Pneumatic tire

Abstract

The invention provides a pneumatic tire capable of improving driving stability while maintaining good durability and rolling resistance. The pneumatic tire is provided with a tread portion (1), a pair of side wall portions (2), and a pair of bead portions (3), a carcass layer (4) is spanned between the pair of bead portions (3, 3), a plurality of layers of belt layers (7) in which belt layer cords intersect each other between the layers are disposed on the outer peripheral side of the carcass layer (4) of the tread portion (1), and a cover layer (8) including cover layer cords (8C) oriented in the tire circumferential direction is disposed on the outer peripheral side of the belt layers (7). Wherein the cover layer cord (8C) is a polyester fiber cord having an elongation in the range of 2.0-4.0% under a load of 2.0 cN / dtex, and the loss elastic modulus E ''of the polyester fiber cord when measured at a frequency of 20 Hz, an initial load of 300 g, a strain of + / -0.1%, and a temperature increase rate of 2 DEG C / min has a peak temperature of 115 DEG C or more and a peak value of 12000 MPa or less. The cord angle theta of the belt layer (7) with respect to the tire circumferential direction is in the range of 27 DEG to 40 DEG.

Description

TECHNICAL FIELD

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

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

[0003] As a cover layer cord for a pneumatic tire for a passenger car and a light truck, a nylon 66 fiber cord is mainstream, but a polyester fiber cord typified by a polyethylene terephthalate (PET) fiber cord is sometimes used. Since the PET fiber cord is higher in elasticity than the nylon 66 fiber cord, when it is used as a cover layer cord, the rigidity of the tread portion of the pneumatic tire becomes high, and the driving stability improves. However, since the PET fiber cord easily generates heat, there is a concern that the durability deteriorates.

[0004] On the other hand, it is known that in the case of a high-angle belt structure in which the cord angle of the belt layer with respect to the tire circumferential direction is set to be large in a pneumatic tire, it is advantageous in terms of heat reduction, weight reduction, and ride comfort. Therefore, in recent years, the demand for high-angle belt structures has increased. However, in the case of a high-angle belt structure, there is a problem that the cornering stiffness of the pneumatic tire decreases, and the driving stability deteriorates.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2023-68374

[0008] [Patent Document 2] Japanese Patent Application Laid-Open No. 2023-68375

[0009] [Patent Document 3] Japanese Patent Application Laid-Open No. 2023-68376

[0010] [Patent Document 4] Japanese Patent Application Laid-Open No. 2023-68377 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] An object of the present application is to provide a pneumatic tire capable of improving driving stability while maintaining durability and rolling resistance in good condition.

[0013] Technical means for solving the problem

[0014] The pneumatic tire of the present application for achieving the above object has a tread portion extending in a tire circumferential direction in a ring shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the tire radial direction inner side of the sidewall portions, a carcass layer is erected between the pair of bead portions, a plurality of belt layers in which belt layer cords intersect each other between layers are disposed on the outer peripheral side of the carcass layer of the tread portion, a cap layer including cap layer cords oriented in the tire circumferential direction is disposed on the outer peripheral side of the belt layer,

[0015] The pneumatic tire is characterized in that the cap layer cords are polyester fiber cords having an elongation at a load of 2.0 cN / dtex in a range of 2.0% to 4.0%, a peak temperature of a loss elastic modulus E" of the polyester fiber cords is 115°C or higher and a peak value is 12000 MPa or lower when measured at a frequency of 20 Hz, an initial load of 300 g, a strain of ±0.1%, and a temperature increase rate of 2°C / minute,

[0016] The belt layer has a cord angle with respect to the tire circumferential direction in a range of 27° to 40°.

[0017] Effects of the invention

[0018] The present inventors have intensively studied a belt layer and a cap layer of a pneumatic tire, and as a result, have found that by using a high-angle belt structure for the belt layer and using polyester fiber cords having specific properties for the cap layer cords of the cap layer, the shortcomings of the two can be compensated for each other while the advantages of the two are maximized, thereby completing the present application.

[0019] That is, in the present application, by using polyester fiber cords having high elasticity as the cap layer cords, even in the case where a high-angle belt structure is used for the belt layer, excellent driving stability can be achieved. In addition, by setting the elongation at a load of 2.0 cN / dtex, the peak temperature of the loss elastic modulus E", and the peak value of the polyester fiber cords in the above ranges, the polyester fiber cords can be inhibited from generating heat, and durability can be inhibited from deteriorating. Furthermore, the high-angle belt structure contributes to reducing the heat generation of the pneumatic tire. Thus, it is possible to improve the driving stability while maintaining the durability and the rolling resistance of the pneumatic tire in good condition.

[0020] In the present application, the belt layer cords preferably have a 1x2 structure. In the case where the belt layer cords having a 1x2 structure are used, the thickness of the belt layer can be reduced, and the weight reduction effect is enhanced, so that the rolling resistance can be reduced. In this case, the thickness of the belt layer is preferably 1.05 mm or less.

[0021] In addition, in the present application, the belt cord preferably has a 2+2 structure. In the case where the belt cord having a 2+2 structure is used, the belt is also sufficiently thin-walled, ensuring a lightweight effect, and thus the rolling resistance is good. In this case, the thickness of the belt is preferably 1.25 mm or less.

[0022] In the present application, the cord angle of the belt with respect to the tire circumferential direction is preferably in the range of 30° to 35°. In the case where the cord angle of the belt is in the above range, the balance of the driving stability, the durability, and the rolling resistance is optimized.

[0023] In the present application, the elongation at 2.0 cN / dtex load is the elongation (%) of the sample cord measured at a load of 2.0 cN / dtex under the conditions of a clamping interval of 250 mm and a tensile speed of 300 ± 20 mm / minute, in accordance with "Test method for tire cord made of chemical fiber" of JIS-L1017. The loss elastic modulus E" is the loss elastic modulus E" (MPa) of the test sample cord measured at a frequency of 20 Hz, an initial load of 300 g, a strain of ±0.1%, and a temperature increase rate of 2°C / minute, in accordance with "Method for determining dynamic properties of vulcanized rubber and thermoplastic rubber" of JIS-K6394. The loss elastic modulus E" is measured, for example, in the temperature range of 0°C to 200°C. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a meridional sectional view showing a pneumatic tire constituted by the embodiment of the present application.

[0025] Figure 2 is an expanded view extracting and showing the belt and the cover of the pneumatic tire of Figure 1

[0026] Figure 3 is a graph showing the temperature dispersion of the loss elastic modulus E" of the polyester cord used in the cover of the pneumatic tire of Figure 1

[0027] Figure 4 (a), (b) are sectional views respectively showing the belt of the pneumatic tire of Figure 1 DETAILED DESCRIPTION

[0028] Hereinafter, the constitution of the present application is explained in detail with reference to the drawings. Figure 1 and Figure 2 are graphs showing a pneumatic tire constituted by the embodiment of the present application.

[0029] As Figure 1 ​​​As shown, the pneumatic tire of this embodiment includes a tread portion 1 extending along the tire circumference and formed in an annular shape, a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3, 3 disposed on the radially inner side of these sidewall portions 2.

[0030] A carcass layer 4 is provided between a pair of bead portions 3, 3. This carcass layer 4 comprises multiple ply cords extending radially along the tire and folded from the inside to the outside of the tire around the bead core 5 disposed in each bead portion 3. Organic fiber cords, such as polyester fiber cords, are preferably used as the ply cords of the carcass layer 4. A sidewall core 6, with a triangular cross-section and made of a rubber composition, is disposed on the outer periphery of the bead core 5.

[0031] On the other hand, multiple belt layers 7 are embedded on the outer periphery of the carcass layer 4 in the tread portion 1. These belt layers 7 are configured to contain multiple belt layer cords 7C inclined relative to the tire circumferential direction, and the belt layer cords 7C intersect each other between layers. Steel cords are preferably used as the belt layer cords 7C of the belt layer 7.

[0032] To improve high-speed durability, a cover layer 8 is provided on the outer periphery of the belt layer 7. This cover layer 8 is formed by arranging the cover layer cords 8C at an angle of, for example, 5° or less relative to the tire circumferential direction. The cover layer 8 can be a full cover layer covering the entire width of the belt layer 7, or a pair of edge cover layers partially covering both ends of the belt layer 7 in the tire width direction, or a combination thereof. Figure 2 As shown, the strip profile 10 is formed by spirally winding it around the tire circumference. The strip profile 10 is formed by pulling at least one covered cord 8C together and covering it with a rubber coating.

[0033] It should be noted that the above description of the internal structure of a tire shows a representative example of a pneumatic tire, but is not limited to it.

[0034] In the aforementioned pneumatic tires, such as Figure 2 As shown, the cord angle θ of the belt layer 7 relative to the tire circumference is set in the range of 27° to 40°. That is, the above-mentioned pneumatic tire has a high-angle belt structure. On the other hand, the belt layer cord 8C constituting the cover layer 8 uses polyester fiber cord with an elongation in the range of 2.0% to 4.0% under a load of 2.0 cN / dtex. As polyester fiber cord, polyethylene terephthalate (PET) fiber cord is preferably used, for example. At least part or all of the PET fiber cord can be composed of recycled polyethylene terephthalate fibers. Figure 3The polyester fiber cord has the following properties: the peak temperature of the loss elastic modulus E" is 115°C or higher and the peak value is 12000 MPa or lower when measured at a frequency of 20 Hz, an initial load of 300 g, a strain of ±0.1%, and a temperature increase rate of 2°C / minute. The polyester fiber cord has a tendency that the higher the crystallinity, the higher the peak temperature of the loss elastic modulus E" and the lower the peak value.

[0035] As described above, by using the polyester fiber cord having high elasticity as the belt cover layer cord 8C of the belt cover layer 8, even in the case where the belt layer 7 adopts a high angle belt structure, excellent driving stability can be exhibited. Further, by setting the elongation at a load of 2.0 cN / dtex, the peak temperature of the loss elastic modulus E", and the peak value of the polyester fiber cord within the above ranges, the polyester fiber cord can be inhibited from generating heat, and deterioration in durability can be inhibited. Moreover, the high angle belt layer structure contributes to reduction in heat generation of the pneumatic tire. Thus, it is possible to improve the driving stability while maintaining the durability and the rolling resistance of the pneumatic tire in good condition.

[0036] Here, if the elongation at a load of 2.0 cN / dtex of the polyester fiber cord used as the belt cover layer cord 8C is less than 2.0%, the polyester fiber cord is easily fatigued and broken, and the durability of the pneumatic tire is reduced, whereas if it is more than 4.0%, the bulging of the belt layer 7 during high speed running increases, and the high speed durability is reduced. If the peak temperature of the loss elastic modulus E" of the polyester fiber cord used as the belt cover layer cord 8C is less than 115°C, the polyester fiber has a loose amorphous structure, and thus is easily subjected to amine deterioration, and the durability of the pneumatic tire is reduced. If the peak value of the loss elastic modulus E" of the polyester fiber cord used as the belt cover layer cord 8C is more than 12000 MPa, the polyester fiber cord is high in heat generation, and the durability of the pneumatic tire is reduced.

[0037] Further, if the cord angle θ of the belt layer 7 with respect to the tire circumferential direction is less than 27°, the rolling resistance is deteriorated, and separation of the cord due to heat generation is induced, whereas if it is more than 40°, the cornering stiffness of the pneumatic tire is reduced, and the driving stability is deteriorated. In particular, it is preferable that the cord angle θ of the belt layer 7 with respect to the tire circumferential direction be within a range of 30° to 38°, and more preferably within a range of 30° to 35°. In this case, the balance of the driving stability, the durability, and the rolling resistance is optimized. Note that the cord angle θ of the belt layer 7 can be measured at the center portion of a shear sample of the tire. At this time, the cord angles of the first layer belt layer 7 and the second layer belt layer 7 counted from the side of the carcass layer 4 are measured respectively, and the average value thereof is set as the cord angle θ of the belt layer 7.

[0038] In the above pneumatic tire, as Figure 4(a) shown, the belt 7 is composed of the belt cord 7C and the cover rubber 7R covering the belt cord 7C. The belt cord 7C preferably has a 1 x 2 structure. The 1 x 2 structure is a structure in which two steel filaments 7F are twisted with each other. In the case where the belt cord 7C having the 1 x 2 structure is used, the thinning of the belt 7 can be achieved, and the effect of weight reduction is enhanced, so that the rolling resistance can be reduced. In this case, the thickness T of the belt 7 is preferably 1.05 mm or less. Thus, the belt 7 is lightened, so that the rolling resistance of the pneumatic tire can be reduced. Note that the thickness T of the belt 7 can be found by measuring the distance between the centers of the belt cords 7C of the two layers of the belt 7 stacked.

[0039] In the above pneumatic tire, as shown in Figure 4 (b) shown, the belt cord 7C can also have a 2 + 2 structure. The 2 + 2 structure is a structure having an inner layer composed of two steel filaments 7F and an outer layer composed of two steel filaments 7F twisted around the inner layer. The two steel filaments 7F constituting the inner layer can be twisted with each other, or can not be twisted. In the case where the belt cord 7C having the 2 + 2 structure is used, the belt 7 is also sufficiently thinned, and the effect of weight reduction is ensured, so that the rolling resistance is good. In this case, the thickness T of the belt 7 is preferably 1.25 mm or less. Thus, the belt 7 is lightened, so that the rolling resistance of the pneumatic tire can be reduced.

[0040] As described above, from the viewpoint of weight reduction, and further from the viewpoint of reduction of the rolling resistance, the belt cord 7C preferably has a 1 x 2 structure or a 2 + 2 structure, but other twisted structures can also be employed. In any case, the thickness T of the belt 7 is desirably 1.25 mm or less, and more desirably 1.05 mm or less. Note that the thickness T of the belt 7 can be measured at the center portion of a shear sample of the tire. At this time, the distance between the centers of the cords of the first belt 7 and the second belt 7 counted from the side of the carcass layer 4 is set as the thickness T of the belt 7.

[0041] Further, the total fineness D of the polyester fiber cord used as the cap ply cord 8C is desirably in the range of 1000 dtex to 4500 dtex. By setting the total fineness D of the polyester fiber cord used as the cap ply cord 8C in the above range, respectively, the characteristics of the cap ply 8 can be optimized. Here, if the total fineness D is less than 1000 dtex, the bulging of the belt 7 at high speed increases, and the durability at high speed decreases, and on the contrary, if it exceeds 4500 dtex, the cap ply 8 becomes thick, and thus the weight of the tire increases, and the rolling resistance can be deteriorated.

[0042] [Example]

[0043] Tires of the conventional example, Comparative Examples 1 to 11, and Examples 1 to 15 were manufactured, which were pneumatic tires having a tire size of 245 / 40R18, provided with a tread portion, a pair of sidewall portions, and a pair of bead portions, a carcass layer interposed between the pair of bead portions, a plurality of belt layers in which belt layer cords cross each other between layers arranged on the outer peripheral side of the carcass layer of the tread portion, and an under cover layer including under cover layer cords oriented in the tire circumferential direction arranged on the outer peripheral side of the belt layers, and the cord material of the under cover layer, the peak temperature and peak value of the loss elastic modulus E" of the cords of the under cover layer, the elongation of the cords of the under cover layer under a load of 2.0 cN / dtex, the cord structure of the belt layers, the thickness of the belt layers, and the cord angle of the belt layers were set as shown in Tables 1 to 4.

[0044] As for the material of the under cover layer cords, the case where nylon 66 fiber cords were used is shown as "N66", and the case where polyethylene terephthalate fiber cords were used is shown as "PET".

[0045] For these test tires, the high-speed driving stability, high-speed durability, and rolling resistance were evaluated by the following evaluation methods, and the results are shown in Tables 1 to 4.

[0046] High-speed driving stability:

[0047] Each test tire was assembled on a wheel having a rim size of 18 x 7.0J, and the air pressure was set to 200 kPa, and mounted on a FR passenger car having a displacement of 2000 cc, and a trained test driver drove at a speed of 120 km / h or more on a test course, and the driving stability was evaluated by the senses. As a relative evaluation with respect to the conventional example, the evaluation results were expressed by the average score of 3 people excluding the highest score and the lowest score, and the score was given on a 5-point scale. The larger the score, the more excellent the high-speed driving stability.

[0048] High-speed durability:

[0049] Each test tire was assembled on a wheel having a rim size of 18 x 7.0J, and the air pressure was set to 220 kPa, and mounted on a drum tester having a smooth drum surface and a diameter of 1707 mm, and a driving test was performed while controlling the environmental temperature to 38 ± 3°C. In the driving test, the initial speed was set to 120 km / h, and the load was set to 88% of the JATMA maximum load, and driving was performed for 20 minutes, and after driving the full course, the speed was increased by only 10 km / h to continue driving for 20 minutes. This was repeated without interruption, and the test was continued until the tire was broken, and the total distance of driving before the breakage was measured. The evaluation results were expressed as an index of 100 for the conventional example. The larger the index value, the more excellent the high-speed durability. Note that if the index value is 95 or more, the permissible level is satisfied.

[0050] Rolling resistance:

[0051] Each test tire was assembled on a wheel having a rim size of 18 x 7.0J, and the air pressure was set to 200 kPa. The test tire was mounted on a drum tester having a smooth drum surface and a diameter of 1707 mm, and the rolling resistance was measured at a speed of 80 km / h under a condition where the tire was pressed against the drum with a load corresponding to 85% of the maximum load according to JATMA. The evaluation results were expressed as an index of 100 for the conventional example. The smaller the index value, the smaller the rolling resistance. Note that the index value was required to be 101 or less to satisfy the permissible level.

[0052] [Table 1]

[0053]

[0054] [Table 2]

[0055]

[0056] [Table 3]

[0057]

[0058] [Table 4]

[0059]

[0060] As is apparent from Tables 1 to 4, the tires of Examples 1 to 15 all improved the high-speed driving stability while maintaining the high-speed durability and the rolling resistance as compared with the conventional example using nylon fiber cords as the belt cover cords.

[0061] On the other hand, the tire of Comparative Example 1, although using a nylon 66 fiber cord as the belt cover cord, adopts a high cord angle belt structure, and thus the high speed driving stability is reduced, and the high speed durability is reduced due to the belt cord rise. The tires of Comparative Examples 2 and 7, although using a PET fiber cord as the belt cover cord, adopt a low cord angle belt structure, and thus the rolling resistance is deteriorated, and the belt edge separation due to heat generation occurs, and the high speed durability is reduced. In the tires of Comparative Examples 3 and 8, the cord angle of the belt cord is too large, and thus the high speed durability is reduced due to the belt cord rise. In the tires of Comparative Examples 4 and 9, the polyester fiber cord used as the belt cover cord has an elongation at 2.0 cN / dtex load that is too small, and thus the high speed durability is reduced due to the cord fatigue fracture. In the tires of Comparative Examples 5 and 10, the polyester fiber cord used as the belt cover cord has a peak temperature of the loss elastic modulus E" that is too low, and thus the high speed durability is reduced due to the cord fatigue fracture. In the tires of Comparative Examples 6 and 11, the polyester fiber cord used as the belt cover cord has a peak of the loss elastic modulus E" that is too high, and thus the belt edge separation due to heat generation occurs, and the high speed durability is reduced.

[0062] BRIEF DESCRIPTION OF DRAWINGS

[0063] 1: tread portion

[0064] 2: sidewall portion

[0065] 3: bead portion

[0066] 4: carcass layer

[0067] 5: bead core

[0068] 6: chafer core

[0069] 7: belt layer

[0070] 7C: belt cord

[0071] 7R: cover rubber

[0072] 7F: steel filament

[0073] 8: belt cover layer

[0074] 8C: belt cover cord

[0075] 10: strip-shaped material

Claims

1. A pneumatic tire comprising: a tread portion extending in a tire circumferential direction in a ring shape; a pair of sidewall portions disposed on both sides of the tread portion; and a pair of bead portions disposed on a tire radial direction inner side of the sidewall portions; a carcass layer is erected between the pair of bead portions, a plurality of belt layers in which belt cords cross each other between layers are disposed on an outer peripheral side of the carcass layer of the tread portion, and a cap layer including cap layer cords oriented in the tire circumferential direction is disposed on an outer peripheral side of the belt layers, the cap layer cord is a polyester fiber cord having an elongation at a load of 2.0 cN / dtex within a range of 2.0% to 4.0%, a peak temperature of a loss elastic modulus E" of the polyester fiber cord is 115°C or higher and a peak value is 12,000 MPa or lower when measured at a frequency of 20 Hz, an initial load of 300 g, a strain of ±0.1%, and a temperature increase rate of 2°C / minute, and a cord angle of the belt layers with respect to the tire circumferential direction is within a range of 27° to 40°. characterized in that The belt cord has a 1 x 2 structure. The thickness of the belt layers is 1.05 mm or lower.

2. The pneumatic tire of claim 1, wherein, The belt cord has a 2 + 2 structure.

3. The pneumatic tire of claim 2, wherein, The thickness of the belt layers is 1.25 mm or lower.

4. The pneumatic tire of claim 1, wherein, The cord angle of the belt layers with respect to the tire circumferential direction is within a range of 30° to 35°.

5. The pneumatic tire of claim 4, wherein, ​ 6. The pneumatic tire of any of claims 1-5, wherein, ​

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