JP2003291610A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of improving drive property (maneuvering stabilizing performance and ride comfort performance) without increasing rolling resistance. <P>SOLUTION: In the pneumatic tire having two layer structure tread comprising a cap tread section and a base tread section, (A) the base tread section comprises solution polimerization butadiene rubber, whose coupling ratio by tin tetrachloride out of rubber components is 25% or more, and molecular weight distribution MW/Mn is 1.2 to 3.0, of 10 to 80 wt.% arranged and a rubber composition, wherein complex modulus of elasticity E* is 5.0 to 8.0 MPa at 70°C and tanδ is 0.12 or less at 70°C, and (B) the cap tread section comprises a rubber composition wherein silica of 40 pts.wt. to rubber component of 100 pts.wt. or more is arranged and complex modulus of elasticity E* is 4.0 to 6.0 MPa at 70°C and tanδ is 0.08 to 0.20 at 70°C. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire. More specifically, while maintaining low fuel consumption performance,
The present invention relates to a pneumatic tire capable of improving a running characteristic. 2. Description of the Related Art In recent years, social demands for reducing fuel consumption of automobiles have increased, and technology for reducing rolling resistance of tires has been actively developed. [0003] On the other hand, various techniques for improving the kinetic characteristics of tires in order to improve the steering stability and riding comfort of vehicles are also known. [0004] In order to reduce the rolling resistance of a tire, there is generally used a technique of using a cap / base two-layer tread in which a tread rubber is formed into a two-layer structure and a lower fuel consumption compound is used for a base tread than a cap tread. However, the purpose of using the base rubber is mainly to reduce the rolling resistance of the tire, so that little consideration is given to the influence on the driving characteristics such as the steering stability and the riding comfort of the vehicle. [0005] For example, Japanese Patent Application Laid-Open No. 7-109384 discloses that a specific diene rubber and carbon black are used in a base tread to improve fuel economy and processability. Is not considered. Further, in order to improve the running characteristics of the tire, Japanese Patent Application Laid-Open No. 10-297214 discusses improving the steering stability of a vehicle by examining the hardness of a base rubber. However, a specific method for reducing the rolling resistance is not clear and insufficient. SUMMARY OF THE INVENTION It is an object of the present invention to provide a vehicle having a motor characteristic (steering stability, steering stability, etc.) without increasing rolling resistance.
An object of the present invention is to provide a pneumatic tire that can improve ride comfort. [0008] As a result of investigations to solve the above problems, a hard base rubber using solution-polymerized butadiene rubber (BR) having a low cis component content and silica were sufficiently filled. The problem was solved by using a tread having a two-layered cap / base structure using a soft cap tread for a tire, thereby achieving the present invention. That is, the present invention relates to a pneumatic tire having a tread having a two-layer structure comprising a cap tread portion and a base tread portion, wherein (A) the base tread portion is coupled with tin tetrachloride in a rubber component. Ratio is 25% or more, and the molecular weight distribution Mw / Mn is 1.2
A solution-polymerized butadiene rubber having a complex elastic modulus E ^* of 5.0 to 3.0 at 70 ° C. is 5.0 to 3.0% by weight.
(B) The cap tread portion is obtained by mixing 40 parts by weight or more of silica with respect to 100 parts by weight of the rubber component, at 80 ° C. and at 70 ° C. 3. The complex elastic modulus E ^* is 4.
0 to 6.0 MPa, tan δ at 70 ° C. is 0.08
The present invention relates to a pneumatic tire comprising a rubber composition having a particle size of about 0.20. [0010] The pneumatic tire of the present invention comprises:
The tread has a two-layer structure of (A) a base tread portion and (B) a cap tread portion. The rubber component of the base rubber in the base tread portion (A) contains 10 to 80% by weight of solution-polymerized butadiene rubber (BR) in the rubber component. 10
If it is less than the weight%, the effect of lowering the heat generation of the compound is small,
On the other hand, when the content exceeds 80% by weight, the rubber material of the unvulcanized rubber deteriorates, and the processability decreases. The solution polymerized BR is preferably contained in the rubber component in an amount of 20 to 70% by weight, more preferably 30 to 60% by weight. The coupling ratio of the solution-polymerized BR with tin tetrachloride is 25% or more. The coupling rate is
It refers to the ratio of the polymer having a tin-butadienyl bond at the reactive end to the total polymer. In addition, the molecular weight distribution Mw of the solution polymerized BR
/ Mn is 1.2 to 3.0. Mw of the molecular weight distribution is
Represents weight average molecular weight, Mn represents number average molecular weight. The solution polymerization BR is prepared by mixing an organic solvent such as n-hexane, cyclohexane, and tetrahydrofuran with butadiene and, for example, using a lithium-based polymerization initiator such as alkyllithium to obtain a desired polymerization temperature, It can be obtained by a usual method of polymerizing in a time and coupling the obtained polymer using a coupling agent. The rubber components other than the solution polymerized BR include:
Although it is not particularly limited as long as it is a diene rubber generally used in tires, natural rubber (NR), isoprene rubber (IR), styrene butadiene rubber ( SBR), and blends thereof. Particularly, natural rubber is preferred. The reinforcing agent to be added to the rubber composition (base rubber composition) of the base tread portion (A) is not particularly limited, but in order to exhibit low fuel consumption performance, the amount of adsorbed iodine is 30 to 100 mg I _2. Of carbon black can be added. Specifically, HAF or FE
It is preferable to mix F-class carbon black and silica. When the carbon black is compounded in the base rubber composition, the compounding amount of the carbon black is preferably 30 to 70 parts by weight based on 100 parts by weight of the rubber component. If the compounding amount of carbon black is less than 30 parts by weight, the reinforcing property of the carbon black tends to be inferior, and if it exceeds 70 parts by weight, the viscosity of the unvulcanized rubber increases, and the moldability tends to deteriorate. is there. In addition to the base rubber composition, other additives generally used in tires, for example, wax, antioxidant, stearic acid, zinc oxide, aroma oil, vulcanizing agent, vulcanization accelerator, etc. are appropriately added. Can be blended. Regarding the viscoelastic properties of the base rubber composition after vulcanization, the complex elastic modulus E ^{* at} 70 ° C. is 5.0.
８8.0 MPa. When E ^* is 5.0 or less, the tire's kinetic characteristics, particularly the initial response of handling, are inferior.
On the other hand, if it is larger than 8.0 MPa, the riding comfort is reduced. More preferably, it is 5.25 to 7.75 MPa, and still more preferably, it is 5.50 to 7.5 MPa. [0020] Further, after vulcanization of the base rubber composition, 7
The loss coefficient tan δ at 0 ° C. is 0.12 or less. If tan δ exceeds 0.12, the effect of reducing the rolling resistance of the tire is lost. Preferably it is 0.10 or less, more preferably 0.08 or less. As long as the durability and other performances of the tire are not adversely affected, there is no lower limit of the value of tan δ, and a smaller value is preferable. The rubber component of the cap rubber composition in the cap tread portion (B) is not particularly limited as long as it can maintain various properties such as rolling resistance, grip performance and wear resistance as a tread for passenger cars. For example, NR,
IR, BR, SBR and blends thereof are preferred. As a reinforcing agent for the cap rubber composition,
By filling 40 parts by weight or more of silica with respect to 100 parts by weight of the rubber component of the cap rubber composition, both the rolling resistance and the grip performance are compatible. The amount of silica is 4
If the amount is less than 0 parts by weight, the wet grip performance is particularly deteriorated. The silica is preferably blended in an amount of 50 parts by weight or more. There is no particular upper limit for the amount of silica to be filled. However, if the total amount of silica and the reinforcing agent other than silica exceeds 100 parts by weight, the viscosity of the unvulcanized rubber increases and the moldability and processability of the rubber deteriorate. The total amount of reinforcing agent is preferably less than 95 parts by weight, more preferably less than 90 parts by weight. The cap rubber composition may contain a silane coupling agent in combination with silica.
The silane coupling agent is not particularly limited as long as it is generally used for tires. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (triethoxysilylpropyl) disulfide, triethoxy Silylpropyl isocyanate, vinyltriethoxysilane, vinyltrimethoxysilane, γ
-Methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ- (polyethyleneamino) -propyltrimethoxysilane, N- β-
(Aminoethyl) -γ-aminopropyltrimethoxysilane, N′-vinylbenzyl-N-trimethoxysilylpropylethylenediamine salt and the like. These may be used alone or in combination of two or more. Among these, bis (3-triethoxysilylpropyl) tetrasulfide and the like are preferable from the viewpoint of achieving both the effect of adding the coupling agent and the cost. The amount of the silane coupling agent is preferably 6 to 10% by weight of the amount of the silica. If the amount of the silane coupling agent is less than 6% by weight, the dispersion of silica tends to deteriorate, and the wear resistance of the rubber tends to decrease. If the amount exceeds 10% by weight, the effect of adding the coupling agent is high. And the cost tends to be high. As a filler other than silica, an inorganic filler such as carbon black, clay and calcium carbonate generally used for tires may be blended. When carbon black is blended with the cap rubber composition, the iodine adsorption amount is 80 to 200 mg I
It is preferable to mix the carbon black of No. ₂ . Specifically, it is preferable to mix SAF, ISAF, and HAF class carbon black. When the above carbon black is blended with the cap rubber composition, the blending amount of the carbon black is based on 100 parts by weight of the rubber component of the cap rubber composition.
It is preferably 3 to 50 parts by weight. If the compounding amount of carbon black is less than 3 parts by weight, the reinforcing property of the rubber composition by carbon black tends to be inferior, and if it exceeds 50 parts by weight, the exothermic characteristics of the rubber composition deteriorate and the rolling resistance tends to increase. is there. It is preferable that the cap rubber contains 5 to 30 parts by weight, more preferably 10 to 20 parts by weight of aroma oil based on 100 parts by weight of the rubber component. If the amount of the aroma oil is less than 5 parts by weight, the compounding viscosity tends to increase and the processability tends to deteriorate, and if it exceeds 30 parts by weight, the abrasion resistance tends to deteriorate. The cap rubber composition may further contain additives generally used in tires, for example, wax, antioxidant, stearic acid, zinc oxide, vulcanizing agent,
A vulcanization accelerator or the like can be appropriately compounded. The complex elastic modulus E ^* of the viscoelasticity after vulcanization of the cap rubber composition is 4.0 to 6.0 MPa. If E ^* is less than 4.0, the steering stability of the tire and the abrasion resistance of the rubber deteriorate, and if it exceeds 6.0, the riding comfort decreases. E ^* is preferably 4.25-5.
75, more preferably 4.50 to 5.70. The loss factor tan δ at 70 ° C. after vulcanization of the cap rubber composition is 0.08 to 0.2.
0. If tan δ is less than 0.08, grip performance is poor, and if tan δ exceeds 0.20, rolling resistance increases. Preferably it is 0.08-0.19, More preferably, it is 0.09-0.18. The pneumatic tire of the present invention is manufactured by a usual method. That is, the rubber compositions of the base tread portion (A) and the cap tread portion (B) are kneaded using a normal tire tread processing method, for example, a roll, a Banbury mixer, a kneader, or the like. The obtained rubber composition is extruded into the shape of a two-layer tread portion composed of a base tread portion and a cap tread portion, and is bonded by a usual method on a tire forming machine to form an unvulcanized tire. The unvulcanized tire is vulcanized in a vulcanizer to obtain a tire. In the tread of the pneumatic tire of the present invention, the ratio of the thickness of the base tread portion (A) to the thickness of the cap tread portion (B) is preferably 1/9 to 3/2. When the thickness ratio is less than 1/9, the effect of the base tread of the present invention is not seen, that is, the steering stability tends to be inferior. When the thickness ratio exceeds 3/2, when the tire tread is worn, the base tread is early. The tread is exposed, and the grip performance of the tire tends to decrease quickly. Further, the thickness of the tread of the pneumatic tire of the present invention depends on the size of the target vehicle and the tire, but is preferably 8 to 12 mm. If the thickness is less than 8 mm, the ride comfort tends to deteriorate.
If it exceeds 2 mm, the heat generation of the tire tread increases, and the rolling resistance tends to increase. The pneumatic tire of the present invention is a solution-polymerized butadiene rubber (B) having the above-mentioned properties and having a low cis component content.
By using a tread having a two-layered cap / base structure using a hard base rubber using R) and a soft cap tread sufficiently filled with silica, the rolling characteristics can be improved without increasing the rolling resistance. Stability and riding comfort). EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to only these Examples. The raw materials used in the examples and comparative examples are shown below. NR: RSS # 3 grade SBR1: SBR1502 (Emulsion polymerization SBR) manufactured by Sumitomo Chemical Co., Ltd. (styrene content: 23.5% by weight, vinyl content: 1)
SBR2: NS116R (solution-polymerized SBR) manufactured by Zeon Corporation (styrene content: 20% by weight, vinyl content 60% by weight, glass transition point: -33 ° C) BR1 : BR150B manufactured by Ube Industries, Ltd. (Solution polymerization B
R) (Mw / Mn: 3.3, high cis component content type (cis component content: 96 mol%)) BR2: BR1250 (solution polymerized BR) manufactured by Zeon Corporation (coupling ratio with tin tetrachloride: 30-40
%, Mw / Mn: 1.6 to 1.7, low cis component content type (cis component content: 45 mol%)) Carbon black: N220 manufactured by Mitsubishi Chemical Corporation (Iodine adsorption amount: 118 m)
gI ₂ / g) N351 manufactured by Mitsubishi Chemical Corporation (Iodine adsorption amount: 68 mg)
I ₂ / g) Silica: Degussa Ultrasil VN3 silane coupling agent: Degussa Si-69 Aroma oil: Idemitsu Kosan Co., Ltd. AH40 Antioxidant 6C: Ozonon made of Seiko Chemical Co., 6C wax: Sannoc wax stearic acid manufactured by Ouchi Shinko Chemical Industry Co., Ltd .: Tungsten oxide manufactured by Nippon Oil & Fats Co., Ltd .: Zinc oxide two kinds of sulfur manufactured by Mitsui Mining & Smelting Co., Ltd .: Karuizawa sulfur Powder sulfur vulcanization accelerator NS: Noxeller NS vulcanization accelerator DPG manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Soccinol D manufactured by Sumitomo Chemical Co., Ltd. Examples and Comparative Examples 1-5 Production method of base tread> The raw materials (base) shown in Table 1 were heated to about 150 ° C. using a usual Banbury mixer.
For 5 to 10 minutes. The vulcanizing agent shown in Table 1 was added to the obtained kneaded material, and the mixture was again heated to 90 ° C. using a Banbury mixer.
For 5 to 7 minutes to obtain a rubber composition. After vulcanizing the obtained rubber composition, a viscoelasticity test was performed. Table 1 shows the results. <Production Method of Cap Tread> The raw materials (Base 1) shown in Table 2 were kneaded at about 130 ° C. for 5 to 8 minutes using an ordinary Banbury mixer. Next, the obtained mixture and the raw materials (base 2) shown in Table 2 were kneaded with a Banbury mixer at about 150 ° C. for 3 to 5 minutes. The vulcanizing agent shown in Table 2 was added to the obtained kneaded material, and the mixture was further added at about 90 ° C.
The mixture was kneaded for about 7 minutes to obtain a rubber composition. After vulcanizing the obtained rubber composition, a viscoelasticity test was performed. Table 2 shows the results. Next, Tables 1 and 2 obtained by the above method were used.
The rubber compositions for the base tread and the cap tread described above are extruded into two layers of treads in the combinations shown in Table 3, and a tire of 175 / 65R1482S size Dunlop SP10 is molded and vulcanized by a conventional method to produce a tire. did. The resulting tire has a tread thickness of 10 m
m, the ratio of the thickness of the base tread portion to the thickness of the cap tread portion in the tread was 1/4. Using the obtained tires of Examples and Comparative Examples 1 to 5, tests of rolling resistance and motion characteristics were respectively performed. Table 3 shows test results
Shown in <Test Method> Viscoelasticity test A tire manufactured by the above method was used to measure a width of 4 mm and a length of 40.
A test piece having a thickness of 2 mm and a thickness of 2 mm was cut out, and physical properties (complex elastic modulus E ^* and loss coefficient tan δ) were measured with a viscoelasticity measuring device manufactured by Iwamoto Seisakusho Co., Ltd. The measurement conditions were an initial strain of 10%, a dynamic strain of 2%, a vibration frequency of 10 Hz, and a temperature of 70 ° C. Rolling resistance Using a rolling resistance tester manufactured by Kobe Steel, Ltd., load 3
The vehicle was run under the conditions of 0 N, a tire internal pressure of 200 kPa, and a speed of 80 km / h, and the rolling resistance was measured. The measured value of Comparative Example 1 was indicated by an index with 100 (reference) being taken. The larger the index, the smaller the rolling resistance and the better the fuel economy performance. The 175 / 65R14 size tire produced was prepared with a displacement of 1
A sensory test was carried out by a test driver on an Okayama test course of Sumitomo Rubber Industries, Ltd. attached to a 600 cc vehicle. In particular, the handling response performance and the riding comfort were evaluated relative to each other with the case of Comparative Example 1 as 6 points (reference). The higher the score, the better the performance. In Comparative Example 1 using the base tread having a low complex elastic modulus, the handling response performance was not improved. In Comparative Example 2 using a base tread having a high complex elastic modulus, the rolling resistance was increased and the riding comfort was reduced. In Comparative Example 3 in which BR having a large molecular weight distribution Mw / Mn was used in the base tread portion, the rolling resistance was increased. In Comparative Example 4 using a cap tread portion containing a small amount of silica, the handling response performance was not improved. In Comparative Example 5 in which a cap tread portion having a high complex elastic modulus was used, riding comfort was reduced. The embodiment in which the base tread portion exhibiting a specific complex elastic modulus and molecular weight distribution and the cap tread portion exhibiting a specific complex elastic modulus and sufficiently containing silica are combined without increasing the rolling resistance , Improved handling response performance. [Table 1] [Table 2] [Table 3] According to the present invention, a hard base rubber using a solution-polymerized butadiene rubber (BR) having a low cis content, and a cap / base using a soft cap tread sufficiently filled with silica. By using a tread having a two-layer structure, it is possible to obtain a pneumatic tire having improved motion characteristics (steering stability and riding comfort) without increasing rolling resistance.

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Claims (1)

Claims 1. A pneumatic tire having a tread having a two-layer structure including a cap tread portion and a base tread portion, wherein (A) the base tread portion includes tin tetrachloride in a rubber component. Of a solution-polymerized butadiene rubber having a coupling ratio of 25% or more and a molecular weight distribution Mw / Mn of 1.2 to 3.0 by 10 to 80% by weight.
Complex elastic modulus E ^* at 5.0 ° C is 5.0 to 8.0 MPa, 7
A rubber composition having a tan δ at 0 ° C. of not more than 0.12;
Complex elastic modulus E ^{* at} 70 ° C. of 4.0 to 6.0 MP
a, A pneumatic tire comprising a rubber composition having a tan δ of 0.08 to 0.20 at 70 ° C.