Patent Description:
In recent years, from the viewpoint of increasing interest in environmental issues and economic efficiency, there has been a growing demand for fuel efficiency in automobiles, and there is a strong demand for improved fuel efficiency also in pneumatic tires (hereinafter, simply referred to as "tires") installed in automobiles.

The fuel efficiency of a tire can be evaluated by rolling resistance, and it is known that the smaller the rolling resistance, the better the fuel efficiency of the tire.

Therefore, conventionally, it has been proposed to reduce the rolling resistance by devising the formulation of the rubber composition constituting the tread portion of the tire (for example, Patent Documents <NUM> to <NUM>).

However, it cannot be said that the tire manufactured by the above-described conventional technology is sufficiently reduced in rolling resistance during high-speed running, and has sufficient durability.

Accordingly, an object of the present invention is to provide a pneumatic tire with sufficiently reduced rolling resistance during high-speed running and excellent durability performance.

The present discloser has diligently studied the solution to the above-mentioned problem, found that the above-mentioned problem can be solved by the invention described below, and has completed the present disclosure.

According to the present invention, it is possible to provide a pneumatic tire with sufficiently reduced the rolling resistance during high-speed running and excellent durability performance.

A tire according to the present invention is a pneumatic tire and has the following characteristics.

First, the tire according to the present invention is characterized in that it is a pneumatic tire having a bead portion, a carcass, and a tread, wherein a bead reinforcing layer that reinforces the bead portion from the outside of the carcass is provided outside the carcass in the tire axial direction.

Further, the tire according to the present invention is also characterized in that it satisfies the following (formula <NUM>) and (formula <NUM>); <MAT> <MAT> where Wt (mm) is the cross-sectional width of the tire, Dt (mm) is the outer diameter, and V (mm<NUM>) is the virtual volume which is the volume of the space occupied by the tire, when the tire is installed on a standardized rim and the internal pressure is <NUM> kPa.

By providing the tire shape with the characteristics described above, a tire with sufficiently reduced rolling resistance during high-speed running and sufficiently excellent durability performance can be provided.

In the above description, the "standardized rim" is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, in the case of JATMA (Japan Automobile Tire Association), it is the standard rim in applicable sizes described in the "JATMA YEAR BOOK", in the case of "ETRTO (The European Tire and Rim Technical Organization)", it is "Measuring Rim" described in "STANDARDS MANUAL", and in the case of TRA (The Tire and Rim Association, Inc. ), it is "Design Rim" described in "YEAR BOOK ". In the case of tires that are not specified in the standard, it refers a rim that can be assembled and can maintain internal pressure, that is, the rim that does not cause air leakage from between the rim and the tire, and has the smallest rim diameter, and then the narrowest rim width.

Further, the outer diameter Dt of the tire is the outer diameter of the tire installed on a standardized rim, having an internal pressure of <NUM> kPa and in a no-load state. The cross-sectional width Wt (mm) of the tire is the width of tire installed on a standardized rim, having an internal pressure of <NUM> kPa and in a no-load state, and is the distance excluding patterns, letters, and the like on the tire side from the linear distance between the side portions (total width of the tire) including all the patterns, letters and the like on the tire side.

Further, the virtual volume V (mm<NUM>) of the tire is, specifically, can be calculated by the following formula: <MAT> based on the outer diameter of tire Dt (mm), the tire cross-sectional height Ht (mm) (distance from the bottom of the bead to the outermost surface of the tread; <NUM>/<NUM> of the difference between the tire outer diameter and the nominal rim diameter), and the cross-sectional width of tire Wt (mm), in the state the tire is installed on a standardized rim, the internal pressure is <NUM> kPa and no load is applied.

In the tire according to the present invention, the mechanism, by which rolling resistance is sufficiently reduced during high-speed running and excellent durability performance is exhibited, is presumed as follows.

As described above, in the present invention, the cross-sectional width Wt (mm) and the outer diameter Dt (mm) of the said tire are tried to satisfy <MAT>.

By increasing the area when the tire is viewed from the lateral direction, [(Dt/<NUM>)<NUM> × π) = (Dt<NUM> × π /<NUM>)], with respect to the cross-sectional width Wt of the tire, and satisfying the numerical range specified in (formula <NUM>), it is considered that the repetition of deformation per unit time is reduced, as a result, the time that can be used for heat exchange is increased, thereby improving the heat release property of the side portion, and the friction between the tread portion and the road surfaces can be reduces. As a result, the rolling resistance of the tire can be reduced (low rolling resistance) and the durability can be improved.

In (formula <NUM>), (Dt <NUM> × π /<NUM>) / Wt is <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, and further preferably <NUM> or more.

However, since such a tire has a large centrifugal force during high-speed running, the side portion tends to be pulled by the tread portion, where a particularly large centrifugal force acts. However, since the side portion is fixed to the rim at the bead portion, the amount of deformation in the vicinity of the bead portion becomes large, which may lead to damage at the bead portion. In addition, centrifugal force rounds the tread portion, causing a change in the tread pattern profile, which may not sufficiently reduce rolling resistance during high-speed running. Therefore, it can be thought there is room for further improvement.

Therefore, in the present invention, the virtual volume V (mm<NUM>) and the cross-sectional width Wt (mm) of the tire are tried to satisfy [(V + <NUM> × <NUM><NUM>) / Wt] ≦ <NUM> × <NUM><NUM> (formula <NUM>).

In this way, it is considered that, by reducing the virtual volume V of the tire in accordance with the decrease in the cross-sectional width Wt of the tire, and reducing the volume of the tire itself, it is possible to reduce the outer diameter growth rate due to the centrifugal force, and the amount of deformation of the side portion in the bead portion can be reduced, and the rounding of the tread portion can also be suppressed.

[(V + <NUM> × <NUM><NUM>) / Wt] is preferably <NUM> × <NUM><NUM> or less, more preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, further preferably <NUM> × <NUM><NUM> or less, and further preferably <NUM> × <NUM><NUM> or less.

At this time, it is more preferable that [(V + <NUM> × <NUM><NUM>) / Wt] ≦ <NUM> × <NUM><NUM> (formula <NUM>), and further preferable that [(V + <NUM> × <NUM><NUM>) / Wt] ≦ <NUM> × <NUM><NUM> (formula <NUM>).

The above [(V + <NUM> × <NUM><NUM>) / Wt] is further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, and further preferably <NUM>×<NUM><NUM> or less.

Further, [(V + <NUM> × <NUM><NUM>) / Wt] is further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, further preferably <NUM>×<NUM><NUM> or less, and further preferably <NUM>×<NUM><NUM> or less.

In the tire according to the present invention, as described above, the bead reinforcing layer that reinforces the bead portion from the outer side of the carcass is provided on the outer side of the carcass in the tire axial direction. By providing such a bead reinforcing layer, it is possible to further suppress the occurrence of deformation in the vicinity of the bead portion, so it is considered that the durability can be further improved. Moreover, as a result, it is possible to suppress the occurrence of deformation in the side portions, so it is considered that rolling resistance during high-speed running can be improved.

The tire according to the present invention can obtain a larger effect by taking the following embodiment.

The tire according to the present invention is preferably a tire having an aspect ratio of <NUM>% or more, whereby, since the height of the side portion of the tire can be increased to suppress local deformation of the tire, the durability of the tire can be further improved.

The aspect ratio (%) described above can be obtained by the following formula using the cross-sectional height Ht (mm) and the cross-sectional width Wt (mm) of the tire when the internal pressure is <NUM> kPa.

The aspect ratio is more preferably <NUM>% or more, further preferably <NUM>% or more, further preferably <NUM>% or more, further preferably <NUM>% or more, further preferably <NUM>% or more, further preferably <NUM>% or more, further preferably <NUM>% or more, further preferably <NUM>% or more, further preferably <NUM>% or more, and further preferably <NUM>% or more. There is no particular upper limit, but for example, it is <NUM>% or less.

When reinforcing the bead portion with the bead reinforcing layer, it is preferable that the loss tangent (tan δ) of the bead reinforcing layer is small from the viewpoint of suppressing heat generation of the bead reinforcing layer. On the other hand, from the viewpoint of suppressing deformation in the vicinity of the bead portion, it is preferable that the rigidity of the bead reinforcing layer, that is, the complex elastic modulus (E*) is large.

Therefore, a favorable relationship between the loss tangent (tan δ) and the complex elastic modulus (E*: MPa) in the bead reinforcing layer has been examined, and it was found that the ratio (tan δ/E*) of the loss tangent (tan δ) to the complex elastic modulus (E*: MPa), of the bead reinforcing layer, measured under the conditions of the temperature of <NUM>, the frequency of <NUM>, the initial strain of <NUM>%, and the dynamic strain rate of <NUM>%, is preferably <NUM> or less. The (tan δ/E*) is more preferably <NUM> or less, further preferably <NUM> or less.

Thereby, heat generation of the bead reinforcing layer during rolling can be suppressed as well as the rigidity of the bead reinforcing layer can be secured satisfactorily, and the growth of the outer diameter of the tire can be further suppressed. It is considered that, as a result, the rolling resistance during high-speed running can be sufficiently reduced, and the durability can be sufficiently improved.

Note that the loss tangent (tan δ) and the complex elastic modulus (E*) described above are taken for rubber cut from at least radially outside the groove bottom of the tire, preferably radially outside half the depth of the deepest circumferential groove. Specifically, for example, it can be measured using a viscoelasticity measuring device such as "Eplexor (registered trademark)" manufactured by GABO.

In a cross-sectional view of the tire in the radial direction, the height of the bead reinforcing layer from below the bead core is preferably <NUM>% or less of the height from below the bead core to the outermost surface of the tread. It was found that, by this, a more pronounced effect can be obtained.

In addition, the larger the area of the side portion of the tire, the greater the amount of heat generated in the side portion where the bead reinforcing layer is arranged, and the more likely the tire is to deteriorate in durability.

The present discloser thought that, in order to prevent this, it is necessary to reduce the heat generation factor of the bead reinforcing layer in accordance with the expansion of the area of the side portion, and has examined the relationship between (tan δ/E*), which is an index related to the heat generation of the bead reinforcing layer, and (V/Wt), which is an index relating to the area of the side portion. As a result, it was found that if <MAT> is satisfied, the heat generation at the side portion can be suppressed, and the durability is further improved. The [(tan δ/E*) × (V/Wt)] is preferably <NUM> or less, more preferably <NUM> or less, and further preferably <NUM> or less.

It was also found that <MAT> is more preferred. The [(tan δ/E*) × (V/Wt)] is more preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, and further preferably <NUM> or less.

The tire according to the present invention preferably has a sidewall formed of rubber composition having a loss tangent (tan δ) of <NUM> or less, more preferably <NUM> or less, measured under conditions of the temperature of <NUM>, the frequency of <NUM>, the initial strain of <NUM>%, and the dynamic strain rate of <NUM>%, in the side portion. As a result, it is possible to suppress deformation of the side portion caused by heat generated during running. As a lower limit, the tan δ is preferably <NUM> or more, for example.

The complex elastic modulus (E*: MPa) of this rubber composition measured under the same conditions is preferably <NUM> MPa or less, more preferably <NUM> MPa or less. As a result, the soft sidewalls are supported by the bead reinforcement layer, the side portion is prevented from being stretched due to centrifugal force during running, and when an impact is applied, by exhibiting flexibility, the impact force can be relaxed, and the durability can be further improved. As a lower limit, it is preferably <NUM> MPa or more, for example, and more preferably <NUM> MPa or more.

In the tire according to the present invention, since the bead reinforcing layer is provided on the outer side of the carcass in the tire axial direction, the deformation during rolling becomes a movement centered on the joint with the rim, and the degree of deformation at the clinch portion is larger than before, and it is considered that the heat generation also becomes larger.

In order to suppress the heat generation in the clinch portion, it is preferable that the clinch portion is formed of a rubber composition having the loss tangent (tan δ) measured under the conditions of the temperature of <NUM>, the frequency of <NUM>, the initial strain of <NUM>%, and the dynamic strain rate of <NUM>% being <NUM> or less, more preferably <NUM> or less. As a result, heat generation in the clinch portion can be reduced and heat transfer to the sidewall (side portion) can be suppressed, so durability can be improved and rolling resistance can be reduced. In addition, as a lower limit, it is preferably <NUM> or more, for example, and more preferably <NUM> or more.

The complex elastic modulus (E*: MPa) of this rubber compositio n measured under the same conditions is preferably <NUM> MPa or more, more preferably <NUM> MPa or more. As a result, the rigidity of the clinch portion, on which deformation tends to concentrate during rolling, is inc reased, so that the occurrence of deformation itself can be suppressed an d heat generation can be reduced. As an upper limit, it is preferably <NUM><NUM> MPa or less, for example, and more preferably <NUM> MPa or less.

The tire according to the present invention has a circumferential groove continuously extending in the tire circumferential direction in the tread portion. The ratio of the groove width L<NUM> at a depth of <NUM>% of the maximum depth of the circumferential groove to the groove width L<NUM> of the circumferential groove on the ground contact surface of the tread portion (L<NUM> / L<NUM>) is preferably <NUM> to <NUM>. As a result, it is possible to suppress the movement of the entire land portion on the bottom surface of the land portion of the tread portion, and, thereby it is considered that occurrence of the chipping in the tread portion can be suppressed. The ratio is more preferably <NUM> to <NUM>, further preferably <NUM> to <NUM>, and particularly preferably <NUM> to <NUM>. The circumferential grooves may be grooves extending continuously in the tire circumferential direction, and non-linear grooves such as zigzag grooves and wavy grooves are also included in the circumferential grooves.

The above-mentioned L<NUM> and L<NUM> refer to the linear distance (L<NUM>) between the groove edges on the tread surface of the tread circumferential groove of a tire, and to the minimum distance (L<NUM>) between the groove walls at a position where the groove depth is <NUM>%, respectively, in a state where the tire is installed on a standardized rim, the internal pressure is <NUM> kPa, and no load is applied. To put it simply, they can be obtained by putting the bead portion of the section cut out in the radial direction with a width of <NUM> to <NUM> in a pressed state according to the rim width.

It is preferable that the tread portion has a plurality of circumferential grooves, and the total cross-sectional area of the plurality of circumferential grooves is <NUM> to <NUM>% of the cross-sectional area of the tread portion. It is considered that this makes it possible to suppress the movement of the tread portion, and occurrence of the chipping in the tread portion during high-speed running can be suppressed. It is more preferably <NUM> to <NUM>%, further preferably <NUM> to <NUM>%, and particularly preferably <NUM> to <NUM>%.

The cross-sectional area of the circumferential groove refers to the total value of the area composed of a straight line connecting the ends of the tread circumferential groove and a groove wall in a tire installed on a standardized rim, having an internal pressure of <NUM> kPa and in a no-load state. To put it simply, they can be obtained by putting the bead portion of the section cut out in the radial direction with a width of <NUM> to <NUM> in a pressed state according to the rim width.

Further, it is preferable that the tread portion has a plurality of lateral grooves extending in the tire axial direction, and the total volume of the plurality of lateral grooves is <NUM> to <NUM>% of the volume of the tread portion. It is considered that this makes it possible to suppress the movement of the tread portion, suppress the uneven wear, and improve the durability. It is more preferably <NUM> to <NUM>%, further preferably <NUM> to <NUM>%, and particularly preferably <NUM> to <NUM>%.

The volume of the lateral groove described above refers to the total volume of the volume composed of the surface connecting the ends of the lateral groove and the groove wall in a tire installed on a standardized rim, having an internal pressure of <NUM> kPa and in a no-load state. To put it simply, it can be obtained by calculating the volume of each lateral groove and multiplying it by the number of grooves, in a state where the bead portion of the section cut out in the radial direction with a width of <NUM> to <NUM> is pressed down according to the rim width. Further, the volume of the tread portion can be calculated by calculating the area of the portion excluding the lateral groove from the section and multiplying it by the outer diameter, then obtaining the difference between the calculation result and the volume of the lateral groove.

In order to suppress occurrence of the chipping in the tread portion and further improve the durability, it is preferred that at least one of these lateral grooves has ratio of groove width Gw to groove depth Gd (Gw/Gd) of <NUM> to <NUM>. The ratio is more preferably <NUM> to <NUM>, further preferably <NUM> to <NUM>, and particularly preferably <NUM> to <NUM>.

The groove width and groove depth of the lateral groove described above refer to the maximum length of the straight lines connecting the tread surface ends of the lateral groove, which are perpendicular to the groove direction, and to the maximum depth of the lateral groove, respectively, in the tire in a state where the internal pressure is <NUM> kPa and no load is applied. To put it simply, it can be calculated in a state where the bead portion of the section cut out in the radial direction with a width of <NUM> to <NUM> is put down in a pressed state according to the rim width.

In the tire of the present invention, when the tire is installed on a standardized rim and the internal pressure is <NUM> kPa, the specific outer diameter Dt (mm) is preferably, for example, <NUM> or more, more preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, and most preferably <NUM> or more.

On the other hand, it is preferably less than <NUM>, more preferably <NUM> or less, further preferably less than <NUM>, further preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, further preferably less than <NUM>, further preferably <NUM> or less, further preferably <NUM> or less, further preferably less than <NUM>, further preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, and further preferably <NUM> or less.

The specific cross-sectional width Wt (mm) is preferably <NUM> or more, more preferably <NUM> or more, further preferably <NUM> or more, further more preferably <NUM> or more, further more preferably <NUM> or more, further more preferably <NUM> or more, further more preferably <NUM> or more, further more preferably <NUM> or more, further more preferably <NUM> or more, further more preferably <NUM> or more, and particularly preferably <NUM>, and most preferably <NUM> or more.

On the other hand, it is preferably less than <NUM>, more preferably less than <NUM>, further preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, further preferably less than <NUM>, further preferably less than <NUM>, further preferably <NUM> or less, further preferably <NUM> or less, further preferably less than <NUM>, and further preferably <NUM> or less.

The specific cross-sectional height Ht (mm) is, for example, preferably <NUM> or more, more preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, and further preferably <NUM> or more.

On the other hand, it is preferably less than <NUM>, more preferably <NUM> or less, further preferably <NUM> or less, further preferably less than <NUM>, further preferably <NUM> or less, further preferably <NUM> or less, and further preferably less than <NUM>.

The specific virtual volume V is preferably <NUM>,<NUM>,<NUM><NUM> or more, more preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>, <NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, further preferably <NUM>,<NUM>,<NUM><NUM> or more, and further preferably <NUM>,<NUM>,<NUM><NUM> or more.

On the other hand, it is preferably less than <NUM>,<NUM>,<NUM><NUM>, more preferably <NUM>,<NUM>,<NUM><NUM> or less, further preferably less than <NUM>,<NUM>,<NUM><NUM>, further preferably <NUM>,<NUM>,<NUM><NUM> or less, further preferably <NUM>,<NUM>,<NUM><NUM> or less, further preferably <NUM>,<NUM>,<NUM><NUM> or less, and further preferably <NUM>,<NUM>,<NUM><NUM> or less.

Further, in the tire of the present invention, considering the stability of the riding comfort during traveling, (Dt - <NUM> × Ht) is preferably <NUM> or more, more preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, further preferably <NUM> or more, and further preferably <NUM> or more.

On the other hand, considering the deformation of the tread portion, it is preferably less than <NUM>, more preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, further preferably <NUM> or less, further preferably less than <NUM>, further preferably less than <NUM>, further preferably <NUM> or less, and further preferably <NUM> or less.

Hereinafter, the present invention will be specifically described based on the embodiments.

In the present invention, the rubber composition forming the bead reinforcing layer can be obtained by appropriately adjusting the types and amounts of various compounding materials such as rubber components, fillers, softeners, and vulcanization accelerators described below.

In the present embodiment, as the rubber component, a rubber (polymer) generally used for manufacturing tires such as styrene-butadiene rubber (SBR), isoprene-based rubber, butadiene rubber (BR), and nitrile rubber (NBR) is used. Among these, it is preferable to contain isoprene-based rubber and styrene-butadiene rubber (SBR). In these rubbers, the rubber phases can be phase-separated and entangled with each other, so that the strain inside the rubber can be reduced.

The content (total content) of the isoprene-based rubber in <NUM> parts by mass of the rubber component is preferably more than <NUM> parts by mass, more preferably more than <NUM> parts by mass, and further preferably more than <NUM> parts by mass, from the viewpoint of good low heat generation and durability. On the other hand, it is preferably less than <NUM> parts by mass, more preferably less than <NUM> parts by mass, and further preferably less than <NUM> parts by mass, and <NUM> parts by mass is particularly preferred. Examples of the isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), reformed NR, modified NR, and modified IR. Among them, NR is preferable from the viewpoint of excellent strength.

As the NR, for example, SIR20, RSS # <NUM>, TSR20 and the like, which are common in the tire industry, can be used. The IR is not particularly limited, and for example, IR <NUM> and the like, which are common in the tire industry, can be used. Reformed NR includes deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and the like. Modified NR includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, and the like. Modified IR includes epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, and the like. These may be used alone or in combination of two or more.

The content of SBR in <NUM> parts by mass of the rubber component is preferably more than <NUM> parts by mass, more preferably more than <NUM> parts by mass, further preferably more than <NUM> parts by mass, and further preferably <NUM> parts by mass or more.

On the other hand, it is preferably less than <NUM> parts by mass, more preferably less than <NUM> parts by mass, and further preferably less than <NUM> parts by mass,.

The weight average molecular weight of SBR is, for example, more than <NUM>,<NUM> and less than <NUM> million. The styrene content of SBR is preferably more than <NUM>% by mass, more preferably more than <NUM>% by mass, and further preferably more than <NUM> % by mass. On the other hand, it is preferably less than <NUM>% by mass, more preferably less than <NUM>% by mass, and further preferably less than <NUM>% by mass. The vinyl bond amount (<NUM>,<NUM>-bonded butadiene unit amount) of SBR is, for example, more than <NUM>% by mass and less than <NUM>% by mass. The structure identification of SBR (measurement of styrene content and vinyl bond amount) can be performed using, for example, an apparatus of the JNM-ECA series manufactured by JEOL Ltd.

The SBR is not particularly limited, and for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR) and the like can be used. The SBR may be either a non-modified SBR or a modified SBR, and these may be used alone or in combination of two or more.

The modified SBR may be any SBR having a functional group that interacts with a filler such as silica. Examples thereof include.

Examples of the functional group include an amino group, an amide group, a silyl group, an alkoxysilyl 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 carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, and an epoxy group. In addition, these functional groups may have a substituent.

Further, as the modified SBR, for example, an SBR modified with a compound (modifying agent) represented by the following formula can be used.

In the formula, R<NUM>, R<NUM> and R<NUM> are the same or different and represent alkyl group, alkoxy group, silyloxy group, acetal group, carboxyl group (-COOH), mercapto group (-SH) or derivatives thereof. R<NUM> and R<NUM> are the same or different and represent hydrogen atoms or alkyl group. R<NUM> and R<NUM> may be combined to form a ring structure with nitrogen atoms. n represents an integer.

As the modified SBR modified by the compound (modifying agent) represented by the above formula, SBR, in which the polymerization end (active end) of the solution-polymerized styrene-butadiene rubber (S-SBR) is modified by the compound represented by the above formula (for example, modified SBR described in <CIT>), can be used.

As R<NUM>, R<NUM> and R<NUM>, an alkoxy group is suitable (preferably an alkoxy group having <NUM> to <NUM> carbon atoms, more preferably an alkoxy group having <NUM> to <NUM> carbon atoms). As R<NUM> and R<NUM>, an alkyl group (preferably an alkyl group having <NUM> to <NUM> carbon atoms) is suitable. n is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and even more preferably <NUM>. Further, when R<NUM> and R<NUM> are combined to form a ring structure together with a nitrogen atom, a <NUM>- to <NUM>-membered ring is preferable. The alkoxy group also includes a cycloalkoxy group (cyclohexyloxy group, and the like) and an aryloxy group (phenoxy group, benzyloxy group, and the like).

Specific examples of the above modifying agent include <NUM>-dimethylaminoethyltrimethoxysilane, <NUM>-dimethylaminopropyltrimethoxysilane, <NUM>-dimethylaminoethyltriethoxysilane, <NUM>-dimethylaminopropyltriethoxysilane, <NUM>-diethylaminoethyltrimethoxysilane, <NUM>-diethylaminopropyltrimethoxysilane, <NUM>-diethylaminoethyltriethoxysilane, and <NUM>-diethylaminopropyltriethoxysilane. These may be used alone or in combination of two or more.

Further, as the modified SBR, a modified SBR modified with the following compound (modifying agent) can also be used. Examples of the modifying agent include.

As the SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co. , JSR Corporation, Asahi Kasei Co. , Nippon Zeon Co. , Ltd, etc. can be used. The SBR may be used alone or in combination of two or more.

Further, as another rubber component, the rubber composition may contain a rubber (polymer) generally used in the production of tires, such as butadiene rubber (BR) and nitrile rubber (NBR).

In the present embodiment, the rubber composition preferably contains a filler. Specific examples of fillers include carbon black, graphite, silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica. Among these, carbon black is preferably used as a reinforcing agent. It is also preferable to use silica as a reinforcing agent, if necessary. In this case, it is preferable to use the silica together with a silane coupling agent.

The rubber composition preferably contains carbon black. The content of carbon black is, for example, preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, and further preferably <NUM> parts by mass or more with respect to <NUM> parts by mass of the rubber component. On the other hand, it is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, further preferably <NUM> parts by mass or less, and further preferably <NUM> parts by mass or less.

The carbon black is not particularly limited, and examples thereof includes furnace black (furnace carbon black) such as SAF, ISAF, HAF, MAF, FEF, SRF, GPF, APF, FF, CF, SCF and ECF; acetylene black (acetylene carbon black); thermal black (thermal carbon black) such as FT and MT; and channel black (channel carbon black) such as EPC, MPC and CC. These may be used alone or in combination of two or more.

Nitrogen adsorption specific surface area (N<NUM>SA) of carbon black is, for example, <NUM><NUM>/g or more and <NUM><NUM>/g or less. The amount of dibutyl phthalate (DBP) absorbed by carbon black is, for example, <NUM>/<NUM> or more and <NUM>/<NUM> or less. The nitrogen adsorption specific surface area of carbon black is measured according to ASTM D4820-<NUM>, and the amount of DBP absorbed is measured according to ASTM D2414-<NUM>.

The specific carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available products include, for example, products of Asahi Carbon Co. , Cabot Japan Co. , Tokai Carbon Co. , Mitsubishi Chemical Corporation, Lion Corporation, Shin Nikka Carbon Co. , Columbia Carbon Co. , etc. These may be used alone or in combination of two or more.

It is preferable that the rubber composition further contain silica, if necessary. The BET specific surface area of the silica is preferably more than <NUM><NUM>/g, more preferably more than <NUM><NUM>/g, from the viewpoint of obtaining good durability performance. On the other hand, from the viewpoint of obtaining good rolling resistance at high-speed running, it is preferably less than <NUM><NUM>/g, and more preferably less than <NUM><NUM>/g. Moreover, the content of the silica with respect to <NUM> parts by mass of the rubber component is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, and further preferably <NUM> parts by mass or more. On the other hand, it is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, and further preferably <NUM> parts by mass or less. The above-mentioned BET specific surface area is the value of N<NUM>SA measured by the BET method according to ASTM D3037-<NUM>.

Examples of silica include dry silica (anhydrous silica) and wet silica (hydrous silica). Among them, wet silica is preferable because it has large number of silanol groups.

As the silica, for example, products of Degussa, Rhodia, Tosoh Silica Co. , Solvay Japan Co. , Tokuyama Corporation, etc. can be used.

As described above, when using silica, it is preferable to use a silane coupling agent together. The silane coupling agent is not particularly limited. Examples of the silane coupling agent include.

As the silane coupling agent, for example, products of Degussa, Momentive, Shinetsu Silicone Co. , Tokyo Chemical Industry Co. , Azumax Co. , Toray Dow Corning Co. , etc. can be used.

The rubber composition may further contain fillers such as graphite, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica, which are generally used in the tire industry, in addition to the above-mentioned carbon black and silica. These contents are, for example, more than <NUM> part by mass and less than <NUM> parts by mass with respect to <NUM> parts by mass of the rubber component.

From the viewpoint of ensuring the rigidity of the bead reinforcing layer, the rubber composition preferably contains a curable resin component. The content of the resin component is, for example, preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, further preferably <NUM> parts by mass or more, further preferably <NUM> parts by mass or more, and further preferably <NUM> parts by mass or more with respect to <NUM> parts by mass of the rubber component. On the other hand, it is preferably <NUM> parts by mass or less, and more preferably <NUM> parts by mass or less.

Examples of the curable resin component include modified resorcinol resins and modified phenolic resins. Examples of specific modified resorcinol resins include Sumikanol <NUM> (modified resorcinol resin) manufactured by Taoka Chemical Co. Examples of modified phenolic resins include PR12686 (Cashew oil-modified phenolic resin) manufactured by Sumitomo Bakelite Co.

When using the modified resorcinol resin, it is preferable to contain a methylene donor together as a curing agent, if necessary. Examples of methylene donors include hexamethylenetetramine (HMT), hexamethoxymethylolmelamine (HMMM) and hexamethylolmelamine pentamethyl ether (HMMPME). It is preferable to contain, for example, about <NUM> parts by mass or more and <NUM> parts by mass or less with respect to <NUM> parts by mass of the curable resin component.

As a specific methylene donor, for example, Sumikanol <NUM> manufactured by Taoka Chemical Co. can be used.

From the viewpoint of workability (imparting tackiness), the rubber composition preferably contains a resin component as necessary. The resin component may be solid or liquid at room temperature, and specific examples of resin components include styrene resin, coumarone resin, terpene resin, C5 resin, C9 resin, C5C9 resin, and acrylic resin. Two or more kinds of the resin components may be used in combination. The content of the resin component with respect to <NUM> parts by mass of the rubber component is preferably more than <NUM> parts by mass and less than <NUM> parts by mass, and more preferably less than <NUM> parts by mass.

The styrene resin is a polymer using a styrene monomer as a constituent monomer, and examples thereof include a polymer obtained by polymerizing a styrene monomer as a main component (<NUM>% by mass or more). Specifically, it includes homopolymers obtained by individually polymerizing styrene monomers (styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, etc.), copolymers obtained by copolymerizing two or more styrene monomers, and, in addition, copolymers obtained by copolymerizing a styrene monomer and other monomers that can be copolymerized with the styrene monomer.

Examples of the other monomers include acrylonitriles such as acrylonitrile and methacrylate; unsaturated carboxylic acids such as acrylic acid and methacrylic acid; unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate; dienes such as chloroprene, butadiene, and isoprene, olefins such as <NUM>-butene and <NUM>-pentene; and α, β-unsaturated carboxylic acids such as maleic anhydride and acid anhydrides thereof.

As the coumarone-based resin, coumarone-indene resin is preferably used. Coumarone-indene resin is a resin containing coumarone and indene as monomer components constituting the skeleton (main chain) of the resin. Examples of the monomer component contained in the skeleton other than coumarone and indene include styrene, α-methylstyrene, methylindene, and vinyltoluene.

The content of the coumarone-indene resin is, for example, more than <NUM> part by mass and less than <NUM> parts by mass with respect to <NUM> parts by mass of the rubber component.

The hydroxyl value (OH value) of the coumarone-indene resin is, for example, more than <NUM> mgKOH/g and less than <NUM> mgKOH/g. The OH value is the amount of potassium hydroxide required to neutralize acetic acid bonded to a hydroxyl group when <NUM> of the resin is acetylated, and is expressed in milligrams. It is a value measured by potentiometric titration method (JIS K <NUM>: <NUM>).

The softening point of the coumarone-indene resin is, for example, higher than <NUM> and lower than <NUM>. The softening point is the temperature at which the ball drops when the softening point defined in JIS K <NUM>-<NUM>: <NUM> is measured by a ring-ball type softening point measuring device.

Examples of the terpene resins include polyterpenes, terpene phenols, and aromatic-modified terpene resins. Polyterpene is a resin obtained by polymerizing a terpene compound and a hydrogenated product thereof. The terpene compound is a hydrocarbon having a composition of (C<NUM>H<NUM>)n or an oxygen-containing derivative thereof, which is a compound having a terpene classified as monoterpenes (C<NUM>H<NUM>), sesquiterpenes (C<NUM>H<NUM>), diterpenes (C<NUM>H<NUM>), etc. as the basic skeleton. Examples thereof include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, osimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, <NUM>,<NUM>-cineol, <NUM>,<NUM>-cineol, α-terpineol, β-terpineol, and γ-terpineol.

Examples of the polyterpene include terpene resins such as α-pinene resin, β-pinene resin, limonene resin, dipentene resin, and β-pinene/limonene resin, which are made from the above-mentioned terpene compound, as well as hydrogenated terpene resin obtained by hydrogenating the terpene resin. Examples of the terpene phenol include a resin obtained by copolymerizing the above-mentioned terpene compound and the phenol compound, and a resin obtained by hydrogenating above-mentioned resin. Specifically, a resin obtained by condensing the above-mentioned terpene compound, the phenol compound and formalin can be mentioned. Examples of the phenol compound include phenol, bisphenol A, cresol, and xylenol. Examples of the aromatic-modified terpene resin include a resin obtained by modifying a terpene resin with an aromatic compound, and a resin obtained by hydrogenating the above-mentioned resin. The aromatic compound is not particularly limited as long as it is a compound having an aromatic ring, and examples thereof include phenol compounds such as phenol, alkylphenol, alkoxyphenol, and unsaturated hydrocarbon group-containing phenol; naphthol compounds such as naphthol, alkylnaphthol, alkoxynaphthol, and unsaturated hydrocarbon group-containing naphthols; styrene derivatives such as styrene, alkylstyrene, alkoxystyrene, unsaturated hydrocarbon group-containing styrene; coumarone; and indene.

The C5 resin refers to a resin obtained by polymerizing a C5 fraction. Examples of the C5 fraction include petroleum fractions having <NUM> to <NUM> carbon atoms such as cyclopentadiene, pentene, pentadiene, and isoprene. As the C5-based petroleum resin, a dicyclopentadiene resin (DCPD resin) is preferably used.

The C9 resin refers to a resin obtained by polymerizing a C9 fraction, and may be hydrogenated or modified. Examples of the C9 fraction include petroleum fractions having <NUM> to <NUM> carbon atoms such as vinyltoluene, alkylstyrene, indene, and methyl indene. As the specific examples, a coumarone-indene resin, a coumarone resin, an indene resin, and an aromatic vinyl resin are preferably used. As the aromatic vinyl resin, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferable because it is economical, easy to process, and excellent in heat generation. A copolymer of α-methylstyrene and styrene is more preferred. As the aromatic vinyl-based resin, for example, those commercially available from Clayton, Eastman Chemical, etc. can be used.

The C5C9 resin refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be hydrogenated or modified. Examples of the C5 fraction and the C9 fraction include the above-mentioned petroleum fraction. As the C5C9 resin, for example, those commercially available from Tosoh Corporation, LUHUA, etc. can be used.

The acrylic resin is not particularly limited, but for example, a solvent-free acrylic resin can be used.

As the solvent-free acrylic resin, a (meth) acrylic resin (polymer) synthesized by a high-temperature continuous polymerization method (high-temperature continuous lump polymerization method (a method described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <NPL>, and the like) without using polymerization initiators, chain transfer agents, organic solvents, etc. as auxiliary raw materials as much as possible, can be mentioned. In the present disclosure, (meth) acrylic means methacrylic and acrylic.

Examples of the monomer component constituting the acrylic resin include (meth) acrylic acid, and (meth) acrylic acid derivatives such as (meth) acrylic acid ester (alkyl ester, aryl ester, aralkyl ester, etc.), (meth) acrylamide, and (meth) acrylamide derivative.

In addition, as the monomer component constituting the acrylic resin, aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, divinylnaphthalene, and the like may be used, together with (meth) acrylic acid or (meth) acrylic acid derivative.

The acrylic resin may be a resin composed of only a (meth) acrylic component or a resin also having a component other than the (meth) acrylic component. Further, the acrylic resin may have a hydroxyl group, a carboxyl group, a silanol group, or the like.

As the resin component, for example, a product of Maruzen Petrochemical Co. , Sumitomo Bakelite Co. , Yasuhara Chemical Co. , Rutgers Chemicals Co. , Arizona Chemical Co. , Nitto Chemical Co. , Nippon Catalyst Co. , JX Energy Co. , Arakawa Chemical Industry Co. , Taoka Chemical Industry Co. can be used.

The rubber composition may contain oil (including extender oil), liquid rubber, or the like as a softener. The total content of the softener is preferably more than <NUM> part by mass, more preferably <NUM> parts by mass or more, and less than <NUM> parts by mass with respect to <NUM> parts by mass of the rubber component. The content of oil also includes the amount of oil contained in the rubber (oil-extended rubber).

Examples of the oil include mineral oils (commonly referred to as process oils), vegetable oils, or mixtures thereof. As the mineral oil (process oil), for example, a paraffinic process oil, an aroma-based process oil, a naphthene process oil, or the like can be used. Examples of the vegetable oils and fats include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, beni-flower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. These may be used alone or in combination of two or more.

Specific examples of process oil (mineral oil) include products of Idemitsu Kosan Co. , Sankyo Yuka Kogyo Co. , Japan Energy Co. , Olisoy Co. , Toyokuni Seiyu Co. , Showa Shell Sekiyu Co. , and Fuji Kosan Co.

The liquid rubber mentioned as the softener is a polymer in a liquid state at room temperature (<NUM>) and is a polymer having a monomer similar to that of solid rubber as a constituent element. Examples of the liquid rubber include farnesene-based polymers, liquid diene-based polymers, and hydrogenated additives thereof.

The farnesene-based polymer is a polymer obtained by polymerizing farnesene, and has a structural unit based on farnesene. Farnesene includes isomers such as α-farnesene ((3E, 7E) -<NUM>,<NUM>,<NUM>-trimethyl-<NUM>,<NUM>,<NUM>,<NUM>-dodecatetraene) and β-farnesene (<NUM>,<NUM>-dimethyl-<NUM>-methylene-<NUM>, <NUM>,<NUM>-dodecatorien).

Examples of the liquid diene polymer include a liquid styrene-butadiene copolymer (liquid SBR), a liquid butadiene polymer (liquid BR), a liquid isoprene polymer (liquid IR), and a liquid styrene isoprene copolymer (liquid SIR).

The liquid diene polymer has a polystyrene-converted weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) of, for example, more than <NUM> × <NUM><NUM> and less than <NUM> × <NUM><NUM>. In the present specification, Mw of the liquid diene polymer is a polystyrene conversion value measured by gel permeation chromatography (GPC).

The content of the liquid rubber (the total content of the liquid farnesene-based polymer, the liquid diene-based polymer, etc.) is, for example, more than <NUM> part by mass and less than <NUM> parts by mass with respect to <NUM> parts by mass of the rubber component.

As the liquid rubber, for example, products of Kuraray Co. and Clay Valley Co. can be used.

The rubber composition preferably contains an anti-aging agent. Content of the anti-aging agent is, for example, more than <NUM> part by mass, <NUM> parts by mass or more, and less than <NUM> parts by mass with respect to <NUM> mass parts of rubber components.

Examples of the antiaging agent include naphthylamine-based antiaging agents such as phenyl-α-naphthylamine; diphenylamine-based antiaging agents such as octylated diphenylamine and <NUM>,<NUM>'-bis (α, α'-dimethylbenzyl) diphenylamine; p-phenylenediamine-based anti-aging agent 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-based anti-aging agent such as a polymer of <NUM>,<NUM>,<NUM>-trimethyl-<NUM>,<NUM>-dihydroquinolin; monophenolic anti-aging agents such as <NUM>,<NUM>-di-t-butyl-<NUM>-methylphenol, styrenated phenol; bis, tris, polyphenolic anti-aging agents such as tetrakis-[methylene-<NUM>- (<NUM>',<NUM>'-di-t-butyl-<NUM>'-hydroxyphenyl)propionate] methane. These may be used alone or in combination of two or more.

As the anti-aging agent, for example, products of Seiko Chemical Co. , Sumitomo Chemical Co. , Ouchi Shinko Chemical Industry Co. , Flexsys Co. , etc. can be used.

Content of stearic acid is, for example, more than <NUM> parts by mass, <NUM> parts by mass or more and less than <NUM> parts by mass with respect to <NUM> parts by mass of the rubber component. As the stearic acid, conventionally known ones can be used, and, for example, products of NOF Corporation, NOF Corporation, Kao Corporation, Fuji film Wako Pure Chemical Industries, Ltd. , and Chiba Fatty Acid Co. , etc. can be used.

Content of zinc oxide is, for example, more than <NUM> parts by mass, <NUM> parts by mass or more and less than <NUM> parts by mass with respect to <NUM> parts by mass of the rubber component. As the zinc oxide, conventionally known ones can be used, for example, products of Mitsui Metal Mining Co. , Toho Zinc Co. , Hakusui Tech Co. , Shodo Chemical Industry Co. , Sakai Chemical Industry Co. , etc. can be used.

The rubber composition preferably contains a cross-linking agent such as sulfur. Content of the cross-linking agent is, for example, more than <NUM> part by mass, <NUM> part by mass or more and less than <NUM> parts by mass with respect to <NUM> parts by mass of the rubber component.

As the sulfur, powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur, which are commonly used in the rubber industry can be used. These may be used alone or in combination of two or more.

As the sulfur, for example, products of Tsurumi Chemical Industry Co. , Karuizawa Sulfur Co. , Shikoku Chemicals Corporation, Flexsys Co. , Nippon Kanryu Kogyo Co. , Hosoi Chemical Industry Co. , etc. can be used.

Examples of the cross-linking agent other than sulfur include vulcanizing agents containing a sulfur atom such as Tackirol V200 manufactured by Taoka Chemical Industry Co. , DURALINK HTS (<NUM>,<NUM>-hexametdihylene-sodium dithiosulfate dihydrate) manufactured by Flexsys, and KA9188 (<NUM>,<NUM>-bis (N, N'-dibenzylthiocarbamoyldithio) hexane) manufactured by Lanxess; and organic peroxides such as dicumylperoxide.

The rubber composition preferably contains a vulcanization accelerator. Content of the vulcanization accelerator is, for example, more than <NUM> parts by mass, <NUM> parts by mass or more, <NUM> parts by mass or more, <NUM> parts by mass or more, and less than <NUM> parts by mass with respect to <NUM> parts by mass of the rubber component.

Examples of the vulcanization accelerator include.

In addition to the above components, the rubber composition may further contain additives generally used in the tire industry, such as fatty acid metal salts, carboxylic acid metal salts, and organic peroxides. Content of these additives is, for example, more than <NUM> part by mass and less than <NUM> parts by mass with respect to <NUM> parts by mass of the rubber component.

The rubber composition is produced by a general method, for example, a manufacturing method including a base kneading step of kneading a rubber component with a filler such as carbon black, and a finish kneading step of kneading the kneaded product obtained in the base kneading step and a cross-linking agent.

The kneading can be performed using a known (sealed) kneader such as a banbury mixer, a kneader, or an open roll.

The kneading temperature in the base kneading step is, for example, higher than <NUM> and lower than <NUM>, and the kneading time is, for example, more than <NUM> seconds and less than <NUM> minutes. In the base kneading process, in addition to the above components, compounding agents conventionally used in the rubber industry, such as softeners such as oil, stearic acid, zinc oxide, antiaging agents, waxes, and vulcanization accelerators, may be appropriately added and kneaded as needed.

In the finish kneading step, the kneaded product obtained in the base kneading step and the cross-linking agent are kneaded. The kneading temperature in the finish kneading step is, for example, above room temperature and lower than <NUM>, and the kneading time is, for example, more than <NUM> minute and less than <NUM> minutes. In the finish kneading step, in addition to the above components, a vulcanization accelerator, zinc oxide and the like may be appropriately added and kneaded as needed.

The tire of the present disclosure is manufactured by a usual method using an unvulcanized rubber composition obtained through the finish kneading step. That is, the bead reinforcing layer obtained by extruding an unvulcanized rubber composition into a predetermined shape is molded together with other tire members by a conventional method on a tire molding machine to produce an unvulcanized tire.

Specifically, on the molded drum, the inner liner as a member to ensure the air-tightness of the tire, the carcass as a member to withstand the load, impact and filling air pressure received by the tire, the belt as a member to strongly tighten the carcass to increase the rigidity of the tread, and the like are wound, both ends of the carcass are fixed to both side edges, a bead part as a member for fixing the tire to the rim is arranged, and they are formed into a toroid shape. Then the tread is pasted on the center of the outer circumference, and a bead reinforcing layer, a clinch portion and a side portion as a member protecting the carcass and resisting bending, is pasted on the radially outside, and an unvulcanized tire is produced.

In the present embodiment, it is preferable to provide with an inclined belt layer that extends at an angle of <NUM>° to <NUM>° with respect to the tire circumferential direction, as the belt. As a result, the durability of the tire is ensured while the rigidity of the tread can be sufficiently maintained. Further, since it can be restrained in the circumferential direction, it becomes easy to suppress the growth of the outer diameter.

Then, the produced unvulcanized tire is heated and pressed in a vulcanizer to obtain a tire. The vulcanization step can be carried out by applying a known vulcanization means. The vulcanization temperature is, for example, higher than <NUM> and lower than <NUM>, and the vulcanization time is, for example, more than <NUM> minutes and less than <NUM> minutes.

<FIG> and <FIG> show examples of the structure in the vicinity of the bead portion of the obtained tire. In <FIG> and <FIG>, <FIG> is a bead reinforcing layer, <NUM> is a sidewall, <NUM> is a clinch portion, <NUM> is a carcass, and <NUM> is an inner liner, <NUM> is a bead apex, and <NUM> is a bead core, and a bead is formed by these. In <FIG>, the bead reinforcing layer <NUM> is covered with the clinch portion <NUM>, and in <FIG>, the bead reinforcing layer <NUM> extends to a height higher than the clinch portion <NUM>.

At this time, the tire is formed into a shape that satisfies the above-mentioned (formula <NUM>) and (formula <NUM>) when the tire is installed on a standardized rim and the internal pressure is set to <NUM> kPa.

Specific tires that can satisfy the above (formula <NUM>) and (formula <NUM>) include tires with size notation of <NUM>/60R18, <NUM>/60R19, <NUM>/55R18, <NUM>/55R19, <NUM>/70R17, <NUM>/70R19, <NUM>/55R20, <NUM>/55R21, <NUM>/60R19, <NUM>/65R19, <NUM>/70R18, <NUM>/55R19, <NUM>/55R20, <NUM>/55R22, <NUM>/60R18, <NUM>/55R19, <NUM>/60R20, <NUM>/50R20, <NUM>/55R20, etc..

In the present embodiment, the tires that can satisfy (formula <NUM>) and (formula <NUM>) are preferably applied to pneumatic tires for passenger cars, and satisfying the above formulas can contribute more favorably to solve the problem in the present disclosure of providing a pneumatic tire with sufficiently reduced rolling resistance during high-speed running and excellent durability.

Hereinafter, the present invention will be described in more specific with reference to Examples.

In this experiment, <NUM> size tires were prepared and evaluated.

First, a rubber composition for bead reinforcing layer was produced.

First, each compounding material shown below was prepared.

Sulfur: powdered sulfur manufactured by Tsurumi Chemical Industry Co.

In accordance with the each formulation shown in Table <NUM> and Table <NUM>, materials other than sulfur and the vulcanization accelerator were kneaded under the conditions of <NUM> for <NUM> minutes using a banbury mixer to obtain a kneaded product. Each compounding amount is a mass part.

Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded at <NUM> for <NUM> minutes using an open roll to obtain a rubber composition for a bead reinforcing layer. A bead reinforcing layer is formed using the obtained tread rubber composition, bonded together with other tire members to form an unvulcanized tire, which is then vulcanized for <NUM> minutes under the condition of <NUM> to produce each test tire having the size of <NUM> type (Examples <NUM>-<NUM> to <NUM>-<NUM> and Comparative Examples <NUM>-<NUM> to <NUM>-<NUM>). At the same time, test tires of Comparative Examples <NUM>-<NUM> and <NUM>-<NUM> were produced as tires having no bead reinforcing layer.

Among the tire members, the sidewall is composed of <NUM> parts by mass of NR (TSR20), <NUM> parts by mass of BR (UBEPOL BR150B manufactured by Ube Industries, Ltd. ), <NUM> parts by mass of carbon black (Show Black N550 manufactured by Cabot Japan Co. ), <NUM> parts by mass of oil (Process X-<NUM> manufactured by Japan Energy Co. ), <NUM> parts by mass of stearic acid (stearic acid "Tsubaki" manufactured by NOF Corporation), <NUM> parts by mass of zinc oxide (Zinc white No. <NUM> manufactured by Mitsui Mining & Smelting Co. , Ltd), <NUM> parts by mass of wax (Sannok wax manufactured by Ouchi Shinko Chemical Industry Co. ), <NUM> parts by mass of anti-aging agent -<NUM> (Nocrac 6C manufactured by Ouchi Shinko Chemical Industry Co. ), <NUM> parts by mass of antioxidant-<NUM> (Antage RD manufactured by Kawaguchi Chemical Industry Co. ), <NUM> parts by mass of sulfur (powdered sulfur manufactured by Tsurumi Chemical Industry Co. ), and <NUM> parts by mass of a vulcanization accelerator (Nocceler NS manufactured by Ouchi Shinko Chemical Industry Co. ), as compounding materials, and they were kneaded to form a rubber composition, which was then molded into a predetermined shape.

And, among the tire members, the clinch part is composed of <NUM> parts by mass of NR (TSR20), <NUM> parts by mass of BR (UBEPOL BR150B manufactured by Ube Industries, Ltd. ), <NUM> parts by mass of carbon black (Showblack N550 manufactured by Cabot Japan Co. ), <NUM> parts by mass of oil (process X-<NUM> manufactured by Japan Energy Co. ), <NUM> parts by mass of stearic acid (stearic acid "Tsubaki" manufactured by NOF Corporation), <NUM> parts by mass of zinc oxide (Zinc white No. <NUM> manufactured by Mitsui Mining & Smelting Co. , Ltd), <NUM> parts by mass of wax (Sannok wax manufactured by Ouchi Shinko Chemical Industry Co. ), <NUM> parts by mass of anti-aging agent -<NUM> (Nocrac 6C manufactured by Ouchi Shinko Chemical Industry Co. ), <NUM> parts by mass of antioxidant-<NUM> (Antage RD manufactured by Kawaguchi Chemical Industry Co. ), <NUM> parts by mass of sulfur (powdered sulfur manufactured by Tsurumi Chemical Industry Co. ) and <NUM> parts by mass of a vulcanization accelerator (Nocceler NS manufactured by Ouchi Shinko Chemical Industry Co. ), as compounding materials, and they were kneaded to form a rubber composition, which was then molded into a predetermined shape.

After that, for each test tire, the outer diameter Dt (mm), the cross-sectional width Wt (mm), the cross-sectional height Ht (mm), and the aspect ratio (%) were obtained, and the virtual volume V (mm<NUM>) is calculated.

In addition, a rubber test piece for viscoelasticity measurement was cut out from the bead reinforcing layer of each test tire of Examples <NUM>-<NUM> to <NUM>-<NUM> and Comparative Examples <NUM>-<NUM> to <NUM>-<NUM>, and, for each rubber test piece, tan δ and E* were measured using Eplexor series by GABO under the conditions of the temperature of <NUM>, the frequency of <NUM>, the initial strain of <NUM>% and the dynamic strain rate of <NUM>%. When the bead reinforcing layer of the test tire had the same composition, the average of each measured value was taken.

At this time, rubber test pieces for viscoelasticity measurement were also cut out from the sidewall and the clinch portion, and tan δ and E * were measured under the same measurement conditions. The measurement results were <NUM> for tan δ and <NUM> MPa for E* at the sidewall and <NUM> for tan δ and <NUM> MPa for E* at the clinch portion.

Then, (Dt-<NUM>×Ht), (Dt<NUM> ×π/<NUM>)/Wt, (V+<NUM>×<NUM><NUM>)/Wt, (V+<NUM>×<NUM><NUM>)/Wt, (V+<NUM>×<NUM><NUM>)/Wt, (tan δ/E*), and (tan δ/E*) × (V/Wt) were obtained. Results are shown in Tables <NUM> and <NUM>.

Each test tire was installed on all wheels of the vehicle (domestic FF vehicle, displacement 2000cc), filled with air so that the internal pressure became 250kPa, and then driven on a dry road surface test course at a speed of <NUM>/h. After making a <NUM> lap, the accelerator was released, and the distance from when the accelerator was turned off until the vehicle stopped was measured as the rolling resistance at high-speed running.

Next, the result in Comparative example <NUM>-<NUM> was set to as <NUM>, and the results were indexed based on the following formula to relatively evaluate the rolling resistance at high-speed running. The larger the value, the longer the distance from when the accelerator is turned off until the vehicle stops and the smaller the rolling resistance in the steady state, and showing excellent fuel efficiency.

After installing each test tire on all wheels of the vehicle (domestic FF vehicle, displacement 2000cc) and filling it with air so that the internal pressure becomes 250kPa, a driving <NUM> laps at a speed of <NUM>/h, followed by climbing onto the unevenness provided on the road surface at a speed of <NUM>/h was repeated on the test course on a dry road surface in an overloaded state. Thereafter, the lap was performed again at a speed of <NUM>/h and then the speed was gradually increased to measure the speed at the time when the driver felt an abnormality.

Next, the result in Comparative example <NUM>-<NUM> was set to as <NUM>, and the durability performance was relatively evaluated by indexing based on the following formula. The larger the value, the better the durability.

The evaluation results of (<NUM>) and (<NUM>) above were totaled to obtain a comprehensive evaluation.

The results of each evaluation are shown in Tables <NUM> and <NUM>.

After producing the test tires of Examples <NUM>-<NUM> to <NUM>-<NUM> and Comparative examples <NUM>-<NUM> to <NUM>-<NUM> shown in Tables <NUM> and <NUM> in the same manner as in Experiment <NUM>, each parameter was calculated by performing the same procedure. Then, in the same manner, a performance evaluation test was conducted and evaluated. In this experiment, the result in Comparative example <NUM>-<NUM> was set as <NUM> for evaluation. The results of each evaluation are shown in Tables <NUM> and <NUM>.

From the results of Experiments <NUM> to <NUM> (Tables <NUM> to <NUM>), for tires of any size, <NUM> size, <NUM> size, <NUM> size, it turns out that it is possible to provide a pneumatic tire with reduced rolling resistance at high-speed running and excellent durability, when the tires have a bead reinforcing layer, and further the above (formula <NUM>) and (formula <NUM>) are satisfied.

Then, it turns out that, by satisfying each of the requirements specified in claim <NUM> and thereafter, it is possible to provide a tire with further reduced rolling resistance at high-speed running and excellent durability performance.

On the other hand, it turns out that when the tires do not have a bead reinforcing layer, or when any of (formula <NUM>) or (formula <NUM>) is not satisfied, the reduced rolling resistance at high-speed running and the excellent durability performance are not sufficiently achieved.

Next, three types of tires (Examples <NUM>-<NUM> to <NUM>-<NUM>), in which the relationship between the virtual volume V and the cross-sectional width Wt did not differ significantly, were produced with the same formulation and were evaluated according to the same manner. Here, in addition to the above-mentioned evaluation of rolling resistance during high-speed running and durability performance, the ride comfort was also evaluated.

Specifically, each test tire was installed on all wheels of the vehicle (domestic FF vehicle, displacement 2000cc), filled with air so that the internal pressure became 250kPa, and then driven on a dry road surface test course. The driver sensory-tested the ride comfort on a <NUM>-point scale when the vehicle has driven <NUM> at a speed of <NUM>/h. After summing up the evaluations by <NUM> drivers, the evaluation was indexed based on the following formula, with the total score in Example <NUM>-<NUM> being set to <NUM>, and the ride comfort was relatively evaluated. A larger value indicates better ride comfort.

Then, as in Experiments <NUM> to <NUM>, each evaluation result was totaled to obtain a comprehensive evaluation. Table <NUM> shows the results of each evaluation.

Table <NUM> shows that, when there is no large difference in the relationship between the virtual volume V and the cross-sectional width Wt, all the rolling resistance at high-speed running and the durability are improved, as the cross-sectional width Wt becomes smaller as from less than <NUM> to less than <NUM>, and as the aspect ratio increases.

Claim 1:
A pneumatic tire having a bead portion, a carcass and a tread, in which a bead reinforcing layer that reinforces the bead portion from the outside of the carcass is provided on the outside of the carcass in the tire axial direction, and
the tire satisfies following (formula <NUM>) and (formula <NUM>): <MAT> <MAT> where the cross-sectional width of the tire is Wt (mm), the outer diameter is Dt (mm), and the volume of the space occupied by the tire is the virtual volume V (mm<NUM>), when the tire is installed on a standardized rim and the internal pressure is <NUM> kPa, wherein the virtual volume V can be calculated by the following formula: V = [(Dt/<NUM>)<NUM> -{(Dt/<NUM>)-Ht}<NUM> ] × π × Wt based on the outer diameter of tire Dt (mm), the tire cross-sectional height Ht (mm) and the cross-sectional width of tire Wt (mm), in the state the tire is installed on a standardized rim, the internal pressure is <NUM> kPa and no load is applied.