tire

Abstract

To provide a tire 2 which can stably exhibit high grip performance.SOLUTION: A tire 2 includes a tread 4 grounded on a road surface. The tread 4 includes in a radial direction: a cap layer 36; and a base layer 38. The cap layer 36 is positioned in the road surface side and laminated on the base layer 38. The base layer 38 includes a pair of end faces 38E contained in an external surface of the tire 2. Thickness TB of the base layer 38 is 0.4 mm or less. The cap layer 36 comprises a cross-link material of a cap rubber containing raw rubber constituent. The base layer 38 comprises a cross-link material of a base rubber containing raw rubber constituent. The raw rubber constituent of the cap rubber and the raw rubber constituent of the base rubber are made of styrene-butadiene rubber.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to tires, and more particularly to tires mounted on vehicles used in racing. [Background technology]

[0002] The road side of the tire tread is made up of a cap layer that takes into account clip performance. For example, high grip performance is required for tires mounted on vehicles that run at their limit, such as racing vehicles. In order to achieve high grip performance, it has been considered to apply a rubber composition containing a large amount of a tackifier (e.g., a softener such as liquid styrene-butadiene rubber) to the cap layer (e.g., Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-76355 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a tire that can stably exhibit high grip performance. [Means for solving the problem]

[0005] The tire according to the present invention comprises a tread that comes into contact with a road surface. The tread comprises a cap layer and a base layer aligned in a radial direction. The cap layer is located on the road surface side and is laminated on the base layer. The base layer has a pair of end faces included in the outer surface of the tire. The thickness of the base layer is 0.4 mm or less. The cap layer is made of a cross-linked product of a cap rubber containing a raw rubber component. The base layer is made of a cross-linked product of a base rubber containing a raw rubber component. The raw rubber component of the cap rubber and the raw rubber component of the base rubber are made of styrene-butadiene rubber. Effect of the Invention

[0006] The tire of the present invention suppresses tread separation even though it employs a thin base layer. Because the base layer is thin, the tire can be configured with a relatively thick cap layer in the tread. The present invention provides a tire that can stably exhibit high grip performance. Since the tire of the present invention can stably exhibit high grip performance, lap times are less likely to decrease, and the frequency of tire replacement during a race can be reduced. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing a portion of a tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing a part of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The tire of the present invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. The tire mounted on the rim is also called a tire-rim assembly. The tire-rim assembly includes a rim and a tire mounted on the rim.

[0009] In the present invention, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the tire is called a standard state. In the case where the subject of the present invention is a tire that cannot be run on public roads, for example, a tire used in a race, the normal state of the tire is when the tire is mounted on a rim having a rim size of 18×13.0J, the internal pressure of the tire is adjusted to 180 kPa, and no load is applied to the tire. The normal rim for this tire is a rim having a rim size of 18×13.0J. The normal internal pressure of this tire is 180 kPa.

[0010] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part in the meridian section of the tire, which cannot be measured when the tire is mounted on a regular rim, are measured on the cut surface of the tire obtained by cutting the tire along a plane including the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads is the same as the distance between the beads of the tire mounted on a regular rim. The tire configuration that cannot be confirmed when the tire is mounted on a regular rim is confirmed on the aforementioned cut surface.

[0011] A genuine rim is a rim that is specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are genuine rims.

[0012] Normal tire pressure means the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0013] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0014] In the present invention, the rubber composition is a material obtained by mixing raw rubber components and chemicals in a kneader such as a Banbury mixer. The rubber composition includes the raw rubber components and chemicals. The crosslinked rubber is a molded product obtained by pressurizing and heating the rubber composition. The crosslinked rubber is a crosslinked product of the rubber composition. The crosslinked rubber includes a crosslinked product of the raw rubber components. The crosslinked rubber is also called vulcanized rubber, and the rubber composition is also called unvulcanized rubber.

[0015] Examples of raw rubber components include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR) and butyl rubber (IIR). Examples of chemicals include reinforcing agents such as carbon black and silica; softeners such as liquid rubbers such as liquid styrene butadiene rubber and process oil; plasticizers; zinc oxide; wax; lubricants such as stearic acid; antioxidants; processing aids; sulfur; and vulcanization accelerators. Selection of raw rubber components and chemicals, and the content of the selected chemicals, etc. are appropriately determined according to the specifications of each element, such as the tread and sidewall, to which the rubber composition is applied. In the present invention, unless otherwise specified, a rubber composition generally used in tires is used.

[0016] In the present invention, the hardness of an element made of crosslinked rubber among elements constituting a tire is measured using a type A durometer under a temperature condition of 23° C. in accordance with the provisions of JIS K6253. In the present invention, the hardness is represented by the hardness at 23° C.

[0017] In the present invention, the loss tangent (tan δ) of the element made of crosslinked rubber among the elements constituting the tire is measured using a viscoelasticity spectrometer in accordance with the provisions of JIS K 6394. The measurement conditions are as follows. Initial distortion = 10% Dynamic distortion = ±1% Frequency = 10Hz Mode = Decompression mode Temperature=100℃ In this measurement, a test piece (length 40 mm x width 4 mm x thickness 1 mm) is sampled from the tire. The length direction of the test piece is aligned with the circumferential direction of the tire. If it is not possible to sample the test piece from the tire, the test piece is sampled from a sheet-like crosslinked rubber, i.e., a rubber sheet, obtained by pressing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes. In the present invention, the loss tangent is represented by the loss tangent at 100°C.

[0018] In the present invention, the tensile strength and elongation at break of the element made of crosslinked rubber among the elements constituting the tire are measured in accordance with the provisions of JIS K6251 under a temperature condition of 100° C. In this measurement, a test piece is sampled from the tire with its length direction coinciding with the circumferential direction of the tire. When it is not possible to sample a test piece from the tire, the test piece is sampled from the above-mentioned rubber sheet. In the present invention, the tensile strength at break and the elongation at break are expressed as the tensile strength at break and the elongation at break at 100°C.

[0019] In the present invention, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that fits onto the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of sidewall portions. The center of the tread is also called the crown. The edges of the tread are also called the shoulders. The boundary between the tread and the sidewall is also called the buttress. The part consisting of the bead and the sidewall is also called the side.

[0020] [Foundations underlying the present invention] The cap layer, which is made of a cross-linked product of a rubber composition containing styrene-butadiene rubber as a raw rubber component and liquid styrene-butadiene rubber, improves the grip performance of the tire. If a thick base layer is used for the tread, a relatively thin cap layer is formed. In this case, the cap layer wears out quickly and the base layer is exposed. As the base layer is exposed, the grip performance decreases. Since the base layer has poor wear resistance, the risk of the tread peeling increases. On the other hand, if a thin base layer is used in the tread, a relatively thick cap layer is constructed, which also has poor adhesion and may result in tread delamination. Although the tread uses a cap layer that contributes to high grip performance, the cap layer is not able to fully demonstrate its function. As the tire is driven, the tread wears away, exposing the base layer and, if the base layer is laminated to a band, the topping rubber of the band. For example, large external forces act on tires mounted on vehicles that run at their limit, such as racing vehicles. When the cap layer is replaced by the base layer, a large shear force is generated at the interface between the cap layer and the base, which may cause peeling in the tread. In order to suppress the growth of cracks that start from this peeling, it is necessary to keep the fracture energy of the interface between the cap layer and the base layer higher than the energy applied by the external force. In order to establish technology that enables tires to stably exhibit high grip performance, the inventors conducted research focusing on the fracture energy at the interface between the cap layer and the base layer, and have completed the invention described below.

[0021] [Overview of the embodiment of the present invention] [Configuration 1] A tire according to one embodiment of the present invention is a tire having a tread that comes into contact with a road surface, the tread having a cap layer and a base layer aligned in a radial direction, the cap layer being located on the road surface side and laminated to the base layer, the base layer having a pair of end faces included in the outer surface of the tire, the base layer having a thickness of 0.4 mm or less, the cap layer being made of a cross-linked product of a cap rubber containing a raw rubber component, the base layer being made of a cross-linked product of a base rubber containing a raw rubber component, the raw rubber component of the cap rubber and the raw rubber component of the base rubber being made of styrene-butadiene rubber.

[0022] By preparing the tires in this way, the tires can stably demonstrate high grip performance.

[0023] [Configuration 2] Preferably, in the tire according to the above-mentioned [Configuration 1], the base rubber does not include a liquid rubber.

[0024] [Configuration 3] Preferably, in the tire according to the above-mentioned [Configuration 1] or [Configuration 2], the hardness of the base layer at 23° C. is 60 or less.

[0025] [Configuration 4] Preferably, in the tire according to any one of the above-mentioned [Configuration 1] to [Configuration 3], the loss tangent of the base layer at 100° C. is 0.30 or more.

[0026] [Configuration 5] Preferably, in the tire according to any one of the above-mentioned [Configuration 1] to [Configuration 4], the base layer has a tensile strength at break at 100° C. of 8.0 MPa or more.

[0027] [Configuration 6] Preferably, in the tire according to any one of [Configuration 1] to [Configuration 5] above, the base layer has an elongation at break at 100° C. of 500% or more.

[0028] [Details of the embodiment of the present invention] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0029] Fig. 1 shows a portion of a tire 2 according to one embodiment of the present invention. This tire 2 is mounted on a racing vehicle (four-wheeled automobile) that runs on a circuit. This tire 2 is a pneumatic tire for racing. In Fig. 1, the tire 2 is mounted on a rim R. The rim R is a regular rim.

[0030] FIG. 1 shows a portion of a cross section of a tire 2 taken along a plane including the rotation axis (not shown) of the tire 2. The cross section shown in FIG. 1 is also called a meridian cross section. The direction indicated by the double arrow AD is the axial direction of the tire 2. The axial direction of the tire 2 means a direction parallel to the rotation axis of the tire 2. The direction indicated by the double arrow RD is the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the circumferential direction of the tire 2. In FIG. 1, a dashed dotted line CL extending in the radial direction represents the equatorial plane of the tire 2.

[0031] 1 is the intersection point between the outer surface of the tire 2 and the equatorial plane. The intersection point PC is also called the equator of the tire 2. When a groove is located on the equatorial plane, the equator PC is determined based on a virtual outer surface obtained by assuming that there is no groove. The equator PC is also the radially outer end of the tire 2.

[0032] Fig. 2 shows a part of a meridian cross section of the tire 2 shown in Fig. 1. Fig. 2 shows a shoulder portion of the tire 2.

[0033] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of clinches 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a band 16 , an inner liner 18 , and a pair of chafers 20 .

[0034] The tread 4 is located radially outside the carcass 12. The tread 4 is made of crosslinked rubber. The outer peripheral surface of the tread 4 includes a tread surface 22. The tread 4 comes into contact with the road surface at the tread surface 22. The tread surface 22 includes the equator PC described above. The tread surface 22 is a part of the outer surface of the tire 2.

[0035] The tread 4 shown in Fig. 1 has no grooves. The tire 2 is a slick type. The tread 4 may have grooves to form a tread pattern.

[0036] Each sidewall 6 is located radially inward of the tread 4. Each sidewall 6 is located axially outward of the carcass 12. The sidewalls 6 are made of crosslinked rubber.

[0037] Each clinch 8 is located axially outside the bead 10, between the carcass 12 and the rim R. The clinch 8 of the tire 2 is covered with the sidewall 6. The clinch 8 is made of crosslinked rubber.

[0038] Each bead 10 is located axially inward of the clinch 8. The bead 10 includes a core 24 and an apex 26. The core 24 is a cable bead having a circular cross-sectional shape. Although not shown, the core 24 includes a core wire and a plurality of sheath wires wound helically around the core wire. The apex 26 is located radially outward of the core 24. The apex 26 is tapered. The apex 26 is made of a crosslinked rubber having high hardness.

[0039] The carcass 12 is located on the inside of the tread 4 and the pair of sidewalls 6. Although one of the beads 10 is not shown in FIG.

[0040] The carcass 12 includes at least one carcass ply 28. The carcass 12 of the tire 2 is composed of two carcass plies 28. Of the two carcass plies 28, the carcass ply 28a located on the inner side is turned up at each bead 10. The carcass ply 28a has a pair of turned-up portions 28af. Each turned-up portion 28af is located between the bead 10 and the clinch 8. The carcass ply 28b located on the outer side is not turned up at the bead 10. The end 28be of the carcass ply 28b is located between the turned up portion 28af and the clinch 8.

[0041] Although not shown, each of the two carcass plies 28 includes a number of carcass cords arranged in parallel. Each carcass cord intersects with the equatorial plane. The angle that the carcass cord makes with the equatorial plane is equal to or greater than 70 degrees and equal to or less than 90 degrees. The carcass 12 of the tire 2 has a radial structure.

[0042] The carcass cord is a cord (organic fiber cord) made of organic fibers, such as nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0043] The belt 14 is located between the tread 4 and the carcass 12 in the radial direction. The belt 14 is laminated on the carcass 12 on the radially inner side of the tread 4. The belt 14 is composed of two belt plies 30 laminated in the radial direction. The belt ply 30 located on the inner side (hereinafter, inner belt ply 30u) has an axial width wider than the axial width of the belt ply 30 located on the outer side (hereinafter, outer belt ply 30s). Although not shown, each of the inner belt ply 30u and the outer belt ply 30s includes a number of belt cords arranged in parallel. Each belt cord is inclined with respect to the equatorial plane. The belt cords are covered with a topping rubber. In the tire 2, the belt cords are steel cords.

[0044] The band 16 is located between the tread 4 and the belt 14 in the radial direction. The band 16 is laminated on the belt 14 on the radially inner side of the tread 4. 2, the band 16 includes a band cord 32. The band cord 32 is covered with a topping rubber 34. Although not described in detail, the topping rubber of the band 16 is composed of a topping rubber generally used as a topping rubber for a band. The raw rubber component contained in the rubber composition for the topping rubber contains natural rubber as a main component. The raw rubber component contained in the rubber composition for the topping rubber covering the belt cord of the belt 14 described above also contains natural rubber as a main component.

[0045] In the tire 2, the band cord 32 is wound in a spiral shape. The band cord 32 extends substantially in the circumferential direction. The angle that the band cord 32 makes with the circumferential direction is 5 degrees or less. The band 16 has a jointless structure. The band cord 32 is an organic fiber cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0046] The band 16 covers the entire belt 14. This band 16 is a full band. This band 16 may be composed of a pair of edge bands that cover each end of the belt 14. This band 16 may be composed of a full band and a pair of edge bands.

[0047] The inner liner 18 is positioned inside the carcass 12. The inner liner 18 constitutes the inner surface of the tire 2. The inner liner 18 is made of crosslinked rubber with excellent air barrier properties. The inner liner 18 maintains the internal pressure of the tire 2.

[0048] Each chafer 20 is located radially inward of the bead 10. A portion of the chafer 20 contacts the rim R. The chafer 20 of the tire 2 is made of a cloth and rubber impregnated into the cloth.

[0049] The tread 4 of the tire 2 includes a cap layer 36 and a base layer 38. The cap layer 36 and the base layer 38 are aligned in the radial direction. The cap layer 36 is located on the road surface side. The cap layer 36 includes the above-mentioned tread surface 22. The cap layer 36 is harder than the base layer 38.

[0050] 2, the position indicated by the reference symbol PP is the axially outer end of the cap layer 36. The cap layer 36 bridges between one axially outer end PP (not shown) and the other axially outer end PP.

[0051] The cap layer 36 is laminated to the base layer 38. The axially outer end PP of the cap layer 36 is also the end of the interface between the cap layer 36 and the base layer 38. The interface is also the inner surface of the cap layer 36 and the outer surface of the base layer 38 in the tire 2. The axially outer end PP of the cap layer 36 is also the end of the outer surface of the base layer 38. The position indicated by the symbol PS in Fig. 2 is the end of the inner surface of the base layer 38. Between the end PP of the outer surface of the base layer 38 and the end PS of the inner surface is an end face 38E of the base layer 38. The base layer 38 bridges between one end face 38E (not shown) and the other end face 38E. The base layer 38 has a uniform thickness between the one end face 38E and the other end face 38E.

[0052] Although not shown, in conventional tires, wings may be provided axially outward from the portion consisting of the cap layer and the base layer for joining to the sidewall. In contrast, in the tread 4 of this tire 2, no wings are provided axially outward from the portion consisting of the cap layer 36 and the base layer 38. Typically, in a tread, the cap layer covers the entire base layer from the outside, so that the base layer is not exposed. In contrast, in this tire 2, the cap layer 36 is laminated on the base layer 38, but the end faces 38E of the base layer 38 are not covered by the cap layer 36. The end faces 38E of the base layer 38 of this tire 2 are exposed. The end faces 38E of the base layer 38 are included in the outer surface of the tire 2. The base layer 38 of this tire 2 has a pair of end faces 38E that are included in the outer surface of the tire 2.

[0053] The length indicated by the double arrow TB in Figure 2 is the thickness of the base layer 38. This thickness TB is measured along a normal to the inner surface of the base layer 38, which passes through the edge PP of the outer surface of the base layer 38, in the cross section shown in Figure 2. The thickness TB is the thickness of the base layer 38 at the edge of the base layer 38.

[0054] In this tire 2, the thickness TB of the base layer 38 is 0.4 mm or less. This base layer 38 is thin. The tread 4 of this tire can be configured with a relatively thick cap layer 36. The thick cap layer 36 can contribute to the tire 2 being able to stably exhibit high grip performance. From this viewpoint, the thickness TB is preferably 0.3 mm or less. More preferably, the thickness TB is 0.25 mm. If the base layer 38 is too thin, there is a concern that the tread 4 may peel off. From the viewpoint of preventing peeling of the tread 4, the thickness TB is preferably 0.1 mm or more, and more preferably 0.2 mm or more.

[0055] 1, the length indicated by the double arrow TT is the thickness of the tread 4 at the equatorial plane. The length indicated by the double arrow TC is the thickness of the cap layer 36 at the equatorial plane. The thicknesses TT and TC are measured along the equatorial plane.

[0056] In the tire 2, the ratio (TC / TT) of the thickness TC of the cap layer 36 to the thickness TT of the tread 4 is preferably equal to or greater than 0.70. This allows the cap layer 36 to effectively contribute to the tire 2 stably exhibiting high grip performance. From this viewpoint, the ratio (TC / TT) is more preferably equal to or greater than 0.75. The ratio (TC / TT) is preferably equal to or less than 0.90. This allows the tire 2 to have a sufficient thickness for the base layer 38, thereby reducing the risk of separation of the tread 4. From this viewpoint, the ratio (TC / TT) is more preferably equal to or less than 0.80.

[0057] As described above, the tread is made of crosslinked rubber, and the cap layer 36 and base layer 38 are each made of crosslinked rubber. The cap layer 36 is made of a crosslinked product of the rubber composition for the cap layer 36. The base layer 38 is made of a crosslinked product of the rubber composition for the base layer 38. In the present invention, the rubber composition for the cap layer 36 is also called a cap rubber, and the rubber composition for the base layer 38 is also called a base rubber.

[0058] <Cap rubber> The cap rubber contains a raw rubber component. In this tire 2, the raw rubber component used in the cap rubber is styrene butadiene rubber (hereinafter, SBR). The raw rubber component of the cap rubber does not contain any rubber component other than SBR. The ratio of the amount of SBR to the total amount of the raw rubber components is 100%. There is no particular limitation on the SBR used as the raw rubber component in the tire 2. Emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. can be used.

[0059] The cap rubber may contain carbon black as a reinforcing agent. Examples of carbon black include, but are not limited to, GPF, FEF, HAF, ISAF, and SAF. These carbon blacks may be used alone or in combination of two or more.

[0060] When the cap rubber contains carbon black, the content of carbon black per 100 parts by mass of the raw rubber component is adjusted in the range of 5 parts by mass to 150 parts by mass, taking into consideration wear resistance and processability.

[0061] The cap rubber may contain a softener, such as a resin component, oil, or liquid rubber.

[0062] The resin component is not particularly limited, but examples thereof include hydrocarbon resins commonly used in the field of tires, such as petroleum resins, terpene resins, rosin resins, and phenol resins. These resin components may be used alone or in combination of two or more.

[0063] When the cap rubber contains a resin component, the content of the resin component is preferably 1 part by mass or more per 100 parts by mass of the raw rubber component from the viewpoint of processability, and is preferably 90 parts by mass or less from the viewpoint of abrasion resistance.

[0064] Examples of the oil include process oil, vegetable oil, and animal oil. Examples of the process oil include paraffin-based process oil, naphthene-based process oil, and aromatic process oil. These oils may be used alone or in combination of two or more.

[0065] When the cap rubber contains oil, the content of the oil per 100 parts by mass of the raw rubber component is preferably 1 part by mass or more, more preferably 5 parts by mass or more, from the viewpoint of processability, and is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, from the viewpoint of abrasion resistance. When the raw rubber component is an oil-extended rubber, the amount of oil contained in the oil-extended rubber is included in the amount of oil per 100 parts by mass of the raw rubber component. In the case of a base rubber described later, the amount of oil contained in the oil-extended rubber is treated in the same way.

[0066] The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), and examples thereof include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), and liquid farnesene rubber. These liquid rubbers may be used alone or in combination of two or more. In the present invention, the liquid state refers to a state in which the substance has a certain volume but does not have a certain shape.

[0067] When the cap rubber contains a liquid rubber, the content of the liquid rubber per 100 parts by mass of the raw rubber component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, from the viewpoint of processability, and is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, from the viewpoint of abrasion resistance.

[0068] As described above, the raw rubber component is SBR. From the viewpoint of exerting high grip performance, when the cap rubber contains liquid rubber, the main component of the liquid rubber is preferably liquid SBR. Specifically, the content of liquid SBR in the liquid rubber is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. Particularly preferably, the content of liquid SBR is 100% by mass. In other words, it is particularly preferable that the cap rubber contains liquid rubber, and that the liquid rubber consists of liquid SBR. The content of liquid SBR in the liquid rubber is expressed as the ratio of the amount of liquid SBR to the total amount of liquid rubber.

[0069] Although not described in detail, the cap rubber may contain, in addition to the above-mentioned components, additives commonly used in the tire industry, such as wax, zinc oxide, lubricants such as stearic acid, antioxidants, sulfur, and vulcanization accelerators.

[0070] <Base rubber> The base rubber contains a raw rubber component. In this tire 2, the raw rubber component used in the base rubber is SBR. The raw rubber component of the base rubber does not contain any rubber component other than SBR. The ratio of the amount of SBR to the total amount of the raw rubber components is 100%. There is no particular limitation on the SBR used as the raw rubber component in the tire 2. Emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. can be used.

[0071] The base rubber may contain carbon black as a reinforcing agent. Examples of carbon black include, but are not limited to, GPF, FEF, HAF, ISAF, and SAF. These carbon blacks may be used alone or in combination of two or more.

[0072] When the base rubber contains carbon black, the content of carbon black per 100 parts by mass of the raw rubber component is adjusted in the range of 10 parts by mass to 150 parts by mass, taking into consideration reinforcing properties and processability.

[0073] The base rubber may contain a softener, such as a resin component, oil, or liquid rubber.

[0074] Examples of the resin component include hydrocarbon resins commonly used in the field of tires, such as petroleum resins, terpene resins, rosin resins, and phenol resins. These resin components may be used alone or in combination of two or more.

[0075] When the base rubber contains a resin component, the content of the resin component per 100 parts by mass of the raw rubber component is preferably 1 part by mass or more, and more preferably 2 parts by mass or more, from the viewpoint of processability, and is preferably 30 parts by mass or less, and more preferably 20 parts by mass or less, from the viewpoint of abrasion resistance.

[0076] The oil includes process oil, vegetable oil, and animal oil. The process oil includes paraffin-based process oil, naphthene-based process oil, and aromatic process oil. These oils may be used alone or in combination of two or more.

[0077] When the base rubber contains oil, the content of the oil per 100 parts by mass of the raw rubber component is preferably 1 part by mass or more, more preferably 5 parts by mass or more, from the viewpoint of processability, and is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, from the viewpoint of abrasion resistance.

[0078] The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C). Examples of the liquid rubber include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), and liquid farnesene rubber. These liquid rubbers may be used alone or in combination of two or more.

[0079] When the base rubber contains a liquid rubber, the content of the liquid rubber per 100 parts by mass of the raw rubber component is preferably 1 part by mass or more, more preferably 5 parts by mass or more, from the viewpoint of processability, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, from the viewpoint of adhesion.

[0080] As described above, the raw rubber component of the cap rubber is SBR, and the raw rubber component of the base rubber is also SBR. When a liquid rubber is blended into the base rubber and the cap rubber contains liquid SBR as the liquid rubber, it is preferable that the liquid rubber blended into the base rubber is liquid SBR.

[0081] Although not described in detail, the base rubber may contain, in addition to the above-mentioned components, additives commonly used in the tire industry, for example, lubricants such as wax, zinc oxide, and stearic acid, antioxidants, sulfur, and vulcanization accelerators.

[0082] In this tire 2, the raw rubber component of the cap rubber and the raw rubber component of the base rubber are made of SBR. This improves the affinity between the cap rubber and the base rubber. The improved affinity contributes to increasing the fracture energy of the interface between the cap layer and the base layer. In this tire 2, the cap layer 36 and the base layer 38 are firmly bonded to each other. In this tire 2, the cap layer 36 is laminated on the base layer 38, and the cap layer 36 is laminated on the base layer 38 that includes a pair of end faces 38E included in the outer surface of the tire 2 and bridges between both end faces 38E. This further increases the fracture energy of the interface between the cap layer and the base layer. The cap layer 36 of this tire 2 is not easily peeled off from the base layer 38. Even if the cap layer 36 is made of a cap rubber containing liquid rubber to achieve high grip performance, the cap layer 36 is not easily peeled off from the base layer 38.

[0083] This tire 2 suppresses peeling of the tread 4 even though it employs a thin base layer 38. Since the base layer 38 is thin, this tire 2 can configure a relatively thick cap layer 36 in the tread 4. This tire 2 can stably exhibit high grip performance. This tire 2 can stably demonstrate high grip performance, so lap times are less likely to deteriorate. This tire 2 also reduces the frequency of tire changes during a race.

[0084] In the tire 2, the base layer 38 is laminated on the band 16. As described above, the band 16 includes the band cord 32, and the band cord 32 is covered with the topping rubber 34. The main component of the raw rubber component of the topping rubber 34 is natural rubber. If the base rubber contains a liquid rubber such as liquid SBR, there is a concern that the bloomed liquid rubber may reduce the adhesion to the band 16. In this case, the risk of the tread 4 peeling off increases. From the viewpoint of increasing the adhesion of the base layer 38, in other words, increasing the fracture energy at the interface between the cap layer and the base layer, and reducing the risk of the tread 4 peeling off, it is preferable that the base rubber does not contain liquid rubber.

[0085] In the present invention, the base rubber does not contain liquid rubber when the base rubber does not contain liquid rubber or when the base layer 38 is subjected to acetone extraction and the extract does not contain any liquid rubber component. The extract is obtained in accordance with JIS K6229.

[0086] In the tire 2, the hardness of the base layer 38 at 23° C. is preferably 70 or less, and more preferably 65 or less. This effectively reduces distortion occurring at the interface between the base layer 38 and the cap layer 36. The base layer 38 can contribute to preventing peeling of the tread 4. If the hardness of the base layer 38 is too low, the strength of the base layer 38 may be insufficient. From the viewpoint of appropriately maintaining the strength of the base layer 38, the hardness of the base layer 38 is preferably 40 or more, and more preferably 45 or more.

[0087] As described above, the cap layer 36 is harder than the base layer 38. If the difference between the hardness of the cap layer 36 and the hardness of the base layer 38 is too large, there is a risk that strain will concentrate between the cap layer 36 and the base layer 38. In this case, the risk of the tread 4 peeling off increases. From the viewpoint of reducing the risk of the tread 4 peeling off, the difference between the hardness of the cap layer 36 and the hardness of the base layer 38 is preferably 20 or less, more preferably 10 or less. If this difference is too small, there is a concern that strain will concentrate between the base layer 38 and the band 16. In this case, too, the risk of the tread 4 peeling off increases. From the viewpoint of reducing the risk of the tread 4 peeling off, the difference between the hardness of the cap layer 36 and the hardness of the base layer 38 is preferably 2 or more, more preferably 4 or more.

[0088] If the topping rubber 34 of the band 16 has a higher rigidity than the base layer 38, the cap layer 36 is harder than the base layer 38, so there is a concern that strain will be concentrated in the base layer 38. In this case, the risk of the tread 4 peeling off increases. From the viewpoint of reducing the risk of the tread 4 peeling off, it is preferable that the topping rubber 34 of the band 16 has the same hardness as the base layer 38 or has a hardness lower than the hardness of the base layer 38. If there is a gap in the difference in hardness between the topping rubber 34 and the base layer 38, there is a concern that strain will be concentrated between the base layer 38 and the band 16. In this case, too, the risk of the tread 4 peeling off increases. From the viewpoint of reducing the risk of the tread 4 peeling off, the difference between the hardness of the base layer 38 and the hardness of the topping rubber 34 of the band 16 is preferably 10 or less, more preferably 5 or less.

[0089] In the tire 2, the loss tangent of the base layer 38 at 100°C is preferably 0.30 or more. The base layer 38 effectively converts energy applied by an external force into thermal energy. The base layer 38 can contribute to dissipating energy applied by an external force. The base layer 38 can reduce the risk of the tread 4 peeling off. From this viewpoint, the loss tangent of the base layer 38 at 100°C is more preferably 0.25 or more, and even more preferably 0.30 or more. From the viewpoint of suppressing thermal deterioration of the topping rubber 34 of the band 16, the loss tangent of the base layer 38 at 100°C is preferably 0.45 or less, and more preferably 0.40 or less.

[0090] In the tire 2, the tensile strength at break of the base layer 38 at 100°C is preferably 8.0 MPa or more. This suppresses the destruction of the base layer 38 due to the action of an external force. The base layer 38 can contribute to reducing the risk of the tread 4 peeling off. From this viewpoint, the tensile strength at break of the base layer 38 at 100°C is more preferably 9.0 MPa or more, and even more preferably 9.5 MPa or more. If the tensile strength at break of the base layer 38 is too high, there is a risk that the action of an external force may affect the topping rubber 34 of the band 16. From the viewpoint of suppressing the influence of the band 16 on the topping rubber 34, the tensile strength at break of the base layer 38 at 100°C is preferably 13 MPa or less.

[0091] In the tire 2, the elongation at break of the base layer 38 at 100°C is preferably 500% or more. This suppresses destruction of the base layer 38 due to the action of external force. The base layer 38 can contribute to reducing the risk of peeling off of the tread 4. From this viewpoint, the elongation at break of the base layer 38 at 100°C is more preferably 600% or more, and even more preferably 650% or more. If the elongation at break of the base layer 38 is too large, there is a risk that the action of external force may affect the topping rubber 34 of the band 16. From the viewpoint of suppressing the influence of the band 16 on the topping rubber 34, the elongation at break of the base layer 38 at 100°C is preferably 800% or less.

[0092] In the tire 2, from the viewpoint of reducing the risk of peeling off of the tread 4, it is more preferable that the tensile strength at break of the base layer 38 at 100° C. is 8.0 MPa or more, and the elongation at break of the base layer 38 at 100° C. is 500% or more. It is even more preferable that the tensile strength at break of the base layer 38 at 100° C. is 8.0 MPa or more, the elongation at break of the base layer 38 at 100° C. is 500% or more, and the hardness of the base layer 38 at 23° C. is 60 or less. And it is even more preferable that the tensile strength at break of the base layer 38 at 100° C. is 8.0 MPa or more, the elongation at break of the base layer 38 at 100° C. is 500% or more, the hardness of the base layer 38 at 23° C. is 60 or less, and the loss tangent of the base layer 38 at 100° C. is 0.30 or more.

[0093] As is clear from the above description, according to the present invention, a tire capable of stably exhibiting high grip performance can be obtained. EXAMPLES

[0094] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0095] [Rubber composition] In order to obtain the cap rubber and base rubber, the following raw rubber components and chemicals were prepared. <Raw rubber components> NR:TSR20 BR: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (cis content = 97 mol%, Mw = 440,000) SBR: HP755B manufactured by JSR Corporation (S-SBR, styrene content = 40 mass%, vinyl content = 38 mol%, contains 37.5 mass parts of oil per 100 mass parts of rubber solids) <Chemicals> Terpene resin: Terpene phenol resin manufactured by Yasuhara Chemical Co., Ltd. Liquid SBR: Ricon 100 by Cray Valley Process oil: Diana Process AH-24 (aroma oil) manufactured by Idemitsu Kosan Co., Ltd. Carbon black 1: Show Black N330 (N) manufactured by Cabot Japan Co., Ltd. 2 SA=75m 2 / g, DBP oil absorption: 102mL / 100g) Carbon black 2: VULCAN10H (N134, N) manufactured by Cabot Japan Co., Ltd. 2 SA:144m 2 / g) Wax: Sannock N manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid camellia manufactured by NOF Corporation Anti-aging agent 1: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Anti-aging agent 2: Nocrac 224 manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur (containing 5% oil) manufactured by Tsurumi Chemical Industry Co., Ltd. Materials other than sulfur and vulcanization accelerator were kneaded for 5 minutes at 150°C using a Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product. Next, sulfur and vulcanization accelerator were added to the kneaded product obtained, and the mixture was kneaded for 5 minutes at 80°C using an open roll to obtain a rubber composition shown in Table 1 below. The loss tangent (tan δ) at 100°C, hardness (H) at 23°C, tensile strength at break (T) at 100°C, and elongation at break (E) at 100°C measured for the crosslinked rubber were as shown in Table 1.

[0096] [Table 1]

[0097] [Example 1] Composition 1 was used as the cap rubber and composition 3 was used as the base rubber, and the tread was prepared and laminated together with other elements to prepare an unvulcanized tire (hereinafter also referred to as a raw tire). The raw tire was pressurized and heated in a mold for 10 minutes under a condition of 170°C. As a result, a pneumatic tire (tire size = 330 / 710R18) having the basic structure shown in Figure 1 and the specifications shown in Table 2 below was obtained. The tread of Example 1 is composed of two layers, a cap layer and a base layer. The tread was constructed so that the end surface of the base layer was exposed as shown in Figure 2. This is shown in Table 2 as "Figure 2" in the tread construction column and "Y" in the exposure column. The thickness of the base layer TB was 0.25 mm. The thickness of the base layer at the equatorial plane was also 0.25 mm.

[0098] [Comparative Example 1] Composition 1 was used as the cap rubber and composition 4 was used as the base rubber, and the tread was prepared and laminated together with other elements to prepare a green tire. The green tire was pressurized and heated in the mold for 10 minutes under a condition of 170°C. In this way, a pneumatic tire (tire size = 330 / 710R18) of Comparative Example 1 having the specifications shown in Table 2 below was obtained. Comparative Example 1 was configured to have the same configuration as the basic configuration shown in Figure 1, except for the tread. The tread of Comparative Example 1 includes a cap layer and a base layer. Although not shown, a wing was provided on the axially outer side of the portion composed of the cap layer and the base layer. Differences from the tread of Example 1 are indicated by "-" in the tread configuration column. The end face of the base layer is not exposed, and is therefore indicated by "N" in the exposure column. The thickness of the base layer was 0.70 mm. In Comparative Example 1, the end faces of the base layer are not exposed, so the thickness of the base layer is expressed as the thickness at the equatorial plane.

[0099] [Comparative Example 2-3] A tire of Comparative Example 2-3 was obtained in the same manner as Comparative Example 1, except that the tread rubber and base rubber were as shown in Table 2.

[0100] [Comparative Example 4] A tire of Comparative Example 4 was obtained in the same manner as in Comparative Example 1, except that the tread was constructed so that no wings were provided and the ends of the base layer were covered with a cap layer.

[0101] [Comparative Example 5] A tire of Comparative Example 5 was obtained in the same manner as in Example 1, except that the base rubber and the thickness TB of the base layer were as shown in Table 2 below.

[0102] [Comparative Example 6] A tire of Comparative Example 5 was obtained in the same manner as in Example 1, except that the base rubber was as shown in Table 2 below.

[0103] [Peeling resistance] An adhesion test was performed using a laminate composed of a cap layer and a base layer to measure peel resistance (N / mm). The peel resistance was measured using an Instron, and the peel resistance index of Comparative Example 1 was set to 100, and the peel resistance of each example was expressed as an index using the following calculation formula. The larger the peeling efficiency value, the more difficult it is to peel. (Peel resistance index)=(peel resistance of each example) / (peel resistance of Comparative Example 1)×100

[0104] [grip] The prototype tire was mounted on a rim (size = 18 x 13.0J), and the tire was filled with air to adjust the internal pressure to 180 kPa. This tire was mounted on a racing vehicle. A driver with professional skills drove the vehicle on a racing circuit, and a sensory evaluation of grip performance was performed. The results are shown in Table 2 below, with Comparative Example 1 set as an index of 100. The higher the value, the better the grip performance.

[0105] [Lap time decrease rate] The prototype tire was mounted on a rim (size = 18 x 13.0J) and the tire was filled with air to adjust the internal pressure to 180 kPa. This tire was mounted on a racing vehicle. A driver with professional skills drove the vehicle on a racing circuit. The vehicle was driven for 30 laps, and the lap times were measured. The ratio of the lap time on the 30th lap to the best time (fastest time) was calculated (the rate of decrease in lap time). The results are shown as an index in Table 2 below. The closer the value is to 100, the more suppressed the decrease in lap time is, which is preferable.

[0106] [Overall performance] The index values ​​obtained from each evaluation were summed up and the results are shown in Table 2 below. The higher the value, the better.

[0107] [Table 2]

[0108] As shown in Table 2, the Examples were rated higher than the Comparative Examples. In particular, it was confirmed that the Examples were able to stably exhibit high grip performance. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0109] The above-described technology for stably achieving high grip performance can be applied to various tires. [Explanation of symbols]

[0110] 2. Tires 4. Tread 6. Sidewall 8. Clinch 10 Bead 12. Carcass 14. Belt 16...Band 22 Tread surface 28, 28a, 28b... Carcass ply 30, 30u, 30s... Belt ply 32 Band cord 34 Topping rubber 36 Cap layer 38...Base layer 38E: End surface of base layer 38 38 End face

Claims

1. A tire having a tread that comes into contact with a road surface, the tread comprises a cap layer and a base layer, the cap layer and the base layer being radially aligned; The cap layer is located on the road surface side and is laminated on the base layer, The base layer has a pair of end faces included in the outer surface of the tire, The thickness of the base layer is 0.4 mm or less, the cap layer is made of a crosslinked product of a cap rubber containing a raw rubber component, the base layer is made of a cross-linked product of a base rubber containing a raw rubber component, The raw rubber component of the cap rubber and the raw rubber component of the base rubber are made of styrene-butadiene rubber. tire.

2. The base rubber does not include liquid rubber.

2. The tire of claim 1.

3. The hardness of the base layer at 23°C is 60 or less.

3. A tire according to claim 1 or 2.

4. The loss tangent of the base layer at 100° C. is 0.30 or more.

3. A tire according to claim 1 or 2.

5. The base layer has a tensile strength at break of 8.0 MPa or more at 100 ° C.

3. A tire according to claim 1 or 2.

6. The base layer has an elongation at break of 500% or more at 100°C.

3. A tire according to claim 1 or 2.

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