JP3802197B2 - Pneumatic radial tire - Google Patents

Description

【０００９】
前記式中、Ｒ¹ 及びＲ² はそれぞれ独立に、水素原子、アルキル基又はアリール基を表すが、Ｒ¹ 及びＲ² が同時に水素原子である場合は除かれる。ここで、Ｒ¹ 、Ｒ² がそれぞれ独立に、水素原子、メチル基、エチル基又はフェニル基を表すものであることが好ましい。
【００１０】
また、この加硫促進剤としては、具体的には、メルカプト−４メチルベンゾチアゾール、メルカプト−５−メチルベンゾチアゾール、ビス（４−メチルベンゾチアゾリル−２）−ジサルファイド及びビス（５−メチルベンゾチアゾリル−２）−ジサルファイドからなる群より選択される少なくとも１種であることが好ましい。
【００１１】
通常、スチールコードとゴム組成物との接着性は、加硫後の残存硫黄量と相関があることが知られており、ベルトコーティングゴム中の残存硫黄量が多い程、タイヤ走行末期の接着性は良好となる。一方、この残存硫黄量は、ゴム組成物中の加硫促進剤残基と反応して再架橋をする（つまり、架橋が進行する）ため、ゴム組成物の耐熱老化性が悪化するという問題がある。本発明の作用機構は明確ではないが、前記特定の加硫促進剤をゴム組成物中に配合することにより再架橋を生起させる加硫促進剤残基を減少させるこができるため、接着性に寄与する残存硫黄量を減少させることなく、耐熱老化性の低下を防止することができ、接着性の改良と劣化の防止とを同時に達成しうるものと考えられる。
【００１２】
【発明の実施の形態】
本発明の空気入りラジアルタイヤのベルトコーティングゴムは前記一般式で表される加硫促進剤をゴム成分１００重量部に対して０．２〜２．０重量部含有するものである。
【００１３】
本発明のタイヤに用いられるベルト層は、スチールコードと該スチールコードを被覆するゴム組成物（ベルトコーティングゴム）とからなる。該ゴム組成物に用いられるゴム成分としては、天然ゴム、ビニル芳香族炭化水素／共役ジエン共重合体、イソプレンゴム、ブタジエンゴム、ブチルゴム、ハロゲン化ブチルゴム、エチレン−プロピレンゴムなど、通常タイヤに用いられるゴム原料の少なくとも１種を、本発明の効果を損なわない範囲において、適宜用いることができるが、ベルトコーティングゴムは、耐破壊性を要求されるため、天然ゴムを７５〜１００重量部含有するゴム成分を用いるのが好ましい。
【００１４】
前記ビニル芳香族炭化水素モノマー及び共役ジエンモノマーの共重合に用いられる共役ジエンモノマーとは１分子当たり炭素原子４〜１２個、好ましくは、４〜８個を含有する共役ジエン炭化水素である。具体的には、例えば１，３−ブタジエン、イソプレン、２，３−ジメチル−１，３−ブタジエン、１，３−ペンタジエン、オクタジエン等が挙げられ。これらは単独でも２種以上混合して用いても良い。特に1,3-ブタジエンモノマーを用いることが好ましい。
【００１５】
共役ジエンモノマーと共重合するビニル芳香族炭化水素モノマーとしては、スチレン、α−メチルスチレン、ｐ−メチルスチレン、ｏ−メチルスチレン、ｐ−ブチルスチレン、ビニルナフタリン及びこれらの誘導体が包含され、特にスチレンが好ましい。
【００１６】
本発明に用いられるゴム成分の製造方法には特に制限はないが、例えば、汎用のビニル芳香族炭化水素単位及び共役ジエン単位を含む共重合体の場合、有機リチウム触媒等による溶液重合法、乳化重合法、懸濁重合法等により、共役ジエンモノマーとビニル芳香族炭化水素モノマーとを共重合する方法等を採用することができる。
【００１７】
この共重合体としては、耐老化性等に優れているブタジエン／スチレン共重合体（以下、適宜、ＳＢＲと称する）が好ましい。
【００１８】
また、本発明に用いられる加硫促進剤は前記一般式に示した構造の加硫促進剤であり、ゴム組成物にゴム成分１００重量部に対して０．２〜２．０重量部の範囲で含有される。含有量が０．２重量部より少ないと、走行末期の接着性低下防止及び耐熱老化性の防止効果が不十分であり、また、２重量部を超えて配合した場合、走行末期の接着性が低下する。
【００１９】
前記一般式中、Ｒ¹ 及びＲ² は互いに水素原子である場合を除き、それぞれ独立に、水素原子、アルキル基又はアリール基を表す。好ましくは、水素原子、炭素原子数１〜６のアルキル基又は炭素原子数６〜１０のアリール基であり、それぞれ水素原子、メチル基、エチル基又はフェニル基であることがより好ましい。
【００２０】
これらの加硫促進剤としては、具体的には、例えば、２−メルカプト−４−メチルベンゾチアゾール、２−メルカプト−４−エチルベンゾチアゾール、２−メルカプト−５−メチルベンゾチアゾール、２−メルカプト−５−エチルベンゾチアゾール、２−メルカプト−６−メチルベンゾチアゾール、２−メルカプト−６−エチルベンゾチアゾール、２−メルカプト−４，５−ジメチルベンゾチアゾール、２−メルカプト−４，５−ジエチルベンゾチアゾール、２−メルカプト−４−フェニルベンゾチアゾール、２−メルカプト−５−フェニルベンゾチアゾール、２−メルカプト−６−フェニルベンゾチアゾール、ビス（４−メチルベンゾチアゾリル−２）−ジサルファイド、ビス（４−エチルベンゾチアゾリル−２）−ジサルファイド、ビス（５−メチルベンゾチアゾリル−２）−ジサルファイド、ビス（５−エチルベンゾチアゾリル−２）−ジサルファイド、ビス（６−メチルベンゾチアゾリル−２）−ジサルファイド、ビス（６−エチルベンゾチアゾリル−２）−ジサルファイド、ビス（４，５−ジメチルベンゾチアゾリル−２）−ジサルファイド、ビス（４，５−ジエチルベンゾチアゾリル−２）−ジサルファイド、ビス（４−フェニルベンゾチアゾリル−２）−ジサルファイド、ビス（５−フェニルベンゾチアゾリル−２）−ジサルファイド、ビス（６−フェニルベンゾチアゾリル−２）−ジサルファイドなどが挙げられる。
【００２１】
中でも、メルカプト−４メチルベンゾチアゾール、メルカプト−５−メチルベンゾチアゾール、ビス（４−メチルベンゾチアゾリル−２）−ジサルファイド及びビス（５−メチルベンゾチアゾリル−２）−ジサルファイドからなる群より選択される少なくとも１種であることが効果の観点から好ましい。
【００２２】
これらの加硫促進剤は単独で用いることも、２種以上の混合物として用いることもできる。
【００２３】
これらの加硫促進剤の製造方法は特に制限されないが、例えば、特開昭４９−９３３６１号公報に記載の方法等により容易に製造することができる。
【００２４】
なお、本発明の空気入りラジアルタイヤのベルトコーティングゴムには、前記ゴム成分及び加硫促進剤とともに、通常用いられるカーボンブラック、シリカなどの充填剤、シリカ用のシランカップリング剤、加硫剤、軟化剤、酸化亜鉛、ステアリン酸、老化防止剤としての酸化防止剤、オゾン劣化防止剤などの添加剤を本発明の効果を損なわない範囲において適宜配合することができる。
【００２５】
加硫剤としては、硫黄等が挙げられ、これらの使用量は、ゴム成分１００重量部に対して硫黄分として２〜１０重量部、好ましくは３〜８重量部である。２重量部未満ではスチールコードとの接着性が十分でなく、１０重量部を超えると熱老化性が大きく低下する。
【００２６】
本発明のタイヤのベルト層に用いられるスチールコードは、汎用のものを使用することができ、タイヤの要求性能に従って、サイズ、撚り数、撚り条件などを適宜選択する。これらのスチールコードはゴム組成物との接着性を向上するためにメッキなどの表面処理を常法に従って施すことができる。
【００２７】
前記のゴム組成物は、ロール、インターナルミキサー等の混練り機を用いて混練りされてシート状に加工され、２枚のゴムシートによってスチールコードを挟んだ状態に成形加工されて、ベルト層が形成される。ベルト層は常法に従ってカーカスプライと積層され、その他の材料と共に本発明の空気入りラジアルタイヤを構成する。
【００２８】
本発明に係るタイヤにおいては、トレッド踏面部、サイドウォール部及びビード部等には通常のタイヤに適用される材料、形状、配置を適宜用いることができる。
【００２９】
【実施例】
以下に実施例を挙げて、本発明をより具体的に説明するが、本発明は下記実施例に限定されるものではない。
【００３０】
なお、実施例において、部及び％は特に断らない限り、重量部及び重量％を意味する。
【００３１】
本発明を実施例および比較例によって以下に説明する。
下記表１に示す配合で実施例、比較例の空気入りラジアルタイヤのベルト層に用いるゴム組成物［１］〜［７］を常法により作製した。
【００３２】
なお、用いた原料は、以下のとおりである。
ＮＲ（天然ゴム）：ＲＳＳ
カーボンブラック：シースト３（商品名）、東海カーボン(株)製
スチール−ゴム接着剤：マノボンドＣ２２．５（商品名）、ＳＨＥＰＨＥＲＤＣＨＥＭＩＣＡＬ社製
【００３３】
【表１】

【００３４】
次にスチールコードと表１のゴム組成物［１］〜［７］によって、ベルト層を形成して、常法によりこのベルト層を配置したラジアルタイヤ：サイズ１８５／７０Ｒ１４を試作してそれぞれ実施例１〜２、比較例１〜５として使用してテストを行った。
【００３５】
各種の評価は下記の方法によった。なお、走行後の評価は、前記タイヤを各５０本作製し、国内市場を８万ｋｍ走行させた後、タイヤを回収し、これを試料として評価を行い、その平均値をとった。
【００３６】
評価方法
（イ）走行後の耐ベルトエンドセパレーション性評価
前記回収したタイヤからベルト層を取り出し、１本のタイヤの半周を任意に切断して、その断面を目視にて観察し、ベルト層中にスチールコードの先端が埋設されている深さを測定した。評価結果は、比較例１の値を１００とした指数で示した。数値が大きい程、耐ベルトエンドセパレーション性が優れていることを示す。
【００３７】
（ロ）走行後の接着性評価
前記回収したタイヤからベルト層を取り出し、ベルト層中のスチールコードを引張試験機によって５０ｍｍ／ｍｉｎの速度で引張り、露出したスチールコード表面に付着したゴムの付着状態を目視にて評価し、下記の基準に従って判定した。試験は１試料当たり、３本のスチールコードを用いて行った。
【００３８】

（ハ）破断伸び保持率
走行前のタイヤ及び前記回収したタイヤから、ＪＩＳ Ｋ ６２５１に従ってベルトコーティングゴムから２ｍｍの厚さにサンプルを切り出して、ダンベル形状の試験片を作成した。これをＪＩＳ Ｋ ６３０１に準拠した引張試験に供し、以下の式にしたがって切断時の伸び保持率を計算した。数値が大きい程熱老化性に対する耐久性が優れていることを示す。
【００３９】
破断時の伸び保持率（％）＝〔（走行後のベルトコーティングゴムの切断時の伸び）／（走行前のベルトコーティングゴムの切断時の伸び）〕×１００
評価結果を下記表２に示した。
【００４０】
【表２】

【００４１】
表２の結果より明らかなように、実施例の空気入りラジアルタイヤは、いずれも国内市場を８万ｋｍ走行させた後も、耐ベルトエンドセパレーション性が良好であり、即ち、スチールコードとゴム組成物との接着性の低下は観察されず、またスチールコード表面へのゴムの付着性も十分で、付着状態も良好であった。また、切断時の伸び保持率も良好で、熱老化による劣化が抑制されていることがわかった。
【００４２】
一方、本発明に係る加硫促進剤を使用しなかったり、使用しても本発明の範囲外である比較例１〜５により得られた空気入りラジアルタイヤは、スチールコードとゴム組成物との接着性又は切断時の伸び保持率のいずれかが低く、接着性と耐熱老化性が両立したものはなく、走行末期の耐久性に問題があることがわかった。
【００４３】
【発明の効果】
本発明の空気入りラジアルタイヤは前記構成としたため、ベルト層におけるスチールコードとゴム組成物との接着性及びゴム組成物の耐熱老化性のいずれも良好であり、タイヤとしての耐久性に優れているという効果を示した。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic radial tire, and more particularly to an improvement in the belt layer of a pneumatic radial tire used for balanced travel, and more particularly to a pneumatic radial tire that achieves durability of the belt layer.
[0002]
[Prior art]
In recent years, the performance required for passenger car tires has become increasingly severe, and further improvements in tire durability are desired. It is important for the belt layer composed of the steel cord used for the radial tire and the rubber composition (belt coating rubber) covering the steel cord to ensure the adhesion between the steel cord and the belt coating rubber. It is known that a decrease in the thickness causes problems in the durability of the belt layer and, in turn, the durability of the tire. Conventionally, in order to improve the adhesion between the steel cord and the rubber composition, the amount of sulfur compounded as a vulcanizing agent in the rubber composition has been increased. According to this method, although the adhesiveness is improved, it has been found that the deterioration of the rubber composition, particularly the heat aging property is promoted, and there arises a problem that separation of the belt end due to this is generated at the end of the running.
[0003]
To prevent the aging of rubber, JP-A-58-87138 discloses a combination of a specific anti-aging agent and a vulcanization accelerator to suppress the aging of tread rubber and side rubber and improve the appearance of the tire at the end of running. However, the present situation is that the adhesiveness with a metal such as a steel cord has not been studied yet.
[0004]
[Problems to be solved by the invention]
As described above, various attempts have been made, but there is a strong demand for the development of tires that are excellent in durability, which is an important performance required for tires, and in particular, that prevent a decrease in strength at the end of traveling due to deterioration of the belt layer. It had been.
[0005]
In view of the above facts, the present invention provides a pneumatic radial tire excellent in durability by preventing deterioration of the belt layer by improving the rubber composition (belt coating rubber) of the belt layer used in the tire. Is the purpose.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventor paid attention to the correlation between the steel cord in the belt layer and the belt coating rubber, and as a result of intensive studies, the following characteristics are satisfied by the following configuration. It has been found that this can be done, and the present invention has been completed.
[0007]
That is, the pneumatic radial tire of the present invention has a tread tread portion, a pair of sidewall portions and a bead portion, a carcass ply reinforced by a cord disposed substantially parallel to the tire radial direction, and the carcass ply In a pneumatic radial tire having a belt layer arranged radially outward, the belt coating rubber of the belt layer contains 0.2 parts of a vulcanization accelerator represented by the following general formula with respect to 100 parts by weight of a rubber component. It is characterized by containing -2.0 parts by weight.
[0008]
[Chemical 2]

[0009]
In the above formula, R ¹ and R ² each independently represents a hydrogen atom, an alkyl group or an aryl group, except that R ¹ and R ² are simultaneously hydrogen atoms. Here, it is preferable that R ¹ and R ² each independently represent a hydrogen atom, a methyl group, an ethyl group, or a phenyl group.
[0010]
Specific examples of the vulcanization accelerator include mercapto-4-methylbenzothiazole, mercapto-5-methylbenzothiazole, bis (4-methylbenzothiazolyl-2) -disulfide and bis (5- It is preferably at least one selected from the group consisting of methylbenzothiazolyl-2) -disulfide.
[0011]
Normally, the adhesion between steel cord and rubber composition is known to correlate with the amount of residual sulfur after vulcanization. The higher the amount of residual sulfur in the belt-coated rubber, the more the adhesion at the end of tire running. Is good. On the other hand, the amount of residual sulfur reacts with the vulcanization accelerator residue in the rubber composition to cause re-crosslinking (that is, crosslinking proceeds), so that the heat aging resistance of the rubber composition deteriorates. is there. Although the mechanism of action of the present invention is not clear, by adding the specific vulcanization accelerator to the rubber composition, it is possible to reduce the vulcanization accelerator residue that causes re-crosslinking. Without reducing the amount of residual sulfur that contributes, it is considered that the heat aging resistance can be prevented from being lowered, and the improvement in adhesion and the prevention of deterioration can be achieved at the same time.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The belt coating rubber of the pneumatic radial tire of the present invention contains 0.2 to 2.0 parts by weight of the vulcanization accelerator represented by the above general formula with respect to 100 parts by weight of the rubber component.
[0013]
The belt layer used in the tire of the present invention comprises a steel cord and a rubber composition (belt coating rubber) that covers the steel cord. As rubber components used in the rubber composition, natural rubber, vinyl aromatic hydrocarbon / conjugated diene copolymer, isoprene rubber, butadiene rubber, butyl rubber, halogenated butyl rubber, ethylene-propylene rubber, etc. are usually used for tires. At least one rubber raw material can be appropriately used within a range that does not impair the effects of the present invention. However, since belt coating rubber is required to have fracture resistance, it contains 75 to 100 parts by weight of natural rubber. It is preferred to use the components.
[0014]
The conjugated diene monomer used for copolymerization of the vinyl aromatic hydrocarbon monomer and the conjugated diene monomer is a conjugated diene hydrocarbon containing 4 to 12, preferably 4 to 8 carbon atoms per molecule. Specific examples include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, octadiene and the like. These may be used alone or in combination of two or more. In particular, it is preferable to use 1,3-butadiene monomer.
[0015]
Examples of the vinyl aromatic hydrocarbon monomer copolymerized with the conjugated diene monomer include styrene, α-methylstyrene, p-methylstyrene, o-methylstyrene, p-butylstyrene, vinylnaphthalene and derivatives thereof. Is preferred.
[0016]
The method for producing the rubber component used in the present invention is not particularly limited. For example, in the case of a copolymer containing general-purpose vinyl aromatic hydrocarbon units and conjugated diene units, a solution polymerization method using an organic lithium catalyst or the like, emulsification A method of copolymerizing a conjugated diene monomer and a vinyl aromatic hydrocarbon monomer by a polymerization method, a suspension polymerization method, or the like can be employed.
[0017]
As this copolymer, a butadiene / styrene copolymer (hereinafter referred to as SBR as appropriate) having excellent aging resistance and the like is preferable.
[0018]
The vulcanization accelerator used in the present invention is a vulcanization accelerator having the structure shown in the general formula, and the rubber composition has a range of 0.2 to 2.0 parts by weight with respect to 100 parts by weight of the rubber component. Contained. When the content is less than 0.2 parts by weight, the effect of preventing the lowering of adhesion at the end of running and the effect of preventing heat aging are insufficient, and when it exceeds 2 parts by weight, the adhesion at the end of running is poor. descend.
[0019]
In the general formula, R ¹ and R ² each independently represent a hydrogen atom, an alkyl group, or an aryl group, except when they are hydrogen atoms. Preferably, they are a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and more preferably a hydrogen atom, a methyl group, an ethyl group, or a phenyl group, respectively.
[0020]
Specific examples of these vulcanization accelerators include 2-mercapto-4-methylbenzothiazole, 2-mercapto-4-ethylbenzothiazole, 2-mercapto-5-methylbenzothiazole, 2-mercapto- 5-ethylbenzothiazole, 2-mercapto-6-methylbenzothiazole, 2-mercapto-6-ethylbenzothiazole, 2-mercapto-4,5-dimethylbenzothiazole, 2-mercapto-4,5-diethylbenzothiazole, 2-mercapto-4-phenylbenzothiazole, 2-mercapto-5-phenylbenzothiazole, 2-mercapto-6-phenylbenzothiazole, bis (4-methylbenzothiazolyl-2) -disulfide, bis (4- Ethylbenzothiazolyl-2) -disulfide, bis 5-methylbenzothiazolyl-2) -disulfide, bis (5-ethylbenzothiazolyl-2) -disulfide, bis (6-methylbenzothiazolyl-2) -disulfide, bis (6- Ethylbenzothiazolyl-2) -disulfide, bis (4,5-dimethylbenzothiazolyl-2) -disulfide, bis (4,5-diethylbenzothiazolyl-2) -disulfide, bis ( Examples include 4-phenylbenzothiazolyl-2) -disulfide, bis (5-phenylbenzothiazolyl-2) -disulfide, and bis (6-phenylbenzothiazolyl-2) -disulfide.
[0021]
Among them, it consists of mercapto-4methylbenzothiazole, mercapto-5-methylbenzothiazole, bis (4-methylbenzothiazolyl-2) -disulfide and bis (5-methylbenzothiazolyl-2) -disulfide. It is preferable from a viewpoint of an effect that it is at least 1 sort (s) selected from a group.
[0022]
These vulcanization accelerators can be used alone or as a mixture of two or more.
[0023]
The method for producing these vulcanization accelerators is not particularly limited, but can be easily produced by, for example, the method described in JP-A-49-93361.
[0024]
In addition, the belt coating rubber of the pneumatic radial tire of the present invention, together with the rubber component and vulcanization accelerator, commonly used fillers such as carbon black and silica, silane coupling agent for silica, vulcanizing agent, Additives such as a softening agent, zinc oxide, stearic acid, an antioxidant as an anti-aging agent, and an ozone deterioration preventing agent can be appropriately blended within a range not impairing the effects of the present invention.
[0025]
Sulfur etc. are mentioned as a vulcanizing agent, and these usage-amounts are 2-10 weight part as a sulfur content with respect to 100 weight part of rubber components, Preferably it is 3-8 weight part. If it is less than 2 parts by weight, the adhesiveness to the steel cord is not sufficient, and if it exceeds 10 parts by weight, the heat aging property is greatly reduced.
[0026]
A general-purpose steel cord can be used for the belt layer of the tire of the present invention, and the size, the number of twists, the twisting conditions, and the like are appropriately selected according to the required performance of the tire. These steel cords can be subjected to a surface treatment such as plating in accordance with a conventional method in order to improve adhesion to the rubber composition.
[0027]
The rubber composition is kneaded using a kneader such as a roll or an internal mixer and processed into a sheet shape, and is molded into a state where a steel cord is sandwiched between two rubber sheets, and a belt layer Is formed. The belt layer is laminated with the carcass ply according to a conventional method, and constitutes the pneumatic radial tire of the present invention together with other materials.
[0028]
In the tire according to the present invention, materials, shapes, and arrangements applicable to ordinary tires can be appropriately used for the tread surface portion, the sidewall portion, the bead portion, and the like.
[0029]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.
[0030]
In Examples, parts and% mean parts by weight and% by weight unless otherwise specified.
[0031]
The present invention will be described below with reference to examples and comparative examples.
Rubber compositions [1] to [7] used in the belt layers of the pneumatic radial tires of Examples and Comparative Examples with the formulation shown in Table 1 below were produced by a conventional method.
[0032]
In addition, the used raw material is as follows.
NR (natural rubber): RSS
Carbon black: Seast 3 (trade name), steel-rubber adhesive manufactured by Tokai Carbon Co., Ltd .: Manobond C22.5 (trade name), manufactured by SHEPHERD CHEMICAL [0033]
[Table 1]

[0034]
Next, a steel tire and a rubber composition [1] to [7] shown in Table 1 were used to form a belt layer, and a radial tire: size 185 / 70R14 in which this belt layer was arranged by a conventional method was prototyped. The test was performed using 1-2 and Comparative Examples 1-5.
[0035]
Various evaluations were based on the following methods. For evaluation after running, 50 tires were produced for each, and the domestic market was run for 80,000 km, and then the tires were collected and evaluated as samples, and the average value was taken.
[0036]
Evaluation method (a) Evaluation of belt end separation resistance after running The belt layer is taken out from the collected tires, a half circumference of one tire is arbitrarily cut, and a cross section thereof is visually observed. The depth at which the tip of the steel cord was embedded was measured. The evaluation results are shown as an index with the value of Comparative Example 1 as 100. The larger the value, the better the belt end separation resistance.
[0037]
(B) Evaluation of adhesion after running The belt layer is taken out from the collected tire, the steel cord in the belt layer is pulled at a speed of 50 mm / min by a tensile tester, and the adhesion state of the rubber adhered to the exposed steel cord surface Was visually evaluated and determined according to the following criteria. The test was performed using three steel cords per sample.
[0038]

(C) Breaking elongation retention rate From the tire before running and the collected tire, a sample was cut out from the belt coating rubber to a thickness of 2 mm in accordance with JIS K 6251 to prepare a dumbbell-shaped test piece. This was subjected to a tensile test based on JIS K 6301, and the elongation retention at the time of cutting was calculated according to the following formula. The larger the value, the better the durability against heat aging.
[0039]
Elongation retention at break (%) = [(Elongation when cutting belt-coated rubber after running) / (Elongation when cutting belt-coated rubber before running)] × 100
The evaluation results are shown in Table 2 below.
[0040]
[Table 2]

[0041]
As is clear from the results in Table 2, the pneumatic radial tires of the examples have good belt end separation resistance even after running 80,000 km in the domestic market, that is, steel cord and rubber composition A decrease in adhesion to the object was not observed, the adhesion of rubber to the steel cord surface was sufficient, and the adhesion state was also good. Moreover, the elongation retention at the time of cutting was also good, and it was found that deterioration due to heat aging was suppressed.
[0042]
On the other hand, the pneumatic radial tires obtained by Comparative Examples 1 to 5 which do not use the vulcanization accelerator according to the present invention or are out of the scope of the present invention even if used are the steel cord and the rubber composition. It was found that either the adhesiveness or the elongation retention at the time of cutting was low, and there was no one that had both adhesiveness and heat aging resistance, and there was a problem in durability at the end of traveling.
[0043]
【The invention's effect】
Since the pneumatic radial tire of the present invention has the above-described configuration, both the adhesion between the steel cord and the rubber composition in the belt layer and the heat aging resistance of the rubber composition are good, and the durability as a tire is excellent. The effect was shown.

Claims (3)

A carcass ply having a tread surface portion, a pair of sidewall portions and a bead portion, reinforced by a cord disposed substantially parallel to the tire radial direction, and a belt layer disposed radially outward of the carcass ply In a pneumatic radial tire having
The rubber composition constituting the belt layer contains 0.2 to 2.0 parts by weight of a vulcanization accelerator represented by the following general formula with respect to 100 parts by weight of a rubber component. tire.

(In the formula, R ¹ and R ² each independently represents a hydrogen atom, an alkyl group or an aryl group, except that R ¹ and R ² are simultaneously hydrogen atoms.) ^2. The pneumatic radial tire according to claim 1, wherein in the vulcanization accelerator represented by the general formula, each of R ¹ and R ² independently represents a hydrogen atom, a methyl group, an ethyl group, or a phenyl group. . (However, the case where R ¹ and R ² are hydrogen atoms at the same time is excluded.) The vulcanization accelerator is mercapto-4-methylbenzothiazole, mercapto-5-methylbenzothiazole, bis (4-methylbenzothiazolyl-2) -disulfide and bis (5-methylbenzothiazolyl-2). The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is at least one selected from the group consisting of: disulfide.