JP4925554B2 - Copolymer, rubber composition and pneumatic tire - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、共重合体、該共重合体を含有するゴム組成物及び該ゴム組成物をトレッドに用いた空気入りタイヤに関し、特にイソブチレン単位とハロゲン基を含有した芳香族ビニル化合物単位とハロゲン基を含有しない芳香族ビニル化合物単位とを含む共重合体に関するものである。
【０００２】
【従来の技術】
従来、高性能乗用車用タイヤのトレッドには、超高分子量スチレン・ブタジエン共重合体ゴム(ＳＢＲ)をマトリックスとし、該マトリックスにグリップ性向上剤として低分子量の液状スチレン・ブタジエン共重合体を配合したゴム組成物が用いられている。
【０００３】
これに対し、グリップ性向上剤として、マトリックスとの相溶性が高く且つマトリックスと架橋しない低分子量の液状スチレン・イソブチレン共重合体を用いることにより、耐破壊性を低下させることなくグリップ性を向上させたタイヤが下記特許文献１に記載されている。しかしながら、昨今、高性能乗用車用タイヤには更なるグリップ性の向上が求められており、この要求に対しては特許文献１に記載のタイヤでも不充分である。また、高性能乗用車用タイヤには、グリップ性の更なる向上の他、耐破壊性の向上も求められており、特許文献１に記載のタイヤは、耐破壊性の点でも改良の余地がある。
【０００４】
【特許文献１】
特開平１１−３１５１７１号公報
【０００５】
【発明が解決しようとする課題】
そこで、本発明の目的は、タイヤのトレッドに用いることにより、上記従来技術のタイヤよりもグリップ性と耐破壊性に優れたタイヤの実現が可能な新規共重合体を提供することにある。また、本発明の他の目的は、かかる共重合体を配合してなるゴム組成物を提供することにある。更に、本発明のその他の目的は、かかるゴム組成物をトレッドに用いた、グリップ性及び耐破壊性に優れたタイヤを提供することにある。
【０００６】
【課題を解決するための手段】
本発明者は、上記目的を達成するために鋭意検討した結果、特定の共重合体を配合してなるゴム組成物をタイヤのトレッドゴムに適用することにより、上記従来技術のタイヤよりもグリップ性及び耐破壊性に優れたタイヤが得られることを見出し、本発明を完成させるに至った。
【０００８】
即ち、本発明の他の共重合体は、（ａ）イソブチレンと、（ｂ）ハロゲン基を含有した芳香族ビニル化合物と、（ｃ）ハロゲン基を含有しない芳香族ビニル化合物とをモノマーとし、カチオン重合開始剤を用いて重合させた共重合体であって、
前記共重合体中の（ｂ）ハロゲン基を含有した芳香族ビニル化合物単位の結合量が5〜70質量％であることを特徴とする。
【０００９】
本発明の共重合体の好適例においては、該共重合体は、重量平均分子量が1000〜200000である。
【００１１】
本発明の共重合体の他の好適例においては、前記共重合体中の（ｃ）ハロゲン基を含有しない芳香族ビニル化合物単位の結合量が65質量％以下である。
【００１２】
本発明の共重合体の他の好適例においては、前記（ｂ）ハロゲン基を含有した芳香族ビニル化合物が実質的にｐ-ハロメチルスチレンである。
【００１３】
また、本発明のゴム組成物は、ジエン系ゴムからなるゴム成分100質量部に対し、上記共重合体5〜200質量部を配合してなることを特徴とする。
【００１４】
本発明のゴム組成物の好適例においては、前記該ジエン系ゴムが合成ゴムであって、ジエン化合物の単独重合体又はジエン化合物と芳香族ビニル化合物との共重合体である。
【００１５】
本発明のゴム組成物の他の好適例においては、ゴム成分に配合される共重合体中の芳香族ビニル化合物単位の結合量は、ゴム成分における芳香族ビニル化合物単位の結合量より多く、ゴム成分における芳香族ビニル化合物単位の結合量より15質量％以上多いのが更に好ましい。ここで、上記共重合体中の芳香族ビニル化合物単位の結合量は、（ｂ）ハロゲン基を含有した芳香族ビニル化合物単位の結合量と（ｃ）ハロゲン基を含有しない芳香族ビニル化合物単位の結合量との合計である。
【００１６】
更に、本発明の空気入りタイヤは、上記ゴム組成物をトレッドの少なくとも接地部分に用いたことを特徴とする。
【００１７】
【発明の実施の形態】
以下に、本発明を詳細に説明する。本発明の共重合体は、（ａ）イソブチレンと、（ｂ）ハロゲン基を含有した芳香族ビニル化合物と、（ｃ）ハロゲン基を含有しない芳香族ビニル化合物とをモノマーとし、カチオン重合開始剤を用いて重合させた三元共重合体である。該共重合体は、熱反応性の高いハロゲン基を含有した芳香族ビニル化合物単位を含むため、ゴム成分との反応性が高い。そのため、該共重合体を含んでなるゴム組成物は、耐熱性が良好で耐破壊性が高く、更にかかるゴム組成物をトレッドに用いたタイヤはグリップの持続性が高い。
【００１８】
本発明の共重合体に用いるハロゲン基を含有した芳香族ビニル化合物としては、ｐ-クロロメチルスチレン、ｐ-ブロモメチルスチレン、ｐ-クロロスチレン、ｐ-ブロモスチレン等が挙げられ、これらの中でもｐ-クロロメチルスチレン、ｐ-ブロモメチルスチレン等のｐ-ハロメチルスチレンが好ましい。本発明の共重合体中の該ハロゲン基を含有した芳香族ビニル化合物単位の結合量は、5〜70質量％であり、10〜70質量％が好ましい。共重合体中のハロゲン基を含有した芳香族ビニル化合物単位の結合量が5質量％未満では、耐破壊性、耐熱性及びグリップ性を向上させる効果が小さく、70質量％を超えると、ゴム組成物の弾性率が高くなりすぎ、ゴム組成物のグリップ性が低下する。
【００１９】
本発明の共重合体に用いるハロゲン基を含有しない芳香族ビニル化合物としては、スチレン、α-メチルスチレン、１-ビニルナフタレン、３-ビニルトルエン、エチルビニルベンゼン、ジビニルベンゼン、４-シクロヘキシルスチレン、２,４,６-トリメチルスチレン等が挙げられ、これらの中でもスチレンが好ましい。本発明の共重合体中の該ハロゲン基を含有しない芳香族ビニル化合物単位の結合量は、65質量％以下が好ましく、45質量％以下が更に好ましい。共重合体中のハロゲン基を含有しない芳香族ビニル化合物単位の結合量が65質量％を超えると、ゴム組成物の弾性率が高くなりすぎ、ゴム組成物のグリップ性が低下する。
【００２０】
本発明の共重合体の製造に用いるカチオン重合開始剤は、陽イオンを成長活性種とする連鎖重合反応であるカチオン重合を開始するための試薬であり、特に限定されるものではないが、例えば、三塩化ホウ素（ＢＣｌ3）、塩化アルミニウム（ＡｌＣｌ3）、四塩化スズ（ＳｎＣｌ4）、四塩化チタン（ＴｉＣｌ4）、五塩化バナジウム（ＶＣｌ5）、三塩化鉄（ＦeＣｌ3）、三フッ化ホウ素（ＢＦ3）、クロロジエチルアルミニウム（Ｅｔ2ＡｌＣｌ）、ジクロロエチルアルミニウム（ＥｔＡｌＣｌ2）等のルイス酸が挙げられ、これらの中でも四塩化チタンが好ましい。
【００２１】
本発明の共重合体の重量平均分子量は1000〜200000であり、2000〜50000が好ましい。上記共重合体の重量平均分子量が1000未満では、耐破壊性が低下し、200000を超えると、ゴム組成物の弾性率が高くなりすぎ、ゴム組成物のグリップ性が低下する。
【００２２】
本発明の共重合体は、例えば、高分子合成の実験法（化学同人社）２０１ページにあるような方法、高分子化学第１８巻３８９〜３９５ページの報告にある方法でカチオン重合することにより製造することができる。
【００２３】
上記共重合体の製造に用いる溶媒としては、通常カチオン重合に用いられる溶剤を適宜用いることができ、例えば脂肪族炭化水素、芳香族炭化水素、ハロゲン化炭化水素等の炭化水素溶媒等が用いられる。この中でも芳香族炭化水素が好ましく、トルエンがより好ましい。かかる脂肪族炭化水素の具体例としては、ペンタン、ヘキサン等を、芳香族炭化水素の具体例としては、ベンゼン、トルエン、キシレン等を、またハロゲン化炭化水素の具体例としては、クロロメタン、クロロエタン、塩化メチレン、１,１-ジクロロエタン、クロロホルム、１,２-ジクロロエタン等を例示できる。これらは、一種単独でも、二種以上を混合して使用してもよい。更に、これらの溶媒と共に少量の他の溶媒、例えば酢酸エチル等の酢酸エステルやニトロエタン等のニトロ基を持つ有機化合物を併用してもよい。
【００２４】
上記共重合体の製造における重合温度は、-100℃〜-30℃が好ましい。-100℃未満では、重合反応の進行が遅く、-30℃を超えると、連鎖移動反応が激しく、分子量が著しく低下する傾向があるので好ましくない。
【００２５】
また、上記共重合体の重合反応は、モノマーを実質的に液相下に保つのに充分な圧力下で行うのが望ましい。即ち、反応圧力は重合される各モノマーや、使用する溶媒及び重合温度にもよるが、所望ならばより高い圧力下で重合させることができ、このような高い圧力は重合反応に関して不活性なガスで反応器を加圧する等の適当な方法で達成される。
【００２６】
上記共重合体の製造においては、一般にモノマー、カチオン重合開始剤、溶媒等の製造に使用する全ての物質から、水、酸素、二酸化炭素等の触媒毒を除去するのが好適である。
【００２７】
なお、本発明の共重合体と一見すると類似している共重合体として、エクソン社のエクスプロ（商品名）が市販されている。しかしながら、本発明の共重合体がモノマーの１つとしてハロゲン基を含有した芳香族ビニル化合物を用いて製造されるのに対し、該エクスプロは、イソブチレンと芳香族ビニル化合物とから共重合体を製造し、その後、ハロゲン化して製造される点で異なる。また、該エクスプロは、ハロゲン化された芳香族ビニル化合物単位の結合量が約2質量％以下と本発明の共重合体よりも著しく低く、且つ分子量も300000〜500000と本発明の共重合体よりも著しく大きい。これら物性の違いは主に製造法の違いに起因し、共重合体を製造した後にハロゲン化するよりも、ハロゲン基を含有した芳香族ビニル化合物をモノマーの１つとして用いる方が、低分子量で且つハロゲン基含有量の高い共重合体を容易に得ることができる。
【００２８】
本発明のゴム組成物は、ジエン系ゴムからなるゴム成分100質量部に対し、上述した本発明の共重合体5〜200質量部を配合してなり、タイヤのトレッド用ゴム組成物として好適である。上記共重合体の配合量が5質量部未満では、耐破壊性、耐熱性及びグリップ性を向上させる効果が小さく、200質量部を超えると、ゴム組成物の耐破壊性が低下する。
【００２９】
本発明のゴム組成物に用いるゴム成分は、天然ゴム(ＮＲ)、ポリイソプレンゴム(ＩＲ)、ポリブタジエンゴム(ＢＲ)、スチレン・ブタジエン共重合体ゴム(ＳＢＲ)、ブチルゴム(ＩＩＲ)、エチレン・プロピレン・ジエン共重合体ゴム(ＥＰＤＭ)、アクリロニトリル・ブタジエン共重合体ゴム(ＮＢＲ)等のジエン系ゴムである。これらジエン系ゴムの中でも、合成ゴムであって、且つ、ジエン化合物の単独重合体であるポリイソプレンゴム、ポリブタジエンゴム等、又はジエン化合物と芳香族ビニル化合物との共重合体であるスチレン・ブタジエン共重合体ゴム等が好ましい。ここで、ジエン化合物としてはイソプレン及び１,３-ブタジエン等が、芳香族ビニル化合物としてはスチレン等が挙げられる。
【００３０】
本発明のゴム組成物において、前記ゴム成分に配合される共重合体中の芳香族ビニル化合物単位の結合量は、前記ゴム成分中の芳香族ビニル化合物単位の結合量より多いのが好ましく、前記ゴム成分中の芳香族ビニル化合物単位の結合量より15質量％以上多いのが更に好ましい。ゴム成分に配合される共重合体中の芳香族ビニル化合物単位の結合量がゴム成分中の芳香族ビニル化合物単位の結合量より多いと、共重合体とゴム成分との相溶性が良好になる。
【００３１】
本発明のゴム組成物は、上記共重合体及びゴム成分の他、通常ゴム業界で用いられている、カーボンブラック、シリカ等の充填剤、アルマチックオイル等の軟化剤、硫黄等の加硫剤、加硫促進剤、老化防止剤、亜鉛華、ステアリン酸等の各種配合剤を、その目的、用途に合わせ、適宜配合することができる。
【００３２】
本発明の空気入りタイヤは、上述したゴム組成物をトレッドの少なくとも接地部分に用いたことを特徴とする。上記本発明のゴム組成物は耐熱性が良好で耐破壊性が高いため、かかるゴム組成物をトレッドの少なくとも接地部分に用いた本発明の空気入りタイヤは、耐破壊性及びグリップ性に優れる。そのため、本発明のタイヤは、高性能乗用車用タイヤとして好適である。
【００３３】
【実施例】
以下に、実施例を挙げて本発明を更に詳しく説明するが、 本発明は下記の実施例に何ら限定されるものではない。
【００３４】
（共重合体Ａ製造例）
乾燥し、窒素置換された300mLのナスフラスコに、トルエン200mL、イソブチレン単量体12.0g、スチレン単量体15.4gを仕込み、これに開始剤ＴｉＣｌ4 0.75mmolを加えた後、-78℃で2.5時間重合を行った。重合系は重合開始から終了まで、全く沈殿は見られず均一で透明であった。重合転化率は、ほぼ100％であった。重合溶液にメチルアルコールを加えて乾燥し、共重合体Ａを得た。この共重合体についてイソブチレン結合量、スチレン結合量及び重量平均分子量を測定し、表１に示す結果を得た。なお、重合体中のイソブチレン結合量及びスチレン結合量は、1Ｈ-ＮＭＲスペクトルの積分比より算出した。また、重量平均分子量（Ｍｗ）は、示差屈折計（ＲＩ）を用いたゲルパーミエイションクロマトグラフィ〔ＧＰＣ；東ソー製ＨＬＣ−８０２０、カラム；東ソー製ＧＭＨ−ＸＬ（２本直列）〕により測定し、単分散ポリスチレンを標準としたポリスチレン換算で示した。
【００３５】
（共重合体Ｂ製造例）
乾燥し、窒素置換された300mLのナスフラスコに、トルエン200mL、イソブチレン単量体13.5g、スチレン単量体7.5g、及びｐ-クロロメチルスチレン単量体9gを仕込み、これに開始剤ＴｉＣｌ4 0.75mmolを加えた後、-78℃で2.5時間重合を行った。重合系は重合開始から終了まで、全く沈殿は見られず均一で透明であった。重合転化率は、ほぼ100％であった。重合溶液にメチルアルコールを加えて乾燥し、共重合体Ｂを得た。この共重合体についてイソブチレン結合量、スチレン結合量、クロロメチルスチレン結合量及び重量平均分子量を測定し、表１に示す結果を得た。なお、重合体中のイソブチレン結合量、スチレン結合量及びクロロメチルスチレン結合量は、1Ｈ-ＮＭＲスペクトルの積分比より算出した。
【００３６】
（共重合体Ｃ製造例）
乾燥し、窒素置換された300mLのナスフラスコに、塩化メチレン200mL、イソブチレン単量体19.3g、及びｐ-クロロメチルスチレン単量体4.8gを仕込み、これに開始剤ＴｉＣｌ4 0.75mmolを加えた後、-78℃で2.5時間重合を行った。重合系は重合開始から終了まで、全く沈殿は見られず均一で透明であった。重合転化率は、ほぼ100％であった。重合溶液にメチルアルコールを加えて乾燥し、共重合体Ｃを得た。この共重合体についてイソブチレン結合量、クロロメチルスチレン結合量及び重量平均分子量を測定し、表１に示す結果を得た。なお、重合体中のイソブチレン結合量及びクロロメチルスチレン結合量は、1Ｈ-ＮＭＲスペクトルの積分比より算出した。
【００３７】
また、ＴｉＣｌ4、イソブチレン、スチレン及びｐ-クロロメチルスチレンの量を変化させる以外は上記共重合体製造例２と同様の製造方法で共重合体Ｄを得た。これらの共重合体について、イソブチレン結合量、スチレン結合量、クロロメチルスチレン結合量及び重量平均分子量を測定し、表１に示す結果を得た。
【００３８】
【表１】
上記のようにして製造した共重合体を用いて、表２に示す配合のゴム組成物を調製し、該ゴム組成物に対し下記に示す方法で耐破壊性及び耐熱性を評価した。また、該ゴム組成物をトレッド接地部分に用い、キャップ／ベース構造のトレッドを持つ、サイズ１８５／７０Ｒ１４のタイヤを作製し、下記に示す方法でグリップ性を評価した。結果を表２に示す。
【００４０】
（１）耐破壊性
ＪＩＳ Ｋ６３０１-１９９５に準拠して破壊強度を測定し、比較例１を100として指数表示し、耐破壊性の指標とした。数値が大きい程、耐破壊性が高いことを示す。
【００４１】
（２）耐熱性
グッドリッチ式フレクソメーターを用い、ＡＳＴＭ-Ｄ-６２３-５８の方法に準拠して行い、試料がブローアウト（ゴム成分が分解して、発泡し、スポンジ状になった状態をいう）したときの温度（単位：℃）（ブローアウトポイント）を測定した。この数値が大きい方が耐熱性に優れ、好ましいことを示す。尚、測定条件は、槽内温度120℃、振動数1800rpm、荷重28kg、歪22.5％であり、サンプル形状は、直径30mm、高さ25.4mmである。
【００４２】
（３）グリップ性
1500ccの乗用車に上記試作タイヤ４輪を装着し、テストコースを１０周した際のベストラップタイムを測定し、比較例１のベストラップタイムの逆数を100として指数表示した。指数値が大きい程、グリップ性が良好であることを示す。
【００４３】
【表２】
表２から、少なくとも分子中にクロロメチルスチレン単位を含む本発明の共重合体を配合した実施例のゴム組成物は、比較例１のゴム組成物より耐破壊性及び耐熱性が優れていることが分かる。また、本発明の共重合体を配合したゴム組成物をトレッドの接地部分に用いた実施例のタイヤは、比較例１のタイヤよりグリップ性が優れていた。
【００４５】
【発明の効果】
本発明によれば、タイヤのトレッドに用いることにより、従来よりもグリップ性及び耐破壊性に優れたタイヤの実現が可能な新規共重合体を提供することができる。また、該共重合体をゴム成分に配合することにより、耐破壊性及び耐熱性に優れたゴム組成物を提供することができる。更に、該ゴム組成物をトレッドの接地部分に用いることにより、耐破壊性が高いと共にグリップ性にも優れたタイヤを提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a copolymer, a rubber composition containing the copolymer, and a pneumatic tire using the rubber composition in a tread, and more particularly, an aromatic vinyl compound unit containing an isobutylene unit and a halogen group, and a halogen group. The present invention relates to a copolymer containing an aromatic vinyl compound unit that does not contain .
[0002]
[Prior art]
Conventionally, treads for high-performance passenger car tires are composed of ultra high molecular weight styrene / butadiene copolymer rubber (SBR) as a matrix, and a low molecular weight liquid styrene / butadiene copolymer as a grip improver is blended in the matrix. A rubber composition is used.
[0003]
On the other hand, by using a low molecular weight liquid styrene / isobutylene copolymer that has high compatibility with the matrix and does not crosslink with the matrix as a gripping property improver, the grip property can be improved without reducing the fracture resistance. A tire is described in Patent Document 1 below. However, recently, high-performance passenger car tires are required to have further improved grip properties, and the tire described in Patent Document 1 is insufficient for this requirement. Further, high-performance passenger car tires are required to have further improved grip resistance as well as improved fracture resistance, and the tire described in Patent Document 1 has room for improvement in terms of fracture resistance. .
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-315171
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a novel copolymer that can be used for a tread of a tire and can realize a tire superior in grip property and fracture resistance as compared with the tire of the prior art. Another object of the present invention is to provide a rubber composition comprising such a copolymer. Furthermore, another object of the present invention is to provide a tire excellent in grip and fracture resistance using such a rubber composition in a tread.
[0006]
[Means for Solving the Problems]
As a result of diligent investigations to achieve the above object, the present inventor applied a rubber composition containing a specific copolymer to a tread rubber of a tire, so that the grip performance is higher than that of the conventional tire. And it discovered that the tire excellent in fracture resistance was obtained, and came to complete this invention.
[0008]
That is , another copolymer of the present invention comprises (a) isobutylene, (b) an aromatic vinyl compound containing a halogen group, and (c) an aromatic vinyl compound not containing a halogen group as monomers. A copolymer polymerized using a polymerization initiator ,
The bond amount of the aromatic vinyl compound unit containing (b) a halogen group in the copolymer is 5 to 70% by mass .
[0009]
In a preferred example of the copolymer of the present invention, the copolymer has a weight average molecular weight of 1000-200000.
[0011]
In another preferred embodiment of the copolymer of the present invention, the binding amount of the aromatic vinyl compound unit not containing (c) halogen group in the copolymer is 65% by mass or less.
[0012]
In another preferred embodiment of the copolymer of the present invention, the (b) aromatic vinyl compound containing a halogen group is substantially p-halomethylstyrene.
[0013]
In addition, the rubber composition of the present invention is characterized by blending 5 to 200 parts by mass of the copolymer with 100 parts by mass of a rubber component made of a diene rubber .
[0014]
In a preferred embodiment of the rubber composition of the present invention, the diene rubber is a synthetic rubber and is a homopolymer of a diene compound or a copolymer of a diene compound and an aromatic vinyl compound.
[0015]
In another preferred embodiment of the rubber composition of the present invention, the amount of the aromatic vinyl compound unit in the copolymer blended with the rubber component is greater than the amount of the aromatic vinyl compound unit in the rubber component. More preferably, the amount is 15% by mass or more than the amount of the aromatic vinyl compound unit in the component. Here, the bonding amount of the aromatic vinyl compound unit in the copolymer is (b) the bonding amount of the aromatic vinyl compound unit containing a halogen group and (c) the aromatic vinyl compound unit containing no halogen group. It is the total with the amount of binding.
[0016]
Furthermore, the pneumatic tire of the present invention is characterized in that the rubber composition is used in at least a ground contact portion of a tread.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below. The copolymer of the present invention comprises (a) isobutylene, (b) an aromatic vinyl compound containing a halogen group, and (c) an aromatic vinyl compound not containing a halogen group as monomers, and a cationic polymerization initiator. It is a terpolymer copolymerized by using. Since the copolymer includes an aromatic vinyl compound unit containing a halogen group having high thermal reactivity, the copolymer has high reactivity with the rubber component. Therefore, a rubber composition comprising the copolymer has good heat resistance and high fracture resistance, and a tire using such a rubber composition as a tread has high grip durability.
[0018]
Examples of the aromatic vinyl compound containing a halogen group used in the copolymer of the present invention include p-chloromethylstyrene, p-bromomethylstyrene, p-chlorostyrene, p-bromostyrene and the like. P-Halomethylstyrene such as -chloromethylstyrene and p-bromomethylstyrene is preferred. The bonding amount of the aromatic vinyl compound unit containing the halogen group in the copolymer of the present invention is 5 to 70% by mass, and preferably 10 to 70% by mass. If the amount of the aromatic vinyl compound unit containing a halogen group in the copolymer is less than 5% by mass, the effect of improving the fracture resistance, heat resistance and grip is small, and if it exceeds 70% by mass, the rubber composition The elastic modulus of the product becomes too high, and the grip properties of the rubber composition are lowered.
[0019]
Examples of the aromatic vinyl compound containing no halogen group used in the copolymer of the present invention include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, , 4,6-trimethylstyrene and the like, and among these, styrene is preferable. The bonding amount of the aromatic vinyl compound unit not containing the halogen group in the copolymer of the present invention is preferably 65% by mass or less, and more preferably 45% by mass or less . When the bond amount of the aromatic vinyl compound unit not containing a halogen group in the copolymer exceeds 65% by mass, the elastic modulus of the rubber composition becomes too high and the grip property of the rubber composition is lowered.
[0020]
The cationic polymerization initiator used in the production of the copolymer of the present invention is a reagent for initiating cationic polymerization, which is a chain polymerization reaction using a cation as a growth active species, and is not particularly limited. Boron trichloride (BCl 3 ), aluminum chloride (AlCl 3 ), tin tetrachloride (SnCl 4 ), titanium tetrachloride (TiCl 4 ), vanadium pentachloride (VCl 5 ), iron trichloride (FeCl 3 ), trifluoride Examples include Lewis acids such as boron fluoride (BF 3 ), chlorodiethylaluminum (Et 2 AlCl), dichloroethylaluminum (EtAlCl 2 ), and among these, titanium tetrachloride is preferable.
[0021]
The weight average molecular weight of the copolymer of the present invention is 1,000 to 200,000, preferably 2000 to 50,000. If the weight average molecular weight of the copolymer is less than 1000, the fracture resistance decreases, and if it exceeds 200,000, the elastic modulus of the rubber composition becomes too high and the grip properties of the rubber composition decrease.
[0022]
The copolymer of the present invention can be obtained by, for example, cationic polymerization by a method as described in page 201 of Experimental Method for Polymer Synthesis (Chemical Doujinsha), or a method described in Polymer Chemistry Vol. 18, pages 389-395. Can be manufactured.
[0023]
As a solvent used for the production of the copolymer, a solvent usually used for cationic polymerization can be appropriately used. For example, hydrocarbon solvents such as aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons and the like are used. . Among these, aromatic hydrocarbons are preferable, and toluene is more preferable. Specific examples of such aliphatic hydrocarbons include pentane and hexane, specific examples of aromatic hydrocarbons include benzene, toluene and xylene, and specific examples of halogenated hydrocarbons include chloromethane and chloroethane. And methylene chloride, 1,1-dichloroethane, chloroform, 1,2-dichloroethane and the like. These may be used singly or in combination of two or more. Furthermore, a small amount of other solvents such as ethyl acetate and other organic compounds having a nitro group such as nitroethane may be used in combination with these solvents.
[0024]
The polymerization temperature in the production of the copolymer is preferably -100 ° C to -30 ° C. If it is less than -100 ° C, the polymerization reaction proceeds slowly, and if it exceeds -30 ° C, the chain transfer reaction is intense and the molecular weight tends to be remarkably lowered.
[0025]
The polymerization reaction of the copolymer is desirably performed under a pressure sufficient to keep the monomer substantially in a liquid phase. That is, the reaction pressure depends on each monomer to be polymerized, the solvent used and the polymerization temperature, but if desired, the polymerization can be carried out at a higher pressure, and such a high pressure is an inert gas for the polymerization reaction. This is accomplished by a suitable method such as pressurizing the reactor.
[0026]
In the production of the copolymer, it is generally preferable to remove catalyst poisons such as water, oxygen and carbon dioxide from all substances used for the production of monomers, cationic polymerization initiators, solvents and the like.
[0027]
Exxon (trade name) manufactured by Exxon is commercially available as a copolymer that is similar to the copolymer of the present invention at first glance. However, whereas the copolymer of the present invention is produced using an aromatic vinyl compound containing a halogen group as one of the monomers, the EXPRO produces a copolymer from isobutylene and an aromatic vinyl compound. However, it is different in that it is then halogenated and manufactured. The EXPRO has a binding amount of halogenated aromatic vinyl compound units of about 2% by mass or less, which is significantly lower than that of the copolymer of the present invention, and a molecular weight of 300,000 to 500,000, which is higher than that of the copolymer of the present invention. Is also significantly larger. The difference in these physical properties is mainly due to the difference in production method. Rather than halogenating after producing a copolymer, it is more low in molecular weight to use an aromatic vinyl compound containing a halogen group as one of the monomers. In addition, a copolymer having a high halogen group content can be easily obtained.
[0028]
The rubber composition of the present invention is formed by blending 5 to 200 parts by mass of the above-described copolymer of the present invention with 100 parts by mass of a rubber component made of a diene rubber, and is suitable as a rubber composition for a tire tread. is there. When the blending amount of the copolymer is less than 5 parts by mass, the effect of improving the fracture resistance, heat resistance and grip properties is small, and when it exceeds 200 parts by mass, the fracture resistance of the rubber composition is lowered.
[0029]
The rubber components used in the rubber composition of the present invention are natural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber (BR), styrene / butadiene copolymer rubber (SBR), butyl rubber (IIR), ethylene / propylene. · diene copolymer rubber (EPDM), diene-based rubber such as acrylonitrile-butadiene copolymer rubber (NBR). Among these diene rubbers, styrene / butadiene copolymer, which is a synthetic rubber and is a homopolymer of a diene compound, such as polyisoprene rubber and polybutadiene rubber, or a copolymer of a diene compound and an aromatic vinyl compound. Polymer rubber or the like is preferable. Here, examples of the diene compound include isoprene and 1,3-butadiene, and examples of the aromatic vinyl compound include styrene.
[0030]
In the rubber composition of the present invention, the bond amount of the aromatic vinyl compound unit in the copolymer blended with the rubber component is preferably larger than the bond amount of the aromatic vinyl compound unit in the rubber component, It is more preferable that the amount of the aromatic vinyl compound unit in the rubber component is 15% by mass or more than the combined amount. If the amount of aromatic vinyl compound units in the copolymer blended with the rubber component is greater than the amount of aromatic vinyl compound units in the rubber component, the compatibility between the copolymer and the rubber component will be good. .
[0031]
The rubber composition of the present invention includes the above copolymer and rubber component, and usually used in the rubber industry, fillers such as carbon black and silica, softeners such as almatic oil, and vulcanizing agents such as sulfur. Various compounding agents such as a vulcanization accelerator, an anti-aging agent, zinc white, and stearic acid can be appropriately mixed according to the purpose and application.
[0032]
The pneumatic tire of the present invention is characterized in that the above-described rubber composition is used in at least a ground contact portion of a tread. Since the rubber composition of the present invention has good heat resistance and high fracture resistance, the pneumatic tire of the present invention in which such a rubber composition is used for at least the ground contact portion of the tread is excellent in fracture resistance and grip properties. Therefore, the tire of the present invention is suitable as a tire for a high-performance passenger car.
[0033]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.
[0034]
(Production example of copolymer A)
In a 300 mL eggplant flask that was dried and purged with nitrogen, 200 mL of toluene, 12.0 g of isobutylene monomer, and 15.4 g of styrene monomer were added, and after adding 0.75 mmol of initiator TiCl 4 to this, 2.5 at −78 ° C. Time polymerization was performed. The polymerization system was uniform and transparent from the start to the end of the polymerization without any precipitation. The polymerization conversion rate was almost 100%. Methyl alcohol was added to the polymerization solution and dried to obtain a copolymer A. With respect to this copolymer, the amount of isobutylene bonds, the amount of styrene bonds and the weight average molecular weight were measured, and the results shown in Table 1 were obtained. The isobutylene bond amount and styrene bond amount in the polymer were calculated from the integral ratio of the 1 H-NMR spectrum. The weight average molecular weight (Mw) was measured by gel permeation chromatography [GPC: Tosoh HLC-8020, column: Tosoh GMH-XL (two in series)] using a differential refractometer (RI). It was shown in terms of polystyrene using monodisperse polystyrene as a standard.
[0035]
(Production example of copolymer B)
A 300 mL eggplant flask that has been dried and purged with nitrogen is charged with 200 mL of toluene, 13.5 g of isobutylene monomer, 7.5 g of styrene monomer, and 9 g of p-chloromethylstyrene monomer, and the initiator is TiCl 4 0.75. After adding mmol, polymerization was performed at -78 ° C for 2.5 hours. The polymerization system was uniform and transparent from the start to the end of the polymerization without any precipitation. The polymerization conversion rate was almost 100%. Methyl alcohol was added to the polymerization solution and dried to obtain a copolymer B. With respect to this copolymer, the amount of isobutylene bonds, the amount of styrene bonds, the amount of chloromethylstyrene bonds and the weight average molecular weight were measured, and the results shown in Table 1 were obtained. The isobutylene bond amount, styrene bond amount, and chloromethylstyrene bond amount in the polymer were calculated from the integral ratio of the 1 H-NMR spectrum.
[0036]
(Production example of copolymer C)
A 300 mL eggplant flask that was dried and purged with nitrogen was charged with 200 mL of methylene chloride, 19.3 g of isobutylene monomer, and 4.8 g of p-chloromethylstyrene monomer, and after adding 0.75 mmol of initiator TiCl 4 to this. Polymerization was performed at −78 ° C. for 2.5 hours. The polymerization system was uniform and transparent from the start to the end of the polymerization without any precipitation. The polymerization conversion rate was almost 100%. Methyl alcohol was added to the polymerization solution and dried to obtain a copolymer C. With respect to this copolymer, the amount of isobutylene bonds, the amount of chloromethylstyrene bonds and the weight average molecular weight were measured, and the results shown in Table 1 were obtained. The amount of isobutylene bonds and the amount of chloromethylstyrene bonds in the polymer were calculated from the integral ratio of 1 H-NMR spectrum.
[0037]
A copolymer D was obtained by the same production method as in the above-mentioned copolymer production example 2 except that the amounts of TiCl 4 , isobutylene, styrene and p-chloromethylstyrene were changed. About these copolymers, the amount of isobutylene bonds, the amount of styrene bonds, the amount of chloromethylstyrene bonds, and the weight average molecular weight were measured, and the results shown in Table 1 were obtained.
[0038]
[Table 1]
Using the copolymer produced as described above, a rubber composition having the composition shown in Table 2 was prepared, and the fracture resistance and heat resistance of the rubber composition were evaluated by the methods described below. Further, tires of size 185 / 70R14 having a tread with a cap / base structure were produced using the rubber composition as a tread grounding portion, and grip properties were evaluated by the method described below. The results are shown in Table 2.
[0040]
(1) Fracture resistance The fracture strength was measured according to JIS K6301-1995, and Comparative Example 1 was displayed as an index, which was used as an index of fracture resistance. It shows that destruction resistance is so high that a numerical value is large.
[0041]
(2) Performed according to ASTM-D-623-58 using a heat-resistant Goodrich flexometer, and the sample was blown out (the rubber component was decomposed and foamed into a sponge-like state) Temperature (unit: ° C.) (blowout point) was measured. A larger value indicates better heat resistance and is preferable. The measurement conditions were a bath temperature of 120 ° C., a frequency of 1800 rpm, a load of 28 kg, a strain of 22.5%, and the sample shape was a diameter of 30 mm and a height of 25.4 mm.
[0042]
(3) Grip properties
The four prototype tires were mounted on a 1500 cc passenger car, the best lap time when the test course was made 10 laps was measured, and the reciprocal of the best lap time of Comparative Example 1 was taken as an index. It shows that grip property is so favorable that an index value is large.
[0043]
[Table 2]
From Table 2, the rubber composition of the Example which mix | blended the copolymer of this invention which contains a chloromethyl styrene unit in a molecule | numerator at least is superior to the rubber composition of the comparative example 1 in fracture resistance and heat resistance. I understand. In addition, the tire of the example using the rubber composition blended with the copolymer of the present invention for the ground contact portion of the tread was superior in grip performance to the tire of Comparative Example 1.
[0045]
【Effect of the invention】
ADVANTAGE OF THE INVENTION According to this invention, the novel copolymer which can implement | achieve the tire excellent in grip property and fracture resistance than before can be provided by using for the tread of a tire. Moreover, the rubber composition excellent in fracture resistance and heat resistance can be provided by mix | blending this copolymer with a rubber component. Furthermore, by using the rubber composition in the ground contact portion of the tread, a tire having high fracture resistance and excellent grip properties can be provided.
Claims (9)
該共重合体中の（ｂ）ハロゲン基を含有した芳香族ビニル化合物単位の結合量が5〜70質量％であることを特徴とする共重合体。A copolymer obtained by polymerizing using (a) isobutylene, (b) an aromatic vinyl compound containing a halogen group, and (c) an aromatic vinyl compound not containing a halogen group as a monomer and using a cationic polymerization initiator Because
The copolymer according to (b), wherein the bond amount of the aromatic vinyl compound unit containing a halogen group in the copolymer is 5 to 70% by mass .
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