Pneumatic tire

Abstract

In this pneumatic tire: first and second belt layers in a tire center part both measure no more than 1.00 mm in thickness; b > a; the length of a first rubber part in the direction toward the tire center part is greater than the length of a second rubber part in the direction toward the tire center part; and reinforcing cords of a belt reinforcement layer are organic fiber cords in which the cutting strength is at least 6.5 cN / dtex, the cutting elongation is at least 10%, and the elastic modulus at 7% elongation is at least 6.0 mN / (dtex %). The belt reinforcement layer is disposed in a tire-width-direction region between at least the end part of the first rubber part on the tire-center side and the end part of the second belt layer as seeb in a cross-sectional view in the tire-width direction.

Description

pneumatic tires

[0001] The present invention relates to a pneumatic tire.

[0002] Conventionally, in order to achieve both weight reduction and belt end durability of a pneumatic tire, a technique has been known in which the belt gauge is made relatively thin and inter-belt rubber is placed at the belt end (for example, Patent Documents 1 and 2).

[0003] JP 2013-159250 A JP 2010-163055 A

[0004] However, with the above-described structure, the hoop effect at the belt ends is insufficient, and the radial growth rate at the ends of the pneumatic tire becomes larger than that at the center, especially when traveling at high speeds, resulting in unevenness across the tire width.

[0005] Therefore, an object of the present invention is to provide a pneumatic tire that achieves both weight reduction and belt end durability while maintaining a uniform radial growth rate in the tire width direction.

[0006] The gist of the present invention is as follows: (1) A tread portion includes a belt including a first belt layer and a second belt layer disposed radially outward of the first belt layer, and a belt reinforcing layer disposed radially outward of the belt, wherein each of the first belt layer and the second belt layer is formed by covering a plurality of belt cords with a belt rubber, and the belt reinforcing layer is formed by covering a plurality of reinforcing cords with a reinforcing layer rubber, and the thickness of the first belt layer and the thickness of the second belt layer in a tire center portion are both 1.00 mm or less, In a cross section in the tire width direction, among distances in the tire radial direction between a first virtual line connecting with a straight line the outermost points in the tire radial direction of the circumscribing circles of the belt cords adjacent to each other of the first belt layer and a second virtual line connecting with a straight line the innermost points in the tire radial direction of the circumscribing circles of the belt cords adjacent to each other of the second belt layer, the maximum value at the tire center is a, and among lengths of line segments connecting with the innermost points in the tire radial direction of the circumscribing circles of the belt cords positioned outermost in the tire width direction of the second belt layer and the first virtual line, b satisfies the following conditions: b>a; at an end of the belt, a first rubber portion is disposed between the first belt layer and the second belt layer, and a second rubber portion is disposed on the outer side of the second belt layer in the tire radial direction; the length of the first rubber portion in the direction toward the tire center portion is longer than the length of the second rubber portion in the direction toward the tire center portion; the belt reinforcing layer is arranged in a tire width direction region between at least an end of the first rubber portion on the tire center side and an end of the second belt layer in a cross section in the tire width direction, and the reinforcing cord of the belt reinforcing layer is an organic fiber cord having a breaking strength of 6.5 cN / dtex or more, a breaking elongation of 10% or more, and an elastic modulus at 7% elongation of 6.0 mN / (dtex·%) or more.

[0007] Here, the term "tire center" refers to the portion of the tire that is located within one-quarter of the tire's contact width from the tire's equatorial plane. The term "tire contact width" refers to the distance in the tire width direction between the contact edges when the tire is mounted on an applicable rim, inflated to the specified internal pressure, and unloaded. The term "contact edges" refers to both ends in the tire width direction of the contact surface that comes into contact with the road when the tire is mounted on an applicable rim, inflated to the specified internal pressure, and under maximum load. Unless otherwise specified, dimensions such as "thickness," "(shortest) distance," and "length" refer to dimensions in the unloaded state. The term "thickness of the first belt layer and the second belt layer at the tire center" refers to the thickness measured in the tire radial direction. The above-mentioned breaking strength, breaking elongation, and modulus of elasticity at 7% elongation are values ​​measured at room temperature (23°C), and the physical properties of the organic fiber cord can be measured in accordance with JIS L 1013, "Test Methods for Chemical Fiber Filament Yarn." The elastic modulus at 7% elongation is calculated by converting the slope (N / %) of the tangent at a point on the load-elongation curve of the cord corresponding to an elongation of 7% into a value per dtex.

[0008] In this specification, the term "applicable rim" refers to the standard rim (referred to as "Measuring Rim" in the ETRTO STANDARDS MANUAL and "Design Rim" in the TRA YEAR BOOK) for the applicable size, which is an industrial standard valid in the region where the tire is produced and used, and which is described in the JATMA YEAR BOOK of the Japan Automobile Tire Manufacturers Association (JATMA) in Japan, the STANDARDS MANUAL of the European Tire and Rim Technical Organization (ETRTO) in Europe, and the YEAR BOOK of the Tire and Rim Association, Inc. (TRA) in the United States, or which will be described in the future. "rim" refers to the rim (i.e., the above "rim" includes not only current sizes but also sizes that may be included in the above industry standards in the future. An example of a "size to be described in the future" is a size listed under "FUTURE DEVELOPMENTS" in the 2013 edition of ETRTO). However, for sizes not listed in the above industry standards, it refers to a rim with a width corresponding to the bead width of the tire. Furthermore, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel for the applicable size / ply rating listed in the above JATMA etc., and for sizes not listed in the above industry standards, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle on which the tire is mounted. Furthermore, "maximum applied load" refers to the load corresponding to the above maximum load capacity.

[0009] According to the present invention, it is possible to provide a pneumatic tire that achieves both weight reduction and belt end durability while maintaining a uniform radial growth rate in the tire width direction.

[0010] FIG. 5A is a schematic cross-sectional view in the tire width direction of a pneumatic tire according to one embodiment of the present invention. FIG. 5B is a schematic cross-sectional view showing an example of an end portion of a belt. FIG. 5C is a schematic cross-sectional view showing another example of an end portion of a belt. FIG. 5D is a schematic cross-sectional view of a tire center portion and an end portion of a belt in a pneumatic tire according to one embodiment of the present invention. FIG. 5E is a schematic cross-sectional view of a tire center portion of a belt in a pneumatic tire according to one embodiment of the present invention. FIG. 5F is a schematic cross-sectional view of a belt end portion in a pneumatic tire obtained according to the manufacturing method of FIG. 5A. FIG. 5G is a schematic cross-sectional view of a belt end portion in a pneumatic tire obtained according to the manufacturing method of FIG. 6A. FIG. 6H is a diagram for explaining a first virtual line and a second virtual line.

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0012] Fig. 1 is a schematic cross-sectional view in the tire width direction of a pneumatic tire according to one embodiment of the present invention. As shown in Fig. 1, a pneumatic tire 1 (hereinafter also simply referred to as "tire") of this embodiment includes a pair of bead portions 2, a pair of sidewall portions 3 continuous with the bead portions 2, and a tread portion 4 continuous between the pair of sidewall portions 3. The tire 1 further includes a carcass 5 that toroidally straddles the pair of bead portions 2. The tire 1 includes, in the tread portion 4, a belt 6 including a first belt layer 6a and a second belt layer 6b arranged radially outward of the first belt layer 6a, and a belt reinforcing layer 7 arranged radially outward of the belt 6.

[0013] A bead core 2 a is embedded in each bead portion 2. Although not shown, a bead filler may be disposed on the radially outer side of the bead core 2 a. The bead filler may have, for example, a triangular cross section.

[0014] The carcass 5 may be made up of one or more carcass plies. The carcass cords of the carcass plies may be made of, for example, organic fiber cords.

[0015] In the illustrated example, there are two belt layers, but there may be three or more layers. In this embodiment, the width of the first belt layer 6a in the tire width direction is larger than the width of the second belt layer 6b in the tire width direction. The belt reinforcing layer 7 may be installed so as to cover only both end portions of the belt 6 in the tire width direction, or may be installed so as to cover the entire belt 6. As shown in FIG. 1 , both a layer installed so as to cover the entire belt 6 and a layer installed so as to cover only both end portions of the belt 6 may be installed. The belt reinforcing layer 7 installed so as to cover only both end portions of the belt 6 is arranged at least in the tire width direction region where the first rubber portion 8B is arranged in the tire width direction. The width of the belt reinforcing layer 7 installed so as to cover the entire belt 6 is larger than the width of the second belt layer 6b in the tire width direction.

[0016] In the tire 1 of this embodiment, the thickness of the first belt layer 6a and the thickness of the second belt layer 6b at the tire center portion are both 1.00 mm or less. By setting the thickness of each belt layer at the tire center portion to 1.00 mm or less, weight reduction and rolling resistance can be achieved. From the same viewpoint, the thickness of the first belt layer 6a at the tire center portion is preferably 0.96 mm or less, and more preferably 0.90 mm or less. Furthermore, the thickness of the second belt layer 6b at the tire center portion is preferably 0.96 mm or less, and more preferably 0.90 mm or less. To achieve such thicknesses, the diameters of the belt cords embedded in the first belt layer 6a and the second belt layer 6b, the coating thickness of the belt rubber, and the like can be appropriately selected.

[0017] 2A is a schematic cross-sectional view showing the end of a belt. As shown in the figure, each of the first belt layer 6a and the second belt layer 6b is made up of a plurality of belt cords (61, 62) covered with belt rubber (63, 64). More generally, these belt layers 6a, 6b are made up of a rubber-steel cord composite in which parallel-wound steel cords (belt cords 61, 62) are covered with belt rubber (63, 64). The belt layers 6a, 6b may be inclined belt layers in which the belt cords cross each other between the layers. The belt cords 61, 62 may extend linearly.

[0018] As shown in the figure, an end rubber 8 is disposed at the end of the belt 6 of the tire 1 of this embodiment. In the illustrated example, a first rubber portion 8B is disposed between the first belt layer 6a and the second belt layer 6b at the end of the belt 6, and a second rubber portion 8C is disposed on the tire radially outer side of the second belt layer 6b. In the illustrated example, a third rubber portion 8A is also disposed between the carcass 5 and the first belt layer 6a at the end of the belt 6, but the third rubber portion 8A does not have to be disposed. By disposing the end rubber 8 at the end of the belt 6 in this manner, it is possible to improve the durability of the belt end. That is, the first rubber portion 8B can suppress failure due to strain between the belt layers, the second rubber portion 8C can suppress failure due to strain between the second belt layer 6b and the belt reinforcing layer 7, and the third rubber portion 8A can suppress failure due to strain between the carcass 5 and the first belt layer 6a.

[0019] Furthermore, in the tire 1 of this embodiment, as shown in the drawing, the first rubber portion 8B has the longest length in the direction toward the tire center portion (which is roughly synonymous with the "length in the tire width direction"). In other words, in the tire 1 of this embodiment, the lengths of the third rubber portion 8A, the first rubber portion 8B, and the second rubber portion 8C in the direction toward the tire center portion are respectively defined as L Ａ , L Ｂ and L Ｃ (See FIG. 2A), L Ａ / L Ｂ is less than 1.0, and L Ｃ / L Ｂis less than 1.0. In addition, in the tire 1 of the present embodiment, as shown in the drawing, the first rubber portion 8B is closest to the tire center portion among the third rubber portion 8A, the first rubber portion 8B, and the second rubber portion 8C.

[0020] The above-described aspect of the end rubber 8 can typically be achieved by manufacturing a tire according to a manufacturing method for a pneumatic tire described later. In the manufacturing method for a pneumatic tire described later, gaps are unlikely to be formed between the first belt layer 6 a and the second belt layer 6 b, and between the second belt layer 6 b and the belt reinforcing layer 7, and this also contributes to improving durability at the belt end.

[0021] In the tire 1 of this embodiment, L Ａ / L Ｂ is 0.5 or less, and L Ｃ / L Ｂ It is preferable that L is 0.5 or less. In this case, the formation of gaps at the belt ends is further suppressed. Ａ / L Ｂ is more preferably 0.4 or less, and L Ｃ / L Ｂ is more preferably 0.4 or less.

[0022] In the tire of FIG. 2A (and FIGS. 1 and 3 ), the third rubber portion 8A, the first rubber portion 8B, and the second rubber portion 8C are integrated as the end rubber 8 and arranged at the end of the belt 6, but such integration is not essential. For example, in the tire of the present invention, the rubber (third rubber portion 8A) on the inner side in the tire radial direction of the first belt layer 6a, the rubber (first rubber portion 8B) between the first belt layer 6a and the second belt layer 6b, and the rubber (second rubber portion 8C) on the outer side in the tire radial direction of the second belt layer 6b may be arranged separately from each other. In addition, in the tire of the present invention, as shown in FIG. 2B , the end rubber 8 (rubber sheet) wrapping the end of the first belt layer 6a and the end rubber 8 (rubber sheet) wrapping the end of the second belt layer 6b may be in contact with each other (without being completely integrated). However, from the viewpoint of further improving the durability of the belt end portion, it is preferable that the third rubber portion 8A, the first rubber portion 8B, and the second rubber portion 8C are integrated as the end rubber 8.

[0023] Fig. 3 is a schematic cross-sectional view of the tire center portion and end portions of the belt 6 in the tire 1 of this embodiment. The end portions of the belt 6 in Fig. 3 correspond to those shown in Fig. 2A. Fig. 7 is a diagram for explaining the first virtual line and the second virtual line. 3 and 7 , in a cross-sectional view in the tire width direction, a first imaginary line 21 is a straight line connecting the radially outermost points of the circumscribing circles of adjacent belt cords 61 of the first belt layer 6a, and a second imaginary line 22 is a straight line connecting the radially innermost points of the circumscribing circles of adjacent belt cords 62 of the second belt layer 6b. The maximum value of the radial distance between the first imaginary line 21 and the second imaginary line 22 is defined as a (although a1 and a2 are illustrated in FIG. 7 , this is the maximum value among countless such radial distances). The minimum value of the length of the line segment connecting the radially innermost point of the circumscribing circle of the belt cord 62 located at the outermost position in the tire width direction of the second belt layer 6b and the first imaginary line 21 is defined as b (although b1, b2, and b3 are illustrated in FIG. 7 , this is the minimum value among countless such radial distances). In this case, b > a in the tire 1 of this embodiment. This is because if b ≦ a, distortion that causes belt edge separation cannot be sufficiently suppressed. In this embodiment, the ratio b / a is more preferably 2.0 or greater and 8.0 or less. By setting the ratio b / a to 2.0 or greater, it is possible to further improve the durability at the belt end, particularly the belt edge separation durability. Furthermore, by setting the ratio b / a to 8.0 or less, it is possible to ensure the sufficiently low rolling resistance desired for the tire. Furthermore, from the same viewpoint, the ratio b / a is more preferably 2.0 or greater and 6.0 or less, and particularly preferably 4.1 or greater and 6.0 or less.

[0024] FIG. 4 is a schematic cross-sectional view of the center portion of the belt 6 in the tire 1 of this embodiment, which corresponds to the portion surrounded by the dashed line in FIG. 3 . In the tire 1 of this embodiment, it is preferable that the distances between the interface of the first belt layer 6a and the belt cord 61 in the tire center portion (i.e., the distance c1 from the upper surface to the belt cord 61 and the distance c2 from the lower surface to the belt cord 61) are both 0.19 mm or less, and the distances between the interface of the second belt layer 6b and the belt cord 6A in the tire center portion (i.e., the distance c3 from the upper surface to the belt cord 62 and the distance c4 from the lower surface to the belt cord 62) are both 0.19 mm or less. By adopting such an embodiment, it is possible to more sufficiently improve the low rolling resistance of the tire 1. From the same viewpoint, the distances between the interface of the first belt layer 6a and the belt cord 61 and the distance between the interface of the second belt layer 6b and the belt cord 62 in the tire center portion are more preferably 0.17 mm or less, and even more preferably 0.14 mm or less.

[0025] The belt reinforcing layer 7 is formed by covering a plurality of reinforcing cords with a reinforcing layer rubber. In this embodiment, the reinforcing cords of the belt reinforcing layer 7 are organic fiber cords having a breaking strength of 6.5 cN / dtex or more, a breaking elongation of 10% or more, and an elastic modulus at 7% elongation of 6.0 mN / (dtex·%) or more. If the elastic modulus at 7% elongation is less than 6.0 mN / (dtex·%), the reinforcing cords of the belt reinforcing layer 7 will not be able to fully exert their reinforcing effect on the hoop of the belt. If the breaking strength is less than 6.5 cN / dtex or the breaking elongation is less than 10%, the durability of the reinforcing cords of the belt reinforcing layer 7 itself will be low, and there is a risk that the reinforcing effect on the hoop of the belt will not be exerted due to cord breakage or the like. In the illustrated example, the belt reinforcing layer 7 is a so-called cap layer, but it may also be a layer disposed only at the belt end.

[0026] As described above, in the tire 1 of this embodiment, the thicknesses of the first belt layer and the second belt layer at the tire center are both 1.00 mm or less, b > a, and the length of the first rubber portion in the direction toward the tire center is longer than the length of the second rubber portion in the direction toward the tire center. This allows for both lightweight and belt end durability. The belt reinforcing layer 7 is disposed radially outward of the belt 6. The reinforcing cords of the belt reinforcing layer 7 are organic fiber cords having a breaking strength of 6.5 cN / dtex or more, a breaking elongation of 10% or more, and a modulus of elasticity at 7% elongation of 6.0 mN / (dtex·%) or more. This reinforces the hoop effect of the belt (particularly the belt end portions) and suppresses the difference in radial growth between the center and the end portions in the tire width direction. Thus, the tire 1 of this embodiment allows for a uniform radial growth rate in the tire width direction while achieving both lightweight and belt end durability. Furthermore, plunger durability and handling stability can also be improved.

[0027] As long as the belt 6 and the belt reinforcing layer 7 are configured as described above, the tire of the present invention is not particularly limited in terms of the specific tire structure and materials. For example, the first belt layer 6a and the second belt layer 6b can be arranged so that the multiple belt cords embedded in the belt rubber are inclined, for example, at an angle of 15 to 40 degrees relative to the tire circumferential direction. The carcass 5 can be made of organic fiber cords extending in a direction substantially perpendicular to the tire circumferential direction, for example, at an angle of 70 to 90 degrees. In the tire 1 shown in the figure, the carcass 5 can be not only folded around the bead cores 2a as shown, but also wound around and secured to the bead cores 2a (not shown), or sandwiched between bead wires on both sides (not shown). The tire of the present invention may also have a tread pattern formed on the surface of the tread portion 4. The tire of the present invention may also have an inner liner (not shown) formed as the innermost layer. The gas to be filled in the tire of the present invention may be normal air or air with a modified oxygen partial pressure, or an inert gas such as nitrogen. The tire of the present invention is suitable for use as a pneumatic tire for a passenger car.

[0028] Next, details of each component used in the tire 1 of this embodiment will be described. The compounds described in this specification may be partially or entirely derived from fossil resources, biological resources such as plant resources, or recycled resources such as used tires. They may also be derived from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0029] (Coating Rubber (Belt Rubber)) The belt rubbers 63, 64 used in the first belt layer 6a and the second belt layer 6b are not particularly limited as long as they are a general rubber composition capable of coating the belt cords 61, 62. Examples of rubber components include diene rubbers, and natural rubber or isoprene rubber is particularly preferred. The belt rubbers 63, 64 may also contain a filler such as carbon black, as long as the filler does not affect the performance of the coating rubber, such as adhesion and durability. HAF-class carbon black is preferred as the carbon black, and the content of carbon black in the belt rubbers 63, 64 may be 50 to 70 parts by mass per 100 parts by mass of the rubber component. In addition to the above-mentioned components, the belt rubbers 63, 64 may also contain, as appropriate, crosslinking agents such as vulcanization accelerators, sulfur, and zinc oxide; adhesion promoters such as cobalt compounds containing cobalt salts; antioxidants; oils; resins; and the like. Examples of the antiaging agent include amine-based antiaging agents such as 6PPD, and bisphenol-based antiaging agents such as o-MBp14. These antiaging agents may be used alone or in combination of two or more.

[0030] The natural rubber used for the belt rubber may be modified. In the case of modified natural rubber, for example, it is preferable that the nitrogen content is 0.1 to 0.3 mass%. Furthermore, it is preferable that the modified natural rubber has had proteins removed by a centrifugation process, enzyme treatment, or urea treatment. Furthermore, it is preferable that the phosphorus content of the modified natural rubber is more than 200 ppm and not more than 900 ppm. The carbon black used for the belt rubber may be recycled carbon black.

[0031] (End rubber) The end rubber 8 (third rubber portion 8A, first rubber portion 8B, second rubber portion 8C) is not particularly limited, but for example, the same rubber composition as the belt rubbers 63, 64 of the first belt layer 6a and the second belt layer 6b can be used.

[0032] (Belt Cord) In the first belt layer 6a and the second belt layer 6b, typically, a plurality of belt cords 61, 62 are arranged in parallel. These belt cords 61, 62 are generally steel cords. The structure of these belt cords is not particularly limited. However, from the viewpoint of effectively achieving both improved tire durability and reduced rolling resistance, the belt cords preferably have a 1×N structure (N is an integer selected from 2 to 6) in which N filaments are twisted together. In particular, for tires with a tire load index of less than 100, the cords more preferably have a 1×2 structure, and for tires with a tire load index of 100 or greater, the cords more preferably have a 1×5 structure. From the same viewpoint, the cords are preferably monofilaments twisted in parallel without being twisted together. In the case of the 1×N structure, the cords may have a 1×N open structure in which the filaments are twisted together without contacting each other and spaced apart. Cords with an open structure have superior fatigue resistance compared to cords in which filaments are twisted together while in contact with each other. A 1×N open structure cord may be formed by sandwiching unvulcanized rubber between filaments and twisting them together, or by coating the surfaces of the filaments with unvulcanized rubber and then twisting them together. Such filaments can also be pre-shaped before twisting. When pre-shaped, the filament shaping pitch is preferably in the range of 8 mm to 16 mm. A shaping pitch in this range can enhance rubber permeability and further improve durability. Furthermore, the ratio Sf / Sc of the filament cross-sectional area Sf in the cord cross section to the area Sc of the circumscribed circle of the cord cross section is preferably in the range of 0.4 to 0.7. Sf / Sc in this range can enhance rubber permeability and further improve durability. The filaments constituting the belt cords 61 and 62 may be surface-treated during wiredrawing. In this case, the amount of phosphoric acid on the surface of the filament after surface treatment is 2.0 mg / m ２The amount of phosphoric acid on the surface of the filament is preferably 2.0 mg / m or less. ２ If it is below this, the adhesive strength between the filament and the coating rubber will be good.

[0033] The filaments constituting the belt cords 61, 62 used in the first belt layer 6a and the second belt layer 6b are preferably classified as ST grade (super tensile strength cord) or UT grade (ultra tensile strength cord) as defined in ISO 17832:2009, and are particularly preferably classified as UT grade. In this case, it is possible to effectively achieve both improved tire durability and low rolling resistance. From the same viewpoint, it is preferable that the belt cords 61, 62 satisfy the following formula (1): 4000-2000X≦Y≦4500-2000X ... (1) where X (mm) is the diameter of the filament constituting the belt cord and Y (MPa) is the tensile strength of the filament. In terms of fatigue resistance, the hardness of the surface layer of the filaments constituting the belt cords 61, 62 is preferably 90 to 110%, and more preferably 100%, of the hardness of the inner layer. Here, the surface layer of the filament refers to a layer (region) extending from the outermost surface of the filament to a depth of 0.01 mm, and the inner layer of the filament refers to a layer (region) inside the surface layer. The hardness can be measured, for example, as Vickers hardness. The hardness of the surface layer of the filament can be measured at a depth of 0.005 mm from the outermost surface of the filament, and the hardness of the inner layer of the filament can be measured at a depth of more than 0.04 mm from the outermost surface of the filament. The manufacturing method of the filaments constituting the belt cords 61, 62 is not particularly limited. The filaments may be obtained, for example, by refining and wiredrawing iron ore, refining and wiredrawing scrap iron, or recycling steel extracted from tires.

[0034] In the first belt layer 6a and the second belt layer 6b, the end density of the belt cords 61, 62 is preferably 50 ends / dm or more and 250 ends / dm or less. In this case, it is possible to effectively achieve both improved tire durability and low rolling resistance. In particular, when the belt cord has a 1×N structure (N is an integer selected from 2 to 6), the end density of the belt cord is preferably 60 ends / dm or more and 95 ends / dm or less. On the other hand, when the cord is a monofilament, the end density of the cord is preferably 180 ends / dm or more and 240 ends / dm or less.

[0035] The diameter of the belt cords 61, 62 used in the first belt layer 6a and the second belt layer 6b is preferably 0.2 mm or more and 1.2 mm or less. In this case, it is possible to effectively achieve both improved tire durability and low rolling resistance. In particular, when the belt cord has a 1×N structure (N is an integer selected from 2 to 6), the diameter of the cord is preferably 0.4 mm or more and 1.2 mm or less, and more preferably 0.5 mm or more and 1.0 mm or less. On the other hand, when the belt cord is a monofilament, the diameter of the belt cord is preferably 0.24 mm or more and 0.28 mm or less.

[0036] (Belt Reinforcement Layer) As described above, the tire 1 of the present invention includes a belt reinforcing layer 7 on the tire radial direction outer side of the belt 6. The belt reinforcing layer 7 is a member formed by covering reinforcing cords (organic fiber cords) arranged substantially parallel to the tire circumferential direction (for example, at an angle of 0 to 5 degrees with respect to the tire circumferential direction) with reinforcing layer rubber (elastomer). The belt reinforcing layer 7 can be formed by continuously spirally winding a narrow strip prepared by covering organic fiber cords with an elastomer in the tire circumferential direction.

[0037] The organic fiber cord used in the belt reinforcing layer has a breaking strength of 6.5 cN / dtex or more, a breaking elongation of 10% or more, and an elastic modulus at 7% elongation of 6.0 mN / (dtex·%) or more.

[0038] An organic fiber cord having a breaking strength of 6.5 cN / dtex or more, a breaking elongation of 10% or more, and a modulus of elasticity at 7% elongation of 6.0 mN / (dtex·%) or more has high strength at break, large elongation at break, and a high modulus of elasticity at 7% elongation. Therefore, by applying an organic fiber cord with such physical properties to the belt reinforcing layer 7 to supplement the rigidity of the belt 6, it is possible to improve the handling stability of the tire while suppressing a decrease in plunger durability that would otherwise be caused by the application of a belt layer containing, for example, a metal monofilament.

[0039] The material of the organic fiber cord is not particularly limited, but examples thereof include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); nylons such as 6-nylon, 6,6-nylon, 4,6-nylon, and 4,10-nylon; and celluloses such as rayon and lyocell. Among these, polyethylene terephthalate is preferred, that is, the organic fiber cords used as reinforcing materials for the belt reinforcing layer are preferably cords made of polyethylene terephthalate (hereinafter, sometimes simply referred to as "polyethylene terephthalate cords"). Polyethylene terephthalate cords have higher rigidity than commonly used nylon cords and are excellent in improving the plunger durability and steering stability of tires.

[0040] The organic fiber cord preferably has a modulus of elasticity of 2.5 mN / (dtex·%) or more at a load of 29.4 N measured at 160°C. Here, the modulus of elasticity at 29.4 N measured at 160°C is calculated by converting the slope (N / %) of the tangent at a point corresponding to a load of 29.4 N on the load-elongation curve of the cord measured at 160°C into a value per dtex. The modulus of elasticity is measured at 160°C because the temperature inside the tire increases with high-speed running, and by the time tire failure occurs during high-speed running, the temperature of the belt reinforcing layer has reached 160°C. In particular, polyethylene terephthalate cords exhibit a significant decrease in modulus of elasticity at high temperatures compared to room temperature. Therefore, even if a cord has high elasticity at room temperature, if it cannot maintain a high modulus of elasticity at high temperatures, it will not be able to exhibit sufficient belt reinforcing effect (improving durability against protrusion input and suppressing belt extrusion). Therefore, the modulus of elasticity at high temperatures is of great significance. By setting the elastic modulus of the cord at a load of 29.4 N measured at 160°C to be 2.5 mN / (dtex·%) or more, the plunger durability of the tire can be improved, and the amount of belt protrusion during high-speed running can be suppressed, reducing stress when the tire presses in and out, thereby improving the handling stability of the tire during high-speed running.

[0041] In order to improve the elastic modulus of the organic fiber cord at 160°C, it is preferable to perform the dipping treatment under high tension. In addition, in order to sufficiently increase the elasticity of the cord, the tension when the cord is subjected to adhesive treatment should be 6.9 × 10 －２ It is preferable to set the elasticity to N / tex or more. However, the method for increasing the elasticity of the cord is not limited to this, and other methods such as reducing the twist of the cord can also be adopted. The adhesive treatment is composed of dry treatment, hot treatment, normalizing treatment, etc., and is a treatment in which temperature and time are appropriately adjusted in addition to tension. The adhesive treatment may be performed by either one-bath treatment or two-bath treatment, but two-bath treatment is preferred, and the elasticity of the cord is 6.9 x 10 －２ It is preferable to apply a tension of at least N / tex to the cord during the hot treatment in the two baths.

[0042] The organic fiber cord preferably has a twist coefficient α, expressed by the following formula: α=T×D1 / 2 (wherein α is the twist coefficient, T is the number of twists (turns / 100 mm), and D is the total cord fineness (dtex)), of 500 to 2500. When the twist coefficient α of the organic fiber cord is 500 or more, the binding force of the filaments becomes strong and adhesion becomes sufficient, and when it is 2500 or less, a sufficient elastic modulus can be exhibited to obtain the effect of improving durability against protrusion input and the effect of suppressing the belt from squeezing out.

[0043] The organic fiber cord preferably has a total fineness of 1000 to 3500 dtex. A total fineness of 1000 dtex or more of the cord can exhibit a sufficient elastic modulus to improve durability against protrusion input and to suppress belt extrusion, while a total fineness of 3500 dtex or less allows for a dense weave, ensuring sufficient rigidity per unit width. The raw materials for the organic fiber cord are not particularly limited, and may be synthetic or biological, or may be derived from mechanical recycling, such as by crushing, melting, and re-spinning PET products such as PET bottles, or chemical recycling, such as by depolymerizing and repolymerizing PET products such as PET bottles.

[0044] (Coating Rubber (Reinforcing Layer Rubber)) The reinforcing layer rubber preferably has a storage modulus E' of 6.0 MPa or less, measured under conditions of a temperature of 24°C, an amplitude of ±1%, and a frequency of 52 Hz. Furthermore, the loss index L of the coating rubber contained per 100 mm of the belt reinforcing layer, defined by L = tan δ × ((100 × D) - π(D / 2)2 × N), (where tan δ is the loss tangent of the reinforcing layer rubber measured under conditions of a temperature of 24°C, an initial strain of 6%, an amplitude of ±1%, and a frequency of 52 Hz, D is the diameter (mm) of the circumscribed circle of the reinforcing cord, and N is the number of reinforcing cords per 100 mm of the belt reinforcing layer), is preferably 4.00 or less. Furthermore, the rubber composition used for the reinforcing layer rubber preferably contains natural rubber and styrene-butadiene rubber as rubber components, and the natural rubber is contained in an amount of 70 parts by mass or more per 100 parts by mass of the rubber component. It is also preferred that the styrene-butadiene rubber in the rubber composition used for the reinforcing layer rubber is non-oil extended. The rubber composition used for the reinforcing layer rubber contains 30 to 60 parts by mass of carbon black per 100 parts by mass of the rubber component, and the nitrogen adsorption specific surface area (N2SA) of the carbon black is 40 m ２ / g or less. Furthermore, it is preferable that the rubber composition used for the reinforcing layer rubber does not contain an oil component derived from a polymer. Furthermore, it is preferable that the oil component in the rubber composition used for the reinforcing layer rubber is 0.2% by mass or less. Furthermore, the natural rubber used for the reinforcing layer rubber may be modified. In the case of modified natural rubber, it is preferable that the nitrogen content is 0.1 to 0.3% by mass. Furthermore, it is preferable that the modified natural rubber has had proteins removed by a centrifugation process, enzyme treatment, or urea treatment. Furthermore, it is preferable that the phosphorus content of the modified natural rubber is more than 200 ppm and 900 ppm or less. The carbon black used for the reinforcing layer rubber may be recycled carbon black.

[0045] In this specification, "recycled carbon black" refers to carbon black recovered from recycled waste raw materials. Examples of recycled waste include rubber products (particularly vulcanized rubber products) containing carbon black, such as used rubber and used tires, and waste oil. "Recycled carbon black" differs from carbon black produced directly from hydrocarbons such as petroleum and natural gas, i.e., non-recycled carbon black. Note that "used" here refers not only to carbon black that has been discarded after actual use, but also to carbon black that has been produced but discarded without actually being used.

[0046] The recycled carbon black used in this embodiment is preferably obtained by pyrolysis of a vulcanized rubber product containing carbon black. In this case, resource recycling becomes possible, further contributing to improving sustainability. Furthermore, the recycled carbon black used in this embodiment is preferably obtained from the solid residue produced by pyrolysis of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is pyrolyzed, a solid residue and a volatile component (oil) are obtained, and recycled carbon black can be recovered from either. However, the recycled carbon black used in this embodiment preferably does not include carbon black recovered from oil.

[0047] The solid residue obtained by pyrolysis of waste materials such as used rubber and used tires contains ash in addition to carbon black. The ash is derived from the non-volatile components contained in the rubber and tires. Therefore, the recycled carbon black obtained from the solid residue has a relatively low carbon black content. On the other hand, considering the various physical properties required for tires manufactured using recycled carbon black, the higher the carbon content in the recycled carbon black, the better. The carbon content of the recycled carbon black used in this embodiment is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, and even more preferably 89% by mass or more. The carbon content of the recycled carbon black used in this embodiment is preferably 97% by mass or less. Note that the above carbon content does not include adsorbed moisture.

[0048] Specific examples of ash include zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, magnesium oxide, and the like. In the case of recycled carbon black produced from solid residues obtained by pyrolysis of waste, a certain amount of ash remains even after various processes for removing the ash. In this embodiment, the recycled carbon black is allowed to contain ash. The lower limit of the ash content of the recycled carbon black used in this embodiment may be 0.5% by mass. Meanwhile, considering the various physical properties required for tires and the quality of the recycled carbon black, the ash content of the recycled carbon black is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 5.0% by mass or less. Having an ash content of 20% by mass or less of the recycled carbon black can improve the various physical properties of rubber products using the rubber composition. Herein, the ash content of carbon black is calculated by burning the carbon black at 550°C ± 25°C to convert it to incineration, and then calculating the mass of the unburned components (ash).

[0049] Recycled carbon black can also be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3,427,975, citing "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, describes that recycled carbon black can be obtained by pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (

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

[0004] of Japanese Patent No. 6,856,781 (Comparison of the Surface Morphology and Chemistry of Pyrolytic Carbon Black and Commercially Available Carbon Black, Powder Technology 160 (2005) pp. 190-193).

[0050] Recycled carbon black may lack functional groups on its surface, or may be treated to include functional groups on its surface. The treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3,173,251, carbon black obtained from a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl and / or carboxyl groups on its surface. Furthermore, in Japanese Patent No. 6,856,781, carbon black obtained from a pyrolysis process is treated with an amino acid compound containing at least one thiol or disulfide group to obtain surface-activated carbon black. The recycled carbon black according to this embodiment also includes carbon blacks that have been treated to include functional groups on their surfaces.

[0051] (Adhesive) The reinforcing cord (organic fiber cord) of the belt reinforcing layer 7 and the reinforcing layer rubber are preferably bonded with an adhesive. From the viewpoint of environmental protection, it is preferable to use a dip treatment liquid that does not contain resorcinol or formalin as the adhesive composition for the organic fiber cord. Examples of such a dip treatment liquid include a composition containing (a) a rubber latex having an unsaturated diene and (b) one or more compounds selected from a compound having a polyether skeleton structure and an amine functional group, a compound having an acrylamide structure, a polypeptide, a polylysine, and a carbodiimide. Examples of such a dip treatment liquid include a composition containing, in addition to the rubber latex (a) having an unsaturated diene and the compound (b), one or more compounds selected from (c) an aqueous compound having a (thermally dissociable blocked) isocyanate group, a polyphenol (d), and a polyvalent metal salt (e).

[0052] Other examples of the dipping treatment liquid that does not contain resorcinol or formalin include a composition containing polyphenols (I) and aldehydes (II). Such a composition may further contain at least one of an isocyanate compound (III) and a rubber latex (IV) in addition to the polyphenols (I) and aldehydes (II).

[0053] The adhesive composition for treating (coating) the organic fiber cord with an adhesive contains polyphenols (I) and aldehydes (II), so that good adhesive properties can be exhibited even when resorcinol is not used in consideration of the environmental load.

[0054] [Polyphenols (I)] The adhesive composition contains polyphenols (I) as a resin component, thereby improving adhesion to organic fiber cords. The polyphenols (I) are typically water-soluble polyphenols, and are not particularly limited as long as they are polyphenols other than resorcinol (resorcinol). The number of aromatic rings or hydroxyl groups in the polyphenols (I) can be appropriately selected.

[0055] From the viewpoint of realizing better adhesive properties, the polyphenols (I) preferably have two or more hydroxyl groups, and more preferably three or more hydroxyl groups. When the polyphenols have three or more hydroxyl groups, the polyphenol or polyphenol condensate is soluble in the adhesive composition (dip treatment liquid) containing water. This allows the polyphenols to be uniformly distributed in the adhesive composition, thereby realizing better adhesive properties. Furthermore, when the polyphenols (I) are polyphenols containing multiple (two or more) aromatic rings, each of the aromatic rings has two or three hydroxyl groups at the ortho, meta, or para positions.

[0056] As the polyphenols (I), for example, those described as polyphenol compounds in WO 2022 / 130879 can be used. These polyphenols (I) may be used alone or in combination of two or more.

[0057] [Aldehydes (II)] When the adhesive composition contains aldehydes (II) as a resin component in addition to the polyphenols (I), high adhesiveness can be achieved together with the polyphenols (I). Here, the aldehydes (II) are not particularly limited and can be appropriately selected depending on the required performance. In this specification, the aldehydes (II) also include derivatives of aldehydes that are generated from aldehydes.

[0058] Examples of the aldehydes (II) include monoaldehydes such as formaldehyde, acetaldehyde, butylaldehyde, acrolein, propionaldehyde, chloral, butylaldehyde, caproaldehyde, and allylaldehyde, and aliphatic dialdehydes such as glyoxal, malonaldehyde, succinaldehyde, glutaraldehyde, and adipaldehyde, aldehydes having an aromatic ring, and dialdehyde starch. These aldehydes (II) may be used singly or in combination of two or more.

[0059] The aldehydes (II) are preferably aldehydes having an aromatic ring or contain aldehydes having an aromatic ring, because this allows for better adhesiveness to be obtained. Furthermore, the aldehydes (II) preferably do not contain formaldehyde. Here, "does not contain formaldehyde" means, for example, that the formaldehyde content of the total mass of the aldehydes is less than 0.5 mass%.

[0060] In the adhesive composition, polyphenols (I) and aldehydes (II) are in a condensed state, and the mass ratio of the polyphenols to the aldehydes having an aromatic ring (content of aldehydes having an aromatic ring / content of polyphenols) is preferably 0.1 or more and 3 or less. In this case, the hardness and adhesive properties of the resin, which is the product of the condensation reaction between the polyphenols and the aldehydes having an aromatic ring, are more suitable. From the same viewpoint, the mass ratio of the polyphenols to the aldehydes having an aromatic ring (content of aldehydes having an aromatic ring / content of polyphenols) in the adhesive composition is more preferably 0.25 or more and more preferably 2.5 or less. Note that the above mass ratio is the mass of the dry product (solid content ratio).

[0061] The total content of polyphenols (I) and aldehydes (II) in the adhesive composition is preferably 3 to 30% by mass. This is because better adhesion can be ensured without deteriorating workability, etc. From the same viewpoint, the total content of polyphenols (I) and aldehydes (II) in the adhesive composition is more preferably 5% by mass or more, and more preferably 25% by mass or less. The above total content is the mass of the dry product (solid content ratio).

[0062] [Isocyanate Compound (III)] The adhesive composition preferably further contains an isocyanate compound (III) in addition to the polyphenols (I) and aldehydes (II) described above. In this case, the adhesive composition can further enhance the adhesiveness due to a synergistic effect with the polyphenols (I) and the aldehydes (II).

[0063] Here, the isocyanate compound (III) is a compound that has the effect of promoting adhesion of the adhesive composition to a resin material (e.g., a phenol / aldehyde resin obtained by condensing polyphenols (I) and aldehydes (II)) that is the adherend, and is a compound that has an isocyanate group as a polar functional group. These isocyanate compounds (III) may be used alone or in combination of two or more.

[0064] The isocyanate compound (III) is not particularly limited, but from the viewpoint of further improving adhesion, it preferably contains a (blocked) isocyanate group-containing aromatic compound. When the adhesive composition contains a (blocked) isocyanate group-containing aromatic compound, the (blocked) isocyanate group-containing aromatic compound is distributed in a position near the interface between the organic fiber cord and the adhesive composition, resulting in a further adhesion-promoting effect, and this effect can further improve the adhesion of the adhesive composition to the organic fiber cord.

[0065] As the (blocked) isocyanate group-containing aromatic compound, those described in Japanese Patent Application No. 2023-040157 and Japanese Patent Application No. 2023-030762 can be used.

[0066] The content of the isocyanate compound (III) in the adhesive composition is not particularly limited, but from the viewpoint of more reliably ensuring excellent adhesion, it is preferably 5 to 65% by mass. From the same viewpoint, the content of the isocyanate compound (III) in the adhesive composition is more preferably 10% by mass or more, and more preferably 45% by mass or less. The above content is the mass of the dry product (solid content ratio).

[0067] [Rubber Latex (IV)] The adhesive composition may further contain substantially rubber latex (IV) in addition to the polyphenols (I), aldehydes (II), and isocyanate compound (III) described above, which can further enhance the adhesiveness of the adhesive composition to rubber members.

[0068] Here, the rubber latex (IV) is not particularly limited, and examples thereof include natural rubber (NR), as well as synthetic rubbers such as polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), halogenated butyl rubber, acrylonitrile-butadiene rubber (NBR), and vinylpyridine-styrene-butadiene copolymer rubber (Vp). These rubber latexes (IV) may be used alone or in combination of two or more.

[0069] When preparing the adhesive composition containing the rubber latex (IV), it is preferable to mix the rubber latex (IV) with the phenol (I) and the aldehyde (II) before compounding the isocyanate compound (III).

[0070] The content of the rubber latex (IV) in the adhesive composition is preferably 20% by mass or more, more preferably 25% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less.

[0071] The method for producing the adhesive composition is not particularly limited, and examples thereof include a method of mixing raw materials such as polyphenols (I), aldehydes (II), and rubber latex (IV) and aging the mixture, or a method of mixing polyphenols (I) and aldehydes (II) and aging the mixture, and then adding rubber latex (IV) and aging the mixture. When an isocyanate compound (III) is contained in the raw materials, the method for producing the adhesive composition may also be a method of adding rubber latex (IV), aging the mixture, and then adding the isocyanate compound (III).

[0072] (Method for Manufacturing Pneumatic Tire) A tire manufacturing method (hereinafter sometimes simply referred to as the "manufacturing method") is a method for manufacturing the pneumatic tire 1 of the present invention described above, and includes a step of laminating the first belt layer 6a and the second belt layer 6b (lamination step). Furthermore, in the manufacturing method of this embodiment, prior to the lamination step, an end of the first belt layer 6a is wrapped with a first rubber sheet, and an end of the second belt layer 6b is wrapped with a second rubber sheet, and at this time, for both the first rubber sheet and the second rubber sheet, the ends of each belt layer are wrapped in a shifted manner so that the length of the rubber sheet portion facing the other belt layer when laminated is longer than the length of the rubber sheet portion facing the other belt layer when laminated. According to this manufacturing method, the pneumatic tire 1 described above can be manufactured while effectively suppressing the formation of gaps between the first belt layer 6a and the second belt layer 6b, and between the second belt layer 6b and the belt reinforcing layer 7.

[0073] The mechanism by which the formation of gaps is suppressed in this embodiment as described above will be described in detail below.

[0074] 5A is a schematic diagram showing the lamination step in the manufacturing method of this embodiment. As shown in the figure, in the lamination step, for example, a first belt layer 6a, a second belt layer 6b, and other layers 16 (including a belt reinforcing layer 7, and also rubber layers, pressure-fitting layers, etc. (not shown)) are laminated in this order, and a roll 15 is pressed from above and moved from the tire center toward the end of each layer to pressure-bond the first belt layer 6a, the second belt layer 6b, and other layers 16. At this time, the end of the first belt layer 6a is wrapped with a first rubber sheet, and the end of the second belt layer 6b is wrapped with a second rubber sheet in advance. At this time, the first rubber sheet wrapping the end of the first belt layer 6a has a length (length in the tire width direction, the same applies hereinafter) (L Ｂ１’ ) is the length of the rubber sheet portion located on the opposite side (L Ａ’) of the second rubber sheet that wraps the end of the second belt layer 6b. As shown in FIG. 5A, the length (L Ｂ２’ ) is the length of the rubber sheet portion located on the opposite side (L ｃ’ 5B ), the first belt layer 6 a is offset so as to enclose the end of the second belt layer 6 b. When the rubber sheets are laminated and pressed in this arrangement, gaps are unlikely to be formed at the belt end between the first belt layer 6 a and the second belt layer 6 b, and between the second belt layer 6 b and the other layer 16.

[0075] On the other hand, in the conventional method, as shown in FIG. 6A, the first rubber sheet that wraps the end of the first belt layer 6a and the second rubber sheet that wraps the end of the second belt layer 6b are both wrapped symmetrically around the end (i.e., L Ａ’ ≒L Ｂ１’ , L Ｂ２’ ≒L Ｃ’ 6B ), when the rubber sheets are laminated and pressed in this arrangement, the first belt layer 6a, the second belt layer 6b, and the other layers 16 cannot be deformed until they are in close contact with each other, and as a result, large gaps (air pockets) tend to form at the belt ends between the first belt layer 6a and the second belt layer 6b, and between the second belt layer 6b and the other layers 16, as shown in FIG.

[0076] The other layer 16 may include, for example, a belt reinforcing layer and may further be a tire constituent member such as a rubber layer.

[0077] The first rubber sheet and the second rubber sheet may be, for example, rectangular rubber sheets.

[0078] In the laminating step, it is preferable to laminate the first belt layer 6a and the second belt layer 6b so that the first rubber sheet and the second rubber sheet are in contact with each other.

[0079] In the manufacturing method of this embodiment, when the first belt layer 6 a and the second belt layer 6 b are laminated, it is preferable that the end of the first rubber sheet located between the first belt layer 6 a and the second belt layer 6 b does not overlap with the end of the second rubber sheet. In other words, the distance L between the end of the first rubber sheet located between the first belt layer 6 a and the second belt layer 6 b is ｘ’ (distance in the tire width direction) (see FIG. 5A ) is preferably greater than 0. This can further suppress the formation of gaps at the belt ends. In this case, the terminal end of the first rubber sheet of the first belt layer 6a may be closer to the tire center portion, or the terminal end of the second rubber sheet of the second belt layer 6b may be closer to the tire center portion as shown in FIG. 5A . However, from the viewpoint of more effective suppression of gap formation, it is more preferable that the terminal end of the second rubber sheet of the second belt layer 6b is closer to the tire center portion as shown in FIG. 5A .

[0080] In this manufacturing method, as long as the arrangement of the rubber sheets around the first belt layer 6a and the second belt layer 6b is as described above and the configuration of the pneumatic tire 1 of the present embodiment is obtained, other specific manufacturing conditions are not particularly limited. For example, the lengths (L Ａ , L Ｂ and L Ｃ ) and the relative positional relationship are determined by the length (L Ａ’ , L Ｂ１’ ~L Ｂ２’ , L Ｃ’ ) and therefore, a person skilled in the art can make appropriate adjustments while keeping this point in mind. Furthermore, for example, in order to adjust the intervals between the belt cords of the first belt layer 6a and the second belt layer 6b in the tire 1 of the present embodiment (and thus to make b > a), it is possible to appropriately adjust, for example, the thickness of the first rubber sheet wrapping the end portion of the first belt layer 6a and / or the thickness of the second rubber sheet wrapping the end portion of the second belt layer 6b.

[0081] The tire of the present invention will be described in more detail below using examples.

[0082] Evaluations of belt edge separation durability and rolling resistance were performed using tires having the belt structures shown in Tables 1 to 3 below and the belt end schematic structure shown in FIG. 2A. The tire sizes used in the tests are shown in Tables 1 to 3, and the cords in each belt layer of each tire were arranged so that they intersected at an angle of ±30° with respect to the tire circumferential direction. In Tables 1 to 3, the cord placement density, cord diameter, filament diameter, thickness of the first belt layer and the second belt layer in the tire center, and the distance between the interface and the cord of the first belt layer and the second belt layer in the tire center are values ​​specified at the time of tire design. "a" indicates the value obtained by doubling the distance between the interface and the cord of the belt layer in the tire center. "b" indicates the value actually measured when the prepared tire was dissected.

[0083] <Belt Edge Separation Durability> After aging, the tires of each example were inflated to internal pressure and mounted on a test passenger vehicle. The vehicle was run over a BES drum with a constant side force (SF) repeatedly applied, and the tire was dissected to measure the length of cracks occurring at the belt layer ends. The crack length of each example was compared with that of a conventional example. If the difference in crack length from the conventional example was less than 0.5 mm, the tire was evaluated as being equivalent to the conventional example, and if the crack length was 0.5 mm or more shorter than the conventional example, the tire was evaluated as being good. The results are shown in Tables 1 to 3.

[0084]

[0085]

[0086]

[0087] <Effect of Belt Reinforcement Layer> In the tires shown in Examples 1 to 4 of the present invention in Tables 1 to 3, by disposing a belt reinforcing layer on the outer side of the belt in the tire radial direction, the belt reinforcing layer is formed by covering cords made of polyethylene terephthalate having a breaking strength of 6.5 cN / dtex or more, a breaking elongation of 10% or more, and an elastic modulus at 7% elongation of 6.0 mN / (dtex·%) or more with an elastomer, and it can be confirmed that the radial growth rate can be made uniform in the tire width direction, and further the plunger durability and handling stability of the tire are improved.

[0088] <Effect of Belt Interlayer Rubber> In the tires shown in Invention Examples 1 to 4 in Tables 1 to 3, a belt reinforcing layer formed by coating cords made of polyethylene terephthalate with an elastomer and having a breaking strength of 6.5 cN / dtex or more, an elongation at break of 10% or more, and an elastic modulus at 7% elongation of 6.0 mN / (dtex·%) or more is disposed on the radially outer side of the belt, and further, belt interlayer rubber is disposed on the end of the belt (between the end of the first belt layer and the end of the second belt layer) to satisfy b>a, whereby it can be confirmed that distortion at the belt end is suppressed and durability of the tire belt end is improved.

[0089] [Contribution to the United Nations-led Sustainable Development Goals (SDGs)] The SDGs have been proposed to realize a sustainable society. One embodiment of the present invention is thought to be a technology that can contribute to goals such as "No. 7: Affordable and Clean Energy for All," "No. 12: Responsible Consumption and Production," and "No. 13: Take Urgent Action Against Climate Change."

[0090] 1: Pneumatic tire, 2: Bead portion, 3: Sidewall portion, 4: Tread portion, 5: Carcass, 6: Belt, 7: Belt reinforcing layer, 8: Edge rubber, 15: Roll, 16: Other layers

Claims

1. A tire comprising a tread portion, a belt including a first belt layer and a second belt layer arranged radially outward of the first belt layer, and a belt reinforcing layer arranged radially outward of the belt, wherein each of the first belt layer and the second belt layer is formed by covering a plurality of belt cords with a belt rubber, and the belt reinforcing layer is formed by covering a plurality of reinforcing cords with a reinforcing layer rubber, and the thickness of the first belt layer and the thickness of the second belt layer in a tire center portion are both 1.00 mm or less, in a cross section in the tire width direction, a maximum value of a distance in the tire radial direction between a first virtual line formed by connecting with a straight line the outermost points in the tire radial direction of the circumscribing circles of the adjacent belt cords of the first belt layer and a second virtual line formed by connecting with a straight line the innermost points in the tire radial direction of the circumscribing circles of the adjacent belt cords of the second belt layer is defined as a, and a minimum value of a length of a line segment connecting the innermost point in the tire radial direction of the circumscribing circle of the belt cord located at the outermost side in the tire width direction of the second belt layer and the first virtual line is defined as b, where b>a, and at an end portion of the belt, a first rubber portion is disposed between the first belt layer and the second belt layer, and a second rubber portion is disposed on the outer side in the tire radial direction of the second belt layer, and a length of the first rubber portion in a direction toward the tire center portion is longer than a length of the second rubber portion in a direction toward the tire center portion, the belt reinforcing layer is disposed in at least a tire width direction region between an end of the first rubber portion on the tire center side and an end of the second belt layer in a cross section in the tire width direction, and the reinforcing cord of the belt reinforcing layer is an organic fiber cord having a breaking strength of 6.5 cN / dtex or more, a breaking elongation of 10% or more, and an elastic modulus at 7% elongation of 6.0 mN / (dtex·%) or more.

2. The pneumatic tire according to claim 1, wherein the belt reinforcing layer is disposed across at least the tire width direction region in which the second belt layer is disposed, in a cross-sectional view in the tire width direction.

3. The pneumatic tire according to claim 1 or 2, wherein the distance between the belt cord and the interface of the first belt layer and the interface of the second belt layer in the tire center portion is 0.19 mm or less.

4. The pneumatic tire according to any one of claims 1 to 3, wherein the belt cord has a 1 x N structure formed by twisting together N filaments, where N is an integer selected from 2 to 6.

5. A pneumatic tire according to any one of claims 1 to 4, wherein the end count of the belt cord is 60 cords / dm or more and 95 cords / dm or less.

6. The pneumatic tire according to any one of claims 1 to 5, wherein the diameter of the belt cord is 0.5 mm or more and 1.0 mm or less.

7. The pneumatic tire according to any one of claims 1 to 6, wherein the ratio b / a is 2.0 or greater and 8.0 or less.

8. A pneumatic tire according to any one of claims 1 to 7, wherein the organic fiber cord serving as the reinforcing cord is a cord made of polyethylene terephthalate.

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