JP4653278B2 - Expandable styrene resin particles - Google Patents
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Description
【０００１】
【技術分野】
本発明は，発泡成形体の原料等として利用する発泡性スチレン系樹脂粒子に関する。
【０００２】
【従来技術】
発泡性スチレン系樹脂粒子から得られる発泡成形体，いわゆる発泡スチロールは，優れた緩衝性，断熱性を有し，成形性も容易で，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，発泡性スチレン系樹脂粒子は，発泡剤としてペンタンやブタン等の炭化水素を含有している。
さらに，発泡性スチレン系樹脂粒子中に発泡性を改良する目的で有機溶剤を可塑剤として添加することが一般的に行われている。この可塑剤となる有機溶剤としては，残存させたスチレンモノマーや，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が広く利用されている。
【０００４】
このため，発泡性スチレン系樹脂粒子中には発泡剤と可塑剤として機能する有機溶剤とを合わせると平均してスチレン系樹脂粒子１００重量部に対して，６〜９重量部の揮発性有機化合物が含有されている。これら発泡剤や有機溶剤は，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６−２５４５６号や特開平６−２５４５８号には，発泡剤量の少ない発泡性スチレン系樹脂粒子及びその製造法が開示されている。しかし，これらの方法より得られた発泡性スチレン系樹脂粒子から成形された発泡成形体には，強度が低いという問題がある。
【０００６】
また，特開平４−２６８３４７号，特開平６−８０７０８号，特開平１０−１７６９８号には，残存スチレンモノマーやベンゼン含有量が少ない発泡性スチレン系樹脂粒子及びその製造法が開示されている。
【０００７】
しかし，残存スチレンモノマー等は発泡性スチレン系樹脂粒子に対して優れた可塑効果を与えることができる。このため，残存スチレンモノマー等を減らすと，発泡性スチレン系樹脂粒子の発泡性が低下し，発泡倍率を高くすることが困難になったり，成形時において粒子同士の融着性が低下するという問題が発生することがある。
また，発泡性を高めるため，発泡性スチレン系樹脂粒子の分子量を低下させることもできる。しかし，得られる発泡成形体の強度が低下するという問題が生じる。
【０００８】
本発明はかかる従来の問題点に鑑み，揮発性有機化合物の含有量が少ないが優れた発泡性を有しており，更に得られる発泡成形体の強度が高く，かつ短い成形サイクルで発泡成形体を成形可能な発泡性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，重量平均分子量が１８万〜４０万のスチレン系樹脂粒子からなると共に，発泡剤及び可塑剤を含有する発泡性スチレン系樹脂粒子であって，
上記発泡剤として沸点が９０℃以下かつ炭素数が３〜６の飽和炭化水素化合物を上記スチレン系樹脂粒子１００重量部に対し２〜５．５重量部含有し，
上記可塑剤として平均炭素数が２０〜３５個でかつ常温で液体のパラフィン類を上記スチレン系樹脂粒子１００重量部に対し０．５〜５重量部含有し，
芳香族炭化水素の含有量が上記スチレン系樹脂粒子１００重量部に対し０．００１〜０．１２重量部であることを特徴とする発泡性スチレン系樹脂粒子にある。
つまり，本発明にかかる発泡性スチレン系樹脂粒子は，スチレン系樹脂粒子１００重量部，発泡剤２〜５．５重量部，可塑剤であるパラフィン類０．５〜５重量部，その他の成分より構成されている。
【００１０】
本発明にかかるスチレン系樹脂粒子の重量平均分子量は１８万〜４０万である。なお，上記重量平均分子量はＧＰＣ（Gel Permeation Chromatography；ゲルパーミエーションクロマトグラフィー）法により測定した値である。
重量平均分子量が１８万未満では，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，成形時にスチレン系樹脂粒子同士が融着しにくくなり，成形品強度が低下するおそれがある。
なお，より好ましくは２０万〜３８万，さらに好ましくは２２万〜３５万である。
【００１１】
本発明にかかる発泡性スチレン系樹脂粒子中には，発泡剤として機能する沸点が９０℃以下の有機化合物がスチレン系樹脂粒子１００重量部に対し２〜５．５重量部含有されている必要がある。
上記沸点が９０℃以下の有機化合物としては，メタン，エタン，プロパン，ｎ−ブタン，イソブタン，シクロブタン，ｎ−ペンタン，イソペンタン，ネオペンタン，シクロペンタン，ｎ−ヘキサン，シクロヘキサン等の飽和炭化水素化合物，メタノール，エタノール等の低級アルコール，ジメチルエーテル，ジエチルエーテル等のエーテル化合物等が挙げられる。
【００１２】
上記発泡剤の含有量が２重量部未満では，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となるおそれがある。５．５重量部を超えると，大気中に放出される揮発性有機化合物の量を減らすという初期の目標を達成することができなくなるおそれがある。
なお，より好ましくは２〜５重量部，さらに好ましくは２〜４．５重量部である。
【００１３】
本発明にかかる発泡性スチレン系樹脂粒子中には，可塑剤として機能する平均炭素数が２０〜３５個でかつ常温で液体のパラフィン類がスチレン系樹脂粒子１００重量部に対し０．５〜５重量部含有されている必要がある。
上記パラフィン類は，ＣmＨn（ｎ＜２ｍ＋１，ｍは炭素数）で示される分岐構造や環構造を有する脂環式炭化水素化合物の混合物で，かつ平均炭素数が２０〜３５個の常温で液体のパラフィン類である。
【００１４】
平均炭素数が２０個未満である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出される揮発性の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。
３５個を超えるとスチレン系樹脂粒子との相溶性が低下し，可塑効果が低くなり，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となるおそれがある。
なお，より好ましくは２０〜３０個である。
【００１５】
また，上記可塑剤の含有量が０．５重量部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となるおそれがある。５重量部を超えると，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０．５〜３．５重量部である。
また，上記発泡剤，可塑剤は発泡性スチレン系樹脂粒子を製造する際に添加される（後述の実施形態例，実施例１参照）。
【００１６】
次に，本発明の作用につき説明する。
本発明にかかる発泡性スチレン系樹脂粒子は，上述したごとき重量平均分子量を有し，また上述したごとき発泡剤と可塑剤とを含有している。
上記可塑剤は上述したごとき特徴を持つため，発泡性スチレン系樹脂粒子の製造時，貯蔵時，発泡成形体の成形工程等において揮発することが殆どない。
上記発泡剤は揮発する可能性があるが，本発明中における発泡剤の含有量は従来知られた発泡性スチレン系樹脂粒子中の揮発性有機化合物の含有量よりも少ない（実施形態例参照）。
【００１７】
また，上記可塑剤の優れた可塑効果により，発泡性に優れ，スチレン系樹脂粒子の重量平均分子量を小さくする必要がないので，発泡成形体の強度が高く，発泡剤の含有量が少ないため成形サイクルが短いという効果を得ることができる。
このため，本発明によれば，上記利点をすべて備えた発泡性スチレン系樹脂粒子を得ることができる。
【００１８】
以上，本発明によれば，揮発性有機化合物の含有量が少ないが優れた発泡性を有しており，更に得られる発泡成形体の強度が高くかつ短い成形サイクルで発泡成形体を成形可能な発泡性スチレン系樹脂粒子を提供することができる
【００１９】
なお，本発明にかかる発泡性スチレン系樹脂粒子より得られた発泡成形品は，各種の食品容器や医療用の容器，物品等に広く用いることができる。
【００２０】
また，本発明にかかる発泡性スチレン系樹脂粒子を得る方法としては，従来から既知の，例えば撹拌装置の付いた密閉容器内にスチレンモノマー等を可塑剤，重合開始剤と共に適当な懸濁剤の存在下で水性媒体中に分散させた後，重合反応を開始し，重合途中あるいは重合完了後に発泡剤を添加して，発泡性スチレン系樹脂粒子を得る方法が挙げられる。なお，上記可塑剤，発泡剤は上述する請求項１に記載した物質を指している。
【００２１】
また，本発明にかかる発泡性スチレン系樹脂粒子は，スチレンモノマーまたはスチレンモノマーを主成分とするビニルモノマーの混合物から製造することができる。
スチレンモノマーと共重合可能なビニルモノマーとして，例えば，α−メチルスチレン，ｐ−メチルスチレン，ｔ−ブチルスチレン，クロロスチレン，ブロモスチレン，ジビニルベンゼン等のスチレン誘導体や，アクリル酸メチル，アクリル酸エチル，アクリル酸ブチル，アクリル酸２−エチルヘキシル，ブタンジオールジアクリレート等のアクリル酸エステル類や，メタクリル酸メチル，メタクリル酸エチル，メタクリル酸ブチル，メタクリル酸２−エチルヘキシル等のメタクリル酸エステル類や，アクリロニトリル，メタクリロニトリル等のニトリル基含有モノマー等が挙げられる。また，ビニルモノマーを２種類以上混合して用いてもよい。
【００２２】
上記重合開始剤としては，例えばビニルモノマーに可溶で１０時間半減期温度が５０〜１２０℃である，クメンヒドロキシパーオキサイド，ジクミルパーオキサイド，ｔ−ブチルパーオキシ−２−エチルヘキサノエート，ｔ−ブチルパーオキシベンゾエート，ベンゾイルパーオキサイド，ｔ−ブチルパーオキシイソプロピルカーボネート，ｔ−アミルパーオキシ−２−エチルヘキシルカーボネート，ヘキシルパーオキシ−２−エチルヘキシルカーボネート，ラウロイルパーオキサイド等の有機過酸化物や，アゾビスイソブチロニトリル等のアゾ化合物等が挙げられる。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。
また，重合開始剤の使用量は，ビニルモノマー１００重量部に対して，０．０１〜３重量部が好ましい。
【００２３】
懸濁剤としては，例えば，ポリビニルアルコール，メチルセルロース，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よい。
なお，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。
【００２４】
懸濁剤の使用量はビニルモノマー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，ビニルモノマー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。
【００２５】
上記スチレンモノマーの重合反応の際には，ヘキサブロモシクロドデカン等の難燃剤，２，３−ジメチル−２，３−ジフェニルブタン等の難燃助剤，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，シリコーン等のセル調整剤，グリセリンジアセトモノラウレート，グリセリントリステアレート等の可塑剤，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。
【００２６】
次に，上記発泡性スチレン系樹脂粒子中には，芳香族炭化水素が上記スチレン系樹脂粒子１００重量部に対し０．００１〜０．１２重量部含有されている。
これにより，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る。
ここでいう芳香族炭化水素とは，例えばスチレン，ベンゼン，トルエン，ｏ−キシレン，ｍ−キシレン，ｐ−キシレン，エチルベンゼン，ｎ−プロピルベンゼン，ｉ−プロピルベンゼン等である。
【００２７】
発泡性スチレン系樹脂粒子中の芳香族炭化水素の含有量が０．１２重量部を超えると，芳香族炭化水素は比較的沸点が高く，発泡成形体に長期間残存するため，例えば，食品が発泡成形体に直接触れるような状態で使用した場合，内容物が汚染されるおそれがある。
また，含有量が０．００１重量部未満である場合，発泡性スチレン系樹脂粒子の製造コストが高くなるおそれがある。
【００２８】
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。
これにより，発泡性に優れた粒子を得ることができる。
【００２９】
炭素数が３〜６個の炭化水素化合物としては，例えばプロパン，ｎ−ブタン，イソブタン，シクロブタン，ｎ−ペンタン，イソペンタン，ネオペンタン，シクロペンタン，ｎ−ヘキサン，シクロヘキサン等が挙げられ，１種類あるいは２種類以上混合して用いることができる。
【００３０】
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速いため，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。
【００３１】
次に，請求項２記載の発明のように，上記発泡性スチレン系樹脂粒子中にセルサイズ調整剤として，ＨＬＢ（Hydrophile-Lipophile Balance；親水性親油性比）が１〜７の界面活性剤が上記スチレン系樹脂１００重量部に対し０．０００１〜０．１重量部含有されていることが好ましい。
これにより，発泡成形体のセルサイズを所望の大きさに調整することができる。通常セルサイズはセルナンバーで表わすと，発泡倍率により増減するが１５〜２５個／ｍｍ程度である（実施形態例参照）。
【００３２】
ＨＬＢが７を超えると，懸濁系が不安定になり重合中に樹脂粒子同士が凝結したり，系全体が凝固するおそれがある。
一方ＨＬＢが１未満である場合，上記効果を得難くなるおそれがある。
なお，より好ましくはＨＬＢが２〜６である。
【００３３】
また，界面活性剤の含有量が０．０００１重量部では上記効果を得難く，０．１重量部を超えると懸濁系が不安定になり，重合中に発泡性スチレン系樹脂粒子同士が凝結したり，系全体が凝固するおそれがある。
なお，より好ましくは，０．０００１〜０．０１重量部である。
【００３４】
ＨＬＢが１〜７の界面活性剤としては，例えばソルビタントリオクトエート，ソルビタンモノステアレート，ソルビタントリオレエート，ソルビタントリステアレート等のソルビタンの脂肪酸エステル類，グリセリンモノラウレート，グリセリンモノステアレート，グリセリンジステアレート等のグリセリンの脂肪酸モノエステル及びジエステル類，Ｎ，Ｎ−ビス（２−ヒドロキシエチル）ヤシアミン等のＮ，Ｎ−ビス（２−ヒドロキシエチル）アルキルアミン類等が挙げられる。
【００３５】
本発明の発泡性スチレン系樹脂粒子から発泡成形体を作製する方法について，例示説明すると，まず発泡性スチレン系樹脂粒子を予備発泡させて予備発泡粒子とする。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，発泡成形体を得ることができる。
また，予め発泡性スチレン系樹脂粒子に熱処理を施すことで，発泡成形体の表面外観を向上させることもできる。
【００３６】
予備発泡の方法としては，例えば，撹拌装置の付いた円筒形の予備発泡機を用いて，スチーム等で加熱し発泡させる方法がある。
また，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，スチーム等で加熱する，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，１５〜３０ｋｇ／ｍ3であるのが好ましい。
【００３７】
【発明の実施の形態】
実施形態例
本発明にかかる発泡性スチレン系樹脂粒子について説明する。
この発泡性スチレン系樹脂粒子は，重量平均分子量が１８万〜４０万のスチレン系樹脂粒子からなると共に，発泡剤として沸点が９０℃以下の有機化合物が上記スチレン系樹脂粒子１００重量部に対し２〜５．５重量部含有され，可塑剤として平均炭素数が２０〜３５個でかつ常温で液体のパラフィン類が上記スチレン系樹脂粒子１００重量部に対し０．５〜５重量部含有されている。
以下に，本発明に関する実施例及び比較例について説明する。
なお，以下の記載において，発泡剤，可塑剤である液体パラフィン，芳香族炭化水素の含有量の数値は，スチレン系樹脂粒子１００重量部に対する重量部である。
【００３８】
実施例１
まず，本例にかかる発泡性スチレン系樹脂粒子の製造方法について説明する。
撹拌装置の付いた内容積が５０リットルのオートクレーブに，脱イオン水１６ｋｇ，懸濁剤として，第３リン酸カルシウム２０ｇ，界面活性剤としてドデシルベンゼンスルホン酸ナトリウム０．８ｇを投入した。
【００３９】
ついで，開始剤としてｔ−ブチルパーオキシ−２−エチルヘキサノエート４０ｇ及びｔ−ブチルパーオキシ−２−エチルヘキシルモノカーボネート２０ｇ，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をスチレンモノマー１７ｋｇに溶解させ，２３０ｒｐｍで撹拌しながらオートクレーブに投入した。オートクレーブ内を窒素置換した後，昇温を開始し，１時間半かけて９０℃まで昇温した。
なお，この流動パラフィンは後述する表１に示すごとく，平均炭素数が２２個である。
【００４０】
９０℃到達後，さらに１００℃まで５時間かけて昇温し，さらに１１０℃まで１時間で昇温し，そのまま１１０℃で５時間保持した。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９０ｇ添加し，９０℃到達４時間目に発泡剤としてブタン（ｎ−ブタンとイソブタンの混合物）８８０ｇをオートクレーブ内に圧入した。その後，３０℃まで約６時間かけて冷却した。
【００４１】
内容物を取り出し，発泡性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，硝酸を添加し第３リン酸カルシウムを溶解させた後，遠心分離機で脱水し，流動乾燥装置で表面に付着した水分を除去し，平均粒径が約１ｍｍの発泡性スチレン系樹脂粒子を得た。
【００４２】
次に，発泡成形体の成形方法について説明する。
得られた発泡性スチレン系樹脂粒子を篩いにかけて０．７〜１．４ｍｍの粒子を取り出し，発泡性スチレン系樹脂粒子１００重量部に対して，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０．００５重量部を添加し，さらにステアリン酸亜鉛０．１重量部，グリセリントリステアレート０．０５重量部，グリセリンモノステアレート０．０５重量部の混合物で被覆した。
【００４３】
得られた発泡性スチレン系樹脂粒子１０ｋｇを加圧バッチ発泡機（ダイセン工業社製ＤＹＨ−８５０）内で，缶内圧力が０．０２ＭＰａになるようにスチームを供給し，約１００秒間加熱した後，６０秒間乾燥させて，嵩密度が約２０ｋｇ／ｍ3（発泡倍率５０倍）の予備発泡粒子を得た。
【００４４】
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のスチーム圧力で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。
【００４５】
上記発泡性スチレン系樹脂粒子の「スチレン系樹脂粒子の重量平均分子量」，「スチレン系樹脂粒子１００重量部に対する発泡剤の含有量（重量部）」，「可塑剤（パラフィン）の平均炭素数」，「スチレン系樹脂粒子１００重量部に対する可塑剤（パラフィン）の含有量（重量部）」，「スチレン系樹脂粒子１００重量部に対する芳香族炭化水素の含有量（重量部）」について，表１に記載した。
【００４６】
また，上記発泡性スチレン系樹脂粒子より得られた発泡成形体の性能を表わす，「成形冷却時間」，「表面外観」，「セルナンバー」，「曲げ強度」，「５０％破壊高さ」について，表１に記載した。
以下にこれらの値を得る方法について説明する。
【００４７】
＜重量平均分子量＞
発泡性スチレン系樹脂粒子をテトラヒドロフランに溶解させ，ゲルパーミエーションクロマトグラフィーで測定し，標準ポリスチレンで校正して求めた。
＜発泡剤の含有量＞
発泡性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ーにて発泡剤の含有量を測定した。
＜可塑剤（パラフィン）の平均炭素数＞
用いたパラフィンの平均炭素数を記載した。
＜可塑剤（パラフィン）の含有量＞
これは発泡性スチレン系樹脂粒子の製造工程中で加えたものが，そのまま完成した発泡性スチレン系樹脂粒子に残留するため，製造工程中で加えた量をそのまま記載した。
＜芳香族炭化水素の含有量＞
発泡性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ーにて，スチレン，トルエン，キシレン，ベンゼン，エチルベンゼン，プロピルベンゼンそれぞれの含有量を測定し，各成分の含有量を合計して求めた。
【００４８】
＜成形冷却時間＞
肉厚５０ｍｍの発泡成形体が得られる金型に面圧計を取り付けておき，スチーム圧力０．０７ＭＰａで２０秒間加熱し５秒間水冷した後，減圧状態で放冷を開始し，発泡成形体の面圧が０．０２ＭＰａになるまでに要した放冷時間を成形冷却時間として測定した。
【００４９】
＜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。
【００５０】
＜セルナンバー＞
発泡成形体の表皮部分をスライサーで切断し，光学顕微鏡にて切断面を撮影した。切断面の写真上に直線を引き，直線と交わっている気泡数を数え，気泡数を直線の長さで除して，１ｍｍ当たりの気泡数を求め，これをセルナンバー（個／ｍｍ）とした。
【００５１】
＜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に準拠して曲げ試験を行い，曲げ強度を測定した。
＜５０％破壊高さ＞
発泡成形体を切断して，縦２００ｍｍ×横４０ｍｍ×厚さ２５ｍｍの試験片を作成し，重量２５５ｇの鋼球を用いる以外は，ＪＩＳ Ｋ ７２１１に準拠して落錘衝撃試験を行い，５０％破壊高さを測定した。これにより発泡成形体の耐衝撃性を評価した。
【００５２】
実施例２
流動パラフィンの添加量を１７０ｇとし，ブタンの添加量を１１００ｇとした以外は実施例１と同様に行った。
実施例３
ｔ−ブチルパーオキシ−２−エチルヘキサノエートの添加量を３０ｇとし，流動パラフィンの添加量を５１０ｇとした以外は実施例１と同様に行った。
【００５３】
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Ｐ１５０，平均炭素数２５個）３４０ｇを添加した以外は，実施例１と同様に行った。
実施例５
セル調整剤としてＮ，Ｎ−ビス（２−ヒドロキシエチル）ヤシアミン（ＨＬＢ４．５）を０．４ｇ添加し，発泡剤としてブタン４００ｇ及びペンタン(ｎ−ペンタンとイソペンタンの混合物)４００ｇを添加した以外は，実施例１と同様に行った。
【００５４】
実施例６
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Ｐ３５０Ｐ，平均炭素数３３個）３４０ｇを添加し，セル調整剤としてソルビタンモノラウレート（ＨＬＢ４．３）を０．４ｇ添加し，発泡剤としてブタン４００ｇ及びペンタン４００ｇを添加した以外は，実施例１と同様に行った。
【００５５】
比較例１
流動パラフィンの量を３４ｇとする以外は実施例１と同様に行った。
比較例２
可塑剤である流動パラフィンは添加せず，連鎖移動剤であるαスチレンダイマーを１５ｇ添加し，重合開始剤であるｔ−ブチルパーオキシ−２−エチルヘキシルモノカーボネートの量を２５ｇとし，発泡剤としてペンタンを８５０ｇ添加した以外は，実施例１と同様に行った。
【００５６】
比較例３
可塑剤として，グリセリントリステアレート１２０ｇを添加し，発泡剤としてシクロヘキサン２５０ｇ，ブタン１３００ｇ添加し，１１０℃での保持時間を１．５時間とする以外は，実施例１と同様に行った。
【００５７】
表１より，本発明にかかる発泡性スチレン系樹脂粒子は，成形冷却時間が短く，表面外観に優れ，セルナンバーが適正で（セルナンバーはセルの大きさを示しており，大きすぎれば強度低下の原因となり，小さすぎれば外観低下の問題が生じる。１５〜２５くらいが適正である。），また曲げ強度，５０％破壊高さがいずれも優れていることが分かった。
比較例１は，成形冷却時間が短いが，表面外観が悪く，また曲げ強度や破壊高さも高くない。比較例２は，表面外観は良いが，セルナンバーが少なく，曲げ強度や５０％破壊高さが低い。また，比較例３は成形冷却時間が長くかかることが分かった。更に，発泡剤が多く含まれていることが分かった。
【００５８】
次に，本例の作用につき説明する。
本例にかかる発泡性スチレン系樹脂粒子は，上述したごとき重量平均分子量を有し，また上述したごとき発泡剤と可塑剤とを含有している。
よって，揮発性有機化合物の含有量が少なく，発泡性に優れ，発泡成形体の強度が高く，成形サイクルが短い，という４つの利点をすべて備えた発泡性スチレン系樹脂粒子を得ることができる（表１参照）。
【００５９】
以上，本例によれば，揮発性有機化合物の含有量が少ないが優れた発泡性を有しており，更に得られる発泡成形体の強度が高くかつ短い成形サイクルで発泡成形体を成形可能な発泡性スチレン系樹脂粒子を提供することができる
【００６０】
【表１】
【発明の効果】
以上より，揮発性有機化合物の含有量が少ないが優れた発泡性を有しており，更に得られる発泡成形体の強度が高くかつ短い成形サイクルで発泡成形体を成形可能な発泡性スチレン系樹脂粒子を提供することができる。[0001]
【Technical field】
The present invention relates to an expandable styrene resin particle used as a raw material for an expanded molded article.
[0002]
[Prior art]
Foam molded products obtained from expandable styrenic resin particles, so-called expanded polystyrene, has excellent buffering and heat insulation properties, is easy to mold, and is a relatively inexpensive material. Widely used.
[0003]
Conventionally, expandable styrene resin particles contain hydrocarbons such as pentane and butane as a foaming agent.
Furthermore, an organic solvent is generally added as a plasticizer for the purpose of improving foamability in the foamable styrene resin particles. As the organic solvent to be used as the plasticizer, the remaining styrene monomer, a small amount of toluene, xylene, cyclohexane and the like are widely used.
[0004]
Therefore, when the foaming styrene resin particles are combined with the foaming agent and the organic solvent functioning as a plasticizer, 6 to 9 parts by weight of the volatile organic compound is averaged with respect to 100 parts by weight of the styrene resin particles. Is contained. These foaming agents and organic solvents are gradually released into the atmosphere in each process such as storage, foaming and molding.
[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 styrene resin particles.
For example, JP-A-6-25456 and JP-A-6-25458 disclose expandable styrene resin particles having a small amount of foaming agent and a method for producing the same. However, there is a problem that the foam molded body molded from the expandable styrene resin particles obtained by these methods has low strength.
[0006]
JP-A-4-268347, JP-A-6-80708, and JP-A-10-17698 disclose expandable styrene resin particles having a small content of residual styrene monomer and benzene and a method for producing the same.
[0007]
However, the residual styrene monomer or the like can give an excellent plastic effect to the expandable styrene resin particles. For this reason, if the residual styrene monomer or the like is reduced, the foamability of the expandable styrene resin particles decreases, making it difficult to increase the expansion ratio, or the fusion between the particles during molding decreases. May occur.
Moreover, in order to improve foamability, the molecular weight of expandable styrene resin particles can also be reduced. However, there arises a problem that the strength of the obtained foamed molded product is lowered.
[0008]
In view of the conventional problems, the present invention has an excellent foaming property with a low content of volatile organic compounds, and the foamed molded product obtained has a high strength and can be molded in a short molding cycle. It is an object of the present invention to provide expandable styrene resin particles that can be molded.
[0009]
[Means for solving problems]
The invention according to claim 1 is an expandable styrene resin particle comprising a styrene resin particle having a weight average molecular weight of 180,000 to 400,000, and containing a foaming agent and a plasticizer,
2 to 5.5 parts by weight of a saturated hydrocarbon compound having a boiling point of 90 ° C. or less and 3 to 6 carbon atoms as the foaming agent with respect to 100 parts by weight of the styrenic resin particles,
0.5 to 5 parts by weight of paraffins having an average carbon number of 20 to 35 and being liquid at room temperature as the plasticizer are contained with respect to 100 parts by weight of the styrene resin particles,
Aromatic hydrocarbonsThe expandable styrenic resin particles are characterized by having a content of 0.001 to 0.12 parts by weight with respect to 100 parts by weight of the styrenic resin particles.
That is, the expandable styrene resin particles according to the present invention comprise 100 parts by weight of styrene resin particles, 2 to 5.5 parts by weight of a foaming agent, 0.5 to 5 parts by weight of paraffins which are plasticizers, and other components. It is configured.
[0010]
The styrene resin particles according to the present invention have a weight average molecular weight of 180,000 to 400,000. The weight average molecular weight is a value measured by GPC (Gel Permeation Chromatography) method.
If the weight average molecular weight is less than 180,000, the strength of the resulting foamed molded product may be lowered. On the other hand, if 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 styrene resin particles are fused to each other during molding. It may become difficult to reduce the strength of the molded product.
In addition, More preferably, it is 200,000-380,000, More preferably, it is 220,000-350,000.
[0011]
In the expandable styrene resin particles according to the present invention, an organic compound having a boiling point of 90 ° C. or less that functions as a foaming agent needs to be contained in an amount of 2 to 5.5 parts by weight with respect to 100 parts by weight of the styrene resin particles. is there.
the aboveOrganic compounds with boiling points below 90 ° CAs, saturated hydrocarbon compounds such as methane, ethane, propane, n-butane, isobutane, cyclobutane, n-pentane, isopentane, neopentane, cyclopentane, n-hexane, cyclohexane, lower alcohols such as methanol and ethanol, dimethyl ether, Ether compounds such as diethyl etherEtc..
[0012]
If the content of the foaming agent is less than 2 parts by weight, the foamability is lowered, and it may be difficult to foam to the target foaming ratio. If it exceeds 5.5 parts by weight, the initial goal of reducing the amount of volatile organic compounds released into the atmosphere may not be achieved.
In addition, 2-5 weight part is more preferable, More preferably, it is 2-4.5 weight part.
[0013]
In the expandable styrene resin particles according to the present invention, paraffins having an average carbon number of 20 to 35 functioning as a plasticizer and liquid at room temperature are 0.5 to 5 parts per 100 parts by weight of the styrene resin particles. It must be contained in parts by weight.
The above paraffins are CmHn(N <2m + 1, where m is the number of carbon atoms) is a mixture of alicyclic hydrocarbon compounds having a branched structure or a ring structure, and paraffins that are liquid at room temperature and have an average carbon number of 20 to 35.
[0014]
Because 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, and molding processes. There exists a possibility that the effect concerning this invention may become difficult to acquire.
If the number exceeds 35, the compatibility with the styrene-based resin particles is lowered, the plastic effect is lowered, and it may be difficult to foam to the target foaming ratio when producing the foamed molded product.
In addition, More preferably, it is 20-30 pieces.
[0015]
Further, when the content of the plasticizer is less than 0.5 parts 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. If it exceeds 5 parts by weight, the strength and heat resistance of the resulting foamed molded product may be lowered, and the production cost may be increased.
More preferably, it is 0.5 to 3.5 parts by weight.
Moreover, the said foaming agent and a plasticizer are added when manufacturing an expandable styrene-type resin particle (refer the below-mentioned embodiment example and Example 1).
[0016]
Next, the operation of the present invention will be described.
The expandable styrene resin particles according to the present invention have a weight average molecular weight as described above, and contain a foaming agent and a plasticizer as described above.
Since the plasticizer has the characteristics as described above, it hardly volatilizes during the production of the expandable styrenic resin particles, during storage, in the molding process of the foamed molded article.
Although the foaming agent may volatilize, the content of the foaming agent in the present invention is less than the content of volatile organic compounds in the conventionally known expandable styrenic resin particles (see embodiment examples). .
[0017]
In addition, because of the excellent plasticizing effect of the plasticizer, it has excellent foaming properties, and it is not necessary to reduce the weight average molecular weight of the styrene resin particles. Therefore, the molded product has high strength and low foaming agent content. The effect that the cycle is short can be obtained.
For this reason, according to this invention, the expandable styrene-type resin particle provided with all the said advantages can be obtained.
[0018]
As described above, according to the present invention, the content of the volatile organic compound is small but the foam has excellent foamability, and the foamed molded product obtained has high strength and can be molded in a short molding cycle. Expandable styrenic resin particles can be provided
[0019]
The foam molded product obtained from the expandable styrene resin particles according to the present invention can be widely used in various food containers, medical containers, articles and the like.
[0020]
In addition, as a method for obtaining the expandable styrene resin particles according to the present invention, for example, a styrene monomer or the like in a sealed container equipped with a stirrer is mixed with a suitable suspending agent together with a plasticizer and a polymerization initiator. Examples thereof include a method of starting the polymerization reaction after dispersing in an aqueous medium in the presence, and adding a foaming agent during or after the polymerization to obtain expandable styrene resin particles. In addition, the said plasticizer and a foaming agent point out the substance described in Claim 1 mentioned above.
[0021]
The expandable styrene resin particles according to the present invention can be produced from a styrene monomer or a mixture of vinyl monomers containing styrene monomer as a main component.
As vinyl monomers copolymerizable with styrene monomers, for example, styrene derivatives such as α-methylstyrene, p-methylstyrene, t-butylstyrene, chlorostyrene, bromostyrene, divinylbenzene, methyl acrylate, ethyl acrylate, Acrylic esters such as butyl acrylate, 2-ethylhexyl acrylate, butanediol diacrylate, methacrylic esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, acrylonitrile, methacrylate Examples include nitrile group-containing monomers such as rhonitrile. Two or more kinds of vinyl monomers may be mixed and used.
[0022]
Examples of the polymerization initiator include cumene hydroxy peroxide, dicumyl peroxide, t-butylperoxy-2-ethylhexanoate, which is soluble in vinyl monomer and has a 10-hour half-life temperature of 50 to 120 ° C. organic peroxides such as t-butylperoxybenzoate, benzoyl peroxide, t-butylperoxyisopropyl carbonate, t-amylperoxy-2-ethylhexyl carbonate, hexylperoxy-2-ethylhexyl carbonate, lauroyl peroxide, Examples include azo compounds such as azobisisobutyronitrile. These polymerization initiators can be used alone or in combination of two or more.
Moreover, the usage-amount of a polymerization initiator has a preferable 0.01-3 weight part with respect to 100 weight part of vinyl monomers.
[0023]
As the suspending agent, for example, hydrophilic polymers such as polyvinyl alcohol, methylcellulose, and polyvinylpyrrolidone, and poorly water-soluble inorganic salts such as tricalcium phosphate and magnesium pyrophosphate can be used. An agent may be used in combination.
When using a poorly water-soluble inorganic salt, it is preferable to use an anionic surfactant such as sodium alkylsulfonate or sodium dodecylbenzenesulfonate in combination.
[0024]
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 where the above slightly water-soluble inorganic salt and an anionic surfactant are used in combination, 0.05 to 3 parts by weight of the slightly water-soluble inorganic salt and 0.0001 anionic surfactant are added per 100 parts by weight of the vinyl monomer. It is preferable to use ˜0.5 parts by weight.
[0025]
In the polymerization reaction of the styrene monomer, a flame retardant such as hexabromocyclododecane, a flame retardant aid such as 2,3-dimethyl-2,3-diphenylbutane, a methyl methacrylate copolymer, a polyethylene wax, Cell modifiers such as talc, silica, ethylenebisstearylamide, silicone, plasticizers such as glycerin diacetomonolaurate, glycerin tristearate, antistatic agents, conductive agents, particle size distribution modifiers, chain transfer agents, polymerization prohibition Additives generally used in the production of expandable styrene resin particles such as an agent, or rubber components such as butadiene rubber and styrene-butadiene rubber can be added.
[0026]
Next, in the above expandable styrene resin particles,Aromatic hydrocarbonsIs contained in an amount of 0.001 to 0.12 parts by weight with respect to 100 parts by weight of the styrene resin particles.
Thereby, it is possible to obtain a foamed molded article with a small amount of aromatic hydrocarbons released into the environment.
The aromatic hydrocarbon here is, for example, styrene, benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, n-propylbenzene, i-propylbenzene or the like.
[0027]
In expandable styrenic resin particlesAromatic hydrocarbonsWhen the content of exceeds 0.12 parts by weight,Aromatic hydrocarbonsHas a relatively high boiling point and remains in the foamed molded product for a long time. For example, when food is used in a state where it directly touches the foamed molded product, the contents may be contaminated.
Moreover, when content is less than 0.001 weight part, there exists a possibility that the manufacturing cost of an expandable styrene-type resin particle may become high.
[0028]
next,The blowing agent is a hydrocarbon compound having 3 to 6 carbon atoms..
Thereby, the particle | grains excellent in foamability can be obtained.
[0029]
Examples of the hydrocarbon compound having 3 to 6 carbon atoms include propane, n-butane, isobutane, cyclobutane, n-pentane, isopentane, neopentane, cyclopentane, n-hexane, cyclohexane, and the like. A mixture of two or more types can be used.
[0030]
Hydrocarbon compounds having 2 or less carbon atoms are likely to have a very short product life due to their rapid dissipation from the expandable styrene resin particles. If the number of carbon atoms is 7 or more, the foaming power may be reduced, making it difficult to foam to the target foaming ratio.
[0031]
Next, the claim2As described in the invention, a surfactant having a HLB (Hydrophile-Lipophile Balance) of 1 to 7 as a cell size adjusting agent in the expandable styrene resin particles is 100 weight of the styrene resin. It is preferable to contain 0.0001-0.1 weight part with respect to a part.
Thereby, the cell size of a foaming molding can be adjusted to a desired magnitude | size. Normally, the cell size is expressed by a cell number, but it increases or decreases depending on the expansion ratio, but is about 15 to 25 cells / mm (see the embodiment example).
[0032]
If the HLB exceeds 7, the suspension system becomes unstable and the resin particles may condense during polymerization or the entire system may solidify.
On the other hand, if the HLB is less than 1, the above effect may be difficult to obtain.
In addition, More preferably, HLB is 2-6.
[0033]
In addition, when the surfactant content is 0.0001 parts by weight, the above effect is difficult to obtain. When the surfactant content exceeds 0.1 parts by weight, the suspension system becomes unstable, and the expandable styrene resin particles condense during the polymerization. Or the entire system may solidify.
In addition, More preferably, it is 0.0001-0.01 weight part.
[0034]
Examples of surfactants having an HLB of 1 to 7 include sorbitan fatty acid esters such as sorbitan trioctoate, sorbitan monostearate, sorbitan trioleate, sorbitan tristearate, glycerin monolaurate, glycerin monostearate, and glycerin. Examples include fatty acid monoesters and diesters of glycerin such as distearate, N, N-bis (2-hydroxyethyl) alkylamines such as N, N-bis (2-hydroxyethyl) cocoamine, and the like.
[0035]
The method for producing a foamed molded product from the expandable styrene resin particles of the present invention will be described by way of example. First, the expandable styrene resin particles are pre-expanded into pre-expanded particles. Thereafter, the pre-foamed particles are heated and foamed, and the pre-foamed particles are fused together to obtain a foam molded article.
Also, the surface appearance of the foamed molded product can be improved by pre-treating the expandable styrene resin particles with heat treatment.
[0036]
As a pre-foaming method, for example, there is a method of heating and foaming with steam or the like using a cylindrical pre-foaming machine equipped with a stirring device.
Moreover, as a method of using pre-expanded particles as a foam-molded product, for example, a method of obtaining a foam-molded product by an in-mold molding method in which a pre-expanded particle is filled in a mold and heated with steam or the like.
The density of the foamed molded article thus obtained is 15-30 kg / m, because the strength is insufficient if the density is low, and conversely it is uneconomical if the density is high.ThreeIs preferred.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Example embodiment
The expandable styrene resin particles according to the present invention will be described.
The expandable styrene resin particles are composed of styrene resin particles having a weight average molecular weight of 180,000 to 400,000, and an organic compound having a boiling point of 90 ° C. or less as a foaming agent is 2 parts by weight with respect to 100 parts by weight of the styrene resin particles. -5.5 parts by weight, and an average carbon number of 20 to 35 as a plasticizer and 0.5 to 5 parts by weight of paraffins that are liquid at room temperature with respect to 100 parts by weight of the styrenic resin particles .
Examples and comparative examples relating to the present invention will be described below.
In the following description, foaming agent, liquid paraffin as plasticizer,Aromatic hydrocarbonsThe numerical value of the content of is a part by weight with respect to 100 parts by weight of the styrene resin particles.
[0038]
Example 1
First, the manufacturing method of the expandable styrene resin particle concerning this example is demonstrated.
In an autoclave with an internal volume of 50 liters equipped with a stirrer, 16 kg of deionized water, 20 g of tricalcium phosphate as a suspending agent, and 0.8 g of sodium dodecylbenzenesulfonate as a surfactant were added.
[0039]
Subsequently, 40 g of t-butylperoxy-2-ethylhexanoate and 20 g of t-butylperoxy-2-ethylhexyl monocarbonate as initiators, and liquid paraffin (Moleco White P60, Matsumura Oil Research Co., Ltd.) 340 g as plasticizers Was dissolved in 17 kg of styrene monomer and charged into an autoclave while stirring at 230 rpm. After the inside of the autoclave was purged with nitrogen, the temperature was raised and the temperature was raised to 90 ° C. over 1 hour and a half.
This liquid paraffin has an average carbon number of 22 as shown in Table 1 described later.
[0040]
After reaching 90 ° C., the temperature was further raised to 100 ° C. over 5 hours, further raised to 110 ° C. over 1 hour, and kept at 110 ° C. for 5 hours. 90g 0.1% aqueous solution of potassium persulfate was added as a suspension aid when the temperature reached 60 ° C during the temperature rising, and 880g butane (mixture of n-butane and isobutane) as a blowing agent was reached 4 hours after reaching 90 ° C. Press-fitted inside. Then, it cooled to 30 degreeC over about 6 hours.
[0041]
Take out the contents and remove the tertiary calcium phosphate adhering to the surface of the expandable styrenic resin particles, add nitric acid to dissolve the tertiary calcium phosphate, dehydrate it with a centrifuge, and apply it to the surface with a fluid dryer. The adhering moisture was removed to obtain expandable styrene resin particles having an average particle diameter of about 1 mm.
[0042]
Next, a method for forming the foam molded body will be described.
The obtained expandable styrenic resin particles are sieved and 0.7 to 1.4 mm particles are taken out, and 100 parts by weight of expandable styrene resin particles, N, N-bis (2- Hydroxyethyl) alkylamine (0.005 parts by weight) was added, and the mixture was further coated with a mixture of zinc stearate (0.1 parts by weight), glycerol tristearate (0.05 parts by weight) and glycerol monostearate (0.05 parts by weight).
[0043]
After 10 kg of the obtained expandable styrenic resin particles are supplied in a pressurized batch foaming machine (DYH-850 manufactured by Daisen Kogyo Co., Ltd.) so that the pressure in the can becomes 0.02 MPa and heated for about 100 seconds. , Dried for 60 seconds, bulk density about 20kg / mThreePre-expanded particles having an expansion ratio of 50 times were obtained.
[0044]
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, cooled for a predetermined time, The product was removed from the mold to obtain a foamed molded product.
[0045]
"The weight average molecular weight of styrene resin particles" of the above expandable styrene resin particles, "Content of foaming agent with respect to 100 parts by weight of styrene resin particles (parts by weight)", "Average carbon number of plasticizer (paraffin)" , “Plasticizer (paraffin) content (parts by weight) with respect to 100 parts by weight of styrene resin particles” and “Aromatic hydrocarbon content (parts by weight) with respect to 100 parts by weight of styrene resin particles” are shown in Table 1. Described.
[0046]
In addition, "molding cooling time", "surface appearance", "cell number", "bending strength", and "50% fracture height" representing the performance of foamed moldings obtained from the above expandable styrene resin particles , Listed in Table 1.
A method for obtaining these values will be described below.
[0047]
<Weight average molecular weight>
The foamable styrene resin particles were dissolved in tetrahydrofuran, measured by gel permeation chromatography, and calibrated with standard polystyrene.
<Content of foaming agent>
Expandable styrene resin particles were dissolved in dimethylformamide, and the content of the foaming agent was measured by gas chromatography.
<Average carbon number of plasticizer (paraffin)>
The average carbon number of the paraffin used was described.
<Plasticizer (paraffin) content>
Since the amount added during the production process of the expandable styrene resin particles remains in the finished expandable styrene resin particles, the amount added during the production process is described as it is.
<Aromatic hydrocarbonsContent of>
Effervescent styrene resin particles were dissolved in dimethylformamide, and the contents of styrene, toluene, xylene, benzene, ethylbenzene, and propylbenzene were measured by gas chromatography, and the contents of each component were summed up. .
[0048]
<Molding cooling time>
A surface pressure gauge is attached to a mold that can obtain a foam molded body having a thickness of 50 mm, heated at a steam pressure of 0.07 MPa for 20 seconds, water cooled for 5 seconds, and then allowed to cool in a reduced pressure state. The cooling time required for the pressure to reach 0.02 MPa was measured as the molding cooling time.
[0049]
<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.
×: 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.
[0050]
<Cell number>
The surface of the foamed product was cut with a slicer, and the cut surface was photographed with an optical microscope. A straight line is drawn on the photograph of the cut surface, the number of bubbles intersecting the straight line is counted, the number of bubbles is divided by the length of the straight line, and the number of bubbles per mm is obtained. This is the cell number (pieces / mm). did.
[0051]
<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, subjected to a bending test in accordance with JIS A 9511, and measured for bending strength.
<50% breaking height>
The foamed molded body was cut to prepare a test piece having a length of 200 mm × width of 40 mm × thickness of 25 mm, and a falling weight impact test was conducted in accordance with JIS K 7211 except that a steel ball having a weight of 255 g was used. The breaking height was measured. This evaluated the impact resistance of the foaming molding.
[0052]
Example 2
The same procedure as in Example 1 was performed except that the addition amount of liquid paraffin was 170 g and the addition amount of butane was 1100 g.
Example 3
The same procedure as in Example 1 was performed except that the addition amount of t-butylperoxy-2-ethylhexanoate was 30 g and the addition amount of liquid paraffin was 510 g.
[0053]
Example 4
The same procedure as in Example 1 was performed except that 340 g of liquid paraffin (Moleco White P150, manufactured by Matsumura Oil Research Co., Ltd., 25 carbon atoms) was added as a plasticizer.
Example 5
0.4 g of N, N-bis (2-hydroxyethyl) coconut amine (HLB4.5) was added as a cell regulator, and 400 g of butane and 400 g of pentane (a mixture of n-pentane and isopentane) were added as a foaming agent. This was carried out in the same manner as in Example 1.
[0054]
Example 6
340 g of liquid paraffin (Moleco White P350P, average carbon number 33) manufactured by Matsumura Oil Research Co., Ltd. was added as a plasticizer, and 0.4 g of sorbitan monolaurate (HLB4.3) was added as a cell modifier. As in Example 1, except that 400 g of butane and 400 g of pentane were added.
[0055]
Comparative Example 1
The same operation as in Example 1 was performed except that the amount of liquid paraffin was changed to 34 g.
Comparative Example 2
Liquid paraffin, which is a plasticizer, is not added, 15 g of α-styrene dimer, which is a chain transfer agent, is added, the amount of t-butylperoxy-2-ethylhexyl monocarbonate, which is a polymerization initiator, is 25 g, and pentane is used as a blowing agent. Was performed in the same manner as in Example 1 except that 850 g was added.
[0056]
Comparative Example 3
The same procedure as in Example 1 was performed except that 120 g of glycerin tristearate was added as a plasticizer, 250 g of cyclohexane and 1300 g of butane were added as a foaming agent, and the holding time at 110 ° C. was 1.5 hours.
[0057]
From Table 1, the expandable styrenic resin particles according to the present invention have a short molding cooling time, excellent surface appearance, and an appropriate cell number. (The cell number indicates the size of the cell. If it is too small, there is a problem of deterioration in appearance. About 15 to 25 is appropriate.) Also, bending strength and 50% fracture height are all excellent.
In Comparative Example 1, the molding cooling time is short, but the surface appearance is poor, and the bending strength and fracture height are not high. In Comparative Example 2, the surface appearance is good, but the cell number is small, the bending strength and the 50% fracture height are low. Moreover, it turned out that the comparative example 3 requires long molding cooling time. Furthermore, it was found that many foaming agents were contained.
[0058]
Next, the operation of this example will be described.
The expandable styrene resin particles according to this example have a weight average molecular weight as described above, and contain a foaming agent and a plasticizer as described above.
Therefore, it is possible to obtain expandable styrene resin particles having all of the four advantages of low content of volatile organic compounds, excellent foamability, high strength of the foamed molded product, and short molding cycle ( (See Table 1).
[0059]
As described above, according to this example, although the content of the volatile organic compound is small, the foamed product has excellent foamability, and the foamed product obtained has high strength and can be molded in a short molding cycle. Expandable styrenic resin particles can be provided
[0060]
[Table 1]
【The invention's effect】
From the above, expandable styrenic resin that has low foaming properties, but has excellent foaming properties, and the foamed molded product obtained has high strength and can be molded in a short molding cycle. Particles can be provided.
Claims (2)
上記発泡剤として沸点が９０℃以下かつ炭素数が３〜６の飽和炭化水素化合物を上記スチレン系樹脂粒子１００重量部に対し２〜５．５重量部含有し，
上記可塑剤として平均炭素数が２０〜３５個でかつ常温で液体のパラフィン類を上記スチレン系樹脂粒子１００重量部に対し０．５〜５重量部含有し，
芳香族炭化水素の含有量が上記スチレン系樹脂粒子１００重量部に対し０．００１〜０．１２重量部であることを特徴とする発泡性スチレン系樹脂粒子。Expandable styrene resin particles comprising a styrene resin particle having a weight average molecular weight of 180,000 to 400,000, and containing a foaming agent and a plasticizer,
2 to 5.5 parts by weight of a saturated hydrocarbon compound having a boiling point of 90 ° C. or less and 3 to 6 carbon atoms as the foaming agent with respect to 100 parts by weight of the styrenic resin particles,
0.5 to 5 parts by weight of paraffins having an average carbon number of 20 to 35 and being liquid at room temperature as the plasticizer are contained with respect to 100 parts by weight of the styrene resin particles.
Expandable styrene resin particles, wherein the aromatic hydrocarbon content is 0.001 to 0.12 parts by weight with respect to 100 parts by weight of the styrene resin particles.
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| JP2002249614A (en) * | 2001-02-23 | 2002-09-06 | Mitsubishi Kagaku Form Plastic Kk | Expandable styrenic resin particle |
| JP2003064212A (en) * | 2001-08-27 | 2003-03-05 | Kanegafuchi Chem Ind Co Ltd | Foamable polystyrene-based resin particle and foam molding of polystyrene-based resin |
| JP4979946B2 (en) * | 2005-12-27 | 2012-07-18 | 栗田工業株式会社 | Method for producing biofilm-forming carrier and biofilm-forming carrier |
| JP6881232B2 (en) * | 2017-10-27 | 2021-06-02 | 株式会社ジェイエスピー | Foamable resin particles |
| JP7121279B2 (en) * | 2018-10-26 | 2022-08-18 | 株式会社ジェイエスピー | Expandable styrene resin particles |
| JP7212263B2 (en) * | 2019-04-26 | 2023-01-25 | 株式会社ジェイエスピー | Expandable styrene resin particles |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS55125129A (en) * | 1979-03-19 | 1980-09-26 | Kanegafuchi Chem Ind Co Ltd | Production of foamable thermoplastic polymer particle |
| JPH0234640A (en) * | 1988-07-26 | 1990-02-05 | Dainippon Ink & Chem Inc | Production of expandable tehermoplastic resin particle |
| JPH03220209A (en) * | 1989-07-19 | 1991-09-27 | Soc Atochem | Manufacture of expandable polymer bead and material obtained therefrom |
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| JPS63193939A (en) * | 1987-02-06 | 1988-08-11 | Hitachi Chem Co Ltd | Expandable styrene resin particle and production thereof |
| JPS6479238A (en) * | 1987-06-09 | 1989-03-24 | Kanegafuchi Chemical Ind | Polystyrene resin foam |
| JPH0627212B2 (en) * | 1988-07-22 | 1994-04-13 | 鐘淵化学工業株式会社 | Expandable styrene resin particles and method for producing the same |
| JPH0967458A (en) * | 1995-08-31 | 1997-03-11 | Daicel Chem Ind Ltd | Production of preliminarily expanded styrene-based resin particle |
| JPH11335435A (en) * | 1998-03-25 | 1999-12-07 | Hitachi Chem Co Ltd | Resin composition giving composite foam, composite foam and production of composite foam |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPS55125129A (en) * | 1979-03-19 | 1980-09-26 | Kanegafuchi Chem Ind Co Ltd | Production of foamable thermoplastic polymer particle |
| JPH0234640A (en) * | 1988-07-26 | 1990-02-05 | Dainippon Ink & Chem Inc | Production of expandable tehermoplastic resin particle |
| JPH03220209A (en) * | 1989-07-19 | 1991-09-27 | Soc Atochem | Manufacture of expandable polymer bead and material obtained therefrom |
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