JP3569082B2

JP3569082B2 - Pneumatic tire

Info

Publication number: JP3569082B2
Application number: JP21513696A
Authority: JP
Inventors: 優一西牧
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 1996-07-26
Filing date: 1996-07-26
Publication date: 2004-09-22
Anticipated expiration: 2016-07-26
Also published as: JPH1035212A

Description

【０００１】
【発明の属する技術分野】
本発明は、空気入りタイヤに関し、詳しくは、カーカスの側面を被覆保護するサイドウォールが外層と内層とでゴム質の異なる２層構造を有し、耐サイドカット性等の耐外傷性を損うことなくサイド部の外観性と耐オゾンクラック性の双方が良好な状態に保たれた空気入りタイヤに関する。
【０００２】
【従来の技術】
従来、空気入りタイヤのサイドウォールは、主鎖中の二重結合の含有割合の高い天然ゴム、イソプレンゴム、ブタジエンゴム、スチレン−ブタジエンゴムなどの高不飽和度ゴムを主要ゴム成分とするゴム組成物で形成されていた。かかる高不飽和度ゴムの二重結合部分はオゾンと反応して解重合する性質があるので、放置または走行により、ゴム表面におけるクラック発生の原因となることが知られている。そこで、これを防ぐために、これまではサイドウォールのゴム組成物にはアミン系の老化防止剤やワックス等のクラック改良剤が配合されていた。しかしながら、アミン系老化防止剤はサイドウォール表面にブルームすると茶褐色に変色する特徴があり、またワックスは表面にブルームすると白色を呈し、いずれの場合も、サイド外観を損ねてしまうという問題があった。
【０００３】
かかる問題点を解決すべく、例えば、特開昭５９−１４５０２号公報においては、タイヤサイド部を内外２層構造とし、外層を、不飽和結合の含有量の少ないゴムを使用して変色の原因物質を減量したゴム組成物で構成することが提案されている。
【０００４】
【発明が解決しようとする課題】
上記特開昭５９−１４５０２号公報に開示されている如き従来の２層サイド構造は、外層は不飽和結合の含有量の少ないゴムを使用していても、内層には通常のサイドウォールをベースとしたゴム組成物を使用していたため、該内層はアミン系老化防止剤やワックス等が使用された配合系となっていた。
【０００５】
これらの物質は拡散速度が非常に速いという特性を有しているため、例え外層に老化防止剤やワックス等が使用されていないゴム組成物を使用しても、すぐに外層にまでこれら物質が移行し、結局は変色を引き起こしていた。それどころか、外層表面に移行した老化防止剤やワックス等は従来の単層サイドウォールよりも却ってより大きな変色を引き起こしていた。従って、内層ゴムに従来のサイドウォールゴムの老化防止剤やワックスを減量した組成物を使用した２層サイド構造においては、例え外層に老化防止剤やワックスが未使用の組成物を使用したとしても、十分な外観性の向上は得られないのが実状であった。
【０００６】
そこで本発明の目的は、タイヤの耐サイドカット性等の耐外傷性を損うことなくサイド部の外観性と耐オゾンクラック性の双方が良好な状態に保たれた空気入りタイヤを提供することにある。
【０００７】
【課題を解決するための手段】
本発明者は、上記課題を解決すべく鋭意検討した結果、サイドウォールを２層構造とし、外層ゴムの特定の低不飽和度ゴムの割合を高め、一方内層ゴムでは特定の高不飽和度ゴムの割合を高め、かつ両層に配合される特定の老化防止剤およびワックスの配合量を所定量以下に抑えることにより、上記目的を達成し得ることを見出し、本発明を完成するに至った。
【０００８】
即ち、本発明の空気入りタイヤは、サイドウォールが外層と内層とでゴム質の異なる２層構造を有する空気入りタイヤにおいて、
上記外層がゴム成分１００重量部対して、ハロゲン化ブチルゴム及びエチレンプロピレンゴムからなる群から選ばれた低不飽和度ゴムの少なくとも１種３０〜７０重量部と、天然ゴム、イソプレンゴム、ブタジエンゴム及びスチレン−ブタジエンゴムからなる群から選ばれた高不飽和度ゴムの少なくとも１種７０〜３０重量部とを配合してなるゴム組成物で構成され、
上記内層がゴム成分１００重量部対して、上記低不飽和度ゴム群から選ばれたゴムの少なくとも１種０〜４０重量部と、上記高不飽和度ゴム群の少なくとも１種１００〜６０重量部とを配合してなるゴム組成物で構成され、
上記内層および外層のゴム組成物ともにフェニレンジアミン系老化防止剤がゴム成分１００重量部に対して０．５重量部以下で、かつワックスが０．５重量部以下で配合されてなることを特徴とするものである。
【０００９】
【発明の実施の形態】
以下、本発明の空気入りタイヤを具体的に説明する。
本発明の空気入りタイヤにおいて、サイドウォールを外層と内層とでゴム質の異なる２層構造とするのは、外層のゴムには老化防止剤およびワックスを極少量配合するかまたは配合しないことで耐オゾンクラック性を良好に保つ機能を持たせ、一方内層のゴムには耐サイドカット性を良好に保つ機能を持たせるためである。
【００１０】
本発明においては、上述の如く外層のゴムは老化防止剤およびワックスを極少量配合するかまたは配合せずに耐オゾンクラック性を良好に維持する必要があるので、耐オゾン性に優れたハロゲン化ブチルゴム（Ｈａｌ−ＩＩＲ）、例えばＣｌ−ＩＩＲ、Ｂｒ−ＩＩＲ及びエチレンプロピレンゴム（ＥＰＭ）からなる群から選ばれた低不飽和度ゴムの少なくとも１種を３０〜７０重量部、より十分な耐オゾンクラック性を得るためには５０〜７０重量部配合することが望ましい。かかる低不飽和度ゴムを７０重量部を超えて配合すると、ゴム自体の強力及び周辺ゴムとの接着力の著しい低下を引き起こし、タイヤ耐久上好ましくない。なお、本発明で低不飽和度ゴムとして使用し得るエチレンプロピレンゴム（ＥＰＭ）には、エチレンとプロピレンの他に第三成分としてジエンモノマーを加え三元共重合体としたゴム（ＥＰＤＭ）を含むものである。
【００１１】
上述の如く、外層のゴムはタイヤサイド部の耐オゾンクラック性に重点をおいているため、従来の高不飽和度ゴムのサイドウォールに比し、耐サイドカット性が劣るものとなっている。従って、本発明においてはこの点を補うために、内層のゴムは耐破壊性を重視して上記高不飽和度ゴムを６０重量部以上、好ましくは７０重量部以上使用する必要がある。
【００１２】
また、本発明においては、十分な外観性を確保するために、外層のみならず内層のアミン系老化防止剤およびワックスの配合量もそれぞれゴム成分１００重量部に対し０．５重量部以下、好ましくは未配合とする必要がある。これは上述の如く、老化防止剤およびワックスがゴム中での拡散速度が速く、例え内層ゴムにのみ使用してもすぐにブルームし、外観性を悪化させるからである。
【００１３】
なお、内層ゴムの破壊性維持を目的としフェノール系老化防止剤を使用することは可能である。
【００１４】
本発明においては、サイドウォールの外層と内層のゴム組成物には上述の配合成分の他に、カーボンブラック、シリカ等の無機充填剤、軟化剤、加硫剤、加硫促進剤、加硫促進助剤等、通常配合される適当量の配合剤を適宜配合することができるのは勿論のことである。
【００１５】
次に、本発明の一例空気入りタイヤを図面に基づき説明する。
図１に示す本発明の一例空気入りラジアルタイヤ１において、サイドウォール部は外層２と内層３の２層構造となっており、タイヤ側面のカーカス４を覆っている。なお、図中、５はベルト部である。
【００１６】
本発明においては、上記外層２と内層３とのゲージ比は、好ましくは１：１〜１：２である。
【００１７】
【実施例】
以下に、本発明を実施例および比較例に基づき具体的に説明する。
（１）外層配合の検討
タイヤのサイドウォールにおける外層用ゴムの検討をするために、下記の表１に示す配合内容の各種ゴム組成物Ａ〜Ｊを調製した。これらゴム組成物について耐オゾンクラック性、変色性、破壊強力およびゴム〜ゴム間接着性について以下のようにして測定試験を行った。
【００１８】
（イ）耐オゾンクラック性および変色性
得られたゴム組成物を１６０℃、２０分間プレス加硫して得たられ試験片を使用し、温度４０℃、オゾン濃度５０ｐｐｈｍの低濃度オゾンを含む空気中において、０〜２０％間、５Ｈｚの繰り返し歪を与え、クラック発生までの時間と、２４時間経過後の変色度合を測定した。
耐オゾンクラックの評価は、Ａは少数、Ｂは多数、Ｃは無数にクラックが発生したことを示し、また１は１０倍のルーペで確認可能、２は肉眼で確認可能、３は亀裂１ｍｍ未満、４は１〜３ｍｍの亀裂、５は３ｍｍ以上の亀裂、をそれぞれ示している。
変色の評価としては、明らかに差の分かるものを変色大、変化が多少認められるものを変色小、それらの中間を変色中、変化の認められないものを不変として評価した。
【００１９】
（ロ）破壊強力
上記試験片を用いて、ＪＩＳＫ６３０１に準拠して破壊強力を測定した。
【００２０】
（ハ）ゴム〜ゴム間接着性
有機繊維で裏打ちした試験ゴムシートをゴム〜ゴム間剥離ができるように重ねて成形した試料をプランジャータイプの金型で１６０℃×２０分加硫し、得られたものを幅１ｃｍに切断した後、ゴム〜ゴム間の接着状態を観察した。
結果を下記の表１に併記する。
【００２１】
【表１】

１）Ｎ−フェニル−Ｎ’−イソプロピル−ｐ−フェニレンジアミン
２）Ｎ−シクロヘキシル−２−ベンゾチアジルスルフェンアミド
３）ジベンゾチアジルジスルフィド
【００２２】
上記表１に示す結果より、外層ゴムとして十分な耐オゾンクラック性と外観性を両立させるためにはＨ〜Ｊのゴム組成物が適当であることが確かめられた。
【００２３】
（２）内層ゴムとの組み合わせ検討
上記Ｈ〜Ｊのゴム組成物をタイヤのサイドウォールにおける外層用ゴムとして用い、一方内層用ゴムとしては下記の表２に示す配合内容のゴム組成物を用い、同表に示す組み合わせにてサイズ１８５／７０Ｒ１４の空気入りラジアルタイヤを製造した。製造された空気入りラジアルタイヤについて耐オゾンクラック性、変色性および外傷性ついて下記のようにして評価を行った。
【００２４】
（Ａ）耐オゾンクラック性および変色性
試験タイヤを屋外ドラムにて５万ｋｍ走行させ、オゾンクラックの発生状況および変色性について観察を行った。
【００２５】
（Ｂ）耐外傷性
試験タイヤを内圧１ｋｇ／ｃｍ^２に設定し、時速１０ｋｍ／ｈで縁石に２０回乗り上げたときのサイド部の状態を観察した。
得られた結果を下記の表２に示す。
【００２６】
【表２】

【００２７】
実施例１〜３の試験結果から分かるように、タイヤサイドウォールの外層に耐オゾンクラック性を重視した配合系を、一方、内層には耐破壊性を重視した配合系をそれぞれ採用したタイヤにおいては、耐オゾンクラック性、変色性、外傷性のすべての性能において良好な結果が得られた。
【００２８】
一方、比較例１および２のように、内層にアミン系老化防止剤およびワックスを所定量以上配合したゴムを配したタイヤでは変色性が悪化し、また比較例２および４のように耐オゾンクラック性を重視し過ぎた配合系を採用してサイド部を構成したタイヤでは十分な耐久性が得られなかった。
【００２９】
本発明の空気入りタイヤ（実施例２）と、従来より市販されているタイヤ（比較例１）を同一車輛に装着し、実地走行２万ｋｍ（約１年後）の状態について検討したところ、耐オゾン性、変色性に関して大幅な向上が確認された。
【００３０】
【発明の効果】
以上説明してきたように本発明の空気入りタイヤにおいては、サイドウォールを２層構造とし、外層ゴムの特定低不飽和度ゴムの割合を高め、一方内層ゴムでは特定高不飽和度ゴムの割合を高め、かつ両層に配合される特定老化防止剤およびワックスの配合量を所定量以下に抑えたことにより、タイヤの耐サイドカット性等の耐外傷性を損うことなくサイド部の外観性と耐オゾンクラック性の双方を良好な状態に保持することができる。
【図面の簡単な説明】
【図１】空気入りラジアルタイヤの左半分断面図である。
【符号の説明】
１大型建設車両用ラジアルタイヤ
２サイドウォール部外層
３サイドウォール部内層
４カーカス
５ベルト部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a pneumatic tire, and more specifically, a sidewall for covering and protecting the side surface of a carcass has a two-layer structure in which an outer layer and an inner layer have different rubber qualities, and impairs trauma resistance such as side cut resistance. The present invention relates to a pneumatic tire in which both the appearance and the ozone crack resistance of a side portion are kept in a good state without any problem.
[0002]
[Prior art]
Conventionally, the sidewall of a pneumatic tire has a rubber composition containing a highly unsaturated rubber such as natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber having a high content of double bonds in a main chain as a main rubber component. It was formed of things. It is known that the double bond portion of such a highly unsaturated rubber has a property of depolymerizing by reacting with ozone, which causes cracks on the rubber surface when left or run. Therefore, in order to prevent this, a rubber composition for the sidewall has heretofore been compounded with an amine-based antioxidant or a crack modifier such as wax. However, the amine-based anti-aging agent has a characteristic that when it blooms on the side wall surface, it turns brown, and when the wax blooms on the surface, it takes on a white color, and in any case, the side appearance is impaired.
[0003]
In order to solve such a problem, for example, in Japanese Patent Application Laid-Open No. Sho 59-14502, the tire side portion has an inner / outer two-layer structure, and the outer layer is formed of a rubber having a low unsaturated bond content, which causes discoloration. It has been proposed to consist of a rubber composition with reduced material.
[0004]
[Problems to be solved by the invention]
In the conventional two-layer side structure disclosed in JP-A-59-14502, even if the outer layer uses a rubber having a low unsaturated bond content, the inner layer is made of a normal side wall. Since the rubber composition described above was used, the inner layer was a compounded system using an amine-based antioxidant, wax, and the like.
[0005]
Since these substances have the property that the diffusion rate is very fast, even if a rubber composition in which an antioxidant or a wax is not used in the outer layer is used, these substances are immediately extended to the outer layer. Migrated, eventually causing discoloration. On the contrary, the antioxidant, wax, and the like transferred to the outer layer surface have caused much greater discoloration than the conventional single-layer sidewall. Therefore, in the two-layer side structure using a composition in which the conventional anti-aging agent and the wax of the sidewall rubber are reduced in the inner layer rubber, even if the anti-aging agent and the wax-free composition are used in the outer layer, In fact, a sufficient improvement in appearance was not obtained.
[0006]
Therefore, an object of the present invention is to provide a pneumatic tire in which both side appearance and ozone crack resistance are kept in a good state without impairing trauma resistance such as side cut resistance of the tire. It is in.
[0007]
[Means for Solving the Problems]
The inventor of the present invention has conducted intensive studies to solve the above-mentioned problems. As a result, the sidewall has a two-layer structure, and the ratio of the specific low unsaturated rubber in the outer rubber is increased, while the specific high unsaturated rubber is used in the inner rubber. It has been found that the above object can be achieved by increasing the ratio of and suppressing the compounding amounts of the specific antioxidant and the wax compounded in both layers to a predetermined amount or less, and completed the present invention.
[0008]
That is, the pneumatic tire of the present invention is a pneumatic tire having a two-layer structure in which sidewalls have different rubber qualities between an outer layer and an inner layer.
The outer layer is 100 parts by weight of a rubber component, and 30 to 70 parts by weight of at least one kind of low unsaturated rubber selected from the group consisting of halogenated butyl rubber and ethylene propylene rubber, natural rubber, isoprene rubber, butadiene rubber and A rubber composition comprising 70 to 30 parts by weight of at least one highly unsaturated rubber selected from the group consisting of styrene-butadiene rubbers,
The inner layer is 100 parts by weight of a rubber component, and 0 to 40 parts by weight of at least one kind of rubber selected from the low unsaturated degree rubber group and 100 to 60 parts by weight of at least one kind of rubber of the high unsaturated degree rubber group. And a rubber composition obtained by blending
The rubber composition of the inner layer and the outer layer is characterized in that the phenylenediamine-based antioxidant is compounded in an amount of 0.5 part by weight or less and 100 parts by weight of wax with respect to 100 parts by weight of the rubber component. Is what you do.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the pneumatic tire of the present invention will be specifically described.
In the pneumatic tire of the present invention, the side wall has a two-layer structure having different rubber qualities between the outer layer and the inner layer. This is because the function of keeping the ozone cracking property good and the function of keeping the side cut resistance good on the inner layer rubber are provided.
[0010]
In the present invention, as described above, the rubber of the outer layer is required to maintain an excellent ozone crack resistance without or with an extremely small amount of an antioxidant and a wax. 30-70 parts by weight of butyl rubber (Hal-IIR), for example, at least one low-unsaturation rubber selected from the group consisting of Cl-IIR, Br-IIR and ethylene propylene rubber (EPM), more sufficient ozone resistance In order to obtain cracking properties, it is desirable to add 50 to 70 parts by weight. If the low-unsaturation rubber is used in an amount exceeding 70 parts by weight, the strength of the rubber itself and the adhesion to the peripheral rubber are significantly reduced, which is not preferable in terms of tire durability. Ethylene propylene rubber (EPM) which can be used as the low-unsaturation rubber in the present invention includes, in addition to ethylene and propylene, a terpolymer obtained by adding a diene monomer as a third component (EPDM). It is a thing.
[0011]
As described above, since the rubber of the outer layer focuses on the ozone crack resistance of the tire side portion, the side cut resistance is inferior to that of the conventional high-unsaturated rubber sidewall. Accordingly, in the present invention, in order to compensate for this point, it is necessary to use the above-mentioned highly unsaturated rubber at 60 parts by weight or more, preferably 70 parts by weight or more, with emphasis on the fracture resistance of the rubber in the inner layer.
[0012]
In the present invention, in order to ensure sufficient appearance, the compounding amount of the amine-based antioxidant and the wax in the inner layer as well as the outer layer is preferably 0.5 parts by weight or less, based on 100 parts by weight of the rubber component. Must be unblended. This is because, as described above, the diffusion rate of the antioxidant and the wax in the rubber is high, and even if it is used only for the inner layer rubber, it blooms immediately and deteriorates the appearance.
[0013]
It is possible to use a phenolic antioxidant for the purpose of maintaining the destructibility of the inner rubber layer.
[0014]
In the present invention, the rubber composition of the outer layer and the inner layer of the side wall includes, in addition to the above-mentioned components, an inorganic filler such as carbon black and silica, a softener, a vulcanizing agent, a vulcanization accelerator, and a vulcanization accelerator. Needless to say, an appropriate amount of a compounding agent usually compounded such as an auxiliary agent can be appropriately compounded.
[0015]
Next, an example pneumatic tire of the present invention will be described with reference to the drawings.
In the example pneumatic radial tire 1 of the present invention shown in FIG. 1, the sidewall portion has a two-layer structure of an outer layer 2 and an inner layer 3 and covers a carcass 4 on a side surface of the tire. In the figure, reference numeral 5 denotes a belt portion.
[0016]
In the present invention, the gauge ratio between the outer layer 2 and the inner layer 3 is preferably 1: 1 to 1: 2.
[0017]
【Example】
Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples.
(1) Examination of outer layer composition In order to examine the rubber for the outer layer in the sidewall of the tire, various rubber compositions A to J having the composition shown in Table 1 below were prepared. These rubber compositions were subjected to measurement tests for ozone crack resistance, discoloration, breaking strength, and adhesion between rubber and rubber as follows.
[0018]
(A) Ozone crack resistance and discoloration resistance Using a test piece obtained by press vulcanizing the obtained rubber composition at 160 ° C. for 20 minutes, air containing low-concentration ozone at a temperature of 40 ° C. and an ozone concentration of 50 pfm is used. In the sample, a repetitive strain of 5 Hz was applied for 0 to 20%, and the time until crack generation and the degree of discoloration after 24 hours were measured.
The evaluation of ozone cracking resistance was as follows: A indicates a small number, B indicates a large number, C indicates an infinite number of cracks, 1 indicates a 10-fold loupe, 2 indicates a naked eye, 3 indicates a crack of less than 1 mm 4 indicates a crack of 1 to 3 mm, and 5 indicates a crack of 3 mm or more.
As for the evaluation of discoloration, those with a clear difference were evaluated as large in discoloration, those with some change were evaluated as small in discoloration, those in between were evaluated as discoloration, and those with no change were evaluated as invariant.
[0019]
(B) Breaking strength Using the above test piece, breaking strength was measured in accordance with JIS K6301.
[0020]
(C) A test rubber sheet lined with a rubber-rubber adhesive organic fiber was laminated and molded so that the rubber-rubber separation could be performed, and a sample was vulcanized at 160 ° C. for 20 minutes using a plunger-type mold. After cutting the obtained piece to a width of 1 cm, the adhesion state between rubber and rubber was observed.
The results are shown in Table 1 below.
[0021]
[Table 1]

1) N-phenyl-N'-isopropyl-p-phenylenediamine 2) N-cyclohexyl-2-benzothiazylsulfenamide 3) dibenzothiazyl disulfide
From the results shown in Table 1 above, it was confirmed that the rubber compositions H to J were suitable for achieving both sufficient ozone crack resistance and appearance as the outer layer rubber.
[0023]
(2) Examination of Combination with Inner Layer Rubber The above rubber compositions H to J are used as rubber for the outer layer in the sidewall of the tire, while the rubber composition for the inner layer is a rubber composition having the composition shown in Table 2 below. Pneumatic radial tires of size 185 / 70R14 were manufactured in the combinations shown in the table. The produced pneumatic radial tires were evaluated for ozone crack resistance, discoloration and trauma as follows.
[0024]
(A) Ozone crack resistance and discoloration test A tire was run for 50,000 km on an outdoor drum, and the occurrence of ozone cracks and discoloration were observed.
[0025]
(B) Trauma resistance test The inner side pressure of the tire was set to 1 kg / cm ^2, and the state of the side portion when riding on the curb 20 times at a speed of 10 km / h was observed.
The results obtained are shown in Table 2 below.
[0026]
[Table 2]

[0027]
As can be seen from the test results of Examples 1 to 3, in the tire adopting the compounding system which emphasized the ozone crack resistance in the outer layer of the tire sidewall, and the compounding system which emphasized the destruction resistance in the inner layer, respectively. Good results were obtained in all of the properties of ozone crack resistance, discoloration, and trauma.
[0028]
On the other hand, in tires in which a rubber in which an amine-based antioxidant and a wax are compounded in a predetermined amount or more is provided in the inner layer as in Comparative Examples 1 and 2, discoloration is deteriorated, and as in Comparative Examples 2 and 4, ozone crack resistance is reduced. Tires having side portions formed by employing a compound system that emphasized the performance too much could not obtain sufficient durability.
[0029]
The pneumatic tire of the present invention (Example 2) and a conventionally marketed tire (Comparative Example 1) were mounted on the same vehicle, and the state of actual running 20,000 km (after about one year) was examined. Significant improvements in ozone resistance and discoloration were confirmed.
[0030]
【The invention's effect】
As described above, in the pneumatic tire of the present invention, the sidewall has a two-layer structure, and the proportion of the specific low unsaturated rubber in the outer rubber is increased, while the proportion of the specific high unsaturated rubber in the inner rubber is increased. By increasing the amount of the specific antioxidant and wax compounded in both layers to a predetermined amount or less, the appearance of the side portion can be improved without impairing the trauma resistance such as the side cut resistance of the tire. Both of the ozone crack resistance can be maintained in a good state.
[Brief description of the drawings]
FIG. 1 is a left half sectional view of a pneumatic radial tire.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Radial tire for large construction vehicles 2 Side wall outer layer 3 Side wall inner layer 4 Carcass 5 Belt part

Claims

In a pneumatic tire having a two-layer structure in which sidewalls have different rubber qualities between an outer layer and an inner layer,
The outer layer against 100 parts by weight of the rubber component, at least one 5 0-70 parts by weight of a low degree of unsaturation rubber selected from the group consisting of halogenated butyl rubber and ethylene propylene rubber, natural rubber, isoprene rubber, butadiene It is composed of a rubber composition obtained by blending at least one 5 0-30 parts by weight of the high degree of unsaturation rubber selected from the group consisting of butadiene rubber, - rubber and styrene
A rubber in which the inner layer is a mixture of at least one kind of the low unsaturated rubber and 0 to 40 parts by weight and at least one kind of the high unsaturated rubber and 100 to 60 parts by weight based on 100 parts by weight of the rubber component. The composition,
The rubber composition of the inner layer and the outer layer is characterized in that the phenylenediamine-based antioxidant is compounded in an amount of 0.5 part by weight or less and 100 parts by weight of wax with respect to 100 parts by weight of the rubber component. Pneumatic tires.

In a pneumatic tire having a two-layer structure in which sidewalls have different rubber qualities between an outer layer and an inner layer,
The outer layer is 100 parts by weight of a rubber component, and 30 to 70 parts by weight of at least one kind of low unsaturated rubber selected from the group consisting of halogenated butyl rubber and ethylene propylene rubber, natural rubber, isoprene rubber, butadiene rubber and A rubber composition comprising 70 to 30 parts by weight of at least one highly unsaturated rubber selected from the group consisting of styrene-butadiene rubbers,
A rubber in which the inner layer is a mixture of at least one kind of the low unsaturated rubber and 0 to 40 parts by weight and at least one kind of the high unsaturated rubber and 100 to 60 parts by weight based on 100 parts by weight of the rubber component. A composition (provided that the blending ratio of the low-unsaturated rubber in the inner layer to 100 parts by weight of the rubber component is lower than the blending ratio of the low-unsaturated rubber in the outer layer).
The rubber composition of the inner layer and the outer layer together with the phenylenediamine-based antioxidant in an amount of 0.5 parts by weight or less based on 100 parts by weight of the rubber component, and a wax in an amount of 0.5 parts by weight or less,
A pneumatic tire, wherein a gauge ratio between the outer layer and the inner layer is from 1: 1 to 1: 2.