to the resin discharge surface of the die 3 5, a cutter chamber 4 having a circulating water inlet / outlet, a circulating water channel 6 provided through the cutter chamber 4, and a solid-liquid separation / The apparatus is provided with a dryer 7 and a circulation pump 8, and a container 11 for storing the foamed particles 9 separated and dried from the solid-liquid separation / dryer 7.
[0011]
The styrene resin used in the present invention is not particularly limited, and includes a newly produced styrene resin, a styrene resin for recycling, and a mixture thereof.
[0012]
Newly manufactured styrene resins include polystyrene homopolymers obtained from styrene monomers only, and random, block or graft copolymers obtained from styrene monomers and other monomers copolymerizable with styrene or derivatives thereof. Coalesced, post-brominated polystyrene, modified polystyrene such as rubber-reinforced polystyrene, and the like. Examples of monomers copolymerizable with styrene include styrene derivatives such as methyl styrene, dimethyl styrene, ethyl styrene, diethyl styrene, and isopropyl styrene, vinyl compounds such as vinyl toluene, vinyl xylene, and divinyl benzene, acrylic acid, methacrylic acid, and acrylic acid. Examples include unsaturated compounds such as methyl, methyl methacrylate, butadiene, and acrylonitrile or derivatives thereof, maleic anhydride, and itaconic anhydride, and these can be used alone or in combination of two or more.
[0013]
The styrene-based resin for recycling is made of a material obtained by collecting expanded polystyrene used in various fields for reuse.
2. Description of the Related Art In recent years, from the viewpoint of reducing environmental load and ecology, active use of recycled materials has been desired. In the case of expanded polystyrene, packing materials for home appliances, fish boxes, and the like are collected and reused. However, styrene-based resins for recycling have been used as raw materials for foamed moldings, and the resulting foamed moldings have poorer mechanical strength and other properties than foamed moldings manufactured using only newly manufactured resins. There was a problem that was difficult to use. In the present invention, the cell structure of the styrene-based resin expanded particles (hereinafter referred to as expanded particles) obtained by expanding the expandable particles has a structure in which fine bubbles and coarse cells are randomly mixed, and the expanded particles are formed. The foamed particles obtained by in-mold molding can improve both the mechanical strength and the heat insulation performance, so that even if a styrene-based resin for recycling is used as a raw material, a foamed molded article with performance comparable to that of conventional products can be manufactured. I can do it. The method for producing the styrene-based resin for recycling is not particularly limited, and a conventionally known production method (regeneration method), for example, dissolving a foam molded product collection such as a packing material and a fish box in limonene is used. A limonene regeneration method or the like is used in which limonene is distilled off by heating in a vacuum and the molten styrene resin is taken out and pelletized.
[0014]
Examples of the blowing agent used in the present invention include chlorinated hydrocarbons such as methyl chloride, methylene chloride, and ethyl chloride; aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and neopentane; -Dichloro-1-fluoroethane (HCFC-141b), 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123), chlorodifluoromethane (HCFC-22), 1-chloro-1,2 Chlorofluorocarbons such as 1,2,2-tetrafluoroethane (HCFC-124), 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a), 1,1,1,1 Various fluorocarbons such as 2-tetrafluoroethane (HFC-134a) and difluoromethane (HFC-32) Alcohol, carbon dioxide, water, and include physical blowing agents such as nitrogen, can be used in combination one or more of these. Of these, particularly preferred blowing agents are n-pentane and isopentane, which are excellent in gas retention and high foaming properties. The addition amount of the foaming agent is in the range of 2 to 15 parts by mass, more preferably 4 to 12 parts by mass, per 100 parts by mass of the styrene resin.
[0015]
The following formula (1) is used as the bubble regulator used in the present invention.
R-CONH ₂ ... (1)
[In the formula, R represents an alkyl group or an alkenyl group having 11 to 21 carbon atoms. A fatty acid amide represented by the following formula (2):
R ¹ -CONH-R ² -NHCO-R ³ ... (2)
[Wherein, R ¹ And R ³ Represents an alkyl group or an alkenyl group having 11 to 21 carbon atoms, which may be the same or different; ² Represents a methylene group or an ethylene group. And at least one selected from the group consisting of fatty acid bisamides represented by the formula: Specific examples of the above-mentioned fatty acid amide include stearic acid amide, oleic acid amide, erucic acid amide, behenic acid amide, palmitic acid amide, myristic acid amide, lauric acid amide and the like. Specific examples of the above fatty acid bisamide include ethylene bisamide stearate, ethylene bisamide oleate, ethylene bisamide erucate, ethylene bisamide behenate, ethylene bisamide palmitate, ethylene bisamide myristate, ethylene bisamide laurate, and the like. Of these, a particularly preferred cell regulator is bisamide stearate, in which fine and coarse cells are particularly prominent.
[0016]
The addition amount of the cell regulator selected and used from the group consisting of the above-mentioned fatty acid amide and fatty acid bisamide is preferably in the range of 0.05 to 1.9 parts by mass, preferably 0.1 to 1 part by mass, per 100 parts by mass of the styrene resin. A range of 0.5 parts by mass is more preferred. If the added amount of the cell regulator is less than the above range, it is not possible to obtain a cell structure in which fine cells and coarse cells are randomly mixed in the expanded particles. On the other hand, when the addition amount of the bubble regulator exceeds the above range, when the molten resin is extruded from the die, the extruded state becomes unstable, and a good product cannot be obtained.
[0017]
The foamable resin of the present invention may contain, as necessary, various additives known in the field of extrusion molding of a styrene-based resin, in addition to the above-mentioned cell regulator, as long as the effects of the present invention are not impaired. it can. Examples of such additives include, but are not limited to, flame retardants, antistatic agents, dyes (pigments), fillers, lubricants, brighteners, and the like.
[0018]
The styrene-based resin, the cell regulator, and additives to be added as necessary are supplied from the hopper 2 into the extruder 1 and melt-kneaded in the extruder 1. The type of the extruder 1 used here is not particularly limited, and various types of extruders conventionally used for molding a thermoplastic resin, for example, a single-screw extruder, a twin-screw extruder, a tandem extruder It can be used by selecting from among others.
[0019]
The resin melt-kneaded in the extruder 1 is injected with a foaming agent in the foaming agent supply unit 10 while being transferred by a screw toward the discharge port. The blowing agent-added molten resin enters the die 3 from the discharge port of the extruder 1 and is extruded from a large number of circular nozzles provided on the resin discharge surface in communication with the cutter chamber 4 and in contact with the circulating water. The blowing agent-added molten resin extruded from the nozzle comes into contact with circulating water circulated and supplied into the cutter chamber 4, is rapidly cooled, and is cut into particles by the cutter 5 immediately after being extruded.
[0020]
The resin cut by the cutter 5 and cooled by contact with the circulating water becomes substantially spherical expandable particles, carried by the circulating water flow, and carried from the cutter chamber 4 to the solid-liquid separation / dryer 7. The expandable particles 9 that have entered the solid-liquid separation / drying device 7 are separated therefrom from the circulating water, dried, taken out, and stored in a container 11. On the other hand, the circulating water separated from the expandable particles 9 is sent to the inlet of the cutter chamber 4 again through the circulation pump 8 and the flow path 6.
[0021]
The foamable particles of the present invention thus produced have a bulk density of 20 kg / m2. ³ It has a feature that micro-bubbles having a bubble diameter of 0.2 mm or less and coarse bubbles having a bubble diameter of 0.35 mm or more are randomly mixed on the cut surface of the foamed particles. FIG. 2 shows an electron microscope observation image of a cut surface of a foamed particle obtained by foaming the expandable particles (Example 1) according to the present invention in Examples described later. As shown in FIG. 2, coarse bubbles and fine bubbles are randomly mixed on the cut surface of the expanded particles.
[0022]
In the cut surface of the expanded particles, the air bubbles are mainly composed of micro air bubbles of 0.2 mm or less and coarse air bubbles of 0.35 mm or more. On the other hand, the number of bubbles having an intermediate bubble diameter, that is, a bubble diameter of more than 0.2 mm and less than 0.35 mm is a small number. In the present invention, it is preferable that the total area of the microbubbles occupies 20 to 80% and the coarse cells occupy 10 to 70% of the total cell area on the cut surface of the expanded particles. When the area ratio of the microbubbles and the area ratio of the coarse cells are out of the above ranges, the mechanical strength and the heat insulating performance of a styrene-based resin foam molded article (hereinafter referred to as a foam molded article) obtained by molding the foamed particles in a mold. The effect of the present invention of improving the resistance is reduced or cannot be sufficiently obtained.
[0023]
The expandable particles of the present invention can be formed into a foamed molded body using a conventionally known in-mold molding method. That is, first, the expandable particles are steam-heated under freely expandable conditions, pre-expanded to a desired expansion ratio to produce expanded particles, and then the inside of a cavity of a mold having a cavity matching the target shape to be molded. Is filled with foamed particles, and the foamed particles are fused by heating with steam, and then cooled and released from the mold to obtain a foam molded article.
[0024]
The foam molded article of the present invention thus produced has a cell structure in which coarse cells and micro cells are randomly mixed, like the expanded particles of the present invention described above, and has good mechanical strength. At the same time, it has good heat insulating performance.
[0025]
As described above, the foamed particles and the foamed molded article of the present invention have a cell structure in which coarse cells and microcells are randomly mixed. As demonstrated in Examples described later, a foamed molded article obtained by molding foamed particles having a cell structure composed of almost only microbubbles has sufficient mechanical strength, but has a high thermal conductivity and a high heat insulating property. Inferior. On the other hand, a foamed molded article obtained by molding foamed particles having a cell structure consisting of almost only coarse cells has low mechanical strength. The foamed molded article of the present invention has sufficient mechanical strength due to the random mixture of coarse cells and fine cells, and has low thermal conductivity and good heat insulating properties.
When a foamed molded article is manufactured using a styrene-based resin for recycling, the mechanical strength of the foamed molded article is lower than that of a newly manufactured resin, but in the present invention, the styrene-based resin for recycling is used as a raw material. A foam molded article having mechanical strength comparable to that of a conventional product can be obtained.
[0026]
Since the foamed molded article of the present invention is manufactured by the in-mold molding method using the expandable particles of the present invention as a raw material, it has a box shape, a thick plate shape having projections and recesses, a complicated shape adapted to the shape of a stored item, and the like. Can be formed into desired shapes, for example, cushioning materials for packing home appliances and precision equipment and their components, heat insulating materials, building materials, tatami mats, food storage containers such as fish boxes, vehicle interior materials, etc. Can be used for various applications.
[0027]
【Example】
Hereinafter, the effects of the present invention will be demonstrated by examples.
In the following Examples and Comparative Examples, measurements of the bubble area occupancy, the thermal conductivity, the bending strength, and the falling ball height were performed as follows.
[0028]
(Bubble area occupancy)
The cell diameter of the cut surface of the expanded particles refers to that measured in the following manner. First, the central part of the foamed particles is cut. Then, the cut surface of the foamed particles is magnified 50 times by using a scanning electron microscope and photographed to obtain an enlarged photograph. Next, of the bubbles appearing on the enlarged photograph, the bubble to be measured is specified, the long diameter distance and the short diameter distance of the specified air bubble are measured, and the bubble diameter distance is calculated from the average value thereof. Divided by the magnification of the photograph is defined as the bubble diameter of the specified bubble.
Next, on the particle cut surface of the foamed particles, the ratio of the total area of the cells to be measured to the total cell area (cell area occupancy) refers to the ratio measured in the following manner. In the bubbles appearing on the enlarged photograph, the total area of the bubbles to be measured blacked out, that is, the total area occupied by the bubbles to be measured is determined. Here, the sum of the areas painted black can be calculated using, for example, a measuring device commercially available from Tamaya Measurement System Co., Ltd. under the trade name “PLANIX5000”.
The ratio of the total area of the microbubbles having a bubble diameter of 0.2 mm or less to the total bubble area (bubble occupancy) is calculated by the following equation.
(Ratio of total area of microbubbles to total bubble area [%])
= 100 x total area of microbubbles / total bubble area
Similarly, the ratio of the total area of the coarse bubbles having a bubble diameter of 0.35 mm or more to the total bubble area (bubble occupancy) is calculated by the following equation.
(Ratio of the total area of coarse bubbles to the total bubble area [%])
= 100 x total area of coarse bubbles / total bubble area
[0029]
(Thermal conductivity)
JIS A 1412-2: 1999 "Measurement method of thermal resistance and thermal conductivity of thermal insulating material-Part 2: Heat flow meter (HFM) method". The specimen had a size of 200 mm in length × 200 mm in width × 10 to 25 mm in thickness, and the average temperature of the specimen was three points of 0 ° C., 20 ° C., and 30 ° C. The measuring device used was HC-071H, manufactured by Eiko Seiki Sangyo Co., Ltd. The measurement was performed by setting the low temperature plate of the device to 10 ° C. lower than the average temperature of the specimen and setting the high temperature plate to 10 ° C. higher than the average temperature of the specimen. A regression line was calculated from the measurement results, and the measured value of the thermal conductivity at 20 ° C. was obtained.
In addition, the extruded polystyrene standard plate (NIST-SRM1453) of the U.S. National Institute of Standards and Technology (NIST-SRM1453) was measured in the same manner, the thermal conductivity λ at 20 ° C. was calculated, and the correction coefficient of the device was obtained from the nominal value of the standard plate. Was. The thermal conductivity λ of the test specimen was calculated by the following equation.
Thermal conductivity λ (W / m · K) = Measurement result of thermal conductivity of test specimen at 20 ° C. × Nominal value of standard plate (NIST) / Result of thermal conductivity measurement of standard plate (NIST) at 20
[0030]
(Bending strength)
It was measured according to the test method defined in JIS A9511 (unit: MPa).
[0031]
(Falling ball impact strength)
It was measured according to the test method specified in JIS K7211 (abbreviated as "falling ball height" in Table 1). A hard sphere having a weight of 255 g was dropped vertically on the foamed molded article, and the drop height at which 50% of the foamed molded article was broken was defined as a unit (unit: cm).
[0032]
[Example 1]
100 parts by mass of polystyrene (manufactured by Toyo Styrene Co., HRM10N) and 0.5 parts by mass of ethylene bisamide stearate as a foam regulator were added, extruded and melted by heating. After kneading, isopentane 5.5 was used as a foaming agent. The mass part was pressed in from the middle of the extruder. A blowing agent-added molten resin is extruded into pressurized water in a cutter chamber from a perforated die in which 300 0.5 mm circular holes attached to an extruder discharge port are arranged, and a cutter installed in close contact with a resin discharge surface of the die. The extrudate was cut with a rotary blade, cooled and dried to obtain expandable particles. The foamed particles were coated with zinc stearate, triglyceride stearate, and monoglyceride stearate, and then heated by steam to obtain pre-expanded particles having a bulk factor of 50. The pre-expanded particles were filled in a cavity of a molding die and subjected to in-mold molding to obtain a foam molded product. The density of the obtained foam molded article is 20 kg / m ³ Met. The cell area occupancy of the foamed particles, the thermal conductivity, the bending strength, and the falling ball height of the foamed molded article were measured. The results are shown in Table 1. FIG. 2 shows an electron microscopic observation image of a cut surface of the pre-expanded particles, and FIG. 5 shows an electron microscopic image of a cut surface of the expanded molded article.
[0033]
[Example 2]
The procedure was performed in the same manner as in Example 1 except that the polystyrene was a styrene resin for recycling (manufactured by Otsuka Sangyo Co., Ltd., limonene recycled material, hereinafter referred to as limonene recycled material). Table 1 shows the results.
[0034]
[Example 3]
The procedure was performed in the same manner as in Example 1 except that the addition amount of the bubble regulator (ethylene bisamide stearate) was 0.1 part by mass. Table 1 shows the results.
[0035]
[Example 4]
The procedure was performed in the same manner as in Example 1 except that the addition amount of the bubble regulator (ethylene bisamide stearate) was changed to 1.0 part by mass. Table 1 shows the results.
[0036]
[Comparative Example 1]
Example 1 was repeated except that talc was added in an amount of 0.8 parts by mass as a cell regulator. Table 1 shows the results. FIG. 4 shows an electron microscopic image of the cut surface of the pre-expanded particles, and FIG. 7 shows an electron microscopic image of the cut surface of the expanded molded article.
[0037]
[Comparative Example 2]
The same operation as in Comparative Example 1 was performed except that limonene regenerated raw material was used as polystyrene. Table 1 shows the results.
[0038]
[Comparative Example 3]
The procedure was performed in the same manner as in Example 1 except that the addition amount of the foam adjuster (ethylene bisamide stearate) was changed to 2.0 parts by mass. Table 1 shows the results. In this example, the extruded state of the blowing agent-added molten resin became unstable, and good products of expandable particles could not be obtained.
[0039]
[Comparative Example 4]
In a 50-liter autoclave equipped with a stirrer, 20 liters of ion-exchanged water, 50 g of tribasic calcium phosphate, 0.6 g of sodium dodecylbenzenesulfonate, and 3.6 g of polyethylene wax (PW-1000, manufactured by Petrolite) were charged. Then, under stirring, 45 g of t-butylperoxy 2-ethylhexanoate, 27 g of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, and 270 g of cyclohexane as a plasticizer were dissolved in 18 kg of styrene monomer. The thing which let you do was thrown. After being left at room temperature for 30 minutes under stirring, the temperature was raised to 90 ° C. over 1 hour. Next, the temperature was raised from 90 ° C. to 100 ° C. over 5 and a half hours, and 700 g of a 25% aqueous sodium chloride solution (the concentration with respect to ion-exchanged water was 0.15 mol / L) was charged into the autoclave over 5 minutes. Thereafter, 1.7 kg of isobutane was injected into the autoclave. Further, the temperature was raised from 100 ° C. to 110 ° C. over one and a half hours and maintained for 2 hours. After cooling to room temperature, the expandable particles were taken out with a centrifuge. The foamed particles were coated with zinc stearate, triglyceride stearate, and monoglyceride stearate, and then heated by steam to obtain pre-expanded particles having a bulk factor of 50. The pre-expanded particles were filled in a cavity of a molding die and subjected to in-mold molding to obtain a foam molded product. The density of the obtained foam molded article is 20 kg / m ³ Met. The cell area occupancy of the foamed particles, the thermal conductivity, the bending strength, and the falling ball height of the foamed molded article were measured. The results are shown in Table 1. FIG. 3 shows an electron microscopic observation image of a cut surface of the pre-expanded particles, and FIG. 6 shows an electron microscopic image of a cut surface of the foam molded article.
[0040]
[Comparative Example 5]
Except that 3.6 g of polypropylene oxide ethylene oxide copolymer (pronon 201, manufactured by NOF CORPORATION) was charged into the autoclave instead of 700 g of 25% aqueous sodium chloride solution (the concentration with respect to ion-exchanged water was 0.15 mol / L). Performed in the same manner as in Comparative Example 4. Table 1 shows the results.
[0041]
[Table 1]

[0042]
From the results shown in Table 1 and FIGS. 2 and 5, in the foamed particles of Examples 1 to 4 according to the present invention, microbubbles having a bubble diameter of 0.2 mm or less and coarse bubbles having a bubble diameter of 0.35 mm or more were random. Had a bubble structure that was mixed. Among Examples 1 to 4 according to the present invention, the foam molded article of Example 1 manufactured using a newly manufactured resin is the foam molded article of Comparative Example 1 using the expandable particles obtained by a conventional extrusion method. It had better mechanical strength than the body. Further, the foamed molded article of Example 1 has a lower thermal conductivity and excellent heat insulating properties as compared with the foamed molded articles of Comparative Examples 4 and 5 using the foamable resin obtained by the suspension polymerization impregnation method. Was. Therefore, it was demonstrated that the foamed molded article obtained by using the expandable particles of the present invention has excellent mechanical strength, and at the same time, has excellent properties having good heat insulating performance.
Further, the foam molded article obtained in Example 2 using the recycled limonene raw material showed mechanical strength and heat insulation performance comparable to Comparative Examples 1, 4, and 5. Therefore, according to the present invention, it has been proved that a foam molded article having sufficient practicality can be obtained using a styrene-based resin for recycling as a raw material.
[0043]
On the other hand, as shown in FIGS. 4 and 7, the foamed particles of Comparative Examples 1 to 3 related to the foamable particles produced by the extrusion method have a cell structure in which many coarse cells are present and a small number of microbubbles are present on the outer periphery. I was The foam molded articles of Comparative Examples 1 to 3 had low mechanical strength.
In addition, the expanded particles of Comparative Examples 4 and 5 related to the expandable particles produced by the suspension polymerization impregnation method had a cell structure including all microbubbles as shown in FIGS. The foamed molded articles of Comparative Examples 4 and 5 had high thermal conductivity and poor heat insulation performance.
[0044]
【The invention's effect】
According to the present invention, while having good mechanical strength, simultaneously with good heat insulating performance, expandable particles capable of producing a foam molded article having excellent properties, expanded particles obtained by expanding the expandable particles, and It is possible to provide a foam molded article obtained by molding the foam particles in a mold.
Further, according to the present invention, a sufficiently practical foam molded article can be obtained using a styrene-based resin for recycling as a raw material, and is extremely useful in reusing a styrene-based resin.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a production apparatus used for a method for producing expandable particles of the present invention.
FIG. 2 is an electron microscope observation image of a cut surface of the foamed particles produced in Example 1.
FIG. 3 is an electron microscope observation image of a cut surface of the foamed particles produced in Comparative Example 1.
FIG. 4 is an electron microscope observation image of a cut surface of the foamed particles produced in Comparative Example 4.
FIG. 5 is an electron microscope observation image of a cut surface of the foam molded article manufactured in Example 1.
FIG. 6 is an electron microscope observation image of a cut surface of the foam molded article manufactured in Comparative Example 1.
FIG. 7 is an electron microscope observation image of a cut surface of the foam molded article manufactured in Comparative Example 4.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Extruder, 2 ... Hopper, 3 ... Die, 4 ... Cutter chamber, 5 ... Cutter, 6 ... Flow path, 7 ... Solid-liquid separation / drying machine, 8 ... Circulation pump, 9 ... Expandable particles, 10 ... Blowing agent supply unit, 11 ... container.

Claims

Styrene characterized in that micro-bubbles having a cell diameter of 0.2 mm or less and coarse cells having a cell diameter of 0.35 mm or more are randomly mixed on a cut surface of foamed particles foamed to a bulk density of 20 kg / m ^3. -Based resin expandable particles.

The styrenic resin foam according to claim 1, wherein the total area of the microbubbles occupies 20 to 80% and the coarse cells occupy 10 to 70% of the total cell area on the particle cut surface of the expanded particles. particle.

A styrene-based resin, 2 to 15 parts by mass of a foaming agent with respect to 100 parts by mass of the styrene-based resin, and the following formula (1)
R-CONH ₂ (1)
[In the formula, R represents an alkyl group or an alkenyl group having 11 to 21 carbon atoms. A fatty acid amide represented by the following formula (2):
R ¹ -CONH-R ² -NHCO-R ³ (2)
[Wherein, R ¹ and R ³ may be the same or different and represent an alkyl group or an alkenyl group having 11 to 21 carbon atoms, and R ² represents a methylene group or an ethylene group. The styrene-based resin expandable particles according to claim 1 or 2, comprising one or more kinds of cell regulators selected from the group consisting of fatty acid bisamides represented by the formula: 0.05 to 1.9 parts by mass. .

The styrene-based resin expandable particles according to claim 3, wherein the cell regulator is ethylene bisamide stearate.

In the extruder, a styrene resin, a foaming agent, and the following formula (1)
R-CONH ₂ (1)
[In the formula, R represents an alkyl group or an alkenyl group having 11 to 21 carbon atoms. A fatty acid amide represented by the following formula (2):
R ¹ -CONH-R ² -NHCO-R ³ (2)
[Wherein, R ¹ and R ³ may be the same or different and represent an alkyl group or an alkenyl group having 11 to 21 carbon atoms, and R ² represents a methylene group or an ethylene group. Is melt-kneaded with 0.05 to 1.9 parts by mass of one or more types of cell regulators selected from the group consisting of fatty acid bisamides represented by Extrude, cut resin in liquid at the same time as extrusion,
Obtaining foamable particles in which microbubbles having a cell diameter of 0.2 mm or less and coarse cells having a cell diameter of 0.35 mm or more are randomly mixed on a cut surface of the foamed particles foamed to a bulk density of 20 kg / m ^3. A method for producing expandable styrene resin particles, comprising:

The method for producing styrene-based resin expandable particles according to claim 5, wherein the cell regulator is ethylene bisamide stearate.

The styrenic resin according to claim 5 or 6, wherein the total area of the microbubbles occupies 20 to 80% and the coarse cells occupy 10 to 70% of the total cell area on the cut surface of the expanded particles. A method for producing expandable particles.

The styrene-based resin expandable particles contain 2 to 15 parts by mass of the blowing agent and 0.05 to 1.9 parts by mass of the cell regulator based on 100 parts by mass of the styrene-based resin. The method for producing expandable styrene resin particles according to any one of the above.

A foamed styrene-based resin particle formed by heating and foaming the foamable styrene-based resin particle according to claim 1.

A styrene-based resin foam molded article formed by filling the foamed particles according to claim 9 into a cavity of a mold having a cavity conforming to the shape of a target molded body, and molding in-mold.