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 welldeveloped 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 is 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, especially during high-speed running, can be imparted to a tire by adjusting the polymer content PC and ash content Ash of the rubber composition to predetermined ranges and, at the same time, focusing on the tire shape to adjust the product of the thickness G (mm) of the tread portion measured on the equator in a cross-section taken in the radial direction of the tire and the ash content Ash (% by mass) to a predetermined value or less.

The present invention relates to a tire, including a tread portion,
the tire satisfying the following relationships (<NUM>) to (<NUM>): <MAT> <MAT> and <MAT> wherein PC and Ash represent a polymer content (% by mass) and an ash content (% by mass), respectively, of a rubber composition contained in the tread portion, and G represents a thickness (mm) of the tread portion measured on an equator in a cross-section taken in a radial direction of the tire.

The tire of the present invention includes a tread portion and satisfies relationships (<NUM>) to (<NUM>) with respect to the polymer content PC (% by mass) and ash content Ash (% by mass) of a rubber composition contained in the tread portion, and the thickness G (mm) of the tread portion measured on the equator in a cross-section taken in the radial direction of the tire. Such a tire has an improved abrasion resistance during high-speed running.

The tire of the present invention satisfies relationships (<NUM>) to (<NUM>) with respect to the polymer content PC (% by mass) and ash content Ash (% by mass) of the rubber composition contained in the tread portion, and the thickness G (mm) of the tread portion measured on the equator in a cross-section taken in the radial direction of the tire.

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

In general, to improve abrasion resistance, the polymer portion forming the matrix of the rubber composition needs to be reinforced by interaction with a reinforcing agent. However, simply increasing the amount of reinforcing agent will increase the amount of polymer constrained by the reinforcing agent, causing hardening of the rubber. Thus, a higher frequency will occur upon contact with the road surface, especially during high-speed running, and further the rubber cannot sufficiently conform to the road surface and will be worn away. As a result, it is considered that abrasion resistance cannot be sufficiently improved.

To overcome this, according to the present invention, the polymer content (PC) is adjusted to <NUM>% by mass or higher (relationship (<NUM>)) to account for more than half the amount of the rubber composition, and further the ash content (Ash) is adjusted to <NUM> to <NUM>% by mass (relationship (<NUM>)). This facilitates the formation of a polymer gel by interaction between the polymer components and ash components in the rubber. At the same time, the proportion of the polymer gel in the polymer components can be increased. Further, as relationship (<NUM>) is satisfied to reduce the proportion of the ash components such as silica, hardening of the micro-domains can be prevented and conforming to the road surface can also be facilitated. As a result, it is considered that abrasion resistance can be improved.

Moreover, the ash content affects the heat generation in the rubber, and the generated heat causes the rubber to soften so that the rubber can be greatly deformed by friction with the road surface and thus can be easily worn away; further, a large thickness G (gauge) of the tread portion facilitates the accumulation of heat due to deformation during running. Thus, it is considered that abrasion resistance can be improved by reducing the ash content with the increase in gauge (or reducing the gauge with the increase in ash content) so that the product of the thickness of the tread portion and the ash content is adjusted to <NUM> or less (relationship (<NUM>)).

Accordingly, it is believed that the present invention improves abrasion resistance during high-speed running by satisfying relationships (<NUM>) to (<NUM>).

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, the relationship (<NUM>): <NUM>% by mass ≤ Ash ≤ <NUM>% by mass, and the relationship (<NUM>): Ash × G ≤ <NUM>, wherein PC and Ash represent the polymer content (% by mass) and the ash content (% by mass), respectively, of the 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. In other words, the parameters of the relationship (<NUM>): PC ≥ <NUM>% by mass, the relationship (<NUM>): <NUM>% by mass ≤ Ash ≤ <NUM>% by mass, and the relationship (<NUM>): Ash × G ≤ <NUM> 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, 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 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, particularly preferably <NUM>% by mass or lower. When Ash is within the range indicated above, the advantageous effect tends to be better achieved.

Here, the polymer content (PC) and ash content (Ash) of the (vulcanized) rubber composition can be measured as described below.

First, the rubber composition (sample) is subjected to acetone extraction 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>.

Next, the sample after the pyrolysis and gasification 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.

PC and Ash may be controlled by methods known to those skilled in the art. For example, PC tends to increase as the amount of rubber components 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 one or more rubber components.

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.

Any rubber component may be used, including those known in the tire field. Examples include diene rubbers such as isoprene-based rubbers, polybutadiene rubbers (BR), styrene-butadiene rubbers (SBR), 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. Among these, the rubber components preferably include any one selected from isoprene-based rubbers, BR, and SBR in order to better achieve the advantageous effect. The rubber components more preferably include a combination of two or more of them, including SBR and BR or a combination of an isoprene-based rubber, BR, and SBR.

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.

When the rubber composition contains isoprene-based rubbers, the amount of isoprene-based rubbers based on <NUM>% by mass of the rubber component content 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, still 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 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 earthcatalyzed 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 component content 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, 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.

Any SBR may be used, and examples include emulsionpolymerized styrene-butadiene rubbers (E-SBR) and solutionpolymerized 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.

When the rubber composition contains SBR, the amount of SBR based on <NUM>% by mass of the rubber component content 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, 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.

When the rubber composition contains SBR and BR, the combined amount of SBR and BR based on <NUM>% by mass of the rubber component content 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, and may be <NUM>% by mass. When the combined 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 preferably contains a filler.

Any filler may be used, including materials known in the rubber field. Examples include inorganic fillers such as silica, carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, and mica. Among these, carbon black or silica 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 component content 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.

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 nitrogen adsorption specific surface area (N<NUM>SA) of the 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. Moreover, the upper limit of the N<NUM>SA of the silica 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 silica per <NUM> parts by mass of the rubber component content 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, 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.

The percentage of silica based on <NUM>% by mass of the filler content 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 carbon black and silica) per <NUM> parts by mass of the rubber component content 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, 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.

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 content 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 desirably contains a resin component in order to better achieve the advantageous effect.

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 component content 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, most 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 terpenestyrene 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 <NPL>) 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 component content 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, most 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 component content 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 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.

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 room temperature (<NUM>)) other than the liquid resins and solid plasticizers (plasticizers which are solid at room temperature (<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 component content 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 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 component content 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. 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 farnesenebutadiene copolymers, all of which are liquid at room temperature (<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 room temperature (<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 component content 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 component content 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 component content 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 component content 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 component content 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 component content 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 component content.

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 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 passenger car tire. Herein, the term "passenger car tire" refers to a tire with a normal internal pressure of <NUM> kPa or lower and a normal load of <NUM> or less.

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.

The tire of the present invention satisfies the following relationship (<NUM>): <MAT> wherein Ash represents the ash 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 upper limit of the value of "Ash × G" is preferably <NUM> or lower, more preferably <NUM> or lower, still more preferably <NUM> or lower, particularly preferably <NUM> or lower, most preferably <NUM> or lower. The lower limit is preferably <NUM> or higher, more preferably <NUM> or higher, still more preferably <NUM> or higher, particularly preferably <NUM> or higher. When the value is within the range indicated above, the advantageous effect tends to be better achieved.

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. 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 G 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.

Moreover, the thickness Gc of the rubber layer of the tread portion measured on the equator of the tire is preferably <NUM> or less, more preferably <NUM> or less, still more preferably <NUM> or less, while the lower limit is preferably <NUM> or more, more preferably <NUM> or more, still more preferably <NUM> or more.

Here, the above-mentioned Gc can be measured as described for the thickness G of the tread portion measured on the equator in a cross-section taken in the radial direction of the tire, and can be determined by measuring the distance from the outermost tread surface to the interface of the rubber layer formed of the above-described rubber composition, which is innermost with respect to the tire.

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

The negative ratio S (%) is preferably <NUM>% or lower, more preferably <NUM>% or lower. The negative ratio S (%) is preferably <NUM>% or higher, more preferably <NUM>% or higher, still 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, particularly 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.

In <FIG>, the vertical direction corresponds to the radial direction of the tire (hereinafter, also referred to simply as radial direction), the horizontal direction corresponds to the axial direction of the tire (hereinafter, also referred to simply as axial direction), and the direction perpendicular to the paper corresponds to the circumferential direction of the tire (hereinafter, also referred to simply as circumferential direction). The tire <NUM> has a shape that is horizontally substantially symmetrical about the center line CL in <FIG>. The center line CL is also referred to as tread center line and defines the equator EQ of the tire <NUM>.

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

The tread portion <NUM> includes a tread face <NUM>. The tread face <NUM> has a radially outwardly convex shape in a cross-section taken in the meridional direction of the tire <NUM>. The tread face <NUM> will contact the road surface. The tread face <NUM> has a plurality of circumferentially extending grooves <NUM> carved therein. The grooves <NUM> define a tread pattern. The axially (widthwise) external part of the tread portion <NUM> is referred to as a shoulder portion <NUM>. The sidewall portion <NUM> extends substantially inwardly in the radial direction from the end of the tread portion <NUM>. The sidewall portion <NUM> consists of a crosslinked rubber or the like.

As shown in <FIG>, the bead portion <NUM> is located radially substantially inward from the sidewall portion <NUM>. 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 along the circumferential direction of the tire. The core <NUM> consists of a wound inextensible wire. Typically, a steel wire is used in the core <NUM>. The apex <NUM> is radially outwardly tapered. The apex <NUM> consists of a very hard crosslinked rubber or the like.

In the present embodiment, the carcass <NUM> consists of a carcass ply <NUM>. The carcass ply <NUM> extends between the opposite bead portions <NUM> along the inner sides of 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 of the tire. Though not shown, the carcass ply <NUM> consists of a large number of parallel cords and a topping rubber. The absolute value of the angle of each cord relative to the equator EQ (CL) is usually <NUM>° to <NUM>°. In other words, the carcass <NUM> has a radial structure.

In the present embodiment, the belt <NUM> is located radially outward of the carcass <NUM>. The belt <NUM> is stacked on the carcass <NUM>. The belt <NUM> reinforces the carcass <NUM>. The belt <NUM> may consist of an inner layer belt <NUM> and an outer layer belt <NUM>. In the present embodiment, the widths of the belts <NUM> and <NUM> are different from each other.

Though not shown, the inner layer belt <NUM> and the outer layer belt <NUM> each usually consist of a large number of parallel cords and a topping rubber. Each cord is desirably inclined to the equator EQ. Desirably, the cords of the inner layer belt <NUM> are inclined in a direction opposite to that of the cords of the outer layer belt.

Though not shown, an embodiment may be used in which a band is stacked on the radially outer side of the belt <NUM>. The width of the band is larger than that of the belt <NUM>. The band may consist of cords and a topping rubber. The cords are spirally wound. The belt is constrained by the cords, so that the belt <NUM> is inhibited from lifting. The cords desirably consist of organic fibers. Preferred examples of the organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

Though not shown, an embodiment may be used in which an edge band is provided radially outward of the belt <NUM> and near the widthwise end (edge portion) of the belt <NUM>. Like the band, the edge band may consist of cords and a topping rubber. An exemplary edge band may be stacked on the upper surface of a step <NUM> of the wider inner layer belt <NUM>. In an exemplary embodiment, the cords of the edge band are inclined in the same direction as the cords of the narrower outer layer belt <NUM> and are biased relative to the cords of the wider inner layer belt <NUM>.

Though not shown, an embodiment may be used in which a cushion rubber layer is stacked on the carcass <NUM> near the widthwise end of the belt <NUM>. In an exemplary embodiment, the cushion layer consists of a soft crosslinked rubber. The cushion layer absorbs the stress on the belt edge.

<FIG> shows a cross-section of the tread portion <NUM> of the tire <NUM> taken along a plane including the tire axis. In <FIG> and <FIG>, a crown center <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> satisfies relationship (<NUM>) with respect to the ash content Ash (% by mass) of the tread rubber composition (vulcanized rubber composition) contained in the tread portion <NUM> and the thickness G of the tread portion <NUM> measured at the crown center <NUM> of the tire <NUM> (the radial dimension from the tread face <NUM> to the upper surface of the outer layer belt <NUM>).

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 each table, the materials other than the sulfur and vulcanization accelerators 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 accelerators 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>/60R18).

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

A rubber test sample cut out of the tread of each test tire is subjected to acetone extraction by a method for measuring the acetone extractable content in accordance with JIS K <NUM>:<NUM>.

The decrease in the amount (mass) of the sample after the acetone extraction 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 sample after the pyrolysis and gasification in the above section "Polymer content (PC)" is heated in the air for oxidative combustion.

Then, the mass of the components which remain unburned in the oxidative combustion (ash) is measured, from which Ash (% by mass) is calculated.

A vehicle equipped with each set of test tires is subjected to <NUM>,<NUM> running at an average speed of <NUM>/h. Then, the groove depth in the tread portion is measured. The amount of wear of the tread portion is calculated from the measured depth and expressed as an index relative to that of the evaluation standard taken as <NUM>. A higher index indicates a smaller amount of wear and better abrasion resistance during high-speed running.

The rolling resistance of each test tire is measured using a rolling resistance tester when it is run under conditions including a <NUM>×6JJ rim, an internal pressure of <NUM> kPa, a load of <NUM> kN, and a speed of <NUM>/h. The 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.

Claim 1:
A tire, comprising a tread portion,
the tire satisfying the following relationships (<NUM>) to (<NUM>): <MAT> <MAT> and <MAT> wherein PC and Ash represent a polymer content (% by mass) and an ash content (% by mass), respectively, of a rubber composition comprised in the tread portion, and G represents a thickness (mm) of the tread portion measured on an equator in a cross-section taken in a radial direction of the tire,
when the polymer content PC is determined in accordance with section <Polymer content (PC)> of the description,
when the ash content Ash is determined in accordance with section <Ash content (Ash)> of the description, and
when G is determined in accordance with section <Thickness G> of the description.