JP2004339433A - Rubber composition for tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tire tread exhibiting excellent braking performance on ice while keeping abrasion resistance and setting resistance. <P>SOLUTION: The rubber composition is produced by compounding 100 pts. wt. of a rubber component composed of at least one kind of diene rubber, 1-10 pts. wt. of staple fibers having an average length of ≤10 mm, (a) pts. wt. of sulfur, (b) pts. wt. of a compounding ingredient B expressed by R<SB>2</SB>N-(C=S)-S-S-(CH<SB>2</SB>)<SB>x</SB>-S-S-(C=S)-NR<SB>2</SB>(R is C<SB>6</SB>H<SB>5</SB>CH<SB>2</SB>; and x is 6) and c pts. wt. of one or more kinds of sulfenamide-based vulcanization promoter in total. The values (a), (b) and (c) satisfies the relationships b≥0.2, 1.2≤a+b/2≤2.0 and 0.5≤c/(a+b/2)≤1.0 at the same time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

によって表される配合剤Ｂをｂ重量部、及び１種以上のスルフェンアミド系加硫促進剤を合計でｃ重量部配合してなるゴム組成物であって、
前記ａ、ｂ、及びｃが、下式
ｂ≧０．２、
１．２≦ａ＋ｂ／２≦２．０、
０．５≦ｃ／（ａ＋ｂ／２）≦１．０
の関係を同時に満足することを特徴とするゴム組成物によって達成される。
【０００８】
【発明の実施の形態】
本発明に係るゴム組成物において使用されるゴム成分としては、天然ゴム（ＮＲ）またはジエン系ゴムのいずれか、あるいはこれらの混合系を用いることができる。ジエン系ゴムとしては、例えば、各種ポリブタジエンゴム（ＢＲ）、各種スチレン−ブタジエン共重合体ゴム（ＳＢＲ）、ポリイソプレンゴム（ＩＲ）、エチレン−プロピレン−ジエン共重合体ゴム等が挙げられる。好ましくは、本発明に係るゴム組成物におけるゴム成分は、天然ゴム（ＮＲ）またはポリブタジエンゴム（ＢＲ）のいずれか、あるいはこれらの混合系である。
【０００９】
本発明に係るタイヤトレッド用ゴム組成物は、上記ゴム成分１００重量部に対して、平均長１０ｍｍ以下の短繊維を１〜１０重量部配合し、更に、硫黄をａ重量部、下式

によって表される配合剤Ｂをｂ重量部、及び１種以上のスルフェンアミド系加硫促進剤を合計でｃ重量部配合してなるゴム組成物であって、
前記ａ、ｂ、及びｃが、下式
ｂ≧０．２、
１．２≦ａ＋ｂ／２≦２．０、
０．５≦ｃ／（ａ＋ｂ／２）≦１．０
の関係を同時に満足することを特徴とするゴム組成物である。
【００１０】
本発明に係るタイヤトレッド用ゴム組成物に配合される上記短繊維を構成する材料の例としては、金属、ガラス、セラミック、カーボン、天然ポリマー及び合成ポリマー等を挙げることができるが、これらに限定されるものではない。好ましくは、上記短繊維を構成する材料は、ポリアミド系ポリマーである。より好ましくは、上記短繊維を構成する材料は、ナイロン６（ポリカプロラクタム）である。
【００１１】
上記短繊維は、平均長が１０ｍｍ以下、好ましくは０．２〜１０ｍｍ、より好ましくは０．５〜５ｍｍであるのが望ましい。上記短繊維の平均長が０．２ｍｍ未満である場合には、加硫後のゴム組成物の氷上制動性能の改良において、短繊維の配合による十分な効果が得られず、逆に、上記短繊維の平均長が１０ｍｍを超える場合には、短繊維の配合により、ゴム組成物の混合加工性が低下し、加硫後のゴム組成物の耐摩耗性が低下するので好ましくない。
【００１２】
また、上記短繊維は、平均直径が１５０μｍ 以下、好ましくは２０〜１５０μｍ 、より好ましくは４０〜１００μｍ であるのが望ましい。上記短繊維の平均直径が２０μｍ 未満である場合には、短繊維の剛性が不十分となり、加硫後のゴム組成物の氷上制動性能の改良において、短繊維の配合による十分な効果が得られず、逆に、上記短繊維の平均直径が１５０μｍ を超える場合には、短繊維の剛性が過大となり、短繊維の配合により、加硫後のゴム組成物の耐疲労性が低下するので好ましくない。
【００１３】
更に、本発明に係るタイヤトレッド用ゴム組成物における上記短繊維の配合量は、上記ゴム成分１００重量部に対して、１〜１０重量部、好ましくは２〜７重量部であるのが望ましい。上記短繊維の配合量が、上記ゴム成分１００重量部に対して、１重量部未満である場合には、加硫後のゴム組成物の氷上制動性能の改良において、短繊維の配合による十分な効果が得られず、逆に、上記短繊維の配合量が、上記ゴム成分１００重量部に対して、１０重量部を超える場合には、短繊維の配合により、ゴム組成物の混合加工性が低下するので好ましくない。
【００１４】
上記の式におけるａ＋ｂ／２は、本発明に係るゴム組成物中の架橋剤成分の配合量に対応する値であり、また、ｃ／（ａ＋ｂ／２）は、本発明に係るゴム組成物中の架橋剤成分の配合量に対する加硫促進剤の配合量の比に対応する値である。上記加硫系成分を、上記の式を同時に満足する条件下で配合することによって、本発明の所与の特性を有するゴム組成物を得ることができる。
【００１５】
上記硫黄及びスルフェンアミド系加硫促進剤としては、ゴム配合技術分野において周知のものを通常の配合量で使用することができ、それぞれ、粉末硫黄並びにＮ−ｔｅｒｔ−ブチル−２−ベンゾチアゾリル−スルフェンアミド（ＴＢＢＳ）（例えば、大内新興化学工業株式会社製「ノクセラーＮＳ−Ｆ」）及びＮ−シクロヘキシル−２−ベンゾチアゾールスルフェンアミド（ＣＢＳ）（例えば、大内新興化学工業株式会社製「ノクセラーＣＺ−Ｇ」）等を例として挙げることができる。
【００１６】
上記配合剤Ｂ自体は、ゴム配合技術分野において既知の化合物であり、例えば、特開 ２００１−２８３３号公報において、ジエン系ゴムおよび常套の添加剤からなる加硫性ゴム組成物に、ゴム１００重量部に対して、ａ）上記配合剤Ｂを０．５〜３．８重量部、ｂ）硫黄を０．５〜２重量部、及びｃ）少なくとも１種の加硫促進剤を０．５〜３．０重量部を配合することによって、加硫後のゴム組成物の発熱性を悪化させること無く、耐引裂性及び耐老化性を向上させることが開示されている。
【００１７】
しかしながら、本発明においては、ゴム成分１００重量部に対する、硫黄、配合剤Ｂ、及び１種以上の特定の加硫促進剤（具体的には、スルフェンアミド系加硫促進剤）の配合量（それぞれ、ａ、ｂ、及びｃ重量部（複数種の加硫促進剤を使用する場合には、それらの合計配分量を表す））を、上記３個の関係式を同時に満足するように規定することにより、ゴム組成物の他の特性を犠牲にすること無く、当該ゴム組成物がトレッド部に使用されているタイヤにおいて、ひときわ優秀な氷上制動性能を実現することができることを見出したものである。
【００１８】
具体的には、ｂが０．２重量部未満である場合には、加硫後のゴム組成物における短繊維の配合による耐セット性の低下を抑制する効果が不十分となる。また、ａ＋ｂ／２が１．２重量部未満である場合には、加硫後のゴム組成物の硬度が低く、ブロック剛性確保には不十分となり、逆に、ａ＋ｂ／２が２．０重量部を超える場合には、加硫後のゴム組成物における短繊維の配合による耐セット性の低下を抑制する効果が不十分となる。更に、ｃ／（ａ＋ｂ／２）が０．５未満である場合には、加硫後のゴム組成物における短繊維の配合による耐セット性の低下を抑制する効果が不十分となり、逆にｃ／（ａ＋ｂ／２）が１．０を超えると、破断伸びが低下し、耐摩耗性の低下が顕著となる。
【００１９】
すなわち、本発明に係るタイヤトレッド用ゴム組成物においては、ゴム成分に上記短繊維を配合し、更に、上記ａ、ｂ、及びｃの値が上記３個の関係式を同時に満足するように、硫黄、配合剤Ｂ、及び１種以上の加硫促進剤を配合することによって、加硫後のゴム組成物において、短繊維の配合による氷上制動性能を更に向上させると同時に、短繊維の配合による耐セット性の低下を十分に抑制することができるのである。
【００２０】
本発明に係るタイヤトレッド用ゴム組成物には、カーボンブラック、充填材（例えば、シリカ）、プロセスオイル、可塑剤、軟化剤、加硫助剤、加硫遅延剤、加硫活性化剤、老化防止剤等、及び／又はゴム配合技術分野において一般的に使用される他の各種添加剤を更に配合することができる。これらの添加剤の配合量も、本発明の目的に反しない限り、従来の一般的な配合量とすることができる。
【００２１】
また、本発明に係るタイヤトレッド用ゴム組成物に、例えば、熱膨張性熱可塑性樹脂粒子、粉砕ゴム、硬質多孔性粒子、及び中空ポリマー等の、昨今のスタッドレスタイヤのトレッド用ゴム組成物において使用されている種々の添加剤を更に配合してもよい。
【００２２】
本発明に係るタイヤトレッド用ゴム組成物は、公知のゴム用混練機械（例えば、ロール、バンバリーミキサー、ニーダー等）を使用して、上記各成分を混合することによって製造することができる。
【００２３】
以下に記載する標準例、比較例、及び実施例によって本発明を更に詳しく説明するけれども、本発明の技術的範囲は、これらの例に限定されるものではない。
【００２４】
【実施例】
標準例、比較例１〜８、及び実施例１〜４
配合成分
後述する各種試験片の調製において使用される各種配合成分を、以下に列記する。
【００２５】
天然ゴム（ＮＲ）：ＳＴＲ−２０
ポリブタジエンゴム（ＢＲ）：日本ゼオン株式会社製「Ｎｉｐｏｌ １２２０」
カーボンブラック（ＣＢ）：昭和キャボット株式会社製「ショウブラックＮ２２０」（ＩＳＡＦ）
アロマオイル：富士興産株式会社製「フレックスＭ」
亜鉛華：正同化学工業株式会社製「酸化亜鉛 ３種」
ステアリン酸：日本油脂株式会社製「ビーズステアリン酸」
老化防止剤（６ＰＰＤ）：Ｆｌｅｘｓｙｓ社製「ＳＡＮＴＯＦＬＥＸ ６ＰＰＤ」（Ｎ−フェニル−Ｎ’−１，３−ジメチルブチル−ｐ−フェニレンジアミン）
ワックス：大内新興化学工業株式会社製「サンノック」
【００２６】

【００２７】
各種試験片の調製
以下の表Ｉに示す、硫黄、配合剤Ｂ、及び加硫促進剤以外の成分を、以下の表Ｉに示す配合量で、バンバリーミキサー及び練りロール機で混合混練し、１６５±５℃に達したときにマスターバッチを放出した。このマスターバッチに、以下の表Ｉに示す配合量の硫黄、配合剤Ｂ（標準例及び比較例１を除く）、及び加硫促進剤を添加し、８インチのオープンロールで混練して、標準例、比較例１〜８、及び実施例１〜４のゴム組成物を得た。次に、各種ゴム組成物を、所定の金型中で１５０℃において４０分間プレス加硫して、目的とする各種試験片を調製した。
【００２８】
【表１】

【００２９】
各種試験片の加硫物性の測定
上記の如く得られた標準例、比較例１〜８、及び実施例１〜４のゴム組成物からなる上記各種試験片の各種加硫物性を、以下の試験方法に従って測定した。
【００３０】
１）硬度（デュロ硬さＡ）：
上記各種試験片について、ＪＩＳ Ｋ６２５３に準拠して測定した。硬度が高いほど、ブロック剛性の増大による偏摩耗抑制効果が高いことを意味する。
【００３１】
２）氷上摩擦指数：
上記各種試験片を、接地圧＝３ｋｇ／ｃｍ^２及び速度＝２５ｋｍ／ｈの条件下で、−３℃の恒温室中に設置された氷盤上で滑らせた際の動摩擦係数を測定し、標準例における測定値を１００とした指数によって表示した。この指数が大きいほど、氷上摩擦係数が大きく、氷上制動性能が良好であることを意味する。
【００３２】
３）耐摩耗性指数：
上記各種試験片について、ＪＩＳ Ｋ６２６４に準拠して、ランボーン摩耗試験機（岩本製作所株式会社製）を使用して、荷重５ｋｇ、スリップ率２５％、時間４分、室温において、ランボーン摩耗指数を測定し、標準例の測定値を１００とした指数にて表示した。この指数が大きいほど、耐摩耗性が良好であることを意味する。
【００３３】
４）耐セット性指数：
上記各種試験片について、ＪＩＳ Ｋ６２６２に準拠して、１００℃において、２５％の圧縮を７２時間にわたって加えた後の圧縮永久歪（％）を測定し、測定値の逆数を算出し、標準例の逆数値を１００とした指数にて表示した。この指数が大きいほど、耐セット性が良好であることを意味する。
【００３４】
各種試験片の加硫物性の評価
上記各種試験片についての、上記１）〜４）の各加硫物性の測定結果は、上記表Ｉに示されている。
【００３５】
標準例の試験片は、短繊維も配合物Ｂも全く含有していない、標準的な組成を有する対照標準となるゴム組成物を使用して調製した試験片である。
【００３６】
比較例１の試験片は、ゴム成分１００重量部に対して５．００重量部の短繊維Ｍを配合したことを除き、標準例のゴム組成物と同じ組成を有する、比較用のゴム組成物を使用して調製した試験片である。短繊維Ｍを配合したことにより、硬度及び氷上摩擦指数が増大したが、耐摩耗性指数が若干減少し、耐セット性指数は大幅に低下した。
【００３７】
実施例１の試験片は、ゴム成分１００重量部に対して、硫黄の配合量（ａ）を１．５０重量部から１．３０重量部に削減する一方で配合物Ｂを０．４０重量部配合して（ｂ＝０．４０）、架橋剤成分の配合量（ａ＋ｂ／２）を一定値（１．５０重量部）に維持し、かつ、加硫促進剤（ＴＢＢＳ）の配合量（ｃ）を１．２０重量部から１．００重量部に削減したことを除き、比較例１のゴム組成物と同じ組成を有する、本発明に係るゴム組成物を使用して調製した試験片である。加硫系成分の各配合量を上記の如く調整することにより、短繊維Ｍを配合したことに起因する高い硬度及び氷上摩擦指数を維持しつつ、短繊維Ｍを配合したことによる耐セット性指数の低下が抑制された。
【００３８】
実施例２の試験片は、硫黄の配合量（ａ）を更に削減し、配合物Ｂの配合量（ｂ）を増大させ、かつ、加硫促進剤（ＴＢＢＳ）の配合量（ｃ）を更に削減したことを除き、実施例１のゴム組成物と同じ組成を有する、本発明に係るゴム組成物を使用して調製した試験片である。配合物Ｂの配合量を増大させながらも、加硫系成分の各配合量を上記の如く調整して、架橋剤成分の配合量（ａ＋ｂ／２）及び架橋剤成分の配合量に対する加硫促進剤の配合量の比（ｃ／（ａ＋ｂ／２））の値を本発明の規定範囲内に収めることによって、短繊維Ｍを配合したことに起因する高い硬度及び氷上摩擦指数を維持しつつ、標準例の試験片よりも高い耐セット性指数が達成された。
【００３９】
実施例３の試験片は、短繊維Ｍの配合量を、ゴム成分１００重量部に対して５．００重量部から１．００重量部に削減したことを除き、実施例１のゴム組成物と同じ組成を有する、本発明に係るゴム組成物を使用して調製した試験片である。短繊維Ｍの配合量を大幅に削減したことにより、氷上摩擦指数及び耐摩耗性指数は標準例の試験片とほぼ同等レベルとなったが、耐セット性指数については、上記実施例２の試験片よりも更に高いレベルが達成された。
【００４０】
次に、比較例２の試験片は、短繊維Ｍの配合量を更に削減して、ゴム成分１００重量部に対して０．５０重量部としたことを除き、実施例３のゴム組成物と同じ組成を有する、比較用のゴム組成物を使用して調製した試験片である。短繊維Ｍの配合量を更に削減したことにより、耐セット性の改良効果は顕著となったが、氷上摩擦指数の改良効果が認められなくなった。
【００４１】
一方、比較例３の試験片は、比較例２とは逆に、短繊維Ｍの配合量を増大させて、ゴム成分１００重量部に対して１１．００重量部としたことを除き、実施例３のゴム組成物と同じ組成を有する、比較用のゴム組成物を使用して調製した試験片である。短繊維Ｍの配合量を大幅に増大させたことにより、硬度及び氷上摩擦指数は大幅に増大したものの、耐摩耗性指数及び耐セット性指数は大幅に低下した。
【００４２】
比較例４の試験片は、配合剤Ｂの配合量（ｂ）を、ゴム成分１００重量部に対して０．４０重量部から０．１０重量部に削減したことを除き、実施例１のゴム組成物と同じ組成を有する、比較用のゴム組成物を使用して調製した試験片である。配合剤Ｂの配合量を大幅に削減したにもかかわらず、架橋剤成分の配合量（ａ＋ｂ／２）及び架橋剤成分の配合量に対する加硫促進剤の配合量の比（ｃ／（ａ＋ｂ／２））の値は本発明の規定範囲内に収まったものの、配合剤Ｂの配合量自体が本発明の規定範囲の下限（０．２）を下回ったため、短繊維Ｍの配合に伴う耐セット性指数の低下を抑制するという配合剤Ｂの配合効果が十分に得られず、耐セット性が不十分であった。
【００４３】
比較例５の試験片は、ゴム成分１００重量部に対して、硫黄の配合量（ａ）を１．００重量部から１．６０重量部に増大させる一方で加硫促進剤（ＴＢＢＳ）の配合量（ｃ）を０．８０重量部から１．０５重量部に増大させたことを除き、実施例２のゴム組成物と同じ組成を有する、比較用のゴム組成物を使用して調製した試験片である。加硫系成分の各配合量を上記の如く調整することにより、架橋剤成分の配合量に対する加硫促進剤の配合量の比（ｃ／（ａ＋ｂ／２））は本発明の規定範囲内に収まったものの、架橋剤成分の配合量（ａ＋ｂ／２）が過大となり、その結果、耐摩耗性指数及び耐セット性指数が不十分であった。
【００４４】
比較例６の試験片は、加硫促進剤（ＴＢＢＳ）の配合量（ｃ）をゴム成分１００重量部に対して１．００重量部から０．７０重量部に削減したことを除き、実施例１のゴム組成物と同じ組成を有する、比較用のゴム組成物を使用して調製した試験片である。加硫促進剤（ＴＢＢＳ）の配合量を大幅に削減したために、架橋剤成分の配合量に対する加硫促進剤の配合量の比（ｃ／（ａ＋ｂ／２））の値が本発明の規定範囲の下限（０．５）を下回り、短繊維Ｍの配合に伴う耐セット性指数の低下を抑制するという配合剤Ｂの配合効果が得られなかった。
【００４５】
比較例７の試験片は、硫黄の配合量（ａ）をゴム成分１００重量部に対して１．３０重量部から０．９０重量部に削減し、かつ、加硫促進剤（ＴＢＢＳ）の配合量（ｃ）をゴム成分１００重量部に対して１．００重量部から１．２０重量部に増大させたことを除き、実施例１のゴム組成物と同じ組成を有する、比較用のゴム組成物を使用して調製した試験片であり、架橋剤成分の配合量（ａ＋ｂ／２）は本発明の規定範囲の下限（１．２）を下回り、架橋剤成分の配合量に対する加硫促進剤の配合量の比（ｃ／（ａ＋ｂ／２））は本発明の規定範囲の上限（１．０）を上回っている。その結果、耐セット性指数は良好であったが、耐摩耗性指数が大幅に低下した。
【００４６】
実施例４の試験片は、短繊維Ｍ（平均長＝３ｍｍ）を短繊維Ｓ（平均長＝０．２ｍｍ）に置き換えたことを除き、実施例１のゴム組成物と同じ組成を有する、本発明に係るゴム組成物を使用して調製した試験片である。ゴム組成物に配合する短繊維の平均長を短くしても、実施例１の試験片とほぼ同等の諸物性を達成することができた。
【００４７】
更に、比較例８の試験片は、実施例４とは逆に、短繊維Ｍ（平均長＝３ｍｍ）を短繊維Ｌ（平均長＝１２ｍｍ）に置き換えたことを除き、実施例１のゴム組成物と同じ組成を有する、比較用のゴム組成物を使用して調製した試験片である。ゴム組成物に配合する短繊維の平均長を、本発明の規定範囲の上限（１０ｍｍ）を超えて長くしたために、硬度及び氷上摩擦指数は大幅に増大したものの、耐摩耗性指数及び耐セット性指数は大幅に低下した。
【００４８】
以上の結果から、本発明の規定に従って、ゴム成分に短繊維を配合し、更に、上記ａ、ｂ、及びｃの値が上記３個の関係式を同時に満足するように、硫黄、配合剤Ｂ、及び１種以上の加硫促進剤を配合することによって、加硫後のゴム組成物において、短繊維の配合による氷上制動性能を更に向上させると同時に、短繊維の配合による耐セット性の低下を十分に抑制することができることが明らかとなった。
【００４９】
【発明の効果】
本発明により、耐摩耗性及び耐セット性を維持しつつ、優れた氷上制動性能を発揮する、タイヤトレッド用ゴム組成物が提供される。本発明に係るゴム組成物は、特にタイヤトレッド用ゴム組成物、とりわけ氷雪路、湿潤路、乾燥路等における走行を目的とする全天候タイヤ及び／又はスタッドレスタイヤのタイヤトレッド用ゴム組成物として有用である。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a rubber composition, particularly a rubber composition for a tire tread, and particularly to a rubber composition for a tire tread of an all-weather tire and / or a studless tire for running on an icy road, a wet road, a dry road, and the like.
[0002]
[Prior art]
2. Description of the Related Art Tires, particularly all-weather tires and / or studless tires for running on icy and snowy roads, wet roads, and dry roads, have tire treads for the purpose of improving braking performance on ice and abrasion resistance on dry roads. It has been conventionally proposed in the art to incorporate short fibers into a rubber composition for use. Examples of such proposals include, for example, JP-A-9-12777 and JP-A-11-28914. And Japanese Patent Application Laid-Open No. 2001-11237.
[0003]
However, in the prior arts including the inventions described in the above publications, the set resistance decreases as the orientation of the short fibers blended in the rubber composition increases, and for example, all weather tires and / or In particular, in a tread pattern having fine blocks and / or sipes such as a studless tire, deformation (smashing) of the block occurs, and the initial groove area and the block shape cannot be maintained. It was often difficult to obtain braking performance on ice.
[0004]
On the other hand, there is a need in the art for further improvements in braking performance on ice, especially in all-weather tires and / or studless tires, and while maintaining wear resistance and set resistance, braking performance on ice. Continuous efforts are being made to further improve
[0005]
Prior art document information related to the invention of this application includes the following.
[Patent Document 1]
Japanese Patent Application Laid-Open No. 9-12777 [Patent Document 2]
JP-A-11-28914 [Patent Document 3]
JP 2001-11237 A
[Problems to be solved by the invention]
An object of the present invention is to provide a rubber composition for a tire tread that exhibits excellent braking performance on ice while maintaining abrasion resistance and set resistance.
[0007]
[Means for Solving the Problems]
The object is as follows: 100 parts by weight of a rubber component composed of at least one diene rubber, 1 to 10 parts by weight of short fibers having an average length of 10 mm or less, and a part by weight of sulfur,

A rubber composition comprising b parts by weight of a compounding agent B represented by the formula and c parts by weight of a total of one or more sulfenamide-based vulcanization accelerators,
Where a, b, and c are as follows:
1.2 ≦ a + b / 2 ≦ 2.0,
0.5 ≦ c / (a + b / 2) ≦ 1.0
Are satisfied at the same time.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
As the rubber component used in the rubber composition according to the present invention, either natural rubber (NR) or diene rubber, or a mixture thereof can be used. Examples of the diene rubber include various polybutadiene rubbers (BR), various styrene-butadiene copolymer rubbers (SBR), polyisoprene rubbers (IR), and ethylene-propylene-diene copolymer rubbers. Preferably, the rubber component in the rubber composition according to the present invention is either natural rubber (NR) or polybutadiene rubber (BR), or a mixture thereof.
[0009]
The rubber composition for a tire tread according to the present invention comprises 1 to 10 parts by weight of a short fiber having an average length of 10 mm or less with respect to 100 parts by weight of the rubber component.

A rubber composition comprising b parts by weight of a compounding agent B represented by the formula and c parts by weight of a total of one or more sulfenamide-based vulcanization accelerators,
Where a, b, and c are as follows:
1.2 ≦ a + b / 2 ≦ 2.0,
0.5 ≦ c / (a + b / 2) ≦ 1.0
Are simultaneously satisfied.
[0010]
Examples of the material constituting the short fibers blended in the rubber composition for a tire tread according to the present invention include, but are not limited to, metals, glass, ceramics, carbon, natural polymers and synthetic polymers. It is not done. Preferably, the material constituting the short fibers is a polyamide-based polymer. More preferably, the material constituting the short fibers is nylon 6 (polycaprolactam).
[0011]
The short fibers preferably have an average length of 10 mm or less, preferably 0.2 to 10 mm, more preferably 0.5 to 5 mm. When the average length of the short fibers is less than 0.2 mm, a sufficient effect of blending the short fibers cannot be obtained in improving the on-ice braking performance of the vulcanized rubber composition. If the average length of the fibers is more than 10 mm, the mixing processability of the rubber composition is reduced due to the incorporation of the short fibers, and the wear resistance of the rubber composition after vulcanization is undesirably reduced.
[0012]
It is desirable that the short fibers have an average diameter of 150 μm or less, preferably 20 to 150 μm, more preferably 40 to 100 μm. When the average diameter of the short fibers is less than 20 μm, the rigidity of the short fibers becomes insufficient, and a sufficient effect of the short fibers is obtained in improving the braking performance on ice of the vulcanized rubber composition. On the contrary, if the average diameter of the short fibers exceeds 150 μm, the rigidity of the short fibers becomes excessively large, and the short fibers are mixed, thereby deteriorating the fatigue resistance of the rubber composition after vulcanization. .
[0013]
Further, the compounding amount of the short fibers in the rubber composition for a tire tread according to the present invention is desirably 1 to 10 parts by weight, preferably 2 to 7 parts by weight based on 100 parts by weight of the rubber component. When the blending amount of the short fiber is less than 1 part by weight based on 100 parts by weight of the rubber component, in improving the braking performance on ice of the rubber composition after vulcanization, the blending of the short fiber is sufficient. When the effect is not obtained and the compounding amount of the short fiber exceeds 10 parts by weight based on 100 parts by weight of the rubber component, the mixing processability of the rubber composition is reduced by the compounding of the short fiber. It is not preferable because it lowers.
[0014]
A + b / 2 in the above formula is a value corresponding to the blending amount of the crosslinking agent component in the rubber composition according to the present invention, and c / (a + b / 2) is the value in the rubber composition according to the present invention. This is a value corresponding to the ratio of the amount of the vulcanization accelerator to the amount of the crosslinking agent component. By compounding the above vulcanization components under conditions that simultaneously satisfy the above formula, a rubber composition having the given properties of the present invention can be obtained.
[0015]
As the sulfur and sulfenamide-based vulcanization accelerators, those well known in the rubber compounding art can be used in usual compounding amounts. Powder sulfur and N-tert-butyl-2-benzothiazolyl-sulfur, respectively, can be used. Phenamide (TBBS) (for example, "Noxeller NS-F" manufactured by Ouchi Shinko Chemical Co., Ltd.) and N-cyclohexyl-2-benzothiazole sulfenamide (CBS) (for example, "Ouchi Shinko Chemical Co., Ltd." Noxeller CZ-G ”) and the like.
[0016]
The compounding agent B itself is a compound known in the rubber compounding technical field. For example, in Japanese Patent Application Laid-Open No. 2001-2833, a vulcanizable rubber composition comprising a diene rubber and a conventional additive is added to a rubber 100% by weight. Parts by weight: a) 0.5 to 3.8 parts by weight of the compounding agent B, b) 0.5 to 2 parts by weight of sulfur, and c) 0.5 to 3.8 parts by weight of at least one vulcanization accelerator. It is disclosed that by incorporating 3.0 parts by weight, the tear resistance and the aging resistance are improved without deteriorating the heat build-up of the rubber composition after vulcanization.
[0017]
However, in the present invention, the compounding amount of sulfur, compounding agent B, and one or more specific vulcanization accelerators (specifically, sulfenamide-based vulcanization accelerators) with respect to 100 parts by weight of the rubber component ( In each case, a, b, and c parts by weight (when a plurality of types of vulcanization accelerators are used, represent the total distribution thereof) are defined so as to simultaneously satisfy the above three relational expressions. By this, it has been found that the rubber composition can realize exceptionally excellent braking performance on ice without sacrificing other properties of the rubber composition, in a tire in which the rubber composition is used for a tread portion. .
[0018]
Specifically, when b is less than 0.2 part by weight, the effect of suppressing a decrease in set resistance due to the incorporation of short fibers in the rubber composition after vulcanization becomes insufficient. On the other hand, when a + b / 2 is less than 1.2 parts by weight, the hardness of the rubber composition after vulcanization is low, which is insufficient for securing the block rigidity. If the amount exceeds the limit, the effect of suppressing a decrease in set resistance due to the incorporation of short fibers in the rubber composition after vulcanization becomes insufficient. Further, when c / (a + b / 2) is less than 0.5, the effect of suppressing the decrease in set resistance due to the incorporation of short fibers in the rubber composition after vulcanization becomes insufficient. When / (a + b / 2) exceeds 1.0, the elongation at break decreases, and the decrease in wear resistance becomes significant.
[0019]
That is, in the rubber composition for a tire tread according to the present invention, the short fibers are blended in a rubber component, and the values of a, b, and c simultaneously satisfy the above three relational expressions. By blending sulfur, blending agent B, and one or more vulcanization accelerators, the rubber composition after vulcanization further improves the braking performance on ice by blending short fibers, and at the same time blends short fibers. It is possible to sufficiently suppress a decrease in set resistance.
[0020]
The rubber composition for a tire tread according to the present invention includes carbon black, filler (for example, silica), process oil, plasticizer, softener, vulcanization aid, vulcanization retarder, vulcanization activator, and aging. Inhibitors and the like and / or other various additives generally used in the rubber compounding technical field can be further compounded. The amounts of these additives may be conventional general amounts as long as the object of the present invention is not adversely affected.
[0021]
Further, in the rubber composition for a tire tread according to the present invention, for example, a rubber composition for a tread of a modern studless tire, such as a heat-expandable thermoplastic resin particle, a crushed rubber, a hard porous particle, and a hollow polymer. Various additives described above may be further added.
[0022]
The rubber composition for a tire tread according to the present invention can be produced by mixing the above components using a known rubber kneading machine (for example, a roll, a Banbury mixer, a kneader, etc.).
[0023]
Although the present invention will be described in more detail with reference to the following standard examples, comparative examples, and examples, the technical scope of the present invention is not limited to these examples.
[0024]
【Example】
Standard Example, Comparative Examples 1 to 8, and Examples 1 to 4
Compounding components Various compounding components used in the preparation of various test pieces described below are listed below.
[0025]
Natural rubber (NR): STR-20
Polybutadiene rubber (BR): "Nipol 1220" manufactured by Zeon Corporation
Carbon black (CB): "Show Black N220" (ISAF) manufactured by Showa Cabot Corporation
Aroma oil: "Flex M" manufactured by Fujikosan Co., Ltd.
Zinc flower: "3 types of zinc oxide" manufactured by Shodo Chemical Co., Ltd.
Stearic acid: "Beads stearic acid" manufactured by NOF Corporation
Anti-aging agent (6PPD): "SANTOFLEX 6PPD" manufactured by Flexsys (N-phenyl-N'-1,3-dimethylbutyl-p-phenylenediamine)
Wax: "Sunnoc" manufactured by Ouchi Shinko Chemical Co., Ltd.
[0026]

[0027]
Preparation of various test pieces The components shown in Table I below, other than sulfur, the compounding agent B, and the vulcanization accelerator, were mixed at the compounding amounts shown in the following Table I using a Banbury mixer and a kneading roll machine. It was kneaded and the masterbatch was released when it reached 165 ± 5 ° C. To this masterbatch, the following amounts of sulfur, compounding agent B (excluding the standard example and comparative example 1), and the vulcanization accelerator shown in Table I were added, and the mixture was kneaded with an 8-inch open roll to obtain a standard. The rubber compositions of Examples, Comparative Examples 1 to 8 and Examples 1 to 4 were obtained. Next, the various rubber compositions were press-vulcanized in a predetermined mold at 150 ° C. for 40 minutes to prepare various target test pieces.
[0028]
[Table 1]

[0029]
Measurement of vulcanization properties of various test pieces The vulcanization properties of the various test pieces comprising the rubber compositions of the standard examples, comparative examples 1 to 8 and examples 1 to 4 obtained as described above were measured. Was measured according to the following test methods.
[0030]
1) Hardness (durometer A):
The above various test pieces were measured in accordance with JIS K6253. The higher the hardness, the higher the effect of suppressing uneven wear due to an increase in block rigidity.
[0031]
2) Friction index on ice:
A coefficient of kinetic friction was measured when each of the above test pieces was slid on an ice plate placed in a constant temperature room at −3 ° C. under the conditions of ground pressure = 3 kg / cm ² and speed = 25 km / h, It was indicated by an index with the measured value in the standard example being 100. The larger the index, the higher the coefficient of friction on ice and the better the braking performance on ice.
[0032]
3) Wear resistance index:
Using the Lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.), a Lambourn abrasion index was measured for each of the above test pieces at a load of 5 kg, a slip ratio of 25%, a time of 4 minutes and room temperature in accordance with JIS K6264. , And an index with the measured value of the standard example being 100. The larger the index, the better the wear resistance.
[0033]
4) Set resistance index:
For each of the above test specimens, the compression set (%) after applying 25% compression for 72 hours at 100 ° C. was measured in accordance with JIS K6262, and the reciprocal of the measured value was calculated. It was indicated by an index with the reciprocal value being 100. The larger the index, the better the set resistance.
[0034]
Evaluation of vulcanization properties of various test pieces The measurement results of the vulcanization properties of each of the above test pieces 1) to 4) are shown in Table I above.
[0035]
The test piece of the standard example is a test piece prepared using a rubber composition serving as a control having a standard composition and containing no short fiber and no compound B.
[0036]
The test piece of Comparative Example 1 had the same composition as the rubber composition of the standard example, except that 5.00 parts by weight of the short fiber M was mixed with 100 parts by weight of the rubber component. Is a test piece prepared using By blending the short fibers M, the hardness and the friction index on ice increased, but the abrasion resistance index decreased slightly and the set resistance index decreased significantly.
[0037]
In the test piece of Example 1, the blending amount (a) of sulfur was reduced from 1.50 parts by weight to 1.30 parts by weight with respect to 100 parts by weight of the rubber component, while compounding B was 0.40 part by weight. (B = 0.40) to maintain the blending amount (a + b / 2) of the crosslinking agent component at a constant value (1.50 parts by weight) and the blending amount (c) of the vulcanization accelerator (TBBS). ) Is a test piece prepared using the rubber composition according to the present invention, having the same composition as the rubber composition of Comparative Example 1 except that the amount of the rubber composition was reduced from 1.20 parts by weight to 1.00 parts by weight. . By adjusting the respective amounts of the vulcanization system components as described above, while maintaining the high hardness and the friction index on ice due to the incorporation of the short fibers M, the set resistance index due to the incorporation of the short fibers M Was suppressed.
[0038]
In the test piece of Example 2, the compounding amount (a) of sulfur was further reduced, the compounding amount (b) of compound B was increased, and the compounding amount (c) of the vulcanization accelerator (TBBS) was further increased. Fig. 4 is a test piece prepared using the rubber composition according to the present invention, having the same composition as the rubber composition of Example 1 except for the reduction. While increasing the compounding amount of the compound B, each compounding amount of the vulcanization system component was adjusted as described above, and vulcanization acceleration with respect to the compounding amount of the crosslinking agent component (a + b / 2) and the compounding amount of the crosslinking agent component. By keeping the value of the ratio (c / (a + b / 2)) of the compounding amount of the agent within the specified range of the present invention, while maintaining the high hardness and friction index on ice caused by compounding the short fibers M, A higher set resistance index than the standard specimen was achieved.
[0039]
The test piece of Example 3 was the same as the rubber composition of Example 1 except that the blending amount of the short fiber M was reduced from 5.00 parts by weight to 1.00 part by weight based on 100 parts by weight of the rubber component. It is a test piece prepared using the rubber composition according to the present invention having the same composition. The friction index on ice and the abrasion resistance index were almost equal to those of the test piece of the standard example due to the drastic reduction of the blending amount of the short fiber M. Even higher levels were achieved than the pieces.
[0040]
Next, the test piece of Comparative Example 2 was the same as the rubber composition of Example 3 except that the blending amount of the short fiber M was further reduced to 0.50 parts by weight with respect to 100 parts by weight of the rubber component. 5 is a test piece prepared using a comparative rubber composition having the same composition. By further reducing the blending amount of the short fibers M, the effect of improving the set resistance became remarkable, but the effect of improving the friction index on ice was not recognized.
[0041]
On the other hand, the test piece of Comparative Example 3 was the same as the Comparative Example 2 except that the amount of the short fiber M was increased to 11.00 parts by weight with respect to 100 parts by weight of the rubber component. 5 is a test piece prepared using a comparative rubber composition having the same composition as the rubber composition of No. 3. Although the hardness and the friction index on ice were greatly increased by greatly increasing the blending amount of the short fibers M, the wear resistance index and the set resistance index were significantly reduced.
[0042]
The test piece of Comparative Example 4 was the same as the rubber of Example 1 except that the blending amount (b) of the compounding agent B was reduced from 0.40 parts by weight to 0.10 parts by weight with respect to 100 parts by weight of the rubber component. It is a test piece prepared using a comparative rubber composition having the same composition as the composition. Despite greatly reducing the compounding amount of compounding agent B, the compounding amount of the crosslinking agent component (a + b / 2) and the ratio of the compounding amount of the vulcanization accelerator to the compounding amount of the crosslinking agent component (c / (a + b / Although the value of 2)) was within the specified range of the present invention, the amount of compounding agent B itself was lower than the lower limit (0.2) of the specified range of the present invention. The compounding effect of compounding agent B, which suppresses a decrease in the property index, was not sufficiently obtained, and the set resistance was insufficient.
[0043]
In the test piece of Comparative Example 5, the compounding amount of sulfur (a) was increased from 1.00 parts by weight to 1.60 parts by weight with respect to 100 parts by weight of the rubber component, while compounding of a vulcanization accelerator (TBBS). A test prepared using a comparative rubber composition having the same composition as the rubber composition of Example 2 except that the amount (c) was increased from 0.80 parts by weight to 1.05 parts by weight. Is a piece. By adjusting the blending amounts of the vulcanizing components as described above, the ratio (c / (a + b / 2)) of the blending amount of the vulcanization accelerator to the blending amount of the crosslinking agent component falls within the range specified in the present invention. Although contained, the blending amount of the crosslinking agent component (a + b / 2) became excessive, and as a result, the wear resistance index and the set resistance index were insufficient.
[0044]
The test piece of Comparative Example 6 was prepared in the same manner as in the Example except that the blending amount (c) of the vulcanization accelerator (TBBS) was reduced from 1.00 part by weight to 0.70 part by weight with respect to 100 parts by weight of the rubber component. 5 is a test piece prepared using a comparative rubber composition having the same composition as the rubber composition of No. 1. Since the amount of the vulcanization accelerator (TBBS) was significantly reduced, the value of the ratio of the amount of the vulcanization accelerator (c / (a + b / 2)) to the amount of the crosslinking agent component was within the specified range of the present invention. Below the lower limit (0.5), the compounding effect of the compounding agent B, which suppresses a decrease in the set resistance index accompanying the compounding of the short fibers M, could not be obtained.
[0045]
In the test piece of Comparative Example 7, the compounding amount of sulfur (a) was reduced from 1.30 parts by weight to 0.90 parts by weight with respect to 100 parts by weight of the rubber component, and the compounding of the vulcanization accelerator (TBBS) was carried out. Comparative rubber composition having the same composition as the rubber composition of Example 1 except that the amount (c) was increased from 1.00 parts by weight to 1.20 parts by weight with respect to 100 parts by weight of the rubber component. A test piece prepared using the product, the amount of the crosslinking agent component (a + b / 2) being below the lower limit (1.2) of the prescribed range of the present invention, and the vulcanization accelerator based on the amount of the crosslinking agent component Is (c / (a + b / 2)), which exceeds the upper limit (1.0) of the specified range of the present invention. As a result, the set resistance index was good, but the wear resistance index was significantly reduced.
[0046]
The test piece of Example 4 has the same composition as the rubber composition of Example 1 except that the short fiber M (average length = 3 mm) was replaced with the short fiber S (average length = 0.2 mm). It is a test piece prepared using the rubber composition according to the present invention. Even when the average length of the short fibers blended in the rubber composition was shortened, it was possible to achieve almost the same physical properties as the test piece of Example 1.
[0047]
Further, the test piece of Comparative Example 8 was the same as the rubber composition of Example 1 except that the short fiber M (average length = 3 mm) was replaced with the short fiber L (average length = 12 mm), contrary to Example 4. 5 is a test piece prepared using a comparative rubber composition having the same composition as the test piece. Since the average length of the short fibers blended in the rubber composition is longer than the upper limit (10 mm) of the specified range of the present invention, the hardness and the friction index on ice are significantly increased, but the wear resistance index and set resistance are increased. The index dropped significantly.
[0048]
From the above results, according to the provisions of the present invention, short fibers are blended with the rubber component, and sulfur and compounding agent B are mixed so that the values of a, b, and c simultaneously satisfy the above three relational expressions. , And by blending one or more vulcanization accelerators, the vulcanized rubber composition further improves the braking performance on ice due to the blending of short fibers, and at the same time, reduces the set resistance due to blending of short fibers. Has been found to be sufficiently suppressed.
[0049]
【The invention's effect】
According to the present invention, there is provided a rubber composition for a tire tread which exhibits excellent braking performance on ice while maintaining abrasion resistance and set resistance. The rubber composition according to the present invention is particularly useful as a rubber composition for a tire tread, particularly a rubber composition for a tire tread of an all-weather tire and / or a studless tire for running on an icy road, a wet road, a dry road or the like. is there.

Claims (1)

For 100 parts by weight of a rubber component composed of at least one diene rubber, 1 to 10 parts by weight of short fibers having an average length of 10 mm or less, and a part by weight of sulfur,

A rubber composition comprising b parts by weight of a compounding agent B represented by the formula and c parts by weight of a total of one or more sulfenamide-based vulcanization accelerators,
Where a, b, and c are as follows:
1.2 ≦ a + b / 2 ≦ 2.0,
0.5 ≦ c / (a + b / 2) ≦ 1.0
A rubber composition characterized by satisfying the relationship at the same time.