JP3592271B2 - Foamed sheet of aromatic monovinyl resin and molded article thereof - Google Patents

Description

〔式中、Ｒ1 は置換若しくは未置換の炭素環式芳香族基、又は置換若しくは未置換の複素環式芳香族基を表し、Ｒ2 、Ｒ3 、Ｒ4 及びＲ5 は、それぞれ独立に、水素原子又は１〜５個の炭素原子を有するアルキル基を示す。〕で表わされる３−アリールベンゾフラノンとからなる芳香族モノビニル系樹脂組成物であって、３−アリールベンゾフラノンの量が（ａ）樹脂重量に対して０．００６〜０．５重量％であり、また、芳香族モノビニル系樹脂組成物における芳香族モノビニル系単量体の残存量が１００ｐｐｍ以下である前記芳香族モノビニル系樹脂組成物からなる、発泡シート及びその成形品に関する。
【０００８】
以下、本発明を詳細に説明する。本発明において、（ａ）芳香族モノビニル系単量体からなる樹脂を得るために、原料として用いる芳香族モノビニル系単量体としては、スチレン単独のみならず、スチレンと共重合可能な他のビニル系単量体とスチレンとの混合物を挙げることができる。ここでスチレンと共重合可能な他のビニル系単量体として、具体的には、メチルメタクリレート、メチルアクリレート、ブチルアクリレート、エチルメタクリレート、ハロゲン含有ビニルモノマー、α一メチルスチレン、ｏ−メチルスチレン、ｍ−メチルスチレン、ｐ−メチルスチレン等があり、これらの１種以上を用いることができる。これらスチレンと共重合し得るビニル系単量体は、通常、全単量体の６０重量％以下、好ましくは５０重量％以下の割合で用いることができる。また、（ａ）芳香族モノビニル系単量体からなる樹脂は、ポリブタジエン、ＳＢＲ、ポリイソプレン、ニトリルゴム、天然ゴム等のゴム成分を含んでいても良い。
【０００９】
本発明においては、熱劣化防止剤として、無酸素下で発生したラジカルを効果的に捕捉安定化することができる構造のもの、すなわち、前記一般式（Ｉ）で表される３−アリールベンゾフラノンを用いる。そして、その量は、樹脂重量に対して０．００６〜０．５重量％、好ましくは０．００８〜０．３重量％、更に好ましくは０．０１〜０．２重量％である。ここで、３−アリールベンゾフラノンの添加量が０．００６重量％未満であると、脱揮工程での芳香族モノビニル系単量体、及びその二量体や三量体の生成抑制効果が不十分となり、これらの少ない成形品を得ることが出来ない。また、添加量が０．００６重量％未満の場合には、発泡シート成形時、さらには二次成形時における樹脂の熱分解によるスチレン単量体生成を抑制する効果が不十分となり、成形品の残留スチレン単量体レベルを低く抑えることが極めて難しくなるため、色調が良好な成形品を得ることができず好ましくない。一方、上記３−アリールベンゾフラノンを０．５重量％より多く添加しても、添加量に見合うだけの効果が得られない。
【００１０】
このような熱劣化防止剤としては、例えば、５，７−ジ−ｔｅｒｔ−ブチル−３−（２，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オン、５，７−ジ−ｔｅｒｔ−ブチル−３−（２，５−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オン、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オン等を挙げることができる。これらの中でも、好ましくは５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンである。
【００１１】
本発明においては、芳香族モノビニル系単量体の残存量は、１００ｐｐｍ以下、好ましくは９５ｐｐｍ以下である。ポリスチレン及び耐衝撃性ポリスチレンで、開口部幅９５ｍｍ、奥行５５ｍｍ、深さ９６ｍｍ、厚み２ｍｍの直方体容器を射出成形で作成し、この容器に９０℃の温湯２００ｍｌを入れ、３分間後にこの温湯の臭気を確認したところ、芳香族モノビニル系単量体の残存量が１００ｐｐｍ以下では、臭気の問題が大幅に改善され、また成形品の色調も大幅に改善される。一方、芳香族モノビニル系単量体の残存量が１００ｐｐｍを超えると、前記３−アリールベンゾフラノンを所定量添加しても、成形品の色調が悪いものとなり、目的を達成することができない。
【００１２】
また、本発明の芳香族モノビニル系樹脂組成物を用いた発泡シート製造時、押出機のマンドレル内の芳香族モノビニル系単量体の凝縮による成形品への影響について確認したが、芳香族モノビニル系単量体の残存量が１００ｐｐｍ以下の場合には、外観不良と印刷性の不良は見られず、成形品の外観が大幅に改善される。また成形品の色調も良好である。一方、１００ｐｐｍを超えると、外観不良や印刷性の不良が見られる。更に、芳香族モノビニル系単量体の二量体及び三量体の残存量の合計が、０．４重量％以下の場合には、成形品の厚み斑が非常に少なく、また発泡シートと成形品の外観も改善された。成形品の表面を光学顕微鏡で拡大して見たところ、気泡破れが少なく、表面が滑らかであることが確認された。
【００１３】
また、本発明においては、（ａ）芳香族モノビニル系単量体からなる樹脂の重量平均分子量は、１５〜７０万が好ましい。より好ましくは１８〜５０万である。１５万未満では、成形品の強度が不充分となり、７０万より大きいと成形性が著しく低下する。本発明の芳香族モノビニル系樹脂組成物には、所望に応じて、通常用いられている添加剤、例えば滑剤、酸化防止剤、紫外線吸収剤、離型剤、可塑剤、染料、顔料、各種充填剤などを添加することができる。また、他の樹脂、例えば一般のポリスチレン、スチレン−ブタジエン共重合エラストマー、部分的にまたは完全に水素添加されたスチレン−ブタジエン共重合エラストマー、ポリフェニレンエーテルなどを配合することもできる。
【００１４】
続いて、本発明の芳香族モノビニル系樹脂組成物の製造方法について述べる。芳香族モノビニル系樹脂、例えば、工業的規模で生産されるポリスチレンは、ほとんどラジカル重合で生産されているが、未反応物及び／又は溶剤を脱揮工程で除去する際に、あるいは脱揮した直後の樹脂が熱分解によって、スチレン単量体及びその二量体や三量体が多く発生し、得られる成形品はこれらを多く含むものとなる。さらにこれらの樹脂を用いて、射出成形、ブロー成形、押出成形等で成形品を得た場合、成形時の熱履歴により、スチレン単量体、その二量体、三量体の量はさらに増加する。
【００１５】
工業的に生産されているポリスチレン中に残留するスチレン単量体の量は、２００〜４００ｐｐｍ程度であり、例えば、１００ｐｐｍ以下のものを得ようとすることは、極めて困難である。従来、ポリスチレンはスチレン単量体の反応で生成する熱開始ラジカル及び／又は重合開始剤ラジカルで重合することが多かった。この場合、重合開始剤ラジカルの割合を増やすことにより、スチレン単量体の二量体及び三量体の量を低減させることはできるが、脱揮工程での樹脂の熱分解により再び発生するため、これらの量の低減には限界があった。
【００１６】
本発明の芳香族モノビニル系樹脂組成物の製造方法は、前記一般式（Ｉ）で表される３−アリールベンゾフラノンを重合工程あるいは脱揮工程において、また重合工程後、脱揮工程前において添加して、芳香族モノビニル系単量体の量、更には、その二量体及び三量体の量が非常に少ない成形品を得る方法である。本発明の（ａ）芳香族モノビニル系単量体からなる樹脂の重合工程における、芳香族モノビニル系単量体の重合方法については、特に制限はなく、従来慣用されている方法、例えば、ラジカル重合法としては、塊状重合法、懸濁重合法、塊状−懸濁重合法のような多段重合法、乳化重合法が可能であり、また、アニオン重合法あるいはメタロセン触媒を用いたイオン重合法等も用いることができる。
【００１７】
ここで、ラジカル重合法である塊状重合法を例に挙げて、本発明の（ａ）芳香族モノビニル系単量体からなる樹脂の重合方法について説明する。上記重合方法で用いられる重合開始剤としては、有機過酸化物、例えば２，２−ビス（ｔ−ブチルペルオキシ）ブタン、２，２−ビス（ｔ−ブチルペルオキシ）オクタン、１，１−ビス（ｔ−ブチルペルオキシ）−３，３，５−トリメチルシクロヘキサン、１，ービス（ｔ−ブチルペルオキシ）シクロヘキサン、ｎーブチルー４，４ービス（ｔ−ブチルペルオキシ）バレレートなどのペルオキシケタール類、ジーｔ−ブチルペルオキシド、ｔ−ブチルクミルペルオキシド、ジクミルペルオキシド、α，α’−ビス（ｔ−ブチルペルオキシイソブロピル）ベンゼン、２，５−ジメチル−２，５−ジ（ｔ−ブチルペルオキシ）ヘキサン、２，５−ジメチルー２，５−ジ（ｔ−ブチルペルオキシ）ヘキシンー３などのジアルキルペルオキシド類、アセチルペルオキシド、イソブチリルペルオキシド、オクタノイルペルオキシド、デカノイルペルオキシド、ラウロイルペルオキシド、３，５，５−トリメチルヘキサノイルペルオキシド、ベンゾイルペルオキシド、２，４−ジクロロベンゾイルペルオキシド、ｍ一トリオイルペルオキシドなどのジアシルペルオキシド類、ジイソプロピルペルオキシジカーボネート、ジー２−エチルヘキシルペルオキシジカーボネート、ジーｎ−プロピルペルオキシジカーボネート、ジミリスチルペルオキシジカーボネート、ジーｎ−エトキシエチルペルオキシジカーボネート、ジメトキシイソプロピルペルオキシジカーボネート、ジー（３−メチル−３−メトキシブチル）ペルオキシジカーボネートなどのペルオキシジカーボネート類、ｔ−ブチルペルオキシアセテート、ｔ―ブチルペルオキシイソブチレート、ｔ−ブチルペルオキシピバレート、ｔ−ブチルペルオキシネオデカノエート、クミルペルオキシネオデカノエート、ｔ−ブチルペルオキシ−２−エチルヘキサノエート、ｔ−プチルペルオキシ−３，３，５−トリメチルヘキサノエート、ｔ−ブチルペルオキシラウレート、ｔ−ブチルペルオキシベンゾエート、ジーｔ−ブチルジペルオキシイソフタレート、２，５−ジメチルー２，５−ジ（ベンゾイルペルオキシ）ヘキサン、ｔ−ブチルペルオキシイソプロピルカーボネートなどのペルオキシエステル類、アセチルアセトンペルオキシド、メチルエチルケトンペルオキシド、シクロヘキサノンペルオキシド、３，３，５−トリメチルシクロヘキサノンペルオキシド、メチルシクロヘキサノンペルオキシドなどのケトンペルオキシド類、ｔ一ブチルヒドロペルオキシド、クメンヒドロペルオキシド、ジイソプロピルペルベンゼンヒドロペルオキシド、ｐ−メンタンヒドロペルオキシド、２，５−ジメチルヘキサン−２，５−ジヒドロペルオキシド、１，１，３，３−テトラメチルブチルヒドロペルオキシドなどのヒドロペルオキシド類等を挙げることができる。
【００１８】
また、アゾ系開始剤である、２，２’ーアゾビスイソブチロニトリル、２，２’−アゾビス（２ーメチルブチロニトリル）、１，１’−アゾビス（１−シクロヘキサンカルボニトリル）等を用いることもできる。これらの有機過酸化物あるいはアゾ系開始剤は、それぞれ単独で用いてもよいし、２種以上を組み合わせて用いてもよい。重合条件としては、重合開始剤としての有機過酸化物の分解温度に応じて、２０〜１８０℃で重合を開始し、塊状重合を行えばよい。この塊状重合系には、連鎖移動剤、溶剤、一般的な酸化防止剤等の熱安定剤、ミネラルオイル、シリコンオイル等を適宜添加することができる。
【００１９】
ここで連鎖移動剤としては、例えばα−メチルスチレンリニアダイマー、ｎ−ドデシルメルカプタン、ｔ−ドデシルメルカプタン、１−フェニルー２−フルオレン、ジベンテン、クロロホルムなどのメルカプタン類、テルペン類、ハロゲン化合物、テレピノーレン等のテレピン類等を挙げることができる。この連鎖移動剤の使用量は、特に制限はないが、一般的には単量体に対して、０．００５〜０．１重量％程度加えれば良い。
【００２０】
必要に応じて用いられる溶剤としては、芳香族炭化水素類、例えばトルエン、キシレン、エチルベンゼン、ジアルキルケトン類、例えばメチルエチルケトンなどが挙げられ、それぞれ単独で用いてもよいし、２種以上を組み合わせて用いてもよい。さらに、重合生成物の溶解性を低下させない範囲で、他の溶剤、例えば脂肪族炭化水素類等を芳香族炭化水素類に混合することができる。これらの溶剤は、単量体に対して、２５重量％を超えない範囲で使用するのが好ましい。溶剤が２５重量％を超えると、重合速度が著しく低下し、かつ、得られる樹脂の衝撃強度の低下が大きくなる。また、溶剤の回収のために、多量のエネルギーを要するので経済性も劣ってくる。溶剤は、重合が進み、比較的高粘度になってから添加してもよいし、あるいは重合前から添加しておいてもよいが、重合前に５〜２０重量％の割合で添加しておく方が、品質が均一化し易く、重合温度制御の点でも好ましい。
【００２１】
また、一般的な安定剤として、例えばオクタデシル−３−（３，５−ターシャリーブチル−４−ヒドロキシフェニル）プロピオネート、４，６−ビス（オクチルチオメチル）−ｏ−クレゾールなどのヒンダートフェノール系酸化防止剤、トリス（２，４−ジ−ターシャリーブチルフェニル）フォスファイトなどのリン系加工熱安定剤等を挙げることができる。これらの安定剤をそれぞれ単独、あるいは２種以上を組み合わせて適宜用いてもよい。添加時期については、特に制限はなく、重合工程又は脱揮工程のいずれでもよい。また、押出機やバンバリミキサー等機械的装置で成形品に安定剤を混合することもできる。なおここで、上記重合工程において用いる装置については、特に制限はなく、芳香族モノビニル系単量体の重合方法に従って適宜選択すれば良い。例えば、塊状重合による場合には、第１反応器、第２反応器及び第３反応器からなる重合装置を、アニオン重合による場合にはオートクレーブ等の重合装置を用いることができる。
【００２２】
本発明の（ａ）芳香族モノビニル系単量体からなる樹脂の製造においては、脱揮工程についても特に制限はない。芳香族モノビニル系単量体の重合を塊状重合で行なう場合は、最終的に未反応の芳香族モノビニル系単量体が、好ましくは５０重量％、より好ましくは４０重量％以下になるまで重合を進め、かかる芳香族モノビニル系単重体などの揮発分を除去するために、公知の方法にて脱揮処理する。この脱揮工程は、重合反応後の反応物から、未反応物及び／又は溶剤を除去するためのものであり、脱揮処理には、例えばフラッシュドラム、二軸脱揮器、薄膜蒸発器、押出機などの通常の脱揮装置を用いることができる。なお、脱揮処理の温度は、通常、１９０〜２８０℃程度であり、また脱揮処理の圧力は通常、１〜１００ｔｏｒｒ（トール）程度である、好ましくは１〜５０ｔｏｒｒであり、さらに好ましくは１〜１０ｔｏｒｒである。脱揮方法としては、例えば加熱下で減圧して除去する方法や、揮発分除去の目的に設計された押出機等を通して除去することが望ましい。
【００２３】
本発明の芳香族モノビニル系樹脂組成物の製造においては、前記一般式（Ｉ）で表される３−アリールベンゾフラノン（熱劣化防止剤）を、重合工程あるいは脱揮工程において添加することが好ましい。つまり、この場合には、本発明の３−アリールベンゾフラノンは、重合反応に用いられる反応器又は押出機等に添加されることになる。また、重合工程の終了後（好ましくは直後）であって脱揮工程の前において添加することがより好ましく、この場合には、重合反応に用いられる反応器の出口において、３−アリールベンゾフラノンの添加が行われることになる。なお、成形時の樹脂の熱分解抑制のため、得られたペレットに、押出機やバンバリミキサー等機械的装置を用いて、さらに３−アリールベンゾフラノンを混合してもよい。
【００２４】
重合工程で得られた重合溶液に３−アリールベンゾフラノン（熱劣化防止剤）を添加した後は、両者を均一に混合することが好ましい。これは、混合性の良くない反応器、または混合手段のない重合ラインに３−アリールベンゾフラノンを添加した場合には、熱劣化防止剤である３−アリールベンゾフラノンの分散が不十分となり、脱揮工程での芳香族モノビニル系単量体及びその二量体や三量体の生成抑制効果はあるものの、その効果が低下して好ましくないからである。
【００２５】
ここで、重合工程で得られた重合溶液と３−アリールベンゾフラノン（熱劣化防止剤）とを均一に混合させるには、例えば、重合装置や脱揮装置の他に、混合装置を別途設けることが好ましい。なお、混合装置の構造については、特に制限はなく、重合工程で得られた重合溶液と３−アリールベンゾフラノンとを均一に混合できるものであればよく、例えば、完全混合型ミキサー、塔型ミキサー等が挙げられる。具体的には、混合装置を上記重合装置（例えば、第３反応器）の後に設けることができる。
【００２６】
重合工程において３−アリールベンゾフラノンを添加する場合は、芳香族モノビニル系単量体の重合率が、５０％以上、特に６０％以上となった時点において、前記一般式（Ｉ）で表される３−アリールベンゾフラノンを添加することが望ましい。これは、重合初期に添加すると、重合反応時のラジカルが捕捉されるため、あまり好ましくないからである。なおここで、重合率とは、原料単量体の重量を１００としたときの重合した樹脂の重量の比率（％）をいう。また、重合工程において３−アリールベンゾフラノンを添加する場合、重合工程の重合温度が１６０℃以下のときに添加することが好ましい。重合温度が１６０℃を超えた後に上記熱劣化防止剤を添加すると、重合反応時のラジカルの捕捉が速くなり、あまり好ましくない。
【００２７】
なお、重合を塊状−懸濁重合で行なう場合は、部分的に重合した反応物を、第三リン酸カルシウムやポリビニルアルコールなどの懸濁安定剤、又はこれと界面活性剤を併用して、水性媒体中に攪拌しながら分散させ、懸濁重合により反応を完結させる。得られた懸濁ポリマー粒子を含んだスラリーを脱水し、洗浄後、乾燥する。その後、脱揮工程で、乾燥した懸濁ポリマー粒子中の未反応物を例えば、押出機などで脱揮し、ペレット化する。この場合、前記一般式（Ｉ）で表される３−アリールベンゾフラノンは、脱揮工程前に添加することが好ましい。
【００２８】
また、アニオン重合を行なう場合は、不活性溶媒中に単量体を溶解させ、重合開始剤として有機アルキル金属化合物、例えば、ｎ−ブチルリチウム、ｓｅｃ−ブチルリチウム、ｔ−ブチルリチウムなどを用いて重合し、重合終了後、メタノール等の活性水素を有する化合物で重合活性末端を失活させ、重合を完結させる。その後、脱揮工程で、重合反応後の反応物から、未反応物及び／又は溶剤を、例えばフラッシュドラム、二軸脱揮器、薄膜蒸発器、押出機などで脱揮し、ペレット化する。この場合、前記一般式（Ｉ）で表される３−アリールベンゾフラノンは、脱揮工程前に添加することが好ましい。
【００２９】
【発明の実施の形態】
次に本発明を実施例及び比較例により、詳しく説明するが、本発明はこれら実施例に限定される訳ではない。
［製造例１］
５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）―３Ｈ−ベンゾフラン−２−オンの製造１，２−ジクロロエタン３００ｍｌ中に、２，４―ジ−ｔｅｒｔ−ブチルフェノール（９７％）２１２．５ｇ（１．００モル）、５０％水性グリオキシル酸１６３．０ｇ（１．１０モル）、ｐ−トルエンスルホン酸１水和物０．５ｇ（２．６ミリモル）の混合物を加え、窒素下において３．５時間、水分離器上で還流した。得られた反応混合物を濃縮し、残留分をヘキサン８００ｍｌ中に取り、３回水洗した。水層をヘキサン３００ｍｌで更に抽出し、有機層と合わせて硫酸マグネシウムで乾燥した後濃縮すると、粘調性化合物が２６０ｇ得られた。
【００３０】
上記化合物にｏ−キシレン５００ｍｌを加え、Ｆｕｌｃａｔ２２Ｂ［ＬａｐｏｒｔｅＡｄｓｏｒｂｅｎｔｓ社製、登録商標、シート状シリケート］を４０ｇ添加して、１．５時間、水分離器上で還流した。次いで、Ｆｕｌｃａｔ２２Ｂをろ過により除き、過剰のｏ−キシレンを留去した。メタノール４００ｍｌから残留分を結晶化し、１７５．５ｇの５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンを得た。
【００３１】
［製造例２］
５，７−ジ−ｔｅｒｔ−ブチル−３−（２，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンの製造１，２−ジクロロエタン３００ｍｌ中に、２，４−ジ−ｔｅｒｔ−ブチルフェノール（９７％）２１２．５ｇ（１．００モル）、５０％水性グリオキシル酸１６３．０ｇ（１．１０モル）、ｐ−トルエンスルホン酸１水和物０．５ｇ（２．６ミリモル）の混合物を加え、窒素下において３．５時間、水分離器上で還流した。反応混合物を濃縮し、残留分をヘキサン８００ｍｌ中に取り、３回水洗した。水層をヘキサン３００ｍｌで更に抽出し、有機層と合わせて硫酸マグネシウムで乾燥した後濃縮すると、粘調性化合物が２６２ｇ得られた。
【００３２】
上記化合物にｍ−キシレン５００ｍｌを加え、Ｆｕｌｃａｔ２２Ｂ［ＬａｐｏｒｔｅＡｄｓｏｒｂｅｎｔｓ社製、登録商標、シート状シリケート］を４０ｇ添加して１．５時間、水分離器上還流した。次いで、Ｆｕｌｃａｔ２２Ｂをろ過により除き、過剰のｍ−キシレンを留去した。メタノール４００ｍｌから残留分を結晶化し、２４２ｇの５，７−ジ−ｔｅｒｔ−ブチル−３−（２，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンが得られた。なお、参考例、参考比較例、実施例及び比較例における樹脂組成物及び成形品の分析方法は、下記の通りである。
【００３３】
（１）重量平均分子量の測定試料調製：テトラヒドロフランに樹脂組成物約１０００ｐｐｍを溶解測定条件機器：昭和電工Ｓｈｏｄｅｘ２１（ゲルパーミエイション・クロマトグラフィー）
カラム：サンプル：ＫＦ−８０６Ｌ２本リファレンス：ＫＦ−８００ＲＬ２本温度：４０℃キャリア：ＴＨＦ１ｍｌ／ｍｉｎ検出器：ＲＩ、ＵＶ：２５４ｎｍ検量線：東ソー製の単分散ＰＳ使用データ処理：Ｓｉｃ―４８０
【００３４】
（２）メルトフローレートの測定ＩＳＯＲ１１３３に準拠して測定（条件：２００℃、荷重５ｋｇｆ）
（３）成形品中の残留スチレン単量体量の測定試料調製：樹脂組成物１ｇをジメチルフォルアミド２５ｍｌに溶解、樹脂がシンジオタクチックの場合のみ樹脂組成物０．１ｇをジクロロベンゼンに溶解測定条件検出方法：ＦＩＤ機器：島津製製作所ＧＣ１４Ｂカラム：ＣＨＲＯＭＡＰＡＣＫＣＰＷＡＸ５２ＣＢ１００ｍ、膜厚２μｍ、０．５２ｍｍφカラム温度：１１０℃−１０分→１５℃／分→１３０℃−２分注入口温度：１５０℃検出器温度：１５０℃キャリアガス：ヘリウム
【００３５】
（４）成形品中の３−アリールベンゾフラノンの測定試料調製：成形品１ｇをメチルエチルケトンに溶解測定条件検出方法：ＦＩＤ機器：島津製製作所ＧＣ１７Ａｐｆカラム：ＤＢ−１（１００％ジメチルポリシロキサン）３０ｍ、膜厚０．１μｍ、０．２５ｍｍφカラム温度：１００℃−２分→５℃／分→２６０℃−５分注入口温度：２００℃検出器温度：２００℃キャリアガス：窒素
【００３６】
（５）成形品中のスチレン単量体の二量体及び三量体の測定（４）と同じ方法成形品の色調、成形品の臭気、金型へのオイル付着状況と、３−アリールベンゾフラノンの添加量、スチレン単量体、その二量体及び三量体の量との関係について、下記、参考例１〜１０、比較参考例１〜８の結果を表１に示す。なお、参考例１〜１０、比較参考例１〜８における樹脂組成物の評価方法は、下記の通りである。
【００３７】
（１）臭気判定方法樹脂組成物から、開口部幅９５ｍｍ、奥行５５ｍｍ、深さ９６ｍｍ、厚み２ｍｍの直方体容器を射出成形で作成し、この容器に９０℃の温湯２００ｍｌを入れ、３分間後にこの温湯の臭気を判定した。
（２）成形品の色調の判定方法（１）の臭気判定に用いた成形品を目視で判定した。
（３）金型へのオイル付着状況の確認方法１５０×５０×２．５ｍｍの短冊型の金型を使用して、充填３．０秒で射出成形時にショートショットさせた。７０ショット終了後、１５分間射出成形を停止し、金型を冷却して、成形体先端部に相当する金型面を観察し、オイルの付着状況を確認した。以後、７０ショット毎に、同様にして金型へのオイル付着状況を確認しつつ、９８０ショットまで成形を繰り返し、金型にオイルが付着し始めたショット数を求めた。
【００３８】
［参考例１］
スチレン９０重量部及びエチルベンゼン１０重量部に、０．０５重量部の重合開始剤（１，１−ビス（ｔ−ブチルペルオキシ）−３，３，５−トリメチルシクロヘキサン）を溶解し、０．５リットル／時の速度で、それぞれの容量が１リットルの第１反応器、第２反応器、第３反応器からなる重合装置に連続的に順次供給した。かかる重合工程が終了した直後、すなわち、第３反応器の出口において、エチルベンゼンに溶解した５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンを、第３反応器により得られた樹脂（重量平均分子量＝２６万）に対して０．１５重量％になるように添加した。次いで、第３反応器の後に設けられた完全混合型ミキサー（容量１５０ミリリットル）で、樹脂と５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンとを均一に混ぜたあと、単軸押出機を直列に２台連結した脱揮装置に移行させ、かかる脱揮工程において揮発分を順次除去し、ペレット化した。
【００３９】
なお、重合工程における重合反応条件は、第１反応器は重合温度１０５〜１１０℃，攪拌機回転数１５０ｒｐｍ、第２反応器は重合温度１１５〜１２５℃、攪拌機回転数５０ｒｐｍ、第３反応器は重合温度１３０〜１５０℃、攪拌機回転数２０ｒｐｍとした。各反応器出口の重合率は、第１反応器出口では３５％、第２反応器出口では６５％、第３反応器出口では９０％であった。また、脱揮工程における、前段の単軸押出機は温度１９０〜２００℃、真空度３０ｔｏｒｒ、後段の単軸押出機は温度２２０〜２４０℃、真空度５ｔｏｒｒとした。
【００４０】
得られたペレットを用いて、臭気判定用の射出成形品を以下の異なる２つの条件で作製した。一つ目の条件としては、通常の連続成形で成形品を採取した（滞留なし品）。他の条件としては、成形を一度止め、シリンダー内に樹脂を３０分間滞留させた後、成形を再開、最初の２ショットを捨て、滞留した樹脂の３ショット目を成形品として採取した（滞留３０分品）。射出成形機の各ゾーンの成形温度はそれぞれ２５０℃、２５０℃、２３０℃、２１０℃とした。さらには射出成形したときの金型へのオイル付着状況を確認した。スチレン単量体の残存量、その二量体及び三量体の残存量の合計、臭気判定結果、並びに目視判定による成形品の色調および金型へのオイル付着状況を、表１に示す。
【００４１】
［参考例２］
参考例１において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンの添加量を０．０５重量％としたこと以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
［参考例３］
参考例１において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンの添加量を０．０２重量％としたこと以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
【００４２】
［参考例４］
参考例１において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンを、脱揮工程における単軸押出機の前段の押出機と後段の押出機との間の位置に添加し、添加量を０．０５重量％としたこと以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
［参考例５］
参考例１において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンの代わりに、製造例２で得られた５，７−ジ−ｔｅｒｔ−ブチル−３−（２，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンを添加し、添加量を０．０５重量％としたこと以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
【００４３】
［参考例６］
参考例１において、スチレン９０重量部の代わりに、スチレン８５重量部及びポリブタジエン（ジエン３５：旭化成製）５重量部を用いた以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
［参考例７］
参考例６において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンの添加量を０．０２重量％としたこと以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
［参考例８］
参考例１において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−１−オンの添加量を０．０１重量％としたこと以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
【００４４】
［参考例９］
乾燥窒素で置換した攪拌機付きオートクレーブ中に脱水したシクロヘキサン６０ｋｇ、脱水したスチレン１０ｋｇを仕込み、反応初期温度５０℃でｎ−ブチルリチウム６ｇを含有する３０重量％のシクロヘキサン溶液を添加し、激しく攪拌しながら重合反応を実施した。５分後、反応器内温は８５℃に上昇した。２０分間反応させ、ガスクロマトグラフィーにより重合率を測定したところ９９．８％であった。次いで、反応器中の重合溶液に、メタノールを１ｋｇ加え、３０分間攪拌後、得られた樹脂に対し、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンを０．０１重量％添加して、２０ｍｍ単軸押出機で、押出機温度２１０〜２３０℃、真空度１５ｔｏｒｒで脱揮、ペレット化した。このペレットを用いた成形品の作製、成形品の評価は、参考例１と同様にして行なった。結果を表１に示す。
【００４５】
［参考例１０］
栗本鉄工所製ＫＲＣ（内容積８．６リットル、ブレード径１００ｍｍ、シリンダー有効長１０００ｍｍ、パドル数４４組、シリンダー内壁とパドルとのクリアランス１ｍｍ）の反応器を使用して、内部温度を８０℃に制御し、また回転数を２００ｒｐｍとした。この反応器にスチレンを１リットル／時の割合で供給するとともに、触媒としてメチルアルミノキサンを７５ミリモル／時、ペンタメチルシクロペンタジエニルチタニウムトリメトキシドを０．１５ミリモル／時の割合で供給しながら５時間連続重合を実施した。反応器出口から出てくる粉体を１重量％の水酸化ナトリウムを溶解したメタノールに浸漬し、洗浄した後、得られた樹脂に対し、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンを０．０１重量％添加して、１８０℃、１０ｔｏｒｒ、１時間、乾燥機で乾燥した。添加剤混合前の樹脂は、１３Ｃ−ＮＭＲによる重合体のラセミペンタッドでのシンジオタクシティーは９７％であった。
【００４６】
この樹脂を２０ｍｍ単軸押出機で、押出機温度２７０〜２９０℃、真空度２０ｔｏｒｒで脱揮、ペレット化した。このペレットを用いて、臭気判定用の射出成形品を２つの異なる条件で作製した。一つ目の条件としては、通常の連続成形で成形品を採取した（滞留なし）。他の条件としては、成形を一度止め、シリンダー内に樹脂を３０分間滞留させた後、成形を再開、最初の２ショットを捨て、滞留した樹脂の３ショット目を成形品として採取した（滞留３０分品）。射出成形機の各ゾーンの成形温度はそれぞれ２９０℃、２９０℃、２８０℃、２７０℃とした。さらには射出成形したときの金型へのオイル付着状況を確認した。スチレン単量体の残存量、臭気判定結果および目視判定による成形品の色調および金型へのオイル付着状況を、表１に示す。
【００４７】
［比較参考例１］
参考例１において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンを添加しなかった以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
［比較参考例２］
参考例１において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンの添加量を０．００５重量％とした以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
【００４８】
［比較参考例３］
参考例１において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンの代わりに、スミライザーＧＳ〔住友化学社製、登録商標、フェノール系熱劣化防止剤、化学名:2-[1-(2-Hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate〕を添加し、添加量を０．０５重量％した以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
［比較参考例４］
参考例１において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンの代わりに、スミライザーＧＳ〔住友化学社製、登録商標、フェノール系熱劣化防止剤〕を添加し、添加量を０．３重量％とした以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
【００４９】
［比較参考例５］
参考例１において、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンの添加量を０．００５重量％とし、また、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンを脱揮工程における単軸押出機の前段の押出機と後段の押出機との間の位置に添加し、更に、樹脂に対して水を１重量％添加した以外は、参考例１と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
【００５０】
［比較参考例６］
参考例２において、後段の単軸押出機の真空度を２０ｔｏｒｒとした以外は、参考例２と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
［比較参考例７］
参考例９において、樹脂乾燥時の真空度を３０ｔｏｒｒにした以外は、参考例９と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
［比較参考例８］
参考例１０において、樹脂乾燥時の真空度を２８ｔｏｒｒにした以外は、参考例１０と同様にしてペレット及び成形品を作製し、物性等の評価を行った。結果を表１に示す。
【００５１】
【表１】

【００５２】
表１より、前記一般式（Ｉ）で表される３―アリールベンゾフラノンを所定量添加して、スチレン単量体の残存量を１００ｐｐｍ以下にすることにより、色調が非常に優れた成形品が得られることが分かる。なお、前記熱劣化防止剤を所定量添加しても、スチレン単量体の残存量が多いと、得られる成形品の色調は非常に悪いものとなる。また、本発明の樹脂組成物においては、成形機での滞留試験の結果においても、スチレン単量体及びその二量体や三量体の増加も少なく、成形品の色調も変わらず、非常に熱安定性に優れるものであった。また、フェノール系熱劣化防止剤（スミラーザーＧＳ）を用いた場合は、得られる成形品の色調が非常に悪い。さらに、添加量を本発明の３−アリールベンゾフラノンと同一量にしても、スチレン単量体及びその二量体や三量体の低減効果は、本発明の３−アリールベンゾフラノンに比べて低いということが分かる。
【００５３】
本発明の樹脂組成物を用いた発泡シート及びその成形品についての評価（その１）を行った。下記実施例１〜９及び比較例１〜３において用いた樹脂の評価方法は下記の通りである。
（１）発泡シートの二次成形性の評価方法発泡シートの二次成形性を確認するために、小型圧空成形機を用い、加熱時間一定にして、炉内温度それぞれ２００℃、２２０℃、２４０℃に変えて、発泡シートから成形品が得られるかどうか確認した。
（２）成形品の厚み斑の測定法第１図に示すように、発泡シートから得た成形品１０サンプルにおいてで、同一側面の４個所（Ａ、Ｂ、Ｃ、Ｄ）の厚みを測定し、その標準偏差を求め、厚み斑の指標とした。
【００５４】
（３）成形品の外観、印刷の転写性の判定方法発泡成形品表面の肌荒れ状態を目視で確認した。また、印刷の転写性は印刷した文字の転写性を目視で確認した。
［実施例１〜９、比較例１〜２］
発泡シートの製造に用いた樹脂は、表２中の「発泡シートの評価に用いた樹脂」欄に記載された、上記参考例１〜９及び比較参考例１〜２でそれぞれ製造されたものである。また、比較例３を下記に示す。
［比較例３］
参考例２において、重合開始剤（１，１−ビス（ｔ−ブチルペルオキシ）−３，３，５−トリメチルシクロヘキサン）を添加せずに、第１反応器は重合温度１２５〜１３０℃，第２反応器は重合温度１３５〜１４５℃、第３反応器は重合温度１５０〜１６５℃（第３反応器出口の重合転化率は９０重量％）にした以外は、参考例２と同様にして樹脂を製造した。
【００５５】
＜芳香族モノビニル系樹脂組成物の発泡シートを用いた成形品の製造方法＞
幅３０ｍｍのＴダイを備えた３０ｍｍ押出発泡機を用いて、芳香族モノビニル系樹脂組成物１００重量部に対して、発泡核剤を１重量部、発泡剤を３重量部添加して、約８倍の発泡シートを得た。樹脂溶融ゾーンの温度は１８０〜２３０℃、ロータリークーラー温度は１５０〜１６０℃、Ｔダイ温度を１２０〜１３０℃に調整した。発泡核剤には日本ミストロン製、ミストロンベーパーを用い、発泡剤にはｎ−ブタン６５重量％とｉ−ブタン３５重量％の混合物を用いた。得られた発泡シートを１週間養生させ、小型圧空成形機を用い、炉内温度を所定の温度にして、１５秒加熱した後、６０℃に調整した金型で１００ｍｍ角、深さ５０ｍｍ、厚さ約２〜３ｍｍの箱型成形品を作成した。二次成形時の成形幅を確認するため、炉内温度２００℃、２２０℃、２４０℃の３点で、成形品の作製が可能かどうか試した。さらに、炉内温度２００℃で得られた成形品の厚み斑の測定及び外観の目視確認を行った。スチレン単量体の残存量、スチレン単量体の二量体及び三量体の残存量の合計、発泡シートの二次成形性、成形品の厚み斑、外観の目視確認結果を表２に示す。
【００５６】
【表２】

【００５７】
本発明の樹脂組成物を用いた発泡シート及びその成形品についての評価（その２）を行った。
［実施例１０］
参考例１において、反応装置がおよそ１０倍大きい装置を用い、５，７−ジ−ｔｅｒｔ−ブチル−３−（３，４−ジメチルフェニル）−３Ｈ−ベンゾフラン−２−オンの添加量を０．０５重量％とした以外は、ほぼ同等の製造造件で樹脂組成物を製造した。このペレットを用いて、下記の方法で、発泡シートおよびその成形品を作製した。
【００５８】
＜芳香族モノビニル系樹脂組成物の発泡シートを用いた成形品の製造方法＞
芳香族モノビニル系樹脂組成物１００重量部に対し、発泡核剤としてタルク０．５重量部、分散助剤としてステアリン酸亜鉛０．３重量部を加えてミキサーでよく攪拌混合した後、６５ｍｍ、Ｌ／Ｄが３３の一軸押出機ホッパーに供給した。その後、押出機スクリューの前段において２３５℃で溶融混練し、その溶融混練物に、押出機中段に設けられた発泡剤注入孔より、全押出量の２．５重量％になるようにｎ−ブタン６５重量％とｉ−ブタン３５重量％の混合物を注入した。
【００５９】
次いで、押出機スクリューの後段において１６０℃に冷却し、リングダイより管状に押出発泡させ、得られた管状発泡シートを押出機のマンドレルで冷却後、カッターにより１面を切り開いて発泡シートを得た。外観検査および成形品作製用の発泡シートは、押出機を連続１時間運転した後に採取し、１週間養生させた。この発泡シートの外観検査の後に、小型圧空成形機を用い、２００℃の炉内で１０秒加熱した後、６０℃に調整した金型で１００ｍｍ角、深さ４０ｍｍの箱型成形品を作製した。この成形品の外観検査の後に、文字の印刷を施し、転写性を確認した。スチレン単量体の残存量、スチレン単量体の二量体及び三量体残存量の合計、発泡シートの外観、成形品の外観、印刷性の結果を表３に示す。
【００６０】
［実施例１１］
実施例１０の樹脂の製造において、脱揮工程における後段の単軸押出機の真空度を１０ｔｏｒｒにした以外は、実施例１０と同様にして樹脂組成物及び成形品を作製し、物性等の評価を行った。結果を表３に示す。
［比較例４］
実施例１０の樹脂の製造において、脱揮工程における後段の単軸押出機の真空度４０ｔｏｒｒとしたこと以外は、実施例１０と同様にして樹脂組成物及び成形品を作製し、物性等の評価を行った。結果を表３に示す。
【００６１】
【表３】

【００６２】
表２及び表３より、スチレン単量体の残存量を１００ｐｐｍ以下とし、スチレン単量体の二量体及び三量体の合計残存量を０．４重量％以下にすることにより、二次成形性に優れた発泡シートが得られ、また、厚み斑が少なく、外観、印刷性に非常に優れた成形品が得られることが分かる。また、本発明の樹脂組成物は、発泡シートの製造においても、非常に熱安定性に優れるものである。
【００６３】
【発明の効果】
本発明の芳香族モノビニル系樹脂組成物の発泡シート及びその成形品は、成形性及び成形時の熱安定性に優れ、色調が良好で且つ臭気の少ないものである。また、本発明の発泡シートから二次性成形で得られる成形品は厚み斑が少なく、直接食品等に接触するような包装材料、容器等に特に好適に使用できる。産業界に果たす役割は大きい。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an aromatic monovinyl resin composition having a small residual amount of an aromatic monovinyl monomer, a dimer and a trimer thereof, and more particularly to a food product having excellent heat stability at the time of molding and direct food production. TECHNICAL FIELD The present invention relates to a foamed sheet of an aromatic monovinyl resin composition which can be suitably used as a material which comes into contact with a molded article, and a molded product thereof. Further, the present invention provides an aromatic monovinyl resin composition which is excellent in secondary moldability, obtains a molded article with less unevenness in thickness, has a good color tone and an excellent appearance, has a low odor, and is excellent in moldability. And a molded article thereof.
[0002]
[Prior art]
BACKGROUND ART A foam of an aromatic monovinyl resin, for example, a polystyrene resin is used for food containers, heat insulating materials, cushioning materials, and the like by utilizing its excellent heat-retaining and lightweight properties. In particular, expanded polystyrene sheets are widely used for food containers, instant noodle containers, and the like because of their excellent secondary moldability by thermoforming. In producing a polystyrene foam molded product, the surface condition of the foam sheet obtained by foam extrusion (primary molding) greatly affects the surface condition of the molded product after secondary molding. For example, surface defects of the foamed sheet such as rough skin and foreign matter on the surface greatly affect the appearance and printing characteristics of a molded article requiring smoothness. In addition, properties of the resin itself, such as molecular weight, molecular weight distribution, and low molecular weight components such as dimers and trimers, greatly affect the productivity and quality of foamed sheets and molded articles at the time of secondary molding.
[0003]
A conventional resin composed of an aromatic monovinyl-based monomer contains a relatively large amount of a styrene monomer and a low molecular weight component such as a dimer or a trimer thereof. ) And high temperature during the secondary molding of the foamed sheet, and the thermal decomposition of polystyrene increases the styrene monomer and its low molecular weight components such as dimers and trimers. In this case, if the amount of styrene monomer is large, the monomer is condensed in a mandrel of an extruder in a mass production machine, particularly when a foamed sheet is produced, and the condensed liquid adheres to the foamed sheet surface (drip phenomenon). However, serious problems such as poor appearance and poor printing of the molded product after the secondary molding may be caused. If the amount of the dimer or the trimer is large, the extensional viscosity of the resin decreases, and the molding width becomes narrow due to drawdown or the like at the time of the secondary molding, and the productivity may decrease.
[0004]
In order to solve these problems, the residual amount of low molecular components such as styrene monomer and its dimer and trimer should be reduced during resin production. Even at times, it is desired that these low molecular components are not formed by the thermal decomposition of polystyrene. At the time of resin production, it is possible to reduce low molecular components to some extent by controlling the conditions of the polymerization step or the devolatilization step. However, in order to suppress the thermal decomposition of the resin at the time of primary or secondary molding, it is necessary to stabilize the resin by adding a thermal deterioration inhibitor or the like.
[0005]
[Problems to be solved by the invention]
The present invention relates to an aromatic monovinyl-based resin composition having a small amount of residual aromatic monovinyl-based monomer, and has excellent thermal stability at the time of molding and can be suitably used for a material that directly comes into contact with food or the like, Furthermore, the present invention provides a foamed sheet of an aromatic monovinyl resin composition and a molded article thereof, which obtains a molded article having a good color tone and appearance, a low odor, and excellent secondary moldability and a small thickness unevenness. Is provided.
[0006]
[Means for Solving the Problems]
In view of the above problems, the present inventors have made intensive studies and as a result, added a specific thermal degradation inhibitor to a resin composed of an aromatic monovinyl-based monomer having a specific molecular weight in a specific ratio to obtain an aromatic monovinyl resin. The present inventors have found that a foamed sheet and a molded article of an aromatic monovinyl resin composition having excellent properties which could not have been predicted can be obtained by reducing the concentration of the system monomer to a specific concentration or less. Was completed.
[0007]
That is, the present invention provides (a) a resin composed of an aromatic monovinyl monomer having a weight average molecular weight of 150,000 to 700,000, and (b) a resin represented by the following general formula (I):
Embedded image

[In the formula, R1 represents a substituted or unsubstituted carbocyclic aromatic group or a substituted or unsubstituted heterocyclic aromatic group, and R2, R3, R4 and R5 each independently represent a hydrogen atom or Indicate alkyl groups having up to 5 carbon atoms. Wherein the amount of the 3-arylbenzofuranone is 0.006 to 0.5% by weight based on the weight of the resin (a). Further, the present invention relates to a foamed sheet comprising the aromatic monovinyl-based resin composition having a residual amount of the aromatic monovinyl-based monomer of 100 ppm or less in the aromatic monovinyl-based resin composition, and a molded article thereof.
[0008]
Hereinafter, the present invention will be described in detail. In the present invention, in order to obtain a resin composed of (a) an aromatic monovinyl monomer, the aromatic monovinyl monomer used as a raw material includes not only styrene alone but also other vinyl copolymerizable with styrene. A mixture of a system monomer and styrene can be given. Here, as other vinyl monomers copolymerizable with styrene, specifically, methyl methacrylate, methyl acrylate, butyl acrylate, ethyl methacrylate, a halogen-containing vinyl monomer, α-methylstyrene, o-methylstyrene, m -Methylstyrene, p-methylstyrene and the like, and one or more of these can be used. These vinyl monomers copolymerizable with styrene can be used usually in a proportion of not more than 60% by weight, preferably not more than 50% by weight of all monomers. Further, (a) the resin composed of an aromatic monovinyl monomer may contain a rubber component such as polybutadiene, SBR, polyisoprene, nitrile rubber, and natural rubber.
[0009]
In the present invention, as a thermal deterioration inhibitor, a 3-arylbenzofuranone having a structure capable of effectively capturing and stabilizing a radical generated under oxygen-free condition, that is, a 3-arylbenzofuranone represented by the above general formula (I) Is used. The amount is 0.006 to 0.5% by weight, preferably 0.008 to 0.3% by weight, and more preferably 0.01 to 0.2% by weight based on the weight of the resin. Here, if the addition amount of the 3-arylbenzofuranone is less than 0.006% by weight, the effect of suppressing the formation of the aromatic monovinyl monomer and its dimer or trimer in the devolatilization step is not sufficient. It is not sufficient to obtain these small molded articles. If the addition amount is less than 0.006% by weight, the effect of suppressing the generation of styrene monomer due to the thermal decomposition of the resin at the time of molding the foamed sheet and further at the time of the secondary molding becomes insufficient, and the molded article becomes Since it is extremely difficult to keep the residual styrene monomer level low, it is not possible to obtain a molded article having a good color tone, which is not preferable. On the other hand, even if the above-mentioned 3-arylbenzofuranone is added in an amount of more than 0.5% by weight, the effect corresponding to the added amount cannot be obtained.
[0010]
Examples of such a thermal deterioration inhibitor include 5,7-di-tert-butyl-3- (2,4-dimethylphenyl) -3H-benzofuran-2-one and 5,7-di-tert-butyl. -3- (2,5-dimethylphenyl) -3H-benzofuran-2-one, 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one and the like. Can be mentioned. Among them, 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one is preferred.
[0011]
In the present invention, the residual amount of the aromatic monovinyl monomer is 100 ppm or less, preferably 95 ppm or less. A rectangular parallelepiped container having a width of 95 mm, a depth of 55 mm, a depth of 96 mm, and a thickness of 2 mm was made by injection molding with polystyrene and impact-resistant polystyrene, and 200 ml of hot water at 90 ° C. was put into the container, and after three minutes, the odor of the hot water As a result, when the residual amount of the aromatic monovinyl monomer was 100 ppm or less, the problem of odor was greatly improved, and the color tone of the molded product was also significantly improved. On the other hand, if the residual amount of the aromatic monovinyl-based monomer exceeds 100 ppm, the color tone of the molded article becomes poor even if the predetermined amount of the 3-arylbenzofuranone is added, and the object cannot be achieved.
[0012]
In addition, during the production of a foamed sheet using the aromatic monovinyl resin composition of the present invention, the influence on the molded article due to condensation of the aromatic monovinyl monomer in the mandrel of the extruder was confirmed. When the residual amount of the monomer is 100 ppm or less, poor appearance and poor printability are not observed, and the appearance of the molded article is greatly improved. The color tone of the molded product is also good. On the other hand, if it exceeds 100 ppm, poor appearance and poor printability are observed. Further, when the total amount of the remaining dimers and trimers of the aromatic monovinyl-based monomer is 0.4% by weight or less, the thickness unevenness of the molded article is very small, and the molded article and the foamed sheet are hardly formed. The appearance of the product has also been improved. When the surface of the molded article was magnified and observed with an optical microscope, it was confirmed that there was little bubble breakage and the surface was smooth.
[0013]
In the present invention, the weight average molecular weight of the resin (a) composed of an aromatic monovinyl monomer is preferably 15 to 700,000. More preferably, it is 180,000 to 500,000. If it is less than 150,000, the strength of the molded product will be insufficient, and if it is more than 700,000, the moldability will be significantly reduced. The aromatic monovinyl resin composition of the present invention may contain, if desired, commonly used additives such as lubricants, antioxidants, ultraviolet absorbers, mold release agents, plasticizers, dyes, pigments, and various fillers. Agents and the like can be added. Further, other resins, for example, general polystyrene, styrene-butadiene copolymer elastomer, partially or completely hydrogenated styrene-butadiene copolymer elastomer, polyphenylene ether, and the like can be blended.
[0014]
Next, a method for producing the aromatic monovinyl resin composition of the present invention will be described. Aromatic monovinyl resins, for example, polystyrene produced on an industrial scale, are mostly produced by radical polymerization, but when unreacted substances and / or solvents are removed in a devolatilization step, or immediately after devolatilization. A large amount of styrene monomer and its dimer or trimer are generated by thermal decomposition of the resin (1), and the resulting molded article contains a large amount of these. Furthermore, when molded products are obtained by injection molding, blow molding, extrusion molding, etc. using these resins, the amount of styrene monomer, its dimer and trimer further increases due to the heat history during molding. I do.
[0015]
The amount of the styrene monomer remaining in industrially produced polystyrene is about 200 to 400 ppm, and it is extremely difficult to obtain, for example, 100 ppm or less. Heretofore, polystyrene has often been polymerized by a thermally initiated radical and / or a polymerization initiator radical generated by the reaction of a styrene monomer. In this case, by increasing the ratio of the polymerization initiator radical, it is possible to reduce the amount of the dimer and trimer of the styrene monomer, but it is generated again by thermal decomposition of the resin in the devolatilization step. However, there was a limit in reducing these amounts.
[0016]
In the method for producing an aromatic monovinyl resin composition of the present invention, the 3-arylbenzofuranone represented by the general formula (I) is added in the polymerization step or the devolatilization step, and after the polymerization step and before the devolatilization step. Then, this is a method for obtaining a molded article having an extremely small amount of the aromatic monovinyl-based monomer, furthermore, the amount of the dimer and the trimer thereof. The method for polymerizing the aromatic monovinyl monomer in the step (a) of polymerizing the resin comprising the aromatic monovinyl monomer of the present invention is not particularly limited, and a conventionally used method such as radical polymerization is used. As a method of polymerization, a bulk polymerization method, a suspension polymerization method, a multi-stage polymerization method such as a bulk-suspension polymerization method, an emulsion polymerization method are possible, and also an anion polymerization method or an ionic polymerization method using a metallocene catalyst. Can be used.
[0017]
Here, the polymerization method of the resin (a) comprising an aromatic monovinyl monomer of the present invention will be described by taking a bulk polymerization method which is a radical polymerization method as an example. Examples of the polymerization initiator used in the above polymerization method include organic peroxides such as 2,2-bis (t-butylperoxy) butane, 2,2-bis (t-butylperoxy) octane, 1,1-bis ( Peroxy ketals such as t-butylperoxy) -3,3,5-trimethylcyclohexane, 1, -bis (t-butylperoxy) cyclohexane, n-butyl-4,4-bis (t-butylperoxy) valerate, and di-t-butyl peroxide , T-butylcumyl peroxide, dicumyl peroxide, α, α'-bis (t-butylperoxyisopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5 Dialkyl peroxides such as -dimethyl-2,5-di (t-butylperoxy) hexyne-3; Diacyl peroxides such as ruperoxide, isobutyryl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide and m-trioil peroxide , Diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-n-propyl peroxydicarbonate, dimyristyl peroxydicarbonate, di-n-ethoxyethyl peroxydicarbonate, dimethoxyisopropyl peroxydicarbonate, di (3-methyl- Peroxydicarbonates such as 3-methoxybutyl) peroxydicarbonate, t-butylperoxya Acetate, t-butyl peroxyisobutyrate, t-butyl peroxy pivalate, t-butyl peroxy neodecanoate, cumyl peroxy neodecanoate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxy -3,3,5-trimethylhexanoate, t-butylperoxylaurate, t-butylperoxybenzoate, di-t-butyldiperoxyisophthalate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, Peroxyesters such as t-butylperoxyisopropyl carbonate, acetylacetone peroxide, methyl ethyl ketone peroxide, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone Ketone peroxides such as peroxides, t-butyl hydroperoxide, cumene hydroperoxide, diisopropyl perbenzene hydroperoxide, p-menthane hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, 1,1,3,3 Hydroperoxides such as -tetramethylbutyl hydroperoxide;
[0018]
Also, azo-based initiators such as 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (1-cyclohexanecarbonitrile) and the like Can also be used. These organic peroxides or azo-based initiators may be used alone or in combination of two or more. As the polymerization conditions, the polymerization may be started at 20 to 180 ° C. in accordance with the decomposition temperature of the organic peroxide as the polymerization initiator, and bulk polymerization may be performed. A chain transfer agent, a solvent, a heat stabilizer such as a general antioxidant, a mineral oil, a silicone oil and the like can be appropriately added to the bulk polymerization system.
[0019]
Here, examples of the chain transfer agent include α-methylstyrene linear dimer, n-dodecylmercaptan, t-dodecylmercaptan, 1-phenyl-2-fluorene, dibenthene, mercaptans such as chloroform, terpenes, halogen compounds, terpinolene and the like. And turpentines. The amount of the chain transfer agent is not particularly limited, but generally may be about 0.005 to 0.1% by weight based on the monomer.
[0020]
As the solvent used as needed, aromatic hydrocarbons, for example, toluene, xylene, ethylbenzene, dialkyl ketones, for example, methyl ethyl ketone, etc., may be used alone, or two or more kinds may be used in combination. May be. Further, other solvents such as aliphatic hydrocarbons and the like can be mixed with the aromatic hydrocarbons as long as the solubility of the polymerization product is not reduced. These solvents are preferably used in an amount not exceeding 25% by weight based on the monomer. When the amount of the solvent exceeds 25% by weight, the polymerization rate is significantly reduced, and the impact strength of the obtained resin is greatly reduced. Further, a large amount of energy is required for the recovery of the solvent, so that the economic efficiency is deteriorated. The solvent may be added after the polymerization proceeds and the viscosity becomes relatively high, or may be added before the polymerization, but is added at a ratio of 5 to 20% by weight before the polymerization. It is easier to make the quality uniform and it is preferable in terms of controlling the polymerization temperature.
[0021]
Examples of general stabilizers include hindered phenols such as octadecyl-3- (3,5-tert-butyl-4-hydroxyphenyl) propionate and 4,6-bis (octylthiomethyl) -o-cresol. Examples include antioxidants and phosphorus-based processing heat stabilizers such as tris (2,4-di-tert-butylphenyl) phosphite. These stabilizers may be used alone or in combination of two or more. The timing of addition is not particularly limited, and may be either the polymerization step or the devolatilization step. Further, the stabilizer can be mixed with the molded product by a mechanical device such as an extruder or a Banbury mixer. Here, the apparatus used in the polymerization step is not particularly limited, and may be appropriately selected according to the polymerization method of the aromatic monovinyl monomer. For example, in the case of bulk polymerization, a polymerization apparatus including a first reactor, a second reactor, and a third reactor can be used, and in the case of anionic polymerization, a polymerization apparatus such as an autoclave can be used.
[0022]
In the production of the resin comprising the aromatic monovinyl monomer (a) of the present invention, the devolatilization step is not particularly limited. When the polymerization of the aromatic monovinyl monomer is carried out by bulk polymerization, the polymerization is continued until the unreacted aromatic monovinyl monomer finally becomes 50% by weight, more preferably 40% by weight or less. In order to remove volatile components such as an aromatic monovinyl monomer, devolatilization is performed by a known method. This devolatilization step is for removing unreacted substances and / or solvents from the reaction product after the polymerization reaction. The devolatilization process includes, for example, a flash drum, a twin-screw devolatilizer, a thin film evaporator, An ordinary devolatilizing device such as an extruder can be used. The temperature of the devolatilization process is usually about 190 to 280 ° C., and the pressure of the devolatilization process is usually about 1 to 100 torr (Torr), preferably 1 to 50 torr, and more preferably 1 to 50 torr. -10 torr. As a devolatilization method, for example, it is desirable to remove under reduced pressure under heating, or to remove through an extruder designed for the purpose of removing volatile components.
[0023]
In the production of the aromatic monovinyl resin composition of the present invention, it is preferable to add the 3-arylbenzofuranone (thermal degradation inhibitor) represented by the general formula (I) in a polymerization step or a devolatilization step. . That is, in this case, the 3-arylbenzofuranone of the present invention is added to a reactor or an extruder used for the polymerization reaction. Further, it is more preferable that the compound is added after (preferably immediately after) the polymerization step and before the devolatilization step. In this case, the 3-arylbenzofuranone is added at the outlet of the reactor used for the polymerization reaction. An addition will be made. In order to suppress the thermal decomposition of the resin during molding, the obtained pellets may be further mixed with a 3-arylbenzofuranone using a mechanical device such as an extruder or a Banbury mixer.
[0024]
After adding the 3-arylbenzofuranone (thermal degradation inhibitor) to the polymerization solution obtained in the polymerization step, it is preferable to mix both uniformly. This is because when 3-arylbenzofuranone is added to a reactor having poor mixing properties or to a polymerization line having no mixing means, the dispersion of the 3-arylbenzofuranone which is a thermal deterioration inhibitor becomes insufficient, and This is because, although it has an effect of suppressing the production of the aromatic monovinyl monomer and its dimer or trimer in the volatilization step, the effect is unfavorably reduced.
[0025]
Here, in order to uniformly mix the polymerization solution obtained in the polymerization step and the 3-arylbenzofuranone (thermal degradation inhibitor), for example, a mixing device is separately provided in addition to the polymerization device and the devolatilization device. Is preferred. The structure of the mixing device is not particularly limited as long as it can uniformly mix the polymerization solution obtained in the polymerization step and the 3-arylbenzofuranone. For example, a complete mixing mixer, a tower mixer And the like. Specifically, a mixing device can be provided after the above-mentioned polymerization device (for example, the third reactor).
[0026]
When the 3-arylbenzofuranone is added in the polymerization step, when the polymerization rate of the aromatic monovinyl monomer reaches 50% or more, particularly 60% or more, it is represented by the general formula (I). It is desirable to add a 3-arylbenzofuranone. This is because if added in the early stage of polymerization, radicals during the polymerization reaction are trapped, which is not very preferable. Here, the polymerization rate means the ratio (%) of the weight of the polymerized resin when the weight of the raw material monomer is 100. In addition, when the 3-arylbenzofuranone is added in the polymerization step, it is preferably added when the polymerization temperature in the polymerization step is 160 ° C. or lower. If the above-mentioned thermal degradation inhibitor is added after the polymerization temperature exceeds 160 ° C, the trapping of radicals during the polymerization reaction is accelerated, which is not so preferable.
[0027]
When the polymerization is carried out by bulk-suspension polymerization, the partially polymerized reactant is added to a suspension stabilizer such as tricalcium phosphate or polyvinyl alcohol, or a surfactant in combination with the suspension stabilizer in an aqueous medium. While stirring to complete the reaction by suspension polymerization. The slurry containing the obtained suspended polymer particles is dehydrated, washed, and dried. Thereafter, in the devolatilization step, the unreacted material in the dried suspended polymer particles is devolatilized by, for example, an extruder and pelletized. In this case, the 3-arylbenzofuranone represented by the general formula (I) is preferably added before the devolatilization step.
[0028]
When performing anionic polymerization, the monomer is dissolved in an inert solvent, and an organic alkyl metal compound such as n-butyllithium, sec-butyllithium, or t-butyllithium is used as a polymerization initiator. After completion of the polymerization, the active terminal of the polymerization is deactivated with a compound having active hydrogen such as methanol, thereby completing the polymerization. Thereafter, in the devolatilization step, unreacted substances and / or solvents are devolatilized from the reaction product after the polymerization reaction by, for example, a flash drum, a twin-screw devolatilizer, a thin film evaporator, an extruder, and the like, and pelletized. In this case, the 3-arylbenzofuranone represented by the general formula (I) is preferably added before the devolatilization step.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to these examples.
[Production Example 1]
Preparation of 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one In 300 ml of 1,2-dichloroethane, 2,4-di-tert-butylphenol (97 %) 212.5 g (1.00 mol), a mixture of 50% aqueous glyoxylic acid 163.0 g (1.10 mol) and p-toluenesulfonic acid monohydrate 0.5 g (2.6 mmol) were added, Reflux on a water separator under nitrogen for 3.5 hours. The obtained reaction mixture was concentrated, and the residue was taken up in 800 ml of hexane and washed three times with water. The aqueous layer was further extracted with 300 ml of hexane, combined with the organic layer, dried over magnesium sulfate, and concentrated to obtain 260 g of a viscous compound.
[0030]
To the above compound was added 500 ml of o-xylene, 40 g of Fucat22B [manufactured by LaporteAdsorbents, registered trademark, sheet silicate] was added, and the mixture was refluxed for 1.5 hours on a water separator. Then, Fucat22B was removed by filtration, and excess o-xylene was distilled off. The residue was crystallized from 400 ml of methanol to obtain 175.5 g of 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one.
[0031]
[Production Example 2]
Preparation of 5,7-di-tert-butyl-3- (2,4-dimethylphenyl) -3H-benzofuran-2-one In 300 ml of 1,2-dichloroethane, 2,4-di-tert-butylphenol (97%) was added. %) 212.5 g (1.00 mol), a mixture of 50% aqueous glyoxylic acid 163.0 g (1.10 mol) and p-toluenesulfonic acid monohydrate 0.5 g (2.6 mmol) were added, Reflux on a water separator under nitrogen for 3.5 hours. The reaction mixture was concentrated, and the residue was taken up in 800 ml of hexane and washed three times with water. The aqueous layer was further extracted with 300 ml of hexane, combined with the organic layer, dried over magnesium sulfate, and concentrated to obtain 262 g of a viscous compound.
[0032]
To the above compound was added 500 ml of m-xylene, 40 g of Fucat22B [registered trademark, sheet silicate manufactured by LaporteAdsorbents] was added, and the mixture was refluxed for 1.5 hours on a water separator. Next, Fucat22B was removed by filtration, and excess m-xylene was distilled off. The residue was crystallized from 400 ml of methanol to obtain 242 g of 5,7-di-tert-butyl-3- (2,4-dimethylphenyl) -3H-benzofuran-2-one. In addition, the analysis method of the resin composition and a molded article in a reference example, a reference comparative example, an example, and a comparative example is as follows.
[0033]
(1) Measurement of weight average molecular weight Preparation of sample: about 1000 ppm of resin composition dissolved in tetrahydrofuran Measurement conditions Equipment: Showa Denko Shodex 21 (gel permeation chromatography)
Column: sample: two KF-806L reference: two KF-800RL temperature: 40 ° C carrier: THF 1 ml / min detector: RI, UV: 254 nm calibration curve: data processing using Tosoh monodisperse PS: Sic-480
[0034]
(2) Melt flow rate measurement Measured in accordance with ISOR1133 (conditions: 200 ° C, load 5 kgf)
(3) Measurement of residual styrene monomer content in molded article Sample preparation: 1 g of resin composition was dissolved in 25 ml of dimethylformamide, and 0.1 g of resin composition was dissolved in dichlorobenzene only when the resin was syndiotactic. Condition detection method: FID equipment: GC14B column manufactured by Shimadzu Corporation: CHROMAPACKCPWAX52CB100 m, film thickness 2 μm, 0.52 mmφ column temperature: 110 ° C. for 10 minutes → 15 ° C./minute→130° C. for 2 minutes Inlet temperature: 150 ° C. Detector temperature : 150 ° C. Carrier gas: helium
(4) Measurement of 3-arylbenzofuranone in molded article Preparation of sample: 1 g of molded article dissolved in methyl ethyl ketone Measurement conditions Detection method: FID equipment: GC17Apf column manufactured by Shimadzu Corporation: DB-1 (100% dimethylpolysiloxane) 30 m, Film thickness 0.1 μm, 0.25 mmφ Column temperature: 100 ° C. for 2 minutes → 5 ° C./minute→260° C. for 5 minutes Injection port temperature: 200 ° C. Detector temperature: 200 ° C. Carrier gas: nitrogen
(5) Measurement of dimer and trimer of styrene monomer in molded article Same method as in (4) Color tone of molded article, odor of molded article, oil adhesion to mold, and 3-arylbenzoic acid Table 1 shows the results of the following Reference Examples 1 to 10 and Comparative Reference Examples 1 to 8 with respect to the relationship between the amount of furanone added and the amounts of the styrene monomer, its dimer and trimer. In addition, the evaluation methods of the resin compositions in Reference Examples 1 to 10 and Comparative Reference Examples 1 to 8 are as follows.
[0037]
(1) Odor determination method From the resin composition, a rectangular parallelepiped container having an opening width of 95 mm, a depth of 55 mm, a depth of 96 mm, and a thickness of 2 mm was prepared by injection molding, 200 ml of 90 ° C hot water was put into the container, and after 3 minutes, The odor of the hot water was determined.
(2) Molded Article Color Tone The molded article used for the odor determination in the method (1) was visually judged.
(3) Method for confirming the state of oil adhesion to mold A short mold was used during injection molding with a filling time of 3.0 seconds using a 150 mm × 50 mm × 2.5 mm rectangular mold. After the 70 shots, the injection molding was stopped for 15 minutes, the mold was cooled, and the mold surface corresponding to the tip of the molded product was observed to confirm the state of oil adhesion. Thereafter, molding was repeated until 980 shots while checking the state of oil attachment to the mold every 70 shots in the same manner, and the number of shots at which oil began to adhere to the mold was determined.
[0038]
[ Reference Example 1 ]
Dissolve 0.05 part by weight of a polymerization initiator (1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane) in 90 parts by weight of styrene and 10 parts by weight of ethylbenzene, and dissolve 0.5 liter. At a rate of / hour, the mixture was continuously and sequentially supplied to a polymerization apparatus comprising a first reactor, a second reactor, and a third reactor, each of which had a capacity of 1 liter. Immediately after the completion of the polymerization step, that is, at the outlet of the third reactor, 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one dissolved in ethylbenzene. Was added so as to be 0.15% by weight based on the resin (weight average molecular weight = 260,000) obtained in the third reactor. Subsequently, the resin and 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2 were mixed in a complete mixing mixer (volume: 150 ml) provided after the third reactor. After the -on was uniformly mixed, the mixture was transferred to a devolatilizer in which two single-screw extruders were connected in series, and in this devolatilization step, volatile components were sequentially removed and pelletized.
[0039]
The polymerization conditions in the polymerization step are as follows: the first reactor has a polymerization temperature of 105 to 110 ° C. and a stirrer rotation speed of 150 rpm; the second reactor has a polymerization temperature of 115 to 125 ° C., a stirrer rotation speed of 50 rpm; The temperature was 130 to 150 ° C. and the rotation speed of the stirrer was 20 rpm. The polymerization rate at the outlet of each reactor was 35% at the outlet of the first reactor, 65% at the outlet of the second reactor, and 90% at the outlet of the third reactor. In the devolatilization step, the temperature of the single-screw extruder in the first stage was 190 to 200 ° C. and the degree of vacuum was 30 torr, and the temperature of the single-screw extruder in the second stage was 220 to 240 ° C. and the degree of vacuum was 5 torr.
[0040]
Using the obtained pellets, injection molded articles for odor determination were produced under the following two different conditions. As the first condition, a molded product was collected by ordinary continuous molding (a product without stagnation). As other conditions, the molding was stopped once, the resin was retained in the cylinder for 30 minutes, the molding was restarted, the first two shots were discarded, and the third shot of the retained resin was collected as a molded product (retention 30 Parts). The molding temperature of each zone of the injection molding machine was 250 ° C, 250 ° C, 230 ° C, and 210 ° C, respectively. Further, the state of oil adhesion to the mold during injection molding was confirmed. Table 1 shows the remaining amount of the styrene monomer, the sum of the remaining amounts of the dimer and the trimer, the odor determination result, and the color tone of the molded product and the state of oil adhesion to the mold by visual determination.
[0041]
[ Reference Example 2 ]
Reference Example 1, except that the 5,7-di -tert- butyl-3 amount of (3,4-dimethylphenyl) -3H- benzofuran-2-one and 0.05 wt% Reference Example Pellets and molded articles were prepared in the same manner as in Example 1, and physical properties and the like were evaluated. Table 1 shows the results.
[ Reference Example 3 ]
Reference Example 1, except that the 5,7-di -tert- butyl-3 amount of (3,4-dimethylphenyl) -3H- benzofuran-2-one and 0.02 wt% Reference Example Pellets and molded articles were prepared in the same manner as in Example 1, and physical properties and the like were evaluated. Table 1 shows the results.
[0042]
[ Reference Example 4 ]
In Reference Example 1 , 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one was added to the extruder at the former stage and the latter stage of the single screw extruder in the devolatilization step. Pellets and molded articles were prepared in the same manner as in Reference Example 1 except that the addition amount was 0.05% by weight, and the physical properties and the like were evaluated. Table 1 shows the results.
[ Reference Example 5 ]
In Reference Example 1 , instead of 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one, 5,7-di- obtained in Production Example 2 was used. Pellets and molding were performed in the same manner as in Reference Example 1 except that tert-butyl-3- (2,4-dimethylphenyl) -3H-benzofuran-2-one was added and the amount added was 0.05% by weight. A product was prepared, and properties and the like were evaluated. Table 1 shows the results.
[0043]
[ Reference Example 6 ]
In Example 1 , pellets and molded articles were prepared in the same manner as in Example 1 except that 85 parts by weight of styrene and 5 parts by weight of polybutadiene (diene 35: manufactured by Asahi Kasei) were used instead of 90 parts by weight of styrene. Evaluation of physical properties and the like was performed. Table 1 shows the results.
[ Reference Example 7 ]
Reference Example 6, except that the 5,7-di -tert- butyl-3 amount of (3,4-dimethylphenyl) -3H- benzofuran-2-one and 0.02 wt% Reference Example Pellets and molded articles were prepared in the same manner as in Example 1, and physical properties and the like were evaluated. Table 1 shows the results.
[ Reference Example 8 ]
Reference Example 1, except that the 5,7-di -tert- butyl-3 amount of (3,4-dimethylphenyl) -3H- benzofuran-1-one and 0.01 wt% Reference Example Pellets and molded articles were prepared in the same manner as in Example 1, and physical properties and the like were evaluated. Table 1 shows the results.
[0044]
[ Reference Example 9 ]
60 kg of dehydrated cyclohexane and 10 kg of dehydrated styrene were charged into an autoclave with a stirrer purged with dry nitrogen, and a 30% by weight cyclohexane solution containing 6 g of n-butyllithium was added at an initial reaction temperature of 50 ° C., followed by vigorous stirring. A polymerization reaction was performed. After 5 minutes, the temperature inside the reactor rose to 85 ° C. The mixture was allowed to react for 20 minutes, and the conversion was measured by gas chromatography to be 99.8%. Next, 1 kg of methanol was added to the polymerization solution in the reactor, and after stirring for 30 minutes, 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H- was added to the obtained resin. Benzofuran-2-one was added in an amount of 0.01% by weight, devolatilized and pelletized with a 20 mm single screw extruder at an extruder temperature of 210 to 230 ° C. and a degree of vacuum of 15 torr. Production of a molded article using the pellets and evaluation of the molded article were performed in the same manner as in Reference Example 1 . Table 1 shows the results.
[0045]
[ Reference Example 10 ]
Using a KRC (Kurimoto Iron Works) reactor (internal volume 8.6 liters, blade diameter 100 mm, cylinder effective length 1000 mm, number of paddles 44, clearance between cylinder inner wall and paddle 1 mm), the internal temperature was reduced to 80 ° C. The rotation speed was controlled at 200 rpm. Styrene was supplied to this reactor at a rate of 1 liter / hour, while methylaluminoxane was supplied as a catalyst at a rate of 75 mmol / hour and pentamethylcyclopentadienyltitanium trimethoxide at a rate of 0.15 mmol / hour. Continuous polymerization was carried out for 5 hours. The powder coming out of the reactor outlet was immersed in methanol in which 1% by weight of sodium hydroxide was dissolved and washed, and then the obtained resin was subjected to 5,7-di-tert-butyl-3- (3 , 4-Dimethylphenyl) -3H-benzofuran-2-one was added in an amount of 0.01% by weight, and dried at 180 ° C. for 10 hours at 10 torr. The resin before mixing with the additive had a polymer syndiotacticity of 97% in racemic pentad by 13 C-NMR.
[0046]
The resin was devolatilized and pelletized with a 20 mm single screw extruder at an extruder temperature of 270 to 290 ° C. and a degree of vacuum of 20 torr. Using these pellets, injection molded articles for odor determination were produced under two different conditions. As the first condition, a molded article was collected by ordinary continuous molding (no stagnation). As other conditions, the molding was stopped once, the resin was retained in the cylinder for 30 minutes, the molding was restarted, the first two shots were discarded, and the third shot of the retained resin was collected as a molded product (retention 30 Parts). The molding temperature of each zone of the injection molding machine was 290 ° C, 290 ° C, 280 ° C, and 270 ° C, respectively. Further, the state of oil adhesion to the mold during injection molding was confirmed. Table 1 shows the residual amount of the styrene monomer, the odor determination result, the color tone of the molded product by visual determination, and the state of oil adhesion to the mold.
[0047]
[ Comparative Reference Example 1 ]
In Reference Example 1 , pellets and pellets were prepared in the same manner as in Reference Example 1 , except that 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one was not added. Molded articles were prepared and physical properties and the like were evaluated. Table 1 shows the results.
[ Comparative Reference Example 2 ]
Reference Example 1 was the same as Reference Example 1 , except that the amount of 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one was 0.005% by weight. Pellets and molded articles were prepared in the same manner as in Example 1 and the properties and the like were evaluated. Table 1 shows the results.
[0048]
[ Comparative Reference Example 3 ]
In Reference Example 1 , in place of 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one, Sumilizer GS [manufactured by Sumitomo Chemical Co., Ltd., registered trademark, phenol-based Thermal degradation inhibitor, chemical name: 2- [1- (2-Hydroxy-3,5-di-tert-pentylphenyl) ethyl] -4,6-di-tert-pentylphenyl acrylate] Pellets and molded articles were prepared in the same manner as in Reference Example 1 except that the amount was 0.05% by weight, and physical properties and the like were evaluated. Table 1 shows the results.
[ Comparative Reference Example 4 ]
In Reference Example 1 , in place of 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one, Sumilizer GS [manufactured by Sumitomo Chemical Co., Ltd., registered trademark, phenol-based Pellets and molded articles were prepared in the same manner as in Reference Example 1 except that the amount of the heat deterioration inhibitor was added and the amount added was 0.3% by weight. Table 1 shows the results.
[0049]
[ Comparative Reference Example 5 ]
In Reference Example 1 , the addition amount of 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one was set to 0.005% by weight. Di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one is added at a position between the former extruder and the latter extruder of the single screw extruder in the devolatilization step. Further, pellets and molded articles were prepared in the same manner as in Reference Example 1 except that 1% by weight of water was added to the resin, and physical properties and the like were evaluated. Table 1 shows the results.
[0050]
[ Comparative Reference Example 6 ]
In Reference Example 2 , pellets and molded articles were prepared and physical properties were evaluated in the same manner as in Reference Example 2 , except that the degree of vacuum of the subsequent single-screw extruder was set to 20 torr. Table 1 shows the results.
[ Comparative Reference Example 7 ]
In Reference Example 9 , pellets and molded articles were prepared in the same manner as in Reference Example 9 except that the degree of vacuum at the time of drying the resin was 30 torr, and physical properties and the like were evaluated. Table 1 shows the results.
[ Comparative Reference Example 8 ]
In Reference Example 10 , pellets and molded articles were prepared and evaluated for physical properties and the like in the same manner as in Reference Example 10 , except that the degree of vacuum during resin drying was set to 28 torr. Table 1 shows the results.
[0051]
[Table 1]

[0052]
From Table 1, it can be seen that by adding a predetermined amount of the 3-arylbenzofuranone represented by the general formula (I) to reduce the residual amount of the styrene monomer to 100 ppm or less, a molded article having a very excellent color tone can be obtained. It can be seen that it can be obtained. Even if a predetermined amount of the thermal degradation inhibitor is added, if the residual amount of the styrene monomer is large, the color tone of the obtained molded article will be extremely poor. In addition, in the resin composition of the present invention, even in the results of the retention test in a molding machine, the increase in the styrene monomer and its dimer or trimer is small, and the color tone of the molded product does not change. The heat stability was excellent. Further, when a phenolic heat deterioration inhibitor (Smilarizer GS) is used, the color tone of the obtained molded product is very poor. Furthermore, even when the addition amount is the same as that of the 3-arylbenzofuranone of the present invention, the effect of reducing the styrene monomer and its dimer or trimer is lower than that of the 3-arylbenzofuranone of the present invention. It turns out that.
[0053]
An evaluation (part 1) of a foamed sheet using the resin composition of the present invention and a molded product thereof was performed. The evaluation methods of the resins used in the following Examples 1 to 9 and Comparative Examples 1 to 3 are as follows.
(1) Method for evaluating secondary formability of foamed sheet In order to confirm the secondary formability of the foamed sheet, a small pressurized air molding machine was used, the heating time was kept constant, and the furnace temperatures were 200 ° C, 220 ° C, and 240 ° C, respectively. The temperature was changed to ° C., and it was confirmed whether a molded product could be obtained from the foamed sheet.
(2) Measurement method of thickness unevenness of molded article As shown in FIG. 1, the thickness of four points (A, B, C, D) on the same side was measured in 10 samples of molded article obtained from a foamed sheet. , And its standard deviation was determined and used as an index of uneven thickness.
[0054]
(3) Method for Determining Appearance of Printed Product and Transferability of Print The surface roughness of the foamed molded product surface was visually checked. The transferability of the print was confirmed by visually checking the transferability of the printed characters.
[ Examples 1 to 9 , Comparative Examples 1 and 2 ]
The resin used in the production of the foamed sheet was the resin produced in Reference Examples 1 to 9 and Comparative Reference Examples 1 to 2 described in the column of “Resin used in the evaluation of the foamed sheet” in Table 2. is there. Comparative Example 3 is shown below.
[ Comparative Example 3 ]
In Reference Example 2 , without adding a polymerization initiator (1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane), the first reactor was subjected to a polymerization temperature of 125 to 130 ° C. and a second The resin was prepared in the same manner as in Reference Example 2 except that the polymerization temperature of the reactor was 135 to 145 ° C., and that of the third reactor was 150 to 165 ° C. (the polymerization conversion rate at the outlet of the third reactor was 90% by weight). Manufactured.
[0055]
<Method for producing molded article using foamed sheet of aromatic monovinyl resin composition>
Using a 30 mm extrusion foaming machine equipped with a T die having a width of 30 mm, 1 part by weight of a foam nucleating agent and 3 parts by weight of a foaming agent were added to 100 parts by weight of an aromatic monovinyl resin composition, and about 8 parts by weight were added. A doubled foam sheet was obtained. The temperature of the resin melting zone was adjusted to 180 to 230 ° C, the temperature of the rotary cooler was adjusted to 150 to 160 ° C, and the T-die temperature was adjusted to 120 to 130 ° C. As a foaming nucleating agent, Mistron Vapor manufactured by Nippon Mistron was used, and as a foaming agent, a mixture of 65% by weight of n-butane and 35% by weight of i-butane was used. The obtained foamed sheet was cured for one week, heated in a furnace at a predetermined temperature using a small air pressure molding machine for 15 seconds, and then heated in a mold adjusted to 60 ° C., 100 mm square, 50 mm deep, and 100 mm thick. A box-shaped molded product having a length of about 2 to 3 mm was prepared. In order to confirm the molding width at the time of the secondary molding, it was examined whether or not a molded product could be produced at three points of the furnace temperature of 200 ° C., 220 ° C., and 240 ° C. Further, the thickness unevenness of the molded article obtained at a furnace temperature of 200 ° C. was measured and the appearance was visually checked. Table 2 shows the remaining amount of the styrene monomer, the sum of the remaining amounts of the dimer and the trimer of the styrene monomer, the secondary formability of the foamed sheet, the thickness unevenness of the molded product, and the results of visual confirmation of the appearance. .
[0056]
[Table 2]

[0057]
Evaluation (2) of a foamed sheet using the resin composition of the present invention and a molded product thereof was performed.
[ Example 10 ]
In Reference Example 1 , the reaction apparatus was used about 10 times larger, and the addition amount of 5,7-di-tert-butyl-3- (3,4-dimethylphenyl) -3H-benzofuran-2-one was 0.1%. A resin composition was manufactured with substantially the same manufacturing conditions except that the amount was set to 05% by weight. Using the pellets, a foamed sheet and a molded product thereof were produced by the following method.
[0058]
<Method for producing molded article using foamed sheet of aromatic monovinyl resin composition>
To 100 parts by weight of the aromatic monovinyl resin composition, 0.5 parts by weight of talc as a foaming nucleating agent and 0.3 parts by weight of zinc stearate as a dispersing aid were added and mixed well with a mixer. / D was fed to a 33 single screw extruder hopper. Thereafter, the mixture is melt-kneaded at 235 ° C. in the former stage of the extruder screw, and n-butane is added to the melt-kneaded material through a foaming agent injection hole provided in the middle stage of the extruder so that the amount becomes 2.5% by weight of the total extruded amount. A mixture of 65% by weight and 35% by weight of i-butane was injected.
[0059]
Next, the extruder was cooled to 160 ° C. at the subsequent stage, extruded and foamed into a tube from a ring die, and the obtained tubular foamed sheet was cooled with a mandrel of the extruder, and one side was cut open by a cutter to obtain a foamed sheet. . The foam sheet for the appearance inspection and the production of the molded article was collected after operating the extruder for one hour continuously and cured for one week. After the appearance inspection of the foamed sheet, using a small pressurized air molding machine, heating was performed in a furnace at 200 ° C. for 10 seconds, and then a box-shaped molded product having a 100 mm square and a depth of 40 mm was prepared using a mold adjusted to 60 ° C. . After the appearance inspection of this molded product, printing of characters was performed, and transferability was confirmed. Table 3 shows the residual amount of the styrene monomer, the total residual amount of the dimer and the trimer of the styrene monomer, the appearance of the foamed sheet, the appearance of the molded product, and the printability.
[0060]
[Example 11]
In the production of the resin of Example 10, a resin composition and a molded article were prepared in the same manner as in Example 10 except that the degree of vacuum of the single-screw extruder at the subsequent stage in the devolatilization step was set to 10 torr, and evaluation of physical properties and the like was performed. Was done. Table 3 shows the results.
[ Comparative Example 4 ]
In the production of the resin of Example 10, a resin composition and a molded product were produced in the same manner as in Example 10 except that the degree of vacuum of the single screw extruder at the latter stage in the devolatilization step was set to 40 torr, and evaluation of physical properties and the like was performed. Was done. Table 3 shows the results.
[0061]
[Table 3]

[0062]
From Tables 2 and 3, the secondary molding was performed by setting the residual amount of the styrene monomer to 100 ppm or less and the total residual amount of the dimer and trimer of the styrene monomer to 0.4% by weight or less. It can be seen that a foamed sheet having excellent properties can be obtained, and a molded article with little unevenness in thickness and excellent in appearance and printability can be obtained. In addition, the resin composition of the present invention has extremely excellent thermal stability even in the production of a foamed sheet.
[0063]
【The invention's effect】
The foamed sheet of the aromatic monovinyl resin composition of the present invention and the molded article thereof are excellent in moldability and heat stability at the time of molding, have good color tone, and have low odor. Further, the molded article obtained by the secondary molding from the foamed sheet of the present invention has a small thickness unevenness and can be particularly suitably used for a packaging material, a container, and the like which come into direct contact with foods or the like. It plays a major role in industry.

Claims (3)

(A) a resin comprising an aromatic monovinyl monomer having a weight average molecular weight of 150,000 to 700,000; and (b) 5,7-di-tert-butyl-3- (2,4-dimethylphenyl) -3H- Benzofuran-2-one, 5,7-di-tert-butyl-3- (2,5-dimethylphenyl) -3H-benzofuran-2-one, 5,7-di-tert-butyl-3- (3, An aromatic monovinyl resin composition comprising a 3-arylbenzofuranone selected from (4-dimethylphenyl) -3H-benzofuran-2-one, wherein the amount of the 3-arylbenzofuranone is based on (a) the weight of the resin. Te is from 0.006 to 0.5 wt%, and the residual amount of the aromatic monovinyl monomer in the aromatic monovinyl resin composition is 100ppm or less than 41 ppm, the aromatic Monobini Foam sheets made from the system resin composition. 2. The aromatic monovinyl resin composition according to claim 1, wherein the total amount of the dimer and trimer of the aromatic monovinyl monomer in the aromatic monovinyl resin composition is 0.4% by weight or less. Foam sheet. A molded article comprising the foamed sheet according to claim 1 .

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