JP4298820B2

JP4298820B2 - Rubber composition for studless tire

Info

Publication number: JP4298820B2
Application number: JP25600798A
Authority: JP
Inventors: 博也戸田
Original assignee: Toyo Tire and Rubber Co Ltd
Current assignee: Toyo Tire Corp
Priority date: 1998-08-25
Filing date: 1998-08-25
Publication date: 2009-07-22
Anticipated expiration: 2018-08-25
Also published as: JP2000063569A

Description

【０００１】
【発明の属する技術分野】
本発明は、雪氷路も走行する自動車、特に乗用車に装着するタイヤ、所謂スタッドレスタイヤに用いるゴム組成物に関する。
【０００２】
【従来の技術】
自動車が雪氷路を滑ることなく走行することを可能にするスタッドレスタイヤは、つぎのような方法を用いて氷上性能を向上させている。すなわち、
▲１▼特開昭６３−３４２０６号公報に記載する銅系金属短繊維、特開平２−２７４７４０号公報に記載するおがくず、胡桃の殻、コルク、落花生の殻、銀杏の殻、籾殻などを粉砕した粒径が０．０１〜５mmの植物性粒状体、特開平２−２８１０５１号公報に記載するアルミナ、花崗岩、石英、石灰岩などを粉砕した粒径が０．０１〜５mmの非金属無機質充填剤、特開平２−１６７３５３号公報に記載する籾殻、麦殻、コルクなどを粉砕した粒径が２０〜６００μm のセルローズ物質を含有する粉体加工品、特開平５−１７９０６９号公報に記載する平均粒子径が２０〜１５０μm のポリエステル樹脂、特開平５−２２２２４７号公報に記載する粒径１０〜５００μm の基材粒子の表面にゴムと接着可能な粒子を埋設した複合化粒子などの防滑材を配合したゴム組成物でトレッドを形成し、トレッド表面に露出した防滑材が奏するミクロスパイク効果で滑りにくくする方法。
▲２▼温度低下に伴う硬さの増加を抑制するためにゴム成分にガラス転移点の低いゴムを用い、雪氷路を走行しない普通タイヤに比して、カーボンブラックの配合量を少なくしたり、軟化剤の配合量を多くしたりして氷点以下の温度での硬さを小さくしたゴム組成物でトレッドを形成し、低温においても硬さが小さく、変形しやすくされたトレッドの表面を路面の凹凸に密着するように変形させて実接地面積を大きくし、接地面積を増大させることよって路面との凝着摩擦を大きくする方法。多くの場合、シリカが配合されて凝着摩擦作用が高められる。
▲３▼トレッド表面に設けられる溝及びサイプ所謂トレッドパターンの横方向成分を多くして、溝及びサイプのエッジを路面に引っ掛けるエッジ効果で滑りにくくする方法。
【０００３】
【発明が解決しようとする課題】
しかしながら、トレッドを形成するゴム組成物の粒状体含有量が多くなれば、摩耗性能が低下するので配合量に限界があり、ゴム組成物が軟らかくなれば、トレッドパターンのブロック剛性が小さくなって耐摩耗性、操縦安定性などのタイヤの一般特性が低下するので、硬さの低下に許容限度があり、ゴムのガラス転移点が低くなれば、湿潤路性能が低下するので、低温硬さを小さくするためのゴム成分のガラス転移点の引き下げに限度があり、溝及びサイプの本数または長さが大になれば、トレッドパターンのブロック剛性が小さくなって耐摩耗性、操縦安定性などのタイヤの一般特性が低下するとともに、サイプの端からブロックに亀裂が生じやすくなるので本数と長さに限界があって、氷上性能は満足できる水準に達しておらず、更なる改良が要請されている。
【０００４】
上記に鑑み本発明は、スタッドレスタイヤに用いられて摩耗性能などを損なうことなく氷上性能を向上させるゴム組成物を提供することを目的にしたものである。
【０００５】
【課題を解決するための手段】
上記課題解決のための手段として、摩耗性能などの一般特性に影響するトレッド全体の小変形時の剛性に関わる動的弾性率を大きくし、凝着摩擦と関係する大変形時の剛性に関わるＪＩＳ硬さを小さくすることにより、耐摩耗性などを従来タイヤと同等又はそれ以上のレベルに維持して氷上性能を向上させることができ、さらにカーボンブラックの一部をシリカで置換することにより氷上性能を大きく向上させることができる。
【０００６】
氷点以下での動的弾性率とＪＩＳ硬さの関係はゴム成分のガラス転移点の影響を受け、比較的ガラス転移点が低いスチレン・ブタジエンゴム、天然ゴム、ブタジエンゴム、イソプレンゴムなどの汎用ゴムがスタッドレスタイヤのトレッドに通常用いられる。これらの汎用ゴムをゴム成分にしてカーボンブラックで補強されたゴム組成物は、カーボンブラック、軟化剤の配合量を調整して硬さを小さくすれば、動的弾性率も低くなる。一般に硬さを変えれば、動的弾性率は大略ＪＩＳ硬さに対して直線的に変わり、汎用ゴムのゴム種を変えても直線関係は大きく変わらないと言われている。しかし、汎用ゴムの一部をガラス転移点が高いシンジオタクチック−１，２−ポリブタジエンで変性したシス−１，４−ポリブタジエンゴムで置換すれば、硬さが同じであっても動的弾性率は汎用ゴムのみの場合より大きくなり、硬さを小さくしながら動的弾性率を高くすることができ、動的弾性率に関係する耐摩耗性などのタイヤの一般特性を高レベルに維持しながら、硬さに関係する凝着摩擦を大きくすることができる。
【０００７】
すなわち本発明は、防滑材を含有するスタッドレスタイヤ用ゴム組成物において、シンジオタクチック−１，２−ポリブタジエンで変性されたシス−１，４−ポリブタジエンゴム１０〜４０重量％と上記の変性シス−１，４−ポリブタジエンゴム以外のジエン系ゴム９０〜６０重量％よりなるゴム成分１００重量部に対し、シリカ配合量とカーボンブラック配合量の和が３５〜６０重量部となる量的関係を満足しながら、シリカが１０〜３０重量部、ＳＡＦ級カーボンブラック及びＩＳＡＦ級カーボンブラックの群から選んだカーボンブラックが２０〜４０重量部配合されてなり、温度１６０℃で１５分間加硫して調製した加硫物について、ＪＩＳＫ６２５３に準拠したタイプＡデュロメーターにより温度−５℃で測定したときのＪＩＳ硬さが４８〜５５であり、かつ、温度−５℃、静歪み１５％、動歪み０．２％及び周波数１００Ｈｚの条件で測定したときの動的弾性率（Ｅ′）が８〜１５MPa であることを特徴にしたスタッドレスタイヤ用ゴム組成物である。
【０００８】
【発明の実施の形態】
本発明に用いるシンジオタクチック−１，２−ポリブタジエンで変性したシス−１，４−ポリブタジエンゴム（以下、本文中においてはシンジオタクチック−１，２−ポリブタジエンで変性したシス−１，４−ポリブタジエンゴムをＶＣＲと言う）は特開昭５５−３１８０２号公報に記載される方法、すなわち有機溶媒中１，２−重合触媒の存在下で１，３−ブタジエンを重合した後、触媒を失活させて得られたシンジオタクチック−１，２−ポリブタジエンの重合液にシス−１，４−ポリブタジエンゴムの有機溶媒溶液を加えて撹拌混合し、混合液からシンジオタクチック−１，２−ポリブタジエンとシス−１，４−ポリブタジエンゴムの混合物を分離することによって得る方法、または特開平５−１９４６５８号公報に記載される方法、すなわち１，３−ブタジエンを最初に１，４−重合触媒の存在下で完全に転化させずに重合してシス１，４−ポリブタジエンにし、次いで重合系に１，２−重合触媒を投入して残余の１，３−ブタジエンを１，２−重合させる方法によって得ることができる。あるいは、宇部興産からＵＢＥＰＯＬＶＣＲの商品名で入手することもできる。ゴム成分中のＶＣＲのブレンド率が１０重量％未満ではＶＣＲがもたらす効果が現れず、４０重量％より多くなると耐摩耗性が低下する。
【０００９】
防滑材として、種子の殻又は果実の核を粉砕した植物性粒状体、石英、アルミナなどを粉砕した非金属無機質粒状体、短繊維などを用いることができる。これらの一般的粒状体はゴムとの接着力が小さいため、タイヤ使用中に脱落し、防滑効果が低下する難点を有しているので、胡桃の殻を粒径１００〜６００μm に粉砕して、レゾルシン・ホルマリン樹脂初期縮合物とラテックスの混合物、所謂ＲＦＬで表面処理し、ゴムとの接着性を向上させた粒状体が防滑材として好適である。配合量は上記の一般的防滑材の場合と同様のゴム成分１００重量部に対し、４〜２０重量部にされる。
【００１０】
氷上性能を向上させるシリカがゴム成分１００重量部に対し１０〜４０重量部の割合で配合され、シリカとゴムの結合をよくするためにシランカップリング剤が定法に従ってシリカ量の約１０重量％添加される。シリカの配合が１０重量部未満であれば、シリカが奏する効果が小さく、４０重量部より多くなると耐摩耗性が低下する。
【００１１】
本発明に使用するカーボンブラック（以下、カーボンブラックを単にカーボンと言う）は、ＡＳＴＭで粒子径によって分類されてコード化された１００番台のＳＡＦ級及び２００番台のＩＳＡＦ級である。これらは補強作用が大きいので少量配合でも優れた耐摩耗性のゴム組成物が得られる。配合量は、ゴム成分１００重量部に対し、シリカ配合量とカーボン配合量の合計が３５〜６０重量部の要件を満たした上、２０〜４０重量部にされる。カーボン配合量が２０重量部未満またはカーボンとシリカの配合合計量が３５重量部未満の場合は耐摩耗性が劣り、カーボン配合量が４０重量部、またはカーボンとシリカの配合合計量が６０重量部より多くなると−５℃におけるＪＩＳ硬さを５５以下にするために多量の軟化剤を配合する必要があり、その結果耐摩耗性が低下する。ＪＩＳ硬さが５５より大になれば、氷上性能が悪くなる。一方ＪＩＳ硬さが４８より小になれば、耐摩耗性が悪くなるので、ＪＩＳ硬さは４８〜５５にされる。
【００１２】
上記の配合要件を満たして−５℃におけるＪＩＳ硬さを４８〜５５にしても、動的弾性率（以下、動的弾性率をＥ′と言う）が８MPa より小さくなれば、タイヤにしたとき、トレッドの剛性が低くなりすぎて耐摩耗性が悪くなり、氷上性能も低下する。１５MPa より大きい場合は、氷上性能が悪くなる。
【００１３】
本発明のゴム組成物は、前記したカーボン、シリカ、粒状体に加えて、タイヤ用ゴム組成物に一般に配合される各種添加剤を任意に配合することができ、その配合量も一般的な量とすることができる。任意に配合する添加剤としては、例えば硫黄、加硫促進剤、亜鉛華、ステアリン酸、などを挙げることができる。
【００１４】
【実施例】
表１に示すゴム成分１００部に対し、表１に示すカーボン、シリカ、シラ社製ンカップリング剤（デグッサ（株）、商品名Ｓｉ６９）、プロセスオイル、胡桃殻を粒径１００〜６００μm に粉砕してＲＦＬ処理を施した胡桃殻粒状体を表１に示す重量部割合（以下、本文中において重量部を単に部と言う）で配合し、さらに亜鉛華３部、ステアリン酸３部、老化防止剤（大内新興化学工業社製商品名ノクラック６Ｃ）１．５部、加硫促進剤ＤＰＧ０．５部、ＣＢＳ１部及び硫黄１．２部を配合してバンバリミキサで定法に従って混合し、混合ゴムを得た。混合ゴムから試料を採取し、ＪＩＳＫ６２５３に準拠してタイプＡデュロメーターによる温度−５℃における硬さ及び下記に示す方法によるＥ′の試験を行った。結果を表１に示した。
【００１５】
【表１】

【００１６】
さらに上記混合ゴムでトレッドを形成したサイズ１８５／７０Ｒ１４タイヤを常法に従って試作した。各試作タイヤについて氷上制動及び耐摩耗性の評価を下記に示す方法で行った。結果を表１に示した。
【００１７】
動的弾性率（Ｅ′）：
温度１６０℃で１５分間加硫して調整した所定形状の試験片を用い、岩本製作所社製の動的粘弾性スペクトロメーターによって温度−５℃、静歪み１５％、動歪み０．２％、周波数１００Hzの条件で測定した。
氷上制動：
乗用車に試作タイヤ４本を装着して５０km慣らし走行した後、気温−８℃の下で、雪氷路を時速４０kmで走行中急ブレーキを掛け、急ブレーキを掛けた地点から停止するまでの停止距離を測定し、結果を下記式で計算した指数で示した。値が大きいほど好ましい。
（比較例１タイヤの停止距離）×１００／（各試作タイヤの停止距離）
耐摩耗性：
１台の乗用車に２種類の試作タイヤを装着して約１万km走行した後、溝深さを測定し、走行前後の溝深さの差から両タイヤの摩耗量を求め、結果を下記式で計算した指数で示した。値が大きいほど好ましい。
（比較例１タイヤの摩耗量）×１００／（各試作タイヤの摩耗量）
【００１８】
従来例であるＶＣＲが用いられていない比較例１と比較して、実施例のゴム組成物で試作されたタイヤは、耐摩耗性を維持または向上させて氷上制動性が向上した。比較例２はＶＣＲのブレンド率が１０重量％未満であるためＥ′が８MPaより小さく、氷上性能の改良効果がない。比較例３はＶＣＲのブレンド率が４０重量％より多いためＥ′が特定範囲内であっても耐摩耗性が悪い。比較例４はカーボン量を多くして特性を特定範囲内にするために軟化剤を多く配合したので、耐摩耗性が悪い。比較例５はカーボン量が２０部未満であるため耐摩耗性が悪い。比較例６はカーボン量とシリカ量の合計が３５部未満であるため耐摩耗性が悪い。比較例７はＪＩＳ硬さが４８より小さいため耐摩耗性が悪い。比較例８は硬さが特定範囲内にあるが、Ｅ′が１５MPa より高いために氷上制動が劣る。比較例９は配合要件を満たして硬さが特定範囲内にあるが、Ｅ′が８MPa より低いため耐摩耗性が悪い。比較例１０はＪＩＳ硬さが５５より大であるので氷上制動が劣る。
【００１９】
【発明の効果】
以上説明したように本発明は、ＶＣＲ１０〜４０重量％とＶＣＲ以外のジエン系ゴム９０〜６０よりなるゴム成分１００部に対し、シリカ配合量とカーボン配合量の和が３５〜６０部となる量的関係を満足しながら、シリカを１０〜３０重量部、ＳＡＦ級カーボン及びＩＳＡＦ級カーボンの群から選んだカーボンを２０〜４０部配合し、温度−５℃で測定された加硫物のＪＩＳ硬さを４８〜５５、動的弾性率（Ｅ′）をが８〜１５MPa にすることにより、スタッドレスタイヤに用いられたとき、耐摩耗性を維持または向上させて氷上性能を向上させる効果を有する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rubber composition used for a vehicle that travels on snowy and icy roads, in particular, a tire that is mounted on a passenger car, a so-called studless tire.
[0002]
[Prior art]
Studless tires that allow an automobile to travel without slipping on a snowy icy road have improved on-ice performance using the following method. That is,
(1) Crushing copper metal short fibers described in JP-A-63-34206, sawdust, walnut shell, cork, peanut shell, ginkgo shell, rice husk described in JP-A-2-274740 Non-metallic inorganic filler having a particle diameter of 0.01 to 5 mm obtained by pulverizing alumina, granite, quartz, limestone, etc. described in JP-A-2-281051 , Powder processed products containing a cellulose substance having a particle size of 20 to 600 μm obtained by pulverizing rice husk, wheat husk, cork and the like described in JP-A-2-167353, and average particles described in JP-A-5-179069 An anti-slip material such as a polyester resin having a diameter of 20 to 150 μm or a composite particle in which particles capable of adhering to rubber are embedded on the surface of a base particle having a particle diameter of 10 to 500 μm described in JP-A-5-222247. A method of forming a tread with a blended rubber composition and making it difficult to slip by the micro spike effect produced by the anti-slip material exposed on the tread surface.
(2) Use rubber with a low glass transition point as a rubber component to suppress the increase in hardness due to temperature drop, and reduce the amount of carbon black compared to ordinary tires that do not run on snowy ice roads. The tread is formed with a rubber composition that has been reduced in hardness at a temperature below the freezing point by increasing the blending amount of the softening agent. A method of increasing adhesion friction with the road surface by increasing the actual contact area by deforming it so that it is in close contact with unevenness. In many cases, silica is blended to increase the adhesion friction effect.
(3) Grooves and sipes provided on the tread surface are increased in the lateral component of the so-called tread pattern, and the edge effect of hooking the edges of the grooves and sipes on the road surface is made difficult to slip.
[0003]
[Problems to be solved by the invention]
However, if the content of the granular material of the rubber composition forming the tread increases, the wear performance decreases, so there is a limit to the blending amount. If the rubber composition becomes soft, the block rigidity of the tread pattern decreases and the resistance to resistance increases. General characteristics of tires such as wearability and steering stability are reduced, so there is an acceptable limit to the reduction in hardness, and if the rubber's glass transition point is lowered, wet road performance is reduced, so low temperature hardness is reduced. There is a limit to lowering the glass transition point of the rubber component, and if the number or length of grooves and sipes increases, the block rigidity of the tread pattern decreases and the tire resistance such as wear resistance and steering stability is reduced. As general properties deteriorate and cracks tend to occur from the end of the sipe, the number and length are limited, and the performance on ice has not reached a satisfactory level. Improvement has been demanded.
[0004]
In view of the above, an object of the present invention is to provide a rubber composition that is used in a studless tire and that improves the performance on ice without impairing the wear performance.
[0005]
[Means for Solving the Problems]
As a means to solve the above problems, the dynamic elastic modulus related to the rigidity at the time of small deformation of the entire tread that affects general characteristics such as wear performance is increased, and JIS related to the rigidity at the time of large deformation related to adhesion friction. By reducing the hardness, it is possible to improve the performance on ice by maintaining the wear resistance etc. at the same level as or higher than that of conventional tires. Furthermore, the performance on ice can be achieved by replacing part of the carbon black with silica. Can be greatly improved.
[0006]
General elastic rubber such as styrene-butadiene rubber, natural rubber, butadiene rubber, and isoprene rubber, which have a relatively low glass transition point due to the influence of the glass transition point of the rubber component. Is usually used for treads of studless tires. A rubber composition reinforced with carbon black using these general-purpose rubbers as a rubber component has a low dynamic elastic modulus when the blending amount of carbon black and a softening agent is adjusted to reduce the hardness. In general, if the hardness is changed, the dynamic elastic modulus changes substantially linearly with respect to the JIS hardness, and it is said that the linear relationship does not change greatly even if the rubber type of the general-purpose rubber is changed. However, if a part of general-purpose rubber is replaced with cis-1,4-polybutadiene rubber modified with syndiotactic-1,2-polybutadiene having a high glass transition point, the dynamic modulus of elasticity is maintained even if the hardness is the same. Is larger than the case of general-purpose rubber alone, can increase the dynamic elastic modulus while reducing the hardness, while maintaining the general characteristics of the tire such as wear resistance related to the dynamic elastic modulus at a high level The adhesion friction related to the hardness can be increased.
[0007]
That is, the present invention relates to a rubber composition for studless tires containing an anti-slip material, 10 to 40% by weight of cis-1,4-polybutadiene rubber modified with syndiotactic-1,2-polybutadiene, and the modified cis- Satisfying the quantitative relationship that the sum of the silica compounding amount and the carbon black compounding amount is 35 to 60 parts by weight with respect to 100 parts by weight of the rubber component consisting of 90 to 60% by weight of diene rubber other than 1,4-polybutadiene rubber. However, 10 to 30 parts by weight of silica and 20 to 40 parts by weight of carbon black selected from the group of SAF grade carbon black and ISAF grade carbon black were blended and vulcanized at a temperature of 160 ° C. for 15 minutes. for vulcanizates, JIS hardness when measured at a temperature -5 ° C. the type a durometer according to JIS K6253 It There are 48 to 55 and a temperature of -5 ° C., Shizuyugami 15%, dynamic strain 0.2% and dynamic elastic modulus when measured at a frequency 100Hz condition (E ') is 8~15MPa A rubber composition for studless tires characterized by the above.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Cis-1,4-polybutadiene rubber modified with syndiotactic-1,2-polybutadiene used in the present invention (hereinafter referred to as cis-1,4-polybutadiene modified with syndiotactic-1,2-polybutadiene) Rubber is referred to as VCR) is a method described in JP-A-55-31802, that is, after polymerization of 1,3-butadiene in the presence of a 1,2-polymerization catalyst in an organic solvent, the catalyst is deactivated. An organic solvent solution of cis-1,4-polybutadiene rubber was added to the polymerization solution of syndiotactic-1,2-polybutadiene obtained by stirring and mixed, and syndiotactic-1,2-polybutadiene and cis were mixed from the mixture. A method obtained by separating a mixture of -1,4-polybutadiene rubber, or a method described in JP-A-5-194658, That is, 1,3-butadiene is first polymerized in the presence of 1,4-polymerization catalyst without being completely converted to cis 1,4-polybutadiene, and then 1,2-polymerization catalyst is charged into the polymerization system. The remaining 1,3-butadiene can be obtained by 1,2-polymerization. Alternatively, it can be obtained from Ube Industries under the trade name UBEPOLVCR. When the blend ratio of the VCR in the rubber component is less than 10% by weight, the effect brought about by the VCR does not appear, and when it exceeds 40% by weight, the wear resistance is lowered.
[0009]
As the anti-slip material, vegetable granules obtained by pulverizing seed shells or fruit nuclei, non-metallic inorganic granules obtained by pulverizing quartz, alumina, etc., short fibers, and the like can be used. Since these general granular materials have a low adhesive force with rubber, they fall off during use of the tire and have a drawback that the anti-slip effect is lowered. Therefore, the walnut shell is crushed to a particle size of 100 to 600 μm, A granule that is surface-treated with a mixture of resorcin / formalin resin initial condensate and latex, so-called RFL, and has improved adhesion to rubber is suitable as an anti-slip material. The compounding amount is 4 to 20 parts by weight with respect to 100 parts by weight of the same rubber component as in the case of the above general anti-slip material.
[0010]
Silica for improving performance on ice is blended at a ratio of 10 to 40 parts by weight with respect to 100 parts by weight of the rubber component, and a silane coupling agent is added in an amount of about 10% by weight of the silica according to a conventional method in order to improve the bond between silica and rubber. Is done. If the amount of silica is less than 10 parts by weight, the effect of silica is small, and if it exceeds 40 parts by weight, the wear resistance is lowered.
[0011]
The carbon black used in the present invention (hereinafter, carbon black is simply referred to as carbon) is a 100th SAF class and a 200th ISAF class that are classified and coded by ASTM according to particle diameter. Since these have a large reinforcing action, an excellent wear-resistant rubber composition can be obtained even in a small amount. The blending amount is set to 20 to 40 parts by weight after the total of the silica blending amount and the carbon blending amount satisfies the requirements of 35 to 60 parts by weight with respect to 100 parts by weight of the rubber component. When the amount of carbon is less than 20 parts by weight or the total amount of carbon and silica is less than 35 parts by weight, the wear resistance is inferior, the amount of carbon is 40 parts by weight, or the total amount of carbon and silica is 60 parts by weight. If it is more, a large amount of a softening agent needs to be added in order to make the JIS hardness at −5 ° C. 55 or less, and as a result, the wear resistance decreases. If the JIS hardness is greater than 55, the performance on ice will deteriorate. On the other hand, if the JIS hardness is less than 48, the wear resistance is deteriorated, so the JIS hardness is set to 48 to 55.
[0012]
If the dynamic modulus of elasticity (hereinafter referred to as the dynamic modulus of elasticity E ') is smaller than 8 MPa even if the JIS hardness at -5 ° C is 48 to 55 while satisfying the above compounding requirements, The rigidity of the tread becomes too low, the wear resistance is deteriorated, and the performance on ice is lowered. If it is greater than 15 MPa, the performance on ice will be poor.
[0013]
The rubber composition of the present invention can be arbitrarily mixed with various additives generally blended in a tire rubber composition in addition to the above-described carbon, silica, and granule, and the blending amount is also a general amount. It can be. Examples of the additive to be arbitrarily added include sulfur, a vulcanization accelerator, zinc white, and stearic acid.
[0014]
【Example】
100 parts of the rubber component shown in Table 1 is pulverized to a particle size of 100 to 600 μm with carbon, silica, Sila Co. coupling agent (Degussa Co., Ltd., trade name: Si69), process oil and walnut shell shown in Table 1. The walnut shell granules subjected to RFL treatment are blended in the proportions by weight shown in Table 1 (hereinafter, the parts by weight are simply referred to as “parts”), and further 3 parts of zinc white, 3 parts of stearic acid, anti-aging 1.5 parts of an agent (trade name NOCRACK 6C manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.), 0.5 part of vulcanization accelerator DPG, 1 part of CBS and 1.2 parts of sulfur are mixed according to a conventional method using a Banbury mixer, and the mixed rubber is mixed. Obtained. A sample was taken from the mixed rubber, and the hardness at a temperature of −5 ° C. by a type A durometer and the E ′ test by the method shown below were performed according to JIS K6253. The results are shown in Table 1.
[0015]
[Table 1]

[0016]
Further, a size 185 / 70R14 tire in which a tread was formed from the above-mentioned mixed rubber was prototyped according to a conventional method. Each prototype tire was evaluated for braking on ice and wear resistance by the following methods. The results are shown in Table 1.
[0017]
Dynamic elastic modulus (E ′):
Using a test piece of a predetermined shape prepared by vulcanization at a temperature of 160 ° C. for 15 minutes, a dynamic viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., temperature −5 ° C., static strain 15%, dynamic strain 0.2%, frequency Measurement was performed at 100 Hz.
Ice braking:
After running for 50 km with 4 prototype tires mounted on a passenger car, suddenly brake while driving on a snowy / ice road at 40 km / h under a temperature of -8 ° C, and the stopping distance from the point where the brake was applied. Was measured and the result was shown as an index calculated by the following formula. Larger values are preferred.
(Comparative example 1 tire stopping distance) × 100 / (stopping distance of each prototype tire)
Abrasion resistance:
After running about 10,000 km with two types of prototype tires mounted on a single passenger car, the groove depth was measured, and the amount of wear on both tires was determined from the difference in groove depth before and after running. It was shown by the index calculated by. Larger values are preferred.
(Comparative Example 1 Tire Amount of Wear) × 100 / (Amount of Wear of Each Prototype Tire)
[0018]
Compared with Comparative Example 1 in which the VCR which is a conventional example is not used, the tire manufactured as a prototype with the rubber composition of the example maintained or improved the wear resistance and improved the braking performance on ice. In Comparative Example 2, since the VCR blend ratio is less than 10% by weight, E ′ is smaller than 8 MPa, and there is no effect of improving the performance on ice. In Comparative Example 3, since the blend ratio of VCR is more than 40% by weight, the wear resistance is poor even if E ′ is within a specific range. In Comparative Example 4, the wear resistance is poor because a large amount of carbon is added and a softening agent is added in order to bring the characteristics into a specific range. In Comparative Example 5, the amount of carbon is less than 20 parts, so the wear resistance is poor. In Comparative Example 6, since the total amount of carbon and silica is less than 35 parts, the wear resistance is poor. Since Comparative Example 7 has a JIS hardness of less than 48, the wear resistance is poor. Although Comparative Example 8 has a hardness within a specific range, braking on ice is inferior because E ′ is higher than 15 MPa. Comparative Example 9 satisfies the compounding requirements and has a hardness within a specific range, but has a poor wear resistance because E ′ is lower than 8 MPa. Since Comparative Example 10 has a JIS hardness greater than 55, braking on ice is inferior.
[0019]
【The invention's effect】
As described above, the present invention is an amount in which the sum of the silica blending amount and the carbon blending amount is 35 to 60 parts with respect to 100 parts by weight of the VCR 10 to 40% by weight and the diene rubber 90 to 60 other than the VCR. JIS hardness of the vulcanizate measured at a temperature of −5 ° C., with 10 to 30 parts by weight of silica and 20 to 40 parts of carbon selected from the group of SAF grade carbon and ISAF grade carbon. When the thickness is 48 to 55 and the dynamic elastic modulus (E ′) is 8 to 15 MPa, when used in a studless tire, it has the effect of maintaining or improving the wear resistance and improving the performance on ice.

Claims

In the rubber composition for studless tires containing an anti-slip material,
For 100 parts by weight of a rubber component consisting of 10 to 40% by weight of cis-1,4-polybutadiene rubber modified with syndiotactic-1,2-polybutadiene and 90 to 60% by weight of diene rubber other than the modified polybutadiene rubber, 20 to 40 parts by weight of carbon black selected from the group of SAF class carbon black and ISAF class carbon black and 10 to 30 parts by weight of silica are blended, and the sum of the blending amounts of carbon black and silica is 35 to 60 parts by weight. Satisfying the quantitative relationship
About the vulcanizate prepared by vulcanizing at a temperature of 160 ° C. for 15 minutes, the JIS hardness when measured at a temperature of −5 ° C. with a type A durometer in accordance with JIS K6253 is 48 to 55 , and a temperature of −5 A rubber composition for a studless tire, characterized by a dynamic elastic modulus (E ') of 8 to 15 MPa when measured under the conditions of C, static strain 15%, dynamic strain 0.2%, and frequency 100 Hz .