Rubber composition and pneumatic tire

Abstract

The present invention provides: a pneumatic tire having an improved balance between dry handling stability and low rolling resistance while maintaining outstanding on-ice performance and wet grip performance; and a rubber composition by which said tire is obtained. The rubber composition contains: a rubber component including natural rubber and a modified styrene-butadiene copolymer rubber having a glass transition temperature of -50°C or less; a resin; a filler including silica having a cetyltrimethylammonium bromide specific surface area of 190 m2 / g or more; and an oil component, wherein the modified styrene-butadiene copolymer rubber content in the rubber component is more than 50 mass %.

Description

Technical Field

[0001] The present invention relates to a rubber composition and a pneumatic tire.

Background Art

[0002] For the purpose of improving the wet grip performance of a tire, there is disclosed a rubber composition containing a rubber component (A), a thermoplastic resin (B), and a filler (C), wherein the rubber component (A) contains 10 to 100 parts by mass of a modified styrene-butadiene copolymer rubber having a glass transition temperature (Tg) of -50°C or lower per 100 parts by mass of the rubber component (A), and the rubber composition contains 5 to 30 parts by mass of the thermoplastic resin (B) per 100 parts by mass of the rubber component (A) (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the rubber composition of Patent Document 1, the balance between ice performance and abrasion resistance was insufficient. Conventionally, in order to improve the balance between wet grip performance and ice performance, large-particle silica has been compounded in a high amount, but this has been in conflict with low rolling resistance and dry handling stability. Recently, environmental regulations have become strict even for tires for SUVs (Sport Utility Vehicles), and more excellent low rolling resistance is required, and also abrasion resistance and dry handling stability are demanded. An object of the present invention is to provide a pneumatic tire having an improved balance between dry handling stability and low rolling resistance while maintaining excellent ice performance and wet grip performance, and a rubber composition from which the tire is obtained, and solving this object is an issue.

Means for Solving the Problem

[0005] <1> A rubber composition containing a rubber component including natural rubber and a modified styrene-butadiene copolymer rubber having a glass transition temperature of -50°C or lower, a resin, a filler containing silica having a cetyltrimethylammonium bromide specific surface area of 190 m 2 / g or more, and an oil component, wherein the content of the modified styrene-butadiene copolymer rubber in the rubber component is more than 50% by mass.

[0006] <2> The rubber composition according to <1>, wherein the silica is contained in an amount of 60 parts by mass or more per 100 parts by mass of the rubber component. <3> The rubber composition according to <1> or <2>, wherein the filler contains aluminum hydroxide. <4> The rubber composition according to <3>, wherein the aluminum hydroxide is contained in an amount of 1 to 20 parts by mass per 100 parts by mass of the rubber component. <5> The rubber composition according to <3> or <4>, wherein the ratio (s / a) of the content (s) of the silica to the content (a) of the aluminum hydroxide is 5 to 10 on a mass basis. <6> The rubber composition according to any one of <1> to <5>, wherein the rubber component further contains 1 to 30% by mass of a modified styrene-butadiene copolymer rubber having a glass transition temperature of -40°C or higher. <7> The rubber composition according to any one of <1> to <6>, wherein the oil component is contained in an amount exceeding 0 part by mass and 20 parts by mass or less per 100 parts by mass of the rubber component. <8> The rubber composition according to any one of <1> to <7>, wherein the resin has a glass transition temperature higher than 60°C.

[0007] <9> A pneumatic tire using the rubber composition according to any one of <1> to <8>.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a pneumatic tire that improves the balance between dry handling stability and low rolling resistance while maintaining excellent ice performance and wet grip performance, and a rubber composition from which the tire is obtained.

Mode for Carrying Out the Invention

[0009] <Rubber Composition> The rubber composition of the present invention contains a rubber component including natural rubber and a modified styrene-butadiene copolymer rubber having a glass transition temperature of -50°C or lower, a resin, a filler containing silica having a cetyltrimethylammonium bromide specific surface area of 190 m 2 / g or more, and an oil component, and the content of the modified styrene-butadiene copolymer rubber in the rubber component is more than 50% by mass. The rubber composition of the present invention may further contain aluminum hydroxide, a modified styrene-butadiene copolymer rubber having a glass transition temperature of -40°C or higher, and the like.

[0010] Hereinafter, the modified styrene-butadiene copolymer rubber having a glass transition temperature of -50°C or lower may be referred to as "low Tg modified SBR"; the cetyltrimethylammonium bromide specific surface area may be referred to as "CTAB specific surface area"; and the modified styrene-butadiene copolymer rubber having a glass transition temperature of -40°C or higher may be referred to as "high Tg modified SBR".

[0011] Also, the handling stability on a dry road surface may be referred to as "DRY handling stability", the braking performance on a wet road surface may be referred to as "WET performance", and the braking performance on an ice and snow road surface may be referred to as "SNOW performance".

[0012] Since the modified styrene-butadiene copolymer rubber is excellent in the dispersibility of silica in the rubber composition, when low Tg modified SBR is included in a high proportion of more than 50% by mass in the rubber component, silica can also be included in a high proportion. In the present invention, as silica, the CTAB specific surface area is 190 m 2By using silica with a particle size of / g or more, it is considered possible to improve the balance between dry handling stability and low rolling resistance while maintaining excellent ice performance. In addition, since the rubber composition contains a resin and an oil component, it is considered possible to maintain the wet grip performance of the tire. Hereinafter, the rubber composition and the pneumatic tire of the present invention will be described in detail.

[0013] 〔Rubber component〕 The rubber component includes natural rubber (NR) and a modified styrene-butadiene copolymer rubber (low Tg modified SBR) having a glass transition temperature of -50°C or lower, and the content of low Tg modified SBR in the rubber component is more than 50% by mass. If the rubber component does not contain natural rubber and more than 50% by mass of low Tg modified SBR, it cannot contain a large amount of silica, cannot exhibit excellent ice performance, and cannot improve the balance between dry handling stability and low rolling resistance. From the viewpoint of further improving the ice performance, dry handling stability and low rolling resistance of the tire, the content of low Tg modified SBR in the rubber component is preferably more than 50% by mass, more preferably 55% by mass or more, still more preferably 57% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or more, still more preferably 75% by mass or less.

[0014] The glass transition temperature (Tg) of the low Tg modified SBR is -50°C or lower. If the Tg of the low Tg modified SBR exceeds -50°C, the SNOW performance cannot be maintained. From the viewpoint of maintaining the SNOW performance, the Tg of the low Tg modified SBR is preferably -60°C or lower, more preferably -60 to -70°C. Tg can be determined by a differential scanning calorimeter.

[0015] The low Tg modified SBR preferably has a bound styrene content of 5 to 25%. By having the bound styrene content of the low-Tg modified SBR be 5% or more, WET performance can be ensured, and by having it be 25% or less, SNOW performance can be ensured. From the perspective of the balance between SNOW performance and WET performance, the bound styrene content of the low-Tg modified SBR is more preferably 7% or more, even more preferably 8% or more, and more preferably 20% or less, even more preferably 15% or less. The bound styrene content can be determined by dissolving the modified SBR in a solvent such as chloroform and measuring the absorption amount of the ultraviolet absorption wavelength (near 254 nm) by the phenyl group of styrene.

[0016] From the perspective of SNOW performance, the content of natural rubber in the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and preferably 45% by mass or less, more preferably 43% by mass or less.

[0017] From the perspective of further improving the wet grip performance and dry handling stability of the tire, the rubber component preferably further contains a modified styrene-butadiene copolymer rubber (high-Tg modified SBR) having a glass transition temperature of -40°C or higher. In the rubber component, the high-Tg modified SBR is preferably 1% or more, more preferably 5% or more, even more preferably 7% or more, and preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less.

[0018] The glass transition temperature (Tg) of the high-Tg modified SBR is -40°C or higher. By having the Tg of the high-Tg modified SBR be -40°C or higher, WET performance can be maintained. From the perspective of the balance between WET performance and low rolling resistance, the Tg of the high-Tg modified SBR is preferably -40°C to -15°C, more preferably -40°C to -20°C, even more preferably -40°C to -30°C.

[0019] The high-Tg modified SBR preferably has a bound styrene content of 30 to 55%. By having the bound styrene content of the high-Tg modified SBR be 30% or more, WET performance can be ensured, and by having it be 55% or less, SNOW performance can be maintained. From the perspective of the SNOW / WET balance, the bound styrene content of the high-Tg modified SBR is more preferably 35% or more, still more preferably 50% or less, even more preferably 45% or less, and even more preferably 40% or less.

[0020] The low-Tg modified SBR and the high-Tg modified SBR are not particularly limited as long as a part (for example, the molecular end, etc.) of the molecular chain of the styrene-butadiene copolymer rubber (SBR) is modified. Among them, from the perspective of having a high affinity for a filler (especially silica), it is preferable that the end of the styrene-butadiene copolymer rubber is modified with a silane compound. Examples of the silane compound include a silane compound having a glycidoxy group, an alkoxysilane compound, a hydrocarbyloxysilane compound, etc.

[0021] Natural rubber, low-Tg modified SBR, and high-Tg modified SBR may each be used alone or in combination of two or more. When both low-Tg modified SBR and high-Tg modified SBR are included, it is preferable that the mass ratio satisfies the following formula. 1.3 ≦ WL / WH ≦ 19 In the above formula, WL represents the mass of the low-Tg SBR, and WH represents the mass of the high-Tg modified SBR. WL / WH is more preferably 1.5 or more, still more preferably 1.8 or more, even more preferably 2.3 or more, even more preferably 2.8 or more, and even more preferably 3.3 or more. Also, WL / WH is more preferably 12 or less, still more preferably 10 or less, even more preferably 9 or less, even more preferably 8.5 or less, even more preferably 8 or less, even more preferably 7.5 or less, and even more preferably 7 or less.

[0022] The rubber component may further contain rubber components other than natural rubber, low Tg modified SBR, and high Tg modified SBR. As other rubber components, for example, synthetic rubbers such as polyisoprene rubber (IR), polybutadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), halogenated butyl rubber, acrylonitrile-butadiene rubber (NBR), etc. can be used. These rubber components may be used alone or in combination of two or more.

[0023] 〔Filler〕 The rubber composition of the present invention contains silica having a cetyltrimethylammonium bromide specific surface area of 190 m 2 / g or more. When the CTAB specific surface area of the silica is less than 190 m 2 / g, the low rolling resistance and ice performance of the tire are not excellent. The upper limit of the CTAB specific surface area of the silica is not particularly limited, but 250 m 2 / g is preferable. From the viewpoint of further improving the low rolling resistance and ice performance of the tire, the CTAB specific surface area of the silica is preferably 195 m 2 / g or more. The CTAB specific surface area of the silica can be measured by a method conforming to the method of ASTM-D3765-80.

[0024] There is no particular limitation on the silica as long as its CTAB specific surface area is 190 m 2 / g or more, and examples include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), colloidal silica, etc. Silica having a CTAB specific surface area of 190 m 2 / g or more may be a commercially available product, and for example, it can be obtained as Zeosil Premium200MP (trade name) of Rhodia and 9500GR (trade name) of Evonik.

[0025] The rubber composition has a CTAB specific surface area of 190 m 2It is preferable to contain 60 parts by mass or more of silica of / g or more with respect to 100 parts by mass of the rubber component. In the rubber composition, the CTAB specific surface area is 190 m 2 By having the content of silica of / g or more be 60 parts by mass or more with respect to 100 parts by mass of the rubber component, the WET performance can be ensured. From the viewpoint of the balance among WET performance, DRY handling stability, and low rolling resistance, in the rubber composition, the content of silica having a CTAB specific surface area of 190 m 2 / g or more is preferably 60 parts by mass or more, more preferably 65 parts by mass or more, and still more preferably 70 parts by mass or more with respect to 100 parts by mass of the rubber component. Also, it is preferably 90 parts by mass or less, and more preferably 85 parts by mass or less.

[0026] Silica having a CTAB specific surface area of 190 m 2 / g or more may be used alone or in a mixture of two or more. Silica having a CTAB specific surface area of less than 190 m 2 / g may also be used alone or in a mixture of two or more. The rubber composition of the present application may contain both silica having a CTAB specific surface area of 190 m 2 / g or more and silica having a CTAB specific surface area of less than 190 m 2 / g, but it is preferable to contain only silica having a CTAB specific surface area of 190 m 2 / g or more. The content of silica having a CTAB specific surface area of 190 m 2 / g or more is preferably 90 mass% or more and 100 mass% or less in the total amount of all silica. Examples of silica having a CTAB specific surface area of less than 190 m 2 / g include "ULTRASIL (registered trademark) VN 3" and the like.

[0027] The filler may further contain other fillers such as aluminum hydroxide and carbon black.

[0028] (aluminum hydroxide) From the perspective of achieving high-dimensional compatibility between the low rolling resistance and wet grip performance of a tire, the filler preferably contains aluminum hydroxide. Unlike reinforcing fillers such as silica and carbon black, aluminum hydroxide is a non-reinforcing filler. Therefore, even if the rubber composition contains it, the viscoelasticity of the rubber composition is less likely to change. Also, after vulcanizing the rubber composition to manufacture a tire, the aluminum hydroxide falls off from the rubber surface, creating roughness on the tire surface, thereby improving the grip on the road surface. As a result, it is possible to achieve high-dimensional compatibility between low rolling resistance and wet grip performance. Note that since aluminum hydroxide is a non-reinforcing filler, the wear resistance of the vulcanized rubber may decrease when the rubber composition contains aluminum hydroxide. However, in the present invention, since low-Tg modified SBR is included in a high proportion of 55% by mass or more in the rubber component, finely divided silica with a CTAB specific surface area of 190 m 2 / g or more can be dispersed in a high proportion and included in the rubber composition. Therefore, a decrease in wear resistance can be suppressed.

[0029] The rubber composition preferably contains 1 to 20 parts by mass of aluminum hydroxide per 100 parts by mass of the rubber component. When the content of aluminum hydroxide in the rubber composition is 1 part by mass or more per 100 parts by mass of the rubber component, it is possible to achieve higher-dimensional compatibility between the low rolling resistance and wet grip performance of the tire. When it is 20 parts by mass or less, a decrease in the wear resistance of the vulcanized rubber can be more effectively suppressed. The content of aluminum hydroxide in the rubber composition is preferably 3 parts by mass or more, more preferably 4 parts by mass or more, and still more preferably 5 parts by mass or more per 100 parts by mass of the rubber component. Also, it is preferably 17 parts by mass or less, more preferably 16 parts by mass or less, and still more preferably 15 parts by mass or less.

[0030] Also, the CTAB specific surface area is 190 m 2The ratio (s / a) of the content (s) of silica to the content (a) of aluminum hydroxide is preferably 5 to 10 on a mass basis. When the ratio (s / a) is 5 or more on a mass basis, the WET performance can be ensured, and when it is 10 or less, the breaking strength can be maintained. From the viewpoint of achieving a higher-dimensional compatibility between the low rolling resistance and wet grip performance of the tire, the ratio (s / a) is preferably 6 or more, more preferably 7 or more, and preferably 10 or less, more preferably 9 or less on a mass basis.

[0031] (Carbon black) The carbon black is not particularly limited and can be appropriately selected according to the purpose. The carbon black is preferably of the FEF, SRF, HAF, ISAF, SAF, or ISAF-HS grade, and more preferably of the HAF, ISAF, SAF, or ISAF-HS grade. The content of carbon black in the rubber composition is preferably 1 part by mass or more, more preferably 2 parts by mass or more, based on 100 parts by mass of the rubber component, from the viewpoint of improving the elastic modulus of the vulcanized rubber. Also, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less.

[0032] [Silane coupling agent] The rubber composition of the present invention contains low-Tg modified SBR as a rubber component. In order to strengthen the bond between the silica-rubber components, further enhance the reinforcing property of the rubber composition, and improve the dispersibility of silica, the rubber composition of the present invention may further use a silane coupling agent. The content of the silane coupling agent in the rubber composition of the present invention is preferably 5 to 15% by mass or less based on the content of silica. When the content of the silane coupling agent is 15% by mass or less based on the content of silica, the effects of improving the reinforcing property and dispersibility of the rubber component can be obtained, and the economy is not easily impaired. Further, when the content of the silane coupling agent is 5% by mass or more based on the content of silica, the dispersibility of silica in the rubber composition can be enhanced.

[0033] The silane coupling agent is not particularly limited, and bis(3-triethoxysilylpropyl)disulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(3-trimethoxysilylpropyl)trisulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)disulfide, bis(2-triethoxysilylethyl)trisulfide, bis(2-triethoxysilylethyl)tetrasulfide, 3-trimethoxysilylpropylbenzothiazole disulfide, 3-trimethoxysilylpropylbenzothiazole trisulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, etc. are preferably mentioned.

[0034] [Softening agent] The rubber composition of the present invention contains a resin and an oil component as a softening agent. Since the rubber composition contains a resin and an oil component in addition to the above-mentioned rubber component and filler, a tire excellent in wet grip performance can be obtained.

[0035] (Resin) The resin preferably has a glass transition temperature (Tg) higher than 60°C. The abrasion resistance can be improved by the glass transition temperature being higher than 60°C. Further, the WET performance can be improved by using a combination of a resin having a glass transition temperature higher than 60°C and aluminum hydroxide. From the viewpoint of processability, the glass transition temperature of the resin is preferably 95°C or lower. The Tg of the resin can be determined by a differential scanning calorimeter. Examples of the resin include C5 resins, terpene resins, C5-C9 resins, C9 resins, terpene-aromatic compound resins, and phenolic resins.

[0036] Examples of the C5 resin include aliphatic hydrocarbon resins and alicyclic hydrocarbon resins. Examples of the aliphatic hydrocarbon resin include petroleum resins produced by polymerizing C5 petroleum fractions. Examples of the alicyclic hydrocarbon resin include cyclopentadiene-based petroleum resins produced mainly from cyclopentadiene extracted from C5 fractions and dicyclopentadiene-based petroleum resins produced mainly from dicyclopentadiene in C5 fractions.

[0037] Examples of the terpene resin include resins produced mainly from naturally derived turpentine oil or orange oil.

[0038] Examples of the C5-C9 resin include petroleum resins selected from one or more of aromatic-modified aliphatic petroleum resins and aliphatic-modified aromatic petroleum resins. The C5-C9 resin is a solid polymer obtained by polymerizing petroleum-derived C5-C11 fractions, and includes aromatic-modified aliphatic petroleum resins and aliphatic-modified aromatic petroleum resins depending on the component ratio.

[0039] Examples of the C9 resin include C9 synthetic petroleum resins, which are solid polymers obtained by polymerization using Friedel-Crafts type catalysts such as AlCl3 and BF3 on C9 fractions.

[0040] Examples of the terpene-aromatic compound resin include terpene phenol resins.

[0041] Examples of the phenolic resin include phenol-formaldehyde resin, resorcinol-formaldehyde resin, cresol-formaldehyde resin, and the like.

[0042] (Oil component) Examples of the oil component include process oil, and paraffin oil, naphthenic oil, liquid paraffin, petroleum asphalt, aroma oil, etc. are exemplified. The rubber composition preferably contains the oil component in a range exceeding 0 part by mass and 20 parts by mass or less with respect to 100 parts by mass of the rubber component. By the content of the oil component in the rubber composition exceeding 0 part by mass with respect to 100 parts by mass of the rubber component, the wet grip performance of the tire can be further improved, and by being 20 parts by mass or less, the dry handling stability can be ensured. From the viewpoints of wet grip performance and dry handling stability, the content of the oil component in the rubber composition is more preferably 7 parts by mass or more, still more preferably 10 parts by mass or more, and also more preferably 18 parts by mass or less, still more preferably 17 parts by mass or less with respect to 100 parts by mass of the rubber component.

[0043] 〔Vulcanizing agent〕 The rubber composition of the present invention preferably contains a vulcanizing agent. The vulcanizing agent is not particularly limited, and usually sulfur is used, and examples thereof include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, etc. In the rubber composition of the present invention, the content of the vulcanizing agent is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the rubber component. By this content being 0.1 part by mass or more, vulcanization can proceed sufficiently, and by being 10 parts by mass or less, the aging property of the vulcanized rubber can be suppressed. The content of the vulcanizing agent in the rubber composition is more preferably 0.5 to 7 parts by mass, still more preferably 0.7 to 4 parts by mass with respect to 100 parts by mass of the rubber component.

[0044] In addition to the above components, the rubber composition of the present invention may, if necessary, appropriately contain compounding agents commonly used in the rubber industry, such as stearic acid, antioxidants, zinc oxide (zinc white), vulcanization accelerators, etc., within the range that does not harm the object of the present invention.

[0045] The rubber composition can be produced by blending each component including a rubber component, a filler, a resin, and an oil component, and kneading them using a kneader such as a Banbury mixer, a roll, an internal mixer, etc. The kneading of each component may be carried out in one stage, or may be carried out in two or more stages. When the kneading is carried out in two or more stages, components that are less likely to contribute to the vulcanization or vulcanization acceleration of the rubber component, such as rubber components, fillers, silane coupling agents, resins, oil components, stearic agents, antioxidants, etc., are kneaded up to a stage before the final stage, and in the final stage, the rubber component is vulcanized, and it is preferable to further blend and knead components that promote vulcanization. The kneading of components that are less likely to contribute to the vulcanization or vulcanization acceleration of the rubber component may be further divided into two or more stages. Also, when kneading in two stages, the maximum temperature in the first stage of kneading is preferably 140 to 160 °C, and the maximum temperature in the second stage is preferably 90 to 120 °C.

[0046] <Pneumatic tire> The pneumatic tire of the present invention is made using the rubber composition of the present invention. It is preferable to manufacture a tire tread using the rubber composition of the present invention and manufacture a tire provided with the tire tread. Since the tire of the present invention uses the rubber composition of the present invention having the above-described configuration, it maintains excellent ice performance and wet grip performance, and is excellent in the balance of dry handling stability and low rolling resistance. The tire may be obtained by vulcanizing after molding using an unvulcanized rubber composition according to the type and member of the tire to be applied, or after passing through a pre-vulcanization process or the like to obtain a semi-vulcanized rubber from an unvulcanized rubber composition once, and then using this to mold and further perform full vulcanization. For example, the rubber composition of the present invention containing various components is processed into a tire tread at the unvulcanized stage, pasted and molded by a normal method on a tire molding machine to form a green tire. This green tire is heated and pressurized in a vulcanizer to obtain a tire.

Examples

[0047] Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for the purpose of exemplifying the present invention and do not limit the present invention in any way.

[0048] <Preparation of Rubber Composition and Manufacture of Tire> 〔Comparative Examples 1 - 8, Examples 1 - 4, and 9 - 12〕 According to the formulations in Tables 1 - 3, each component was blended and kneaded to obtain the rubber compositions of Comparative Examples 1 - 8, Examples 1 - 4, and 9 - 12. In the tables, a blank means that the blending amount is 0 parts by mass.

[0049] 〔Examples 5 - 8〕 According to the formulation in Table 2, each component was blended and kneaded to obtain the rubber compositions of Examples 5 - 8. In the table, a blank means that the blending amount is 0 parts by mass. Details of the components in the tables are as follows.

[0050] (Rubber Component) NR: Natural Rubber Low Tg Unmodified SBR: Unmodified styrene - butadiene copolymer rubber, manufactured by JSR Corporation, trade name "JSR 1723", Tg = -55°C, bound styrene content = 23.5% Low Tg Modified SBR: Modified styrene - butadiene copolymer rubber manufactured in Production Example 1 below, Tg = -65°C, bound styrene content = 10% High Tg Modified SBR: Modified styrene - butadiene copolymer rubber manufactured in Production Example 2 below, Tg = -38°C, bound styrene content = 35%

[0051] (Filler, etc.) Carbon Black: Manufactured by Tokai Carbon Co., Ltd., ISAF - HS, trade name "Seast 7HM" Highlight: Aluminum hydroxide, manufactured by Nippon Light Metal Co., Ltd., product name "Aluminum hydroxide" Silica 1: CTAB specific surface area = 155 m 2 / g of silica Silica 2: CTAB specific surface area = 200 m 2 / g of silica Silica 3: CTAB specific surface area = 110 m 2 / g of silica Silane coupling agent: Silane coupling agent manufactured by Evonik, product name "Si75"

[0052] (Softening agent, etc.) Resin 1: Tg = 89 °C, C9 resin, manufactured by ENEOS Corporation, product name "Nisseki Neopolymer 140" Resin 2: Tg = 48 °C, C5C9 resin, manufactured by ExxonMobil Chemical Company, product name "ECR213" Resin 3: Tg = 75 °C, hydrogenated C5 resin, manufactured by Eastman, product name "Registered trademark Impera E1780" Oil: Manufactured by Sankyo Yuka Kogyo Co., Ltd., product name "A / O Mix" Wax: Microcrystalline wax, manufactured by Nippon Seiro Co., Ltd., product name "Ozace 0701" Antioxidant package: Includes "No Crack 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Zinc white: Zinc oxide Vulcanization accelerator package: Includes "Sunceler D" manufactured by Sanshin Chemical Industry Co., Ltd.

[0053] (Measurement of each physical property) 1. Glass transition temperature (Tg) and bound styrene content of styrene-butadiene copolymer rubber (1) Glass transition temperature (Tg) Using the modified styrene-butadiene copolymer rubber as a sample, DSC250 manufactured by TA Instruments was used. While flowing helium at 50 mL / min, the temperature was raised from -100 °C at 20 °C / min, and the DSC curve was recorded. The peak top (Inflection point) of the DSC differential curve was taken as the glass transition temperature.

[0054] (2) Bound styrene content Using a modified styrene-butadiene copolymer rubber as a sample, 100 mg of the sample was made up to 100 mL with chloroform, dissolved, and used as a measurement sample. The amount of bound styrene (% by mass) relative to 100% by mass of the sample was measured based on the absorption amount of the ultraviolet absorption wavelength (near 254 nm) by the phenyl group of styrene (using a spectrophotometer "UV-2450" manufactured by Shimadzu Corporation).

[0055] The glass transition temperature (Tg) and the amount of bound styrene of the low-Tg unmodified SBR are the manufacturer's catalog values.

[0056] 2. Cetyltrimethylammonium bromide specific surface area (CTAB specific surface area) of silica The CTAB specific surface areas of Silicas 1 to 3 were measured by a method conforming to the method of ASTM-D3765-80.

[0057] (Production Example of Modified SBR) 1. Production Example 1 (Production Example of Low-Tg Modified SBR) Into a dried and nitrogen-substituted 800 mL pressure-resistant glass container, a cyclohexane solution of 1,3-butadiene and a cyclohexane solution of styrene were added so that the amounts became 67.5 g of 1,3-butadiene and 7.5 g of styrene. Further, 0.09 mmol of 2,2-ditetrahydrofurylpropane was added to the pressure-resistant glass container, and 0.7 mmol of n-butyllithium was added. Then, polymerization was carried out at 50 °C for 1.5 hours. To the polymerization reaction system in which the polymerization conversion rate at this time became almost 100%, 0.63 mmol of N,N-bis(trimethylsilyl)-3-[diethoxy(methyl)silyl]propylamine was added as a modifier, and a modification reaction was carried out at 50 °C for 30 minutes. Then, 2 mL of a 5% by mass solution of 2,6-di-t-butyl-p-cresol (BHT) in isopropanol was added to stop the reaction, and it was dried according to a conventional method to obtain a modified SBR. As a result of measuring the microstructure of the obtained modified SBR (low-Tg modified SBR), the amount of bound styrene was 10%, the amount of vinyl bonds in the butadiene portion was 40%, and the peak molecular weight was 200,000.

[0058] 2. Production Example 2 (Production Example of High Tg Modified SBR) Into a dried and nitrogen-substituted 800 mL pressure-resistant glass container, a cyclohexane solution of 1,3-butadiene and a cyclohexane solution of styrene were added so that the amounts became 70.2 g of 1,3-butadiene and 39.5 g of styrene. Further, 0.19 mmol of 2,2-ditetrahydrofurylpropane was added to the pressure-resistant glass container, and 1.56 mmol of n-butyllithium was added. Thereafter, polymerization was carried out at 50 °C for 1.5 hours. To the polymerization reaction system in which the polymerization conversion rate at this time was almost 100%, 1.40 mmol of N-(1,3-dimethylbutylidene)-3-triethoxysilyl-1-propanamine was added as a modifier, and a modification reaction was carried out at 50 °C for 30 minutes. Thereafter, 2 mL of a 5 mass% solution of 2,6-di-t-butyl-p-cresol (BHT) in isopropanol was added to stop the reaction, and it was dried according to a conventional method to obtain a modified SBR. As a result of measuring the microstructure of the obtained modified SBR (high Tg modified SBR), the bound styrene amount was 35 mass%.

[0059] <Evaluation> [Comparative Examples 1 to 8, Examples 1 to 4, and 9 to 12] Vulcanized rubbers were obtained from the rubber compositions of Comparative Examples 1 to 8, Examples 1 to 4, and 9 to 12. The following performances of the obtained vulcanized rubbers were evaluated. The evaluation results are shown in Tables 1 to 3.

[0060] [Examples 5 to 8] Vulcanized rubbers are obtained from the rubber compositions of Examples 5 to 8. The following performances of the obtained vulcanized rubbers are evaluated. The evaluation results are shown in Table 2. The evaluations of the performances of Examples 5 to 8 are predicted values.

[0061] (1) Wet Grip Performance (Braking Performance on Wet Road Surface) Using a vulcanized rubber obtained by vulcanizing the rubber composition at 145 °C for 33 minutes, the resistance value of a test piece (vulcanized rubber) against a wet concrete road surface was measured using a British Portable Skid Tester. The evaluation results were expressed as an index with the value of Comparative Example 1 being 100. The larger the numerical value, the better the wet grip property. The allowable range is 94 or more.

[0062] (2) Dry handling stability The storage elastic modulus (E’) of the vulcanized rubber was measured using a spectrometer manufactured by Ueshima Seisakusho under the conditions of a temperature of 30°C, an initial strain of 2%, a dynamic strain of 1%, and a frequency of 52 Hz. The storage elastic modulus (E’) of Comparative Example 1 was set to 100 and expressed exponentially. The larger the exponent, the better the dry handling stability of the tire obtained from the vulcanized rubber. The allowable range is 101 or more.

[0063] (3) Low rolling resistance Using a viscoelasticity measuring device [manufactured by Rheometric Scientific], the loss tangent (tanδ) of the vulcanized rubber was measured at a temperature of 50°C, a strain of 5%, and a frequency of 15 Hz. The evaluation result of Comparative Example 1 was set to 100 for relative evaluation. The larger the numerical value, the lower the rolling resistance, which means that the low rolling resistance of the tire obtained from the vulcanized rubber is good. The allowable range is 100 or more.

[0064] (4) Ice performance The storage elastic modulus (E’) of the vulcanized rubber was measured using a spectrometer manufactured by Ueshima Seisakusho under the conditions of a temperature of -20°C, an initial strain of 2%, a dynamic strain of 1%, and a frequency of 52 Hz, and the result was calculated based on this. The allowable range is 100 or more.

[0065] (5) Abrasion resistance For the vulcanized rubber, the amount of wear at a slip rate of 60% at room temperature was measured using a Lambourne type abrasion tester. The reciprocal of the wear amount of the vulcanized rubber in Comparative Example 1 was set to 100 and expressed exponentially. The larger the exponential value, the smaller the wear amount, indicating excellent abrasion resistance. The allowable range is 102 or more.

[0066]

Table 1

[0067]

Table 2

[0068]

Table 3

[0069] As can be seen from Table 2, in the examples, the index of wet grip performance is 94 or more, the index of dry handling stability is 101 or more, the index of low rolling resistance is 100 or more, and the index of ice performance is 100 or more. That is, it can be seen that from the rubber compositions of the examples, a pneumatic tire having an improved balance between dry handling stability and low rolling resistance while maintaining excellent ice performance and wet grip performance can be obtained. Further, the examples have an abrasion resistance index of 102 or more, and the vulcanized rubber obtained from the rubber compositions of the examples is also excellent in abrasion resistance. Also, as can be seen from the comparison between Examples 5 to 8 containing natural rubber, low Tg modified SBR, resin, silica having a CTAB specific surface area of 190 m 2 / g or more and an oil component, and Examples 1 to 4 further containing aluminum hydroxide, the wet grip performance is greatly improved in Examples 1 to 4.

[0070] Similarly, as can also be seen from the comparison between Example 9 and Example 11, and the comparison between Example 10 and Example 12, it can be seen that the systems containing aluminum hydroxide (Examples 9 and 10) have improved wet grip performance compared to the systems not containing aluminum hydroxide (Examples 11 and 12). Further, from the comparison between the system containing a resin having a glass transition temperature higher than 60°C (Resins 1 and 3) and the system containing a resin having a glass transition temperature of 60°C or lower (Resin 2), it can be seen that the system containing a resin having a glass transition temperature higher than 60°C is superior in abrasion resistance. Specifically, from the comparison between Examples 1 and 10 and Example 9 (comparison in the aspect containing aluminum hydroxide), and the comparison between Examples 5 and 12 and Example 11 (comparison in the aspect not containing aluminum hydroxide), the improvement in abrasion resistance can be grasped.

[0071] In contrast, the rubber compositions of Comparative Examples 1 to 8 shown in Table 1 do not contain any one or more of silica having a CTAB specific surface area of 190 m 2 / g or more, resin, oil, low-Tg modified SBR, and natural rubber, and any one or more of wet grip performance, dry handling stability, low rolling resistance, and ice performance were below the allowable range.

Claims

1. A rubber component containing natural rubber and a modified styrene-butadiene copolymer rubber modified with a silane compound having a glass transition temperature of -50°C or lower, a resin, Aluminum hydroxide and cetyltrimethylammonium bromide A filler containing silica with a specific surface area of 190 m ２ / g or more, and an oil component, and containing wherein the resin is at least one selected from the group consisting of C5 resins, terpene resins, C5C9 resins, C9 resins, terpene-aromatic compound resins, and phenolic resins, wherein the silica is contained in an amount of 60 parts by mass or more per 100 parts by mass of the rubber component, wherein the oil component is contained in an amount exceeding 0 part by mass and 20 parts by mass or less per 100 parts by mass of the rubber component, wherein the ratio (s / a) of the content (s) of the silica to the content (a) of the aluminum hydroxide is 7 to 10 on a mass basis, wherein the resin has a glass transition temperature higher than 60°C, and a rubber composition in which the content of the modified styrene-butadiene copolymer rubber in the rubber component is more than 50% by mass.

2. The rubber composition according to claim 1, wherein the aluminum hydroxide is contained in an amount of 1 to 20 parts by mass per 100 parts by mass of the rubber component.

3. The rubber composition according to claim 1 or 2, wherein the rubber component further contains 1 to 30% by mass of a modified styrene-butadiene copolymer rubber modified with a silane compound having a glass transition temperature of -40°C or higher.

4. A pneumatic tire using the rubber composition according to claim 1 or 2.

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