JP2004051797A

JP2004051797A - Tire tread rubber composition

Info

Publication number: JP2004051797A
Application number: JP2002211473A
Authority: JP
Inventors: Takashi Shirokawa; 城川　隆; Shingo Midorikawa; 緑川　真吾
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: JP4148715B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire tread rubber composition improved in dispersibility and processability in a highly silica filled system and improved in abrasion resistance and wet performances. <P>SOLUTION: The rubber composition contains 30-60 pts.wt. specified styrene/butadiene copolymer rubber (SBR), 10-30 pts.wt. natural rubber (NR) or polyisoprene rubber (IR), 25-45 pts. wt. butadiene rubber (BR), and 50-100 pts.wt., per 100 pts.wt. total weight of the rubber components, silica. 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、シリカ多量配合系での分散性および加工性を改善し、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、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、これらの従来技術において、シリカを多量に配合したゴム組成物でも、その分散性および加工性が改善されるという知見は無く、勿論タイヤ性能が向上するという記述もない。
【０００４】
【発明が解決しようとする課題】
したがって、本発明では、シリカ多量配合系でのゴム組成物における分散性および加工性を改善し、また当該ゴム組成物の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を提供することを目的とする。
【０００５】
【課題を解決するための手段】
本発明によれば、スチレン量２０〜４０重量％、ビニル量３０〜７５重量％を含み、重量平均分子量が５００，０００〜１，５００，０００で、ガラス転移温度が−４０〜−２０℃であるスチレン−ブタジエン共重合体ゴム（ＳＢＲ）３０〜６０重量部、天然ゴム（ＮＲ）またはポリイソプレンゴム（ＩＲ）１０〜３０重量部、ブタジエンゴム（ＢＲ）２５〜４５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５０〜１００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。
【０００６】
【発明の実施の形態】
本発明では、シリカ多量配合系において、特定のＳＢＲ，ＮＲまたはＩＲ、および特定のＢＲを特定比率で含む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を特定量配合することで、高シリカ配合系の当該ゴム組成物のシリカ分散性および加工性が改善され、またその耐摩耗性およびウェット性能の向上も達成できることを見出したものである。
【０００７】
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２０〜４０重量％、ビニル量３０〜７５重量％を含み、重量平均分子量が５００，０００〜１，５００，０００で、ガラス転移温度が−４０〜−２０℃であるスチレン−ブタジエン共重合体ゴム（ＳＢＲ）３０〜６０重量部、天然ゴム（ＮＲ）またはポリイソプレンゴム（ＩＲ）１０〜３０重量部、ブタジエンゴム（ＢＲ）２５〜４５重量部からなるゴム配合物が使用され、ここで、当該ブタジエンゴム（ＢＲ）としては、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。これら種類のゴム成分の選定、配合量の特定およびプリブレンドＢＲの使用は、本発明のシリカ多量配合系のゴム組成物について所期の目的を達成する上で重要な要件である。
【０００８】
本発明のタイヤトレッド用ゴム組成物では、補強剤として上記ブレンドゴム成分１００重量部に対して５０〜１００重量部のシリカが配合された、高配合シリカゴム組成物として使用されることが特徴である。シリカ配合量が少ないと、期待されるウェット性能が発揮できず、シリカ配合量が多過ぎると、混練が困難となる。シリカの好ましい配合量は、ゴム成分の総重量１００重量部当たり６０〜９０重量部である。このシリカとしては、各種のシリカを使用することができるが、特に、沈降シリカの使用が好ましい。また、このシリカとカーボンブラックを併用することが好ましく、その場合の総量は、ゴム成分１００重量部当たり６０〜１００重量部であることがよく、シリカとしては、Ｎ_２ＳＡが１００〜３００ｍ^２／ｇのものが好ましく使用される。
【０００９】
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。
【００１０】
【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。
【００１１】
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。
【００１２】
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。
【００１３】
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点法によって加工性を評価した。点数が高いほど、密着少なく、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。
【００１４】
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。
【００１５】
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。
【００１６】
実施例１〜２および比較例１〜６
結果を表１に示す。
【表１】

【００１７】
【発明の効果】
以上の結果によると、本発明のシリカ多量配合系のゴム組成物では、シリカ分散性、混合加工性が良好で、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、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 relates to a rubber composition for a tire tread, and more particularly, to a rubber composition for a tire tread which has improved dispersibility and processability in a system containing a large amount of silica, and has improved abrasion resistance and wet performance. .
[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 poorly dispersed lumps 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]
In addition, a technique for improving grip performance on ice and wet road surfaces (for example, Japanese Patent Application Laid-Open No. 2001-11237) and a technique for suppressing changes in physical properties by blending a low molecular weight polymer such as SBR or BR (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, in these conventional techniques, there is no finding that even in a rubber composition containing a large amount of silica, the dispersibility and processability are improved, and of course, there is no description that the tire performance is improved.
[0004]
[Problems to be solved by the invention]
Accordingly, the present invention provides a rubber composition for a tire tread in which the dispersibility and processability of a rubber composition containing a large amount of silica are improved, and the abrasion resistance and wet performance of the rubber composition are improved. The purpose is to do.
[0005]
[Means for Solving the Problems]
According to the present invention, the composition contains 20 to 40% by weight of styrene, 30 to 75% by weight of vinyl, has a weight average molecular weight of 500,000 to 1,500,000, and has a glass transition temperature of -40 to -20 ° C. 30-60 parts by weight of certain styrene-butadiene copolymer rubber (SBR), 10-30 parts by weight of natural rubber (NR) or polyisoprene rubber (IR), 25-45 parts by weight of butadiene rubber (BR), and these rubber components A rubber composition for a tire tread containing 50 to 100 parts by weight of silica with respect to 100 parts by weight of the total of the above, wherein the BR is a high molecular weight BR having a weight average molecular weight of 500,000 to 1,000,000 and a weight average molecular weight A low molecular weight BR of 6,000 to 60,000 is pre-blended in a solvent, and the low molecular weight BR is contained in 20 to 40% by weight of the total BR amount. The rubber composition for a tire tread, characterized in Rukoto is provided.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, in a rubber composition containing a specific SBR, NR or IR, and a specific BR in a specific ratio in a large amount of silica compounding system, a high molecular weight BR and a low molecular weight BR of a specific compounding ratio are previously specified as the BR component. By mixing a specific amount of the pre-blend BR blended in the solution, the silica dispersibility and processability of the rubber composition having a high silica content can be improved, and the abrasion resistance and wet performance can also be improved. It was found.
[0007]
The rubber component in the rubber composition for a tire tread of the present invention contains 20 to 40% by weight of styrene and 30 to 75% by weight of vinyl, has a weight average molecular weight of 500,000 to 1,500,000, and has a glass transition. 30-60 parts by weight of styrene-butadiene copolymer rubber (SBR) having a temperature of -40 to -20 ° C, 10 to 30 parts by weight of natural rubber (NR) or polyisoprene rubber (IR), and 25 of butadiene rubber (BR) A butadiene rubber (BR) having a weight average molecular weight of 500,000 to 1,000,000 and a weight average molecular weight of 6,000. And a low molecular weight BR of about 60,000, pre-blended in a solvent such that the low molecular weight BR is contained in an amount of 20 to 40% by weight of the total BR. It is. Selection of these types of rubber components, specification of the compounding amount, and use of the pre-blend BR are important requirements for achieving the intended purpose of the rubber composition containing a large amount of silica of the present invention.
[0008]
The rubber composition for a tire tread of the present invention is characterized in that it is used as a highly blended silica rubber composition in which 50 to 100 parts by weight of silica is blended with respect to 100 parts by weight of the above blended rubber component as a reinforcing agent. . If the amount of silica is small, the expected wet performance cannot be exhibited, and if the amount of silica is too large, kneading becomes difficult. The preferred amount of silica is 60 to 90 parts by weight per 100 parts by weight of the total weight of the rubber component. As the silica, various types of silica can be used, and the use of precipitated silica is particularly preferable. In addition, it is preferable to use the silica and carbon black in combination, and in that case, the total amount is preferably 60 to 100 parts by weight per 100 parts by weight of the rubber component, and N ₂ SA is 100 to 300 m ² / g are preferably used.
[0009]
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.
[0010]
【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.
[0011]
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, this 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 wear resistance test. 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.
[0012]
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 observed.
2 points: A state in which the silica is uniformly dispersed, but visible defective silica lump is scattered at 10 to 100/10 cm ² .
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.
[0013]
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 the processability was 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 good, and it comes out of the mixer easily.
3 points: Slightly adhered to the inside of the mixer, but came out of the mixer naturally.
2 points: A state in which it comes into close contact with the mixer and can be taken out of the mixer in a separated state.
1 point: completely adhered to one side inside the mixer, and does not come out of the mixer naturally.
[0014]
3) Abrasion resistance: The wear loss was measured using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho) at a temperature of 20 ° C. and a slip rate of 50%. The larger the value, the better the wear resistance.
[0015]
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.
[0016]
Examples 1-2 and Comparative Examples 1-6
Table 1 shows the results.
[Table 1]

[0017]
【The invention's effect】
From the above results, it can be seen that the rubber composition containing a large amount of silica of the present invention has good silica dispersibility and mixing processability, and has excellent wear resistance and wet braking. Therefore, this rubber composition is extremely useful as a rubber composition for a tire tread.

Claims

A styrene-butadiene copolymer having a styrene content of 20 to 40% by weight, a vinyl content of 30 to 75% by weight, a weight average molecular weight of 500,000 to 1,500,000 and a glass transition temperature of -40 to -20 ° C. 30 to 60 parts by weight of united rubber (SBR), 10 to 30 parts by weight of natural rubber (NR) or polyisoprene rubber (IR), 25 to 45 parts by weight of butadiene rubber (BR), and 100 parts by weight of these rubber components A rubber composition for a tire tread containing 50 to 100 parts by weight of silica, wherein the BR is a high molecular weight BR having a weight average molecular weight of 500,000 to 1,000,000 and a weight average molecular weight of 6,000 to 60, 000 low molecular weight BR is pre-blended in a solvent, and the low molecular weight BR is contained in 20 to 40% by weight of the total BR amount. Tire tread rubber composition for that.

_2. The tire tread according to claim 1, wherein the silica has an N ₂ SA of 100 to 300 m ² / g, and the total amount of the silica and carbon black is 60 to 100 parts by weight per 100 parts by weight of the rubber component. Rubber composition.