JP5654410B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

The present invention relates to a tire rubber composition and a pneumatic tire.

In recent years, due to environmental problems such as global warming, social demands for lower fuel consumption have increased, and development of fuel-efficient tires with reduced rolling resistance has been demanded in response to lower fuel consumption of automobiles. Accordingly, low heat generation is also required for the rubber composition used for each member constituting the tire, and excellent low heat generation is also required for the rubber composition covering the tire cord. Yes.

As a method for improving the low heat buildup of the rubber composition, a method of reducing the reinforcing filler is known. However, this method has a problem that the rigidity of the rubber is lowered and the steering stability is lowered.

Patent Document 1 improves the on-ice performance and wear resistance of studless tires by using an epoxidized natural rubber with an epoxidation rate of about 5% and an epoxidized butadiene rubber with an epoxidation rate of about 5%. It describes what you can do. However, the point of obtaining a good balance between low exothermic property, steering stability, and the epoxidation rate have not been studied in detail.

JP 2011-12161 A

The present invention solves the above-mentioned problems and provides a rubber composition for tires that provides a well-balanced kneadability, low heat build-up, bending fatigue resistance, adhesion to cords, air permeation resistance, and steering stability, and An object is to provide a pneumatic tire using the same.

The present invention includes an epoxidized natural rubber having an epoxidation rate of 15 to 65 mol% and an epoxidized butadiene rubber having an epoxidation rate of 15 to 65 mol%. The tire has a total content of 65% by mass or more in 100% by mass of the rubber component, and includes 20 to 100 parts by mass of silica and 0.2 to 8.0 parts by mass of the modified resorcin resin with respect to 100 parts by mass of the rubber component. The present invention relates to a rubber composition.

（式中、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、メルカプト基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。）で表される化合物により変性されたジエン系ゴムを含むことが好ましい。 The tire rubber composition has the following formula (1):

(Wherein R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group or a derivative thereof. R ⁴ and R ⁵ are It is the same or different and represents a hydrogen atom or an alkyl group. N represents an integer.) It is preferable to include a diene rubber modified with a compound represented by:

The tire rubber composition preferably contains rod-like silica having an average width of 3 to 35 nm and an average length of 50 nm to 5 μm.

The rod-like silica is preferably obtained by defibrating sepiolite mineral.

In the tire rubber composition, the content of the epoxidized natural rubber in 100% by mass of the rubber component is preferably 10 to 90% by mass, and the content of the epoxidized butadiene rubber is preferably 10 to 90% by mass.

The epoxidized butadiene rubber is preferably obtained by epoxidizing a butadiene rubber having a cis content of 80% by mass or more.

（式中、Ｒは、同一若しくは異なって、アルキル基又は水酸基を表し、ｍ個のＲのうち少なくとも１つはアルキル基である。ｍは整数を表す。） The modified resorcin resin is preferably a resin represented by the following formula (2).

(In the formula, R is the same or different and represents an alkyl group or a hydroxyl group, and at least one of m Rs is an alkyl group. M represents an integer.)

The rubber composition is preferably used as a tire cord covering rubber composition.

The present invention also relates to a pneumatic tire using the rubber composition.

According to the present invention, an epoxidized natural rubber having a specific epoxidation rate and an epoxidized butadiene rubber having a specific epoxidation rate, the total content of which is greater than or equal to a specific amount, and silica, a modified resorcin resin Therefore, kneading processability, low heat build-up, bending fatigue resistance, adhesion to cords, air permeability resistance, and steering stability can be obtained in a well-balanced manner. Therefore, by using the rubber composition for each member of a tire such as a member obtained by coating a tire cord with rubber (for example, carcass, breaker, band, etc.), a pneumatic tire having excellent performance as described above can be produced. Can provide well. Further, by using a combination of an epoxidized natural rubber having a specific epoxidation rate and an epoxidized butadiene rubber having a specific epoxidation rate, it is possible to synergistically improve adhesiveness, air permeation resistance, and steering stability.

It is a schematic diagram which shows schematic structure of rod-shaped silica (sepiolite).

The tire rubber composition of the present invention includes an epoxidized natural rubber (ENR) having a specific epoxidation rate and an epoxidized butadiene rubber (EBR) having a specific epoxidation rate, and the total content thereof is a specific amount. In addition, specific amounts of silica and modified resorcin resin are included.

The ENR is not particularly limited, and may be a commercially available epoxidized natural rubber or an epoxidized natural rubber (NR). The method for epoxidizing natural rubber is not particularly limited, and examples thereof include a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, a peracid method, and the like (Japanese Patent Publication No. 4-26617, Japanese Patent Application Laid-Open No. Hei 2). No. 110182, British Patent No. 2113692, etc.). Examples of the peracid method include a method of reacting natural rubber with an organic peracid such as peracetic acid or performic acid. In addition, epoxidized natural rubber having various epoxidation rates can be prepared by adjusting the amount of organic peracid and the reaction time.
In the present invention, the epoxidation rate is the ratio (mol%) of the number of epoxidized double bonds to the total number of double bonds in the rubber before being epoxidized. Moreover, in this invention, an epoxidation rate is a value obtained by the measuring method as described in the Example mentioned later.

The natural rubber to be epoxidized is not particularly limited. For example, SIR20, RSS # 3, TSR20, deproteinized natural rubber (DPNR), high-purity natural rubber (HPNR), and the like used in the tire industry are used. it can.

The epoxidation rate of ENR is 15 mol% or more, preferably 20 mol% or more. When the epoxidation rate is less than 15 mol%, the air permeation resistance, the adhesion to the cord, and the steering stability tend not to be sufficiently obtained. The epoxidation rate is 65 mol% or less, preferably 50 mol% or less, more preferably 35 mol% or less. When the epoxidation rate exceeds 65 mol%, kneadability, low heat build-up, bending fatigue resistance, and adhesion to cords tend to be greatly deteriorated. When the epoxidation rate is within the above range, kneadability, low heat build-up, bending fatigue resistance, adhesion to cord, air permeation resistance, and steering stability can be obtained in a well-balanced manner.

The content of ENR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 40% by mass or more. If it is less than 10% by mass, the bending fatigue resistance and the air permeation resistance tend to be insufficient. The content of ENR is preferably 90% by mass or less, more preferably 80% by mass or less. When it exceeds 90% by mass, the bending fatigue resistance and the low heat build-up tend to decrease.

The EBR is not particularly limited, and may be a commercially available epoxidized butadiene rubber or an epoxidized butadiene rubber (BR). Examples of the method for epoxidizing butadiene rubber include the same method as the method for epoxidizing natural rubber described above. Similarly to the case of ENR, epoxidized butadiene rubbers having various epoxidation rates can be prepared by adjusting the amount of organic peracid and the reaction time.

The BR to be epoxidized is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B and other high cis content BR, manufactured by Ube Industries, Ltd. BR containing syndiotactic polybutadiene crystals such as VCR 412 and VCR 617 can be used.

The cis content of BR to be epoxidized is 80% by mass because kneadability, low heat build-up, bending fatigue resistance, cord adhesion, air permeation resistance, and steering stability are well balanced. The above is preferable, 90 mass% or more is more preferable, and 95 mass% or more is still more preferable.
The cis content (cis-1,4-bonded butadiene unit amount) can be measured by infrared absorption spectrum analysis.

The epoxidation rate of EBR is 15 mol% or more, preferably 20 mol% or more. When the epoxidation rate is less than 15 mol%, the air permeation resistance, the adhesion to the cord, and the steering stability tend not to be sufficiently obtained. The epoxidation rate is 65 mol% or less, preferably 50 mol% or less, more preferably 35 mol% or less. When the epoxidation rate exceeds 65 mol%, kneadability, low heat build-up, bending fatigue resistance, and adhesion to cords tend to be greatly deteriorated. When the epoxidation rate is within the above range, kneadability, low heat build-up, bending fatigue resistance, adhesion to cord, air permeation resistance, and steering stability can be obtained in a well-balanced manner.

The number average molecular weight (Mn) of EBR is preferably 100,000 or more, more preferably 120,000 or more, and still more preferably 150,000 or more. The Mn of EBR is preferably 800000 or less, more preferably 600000 or less, and still more preferably 300000 or less. When the Mn of EBR is within the above range, kneadability, low heat build-up, bending fatigue resistance, adhesion to cords, air permeation resistance, and steering stability can be obtained in a well-balanced manner.
In the present invention, the number average molecular weight (Mn) is a value measured by the method described in Examples.

The content of EBR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more. If it is less than 10% by mass, the bending fatigue resistance and the air permeation resistance tend to be insufficient. The content of EBR is preferably 90% by mass or less, more preferably 60% by mass or less, and still more preferably 40% by mass or less. If it exceeds 90% by mass, the rubber mass at the time of kneading is deteriorated, and the kneading processability tends to be lowered.

The total content of ENR and EBR in 100% by mass of the rubber component is 65% by mass or more, preferably 70% by mass or more, and may be 100% by mass.
If it is less than 65% by mass, sufficient adhesion to the cord and air permeation resistance cannot be obtained.

Examples of rubber components other than ENR and EBR used in rubber compositions include diene rubbers, such as NR, BR, styrene butadiene rubber (SBR), epoxidized styrene butadiene rubber (ESBR), and isoprene rubber (IR). Butyl rubber (IIR), halogenated butyl rubber (X-IIR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), styrene-isoprene-butadiene copolymer rubber (SIBR), and the like can be used. Among these, ESBR is preferable because it can reduce reversion during vulcanization.

Moreover, as rubber components other than ENR and EBR, NR is preferable because good kneading processability, low heat build-up property, and adhesiveness with cords can be obtained. As NR, the same natural rubber as the above-mentioned epoxidized can be used.

When the rubber composition of the present invention contains NR, the content of NR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more. The content of NR is preferably 35% by mass or less. When the content of NR is within the above range, good kneading processability, low heat build-up, and adhesiveness with cords can be obtained.

（式中、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（好ましくは炭素数１〜８、より好ましくは炭素数１〜６、更に好ましくは炭素数１〜４のアルコキシ基）、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（好ましくは炭素数１〜４のアルキル基）を表す。ｎは整数（好ましくは１〜５、より好ましくは２〜４、更に好ましくは３）を表す。）で表される化合物により上記ジエン系ゴムが変性された変性ジエン系ゴムが好ましく、上記式（１）で表される化合物によりＢＲ、ＳＢＲが変性された変性ＢＲ、変性ＳＢＲ（特開２０１０−１１１７５３号公報に記載の変性ＢＲ、変性ＳＢＲ）がより好ましい。 Further, as rubber components other than ENR and EBR, the following formula (1); from the reason that good kneading processability, low exothermic property, adhesion to cords, and steering stability are obtained.

(In formula, R < ¹ >, R < ² > and R < ³ > are the same or different, and are an alkyl group and an alkoxy group (preferably C1-C8, More preferably C1-C6, More preferably C1-C4 An alkoxy group), a silyloxy group, an acetal group, a carboxyl group (—COOH), a mercapto group (—SH), or a derivative thereof, and R ⁴ and R ⁵ are the same or different and represent a hydrogen atom or an alkyl group (preferably Represents an alkyl group having 1 to 4 carbon atoms, and n represents an integer (preferably 1 to 5, more preferably 2 to 4 and still more preferably 3). Modified diene rubber is preferable, and modified BR and modified SBR in which BR and SBR are modified by the compound represented by the above formula (1) (described in JP 2010-111753 A). Modified BR, the modified SBR) is more preferable.

As R ¹ , R ² and R ³ , an alkoxy group is desirable, and as R ⁴ and R ⁵ , an alkyl group is desirable. As a result, good kneading workability, low heat build-up, adhesion to the cord, and steering stability can be obtained.

Specific examples of the compound represented by the above formula (1) include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 2-dimethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 3 -Dimethylaminopropyltrimethoxysilane etc. are mentioned. These may be used alone or in combination of two or more.

Examples of the method for modifying the diene rubber with the compound (modifier) represented by the above formula (1) are described in JP-B-6-53768, JP-B-6-57767, JP-T2003-514078, and the like. A conventionally known method such as a known method can be used. For example, a diene rubber may be brought into contact with a modifying agent. After synthesizing a diene rubber by anionic polymerization, a predetermined amount of a modifying agent is added to the diene rubber solution, and the polymerization terminal of the diene rubber (active And a method in which a modifier is added to the diene rubber solution and reacted.

The weight average molecular weight (Mw) of the modified diene rubber is preferably 100,000 or more, more preferably 200,000 or more. If it is less than 100,000, the fracture strength, wear resistance, and bending fatigue resistance tend to decrease. Mw is preferably 2000000 or less, more preferably 1000000 or less, and still more preferably 600000 or less. If it exceeds 2,000,000, the kneading processability is lowered, the dispersibility is deteriorated accordingly, and the fracture strength and the bending fatigue resistance may be lowered.
In the present invention, the weight average molecular weight (Mw) is a value measured by the method described in Examples.

The vinyl content of the modified BR is preferably 40% by mass or less, more preferably 35% by mass or less. If the vinyl content exceeds 40% by mass, low heat build-up and bending fatigue resistance may be reduced. Although the minimum of the said vinyl content is not specifically limited, 1 mass% or more, 5 mass% or more, 10 mass% or more may be sufficient. If it is less than 1% by mass, heat resistance and deterioration resistance may be lowered.
The vinyl content (1,2-bond butadiene unit amount) can be measured by infrared absorption spectrum analysis.

When the rubber composition of the present invention contains a modified diene rubber, the content of the modified diene rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15%. It is at least mass%. The content of the modified diene rubber is preferably 35% by mass or less. When the content of the modified diene rubber is within the above range, good kneading processability, low exothermic property, adhesion to the cord, and steering stability can be obtained.

The rubber composition of the present invention contains silica (spherical silica). As a result, kneadability, low heat build-up, bending fatigue resistance, adhesion to the cord, air permeation resistance, and steering stability can be obtained in a well-balanced manner. The silica is not particularly limited, and examples thereof include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and the like, but wet process silica is preferable because of its large number of silanol groups. Silica may be used alone or in combination of two or more. In this specification, when it is simply described as silica, it means spherical silica unless otherwise specified.

The nitrogen adsorption specific surface area (N ₂ SA) of the silica is preferably 50 m ² / g or more, more preferably 80 m ² / g or more, and still more preferably 120 m ² / g or more. If it is less than 50 m ² / g, the reinforcing effect due to the blending of silica is not sufficient, and the bending fatigue resistance and the wear resistance tend to decrease. Further, N ₂ SA of silica is preferably 300 m ² / g or less, more preferably 250 m ² / g or less, and further preferably 200 m ² / g or less. When it exceeds 300 m ² / g, the dispersibility and low heat build-up of silica tend to deteriorate.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The content of silica is 20 parts by mass or more, preferably 40 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, the effect of silica blending cannot be sufficiently obtained. The content of the silica is 100 parts by mass or less, preferably 80 parts by mass or less. When it exceeds 100 parts by mass, the viscosity increases, so that the kneading processability is lowered.

The rubber composition of the present invention contains a modified resorcin resin. As a result, it is possible to improve the adhesion to the cord while maintaining good kneading workability, low heat generation, bending fatigue resistance, air permeation resistance and steering stability, and kneading workability, low heat generation resistance, Bending fatigue, adhesion to cord, air permeation resistance, and steering stability can be obtained in a well-balanced manner.

Examples of the modified resorcin resin include resorcin / alkylphenol / formalin copolymer (condensate), resorcin / formalin reaction product penacolite resin, RSM (mixture of about 60% by mass resorcin and about 40% by mass stearic acid). Etc. Specifically, Penacolite resins B-18-S and B-20 manufactured by India Spec Co., Sumikanol 620 manufactured by Sumitomo Chemical Co., Ltd., R-6 manufactured by Uniroyal Corporation, and SRF1501 manufactured by Schenectady Chemical Co., Ltd. And Arofine 7209 manufactured by Ashland Chemical Co., Ltd. Of these, a resorcin / alkylphenol / formalin copolymer is preferable, and a resin represented by the following formula (2) is more preferable.

（式中、Ｒは、同一若しくは異なって、アルキル基又は水酸基（−ＯＨ）を表し、ｍ個のＲのうち少なくとも１つはアルキル基である。ｍは整数を表す。）

(In the formula, R is the same or different and represents an alkyl group or a hydroxyl group (—OH), and at least one of m R is an alkyl group. M represents an integer.)

Examples of the alkyl group for R include alkyl groups having 1 to 9 carbon atoms (preferably 2 to 8 carbon atoms) such as a methyl group, an ethyl group, and an octyl group. The bonding position of R is preferably a meta position or a para position with respect to a hydroxyl group bonded to the aromatic ring. Further, when R is a hydroxyl group, the bonding position of R is more preferably a meta position with respect to the hydroxyl group bonded to the aromatic ring.

m is preferably 2 to 5 from the viewpoint of good dispersibility in rubber.

The content of the modified resorcin resin is 0.2 parts by mass or more, preferably 1.2 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.2 parts by mass, sufficient adhesion with the cord cannot be obtained, and the durability of the tire is lowered. The content of the modified resorcin resin is 8.0 parts by mass or less, preferably 5.0 parts by mass or less. If it exceeds 8.0 parts by mass, the low heat build-up and the breaking strength are reduced.

In the present invention, it is preferable to use a methylene donor together with the modified resorcin resin. Thereby, it is possible to further improve the adhesion with the cord while maintaining good kneading workability, low heat generation, bending fatigue resistance, air permeation resistance, steering stability, kneading workability, low heat generation, Bending fatigue resistance, cord adhesion, air permeation resistance, and steering stability can be obtained in a more balanced manner.

Examples of the methylene donor include hexamethylenetetramine (HMT), hexamethoxymethylol melamine (HMMM), hexamethylol melamine pentamethyl ether (HMMPME), and Sumikanol 507A.

The content of the methylene donor is preferably 0.2 parts by mass or more, more preferably 1.2 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 0.2 parts by mass, sufficient adhesion with the cord cannot be obtained, and the durability of the tire tends to decrease. The content of the methylene donor is preferably 5.0 parts by mass or less, and preferably 4.0 parts by mass or less. When it exceeds 5.0 parts by mass, kneadability, low heat build-up, and breaking strength tend to decrease.

In the present invention, it is preferable to use a specific rod-like silica. Thereby, good air permeation resistance and steering stability can be obtained. In particular, when the above-mentioned modified diene rubber (particularly the above-mentioned modified BR and the above-mentioned modified SBR) is blended with a specific rod-like silica, the steering stability can be improved synergistically, and further, kneadability and low heat build-up can be achieved. It can be improved.

Unlike ordinary silica having a spherical shape, rod-shaped silica is an inorganic material (silica) having a rod-like or needle-like shape and having a silanol group on the surface thereof. Examples of the rod-like silica include sepiolite, palygorskite, attapulgite, sirotile, rafrinite, falconite, imogolite and the like. Of these, sepiolite and attapulgite are preferred because they have few impurities and many silanol groups.

Silanol groups are present on the surface of the rod-like silica. Therefore, by mix | blending a silane coupling agent, a rubber molecule and rod-shaped silica can be couple | bonded through a silane coupling agent, and the effect which mix | blended rod-shaped silica can fully be acquired. Further, when used in combination with the modified diene rubber, a strong interaction can be directly formed between the modified diene rubber and the rod-like silica. Therefore, the effect of blending rod-like silica can be obtained more sufficiently.

Rod-like silica, can be suitably used those obtained by fibrillating sepiolite mineral is fibrous material _{[Mg 8 Si 12 O 30 (} OH) 4 (H 2 O) 4 · 8 (H 2 O)] . The structure of sepiolite mineral is formed by connecting three Si-O tetrahedrons to form a Si-O tetrahedral ribbon parallel to the fiber direction. The ribbons are connected by octahedrally coordinated magnesium ions and resemble a talc structure. Form a 2: 1 mold. These adhere to each other to form a fiber bundle, which can form an aggregate.

The agglomerates can be broken (defibrated) by industrial processes such as pulverization (grinding) or chemical modification (see for example EP 170299), whereby fibers of nanometer diameter, That is, exfoliated (defibrated) rod-like silica (sepiolite) can be produced. In the present invention, the method for defibrating sepiolite minerals is not particularly limited, but it is preferable to defibrate without substantially breaking the shape of rod-like silica (sepiolite) as a fiber. Examples of such a defibrating method include a wet pulverization method (for example, a method described in European Patent No. 170299, Japanese Patent Laid-Open No. 5-97488, European Patent No. 85200094-4, etc.) and the like. .

An example of the wet pulverization method will be specifically described. First, rod-shaped silica (sepiolite) containing water is pulverized to a particle size of 2 mm or less. After pulverization, water is added so that the solid content concentration of the suspension is 5 to 25%, and then a dispersant (for example, an alkali salt of hexametaphosphate) is added. The suspension is then stirred for 5-15 minutes using a stirrer with high shear. At the time of stirring, the mixture is first stirred for 2 to 7 minutes at a low rotation, and then stirred for 2 to 8 minutes at a high rotation. Next, by separating the supernatant by decantation or centrifugation, rod-shaped silica (sepiolite) that has been defibrated without substantially breaking the shape as a fiber can be obtained.

The sepiolite in the present invention is a concept including attapulgite (also known as palygorskite). Attapulgite is structurally and chemically almost identical to sepiolite, except that the unit cell of attapulgite is slightly smaller (fiber length is shorter).

The average width of the rod-like silica is preferably 3 nm or more, more preferably 5 nm or more. If it is less than 3 nm, the surface area tends to be large, and the dispersion into rubber tends to be poor. The average width of the rod-like silica is preferably 35 nm or less, more preferably 30 nm or less. If it exceeds 35 nm, the aspect ratio tends to be small, and sufficient low heat build-up tends not to be obtained.

The average length of the rod-like silica is preferably 50 nm or more, more preferably 100 nm or more, and more preferably 300 nm or more. If it is less than 50 nm, the aspect ratio tends to be small, and sufficient low heat build-up tends not to be obtained. The average length of the rod-like silica is preferably 5 μm or less, more preferably 3 μm or less, and still more preferably 2 μm or less. If it exceeds 5 μm, it becomes a starting point of fracture, so that the bending fatigue resistance tends to deteriorate.

The aspect ratio (average length / average width) of the rod-like silica is preferably 2 or more, more preferably 5 or more. If it is less than 2, there is a tendency that sufficient low exothermic property cannot be obtained. The upper limit of the aspect ratio of the rod-like silica is not particularly limited, and it is preferably as large as possible within the range of the above shape.

FIG. 1 is a schematic diagram showing a schematic structure of rod-like silica (sepiolite). As shown in FIG. 1, rod-like silica (sepiolite) has a needle shape or a long fiber shape (rod shape). The width, thickness, and length of sepiolite correspond to X, Y, and Z in FIG. In other words, the sepiolite width (X) is the length of the short side of the main surface (the surface having the largest area when viewed in plan), and the sepiolite thickness (Y) is the normal to the main surface. It is the length in the direction, and the sepiolite length (Z) is the length of the long side of the main surface.

In the present specification, the average width of the rod-shaped silica is an average value of X of the rod-shaped silica measured by a transmission electron microscope (for example, an average value calculated by measuring X of 100 rod-shaped silica). In the present specification, the average length of the rod-shaped silica is an average value of Z of the rod-shaped silica measured by a transmission electron microscope (for example, an average value calculated by measuring Z of 100 rod-shaped silica). .

The content of the rod-like silica is preferably 1 part by mass or more, more preferably 2 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the effect of blending rod-like silica may not be sufficiently obtained. Further, the content of the rod-like silica is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less. If it exceeds 50 parts by mass, kneadability, low heat build-up, and bending fatigue resistance tend to deteriorate.

The rubber composition of the present invention preferably contains a silane coupling agent together with rod-like silica and silica.
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 type, mercapto type, vinyl type, amino type, glycidoxy type, nitro type And chloro-based silane coupling agents. Among these, a sulfide system is preferable because the effects of the present invention can be obtained satisfactorily.

As the sulfide-based silane coupling agent, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3- Triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, and 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide are preferable, and bis (3-triethoxysilylpropyl) disulfide is more preferable.

In order to improve low heat buildup, it is effective to use a mercapto-based silane coupling agent in combination. Specifically, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercapto Examples include ethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the like. Examples of the trade name include Si363 manufactured by Degussa, NXT-Z45 manufactured by Momentive, and the like.

The content of the silane coupling agent is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, with respect to 100 parts by mass of the total content of rod-like silica and silica. If the amount is less than 3 parts by mass, the rod-like silica and silica cannot be sufficiently dispersed, and the low heat buildup and the bending fatigue resistance may be deteriorated. Further, the content of the silane coupling agent is preferably 15 parts by mass or less, more preferably 10 parts by mass or less. When the amount exceeds 15 parts by mass, an excess silane coupling agent remains, which may cause deterioration of kneading processability and bending fatigue resistance of the resulting rubber composition.

The rubber composition of the present invention preferably contains carbon black. As a result, the bending fatigue resistance can be improved, and kneadability, low heat generation, bending fatigue resistance, adhesion to the cord, air permeation resistance, and steering stability can be obtained in a more balanced manner. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. Carbon black may be used independently and may use 2 or more types together.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 50 m ² / g or more, and more preferably 90 m ² / g or more. When N ₂ SA is less than 50 m ² / g, sufficient reinforcing property cannot be obtained, and sufficient bending fatigue resistance tends to be not obtained. Also, _N 2 SA of carbon black is preferably 150 meters ² / g or less, more preferably 130m ² / g. When N ₂ SA exceeds 150 m ² / g, the viscosity at the time of unvulcanization becomes very high, and the kneading processability tends to deteriorate. In addition, low exothermicity tends to deteriorate.
In addition, the nitrogen adsorption specific surface area of carbon black is measured according to JIS K6217-2: 2001.

When carbon black is blended in the rubber composition of the present invention, the carbon black content is preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 3 parts by mass, the effect of blending carbon black may not be sufficiently obtained. The carbon black content is preferably 60 parts by mass or less, more preferably 20 parts by mass or less, and still more preferably 10 parts by mass or less. When it exceeds 60 parts by mass, low heat build-up and kneading workability tend to deteriorate.

In addition to the above components, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions, such as reinforcing fillers such as clay, zinc oxide, stearic acid, various anti-aging agents, oils Further, vulcanizing agents such as wax and sulfur, vulcanization accelerators and the like can be appropriately blended.

Examples of the vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl-2- Examples include benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), N, N′-diphenylguanidine (DPG), and the like. Of these, sulfenamide-based vulcanization accelerators such as TBBS, CBS, and DZ are preferred, and TBBS is more preferred because the effects of the present invention can be obtained satisfactorily.

As a method for producing the rubber composition of the present invention, a known method can be used. For example, the above components are kneaded using a rubber kneader such as an open roll or a Banbury mixer, and then vulcanized. Can be manufactured.

The rubber composition of the present invention can be used for each member of a tire. Among them, a member obtained by coating a tire cord with rubber (for example, carcass, breaker (belt), band, etc.) (particularly carcass). It can be suitably applied. Specifically, the carcass shown in the drawings of JP 2009-13220 A, the breaker shown in the drawings of JP 2003-94918 A, the band shown in the drawings of JP 6-270606 A, etc. Used for.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, if necessary, a rubber composition containing various additives is coated on a tire cord at an unvulcanized stage and formed into a shape such as a carcass, and then bonded together with other tire members to form an unvulcanized tire. After forming, a tire can be manufactured by heating and pressurizing in a vulcanizer.

Examples of tire cords that can be used in the present invention include organic fiber cords, steel cords, and hybrid cords of organic fibers and steel. Specifically, steel cords for tires, 2 + 2 / 0.23 (tire cords obtained by adding and twisting two cords having a wire diameter of 0.23 mm), high-tension cords with brass plating, and the like can be given. .

In the pneumatic tire of the present invention, the tire cord is coated with rubber using the above rubber composition that provides a good balance between low heat build-up, bending fatigue resistance, cord adhesion, air permeability resistance, and steering stability. Therefore, the inner liner layer can be reduced in weight, and the fuel efficiency of the pneumatic tire can be further improved.

The pneumatic tire of the present invention is preferably used as a tire for passenger cars, a tire for trucks and buses, a tire for motorcycles, a tire for competition, and the like, and more preferably used as a tire for passenger cars.

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 the production examples will be described together. In addition, the chemical | medical agent refine | purified according to the usual method as needed.
High ammonia type natural rubber latex: Hytex made by Nomura Trading Co., Ltd.
Nonionic emulsifier: Emulgen 106 manufactured by Kao Corporation
Cyclohexane: Kanto Chemical Co., Ltd. 1,3-Butadiene: Tokyo Chemical Industry Co., Ltd. Tetramethylethylenediamine: Kanto Chemical Co., Ltd. n-Butyllithium: Kanto Chemical Co., Ltd. 1.6M n-Butyllithium Hexane solution modifier: 3-dimethylaminopropyltrimethoxysilane manufactured by AMAX Co. (in formula (1), R ¹ , R ² and R ³ = methoxy group, R ⁴ and R ⁵ = methyl group, n = 3)
2,6-di-tert-butyl-p-cresol: NOCRACK 200 manufactured by Ouchi Shinsei Chemical Co., Ltd.

The following evaluation was performed on ENR, EBR, and modified BR obtained in the following production examples.
(Epoxidation rate)
The obtained ENR or EBR is dissolved in deuterated chloroform and epoxidized with the number of non-epoxidized diene units by nuclear magnetic resonance (NMR (JNM-ECA series manufactured by JEOL Ltd.)) spectroscopic analysis. The ratio of the number of diene units was determined and calculated using the following formula.
(Epoxidation rate E%) = (number of epoxies contained in the main chain of rubber) / (number of diene units contained in the main chain of rubber (including epoxidized units)) × 100
(Number average molecular weight (Mn), weight average molecular weight (Mw))
The number average molecular weight (Mn) and the weight average molecular weight (Mw) are gel permeation chromatograph (GPC) (HLC-8220GPC manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE manufactured by Tosoh Corporation). HZ-M) and converted from standard polystyrene.
(Vinyl content)
The vinyl content (1,2-bonded butadiene unit amount) was measured by infrared absorption spectrum analysis.

(Production Example 1)
1500 g of high ammonia type natural rubber latex (solid content 60%) is put into a 5 L container equipped with a stir bar, dropping funnel and condenser, and diluted with 1.5 L of distilled water so that the solid content becomes 30%. And adjusted to 20 ° C. To this, 9 g of nonionic emulsifier was added with stirring. Next, 800 g of peracetic acid with a concentration of 2.5 mol / L was slowly added while adjusting with 2.8% aqueous ammonia so that the pH of the latex was in the range of 5-6. After the addition, the mixture was reacted at room temperature for 5 hours, and then formic acid or methanol was added little by little to solidify only the rubber component, and then washed several times with distilled water and dried to prepare ENR (Polymer 1). The epoxidation rate of the obtained ENR was 4.9 mol%.

(Production Example 2)
1500 g of high ammonia type natural rubber latex (solid content 60%) is put into a 5 L container equipped with a stir bar, dropping funnel and condenser, and diluted with 1.5 L of distilled water so that the solid content becomes 30%. And adjusted to 20 ° C. To this, 9 g of nonionic emulsifier was added with stirring. Next, 800 g of peracetic acid having a concentration of 12.5 mol / L was slowly added while adjusting with 2.8% aqueous ammonia so that the pH of the latex was in the range of 5-6. After the addition, the mixture was reacted at room temperature for 5 hours, and then formic acid or methanol was added little by little to solidify only the rubber component, and then washed several times with distilled water and dried to prepare ENR (polymer 2). The epoxidation rate of the obtained ENR was 25.1 mol%.

(Production Example 3)
In a 5 L container equipped with a stirrer, a dropping funnel and a condenser, 300 g of BR (BRI50B manufactured by Ube Industries, Ltd. (number average molecular weight (Mn) = 19000, cis content = 98 mass%)) was dissolved in 3 L of toluene. After adding 4 g of formic acid, 12 g of hydrogen peroxide solution having a concentration of 30% by mass was added dropwise and reacted at a temperature of 40 ° C. with stirring for 4 hours. After the reaction, an aqueous calcium carbonate solution was added to adjust the polymer solution to pH 7. Then, the solution was dropped into ethanol, and the precipitated polymer was separated and dried to prepare EBR (Polymer 3). The obtained EBR had an epoxidation rate of 4.1 mol% and a number average molecular weight (Mn) of 190000.

(Production Example 4)
In a 5 L vessel equipped with a stir bar, dropping funnel and condenser, 300 g of BR (BR150B manufactured by Ube Industries, Ltd. (number average molecular weight (Mn) = 19000, cis content = 98 mass%)) was dissolved in 3 L of toluene. After adding 4 g of formic acid, 60 g of hydrogen peroxide solution having a concentration of 30% by mass was added dropwise and reacted at a temperature of 40 ° C. with stirring for 4 hours. After the reaction, an aqueous calcium carbonate solution was added to adjust the polymer solution to pH 7. Then, the solution was dropped into ethanol, and the precipitated polymer was separated and dried to prepare EBR (polymer 4). The obtained EBR had an epoxidation rate of 25.3 mol% and a number average molecular weight (Mn) of 190000.

(Production Example 5)
1500 g of high ammonia type natural rubber latex (solid content 60%) is put into a 5 L container equipped with a stir bar, dropping funnel and condenser, and diluted with 1.5 L of distilled water so that the solid content becomes 30%. And adjusted to 20 ° C. To this, 9 g of nonionic emulsifier was added with stirring. Next, 1200 g of peracetic acid having a concentration of 25 mol / L was slowly added while adjusting with 2.8% aqueous ammonia so that the pH of the latex was in the range of 5-6. After the addition, the mixture was reacted at room temperature for 5 hours, and then formic acid or methanol was added little by little to coagulate the rubber component, followed by washing several times with distilled water and drying to prepare ENR (polymer 5). The epoxidation rate of the obtained ENR was 72.4 mol%.

(Production Example 6)
15000 ml of cyclohexane, 900 mmol of 1,3-butadiene, 0.2 mmol of tetramethylethylenediamine and 0.12 mmol of n-butyllithium were added to a pressure-resistant container sufficiently purged with nitrogen, and stirred at 40 ° C. for 48 hours. Thereafter, 0.12 mmol of a modifier was added to stop the reaction, 1 g of 2,6-di-tert-butyl-p-cresol was added to the reaction solution, and then modified butadiene rubber (modified BR) (polymer 6) by reprecipitation purification. ) The weight average molecular weight (Mw) was 460000, and the vinyl content was 34% by mass.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR20
BR: BR150B manufactured by Ube Industries, Ltd.
Polymer 1: Epoxidized natural rubber polymer produced in Production Example 1 above: Epoxidized natural rubber polymer produced in Production Example 2 above: Epoxidized butadiene rubber polymer produced in Production Example 3 above: Epoxidized butadiene rubber polymer produced in Production Example 4: Epoxidized natural rubber polymer produced in Production Example 5 above: Modified butadiene rubber produced in Production Example 6 (terminally modified butadiene rubber)
Rod-like silica: PANGEL AD (length: 200 to 2000 nm, width: 5 to 30 nm, wet pulverized product of sepiolite mineral) manufactured by TOLSA
Carbon black: N220 manufactured by Cabot Japan Co., Ltd. (DBP oil absorption: 115 ml / 100 g, nitrogen adsorption specific surface area (N ₂ SA): 110 m ² / g)
Silica: ULTRASIL VN3 manufactured by Degussa (spherical silica, nitrogen adsorption specific surface area (N ₂ SA): 175 m ² / g)
Silane coupling agent: Si75 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Aroma oil: Process X-140 manufactured by Japan Energy
Modified resorcin resin: Sumikanol 620 (resorcin / alkylphenol / formalin copolymer (R: alkyl group in the above formula (2), m: resin of 2 to 5)) manufactured by Sumitomo Chemical Co., Ltd.)
Methylene donor: Sumicanol 507A (mixture of about 65% by weight methylol melamine resin with about 35% by weight silica and oil)
Anti-aging agent: Santoflex 13 from Flexis
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Zinc oxide: Zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) -2-Benzothiazolylsulfenamide)

Examples and Comparative Examples In accordance with the formulation shown in Table 2, materials other than sulfur and a vulcanization accelerator were kneaded for 4 minutes at 150 ° C. 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 for 4 minutes under the condition of 80 ° C. using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized with a 2 mm thick mold at 170 ° C. for 12 minutes to obtain a vulcanized rubber composition.

The obtained unvulcanized rubber composition was processed into a sheet having a thickness of about 1 mm, and a carcass was created by overlapping the cord array shown in Table 1 from above and below. Using this carcass, it was bonded to other tire members to produce a raw tire, and vulcanized under the conditions of 150 ° C., 35 minutes, 25 kgf to produce a test tire of 195 / 65R15 size.

The following tests were performed using the obtained unvulcanized rubber composition, vulcanized rubber composition, and test tire.

(Kneading workability index)
The Mooney viscosity of a predetermined unvulcanized rubber composition was measured at 130 ° C. according to JIS K6300. The measurement results are shown as an index with Comparative Example 1 as 100. The larger the index, the lower the Mooney viscosity and the easier the processing (excellent kneading processability).
(Kneading workability index) = (Mooney viscosity of Comparative Example 1) / (Mooney viscosity of each formulation) × 100

(Low exothermic index)
The loss tangent tan δ of the vulcanized rubber composition at 70 ° C. was measured under the conditions of a frequency of 10 Hz, an initial strain of 10% and a dynamic strain of 2% using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. The low exothermic index of 1 was set to 100, and tan δ of each formulation was expressed as an index according to the following formula.
In addition, it shows that it is excellent in low exothermic property (low fuel consumption property), so that heat_generation | fever is so small that a low exothermic index is large.
(Low exothermic index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Bending fatigue resistance index)
Using a constant stress / constant strain fatigue tester (FT-3100) manufactured by Ueshima Seisakusho Co., Ltd., the test was conducted in accordance with the method of ISO6943. Using a test piece (vulcanized rubber composition) of Dumbbell No. 3, 1 Hz, 30% strain was continuously applied repeatedly, the number of times until the test piece broke was determined, and Comparative Example 1 was set as 100. It shows that it is excellent in bending fatigue resistance, so that an index | exponent is large.

(Adhesiveness with cord)
The steel cord was coated with an unvulcanized rubber composition, molded, and then vulcanized at 150 ° C. for 30 minutes to prepare a steel cord-coated rubber composition. The obtained rubber composition was subjected to wet heat deterioration under conditions of a temperature of 80 ° C. and a humidity of 95% for 150 hours, and then the rubber coverage (%) of each rubber composition was measured.
The rubber coverage was the ratio of the rubber covered on the peeled surface when the steel cord and rubber were peeled, and was evaluated according to the following criteria.
5: 100% of the entire surface is covered 0: Not covered at all

(Air permeability resistance index)
The test tire was assembled into a JIS standard rim 15 × 6 JJ, sealed with an initial air pressure of 300 KPa, left at room temperature for 90 days, and the rate of decrease in air pressure was calculated. The rate of decrease in air pressure of Comparative Example 1 was set to 100, and the rate of decrease in air pressure of each formulation was displayed as an index according to the following formula. It shows that it is excellent in air permeation resistance, so that an index | exponent is large.
(Air permeability resistance index) = (Air pressure decrease rate of Comparative Example 1) / (Air pressure decrease rate of each formulation) × 100

(Maneuvering stability)
The test tires were mounted on all domestic FF2000cc wheels, the vehicle was run on the test course, and the handling stability was evaluated by sensory evaluation of the driver. Evaluation was made into a 10-point full scale, and the comparative example 1 was made into 6 points and relative evaluation was carried out. The greater the score, the better the steering stability.

From Table 2, it contains epoxidized natural rubber (ENR) having a specific epoxidation rate and epoxidized butadiene rubber (EBR) having a specific epoxidation rate, and the total content thereof is a specific amount or more, and further silica. In the examples containing specific amounts of the modified resorcin resins, kneadability, low heat generation, bending fatigue resistance, adhesion to cords, air permeability resistance, and steering stability were obtained in a well-balanced manner.

From Comparative Examples 4, 9, 10 and Example 2, the adhesiveness can be obtained by using epoxidized natural rubber (ENR) having a specific epoxidation rate and epoxidized butadiene rubber (EBR) having a specific epoxidation rate. It was found that the air permeation resistance and the steering stability can be synergistically improved.

Claims (9)

An epoxidized natural rubber having an epoxidation rate of 15 to 65 mol%, and an epoxidized butadiene rubber having an epoxidation rate of 15 to 65 mol%,
The total content of the epoxidized natural rubber and the epoxidized butadiene rubber is 65% by mass or more in 100% by mass of the rubber component,
20 to 100 parts by mass of spherical silica having a spherical shape with respect to 100 parts by mass of the rubber component,
A tire rubber composition containing 0.2 to 8.0 parts by mass of a modified resorcin resin. Following formula (1);

(Wherein R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group or a derivative thereof. R ⁴ and R ⁵ are The tire rubber composition according to claim 1, comprising a diene rubber modified with a compound represented by the same or different and each represents a hydrogen atom or an alkyl group, and n represents an integer. The rubber composition for a tire according to claim 1 or 2, comprising rod- like silica having a rod- like or needle-like shape having an average width of 3 to 35 nm and an average length of 50 nm to 5 µm. The rubber composition for a tire according to claim 3, wherein the rod-like silica is obtained by defibrating sepiolite mineral. The tire according to any one of claims 1 to 4, wherein a content of the epoxidized natural rubber in 10% by mass of a rubber component is 10 to 90% by mass, and a content of the epoxidized butadiene rubber is 10 to 90% by mass. Rubber composition. The tire rubber composition according to any one of claims 1 to 5, wherein the epoxidized butadiene rubber is obtained by epoxidizing a butadiene rubber having a cis content of 80% by mass or more. The tire rubber composition according to any one of claims 1 to 6, wherein the modified resorcin resin is a resin represented by the following formula (2).

(In the formula, R is the same or different and represents an alkyl group or a hydroxyl group, and at least one of m Rs is an alkyl group. M represents an integer.) The tire rubber composition according to any one of claims 1 to 7, which is used as a rubber composition for covering a tire cord. A pneumatic tire using the rubber composition according to claim 1.

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