JP4098391B2 - Pneumatic tire - Google Patents

Description

【００２９】
【表２】

【００３０】
次にこれらのキャップゴム体、ベースゴム体を組み合わせてタイヤサイズが１１０／９０−１９でありかつ図１、表３に示すような不整地走行用の自動二輪車用空気入りタイヤを試作し（実施例）、操縦安定性耐久性、耐チャンキング性能をテストした。なお本発明に含まれない不整地走行用の自動二輪車用空気入りタイヤについても併せて試作し（比較例１〜８）性能を比較した。なお比較例１は、トレッド部のゴムを１層構造とした。
テスト方法は次の通りである。
【００３１】
＜操縦安定性能＞
供試タイヤを２５０ｃｃのモトクロス用の自動二輪車の後輪に装着し、広島県グリーンパーク弘楽園のモトクロスコースを約２時間走行し、駆動性、制動性、コントロール性などを総合評価し、ドライバーの官能により比較例１を１００とする指数で評価した。数値が大きいほど良好である。
【００３２】
＜キャップゴムの耐久性＞
操縦安定性テスト後のタイヤのブロックを観察すると、図３に示すようにブロックのエッジが丸く摩耗しているが、このエッジの減り量ａを測定し比較例１を１００とする指数で評価した。数値が大きいほど良好である。
【００３３】
＜耐チャンキング性＞
操縦安定性テスト後のタイヤのブロックを観察し、チャンキングによりブロックが根本からちぎれた数を全体のブロック数に対する比率で調べ、比較例１を１００とする指数で評価した。数値が大きいほど良好である。
テストの結果などを表３に示す。
【００３４】
【表３】

【００３５】
なお表中の＊１〜＊１１は、次の通りである。
＊１ 住友化学製１５０２
＊２ 三菱化学製 ダイヤブラックｌ
＊３ デグサ製 ウルトラシルＶＮ３
＊４ デグサ製 Ｓｉ６９
＊５ フレキシス製 サントフレックス１３
＊６ 大内新興製 サンノックスＮ
＊７ 日本油脂製 ステアリン酸桐
＊８ 三井金属製 酸化亜鉛
＊９ 軽井沢硫黄製 粉末硫黄
＊１０ 大内新興製 ノクセラ−ＣＺ
＊１１ 出光興産製 ダイアナプロセスオイル
【００３６】
テストの結果、実施例のタイヤは、不整地走行時の操縦安定性を向上しつつ耐チャンキング性を高めていることが確認できた。
【００３７】
【発明の効果】
以上説明したように請求項１記載の発明では、不整地走行時の操縦安定性を向上しつつ耐チャンキング性を高めうる。
【００３８】
また請求項２記載の発明では、キャップゴム体の優れた路面グリップ力を活かしつつブロックの内部がＪＩＳＡ硬度が７７°以上の硬度を有するベースゴム体の増厚部にて好的に補強されることにより、さらに耐チャンキング性能が向上しうる。
【図面の簡単な説明】
【図１】本発明の実施の一形態を示す空気入りタイヤの断面図である。
【図２】そのトレッド溝付近の拡大図である。
【図３】ブロックの摩耗状態を示す断面図である。
【符号の説明】
２ トレッド部
３ サイドウォール部
４ ビード部
５ ビードコア
６ カーカス
７ キャップゴム体
９ ベースゴム体
９ａ 層状部
９ｂ 増厚部
Ｔ トレッド溝
Ｂ ブロック[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic tire having improved chunking resistance while improving steering stability when traveling on rough terrain.
[0002]
[Background Art and Problems to be Solved by the Invention]
When driving on rough terrain, such as sand, rocks, and rubble, cracks may occur in the tread of the tire, for example, at the base of the block, and this may grow and cause damage called chunking where the block scatters while driving . When such chunking occurs, the life of the tire is shortened and the road surface grip is suddenly lost, which greatly affects the running performance.
[0003]
Conventionally, in order to prevent such chunking, improvements have been made in the direction of hardening the rubber by increasing the amount of carbon black in the tread rubber or decreasing the oil content.
[0004]
However, if the tread rubber is reinforced so hard, the chunking performance can be expected to improve to some extent, but the tire grip performance is greatly reduced. There was a problem that the performance was greatly reduced.
[0005]
The present invention has been devised in view of the above problems, and the tread portion is composed of a cap rubber body forming a tread surface and a base rubber body disposed on the inner side in the radial direction. The purpose is to provide a pneumatic tire that can improve the anti-chunking performance without deteriorating the steering stability performance, in particular, a pneumatic tire that frequently travels on rough terrain, based on specifying the formulation and physical properties of Yes.
[0006]
[Means for Solving the Problems]
The invention according to claim 1 of the present invention is a pneumatic tire having a carcass extending from a tread portion to a bead core of a bead portion through a sidewall portion, wherein the tread portion is an outer surface of the tread portion. A cap rubber body that forms a surface, and a base rubber body that is disposed on the inner side in the tire radial direction of the cap rubber body. The cap rubber body is composed of silica with respect to 100 parts by weight of the rubber component of the cap rubber body. The total blending amount (α + β) of the amount α and the blending amount β of carbon black is 70 to 120 parts by weight, and the proportion γ of the blending amount α of silica in the total blending amount (α + β) of this silica and carbon black γ (= Α / (α + β)) is 20 to 80%, and further contains 5 to 10% of a silane coupling agent of the amount α of silica, and the base rubber body is It is characterized in that the dynamic storage modulus after curing (E ') is 9.5 (MPa) or more and JISA hardness of 77 ° or more.
[0007]
According to a second aspect of the present invention, the tread portion is provided with a tread groove and a plurality of blocks defined by the tread groove, and the base rubber body extends substantially along the groove bottom surface of the tread groove. 2. The pneumatic tire according to claim 1, further comprising a layered portion and a thickened portion connected to the layered portion and increasing in thickness within the block.
[0008]
In this specification, the dynamic storage elastic modulus (E ′) is obtained by cutting a strip-shaped sample 4 mm wide × 30 mm long × 2 2.0 mm thick and using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. The value measured under the conditions of initial strain 10%, frequency 10 Hz, amplitude 2%, and measurement temperature 70 ° C. is used. The JISA hardness is measured based on the JISK6253 durometer hardness test (type A).
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the pneumatic tire of the present embodiment includes a carcass 6 formed of a carcass ply that is folded and locked around a bead core 5 of a bead portion 4 from a tread portion 2 through a sidewall portion 3. It is.
[0010]
The pneumatic tire of this example is a motorcycle for running on rough terrain used in, for example, motocross and rally where the tread width, which is the distance in the tire axial direction between the edges E of the tread portion 2, forms the maximum tire width. The pneumatic tire for is illustrated.
[0011]
The carcass 6 is composed of, for example, an organic fiber cord, and a carcass ply having a multi-layer bias structure in which the cord is inclined with respect to the tire equator C at an angle of, for example, 30 to 65 °.
[0012]
In the present embodiment, the tread portion 2 has a tread groove T formed deeply and a plurality of blocks B partitioned by the tread groove T, and is configured to transmit a driving force on rough terrain. The tread portion 2 has a two-layer structure including a cap rubber body 7 that forms a tread surface 2a that is an outer surface of the tread portion 2, and a base rubber body 9 that is disposed on the inner side in the tire radial direction of the cap rubber body. The thing is illustrated.
[0013]
In order to improve the grip performance when running on rough terrain in the cap rubber body 9, the present inventors blended the silica blend amount α and carbon black with respect to 100 parts by weight of the rubber component of the cap rubber body 9. The ratio γ (= α / (α + β) of the compounding amount α of silica in the total compounding amount (α + β) with the amount β is 70 to 120 parts by weight and the total compounding amount (α + β) of the silica and carbon black ) Is 20 to 80%, and it was found that it is preferable to contain 5 to 10% of a silane coupling agent with respect to the blending amount α of the silica.
[0014]
First, if the total blending amount (α + β) of the blending amount α of silica and the blending amount β of carbon black is less than 70 parts by weight with respect to 100 parts by weight of the rubber component of the cap rubber body 7, On the other hand, if the total blending amount (α + β) exceeds 120 parts by weight, sufficient heat buildup on running on leveling can not be obtained and the durability decreases. The temperature of the cap rubber body 9 rises due to the history due to strain, and is liable to cause thermal destruction.
[0015]
At this time, if the ratio γ (= α / (α + β)) of the silica blend amount α in the total blend amount (α + β) of silica and carbon black is less than 20%, there is a large difference from the reinforcement by the conventional carbon black. On the other hand, it is difficult to expect improvement in steering stability performance due to silica due to a decrease in road surface grip force. On the other hand, when the ratio γ exceeds 80%, there is a problem in that the fracture characteristics at high temperatures are significantly deteriorated.
[0016]
In other words, silica is difficult to improve dispersion in rubber compared to carbon black, and especially when the proportion γ of silica is increased, it is very difficult to improve dispersion. When the temperature of the rubber becomes high, the fracture characteristics are greatly reduced.
[0017]
Further, the effect of improving the grip by silica requires a sufficient bond with the polymer, and for that purpose, it is necessary to blend a silane coupling agent. And the compounding quantity of this silane cup agent is determined according to the compounding quantity (alpha) of a silica, and it is necessary to set it as 5 to 10% of the compounding quantity (alpha) of a silica in this invention.
[0018]
When the blending amount of the silane coupling agent is less than 5% of the blending amount α of silica, the bond between the silica and the polymer is weak and the grip improvement or reinforcement cannot be effectively exhibited, and conversely exceeds 10%. If blended, the elastic modulus of the rubber will be significantly increased, and the durability will be greatly reduced.
[0019]
Here, as the rubber component, various diene rubbers can be suitably employed. For example, natural rubber (NR), butadiene rubber (BR), so-called emulsion polymerization styrene butadiene rubber (E-SBR), solution polymerization, and the like. Examples include styrene butadiene rubber (S-SBR), synthetic polyisoprene rubber (IR), nitrile rubber (NBR) which is a copolymer of butadiene and acrylonitrile, and chloroprene rubber (CR) which is a polymer of chloroprene. It is preferable to use a rubber obtained by blending one or more of these.
[0020]
The silica has a colloidal characteristic with a nitrogen adsorption specific surface area (BET) in the range of 100 to 250 m ² / g and a dibutyl phthalate (DBP) oil absorption of 150 ml / 100 g or more. In view of rubber processability and the like. Silica having improved dispersibility can also be suitably employed.
[0021]
As the carbon black, various commercially available carbon blacks can be used. Further, as the silane coupling agent, for example, bis (triethoxysilylpropyl) tetrasulfide and α-mercaptopropyltrimethoxysilane are suitable.
[0022]
The base rubber body 9 disposed on the inner side in the radial direction of the cap rubber body 7 must particularly improve the anti-chunking performance. It was found that the storage elastic modulus (E ′) is required to be 9.5 (MPa) or higher and the JISA hardness is 77 ° or higher.
[0023]
When the dynamic storage elastic modulus (E ′) of the base rubber body 9 is less than 9.5 (MPa) or the JISA hardness is less than 77 °, it is difficult to improve the anti-chunking performance. Become. The dynamic storage elastic modulus (E ′) of the base rubber body 9 is preferably in the range of 9.5 to 12.0, and the JISA hardness is preferably in the range of 77 to 88.
[0024]
The dynamic elastic modulus (E ') and JISA hardness of the cap rubber body 7 are preferably smaller than that of the base rubber body in order to increase the grip force on the road surface.
[0025]
In the present embodiment, the base rubber body 9 has a layered portion 9a extending substantially along the groove bottom surface 10 of the tread groove T, and the block B in the block B as shown in FIG. And a preferred embodiment having a thickened portion 9b that increases the thickness in the tire radial direction. Thus, the inside of the block B is particularly effectively reinforced by the thickened portion 9b of the base rubber body 9 having a hardness of 77 ° or more while utilizing the excellent road surface grip force of the cap rubber body 7. This further improves the handling stability and anti-chunking performance when traveling on rough terrain.
[0026]
Further, at the position of the groove bottom surface 10 of the tread groove T, the thickness ratio tc: tb between the cap rubber body 7 and the base rubber body 9 is preferably about 30:70 to 70:30, for example.
[0027]
【Example】
Tables 1 and 2 show the composition of rubber used for the cap rubber body and the base rubber body.
[0028]
[Table 1]

[0029]
[Table 2]

[0030]
Next, by combining these cap rubber body and base rubber body, a pneumatic tire for motorcycles having a tire size of 110 / 90-19 and running on rough terrain as shown in FIG. Eg), steering stability durability, anti-chunking performance was tested. A pneumatic tire for motorcycles on rough terrain that is not included in the present invention was also prototyped (Comparative Examples 1 to 8) and the performance was compared. In Comparative Example 1, the rubber in the tread portion has a single layer structure.
The test method is as follows.
[0031]
<Steering stability>
The test tire is mounted on the 250cc motocross motorcycle, and the motocross course of Hiroshima Green Park Korakuen is run for about 2 hours. The driver's driving performance, braking performance and control performance are comprehensively evaluated. Sensory evaluation was performed using an index with Comparative Example 1 as 100. The larger the value, the better.
[0032]
<Durability of cap rubber>
When the tire block after the steering stability test was observed, the edge of the block was worn round as shown in FIG. 3. The reduction amount a of the edge was measured, and the evaluation was made with an index of Comparative Example 1 being 100. . The larger the value, the better.
[0033]
<Chunking resistance>
The blocks of the tire after the steering stability test were observed, the number of blocks that were torn apart by chunking was examined by the ratio to the total number of blocks, and the index of Comparative Example 1 was set to 100. The larger the value, the better.
Table 3 shows the test results.
[0034]
[Table 3]

[0035]
In the table, * 1 to * 11 are as follows.
* 1 1502 made by Sumitomo Chemical
* 2 Diamond Black 1 manufactured by Mitsubishi Chemical
* 3 Degussa Ultrasil VN3
* 4 Degussa Si69
* 5 Santoflex 13 made by Flexis
* 6 Sannox N
* 7 Made by Nippon Oil & Fats, Stearic Acid Tungsten * 8 Made by Mitsui Metals Zinc Oxide * 9 Made by Karuizawa Sulfur Powdered Sulfur * 10 Emerging Ouchi Noxera-CZ
* 11 Diana process oil manufactured by Idemitsu Kosan Co., Ltd. [0036]
As a result of the test, it was confirmed that the tires of the examples had improved chunking resistance while improving steering stability during running on rough terrain.
[0037]
【The invention's effect】
As described above, according to the first aspect of the present invention, the anti-chunking property can be improved while improving the steering stability when traveling on rough terrain.
[0038]
In the invention according to claim 2, the inside of the block is favorably reinforced by the thickened portion of the base rubber body having a JIS hardness of 77 ° or more while utilizing the excellent road surface grip force of the cap rubber body. As a result, the anti-chunking performance can be further improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a pneumatic tire showing an embodiment of the present invention.
FIG. 2 is an enlarged view of the vicinity of the tread groove.
FIG. 3 is a sectional view showing a worn state of a block.
[Explanation of symbols]
2 Tread portion 3 Side wall portion 4 Bead portion 5 Bead core 6 Carcass 7 Cap rubber body 9 Base rubber body 9a Layered portion 9b Thickened portion T Tread groove B Block

Claims (2)

A pneumatic tire having a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion,
The tread portion includes a cap rubber body that forms a tread surface that is an outer surface of the tread portion, and a base rubber body that is disposed on the inner side in the tire radial direction of the cap rubber body,
The cap rubber body has a total blending amount (α + β) of 70 to 120 parts by weight of the blending amount α of silica and the blending amount β of carbon black with respect to 100 parts by weight of the rubber component of the cap rubber body.
And the ratio γ (= α / (α + β)) of the blending amount α of silica in the total blending amount (α + β) of the silica and carbon black is 20 to 80%, and 5 to 5 of the blending amount α of the silica. Containing 10% silane coupling agent,
The pneumatic rubber characterized in that the base rubber body has a dynamic storage elastic modulus (E ′) after vulcanization of 9.5 (MPa) or more and a JISA hardness of 77 ° or more. The tread portion is provided with a tread groove and a plurality of blocks defined by the tread groove,
2. The air according to claim 1, wherein the base rubber body has a layered portion extending substantially along the groove bottom surface of the tread groove, and a thickened portion connected to the layered portion and increasing in thickness in the block. Enter tire.

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