JP2009007454A - Tread rubber composition and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tread rubber composition friendly to the earth and prepared for the decrease in the amount of petroleum supply in the future by increasing the content of resources other than petroleum, and giving tires maintaining sufficient brake performance on both wet and dry road surfaces and reduced in rolling resistance. <P>SOLUTION: The tread rubber composition comprises 100 pts.wt. of a rubber component containing 50 mass% or more of a natural rubber and/or an epoxidized natural rubber, 5 pts.mass or more of a resin and 30-150 pts.mass of a filler comprising 80 wt.% or more of a white filler, wherein the resin has at least two peaks in its molecular weight distribution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention employs a tread rubber composition and a pneumatic tire using the same in the tread portion, particularly a rubber composition using natural resources as a tread portion to improve braking performance and reduce rolling resistance. Related to pneumatic tires.

  In recent years, exhaustion of petroleum resources has been a problem. Since the supply of petroleum raw materials has been decreasing year by year, oil prices are expected to rise in the future, and supply of raw materials consisting of petroleum resources such as synthetic rubber such as styrene-butadiene rubber and carbon black will be insufficient in the future. Is expected to. In the future, assuming short supply of petroleum resources, it will be necessary to use raw materials of natural resources such as natural rubber, white fillers such as silica and calcium carbonate.

  Conventionally, with a tread rubber compound mainly composed of natural rubber, the running performance on wet road surfaces and dry road surfaces is inferior to that of the commonly used styrene-butadiene rubber. Therefore, there is a method of improving the running performance on the wet road surface by using a white filler such as silica, calcium carbonate, aluminum hydroxide as the filler, but in that case, the running performance on the dry road surface becomes insufficient.

  Patent Document 1 discloses a technique that indicates a tire raw material that is assumed when oil is depleted, but does not disclose a tread rubber composition that exhibits sufficient running performance on wet and dry road surfaces. .

Patent Document 2 discloses a rubber tread for a tire that is gentle on the earth by increasing the content ratio of non-oil resources and that has sufficient running performance on wet and dry road surfaces in preparation for a future reduction in oil supply. A composition is disclosed.
JP 2003-63206 A JP 2006-63093 A

  The present invention uses natural resource raw materials instead of petroleum resource raw materials, in particular, using natural rubber and / or modified natural rubber, further blending a predetermined amount of resin, and adjusting its molecular weight distribution, A tread rubber composition having improved braking performance and reduced rolling resistance and a pneumatic tire using the tread rubber composition are proposed.

The present invention relates to a resin containing at least two peaks of molecular weight distribution with respect to 100 parts by mass of a rubber component containing 50% by mass or more of natural rubber and / or modified natural rubber, which is on the low molecular weight side of the peak. Peak height (H1) of the maximum peak (P1) and maximum peak on the polymer side (
5 parts by mass or more of the resin having a peak height (H2) ratio of P2) in the following relationship, and 0.5 ≦ (H2 / H1) ≦ 2.0
It is a tread rubber composition containing 30 to 150 parts by mass of a filler containing 80% by mass or more of a white filler. The resin is preferably a terpene polymer or a terpene copolymer.

  The molecular weight distribution peak of the resin is preferably 3000 or less, at least one molecular weight distribution peak is 1000 or more, and at least one molecular weight distribution is preferably less than 1000. The modified natural rubber is an epoxidized natural rubber, and the epoxidation rate is desirably 12 mol% or more.

  Furthermore, the present invention is a pneumatic tire using the tread rubber composition.

  According to the present invention, it is possible to provide a tread rubber composition used for a tire that is gentle to the earth by using raw materials of natural resources and is prepared for a future reduction in the supply of petroleum, and further, the tread rubber composition of the present invention. A pneumatic tire obtained from an object has excellent braking performance on wet and dry road surfaces, and rolling resistance is also reduced.

  The present invention relates to 100 parts by mass of a rubber component containing 50% by mass or more of natural rubber and / or modified natural rubber, 5 parts by mass or more of a resin containing at least two peaks of molecular weight distribution, and a white filler Is a tread rubber composition containing 30 to 150 parts by mass of a filler containing 80% by mass or more.

<Rubber component>
As the rubber component in the rubber composition for a tread of the present invention, natural rubber (NR) and / or modified natural rubber is used.

  As the natural rubber, cis 1,4 polyisoprene is used, but trans 1,4 polyisoprene can be appropriately mixed.

  As the modified natural rubber, epoxidized natural rubber (ENR) or deproteinized natural rubber is used. Epoxidized natural rubber refers to an epoxidized natural rubber double bond. Epoxidized natural rubber is also available as a commercial product. As a method for epoxidizing natural rubber, a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, a peracid method, or the like can be used. Examples thereof include a method of reacting natural rubber with an organic peracid such as peracetic acid or performic acid.

  The average epoxidation rate of the epoxidized natural rubber is preferably 12 mol% or more, more preferably 15 mol% or more. If the average of the epoxidation rate is less than 12 mol%, the coefficient of friction on the wet and dry road surfaces of the tread rubber composition becomes low and the braking performance cannot be improved. The average epoxidation rate is preferably 80 mol% or less, and more preferably 60 mol% or less. When the average of the epoxidation rate exceeds 80 mol%, gelation of the rubber component occurs.

  The content of natural rubber and / or modified natural rubber in the rubber component is 50% by mass or more, preferably 80% by mass or more. When the content is less than 50% by mass, the ratio of non-petroleum resources becomes small. By setting the content of the natural rubber and / or modified natural rubber in the rubber component to 100% by mass in particular, it is possible to achieve both improvement in braking characteristics and reduction in rolling resistance.

<Other rubber components>
In the present invention, as rubber components, there are the following rubber components used in addition to natural rubber, epoxidized natural rubber or deproteinized natural rubber. For example, styrene-butadiene rubber (SBR), polybutadiene rubber (BR), polyisoprene rubber (IR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), a copolymer of isobutylene and p-methylstyrene. Halides, acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR) and the like can be mentioned. The ethylene-propylene-diene rubber (EPDM) is an ethylene-propylene rubber (EPM) containing a third diene component. Examples of the third diene component include non-conjugated dienes having 5 to 20 carbon atoms such as 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, and 2,5-dimethyl-1,5. -Hexadiene and 1,4-octadiene, or cyclic dienes such as 1,4-cyclohexadiene, cyclooctadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 5-butylidene-2-norbornene, 2-methallyl-5 Examples thereof include alkenyl norbornene such as -norbornene and 2-isopropenyl-5-norbornene. In particular, dicyclopentadiene, 5-ethylidene-2-norbornene and the like can be used.

<Resin>
In the rubber composition for a tread of the present invention, the resin is blended in an amount of 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the rubber component.

  Examples of the resin include aromatic petroleum resins (resin using C9 fraction), coumarone indene resin (coal coumarone indene resin, etc.), terpene resin, aromatic modified terpene resin (natural aromatic terpene, etc.), rosin resin, Examples thereof include phenolic resins and petroleum resins (resins using C5 fraction). Of these, natural resins obtained from natural resources other than petroleum such as natural aromatic terpenes and coal coumarone indene resins are preferred.

  For example, a terpene system obtained by homopolymerization or copolymerization of terpenes such as dipentenes such as limonene, monoterpenes such as α-pinene, β-pinene, 3-carene, terpinolene and myrcene, and terpenes such as sesquiterpenes such as longifolene and caryophyllene. The (co) polymer is excellent. The terpene-based (co) polymer can be a homopolymer or a copolymer of only the terpene monomer, but can also be a copolymer using a terpene monomer and a monomer other than the terpene.

  The content of the terpene homopolymer or copolymer in the terpene (co) polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. When the (co) polymer of terpenes is less than 50% by mass, the effect of improving the dispersibility of the filler and improving the wear resistance cannot be expected.

  As the terpene-based (co) polymer, a homopolymer of one or more monomers selected from the group of limonene, α-pinene, β-pinene and terpinolene, or a copolymer is a modified natural such as natural rubber or ENR It is excellent in compatibility with rubber and synthetic rubber such as SBR, and is preferably used. In particular, the (co) polymer of β-pinene and / or limonene has a glass transition temperature of −30 ° C. to −45 ° C. and is excellent in compatibility with the rubber component. The terpene (co) polymer can be subjected to a hydrogenation treatment in order to improve heat aging resistance, weather resistance, and ozone resistance.

  In addition to terpenes, natural resins such as rosin, monomers derived from petroleum resources such as isoprene and phenol, and monomers derived from coal such as coumarone can be used as the resin. In particular, it is preferable to avoid the use of monomers derived from petroleum resources and monomers derived from coal resources from the viewpoint of environmental considerations.

The measurement conditions of the gel permeation chromatogram of the resin are as follows.
Column: TSKgerG2000H8 (60 cm × 2 (120 cm)) manufactured by Tosoh Corporation
Detector: RI (40 ° C) manufactured by Tosoh Corporation
Flow rate: 1 ml / min THF,
Pressure: 22-23 kg / cm ² ,
Mobile phase: 1% THF,
Apparatus: TOYOSODA HLC-801A manufactured by Tosoh Corporation.

  The molecular weight distribution obtained under the above measurement conditions has at least two peaks. FIG. 1 shows the molecular weight distribution of two types of resins, resin A and resin B, used in the present invention. For example, the resin A has peaks P1 and P2 in the molecular weight distribution, on the high molecular weight side having a polystyrene equivalent molecular weight of 1000 or more in GPC measurement and on the low molecular weight side having a polystyrene equivalent molecular weight of less than 1000, respectively. When the position of the low molecular weight peak (P1) is 1000 or more, it is difficult to reduce the rolling resistance, and when the position of the high molecular weight peak (P2) is 1000 or less, the braking performance is improved. Can not do it.

  In addition, when a conventional resin having one peak in the molecular weight distribution is used, depending on the position of the molecular weight that shows the peak, it is biased toward either the reduction of rolling resistance or the improvement of the group performance, and the balance between the two characteristics is achieved. Is difficult. It should be noted that at least two peaks in the molecular weight distribution are required, but one or more additional intermediate molecular weight peaks (Pm) between the maximum peak (P1) on the low molecular weight side and the maximum peak (P2) on the high molecular weight side. Can have. Moreover, it can also have a peak on the high molecular weight side from the low molecular weight side maximum peak (P1) or the high molecular weight side maximum peak (P2).

  Here, the maximum peak (P1) on the low molecular weight side means a peak having the maximum peak height (H1) on the low molecular weight side, and the maximum peak (P2) on the high molecular weight side is the maximum on the high molecular weight side. A peak having a peak height (H2) of.

  In the present invention, the ratio (H2 / H1) of the peak heights of the maximum peak (P1) on the low molecular weight side and the maximum peak (P2) on the high molecular weight side is in the range of 0.5 to 2.0. The range is preferably 0.8 or more and 1.5 or less. When the ratio of peak heights (H2 / H1) is less than 0.5, grip properties tend to decrease, while when it exceeds 2.0, rolling resistance tends to deteriorate.

  Here, the ratio of the peak height is the height of the peak height (H1) of the maximum peak (P1) on the low molecular weight side in the graph showing the relationship between the molecular weight and the peak intensity obtained by GPC measurement as shown in FIG. It is defined as the ratio (H2 / H1) of the maximum peak (P2) on the molecular weight side to the peak height (H2). In FIG. 1, the maximum peak (P2) on the high molecular weight side preferably has a molecular weight of 3000 or less. When a peak exists in the region where the molecular weight exceeds 3000, the hardness of the rubber composition increases and the braking performance tends to decrease.

  In the present invention, the softening point of the resin is preferably 50 ° C. or higher, and more preferably 80 ° C. or higher. When the softening point is less than 50 ° C., the tackiness in the manufacturing process becomes strong, and the work in manufacturing the tire tends to be difficult. The softening point of the resin is preferably 150 ° C. or less, and more preferably 140 ° C. or less. When the softening point exceeds 150 ° C., the wet braking performance becomes insufficient and the effect of blending the resin tends to be lost.

  The content of the resin is 5 parts by mass or more, preferably 8 parts by mass or more with respect to 100 parts by mass of the rubber component. When the content is less than 5 parts by mass, the effect of improving the braking performance is reduced. Moreover, content is 50 mass parts or less, Preferably it is 35 mass parts or less. When the content exceeds 50 parts by mass, the hardness increases.

<Filler>
Examples of the filler used in the rubber composition for a tread of the present invention include silica, calcium carbonate, sericite, carbon black, aluminum hydroxide, and clay. As the tread rubber composition of the present invention, it is preferable to use a white filler such as silica, calcium carbonate or sericite. By using these white fillers, unlike the case of fillers such as carbon black, the effect of reducing rolling resistance and increasing the ratio of non-petroleum resources can be obtained.

  The content of the white filler in the filler is 80% by mass or more, preferably 90% by mass or more. If the content is less than 80% by mass, the ratio of non-petroleum resources decreases, which is not preferable. The content of the white filler is preferably 100% by mass.

When carbon black is used in the present invention, the nitrogen adsorption specific surface area of the carbon black, 100 m ² / g or more 1500 m ² / g or less. When the nitrogen adsorption specific surface area is 100 m ² / g or more, the mechanical strength of the rubber composition is improved, and when the nitrogen adsorption specific surface area is 1500 m ² / g or less, it is preferable from the viewpoint of ensuring processability during production. The nitrogen adsorption specific surface area is more preferably 105 m ² / g or more, more preferably 1300 m ² / g or less, and still more preferably 1000 m ² / g or less.

Moreover, when using silica, it is preferable that the nitrogen adsorption specific surface area (BET method) of a silica exists in the range of 100-300 m < ² > / g, for example, and also 150-250 m < ² > / g. When the nitrogen adsorption specific surface area of silica is 100 m ² / g or more, the abrasion resistance of the tire is improved satisfactorily by obtaining a sufficient reinforcing effect. On the other hand, when the nitrogen adsorption specific surface area is 300 m ² / g or less, the processability during production of each rubber is good, and the steering stability of the tire is also ensured. The nitrogen adsorption specific surface area is measured by the BET method according to ASTM D3037-81.

<Silane coupling agent>
When silica is used as the white filler, it is preferable to use a silane coupling agent in combination. It is preferable that the compounding quantity of a silane coupling agent shall be 1-20 mass parts with respect to 100 mass parts of silica. If the blending amount is less than 1 part by mass, the wear resistance tends to deteriorate. On the other hand, if the blending amount of the silane coupling agent is 20% by mass or more, scorching may occur in the rubber kneading and extrusion processes. There is sex.

  As sulfur-containing silane coupling agents, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl-tetrasulfide, trimethoxysilylpropyl-mercaptobenzothiazole tetrasulfide, triethoxysilylpropyl-methacrylate-monosulfide, dimethoxymethyl Examples include silylpropyl-N, N-dimethylthiocarbamoyl-tetrasulfide, bis- [3- (triethoxysilyl) -propyl] tetrasulfide, 3-mercaptopropyltrimethoxysilane and the like. Other silane coupling agents include vinyltrichlorosilane, vinyltris (2-methoxyethoxy) silane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ- (2-aminoethyl) Aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and the like can be used.

<Other ingredients>
In addition to the above, it is possible to add a vulcanizing agent, a vulcanization accelerator, a softening agent, a plasticizer, an anti-aging agent, an anti-scorch agent, and the like to the rubber composition.

  As the vulcanizing agent, an organic peroxide or a sulfur vulcanizing agent can be used. Examples of the organic peroxide include benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 2,5-dimethyl-2, 5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne- 3 or 1,3-bis (t-butylperoxypropyl) benzene, di-t-butylperoxy-diisopropylbenzene, t-butylperoxybenzene, 2,4-dichlorobenzoyl peroxide, 1,1- Di-t-butylperoxy-3,3,5-trimethylsiloxane, n-butyl-4, - it can be used such as di -t- butyl peroxy valerate. Of these, dicumyl peroxide, t-butylperoxybenzene and di-t-butylperoxy-diisopropylbenzene are preferred. Moreover, as a sulfur type vulcanizing agent, sulfur, morpholine disulfide, etc. can be used, for example. Of these, sulfur is preferred.

  Vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine, aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Those containing at least one of them can be used.

  As the anti-aging agent, amine-based, phenol-based, and imidazole-based compounds, carbamic acid metal salts, waxes, and the like can be appropriately selected and used.

  In the present invention, a softener may be used in combination in order to further improve kneading processability. Softeners include process oil, lubricating oil, paraffin, liquid paraffin, petroleum asphalt, petroleum jelly such as petroleum jelly, fatty oil softener such as castor oil, linseed oil, rapeseed oil, coconut oil, tall oil, , Waxes such as beeswax, carnauba wax and lanolin, and fatty acids such as linoleic acid, palmitic acid, stearic acid and lauric acid.

  As plasticizers, DMP (dimethyl phthalate), DEP (diethyl phthalate), DBP (dibutyl phthalate), DHP (diheptyl phthalate), DOP (dioctyl phthalate), DINP (diisononyl phthalate), DIDP (phthalate) Acid diisodecyl), BBP (butyl benzyl phthalate), DLP (dilauryl phthalate), DCHP (dicyclohexyl phthalate), hydrophthalic anhydride, DOZ (di-2-ethylhexyl azelate), DBS (dibutyl sebacate), DOS (Dioctyl sebacate), acetyl triethyl citrate, acetyl tributyl citrate, DBM (dibutyl maleate), DOM (2-ethylhexyl maleate), DBF (dibutyl fumarate) and the like.

  As the scorch preventing agent for preventing or delaying scorch, for example, organic acids such as phthalic anhydride, salicylic acid and benzoic acid, nitroso compounds such as N-nitrosodiphenylamine, N-cyclohexylthiophthalimide and the like can be used.

<Tire structure>
The structure of the pneumatic tire of the present invention is exemplified in the upper right half of the tire cross section of FIG. The tire 1 includes a tread rubber 7 constituting a tread portion, a pair of sidewall portions 8 extending inward in the tire radial direction from both ends thereof, a clinch portion 3 positioned at an inner end of each sidewall portion, and an upper portion of a rim. The chafer part 2 is provided. A carcass 10 is bridged between the pair of bead cores 4, and a breaker portion 9 is disposed outside the carcass 10 in the tire radial direction. The carcass 10 is formed of one or more carcass plies on which carcass cords are arranged. The carcass ply includes a bead core 4 extending from a tread portion through a sidewall portion and a bead core 4 extending from the upper end of the bead core 4 toward the sidewall. Around the apex 5 is folded from the inner side to the outer side in the tire axial direction, and is locked by the folded portion. The breaker portion is composed of two or more breaker plies in which breaker cords are arranged, and each breaker cord is arranged so as to intersect between the breaker plies.

  By using the rubber composition for a tread of the present invention, a tire containing a tread composed of the rubber composition can be produced by a usual method. That is, the rubber composition for a tread of the present invention, which is blended with the chemicals as necessary, is extruded according to the shape of the tread of the tire at an unvulcanized stage, and molded by a normal method on a tire molding machine. By doing so, an unvulcanized tire is formed. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

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

Examples 1 and 2 and Comparative Examples 1 to 3
Various chemicals other than sulfur and vulcanization accelerators listed in Table 1 were filled in a 1.7 L Banbury manufactured by Kobe Steel, Ltd., and kneaded at 77 rpm until reaching 145 ° C. To the obtained kneaded product, sulfur and a vulcanization accelerator were blended in the amounts shown in Table 1, and kneaded at 80 ° C. for 6 minutes with an open roll to obtain an unvulcanized rubber composition. The unvulcanized rubber composition was molded into a tread shape on a tire molding machine and bonded to another tire member to produce an unvulcanized tire. A tire was manufactured by vulcanizing it at 160 ° C. for 20 minutes.

  Using a tread rubber composition adjusted with the rubber composition shown in Table 1, vulcanization molding was carried out by a conventional method to produce a pneumatic tire of size 195 / 65R15 having the structure shown in FIG. Here, the basic structure of the prototype tire is as follows.

Carcass ply Cord angle 88 degrees in the tire circumferential direction Cord material Polyester 1670/2 dtex
Breaker Cord angle 20 degrees x -20 degrees in the tire circumferential direction Cord material Steel cord

The various chemicals used in the examples are described in detail below.
(Note 1) ENR-25: Epoxidized natural rubber manufactured by GATHRIE POLYMER SDN. BHD (epoxidation rate: 25 mol%)
(Note 2) NR: RSS # 1
(Note 3) Carbon Black: Show Black N220 manufactured by Showa Cabot Corporation
(Note 4) Silica: Ultrasil VN3 (BET specific surface area: 175 m ² / g) manufactured by Tegussa
(Note 5) Silane coupling agent: Si-69 manufactured by Tegussa
(Note 6) Oil: Vegetable oil: Refined palm oil J (S) manufactured by Nisshin Oil Co., Ltd.
(Note 7) Resin A: PX300N (β-pinene polymer resin, manufactured by Yasuhara Chemical Co., Ltd., molecular weight distribution: high molecular weight side peak position Mw = 2750, low molecular weight side peak position Mw = 540, peak intensity ratio (H2 / H1 = 0.81)
(Note 8) Resin B: PX1150N manufactured by Yasuhara Chemical Co., Ltd. (β-pinene polymer resin, molecular weight distribution: peak position on the high molecular weight side is Mw = 2600, peak position on the low molecular weight side is Mw = 210, peak intensity ratio (H2 / H1 = 2.83)
(Note 9) Wax: Sunnock wax manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. (Note 10) Anti-aging agent: Ozonon 6C manufactured by Seiko Chemical Co., Ltd.
(Note 11) Stearic acid: Stearic acid manufactured by NOF Corporation (Note 12) Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. (Note 13) Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. (Note 14) Vulcanization accelerator TBBS: Noxeller NS manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Of these chemicals, non-petroleum resources are NR, ENR, silica, sulfur, oil, Resin A, Resin B, stearic acid, and zinc oxide.

The following tests were performed using the obtained tires.
<Dry braking index, wet braking index>
The test tire was mounted on a vehicle, and the braking stop distance from 100 km / h was measured on the dry asphalt road surface and the wet asphalt road surface, and the friction coefficient μ was obtained from the measured value. The index was displayed with μ in Comparative Example 1 as 100. The larger the index, the better the performance.

<Rolling resistance index>
The test tire was mounted on a 15 × 6 JJ rim, filled with an air temperature of 25 ° C. and an internal pressure of 230 KPa, and the rolling resistance was measured using a rolling resistance tester under a load of 3.43 kN and a speed of 80 km / h. About rolling resistance coefficient (RRC) which remove | divided the measured value of rolling resistance with the load, the rolling resistance of Examples 1, 2, and Comparative Examples 2 and 3 was displayed as Comparative Example 1 (reference | standard mixing | blending) as 100 by the following formula | equation. . The larger the value, the smaller the rolling resistance and the better the performance. The results are shown in Table 1.
Rolling resistance index = Rolling resistance of standard composition / Rolling resistance coefficient of each composition × 100
<Performance evaluation>
In Table 1, Examples 1 and 2 of the present invention show resin A having two peaks in which the ratio of peak height (H2 / H1) is in the range of 0.5 to 2.0 in the molecular weight distribution. 8 parts by mass of (H2 / H1 = 0.81) is blended, and the dry braking performance, wet braking performance, and rolling resistance index are comprehensively excellent.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a graph which shows the molecular weight distribution of the resin used for this invention. It is a right half of sectional drawing of the pneumatic tire of this invention.

Explanation of symbols

  1 tire, 2 chafer, 3 clinch rubber, 4 bead core, 5 bead apex, 7 tread part, 8 side wall part, 9 breaker part, 10 carcass.

Claims (5)

For 100 parts by mass of a rubber component containing 50% by mass or more of natural rubber and / or modified natural rubber,
A resin comprising at least two peaks of molecular weight distribution, wherein the peak height (H1) of the maximum peak (P1) on the low molecular weight side and the peak height (H2) of the maximum peak (P2) on the polymer side of the peaks ) In the following relationship: 5 parts by mass or more, and 0.5 ≦ (H2 / H1) ≦ 2.0
A tread rubber composition containing 30 to 150 parts by mass of a filler containing 80% by mass or more of a white filler.   The tread rubber composition according to claim 1, wherein the resin is a terpene polymer or a terpene copolymer.   3. The tread rubber composition according to claim 1 or 2, wherein the resin has a molecular weight distribution peak of 3000 or less, at least one molecular weight distribution peak is 1000 or more, and at least one molecular weight distribution is less than 1000. .   The tread rubber composition according to any one of claims 1 to 3, wherein the modified natural rubber is an epoxidized natural rubber and has an average epoxidation rate of 12 mol% or more.   A pneumatic tire using the tread rubber composition according to claim 1.

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