JP3670980B2 - Thermally foamable microsphere and method for producing the same - Google Patents

Description

【００６８】
【数２】

【００６９】
（式中、μ＝平均値、ｘ_j ＝粒子径、ｑ_j ＝頻度分布）
【００７０】
本発明の熱発泡性マイクロスフェアーにおける発泡剤の含有量は、全重量基準で、通常５〜５０重量％、好ましくは７〜３５重量％である。発泡剤の含有量が少なすぎると、発泡倍率が不充分となり、大きすぎると、外殻の厚みが薄くなって、加工時に加熱下での剪断力を受けて早期発泡や外殻の破裂を起こしやすくなる。発泡剤としては、低沸点有機溶剤、加熱により分解してガスを発生する化合物などがあり、これらの中でも、低沸点有機溶剤が好ましい。発泡剤は、外殻を形成する重合体の軟化点以下の温度でガス状になるものから選択される。
【００７１】
本発明の熱発泡性マイクロスフェアーの外殻は、通常、ガスバリア性と耐熱性に優れた重合体から形成される。具体的には、前記した通り、アクリル酸エステル、（メタ）アクリロニトリル、塩化ビニリデン、塩化ビニル、スチレンなどの種々の重合性単量体を用いて形成することができる。これらの中でも、塩化ビニリデン（共）重合体及び（メタ）アクリロニトリル（共）重合体は、ガスバリア性、耐溶剤性、耐熱性、発泡性などを高度にバランスさせる上で好ましい。本発明によれば、使用する重合性単量体の組み合わせや組成比の制御と、発泡剤の種類の選択により、様々な発泡挙動を示す熱発泡性マイクロスフェアーを得ることができる。
【００７２】
本発明の熱発泡性マイクロスフェアーは、特に加工特性に優れており、かつ、発泡特性（熱膨張性）と加工特性とのバランスが良好である。本発明の熱発泡性マイクロスフェアーは、架橋剤を１重量％を越える割合で用いているにもかかわらず、熱膨張性が喪失しておらず、最大発泡倍率が５倍以上である。最大発泡倍率は、好ましくは１０倍以上、より好ましくは２０倍以上であり、多くの場合、３０〜６０倍程度の最大発泡倍率を達成することが可能である。
【００７３】
本発明の熱発泡性マイクロスフェアーは、重合体から形成された外殻の弾性率の温度依存性が小さい。また、本発明の熱発泡性マイクロスフェアーは、加工の適正温度域が広い。さらに、本発明の熱発泡性マイクロスフェアーは、極性溶剤や可塑剤などに対して、耐性（耐薬品性、耐溶剤性）と発泡特性の保持能力が高い。本発明の熱発泡性マイクロスフェアーが有するこれらの特性は、実施例に具体的に示されている。
【００７４】
本発明の熱発泡性マイクロスフェアーの特性の具体例として、発泡の温度依存性の小さいことが挙げられる。例えば、本発明の熱発泡性マイクロスフェアーの外殻重合体が前述の如き塩化ビニリデン（共）重合体である場合、最大発泡倍率Ｒ₁ に対するそのときの温度から１０℃高い温度での発泡倍率Ｒ₂ の比（Ｒ₂ ／Ｒ₁ ）は、通常０．８〜０．４、好ましくは０．９〜０．５、より好ましくは１〜０．５である。
【００７５】
本発明の熱発泡性マイクロスフェアーの外殻重合体が前述の如き（メタ）アクリロニトリル共重合体〔（メタ）アクリロニトリルの共重合割合＝３０重量％以上８０重量％未満〕である場合、最大発泡倍率Ｒ₁ に対するそのときの温度から５℃高い温度での発泡倍率Ｒ₂ の比（Ｒ₂ ／Ｒ₁ ）は、通常１〜０．８、好ましくは１〜０．８５、より好ましくは１〜０．９である。
【００７６】
本発明の熱発泡性マイクロスフェアーの外殻重合体が（メタ）アクリロニトリル（共）重合体〔（メタ）アクリロニトリルの割合＝８０〜１００重量％〕である場合、架橋性単量体として、特に、前記の屈曲性連鎖を有する二官能架橋性単量体を１重量％超過５重量％以下の割合で使用することにより、発泡性を高度に維持しつつ、外殻重合体の弾性率の温度依存性が小さく、加工性や耐薬品性に優れた熱発泡性マイクロスフェアーを得ることができる。
【００７７】
本発明の熱発泡性マイクロスフェアーは、１９０℃以上における外殻重合体の弾性率が１０⁶Ｎ/ｍ²以上かつ１０⁹Ｎ/ｍ²以下のものであると、高温かつ高剪断化での耐性に優れる。外殻重合体の弾性率は、より好ましくは５．０×１０⁶Ｎ/ｍ²以上かつ１０⁹Ｎ/ｍ²以下、特に好ましくは１０⁷Ｎ/ｍ²以上かつ１０⁸Ｎ/ｍ²以下である。
【００７８】
３．用途
本発明の熱発泡性マイクロスフェアーは、加熱発泡（熱膨脹）させて、あるいは未発泡のままで、各種分野に使用される。熱発泡性マイクロスフェアーは、例えば、その膨脹性を利用して、自動車等の塗料の充填剤、壁紙、発泡インク（Ｔ−シャツ等のレリーフ模様付け）の発泡剤、収縮防止剤などに使用される。熱発泡性マイクロスフェアーは、発泡による体積増加を利用して、プラスチック、塗料、各種資材などの軽量化や多孔質化、各種機能性付与（例えば、スリップ性、断熱性、クッション性、遮音性等）の目的で使用される。本発明の熱発泡性マイクロスフェアーは、表面性や平滑性が要求される塗料、壁紙、インク分野に好適に用いることができる。本発明の熱発泡性マイクロスフェアーは、加工特性に優れているので、混練加工、カレンダー加工、押出加工、射出成形などの加工工程を必要とする用途分野に好適に適用することができる。
【００７９】
【実施例】
以下、実施例及び比較例を挙げて、本発明についてより具体的に説明する。
物性及び特性の測定方法は、次の通りである。
（１）発泡倍率及び最大発泡倍率
熱発泡性マイクロスフェアー０．７ｇを、ギア式オーブン中に入れ、所定温度（発泡温度）で２分間加熱して発泡させる。得られた発泡体をメスシリンダーに入れて体積を測定し、未発泡時の体積で割って発泡倍率とする。この際、発泡倍率を１００℃から５℃刻みで昇温して測定し、最大の発泡倍率が得られた時の発泡温度での当該発泡倍率を最大発泡倍率と定義する。
【００８０】
（２）平均粒径
島津製作所製の粒径分布測定器ＳＡＬＤ−３０００Ｊを用いて、重量基準でのメディアン径を測定し、平均粒径とした。
（３）弾性率
熱発泡性マイクロスフェアーを発泡させ、内包された発泡剤をできるだけ抜いた後、熱プレス機で熱プレスシートを調製し、１ｃｍ×１．５ｃｍ×０．２５ｃｍの試験片に切り出した。この試験片を東洋精機製作所のレオグラフ・ソリッドを用いて、窒素雰囲気下、周波数１０ヘルツ、３℃／分の昇温速度で加熱して、弾性率を測定した。
【００８１】
（４）バインダー系での発泡倍率
エチレン・酢酸ビニル共重合体（ＥＶＡ；エチレン／酢酸ビニル＝３０／７０重量％）を含有するＥＶＡ系エマルジョン（濃度５５重量％）に、ＥＶＡ５重量部に対して、熱発泡性マイクロスフェアー１重量部を加えて塗布液を調製する。この塗布液を両面アート紙に２００μｍのギャップを有するコーターで塗布、乾燥し、次いで、所定温度のオーブンに入れて２分間加熱する。発泡前後の厚み比でもって、発泡倍率とする。
（５）耐薬品性
ガラス製試験管に、可塑剤としてフタル酸ジイソノリル２重量部と熱発泡性マイクロスフェアー１重量部を加えて可塑剤液を調製する。この可塑剤液を、オイルバスを用いて１４０℃で加熱し、経時による発泡の有無と可塑剤液の増粘の程度を観察する。
【００８２】
（６）可塑化ＰＶＣシートでの発泡倍率
ポリ塩化ビニル樹脂（呉羽化学工業製Ｓ９０３）５０重量部とジオクチルフタレート（ＤＯＰ）５０重量部に対して、熱発泡性マイクロスフェアー３重量部を加えて、コンパウンドを調製する。コンパウンドを１２０℃で２分間ロール練りして、１ｍｍ厚さのシートを作成する。このシートを３×４ｃｍ角の大きさに裁断して試料とし、この試料を２００℃のオーブン中で、５分間及び１０分間、それぞれ発泡させる。発泡前後の比重を測定して、発泡倍率（％）を算出する。
（７）ＴＭＡ（Thermo Mechnical Analysis）
パーキンエルマー社製のＴＭＡ-７型を用いてＴＭＡ測定を行った。サンプル約０．２５ｍｇを使用した。昇温速度は、５℃／分及び２０℃／分とした。
【００８３】
［比較例１］
固形分２０％のコロイダルシリカ８０．５ｇ、ジエタノールアミン−アジピン酸縮合物５０％水溶液３．０ｇ、塩化ナトリウム１６４．１ｇ、重クロム酸カリ２．５％水溶液２．２ｇ、塩酸０．１ｇ、及び脱イオン水からなる合計４７０ｇの水系分散媒体を調製した。
【００８４】
一方、アクリロニトリル１４１．７ｇ、メタクリロニトリル６７．１ｇ、メタクリル酸メチル１１．２ｇ、三官能架橋性単量体のトリメタクリル酸トリメチロールプロパン０．６７ｇ、ｎ−ペンタン２６．１ｇ、石油エーテル１４．９ｇ、及びアゾビスイソブチロニトリル１．１ｇからなる重合性混合物を調製した（単量体成分の重量％＝アクリロニトリル／メタクリロニトリル／メタクリル酸メチル＝６４．４／３０．５／５．１；架橋性単量体使用量＝単量体成分の０．３重量％）。
【００８５】
この重合性混合物と水系分散媒体とを、図４に示す回分式高速回転高剪断型分散機で攪拌混合して重合性混合物の微小な液滴を造粒した。この重合性混合物の微小な液滴を含有する水系分散媒体を、攪拌機付きの重合缶（１．５Ｌ）に仕込み、温水バスを用いて６０℃で２０時間反応させた。得られた反応生成物を遠心分離機を用いる濾過と水洗に繰り返し付してケーキ状物とし、これを一昼夜乾燥して、平均粒径が約２５μｍ、粒径分布の変動係数が１．７％である熱発泡性マイクロスフェアー（ＭＳ−Ａ）を得た。ＭＳ−Ａの１７０℃での発泡倍率（最大発泡倍率）は、約５０倍であった。結果を表１に示す。この比較例１は、特公平５−１５４９９号公報の実施例２に準じたものである。
【００８６】
［実施例１］
三官能架橋性単量体のトリメタクリル酸トリメチロールプロパン０．６７ｇに代えて、二官能架橋性単量体のジエチレングリコールジメタクリレート３．５ｇ（架橋性単量体使用量＝単量体成分の１．６重量％）を用いたこと以外は、比較例１と同様にして、平均粒径が約２６μｍ、粒径分布の変動係数が１．７％である熱発泡性マイクロスフェアー（ＭＳ−１）を得た。ＭＳ−１の１７０℃での発泡倍率（最大発泡倍率）は、約５０倍であった。結果を表１に示す。
【００８７】
［比較例２］
三官能架橋性単量体のトリメタクリル酸トリメチロールプロパンの使用量０．６７ｇを３．５ｇにしたこと以外は比較例１と同様にして、平均粒径が約２６μｍの熱発泡性マイクロスフェアー（ＭＳ−Ｂ）を得た。ＭＳ−Ｂは、その外殻層を形成する樹脂成分が熱可塑性樹脂としての特性を大幅に失ったため、１４０℃以上のどの温度域でもほとんど発泡しなかった。結果を表１に示す。
【００８８】
【表１】

【００８９】
（脚注）
(*1)熱発泡性マイクロスフェアー含有ＥＶＡ系エマルジョン塗布層の発泡前後の厚み比。
(*2)可塑剤液＝フタル酸ジイソノニル２部／熱発泡性マイクロスフェアー１部
【００９０】
（考察）
実施例１のＭＳ−１は、架橋性単量体の使用量が単量体成分の１重量％を超過しているにかかわらず、最大発泡倍率（発泡温度１７０℃）が５０倍と良好である。これに対して、三官能架橋性単量体を単量体成分の１．６重量％の割合で用いたＭＳ−Ｂ（比較例２）は、外殻層を形成する重合体が高度に架橋して、熱発泡性を実質的に喪失している。
【００９１】
ＥＶＡ系エマルジョン中での発泡挙動では、実施例１のＭＳ−１は、架橋性単量体の使用量を比較例１のＭＳ−Ａに比べて、重量で５．２倍（モル数で５．２倍）と多くしたにもかかわらず、最大発泡倍率が得られた１７０℃での発泡倍率が５．５倍であり、ＭＳ−Ａと同じ高発泡倍率を保持している。しかも、さらに高温の１９０℃でのＭＳ−１の発泡倍率は４．３倍であり、ＭＳ−Ａの３．７倍に比べて発泡倍率の低下が少なく、耐熱性に優れていることが分かる。
【００９２】
１４０℃での外殻重合体の弾性率を比較すると、実施例１のＭＳ−１は、代表的な従来技術の熱発泡性マイクロスフェアーである比較例１のＭＳ−Ａに比べて、１．４倍の弾性率を有している。すなわち、本発明の熱発泡性マイクロスフェアーは、より高い剪断力に対する耐性があり、かつ、耐熱性に優れていることが分かる。さらに高温の１９０℃で比較すると、実施例１のＭＳ−１は、比較例１のＭＳ−Ａに比べて、外殻重合体の弾性率が１．６倍である。このことは、本発明の熱発泡性マイクロスフェアーが、粒子の収縮が起こり難く、高発泡倍率を保持できること、並びに、加工適性温度域を従来に比べ広く取れることを意味している。
【００９３】
耐薬品性の評価では、比較例１のＭＳ−Ａを含有する可塑剤液は、１４０℃で６分加熱後に一部発泡が起こり、著しく増粘した。これに対して、実施例１のＭＳ−１の場合は、１４０℃で６分加熱後に部分発泡は認められず、さらに７分経過しても部分発泡しなかった。
【００９４】
［比較例３］
コロイダルシリカ１２ｇ、ジエタノールアミン−アジピン酸縮合物１．４ｇ、塩化ナトリウム１５４ｇ、亜硝酸ナトリウム０．１２ｇ、塩酸０．２ｇ、及び脱イオン水からなる合計５２０ｇの水系分散媒体を調製した。
【００９５】
一方、アクリロニトリル１３０ｇ、メタクリロニトリル６０ｇ、イソボニルメタクリレート１０ｇ、三官能架橋性単量体のトリメタクリル酸トリメチロールプロパン１ｇ、ｎ−ペンタン３８ｇ、及びアゾビスイソブチロニトリル１．２ｇからなる重合性混合物を調製した（単量体成分の重量％＝アクリロニトリル／メタクリロニトリル／イソボニルメタクリレート＝６５／３０／５、架橋性単量体使用量＝単量体成分の０．５重量％）。この重合性混合物と水系分散媒体とを、図４に示す回分式高速回転高剪断型分散機で攪拌混合して重合性混合物の微小な液滴を造粒した。
【００９６】
この重合性混合物の微小な液滴を含有する水系分散媒体を、攪拌機付きの重合缶（１．５Ｌ）に仕込み、温水バスを用いて６０℃で２２時間反応させた。得られた反応生成物を遠心分離機を用いる濾過と水洗に繰り返し付してケーキ状物とし、このケーキ状物を一昼夜乾燥して、平均粒径が約２８μｍ、粒径分布の変動係数が１．８％である熱発泡性マイクロスフェアー（ＭＳ−Ｃ）を得た。ＭＳ−Ｃの１７０℃での発泡倍率（最大発泡倍率）は、約５５倍であった。この比較例３は、特開平５−２８５３７６号公報の実施例２に準じたものである。結果を表２に示す。
【００９７】
［実施例２］
三官能架橋性単量体のトリメタクリル酸トリメチロールプロパン１ｇに代えて、二官能架橋性単量体のジエチレングリコールジメタクリレート３．５ｇ（架橋性単量体使用量＝単量体成分の１．６重量％）を用いたこと以外は、比較例３と同様にして、平均粒径が約３０μｍ、粒径分布の変動係数が１．６％である熱発泡性マイクロスフェアー（ＭＳ−２）を得た。このＭＳ−２の１７０℃での発泡倍率（最大発泡倍率）は、約５５倍であった。結果を表２に示す。
【００９８】
【表２】

【００９９】
（考察）
外殻重合体の弾性率を比較すると、実施例２のＭＳ−２は、測定温度が１９４℃の場合、代表的な従来技術の熱発泡性マイクロスフェアーである比較例３のＭＳ−Ｃと同じであった。しかし、高温の２１０℃の測定温度で比較すると、ＭＳ−２の外殻重合体の弾性率は、ＭＳ−Ａの２．６倍である。また、実施例２のＭＳ−２は、１９４℃から２１０℃の温度域での外殻重合体の弾性率の低下が極めて小さい。このことは、本発明の熱発泡性マイクロスフェアーが、高温度域において粒子の収縮が起こり難く、高発泡倍率を保持できること、並びに、加工温度域を従来に比べ広く取れることを意味する。別な見方をすれば、より高い剪断力に対する耐性があり、耐熱性があることをも意味している。
【０１００】
［実施例３］
攪拌機付の重合缶（１．５Ｌ）にコロイダルシリカ１６．５ｇ、ジエタノールアミン−アジピン酸縮合生成物 １．６ｇ、食塩１６９．８ｇ、亜硝酸ナトリウム０．１１ｇ、及び水を合計で５５７ｇになるように仕込み、水系分散媒体を調製した。水系分散体のｐＨが３．２になるように、塩酸を添加して調整した。
【０１０１】
一方、アクリロニトリル１４７．４ｇ、メタクリロニトリル７０．４ｇ、メタクリル酸メチル２．２ｇ、ジエチレングリコールジメタクリレート３．５ｇ、イソペンタン４１．８ｇ、及びアゾビスイソブチロニトリル１．３２ｇからなる重合性混合物を調製した（単量体成分の重量％＝アクリロニトリル／メタクリロニトリル／メタクリル酸メチル＝６７／３２／１、架橋性単量体使用量＝単量体成分の１．６重量％）。この重合性混合物と前記で調製した水系分散媒体とを、図４に示す回分式高速回転高剪断型分散機で攪拌混合して、重合性混合物の微小な液滴を造粒した。
【０１０２】
この重合性混合物の微小な液滴を含有する水系分散媒体を、攪拌機付きの重合缶（１．５Ｌ）に仕込み、温水バスを用いて６０℃で４５時間反応させた。得られた反応生成物を濾過と水洗を繰り返し、平均粒径が約３０μｍ、粒径分布の変動係数が１．８％である熱発泡性マイクロスフェアー（ＭＳ−３）を得た。ＭＳ−３の１７０℃での発泡倍率（最大発泡倍率）は、約５０倍であった。結果を表３に示す。
【０１０３】
［実施例４］
単量体成分の仕込み重量比を、アクリロニトリル／メタクリロニトリル＝７０／３０になるように、単量体の仕込み量を変えたこと以外は、実施例３と同様にして、平均粒径が約３０μｍ、粒径分布の変動係数が２．１％である熱発泡性マイクロスフェアー（ＭＳ−４）を得た。このＭＳ−４の１７０℃での発泡倍率（最大発泡倍率）は、約５０倍であった。結果を表３に示す。
【０１０４】
［比較例４］
二官能架橋性単量体のジエチレングリコールジメタクリレート３．５ｇに代えて、三官能架橋性単量体のトリメタクリル酸トリメチロールプロパン０．６ｇ（架橋性単量体使用量＝単量体成分の０．３重量％）を用いたこと以外は、実施例３と同様にして、平均粒径が約３０μｍ、粒径分布の変動係数が１．６％である熱発泡性マイクロスフェアー（ＭＳ−Ｄ）を得た。このＭＳ−Ｄの１７０℃での発泡倍率（最大発泡倍率）は、約５０倍であった。結果を表３に示す。
【０１０５】
［比較例５］
二官能架橋性単量体のジエチレングリコールジメタクリレート３．５ｇに代えて、三官能架橋性単量体のトリメタクリル酸トリメチロールプロパン０．６ｇ（架橋性単量体使用量＝単量体成分の０．３重量％）を用いたこと以外は、実施例４と同様にして、平均粒径が約３０μｍ、粒径分布の変動係数が１．９％である熱発泡性マイクロスフェアー（ＭＳ−Ｅ）を得た。このＭＳ−Ｅの１７０℃での発泡倍率（最大発泡倍率）は、約５０倍であった。結果を表３に示す。
【０１０６】
【表３】

【０１０７】
（脚注）
(*1)ＰＶＣ５０部／ＤＯＰ５０部／熱発泡性マイクロスフェアー３部からなる混合物１００ｇを１２０℃の回転ロールにて２分間混練して調製した１ｍｍ厚のシート
(*2)３×４ｃｍ角のシートを２００℃のオーブン中で発泡させ、発泡前後の比重の測定値から発泡倍率（％）を算出した。
【０１０８】
（考察）
実施例３及び４の熱発泡性マイクロスフェアー（ＭＳ−３及びＭＳ−４）を含有する各可塑化ＰＶＣシートは、それぞれ２００℃／５分後に高度の発泡倍率を示し、２００℃／１０分後にも高い発泡倍率を維持している。これに対して、比較例４及び５の熱発泡性マイクロスフェアー（ＭＳ−Ｄ及びＭＳ−Ｅ）を含有する各可塑化ＰＶＣシートは、１２０℃での発泡が著しく、２００℃／５分後の発泡倍率が小さく、さらには、２００℃／１０分後の発泡倍率が著しく低下して、いわゆるヘタリ現象が観察された。
【０１０９】
［比較例６］
コロイダルシリカ５ｇ、ジエタノールアミン−アジピン酸縮合生成物０．５ｇ、亜硝酸ナトリウム０．１２ｇ、及び水が合計で６００ｇになるように計量し、水系分散媒体を調製した。水系分散媒体のｐＨが３．２になるように、塩酸を添加して調整した。
【０１１０】
一方、アクリロニトリル１２０ｇ、メタクリル酸メチル１２０ｇ、三官能架橋性単量体のトリメタクリル酸トリメチロールプロパン０．４ｇ、イソペンタン７０ｇ、及び２，２′−アゾビス（２，４−ジメチルバレロニトリル）１．２ｇからなる重合性混合物を調製した（単量体成分の重量％＝アクリロニトリル／メタクリル酸メチル＝５０／５０、架橋性単量体使用量＝単量体成分の０．２重量％）。この重合性混合物と水系分散媒体とを、図４に示す回分式高速回転高剪断型分散機で攪拌混合して重合性混合物の微小な液滴を調製した。
【０１１１】
この重合性混合物の微小な液滴を含有する水系分散媒体を、攪拌機付きの重合缶（１．５Ｌ）に仕込み、温水バスを用いて５３℃で２２時間反応させた。得られたｐＨ６．３の反応生成物を濾過・水洗し、これを繰り返した後、乾燥して、平均粒径が１４μｍ、粒径分布の変動係数が１．６％である熱発泡性マイクロスフェアー（ＭＳ−Ｆ）を得た。ＭＳ−Ｆの１４５℃での発泡倍率（最大発泡倍率）は、約１８倍であり、１５０℃での発泡倍率は、約１２倍であった。結果を表４に示す。
【０１１２】
［実施例５］
三官能架橋性単量体のトリメタクリル酸トリメチロールプロパン０．４ｇの代わりに、二官能架橋性単量体のジエチレングリコールジメタクリレート３．２ｇ（架橋性単量体使用量＝単量体成分の１．６重量％）を用いたこと以外は、比較例６と同様にして平均粒径が約１５μｍ、粒径分布の変動係数が１．７％である熱発泡性マイクロスフェアー（ＭＳ−５）を得た。このＭＳ−５の１４５℃での発泡倍率（最大発泡倍率）は、約４０倍であり、１５０℃に発泡温度を上げても約４０倍の最大発泡倍率を維持していた。結果を表４に示す。
【０１１３】
【表４】

【０１１４】
［比較例７］
コロイダルシリカ８．８ｇ、ジエタノールアミン−アジピン酸縮合生成物０．８ｇ、亜硝酸ナトリウム０．１３ｇ、及び水が合計で５２８ｇになるように計量し、水系分散媒体を調製した。
【０１１５】
一方、塩化ビニリデン１４３ｇ、アクリロニトリル６６ｇ、メタクリル酸メチル１１ｇ、トリメタクリル酸トリメチロールプロパン０．３３ｇ、イソプロピルパーオキシジカーボネート２．２ｇ、及びイソブタン３５．２ｇからなる重合性混合物を調製した（単量体成分の重量％＝塩化ビニリデン／アクリロニトリル／メタクリル酸メチル＝６５／３０／５、架橋性単量体使用量＝単量体成分の０．１５重量％）。次いで、この重合性混合物と上記で調製した水系分散媒体とを、図４に示す回分式高速回転高剪断型分散機で攪拌混合して、重合性混合物の微小な液滴を造粒した後、重合缶に仕込み、５０℃で２２時間反応させた。得られた反応生成物を濾過と水洗を繰り返し、平均粒径が約１５μｍ、粒径分布の変動係数が１．６％である熱発泡性マイクロスフェアー（ＭＳ−Ｇ）を得た。このＭＳ−Ｇは、１２０℃での発泡倍率（最大発泡倍率）が約５０倍であったが、発泡温度を１３０℃に上げると、発泡倍率が約１８倍に著しく低下した。結果を表５に示す。
【０１１６】
［実施例６］
三官能架橋性単量体のトリメタクリル酸トリメチロールプロパン０．３３ｇの代わりに、二官能架橋性単量体のジエチレングリコールジメタクリレート３．５ｇ（架橋性単量体使用量＝単量体成分の１．６重量％）を用いたこと以外は、比較例７と同様にして平均粒径が約１５μｍ、粒径分布の変動係数が１．７％である熱発泡性マイクロスフェアーＭＳ−６を得た。このＭＳ−６の１２０℃での発泡倍率（最大発泡倍率）は、約５０倍であり、発泡温度を１３０℃に上げても、約３５倍の高い発泡倍率を示した。結果を表５に示す。
【０１１７】
【表５】

【０１１８】
［実施例７］
三官能架橋性単量体のトリメタクリル酸トリメチロールプロパン０．６７ｇに代えて、二官能架橋性単量体のジエチレングリコールジメタクリレート３．５ｇ（架橋性単量体使用量＝単量体成分の１．６重量％）を用い、この重合性混合物と水系分散媒体とを攪拌混合する際に、図２に示すように、水系分散媒体と重合性混合物をそれぞれ別の槽に保持し、そして、これらをある一定の比率で連続的に連続式高速回転高剪断型攪拌分散機を通過させた後、懸濁重合を行うこと以外は、比較例１と同様にして、平均粒径が約２５μｍ、粒径分布の変動係数が０．３％である熱発泡性マイクロスフェアー（ＭＳ−７）を得た。ＭＳ−７の１７０℃での発泡倍率（最大発泡倍率）は、約５０倍であった。このＭＳ−７を含有する可塑剤液は、１４０℃で８分間保持しても部分発泡しなかった。一方、実施例１のＭＳ−１の場合は、８分間を過ぎるとやや部分発泡が認められ始めた。これは、架橋性単量体の種類と使用量の効果に加えて、ＭＳ−７の粒径分布がＭＳ−１に比べてシャープであることに起因する。
【０１１９】
［実施例８］
重合性混合物と水系分散媒体とを攪拌混合する際に、図２に示すように、水系分散媒体と重合性混合物をそれぞれ別の槽に保持し、そして、これらをある一定の比率で連続的に連続式高速回転高剪断型分散機を通過させた後、懸濁重合を行うこと以外は、実施例３と同様にして、平均粒径が約３０μｍ、粒径分布の変動係数が０．３％である粒径分布のシャープな熱発泡性マイクロスフェアー（ＭＳ−８）を得た。ＭＳ−８の１７０℃での発泡倍率（最大発泡倍率）は、約５０倍であった。
【０１２０】
実施例３のＭＳ−３を含有する可塑化ＰＶＣシート（表３参照）は、１２０℃の回転ロールにて２分間混練して調製した１ｍｍ厚のシートの厚みが、ＭＳ−３を含有しない可塑化ＰＶＣシートに比べ１０％程度厚みが増加した。これに対して、ＭＳ−８を含有する可塑化ＰＶＣシートは、１２０℃の回転ロールにて２分間混練して調製した１ｍｍ厚のシートの厚みが、ＭＳ−８を含有しない可塑化ＰＶＣシートに比べ殆ど厚み変化がなかった。つまり、ＭＳ−８は、ロール混練時の部分発泡特性に優れる（部分発泡しにくい）と言える。
【０１２１】
［実施例９］
重合性混合物と水系分散媒体とを攪拌混合する際に、図２に示すように、水系分散媒体と重合性混合物をそれぞれ別の槽に保持し、そして、これらをある一定の比率で連続的に連続式高速回転高剪断型分散機を通過させた後、懸濁重合を行うこと以外は、実施例５と同様にして、平均粒径が約１５μｍ、粒径分布の変動係数が０．５％である粒径分布のシャープな熱発泡性マイクロスフェアー（ＭＳ−９）を得た。ＭＳ−９の１４５℃での発泡倍率（最大発泡倍率）は、約４０倍であり、１５０℃に発泡温度を上げても、約４０倍の最大発泡倍率を維持していた。
【０１２２】
このＭＳ−９とＭＳ−５（実施例５）をそれぞれバインダー系での発泡倍率の測定方法に従い、両面アート紙に塗布した。これらのウエット塗布紙を乾燥機にて１℃／分の昇温速度で乾燥したところ、ＭＳ−５は、ＭＳ−９より低い温度で発泡してしまった。このことは、ＭＳ−９のような粒径分布のシャープな熱発泡性マイクロスフェアーを使用すると、加工速度がアップできる（高温で短時間で乾燥できる）ことを意味する。
【０１２３】
［実施例１０］
重合性混合物と水系分散媒体とを攪拌混合する際に、図２に示すように、水系分散媒体と重合性混合物をそれぞれ別の槽に保持し、そして、これらをある一定の比率で連続的に連続式高速回転高剪断型分散機を通過させた後、懸濁重合を行うこと以外は、実施例６と同様にして、平均粒径が約１５μｍ、粒径分布の変動係数が０．２％である粒径分布のシャープな熱発泡性マイクロスフェアー（ＭＳ−１０）を得た。ＭＳ−１０の１２０℃での発泡倍率（最大発泡倍率）は、約５０倍であり、１３０℃に発泡温度を上げても、約３５倍の最大発泡倍率を維持していた。ホットステージ付き顕微鏡で５℃／分の速度で昇温しながら、その発泡挙動を観察したところ、ＭＳ−１０は、実施例６のＭＳ−６に比べて発泡する温度が高かった。したがって、ＭＳ−１０は、発泡がシャープに起きていると判断される。
【０１２４】
［実施例１１］
イソペンタン４１．８ｇに代えて、発泡剤としてイソペンタン／２，２，４-トリメチルペンタン（重量比＝２０／１０）６６ｇを用いたこと以外は、実施例８と同様にして、平均粒径が約３０μｍ、粒径分布の変動係数が０．５％である熱発泡性マイクロスフェアー（ＭＳ−１１）を得た。ＭＳ−１１の１８０℃での発泡倍率は、約４０倍であった。
【０１２５】
ＭＳ−１１を含有する可塑化ＰＶＣシートは、１２０℃の回転ロールにて２分間混練して調製した１ｍｍ厚のシートの厚みが、ＭＳ−１１を含有しない可塑化ＰＶＣシートに比べ殆ど厚み変化がなかった。つまり、ＭＳ−１１は、ロール混練時の部分発泡特性に優れる（部分発泡しにくい）と言える。
【０１２６】
［実施例１２］
イソペンタン４１．８ｇに代えて、発泡剤としてイソペンタン／２，２，４-トリメチルペンタン（重量比＝１５／１５）６６ｇを用いたこと以外は、実施例８と同様にして、平均粒径が約３１μｍ、粒径分布の変動係数が０．４％である熱発泡性マイクロスフェアー（ＭＳ−１２）を得た。
【０１２７】
ＭＳ−１２を含有する可塑化ＰＶＣシートは、１２０℃の回転ロールにて２分間混練して調製した１ｍｍ厚のシートの厚みが、ＭＳ−１２を含有しない可塑化ＰＶＣシートに比べ殆ど厚み変化がなかった。つまり、ＭＳ−１２は、ロール混練時の部分発泡特性に優れる（部分発泡しにくい）と言える。
【０１２８】
［実施例１３］
イソペンタン４１．８ｇに代えて、発泡剤としてイソペンタン／２，２，４-トリメチルペンタン（重量比＝１０／２０）６６ｇを用いたこと以外は、実施例８と同様にして、平均粒径が約３０μｍ、粒径分布の変動係数が０．３％である熱発泡性マイクロスフェアー（ＭＳ−１３）を得た。
【０１２９】
ＭＳ−１３を含有する可塑化ＰＶＣシートは、１２０℃の回転ロールにて２分間混練して調製した１ｍｍ厚のシートの厚みが、ＭＳ−１３を含有しない可塑化ＰＶＣシートに比べ殆ど厚み変化がなかった。つまり、ＭＳ−１３は、ロール混練時の部分発泡特性に優れる（部分発泡しにくい）と言える。
【０１３０】
［実施例１４］
イソペンタン４１．８ｇに代えて、発泡剤としてイソペンタン／２，２，４-トリメチルペンタン（重量比＝６／２４）６６ｇを用いたこと以外は、実施例８と同様にして、平均粒径が約３０μｍ、粒径分布の変動係数が０．５％である熱発泡性マイクロスフェアー（ＭＳ−１４）を得た。
【０１３１】
［実施例１５］
イソペンタン４１．８ｇに代えて、発泡剤として２，２，４-トリメチルペンタン６６ｇを用いたこと以外は、実施例３と同様にして、平均粒径が約２９μｍ、粒径分布の変動係数が０．２％である熱発泡性マイクロスフェアー（ＭＳ−１５）を得た。
【０１３２】
［実施例１６］
イソペンタン４１．８ｇに代えて、発泡剤としてヘプタン６６ｇを用いたこと以外は、実施例３と同様にして、平均粒径が約３２μｍ、粒径分布の変動係数が０．３％である熱発泡性マイクロスフェアー（ＭＳ−１６）を得た。
【０１３３】
［実施例１７］
上記の実施例で調製したサンプルＭＳ−３、ＭＳ−１１〜ＭＳ−１５についてＴＭＡ測定を行った。結果を表６に示す。
【０１３４】
【表６】

(*)膨張による変位量の相対比較
【０１３５】
［実施例１８］
比較例４で調製したＭＳ−Ｄ、及び実施例１４〜１６で調製したＭＳ−１４〜１６を、水９９ｇにそれぞれ１ｇ分散した後、１００℃で１０分間煮沸した。水面に発泡した粒子が浮いているかを観察し、その結果を表７に示す。
【０１３６】
【表７】

【０１３７】
【発明の効果】
本発明によれば、強い剪断力が加えられる混練加工、カレンダー加工、押出加工、射出成形などの加工に適した熱発泡性マイクロスフェアーとその製造方法が提供される。また、本発明によれば、重合体から形成された外殻の弾性率の温度依存性が小さい熱発泡性マイクロスフェアーとその製造方法が提供される。本発明の熱発泡性マイクロスフェアーは、加工の適性温度域が広く、耐薬品性や耐溶剤性と発泡特性の保持能力が高い。さらに、本発明によれば、前記諸特性を有することに加えて、粒径分布の変動係数が極めて小さく、発泡がシャープな熱発泡性マイクロスフェアーが提供される。
【図面の簡単な説明】
【図１】図１は、熱発泡性マイクロスフェアーの外殻重合体の弾性率と測定温度との関係を示すグラフである。
【図２】図２は、連続式高速回転高剪断型分散機を用いた熱発泡性マイクロスフェアーの製造方法の一例を示す説明図である。
【図３】図３は、連続式高速回転高剪断型分散機を用いた熱発泡性マイクロスフェアーの製造方法の他の例を示す説明図である。
【図４】図４は、回分式高速回転高剪断型分散機を用いた熱発泡性マイクロスフェアーの製造方法の一例を示す説明図である。
【符号の説明】
１：水系分散媒体
２：単量体混合物
３：槽
４：槽
５：ポンプ
６：ライン
７：ポンプ
８：ライン
９：連続式高速回転高剪断型攪拌分散機
１０：ライン
１１：重合槽
１２：分散槽
１３：ポンプ
１４：ライン
１５：ライン
１６：回分式高速回転高剪断型分散機
１７：ポンプ
１８：ライン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat-foamable microsphere having a structure in which a foaming agent is enclosed in an outer shell formed of a polymer, and more particularly, a heat-foamable microsphere with significantly improved processing characteristics, and It relates to the manufacturing method.
[0002]
[Prior art]
Thermally foamable microspheres, also called thermally expandable microcapsules, are used in various fields such as paints and plastic fillers for weight reduction, including applications in foamed inks. ing. Thermally foamable microspheres are usually obtained by microencapsulating a volatile liquid foaming agent with a polymer. Such blowing agents are also called physical blowing agents or volatile swelling agents. If desired, a chemical foaming agent that decomposes when heated to generate gas may be used. Thermally foamable microspheres can generally be produced by a suspension polymerization method of a polymerizable mixture containing at least a foaming agent and a polymerizable monomer in an aqueous medium. As the polymerization reaction proceeds, an outer shell is formed by the produced polymer, and a thermally foamable microsphere having a structure in which a foaming agent is enclosed in the outer shell is obtained.
[0003]
As the polymer forming the outer shell, a thermoplastic resin having a good gas barrier property is generally used. The polymer forming the outer shell softens when heated. As the foaming agent, one that is gaseous at a temperature below the softening point of the polymer is selected. When the heat-foamable microsphere is heated, the foaming agent vaporizes and expands and acts on the outer shell, but at the same time, the elastic modulus of the polymer forming the outer shell rapidly decreases. Therefore, sudden expansion occurs at a certain temperature. This temperature is called the foaming temperature. That is, when the thermally foamable microsphere is heated to the foaming temperature, it expands itself to form closed cells (foam particles).
[0004]
Thermally expandable microspheres have been developed for use in a wide range of fields as a designability-imparting agent, a functionality-imparting agent, a weight-reducing agent, and the like by utilizing the property of forming closed cells. In addition, as higher performance is required in each application field, the required level for thermally foamable microspheres is also increasing. Improvement in processing characteristics is an example of the required performance for thermally foamable microspheres.
[0005]
For example, a composition in which a thermoplastic foam is blended with a thermoplastic resin is kneaded, calendered, extruded, or injection molded, and the thermally foamable microsphere is foamed in the process to reduce the weight. There is a method for obtaining a molded article or sheet having a design or design. However, in the case of thermally foamable microspheres, the polymer layer of the outer shell becomes very thin as the volume expands during foaming, and the elasticity of the polymer that forms the outer shell due to high temperature and high shearing force due to processing. Since the rate suddenly drops and the outer shell becomes soft, the heat-foamable microspheres were easily destroyed and it was extremely difficult to achieve the intended purpose.
[0006]
In addition, the heat-foamable microsphere has a problem that an appropriate temperature range for processing is very narrow because the temperature dependence of the elastic modulus of the polymer forming the outer shell is large. Furthermore, conventional heat-foamable microspheres have poor resistance (solvent resistance, chemical resistance) to polar solvents and plasticizers, and for example, their use in fields commonly used with polar organic solvents has been limited.
[0007]
Japanese Patent Application Laid-Open No. 11-60868 discloses a soft vinyl chloride resin composition for foam extrusion molding in which a thermally expandable microcapsule is blended with a vinyl chloride resin containing a plasticizer. In JP-A-2000-17103, as a first step, a resin composition containing a thermoplastic resin having a melting point or a softening point of 100 ° C. or less and a thermally expandable microcapsule that expands at 100 to 200 ° C. A method for producing a resin composition is disclosed in which the obtained resin composition is added to a thermoplastic resin and kneaded or molded as a second step.
[0008]
However, in fact, in order for the thermally foamable microspheres to be applicable to such foam extrusion molding and kneading / molding, in addition to having an outer shell having a high foaming temperature and excellent heat resistance, The temperature dependence of the elastic modulus of the polymer forming the outer shell is small, the appropriate temperature range for processing is large, and the resistance to polar solvents and plasticizers is excellent.
[0009]
Conventionally, as a method for producing heat-foamable microspheres having high heat resistance, a polymer layer of an outer shell is obtained by adding a crosslinkable monomer to a polymerizable monomer composed of a vinyl monomer and polymerizing it. Have been proposed (Japanese Patent Publication No. 42-26524, Japanese Patent Publication No. 5-15499, Japanese Patent No. 2894990, Japanese Patent Application Laid-Open No. 5-285376). By using a crosslinkable monomer, a crosslinked structure is introduced into the polymer forming the outer shell, thereby improving the heat resistance and melt fluidity of the thermally foamable microsphere.
[0010]
However, when the degree of crosslinking of the polymer forming the outer shell is increased, the thermal expansion of the thermally foamable microspheres is impaired. Therefore, in each of the examples of these prior art documents, the crosslinking agent is used as a polymerizable monomer. It is only used in a very small proportion of 1% by weight or less, preferably 0.2 to 0.6% by weight. However, if the proportion of the crosslinking agent used is small, it is not possible to obtain thermally foamable microspheres with sufficiently improved processing characteristics. Moreover, since the outer shell formed from the conventional crosslinked polymer has a large temperature dependence of the elastic modulus, the appropriate temperature range for processing is very narrow and the processing characteristics are inferior. Furthermore, the outer shell formed from a conventional crosslinked polymer has insufficient resistance to polar solvents and plasticizers. In addition, since the outer shell formed from the conventional crosslinked polymer is actually limited to a polymer having a specific composition, the thermally foamable microsphere having excellent compatibility with the thermoplastic resin to be used. It was difficult to design.
[0011]
[Problems to be solved by the invention]
An object of the present invention is to provide a thermally foamable microsphere suitable for processing such as kneading processing, calendering processing, extrusion processing, injection molding and the like to which a strong shearing force is applied, and a method for producing the same.
[0012]
In particular, an object of the present invention is to provide a thermally foamable microsphere having a small temperature dependence of the elastic modulus of an outer shell formed from a polymer and having a wide processing temperature range and a method for producing the same.
[0013]
Another object of the present invention is to provide a heat-foamable microsphere having high resistance (chemical resistance, solvent resistance) and foaming property retention ability to polar solvents and plasticizers, and a method for producing the same. It is in.
[0014]
As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the outer shell of the thermally foamable microspheres exceeds 1% by weight based on the polymerizable monomer and the polymerizable monomer. Surprisingly, by forming a polymer obtained by polymerizing a crosslinkable monomer in a proportion of less than% by weight, the thermal foaming property has been remarkably improved without sacrificing the thermal expansibility. I found out that microspheres can be obtained. As the crosslinkable monomer, a bifunctional crosslinkable monomer is preferable, and a compound having a structure in which two polymerizable carbon-carbon double bonds are connected via a flexible chain is particularly preferable. The present invention has been completed based on these findings.
[0015]
[Means for Solving the Problems]
  According to the present invention, in a thermally foamable microsphere having a structure in which a foaming agent is enclosed in an outer shell formed of a polymer,
(1) The outer shell formed from the polymer has a ratio of more than 1% by weight and less than 5% by weight based on the polymerizable monomer and the polymerizable monomer.Bifunctional having two polymerizable carbon-carbon double bondsIt is formed from a polymer obtained by polymerizing a crosslinkable monomer, and
(2) Maximum expansion ratio is 5 times or more
A thermally foamable microsphere characterized by the above is provided.
[0016]
  Further, according to the present invention, the polymer is formed from the resulting polymer by suspension polymerization of a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, and a crosslinkable monomer in an aqueous dispersion medium. In a method for producing a foamable microsphere having a structure in which a foaming agent is enclosed in an outer shell, the proportion is more than 1% by weight and less than 5% by weight based on the polymerizable monomer.Bifunctional having two polymerizable carbon-carbon double bondsProvided is a method for producing a thermally foamable microsphere characterized by suspension polymerization of a polymerizable mixture containing a crosslinkable monomer to obtain a thermally foamable microsphere having a maximum foaming ratio of 5 times or more. Is done.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
1.Method for producing thermally foamable microspheres
  The thermally foamable microsphere of the present invention is obtained by suspension polymerization of a polymerizable mixture containing at least a foaming agent, a polymerizable monomer, and a crosslinkable monomer in an aqueous dispersion medium, and from the resulting polymer. In a method for producing a thermally foamable microsphere having a structure in which a foaming agent is enclosed in a formed outer shell, the proportion is more than 1% by weight and less than 5% by weight based on the polymerizable monomer.Bifunctional crosslinkable monomer having two polymerizable carbon-carbon double bondsCan be obtained by suspension polymerization of a polymerizable mixture containing. Type of polymerizable monomer,Crosslinkable monomerBy adjusting the type and ratio of use, it is possible to obtain a thermally foamable microsphere having a maximum expansion ratio of 5 times or more, preferably 10 times or more. In the present invention, the maximum expansion ratio means the expansion ratio at the expansion temperature at which the maximum expansion ratio of the thermally foamable microsphere is obtained. A method for measuring the maximum expansion ratio will be described later.
[0018]
(1) Foaming agent
The foaming agent used in the present invention is usually a substance that becomes gaseous at a temperature below the softening point of the polymer forming the outer shell. As such a foaming agent, a low-boiling organic solvent having a boiling point of usually 150 ° C. or lower, preferably 130 ° C. or lower, more preferably 120 ° C. or lower, particularly preferably 110 ° C. or lower is suitable.
[0019]
Specific examples of the blowing agent together with the boiling point are ethane (−89 ° C.), ethylene (−102.4 ° C.), propane (−42.1 ° C.), propene (−47.7 ° C.), n-butane (− 0.5 ° C), isobutane (-12 ° C), butene (-6.47 ° C), isobutene (-6.6 ° C), n-pentane (36 ° C), isopentane (27.85 ° C), neopentane (9 0.5 ° C), 2,2,4-trimethylpentane (99.25 ° C), n-hexane (69 ° C), isohexane (60.3 ° C), petroleum ether (27-67 ° C), heptane (98.4). C)), etc .; CCl_ThreeChlorofluorocarbons such as F (23.8 ° C.); tetraalkylsilanes such as tetramethylsilane (26.6 ° C.); These foaming agents can be used alone or in combination of two or more.
[0020]
In particular, when a heat-foamable microsphere that is not easily broken under high temperature and high shear conditions during processing is desired, for example, boiling point of n-hexane, isohexane, heptane, 2,2,4-trimethylpentane, etc. Is preferably foamed using a hydrocarbon foaming agent having a temperature of 60 ° C. or higher. Among these, it is particularly preferable to use a hydrocarbon-based blowing agent having a boiling point of 70 ° C. or higher, such as heptane and 2,2,4-trimethylpentane. The boiling point range of these foaming agents is preferably 60 to 130 ° C, more preferably 60 to 120 ° C, and particularly preferably 70 to 110 ° C.
[0021]
The hydrocarbon-based blowing agents having a boiling point of 60 ° C. or higher may be used alone, but when used in combination with a hydrocarbon-based blowing agent having a boiling point of less than 60 ° C., a higher expansion ratio can be obtained. . That is, when the same amount of foaming agent is used, the low-boiling point hydrocarbon-based foaming agent of less than 60 ° C. contributes to an increase in the expansion ratio because the number of moles increases, and the hydrocarbon-based foaming having a boiling point of 60 ° C. or more. The agent contributes to heat resistance and foaming characteristics at higher temperatures. The proportion of the hydrocarbon-based blowing agent having a boiling point of 60 ° C. or higher is preferably 10% by weight to 100% by weight, more preferably 15% by weight to 95% by weight, particularly preferably, based on the total weight of the foam. 20% by weight or more and 90% by weight or less.
[0022]
(2) Polymerizable monomer and polymer
Examples of polymerizable monomers include acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and dicyclopentenyl acrylate; methacrylic acid such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and isobornyl methacrylate. Esters; vinyl monomers such as acrylonitrile, methacrylonitrile, vinylidene chloride, vinyl chloride, styrene, vinyl acetate, α-methylstyrene, chloroprene, neoprene, butadiene and the like. These polymerizable monomers can be used alone or in combination of two or more.
[0023]
As the thermally foamable microspheres, those in which the polymer forming the outer shell is thermoplastic and has gas barrier properties are preferred. From these viewpoints, vinylidene chloride (co) polymer and (meth) acrylonitrile (co) polymer are preferable as the polymer forming the outer shell.
[0024]
As the vinylidene chloride (co) polymer, a (co) polymer obtained by using, as a polymerizable monomer, vinylidene chloride alone or a mixture of vinylidene chloride and a vinyl monomer copolymerizable therewith is used. Can be mentioned. Examples of the monomer copolymerizable with vinylidene chloride include acrylonitrile, methacrylonitrile, methacrylic acid ester, acrylic acid ester, styrene, and vinyl acetate.
[0025]
Such vinylidene chloride (co) polymers include, as polymerizable monomers, (A) 30-100% by weight of vinylidene chloride, and (B) acrylonitrile, methacrylonitrile, acrylic acid ester, methacrylic acid ester, styrene. And a (co) polymer obtained using 0 to 70% by weight of at least one monomer selected from the group consisting of vinyl acetate. If the copolymerization ratio of vinylidene chloride is less than 30% by weight, the gas barrier property of the outer shell is too low, which is not preferable.
[0026]
The vinylidene chloride (co) polymer has, as a polymerizable monomer, (A1) 40 to 80% by weight of vinylidene chloride, and (B1) at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile. A copolymer obtained by using 0 to 60% by weight of the polymer and 0 to 60% by weight of at least one monomer selected from the group consisting of (B2) acrylic acid ester and methacrylic acid ester is preferable. By setting it as such a copolymer, design of foaming temperature is easy and it is easy to achieve a high foaming ratio.
[0027]
When solvent resistance or foamability at high temperature is desired, it is preferable to form the outer shell with a (meth) acrylonitrile (co) polymer. The (meth) acrylonitrile (co) polymer is obtained by using (meth) acrylonitrile alone or (meth) acrylonitrile and a vinyl monomer copolymerizable therewith as the polymerizable monomer (co). A polymer can be mentioned. Examples of the vinyl monomer copolymerizable with (meth) acrylonitrile include vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate.
[0028]
As such (meth) acrylonitrile (co) polymer, as a polymerizable monomer, (C) at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile, 30 to 100% by weight, (D) A (co) polymer obtained using 0 to 70% by weight of at least one monomer selected from the group consisting of vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate is preferred. When the copolymerization ratio of (meth) acrylonitrile is less than 30% by weight, the solvent resistance and heat resistance are insufficient.
[0029]
(Meth) acrylonitrile (co) polymer has a high proportion of (meth) acrylonitrile and a high foaming temperature (co) polymer, a small proportion of (meth) acrylonitrile and a low foaming temperature (co) heavy Can be divided into coalescence. As the (co) polymer having a large use ratio of (meth) acrylonitrile, as a polymerizable monomer, at least one monomer selected from the group consisting of (C) acrylonitrile and methacrylonitrile is 80 to 100% by weight. (D) a (co) polymer obtained using 0 to 20% by weight of at least one monomer selected from the group consisting of vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate. Can be mentioned. On the other hand, the (co) polymer with a small proportion of (meth) acrylonitrile used is at least 30% by weight of at least one monomer selected from the group consisting of (C) acrylonitrile and methacrylonitrile as a polymerizable monomer. Obtained by using less than 80% by weight and (D) at least one monomer selected from the group consisting of vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate in excess of 20% by weight and 70% by weight or less. And a copolymer obtained.
[0030]
The (meth) acrylonitrile (co) polymer has, as a polymerizable monomer, 51 to 100% by weight of at least one monomer selected from the group consisting of (C1) acrylonitrile and methacrylonitrile, and (D1) A (co) polymer obtained using 0 to 40% by weight of vinylidene chloride and 0 to 48% by weight of at least one monomer selected from the group consisting of (D2) acrylic acid ester and methacrylic acid ester is preferable. .
[0031]
When a (co) polymer containing no vinylidene chloride is desired as the outer shell polymer, (E) at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile is used as the polymerizable monomer. (Meth) acrylonitrile (co) heavy obtained using 30 to 100% by weight of the body and 0 to 70% by weight of at least one monomer selected from the group consisting of (F) acrylates and methacrylates Coalescence is preferred. The polymerizable monomer is at least selected from the group consisting of (E1) acrylonitrile 1 to 99% by weight, (E2) methacrylonitrile 1 to 99% by weight, and (F) an acrylate ester and a methacrylate ester. Copolymers obtained using 0 to 70% by weight of a single monomer are preferred.
[0032]
Furthermore, in order to obtain thermally foamable microspheres with particularly excellent processability, foamability, gas barrier properties, and solvent resistance, the outer shell (meth) acrylonitrile (co) polymer is used as a polymerizable monomer. , (E1) acrylonitrile 20 to 80% by weight, (E2) methacrylonitrile 20 to 80% by weight, and (F) at least one monomer selected from the group consisting of acrylates and methacrylates 0 to 20 It is preferable that it is a copolymer obtained by using% by weight.
[0033]
(3) Crosslinkable monomer
  In the present invention, in addition to the polymerizable monomer as described above, a crosslinkable monomer is used in order to improve processing characteristics, foaming characteristics, heat resistance, solvent resistance (chemical resistance) and the like. As a crosslinkable monomer,TwoA polyfunctional compound having a polymerizable carbon-carbon double bond is used. Examples of the polymerizable carbon-carbon double bond include a vinyl group, a methacryl group, an acrylic group, and an allyl group. 2HornThe polymerizable carbon-carbon double bonds may be the same or different from each other.
[0034]
  Specifically, examples of the crosslinkable monomer include aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, and derivatives thereof; and diethylenically unsaturated compounds such as ethylene glycol di (meth) acrylate and diethylene glycol di (meth) acrylate. Bifunctional crosslinks such as carboxylic acid esters; (meth) acrylates derived from aliphatic terminal alcohols such as 1,4-butanediol and 1,9-nonanediol; divinyl compounds such as N, N-divinylaniline and divinyl ether; Sexual monomer.
[0035]
Among the crosslinkable monomers, a bifunctional crosslinkable monomer having two polymerizable carbon-carbon double bonds is preferable from the viewpoint of easily balancing the foamability and processing characteristics. In the case of a trifunctional or higher polyfunctional crosslinkable monomer, when the ratio of use increases, the polymer forming the outer shell loses its properties as a thermoplastic resin, and foaming may not occur even when heated.
[0036]
The bifunctional crosslinkable monomer may be directly or indirectly via a flexible chain derived from a diol compound selected from the group consisting of polyethylene glycol, polypropylene glycol, alkyl diol, alkyl ether diol, and alkyl ester diol. In particular, the compound is preferably a compound having a structure in which two polymerizable carbon-carbon double bonds are linked.
[0037]
When a bifunctional crosslinkable monomer having such a flexible chain is used as a crosslinkable monomer in a proportion of more than 1% by weight and 5% by weight or less, while maintaining a high expansion ratio, The temperature dependence of the modulus of elasticity of the polymer can be reduced, and even in the process of kneading, calendering, extrusion, injection molding, etc., even when subjected to shearing force, the outer shell breaks down or the inclusion gas It is possible to obtain a thermally foamable microsphere that hardly dissipates.
[0038]
When a bifunctional crosslinkable monomer having a flexible chain is used at a specific ratio, it is presumed that good scratch-hardening physical properties can be imparted to the outer shell polymer layer. Strain curability is a characteristic that requires a larger deformation stress in order to further deform as the amount of deformation increases. That is, as the foaming starts and proceeds, the outer polymer layer is stretched. At that time, not only the thinned portion of the polymer layer is further stretched by the deformation stress, but the thick portion of the polymer layer that is still small in deformation and small in deformation stress is preferentially stretched. Thereby, even if the degree of cross-linking of the outer shell polymer layer is high, a high expansion ratio can be obtained. In addition, since the thickness of the outer shell polymer layer is uniform, the temperature, shearing force, and resistance to solvents are increased. On the other hand, if the site connecting the polymerizable carbon-carbon double bonds has a rigid structure, or if the amount of the crosslinkable monomer used is too large, the curability of the strain becomes too large, and the expansion ratio If it drops significantly or is severe, it will not foam at all.
[0039]
Examples of the bifunctional crosslinkable monomer having a structure in which two polymerizable carbon-carbon double bonds are linked via the above-described flexible chain include polyethylene glycol di (meth) acrylate, polypropylene glycol di (meta) ) Acrylate, alkyl diol di (meth) acrylate, alkyl ether diol di (meth) acrylate, alkyl ester diol di (meth) acrylate, and mixtures of two or more thereof.
[0040]
More specifically, examples of the bifunctional crosslinkable monomer include polyethylene glycol di (meth) acrylates such as diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and tetraethylene glycol di (meth) acrylate [ethylene oxide Unit (-CH₂ CH₂ O-) usually 2 to 15]; polypropylene glycol di (meth) acrylate such as dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetrapropylene glycol di (meth) acrylate [propylene oxide unit [-CH (CH_Three ) CH₂ O-] or [-CH₂ CH (CH_Three ) O-] is usually 2 to 20]; ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,3-propanediol di (meth) acrylate, 1,4-butanediol di (meth) Acrylate, 1,3-butylene diol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 3-methyl -1,5-pentanediol di (meth) acrylate, 2-methyl-1,8-octanediol di (meth) acrylate, 2,4-diethyl-1,5-pentanediol di (meth) acrylate, 2-hydroxy Alkyldiols such as -1,3-propanediol di (meth) acrylate (Meth) acrylate (refractive chain is composed of aliphatic carbon, and usually has 2 to 20 carbon atoms in the connecting portion); alkyl ether diol such as 3-oxa-1,6-hexanediol di (meth) acrylate Di (meth) acrylate [flexible chain is composed of aliphatic carbon and ether bond. When there is one ether bond (-R₁ -O-R₂ -) Is usually not the same for each aliphatic carbon (R₁ ≠ R₂ ). ] Alkyl ester diol di (meth) acrylate such as neopentyl glycol di (meth) acrylate hydroxypivalate [a flexible chain is composed of aliphatic carbon and an ester bond. (-R₁ -COO-R₂ -)]; And the like.
[0041]
The lower limit of the use ratio of the crosslinkable monomer is based on the polymerizable monomer (polymerizable monomer = 100 wt%), more than 1 wt%, preferably 1.1 wt%, more preferably 1.2% by weight, particularly preferably 1.3% by weight. The upper limit of the proportion of the crosslinkable monomer used is 5% by weight, preferably 4% by weight, more preferably 3% by weight. In particular, in the case of using a bifunctional copolymerizable monomer having a structure in which two polymerizable carbon-carbon double bonds are linked via the flexible chain, in many cases, a crosslinkable monomer is used. Good results can be easily obtained when the proportion of is in the range of 1.4 to 4% by weight, and further 1.5 to 3% by weight.
[0042]
When the use ratio of the crosslinkable monomer is 1% by weight or less, only processing characteristics similar to those of the conventional thermally foamable microsphere can be obtained. On the other hand, if the use ratio of the crosslinking agent is excessive, the outer shell polymer loses its thermoplasticity and foaming becomes difficult.
[0043]
(4) Polymerization initiator
The polymerization initiator is not particularly limited, and those generally used in this field can be used, but an oil-soluble polymerization initiator that is soluble in the polymerizable monomer is preferable. More specifically, examples of the polymerization initiator include dialkyl peroxide, diacyl peroxide, peroxyester, peroxydicarbonate, and azo compound. The polymerization initiator is usually contained in the monomer mixture. However, when it is necessary to suppress early polymerization, a part or all of the polymerization initiator is added to the aqueous dispersion medium during or after the granulation step. It may be added and transferred into droplets of the polymerizable mixture. The polymerization initiator is usually used in a proportion of 0.0001 to 3% by weight based on the aqueous dispersion medium.
[0044]
(5) Aqueous dispersion medium
Suspension polymerization is usually carried out in an aqueous dispersion medium containing a dispersion stabilizer. Examples of the dispersion stabilizer include inorganic fine particles such as silica and magnesium hydroxide. In addition, auxiliary stabilizers such as a condensation product of diethanolamine and an aliphatic dicarboxylic acid, polyvinyl pyrrolidone, polyethylene oxide, various emulsifiers and the like can be used. The dispersion stabilizer is usually used at a ratio of 0.1 to 20 parts by weight with respect to 100 parts by weight of the polymerizable monomer.
[0045]
An aqueous dispersion medium containing a dispersion stabilizer is usually prepared by blending a dispersion stabilizer or an auxiliary stabilizer with deionized water. The pH of the aqueous phase at the time of polymerization is appropriately determined depending on the type of dispersion stabilizer and auxiliary stabilizer used. For example, when silica such as colloidal silica is used as a dispersion stabilizer, polymerization is performed in an acidic environment. In order to make the aqueous dispersion medium acidic, an acid is added as necessary to adjust the pH of the system to 6 or less, preferably about pH 3-4. In the case of a dispersion stabilizer that dissolves in an aqueous dispersion medium in an acidic environment such as magnesium hydroxide or calcium phosphate, the polymerization is performed in an alkaline environment.
[0046]
One preferred combination of dispersion stabilizers is a combination of colloidal silica and a condensation product. As the condensation product, a condensation product of diethanolamine and an aliphatic dicarboxylic acid is preferable, and a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid is particularly preferable. The acid value of the condensation product is preferably 60 or more and less than 95, and more preferably 65 to 90. Furthermore, when an inorganic salt such as sodium chloride or sodium sulfate is added, a thermally foamable microsphere having a more uniform particle shape can be easily obtained. As the inorganic salt, sodium chloride is usually preferably used.
[0047]
Although the usage-amount of colloidal silica changes also with the particle diameter, it is a ratio of 1-20 weight part normally with respect to 100 weight part of polymerizable monomers, Preferably it is a ratio of 2-15 weight part. The condensation product is usually used at a ratio of 0.05 to 2 parts by weight with respect to 100 parts by weight of the polymerizable monomer. The inorganic salt is used in a ratio of 0 to 100 parts by weight with respect to 100 parts by weight of the polymerizable monomer.
[0048]
Another preferred combination of the dispersion stabilizer includes a combination of colloidal silica and a water-soluble nitrogen-containing compound. Among these, a combination of colloidal silica and polyvinylpyrrolidone is preferably used. Furthermore, another preferred combination is a combination of magnesium hydroxide and / or calcium phosphate and an emulsifier.
[0049]
As a dispersion stabilizer, a hardly water-soluble metal hydroxide (for example, obtained by reaction in a water phase of a water-soluble polyvalent metal salt compound (for example, magnesium chloride) and an alkali metal hydroxide (for example, sodium hydroxide)) , Magnesium hydroxide) colloid. Moreover, as calcium phosphate, the reaction product in the aqueous phase of sodium phosphate and calcium chloride can be used.
[0050]
Although an emulsifier is not generally used, an anionic surfactant such as a dialkyl sulfosuccinate or a polyoxyethylene alkyl (allyl) ether phosphate may be used if desired.
[0051]
As the polymerization aid, at least one compound selected from the group consisting of alkali metal nitrite, stannous chloride, stannic chloride, water-soluble ascorbic acids, and boric acid can be present in the aqueous dispersion medium. . When suspension polymerization is performed in the presence of these compounds, polymerization particles do not agglomerate at the time of polymerization, the polymer does not adhere to the polymerization can wall, and is stable while efficiently removing heat generated by polymerization. Thus, a thermally foamable microsphere can be produced.
[0052]
Among the alkali metal nitrites, sodium nitrite and potassium nitrite are preferable in terms of availability and price. Examples of ascorbic acids include ascorbic acid, metal salts of ascorbic acid, esters of ascorbic acid, and the like. Among these, water-soluble ones are preferably used. Here, water-soluble ascorbic acids have a solubility in water at 23 ° C. of 1 g / 100 cm.^Three It means the above, and ascorbic acid and its alkali metal salt are preferable. Among these, L-ascorbic acid (vitamin C), sodium ascorbate, and potassium ascorbate are particularly preferably used in terms of availability, price, and action and effect. These compounds are generally used in a proportion of 0.001 to 1 part by weight, preferably 0.01 to 0.1 part by weight, per 100 parts by weight of the polymerizable monomer.
[0053]
(6) Suspension polymerization
The order of adding each component to the aqueous dispersion medium is arbitrary, but usually an aqueous dispersion containing a dispersion stabilizer by adding water and a dispersion stabilizer, and if necessary, a stabilizer or a polymerization assistant. Prepare the medium. On the other hand, the foaming agent, the polymerizable monomer, and the crosslinkable monomer may be separately integrated in the aqueous dispersion medium in addition to the aqueous dispersion medium to form a polymerizable mixture (oil-based mixture). Usually, these are mixed in advance and then added to the aqueous dispersion medium. The polymerization initiator can be used by adding it to the polymerizable monomer in advance, but when it is necessary to avoid early polymerization, for example, the polymerizable mixture is added to the aqueous dispersion medium and stirred. However, a polymerization initiator may be added and integrated in an aqueous dispersion medium. The polymerization mixture and the aqueous dispersion medium may be mixed in a separate container, mixed with a stirrer or a disperser having high shearing force, and then charged into a polymerization can.
[0054]
By stirring and mixing the polymerizable mixture and the aqueous dispersion medium, droplets of the polymerizable mixture are granulated in the aqueous dispersion medium. The average particle diameter of the droplets is preferably approximately the same as the average particle diameter of the target thermally foamable microsphere, but is usually about 3 to 100 μm. In order to obtain a heat-foamable microsphere having a very sharp particle size distribution, an aqueous dispersion medium and a polymerizable mixture are fed into a continuous high-speed rotation / high shear type agitator / disperser, and both are continuously fed in the agitator / disperser. It is preferable to employ a method in which the obtained dispersion is poured into a polymerization tank and suspension polymerization is performed in the polymerization tank after being stirred and dispersed.
[0055]
More specifically, in the step of supplying the aqueous dispersion medium and the polymerizable mixture into the continuous high-speed rotation and high shear type stirring and dispersing machine, (1) the aqueous dispersion medium and the polymerizable mixture are separately flowed at a certain ratio. In the continuous high-speed rotation high shear type stirring and dispersing machine, and (2) the aqueous dispersion medium and the polymerizable mixture are injected into the dispersing tank, and both are stirred in the dispersing tank for primary dispersion. Then, there is a method of supplying the obtained primary dispersion into a continuous high-speed rotation high-shearing type stirring and dispersing machine.
[0056]
In the method of (1), for example, as shown in FIG. 2, in the step of supplying the aqueous dispersion medium and the polymerizable mixture into the continuous high-speed rotation high shear type stirring and dispersing machine, the aqueous dispersion medium 1 and the polymerizable mixture 2 are As separate flows, they are continuously fed into a continuous high speed rotating high shear type stirring and dispersing machine at a constant ratio. Specifically, the aqueous dispersion medium 1 is held in the storage tank 3, and the polymerizable mixture 2 is held in the storage tank 4. The aqueous dispersion medium 1 is supplied from the line 6 using the pump 5 and the polymerizable mixture 2 is supplied from the line 8 using the pump 7 as separate flows into the continuous high-speed rotation high shear type stirring and dispersing machine 9. The supply ratio of the aqueous dispersion medium 1 and the polymerizable mixture 2 is usually in the range of 1: 1 to 6: 1, more preferably in the range of 2: 1 to 4: 1. Both are continuously stirred and dispersed in the stirring and dispersing machine 9, and then the obtained dispersion is injected into the polymerization tank 11 through the line 10, and suspension polymerization is performed in the polymerization tank 11.
[0057]
In the method (2), as shown in FIG. 3, the aqueous dispersion medium 1 and the polymerizable mixture 2 are dispersed in the step of supplying the aqueous dispersion medium and the polymerizable mixture into the continuous high-speed rotation high shear type stirring and dispersing machine. It inject | pours in the tank 12, and stirs both in the dispersion tank 12, and makes primary dispersion | distribution. The dispersion tank 12 is usually provided with a general stirring blade. The ratio of the aqueous dispersion medium 1 to the heavy mixture 2 is usually in the range of 1: 1 to 6: 1, more preferably in the range of 2: 1 to 4: 1. The primary dispersion obtained by stirring in the dispersion tank is supplied into the continuous high-speed rotation high shear type stirring and dispersing machine 9 through the line 14 using the pump 13. After the primary dispersion is further stirred and dispersed in the stirring and dispersing machine 9, the obtained dispersion is poured into the polymerization tank 11 through the line 15, and suspension polymerization is performed in the polymerization tank 11. According to the above method (2), it is possible to stably obtain a thermally foamable microsphere having a sharp particle size distribution.
[0058]
By adopting such a method, the average particle size is 3 to 100 μm, and the variation coefficient of the particle size distribution is preferably 1.50% or less, more preferably 1.30% or less, and particularly preferably 1.10. It is possible to obtain thermally foamable microspheres having a sharp particle size distribution of not more than%. Thermally foamable microspheres with a sharp particle size distribution have sharp foaming and can give uniform foams and foamed molded products.
[0059]
In the present invention, a batch-type high-speed rotation high shear disperser as shown in FIG. 4 can be used. In the method using a batch-type high-speed rotation / high-shear disperser, the aqueous dispersion medium 1 and the polymerizable mixture 2 are put into the batch-type high-speed rotation / high-shear disperser 16 and stirred to disperse. The droplets are granulated, and then the dispersion is injected into the polymerization tank 11 via the line 18 using the pump 17 and suspension polymerization is performed in the polymerization tank.
[0060]
Suspension polymerization is usually performed by degassing the inside of the reaction vessel or replacing it with an inert gas and raising the temperature to 30 to 100 ° C. After suspension polymerization, the aqueous phase is removed, for example, by filtration, centrifugation, and sedimentation. The thermally foamable microspheres are collected in a wet cake state after being filtered and washed. If necessary, the thermally foamable microspheres are dried at a relatively low temperature such that the foaming agent is not gasified. The heat-foamable microspheres can be surface-treated with various compounds as desired, and inorganic fine powders can be attached thereto. Furthermore, the surface can be coated with various materials other than the inorganic fine powder.
[0061]
2.Thermal foaming microsphere
  The thermally foamable microsphere of the present invention has a structure in which a foaming agent is enclosed in an outer shell formed from a polymer, and the outer shell polymer is a polymerizable monomer (usually a vinyl-based monomer). In the present invention, it is more than 1 wt% and not more than 5 wt% based on the polymerizable monomer.Bifunctional having two polymerizable carbon-carbon double bondsIt is formed by polymerizing with a crosslinkable monomer.
[0062]
  The thermally foamable microsphere of the present invention has a relatively large amount of outer shell polymer in addition to the polymerizable monomer.TwoSince it is formed using a functional crosslinkable monomer, the temperature dependence of the elastic modulus of the outer shell polymer is small. Therefore, for example, when a resin composition obtained by blending the heat-foamable microspheres of the present invention with a thermoplastic resin is subjected to processing such as kneading, calendering, extrusion, injection molding, etc., destruction of the outer shell or inclusion gas Dissipation is difficult to occur.
[0063]
In addition, the thermally foamable microspheres of the present invention have a small temperature dependency of the elastic modulus of the outer shell polymer, and therefore can have a wide processing suitability temperature range for uniform foaming. In this regard, please refer to FIG. FIG. 1 is a graph showing the relationship between the elastic modulus of the outer shell polymer and the measurement temperature. The outer shell polymer (a) of the conventional heat-foamable microsphere has an elastic modulus that rapidly decreases as the temperature rises. Therefore, the temperature range (a2-a1) of the elastic modulus region in which appropriate foaming (uniform foaming) is performed. ) Is narrow. On the other hand, the outer shell polymer (b) of the heat-foamable microsphere of the present invention has a wide temperature range (b2-b1) in the elastic modulus region for appropriate foaming, so that it can foam uniformly. A wide processing suitability temperature range can be taken.
[0064]
The average particle size of the thermally foamable microspheres of the present invention is not particularly limited, but is usually 3 to 100 μm, preferably 5 to 50 μm. If this average particle size is too small, foamability becomes insufficient. If the average particle size is too large, it is not preferable because the surface becomes rough in a field where a beautiful appearance is required, and the resistance to shearing force is insufficient.
[0065]
The coefficient of variation of the particle size distribution of the heat-foamable microsphere of the present invention is not particularly limited, but it is preferable that the coefficient of variation is 1.50% or less particularly in applications where sharp foaming is required. The variation coefficient of the particle size distribution is more preferably 1.30% or less, and particularly preferably 1.10% or less. If this coefficient of variation is too large, large particle diameter and small particle diameter thermally foamable microspheres will be mixed. Larger particle size tends to lower the foaming start temperature than small particle size, so to prevent early foaming and obtain uniform foaming, it is desirable to reduce the coefficient of variation of the thermally foamable microspheres . Examples of a method for obtaining a thermally foamable microsphere having a very small variation coefficient of the particle size distribution include the methods (1) and (2) described above.
[0066]
In the present invention, the variation coefficient of the particle size distribution is a value calculated based on the following formulas (1) and (2).
[0067]
[Expression 1]

[0068]
[Expression 2]

[0069]
(Where, μ = average value, x_j = Particle diameter, q_j = Frequency distribution)
[0070]
The content of the foaming agent in the thermally foamable microsphere of the present invention is usually 5 to 50% by weight, preferably 7 to 35% by weight, based on the total weight. If the foaming agent content is too low, the expansion ratio will be insufficient, and if it is too high, the thickness of the outer shell will be reduced, causing shearing under heating during processing and causing early foaming or rupture of the outer shell. It becomes easy. Examples of the foaming agent include a low-boiling organic solvent and a compound that decomposes by heating to generate a gas. Among these, a low-boiling organic solvent is preferable. The foaming agent is selected from those which become gaseous at a temperature below the softening point of the polymer forming the outer shell.
[0071]
The outer shell of the thermally foamable microsphere of the present invention is usually formed from a polymer having excellent gas barrier properties and heat resistance. Specifically, as described above, it can be formed using various polymerizable monomers such as acrylic acid ester, (meth) acrylonitrile, vinylidene chloride, vinyl chloride, and styrene. Among these, vinylidene chloride (co) polymers and (meth) acrylonitrile (co) polymers are preferable for highly balancing gas barrier properties, solvent resistance, heat resistance, foaming properties, and the like. According to the present invention, thermally foamable microspheres exhibiting various foaming behaviors can be obtained by controlling the combination and composition ratio of polymerizable monomers to be used and selecting the type of foaming agent.
[0072]
The thermally foamable microspheres of the present invention are particularly excellent in processing characteristics, and have a good balance between foaming characteristics (thermal expansion properties) and processing characteristics. The heat-expandable microspheres of the present invention do not lose thermal expansibility and have a maximum expansion ratio of 5 times or more despite the use of a crosslinking agent in a proportion exceeding 1% by weight. The maximum expansion ratio is preferably 10 times or more, more preferably 20 times or more. In many cases, it is possible to achieve a maximum expansion ratio of about 30 to 60 times.
[0073]
The thermally foamable microsphere of the present invention has a small temperature dependency of the elastic modulus of the outer shell formed from a polymer. Moreover, the heat-foamable microsphere of the present invention has a wide temperature range for processing. Furthermore, the thermally foamable microspheres of the present invention have high resistance (chemical resistance, solvent resistance) and foaming property retention capability against polar solvents and plasticizers. These characteristics of the thermally foamable microspheres of the present invention are specifically shown in the examples.
[0074]
A specific example of the characteristics of the thermally foamable microsphere of the present invention is that the temperature dependence of foaming is small. For example, when the outer shell polymer of the thermally foamable microsphere of the present invention is a vinylidene chloride (co) polymer as described above, the maximum foaming ratio R₁ Foaming ratio R at a temperature 10 ° C higher than the current temperature₂ Ratio (R₂ / R₁ ) Is usually 0.8 to 0.4, preferably 0.9 to 0.5, more preferably 1 to 0.5.
[0075]
When the outer shell polymer of the thermally foamable microsphere of the present invention is a (meth) acrylonitrile copolymer (copolymerization ratio of (meth) acrylonitrile = 30 wt% or more and less than 80 wt%) as described above, the maximum foaming Magnification R₁ Foaming ratio R at a temperature 5 ° C higher than the temperature at that time₂ Ratio (R₂ / R₁ ) Is usually 1 to 0.8, preferably 1 to 0.85, more preferably 1 to 0.9.
[0076]
When the outer shell polymer of the thermally foamable microsphere of the present invention is a (meth) acrylonitrile (co) polymer [(meth) acrylonitrile ratio = 80 to 100% by weight], particularly as a crosslinkable monomer, By using the above-mentioned bifunctional crosslinkable monomer having a flexible chain in an amount of more than 1% by weight and not more than 5% by weight, the temperature of the elastic modulus of the outer shell polymer is maintained while maintaining a high foaming property. Thermally foamable microspheres with low dependence and excellent workability and chemical resistance can be obtained.
[0077]
The thermally foamable microsphere of the present invention has an elastic modulus of the outer shell polymer at 190 ° C. or higher of 10⁶N / m²And 10⁹N / m²The following are excellent in resistance at high temperature and high shear. The elastic modulus of the outer shell polymer is more preferably 5.0 × 10⁶N / m²And 10⁹N / m²Below, particularly preferably 10⁷N / m²And 10⁸N / m²It is as follows.
[0078]
3.Application
The heat-foamable microspheres of the present invention are used in various fields after being heated and foamed (thermally expanded) or unfoamed. Thermally foamable microspheres are used, for example, as fillers for paints for automobiles, wallpaper, foaming agents for foamed inks (relief patterns such as T-shirts), shrinkage prevention agents, etc. Is done. Thermally foamable microspheres use the volume increase caused by foaming to reduce the weight and porosity of plastics, paints, and various materials, and to provide various functions (for example, slip properties, heat insulation properties, cushion properties, and sound insulation properties). Etc.). The thermally foamable microspheres of the present invention can be suitably used in the paint, wallpaper, and ink fields that require surface properties and smoothness. Since the thermally foamable microsphere of the present invention is excellent in processing characteristics, it can be suitably applied to application fields that require processing steps such as kneading, calendering, extrusion, and injection molding.
[0079]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
The measuring methods of physical properties and characteristics are as follows.
(1) Foaming ratio and maximum foaming ratio
0.7 g of thermally foamable microspheres is placed in a gear-type oven and heated at a predetermined temperature (foaming temperature) for 2 minutes to cause foaming. The obtained foam is put into a graduated cylinder, the volume is measured, and divided by the volume when not foamed to obtain the expansion ratio. At this time, the expansion ratio is measured by increasing the temperature from 100 ° C. in increments of 5 ° C., and the expansion ratio at the expansion temperature when the maximum expansion ratio is obtained is defined as the maximum expansion ratio.
[0080]
(2) Average particle size
Using a particle size distribution measuring instrument SALD-3000J manufactured by Shimadzu Corporation, the median diameter on a weight basis was measured to obtain an average particle diameter.
(3) Elastic modulus
After foaming the thermally foamable microspheres and removing the encapsulated foaming agent as much as possible, a hot press sheet was prepared with a hot press machine and cut into test pieces of 1 cm × 1.5 cm × 0.25 cm. This test piece was heated using a rheograph solid manufactured by Toyo Seiki Seisakusho under a nitrogen atmosphere at a frequency of 10 hertz and a heating rate of 3 ° C./min, and the elastic modulus was measured.
[0081]
(4) Foaming ratio in binder system
1 weight of thermally foamable microspheres in 5 weight parts of EVA in EVA emulsion (concentration 55 weight%) containing ethylene / vinyl acetate copolymer (EVA; ethylene / vinyl acetate = 30/70 weight%) Part is added to prepare a coating solution. This coating solution is applied to a double-sided art paper with a coater having a gap of 200 μm, dried, and then placed in an oven at a predetermined temperature and heated for 2 minutes. The expansion ratio is determined by the thickness ratio before and after foaming.
(5) Chemical resistance
A plasticizer solution is prepared by adding 2 parts by weight of diisonolyl phthalate and 1 part by weight of thermally foamable microspheres as a plasticizer to a glass test tube. This plasticizer liquid is heated at 140 ° C. using an oil bath, and the presence or absence of foaming over time and the degree of thickening of the plasticizer liquid are observed.
[0082]
(6) Foaming ratio in plasticized PVC sheet
A compound is prepared by adding 3 parts by weight of thermally foamable microspheres to 50 parts by weight of a polyvinyl chloride resin (S903 manufactured by Kureha Chemical Industry) and 50 parts by weight of dioctyl phthalate (DOP). The compound is roll-kneaded at 120 ° C. for 2 minutes to prepare a sheet having a thickness of 1 mm. The sheet is cut into a size of 3 × 4 cm square to make a sample, and the sample is foamed in an oven at 200 ° C. for 5 minutes and 10 minutes, respectively. The specific gravity before and after foaming is measured to calculate the foaming ratio (%).
(7) TMA (Thermo Mechanical Analysis)
TMA measurement was performed using a TMA-7 model manufactured by PerkinElmer. About 0.25 mg of sample was used. The heating rate was 5 ° C./min and 20 ° C./min.
[0083]
[Comparative Example 1]
Colloidal silica with a solid content of 20% 80.5 g, diethanolamine-adipic acid condensate 50% aqueous solution 3.0 g, sodium chloride 164.1 g, potassium dichromate 2.5% aqueous solution 2.2 g, hydrochloric acid 0.1 g A total of 470 g of an aqueous dispersion medium consisting of ionic water was prepared.
[0084]
On the other hand, 141.7 g of acrylonitrile, 67.1 g of methacrylonitrile, 11.2 g of methyl methacrylate, 0.67 g of trimethylolpropane trimethacrylate as a trifunctional crosslinkable monomer, 26.1 g of n-pentane, 14.4 g of petroleum ether. A polymerizable mixture comprising 9 g and 1.1 g of azobisisobutyronitrile was prepared (weight% of monomer component = acrylonitrile / methacrylonitrile / methyl methacrylate = 64.4 / 30.5 / 5.1). The amount of crosslinkable monomer used = 0.3% by weight of the monomer component).
[0085]
The polymerizable mixture and the aqueous dispersion medium were agitated and mixed with a batch-type high-speed rotary high shear type disperser shown in FIG. 4 to granulate fine droplets of the polymerizable mixture. An aqueous dispersion medium containing fine droplets of this polymerizable mixture was charged into a polymerization can (1.5 L) equipped with a stirrer and reacted at 60 ° C. for 20 hours using a hot water bath. The obtained reaction product is repeatedly subjected to filtration using a centrifuge and washed with water to form a cake, which is dried for a whole day and night. The average particle size is about 25 μm, and the variation coefficient of the particle size distribution is 1.7%. A thermally foamable microsphere (MS-A) was obtained. The expansion ratio (maximum expansion ratio) of MS-A at 170 ° C. was about 50 times. The results are shown in Table 1. Comparative Example 1 is in accordance with Example 2 of Japanese Patent Publication No. 5-15499.
[0086]
[Example 1]
In place of 0.67 g of trimethylolpropane trimethacrylate which is a trifunctional crosslinkable monomer, 3.5 g of diethylene glycol dimethacrylate which is a bifunctional crosslinkable monomer (crosslinkable monomer use amount = one monomer component) .6 wt%) in the same manner as Comparative Example 1 except that the average particle size is about 26 μm and the coefficient of variation of the particle size distribution is 1.7% (MS-1 ) The expansion ratio (maximum expansion ratio) of MS-1 at 170 ° C. was about 50 times. The results are shown in Table 1.
[0087]
[Comparative Example 2]
Thermally foamable microspheres having an average particle size of about 26 μm in the same manner as in Comparative Example 1 except that the amount of trimethylolpropane trimethacrylate, a trifunctional crosslinkable monomer, was changed from 0.67 g to 3.5 g. (MS-B) was obtained. MS-B hardly foamed in any temperature range of 140 ° C. or higher because the resin component forming the outer shell layer significantly lost the properties as a thermoplastic resin. The results are shown in Table 1.
[0088]
[Table 1]

[0089]
(footnote)
(* 1) Thickness ratio before and after foaming of thermally foamable microsphere-containing EVA emulsion coating layer.
(* 2) Plasticizer liquid = 2 parts of diisononyl phthalate / 1 part of thermally foamable microspheres
[0090]
(Discussion)
MS-1 of Example 1 had a good maximum foaming ratio (foaming temperature of 170 ° C.) of 50 times regardless of the amount of the crosslinkable monomer used exceeding 1% by weight of the monomer component. is there. In contrast, MS-B (Comparative Example 2) using a trifunctional crosslinkable monomer in a proportion of 1.6% by weight of the monomer component is highly crosslinked by the polymer forming the outer shell layer. Thus, the thermal foaming property is substantially lost.
[0091]
In the foaming behavior in the EVA emulsion, MS-1 of Example 1 was 5.2 times the weight of the crosslinkable monomer used by MS-A of Comparative Example 1 (5 moles). (2 times), the foaming ratio at 170 ° C. at which the maximum foaming ratio was obtained was 5.5 times, and the same high foaming ratio as MS-A was maintained. Moreover, the expansion ratio of MS-1 at 190 ° C., which is even higher, is 4.3 times, indicating that the expansion ratio is less than that of MS-A and the heat resistance is excellent. .
[0092]
Comparing the elastic modulus of the outer shell polymer at 140 ° C., the MS-1 of Example 1 is less than the MS-A of Comparative Example 1 which is a typical prior art thermal foamable microsphere. .4 times the elastic modulus. That is, it can be seen that the thermally foamable microspheres of the present invention are resistant to higher shearing force and excellent in heat resistance. When compared at a higher temperature of 190 ° C., MS-1 of Example 1 has a modulus of elasticity of the outer shell polymer of 1.6 times that of MS-A of Comparative Example 1. This means that the thermally foamable microspheres of the present invention are less susceptible to particle shrinkage, can maintain a high expansion ratio, and can take a wider processing suitability temperature range than before.
[0093]
In the evaluation of chemical resistance, the plasticizer liquid containing MS-A of Comparative Example 1 was partially foamed after heating at 140 ° C. for 6 minutes, and the viscosity was remarkably increased. On the other hand, in the case of MS-1 of Example 1, partial foaming was not observed after heating at 140 ° C. for 6 minutes, and further, even after 7 minutes, partial foaming did not occur.
[0094]
[Comparative Example 3]
A total of 520 g of an aqueous dispersion medium comprising 12 g of colloidal silica, 1.4 g of diethanolamine-adipic acid condensate, 154 g of sodium chloride, 0.12 g of sodium nitrite, 0.2 g of hydrochloric acid, and deionized water was prepared.
[0095]
On the other hand, polymerizability comprising acrylonitrile 130 g, methacrylonitrile 60 g, isobornyl methacrylate 10 g, trifunctional cross-linking monomer trimethylolpropane trimethacrylate 1 g, n-pentane 38 g, and azobisisobutyronitrile 1.2 g. A mixture was prepared (wt% of monomer component = acrylonitrile / methacrylonitrile / isobornyl methacrylate = 65/30/5, amount of crosslinkable monomer = 0.5 wt% of monomer component). The polymerizable mixture and the aqueous dispersion medium were agitated and mixed with a batch-type high-speed rotary high shear type disperser shown in FIG. 4 to granulate fine droplets of the polymerizable mixture.
[0096]
An aqueous dispersion medium containing fine droplets of this polymerizable mixture was charged into a polymerization can (1.5 L) equipped with a stirrer and reacted at 60 ° C. for 22 hours using a hot water bath. The obtained reaction product is repeatedly subjected to filtration using a centrifuge and washed with water to form a cake. The cake is dried overnight, the average particle size is about 28 μm, and the variation coefficient of the particle size distribution is 1. Thermal foaming microspheres (MS-C) of 8% were obtained. The expansion ratio (maximum expansion ratio) of MS-C at 170 ° C. was about 55 times. Comparative Example 3 is in accordance with Example 2 of JP-A-5-285376. The results are shown in Table 2.
[0097]
[Example 2]
Instead of 1 g of trimethylolpropane trimethacrylate, a trifunctional crosslinkable monomer, 3.5 g of diethylene glycol dimethacrylate, a difunctional crosslinkable monomer (amount of crosslinkable monomer = 1.6 of monomer component) In the same manner as in Comparative Example 3 except that the weight%) was used, a thermally foamable microsphere (MS-2) having an average particle size of about 30 μm and a coefficient of variation of the particle size distribution of 1.6% was obtained. Obtained. The expansion ratio of MS-2 at 170 ° C. (maximum expansion ratio) was about 55 times. The results are shown in Table 2.
[0098]
[Table 2]

[0099]
(Discussion)
Comparing the elastic modulus of the outer shell polymer, MS-2 of Example 2 was compared with MS-C of Comparative Example 3, which is a typical prior art thermal foaming microsphere, when the measurement temperature was 194 ° C. It was the same. However, when compared at a high measurement temperature of 210 ° C., the elastic modulus of the outer polymer of MS-2 is 2.6 times that of MS-A. In addition, in MS-2 of Example 2, the decrease in the elastic modulus of the outer shell polymer in the temperature range of 194 ° C. to 210 ° C. is extremely small. This means that the thermally foamable microspheres of the present invention are less likely to shrink particles in a high temperature range, can maintain a high expansion ratio, and can take a wider processing temperature range than in the past. From another point of view, it also means that it is resistant to higher shear forces and is heat resistant.
[0100]
[Example 3]
A total of 557 g of colloidal silica (16.5 g), diethanolamine-adipic acid condensation product (1.6 g), sodium chloride (169.8 g), sodium nitrite (0.11 g), and water is added to a polymerization vessel (1.5 L) equipped with a stirrer. The aqueous dispersion medium was prepared. Hydrochloric acid was added and adjusted so that the pH of the aqueous dispersion was 3.2.
[0101]
Meanwhile, a polymerizable mixture comprising 147.4 g of acrylonitrile, 70.4 g of methacrylonitrile, 2.2 g of methyl methacrylate, 3.5 g of diethylene glycol dimethacrylate, 41.8 g of isopentane, and 1.32 g of azobisisobutyronitrile is prepared. (Wt% of monomer component = acrylonitrile / methacrylonitrile / methyl methacrylate = 67/32/1, amount of crosslinkable monomer used = 1.6 wt% of monomer component). The polymerizable mixture and the aqueous dispersion medium prepared above were agitated and mixed with a batch-type high-speed rotary high shear type disperser shown in FIG. 4 to granulate fine droplets of the polymerizable mixture.
[0102]
An aqueous dispersion medium containing minute droplets of this polymerizable mixture was charged into a polymerization can (1.5 L) equipped with a stirrer and reacted at 60 ° C. for 45 hours using a hot water bath. The obtained reaction product was repeatedly filtered and washed with water to obtain thermally foamable microspheres (MS-3) having an average particle size of about 30 μm and a coefficient of variation of the particle size distribution of 1.8%. The expansion ratio (maximum expansion ratio) of MS-3 at 170 ° C. was about 50 times. The results are shown in Table 3.
[0103]
[Example 4]
The average particle size was about the same as in Example 3 except that the monomer charge amount was changed so that the monomer component charge ratio was acrylonitrile / methacrylonitrile = 70/30. A thermally foamable microsphere (MS-4) having a coefficient of variation of 30% and a particle size distribution of 2.1% was obtained. The expansion ratio (maximum expansion ratio) of this MS-4 at 170 ° C. was about 50 times. The results are shown in Table 3.
[0104]
[Comparative Example 4]
Instead of 3.5 g of the difunctional crosslinkable monomer diethylene glycol dimethacrylate, the trifunctional crosslinkable monomer trimethylol propane trimethacrylate 0.6 g (crosslinkable monomer use amount = 0 of monomer component) .3 wt%) in the same manner as in Example 3, except that the average particle size was about 30 μm and the coefficient of variation of the particle size distribution was 1.6% (MS-D ) The expansion ratio (maximum expansion ratio) of this MS-D at 170 ° C. was about 50 times. The results are shown in Table 3.
[0105]
[Comparative Example 5]
Instead of 3.5 g of the difunctional crosslinkable monomer diethylene glycol dimethacrylate, the trifunctional crosslinkable monomer trimethylol propane trimethacrylate 0.6 g (crosslinkable monomer use amount = 0 of monomer component) .3 wt%) in the same manner as in Example 4 except that the average particle size was about 30 μm and the coefficient of variation of the particle size distribution was 1.9% (MS-E ) The expansion ratio (maximum expansion ratio) of this MS-E at 170 ° C. was about 50 times. The results are shown in Table 3.
[0106]
[Table 3]

[0107]
(footnote)
(* 1) A sheet of 1 mm thickness prepared by kneading 100 g of a mixture of 50 parts PVC / 50 parts DOP / 3 parts thermally foamable microspheres for 2 minutes with a rotating roll at 120 ° C.
(* 2) A 3 × 4 cm square sheet was foamed in an oven at 200 ° C., and the foaming ratio (%) was calculated from the measured specific gravity before and after foaming.
[0108]
(Discussion)
Each plasticized PVC sheet containing the thermally foamable microspheres (MS-3 and MS-4) of Examples 3 and 4 showed a high foaming ratio after 200 ° C / 5 minutes, respectively, and 200 ° C / 10 minutes. The high expansion ratio is maintained afterwards. On the other hand, each plasticized PVC sheet containing the thermally foamable microspheres (MS-D and MS-E) of Comparative Examples 4 and 5 was significantly foamed at 120 ° C., after 200 ° C./5 minutes. The foaming ratio was small, and the foaming ratio after 200 ° C./10 minutes was remarkably lowered, so-called sag phenomenon was observed.
[0109]
[Comparative Example 6]
An aqueous dispersion medium was prepared by weighing 5 g of colloidal silica, 0.5 g of diethanolamine-adipic acid condensation product, 0.12 g of sodium nitrite, and 600 g in total. Hydrochloric acid was added and adjusted so that the pH of the aqueous dispersion medium was 3.2.
[0110]
On the other hand, 120 g of acrylonitrile, 120 g of methyl methacrylate, 0.4 g of trimethylol propane trimethacrylate, 70 g of isopentane, and 1.2 g of 2,2′-azobis (2,4-dimethylvaleronitrile) A polymerizable mixture was prepared (weight% of monomer component = acrylonitrile / methyl methacrylate = 50/50, amount of crosslinkable monomer used = 0.2% by weight of monomer component). The polymerizable mixture and the aqueous dispersion medium were stirred and mixed with a batch-type high-speed rotary high shear type disperser shown in FIG. 4 to prepare fine droplets of the polymerizable mixture.
[0111]
An aqueous dispersion medium containing fine droplets of this polymerizable mixture was charged into a polymerization can equipped with a stirrer (1.5 L) and reacted at 53 ° C. for 22 hours using a hot water bath. The obtained reaction product having a pH of 6.3 was filtered and washed with water, and this was repeated, followed by drying, and a thermally foamable microscopic product having an average particle size of 14 μm and a coefficient of variation of the particle size distribution of 1.6%. Fair (MS-F) was obtained. The expansion ratio of MS-F at 145 ° C. (maximum expansion ratio) was about 18 times, and the expansion ratio at 150 ° C. was about 12 times. The results are shown in Table 4.
[0112]
[Example 5]
Instead of 0.4 g of trimethylolpropane trimethacrylate, a trifunctional crosslinkable monomer, 3.2 g of diethylene glycol dimethacrylate, a bifunctional crosslinkable monomer (crosslinkable monomer use amount = one monomer component) .6 wt%), the same as Comparative Example 6, except that the average particle size is about 15 μm, and the coefficient of variation of the particle size distribution is 1.7% (MS-5) Got. The expansion ratio of MS-5 at 145 ° C. (maximum expansion ratio) was about 40 times, and the maximum expansion ratio of about 40 times was maintained even when the foaming temperature was increased to 150 ° C. The results are shown in Table 4.
[0113]
[Table 4]

[0114]
[Comparative Example 7]
An aqueous dispersion medium was prepared by weighing 8.8 g of colloidal silica, 0.8 g of a diethanolamine-adipic acid condensation product, 0.13 g of sodium nitrite, and 528 g of water in total.
[0115]
Meanwhile, a polymerizable mixture comprising 143 g of vinylidene chloride, 66 g of acrylonitrile, 11 g of methyl methacrylate, 0.33 g of trimethylolpropane trimethacrylate, 2.2 g of isopropyl peroxydicarbonate, and 35.2 g of isobutane was prepared (monomer % By weight of component = vinylidene chloride / acrylonitrile / methyl methacrylate = 65/30/5, amount of crosslinkable monomer = 0.15% by weight of monomer component). Next, the polymerizable mixture and the aqueous dispersion medium prepared above were stirred and mixed with a batch-type high-speed rotary high shear type disperser shown in FIG. 4 to granulate fine droplets of the polymerizable mixture. The polymerization can was charged and reacted at 50 ° C. for 22 hours. The obtained reaction product was repeatedly filtered and washed with water to obtain thermally foamable microspheres (MS-G) having an average particle size of about 15 μm and a coefficient of variation of the particle size distribution of 1.6%. This MS-G had a foaming ratio at 120 ° C. (maximum foaming ratio) of about 50 times, but when the foaming temperature was raised to 130 ° C., the foaming ratio was significantly reduced to about 18 times. The results are shown in Table 5.
[0116]
[Example 6]
Instead of 0.33 g of trimethylolpropane trimethacrylate, a trifunctional crosslinkable monomer, 3.5 g of diethylene glycol dimethacrylate, a bifunctional crosslinkable monomer (the amount of crosslinkable monomer used = one monomer component) .6 wt%) was obtained in the same manner as in Comparative Example 7 to obtain a thermally foamable microsphere MS-6 having an average particle size of about 15 μm and a coefficient of variation of the particle size distribution of 1.7%. It was. The expansion ratio of MS-6 at 120 ° C. (maximum expansion ratio) was about 50 times, and even when the foaming temperature was increased to 130 ° C., a high expansion ratio of about 35 times was exhibited. The results are shown in Table 5.
[0117]
[Table 5]

[0118]
[Example 7]
In place of 0.67 g of trimethylolpropane trimethacrylate which is a trifunctional crosslinkable monomer, 3.5 g of diethylene glycol dimethacrylate which is a bifunctional crosslinkable monomer (crosslinkable monomer use amount = one monomer component) 6 wt%), when stirring and mixing the polymerizable mixture and the aqueous dispersion medium, as shown in FIG. 2, the aqueous dispersion medium and the polymerizable mixture are respectively held in separate tanks, and these In the same manner as in Comparative Example 1 except that the suspension polymerization is carried out after continuously passing through a continuous high-speed rotation high-shear stirring and dispersing machine at a certain ratio. A thermally foamable microsphere (MS-7) having a coefficient of variation in diameter distribution of 0.3% was obtained. The expansion ratio (maximum expansion ratio) of MS-7 at 170 ° C. was about 50 times. This plasticizer liquid containing MS-7 did not partially foam even when held at 140 ° C. for 8 minutes. On the other hand, in the case of MS-1 of Example 1, partial foaming was slightly recognized after 8 minutes. This is due to the fact that the particle size distribution of MS-7 is sharper than that of MS-1 in addition to the effects of the type and amount of crosslinkable monomer.
[0119]
[Example 8]
When stirring and mixing the polymerizable mixture and the aqueous dispersion medium, as shown in FIG. 2, the aqueous dispersion medium and the polymerizable mixture are held in separate tanks, and these are continuously added at a certain ratio. The average particle size is about 30 μm and the coefficient of variation of the particle size distribution is 0.3% in the same manner as in Example 3 except that the suspension polymerization is performed after passing through a continuous high-speed rotation high shear type disperser. Thus, a thermally foamable microsphere (MS-8) having a sharp particle size distribution was obtained. The expansion ratio (maximum expansion ratio) of MS-8 at 170 ° C. was about 50 times.
[0120]
The plasticized PVC sheet containing MS-3 of Example 3 (see Table 3) was prepared by kneading with a rotating roll at 120 ° C. for 2 minutes, so that the thickness of the 1 mm thick sheet does not contain MS-3. The thickness increased by about 10% compared to the modified PVC sheet. On the other hand, the plasticized PVC sheet containing MS-8 is a plasticized PVC sheet containing 1-8 mm thick prepared by kneading for 2 minutes with a rotating roll at 120 ° C. There was almost no change in thickness. That is, it can be said that MS-8 is excellent in partial foaming characteristics during roll kneading (partial foaming is difficult).
[0121]
[Example 9]
When stirring and mixing the polymerizable mixture and the aqueous dispersion medium, as shown in FIG. 2, the aqueous dispersion medium and the polymerizable mixture are held in separate tanks, and these are continuously added at a certain ratio. The average particle size was about 15 μm and the coefficient of variation in particle size distribution was 0.5%, as in Example 5, except that the suspension polymerization was performed after passing through a continuous high-speed rotation high shear type disperser. Thus, a thermally foamable microsphere (MS-9) having a sharp particle size distribution was obtained. The expansion ratio of MS-9 at 145 ° C. (maximum expansion ratio) was about 40 times, and even when the foaming temperature was increased to 150 ° C., the maximum expansion ratio of about 40 times was maintained.
[0122]
MS-9 and MS-5 (Example 5) were each applied to double-sided art paper according to the method for measuring the expansion ratio in a binder system. When these wet coated papers were dried with a dryer at a rate of 1 ° C./min, MS-5 foamed at a lower temperature than MS-9. This means that when a thermally foamable microsphere having a sharp particle size distribution such as MS-9 is used, the processing speed can be increased (can be dried at a high temperature in a short time).
[0123]
[Example 10]
When stirring and mixing the polymerizable mixture and the aqueous dispersion medium, as shown in FIG. 2, the aqueous dispersion medium and the polymerizable mixture are held in separate tanks, and these are continuously added at a certain ratio. The average particle size is about 15 μm and the coefficient of variation of the particle size distribution is 0.2% in the same manner as in Example 6 except that the suspension polymerization is performed after passing through the continuous high-speed rotation high shear type disperser. Thus, a thermally foamable microsphere (MS-10) having a sharp particle size distribution was obtained. The expansion ratio of MS-10 at 120 ° C. (maximum expansion ratio) was about 50 times, and even when the foaming temperature was increased to 130 ° C., the maximum expansion ratio of about 35 times was maintained. When the foaming behavior was observed while raising the temperature at a rate of 5 ° C./min with a microscope with a hot stage, the temperature at which MS-10 foamed was higher than that of MS-6 in Example 6. Therefore, MS-10 is judged to be sharply foaming.
[0124]
[Example 11]
The average particle size was about the same as in Example 8 except that 66 g of isopentane / 2,2,4-trimethylpentane (weight ratio = 20/10) was used as a blowing agent instead of 41.8 g of isopentane. A thermally foamable microsphere (MS-11) having a coefficient of variation of 30% and a particle size distribution of 0.5% was obtained. The expansion ratio of MS-11 at 180 ° C. was about 40 times.
[0125]
As for the plasticized PVC sheet containing MS-11, the thickness of a 1 mm-thick sheet prepared by kneading for 2 minutes with a rotating roll at 120 ° C. is almost the same as that of a plasticized PVC sheet not containing MS-11. There wasn't. That is, it can be said that MS-11 is excellent in partial foaming characteristics during roll kneading (partial foaming is difficult).
[0126]
[Example 12]
The average particle size was about the same as in Example 8 except that 66 g of isopentane / 2,2,4-trimethylpentane (weight ratio = 15/15) was used as a blowing agent instead of 41.8 g of isopentane. A thermally foamable microsphere (MS-12) having a coefficient of variation of 31 μm and a particle size distribution of 0.4% was obtained.
[0127]
The plasticized PVC sheet containing MS-12 has a thickness of 1 mm, which is prepared by kneading for 2 minutes with a rotating roll at 120 ° C., and the thickness changes almost as compared with the plasticized PVC sheet not containing MS-12. There wasn't. That is, it can be said that MS-12 is excellent in partial foaming characteristics during roll kneading (partial foaming is difficult).
[0128]
[Example 13]
The average particle size was about the same as in Example 8 except that 66 g of isopentane / 2,2,4-trimethylpentane (weight ratio = 10/20) was used as a blowing agent instead of 41.8 g of isopentane. A heat-foamable microsphere (MS-13) having 30 μm and a coefficient of variation of the particle size distribution of 0.3% was obtained.
[0129]
The plasticized PVC sheet containing MS-13 has a thickness of 1 mm, which is prepared by kneading for 2 minutes with a rotating roll at 120 ° C., and the thickness of the plasticized PVC sheet is almost the same as that of the plasticized PVC sheet not containing MS-13. There wasn't. That is, it can be said that MS-13 is excellent in partial foaming characteristics during roll kneading (partial foaming is difficult).
[0130]
[Example 14]
The average particle size was about the same as in Example 8 except that 66 g of isopentane / 2,2,4-trimethylpentane (weight ratio = 6/24) was used as a blowing agent instead of 41.8 g of isopentane. A thermally foamable microsphere (MS-14) having a coefficient of variation of 30% and a particle size distribution of 0.5% was obtained.
[0131]
[Example 15]
In the same manner as in Example 3 except that 66 g of 2,2,4-trimethylpentane was used as a foaming agent in place of 41.8 g of isopentane, the average particle size was about 29 μm and the variation coefficient of the particle size distribution was 0. Thermally foamable microspheres (MS-15) of 2% were obtained.
[0132]
[Example 16]
Thermal foaming having an average particle size of about 32 μm and a coefficient of variation of the particle size distribution of 0.3% in the same manner as in Example 3 except that 66 g of heptane was used as the blowing agent instead of 41.8 g of isopentane. Microspheres (MS-16) were obtained.
[0133]
[Example 17]
TMA measurement was performed on samples MS-3 and MS-11 to MS-15 prepared in the above examples. The results are shown in Table 6.
[0134]
[Table 6]

(*) Relative comparison of displacement due to expansion
[0135]
[Example 18]
1 g of MS-D prepared in Comparative Example 4 and MS-14-16 prepared in Examples 14-16 were dispersed in 99 g of water and then boiled at 100 ° C. for 10 minutes. It was observed whether the foamed particles floated on the water surface, and the results are shown in Table 7.
[0136]
[Table 7]

[0137]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the thermally foamable microsphere suitable for processes, such as a kneading process, a calendar process, an extrusion process, and injection molding to which a strong shear force is applied, and its manufacturing method are provided. Moreover, according to this invention, the thermal foamable microsphere with small temperature dependence of the elasticity modulus of the outer shell formed from the polymer, and its manufacturing method are provided. The heat-foamable microsphere of the present invention has a wide processing temperature range, and has high chemical resistance, solvent resistance, and a high ability to retain foaming properties. Furthermore, according to the present invention, in addition to the above characteristics, a thermally foamable microsphere having a very small coefficient of variation in particle size distribution and sharp foaming is provided.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the elastic modulus of a shell polymer of a thermally foamable microsphere and the measurement temperature.
FIG. 2 is an explanatory view showing an example of a method for producing thermally foamable microspheres using a continuous high-speed rotating high shear type disperser.
FIG. 3 is an explanatory view showing another example of a method for producing thermally foamable microspheres using a continuous high-speed rotation high shear type disperser.
FIG. 4 is an explanatory diagram showing an example of a method for producing thermally foamable microspheres using a batch-type high-speed rotation high shear type disperser.
[Explanation of symbols]
1: Aqueous dispersion medium
2: Monomer mixture
3: Tank
4: Tank
5: Pump
6: Line
7: Pump
8: Line
9: Continuous high-speed rotation high-shear type stirring and dispersing machine
10: Line
11: Polymerization tank
12: Dispersion tank
13: Pump
14: Line
15: Line
16: Batch type high speed rotation high shear type disperser
17: Pump
18: Line

Claims (18)

In a thermally foamable microsphere having a structure in which a foaming agent is enclosed in an outer shell formed of a polymer,
(1) The outer shell formed from a polymer contains 2 polymerizable carbon-carbon double bonds in excess of 1% by weight and 5% by weight or less based on the polymerizable monomer. It is formed from a polymer obtained by polymerizing two difunctional crosslinkable monomers, and
(2) A thermally foamable microsphere characterized by having a maximum foaming ratio of 5 times or more. The bifunctional crosslinkable monomer has two polymerizable properties via a flexible chain derived from a diol compound selected from the group consisting of polyethylene glycol, polypropylene glycol, alkyl diol, alkyl ether diol, and alkyl ester diol. carbon - thermally foamable microspheres according to claim 1, wherein carbon double bond is a compound of the connecting structure. The compound which is a bifunctional crosslinkable monomer is polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, alkyl diol di (meth) acrylate, alkyl ether diol di (meth) acrylate, and alkyl ester diol The thermally foamable microsphere according to claim 2 , which is at least one compound selected from the group consisting of di (meth) acrylates. An outer shell formed from a polymer,
(A) As a polymerizable monomer, vinylidene chloride alone or a mixture of vinylidene chloride and a vinyl monomer copolymerizable therewith, and a bifunctional crosslinkable monomer having two polymerizable carbon-carbon double bonds And (b) (meth) acrylonitrile alone or a mixture of (meth) acrylonitrile and a vinyl monomer copolymerizable therewith as a polymerizable monomer, polymerizable carbon - obtained by polymerizing a bifunctional crosslinkable monomer having two carbon-carbon double bond (meth) acrylonitrile (co) any one of claims 1 and is formed from a polymer 3 1 The thermally foamable microsphere according to Item. A vinylidene chloride (co) polymer is used as the polymerizable monomer: (A) 30-100% by weight of vinylidene chloride; (B) acrylonitrile, methacrylonitrile, acrylic ester, methacrylic ester, styrene, and vinyl acetate The thermally foamable microsphere according to claim 4, which is a (co) polymer obtained by using 0 to 70% by weight of at least one monomer selected from the group consisting of: The vinylidene chloride (co) polymer is, as a polymerizable monomer, at least one monomer selected from the group consisting of (A1) vinylidene chloride 40 to 80% by weight and (B1) acrylonitrile and methacrylonitrile 0 The heat according to claim 4, which is a copolymer obtained by using 60% by weight and 0-60% by weight of at least one monomer selected from the group consisting of (B2) acrylic acid ester and methacrylic acid ester. Effervescent microsphere. The (meth) acrylonitrile (co) polymer is, as a polymerizable monomer, at least one monomer selected from the group consisting of (C) acrylonitrile and methacrylonitrile, and (D) vinylidene chloride. , acrylic acid esters, methacrylic acid esters, styrene, and at least one obtained using a monomer 0 to 70% by weight (co) of claim 4 wherein a polymer selected from the group consisting of vinyl acetate Thermal foaming microsphere. The (meth) acrylonitrile (co) polymer is, as a polymerizable monomer, at least one monomer selected from the group consisting of (C) acrylonitrile and methacrylonitrile, and (D) vinylidene chloride. , acrylic acid esters, methacrylic acid esters, styrene, and at least one a monomer 0 to 20 wt% were obtained using the (co) according to claim 7, wherein a polymer selected from the group consisting of vinyl acetate Thermal foaming microsphere. The (meth) acrylonitrile (co) polymer has, as a polymerizable monomer, at least one monomer selected from the group consisting of (C) acrylonitrile and methacrylonitrile and at least 30% by weight and less than 80% by weight (D ) A copolymer obtained by using at least one monomer selected from the group consisting of vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, and vinyl acetate in excess of 20% by weight and 70% by weight or less. Item 8. The thermally foamable microsphere according to Item 7 . The (meth) acrylonitrile (co) polymer is, as a polymerizable monomer, at least one monomer selected from the group consisting of (C1) acrylonitrile and methacrylonitrile, and (D1) vinylidene chloride. A (co) polymer obtained using 0 to 40% by weight and 0 to 48% by weight of at least one monomer selected from the group consisting of (D2) acrylic acid esters and methacrylic acid esters. 4. The thermally foamable microsphere according to 4 . The (meth) acrylonitrile (co) polymer is, as a polymerizable monomer, at least one monomer selected from the group consisting of (E) acrylonitrile and methacrylonitrile, and (F) acrylic acid. The thermally foamable microsphere according to claim 4, which is a (co) polymer obtained using 0 to 70% by weight of at least one monomer selected from the group consisting of esters and methacrylates. The (meth) acrylonitrile (co) polymer has, as polymerizable monomers, (E1) acrylonitrile 1 to 99% by weight, (E2) methacrylonitrile 1 to 99% by weight, (F) acrylic acid ester and methacrylic acid. The thermally foamable microsphere according to claim 4, which is a copolymer obtained by using 0 to 70% by weight of at least one monomer selected from the group consisting of acid esters. The (meth) acrylonitrile (co) polymer has, as polymerizable monomers, 20 to 80% by weight of (E1) acrylonitrile, 20 to 80% by weight of (E2) methacrylonitrile, (F) acrylic acid ester and methacrylic acid. The thermally foamable microsphere according to claim 4, which is a copolymer obtained using 0 to 20% by weight of at least one monomer selected from the group consisting of acid esters. Modulus of the shell formed from the polymer, blowing according to any one of claims 1 to 13, characterized in that 10 6 N ^/ m ² or more and 10 9 ^{N /} m ² or less Microspheres. The thermally foamable microsphere according to any one of claims 1 to 14 , wherein the foaming agent contains a hydrocarbon-based foaming agent having a boiling point of 60 ° C or higher. Suspension polymerization of a polymerizable mixture containing at least a blowing agent, a polymerizable monomer, and a crosslinkable monomer in an aqueous dispersion medium, and the blowing agent is enclosed in the outer shell formed from the resulting polymer. Bifunctional having two polymerizable carbon-carbon double bonds in a ratio of more than 1% by weight and not more than 5% by weight based on the polymerizable monomer in a method for producing a foamable microsphere having a structured structure A method for producing a thermally foamable microsphere, wherein a polymerizable mixture containing a crosslinkable monomer is subjected to suspension polymerization to obtain a thermally foamable microsphere having a maximum foaming ratio of 5 times or more. The polymerizable monomer is (a) vinylidene chloride alone or a mixture of vinylidene chloride and a copolymerizable vinyl monomer, and (b) (meth) acrylonitrile alone or (meth) acrylonitrile and copolymerizable with it. The production method according to claim 16 , which is a monomer or a monomer mixture selected from the group consisting of mixtures with various vinyl monomers. The method for producing a thermally foamable microsphere according to claim 16 or 17, wherein the foaming agent contains a hydrocarbon-based foaming agent having a boiling point of 60 ° C or higher.

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