Patent Description:
It is desirable for tires to have improved wet grip performance (braking performance on wet roads) for safety.

For example, Patent Literature <NUM> discloses a rubber composition containing a predetermined amount of two specific types of silica to improve wet grip performance.

Patent Literature <NUM> describes cross-linkable rubber compositions comprising, per hundred parts by weight of rubber (phr): ≥ <NUM> phr to ≤ <NUM> phr of a styrene-butadiene rubber component; ≥ 1phr to ≤ <NUM> phr of a polybutadiene rubber component, having a branching index G of ≥ <NUM> to ≤ <NUM> and a polydispersity index Mw/Mn of ≥ <NUM> and ≤ <NUM>; and ≥ <NUM> phr to ≤ <NUM> phr of a polyterpene resin component having a molecular weight Mw of ≥ <NUM> to ≤ <NUM>/mol.

As a result of extensive research and experimentation, the present inventor has found that conventional techniques leave room for improvement in reducing deterioration of wet grip performance and abrasion resistance over time.

The present disclosure aims to solve the new problem found by the inventor and provide a tire rubber composition and a tire which have good wet grip performance and an excellent ability to reduce deterioration of wet grip performance and abrasion resistance over time.

The present disclosure relates to a tire rubber composition, containing: one or more rubber components having a combined content of styrene-butadiene rubber and polybutadiene of <NUM>% by mass or more; one or more fillers; and one or more vulcanizing agents, the rubber composition as a whole having a vinyl content of <NUM> mol% or higher and a trans content of <NUM> mol% or higher, each based on <NUM> mol% of a combined amount of butadiene-based structural units in a butadiene portion of the styrene-butadiene rubber and the polybutadiene.

Preferably, the vinyl content is <NUM> mol% or higher, more preferably <NUM> mol% or higher, still more preferably <NUM> mol% or higher.

Preferably, the rubber composition contains <NUM> parts by mass or more of silica per <NUM> parts by mass of the rubber components.

Preferably, the rubber composition contains the styrene-butadiene rubber and the polybutadiene.

Preferably, the rubber composition contains syndiotactic <NUM>,<NUM>-polybutadiene.

The present disclosure also relates to a tire, including a tread including the rubber composition.

The present disclosure provides a tire rubber composition containing one or more rubber components having a combined content of styrene-butadiene rubber and polybutadiene of <NUM>% by mass or more, one or more fillers, and one or more vulcanizing agents, the rubber composition as a whole having a vinyl content of <NUM> mol% or higher and a trans content of <NUM> mol% or higher, each based on <NUM> mol% of the combined amount of the butadiene-based structural units in the butadiene portion of the styrene-butadiene rubber and the polybutadiene. Such a tire rubber composition has good wet grip performance and an excellent ability to reduce deterioration of wet grip performance and abrasion resistance over time.

The tire rubber composition of the present disclosure contains one or more rubber components having a combined content of styrene-butadiene rubber and polybutadiene of <NUM>% by mass or more, one or more fillers, and one or more vulcanizing agents. Further, the rubber composition as a whole has a vinyl content of <NUM> mol% or higher and a trans content of <NUM> mol% or higher, each based on <NUM> mol% of the combined amount of the butadiene-based structural units in the butadiene portion of the styrene-butadiene rubber and the polybutadiene. Thus, it is possible to have good wet grip performance and to improve the ability to reduce deterioration of wet grip performance over time and the ability to reduce deterioration of abrasion resistance over time.

The tire rubber composition provides the above-mentioned effect. The reason for this advantageous effect is not exactly clear but may be explained as follows.

The tire rubber composition contains one or more rubber components based on styrene-butadiene rubber (SBR) and/or polybutadiene (BR). The rubber composition as a whole has a vinyl content (hereinafter, also referred to as vinyl content of the rubber composition) of <NUM> mol% or higher and a trans content (hereinafter, also referred to as trans content of the rubber composition) of <NUM> mol% or higher, each based on <NUM> mol% of the combined amount of the butadiene-based structural units in the butadiene portion of the styrene-butadiene rubber and the polybutadiene.

Here, as such butadiene-based structural units, there are cis-<NUM>,<NUM>-units, trans-<NUM>,<NUM>-units, and vinyl-<NUM>,<NUM>-units. The cis-<NUM>,<NUM>-units and trans-<NUM>,<NUM>-units have a double bond in the backbone, whereas the vinyl-<NUM>,<NUM>-units have no double bond in the backbone.

Moreover, the vinyl content of the rubber composition refers to the amount of vinyl-<NUM>,<NUM>-units based on <NUM> mol% of the combined amount of the butadiene-based structural units derived from the styrene-butadiene rubber and polybutadiene. The trans content of the rubber composition refers to the amount of trans-<NUM>,<NUM>-units based on <NUM> mol% of the combined amount of the butadiene-based structural units derived from the styrene-butadiene rubber and polybutadiene. The below-mentioned cis content of the rubber composition refers to the amount of cis-<NUM>,<NUM>-units based on <NUM> mol% of the combined amount of the butadiene-based structural units derived from the styrene-butadiene rubber and polybutadiene.

When the vinyl content of the rubber composition is <NUM> mol% or higher, the amount of double bonds in the polymer backbone is reduced so that the molecular chains of the polymer are less likely to be broken by ozone attack, thereby making it possible to reduce deterioration of wet grip performance and abrasion resistance over time. Thus, good wet grip performance can also be obtained.

When the trans content of the rubber composition is <NUM> mol% or higher, highly polar functional groups can be more exposed to the tire surface, thereby improving the hydrophilicity of the entire tire. Thus, better wet grip performance can be obtained.

Furthermore, when the vinyl content of the rubber composition is <NUM> mol% or higher and at the same time the trans content of the rubber composition is <NUM> mol% or higher, wet grip performance is synergistically improved and good wet grip performance can be maintained for a long time.

As described above, the tire rubber composition contains one or more rubber components based on styrene-butadiene rubber and polybutadiene and has a vinyl content of <NUM> mol% or higher and a trans content of <NUM> mol% or higher to have good wet grip performance and to improve the ability to reduce deterioration of wet grip performance over time and the ability to reduce deterioration of abrasion resistance over time.

The tire rubber composition as a whole has a vinyl content (vinyl content of the rubber composition) of <NUM> mol% or higher, preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher, still more preferably <NUM> mol% or higher, particularly preferably <NUM> mol% or higher, most preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, but preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower, still more preferably <NUM> mol% or lower, particularly preferably <NUM> mol% or lower, most preferably <NUM> mol% or lower, still most preferably <NUM> mol% or lower, further most preferably <NUM> mol% or lower, based on <NUM> mol% of the combined amount of the butadiene-based structural units in the butadiene portion of the styrene-butadiene rubber and the polybutadiene. When the vinyl content is within the range indicated above, the advantageous effect can be more suitably achieved.

The tire rubber composition as a whole has a trans content (trans content of the rubber composition) of <NUM> mol% or higher, preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher, still more preferably <NUM> mol% or higher, particularly preferably <NUM> mol% or higher, most preferably <NUM> mol% or higher, further most preferably <NUM> mol% or higher, but preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower, still more preferably <NUM> mol% or lower, particularly preferably <NUM> mol% or lower, most preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, based on <NUM> mol% of the combined amount of the butadiene-based structural units in the butadiene portion of the styrene-butadiene rubber and the polybutadiene. When the trans content is within the range indicated above, the advantageous effect can be more suitably achieved.

The tire rubber composition as a whole preferably has a cis content (cis content of the rubber composition) of <NUM> mol% or higher, more preferably <NUM> mol% or higher, still more preferably <NUM> mol% or higher, particularly preferably <NUM> mol% or higher, most preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, further preferably <NUM> mol% or higher, but preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower, still more preferably <NUM> mol% or lower, particularly preferably <NUM> mol% or lower, most preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, further preferably <NUM> mol% or lower, based on <NUM> mol% of the combined amount of the butadiene-based structural units in the butadiene portion of the styrene-butadiene rubber and the polybutadiene. When the cis content is within the range indicated above, the advantageous effect can be more suitably achieved.

The vinyl content of the rubber composition, the trans content of the rubber composition, and the cis content of the rubber composition indicated above may be achieved by using an appropriate combination of SBR and/or BR.

For example, rubber components such as SBR with a high trans content, BR with a high trans content, and BR with a high vinyl content may be combined.

Chemicals that may be used in the rubber composition are described below.

The tire rubber composition contains styrene-butadiene rubber (SBR) and/or polybutadiene (BR). To more suitably achieve the advantageous effect, the tire rubber composition preferably contains SBR and BR.

Any SBR may be used. Examples include those commonly used in the tire industry, such as emulsion-polymerized SBR (E-SBR) and solution-polymerized SBR (S-SBR). These may be used alone or in combinations of two or more. Preferred among these are combinations of two or more types of SBR having different vinyl contents and/or different trans contents.

The styrene content of the SBR is preferably <NUM>% by mass or higher, more preferably <NUM>% by mass or higher, still more preferably <NUM>% by mass or higher, but is preferably <NUM>% by mass or lower, more preferably <NUM>% by mass or lower, still more preferably <NUM>% by mass or lower, particularly preferably <NUM>% by mass or lower. When the styrene content is within the range indicated above, the advantageous effect tends to be more suitably achieved.

The vinyl content of the SBR is preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher, still more preferably <NUM> mol% or higher, but is preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower, still more preferably <NUM> mol% or lower, particularly preferably <NUM> mol% or lower. When the vinyl content is within the range indicated above, the advantageous effect tends to be more suitably achieved.

The trans content of the SBR is preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher, still more preferably <NUM> mol% or higher, particularly preferably <NUM> mol% or higher, most preferably <NUM> mol% or higher, but is preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower, still more preferably <NUM> mol% or lower. When the trans content is within the range indicated above, the advantageous effect tends to be more suitably achieved.

By using SBR with a trans content within the range indicated above (high trans content), highly polar functional groups can be more exposed to the tire surface, thereby improving the hydrophilicity of the entire tire. Thus, better wet grip performance can be obtained.

The cis content of the SBR is preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher, still more preferably <NUM> mol% or higher, but is preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower. When the cis content is within the range indicated above, the advantageous effect tends to be more suitably achieved.

Herein, the vinyl content, trans content, and cis content of the SBR each refer to the content based on <NUM> mol% of the butadiene-based structural units in the SBR.

The SBR may be either unmodified or modified SBR.

The modified SBR may be any SBR having a functional group interactive with a filler such as silica. Examples include: chain end-modified SBR obtained by modifying at least one chain end of SBR with a compound (modifier) having the functional group (i.e., chain end-modified SBR terminated with the functional group); backbone-modified SBR having the functional group in the backbone; backbone- and chain end-modified SBR having the functional group in both the backbone and chain end (e.g., backbone- and chain end-modified SBR in which the backbone has the functional group and at least one chain end is modified with the modifier); and chain end-modified SBR into which a hydroxy or epoxy group has been introduced by modification (coupling) with a polyfunctional compound having two or more epoxy groups in the molecule. These may be used alone or in combinations of two or more.

Examples of the functional group include amino, amide, silyl, alkoxysilyl, isocyanate, imino, imidazole, urea, ether, carbonyl, oxycarbonyl, mercapto, sulfide, disulfide, sulfonyl, sulfinyl, thiocarbonyl, ammonium, imide, hydrazo, azo, diazo, carboxyl, nitrile, pyridyl, alkoxy, hydroxy, oxy, and epoxy groups. These functional groups may have substituent groups. Preferred among these are amino groups (preferably amino groups whose hydrogen atom is replaced with a C1-C6 alkyl group), alkoxy groups (preferably C1-C6 alkoxy groups), alkoxysilyl groups (preferably C1-C6 alkoxysilyl groups), and amide groups.

SBR products manufactured or sold by Sumitomo Chemical Co. , JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. may be used as the SBR.

The SBR is preferably SBR <NUM> having a styrene content of <NUM>% by mass or higher and a trans content of <NUM> mol% or lower or SBR <NUM> having a styrene content of <NUM>% by mass or lower and a trans content of <NUM> mol% or higher, more preferably a combination of SBR <NUM> and SBR <NUM>.

The styrene content of the SBR <NUM> is preferably <NUM>% by mass or higher but is preferably <NUM>% by mass or lower, more preferably <NUM>% by mass or lower. Moreover, the trans content of the SBR <NUM> is preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher, still more preferably <NUM> mol% or higher, particularly preferably <NUM> mol% or higher.

The styrene content of the SBR <NUM> is preferably <NUM>% by mass or higher, more preferably <NUM>% by mass or higher, still more preferably <NUM>% by mass or higher. Moreover, the trans content of the SBR <NUM> is preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower, still more preferably <NUM> mol% or lower.

The vinyl content and cis content of the SBR <NUM> and SBR <NUM> are as described for the vinyl content and cis content of the SBR described above.

The amount of SBR based on <NUM>% by mass of the rubber components is preferably <NUM>% by mass or more, preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, still more preferably <NUM>% by mass or more, particularly preferably <NUM>% by mass or more, and may be <NUM>% by mass, but is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The amount of SBR <NUM> based on <NUM>% by mass of the rubber components is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, but is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Any polybutadiene (BR) may be used, and examples include those commonly used in the tire industry, such as high-cis BR having a high cis content, low-cis BR having a low cis content, BR containing syndiotactic polybutadiene crystals, and BR synthesized using rare earth catalysts (rare earth-catalyzed BR). Crystalline BR such as syndiotactic <NUM>,<NUM>-polybutadiene may also be used. These may be used alone or in combinations of two or more.

Moreover, the BR may be either unmodified or modified BR. Examples of the modified BR include those into which the above-mentioned functional groups are introduced. Preferred embodiments of the modified BR are as described for the modified SBR.

The BR may be commercially available from Ube Industries, Ltd. , JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc..

In particular, the BR is preferably BR <NUM> having a trans content of <NUM> mol% or higher or syndiotactic <NUM>,<NUM>-polybutadiene (BR <NUM>), more preferably syndiotactic <NUM>,<NUM>-polybutadiene (BR <NUM>). The BR is also preferably a combination of BR <NUM> having a trans content of <NUM> mol% or higher and syndiotactic <NUM>,<NUM>-polybutadiene (BR <NUM>).

Particularly by incorporating syndiotactic <NUM>,<NUM>-polybutadiene, the amount of double bonds in the polymer backbone is reduced so that the molecular chains of the polymer are less likely to be broken by ozone attack, thereby making it possible to more suitably reduce deterioration of wet grip performance and abrasion resistance over time. BR containing syndiotactic polybutadiene crystals (for example, VCR available from Ube Industries, Ltd. ) is also conventionally used and has a cis-<NUM>,<NUM>-linked backbone, whereas the syndiotactic <NUM>,<NUM>-polybutadiene (BR <NUM>) has a vinyl-<NUM>,<NUM>-linked backbone, thereby making it possible to more suitably reduce deterioration of wet grip performance and abrasion resistance over time.

The trans content of the BR <NUM> is preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher. The trans content is also preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower, still more preferably <NUM> mol% or lower. When the trans content is within the range indicated above, the advantageous effect tends to be better achieved.

The vinyl content of the BR <NUM> is preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower. The vinyl content is also preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher. When the vinyl content is within the range indicated above, the advantageous effect tends to be better achieved.

The cis content of the BR <NUM> is preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher. The cis content is also preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower. When the cis content is within the range indicated above, the advantageous effect tends to be better achieved.

The vinyl content of the syndiotactic <NUM>,<NUM>-polybutadiene (SPB, BR <NUM>) is preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher, still more preferably <NUM> mol% or higher, particularly preferably <NUM> mol% or higher, and may be <NUM> mol%. When the vinyl content is within the range indicated above, the advantageous effect tends to be better achieved.

The trans content and cis content of the BR <NUM> are each preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower, and may be <NUM> mol%. When the trans and cis contents are each within the range indicated above, the advantageous effect tends to be better achieved.

The melting point of the BR <NUM> is not limited, but it is preferably <NUM> or higher, more preferably <NUM> or higher, still more preferably <NUM> or higher, but is preferably <NUM> or lower, more preferably <NUM> or lower, still more preferably <NUM> or lower. When the melting point is within the range indicated above, the advantageous effect tends to be better achieved.

Herein, the melting point of the BR refers to the melting peak temperature in the DSC curve measured in accordance with JIS K7121.

The degree of crystallization of the BR <NUM> is not limited, but it is preferably <NUM>% or higher, more preferably <NUM>% or higher, but is preferably <NUM>% or lower, more preferably <NUM>% or lower. When the degree of crystallization is within the range indicated above, the advantageous effect tends to be better achieved.

Herein, the degree of crystallization is calculated from the density measured by the water displacement method in which the density of <NUM>,<NUM>-polybutadiene with a degree of crystallization of <NUM>% is <NUM>/cm<NUM> and the density of <NUM>,<NUM>-polybutadiene with a degree of crystallization of <NUM>% is <NUM>/cm<NUM>.

The amount of BR based on <NUM>% by mass of the rubber components is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, still more preferably <NUM> by mass or more, but is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The amount of BR <NUM> based on <NUM>% by mass of the rubber components is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, but is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The amount of BR <NUM> (SPB) based on <NUM>% by mass of the rubber components is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, but is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The combined amount of SBR and BR based on <NUM>% by mass of the rubber components is <NUM>% by mass or more, preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, and may be <NUM>% by mass. When the combined amount is within the range indicated above, the advantageous effect tends to be better achieved.

Examples of usable rubber components other than SBR and BR include diene rubber such as isoprene-based rubber, styrene-isoprene-butadiene rubber (SIBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), and butyl rubber (IIR). The rubber components may be used alone or in combinations of two or more. Diene rubber is preferred among these, with isoprene-based rubber being more preferred.

The term "rubber component" preferably refers to rubber having a weight average molecular weight (Mw) of <NUM>,<NUM> or more, more preferably <NUM>,<NUM> or more. The upper limit of the Mw is not limited, but it is preferably <NUM>,<NUM>,<NUM> or less, more preferably <NUM>,<NUM>,<NUM> or less.

Examples of the isoprene-based rubber include natural rubber (NR), polyisoprene rubber (IR), refined NR, modified NR, and modified IR. The NR may be ones commonly used in the tire industry, such as SIR20, RSS#<NUM>, or TSR20. Any IR may be used, and examples include those commonly used in the tire industry, such as IR2200. Examples of the refined NR include deproteinized natural rubber (DPNR) and highly purified natural rubber (UPNR). Examples of the modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of the modified IR include epoxidized polyisoprene rubber, hydrogenated polyisoprene rubber, and grafted polyisoprene rubber. These may be used alone or in combinations of two or more. NR is preferred among these.

Herein, the weight average molecular weight (Mw) and number average molecular weight (Mn) can be determined by gel permeation chromatography (GPC) (GPC-<NUM> series available from Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M available from Tosoh Corporation) calibrated with polystyrene standards.

The cis content, vinyl content, and trans content can be measured by <NUM>C-NMR analysis. Moreover, the styrene content can be measured by <NUM>H-NMR analysis.

The vinyl content of the rubber composition, the trans content of the rubber composition, and the cis content of the rubber composition may be measured directly on the rubber composition by <NUM>C-NMR analysis, or may be calculated from the vinyl content, trans content, and cis content, respectively, measured on the material rubber and in proportion to the amount of the material rubber.

The rubber composition contains one or more fillers (reinforcing fillers).

Any filler may be used, and examples include silica, carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica. These may be used alone or in combinations of two or more. Preferred among these are silica and carbon black, with silica being more preferred. A combination of silica and carbon black is also preferred.

The amount of fillers per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less, particularly preferably <NUM> parts by mass or less, most preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Any carbon black may be used, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. These may be used alone or in combinations of two or more.

The nitrogen adsorption specific surface area (N<NUM>SA) of the carbon black is preferably <NUM><NUM>/g or more, more preferably <NUM><NUM>/g or more, but is preferably <NUM><NUM>/g or less, more preferably <NUM><NUM>/g or less, still more preferably <NUM><NUM>/g or less. When the N<NUM>SA is within the range indicated above, the advantageous effect tends to be better achieved.

Herein, the N<NUM>SA of the carbon black is measured in accordance with JIS K6217-<NUM>:<NUM>.

The carbon black may be commercially available from Asahi Carbon Co. , Cabot Japan K. , Tokai Carbon Co. , Mitsubishi Chemical Corporation, Lion Corporation, NSCC Carbon Co. , Columbia Carbon, etc..

The amount of carbon black per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less, particularly preferably <NUM> parts by mass or less, most preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Examples of the silica include dry silica (anhydrous silicic acid) and wet silica (hydrous silicic acid). Wet silica is preferred because it has a large number of silanol groups. These may be used alone or in combinations of two or more.

The nitrogen adsorption specific surface area (N<NUM>SA) of the silica is <NUM><NUM>/g or more, preferably <NUM><NUM>/g or more, more preferably <NUM><NUM>/g or more, still more preferably <NUM><NUM>/g or more, particularly preferably <NUM><NUM>/g or more. The N<NUM>SA is also preferably <NUM><NUM>/g or less, more preferably <NUM><NUM>/g or less, still more preferably <NUM><NUM>/g or less, particularly preferably <NUM><NUM>/g or less. When the N<NUM>SA is within the range indicated above, the advantageous effect tends to be more suitably achieved.

The N<NUM>SA of the silica is measured by the BET method in accordance with ASTM D3037-<NUM>.

The silica may be commercially available from Degussa, Rhodia, Tosoh Silica Corporation, Solvay Japan, Tokuyama Corporation, etc..

The amount of silica per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more, particularly preferably <NUM> parts by mass or more, most preferably <NUM> parts by mass or more, further preferably <NUM> parts by mass or more, further preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less, particularly preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The amount of silica based on <NUM>% by mass of the fillers (reinforcing fillers) in the rubber composition is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, still more preferably <NUM>% by mass or more, particularly preferably <NUM>% by mass or more, most preferably <NUM>% by mass or more, and may be <NUM>% by mass. When the amount is within the range indicated above, the advantageous effect tends to be more suitably achieved.

The rubber composition containing silica preferably further contains one or more silane coupling agents.

Any silane coupling agent may be used. Examples include sulfide silane coupling agents such as bis(<NUM>-triethoxysilylpropyl)tetrasulfide, bis(<NUM>-triethoxysilylethyl)tetrasulfide, bis(<NUM>-triethoxysilylbutyl)tetrasulfide, bis(<NUM>-trimethoxysilylpropyl)tetrasulfide, bis(<NUM>-trimethoxysilylethyl)tetrasulfide, bis(<NUM>-triethoxysilylethyl)trisulfide, bis(<NUM>-trimethoxysilylbutyl)trisulfide, bis(<NUM>-triethoxysilylpropyl)disulfide, bis(<NUM>-triethoxysilylethyl)disulfide, bis(<NUM>-triethoxysilylbutyl)disulfide, bis(<NUM>-trimethoxysilylpropyl)disulfide, bis(<NUM>-trimethoxysilylethyl)disulfide, bis(<NUM>-trimethoxysilylbutyl)disulfide, <NUM>-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, <NUM>-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and <NUM>-triethoxysilylpropyl methacrylate monosulfide; mercapto silane coupling agents such as <NUM>-mercaptopropyltrimethoxysilane and <NUM>-mercaptoethyltriethoxysilane; vinyl silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino silane coupling agents such as <NUM>-aminopropyltriethoxysilane and <NUM>-aminopropyltrimethoxysilane; glycidoxy silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro silane coupling agents such as <NUM>-nitropropyltrimethoxysilane and <NUM>-nitropropyltriethoxysilane; and chloro silane coupling agents such as <NUM>-chloropropyltrimethoxysilane and <NUM>-chloropropyltriethoxysilane. Commercial products available from Degussa, Momentive, Shin-Etsu Silicone, Tokyo Chemical Industry Co. , DuPont Toray Specialty Materials K. , etc. may be used. These may be used alone or in combinations of two or more. Sulfide silane coupling agents are preferred among these, with disulfide silane coupling agents having a disulfide bond, such as bis(<NUM>-triethoxysilylpropyl)disulfide, being more preferred, because the advantageous effect tends to be better achieved.

The amount of silane coupling agents per <NUM> parts by mass of the silica is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The rubber composition preferably contains sulfur as a crosslinking agent (vulcanizing agent).

Examples of the sulfur include those commonly used in the rubber industry, such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. These may be used alone or in combinations of two or more.

Examples of vulcanizing agents other than sulfur include organic peroxides.

The sulfur may be commercially available from Tsurumi Chemical Industry Co. , Karuizawa Sulfur Co. , Shikoku Chemicals Corporation, Flexsys, Nippon Kanryu Industry Co. , Hosoi Chemical Industry Co.

The amount of vulcanizing agents (preferably sulfur) per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more, particularly preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less, particularly preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The rubber composition preferably contains one or more vulcanization accelerators.

Examples of the vulcanization accelerators include thiazole vulcanization accelerators such as <NUM>-mercaptobenzothiazole, di-<NUM>-benzothiazolyl disulfide, and N-cyclohexyl-<NUM>-benzothiazylsulfenamide; thiuram vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(<NUM>-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide vulcanization accelerators such as N-cyclohexyl-<NUM>-benzothiazole sulfenamide, N-t-butyl-<NUM>-benzothiazolylsulfenamide, N-oxyethylene-<NUM>-benzothiazole sulfenamide, and N,N'-diisopropyl-<NUM>-benzothiazole sulfenamide; and guanidine vulcanization accelerators such as diphenylguanidine, diorthotolylguanidine, and orthotolylbiguanidine. These may be used alone or in combinations of two or more. Preferred among these are sulfenamide and/or guanidine vulcanization accelerators, with combinations of sulfenamide and guanidine vulcanization accelerators being more preferred.

The vulcanization accelerators may be commercially available from Kawaguchi Chemical Industry Co. , Ouchi Shinko Chemical Industrial Co. , Rhein Chemie, etc..

The amount of vulcanization accelerators per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> part by mass or more, still more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The rubber composition may contain one or more resins.

Any resin may be used, and examples include solid alkylphenol resins, styrene resins, coumarone-indene resins, terpene resins, rosin resins, acrylic resins, and dicyclopentadiene resins (DCPD resins). These may be used alone or in combinations of two or more.

The resins may be commercially available from Maruzen Petrochemical Co. , Sumitomo Bakelite Co. , Yasuhara Chemical Co. , Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical, Nitto Chemical Co. , Nippon Shokubai Co. , JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries, Ltd. , Taoka Chemical Co.

The amount of resins per <NUM> parts by mass of the rubber components is preferably <NUM> part by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more. The amount is also preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less.

The rubber composition may contain one or more softeners.

Any softener may be used, and examples include oils and liquid diene polymers. These may be used alone or in combinations of two or more.

Examples of the oils include process oils, vegetable oils, and mixtures thereof. Examples of the process oils include paraffinic process oils, aromatic process oils, and naphthenic process oils. Examples of the vegetable oils include castor oil, cotton seed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. These may be used alone or in combinations of two or more. To achieve the advantageous effect well, process oils are preferred among these, with aromatic process oils being more preferred.

The oils may be commercially available from Idemitsu Kosan Co. , Sankyo Yuka Kogyo K. , Japan Energy Corporation, Olisoy, H&R, Hokoku Corporation, Showa Shell Sekiyu K. , Fuji Kosan Co.

Liquid diene polymers refer to diene polymers that are liquid at room temperature (<NUM>).

The weight average molecular weight (Mw) of the liquid diene polymers is preferably <NUM>×<NUM><NUM> or more, more preferably <NUM>×<NUM><NUM> or more, but is preferably <NUM>×<NUM><NUM> or less, more preferably <NUM>×<NUM><NUM> or less. When the Mw is within the range indicated above, the advantageous effect can be more suitably achieved.

Examples of the liquid diene polymers include liquid styrene-butadiene copolymers (liquid SBR), liquid polybutadiene polymers (liquid BR), liquid polyisoprene polymers (liquid IR), and liquid styrene-isoprene copolymers (liquid SIR). These may be used alone or in combinations of two or more. To more suitably achieve the advantageous effect, liquid SBR is preferred among these.

The liquid diene polymers may be commercially available from Sartomer, Kuraray Co.

The amount of softeners (preferably oils) per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved. Herein, the amount of softeners includes the amount of oils contained in the rubber (oil extended rubber), if used.

The rubber composition may contain one or more waxes.

Any wax may be used, and examples include petroleum waxes such as paraffin waxes and microcrystalline waxes; naturally-occurring waxes such as plant waxes and animal waxes; and synthetic waxes such as polymers of ethylene, propylene, or other similar monomers. These may be used alone or in combinations of two or more. Petroleum waxes are preferred among these, with paraffin waxes being more preferred.

The waxes may be commercially available from Ouchi Shinko Chemical Industrial Co. , Nippon Seiro Co. , Seiko Chemical Co.

The amount of waxes per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The rubber composition may contain one or more antioxidants.

Examples of the antioxidants include naphthylamine antioxidants such as phenyl-α-naphthylamine; diphenylamine antioxidants such as octylated diphenylamine and <NUM>,<NUM>'-bis(α,α'-dimethylbenzyl)diphenylamine; p-phenylenediamine antioxidants such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-(<NUM>,<NUM>-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-<NUM>-naphthyl-p-phenylenediamine; quinoline antioxidants such as polymerized <NUM>,<NUM>,<NUM>-trimethyl-<NUM>,<NUM>-dihydroquinoline; monophenolic antioxidants such as <NUM>,<NUM>-di-t-butyl-<NUM>-methylphenol and styrenated phenol; and bis-, tris-, or polyphenolic antioxidants such as tetrakis[methylene-<NUM>-(<NUM>',<NUM>'-di-t-butyl-<NUM>'-hydroxyphenyl)propionate]methane. These may be used alone or in combinations of two or more. Preferred among these are p-phenylenediamine and/or quinoline antioxidants, with combinations of p-phenylenediamine and quinoline antioxidants being more preferred.

The antioxidants may be commercially available from Seiko Chemical Co. , Sumitomo Chemical Co. , Ouchi Shinko Chemical Industrial Co. , Flexsys, etc..

The amount of antioxidants per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> part by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Conventional stearic acid may be used, such as those available from NOF Corporation, Kao Corporation, FUJIFILM Wako Pure Chemical Corporation, Chiba Fatty Acid Co.

The amount of stearic acid per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> part by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Conventional zinc oxide may be used, such as those available from Mitsui Mining & Smelting Co. , Toho Zinc Co. , Hakusui Tech Co. , Seido Chemical Industry Co. , Sakai Chemical Industry Co.

The amount of zinc oxide per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> part by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

In addition to the above-described components, the rubber composition may further contain additives commonly used in the tire industry. The amount of such additives is preferably <NUM> to <NUM> parts by mass per <NUM> parts by mass of the rubber components.

The rubber composition may be prepared, for example, by kneading the components in a rubber kneading machine such as an open roll mill or a Banbury mixer, and then vulcanizing the kneaded mixture.

The kneading conditions are as follows. In a base kneading step of kneading additives other than vulcanizing agents and vulcanization accelerators, the kneading temperature is usually <NUM> to <NUM>, preferably <NUM> to <NUM>. In a final kneading step of kneading vulcanizing agents and vulcanization accelerators, the kneading temperature is usually <NUM> or lower, preferably from <NUM> to <NUM>. Moreover, the composition obtained after kneading vulcanizing agents and vulcanization accelerators is usually vulcanized by press vulcanization, for example. The vulcanization temperature is usually <NUM> to <NUM>, preferably <NUM> to <NUM>. The vulcanization time is usually <NUM> to <NUM> minutes.

The rubber composition may be used in tire components (i.e., as a tire rubber composition), including, for example, treads (cap treads), sidewalls, base treads, undertreads, clinches, bead apexes, breaker cushion rubbers, rubbers for carcass cord topping, insulations, chafers, and innerliners, and side reinforcement layers of run-flat tires. The rubber composition is especially suitable for use in treads.

The tire (e.g., pneumatic tire) of the present disclosure may be produced from the rubber composition by usual methods. Specifically, the unvulcanized rubber composition containing additives as needed may be extruded into the shape of a tire component (in particular, a tread (cap tread)) and then formed and assembled with other tire components in a usual manner in a tire building machine to build an unvulcanized tire, which may then be heated and pressurized in a vulcanizer to produce a tire.

Non-limiting examples of the tire include pneumatic tires, solid tires, and airless tires. Preferred among these are pneumatic tires.

The tire can be suitably used as any of the following tires: tires for passenger cars, tires for large passenger cars, tires for large SUVs, tires for trucks and buses, tires for two-wheeled vehicles, racing tires, winter tires (studless winter tires, snow tires, studded tires), all-season tires, run-flat tires, aircraft tires, mining tires, etc..

The present disclosure is specifically described with reference to, but not limited to, examples.

A nitrogen-purged autoclave reactor was charged with cyclohexane, tetrahydrofuran, styrene, and <NUM>,<NUM>-butadiene. The temperature of the contents of the reactor was adjusted to <NUM>, and then n-butyllithium was added to initiate polymerization. The polymerization was carried out under adiabatic conditions, and the maximum temperature reached <NUM>. Once the polymerization conversion ratio reached <NUM>%, <NUM>,<NUM>-butadiene was further added, followed by polymerization for five minutes. Subsequently, N,N-bis(trimethylsilyl)-<NUM>-aminopropyltriethoxysilane was added as a modifier, and a reaction was performed. After completion of the polymerization reaction, <NUM>,<NUM>-di-tert-butyl-p-cresol was added. Thereafter, the solvent was removed by steam stripping. The product was dried on hot rolls adjusted at <NUM> to obtain SBR <NUM>.

To a graduated flask in a nitrogen atmosphere were added <NUM>-dimethylaminopropyltrimethoxysilane and then anhydrous hexane to prepare a terminal modifier.

A sufficiently nitrogen-purged pressure-proof vessel was charged with n-hexane, butadiene, and TMEDA, followed by heating to <NUM>. Next, butyllithium was added, and the mixture was then heated to <NUM> and stirred for three hours. Subsequently, the terminal modifier was added, and the mixture was stirred for <NUM> minutes. To the reaction solution were added methanol and <NUM>,<NUM>-tert-butyl-p-cresol, and the resulting reaction solution was put into a stainless steel vessel containing methanol. Then, aggregates were collected. The aggregates were dried under reduced pressure for <NUM> hours to obtain a modified polybutadiene rubber (BR <NUM>).

The chemicals other than the sulfur and vulcanization accelerators according to the formulation shown in Table <NUM> were kneaded in a <NUM> Banbury mixer (Kobe Steel, Ltd. ) at <NUM> for four minutes to give a kneaded mixture. Then, the sulfur and vulcanization accelerators were added to the kneaded mixture, and they were kneaded in an open roll mill at <NUM> for four minutes to prepare an unvulcanized rubber composition. Then, the unvulcanized rubber composition was press-vulcanized in a <NUM>-thick die at <NUM> for <NUM> minutes to give a vulcanized rubber composition.

Moreover, an unvulcanized rubber composition prepared as above was formed into the shape of a tread and assembled with other tire components to build an unvulcanized tire. The unvulcanized tire was press-vulcanized at <NUM> for <NUM> minutes to prepare a test tire (size: <NUM>/65R15).

The vulcanized rubber compositions and test tires prepared as above were left in an oven at <NUM> for <NUM> days to prepare aged vulcanized rubber compositions and test tires.

The vulcanized rubber compositions (new), vulcanized rubber compositions (after aging), test tires (new), and test tires (after aging) were subjected to the evaluations below. Table <NUM> shows the results.

The vulcanized rubber compositions were analyzed using a portable skid tester (Stanley) in accordance with ASTM E303-<NUM>. The results are expressed as an index (wet grip performance index) relative to the vulcanized rubber composition (new) of Example <NUM>, which is taken as <NUM>. A higher index indicates a shorter braking distance and thus better wet skid performance (wet grip performance). Here, a wet grip performance (before aging) index of <NUM> or higher is considered to represent good wet grip performance.

Moreover, a wet grip performance retention ratio was calculated from the evaluation results of the new and aged vulcanized rubber compositions. A higher wet grip performance retention ratio indicates a better ability to reduce deterioration of wet grip performance over time. Here, a wet grip performance retention ratio of <NUM> or higher is considered to represent a good ability to reduce deterioration of wet grip performance over time.

A set of test tires (new) or test tires (after aging) were mounted on a front-engine, front-wheel-drive car made in Japan. After running <NUM>,<NUM>, the groove depth in the tire tread portion was measured. A distance that caused a <NUM> decrease in tire groove depth was calculated and expressed as an index (abrasion resistance index) relative to Example <NUM> which is taken as <NUM>. A higher index indicates a longer distance that caused a <NUM> decrease in tire groove depth and thus better abrasion resistance.

Moreover, an abrasion resistance retention ratio was calculated from the evaluation results of the new and aged test tires. A higher abrasion resistance retention ratio indicates a better ability to reduce deterioration of abrasion resistance over time. Here, an abrasion resistance retention ratio of <NUM> or higher is considered to represent a good ability to reduce deterioration of abrasion resistance over time.

Claim 1:
A tire rubber composition, comprising:
one or more rubber components having a combined content of styrene-butadiene rubber and polybutadiene of <NUM>% by mass or more;
one or more fillers; and
one or more vulcanizing agents,
the rubber composition as a whole having a vinyl content of <NUM> mol% or higher and a trans content of <NUM> mol% or higher, each based on <NUM> mol% of a combined amount of butadiene-based structural units in a butadiene portion of the styrene-butadiene rubber and the polybutadiene.