JP3926289B2 - Styrenic expandable resin particles, expanded beads and expanded molded products - Google Patents
Styrenic expandable resin particles, expanded beads and expanded molded products Download PDFInfo
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- JP3926289B2 JP3926289B2 JP2003129891A JP2003129891A JP3926289B2 JP 3926289 B2 JP3926289 B2 JP 3926289B2 JP 2003129891 A JP2003129891 A JP 2003129891A JP 2003129891 A JP2003129891 A JP 2003129891A JP 3926289 B2 JP3926289 B2 JP 3926289B2
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- Prior art keywords
- styrene
- molecular weight
- polymerization
- resin particles
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- 239000002245 particle Substances 0.000 title claims description 92
- 229920005989 resin Polymers 0.000 title claims description 66
- 239000011347 resin Substances 0.000 title claims description 66
- 239000011324 bead Substances 0.000 title description 13
- PPBRXRYQALVLMV-UHFFFAOYSA-N Styrene Chemical group C=CC1=CC=CC=C1 PPBRXRYQALVLMV-UHFFFAOYSA-N 0.000 claims description 141
- 238000006116 polymerization reaction Methods 0.000 claims description 77
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 32
- 239000001301 oxygen Substances 0.000 claims description 32
- 229910052760 oxygen Inorganic materials 0.000 claims description 32
- 239000004088 foaming agent Substances 0.000 claims description 17
- GPRLSGONYQIRFK-UHFFFAOYSA-N hydron Chemical compound [H+] GPRLSGONYQIRFK-UHFFFAOYSA-N 0.000 claims description 17
- 238000004519 manufacturing process Methods 0.000 claims description 15
- 229910017053 inorganic salt Inorganic materials 0.000 claims description 8
- 238000010557 suspension polymerization reaction Methods 0.000 claims description 8
- 238000006243 chemical reaction Methods 0.000 claims description 7
- 239000006185 dispersion Substances 0.000 claims description 3
- 238000001179 sorption measurement Methods 0.000 claims 1
- 239000001506 calcium phosphate Substances 0.000 description 40
- QORWJWZARLRLPR-UHFFFAOYSA-H tricalcium bis(phosphate) Chemical compound [Ca+2].[Ca+2].[Ca+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O QORWJWZARLRLPR-UHFFFAOYSA-H 0.000 description 40
- 229940078499 tricalcium phosphate Drugs 0.000 description 40
- 229910000391 tricalcium phosphate Inorganic materials 0.000 description 40
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 30
- GVGUFUZHNYFZLC-UHFFFAOYSA-N dodecyl benzenesulfonate;sodium Chemical compound [Na].CCCCCCCCCCCCOS(=O)(=O)C1=CC=CC=C1 GVGUFUZHNYFZLC-UHFFFAOYSA-N 0.000 description 27
- 229940080264 sodium dodecylbenzenesulfonate Drugs 0.000 description 27
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- OMPJBNCRMGITSC-UHFFFAOYSA-N Benzoylperoxide Chemical compound C=1C=CC=CC=1C(=O)OOC(=O)C1=CC=CC=C1 OMPJBNCRMGITSC-UHFFFAOYSA-N 0.000 description 14
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- FTQWRYSLUYAIRQ-UHFFFAOYSA-N n-[(octadecanoylamino)methyl]octadecanamide Chemical compound CCCCCCCCCCCCCCCCCC(=O)NCNC(=O)CCCCCCCCCCCCCCCCC FTQWRYSLUYAIRQ-UHFFFAOYSA-N 0.000 description 7
- NNPPMTNAJDCUHE-UHFFFAOYSA-N isobutane Chemical compound CC(C)C NNPPMTNAJDCUHE-UHFFFAOYSA-N 0.000 description 6
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- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 description 3
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- ZEMPKEQAKRGZGQ-XOQCFJPHSA-N glycerol triricinoleate Natural products CCCCCC[C@@H](O)CC=CCCCCCCCC(=O)OC[C@@H](COC(=O)CCCCCCCC=CC[C@@H](O)CCCCCC)OC(=O)CCCCCCCC=CC[C@H](O)CCCCCC ZEMPKEQAKRGZGQ-XOQCFJPHSA-N 0.000 description 3
- 238000002347 injection Methods 0.000 description 3
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- 239000001282 iso-butane Substances 0.000 description 3
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- 229920001296 polysiloxane Polymers 0.000 description 3
- XOOUIPVCVHRTMJ-UHFFFAOYSA-L zinc stearate Chemical compound [Zn+2].CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O XOOUIPVCVHRTMJ-UHFFFAOYSA-L 0.000 description 3
- 239000004604 Blowing Agent Substances 0.000 description 2
- SOGAXMICEFXMKE-UHFFFAOYSA-N Butylmethacrylate Chemical compound CCCCOC(=O)C(C)=C SOGAXMICEFXMKE-UHFFFAOYSA-N 0.000 description 2
- RGSFGYAAUTVSQA-UHFFFAOYSA-N Cyclopentane Chemical compound C1CCCC1 RGSFGYAAUTVSQA-UHFFFAOYSA-N 0.000 description 2
- 239000004372 Polyvinyl alcohol Substances 0.000 description 2
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 description 2
- 230000032683 aging Effects 0.000 description 2
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- QWTDNUCVQCZILF-UHFFFAOYSA-N isopentane Chemical compound CCC(C)C QWTDNUCVQCZILF-UHFFFAOYSA-N 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000012856 packing Methods 0.000 description 2
- 239000004014 plasticizer Substances 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 239000002685 polymerization catalyst Substances 0.000 description 2
- 229920002451 polyvinyl alcohol Polymers 0.000 description 2
- 238000007639 printing Methods 0.000 description 2
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- QEQBMZQFDDDTPN-UHFFFAOYSA-N (2-methylpropan-2-yl)oxy benzenecarboperoxoate Chemical compound CC(C)(C)OOOC(=O)C1=CC=CC=C1 QEQBMZQFDDDTPN-UHFFFAOYSA-N 0.000 description 1
- RNFJDJUURJAICM-UHFFFAOYSA-N 2,2,4,4,6,6-hexaphenoxy-1,3,5-triaza-2$l^{5},4$l^{5},6$l^{5}-triphosphacyclohexa-1,3,5-triene Chemical compound N=1P(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP=1(OC=1C=CC=CC=1)OC1=CC=CC=C1 RNFJDJUURJAICM-UHFFFAOYSA-N 0.000 description 1
- SBYMUDUGTIKLCR-UHFFFAOYSA-N 2-chloroethenylbenzene Chemical compound ClC=CC1=CC=CC=C1 SBYMUDUGTIKLCR-UHFFFAOYSA-N 0.000 description 1
- YIVJZNGAASQVEM-UHFFFAOYSA-N Lauroyl peroxide Chemical compound CCCCCCCCCCCC(=O)OOC(=O)CCCCCCCCCCC YIVJZNGAASQVEM-UHFFFAOYSA-N 0.000 description 1
- 229920001890 Novodur Polymers 0.000 description 1
- 239000004793 Polystyrene Substances 0.000 description 1
- BCKXLBQYZLBQEK-KVVVOXFISA-M Sodium oleate Chemical compound [Na+].CCCCCCCC\C=C/CCCCCCCC([O-])=O BCKXLBQYZLBQEK-KVVVOXFISA-M 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N acrylic acid group Chemical group C(C=C)(=O)O NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- XYLMUPLGERFSHI-UHFFFAOYSA-N alpha-Methylstyrene Chemical compound CC(=C)C1=CC=CC=C1 XYLMUPLGERFSHI-UHFFFAOYSA-N 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000003945 anionic surfactant Substances 0.000 description 1
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- 238000005452 bending Methods 0.000 description 1
- 235000021028 berry Nutrition 0.000 description 1
- VBICKXHEKHSIBG-UHFFFAOYSA-N beta-monoglyceryl stearate Natural products CCCCCCCCCCCCCCCCCC(=O)OCC(O)CO VBICKXHEKHSIBG-UHFFFAOYSA-N 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- CQEYYJKEWSMYFG-UHFFFAOYSA-N butyl acrylate Chemical compound CCCCOC(=O)C=C CQEYYJKEWSMYFG-UHFFFAOYSA-N 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 230000008094 contradictory effect Effects 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- AFABGHUZZDYHJO-UHFFFAOYSA-N dimethyl butane Natural products CCCC(C)C AFABGHUZZDYHJO-UHFFFAOYSA-N 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- WNAHIZMDSQCWRP-UHFFFAOYSA-N dodecane-1-thiol Chemical compound CCCCCCCCCCCCS WNAHIZMDSQCWRP-UHFFFAOYSA-N 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- SUPCQIBBMFXVTL-UHFFFAOYSA-N ethyl 2-methylprop-2-enoate Chemical compound CCOC(=O)C(C)=C SUPCQIBBMFXVTL-UHFFFAOYSA-N 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- DMEGYFMYUHOHGS-UHFFFAOYSA-N heptamethylene Natural products C1CCCCCC1 DMEGYFMYUHOHGS-UHFFFAOYSA-N 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
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- 238000009413 insulation Methods 0.000 description 1
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- 239000000314 lubricant Substances 0.000 description 1
- GVALZJMUIHGIMD-UHFFFAOYSA-H magnesium phosphate Chemical compound [Mg+2].[Mg+2].[Mg+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O GVALZJMUIHGIMD-UHFFFAOYSA-H 0.000 description 1
- 239000004137 magnesium phosphate Substances 0.000 description 1
- 229960002261 magnesium phosphate Drugs 0.000 description 1
- 229910000157 magnesium phosphate Inorganic materials 0.000 description 1
- 235000010994 magnesium phosphates Nutrition 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
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- 125000005641 methacryl group Chemical group 0.000 description 1
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- 229920000609 methyl cellulose Polymers 0.000 description 1
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 description 1
- 239000001923 methylcellulose Substances 0.000 description 1
- 235000010981 methylcellulose Nutrition 0.000 description 1
- 239000002736 nonionic surfactant Substances 0.000 description 1
- 239000002667 nucleating agent Substances 0.000 description 1
- KZCOBXFFBQJQHH-UHFFFAOYSA-N octane-1-thiol Chemical compound CCCCCCCCS KZCOBXFFBQJQHH-UHFFFAOYSA-N 0.000 description 1
- 230000000379 polymerizing effect Effects 0.000 description 1
- 229920002223 polystyrene Polymers 0.000 description 1
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- HJWLCRVIBGQPNF-UHFFFAOYSA-N prop-2-enylbenzene Chemical compound C=CCC1=CC=CC=C1 HJWLCRVIBGQPNF-UHFFFAOYSA-N 0.000 description 1
- 239000001294 propane Substances 0.000 description 1
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- DCXXMTOCNZCJGO-UHFFFAOYSA-N tristearoylglycerol Chemical compound CCCCCCCCCCCCCCCCCC(=O)OCC(OC(=O)CCCCCCCCCCCCCCCCC)COC(=O)CCCCCCCCCCCCCCCCC DCXXMTOCNZCJGO-UHFFFAOYSA-N 0.000 description 1
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Description
【０００１】
【発明の属する技術分野】
本発明は、スチレン系発泡性樹脂粒子とその製造方法、さらにスチレン系発泡ビーズ及び発泡成形品に関する。
【０００２】
【従来の技術】
スチレン系発泡性樹脂は、優れた断熱性、経済性、衛生性を特徴として多くの食品容器、梱包材、緩衝材等に用いられている。これらの発泡成形品は、スチレン系発泡性樹脂粒子をスチーム等により加熱、所望の嵩密度まで予備発泡し、熟成工程を経た後、成形金型に充填し再度加熱発泡成形する方法により製造される。このスチレン系発泡性樹脂粒子は、予備発泡段階や金型内での加熱発泡成形段階において、良好な発泡性を示し、また、成形品としたときの成形品強度の大きいことが求められている。
【０００３】
従来、発泡成形品の強度を大きくするためには、成形品密度を高密度化する方法や成形品自体の肉厚を厚くする方法等が行われていた。しかし、これらいずれの方法も成形品重量がかさむため経済的とは言い難く、環境的視点からも問題である。また、スチレン系発泡性樹脂粒子においては、分子量を高分子量化する、また、樹脂粒子を可塑化する可塑剤の種類や添加量を減量調整する等の方法が行われてきた。
【０００４】
一方、スチレン系発泡性樹脂粒子の発泡性を向上させる方法として、分子量を低分子化する方法や樹脂粒子を可塑化する方法、さらには発泡剤の組成比を変更する方法等が検討されてきた。
【０００５】
このような発泡成形品の強度を大きくするための方法及び発泡性を向上させる方法は、一般的に相反し両立させることは困難であった。
【０００６】
これら問題点を解決する方法として、粒子最表層部と粒子中心部が低分子量であり、粒子中間部が高分子量となる樹脂粒子が提案されている（例えば、特許文献１参照）。
しかし、この粒子は、粒子最表層部の分子量が粒子中心部同様に低分子量であるため、加熱発泡成形時において熱融着が促進しすぎて、成形品の表面仕上がりを悪化させるという欠点があった。
【０００７】
また、表層部の分子量が粒子全体の分子量より高い樹脂粒子も開示されている（例えば、特許文献２参照）。
この特許文献には、表層部をあまり高分子量化すると発泡性能が低下し成形品の外観が損なわれ、その結果として、強度が低下することが記載されている。これは、ここに開示されている粒子が、表層部を高分子量化するとそれに伴い中心部も高分子量化してしまうためと考えられる。即ち、この樹脂粒子には、表層部を十分に高分子量化できないという欠点があった。
【０００８】
【特許文献１】
特開平８−２９５７５６号公報
【特許文献２】
特開平７−１８８４５４号公報
【０００９】
【発明が解決しようとする課題】
本発明は、成形品の強度が大きく、発泡性に優れたスチレン系発泡性樹脂粒子、発泡ビーズ及び発泡成形品を提供することを目的とする。
【００１０】
【課題点を解決するための手段】
本発明の第１の態様によれば、粒子の表面から中心に向かって５等分した表面から１／５までを形成する表面部分の重量平均分子量が、中心から表面に向かって中心から１／５までを形成する中心部分の重量平均分子量より高く、表面部分のゲルパーミエーションクロマトグラフ法のチャートが二山又はショルダーを有することを特徴とするスチレン系発泡性樹脂粒子が提供される。
【００１２】
本発明の第２の態様によれば、粒子の表面から中心に向かって５等分した表面から１／５までを形成する表面部分の、ＧＰＣ／ＭＡＬＬＳ法により測定したｌｏｇ（Ｒ．Ｍ．Ｓ半径）とｌｏｇ（ＭＷ）との相関式の傾きが、０．５３以下であることを特徴とするスチレン系発泡性樹脂粒子が提供される。
【００１４】
本発明の第３の態様によれば、スチレン系単量体の懸濁重合において、重合率が６０％以上のとき、反応槽内の酸素濃度を７体積％以下に保ちつつ、スチレン系発泡性樹脂粒子の５重量％〜３０重量％のスチレン系単量体を添加し、重合途中にあるスチレン樹脂粒子に吸着させて重合反応を進め、重合反応の完了前または重合反応の完了後に、発泡剤を含浸することを特徴とするスチレン系発泡性樹脂粒子の製造方法が提供される。
【００１５】
本発明の第４の態様によれば、上記の製造方法により得られることを特徴とするスチレン系発泡性樹脂粒子が提供される。
【００１６】
本発明の第５の態様によれば、上記のスチレン系発泡性樹脂粒子を発泡させて得られることを特徴とするスチレン系発泡ビーズが提供される。
【００１７】
本発明の第６の態様によれば、上記のスチレン系発泡ビーズを成形させて得られることを特徴とするスチレン系発泡成形品が提供される。
【００１８】
【発明の実施の形態】
本発明のスチレン系発泡性樹脂粒子、発泡ビーズ及び発泡成形品について詳しく説明する。
スチレン系発泡性樹脂粒子は、スチレン系単量体を重合して得られるものである。スチレン系単量体として、スチレン、又はスチレンを主成分とし、α―メチルスチレン、クロルスチレン、ビニルトルエン等のスチレン誘導体、アクリル酸メチル、アクリル酸メチル、アクリル酸ブチル等のアクリル酸エステル類、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等のメタクリル酸エステル類との混合単量体を使用できる。
【００１９】
スチレン系発泡性樹脂粒子を製造する方法は懸濁重合が好ましく、これは従来公知の方法を採用することができる。即ち、一般に、分散剤を含む水性媒体中に有機過酸化物等の触媒を溶解したスチレン系単量体を分散してラジカルを発生させて重合を行なう。
【００２０】
分散剤として、難溶性無機塩と界面活性剤を併用してもよいし、ＰＶＡ等の有機分散剤等従来公知のものを使用することができる。
難溶性無機塩として、リン酸マグネシウム、リン酸三カルシウム等が使用できる。界面活性剤として、オレイン酸ナトリウム、ドデシルベンゼンスルホン酸ナトリウム、その他懸濁重合に一般的に使用されるアニオン系界面活性剤、ノニオン系界面活性剤のいずれでも使用できる。有機分散剤として、ポリビニルアルコール、ポリビニルピロリドン、メチルセルロース等が使用できる。
有機過酸化物は、１０時間半減分解温度が５０〜１００℃である従来公知のものを使用できる。例えば、ラウロイルパーオキサイド、ベンゾイルパーオキサイド、ｔ―ブチルパーオキシベンゾエート、ｔ―ブチルパーオキシイソプロピルカーボネイト等がある。有機過酸化物は、重合性単量体に対して０．００１重量％〜０．５重量％使用されるのが好ましい。有機過酸化物は一又は二以上用いることができる。
【００２１】
全体の分子量は、触媒濃度を調整するか、連鎖移動剤を併用するか、又はこれら両方により調整できる。
連鎖移動剤としては、オクチルメルカプタン、ドデシルメルカプタン、α―メチルスチレンダイマー等の従来公知のものが使用できる。連鎖移動剤の添加量は、重合性単量体に対して２０ｐｐｍ〜１００ｐｐｍ使用することが好ましい。
【００２２】
本発明の製造方法においては、少なくとも、重合後期のとき、反応槽内の酸素濃度を低く保ちつつ、スチレン系単量体を添加する。
この方法では、重合開始又は重合途中より、反応槽内を低酸素濃度にしてもよいが、少なくとも重合後期には低酸素濃度にする。また、酸素濃度を、例えば重合後期だけ特に低くするように、変化させてもよい。
【００２３】
好ましくは重合率が６０％以上、より好ましくは６０％以上９７％未満において、スチレン系単量体を添加する。また、好ましくは、反応槽内の酸素濃度は７体積％以下に保ちつつ、スチレン系単量体を添加する。
酸素濃度が７体積％を超えると、スチレン系単量体を添加して反応を進める際に、スチレン系樹脂粒子の表面層で低分子量物が形成される。表皮での低分子量物の生成は、発泡成形時において熱融着が促進しすぎて、成形品の強度を低下させると共に表面仕上がりを悪化させる。好ましくは、酸素濃度は５体積％以下ある。酸素濃度は窒素等の不活性ガスで置き換えることにより調節できる。
【００２４】
重合率が６０％より低い場合、スチレン系樹脂粒子へのスチレン系単量体の吸収が促進し、中心部分の分子量が高分子量化するため、発泡力及び成形品の融着が低下する。また、重合率が９７％以上の場合、樹脂粒子へのスチレン系単量体の吸収が低下し、樹脂粒子内のラジカル量及び重合触媒量が減少し、樹脂粒子最表面部の分子量が低分子量化するため、発泡成形時において熱融着が促進しすぎて、成形品の強度を低下させると共に表面仕上がりを悪化させる恐れがある。重合率８５以上９７％未満での追加がより好ましい。
【００２５】
スチレン系単量体の添加量は、最終的に得られるスチレン系樹脂粒子に対して５重量％〜３０重量％であることが好ましい。より好ましくは、１０重量％〜１５重量％の範囲である。
添加量が５重量％より少ない量では、スチレン系樹脂粒子における最表面部の高分子量化効果が小さく、強度向上効果を十分に得られない場合がある。反面、添加量が３０重量％より多い量では、樹脂粒子を軟化し、スチレン系単量体の吸収が促進され中心部の分子量が高分子量化する等粒子内の最も高分子量化する部分が中心部へ移動するため、発泡力が低下し成形品で融着しにくくなる場合がある。
【００２６】
懸濁重合温度は、一般に、８０℃〜９５℃である。スチレン系単量体の添加温度は、そのままの温度でもよく昇温してもよい。最終的に得られるスチレン系発泡性樹脂粒子において残存するスチレン系単量体の量を少なくするという、工業的な製造効率からは、重合温度は９０℃以上が好ましく、スチレン系単量体添加温度は昇温中に行うことが好ましい。
【００２７】
本発明の製造方法においては、水分散液の水素イオン濃度が８〜１０で重合を開始させ、重合率２０％〜５０％で少なくとも１回以上の難溶性無機塩を追加することが好ましい。水分散液は連続相であることが好ましい。
水素イオン濃度が上記の範囲外であると、懸濁重合終了時の粒度分布がシャープとならない恐れがある。水素イオン濃度は塩基性無機塩により調節することができる。
また、同様の理由により重合率２０％〜５０％で難溶性無機塩を追加することができる。
難溶性無機塩は少なくとも一回以上、例えば、２〜３回追加することができる。また、難溶性無機塩はさらに重合が進んでから追加することもできる。
【００２８】
昜揮発性発泡剤は、スチレン系単量体の添加と平行して圧入することもできるが、一般的には、スチレン系単量体添加後に行うことが好ましく、重合反応の完結前又は完結後に、易揮発性発泡剤をスチレン系樹脂粒子に含浸することが好ましい。
【００２９】
昜揮発性発泡剤としては、プロパン、イソブタン、ノルマルブタン、イソペンタン、ノルマルペンタン、シクロペンタン等の脂肪族炭化水素の中から選ばれる。また、発泡助剤として脂肪族炭化水素の他に、シクロヘキサン等の脂環式炭化水素や芳香族炭化水素を昜揮発性発泡剤と併用することもできる。
【００３０】
重合に際し、溶剤、可塑剤、発泡セル造核剤、充填剤、難燃剤、難燃助剤、滑剤、着色剤等、スチレン系発泡性樹脂粒子を製造する際に用いられる添加剤を、必要に応じて適宜使用してもよい。
【００３２】
スチレン系発泡性樹脂粒子は、発泡剤の含浸が完了し、重合系内より排出され、さらに脱水乾燥した後、必要に応じて表面被覆剤を被覆することができる。かかる被覆剤は、従来公知である発泡スチレン系樹脂粒子に用いられるものが適用できる。例えば、ジンクステアレート、ステアリン酸トリグリセライド、ステアリン酸モノグリセライド、ひまし硬化油、アミド化合物、シリコーン類、静電防止剤等である。
【００３３】
通常、懸濁重合により製造されるスチレン系発泡性樹脂粒子は、重量平均分子量（分子量）は重合触媒の量により決定され、粒子中心部、中間部、及び表層部の分子量は、ほぼ一定である。
しかしながら、本発明の製造方法によれば、樹脂粒子の表面部分の分子量が、中心部分の分子量より高いスチレン系発泡性樹脂粒子が得られる。中心から表面までの分子量勾配は、徐々に一定の比率で高くなるのではなく、表面付近で急に高くなる。
本発明の製造方法により得られるスチレン系発泡性樹脂粒子では、分子量が表面付近で急に高くなっているので、中心部分を低分子量に保ちながら、表面部分を高分子量にできる。一般に、中心部分が低分子量であると良好な発泡性が発揮でき、表面部分が高分子量であると成形品の強度が大きくなる。従って、本発明の粒子では、発泡性と成形品強度を共に満足させることができる。例えば、ある程度の発泡性を保ちながら、かなり高い成形品強度を得ることができる。
【００３４】
特に、本発明のスチレン系発泡性樹脂粒子は、樹脂粒子表面から中心に向かって５等分した表面から１／５までを形成する表面部分の重量平均分子量が、中心から表面に向かって中心から１／５までを形成する中心部分の重量平均分子量より高いことが好ましい。
ここで、表面部分及び中心部分について、図面を用いて説明する。図１に示すように、樹脂粒子１０の表面から中心に向かって５等分する。最も外側にある、表面から１／５までを形成する部分１が、表面部分である。表面部分の重量平均分子量は、この部分１の重量平均分子量である。最も内側にある、中心から１／５までを形成する部分５が、中心部分である。中心部分の重量平均分子量は、この部分５を５等分した中心の重量平均分子量である。
さらに、表面部分のゲルパーミエーションクロマトグラフ法によるチャートが二山又はショルダーを有することが好ましい。二山又はショルダーを有することは、分子量が急激に変化していることを意味する。ショルダーは変曲点により形成される。本発明において、ゲルパーミエーションクロマトグラフ法によるチャートは、日立化成工業（株）社製のカラム、ＧＬ−Ｒ４００Ｍ、を２本用いて測定する。尚、通常チャートの両すそにも変曲点が発生するが、本発明でいうショルダーにはこれらは含まれない（図３参照）。
【００３５】
さらに、本発明は、中心部分の重量平均分子量が、２００，０００〜３００，０００の範囲であり、表面部分の重量平均分子量が３００，０００〜４５０，０００の範囲であると共に、表面部分の重量平均分子量が中心部分の重量平均分子量に対して１．２倍以上大きいことが好ましい。
【００３６】
中心部分の分子量が２００，０００より小さい場合、成形品強度が低くなる恐れがある。また、分子量を２００，０００より小さくするためには、製造過程において、触媒の使用量を増加しなければならず好ましくない。
中心部分の分子量が３００，０００より大きい場合、発泡性が低くなる恐れがある。
また、好ましくは、中心部分の重量平均分子量は、２００，０００〜２５０，０００である。好ましくは、中心から３／５を形成する部分の分子量がほぼ均一である。
【００３７】
表面部分の分子量が３００，０００より小さい場合、十分な成形品強度が得られない恐れがある。
表面部分の分子量が４５０，０００より大きい場合、発泡力が低下し熱溶融が促進せず成形品の表面仕上がりが悪くなり融着しにくくなる。
また、好ましくは、表面部分の重量平均分子量は、３５０，０００〜４５０，０００である。
【００３８】
中心部分の重量平均分子量に対して表面部分の重量平均分子量（分子量比）はより好ましくは、１．５倍以上である。通常、２．２倍以下である。
【００３９】
このようなスチレン系発泡性樹脂粒子は上記の本発明の製造方法により酸素濃度を低くして製造できる。
【００４０】
また、本発明の製造方法によれば、表面部分に、従来のスチレンのラジカル重合では起こらないと考えられていたグラフト化が起こり、高分子量の枝分かれ構造を生成させることが可能となった。
このように、表面部分が枝分かれ構造を有していることは、例えば、粒子の表面から中心に向かって５等分した表面から１／５までを形成する表面部分をＧＰＣ／ＭＡＬＬＳ法により測定すると、ｌｏｇ（Ｒ．Ｍ．Ｓ半径）とｌｏｇ（ＭＷ）との相関式の傾きが０．５３以下、好ましくは０．５２以下、より好ましくは０．５０以下であることから分かる。ここで、ＧＰＣはゲルパーミエーションクロマトグラフィーを、ＭＡＬＬＳ（Ｍｕｌｔｉ
Ａｎｇｌｅ Ｌａｓｅｒ Ｌｉｇｈｔ Ｓｃａｔｔｅｒｉｎｇ）は、多角度光散乱検出器を、Ｒ．Ｍ．Ｓ（Ｒｏｏｔ Ｍｅａｎ Ｓｑｕａｒｅ）半径は、根平均二乗半径を、ＭＷは、絶対分子量をそれぞれ意味する。
尚、この傾きは、通常のラジカル重合（懸濁系）により得られた直鎖構造のポリスチレンでは、０．５５〜０．６０である。
また、この表面部分の重量平均分子量は、上記と同様の理由により、３００，０００以上４５０，０００以下が好ましい。
【００４１】
本発明の樹脂粒子では、上述したように、表面部分における低分子量物の発生が抑制され、また、この表面部分に高分子量の枝分かれ構造を有しているため、酸素濃度を抑制しない通常の重合により製造される発泡成形品に比較し、粒子表面部分の耐熱性が向上し、外観及び機械強度の良好な発泡成形品を得ることができる。
【００４２】
尚、本発明のスチレン系発泡性樹脂粒子の平均粒子径は、通常、０．０５〜２．０ｍｍである。
【００４３】
本発明の発泡ビーズは、スチレン系発泡性樹脂粒子を発泡して製造する。また、本発明の発泡成形品は、この発泡ビーズを成形して製造する。
一般には、スチレン系発泡性樹脂粒子を、スチーム等により加熱して所定の嵩密度まで予備発泡し、熟成工程を経て発泡ビーズを製造する。その後、発泡ビーズを成形金型に充填し再度加熱発泡成形して、発泡成形品を製造する。
【００４４】
本発明では、スチレン系発泡性樹脂粒子の発泡性と、それから得られる成形品の強度のバランスに優れている。本発明の成形品は、食品容器、梱包材、緩衝材等に好適に使用できる。
【００４５】
【実施例】
実施例及び比較例における特性評価方法は以下の通りであった。
（１）重量平均分子量（分子量）
スチレン系発泡性樹脂粒子の分子量は粒子を発泡させて測定した。
スチレン系発泡性樹脂粒子を飽和水蒸気中で嵩倍数８０ｍｌ／ｇに発泡した。
任意の発泡粒子２〜３粒を採取し、剃刀で図１に示すように粒子１を半分等間隔に５等分して、外側から、部分１，２，３，４，５を形成した。最も表面側の部分１（表面部分）についてはそのまま、最も内側の部分５（中心部分）についてはこの部分を５等分した中心を注射針で繰り抜いて取り出し、分子量を測定した。部分３（中心より３／５部分）については部分５と同じ中心を注射針で繰り抜いて取り出し、分子量を測定した。
尚、分子量は、ゲルパーミエーションクロマトグラフ（ＧＰＣ）法により測定した。
また、表面部分について、ＧＰＣ法によるチャート（ＧＰＣチャート）を得た。そのとき、以下の装置及び条件で測定した。
測定装置：（株）日立製作所社製
溶離液：ＴＨＦ、流量：２ｍｌ／分
検出器：ＵＶ ２２０ｎｍ
カラム：日立化成工業（株）社製 ＧＬ−Ｒ４００Ｍ ２本
【００４６】
（２）発泡性
発泡性は、スチレン系発泡性樹脂粒子の揮発性成分量が７．０重量％のときの１００℃沸騰水中で３分間発泡させた際の嵩密度（発泡度）を測定した。
【００４７】
（３）曲げ強度
スチレン系発泡性樹脂粒子を、日立テクノプラント（株）製のＨＢＰ−７００発泡機を用いて発泡させて発泡ビーズを得た。さらに、この発泡ビーズを、ダイセン工業（株）製のＶＳ−５００成形機を用い、スチーム圧力を０．０８ＭＰａで成形して、５５０ｍｍ×３３５ｍｍ×１５０ｍｍの成形品を得た。
成形品の曲げ強度は、密度６０ｍｌ／ｇの発泡成形体をＪＩＳ−Ａ−９５１１に準じて測定した。
【００４８】
（４）ＧＰＣ／ＭＡＬＬＳ法による粒子表面部分のポリマー構造解析
図１に示す表面部分１を測定用試料とした。ＧＰＣ／ＭＡＬＬＳ法は、以下の装置及び条件で行い、これから、ｌｏｇ（Ｒ．Ｍ．Ｓ半径）とｌｏｇ（ＭＷ）との相関式の傾きを求めた。
カラム：Shodex、ＫＦ−８０７Ｌ×２本
カラム温度：４０℃
溶離液：ＴＨＦ
流速：１．００ｍｌ／ｍｉｎ
注入量：１００μＬ
検出器：ＲＩ及びWyatt Technology、ＤＡＷＮ ＤＳＰ-Ｆ
（レーザー波長：６３２．８nm）
多角度フィット法：Ｂｅｒｒｙ法
【００４９】
（５）外観（表面平滑率）
（３）と同様にして製造した成形品の表面部分に黒色印刷インクをローラーで薄く塗り、この表面部分を画像処理装置にかけた。表面部分の空隙には印刷インクが塗布されないことから、全塗布面積に対する黒色部分の面積を求め表面平滑率とし、外観の評価数値とした。
【００５０】
（６）重合率
重合率は、合成中の樹脂粒子を採取し、以下の装置及び条件にて測定した。
測定装置：（株）日立製作所社製
溶離液：アセトニトリル／蒸留水＝７０／３０、流量：１ｍｌ／分
検出器：ＵＶ ２３０ｎｍ
カラム：Ｉｎｅｒｔｓｉｌ ＯＤＳ−２
【００５１】
実施例１
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン５４００ｇ、ベンゾイルパーオキサイド２２．０ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。
仕込み完了後、重合槽内を密閉した。９０℃まで昇温し、昇温完了２時間及び３時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ４０％，４６％であった。
引き続き、９０℃で２時間保温した時点で再度燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの重合率は９５％であった。重合槽内を窒素で２００〜３００ｍｌ／分の速度で１０分間置換した。このときの重合槽内における酸素濃度は３．１体積％であった。この後、スチレン６００ｇを１００℃に昇温しながら３時間かけて連続的に滴下した。
【００５２】
引き続き、シクロヘキサン９０ｇ、さらに１時間後に、ブタン（イソブタン／ノルマルブタン比＝４／６）４２０ｇを１時間で圧入し、さらに４時間保温した。その後、室温まで冷却しオートクレーブより取り出した。
【００５３】
取り出したスラリーを洗浄、脱水、乾燥と各工程を行った後、１４メッシュ通過、２６メッシュ残で分級し、さらにジンクステアレート０．０８％、ひまし硬化油０．０５％、ジメチルシリコーン０．０２％を表面被覆しスチレン系発泡性樹脂粒子を得た。
【００５４】
得られたスチレン系発泡性樹脂粒子の分子量及び特性を測定しその結果を表１に示す。また、中心から表面に向かった分子量変化を図２に示す。
さらに、表面部分について、ＧＰＣ法によるチャート（ＧＰＣチャート）を測定した。チャートを図３（ａ）に示す。
【００５５】
実施例２
攪拌機付属の１４リットルオートクレーブ槽内に、窒素を５００〜６００ｍｌ／分の速度で３０分間置換した後、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン５４００ｇ、ベンゾイルパーオキサイド２３．６ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。
仕込み完了後、重合槽内を密閉し、ブロー用配管を開放した後、窒素を２００〜３００ｍｌ／分の速度で流した。９０℃まで昇温し、昇温完了１．５時間及び２．５時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ３９％，４６％であった。
引き続き、９０℃で２時間保温した時点で再度燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときまで、窒素は継続し流し続けており、このときの重合率は９６％であり、酸素濃度を測定したところ０．１体積％であった。酸素濃度測定後、窒素を止めブロー用配管を閉めた後、スチレン６００ｇを１００℃に昇温しながら３時間かけて連続的に滴下した。
発泡剤の含浸以降は、実施例１と同様に行った。
【００５６】
分子量及び特性を測定しその結果を表１に示す。
さらに、表面部分について、ＧＰＣ法によるチャート（ＧＰＣチャート）を測定した。チャートを図３（ｂ）に示す。
【００５７】
比較例１
スチレン系発泡性樹脂粒子（商品名Ｓ−ＨＣＭ−Ｋ、湘南積水工業（株））の分子量及び特性を測定しその結果を表１に示す。また、中心から表面に向かった分子量変化を図２に示す。
さらに、表面部分について、ＧＰＣ法によるチャート（ＧＰＣチャート）を測定した。チャートを図３（ｃ）に示す。
【００５８】
図２に示されるように、実施例１の粒子も比較例１の粒子も、中心から表面に向かって、分子量が高くなっていた。しかし、比較例１の粒子が徐々に高くなるのに対し、実施例１の粒子は、中心から３／５まではほぼ均一であまり変化しないで、表面付近で急に分子量が高くなっていた。従って、実施例１の粒子では、中心付近の分子量を低く維持した状態で表面付近の分子量が高くなっているのが分かる。
また、図３（ａ），（ｂ），（ｃ）に示されるように、実施例１，２のように急に分子量が高くなる粒子は、ＧＰＣチャートがショルダーを有していた。これらショルダーに変曲点が存在している。ショルダーは、高分子ポリマー比率が多いため形成される。一方、比較例１のように分子量が少しずつ上がる粒子は、ＧＰＣチャートに若干の膨らみが見られるものの、変曲点が無くショルダーを形成していなかった。
【００５９】
実施例３
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン５４００ｇ、ベンゾイルパーオキサイド２０．４ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。
仕込み完了後、重合槽内を密閉した。９０℃まで昇温し、昇温完了２時間及び３時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ３５％，４４％であった。
引き続き、９０℃で２時間保温した時点で再度燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの重合率は９１％であり、重合槽内を窒素で２００〜３００ｍｌ／分の速度で１０分間置換した後測定した酸素濃度は４．８体積％であった。この後、スチレン６００ｇを１００℃に昇温しながら３時間かけて連続的に滴下した。
発泡剤の含浸以降は、実施例１と同様に行った。
分子量及び特性を測定しその結果を表１に示す。
【００６０】
実施例４
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン５７００ｇ、ベンゾイルパーオキサイド２０．４ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。
仕込み完了後、重合槽内を密閉した。９０℃まで昇温し、昇温完了２時間及び３時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ３５％，４４％であった。
引き続き、９０℃で２時間保温した時点で再度燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの重合率は、９０％であり、重合槽内を窒素で２００〜３００ｍｌ／分の速度で１０分間置換した後測定した酸素濃度は４．５体積％であった。この後、スチレン３００ｇを１００℃に昇温しながら１．５時間かけて連続的に滴下した。
発泡剤の含浸以降は、実施例１と同様に行った。
分子量及び特性を測定しその結果を表１に示す。
【００６１】
実施例５
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン５４００ｇ、ベンゾイルパーオキサイド２０．０ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。仕込み完了後、重合槽内を密閉した。９０℃まで昇温し、昇温完了２時間及び３時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ３４％，４３％であった。
引き続き、９０℃で２時間保温した時点で再度燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの重合率は、９０％であり、重合槽内を窒素で２００〜３００ｍｌ／分の速度で１０分間置換した後測定した酸素濃度は４．０体積％であった。この後、スチレン６００ｇを１００℃に昇温しながら３時間かけて連続的に滴下した。
発泡剤の含浸以降は、実施例１と同様に行った。
分子量及び特性を測定しその結果を表１に示す。
【００６２】
実施例６
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いてスチレン５４００ｇ、ベンゾイルパーオキサイド２２．４ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。仕込み完了後、重合糟内を密閉した。９０℃まで昇温し、昇温完了後２時間及び２．５時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ３８％，４３％であった。
引き続き、９０℃で０．５時間保温した時点で再度燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの重合率は、６１％であり、重合槽内を窒素で２００〜３００ｍｌ／分の速度で１０分間置換した後測定した酸素濃度は４．１体積％であった。この後、スチレン６００ｇを１００℃に昇温しながら５時間かけて連続的に滴下した。
発泡剤の含浸以降は、実施例１と同様に行った。
分子量及び特性を測定しその結果を表１に示す。
【００６３】
実施例７
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン４２００ｇ、ベンゾイルパーオキサイド２１．７ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。仕込み完了後、重合糟内を密閉した。９０℃まで昇温し、昇温完了後１．５時間及び２時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ３５％，４０％であった。
引き続き、９０℃で１．５時間保温した時点で再度燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの重合率は、９６％であり、重合槽内を窒素で２００〜３００ｍｌ／分の速度で１０分間置換した後測定した酸素濃度は３．８体積％であった。この後、スチレン１８００ｇを１００℃に昇温しながら６時間かけて連続的に滴下した。
発泡剤の含浸以降は、実施例１と同様に行った。
分子量及び特性を測定しその結果を表１に示す。
【００６４】
実施例８
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いてスチレン５４００ｇ、ベンゾイルパーオキサイド２２．４ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。仕込み完了後、重合糟内を密閉した。９０℃まで昇温し、昇温完了後２時間及び２．５時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ３８％，４３％であった。
引き続き、９０℃で０．５時間保温した時点で再度燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの重合率は、６１％であり、重合槽内を窒素で２００〜３００ｍｌ／分の速度で１０分間置換した後測定した酸素濃度は６．５体積％であった。この後、スチレン６００ｇを１００℃に昇温しながら５時間かけて連続的に滴下した。
発泡剤の含浸以降は、実施例１と同様に行った。
分子量及び特性を測定しその結果を表１に示す。
【００６７】
比較例２
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン６０００ｇ、ベンゾイルパーオキサイド２０．８ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。
仕込み完了後、重合糟内を密閉した。９０℃まで昇温し、昇温完了後２時間及び３時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ３８％，４４％であった。
引き続き、９０℃で２．５時間保温し時点で再度燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの重合率は９５％であり、酸素濃度は１８．７体積％であった。この後、１００℃に１時間かけて昇温した。
発泡剤の含浸以降は、実施例１と同様に行った。
分子量及び特性を測定しその結果を表１に示す。
【００６８】
比較例３
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン５７００ｇ、ベンゾイルパーオキサイド２４．８ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。仕込み完了後、重合槽内を密閉した。９０℃まで昇温し、昇温完了１時間及び２時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ３９％，４８％であった。
引き続き、９０℃で２時間保温した時点で再度燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの重合率は、９８％であり、測定した酸素濃度は１９．０体積％であった。この後、スチレン３００ｇを１００℃に昇温しながら１．５時間かけて連続的に滴下した。
発泡剤の含浸以降は、実施例１と同様に行った。
分子量及び特性を測定しその結果を表１に示す。
【００６９】
【表１】
実施例１０
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン５４００ｇ、ベンゾイルパーオキサイド２２．４ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。
仕込み完了後、重合槽内を密閉し、ブロー配管を開け、窒素置換を行った。このときの酸素濃度は１２体積％であった。窒素置換終了後ブロー配管を閉め密閉状態としたのち、９０℃まで昇温し、昇温完了後２時間及び３時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ４０％，４９％であった。
引き続き、９０℃で２．５時間保温し重合率９５％まで進んだ時点で燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの酸素濃度は３．１体積％であった。この後、スチレン６００ｇを１００℃に昇温しながら３時間かけて連続的に滴下した。
引き続き、シクロヘキサン９０ｇ、さらに１時間後に、ブタン（イソブタン／ノルマルブタン比＝４／６）４２０ｇを１時間で圧入し、さらに４時間保温した。その後、室温まで冷却しオートクレーブより取り出した。
取り出したスラリーを洗浄、脱水、乾燥と各工程を行った後、１４メッシュ通過、２６メッシュ残で分級し、さらにジンクステアレート０．０８％、ひまし硬化油０．０５％、ジメチルシリコーン０．０２％を表面被覆しスチレン系発泡性樹脂粒子を得た。
得られたスチレン系発泡性樹脂粒子の分子量及び特性を測定しその結果を表２に示す。また、中心から表面に向かった分子量変化を図６に示す。
【００７１】
実施例１１
攪拌機付属の１４リットルオートクレーブ中を、窒素で置換した後、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン５４００ｇ、ベンゾイルパーオキサイド２２．４ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。
仕込み完了後、重合槽内を密閉し、ブロー配管を開け、再度窒素置換を行った。このとき酸素濃度計を用い測定した酸素濃度は５．４体積％であった。９０℃まで昇温し、昇温完了後２時間及び３時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ４０％，４９％であった。
引き続き、９０℃で２．５時間保温し重合率９５％まで進んだ時点で燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの酸素濃度は４．８体積％であった。この後、スチレン６００ｇを１００℃に昇温しながら３時間かけて連続的に滴下した。
発泡剤の添加量や含浸時間温度以降、得られたスチレン系発泡性樹脂粒子の処理及び表面処理を含め、実施例１０同様に行った。
分子量及び特性を測定しその結果を表２に示す。
【００７２】
実施例１２
攪拌機付属の１４リットルオートクレーブ中に、純水６０００ｇ、燐酸三カルシウム９ｇ、ドデシルベンゼンスルホン酸ソーダ０．３ｇを入れ２３０回転／分で攪拌しながら仕込んだ。このときの水素イオン濃度は８．０であった。
続いて、スチレン５４００ｇ、ベンゾイルパーオキサイド２２．４ｇ（Ｗｅｔ７５％）、ｔ−ブチルパーオキシイソプロピルカーボネイト２．４ｇ、エチレンビスアミド３ｇを攪拌しながら仕込んだ。
仕込み完了後、重合槽内を密閉し、ブロー配管を開け、窒素置換を行った。このときの酸素濃度は１１体積％であった。窒素置換終了後ブロー配管を閉め密閉状態としたのち、９０℃まで昇温し、昇温完了後２時間及び３時間後、それぞれ燐酸三カルシウムを３ｇ追加した。このときの重合率はそれぞれ４０％，４９％であった。
引き続き、９０℃で２．５時間保温し重合率９５％まで進んだ時点で燐酸三カルシウム６ｇとドデシルベンゼンスルホン酸ソーダ０．３ｇを追加した。このときの酸素濃度は５体積％であった。この後、窒素置換を実施し酸素濃度を０．５体積％まで減少させた後、スチレン６００ｇを１００℃に昇温しながら３時間かけて連続的に滴下した。
発泡剤の添加量や含浸時間温度以降、得られたスチレン系発泡性樹脂粒子の処理及び表面処理を含め、実施例１０同様に行った。
分子量及び特性を測定しその結果を表２に示す。
【００７３】
【表２】
【発明の効果】
本発明によれば、成形品の強度が大きく、発泡性に優れたスチレン系発泡性樹脂粒子、発泡ビーズ及び発泡成形品を提供できる。
【図面の簡単な説明】
【図１】本発明の表面部分と中心部分、さらに、これらの分子量の測定方法を説明するための図である。
【図２】実施例１及び比較例１の中心から表面までの分子量変化を示すグラフである。
【図３】実施例１，２及び比較例１のＧＰＣチャートである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a styrene-based expandable resin particle and a method for producing the same, and further relates to a styrene-based expanded bead and an expanded molded article.
[0002]
[Prior art]
Styrenic foamable resins are used in many food containers, packing materials, cushioning materials, and the like because of their excellent heat insulation, economic efficiency, and hygiene. These foam-molded products are manufactured by a method in which styrene-based expandable resin particles are heated with steam or the like, pre-foamed to a desired bulk density, passed through an aging step, filled into a molding die, and heated and foam-molded again. . The styrene-based expandable resin particles are required to exhibit good foamability in the pre-foaming stage and the heat-foaming molding stage in the mold and to have a high strength of the molded product when formed into a molded product. .
[0003]
Conventionally, in order to increase the strength of a foam molded product, a method of increasing the density of the molded product, a method of increasing the thickness of the molded product itself, and the like have been performed. However, any of these methods is not economical because the weight of the molded product increases, and it is also a problem from an environmental point of view. In styrene-based expandable resin particles, methods such as increasing the molecular weight and adjusting the amount and amount of plasticizers that plasticize the resin particles have been performed.
[0004]
On the other hand, as a method for improving the foamability of styrene-based foamable resin particles, a method for lowering the molecular weight, a method for plasticizing resin particles, and a method for changing the composition ratio of the foaming agent have been studied. .
[0005]
In general, the method for increasing the strength of the foamed molded product and the method for improving the foaming property are contradictory and it is difficult to achieve both.
[0006]
As a method for solving these problems, resin particles have been proposed in which the outermost layer part of the particle and the center part of the particle have a low molecular weight and the middle part of the particle has a high molecular weight (for example, see Patent Document 1).
However, this particle has a disadvantage that the surface finish of the molded product is deteriorated because the molecular weight of the outermost layer of the particle is as low as that of the center of the particle, and heat fusion is promoted too much at the time of hot foam molding. It was.
[0007]
Moreover, the resin particle whose molecular weight of a surface layer part is higher than the molecular weight of the whole particle | grain is also disclosed (for example, refer patent document 2).
This patent document describes that if the surface layer is made too high in molecular weight, the foaming performance is lowered and the appearance of the molded product is impaired, and as a result, the strength is lowered. This is presumably because the particles disclosed herein increase the molecular weight of the central layer when the surface layer increases in molecular weight. That is, this resin particle has a drawback that the surface layer portion cannot be sufficiently high molecular weight.
[0008]
[Patent Document 1]
JP-A-8-295756 [Patent Document 2]
Japanese Patent Laid-Open No. 7-188454
[Problems to be solved by the invention]
An object of the present invention is to provide styrene-based expandable resin particles, expanded beads, and expanded molded products having high strength of molded products and excellent foamability.
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, the weight average molecular weight of the surface portion forming 1/5 from the surface divided equally from the surface of the particle to the center by 5 is 1/5 from the center toward the surface. There is provided a styrenic expandable resin particle which is higher than the weight average molecular weight of the central part forming up to 5, and has a gel permeation chromatography chart on the surface part having two peaks or shoulders.
[0012]
According to the second aspect of the present invention, the log (RMS) measured by the GPC / MALLS method of the surface portion forming from the surface of the particle divided into 5 equal parts toward the center to 1/5. Styrenic expandable resin particles are provided, wherein the slope of the correlation equation between (radius) and log (MW) is 0.53 or less.
[0014]
According to the third aspect of the present invention, in suspension polymerization of a styrene monomer, when the polymerization rate is 60% or more, the oxygen concentration in the reaction vessel is maintained at 7% by volume or less, while the styrene foaming property is maintained . Add 5% to 30% by weight of the styrene monomer of the resin particles and adsorb it to the styrene resin particles in the middle of the polymerization to advance the polymerization reaction. Before or after the completion of the polymerization reaction, the foaming agent A method for producing styrenic expandable resin particles is provided.
[0015]
According to the 4th aspect of this invention, the styrene-type expandable resin particle characterized by being obtained by said manufacturing method is provided.
[0016]
According to a fifth aspect of the present invention, there is provided a styrene foam bead obtained by foaming the above styrene foam resin particle.
[0017]
According to a sixth aspect of the present invention, there is provided a styrenic foam molded article obtained by molding the above styrenic foam beads.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The styrenic expandable resin particles, expanded beads and expanded molded article of the present invention will be described in detail.
Styrenic expandable resin particles are obtained by polymerizing styrene monomers. Styrene monomer, styrene or styrene as a main component, styrene derivatives such as α-methylstyrene, chlorostyrene, vinyltoluene, acrylic esters such as methyl acrylate, methyl acrylate, butyl acrylate, methacryl Mixed monomers with methacrylic acid esters such as methyl acid, ethyl methacrylate and butyl methacrylate can be used.
[0019]
The method for producing the styrene-based expandable resin particles is preferably suspension polymerization, and conventionally known methods can be adopted. That is, in general, polymerization is performed by dispersing a styrene monomer in which a catalyst such as an organic peroxide is dissolved in an aqueous medium containing a dispersant to generate radicals.
[0020]
As the dispersant, a hardly soluble inorganic salt and a surfactant may be used in combination, and conventionally known ones such as an organic dispersant such as PVA may be used.
As the hardly soluble inorganic salt, magnesium phosphate, tricalcium phosphate or the like can be used. As the surfactant, any of sodium oleate, sodium dodecylbenzenesulfonate, and other anionic surfactants and nonionic surfactants generally used for suspension polymerization can be used. As the organic dispersant, polyvinyl alcohol, polyvinyl pyrrolidone, methyl cellulose and the like can be used.
As the organic peroxide, a conventionally known one having a 10-hour half-life decomposition temperature of 50 to 100 ° C. can be used. For example, lauroyl peroxide, benzoyl peroxide, t-butyl peroxybenzoate, t-butyl peroxyisopropyl carbonate, and the like. The organic peroxide is preferably used in an amount of 0.001% to 0.5% by weight based on the polymerizable monomer. One or more organic peroxides can be used.
[0021]
The overall molecular weight can be adjusted by adjusting the catalyst concentration, using a chain transfer agent together, or both.
As the chain transfer agent, conventionally known ones such as octyl mercaptan, dodecyl mercaptan, α-methylstyrene dimer can be used. The addition amount of the chain transfer agent is preferably 20 ppm to 100 ppm with respect to the polymerizable monomer.
[0022]
In the production method of the present invention, at least in the late stage of polymerization, the styrene monomer is added while keeping the oxygen concentration in the reaction vessel low.
In this method, the inside of the reaction vessel may be set to a low oxygen concentration from the start of polymerization or during the polymerization, but at a low oxygen concentration at least late in the polymerization. Further, the oxygen concentration may be changed, for example, so as to be particularly low only at the latter stage of polymerization.
[0023]
Preferably, the styrene monomer is added at a polymerization rate of 60% or more, more preferably 60% or more and less than 97%. Preferably, the styrene monomer is added while maintaining the oxygen concentration in the reaction vessel at 7% by volume or less.
When the oxygen concentration exceeds 7% by volume, a low molecular weight substance is formed on the surface layer of the styrene resin particles when the styrene monomer is added and the reaction proceeds. Formation of a low molecular weight product in the skin causes excessive heat fusion during foam molding, thereby reducing the strength of the molded product and worsening the surface finish. Preferably, the oxygen concentration is less than 5 vol%. The oxygen concentration can be adjusted by replacing with an inert gas such as nitrogen.
[0024]
When the polymerization rate is lower than 60%, absorption of the styrenic monomer into the styrenic resin particles is promoted, and the molecular weight of the central portion is increased, so that the foaming force and the fusion of the molded product are lowered. In addition, when the polymerization rate is 97% or more, the absorption of the styrene monomer to the resin particles decreases, the amount of radicals and polymerization catalyst in the resin particles decreases, and the molecular weight of the outermost surface portion of the resin particles is low molecular weight. Therefore, heat fusion is promoted too much during foam molding, which may reduce the strength of the molded product and deteriorate the surface finish. Addition at a polymerization rate of 85 or more and less than 97% is more preferable.
[0025]
The addition amount of the styrene monomer is preferably 5% by weight to 30% by weight with respect to the styrene resin particles finally obtained. More preferably, it is in the range of 10% by weight to 15% by weight.
When the addition amount is less than 5% by weight, the effect of increasing the molecular weight of the outermost surface portion of the styrene resin particles is small, and the strength improvement effect may not be sufficiently obtained. On the other hand, when the added amount is more than 30% by weight, the resin particles are softened, the absorption of the styrenic monomer is promoted, and the molecular weight of the central part is increased. Therefore, the foaming force may be reduced, and it may be difficult to fuse the molded product.
[0026]
The suspension polymerization temperature is generally 80 ° C to 95 ° C. The addition temperature of the styrene monomer may be as it is or may be increased. From the industrial production efficiency of reducing the amount of styrene monomer remaining in the finally obtained styrene foam resin particles, the polymerization temperature is preferably 90 ° C. or higher, and the styrene monomer addition temperature. Is preferably performed during the temperature rise.
[0027]
In the production method of the present invention, it is preferable to start the polymerization when the hydrogen ion concentration of the aqueous dispersion is 8 to 10, and add at least one hardly soluble inorganic salt at a polymerization rate of 20% to 50%. The aqueous dispersion is preferably a continuous phase.
If the hydrogen ion concentration is outside the above range, the particle size distribution at the end of suspension polymerization may not be sharp. The hydrogen ion concentration can be adjusted with a basic inorganic salt.
For the same reason, a hardly soluble inorganic salt can be added at a polymerization rate of 20% to 50%.
The hardly soluble inorganic salt can be added at least once, for example, 2 to 3 times. Further, the hardly soluble inorganic salt can be added after further polymerization.
[0028]
昜 The volatile foaming agent can be injected in parallel with the addition of the styrenic monomer, but in general, it is preferably performed after the addition of the styrenic monomer, before or after the completion of the polymerization reaction. The styrene resin particles are preferably impregnated with a readily volatile foaming agent.
[0029]
昜 The volatile blowing agent is selected from aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, normal pentane, and cyclopentane. In addition to aliphatic hydrocarbons, alicyclic hydrocarbons such as cyclohexane and aromatic hydrocarbons can also be used in combination with highly volatile blowing agents as foaming aids.
[0030]
In the case of polymerization, it is necessary to use additives used in the production of styrene-based expandable resin particles, such as solvents, plasticizers, foamed cell nucleating agents, fillers, flame retardants, flame retardant aids, lubricants, colorants, etc. It may be used as appropriate.
[0032]
The styrenic foamable resin particles can be coated with a surface coating agent as necessary after impregnation with the foaming agent, discharged from the polymerization system, and further dehydrated and dried. As this coating agent, those used for conventionally known expanded styrene resin particles can be applied. For example, zinc stearate, stearic acid triglyceride, stearic acid monoglyceride, castor oil, amide compound, silicones, antistatic agent and the like.
[0033]
Usually, in the styrene-based expandable resin particles produced by suspension polymerization, the weight average molecular weight (molecular weight) is determined by the amount of the polymerization catalyst, and the molecular weights of the particle central portion, intermediate portion, and surface layer portion are almost constant. .
However, according to the production method of the present invention, styrene-based expandable resin particles in which the molecular weight of the surface portion of the resin particles is higher than the molecular weight of the central portion can be obtained. The molecular weight gradient from the center to the surface does not gradually increase at a constant rate but suddenly increases near the surface.
In the styrenic expandable resin particles obtained by the production method of the present invention, the molecular weight is abruptly increased in the vicinity of the surface, so that the surface portion can have a high molecular weight while keeping the central portion at a low molecular weight. In general, when the center portion has a low molecular weight, good foamability can be exhibited, and when the surface portion has a high molecular weight, the strength of the molded product increases. Therefore, in the particles of the present invention, both foamability and molded product strength can be satisfied. For example, a considerably high strength of the molded product can be obtained while maintaining a certain degree of foamability.
[0034]
In particular, in the styrene-based expandable resin particles of the present invention, the weight average molecular weight of the surface portion that forms 1/5 from the surface divided into 5 equal parts from the resin particle surface toward the center is from the center toward the surface. It is preferably higher than the weight average molecular weight of the central part forming up to 1/5.
Here, the surface portion and the central portion will be described with reference to the drawings. As shown in FIG. 1, the
Furthermore, it is preferable that the chart of the surface portion by gel permeation chromatography has two peaks or a shoulder. Having two peaks or shoulders means that the molecular weight is changing rapidly. The shoulder is formed by an inflection point. In the present invention, the chart by gel permeation chromatography is measured using two columns, GL-R400M, manufactured by Hitachi Chemical Co., Ltd. Note that inflection points are also generated at both tails of the normal chart, but these are not included in the shoulder in the present invention (see FIG. 3).
[0035]
Further, according to the present invention, the weight average molecular weight of the central portion is in the range of 200,000 to 300,000, the weight average molecular weight of the surface portion is in the range of 300,000 to 450,000, and the weight of the surface portion. The average molecular weight is preferably 1.2 times or more larger than the weight average molecular weight of the central portion.
[0036]
When the molecular weight of the central part is smaller than 200,000, the strength of the molded product may be lowered. Further, in order to make the molecular weight smaller than 200,000, the amount of catalyst used must be increased in the production process, which is not preferable.
When the molecular weight of the central part is larger than 300,000, foamability may be lowered.
Moreover, Preferably, the weight average molecular weight of a center part is 200,000-250,000. Preferably, the molecular weight of the portion forming 3/5 from the center is substantially uniform.
[0037]
When the molecular weight of the surface portion is smaller than 300,000, there is a possibility that sufficient molded product strength cannot be obtained.
When the molecular weight of the surface portion is larger than 450,000, the foaming force is lowered, the thermal melting is not promoted, the surface finish of the molded product is deteriorated, and the fusion is difficult.
Moreover, Preferably, the weight average molecular weight of a surface part is 350,000-450,000.
[0038]
The weight average molecular weight (molecular weight ratio) of the surface portion is more preferably 1.5 times or more with respect to the weight average molecular weight of the central portion. Usually, it is 2.2 times or less.
[0039]
Such styrenic expandable resin particles can be produced by reducing the oxygen concentration by the production method of the present invention.
[0040]
Further, according to the production method of the present invention, grafting, which was considered not to occur in the conventional radical polymerization of styrene, occurred on the surface portion, and a high molecular weight branched structure could be generated.
In this way, the surface portion has a branched structure, for example, when the surface portion that forms 1/5 from the surface divided into five equal parts from the surface of the particle toward the center is measured by the GPC / MALLS method. , Log (RMS radius) and log (MW), the slope of the correlation equation is 0.53 or less, preferably 0.52 or less, more preferably 0.50 or less. Here, GPC performs gel permeation chromatography using MALLS (Multi
(Angle Laser Light Scattering) is a multi-angle light scattering detector. M.M. S (Root Mean Square) radius means the root mean square radius, and MW means absolute molecular weight.
In addition, this inclination is 0.55-0.60 in the polystyrene of the linear structure obtained by normal radical polymerization (suspension system).
Further, the weight average molecular weight of the surface portion is preferably 300,000 or more and 450,000 or less for the same reason as described above.
[0041]
In the resin particles of the present invention, as described above, the occurrence of low molecular weight substances in the surface portion is suppressed, and since the surface portion has a high molecular weight branched structure, normal polymerization that does not suppress the oxygen concentration Compared with the foam molded product produced by the above, the heat resistance of the particle surface portion is improved, and a foam molded product having good appearance and mechanical strength can be obtained.
[0042]
In addition, the average particle diameter of the styrenic expandable resin particles of the present invention is usually 0.05 to 2.0 mm.
[0043]
The expanded beads of the present invention are produced by expanding styrene-based expandable resin particles. The foamed molded product of the present invention is produced by molding the foamed beads.
In general, styrene-based expandable resin particles are heated with steam or the like to be pre-expanded to a predetermined bulk density, and expanded beads are produced through an aging step. Thereafter, the foamed beads are filled into a molding die and heated and foamed again to produce a foamed molded product.
[0044]
In this invention, it is excellent in the balance of the foamability of a styrene-type expandable resin particle, and the intensity | strength of the molded article obtained from it. The molded product of the present invention can be suitably used for food containers, packing materials, cushioning materials and the like.
[0045]
【Example】
The characteristic evaluation methods in the examples and comparative examples were as follows.
(1) Weight average molecular weight (molecular weight)
The molecular weight of the styrene-based expandable resin particles was measured by foaming the particles.
Styrenic foamable resin particles were foamed in saturated water vapor to a bulk multiple of 80 ml / g.
Arbitrary foamed particles 2 to 3 were collected, and with a razor, the particles 1 were equally divided into 5 at half equal intervals to form
The molecular weight was measured by a gel permeation chromatograph (GPC) method.
Moreover, the chart (GPC chart) by GPC method was obtained about the surface part. At that time, it measured with the following apparatuses and conditions.
Measuring device: manufactured by Hitachi, Ltd. Eluent: THF, flow rate: 2 ml / min detector: UV 220 nm
Column: 2 GL-R400M manufactured by Hitachi Chemical Co., Ltd.
(2) Foaming foaming property measured the bulk density (foaming degree) at the time of making it foam for 3 minutes in 100 degreeC boiling water when the amount of volatile components of a styrene-type foaming resin particle is 7.0 weight%. .
[0047]
(3) Flexural strength Styrenic expandable resin particles were foamed using an HBP-700 foaming machine manufactured by Hitachi Technoplant Co., Ltd. to obtain expanded beads. Furthermore, this foamed bead was molded at a steam pressure of 0.08 MPa using a VS-500 molding machine manufactured by Daisen Industry Co., Ltd. to obtain a molded product of 550 mm × 335 mm × 150 mm.
The bending strength of the molded product was measured according to JIS-A-9511 for a foamed molded product having a density of 60 ml / g.
[0048]
(4) Polymer structure analysis of particle surface portion by GPC / MALLS method Surface portion 1 shown in FIG. 1 was used as a sample for measurement. The GPC / MALLS method was performed with the following apparatus and conditions, and the slope of the correlation equation between log (RMS radius) and log (MW) was determined from this.
Column: Shodex, KF-807L × 2 Column temperature: 40 ° C.
Eluent: THF
Flow rate: 1.00 ml / min
Injection volume: 100 μL
Detector: RI and Wyatt Technology, DAWN DSP-F
(Laser wavelength: 632.8 nm)
Multi-angle fitting method: Berry method
(5) Appearance (surface smoothness)
A black printing ink was thinly applied to the surface portion of the molded product produced in the same manner as (3) with a roller, and this surface portion was applied to an image processing apparatus. Since printing ink was not applied to the voids in the surface portion, the area of the black portion with respect to the total application area was determined and used as the surface smoothness, and the appearance evaluation value.
[0050]
(6) Polymerization rate The polymerization rate was measured using the following apparatus and conditions after collecting resin particles during synthesis.
Measuring apparatus: manufactured by Hitachi, Ltd. Eluent: acetonitrile / distilled water = 70/30, flow rate: 1 ml / min detector: UV 230 nm
Column: Inertsil ODS-2
[0051]
Example 1
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5400 g of styrene, 22.0 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylene bisamide were charged with stirring.
After completion of the charging, the inside of the polymerization tank was sealed. The temperature was raised to 90 ° C., and 2 hours and 3 hours after completion of the temperature increase, 3 g of tricalcium phosphate was added. The polymerization rates at this time were 40% and 46%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again when the temperature was kept at 90 ° C. for 2 hours. At this time, the polymerization rate was 95%. The inside of the polymerization tank was replaced with nitrogen at a rate of 200 to 300 ml / min for 10 minutes. At this time, the oxygen concentration in the polymerization tank was 3.1% by volume. Thereafter, 600 g of styrene was continuously dropped over 3 hours while raising the temperature to 100 ° C.
[0052]
Subsequently, 90 g of cyclohexane and another 1 hour later, 420 g of butane (isobutane / normal butane ratio = 4/6) were injected in 1 hour, and the temperature was further maintained for 4 hours. Then, it cooled to room temperature and took out from the autoclave.
[0053]
The extracted slurry was washed, dewatered, and dried, and then classified by passing 14 meshes and remaining 26 meshes. Further, zinc stearate 0.08%, castor oil 0.05%, dimethyl silicone 0. 02% of the surface was coated to obtain styrene-based expandable resin particles.
[0054]
The molecular weight and characteristics of the obtained styrenic expandable resin particles were measured, and the results are shown in Table 1. Moreover, the molecular weight change from the center toward the surface is shown in FIG.
Furthermore, the chart (GPC chart) by GPC method was measured about the surface part. The chart is shown in FIG.
[0055]
Example 2
In a 14 liter autoclave tank attached to a stirrer, nitrogen was replaced at a rate of 500 to 600 ml / min for 30 minutes, and then 6000 g of pure water, 9 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added at 230 rpm. Charged with stirring. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5400 g of styrene, 23.6 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylene bisamide were charged with stirring.
After completion of the charging, the inside of the polymerization tank was sealed, the blow piping was opened, and then nitrogen was flowed at a rate of 200 to 300 ml / min. The temperature was raised to 90 ° C., and 1.5 g and 2.5 hours after completion of the temperature raising, 3 g of tricalcium phosphate was added. The polymerization rates at this time were 39% and 46%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again when the temperature was kept at 90 ° C. for 2 hours. Until this time, nitrogen continued to flow, the polymerization rate at this time was 96%, and the oxygen concentration measured was 0.1% by volume. After measuring the oxygen concentration, nitrogen was stopped and the blow piping was closed, and then 600 g of styrene was continuously dropped over 3 hours while raising the temperature to 100 ° C.
After impregnation with the foaming agent, the same procedure as in Example 1 was performed.
[0056]
The molecular weight and properties were measured and the results are shown in Table 1.
Furthermore, the chart (GPC chart) by GPC method was measured about the surface part. The chart is shown in FIG.
[0057]
Comparative Example 1
The molecular weight and characteristics of styrene-based expandable resin particles (trade name S-HCM-K, Shonan Sekisui Industry Co., Ltd.) were measured, and the results are shown in Table 1. Moreover, the molecular weight change from the center toward the surface is shown in FIG.
Furthermore, the chart (GPC chart) by GPC method was measured about the surface part. The chart is shown in FIG.
[0058]
As shown in FIG. 2, the molecular weight of both the particles of Example 1 and Comparative Example 1 increased from the center toward the surface. However, while the particles of Comparative Example 1 gradually increased, the particles of Example 1 were almost uniform from the center to 3/5 and did not change much, and the molecular weight suddenly increased near the surface. Therefore, it can be seen that in the particles of Example 1, the molecular weight in the vicinity of the surface is high while the molecular weight in the vicinity of the center is kept low.
Further, as shown in FIGS. 3A, 3B, and 3C, the GPC chart had a shoulder in the particles that suddenly increased in molecular weight as in Examples 1 and 2. Inflection points exist in these shoulders. The shoulder is formed because of the high polymer ratio. On the other hand, the particles whose molecular weight gradually increased as in Comparative Example 1 did not have inflection points and did not form a shoulder although a slight swelling was seen on the GPC chart.
[0059]
Example 3
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5400 g of styrene, 20.4 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylene bisamide were charged with stirring.
After completion of the charging, the inside of the polymerization tank was sealed. The temperature was raised to 90 ° C., and 2 hours and 3 hours after completion of the temperature increase, 3 g of tricalcium phosphate was added. The polymerization rates at this time were 35% and 44%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again when the temperature was kept at 90 ° C. for 2 hours. The polymerization rate at this time was 91%, and the oxygen concentration measured after replacing the inside of the polymerization tank with nitrogen at a rate of 200 to 300 ml / min for 10 minutes was 4.8% by volume. Thereafter, 600 g of styrene was continuously dropped over 3 hours while raising the temperature to 100 ° C.
After impregnation with the foaming agent, the same procedure as in Example 1 was performed.
The molecular weight and properties were measured and the results are shown in Table 1.
[0060]
Example 4
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5700 g of styrene, 20.4 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylenebisamide were charged with stirring.
After completion of the charging, the inside of the polymerization tank was sealed. The temperature was raised to 90 ° C., and 2 hours and 3 hours after completion of the temperature increase, 3 g of tricalcium phosphate was added. The polymerization rates at this time were 35% and 44%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again when the temperature was kept at 90 ° C. for 2 hours. The polymerization rate at this time was 90%, and the oxygen concentration measured after substituting the inside of the polymerization tank with nitrogen at a rate of 200 to 300 ml / min for 10 minutes was 4.5% by volume. Thereafter, 300 g of styrene was continuously added dropwise over 1.5 hours while the temperature was raised to 100 ° C.
After impregnation with the foaming agent, the same procedure as in Example 1 was performed.
The molecular weight and properties were measured and the results are shown in Table 1.
[0061]
Example 5
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5400 g of styrene, 20.0 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylenebisamide were charged with stirring. After completion of the charging, the inside of the polymerization tank was sealed. The temperature was raised to 90 ° C., and 2 hours and 3 hours after completion of the temperature increase, 3 g of tricalcium phosphate was added. The polymerization rates at this time were 34% and 43%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again when the temperature was kept at 90 ° C. for 2 hours. The polymerization rate at this time was 90%, and the oxygen concentration measured after replacing the inside of the polymerization tank with nitrogen at a rate of 200 to 300 ml / min for 10 minutes was 4.0% by volume. Thereafter, 600 g of styrene was continuously dropped over 3 hours while raising the temperature to 100 ° C.
After impregnation with the foaming agent, the same procedure as in Example 1 was performed.
The molecular weight and properties were measured and the results are shown in Table 1.
[0062]
Example 6
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5400 g of styrene, 22.4 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylene bisamide were charged with stirring. After completion of the charging, the inside of the polymerization vessel was sealed. The temperature was raised to 90 ° C., and 3 g of tricalcium phosphate was added 2 hours and 2.5 hours after completion of the temperature rise. The polymerization rates at this time were 38% and 43%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again when the temperature was kept at 90 ° C. for 0.5 hour. The polymerization rate at this time was 61%, and the oxygen concentration measured after replacing the inside of the polymerization tank with nitrogen at a rate of 200 to 300 ml / min for 10 minutes was 4.1% by volume. Thereafter, 600 g of styrene was continuously dropped over 5 hours while raising the temperature to 100 ° C.
After impregnation with the foaming agent, the same procedure as in Example 1 was performed.
The molecular weight and properties were measured and the results are shown in Table 1.
[0063]
Example 7
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 4200 g of styrene, 21.7 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylene bisamide were charged with stirring. After completion of the charging, the inside of the polymerization vessel was sealed. The temperature was raised to 90 ° C., and 1.5 g and 2 hours after completion of the temperature raising, 3 g of tricalcium phosphate was added. The polymerization rates at this time were 35% and 40%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again when the temperature was kept at 90 ° C. for 1.5 hours. The polymerization rate at this time was 96%, and the oxygen concentration measured after substituting the inside of the polymerization tank with nitrogen at a rate of 200 to 300 ml / min for 10 minutes was 3.8% by volume. Thereafter, 1800 g of styrene was continuously dropped over 6 hours while raising the temperature to 100 ° C.
After impregnation with the foaming agent, the same procedure as in Example 1 was performed.
The molecular weight and properties were measured and the results are shown in Table 1.
[0064]
Example 8
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5400 g of styrene, 22.4 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylene bisamide were charged with stirring. After completion of the charging, the inside of the polymerization vessel was sealed. The temperature was raised to 90 ° C., and 3 g of tricalcium phosphate was added 2 hours and 2.5 hours after completion of the temperature rise. The polymerization rates at this time were 38% and 43%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again when the temperature was kept at 90 ° C. for 0.5 hour. The polymerization rate at this time was 61%, and the oxygen concentration measured after replacing the inside of the polymerization tank with nitrogen at a rate of 200 to 300 ml / min for 10 minutes was 6.5% by volume. Thereafter, 600 g of styrene was continuously dropped over 5 hours while raising the temperature to 100 ° C.
After impregnation with the foaming agent, the same procedure as in Example 1 was performed.
The molecular weight and properties were measured and the results are shown in Table 1.
[0067]
Comparative Example 2
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 6000 g of styrene, 20.8 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylenebisamide were charged with stirring.
After completion of the charging, the inside of the polymerization vessel was sealed. The temperature was raised to 90 ° C., and 3 g of tricalcium phosphate was added 2 hours and 3 hours after completion of the temperature rise. The polymerization rates at this time were 38% and 44%, respectively.
Subsequently, the mixture was kept at 90 ° C. for 2.5 hours, and 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again. The polymerization rate at this time was 95%, and the oxygen concentration was 18.7% by volume. Thereafter, the temperature was raised to 100 ° C. over 1 hour.
After impregnation with the foaming agent, the same procedure as in Example 1 was performed.
The molecular weight and properties were measured and the results are shown in Table 1.
[0068]
Comparative Example 3
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5700 g of styrene, 24.8 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylene bisamide were charged with stirring. After completion of the charging, the inside of the polymerization tank was sealed. The temperature was raised to 90 ° C., and 1 hour and 2 hours after completion of the temperature increase, 3 g of tricalcium phosphate was added. The polymerization rates at this time were 39% and 48%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added again when the temperature was kept at 90 ° C. for 2 hours. The polymerization rate at this time was 98%, and the measured oxygen concentration was 19.0% by volume. Thereafter, 300 g of styrene was continuously added dropwise over 1.5 hours while the temperature was raised to 100 ° C.
After impregnation with the foaming agent, the same procedure as in Example 1 was performed.
The molecular weight and properties were measured and the results are shown in Table 1.
[0069]
[Table 1]
Example 10
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5400 g of styrene, 22.4 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylenebisamide were charged with stirring.
After completion of the charging, the inside of the polymerization tank was sealed, the blow pipe was opened, and nitrogen substitution was performed. At this time, the oxygen concentration was 12% by volume. After completion of the nitrogen substitution, the blow pipe was closed and sealed, and then the temperature was raised to 90 ° C., and 3 g of tricalcium phosphate was added 2 hours and 3 hours after the completion of the temperature rise. The polymerization rates at this time were 40% and 49%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added when the temperature was maintained at 90 ° C. for 2.5 hours and the polymerization rate reached 95%. At this time, the oxygen concentration was 3.1% by volume. Thereafter, 600 g of styrene was continuously dropped over 3 hours while raising the temperature to 100 ° C.
Subsequently, 90 g of cyclohexane and another 1 hour later, 420 g of butane (isobutane / normal butane ratio = 4/6) were injected in 1 hour, and the temperature was further maintained for 4 hours. Then, it cooled to room temperature and took out from the autoclave.
The extracted slurry was washed, dewatered, and dried, and then classified by passing 14 meshes and remaining 26 meshes. Further, zinc stearate 0.08%, castor oil 0.05%, dimethyl silicone 0. 02% of the surface was coated to obtain styrene-based expandable resin particles.
The molecular weight and characteristics of the obtained styrenic expandable resin particles were measured, and the results are shown in Table 2. Moreover, the molecular weight change from the center toward the surface is shown in FIG.
[0071]
Example 11
The 14 liter autoclave attached to the stirrer was purged with nitrogen, and then 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were added while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5400 g of styrene, 22.4 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylenebisamide were charged with stirring.
After completion of the charging, the inside of the polymerization tank was sealed, the blow pipe was opened, and nitrogen substitution was performed again. At this time, the oxygen concentration measured using an oxygen concentration meter was 5.4% by volume. The temperature was raised to 90 ° C., and 3 g of tricalcium phosphate was added 2 hours and 3 hours after completion of the temperature rise. The polymerization rates at this time were 40% and 49%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added when the temperature was maintained at 90 ° C. for 2.5 hours and the polymerization rate reached 95%. The oxygen concentration at this time was 4.8% by volume. Thereafter, 600 g of styrene was continuously dropped over 3 hours while raising the temperature to 100 ° C.
After the addition amount of the foaming agent and the impregnation time temperature, the same procedures as in Example 10 were performed including the treatment and surface treatment of the obtained styrene-based foamable resin particles.
The molecular weight and properties were measured and the results are shown in Table 2.
[0072]
Example 12
In a 14 liter autoclave attached to a stirrer, 6000 g of pure water, 9 g of tricalcium phosphate, and 0.3 g of sodium dodecylbenzenesulfonate were placed while stirring at 230 rpm. The hydrogen ion concentration at this time was 8.0.
Subsequently, 5400 g of styrene, 22.4 g of benzoyl peroxide (Wet 75%), 2.4 g of t-butylperoxyisopropyl carbonate, and 3 g of ethylenebisamide were charged with stirring.
After completion of the charging, the inside of the polymerization tank was sealed, the blow pipe was opened, and nitrogen substitution was performed. At this time, the oxygen concentration was 11% by volume. After completion of the nitrogen substitution, the blow pipe was closed and sealed, and then the temperature was raised to 90 ° C., and 3 g of tricalcium phosphate was added 2 hours and 3 hours after the completion of the temperature rise. The polymerization rates at this time were 40% and 49%, respectively.
Subsequently, 6 g of tricalcium phosphate and 0.3 g of sodium dodecylbenzenesulfonate were added when the temperature was maintained at 90 ° C. for 2.5 hours and the polymerization rate reached 95%. At this time, the oxygen concentration was 5% by volume. Thereafter, nitrogen substitution was performed to reduce the oxygen concentration to 0.5% by volume, and then 600 g of styrene was continuously dropped over 3 hours while the temperature was raised to 100 ° C.
After the addition amount of the foaming agent and the impregnation time temperature, the same procedures as in Example 10 were performed including the treatment and surface treatment of the obtained styrene-based foamable resin particles.
The molecular weight and properties were measured and the results are shown in Table 2.
[0073]
[Table 2]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the intensity | strength of a molded article is large and can provide the styrene-type expandable resin particle, the expanded bead, and the expanded molded article which were excellent in foamability.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram for explaining a surface portion and a central portion of the present invention and a method for measuring their molecular weights.
2 is a graph showing changes in molecular weight from the center to the surface of Example 1 and Comparative Example 1. FIG.
3 is a GPC chart of Examples 1 and 2 and Comparative Example 1. FIG.
Claims (3)
重合率が６０％以上のとき、反応槽内の酸素濃度を７体積％以下に保ちつつ、スチレン系発泡性樹脂粒子の５重量％〜３０重量％のスチレン系単量体を添加し、重合途中にあるスチレン樹脂粒子に吸着させて重合反応を進め、
重合反応の完了前または重合反応の完了後に、発泡剤を含浸することを特徴とするスチレン系発泡性樹脂粒子の製造方法。In suspension polymerization of styrene monomer,
When the polymerization rate is 60% or more, 5% to 30% by weight of a styrene-based expandable resin particle is added while maintaining the oxygen concentration in the reaction vessel at 7% by volume or less. Adsorption to styrene resin particles in the
A method for producing styrenic expandable resin particles, wherein the foaming agent is impregnated before or after the completion of the polymerization reaction.
重合率２０％〜５０％で、少なくとも１回以上、難溶性無機塩を加えることを特徴とする請求項１又は２記載のスチレン系発泡性樹脂粒子の製造方法。In the suspension polymerization of the styrene monomer, the polymerization starts when the hydrogen ion concentration of the aqueous dispersion is 8 to 10,
The method for producing styrene-based expandable resin particles according to claim 1 or 2 , wherein the hardly soluble inorganic salt is added at least once or more at a polymerization rate of 20% to 50%.
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| JP2006160905A (en) * | 2004-12-08 | 2006-06-22 | Hitachi Chem Co Ltd | Reclaimed foamable sytrenic resin particle, method for producing the same, reclaimed styrenic foamed bead and reclaimed foamed styrenic resin molded article |
| JP2006316240A (en) * | 2005-04-11 | 2006-11-24 | Hitachi Chem Co Ltd | Foamed styrenic block molded product |
| JP2006307016A (en) * | 2005-04-28 | 2006-11-09 | Hitachi Chem Co Ltd | Method for producing recycled foaming styrenic resin particle |
| JP2006316176A (en) * | 2005-05-13 | 2006-11-24 | Hitachi Chem Co Ltd | Method for producing regenerated foaming styrene resin particle |
| JP4891586B2 (en) * | 2005-09-28 | 2012-03-07 | 積水化成品工業株式会社 | Expandable thermoplastic resin particles and process for producing the same, thermoplastic resin pre-expanded particles, and foam molded article |
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| JP5732358B2 (en) * | 2011-09-12 | 2015-06-10 | 積水化成品工業株式会社 | Polystyrene-based resin particles, expandable resin particles, expanded particles, expanded molded articles, and methods for producing them |
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