Pneumatic tire

Abstract

The present application provides a pneumatic tire which can improve impact burst resistance while maintaining steering stability at high speed, and which highly balances these properties. In a pneumatic tire provided with a carcass layer (4) and a belt layer (7), the carcass layer (4) contains organic fiber cords having an elongation at break of 20% to 30%, an elongation at a load of 2.0 cN / dtex at the side portion of 5.5% to 8.0%, and a product A=D×Ec of a public fineness D [unit: dtex / strand] and an implanted number of strands Ec [unit: strands / 50 mm] of 1.8×10 5 dtex / 50 mm to 3.0×10 5 dtex / 50 mm, and the belt layer contains steel cords having a breaking stress of 3300 MPa or more and a product B=S×Eb of a sectional area S [unit: mm 2 / strand] and an implanted number of strands Eb [unit: strands / 50 mm] of 6.0 mm 2 / 50 mm to 7.5 mm 2 / 50 mm.

Description

TECHNICAL FIELD

[0001] The present application relates to a pneumatic tire provided with a carcass layer including organic fiber cords. BACKGROUND

[0002] A pneumatic tire generally has a carcass layer that is erected between a pair of bead portions, and the carcass layer includes a plurality of reinforcing cords (carcass cords). As the carcass cords, organic fiber cords are mainly used. In particular, in a tire that requires excellent handling stability at high speed, a high-rigidity rayon fiber cord is sometimes used (for example, refer to Patent Literature 1).

[0003] On the other hand, in recent years, the demand for weight reduction and reduction of rolling resistance of a tire has increased, and the rubber thickness of a tread portion is being studied to be made thinner. However, in the case of a tire provided with a carcass layer including the above-described rayon fiber cord, with the thinning of the tread portion, the impact burst resistance can possibly decrease. Note that the impact burst resistance refers to the durability against damage (impact burst) of the carcass due to a large impact on the tire during running, and, for example, a plunger energy test (a test for measuring the breaking energy when a tire is broken by pressing a plunger of a predetermined size against the center portion of the tread) becomes an index. Therefore, in order to improve the impact burst resistance while ensuring the same performance as in the case of using a rayon fiber cord, the use of a polyester fiber cord provided with a predetermined property is being studied. However, if only such a polyester fiber cord is used instead of a rayon fiber cord, there is a problem that sufficient handling stability (high-speed handling stability) cannot necessarily be ensured due to the difference in the property thereof.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Laid-Open No. 2017-031381 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] An object of the present application is to provide a pneumatic tire that can improve the impact burst resistance while maintaining the handling stability at high speed, and highly balance these performances.

[0009] MEANS FOR SOLVING THE PROBLEMS

[0010] The pneumatic tire of the present invention for achieving the above-mentioned purpose comprises: a tread portion, the tread portion extending in a ring shape along the tire circumferential direction; a pair of sidewall portions, the pair of sidewall portions being arranged on both sides of the tread portion; and a pair of bead portions, the pair of bead portions being arranged on the radial inner side of these sidewall portions, the pneumatic tire comprising: at least one carcass layer, the at least one carcass layer being spanned between the pair of bead portions; and a multi-layer belt layer, the multi-layer belt layer being arranged on the outer peripheral side of the carcass layer at the tread portion, the pneumatic tire being characterized in that The carcass layer includes a carcass cord composed of an organic fiber cord, the breaking elongation of the carcass cord is 20% to 30%, the elongation of the carcass cord at the sidewall portion under a load of 2.0 cN / dtex is 5.5% to 8.0%, and the product A = D × Ec of the nominal fineness D (unit: dtex / cord) of each carcass cord and the number of carcass cords implanted per 50 mm in a direction perpendicular to the extension direction of the carcass cord (unit: cords / 50 mm) is 1.8 × 10 5 dtex / 50mm~3.0×10 5 dtex / 50mm, the belt layer comprises belt cords composed of steel cords, the breaking stress of the belt cords is 3300 MPa or more, and the cross-sectional area S of each belt cord [unit: mm 2 The product of the number of implanted belt cords per 50 mm in a direction perpendicular to the extending direction of the belt cords (unit: cords / 50 mm) and the number of implanted belt cords per 50 mm (unit: cords / 50 mm) is 6.0 mm. 2 / 50mm~7.5mm 2 / 50mm.

[0011] Effects of the Invention

[0012] In the present invention, the carcass cords comprising the carcass layer are polyester fiber cords having the aforementioned properties. This allows for improved high-speed handling stability, comparable to that achieved using rayon fiber cords, while also improving impact and burst resistance. Specifically, since the carcass cords have an elongation at break and an elongation at a load of 2.0 cN / dtex at the sidewall within the aforementioned ranges, they maintain appropriate carcass cord rigidity, enabling excellent high-speed handling stability. Furthermore, since the carcass cords have the aforementioned elongation at break, they easily follow local deformation and can fully tolerate deformation during a plunger energy test (when pressed by a plunger), thereby increasing the breaking energy. In other words, the carcass cords exhibit improved durability against protruding inputs from the tread during driving, thereby enhancing impact and burst resistance. Furthermore, since the product A, or the carcass cord fineness per unit width, is within the aforementioned range, both durability and braking performance are achieved, resulting in improved impact and burst resistance and high-speed handling stability. On the other hand, the belt structure described above reduces the overall strength of the belt, compensating for the disadvantages of using polyester fiber cords as the carcass cords and improving high-speed handling stability. This synergy allows for a high degree of both high-speed handling stability and impact and burst resistance.

[0013] Note that the "elongation at break" and "elongation at a load of 1.5 cN / dtex" for carcass cords (polyester fiber cords) are the elongations (%) of the sample cords measured in a tensile test conducted in accordance with JIS L1017, "Testing Methods for Chemical Fiber Tire Cords," under the conditions of a clamping gap of 250 mm and a tensile speed of 300 ± 20 mm / min. The "elongation at break" is the value measured at cord break, and the "elongation at a load of 1.5 cN / dtex" is the value measured at a load of 1.5 cN / dtex. Furthermore, the "breaking stress" for belt cords (steel cords) is the value obtained by dividing the tensile strength at cord break by the cord's cross-sectional area.

[0014] In the present invention, the belt cord preferably has an N+M structure, with the number of wires N in the inner layer being 2 to 4 and the number of wires M in the outer layer being 2 to 7. A 2+2 structure, with the number of wires N in the inner layer being 2 and the number of wires M in the outer layer being 2, is particularly preferred. Using a belt cord with such a specific structure is advantageous for optimizing the strength of the belt layer and improving high-speed steering stability.

[0015] In addition, in the above-mentioned belt cords, it is preferable that the wires constituting the inner layer are aligned in an untwisted state. By using belt cords with such a specific structure, it is advantageous to optimize the strength of the belt layer and improve high-speed steering stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1This is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention.

[0017] Figure 2 It is an explanatory diagram schematically showing the structure of a belt cord. DETAILED DESCRIPTION

[0018] Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

[0019] like Figure 1 As shown in FIG, the pneumatic tire of the present invention comprises a tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged on the inner side of the sidewall portions 2 in the tire radial direction. Figure 1 , reference symbol CL represents the tire equator. Figure 1 This is a meridian cross-sectional view and therefore is not depicted, but the tread portion 1, the sidewall portion 2, and the bead portion 3 extend in a ring shape along the tire circumferential direction, thereby constituting the basic ring-shaped structure of the pneumatic tire. Figure 1 The description is basically based on the meridian cross-sectional shape shown in the figure, but each tire component extends in the tire circumferential direction and has a ring shape.

[0020] A carcass layer 4 comprising a plurality of reinforcing cords (hereinafter referred to as carcass cords) extending in the radial direction of the tire is provided between a pair of left and right bead portions 3. A bead core 5 is embedded in each bead portion, and a bead filler 6 having a roughly triangular cross-section is arranged on the outer periphery of the bead core 5. The carcass layer 4 is folded back around the bead core 5 from the inner side to the outer side in the tire width direction. As a result, the bead core 5 and the bead filler 6 are enclosed by the main body of the carcass layer 4 (the portion extending from the tread portion 1 through each sidewall portion 2 to each bead portion 3) and the folded back portion (the portion folded back around the bead core 5 at each bead portion 3 and extending toward each sidewall portion 2).

[0021] Meanwhile, multiple (two in the illustrated example) belt layers 7 are embedded in the outer circumference of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes multiple reinforcing cords (hereinafter referred to as belt cords) that are inclined relative to the tire circumferential direction, and the belt cords are arranged so that the belt cords intersect each other between the layers. In these belt layers 7, the inclination angle of the belt cords relative to the tire circumferential direction is set, for example, in the range of 10° to 40°.

[0022] Moreover, a belt reinforcing layer 8 is provided on the outer peripheral side of the belt layer 7 for the purpose of improving high-speed durability. The belt reinforcing layer 8 contains reinforcing cords (hereinafter referred to as cover cords) oriented in the tire circumferential direction. As the cover cords, for example, organic fiber cords can be used. In the belt reinforcing layer 8, the angle of the cover cords with respect to the tire circumferential direction is set to, for example, 0° to 5°. As the belt reinforcing layer 8, a full cover layer 8a that covers the entire region of the width direction of the belt layer 7, a pair of edge cover layers 8b that partially cover both end portions of the tire width direction of the belt layer 7, or the like can be provided separately (in the example shown, both the full cover layer 8a and the edge cover layers 8b are provided). The belt reinforcing layer 8 can be formed, for example, by spirally winding a belt material in which at least one cover cord is aligned and covered with a cover rubber in the tire circumferential direction.

[0023] The present application is mainly related to the cords (carcass cords, belt cords) that constitute the above-described carcass layer 4 and belt layer 7, respectively, and thus the basic structure of the tire is not limited to the above-described structure.

[0024] In the present application, the carcass cords that constitute the carcass layer 4 are formed of polyester fiber cords in which a bundle of polyester fibers is twisted. The elongation at break of the carcass cords (polyester fiber cords) is 20% to 30%, and preferably 22% to 28%. In addition, the elongation at a load of 2.0 cN / dtex at the side portion of the carcass cords is 5.5% to 8.0%, and preferably 6.5% to 7.5%. Since the carcass cords (polyester fiber cords) having such properties are used for the carcass layer 4, it is possible to improve the impact burst resistance while ensuring good handling stability to the same extent as in the case where a conventional rayon fiber cord is used. That is, since the carcass cords have the above-described elongation characteristics, it is possible to moderately ensure the rigidity of the carcass cords and to exhibit good handling stability. In addition, since the carcass cords have the above-described elongation characteristics, the carcass cords easily follow local deformation, it is possible to sufficiently allow deformation at the time of the plunger energy test (when pressed by the plunger), and it is possible to improve the breaking energy. That is, the damage durability against the protrusion of the tread portion at the time of running is improved, and thus it is possible to improve the impact burst resistance. If the elongation at break of the carcass cords is less than 20%, it is not possible to obtain the effect of improving the impact burst resistance. If the elongation at break of the carcass cords exceeds 30%, there is a tendency for the intermediate elongation to also increase, and thus there is a possibility that the rigidity will decrease and the handling stability will decrease. If the elongation at a load of 2.0 cN / dtex is less than 5.5%, the cord rigidity becomes high, the compression strain of the rolled end portion of the carcass layer 4 at the ground contact region directly below increases, and there is a possibility that the cord will break (that is, there is a possibility that the durability will be impaired). If the elongation at a load of 2.0 cN / dtex exceeds 8.0%, it is difficult to ensure the rigidity, and it is not possible to sufficiently obtain the effect of improving the high-speed handling stability.

[0025] In the carcass layer 4, the product of the nominal fineness D (unit: dtex / cord) of each carcass cord and the number of carcass cords implanted per 50 mm in the direction perpendicular to the extending direction of the carcass cord Ec (unit: cords / 50 mm) is A = D × Ec, which is 1.8 × 10 5 dtex / 50mm~3.0×10 5 dtex / 50mm, preferably 2.2×10 5 dtex / 50mm~2.7×10 5 dtex / 50mm. The product A is the fineness of the carcass cord per unit width in the carcass layer 4. Therefore, by making it meet the above range, the durability and braking performance can be improved, which is conducive to improving the impact resistance and high-speed handling stability. If the product A is less than 1.8×10 5 dtex / 50mm, the braking performance may be deteriorated. If the product A exceeds 3.0×10 5 dtex / 50mm, the intervals between the carcass cords become narrower, making it difficult to maintain durability. It should be noted that the ranges of the above-mentioned common fineness D and the number of implanted cords Ec are not particularly limited as long as the product A satisfies the above-mentioned ranges.

[0026] Furthermore, the heat shrinkage of the carcass cord is preferably 0.5% to 2.5%, more preferably 1.0% to 2.0%. It should be noted that "heat shrinkage" refers to the dry heat shrinkage (%) of the sample cord measured after heating at 150°C for 30 minutes with a sample length of 500 mm in accordance with JIS L1017 "Test Methods for Chemical Fiber Tire Cords". By using a cord with such a heat shrinkage, it is possible to suppress the generation of kinks (twisting, bending, distortion, deformation, etc.) in the cord during vulcanization, thereby reducing durability and uniformity. In this case, if the heat shrinkage of the cord is less than 0.5%, kinks are likely to occur during vulcanization, making it difficult to maintain good durability. If the heat shrinkage of the cord exceeds 2.5%, uniformity may deteriorate.

[0027] The twist coefficient K of the carcass cord, represented by the following formula (1), is preferably 2000 to 2500, and more preferably 2100 to 2400. It should be noted that this twist coefficient K is a value for the cord after the dipping treatment. By using a cord having such a twist coefficient K, the cord fatigue resistance can be improved, thereby ensuring excellent durability. In this case, if the twist coefficient K of the cord is less than 2000, the cord fatigue resistance is reduced, making it difficult to ensure durability. If the twist coefficient K of the cord exceeds 2500, the productivity of the cord is deteriorated.

[0028] K=T×D 1 / 2 ...(1)

[0029] (Wherein, T is the twist number (re-twist number) of the cord [times / 10cm], and D is the total fineness of the cord [dtex]).

[0030] As mentioned above, the carcass cord is made of polyester fiber. As polyester fiber, polyethylene terephthalate fiber (PET fiber), polyethylene naphthalate fiber (PEN fiber), polybutylene terephthalate fiber (PBT), polybutylene naphthalate fiber (PBN) can be exemplified, and PET fiber can be preferably used. When using any fiber, according to the physical properties of each fiber, it is all conducive to a well-balanced high-speed durability and handling stability. Particularly, in the case of PET fiber, PET fiber is cheap, so it is possible to achieve low cost of pneumatic tires. In addition, it is also possible to improve the workability when manufacturing the cord.

[0031] In the present invention, Figure 2 As shown, the belt cord 7C constituting the belt layer 7 has an N+M structure (a 2+2 structure in the illustrated example) consisting of an inner layer 7n (core) composed of N wires and an outer layer 7m (sheath) composed of M wires twisted around the inner layer 7n. The number N of wires in the inner layer 7n is 2 to 4, and the number M of wires in the outer layer 7m is 2 to 7. In particular, the illustrated 2+2 structure is preferably employed. Furthermore, the twist directions of the inner layer 7n and the outer layer 7m are not necessarily the same; they are preferably different. Specifically, if the inner layer 7n is S-twisted, the outer layer 7m is preferably Z-twisted; if the inner layer 7n is Z-twisted, the outer layer 7m is preferably S-twisted; and if the inner layer 7n is untwisted, the outer layer 7m is preferably S-twisted or Z-twisted. In particular, in the present invention, it is preferred that the inner layer 7n be untwisted (the wires are not twisted but aligned). If the number N of wires constituting the inner layer of the steel cords 7C of the belt layer 7 is less than 2, the initial elongation of the cords deteriorates. If the number N of wires constituting the inner layer of the steel cords 7C of the belt layer 7 exceeds 4, the twisting structure becomes unstable. If the number M of wires constituting the outer layer of the steel cords 7C of the belt layer 7 is less than 2, the cord strength becomes insufficient. If the number M of wires constituting the outer layer of the steel cords 7C of the belt layer 7 exceeds 7, the twisting structure becomes unstable.

[0032] The breaking stress of the belt cord of the present invention is 3300 MPa or more, preferably 3300 MPa to 3800 MPa. In the belt layer 7, the cross-sectional area S of each belt cord (unit: mm) is 2 The product of the number of belt cords implanted per 50 mm in the direction perpendicular to the extending direction of the belt cords (unit: cords / 50 mm) (B = S × Eb) is 6.0 mm. 2 / 50mm~7.5mm 2 / 50mm, preferably 6.2mm 2 / 50mm~7.2mm 2 / 50mm. By constructing the belt layer 7 in this way, the overall strength of the belt layer 7 can be suppressed, which can compensate for the disadvantages of using the above-mentioned polyester fiber cords for the carcass cords and improve high-speed handling stability. In this case, if the breaking stress of the belt cords is less than 3300MPa, it is necessary to increase the number of implanted cords Eb in order to ensure the belt strength, thereby increasing the tire weight and reducing the high-speed handling stability. If the product B = S × Eb is less than 6.0mm 2 / 50mm, the belt strength is insufficient, so the plunger strength is reduced. If the product B = S × Eb exceeds 7.5mm 2 / 50mm, the tire weight increases and high-speed handling stability decreases. It should be noted that the ranges of the above-mentioned cross-sectional area S and the number of implants Eb are not particularly limited as long as the product B satisfies the above-mentioned ranges.

[0033] Hereinafter, the present invention will be further described with reference to examples, but the scope of the present invention is not limited to these examples.

[0034] Example

[0035] The tire size is 245 / 45R20, with Figure 1 The basic structure shown in Table 1 is as follows: for the carcass layer, the material of the carcass cord, the cord structure, the nominal fineness D of each carcass cord (unit: dtex / cord), the number of cords implanted per 50 mm in the direction perpendicular to the extension direction of the carcass cord (unit: cord / 50 mm), their product A = D × E, the elongation at break (unit: %), and the elongation at a load of 1.5 cN / dtex (unit: %) are set; and for the belt layer, the structure of the belt cord, the breaking stress (unit: MPa), and the cross-sectional area S of each belt cord (unit: mm) are set as shown in Table 1. 2 / pieces], the number of implanted belt cords per 50 mm in the direction perpendicular to the extending direction of the belt cords Eb [unit: pieces / 50 mm], and their product B = S × Eb for the pneumatic tires of Conventional Example 1, Comparative Examples 1 to 4, and Examples 1 to 11.

[0036] In Table 1, the "elongation at break" and "elongation at a load of 1.5 cN / dtex" for the carcass cords were measured in accordance with JIS L1017, "Testing methods for chemical fiber tire cords," using a tensile test with a clamping distance of 250 mm and a tensile speed of 300 ± 20 mm / min. Specifically, "elongation at break" is the elongation (%) of the sample cord measured at the time of cord break, and "elongation at a load of 1.5 cN / dtex" is the elongation (%) of the sample cord measured at a load of 1.5 cN / dtex. The "breaking stress" of the belt cords was calculated by dividing the tensile strength at break by the cord's cross-sectional area.

[0037] In the column of the material of the carcass cord in Table 1, the case where a rayon fiber cord was used is indicated as "rayon", and the case where a polyethylene terephthalate fiber cord was used is indicated as "PET".

[0038] These test tires were evaluated for impact burst resistance (plunger energy), high-speed steering stability, and tire weight by the following evaluation methods. The results are collectively shown in Table 1.

[0039] Impact blast resistance (plunger energy)

[0040] Each test tire was assembled on a wheel with a rim size of 20×8J, and the air pressure was set to 220kPa. According to JIS K6302, a tire destruction test (plunger destruction test) was performed in which a plunger with a plunger diameter of 19±1.6mm was pressed against the center of the tread at a load speed (plunger insertion speed) of 50.0±1.5m / min to measure the tire strength (tire destruction energy). The evaluation results were expressed as an index with the measured value of Example 1 being set to 100. The larger the value, the greater the destruction energy (plunger energy) and the better the impact blast resistance. In particular, when the index value is "130" or above, it means that good performance has been obtained.

[0041] High-speed handling stability

[0042] Each test tire was assembled onto a 20×8J wheel rim, set to an air pressure of 200 kPa, and installed in a 2000cc test vehicle. With two passengers aboard, the vehicle was subjected to sensory evaluation of high-speed handling stability by the test driver on a dry road test course. The results were evaluated on a 5-point scale, with Conventional Example 1 set to 3.0 (baseline), and expressed as the average of the five scores, excluding the highest and lowest scores. A higher score indicates superior high-speed handling stability.

[0043] Tire weight

[0044] The weight of each test tire was measured, and the evaluation results were expressed as an index with the measured value of Conventional Example 1 being 100. A smaller index value means a smaller tire weight.

[0045] [Table 1]

[0046]

[0047] [Table 2]

[0048]

[0049] As shown in Table 1, the tires of Examples 1 to 11, when compared to Conventional Example 1, demonstrate excellent high-speed handling stability while improving impact and burst resistance and reducing tire weight. On the other hand, in Comparative Example 1, because the carcass cords are rayon fiber cords, even though the belt cords meet the requirements of the present invention, impact and burst resistance cannot be improved. In Comparative Example 2, the carcass cords have low elongation at break and elongation at a load of 1.5 cN / dtex, and the belt cords have low breaking stress and high product B, resulting in reduced high-speed handling stability. In Comparative Example 3, the carcass cords have low elongation at break and elongation at a load of 1.5 cN / dtex, failing to achieve the effect of improving high-speed handling stability. In Comparative Example 4, the belt cords have low breaking stress and high product B, resulting in reduced high-speed handling stability.

[0050] Description of Reference Numerals

[0051] 1. Tread

[0052] 2 Sidewall

[0053] 3 Bead

[0054] 4 carcass layers

[0055] 5 Bead core

[0056] 6 Bead filler

[0057] 7 Belt

[0058] 7c belt cord

[0059] 8 belt reinforcement layer

[0060] CL Tire Equator

Claims

1. A pneumatic tire comprising: a tread portion extending in a ring shape along the tire circumferential direction; a pair of sidewall portions, the pair of sidewall portions being arranged on both sides of the tread portion; and a pair of bead portions, the pair of bead portions being arranged radially inward of the sidewall portions, the pneumatic tire comprising: at least one carcass layer, the at least one carcass layer being spanned between the pair of bead portions; and a multi-layer belt layer, the multi-layer belt layer being arranged on the outer circumferential side of the carcass layer at the tread portion, The pneumatic tire is characterized in that The carcass layer includes a carcass cord composed of an organic fiber cord, the breaking elongation of the carcass cord is 20% to 30%, the elongation of the carcass cord at a load of 2.0 cN / dtex at the sidewall portion is 5.5% to 8.0%, and the product A=D×Ec of the common fineness D of each carcass cord and the number of implanted carcass cords Ec per 50 mm in a direction perpendicular to the extension direction of the carcass cord is 2.2×10 5 dtex / 50mm~3.0×10 5 dtex / 50mm, the unit of the common fineness D of each carcass cord is dtex / cord, and the unit of the number of implanted carcass cords Ec per 50mm is cord / 50mm, The belt layer includes belt cords composed of steel cords, the breaking stress of the belt cords is 3300 MPa or more, and the product of the cross-sectional area S of each belt cord and the number of implanted belt cords Eb per 50 mm in a direction perpendicular to the extending direction of the belt cords (B = S × Eb) is 6.0 mm 2 / 50mm~7.5mm 2 / 50mm, the unit of the cross-sectional area S of each of the belt cords is mm 2 / piece, and the unit of the number of implanted belt cords Eb per 50 mm is piece / 50 mm.

2. The pneumatic tire according to claim 1, wherein: The belt cord has an N+M structure in which the number N of wires in the inner layer is 2 to 4 and the number M of wires in the outer layer is 2 to 7.

3. The pneumatic tire according to claim 2, wherein: The belt cord has a 2+2 structure in which the number of wires N in the inner layer is two and the number of wires M in the outer layer is two.

4. The pneumatic tire according to claim 2 or 3, characterized in that: The wires constituting the inner layer are aligned in an untwisted state.

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