Patent Description:
An exemplary method for simultaneously providing abrasion resistance to a tire is to improve the order of introduction of chemicals in rubber mixing (for example, Patent Literature <NUM>). However, in these days of well-developed automobile highways and increasingly sophisticated automobiles, repeated high-speed running is not uncommon, and therefore it is believed that there is room for further improvement in terms of abrasion resistance during high-speed running.

The present invention aims to solve the above problem and provide a tire having an improved abrasion resistance during high-speed running.

Although tire rubber properties greatly affect tire performance, not only the rubber properties but also tire shape (tread gauge, etc.) have a large influence on the development of tire performance. To improve the resistance to abrasion, which partially constitutes a fracture event, the amount of filler and its dispersion are important, and the reinforcement of a tire cannot be ensured unless at least a certain amount of filler is added. However, the amount of filler and abrasion resistance do not have a complete proportional relationship, and too much filler will deteriorate the performance.

In view of the above, the present invention was completed based on the finding that excellent abrasion resistance during high-speed running can be imparted to a tire by incorporating predetermined amounts of an isoprene-based rubber, a styrene-butadiene rubber, silica having a specific particle size, and a resin component while adjusting the polymer content PC and acetone extractable content AE of the rubber composition to specific ranges, and further that particularly excellent abrasion resistance during high-speed running can be imparted by further focusing on the tire shape to adjust the product of the thickness G of the tread portion measured on the equator in a cross-section taken in the radial direction of the tire and the polymer content PC to a predetermined value or more.

The present invention relates to a tire, including a tread portion,.

wherein PC and AE represent a polymer content (% by mass) and an acetone extractable content (% by mass), respectively, of the rubber composition.

The tire of the present invention includes a tread portion containing a rubber composition which contains predetermined amounts of rubber components including an isoprene-based rubber and a styrene-butadiene rubber, silica having an average primary particle size of <NUM> or less, and a resin component, and satisfies relationships (<NUM>) and (<NUM>). Such a tire provides an improved abrasion resistance during high-speed running.

The present invention provides a tire including a tread portion containing a rubber composition which contains predetermined amounts of rubber components including an isoprene-based rubber and a styrene-butadiene rubber, silica having an average primary particle size of <NUM> or less, and a resin component, and satisfies relationships (<NUM>) and (<NUM>).

The mechanism of this advantageous effect is not clear but is believed to be as follows.

The formation of a polymer gel made of a polymer bound to a reinforcing agent is considered to be important to improve abrasion resistance. Thus, when a rubber composition contains silica having an average primary particle size of <NUM> or less and has a polymer content PC of <NUM>% by mass or higher and an acetone extractable content AE reduced to <NUM>% by mass or lower, shear deformation during rubber mixing can readily propagate so that the formation of a polymer gel made of the polymer component bound to the silica can be facilitated, and at the same time the proportion of the polymer gel in the rubber composition can be increased.

Further, the gel formation in the polymer components can be further facilitated by increasing the isoprene-based rubber content in the polymer components and also incorporating a styrene-butadiene rubber which is highly reactive with silica.

Moreover, the simultaneous incorporation of a resin component improves the compatibility between the isoprene-based rubber and styrene-butadiene rubber, so that the distribution of the silica to the polymers can be improved to improve the dispersion of the silica, thereby further facilitating the polymer gel formation.

Accordingly, it is believed that the present invention provides good abrasion resistance during high-speed running by making it possible to form a polymer gel in the tread portion and increase the proportion of the polymer gel.

Thus, the present tire solves the problem (purpose) of improving abrasion resistance during high-speed running by a formulation satisfying the relationship (<NUM>): PC ≥ <NUM>% by mass and the relationship (<NUM>): AE ≤ <NUM>% by mass, wherein PC and AE represent the polymer content (% by mass) and the acetone extractable content (% by mass), respectively, of the rubber composition contained in the tread portion. In other words, the parameters of the relationship (<NUM>): PC ≥ <NUM>% by mass and the relationship (<NUM>): AE ≤ <NUM>% by mass do not define the problem (purpose), and the problem herein is to improve abrasion resistance during high-speed running. In order to solve this problem, the tire has been formulated to satisfy the parameters.

The tire of the present invention includes a tread portion which contains a tread rubber composition (vulcanized rubber composition) satisfying the following relationship (<NUM>): <MAT> wherein PC represents the polymer content (% by mass) of the rubber composition.

The lower limit of PC is preferably <NUM>% by mass or higher, more preferably <NUM>% by mass or higher, still more preferably <NUM>% by mass or higher, particularly preferably <NUM>% by mass or higher. The upper limit 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 PC is within the range indicated above, a polymer gel can be formed, and at the same time the proportion of the polymer gel in the rubber composition can be increased. Thus, the advantageous effect tends to be better achieved.

The tire of the present invention includes a tread portion which contains a tread rubber composition (vulcanized rubber composition) satisfying the following relationship (<NUM>): <MAT> wherein AE represents the acetone extractable content (% by mass) of the rubber composition.

The upper limit of AE 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. The lower limit is preferably <NUM>% by mass or higher, more preferably <NUM>% by mass or higher, still more preferably <NUM>% by mass or higher, particularly preferably <NUM>% by mass or higher. When AE is within the range indicated above, more shear energy can be obtained during mixing, thereby facilitating the polymer gel formation. Thus, the advantageous effect tends to be better achieved.

The tire of the present invention includes a tread portion which contains a tread rubber composition (vulcanized rubber composition) desirably satisfying the following relationship in order to better achieve the advantageous effect: <MAT> wherein Ash represents the ash content (% by mass) of the rubber composition.

The lower limit of Ash is preferably <NUM>% by mass or higher, more preferably <NUM>% by mass or higher, still more preferably <NUM>% by mass or higher, particularly preferably <NUM>% by mass or higher. The upper limit is preferably <NUM>% by mass or lower, more preferably <NUM>% by mass or lower, still more preferably <NUM>% by mass or lower. When Ash is within the range indicated above, the advantageous effect tends to be better achieved.

The tire of the present invention includes a tread portion which contains a tread rubber composition (vulcanized rubber composition) desirably satisfying the following relationship in order to better achieve the advantageous effect: <MAT> wherein BC represents the carbon black content (% by mass) of the rubber composition.

The upper limit of BC 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. The lower limit is preferably <NUM>% by mass or higher, more preferably <NUM>% by mass or higher, still more preferably <NUM>% by mass or higher, particularly preferably <NUM>% by mass or higher. When BC is within the range indicated above, the advantageous effect tends to be better achieved.

Here, the polymer content (PC), acetone extractable content (AE), carbon black content (BC), and ash content (Ash) of the (vulcanized) rubber composition can be measured as described below.

First, the acetone extractable content (AE, unit: % by mass based on the rubber composition (sample)) of the rubber composition (sample) is measured by a method for measuring the acetone extractable content in accordance with JIS K <NUM>:<NUM>.

The polymer content (PC, unit: % by mass based on the rubber composition (sample)) is calculated from the decrease in the amount (mass) of the sample remaining after the acetone extraction when it is heated (from room temperature to <NUM>) in nitrogen for pyrolysis and gasification of organic matter in accordance with JIS K <NUM>-<NUM>:<NUM>.

The carbon black content (BC, unit: % by mass based on the rubber composition (sample)) is calculated from the decrease in the amount (mass) of the sample after the pyrolysis and gasification when it is heated in the air for oxidative combustion.

The ash content (Ash, unit: % by mass based on the rubber composition (sample)) is calculated from the mass of the components which remain unburned in the oxidative combustion (ash).

Here, the sample used in the measurements is collected from the tread portion of the tire.

AE, PC, BC, and Ash may be controlled by methods known to those skilled in the art. For example, AE tends to increase as the amount of softeners such as oils in the rubber composition increases. PC tends to increase as the amount of elastomer components in the rubber composition increases. BC tends to increase as the amount of carbon black in the rubber composition increases. Ash tends to increase as the amount of components which remain unburned in oxidative combustion, such as silica, in the rubber composition increases.

The tread rubber composition contains rubber components including an isoprene-based rubber and a styrene-butadiene rubber (SBR).

The rubber components in the rubber composition contribute to cross-linking and generally correspond to polymers having a weight average molecular weight (Mw) of <NUM>,<NUM> or more.

The weight average molecular weight of the rubber components is preferably <NUM>,<NUM> or more, more preferably <NUM>,<NUM> or more, still more preferably <NUM>,<NUM> or more, but is preferably <NUM>,<NUM>,<NUM> or less, more preferably <NUM>,<NUM>,<NUM> or less, still more preferably <NUM>,<NUM>,<NUM> or less. When the weight average molecular weight is within the range indicated above, the advantageous effect tends to be better achieved.

Herein, the weight average molecular weight (Mw) 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.

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

The amount of isoprene-based rubbers based on <NUM>% by mass of the rubber components in the rubber composition is <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. The upper limit 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 SBR may be used, and examples include emulsion-polymerized styrene-butadiene rubbers (E-SBR) and solution-polymerized styrene-butadiene rubbers (S-SBR). Hydrogenated SBR may also be used in which the double bonds of the butadiene portions are appropriately hydrogenated. Examples of commercial products include those available from Sumitomo Chemical Co. , JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc..

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

Herein, the styrene content of the SBR can be determined by <NUM>H-NMR analysis.

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

Herein, the vinyl content (<NUM>,<NUM>-butadiene unit content) of the SBR can be measured by infrared absorption spectrometry.

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

Usable rubber components other than isoprene-based rubbers and SBR are not limited and include those known in the tire field. Examples include diene rubbers such as polybutadiene rubbers (BR), acrylonitrile-butadiene rubbers (NBR), chloroprene rubbers (CR), butyl rubbers (IIR), and styrene-isoprene-butadiene copolymer rubbers (SIBR). Each of these may be used alone, or two or more of these may be used in combination. To better achieve the advantageous effect, BR is preferred among these.

Any BR may be used, and examples include those commonly used in the tire industry, including: high cis BR such as BR1220 available from Zeon Corporation, BR150B available from Ube Industries, Ltd. , and BR1280 available from LG Chem; BR containing <NUM>,<NUM>-syndiotactic polybutadiene crystals (SPB) such as VCR412 and VCR617 both available from Ube Industries, Ltd. ; and polybutadiene rubbers synthesized using rare earth catalysts (rare earth-catalyzed BR). Each of these may be used alone, or two or more of these may be used in combination.

The cis content of the BR 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. When the cis content is within the range indicated above, the advantageous effect tends to be better achieved.

Here, the cis content of the BR can be measured by infrared absorption spectrometry.

When the rubber composition contains BR, 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, but is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, still more preferably <NUM>% by mass or less, particularly preferably <NUM>% by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The rubber components may include oil extended rubbers prepared by oil extension. These may be used alone or in combinations of two or more. The oils used in oil extended rubbers may be as described later. Moreover, the oil content of the oil extended rubbers is not limited but is usually about <NUM> to <NUM> parts by mass per <NUM> parts by mass of the rubber solids content.

The rubber components may be modified to introduce therein a functional group interactive with filler such as silica.

Examples of the functional group include a silicon-containing group (-SiR<NUM> where each R is the same or different and represents a hydrogen atom, a hydroxy group, a hydrocarbon group, an alkoxy group, or the like), an amino group, an amide group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxy group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxy group, an oxy group, and an epoxy group, each of which may be substituted. Preferred among these is a silicon-containing group. More preferred is - SiR<NUM> where each R is the same or different and represents a hydrogen atom, a hydroxy group, a hydrocarbon group (preferably a C1-C6 hydrocarbon group, more preferably a C1-C6 alkyl group), or an alkoxy group (preferably a C1-C6 alkoxy group), and at least one R is a hydroxy group.

Specific examples of the compound (modifier) used to introduce the functional group include <NUM>-dimethylaminoethyltrimethoxysilane, <NUM>-dimethylaminopropyltrimethoxysilane, <NUM>-dimethylaminoethyltriethoxysilane, <NUM>-dimethylaminopropyltriethoxysilane, <NUM>-diethylaminoethyltrimethoxysilane, <NUM>-diethylaminopropyltrimethoxysilane, <NUM>-diethylaminoethyltriethoxysilane, and <NUM>-diethylaminopropyltriethoxysilane.

The rubber composition contains silica having an average primary particle size of <NUM> or less (hereinafter, also referred to as "fine particle silica").

The average primary particle size is preferably <NUM> or less, more preferably <NUM> or less, still more preferably <NUM> or less. The lower limit is preferably <NUM> or more, more preferably <NUM> or more, still more preferably <NUM> or more. When the average primary particle size is within the range indicated above, the advantageous effect tends to be better achieved.

Here, the average primary particle size can be determined by measuring the particle sizes of at least <NUM> primary particles of silica observed in the visual field of a transmission or scanning electron microscope and averaging them.

The nitrogen adsorption specific surface area (N<NUM>SA) of the fine particle silica is 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 upper limit is not limited 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.

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

The amount of fine particle silica per <NUM> parts by mass of the rubber components in the rubber composition is <NUM> parts by mass or more, preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more. The upper limit of the amount 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 may contain silica other than the fine particle silica.

The total amount of silica (the combined amount of fine particle silica and silica other than fine particle silica) per <NUM> parts by mass of the rubber components in the rubber composition is <NUM> parts by mass or more, preferably <NUM> parts by mass or more, more preferably more than <NUM> parts by mass, still more preferably <NUM> parts by mass or more. The upper limit of the total amount 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 total amount is within the range indicated above, the advantageous effect tends to be better achieved.

Examples of usable silica include dry silica (anhydrous silica) and wet silica (hydrous silica). Wet silica is preferred among these because it contains a large number of silanol groups. Moreover, besides such anhydrous silica and hydrous silica, silica produced from biomass materials such as rice husks may be appropriately used. Usable commercial products are available from Degussa, Rhodia, Tosoh Silica Corporation, Solvay Japan, Tokuyama Corporation, etc. These may be used alone or in combinations of two or more.

The rubber composition which contains silica preferably further contains a silane coupling agent.

Any silane coupling agent may be used, including those known in the rubber field. 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-dimethylthiocarbamoyltetrasulfide, <NUM>-triethoxysilylethyl-N,N-dimethylthiocarbamoyltetrasulfide, and <NUM>-triethoxysilylpropyl methacrylate monosulfide; mercapto silane coupling agents such as <NUM>-mercaptopropyltrimethoxysilane, <NUM>-mercaptoethyltriethoxysilane, and NXT and NXT-Z both available from Momentive; 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. Usable commercial products are available from Degussa, Momentive, Shin-Etsu Silicone, Tokyo Chemical Industry Co. , Dow Corning Toray Co. , etc. These may be used alone or in combinations of two or more.

The amount of silane coupling agents per <NUM> parts by mass of the silica in the rubber composition 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. The upper limit of the amount 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 may contain fillers other than silica.

Any filler other than silica may be used, including materials known in the rubber field. Examples include inorganic fillers such as carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, and mica. Among these, carbon black is preferred in order to better achieve the advantageous effect.

Any carbon black may be used in the rubber composition, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Besides such carbon black produced by burning mineral oils, carbon black produced by burning biomass-derived materials such as lignin may also be appropriately used. Usable commercial products are available from Asahi Carbon Co. , Cabot Japan K. , Tokai Carbon Co. , Mitsubishi Chemical Corporation, Lion Corporation, NIPPON STEEL Carbon Co. , Columbia Carbon, etc. 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, still more 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, further 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.

The amount of carbon black per <NUM> parts by mass of the rubber components in the rubber composition 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 upper limit of the amount 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 percentage of silica based on <NUM>% by mass of the fillers contained in the rubber composition is preferably <NUM>% by mass or higher, more preferably <NUM>% by mass or higher, still more preferably <NUM>% by mass or higher, particularly preferably <NUM>% by mass or higher. The upper limit is not limited but is preferably <NUM>% by mass or lower, more preferably <NUM>% by mass or lower, still more preferably <NUM>% by mass or lower. When the percentage of silica is within the range indicated above, the advantageous effect tends to be better achieved.

The amount of fillers (the total amount of fillers including fine particle silica, other silica, carbon black, etc.) per <NUM> parts by mass of the rubber components in the rubber composition 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. The upper limit of the amount 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 contains a resin component.

The resin component may be either a liquid resin which is liquid at room temperature (<NUM>) or a solid resin which is solid at room temperature (<NUM>). Among these, the solid resin is desirable in order to better achieve the advantageous effect.

The amount of resin components (the combined amount of liquid resins which are liquid at <NUM> and solid resins which are solid at <NUM>) per <NUM> parts by mass of the rubber components in the rubber composition 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. The upper limit 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.

Examples of the solid resins include petroleum resins, terpene resins, aromatic vinyl polymers, coumarone-indene resins, coumarone resins, indene resins, phenol resins, rosin resins, and acrylic resins, all of which are solid at room temperature (<NUM>). These resin components may also be hydrogenated. These may be used alone or in combinations of two or more. Petroleum resins, terpene resins, and aromatic vinyl polymers are preferred among these.

The softening point of the resin components is preferably <NUM> or higher, more preferably <NUM> or higher, still more preferably <NUM> or higher. The upper limit is preferably <NUM> or lower, more preferably <NUM> or lower, still more preferably <NUM> or lower. When the softening point is within the range indicated above, the advantageous effect tends to be better achieved.

Here, the softening point of the resin components is determined as set forth in JIS K <NUM>-<NUM>:<NUM> using a ring and ball softening point measuring apparatus and defined as the temperature at which the ball drops down. Moreover, the softening point of the resin components is usually higher by about <NUM> ± <NUM> than the glass transition temperature of the resin components.

Examples of the petroleum resins include C5 resins, C9 resins, C5/C9 resins, and dicyclopentadiene (DCPD) resins. Hydrogenated products of these resins are also usable.

The terpene resins refer to polymers containing terpenes as structural units. Examples include polyterpene resins produced by polymerizing terpene compounds, and aromatic modified terpene resins produced by polymerizing terpene compounds and aromatic compounds. Hydrogenated products of these resins are also usable.

The polyterpene resins refer to resins produced by polymerizing terpene compounds. The terpene compounds refer to hydrocarbons having a composition represented by (C<NUM>H<NUM>)n or oxygen-containing derivatives thereof, each of which has a terpene backbone and is classified as a monoterpene (C<NUM>H<NUM>), sesquiterpene (C<NUM>H<NUM>), diterpene (C<NUM>H<NUM>), or other terpene. Examples of the terpene compounds include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, <NUM>,<NUM>-cineole, <NUM>,<NUM>-cineole, α-terpineol, β-terpineol, and γ-terpineol.

Examples of the polyterpene resins include resins made from the above-mentioned terpene compounds, such as pinene resins, limonene resins, dipentene resins, and pinene-limonene resins. Pinene resins are preferred among these. Pinene resins, which usually contain two isomers, α-pinene and β-pinene, are classified as β-pinene resins mainly containing β-pinene and α-pinene resins mainly containing α-pinene, depending on the proportions of the components in the resins.

Examples of the aromatic modified terpene resins include terpene-phenol resins made from the above-mentioned terpene compounds and phenolic compounds, and terpene-styrene resins made from the above-mentioned terpene compounds and styrene compounds. Terpene-phenol-styrene resins made from the terpene compounds, phenolic compounds, and styrene compounds are also usable. Here, examples of the phenolic compounds include phenol, bisphenol A, cresol, and xylenol, and examples of the styrene compounds include styrene and α-methylstyrene.

The aromatic vinyl polymers refer to polymers containing aromatic vinyl monomers as structural units. Examples include resins produced by polymerizing α-methylstyrene and/or styrene. Specific examples include styrene homopolymers (styrene resins), α-methylstyrene homopolymers (α-methylstyrene resins), copolymers of α-methylstyrene and styrene, and copolymers of styrene and other monomers.

The coumarone-indene resins refer to resins containing coumarone and indene as the main monomer components forming the skeleton (backbone) of the resins. Examples of monomer components which may be contained in the skeleton in addition to coumarone and indene include styrene, α-methylstyrene, methylindene, and vinyltoluene.

The coumarone resins refer to resins containing coumarone as the main monomer component forming the skeleton (backbone) of the resins.

The indene resins refer to resins containing indene as the main monomer component forming the skeleton (backbone) of the resins.

Examples of the phenol resins include known polymers produced by reaction of phenol with aldehydes such as formaldehyde, acetaldehyde, or furfural using acid or alkali catalysts. Preferred among these are those produced by reaction using acid catalysts (e.g., novolac-type phenol resins).

Examples of the rosin resins include rosin-based resins typified by natural rosins, polymerized rosins, modified rosins, and esterified compounds thereof, and hydrogenated products thereof.

The acrylic resins refer to polymers containing acrylic monomers as structural units. Examples include styrene acrylic resins such as those which contain carboxy groups and are produced by copolymerizing aromatic vinyl monomer components and acrylic monomer components. Solvent-free, carboxy group-containing styrene acrylic resins are suitable among these.

The solvent-free, carboxy group-containing styrene acrylic resins may be (meth)acrylic resins (polymers) synthesized by high temperature continuous polymerization (high temperature continuous bulk polymerization as described in, for example, <CIT>, <CIT>,<CIT>, <CIT>, <CIT>, and annual research report TREND <NUM> issued by Toagosei Co. <NUM>-<NUM>) using no or minimal amounts of auxiliary raw materials such as polymerization initiators, chain transfer agents, and organic solvents. Herein, the term "(meth)acrylic" means methacrylic and acrylic.

Examples of the acrylic monomer components of the acrylic resins include (meth)acrylic acid and (meth)acrylic acid derivatives such as (meth)acrylic acid esters (e.g., alkyl esters, aryl esters, and aralkyl esters, such as <NUM>-ethylhexyl acrylate), (meth)acrylamide, and (meth)acrylamide derivatives. Here, the term "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid.

Examples of the aromatic vinyl monomer components of the acrylic resins include aromatic vinyls such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, and divinylnaphthalene.

In addition to the (meth)acrylic acid or (meth)acrylic acid derivatives and aromatic vinyls, other monomer components may also be used as the monomer components of the acrylic resins.

The amount of solid resins per <NUM> parts by mass of the rubber components in the rubber composition 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. The upper limit 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. Here, the amount of petroleum resins, the amount of terpene resins, and the amount of aromatic vinyl polymers are each also desirably within the range as indicated above.

Examples of the liquid resins include terpene resins (including terpene-phenol resins and aromatic modified terpene resins), rosin resins, styrene resins, C5 resins, C9 resins, C5/C9 resins, dicyclopentadiene (DCPD) resins, coumarone-indene resins (including resins based on coumarone or indene alone), phenol resins, olefin resins, polyurethane resins, and acrylic resins, all of which are liquid at room temperature (<NUM>). Hydrogenated products of these resins are also usable.

The amount of liquid resins per <NUM> parts by mass of the rubber components in the rubber composition 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. The upper limit 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.

Besides the above-mentioned resin components, the rubber composition may contain other plasticizers capable of imparting plasticity to rubber components. Examples of such other plasticizers include liquid plasticizers (plasticizers which are liquid at <NUM>) other than the liquid resins and solid plasticizers (plasticizers which are solid at <NUM>) other than the solid resins. These plasticizers may be used alone or in combinations of two or more.

The total amount of plasticizers (the combined amount of liquid resins and other liquid plasticizers, and solid resins and other solid plasticizers) per <NUM> parts by mass of the rubber components in the rubber composition 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. The upper limit 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.

Non-limiting examples of the above-mentioned other liquid plasticizers (plasticizers which are liquid at room temperature (<NUM>)) include oils and liquid polymers other than the liquid resins, such as liquid diene polymers and liquid farnesene polymers. Oils are desirable among these. These may be used alone or in combinations of two or more.

When the rubber composition contains the above-mentioned other liquid plasticizers, the amount of the other liquid plasticizers per <NUM> parts by mass of the rubber components 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, and may be <NUM> parts by mass. The amount of oils is also desirably within the range as indicated above. Here, the amount of liquid plasticizers includes the amount of the oils contained in extender oils.

Examples of oils include process oils, plant oils, and mixtures thereof. Examples of process oils include paraffinic process oils, aromatic process oils, and naphthenic process oils. Examples of plant 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. In addition to these oils, oils after being used as lubricating oils in mixers for processing rubber, engines, or other applications, or oils obtained by purifying waste cooking oils used in cooking establishments may also be appropriately used from the standpoint of life cycle assessment.

Examples of liquid diene polymers include liquid styrene-butadiene copolymers (liquid SBR), liquid polybutadiene polymers (liquid BR), liquid polyisoprene polymers (liquid IR), liquid styrene-isoprene copolymers (liquid SIR), liquid styrene-butadiene-styrene block copolymers (liquid SBS block polymers), liquid styrene-isoprene-styrene block copolymers (liquid SIS block polymers), liquid farnesene polymers, and liquid farnesene-butadiene copolymers, all of which are liquid at <NUM>. These polymers may be modified at the chain end or backbone with a polar group. Hydrogenated products of these polymers are also usable.

The above-mentioned other solid plasticizers (plasticizers which are solid at <NUM>) may be materials other than the solid resins which are capable of imparting plasticity to rubber components.

The plasticizers may be commercially available from, for example, Maruzen Petrochemical Co. , Sumitomo Bakelite Co. , Yasuhara Chemical Co. , Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical, Nitto Chemical Co. , Nippon Shokubai Co. , ENEOS Corporation, Arakawa Chemical Industries, Ltd. , Taoka Chemical Co.

The rubber composition may contain an antioxidant.

Examples of 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. Usable commercial products are available from Seiko Chemical Co. , Sumitomo Chemical Co. , Ouchi Shinko Chemical Industrial Co. , Flexsys, etc. Each of these may be used alone, or two or more of these may be used in combination.

The amount of antioxidants per <NUM> parts by mass of the rubber components in the rubber composition 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. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The rubber composition may contain a wax.

Any wax may be used, and examples include petroleum waxes such as paraffin waxes and microcrystalline waxes; and synthetic waxes such as polymers of ethylene, propylene, or other similar monomers. Usable commercial products are available from Ouchi Shinko Chemical Industrial Co. , Nippon Seiro Co. , Seiko Chemical Co. , etc. Each of these may be used alone, or two or more of these may be used in combination.

The amount of waxes per <NUM> parts by mass of the rubber components in the rubber composition is preferably <NUM> part 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.

Conventional stearic acid may be used. Usable commercial products are available from NOF Corporation, Kao Corporation, FUJIFILM Wako Pure Chemical Corporation, Chiba Fatty Acid Co. , etc. Each of these may be used alone, or two or more of these may be used in combination.

The amount of stearic acid per <NUM> parts by mass of the rubber components in the rubber composition 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. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Conventional zinc oxide may be used. Usable commercial products are available from Mitsui Mining & Smelting Co. , Toho Zinc Co. , HakusuiTech Co. , Seido Chemical Industry Co. , Sakai Chemical Industry Co. , etc. Each of these may be used alone, or two or more of these may be used in combination.

The amount of zinc oxide per <NUM> parts by mass of the rubber components in the rubber composition 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. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Examples of sulfur include those commonly used as crosslinking agents in the rubber industry, such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. Usable commercial products are available from Tsurumi Chemical Industry Co. , Karuizawa sulfur Co. , Shikoku Chemicals Corporation, Flexsys, Nippon Kanryu Industry Co. , Hosoi Chemical Industry Co. , etc. These may be used alone or in combinations of two or more.

The amount of sulfur per <NUM> parts by mass of the rubber components in the rubber composition 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. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The rubber composition may contain a vulcanization accelerator.

Examples of vulcanization accelerators include thiazole vulcanization accelerators such as <NUM>-mercaptobenzothiazole and di-<NUM>-benzothiazolyl disulfide; thiuram vulcanization accelerators such as tetramethylthiuram disulfide (TMTD) and tetrakis(<NUM>-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide vulcanization accelerators such as N-cyclohexyl-<NUM>-benzothiazylsulfenamide (CBS), N-tert-butyl-<NUM>-benzothiazolylsulfenamide (TBBS), N-oxyethylene-<NUM>-benzothiazole sulfenamide, and N,N'-diisopropyl-<NUM>-benzothiazole sulfenamide; and guanidine vulcanization accelerators such as diphenylguanidine, diorthotolylguanidine, and orthotolylbiguanidine. Usable commercial products are available from Sumitomo Chemical Co. , Ouchi Shinko Chemical Industrial Co. , etc. These may be used alone or in combinations of two or more.

The amount of vulcanization accelerators per <NUM> parts by mass of the rubber components in the rubber composition 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. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

In addition to the above-mentioned components, the rubber composition may further contain additives commonly used in the tire industry, such as organic peroxides. The amounts of such additives are each 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 above-mentioned components using 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 <NUM> to <NUM>. Then, 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 above-described rubber composition (tread rubber composition) is used in a tread portion of a tire.

Examples of tires applicable in the present invention include pneumatic tires and non-pneumatic tires, with pneumatic tires being preferred. In particular, summer tires, winter tires (e.g., studless winter tires, snow tires, cold weather tires, studded tires), and all-season tires are suitable. For example, the present tire may be used as a tire for passenger cars, large passenger cars, large SUVs, heavy duty vehicles such as trucks and buses, light trucks, or motorcycles, or as a racing tire (high performance tire). Among these, the tire is desirably used as a heavy duty tire. Herein, the term "heavy duty tire" refers to a tire with a normal internal pressure of higher than <NUM> kPa and a normal load of more than <NUM>.

The tire can be produced from the above-described rubber composition by usual methods. For example, an unvulcanized rubber composition containing various materials may be extruded into the shape of a tread portion and then formed together with other tire components in a usual manner on a tire building machine to build an unvulcanized tire, which may then be heated and pressurized in a vulcanizer to produce a tire.

To better achieve the advantageous effect, the tire of the present invention desirably satisfies the following relationship: <MAT> wherein PC represents the polymer content (% by mass) of the tread rubber composition (vulcanized rubber composition) contained in the tread portion, and G represents the thickness (mm) of the tread portion measured on the equator in a cross-section taken in the radial direction of the tire.

The lower limit of the value of "PC × G" is preferably <NUM> or higher, more preferably <NUM> or higher, still more preferably <NUM> or higher, particularly preferably <NUM> or higher. The upper limit is preferably <NUM> or lower, more preferably <NUM> or lower, still more preferably <NUM> or lower. When the value is within the range indicated above, the advantageous effect tends to be better achieved.

As described earlier, the polymer content is considered to be a factor that affects the amount of the polymer gel. Meanwhile, a tread portion with a smaller gauge has a higher rigidity and thus is less likely to be deformed and more likely to be worn away by the road surface. Hence, it is believed that by adjusting the product of the polymer content, which affects the amount of the polymer gel, and the gauge to a certain value or more, good abrasion resistance during high-speed running can be provided even when the thickness is small.

In the tire of the present invention, the thickness G (mm) of the tread portion measured on the equator in a cross-section taken in the radial direction of the tire is preferably <NUM> or less, more preferably <NUM> or less, still more preferably <NUM> or less, particularly preferably <NUM> or less, most preferably <NUM> or less. The lower limit is preferably <NUM> or more, more preferably <NUM> or more, still more preferably <NUM> or more, particularly preferably <NUM> or more. When the thickness is within the range indicated above, the advantageous effect tends to be better achieved.

Herein, the term "thickness G of the tread portion measured on the equator in a cross-section taken in the radial direction of the tire" refers to the distance from the tread surface to the interface of the belt-reinforcing layer, belt layer, carcass layer, or other reinforcing layer containing a fiber material, which is outermost with respect to the tire, as measured on the equator in a cross-section taken along a plane including the axis of the tire. Here, when the tread portion has a groove on the equator of the tire, the thickness G is the linear distance from the intersection of the equator and a straight line connecting the edges of the groove which are outermost in the radial direction of the tire.

In the tire of the present invention, the tread portion desirably has a negative ratio S (%) of <NUM>% or lower.

S is preferably <NUM>% or lower, more preferably <NUM>% or lower, still more preferably <NUM>% or lower, particularly preferably <NUM>% or lower. The negative ratio is preferably <NUM>% or higher, more preferably <NUM>% or higher. When S is within the range indicated above, the advantageous effect tends to be better achieved.

Here, the negative ratio (negative ratio within the ground contact surface of the tread portion) refers to the ratio of the total groove area within the ground contact surface relative to the total area of the ground contact surface and is determined as described below.

Herein, when the tire is a pneumatic tire, the negative ratio is calculated from the contact patch of the tire under conditions including a normal rim, a normal internal pressure, and a normal load. When the tire is a non-pneumatic tire, the negative ratio can be similarly determined without the need of a normal internal pressure.

The term "normal rim" refers to a rim specified for each tire by the standard in a standard system including standards according to which tires are provided, and may be, for example, the standard rim in JATMA, "design rim" in TRA, or "measuring rim" in ETRTO.

The term "normal internal pressure" refers to an air pressure specified for each tire by the standard and may be the maximum air pressure in JATMA, the maximum value shown in Table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA, or "inflation pressure" in ETRTO.

The term "normal load" refers to a load specified for each tire by the standard and may be the maximum load capacity in JATMA, the maximum value shown in Table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA, or "load capacity" in ETRTO.

The contact patch may be determined by mounting the tire on a normal rim, applying a normal internal pressure to the tire, and allowing the tire to stand at <NUM> for <NUM> hours, followed by applying black ink to the tread surface of the tire and pressing the tread surface against a cardboard at a normal load (camber angle: <NUM>°) for transfer to the cardboard.

The transfer may be performed on the tire in five positions, each rotated by <NUM>° in the circumferential direction. Namely, the contact patch may be determined five times.

The contour points of each of the five contact patches are smoothly connected to draw a figure, the area of which is defined as the total area, and the transferred area as a whole constitutes the ground contact area. The average of the results of the five positions is determined and then the negative ratio (%) is calculated by the equation: [<NUM>-{Average of areas of five contact patches transferred to cardboard (parts with black ink)}/{Average of five total areas transferred to cardboard (figures obtained from contour points)}] × <NUM> (%).

Here, the average length or area is the simple average of the five values.

In the tire of the present invention, the groove depth D of a circumferential groove formed in the tread portion is preferably <NUM> or less, more preferably <NUM> or less, still more preferably <NUM> or less, but is preferably <NUM> or more, more preferably <NUM> or more, still more preferably <NUM> or more. When D is within the range indicated above, the advantageous effect tends to be better achieved.

Herein, the groove depth D of the circumferential groove is measured along the normal of a plane extended from the outermost tread surface forming the ground contact surface, and refers to the distance from the plane extended from the surface forming the ground contact surface to the deepest groove bottom, which is the largest among the groove depths of the circumferential grooves provided.

<FIG> shows a cross-section of a part of a pneumatic tire <NUM> according to one embodiment of the present invention taken in the meridional direction. Here, the tire of the present invention is not limited to the following embodiment.

<FIG> shows an example of a heavy duty pneumatic tire <NUM>. In <FIG>, the vertical direction corresponds to the radial direction of the tire <NUM>, the horizontal direction corresponds to the axial direction of the tire <NUM>, and the direction perpendicular to the paper corresponds to the circumferential direction of the tire <NUM>. In <FIG>, the center line CL of the tire <NUM> also represents the equator EQ of the tire <NUM>. The shape of the tire <NUM> is symmetrical about the equator EQ, except for the tread pattern.

The tire <NUM> includes a tread portion <NUM>, a sidewall portion <NUM>, a chafer <NUM>, a bead portion <NUM>, a carcass <NUM>, an innerliner <NUM>, a filler <NUM>, and a belt <NUM>. The tire <NUM> is a tubeless tire.

The tread portion <NUM> has a radially outwardly convex shape. The tread portion <NUM> forms a tread face <NUM> that will contact the road surface. The tread face <NUM> is provided with five circumferential grooves <NUM> (hereinafter, also referred to as main grooves). The main grooves <NUM> consist of one center main groove 24c located in the axial center (substantially corresponding to the equator EQ), a pair of shoulder main grooves <NUM> located at opposite axially outer sides, and a pair of middle main grooves <NUM> each located between the center main groove 24c and the shoulder main groove <NUM>. The five main grooves 24c, <NUM> and <NUM> define six circumferentially extending ribs.

The six ribs are desirably each provided with axial grooves (lug grooves) (not shown). The main grooves <NUM> and the lug grooves (not shown) define a tread pattern with six rows of blocks <NUM>, specifically, center blocks 40c, middle blocks <NUM>, and shoulder blocks <NUM>. Here, the shoulder main groove <NUM>, the center main groove 24c, and the shoulder groove <NUM> may not have the same width.

The sidewall portion <NUM> radially substantially inwardly extends from the end of the tread portion <NUM>. The radially outer part of the sidewall portion <NUM> is bound to the tread portion <NUM>. The radially inner part of the sidewall portion <NUM> is bound to the chafer <NUM>. As is clear from <FIG>, the sidewall portion <NUM> is located axially outward from the carcass <NUM>. The sidewall portion <NUM> desirably consists of a crosslinked rubber.

The chafer <NUM> radially substantially inwardly extends from the sidewall portion <NUM>. The chafer <NUM> will come into contact with a rim flange.

The bead portion <NUM> includes a core <NUM> and an apex <NUM> radially outwardly extending from the core <NUM>. The core <NUM> has a ring shape and includes a wound inextensible wire. Typical examples of the material of the wire include steel. The apex <NUM> is radially outwardly tapered.

The carcass <NUM> consists of a carcass ply <NUM>. The carcass ply <NUM> extends between the opposite bead portions <NUM> along the tread portion <NUM> and the sidewall portions <NUM>. The carcass ply <NUM> is folded around the core <NUM> from the inside to the outside in the axial direction. The carcass ply <NUM> may consist of a large number of parallel cords and a topping rubber. The carcass <NUM> may be formed of two or more carcass plies <NUM>.

The filler <NUM> is located near the bead portion <NUM>. The filler <NUM> is stacked on the carcass <NUM>. The filler <NUM> is folded around the core <NUM> of the bead portion <NUM> while being inside the carcass ply <NUM>. The filler <NUM> may consist of a large number of parallel cords and a topping rubber.

The innerliner <NUM> is located inside the carcass <NUM>. The innerliner <NUM> desirably consists of a crosslinked rubber.

In the cross-section shown in <FIG>, the belt <NUM> extends in the axial direction. The belt <NUM> is located radially inward of the tread portion <NUM>. The belt <NUM> is located radially outward of the carcass <NUM>. The belt <NUM> reinforces the carcass <NUM>. In the tire <NUM>, the belt <NUM> includes four layers. The belt <NUM> consists of a first ply 18a, a second ply 18b, a third ply 18c, and a fourth ply 18d which are stacked in said order from the radially inside. The first ply 18a is stacked on the carcass <NUM> at the equator. Each ply may consist of a large number of parallel cords and a topping rubber. In the tire <NUM>, the second ply 18b has the largest width in the axial direction among the four layers. In the tire <NUM>, the fourth ply 18d has the smallest width in the axial direction among the four layers. The belt <NUM> may include three layers.

<FIG> shows an enlarged cross-section in the vicinity of a shoulder portion <NUM> of the tire <NUM> shown in <FIG>.

In <FIG> and <FIG>, a crown center CL (the center line CL of the tire <NUM>) located at the equator EQ corresponds to "the equator in a cross-section of the tread portion <NUM> taken in the radial direction of the tire".

The tire <NUM> desirably satisfies the relationship: PC × G ≥ <NUM>, wherein PC represents the polymer content (% by mass) of the tread rubber composition (vulcanized rubber composition) contained in the tread portion <NUM>, and G represents the thickness of the tread portion <NUM> measured at the center line CL of the tire <NUM> (the radial dimension from the tread face <NUM> to the upper surface of the fourth ply 18d).

The tread portion <NUM> of the tire <NUM> includes circumferential grooves <NUM>. In the tire <NUM>, the groove depth D of the circumferential grooves <NUM> refers to the distance in the normal direction from a plane extended from the tread face <NUM> forming the ground contact surface to the deepest groove bottom and also refers to the depth of the deepest groove among the circumferential grooves <NUM> provided.

The present invention will be specifically described with reference to, but not limited to, examples.

According to the formulation recipe shown in Table <NUM>, the materials other than the sulfur and vulcanization accelerator are kneaded for five minutes at <NUM> using a <NUM> Banbury mixer (Kobe Steel, Ltd. ) to give a kneaded mixture. Next, the sulfur and vulcanization accelerator are added to the kneaded mixture, and they are kneaded for five minutes at <NUM> using an open roll mill to obtain an unvulcanized rubber composition. The unvulcanized rubber composition is formed into the shape of a tread portion and assembled with other tire components to build an unvulcanized tire. The unvulcanized tire is press-vulcanized at <NUM> for <NUM> minutes to prepare a test tire (size: <NUM>/80R22.

The test tires prepared as above are subjected to physical property measurements and evaluations as described below. The results are shown in Table <NUM>. Here, the standard comparative examples in Table <NUM> are as follows.

The amount of the substances extracted with acetone from a rubber specimen cut out of the tread of each test tire is measured by a method for measuring the acetone extractable content in accordance with JIS K <NUM>. Acetone extractable content (% by mass) = (Mass of sample before extraction - Mass of sample after extraction)/Mass of sample before extraction × <NUM>.

The decrease in the amount (mass) of the sample after the acetone extraction in the above section "Acetone extractable content (AE)" is measured when it is heated (from room temperature to <NUM>) in nitrogen for pyrolysis and gasification of organic matter in accordance with JIS K <NUM>-<NUM>:<NUM>, and PC (% by mass) is calculated therefrom.

The decrease in the amount (mass) of the sample after the pyrolysis and gasification in the above section "Polymer content (PC)" is measured when it is heated in the air for oxidative combustion, and BC (% by mass) is calculated therefrom.

The mass of the components which remain unburned in the oxidative combustion (ash) in the above section "Carbon black content (BC)" is measured, from which Ash (% by mass) is calculated.

Rolling resistance is measured using a rolling resistance tester under the following conditions.

The measurement results are expressed as an index (fuel economy index) relative to that of the standard comparative example taken as <NUM>. A higher index indicates a smaller rolling resistance and better fuel economy.

Each test tire mounted on a rim is installed on a rear wheel of a truck as a test car. A road test is conducted using the test car. The test conditions are as follows.

The groove depth of the test tire is measured after the running to determine the amount of wear from the start of running. The amount of wear of the tread portion is calculated from the measured depth and expressed as an index relative to that of the standard comparative example taken as <NUM>. A higher index indicates a smaller amount of wear and better abrasion resistance during high-speed running.

Claim 1:
A tire, comprising a tread portion,
the tread portion comprising a rubber composition comprising: rubber components including at least one isoprene-based rubber and at least one styrene-butadiene rubber; at least one silica having an average primary particle size of <NUM> or less; and at least one resin component,
the rubber composition comprising the isoprene-based rubber in an amount of <NUM>% by mass or more based on <NUM>% by mass of the rubber components and the silica in an amount of <NUM> parts by mass or more per <NUM> parts by mass of the rubber components,
the tire satisfying the following relationships (<NUM>) and (<NUM>): <MAT> and <MAT> wherein PC and AE represent a polymer content (% by mass) and an acetone extractable content (% by mass), respectively, of the rubber composition,
wherein the acetone extractable content is measured in accordance with JIS K <NUM>:<NUM>, and
wherein the polymer content is calculated from the decrease in the amount of a sample from the rubber composition remaining after the acetone extraction when it is heated from room temperature to <NUM> in nitrogen for pyrolysis and gasification of organic matter in accordance with JIS K <NUM>-<NUM>:<NUM>.