pneumatic tires

Abstract

To provide a pneumatic tire that improves handling stability while maintaining good durability and rolling resistance. [Solution] A pneumatic tire comprising a tread portion 1, a pair of sidewall portions 2, and a pair of bead portions 3, with a carcass layer 4 mounted between the pair of bead portions 3, 3, a plurality of belt layers 7 arranged on the outer circumference of the carcass layer 4 in the tread portion 1, in which belt cords intersect with each other between the layers, and a belt cover layer 8 including a belt cover cord 8C oriented in the tire circumferential direction arranged on the outer circumference of the belt layer 7, wherein the belt cover cord 8C is a polyester fiber cord whose elongation under a 2.0 cN / dtex load is in the range of 2.0% to 4.0%, the peak temperature of the loss modulus of elasticity E'' of the polyester fiber cord measured at a frequency of 20 Hz, an initial load of 300 g, a strain of ±0.1%, and a heating rate of 2 °C / min is 115 °C or higher and the peak value is 12,000 MPa or lower, and the cord angle θ of the belt layer 7 with respect to the tire circumferential direction is in the range of 27° to 40°.

Description

Technical Field

[0001] The present invention relates to a pneumatic tire provided with a belt layer and a belt cover layer on the outer peripheral side of a carcass layer, and more particularly to a pneumatic tire capable of improving handling stability while maintaining good durability and rolling resistance.

Background Art

[0002] In a pneumatic tire, a carcass layer is mounted between a pair of bead portions, and a plurality of belt layers in which belt cords cross each other in layers are arranged on the outer peripheral side of the carcass layer in the tread portion, and a belt cover layer including a belt cover cord oriented in the tire circumferential direction is arranged on the outer peripheral side of the belt layer (see, for example, Patent Documents 1 to 4).

[0003] As the belt cover cord for pneumatic tires for passenger cars and light trucks, nylon 66 fiber cords are the mainstream, but polyester fiber cords typified by polyethylene terephthalate (PET) fiber cords may be used. Since the PET fiber cord has higher elasticity than the nylon 66 fiber cord, when this is used as the belt cover cord, the rigidity of the tread portion of the pneumatic tire increases and the handling stability improves. However, since the PET fiber cord is likely to generate heat, there is a concern that the durability deteriorates.

[0004] On the other hand, in a pneumatic tire, when a high-angle belt structure in which the cord angle of the belt layer with respect to the tire circumferential direction is set large is adopted, it is known to be advantageous from the viewpoints of low heat generation, weight reduction, and riding comfort. Therefore, in recent years, the demand for the high-angle belt structure has been increasing. However, in the case of the high-angle belt structure, there is a problem that the cornering power of the pneumatic tire decreases and the handling stability deteriorates.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-68374 [Patent Document 2] Japanese Patent Publication No. 2023-68375 [Patent Document 3] Japanese Patent Publication No. 2023-68376 [Patent Document 4] Japanese Patent Publication No. 2023-68377 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide a pneumatic tire that improves handling stability while maintaining good durability and rolling resistance. [Means for solving the problem]

[0007] The pneumatic tire of the present invention for achieving the above objective comprises a tread portion extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged radially inward of these sidewall portions, a carcass layer mounted between these pair of bead portions, a plurality of belt layers arranged on the outer circumference of the carcass layer in the tread portion, in which belt cords intersect each other between the layers, and a belt cover layer including belt cover cords oriented in the circumferential direction of the tire arranged on the outer circumference of the belt layers, The belt cover cord is a polyester fiber cord having an elongation of 2.0% to 4.0% under a 2.0 cN / dtex load, and the peak temperature of the loss modulus E'' of the polyester fiber cord, measured at a frequency of 20 Hz, initial load of 300 g, strain of ±0.1%, and heating rate of 2 °C / min, is 115 °C or higher and the peak value is 12,000 MPa or lower. The aforementioned belt layer is characterized by having a cord angle with respect to the tire circumferential direction that is in the range of 27° to 40°. [Effects of the Invention]

[0008] The inventors of the present invention conducted extensive research on the belt layer and belt cover layer of pneumatic tires and discovered that by employing a high-angle belt structure for the belt layer and using polyester fiber cords with specific physical properties for the belt cover cord of the belt cover layer, it is possible to complement each other's shortcomings while maximizing the advantages of both, leading to the present invention.

[0009] In other words, in this invention, by using a highly elastic polyester fiber cord as the belt cover cord, excellent handling stability can be achieved even when a high-angle belt structure is adopted for the belt layer. Furthermore, by setting the elongation, peak temperature, and peak value of the polyester fiber cord at a load of 2.0 cN / dtex within the above range, heat generation of the polyester fiber cord can be suppressed, and deterioration of durability can be suppressed. Moreover, the high-angle belt structure contributes to reducing heat generation in pneumatic tires. As a result, it becomes possible to improve handling stability while maintaining good durability and rolling resistance of pneumatic tires.

[0010] In the present invention, it is preferable that the belt cord has a 1x2 structure. When a belt cord with a 1x2 structure is used, the thickness of the belt layer can be reduced, resulting in a greater weight reduction effect and thus reducing rolling resistance. In this case, the thickness of the belt layer should preferably be 1.05 mm or less.

[0011] Furthermore, in the present invention, it is preferable that the belt cord has a 2+2 structure. Even when a belt cord with a 2+2 structure is used, the belt layer is sufficiently thinned, ensuring a weight reduction effect, and thus the rolling resistance is good. In this case, the thickness of the belt layer is preferably 1.25 mm or less.

[0012] In this invention, the cord angle of the belt layer with respect to the tire circumferential direction is preferably in the range of 30° to 35°. When the cord angle of the belt layer is within this range, the balance between handling stability, durability, and rolling resistance is optimized.

[0013] In this invention, the elongation under a 2.0 cN / dtex load is the elongation rate (%) of the sample cord measured under a 2.0 cN / dtex load, in accordance with JIS-L1017 "Test Method for Chemical Fiber Tire Cords," by conducting a tensile test under the conditions of a gripping distance of 250 mm and a tensile speed of 300 ± 20 mm / min. The loss modulus E" is the loss modulus E" (MPa) of the sample cord measured under JIS-K6394 "Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Dynamic Properties," by a frequency of 20 Hz, an initial load of 300 g, a strain of ±0.1%, and a heating rate of 2 °C / min. The loss modulus E" is measured, for example, in a temperature range of 0 °C to 200 °C. [Brief explanation of the drawing]

[0014] [Figure 1] This is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. [Figure 2] Figure 1 is an unfolded view showing the belt layer and belt cover layer of the pneumatic tire, extracted from the original figure. [Figure 3] Figure 1 is a graph showing the temperature dispersion of the loss modulus E'' of the polyester fiber cord used in the belt cover layer of a pneumatic tire. [Figure 4] (a) and (b) are cross-sectional views showing the belt layer of the pneumatic tire in Figure 1, respectively. [Modes for carrying out the invention]

[0015] The configuration of the present invention will be described in detail below with reference to the attached drawings. Figures 1 and 2 show a pneumatic tire according to an embodiment of the present invention.

[0016] As shown in Figure 1, the pneumatic tire of this embodiment comprises a tread portion 1 that extends in the circumferential direction of the tire and forms an annular shape, a pair of sidewall portions 2, 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3, 3 arranged radially inward of these sidewall portions 2.

[0017] A carcass layer 4 is mounted between a pair of bead portions 3, 3. This carcass layer 4 includes a plurality of carcass cords extending in the tire radial direction, and is folded back from the inner side to the outer side of the tire around a bead core 5 disposed in each bead portion 3. As the carcass cords of the carcass layer 4, organic fiber cords such as polyester fiber cords are preferably used. A bead filler 6 made of a rubber composition having a triangular cross-section is disposed on the outer periphery of the bead core 5.

[0018] On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 include a plurality of belt cords 7C inclined with respect to the tire circumferential direction, and are arranged such that the belt cords 7C cross each other between the layers. As the belt cords 7C of the belt layer 7, steel cords are preferably used.

[0019] On the outer peripheral side of the belt layer 7, a belt cover layer 8 is disposed which is formed by arranging belt cover cords 8C at an angle of, for example, 5° or less with respect to the tire circumferential direction for the purpose of improving high-speed durability. As the belt cover layer 8, a full cover layer covering the entire width direction of the belt layer 7, or a pair of edge cover layers locally covering both ends in the tire width direction of the belt layer 7 can be provided individually or in combination. The belt cover layer 8 can be configured, for example, as shown in FIG. 2, by spirally winding a strip material 10 in which at least one belt cover cord 8C is aligned and covered with coating rubber in the tire circumferential direction.

[0020] Note that the above-described tire internal structure shows a typical example in a pneumatic tire, but is not limited thereto.

[0021] In the pneumatic tire described above, as shown in Figure 2, the cord angle θ of the belt layer 7 with respect to the tire circumferential direction is set in the range of 27° to 40°. That is, the pneumatic tire has a high-angle belt structure. On the other hand, the belt cover cord 8C constituting the belt cover layer 8 uses a polyester fiber cord having an elongation in the range of 2.0% to 4.0% under a 2.0 cN / dtex load. As the polyester fiber cord, for example, polyethylene terephthalate (PET) fiber cord is preferably used. The PET fiber cord may be composed of at least part or all of recycled polyethylene terephthalate fibers. As shown in Figure 3, the polyester fiber cord has physical properties such that the peak temperature of the loss modulus E'' measured at a frequency of 20 Hz, an initial load of 300 g, a strain of ±0.1%, and a heating rate of 2°C / min is 115°C or higher, and its peak value is 12000 MPa or lower. The higher the crystallinity of the polyester fiber cord, the higher the peak temperature of the loss modulus E'' and the lower its peak value tends to be.

[0022] As described above, by using a highly elastic polyester fiber cord as the belt cover cord 8C of the belt cover layer 8, excellent handling stability can be achieved even when a high-angle belt structure is adopted for the belt layer 7. Furthermore, by setting the elongation, loss modulus E'' peak temperature, and peak value of the polyester fiber cord under a 2.0 cN / dtex load within the above range, heat generation of the polyester fiber cord can be suppressed, and deterioration of durability can be prevented. Moreover, the high-angle belt structure contributes to reducing heat generation in pneumatic tires. This makes it possible to improve handling stability while maintaining good durability and rolling resistance of pneumatic tires.

[0023] Here, if the elongation of the polyester fiber cord used as belt cover cord 8C under a 2.0 cN / dtex load is less than 2.0%, the polyester fiber cord becomes more prone to fatigue fracture, reducing the durability of the pneumatic tire. Conversely, if it is greater than 4.0%, the belt layer 7 will rise more during high-speed driving, reducing high-speed durability. If the peak temperature of the loss modulus E'' of the polyester fiber cord used as belt cover cord 8C is lower than 115°C, the polyester fibers have a loose amorphous structure, making them more susceptible to amine degradation, reducing the durability of the pneumatic tire. If the peak value of the loss modulus E'' of the polyester fiber cord used as belt cover cord 8C is greater than 12000 MPa, the heat generation of the polyester fiber cord increases, reducing the durability of the pneumatic tire.

[0024] Furthermore, if the cord angle θ of the belt layer 7 with respect to the tire circumferential direction is less than 27°, rolling resistance will worsen and cord separation due to heat generation will be induced. Conversely, if it is greater than 40°, the cornering power of the pneumatic tire will decrease and handling stability will deteriorate. In particular, the cord angle θ of the belt layer 7 with respect to the tire circumferential direction should be in the range of 30° to 38°, more preferably in the range of 30° to 35°. In this case, the balance between handling stability, durability, and rolling resistance is optimized. The cord angle θ of the belt layer 7 can be measured at the center of a cut sample of the tire. At that time, the cord angles of the first belt layer 7 and the second belt layer 7, counting from the carcass layer 4 side, are measured, and the average value is taken as the cord angle θ of the belt layer 7.

[0025] In the above-described pneumatic tire, as shown in Figure 4(a), the belt layer 7 is composed of belt cords 7C and a coating rubber 7R covering them. The belt cords 7C preferably have a 1x2 structure. The 1x2 structure is a structure in which two steel filaments 7F are twisted together. When belt cords 7C with a 1x2 structure are used, the belt layer 7 can be made thinner, resulting in a greater weight reduction effect and thus reducing rolling resistance. In this case, the thickness T of the belt layer 7 should preferably be 1.05 mm or less. This reduces the weight of the belt layer 7, thereby reducing the rolling resistance of the pneumatic tire. The thickness T of the belt layer 7 can be determined by measuring the distance between the centers of the belt cords 7C of the two stacked belt layers 7.

[0026] In the above-described pneumatic tire, the belt cord 7C may have a 2+2 structure, as shown in Figure 4(b). The 2+2 structure has an inner layer consisting of two steel filaments 7F and an outer layer consisting of two steel filaments 7F twisted around the inner layer. The two steel filaments 7F that make up the inner layer may be twisted together or may not be twisted. Even when a belt cord 7C with a 2+2 structure is used, the belt layer 7 is sufficiently thinned, ensuring a weight reduction effect, and thus the rolling resistance is improved. In this case, the thickness T of the belt layer 7 should be 1.25 mm or less. As a result, the weight of the belt layer 7 is reduced, and the rolling resistance of the pneumatic tire can be reduced.

[0027] As described above, the belt cord 7C preferably has a 1x2 structure or a 2+2 structure from the viewpoint of weight reduction and, consequently, the viewpoint of reducing rolling resistance, but other twisted structures can also be adopted. In any case, the thickness T of the belt layer 7 is preferably 1.25 mm or less, more preferably 1.05 mm or less. The thickness T of the belt layer 7 can be measured at the center of a cut sample of the tire. In this case, the distance between the cord centers of the first belt layer 7 and the second belt layer 7, counted from the carcass layer 4 side, is defined as the thickness T of the belt layer 7.

[0028] Furthermore, the total fineness D of the polyester fiber cord used as the belt cover cord 8C should ideally be in the range of 1000 dtex to 4500 dtex. By setting the total fineness D of the polyester fiber cord used as the belt cover cord 8C within the above range, the characteristics of the belt cover layer 8 can be optimized. Here, if the total fineness D is less than 1000 dtex, the belt layer 7 will rise up more during high-speed driving, reducing high-speed durability. Conversely, if it exceeds 4500 dtex, the belt cover layer 8 will become thicker, increasing tire weight and potentially worsening rolling resistance. [Examples]

[0029] In a pneumatic tire with a tire size of 245 / 40R18, comprising a tread section, a pair of sidewall sections, and a pair of bead sections, with a carcass layer mounted between these pair of bead sections, multiple belt layers arranged on the outer circumference of the carcass layer in the tread section, with belt cords intersecting each other between the layers, and a belt cover layer including belt cover cords oriented in the circumferential direction of the tire arranged on the outer circumference of the belt layers, tires of the Conventional Example, Comparative Examples 1-11 and Examples 1-15 were manufactured with the following settings: the cord material of the belt cover layer, the peak temperature and peak value of the loss modulus of elasticity E'' of the cords of the belt cover layer, the elongation of the cords of the belt cover layer under a 2.0 cN / dtex load, the cord structure of the belt layer, the thickness of the belt layer, and the cord angle of the belt layer.

[0030] Regarding the cord material of the belt cover layer, if nylon 66 fiber cord is used, it is indicated as "N66," and if polyethylene terephthalate fiber cord is used, it is indicated as "PET."

[0031] These test tires were evaluated for high-speed handling stability, high-speed durability, and rolling resistance using the evaluation method described below, and the results are shown in Tables 1 to 4.

[0032] High-speed handling stability: Each test tire was mounted on a wheel with a rim size of 18 x 7.0J, and fitted to a 2000cc FR passenger car with an air pressure of 200kPa. Five trained test drivers drove the car on a test course at speeds exceeding 120km / h, and subjective evaluations of handling stability were conducted. The evaluation results were presented as a relative evaluation to previous examples, scored on a 5-point scale, and shown as the average score of the three drivers after excluding the highest and lowest scores. A higher score indicates better high-speed handling stability.

[0033] Fast durability: Each test tire was mounted on a wheel with a rim size of 18 x 7.0J, and the air pressure was set to 220kPa. The tire was then mounted on a drum testing machine with a smooth steel drum surface and a diameter of 1707mm, and a running test was conducted while controlling the ambient temperature to 38±3℃. In the running test, the tire was driven for 20 minutes at an initial speed of 120km / h and a load of 88% of the JATMA maximum load. After completing the run, the speed was increased by 10km / h and the tire was driven for another 20 minutes. This process of increasing speed and driving for 20 minutes was repeated without interruption until the tire failed, and the total distance traveled until failure was measured. The evaluation results are shown as an index with the conventional example set to 100. A higher index value indicates better high-speed durability. An index value of 95 or higher satisfies the acceptable level.

[0034] Rolling resistance: Each test tire was mounted on a wheel with a rim size of 18 x 7.0J, inflated to 200kPa, and placed on a drum testing machine with a smooth steel drum surface and a diameter of 1707mm. The rolling resistance was measured while the machine was driven at a speed of 80km / h with a load equivalent to 85% of the JATMA maximum load applied and pressed against the drum. The evaluation results are shown as an index with the conventional example set to 100. A smaller index value indicates lower rolling resistance. An index value of 101 or less satisfies the acceptable level.

[0035] [Table 1]

[0036] [Table 2]

[0037] [Table 3]

[0038] [Table 4]

[0039] As can be seen from Tables 1 to 4, the tires of Examples 1 to 15 all improved high-speed handling stability while maintaining good high-speed durability and rolling resistance compared to conventional examples that used nylon fiber cord as the belt cover cord.

[0040] On the other hand, in the tire of Comparative Example 1, while nylon 66 fiber cord was used as the belt cover cord, a high-angle belt structure was adopted, resulting in reduced high-speed handling stability and decreased high-speed durability due to belt layer lifting. In the tires of Comparative Examples 2 and 7, while PET fiber cord was used as the belt cover cord, a low-angle belt structure was adopted, resulting in worsening rolling resistance and decreased high-speed durability due to belt edge separation caused by heat generation. In the tires of Comparative Examples 3 and 8, the cord angle of the belt layer was too large, resulting in decreased high-speed durability due to belt layer lifting. In the tires of Comparative Examples 4 and 9, the elongation of the polyester fiber cord used as the belt cover cord under a 2.0 cN / dtex load was too small, resulting in decreased high-speed durability due to cord fatigue fracture. In the tires of Comparative Examples 5 and 10, the peak temperature of the loss modulus E'' of the polyester fiber cord used as the belt cover cord was too low, resulting in reduced high-speed durability due to fatigue fracture of the cord. In the tires of Comparative Examples 6 and 11, the peak value of the loss modulus E'' of the polyester fiber cord used as the belt cover cord was too high, causing belt edge separation due to heat generation, resulting in reduced high-speed durability. [Explanation of Symbols]

[0041] 1. Tread section 2 Sidewall section 3. Bead section 4. Carcass layer 5 Bead core 6. Bead Filler 7 Belt layer 7C Belt Cord 7R coated rubber 7F Steel Filament 8 Belt cover layer 8C Belt Cover Cord 10 strip material

Claims

1. In a pneumatic tire comprising a tread portion extending in the circumferential direction of the tire and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged radially inward of these sidewall portions, a carcass layer mounted between these pair of bead portions, a plurality of belt layers arranged on the outer circumference of the carcass layer in the tread portion, in which belt cords intersect each other between the layers, and a belt cover layer including belt cover cords oriented in the circumferential direction of the tire arranged on the outer circumference of the belt layers, The belt cover cord is a polyester fiber cord having an elongation of 2.0% to 4.0% under a 2.0 cN / dtex load, and the peak temperature of the loss modulus E'' of the polyester fiber cord, measured at a frequency of 20 Hz, initial load of 300 g, strain of ±0.1%, and heating rate of 2°C / min, is 115°C or higher and the peak value is 12000 MPa or lower. A pneumatic tire characterized in that the cord angle of the belt layer with respect to the tire circumferential direction is in the range of 27° to 40°.

2. The pneumatic tire according to claim 1, characterized in that the belt cord has a 1x2 structure.

3. The pneumatic tire according to claim 2, characterized in that the thickness of the belt layer is 1.05 mm or less.

4. The pneumatic tire according to claim 1, characterized in that the belt cord has a 2+2 structure.

5. The pneumatic tire according to claim 4, characterized in that the thickness of the belt layer is 1.25 mm or less.

6. The pneumatic tire according to any one of claims 1 to 5, characterized in that the cord angle of the belt layer with respect to the tire circumferential direction is in the range of 30° to 35°.

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