JP2004051798A

JP2004051798A - Tire tread rubber composition

Info

Publication number: JP2004051798A
Application number: JP2002211492A
Authority: JP
Inventors: Takashi Shirokawa; 城川　隆
Original assignee: Yokohama Rubber Co Ltd
Current assignee: Yokohama Rubber Co Ltd
Priority date: 2002-07-19
Filing date: 2002-07-19
Publication date: 2004-02-19
Anticipated expiration: 2022-07-19
Also published as: JP4111765B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire tread rubber composition which realizes a low fuel consumption and a high balance between wet performance and low-temperature brittleness temperature. <P>SOLUTION: The rubber composition contains 55-75 pts.wt. specified styrene/butadiene copolymer rubber (SBR), 6-25 pts.wt. natural rubber (NR) or polyisoprene rubber (IR), 5-15 pts.wt. butadiene rubber (BR), and 20-50 pts.wt. silica and 20-50 pts.wt. carbon black, per 100 pts.wt. total weight of the rubber components. The BR is obtained by preblending a high-molecular-weight BR having a weight-average molecular weight of 500,000-1,000,000 with a low-molecular-weight BR having a weight-average molecular weight of 6,000-60,000 in a solvent. The low-molecular-weight BR is contained in an amount of 20-40 wt.% based on the total BR weight. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、タイヤトレッド用ゴム組成物、更に詳細には、カーボンブラックを含むシリカ配合系での分散性、加工性および低温脆化を改善し、また耐摩耗性およびウェット性能の向上を図ったタイヤトレッド用ゴム組成物に関する。
【０００２】
【従来の技術】
従来より、シリカを配合することによりウェット性能を向上させる技術（例えば、特開平１１−１２４４７４号、特開平１１−２６９３０５号および特開平１３−１７２４３２号公報）はよく知られている。しかしながら、シリカを多量に配合すると、その分散が難しく、不良分散塊が多くなる。この結果、耐摩耗性が悪化し易く、また、期待するウェット性能が発現しないという問題がある。
【０００３】
また、低燃費性とウェット性能およびスノー性能とのバランスを目的にシリカを多量に配合することも、一般的に行なわれている手法である。しかしながら、これらの従来技術において、多量のシリカを配合したゴム組成物では、そのシリカの分散性およびゴム組成物の加工性等に難があり、また耐摩耗性が悪くなるという問題があった。更に、ウェット性能とスノー性能とを両立する上で耐低温脆化性を確保することが、非常に難しかった。
【０００４】
更に、ＳＢＲやＢＲ等の低分子量ポリマーを配合することによって、氷上および湿潤路面におけるグリップ性能を改善する技術（例えば、特開２００１−１１２３７号公報）、物性の変化を抑制する技術（例えば、特開平６−２７８４１０号公報）およびロール加工性を改善する技術（例えば、特開平１０−５３６７１号公報）が提案されている。しかしながら、これらＳＢＲやＢＲの低分子量ポリマーを配合利用する発明は、いずれも本発明とはその構成および目的が全く異なり、しかも、その解決手段を異にするものである。
【０００５】
【発明が解決しようとする課題】
本発明では、カーボンブラックを含むシリカ配合系でのゴム組成物における分散性、加工性および低温脆化性を改善し、またその耐摩耗性およびウェット性能の向上を図ると共に、低燃費性とウェット性能および低温脆化温度との高バランス化を達成したタイヤトレッド用ゴム組成物を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明によれば、特定のスチレン−ブタジエン共重合体ゴム（ＳＢＲ）５５〜７５重量部、天然ゴム（ＮＲ）またはポリイソプレンゴム（ＩＲ）６〜２５重量部、ブタジエンゴム（ＢＲ）５〜１５重量部、およびこれらゴム成分の総量１００重量部に対してシリカ２０〜５０重量部およびカーボンブラック２０〜５０重量部を含むタイヤトレッド用ゴム組成物であって、前記ＢＲは、重量平均分子量５００，０００〜１，０００，０００の高分子量ＢＲと重量平均分子量６，０００〜６０，０００の低分子量ＢＲとが溶媒中でプリブレンドされており、かつ当該低分子量ＢＲが全ＢＲ量の２０〜４０重量％含まれていることを特徴とするタイヤトレッド用ゴム組成物が提供される。
【０００７】
【発明の実施の形態】
本発明では、所定量のカーボンブラックを含むシリカ配合系の特定のＳＢＲ、ＮＲまたはＩＲ、および特定のＢＲを特定配合比で含んでなるゴム組成物において、当該ＢＲ成分として特定配合比の高分子量ＢＲと低分子量ＢＲとを予め溶液中でブレンドしたプリブレンドＢＲを少量配合することで、シリカ配合系の当該ゴム組成物におけるシリカの分散性、ゴム組成物の加工性および低温脆化性が改善され、またその耐摩耗性およびウェット性能の向上が図られると共に、低燃費性とウェット性能および低温脆化温度との高バランス化も同時に達成できることを見出したものである。
【０００８】
本発明のタイヤトレッド用ゴム組成物におけるゴム成分には、スチレン量が１５〜３５重量％、ビニル量が３０〜７５重量％を含み、重量平均分子量が５００，０００〜１，０００，０００で、ガラス転移温度が−５０〜−３０℃であるＳＢＲ５５〜７５重量部、ＮＲまたはＩＲ６〜２５重量部、および高分子量と低分子量のＢＲを含むプリブレンドゴムが全量で５〜１５重量部、特に好ましくは６〜１２重量部からなるプリブレンドゴムが用いられる。ここで、当該ＢＲ成分には、重量平均分子量で５００，０００〜１，０００，０００の高分子量ＢＲと重量平均分子量で６，０００〜６０，０００の低分子量ＢＲとを、この低分子量ＢＲが全ＢＲの２０〜４０重量％の量で含まれるように溶媒中でプリブレンドしたＢＲが用いられる。また、当該所定比のプリブレンドゴムの配合量が全量で１５重量部を超えると、ウェット性能が低下し、逆に５重量部未満では、良好な低温脆化温度、シリカの分散性、並びにゴム組成物の良好な加工性と耐摩耗性が得られない。よって、これら種類のゴム成分および配合量の選定、並びに当該プリブレンドＢＲの使用は、以下の特定量のシリカとカーボンブラックの配合と相俟って、本発明のカーボンブラックを含むシリカ配合系のゴム組成物が所期の低燃費性とウェット性能および低温脆化温度の高バランス化を達成する上で、極めて重要な要件である。
【０００９】
本発明のタイヤトレッド用ゴム組成物には、更に、補強剤として、上記ブレンドゴム成分１００重量部に対して、シリカ２０〜５０重量部、好ましくは３０〜４０重量部とカーボンブラック２０〜５０重量部とが配合される。特に、本願発明では、Ｎ_２ＳＡ１００〜３００ｍ^２／ｇのシリカとＮ_２ＳＡ７０〜１００ｍ^２／ｇのカーボンブラックとを併用して、ゴム成分１００重量部当たり総量５０〜７０重量部の配合量で用いることが、所期の目的達成の上で好ましい。前記シリカの配合量が２０重量部未満では、ウェット性能が低くなり、逆に５０重量部を超えると、耐摩耗性が悪くなる。
【００１０】
本発明のタイヤトレッド用ゴム組成物には、前記した成分に加えて、加硫または架橋剤、加硫または架橋促進剤、シランカップリング剤、各種オイル、老化防止剤、可塑剤などのタイヤ用ゴムに一般に配合されている各種配合剤を配合することができ、かかる配合剤は一般的な方法で混練、加硫してゴム組成物とし、加硫または架橋するのに使用することができる。これら配合剤の配合量も、本発明の目的に反しない限り、一般的な配合量とすることができる。
【００１１】
【実施例】
以下、実施例および比較例によって本発明を更に説明するが、本発明の技術的範囲をこれらの実施例によって限定するものでないことは言うまでもない。
【００１２】
試験サンプルの作製
以下の表１に示す各例の配合において、硫黄と加硫促進剤を除く成分を１．７リットルの密閉型ミキサーにて５分間混合した後、ミキサーよりゴム組成物を放出した。このゴム組成物をシリカ分散性の観察に供し、また、放出するときのミキサー内部への密着度合いを観察した。別途、同じく硫黄と加硫促進剤を除く成分を１．７リットルの密閉型ミキサーで５分間混合し、１６０℃に達したときに放出した。このマスターバッチに硫黄と加硫促進剤を加えて８インチのオープンロールで混練してゴム組成物を得た。次いで、このゴム組成物を１５ｃｍ×１５ｃｍ×０．２ｃｍの金型中で１６０℃、２０分間プレス加硫して試験片（ゴムシート）を作製し、これを低温脆化温度試験および耐摩耗性試験に供した。また、上記配合物をキャップトレッドに用いて、サイズ１８５／６５Ｒ１４の試験タイヤを作製し、制動試験に供した。
【００１３】
試験法
１）シリカ分散性：　加硫系と硫黄を混合する前に放出した混練ゴム組成物の破断面におけるシリカの分散性について目視にて観察し、以下の４点法によって評価した。点数が高いほど、分散性が良好である。
４点：目視可能なシリカの不良分散塊が全く見られず、均一分散している状態。
３点：均一に分散しているが、目視可能なシリカの不良分散塊が数個／１０ｃｍ^２で散見される状態。
２点：均一に分散しているが、目視可能なシリカの不良分散塊が１０〜１００個／１０ｃｍ^２で散見される状態。
１点：不良分散塊が無数にあり、０．５ｍｍ以上の不良分散塊も多数存在し、表面から粉が見える状態。
【００１４】
２）混合加工性：　加硫系と硫黄を混合する前の混練ゴム組成物の放出時におけるミキサー内部への密着度合いを目視にて観察し、以下の４点法によって評価した。点数が高いほど、密着が少なく、加工し易い。
４点：全くミキサー内部に密着せず、ゴムまとまりもよく、簡単にミキサーより出てくる状態。
３点：若干ミキサー内部に密着するが、自然にミキサーより出てくる状態。
２点：かなりミキサーに密着し、ばらばらの状態で何とかミキサーより出せる状態。
１点：ミキサー内部に一面に完全に密着して、自然にはミキサーより出てこない状態。
【００１５】
３）低温脆化温度：　ＪＩＳ　Ｋ６２６１の低温衝撃脆化試験法に準拠して測定した。
【００１６】
３）耐摩耗性：　ランボーン摩耗試験機（岩本製作所製）を用いて、温度２０℃、スリップ率５０％の条件で摩耗減量を測定し、比較例１を１００として指数表示した。数値が大なるほど、耐摩耗性が良好であることを示す。
【００１７】
４）ウェット制動性：　試験タイヤ４本を排気量１８００ｃｃの乗用車に装着して、散水したアスファルト路面上で初速度１００ｋｍ／時間からの制動距離を測定し、比較例１を１００として指数表示した。数値が大なるほど、ウェット制動性が良好であることを示す。
【００１８】
実施例１〜２および比較例１〜６
結果を表１に示す。
【表１】

【００１９】
【発明の効果】
以上の結果によると、本発明のカーボンブラックを含むシリカ配合系のゴム組成物では、シリカ分散性、混合密着性および低温脆化温度が良好で、その耐摩耗性およびウェット制動が優れていることが判る。よって、このゴム組成物は、低燃費性とウェット性能および低温脆化温度（スノー性能）とのバランスを高次に図ったタイヤトレッド用ゴム組成物として極めて有用である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention has improved the dispersibility, workability and low-temperature embrittlement of a rubber composition for a tire tread, more specifically, a silica-containing system containing carbon black, and has also improved wear resistance and wet performance. The present invention relates to a rubber composition for a tire tread.
[0002]
[Prior art]
Conventionally, techniques for improving wet performance by blending silica (for example, JP-A-11-124474, JP-A-11-269305, and JP-A-13-172432) are well known. However, when silica is blended in a large amount, it is difficult to disperse the silica, and the number of defective dispersed masses increases. As a result, there is a problem that the abrasion resistance is liable to be deteriorated and the expected wet performance is not exhibited.
[0003]
It is also a commonly practiced method to incorporate a large amount of silica for the purpose of balancing fuel economy, wet performance and snow performance. However, in these conventional techniques, a rubber composition containing a large amount of silica has problems in that the silica dispersibility and the processability of the rubber composition are difficult, and that abrasion resistance is deteriorated. Furthermore, it was very difficult to ensure low-temperature embrittlement resistance in order to achieve both wet performance and snow performance.
[0004]
Furthermore, by blending a low molecular weight polymer such as SBR or BR, a technique for improving grip performance on ice and wet road surfaces (for example, JP-A-2001-11237), a technique for suppressing changes in physical properties (for example, Japanese Unexamined Patent Publication No. Hei 6-278410) and a technique for improving roll workability (for example, Japanese Unexamined Patent Publication No. Hei 10-53671) have been proposed. However, the inventions in which the low molecular weight polymers of SBR and BR are blended and used have completely different constitutions and objects from the present invention, and have different means for solving them.
[0005]
[Problems to be solved by the invention]
In the present invention, the dispersibility, processability, and low-temperature embrittlement of a rubber composition in a silica compounding system containing carbon black are improved, and the abrasion resistance and wet performance are improved. An object of the present invention is to provide a rubber composition for a tire tread that achieves a high balance between performance and low-temperature embrittlement temperature.
[0006]
[Means for Solving the Problems]
According to the present invention, 55 to 75 parts by weight of a specific styrene-butadiene copolymer rubber (SBR), 6 to 25 parts by weight of natural rubber (NR) or polyisoprene rubber (IR), 5 to 15 parts by weight of butadiene rubber (BR) A rubber composition for a tire tread comprising 20 to 50 parts by weight of silica and 20 to 50 parts by weight of carbon black based on 100 parts by weight of the rubber component, and wherein the BR has a weight average molecular weight of 500, A high molecular weight BR of 000 to 1,000,000 and a low molecular weight BR of a weight average molecular weight of 6,000 to 60,000 are pre-blended in a solvent, and the low molecular weight BR is 20 to 40% of the total BR amount. A rubber composition for a tire tread, characterized in that the rubber composition is contained in a weight percent.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, in a rubber composition containing a specific SBR, NR or IR of a silica compound containing a predetermined amount of carbon black, and a specific BR at a specific compounding ratio, a high molecular weight of a specific compounding ratio is used as the BR component. By blending a small amount of pre-blend BR in which BR and low molecular weight BR are previously blended in a solution, silica dispersibility in the silica-containing rubber composition, processability of rubber composition, and low-temperature embrittlement are improved. In addition, it has been found that the abrasion resistance and the wet performance are improved, and that a high balance between low fuel consumption, wet performance and low temperature embrittlement temperature can be achieved at the same time.
[0008]
The rubber component in the rubber composition for a tire tread of the present invention has a styrene content of 15 to 35% by weight, a vinyl content of 30 to 75% by weight, a weight average molecular weight of 500,000 to 1,000,000, 55 to 75 parts by weight of SBR having a glass transition temperature of -50 to -30 ° C, 6 to 25 parts by weight of NR or IR, and 5 to 15 parts by weight of a pre-blend rubber containing a high molecular weight and low molecular weight BR are particularly preferable. Is a pre-blended rubber consisting of 6 to 12 parts by weight. Here, the BR component includes a high molecular weight BR having a weight average molecular weight of 500,000 to 1,000,000 and a low molecular weight BR having a weight average molecular weight of 6,000 to 60,000. A BR preblended in a solvent to be included in an amount of 20 to 40% by weight of the total BR is used. On the other hand, if the total amount of the pre-blend rubber in the predetermined ratio exceeds 15 parts by weight, the wet performance is deteriorated, and if it is less than 5 parts by weight, favorable low-temperature embrittlement temperature, silica dispersibility, and rubber Good workability and abrasion resistance of the composition cannot be obtained. Therefore, the selection of these types of rubber components and the blending amount, and the use of the pre-blend BR, together with the following blending of the specific amounts of silica and carbon black, together with the silica blending system containing carbon black of the present invention. It is a very important requirement for the rubber composition to achieve a desired balance between low fuel consumption, wet performance and low-temperature embrittlement temperature.
[0009]
The rubber composition for a tire tread of the present invention further comprises, as a reinforcing agent, 20 to 50 parts by weight of silica, preferably 30 to 40 parts by weight, and 20 to 50 parts by weight of carbon black based on 100 parts by weight of the blend rubber component. Parts are blended. In particular, in the present _invention, N ² _SA100~300m 2 / g in combination with carbon black silica and _N ² _SA70~100m 2 / g, in the amount of 50 to 70 parts by weight total per 100 parts by weight of the rubber component It is preferable to use it for achieving the intended purpose. If the amount of the silica is less than 20 parts by weight, the wet performance will be low, and if it exceeds 50 parts by weight, the wear resistance will be poor.
[0010]
In the rubber composition for a tire tread of the present invention, in addition to the above-described components, a vulcanizing or crosslinking agent, a vulcanizing or crosslinking accelerator, a silane coupling agent, various oils, an antioxidant, a tire for a tire such as a plasticizer. Various compounding agents generally compounded in rubber can be compounded, and such compounding agents can be kneaded and vulcanized by a general method into a rubber composition, and used for vulcanization or crosslinking. The compounding amount of these compounding agents can be a general compounding amount as long as the object of the present invention is not adversely affected.
[0011]
【Example】
Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but it goes without saying that the technical scope of the present invention is not limited by these Examples.
[0012]
Preparation of test sample In each of the formulations shown in Table 1 below, components other than sulfur and the vulcanization accelerator were mixed in a 1.7-liter closed mixer for 5 minutes, and then the rubber composition was mixed with the mixer. Things were released. This rubber composition was used for observation of silica dispersibility, and the degree of adhesion to the inside of the mixer when releasing was observed. Separately, components other than sulfur and the vulcanization accelerator were similarly mixed in a 1.7-liter closed mixer for 5 minutes, and released when the temperature reached 160 ° C. Sulfur and a vulcanization accelerator were added to this master batch and kneaded with an 8-inch open roll to obtain a rubber composition. Next, the rubber composition was press-vulcanized in a mold of 15 cm × 15 cm × 0.2 cm at 160 ° C. for 20 minutes to prepare a test piece (rubber sheet), which was subjected to a low-temperature embrittlement temperature test and abrasion resistance. Tested. In addition, a test tire having a size of 185 / 65R14 was prepared using the above-mentioned composition for a cap tread, and subjected to a braking test.
[0013]
Test Method 1) Dispersibility of Silica: The dispersibility of silica in the fracture surface of the kneaded rubber composition released before mixing the vulcanized system with sulfur was visually observed and evaluated by the following four-point method. The higher the score, the better the dispersibility.
4 points: A state in which no visible defective dispersion mass of silica was observed at all, and the silica was uniformly dispersed.
3 points: A state in which the dispersed silica particles are uniformly dispersed, but are visible at several particles / 10 cm ² , which are visually observable.
2 points: A state in which the dispersed silica particles are uniformly dispersed, but are visible at 10 to 100 particles / 10 cm ² , which are visible.
1 point: The number of defective dispersed masses is innumerable, a large number of defective dispersed masses of 0.5 mm or more are present, and powder is visible from the surface.
[0014]
2) Mixing processability: The degree of adhesion to the inside of the mixer at the time of release of the kneaded rubber composition before mixing the vulcanization system and sulfur was visually observed and evaluated by the following four-point method. The higher the score, the less the adhesion and the easier the processing.
4 points: The rubber does not adhere to the inside of the mixer at all, the rubber is well united, and easily comes out of the mixer.
3 points: Slightly adhered to the inside of the mixer, but came out of the mixer naturally.
2 points: Very close to the mixer, and can be put out of the mixer in a separated state.
1 point: completely adhered to the inside of the mixer, and does not come out of the mixer naturally.
[0015]
3) Low temperature embrittlement temperature: Measured in accordance with JIS K6261 low temperature impact embrittlement test method.
[0016]
3) Abrasion resistance: The wear loss was measured using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho) under the conditions of a temperature of 20 ° C. and a slip ratio of 50%. The larger the value, the better the wear resistance.
[0017]
4) Wet braking performance: Four test tires were mounted on a passenger car with a displacement of 1800 cc, and the braking distance from an initial speed of 100 km / hour was measured on a sprinkled asphalt road surface. The higher the value, the better the wet braking performance.
[0018]
Examples 1-2 and Comparative Examples 1-6
Table 1 shows the results.
[Table 1]

[0019]
【The invention's effect】
According to the above results, the silica compound-containing rubber composition containing carbon black of the present invention has good silica dispersibility, mixed adhesion and low-temperature embrittlement temperature, and has excellent wear resistance and wet braking. I understand. Therefore, this rubber composition is extremely useful as a rubber composition for a tire tread in which the balance between low fuel consumption, wet performance, and low-temperature embrittlement temperature (snow performance) is attained to a high degree.

Claims

Styrene-butadiene having a styrene content of 15 to 35% by weight, a vinyl content of 30 to 75% by weight, a weight average molecular weight of 500,000 to 1,000,000, and a glass transition temperature of -50 to -30C. 55 to 75 parts by weight of copolymer rubber (SBR), 6 to 25 parts by weight of natural rubber (NR) or polyisoprene rubber (IR), 5 to 15 parts by weight of butadiene rubber (BR), and a total amount of these rubber components of 100 parts by weight A rubber composition for a tire tread, comprising 20 to 50 parts by weight of silica and 20 to 50 parts by weight of carbon black with respect to parts by weight, wherein the BR is a high molecular weight BR having a weight average molecular weight of 500,000 to 1,000,000. And a low molecular weight BR having a weight average molecular weight of 6,000 to 60,000 are preblended in a solvent, and the low molecular weight BR is 20% of the total BR amount. Tire tread rubber composition which is characterized in that it contains 40 wt%.

_N 2 SA is 100 to 300 m ² / g of the silica, a _N 2 SA of the carbon black is 70~100m ² / g, further silica and 50 to 70 parts by weight per 100 parts by weight of the rubber component to the total amount of carbon black The rubber composition for a tire tread according to claim 1, comprising: