JP2004051822A - Rubber composition and tire using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition that prevents the occurrence of a crack tear at the bottom of defence grooves while maintaining resistance against uneven wear and a tire using the composition. <P>SOLUTION: The rubber composition is for preventing cracking, is arranged at the bottom of defence grooves on a tire tread and has a dynamic modulus of ≥ 6 MPa and an elongation at break of ≥ 550%. Presented is a tire having defence grooves with the crack-preventive rubber composition arranged at the bottom of the defence grooves to prevent cracks. <P>COPYRIGHT: (C)2004,JPO

Description

（式（Ｉ）中、Ｒ^１及びＲ^２は炭素数１〜１８までのアルキル基、シクロアルキル基、アリール基で、Ｏ、Ｓ、Ｎ原子を含んでいてもよい。）
【化５】

（式（ＩＩ）中、Ａは芳香族環、置換されているか置換されていないヒダントイン環、炭素数１〜１８の飽和又は不飽和直鎖状炭化水素からなる群より選んだ１種であり、Ｘはヒドロキシ基、アミノ基、下記式（ＩＩＩ）：
【化６】

で表される基より選んだ少なくとも１種であり、Ｒ^３、Ｒ^４、Ｒ^５及びＲ^６は水素及び炭素数１〜１８からなる直鎖状又は分岐状のアルキル基、シクロアルキル基、芳香族環であり、それぞれ同じでも異なっていてもよい。）
【０００９】
ここで、上記天然ゴム／スチレン−ブタジエンゴムの質量比は、９０／１０〜６０／４０であるのがより好ましい。また、前記式（Ｉ）で表される化合物は、１−ヒドロキシ−Ｎ’−（１−メチルエチリデン）−２−ナフトエ酸ヒドラジド、１−ヒドロキシ−Ｎ’−（１−メチルプロピリデン）−２−ナフトエ酸ヒドラジド、１−ヒドロキシ−Ｎ’−（１，３−ジメチルブチリデン）−２−ナフトエ酸ヒドラジド、１−ヒドロキシ−Ｎ’−（２−フリルメチレン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（１−メチルエチリデン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（１−メチルプロピリデン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（１，３−ジメチルブチリデン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（２−フリルメチレン）−２−ナフトエ酸ヒドラジドであり、前記式（ＩＩ）で表される化合物は、Ｎ’−（１−メチルエチリデン）サリチル酸ヒドラジド、Ｎ’−（１−メチルプロピリデン）サリチル酸ヒドラジド、Ｎ’−（１，３−ジメチルブチリデン）サリチル酸ヒドラジド、Ｎ’−（２−フリルメチレン）サリチル酸ヒドラジドであるのがより好ましい。
【００１０】
また、本発明のタイヤは、トレッドにディフェンスグルーブを備えるタイヤにおいて、上記亀裂抑制用ゴム組成物を該ディフェンスグルーブの溝底に亀裂抑制ゴム部材として配設したことを特徴とする。
【００１１】
本発明のタイヤの好適例においては、前記亀裂抑制ゴム部材は、前記ディフェンスグルーブの溝底から開口部へ向けて、ディフェンスグルーブの深さの１０％以上に渡って配設されている。
【００１２】
本発明のタイヤの他の好適例においては、前記亀裂抑制ゴム部材は、厚さが１ｍｍ以上である。
【００１３】
【発明の実施の形態】
以下に、本発明を詳細に説明する。本発明の亀裂抑制用ゴム組成物は、動的弾性率（貯蔵弾性率）が６ＭＰａ以上で且つ切断時伸びが５５０％以上であり、タイヤトレッドのディフェンスグルーブの溝底に配設される。切断時伸びが５５０％以上であれば、大きな横力や路面の凹凸等によりディフェンスグルーブの横の陸部が大きく変形した際の溝底付近のクラック・テアー等の破壊を防止することができる。また、動的弾性率が６ＭＰａ以上であれば、ディフェンスグルーブの溝幅が広がるのを抑制して、該ディフェンスグルーブの外側のゴムの横への変形を抑制することができる。このため、クラック・テアーの進展による陸部の欠けやトレッドとベルトとの間でのセパレーションの発生を抑制することができる。
【００１４】
上記ゴム組成物のゴム成分はジエン系ゴムが好ましく、該ジエン系ゴムとしては、天然ゴム（ＮＲ）、ブタジエンゴム（ＢＲ）、スチレン−ブタジエンゴム（ＳＢＲ）等が挙げられる。この中でも、天然ゴム／スチレン−ブタジエンゴムの質量比が１００／０〜５０／５０であるゴムが好ましい。
【００１５】
耐破壊性を高めるためには、ゴム成分が天然ゴムのみである配合を用いる場合が多いが、スチレン−ブタジエンゴムを併用することにより、耐破壊性を維持しながら、動的弾性率を向上させることができる。但し、ゴム成分に占めるスチレン−ブタジエンゴムの比率が５０質量％を超えると耐破壊性が大きく低下し、同時に発熱性が悪化するため好ましくない。天然ゴム／スチレン−ブタジエンゴムの好ましい質量比は、９０／１０〜６０／４０である。
【００１６】
また、ゴム成分にヒドラジド化合物を配合することで、動的弾性率及び切断時伸びの両方を高めることができる。但し、該ヒドラジド化合物の配合量が少ないと動的弾性率及び切断時伸びを高める効果が小さく、多くなると粘度が上昇し作業性が低下する傾向にある。該ヒドラジド化合物の好ましい配合量は、ゴム成分１００質量部に対し０．５〜５質量部であり、更に好ましくは１〜５質量部である。
【００１７】
本発明で用いられるヒドラジド化合物は、特に限定されないが、前記式（Ｉ）又は（ＩＩ）で表される化合物であることが好ましい。式（Ｉ）で表わされる化合物としては、例えば、１−ヒドロキシ−Ｎ’−（１−メチルエチリデン）−２−ナフトエ酸ヒドラジド、１−ヒドロキシ−Ｎ’−（１−メチルプロピリデン）−２−ナフトエ酸ヒドラジド、１−ヒドロキシ−Ｎ’−（１−メチルブチリデン）−２−ナフトエ酸ヒドラジド、１−ヒドロキシ−Ｎ’−（１，３−ジメチルブチリデン）−２−ナフトエ酸ヒドラジド、１−ヒドロキシ−Ｎ’−（２−フリルメチレン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（１−メチルエチリデン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（１−メチルプロピリデン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（１−メチルブチリデン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（１，３−ジメチルブチリデン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（２−フリルメチレン）−２−ナフトエ酸ヒドラジド等が挙げられる。
【００１８】
また、式（ＩＩ）で表わされる化合物としては、例えば、Ｎ^２，Ｎ^４−ジ（１−メチルエチリデン）イソフタル酸ジヒドラジド、Ｎ^２，Ｎ^４−ジ（１−メチルプロピリデン）イソフタル酸ジヒドラジド、Ｎ^２，Ｎ^４−ジ（１，３−ジメチルブチリデン）イソフタル酸ジヒドラジド、Ｎ’−（１−メチルエチリデン）サリチル酸ヒドラジド、Ｎ’−（１−メチルプロピリデン）サリチル酸ヒドラジド、Ｎ’−（１−メチルブチリデン）サリチル酸ヒドラジド、Ｎ’−（１，３−ジメチルブチリデン）サリチル酸ヒドラジド、Ｎ’−（２−フリルメチレン）サリチル酸ヒドラジド等が挙げられる。
【００１９】
上記式（Ｉ）又は（ＩＩ）で表される化合物は、原料となる３−ヒドロキシ−２−ナフトエ酸ヒドラジド等と、アセトン、メチルイソブチルケトン等とを加温して反応させることにより容易に合成することができる。
【００２０】
動的弾性率及び切断時伸びの向上効果、合成の容易性並びにコスト面から、式（Ｉ）で表される化合物の中でも、１−ヒドロキシ−Ｎ’−（１−メチルエチリデン）−２−ナフトエ酸ヒドラジド、１−ヒドロキシ−Ｎ’−（１−メチルプロピリデン）−２−ナフトエ酸ヒドラジド、１−ヒドロキシ−Ｎ’−（１，３−ジメチルブチリデン）−２−ナフトエ酸ヒドラジド、１−ヒドロキシ−Ｎ’−（２−フリルメチレン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（１−メチルエチリデン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（１−メチルプロピリデン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（１，３−ジメチルブチリデン）−２−ナフトエ酸ヒドラジド、３−ヒドロキシ−Ｎ’−（２−フリルメチレン）−２−ナフトエ酸ヒドラジドが望ましく、また、式（ＩＩ）で表される化合物の中でも、Ｎ’−（１−メチルエチリデン）サリチル酸ヒドラジド、Ｎ’−（１−メチルプロピリデン）サリチル酸ヒドラジド、Ｎ’−（１，３−ジメチルブチリデン）サリチル酸ヒドラジド、Ｎ’−（２−フリルメチレン）サリチル酸ヒドラジドが望ましい。
【００２１】
本発明の亀裂抑制用ゴム組成物には、上記ゴム成分及びヒドラジド化合物の他、通常ゴム業界で用いられるカーボンブラック等の充填剤、その他の各種配合剤を適宜配合することができる。
【００２２】
本発明のタイヤは、トレッドにディフェンスグルーブを備え、上述した亀裂抑制用ゴム組成物を該ディフェンスグルーブの溝底に亀裂抑制ゴム部材として配設したことを特徴とする。そのため、横力や路面の凹凸等によりディフェンスグルーブの横の陸部が大きく変形した際の溝底付近のクラック・テアー等の破壊を防止でき、また、ディフェンスグルーブの溝幅が広がるのを抑制して、該ディフェンスグルーブの外側のゴムの横への変形を抑制することができる。
【００２３】
上記亀裂抑制ゴム部材は溝底及びその近傍に配設されることが好ましく、ディフェンスグルーブの溝底から開口部へ向けて、ディフェンスグルーブの深さの１０％以上に渡って配設されているのが好ましい。クラック・テアーは応力の集中しやすい溝底（最深部）付近から進展することが多いが、溝底（最深部）から多少上側に発生したクラック・テアーが進展することもある。これに対し、亀裂抑制ゴム部材をディフェンスグルーブの溝底から溝開口部へ向けて、ディフェンスグルーブの溝深さの１０％以上に渡って設けることにより、溝底（最深部）から多少上側に発生したクラック・テアーの進展を抑制できる。
【００２４】
上記亀裂抑制ゴム部材は、厚さが１ｍｍ以上であるのが好ましい。亀裂抑制ゴム部材の厚さが１ｍｍ未満では、クラック・テアーの進展を抑制できなくなることがある。
【００２５】
次　に、図１を参照して本発明のタイヤを詳細に説明する。図１は、本発明のタイヤの　好適実施例におけるトレッドの部分断面図である。図示例のタイヤのトレッド１には、タイヤ周方向に沿って直線状に延びる周方向主溝２が形成されており、また、ショルダーリブ３にはショルダー寄りに周方向に沿って直線状に延び且つ周方向主溝２よりも幅狭のディフェンスグルーブ４が形成されている。
【００２６】
ディフェンスグルーブ４の溝幅Ｗ１は、ショルダーリブ３内に接地圧の急激な段差が生じないように、トレッド幅Ｗの３％以下の溝幅とすることが好ましく、タイヤの負荷転動時、接地領域において溝壁同士が実質上接触するようにトレッド幅Ｗの０．３〜２％程度とすることが更に好ましい。また、偏摩耗防止の効果を得るためには、ディフェンスグルーブ４の溝深さＤ１は、隣接する周方向主溝２の深さＤの３０％以上であることが好ましく、更に好ましくは１００％以内である。
【００２７】
図示例のタイヤのトレッド１は、路面側のキャップゴム１Ａと、キャップゴム１Ａのタイヤ径方向内側に配置されるベースゴム１Ｂとからなる、所謂キャップ・ベース構造である。キャップゴム１Ａ及びベースゴム１Ｂのゴムの種類は従来通りであり、キャップゴム１Ａには主に耐摩耗性を考慮したゴム、ベースゴム１Ｂには発熱耐久性を考慮したゴムが用いられる。なお、図示例のトレッドはキッャプ・ベース構造であるが、本発明のタイヤのトレッドの構造はこれに限られず、単一のゴムで構成されても、三種類以上のゴムで構成されてもよい。
【００２８】
本実施形態では、ディフェンスグルーブ４の溝底付近にクラック・テアー等の破壊を防止するための亀裂抑制ゴム部材１Ｃが配設されている。この亀裂抑制ゴム部材１Ｃに用いるゴム組成物は、動的弾性率が６ＭＰａ以上で且つ切断時伸びが５５０％以上である。ここで、亀裂抑制ゴム部材１Ｃは、ディフェンスグルーブ４の溝底（最深部）から開口部へ向けて、ディフェンスグルーブ４の溝深さＤ１の１０％以上に渡って設けることが好ましい。
【００２９】
また、クラック・テアー抑制効果を得る観点から、亀裂抑制ゴム部材１Ｃの厚さｔ１は、溝底付近（少なくとも溝底のタイヤ径方向内側及び溝底のタイヤ幅方向）において１ｍｍ以上確保することが好ましく、２〜５ｍｍがより好ましい。亀裂抑制ゴム部材１Ｃの厚さｔ１が５ｍｍを超えると、発熱性等の他の性能とのバランスが悪化するため好ましくない。
【００３０】
ディフェンスグルーブ４の溝底付近の溝壁は、亀裂抑制ゴム部材１Ｃが露出していることが好ましいが、薄肉であればキャップゴム１Ａが亀裂抑制ゴム部材１Ｃの溝壁側に配置されていてもよい。図示例では、亀裂抑制ゴム部材１Ｃの溝壁側に、キャップゴム１Ａが薄膜状に配置されている。このように、亀裂抑制ゴム部材１Ｃが溝壁に露出しない場合、亀裂抑制ゴム部材１Ｃを覆う薄膜状のキャップゴム１Ａの厚さｔは、１ｍｍ以下が好ましく、０．５ｍｍ以下が更に好ましい。
【００３１】
図示例のタイヤでは、該タイヤに横力が働いた場合、ショルダーリブ３にかかる接地圧をディフェンスグルーブ４が適正に減少させ、ショルダーリブ３の接地圧分布をより均一化することによって、偏摩耗の核たる局部摩耗が発生するのを抑制すると共に、発生した局部摩耗がショルダーリブ３のタイヤ軸方向内側（タイヤ赤道面側）へ成長進行することを抑制する。
【００３２】
また、ディフェンスグルーブ４の溝底及びその近傍に、動的弾性率が６ＭＰａ以上で且つ切断時伸びが５５０％以上であるゴム組成物よりなる亀裂抑制ゴム部材１Ｃを配設したので、大きな横力や路面の凹凸等によりディフェンスグルーブ４の外側の陸部が大きく変形した際の溝底付近のクラック・テアー等の破壊を防止することができ、その結果、ディフェンスグルーブ４の外側の陸部の欠けや、トレッド１のセパレーションを抑制することができる。
【００３３】
なお、溝底（最深部）から多少上側より発生したクラック・テアーが進展することもあるが、亀裂抑制ゴム部材１Ｃをディフェンスグルーブ４の溝底から溝開口部へ向けて、ディフェンスグルーブ４の溝深さＤの１０％以上に渡って設けることにより、このようなクラック・テアーの進展を抑制できる。また、亀裂抑制ゴム部材１Ｃは、ディフェンスグルーブ４の底部付近にのみ少量使用されているので、トレッド１の基本性能を低下させることがない。
【００３４】
【実施例】
以下に、実施例及び比較例を挙げて本発明を更に詳しく説明するが、本発明はこれらの例によりその範囲を限定されるものではない。
【００３５】
表１の配合のゴム組成物を調製し、下記の方法により切断時伸び及び動的弾性率を測定した。測定結果を表１に示す。
【００３６】
（１）切断時伸び
ＪＩＳ＃３号型試験片を用いて、ＪＩＳ　Ｋ　６２５１に準拠して引張試験を行い、切断時の伸び（％）を測定した。
【００３７】
（２）動的弾性率
スペクトロメーターを用い、室温、初期荷重１００ｇ、歪１％の条件で動的弾性率（ＭＰａ）を測定した。
【００３８】
更に、該ゴム組成物を図１に記載のディフェンスグルーブ底に配置される亀裂抑制ゴム部材に用い、タイヤサイズ２９５／７５Ｒ２２．５のトラック・バス用ラジアルタイヤ（ＴＢＲ）を試作し、実車にて２０万ｋｍ走行後のタイヤのショルダーリブ部に発生したテアーの総長さを測定した。測定結果を表１に示す。なお、亀裂抑制ゴム部材は、厚さが溝底付近で２ｍｍ、溝底からの高さが溝深さの４０％（６ｍｍ）、亀裂抑制ゴム部材を覆う薄膜状のキャップゴムの厚さｔが０．５ｍｍである。
【００３９】
【表１】

【００４０】
比較例１のタイヤは、切断時伸び及び動的弾性率共に低いため、ディフェンスグルーブ内にテアーの発生が見られた。動的弾性率のみを向上させた比較例２のタイヤは、比較例１に比しテアーの発生が若干改善されているものの、テアーの発生の防止までには至っていなかった。また、切断時伸びを向上させた比較例３のタイヤは、比較例１に比しテアーの発生がかなり改善されているものの、テアーの発生の防止までには至っていなかった。
【００４１】
これに対し、実施例１〜３のタイヤは、切断時伸び及び動的弾性率共に充分高いため、ディフェンスグルーブ内のテアーの発生が完全に防止できた。
【００４２】
【発明の効果】
本発明によれば、動的弾性率が６ＭＰａ以上で且つ切断時伸びが５５０％以上であるゴム組成物をタイヤトレッドのディフェンスグルーブの溝底及びその近傍に配設することにより、クラック・テアーの発生を防止することができ、タイヤが完全に摩耗するまで良好な状態で使用することができる。
【図面の簡単な説明】
【図１】本発明のタイヤの一実施態様のトレッドの部分断面図である。
【符号の説明】
１　トレッド
１Ａ　キャップゴム
１Ｂ　ベースゴム
１Ｃ　亀裂抑制ゴム部材
２　周方向主溝
３　ショルダーリブ
４　ディフェンスグルーブ
Ｗ　トレッド幅
Ｗ１　ディフェンスグルーブの溝幅
Ｄ　周方向主溝の深さ
Ｄ１　ディフェンスグルーブの溝深さ
ｔ　亀裂抑制ゴム部材を覆う薄膜状のキャップゴムの厚さ
ｔ１　亀裂抑制ゴム部材の厚さ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a rubber composition and a tire using the same, and more particularly to a rubber composition for preventing cracks provided at a groove bottom of a defense groove of a tire tread.
[0002]
[Prior art]
Since a radial tire (TBR) for trucks and buses is required to have uneven wear resistance, a relatively narrow (1 to 4 mm) groove extending in the tire circumferential direction called a defense groove near a shoulder portion of a tread of the tire. Is provided.
[0003]
Since the defense groove is formed relatively close to the shoulder portion, the rigidity of the land portion outside the defense groove in the tire width direction is smaller than that of the other land portions. In addition, due to its structure, the radius of curvature of the bottom of the defense groove must be small (about 1 to 3 mm), and cracks and tears are generated at the bottom of the groove of the defense groove due to deterioration of rubber due to running. There was a problem that it was easy. Here, if the crack tear extends to the shoulder side, the outer rib part of the defense groove may be chipped, and if the crack tear extends to the belt side, a separation occurs between the tread and the belt and a tire burst occurs. May be reached.
[0004]
In order to solve this problem, there have been proposed tires in which the tread rubber is improved or the vicinity of the groove bottom of the defense groove has a substantially circular cross section. However, when the crack and tear are suppressed by improving the tread rubber, the uneven wear resistance is reduced, and a problem arises that the original effect of the defense groove cannot be sufficiently exhibited.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems of the prior art, and to use a rubber composition for preventing crack and tear from being generated at a groove bottom of a defense groove while maintaining uneven wear resistance, and using the same. To provide tires.
[0006]
[Means for Solving the Problems]
The present inventor has conducted intensive studies to achieve the above object, and as a result, has found that the occurrence of cracks and tears can be suppressed by applying a rubber composition for suppressing cracks having specific physical properties to the groove bottoms. Was completed.
[0007]
That is, the rubber composition for crack suppression according to the present invention is disposed at the groove bottom of the defense groove of the tire tread, and has a dynamic elastic modulus of 6 MPa or more and an elongation at break of 550% or more.
[0008]
In a preferred example of the rubber composition for suppressing cracks according to the present invention, the rubber composition comprises a rubber component having a natural rubber / styrene-butadiene rubber mass ratio of 100/0 to 50/50, and a rubber component of 100 mass%. Parts by weight, and 0.5 to 5 parts by mass of at least one hydrazide compound represented by the following formula (I) or (II).
Embedded image

(In the formula (I), R ¹ and R ² are an alkyl group, a cycloalkyl group, or an aryl group having 1 to 18 carbon atoms, which may contain O, S, and N atoms.)
Embedded image

(In the formula (II), A is one selected from the group consisting of an aromatic ring, a substituted or unsubstituted hydantoin ring, a saturated or unsaturated linear hydrocarbon having 1 to 18 carbon atoms, X is a hydroxy group, an amino group, the following formula (III):
Embedded image

Wherein R ³ , R ⁴ , R ⁵ and R ⁶ are hydrogen and a linear or branched alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an aromatic group, Group rings, which may be the same or different. )
[0009]
Here, the mass ratio of the natural rubber / styrene-butadiene rubber is more preferably 90/10 to 60/40. Compounds represented by the formula (I) include 1-hydroxy-N ′-(1-methylethylidene) -2-naphthoic acid hydrazide, 1-hydroxy-N ′-(1-methylpropylidene) -2 -Naphthoic acid hydrazide, 1-hydroxy-N '-(1,3-dimethylbutylidene) -2-naphthoic acid hydrazide, 1-hydroxy-N'-(2-furylmethylene) -2-naphthoic acid hydrazide, 3- Hydroxy-N ′-(1-methylethylidene) -2-naphthoic acid hydrazide, 3-hydroxy-N ′-(1-methylpropylidene) -2-naphthoic acid hydrazide, 3-hydroxy-N ′-(1,3 -Dimethylbutylidene) -2-naphthoic acid hydrazide, 3-hydroxy-N '-(2-furylmethylene) -2-naphthoic acid hydrazide, and represented by the formula (II) Are N '-(1-methylethylidene) salicylic hydrazide, N'-(1-methylpropylidene) salicylic hydrazide, N '-(1,3-dimethylbutylidene) salicylic hydrazide, N'-(2-furylmethylene) ) Salicylic acid hydrazide is more preferred.
[0010]
Further, the tire of the present invention is characterized in that in the tire provided with a defense groove in the tread, the above-described rubber composition for suppressing cracks is disposed as a crack-suppressing rubber member at the groove bottom of the defense groove.
[0011]
In a preferred example of the tire according to the present invention, the crack suppressing rubber member is disposed from the groove bottom of the defense groove toward the opening over 10% of the depth of the defense groove.
[0012]
In another preferred embodiment of the tire of the present invention, the crack suppressing rubber member has a thickness of 1 mm or more.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail. The rubber composition for crack suppression of the present invention has a dynamic elastic modulus (storage elastic modulus) of 6 MPa or more and an elongation at break of 550% or more, and is disposed at the groove bottom of the defense groove of the tire tread. If the elongation at break is 550% or more, it is possible to prevent cracks, tears, and the like near the groove bottom when the lateral land portion of the defense groove is greatly deformed due to a large lateral force or unevenness of the road surface. Further, when the dynamic elastic modulus is 6 MPa or more, it is possible to suppress the groove width of the defense groove from expanding, and to suppress lateral deformation of the rubber outside the defense groove. For this reason, it is possible to suppress chipping of the land due to the development of the crack tear and occurrence of separation between the tread and the belt.
[0014]
The rubber component of the rubber composition is preferably a diene rubber, and examples of the diene rubber include natural rubber (NR), butadiene rubber (BR), and styrene-butadiene rubber (SBR). Among them, a rubber having a natural rubber / styrene-butadiene rubber mass ratio of 100/0 to 50/50 is preferable.
[0015]
In order to increase the fracture resistance, a rubber component is often used only in the composition of natural rubber, but by using a styrene-butadiene rubber in combination, the dynamic elastic modulus is improved while maintaining the fracture resistance. be able to. However, when the ratio of the styrene-butadiene rubber in the rubber component exceeds 50% by mass, the fracture resistance is greatly reduced, and at the same time, the heat generation is unfavorably deteriorated. The preferred mass ratio of natural rubber / styrene-butadiene rubber is 90/10 to 60/40.
[0016]
Further, by blending the hydrazide compound with the rubber component, both the dynamic elastic modulus and the elongation at break can be increased. However, when the amount of the hydrazide compound is small, the effect of increasing the dynamic elastic modulus and elongation at break is small, and when the amount is large, the viscosity tends to increase and the workability tends to decrease. The preferred amount of the hydrazide compound is 0.5 to 5 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.
[0017]
The hydrazide compound used in the present invention is not particularly limited, but is preferably a compound represented by the formula (I) or (II). Examples of the compound represented by the formula (I) include 1-hydroxy-N '-(1-methylethylidene) -2-naphthoic acid hydrazide, 1-hydroxy-N'-(1-methylpropylidene) -2- Naphthoic acid hydrazide, 1-hydroxy-N '-(1-methylbutylidene) -2-naphthoic acid hydrazide, 1-hydroxy-N'-(1,3-dimethylbutylidene) -2-naphthoic acid hydrazide, 1- Hydroxy-N '-(2-furylmethylene) -2-naphthoic acid hydrazide, 3-hydroxy-N'-(1-methylethylidene) -2-naphthoic acid hydrazide, 3-hydroxy-N '-(1-methylpropy Ridene) -2-naphthoic acid hydrazide, 3-hydroxy-N '-(1-methylbutylidene) -2-naphthoic acid hydrazide, 3-hydroxy-N'-(1,3-di Chirubuchiriden) -2-naphthoic acid hydrazide, 3-hydroxy -N '- (2-furyl-methylene) -2-naphthoic acid hydrazide, and the like.
[0018]
The compound represented by Formula (II), for ^example, N 2, ^{N 4} - di (1-methylethylidene) isophthalic acid ^dihydrazide, N 2, ^{N 4} - di (1-methyl-propylidene) isophthalic acid dihydrazide, N ² , N ⁴ -Di (1,3-dimethylbutylidene) isophthalic dihydrazide, N ′-(1-methylethylidene) salicylic hydrazide, N ′-(1-methylpropylidene) salicylic hydrazide, N ′-(1 -Methylbutylidene) salicylic hydrazide, N '-(1,3-dimethylbutylidene) salicylic hydrazide, N'-(2-furylmethylene) salicylic hydrazide and the like.
[0019]
The compound represented by the above formula (I) or (II) is easily synthesized by reacting 3-hydroxy-2-naphthoic acid hydrazide or the like as a raw material with acetone, methyl isobutyl ketone or the like by heating. can do.
[0020]
Among the compounds represented by the formula (I), 1-hydroxy-N ′-(1-methylethylidene) -2-naphthoe is preferred from the viewpoints of improving dynamic elastic modulus and elongation at break, ease of synthesis and cost. Acid hydrazide, 1-hydroxy-N ′-(1-methylpropylidene) -2-naphthoic acid hydrazide, 1-hydroxy-N ′-(1,3-dimethylbutylidene) -2-naphthoic acid hydrazide, 1-hydroxy -N '-(2-furylmethylene) -2-naphthoic acid hydrazide, 3-hydroxy-N'-(1-methylethylidene) -2-naphthoic acid hydrazide, 3-hydroxy-N '-(1-methylpropylidene) ) -2-Naphthoic acid hydrazide, 3-hydroxy-N '-(1,3-dimethylbutylidene) -2-naphthoic acid hydrazide, 3-hydroxy-N'-(2-furylmethylene -2-Naphthoic acid hydrazide is desirable, and among the compounds represented by formula (II), N '-(1-methylethylidene) salicylic acid hydrazide, N'-(1-methylpropylidene) salicylic acid hydrazide, N ' -(1,3-Dimethylbutylidene) salicylic hydrazide and N '-(2-furylmethylene) salicylic hydrazide are preferred.
[0021]
In addition to the rubber component and the hydrazide compound, a filler such as carbon black, which is usually used in the rubber industry, and other various compounding agents can be appropriately added to the crack-inhibiting rubber composition of the present invention.
[0022]
The tire according to the present invention is characterized in that the tread is provided with a defense groove, and the above-described rubber composition for crack suppression is disposed as a crack suppression rubber member at the groove bottom of the defense groove. Therefore, cracks and tears near the groove bottom can be prevented from being destroyed when the land portion beside the defense groove is greatly deformed due to lateral force or unevenness of the road surface, etc.In addition, the groove width of the defense groove is suppressed from expanding. Thus, the lateral deformation of the rubber outside the defense groove can be suppressed.
[0023]
The crack suppressing rubber member is preferably provided at and near the groove bottom, and is provided from the groove bottom of the defense groove toward the opening over 10% or more of the depth of the defense groove. Is preferred. Crack tear often develops near the groove bottom (deepest part) where stress tends to concentrate, but crack tear generated slightly above the groove bottom (deepest part) may also develop. On the other hand, by providing the crack suppressing rubber member from the groove bottom of the defense groove toward the groove opening over 10% or more of the groove depth of the defense groove, the rubber member is generated slightly above the groove bottom (deepest part). Crack tear progress can be suppressed.
[0024]
The crack suppressing rubber member preferably has a thickness of 1 mm or more. If the thickness of the crack suppressing rubber member is less than 1 mm, it may not be possible to suppress the progress of the crack and tear.
[0025]
Next, the tire of the present invention will be described in detail with reference to FIG. FIG. 1 is a partial sectional view of a tread in a preferred embodiment of the tire of the present invention. The tread 1 of the illustrated example tire has a circumferential main groove 2 extending linearly along the tire circumferential direction, and the shoulder rib 3 linearly extends along the circumferential direction toward the shoulder. In addition, a defense groove 4 narrower than the circumferential main groove 2 is formed.
[0026]
The groove width W1 of the defense groove 4 is preferably 3% or less of the tread width W so as to prevent a sharp step in the contact pressure in the shoulder rib 3 from occurring. More preferably, the width is set to about 0.3 to 2% of the tread width W so that the groove walls substantially contact each other in the region. In order to obtain the effect of preventing uneven wear, the groove depth D1 of the defense groove 4 is preferably 30% or more of the depth D of the adjacent circumferential main groove 2, and more preferably 100% or less. It is.
[0027]
The tread 1 of the illustrated tire has a so-called cap-base structure including a cap rubber 1A on the road surface side and a base rubber 1B disposed inside the cap rubber 1A in the tire radial direction. The types of the rubber of the cap rubber 1A and the base rubber 1B are the same as those of the related art. The cap rubber 1A is mainly made of rubber in consideration of wear resistance, and the base rubber 1B is made of rubber in consideration of heat resistance. Although the tread in the illustrated example has a cap-based structure, the structure of the tread of the tire of the present invention is not limited to this, and may be formed of a single rubber or may be formed of three or more types of rubber. .
[0028]
In the present embodiment, a crack suppressing rubber member 1C for preventing breakage of cracks and tears is provided near the groove bottom of the defense groove 4. The rubber composition used for the crack suppressing rubber member 1C has a dynamic elastic modulus of 6 MPa or more and an elongation at break of 550% or more. Here, the crack suppressing rubber member 1C is preferably provided from the groove bottom (deepest part) of the defense groove 4 to the opening over 10% or more of the groove depth D1 of the defense groove 4.
[0029]
In addition, from the viewpoint of obtaining a crack and tear suppressing effect, the thickness t1 of the crack suppressing rubber member 1C is preferably 1 mm or more near the groove bottom (at least in the tire radial direction inside the groove bottom and in the tire width direction at the groove bottom). Preferably, 2-5 mm is more preferable. If the thickness t1 of the crack suppressing rubber member 1C exceeds 5 mm, it is not preferable because the balance with other properties such as heat generation deteriorates.
[0030]
It is preferable that the crack suppressing rubber member 1C is exposed on the groove wall near the groove bottom of the defense groove 4. However, if the cap rubber 1A is thin, even if the cap rubber 1A is arranged on the groove wall side of the crack suppressing rubber member 1C. Good. In the illustrated example, the cap rubber 1A is disposed in a thin film shape on the groove wall side of the crack suppressing rubber member 1C. Thus, when the crack suppressing rubber member 1C is not exposed to the groove wall, the thickness t of the thin cap rubber 1A covering the crack suppressing rubber member 1C is preferably 1 mm or less, more preferably 0.5 mm or less.
[0031]
In the illustrated tire, when a lateral force acts on the tire, the contact pressure applied to the shoulder rib 3 is appropriately reduced by the defense groove 4, and the contact pressure distribution of the shoulder rib 3 is made more uniform, thereby causing uneven wear. In addition to suppressing the occurrence of local wear, which is the core of the tire, the growth of the generated local wear toward the inside of the shoulder rib 3 in the tire axial direction (tire equatorial plane side) is suppressed.
[0032]
In addition, a crack suppressing rubber member 1C made of a rubber composition having a dynamic elastic modulus of 6 MPa or more and an elongation at break of 550% or more is provided at and near the groove bottom of the defense groove 4, so that a large lateral force is applied. When the land on the outside of the defense groove 4 is greatly deformed due to irregularities or road surface irregularities, it is possible to prevent cracks, tears, etc. near the groove bottom from being broken, and as a result, the land on the outside of the defense groove 4 is chipped. Also, the separation of the tread 1 can be suppressed.
[0033]
In addition, cracks and tears generated from the groove bottom (deepest part) slightly from above may develop. However, the crack suppressing rubber member 1C is moved from the groove bottom of the defense groove 4 toward the groove opening, and the groove of the defense groove 4 is formed. By providing over 10% of the depth D, such crack tear can be suppressed from developing. In addition, since the crack suppressing rubber member 1C is used only in a small amount near the bottom of the defense groove 4, the basic performance of the tread 1 does not decrease.
[0034]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these examples.
[0035]
A rubber composition having the composition shown in Table 1 was prepared, and the elongation at break and the dynamic elastic modulus were measured by the following methods. Table 1 shows the measurement results.
[0036]
(1) Elongation at break Using a JIS # 3 type test piece, a tensile test was performed in accordance with JIS K6251, and the elongation at break (%) was measured.
[0037]
(2) Using a dynamic elastic modulus spectrometer, the dynamic elastic modulus (MPa) was measured under the conditions of room temperature, initial load of 100 g, and strain of 1%.
[0038]
Further, a radial tire (TBR) for trucks and buses having a tire size of 295 / 75R22.5 was prototyped using the rubber composition as a crack suppressing rubber member disposed on the bottom of the defense groove shown in FIG. The total length of the tear generated on the shoulder rib portion of the tire after traveling 200,000 km was measured. Table 1 shows the measurement results. The thickness of the crack suppressing rubber member is 2 mm near the groove bottom, the height from the groove bottom is 40% (6 mm) of the groove depth, and the thickness t of the thin cap rubber covering the crack suppressing rubber member is t 0.5 mm.
[0039]
[Table 1]

[0040]
In the tire of Comparative Example 1, since both the elongation at break and the dynamic elastic modulus were low, the occurrence of tear in the defense groove was observed. In the tire of Comparative Example 2 in which only the dynamic elastic modulus was improved, although the occurrence of tare was slightly improved as compared with Comparative Example 1, the occurrence of tare was not yet prevented. Further, in the tire of Comparative Example 3 in which the elongation at break was improved, although the occurrence of tare was considerably improved as compared with Comparative Example 1, the occurrence of tare was not yet attained.
[0041]
On the other hand, in the tires of Examples 1 to 3, both the elongation at break and the dynamic elastic modulus were sufficiently high, so that the occurrence of tear in the defense groove was completely prevented.
[0042]
【The invention's effect】
According to the present invention, a rubber composition having a dynamic elastic modulus of 6 MPa or more and an elongation at break of 550% or more is provided at the groove bottom of the defense groove of the tire tread and in the vicinity thereof, so that the crack tear can be reduced. Generation can be prevented and the tire can be used in a good condition until it is completely worn.
[Brief description of the drawings]
FIG. 1 is a partial sectional view of a tread of one embodiment of a tire of the present invention.
[Explanation of symbols]
Reference Signs List 1 tread 1A cap rubber 1B base rubber 1C crack suppressing rubber member 2 circumferential main groove 3 shoulder rib 4 defense groove W tread width W1 groove width of defense groove D circumferential main groove depth D1 defense groove groove depth t crack The thickness t1 of the thin film cap rubber covering the suppression rubber member The thickness of the crack suppression rubber member

Claims (7)

A rubber composition for crack suppression, which is disposed at a groove bottom of a defense groove of a tire tread and has a dynamic elastic modulus of 6 MPa or more and an elongation at break of 550% or more. A rubber component having a natural rubber / styrene-butadiene rubber mass ratio of 100/0 to 50/50, and 0.5 to 5 parts by mass of the following formula (I) or formula (II) based on 100 parts by mass of the rubber component. The crack-inhibiting rubber composition according to claim 1, wherein the rubber composition comprises at least one hydrazide compound represented by the formula:

(In the formula (I), R ¹ and R ² are an alkyl group, a cycloalkyl group, or an aryl group having 1 to 18 carbon atoms, which may contain O, S, and N atoms.)

(In the formula (II), A is one selected from the group consisting of an aromatic ring, a substituted or unsubstituted hydantoin ring, a saturated or unsaturated linear hydrocarbon having 1 to 18 carbon atoms, X is a hydroxy group, an amino group, the following formula (III):

Wherein R ³ , R ⁴ , R ⁵ and R ⁶ are hydrogen and a linear or branched alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an aromatic group, Group rings, which may be the same or different. ) The rubber composition for crack suppression according to claim 2, wherein the mass ratio of the natural rubber / styrene-butadiene rubber is 90/10 to 60/40. When the compound represented by the formula (I) is 1-hydroxy-N ′-(1-methylethylidene) -2-naphthoic acid hydrazide, 1-hydroxy-N ′-(1-methylpropylidene) -2-naphthoe Acid hydrazide, 1-hydroxy-N '-(1,3-dimethylbutylidene) -2-naphthoic acid hydrazide, 1-hydroxy-N'-(2-furylmethylene) -2-naphthoic acid hydrazide, 3-hydroxy- N '-(1-methylethylidene) -2-naphthoic acid hydrazide, 3-hydroxy-N'-(1-methylpropylidene) -2-naphthoic acid hydrazide, 3-hydroxy-N '-(1,3-dimethyl (Butylidene) -2-naphthoic acid hydrazide and 3-hydroxy-N ′-(2-furylmethylene) -2-naphthoic acid hydrazide, represented by the formula (II). The compound is N '-(1-methylethylidene) salicylic acid hydrazide, N'-(1-methylpropylidene) salicylic acid hydrazide, N '-(1,3-dimethylbutylidene) salicylic acid hydrazide, N'-(2- The rubber composition according to claim 2, which is (furylmethylene) salicylic acid hydrazide. A tire provided with a defense groove in a tread, wherein the rubber composition for crack suppression according to any one of claims 1 to 4 is provided as a crack suppression rubber member at a groove bottom of the defense groove. The tire according to claim 5, wherein the crack suppressing rubber member is provided from the groove bottom of the defense groove toward the opening over 10% or more of the depth of the defense groove. The tire according to claim 5, wherein the crack suppressing rubber member has a thickness of 1 mm or more.

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