JP5346357B2 - Sidewall rubber composition and pneumatic tire - Google Patents

Description

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

In recent years, a rubber composition used for a sidewall of an automobile tire is required to have excellent fuel efficiency. As a method for improving fuel economy, a method using a butadiene rubber modified with a modifier, a neodymium catalyst high cis BR or a hybrid crosslinking agent is known.

On the other hand, steering stability and ride comfort are also required for the sidewall. In general, steering stability is superior as the complex elastic modulus E * is higher, and riding comfort is better as the complex elastic modulus E * is lower. Therefore, steering stability and riding comfort are in a trade-off relationship.

It is known to use fine fibers such as polyethylene terephthalate, fine paper fiber, and aramid fiber as a method for obtaining a good balance between driving stability and ride comfort, but the fine fibers are not bonded to the rubber matrix. Therefore, it may become a starting point of notch or fracture, and there is a problem in terms of crack growth resistance.

In addition, a high-viscosity high cis-butadiene rubber is usually used for the sidewall, but there is a problem in fuel efficiency due to poor processability and poor filler dispersion. As described above, it is difficult to improve the fuel efficiency, the handling stability, the riding comfort and the workability at the same time in a well-balanced manner.

Patent Document 1 proposes a method for improving fuel economy, crack growth resistance, and the like by using butadiene rubber, natural rubber, or the like containing 1,2-syndiotactic polybutadiene crystals. There is still no technology that satisfies the handling stability, ride comfort and processability at the same time.

JP 2006-63143 A

An object of the present invention is to solve the above-mentioned problems and to provide a rubber composition that can improve fuel economy, handling stability, riding comfort and processability in a well-balanced manner, and a pneumatic tire using the rubber composition.

The present invention includes a butadiene rubber containing 1,2-syndiotactic polybutadiene crystals, a terminal-modified butadiene rubber, an isoprene-based rubber, and a resin, and the 1,2-syndiotactic polybutadiene crystals in 100% by mass of the rubber component. A sidewall comprising a rubber composition having a butadiene rubber content of 10 to 60% by mass, a content of the terminal-modified butadiene rubber of 7 to 60% by mass, and a content of the isoprene-based rubber of 20 to 70% by mass. It relates to a pneumatic tire having

The sidewall has a ratio (E * a / E * b) of the complex elastic modulus E * a in the tire circumferential direction and the complex elastic modulus E * b in the tire radial direction measured at a temperature of 70 ° C. and a dynamic strain of 2%. It is preferable that it is 1.03-2.0. The sidewall preferably has a tan δ measured at a temperature of 70 ° C. and a dynamic strain of 2% of less than 0.125.

The content of butadiene rubber containing 1,2-syndiotactic polybutadiene crystals in 100% by mass of the rubber component is 10 to 40% by mass, the content of the terminal-modified butadiene rubber is 25 to 50% by mass, and the isoprene-based The rubber content is preferably 30 to 60% by mass.
Moreover, it is preferable that the said terminal modified butadiene rubber is a tin terminal modified butadiene rubber, and the said rubber composition contains 1.61-2.3 mass parts of sulfur with respect to 100 mass parts of said rubber components.
The rubber composition contains carbon black having a nitrogen adsorption specific surface area of 25 to 120 m ² / g and / or silica having a nitrogen adsorption specific surface area of 80 to 240 m ² / g, and 100 parts by mass of the rubber component, The total content of the carbon black and the silica is preferably 20 to 40 parts by mass.

According to the present invention, since it is a pneumatic tire having a sidewall made of a rubber composition containing a 1,2-syndiotactic polybutadiene crystal-containing butadiene rubber, terminal-modified butadiene rubber, isoprene-based rubber, and resin, Fuel economy, handling stability, ride comfort and processability can be improved in a well-balanced manner.

The pneumatic tire of the present invention has a sidewall made of a rubber composition containing a specific amount of 1,2-syndiotactic polybutadiene crystals, a butadiene rubber, a terminal-modified butadiene rubber, an isoprene-based rubber, and a resin.

In the rubber composition constituting the sidewall, as the butadiene rubber containing 1,2-syndiotactic polybutadiene crystal (SPB-containing BR), a general-purpose product in tire production can be used, but the above-mentioned performance is obtained favorably. From this point, it is preferable that 1,2-syndiotactic polybutadiene crystals are chemically bonded to BR and dispersed.

The melting point of the 1,2-syndiotactic polybutadiene crystal is preferably 180 ° C. or higher, more preferably 190 ° C. or higher, and preferably 220 ° C. or lower, more preferably 210 ° C. or lower. If it is less than the lower limit, the effect of improving the steering stability by the SPB-containing BR may not be sufficiently obtained, and if it exceeds the upper limit, the workability tends to deteriorate.

In the SPB-containing BR, the content of 1,2-syndiotactic polybutadiene crystals (the content of boiling n-hexane insoluble matter) is preferably 2.5% by mass or more, more preferably 10% by mass or more. If it is less than 2.5% by mass, the reinforcing effect (E *) may not be sufficient. The content is preferably 20% by mass or less, more preferably 18% by mass or less. When it exceeds 20 mass%, workability tends to deteriorate.

In 100% by mass of the rubber component of the rubber composition, the content of 1,2-syndiotactic polybutadiene crystals derived from SPB-containing BR (content of boiling n-hexane insoluble matter) is preferably 1% by mass or more, More preferably, it is 4 mass% or more, Preferably it is 15 mass% or less, More preferably, it is 10 mass% or less. Within the above range, E * a / E * b, which will be described later, can be adjusted well, and the effects of the present invention can be obtained well.

The content of SPB-containing BR in 100% by mass of the rubber component is 10% by mass or more, preferably 20% by mass or more. If the amount is less than 10% by mass, sufficient crack growth resistance and workability may not be obtained. The content is 60% by mass or less, preferably 40% by mass or less. If it exceeds 60% by mass, sufficient fuel economy may not be obtained.

The terminal-modified butadiene rubber (terminal-modified BR) is not particularly limited, and can be selected according to the type of filler (carbon black, silica, etc.) that can be used. Butadiene rubber (tin-modified BR) and modified butadiene rubber (S-modified BR) modified with a compound represented by the following formula (1) are preferable, and tin-modified BR is more preferable.

（式（１）中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、アルキル基、アルコキシ基、シリルオキシ基、アセタール基、カルボキシル基（−ＣＯＯＨ）、メルカプト基（−ＳＨ）又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子又はアルキル基を表す。ｎは整数を表す。）

(In formula (1), R ¹ , R ² and R ³ are the same or different and are alkyl group, alkoxy group, silyloxy group, acetal group, carboxyl group (—COOH), mercapto group (—SH) or these R ⁴ and R ⁵ are the same or different and each represents a hydrogen atom or an alkyl group, and n represents an integer.

The tin-modified BR is not particularly limited, but a tin-modified BR that is polymerized with a lithium initiator, has a tin atom content of 50 to 3000 ppm, a vinyl content of 5 to 50% by mass, and a molecular weight distribution of 2 or less is preferable.

The tin-modified BR is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and the end of the tin-modified BR molecule is bonded with a tin-carbon bond. It is preferable.

Examples of the lithium initiator include lithium compounds such as alkyl lithium and aryl lithium. Examples of tin compounds include tin tetrachloride and butyltin trichloride.

The tin atom content of the tin-modified BR is 50 ppm or more. If it is less than 50 ppm, tan δ tends to increase. The tin atom content is 3000 ppm or less, preferably 300 ppm or less. If it exceeds 3000 ppm, the processability of the kneaded product tends to deteriorate.

The molecular weight distribution (Mw / Mn) of the tin-modified BR is 2 or less. When Mw / Mn exceeds 2, tan δ tends to increase. The lower limit of the molecular weight distribution is not particularly limited, but is preferably 1 or more.
In the present specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation), detector: differential refractometer, column: It can be determined by standard polystyrene conversion based on the measured value by TSKEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation.

The vinyl content of the tin-modified BR is 5% by mass or more. If it is less than 5% by mass, it is difficult to produce tin-modified BR. The vinyl content is 50% by mass or less, preferably 20% by mass or less. If it exceeds 50% by mass, the dispersibility of carbon black tends to be poor, and the fuel economy and tensile strength tend to decrease.
In the present specification, the vinyl content (1,2-bond butadiene unit amount) can be measured by infrared absorption spectrum analysis.

As said S modified BR, what is described in Unexamined-Japanese-Patent No. 2010-111753 etc. is mentioned.

In the formula (1), an alkoxy group is preferable as R ¹ , R ² and R ^{3 in} terms of obtaining excellent rolling resistance characteristics and breaking strength (preferably having 1 to 8 carbon atoms, more preferably carbon. 1 to 4 alkoxy groups). R ⁴ and R ⁵ are preferably an alkyl group (preferably an alkyl group having 1 to 3 carbon atoms). n is preferably 1 to 5, more preferably 2 to 4, and still more preferably 3. By using a preferable compound, low fuel consumption, handling stability, riding comfort and processability can be obtained in a well-balanced manner.

Specific examples of the compound represented by the formula (1) include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, and 3-dimethylaminopropyltriethoxysilane. 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane, and the like. Of these, 3-dimethylaminopropyltrimethoxysilane, 3-dimethylaminopropyltriethoxysilane, and 3-diethylaminopropyltrimethoxysilane are preferable because the above-described performance can be improved satisfactorily. These may be used alone or in combination of two or more.

As a method for modifying the butadiene rubber with the compound represented by the formula (1), conventionally known methods such as the methods described in JP-B-6-53768 and JP-B-6-57767 can be used. For example, it can be modified by bringing the butadiene rubber into contact with the compound. Specifically, after the preparation of the butadiene rubber by anionic polymerization, a predetermined amount of the compound is added to the rubber solution, and the polymerization terminal of the butadiene rubber (active And the like, and the like.

The vinyl content of the S-modified BR is preferably 35% by mass or less, more preferably 30% by mass or less. If the vinyl content exceeds 35% by mass, fuel efficiency may be reduced. Although the minimum of the said vinyl content is not specifically limited, Preferably it is 1 mass% or more, More preferably, it is 20 mass% or more. If it is less than 1% by mass, heat resistance and deterioration resistance may be lowered.

The weight average molecular weight (Mw) of the S-modified BR is preferably 100,000 or more, more preferably 400,000 or more. If it is less than 100,000, sufficient fracture strength and resistance to bending fatigue may not be obtained. Mw is preferably 2 million or less, more preferably 800,000 or less. If it exceeds 2,000,000, the workability is lowered and poor dispersion is caused, and there is a possibility that sufficient fracture strength cannot be obtained.

The content of the terminal-modified BR in 100% by mass of the rubber component is preferably 7% by mass or more, more preferably 25% by mass or more. If it is less than 7% by mass, sufficient fuel economy may not be obtained. The content is preferably 60% by mass or less, more preferably 50% by mass or less. If it exceeds 60% by mass, the workability tends to decrease.

Examples of the isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), liquid isoprene rubber (L-IR), epoxidized natural rubber (ENR), and the like. The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, ENR25 can be used. Moreover, it does not specifically limit as IR, A general thing can be used in the tire industry. Among them, NR is preferable from the viewpoint that good elongation at break is obtained and roll workability is excellent. Moreover, combined use of NR and IR is more preferable from the viewpoint that superior processability can be obtained.

The content of isoprene-based rubber in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more. If it is less than 20% by mass, the elongation at break may not be sufficiently obtained. The content is preferably 70% by mass or less, more preferably 60% by mass or less. When it exceeds 70 mass%, there exists a possibility that low-fuel-consumption property may fall.

Examples of rubber components that can be used in the rubber composition other than SPB-containing BR, terminal-modified BR, and isoprene-based rubber include, for example, styrene butadiene rubber (SBR), ethylene-propylene-diene rubber (EPDM), butyl rubber (IIR), and halogen. And diene rubbers such as butyl rubber (X-IIR) and chloroprene rubber (CR).

The resin is not particularly limited, but C5 petroleum resin, phenolic resin, and coumarone indene resin are preferred because low fuel consumption, handling stability, riding comfort, and processability can be obtained in a balanced manner.

Examples of the C5 petroleum resin include aliphatic petroleum resins made mainly of olefins and diolefins in the C5 fraction obtained by naphtha cracking.

Examples of phenolic resins include phenolic resins and modified phenolic resins. The phenolic resin is obtained by reacting phenol with aldehydes such as formaldehyde, acetaldehyde, furfural, etc. with an acid or alkali catalyst. The modified phenolic resin includes cashew oil, tall oil, linseed oil, various kinds It is a phenolic resin modified with compounds such as animal and vegetable oils, unsaturated fatty acids, rosin, alkylbenzene resins, aniline, and melamine.

The phenolic resin is preferably a modified phenolic resin, more preferably a cashew oil-modified phenolic resin or a rosin-modified phenolic resin, from the viewpoint that good hardness can be obtained by a curing reaction.

As said cashew oil modified phenol resin, what is shown by following formula (2) can be used conveniently.

In formula (2), p is an integer of 1 to 9 and preferably 5 to 6 in that the reactivity is good and the dispersibility is improved.

Moreover, a non-reactive alkylphenol resin can be suitably used as the phenolic resin. The non-reactive alkylphenol resin refers to an alkylphenol resin having no reactive sites at the ortho position and para position (particularly the para position) of the hydroxyl group of the benzene ring in the chain. Here, as a non-reactive alkylphenol resin, what is shown by following formula (3) or (4) can be used conveniently.

In formula (3), m is an integer. M is preferably 1 to 10 and more preferably 2 to 9 in terms of moderate bloom property. R ⁶ is the same or different and represents an alkyl group, and the number of carbon atoms is preferably 4 to 15 and more preferably 6 to 10 in terms of affinity with rubber.

In formula (4), r is an integer. In terms of moderate bloom property, r is preferably 1 to 10, and more preferably 2 to 9.

As the phenolic resin, a product obtained by reacting an alkylphenol such as butylphenol and an alkyne such as acetylene (condensate) can also be suitably used.

The softening point of the C5 petroleum resin is preferably 50 ° C or higher, more preferably 80 ° C or higher, preferably 150 ° C or lower, more preferably 120 ° C or lower. Within the above range, fuel economy, handling stability, riding comfort and processability can be improved in a well-balanced manner.

The softening point of the phenolic resin is preferably 50 ° C. or higher, more preferably 80 ° C. or higher, preferably 150 ° C. or lower, more preferably 110 ° C. or lower. Within the above range, fuel economy, handling stability, riding comfort and processability can be improved in a well-balanced manner.

The softening point of the coumarone indene resin is preferably −20 ° C. or higher, more preferably 0 ° C. or higher, preferably 60 ° C. or lower, more preferably 35 ° C. or lower, and further preferably 15 ° C. or lower. Within the above range, fuel economy, handling stability, riding comfort and processability can be improved in a well-balanced manner.

In this specification, the softening point is a temperature at which a sphere descends when a softening point defined in JIS K6220: 2001 is measured by a ring and ball softening point measuring apparatus.

The content of the resin is preferably 0.5 parts by mass or more, more preferably 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 0.5 parts by mass, the fuel economy, handling stability, riding comfort and workability may not be improved in a well-balanced manner. Moreover, this content becomes like this. Preferably it is 10 mass parts or less, More preferably, it is 5 mass parts or less, More preferably, it is 2.5 mass parts or less. If it exceeds 10 parts by mass, sufficient fuel economy tends not to be obtained.

The rubber composition preferably contains a curing agent having a curing action such as a phenol resin. The curing agent is not particularly limited as long as it has the curing action described above. For example, hexamethylenetetramine (HMT), hexamethoxymethylol melamine (HMMM), hexamethoxymethylol pantamethyl ether (HMMPME), melamine, methylol. Examples include melamine. Among these, HMT, HMMM, and HMMPME are preferable because they are excellent in the action of increasing the hardness of the phenol resin.

The lower limit of the content of the curing agent is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and the upper limit is preferably 50 parts by mass with respect to 100 parts by mass of the total amount of the phenol resin and the modified phenol resin. Hereinafter, it is more preferably 15 parts by mass or less. If it is less than the lower limit, it may not be sufficiently cured, and if it exceeds the upper limit, the curing may be uneven, and burning may occur during extrusion.

The rubber composition preferably contains carbon black. As a result, good reinforcement can be obtained, and low fuel consumption, handling stability, riding comfort and workability can be obtained in a well-balanced manner.

Nitrogen adsorption specific surface area _(N 2 SA) of carbon black is preferably not less than ^{25 m} 2 / g, more preferably at least ^{30 m} 2 / g, preferably 120 m ² / g or less, more preferably ^{50 m} 2 / g. If it is less than the lower limit, sufficient elongation at break may not be obtained, and if it exceeds the upper limit, fuel economy tends to deteriorate.
Incidentally, _N 2 SA of carbon black, JIS K 6217-2: determined by 2001.

Further, two types of carbon blacks (1) and (2) having different N ₂ SA may be used in combination, thereby significantly improving fuel efficiency and elongation at break. In this case, _N 2 SA is preferably 25~50m ² / g of carbon black (1), _N 2 SA of the carbon black (2) is 100~120m ² / g are preferred. Here, the content of the carbon black (1) is preferably 5 to 30 parts by mass with respect to 100 parts by mass of the rubber component because the above-described improvement effect can be satisfactorily obtained, and the carbon black (2) The content of is preferably 5 to 30 parts by mass.

The content of carbon black (when two types of carbon black are used, the total content thereof) is preferably 10 parts by mass or more, more preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 10 parts by mass, sufficient steering stability may not be obtained. The content is preferably 60 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 30 parts by mass or less. When it exceeds 60 parts by mass, there is a possibility that sufficient low fuel efficiency cannot be obtained.
In addition, since the rubber composition contains the above-described components, even if it is a small amount of carbon black within the above range, good fuel economy, handling stability, riding comfort and processability can be obtained. .

The rubber composition may contain silica. Thereby, low fuel consumption can be improved. Examples of the silica include dry method silica (anhydrous silica), wet method silica (hydrous silica), and the like. Of these, wet-process silica is preferred because it has many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 80 m ² / g or more, more preferably 160 m ² / g or more. If it is less than 80 m ² / g, sufficient fracture strength may not be obtained. Further, N ₂ SA of silica is preferably 240 m ² / g or less, more preferably 220 m ² / g or less. When it exceeds 240 m < ² > / g, it becomes difficult to disperse | distribute a silica and there exists a possibility that workability may deteriorate.
The _N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

The content of silica is preferably 5 parts by mass or more and more preferably 15 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, the effects of reducing tan δ and improving elongation at break by blending silica may not be sufficiently obtained. The silica content is preferably 40 parts by mass or less, more preferably 30 parts by mass or less. If it exceeds 40 parts by mass, the silica is difficult to disperse and the workability may be deteriorated. Moreover, the extrudate may shrink unevenly with cooling after extrusion, and the uniformity may deteriorate.

The rubber composition preferably contains a silane coupling agent together with silica.
As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry, and examples thereof include sulfide systems such as bis (3-triethoxysilylpropyl) disulfide, 3- Mercapto type such as mercaptopropyltrimethoxysilane, vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type of γ-glycidoxypropyltriethoxysilane, 3-nitropropyltrimethoxy Examples thereof include nitro compounds such as silane and chloro compounds such as 3-chloropropyltrimethoxysilane. Among these, sulfide type is preferable, and bis (3-triethoxysilylpropyl) disulfide is more preferable. The content of the silane coupling agent is preferably 1 to 15 parts by mass with respect to 100 parts by mass of silica. Within the above range, fuel economy, handling stability, riding comfort and processability can be improved in a well-balanced manner.

The total content of carbon black and silica is preferably 20 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 20 parts by mass, sufficient steering stability may not be obtained. The total content is preferably 40 parts by mass or less. If it exceeds 40 parts by mass, sufficient fuel economy may not be obtained.

In addition to the components described above, compounding agents conventionally used in the rubber industry, such as oil, zinc white, stearic acid, various anti-aging agents, sulfur, vulcanization accelerators, and the like can be appropriately blended with the rubber composition.

The rubber composition usually contains sulfur. The sulfur content is not particularly limited, but the difference in sulfur concentration from the ply can be appropriately maintained, and good fracture characteristics and the like can be obtained. .3 parts by mass is preferred.
The sulfur content is a pure sulfur content, and when insoluble sulfur is used, it is a content excluding the oil content.

In the sidewall of the pneumatic tire of the present invention, the complex elastic modulus E * a in the tire circumferential direction measured at a temperature of 70 ° C. and a dynamic strain of 2%, and the tire radial direction (radial) measured at a temperature of 70 ° C. and a dynamic strain of 2% The ratio (E * a / E * b) to the complex elastic modulus E * b of (direction) is usually 1.03 to 2.0. By adjusting E * a / E * b within the above range, low fuel consumption, steering stability, riding comfort and workability can be obtained in a well-balanced manner. More preferably, E * a / E * b is adjusted to 1.1 to 2.0.
In the present specification, the tire circumferential direction and the tire radial direction are specifically the directions described in FIG. 1 of JP-A-2009-202865.
In the present specification, E * a and E * b are measured by the method described in Examples described later.

E * a / E * b can be adjusted by the amount of 1,2-syndiotactic polybutadiene crystals derived from SPB-containing BR, the orientation direction of 1,2-syndiotactic polybutadiene crystals, the extrusion pressure, and the like.
Specifically, E * a / E * b can be increased as the 1,2-syndiotactic polybutadiene crystal is oriented in the tire circumferential direction and as the amount of 1,2-syndiotactic polybutadiene crystal is increased. . Moreover, E * a / E * b can be increased by extruding a rubber strip at a high pressure by a strip wind type extruder.

E * a is preferably 3.8 to 5.5 MPa. Moreover, as E * b, 3-3.8 MPa is preferable. When it is within the above range, steering stability, riding comfort, and crack growth resistance can be obtained satisfactorily.

In the sidewall of the pneumatic tire of the present invention, tan δ measured at a temperature of 70 ° C. and a dynamic strain of 2% is preferably less than 0.125.
In the present specification, tan δ is measured by the method described in Examples described later.

The pneumatic tire of the present invention can be suitably used as a passenger car tire or the like.

The pneumatic tire of the present invention can be produced by a usual method using the rubber composition. That is, a rubber composition prepared by kneading each of the above components using a rubber kneading apparatus such as an open roll or a Banbury mixer is extruded to match the shape of the sidewall of the tire at an unvulcanized stage, thereby forming a tire. An unvulcanized tire can be formed by pasting together with other tire members on the machine, and this unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire. Thereby, the tire which has a side wall (vulcanized rubber composition) which mix | blended the above-mentioned component is obtained.

In particular, a 1,2-syndiotactic polybutadiene crystal can be oriented in the tire circumferential direction, and excellent steering stability and ride comfort can be obtained due to the anisotropic effect of the complex elastic modulus E *. Step 1 for producing a rubber sheet having a thickness of 0.2 to 1.5 mm from the rubber composition (unvulcanized) using a known roll, and laminating the rubber sheet on a tire molding machine, A production method including the step 2 of molding is preferable. As this manufacturing method, the manufacturing method as described in Unexamined-Japanese-Patent No. 2009-202865 etc. is mentioned.

The upper limit of the thickness of the rubber sheet is more preferably 1.2 mm. As a result, the 1,2-syndiotactic polybutadiene crystal is oriented at a high pressure in the tire circumferential direction, so that a desired E * a / E * b is obtained.

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: TSR20
IR: IR2200 manufactured by JSR Corporation
Modified BR1: BR1250H manufactured by Nippon Zeon Co., Ltd. (tin-modified BR polymerized using a lithium initiator, vinyl content: 10 to 13% by mass, Mw / Mn: 1.5, tin atom content: 250 ppm)
Modified BR2: N103 manufactured by Asahi Kasei Chemicals Corporation (modified BR polymerized using a lithium initiator, vinyl content: 12% by mass, Mw / Mn: 1.19, Mw: 550,000)
Modified BR3: Modified butadiene rubber manufactured by Sumitomo Chemical Co., Ltd. (modified BR polymerized using a lithium initiator, vinyl content: 26 mass%, Mw / Mn: 1.34, Mw: 670,000) (R ¹ , R ² and R ³ = —OCH ₃ , R ⁴ and R ⁵ = —CH ₂ CH ₃ , n = 3)
BR150B: BR150B (Hisys BR) manufactured by Ube Industries, Ltd.
SPB-containing BR1: VCR450 manufactured by Ube Industries, Ltd. (SPB-containing BR, SPB content: 3.8% by mass, SPB melting point: 200 ° C., boiling n-hexane insoluble matter content: 3.8% by mass )
SPB-containing BR2: VCR412 manufactured by Ube Industries, Ltd. (SPB-containing BR, SPB content: 12% by mass, SPB melting point: 200 ° C., boiling n-hexane insoluble matter content: 12% by mass)
SPB-containing BR3: VCR617 manufactured by Ube Industries, Ltd. (SPB-containing BR, SPB content: 17% by mass, SPB melting point: 200 ° C., boiling n-hexane insoluble content: 15-18% by mass)
Carbon Black N220: Show Black N220 (N ₂ SA: 114 m ² / g) manufactured by Cabot Japan
Carbon black N660: Seast V (N660) manufactured by Tokai Carbon Co., Ltd. (N ₂ SA: 35 m ² / g)
Carbon Black N550: Show Black N550 (N ₂ SA: 40 m ² / g) manufactured by Cabot Japan
Silica: Z1085Gr (N ₂ SA: 90 m ² / g) manufactured by Rhodia
Silane coupling agent: Si75 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Resin 1: Marukaretsu T-100AS manufactured by Maruzen Petrochemical Co., Ltd. (C5 petroleum resin: aliphatic petroleum resin mainly composed of olefins and diolefins in C5 fraction obtained by naphtha decomposition) (softening point) : 100 ° C)
Resin 2: NOVARES C10 (Coumarone indene resin, softening point: 5 to 15 ° C.) manufactured by Rutgers Chemicals
Resin 3: NOVARES C30 (coumarone indene resin, softening point: 30 ° C.) manufactured by Rutgers Chemicals
Resin 4: Koresin (condensate of butylphenol and acetylene, softening point: 142 ° C.) manufactured by BASF
Resin 5: SP1068 manufactured by Nippon Shokubai Co., Ltd. (non-reactive alkylphenol resin represented by the above formula (3): integer of m = 1 to 10, R ⁶ = octyl group) (softening point: 90 ° C.)
Resin 6: PR12686 manufactured by Sumitomo Bakelite Co., Ltd. (cashew oil-modified phenol resin represented by the above formula (2), softening point: 100 ° C.)
Oil: VivaTec500 (TDAE oil) manufactured by H & R Co., Ltd.
Zinc Hana: Mitsui Mining & Mining Co., Ltd. 2 types of Zinc Hua stearic acid: NOF anti-aging agent 6PPD: Sumitomo Chemical Co., Ltd. Antigen 6C (N-phenyl-N '-(1 , 3-Dimethylbutyl) -p-phenylenediamine)
10% oil-containing insoluble sulfur: Seimisulfur manufactured by Nippon Kiboshi Kogyo Co., Ltd. (60% or more insoluble sulfur by carbon disulfide, oil content: 10% by mass) (The values in Tables 1-2 are the pure sulfur content. Indicates)
HMT (curing agent): Sunseller HT (hexamethylenetetramine) manufactured by Sanshin Chemical Industry Co., Ltd.
TBBS: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-11, 15-28 and Comparative Examples 1-10
According to the formulation shown in Tables 1 and 2, chemicals other than sulfur and a vulcanization accelerator were kneaded using a 1.7 L Banbury mixer. Next, using a roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded to obtain an unvulcanized rubber composition. Using the obtained unvulcanized rubber composition as a sidewall, an unvulcanized tire was produced and vulcanized to produce a test tire (size: 245 / 40R18).

Examples 12-14
Using a strip wind type extruder, a rubber sheet (unvulcanized rubber composition) having a width of 20 mm and a thickness of 1 mm is extruded, and the rubber sheet is laminated on a tire molding machine in a high temperature state. A test tire was obtained in the same manner as described above except that a thick sidewall was formed.

The obtained unvulcanized rubber composition and the test tire were evaluated as follows, and the results are shown in Tables 1 and 2.

(Viscoelasticity test)
From the obtained test tire, a strip-shaped rubber test piece was cut out so that the circumferential direction was a long side about the tire axis, and a rubber test piece 1 (size: 20 mm long, 3 mm wide, 2 mm thick) was obtained. . Further, a strip-shaped rubber test piece was cut out so that the radial direction (radial direction) was a long side about the tire axis, and a rubber test piece 2 (size: similar to the rubber test piece 1) was obtained.
Using the obtained rubber test pieces 1 and 2, using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd., temperature 70 ° C., frequency 10 Hz, initial strain 10% and dynamic strain 2% (long side direction) Strain), loss tangent tan δ, tire elastic modulus E * a (MPa), and tire radial elastic modulus E * b (MPa) were measured.
The smaller tan δ, the lower the exothermic property and the better the fuel efficiency. It shows that rigidity is so high that E * is large.
The larger E * a, the better the steering response at a small steering angle, and the better the steering stability. The smaller E * b, the better the road surface unevenness absorbability and the better the ride comfort. The larger E * a / E * b, the better the transient characteristics (good vehicle return when the steering wheel is returned straight after cornering with a steering angle).

Moreover, about the tan-delta measured by the above-mentioned evaluation method, the comparative example 1 was set to 100, and tan-delta of each mixing | blending was displayed as the index | exponent. The larger the tan δ (70 ° C.) index, the better the fuel efficiency.

(Sheet processability)
For each unvulcanized rubber composition, visually check the edge state of the molded product obtained by molding each unvulcanized rubber composition after extrusion into a predetermined sidewall shape, the degree of rubber burn, the degree of adhesion between rubbers, and the flatness. Evaluation was made by tactile sensation, and indexed with Comparative Example 1 as 100. The larger the value, the better the sheet processability.
As for the edge state, the state where the edge is straight and smooth is considered good, and the degree of burnt rubber is good when there is no unevenness due to Pitt's burnt rubber lump in a 15 cm square 2 mm sheet cut out from the molded product. As for the flatness, the state in which the sheet is flat and in close contact with the flat plate was evaluated as good.

(Maneuvering stability, ride comfort)
Test tires were mounted on all wheels of a vehicle (3000 cc), and actual vehicles were run on a test course under general driving conditions. The test driver evaluated the control stability during steering (steering stability) and ride comfort, and the index was displayed with Comparative Example 1 as 100. The larger the steering stability index, the better the steering stability, and the higher the riding comfort index, the better the riding comfort.

From Tables 1-2, in the pneumatic tire of the Example which has a side wall which mix | blended predetermined amount SPB containing BR, terminal modified BR, and isoprene-type rubber | gum, and predetermined amount, low fuel consumption, sheet | seat processability, steering A good balance between stability and ride comfort. Particularly in Examples 12 to 14 using the strip wind molding machine, the handling stability and the ride comfort were greatly improved.

On the other hand, in Comparative Example 1 in which SPB-containing BR and terminal-modified BR are not blended, four performances are generally low, in Comparative Examples 2 and 4 in which modified BR is not blended, and in Comparative Example 6 in which the blending amount is small. The tan δ (70 ° C.) index did not exceed the target (> 120), the fuel efficiency was poor, and the performance balance was poor. In Comparative Example 3 in which the SPB-containing BR was not blended and Comparative Example 5 in which the blending amount was small, the steering stability index did not exceed the target (> 104), the steering stability was inferior, and the workability was also slightly inferior. Further, in Comparative Example 7 including a large amount of NR and Comparative Example 8 including a small amount of NR, the steering stability index did not exceed the target (> 104), the steering stability was inferior, and the performance balance was poor. Furthermore, in Comparative Example 9 containing a large amount of SPB-containing BR, the tan δ (70 ° C.) index did not exceed the target (> 120), the fuel efficiency was poor, and the workability was also poor. In Comparative Example 10 in which no resin was blended, the steering stability index did not exceed the target (> 104), and the steering stability was poor. In addition, the sheet workability index does not exceed the target (> 60), the adhesiveness is insufficient, and the tire molding process is difficult. In the obtained test tire, residual air is generated between the sidewall and the case, and there is a problem. Occurred.

Claims (7)

Butadiene rubber containing 1,2-syndiotactic polybutadiene crystals, terminal-modified butadiene rubber, isoprene-based rubber , containing carbon black and resin having a nitrogen adsorption specific surface area of 25 to 50 m ² / g ,
The content of the butadiene rubber containing the 1,2-syndiotactic polybutadiene crystal in 100% by mass of the rubber component is 10 to 60% by mass, the content of the terminal-modified butadiene rubber is 7 to 60% by mass, and the isoprene-based rubber. The content of is 20 to 70% by mass ,
The said resin is a pneumatic tire which has a sidewall which consists of a rubber composition which is at least 1 sort (s) selected from the group which consists of C5 type | system | group petroleum resin, a phenol-type resin, and a coumarone indene resin . The sidewall has a ratio (E * a / E * b) of the complex elastic modulus E * a in the tire circumferential direction and the complex elastic modulus E * b in the tire radial direction measured at a temperature of 70 ° C. and a dynamic strain of 2%. The pneumatic tire according to claim 1, which is 1.03 to 2.0. The pneumatic tire according to claim 1, wherein the sidewall has a tan δ measured at a temperature of 70 ° C. and a dynamic strain of 2% is less than 0.125. The content of butadiene rubber containing 1,2-syndiotactic polybutadiene crystals in 100% by mass of the rubber component is 10 to 40% by mass, the content of the terminal-modified butadiene rubber is 25 to 50% by mass, and the isoprene-based The pneumatic tire according to any one of claims 1 to 3, wherein the rubber content is 30 to 60 mass%. The terminal modified butadiene rubber is a tin terminal modified butadiene rubber;
The pneumatic tire according to any one of claims 1 to 4, wherein the rubber composition contains 1.61 to 2.3 parts by mass of sulfur with respect to 100 parts by mass of the rubber component. The rubber composition, adsorption specific surface area nitrogen containing silica 80~240m ² / g,
The pneumatic tire according to any one of claims 1 to 5, wherein a total content of the carbon black and the silica is 20 to 40 parts by mass with respect to 100 parts by mass of the rubber component. The pneumatic tire according to any one of claims 1 to 6, wherein the sidewall is obtained by using a strip wind type extruder.