JP2022086476A - tire - Google Patents

Abstract

To provide a tire improved in overall performance, i.e., low fuel consumption performance, wet grip performance when the tire is new, and wet grip performance after the tire wears.SOLUTION: A tire has a tread having at least a first layer 6 composing a tread surface 3 and a second layer 7 adjacent to a radially inner side of the first layer; wherein the tread has a land portion 2 partitioned by a plurality of circumferential grooves 1 continuously extending in a tire circumferential direction; wherein the first layer and the second layer are composed of a rubber composition containing a rubber component and a plasticizer; and wherein a ratio of a complex elastic modulus at 30°C of the first layer to a complex elastic modulus at 30°C of the second layer is equal to or larger than 0.85, and a ratio of tan δ at 30°C of the first layer to tan δ at 30°C of the second layer is equal to or larger than 1.0.SELECTED DRAWING: Figure 1

Description

The present invention relates to a tire.

In Patent Document 1, the tread portion has a two-layer structure (so-called cap / base structure) of a base rubber located inside the tire radial direction and a cap rubber located outside the tire radial direction, and is in direct contact with the base rubber. It has been described that the application of a small rubber composition of (tan δ) improves the steering stability performance and the fuel efficiency performance of the tire.

Japanese Patent No. 3213127

In the case of the above-mentioned tire, the loss tangent tan δ of the cap rubber layer is high, so that the wet grip performance at the time of new product is high. However, with each run, the cap rubber layer undergoes thermal deterioration due to the effect of self-heating and becomes harder, the groove volume of the groove becomes smaller, the rigidity of the tread contact patch becomes higher, the followability to the road surface is lost, and the wet There is a concern that the grip performance will deteriorate.

An object of the present invention is to provide a tire having improved fuel efficiency, wet grip performance when new, and wet grip performance after wear.

As a result of diligent studies, the present inventor has solved the above-mentioned problems by providing two or more rubber layers in the tread portion and setting the complex elastic modulus E * and the loss tangent tan δ of the rubber layers to a predetermined relationship. We found that and completed the present invention.

That is, the present invention
[1] A tire having a tread having at least a first layer constituting a tread surface and a second layer adjacent to the inner side in the radial direction of the first layer, and the treads are continuous in the tire circumferential direction. It has a land portion partitioned by a plurality of circumferential grooves extending from the tire, and the first layer and the second layer are composed of a rubber composition containing a rubber component and a plasticizer, and the second layer at 30 ° C. The ratio of the complex elastic modulus of the first layer to the complex elastic modulus at 30 ° C. is 0.85 or more, and the ratio of the tan δ of the first layer at 30 ° C. to the tan δ of the second layer at 30 ° C. is 1.0. Tires that are above
[2] The tire according to [1] above, wherein the ratio of tan δ at 30 ° C. of the first layer to tan δ at 30 ° C. of the second layer is 1.2 or more.
[3] The tire according to the above [1] or [2], wherein the ratio of the tan δ of the first layer at 30 ° C. to the tan δ of the second layer at 30 ° C. is 1.4 to 2.0.
[4] The tire according to any one of [1] to [3] above, wherein the content of butadiene rubber in the rubber component constituting the first layer is 35% by mass or less.
[5] Difference between the acetone extraction amount AE ₁ of the rubber composition constituting the first layer and the acetone extraction amount AE ₂ of the rubber composition constituting the second layer | AE ₁ -AE ₂ | is 10% by mass. The tire according to any one of the above [1] to [4], which is as follows.
[6] The tire according to any one of [1] to [5] above, wherein the rubber composition constituting the first layer and the rubber composition constituting the second layer each contain a resin component.
[7] Any one of the above [1] to [6], wherein at least one of the rubber composition constituting the first layer and the rubber composition constituting the second layer contains an aromatic petroleum resin. Tires listed in,
[8] The content of the resin component with respect to 100 parts by mass of the rubber component of the rubber composition constituting the first layer, and the content of the resin component with respect to 100 parts by mass of the rubber component of the rubber composition constituting the second layer. The tire according to any one of [1] to [7] above, wherein the ratio is 2.4 or less.
[9] The tire according to any one of [1] to [8] above, which comprises a third layer adjacent to the inside of the second layer in the radial direction.
[10] The tire according to any one of [1] to [9] above, wherein the ratio of the thickness of the first layer to the total thickness of the first layer and the second layer is 0.40 or more.
[11] The tire according to any one of [1] to [10] above, wherein the complex elastic modulus of the second layer at 30 ° C. is 5 MPa or more.
[12] The tire according to any one of [1] to [11] above, wherein the tan δ of the second layer at 30 ° C. is 0.30 or less.
[13] The tire according to any one of [1] to [12] above, wherein the glass transition temperature of the first layer is −15 ° C. or higher.
[14] The shore hardness (Hs) of the second layer is 50 to 80 as measured at a temperature of 23 ° C. using a durometer type A in accordance with JIS K 6253-3: 2012. The tire according to any one of [13].
[15] The tire according to any one of [1] to [14] above, wherein the modulus of the first layer at 100% stretching is larger than that of the second layer at 100% stretching.
[16] The deepest portion of the groove bottom of any one of the circumferential grooves is formed so as to be located inside the tire radial direction with respect to the outermost portion of the second layer in the land portion adjacent to the circumferential groove. The tire according to any one of the above [1] to [15].
[17] The tire according to any one of [1] to [16] above, wherein the land portion has sipes having both ends not opened in the circumferential groove.
[18] The tire according to any one of [1] to [17] above, which has a portion where the length in the width direction of the land portion closest to the equatorial plane of the tire increases from the outside to the inside in the radial direction of the tire. Regarding.

According to the present invention, there is provided a tire having improved fuel efficiency, wet grip performance when new, and wet grip performance after wear.

It is an enlarged sectional view which showed a part of the tread of the tire which concerns on one Embodiment of this disclosure. It is an enlarged sectional view which showed a part of the tread of the tire which concerns on one Embodiment of this disclosure. It is an enlarged sectional view which showed a part of the tread of the tire which concerns on one Embodiment of this disclosure. It is an enlarged sectional view which showed a part of the tread of the tire which concerns on one Embodiment of this disclosure. It is an enlarged sectional view which showed a part of the tread of the tire which concerns on one Embodiment of this disclosure. It is an enlarged sectional view which showed a part of the tread of the tire which concerns on one Embodiment of this disclosure. It is a schematic diagram of the contact patch of a tire when the tread is pressed against a flat surface. It is a schematic diagram of the contact patch of a tire when the tread is pressed against a flat surface.

A tire according to an embodiment of the present disclosure is a tire having a tread having at least a first layer constituting a tread surface and a second layer adjacent to the inner side in the radial direction of the first layer, and the tread. The tire has a land portion partitioned by a plurality of circumferential grooves continuously extending in the circumferential direction of the tire, and the first layer and the second layer are composed of a rubber composition containing a rubber component and a plasticizing agent. The ratio of the complex elastic modulus of the first layer at 30 ° C. to the complex elastic modulus of the second layer at 30 ° C. is 0.85 or more, and the ratio of the first layer to tan δ at 30 ° C. of the second layer is 30 ° C. The tire has a tan δ ratio of 1.0 or more (preferably 1.2 or more, more preferably 1.4 to 2.0).

Although not intended to be bound by theory, in the present disclosure, the following can be considered as a mechanism capable of suppressing a decrease in wet grip performance after tire wear.

In the tread of the present disclosure, when the ratio of the complex elastic modulus of the first layer at 30 ° C. to the complex elastic modulus of the first layer at 30 ° C. is 0.85 or more and less than 1.00, the first layer is soft when new. Indicates that it is. At this time, at the time of braking, the first layer easily follows the road surface and the amount of deformation is large, and the tan δ at 30 ° C. is also larger than that of the second layer. The motility inside the first layer is increased, and the plasticizer is easily transferred from the first layer to the second layer. As a result, when the second layer is exposed, the second layer is also in a soft state, so that good followability can be obtained even if the tread capacity is reduced, and good wet grip even when worn. Performance is expected to be obtained.

When the ratio of the complex elastic modulus of the first layer at 30 ° C to the complex elastic modulus of the second layer at 30 ° C is 1.00 or more, the entire land area moves so as to be centered on the second layer during braking. It is considered that wet grip performance can be obtained by generating heat from the first layer to the road surface. Further, when the second layer is exposed, the second layer is in a soft state, so that good followability can be obtained even if the tread volume is reduced, and good wet grip performance is obtained even when worn. It is thought that it will be obtained.

On the other hand, if the ratio of the complex elastic modulus of the first layer at 30 ° C. to the complex elastic modulus of the second layer at 30 ° C. is less than 0.85, the first layer becomes too soft with respect to the second layer. In the land area, the amount of deformation of the first layer becomes too large, causing chunking from the part that cannot withstand the deformation, and the contact area decreases early when new, and good wet grip performance cannot be obtained. Conceivable. In addition, since the transfer of the plasticizer into the second layer is not sufficient, it is considered that the wet grip performance at the time of wear is not sufficient.

In the tire of the present disclosure, the deepest portion of the groove bottom of any one of the circumferential grooves is located inside the tire radial direction with respect to the outermost portion of the second layer in the land portion adjacent to the circumferential groove. It is preferably formed.

The land portion preferably has sipes at both ends that do not open into the circumferential groove.

The tire of the present disclosure preferably has a portion where the widthwise length of the land portion closest to the tire equatorial plane increases from the outside to the inside in the tire radial direction.

A tire according to an embodiment of the present disclosure will be described in detail below. However, the following description is an example for explaining the present disclosure, and is not intended to limit the technical scope of the present invention to this description range only. In this specification, when a numerical range is indicated by using "-", the numerical values at both ends thereof are included.

1 to 6 are enlarged cross-sectional views showing a part of a tire tread. In FIGS. 1 to 6, the vertical direction is the tire radial direction, the left-right direction is the tire width direction, and the direction perpendicular to the paper surface is the tire circumferential direction.

As shown, the tread portion of the tire of the present disclosure may include a first rubber layer 6 and a second rubber layer 7 and may have a third rubber layer 8 (hereinafter, simply "first". Layer 6 ”,“ second layer 7 ”,“ third layer 8 ”), the outer surface of the first layer 6 constitutes the tread surface 3, and the second layer 7 is the radius of the first layer 6. Adjacent to the inside of the direction, the third layer 8 is adjacent to the inside of the second layer 7 in the radial direction. The first layer 6 typically corresponds to a cap tread. The third layer 8 typically corresponds to a base tread or under tread. Since the typical shape of the second layer 7 has not been determined, the second layer 7 may be a base tread or an under tread. Further, as long as the object of the present disclosure is achieved, one or more rubber layers may be further provided between the third layer 8 and the belt layer. In FIGS. 1, 2, 3, and 6, the tread is composed of the first layer 6, the second layer 7, and the third layer 8, and in FIGS. 4 and 5, the tread is the first layer 6. And the second layer 7.

In FIGS. 1 to 6, double-headed arrow t1 is the maximum thickness of the first layer 6, double-headed arrow t2 is the maximum thickness of the second layer 7, and double-headed arrow t3 is the maximum thickness of the third layer 8. In FIGS. 1 to 6, any point on the tread surface in which the groove is not formed is indicated by the symbol P. The straight line represented by the symbol N is a straight line (normal line) that passes through the point P and is perpendicular to the tangent plane at this point P. As used herein, the thicknesses t1, t2 and t3 are measured along a normal line N drawn from a point P on the tread surface at a position where no groove is present in the cross sections of FIGS. 1-6.

In the present disclosure, the maximum thickness t1 of the first layer 6 is not particularly limited, but from the viewpoint of wet grip performance, 1.0 mm or more is preferable, 1.5 mm or more is more preferable, and 2.0 mm or more is further preferable. On the other hand, from the viewpoint of heat generation, the maximum thickness t1 of the first layer 6 is preferably 7.0 mm or less, more preferably 6.5 mm or less, still more preferably 6.0 mm or less.

In the present disclosure, the maximum thickness t2 of the second layer 7 is not particularly limited, but is preferably 1.0 mm or more, and more preferably 1.5 mm or more. The maximum thickness t2 of the second layer 7 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

In the present disclosure, the maximum thickness t3 of the third layer 8 is not particularly limited, but is preferably 1.0 mm or more, more preferably 1.5 mm or more, still more preferably 2.0 mm or more. The maximum thickness t3 of the third layer 8 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

The ratio of the thickness of the second layer 7 to the total thickness of the first layer 6 and the second layer 7 (t2 / (t1 + t2) is preferably 0.30 or more, preferably 0.40 or more, from the viewpoint of the effect of the present disclosure. Is more preferable, and 0.45 or more is further preferable.

The tread of the present disclosure has a land portion 2 partitioned by a circumferential groove 1 in the tire width direction.

The groove depth H1 of the circumferential groove 1 is obtained by the distance between the extension line 4 of the land portion 2 and the extension line 5 of the deepest portion of the groove bottom of the circumferential groove 1. The groove depth H1 is, for example, when there are a plurality of circumferential grooves 1, the extension line 4 of the land portion 2 and the groove bottom of the circumferential groove 1 having the deepest groove depth among the plurality of circumferential grooves 1. It can be the distance from the extension line 5 of the deepest part of.

In FIGS. 1 and 2, the deepest portion of the groove bottom of the circumferential groove 1 having the deepest groove depth among the plurality of circumferential grooves 1 is the third layer 8 in the land portion 2 adjacent to the circumferential groove. It is formed so as to be located inside the tire radial direction from the outermost part of the tire. That is, the extension line 5 of the deepest portion of the groove bottom of the circumferential groove 1 having the deepest groove depth among the plurality of circumferential grooves 1 is the third layer 8 in the land portion 2 adjacent to the circumferential groove. It is located inside the tire radial direction from the outermost extension line 10. Immediately below the circumferential groove 1 having the deepest groove depth among the plurality of circumferential grooves 1 (inside in the radial direction of the tire), with respect to the outermost side of the third layer 8 in the land portion 2 adjacent to the circumferential groove. It has a recessed portion inward in the radial direction of the tire, and a part of the first layer 6 and the second layer 7 is formed in the recessed portion of the third layer 8 with a predetermined thickness.

In FIGS. 3 to 6, the deepest portion of the groove bottom of the circumferential groove 1 having the deepest groove depth among the plurality of circumferential grooves 1 is the second layer 7 in the land portion 2 adjacent to the circumferential groove. It is formed so as to be located inside the tire radial direction from the outermost part of the tire. That is, the extension line 5 of the deepest portion of the groove bottom of the circumferential groove 1 having the deepest groove depth among the plurality of circumferential grooves 1 is the second layer 7 in the land portion 2 adjacent to the circumferential groove. It is located inside the tire radial direction from the outermost extension line 9. Immediately below the circumferential groove 1 having the deepest groove depth among the plurality of circumferential grooves 1 (inside in the radial direction of the tire), with respect to the outermost side of the second layer 7 in the land portion 2 adjacent to the circumferential groove. It has a recessed portion inward in the radial direction of the tire, and a part of the first layer 6 is formed in the recessed portion of the second layer 7 with a predetermined thickness.

By forming the first layer 6, the second layer 7, and the third layer 8 as described above, the complex elastic modulus of the first layer 6 remaining around the circumferential groove 1 after the tire wear is the second layer 7. Since it is higher than the complex elastic modulus, it becomes easier to function as an edge when turning, and it is considered that snow traction and the like are improved.

As shown in FIGS. 1 to 4, the tire of the present disclosure preferably has a portion where the widthwise length of at least one land portion 2 increases from the outside to the inside in the radial direction of the tire. It is more preferable that the length of the land portion 2 in the width direction gradually increases from the outside to the inside in the radial direction of the tire. With such an aspect, the contact area can be widened along with the wear due to running, so that the wet grip performance can be maintained until the end of running. The groove wall of the circumferential groove 1 of the present disclosure extends linearly from the outside in the radial direction of the tire toward the inside, but the present invention is not limited to such an embodiment, and is not limited to such an embodiment, for example, a curved shape or a stepped shape. May extend to.

As shown in FIG. 1, in the tire of the present disclosure, at least one of the land portions 2 is formed asymmetrically with respect to the normal line N passing through the center in the tire width direction in the tire meridian cross section including the tire rotation axis. It may have the third layer 8. By forming the third layer 8 asymmetrically, the hardness distribution in the land portion is biased, which affects the ground contact pressure. In the portion where the contact pressure is high, there is a place where the water film touches the ground without riding on it, and the wet grip performance is improved. Therefore, the difference between the wet grip performance when the product is new and when it is worn can be reduced. The land portion 2 having such asymmetrical third layer 8 may be the land portion 2 located on the outside of the vehicle when the tire equator is mounted on the vehicle, and may be mounted on the vehicle on the tire equator. Sometimes it may be the land portion 2 located inside the vehicle. Further, the land portion 2 having the asymmetrical third layer 8 may be a land portion sandwiched between a plurality of circumferential grooves 1, and may be a shoulder land portion sandwiched between the circumferential groove 1 and the tread ground contact end. Although it may be present, it is preferably a land portion sandwiched between a plurality of circumferential grooves 1.

7 and 8 show a schematic view of the ground plane when the tread is pressed against a flat surface. As shown in FIGS. 7 and 8, the tread 10 constituting the tire according to the present disclosure includes a circumferential groove 1 continuously extending in the tire circumferential direction C, a lateral groove 21 extending in the width direction, and sipes 22 and 23. Have.

The tread has a plurality of circumferential grooves 1 continuously extending in the circumferential direction C. In FIGS. 7 and 8, three circumferential grooves 1 are provided, but the number of circumferential grooves is not particularly limited, and may be, for example, two to five. Further, in the present disclosure, the circumferential groove 1 extends linearly along the circumferential direction C, but is not limited to such an embodiment, and is not limited to such an aspect. For example, the circumferential groove 1 has a wavy shape or a sinusoidal shape along the circumferential direction C. Or may extend in a zigzag shape.

The tread has a land portion 2 partitioned by a plurality of circumferential grooves 1 in the tire width direction W. The shoulder land portion 11 is a pair of land portions formed between the circumferential groove 1 and the tread end Te. The center land portion 12 is a land portion formed between a pair of shoulder land portions 11. In FIGS. 7 and 8, two center land portions 12 are provided, but the number of center land portions is not particularly limited, and may be, for example, one to five.

It is preferable that the land portion 2 is provided with a lateral groove and / or a sipe that crosses the land portion 2. Further, it is more preferable that the land portion 2 has sipes whose ends are not opened in the circumferential groove 1. In FIG. 1, the shoulder land portion 11 is provided with a plurality of shoulder lateral grooves 21 whose ends are open in the circumferential groove 1 and a plurality of shoulder sipes 22 whose one end is open in the circumferential groove 1. The center land portion 12 is provided with a plurality of center sipes 23 having one end open in the circumferential groove 1. In FIG. 2, the shoulder land portion 11 is provided with a plurality of shoulder lateral grooves 21 whose ends are open to the circumferential groove 1 and a plurality of shoulder sipes 22 whose ends are not open to the circumferential groove 1. The center land portion 12 is provided with a plurality of center sipes 23 having one end open in the circumferential groove 1.

In the present specification, the "groove" including the circumferential groove and the lateral groove means a dent having a width larger than at least 2.0 mm. On the other hand, in the present specification, "sipe" refers to a narrow notch having a width of 2.0 mm or less, preferably 0.5 to 2.0 mm.

In the present disclosure, unless otherwise specified, the dimensions of each member of a tire are measured with the tire incorporated into a regular rim and the tire filled with air to provide regular internal pressure. At the time of measurement, no load is applied to the tire.

A "regular rim" is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, "Measuring Rim". In the case of a tire of a size not specified in the above standard system, the narrowest rim can be assembled to the tire and has the smallest diameter that does not cause air leakage between the rim and the tire. Shall point to.

"Regular internal pressure" is the air pressure defined for each tire in the standard system including the standard on which the tire is based. For JATTA, "maximum air pressure", for TRA, the table "TIRE LOAD LIMITS AT" The maximum value described in "VARIOUS COLD INFLATION PRESSURES", or "INFLATION PRESSURE" for ETRTO. In the case of a tire of a size not specified in the above standard system, the normal internal pressure is 250 kPa.

"30 ° C.E *" in the present disclosure refers to a complex elastic modulus E * under the conditions of a temperature of 30 ° C., an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10 Hz. The 30 ° C.E * of the first layer 6 is preferably 7 MPa or more, more preferably 8 MPa or more, further preferably 9 MPa or more, and particularly preferably 10 MPa or more, from the viewpoint of steering stability performance. The 30 ° C.E * of the second layer 7 is preferably 4 MPa or more, more preferably 5 MPa or more, still more preferably 6 MPa or more, from the viewpoint of steering stability performance. The 30 ° C. E * of the third layer 8 is preferably 4 MPa or more, more preferably 5 MPa or more, and even more preferably 6 MPa or more. On the other hand, the 0 ° C.E * of the first layer 6, the second layer 7, and the third layer 8 is preferably 25 MPa or less, more preferably 20 MPa or less, still more preferably 18 MPa or less, from the viewpoint of wet grip performance. In the present disclosure, the ratio of 30 ° C.E * of the first layer 6 to 30 ° C.E * of the second layer 7 is 0.85 or more, preferably 1.0 or more, more preferably 1.1 or more. 2 or more is more preferable, 1.3 or more is further preferable, and 1.4 or more is particularly preferable. When the ratio of 30E * of the first layer 6 to 30 ° CE * of the second layer 7 is 0.85 or more and less than 1.00, good wet grip performance can be obtained at the time of new product, and at the same time, the inside of the first layer 6 is obtained. The motility of the plasticizer is increased, and the plasticizer is easily transferred from the first layer 6 to the second layer 7. As a result, when the second layer 7 is exposed, the second layer 7 is also in a soft state, so that good followability can be obtained even if the tread capacity is reduced, and it is also good at the time of wear. Wet grip performance is considered to be obtained. When the ratio of the complex elastic modulus of the first layer 6 at 30 ° C to the complex elastic modulus of the second layer 7 at 30 ° C is 1.00 or more, the entire land area is formed around the second layer 7 at the time of braking. It is considered that the wet grip performance can be obtained by generating heat from the first layer 6 to the road surface while moving to. Further, when the second layer 7 is exposed, the second layer 7 is in a soft state, so that good followability can be obtained even if the tread volume is reduced, and a good wet grip even when worn. Performance is expected to be obtained. The upper limit of the ratio of 30 ° C.E * of the first layer 6 to 30 ° C.E * of the second layer 7 is not particularly limited, but is preferably 3.0 or less, more preferably 2.5 or less, and 2.2 or less. Is more preferable, and 2.0 or less is particularly preferable. The 30 ° C.E * of each rubber layer can be appropriately adjusted depending on the type and blending amount of the rubber component, filler, plasticizer and the like (particularly the plasticizer) described later.

The “30 ° C. tan δ” in the present disclosure refers to a loss tangent tan δ under the conditions of a temperature of 30 ° C., an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10 Hz. From the viewpoint of wet grip performance, the 30 ° C. tan δ of the first layer 6 is preferably 0.18 or more, more preferably 0.20 or more, further preferably 0.22 or more, and particularly preferably 0.24 or more. The 30 ° C. tan δ of the second layer 7 is preferably 0.10 or more, more preferably 0.12 or more, and even more preferably 0.14 or more. The 30 ° C. tan δ of the third layer 8 is preferably 0.10 or more, more preferably 0.12 or more, and even more preferably 0.14 or more. On the other hand, the 30 ° C. tan δ of the rubber composition constituting the first layer 6, the second layer 7, and the third layer 8 is preferably 0.40 or less, more preferably 0.35 or less, from the viewpoint of fuel efficiency. , 0.30 or less is more preferable. In the present disclosure, the ratio of 30 ° C. tan δ of the first layer 6 to 30 ° C. tan δ of the second layer 7 is 1.0 or more, preferably 1.1 or more, more preferably 1.2 or more, and 1.3 or more. Is more preferable, and 1.4 or more is particularly preferable. When the ratio of the 30 ° C. tan δ of the first layer 6 to the 30 ° C. tan δ of the second layer 7 is 1.0 or more, the heat generated in the first layer becomes large during running, and good wet grip performance can be obtained. At the same time, when the complex elastic modulus E * of the first layer is smaller than the complex elastic modulus E * of the second layer, the motility inside the first layer is enhanced and the effect of transferring the plasticizer to the second layer is obtained. It is thought that it will be possible. The upper limit of the ratio of 30 ° C. tan δ of the first layer 6 to 30 ° C. tan δ of the second layer 7 is not particularly limited, but is preferably 2.5 or less, more preferably 2.2 or less, and 2.0 or less. More preferably, 1.8 or less is particularly preferable. The 30 ° C. tan δ of each rubber layer can be appropriately adjusted depending on the type and blending amount of the rubber component, filler, plasticizer and the like (particularly the plasticizer) described later.

The amount of acetone extracted in the present disclosure is an index of the concentration of the organic low molecular weight compound in the plasticizer contained in the vulcanized rubber composition. The amount of acetone extracted is determined by immersing each vulcanized rubber test piece in acetone for 24 hours to extract soluble components in accordance with JIS K 6229-3: 2015, and measuring the mass of each test piece before and after extraction. It can be calculated by an equation.
Acetone extraction amount (%) = {(mass of rubber test piece before extraction-mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} × 100

Difference between the acetone extraction amount AE ₁ of the rubber composition constituting the first layer 6 and the acetone extraction amount AE ₂ of the rubber composition constituting the second layer 7 | AE ₁ -AE ₂ | is 10% by mass or less. It is preferably 8% by mass or less, more preferably 6% by mass or less, and particularly preferably 4% by mass or less. By setting the difference in the amount of acetone extraction within the above range, the transfer of the acetone extraction component from the second layer 7 to the first layer 6 is suppressed during running, so that the hardness of the tread rubber is maintained even after wear. , It is thought that it will be possible to maintain wet grip performance for a long period of time. It should be noted that either value of AE ₁ and AE ₂ may be large as long as the difference is within the above range. The values of AE ₁ and AE ₂ are not particularly limited, but are preferably 1 to 40% by mass, more preferably 5 to 30% by mass, respectively.

The glass transition temperature (Tg) in the present disclosure refers to the tan δ peak temperature measured by the following method. That is, the elastic test piece (for example, length 20 mm × width 4 mm × thickness 1 mm) produced by cutting out from the inside of the rubber layer of the tread portion of each test tire so that the tire circumferential direction is the long side is dynamically. Using a viscoelasticity evaluation device (for example, Iplexer series manufactured by GABO), the temperature distribution curve of tan δ was measured under the conditions of initial strain of 10%, kinetic strain of 1%, and frequency of 10 Hz, and the obtained temperature distribution curve was obtained. The temperature corresponding to the largest tan δ value in tan δ (tan δ peak temperature) is defined as the glass transition temperature (Tg) in the present disclosure. The Tg of the first layer 6 is preferably −15 ° C. or higher, more preferably −13 ° C. or higher, from the viewpoint of wet grip performance. -11 ° C or higher is more preferable. Further, the Tg of the second layer 7 is preferably −20 ° C. or higher, more preferably −15 ° C. or higher, still more preferably −12 ° C. or higher, from the viewpoint of wet grip performance. The upper limit of Tg of the first layer 6 and the second layer 7 is not particularly limited, but is preferably 20 ° C. or lower, more preferably 15 ° C. or lower, still more preferably 10 ° C. or lower. The Tg of each rubber layer can be appropriately adjusted depending on the type and blending amount of the rubber component and the like.

The rubber hardness in the present disclosure refers to the shore hardness (Hs) measured at a temperature of 23 ° C. using a durometer type A in accordance with JIS K 6253-3: 2012. The shore hardness (Hs) of the first layer 6 is preferably 80 or less, more preferably 75 or less, and even more preferably 70 or less. The shore hardness (Hs) of the second layer 7 is preferably 80 or less, more preferably 75 or less, and even more preferably 70 or less. By setting the shore hardness (Hs) of the first layer 6 and the second layer 7 within the above range, the followability to the road surface is not impaired and the reaction force can be easily obtained, so that the wet grip performance at the time of a new product is improved. Moreover, since sufficient followability can be easily obtained even after wear, it is considered that deterioration of wet grip performance after tire wear can be suppressed. On the other hand, the shore hardness (Hs) of the first layer 6 and the second layer 7 is preferably 50 or more, and more preferably 55 or more, from the viewpoint of maintaining the block rigidity of the tire. The rubber hardness of each rubber layer can be appropriately adjusted depending on the type and amount of the rubber component, filler, plasticizer, etc. described later.

The modulus at 100% stretching in the present disclosure is measured in the columnar direction (extruded or sheared) under the condition of a tensile speed of 3.3 mm / sec in an atmosphere of 23 ° C. according to JIS K 6251: 2017. It refers to the tensile stress at 100% elongation in the rolling direction when forming the rubber sheet). The modulus of the first layer 6 at 100% stretching is preferably 1.0 MPa or more, more preferably 1.2 MPa or more, further preferably 1.4 MPa or more, and particularly preferably 1.6 MPa or more. The modulus of the second layer 7 when stretched at 100% is preferably 1.0 MPa or more, more preferably 1.2 MPa or more, further preferably 1.4 MPa or more, and particularly preferably 1.6 MPa or more. The upper limit of the modulus of the first layer 6 and the second layer 7 at the time of 100% stretching is not particularly limited, but is usually 4.0 MPa or less, preferably 3.5 MPa or less. In the present disclosure, it is preferable that the modulus of the first layer 6 at 100% stretching is larger than that of the second layer 7 at 100% stretching. The difference between the 100% stretched modulus of the second layer 7 and the 100% stretched modulus of the first layer 6 is preferably 0.1 MPa or more, more preferably 0.2 MPa or more, and further preferably 0.3 MPa or more. preferable. The modulus of each rubber layer at the time of 100% stretching can be appropriately adjusted depending on the type and blending amount of the rubber component, filler, plasticizer and the like described later.

[Rubber composition]
In the tire of the present disclosure, the structure of the tire described above, particularly the shape of the tread, and the physical properties of the rubber composition constituting each layer of the tread cooperate with each other to further reduce the wet grip performance after tire wear. It can be effectively suppressed.

<Rubber component>
The rubber composition according to the present disclosure preferably contains at least one selected from the group consisting of isoprene-based rubber, styrene-butadiene rubber (SBR) and butadiene rubber (BR) as a rubber component. The rubber component constituting the first layer 6 and the second layer 7 preferably contains SBR, more preferably contains SBR and BR, and may be a rubber component composed of only SBR and BR. The rubber component constituting the third layer 8 preferably contains isoprene-based rubber, more preferably contains isoprene-based rubber and BR, and may be a rubber component composed of only isoprene-based rubber and BR.

(Isoprene rubber)
As the isoprene-based rubber, for example, isoprene rubber (IR), natural rubber, and other rubbers commonly used in the tire industry can be used. Natural rubber includes non-modified natural rubber (NR), epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. Also included are modified natural rubber and the like. These isoprene-based rubbers may be used alone or in combination of two or more.

The NR is not particularly limited, and a tire that is common in the tire industry can be used, and examples thereof include SIR20, RSS # 3, and TSR20.

When the rubber components constituting the first layer 6 and the second layer 7 contain isoprene-based rubber (preferably natural rubber, more preferably non-modified natural rubber (NR)), the content in the rubber component is From the viewpoint of wet grip performance, 50% by mass or less is preferable, 40% by mass or less is more preferable, 30% by mass or less is further preferable, and 20% by mass or less is particularly preferable. On the other hand, the lower limit of the content of the isoprene-based rubber in the rubber component is not particularly limited, but is, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, and 15% by mass or more. Can be done.

When the rubber component constituting the third layer 8 contains isoprene-based rubber (preferably natural rubber, more preferably non-modified natural rubber (NR)), the content in the rubber component is 20% by mass or more. Is preferable, 30% by mass or more is more preferable, and 40% by mass or more is further preferable. Further, the upper limit of the content of the isoprene-based rubber in the rubber component is not particularly limited and may be 100% by mass.

(SBR)
The SBR is not particularly limited, and examples thereof include solution polymerization SBR (S-SBR), emulsion polymerization SBR (E-SBR), and modified SBR (modified S-SBR, modified E-SBR) thereof. Examples of the modified SBR include modified SBRs (condensates, those having a branched structure, etc.) coupled with SBRs having modified terminals and / or backbones, tin, silicon compounds, and the like. Of these, S-SBR and modified SBR are preferable. Further, hydrogenated additives of these SBRs (hydrogenated SBR) and the like can also be used. These SBRs may be used alone or in combination of two or more.

Examples of the S-SBR that can be used in the present disclosure include S-SBR manufactured and sold by JSR Co., Ltd., Sumitomo Chemical Co., Ltd., Ube Kosan Co., Ltd., Asahi Kasei Co., Ltd., ZS Elastomer Co., Ltd., and the like. ..

The styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 20% by mass or more, from the viewpoint of wet grip performance and wear resistance performance. Further, from the viewpoint of temperature dependence of grip performance and blow resistance, 60% by mass or less is preferable, 55% by mass or less is more preferable, and 50% by mass or less is further preferable. In this specification, the styrene content of SBR is calculated by ¹ H-NMR measurement.

The vinyl content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and further 20 mol% or more from the viewpoint of ensuring reactivity with silica, wet grip performance, rubber strength, and wear resistance. preferable. The vinyl content of SBR is preferably 70 mol% or less, more preferably 65 mol% or less, still more preferably 60 mol% or less, from the viewpoints of preventing increase in temperature dependence, elongation at break, and wear resistance. In the present specification, the vinyl content (1,2-bonded butadiene unit amount) of SBR is measured by infrared absorption spectrum analysis.

The weight average molecular weight (Mw) of SBR is preferably 200,000 or more, more preferably 250,000 or more, still more preferably 300,000 or more, from the viewpoint of wet grip performance. Further, from the viewpoint of cross-linking uniformity, the weight average molecular weight is preferably 2 million or less, more preferably 1.8 million or less, still more preferably 1.5 million or less. In the present specification, the weight average molecular weight of SBR is defined by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: manufactured by Tosoh Corporation. It can be obtained by standard polystyrene conversion based on the measured value by TSKGEL SUPERMALTIPORE HZ-M).

In the rubber components constituting the first layer 6 and the second layer 7, the content in the rubber component when SBR is contained is preferably 50% by mass or more, more preferably 60% by mass or more from the viewpoint of wet grip performance. It is preferable, 65% by mass or more is more preferable, and 70% by mass or more is particularly preferable. 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. In the rubber component constituting the third layer 8, the content in the rubber component when SBR is contained is not particularly limited.

(BR)
The BR is not particularly limited, and is synthesized by using, for example, BR (low cis BR) having a cis content of less than 50% by mass, BR (high cis BR) having a cis content of 90% by mass or more, and a rare earth element-based catalyst. Rare earth-based butadiene rubber (rare earth-based BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (Hisys-modified BR, Locis-modified BR), etc., which are common in the tire industry can be used. can. Examples of the modified BR include BRs modified with a functional group or the like similar to those described in the above SBR. These BRs may be used alone or in combination of two or more.

As the high cis BR, for example, those commercially available from Nippon Zeon Corporation, Ube Kosan Co., Ltd., JSR Corporation and the like can be used. By containing HISIS BR, low temperature characteristics and wear resistance can be improved. The cis content is preferably 95% by mass or more, more preferably 96% by mass or more, still more preferably 97% by mass or more, and particularly preferably 98% by mass or more. In the present specification, the cis content (cis-1,4-bonded butadiene unit amount) is a value calculated by infrared absorption spectrum analysis.

The rare earth element BR is synthesized by using a rare earth element catalyst, and has a vinyl content of preferably 1.8 mol% or less, more preferably 1.0 mol% or less, still more preferably 0.8% mol or less. The cis content is preferably 95% by mass or more, more preferably 96% by mass or more, still more preferably 97% by mass or more, and particularly preferably 98% by mass or more. As the rare earth BR, for example, one commercially available from LANXESS Co., Ltd. or the like can be used.

Examples of the SPB-containing BR include those in which 1,2-syndiotactic polybutadiene crystals are not simply dispersed in BR, but are dispersed after being chemically bonded to BR. As such an SPB-containing BR, one commercially available from Ube Kosan Co., Ltd. or the like can be used.

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

Other modified BRs are obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and further, the end of the modified BR molecule is bonded by a tin-carbon bond. (Tin-modified BR) and the like. Further, 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.

The weight average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, still more preferably 400,000 or more, from the viewpoint of wear resistance performance. Further, from the viewpoint of cross-linking uniformity and the like, 2 million or less is preferable, and 1 million or less is more preferable. Mw is measured 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). It can be obtained by standard polystyrene conversion based on the value.

In the rubber components constituting the first layer 6 and the second layer 7, the content in the rubber component when BR is contained is preferably 50% by mass or less, more preferably 40% by mass or less from the viewpoint of wet grip performance. It is preferable, 30% by mass or less is more preferable, and 20% by mass or less is particularly preferable. On the other hand, the lower limit of the content of BR in the rubber component is not particularly limited, but may be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, and 15% by mass or more. ..

In the rubber component constituting the third layer 8, when BR is contained, the content in the rubber component is preferably 80% by mass or less, more preferably 70% by mass or less, further preferably 65% by mass or less, and further preferably 60% by mass. % Or less is particularly preferable. On the other hand, the lower limit of the content of BR in the rubber component is not particularly limited, but may be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, and 15% by mass or more. ..

(Other rubber components)
As the rubber component according to the present disclosure, a rubber component other than the above-mentioned isoprene-based rubber, SBR, and BR may be contained. As another rubber component, a crosslinkable rubber component generally used in the tire industry can be used, for example, a styrene-isoprene-butadiene copolymer rubber (SIBR), a styrene-isobutylene-styrene block copolymer ( SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydride nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, polyethylene chloride rubber, fluororubber (FKM) , Acrylic rubber (ACM), hydrin rubber and the like. These other rubber components may be used alone or in combination of two or more.

<Filler>
As the rubber composition according to the present disclosure, a filler containing carbon black and / or silica is preferably used. The rubber composition constituting the first layer 6 and the second layer 7 more preferably contains silica as a filler, more preferably contains carbon black and silica, and may be a filler composed of only carbon black and silica. The rubber composition constituting the third layer 8 preferably contains carbon black as a filler, and may be a filler composed of only carbon black.

(Carbon black)
As the carbon black, those commonly used in the tire industry can be appropriately used, and examples thereof include GPF, FEF, HAF, ISAF, and SAF. These carbon blacks may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 10 m ² / g or more, more preferably 30 m ² / g or more, still more preferably 50 m ² / g or more, from the viewpoint of reinforcing property. Further, from the viewpoint of fuel efficiency and workability, 200 m ² / g or less is preferable, 150 m ² / g or less is more preferable, and 125 m ² / g or less is further preferable. The N ₂ SA of carbon black is a value measured according to JIS K 6217-2: 2017 "Basic characteristics of carbon black for rubber-Part 2: How to obtain specific surface area-Nitrogen adsorption method-Single point method". Is.

When the rubber composition constituting the first layer 6 and the second layer 7 contains carbon black, the content with respect to 100 parts by mass of the rubber component is preferably 1 part by mass or more from the viewpoint of wear resistance and wet grip performance. 3 parts by mass or more is more preferable, and 5 parts by mass or more is further preferable. From the viewpoint of fuel efficiency, 50 parts by mass or less is preferable, 35 parts by mass or less is more preferable, 20 parts by mass or less is further preferable, and 10 parts by mass or less is particularly preferable.

When the rubber composition constituting the third layer 8 contains carbon black, the content with respect to 100 parts by mass of the rubber component is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and 50 parts by mass from the viewpoint of reinforcing property. More than parts by mass is more preferable. From the viewpoint of fuel efficiency, 100 parts by mass or less is preferable, 90 parts by mass or less is more preferable, and 80 parts by mass or less is further preferable.

(silica)
The silica is not particularly limited, and for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), and the like, which are common in the tire industry, can be used. Of these, hydrous silica prepared by a wet method is preferable because it has a large number of silanol groups. These silicas may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 140 m ² / g or more, more preferably 170 m ² / g or more, still more preferably 200 m ² / g or more, from the viewpoint of fuel efficiency and wear resistance. Further, from the viewpoint of fuel efficiency and workability, 350 m ² / g or less is preferable, 300 m ² / g or less is more preferable, and 250 m ² / g or less is further preferable. The N ₂ SA of silica in the present specification is a value measured by the BET method according to ASTM D3037-93.

When the rubber composition constituting the first layer 6 and the second layer 7 contains silica, the content with respect to 100 parts by mass of the rubber component is preferably 20 parts by mass or more, preferably 40 parts by mass or more from the viewpoint of wet grip performance. Is more preferable, 50 parts by mass or more is further preferable, and 60 parts by mass or more is particularly preferable. Further, from the viewpoint of wear resistance, 130 parts by mass or less is preferable, 120 parts by mass or less is more preferable, and 110 parts by mass or less is further preferable. When the rubber composition constituting the third layer 8 contains silica, the content with respect to 100 parts by mass of the rubber component is not particularly limited.

In the rubber composition constituting the first layer 6 and the second layer 7, the total content of silica and carbon black with respect to 100 parts by mass is preferably 40 parts by mass or more, preferably 50 parts by mass, from the viewpoint of wear resistance performance. The above is more preferable, and 60 parts by mass or more is further preferable. Further, from the viewpoint of fuel efficiency performance and elongation at break, 160 parts by mass or less is preferable, 140 parts by mass or less is more preferable, and 120 parts by mass or less is further preferable.

The rubber composition constituting the first layer 6 and the second layer 7 contains carbon black in terms of the content of silica per 100 parts by mass of the rubber component from the viewpoint of the balance between fuel efficiency, wet grip performance, and wear resistance. Preferably more than the amount. The ratio of silica to the total content of silica and carbon black in the first layer 6 and the second layer 7 is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and 85% by mass. The above is particularly preferable. The content ratio of silica and carbon black in the rubber composition constituting the third layer 8 is not particularly limited.

(Other fillers)
As the filler other than silica and carbon black, aluminum hydroxide, calcium carbonate, alumina, clay, talc and the like, which have been generally used in the tire industry, can be blended.

(Silane coupling agent)
Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and in the tire industry, any silane coupling agent conventionally used in combination with silica can be used. For example, the following mercapto-based silane coupling agent; bis (3). -Brust-based silane coupling agents such as triethoxysilylpropyl) disulfide and bis (3-triethoxysilylpropyl) tetrasulfide; vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; 3-aminopropyl Amino-based silane coupling agents such as triethoxysilane, 3-aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane; γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyl Glycydoxy-based silane coupling agents such as trimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxy Examples thereof include chloro-based silane coupling agents such as silane. Among them, a sulfide-based silane coupling agent and / or a mercapto-based silane coupling agent is preferable, and a mercapto-based silane coupling agent is more preferable. 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 contains a compound represented by the following formula (1) and / or a binding unit A represented by the following formula (2) and a binding unit B represented by the following formula (3). It is preferably a compound.

(In the formula, R ¹⁰¹ , R ¹⁰² , and R ¹⁰³ are each independently an alkyl having 1 to 12 carbon atoms, an alkoxy having 1 to 12 carbon atoms, or -O- (R ¹¹¹ -O) _z -R ¹¹² . (Z R ^111s independently represent divalent hydrocarbon groups having 1 to 30 carbon atoms; R ¹¹² is an alkyl having 1 to 30 carbon atoms, an alkenyl having 2 to 30 carbon atoms, and a carbon number of carbon atoms. Represents an aryl of 6 to 30 or an aralkyl having 7 to 30 carbon atoms; z represents an integer of 1 to 30); R ¹⁰⁴ represents an alkylene having 1 to 6 carbon atoms. .)

(In the equation, x represents an integer of 0 or more; y represents an integer of 1 or more; R ²⁰¹ is an alkyl having 1 to 30 carbon atoms which may be substituted with a hydrogen atom, a halogen atom, a hydroxyl or a carboxyl. Represents an alkenyl having 2 to 30 carbon atoms or an alkynyl having 2 to 30 carbon atoms; 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; Here, a ring structure may be formed by R ²⁰¹ and R ^202. )

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

Examples of the compound containing the binding unit A represented by the formula (2) and the binding unit B represented by the formula (3) include those manufactured and sold by Momentive and the like. These may be used alone or in combination of two or more.

When the silane coupling agent is contained, the total content of the rubber component with respect to 100 parts by mass is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, from the viewpoint of enhancing the dispersibility of silica. 0 parts by mass or more is more preferable, and 4.0 parts by mass or more is particularly preferable. Further, from the viewpoint of preventing deterioration of wear resistance performance, 20 parts by mass or less is preferable, 12 parts by mass or less is more preferable, 10 parts by mass or less is further preferable, and 9.0 parts by mass or less is particularly preferable.

The content of the silane coupling agent with respect to 100 parts by mass of silica (total amount of all silane coupling agents when used in combination) is preferably 1.0 part by mass or more from the viewpoint of enhancing the dispersibility of silica. .0 parts by mass or more is more preferable, and 5.0 parts by mass or more is further preferable. Further, from the viewpoint of cost and workability, 20 parts by mass or less is preferable, 15 parts by mass or less is more preferable, and 12 parts by mass or less is further preferable.

As the filler, other fillers may be used in addition to carbon black and silica. The filler is not particularly limited, and any filler generally used in this field such as aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, and clay can be used. can. These fillers may be used alone or in combination of two or more.

<Plasticizer>
The rubber composition according to the present disclosure preferably contains a plasticizer. Examples of the plasticizer include resin components, oils, liquid rubbers, ester-based plasticizers, and the like.

The rubber composition constituting the first layer 6 and the second layer 7 preferably contains a resin component. The resin component is not particularly limited, and examples thereof include petroleum resins, terpene-based resins, rosin-based resins, and phenol-based resins commonly used in the tire industry. These resin components may be used alone or in combination of two or more. It is preferable that at least one of the rubber composition constituting the first layer 6 and the rubber composition constituting the second layer 7 contains an aromatic petroleum resin.

As used herein, the term "C5 based petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of the C5 fraction include petroleum fractions having 4 to 5 carbon atoms such as cyclopentadiene, pentene, pentadiene, and isoprene. As the C5 type petroleum resin, a dicyclopentadiene resin (DCPD resin) is preferably used.

As used herein, the term "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, which may be hydrogenated or modified. Examples of the C9 fraction include petroleum fractions having 8 to 10 carbon atoms such as vinyltoluene, alkylstyrene, indene, and methyl indene. Specific examples of aromatic petroleum resins include, for example,
Kumaron inden resin, Kumaron resin, inden resin, and aromatic vinyl-based resin are preferably used. As the aromatic vinyl resin, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferable because it is economical, easy to process, and excellent in heat generation. , A polymer of α-methylstyrene and styrene is more preferred. As the aromatic vinyl-based resin, for example, those commercially available from Clayton, Eastman Chemical, etc. can be used.

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

The terpene-based resin is a polyterpene resin consisting of at least one selected from terpene compounds such as α-pinene, β-pinene, limonene, and dipentene; an aromatic-modified terpene resin made from the terpene compound and an aromatic compound; Examples thereof include terpene phenol resins made from terpene compounds and terpene compounds; and terpene resins obtained by subjecting these terpene resins to hydrogenation treatment (hydrogenated terpene resins). Examples of the aromatic compound used as a raw material for the aromatic-modified terpene resin include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of the phenolic compound which is a raw material of the terpene phenol resin include phenol, bisphenol A, cresol, xylenol and the like.

The rosin-based resin is not particularly limited, and examples thereof include natural resin rosin, and rosin-modified resin obtained by modifying it by hydrogenation, disproportionation, dimerization, esterification, or the like.

The phenol-based resin is not particularly limited, and examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, and oil-modified phenol formaldehyde resin.

The softening point of the resin component is preferably 60 ° C. or higher, more preferably 65 ° C. or higher, from the viewpoint of wet grip performance. Further, from the viewpoint of workability and improvement of dispersibility between the rubber component and the filler, 150 ° C. or lower is preferable, 140 ° C. or lower is more preferable, and 130 ° C. or lower is further preferable. In the present specification, the softening point can be defined as the temperature at which the sphere has fallen by measuring the softening point defined in JIS K 62201: 2001 with a ring-shaped softening point measuring device.

When the resin component is contained, the content of the rubber component with respect to 100 parts by mass is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more from the viewpoint of wet grip performance. Further, from the viewpoint of suppressing heat generation, 60 parts by mass or less is preferable, 50 parts by mass or less is more preferable, 40 parts by mass or less is further preferable, and 30 parts by mass or less is particularly preferable.

The ratio of the content of the resin component to 100 parts by mass of the rubber component of the rubber composition constituting the first layer 6 to the content of the resin component to 100 parts by mass of the rubber component of the rubber composition constituting the second layer 7. 3.0 or less is preferable, 2.4 or less is more preferable, 1.9 or less is further preferable, and 1.4 or less is particularly preferable. When the content ratio exceeds 3.0, a local rigidity difference is likely to occur at the interface between the first layer 6 and the second layer 7, and the first layer 6 has a larger amount of deformation. Therefore, there is a concern that the first layer 6 is likely to be partially peeled off and the wet grip performance is deteriorated. The content ratio is preferably 0.3 or more, more preferably 0.5 or more, further preferably 0.7 or more, and particularly preferably 1.0 or more. If the content ratio is less than 0.3, the amount of liquid component as a plasticizer in the second layer increases, and there is a concern that the plasticizer shifts from the second layer 7 to the first layer 6 during traveling. To.

Examples of the oil include process oils, vegetable oils and fats, animal oils and fats and the like. Examples of the process oil include paraffin-based process oils, naphthen-based process oils, aromatic process oils and the like. Further, as an environmental measure, a process oil having a low content of a polycyclic aromatic compound (PCA) compound can also be used. Examples of the low PCA content process oil include mild extraction solvates (MES), treated distillates aromatic extracts (TDAE), heavy naphthenic oils and the like.

When oil is contained, the content of the rubber component with respect to 100 parts by mass is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 15 parts by mass or more, from the viewpoint of processability. Further, from the viewpoint of wear resistance, 120 parts by mass or less is preferable, 100 parts by mass or less is more preferable, and 90 parts by mass or less is further preferable. In the present specification, the oil content also includes the amount of oil contained in the oil-extended rubber.

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

When the liquid rubber is contained, the content with respect to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. The content of the liquid rubber is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and further preferably 20 parts by mass or less.

Examples of the ester-based plasticizer include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di2-ethylhexyl adipicate (DOZ), dibutyl sebacate (DBS), and diisononyl adipate. (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sevacinate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TBP) TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), trixylenyl phosphate (TXP) and the like. These ester-based plasticizers may be used alone or in combination of two or more.

The content of the plasticizer with respect to 100 parts by mass of the rubber component (total amount of all when a plurality of plasticizers are used in combination) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, from the viewpoint of wet grip performance. More than 15 parts by mass is more preferable. From the viewpoint of processability, 120 parts by mass or less is preferable, 100 parts by mass or less is more preferable, 90 parts by mass or less is further preferable, and 80 parts by mass or less is particularly preferable.

<Other compounding agents>
In addition to the above-mentioned components, the rubber composition according to the present disclosure includes compounding agents generally used in the tire industry, for example, wax, processing aid, stearic acid, zinc oxide, antiaging agent, vulcanizing agent, and addition. A sulfurization accelerator or the like can be appropriately contained.

When wax is contained, the content of the rubber component with respect to 100 parts by mass is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and 1.5 parts by mass or more from the viewpoint of weather resistance of rubber. More preferred. Further, from the viewpoint of preventing whitening of the tire by bloom, 10 parts by mass or less is preferable, and 5.0 parts by mass or less is more preferable.

Examples of the processing aid include fatty acid metal salts, fatty acid amides, amide esters, silica surface active agents, fatty acid esters, mixtures of fatty acid metal salts and amide esters, and mixtures of fatty acid metal salts and fatty acid amides. These processing aids may be used alone or in combination of two or more. As the processing aid, for example, those commercially available from Schill + Seilacher, Performance Additives and the like can be used.

When the processing aid is contained, the content of the rubber component with respect to 100 parts by mass is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and 1.5 parts by mass from the viewpoint of exerting the effect of improving workability. More than a portion is more preferable. Further, from the viewpoint of wear resistance and breaking strength, 10 parts by mass or less is preferable, and 8.0 parts by mass or less is more preferable.

The antiaging agent is not particularly limited, and examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, and antiaging agents such as carbamate metal salts. -(1,3-Dimethylbutyl) -N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N, N'-diphenyl-p-phenylenediamine, N, N' -Phenylenediamine-based antiaging agents such as di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, and 2,2,4-trimethyl-1,2-dihydroquinoline weight. Phenylene-based antioxidants such as coalesced, 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinolin are preferred. These anti-aging agents may be used alone or in combination of two or more.

When the anti-aging agent is contained, the content of the rubber component with respect to 100 parts by mass is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and 1.5 parts by mass, from the viewpoint of ozone crack resistance of rubber. More than parts by mass is more preferable. Further, from the viewpoint of wear resistance and wet grip performance, 10 parts by mass or less is preferable, and 5 parts by mass or less is more preferable.

When stearic acid is contained, the content of the rubber component with respect to 100 parts by mass is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and further preferably 1.5 parts by mass or more from the viewpoint of processability. preferable. Further, from the viewpoint of the vulcanization rate, 10 parts by mass or less is preferable, and 5.0 parts by mass or less is more preferable.

When zinc oxide is contained, the content of the rubber component with respect to 100 parts by mass is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and further preferably 1.5 parts by mass or more from the viewpoint of processability. preferable. Further, from the viewpoint of wear resistance, 10 parts by mass or less is preferable, and 5.0 parts by mass or less is more preferable.

Sulfur is preferably used as the vulcanizing agent. As the sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur and the like can be used.

When sulfur is contained as a vulcanizing agent, the content with respect to 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.3 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. More preferably, 0.5 part by mass or more. From the viewpoint of preventing deterioration, 5.0 parts by mass or less is preferable, 4.0 parts by mass or less is more preferable, and 3.0 parts by mass or less is further preferable. When oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of pure sulfur contained in the oil-containing sulfur.

Examples of the vulcanizing agent other than sulfur include alkylphenol / sulfur chloride condensate, 1,6-hexamethylene-sodium dithiosulfate / dihydrate, and 1,6-bis (N, N'-dibenzylthiocarbamoyldithio). ) Hexane and the like can be mentioned. As these vulcanizing agents other than sulfur, those commercially available from Taoka Chemical Industry Co., Ltd., LANXESS Co., Ltd., Flexis Co., Ltd. and the like can be used.

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, and xantate-based vulcanization accelerators. And so on. These vulcanization accelerators may be used alone or in combination of two or more. Among them, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators are preferable, and sulfenamide-based vulcanization accelerators are more preferable.

Examples of the sulfenamide-based vulcanization accelerator include N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS), N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS), N, N. -Dicyclohexyl-2-benzothiazolyl sulfenamide (DCBS) and the like can be mentioned. Of these, N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS) is preferable.

Examples of the guanidine-based vulcanization accelerator include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, and di-o-tolylguanidine salt of dicatecholbolate. , 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine and the like. Of these, 1,3-diphenylguanidine (DPG) is preferable.

Examples of the thiazole-based vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide and the like. Of these, 2-mercaptobenzothiazole is preferable.

When the vulcanization accelerator is contained, the content with respect to 100 parts by mass of the rubber component is preferably 1 part by mass or more, and more preferably 2 parts by mass or more. The content of the vulcanization accelerator with respect to 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and further preferably 6 parts by mass or less. By setting the content of the vulcanization accelerator within the above range, the fracture strength and elongation tend to be ensured.

The rubber composition according to the present disclosure can be produced by a known method. For example, it can be produced by kneading each of the above components using a rubber kneading device such as an open roll or a closed kneader (Banbury mixer, kneader, etc.).

In the kneading step, for example, a base kneading step of kneading a compounding agent and an additive other than the vulcanizing agent and the vulcanization accelerator, and a vulcanizing agent and a vulcanization accelerator are added to the kneaded product obtained in the base kneading step. It includes a final kneading (F kneading) step of adding and kneading. Further, the base kneading step can be divided into a plurality of steps, if desired.

The kneading conditions are not particularly limited, but for example, in the base kneading step, kneading is performed at a discharge temperature of 150 to 170 ° C. for 3 to 10 minutes, and in the final kneading step, kneading is performed at 70 to 110 ° C. for 1 to 5 minutes. There is a method of kneading. The vulcanization conditions are not particularly limited, and examples thereof include a method of vulcanizing at 150 to 200 ° C. for 10 to 30 minutes.

[tire]
The tire according to the present disclosure includes a tread including a first layer 6, a second layer 7, and a third layer 8, and may be a pneumatic tire or a non-pneumatic tire. Further, it is suitable for competition tires, passenger car tires, large passenger car tires, large SUV tires, and motorcycle tires, and can be used as summer tires, winter tires, and studless tires, respectively.

A tire having a tread including a first layer 6, a second layer 7, and a third layer 8 can be manufactured by a conventional method using the above rubber composition. That is, the unvulcanized rubber composition in which each of the above components is blended with the rubber component as needed is subjected to the first layer 6, the second layer 7, and the third layer by an extruder equipped with a mouthpiece having a predetermined shape. An unvulcanized tire is formed by extruding according to the shape of layer 8, bonding with other tire members on a tire molding machine, and molding by a usual method, and the unvulcanized tire is vulcanized. Tires can be manufactured by heating and pressurizing in the machine.

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

Hereinafter, various chemicals used in Examples and Comparative Examples are collectively shown.
NR: TSR20
SBR1: Toughden 4850 manufactured by Asahi Kasei Corporation (unmodified S-SBR, styrene content: 40% by mass, vinyl content: 46 mol%, Mw: 350,000, rubber solid content 100 parts by mass, oil content 50 parts by mass) Contains)
SBR2: Modified S-SBR produced in Production Example 1 described later (styrene content: 40% by mass, vinyl content: 25 mol%, Mw: 1 million, non-oil-extended product)
SBR3: Modified S-SBR produced in Production Example 2 described later (styrene content: 25% by mass, vinyl content: 25 mol%, Mw: 1 million, non-oil-extended product)
BR: UBEPOL BR (registered trademark) 150B manufactured by Ube Kosan Co., Ltd. (vinyl content: 1.5 mol%, cis content: 97% by mass, Mw: 440,000)
Carbon Black 1: Show Black N330 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 75m ² / g)
Carbon Black 2: Show Black N220 (N ₂ SA: 110m ² / g) manufactured by Cabot Japan Co., Ltd.
Silica: Ultrasil VN3 manufactured by Evonik Degussa (N ₂ SA: 175m ² / g)
Silane coupling agent 1: NXT-Z45 (mercapto-based silane coupling agent) manufactured by Momentive.
Silane coupling agent 2: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa
Oil: VivaTec500 (TDAE oil) manufactured by H & R
Resin component: Sylvares SA85 manufactured by Clayton (copolymer of α-methylstyrene and styrene, softening point: 85 ° C)
Anti-aging agent: Antigen 6C (N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Wax: Sunknock N manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Stearic acid: Beads made by Nichiyu Co., Ltd. Tsubaki Zinc oxide: Zinc oxide type 2 made by Mitsui Metal Mining Co., Ltd .: Sulfur powder from Karuizawa Sulfur Co., Ltd. 1: Ouchi Shinko Kagaku Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Kogyo Co., Ltd.
Vulcanization accelerator 2: Noxeller D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

Production Example 1: Synthesis of SBR2 Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene were charged into a nitrogen-substituted autoclave reactor. The ratio of styrene and 1,3-butadiene was adjusted so that the styrene content was 40% by mass. After adjusting the temperature of the contents of the reactor to 20 ° C., n-butyllithium was added to initiate polymerization. Polymerization was carried out under adiabatic conditions, and the maximum temperature reached 80 ° C. When the polymerization conversion reaches 99%, 1,3-butadiene is added, and after further polymerization for 5 minutes, N, N-bis (trimethylsilyl) -3-aminopropyltrimethoxysilane is added as a denaturant. The reaction was carried out. After completion of the polymerization reaction, 2,6-di-tert-butyl-p-cresol is added. Then, the solvent was removed by steam stripping and dried by a heat roll adjusted to 110 ° C. to obtain SBR2.

Production Example 2: Synthesis of SBR3 SBR3 was obtained in the same manner as in Production Example 1 except that the ratio of styrene and 1,3-butadiene was adjusted so that the styrene content was 25% by mass.

(Examples and comparative examples)
According to the formulation shown in Table 1, Table 2, and Table 4, a 1.7 L closed-type Banbury mixer was used to discharge chemicals other than sulfur and vulcanization accelerator from 1 to 10 until the discharge temperature reached 150 to 160 ° C. It was kneaded for a minute to obtain a kneaded product. Next, using a twin-screw open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded for 4 minutes until the temperature reached 105 ° C. to obtain an unvulcanized rubber composition. Using the obtained unvulcanized rubber composition, it was molded according to the shape of the first layer, the second layer and the third layer of the tread, and bonded together with other tire members to prepare an unvulcanized tire. Vulcanization was performed at 170 ° C. to obtain the test tires (size: 195 / 65R15, rim: 15 × 6.0J, internal pressure: 230 kPa) shown in Tables 3 and 5.

<Measurement of loss tangent tan δ, complex elastic modulus E *, and glass transition temperature (Tg)>
GABO's ip for each rubber test piece produced by cutting out from the inside of the rubber layer of the tread part of each test tire in a length of 20 mm × width 4 mm × thickness 1 mm so that the tire circumference direction is the long side. Using the Lexer series, the loss tangent tan δ and the complex elastic modulus E * were measured under the conditions of a temperature of 30 ° C., an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10 Hz. Further, the temperature distribution curve of the loss tangent tan δ was measured under the conditions of initial strain 10%, dynamic strain 1%, and frequency 10 Hz, and the temperature corresponding to the largest tan δ value in the obtained temperature distribution curve (tan δ peak temperature). Was defined as the glass transition temperature (Tg). The thickness direction of the sample was the tire radial direction.

<Measurement of acetone extraction amount (AE amount)>
Each rubber test piece after vulcanization was immersed in acetone for 24 hours to extract soluble components. The mass of each test piece before and after extraction was measured, and the amount of acetone extracted was determined by the following formula.
Acetone extraction amount (%) = {(mass of rubber test piece before extraction-mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} × 100

As each rubber test piece, a piece cut out from the inside of the rubber layer of the tread portion of each test tire was used.

<Measurement of rubber hardness (Hs)>
According to JIS K 6253-3: 2012, the shore hardness (Hs) of each rubber test piece at a temperature of 23 ° C. was measured using a durometer type A. As each rubber test piece, a piece cut out from the inside of the rubber layer of the tread portion of each test tire was used.

<Tensile test>
From the inside of the rubber layer of the tread part of each test tire, a dumbbell-shaped No. 7 test piece with a thickness of 1 mm was cut out so that the tire circumferential direction was the tensile direction, and JIS K 6251: 2017 "vulcanized rubber" was prepared. And thermoplastic rubber-How to determine the tensile test characteristics ”, a tensile test was conducted under the condition of a tensile speed of 3.3 mm / sec in an atmosphere of 23 ° C, and the modulus (MPa) at 100% stretching was measured. did. The thickness direction of the sample was the tire radial direction.

<Fuel efficiency performance>
Using a rolling resistance tester, we measured the rolling resistance of each new test tire when it was run under the conditions of rim 15 x 6.0 J, internal pressure 230 kPa, load 4.24 kN, and speed 80 km / h. The reciprocal was indexed with the reference comparative example (Comparative Example 1 in Table 3, Comparative Example 3 in Table 5, and the same applies hereinafter) as 100. The larger the value, the smaller the rolling resistance and the better the fuel efficiency.

<Wet grip performance when new tires and after wear>
Each test tire (size: 195 / 65R15, rim: 15 x 6.0J, internal pressure: 230kPa) was attached to all wheels of the vehicle (domestic FF2000cc) and braked at a speed of 100km / h on a wet asphalt road surface. The braking distance from the point was measured. Further, after the tire was thermally deteriorated at 80 ° C. for 7 days, each test tire in which the tread portion was worn along the tread radius so that the thickness of the tread portion became 50% of that of a new tire was used. The braking distance was measured from the point where the brake was applied at a speed of 100 km / h on a wet asphalt road surface mounted on all the wheels of the vehicle. The braking distances of the test tires of Comparative Example 1 when new and after wear were set to 100, respectively, and the wet grip performance of each tire when the tire was new and after wear was expressed as an index by the following formula. The larger the index, the better the wet grip performance.
(Wet grip performance index when new) =
(Braking distance when the tire of the standard comparison example is new) / (Braking distance when the tire for each test is new) x 100
(Wet grip performance index after wear) =
(Brake distance after tire wear in standard comparison example) / (Brake distance after wear of each test tire) x 100

The total performance of fuel efficiency, wet grip performance when new, and wet grip performance after wear (total of fuel efficiency performance index, wet grip performance index when new, and wet grip performance index after wear) is over 300. Is the performance target value.

From the results of Tables 1 to 5, the tires of the present disclosure, in which two or more rubber layers are provided on the tread portion and the complex elastic modulus E * and the loss tangent tan δ of the rubber layers are in a predetermined relationship, have low fuel consumption performance. It can be seen that the overall performance of the wet grip performance when new and the wet grip performance after wear is improved.

1 ... Circumferential groove 2 ... Land 3 ... Tread surface 4 ... Extension of land 5 ... Extension of the deepest part of the groove bottom of the circumferential groove 6 ... First Layer 7 ... Second layer 8 ... Third layer 9 ... Outermost extension of the second layer 10 ... Outermost extension of the third layer 11 ... Shoulder land area 12.・ ・ Center land area 21 ・ ・ ・ Shoulder tread 22 ・ ・ ・ Shoulder sipe 23 ・ ・ ・ Center sipe

Claims (18)

A tire having a tread having at least a first layer constituting a tread surface and a second layer adjacent to the inside of the first layer in the radial direction.
The tread has a land portion partitioned by a plurality of circumferential grooves extending continuously in the tire circumferential direction.
The first layer and the second layer are composed of a rubber composition containing a rubber component and a plasticizer.
The ratio of the complex elastic modulus of the first layer at 30 ° C. to the complex elastic modulus of the second layer at 30 ° C. is 0.85 or more.
A tire in which the ratio of tan δ at 30 ° C. of the first layer to tan δ at 30 ° C. of the second layer is 1.0 or more. The tire according to claim 1, wherein the ratio of tan δ at 30 ° C. of the first layer to tan δ at 30 ° C. of the second layer is 1.2 or more. The tire according to claim 1 or 2, wherein the ratio of the tan δ of the first layer to the tan δ at 30 ° C. of the second layer is 1.4 to 2.0. The tire according to any one of claims 1 to 3, wherein the content of butadiene rubber in the rubber component constituting the first layer is 35% by mass or less. The difference between the acetone extraction amount AE ₁ of the rubber composition constituting the first layer and the acetone extraction amount AE ₂ of the rubber composition constituting the second layer | AE ₁ -AE ₂ | is 10% by mass or less. , The tire according to any one of claims 1 to 4. The tire according to any one of claims 1 to 5, wherein the rubber composition constituting the first layer and the rubber composition constituting the second layer each contain a resin component. The tire according to any one of claims 1 to 6, wherein at least one of the rubber composition constituting the first layer and the rubber composition constituting the second layer contains an aromatic petroleum resin. .. The ratio of the content of the resin component to 100 parts by mass of the rubber component of the rubber composition constituting the first layer to 100 parts by mass of the rubber component of the rubber composition constituting the second layer is 2. .4 The tire according to any one of claims 1 to 7, which is 4 or less. The tire according to any one of claims 1 to 8, further comprising a third layer adjacent to the inner side in the radial direction of the second layer. The tire according to any one of claims 1 to 9, wherein the ratio of the thickness of the first layer to the total thickness of the first layer and the second layer is 0.40 or more. The tire according to any one of claims 1 to 10, wherein the complex elastic modulus of the second layer at 30 ° C. is 5 MPa or more. The tire according to any one of claims 1 to 11, wherein the tan δ of the second layer at 30 ° C. is 0.30 or less. The tire according to any one of claims 1 to 12, wherein the glass transition temperature of the first layer is −15 ° C. or higher. Any of claims 1 to 13, wherein the shore hardness (Hs) of the second layer is 50 to 80 as measured at a temperature of 23 ° C. using a durometer type A in accordance with JIS K 6253-3: 2012. The tire described in item 1. The tire according to any one of claims 1 to 14, wherein the modulus of the first layer at 100% stretching is larger than that of the second layer at 100% stretching. A claim that the deepest portion of the groove bottom of any one of the circumferential grooves is formed so as to be located inside the tire radial direction with respect to the outermost portion of the second layer in the land portion adjacent to the circumferential groove. The tire according to any one of Items 1 to 15. The tire according to any one of claims 1 to 16, wherein the land portion has sipes having both ends not opened in the circumferential groove. The tire according to any one of claims 1 to 17, wherein the length in the width direction of the land portion closest to the equatorial plane of the tire increases from the outside to the inside in the radial direction of the tire.

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