Tire

Abstract

Provided is a tire with improved comprehensive performance in terms of handling stability on wet roads and total wear resistance until the end of travel. A tire having a tread, the tire at least having a first layer constituting a tread surface, a second layer disposed in abutment on the radially inner side of the first layer, and a third layer disposed in abutment on the radially inner side of the second layer, wherein the first layer, the second layer, and the third layer are composed of a rubber composition containing a rubber component, the amount of free sulfur of the rubber composition constituting the third layer is greater than the amount of free sulfur of the rubber composition constituting the second layer, and the amount of free sulfur of the rubber composition constituting the second layer is greater than the amount of free sulfur of the rubber composition constituting the first layer.

Description

TECHNICAL FIELD

[0001] The present application relates to a tire. BACKGROUND

[0002] Patent Document 1 discloses a tire provided with a tread portion having a cap rubber that grounds on a road surface and a base rubber that is provided on an inner side in a tire radial direction of the cap rubber, the cap rubber is configured as a rubber layer having relatively high rigidity, the base rubber is configured as a rubber layer having relatively low rigidity, and the thickness of the base rubber is biased in a tire width direction to reduce a difference in ground pressure and improve braking performance.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENT

[0005] Patent Document 1: JP 2014-162242 A SUMMARY

[0006] [PROBLEMS TO BE SOLVED BY THE INVENTION]

[0007] However, in the tire disclosed in Patent Document 1, since the cap rubber having relatively high rigidity easily loses followability to a road surface, and the base rubber having low rigidity cannot generate sufficient reaction force, there is room for improvement in steering stability on a wet road surface. Further, there is also a concern that abrasion resistance deteriorates sharply when the base rubber is exposed, so there is also room for improvement in total abrasion resistance until the end of travel.

[0008] An object of the present application is to provide a tire in which the steering stability on a wet road surface and the total abrasion resistance until the end of travel are improved in a comprehensive manner.

[0009] [MEANS FOR SOLVING THE PROBLEMS]

[0010] The present inventors have found, as a result of intensive studies, that the aforementioned problems can be solved by providing three or more rubber layers in the tread portion and forming a concentration gradient of a free sulfur amount from the rubber layer on the inner side in the tire radial direction toward the rubber layer on the outer side in the tire radial direction, and have thus completed the present application.

[0011] In other words, the present application relates to:

[0012] [1] A tire having a tread, the tread at least having a first layer constituting a tread surface, a second layer disposed in abutment on a radially inner side of the first layer, and a third layer disposed in abutment on a radially inner side of the second layer, wherein the first layer, the second layer, and the third layer are constituted by rubber compositions containing a rubber component, the amount of free sulfur of the rubber composition constituting the third layer is greater than the amount of free sulfur of the rubber composition constituting the second layer, and the amount of free sulfur of the rubber composition constituting the second layer is greater than the amount of free sulfur of the rubber composition constituting the first layer.

[0013] [2] The tire according to [1], wherein the difference (X1-X2) between the mass change rate X1 (%) of the rubber composition constituting the first layer before and after immersion in toluene at 23°C for 24 hours measured according to JIS K 6258:2016 and the mass change rate X2 (%) of the rubber composition constituting the second layer before and after immersion in toluene at 23°C for 24 hours measured according to JIS K 6258:2016 is 50% or less.

[0014] [3] The tire according to [1] or [2], wherein tan δ at 0°C of the rubber composition constituting the first layer and tan δ at 0°C of the rubber composition constituting the second layer are each 0.45 or more.

[0015] [4] The tire according to any one of [1] to [3], wherein the difference between the hardness of the rubber composition constituting the second layer and the hardness of the rubber composition constituting the first layer is 5 or less.

[0016] [5] The tire according to any one of [1] to [4], wherein the specific gravity of the rubber composition constituting the first layer and the specific gravity of the rubber composition constituting the second layer are each 1.25 or less.

[0017] [6] The tire according to any one of [1] to [5], wherein the specific gravity of the rubber composition constituting the second layer is less than 1.20.

[0018] [7] The tire according to any one of [1] to [6], wherein the acetone extract amount AE2 of the rubber composition constituting the second layer is greater than the acetone extract amount AE1 of the rubber composition constituting the first layer.

[0019] [8] The tire according to any one of [1] to [7], wherein the modulus at 23°C when extended by 100% of the rubber composition constituting the second layer is greater than the modulus at 23°C when extended by 100% of the rubber composition constituting the first layer.

[0020] [9] The tire according to any one of [1] to [8], wherein each of the rubber composition constituting the first layer and the rubber composition constituting the second layer contains butadiene rubber.

[0021]

[10] The tire according to any one of [1] to [9], wherein each of the rubber composition constituting the first layer and the rubber composition constituting the second layer contains a reinforcing filler and a silane coupling agent, and the amount of silica contained in the reinforcing filler in the rubber composition constituting the first layer and the amount of silica contained in the reinforcing filler in the rubber composition constituting the second layer are each 80% by mass or more.

[0022]

[11] The tire according to

[10] , wherein each of the silane coupling agent contained in the rubber composition constituting the first layer and the silane coupling agent contained in the rubber composition constituting the second layer is a mercapto-based silane coupling agent.

[0023]

[12] The tire according to any one of [1] to

[11] , wherein the rubber composition constituting the second layer contains a resin component.

[0024]

[13] The tire according to any one of [1] to

[12] , wherein the third layer has a smaller thickness than both the thickness of the first layer and the thickness of the second layer.

[0025]

[14] The tire according to any one of [1] to

[13] , wherein the tread has a land part partitioned by a plurality of circumferential grooves, and the deepest part of the groove bottom of at least one of the circumferential grooves is formed at a position inside the tire radial direction of the outermost part of the second layer.

[0026]

[15] The tire according to

[14] , wherein the land part is provided with a sipe that does not open to the circumferential grooves at both ends.

[0027] [Effects of Invention]

[0028] According to the present application, a tire is provided in which the comprehensive performance of the handling stability on wet road surfaces and the total abrasion resistance until the end of travel is improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is an enlarged cross-sectional view showing a part of a tread of a tire according to an embodiment of the present application.

[0030] Figure 2 is a schematic view of a ground contact surface of a tire when the tread is pressed against a flat surface.

[0031] [REFERENCE NUMERALS]

[0032] 1 … circumferential groove

[0033] 2 land portion

[0034] 3 tread surface

[0035] 4 extension line of the deepest portion of the groove bottom of the circumferential groove

[0036] 5 extension line of the deepest portion of the groove bottom of the circumferential groove

[0037] 6 first layer

[0038] 7 second layer

[0039] 8 third layer

[0040] 9 extension line of the outermost portion of the second layer

[0041] 11 shoulder land portion

[0042] 12 center land portion

[0043] 21 shoulder transverse groove

[0044] 22 shoulder sipe

[0045] 23 center sipe DETAILED DESCRIPTION

[0046] A tire according to an embodiment of the present application has a tread including at least a first layer constituting a tread surface, a second layer disposed in abutment on a radially inner side of the first layer, and a third layer disposed in abutment on a radially inner side of the second layer, wherein the first layer, the second layer, and the third layer are composed of a rubber composition containing a rubber component, the amount of free sulfur of the rubber composition constituting the third layer is greater than the amount of free sulfur of the rubber composition constituting the second layer, and the amount of free sulfur of the rubber composition constituting the second layer is greater than the amount of free sulfur of the rubber composition constituting the first layer.

[0047] In a vulcanized rubber composition that has been vulcanized with sulfur, there is contained unreacted sulfur, i.e., free sulfur, which exists in a state not chemically combined with a rubber component and does not participate in crosslinking reaction of the rubber component. In the present application, "free sulfur" refers to free sulfur existing in a state not chemically combined with a rubber component and not participating in crosslinking reaction, and "amount of free sulfur" refers to the amount of free sulfur contained in a vulcanized rubber composition.

[0048] Although not intended to be bound by theory, in the present application, the mechanism by which the handling stability on a wet road and the wear resistance can be improved in a well-balanced manner can be as follows.

[0049] Free sulfur not chemically combined with the rubber component and not participating in the cross-linking reaction on the uppermost surface (tread surface) in contact with the road surface reacts with the rubber component due to heat during running. As a result, the wear resistance on the tread surface can be improved, and the rubber composition constituting the first layer can be maintained at the same hardness as immediately after vulcanization.

[0050] Thus, the sulfur in the rubber composition constituting the first layer is consumed due to heat during running, but the sulfur in the rubber composition moves between the rubber layers due to the concentration gradient. Thereby, by forming a concentration gradient of the amount of free sulfur from the rubber layer on the tire radial inner side toward the rubber layer on the tire radial outer side, a predetermined amount of sulfur can be continuously brought to the first layer, and the friction between the tread surface and the road surface makes it easy for the free sulfur to partially combine with the rubber component on the tread surface, thereby enabling the rigidity to be improved so that the reaction force is easily generated. Furthermore, the rubber layer as a whole does not accompany a large change in rigidity, and the followability to the road surface is not impaired, thereby enabling the handling stability on a wet road surface to be improved. Furthermore, at this time, the wear resistance of the tread surface portion is considered to be improved. Further, when the second layer is exposed, since a cross-linking form equivalent to that of the first layer is ensured, a sharp decrease in wear resistance can be prevented, and thus it is considered that a sharp deterioration in wear resistance does not occur, and the total wear resistance until the end of running can be maintained and improved.

[0051] On the contrary, forming a concentration gradient of the amount of free sulfur from the rubber layer on the tire radial outer side toward the rubber layer on the tire radial inner side results in an increase in the amount of free sulfur consumed in the first layer, resulting in the cross-linking density of the first layer becoming too large, and thus the handling stability on a wet road surface is considered to be deteriorated. Furthermore, it is also considered to result in a large decrease in wear resistance after abrasion of the first layer.

[0052] The difference (X1-X2) between the mass change rate X1 (%) of the rubber composition constituting the first layer before and after immersion in toluene at 23°C for 24 hours measured according to JIS K 6258:2016 and the mass change rate X2 (%) of the rubber composition constituting the second layer before and after immersion in toluene at 23°C for 24 hours measured according to JIS K 6258:2016 is preferably 50% or less.

[0053] Each of the tan δ at 0°C of the rubber composition constituting the first layer and the rubber composition constituting the second layer is preferably 0.45 or more.

[0054] The difference between the hardness of the rubber composition constituting the second layer and the hardness of the rubber composition constituting the first layer is preferably 5 or less.

[0055] The specific gravity of the rubber composition constituting the first layer and the specific gravity of the rubber composition constituting the second layer are each preferably 1.25 or less. The specific gravity of the rubber composition constituting the first layer is more preferably 1.24 or less, further preferably 1.23 or less, particularly preferably 1.22 or less. The specific gravity of the rubber composition constituting the second layer is more preferably 1.23 or less, further preferably 1.21 or less, particularly preferably less than 1.20. It is considered that by setting the specific gravity within the ranges described earlier, the energy applied to the tread when the tire is rolling can be reduced, the depletion of free sulfur inside the rubber layer can be prevented, and the handling stability on wet road surfaces and the total abrasion resistance until the end of running can be improved.

[0056] The acetone extract amount AE2 of the rubber composition constituting the second layer is preferably greater than the acetone extract amount AE1 of the rubber composition constituting the first layer.

[0057] The modulus at 100% elongation at 23°C of the rubber composition constituting the second layer is preferably greater than the modulus at 100% elongation at 23°C of the rubber composition constituting the first layer.

[0058] The rubber composition constituting the first layer and the rubber composition constituting the second layer each preferably contain a butadiene rubber.

[0059] Preferably, the rubber composition constituting the first layer and the rubber composition constituting the second layer each contain a reinforcing filler and a silane coupling agent, and the content of silica contained in the reinforcing filler in the rubber composition constituting the first layer and the content of silica contained in the reinforcing filler in the rubber composition constituting the second layer are each 80% by mass or more.

[0060] The silane coupling agent contained in the rubber composition constituting the first layer and the silane coupling agent contained in the rubber composition constituting the second layer are each preferably a mercapto-based silane coupling agent.

[0061] The rubber composition constituting the second layer preferably contains a resin component.

[0062] The thickness of the third layer is preferably smaller than the thickness of each of the first layer and the second layer.

[0063] Preferably, the tread has a land portion separated by a plurality of circumferential grooves, and the deepest part of the groove bottom of at least one of the circumferential grooves is formed on the tire radial direction inner side of the outermost portion of the second layer.

[0064] Preferably, in the land portion, a sipe that does not open to the circumferential grooves at both ends is provided.

[0065] The following will describe a manufacturing process of a tire as an embodiment of the present application in detail. Note that the following description is an example for explaining the present application and is not intended to limit the technical scope of the present application to the described range. Also, in the description, a numerical range indicated by "~" includes both numerical values at the ends.

[0066] Figure 1 is an enlarged cross-sectional view showing a portion of the tread of the tire. In Figure 1 , the up-down 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.

[0067] As shown in the figure, the tread portion of the tire of the present application has a first layer 6, a second layer 7, and a third layer 8, the outer surface of the first layer 6 constituting the tread surface 3, the second layer 7 being disposed in abutment on the inner side in the radial direction of the first layer 6, and the third layer 8 being disposed in abutment on the inner side in the radial direction of the second layer 7. The first layer 6 corresponds typically to the cap tread. The second layer 7 and the third layer 8 correspond typically to the base tread or the under tread. Also, one or more rubber layers can be further provided between the third layer 8 and the belt layer as long as the object of the present application is achieved.

[0068] In Figure 1 , the bidirectional arrow t1 is the thickness of the first layer 6, the bidirectional arrow t2 is the thickness of the second layer 7, and the bidirectional arrow t3 is the thickness of the third layer 8. In Figure 1 , an arbitrary point on the tread surface on which no groove is formed is shown by the symbol P. The straight line shown by the symbol N passing through the point P is a straight line (normal line) perpendicular to the contact plane at the point P. In the description, the thicknesses t1, t2, and t3 are measured in the cross section of Figure 1 along the normal line N drawn from the point P on the tread surface at the position where no groove is present.

[0069] In the present application, the thickness t1 of the first layer 6 is not particularly limited, but from the viewpoint of wet grip performance, it is preferably 1.0 mm or more, more preferably 1.5 mm or more, and further preferably 2.0 mm or more. On the other hand, from the viewpoint of heat generation, the thickness t1 of the first layer 6 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and further preferably 8.0 mm or less.

[0070] In the present application, the thickness t2 of the second layer 7 is not particularly limited, but it is preferably 1.5 mm or more, more preferably 2.0 mm or more, and further preferably 2.5 mm or more. Also, the thickness t2 of the second layer 7 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and further preferably 8.0 mm or less.

[0071] In the present invention, the 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. In addition, the thickness t3 of the third layer 8 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and further preferably 8.0 mm or less.

[0072] The tread of the present invention has a plurality of circumferential grooves 1 that extend continuously in the tire circumferential direction. Although the circumferential grooves 1 extend linearly along the circumference, they are not limited to such a form. For example, they may extend in a wavy, sinusoidal, or zigzag manner along the circumference.

[0073] The tread of the present invention has land portions 2 partitioned by circumferential grooves 1 in the tire width direction.

[0074] The groove depth H of the circumferential groove 1 is determined by the distance between the extension line 4 of the land portion 2 and the extension line 5 of the deepest part of the groove bottom of the circumferential groove 1. In addition, for example, when there are multiple circumferential grooves 1, the groove depth H is the distance between the extension line 4 of the land portion 2 and the circumferential groove 1 having the largest groove depth among the multiple circumferential grooves 1 ( Figure 1 The middle is the distance between the extension lines 5 of the deepest part of the groove bottom of the left circumferential groove 1).

[0075] In the present invention, circumferential groove 1 is formed so that the deepest portion of its bottom is located radially inward of the outermost portion of second layer 7 of land portion 2. Specifically, directly below circumferential groove 1 (inward in the tire radial direction), second layer 7 has a recessed portion that is recessed radially inward of the outermost portion, and a portion of first layer 6 is formed with a predetermined thickness within the recessed portion of second layer 7. Circumferential groove 1 is formed so that it extends beyond the outermost portion of second layer 7 and into the inner side of the recessed portion of second layer 7.

[0076] Figure 2 This is a diagram of the contact patch when the tread is pressed against a flat surface. Figure 1 and Figure 2 As shown, the tread 10 constituting the tire of the present invention has: Figure 2 In the example of FIG, a circumferential groove 1 extending linearly along the tire circumferential direction, and a transverse groove 21 and sipes 22, 23 extending in the width direction.

[0077] The tread 10 has a plurality of circumferential grooves 1 that extend continuously in the tire circumferential direction C. Figure 2 Three circumferential grooves 1 are provided in the embodiment of the present invention, but the number of circumferential grooves is not particularly limited, and for example, it can be 2 to 5. In addition, although the circumferential grooves 1 extend in a straight line along the circumference in the present invention, this is not limited to such a form. For example, the circumferential grooves 1 can extend in a wavy, sinusoidal, or sawtooth manner along the circumference.

[0078] The tread 10 has land portions 2 separated by a plurality of circumferential grooves 1 in the tire width direction W. The shoulder land portions 11 are a pair of land portions formed between the circumferential grooves 1 and the tread end Te. The center land portion 12 is a land portion formed between the pair of shoulder land portions 11. Although two center land portions 12 are provided in Figure 2 the number of center land portions is not particularly limited, and for example, it can be one to five.

[0079] Preferably, in the land portion 2, a transverse groove and / or a sipe that crosses the land portion 2 is provided. Further, more preferably, in the land portion 2, a sipe whose both ends do not open to the circumferential groove 1 is provided. In Figure 2 the shoulder land portion 11, a plurality of shoulder transverse grooves 21 whose ends open to the circumferential groove 1 and a plurality of shoulder sipes 22 whose both ends do not open to the circumferential groove 1 are provided, and in the center land portion 12, a plurality of center sipes 23 whose one end opens to the circumferential groove 1 are provided, but they are not limited to such forms.

[0080] Further, in the present specification, the "groove" including the circumferential groove and the transverse groove refers to a recess whose width is at least greater than 2.0 mm. On the other hand, in the present specification, the "sipe" refers to a fine cut whose width is 2.0 mm or less (preferably 0.5 to 2.0 mm).

[0081] In the present application, unless otherwise specified, the dimensions and angles of each component of the tire are measured in a state in which the tire is assembled in a normal rim and the tire is filled with air to achieve a normal internal pressure. At the time of measurement, no load is applied to the tire. Further, in the present specification, the "normal rim" is a rim that is prescribed differently for each tire in a standard system including a standard to which the tire conforms, for example, for JATMA, it is a standard rim, for TRA, it is a "Design Rim", and for ETRTO, it is a "Measuring Rim". In the present specification, the "normal internal pressure" is an air pressure that is prescribed differently for each tire in the above-mentioned standard, for JATMA, it is a maximum air pressure, for TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and for ETRTO, it is an "INFLATION PRESSURE".

[0082] The "free sulfur amount" in the present application can be determined as follows. The sulfur amount Ts (mass %) in the vulcanized rubber test piece after curing is calculated by using the oxygen flask combustion method based on Japanese Industrial Standard JIS K6233:2016 "Rubber - Determination of total sulfur content by ion chromatography (quantitative)". Next, the aforementioned test piece is immersed in acetone for 24 hours to extract the soluble component according to Japanese Industrial Standard JIS K 6229:2015 "Rubber - Determination of solvent extract (quantitative)". The test piece after extraction of the soluble component is heated and dried to remove the solvent in the test piece, and then the sulfur amount As (mass %) in the test piece is calculated using the oxygen flask combustion method according to Japanese Industrial Standard JIS K6233:2016. By calculating the difference (Ts-As) between the sulfur amount Ts and the sulfur amount As, the free sulfur amount can be determined. Furthermore, the free sulfur amount in the rubber composition can be appropriately adjusted depending on the compounding amount of sulfur, the type and compounding amount of the vulcanization accelerator.

[0083] In the present application, the free sulfur amount of the rubber composition constituting the third layer 8 is greater than the free sulfur amount of the rubber composition constituting the second layer 7, and the free sulfur amount of the rubber composition constituting the second layer 7 is greater than the free sulfur amount of the rubber composition constituting the first layer 6. The difference between the free sulfur amount of the rubber composition constituting the third layer 8 and the free sulfur amount of the rubber composition constituting the second layer 7 is preferably 0.1% or more, more preferably 0.2% or more, and further preferably 0.3% or more. The difference between the free sulfur amount of the rubber composition constituting the second layer 7 and the free sulfur amount of the rubber composition constituting the first layer 6 is preferably 0.1% or more, more preferably 0.2% or more, and further preferably 0.3% or more.

[0084] The "acetone extract amount" in the present application can be calculated using the following equation by measuring the mass of each vulcanized rubber test piece before and after extraction according to Japanese Industrial Standard JIS K 6229:2015, in which each vulcanized rubber test piece is immersed in acetone for 24 hours to extract the soluble component. Furthermore, the acetone extract amount becomes an index of the concentration of the organic low molecular compound in the plasticizer contained in the vulcanized rubber composition. Furthermore, in the present application, unless otherwise specified, the acetone extract amount is a value measured by cutting a sample from a tire.

[0085] Acetone extract amount (mass %) = {(mass of the rubber test piece before extraction - mass of the rubber test piece after extraction) / (mass of the rubber test piece before extraction)} x 100

[0086] The acetone extract amount AE2 of the rubber composition constituting the second layer 7 is preferably greater than the acetone extract amount AE1 of the rubber composition constituting the first layer 6. The difference (AE2-AE1) between the acetone extract amount AE2 of the rubber composition constituting the second layer 7 and the acetone extract amount AE2 of the rubber composition constituting the first layer 6 is preferably 1 to 20 mass%, more preferably 2 to 15 mass%, further preferably 3 to 10 mass%. This is because, by setting the difference in the acetone extract amount within the aforementioned range, free sulfur is easily moved in the plasticizer component in the second layer 7, and thus free sulfur is easily transferred from the second layer 7 to the first layer 6 during running.

[0087] The ratio (AE2 / AE1) of the acetone extract amount AE2 of the rubber composition constituting the second layer 7 to the acetone extract amount AE1 of the rubber composition constituting the first layer 6 is preferably 1.05 to 2.00, more preferably 1.10 to 1.80, further preferably 1.15 to 1.60, particularly preferably 1.20 to 1.40. This is because, by setting the ratio of the acetone extract amount within the aforementioned range, free sulfur is easily moved in the plasticizer component in the second layer 7, and thus free sulfur is easily transferred from the second layer 7 to the first layer 6 during running.

[0088] In the present application, as a scale reflecting the crosslinking density of the rubber composition, the mass change rate before and after toluene swelling is used. In the present application, the mass change rate before and after toluene swelling can be calculated by measuring the mass change rate (%) of each test rubber composition after vulcanization before and after immersion in toluene at 23°C for 24 hours according to Japanese Industrial Standard JIS K 6258:2016 "Vulcanized or thermoplastic rubber - Determination of resistance to liquids". The smaller the value, the higher the crosslinking density. Furthermore, in the present application, unless otherwise specified, the mass change rate before and after toluene swelling is a value measured by cutting a sample from a tire.

[0089] In the present application, the difference (X1-X2) between the mass change rate X1 (%) before and after immersion in toluene at 23°C for 24 hours of the rubber composition constituting the first layer 6 measured according to JIS K 6258:2016 and the mass change rate X2 (%) before and after immersion in toluene at 23°C for 24 hours of the rubber composition constituting the second layer 7 measured according to JIS K 6258:2016 is preferably 50% or less, more preferably 40% or less, further preferably 35% or less, particularly preferably 30% or less. This is because, by setting the difference in the mass change rate within the aforementioned range, the crosslinking density of the first layer 6 is low, and the difference in the crosslinking density from the second layer 7 is reduced, a predetermined amount of free sulfur can be continuously made to reach the first layer 6, and thus good wet road handling stability and wear resistance can be maintained.

[0090] The modulus at 100% elongation in the present application refers to the tensile stress at 100% elongation in the grain direction, and the modulus is measured according to JIS K 6251:2017 "Vulcanized rubber or thermoplastic rubber - Determination of tensile stress-strain properties" under the conditions of an atmosphere of 23°C and a tensile speed of 3.3 mm / sec. The sample can be, for example, a dumbbell type No. 7. The modulus at 100% elongation of the rubber composition constituting the first layer 6 is preferably 1.6 MPa or greater, more preferably 1.8 MPa or greater, and further preferably 2.0 MPa or greater. In addition, the modulus at 100% elongation of the rubber composition constituting the second layer 7 is preferably 1.8 MPa or greater, more preferably 2.0 MPa or greater, and further preferably 2.2 MPa or greater. In addition, the upper limit of the modulus at 100% elongation of the rubber composition constituting the first layer 6, the second layer 7, and the third layer 8 is not particularly limited. In addition, from the viewpoint of the effects of the present application, the modulus at 100% elongation at 23°C of the rubber composition constituting the second layer 7 is preferably greater than the modulus at 100% elongation at 23°C of the rubber composition constituting the first layer 6. In addition, in the present specification, the "grain direction" refers to the calendering direction when a rubber sheet is formed by an extrusion or a shearing process, and coincides with the tire circumferential direction.

[0091] The "0°C tan δ" in the present application refers to the loss tangent tan δ under the conditions of a temperature of 0°C, an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10 Hz. In the case where a test rubber composition is manufactured by being cut out from a tire (for example, it can be manufactured to have a length of 20 mm x a width of 4 mm x a thickness of 1 mm), it is cut out from the tread portion of the tire with the tire circumferential direction as the long side and the tire radial direction as the thickness direction. The 0°C tan δ of the rubber composition constituting the first layer 6 is preferably 0.45 or greater, more preferably 0.50 or greater, further preferably 0.55 or greater, and particularly preferably 0.60 or greater. In addition, the 0°C tan δ of the rubber composition constituting the second layer 7 is preferably 0.45 or greater, more preferably 0.50 or greater, and further preferably 0.55 or greater. By setting the 0°C tan δ within the above range, not only is a good wet grip performance obtained due to hysteresis loss, but also heat is able to be generated on the tread surface 3 even when traveling on a wet road surface or on a low-temperature road surface, and thus the wear resistance is able to be further improved. On the other hand, from the viewpoint of fuel efficiency, the 0°C tan δ of the rubber composition constituting the first layer 6, the second layer 7, and the third layer 8 is preferably 1.60 or less, more preferably 1.40 or less, further preferably 1.20 or less, and particularly preferably 1.00 or less. In addition, the value of the 0°C tan δ of the rubber composition constituting the first layer 6 is preferably greater than the value of the 0°C tan δ of the rubber composition constituting the second layer 7.

[0092] The rubber hardness in the present application refers to the Shore hardness (Hs) measured at 23°C atmosphere using a type A durometer according to Japanese Industrial Standard JIS K 6253-3:2012 "Vulcanized or thermoplastic rubber - Determination of hardness". Specifically, the Shore hardness (Hs) at 23°C of each rubber layer after vulcanization can be measured by cutting the tire in the radial direction with a width of 20 mm, smoothing the cut surface, and then pressing a type A durometer against the tire from the cross-sectional direction. In the present application, the difference between the rubber hardness of the rubber composition constituting the first layer 6 and the rubber hardness of the rubber composition constituting the second layer 7 is preferably 6 or less, more preferably 5 or less, further preferably 4 or less, and particularly preferably 3 or less. This is because, by setting the difference in rubber hardness within the above range, excessive change in performance when the second layer 7 becomes the uppermost surface due to wear can be suppressed.

[0093] <Rubber component>

[0094] The rubber composition (tread rubber composition) constituting each rubber layer of the tread according to the present application preferably contains at least one selected from 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, or can be a rubber component consisting only of SBR and BR. The rubber component constituting the third layer 8 preferably contains isoprene-based rubber, more preferably contains isoprene-based rubber and BR, or can be a rubber component consisting only of isoprene-based rubber and BR.

[0095] (Isoprene-based rubber)

[0096] Examples of the isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, and the like. As the NR, for example, SIR20, RSS#3, TSR20, and the like, which are conventional in the tire industry, can be used. The IR is not particularly limited, and as the IR, for example, IRs conventionally used in the tire industry, such as IR2200 and the like, can be used. Examples of the modified NR include deproteinized natural rubber (DPNR), ultra-pure natural rubber, and the like, examples of the modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, and the like, and examples of the modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, and the like. These isoprene-based rubbers can be used alone or two or more thereof can be used in combination.

[0097] In the rubber component constituting the first layer 6 and the second layer 7, when the rubber composition contains isoprene rubber (preferably NR), the content of isoprene rubber (preferably NR) in the rubber component 100 mass% is preferably 50 mass% or less, more preferably 40 mass% or less, further preferably 30 mass% or less, particularly preferably 20 mass% or less, from the viewpoint of wet grip performance. Furthermore, although the lower limit of the content of isoprene rubber is not particularly limited when the rubber composition contains isoprene rubber, it can be, for example, 1 mass% or more, 3 mass% or more, 5 mass% or more, 10 mass% or more, 15 mass% or more.

[0098] In the rubber component constituting the third layer 8, when the rubber composition contains isoprene rubber (preferably NR), the content of isoprene rubber (preferably NR) in the rubber component 100 mass% is preferably 30 mass% or more, more preferably 40 mass% or more, further preferably 50 mass% or more. Furthermore, the upper limit of the content of isoprene rubber in the rubber component is not particularly limited, and it can be 100 mass%.

[0099] (SBR)

[0100] The SBR is not particularly limited, and examples thereof include solution polymerized SBR (S-SBR), emulsion polymerized SBR (E-SBR), modified SBRs thereof (modified S-SBR, modified E-SBR), and the like. Examples of the modified SBR include SBRs modified at the terminal and / or main chain thereof, modified SBRs coupled with tin, silicon compounds, and the like (modified SBRs of condensates or modified SBRs having a branched structure, and the like), and the like. Furthermore, hydrogenates of these SBRs (hydrogenated SBRs), and the like can also be used. Among them, S-SBR is preferred, and modified S-SBR is more preferred.

[0101] Examples of the modified SBR include modified SBRs in which a functional group commonly used in the field is introduced. Examples of the above-mentioned functional group include, for example, amino group (preferably C 1-6 alkyl-substituted amino group), amido group, silyl group, alkoxy silyl group (preferably C 1-6 alkoxy silyl group), isocyanate group, imino group, imidazole group, ureido group, ether group, carbonyl group, oxycarbonyl group, mercapto group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, ammonium group, imide group, hydrazo group, azo group, diazo group, carboxyl group, nitrile group, pyridyl group, alkoxy group (preferably C 1-6hydroxyl group, an oxyl group, an epoxy group, and the like. In addition, these functional groups can have a substituent. Examples of the substituent include, for example, a functional group such as an amino group, an amido group, an alkoxysilyl group, a carboxyl group, and a hydroxyl group. In addition, examples of the modified SBR include a hydrogenated SBR, an epoxidized SBR, a tin-modified SBR, and the like.

[0102] As the SBR, an oil-extended SBR can be used, or a non-oil-extended SBR can be used. When an oil-extended SBR is used, the amount of oil extension of the SBR, that is, the content of oil filling contained in the SBR, is preferably 10 to 50 parts by mass with respect to 100 parts by mass of the rubber solid component of the SBR.

[0103] The aforementioned listed SBRs can be used alone, or two or more of them can be used in combination. As the aforementioned listed SBRs, for example, those manufactured / sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, ZSElastomer Corporation, and the like can be used.

[0104] From the viewpoint of ensuring the damping in the tread portion and the wet grip, the styrene content of the SBR is preferably 15% by mass or more, more preferably 20% by mass or more. In addition, from the viewpoint of the temperature dependence of the grip and the abrasion resistance, the content is preferably 60% by mass or less, more preferably 50% by mass or less. In addition, in the present specification, the styrene content of the SBR is calculated by H-NMR measurement. 1 H-NMR measurement.

[0105] From the viewpoint of ensuring the reactivity with silica, the rubber strength, and the abrasion resistance, the vinyl content of the SBR is preferably 10% by mole or more, more preferably 13% by mole or more, further preferably 16% by mole or more. In addition, from the viewpoint of preventing an increase in the temperature dependence, the wet grip performance, the elongation at break, and the abrasion resistance, the vinyl content of the SBR is preferably 70% by mole or less, more preferably 65% by mole or less, further preferably 60% by mole or less. In addition, in the present specification, the vinyl content (1,2-bound butadiene unit amount) of the SBR is measured by infrared absorption spectroscopy.

[0106] From the viewpoint of abrasion resistance, the weight average molecular weight (Mw) of the SBR is preferably 150,000 or more, more preferably 200,000 or more, and further preferably 250,000 or more. In addition, from the viewpoint of uniformity of crosslinking and the like, the Mw is preferably 2,500,000 or less, and more preferably 2,000,000 or less. In addition, the Mw can be determined based on a measured value obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation), and converted according to a standard polystyrene.

[0107] In the rubber component constituting the first layer 6 and the second layer 7, when the rubber composition contains the SBR, the content of the SBR in the rubber component 100% by mass is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 65% by mass or more, and particularly preferably 70% by mass or more, from the viewpoint of wet grip performance. In addition, the upper limit of the content of the SBR in the rubber component is not particularly limited, and it can be 100% by mass. In addition, when the rubber composition constituting the third layer 8 contains the SBR, the content of the SBR in the rubber component 100% by mass is not particularly limited.

[0108] (BR)

[0109] The BR is not particularly limited, and those generally used in the tire industry, such as BR having a cis content of less than 50 mol% (low-cis BR), BR having a cis content of 90 mol% or more (high-cis BR), rare-earth-based butadiene rubber synthesized using a rare-earth element-based catalyst (rare-earth-based BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis modified BR, low-cis modified BR), and the like, can be used. Examples of the modified BR include BR modified with the same functional group as the functional group described in the SBR described above, and the like. These BRs can be used alone, or two or more can be used in combination.

[0110] As the high-cis BR, for example, those commercially available from Zeon Corporation, Ube Industries, Ltd., JSR Corporation, and the like can be used. When the high-cis BR is contained, the abrasion resistance can be improved. The cis content is preferably 95 mol% or more, more preferably 96 mol% or more, further preferably 97 mol% or more, and particularly preferably 98 mol% or more. In addition, in the present specification, the cis content (amount of cis-1,4-bound butadiene units) is a value calculated by infrared absorption spectroscopy.

[0111] As the rare-earth-based BR, those synthesized with a rare-earth element-based catalyst and having a vinyl group content of preferably 1.8 mol% or less, more preferably 1.0 mol% or less, further preferably 0.8 mol% or less, and a cis content of preferably 95 mol% or more, more preferably 96 mol% or more, further preferably 97 mol% or more, particularly preferably 98 mol% or more can be used. As the rare-earth-based BR, for example, those commercially available from LANXESS KK or the like can be used.

[0112] Examples of the BR containing SPB include those in which 1,2-syndiotactic polybutadiene crystals are chemically bound to BR and dispersed in BR, but exclude those in which the crystals are simply dispersed in BR. As such a BR containing SPB, for example, those commercially available from Ube Industries, Ltd. or the like can be used.

[0113] As the modified BR, a modified butadiene rubber in which the terminal and / or main chain thereof is modified with a functional group containing at least one element selected from silicon, nitrogen, and oxygen can be suitably used.

[0114] Examples of other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and in which the terminal of the modified BR molecule is bound by a tin-carbon bond (tin-modified BR), and the like. In addition, the modified BR can be hydrogenated or not.

[0115] The aforementioned listed BRs can be used alone, or two or more thereof can be used in combination.

[0116] From the viewpoint of preventing low-temperature brittleness, the glass transition temperature (Tg) of the BR is preferably -14°C or lower, more preferably -17°C or lower, further preferably -20°C or lower. On the other hand, although the lower limit of the Tg is not particularly limited, from the viewpoint of abrasion resistance, it is preferably -150°C or higher, more preferably -120°C or higher, further preferably -110°C or higher. In addition, the glass transition temperature of the BR is a value determined using differential scanning calorimetry (DSC) under the conditions of a temperature increase rate of 10°C / min according to Japanese Industrial Standards JIS K 7121.

[0117] From the viewpoint of abrasion resistance, the weight average molecular weight (Mw) of the BR is preferably 300,000 or greater, more preferably 350,000 or greater, and further preferably 400,000 or greater. In addition, from the viewpoint of uniformity of crosslinking and the like, it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. In addition, the Mw can be determined based on a measurement value obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation), according to a standard polystyrene conversion.

[0118] In the rubber component constituting the first layer 6 and the second layer 7, when the rubber composition contains BR, the content of BR in the rubber component 100% by mass is preferably 50% by mass or less, more preferably 40% by mass or less, further preferably 30% by mass or less, and particularly preferably 20% by mass or less, from the viewpoint of wet grip performance. In addition, when the rubber composition contains BR, the lower limit of the content of BR is not particularly limited, and it can be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more. In addition, when the rubber composition constituting the third layer 8 contains BR, the content of BR in the rubber component 100% by mass is not particularly limited.

[0119] (other rubber component)

[0120] As the rubber component according to the present application, other rubber components than the above-mentioned isoprene-based rubber, SBR, and BR can be contained. As the other rubber component, a crosslinkable rubber component generally used in the tire industry, such as styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), epichlorohydrin rubber, and the like can be used. These other rubber components can be used alone, or two or more of them can be used in combination.

[0121] <reinforcing filler>

[0122] The rubber composition for the tread of the present application preferably contains a reinforcing filler including carbon black and / or silica. Furthermore, the reinforcing filler can be a reinforcing filler consisting only of carbon black and silica. The rubber composition constituting the first layer 6 and the second layer 7 preferably contains silica (more preferably contains carbon black and silica) as a reinforcing filler. The rubber composition constituting the third layer 8 preferably contains carbon black as a reinforcing filler.

[0123] (Carbon black)

[0124] The carbon black is not particularly limited, and those conventionally used in the tire industry, such as GPF, FEF, HAF, ISAF, SAF, and the like, or specifically, N110, N115, N120, N125, N134, N135, N219, N220, N231, N234, N293, N299, N326, N330, N339, N343, N347, N351, N356, N358, N375, N539, N550, N582, N630, N642, N650, N660, N683, N754, N762, N765, N772, N774, N787, N907, N908, N990, N991, and the like, can be appropriately used, and in addition thereto, in-house synthetic products and the like can be appropriately used. These carbon blacks can be used alone, or two or more kinds thereof can be used in combination.

[0125] From the viewpoint of weather resistance and reinforcing property, the nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 50 m 2 / g or more, more preferably 80 m 2 / g or more, further preferably 100 m 2 / g or more. Furthermore, from the viewpoint of dispersibility, fuel efficiency, fracture property, and pinch cut resistance, it is preferably 250 m 2 / g or less, more preferably 220 m 2 / g or less. Furthermore, the N2SA of the carbon black in the present specification is a value measured according to the method A of Japanese Industrial Standards JIS K6217-2 "Carbon black for rubber - General characteristics - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method".

[0126] When the rubber composition constituting the first layer 6 and the second layer 7 contains carbon black, the content of the carbon black 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, relative to 100 parts by mass of the rubber component, from the viewpoint of weather resistance and reinforcing property. In addition, the content is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, further preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, from the viewpoint of improvement in chunk resistance due to suppression of heat generation in the tread portion. When the rubber composition constituting the third layer 8 contains carbon black, the content of the carbon black is preferably 20 to 100 parts by mass, more preferably 25 to 80 parts by mass, and further preferably 30 to 60 parts by mass, relative to 100 parts by mass of the rubber component.

[0127] (Silica)

[0128] The silica is not particularly limited, and those conventionally used in the tire industry, such as silica modulated by a dry method (anhydrous silica), silica modulated by a wet method (hydrous silica), and the like, can be used. Among them, the hydrous silica modulated by a wet method is preferred because it has many silanol groups. These silicas can be used alone, or two or more kinds thereof can be used in combination.

[0129] From the viewpoint of reinforcing property and securing of damping in the tread portion, the nitrogen adsorption specific surface area (N2SA) of the silica is preferably 140 m 2 / g or more, more preferably 150 m 2 / g or more, further preferably 160 m 2 / g or more, and particularly preferably 170 m 2 / g or more. In addition, from the viewpoint of heat generation and processability, it is preferably 350 m 2 / g or less, more preferably 300 m 2 / g or less, further preferably 250 m 2 / g or less. In addition, the N2SA of the silica in the present specification is a value measured by the BET method according to ASTM D3037-93.

[0130] The average primary particle diameter of the silica is preferably 20 nm or less, and more preferably 18 nm or less. The lower limit of the average primary particle diameter is not particularly limited, and is preferably 1 nm or more, more preferably 3 nm or more, and further preferably 5 nm or more. When the average primary particle diameter of the silica is within the above range, the dispersibility of the silica can be further improved, and the reinforcing property, the breaking property, and the wear resistance can be further improved. In addition, the average primary particle diameter of the silica can be determined by observing the average primary particle diameter of the silica with a transmission or scanning electron microscope, measuring the primary particle diameters of 400 or more of the silicas observed within the field of view, and averaging them.

[0131] From the viewpoint of ensuring the damping of the tread portion and the wet grip performance, the content of silica in the rubber composition constituting the first layer 6 and the second layer 7 is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, further preferably 70 parts by mass or more, and particularly preferably 80 parts by mass or more, relative to 100 parts by mass of the rubber component. In addition, from the viewpoint of reducing the specific gravity of the rubber and achieving weight reduction, and the viewpoint of improving the cut resistance by suppressing the heat generation of the tread portion, it is preferably 120 parts by mass or less, more preferably 110 parts by mass or less, further preferably 105 parts by mass or less, and particularly preferably 100 parts by mass or less. In addition, in the rubber composition constituting the third layer 8, the content of silica is not particularly limited, relative to 100 parts by mass of the rubber component.

[0132] (Other reinforcing fillers)

[0133] As the other reinforcing fillers other than silica and carbon black, those conventionally used in the tire industry can be used, such as aluminum hydroxide, calcium carbonate, alumina, clay, talc, and the like.

[0134] In the rubber composition constituting the first layer 6 and the second layer 7, the content of silica is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and particularly preferably 85% by mass or more, in 100% by mass of the total of silica and carbon black. In addition, the content of silica is preferably 99% by mass or less, more preferably 97% by mass or less, and further preferably 95% by mass or less. This is because, by setting the content of silica within the aforementioned range, the interaction between the reinforcing fillers and the free sulfur is reduced, and the transfer of the free sulfur to the first layer 6 becomes easy.

[0135] In the rubber composition constituting the third layer 8, the content of carbon black is preferably 50% by mass or more, more preferably 75% by mass or more, further preferably 90% by mass or more, and particularly preferably 100% by mass, in 100% by mass of the total of silica and carbon black.

[0136] From the viewpoint of reducing the specific gravity of the rubber and weight reduction, the total content of the reinforcing fillers is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, further preferably 110 parts by mass or less, and particularly preferably 105 parts by mass or less, relative to 100 parts by mass of the rubber component. In addition, from the viewpoint of reinforcing properties and ensuring the damping of the tread portion, it is preferably 55 parts by mass or more, more preferably 65 parts by mass or more, further preferably 75 parts by mass or more, and particularly preferably 85 parts by mass or more.

[0137] (Silane coupling agent)

[0138] The silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent conventionally used in combination with silica in the tire industry can be used, examples of which include, for example, the following mercapto-based silane coupling agents; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; thioester-based silane coupling agents such as 3-octanoylthio-1-propyl triethoxysilane, 3-hexanoylthio-1-propyl triethoxysilane, and 3-octanoylthio-1-propyl trimethoxysilane; vinyl-based silane coupling agents such as vinyl triethoxysilane and vinyl trimethoxysilane; amino-based silane coupling agents such as 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane, and 3-(2-aminoethyl) aminopropyl triethoxysilane; glycidoxypropoxy-based silane coupling agents such as γ-glycidoxypropyl triethoxysilane and γ-glycidoxypropyl trimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyl trimethoxysilane and 3-nitropropyl triethoxysilane; chloro-based silane coupling agents such as 3-chloropropyl trimethoxysilane and 3-chloropropyl triethoxysilane, and the like. Of these, a silane coupling agent containing a sulfide-based silane coupling agent and / or a mercapto-based silane coupling agent is preferred. These silane coupling agents can be used alone or two or more thereof can be used in combination.

[0139] The mercapto-based silane coupling agent is preferably a compound represented by the following formula (1) and / or a compound containing a binding unit A represented by the following formula (2) and a binding unit B represented by the following formula (3):

[0140] [Chemical Formula 1]

[0141]

[0142] (In the formula, R 101 , R 102 , and R 103 each independently represent an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or a group represented by -O-(R 111 -O)z-R 112 (z number of R 111 each independently represent a divalent hydrocarbon group having 1 to 30 carbon atoms; R 112 represents an alkyl group having 1 to 30 carbon atoms, an (chain)alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms; and z represents an integer of 1 to 30) ; R 104 represents an alkylene group having 1 to 6 carbon atoms.)

[0143] [Chemical Formula 2]

[0144]

[0145] [Chemical Formula 3]

[0146]

[0147] (In the formula, x represents an integer of 0 or more; y represents an integer of 1 or more; R 201 represents a hydrogen atom, an alkyl group having 1 to 30 carbon atoms which is optionally substituted with a halogen atom, a hydroxyl group, or a carboxyl group, an (chain)alkenyl group having 2 to 30 carbon atoms, or an alkynyl group having 2 to 30 carbon atoms; R 202 represents an alkylene group having 1 to 30 carbon atoms, an alkenylene group having 2 to 30 carbon atoms, or an alkynylene group having 2 to 30 carbon atoms; and R 201 and R 202 may form a ring structure together.)

[0148] Examples of the compound represented by formula (1) include, for example, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and a compound represented by formula (4) (Si363 manufactured by Evonik Degussa), and a compound represented by the following formula (4) can be suitably used. They can be used alone, or two or more of them can be used in combination.

[0149] [Chemical Formula 4]

[0150]

[0151] Examples of the compound containing the binding unit A represented by formula (2) and the binding unit B represented by formula (3) include those manufactured and / or sold by Momentive Performance Materials Inc. and the like. They can be used alone, or two or more of them can be used in combination.

[0152] When the rubber composition contains a silane coupling agent, from the viewpoint of improving the dispersibility of silica, the content of the silane coupling agent is preferably 1.0 parts by mass or more, more preferably 3.0 parts by mass or more, and further preferably 5.0 parts by mass or more, relative to 100 parts by mass of silica. In addition, from the viewpoint of preventing a decrease in wear resistance, it is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and further preferably 15 parts by mass or less.

[0153] <Plasticizer>

[0154] The rubber composition for a tread of the present application preferably contains a plasticizer. Examples of the plasticizer include, for example, a resin component, an oil, a liquid rubber, and the like.

[0155] The rubber composition constituting 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, phenol-based resins, and the like, which are commonly used in the tire industry, and they can be hydrogenated. These resin components can be used alone, or two or more thereof can be used in combination.

[0156] In the present specification, "C5-based petroleum resins" refer to resins obtained by polymerizing a C5 fraction. Examples of the C5 fraction include, for example, petroleum fractions corresponding to 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, isoprene, and the like. As the C5-based petroleum resins, a cyclopentadiene-based resin is suitably used. Examples of the cyclopentadiene-based resin include dicyclopentadiene resin (DCPD resin), cyclopentadiene resin, methylcyclopentadiene resin (unhydrogenated cyclopentadiene-based resin), and those obtained by subjecting these cyclopentadiene-based resins to a hydrogenation treatment (hydrogenated cyclopentadiene-based resin). As the cyclopentadiene-based resin, for example, those commercially available from ExxonMobil Chemical Company and the like can be used.

[0157] In the present specification, "aromatic-based petroleum resins" refer to resins obtained by polymerizing a C9 fraction, and they can be hydrogenated or modified. Examples of the C9 fraction include, for example, petroleum fractions corresponding to 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. As specific examples of the aromatic-based petroleum resins, for example, a benzofuran-indene resin, a benzofuran resin, an indene resin, and an aromatic vinyl-based resin are suitably used. As the aromatic vinyl-based resin, for economic, ease of processing, and good heat generation reasons, a homopolymer of α-methylstyrene or styrene, or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred. As the aromatic vinyl-based resin, for example, those commercially available from Kraton Corporation, Eastman Chemical Company, and the like can be used.

[0158] In the present specification, "C5-C9-based petroleum resins" refer to resins obtained by copolymerizing the aforementioned C5 fraction and the aforementioned C9 fraction, and they can be hydrogenated or modified. Examples of the C5 fraction and the C9 fraction include the aforementioned petroleum fractions. As the C5-C9-based petroleum resins, for example, those commercially available from Toagosei Co., Ltd., Zibo Luohua Hongjin New Material Co., Ltd., and the like can be used.

[0159] Examples of the terpene-based resin include polyterpene (ene) resins composed of at least one selected from terpene compounds such as a-pinene, β-pinene, limonene, dipentene, and the like; aromatic-modified terpene resins made from terpene compounds and aromatic compounds; terpene (ene) phenol resins made from terpene compounds and phenol-based compounds; and (hydrogenated terpene-based resins) obtained by hydrogenating these terpene-based resins. Examples of the aromatic compounds used as raw materials for the aromatic-modified terpene resins include, for example, styrene, a-methylstyrene, vinyltoluene, divinyltoluene, and the like. Examples of the phenol-based compounds used as raw materials for the terpene (ene) phenol resins include, for example, phenol, bisphenol A, cresol, xylenol, and the like. As the terpene-based resin, for example, those commercially available from AnGou Chemical Co., Ltd., and the like can be used.

[0160] The rosin-based resin is not particularly limited, and examples thereof include, for example, natural resin rosin and modified rosin resins. As the rosin-based resin, for example, those commercially available from Arakawa Chemical Industries, Ltd., Harima Chemicals, Inc., and the like can be used.

[0161] The phenol-based resin is not particularly limited, and examples thereof include phenol resins, alkylphenol resins, alkylphenol acetylene resins, oil-modified phenol resins, and the like.

[0162] From the viewpoint of wet grip performance, the softening point of the resin component is preferably 60°C or higher, more preferably 65°C or higher. In addition, from the viewpoint of processability and improvement in dispersibility of the rubber component and the filler, it is preferably 150°C or lower, more preferably 140°C or lower, and further preferably 130°C or lower. In addition, in the present specification, the softening point can be defined as the temperature at which the ball falls down when the softening point prescribed in Japanese Industrial Standards JIS K 6220-1:2001 is measured using a ring-and-ball type softening point measuring device.

[0163] When the rubber composition contains the resin component, from the viewpoint of wet grip performance, the content of the resin component is preferably 1 part by mass or more, more preferably 5 parts by mass or more, further preferably 10 parts by mass or more, and particularly preferably 12 parts by mass or more, relative to 100 parts by mass of the rubber component. In addition, from the viewpoint of suppressing heat generation, it is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, further preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0164] Examples of the oil include, for example, an operating oil, a vegetable fat, an animal fat, and the like. Examples of the operating oil include a paraffin-based operating oil, a naphthene-based operating oil, an aromatic-based operating oil, and the like. Furthermore, as an environmental countermeasure, an operating oil having a low content of polycyclic aromatic compounds (PCA) can also be used. Examples of the operating oil having a low content of PCA include a mild extract solvent (MES), a treated distillate aromatic extract (TDAE), a heavy naphthene-based oil, and the like.

[0165] When the rubber composition contains the oil, from the viewpoint of processability, the content of the oil is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and further preferably 15 parts by mass or more, relative to 100 parts by mass of the rubber component. In addition, from the viewpoint of wear resistance, it is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and further preferably 60 parts by mass or less. Furthermore, in the present specification, the content of the oil also includes the amount of the oil contained in the oil-extended rubber.

[0166] The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), and examples of the liquid rubber include, for example, liquid butadiene rubber (liquid BR), liquid styrene-butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene-isoprene rubber (liquid SIR), liquid farnesene rubber, and the like. These can be used alone, or two or more kinds thereof can be used in combination.

[0167] When the rubber composition contains the liquid rubber, the content of the liquid rubber 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, relative to 100 parts by mass of the rubber component. In addition, 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.

[0168] When the rubber composition contains the plasticizer, from the viewpoint of wet grip performance, the content of the plasticizer (when a plurality of plasticizers is used, the total content of all the plasticizers) is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and further preferably 25 parts by mass or more, relative to 100 parts by mass of the rubber component. In addition, from the viewpoint of processability, it is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, further preferably 110 parts by mass or less, further preferably 70 parts by mass or less, and particularly preferably 50 parts by mass or less.

[0169] <Other additives>

[0170] The rubber composition for a tire tread according to the present application can appropriately contain, in addition to the aforementioned components, compounding agents conventionally used in the tire industry, for example, waxes, processing aids, stearic acid, zinc oxide, anti-aging agents, vulcanizing agents, vulcanization accelerators, and the like.

[0171] When the rubber composition contains a wax, the content of the wax is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the rubber component, from the viewpoint of the weather resistance of the rubber. Furthermore, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of preventing whitening of the tire due to blooming.

[0172] Examples of the processing aid include, for example, 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, mixtures of fatty acid metal salts and fatty acid amides, and the like. These processing aids can be used alone or two or more thereof can be used in combination. As the processing aid, those commercially available from, for example, Schill & Seilacher Company, Performance Additives Company, and the like can be used.

[0173] When the rubber composition contains a processing aid, the content of the processing aid is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the rubber component, from the viewpoint of the improvement effect of the processability. Furthermore, it is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, from the viewpoint of the abrasion resistance and the breaking strength.

[0174] The anti-aging agent is not particularly limited, and examples thereof include, for example, each of compounds of amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based, and anti-aging agents such as metal salt of carbamic acid, and preferably a phenylenediamine-based anti-aging agent such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, and the like; and a quinoline-based anti-aging agent such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, and the like. These anti-aging agents can be used alone or two or more thereof can be used in combination.

[0175] When the rubber composition contains an anti-aging agent, the content of the anti-aging agent is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the rubber component, from the viewpoint of the ozone cracking resistance of the rubber. Furthermore, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of the abrasion resistance and the wet grip performance.

[0176] When the rubber composition contains stearic acid, the content of stearic acid is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the rubber component, from the viewpoint of processability. In addition, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of vulcanization rate.

[0177] When the rubber composition contains zinc oxide, the content of zinc oxide is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the rubber component, from the viewpoint of processability. In addition, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of wear resistance.

[0178] Sulfur is suitably used as a 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.

[0179] When the rubber composition contains sulfur as a vulcanizing agent, the content of sulfur is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, relative to 100 parts by mass of the rubber component, from the viewpoint of ensuring sufficient vulcanization reaction. In addition, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, further preferably 3.0 parts by mass or less, from the viewpoint of preventing deterioration. Furthermore, when oil-containing sulfur is used as a vulcanizing agent, the content of the vulcanizing agent should be the total content of the pure sulfur component contained in the oil-containing sulfur.

[0180] Examples of the vulcanizing agent other than sulfur include, for example, alkylphenol-sulfur chloride condensates, 1,6-hexamethylene-bis(thiocarbamoyl disulfide) sodium dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyl disulfide) hexane, and the like. As these vulcanizing agents other than sulfur, those commercially available from NOKA CHEMICAL CO., LTD., LANXESS KK, Flexsys Corporation, and the like can be used.

[0181] Examples of the vulcanization accelerator include, for example, sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators. These vulcanization accelerators can be used alone, or two or more thereof can be used in combination. Among them, sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators are preferred, and the combination use of sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators is more preferred.

[0182] Examples of the sulfenamide-based vulcanization accelerator include, for example, N-tert-butyl-2-benzothiazyl sulfenamide (TBBS), N-cyclohexyl-2-benzothiazyl sulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazyl sulfenamide (DCBS), and the like. Among them, N-cyclohexyl-2-benzothiazyl sulfenamide (CBS) is preferred.

[0183] Examples of the guanidine-based vulcanization accelerator include, for example, 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of di- catechol borate, 1,3-di-o-isopropylphenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o- isopropylphenyl-2-propionylguanidine, and the like. Of these, 1,3-diphenylguanidine (DPG) is preferred.

[0184] Examples of the thiazole-based vulcanization accelerator include, for example, 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazyl disulfide, and the like. Of these, 2-mercaptobenzothiazole is preferred.

[0185] When the rubber composition contains a vulcanization accelerator, the content of the vulcanization accelerator is preferably 1.0 parts by mass or more, more preferably 1.5 parts by mass or more, with respect to 100 parts by mass of the rubber component. In addition, the content of the vulcanization accelerator is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, further preferably 6 parts by mass or less, with respect to 100 parts by mass of the rubber component. When the content of the vulcanization accelerator is within the above range, there is a tendency to be able to ensure the breaking strength and the elongation.

[0186] The rubber composition according to the present application can be manufactured by a publicly known method. For example, it can be manufactured by mixing the aforementioned components using, for example, an open roll, a closed mixer (Banbury mixer, kneader, or the like), or the like.

[0187] The mixing step includes, for example, a basic kneading step of mixing the compounding agents and the additives other than the vulcanizing agent and the vulcanization accelerator, and a final kneading (F-kneading) step of adding the vulcanizing agent and the vulcanization accelerator to the mixture obtained in the basic kneading step and mixing them. In addition, the basic kneading step can be divided into a plurality of steps as necessary.

[0188] The mixing conditions are not particularly limited, and, for example, a method of mixing at an discharge temperature of 150 to 170°C for 3 to 10 minutes in the basic kneading step, and mixing at 70 to 110°C for 1 to 5 minutes in the final kneading step can be given. The vulcanization conditions are not particularly limited, and, for example, a method of vulcanizing at 150 to 200°C for 10 to 30 minutes can be given.

[0189] [Tire]

[0190] The tire of the present application is provided with a tread having a first layer 6, a second layer 7, and a third layer 8, and can be a pneumatic tire or a non-pneumatic tire. Further, examples of the pneumatic tire include a passenger car tire, a truck / bus tire, a motorcycle tire, a high-performance tire, and the like. Further, the high-performance tire in the present specification is a tire with particularly excellent grip performance, and is a concept including a racing tire for a racing car.

[0191] The tire provided with a tread having a first layer 6, a second layer 7, and a third layer 8 can be manufactured by a conventional method using the aforementioned rubber composition. In other words, the tire can be manufactured by a method of extrusion-machining a raw rubber composition in which the aforementioned components are added to a rubber component as needed into the shape of the first layer 6, the second layer 7, and the third layer 8 using an extruder provided with a die having a predetermined shape, fitting them together with other tire components on a tire building machine, molding them by a conventional method to form an unvulcanized tire, and subsequently heating and pressurizing the unvulcanized tire in a vulcanizer.

[0192] In the tire of the present application, in the tire inner cavity, a sealing material, a noise damping body, a sensor or a tag for tire monitoring, and a mounting member thereof can be provided.

[0193] As the sealing material, those sealing materials that are generally used for the inner peripheral surface of the tread portion for the purpose of preventing puncture can be appropriately used. Specific examples of such a sealing material layer include, for example, the material layer disclosed in JP 2020-023152 A. In general, the thickness of the sealing material is preferably 1 to 10 mm. The width of the sealing material is generally preferably 85 to 115% of the maximum width of the belt layer, and more preferably 95 to 105% of the maximum width of the belt layer.

[0194] The sound deadener can suitably use any sound deadener as long as it can exert a sound deadening effect in the tire inner cavity. Specific examples of such a sound deadener include, for example, the examples disclosed in JP 2019-142503 A. The sound deadener is, for example, composed of a porous sponge material. The sponge material is a sponge-like porous structure, including, for example, in addition to a so-called sponge itself having interconnected cells (continuous bubbles) formed by foaming rubber or synthetic resin, a mesh body formed by integrally interweaving animal fibers, plant fibers, or synthetic fibers, or the like. Furthermore, the "porous structure" includes not only a structure having interconnected cells (continuous bubbles), but also a structure having closed cells (independent bubbles). Examples of the sound deadener include a sponge material having interconnected cells (continuous bubbles) made of polyurethane. As the sponge material, for example, synthetic resin sponges such as ether-based polyurethane sponge, ester-based polyurethane sponge, polyethylene sponge, and rubber sponges such as chloroprene rubber sponge (CR sponge), ethylene-propylene-diene rubber sponge (EDPM sponge), nitrile rubber sponge (NBR sponge), and the like can be suitably used, and in particular, from the viewpoints of sound deadening property, light weight, controllability of foaming, durability, and the like, a sponge of polyurethane-based or polyethylene-based or the like including ether-based polyurethane sponge is preferable.

[0195] The sound deadener is in a long band shape, has a bottom surface fixed to the inner cavity surface of the tread portion, and extends in the tire circumferential direction. At this time, the outer end portions in the circumferential direction can be brought into contact with each other to form a substantially toroidal shape, or the outer end portions can be spaced apart in the circumferential direction.

[0196] Examples

[0197] The present application is explained based on examples, but the present application is not limited to these examples.

[0198] The various chemicals used in the examples and comparative examples are shown below.

[0199] NR: TSR20

[0200] SBR1: Modified S-SBR (styrene content: 30% by mass, vinyl group content: 52 mol%, Mw: 250,000, non-extended product) manufactured in Production Example 1 described later

[0201] SBR2: Modified S-SBR (styrene content: 40% by mass, vinyl group content: 25 mol%, Mw: 1,100,000, non-extended product)

[0202] BR: UBEPOL BR (registered trademark) 150B (vinyl group content: 1.5 mol%, cis content: 97 mol%, Tg: -108°C, Mw: 440,000) manufactured by Ube Industries, Ltd.

[0203] Carbon black: Diablack N220 (N2SA: 115 m 2 / g)

[0204] Silica: ULTRASIL VN3 (N2SA: 175 m 2 / g, average primary particle diameter: 18 nm)

[0205] Silane coupling agent 1: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa

[0206] Silane coupling agent 2: NXT-Z45 (mercapto-based silane coupling agent) manufactured by Momentive Performance Materials

[0207] Oil: VivaTec 500 (TDAE oil) manufactured by H&R Group

[0208] Resin component: PetroTac 100V (C5-C9 petroleum resin, softening point: 96°C) manufactured by DKS

[0209] Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical

[0210] Wax: Sunnock N manufactured by Ouchi Shinko Chemical Industrial

[0211] Stearic acid: Bead stearic acid "Tsubaki" manufactured by NOF

[0212] Zinc oxide: Zinc oxide No. 2 manufactured by Mitsui Mining

[0213] Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur

[0214] Vulcanization accelerator 1: Nocceler CZ (N-cyclohexyl-2-benzothiazyl sulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industrial

[0215] Vulcanization accelerator 2: Nocceler D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industrial

[0216] Production Example 1: Synthesis of SBR1

[0217] Cyclohexane, tetrahydrofuran, styrene and 1,3-butadiene were charged into a nitrogen-replaced autoclave reactor. The temperature of the contents of the reactor was adjusted to 20°C, n-butyllithium was added to initiate polymerization. The polymerization was carried out under adiabatic conditions, the temperature reaching a maximum of 85°C. When the polymerization conversion reached 99%, 1,3-butadiene was added, and after further polymerization for 5 minutes, N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane was added as a modifier to carry out the reaction. After the polymerization reaction was completed, 2,6-di-tert-butyl-p-cresol was added. Next, the mixture was stripped to remove the solvent, dried by passing through a hot roll with the temperature adjusted to 110°C, and SBR1 was obtained.

[0218] (Examples and Comparative Examples)

[0219] According to the mixing formulation shown in Table 1, all chemicals except sulfur and vulcanization accelerators were mixed for 1 to 10 minutes using a 1.7L closed Banbury mixer until the discharge temperature reached 150 to 160°C, and a mix was obtained. Next, using a twin-screw roll mill, sulfur and vulcanization accelerators were added to the obtained mix, and the mixture was mixed for 4 minutes until the temperature reached 105°C, and an unvulcanized rubber composition was obtained. Using the obtained unvulcanized rubber composition, the unvulcanized rubber composition was extruded into a shape of a first layer (thickness: 3 mm), a second layer (thickness: 3 mm), and a third layer (thickness: 1 mm) of a tread using an extruder equipped with a die of a predetermined shape, and was laminated with other tire components to produce an unvulcanized tire, and then the unvulcanized tire was press-vulcanized at 170°C for 12 minutes to obtain each test tire (size: 205 / 65R15, rim: 15 x 6JJ, internal pressure: 230 kPa) shown in Table 2. In addition, the groove depth of the circumferential groove was set to 6 mm.

[0220] <Measurement of Free Sulfur Amounts of the First Layer, the Second Layer, and the Third Layer>

[0221] The amount of sulfur Ts (mass%) in each rubber test piece after vulcanization was calculated using the oxygen flask combustion method according to Japanese Industrial Standard JIS K 6233:2016. Next, according to Japanese Industrial Standard JIS K 6229-3:2015, the aforementioned test piece was immersed in acetone for 24 hours to extract a soluble component. The test piece after extraction of the soluble component was placed in an oven and heated at 100°C for 30 minutes to remove the solvent in the test piece, and then the amount of sulfur As (mass%) in the test piece was calculated using the oxygen flask combustion method according to Japanese Industrial Standard JIS K 6233:2016. Then, the difference (Ts-As) between the amount of sulfur Ts and the amount of sulfur As was calculated to determine the free sulfur amount. Furthermore, for each rubber test piece of the first layer, the second layer, and the third layer, a portion cut out from the tread portion of each test tire was used.

[0222] Measurement of Acetone Extraction Amount (AE amount) of First Layer, Second Layer and Third Layer

[0223] According to Japanese Industrial Standard JIS K 6229:2015, 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 acetone extraction amount was calculated using the following calculation formula. In addition, for each rubber test piece of the first layer, the second layer and the third layer, it was cut out from the tread portion of each test tire.

[0224] Acetone extraction amount (% by mass) = {(mass of rubber test piece before extraction - mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} x 100

[0225] Measurement of Toluene Swelling Index and Mass Change Rate

[0226] According to Japanese Industrial Standard JIS K 6258:2016, the mass of each rubber test piece after vulcanization before and after immersion in acetone for 24 hours was measured, and the toluene swelling index was calculated using the following equation. The results are shown in Table 1. The value obtained by subtracting 100 from the calculated toluene swelling index is the mass change rate (%). The smaller the toluene swelling index and the mass change rate, the higher the crosslinking density.

[0227] (Toluene swelling index) = (weight after immersion) / (weight before immersion) x 100

[0228] Tensile Test

[0229] Each rubber layer was cut out from the tread portion of each test tire and a No. 7 dumbbell-shaped test piece was prepared with the tire circumferential direction as the tensile direction. According to JIS K 6251:2017 "Vulcanized Rubber or Thermoplastic Rubber - Determination of Tensile Stress-Strain Properties", a tensile test was performed on the No. 7 dumbbell-shaped test piece at 23°C atmosphere and a tensile speed of 3.3 mm / second, and the modulus (MPa) at 100% elongation was measured.

[0230] Measurement of Loss Tangent tan δ

[0231] Each rubber test piece of 20 mm long x 4 mm wide x 1 mm thick was cut out from each rubber layer of the tread portion of each test tire with the tire circumferential direction as the long side. Using an EPLEXOR series manufactured by GABO Qualimeter Testanlagen GmbH, the loss tangent tan δ of each rubber test piece was measured at a temperature of 0°C, an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10 Hz. In addition, the thickness direction of the sample was set as the tire radial direction.

[0232] Measurement of Rubber Hardness

[0233] The tire was cut in the radial direction at a width of 20 mm, the cut surface was smoothed, and then an A-type durometer was pressed against the rubber from the cross-sectional direction to measure the Shore hardness (Hs) of each rubber layer after vulcanization at 23°C.

[0234] <Wet handling stability>

[0235] Each test tire was mounted on all wheels of a vehicle (Japanese FF, displacement 2,000 cc), and the vehicle was driven on a test course having a wet asphalt pavement for 10 laps. Based on the feeling of 10 test drivers for the respective handling stability at the time of entry, rotation, and exit at a turn, the scores were rated in 10 levels, the total score was calculated, and then the score of Comparative Example 1 was taken as 100 to convert the total score into an index. The larger the value, the better the handling stability on a wet pavement.

[0236] <Overall wear resistance>

[0237] Each test tire was mounted on all wheels of a vehicle (Japanese FF, displacement 2,000 cc), and the driving distance until the wear indicator was exposed was measured, the driving distance of Comparative Example 1 was taken as 100 to convert the driving distance into an index. The larger the value, the better the overall wear resistance until the end of driving.

[0238]

[0239]

[0240] [Table 2]

[0241] Table 2

[0242]

[0243] From the results of Table 1 and Table 2, it was found that the tire of the present application (in which, in the tread portion, three or more rubber layers are provided, and a concentration gradient of free sulfur amount is formed from the rubber layer on the inner side in the tire radial direction toward the rubber layer on the outer side in the tire radial direction) has improved comprehensive performance (the sum of the wet handling stability and the overall wear resistance index) of the handling stability on a wet pavement and the overall wear resistance until the end of driving.

Claims

1. A tire having a tread, the tread at least having a first layer constituting a tread surface, a second layer disposed in abutment on a radially inner side of the first layer, and a third layer disposed in abutment on a radially inner side of the second layer, characterized in that, the first layer, the second layer, and the third layer are constituted by rubber compositions containing a rubber component, the free sulfur amount of the rubber composition constituting the third layer is greater than the free sulfur amount of the rubber composition constituting the second layer, the free sulfur amount of the rubber composition constituting the second layer is greater than the free sulfur amount of the rubber composition constituting the first layer, the difference between the free sulfur amount of the rubber composition constituting the third layer and the free sulfur amount of the rubber composition constituting the second layer is 0.1% or greater, the difference between the mass change rate Xl (%) before and after immersion in toluene at 23°C for 24 hours of the rubber composition constituting the first layer measured according to JIS K 6258:2016 and the mass change rate X2 (%) before and after immersion in toluene at 23°C for 24 hours of the rubber composition constituting the second layer measured according to JIS K 6258:2016, i.e., Xl-X2, is 50% or less, the tan δ at 0°C of the rubber composition constituting the first layer and the tan δ at 0°C of the rubber composition constituting the second layer are each 0.45 or greater, the difference between the hardness of the rubber composition constituting the second layer and the hardness of the rubber composition constituting the first layer is 5 or less, the specific gravity of the rubber composition constituting the first layer and the specific gravity of the rubber composition constituting the second layer are each 1.25 or less, the specific gravity of the rubber composition constituting the second layer is less than 1.20, the acetone extract amount AE2 of the rubber composition constituting the second layer is greater than the acetone extract amount AE1 of the rubber composition constituting the first layer, the modulus at 23°C when extended by 100% of the rubber composition constituting the second layer is greater than the modulus at 23°C when extended by 100% of the rubber composition constituting the first layer, the rubber composition constituting the first layer and the rubber composition constituting the second layer each contain a butadiene rubber, the rubber composition constituting the first layer and the rubber composition constituting the second layer each contain a reinforcing filler and a silane coupling agent, the amount of silica contained in the reinforcing filler in the rubber composition constituting the first layer and the amount of silica contained in the reinforcing filler in the rubber composition constituting the second layer are each 80% by mass or greater, the silane coupling agent contained in the rubber composition constituting the first layer and the silane coupling agent contained in the rubber composition constituting the second layer are each a mercapto-based silane coupling agent, the rubber composition constituting the second layer contains a resin component, the thickness of the third layer is smaller than both the thickness of the first layer and the thickness of the second layer, and the tread has land portions separated by a plurality of circumferential grooves, the deepest part of the groove bottom of at least one circumferential groove is formed to be located on a radially inner side of the outermost portion of the second layer.

14. The tire according to claim 1 or 2, characterized in that, the tread has land portions separated by a plurality of circumferential grooves, the deepest part of the groove bottom of at least one circumferential groove is formed to be located on a radially inner side of the outermost portion of the second layer. ​ ​ ​ 2. Tyre according to Claim 1, characterized in that, ​ 3. Tyre according to Claim 1 or 2, characterised in that, ​ 4. Tyre according to claim 1 or 2, characterised in that, ​ 5. Tyre according to claim 1 or 2, characterised in that, ​ 6. Tyre according to claim 1 or 2, characterised in that, ​ 7. A tyre according to claim 1 or 2, characterised in that, ​ 8. A tyre according to claim 1 or 2, characterised in that, ​ 9. Tyre according to claim 1 or 2, characterised in that, ​ ​ ​ ​ 11. Tyre according to Claim 10, characterized in that, ​ 12. A tyre according to claim 1 or 2, characterised in that, ​ 13. A tyre according to claim 1 or 2, characterised in that, ​ ​ ​ ​ 15. Tyre according to Claim 14, characterized in that, The land portion is provided with a sipe which is not open at both ends to the circumferential groove.

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