JP2024102800A - tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire having improved wet grip performance in high speed turning.

SOLUTION: A tire has a tread part and a belt layer, wherein the tread part includes at least a first rubber layer on an outermost side in a tire radial direction, and a second rubber layer adjacent to the inside in the tire radial direction of the first rubber layer, the belt layer includes at least a first belt layer having the widest width in the tire width direction and a second belt layer adjacent to the first belt layer, when a glass transition temperature (°C) of the first rubber layer is represented by Tg1, a glass transition temperature (°C) of the second rubber layer is represented by Tg2, a tire sectional width (mm) in a cross section passing through a tire rotary shaft is represented by Wt, a first belt layer sectional width (mm) in the cross section is represented by W1, and a second belt layer sectional width (mm) in the cross section is represented by W2, Tg1, Tg2, Wt, W1 and W2 satisfy following relations: (1) Tg1-Tg2<0; (2) (W1-16)/Wt≤0.75; and (3) Tg2/(W2/W1)≤-8.0.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a tire.

Known techniques for improving the wet grip performance of tires include blending silica into the tread rubber composition, increasing the amount of low-softening point resin or liquid polymer blended, and blending a cold-resistant plasticizer (see, for example, Patent Document 1).

JP 2000-159935 A

However, with the construction of expressways and improvements to vehicle performance in recent years, and the fact that it is not uncommon to travel at high speeds, it is believed that there is a demand for further improvements in wet grip performance when cornering at high speeds.

The purpose of this invention is to improve wet grip performance during high-speed cornering.

The present invention relates to the following tire.
A tire having a tread portion and a belt layer,
The tread portion includes at least a first rubber layer that is an outermost layer in the radial direction of the tire, and a second rubber layer that is adjacent to the inner side of the first rubber layer in the radial direction of the tire,
The belt layer includes at least a first belt layer having a widest width in the tire width direction and a second belt layer adjacent to the first belt layer,
A tire in which Tg1, Tg2, Wt, W1 and W2 satisfy the following relationship, where Tg1 is the glass transition temperature (°C) of the first rubber layer, Tg2 is the glass transition temperature (°C) of the second rubber layer, Wt is the tire cross-sectional width (mm) in a cross section passing through the tire rotation axis, W1 is the first belt layer cross-sectional width (mm) in the cross section, and W2 is the second belt layer cross-sectional width (mm) in the cross section.
(1) Tg1-Tg2<0
(2) (W1-16)/Wt≦0.75
(3) Tg2/(W2/W1)≦-8.0

The present invention can improve wet grip performance during high-speed cornering.

1 is a cross-sectional view of a tire according to one embodiment of the present invention. 1 is a development view of a portion of a tread of a tire according to an embodiment of the present invention. 1 is a development view of a portion of a tread of a tire according to an embodiment of the present invention. 4 is a cross-sectional view of the widened circumferential main groove of FIG. 3 taken along a plane passing through the tire rotation axis. FIG. 2 is a development view of a portion of a tread of a tire according to one embodiment of the present invention, the tire having widened circumferential narrow grooves in a land portion closest to the tire centerline. 1 is a development view of a portion of a tread of a tire according to one embodiment of the present invention, the tire having a small hole in a shoulder land portion. 1 is a development view of a portion of a tread of a tire according to one embodiment of the present invention, the tire having circumferential narrow grooves in shoulder land portions.

A tire according to one embodiment of the present invention is a tire having a tread portion and a belt layer, the tread portion comprising at least a first rubber layer outermost in the tire radial direction and a second rubber layer adjacent to the first rubber layer on the radially inner side of the tire, the belt layer comprising at least a first belt layer having the widest width in the tire width direction and a second belt layer adjacent to the first belt layer, wherein Tg1, Tg2, Wt, W1 and W2 satisfy the following relationship, where Tg1 is the glass transition temperature (°C) of the first rubber layer, Tg2 is the glass transition temperature (°C) of the second rubber layer, Wt is the tire cross-sectional width (mm) in a cross section passing through the tire rotation axis, W1 is the first belt layer cross-sectional width (mm) in the cross section, and W2 is the second belt layer cross-sectional width (mm) in the cross section.
(1) Tg1-Tg2<0
(2) (W1-16)/Wt≦0.75
(3) Tg2/(W2/W1)≦-8.0

While not intending to be bound by theory, the following is believed to be the mechanism by which wet grip performance during high-speed cornering is improved in the present invention.

That is, (a) by satisfying the relationship of formula (1) that the glass transition temperature (Tg1) of the first rubber layer of the tread portion is lower than the glass transition temperature (Tg2) of the second rubber layer, the first rubber layer can easily follow the road surface even at low temperatures and high frequencies, while the second rubber layer can easily cause energy loss due to deformation of the tread portion. Therefore, the first rubber layer follows the road surface, and the second rubber layer can cause energy loss for the deformation associated with it, which is considered to improve the grip performance of the tread portion. (b) Furthermore, by narrowing the cross-sectional width (W1) of the first belt layer relative to the cross-sectional width Wt so as to satisfy the relationship of formula (2), the shoulder portion of the tread becomes more likely to deform when it comes into contact with the road surface, improving the ground contact, and it is considered that it becomes easier to follow the road surface. (c) Furthermore, when the ratio of the cross-sectional width (W2) of the second belt layer to W1 is large, the rigidity of the belt layer is increased, the deformation of the second tread layer is reduced, and heat generation is less likely to occur. Therefore, by satisfying the relationship of formula (3) so that Tg2 is equal to or less than a certain value relative to W2/W1, it is believed that deformation and heat generation can be sufficiently facilitated in the second tread layer. Furthermore, it is believed that the cooperation of the above (a) to (c) enhances the improvement of ground contact at the tread surface (first tread layer) and the improvement of heat generation inside the tread (second tread layer), resulting in improved wet grip performance during high-speed cornering.

The rubber composition of the second rubber layer preferably contains a filler, and the silica content of the filler is preferably 80% by mass or more.

By increasing the silica content in the filler of the second rubber layer, heat generation during rolling is suppressed. Generally, energy loss decreases as temperature increases, so it is believed that suppressing heat generation during rolling can make it easier for energy loss to occur when deformation occurs during turning. Therefore, it is believed that it can be easier to improve wet grip performance during high-speed turning.

The right side of equation (1) is preferably -1.0, and more preferably -3.0.

By making the Tg of the first rubber layer lower than the Tg of the second rubber layer to a certain extent, it is believed that it becomes easier to ensure conformability in the first rubber layer and prevent energy loss in the second rubber layer.

It is preferable that Tg1, Tg2, W1 and W2 satisfy the following relationship.
(4) (Tg2/Tg1)/(W2/W1)≦1.00
(However, Tg2 is less than 0.)

By satisfying the relationship in formula (4), the heat generation properties of the second rubber layer can be largely maintained during cornering on wet roads, where the strain in the second rubber layer becomes large, and it is believed that this makes it easier to improve wet grip performance during high-speed cornering.

It is preferable that Tg2 is less than -10°C.

This ensures deformability in the second rubber layer while increasing heat generation, which is thought to contribute to improved wet grip performance during high-speed cornering.

When the total styrene content (mass%) of the rubber components contained in the rubber composition of the first rubber layer is St1 and the total styrene content (mass%) of the rubber components contained in the rubber composition of the second rubber layer is St2, it is preferable that at least one of St1 and St2 is less than 25.0.

By reducing the total amount of styrene in the rubber components contained in the rubber composition constituting the first rubber layer and the second rubber layer, it is believed that it is possible to suppress the deformation of the rubber layer from becoming small due to styrene domains generated in the rubber composition, and to easily obtain the ability to conform to the road surface and heat generation.

When the total styrene amount (mass%) of the rubber component contained in the rubber composition of the first rubber layer is St1, the total styrene amount (mass%) of the rubber component contained in the rubber composition of the second rubber layer is St2, the thickness of the first rubber layer is H1, and the thickness of the second rubber layer is H2, it is preferable that St1, St2, H1 and H2 satisfy the following relationship:
(5) {St1×H1+St2×H2}/(H1+H2)<25.0

By reducing the total amount of styrene in the rubber components contained in the rubber composition constituting the first rubber layer and the second rubber layer, it is believed that it is possible to suppress the deformation of the rubber layer from becoming small due to styrene domains generated in the rubber composition, and to easily obtain conformability to the road surface and heat generation properties.

It is preferable that at least one of the rubber components contained in the rubber composition of the first rubber layer and the rubber components contained in the rubber composition of the second rubber layer contains an isoprene-based rubber.

By including isoprene-based rubber in the rubber composition that constitutes the first rubber layer and the second rubber layer, the excellent strength of the isoprene-based rubber makes it easier to generate reaction force, and the improved responsiveness is thought to facilitate improved wet grip performance during high-speed cornering.

It is preferable that the tread surface of the tread portion has a widening circumferential groove that extends in the circumferential direction of the tire and has a groove width that widens radially inward of the tire, and that the widening circumferential groove is at least one selected from the group consisting of a widening circumferential main groove, a widening circumferential narrow groove, and a widening circumferential sipe.

By making the groove width on the radially inner side of the tread larger than that on the surface of the tread, deformation can be more easily generated from the radially inner side of the tread when cornering, which is thought to facilitate energy loss in the second layer and contribute to improved wet grip performance during high-speed cornering.

The tread surface of the tread portion has two or more circumferential main grooves that extend continuously in the circumferential direction of the tire and a land portion defined by the circumferential main grooves, and it is preferable that at least one of the circumferential main grooves is a widening circumferential main groove whose groove width is wider on the radially inner side of the tire.

By making the groove width on the radially inner side of the tread larger than that on the surface of the tread, deformation can be more easily generated from the radially inner side of the tread when cornering, which is thought to facilitate energy loss in the second layer and contribute to improved wet grip performance during high-speed cornering.

The tread surface of the tread portion has two or more circumferential main grooves that extend continuously in the tire circumferential direction and land portions defined by the circumferential main grooves, at least one of the land portions has a widening circumferential narrow groove that extends in the tire circumferential direction and has a groove width that widens radially inward of the tire, and it is preferable that at least one land portion having the widening circumferential narrow groove is a land portion located on the tire centerline, or, if a circumferential main groove exists on the tire centerline, is a land portion closest to the tire centerline.

By having the widened circumferential groove in the center of the contact area of the tread, it is believed that deformation occurs more easily from inside the tread at the center of deformation during cornering, making it easier to improve wet grip performance during high-speed cornering.

The tread surface has two or more circumferential main grooves extending continuously in the tire circumferential direction and land portions defined by the circumferential main grooves, and when a pair of land portions defined by a pair of circumferential main grooves that are outermost in the tire width direction among the two or more circumferential main grooves are defined as shoulder land portions, it is preferable that the shoulder land portion has one or more small holes having an opening area of more than 0.1 and less than 15 ^mm2 .

The small holes contribute to improved drainage, which is thought to improve drainage in the shoulder area, make it easier for the tread to make contact with the ground, and improve wet grip performance during high-speed cornering.

The tread surface has two or more circumferential main grooves that extend continuously in the tire circumferential direction and a land portion defined by the circumferential main grooves. When the pair of land portions that are the outermost in the tire width direction and are defined by the pair of circumferential main grooves that are the outermost in the tire width direction among the two or more circumferential main grooves are defined as shoulder land portions, it is preferable that the shoulder land portions have at least one or more circumferential narrow grooves.

By providing circumferential narrow grooves in the shoulder land portion, the rigidity of the shoulder land portion can be reduced, and the tread portion deforms around the narrow grooves during high-speed cornering, making it easier for the tire to make contact with the ground. This is thought to improve wet grip performance during high-speed cornering.

[Definition]
"Normal condition" refers to a condition in which the tire is mounted on a normal rim, inflated to normal internal pressure, and unloaded. Unless otherwise specified, "the dimensions, etc. of each part of the tire" refer to values that are specified for those that appear on the outer surface of the tire in the normal condition. Meanwhile, those that exist inside the tire or on a cut surface of the tire refer to values that are specified, for example, when the tire is cut on a plane that includes the tire rotation axis and the cut piece of tire is maintained within the rim width of a normal rim.

"Genuine rim" refers to a rim that is specified for each tire by the standard system that includes the standard on which the tire is based. For example, for JATMA (Japan Automobile Tire Manufacturers Association), it refers to the standard rim for the applicable size listed in the "JATMA YEAR BOOK", for ETRTO (The European Tire and Rim Technical Organisation), it refers to the "Measuring Rim" listed in the "STANDARDS MANUAL", and for TRA (The Tire and Rim Association, Inc.), it refers to the "Design Rim" listed in the "YEAR BOOK". JATMA, ETRTO, TRA are referred to in that order, and if there is an applicable size at the time of reference, that standard is followed. And for tires not specified in the standard, it refers to a rim that can be assembled to a rim and can hold internal pressure, that is, a rim that does not leak air from between the rim and tire, with the smallest rim diameter and the next narrowest rim width.

"Regular internal pressure" refers to the air pressure set for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure." For TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." For ETRTO, it is the "INFLATION PRESSURE." As with regular rims, refer to JATMA, ETRTO, and TRA in that order, and follow the standard if there is an applicable size at the time of reference. In the case of a tire not specified in the standard, it refers to the regular internal pressure (250 KPa or more) of another tire size (defined in the standard) that is listed with the regular rim as the standard rim. Note that if multiple regular internal pressures of 250 KPa or more are listed, it refers to the smallest value among them.

"Normal load" means a load defined in a standard system including the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads, and like the normal rim and normal internal pressure, JATMA, ETRTO, and TRA are referenced in that order, and if there is an applicable size at the time of reference, that standard is followed. In the case of a tire not specified in the above standards, the normal load W _L is calculated as follows. V is the virtual volume of the tire (mm ³ ), Dt is the outer diameter of the tire in the normal state (mm), Ht is the cross-sectional height of the tire in the radial direction of the tire in the cross section of the tire on a plane including the tire rotation axis (mm), and Wt is the cross-sectional width of the tire in the normal state (mm). Ht can be calculated by (Dt-R)/2, where R is the rim diameter of the tire. When there is a pattern or lettering on the side of the tire, the value Wt is obtained by excluding the pattern or lettering. In this specification, the "maximum load capacity" is the same as the normal load.

"Tire section width Wt" refers to the maximum width of the tire section in its normal state. However, if there are patterns or letters on the side of the tire, this is the maximum width between the outer surfaces of the sidewalls, excluding these. In other words, the tire section width Wt can be measured by determining the maximum distance in the width direction, excluding letters on the sidewalls, in the tire cross section passing through the tire rotation axis, with the distance between the beads aligned to the normal rim width.

The "belt layer cross-sectional width" is the maximum length of the belt layer in the tire width direction in the normal state. That is, the belt layer cross-sectional width can be measured in the same manner as the tire cross-sectional width described above, by determining the widthwise distance between the end points of the belt layer in a state where the bead portions are aligned to the normal rim width in a cross section of the tire passing through the tire rotation axis. The belt layer is composed of at least two layers, and the belt layer with the widest belt layer cross-sectional width is called the first belt layer, and its cross-sectional width is called the "first belt layer cross-sectional width W1". The belt layer adjacent to the first belt layer is called the second belt layer, and its cross-sectional width is called the "second belt layer cross-sectional width W2". In addition, when there are three or more belt layers and there are two or more belt layers adjacent to the first belt layer, the belt layer with the wider cross-sectional width is called the second belt layer.

"Tread surface" refers to the area of the tread that can come into contact with the ground, and is the area between a pair of tread edges and located on the inner side in the tire width direction than the tread edges.

"Circumferential main groove" refers to a groove that extends continuously in the circumferential direction of the tire and has a groove width in the tire width direction on the tread surface of 4 mm or more. The circumferential main groove may extend linearly in the circumferential direction, or may extend in a wavy, sinusoidal, or zigzag shape in the circumferential direction. However, this does not include the widened circumferential grooves described below.

A "land portion" is an area on the tread surface that is defined by circumferential main grooves. When the tread surface has two or more circumferential grooves, the pair of land portions that are defined by the pair of circumferential grooves that are the outermost in the tire width direction are specifically referred to as "shoulder land portions."

"Circumferential narrow groove" refers to a groove that extends continuously in the circumferential direction of the tire and has a groove width in the tire width direction on the tread surface of less than 4 mm. Circumferential narrow grooves may extend linearly in the circumferential direction, or may extend in a wavy, sinusoidal, or zigzag shape in the circumferential direction. However, this does not include widened circumferential grooves, as described below.

A "widened circumferential groove" is a groove that extends continuously in the circumferential direction of the tire, and is configured such that the groove width in the tire width direction is the smallest on the tread surface and expands radially inward. The widened circumferential groove may extend linearly along the circumferential direction, or may extend wavy, sinusoidal, or zigzag along the circumferential direction. The widened circumferential groove includes a "widened circumferential main groove" with a groove width in the tire width direction on the tread surface of 4 mm or more, a "widened circumferential narrow groove" with a groove width in the tire width direction on the tread surface of less than 4 mm, and a "widened circumferential sipe" with a groove width in the tire width direction on the tread surface of less than 2 mm. Note that the groove width of the widened circumferential groove changes due to wear of the tread portion, so that one widened circumferential groove may change from a widened circumferential sipe to a widened circumferential narrow groove, or from a widened circumferential narrow groove to a widened circumferential main groove as wear progresses.

"Total styrene content (mass%) of rubber component" is calculated by multiplying the styrene content of each rubber that makes up the entire rubber component (100 mass%) by its percentage of the total rubber component, and then adding them all together.

"Small holes" are small holes on the tread surface that extend from inside the tread and open to the tread surface. Small holes exist independently and are not connected to circumferential grooves, lateral grooves, etc.

The "thickness (H) of the rubber layer constituting the tread portion" is the thickness of the rubber layer measured along a normal line drawn from the tire centerline. In cases where the tire has circumferential main grooves, circumferential narrow grooves, etc. on the tire centerline, the thickness is measured along a normal line drawn from the land centerline of the land portion closest to the tire centerline. Here, the "land centerline" is a straight line that passes through the center of the land portion in the tire width direction and extends continuously in the tire circumferential direction. Examples of rubber layers constituting the tread portion include a first rubber layer, a second rubber layer, etc.

[Measuring method]
The "glass transition temperature (Tg) (°C) of the rubber composition" is the temperature (tan δ peak temperature) corresponding to the largest tan δ value in the temperature distribution curve obtained in the range of -60°C to 40°C, measured using a GABO Iplexer series under the conditions of a frequency of 10 Hz, an initial strain of 10%, an amplitude of ±0.5%, and a heating rate of 2°C/min. For example, if there is one point showing the largest tan δ value between -60°C and 40°C, the temperature showing that value is the glass transition temperature of the rubber composition. In addition, if the temperature distribution curve of tan δ in the range of -60°C to 40°C gradually increases or decreases with increasing temperature, the glass transition temperature of the rubber composition is 40°C or -60°C, respectively, according to the above definition. Note that, if there are two or more points at which the glass transition temperature is maximum in the range of -60°C to 40°C, the lowest temperature among these is treated as the glass transition temperature of the rubber composition. The measurement sample is prepared in the same manner as the loss tangent measurement sample.

"Styrene content (mass %)" is calculated by ¹ H-NMR measurement.

"Vinyl content (amount of 1,2-bonded butadiene units) (mol%)" is calculated by infrared absorption spectrum analysis in accordance with JIS K 6239-2:2017.

"Cis content (amount of cis-1,4-bonded butadiene units) (mol%)" is calculated by infrared absorption spectrum analysis in accordance with JIS K 6239-2:2017.

The "glass transition temperature (Tg) (°C)" is measured in accordance with JIS K 7121 using a differential scanning calorimeter (Q200) manufactured by TA Instruments Japan, Ltd., while increasing the temperature at a rate of 10°C/min. In the present invention, the Tg of styrene-butadiene rubber is particularly measured.

The "weight average molecular weight (Mw)" can be calculated based on the measured value obtained by gel permeation chromatography (GPC) (e.g., GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation) and converted into standard polystyrene.

"N ₂ SA of carbon black" is measured in accordance with JIS K 6217-2:2017.

"N ₂ SA of silica" is measured by the BET method in accordance with ASTM D3037-93.

The "average primary particle diameter" can be determined by observing with a transmission or scanning electron microscope, measuring 400 or more primary particles observed within the field of view, and taking the average. If the particle shape is nearly circular, the diameter of the circle is taken as the particle diameter, if it is needle-like or rod-like, the minor axis is taken as the particle diameter, and in other cases, the equivalent circle diameter is calculated from the electron microscope image. The equivalent circle diameter is calculated as "4 x (particle area) / positive square root of π". This applies to carbon black, silica, etc.

The "softening point" is defined as the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point tester.

"Plasticizer content" includes the amount of plasticizer in the rubber component that has been extended by the plasticizer. Similarly, "oil content" includes the amount of oil contained in the oil-extended rubber.

[tire]
The tire of the present invention will be described below with reference to the drawings as appropriate. However, the drawings are merely examples, and the present invention should not be interpreted as being limited based on the drawings.

The tire of the present invention has a tread portion and a belt layer, and the tread portion has at least a first rubber layer that is outermost in the tire radial direction and a second rubber layer adjacent to the tire radially inward of the first rubber layer, and the belt layer has at least a first belt layer that is widest in the tire width direction and a second belt layer adjacent to the first belt layer.

1 is a cross-sectional view of a tire according to an embodiment of the present invention. In FIG. 1, the tire 1 has a cross-sectional width Wt. The tire 1 also includes a first rubber layer 2 that is the outermost in the radial direction of the tire and that constitutes the tread portion, and a second rubber layer 3 that is adjacent to the first rubber layer 2 on the inner side in the radial direction of the tire. The tire 1 also includes a first belt layer 5 that is the widest in the radial direction of the tire, having a cross-sectional width W1 in the tire width direction, and a second belt layer 4 that is adjacent to the outer side of the first belt layer 5 in the tire radial direction and has a cross-sectional width W2 in the tire width direction. The rubber layer that constitutes the tread portion may include at least two layers, the first rubber layer and the second rubber layer, and may further include an additional layer on the inner side in the radial direction of the tire, making it possible to have three or more layers in total. The belt layer may also include at least the first belt layer and the second belt layer, and may further include an additional layer on the inner side or outer side in the radial direction of the tire, making it possible to have three or more layers in total. In FIG. 1, the thickness of the first rubber layer 2 is indicated by H1, and the thickness of the second rubber layer 3 is indicated by H2.

Figure 2 is a development of a portion of the tread of a tire according to one embodiment of the present invention. In Figure 2, the tread surface has three circumferential main grooves 6 that extend continuously in the tire circumferential direction, and four land portions 7 defined by the circumferential main grooves 6. Of these circumferential main grooves 6, the pair of land portions 7 on the outermost side in the tire width direction defined by the pair of circumferential main grooves on the outermost side in the tire width direction are shoulder land portions. In Figure 2, all of the circumferential main grooves 6 are formed in a straight line, but the circumferential main grooves may extend in a wavy, sinusoidal, or zigzag shape along the circumferential direction, for example.

In the tire of the present invention, when the glass transition temperature (°C) of the first rubber layer is Tg1, the glass transition temperature (°C) of the second rubber layer is Tg2, the tire cross-sectional width (mm) in a cross section passing through the tire rotation axis is Wt, the first belt layer cross-sectional width (mm) in the cross section is W1, and the second belt layer cross-sectional width (mm) in the cross section is W2, Tg1, Tg2, Wt, W1, and W2 satisfy the following relationship:
(1) Tg1-Tg2<0
(2) (W1-16)/Wt≦0.75
(3) Tg2/(W2/W1)≦-8.0

In the tire of the present invention, it is preferable that Tg1, Tg2, W1 and W2 satisfy the following relationship.
(4) (Tg2/Tg1)/(W2/W1)≦1.00
(However, Tg2 is less than 0.)

In addition, in the tire of the present invention, when the total styrene amount (mass%) of the rubber component contained in the rubber composition of the first rubber layer is St1, the total styrene amount (mass%) of the rubber component contained in the rubber composition of the second rubber layer is St2, the thickness of the first rubber layer is H1, and the thickness of the second rubber layer is H2, it is preferable that St1, St2, H1, and H2 satisfy the following relationship:
(5) {St1×H1+St2×H2}/(H1+H2)<25.0

<Formula (1)>
In the tire of the present invention, the right side of formula (1) is preferably -0.5, more preferably -0.9, even more preferably -1.0, even more preferably -1.5, even more preferably -1.9, even more preferably -2.0, even more preferably -2.5, even more preferably -2.9, even more preferably -3.0. On the other hand, with respect to the value of Tg1-Tg2, there is no particular restriction on the lower limit from the viewpoint of the effects of the invention, but it may usually be about -5.0. Both Tg1 and Tg2 can be appropriately adjusted by the type and amount of the rubber component constituting the rubber composition, and the type and amount of additives other than the rubber component.

<Formula (2)>
In the tire of the present invention, the right side of formula (2) is preferably 0.74, more preferably 0.73, still more preferably 0.72, still more preferably 0.70, still more preferably 0.68, and still more preferably 0.65. On the other hand, with respect to the value of (W1-16)/Wt, there is no particular restriction on the lower limit from the viewpoint of the effects of the invention, but it may usually be about 0.60.

The tire cross-sectional width Wt is preferably 125 mm or more, more preferably 150 mm or more, and even more preferably 175 mm or more. The tire cross-sectional width Wt is preferably less than 305 mm, more preferably less than 245 mm, and even more preferably less than 210 mm.

<Formula (3)>
In the tire of the present invention, the right side of formula (3) is preferably -9.0, more preferably -10.0, even more preferably -11.0, even more preferably -12.0, even more preferably -13.0, and even more preferably -14.0. On the other hand, with respect to the value of Tg2/(W2/W1), there is no particular lower limit from the viewpoint of the effects of the invention, but it may usually be about -17.0. The adjustment of Tg2 is as described above.

The value of W2/W1 is less than 1, preferably less than 0.98, more preferably less than 0.96, and even more preferably less than 0.95. On the other hand, the value of W2/W1 is preferably greater than 0.70, more preferably greater than 0.75, and even more preferably greater than 0.80.

<Formula (4)>
In the tire of the present invention, the right side of formula (4) is preferably 0.98, more preferably 0.96, even more preferably 0.94, even more preferably 0.92, even more preferably 0.90, and even more preferably 0.89. On the other hand, the value of (Tg2/Tg1)/(W2/W1) is not particularly limited in terms of the lower limit from the viewpoint of the effects of the invention, but may usually be about 0.40 or 0.50. The adjustment of Tg1 and Tg2 is as described above.

<Tg2>
In the tire of the present invention, when the glass transition temperature (°C) of the second rubber composition is Tg2, Tg2 is preferably less than 0°C. Tg2 is more preferably less than -5.0°C, even more preferably less than -7.0°C, even more preferably less than -9.0°C, even more preferably less than -10.0°C, even more preferably less than -10.0°C, even more preferably less than -11.0°C, even more preferably less than -12.0°C, even more preferably less than -13.0°C. From the viewpoint of the effects of the invention, there is no particular restriction on the lower limit of the value of Tg2, but it may usually be about -20.0°C or -17.0°C. The adjustment of Tg2 is as described above.

<Formula (5)>
In the tire of the present invention, the right side of formula (5) is preferably 23.0, more preferably 21.0, even more preferably 19.0, even more preferably 17.0, even more preferably 15.0, and even more preferably 13.0. On the other hand, with respect to the value of {St1×H1+St2×H2}/(H1+H2), there is no particular restriction on the lower limit from the viewpoint of the effects of the invention, but it may usually be about 10.0.

<Stage 1, Stage 2>
In the tire of the present invention, it is preferable that at least one of the total styrene amount (mass%) St1 of the rubber component contained in the first rubber composition and the total styrene amount (mass%) St2 of the rubber component contained in the second rubber composition is less than 25.0, and it is more preferable that both St1 and St2 are less than 25.0.

Moreover, the value of at least one of St1 and St2, or both of St1 and St2, is more preferably less than 21.0, even more preferably less than 19.0, even more preferably less than 17.0, even more preferably less than 15.0, even more preferably less than 13.0. On the other hand, from the viewpoint of the effect of the invention, there is no particular restriction on the lower limit of the value of at least one of St1 and St2, or both of St1 and St2, but it may usually be about 10.0.

<H1, H2>
In the tire of the present invention, H1 is preferably more than 1.5 mm, more preferably 2 mm or more, and further preferably 3 mm or more. On the other hand, H1 is preferably less than 6.5 mm, more preferably 6 mm or less, and further preferably 5 mm or less. H2 is the same as H1.

<Wide circumferential groove>
In the tire of the present invention, it is preferable that the tread surface has a widened circumferential groove whose groove width is wider on the radially inner side of the tire. By making the groove width on the radially inner side of the tread portion larger than that on the tread portion surface, it is possible to easily cause deformation from the radially inner side of the tread portion during cornering, which is thought to make it easier to cause energy loss in the second layer and improve wet grip performance during high-speed cornering. It is preferable that the widened circumferential groove is at least one selected from the group consisting of a widened circumferential main groove, a widened circumferential narrow groove, and a widened circumferential sipe.

Figure 3 is a development of a portion of the tread of a tire according to one embodiment of the present invention. The tread surface in Figure 3 differs from that in Figure 2 in that the circumferential main groove on the tire centerline CL is an expanded circumferential main groove 8. Therefore, the description of the portions other than the expanded circumferential main groove 8 is the same as that in Figure 2. In Figure 3, the expanded circumferential main groove 8 is only formed on the tire centerline CL, but this is not limited to this form, and other circumferential main grooves 6 may be expanded circumferential main grooves 8. In Figure 3, the dashed line of the expanded circumferential main groove 8 represents the maximum width of the expanded circumferential main groove 8 present on the radially inner side of the tire.

Figure 4 shows a cross section of the widened circumferential main groove 8. In Figure 4, the groove width of the widened circumferential main groove increases uniformly toward the inside in the tire radial direction, but the increase in groove width is not limited to this manner, and may increase, for example, by repeating small increases and decreases in a curved or stepped manner.

Figure 5 is a development of a portion of the tread of a tire according to an embodiment of the present invention, which has a widened circumferential narrow groove in the land portion closest to the tire centerline. In Figure 5, widened circumferential narrow grooves 9 are formed on each of two land portions 7 adjacent to a circumferential main groove 6 that passes along the tire centerline. These widened circumferential narrow grooves 9 are linear, but are not limited to this, and may extend, for example, in a wavy, sinusoidal, or zigzag shape along the circumferential direction. There are no particular restrictions on the land portion on which the widened circumferential narrow grooves are formed, but they are preferably formed on the land portion located on the tire centerline, or, if a circumferential main groove exists on the tire centerline, they are preferably formed on the land portion closest to the tire centerline, as in the widened circumferential narrow groove 9 in Figure 5.

＜Small hole＞
In the tire of the present invention, the shoulder land portion of the tread surface preferably has one or more small holes having an opening area of more than 0.1 ^mm2 and less than 15 ^mm2 . In FIG. 6, small holes 10 are formed on a pair of shoulder land portions 7. FIG. 6 is similar to FIG. 2 except that small holes are formed in this way. The small holes contribute to improving drainage, so that the drainage in the shoulder land portion is improved, the ground contact in the shoulder portion is improved, and it is considered that it contributes to improving the wet grip performance during high-speed cornering. The opening area of the small holes on the tread surface is preferably more than 0.1 ^mm2 , more preferably more than 0.5 ^mm2 , even more preferably more than 1.0 ^mm2 , and particularly preferably more than 1.5 ^mm2 . In addition, the opening area of the small holes on the tread surface is preferably less than ¹⁵ mm2, more preferably less than ¹⁰ mm2, even more preferably less than 7.0 ^mm2 , and particularly preferably less than 5.0 ^mm2 . The depth of the deepest portion of the small hole is preferably 3% or more, more preferably 5% or more, of the depth of the deepest portion of the circumferential main groove, and is preferably 80% or less, more preferably 60% or less, and even more preferably 40% or less, of the depth of the deepest portion of the circumferential main groove.

<Circumferential narrow groove>
In the tire of the present invention, the shoulder land portion of the tread surface preferably has at least one circumferential narrow groove. In Fig. 7, a circumferential narrow groove 11 is formed on a pair of shoulder land portions 7. Fig. 7 is the same as Fig. 2 except for the circumferential narrow groove. The rigidity of the shoulder land portion can be reduced, and the tread portion deforms around the narrow groove during high-speed cornering, making it easier for the tire to contact the ground, which contributes to improving wet grip performance during high-speed cornering.

[Rubber composition]
Hereinafter, the rubber composition according to the tire of the present invention, that is, the first rubber composition constituting the first rubber layer of the tread portion and the second rubber composition constituting the second rubber layer will be described. The following description can be applied to both the first rubber composition and the second rubber composition unless otherwise specified. Therefore, when simply referring to the rubber composition, it is meant to include both the first rubber composition and the second rubber composition.

<Rubber component>
The rubber composition according to the present invention, that is, the first rubber composition and the second rubber composition, each preferably contains styrene-butadiene rubber as a rubber component. At least one of the rubber components contained in the first rubber composition and the second rubber composition preferably contains isoprene-based rubber. At least one of the rubber components contained in the first rubber composition and the second rubber composition preferably contains butadiene rubber. At least one of the rubber components contained in the first rubber composition and the second rubber composition preferably contains butadiene rubber and isoprene-based rubber. At least one of the rubber components contained in the first rubber composition and the second rubber composition preferably contains styrene-butadiene rubber, butadiene rubber, and isoprene-based rubber. At least one of the rubber components contained in the first rubber composition and the second rubber composition preferably contains styrene-butadiene rubber, butadiene rubber, and isoprene-based rubber. At least one of the rubber components contained in the first rubber composition and the second rubber composition preferably consists of styrene-butadiene rubber, butadiene rubber, and isoprene-based rubber.

(SBR)
The SBR is not particularly limited, and examples thereof include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Examples of modified SBR include SBR whose ends and/or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin, silicon compounds, etc. Among these, S-SBR and modified SBR are preferred. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR), etc. can also be used. These SBRs may be used alone or in combination of two or more types.

Examples of S-SBR that can be used in the present invention include S-SBR manufactured and sold by JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, ZS Elastomers Co., Ltd., etc.

The styrene content of SBR is appropriately selected according to the values of St1 and St2, and as an example, from the viewpoints of wet grip performance and abrasion resistance, it is preferably more than 10 mass%, more preferably more than 15 mass%, and even more preferably more than 20 mass%. From the viewpoints of the temperature dependency of grip performance and blow resistance, it is preferably less than 41 mass%, more preferably less than 35 mass%, and even more preferably less than 26 mass%. In this specification, the styrene content of SBR is calculated by ¹ H-NMR measurement.

From the viewpoints of ensuring reactivity with silica, wet grip performance, rubber strength, and abrasion resistance, the vinyl content of SBR is preferably more than 10 mol%, more preferably more than 13 mol%, and even more preferably more than 15 mol%. Also, from the viewpoints of preventing an increase in temperature dependency, elongation at break, and abrasion resistance, the vinyl content of SBR is preferably less than 70 mol%, more preferably less than 50 mol%, and even more preferably less than 40 mol%. In this specification, the vinyl content of SBR (amount of 1,2-bonded butadiene units) is measured by infrared absorption spectroscopy.

From the viewpoint of wet grip performance, the weight average molecular weight (Mw) of SBR is preferably more than 200,000, more preferably more than 250,000, and even more preferably more than 300,000. From the viewpoint of crosslinking uniformity, the weight average molecular weight is preferably less than 2,000,000, more preferably less than 1,800,000, and even more preferably less than 1,500,000. In this specification, the weight average molecular weight of SBR can be determined in standard polystyrene equivalent based on the measured value obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

From the viewpoint of wet grip performance, the content of SBR in the rubber component is preferably more than 45% by mass, more preferably 50% by mass or more, even more preferably more than 70% by mass, and even more preferably 80% by mass or more. On the other hand, the upper limit of the content of SBR in the rubber component is not particularly limited and may be 100% by mass.

(BR)
The BR is not particularly limited, and may be, for example, a BR having a cis content of less than 50 mol% (low cis BR), a BR having a cis content of more than 90 mol% (high cis BR), a rare earth butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, a BR containing syndiotactic polybutadiene crystals (SPB-containing BR), or a modified BR (high cis modified BR, low cis modified BR), which are commonly used in the tire industry. The modified BR may be a BR modified with the same functional groups as those described above for the SBR. These BRs may be used alone or in combination of two or more.

As the high cis BR, for example, commercially available products from Zeon Corporation, Ube Industries, Ltd., JSR Corporation, etc. can be used. By including high cis BR, it is possible to improve low temperature properties and wear resistance. The cis content is preferably more than 95 mol%, more preferably more than 96 mol%, and even more preferably 97 mol% or more. In this specification, the cis content (amount of cis-1,4-bonded butadiene units) is a value calculated by infrared absorption spectrum analysis.

The rare earth BR is synthesized using a rare earth catalyst, has a vinyl content of preferably less than 1.8 mol%, more preferably less than 1.6 mol%, and even more preferably 1.5 mol% or less, and has a cis content of preferably more than 95 mol%, more preferably more than 96 mol%, and even more preferably 97 mol% or more. The rare earth BR may be, for example, commercially available from LANXESS Co., Ltd.

SPB-containing BR is one in which 1,2-syndiotactic polybutadiene crystals are not simply dispersed in BR, but are dispersed after being chemically bonded to the BR. Such SPB-containing BR can be commercially available from Ube Industries, Ltd., etc.

As the modified BR, a modified butadiene rubber (modified BR) in which the terminals and/or the main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen is preferably used.

Other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, in which the ends of the modified BR molecules are further bonded with tin-carbon bonds (tin-modified BR). In addition, the modified BR may be either non-hydrogenated or hydrogenated.

The BRs listed above may be used alone or in combination of two or more.

From the viewpoint of abrasion resistance, the weight average molecular weight (Mw) of BR is preferably more than 300,000, more preferably more than 350,000, and even more preferably more than 400,000. From the viewpoint of crosslinking uniformity, etc., it is preferably less than 2,000,000, more preferably less than 1,000,000, and even more preferably less than 500,000. Note that Mw can be calculated based on the measured value obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation) in terms of standard polystyrene.

When BR is included, the content in the rubber component is preferably less than 50% by mass, more preferably less than 40% by mass, and even more preferably less than 30% by mass, from the viewpoint of wet grip performance. On the other hand, the lower limit of the content of BR in the rubber component is not particularly limited and may be 0% by mass, but it can also be, for example, more than 1% by mass, more than 5% by mass, more than 10% by mass, or more than 15% by mass.

(Isoprene rubber)
As the isoprene-based rubber, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. In addition to unmodified natural rubber (NR), natural rubber also includes modified natural rubber such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. These isoprene-based rubbers may be used alone or in combination of two or more.

There are no particular limitations on NR, and any commonly used NR in the tire industry can be used, such as SIR20, RSS#3, TSR20, etc.

When isoprene-based rubber is contained, the content in the rubber component is preferably less than 50% by mass, more preferably less than 45% by mass, even more preferably less than 40% by mass, and even more preferably 30% by mass or less, from the viewpoint of wet grip performance. On the other hand, the lower limit of the content of isoprene-based rubber in the rubber component is not particularly limited and may be 0% by mass, but it can also be, for example, more than 1% by mass, more than 5% by mass, more than 10% by mass, more than 20% by mass, more than 25% by mass, or 30% by mass or more.

(Other rubber components)
The rubber component according to the present invention may contain rubber components other than the isoprene-based rubber, SBR, and BR. As the other rubber components, crosslinkable rubber components generally used in the tire industry can be used, and examples thereof include styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used alone or in combination of two or more.

<Filler>
The rubber composition according to the present invention may contain a filler containing carbon black and/or silica. The filler preferably contains silica, more preferably contains carbon black and silica, and may be a filler consisting of only carbon black and silica.

(Carbon black)
Carbon black generally used in the tire industry can be appropriately used, and examples of the carbon black include GPF, FEF, HAF, ISAF, and SAF. In addition, recycled carbon black can also be used as the carbon black. The term "recycled carbon black" refers to carbon black obtained by crushing a product such as a used tire containing carbon black and calcining the crushed product, and the carbon black has a mass ratio (ash content) of 13% by mass or more of ash, which is a component that does not burn, when it is oxidized and burned in air by heating in a thermogravimetric measurement method conforming to JIS K 6226-2:2003. That is, the mass (carbon content) of the weight loss due to the oxidative combustion is less than 87% by mass. Recycled carbon black is also called recycled carbon black, and may be represented by rCB. These carbon blacks may be used alone or in combination of two or more types.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably more than 10 m ² /g, more preferably more than 30 m ² /g, and even more preferably more than 50 m ² /g from the viewpoint of reinforcing properties. Also, from the viewpoint of fuel efficiency and processability, it is preferably less than 200 m ² /g, more preferably less than 175 m ² /g, and even more preferably less than 150 m ² /g. The N ₂ SA of carbon black is a value measured in accordance with JIS K 6217-2:2017 "Basic properties of carbon black for rubber - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method".

The average primary particle diameter of carbon black is preferably greater than 10 nm, more preferably greater than 12 nm, and even more preferably greater than 14 nm. The average primary particle diameter is preferably less than 26 nm, more preferably less than 24 nm, and even more preferably 22 nm or less. The average primary particle diameter of carbon black is measured by the above-mentioned measurement method.

When carbon black is contained, the content per 100 parts by mass of the rubber component is preferably more than 1 part by mass, more preferably 5 parts by mass or more, even more preferably more than 10 parts by mass, even more preferably more than 20 parts by mass, even more preferably more than 30 parts by mass, and even more preferably 40 parts by mass or more, from the viewpoint of low fuel consumption performance. In addition, the content is preferably less than 50 parts by mass, more preferably less than 45 parts by mass, and even more preferably 40 parts by mass or less, from the viewpoint of low fuel consumption performance.

(silica)
The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrated silica), or other silica commonly used in the tire industry. In addition to these silicas, silica made from biomass materials such as rice husks can also be used. Among them, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. These silicas can be used alone or in combination of two or more.

From the viewpoints of fuel economy and wear resistance, the nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably more than 140 m ² /g, more preferably more than 150 m ² /g, even more preferably more than 160 m ² /g, and even more preferably 175 m ² /g or more. From the viewpoints of fuel economy and processability, it is preferably less than 350 m ² /g, more preferably less than 300 m ² /g, and even more preferably less than 250 m ² /g. The N ₂ SA of silica in this specification is a value measured by the BET method in accordance with ASTM D3037-93.

The average primary particle diameter of silica is preferably greater than 10 nm, more preferably greater than 12 nm, and even more preferably greater than 14 nm. The average primary particle diameter is preferably less than 26 nm, more preferably less than 24 nm, and even more preferably 22 nm or less. The average primary particle diameter of silica is measured by the above-mentioned measurement method.

When silica is contained, the content per 100 parts by mass of the rubber component is preferably more than 20 parts by mass, more preferably more than 30 parts by mass, even more preferably more than 40 parts by mass, and even more preferably 45 parts by mass or more, from the viewpoint of wet grip performance. Also, from the viewpoint of abrasion resistance, the content is preferably less than 130 parts by mass, more preferably less than 120 parts by mass, and even more preferably less than 110 parts by mass.

When both silica and carbon black are contained, the total content of silica and carbon black per 100 parts by mass of the rubber component is preferably more than 40 parts by mass, more preferably more than 50 parts by mass, and even more preferably more than 60 parts by mass, from the viewpoint of abrasion resistance performance. Also, from the viewpoint of fuel efficiency performance and elongation at break, it is preferably less than 160 parts by mass, more preferably less than 140 parts by mass, and even more preferably less than 120 parts by mass.

When both silica and carbon black are contained, the content of silica is preferably greater than the content of carbon black from the viewpoint of the balance of fuel economy, wet grip performance, and abrasion resistance. The ratio of silica to the total content of silica and carbon black is preferably greater than 50% by mass, more preferably greater than 70% by mass, even more preferably 80% by mass or more, even more preferably greater than 80% by mass, even more preferably 90% by mass or more, and even more preferably greater than 90% by mass.

(Other fillers)
As the filler, in addition to carbon black and silica, other fillers may be used. Such fillers are not particularly limited, and any fillers that have been conventionally and generally used in the tire industry, such as aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, etc., may be used. These fillers may be used alone or in combination of two or more.

(Silane coupling agent)
Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent conventionally used in combination with silica in the tire industry can be used, for example, thioester-based silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane, mercapto-based silane coupling agents such as those represented by the following chemical formula, sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide, bis(3-triethoxysilylpropyl) tetrasulfide, vinyltriethoxysilane, Examples of the silane coupling agents include vinyl-based silane coupling agents such as vinyltrimethoxysilane; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, thioester-based silane coupling agents and/or sulfide-based silane coupling agents are preferred. These silane coupling agents may be used alone or in combination of two or more.

（式中、Ｒ¹⁰¹、Ｒ¹⁰²、およびＲ¹⁰³は、それぞれ独立して、炭素数１～１２のアルキル、炭素数１～１２のアルコキシ、または－Ｏ－（Ｒ¹¹¹－Ｏ）_z－Ｒ¹¹²（ｚ個のＲ¹¹¹は、それぞれ独立して、炭素数１～３０の２価の炭化水素基を表し；Ｒ¹¹²は、炭素数１～３０のアルキル、炭素数２～３０のアルケニル、炭素数６～３０のアリール、または炭素数７～３０のアラルキルを表し；ｚは、１～３０の整数を表す。）で表される基を表し；Ｒ¹⁰⁴は、炭素数１～６のアルキレンを表す。）

（式中、ｘは０以上の整数を表し；ｙは１以上の整数を表し；Ｒ²⁰¹は、水素原子、ハロゲン原子、ヒドロキシルもしくはカルボキシルで置換されていてもよい炭素数１～３０のアルキル、炭素数２～３０のアルケニル、または炭素数２～３０のアルキニルを表し；Ｒ²⁰²は、炭素数１～３０のアルキレン、炭素数２～３０のアルケニレン、または炭素数２～３０のアルキニレンを表し；ここにおいて、Ｒ²⁰¹とＲ²⁰²とで環構造を形成してもよい。） The mercapto-based silane coupling agent is preferably a compound represented by the following chemical formula (1) and/or a compound containing a bonding unit A represented by the following chemical formula (2) and a bonding unit B represented by the following chemical formula (3).

(In the formula, R ¹⁰¹ , R ¹⁰² , and R ¹⁰³ each independently represent an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or a group represented by -O-(R ¹¹¹ -O) _z -R ¹¹² (z R ¹¹¹ each independently represent a divalent hydrocarbon group having 1 to 30 carbon atoms; R ¹¹² represents an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms; and z represents an integer from 1 to 30); and R ¹⁰⁴ represents an alkylene group having 1 to 6 carbon atoms.)

(In the formula, x represents an integer of 0 or more; y represents an integer of 1 or more; R ²⁰¹ represents an alkyl having 1 to 30 carbon atoms, an alkenyl having 2 to 30 carbon atoms, or an alkynyl having 2 to 30 carbon atoms, which may be substituted with a hydrogen atom, a halogen atom, a hydroxyl, or a carboxyl; R ²⁰² represents an alkylene having 1 to 30 carbon atoms, an alkenylene having 2 to 30 carbon atoms, or an alkynylene having 2 to 30 carbon atoms; and R ²⁰¹ and R ²⁰² may together form a ring structure.)

Examples of the compound represented by formula (1) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the compound represented by the following chemical formula (4) (Si363 manufactured by Evonik Degussa), and the compound represented by the following chemical formula (4) can be preferably used. These may be used alone or in combination of two or more kinds.

Compounds containing a bond unit A represented by chemical formula (2) and a bond unit B represented by chemical formula (3) include, for example, those manufactured and sold by Momentive, Inc. These may be used alone or in combination of two or more types.

When a silane coupling agent is contained, the content per 100 parts by mass of the rubber component (the total amount when multiple silane coupling agents are used in combination) is preferably more than 0.5 parts by mass, more preferably more than 1.0 parts by mass, even more preferably more than 2.0 parts by mass, and even more preferably more than 3.0 parts by mass, from the viewpoint of improving the dispersibility of silica. Also, from the viewpoint of preventing a decrease in abrasion resistance, it is preferably less than 20 parts by mass, more preferably less than 12 parts by mass, even more preferably less than 10 parts by mass, and even more preferably less than 9.0 parts by mass.

The content of the silane coupling agent relative to 100 parts by mass of silica is preferably more than 1.0 part by mass, more preferably more than 3.0 parts by mass, and even more preferably more than 5.0 parts by mass, from the viewpoint of increasing the dispersibility of the silica. Also, from the viewpoint of cost and processability, it is preferably less than 20 parts by mass, more preferably less than 15 parts by mass, and even more preferably less than 12 parts by mass.

<Plasticizer>
The rubber composition according to the present invention preferably contains a plasticizer. Examples of the plasticizer include resin, oil, liquid rubber, and ester-based plasticizers. The total amount of plasticizer is the total amount of all of these plasticizers. The total amount of plasticizer also includes the amount of plasticizer in the rubber component extended by the plasticizer. For example, the oil content also includes the amount of oil contained in the oil-extended rubber.

(resin)
The resin is not particularly limited, but examples thereof include petroleum resins, terpene resins, rosin resins, phenol resins, etc., which are commonly used in the tire industry. These resins may be used alone or in combination of two or more.

<Petroleum resin>
As the petroleum resin, C5 petroleum resin, aromatic petroleum resin, C5C9 petroleum resin, etc. These resins may be used alone or in combination of two or more.

C5 petroleum resin refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions with 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as a C5 petroleum resin.

Aromatic petroleum resin refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified product. Examples of C9 fractions include petroleum fractions with 8 to 10 carbon atoms, such as vinyl toluene, alkyl styrene, indene, and methyl indene. Specific examples of aromatic petroleum resins that are preferably used include coumarone-indene resin, coumarone resin, indene resin, and aromatic vinyl resin.

As the aromatic vinyl resin, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred, because they are economical, easy to process, and have excellent heat generation properties. As the aromatic vinyl resin, for example, commercially available products from Kraton Corporation, Eastman Chemical Company, etc. can be used.

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

<Terpene resin>
Examples of the terpene resin include polyterpene resins consisting of at least one selected from terpene compounds such as α-pinene, β-pinene, limonene, and dipentene; aromatic modified terpene resins made from the terpene compounds and aromatic compounds; terpene phenolic resins made from terpene compounds and phenolic compounds; and terpene resins obtained by subjecting these terpene resins to hydrogenation treatment (hydrogenated terpene resins). Examples of aromatic compounds that are raw materials for aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds that are raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol. These resins may be used alone or in combination of two or more.

<Rosin-based resin>
The rosin-based resin is not particularly limited, but examples thereof include natural resin rosin and rosin-modified resins obtained by modifying natural resin rosin through hydrogenation, disproportionation, dimerization, esterification, etc. These resins may be used alone or in combination of two or more kinds.

<Phenol-based resin>
The phenol-based resin is not particularly limited, but examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, oil-modified phenol formaldehyde resin, etc. These resins may be used alone or in combination of two or more kinds.

<Softening point>
From the viewpoint of wet grip performance, the softening point of the resin is preferably more than 60° C., more preferably more than 70° C., and even more preferably more than 80° C. In addition, from the viewpoint of processability and improvement of dispersibility between the rubber component and the filler, it is preferably less than 150° C., more preferably less than 140° C., and even more preferably less than 130° C. In this specification, the softening point may be defined as the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point measuring device.

<Content>
In the case where a resin is contained, the content per 100 parts by mass of the rubber component is preferably more than 1 part by mass, more preferably more than 3 parts by mass, and even more preferably 5 parts by mass or more, from the viewpoint of wet grip performance, and is preferably less than 80 parts by mass, more preferably less than 60 parts by mass, even more preferably less than 50 parts by mass, and even more preferably 40 parts by mass or less, from the viewpoint of suppressing heat buildup.

(oil)
Examples of the oil include process oil, vegetable oil, and animal oil. Examples of the process oil include paraffin-based process oil, naphthenic process oil, and aromatic process oil. In addition, a process oil having a low content of polycyclic aromatic compounds (PCA) compounds can be used as an environmental measure. Examples of the low PCA content process oil include mild extract solvates (MES), treated distillate aromatic extracts (TDAE), and heavy naphthenic oil. In addition, from the viewpoint of life cycle assessment, waste oil after use in rubber mixers and engines, or refined waste edible oil used in restaurants may be used.

When oil is contained, the content per 100 parts by mass of the rubber component is preferably more than 5 parts by mass, more preferably more than 10 parts by mass, and even more preferably 15 parts by mass or more, from the viewpoint of processability. Also, from the viewpoint of abrasion resistance, it is preferably less than 120 parts by mass, more preferably less than 80 parts by mass, and even more preferably less than 40 parts by mass. In this specification, the oil content includes the amount of oil contained in the oil-extended rubber.

(Liquid rubber)
The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25° C.), and examples thereof include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. These liquid rubbers may be used alone or in combination of two or more kinds.

When liquid rubber is contained, the content per 100 parts by mass of the rubber component is preferably more than 1 part by mass, more preferably more than 2 parts by mass, even more preferably more than 3 parts by mass, and even more preferably more than 5 parts by mass. The content of liquid rubber is preferably less than 50 parts by mass, more preferably less than 40 parts by mass, and even more preferably less than 20 parts by mass.

(Ester plasticizer)
Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), trixylenyl phosphate (TXP), etc. These ester-based plasticizers may be used alone or in combination of two or more.

(Total amount of plasticizer)
The content of the plasticizer per 100 parts by mass of the rubber component is preferably more than 5 parts by mass, more preferably more than 10 parts by mass, and even more preferably more than 15 parts by mass from the viewpoint of wet grip performance, and is preferably less than 120 parts by mass, more preferably less than 80 parts by mass, and even more preferably less than 40 parts by mass from the viewpoint of processability.

<Other compounding agents>
In addition to the above-mentioned components, the rubber composition according to the present invention may appropriately contain compounding agents generally used in the tire industry, such as wax, processing aids, antioxidants, stearic acid, zinc oxide, vulcanizing agents, and vulcanization accelerators.

(wax)
When the wax is contained, the content thereof per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, and even more preferably 1.5 parts by mass or more, from the viewpoint of weather resistance of the rubber, and is preferably less than 10 parts by mass, more preferably less than 7.0 parts by mass, and even more preferably less than 5.0 parts by mass, from the viewpoint of preventing whitening of the tire due to bloom.

(Processing aids)
Examples of the processing aid include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, mixtures of fatty acid metal salts and fatty acid amides, etc. These processing aids may be used alone or in combination of two or more. Examples of the processing aids that can be used include those commercially available from Schill+Seilacher, Performance Additives, etc.

When a processing aid is contained, the content per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1 part by mass, and even more preferably more than 1.5 parts by mass, from the viewpoint of improving processability. Also, from the viewpoint of abrasion resistance and breaking strength, the content is preferably less than 10 parts by mass, more preferably less than 8.0 parts by mass, and even more preferably less than 5.0 parts by mass.

(Anti-aging agent)
The antiaging agent is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, and carbamic acid metal salts, and among these, preferred are phenylenediamine-based antiaging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based antiaging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These antiaging agents may be used alone or in combination of two or more.

When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 parts by mass, and even more preferably more than 1.5 parts by mass, from the viewpoint of the ozone crack resistance of the rubber. Also, from the viewpoint of abrasion resistance and wet grip performance, the content is preferably less than 10 parts by mass, more preferably less than 7 parts by mass, and even more preferably less than 5 parts by mass.

(stearic acid)
When stearic acid is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less from the viewpoint of vulcanization speed.

(Zinc Oxide)
When zinc oxide is contained, the content per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 parts by mass, and even more preferably more than 1.5 parts by mass from the viewpoint of processability, and is preferably less than 10 parts by mass, more preferably less than 7 parts by mass, and even more preferably less than 5 parts by mass from the viewpoint of abrasion resistance.

(Vulcanizing agent)
As the vulcanizing agent, sulfur is preferably used, and examples of the sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

When sulfur is used as a vulcanizing agent, the content per 100 parts by mass of the rubber component is preferably more than 0.1 parts by mass, more preferably more than 0.3 parts by mass, and even more preferably more than 0.5 parts by mass, from the viewpoint of ensuring a sufficient vulcanization reaction. From the viewpoint of preventing deterioration, the content is preferably less than 5.0 parts by mass, more preferably less than 4.0 parts by mass, and even more preferably less than 3.0 parts by mass. Note that when oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of the pure sulfur contained in the oil-containing sulfur.

Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. These vulcanizing agents other than sulfur can be commercially available from Taoka Chemical Co., Ltd., LANXESS Co., Ltd., Flexis, etc.

(Vulcanization accelerator)
Examples of the vulcanization accelerator include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, or xanthate-based vulcanization accelerators, etc. These vulcanization accelerators may be used alone or in combination of two or more.

Among these, it is preferable that the composition contains one or more vulcanization accelerators selected from the group consisting of sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators, and it is more preferable that the composition contains a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator.

Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS). Of these, N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) is preferred.

Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, etc. Among these, 1,3-diphenylguanidine (DPG) is preferred.

Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, and di-2-benzothiazolyl disulfide. Of these, 2-mercaptobenzothiazole is preferred.

When a vulcanization accelerator is contained, the content per 100 parts by mass of the rubber component is preferably more than 1 part by mass, more preferably more than 1.5 parts by mass, and even more preferably more than 2 parts by mass. The content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably less than 8 parts by mass, more preferably less than 7 parts by mass, and even more preferably less than 6 parts by mass. By keeping the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be ensured.

[Manufacturing]
The rubber composition according to the present invention, i.e., the first rubber composition constituting the first rubber layer and the second rubber composition constituting the second rubber layer, can both be produced by a known method, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or an internal kneader (Banbury mixer, kneader, etc.).

The kneading process includes, for example, a base kneading process in which compounding ingredients and additives other than the vulcanizing agent and vulcanization accelerator are kneaded, and a final kneading (F kneading) process in which the vulcanizing agent and vulcanization accelerator are added to the kneaded product obtained in the base kneading process and kneaded. Furthermore, the base kneading process can be divided into multiple processes as desired.

The kneading conditions are not particularly limited, but for example, in the base kneading process, the mixture is kneaded for 3 to 10 minutes at a discharge temperature of 150 to 170°C, and in the final kneading process, the mixture is kneaded for 1 to 5 minutes at a temperature of 70 to 110°C.

The tire of the present invention can be manufactured by a conventional method using the first and second rubber compositions. That is, the tire of the present invention can be manufactured by extruding the unvulcanized first and second rubber compositions in an extruder equipped with a die of a predetermined shape to match the shapes of the first and second rubber layers, laminating them together with other tire components on a tire building machine, and molding them by a conventional method to form an unvulcanized tire, and then heating and pressurizing the unvulcanized tire in a vulcanizer. The vulcanization conditions are not particularly limited, and examples include a method of vulcanizing at 150 to 200°C for 10 to 30 minutes.

[Application]
The tire of the present invention can be used for any purpose, regardless of whether it is a pneumatic tire or a non-pneumatic tire. It can also be used as a racing tire, a passenger car tire, a large passenger car tire, a large SUV tire, or a motorcycle tire. Among these, a passenger car tire is preferable. Here, a passenger car tire refers to a tire that is intended to be mounted on a four-wheeled automobile and has a maximum load capacity of 1000 kg or less.

The tire of the present invention can also be used as a summer tire, winter tire, or studless tire for each of the above tires.

The present invention will be described based on examples, but the present invention is not limited to only the examples.

The various chemicals used in the examples and comparative examples are listed below.
NR: TSR20
SBR1: Modified S-SBR synthesized in Production Example 1 below (styrene content: 40% by mass, vinyl content: 25% by mole, non-oil extended product)
SBR2: Styrene-butadiene rubber synthesized in Production Example 2 below (modified S-SBR, styrene content: 25% by mass, vinyl content: 25% by mol, non-oil extended product)
BR: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (vinyl content: 1.5 mol%, cis content: 97 mol%, Mw: 440,000)
CB (carbon black): N220 manufactured by Birla Carbon Brasil Ltda ( _N2SA : 115 ^m2 /g, average primary particle size: 22 nm)
Silica: ULTRASIL (registered trademark) VN3 manufactured by Evonik Degussa ( _N2SA : 175 ^m2 /g, average primary particle size: 18 nm)
Coupling agent (silane coupling agent): Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa
Oil: H&R VivaTec 500 (TDAE oil)
Resin: Sylvares SA85 manufactured by Kraton (a copolymer of α-methylstyrene and styrene, softening point: 85° C.)
Antioxidant 1: Antigen 6C (6PPD, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Antioxidant 2: Nocrac RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Wax: Sannock N manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Stearic acid: Beads stearic acid camellia manufactured by NOF Corp. Zinc oxide: Zinc oxide type 2 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder manufactured by Karuizawa Sulfur Co., Ltd. Sulfur vulcanization accelerator 1: Noccela CZ (CBS, N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noccelaer D (DPG, 1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

Production Example 1: Synthesis of SBR1 The ratio of styrene and 1,3-butadiene is adjusted so that the styrene content in the target product is 40% by mass. Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene are charged into a nitrogen-substituted autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium is added to initiate polymerization. Polymerization is performed under adiabatic conditions, and when the polymerization conversion rate reaches 99%, 1,3-butadiene is added and further polymerized, and then N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane is added as a modifier to carry out the reaction. After the polymerization reaction is completed, 2,6-di-tert-butyl-p-cresol is added. Next, the solvent is removed by steam stripping, and the mixture is dried with a heated roll adjusted to 110°C to obtain SBR1.

Production Example 2: Synthesis of SBR2 The ratio of styrene and 1,3-butadiene is adjusted so that the styrene content in the target product is 25% by mass. Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene are charged into a nitrogen-substituted autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium is added to initiate polymerization. Polymerization is carried out under adiabatic conditions, and when the polymerization conversion rate reaches 99%, 1,3-butadiene is added and further polymerized, and then a mixture of 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (monomer) and its oligomer components is added as a modifier to carry out a modification reaction. After the reaction is completed, 2,6-di-tert-butyl-p-cresol is added. Next, the solvent is removed by steam stripping, and the mixture is dried with a heat roll adjusted to 110°C to obtain SBR2.

[Examples and Comparative Examples]
According to the compounding recipe shown in Table 1, chemicals other than sulfur and vulcanization accelerator are kneaded for 1 to 10 minutes using a 1.7 L closed type Banbury mixer until the discharge temperature reaches 150 to 160°C, to obtain a kneaded product. Next, sulfur and vulcanization accelerator are added to the kneaded product obtained using a two-axis open roll, and kneaded for 4 minutes until the temperature reaches 105°C, to obtain an unvulcanized rubber composition. The unvulcanized rubber composition obtained is molded according to the shape of the first and second layers of the tread, and laminated together with other tire components including the belt layer to prepare an unvulcanized tire, which is vulcanized at 170°C to obtain a test tire of tire size A (205/55R16) described in Table 2-1 and a test tire of tire size B (195/65R15) described in Table 2-2.

Regarding the positional relationship between the first belt layer and the second belt layer, the first belt layer is disposed on the radially inner side of the tire, and the second belt layer is disposed on the radially outer side of the first belt layer. However, only in Example 16, the arrangement is reversed. That is, in Example 16, in the tire of Example 8, the first belt layer is disposed on the radially outer side of the tire, and the second belt layer is disposed on the radially inner side of the first belt layer.

Each test tire has four tread patterns. Type I has no widened circumferential grooves, small holes, or narrow circumferential grooves, as shown in Figure 2; Type II has one widened circumferential narrow groove on each of the pair of land portions closest to the tire centerline, as shown in Figure 5, and is otherwise the same as Type I; Type III has small holes on each of the pair of shoulder land portions, as shown in Figure 6, and is otherwise the same as Type I; Type IV has one circumferential narrow groove on each of the pair of shoulder land portions, as shown in Figure 7, and is otherwise the same as Type I.

<Properties of Rubber Layer>
The physical properties of each rubber layer constituting the tire are measured by the following methods. The results are also shown in the corresponding columns of Table 1 for the rubber composition constituting each rubber layer.

(Glass Transition Temperature (Tg) of Rubber Composition)
For each rubber test piece prepared by cutting out from inside a predetermined rubber layer (second rubber layer) in the tread portion of each test tire a length of 20 mm, width of 4 mm, and thickness of 1 mm so that the long side is in the tire circumferential direction and the thickness is in the tire radial direction, a temperature distribution curve of loss tangent tan δ was measured using an Iplexer series manufactured by GABO Corporation under conditions of a frequency of 10 Hz, an initial strain of 10%, an amplitude of ±0.5%, and a heating rate of 2°C/min, and the temperature corresponding to the largest tan δ value in the obtained temperature distribution curve (tan δ peak temperature) was determined as the glass transition temperature (Tg).

<Tire evaluation>
Each test tire is evaluated by the following methods. The results are shown in Tables 2-1 and 2-2.

(High speed WET turning performance)
The obtained test tire A is mounted on a regular rim, inflated with 250 kPa air, and then attached to all wheels of a domestically produced FF vehicle (2000 cc). With the test tire mounted, the vehicle is driven on a wet road surface at a speed of 100 km/h. The cornering performance of the vehicle was evaluated on a scale of 1 to 5, and 20 drivers performed the same evaluation, and the total score of the evaluation results was calculated. The calculation results were indexed with the standard comparative example set at 100, and each Obtain tire evaluation results.
(High-speed wet cornering performance index) = (total score of each evaluated tire) / (total score of reference comparative example) x 100

For test tires of tire size B, evaluation results are obtained in the same manner as for test tires of tire size B, except that the air pressure is set to 230 kPa.

In Tables 2-1 and 2-2 above, "○" means that the given conditions are met, and "×" means that the conditions are not met.

<Embodiment>
The following are preferred embodiments.

[1] A tire having a tread portion and a belt layer,
The tread portion includes at least a first rubber layer that is an outermost layer in the radial direction of the tire, and a second rubber layer that is adjacent to the inner side of the first rubber layer in the radial direction of the tire,
The belt layer includes at least a first belt layer having a widest width in the tire width direction and a second belt layer adjacent to the first belt layer,
A tire in which Tg1, Tg2, Wt, W1 and W2 satisfy the following relationship, where Tg1 is the glass transition temperature (°C) of the first rubber layer, Tg2 is the glass transition temperature (°C) of the second rubber layer, Wt is the tire cross-sectional width (mm) in a cross section passing through the tire rotation axis, Wt is the first belt layer cross-sectional width (mm) in the cross section, and W2 is the second belt layer cross-sectional width (mm) in the cross section, and preferably, at least the right side of formula (1) is −0.5, or the right side of formula (2) is 0.74 or 0.73, or the right side of formula (3) is −9.0 or −10.0.
(1) Tg1-Tg2<0
(2) (W1-16)/Wt≦0.75
(3) Tg2/(W2/W1)≦-8.0
[2] The tire according to the above-mentioned [1], wherein the rubber composition of the second rubber layer contains a filler, and the silica content of the filler is 80 mass% or more, preferably more than 80 mass%, more preferably 90 mass% or more, and even more preferably more than 90 mass%.
[3] The tire according to the above [1] or [2], wherein the right side of formula (1) is −0.9, preferably −1.0, more preferably −1.5, even more preferably −1.9, still more preferably −2.0, and even more preferably −2.5.
[4] The tire according to the above [1] or [2], wherein the right side of formula (1) is −2.9, preferably −3.0.
[5] The tire according to any one of the above [1] to [4], wherein the right side of formula (2) is 0.72, preferably 0.70, more preferably 0.68, and even more preferably 0.65.
[6] The tire according to any one of the above [1] to [5], wherein the right side of formula (3) is −11.0, preferably −12.0, more preferably −13.0, and even more preferably −14.0.
[7] The tire according to any one of the above [1] to [6], wherein Tg1, Tg2, W1, and W2 satisfy the following relationship, and preferably, at least, the right side of formula (4) is 0.98, more preferably 0.96, even more preferably 0.94, even more preferably 0.92, even more preferably 0.90, and even more preferably 0.89; or Tg2 is less than -5.0°C, more preferably less than -7.0°C, and even more preferably less than -9.0°C.
(4) (Tg2/Tg1)/(W2/W1)≦1.00
(However, Tg2 is less than 0.)
[8] The tire according to any one of the above [1] to [7], wherein Tg2 is −10.0 or less, preferably less than −10.0, more preferably −11.0 or less, even more preferably −12.0 or less, and still more preferably −13.0 or less.
[9] The tire according to any one of the above [1] to [8], wherein the total styrene amount (mass%) of the rubber component contained in the rubber composition of the first rubber layer is St1 and the total styrene amount (mass%) of the rubber component contained in the rubber composition of the second rubber layer is St2, and at least one of St1 and St2 or both of St1 and St2 are less than 25.0, preferably less than 21.0, more preferably less than 19.0, even more preferably less than 17.0, even more preferably less than 15.0, and even more preferably less than 13.0.
[10] The tire according to any one of the above [1] to [9], wherein St1 is a total styrene amount (mass%) of a rubber component contained in a rubber composition of the first rubber layer, St2 is a total styrene amount (mass%) of a rubber component contained in a rubber composition of the second rubber layer, H1 is a thickness of the first rubber layer, and H2 is a thickness of the second rubber layer. St1, St2, H1, and H2 satisfy the following relationship, and preferably the right side of formula (5) is 23.0, more preferably 21.0, even more preferably 19.0, even more preferably 17.0, even more preferably 15.0, and even more preferably 13.0.
(5) {St1×H1+St2×H2}/(H1+H2)<25.0
[11] The tire according to any one of the above [1] to [10], wherein at least one of the rubber components contained in the rubber composition of the first rubber layer and the rubber components contained in the rubber composition of the second rubber layer contains an isoprene-based rubber.
[12] A tread surface of the tread portion has a widening circumferential groove extending in the tire circumferential direction and having a groove width widened on the radially inner side of the tire,
The tire according to any one of the above [1] to [11], wherein the widening circumferential groove is at least one selected from the group consisting of a widening circumferential main groove, a widening circumferential narrow groove, and a widening circumferential sipe.
[13] A tread surface of the tread portion has two or more circumferential main grooves extending continuously in the tire circumferential direction and a land portion defined by the circumferential main grooves,
The tire according to any one of the above-mentioned [1] to [11], wherein at least one of the circumferential main grooves is a widening circumferential main groove having a groove width that is wider on the radially inner side of the tire.
[14] A tread surface of the tread portion has two or more circumferential main grooves extending continuously in the tire circumferential direction and a land portion defined by the circumferential main grooves,
At least one of the land portions extends in the tire circumferential direction and has a widened circumferential narrow groove whose groove width is wider on the inner side in the tire radial direction,
The tire according to any one of the above [1] to [11], wherein at least one land portion having the widened circumferential narrow groove is a land portion located on the tire center line, or, if a circumferential main groove is present on the tire center line, is a land portion closest to the tire center line.
[15] The tread surface has two or more circumferential main grooves extending continuously in the tire circumferential direction and a land portion defined by the circumferential main grooves,
The tire according to any one of the above-mentioned [1] to [14], wherein when a pair of land portions on the outermost side in the tire width direction defined by a pair of circumferential main grooves on the outermost side in the tire width direction among the ^two or more circumferential main grooves is defined as a shoulder land portion, the shoulder land portion has one or more small holes having an opening area of more than 0.1 and less than 15 ^mm2 , preferably more than 0.5 and less than ¹⁰ mm2, more preferably more than 1.0 and less than 7.0 ^mm2 , and even more preferably more than 1.5 and less than 5.0 mm2.
[16] The tread surface has two or more circumferential main grooves extending continuously in the tire circumferential direction and a land portion defined by the circumferential main grooves,
The tire according to any one of the above-mentioned [1] to [15], wherein a pair of land portions on the outermost side in the tire width direction defined by a pair of circumferential main grooves on the outermost side in the tire width direction among the two or more circumferential main grooves is defined as a shoulder land portion, and the shoulder land portion has at least one or more circumferential narrow grooves.

Description of the Preferred Embodiments CL: Tire center line Wt: Tire cross-sectional width W1: First belt layer cross-sectional width W2: Second belt layer cross-sectional width H1: Thickness of first rubber layer H2: Thickness of second rubber layer Te: Tread edge C: Tire circumferential direction W: Tire width direction 1: Tire 2: First rubber layer 3: Second rubber layer 4: First belt layer 5: Second belt layer 6: Circumferential main groove 7: Land portion 8: Widened circumferential main groove 9: Widened circumferential narrow groove 10: Small hole 11: Circumferential narrow groove

Claims (16)

A tire having a tread portion and a belt layer,
The tread portion includes at least a first rubber layer that is an outermost layer in the radial direction of the tire, and a second rubber layer that is adjacent to the inner side of the first rubber layer in the radial direction of the tire,
The belt layer includes at least a first belt layer having a widest width in the tire width direction and a second belt layer adjacent to the first belt layer,
A tire in which Tg1, Tg2, Wt, W1 and W2 satisfy the following relationship, where Tg1 is the glass transition temperature (°C) of the first rubber layer, Tg2 is the glass transition temperature (°C) of the second rubber layer, Wt is the tire cross-sectional width (mm) in a cross section passing through the tire rotation axis, W1 is the first belt layer cross-sectional width (mm) in the cross section, and W2 is the second belt layer cross-sectional width (mm) in the cross section.
(1) Tg1-Tg2<0
(2) (W1-16)/Wt≦0.75
(3) Tg2/(W2/W1)≦-8.0 The tire according to claim 1, wherein the rubber composition of the second rubber layer contains a filler, and the silica content of the filler is 80 mass% or more. The tire of claim 1, in which the right-hand side of formula (1) is -1.0. The tire of claim 1, in which the right-hand side of formula (1) is -3.0. The tire of claim 1, wherein the right-hand side of equation (2) is 0.72. The tire of claim 1, in which the right-hand side of formula (3) is -11.0. The tire of claim 1 , wherein Tg1, Tg2, W1 and W2 satisfy the following relationship:
(4) (Tg2/Tg1)/(W2/W1)≦1.00
(However, Tg2 is less than 0.) The tire according to claim 1, in which Tg2 is -10 or less. The tire according to claim 1, wherein the total styrene amount (mass%) of the rubber components contained in the rubber composition of the first rubber layer is St1, and the total styrene amount (mass%) of the rubber components contained in the rubber composition of the second rubber layer is St2, and at least one of St1 and St2 is less than 25.0. 2. The tire according to claim 1, wherein a total styrene amount (mass%) of a rubber component contained in a rubber composition of the first rubber layer is St1, a total styrene amount (mass%) of a rubber component contained in a rubber composition of the second rubber layer is St2, a thickness of the first rubber layer is H1, and a thickness of the second rubber layer is H2, St1, St2, H1, and H2 satisfy the following relationship:
(5) {St1×H1+St2×H2}/(H1+H2)<25.0 The tire according to claim 1, wherein at least one of the rubber components contained in the rubber composition of the first rubber layer and the rubber components contained in the rubber composition of the second rubber layer contains an isoprene-based rubber. A tread surface of the tread portion has a widening circumferential groove extending in a tire circumferential direction and having a groove width widened on the inner side in the tire radial direction,
The tire according to any one of claims 1 to 11, wherein the widening circumferential groove is at least one selected from the group consisting of a widening circumferential main groove, a widening circumferential narrow groove, and a widening circumferential sipe. The tread surface of the tread portion has two or more circumferential main grooves extending continuously in the tire circumferential direction and a land portion defined by the circumferential main grooves,
The tire according to any one of claims 1 to 11, wherein at least one of the circumferential main grooves is a widening circumferential main groove whose groove width is wider on the inner side in the tire radial direction. The tread surface of the tread portion has two or more circumferential main grooves extending continuously in the tire circumferential direction and a land portion defined by the circumferential main grooves,
At least one of the land portions extends in the tire circumferential direction and has a widened circumferential narrow groove whose groove width is wider on the inner side in the tire radial direction,
The tire according to any one of claims 1 to 11, wherein at least one land portion having the widened circumferential narrow groove is a land portion located on a tire center line, or, if a circumferential main groove is present on the tire center line, is a land portion closest to the tire center line. The tread surface has two or more circumferential main grooves extending continuously in the tire circumferential direction and a land portion defined by the circumferential main grooves,
The tire according to any one of claims 1 to 11, wherein a pair of land portions on the outermost side in the tire width direction defined by a pair of circumferential main grooves on the outermost side in the tire width direction among the two or more circumferential main grooves is defined as a shoulder land portion, and the shoulder land portion has one or more small holes having an opening area of more than 0.1 and less than 15 ^mm2 . The tread surface has two or more circumferential main grooves extending continuously in the tire circumferential direction and a land portion defined by the circumferential main grooves,
The tire according to any one of claims 1 to 11, wherein a pair of land portions on the outermost side in the tire width direction defined by a pair of circumferential main grooves on the outermost side in the tire width direction among the two or more circumferential main grooves is defined as a shoulder land portion, and the shoulder land portion has at least one or more circumferential narrow grooves.

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