JP2011144322A - Rubber composition for base tread and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tread, which can be improved well balancedly in rolling resistance characteristics and extrusion processability; and to provide a pneumatic tire having the tread fabricated using the same. <P>SOLUTION: The rubber composition for a base tread contains rubber components of a natural rubber and butadiene rubber whose total content is ≥80 mass%, a liquid resin whose softening point is -20 to 20°C, and carbon black and/or silica, wherein with respect to 100 pts.mass of the rubber components, the content of the liquid resin is 1 to 6 pts.mass, and the total content of the carbon black and the silica is ≤55 pts.mass. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a rubber composition for a base tread and a pneumatic tire using the same.

In recent years, in pneumatic tires, in order to reduce rolling resistance, tire blending design that suppresses tire energy loss and improves rolling resistance characteristics has been performed.

As a method for improving rolling resistance characteristics, for example, a method of reducing the blending amount of reinforcing agents such as carbon black and silica is known. However, when the amount of the reinforcing agent is reduced, the shape of the rubber composition is not stable, and the extrusion processability tends to deteriorate.

As a method for suppressing the deterioration of the extrusion processability, a method of blending oil or solid resin is known. However, when oil or a solid resin is blended, rolling resistance characteristics tend to deteriorate.

Thus, rolling resistance characteristics and extrusion processability are in a contradictory relationship, and a method for improving both performances in a well-balanced manner has been desired.

Patent Document 1 proposes to improve the grip performance and wear resistance in a well-balanced manner using an indene resin having a melting point of 100 to 150 ° C., and Patent Document 2 tackifies coumarone indene resin or the like. It has been proposed to improve grip performance as an agent. However, in these documents, it has not been studied to improve the rolling resistance characteristics and the extrusion processability in a balanced manner.

JP 2006-124601 A JP 2001-240704 A

An object of the present invention is to solve the above problems and provide a rubber composition for a tread that can improve the rolling resistance characteristics and extrusion processability in a well-balanced manner, and a pneumatic tire having a tread produced by using the rubber composition.

The present invention contains a rubber component having a total content of natural rubber and butadiene rubber of 80% by mass or more, a liquid resin having a softening point of -20 to 20 ° C., carbon black and / or silica, and The present invention relates to a rubber composition for a base tread in which the content of the liquid resin is 1 to 6 parts by mass and the total content of the carbon black and the silica is 55 parts by mass or less with respect to 100 parts by mass of the rubber component.

The content of the silica in the total content of the carbon black and the silica of 100% by mass is preferably 40% by mass or more.

The present invention also relates to a pneumatic tire having a base tread produced using the rubber composition.

According to the present invention, rubber in which a predetermined amount of liquid resin having a specific softening point and carbon black and / or silica is blended with a rubber component having a total content of natural rubber and butadiene rubber of a certain level or more. Since it is a composition, a rolling resistance characteristic and extrusion processability are obtained with good balance. Therefore, by using the rubber composition for the base tread, a pneumatic tire having good rolling resistance characteristics and easy to manufacture can be provided.

The present invention provides a liquid resin having a specific softening point and carbon black and / or silica for a rubber component having a total content of natural rubber (NR) and butadiene rubber (BR) of a certain level or more. It is a rubber composition containing a fixed amount. By using these components in combination, rolling resistance characteristics and extrusion processability can be obtained in a well-balanced manner.

The rubber composition of the present invention contains NR and / or BR as a rubber component. Thereby, rolling resistance characteristics can be improved. Moreover, it is preferable to use NR from the point that favorable mechanical strength and extrusion processability are obtained. Furthermore, it is preferable to use NR and BR together from the standpoint that rolling resistance characteristics and extrusion processability can be obtained in a well-balanced manner, and that good crack growth resistance can also be obtained. In addition, it does not specifically limit as NR and BR, A thing common in a tire industry can be used.

The content of NR in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 50% by mass or more, and still more preferably 80% by mass or more. If it is less than 20% by mass, the rolling resistance characteristics and the extrusion processability may not be obtained in a well-balanced manner. In addition, the mechanical strength may not be sufficiently improved. The NR content is preferably 95% by mass or less, more preferably 90% by mass or less. If it exceeds 95% by mass, the BR content decreases, and sufficient crack growth resistance may not be obtained.

The content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more. If it is less than 5% by mass, sufficient crack growth resistance may not be obtained. The BR content is preferably 50% by mass or less, more preferably 40% by mass or less, and still more preferably 30% by mass or less. If it exceeds 50% by mass, the NR content decreases, and there is a possibility that the rolling resistance characteristics and the extrusion processability cannot be obtained in a well-balanced manner. In addition, the mechanical strength may not be sufficiently improved.

The total content of NR and BR in 100% by mass of the rubber component is 80% by mass or more, preferably 85% by mass or more, and more preferably 90% by mass or more. If it is less than 80% by mass, sufficient rolling resistance characteristics may not be obtained. In addition, the upper limit of the total content of NR and BR is not particularly limited, and may be 100% by mass.

The rubber composition of the present invention may use rubber components other than NR and BR. For example, epoxidized natural rubber (ENR), styrene butadiene rubber (SBR), isoprene rubber (IR), ethylene-propylene- Tire industry such as diene rubber (EPDM), butyl rubber (IIR), halogenated butyl rubber (X-IIR), chloroprene rubber (CR), acrylonitrile (NBR), halide of copolymer of isomonoolefin and paraalkyl styrene Common ones can be used.

The rubber composition of the present invention contains a liquid resin having a specific softening point. The liquid resin has a softening point lower than that of the solid resin, and is liquid at 70 ° C., which is considered to have a correlation in rolling resistance characteristics. Therefore, it is considered that when a liquid resin is blended, the polymer becomes easy to move, energy loss is reduced, and rolling resistance characteristics are improved.

Examples of the liquid resin include liquid petroleum-based or coal-based resins such as liquid coumarone indene resin, liquid indene resin, liquid α-methylstyrene resin, liquid vinyltoluene resin, and liquid polyisopentane resin. Among these, liquid coumarone indene resin is preferable from the viewpoint that the rolling resistance of the rubber composition using both NR and BR can be reduced.

The softening point of the liquid resin is −20 ° C. or higher, preferably −5 ° C. or higher, more preferably 0 ° C. or higher. When the temperature is lower than -20 ° C, the viscosity of the liquid resin becomes too low, and the kneadability with the rubber component tends to deteriorate. The softening point of the liquid resin is 20 ° C. or lower, preferably 19 ° C. or lower, more preferably 17 ° C. or lower. When it exceeds 20 ° C., energy loss increases and rolling resistance characteristics tend to deteriorate.
In this specification, the softening point is a temperature at which a sphere descends when the softening point defined in JIS K 6220 is measured with a ring and ball softening point measuring device.

Content of the said liquid resin is 1 mass part or more with respect to 100 mass parts of rubber components, Preferably it is 2 mass parts or more. If it is less than 1 part by mass, rolling resistance characteristics may not be sufficiently improved. Moreover, content of the said liquid resin is 6 mass parts or less, Preferably it is 5 mass parts or less. When the amount exceeds 6 parts by mass, the effect of improving the extrudability increases, while the rolling resistance characteristic tends to deteriorate.

The rubber composition of the present invention contains carbon black and / or silica as a reinforcing agent. Thereby, reinforcement is obtained and good extrudability can be secured.

Carbon black is not particularly limited, and those generally used in the tire industry such as SAF, ISAF, HAF, FF, GPF can be used.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 30 m ² / g or more, more preferably 50 m ² / g or more. If it is less than 30 m ² / g, there is a possibility that sufficient reinforcing properties cannot be obtained. Also, _N 2 SA of carbon black is preferably 120 m ² / g, more preferably at most ^{80 m} 2 / g. When it exceeds 120 m ² / g, the viscosity of the unvulcanized rubber composition increases, and the kneadability tends to deteriorate.
The N ₂ SA of carbon black is determined by the A method of JIS K6217.

The silica is not particularly limited, and those generally used in the tire industry such as wet method silica (hydrous silica) and dry method silica (anhydrous silica) can be used.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 80 m ² / g or more, more preferably 120 m ² / g or more, and further preferably 150 m ² / g or more. If it is less than 80 m ² / g, there is a possibility that sufficient reinforcing properties cannot be obtained. Further, N ₂ SA of silica is preferably 250 m ² / g or less, more preferably 200 m ² / g or less. When it exceeds 250 m ² / g, the viscosity of the unvulcanized rubber composition increases, and the kneadability tends to deteriorate.
The _N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

When the rubber composition of the present invention contains silica, the content of silica is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and further preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. It is. If the amount is less than 10 parts by mass, a sufficient reinforcing effect may not be obtained. The silica content is preferably 55 parts by mass or less. If it exceeds 55 parts by mass, the viscosity of the unvulcanized rubber composition increases, and the kneadability may deteriorate. Further, the rolling resistance characteristics may be deteriorated.

When carbon black is contained in the rubber composition of the present invention, the carbon black content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 20 parts by mass with respect to 100 parts by mass of the rubber component. More than a part. If it is less than 5 parts by mass, a sufficient reinforcing effect may not be obtained. The carbon black content is preferably 55 parts by mass or less, and preferably 40 parts by mass or less. When it exceeds 55 mass parts, there exists a tendency for a rolling resistance characteristic to deteriorate.

The total content of silica and carbon black is 55 parts by mass or less, preferably 45 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 35 parts by mass or less with respect to 100 parts by mass of the rubber component. If the amount exceeds 55 parts by mass, the rolling resistance characteristics may be deteriorated, and the rolling resistance characteristics and the extrusion processability may not be compatible. The total content is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and further preferably 25 parts by mass or more. If the amount is less than 10 parts by mass, sufficient extrudability may not be ensured.

The content of silica in the total content of 100% by mass of silica and carbon black is preferably 40% by mass or more. If it is less than 40% by mass, the effect of blending silica may not be sufficiently obtained.

Silica is preferably used in combination with a silane coupling agent. As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, sulfide systems such as bis (3-triethoxysilylpropyl) tetrasulfide, 3 -Mercapto type such as mercaptopropyltrimethoxysilane, vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type of γ-glycidoxypropyltriethoxysilane, 3-nitropropyltri Examples thereof include nitro compounds such as methoxysilane and chloro compounds such as 3-chloropropyltrimethoxysilane. These may be used alone or in combination of two or more. Among these, sulfide type is preferable, and bis (3-triethoxysilylpropyl) tetrasulfide is more preferable.

The content of the silane coupling agent is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and further preferably 4 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 1 part by mass, sufficient rubber strength may not be ensured. Further, the content of the silane coupling agent is preferably 20 parts by mass or less, more preferably 10 parts by mass or less. When it exceeds 20 parts by mass, there is a tendency that an effect commensurate with the increase in cost cannot be obtained.

In addition to the above components, the rubber composition of the present invention requires compounding agents conventionally used in the rubber industry, such as stearic acid, antioxidants, anti-aging agents, vulcanization accelerators, waxes, softeners and the like. You may mix according to.

The liquid resin has an action of softening the rubber composition. Therefore, by using the above liquid resin, the amount of oil in the rubber composition can be reduced, and performance degradation (increased rolling resistance, etc.) due to the oil can be prevented.

The oil content is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, still more preferably 3.5 parts by mass or less, and particularly preferably 3.2 parts by mass or less with respect to 100 parts by mass of the rubber component. is there. The oil content may be 0 part by mass (not contained).

Using the rubber composition of the present invention, the pneumatic tire of the present invention can be produced by an ordinary method. That is, it can be produced by producing a base tread using the rubber composition, pasting together with other members, and heating and pressing on a tire molding machine.

The pneumatic tire of the present invention can be used for passenger cars, trucks, buses and the like.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: RSS # 3
BR: BR150B manufactured by Ube Industries, Ltd.
SBR: SBR1502 manufactured by JSR Corporation
Carbon black: N351 (N ₂ SA: 69 m ² / g) manufactured by Cabot Japan
Silica: Ultrasil VN3 (N ₂ SA: 175 m ² / g) manufactured by Degussa Corporation
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Oil: Diana Process AH-24 manufactured by Idemitsu Kosan Co., Ltd.
Solid Resin: Exxon Chemical Co. of Escorez 1102 _{(C 5} resin, softening point: 97 to 103 ° C.)
Liquid resin: Novares C10 manufactured by Rutgers Chemicals (liquid coumarone indene resin, softening point: 5 to 15 ° C.)
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Anti-aging agent: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Zinc oxide: Zinc oxide sulfur manufactured by Mitsui Mining & Smelting Co., Ltd .: Powder sulfur vulcanization accelerator manufactured by Karuizawa Sulfur Co., Ltd. NS: Noxeller NS manufactured by Ouchi Shinsei Chemical Co., Ltd.

Examples 1-3 and Comparative Examples 1-8
In accordance with the formulation shown in Table 1, a chemical other than sulfur and a vulcanization accelerator was kneaded using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded using an open roll to obtain an unvulcanized rubber composition. Furthermore, the obtained unvulcanized rubber composition was press vulcanized at 150 ° C. for 30 minutes using a 2 mm thick mold to obtain a vulcanized rubber sheet.

The following evaluation was performed using the unvulcanized rubber composition and the vulcanized rubber sheet. The results are shown in Table 1.

(Rolling resistance index)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of the vulcanized rubber sheet was measured under the conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2%. The resistance index was set to 100, and the index was displayed by the following calculation formula. The larger the index, the better the rolling resistance characteristics.
(Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Extrudability)
The ease of passing through the roll of the unvulcanized rubber composition and the rubber skin (surface shape) after extrusion were visually observed and evaluated on a 5-point scale. The closer to 5, the better the extrudability.

From Table 1, the Example which mix | blended the predetermined amount of liquid resin was favorable in rolling resistance characteristic and extrusion processability rather than the corresponding comparative example, respectively.

In Comparative Example 2, the rolling resistance characteristic was improved by reducing the amount of carbon black from the formulation of Comparative Example 1, but the extrusion processability was deteriorated.

In Comparative Example 3, the extrusion processability was improved by substituting part of the oil with the solid resin from the formulation of Comparative Example 2, but the rolling resistance characteristic was deteriorated.

In Comparative Example 4, the extrusion processability was improved by increasing the amount of oil from the formulation of Comparative Example 2, but the rolling resistance characteristics were deteriorated.

In Comparative Example 5, since the content of carbon black was large, the rolling resistance characteristics were not improved even when a liquid resin was blended, and the extrusion processability was also deteriorated.

In Comparative Example 6, the extrusion processability was improved because the liquid resin content was large, but the rolling resistance characteristics were deteriorated.

In Comparative Example 7, the extrusion processability was improved by substituting BR with SBR from the formulation of Comparative Example 2, but the rolling resistance characteristics deteriorated.

In Comparative Example 8, rolling resistance characteristics were improved by replacing carbon black with silica from the formulation of Comparative Example 1, but extrudability deteriorated.

Claims (3)

A rubber component having a total content of natural rubber and butadiene rubber of 80% by mass or more, a liquid resin having a softening point of -20 to 20 ° C., carbon black and / or silica,
A rubber composition for a base tread, wherein the content of the liquid resin is 1 to 6 parts by mass and the total content of the carbon black and the silica is 55 parts by mass or less with respect to 100 parts by mass of the rubber component. The rubber composition for a base tread according to claim 1, wherein a content of the silica in a total content of 100% by mass of the carbon black and the silica is 40% by mass or more. A pneumatic tire having a base tread produced using the rubber composition according to claim 1.