Airless tire

Abstract

To provide an airless tire with an improved vibration performance by suppressing generation of flat spots.SOLUTION: Provided is an airless tire 1 including an annular tread ring 2 having a contact surface 2a, a hub 3 arranged in a radially inside of the tire of the tread ring 2, and a spoke part 4 connecting the tread ring 2 and the hub 3. The spoke part 4 includes a thermoplastic resin 8. In the thermoplastic resin 8, tension permanent set at 40°C conforming to JIS K6273 is equal to or less than 60% and compression permanent set at 40°C conforming to JIS K6262 is equal to or less than 50%.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an airless tire. [Background technology]

[0002] Patent Document 1 below describes an airless tire. The airless tire includes a tread ring, a hub, and spokes that connect the tread ring and the hub. The spokes are made of a thermoplastic resin. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-34665 Summary of the Invention [Problem to be solved by the invention]

[0004] When an airless tire is mounted on a vehicle, compressive stress acts on the spokes below the tire's rotation axis, and tensile stress acts on the spokes above the tire's rotation axis. For this reason, if the vehicle is parked for a long period of time, compression set may occur in the lower spokes, and tensile set may occur in the upper spokes. In particular, after the vehicle has been driven, the spokes made of resin become hot and their modulus decreases, so that compression set and tensile set are likely to become large. The permanent strain generated in the spokes causes the contact surface of the tread ring to deform flat, resulting in so-called flat spots, which deteriorate the vibration performance of the airless tire.

[0005] The present invention has been devised in view of the above-mentioned circumstances, and has as its main object to provide an airless tire that can suppress the occurrence of flat spots and improve vibration performance. [Means for solving the problem]

[0006] The present invention is an airless tire comprising: an annular tread ring having a contact surface; a hub disposed radially inward of the tread ring; and spoke portions connecting the tread ring and the hub, wherein the spoke portions contain a thermoplastic resin having a tensile permanent set of 60% or less at 40°C in accordance with JIS K6273 and a compression permanent set of 50% or less at 40°C in accordance with JIS K6262. Effect of the Invention

[0007] By employing the above-described configuration, the airless tire of the present invention can suppress the occurrence of flat spots and improve vibration performance. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of an airless tire manufactured by the manufacturing method of the present embodiment. [Diagram 2] FIG. 2 is an enlarged view of a cross section taken along line AA in FIG. [Diagram 3] FIG. [Figure 4] FIG. 2 is a flow diagram of a manufacturing method according to the present embodiment. [Diagram 5] FIG. 11 is a plan view of the mold in the placement process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The drawings include exaggerated expressions and expressions different from the dimensional ratio of the actual structure in order to facilitate understanding of the present invention. In addition, when there are multiple embodiments, the same or common elements are given the same reference numerals throughout the specification, and duplicated explanations are omitted.

[0010] [Basic structure of airless tires] Fig. 1 is a perspective view of one embodiment of an airless tire (hereinafter, may be simply referred to as "tire") 1 of the present invention. Fig. 2 is an enlarged view of a cross section of the tire 1 taken along line AA in Fig. 1. As shown in Figs. 1 and 2, the tire 1 includes a tread ring 2 having a contact surface 2a that contacts the road surface, a hub 3 disposed radially inward of the tread ring 2, and spoke portions 4 that connect the tread ring 2 and the hub 3.

[0011] The tread ring 2 is an annular rubber member. Well-known rubber members such as natural rubber, butadiene rubber, and isoprene rubber are used as the rubber members. The tread ring 2 is formed of, for example, vulcanized rubber. Spoke portions 4 are connected to an inner peripheral surface 2b of the tread ring 2 in the tire radial direction. In this embodiment, the tread ring 2 is bonded to the spoke portions 4 with a first adhesive 31.

[0012] The tread ring 2 may have, for example, a reinforcing cord 2c (shown in FIG. 3) disposed therein. The reinforcing cord 2c may be, for example, a plurality of organic fiber cords or steel cords oriented in a predetermined direction. A resin material may be added to or compounded with a part of the tread ring 2.

[0013] The hub 3 is connected to an axle (drive shaft) of a vehicle (not shown). The hub 3 in this embodiment is made of metal. Well-known metals such as aluminum, magnesium, copper, and titanium are used as the metal. The hub 3 includes, for example, a disk portion 3a and a cylindrical portion 3b formed on the outer side in the tire radial direction. The disk portion 3a is disposed concentrically with the tread ring 2. The spoke portions 4 are connected to the outer peripheral surface 3e of the cylindrical portion 3b. The hub 3 is bonded to the spoke portions 4 with a second adhesive 32.

[0014] The spoke portion 4 of this embodiment contains a thermoplastic resin 8. Such a spoke portion 4 absorbs vibrations generated when the tire is running and has high vibration performance. In this embodiment, the spoke portion 4 is made of a hardened thermoplastic resin 8.

[0015] The thermoplastic resin 8 has a tensile permanent set at 40°C according to JIS K6273:2018 of 60% or less, and a compression permanent set at 40°C according to JIS K6262:2013 of 50% or less. In this way, in the present invention, the tensile permanent set at 40°C and the compression permanent set at 40°C are limited to a certain range, so that even if the vehicle is parked for a long time after driving, the permanent set occurring in the spoke portion 4 can be reduced. Therefore, the airless tire of the present invention can suppress flat spots on the tread ring 2, and thus can improve vibration performance. In addition, in recent years, the outside air temperature in summer is about 40°C. Therefore, by adopting the tensile permanent set at 40°C and the compression permanent set at 40°C, it is possible to effectively suppress flat spots on the tread ring 2 after the vehicle is driven and parked for a long time in summer, when both permanent sets tend to be large.

[0016] The tensile set at 40°C is calculated by using a rectangular test piece (thermoplastic resin 8) of the following size, fixing the rectangular test piece at 10% elongation in an atmosphere at 40°C for 22 hours, releasing it, and measuring the value after 30 minutes have passed. The compression set at 40°C is calculated by using a cylindrical test piece (thermoplastic resin) of the following size, fixing the cylindrical test piece at 10% compression in an atmosphere at 40°C for 22 hours, releasing it, and measuring the value after 30 minutes have passed. Strip-shaped test piece (length x width x thickness): 100mm x 10mm x 2mm Cylindrical test piece (diameter x thickness): 29mm x 12mm

[0017] If the tensile permanent set and compression permanent set at 40°C are excessively small, the thermoplastic resin 8 tends to lose elasticity and become excessively hard, which may deteriorate the ride comfort. In order to achieve both vibration performance and ride comfort, the tensile permanent set at 40°C is preferably 55% or less, more preferably 1.0% or more, and more preferably 2.0% or more. The compression permanent set at 40°C is preferably 45% or less, more preferably 1.0% or more, and more preferably 2.0% or more.

[0018] The complex modulus of the thermoplastic resin 8 (after curing) at 30°C is preferably 50 MPa or more, more preferably 100 MPa or more, and more preferably 300 MPa or less, and even more preferably 250 MPa or less. Since the complex modulus is 50 MPa or more, the rigidity of the tire 1 is maintained. Since the complex modulus is 300 MPa or less, the vibration performance can be maintained at a high level.

[0019] From the same viewpoint, the loss tangent of the thermoplastic resin 8 at 30°C is preferably 0.001 or more, more preferably 0.005 or more, and more preferably 0.1 or less, and even more preferably 0.08 or less. In this specification, the complex modulus and the loss tangent are values ​​measured under the conditions shown below using a viscoelasticity spectrometer such as "IPLEXER (registered trademark)" manufactured by GABO Co., Ltd. in accordance with JIS K6394:2007. The complex modulus and the loss tangent are measured at 30°C because the temperature of the spoke portion 4 of the tire 1 during running is lower than 30°C. Initial strain: 5% Amplitude: ±1% Frequency: 10Hz Deformation mode: tension Temperature: 30℃

[0020] The softening point of the thermoplastic resin 8 is preferably 80°C or higher, more preferably 100°C or higher, and more preferably 200°C or lower, and even more preferably 180°C or lower. Since the softening point is 80°C or higher, the high-speed durability performance of the tire 1 can be ensured. Since the softening point is 200°C or lower, the hardness of the spoke portion 4 is prevented from becoming too high, and vibration performance can be improved. The softening point is measured by the Vicat method specified in ASTM-D1525.

[0021] Furthermore, the breaking elongation of the thermoplastic resin 8 at 23°C is preferably 350% or more, more preferably 400% or more, more preferably 800% or less, and even more preferably 700% or less. Since the breaking elongation at 23°C is 350% or more, the strength of the thermoplastic resin 8 is high and high-speed durability performance can be maintained. Since the breaking elongation at 23°C is 800% or less, the tensile permanent set and compression permanent set are kept small and vibration performance can be improved. The breaking elongation can be measured by performing a tensile test at 23°C using a No. 3 dumbbell-shaped test piece made of the cured thermoplastic resin 8 in accordance with JIS K6251:2017.

[0022] The thermoplastic resin 8 desirably has a yield stress at 23°C greater than the modulus at 100% stretch. A spoke portion 4 made of such a thermoplastic resin 8 can reduce deformation (permanent set) caused by parking for a long period of time after driving. The yield stress is desirably 5.0 MPa or more, more desirably 6.5 MPa or more, desirably 10.0 MPa or less, and more desirably 9.0 MPa or less. The difference (σ1-σ2) between the yield stress σ1 at 23°C and the modulus σ2 at 100% stretch is desirably 0.5 MPa or more, more desirably 1.0 MPa or more, desirably 5.0 MPa or less, and more desirably 4.0 MPa or less.

[0023] The modulus at 100% stretch is the tensile stress at 100% elongation in the grain direction (the rolling direction when forming thermoplastic resin 8 by extrusion or shearing) measured in accordance with JIS K6251:2017 under conditions of a tensile speed of 3.3 mm / sec in an atmosphere of 23°C. The sample for measuring the modulus at 100% stretch is a dumbbell-shaped No. 7 test piece having a thickness of 1 mm. The yield stress is measured from a stress-strain curve obtained by a tensile test measured in accordance with JIS K6251:2017. Specifically, a sheet having a thickness of 2 mm was prepared by injection molding using thermoplastic resin 8, and a dumbbell-shaped test piece was prepared from the sheet stored at 23°C for 2 weeks, and the stress-strain curve was obtained for this test piece. Using this obtained curve, the initial stress at which the stress decreased with increasing strain was determined as the yield stress.

[0024] As such a thermoplastic resin 8, for example, polyolefin, polyvinyl chloride, methacrylic resin, etc. are preferable, and in particular, polyester resin, polyamide resin, or polyurethane resin is preferably adopted. Note that "resin" includes elastomer.

[0025] The "thermoplastic resin" means a thermoplastic resin material made of a copolymer of a polymer having elasticity, a crystalline hard segment with a high melting point, and a non-crystalline soft segment with a low glass transition temperature. The crystalline hard segment with a high melting point of the thermoplastic resin acts as a pseudo cross-linking point and exhibits elasticity. The thermoplastic resin can be reused because the pseudo cross-linking point can be regenerated by heating the hard segment to melt it once and then cooling it. The hard segment is, for example, a portion derived from a low molecular weight polyol. The soft segment is, for example, a portion derived from a polyether polyol or a polycarbonate polyol. The thermoplastic resin of the present invention does not contain a rubber component.

[0026] The methods for adjusting the tensile set, compression set, complex modulus, loss tangent, softening point temperature, elongation at break, yield stress, and modulus at 100% stretching are, for example, as follows. The adjustment methods include, for example, a method of appropriately selecting the types of hard segments and soft segments in a thermoplastic resin, and a method of adjusting the amounts of constituent units of hard segments and soft segments in a thermoplastic resin. In addition, the adjustment methods may include, for example, a method of combining two or more types of soft segments, a method of combining a thermoplastic resin with a crosslinking agent as an additive, and a method of adjusting the type and content of a filler. Furthermore, the adjustment methods include, as preferred embodiments, blending a thermoplastic resin having hard segments and soft segments, or combining a thermoplastic resin with a crosslinking agent (additive).

[0027] The spoke portion 4 made of such a thermoplastic resin 8 includes, for example, an outer ring portion 4a on the outside in the tire radial direction, an inner ring portion 4b on the inside in the tire radial direction, and a plurality of spoke elements 4c. The outer ring portion 4a is, for example, an annular body connected to the inner peripheral surface 2b of the tread ring 2. The inner ring portion 4b is, for example, an annular body connected to the outer peripheral surface 3e of the cylindrical portion 3b of the hub 3. In this manner, the tread ring 2 is connected to the outside of the spoke portion 4 in the tire radial direction, and the hub 3 is connected to the inside of the spoke portion 4 in the tire radial direction. Each spoke element 4c is, for example, a plate-like body extending in the tire radial direction, and is connected to the outer ring portion 4a and the inner ring portion 4b. The spoke element 4c is not limited to the illustrated embodiment, and various well-known forms may be adopted.

[0028] [Manufacturing method of airless tires] Next, a method for manufacturing the tire 1 will be described. A mold 10 is used to manufacture the tire 1. FIG. 3 is a cross-sectional view of one embodiment of the mold 10. As shown in FIG. 3, the mold 10 includes a lower mold 10A and an upper mold 10B that is movable in the vertical direction relative to the lower mold 10A. The lower mold 10A includes a cavity 20 formed of a cylindrical recess and a mating surface 11 with which the upper mold 10B is mated. Specifically, FIG. 3 is a cross-sectional view of the upper mold 10B and the lower mold 10A when they are closed and cut at the mating surface 11, and shows the lower mold 10A and a portion 10e of the upper mold 10B located below the mating surface 11. The mold 10 includes, for example, an injection gate 26 of a known structure for injecting a thermoplastic resin 8 into the cavity 20.

[0029] The cavity 20 includes, for example, an area in which the tread ring 2 and the hub 3 are disposed, and an area in which the thermoplastic resin 8 for molding the spoke portion 4 is filled. As described above, in this embodiment, the mold 10 has a well-known structure.

[0030] Fig. 4 is a flow diagram of the manufacturing method of this embodiment. As shown in Fig. 4, the manufacturing method in this embodiment includes a preparation step S1, a treatment step S2, a first application step S3, a second application step S4, a placement step S5, an injection step S6, a molding step S7, and an annealing step S8. The manufacturing method also includes, for example,

[0031] In the manufacturing method of this embodiment, first, a preparation step S1 is performed. In the preparation step S1, for example, a tread ring 2 and a hub 3 are prepared. The tread ring 2 is obtained, for example, according to a conventional method, by molding an unvulcanized rubber member, a reinforcing cord 2c, etc. into a predetermined shape and vulcanizing it in a mold or the like. On the other hand, the hub 3 is manufactured by various well-known methods such as casting, forging, cutting, etc. (not shown).

[0032] Next, a treatment step S2 is performed. The treatment step S2 is, for example, a step of blasting the outer peripheral surface 3e (shown in FIG. 2) of the hub 3. The blasting step is, for example, a step of roughening the outer peripheral surface 3e by spraying non-metallic particles or metallic particles at high speed onto the outer peripheral surface 3e. This makes it possible to increase the adhesive strength between the hub 3 and the spoke portion 4. In the treatment step S2 in this embodiment, the inner peripheral surface 2b of the tread ring 2 may be blasted. Note that in the manufacturing method of the present invention, a well-known roughening treatment step S2 other than the blasting treatment may be performed, or the treatment step may be omitted.

[0033] Next, a first application step S3 is performed. In the first application step S3, in this embodiment, a second adhesive 32 (shown in FIG. 2) is applied to the outer circumferential surface 3e of the hub 3. In this embodiment, the second adhesive 32 is applied to the outer circumferential surface 3e by a well-known method.

[0034] The second adhesive 32 is preferably a vulcanizing adhesive to increase adhesive strength. Specifically, the second adhesive 32 is preferably made of products such as "CHEMLOC 218E" and "IMB1040" manufactured by LORD Far East Corporation, or "METALOC UA" and "METALOC C-12" manufactured by Toyo Kagaku Kenkyusho Co., Ltd.

[0035] In the first application step S3, it is preferable that the second adhesive 32 is applied to a thickness d1 (shown in FIG. 2) of 30 to 100 μm. Since the thickness d1 is 30 μm or more, the second adhesive 32 is sufficiently applied to the outer peripheral surface 3e, and therefore the adhesive strength can be ensured. Since the thickness d1 is 100 μm or less, the second adhesive 32 is prevented from being swept away by the thermoplastic resin 8 when the thermoplastic resin 8 is injected in the injection step, and the adhesive strength can be increased. The second adhesive 32 applied to the thickness d1 remains in the same thickness range even after the molding step S7.

[0036] In the first application step S3, it is preferable to apply the second adhesive 32, which has been preheated in advance, to the outer circumferential surface 3e of the hub 3. This allows the second adhesive 32 to be spread and improves adhesion to the metal hub 3, and also makes it possible to remove the solvent contained in the second adhesive 32. The second adhesive 32 is heated to 30 to 150°C by a known heater (not shown) for a preheating time of 10 to 60 minutes, for example.

[0037] Next, the second application step S4 is performed. In the second application step S4, in this embodiment, the first adhesive 31 (shown in FIG. 2) is applied to the inner circumferential surface 2b of the tread ring 2. In this embodiment, the first adhesive 31 is applied to the inner circumferential surface 2b by a well-known method. The first adhesive 31 may be, for example, the same as the second adhesive 32. The first adhesive 31 may also be a vulcanization adhesive different from the second adhesive 32. Specifically, the first adhesive 31 is preferably manufactured by Lord Far East Corporation under the trade names "Chemlock 210" and "Chemlock 6108" or manufactured by Toyo Kagaku Kenkyusho Co., Ltd. under the trade names "Metalock UA" and "Metalock C-12". The second application step S4 may be performed between the treatment step S2 and the arrangement step S5.

[0038] The thickness d2 of the first adhesive 31 may be smaller than the thickness d1 of the second adhesive 32. In general, due to the flow path of the thermoplastic resin 8, the adhesion between the spoke portion 4 formed of the thermoplastic resin 8 and the tread ring 2 formed of vulcanized rubber is delayed from the adhesion between the spoke portion 4 and the metal hub 3. As a result, the pressure of the thermoplastic resin 8 adhering to the tread ring 2 is relatively small, and the first adhesive 31 flowed by the thermoplastic resin 8 becomes small. Therefore, by making the thickness d2 of the first adhesive 31 smaller than the thickness d1 of the second adhesive 32, it is possible to reduce the amount of the first adhesive 31 used while making the adhesive strength between the spoke portion 4 and the tread ring 2 and the adhesive strength between the spoke portion 4 and the hub 3 approximately equal. From this viewpoint, in the second application step S4, it is desirable to apply the first adhesive 31 to a thickness d2 of 10 to 50 μm.

[0039] Next, the arrangement step S5 is performed. FIG. 5 is a plan view of the lower die 10A of the mold 10 in the arrangement step S5. As shown in FIG. 5, in the arrangement step S5 in this embodiment, the hub 3 to which the second adhesive 32 is applied is arranged at a predetermined position in the cavity 20 of the lower die 10A. Also, in the arrangement step S5, for example, the tread ring 2 to which the first adhesive 31 is applied may be arranged in the cavity 20. This tread ring 2 is arranged at a predetermined position in the cavity 20, for example. Thereafter, the upper die 10B is fitted into the lower die 10A, and the mold 10 is closed.

[0040] Next, the injection process S6 is performed. In the injection process S6, in this embodiment, the thermoplastic resin 8 is injected into the cavity 20. In the injection process S6, for example, the thermoplastic resin 8 is filled into a predetermined position in the cavity 20 through an injection gate 26 (shown in FIG. 3).

[0041] To inject the thermoplastic resin 8, for example, an injection molding machine (not shown) of a known structure is used. This injection molding machine includes a cylinder (not shown) for heating the thermoplastic resin 8, and a screw (not shown) that rotates inside the cylinder and injects the thermoplastic resin 8 while applying pressure to it. The cylinder is configured so that its temperature can be controlled by a heating means such as a heater. As a result, the thermoplastic resin 8 is injected in a state softened by heating.

[0042] The temperature of the cylinder is desirably 180° C. or higher, more desirably 200° C. or higher, desirably 300° C. or lower, and desirably 220° C. or lower. Since the temperature of the cylinder is controlled to 300° C. or lower, it is possible to prevent the thermoplastic resin 8 from being heated to a temperature higher than necessary, and therefore it is possible to prevent thermal deterioration of the tread ring 2, the second adhesive 32, and the first adhesive 31. Since the temperature of the cylinder is controlled to 180° C. or higher, the heat of the thermoplastic resin 8 is imparted to the second adhesive 32 and the first adhesive 31, and the activity of the reactive groups is increased, thereby improving the adhesive strength.

[0043] Next, a molding step S7 is performed. In this embodiment, the molding step S7 involves hardening the thermoplastic resin 8 in the cavity 20 to form the spoke portions 4. This results in a spoke complex 7 in which the spoke portions 4 are connected to the hub 3 (as shown in FIG. 2). In this embodiment, the thermoplastic resin 8 is hardened by cooling, for example, by natural cooling. In this embodiment, the spoke complex 7 is formed by connecting the outer circumferential surface 3e of the cylindrical portion 3b and the inner ring portion 4b via the second adhesive 32. A well-known method is used to harden the thermoplastic resin 8.

[0044] Furthermore, since the tread ring 2 is placed in the mold 10 in the placement step S5, the tread ring 2 is connected to the spoke complex 7 in the molding step S7 of this embodiment. In the molding step S7, for example, the inner circumferential surface 2b of the tread ring 2 and the outer ring portion 4a of the spoke portion 4 are connected via the first adhesive 31. As a result, in the molding step S7 of this embodiment, a tire 1 is formed in which the tread ring 2, the hub 3, and the spoke portion 4 are integrally molded.

[0045] Next, the annealing step S8 is performed. In the annealing step S8, heat is supplied to the spoke complex 7. As a result, the reactive groups of the second adhesive 32, which tend to be insufficiently reacted with the heat from the thermoplastic resin 8 in the injection step S6, are sufficiently activated by the heat supply in the annealing step S8. Therefore, the manufacturing method of the airless tire 1 of the present invention can further increase the adhesive strength of the second adhesive 32 of the spoke complex 7. In addition, the annealing step S8 increases the activity of the reactive groups of the first adhesive 31.

[0046] In the annealing step S8, in this embodiment, the spoke composite 7, or in this embodiment, the tire 1, is placed in an atmosphere of 50 to 100° C. for 10 to 90 minutes. This increases the adhesive strength and suppresses deterioration of the thermoplastic resin 8 and deformation of the spoke portion 4.

[0047] The annealing step S8 is performed, for example, after the spoke complex 7, or in this embodiment, the tire 1, is removed from the mold 10. This ensures that the spoke complex 7 is cooled. Furthermore, cooling the spoke complex 7 within the mold 10 prevents the thermoplastic resin 8 from sticking to the mold 10. In this embodiment, the annealing step involves placing at least one tire 1, and preferably multiple tires 1, in a heating device of known structure, such as a hot air dryer, and annealing the tires.

[0048] Although a particularly preferred embodiment of the present invention has been described above in detail, the present invention is not limited to the illustrated embodiment and can be modified and embodied in various ways. In this embodiment, the tire 1 in which the hub 3, the tread ring 2, and the spoke portion 4 made of thermoplastic resin 8 are integrally molded in a mold 10 is annealed. However, for example, only the spoke complex 7 integrally molded with the hub 3 and the spoke portion 4 made of thermoplastic resin 8 is annealed. Then, the tire 1 may be molded by bonding the tread ring 2 to which the first adhesive 31 is applied to the annealed spoke complex 7 (not shown). Also, the annealed spoke complex 7 and the tread ring 2 to which the first adhesive 31 is applied may be placed in the mold 10, and the thermoplastic resin 8 may be injected between the spoke complex 7 and the tread ring 2 to mold the tire 1 (not shown). EXAMPLES

[0049] An airless tire (corresponding to a tire size of 145 / 70R12) having the basic structure shown in Fig. 1 and Fig. 2 was prototyped. Then, the durability of each test tire was tested. The test method was as follows.

[0050] <Vibration performance> Using a drum tester, each tire was run under the following specifications, and then naturally cooled for two weeks while the running load was applied. Then, the tire was run under the same specifications, and the radial force variation (RFV) was measured before and after the run. The result was calculated as the difference (RFV1-RFV2) between the radial force variation before the run (RFV1) and the radial force variation after the run (RFV2), and expressed as an index with the difference (RFV1-RFV2) of Comparative Example 1 set to 100. The larger the value, the better the vibration performance. The radial force variation was obtained by using a tire uniformity tester and setting the running speed of the tire to 60 km / h in accordance with JASO C607:2000 "Test method for uniformity of automobile tires". Load: 3.4kN Speed: 60km / h Travel time: 1 hour

[0051] <High-speed durability performance> Using a drum testing machine, each tire was run under the following conditions until damage such as peeling or cracks occurred in the spokes. The results were evaluated using a speed (called the breaking speed) that was 10 km / h lower than the speed at which the tire was damaged, and the breaking speed of Comparative Example 1 was set to 100 as an index. The higher the value, the better the high-speed durability performance. Load: 3.4kN Speed: Initial speed 100km / h, add 10km / h every 10 minutes The results of the tests are shown in Table 1.

[0052] [Table 1]

[0053] From the test results, it is understood that the tires of the examples have better vibration performance than the tires of the comparative examples. It is also understood that the tires of the examples maintain high-speed durability. Furthermore, tires with complex modulus, loss tangent, softening point, and breaking elongation at 23°C each within a preferred range, or with a yield stress greater than the modulus at 100% elongation, have even better vibration performance.

[0054] [Note] The present invention includes the following aspects.

[0055] [Invention 1] An airless tire, The tire has an annular tread ring having a ground contact surface, a hub disposed radially inward of the tread ring, and spoke portions connecting the tread ring and the hub, the spoke portion includes a thermoplastic resin, The thermoplastic resin has a tensile set of 60% or less at 40°C according to JIS K6273 and a compression set of 50% or less at 40°C according to JIS K6262. Airless tires. [Invention 2] The airless tire according to Invention 1, wherein the thermoplastic resin has a complex modulus at 30°C of 50 to 300 MPa and a loss tangent at 30°C of 0.1 or less. [Invention 3] 3. The airless tire according to claim 1 or 2, wherein the thermoplastic resin includes a polyester resin, a polyamide resin, or a polyurethane resin. [Invention 4] The airless tire according to any one of Inventions 1 to 3, wherein the thermoplastic resin has a softening point of 80 to 200°C. [Invention 5] 5. The airless tire according to any one of claims 1 to 4, wherein the thermoplastic resin has a breaking elongation at 23°C of 350% or more. [Invention 6] 6. The airless tire according to any one of Inventions 1 to 5, wherein the thermoplastic resin has a yield stress at 23° C. that is greater than the modulus at 100% elongation. [Explanation of symbols]

[0056] 1. Airless tires 2 Tread Ring 2a Ground plane 3. Hub 4 Spoke section 8 Thermoplastic resin

Claims

1. An airless tire, The tire has an annular tread ring having a ground contact surface, a hub disposed radially inward of the tread ring, and spoke portions connecting the tread ring and the hub, the spoke portion includes a thermoplastic resin, The thermoplastic resin has a tensile set of 60% or less at 40°C according to JIS K6273 and a compression set of 50% or less at 40°C according to JIS K6262. Airless tires.

2. 2. The airless tire according to claim 1, wherein the thermoplastic resin has a complex modulus of elasticity at 30° C. of 50 to 300 MPa and a loss tangent at 30° C. of 0.1 or less.

3. The airless tire according to claim 2 , wherein the thermoplastic resin includes a polyester resin, a polyamide resin, or a polyurethane resin.

4. The airless tire according to any one of claims 1 to 3, wherein the thermoplastic resin has a softening point of 80 to 200°C.

5. 4. The airless tire according to claim 1, wherein the thermoplastic resin has a breaking elongation of 350% or more at 23°C.

6. 4. The airless tire according to claim 1, wherein the thermoplastic resin has a yield stress at 23° C. that is greater than a modulus at 100% elongation.

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