tire

Abstract

To provide a tire improved in on-ice grip performance during high-speed running.SOLUTION: A tire comprises a tread part. The tread part has a first layer constituting a trad surface and a second layer formed adjacently to inside in a tire radial direction of the first layer, where the first layer and the second layer respectively are constituted by rubber compositions containing rubber components and regenerative carbon blacks. When contents of the regenerative carbon blacks with respect to 100 parts by mass of rubber components of the rubber compositions constituting the first layer are defined as C (mass parts) and contents of the regenerative carbon blacks with respect to 100 parts by mass of rubber components of the rubber compositions constituting the second layer are defined as B (mass parts), B / C is below 1.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to tires. [Background technology]

[0002] Tires are the only automotive parts that transmit force to the road surface, and it is desirable that they enhance braking performance without slipping, even on icy roads.

[0003] Patent Document 1 discloses a method for improving braking performance on icy roads by incorporating eggshell powder or the like into the rubber layer that constitutes the tread contact surface to obtain a scratching effect. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-167410 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, further improvements are needed in braking performance when driving on ice that is difficult for drivers to see (black ice). Also, with the improvement of highways and vehicle performance, high-speed driving has become commonplace, and it is now expected that vehicles will be driving at high speeds on black ice.

[0006] In view of the above problems, the present invention aims to improve the grip performance of tires on ice during high-speed driving. [Means for solving the problem]

[0007] This invention relates to the following tires. A tire having a tread section, The tread portion comprises a first layer that constitutes the tread surface and a second layer adjacent to the first layer on the radially inward side of the tire. The first layer and the second layer are each composed of a rubber composition containing a rubber component and recycled carbon black, A tire in which, when the amount of recycled carbon black per 100 parts by mass of rubber component in the rubber composition constituting the first layer is C (parts by mass), and the amount of recycled carbon black per 100 parts by mass of rubber component in the rubber composition constituting the second layer is B (parts by mass), the ratio B / C is 1.0 or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to improve the grip performance of tires on ice during high-speed driving. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing a cross-section of the tire tread passing through the tire's axis of rotation. [Figure 2] This is a schematic diagram of the contact surface when the tread portion of a tire according to one embodiment of the present invention is pressed against a flat surface. [Figure 3] This is a schematic diagram of the contact surface when the tread portion of a tire according to another embodiment of the present invention is pressed against a flat surface. [Modes for carrying out the invention]

[0010] A tire according to one embodiment of the present invention is a tire having a tread portion, wherein the tread portion has a first layer constituting the tread surface and a second layer adjacent to the radially inward side of the first layer, and the first layer and the second layer are each composed of a rubber composition containing a rubber component and recycled carbon black, and when the amount of recycled carbon black per 100 parts by mass of rubber component in the rubber composition constituting the first layer is C (parts by mass) and the amount of recycled carbon black per 100 parts by mass of rubber component in the rubber composition constituting the second layer is B (parts by mass), the ratio B / C is 1.0 or less.

[0011] While not intended to be constrained by theory, the following are some possible mechanisms for improving ice grip performance at high speeds in the tire of the present invention.

[0012] Recycled carbon black, due to the influence of hydrocarbons and other substances contained in the raw materials such as rubber products, is thought to have more surface irregularities and lower surface activity compared to ordinary carbon black. Therefore, by including recycled carbon black in the first layer of rubber composition that makes up the tread, (1) even on icy road surfaces with few irregularities, the irregularities of the recycled carbon black can grip and provide a scratching effect. Furthermore, (2) the physical adsorption of recycled carbon black provides a reinforcing effect on the rubber components, making it easier to transmit deformation caused by gripping into the rubber interior. In addition, due to the reduced surface activity, (3) friction occurs between the recycled carbon black and rubber molecular chains around the recycled carbon black, generating heat around the recycled carbon black, and making it easier for the domains centered on the recycled carbon black to bite into the icy road surface. Moreover, by including recycled carbon black in the rubber composition that makes up the second layer, (4) even inside the tread, friction occurs between the recycled carbon black and rubber molecular chains due to the force transmitted from the road surface through the tread surface, generating heat around the recycled carbon black, converting the vehicle's kinetic energy into heat inside the rubber, resulting in good grip performance even at high speeds. Furthermore, by setting the B / C ratio to 1.0 or less, (5) the heat generation of the second layer, which is prone to heat accumulation, can be reduced compared to the first layer, preventing the tire from slipping due to melted ice on the road surface caused by excessive heat accumulation in the second layer. From the above, it is believed that the cooperation of (1) to (5) above allows for a scratching effect derived from recycled carbon black on the surface of the tread without excessively melting the ice on the road surface, and that this deformation is transmitted to the inside of the tread, causing energy loss inside the tread as well. Therefore, it is believed that the tire of the present invention can improve the grip performance on ice at high speeds.

[0013] The ratio (70℃E*1 / 70℃E*2) of the complex elastic modulus (MPa) (70℃E*1) of the rubber composition constituting the first layer to the complex elastic modulus (MPa) (70℃E*2) of the rubber composition constituting the second layer at 70°C is preferably 0.70 or less.

[0014] Since the rubber composition constituting the first layer is softer than the rubber composition constituting the second layer, when the tire contacts the road surface, the first layer is pushed into the second layer, so it is considered that the grip performance due to the domain centered on recycled carbon black in the first layer is further improved.

[0015] The 100% modulus of the rubber composition constituting the second layer is preferably greater than the 100% modulus of the rubber composition constituting the first layer.

[0016] Since the rubber composition constituting the first layer is softer than the rubber composition constituting the second layer, when the tire contacts the road surface, the first layer is pushed into the second layer, so it is considered that the grip performance due to the domain centered on recycled carbon black in the first layer is further improved.

[0017] When the thickness of the first layer is t1 (mm) and the thickness of the second layer is t2 (mm), the ratio of t1 to the sum of t1 and t2 (t1 / (t1 + t2)) is preferably 0.80 or less.

[0018] By making the ratio of the thickness of the first layer below a certain level, it is considered that the first layer stores heat during high-speed driving, suppresses the melting of ice on the road, and can prevent slipping, so the grip performance on ice can be further improved.

[0019] When the thickness of the first layer is t1 (mm) and the thickness of the second layer is t2 (mm), the product of C (parts by mass) and the ratio of t1 to the sum of t1 and t2 (C×t1 / (t1 + t2)) is preferably 20.0 or less.

[0020] By setting C×t1 / (t1+t2) within the aforementioned range, the first layer accumulates excessive heat during high-speed driving, and this heat melts the ice on the road, generating a water film. This water film prevents the tire from slipping, thus further improving grip performance on ice.

[0021] Preferably, the tread portion has one or more circumferential grooves that extend continuously in the circumferential direction of the tire, and the product of the groove depth H (mm) and C (mass portion) of the deepest part of the circumferential groove (H × C) is 200 or less.

[0022] The deeper the grooves in the tread, the more easily the land areas separated by adjacent circumferential grooves and the land areas separated by the circumferential grooves and the contact edges of the tread become deformable and generate heat. Therefore, by reducing the product of these to below a certain level, it is possible to suppress heat generation and heat accumulation in the first layer of the tread during driving. This heat can melt the ice on the road, creating a water film, which prevents the tire from slipping, thus further improving grip performance on ice.

[0023] Preferably, the tread portion has grooves inclined in the tire circumferential direction or tire width direction, and the ratio of the maximum width L (mm) of the grooves inclined in the tire circumferential direction or tire width direction to C (mass portion) (L / C) is 0.30 or more.

[0024] The inclined grooves allow air to pass more easily across the tire's width as it rolls, which is thought to provide a cooling effect on the tread surface. Furthermore, by making the groove width sufficiently wide relative to the recycled carbon black content C in the first layer, it is thought that cooling efficiency can be improved and heat accumulation in the first layer of the tread can be more easily suppressed.

[0025] The tanδ (70°C tanδ²) of the rubber composition constituting the second layer is preferably greater than 0.02 and less than 0.20.

[0026] By setting the 70°C tanδ of the second layer within the aforementioned range, the heat generation of the second layer can be reduced, heat accumulation in the second layer can be suppressed, and it is believed that the grip performance on ice during high-speed driving will be further improved.

[0027] It is preferable that the Shore hardness (Hs) of the rubber composition constituting the above-mentioned layer is greater than 55 and less than 80.

[0028] By setting the rubber hardness within the aforementioned range, it is believed that the grip performance on ice during high-speed driving will be further improved.

[0029] When the content of isoprene-based rubber in the rubber component of the rubber composition constituting the above layer is I (mass%), it is preferable that the ratio of I to C (I / C) is 1.20 or more.

[0030] By setting the I / C within the aforementioned range, the dispersibility of recycled carbon black in the rubber component in the first layer is improved, which is expected to further enhance ice grip performance during high-speed driving.

[0031] Preferably, the recycled carbon black is recycled carbon black obtained by calcining waste tires and / or waste tire tubes.

[0032] By using recycled carbon black obtained by calcining waste tires and / or waste tire tubes, it is believed that the recycled carbon black will disperse more easily within the rubber components of the rubber composition.

[0033] It is preferable that the aforementioned waste tire and / or tube for waste tires contains diene-based rubber.

[0034] It is believed that the inclusion of diene-based rubber in waste tires and / or tubes for waste tires facilitates the dispersion of recycled carbon black within the rubber components of the rubber composition.

[0035] <Definition> The "tread portion" is the part that forms the contact surface of the tire, and in the radial cross-section of the tire, if the tire has components that form the tire skeleton using steel or textile materials such as belt layers, belt reinforcement layers, and carcass layers, the tread portion is the component that is radially outward from these components.

[0036] "Tread thickness" refers to the thickness of each rubber layer on the tire equator in a cross-section obtained by cutting the tire in a plane containing the tire's axis of rotation. It is the average of the tread thicknesses obtained at five locations by rotating the tire circumferentially by 72°. For example, the thickness of the first layer refers to the straight-line distance in the radial direction of the tire from the outermost surface of the tread to the inner radial interface of the first layer on the tire equator. If there are circumferential grooves on the tire equator, the thickness of each rubber layer constituting the tread is the thickness of each rubber layer at the center of the tire width direction of the land area closest to the tire equator. "Land area closest to the tire equator" refers to the land area with the groove edge closest to the tire equator of the circumferential grooves present on the tire equator. If there are multiple such land areas, the thickness of each rubber layer constituting the tread is the average of the thicknesses of each rubber layer at the center of the tire width direction of the two such land areas. Furthermore, if conductive materials or other elements exist on the land portion of the tire equator, and the interface is unclear, the interface obstructed by the conductive materials or other elements shall be virtually connected and measured.

[0037] The "maximum width of the inclined groove" refers to the largest groove opening width at the outermost surface of the tread in a cross-section perpendicular to the centerlines of both ends of the tread extending in the direction of groove extension. The opening width is the straight-line distance from one end of the tread to the other at the outermost surface of the tread. Here, the "direction of groove extension" refers to the direction in which the groove extends continuously; for example, in the case of a circumferential groove, it is the circumferential direction, and in the case of a groove inclined in the tire width direction, it is the direction along the inclination in the tire width direction.

[0038] "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 mass of carbon lost due to oxidative combustion is less than 87% by mass. Recycled carbon black is also called recycled carbon black and is sometimes represented as rCB.

[0039] A "softener" is a material that imparts plasticity to rubber components and is extracted from rubber compositions using acetone. Softeners include those that are liquid at 25°C and those that are solid at 25°C. However, waxes and stearic acid commonly used in the tire industry are excluded.

[0040] "Softener content" includes the amount of softener contained in the stretchable rubber component that has been pre-stretched with softeners such as oil, resin components, and liquid rubber components. The same applies to the oil content, resin component content, and liquid rubber content; for example, if the stretchable component is oil, the stretchable oil is included in the oil content.

[0041] <Measurement method> "70℃tanδ" is the loss tangent measured using a dynamic viscoelasticity measuring device (e.g., the Iplexer series from GABO) under the conditions of a temperature of 70℃, a frequency of 10Hz, an initial strain of 5%, a dynamic strain of ±1%, and the extension mode. The sample for loss tangent measurement is a vulcanized rubber composition measuring 20mm in length, 4mm in width, and 1mm in thickness. When preparing the sample by cutting it from a tire, it should be cut from the tire tread so that the tire circumference is the longer side and the tire radius is the thickness direction.

[0042] "70℃E*" is the complex modulus of elasticity measured using a dynamic viscoelasticity analyzer (e.g., GABO's Iplexer series) under the conditions of 70℃ temperature, 10Hz frequency, 5% initial strain, ±1% dynamic strain, and extension mode. The sample for this measurement is prepared in the same manner as for 30℃tanδ.

[0043] "Styrene content" is, 1 This value is calculated by 1H-NMR measurement and applies, for example, to rubber components having repeating units derived from styrene, such as SBR. "Cis content (amount of cis-1,4-bonded butadiene units)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2:2017 and applies, for example, to rubber components having repeating units derived from butadiene, such as BR.

[0044] Shore hardness is measured in accordance with JIS K 6253 by pressing a Type A durometer against the sample from the contact surface side at 23°C. When preparing a hardness measurement sample from a test tire, cut out the tread portion that forms the contact surface of the test tire so that the tire radius direction is the thickness direction.

[0045] "100% modulus" refers to the 100% tensile stress (MPa) obtained when a tensile test is performed on a 1 mm thick, No. 7 dumbbell-shaped test specimen in accordance with JIS K 6251 "Vulcanized rubber and thermoplastic rubber - Method for determining tensile test properties" at a 23°C atmosphere and a tensile speed of 3.3 mm / second. When preparing a measurement sample from a test tire, the tread portion that forms the contact surface of the test tire is cut out so that the tire radius direction is the thickness direction.

[0046] 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 from Tosoh Corporation, with a differential refractometer as the detector and TSKGEL SUPERMALTIPORE HZ-M column from Tosoh Corporation) to a standard polystyrene equivalent. This method is applicable, for example, to SBR, BR, etc.

[0047] The nitrogen adsorption specific surface area (N2SA) of carbon black is measured in accordance with JIS K 6217-2:2017. The nitrogen adsorption specific surface area (N2SA) of silica is measured by the BET method in accordance with ASTM D3037-93.

[0048] A tire manufacturing procedure according to one embodiment of the present invention will be described in detail below. However, the following description is illustrative for explaining the present invention and is not intended to limit the technical scope of the present invention to this scope only.

[0049] [tire] A tire according to one embodiment of the present invention will be described below with reference to the drawings. Note that the embodiments shown below are merely examples, and the tire of the present invention is not limited to the embodiments described below.

[0050] Figure 1 is a diagram showing a cross-section of the tire tread passing through the tire's axis of rotation. In Figure 1, the vertical direction is the tire radius, the horizontal direction is the tire width, and the direction perpendicular to the plane of the paper is the tire circumferential direction.

[0051] In this embodiment, the tire tread preferably has circumferential grooves 1 extending in the circumferential direction of the tire. The circumferential grooves 1 may extend in a straight line along the circumferential direction, or they may extend in a zigzag pattern along the circumferential direction. It is not necessary for the circumferential grooves 1 to be continuous without interruption in the circumferential direction; for example, they may be interrupted by lateral grooves.

[0052] The groove depth H of the circumferential groove 1 is determined by the distance between the extension line 4 connecting two adjacent land areas 2 to the circumferential groove 1 and the extension line 5 of the deepest part of the groove bottom of the circumferential groove 1. Note that, for example, if there are multiple circumferential grooves 1, the groove depth H can be the groove depth of the circumferential groove with the deepest groove depth.

[0053] As shown in the figures, the tread portion 8 of the tire according to this embodiment comprises a first layer 6 and a second layer 7, the outer surface of the first layer 6 constituting the tread surface 3, and the second layer 7 adjacent to the radially inward side of the first layer 6. The first layer 6 typically corresponds to a cap tread. The second layer 7 does not have a typical shape and may be a cap tread or a base tread. Furthermore, as long as the objective of the present invention is achieved, there may be one or more additional rubber layers between the second layer 7 and the belt layer. If the tread portion 8 has three or more layers, the cap tread or inner layer (base tread) may be composed of two or more layers. For example, if there are two cap tread layers, the rubber layer located radially inward of the cap tread corresponds to the second layer of the present invention, and if there are two base tread layers, the rubber layer located radially outward of the base tread corresponds to the second layer of the present invention.

[0054] In Figure 1, the deepest part of the groove bottom of the circumferential groove 1 having the deepest groove depth among the multiple circumferential grooves 1 is formed to be located radially inward of the tire beyond the outermost part of the second layer 7 in the land area 2 adjacent to that circumferential groove. However, the configuration is not limited to this, and the deepest part of the groove bottom of the circumferential groove 1 may remain within the range of the first layer 6 in the land area 2 adjacent to that circumferential groove.

[0055] In Figure 1, the groove width of the circumferential groove 1 is constant from the outside to the inside in the radial direction of the tire, but the design is not limited to this configuration and may vary from the outside to the inside in the radial direction of the tire. Also, the groove wall 10 of the circumferential groove extends linearly from the outside to the inside in the radial direction of the tire, but the design is not limited to this configuration and may extend in a curved or stepped shape, for example.

[0056] In this embodiment, the total thickness of the tread portion, which in Figure 1 is the sum of the thickness t1 of the first layer 6 and the thickness t2 of the second layer 7 (t1+t2), is preferably 6.0 mm or more, more preferably 7.0 mm or more, even more preferably 8.0 mm or more, even more preferably 9.0 mm or more, and particularly preferably 9.5 mm or more, from the viewpoint of ice grip performance and durability. Furthermore, from the viewpoint of the effects of the present invention, the total thickness of the tread portion is preferably 15.0 mm or less, more preferably 13.0 mm or less, and even more preferably 11.0 mm or less.

[0057] In this embodiment, the thickness t1 of the first layer 6 is preferably 4.0 mm or more, more preferably 5.0 mm or more, and even more preferably 6.0 mm or more, from the viewpoint of improving ice grip performance by allowing the first layer to easily bite into the icy road surface due to the heat generated by the first layer. Furthermore, the thickness t1 of the first layer 6 is preferably 12.0 mm or less, more preferably 10.0 mm or less, even more preferably 9.0 mm or less, and particularly preferably 8.0 mm or less.

[0058] In this embodiment, the thickness t2 of the second layer 7 is preferably 0.5 mm or more, more preferably 0.7 mm or more, and even more preferably 1.0 mm or more, from the viewpoint of ensuring the heat generation of the second layer and improving ice grip performance during high-speed driving. Furthermore, the thickness t2 of the second layer 7 is preferably 6.0 mm or less, more preferably 4.0 mm or less, even more preferably 3.0 mm or less, and particularly preferably 2.5 mm or less, from the viewpoint of suppressing heat generation during driving.

[0059] The ratio of t1 to the sum of the thickness t1 of the first layer 6 and the thickness t2 of the second layer 7 (t1 / (t1+t2)) is preferably 0.80 or less, more preferably 0.75 or less, and even more preferably 0.72 or less, from the viewpoint of keeping the ratio of the thickness of the first layer below a certain level, suppressing heat accumulation in the first layer during high-speed driving and melting of ice on the road, preventing slippage, and improving grip performance on ice. Furthermore, t1 / (t1+t2) is preferably 0.50 or more, more preferably 0.55 or more, and even more preferably 0.65 or more, from the viewpoint of allowing the first layer to deform appropriately.

[0060] The 70°C tanδ (70°C tanδ1) of the first layer 6 is preferably 0.21 or less, more preferably 0.20 or less, and even more preferably 0.19 or less, from the viewpoint of suppressing excessive heat generation in the tread area even during high-speed driving and preventing slippage. Furthermore, the lower limit of 70°C tanδ1 is preferably 0.02 or more, more preferably 0.04 or more, and even more preferably 0.06 or more.

[0061] The 70°C tanδ (70°C tanδ²) of the second layer 7 is preferably less than 0.20, and more preferably 0.19 or less, from the viewpoint of suppressing excessive heat generation inside the tread. The lower limit is not particularly limited, but the 70°C tanδ² is preferably greater than 0.02, more preferably greater than 0.03, and even more preferably greater than 0.04.

[0062] The complex modulus of elasticity (MPa) (70°CE*1) of the first layer 6 at 70°C is preferably 8.0 MPa or less, more preferably 6.0 MPa or less, even more preferably 5.0 MPa or less, and particularly preferably 4.5 MPa or less, from the viewpoint of ice grip performance. Furthermore, the 70°CE*1 is preferably 3.0 MPa or more, more preferably 3.5 MPa or more, and even more preferably 4.0 MPa or more, from the viewpoint of suppressing excessive heat generation in the first layer and preventing slippage.

[0063] The 70°CE*2 of the second layer 7 is preferably greater than the 70°CE* of the first layer 6. That is, the ratio of the 70°CE*1 of the first layer 6 to the 70°CE*2 of the second layer 7 (70°CE*1 / 70°CE*2) is preferably less than 1.00. Specifically, the 70°CE*2 of the second layer 7 is preferably 9.0 MPa or less, more preferably 8.0 MPa or less, even more preferably 7.0 MPa or less, and particularly preferably 6.5 MPa or less. Furthermore, the 70°CE*2 is preferably 3.0 MPa or more, more preferably 4.0 MPa or more, and even more preferably 4.5 MPa or more.

[0064] The 70℃E*1 / 70℃E*2 ratio is preferably less than 1.00, more preferably 0.80 or less, even more preferably 0.70 or less, and particularly preferably 0.65 or less. The lower limit of the 70℃E*1 / 70℃E*2 ratio is preferably 0.40 or higher, more preferably 0.50 or higher, and even more preferably 0.55 or higher.

[0065] The values ​​of 70°C tanδ and 70°C E* can be appropriately adjusted depending on the type and amount of rubber components, fillers, softeners, vulcanizing agents, and vulcanization accelerators. For example, increasing the total amount of styrene in the rubber components, increasing the amount of fillers, decreasing the vulcanizing agents and vulcanization accelerators, and using resins with a high glass transition temperature as softeners tend to increase the value of 70°C tanδ. Similarly, increasing the total amount of styrene in the rubber components, increasing the amount of fillers, increasing the vulcanizing agents and vulcanization accelerators, using resins with a high glass transition temperature as softeners, and decreasing the amount of softeners tend to increase the value of 70°C E*. Furthermore, reducing the amount of recycled carbon black tends to decrease the values ​​of 70°C tanδ and 70°C E*.

[0066] The Shore hardness (Hs) of the rubber composition constituting the first layer 6 is preferably 50.0 or higher, more preferably 55.0 or higher, even more preferably 60.0 or higher, and particularly preferably 61.5 or higher, from the viewpoint of ice grip performance. Furthermore, the rubber hardness is preferably 80.0 or lower, more preferably 75.0 or lower, and even more preferably 70.0 or lower, from the viewpoint of ice grip performance during high-speed driving.

[0067] The Shore hardness (Hs) of the rubber composition constituting the second layer 7 is preferably 55.0 or higher, more preferably 60.0 or higher, even more preferably 62.0 or higher, and particularly preferably 63.5 or higher, from the viewpoint of ice grip performance. Furthermore, from the viewpoint of ice grip performance during high-speed driving, the rubber hardness is preferably 80.0 or lower, more preferably 70.0 or lower, and even more preferably 65.0 or lower.

[0068] The Shore hardness of each rubber layer can be adjusted as appropriate by changing the type and amount of rubber components, fillers, softeners, etc. For example, the Shore hardness can be increased by increasing the total amount of styrene in the rubber components, increasing the amount of fillers, increasing the amount of vulcanizing agents and vulcanization accelerators, using resins with a high glass transition temperature as softeners, or decreasing the amount of softeners. Conversely, the Shore hardness can be decreased by decreasing the total amount of styrene in the rubber components, decreasing the amount of fillers, decreasing the amount of vulcanizing agents and vulcanization accelerators, using plasticizers with a low glass transition temperature as softeners, or increasing the amount of softeners.

[0069] The 100% modulus of the rubber composition constituting the first layer 6 is preferably smaller than the 100% modulus of the rubber composition constituting the second layer 7. This is thought to further improve the grip performance of the domains centered on recycled carbon black in the first layer, as the first layer is pressed into the second layer when the tire makes contact with the road surface. The 100% modulus of the rubber composition constituting the first layer 6 is preferably 1.0 MPa or higher, more preferably 1.1 MPa or higher, even more preferably 1.2 MPa or higher, and particularly preferably 1.3 MPa or higher. Furthermore, the 100% modulus is preferably 3.0 MPa or lower, more preferably 2.5 MPa or lower, and even more preferably 2.3 MPa or lower.

[0070] The 100% modulus of the rubber composition constituting the second layer 7 is preferably 1.0 MPa or higher, more preferably 1.5 MPa or higher, and even more preferably 2.0 MPa or higher. Furthermore, the 100% modulus is preferably 5.5 MPa or lower, more preferably 5.0 MPa or lower, even more preferably 4.5 MPa or lower, and particularly preferably 4.0 MPa or lower.

[0071] Furthermore, the 100% modulus can be adjusted as appropriate by changing the type and amount of fillers, plasticizers, vulcanizing agents, vulcanization accelerators, etc. For example, the 100% modulus of a rubber composition can be increased by increasing the total amount of styrene in the rubber component, increasing the amount of fillers, increasing the amount of vulcanizing agents and vulcanization accelerators, using resins with a high glass transition temperature as softeners, or decreasing the amount of softeners.

[0072] From the viewpoint of ice grip performance, the groove depth H of the circumferential grooves is preferably 5.0 mm or more, more preferably 6.0 mm or more, even more preferably 6.5 mm or more, even more preferably 7.0 mm or more, and even more preferably 7.5 mm or more. 8.0 mm or more is particularly preferred. Furthermore, from the viewpoint of durability performance, the groove depth H of the circumferential grooves is preferably 12.0 mm or less, more preferably 11.0 mm or less, and even more preferably 10.0 mm or less.

[0073] From the viewpoint of the effects of the present invention, the ratio t1 / H of the thickness t1 (mm) of the first layer 6 to the groove depth H (mm) of the circumferential groove is preferably less than 1.00, more preferably less than 0.90, and even more preferably less than 0.88. Furthermore, t1 / H is preferably greater than 0.30, more preferably greater than 0.40, and even more preferably greater than 0.45.

[0074] In this embodiment, the tread portion 8 of the tire preferably has grooves (inclined grooves) that are inclined in the circumferential direction or the width direction of the tire. Specifically, the grooves (inclined grooves) that are inclined in the circumferential direction or the width direction of the tire are lateral grooves that extend in the width direction, and these lateral grooves bend or curve as they extend in the width direction. The width of the lateral grooves is not particularly limited, but is usually 8 mm or less. Among the lateral grooves, those with a width of 2 mm or less are specifically called sipes.

[0075] Figure 2 shows a schematic diagram of the contact surface when the tread portion of a tire according to one embodiment of the present invention is pressed against a flat surface. In Figure 2, the tread surface 3 has a plurality of zigzag-shaped circumferential grooves 1 that extend continuously in the circumferential direction. The lateral grooves 11 are curved so as they shift to one side in the circumferential direction of the tire as they approach the tire equator C. In Figure 2, at the bends in the circumferential grooves 1, the lateral grooves 11 intersect and extend with the circumferential grooves 1. Also in Figure 2, the shoulder land portion 12 is provided with a plurality of straight shoulder sipes 22, one end of which opens into the circumferential grooves 1, and the center land portion 13 is provided with a plurality of straight center sipes 23, one end of which opens into the circumferential grooves 1.

[0076] The maximum width L of the grooves (inclined grooves) that are inclined in the circumferential or widthwise direction of the tire is preferably 3.0 mm or more, more preferably 4.0 mm or more, and even more preferably 5.0 mm or more, from the viewpoint of cooling the first layer and suppressing heat accumulation. On the other hand, the upper limit of L is preferably 15.0 mm or less, more preferably 10.0 mm or less, and even more preferably 8.0 mm or less.

[0077] Figure 3 shows a schematic diagram of the contact surface when the tread portion of a tire according to another embodiment of the present invention is pressed against a flat surface. In Figure 3, the tire has a circumferential groove 1 that extends linearly and continuously along the tire equator C, and transverse grooves 21 and sipes 22, 23 that extend in the width direction. The tread portion of the tire in the embodiment shown in Figure 3 does not have transverse grooves that bend or curve, that is, it does not have inclined grooves.

[0078] [Rubber composition] Each rubber composition constituting the tread layer according to this embodiment can be manufactured using the raw materials described below, according to the required 100% modulus, Shore hardness, 70°C tanδ, 70°C E*, etc. These will be described in detail below. Unless otherwise specified below, the types and amounts of various compounding agents described are common to the rubber compositions constituting the first and second layers of the tread.

[0079] <Rubber components> The rubber composition according to this embodiment preferably contains at least one selected from the group consisting of isoprene rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR) as a rubber component. The rubber composition constituting the first layer preferably contains BR as a rubber component, more preferably contains BR and isoprene rubber, and may consist only of BR and isoprene rubber. The rubber composition constituting the second layer preferably contains isoprene rubber as a rubber component, more preferably contains isoprene rubber and BR, and may consist only of isoprene rubber and BR. Furthermore, these rubber components may be stretched rubber that has been pre-stretched with a plasticizer component. Furthermore, these rubber components may be modified with functional groups that can interact with filler components such as silica and carbon black, and from the viewpoint of optimizing the crosslinking form and suppressing degradation, a part of the unsaturated bond portion may be hydrogenated to become a saturated bond.

[0080] (Isoprene 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, and grafted natural rubber. These isoprene-based rubbers may be used individually or in combination of two or more types.

[0081] NR is not particularly limited and can be any tire that is common in the tire industry, such as SIR20, RSS#3, and TSR20.

[0082] From the viewpoint of the effects of the present invention, the content I of isoprene-based rubber in the rubber component of the rubber composition constituting the first layer is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and particularly preferably 40% by mass or more. Furthermore, there is no particular upper limit to the content, but it is preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less, and particularly preferably 55% by mass or less.

[0083] From the viewpoint of the effects of the present invention, the content of isoprene-based rubber in the rubber component constituting the second layer is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and particularly preferably 40% by mass or more. Furthermore, there is no particular upper limit to the content, but it is preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less, and particularly preferably 55% by mass or less.

[0084] (BR) 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. These BRs may be used individually or in combination of two or more types.

[0085] High-cis BR can be commercially available from companies such as Nippon Zeon Co., Ltd., Ube Industries, Ltd., and JSR Corporation. Including high-cis BR can improve low-temperature properties and wear resistance. The cis content is preferably 95 mol% or more, more preferably 96 mol% or more, and even more preferably 97 mol% or more. The cis content of BR is measured by the measurement method described above.

[0086] As the modified BR, a modified butadiene rubber (modified BR) is preferably used 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.

[0087] 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.

[0088] From the viewpoint of wear resistance, the weight-average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more. From the viewpoint of crosslinking uniformity, it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. The weight-average molecular weight of BR is measured by the measurement method described above.

[0089] The BR content in the rubber components of the rubber composition constituting the first layer (total BR content when two or more types are used in combination) is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, and particularly preferably 50% by mass or more. On the other hand, the BR content in the rubber components constituting the first layer is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 65% ​​by mass or less.

[0090] The BR content in the rubber components of the rubber composition constituting the second layer (total BR content when two or more types are used in combination) is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, and particularly preferably 50% by mass or more. On the other hand, the BR content in the rubber components constituting the first layer is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 65% ​​by mass or less.

[0091] (SBR) There are no particular limitations on SBR, and examples include unmodified solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Modified SBRs include SBRs with modified terminals and / or main chains, and modified SBRs coupled with tin, silicon compounds, etc. (condensates, those with branched structures, etc.). Among these, S-SBR and modified SBRs are preferred. Furthermore, hydrogenated versions of these SBRs (hydrogenated SBRs) can also be used. These SBRs may be used individually or in combination of two or more types.

[0092] The SBRs listed above may be used individually or in combination of two or more. Examples of the SBRs listed above include those commercially available from companies such as Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Corporation, and ZS Elastomer Co., Ltd.

[0093] The SBR content in the rubber components constituting the first and second layers is not particularly limited and can be, for example, 5.0% by mass or more, 10% by mass or more, etc.

[0094] (Other rubber components) The rubber component according to this embodiment may contain rubber components other than the isoprene-based rubber, BR, and SBR mentioned above. Other rubber components that can be crosslinked are commonly used in the tire industry and include isoprene-based rubbers such as styrene-isoprene rubber (SIR), styrene-isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR), diene-based rubbers other than SBR and BR; and non-diene rubbers such as butyl rubber (IIR), halogenated 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. The rubber component according to this embodiment preferably contains 80% by mass or more of diene-based rubber, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more, and may consist only of diene-based rubber. In addition to the rubber components mentioned above, the product may or may not contain known thermoplastic elastomers.

[0095] <Filler> The rubber composition according to this embodiment contains recycled carbon black as a filler, and it is preferable to use recycled carbon black in combination with carbon black and / or silica.

[0096] (Recycled carbon black) Recycled carbon black can be obtained by crushing used pneumatic tires (waste tires) or used tire tubes (waste tire tubes) and calcining the crushed material. These waste tires and waste tire tubes preferably contain diene rubber. For example, European Patent Application Publication No. 3427975, referring 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 thermal decomposition of organic materials at 550-800°C in the absence of oxygen, or by vacuum thermal decomposition at relatively low temperatures (

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

[0004] of Patent No. 6856781 (Comparison of Surface Morphology and Chemistry of Thermally Decomposed Carbon Black and Commercially Available Carbon Black, Powder Technology 160 (2005) 190-193).

[0097] The recycled carbon black of the present invention has an ash content of 13% by mass or more. Because recycled carbon black has a high ash content, it has the characteristic of being less likely to absorb oil. The ash content is preferably 14% by mass or more, more preferably 15% by mass or more, even more preferably 16% by mass or more, and particularly preferably 17% by mass or more. The ash content is as defined above.

[0098] Recycled carbon black may lack functional groups on its surface, or it may be treated to contain functional groups on its surface. Treatment to contain 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 thermal decomposition 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 No. 6856781, carbon black obtained from a thermal decomposition 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 contain functional groups on its surface.

[0099] Recycled carbon black can be purchased from companies such as Strable Green Carbon and LDCarbon.

[0100] The amount of recycled carbon black (C) per 100 parts by mass of rubber component in the first layer of the rubber composition is preferably 7.0 parts by mass or more, more preferably 9.0 parts by mass or more, even more preferably 10.0 parts by mass or more, even more preferably 15.0 parts by mass or more, even more preferably 20.0 parts by mass or more, and particularly preferably 25 parts by mass or more. Furthermore, from the viewpoint of reinforcing properties, it is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 60 parts by mass or less, and particularly preferably 50 parts by mass or less.

[0101] In the present invention, the amount of recycled carbon black B per 100 parts by mass of rubber component in the rubber composition constituting the second layer is less than the amount of recycled carbon black C per 100 parts by mass of rubber component in the rubber composition constituting the first layer. That is, B / C is 1.0 or less. By setting B / C to 1.0 or less, the heat generation of the second layer can be reduced compared to the first layer, preventing the tire from slipping due to melted ice on the road surface caused by excessive heat accumulation in the second layer, and improving ice grip performance at high speeds.

[0102] The content B of recycled carbon black per 100 parts by mass of rubber component in the rubber composition constituting the second layer is preferably 3.0 parts by mass or more, more preferably 5.0 parts by mass or more, and even more preferably 7.0 parts by mass or more. Furthermore, from the viewpoint of reinforcing properties, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 25 parts by mass or less.

[0103] The B / C ratio is 1.00 or less, preferably 0.90 or less, more preferably 0.80 or less, even more preferably 0.75 or less, and particularly preferably 0.60 or less. On the other hand, the lower limit of the B / C ratio is preferably greater than 0.10, more preferably greater than 0.20, and even more preferably greater than 0.30.

[0104] The product of C (mass portion) and the ratio of t2 to the sum of the thickness t1 of the first layer and the thickness t2 of the second layer (t1 / (t1+t2)) (C×(t1 / t1+t2)) is preferably 20.0 or less, more preferably 15.0 or less, even more preferably 10.0 or less, and even more preferably 9.0 or less. 7.0 or less is particularly preferred. Furthermore, the lower limit of C×(t1 / t1+t2) is preferably 1.0 or more, more preferably 1.5 or more, and even more preferably 2.0 or more. By setting C×t1 / (t1+t2) within the above range, the first layer accumulates excessive heat during high-speed driving, and this heat melts the ice on the road, generating a water film. This water film prevents the tire from slipping, thus further improving ice grip performance.

[0105] The ratio of the isoprene-based rubber content I (mass%) in the first layer's rubber component to C (mass) (I / C) is preferably 1.0 or higher, more preferably 1.20 or higher, even more preferably 2.0 or higher, and still more preferably 3.0 or higher. On the other hand, the upper limit of I / C is preferably 15.0 or lower, more preferably 12.0 or lower, and even more preferably 10.0 or lower. By setting I / C within the above range, the dispersibility of recycled carbon black in the rubber component of the first layer is improved, and it is believed that the grip performance on ice during high-speed driving is further improved.

[0106] The product of the groove depth H (mm) and C at the deepest part of the circumferential groove (H × C) is preferably 200 or less, more preferably 150 or less, and even more preferably 100 or less. On the other hand, the lower limit of H × C is preferably 20 or more, more preferably 50 or more, and even more preferably 60 or more.

[0107] The ratio (L / C) of the maximum width L (mm) of the grooves inclined in the tire circumferential or tire width direction to C (mass portion) is preferably 0.25 or more, more preferably 0.3 or more, and even more preferably 0.5 or more. On the other hand, the upper limit of L / C is preferably 2.0 or less, more preferably 1.8 or less, and even more preferably 1.2 or less.

[0108] (Carbon black other than rCB) Other carbon blacks besides rCB are not particularly limited, and common types used in the tire industry such as GPF, FEF, HAF, ISAF, and SAF can be used. In addition to carbon black produced by burning common mineral oil, carbon black made from biomass materials such as lignin may also be used. These carbon blacks may be used individually or in combination of two or more types.

[0109] The nitrogen adsorption specific surface area (N2SA) of carbon black is 10 m² from the perspective of reinforcing properties. 2 Preferably 30m / g or more. 2 More preferably 50m 2 A value of 200m or more is even more preferable. Furthermore, from the viewpoint of low fuel consumption and processability, 200m2 Preferably less than / g, 150m 2 / g or less is more preferable, 120m 2 A value of less than / g is even more preferable. The N2SA of carbon black is measured by the measurement method described above.

[0110] From the viewpoint of reinforcing properties, the content of carbon black other than rCB per 100 parts by mass of rubber component in the rubber composition constituting the first layer is preferably 3.0 parts by mass or more, more preferably 5.0 parts by mass or more, and even more preferably 6.0 parts by mass or more. Furthermore, from the viewpoint of the effects of the present invention, it is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 15 parts by mass or less.

[0111] From the viewpoint of heat generation, the content of carbon black other than rCB per 100 parts by mass of rubber component in the rubber composition constituting the second layer is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more. Furthermore, the content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 70 parts by mass or less.

[0112] From the viewpoint of reinforcing properties, the total carbon black content (total content of rCB and non-rCB carbon black) per 100 parts by mass of rubber component in the rubber composition constituting the first layer is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more. Furthermore, from the viewpoint of the effects of the present invention, the total carbon black content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 60 parts by mass or less, and particularly preferably 50 parts by mass or less.

[0113] From the perspective of reinforcement, the total content of carbon black (the sum of rCB and the content of carbon black other than rCB) per 100 parts by mass of the rubber component of the rubber composition constituting the second layer is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and still more preferably 20 parts by mass or more. Also, from the perspective of the effects of the present invention, the total content of the carbon black is preferably 90 parts by mass or less, more preferably 85 parts by mass or less, still more preferably 80 parts by mass or less, and particularly preferably 75 parts by mass or less.

[0114] The ratio of the content of rCB to the total content of carbon black (C / total carbon black content) per 100 parts by mass of the rubber component of the rubber composition constituting the first layer is preferably 0.40 or more, more preferably 0.50 or more, and still more preferably 0.60 or more. The ratio of the content of rCB to the total content of carbon black (B / total carbon black content) per 100 parts by mass of the rubber component of the rubber composition constituting the second layer is preferably 0.12 or more, more preferably 0.20 or more, and still more preferably 0.33 or more.

[0115] (Silica) The silica is not particularly limited, and for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), etc., which are common in the tire industry, can be used. Among them, hydrous silica prepared by a wet method is preferred because it has many silanol groups. In addition to the above silica, silica made from biomass materials such as rice husks may be appropriately used as raw materials. These silicas may be used alone or in combination of two or more.

[0116] The nitrogen adsorption specific surface area (N2SA) of the silica is preferably 120 m 2 / g or more, more preferably 150 m 2 / g or more, and still more preferably 170 m 2 / g or more from the perspectives of low fuel consumption performance and abrasion resistance performance. Also, from the perspectives of low fuel consumption performance and processability, it is preferably 350 m 2 / g or less, and more preferably 300 m 2More preferably less than / g, 250m 2 A value of less than / g is even more preferable. The N2SA of silica is measured by the measurement method described above.

[0117] From the viewpoint of reinforcing properties, the silica content of the rubber composition constituting the first layer, relative to 100 parts by mass of rubber components, is preferably 40 parts by mass or more, more preferably 45 parts by mass or more, and even more preferably 50 parts by mass or more. From the viewpoint of processability, it is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 70 parts by mass or less.

[0118] The silica content of the rubber composition constituting the second layer, relative to 100 parts by mass of rubber components, is not particularly limited and may be 0 parts by mass. From the viewpoint of reinforcing properties, 10 parts by mass or more is preferred, 15 parts by mass or more is more preferred, and 30 parts by mass or more is even more preferred. From the viewpoint of processability, 100 parts by mass or less is preferred, 90 parts by mass or less is more preferred, 80 parts by mass or less is even more preferred, and 70 parts by mass or less is particularly preferred.

[0119] The total content of carbon black (rCB and non-rCB carbon black) and silica per 100 parts by mass of rubber component in the first layer of the rubber composition is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and even more preferably 70 parts by mass or more. The total content of carbon black (rCB and non-rCB carbon black) and silica per 100 parts by mass of rubber component in the second layer of the rubber composition is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 60 parts by mass or more. Furthermore, from the viewpoint of processability, the upper limit of the total content of carbon black and silica in the rubber compositions of the first and second layers is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 100 parts by mass or less.

[0120] (Other fillers) The recycled carbon black, carbon black other than rCB, and fillers other than silica are not particularly limited and can be blended with, for example, aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, biochar, etc., which are commonly used in the tire industry. These other fillers may be used individually or in combination of two or more.

[0121] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent that has conventionally been used in combination with silica in the tire industry can be used, for example: mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxy Examples include thioester silane coupling agents such as silanes; vinyl silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. In particular, it is preferable to contain a sulfide silane coupling agent and / or a mercapto silane coupling agent. As silane coupling agents, for example, those commercially available from Momentive, etc., can be used. These silane coupling agents may be used individually or in combination of two or more.

[0122] From the viewpoint of improving silica dispersibility, the content of the silane coupling agent per 100 parts by mass of silica is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more. Furthermore, from the viewpoint of cost and processability, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less.

[0123] <Other compounding agents> In addition to the components mentioned above, the rubber composition according to this embodiment may appropriately contain compounding agents commonly used in the tire industry, such as softeners, waxes, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0124] (Softener) The rubber composition according to this embodiment preferably contains a softening agent. Examples of softening agents include resin components, oils, and liquid rubber. These softening agents also include the stretching components used when the aforementioned stretchable rubber is used.

[0125] The resin components are not particularly limited, but examples include hydrocarbon resins commonly used in the tire industry, such as petroleum resins, terpene resins, rosin resins, and phenolic resins.

[0126] When a resin component is included, its content per 100 parts by mass of the rubber component is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more. Furthermore, the content of the resin component is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 40 parts by mass or less.

[0127] Examples of oils include paraffinic process oils, naphthenic process oils, and aromatic process oils. Furthermore, for environmental reasons, process oils with a low content of polycyclic aromatic compounds (PCA) can be used. Examples of such low-PCA process oils include light extraction solvates (MES), processed distillate aromatic extracts (TDAEs), and heavy naphthenic oils. Additionally, from a life cycle assessment perspective, refined waste oil from rubber mixers and engines, or waste cooking oil used in restaurants, may be used.

[0128] When oil 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 content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less.

[0129] Liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (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. These liquid rubbers may be used individually or in combination of two or more.

[0130] When liquid rubber is included, the 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. Furthermore, the 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.

[0131] The content of the softener relative to 100 parts by mass of the rubber component in the first layer of the rubber composition is preferably 5 parts by mass or more, more preferably 6 parts by mass or more, even more preferably 7 parts by mass or more, and particularly preferably 8 parts by mass or more. Furthermore, the content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 45 parts by mass or less, and particularly preferably 40 parts by mass or less.

[0132] The content of the softener in the rubber composition constituting the second layer, relative to 100 parts by mass of the rubber component, is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more. Furthermore, the content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less.

[0133] 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, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts 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 5.0 parts by mass or less.

[0134] 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. These processing aids may be used individually or in combination of two or more. Examples of processing aids that can be used are those commercially available from companies such as Schill+Seilacher and Performance Additives.

[0135] When processing aids are included, the content per 100 parts by mass of rubber components 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 exhibiting an effect of improving processability. Furthermore, from the viewpoint of abrasion resistance and fracture strength, it is preferably 10 parts by mass or less, and more preferably 8.0 parts by mass or less.

[0136] While not particularly limited, examples of anti-aging agents include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as metal carbamate salts. Phenylenediamine-based anti-aging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine are preferred, as are quinoline-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These anti-aging agents may be used individually or in combination of two or more.

[0137] When an anti-aging agent is included, the content per 100 parts by mass of the 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 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 5.0 parts by mass or less.

[0138] When stearic acid 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 vulcanization rate, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0139] 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 10.0 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0140] Sulfur is preferably used as a vulcanizing agent. Suitable sulfur varieties include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0141] 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, even more preferably 3.0 parts by mass or less, and particularly preferably 2.5 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.

[0142] 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 purchased commercially from companies such as Taoka Chemical Industries, Ltd., Lanxess Corporation, and Flexis.

[0143] Examples of vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamate, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. These vulcanization accelerators may be used individually or in combination of two or more. Among these, one or more vulcanization accelerators selected from the group consisting of sulfenamide, guanidine, and thiazole vulcanization accelerators are preferred, with sulfenamide vulcanization accelerators being more preferred.

[0144] 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-cyclohexyl-2-benzothiazolyl sulfenamide (CBS) is preferred.

[0145] 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. Among these, 1,3-diphenylguanidine (DPG) is preferred.

[0146] Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, and di-2-benzothiazolyl disulfide. Among these, 2-mercaptobenzothiazole is preferred.

[0147] When a vulcanization accelerator is included, the content per 100 parts by mass of the rubber component (total amount if multiple vulcanization accelerators are used in combination) is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more. Furthermore, the content is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 6.0 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.

[0148] <Manufacturing> The rubber composition according to this embodiment can be manufactured by known methods. For example, it can be manufactured by kneading each of the above components using a rubber kneading device such as an open roll or a closed kneader (Banbury mixer, kneader, etc.).

[0149] The mixing process includes, for example, a base mixing process in which compounding agents and additives other than the vulcanizing agent and vulcanization accelerator are mixed, and a final mixing (F mixing) process in which the vulcanizing agent and vulcanization accelerator are added to the mixture obtained in the base mixing process and mixed. Furthermore, the base mixing process can be divided into multiple processes as desired.

[0150] There are no particular limitations on the mixing conditions, but for example, in the base mixing process, mixing is performed at a discharge temperature of 150-170°C for 3-10 minutes, and in the final mixing process, mixing is performed at 70-110°C for 1-5 minutes. There are no particular limitations on the vulcanization conditions, but for example, vulcanization is performed at 150-200°C for 10-30 minutes.

[0151] A tire having a tread including a first layer 6 and a second layer 7 can be manufactured by conventional methods using the corresponding rubber compositions. Specifically, the unvulcanized rubber compositions corresponding to each rubber layer obtained by the above method are extruded in an extruder equipped with a die of a predetermined shape to match the shape of each rubber layer, bonded together with other tire components on a tire molding machine, and molded in conventional methods to form an unvulcanized tire. This unvulcanized tire is then heated and pressurized in a vulcanizer to manufacture the tire. The vulcanization conditions are not particularly limited, and for example, a method of vulcanization at 150 to 200°C for 10 to 30 minutes can be used.

[0152] <Application> The tire according to this embodiment can be suitably used for passenger car tires, truck and bus tires, motorcycle tires, and racing tires, and is particularly preferred for use as a passenger car tire. A passenger car tire is a tire intended to be mounted on a four-wheeled vehicle and has a maximum load capacity of 1000 kg or less. Furthermore, the tire according to this embodiment can be used for all-season tires, summer tires, and winter tires such as studless tires. [Examples]

[0153] The present invention will be described based on examples, but the present invention is not limited to these examples.

[0154] Assuming a tire with a tread made of rubber compositions obtained according to Table 1 using the various chemicals listed below, the results calculated based on the evaluation method described below are shown in Tables 1 and 2. NR:TSR20 BR1: BR150B manufactured by Ube Industries, Ltd. (Unmodified high-cis BR, cis content: 97 mol%, Mw: 440,000) BR2: BR730 manufactured by JSR Corporation (unmodified high-cis BR, cis content: 95 mol%, Mw: 580,000) Carbon Black 1: Show Black N330 (N2SA: 75m) manufactured by Cabot Japan Co., Ltd. 2 / g Carbon Black 2: Show Black N220 (N2SA: 111m) manufactured by Cabot Japan Co., Ltd. 2 / g) Recycled carbon black: Carbon black obtained by crushing and calcining waste tires (ash content: 17% by mass) Silica: Evonik Degussa's UltraSil VN3 (N2SA: 175m 2 / g) Coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Evonik Degussa. Oil: Process X-140 manufactured by ENEOS Corporation Resin component: SYLVATRAXX 4401 manufactured by KRATON (softening point: 85°C, glass transition temperature: 39°C) Wax: Hi-Mic-1080 (microcrystalline wax) manufactured by Nippon Seiro Co., Ltd. Anti-aging agent: Nocrack 6C(N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid manufactured by NOF Corporation Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 (5% oil-containing powdered sulfur) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Noxellar CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noxellar D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0155] (Examples and Comparative Examples) According to the formulation shown in Table 1, the chemicals other than sulfur and vulcanization accelerator are mixed in a 1.7 L closed Banbury mixer for 1 to 10 minutes until the discharge temperature reaches 150 to 160°C to obtain a mixture. Next, using a twin-screw open roll mixer, sulfur and vulcanization accelerator are added to the obtained mixture and mixed for 4 minutes until the temperature reaches 105°C to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition is molded to match the shape of the first and / or second layers of the tread, and bonded together with other tire components to produce an unvulcanized tire, which is then vulcanized at 170°C to obtain the test tires listed in Table 2. The groove depth H of the circumferential grooves, the presence or absence of inclined grooves, and the maximum width L of the inclined grooves are as shown in Table 2.

[0156] <Measurement of 70°C E* and 70°C tanδ> For each vulcanized rubber test piece, measuring 20 mm in length, 4 mm in width, and 1 mm in thickness, taken from inside the first or second layer of the tread of each test tire, with the tire circumference being the longer side and the tire radius being the thickness direction, the complex modulus E* and loss tangent tanδ were measured in accordance with JIS K 6394:2007 under the conditions of a temperature of 70°C, a frequency of 10 Hz, an initial strain of 5%, a dynamic strain of ±1%, and the extension mode.

[0157] <Shore hardness measurement> Hardness measurement samples are prepared from within the first or second tread layer of each test tire, such that the tire radius direction is the thickness direction. The rubber hardness is measured in accordance with JIS K 6253 by pressing a Type A durometer onto the sample from the contact surface side at 23°C.

[0158] <Tensile Test> From the first or second tread layer of each test tire, a 1 mm thick, dumbbell-shaped test specimen (size 7) is cut out so that the circumferential direction of the tire is the tensile direction. A tensile test is then performed in accordance with JIS K 6251:2017 "Vulcanized rubber and thermoplastic rubber - Method for determining tensile test properties" at a 23°C atmosphere and a tensile speed of 3.3 mm / second, and the modulus (MPa) at 100% elongation is measured. The thickness direction of the sample is the radial direction of the tire.

[0159] <Grip performance on ice at high speeds> Each test tire is inflated to 250 kPa and mounted on a 2000cc vehicle. The vehicle is then driven on an icy surface at an initial speed of 60 km / h, and the braking distance is measured by applying the brakes. The reciprocal of the braking distance is expressed exponentially, with the braking distance of Comparative Example 4 set to 100. A higher exponent indicates superior wet grip performance at high speeds.

[0160] [Table 1]

[0161] [Table 2]

[0162] <Embodiment> Examples of embodiments of the present invention are shown below. [1] A tire having a tread section, The tread portion comprises a first layer that constitutes the tread surface and a second layer adjacent to the first layer on the radially inward side of the tire. The first layer and the second layer are each composed of a rubber composition containing a rubber component and recycled carbon black, A tire in which, when the amount of recycled carbon black per 100 parts by mass of rubber component in the rubber composition constituting the first layer is C (parts by mass), and the amount of recycled carbon black per 100 parts by mass of rubber component in the rubber composition constituting the second layer is B (parts by mass), the ratio B / C is 1.0 or less. [2] The tire according to [1] above, wherein the ratio (70°CE*1 / 70°CE*2) of the complex modulus of elasticity (MPa) (70°CE*2) of the rubber composition constituting the first layer at 70°C to the complex modulus of elasticity (MPa) (70°CE*2) of the rubber composition constituting the second layer at 70°C is 0.70 or less. [3] The tire according to [1] or [2] above, wherein the 100% modulus of the rubber composition constituting the second layer is greater than the 100% modulus of the rubber composition constituting the first layer. [4] The tire according to any one of [1] to [3] above, wherein when the thickness of the first layer is t1 (mm) and the thickness of the second layer is t2 (mm), the ratio of t1 to the sum of t1 and t2 (t1 / (t1+t2)) is 0.80 or less (preferably 0.75 or less, more preferably 0.72 or less). [5] The tire according to any one of [1] to [4] above, wherein when the thickness of the first layer is t1 (mm) and the thickness of the second layer is t2 (mm), the product of C (mass portion) and the ratio of t1 to the sum of t1 and t2 (t1 / (t1+t2)) (C × t1 / (t1+t2)) is 20.0 or less (preferably 15.0 or less, more preferably 12.0 or less, and even more preferably 10.0 or less). [6] The tire according to any one of [1] to [5] above, wherein the tread portion has one or more circumferential grooves that extend continuously in the circumferential direction of the tire, and the product of the groove depth H (mm) of the deepest part of the circumferential groove and C (mass portion) (H × C) is 200 or less. [7] The tire according to any one of [1] to [6] above, wherein the tread portion has grooves inclined in the tire circumferential direction or the tire width direction, and the ratio (L / C) of the maximum width L (mm) of the grooves inclined in the tire circumferential direction or the tire width direction to C (mass portion) is 0.30 or more (preferably 0.4 or more, more preferably 0.5 or more). [8] The tire according to any one of [1] to [7] above, wherein the tanδ (70°C tanδ²) of the rubber composition constituting the second layer is greater than 0.02 and less than 0.20. [9] The tire according to any one of [1] to [8] above, wherein the Shore hardness (Hs) of the rubber composition constituting the preceding layer is greater than 55 and less than 80.

[10] The tire according to any one of [1] to [9] above, wherein when the content of isoprene-based rubber in the rubber component of the rubber composition constituting the above layer is I (mass%), the ratio of I to C (I / C) is 1.20 or more (preferably 2.0 or more, more preferably 3.0 or more).

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

[10] above, wherein the recycled carbon black is recycled carbon black obtained by firing waste tires and / or tubes for waste tires.

[12] The tire described in

[11] above, wherein the waste tire and / or tube for the waste tire contains diene rubber.

[13] A tire as described in any of [1] to

[12] above, wherein the tire is a passenger car tire. [Explanation of symbols]

[0163] 1 Circumferential groove 2 Land 3. Tread surface 4. Extension of the land area 5. Extension of the deepest part of the groove bottom 6 First layer 7 Second layer 8 Tread section 9. The outermost extension of the second layer 10 Groove edge 11. Transverse grooves (inclined grooves) 12 Shoulder Track and Field Club 13 Center Track and Field Club 21 Yokomizo 22 Shoulder Sipes 23 Center Sipe t1 Thickness of the first layer t2 Thickness of the second layer H Groove depth of circumferential groove C Tire Equator W (Tire width direction) Te tread edge

Claims

1. A tire having a tread section, The tread portion comprises a first layer that constitutes the tread surface and a second layer adjacent to the first layer on the radially inward side of the tire. The first layer and the second layer are each composed of a rubber composition containing a rubber component and recycled carbon black, A tire in which, when the amount of recycled carbon black per 100 parts by mass of rubber component in the rubber composition constituting the first layer is C (parts by mass), and the amount of recycled carbon black per 100 parts by mass of rubber component in the rubber composition constituting the second layer is B (parts by mass), the ratio B / C is 1.0 or less.

2. The tire according to claim 1, wherein the ratio (70°CE*1 / 70°CE*2) of the complex modulus of elasticity (MPa) (70°CE*2) of the rubber composition constituting the first layer at 70°C to the complex modulus of elasticity (MPa) (70°CE*2) of the rubber composition constituting the second layer at 70°C is 0.70 or less.

3. The tire according to claim 1, wherein the 100% modulus of the rubber composition constituting the second layer is greater than the 100% modulus of the rubber composition constituting the first layer.

4. The tire according to claim 1, wherein, when the thickness of the first layer is t1 (mm) and the thickness of the second layer is t2 (mm), the ratio of t1 to the sum of t1 and t2 (t1 / (t1+t2)) is 0.80 or less.

5. The tire according to claim 1, wherein, when the thickness of the first layer is t1 (mm) and the thickness of the second layer is t2 (mm), the product of C (mass portion) and the ratio of t1 to the sum of t1 and t2 (t1 / (t1+t2)) (C × t1 / (t1+t2)) is 20.0 or less.

6. The tire according to claim 1, wherein the tread portion has one or more circumferential grooves that extend continuously in the circumferential direction of the tire, and the product of the groove depth H (mm) and C (mass portion) of the deepest part of the circumferential groove (H × C) is 200 or less.

7. The tire according to claim 1, wherein the tread portion has grooves inclined in the tire circumferential direction or the tire width direction, and the ratio (L / C) of the maximum width L (mm) of the grooves inclined in the tire circumferential direction or the tire width direction to C (mass portion) is 0.30 or more.

8. The tire according to claim 1, wherein the tanδ (70°C tanδ²) of the rubber composition constituting the second layer is greater than 0.02 and less than 0.

20.

9. The tire according to claim 1, wherein the Shore hardness (Hs) of the rubber composition constituting the preceding layer is greater than 55 and less than 80.

10. The tire according to claim 1, wherein when the content of isoprene-based rubber in the rubber component of the rubber composition constituting the above layer is I (mass%), the ratio of I to C (I / C) is 1.20 or more.

11. The tire according to claim 1, wherein the recycled carbon black is recycled carbon black obtained by firing waste tires and / or waste tire tubes.

12. The tire according to claim 11, wherein the waste tire and / or tube for waste tires contains diene rubber.

13. The tire according to claim 1, wherein the tire is a passenger car tire.

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