JP4030347B2 - Expandable polystyrene resin particles - Google Patents
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Description
【０００１】
【技術分野】
本発明は，スチレン，トルエン等の芳香族炭化水素類の含有量が少なく，優れた発泡性を有しており，得られる発泡成形体が高い強度を有するとともに優れた柔軟性を有する発泡成形体を製造することができる，発泡性ポリスチレン系樹脂粒子に関する。
【０００２】
【従来技術】
スチレン系の発泡成形体は，スチレン系樹脂に発泡剤および発泡性改良のための可塑剤を添加して発泡性ポリスチレン系樹脂粒子を作製し，これを予備発泡した後に金型内で発泡成形することにより得られる。この発泡成形体は，優れた緩衝性，断熱性を有し，成形も容易で，さらに比較的安価な材料であるため，包装材，断熱材として広く用いられている。
【０００３】
従来，発泡剤としては，ペンタンやブタン等の炭化水素が用いられている。可塑剤としては，発泡性ポリスチレン系樹脂粒子中に残存させたスチレンや，少量添加されたトルエンやキシレン，またシクロヘキサン等の有機溶剤が広く利用されている。このような発泡剤や可塑剤の多くは，揮発性有機化合物である。
【０００４】
従来，発泡剤や可塑剤として機能する揮発性有機化合物は，平均して，スチレン系樹脂粒子に対して６〜９重量％含有されており，貯蔵，発泡，成形，加工等の各プロセスにおいて徐々に大気中に放出される。
【０００５】
【解決しようとする課題】
最近，地球環境に対する配慮から，発泡性ポリスチレン系樹脂粒子中の発泡剤や有機溶剤を減量する試みがなされている。例えば，特開平４−２６８３４７号，特開平６−８０７０８号，特開平１０−１７６９８号には，残存スチレンやベンゼンの含有量が少ない発泡性ポリスチレン系樹脂粒子及びその製造法が開示されている。
【０００６】
従来，スチレン系発泡性樹脂粒子は，スチレン系樹脂に対して優れた可塑効果を有するスチレン，トルエン，キシレン，エチルベンゼン，プロピルベンゼン，フタル酸エステル類といった芳香族炭化水素類等が可塑剤として用いられる。
【０００７】
上記のように，近年，環境衛生に対する配慮から，上記のスチレン，トルエン等の芳香族炭化水素類の放散量の少ない材料の要望が強くなっている。
しかしながら，スチレン系発泡性樹脂粒子において，これら芳香族成分の含有量を単に低下させてしまうと，発泡性樹脂粒子の発泡性が悪くなったり，成形時における予備発泡粒子同士の融着が低下するという問題がある。
また，その対策としてスチレン系発泡性樹脂粒子の基材樹脂の分子量を低下させることも考えられるが，この場合には機械的強度が低下するという問題があった。
【０００８】
本発明はかかる従来の問題点に鑑み，スチレン，トルエン等の芳香族炭化水素類の含有量及び放散量が少なく，優れた発泡性を有しており，得られる発泡成形体が高い強度と柔軟性を有する発泡性ポリスチレン系樹脂粒子を提供しようとするものである。
【０００９】
【課題の解決手段】
請求項１記載の発明は，スチレン，またはスチレンを主成分とするビニルモノマーとの混合物を，可塑剤及び重合開始剤と共に水性媒体中に分散させて重合反応を開始してスチレン系樹脂とするとともに，重合途中あるいは重合完了後に発泡剤を添加することにより得られる発泡性ポリスチレン系樹脂粒子において，
該発泡性ポリスチレン系樹脂粒子は，重量平均分子量が２０万〜４０万のスチレン系樹脂と，
該スチレン系樹脂１００重量％に対して，発泡剤として沸点が９０℃以下の有機化合物が３〜１０重量％と，
該スチレン系樹脂の中に含まれている可塑剤としての平均炭素数が２０〜３５個の流動パラフィン０．０１〜２重量％及び，
同じく該スチレン系樹脂の中に含まれている可塑剤としての常温で固体の脂肪酸エステル０．０１〜２重量％とを含有することを特徴とする発泡性ポリスチレン系樹脂粒子である。
【００１０】
本発明によれば，上記特定のスチレン系樹脂と，該スチレン系樹脂１００重量％に対して上記発泡剤と可塑剤とを上記重量％の範囲で含有している。
そのため，スチレン，トルエン，キシレン，エチルベンゼン，プロピルベンゼン，フタル酸エステル類の１種以上からなる芳香族炭化水素類の含有量が少なく，優れた発泡性を有しており，得られる発泡成形体が高い強度と優れた柔軟性を有するとともに外観が良く，収縮しにくい，発泡性ポリスチレン系樹脂粒子を提供することができる。
【００１１】
【発明の実施の形態】
請求項１の発明において，上記スチレン系樹脂は，重量平均分子量が２０万〜４０万である。これにより，高い発泡性を維持しつつ，優れた強度を有する発泡成形体を作成することができる。上記重量平均分子量はＧＰＣ（Ｇｅｌ Ｐｅｒｍｅａｔｉｏｎ Ｃｈｒｏｍａｔｏｇｒａｐｈｙ；ゲルパ−ミエ−ションクロマトグラフィ−）法により測定した値である。
【００１２】
上記重量平均分子量が２０万未満では，得られる発泡成形体の強度が低下するおそれがある。一方，重量平均分子量が４０万を超えると，発泡性が低下し，目標の発泡倍率（例えば５０〜６０倍）まで発泡させることが困難になったり，成形時に発泡粒子同士が融着しにくくなり，発泡成形体の強度が低下するおそれがある。
より好ましくは，スチレン系樹脂粒子の重量平均分子量は２０万〜３８万，更に好ましくは２２万から３５万である。
【００１３】
次に，発泡性ポリスチレン系樹脂粒子の中には，上記スチレン系樹脂１００重量％に対して，発泡剤として機能する沸点が９０℃以下の有機化合物が，３〜１０重量％含有されている。
上記発泡剤として，沸点が９０℃以下の有機化合物としては，例えばプロパン，ノルマルブタン，イソブタン，ノルマルペンタン，イソペンタン，ネオペンタン，ヘキサン等の脂肪族炭化水素，シクロブタン，シクロペンタン等の脂環系炭化水素等の炭素数３〜６個の炭化水素化合物，アセトン，メチルエチルケトン等のケトン類，メタノール，エタノール，イソプロピルアルコール等のアルコール類がある。
【００１４】
上記発泡剤の含有量が３重量％未満では，発泡性ポリスチレン系樹脂粒子の発泡性が低下し，目標の発泡倍率まで発泡させることが困難になるおそれがある。１０重量％を超えると，ポリスチレン樹脂に対する溶解性に限界があるため経済的に無駄であり，さらに大気中に放出される揮発性有機化合物の量が多くなり，大気環境を汚染する恐れがある。
なお，より好ましくは，上記発泡剤の含有量は，５〜１０重量％である。
【００１５】
また，本発明にかかる発泡性ポリスチレン系樹脂粒子を製造するに当っては，スチレン系単量体を重合開始剤及び懸濁剤と界面活性剤の存在下で水性媒体中に分散させた後に重合反応を開始し，懸濁重合中に発泡剤を添加したり，または懸濁重合完了後に発泡剤を含浸させることができる。
スチレン系単量体を水性媒体に分散させる際には，予め両者を一括して仕込んでもよいし，徐々に添加しながら行ってもよい。
【００１６】
次に，発泡性ポリスチレン系樹脂粒子の中には，スチレン系樹脂１００重量％に対して，可塑剤として機能する平均炭素数２０〜３５個の流動パラフィンが０．０１〜２重量％含有されている。
上記流動パラフィンの含有量が０．０１重量％未満では可塑効果が少なく，発泡成形体作製の際に目標の発泡倍率まで発泡させることが困難になるおそれがある。一方，２重量％を超えると，得られる発泡成形体の表面外観が悪化し，強度や耐熱性が低下し，製造コストも高くなるおそれがある。なお，より好ましくは，上記流動パラフィンの含有量は０．１〜１．５重量％である。
【００１７】
上記流動パラフィン類は，ＣｍＨｎ（ｎ＜２ｍ＋１，ｎ，ｍは自然数）で示される飽和炭化水素の混合物で，かつ平均炭素数が２０〜３５個であり，常温で液体のパラフィン類である。常温とは，１０〜３０℃をいう。
【００１８】
平均炭素数が２０個未満である流動パラフィン類は揮発性があるため，貯蔵，発泡，成形加工等の各プロセスにおいて徐々に大気中に放散される揮発性有機化合物となる可能性があるため，本発明にかかる効果が得難くなるおそれがある。
また，平均炭素数が３５個以上では，目標の可塑効果が得られない場合や，粘度が高く扱い難いという問題がある。
これにより，成形加工中に，有機化合物が大気中に放散することを抑制するとともに，発泡成形性に優れた発泡性ポリスチレン系樹脂粒子を得ることができる
【００１９】
また，発泡性ポリスチレン系樹脂粒子の中には，スチレン系樹脂１００重量％に対して上記流動パラフィンと併用して，可塑剤として機能する常温で固体の脂肪酸エステルを０．０１〜２重量％含有されている。
上記脂肪酸エステルのみを可塑剤として使用すると，比較的高温となる発泡および成形時は，脂肪酸エステルが可塑剤として働き発泡性・成形性の改善に寄与する。しかし，発泡成形体としたときは，樹脂内で脂肪酸エステルが凝集するため，成形品強度や耐熱性の低下は流動パラフィンと比べ小さく，成形品の収縮性も優れるが，得られた発泡成形体の柔軟性が劣るおそれがある。
【００２０】
上記常温で固体の脂肪酸エステルの含有量が０．０１重量％未満では可塑効果が少なく，発泡成形体作製の際に目標の発泡倍率まで発泡させることが困難になるおそれがある。
一方，２重量％を超えると，得られる発泡成形体の強度や耐熱性が低下し，製造コストも高くなるおそれがある。なお，より好ましくは，上記常温で固体の脂肪酸エステルの含有量は０．１〜１．５重量％である。
【００２１】
上記常温で固体の脂肪酸エステルとしては，高級脂肪酸と高級脂肪族１価アルコールとのエステルや高級脂肪酸とソルビタンとのエステル，高級脂肪酸とグリセリンのエステルが挙げられる。例えば，ステアリン酸，ミリスチン酸，パルミチン酸，ベヘニン酸，オレイン酸等のグリセリド，牛脂極度硬化油，ヒマシ硬化油，極度硬化大豆油，ミリスチン酸ミリスチル，ステアリン酸ステアリル，ベヘニン酸オクチルドデシル，ベヘニン酸ベヘニル，ソルビタンモノパルミテート，ソルビタンモノステアレート，ソルビタントリステアレート，ソルビタンジステアレート，ソルビタンモノベヘネートなどがある。
【００２２】
本発明は，可塑剤として平均炭素数が２０〜３５個の流動パラフィンを０．０１〜２重量％含有し，かつ常温で固体の脂肪酸エステルを０．０１〜２重量％含有している。これにより，それぞれの可塑剤を単独で用いた時の欠点を補い合い，優れた発泡性を有し，得られる発泡成形体が高い強度を有すると共に，外観が良く収縮しにくく，かつ柔軟性を有する発泡性スチレン系樹脂粒子を提供することができる。
【００２３】
上記発泡性ポリスチレン系樹脂粒子を製造する方法としては，例えば，撹拌装置の付いた密閉容器内に，スチレンを，可塑剤及び重合開始剤と共に適当な懸濁剤の存在下で水性溶媒中に分散させて重合反応を開始してスチレン系樹脂とするとともに，重合途中あるいは重合完了後に発泡剤を添加して，発泡性ポリスチレン系樹脂粒子を得る方法が挙げられる。
【００２４】
上記発泡性ポリスチレン系樹脂粒子は，スチレン，またはスチレンを主成分とするビニルモノマ−の混合物から製造することができる。スチレンと共重合可能なビニルモノマ−として，例えば，α−メチルスチレン，ｏ−メチルスチレン，ｍ−メチルスチレン，ｐ−メチルスチレン，ビニルトルエン，ｐ−エチルスチレン，２，４−ジメチルスチレン，ｐ−メトキシスチレン，ｐ−フェニルスチレン，ｏ−クロロスチレン，ｍ−クロロスチレン，ｐ−クロロスチレン，２，４−ジクロロスチレン，ｐ−ｎ−ブチルスチレン，ｐ−ｔ−ブチルスチレン，ｐ−ｎ−ヘキシルスチレン，ｐ−オクチルスチレン，スチレンスルホン酸，スチレンスルホン酸ナトリウム等が挙げられ，これらのビニルモノマ−を２種類以上混合して用いてもよい。
【００２５】
上記重合開始剤としては，例えばアゾビスイソブチロニトリル等のアゾ系化合物，クメンヒドロパ−オキサイド，ジクミルパ−オキサイド，ｔ−ブチルパ−オキシ−２−エチルヘキサノエ−ト，ｔ−ブチルパ−オキシベンゾエ−ト，ベンゾイルパ−オキサイド，ｔ−ブチルパ−オキシイソプロピルカ−ボネ−ト，ｔ−ブチルパ−オキシ２−エチルヘキシルモノカ−ボネ−ト，１，１−ジメチルプロピルパ−オキシ−２−エチルヘキシルモノカ−ボネ−ト，１，１−ジメチルブチルパ−オキシ−２−エチルヘキシルモノカ−ボネ−ト，ペンチルパ−オキシ２−エチルヘキシルモノカ−ボネ−ト，ヘキシルパ−オキシ２−エチルヘキシルモノカ−ボネ−ト，ラウロイルパ−オキサイド，１，１−ビス（ｔ−ブチルパ−オキシ）−３，３，５−トリメチルシクロヘキサン，１，１−ジ−ｔ−ブチルパ−オキシ−２−メチルシクロヘキサン等のスチレン系単量体に可溶な開始剤が挙げられる。これらの重合開始剤は，１種類または２種類以上組み合わせて用いることができる。
重合開始剤の使用量は，ビニルモノマ−１００重量部に対して，０．０１〜３重量部が好ましい。
【００２６】
上記懸濁剤としては，例えば，ポリビニルアルコ−ル，メチルセルロ−ス，ポリビニルピロリドン等の親水性高分子や，第３リン酸カルシウム，ピロリン酸マグネシウム等の難水溶性無機塩等を用いることができ，必要に応じて界面活性剤を併用しても良い。
難水溶性無機塩を使用する場合は，例えばアルキルスルホン酸ナトリウムやドデシルベンゼンスルホン酸ナトリウム等のアニオン系界面活性剤を併用することが好ましい。
【００２７】
懸濁剤の使用量はビニルモノマ−１００重量部に対して０．０１〜５重量部が好ましい。前記の難水溶性無機塩とアニオン性界面活性剤を併用する場合は，ビニルモノマ−１００重量部に対して，難水溶性無機塩を０．０５〜３重量部，アニオン性界面活性剤を０．０００１〜０．５重量部用いることが好ましい。
【００２８】
上記ビニルモノマ−の重合反応の際には，有機臭素化合物の難燃剤，ジクミルパ−オキサイド，ビスクミル，クメンヒドロパ−オキサイド，三酸化アンチモン等の難燃助剤，メタクリル酸メチル系共重合体，ポリエチレンワックス，タルク，シリカ，エチレンビスステアリルアミド，シリコ−ン等のセル調整剤，帯電防止剤，導電化剤，粒度分布調整剤，連鎖移動剤，重合禁止剤等の，一般的に発泡性ポリスチレン系樹脂粒子の製造に使用されている添加剤を添加したり，ブタジエンゴム，スチレン−ブタジエンゴム等のゴム成分を添加することができる。
【００２９】
上記難燃剤としては，例えば１，２，３，４−テトラブロモブタン，１，２，４−トリブロモブタン，テトラブロモペンタン，テトラブロモビスフェノ−ルＡ，２，２−ビス（４−アリルオキシ−３，５−ジブロモフェニル）プロパン，２，２−ビス（４−ヒドロキシエトキシ−３，５−ジブロモフェニル）プロパン，２，２−ビス（４−（２，３−ジブロモ）プロピルオキシ−３，５−ジブロモフェニル）プロパン，ペンタブロモジフェニルエ−テル，ヘキサブロモジフェニルエ−テル，オクタブロモジフェニルエ−テル，デカブロモジフェニルエ−テル，トリブロモフェノ−ル，ジブロムエチルベンゼンや，１，２，３，４，５，６−ヘキサブロモシクロヘキサン，１，２，５，６，９，１０−ヘキサブロモシクロドデカン，オクタブロモシクロヘキサデカン，１−クロロ−２，３，４，５，６−ペンタブロモシクロヘキサンの様な臭素置換シクロアルカン等が挙げられる。
また，トリス−（２，３−ジブロモプロピル）−ホスフェ−トのようなジブロムプロパノ−ルのエステルもしくはアセタ−ル，トリブロモフェノ−ルアリルエ−テル，トリブロモスチレン等があげられる。
この中でもヘキサブロモシクロドデカン，２，２−ビス（４−ヒドロキシエトキシ−３，５−ジブロモフェニル）プロパン，２，２−ビス（４−（２，３−ジブロモ）プロピルオキシ−３，５−ジブロモフェニル）プロパン，トリブロモフェノ−ルアリルエ−テルは少量の添加でも自己消火性を発現できることから好ましい。
【００３０】
本発明にかかる発泡性スチレン系樹脂より得られた発泡成形体は，上記した様なスチレン，トルエン等の芳香族炭化水素類の含有量が少なく，成形品から放出されるこれら物質の放散量も少ないため衛生性，安全性が高く，たとえば，各種の食品容器や医療用の容器，建材，物品等に広く用いることができる。
【００３１】
本発明の発泡性ポリスチレン系樹脂粒子は，これを予備発泡させて予備発泡粒子とし，その後予備発泡粒子を加熱発泡させて予備発泡粒子同士を融着させて，発泡成形体とする。予備発泡の方法としては，例えば，攪拌装置の付いた円筒形の予備発泡機を用いて，スチ−ムなどで加熱し発泡させる方法がある。
予備発泡粒子を発泡成形体とする方法として，例えば，金型内に予備発泡粒子を充填し，スチ−ムなどで加熱する，型内成形法で発泡成形体を得る方法が挙げられる。
このようにして，得られた発泡成形体の密度は，密度が低いと強度が不足し，逆に密度が高いと不経済であるため，一般的には１０〜５０ｋｇ／ｍ3であるのが好ましい。
【００３２】
次に，上記脂肪酸エステルは脂肪酸グリセリドであることが好ましい（請求項２）。
この場合には，融点が比較的高温の脂肪酸グリセリドが，比較的高温となる発泡および成形時に可塑剤として優れた働きを示し，発泡性，成形性の改善に大きく寄与する。また，発泡成形体としたとき，柔軟性はやや劣るものの，適度な可塑性のため収縮し難くなるという効果が得られる。
【００３３】
次に，上記脂肪酸エステルは脂肪酸トリグリセリドであることが好ましい（請求項３）。
脂肪酸トリグリセリドは，脂肪酸モノグリセリド，ジグリセリドのように親水基を有していないため，ポリスチレンに対して可塑効果が強いという効果が得られる。
【００３４】
次に，上記脂肪酸エステルは飽和脂肪酸エステルであることが好ましい（請求項４）。
この場合には，重合時の安定性を図ることができる。なお，不飽和脂肪酸エステルの場合，発泡粒子の発泡性，成型性という面では効果の差は小さいものの製造時に添加された際，重合の条件によっては重合を不安定化させる場合がある。
【００３５】
次に，上記発泡剤は，炭素数３〜６個の炭化水素化合物であることが好ましい（請求項５）。
この場合には，製品ライフが長く，発泡倍率も高い。
炭素数が２個以下の炭化水素化合物は，発泡性スチレン系樹脂粒子からの逸散が早いため，製品ライフが非常に短くなるおそれがある。炭素数が７個以上では発泡力が低下し，目標の発泡倍率まで発泡させることが困難になるおそれがある。
【００３６】
上記炭素数３〜６個の炭化水素化合物としては，例えばプロパン，ノルマルブタン，イソブタン，ノルマルペンタン，イソペンタン，ネオペンタン，ヘキサン等の脂肪族炭化水素，シクロブタン，シクロペンタン等の脂環族炭化水素等が挙げられる。
なお，より好ましくは，発泡剤は炭素数４個あるいは５個の炭化水素化合物である。
これらの発泡剤は１種類を単独で，又は２種以上を併用して使用できる。
【００３７】
次に，発泡性ポリスチレン系樹脂粒子中における，スチレン，トルエン，キシレン，エチルベンゼン，プロピルベンゼン，フタル酸エステル類の１種以上からなる芳香族炭化水素類の含有量は，０．２重量％以下であることが好ましい（請求項６）。
【００３８】
この場合には，上記芳香族炭化水素類の環境中への逸散量が少ない発泡成形体を得ることができ，また得られる発泡成形体からの上記芳香族炭化水素類の放散速度が，ＡＤＰＡＣで測定したときに１００μｇ／ｍ2・ｈｒ以下とすることができる。
なお，樹脂粒子中のこれら芳香族炭化水素類の含有量を少なくする方法は任意であるが，例えばスチレンは重合後残存する量が少なくなる重合方法を用いる。トルエン，キシレン，フタル酸エステル類といった物質は，重合時に添加しなければ含有量を微量にすることができる。
上記芳香族炭化水素類の含有量が０．２重量％を超える場合には，上記のごとく大気への放出量が多くなるおそれがある。
【００３９】
上記フタル酸エステル類としては，フタル酸ブチルベンジル，フタル酸−ｎ−ジブチル，フタル酸ジシクロヘキシル，フタル酸ジエチルヘキシル，フタル酸ジエチル，フタル酸ジヘキシル，フタル酸ジペンチル，フタル酸ジプロピルが挙げられる。
【００４０】
発泡成形体中におけるスチレン，トルエン，キシレン，エチルベンゼン，プロピルベンゼン，フタル酸エステル類の１種以上からなる芳香族炭化水素類を測定する方法としては，チャンバ−法を用いる。
チャンバ−法には，例えばＦＬＥＣ，ＡＤＰＡＣ，Ｓｍａｌｌ Ｔｅｓｔ Ｃｈａｍｂｅｒ，大型チャンバ−法などがあるが，本発明での測定にはＡＤＰＡＣを用いる。
【００４１】
ＡＤＰＡＣとは，小型チャンバ−内に材料を設置して測定する方法で，内部拡散支配型放散のサンプルからの化学物質放散速度は，建材内部での化学物質拡散性状に支配され，建材表面での流れ場は化学物質の放散性状に大きく影響を与えないため，チャンバ−内での流れ性状を無視し，完全混合を仮定している方法であり，ＡＳＴＭ及びＥＣＡの規格に準じている。
【００４２】
次に，上記発泡性ポリスチレン系樹脂粒子は，これを用いて成形した成形品中における，スチレン，トルエン，キシレン，エチルベンゼン，プロピルベンゼン，フタル酸エステル類の１種以上からなる芳香族炭化水素類の放散速度が，ＡＤＰＡＣで測定した場合に１００μｇ／ｍ2・ｈｒ以下であることが好ましい（請求項７）。
この場合には，大気環境中に放散される上記芳香族炭化水素類が少ないため，大気環境汚染を防止するという効果が得られる。
【００４３】
【実施例】
本発明の実施例及び比較例について説明する。
【００４４】
実施例１
撹拌装置のついた内容積が５０Ｌのオ−トクレ−ブに，脱イオン水１５．５ｋｇ，懸濁剤として第３リン酸カルシウム８７ｇ，界面活性剤としてドデシルジフェニルエーテルスルホン酸ジナトリウム２０ｇ，及び，ドデシルベンゼンスルホン酸ナトリウム６０ｇを投入した。
次いで，重合開始剤としてベンゾイルパ−オキサイド３９ｇ，及び，ｔ−ブチルパ−オキシ−２−エチルヘキシルカ−ボネ−ト２２ｇ，可塑剤として流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０，平均炭素数２２個）１７．０ｇと牛脂極度硬化油（脂肪酸エステル）２５５ｇ（日本油脂株式会社製）をスチレン１６．５ｋｇに溶解させ，１９０ｒｐｍで攪拌しながらオ−トクレ−ブに投入した。オ−トクレ−ブ内を窒素置換した後，昇温を開始し，１時間１５分かけて９０℃まで昇温した。
【００４５】
９０℃到達後，さらに１００℃まで５時間かけて昇温し，さらに最終重合温度として１２０℃まで１時間３０分で昇温し，そのまま１２０℃で３時間保持（最終重合温度）した。昇温途中，６０℃到達時に懸濁助剤として過硫酸カリウムの０．１％水溶液を８５ｇ添加し，９０℃到達４時間３０分目に発泡剤としてブタン（ｎ−ブタン７０％とイソブタン３０％の混合物）１２７５ｇをオ−トクレ−ブ内に圧入した。その後，３０℃まで約８時間かけて冷却した。
【００４６】
内容物を取り出し，発泡性ポリスチレン系樹脂粒子の表面に付着した第３リン酸カルシウムを除去するため，硝酸を添加して第３リン酸カルシウムを溶解させた後，遠心分離で脱水した。次に，発泡性ポリスチレン系樹脂粒子１００重量％に対して，帯電防止剤であるＮ，Ｎ−ビス（２−ヒドロキシエチル）アルキルアミン０．００８重量％を添加した後，気流乾燥機により乾燥させた。
【００４７】
得られた発泡性スチレン系樹脂を篩いにかけて０．７〜１．４ｍｍの粒子を取り出した。０．７〜１．４ｍｍの粒子に，さらにグリセリンモノステアレ−ト０．０５重量％，グリセリントリステアレ−ト０．０５重量％，ステアリン酸亜鉛０．１５重量％及びグリセリン０．０２５重量％により被覆した。
【００４８】
次いで，発泡性ポリスチレン系樹脂粒子１０ｋｇを，上下に１００メッシュの金網の付いた直径３５ｃｍの筒型金網容器に入れ，流量５５ｍ3／ｈｒで，４０℃の温風空気を筒型金属容器下部より導入し，そのまま９０分処理して発泡性ポリスチレン系樹脂粒子を得た。
【００４９】
得られた発泡性ポリスチレン系樹脂粒子３．３ｋｇを加圧バッチ予備発泡機（ダイセン工業社製ＤＹＨＬ５００Ｕ）内で，缶内圧力が０．０４ＭＰａになるようにスチ−ムを供給し，約９０秒間加熱した後，６０秒間乾燥させて，嵩密度が約１７ｋｇ／ｍ3（発泡倍率 約６０倍）の予備発泡粒子を得た。得られた予備発泡粒子を室温で１日熟成後，型物成形機（ダイセン工業社製，ＶＳ５００）の金型に充填し，０．０７ＭＰａのスチ−ム圧力で２０秒間加熱し，所定時間冷却後，金型から取り出し，発泡成形体を得た。
【００５０】
上記のようにして得られた発泡性ポリスチレン系樹脂粒子における，発泡剤の含有量，残存スチレン量，重量平均分子量，芳香族炭化水素類の含有量，発泡性，また得られた発泡成形体の芳香族炭化水素類放散速度，柔軟性，収縮性，表面外観，曲げ強度は以下の方法で評価した。
【００５１】
＜発泡剤の含重量＞
発泡性ポリスチレン系樹脂粒子をジメチルホルムアミドに溶解させ，ガスクロマトグラフィ−にて発泡剤の含有量を測定した。
【００５２】
＜残存スチレン量＞＜芳香族炭化水素類の含有量＞
発泡性ポリスチレン系樹脂粒子をジメチルホルムアミドに溶解させ，ガスクロマトグラフィ−にて，残存スチレン量，ならびにトルエン，キシレン，ベンゼン，エチルベンゼン，フタル酸エステル類及びプロピルベンゼンそれぞれの含有量を測定した。各成分の含有量を合計して芳香族炭化水素類の含有量とした。
【００５３】
＜重量平均分子量＞
発泡性ポリスチレン系樹脂粒子をテトラヒドロフランに溶解させ，ゲルパ−ミエ−ションクロマトグラフィ−で測定し，標準ポリスチレンで校正して求めた。
【００５４】
＜発泡性＞
得られた発泡性ポリスチレン系樹脂粒子を箱形バッチ予備発泡機（昭和５７年８月３日 特許庁発行の周知慣用技術集（発泡成形）第３８項参照）に入れ，圧力が０．０３ＭＰａのスチ−ムを導入し，２７０秒間加熱して発泡させた。得られた発泡粒子を室温にて８時間以上自然乾燥させてから嵩密度を測定し，発泡性を評価した。嵩密度が小さいほど，発泡性が良い。
【００５５】
＜芳香族炭化水素類の放散速度＞
６０倍の発泡成形体を，容積２０Ｌのスモ−ルチャンバ−に入れ，換気回数を０．５回／ｈｒ，相対湿度を５０％（２５℃）に設定し，１４日目までの残存スチレン量ならびにトルエン，キシレン，エチルベンゼン，フタル酸エステル類及びプロピルベンゼンの放散速度を測定した。チャンバ−内空気をＴｅｎａｘ管で採取し，加熱脱着後，ガスクロマトグラフィ−／質量分析器にて，残存スチレン量，ならびにトルエン，キシレン，エチルベンゼン，フタル酸エステル類及びプロピルベンゼンそれぞれの含有量を測定した。
【００５６】
＜柔軟性＞
得られた発泡成形体を６０℃の乾燥室で半日乾燥させた後，室温で１日養生後その成形体をニクロム切断機を用いて，大きさ２００ｍｍ×３０ｍｍ×２０ｍｍにニクロム線の温度を約２００℃にして切断し，ＪＩＳ Ｋ６７６７に準拠した柔軟性試験を１０個の試料について実施し，試験片が破断したり，ひびが発生しなかったものを合格として判定し，合格した割合（合格率，％）で柔軟性を評価した。
【００５７】
＜収縮性＞
得られた発泡成形体を常温（２３℃）にて１日放置した後，次に述べる方法で成形体の収縮を測定した。
即ち，発泡成形体として，外側の幅２８０ｍｍ，外側の長さ３３０ｍｍ，高さ１５０ｍｍで，内側の幅２３０ｍｍ（肉厚２５ｍｍ），内側の長さ３００ｍｍ（肉厚１５ｍｍ）の角筒状成形体を成形した。成形体を金型から取り出して上記のように放置し，上記幅方向（つまり２８０ｍｍ方向）の寸法収縮度合いを測定した。寸法収縮率が１％以下を○，１〜２％を△，２％以上を×とした。
【００５８】
＜表面外観＞
発泡成形体の表面外観を目視により，下記基準にて評価した。
○：発泡粒子間の間隙がなく，表面が溶融した発泡粒子もなく，表面が平滑で見栄えがよい。
△：発泡粒子間の間隙が少なく，表面が溶融した発泡粒子が僅かに存在し，比較的表面は平滑であるが，見栄えが劣る。
×：発泡粒子間の間隙が多く，あるいは表面に溶融した発泡粒子が多数存在し，表面が凸凹し見栄えが非常に悪い。あるいは発泡成形体が得られない。
【００５９】
＜曲げ強度＞
発泡成形体を切断して，縦３００ｍｍ×横７５ｍｍ×厚さ２５ｍｍの試験片を作成し，ＪＩＳ Ａ ９５１１に準拠して３点曲げ試験を行い，曲げ強度（ＫＰａ）を測定した。
【００６０】
実施例２
可塑剤として流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）２５５ｇと牛脂極度硬化油１７．０ｇ（日本油脂株式会社製）を添加した以外は，実施例１と同様に行った。
【００６１】
実施例３
可塑剤として流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）２５５ｇと牛脂極度硬化油２５５ｇ（日本油脂株式会社製）を添加した以外は，実施例１と同様に行った。
【００６２】
実施例４
可塑剤として流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）１７０ｇと牛脂極度硬化油（日本油脂株式会社製）１７０ｇを添加した以外は，実施例１と同様に行った。
【００６３】
実施例５
可塑剤として流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）８５ｇと牛脂極度硬化油（日本油脂株式会社製）８５ｇを添加した以外は，実施例１と同様に行った。
【００６４】
実施例６
可塑剤として，牛脂極度硬化油の代わりに，ヒマシ硬化油（日本油脂株式会社製 カスターワックスＡ）を１７０ｇ用いると共に流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）を１７０ｇ添加した以外は，実施例１と同様に行った。
【００６５】
実施例７
可塑剤として，牛脂極度硬化油の代わりにミリスチン酸ミリスチル（花王株式会社製 エキセパールＭＹ−Ｍ）を１７０ｇ用いると共に，流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）を１７０ｇ添加した以外は，実施例１と同様に行った。
【００６６】
実施例８
重合開始剤としてのｔ−ブチルパ−オキシ−２−エチルヘキシルカ−ボネ−トの量を１７ｇ添加し，最終重合温度及び時間を１１２℃で１時間３０分とした以外は，実施例１と同様に行った。
【００６７】
実施例９
可塑剤として，流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）の代わりに他の流動パラフィン（松村石油研究所社製 モレスコホワイトＰ１５０，平均炭素数２５個）を１７０ｇ用いると共に，牛脂極度硬化油（日本油脂株式会社製）１７０ｇを添加した以外は，実施例１と同様に行った。
【００６８】
実施例１０
可塑剤として，流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）の代わりに他の流動パラフィン（松村石油研究所社製 モレスコホワイトＰ１５０，平均炭素数２５個）を２５５ｇを用いると共に，牛脂極度硬化油（日本油脂株式会社製）１７．０ｇを添加した以外は，実施例１と同様に行った。
【００６９】
実施例１１
可塑剤として，流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）の代わりに他の流動パラフィン（松村石油研究所社製 モレスコホワイトＰ３５０，平均炭素数３３個）を１７０ｇを用いると共に，，牛脂極度硬化油（日本油脂株式会社製）１７０ｇを添加した以外は，実施例１と同様に行った。
【００７０】
実施例１２
可塑剤として，流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）の代わりに他の流動パラフィン（松村石油研究所社製 モレスコホワイトＰ３５０，平均炭素数３３個）を２５５ｇを用いると共に，，牛脂極度硬化油（日本油脂株式会社製）１７．０ｇを添加した以外は，実施例１と同様に行った。
【００７１】
実施例１３
可塑剤として，牛脂極度硬化油の代わりに，ステアリン酸モノグリセリド（花王株式会社製 エキセルＴ−９５）を１７０ｇ用いると共に，流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）を１７０ｇ添加した以外は，実施例１と同様に行なった。
【００７２】
比較例１
可塑剤として，可塑剤として流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）３４０ｇのみを添加した以外は，実施例１と同様に行った。
【００７３】
比較例２
可塑剤として，牛脂極度硬化油３４０ｇのみを添加した以外は，実施例１と同様に行った。
【００７４】
比較例３
可塑剤として流動パラフィン（松村石油研究所社製 モレスコホワイトＰ６０）５１０ｇのみを添加した以外は，実施例１と同様に行った。
【００７５】
比較例４
可塑剤として牛脂極度硬化油（日本油脂株式会社製）５１０ｇのみを添加した以外は，実施例１と同様に行った。
【００７６】
比較例５
可塑剤として牛脂極度硬化油（日本油脂株式会社製）３４０ｇのみを添加し，重合開始剤としてのｔ−ブチルパーオキシ−２−エチルヘキシルカーボネートを１７ｇ添加し，最終重合温度及び時間を１１２℃，１時間３０分とした以外は実施例１と同様に行なった。
【００７７】
以上の各実施例及び各比較例における，上記の各測定結果を表１〜表３に示した。
表１〜表３において，可塑剤等の量（重量％）はスチレン系樹脂１００重量％に対する割合である。
表１〜表３より明らかなように，本発明の実施例１〜７，９〜１３に係る発泡性ポリスチレン系樹脂粒子は，芳香族炭化水素類の含有量が０．２重量％以下で，発泡性にも優れている。
また，この発泡性ポリスチレン系樹脂粒子を用いて成形した発泡成形体は，上記の放散速度が小さく，柔軟性，収縮性，表面外観，曲げ強度がいずれも優れていた。
【００７８】
また，実施例８，比較例５は，重合開始剤量，最終重合温度及び時間（１１２℃，１．５時間）を変更したため，芳香族炭化水素類の含有量及び放散量が多くなった。
一方，比較例１及び３は，可塑剤として流動パラフィンのみを使用したため，収縮性，表面外観が劣っていた。比較例２，４及び５は，可塑剤として牛脂極度硬化油のみを使用したため，柔軟性，表面外観が劣っていた。
【００７９】
【表１】
【表２】
【表３】
【Technical field】
The present invention relates to a foamed molded product having a low content of aromatic hydrocarbons such as styrene and toluene, excellent foaming properties, and a foamed molded product having high strength and excellent flexibility. Relates to expandable polystyrene resin particles.
[0002]
[Prior art]
Styrenic foam moldings are made by adding a foaming agent and a plasticizer for improving foamability to a styrene resin to produce expandable polystyrene resin particles, which are pre-foamed and then foam-molded in a mold. Can be obtained. This foam molded article has excellent buffering properties and heat insulation properties, is easy to mold, and is a relatively inexpensive material, so it is widely used as a packaging material and heat insulation material.
[0003]
Conventionally, hydrocarbons such as pentane and butane have been used as blowing agents. As the plasticizer, styrene left in the expandable polystyrene resin particles, a small amount of toluene, xylene, or an organic solvent such as cyclohexane is widely used. Many of such foaming agents and plasticizers are volatile organic compounds.
[0004]
Conventionally, a volatile organic compound that functions as a foaming agent or a plasticizer is contained on an average of 6 to 9% by weight based on the styrene resin particles, and gradually in each process such as storage, foaming, molding, and processing. Released into the atmosphere.
[0005]
[Problems to be solved]
Recently, in consideration of the global environment, attempts have been made to reduce the amount of foaming agents and organic solvents in expandable polystyrene resin particles. For example, JP-A-4-268347, JP-A-6-80708, and JP-A-10-17698 disclose expandable polystyrene resin particles having a small content of residual styrene and benzene and methods for producing the same.
[0006]
Conventionally, styrene-based expandable resin particles used as plasticizers are aromatic hydrocarbons such as styrene, toluene, xylene, ethylbenzene, propylbenzene, and phthalates that have an excellent plasticizing effect on styrene-based resins. .
[0007]
As described above, in recent years, due to considerations for environmental sanitation, there is a strong demand for materials with a low emission amount of the above aromatic hydrocarbons such as styrene and toluene.
However, if the content of these aromatic components is simply reduced in the styrene-based expandable resin particles, the expandability of the expandable resin particles is deteriorated and the fusion between the pre-expanded particles at the time of molding is decreased. There is a problem.
As a countermeasure, it is conceivable to lower the molecular weight of the base resin of the styrene-based expandable resin particles, but in this case, there is a problem that the mechanical strength is lowered.
[0008]
In view of such conventional problems, the present invention has a low content and emission amount of aromatic hydrocarbons such as styrene and toluene, has excellent foamability, and the resulting foamed molded product has high strength and flexibility. It is an object of the present invention to provide expandable polystyrene resin particles having properties.
[0009]
[Means for solving problems]
The invention described in claim 1Styrene or a mixture of vinyl monomers containing styrene as a main component is dispersed in an aqueous medium together with a plasticizer and a polymerization initiator to initiate a polymerization reaction to form a styrene resin, and foaming during or after completion of the polymerization In expandable polystyrene resin particles obtained by adding an agent,
The expandable polystyrene resin particles are:A styrene resin having a weight average molecular weight of 200,000 to 400,000,
3 to 10% by weight of an organic compound having a boiling point of 90 ° C. or less as a foaming agent with respect to 100% by weight of the styrenic resin,
Contained in the styrenic resinAs a plasticizerof0.01 to 2% by weight of liquid paraffin having an average carbon number of 20 to 35 and,
Similarly as a plasticizer contained in the styrenic resinIt is an expandable polystyrene resin particle characterized by containing 0.01 to 2% by weight of a fatty acid ester that is solid at room temperature.
[0010]
According to this invention, the said foaming agent and a plasticizer are contained in the said weight% range with respect to the said specific styrene resin and 100 weight% of this styrene resin.
Therefore, the content of aromatic hydrocarbons consisting of at least one of styrene, toluene, xylene, ethylbenzene, propylbenzene, and phthalates is low, and has excellent foaming properties. It is possible to provide expandable polystyrene resin particles having high strength, excellent flexibility, good appearance, and hardly shrinking.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the invention of claim 1, the styrenic resin has a weight average molecular weight of 200,000 to 400,000. Thereby, the foaming molding which has the outstanding intensity | strength can be created, maintaining high foamability. The said weight average molecular weight is the value measured by GPC (Gel Permeation Chromatography; gel permeation chromatography) method.
[0012]
If the said weight average molecular weight is less than 200,000, there exists a possibility that the intensity | strength of the foaming molding obtained may fall. On the other hand, when the weight average molecular weight exceeds 400,000, the foaming property is lowered, and it becomes difficult to foam to a target foaming ratio (for example, 50 to 60 times), or the foamed particles are difficult to fuse at the time of molding. , There is a risk that the strength of the foamed molded product is lowered.
More preferably, the styrene resin particles have a weight average molecular weight of 200,000 to 380,000, and more preferably 220,000 to 350,000.
[0013]
Next, the expandable polystyrene resin particles contain 3 to 10% by weight of an organic compound having a boiling point of 90 ° C. or less that functions as a foaming agent with respect to 100% by weight of the styrene resin.
As the foaming agent, organic compounds having a boiling point of 90 ° C. or lower include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, and hexane, and alicyclic hydrocarbons such as cyclobutane and cyclopentane. And hydrocarbon compounds having 3 to 6 carbon atoms, ketones such as acetone and methyl ethyl ketone, and alcohols such as methanol, ethanol and isopropyl alcohol.
[0014]
When the content of the foaming agent is less than 3% by weight, the foamability of the expandable polystyrene resin particles is lowered, and it may be difficult to foam to the target foaming ratio. If it exceeds 10% by weight, there is a limit to the solubility in polystyrene resin, which is economically wasteful, and the amount of volatile organic compounds released into the atmosphere increases, which may contaminate the air environment.
In addition, More preferably, content of the said foaming agent is 5 to 10 weight%.
[0015]
In producing the expandable polystyrene resin particles according to the present invention, the styrene monomer is dispersed in an aqueous medium in the presence of a polymerization initiator, a suspending agent and a surfactant, and then polymerized. The reaction can be initiated and a blowing agent can be added during suspension polymerization or impregnated with the blowing agent after suspension polymerization is complete.
When the styrenic monomer is dispersed in the aqueous medium, both may be charged in advance or may be gradually added.
[0016]
Next, the expandable polystyrene resin particles contain 0.01 to 2% by weight of liquid paraffin having an average carbon number of 20 to 35 and functioning as a plasticizer with respect to 100% by weight of the styrene resin. Yes.
If the content of the liquid paraffin is less than 0.01% by weight, the plastic effect is small, and it may be difficult to foam to the target foaming ratio when producing a foamed molded product. On the other hand, if it exceeds 2% by weight, the surface appearance of the obtained foamed molded article is deteriorated, the strength and heat resistance are lowered, and the production cost may be increased. More preferably, the content of the liquid paraffin is 0.1 to 1.5% by weight.
[0017]
The liquid paraffin is a mixture of saturated hydrocarbons represented by CmHn (n <2m + 1, n and m are natural numbers) and has an average carbon number of 20 to 35, and is liquid paraffin at room temperature. Normal temperature means 10-30 degreeC.
[0018]
Since liquid paraffins with an average carbon number of less than 20 are volatile, they may become volatile organic compounds that are gradually released into the atmosphere during storage, foaming, molding, and other processes. There exists a possibility that the effect concerning this invention may become difficult to acquire.
In addition, when the average number of carbon atoms is 35 or more, there are problems that the target plastic effect cannot be obtained or that the viscosity is high and difficult to handle.
As a result, it is possible to obtain expandable polystyrene resin particles having excellent foam moldability while suppressing the diffusion of organic compounds into the atmosphere during the molding process.
[0019]
The expandable polystyrene resin particles contain 0.01 to 2% by weight of a fatty acid ester that is solid at room temperature and functions as a plasticizer in combination with the above liquid paraffin with respect to 100% by weight of the styrene resin. Has been.
When only the above fatty acid ester is used as a plasticizer, the fatty acid ester acts as a plasticizer at the time of foaming and molding at a relatively high temperature and contributes to improvement of foamability and moldability. However, when foamed molded products are used, fatty acid esters agglomerate in the resin, so the decrease in molded product strength and heat resistance is smaller than that of liquid paraffin, and the molded product has excellent shrinkage. There is a possibility that the flexibility of is inferior.
[0020]
If the content of the fatty acid ester that is solid at room temperature is less than 0.01% by weight, the plastic effect is small, and it may be difficult to foam to the target foaming ratio when producing the foamed molded product.
On the other hand, if it exceeds 2% by weight, the strength and heat resistance of the obtained foamed molded product may be lowered, and the production cost may be increased. More preferably, the content of the fatty acid ester solid at normal temperature is 0.1 to 1.5% by weight.
[0021]
Examples of the fatty acid ester solid at normal temperature include esters of higher fatty acids and higher aliphatic monohydric alcohols, esters of higher fatty acids and sorbitan, and esters of higher fatty acids and glycerin. For example, glycerides such as stearic acid, myristic acid, palmitic acid, behenic acid, oleic acid, beef tallow extremely hardened oil, castor hardened oil, extremely hardened soybean oil, myristyl myristate, stearyl stearate, octyldodecyl behenate, behenyl behenate Sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan distearate, sorbitan monobehenate and the like.
[0022]
The present invention contains 0.01 to 2% by weight of liquid paraffin having an average carbon number of 20 to 35 as a plasticizer, and 0.01 to 2% by weight of a fatty acid ester that is solid at room temperature. This compensates for the disadvantages when each plasticizer is used alone, has excellent foamability, and the resulting foamed molded article has high strength, good appearance, hardly shrinks, and flexibility. Expandable styrenic resin particles can be provided.
[0023]
As a method for producing the expandable polystyrene resin particles, for example, styrene is dispersed in an aqueous solvent in the presence of a suitable suspending agent together with a plasticizer and a polymerization initiator in a closed container equipped with a stirrer. The polymerization reaction is started to obtain a styrene resin, and a foaming agent is added during or after the polymerization to obtain expandable polystyrene resin particles.
[0024]
The expandable polystyrene resin particles can be produced from styrene or a mixture of vinyl monomers mainly composed of styrene. Examples of vinyl monomers copolymerizable with styrene include α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, p-ethylstyrene, 2,4-dimethylstyrene, and p-methoxy. Styrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4-dichlorostyrene, pn-butylstyrene, pt-butylstyrene, pn-hexylstyrene, Examples thereof include p-octyl styrene, styrene sulfonic acid, sodium styrene sulfonate, and the like. Two or more kinds of these vinyl monomers may be used in combination.
[0025]
Examples of the polymerization initiator include azo compounds such as azobisisobutyronitrile, cumene hydroperoxide, dicumyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxybenzoate, Benzoyl peroxide, t-butyl peroxyisopropyl carbonate, t-butyl peroxy 2-ethylhexyl monocarbonate, 1,1-dimethylpropyl peroxy-2-ethylhexyl monocarbonate, 1 1,1-dimethylbutyl peroxy-2-ethylhexyl monocarbonate, pentyl peroxy 2-ethylhexyl monocarbonate, hexyl peroxy 2-ethylhexyl monocarbonate, lauroyl peroxide, 1,1- Bis (t-butylperoxy) -3,3,5-tri Chill cyclohexane, 1,1-di -t- Buchirupa - soluble initiators mentioned styrene monomers such as oxy-2-methylcyclohexane. These polymerization initiators can be used alone or in combination of two or more.
The amount of the polymerization initiator used is preferably 0.01 to 3 parts by weight with respect to 100 parts by weight of the vinyl monomer.
[0026]
Examples of the suspending agent that can be used include hydrophilic polymers such as polyvinyl alcohol, methyl cellulose, and polyvinyl pyrrolidone, and poorly water-soluble inorganic salts such as tricalcium phosphate and magnesium pyrophosphate. Depending on the case, a surfactant may be used in combination.
When using a slightly water-soluble inorganic salt, it is preferable to use an anionic surfactant such as sodium alkylsulfonate or sodium dodecylbenzenesulfonate in combination.
[0027]
The amount of the suspending agent used is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the vinyl monomer. In the case of using the sparingly water-soluble inorganic salt and the anionic surfactant in combination, 0.05 to 3 parts by weight of the sparingly water-soluble inorganic salt and 0.1% of the anionic surfactant are used with respect to 100 parts by weight of the vinyl monomer. It is preferable to use 0001 to 0.5 parts by weight.
[0028]
In the polymerization reaction of the vinyl monomer, flame retardants such as organic bromine compounds, dicumyl peroxide, biscumyl, cumene hydroperoxide, antimony trioxide, methyl methacrylate copolymer, polyethylene wax, talc , Silica, ethylenebisstearylamide, silicone and other cell regulators, antistatic agents, conductive agents, particle size distribution regulators, chain transfer agents, polymerization inhibitors, etc. Additives used in production can be added, and rubber components such as butadiene rubber and styrene-butadiene rubber can be added.
[0029]
Examples of the flame retardant include 1,2,3,4-tetrabromobutane, 1,2,4-tribromobutane, tetrabromopentane, tetrabromobisphenol A, 2,2-bis (4-allyloxy). -3,5-dibromophenyl) propane, 2,2-bis (4-hydroxyethoxy-3,5-dibromophenyl) propane, 2,2-bis (4- (2,3-dibromo) propyloxy-3, 5-dibromophenyl) propane, pentabromodiphenyl ether, hexabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, tribromophenol, dibromoethylbenzene, 1,2, 3,4,5,6-hexabromocyclohexane, 1,2,5,6,9,10-hexabromocyclododecane, octabro Cyclohexadecane, 1-chloro-2,3,4,5,6-brominated cycloalkanes such, such as penta-bromo cyclohexane.
Further, examples include esters or acetal of dibromopropanol such as tris- (2,3-dibromopropyl) -phosphate, tribromophenol allyl ether, tribromostyrene, and the like.
Among these, hexabromocyclododecane, 2,2-bis (4-hydroxyethoxy-3,5-dibromophenyl) propane, 2,2-bis (4- (2,3-dibromo) propyloxy-3,5-dibromo Phenyl) propane and tribromophenol allyl ether are preferred because they can exhibit self-extinguishing properties even when added in a small amount.
[0030]
The foamed molded product obtained from the expandable styrenic resin according to the present invention has a low content of aromatic hydrocarbons such as styrene and toluene as described above, and the amount of these substances released from the molded product is also reduced. Since it is small, it has high hygiene and safety, and can be widely used for various food containers, medical containers, building materials, articles, and the like.
[0031]
The expandable polystyrene resin particles of the present invention are pre-expanded to be pre-expanded particles, and then the pre-expanded particles are heated and foamed to fuse the pre-expanded particles together to obtain a foam molded article. As a pre-foaming method, for example, there is a method of foaming by heating with a steam or the like using a cylindrical pre-foaming machine equipped with a stirring device.
Examples of a method of using pre-expanded particles as a foam-molded product include a method of obtaining a foam-molded product by an in-mold molding method in which pre-expanded particles are filled in a mold and heated with a steam or the like.
In this way, the density of the obtained foamed molded article is insufficient when the density is low, and conversely, it is uneconomical when the density is high.ThreeIs preferred.
[0032]
Next, the fatty acid ester is preferably a fatty acid glyceride (claim 2).
In this case, fatty acid glycerides having a relatively high melting point exhibit an excellent function as a plasticizer during foaming and molding at relatively high temperatures, and greatly contribute to the improvement of foamability and moldability. Moreover, when it is made into a foamed molded product, although the flexibility is somewhat inferior, the effect that it becomes difficult to shrink due to moderate plasticity is obtained.
[0033]
Next, the fatty acid ester is preferably a fatty acid triglyceride.
Since fatty acid triglyceride does not have a hydrophilic group like fatty acid monoglyceride and diglyceride, an effect that a plasticizing effect is strong with respect to polystyrene is obtained.
[0034]
Next, the fatty acid ester is preferably a saturated fatty acid ester.
In this case, stability during polymerization can be achieved. In the case of unsaturated fatty acid esters, the difference in effect is small in terms of foamability and moldability of the foamed particles, but when added during production, the polymerization may be destabilized depending on the polymerization conditions.
[0035]
Next, the foaming agent is preferably a hydrocarbon compound having 3 to 6 carbon atoms.
In this case, the product life is long and the expansion ratio is high.
Hydrocarbon compounds having 2 or less carbon atoms are likely to have a very short product life because they dissipate quickly from the expandable styrene resin particles. When the number of carbon atoms is 7 or more, the foaming power is reduced, and it may be difficult to foam to the target foaming ratio.
[0036]
Examples of the hydrocarbon compound having 3 to 6 carbon atoms include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, and hexane, and alicyclic hydrocarbons such as cyclobutane and cyclopentane. Can be mentioned.
More preferably, the blowing agent is a hydrocarbon compound having 4 or 5 carbon atoms.
These foaming agents can be used alone or in combination of two or more.
[0037]
Next, the content of aromatic hydrocarbons composed of one or more of styrene, toluene, xylene, ethylbenzene, propylbenzene, and phthalates in the expandable polystyrene resin particles is 0.2% by weight or less. It is preferable that there is (Claim 6).
[0038]
In this case, it is possible to obtain a foamed molded article with a small amount of the aromatic hydrocarbons released into the environment, and the diffusion rate of the aromatic hydrocarbons from the obtained foamed molded article is determined by the ADPAC. 100 μg / m when measured with2-It can be less than hr.
Any method can be used to reduce the content of these aromatic hydrocarbons in the resin particles. For example, a polymerization method in which the amount of styrene remaining after polymerization is reduced is used. Substances such as toluene, xylene, and phthalates can be contained in minute amounts unless added during polymerization.
When the content of the aromatic hydrocarbons exceeds 0.2% by weight, the amount released to the atmosphere may increase as described above.
[0039]
Examples of the phthalic acid esters include butylbenzyl phthalate, n-dibutyl phthalate, dicyclohexyl phthalate, diethylhexyl phthalate, diethyl phthalate, dihexyl phthalate, dipentyl phthalate, and dipropyl phthalate.
[0040]
A chamber method is used as a method for measuring aromatic hydrocarbons composed of one or more of styrene, toluene, xylene, ethylbenzene, propylbenzene, and phthalates in the foamed molded article.
The chamber method includes, for example, FLEC, ADPAC, Small Test Chamber, large chamber method, etc. ADPAC is used for measurement in the present invention.
[0041]
ADPAC is a method in which materials are placed in a small chamber and measured. The chemical diffusion rate from the internal diffusion-dominated diffusion sample is governed by the chemical diffusion properties inside the building material, and is measured on the surface of the building material. Since the flow field does not significantly affect the chemical release properties, it ignores the flow properties in the chamber and assumes complete mixing, and conforms to ASTM and ECA standards.
[0042]
Next, the expandable polystyrene resin particles are made of aromatic hydrocarbons composed of one or more of styrene, toluene, xylene, ethylbenzene, propylbenzene, and phthalates in a molded product molded using the same. The emission rate is 100 μg / m as measured by ADPAC.2-It is preferable that it is below hr (claim 7).
In this case, since the aromatic hydrocarbons released into the atmospheric environment are small, an effect of preventing atmospheric pollution is obtained.
[0043]
【Example】
Examples of the present invention and comparative examples will be described.
[0044]
Example 1
Into an autoclave with a stirrer of 50L, 15.5 kg of deionized water, 87 g of tricalcium phosphate as a suspending agent, 20 g of disodium dodecyl diphenyl ether sulfonate as a surfactant, and dodecyl benzene sulfone 60 g of sodium acid was added.
Subsequently, 39 g of benzoyl peroxide as a polymerization initiator and 22 g of t-butyl peroxy-2-ethylhexyl carbonate, liquid paraffin as a plasticizer (Moleco White P60 manufactured by Matsumura Oil Research Co., Ltd., average carbon number 22) 17.0 g and beef tallow extremely hardened oil (fatty acid ester) 255 g (manufactured by Nippon Oil & Fats Co., Ltd.) were dissolved in 16.5 kg of styrene and charged into an autoclave while stirring at 190 rpm. After replacing the inside of the autoclave with nitrogen, the temperature increase was started and the temperature was increased to 90 ° C. over 1 hour and 15 minutes.
[0045]
After reaching 90 ° C., the temperature was further raised to 100 ° C. over 5 hours. Further, the final polymerization temperature was raised to 120 ° C. over 1 hour 30 minutes, and maintained at 120 ° C. for 3 hours (final polymerization temperature). During the temperature increase, when reaching 60 ° C., 85 g of a 0.1% aqueous solution of potassium persulfate was added as a suspension aid, and after 90 hours at 90 ° C., butane was added as a blowing agent (butane 70% and isobutane 30% 1275 g) was pressed into the autoclave. Then, it cooled to 30 degreeC over about 8 hours.
[0046]
The contents were taken out, and in order to remove the tertiary calcium phosphate adhering to the surface of the expandable polystyrene resin particles, nitric acid was added to dissolve the tertiary calcium phosphate, and then dehydrated by centrifugation. Next, after adding 0.008% by weight of N, N-bis (2-hydroxyethyl) alkylamine, which is an antistatic agent, to 100% by weight of expandable polystyrene resin particles, it is dried by an air dryer. It was.
[0047]
The obtained expandable styrenic resin was sieved and particles of 0.7 to 1.4 mm were taken out. In addition to 0.7-1.4 mm particles, 0.05% by weight of glycerol monostearate, 0.05% by weight of glycerol tristearate, 0.15% by weight of zinc stearate and 0.025% by weight of glycerol Coated.
[0048]
Next, 10 kg of expandable polystyrene resin particles are put into a cylindrical wire mesh container having a diameter of 35 cm with a 100 mesh wire mesh on the top and bottom, and the flow rate is 55 m.Three/ Hr, hot air of 40 ° C. was introduced from the bottom of the cylindrical metal container, and treated as it was for 90 minutes to obtain expandable polystyrene resin particles.
[0049]
In a pressurized batch pre-foaming machine (DYHL 500U, manufactured by Daisen Kogyo Co., Ltd.), a steam was supplied to the obtained expandable polystyrene resin particles (3.3 kg) so that the internal pressure of the can becomes 0.04 MPa. After heating, it is dried for 60 seconds, and the bulk density is about 17kg / mThreePre-expanded particles having an expansion ratio of about 60 times were obtained. The pre-expanded particles obtained were aged at room temperature for 1 day, filled in a mold of a molding machine (Daisen Kogyo Co., Ltd., VS500), heated at a steam pressure of 0.07 MPa for 20 seconds, and cooled for a predetermined time. Thereafter, it was removed from the mold to obtain a foamed molded product.
[0050]
In the expandable polystyrene resin particles obtained as described above, the content of the foaming agent, the amount of residual styrene, the weight average molecular weight, the content of aromatic hydrocarbons, the foamability, and the obtained foamed molded product The aromatic hydrocarbons release rate, flexibility, shrinkage, surface appearance, and bending strength were evaluated by the following methods.
[0051]
<Weight content of foaming agent>
Expandable polystyrene resin particles were dissolved in dimethylformamide, and the content of the foaming agent was measured by gas chromatography.
[0052]
<Residual styrene content> <Aromatic hydrocarbon content>
Expandable polystyrene resin particles were dissolved in dimethylformamide, and the amount of residual styrene and the contents of toluene, xylene, benzene, ethylbenzene, phthalates and propylbenzene were measured by gas chromatography. The content of each component was summed to obtain the content of aromatic hydrocarbons.
[0053]
<Weight average molecular weight>
The expandable polystyrene resin particles were dissolved in tetrahydrofuran, measured by gel permeation chromatography, and calibrated with standard polystyrene.
[0054]
<Foaming properties>
The obtained expandable polystyrene resin particles are put into a box-type batch pre-foaming machine (refer to paragraph 38 of well-known conventional technology (foam molding) published on August 3, 1982) and the pressure is 0.03 MPa. A steam was introduced and foamed by heating for 270 seconds. The obtained foamed particles were naturally dried at room temperature for 8 hours or more, and then the bulk density was measured to evaluate foamability. The smaller the bulk density, the better the foamability.
[0055]
<Emission rate of aromatic hydrocarbons>
A 60-fold expanded molded article is put in a 20 L volume small chamber, the ventilation frequency is set to 0.5 times / hr, the relative humidity is set to 50% (25 ° C.), and the amount of residual styrene by the 14th day. The emission rates of toluene, xylene, ethylbenzene, phthalates and propylbenzene were measured. The air in the chamber was sampled with a Tenax tube, and after heat desorption, the amount of residual styrene and the contents of toluene, xylene, ethylbenzene, phthalates and propylbenzene were measured with a gas chromatography / mass spectrometer. .
[0056]
<Flexibility>
The obtained foamed molded product was dried in a drying room at 60 ° C. for half a day, then cured at room temperature for one day, and then the molded product was subjected to a nichrome cutting machine to a size of 200 mm × 30 mm × 20 mm and the temperature of the nichrome wire was reduced to about The sample was cut at 200 ° C., a flexibility test in accordance with JIS K6767 was performed on 10 samples, and the test piece was judged to be acceptable if it did not break or cracked. ,%) Was evaluated for flexibility.
[0057]
<Shrinkability>
The obtained foamed molded product was allowed to stand at room temperature (23 ° C.) for 1 day, and then the shrinkage of the molded product was measured by the method described below.
That is, as the foam molded body, a rectangular tube-shaped molded body having an outer width of 280 mm, an outer length of 330 mm, a height of 150 mm, an inner width of 230 mm (thickness of 25 mm), and an inner length of 300 mm (thickness of 15 mm). Molded. The molded body was taken out from the mold and allowed to stand as described above, and the degree of dimensional shrinkage in the width direction (that is, 280 mm direction) was measured. The dimensional shrinkage ratio is 1% or less, ◯, 1-2% is Δ, and 2% or more is ×.
[0058]
<Surface appearance>
The surface appearance of the foamed molded product was evaluated visually according to the following criteria.
○: There are no gaps between the expanded particles, the expanded surface has no expanded particles, and the surface is smooth and attractive.
(Triangle | delta): The space | gap between foaming particles is few, there exist few foaming particles which the surface fuse | melted, and the surface is comparatively smooth, but the appearance is inferior.
×: There are many gaps between the expanded particles, or there are many expanded particles melted on the surface, the surface is uneven, and the appearance is very bad. Or a foaming molding cannot be obtained.
[0059]
<Bending strength>
The foamed molded body was cut to prepare a test piece having a length of 300 mm × width of 75 mm × thickness of 25 mm, a three-point bending test was performed in accordance with JIS A 9511, and the bending strength (KPa) was measured.
[0060]
Example 2
The same procedure as in Example 1 was performed except that 255 g of liquid paraffin (Moleco White P60 manufactured by Matsumura Oil Research Co., Ltd.) and 17.0 g of beef tallow extremely hardened oil (manufactured by Nippon Oil & Fats Co., Ltd.) were added as plasticizers.
[0061]
Example 3
The same procedure as in Example 1 was conducted except that 255 g of liquid paraffin (Moleco White P60 manufactured by Matsumura Oil Research Co., Ltd.) and 255 g of beef tallow extremely hardened oil (manufactured by Nippon Oil & Fats Co., Ltd.) were added as plasticizers.
[0062]
Example 4
The same procedure as in Example 1 was performed except that 170 g of liquid paraffin (Moleco White P60 manufactured by Matsumura Oil Research Co., Ltd.) and 170 g of beef tallow extremely hardened oil (manufactured by Nippon Oil & Fats Co., Ltd.) were added as plasticizers.
[0063]
Example 5
The same procedure as in Example 1 was performed except that 85 g of liquid paraffin (Moleco White P60 manufactured by Matsumura Oil Research Co., Ltd.) and 85 g of beef tallow extremely hardened oil (manufactured by Nippon Oil & Fats Co., Ltd.) were added as plasticizers.
[0064]
Example 6
As a plasticizer, 170 g of castor hardened oil (Caster Wax A manufactured by Nippon Oil & Fats Co., Ltd.) is used instead of beef fat extremely hardened oil, and 170 g of liquid paraffin (Molemura White P60 manufactured by Matsumura Oil Research Co., Ltd.) is added. The same operation as in Example 1 was performed.
[0065]
Example 7
As a plasticizer, 170 g of myristyl myristate (Exepal MY-M manufactured by Kao Corporation) is used in place of beef tallow extremely hardened oil, and 170 g of liquid paraffin (Molesco White P60 manufactured by Matsumura Oil Research Co., Ltd.) is added. The same operation as in Example 1 was performed.
[0066]
Example 8
As in Example 1, except that 17 g of t-butyl peroxy-2-ethylhexyl carbonate as a polymerization initiator was added and the final polymerization temperature and time were 112 ° C. and 1 hour 30 minutes. went.
[0067]
Example 9
As a plasticizer, 170 g of other liquid paraffin (Morethco White P150, Matsumura Oil Research Co., Ltd., Morocco White P150, average carbon number 25) is used instead of liquid paraffin (Matsumura Oil Research Co., Ltd. Moresco White P60) It carried out like Example 1 except having added 170g of hardened oil (made by Nippon Oil & Fat Co., Ltd.).
[0068]
Example 10
As a plasticizer, instead of liquid paraffin (Morethco White P60, Matsumura Oil Research Co., Ltd.), 255 g of other liquid paraffin (Morezco White P150, Matsumura Oil Research Co., Ltd., average carbon number 25) is used, and beef tallow The same operation as in Example 1 was performed except that 17.0 g of extremely hardened oil (manufactured by Nippon Oil & Fats Co., Ltd.) was added.
[0069]
Example 11
As a plasticizer, 170 g of other liquid paraffin (Morezco White P350, Matsumura Oil Research Co., Ltd., Moresco White P350, average carbon number 33) is used instead of liquid paraffin (Morseco White P60, manufactured by Matsumura Oil Research Co., Ltd.) The same procedure as in Example 1 was performed except that 170 g of beef tallow extremely hardened oil (Nippon Yushi Co., Ltd.) was added.
[0070]
Example 12
As a plasticizer, 255 g of other liquid paraffin (Morethco White P350, Matsumura Oil Research Co., Ltd., Morseco White P350, average carbon number 33) is used instead of liquid paraffin (Morsoco White P60, manufactured by Matsumura Oil Research Co., Ltd.) The same procedure as in Example 1 was conducted except that 17.0 g of beef tallow extremely hardened oil (manufactured by Nippon Oil & Fats Co., Ltd.) was added.
[0071]
Example 13
As a plasticizer, 170 g of stearic acid monoglyceride (Excel T-95 manufactured by Kao Corporation) was used instead of beef tallow extremely hardened oil, and 170 g of liquid paraffin (Morezco White P60 manufactured by Matsumura Oil Research Co., Ltd.) was added. This was carried out in the same manner as in Example 1.
[0072]
Comparative Example 1
As a plasticizer, the same procedure as in Example 1 was performed except that only 340 g of liquid paraffin (Moleco White P60 manufactured by Matsumura Oil Research Co., Ltd.) was added as a plasticizer.
[0073]
Comparative Example 2
The same procedure as in Example 1 was performed except that only 340 g of beef tallow extremely hardened oil was added as a plasticizer.
[0074]
Comparative Example 3
The same procedure as in Example 1 was performed except that only 510 g of liquid paraffin (Moleco White P60 manufactured by Matsumura Oil Research Co., Ltd.) was added as a plasticizer.
[0075]
Comparative Example 4
The same operation as in Example 1 was performed except that only 510 g of beef tallow extremely hardened oil (manufactured by Nippon Oil & Fats Co., Ltd.) was added as a plasticizer.
[0076]
Comparative Example 5
Only 340 g of beef tallow extremely hardened oil (manufactured by Nippon Oil & Fats Co., Ltd.) is added as a plasticizer, 17 g of t-butylperoxy-2-ethylhexyl carbonate is added as a polymerization initiator, and the final polymerization temperature and time are 112 ° C., 1 The same operation as in Example 1 was performed except that the time was 30 minutes.
[0077]
Tables 1 to 3 show the measurement results of the above examples and comparative examples.
In Tables 1 to 3, the amount (% by weight) of the plasticizer and the like is a ratio with respect to 100% by weight of the styrene resin.
As is clear from Tables 1 to 3, the expandable polystyrene resin particles according to Examples 1 to 7 and 9 to 13 of the present invention have an aromatic hydrocarbon content of 0.2% by weight or less, Excellent foamability.
In addition, the foamed molded body molded using the expandable polystyrene resin particles had a low diffusion rate and was excellent in flexibility, shrinkage, surface appearance, and bending strength.
[0078]
In Example 8 and Comparative Example 5, since the polymerization initiator amount, final polymerization temperature and time (112 ° C., 1.5 hours) were changed, the content and emission amount of aromatic hydrocarbons increased.
On the other hand, Comparative Examples 1 and 3 were inferior in shrinkage and surface appearance because only liquid paraffin was used as a plasticizer. In Comparative Examples 2, 4 and 5, since only beef tallow extremely hardened oil was used as a plasticizer, flexibility and surface appearance were inferior.
[0079]
[Table 1]
[Table 2]
[Table 3]
Claims (7)
該発泡性ポリスチレン系樹脂粒子は，重量平均分子量が２０万〜４０万のスチレン系樹脂と，
該スチレン系樹脂１００重量％に対して，発泡剤として沸点が９０℃以下の有機化合物が３〜１０重量％と，
該スチレン系樹脂の中に含まれている可塑剤としての平均炭素数が２０〜３５個の流動パラフィン０．０１〜２重量％及び，
同じく該スチレン系樹脂の中に含まれている可塑剤としての常温で固体の脂肪酸エステル０．０１〜２重量％とを含有することを特徴とする発泡性ポリスチレン系樹脂粒子。 Styrene or a mixture of vinyl monomers containing styrene as a main component is dispersed in an aqueous medium together with a plasticizer and a polymerization initiator to initiate a polymerization reaction to form a styrene resin, and foaming during or after completion of the polymerization In expandable polystyrene resin particles obtained by adding an agent,
The expandable polystyrene resin particles include a styrene resin having a weight average molecular weight of 200,000 to 400,000,
3 to 10% by weight of an organic compound having a boiling point of 90 ° C. or less as a blowing agent with respect to 100% by weight of the styrenic resin,
0.01 to 2% by weight of liquid paraffin having an average carbon number of 20 to 35 as a plasticizer contained in the styrenic resin ;
Expandable polystyrene resin particles characterized by containing 0.01 to 2% by weight of a fatty acid ester which is solid at normal temperature as a plasticizer which is also contained in the styrene resin.
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