JP5898007B2 - Rubber composition for bead apex and pneumatic tire - Google Patents

Description

The present invention relates to a bead apex rubber composition and a pneumatic tire produced using the same.

In recent years, due to soaring fuel costs and the introduction of environmental regulations, the demand for lower fuel consumption of vehicles has become stronger, and among the tires, not only tread with a particularly high occupation ratio but also excellent fuel efficiency for bead apex Sex is required. Conventionally, bead apex has been used as a filler, carbon black, which can easily interact with the rubber component and has an excellent reinforcing effect, but in order to improve fuel efficiency, silica is used instead. It is being considered for use.

However, silica has lower affinity with natural rubber, butadiene rubber, styrene butadiene rubber, etc., which are widely used for tires, and is inferior to carbon black in terms of mechanical strength (tensile strength and elongation at break). Many.

As a method for solving this problem, it has been proposed to use a silane coupling agent having reactivity with a rubber component or silica, but it is difficult to sufficiently advance the reaction with silica, and unreacted silica. May remain poorly dispersed and the desired performance may not be exhibited. Further, in order to prevent this, if a large amount of silane coupling agent is blended, due to the residual silane coupling agent, rubber burning during processing, degradation performance of vulcanized rubber, and the like may be caused.

Patent Document 1 discloses a tire rubber composition containing a basic aqueous solution having a pH of 8 to 12 and silica for the purpose of enhancing the compatibility between silica and rubber, but the interaction between rubber and silica is disclosed. Cannot be sufficiently obtained, and the improvement effect such as low fuel consumption is not satisfactory. Therefore, it is desired to provide a silica-containing rubber that can improve fuel economy and rubber strength in a well-balanced manner.

JP 2000-219779 A

The object of the present invention is to solve the above-mentioned problems and to provide a bead apex rubber composition that improves the fuel efficiency and rubber strength in a well-balanced manner, and a pneumatic tire using the same.

The present invention relates to a rubber composition for bead apex containing 0.1 to 100 parts by mass of silica and 0.1 to 60 parts by mass of cyclized rubber with respect to 100 parts by mass of a rubber component.

The cyclization rate of the cyclized rubber is preferably 0.1 to 40%.
The cyclized rubber is preferably at least one selected from the group consisting of cyclized natural rubber, cyclized isoprene rubber, and cyclized butadiene rubber.

It is preferable that 1-100 mass parts of carbon black is included with respect to 100 mass parts of said rubber components.
The present invention relates to a pneumatic tire having a bead apex produced using the rubber composition.

According to the present invention, since it is a rubber composition for bead apex containing 0.1 to 100 parts by mass of silica and 0.1 to 60 parts by mass of cyclized rubber with respect to 100 parts by mass of the rubber component, low fuel consumption Property and rubber strength can be improved in a well-balanced manner.

The rubber composition for bead apex of the present invention is a mixture of silica and cyclized rubber in a predetermined amount with respect to a rubber component.

Silica compound rubber generally has low dispersibility of silica and it is difficult to obtain desired performance. However, in the present invention, the interaction between silica and a rubber component is enhanced by compounding cyclized rubber. Therefore, the dispersibility of the silica is improved, and both the low fuel consumption and the rubber strength can be achieved, and the performance balance can be improved synergistically.

Further, by using a cyclized rubber having a predetermined cyclization rate, the dispersibility of silica is dramatically improved, and the performance balance can be remarkably improved.

Rubber components include natural rubber (NR), epoxidized natural rubber (ENR), isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), diene rubbers such as butadiene isoprene rubber, and chlorinated butyl rubber. Butyl rubbers such as those obtained by condensing or modifying these rubbers can also be used. Among these, NR and BR are preferable from the viewpoint of the performance balance, and it is more preferable to use these in combination. These rubber components may be used alone or in combination of two or more.

Natural rubber (NR) is not particularly limited, and for example, SIR20, RSS # 3, TSR20, deproteinized natural rubber (DPNR), high-purity natural rubber (HPNR), etc., which are common in the tire industry can be used.

The content of NR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more. If it is less than 5% by mass, the fuel efficiency tends to decrease. The NR content is preferably 50% by mass or less, more preferably 30% by mass. If it exceeds 50 mass%, the rubber strength tends to decrease.

The BR is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd. Commonly used in the tire industry such as BR containing syndiotactic polybutadiene crystals can be used.

The content of BR in 100% by mass of the rubber component is preferably 40% by mass or more, more preferably 60% by mass or more. If it is less than 40% by mass, the rubber strength tends to decrease. The BR content is preferably 90% by mass or less, more preferably 80% by mass or less. When it exceeds 90 mass%, there exists a tendency for low-fuel-consumption property to fall.

In the present invention, from the viewpoint of the performance balance, the total content of NR and BR in 100% by mass of the rubber component is preferably 70% by mass or more, more preferably 90% by mass or more, and further preferably 100% by mass. .

The silica used in the present invention is not particularly limited, and examples thereof include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid) and the like, but because of the large number of silanol groups, wet process silica. Is preferred.

Nitrogen adsorption specific surface area of the silica _(N 2 SA) of preferably at least ^{40 m} 2 / g, more preferably at least ^{50m 2 / g, 100m 2 /} g or more, and particularly preferably equal to or greater than 150m ² / g. If it is less than 40 m ² / g, the rubber strength after vulcanization tends to decrease. The _N 2 SA of the silica is preferably not more than 500 meters ² / g, more preferably at most 300m ² / g. When it exceeds 500 m ² / g, there is a tendency that low heat build-up and rubber processability are lowered.
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 0.1 parts by mass or more, preferably 10 parts by mass or more, and more preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.1 parts by mass, the low heat build-up may be insufficient. Moreover, this content is 100 mass parts or less, Preferably it is 80 mass parts or less, More preferably, it is 60 mass parts or less. When the amount exceeds 100 parts by mass, it becomes difficult to disperse the filler into the rubber, and the processability of the rubber tends to deteriorate.

The rubber composition of the present invention may contain a silane coupling agent.
The silane coupling agent is not particularly limited, and conventionally known silane coupling agents can be used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-tri Methoxysilylpropyl) sulfide type such as tetrasulfide; mercapto type such as 3-mercaptopropyltrimethoxysilane; vinyl type such as vinyltriethoxysilane; amino type such as 3-aminopropyltriethoxysilane; γ-glycidoxypropyl Examples thereof include glycidoxy type such as triethoxysilane; nitro type such as 3-nitropropyltrimethoxysilane; chloro type such as 3-chloropropyltrimethoxysilane.

The content of the silane coupling agent is preferably 0 to 20 parts by mass with respect to 100 parts by mass of the rubber component. If the amount exceeds 20 parts by mass, the effect of dispersing the filler cannot be obtained for an increase in cost, and further, the reinforcing property and rubber strength may be lowered, and the unreacted silane coupling agent remains. There is also a risk that the rubber strength of the rubber after processing and the rubber strength after vulcanization may be lowered. The lower limit is more preferably 1 part by mass or more, still more preferably 3 parts by mass or more, and the upper limit is more preferably 15 parts by mass or less, still more preferably 10 parts by mass or less.

It is preferable that carbon black is blended in the rubber composition of the present invention. Thereby, the outstanding reinforcement property is obtained, rubber strength improves, and the said performance balance can be improved notably. Carbon black is not particularly limited, and examples thereof include SAF, ISAF, HAF, FF, and GPF.

Carbon black having an average particle size of 31 nm or less and / or a DBP oil absorption of 100 ml / 100 g or more is preferable. By blending such carbon black, necessary reinforcing properties are imparted, block rigidity and rubber strength are secured, and the effects of the present invention are remarkably obtained.

If the average particle size of the carbon black exceeds 31 nm, the rubber strength may be significantly deteriorated. The average particle diameter is more preferably 25 nm or less, and further preferably 23 nm or less. The average particle size is preferably 15 nm or more, and more preferably 19 nm or more. If it is less than 15 nm, the viscosity of the blended rubber is significantly increased, and the processability may be deteriorated. In the present invention, the average particle diameter is a number average particle diameter and is measured by a transmission electron microscope.

If the DBP oil absorption amount (dibutyl phthalate oil absorption amount) of carbon black is less than 100 ml / 100 g, the reinforcing property is low, and it may be difficult to ensure rigidity (elastic modulus). The DBP oil absorption is more preferably 105 ml / 100 g or more, and even more preferably 110 ml / 100 g or more. The DBP oil absorption is preferably 160 ml / 100 g or less, and more preferably 150 ml / 100 g or less. If it exceeds 160 ml / 100 g, it is difficult to produce carbon black itself. The DBP oil absorption of carbon black is measured according to JIS K6217-4: 2001.

The content of carbon black is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and still more preferably 10 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 reinforcing property may be inferior. The content is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and still more preferably 30 parts by mass or less. If it exceeds 100 parts by mass, the rigidity becomes too high and the fuel efficiency tends to deteriorate.

50 mass% or more is preferable, as for the silica content (content rate) in a total of 100 mass% of a silica and carbon black, 65 mass% or more is more preferable, and 75 mass% or more is still more preferable. If it is less than 50% by mass, the fuel efficiency tends to decrease. In addition, the content is preferably 90% by mass or less, and more preferably 80% by mass or less. If it exceeds 90% by mass, the rubber strength may decrease.

The rubber composition of the present invention may contain other fillers, and examples include, but are not limited to, calcium carbonate, aluminum hydroxide, montmorillonite, cellulose, various short fibers, glass balloons and eggshells. It is not something.

As the cyclized rubber, compounds having various chemical structures have been proposed, but the cyclized rubber in the present invention is not limited to any of them, and any compound can be used. In the present invention, the cyclized rubber is not a rubber component but an additive (silica dispersion improver) having an action of improving the compatibility between silica and the rubber component and improving the silica dispersibility.

The cyclization rate of the cyclized rubber is preferably 0.1% or more, more preferably 1% or more, and further preferably 3% or more. If it is less than 0.1%, sufficient interaction with silica cannot be obtained, and the fuel efficiency may be deteriorated. The cyclization rate is preferably 40% or less, more preferably 35% or less, and still more preferably 30% or less. If it exceeds 40%, the cyclized rubber may gel or adhere to the kneader.

The cyclization rate is the ratio of double bonds reacted by the cyclization reaction to the number of double bonds of the raw rubber component (conjugated diene polymer) before the cyclization reaction. For example, by measuring the peak areas of protons derived from double bonds before and after the cyclization reaction of the conjugated diene polymer used as a raw material by ¹ H-NMR analysis, the cyclization reaction when the pre-cyclization reaction is 100 The ratio of the double bond remaining in the subsequent cyclized product is obtained, and can be measured as a value (%) represented by the calculation formula = (100−the ratio of the double bond remaining in the cyclized product).

The number average molecular weight (Mn) of the cyclized rubber is preferably 1,000 to 1,300,000, more preferably 5,000 to 500,000, and 10,000 to 300,000. More preferably. If it is less than 1,000, the fuel efficiency may be deteriorated, and if it exceeds 1,300,000, the viscosity increases and the processability may be deteriorated.

The molecular weight distribution of the cyclized rubber, that is, the weight average molecular weight / number average molecular weight (Mw / Mn) is preferably 4 or less.
In addition, Mw / Mn is a standard polystyrene conversion value measured by GPC.

The glass transition temperature (Tg) of the cyclized rubber is not particularly limited and is usually −100 to 100 ° C., but preferably −90 to 80 ° C., more preferably −90 to 40 from the viewpoint of the effect of the present invention. ° C, more preferably -90 to 20 ° C, particularly preferably -90 to 5 ° C.

The gel amount of the cyclized rubber is preferably 10% by mass or less, more preferably 5% by mass or less from the viewpoint of the effect of the present invention, and a gel having substantially no gel is particularly preferable.

As the cyclized rubber, a conjugated diene polymer cyclized product can be preferably used. The conjugated diene polymer cyclized product is prepared by (co) polymerizing a conjugated diene monomer or a conjugated diene monomer and another monomer copolymerizable with the conjugated diene monomer by a known method. And the like obtained by cyclizing the conjugated diene polymer.

Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2-methyl- Examples include 1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, and the like. These monomers may be used alone or in combination of two or more.

Examples of other monomers copolymerizable with the conjugated diene monomer include styrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, and p-tert. -Butylstyrene, α-methylstyrene, α-methyl-p-methylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, p-bromostyrene, 2-methyl-1,4-dichlorostyrene, Aromatic vinyl monomers such as 2,4-dibromostyrene and vinylnaphthalene; Chain olefin monomers such as ethylene, propylene and 1-butene; Cyclic olefin monomers such as cyclopentene and 2-norbornene; 1,5 -Hexadiene, 1,6-heptadiene, 1,7-octadiene, dicyclopentadiene, 5-ethylidene-2-no Non-conjugated diene monomers such as rubornene; (meth) acrylic acid esters such as methyl (meth) acrylate and ethyl (meth) acrylate; (meth) acrylonitrile, (meth) acrylamide and the like. These monomers may be used alone or in combination of two or more.

The content of the conjugated diene monomer unit in the conjugated diene polymer may be appropriately selected within a range not impairing the effects of the present invention, but is preferably 40 mol% or more, more preferably 60 mol% or more, and still more preferably. Is 80 mol% or more.

As the cyclized rubber, the conjugated diene polymer cyclized product described above can be used. Among them, cyclized natural rubber, cyclized isoprene rubber, cyclized butadiene rubber and the like are particularly preferable from the viewpoint of the effect of the present invention.

As described above, the conjugated diene polymer cyclized product can be prepared by cyclizing the conjugated diene polymer, but this cyclization reaction can be carried out by a known method, for example, after the (co) polymerization reaction, one-pot reaction as it is. And a method of cyclization by adding a cyclization catalyst in (3), (co) polymerization, a method of re-creating a solution from a dried conjugated diene polymer, and the like.

Here, in the cyclization reaction, for example, a known cyclization catalyst is allowed to act directly on raw rubber or on a rubber solution, and a part of chain molecules in the rubber molecule is cyclized to reduce double bonds. Thereby obtaining a cyclized rubber. Examples of the cyclization catalyst include organic sulfonic acids such as sulfuric acid and p-toluenesulfonic acid, and chlorosulfonic acid.

The content of the cyclized rubber is 0.1 parts by mass or more, preferably 2 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. Moreover, this content is 60 mass parts or less, Preferably it is 40 mass parts or less, More preferably, it is 30 mass parts or less. If the amount is less than 0.1 parts by mass, the effect of silica dispersion is not sufficient, and the effect of improving fuel economy tends to be difficult to obtain. If it exceeds 60 parts by mass, the physical properties of the rubber may be reduced.

In addition to the above components, the rubber composition of the present invention includes oils, waxes, anti-aging agents, additives such as stearic acid and zinc oxide, vulcanizing agents such as sulfur, vulcanization accelerators, vulcanization acceleration aids, etc. May be appropriately blended.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a kneader such as a Banbury mixer, a kneader, or an open roll and then vulcanizing. The rubber composition is used for bead apex. The bead apex is a member arranged inside the tire clinch so as to extend radially outward from the bead core. Specifically, FIGS. 1 to 3 of Japanese Patent Application Laid-Open No. 2008-38140, and Japanese Patent Application Laid-Open No. 2004. This is the member shown in FIG.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, by extruding a rubber composition containing the above components in accordance with the shape of the bead apex at an unvulcanized stage, and molding it on a tire molding machine together with other tire members by a normal method. To form an unvulcanized tire. The pneumatic tire of the present invention can be manufactured by heating and pressurizing the unvulcanized tire in a vulcanizer.

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

(Production Example 1)
A pressure-resistant reactor equipped with a stirrer substituted with nitrogen was charged with 1400 g of dehydrated toluene and 18 mmol of n-butyllithium, and the internal temperature was maintained at 60 ° C. 487 g of isoprene was continuously added to the reactor over 15 minutes, and the internal temperature was controlled not to exceed 75 ° C. Thereafter, the mixture was reacted at 70 ° C. for 10.5 hours, and then 1.4 mmol of methanol was added as a polymerization terminator to terminate the polymerization reaction.
After stopping the polymerization reaction, the temperature was raised to 80 ° C., 4.24 g of p-toluenesulfonic acid was added, and the cyclization reaction was performed for 1 hour while maintaining the temperature at 80 ° C. Subsequently, an aqueous solution in which 1.70 g of sodium carbonate was dissolved in 5.1 g of water was added to stop the cyclization reaction, and the reaction solution was filtered to remove the catalyst residue. After adding 0.4 g of an anti-aging agent (Irganox 1010: manufactured by Ciba Specialty Chemicals) to this solution, toluene was distilled off and dried under reduced pressure to obtain a cyclized rubber 1.

(Production Example 2)
In a pressure vessel equipped with a stirrer substituted with nitrogen, 300 g of liquid polyisoprene (Kuraray LIR-30: Mn = 28,000) and 700 g of toluene were charged. The mixture was heated to 80 ° C. to completely dissolve polyisoprene, and then 2 g of p-toluenesulfonic acid was added to carry out a cyclization reaction while maintaining the internal temperature at 80 ° C. After reacting for 1 hour, a 25% aqueous solution of sodium carbonate containing 0.8 g of sodium carbonate was added to stop the reaction, stirred at 80 ° C. for 30 minutes, and then filtered to remove the catalyst residue. After adding 0.3 g of an anti-aging agent (Irganox 1010: manufactured by Ciba Specialty Chemicals) to this solution, toluene was distilled off and dried under reduced pressure to obtain a cyclized rubber 2.

(Production Example 3)
A cyclized rubber 3 was obtained in the same manner as in Production Example 2, except that liquid polybutadiene (manufactured by Sartomer, Rycon 150, Mn = 5,200) was used instead of liquid polyisoprene.

(Production Example 4)
Instead of liquid polyisoprene, polybutadiene (Ube Industries, UBEPOL 150L, Mn = 250,000) was used, and the cyclized rubber 4 was prepared in the same manner as in Production Example 2 except that the cyclization reaction time was changed to 3 hours. Obtained.

The physical properties of the obtained cyclized rubber were measured by the following methods, and the results are shown in Table 1.

(Cyclization rate of cyclized rubber)
The cyclization rate of the cyclized rubber was determined by the peak area ratio of protons in the polymer before and after the cyclization reaction by ¹ H-NMR measurement using an AV400 NMR apparatus manufactured by BRUKER, data analysis software TOP SPIN2.1. . In addition, the detailed cyclization rate calculation method is as having described in the following literature.
Y. Tanaka and H.M. Sato, J .; Polym. Sci: Poly. Chem. Ed. , 17, 3027 (1979)

(Number average molecular weight (Mn) and weight average molecular weight (Mw) of cyclized rubber)
The calibration curve obtained from the molecular weight distribution curve obtained by performing gel permeation (permeation) chromatography of cyclized rubber (GPC, manufactured by Tosoh Corporation) using polystyrene as a standard substance and tetrahydrofuran as a solvent at a temperature of 40 ° C. Mn and Mw were calculated.

(Glass transition temperature Tg of cyclized rubber)
The glass transition temperature of the cyclized rubber was measured using a differential scanning calorimeter (manufactured by Seiko Denshi Kogyo Co., Ltd .: SSC5200) under the conditions of a starting temperature of −100 ° C. and a heating rate of 10 ° C./min.

(Gel amount of cyclized rubber)
After 0.2 g of a sample cut to 2 mm square was immersed in 100 ml of toluene for 48 hours, the ratio of the dry weight of the gel remaining on the 80-mesh wire net was shown as a percentage.

The chemicals used in the examples and comparative examples are summarized below.
NR: RSS # 3
BR: UBEPOL BR150B manufactured by Ube Industries, Ltd. (cis 1,4 bond amount 97%, ML _{1 + 4} (100 ° C.) 40, Mw / Mn 3.3)
Cyclized rubber 1-4: Production Examples 1-4
Carbon black: Dia Black I manufactured by Mitsubishi Chemical Corporation (ISAF carbon, average particle size 23 nm, DBP oil absorption 114 ml / 100 g)
Silica: Ultrasil VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by EVONIK-DEGUSSA
Oil: Process X-140 (aromatic process oil) manufactured by Japan Energy Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Stearic acid: Stearic acid “paulownia” manufactured by NOF Corporation
Zinc oxide: Zinc oxide type 2 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylene) manufactured by Ouchi Shinsei Chemical Diamine)
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples and Comparative Examples>
In accordance with the formulation of Table 2, using a 1.7L Banbury mixer manufactured by Kobe Steel Co., Ltd., chemicals other than sulfur and a vulcanization accelerator were filled to a filling rate of 58%, and 140 rpm at 140 rpm. A kneaded product was obtained by kneading until reaching 0C. Next, using an open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded to obtain an unvulcanized rubber composition.
Further, the obtained unvulcanized rubber composition was molded into a predetermined size, and a vulcanized rubber composition was obtained by press vulcanization at 150 ° C. for 20 minutes, and a vulcanization of about 2 mm × 130 mm × 130 mm was obtained. A rubber slab sheet was prepared.

The following evaluation was performed about the obtained unvulcanized rubber composition and vulcanized rubber slab sheet. The results are shown in Table 2.

(Rubber strength)
The vulcanized rubber composition (vulcanized rubber slab sheet) was measured for tensile strength at the time of cutting based on JIS K6251, and the rubber strength index was calculated from the following formula using Comparative Example 1 as a reference. The larger the index, the higher the rubber strength.
(Rubber strength index) = (Tensile strength at cutting of each compound) / (Tensile strength at cutting in Comparative Example 1) × 100

(Viscoelasticity test)
Tensile modulus (E ^* ) of vulcanized rubber slab sheet using viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd. under conditions of temperature 70 ° C., initial strain 10%, dynamic strain ± 1% and frequency 10 Hz. The loss tangent (tan δ) was measured, and Comparative Example 1 was set to 100, and the elastic modulus and rolling resistance were indicated by an index according to the following formula. The larger the elastic modulus index is, the harder the rubber is, and the more preferable it is as a bead apex. The larger the rolling resistance index is, the better the rolling resistance is reduced.
(Modulus index = each formulation ^E *) / (Comparative Example 1 ^{E *)} × 100
(Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

In the example in which cyclized rubber was added to the silica-blended rubber of Comparative Example 1, each performance of rubber strength, elastic modulus, and low fuel consumption (rolling resistance) could be improved at the same time, and these performance balances could be improved synergistically. It became clear.

Claims (5)

A rubber composition for bead apex containing 0.1 to 100 parts by mass of silica and 0.1 to 60 parts by mass of cyclized rubber with respect to 100 parts by mass of the rubber component. The bead apex rubber composition according to claim 1, wherein the cyclized rubber has a cyclization rate of 0.1 to 40%. The bead apex rubber composition according to claim 1 or 2, wherein the cyclized rubber is at least one selected from the group consisting of cyclized natural rubber, cyclized isoprene rubber and cyclized butadiene rubber. The rubber composition for bead apex according to any one of claims 1 to 3, comprising 1 to 100 parts by mass of carbon black with respect to 100 parts by mass of the rubber component. The pneumatic tire which has the bead apex produced using the rubber composition in any one of Claims 1-4.