JP7305991B2 - pneumatic tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pneumatic tire having a carcass layer made of organic fiber cords, and more particularly to a pneumatic tire capable of achieving both shock burst resistance and high-speed durability.

As one of the causes of failure of pneumatic tires, damage (shock burst) in which the carcass is destroyed due to a large shock to the tire during running is known. Durability against such damage (shock burst resistance) can be determined, for example, by a plunger energy test. That is, the plunger energy test is a test to measure the breaking energy when a plunger of a predetermined size is pressed against the center of the tread to break the tire. It can be used as an index of breaking energy (breaking durability against projection input of the tread portion).

As a method of obtaining good results (that is, improving shock burst resistance) in such a plunger energy test, for example, it is known to increase the rubber gauge at the tire equator where the plunger abuts during the test. (See Patent Document 1, for example). However, these methods may increase the amount of rubber used, resulting in an increase in tire weight. Therefore, it is being studied to use an organic fiber cord having a large breaking elongation as the carcass cord constituting the carcass layer to allow deformation during the test (when pressed by the plunger). However, in this case, since the rigidity of the carcass layer is lowered, there is a possibility that the high-speed durability is lowered. Therefore, in a pneumatic tire having a carcass layer made of organic fiber cords, there is a demand for a countermeasure that achieves a high degree of both shock burst resistance and high-speed durability.

Japanese Unexamined Patent Application Publication No. 2010-247700

An object of the present invention relates to a pneumatic tire having a carcass layer made of organic fiber cords, and more specifically, to provide a pneumatic tire capable of achieving both shock burst resistance and high-speed durability. be.

The pneumatic tire of the present invention for achieving the above object comprises a tread portion extending in the tire circumferential direction and forming an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and these sidewall portions. A pair of bead portions arranged radially inward of the tire, at least one carcass layer mounted between the pair of bead portions, and an outer peripheral side of the carcass layer in the tread portion In a pneumatic tire having a plurality of belt layers and a belt reinforcing layer arranged on the outer peripheral side of the belt layer, the carcass layer is a carcass cord made of organic fiber cords obtained by twisting organic fiber filament bundles. The carcass cord has an elongation at break of 20% or more, and an elongation at a sidewall portion of the carcass cord under a load of 1.5 cN/dtex is 6.5% to 7.0% , and the belt reinforcing layer The belt reinforcing cord is composed of an organic fiber cord obtained by twisting filament bundles of polyethylene terephthalate fibers , and the elongation of the belt reinforcing cord under a load of 2.0 cN/dtex is 2.0% to 4.0%. Characterized by

In the present invention, as described above, since the breaking elongation of the carcass cords constituting the carcass layer is 20% or more, deformation during the plunger energy test (when pressed by the plunger) can be sufficiently allowed. It is possible to improve the breaking energy (breaking durability against projection input of the tread portion). That is, the shock burst resistance of the pneumatic tire can be improved. On the other hand, the elongation of the sidewall portion of the carcass cord at a load of 1.5 cN/dtex is 6.5% to 7.0% , and the rigidity of the carcass layer in the sidewall portion is kept low, so high-speed Good durability can be maintained. Furthermore, since the elongation of the belt reinforcing cords constituting the belt cover layer under a load of 2.0 cN/dtex is 2.0% to 4.0%, the rise of the belt ends during high-speed running is effectively suppressed. It is advantageous to improve high-speed durability. By cooperating with each other, the pneumatic tire of the present invention can highly achieve both shock burst resistance and high-speed durability.

In the present invention, the breaking elongation of the carcass cords is preferably 22% to 24% . Furthermore , it is preferable that the twist coefficient K of the carcass cord after dip treatment represented by the following formula (1) is 2,000 to 2,500. By setting each physical property value in this manner, the physical properties of the carcass cord are further improved, which is advantageous in achieving both high shock burst resistance and high-speed durability.
K=T×D ^1/2 (1)
(However, T is the number of twists of the cord (twist/10cm) and D is the total fineness of the cord (dtex).)

In the present invention, the elongation of the belt reinforcing cord under a load of 2.0 cN/dtex is preferably 2.5% to 3.5%. As a result, the physical properties of the belt reinforcing cord are further improved, which is advantageous in achieving both high shock burst resistance and high-speed durability.

In the present invention, the organic fibers forming the carcass cords are preferably polyethylene terephthalate fibers. Also, the organic fibers constituting the belt reinforcing cords are polyethylene terephthalate fibers . By using polyethylene terephthalate fibers in each layer in this way, it is advantageous in achieving both high shock burst resistance and high-speed durability due to its excellent physical properties (high elastic modulus).

In the present invention, it is preferable that the belt reinforcing cord covers the entire area of the belt layer in the tire width direction. Such an arrangement makes it possible to exhibit the effect of the belt reinforcing cords more satisfactorily.

1 is a meridional cross-sectional view showing a pneumatic radial tire according to an embodiment of the present invention; FIG.

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

As shown in FIG. 1, the pneumatic tire of the present invention includes a tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of sidewall portions 2 arranged radially inward of the sidewall portions 2. and a pair of bead portions 3. In FIG. 1, symbol CL indicates the tire equator. Although FIG. 1 is a meridional sectional view and is not depicted, the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction and form an annular shape, thereby forming a toroidal pneumatic tire. A basic structure of the shape is constructed. The following explanation using FIG. 1 is basically based on the meridian cross-sectional shape shown in the drawing, but each tire constituent member extends in the tire circumferential direction and forms an annular shape.

In the illustrated example, a plurality of (four in the illustrated example) main grooves extending in the tire circumferential direction are formed on the outer surface of the tread portion 1, but the number of main grooves is not particularly limited. In addition to the main grooves, various grooves and sipes including lug grooves extending in the tire width direction can also be formed.

A carcass layer 4 including a plurality of reinforcing cords (carcass cords) extending in the tire radial direction is mounted between the 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 substantially 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 form the main portion of the carcass layer 4 (the portion extending from the tread portion 1 through the sidewall portions 2 to the bead portions 3) and the turn-up portions (the portions around the bead core 5 in each bead portion 3). folded back and extending toward each side wall portion 2).

On the other hand, a plurality of belt layers 7 (two layers in the illustrated example) are embedded in the outer peripheral side of the carcass layer 4 in the tread portion 1 . Each belt layer 7 includes a plurality of reinforcing cords (belt cords) that are inclined with respect to the tire circumferential direction, and 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 with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Steel cords, for example, are used as belt cords.

A belt cover layer 8 is provided on the outer peripheral side of the belt layer 7 for the purpose of improving high-speed durability and reducing road noise. The belt reinforcing layer 8 includes reinforcing cords (belt reinforcing cords) oriented in the tire circumferential direction. In the belt reinforcing layer 8, the belt reinforcing cords are set at an angle of, for example, 0° to 5° with respect to the tire circumferential direction. In the present invention, the belt cover layer 8 must include a full cover layer 8a that covers the entire belt layer 7, and optionally include a pair of edge cover layers 8b that locally cover both ends of the belt layer 7. (the illustrated example includes both the full cover layer 8a and the edge cover layer 8b). The belt cover layer 8 is preferably constructed by spirally winding a strip material in which at least one belt reinforcing cord is aligned and covered with a coating rubber in the tire circumferential direction, and particularly preferably has a jointless structure.

Since the present invention relates to the carcass cords forming the carcass layer 4 and the belt cords forming the belt reinforcing layer 8, the basic structure of the entire tire is not limited to the above.

In the present invention, the carcass cords constituting the carcass layer 4 are composed of organic fiber cords obtained by twisting organic fiber filament bundles. The breaking elongation of this carcass cord (organic fiber cord) is 20% or more, preferably 22% to 24%. Further, the elongation of the side wall portion 2 of the carcass cord under a load of 1.5 cN/dtex is 5.0% or more, preferably 5.0% to 6.5%. Although the type of organic fibers constituting the carcass cords is not particularly limited, for example, polyester fibers, nylon fibers, aramid fibers, etc. can be used, and among these, polyester fibers can be preferably used. Examples of polyester fibers include polyethylene terephthalate fibers (PET fibers), polyethylene naphthalate fibers (PEN fibers), polybutylene terephthalate fibers (PBT), and polybutylene naphthalate fibers (PBN). It can be used preferably. The "breaking elongation" and "elongation at 1.5 cN/dtex load" conform to JIS L1017 "Chemical fiber tire cord test method" under the conditions of a grip interval of 250 mm and a tensile speed of 300 ± 20 mm / min. It is the elongation (%) of the sample cord measured by conducting a tensile test. /dtex load.

In the present invention, the belt reinforcing cords constituting the belt cover layer 8 are composed of organic fiber cords obtained by twisting organic fiber filament bundles. The elongation of this belt reinforcing cord (organic fiber cord) under a load of 2.0 cN/dtex is 2.0% to 4.0%, preferably 2.5% to 3.5%. The type of organic fiber that constitutes the belt reinforcing cord is not particularly limited, but polyester fiber, nylon fiber, aramid fiber, and the like can be used, for example, and among these, polyester fiber can be preferably used. Examples of polyester fibers include polyethylene terephthalate fibers (PET fibers), polyethylene naphthalate fibers (PEN fibers), polybutylene terephthalate fibers (PBT), and polybutylene naphthalate fibers (PBN). It can be used preferably. In the present invention, the elongation under a load of 2.0 cN/dtex conforms to JIS L1017 "Chemical fiber tire cord test method", and a tension test is performed under the conditions of a grip interval of 250 mm and a tensile speed of 300 ± 20 mm / min. It is the elongation rate (%) of the sample cord measured under a load of 2.0 cN/dtex.

As described above, by using the carcass layer 4 made of organic fiber cords having specific physical properties and the belt cover layer 8 made of organic fiber cords having specific physical properties in combination, the pneumatic tire of the present invention has shock burst resistance. It is possible to achieve a high degree of compatibility between durability and high-speed durability. That is, in the carcass layer 4, since the breaking elongation of the carcass cords is large, it is possible to sufficiently allow deformation during the plunger energy test (when pressed by the plunger), and the breaking energy (the protrusion of the tread portion (destruction durability against input) can be improved, and the shock burst resistance of the pneumatic tire can be improved. On the other hand, since the rigidity of the carcass layer 4 in the sidewall portion 2 is kept low, high-speed durability can be maintained satisfactorily. Further, in the belt cover layer 8, the reinforcing cords having the above-mentioned physical properties can effectively suppress the rising of the belt ends during high-speed running, thereby improving the high-speed durability.

At this time, if the breaking elongation of the carcass cord (organic fiber cord) is less than 20%, the deformation during the plunger energy test cannot be sufficiently allowed, and the shock burst resistance cannot be improved. When the elongation of the sidewall portion 2 of the carcass cord under a load of 1.5 cN/dtex is less than 5.0%, the rigidity of the carcass layer in the sidewall portion 2 increases, and the rolled-up end of the carcass layer immediately below the contact area. The compressive strain of the portion increases, and there is a risk of breakage of the cord (that is, there is a risk of loss of durability). When the elongation of the belt reinforcing cord (organic fiber cord) under a load of 2.0 cN/dtex is less than 2.0%, the rigidity of the belt reinforcing layer 8 increases, the fatigue resistance of the cord decreases, and the durability against separation deteriorates. There is a risk that the performance will decrease. If the elongation of the belt reinforcing cord (organic fiber cord) under a load of 2.0 cN/dtex is greater than 4.0%, the rigidity of the belt reinforcing layer 8 will be low, and the lifting of the belt edge during high-speed running will be suppressed. Limited effect.

In addition to the physical properties described above, the carcass cord of the present invention preferably has a twist coefficient K of 2000 to 2500, which is represented by the following formula (1). The twist coefficient K is the numerical value of the carcass cord after dipping. Setting the twist coefficient K to a large value in this manner is advantageous for improving high-speed durability. When the twist coefficient K is less than 2000, fatigue is likely to occur in the carcass layer 4 due to repeated compressive deformation of the wound-up portion of the carcass layer 4 due to collapse of the bead portion when the tire rolls, improving high-speed durability. There is a possibility that a sufficient effect cannot be obtained.
K=T×D ^1/2 (1)
(However, T is the number of twists of the cord (twist/10cm) and D is the total fineness of the cord (dtex).)

The tire size is 275/40ZR20, and it has the basic structure illustrated in FIG. , Conventional Example 1, Comparative Examples 1 to 5 , and Example 1 in which the materials and physical properties (elongation at a load of 2.0 cN/dtex) of the belt reinforcing cords constituting the belt protective layer were varied as shown in Tables 1 and 2. I made ~ 6 pneumatic tires.

In any example, the belt cover layer is a joint obtained by spirally winding a strip formed by arranging one organic fiber cord (nylon 66 fiber cord or PET fiber cord) and covering it with a coat rubber in the tire circumferential direction. It has a less structure. The cording density in the strip is 50 lines/50 mm. Also, organic fiber cords (nylon 66 fiber cords or PET fiber cords) each have a structure of 1100 dtex/2.

In the column for the type of organic fiber, "N66" is indicated for nylon 66 fiber cords, and "PET" is indicated for PET fiber cords.

These test tires were evaluated for shock burst resistance, high-speed durability, and the presence or absence of separation according to the following evaluation methods. Tables 1 and 2 also show the results.

Shock burst resistance Each test tire was mounted on a rim size 9 1/2 J wheel (ETRTO standard rim), air pressure was set to 240 kPa (Reinforced/Extra Load Tires), and a plunger with a plunger diameter of 19 ± 1.6 mm was applied at a load speed. (Plunger pushing speed) A tire breaking test was conducted by pressing against the tread central portion under the condition of 50.0±1.5 m/min, and the tire strength (tire breaking energy) was measured. The evaluation results are shown as an index with the measured value of Conventional Example 1 set to 100. The larger this value is, the larger the fracture energy is, which means that the shock burst resistance is excellent. Incidentally, if this index value is "110" or less, it means that a sufficient improvement effect was not obtained.

High Speed Durability Each test tire was mounted on a wheel with a rim size of 9 1/2 J and stored for 30 days in a chamber maintained at a temperature of 70°C and a humidity of 95% with an internal pressure of 240 kPa and oxygen sealed. The test tire thus pretreated is mounted in a drum tester with a smooth-faced steel drum with a diameter of 1707 mm, the ambient temperature is controlled at 38±3° C., and the speed is 120 km/h for 30 minutes. The vehicle was accelerated by 10 km/h each time, and the distance traveled until tire failure occurred was measured. The evaluation results are shown as an index with the measured value of Conventional Example 1 set to 100. A higher index value means better high-speed durability. Incidentally, if this index value is "105" or less, it means that a sufficient improvement effect was not obtained.

Presence or Absence of Separation After conducting the high-speed durability test, each test tire was dismantled to confirm the presence or absence of a separation at the rolled-up end portion of the carcass layer. The evaluation results were indicated as "present" when separation occurred, and "absent" when separation did not occur.

As can be seen from Tables 1 and 2, the tires of Examples 1 to 6 achieved a high level of both shock burst resistance and high-speed durability in comparison with Conventional Example 1, which serves as a reference. Moreover, no separation occurred even after the high-speed durability test. On the other hand, in Comparative Example 1, since the breaking elongation of the carcass cord was small, the breaking energy of the tire measured by the plunger test was small, and the effect of improving the shock burst resistance was not sufficiently obtained. In Comparative Example 2, elongation of the sidewall portion of the carcass cord under a load of 1.5 cN/dtex was small, so the rigidity of the sidewall portion was increased, and the effect of improving high-speed durability was not sufficiently obtained. Also, separation occurred in the tire after the high-speed durability test. In Comparative Example 3, the elongation of the belt reinforcing cord under a load of 2.0 cN/dtex was small, so the effect of improving shock burst resistance was not sufficiently obtained. In Comparative Example 4, the elongation of the belt reinforcing cord under a load of 2.0 cN/dtex was large, so the effect of improving high-speed durability was not sufficiently obtained.

1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt cover layer CL tire equator

Claims (6)

A tread portion extending in the tire circumferential direction 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 inside the tire radial direction of the sidewall portions. At least one carcass layer mounted between the pair of bead portions, a plurality of belt layers arranged on the outer peripheral side of the carcass layer in the tread portion, and a plurality of belt layers arranged on the outer peripheral side of the belt layer In a pneumatic tire having a belt reinforcing layer and
The carcass layer is composed of carcass cords made of organic fiber cords obtained by twisting organic fiber filament bundles, the breaking elongation of the carcass cords is 20% or more, and the sidewall portion of the carcass cords has a load of 1.5 cN/dtex. Elongation at time is 6.5% to 7.0% ,
The belt reinforcing layer is composed of belt reinforcing cords made of organic fiber cords obtained by twisting filament bundles of polyethylene terephthalate fibers . A pneumatic tire that is 0%. The pneumatic tire according to claim 1, wherein the breaking elongation of the carcass cords is 22% to 24%. The pneumatic tire according to claim 1 or 2, wherein the twist coefficient K of the carcass cords after dip treatment represented by the following formula (1) is 2000 to 2500.
K=T×D ^1/2 (1)
(However, T is the number of twists of the cord (twist/10cm) and D is the total fineness of the cord (dtex).) The pneumatic tire according to any one of claims 1 to 3 , wherein the organic fibers constituting the carcass cords are polyethylene terephthalate fibers. The pneumatic tire according to any one of claims 1 to 4, wherein the belt reinforcing cord has an elongation of 2.5% to 3.5% under a load of 2.0 cN/dtex. The pneumatic tire according to any one of claims 1 to 5 , wherein the belt reinforcing cord covers the entire width of the belt layer in the tire width direction.

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