JP2004284375A - Pneumatic radial tire for high speed heavy load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radial tire for an aircraft enhancing abrasion resistance and durability while retaining low heat generation property and high rupture strength. <P>SOLUTION: A belt ply comprises a fiber obtained by mixing and twisting an aromatic polyamide based fiber and an aliphatic polyamide based fiber. A covering rubber is a rubber composition comprising (1) 70-100 parts of natural rubber and/or synthesized isoprene rubber; (2) 30-0 parts of styrene-butadiene copolymer rubber obtained by solution polymerization and having a tin atom in the molecule, having a bonded styrene amount of 3-10% and 1,2-vinyl bonding amount of polybutadiene of 40% or lower; and (3) 40-65 parts of carbon black having a nitrogen adsorption specific surface area of 65-92 m<SP>2</SP>/g and DBP oil absorption amount of 70-132×10<SP>-5</SP>m<SP>3</SP>/kg; and has 100% modulus of 5.0-10.0 MPa and elongation of 300% or higher. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

〔式（Ｉ）中、Ｒ^１とＲ^２は炭素数１〜２０の脂肪族、脂環族、芳香族の炭化水素基から選ばれる基を表し、該基は同一であっても異なっていてもよい。〕
【００２７】
【化２】

〔式（ＩＩ）中、Ｘは次の構造基から選ばれる。Ｘ−Ｉ：（ＣＲ^３Ｒ^４）_ｎからなる飽和型環状構造基、Ｘ−ＩＩ：（Ｒ^５Ｒ^６）_ｍ−Ｙ−（Ｒ^５Ｒ^６）_ｌ（但し、該ＹはＮＲ^７、Ｏ、又は炭素−炭素２重結合を有するイミン化合物である）。ここで、Ｒ^３〜Ｒ^６は水素及び炭素数１〜１０の脂肪族、炭素数３〜１０の脂環族、炭素数６〜１０の芳香族の炭化水素基から選ばれる基を表し、また、Ｒ^７は炭素数１〜１０の脂肪族、炭素数３〜１０の脂環族、炭素数５〜１０の芳香族の炭化水素基から選ばれる基を表し、該基は同一であっても異なっていてもよい。ｎは３〜１０の整数を表し、ｍとｌの合計は２〜９の整数である。〕
【００２８】
これらの中でも、好ましいトリオルガノアミドスズリチウムとしては、例えば、トリピロリジドスズリチウム、トリヘキサメチレンイミドスズリチウム、トリジエチルアミドスズリチウム、及びトリ（ジプロピルアミド）スズリチウム等が挙げられる。
【００２９】
尚、上記において、トリオルガノアミドスズリチウムについては米国特許第５５０２１２９号明細書に記載されており、トリオルガノアミドスズリチウム及びトリオルガノイミドスズリチウムについては米国特許第５４６３００３号明細書に記載されている。また、前記第５の方法として、目的とするスチレン−ブタヂエン共重合体は、スズ原子を有する第３モノマーを導入することによっても得ることができる。ここで、スチレンやブタヂエンと共重合される第３モノマーとしては、下記の一般式（ＩＩＩ）又は（ＩＶ）で表される化合物が好適に用いられる。
【００３０】
【化３】

〔式（ＩＩＩ）中、Ｒ^８〜Ｒ^１０は炭素数１〜３０の脂肪族、脂環族又は芳香族の炭化水素基を表し、該基は同一であっても異なっていてもよい。〕
【００３１】
【化４】

〔式（ＩＶ）中、Ｒ^１１（Ｒ^１２）Ｃ＝ＣＲ^１３−、Ｒ^１４〜Ｒ^１７はベンゼン環に結合する基であり、Ｒ^１１〜Ｒ^２２は、水素原子又は炭素数１〜３０の脂肪族、脂環族又は芳香族の炭化水素基を表し、該基は同一であっても異なっていてもよい。但し、Ｒ^２０〜Ｒ^２２はは水素原子を含まない。〕
【００３２】
具体的には、前記一般式（ＩＩＩ）で表される化合物としては、２−トリブチルスタニル−１，３−ブタジエン、２−トリオクチルスタニル−１，３−ブタジエン、２−トリシクロヘキシルスタニル−１，３−ブタジエン、２−トリフェニルスタニル−１，３−ブタジエン、２−ジブチルフェニルスタニル−１，３−ブタジエン、２−ジフェニルオクチルスタニル−１，３−ブタジエン等が挙げらる。また、前記一般式（ＩＶ）で表わされる化合物としては、ｍ−ビニルベンジルトリブチルスズ、ｍ−ビニルベンジルトリオクチルスズ、ｍ−ビニルベンジルトリフェニルスズ、ｍ−（１−フェニルビニル）ベンヂルトリブチルスズ、及びこれらのｐ−体、ｍ−体／ｐ−体の混合物などが好適に挙げられる。
【００３３】
前記リチウム化合物を重合開始剤として用い、アニオン重合によってスチレン−ブタジエン共重合体（スチレン又はブタジエンのモノマー単位中にスズ原子を導入した共重合体を含む）を製造する方法としては特に制限はなく、従来より公知の方法を用いることができる。具体的には、反応に不活性な有機溶剤、例えば脂肪族、脂環族、芳香族炭化水素化合物などの炭化水素系溶剤中において、スチレンと１，３−ブタジエンを、前記有機リチウム化合物を重合開始剤として、所望により、用いられるランダマイザーの存在下にアニオン重合させることにより、目的のスチレン−ブタジエン共重合体が得られる。この重合反応における温度は、通常−８０〜１５０℃、好ましくは−２０〜１００℃の範囲で適宜に選定される。上記重合反応は、発生圧力下で行うことができるが、通常は単量体を実質的に液相に保つ十分な圧力で操作することが望ましい。所望ならば更に高い圧力を用いることができ、この様な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得られる。
【００３４】
この様にして得られた、重合開始末端にヒドロカルビル基又は窒素含有基を有し、且つ他方の末端が重合活性である変性前のスチレン−ブタジエン共重合体（スチレン又はブタジエンのモノマー単位中にスズ原子を導入した共重合体を含む）の該重合活性末端に、スズ化合物を反応させることにより、所望の変性スチレン−ブタジエン共重合体ゴムが得られる。
上記のスズ化合物としては、例えば、四塩化スズ、トリブチルスズクロリド、トリオクチルスズクロリド、ジオクチルスズジクロリド、ジブチルスズジクロリド、塩化トリフェニルスズなどが挙げられる。また、変性剤を使用せず反応を停止しても分子中にスズ原子が導入されている。
【００３５】
本発明のゴム組成物に用いられる溶液重合ＳＢＲは、分子内に少なくとも１個のスズ原子を有し、分子内の結合スチレン含量が３〜１０質量％であり、且つポリブタジエン鎖部の１，２−ビニル結合量が４０質量％以下である変性スチレン−ブタジエン共重合体ゴムである。結合スチレン含量が上記範囲未満では、ゴムの硬度が不足となり、また上記範囲を越えると破断伸び及び発熱特性が悪化する。また、１，２−ビニル結合量が上記範囲を越えると破断伸び及び発熱特性の低下を招く。
【００３６】
本発明のゴム組成物においては、前記成分（３）の補強材ないし充填材として、上述のゴム成分１００質量部に対して、窒素吸着比表面積が６５〜９２ｍ^２／ｇで且つＤＢＰ吸油量が７０〜１３２×１０^−５ｍ^３／ｋｇであるカーボンブラックの４０〜６５質量部が配合される。上記特性のカーボンブラックを上記範囲で配合することにより、抗破壊物性や耐亀裂成長性及びモジュラス等を向上できる。尚、該カーボンブラックの配合量は、上記効果を高める為に、４５〜６０質量部の範囲がより好ましい。該カーボンブラックの配合量が４０質量部に満たないと、上記改善効果が不十分であり、一方、該配合量が６５質量部を越えて配合すると、抗破壊物性や耐亀裂成長性及び発熱特性の低下を来たす。
【００３７】
本発明に用いるカーボンブラックとしては、窒素吸着比表面積及びＤＢＰ吸油量が上記範囲を満足する物であれば特に制限はなく、具体的には、例えば、Ｓ３１５、Ｎ３２６（ＩＳＡＦ−ＬＳ）、Ｎ３３０（ＨＡＦ）、Ｎ３３５、Ｎ３３９、Ｎ３４３、Ｎ３４７（ＨＡＦ−ＨＳ）、Ｎ３５１、Ｎ３５６、Ｎ３５８、Ｎ３７５、Ｎ５３９、Ｎ５５０（ＦＥＦ）、Ｎ５８２等のカーボンブラック等を挙げることができる。これらのカーボンブラックの中でも、高モジュラスと高破壊特性を両立させて向上させる観点より、Ｎ３２６（ＩＳＡＦ−ＬＳ）、Ｎ３３０（ＨＡＦ）、Ｎ３３５、Ｎ３３９、Ｎ３４３、Ｎ３４７（ＨＡＦ−ＨＳ）カーボンが好ましく、特にＮ３３０（ＨＡＦ）とＮ３２６（ＩＳＡＦ−ＬＳ）カーボンがより好ましい。上記のカーボンブラックは、１種を単独で使用してもよいし、２種以上を併用して用いてもよい。
【００３８】
本発明のゴム組成物においては、所望により、更にシリカを配合することもできる。このシリカは、窒素吸着比表面積（Ｎ_２ＳＡ）が１６０〜２６０ｍ^２／ｇの範囲にあり、且つジブチルフタレート吸油量（ＤＢＰ）が１８０〜２６０ｍＬ／１００ｇの範囲にあるものが好適である。この（Ｎ_２ＳＡ）が１６０ｍ^２／ｇ未満や（ＤＢＰ）が１８０ｍＬ／１００ｇ未満では耐摩耗性が不充分になる恐れがあり、一方、（Ｎ_２ＳＡ）が２６０ｍ^２／ｇを超えたり、（ＤＢＰ）が２６０ｍＬ／１００ｇを超えると分散不良を引き起こし、低発熱性能及び耐摩耗性が低下する原因となることがある。ここで、上記（Ｎ_２ＳＡ）は、３００℃で１時間乾燥した後、ＡＳＴＭ Ｄ４８２０−９３に準拠して測定した値であり、（ＤＢＰ）は、ＡＳＴＭ Ｄ２４１４−９３に準拠して測定した値である。
【００３９】
上記シリカとしては、例えば湿式シリカ（含水ケイ酸）、乾式シリカ（無水ケイ酸）、ケイ酸カルシウム、ケイ酸アルミニウムなどが挙げられるが、これらの中で、特に湿式シリカが好適である。本発明においては、このシリカは、前記（Ａ）或いは（Ａ）のゴム成分１００質量部に対し、３０質量部以下の範囲で配合されることが好ましい。この配合量が３０質量部を超えると低発熱性能が低下する恐れがある。更に好ましいシリカの配合量は２０質量部以下の範囲である。
【００４０】
本発明のゴム組成物には、前記（１）及び（２）のゴム成分と（３）のカーボンブラックの他に、目的及び必要に応じて、更に、通常の工業用ゴム配合に常用される加硫剤、加硫促進剤、加硫助剤、老化防止剤、酸化防止剤、プロセス油、軟化剤、その他ゴム配合剤を適宜に配合することができる。特に、１００％伸長時の弾性率もしくはモジュラスを高めるために、ゴム成分１００質量部に対して、加硫剤としての硫黄及び／又は含硫黄化合物を１〜８質量部、好ましくは２〜６質量部、より好ましくは２．５〜５質量部を配合することが望ましい。尚、上記の様に硫黄の配合量が多くてブルームの恐れがある場合には、使用する硫黄の一部或いは全部を不溶性硫黄（高分子タイプ）に置き換えることも望ましい。
【００４１】
また、本発明のゴム組成物には、耐熱性や耐熱老化性及び動的貯蔵弾性率（Ｅ′）等を向上させる為に、ビスマレイミド化合物を配合するができる。該ビスマレイミド化合物としては、例えば、Ｎ，Ｎ′−１，２−フェニレンジマレイミド、Ｎ，Ｎ′−１，３−フェニレンジマレイミド、Ｎ，Ｎ′−１，４−フェニレンジマレイミド、Ｎ，Ｎ′−（４，４′−ジフェニルメタン）ビスマレイミド、２、２−ビス［４−（４−マレイミドフェノキシ）フェニル］プロパン、ビス（３−エチル−５−メチル−４−マレイミドフェニル］メタン等を挙げることができる。これらの中でも、Ｎ，Ｎ′−１，２−フェニレンジマレイミド、Ｎ，Ｎ′−１，３−フェニレンジマレイミド、Ｎ，Ｎ′−１，４−フェニレンジマレイミドが好ましく、特にＮ，Ｎ′−（４，４′−ジフェニルメタン）ビスマレイミドが効果が顕著な点で更に好ましい。ビスマレイミド化合物の配合量は、ゴム成分１００質量部に対して１〜３質量部が好ましく、また、１種を単独で使用してもよいし、２種以上を併用して用いてもよい。
【００４２】
本発明のゴム組成物は、上述した配合からなるものであるが、更にその物性の内、特にタイヤ周方向における１００％伸長時のモジュラス（Ｍ_１００）が５．０〜１０．０ＭＰａの範囲にあり且つ破断伸び（Ｅｂ）が３００％以上であることを必要な要件とする。この１００％伸長時のモジュラス（Ｍ_１００）が上記の範囲未満であると、高内圧で高速走行時のタイヤの径膨張を所定の値以下に抑制することができなくなり、また破断伸び（Ｅｂ）が３００％未満であると、ベルト端部での亀裂の発生及び成長を抑制することができなくなる。
【００４３】
尚、本発明の高速重荷重用ラジアルタイヤは、後述する様に、ベルト層のタイヤ半径方向外側に所定のゴム厚みを隔てて有機繊維コードからなる保護ベルトを配設することができるが、本発明の前記ゴム組成物の１００％伸長時のモジュラス（Ｍ_１００）は、該保護ベルトの被覆ゴムの１００％伸長時のモジュラス（Ｍ_１００）より１．２〜１．５倍ほど高いことが好ましい。上記モジュラス（Ｍ_１００）の比率が１．２倍未満では、保護ベルトの配設による緩衝効果が減少する懸念があり、また該比率が１．５倍を越えると、ベルト層と保護ベルトの間において剥離故障が生じる恐れがある。
【００４４】
本発明の重荷重用空気入りラジアルタイヤは、この様なゴム組成物をベルト層のベルトプライ用の被覆ゴムとして用い、通常の加硫条件に従って加硫成形することにより、製造することができる。ここにおいて、本発明の前記ゴム組成物は、ベルト層を構成するベルトプライの総てに適用してもよいが、特に航空機用ラジアルタイヤにおいて、重量増及びコスト増を極力避けながら、高内圧で高速走行時の径成長を抑制し抗破壊特性及び耐久寿命を向上させる観点より、該ベルト層を構成するベルトプライの２枚以上からなる主ベルト層の被覆ゴムに適用することが好ましい。
尚、本発明の上記タイヤに充填される気体には、空気或いは窒素などの不活性なガスが用いられる。
【００４５】
（高速重荷重用ラジアルタイヤ）
上述したゴム組成物をタイヤのベルトゴムに適用した、本発明の高速重荷重用空気入りラジアルタイヤについて、以下に詳細に説明する。
本発明者等が、ベルト層の張力負担を詳細に調べた結果、図３のグラフに示すように、１００％内圧（ＴＲＡ規定内圧）の無負荷状態では１点鎖線の様な分布になっていた。尚、図３において、縦軸は張力、横軸はベルト幅方向の位置、ＳＢＷはベルト層の最大幅を示す。
ところで、航空機用タイヤの場合、無負荷状態において、規定内圧の４００％の耐圧性が必要である。該４００％内圧充填時の張力分布を調べた結果、実線の様になることが分かった。一方、荷重負荷状態では、ベルト層の張力分布は２点鎖線のようになることが分かった。このことから、該ベルト層は、両方の条件を満たす強度を有することが必要となることが分かる。
発明者等は種々の実験、調査から、無負荷時の張力に対し、赤道面の強力をベルト層の最大幅の２／３の位置の強力よりも大きく規定することで、径成長の抑制と質量減の両立を達成できることを見出した。
請求項４に記載の発明は上記事実に鑑みてなされたものであって、一対のビードコアと、一方ビードコアから他方のビードコアに向けてトロイド状に延びる少なくとも１枚以上のカーカスプライからなるカーカス層と、前記カーカス層のタイヤ半径方向外側のクラウン域外周面に、有機繊維コードを含む少なくとも１枚以上のベルトプライからなるベルト層と、該ベルト層のタイヤ半径方向外側に踏面部を構成するトレッドゴム層と、を備えた空気入りラジアルタイヤであって、タイヤ赤道面位置Ｐ０での単位幅当りにおける前記ベルト層のタイヤ周方向の総強力をＫ０、タイヤ赤道面を中心として前記ベルト層の最大幅の２／３の幅位置Ｐ２での単位幅当りにおける前記ベルト層のタイヤ周方向の総強力をＫ２としたときに、Ｋ２＜Ｋ０を満足する、ことを特徴としている。
次に、請求項４に記載の空気入りラジアルタイヤの作用を説明する。
請求項４に記載の空気入りラジアルタイヤでは、タイヤ赤道面位置Ｐ０での単位幅当りにおけるベルト層のタイヤ周方向の総強力Ｋ０を、タイヤ赤道面を中心としてベルト層の最大幅の２／３の幅位置Ｐ２での単位幅当りにおけるベルト層のタイヤ周方向の総強力より大きく設定したので、ベルト層の材料使用量を抑えつつ、標準内圧の充填時及び高速回転時に、トレッド中央域でのトレッドゴムの周方向伸張量を抑制し、タイヤの径成長を抑制することができる。トレッドゴムの周方向伸張量が抑制されることでゴムの緊張度合いが低下するので、異物の進入に対する抵抗力が増大し、また、万一異物が刺さり込んだ場合であっても、亀裂の成長を抑えることが出来る。
尚、請求項４に記載の空気入りラジアルタイヤにおいて、前述した本発明のゴム組成物は、ベルト層のベルトプライの全体に適用されてもよく、少なくとも主ベルトプライに適用されてもよい。
【００４６】
（総強力の定義）ここでいう総強力とは、ベルト層の周方向の強力を指しており、１本のコードの強力に単位幅当り（ここでは１０ｍｍ）の本数を掛けて算出したものである。なお、コードが周方向に対して角度θで傾斜している場合の総強力は、上記単位幅当りの総強力にｃｏｓθを掛けて算出してものとする。また、タイヤ内のコードがタイヤ周方向に波型（ジグザグ状）に伸びている場合は、真っ直ぐに伸ばして強力を算出するのではなく、タイヤに埋設されている形状、即ち、波状に型付けされたものを周方向に伸ばした時の強力を算出する。
【００４７】
請求項５に記載の発明は、請求項４に記載の空気入りラジアルタイヤにおいて、０．２≦Ｋ２／Ｋ０≦０．８を満足する、ことを特徴としている。
次に、請求項５に記載の空気入りラジアルタイヤの作用を説明する。
強力の比（Ｋ２／Ｋ０）が０．２を下回ると、ショルダー部付近に位置する有機繊維コードに過大な張力が負担されることによる耐圧性能の低下を引き起こす虞がある。一方、強力の比（Ｋ２／Ｋ０）が０．８を上回ると、２／３点に配置したベルトプライの有機繊維コードが有効に活用されず、空気入りラジアルタイヤの質量増につながる。従って、強力の比（Ｋ２／Ｋ０）は、０．２≦Ｋ２／Ｋ０≦０．８を満足することが好ましい。
【００４８】
請求項６に記載の発明は、請求項４または請求項５に記載の空気入りラジアルタイヤにおいて、前記ベルト層において、前記有機繊維コードの積層厚みを前記タイヤ赤道面位置Ｐ０で最も厚くし、前記タイヤ赤道面位置Ｐ０での前記有機繊維コードの積層厚みをＧ０、前記ベルト層の最大幅の２／３の幅位置Ｐ２での前記有機繊維コードの積層厚みをＧ２としたときに、Ｇ２＜Ｇ０を満足する、ことを特徴としている。
次に、請求項６に記載の空気入りラジアルタイヤの作用を説明する。
ベルト層の最大幅の２／３の幅位置Ｐ２での有機繊維コードの積層厚みＧ２を、タイヤ赤道面位置Ｐ０での有機繊維コードの積層厚みＧ０よりも大きく設定することで、Ｋ２＜Ｋ０を容易に達成することができる。尚、有機繊維コードの積層厚みとは、ベルト層をタイヤ径方向断面で見たときのタイヤ径方向に積層されている有機繊維コードの総径寸法である。例えば、直径がＡの有機繊維コードが１２本積層されている場合には、積層厚みはＡ×１２となる。
【００４９】
請求項７に記載の発明は、請求項６に記載の空気入りラジアルタイヤにおいて、０．３５≦Ｇ２／Ｇ０≦０．８５を満足することを特徴としている。
次に、請求項７に記載の空気入りラジアルタイヤの作用を説明する。
有機繊維コードの積層厚みの比Ｇ２／Ｇ０が、０．３５を下回ると、ショルダー部付近に位置する有機繊維コードに過大な張力が負担されることによる耐圧性能の低下を引き起こす虞がある。一方、有機繊維コードの積層厚みの比Ｇ２／Ｇ０が０．８５を上回ると、２／３点に配置したベルトプライの有機繊維コードが有効に活用されず、空気入りラジアルタイヤの質量増につながる。従って、有機繊維コードの積層厚みの比Ｇ２／Ｇ０は、０．３５≦Ｇ２／Ｇ０≦０．８５を満足することが好ましい。
【００５０】
請求項８に記載の発明は、請求項４〜請求項７の何れか１項に記載の空気入りラジアルタイヤにおいて、前記ベルト層において、前記ベルト層の最大幅の２／３の幅位置Ｐ２での前記有機繊維コードの積層厚みをＧ２とした時に、前記ベルト層には、前記ベルト層の最大幅の２／３の幅位置Ｐ２よりもタイヤ幅方向外側の領域において、前記積層厚みＧ２よりも積層厚みの厚い部分が設けられている、ことを特徴としている。
次に、請求項８に記載の空気入りラジアルタイヤの作用を説明する。
ベルト層の最大幅の２／３の幅位置Ｐ２よりもタイヤ幅方向外側の領域において、積層厚みＧ２よりも積層厚みの厚い部分を設けると、高速走行時、特にタイヤ幅方向の外力に晒される様な場合に、タイヤ両側部の大きな張力変動を柔軟に吸収せしめることが可能となり、空気入りラジアルタイヤの寿命を著しく低下させ得るスタンディングウエーブの発生を効果的に抑制することができる。
【００５１】
請求項９に記載の発明は、請求項４〜請求項８の何れか１項に記載の空気入りラジアルタイヤにおいて、前記ベルト層は、引張破断強度が６．３ｃＮ／ｄｔｅｘ以上、伸張方向に０．３ｃＮ／ｄｔｅｘ荷重時の伸び率が０．２〜２．０％、伸張方向に２．１ｃＮ／ｄｔｅｘ荷重時の伸び率が１．５〜７．０％、伸張方向に３．２ｃＮ／ｄｔｅｘ荷重時の伸び率が２．２〜９．３％とされた有機繊維コードを含むベルトプライの少なくとも２枚以上で構成された主ベルト層を有する、ことを特徴としている。
次に、請求項９に記載の空気入りラジアルタイヤの作用を説明する。
本発明の様に、ベルト層の強度分布を規定することで、径成長抑制と質量減の両立を達成できるが、ナイロンの様な低弾性のコードを用いると、径成長を抑えるために多層にする必要があり、タイヤの質量増につながる。
【００５２】
請求項９に記載の空気入りラジアルタイヤでは、主ベルト層を、引張破断強度が６．３ｃＮ／ｄｔｅｘ以上とされた高弾性の有機繊維コードを含む少なくとも２枚以上のベルトプライで構成することにより、必要な耐圧性能を満足することができる。ここで、有機繊維コードの伸張方向に２．１ｃＮ／ｄｔｅｘ荷重時の伸び率を１．５〜７．０％、伸張方向に３．２ｃＮ／ｄｔｅｘ荷重時の伸び率を２．２〜９．３％とすることにより、目標の径成長の抑制を容易に達成することができた。
その理由は、航空機用の空気入りラジアルタイヤでは、標準状態の内圧負荷時におよそ２．１ｃＮ／ｄｔｅｘのコード張力が加わり、高速走行時におよそ３．２ｃＮ／ｄｔｅｘのコード張力が加わるが、有機繊維コードの伸び率が上記範囲を上回る場合、タイヤ内圧充填時においてタイヤ径方向の膨出を効果的に抑えられず、異物の刺さり込みに対する性能を期待できなくなるからである。
一方、有機繊維コードの伸び率が上記範囲を下回る場合、ベルトプライのタガ効果が大き過ぎるため、カーカスプライが必要以上にタイヤ幅方向に膨出する結果となり好ましくない。
更に、有機繊維コードの伸張方向に０．３ｃＮ／ｄｔｅｘ荷重時の伸び率を０．２〜２．０％とした理由は、以下に述べる通りである。先ず、空気入りラジアルタイヤを加硫するに当り、航空機用空気入りラジアルタイヤの場合、通常タイヤモールド内にて生タイヤが０．２〜２．０％ほど伸張する様にタイヤ外径が設定される。これは、加硫時に生タイヤ内部より負荷される圧力によってタイヤを均等に伸張せしめることによってコードの方向を揃え、コード打込みのばらつきを是正するためのものである。然る該工程においては、０．３ｃＮ／ｄｔｅｘ程度の比較的小さい張力が有機繊維コードに作用するが、この時の有機繊維コードの伸び率が２．０％より大きいと、コード性状是正の効果が薄く、また、伸び率が０．２％より小さい場合には、加硫時の膨張時にコード張力が大となり、有機繊維コードがタイヤ径方向内側のゴムに食い込むなどの不都合が生じるからである。
【００５３】
（標準状態の内圧負荷時の定義）ここでの内圧及び荷重は、ＴＲＡ ＹＥＡＲＢＯＯＫ（２００２年度版）に規定されている内圧、及び荷重を採用している。例えば、航空機用ラジアルタイヤ１２７０×４５５Ｒ２２ ３２ＰＲの場合、規定内圧は１６２０ｋＰａ、規定荷重は２４８６０ｋｇである。
尚、有機繊維コードは、伸張方向に０．３ｃＮ／ｄｔｅｘ荷重時の伸び率が０．２〜１．５％、伸張方向に２．１ｃＮ／ｄｔｅｘ荷重時の伸び率が１．５〜６．５％、伸張方向に３．２ｃＮ／ｄｔｅｘ荷重時の伸び率が２．２〜８．３％のものがより好ましい。
【００５４】
請求項１０に記載の発明は、請求項９に記載の空気入りラジアルタイヤにおいて、前記主ベルト層のタイヤ幅方向端部では、少なくとも前記ベルトプライが２層以上積層されている、ことを特徴としている。
次に、請求項１０に記載の空気入りラジアルタイヤの作用を説明する。
主ベルト層のタイヤ幅方向端部において、ベルトプライを２層以上積層することで、タイヤ走行時、特に、タイヤ幅方向に外力が作用する場合のように、タイヤ接地面の幅方向両端付近の有機繊維コードに激しい張力変動を伴う様な条件下においても、その弾力性を持って衝撃を効果的に分散することが可能となり、苛酷な使用条件下におけるタイヤの信頼性向上に効果的である。
【００５５】
請求項１１に記載の発明は、請求項９又は請求項１０に記載の空気入りラジアルタイヤにおいて、前記主ベルト層は、芳香族ポリアミド系の繊維から構成され、下撚り係数が０．１２〜０．８５、上撚り係数が０．４０〜０．８０とされた有機繊維コードを含むベルトプライを有する、ことを特徴としている。
次に、請求項１１に記載の空気入りラジアルタイヤの作用を説明する。
主ベルト層を構成する有機繊維コードを芳香族ポリアミド系の繊維から構成し、下撚り係数を０．１２〜０．８５、好ましくは０．１７〜０．５１、上撚り係数を０．４０〜０．８０とすることで、有機繊維コードを請求項６に規定の物性、即ち、引張破断強度を６．３ｃＮ／ｄｔｅｘ以上、伸張方向に０．３ｃＮ／ｄｔｅｘ荷重時の伸び率を０．２〜２．０％、伸張方向に２．１ｃＮ／ｄｔｅｘ荷重時の伸び率を１．５〜７．０％、伸張方向に３．２ｃＮ／ｄｔｅｘ荷重時の伸び率を２．２〜９．３％に設定することができる。
【００５６】
（撚り係数の定義）ここでいう撚り係数とは、以下の式から算出されるものである。
ＮＴ＝Ｎ×（０．１３９×Ｄ／ρ）^１／２×１０^−３
Ｎ：有機繊維コード１００ｍｍ当りの撚り数
Ｄ：総表示デシテックス（ｄｔｅｘ）数
ρ：有機繊維コードの比重（ｇ／ｃｍ^３）
【００５７】
請求項１２に記載の発明は、請求項９〜請求項１１の何れか１項に記載の空気入りラジアルタイヤにおいて、前記主ベルト層は、芳香族ポリアミド系の繊維と脂肪族ポリアミド系の繊維とを含み、芳香族ポリアミド系の繊維と脂肪族ポリアミド系の繊維との質量比が１００：１０〜１７０とされた有機繊維コードを含むベルトプライを有する、ことを特徴としている。
次に、請求項１２に記載の空気入りラジアルタイヤの作用を説明する。
主ベルト層を構成する有機繊維コードを芳香族ポリアミド系の繊維と脂肪族ポリアミド系の繊維とから構成し、かつ芳香族ポリアミド系の繊維と脂肪族ポリアミド系の繊維との質量比を１００：１０〜１７０とすることで、有機繊維コードを請求項９に規定の物性、即ち、引張破断強度が６．３ｃＮ／ｄｔｅｘ以上、伸張方向に０．３ｃＮ／ｄｔｅｘ荷重時の伸び率が０．２〜２．０％、伸張方向に２．１ｃＮ／ｄｔｅｘ荷重時の伸び率が１．５〜７．０％、伸張方向に３．２ｃＮ／ｄｔｅｘ荷重時の伸び率が２．２〜９．３％に設定することができる。
ここで、芳香族ポリアミド系の繊維の質量１００に対して脂肪族ポリアミド系の繊維の質量が１０を下回ると、上記荷重を負荷したときに、コード伸張が小さくなるため請求項９に規定の物性を達成することが困難となる。一方、芳香族ポリアミド系の繊維の質量１００に対して脂肪族ポリアミド系の繊維の質量が１７０を上回ると、上記荷重を負荷したときに、コード伸張が大きくなるため請求項９に規定の物性を達成することが困難となる。
【００５８】
尚、芳香族ポリアミド系の繊維と脂肪族ポリアミド系の繊維との質量比は、より好ましくは１００：１７〜８６である。ここで、脂肪族ポリアミド系の繊維とは、例えば、６−ナイロン、６，６−ナイロン、４，６−ナイロン繊維等である。ここで、有機繊維コードは、芳香族ポリアミド系の繊維と脂肪族ポリアミド系の繊維とから構成されていればよく、芳香族ポリアミド系有機繊維コードと脂肪族ポリアミド系有機繊維コードとを撚り合わせてもよく、芳香族ポリアミド系の繊維と脂肪族ポリアミド系の繊維とを合わせてから撚りをかけてもよい。
また、芳香族ポリアミド系有機繊維コードをＡ、脂肪族ポリアミド系有機繊維コードをＢとした場合、ＡまたはＢを下撚り（Ｚ撚り）後、引き揃えて、下撚りと逆方向に上撚り（Ｓ撚り）をかけることで主ベルト層を構成する有機繊維コードを得ることができる。尚、下撚り時は、ＡまたはＢをそれぞれ単独で撚ってもよいし、ＡとＢを併せた後撚ってもよい。下撚り又は上撚り時のＡ、Ｂ又はＡＢ（合糸）の本数は１本ずつでも複数本ずつでもよい。Ａ又はＢ原糸の太さは同じでもよいし異なっていてもよい。混撚糸の形態は、芯となる糸の回りにループを作ったものなどでもよい。
【００５９】
請求項１３に記載の発明は、請求項１２に記載の空気入りラジアルタイヤにおいて、前記主ベルト層は、芳香族ポリアミド系のコードと脂肪族ポリアミド系のコードとが撚り合わされ、且つ前記芳香族ポリアミド系のコードの下撚り係数が０．１２〜０．８５とされた有機繊維コードを含むベルトプライを有する、ことを特徴としている。
次に、請求項１３に記載の空気入りラジアルタイヤの作用を説明する。
芳香族ポリアミド系のコードの下撚り係数を０．１２〜０．８５とすることにより、請求項９に規定の物性を達成することが容易になる。尚、芳香族ポリアミド系のコードの下撚り係数を０．１７〜０．５１とすることが更に好ましい。
【００６０】
請求項１４に記載の発明は、請求項９〜請求項１３の何れか１項に記載の空気入りラジアルタイヤにおいて、前記主ベルト層は、タイヤ赤道面に対して略０°の角度で螺旋状に巻回された有機繊維コードを含むベルトプライを有する、ことを特徴としている。
次に、請求項１４に記載の空気入りラジアルタイヤの作用を説明する。
有機繊維コードのタイヤ赤道面に対する角度が略０°に設定することで、主ベルト層の周方向剛性を確保するために使用する有機繊維コードの強力を最大限に活用することが可能となり、空気入りラジアルタイヤの軽量化を図ることが出来る。尚、ここでいう略０°とは、２．０°以下を含むものとする。
【００６１】
請求項１５に記載の発明は、請求項４〜請求項１４の何れか１項に記載の空気入りラジアルタイヤにおいて、前記主ベルト層は、タイヤ赤道面に対して２〜２５°の角度で傾斜し、それぞれのプライ端で反対方向に傾斜するように同一面内で屈曲されてタイヤ周方向にジグザグ状に延びる有機繊維コードを含むベルトプライを有する、ことを特徴としている。
次に、請求項１５に記載の空気入りラジアルタイヤの作用を説明する。
タイヤ赤道面に対して２〜２５°の角度で傾斜し、それぞれのプライ端で反対方向に傾斜するように同一面内で屈曲されてタイヤ周方向にジグザグ状に延びる有機繊維コードを含むベルトプライを用いることで、主ベルト層の周方向剛性を大きく低下させることなくしてタイヤ幅方向の剛性を確保することができ、その結果、優れた耐摩耗性を実現することが可能となる。
【００６２】
タイヤ幅方向の剛性を確保することで、優れた耐摩耗性が実現される理由は以下の通りである。一般に、内圧充填時のタイヤ形状において、クラウンセンター部とショルダー部との径差が大きいと、いわゆる「引きずり摩耗」を起こす可能性が高くなる。タイヤ回転中に接地したセンター部とショルダー部は、接地長の分だけ回転するが、一定の周長に対応するタイヤ回転角度は径の小さいショルダー部の方が大きくなる。このため、路面を離れるまでにショルダー部は回転方向後方に拘束された状態となり、トレッド接地面内にてセンター部とショルダー部とが剪断変形する。この変形を是正するためにショルダー部が路面に対して相対的に滑る現象が「引きずり摩耗」である。
上記周方向位置のずれの大きさは、上記センター部とショルダー部との径差、及びトレッド面内の周方向剪断剛性に依存し、径差が大きく剪断剛性が小さいほど引きずり摩耗の程度が大きくなる。スパイラルベルトは、コードがほぼ周方向を向いているため、上記剪断剛性が小さく、引きずり摩耗に関しては有効ではない。これを補うため、タイヤ周方向に対する角度が大きいコードを有するベルトを追加することで、タイヤ幅方向剛性を確保でき、摩耗特性の改善が図られる。
ここで、有機繊維コードのタイヤ赤道面に対する角度が２°を下回ると、幾何学的にジグザグ状にベルトを巻回することが困難となる（即ち、スパイラル状になってしまう。）。一方、有機繊維コードのタイヤ赤道面に対する角度が２５°を上回ると、有機繊維コードがタイヤ周方向に発揮し得る張力が相対的に減少し、空気入りラジアルタイヤの内圧を負担する効率が悪化する。
【００６３】
（１つの実施形態）
以下、本発明の航空機用空気入りラジアルタイヤの１つの実施形態を、添付した図１に基づいて説明する。
図１に示す様に、本実施形態の航空機用の空気入りラジアルタイヤ１０１（タイヤサイズ：１２７０×４５５Ｒ２２ ３２ＰＲ）は、ビード部１２に丸型断面を有するビードコア１４を備えていて、ゴム被覆された有機繊維コードがラジアル方向に配列された６枚のカーカスプライよりなるカーカス層１６がこのビードコア１４に係留されている。
カーカス層１６のタイヤ半径方向外側のクラウン域外周面には、ベルト層２０、ベルト層２０のタイヤ径方向外側にはトレッド部を構成するトレッドゴム層（３１〜３３）が設けられている。また、カーカス層のタイヤ幅方向外側には、サイドウォール部２５を構成するサイドゴム層２７が設けられている。尚、本実施の形態では、ベルト層２０は、タイヤ径方向内側の主ベルト層２６と、主ベルト層２６のタイヤ径方向外側に設けられる副ベルト層２８、副ベルト層２８のタイヤ径方向外側に設けられる保護ベルト層２２とから構成されている。
【００６４】
主ベルト層２６は、複数枚のベルトプライ、本実施形態では、８枚のベルトプライから構成されている。主ベルト層２６を構成するこれらプライは、複数本の有機繊維コードをゴム被覆することにより形成されている。これらの有機繊維コードは、引張破断強度を６．３ｃＮ／ｄｔｅｘ以上とすることが好ましく、伸張方向に０．３ｃＮ／ｄｔｅｘ荷重時の伸び率が０．２〜２．０％、伸張方向に２．１ｃＮ／ｄｔｅｘ荷重時の伸び率が１．５〜７．０％、伸張方向に３．２ｃＮ／ｄｔｅｘ荷重時の伸び率が２．２〜９．３％であることが好ましい。
本実施形態の有機繊維コードは、芳香族ポリアミド系の繊維から構成されている。有機繊維コードを芳香族ポリアミド系の繊維から構成した場合、下撚り係数は０．１２〜０．８５、好ましくは０．１７〜０．５１、上撚り係数は０．４０〜０．８０に設定することが好ましい。本実施形態では、芳香族ポリアミド系の繊維、具体的にはデュポン社製ポリアミド繊維（商品タイプ名：ＫＥＶＬＡＲ（Ｒ）２９、公称繊度３０００デニール。以後、適宜ケブラーと呼ぶ。）からなる有機繊維コードを用いている。なお、本実施形態では、有機繊維コードの傾斜角度はタイヤ赤道面ＣＬに対して略０°である。なお、ベルトプライにおいて、有機繊維コードの打込み数は、４〜１０本／１０ｍｍの範囲内が好ましい。本実施形態では、ベルトプライ２６において、有機繊維コードの打込み数が６．３本／１０ｍｍである。
【００６５】
本実施形態のように副ベルト層２８を設ける場合、その範囲は、タイヤ赤道面ＣＬから主ベルト層２６の幅ＢＷの１４０％位置までの範囲内に設けることが好ましい。本実施形態では、副ベルト層２８の幅ＳＢＷは主ベルト層２６の幅ＢＷの１０３％である。副ベルト層２８は、本実施形態では１枚のベルトプライから構成されている。本実施形態のベルトプライは、１又は複数本の有機繊維コードをゴム被覆して構成した帯状の細長体を準備し、この細長体をほぼ１周する毎に両プライ端間を１度だけ往復させながらタイヤ赤道面に対して２〜２５°の角度で傾斜させて周方向に巻き付けると共に、このような巻付けを細長体間に隙間が生じないよう周方向にほぼ細長体の幅だけずらして多数回巻回することで形成している（以後、適宜無端ジグザグ巻きベルトと呼ぶ。）。この結果、ベルトプライ内には両プライ端において折り曲げ方向を変えることによりジグザグしながらほぼ周方向に延びる有機繊維コードが、該ベルトプライの全領域においてほぼ均一に埋設されることになる。
【００６６】
このベルトプライには、主ベルト層２６に含まれる有機繊維コードに対して弾性率が同等、あるいは小さい有機繊維コード（主ベルト層２６の有機繊維コードに対して２．１ｃＮ／ｄｔｅｘ荷重時の伸び率が略同等以上である有機繊維コード）を用いることが好ましい。副ベルト層２８を構成するベルトプライに用いる有機繊維コードとしては、ナイロン等の脂肪族ポリアミド系の繊維からなるコード、アラミド等の芳香族ポリアミド系の繊維とナイロン等の脂肪族ポリアミド系の繊維とを含むコード等が好ましく、本実施形態では、ナイロンコード（撚り数：１２６０Ｄ／／２／３、打込み数７．３本／１０ｍｍ）を用いている。また、無端ジグザグ巻きベルトである本実施形態のベルトプライにおいて、その有機繊維コードの傾斜角度はタイヤ赤道面ＣＬに対して２〜４５°の範囲内が好ましく、本実施形態では８°に設定されている。
【００６７】
【実施例】
以下に、本発明を実施例により具体的に説明するが、本発明はこれらの実施例に限定されるものではない。ここで用いたビスマレイミド、老化防止剤、加硫促進剤等のゴム用薬品は一例を示すものであって、目的に応じて他の任意の配合薬品に変更することができる。尚、本実施例中の「部数」及び「％」は全て、「質量部」及び「質量％」を表す。
【００６８】
［実施例１〜３及び比較例１〜２］
下記の表１に示す配合処方に従って、実施例１〜３及び比較例１〜２のゴム組成物を調合して、２５０ｍＬのラボプラストミル（（株）東洋精機製作所製）を用いて混練した後、３インチロールで各ゴム組成物のシート物を作製した。次いで、温度１５０℃で、加硫反応によるトルクの上昇が最高値の９０％に達するまでの時間（ｔ_９０）の１．５倍にあたる加硫時間で加硫して、下記の物性測定用の供試サンプルを得た。
【００６９】
【表１】

【００７０】
上記の表１に記載の配合成分は、下記の仕様（スペック）のものである。
・溶液重合ＳＢＲ………ＪＳＲ（株）製の溶液重合ＳＢＲ（スチレン含量：３〜１０質量％、ビニル結合量：４０質量％以下）
・カーボンブラック（Ａ）………旭カーボン（株）製の「ＨＡＦ」（窒素吸着比表面積：７１ｍ^２／ｇ、ＤＢＰ吸油量：１０３×１０^−５ｍ^３／ｋｇ）
・カーボンブラック（Ｂ）………旭カーボン（株）製の「Ｎ３２６」（窒素吸着比表面積：８４ｍ^２／ｇ、ＤＢＰ吸油量：７５×１０^−５ｍ^３／ｋｇ）
また、使用したビスマレイミド、老化防止剤、加硫促進剤は下記のものである。
・ビスマレイミド（ＰＢＭ）………三井化学（株）製の商品名「ＢＭＩ−Ｓ」（Ｎ，Ｎ’−（４，４’−ジフェニルメタン）ビスマレイミド）
・老化防止剤（６ＰＰＤ）………Ｎ−（１，３−ジメチルブチル）−Ｎ’−フェニル−ｐ−フェニレンジアミン
・加硫促進剤（ＴＢＢＳ）………Ｎ−ｔ−ブチル−２−ベンゾチアゾリルスルフェンアミド
【００７１】
上記で得られた各加硫ゴム試料につき、以下の様に評価試験を実施して、その結果を下記の表２に記入した。
（１）引張り試験
ＪＩＳ Ｋ６３０１（１９９５）に準拠して、室温（２５℃）において、ダンベル３号の打抜きサンプルを用いて引張り試験を行い、１００％伸張時のモジュラス（ＭＰａ）及び破断伸び（％）を測定した。
【００７２】
更に、上記表１に示す各配合のゴム組成物を、図１に示す航空機用空気入りラジアルタイヤ（サイズ：ＡＰＲ １２７０×４５５Ｒ２２ ３２ＰＲ）の主ベルト層（図１の２６で示す。）のベルトプライに適用して、通常の航空機用ラジアルタイヤの製造プロセスに従って、供試用タイヤを作製し、下記の評価試験を実施した。
（２）ベルト端亀裂の評価
各供試タイヤにつき、正規リム（４６×１７Ｒ２０／３０）に組み付け、最大空気圧（１２．７ｋｇ／ｃｍ^２）の内圧を充填し、最大負荷能力の８０％の荷重を負荷して、速度６４．５ｋｍ／ｈで４分間のドラム走行を１時間サイクルで８００回実施した後、試験タイヤを解剖してベルトプライ端部の亀裂の有無を観察した。
【００７３】
（３）タイヤ径成長率の評価
各供試タイヤにつき、正規リム（４６×１７Ｒ２０／３０）に組み付け、最大空気圧（１２．７ｋｇ／ｃｍ^２）の内圧を充填した時の、該内圧充填の前後のトレッドセンターの外径の増加率（％）を測定した。この外径増加率が小さい程、タイヤの径成長が抑制され好ましいことを意味する。
【００７４】
【表２】

【００７５】
上記の表２の結果から明らかな様に、本発明のゴム組成物（実施例１〜３）は、比較例のものに比べて、モジュラス及び破断特性に優れていることが判明した。また、これらのゴム組成物を主ベルトのプライ被覆ゴムに適用した本発明の航空機用ラジアルタイヤ（実施例１〜３）は、比較例のタイヤに比べて、耐亀裂性及び径膨張抑制に優れていることが実証された。
【００７６】
【発明の効果】
本発明のゴム組成物及びタイヤ構造をベルト層に適用することに依って、タイヤの径膨張が抑制され耐亀裂性が改善され、耐久寿命に優れた重荷重用空気入りラジアルタイヤ、特に航空機用ラジアルタイヤを提供することが可能になった。
【図面の簡単な説明】
【図１】第１の実施形態に係る本発明の航空機用空気入りラジアルタイヤ（１０１）の断面図である。
【図２】従来例に係る空気入りラジアルタイヤ（１０２）の断面図である。
【図３】ベルト層にかかる張力を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a radial tire for high-speed heavy load, and more particularly to a pneumatic radial tire suitable for aircraft which suppresses the growth of diameter at high internal pressure at high speed running and has improved anti-destructive characteristics and durability life.
[0002]
[Prior art]
Conventional high-speed heavy-load radial tires, particularly aircraft radial tires, have a large radial protrusion on the tread surface due to the action of high internal pressure and centrifugal force during high-speed rotation. When the tread surface protrudes in the radial direction in this manner, the tread rubber is stretched in the circumferential direction of the tire, and the property that the tread is not damaged when the tire passes over a foreign matter, so-called "envelope". There is a problem that the foreign matter that is stomached easily penetrates into the tread rubber and easily damages the tire. In addition, in the radial protrusion, a difference in diameter caused by being larger than the vicinity of both ends (shoulders) in the tire width direction at the center portion in the tire width direction causes a drag phenomenon on a tread surface of the rotating tire, and a tread is generated. There is also a problem that a so-called “uneven wear phenomenon” occurs in which the vicinity of the shoulder region (shoulder portion) wears faster than the central portion of the tire and shortens the life of the tire.
[0003]
As a conventional method of improving the uneven wear, the crown shape of the tread portion of the tire is changed so that the contact shape of the tire tread is made larger near the shoulder portion than the center portion of the tire, that is, a so-called “butterfly type” is devised. Have been. With this crown shape,
The contact pressure in the vicinity of the tire shoulder is increased, the drag phenomenon is reduced and the abrasion resistance is improved, but the heat generation in the tire shoulder becomes extremely large, resulting in an undesired result of shortening the durability life of the tire. ing.
[0004]
As a conventional technique for suppressing the bulging deformation of the tread and improving the wear characteristics of the tread and improving the envelope property, as shown in the cross-sectional view of FIG. The belt layer 20 disposed between the area and the tread rubber layer 30 is formed of a conventional general main belt layer 26 made of a wide belt ply and a narrow belt ply added to the outer peripheral side of the main belt layer 26. And a sub-belt layer 28 formed at the center of the main belt layer 26, thereby increasing the belt rigidity by the sub-belt layer 28, and in particular, a technology that restrains the bulging deformation in the central region of the tread. A pneumatic radial tire (102) has been considered.
[0005]
Further, in order to suppress the protrusion due to the internal pressure in the central portion in the width direction of the tire, as a conventionally used technique, a ply cord is replaced with an aromatic polyamide cord having a relatively high elastic modulus (for example, see Patent Reference 1). This aromatic polyamide cord exerts a high tension even in the low elongation area compared with the aliphatic polyamide that has been generally used in aircraft tires so far to maintain the internal pressure, so that the tire can be effectively protruded. It is said that it can be suppressed.
[0006]
As a conventional method for suppressing the protrusion at the center in the width direction of the tire, for example, a pneumatic radial tire in which a narrow reinforcing layer (cord is steel) is additionally arranged on a belt has been proposed (for example, Patent Document 2). Further, as another conventional example, a pneumatic radial tire having a reinforcing layer formed of a cord reinforced with a high-strength cord such as glass, metal, or aramid on the outermost layer of a belt made of organic fibers has been proposed. (For example, see Patent Document 3).
[0007]
In these conventional inventions, a belt having a large tension is further added. However, according to the prior art shown in FIG. 2, by securing a required rubber thickness H (thickness of rubber only, excluding cords) in the central region of the tread where the total thickness of the belt layer is the thickest, Besides the increase in tire weight for the rubber thickness H ₀ of the side region is too thick is forced, because the calorific value of the tread side region is increased, high-speed durability is lowered.
[0008]
Further, in the conventional belt structure, simply using a relatively high-elasticity cord for the belt ply cannot exert the performance fully utilizing the cord characteristic, and the amount of members to be used must be minimized. It was difficult to achieve a balance with the problem of weight reduction. In the first place, there is a need to avoid increasing the number of aircraft tires because the number of belts is originally large, and to reduce the mass of the tread portion because a large centrifugal force is applied when rolling.
[0009]
Therefore, in order to overcome these problems, it is necessary to adopt a new belt arrangement and structure that can utilize the characteristics of cords without waste. In consideration of the above facts, the present invention suppresses the radial growth of the tread surface, improves the durability against cutting of foreign matters, and at the same time, achieves a pneumatic radial tire belt suitable for an aircraft capable of achieving weight reduction. The purpose is to provide an arrangement structure.
[0010]
Furthermore, in heavy-duty pneumatic tires used in aircraft, in order to improve wear resistance and extend the life of the tire, while improving the rigidity of the tread, suppressing the decrease in the life due to external injury, It is also important to suppress the temperature rise of the tread rubber due to the strain applied repeatedly. Conventionally, in order to improve rigidity, for example, measures such as increasing the filling amount of carbon black, increasing the amount of resin added, and increasing the amount of a vulcanizing agent such as sulfur or a vulcanization accelerator are employed. However, when the filling amount of carbon black is increased, the wear resistance is improved, but the low heat generation performance and the anti-destructive property are inevitably deteriorated. In addition, increasing the amount of a vulcanizing agent such as sulfur or vulcanization accelerator does not significantly change the low heat generation performance and abrasion resistance, but rather decreases the anti-destructive property, and increases the amount of added resin increases the anti-destructive property. However, there is a problem that abrasion resistance and low heat generation performance decrease.
[0011]
Therefore, in order to achieve both abrasion resistance and low heat generation performance at a high level, tread rubber of heavy duty pneumatic tires is generally based on isoprene-based rubber such as natural rubber, and carbon black / carbon black is used as a reinforcing filler. It has been practiced to incorporate a silica combination system. However, those mainly composed of isoprene-based rubber as the rubber component are not preferable because the elastic modulus is reduced due to re-vulcanization due to over-vulcanization, low heat generation performance is easily deteriorated, and abrasion resistance is reduced. Invite the situation.
Further, in order to improve the low heat generation performance of the heavy duty tire, a low loss agent (low heat generation imparting agent) typified by 5-nitroso-8-hydroxyquinoline is further added to the composition. I have. However, these loss reducing agents have a degree of vulcanization dependency, and the resulting overvulcanization has a problem that the elastic modulus is reduced and the effect of improving the low heat generation performance is not sufficiently exhibited.
[0012]
As a technique for solving the above problems, a rubber component for a tread comprising a modified styrene-butadiene copolymer rubber obtained by solution polymerization and a hydrazide compound mixed with a rubber component composed of natural rubber or isoprene rubber is disclosed. It is described that in tires for trucks and buses, an effect of improving abrasion resistance, low heat generation performance and anti-destructive property was obtained (for example, see Patent Document 4). However, especially for heavy-duty radial tires for aircraft, there is a limit to the improvement effect of the rubber composition alone, and there is a strong demand for the development of a further high-performance material and a belt layer structure utilizing characteristics of the material. Have been.
[0013]
[Patent Document 1]
JP-A-61-178204 [Patent Document 2]
JP-A-8-58310 [Patent Document 3]
US Pat. No. 4,216,813 [Patent Document 4]
Japanese Patent Application Laid-Open No. 2002-146102
[Problems to be solved by the invention]
Under such circumstances, the present invention improves the anti-destructive properties and low heat generation performance, and further improves the abrasion resistance, particularly the uneven wear resistance, for heavy loads formed by applying a rubber composition suitable as a tread rubber. An object of the present invention is to provide a pneumatic radial tire.
[0015]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to achieve the above object, and as a result, as a rubber component, a specific modified styrene-butadiene copolymer obtained by solution polymerization and having at least one tin atom in the molecule. A rubber composition containing rubber and reinforced with carbon black having a specific nitrogen adsorption specific surface area and DBP oil absorption, and further specifying its modulus (M ₁₀₀ ) and elongation at break (Eb), It has been found that the present invention can be adapted to the purpose, and the present invention has been completed. That is, the present invention
[0016]
<1> At least one belt ply constituting the belt layer is made of a cord in which an aromatic polyamide-based fiber and an aliphatic polyamide-based fiber are mixed and twisted to form a rubber-coated cord. 1) 70 to 100 parts by mass of natural rubber and / or synthetic isoprene rubber; (2) obtained by solution polymerization, having at least one tin atom in the molecule, and having a bound styrene content in the molecule of 3 to 10% by mass. And 30 to 0 parts by mass of a modified styrene-butadiene copolymer rubber having a 1,2-vinyl bond amount of 40% by mass or less in a polybutadiene chain portion, and (3) a nitrogen adsorption specific surface area of 65 to 92 m ² / 40-65 parts by weight of carbon black and a DBP oil absorption g is ^{70~132 × 10 -5 m 3 / kg} , a rubber composition comprising, in its tire circumferential direction Fast heavy duty pneumatic radial tire kicking at 100% elongation modulus _{(M 100)} is characterized in that there and elongation at break in the range of 5.0~10.0MPa (Eb) is 300% or more.
<2> The pneumatic device for high-speed heavy load according to <1>, wherein the rubber composition is applied to at least a coating rubber of a main belt layer composed of two or more belt plies constituting a belt layer. Radial tire.
<3> The modulus (M ₁₀₀ ) of the rubber composition at the time of 100% elongation of the rubber coated with the protective belt made of an organic fiber cord disposed at a predetermined rubber thickness outside the belt layer in the tire radial direction with a predetermined rubber thickness. The pneumatic radial tire for a high-speed heavy load according to the above <1> or <2>, wherein the pneumatic radial tire is 1.2 to 1.5 times higher than the modulus (M ₁₀₀ ) at 100% elongation.
<4> The radial tire includes a pair of bead cores, a carcass layer including at least one or more carcass plies extending in a toroidal shape from one bead core to the other bead core, and a crown in a tire radial outside of the carcass layer. A pneumatic radial tire comprising: a belt layer comprising at least one or more belt plies containing an organic fiber cord on an outer peripheral surface of a region; and a tread rubber layer constituting a tread portion on a radially outer side of the belt layer. The total strength of the belt layer in the tire circumferential direction per unit width at the tire equatorial plane position P0 is K0, and the unit width at the width position P2 which is 2/3 of the maximum width of the belt layer around the tire equatorial plane. K1 <K0, wherein K2 <K0 is satisfied when the total strength of the belt layer in the tire circumferential direction at the time of hitting is K2. The pneumatic radial tire for high-speed heavy loads according to any one of <1> to <3>.
<5> The pneumatic radial tire for high-speed heavy load according to <4>, wherein the belt layer satisfies 0.2 ≦ K2 / K0 ≦ 0.8.
<6> In the belt layer, the lamination thickness of the organic fiber cord is the thickest at the tire equatorial plane position P0, the lamination thickness of the organic fiber cord at the tire equatorial plane position P0 is G0, and the lamination thickness of the belt layer is G0. The high-speed load described in the above item <4> or <5>, wherein G2 <G0 is satisfied when the laminated thickness of the organic fiber cord at a large 2/3 width position P2 is G2. Heavy duty pneumatic radial tire.
<7> The pneumatic radial tire for high-speed heavy load according to <6>, wherein the belt layer satisfies 0.35 ≦ G2 / G0 ≦ 0.85.
<8> In the belt layer, when the lamination thickness of the organic fiber cord at a width position P2 of ２ of the maximum width of the belt layer is G2, the maximum width of the belt layer is Any of the above items <4> to <7>, wherein a portion having a thickness greater than the thickness G2 is provided in a region outside the width position P2 of 2/3 in the tire width direction. The pneumatic radial tire for high-speed heavy loads described in 1.
<9> The belt layer has a tensile breaking strength of 6.3 cN / dtex or more, an elongation of 0.2 to 2.0% under a 0.3 cN / dtex load in the elongation direction, and 2.1 cN / dtex in the elongation direction. At least 2 of the belt plies including an organic fiber cord having an elongation of 1.5 to 7.0% under load and an elongation of 2.2 to 9.3% under 3.2 cN / dtex in the elongation direction. The high-speed heavy-load pneumatic radial tire according to any one of the above items <4> to <8>, comprising a main belt layer composed of at least one sheet.
<10> The pneumatic radial tire for high-speed heavy load according to <9>, wherein at least two or more layers of the belt ply are laminated at an end in the tire width direction of the main belt layer.
<11> The main belt layer is made of an aromatic polyamide-based fiber, and includes an organic fiber cord having a lower twist coefficient of 0.12 to 0.85 and an upper twist coefficient of 0.40 to 0.80. The high-speed heavy-load pneumatic radial tire according to the above <9> or <10>, further comprising a belt ply.
<12> The main belt layer contains an aromatic polyamide-based fiber and an aliphatic polyamide-based fiber, and the mass ratio of the aromatic polyamide-based fiber to the aliphatic polyamide-based fiber is 100: 10 to 170. The pneumatic radial tire for high-speed heavy loads according to any one of the above items <9> to <11>, comprising a belt ply including an organic fiber cord.
<13> In the main belt layer, an aromatic polyamide cord and an aliphatic polyamide cord are twisted together, and a lower twist coefficient of the aromatic polyamide cord is set to 0.12 to 0.85. The pneumatic radial tire for high-speed heavy load according to the item <12>, further comprising a belt ply including an organic fiber cord.
<14> The above <9> to <13>, wherein the main belt layer has a belt ply including an organic fiber cord spirally wound at an angle of about 0 ° with respect to the tire equatorial plane. > The pneumatic radial tire for high-speed heavy load according to any one of <1> to <3>.
<15> The main belt layer is inclined at an angle of 2 to 25 ° with respect to the tire equatorial plane, is bent in the same plane so as to be inclined in the opposite direction at each ply end, and is zigzag in the tire circumferential direction. The pneumatic radial tire for a high-speed heavy load according to any one of the above <9> to <14>, further comprising a belt ply including an organic fiber cord extending to the tire.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
(Rubber composition)
At least one belt ply constituting the belt layer of the pneumatic radial tire for high-speed heavy load of the present invention is made of a cord in which an aromatic polyamide-based fiber and an aliphatic polyamide-based fiber are mixed, and a twisted organic fiber is rubber-coated. The rubber composition applied to the belt-coated rubber has (1) 70 to 100 parts by mass of natural rubber and / or synthetic isoprene rubber, and (2) at least one tin atom in the molecule obtained by solution polymerization. 30 to 0 parts by mass of a modified styrene-butadiene copolymer rubber having a bonded styrene content in a molecule of 3 to 10% by mass and a 1,2-vinyl bond amount of a polybutadiene chain part of 40% by mass or less. , and (3) 40 nitrogen adsorption specific surface area and DBP oil absorption 65~92m ² / g is carbon black which is 70~132 × ¹⁰ -5 ^m 3 / kg 65 parts by weight, a rubber composition comprising, modulus at 100% elongation in the circumferential direction of the tire _{(M 100)} is in the range of 5.0~10.0MPa and elongation at break (Eb) is more than 300% It is characterized by being.
[0018]
The natural rubber of the above (1) may be a sheet rubber or a block rubber, and all of RSS # 1 to # 5 and all grades of TSR can be used. The synthetic isoprene rubber (IR) of the above (1) is obtained by polymerization of isoprene monomer. Among them, IR having a cis 1,4-bond of about 98% has a molecular structure very similar to natural rubber. Therefore, it shows the same physical properties as natural rubber and is preferable.
[0019]
The modified styrene-butadiene copolymer rubber of the above (2) is obtained by solution polymerization, and is modified by introducing a tin atom into at least one of a polymerization initiation terminal or a polymerization active terminal of a molecular chain or a molecular chain. SBR rubber. Such a modified styrene-butadiene copolymer rubber can be preferably produced, for example, by the following method. That is,
In the first and second methods, 1,3-butadiene and styrene are used as raw materials, an alkali metal compound, preferably a lithium compound is used as a polymerization initiator, and solution polymerization (anion polymerization) is performed, so that the terminal is a polymerization active terminal. A base polymer comprising a styrene-butadiene copolymer is obtained. The desired modified styrene-butadiene copolymer can be obtained by modifying the base polymer thus obtained with a tin compound.
[0020]
In the third method, 1,3-butadiene and styrene are used as raw materials, an alkali metal compound having a tin atom, preferably a lithium compound is used as a polymerization initiator, and solution polymerization (anion polymerization) is performed, so that the terminal is a polymerization active terminal. A base polymer comprising a styrene-butadiene copolymer is obtained. Subsequently, the active terminal is modified with a modifying agent such as a tin compound, an alkoxysilane compound, or a nitrogen-containing compound. In this case, the reaction may be stopped without using a denaturing agent.
[0021]
In a fourth method, 1,3-butadiene and styrene are used as raw materials, and an alkali metal compound having a tin atom and a nitrogen atom, preferably a lithium compound, is used as a polymerization initiator and solution polymerization (anion polymerization) is performed. A styrene-butadiene copolymer having a tin atom and a nitrogen atom introduced therein is obtained.
The fifth method uses 1,3-butadiene, styrene and a compound containing a tin atom (monomer) as a raw material, and uses an alkali metal compound, preferably a lithium compound as a polymerization initiator, and performs solution polymerization (anionic polymerization) to obtain a terminal. Is a polymerization active terminal to obtain a base polymer comprising a styrene-butadiene copolymer. Subsequently, the active terminal is modified with a modifying agent such as a tin compound, an alkoxysilane compound, or a nitrogen-containing compound. In this case, the reaction may be stopped without using a denaturing agent.
The above methods can be combined as appropriate. Further, in the above third to fifth methods, a copolymer into which a tin atom has been introduced can be obtained without performing a terminal modification step using a modifying agent.
[0022]
In the above first, second and fifth methods, as the lithium compound of the polymerization initiator, hydrocarbyl lithium and lithium amide compound are preferably used. When the former hydrocarbyl lithium is used, the polymerization initiation terminal is a hydrocarbyl group. A base polymer of a certain styrene-butadiene copolymer (including a copolymer having tin atoms introduced into styrene or butadiene monomer units) is obtained. When the latter lithium amide compound is used, the base of a styrene-butadiene copolymer having a nitrogen-containing group at a polymerization initiation terminal (including a copolymer in which a tin atom is introduced into a monomer unit of styrene or butadiene) is used. A polymer is obtained. Here, the base polymer means a copolymer having an active terminal before termination of the reaction.
[0023]
As the above hydrocarbyl lithium, those having a hydrocarbyl group having 2 to 20 carbon atoms are preferable. For example, ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, t-butyl lithium, tert-octyl Lithium, n-decyllithium, phenyllithium, 2-naphthyllithium, 2-butyl-phenyllithium, 4-phenyl-butyllithium, cyclohexyllithium, cyclopentyllithium, reaction products of diisopropenylbenzene and butyllithium, and the like. Of these, n-butyllithium is preferred.
[0024]
On the other hand, as the lithium amide compound, for example, lithium hexamethylene imide, lithium pyrrolidide, lithium piperidide, lithium heptamethylene imide, lithium dodecamethylene imide, lithium dimethyl amide, lithium diethyl amide, lithium dibutyl amide, lithium dipropyl amide, Lithium diheptylamide, lithium dihexylamide, lithium dioctylamide, lithium bis-2-ethylhexylamide, lithium didecylamide, lithium-N-methylpiperazide, lithium ethylpropylamide, lithium ethylbutylamide, lithium methylbutylamide, lithium ethylbenzyl Amide, lithium methylphenethylamide and the like. Among them, cyclic lithium amides such as lithium hexamethylene imide, lithium pyrrolidide, lithium piperidide, lithium heptamethylene imide and lithium dodecamethylene imide are preferable, and lithium hexamethylene imide and lithium pyrrolidide are particularly preferable.
[0025]
In the third method, as the lithium compound used for the polymerization initiator, a lithium triorganotin compound such as lithium tributyltin and lithium trioctyltin is preferably used. Further, in the fourth method, as the lithium compound having a tin atom and a nitrogen atom used for the polymerization initiator, the lithium triorganoamidotin represented by the following general formula (I) or the following general formula (II) ) Is preferably used.
[0026]
Embedded image

[In the formula (I), R ¹ and R ² each represent a group selected from aliphatic, alicyclic and aromatic hydrocarbon groups having 1 to 20 carbon atoms. Is also good. ]
[0027]
Embedded image

[In the formula (II), X is selected from the following structural groups. XI: a saturated cyclic structure group consisting of (CR ³ R ⁴ ) _n , X-II: (R ⁵ R ⁶ ) _m -Y- (R ⁵ R ⁶ ) ₁ (where Y is NR ⁷ , O Or an imine compound having a carbon-carbon double bond). Here, R ^{3 to} R ⁶ represent a group selected from hydrogen and an aliphatic hydrocarbon group having 1 to 10 carbon atoms, an alicyclic group having 3 to 10 carbon atoms, and an aromatic hydrocarbon group having 6 to 10 carbon atoms; , R ⁷ represents a group selected from an aliphatic group having 1 to 10 carbon atoms, an alicyclic group having 3 to 10 carbon atoms, and an aromatic hydrocarbon group having 5 to 10 carbon atoms. It may be different. n represents an integer of 3 to 10, and the sum of m and l is an integer of 2 to 9. ]
[0028]
Among these, preferred lithium triorganamidotin include, for example, lithium tripyrrolidide tin, lithium trihexamethylene imido tin, lithium tridiethylamidotin, and lithium tri (dipropylamido) tin.
[0029]
In the above, lithium triorganamidotin is described in U.S. Pat. No. 5,502,129, and lithium triorganamidotin and lithium triorganoimidin are described in U.S. Pat. No. 5,463,003. . In the fifth method, the intended styrene-butadiene copolymer can also be obtained by introducing a third monomer having a tin atom. Here, as the third monomer copolymerized with styrene or butadiene, a compound represented by the following general formula (III) or (IV) is preferably used.
[0030]
Embedded image

[In formula (III), R ^{8 to} R ¹⁰ represent an aliphatic, alicyclic, or aromatic hydrocarbon group having 1 to 30 carbon atoms, and the groups may be the same or different. ]
[0031]
Embedded image

[In the formula (IV), R ¹¹ (R ¹² ) CＣＲCR ¹³ —, R ^{14 to} R ¹⁷ are groups bonded to a benzene ring, and R ^{11 to} R ²² are a hydrogen atom or a carbon atom having 1 to 30 carbon atoms. Represents an aliphatic, alicyclic or aromatic hydrocarbon group, which may be the same or different. However, R ^{20 to} R ²² do not contain a hydrogen atom. ]
[0032]
Specifically, as the compound represented by the general formula (III), 2-tributylstannyl-1,3-butadiene, 2-trioctylstannyl-1,3-butadiene, 2-tricyclohexylstannyl -1,3-butadiene, 2-triphenylstannyl-1,3-butadiene, 2-dibutylphenylstannyl-1,3-butadiene, 2-diphenyloctylstanyl-1,3-butadiene and the like. . Examples of the compound represented by the general formula (IV) include m-vinylbenzyltributyltin, m-vinylbenzyltrioctyltin, m-vinylbenzyltriphenyltin, m- (1-phenylvinyl) benzyltributyltin, and P- and m- / p-mixtures are preferred.
[0033]
There is no particular limitation on the method for producing a styrene-butadiene copolymer (including a copolymer in which a tin atom is introduced into a monomer unit of styrene or butadiene) by anionic polymerization using the lithium compound as a polymerization initiator, A conventionally known method can be used. Specifically, styrene and 1,3-butadiene are polymerized with the organic lithium compound in an organic solvent inert to the reaction, for example, an aliphatic, alicyclic, or aromatic hydrocarbon compound. If desired, the desired styrene-butadiene copolymer is obtained by anionic polymerization in the presence of a randomizer used, if desired. The temperature in this polymerization reaction is appropriately selected in the range of usually -80 to 150C, preferably -20 to 100C. Although the above polymerization reaction can be carried out under the generated pressure, it is usually desirable to operate at a pressure sufficient to keep the monomer substantially in a liquid phase. Higher pressures can be used if desired, and such pressures can be obtained by any suitable method, such as by pressurizing the reactor with a gas that is inert with respect to the polymerization reaction.
[0034]
The unmodified styrene-butadiene copolymer (having a tin in the styrene or butadiene monomer unit) having a hydrocarbyl group or a nitrogen-containing group at the polymerization initiation terminal and having the other terminal active for polymerization, thus obtained. By reacting a tin compound with the polymerized active terminal of the compound (including a copolymer into which atoms have been introduced), a desired modified styrene-butadiene copolymer rubber can be obtained.
Examples of the tin compound include tin tetrachloride, tributyltin chloride, trioctyltin chloride, dioctyltin dichloride, dibutyltin dichloride, and triphenyltin chloride. Even if the reaction is stopped without using a denaturing agent, tin atoms are introduced into the molecule.
[0035]
The solution-polymerized SBR used in the rubber composition of the present invention has at least one tin atom in the molecule, has a bound styrene content in the molecule of 3 to 10% by mass, and has 1,2 in the polybutadiene chain portion. -A modified styrene-butadiene copolymer rubber having a vinyl bond amount of 40% by mass or less. If the bound styrene content is less than the above range, the hardness of the rubber will be insufficient, and if it exceeds the above range, the elongation at break and the exothermic properties will deteriorate. On the other hand, when the amount of 1,2-vinyl bond exceeds the above range, elongation at break and deterioration of heat generation characteristics are caused.
[0036]
In the rubber composition of the present invention, as a reinforcing material or a filler of the component (3), the nitrogen adsorption specific surface area is 65 to 92 m ² / g and the DBP oil absorption is 100 parts by mass of the rubber component. 40 to 65 parts by mass of carbon black of 70 to 132 × 10 ⁻⁵ m ³ / kg is blended. By blending the carbon black having the above properties in the above range, the anti-fracture properties, crack growth resistance, modulus and the like can be improved. In addition, the compounding amount of the carbon black is more preferably in the range of 45 to 60 parts by mass in order to enhance the above effect. When the compounding amount of the carbon black is less than 40 parts by mass, the above-mentioned improvement effect is insufficient. On the other hand, when the compounding amount exceeds 65 parts by mass, the anti-destructive properties, the crack growth resistance and the exothermic properties are obtained. Comes down.
[0037]
The carbon black used in the present invention is not particularly limited as long as the nitrogen adsorption specific surface area and the DBP oil absorption satisfy the above ranges. Specifically, for example, S315, N326 (ISAF-LS), N330 ( HAAF), carbon blacks such as N335, N339, N343, N347 (HAF-HS), N351, N356, N358, N375, N539, N550 (FEF) and N582. Among these carbon blacks, N326 (ISAF-LS), N330 (HAF), N335, N339, N343, and N347 (HAF-HS) carbons are preferable from the viewpoint of simultaneously improving high modulus and high destruction characteristics. In particular, N330 (HAF) and N326 (ISAF-LS) carbon are more preferable. One of the above carbon blacks may be used alone, or two or more thereof may be used in combination.
[0038]
In the rubber composition of the present invention, silica can be further compounded, if desired. The silica preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 160 to 260 m ² / g and a dibutyl phthalate oil absorption (DBP) of 180 to 260 mL / 100 g. If the (N ₂ SA) is less than 160 m ² / g or (DBP) is less than 180 mL / 100 g, the abrasion resistance may be insufficient, while the (N ₂ SA) may exceed 260 m ² / g, When (DBP) exceeds 260 mL / 100 g, poor dispersion may be caused, and low heat generation performance and abrasion resistance may be reduced. Here, (N ₂ SA) is a value measured according to ASTM D4820-93 after drying at 300 ° C. for 1 hour, and (DBP) is a value measured according to ASTM D2414-93. It is.
[0039]
Examples of the silica include wet silica (hydrous silicic acid), dry silica (silicic anhydride), calcium silicate, aluminum silicate, and the like. Of these, wet silica is particularly preferable. In the present invention, the silica is preferably blended in an amount of 30 parts by mass or less based on 100 parts by mass of the rubber component (A) or (A). If the amount exceeds 30 parts by mass, the low heat generation performance may be reduced. A more preferred amount of silica is in the range of 20 parts by mass or less.
[0040]
In the rubber composition of the present invention, in addition to the rubber component of (1) and (2) and the carbon black of (3), if necessary and necessary, the rubber composition is commonly used in general industrial rubber compounding. Vulcanizing agents, vulcanization accelerators, vulcanization aids, antioxidants, antioxidants, process oils, softeners, and other rubber compounding agents can be appropriately compounded. In particular, in order to increase the elastic modulus or modulus at 100% elongation, 1 to 8 parts by mass, preferably 2 to 6 parts by mass of sulfur and / or a sulfur-containing compound as a vulcanizing agent is used with respect to 100 parts by mass of the rubber component. Parts, more preferably 2.5 to 5 parts by mass. When the amount of sulfur is large and there is a possibility of blooming as described above, it is also desirable to replace some or all of the sulfur used with insoluble sulfur (polymer type).
[0041]
Further, a bismaleimide compound can be added to the rubber composition of the present invention in order to improve heat resistance, heat aging resistance, dynamic storage modulus (E ′), and the like. Examples of the bismaleimide compound include N, N'-1,2-phenylenedimaleimide, N, N'-1,3-phenylenedimaleimide, N, N'-1,4-phenylenedimaleimide, N '-(4,4'-diphenylmethane) bismaleimide, 2,2-bis [4- (4-maleimidophenoxy) phenyl] propane, bis (3-ethyl-5-methyl-4-maleimidophenyl] methane, etc. Among these, N, N'-1,2-phenylenedimaleimide, N, N'-1,3-phenylenedimaleimide, and N, N'-1,4-phenylenedimaleimide are preferred, In particular, N, N '-(4,4'-diphenylmethane) bismaleimide is more preferred because of its remarkable effect.The compounding amount of the bismaleimide compound is 100 parts by mass of the rubber component. It is preferably from 1 to 3 parts by weight for, also may be used alone or may be used in combination of two or more.
[0042]
The rubber composition of the present invention has the above-mentioned composition, and further has a physical property, particularly, a modulus (M ₁₀₀ ) at the time of 100% elongation in the tire circumferential direction of 5.0 to 10.0 MPa. It is a necessary requirement that the material has a breaking elongation (Eb) of 300% or more. If the modulus (M ₁₀₀ ) at the time of 100% elongation is less than the above range, the radial expansion of the tire during high-speed running at a high internal pressure cannot be suppressed below a predetermined value, and the elongation at break (Eb) Is less than 300%, the generation and growth of cracks at the belt end cannot be suppressed.
[0043]
In the radial tire for high-speed heavy load according to the present invention, a protective belt made of an organic fiber cord can be disposed at a predetermined rubber thickness outside the belt layer in the tire radial direction, as described later. The modulus (M ₁₀₀ ) at 100% elongation of the rubber composition is preferably 1.2 to 1.5 times higher than the modulus (M ₁₀₀ ) at 100% elongation of the coating rubber of the protective belt. If the ratio of the modulus (M ₁₀₀ ) is less than 1.2 times, there is a concern that the cushioning effect due to the provision of the protective belt may be reduced, and if the ratio exceeds 1.5 times, the distance between the belt layer and the protective belt may be reduced. May cause a peeling failure.
[0044]
The heavy-duty pneumatic radial tire of the present invention can be manufactured by vulcanizing and molding according to ordinary vulcanization conditions using such a rubber composition as a coating rubber for a belt ply of a belt layer. Here, the rubber composition of the present invention may be applied to all of the belt plies constituting the belt layer.In particular, in a radial tire for an aircraft, while avoiding an increase in weight and cost as much as possible, at a high internal pressure. From the viewpoint of suppressing the diameter growth during high-speed running and improving the anti-destructive properties and the durability life, it is preferable to apply the present invention to the coating rubber of the main belt layer composed of two or more belt plies constituting the belt layer.
In addition, an inert gas such as air or nitrogen is used as the gas filled in the tire of the present invention.
[0045]
(Radial tire for high-speed heavy load)
The high-speed heavy-load pneumatic radial tire of the present invention in which the above rubber composition is applied to a tire rubber belt will be described in detail below.
As a result of a detailed examination of the tension load of the belt layer by the present inventors, as shown in the graph of FIG. 3, the distribution is like a one-dot chain line in a no-load state of 100% internal pressure (TRA prescribed internal pressure). Was. In FIG. 3, the vertical axis represents the tension, the horizontal axis represents the position in the belt width direction, and SBW represents the maximum width of the belt layer.
By the way, in the case of an aircraft tire, in an unloaded state, a pressure resistance of 400% of a specified internal pressure is required. As a result of examining the tension distribution at the time of 400% internal pressure filling, it was found that the distribution was as shown by a solid line. On the other hand, it was found that under the load condition, the tension distribution of the belt layer was like a two-dot chain line. This indicates that the belt layer needs to have a strength that satisfies both conditions.
From various experiments and investigations, the inventors have determined that the elongation at the equatorial plane is larger than the strength at the position of 2/3 of the maximum width of the belt layer with respect to the tension at no load, thereby suppressing the growth of the diameter. It has been found that both reductions in mass can be achieved.
The invention according to claim 4 has been made in view of the above fact, and includes a pair of bead cores and a carcass layer including at least one or more carcass plies extending in a toroidal shape from one bead core to the other bead core. A belt layer comprising at least one or more belt plies containing organic fiber cords on the outer peripheral surface of a crown region of the carcass layer in the tire radial direction; and a tread rubber forming a tread portion on the tire radial direction outside of the belt layer. A total strength in the tire circumferential direction of the belt layer per unit width at a tire equatorial plane position P0, and a maximum width of the belt layer around the tire equatorial plane. When the total strength in the tire circumferential direction of the belt layer per unit width at a width position P2 of 2/3 of the above is K2, K2 <K0 is satisfied. To foot, it is characterized in that.
Next, the operation of the pneumatic radial tire according to claim 4 will be described.
In the pneumatic radial tire according to claim 4, the total strength K0 of the belt layer in the tire circumferential direction per unit width at the tire equatorial plane position P0 is 2/3 of the maximum width of the belt layer around the tire equatorial plane. Is set to be larger than the total strength of the belt layer in the tire circumferential direction per unit width at the width position P2 of the tread. It is possible to suppress the amount of circumferential extension of the tread rubber, thereby suppressing the tire from growing in diameter. The suppression of the tread rubber in the circumferential direction reduces the degree of tension of the rubber, thereby increasing the resistance to the intrusion of foreign matter, and the growth of cracks even if foreign matter is stabbed. Can be suppressed.
In the pneumatic radial tire according to claim 4, the above-described rubber composition of the present invention may be applied to the entire belt ply of the belt layer, or may be applied to at least the main belt ply.
[0046]
(Definition of total strength) The total strength here refers to the circumferential strength of the belt layer, and is calculated by multiplying the strength of one cord by the number of cords per unit width (here, 10 mm). is there. The total strength when the cord is inclined at an angle θ with respect to the circumferential direction is calculated by multiplying the total strength per unit width by cos θ. When the cord in the tire extends in a wave shape (zigzag shape) in the tire circumferential direction, the strength is not calculated by straightening the cord, but the shape embedded in the tire, that is, the wave shape is applied. Calculate the strength when the object is extended in the circumferential direction.
[0047]
According to a fifth aspect of the present invention, in the pneumatic radial tire according to the fourth aspect, 0.2 ≦ K2 / K0 ≦ 0.8 is satisfied.
Next, the operation of the pneumatic radial tire according to claim 5 will be described.
When the strength ratio (K2 / K0) is less than 0.2, there is a possibility that the organic fiber cord located in the vicinity of the shoulder portion is subjected to excessive tension, thereby causing a decrease in pressure resistance. On the other hand, when the strength ratio (K2 / K0) exceeds 0.8, the organic fiber cords of the belt plies arranged at 2/3 points are not effectively used, which leads to an increase in the mass of the pneumatic radial tire. Therefore, the strength ratio (K2 / K0) preferably satisfies 0.2 ≦ K2 / K0 ≦ 0.8.
[0048]
The invention according to claim 6 is the pneumatic radial tire according to claim 4 or 5, wherein in the belt layer, the lamination thickness of the organic fiber cord is the largest at the tire equatorial plane position P0, When the laminated thickness of the organic fiber cord at the tire equatorial plane position P0 is G0, and the laminated thickness of the organic fiber cord at the width position P2 of の of the maximum width of the belt layer is G2, G2 <G0. Is satisfied.
Next, the operation of the pneumatic radial tire according to claim 6 will be described.
By setting the lamination thickness G2 of the organic fiber cord at the width position P2 of 2/3 of the maximum width of the belt layer to be larger than the lamination thickness G0 of the organic fiber cord at the tire equatorial plane position P0, K2 <K0. Can be easily achieved. In addition, the lamination | stacking thickness of an organic fiber cord is the total diameter dimension of the organic fiber cord laminated | stacked in the tire radial direction when a belt layer is seen in a tire radial direction cross section. For example, when 12 organic fiber cords having a diameter of A are laminated, the laminated thickness is A × 12.
[0049]
According to a seventh aspect of the present invention, in the pneumatic radial tire according to the sixth aspect, 0.35 ≦ G2 / G0 ≦ 0.85 is satisfied.
Next, the operation of the pneumatic radial tire according to claim 7 will be described.
When the ratio G2 / G0 of the laminated thickness of the organic fiber cords is less than 0.35, there is a possibility that an excessive tension is applied to the organic fiber cords located in the vicinity of the shoulder portion, thereby lowering the pressure resistance. On the other hand, if the ratio G2 / G0 of the laminated thickness of the organic fiber cords exceeds 0.85, the organic fiber cords of the belt plies arranged at 2/3 points are not effectively utilized, which leads to an increase in the mass of the pneumatic radial tire. . Therefore, the ratio G2 / G0 of the laminated thickness of the organic fiber cord preferably satisfies 0.35 ≦ G2 / G0 ≦ 0.85.
[0050]
According to an eighth aspect of the present invention, in the pneumatic radial tire according to any one of the fourth to seventh aspects, in the belt layer, at a width position P2 of 2/3 of a maximum width of the belt layer. When the lamination thickness of the organic fiber cord is G2, the belt layer has a thickness greater than the lamination thickness G2 in a region outside the width position P2 of 2/3 of the maximum width of the belt layer in the tire width direction. It is characterized in that a portion having a large lamination thickness is provided.
Next, the operation of the pneumatic radial tire according to claim 8 will be described.
In a region outside the width position P2 of 2/3 of the maximum width of the belt layer in the tire width direction, if a portion having a stack thickness greater than the stack thickness G2 is provided, the tire is exposed to an external force in the tire width direction, particularly during high-speed running. In such a case, it is possible to flexibly absorb a large fluctuation in tension at both sides of the tire, and it is possible to effectively suppress the occurrence of a standing wave that can significantly reduce the life of the pneumatic radial tire.
[0051]
According to a ninth aspect of the present invention, in the pneumatic radial tire according to any one of the fourth to eighth aspects, the belt layer has a tensile breaking strength of 6.3 cN / dtex or more and 0 in the extension direction. The elongation percentage under a load of 0.3 cN / dtex is 0.2 to 2.0%, the elongation percentage under a 2.1 cN / dtex load is 1.5 to 7.0% in the extension direction, and 3.2 cN / dtex in the extension direction. It is characterized by having a main belt layer composed of at least two or more belt plies including an organic fiber cord having an elongation under load of 2.2 to 9.3%.
Next, the operation of the pneumatic radial tire according to claim 9 will be described.
As in the present invention, by regulating the strength distribution of the belt layer, it is possible to achieve both the suppression of diameter growth and the reduction in mass.However, if a low-elastic cord such as nylon is used, a multilayer structure is used to suppress the diameter growth. It is necessary to increase the mass of the tire.
[0052]
In the pneumatic radial tire according to the ninth aspect, the main belt layer is constituted by at least two or more belt plies including a high elasticity organic fiber cord having a tensile breaking strength of 6.3 cN / dtex or more. The required pressure resistance performance can be satisfied. Here, the elongation rate of the organic fiber cord under a 2.1 cN / dtex load in the extension direction is 1.5 to 7.0%, and the elongation rate under a 3.2 cN / dtex load in the extension direction is 2.2 to 9.9. By setting it to 3%, the target suppression of diameter growth could be easily achieved.
The reason is that in a pneumatic radial tire for an aircraft, a cord tension of about 2.1 cN / dtex is applied when the internal pressure is loaded in a standard state, and a cord tension of about 3.2 cN / dtex is applied during high-speed running. If the elongation percentage exceeds the above range, bulging in the tire radial direction cannot be effectively suppressed at the time of filling the tire with the internal pressure, so that the performance against sticking of foreign matter cannot be expected.
On the other hand, if the elongation percentage of the organic fiber cord is less than the above range, the hoop effect of the belt ply is too large, and the carcass ply undesirably expands in the tire width direction, which is not preferable.
Further, the reason why the elongation percentage under a load of 0.3 cN / dtex in the elongation direction of the organic fiber cord is set to 0.2 to 2.0% is as described below. First, when vulcanizing a pneumatic radial tire, in the case of a pneumatic radial tire for an aircraft, the tire outer diameter is set so that the raw tire is stretched by about 0.2 to 2.0% in a normal tire mold. You. This is to uniformly expand the tire by the pressure applied from the inside of the raw tire during vulcanization, thereby aligning the cord directions, and correcting variations in cord driving. In this step, a relatively small tension of about 0.3 cN / dtex acts on the organic fiber cord. If the elongation percentage of the organic fiber cord at this time is greater than 2.0%, the effect of correcting the cord properties is reduced. If the elongation is too small and the elongation is less than 0.2%, the cord tension becomes large during expansion during vulcanization, which causes inconvenience such that the organic fiber cord bites into the rubber inside the tire in the radial direction. .
[0053]
(Definition of Internal Pressure Load in Standard State) The internal pressure and load specified in TRAYEARBOOK (2002 version) are adopted as the internal pressure and load. For example, in the case of an aircraft radial tire 1270 × 455R22 32PR, the specified internal pressure is 1620 kPa and the specified load is 24860 kg.
The organic fiber cord has an elongation of 0.2 to 1.5% under a load of 0.3 cN / dtex in the elongation direction, and an elongation of 1.5 to 6.6 under a load of 2.1 cN / dtex in the elongation direction. More preferably, the elongation at the time of load of 3.2 cN / dtex in the extension direction is 2.2 to 8.3%.
[0054]
According to a tenth aspect of the present invention, in the pneumatic radial tire according to the ninth aspect, at least two or more of the belt plies are stacked at an end portion in the tire width direction of the main belt layer. I have.
Next, the operation of the pneumatic radial tire according to claim 10 will be described.
By laminating two or more belt plies at the end of the main belt layer in the width direction of the tire, during running of the tire, particularly in the case where an external force acts in the width direction of the tire, the vicinity of both ends in the width direction of the tire tread surface. It is possible to effectively disperse the impact with its elasticity even under conditions where the organic fiber cord is subject to severe tension fluctuations, which is effective in improving tire reliability under severe use conditions. .
[0055]
According to an eleventh aspect of the present invention, in the pneumatic radial tire according to the ninth or tenth aspect, the main belt layer is made of an aromatic polyamide-based fiber and has a lower twist coefficient of 0.12 to 0. .85, and a belt ply including an organic fiber cord having a twist factor of 0.40 to 0.80.
Next, the operation of the pneumatic radial tire according to claim 11 will be described.
The organic fiber cord constituting the main belt layer is composed of an aromatic polyamide-based fiber, and has a lower twist coefficient of 0.12 to 0.85, preferably 0.17 to 0.51, and a lower twist coefficient of 0.40 to 0.40. By setting it to 0.80, the organic fiber cord has the physical properties defined in claim 6, namely, a tensile strength at break of 6.3 cN / dtex or more, and an elongation percentage under a load of 0.3 cN / dtex in the elongation direction of 0.2. ２．０2.0%, elongation rate under a 2.1 cN / dtex load in the extension direction is 1.5-7.0%, and elongation rate under a 3.2 cN / dtex load in the extension direction is 2.2-9.3. % Can be set.
[0056]
(Definition of Twist Coefficient) The twist coefficient referred to here is calculated from the following equation.
NT = N × (0.139 × D / ρ) ^1/2 × 10 ^-3
N: number of twists per 100 mm of organic fiber cord D: total indicated decitex (dtex) number ρ: specific gravity of organic fiber cord (g / cm ³ )
[0057]
According to a twelfth aspect of the present invention, in the pneumatic radial tire according to any one of the ninth to eleventh aspects, the main belt layer includes an aromatic polyamide-based fiber and an aliphatic polyamide-based fiber. And a belt ply including an organic fiber cord having a mass ratio of aromatic polyamide-based fiber to aliphatic polyamide-based fiber of 100: 10 to 170.
Next, the operation of the pneumatic radial tire according to claim 12 will be described.
The organic fiber cord constituting the main belt layer is composed of an aromatic polyamide fiber and an aliphatic polyamide fiber, and the mass ratio of the aromatic polyamide fiber to the aliphatic polyamide fiber is 100: 10. By setting it to 170, the organic fiber cord has the physical properties defined in claim 9, that is, a tensile strength at break of 6.3 cN / dtex or more, and an elongation percentage under a load of 0.3 cN / dtex in the stretching direction of 0.2 to 0.2. 2.0%, elongation rate under a 2.1 cN / dtex load in the extension direction is 1.5 to 7.0%, and elongation rate under a 3.2 cN / dtex load in the extension direction is 2.2 to 9.3%. Can be set to
Here, when the mass of the aliphatic polyamide fiber is less than 10 with respect to the mass of the aromatic polyamide fiber of 100, the cord elongation is reduced when the above load is applied, and thus the physical properties specified in claim 9 are satisfied. Is difficult to achieve. On the other hand, when the mass of the aliphatic polyamide-based fiber exceeds 170 with respect to the mass of the aromatic polyamide-based fiber of 100, the cord elongation becomes large when the above-mentioned load is applied. It is difficult to achieve.
[0058]
The mass ratio of the aromatic polyamide-based fiber to the aliphatic polyamide-based fiber is more preferably 100: 17 to 86. Here, the aliphatic polyamide fiber is, for example, 6-nylon, 6,6-nylon, 4,6-nylon fiber or the like. Here, the organic fiber cord may be composed of an aromatic polyamide-based fiber and an aliphatic polyamide-based fiber, and is obtained by twisting the aromatic polyamide-based organic fiber cord and the aliphatic polyamide-based organic fiber cord. Alternatively, the aromatic polyamide fiber and the aliphatic polyamide fiber may be combined and then twisted.
When the aromatic polyamide-based organic fiber cord is A and the aliphatic polyamide-based organic fiber cord is B, after A or B is twisted (Z twist), they are aligned and then twisted in the opposite direction to the twisting ( By applying S twist), an organic fiber cord constituting the main belt layer can be obtained. At the time of bottom twisting, A or B may be twisted alone, or A and B may be twisted together. The number of A, B, or AB (combined yarn) at the time of the first twist or the first twist may be one or more. The thickness of the A or B raw yarn may be the same or different. The form of the twisted yarn may be such that a loop is formed around the core yarn.
[0059]
According to a thirteenth aspect of the present invention, in the pneumatic radial tire according to the twelfth aspect, the main belt layer is formed by twisting an aromatic polyamide cord and an aliphatic polyamide cord with each other, and A belt ply including an organic fiber cord having a ply twist coefficient of 0.12 to 0.85;
Next, the operation of the pneumatic radial tire according to claim 13 will be described.
By setting the ply twist coefficient of the aromatic polyamide cord to 0.12 to 0.85, it becomes easy to achieve the physical properties defined in claim 9. In addition, it is more preferable that the ply twist coefficient of the aromatic polyamide cord be 0.17 to 0.51.
[0060]
According to a fourteenth aspect of the present invention, in the pneumatic radial tire according to any one of the ninth to thirteenth aspects, the main belt layer is spirally formed at an angle of approximately 0 ° with respect to the tire equatorial plane. And a belt ply including an organic fiber cord wound around.
Next, the operation of the pneumatic radial tire according to claim 14 will be described.
By setting the angle of the organic fiber cord to the tire equatorial plane at about 0 °, the strength of the organic fiber cord used to secure the circumferential rigidity of the main belt layer can be maximized, and The weight of the radial tire can be reduced. Here, the term “approximately 0 °” includes 2.0 ° or less.
[0061]
The invention according to claim 15 is the pneumatic radial tire according to any one of claims 4 to 14, wherein the main belt layer is inclined at an angle of 2 to 25 ° with respect to the tire equatorial plane. Further, a belt ply including an organic fiber cord bent in the same plane so as to be inclined in the opposite direction at each ply end and extending in a tire circumferential direction in a zigzag manner is provided.
Next, the operation of the pneumatic radial tire according to claim 15 will be described.
Belt ply that includes an organic fiber cord that is inclined in the same plane so as to be inclined at an angle of 2 to 25 degrees with respect to the tire equatorial plane and inclined in the opposite direction at each ply end, and extends in a tire circumferential direction in a zigzag manner. By using, the rigidity in the tire width direction can be secured without greatly reducing the circumferential rigidity of the main belt layer, and as a result, excellent wear resistance can be realized.
[0062]
The reason why excellent wear resistance is realized by securing rigidity in the tire width direction is as follows. In general, if the diameter difference between the crown center portion and the shoulder portion is large in the tire shape at the time of internal pressure filling, the possibility of causing so-called “dragging wear” increases. The center portion and the shoulder portion that contact the ground during rotation of the tire rotate by an amount corresponding to the contact length, but the rotation angle of the tire corresponding to a constant circumference is larger in the shoulder portion having a smaller diameter. Therefore, the shoulder portion is restrained rearward in the rotational direction before leaving the road surface, and the center portion and the shoulder portion are sheared and deformed in the tread contact surface. A phenomenon in which the shoulder portion slides relatively to the road surface to correct this deformation is “drag wear”.
The magnitude of the deviation of the circumferential position depends on the diameter difference between the center portion and the shoulder portion, and the circumferential shear rigidity in the tread surface, and the degree of the drag wear increases as the diameter difference increases and the shear rigidity decreases. Become. The spiral belt has a low shear rigidity because the cord is oriented substantially in the circumferential direction, and is not effective with respect to drag wear. In order to compensate for this, by adding a belt having a cord having a large angle with respect to the tire circumferential direction, rigidity in the tire width direction can be ensured and wear characteristics can be improved.
Here, if the angle of the organic fiber cord with respect to the tire equatorial plane is less than 2 °, it becomes difficult to wind the belt geometrically in a zigzag manner (that is, it becomes spiral). On the other hand, if the angle of the organic fiber cord with respect to the tire equatorial plane exceeds 25 °, the tension that the organic fiber cord can exert in the tire circumferential direction relatively decreases, and the efficiency of bearing the internal pressure of the pneumatic radial tire deteriorates. .
[0063]
(One embodiment)
Hereinafter, one embodiment of a pneumatic radial tire for an aircraft of the present invention will be described with reference to FIG.
As shown in FIG. 1, the pneumatic radial tire 101 for an aircraft (tire size: 1270 × 455R22 32PR) according to the present embodiment includes a bead core 14 having a round cross section in a bead portion 12 and is coated with rubber. A carcass layer 16 composed of six carcass plies in which organic fiber cords are arranged in the radial direction is moored to the bead core 14.
A belt layer 20 is provided on the outer peripheral surface of the crown area of the carcass layer 16 in the tire radial direction, and tread rubber layers (31 to 33) constituting a tread portion are provided on the outer side of the belt layer 20 in the tire radial direction. Further, a side rubber layer 27 constituting the sidewall portion 25 is provided outside the carcass layer in the tire width direction. In the present embodiment, the belt layer 20 includes a main belt layer 26 on the inner side in the tire radial direction, an auxiliary belt layer 28 provided on the outer side in the tire radial direction of the main belt layer 26, and an outer side in the tire radial direction on the auxiliary belt layer 28. And a protective belt layer 22 provided on the second side.
[0064]
The main belt layer 26 includes a plurality of belt plies, in this embodiment, eight belt plies. These plies constituting the main belt layer 26 are formed by coating a plurality of organic fiber cords with rubber. These organic fiber cords preferably have a tensile breaking strength of 6.3 cN / dtex or more, an elongation of 0.2 to 2.0% under a load of 0.3 cN / dtex in the elongation direction, and 2% in the elongation direction. It is preferable that the elongation percentage under a load of 0.1 cN / dtex is 1.5 to 7.0% and the elongation percentage under a 3.2 cN / dtex load in the extension direction is 2.2 to 9.3%.
The organic fiber cord of the present embodiment is composed of aromatic polyamide-based fibers. When the organic fiber cord is composed of aromatic polyamide-based fiber, the lower twist coefficient is set to 0.12 to 0.85, preferably 0.17 to 0.51, and the upper twist coefficient is set to 0.40 to 0.80. Is preferred. In the present embodiment, an organic fiber cord made of an aromatic polyamide-based fiber, specifically, a polyamide fiber manufactured by DuPont (product type name: KEVLAR (R) 29, nominal fineness: 3000 denier, hereinafter appropriately referred to as Kevlar). Is used. In the present embodiment, the inclination angle of the organic fiber cord is substantially 0 ° with respect to the tire equatorial plane CL. In the belt ply, the number of organic fiber cords to be driven is preferably in the range of 4 to 10/10 mm. In the present embodiment, the number of driving organic fiber cords in the belt ply 26 is 6.3 / 10 mm.
[0065]
When the sub-belt layer 28 is provided as in the present embodiment, the range is preferably provided within a range from the tire equatorial plane CL to a position 140% of the width BW of the main belt layer 26. In the present embodiment, the width SBW of the sub belt layer 28 is 103% of the width BW of the main belt layer 26. The sub-belt layer 28 is composed of one belt ply in the present embodiment. The belt ply of the present embodiment prepares a strip-shaped elongated body constituted by coating one or a plurality of organic fiber cords with rubber, and reciprocates between both ply ends only once every time the elongated body is rotated substantially once. At the same time, it is inclined at an angle of 2 to 25 ° with respect to the tire equatorial plane and wound in the circumferential direction, and such winding is shifted in the circumferential direction by almost the width of the elongated body so that no gap is formed between the elongated bodies. It is formed by winding a number of times (hereinafter referred to as an endless zigzag winding belt as appropriate). As a result, in the belt ply, the organic fiber cords extending substantially in the circumferential direction while zigzag by changing the bending direction at both ply ends are embedded almost uniformly in the entire area of the belt ply.
[0066]
This belt ply has an organic fiber cord having an elastic modulus equal to or smaller than that of the organic fiber cord included in the main belt layer 26 (elongation of the organic fiber cord of the main belt layer 26 under a 2.1 cN / dtex load). It is preferable to use an organic fiber cord whose ratio is substantially equal to or higher. Examples of the organic fiber cord used for the belt ply constituting the sub-belt layer 28 include cords made of aliphatic polyamide-based fibers such as nylon, aromatic polyamide-based fibers such as aramid, and aliphatic polyamide-based fibers such as nylon. Is preferable. In the present embodiment, a nylon cord (twisting number: 1260 D // 2/3, driving number: 7.3 / 10 mm) is used. In the belt ply of the present embodiment, which is an endless zigzag winding belt, the inclination angle of the organic fiber cord is preferably within a range of 2 to 45 ° with respect to the tire equatorial plane CL, and is set to 8 ° in the present embodiment. ing.
[0067]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples. The rubber chemicals such as bismaleimide, an antioxidant, and a vulcanization accelerator used here are merely examples, and can be changed to other arbitrary chemicals according to the purpose. In this example, “parts” and “%” all represent “parts by mass” and “% by mass”.
[0068]
[Examples 1-3 and Comparative Examples 1-2]
According to the formulation shown in Table 1 below, the rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 2 were prepared and kneaded using a 250 mL Labo Plastomill (manufactured by Toyo Seiki Seisakusho). Then, a sheet of each rubber composition was prepared with a 3-inch roll. Next, at a temperature of 150 ° C., vulcanization was performed for a vulcanization time corresponding to 1.5 times the time (t ₉₀ ) until the increase in torque due to the vulcanization reaction reached 90% of the maximum value, and the following physical properties were measured. A test sample was obtained.
[0069]
[Table 1]

[0070]
The components listed in Table 1 above have the following specifications (specs).
-Solution polymerization SBR: Solution polymerization SBR manufactured by JSR Corporation (styrene content: 3 to 10% by mass, vinyl bond amount: 40% by mass or less)
-Carbon black (A): "HAF" manufactured by Asahi Carbon Co., Ltd. (nitrogen adsorption specific surface area: 71 m ² / g, DBP oil absorption: 103 × 10 ⁻⁵ m ³ / kg)
-Carbon black (B): "N326" manufactured by Asahi Carbon Co., Ltd. (nitrogen adsorption specific surface area: 84 m ² / g, DBP oil absorption: 75 × 10 ⁻⁵ m ³ / kg)
The bismaleimide, antioxidant and vulcanization accelerator used are as follows.
・ Bismaleimide (PBM): trade name “BMI-S” (N, N ′-(4,4′-diphenylmethane) bismaleimide) manufactured by Mitsui Chemicals, Inc.
-Antioxidant (6PPD)-N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine-Vulcanization accelerator (TBBS)-Nt-butyl-2-benzo Thiazolylsulfenamide
An evaluation test was performed on each of the vulcanized rubber samples obtained as described above, and the results were recorded in Table 2 below.
(1) Tensile test In accordance with JIS K6301 (1995), at room temperature (25 ° C.), a tensile test was performed using a punched sample of dumbbell No. 3, and the modulus (MPa) and the elongation at break (%) at 100% elongation. ) Was measured.
[0072]
Further, the rubber composition of each composition shown in Table 1 above was used as a belt ply for the main belt layer (indicated by 26 in FIG. 1) of the pneumatic radial tire for an aircraft (size: APR 1270 × 455R22 32PR) shown in FIG. , A test tire was manufactured in accordance with a normal manufacturing process of an aircraft radial tire, and the following evaluation test was performed.
(2) Evaluation of belt end crack For each test tire, assemble it with a regular rim (46 × 17R20 / 30), fill it with the internal pressure of the maximum air pressure (12.7 kg / cm ² ), and load 80% of the maximum load capacity. And the drum was run at a speed of 64.5 km / h for 4 minutes for 800 times in a one-hour cycle, and the test tire was dissected to check for cracks at the end of the belt ply.
[0073]
(3) Evaluation of growth rate of tire diameter For each test tire, before and after filling with the internal pressure of the maximum air pressure (12.7 kg / cm ² ), assembling it with a regular rim (46 × 17R20 / 30) The rate of increase (%) in the outer diameter of the tread center was measured. The smaller the increase rate of the outer diameter is, the more preferable it is because the diameter growth of the tire is suppressed.
[0074]
[Table 2]

[0075]
As is clear from the results in Table 2 above, it was found that the rubber compositions (Examples 1 to 3) of the present invention were superior to those of Comparative Examples in the modulus and the breaking characteristics. In addition, the radial tires for aircraft (Examples 1 to 3) of the present invention in which these rubber compositions are applied to the ply-covered rubber of the main belt are more excellent in crack resistance and radial expansion suppression than the comparative tires. It was proved that.
[0076]
【The invention's effect】
By applying the rubber composition and the tire structure of the present invention to a belt layer, the radial expansion of the tire is suppressed, crack resistance is improved, and a heavy-duty pneumatic radial tire excellent in durability life, particularly an aircraft radial It is now possible to provide tires.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a pneumatic radial tire for an aircraft (101) according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of a conventional pneumatic radial tire (102).
FIG. 3 is a graph showing tension applied to a belt layer.

Claims (15)

At least one belt ply constituting the belt layer is made of a cord in which an aromatic polyamide-based fiber and an aliphatic polyamide-based fiber are mixed and twisted to form a rubber-coated cord. 70 to 100 parts by mass of rubber and / or synthetic isoprene rubber, (2) obtained by solution polymerization, having at least one tin atom in the molecule, having a bound styrene content in the molecule of 3 to 10% by mass, and 30 to 0 parts by mass of a modified styrene-butadiene copolymer rubber having a 1,2-vinyl bond amount of 40% by mass or less in a polybutadiene chain portion, and (3) a nitrogen adsorption specific surface area of 65 to 92 m ² / g and 40-65 parts by weight of carbon black DBP oil absorption amount is ^{70~132 × 10 -5 m 3 / kg} , a rubber composition comprising, in the tire circumferential direction Fast heavy duty pneumatic radial tire 00% elongation during the modulus _{(M 100)} is characterized in that and elongation at break in the range of 5.0~10.0MPa (Eb) is 300% or more. 2. The pneumatic radial tire for high-speed heavy load according to claim 1, wherein the rubber composition is applied at least to a coating rubber of a main belt layer composed of two or more belt plies constituting a belt layer. 3. The modulus (M ₁₀₀ ) at the time of 100% elongation of the rubber composition is 100% elongation of the coating rubber of the protective belt made of an organic fiber cord disposed at a predetermined rubber thickness outside the belt layer in the tire radial direction. fast heavy duty pneumatic radial tire according to claim 1 or 2, characterized in that 1.2 to 1.5 times higher than the modulus _{(M 100)} when. The radial tire has a pair of bead cores, a carcass layer including at least one or more carcass plies extending in a toroidal shape from one bead core to the other bead core, and a crown area outer peripheral surface of the carcass layer in a tire radial direction outside. A pneumatic radial tire comprising: a belt layer comprising at least one or more belt plies containing an organic fiber cord; and a tread rubber layer constituting a tread portion on the tire radial outside of the belt layer. The total strength of the belt layer in the tire circumferential direction per unit width at the equatorial plane position P0 is K0, and the total strength per unit width at a width position P2 of 2/3 of the maximum width of the belt layer around the tire equatorial plane is K0. 4. The tire according to claim 1, wherein K2 <K0 is satisfied when the total strength of the belt layer in the tire circumferential direction is K2. High-speed heavy-duty pneumatic radial tire according to any Re. The pneumatic radial tire for high-speed heavy load according to claim 4, wherein the belt layer satisfies 0.2 ≦ K2 / K0 ≦ 0.8. In the belt layer, the lamination thickness of the organic fiber cord is the thickest at the tire equatorial plane position P0, the lamination thickness of the organic fiber cord at the tire equatorial plane position P0 is G0, and the maximum width of the belt layer is two. 6. The pneumatic radial tire for high-speed heavy load according to claim 4, wherein, when the laminated thickness of the organic fiber cords at the width position P2 of / 3 is G2, G2 <G0 is satisfied. 7. The pneumatic radial tire for high-speed heavy load according to claim 6, wherein the belt layer satisfies 0.35≤G2 / G0≤0.85. In the belt layer, when the lamination thickness of the organic fiber cord is G2 at a width position P2 that is 2/3 of the maximum width of the belt layer, the belt layer has two-thirds of the maximum width of the belt layer. 8. A high-speed heavy load according to any one of claims 4 to 7, wherein a portion thicker than the lamination thickness G2 is provided in a region outside the width position P2 of the tire in the tire width direction. Pneumatic radial tire. The belt layer has a tensile rupture strength of 6.3 cN / dtex or more, an elongation of 0.2 to 2.0% at a load of 0.3 cN / dtex in the elongation direction, and an elongation of 2.1 cN / dtex at a load in the elongation direction. At least two or more belt plies containing an organic fiber cord having an elongation of 1.5 to 7.0% and an elongation of 2.2 to 9.3% under a 3.2 cN / dtex load in the elongation direction. The pneumatic radial tire for high-speed heavy load according to any one of claims 4 to 8, comprising a main belt layer configured. The pneumatic radial tire for high-speed heavy load according to claim 9, wherein at least two or more of the belt plies are laminated at an end of the main belt layer in the tire width direction. The main belt layer is made of an aromatic polyamide fiber, and has a lower twist coefficient of 0.12 to 0.85 and a lower twist coefficient of 0.45 to 0.80. The pneumatic radial tire for high-speed heavy loads according to claim 9 or 10, wherein The main belt layer includes an aromatic polyamide-based fiber and an aliphatic polyamide-based fiber, and has a mass ratio of the aromatic polyamide-based fiber to the aliphatic polyamide-based fiber of 100: 10 to 170. The pneumatic radial tire for high-speed heavy loads according to any one of claims 9 to 11, comprising a belt ply including a fiber cord. The main belt layer is an organic fiber cord in which an aromatic polyamide cord and an aliphatic polyamide cord are twisted, and a lower twist coefficient of the aromatic polyamide cord is 0.12 to 0.85. The pneumatic radial tire for high-speed heavy load according to claim 12, comprising a belt ply including: The main belt layer has a belt ply including an organic fiber cord spirally wound at an angle of about 0 ° with respect to the tire equatorial plane, wherein the belt ply includes an organic fiber cord. Pneumatic radial tire for high-speed heavy loads. The main belt layer is inclined at an angle of 2 to 25 ° with respect to the tire equatorial plane, bent in the same plane so as to be inclined in the opposite direction at each ply end, and extends in a zigzag manner in the tire circumferential direction. The pneumatic radial tire for high-speed heavy load according to any one of claims 9 to 14, further comprising a belt ply including a fiber cord.

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