pneumatic tires

Abstract

We offer tires with improved durability. [Solution] A pneumatic tire having a tread portion, wherein the tread portion includes a cap rubber layer including the tread contact surface and a heat dissipation rubber layer, the heat dissipation rubber layer extends in the tire axial direction while at least a portion of its entire length is in contact with the cap rubber layer and is arranged to be exposed on the tire side surface, the thermal conductivity of the heat dissipation rubber layer is greater than the thermal conductivity of the cap rubber layer, the length (mm) of the heat dissipation rubber layer is Ld, and the loss loss tangent of the heat dissipation rubber layer at 70°C is 70°C tanδ D The loss loss tangent of the cap rubber layer at 70°C is defined as 70°C tanδ. C In this case, Ld and 70°C tanδ D and 70℃ tanδ C A pneumatic tire that satisfies the relationship in equation (1). (1) Ld × (70℃ tanδ D / 70℃ tanδ C )>10

Description

[Technical Field]

[0001] This invention relates to a pneumatic tire. [Background technology]

[0002] Tires deform and generate heat when rolling. This heat generated by tire components is believed to accelerate the deterioration of the rubber. Therefore, efforts are being made to improve tire durability by releasing heat from within the tire. For example, Patent Document 1 describes a tire in which a heat-conductive component containing a fibrous material with a higher thermal conductivity than rubber is placed from the inside of the tire to near the surface of the sidewall. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-107953 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention aims to provide a tire with improved durability. [Means for solving the problem]

[0005] This invention relates to the following tires. A pneumatic tire having a tread section, The tread portion includes a cap rubber layer including the tread contact surface and a heat dissipation rubber layer. The heat-dissipating rubber layer extends in the tire axial direction, with at least a portion of it in contact with the cap rubber layer over its entire length, and is arranged to be exposed on the tire side surface. The thermal conductivity of the heat-dissipating rubber layer is greater than that of the cap rubber layer. Let Ld be the extended length (mm) of the heat dissipation rubber layer, and let 70°C tanδ be the loss tangent of the heat dissipation rubber layer at 70°C. Dand the loss tangent of the cap rubber layer at 70°C is 70°C tanδ C When this is the case, Ld and 70°C tanδ D and 70°C tanδ C and 70°C tanδ (1) Ld × (70°C tanδ D / 70°C tanδ C ) > 10 [Advantages of the Invention]

[0006] According to the present invention, it is possible to provide a tire that suppresses heat accumulation in the tire and has improved durability. [Brief Description of the Drawings]

[0007] [Figure 1] It is a cross-sectional view taken along a plane including the tire rotation axis of the tire according to an embodiment of the present invention. [Figure 2] It is a partial perspective view of the tire according to an embodiment of the present invention. [Modes for Carrying Out the Invention]

[0008] A tire according to an embodiment of the present invention will be described. The tire of this embodiment is a pneumatic tire provided with a tread portion, and the tread portion includes a cap rubber layer including a tread contact surface and a heat dissipation rubber layer. The heat dissipation rubber layer extends in the tire axial direction while at least a part thereof is in contact with the cap rubber layer throughout its entire extension length and is arranged so as to be exposed on the tire side surface. The thermal conductivity of the heat dissipation rubber layer is greater than the thermal conductivity of the cap rubber layer. The extension length (mm) of the heat dissipation rubber layer is Ld, and the loss tangent of the heat dissipation rubber layer at 70°C is 70°C tanδ D and the loss tangent of the cap rubber layer at 70°C is 70°C tanδ C When this is the case, Ld and 70°C tanδ D and 70°C tanδ C and 70°C tanδ (1) Ld × (70°C tanδ D / 70°C tanδC )>10

[0009] While not intended to be constrained by theory, the following mechanisms are considered to improve durability in this invention: (A) A heat-dissipating rubber layer with a higher thermal conductivity than the cap rubber layer is provided in the tread area, and the heat-dissipating rubber layer extends from the inside of the cap rubber layer to the side of the tire, so that heat accumulated inside the tread area, especially near both ends of the tread area in the width direction of the tire, can be released to the outside when the tire is running. (B) The loss tangent (70°C tanδ) of the rubber composition constituting the heat-dissipating rubber layer at 70°C. D ) and the loss loss tangent (70°C tanδ) of the rubber composition constituting the cap rubber layer at 70°C. C Focusing on the relationship with ), 70℃ tanδ D / 70℃ tanδ C If the value is large, it is thought that the heat dissipation effect of the heat dissipation rubber layer can suppress heat accumulation in the shoulder area. (C)70℃tanδ D / 70℃ tanδ C Even when is small, if the extension length (Ld) of the heat-dissipating rubber layer is large enough to satisfy the relationship in equation (1), the volume of the heat-dissipating rubber layer increases, creating a state in which heat from inside the tire is dissipated to the tire surface and the outside air, and heat accumulation in the tread can be effectively suppressed. It is thought that (A), (B), and (C) work together to improve the durability of the tire.

[0010] It is more preferable that the rubber composition constituting the cap rubber layer contains 20 parts by mass or more of silica per 100 parts by mass of the rubber component.

[0011] It is believed that by including a predetermined amount or more of silica in the rubber composition constituting the cap rubber layer, heat accumulation in the cap rubber layer can be suppressed, thereby improving durability.

[0012] Preferably, at least a portion of the heat-dissipating rubber layer is located between the cap rubber layer and the base rubber layer in the radial direction of the tire.

[0013] It is believed that the heat transfer path extending from the inside of the cap rubber layer to the side of the tire is formed as a heat dissipation rubber layer, allowing heat accumulated inside the tread during tire operation to be released to the outside.

[0014] The aforementioned 70℃ tanδ C It is preferable that the value is 0.15 or less.

[0015] By using a rubber composition with a 70°C tanδ of less than or equal to a predetermined value as the rubber composition constituting the cap rubber layer, it is believed that the heat generation of the rubber composition will be suppressed, and consequently, the durability of the tire will be improved.

[0016] It is preferable that the right-hand side of equation (1) is 20.

[0017] Tires that meet equation (1) under more stringent conditions are likely to have even greater durability.

[0018] Preferably, the rubber composition constituting the heat-dissipating rubber layer contains 50 parts by mass or more of a thermally conductive filler per 100 parts by mass of the rubber component.

[0019] The increased thermal conductivity of the heat-dissipating rubber layer enhances heat dissipation, which is expected to contribute to improved tire durability.

[0020] It is preferable that the thermal conductivity (W / m·K) of the heat-dissipating rubber layer is 0.40 or higher.

[0021] This is expected to improve heat dissipation and contribute to increased tire durability.

[0022] The aforementioned 70℃ tanδ D It is preferable that the value is 0.16 or higher.

[0023] It is believed that using a rubber composition with a 70°C tanδ of 70°C or higher as the rubber composition constituting the heat dissipation rubber layer will improve the heat dissipation performance and durability of the heat dissipation rubber layer.

[0024] When TW is the contact width of the tread portion in the axial direction of the tire, it is preferable that the ratio of Ld to TW (Ld / TW) is 0.04 or more and less than 0.20.

[0025] By setting the extension length of the heat-dissipating rubber layer to a predetermined ratio with respect to the tire's contact width, heat dissipation is improved, which is thought to contribute to improved tire durability.

[0026] Preferably, the outer surface of the tire radially inward from the exposed position of the heat-dissipating rubber layer is provided with a row of recesses formed along the circumferential direction of the tire, and preferably the recesses are arranged at equal intervals in the circumferential direction of the tire. Furthermore, preferably the row of recesses is arranged radially inward from the maximum width position of the tire, and preferably the ratio of the circumferential length w of the recesses to the circumferential spacing P of the recesses (w / P) is 0.60 to 0.90.

[0027] This effectively generates turbulence on the outer surface of the tire, allowing heat generated in the tire to be effectively released to the outside. As a result, the heat dissipation efficiency of the heat conducted by the heat-dissipating rubber layer is improved, which is thought to enhance the tire's durability.

[0028] In this specification, the upper and lower numerical limits related to "greater than or equal to" and "less than or equal to" in the description of numerical ranges are numbers that can be arbitrarily combined, and in addition, the numerical values ​​in the examples can also be combined with these upper and lower limits. Furthermore, in this specification, a numerical range shown as including both ends of the range is understood to simultaneously indicate a numerical range that does not include either of the two ends of the range, and even a numerical range that does not include either of the two ends of the range, as long as this does not contradict the spirit of the present invention.

[0029] [Definition] The "tread portion" refers to a component that includes the part that forms the contact surface of the tire. In a cross-section of the tire with a plane including the tire's axis of rotation, if the tire has components that reinforce and form the tire's structure, such as a belt layer, belt reinforcement layer, or carcass layer, located on the radially inner side of the tire, the tread portion is a component that is positioned radially outward from these components.

[0030] "Standard condition" refers to a state of no load where the tire is mounted on a standard rim and filled with air at the standard internal pressure. Unless otherwise specified, tires in the standard condition should be used.

[0031] Unless otherwise specified, the "dimensions of each part of the tire" refer to values ​​that are determined in the normal state for those visible on the outer surface of the tire, while those located inside the tire or on the cut surface of the tire refer to values ​​that are determined, for example, by cutting the tire in a plane including the tire's axis of rotation and holding the cut tire piece within the rim width of the normal rim.

[0032] A "standard rim" refers to the rim specified for each tire within the standards system that the tire is based on. For example, for JATMA (Japan Automobile Tire Manufacturers Association), it refers to the standard rim for the applicable size listed in the "JATMA YEAR BOOK," for ETRTO (The European Tyre and Rim Technical Organisation), it refers to the "Measuring Rim" listed in the "STANDARDS MANUAL," and for TRA (The Tire and Rim Association, Inc.), it refers to the "Design Rim" listed in the "YEAR BOOK." Refer to JATMA, ETRTO, and TRA in that order, and if an applicable size is available at the time of reference, follow that standard. In the case of a tire not specified in the above standards, it refers to the narrowest rim width among the smallest diameter rims that can be mounted on that tire and that can maintain internal pressure (i.e., do not cause air leakage between the rim and tire).

[0033] "Regular internal pressure" refers to the air pressure specified for each tire in the standards system, including the standard on which the tire is based. For example, for JATMA it refers to "maximum air pressure," for ETRTO it refers to "INFLATION PRESSURE," and for TRA it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." As with regular rims, refer to JATMA, ETRTO, and TRA in that order, and if there is an applicable size at the time of reference, follow that standard. In the case of tires not specified in the above standards, it refers to the regular internal pressure (but at least 250kPa) of another tire size (but specified in the standard) that is listed with the aforementioned regular rim as the standard rim. If multiple regular internal pressures of 250kPa or higher are listed, refer to the lowest value among them.

[0034] "Regular load (kg)" refers to the load specified for each tire in the standard system that the tire is based on. For example, for JATMA it is "Maximum Load Capacity," for ETRTO it is "LOAD CAPACITY," and for TRA it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." As with regular rims and regular in-tire pressure, refer to JATMA, ETRTO, and TRA in that order, and if an applicable size is available at the time of reference, follow that standard. For tires not specified in the above standards, the maximum load capacity (kg) is calculated separately. L This is considered the normal load.

[0035] "Maximum load capacity W L The weight (kg) is calculated using the following formula: "V" is the virtual volume of the tire (mm²). 3), "Dt" is the outer diameter of the tire in the normal state (mm), "Ht" is the height of the tire's cross-section in the radial direction in a plane containing the tire's axis of rotation (mm), and "Wt" is the width of the tire's cross-section in the normal state (mm). Ht can be calculated by (Dt-R) / 2, where R is the rim diameter of the tire. Wt is the value obtained by removing any patterns or letters on the tire's sidewall. Note that the maximum load capacity is synonymous with the normal load mentioned above.

[0036]

number

[0037] "Tire outer diameter Dt" refers to the outer diameter of the tire in its normal state.

[0038] "Tire section width Wt" refers to the maximum width between the outer surfaces of the sidewalls in a normal state (excluding patterns or letters on the tire sidewall if any).

[0039] "Tire section height Ht" refers to the height in the radial direction of the tire's cross-section, defined by the plane containing the tire's axis of rotation. When the tire's rim diameter is R, it corresponds to half the difference between the tire's outer diameter Dt and its rim diameter R. In other words, the section height Ht can be calculated using (Dt-R) / 2.

[0040] "Tire weight G" refers to the weight (kg) of the tire alone, excluding the weight of the rim. However, if the tire's internal cavity contains components such as sponge, sealant, or sensor components, the weight includes these components.

[0041] "Contact width TW" is the maximum width of the contact area in the tire width direction. TW is determined by mounting the tire to a standard rim, filling it to the standard internal pressure, letting it stand at 25°C for 24 hours, then applying ink to the tire tread surface, applying a standard load (a load equal to the maximum load capacity) to the tire, pressing it perpendicularly onto cardboard (camber angle 0°), transferring the ink to create a copy of the contact area, and then filtering the resulting contact area to determine the maximum width in the tire width direction. However, the same transfer process is performed at a total of 5 locations, rotating the tire 72 degrees each time, and the average of these 5 maximum width values ​​is taken as TW.

[0042] "Extended length Ld" is the longitudinal length of the heat-dissipating rubber layer in the tire cross-section along the tire meridian. This corresponds to Ld in Figure 1.

[0043] [Measurement method] "Styrene content" can be determined by pyrolysis gas chromatography or NMR measurement. 1 H-NMR and 13 It is calculated by 13C-NMR. Unlike physical properties such as the complex modulus (E*), the amounts of components such as "styrene content" have true values ​​that do not depend on the measurement method, so it is preferable to use a measurement method that is as accurate as possible. In this specification, "pyrolysis gas chromatography" refers to a method in which a sample is heated by a pyrolysis apparatus, the individual components contained in the gas phase components produced by this heating are separated by a separation column, and each isolated component is analyzed.

[0044] "Vinyl content (amount of 1,2-bonded butadiene units)" can be determined by pyrolysis gas chromatography or NMR measurement. 1 H-NMR and 13 It is calculated using 1C-NMR. Similar to "styrene content," a true value exists for "vinyl content" that is independent of the measurement method, so it is preferable to use the most accurate measurement method possible.

[0045] "Cis content (amount of cis-1,4-bonded butadiene units)" is determined by infrared absorption spectroscopy or NMR measurement in accordance with JIS K 6239-2:2017. 1 H-NMR and13 This value is measured by 13C-NMR and is applied, for example, to rubber components having repeating units derived from butadiene, such as BR. Similar to "styrene content," a true value exists for "cis content" that is independent of the measurement method, so it is preferable to use the most accurate measurement method possible.

[0046] The "loss tangent of the rubber composition" is the loss tangent (tanδ) measured in extension mode under various conditions using a dynamic viscoelasticity measuring device (e.g., the Iplexer series from GABO). The measurement sample is prepared by cutting a 20mm long x 4mm wide x 1mm thick sample from a tire component such as the tire cap rubber layer or heat dissipation rubber layer. In all cases, the sample is prepared as close to the specified dimensions as possible. This is because the strain applied to the sample is normalized with respect to its length, and the measured tanδ is normalized with respect to the width and thickness of the sample, so it is considered that there is no influence from the size of the sample.

[0047] "70℃tanδ" is the loss tangent (tanδ) measured under the conditions of a temperature of 70℃, a frequency of 10Hz, an initial strain of 10%, a dynamic strain of ±1%, and extension mode.

[0048] The "weight-average molecular weight (Mw)" can be determined by converting the measured value using gel permeation chromatography (GPC) (for example, the GPC-8000 series manufactured by Tosoh Corporation, with a differential refractometer as the detector and TSKgel® SuperMultiporeHZ-M column manufactured by Tosoh Corporation) to a standard polystyrene equivalent. This method is applicable, for example, to SBR, BR, etc.

[0049] The nitrogen adsorption specific surface area (N2SA) of carbon black is measured in accordance with JIS K 6217-2:2017.

[0050] The nitrogen adsorption specific surface area (N2SA) of silica is measured by the BET method in accordance with ASTM D3037-93.

[0051] The "average primary particle diameter" is a value obtained by photographing particles with a transmission or scanning electron microscope and taking the arithmetic mean of the particle diameters of 400 particles. If the particle shape is spherical, the diameter of the sphere is used as the particle diameter; if it is not spherical, the equivalent diameter of a circle (the positive square root of {4 × (particle area) / π}) is calculated from the microscope image and used as the particle diameter. The average primary particle diameter is applied to silica, carbon black, and other materials.

[0052] The "thermal conductivity (W / m·K)" is a value measured according to the hot-wire method specified in JIS R 2616 (measurement temperature: 23°C). Specifically, it can be measured using a rapid thermal conductivity meter such as the "kemtherm QTM-500" manufactured by Kyoto Electronics Manufacturing Co., Ltd., or a thermal conductivity measuring device such as the "TCM1001" manufactured by Resca Co., Ltd. The measurement sample may be a vulcanized rubber composition of the tire component to be measured, or it may be cut out from the tire. When creating a vulcanized rubber composition by press-vulcanizing the unvulcanized rubber composition of the tire component, the sample should be made of the vulcanized rubber composition with dimensions of 100 mm in length, 50 mm in width, and 10 mm in thickness. When cutting out from a tire, the sample should be cut out to a thickness of 10 mm or more.

[0053] A "plasticizer" is a material that imparts plasticity to rubber components and is extracted from rubber compositions using acetone. This definition includes both liquid plasticizers at 25°C and solid plasticizers at 25°C. However, it excludes waxes and stearic acid commonly used in the tire industry.

[0054] The "softening point of the resin component" is the temperature at which the sphere descends when the softening point specified in JIS K 6220-1:2015 7.7 is measured using a ring-type softening point measuring device.

[0055] [tire] A tire, which is one embodiment of the present invention, will be described below with reference to the drawings as appropriate. However, the drawings used are merely specific examples of one embodiment, and the present invention is not limited by these drawings.

[0056] The tire according to this embodiment comprises a tread portion having a cap rubber layer and a heat dissipation rubber layer made of a predetermined rubber composition, wherein at least a portion of the heat dissipation rubber layer extends in the tire axial direction while in contact with the cap rubber layer over its entire length, and is preferably arranged to be exposed on the tire side surface. The thermal conductivity of the heat dissipation rubber layer is greater than that of the cap rubber layer, Ld, 70℃ tanδ D , 70℃ tanδ C This satisfies the relationship in equation (1).

[0057] Figure 1 is a schematic diagram showing a portion of the cross-section (upper right portion of the cross-section) of a tire according to one embodiment of the present invention, along the tire meridian. In Figure 1, the tread portion 3 has a cap rubber layer 4 that constitutes the tread surface 2 and a base rubber layer 5 that is located inside the cap rubber layer. The heat dissipation rubber layer 6 is located between the cap rubber layer 4 and the base rubber layer 5 in the radial direction of the tire, is in contact with the cap rubber layer 2, extends in the axial direction of the tire with a length Ld, and is exposed on the side surface of the tire. The contact width of the tread portion is shown as TW.

[0058] As shown in Figure 1, it is preferable that at least a portion of the heat dissipation rubber layer is located between the cap rubber layer and the base rubber layer in the radial direction of the tire. Furthermore, regarding the exposed position of the heat dissipation rubber layer, as long as at least a portion of the heat dissipation rubber layer is in contact with the cap rubber layer over its entire length, there are no particular restrictions on the exposed position as long as the heat dissipation rubber layer is exposed on the side of the tire. However, it is preferable that it be more than 30 mm away from the maximum width position of the tire, more preferably more than 40 mm away, and even more preferably more than 50 mm away.

[0059] (Ld) The extended length L (mm) of the heat-dissipating rubber layer is preferably more than 5 mm, more preferably more than 7 mm, even more preferably more than 10 mm, even more preferably 12 mm or more, and even more preferably 15 mm or more. There is no particular upper limit, but for example it may be less than 50 mm, preferably less than 40 mm, more preferably less than 30 mm, and even more preferably less than 25 mm. Being within this range allows heat from inside the tire, such as the cap rubber layer, to be efficiently transferred to the outer surface of the tire and released to the outside of the tire.

[0060] (Thermal conductivity) In this embodiment, the thermal conductivity of the heat-dissipating rubber layer is greater than that of the cap rubber layer. As a result, the heat generated in the cap rubber layer is released to the outside of the tire through the heat-dissipating rubber layer, which is thought to suppress the deterioration of the cap rubber layer and improve its durability.

[0061] <Thermal conductivity of the cap rubber layer> In this embodiment, the thermal conductivity of the rubber composition for the cap rubber is 0.15 W / m·K or higher. Preferably, the thermal conductivity is 0.18 W / m·K or higher, more preferably 0.20 W / m·K or higher, and even more preferably 0.24 W / m·K or higher. There is no particular upper limit, but for example, it may be 2.0 W / m·K or lower, or 1.0 W / m·K or lower. The thermal conductivity of the rubber composition is measured based on the method described above.

[0062] <Thermal conductivity of the heat-dissipating rubber layer> In this embodiment, the thermal conductivity of the rubber composition for the heat-dissipating rubber layer is preferably 0.30 W / m·K or higher. This allows heat generated in the cap rubber to be efficiently released to the outside of the tire, which is thought to improve the tire's durability. The thermal conductivity is more preferably 0.40 W / m·K or higher, and even more preferably 0.50 W / m·K or higher. A higher thermal conductivity is preferable, and there is no particular upper limit, but for example, it may be 3.0 W / m·K or lower, or 2.0 W / m·K or lower. The thermal conductivity of the heat-dissipating rubber layer is preferably 1.5 to 10 times, more preferably 1.7 to 9 times, and even more preferably 2 to 8 times, compared to the thermal conductivity of the cap rubber layer. The thermal conductivity of the rubber composition is measured based on the method described above.

[0063] The thermal conductivity of a rubber composition can be adjusted by changing the type and amount of fillers and other compounding agents described below. For example, by adding a large amount of additives that have little effect on increasing thermal conductivity (such as silica, titanium dioxide, and calcium carbonate), the thermal conductivity can be kept low. Similarly, by reducing or omitting the amount of carbon black, the thermal conductivity can be further reduced. Conversely, for example, by adding a large amount of carbon black and reducing or omitting the amount of silica, the thermal conductivity of the rubber composition can be increased. Furthermore, the thermal conductivity can also be increased by incorporating highly conductive fillers into the rubber composition.

[0064] (Formula (1)) The right-hand side of equation (1) is preferably 15, more preferably 17, even more preferably 20, even more preferably 23, even more preferably 25, and even more preferably 30. The value of the left-hand side of equation (1) has no particular upper limit, but is, for example, less than 150, preferably less than 120, more preferably less than 100, and even more preferably less than 70.

[0065] Regarding equation (1), 70℃ tanδ C The value and 70℃ tanδ DThe value of 70°C tanδ can be adjusted as appropriate by conventional methods in the tire industry. Specifically, it can be adjusted by changing the type and amount of chemicals (e.g., rubber components, fillers, softeners, sulfur, vulcanization accelerators, silane coupling agents, etc.) blended into the tire rubber composition. For example, by reducing the content of silica or aromatic petroleum resins, the 70°C tanδ can be adjusted. C The value and 70℃ tanδ D The value of can be made smaller. Also, by increasing it, 70℃tanδ C The value and 70℃ tanδ D The value of can be increased. Therefore, those skilled in the art can increase the target 70°C tanδ. D / 70℃ tanδ C Depending on the value, 70℃ tanδ C The value and 70℃ tanδ D The value of can be adjusted as appropriate. Also, as Ld increases, the value on the left side of equation (1) increases, and conversely, as it decreases, the value of the same thing decreases. Focusing on this relationship, Ld, 70℃ tanδ C and 70℃ tanδ D By adjusting this, the value on the left side of equation (1) can be adjusted.

[0066] (Ld / TW) When the contact width of the tread portion in the axial direction of the tire is denoted as TW, the ratio of Ld to TW (Ld / TW) is preferably greater than 0.03, more preferably 0.04 or greater, even more preferably 0.05 or greater, and still more preferably 0.06 or greater. Furthermore, Ld / TW is preferably less than 0.20, more preferably less than 0.18, and even more preferably less than 0.15.

[0067] Figure 2 is a partial perspective view of tire 1. As shown in Figure 2, in this embodiment, it is preferable that a series of recesses 9R are formed along the circumferential direction of the tire on the outer surface 7 of the tire, which is radially inward from the exposed position of the heat-dissipating rubber layer 6. Such a series of recesses 9R generates turbulence f on the outer surface 7 of the tire when the tire 1 is running. This turbulence f is thought to draw in cold air from outside the tire onto the outer surface 7. This cold air is then moved outward in the radial direction of the tire by the centrifugal force caused by the tire rotation, cooling the area outside the radial direction of the tire and contributing to improved tire durability.

[0068] The depth of the recess 9 should preferably be between 1.0 and 5.0 mm. A depth of 1.0 mm or more can generate turbulence on the outer surface 7 of the tire, while a depth of 5.0 mm or less is thought to prevent the generation of excessively large turbulence, thus having little effect on the rolling resistance of the tire 1.

[0069] The recesses 9 are arranged, for example, at equal intervals in the circumferential direction of the tire. As a result, turbulence f is generated at equal intervals by the recesses 9, which is thought to effectively cool the outer surface 7 of the tire and contribute to improving the durability of the tire.

[0070] The ratio of the spacing P (mm) of the recess 9 in the tire circumferential direction to the depth (mm) of the recess 9 is preferably 1.0 to 30.0. Setting it within this range is thought to effectively generate turbulence f on the outer surface 7 of the tire, promoting heat dissipation from the tire and contributing to improved tire durability. A ratio of 3.0 or higher is more preferable, and 5.0 or higher is even more preferable.

[0071] The ratio (w / P) of the length w (mm) of the recess 9 in the tire circumferential direction to the spacing P (mm) of the recess 9 is preferably, for example, 0.60 to 0.90. A ratio (w / P) of 0.60 or higher is thought to effectively generate turbulence f, promote heat dissipation from the tire, and contribute to improving tire durability.

[0072] [Rubber composition for cap rubber layer] The components of the rubber composition for the cap rubber layer will be described below.

[0073] (Rubber component) The rubber composition for the cap rubber layer preferably contains isoprene-based rubber (IR-based rubber) and butadiene rubber (BR). In this case, the rubber components may include other rubber components in addition to isoprene-based rubber and butadiene rubber. Alternatively, it may consist only of isoprene-based rubber and butadiene rubber.

[0074] <Isoprene-based rubber> As isoprene-based rubbers, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. Natural rubber includes not only unmodified natural rubber (NR), but also modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and grafted natural rubber. These isoprene-based rubbers may be used individually or in combination of two or more types.

[0075] NR is not particularly limited and can be any tire that is common in the tire industry, such as SIR20, RSS#3, and TSR20.

[0076] The content of isoprene-based rubber in the rubber component is preferably more than 30% by mass, more preferably more than 35% by mass, and even more preferably 40% by mass or more. Furthermore, the content is preferably less than 80% by mass, more preferably less than 70% by mass, even more preferably less than 65% by mass, and even more preferably 60% by mass or less.

[0077] BR is not particularly limited, and for example, BR with a cis content of less than 50 mol% (low-cis BR), BR with a cis content of 90 mol% or more (high-cis BR), rare-earth butadiene rubber synthesized using a rare-earth element catalyst (rare-earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis modified BR, low-cis modified BR), etc., which are common in the tire industry, can be used. BR may be used alone or in combination of two or more types.

[0078] High-cis BR can be commercially available from companies such as Nippon Zeon Co., Ltd., UBE Corporation, and JSR Corporation. Including high-cis BR can improve low-temperature properties and wear resistance. The cis content of high-cis BR is preferably more than 90 mol%, more preferably more than 95 mol%, and even more preferably 96 mol% or more. The cis content of BR is measured by the measurement method described above.

[0079] Rare earth-based BR is synthesized using a rare earth element catalyst, and has a vinyl content of preferably less than 1.8 mol%, more preferably less than 1.5 mol%, and even more preferably less than 1.2 mol%, and a cis content of preferably more than 90 mol%, more preferably more than 95 mol%, and even more preferably 96 mol% or more. As rare earth-based BR, commercially available products from companies such as Lanxess can be used.

[0080] SPB-containing BR refers to a type in which 1,2-syndiotactic polybutadiene crystals are not simply dispersed in BR, but are chemically bonded to and dispersed in BR. Such SPB-containing BR can be commercially available from companies such as UBE Corporation.

[0081] Examples of modified BR include BR modified with functional groups similar to those described for SBR above, as well as modified butadiene rubber (modified BR) in which the terminal and / or main chain is modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen.

[0082] 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 ends of the modified BR molecule are linked by a tin-carbon bond (tin-modified BR). Furthermore, the modified BR may be either unhydrogenated or hydrogenated.

[0083] The weight-average molecular weight (Mw) of BR is preferably greater than 300,000, more preferably greater than 350,000, and even more preferably greater than 400,000. Furthermore, from the viewpoint of crosslinking uniformity, it is preferably less than 2,000,000, more preferably less than 1,000,000, and even more preferably less than 700,000. The Mw of BR can be determined by the method described above.

[0084] The content of BR in the rubber component is preferably more than 5% by mass, more preferably more than 10% by mass, and even more preferably more than 15% by mass. Furthermore, the content is preferably less than 50% by mass, more preferably less than 40% by mass, even more preferably less than 30% by mass, and even more preferably less than 25% by mass.

[0085] The rubber component contains IR rubber and BR, preferably with an IR rubber content of 30% by mass or more of the total rubber component by mass, and a BR content of 5% by mass or more of the total rubber component by mass. More preferably, the IR rubber content is 35% by mass or more and the BR content is 10% by mass or more. Even more preferably, the IR rubber content is 40% by mass or more and the BR content is 15% by mass or more.

[0086] (Other rubber components) The rubber component may contain other rubber components as long as they do not affect the effects of the invention. Examples of such rubber components include those commonly used in the tire industry, such as styrene-butadiene rubber (SBR), butyl rubber, ethylene-propylene rubber, polynorbornene rubber, silicone rubber, polyethylene chloride rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used individually or in combination of two or more. Furthermore, known thermoplastic elastomers may or may not be included in addition to the above-mentioned rubber components.

[0087] <sbr> Styrene-butadiene rubber (SBR) is not particularly limited and can include, for example, unmodified emulsion-polymerized styrene-butadiene rubber (E-SBR) and solution-polymerized styrene-butadiene rubber (S-SBR), as well as modified SBRs such as modified emulsion-polymerized styrene-butadiene rubber (modified E-SBR) and modified solution-polymerized styrene-butadiene rubber (modified S-SBR). Modified SBRs include modified SBRs in which the terminals and / or main chain are modified, and modified SBRs coupled with tin, silicon compounds, etc. (such as those having condensates or branched structures). Furthermore, SBRs can be of the oil-expandable type, in which flexibility is adjusted by adding an expanding oil, or of the non-oil-expandable type, in which no expanding oil is added, and both types can be used. Examples of such SBRs can be those manufactured by JSR Corporation, Asahi Kasei Chemicals Corporation, Nippon Zeon Co., Ltd., and ZS Elastomer Co., Ltd. SBRs can be used individually or in combination of two or more types.

[0088] From the viewpoint of rubber strength and grip performance, the styrene content of SBR is preferably more than 15.0% by mass, more preferably more than 20.0% by mass, and even more preferably more than 23.0% by mass. Furthermore, from the viewpoint of low fuel consumption, the styrene content is preferably less than 40.0% by mass, more preferably less than 30.0% by mass, and even more preferably less than 25.0% by mass. Note that the styrene content of SBR is 1 This value is calculated by 1H-NMR measurement.

[0089] The vinyl content (amount of 1,2-bonded butadiene units) of SBR is preferably greater than 10.0 mol%, more preferably greater than 15.0%, and even more preferably 18.0 mol% or higher, from the viewpoint of rubber strength and grip performance. Furthermore, from the viewpoint of low fuel consumption, the vinyl content is preferably less than 80.0 mol%, more preferably less than 50.0 mol%, and even more preferably less than 30.0 mol%. The vinyl content of SBR is measured by infrared absorption spectroscopy.

[0090] ·Content The SBR content in 100% by mass of the rubber component is preferably more than 5% by mass, more preferably more than 10% by mass, and even more preferably more than 15% by mass. Furthermore, the content is preferably less than 60% by mass, more preferably less than 55% by mass, even more preferably less than 50% by mass, and even more preferably less than 45% by mass.

[0091] (Rubber components synthesized from recycled and biomass-derived raw materials) Monomers, which are the constituent units of synthetic rubbers such as IR, SBR, and BR, may be derived from underground resources such as petroleum and natural gas, or they may be recycled from rubber products such as tires or non-rubber products such as polystyrene. The monomers obtained by recycling (recycled monomers) are not particularly limited, but include recycled polyisoprene, recycled butadiene, and recycled aromatic vinyl compounds. Examples of butadiene include 1,2-butadiene and 1,3-butadiene. Examples of aromatic vinyl compounds are not particularly limited, but include styrene. In particular, it is preferable to use recycled polyisoprene (recycled isoprene), recycled butadiene (recycled butadiene), and / or recycled styrene (recycled styrene) as raw materials.

[0092] The method for producing recycled monomer is not particularly limited, and for example, it can be synthesized from recycled naphtha obtained by decomposing rubber products such as tires. Furthermore, the method for producing recycled naphtha is not particularly limited, and for example, rubber products such as tires may be decomposed under high temperature and pressure, decomposed by microwaves, or extracted after mechanical grinding.

[0093] Furthermore, the monomers that make up polymers such as IR, SBR, and BR may be derived from biomass. In this specification, biomass refers to substances derived from natural resources such as plants. Biomass is not particularly limited, but examples include agricultural, forestry, and fishery products, sugars, wood chips, plant residues after obtaining useful components, plant-derived ethanol, and biomass naphtha.

[0094] The biomass-derived monomer (biomass monomer) is not particularly limited and includes biomass-derived butadiene and biomass-derived aromatic vinyl compounds. Examples of the butadiene include 1,2-butadiene and 1,3-butadiene. Examples of the aromatic vinyl compound are not particularly limited but include styrene. Furthermore, the method for producing the biomass monomer is not particularly limited and includes, for example, biological and / or chemical and / or physical transformations of plants and animals. Typical biological transformations include fermentation by microorganisms, while chemical and / or physical transformations include those by catalysts, high heat, high pressure, electromagnetic waves, critical liquids, and combinations thereof.

[0095] The polymer synthesized from biomass monomer components (biomass polymer) is not particularly limited, and examples include polybutadiene rubber synthesized from biomass-derived butadiene, and aromatic vinyl / butadiene copolymers synthesized from biomass-derived butadiene and / or biomass-derived aromatic vinyl compounds. Examples of the aromatic vinyl / butadiene copolymer include styrene-butadiene rubber synthesized from biomass-derived butadiene and / or biomass-derived styrene.

[0096] Whether the raw materials for a polymer are biomass-derived can be determined by measuring pMC (percent Modern Carbon) according to ASTM D6866-10. pMC refers to the percentage of modern standard reference carbon. 14 Sample relative to C concentration 14 This is a ratio of C concentrations and is used as an indicator of the biomass ratio of a compound. The significance of this value is described below.

[0097] 1 mole of carbon atoms (6.02 × 10⁻¹⁰) 23 (Each) contains approximately 6.02 × 10¹⁶ atoms, which is about one trillionth of the amount of carbon atoms in a normal atom. 11 individual 14 C exists. 14 The half-life of C is 5730 years. 14 C is decreasing regularly. Therefore, in fossil fuels such as coal, oil, and natural gas, which are thought to have been fixed after more than 226,000 years have passed since atmospheric carbon dioxide was taken in and fixed by plants, etc., C was initially included in these as well. 14 All elements of C have decayed. Therefore, in the 21st century, fossil fuels such as coal, oil, and natural gas are no longer viable. 14 It contains absolutely no element C. Therefore, chemical substances produced using these fossil fuels as raw materials also contain C. 14 It contains absolutely no element C.

[0098] on the other hand, 14 C is continuously produced when cosmic rays undergo nuclear reactions in the atmosphere. Therefore, 14 In the Earth's atmospheric environment, carbon (C) is produced in a state where its decrease due to radioactive decay and its production through nuclear reactions are in equilibrium. 14 The amount of C is constant. Therefore, the amount of biomass resource-derived substances currently circulating in the environment 14 As mentioned above, the carbon concentration is approximately 1 × 10¹⁶ of the total carbon atoms. -12 These values ​​are approximately in mole percent. Therefore, the difference between these values ​​can be used to calculate the biomass ratio in a given compound.

[0099] this 14 C is typically measured as follows: Using accelerator mass spectrometry based on a tandem accelerator, 13 C concentration ( 13 C / 12 C), 14 C concentration ( 14 C / 12 Perform measurement C). In the measurement, 14 As a modern standard reference for the concentration of C, the amount of cyclic carbon in nature as of 1950 14 The C concentration will be used. The specific standard material will be the oxalic acid standard provided by NIST (National Institute of Standards and Technology). The specific radioactivity of carbon in this oxalic acid (per gram of carbon) will be used. 14 The radioactivity intensity of C is separated by carbon isotope, 13 The standard value is obtained by correcting C to a constant value and applying decay correction from 1950 AD to the measurement date. 14 This value is used as the C concentration value (100%). The ratio of this value to the value of the sample actually measured is the pMC value.

[0100] Therefore, if rubber is made from 100% biomass-derived materials, although there are regional differences, under normal conditions it will often not reach 100, and will show a value of approximately 110 pMC. On the other hand, regarding chemical substances derived from fossil fuels such as petroleum, 14 When the C concentration is measured, it will show a value of approximately 0 pMC (for example, 0.3 pMC). This value corresponds to the aforementioned biomass ratio of 0%.

[0101] For the reasons stated above, using materials such as rubber with a high pMC value, that is, materials such as rubber with a high biomass ratio, in rubber compositions is preferable from an environmental protection standpoint.

[0102] (Filler) The rubber composition preferably contains a filler. The filler preferably contains silica, and more preferably contains silica and carbon black. The filler may contain other fillers besides silica and carbon black, but it may also consist solely of silica and carbon black. The filler may be used alone or in combination of two or more types.

[0103] <Silica> The silica used is not particularly limited, and common silica used in the tire industry can be used, such as silica prepared by a dry process (anhydrous silica) or silica prepared by a wet process (hydrated silica). The raw material for silica is not particularly limited, and may be a mineral-derived raw material such as quartz, or a biological-derived raw material such as rice husks (for example, silica made from biomass materials such as rice husks), or silica recycled from silica-containing products may be used. Among these, hydrated silica prepared by a wet process is preferred because it contains a large number of silanol groups. Silica may be used alone or in combination of two or more types.

[0104] Silica derived from biomass materials can be obtained, for example, by extracting silicates from rice husk ash obtained by burning rice husks using a sodium hydroxide solution, and then using these silicates to react with sulfuric acid in the same way as conventional wet silica, the precipitate of silicon dioxide is filtered, washed with water, dried, and pulverized.

[0105] The silica recycled from silica-containing products can be, for example, silica recovered from products containing silica such as semiconductors and other electronic components, tires, desiccants, and diatomaceous earth and other filter materials. The recovery method is not particularly limited and can include thermal decomposition and decomposition by electromagnetic waves. Among these, silica recovered from semiconductors and other electronic components or tires is preferred.

[0106] When silica crystallizes, it becomes insoluble in water, and its component, silicic acid, cannot be utilized. By controlling the combustion temperature and combustion time, the crystallization of silica in rice husk ash can be suppressed (see Japanese Patent Publication No. 2009-2594, Akita Prefectural University Web Journal B / 2019, vol.6, pp.216-222, etc.).

[0107] Amorphous silica extracted from rice husks can be commercially available from companies such as Wilmar.

[0108] The specific surface area (N2SA) of silica for nitrogen adsorption is 130 m². 2 Preferably more than / g, 150m 2 More preferably than / g, 170m 2 More preferably than / g, 175m 2 More preferably 185m / g or more. 2 More preferably than / g, 195m 2 A value exceeding / g is even more preferable. Also, N2SA is preferable to 500m from the viewpoint of processability. 2 Preferably less than / g, 350m 2 Less than / g is more preferable, 300m 2 It is even more preferable that the amount be less than / g, and 250m 2 A value less than / g is even more preferable. The N2SA of silica is the value measured by the measurement method described above.

[0109] From the viewpoint of the effects of the present invention, the average primary particle diameter of silica is preferably less than 18 nm, more preferably less than 17 nm, and even more preferably less than 16 nm. Furthermore, from the viewpoint of processability, the average primary particle diameter is preferably greater than 12 nm, more preferably greater than 13 nm, and even more preferably greater than 14 nm. The average primary particle diameter of silica is measured by the measurement method described above.

[0110] The silica content is 20 parts by mass or more, preferably 25 parts by mass or more, and more preferably 30 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the silica content is preferably less than 80 parts by mass, more preferably less than 70 parts by mass, and even more preferably less than 60 parts by mass.

[0111] <Silane coupling agent> Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, but examples include: sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; silane coupling agents having a mercapto group such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane; vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; and 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane. Examples of silane coupling agents include amino-based silane coupling agents such as 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. In particular, it is preferable to contain a sulfide-based silane coupling agent and / or a silane coupling agent having a mercapto group. As silane coupling agents, for example, those commercially available from Evonik Industries, Momentive, etc., can be used. The silane coupling agent may be used alone or in combination of two or more.

[0112] From the viewpoint of improving silica dispersibility, the content of the silane coupling agent per 100 parts by mass of silica is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and even more preferably 8 parts by mass or more. Furthermore, from the viewpoint of cost and processability, it is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and even more preferably 16 parts by mass or less.

[0113] <Carbon Black> The carbon black used is not particularly limited and includes N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N660, N762, etc. The raw materials for carbon black may be biomass materials such as lignin and vegetable oil, or pyrolysis oil obtained by thermal decomposition of waste tires. The manufacturing method for carbon black may be combustion such as the furnace method, hydrothermal carbonization (HTC), or thermal decomposition of methane such as the thermal black method. Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., and Columbia Carbon Corporation. These may be used individually or in combination of two or more types.

[0114] In addition to the above, recycled carbon black, obtained by thermally decomposing and refining products containing carbon black, such as tires, may also be used as carbon black, from the perspective of life cycle assessment.

[0115] "Recycled carbon black" refers to carbon black obtained by crushing used tires and other products containing carbon black, and then calcining the crushed material. According to the thermogravimetric method compliant with JIS K 6226-2:2003, when oxidative combustion occurs in air, the proportion of ash (non-combustible components) is 13% by mass or more. In other words, the proportion of carbon loss due to oxidative combustion in recycled carbon black is 87% by mass or less. Recycled carbon black is also called recovered carbon black and is sometimes represented as rCB.

[0116] Recycled carbon black can be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, which refers to "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, states that it can be obtained by the pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (

[0027] ). Carbon black obtained from such pyrolysis processes usually lacks functional groups on its surface, as referred to in

[0004] of Japanese Patent Publication No. 6856781 (Comparison of Surface Morphology and Chemistry of Pyrolysis Carbon Black and Commercial Carbon Black, Powder Technology 160 (2005) 190-193).

[0117] Recycled carbon black may lack functional groups on its surface, or it may be treated to include functional groups on its surface. Treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3173251, carbon black obtained from a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl and / or carboxyl groups on its surface. In addition, in Japanese Patent Publication No. 6856781, carbon black obtained from a pyrolysis process is treated with an amino acid compound containing at least one thiol group or disulfide group to obtain carbon black with an activated surface. The recycled carbon black according to this embodiment also includes carbon black treated to include functional groups on its surface.

[0118] Recycled carbon black can be purchased from companies such as Strable Green Carbon and LDCarbon.

[0119] The nitrogen adsorption specific surface area (N2SA) of carbon black is 50m², considering its weather resistance and reinforcing properties. 2 Preferably more than / g, 80m 2 More preferably than / g, 100m 2 A value exceeding / g is even more preferable. Furthermore, N2SA is preferable in terms of dispersibility, low fuel consumption performance, fracture characteristics and durability, at 250m 2 Preferably less than / g, 220m 2 Less than / g is more preferable, 180m 2 It is even more preferable that the amount be less than / g, and 150m 2 A value of less than / g is even more preferable. The N2SA of carbon black is measured by the measurement method described above.

[0120] The average primary particle size of carbon black is preferably greater than 12 nm, more preferably greater than 15 nm, and even more preferably greater than 17 nm, from the viewpoint of weather resistance and reinforcing properties. Furthermore, from the viewpoint of dispersibility, low fuel consumption performance, fracture characteristics, and durability, the average primary particle size is preferably less than 30 nm, more preferably less than 25 nm, and even more preferably 22 nm or less. The average primary particle size of carbon black is measured by the measurement method described above.

[0121] The carbon black content per 100 parts by mass of rubber component is preferably more than 1 part by mass, more preferably more than 3 parts by mass, and even more preferably 5 parts by mass or more. The amount of carbon black blended is also preferably less than 50 parts by mass, more preferably less than 45 parts by mass, even more preferably less than 40 parts by mass, and even more preferably 30 parts by mass or less.

[0122] <Other fillers> The filler may contain other fillers besides silica and carbon black. These other fillers are not particularly limited, but may include, for example, aluminum hydroxide, calcium carbonate, alumina, clay, talc, and other materials commonly used in the tire industry.

[0123] (Other combination drugs) In addition to rubber components and fillers, the rubber composition may appropriately contain compounding agents commonly used in the tire industry, such as plasticizers, processing aids, vulcanized rubber particles, waxes, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0124] <Plasticizer> A plasticizer is a material that imparts plasticity to rubber components, and the concept includes both liquid and solid plasticizers at 25°C. Examples of plasticizers include resin components, oils, liquid rubber, and ester-based plasticizers. These plasticizers may be derived from mineral resources such as petroleum and natural gas, from biomass, or from naphtha recycled from rubber or non-rubber products. Low molecular weight hydrocarbon components obtained by thermal decomposition and extraction of used tires or products containing various components may also be used as plasticizers. Plasticizers may be used individually or in combination of two or more types.

[0125] ≪Resin components≫ The rubber composition according to this embodiment may also contain a resin component. The resin component that can be used in this embodiment is not particularly limited, but resins commonly used in the tire industry can be used, such as C9 resins, C5 resins, C5C9 resins, dicyclopentadiene resins, aromatic vinyl resins, coumarone resins, indene resins, terpene resins, rosin resins, phenolic resins, etc. These resin components may be used individually or in combination of two or more. Each resin component may also be used individually or in combination of two or more.

[0126] ·C9 resin A "C9 resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a polymer obtained by polymerizing the C9 fraction alone, or a copolymer obtained by copolymerizing the C9 fraction with other components. For example, a resin obtained by copolymerizing dicyclopentadiene (DCPD) and a C9 fraction is called a DCPD / C9 resin. Furthermore, the C9 resin may be a hydrogenated or modified version of these resins. Examples of C9 fractions include petroleum fractions with 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, coumarone, indene, methylindene, and dicyclopentadiene. As for C9 resins, commercially available products from companies such as BASF, Zeon Corporation, and ENEOS Corporation can be used.

[0127] ·C5 resin "C5 resins" refer to resins obtained by polymerizing C5 fractions, and may be hydrogenated or modified resins. Examples of C5 fractions other than dicyclopentadiene include petroleum fractions with 4 to 5 carbon atoms, such as cyclopentadiene, isoprene, piperylene, 2-methyl-1-butene, 2-methyl-2-butene, and 1-pentene. As C5 resins, commercially available products from companies such as Structol, Nippon Zeon Co., Ltd., and ENEOS Corporation can be used.

[0128] C5C9 resin "C5C9 resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be hydrogenated or modified. As C5C9 petroleum resin, commercially available products from companies such as Tosoh Corporation and LUHUA can be used.

[0129] • Dicyclopentadiene resins A "dicyclopentadiene-based resin" refers to a resin in which cyclopentadiene (CPD) and / or dicyclopentadiene (DCPD) are the most abundant monomer components, and these may be hydrogenated or modified resins. Preferred dicyclopentadiene-based resins include polymers obtained by polymerizing only dicyclopentadiene as a monomer, and copolymers (DCPD / C9 resins) obtained by copolymerizing dicyclopentadiene with the C9 fraction. Commercially available dicyclopentadiene-based resins from companies such as ExxonMobil, ENEOS Corporation, Nippon Zeon Corporation, and Maruzen Petrochemical Co., Ltd. can be used.

[0130] Aromatic vinyl resin "Aromatic vinyl resin" refers to a resin in which aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and p-chlorostyrene are the most abundant monomer components, and these may be hydrogenated or modified. As aromatic vinyl resins, α-methylstyrene or a homopolymer of styrene or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred, for reasons of being economical, easy to process, and having excellent heat generation properties. As aromatic vinyl resins, commercially available products from companies such as Kraton, Eastman Chemical Company, and Mitsui Chemicals, Inc. can be used.

[0131] • Coumaron resin "Coumarone-based resin" refers to a resin containing coumarone as a monomer component, and may be hydrogenated or modified. Preferred coumarone-based resins include, for example, coumarone resin, which is a polymer with coumarone as the monomer component; coumarone-indene resin, which is a copolymer with coumarone and indene as monomer components; and coumarone-indene-styrene resin, which is a copolymer with coumarone, indene, and styrene as monomer components. As coumarone-based resins, commercially available products from companies such as Rutgers, Nippon Paint Chemical Co., Ltd., and Mitsui Chemicals, Inc. can be used.

[0132] • Indene resin "Indene-based resin" refers to a resin containing indene as a monomer component, and may be hydrogenated or modified resins. Preferred indene-based resins include, for example, coumarone-indene resin, which is a copolymer of coumarone and indene as monomer components, and coumarone-indene-styrene resin, which is a copolymer of coumarone, indene, and styrene as monomer components. Commercially available indene-based resins from companies such as Rutgers, Nippon Paint Chemical Co., Ltd., and Mitsui Chemicals, Inc. can be used.

[0133] • Terpene resins "Terpene resin" refers to a resin containing terpene compounds such as α-pinene, β-pinene, limonene, and dipentene as monomer components, and may be hydrogenated or modified. Preferred terpene resins include, for example, polyterpene resins, which are polymers in which one or more of the aforementioned terpene compounds are used as monomer components; aromatically modified terpene resins, which are copolymers in which the aforementioned terpene compounds and aromatic compounds are used as monomer components; and terpene phenol resins, which are copolymers in which the aforementioned terpene compounds and phenol compounds are used as monomer components. Examples of aromatic compounds that serve as monomer components in aromatically modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenol compounds that serve as monomer components in terpene phenol resins include phenol, bisphenol A, cresol, and xylenol. As terpene resins, commercially available products from companies such as Yasuhara Chemical Co., Ltd., Arakawa Chemical Industries, Ltd., and Nippon Terpene Chemical Co., Ltd. can be used.

[0134] • Rosin-based resin "Rosin-based resin" refers to a resin containing rosin acid compounds such as abietic acid, neoabietic acid, palastic acid, and isopimal acid, and may be hydrogenated or modified. Rosin-based resins are not particularly limited, but examples include natural resin rosin and rosin-modified resins obtained by hydrogenating, disproportionating, dimerizing, esterifying, etc. As rosin-based resins, commercially available products from companies such as Harima Chemical Industries, Ltd., Arakawa Chemical Industries, Ltd., and IREC Co., Ltd. can be used.

[0135] • Phenolic resins "Phenol-based resins" refer to resins containing phenol compounds such as phenol and cresol as monomer components, and may also be hydrogenated or modified resins. Phenolic resins are not particularly limited, but examples include phenol-formaldehyde resins, alkylphenol-formaldehyde resins, alkylphenol-acetylene resins, oil-modified phenol-formaldehyde resins, and terpene-phenol resins. Phenolic resins that are commercially available from companies such as Sumitomo Bakelite Co., Ltd., DIC Corporation, and Asahi Organic Materials Co., Ltd. can be used.

[0136] ·Content The resin content per 100 parts by mass of rubber component is preferably more than 1 part by mass, more preferably more than 5 parts by mass, and even more preferably 5 parts by mass or more. On the other hand, from the viewpoint of suppressing heat generation, the content is preferably less than 60 parts by mass, more preferably less than 30 parts by mass, and even more preferably less than 20 parts by mass.

[0137] (Plasticizers other than resin components) This section explains plasticizers other than resin components, such as oils, liquid rubbers, and ester-based plasticizers.

[0138] ≪Oil≫ Examples of oils include mineral oil, vegetable oil, and animal oil. Furthermore, from a life cycle assessment perspective, waste oil from rubber mixers and engines, or refined waste cooking oil from restaurants, may also be used. Oils may be used individually or in combination of two or more types.

[0139] In this specification, mineral oil refers to oil derived from mineral resources such as petroleum and natural gas. Examples of mineral oil include paraffinic oils (mineral oil), naphthenic oils, and aromatic oils. Specific examples of mineral oil include MES (Mild Extracted Solvate), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), and RAE (Residual Aromatic Extract). Furthermore, for environmental reasons, oils with a low content of polycyclic aromatic compounds (PCA) can be used. Examples of low-PCA oils include MES, TDAE, and heavy naphthenic oils. Mineral oil may be used alone or in combination of two or more types.

[0140] In this specification, vegetable oils include, for example, linseed oil, rapeseed oil, safflower oil, soybean oil, corn oil, cottonseed oil, rice oil, tall oil, sesame oil, perilla oil, castor oil, tung oil, pine oil, pine tar oil, sunflower oil, coconut oil, palm oil, palm kernel oil, olive oil, camellia oil, jojoba oil, macadamia nut oil, peanut oil, grapeseed oil, and wood wax. Furthermore, vegetable oils may also include refined oils (such as salad oil) obtained by refining the above oils, transesterified oils obtained by transesterifying the above oils, hydrogenated oils obtained by hydrogenating the above oils, thermally polymerized oils obtained by thermally polymerizing the above oils, oxidized polymerized oils obtained by oxidizing the above oils, and waste cooking oils recovered from use as edible oils. Note that vegetable oils may be liquid or solid at 25°C. Vegetable oils may be used individually or in combination of two or more types.

[0141] The vegetable oil according to this embodiment preferably contains acyl glycerol, and more preferably contains triacyl glycerol. In this specification, acyl glycerol refers to a compound in which the hydroxy group of glycerin and a fatty acid are ester-bonded. The acyl glycerol is not particularly limited, and may be 1-monoacyl glycerol, 2-monoacyl glycerol, 1,2-diacyl glycerol, 1,3-diacyl glycerol, or triacyl glycerol. Further, the acyl glycerol may be a monomer, a dimer, or a multimer of three or more units. Note that acyl glycerols of two or more units can be obtained by thermal polymerization, oxidative polymerization, or the like. Also, the acyl glycerol may be liquid or solid at 25°C.

[0142] The method for confirming whether the acyl glycerol is contained in the rubber composition is not particularly limited, but 1 it can be confirmed by 1H-NMR measurement. For example, a rubber composition containing triacyl glycerol is immersed in deuterated chloroform at 25°C for 24 hours. After removing the rubber composition, 1 1H-NMR is measured. When the signal of tetramethylsilane (TMS) is set to 0.00 ppm, signals around 5.26 ppm, around 4.28 ppm, and around 4.15 ppm are observed, and these signals are presumed to be signals derived from hydrogen atoms bonded to carbon atoms adjacent to the oxygen atom of the ester group. In this paragraph, "around" means a range of ±0.10 ppm.

[0143] The fatty acid is not particularly limited, and may be an unsaturated fatty acid or a saturated fatty acid. Examples of the unsaturated fatty acid include monounsaturated fatty acids such as oleic acid, and polyunsaturated fatty acids such as linoleic acid and linolenic acid. Examples of the saturated fatty acid include butyric acid and lauric acid.

[0144] In particular, it is desirable that the fatty acid contains fatty acids with few double bonds, i.e., saturated fatty acids or monounsaturated fatty acids, and oleic acid is preferred. As a vegetable oil containing such fatty acids, for example, a vegetable oil containing saturated fatty acids or monounsaturated fatty acids may be used, or a vegetable oil that has been modified by transesterification or other means may be used. Furthermore, in order to produce a vegetable oil containing such fatty acids, plants may be improved by breeding, genetic modification, genome editing, etc.

[0145] As for vegetable oils, commercially available products from companies such as Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoy Co., Ltd., H&R Co., Ltd., Toyokuni Oil Co., Ltd., Fuji Kosan Co., Ltd., and Nisshin Oillio Group Ltd. can be used.

[0146] Examples of animal oils include fish oil, beef tallow, or oleyl alcohol derived from them.

[0147] When oil is included, the oil content per 100 parts by mass of rubber component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, from the viewpoint of processability. Furthermore, 30 parts by mass or less is preferred, 25 parts by mass or less is more preferred, and 20 parts by mass or less is even more preferred. The oil content also includes the amount of oil contained in the oil-spread rubber.

[0148] Liquid Rubber The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at 25°C, but examples include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. The liquid rubber may be used alone or in combination of two or more types.

[0149] When liquid rubber is included, its content per 100 parts by mass of rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. Furthermore, the liquid rubber content is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less.

[0150] Ester-based plasticizers Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelaate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), and trixylenyl phosphate (TXP). Ester-based plasticizers may be used individually or in combination of two or more.

[0151] When an ester-based plasticizer is included, its content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. The liquid rubber content is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less. The ester-based plasticizer content also includes the amount of stretched ester-based plasticizer used to stretch the rubber component.

[0152] Vulcanized rubber particles Vulcanized rubber particles are particles made of vulcanized rubber, and specifically, rubber powder as specified in JIS K 6316:2017 can be used. From the viewpoint of environmental considerations and cost, recycled rubber powder produced from crushed waste tires is preferred. One type of vulcanized rubber particle may be used alone, or two or more types may be used in combination.

[0153] The vulcanized rubber particles are not particularly limited and may be either unmodified vulcanized rubber particles or modified vulcanized rubber particles.

[0154] Commercially available vulcanized rubber products can be used, such as those from Lehigh, Muraoka Rubber Industries, and others.

[0155] When vulcanized rubber particles are included, the content per 100 parts by mass of the rubber component can be appropriately adjusted, for example, within a range of more than 1 part by mass and less than 80 parts by mass.

[0156] Anti-aging agent The anti-aging agents are not particularly limited, but include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-diphenyl-p-phenylenediamine (DPPD), and N,N'-ditril-p-phenylenediamine. Examples include p-phenylenediamine-based antioxidants such as amines (DTPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), and N,N'-di-2-naphthyl-p-phenylenediamine (DNPD); quinoline-based antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine-based antioxidants and quinoline-based antioxidants are preferred, and polymers of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. Commercially available products include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., Flexis, and others. The antioxidant may be used alone or in combination of two or more.

[0157] When an anti-aging agent is included, the content per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of the rubber's resistance to ozone cracking. Furthermore, from the viewpoint of wear resistance and wet grip performance, it is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

[0158] ≪Wax≫ The wax is not particularly limited, and any wax commonly used in the tire industry can be suitably used, such as mineral waxes and plant-derived waxes. Mineral waxes refer to waxes derived from mineral resources such as oil and natural gas. Plant-derived waxes refer to waxes derived from natural resources such as plants. Among these, mineral waxes are preferred. Examples of plant-derived waxes include rice wax, carnauba wax, and candelilla wax. Examples of mineral waxes include paraffin wax, microcrystalline wax, and selected special waxes thereof, with paraffin wax being preferred. The wax according to this embodiment does not contain stearic acid. The wax can be commercially available from companies such as Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Paramelt Co., Ltd. The wax may be used alone or in combination of two or more types.

[0159] When wax is included, the amount of wax per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of weather resistance of the rubber. Furthermore, from the viewpoint of preventing whitening of the tire due to bloom, it is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

[0160] Processing aids Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, and mixtures of fatty acid metal salts and fatty acid amides. For example, commercially available processing aids from companies such as Schill+Seilacher and Performance Additives can be used. Processing aids may be used individually or in combination of two or more.

[0161] When processing aids are included, the content per 100 parts by mass of rubber components is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of exhibiting an effect of improving processability. Furthermore, from the viewpoint of wear resistance and fracture strength, it is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less.

[0162] ≪Stearic Acid≫ When stearic acid is included, its content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of processability. Furthermore, from the viewpoint of vulcanization rate, it is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

[0163] ≪Zinc Oxide≫ When zinc oxide is included, its content per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of processability. Furthermore, from the viewpoint of wear resistance, it is preferably 5.0 parts by mass or less, more preferably 4.5 parts by mass or less, and even more preferably 4.0 parts by mass or less.

[0164] ≪Sulfurizing agent≫ Sulfur is preferably used as a vulcanizing agent. Suitable sulfurs include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur. The vulcanizing agent may be used alone or in combination of two or more types.

[0165] When sulfur is included as a vulcanizing agent, the amount of sulfur per 100 parts by mass of rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. When oil-containing sulfur is used as the vulcanizing agent, the amount of vulcanizing agent is the total amount of pure sulfur contained in the oil-containing sulfur.

[0166] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, 1,6-hexamethylene-dithiosulfate sodium dihydrate, and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane). These non-sulfur vulcanizing agents can be commercially available from companies such as Taoka Chemical Industries, Ltd., Lanxess Corporation, and Flexis. The vulcanizing agent may be used alone or in combination of two or more types.

[0167] <<Vulcanization accelerator>> The vulcanization accelerator is not particularly limited, but examples include sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, guanidine-based vulcanization accelerators, thiram-based vulcanization accelerators, thiourea-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, aldehyde-amine-based vulcanization accelerators, aldehyde-ammonia-based vulcanization accelerators, imidazoline-based vulcanization accelerators, xanthate-based vulcanization accelerators, caprolactam disulfide, and the like. The vulcanization accelerator may be used alone or in combination of two or more. Among these, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, and guanidine-based vulcanization accelerators are preferred because they more favorably produce the desired effect. The vulcanization accelerator may be used alone or in combination of two or more.

[0168] Examples of sulfenamide-based vulcanization accelerators include N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS), N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolyl sulfenamide (DCBS). Among these, N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS) is preferred.

[0169] Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole (MBT) or its salts, di-2-benzothiazolyl disulfide (MBTS), 2-(2,4-dinitrophenyl)mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinothio)benzothiazole.

[0170] Examples of guanidine-based vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salts of dicatecholborate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-cumenyl-2-propionylguanidine.

[0171] Examples of thiram-based vulcanization accelerators include tetrakis(2-ethylhexyl)thiram disulfide (TOT-N), tetramethylthiram disulfide (TMTD), tetraethylthiram disulfide, tetramethylthiram monosulfide (TMTM), dipentamethylenethiram disulfide, and dipentamethylenethiram tetrasulfide.

[0172] Examples of thiourea-based vulcanization accelerators include thiourea compounds such as thiacarbamide, diethylthiourea, dibutylthiourea, trimethylthiourea, and dioltotrilthiourea, as well as N,N'-diphenylthiourea, trimethylthiourea, and N,N'-diethylthiourea.

[0173] Examples of dithiocarbamate-based vulcanization accelerators include piperidinium pentamethylenedithiocarbamate (PPDC), zinc dimethyldithiocarbamate (ZnMDC), zinc diethyldithiocarbamate (ZnEDC), zinc dibutyldithiocarbamate (ZnBDC), zinc dibenzyldithiocarbamate (ZDBzC), zinc N-ethyl-N-phenyldithiocarbamate (ZnEPDC), zinc N-pentamethylenedithiocarbamate (ZnPDC), sodium dibutyldithiocarbamate (NaBDC), copper dimethyldithiocarbamate (CuMDC), iron dimethyldithiocarbamate (FeMDC), and tellurium diethyldithiocarbamate (TeEDC).

[0174] When a vulcanization accelerator is included, its content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, and more preferably 1.5 parts by mass or more. Furthermore, the content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By keeping the content of the vulcanization accelerator within the above range, it tends to be possible to ensure fracture strength and elongation.

[0175] <70℃ tanδ C > 70℃ tanδ C The value is preferably 0.03 or higher, more preferably 0.05 or higher, and even more preferably 0.08 or higher. Furthermore, it is preferably 0.18 or lower, more preferably 0.15 or lower, even more preferably 0.12 or lower, and even more preferably 0.10 or lower. 70℃ tanδ C This can be adjusted as appropriate by conventional methods in the tire industry, specifically by changing the type and amount of chemicals (e.g., rubber components, fillers, softeners, sulfur, vulcanization accelerators, silane coupling agents, etc.) incorporated into the tire rubber composition.

[0176] [Rubber composition for heat dissipation rubber layer] The rubber composition for the heat dissipation rubber layer will now be described. The rubber composition for the heat dissipation rubber layer is as follows, and the same description as for the rubber composition for the cap rubber layer also applies.

[0177] (Rubber component) It is preferable that the composition contains isoprene rubber (IR rubber) and butadiene rubber (BR). In this case, the rubber components may include other rubber components in addition to isoprene rubber and butadiene. Alternatively, it may consist only of isoprene rubber and butadiene rubber. SBR is preferably used as the other rubber component. The rubber components are described below, as well as in the rubber composition for the cap rubber layer.

[0178] ≪Content≫ The explanation regarding the content of rubber components is as described in the section on the rubber composition constituting the cap rubber layer. The content of IR-based rubber in 100% by mass of rubber components is, for example, more than 40% by mass, preferably more than 50% by mass, more preferably more than 55% by mass, and even more preferably 60% by mass or more. On the other hand, the content is, for example, 100% by mass or less, preferably less than 90% by mass, and more preferably less than 80% by mass.

[0179] Furthermore, the BR content in 100% by mass of the rubber component is preferably more than 5% by mass, more preferably more than 10% by mass, and even more preferably more than 15% by mass. The content is also preferably less than 50% by mass, more preferably less than 40% by mass, even more preferably less than 30% by mass, and even more preferably less than 25% by mass.

[0180] The rubber component contains IR rubber and BR, preferably with an IR rubber content of 50% by mass or more of the total rubber component by mass, and a BR content of 5% by mass or more of the total rubber component by mass. More preferably, the IR rubber content is 55% by mass or more and the BR content is 10% by mass or more. Even more preferably, the IR rubber content is 60% by mass or more and the BR content is 15% by mass or more.

[0181] The SBR content in 100% by mass of the rubber component is preferably more than 5% by mass, more preferably more than 10% by mass, and even more preferably more than 15% by mass. Furthermore, the content is preferably less than 50% by mass, more preferably less than 45% by mass, even more preferably less than 40% by mass, and even more preferably less than 35% by mass.

[0182] (Filler) In this embodiment, the thermal conductivity of the heat-dissipating rubber layer is higher than that of the cap rubber layer. To increase the thermal conductivity, it is preferable to reduce the amount of silica and other materials that do not significantly increase thermal conductivity in the rubber composition for the heat-dissipating rubber layer, and increase the amount of carbon black, compared to the amount of silica used in the rubber composition for the cap rubber layer. In addition, for example, the thermal conductivity can also be increased by incorporating a highly conductive filler into the rubber composition.

[0183] The filler preferably contains carbon black. In addition to carbon black, the filler may also contain silica. If the filler contains silica, it may further contain a silane coupling agent. The filler may further contain other fillers besides carbon black and silica. A description of each component that may constitute the filler is provided in the section on the rubber composition constituting the cap rubber layer. To increase thermal conductivity, the rubber composition constituting the heat-dissipating rubber layer may also contain a highly conductive filler.

[0184] Carbon black content When carbon black is included, the total carbon black content is, for example, more than 30 parts by mass, preferably more than 40 parts by mass, more preferably 50 parts by mass or more, and even more preferably 60 parts by mass or more, per 100 parts by mass of the rubber component. On the other hand, the total content is preferably less than 150 parts by mass, more preferably less than 110 parts by mass, and even more preferably less than 80 parts by mass. When the carbon black content is within the above range, sufficient reinforcing properties and good dispersion in the rubber tend to be obtained, as well as thermal conductivity suitable for the heat dissipation rubber layer.

[0185] Furthermore, the explanation given for the rubber composition for the cap rubber layer can be similarly applied to carbon black.

[0186] ≪Silica Content≫ When silica is included, its content per 100 parts by mass of rubber component is preferably less than 30 parts by mass, more preferably less than 20 parts by mass, even more preferably less than 10 parts by mass, and still more preferably less than 5 parts by mass, from the viewpoint of thermal conductivity. There is no particular lower limit, and it may be 0 parts by mass.

[0187] ≪Highly conductive filler≫ The rubber composition preferably contains a highly conductive filler. This further enhances its thermal conductivity. There are no particular restrictions on the highly conductive filler, and commonly used ones can be used, but carbon-based conductive fillers are preferred, such as carbon nanotubes, carbon fibers, and acetylene black.

[0188] The content of the highly conductive filler is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, even more preferably 80 parts by mass or more, and even more preferably 100 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, it is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 110 parts by mass or less.

[0189] (Other compounding agents) For any other information, the explanation given for rubber compositions for cap rubbers can be applied similarly.

[0190] <70℃ tanδ D > 70℃ tanδ D is preferably 0.04 or more, more preferably 0.05 or more, still more preferably 0.07 or more, still more preferably 0.10 or more, still more preferably 0.13 or more, still more preferably 0.16 or more, still more preferably 0.18 or more. Also, it is preferably 0.28 or less, more preferably 0.25 or less, still more preferably 0.22 or less. 70 °C tanδ D D can be appropriately adjusted by a conventional method in the tire industry. Specifically, it can be adjusted by changing the type and amount of chemicals (for example, rubber components, fillers, softeners, sulfur, vulcanization accelerators, silane coupling agents, etc.) incorporated into the rubber composition for tires.

[0191] <Various materials containing carbon atoms> In this specification, various materials containing carbon atoms (for example, rubber, oil, resin, vulcanization accelerator, anti-aging agent, surfactant, etc.) may be derived from carbon dioxide in the atmosphere. As a method for obtaining the various materials from carbon dioxide, carbon dioxide may be directly converted, or methane obtained through a methanation process of synthesizing methane from carbon dioxide may be converted.

[0192] [Manufacturing method] Both the rubber composition for the cap rubber and the rubber composition for the heat dissipation rubber layer can be manufactured by known methods. For example, they can be manufactured by kneading the above-mentioned respective components using a rubber kneading apparatus such as an open roll, a closed kneader (Banbury mixer, kneader, etc.).

[0193] The kneading process includes, for example, a base kneading process of kneading compounding agents and additives other than the vulcanizing agent and the vulcanization accelerator, and a final kneading (F kneading) process of adding the vulcanizing agent and the vulcanization accelerator to the kneaded product obtained in the base kneading process and kneading them. Further, the base kneading process can be divided into a plurality of processes if desired.

[0194] While there are no particular limitations on the mixing conditions, for example, in the case of a rubber composition for cap rubber, one method is to mix the base mixture at a discharge temperature of 150-170°C for 3-10 minutes, and then mix the final mixture at 70-110°C for 1-5 minutes. Similarly, in the case of a rubber composition for a heat dissipation rubber layer, one method is to mix the base mixture at a discharge temperature of 150-170°C for 3-10 minutes, and then mix the final mixture at 70-110°C for 1-5 minutes.

[0195] The tire according to this embodiment can be manufactured by conventional methods using the rubber composition. Specifically, the unvulcanized rubber composition is extruded in an extruder equipped with a die of a predetermined shape to match the shape of the cap rubber layer and the heat dissipation rubber layer, and then bonded together with other tire components on a tire molding machine while adjusting to form a predetermined tire structure, thereby forming an unvulcanized tire by conventional methods. This unvulcanized tire is then heated and pressurized in a vulcanizing machine to manufacture the tire. The vulcanization conditions are not particularly limited, but for example, a method of vulcanizing at 140 to 170°C for 10 to 40 minutes can be used.

[0196] [Application] In this specification, tires, whether pneumatic or non-pneumatic, can be used for any application and can be used as passenger car tires, large passenger car tires, large SUV tires, racing tires, motorcycle tires, heavy-duty tires, and run-flat tires. They are particularly suitable for use as heavy-duty tires for trucks and buses. Heavy-duty tires are defined as tires intended for use on four-wheeled vehicles and have a maximum load capacity of 1000 kg or more. The maximum load capacity of heavy-duty tires is preferably 1200 kg or more, and more preferably 1400 kg or more. [Examples]

[0197] The following examples (case studies) are shown as preferred for implementation, but the scope of the present invention is not limited to these examples. According to each table, we examined a tire having a cap rubber layer, a heat-dissipating rubber layer, and a tire structure obtained using the various chemicals shown below, and the results calculated based on the evaluation method described below are shown at the bottom of the table.

[0198] [Various medicines] The various chemicals used in the examples and comparative examples are summarized below. NR:TSR20 SBR: HPR840 manufactured by JSR Corporation (styrene content: 10% by weight, vinyl content: 41 mol%, non-oil-based product) BR: Nipol BR1220 (High-cis BR, cis content: 97 mol%, trans content: 2 mass%, vinyl content: 1 mol%) manufactured by Nippon Zeon Co., Ltd. CB (Carbon Black) 1: Dia Black N220 (N2SA114m) manufactured by Mitsubishi Chemical Corporation. 2 / g, average primary particle diameter 22nm; ash content: 1.0% by mass or less) CB2: Lion Specialty Chemicals Ketjenblack EC600JD (N2SA1270m 2 / g, average primary particle size 34nm) Silica: ULTRASIL(registered trademark) VN3 (N2SA: 175m) manufactured by Evonik Industries. 2 / g, average primary particle diameter: 18nm) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Industries. Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Anti-aging agent: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid manufactured by NOF Corporation Wax: Ozoace 0355 (paraffin wax) manufactured by Nippon Seiro Co., Ltd. Sulfur: HK-200-5 (5% oil-containing powdered sulfur) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator: Noxellar NS (N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0199] [Examples and Comparative Examples] (Preparation of unvulcanized rubber composition for cap rubber layer) According to the formulations shown in Table 1, formulations A to D, all chemicals except sulfur and vulcanization accelerator are mixed in a 1.7 L sealed Banbury mixer for 5 minutes until the discharge temperature reaches 170°C to obtain a mixture. Next, sulfur and vulcanization accelerator are added to the mixture using a twin-screw open roll mixer and mixed for 4 minutes until the temperature reaches 105°C to obtain an unvulcanized rubber composition for the cap rubber layer.

[0200] (Preparation of unvulcanized rubber composition for heat dissipation rubber layer) According to the formulations shown in Table 1, formulations E to G, all chemicals except sulfur and vulcanization accelerator are mixed in a 1.7 L sealed Banbury mixer for 5 minutes until the discharge temperature reaches 170°C to obtain a mixture. Next, sulfur and vulcanization accelerator are added to the mixture using a twin-screw open roll mixer and mixed for 4 minutes until the temperature reaches 105°C to obtain an unvulcanized rubber composition for the heat dissipation rubber layer.

[0201] (Preparation of vulcanized rubber composition for heat dissipation rubber layer for thermal conductivity measurement) The unvulcanized rubber composition for the heat-dissipating rubber layer obtained above is press-vulcanized for 12 minutes under conditions of 170°C to produce a vulcanized rubber composition.

[0202] (Manufacturing of test tires) Each unvulcanized rubber composition for the cap rubber and the unvulcanized rubber composition for the heat dissipation rubber layer obtained above are extruded using an extruder equipped with a die of a predetermined shape, bonded together with other tire components to form an unvulcanized tire, and then press-vulcanized at 170°C for 12 minutes to produce each test tire (tire size: 295 / 80R22.5, tread contact width TW: 250 mm).

[0203] [evaluation] For each test tire, the results measured using the following method are recorded in the corresponding column of the table below. Unless otherwise specified, each test tire is used after being brought to its normal state.

[0204] <70℃ tanδ C Measurement > Samples are prepared by cutting out pieces measuring 20 mm in length, 4 mm in width, and 1 mm in thickness from the rubber cap layer of each test tire. For each sample, the loss tangent (tanδ) is measured using a GABO iplexer series under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of ±1%, and frequency of 10 Hz.

[0205] <70℃ tanδ D Measurement > Samples are prepared by cutting out pieces measuring 20 mm in length, 4 mm in width, and 1 mm in thickness from the heat dissipation rubber layer of each test tire. For each sample, the loss tangent (tanδ) is measured using a GABO Iplexer series under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of ±1%, and frequency of 10 Hz.

[0206] <Thermal conductivity> Samples are prepared by cutting 10 mm thick pieces from the cap rubber layer and heat dissipation rubber layer of each test tire. The thermal conductivity (W / m·K) of the obtained samples is measured using a thermal conductivity meter (QTM-500 manufactured by Kyoto Electronics Manufacturing Co., Ltd.) in accordance with JIS R 2616, under the conditions of a measurement temperature of 25°C and a measurement time of 60 seconds.

[0207] <Durability> Each test tire, inflated with 230 kPa of air, is mounted on a drum-type running test machine. A longitudinal load of 18.75 kN is applied to the tire, and it is driven on the drum at a speed of 80 km / h. The distance traveled until the tire breaks is measured. The results are expressed as an index, with the reference comparison set to 100. A higher index indicates superior durability.

[0208] [Table 1]

[0209] [Table 2]

[0210] [Embodiment] Examples of embodiments of the present invention are shown below.

[0211] [1] A pneumatic tire having a tread section, The tread portion includes a cap rubber layer including the tread contact surface and a heat dissipation rubber layer. The heat-dissipating rubber layer extends in the tire axial direction, with at least a portion of it in contact with the cap rubber layer over its entire length, and is arranged to be exposed on the tire side surface. The thermal conductivity of the heat-dissipating rubber layer is greater than that of the cap rubber layer. Let Ld be the extended length (mm) of the heat dissipation rubber layer, and let 70°C tanδ be the loss tangent of the heat dissipation rubber layer at 70°C. D The loss loss tangent of the cap rubber layer at 70°C is defined as 70°C tanδ. C In this case, Ld and 70°C tanδ D and 70℃ tanδ C A pneumatic tire that satisfies the relationship in equation (1). (1) Ld × (70℃ tanδ D / 70℃ tanδ C )>10 Here, the right-hand side of equation (1) is preferably 15, and more preferably 17. [2] The pneumatic tire according to [1] above, wherein the rubber composition constituting the cap rubber layer contains 20 parts by mass or more, preferably 25 parts by mass or more, and more preferably 30 parts by mass or more, of silica per 100 parts by mass of the rubber component. [3] The pneumatic tire according to [1] or [2] above, wherein at least a portion of the heat dissipation rubber layer is located between the cap rubber layer and the base rubber layer in the radial direction of the tire. [4] The 70°C tanδ C A pneumatic tire according to any of the above [1] to [3], wherein the ratio is 0.15 or less, preferably 0.12 or less, and more preferably 0.10 or less. [5] The pneumatic tire according to any of [1] to [4] above, wherein the right-hand side of equation (1) is 20, preferably 23, more preferably 25, and even more preferably 30. [6] The pneumatic tire according to any one of [1] to [5] above, wherein the rubber composition constituting the heat dissipation rubber layer contains 50 parts by mass or more, preferably 60 parts by mass or more, more preferably 80 parts by mass or more, and even more preferably 100 parts by mass or more of a highly conductive filler per 100 parts by mass of the rubber component. [7] The pneumatic tire according to any one of [1] to [6], wherein the thermal conductivity (W / m·K) of the heat-dissipating rubber layer is 0.40 or higher, preferably 0.50 or higher, and more preferably 0.60 or higher. [8] The 70°C tanδ D A pneumatic tire according to any of the above [1] to [7], wherein the ratio is 0.16 or higher, preferably 0.18 or higher. [9] A pneumatic tire according to any of [1] to [8] above, wherein when the contact width of the tread portion in the axial direction of the tire is TW, the ratio of Ld to TW (Ld / TW) is 0.04 or more, preferably 0.05 or more, more preferably 0.06 or more, and less than 0.20.

[10] A pneumatic tire according to any one of [1] to [9] above, wherein the outer surface of the tire, which is radially inward from the exposed position of the heat-dissipating rubber layer, is provided with a row of recesses formed along the circumferential direction of the tire.

[11] The pneumatic tire according to

[10] above, wherein the recesses are arranged at equal intervals in the circumferential direction of the tire.

[12] The pneumatic tire according to

[10] or

[11] , wherein the row of recesses is located radially inward from the tire's maximum width position.

[13] The pneumatic tire according to any one of the above

[10] to

[12] , wherein the ratio of the tire circumferential length w of the recess to the tire circumferential spacing P of the recess (w / P) is 0.60 to 0.90. [Explanation of Symbols]

[0212] 1 Tire 2 Tread surface 3 Tread part 4 Cap rubber layer 5 Base rubber layer 6 Heat dissipation rubber layer 7 Tire outer surface 9 Recess 9a Row of recesses C Tire center line (equator) Ld Extension length of the heat dissipation rubber layer P Tire circumferential interval of the recess TW Contact width f Turbulent flow w Tire circumferential length of the recess< / sbr>

Claims

1. A pneumatic tire having a tread section, The tread portion includes a cap rubber layer including the tread contact surface and a heat dissipation rubber layer. The heat-dissipating rubber layer extends in the tire axial direction, with at least a portion of it in contact with the cap rubber layer over its entire length, and is arranged to be exposed on the tire side surface. The thermal conductivity of the heat-dissipating rubber layer is greater than that of the cap rubber layer. Let Ld be the extended length (mm) of the heat dissipation rubber layer, and let 70°C tanδ be the loss tangent of the heat dissipation rubber layer at 70°C. D The loss tangent of the cap rubber layer at 70°C is defined as 70°C tanδ. C In this case, Ld and 70°C tanδ D and 70°C tanδ C A pneumatic tire that satisfies the relationship in equation (1). (1)Ld×(70℃tanδ D / 70℃tanδ C )>10

2. The pneumatic tire according to claim 1, wherein the rubber composition constituting the cap rubber layer contains 20 parts by mass or more of silica per 100 parts by mass of the rubber component.

3. The pneumatic tire according to claim 1 or 2, wherein at least a portion of the heat-dissipating rubber layer is located between the cap rubber layer and the base rubber layer in the radial direction of the tire.

4. The aforementioned 70°C tanδ C A pneumatic tire according to claim 1 or 2, wherein the coefficient is 0.15 or less.

5. The pneumatic tire according to claim 1 or 2, wherein the right-hand side of equation (1) is 20.

6. The pneumatic tire according to claim 1 or 2, wherein the rubber composition constituting the heat-dissipating rubber layer contains 50 parts by mass or more of a highly conductive filler per 100 parts by mass of the rubber component.

7. The pneumatic tire according to claim 1 or 2, wherein the thermal conductivity (W / m·K) of the heat-dissipating rubber layer is 0.40 or higher.

8. The aforementioned 70°C tanδ D A pneumatic tire according to claim 1 or 2, wherein the ratio is 0.16 or greater.

9. The pneumatic tire according to claim 1 or 2, wherein when TW is the contact width of the tread portion in the axial direction of the tire, the ratio of Ld to TW (Ld / TW) is 0.04 or more and less than 0.

20.

10. The pneumatic tire according to claim 1 or 2, further comprising a row of recesses formed along the circumferential direction of the tire on the outer surface of the tire, which is radially inward from the exposed position of the heat-dissipating rubber layer.

11. The pneumatic tire according to claim 10, wherein the recesses are arranged at equal intervals in the circumferential direction of the tire.

12. The pneumatic tire according to claim 10, wherein the row of recesses is located radially inward from the tire's maximum width position.

13. The pneumatic tire according to claim 10, wherein the ratio of the circumferential length w of the recess to the spacing P of the recess in the tire circumferential direction (w / P) is 0.60 to 0.90.

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