JP2021024509A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire that can improve durability under a moist-heat condition, while reducing road noise.SOLUTION: A belt cover layer 8 made of an organic fiber cord spirally wound around along a tire circumferential direction is provided at outer periphery sides of belt layers 7 in a tread part 1. As the organic fiber cord, a polyethylene terephthalate fiber cord is used having an elastic modulus under load of 2.0cN/dtex at 100°C in a range of 3.5cN/(tex.%) to 5.5cN/(tex.%). As a coat rubber coating the organic fiber cord, a rubber is used whose tanδ measured under a condition that an initial strain is 10%, vibrational amplitude is ±2%, a frequency is 20 Hz and a temperature is 60°C is 0.03 or more and less than 0.15.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pneumatic tire using a polyethylene terephthalate (PET) fiber cord for the belt cover layer.

Pneumatic tires for passenger cars or light trucks generally have a carcass layer mounted between a pair of bead portions, and a plurality of belt layers are arranged on the outer peripheral side of the carcass layer in the tread portion to form a belt layer. It has a structure in which a belt cover layer containing a plurality of organic fiber cords spirally wound along the tire circumferential direction is arranged on the outer peripheral side. In this structure, the belt cover layer contributes to the improvement of high-speed durability and also contributes to the reduction of medium-frequency road noise.

Conventionally, nylon fiber cords are the mainstream of organic fiber cords used for belt cover layers, but polyethylene terephthalate fiber cords (hereinafter referred to as PET fiber cords), which are more elastic and inexpensive than nylon fiber cords, are used. It has been proposed to be used (see, for example, Patent Document 1). However, the PET fiber cord has a problem that it tends to generate heat more easily than the conventional nylon fiber cord. Therefore, in order to reduce road noise by using a PET fiber cord, measures are required to suppress heat generation and improve durability under moist heat conditions.

Japanese Unexamined Patent Publication No. 2001-63312

An object of the present invention is to provide a pneumatic tire capable of improving durability under moist heat conditions in reducing road noise by using a PET fiber cord for a belt cover layer.

The pneumatic tire of the present invention for achieving the above object has a tread portion extending in the tire circumferential direction to form 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 inside in the tire radial direction, a carcass layer mounted between the pair of bead portions, and a plurality of layers of belts arranged on the outer peripheral side of the carcass layer in the tread portion. In a pneumatic tire having a layer and a belt cover layer arranged on the outer peripheral side of the belt layer, the belt cover layer spirally winds an organic fiber cord coated with a coated rubber along the tire circumferential direction. The organic fiber cord is a polyethylene terephthalate fiber having an elastic coefficient in the range of 3.5 cN / (tex ·%) to 5.5 cN / (tex ·%) under a load of 2.0 cN / dtex at 100 ° C. It is a code, and is characterized in that the tan δ of the coated rubber measured under the conditions of an initial strain of 10%, an amplitude of ± 2%, a frequency of 20 Hz, and a temperature of 60 ° C. is 0.03 or more and less than 0.15.

As a result of diligent research on a pneumatic tire provided with a belt cover layer made of PET fiber cord, the present inventor has optimized the dip treatment of PET fiber cord and determined the elastic modulus under a 2.0 cN / dtex load at 100 ° C. It was found that the fatigue resistance and the tagging effect of the cord suitable for the belt cover layer can be obtained by setting the value in the range of, and the present invention has been reached. That is, in the present invention, the elastic modulus of the organic fiber cord constituting the belt cover layer under a load of 2.0 cN / dtex at 100 ° C. is 3.5 cN / (tex ·%) to 5.5 cN / (tex ·%). By using the PET fiber cord in the range of), road noise can be effectively reduced while maintaining good durability of the pneumatic tire.

Further, as the coated rubber for coating this PET fiber cord, a tire having a tan δ of 0.03 or more and less than 0.15 measured under the conditions of an initial strain of 10%, an amplitude of ± 2%, a frequency of 20 Hz, and a temperature of 60 ° C. is used. , Heat generation can be suppressed, and tire durability and rolling resistance can be improved.

In the present invention, the rubber composition constituting the coated rubber contains at least one selected from natural rubber, styrene-butadiene rubber, and butadiene rubber as the rubber component, and the blending amount of the natural rubber in the rubber component is 20% by mass to 65. the mass%, it is intended that the nitrogen adsorption specific surface area N ₂ SA is relative to 100 parts by mass of the rubber component is 25m ² / g~50m ² / g carbon black is 30 parts by mass to 80 parts by mass preferable. By using a rubber composition having such a composition, the physical characteristics of the coated rubber are improved, which is advantageous in achieving both reduction of road noise and improvement of tire durability.

In the present invention, the cord tension of the organic fiber cord in the tire is preferably 0.9 cN / dtex or more. This is advantageous for suppressing heat generation and improving the durability of the tire.

In the present invention, when the region of 70% of the ground contact width centered on the equator of the tire is the center region and the region outside the tire width direction is the shoulder region, the inside of the tire of the organic fiber cord arranged in the center region. The ratio Ce / Sh of the cord tension Ce to the cord tension Sh in the tire of the organic fiber cord arranged in the shoulder region is preferably 1.0 or more and 2.0 or less. By setting the tension for each portion in the tire width direction in this way, heat generation can be suppressed and tire durability can be improved.

In the present invention, the "ground contact width" is the distance between the ground contact ends on both sides in the tire width direction. The "ground contact ends" are both ends of the ground contact area in the tire axial direction that are formed when the tire is rim-assembled on the regular rim, placed vertically on a flat surface with the regular internal pressure applied, and a regular load is applied. is there. A "regular rim" is a rim defined for each tire in a standard system including a standard on which a tire is based. For example, a standard rim for JATTA, "DesignRim" for TRA, or ETRTO. If so, it is set to "Measuring Rim". "Regular internal pressure" is the air pressure defined for each tire in the standard system including the standard on which the tire is based. For JATMA, the maximum air pressure, and for TRA, the table "TIRE ROAD LIMITED AT VARIOUS". The maximum value described in "COLD INFLATION PRESSURES" is "INFLATION PRESSURE" for ETRTO, but 180 kPa when the tires are for passenger cars. "Regular load" is the load defined for each tire in the standard system including the standard on which the tire is based. JATMA has the maximum load capacity, and TRA has the table "TIRE ROAD LIMITS AT VARIOUS". The maximum value described in "COLD INFLATION PRESSURES" is "LOAD CAPACITY" in the case of ETRTO, but when the tire is for a passenger car, the load is equivalent to 88% of the above load.

It is a meridian cross-sectional view which shows the pneumatic radial tire which concerns on embodiment of this invention.

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 is arranged inside the tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and the sidewall portion 2 in the tire radial direction. It is provided with a pair of bead portions 3. In FIG. 1, reference numeral CL indicates a tire equator, reference numeral E indicates a ground contact end, and reference numeral W indicates a ground contact width. Although FIG. 1 is a cross-sectional view of the meridian, it is not depicted, but the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction to form an annular shape, whereby the toroidal of the pneumatic tire is formed. The basic structure of the shape is constructed. Hereinafter, the description using FIG. 1 is basically based on the illustrated meridian cross-sectional shape, but all the tire constituent members extend in the tire circumferential direction to form an annular shape.

In the illustrated example, a plurality of main grooves (4 in the illustrated example) 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. Further, in addition to the main groove, various grooves and sipes including a lug groove extending in the tire width direction can be formed.

A carcass layer 4 including a plurality of reinforcing 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 around the bead core 5 from the inside to the outside in the tire width direction. As a result, the bead core 5 and the bead filler 6 are formed around the main body portion of the carcass layer 4 (the portion extending from the tread portion 1 to each bead portion 3 via each sidewall portion 2) and the folded portion (in each bead portion 3 around the bead core 5). It is wrapped by a portion) that is folded back and extends toward each sidewall portion 2 side. As the reinforcing cord of the carcass layer 4, for example, a polyester cord is preferably used.

On the other hand, a plurality of layers (two layers in the illustrated example) of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to intersect each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in the range of, for example, 10 ° to 40 °. As the reinforcing cord of the belt layer 7, for example, a steel cord is preferably used.

Further, 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 contains an organic fiber cord oriented in the tire circumferential direction. In the belt reinforcing layer 8, the angle of the organic fiber cord with respect to the tire circumferential direction is set to, for example, 0 ° to 5 °. In the present invention, the belt cover layer 8 always includes a full cover layer 8a that covers the entire area of the belt layer 7, and optionally includes a pair of edge cover layers 8b that locally cover both ends of the belt layer 7. (In the illustrated example, both the full cover layer 8a and the edge cover layer 8b are included). The belt cover layer 8 may be formed by spirally winding a strip material in which at least one organic fiber cord is aligned and coated with a coated rubber in the tire circumferential direction, and it is particularly desirable to have a jointless structure.

In the present invention, the organic fiber cord constituting the belt cover layer 8 has an elastic modulus of 3.5 cN / (tex ·%) to 5.5 cN / (tex ·%) under a load of 2.0 cN / dtex at 100 ° C. Polyethylene terephthalate fiber cords (PET fiber cords) in the range are used. By using a specific PET fiber cord as the organic fiber cord constituting the belt cover layer 8 in this way, road noise can be effectively reduced while maintaining good durability of the pneumatic tire. If the elastic modulus of this PET fiber cord under a load of 2.0 cN / dtex at 100 ° C. is less than 3.5 cN / (tex ·%), the medium frequency road noise cannot be sufficiently reduced. If the elastic modulus of the PET fiber cord under a load of 2.0 cN / dtex at 100 ° C. exceeds 5.5 cN / (tex ·%), the fatigue resistance of the cord is lowered and the durability of the tire is lowered. In the present invention, the elastic modulus [N / (tex ·%)] under a load of 2.0 cN / dtex at 100 ° C. conforms to JIS-L1017 “Chemical fiber tire cord test method” and has a grip interval of 250 mm. It is calculated by conducting a tensile test under the condition of a tensile speed of 300 ± 20 mm / min and converting the slope of the tangent line at the point corresponding to the load 2.0 cN / dtex of the load-elongation curve into a value per tex. ..

Further, when this organic fiber cord (PET fiber cord) is used as the belt cover layer 8, the cord tension in the tire is preferably 0.9 cN / dtex or more, more preferably 1.5 cN / dtex to 2.0 cN / dtex. It is good to be. By setting the cord tension in the tire in this way, heat generation can be suppressed and tire durability can be improved. If the cord tension of this organic fiber cord (PET fiber cord) in the tire is less than 0.9 cN / dtex, the peak of tan δ rises, and the effect of improving the durability of the tire cannot be sufficiently obtained. The cord tension of the organic fiber cord (PET fiber cord) constituting the belt cover layer 8 in the tire shall be measured at least two laps inside the end of the strip material constituting the belt cover layer in the tire width direction.

In particular, as shown in FIG. 1, when the region of 70% of the contact width W centered on the tire equator CL is the center region A and the regions outside the tire width direction are the shoulder regions B, the center region A is set. The ratio Ce / Sh of the cord tension Ce in the tire of the arranged organic fiber cord to the cord tension Sh in the tire of the organic fiber cord arranged in the shoulder region B must be 1.0 or more and 2.0 or less. preferable. By setting the tension relationship for each part in the tire width direction in this way, heat generation can be suppressed and tire durability can be improved. When the ratio Ce / Sh exceeds 2.0, when the cord tension in the shoulder region becomes too low, the heat generated by the cord increases, cord melt is generated, and the high-speed durability is lowered. If the ratio Ce / Sh is less than 1.0, the rigidity of the shoulder portion becomes too high when the cord tension in the shoulder region becomes too high, the ground contact shape becomes round, and the belt layer 7 and the belt cover layer 8 during running. The separation between the tire and the tire is likely to proceed, and the tire durability is reduced. The tensions Ce and Sh are not particularly limited as long as they satisfy the above-mentioned relationship, but the tension Ce is, for example, 1.2 cN / dtex to 2.5 cN / dtex, and the tension Sh is, for example, 0.9 cN / dtex to 2.0 cN / dtex. Can be set to. The relationship between the tensions Ce and Sh has, for example, a curvature drum (a portion corresponding to the shoulder portion of the tire to be manufactured has a smaller peripheral length than a portion corresponding to the center portion of the tire to be manufactured) during tire molding. This can be achieved by using a drum) or by controlling the winding tension of the belt cover material. The tension Ce is a value measured in five fiber cords located at the center of the outermost belt layer 7, and the tension Sh is two or more turns in the tire width direction from the end of the strip material constituting the belt cover layer. It is a value measured in five fiber cords located in the shoulder portion of the inner and outermost belt layer 7.

The PET fiber cord used as the organic fiber cord constituting the belt cover layer 8 preferably has a heat shrinkage stress of 0.6 cN / tex or more at 100 ° C. By setting the heat shrinkage stress at 100 ° C. in this way, it is possible to effectively reduce road noise while maintaining good durability of the pneumatic radial tire more effectively. If the heat shrinkage stress of the PET fiber cord at 100 ° C. is smaller than 0.6 cN / tex, the tagging effect during running cannot be sufficiently improved, and it becomes difficult to sufficiently maintain high-speed durability. The upper limit of the heat shrinkage stress of the PET fiber cord at 100 ° C. is not particularly limited, but may be set to 2.0 cN / tex, for example. In the present invention, the heat shrinkage stress (cN / tex) at 100 ° C. conforms to the "chemical fiber tire cord test method" of JIS-L1017, and has a sample length of 500 mm and a heating condition of 100 ° C. for 5 minutes. This is the heat shrinkage stress of the sample cord measured when heated in.

In order to obtain a PET fiber cord having the above-mentioned physical characteristics, for example, it is advisable to optimize the dip treatment. That is, prior to the calendar process, the PET fiber cord is dipped with an adhesive, but in the normalization process after the two-bath treatment, the ambient temperature is set within the range of 210 ° C to 250 ° C, and the cord tension is applied. Is preferably set in the range of 2.2 × 10 ⁻² N / tex to 6.7 × 10 ^{−2 N / tex.} This makes it possible to impart the desired physical properties as described above to the PET fiber cord. If the cord tension in the normalization process ^{is smaller than 2.2 × 10 −2} N / tex, the cord elastic modulus becomes low, and the medium frequency road noise cannot be sufficiently reduced, and conversely, 6.7 × 10 ^{− If} it is larger than 2 N / tex, the elastic modulus of the cord becomes high and the fatigue resistance of the cord decreases.

In the tread portion 1, the tread rubber layer 10 is arranged on the outer peripheral side of the above-mentioned tire constituent members (carcus layer 4, belt layer 7, belt cover layer 8). In particular, in the present invention, the tread rubber layer 10 has a structure in which two types of rubber layers having different physical properties (cap tread layer 11 and under tread layer 12) are laminated in the tire radial direction. The side rubber layer 20 is arranged on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the sidewall portion 2, and the rim cushion rubber layer is arranged on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the bead portion 3. 30 are arranged.

The organic fiber cord (PET fiber cord) constituting the belt cover layer 8 is coated with a coated rubber (hereinafter, referred to as a belt cover coated rubber). As this belt cover coat rubber, the tan δ measured under the conditions of initial strain 10%, amplitude ± 2%, frequency 20 Hz, and temperature 60 ° C. is 0.03 or more and less than 0.15, preferably 0.08 or more and 0.13 or less. Use rubber that is. By adopting the belt cover coated rubber having specific physical properties in this way, it is possible to suppress the heat generation of the coated rubber, and when combined with the above-mentioned organic fiber cord (PET fiber cord), the durability of the tire and Rolling resistance can be effectively improved. If the above-mentioned tan δ is 0.15 or more, heat generation cannot be suppressed, and the effect of improving tire durability and rolling resistance cannot be obtained.

In the rubber composition constituting the belt cover coat rubber, the rubber component is a diene-based rubber, and it is preferable that the rubber component contains at least one selected from natural rubber, styrene-butadiene rubber, and butadiene rubber. In particular, it is preferable to mix 20% by mass to 65% by mass, preferably 40% by mass to 65% by mass of natural rubber in the rubber component, and use styrene-butadiene rubber and / or butadiene rubber in combination as the remaining rubber component. More preferably, three types of natural rubber, styrene-butadiene rubber, and butadiene rubber may be used in combination. In this case, the blending amount of the natural rubber is 30% by mass to 60% by mass, and the blending amount of the styrene-butadiene rubber is 20% by mass to 45. The blending amount of butadiene rubber may be 5% by mass to 30% by mass. In any case, if the blending amount of the natural rubber is out of the above range, the desired effect of the present invention cannot be sufficiently obtained. As the natural rubber, styrene-butadiene rubber, and butadiene rubber, those usually used for pneumatic tires (particularly, belt cover coat rubber) can be used.

In the present invention, carbon black can be further added to the rubber composition constituting the belt cover coat rubber. The blending amount of carbon black is preferably 30 parts by mass to 80 parts by mass, and more preferably 40 parts by mass to 70 parts by mass with respect to 100 parts by mass of the rubber component. By blending carbon black in this way, hardness and strength can be increased, and it becomes possible to suitably use it for belt cover coat rubber. If the amount of carbon black blended is less than 30 parts by mass, it becomes difficult to sufficiently secure the hardness and strength of the belt cover coat rubber, and the durability of the tire may decrease. If the amount of carbon black compounded exceeds 80 parts by mass, heat generation cannot be sufficiently suppressed, and the durability and rolling resistance of the tire may deteriorate.

Case of blending carbon black as described above, the nitrogen adsorption specific surface area N ₂ SA of carbon black is preferably 25m ² / g~50m ² / g, more preferably 30m ² / g~45m ² / g. By using the specific carbon black in this way, the hardness and strength of the belt cover coat rubber can be appropriately increased. If the nitrogen adsorption specific surface area N ₂ SA of ^{carbon black is less than 25 m 2} / g, it becomes difficult to sufficiently secure the hardness and strength of the belt cover coat rubber, and the durability of the tire may decrease. If the nitrogen adsorption specific surface area N ₂ SA of ^{carbon black exceeds 50 m 2} / g, heat generation cannot be sufficiently suppressed, and the durability and rolling resistance of the tire may deteriorate. In the present invention, the nitrogen adsorption specific surface area N ₂ SA of carbon black is measured according to JIS K6217-7.

In the present invention, sulfur can be further added to the rubber composition constituting the belt cover coat rubber. The blending amount of sulfur is preferably 2.0 parts by mass to 3.5 parts by mass, and more preferably 2.3 parts by mass to 3.2 parts by mass with respect to 100 parts by mass of the rubber component. By blending sulfur in this way, the hardness of the belt cover coat rubber can be appropriately increased. If the amount of sulfur compounded is less than 2.0 parts by mass, it becomes difficult to secure sufficient hardness of the belt cover coat rubber. If the amount of sulfur compounded exceeds 3.5 parts by mass, the elongation of the belt cover coat rubber may decrease.

In the present invention, a vulcanization accelerator can be further added to the rubber composition constituting the belt cover coat rubber. The blending amount of the vulcanization accelerator is preferably 0.5 parts by mass to 2.0 parts by mass, and more preferably 0.7 parts by mass to 1.5 parts by mass with respect to 100 parts by mass of the rubber component. By blending the vulcanization accelerator in this way, the hardness of the belt cover coat rubber can be appropriately increased. If the blending amount of the vulcanization accelerator is less than 0.5 parts by mass, it becomes difficult to sufficiently secure the hardness of the belt cover coat rubber. If the blending amount of the vulcanization accelerator exceeds 2.0 parts by mass, the elongation of the belt cover coat rubber may decrease.

The belt cover coat rubber preferably has a storage elastic modulus E1 (100 ° C.) measured under the conditions of static strain 10%, dynamic strain ± 2%, frequency 20 Hz, and temperature 100 ° C. in accordance with JIS K6394: 2007. Is 3.0 MPa or more and 6.0 MPa or less, more preferably 3.5 MPa or more and 5.5 MPa or less. By setting the storage elastic modulus in this way, high-speed durability can be improved. If the storage elastic modulus E1 (100 ° C.) deviates from the above range, it becomes difficult to satisfactorily exhibit high-speed durability.

The organic fiber cord (PET fiber cord) having a tire size of 225 / 60R18 and having the basic structure illustrated in FIG. 1 and constituting the belt cover layer has an elastic coefficient at 100 ° C. under a 2.0 cN / dtex load [ cN / (tex ·%)], cord tension [cN / dtex] in the tire, cord tension Ce in the tire of the organic fiber cord arranged in the center region, and the cord tension Ce in the tire of the organic fiber cord arranged in the shoulder region in the tire. The ratio Ce / Sh to the cord tension Sh is set as shown in Tables 1 and 2, and the coated rubber (belt cover coated rubber) that coats the organic fiber cord (PET fiber cord) constitutes the coated rubber. Tires of Conventional Example 1, Comparative Examples 1 to 5, and Examples 1 to 12 in which the composition of the rubber composition and tan δ (60 ° C.) were different as shown in Tables 1 and 2 were produced.

In each example, the belt cover layer has a jointless structure in which a strip formed by aligning one organic fiber cord (PET fiber cord) and covering it with coated rubber is spirally wound in the tire circumferential direction. ing. The cord driving density in the strip is 50 lines / 50 mm. Further, each organic fiber cord (PET fiber cord) has a structure of 1100 dtex / 2.

In each example, the elastic modulus [cN / (tex ·%)] under a load of 2.0 cN / dtex at 100 ° C. conforms to JIS-L1017 “Chemical fiber tire cord test method”, grip interval 250 mm, tensile speed. The tensile test was carried out under the condition of 300 ± 20 mm / min, and the calculation was performed by converting the slope of the tangent line at the point corresponding to the load 2.0 cN / dtex of the load-elongation curve into the value per tex. Further, the cord tension [cN / dtex] in the tire is obtained by removing the tread rubber from the tread portion 1 to expose the belt cover layer, peeling the fiber cord from a predetermined length range of the belt cover layer, and after collecting the tread rubber. The length was measured and the amount of shrinkage with respect to the length before collection was determined. In particular, the average value of the shrinkage amount was calculated for the five fiber cords located at the center of the outermost belt layer. Then, the load corresponding to the shrinkage amount (%) was obtained from the SS curve and measured by converting it into a value per 1 dtex. The tension Ce was measured on the five fiber cords located at the center of the outermost belt layer 7, and the tension Sh was measured on the five fiber cords located on the shoulder of the outer belt layer 7.

For each example, the belt cover coat rubber tan δ (60 ° C.) is obtained by vulcanizing the rubber composition of each example at 180 ° C. for 5 minutes using a mold having a predetermined shape, and then using a 2 mm thick sheet-shaped vulcanized rubber. A test piece was prepared and used for measurement by the following method.

tan δ (60 ° C)
Using the vulcanized rubber test pieces of each example, in accordance with JIS K6394, using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.), elongation deformation strain rate 10% ± 2%, frequency 20 Hz, temperature 60 Tan δ was measured under the condition of ° C.

These test tires were evaluated for road noise, moist heat durability, and the presence or absence of belt cover separation by the following evaluation methods, and the results are also shown in Tables 1 and 2.

Road noise Each test tire is assembled to a wheel with a rim size of 18 x 7J, mounted as the front and rear wheels of a passenger car (front wheel drive vehicle) with a displacement of 2.5L, the air pressure is set to 230kPa, and the sound collecting microphone is inside the driver's seat window. The sound pressure level around 315 Hz was measured when the test course composed of the asphalt road surface was run under the condition of an average speed of 50 km / h. As the evaluation result, the amount of change (dB) with respect to the standard was shown with reference to the conventional example 1.

Moisture and heat durability Each test tire was assembled on a wheel having a rim size of 18 × 7J, and stored in a chamber maintained at a temperature of 70 ° C. and a humidity of 95% in a state where oxygen was sealed at an internal pressure of 230 kPa for 30 days. The test tire thus pretreated was mounted on a drum tester equipped with a drum made of steel with a smooth surface and a diameter of 1707 mm, the ambient temperature was controlled to 38 ± 3 ° C., and the speed was 120 km / h for 24 hours. The vehicle was accelerated by 50 km / h and the mileage until the tire failed was measured. The evaluation result is shown by an index with the conventional example 1 as 100 using the measured value of the mileage. The larger the index value, the longer the mileage until a failure occurs, and the better the wet and heat durability.

Presence or absence of belt cover separation After conducting the above-mentioned wet and heat durability test, each test tire was disassembled and the presence or absence of separation (belt cover separation) in the belt reinforcing layer was visually confirmed. The evaluation results showed "yes" when the belt cover separation occurred and "no" when the belt cover separation did not occur.

The types of raw materials used in Tables 1 and 2 are shown below.
・ NR: Natural rubber, STR20
-BR: butadiene rubber, Nippon Zeon Nipol 1220
-SBR: Styrene butadiene rubber, SBR1502 manufactured by Zeon Corporation
・ CB1: Carbon black (ISAF), Cabot Japan Show Black N234 (Nitrogen adsorption specific surface area N ₂ SA: ^{119m 2} / g)
-CB2: Carbon black (GPF), Tokai Carbon Co., Ltd. Seast V (Nitrogen adsorption specific surface area N ₂ SA: 35 m ² / g)
・ Zinc oxide: Zinc oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. ・ Stearic acid: Bead stearic acid NY manufactured by NOF CORPORATION
-Anti-aging agent: Nocrack 224 manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
・ Aroma oil: Showa Shell Sekiyu Co., Ltd. Extract No. 4 ・ Vulcanization accelerator: Sanshin Chemical Industry Co., Ltd. NS-G
-Sulfur: Shikoku Kasei Kogyo Co., Ltd. Mucron OT-20 (sulfur content: 80% by mass)

As can be seen from Tables 1 and 2, the tires of Examples 1 to 12 reduced road noise and improved moist heat durability in comparison with the standard Conventional Example 1. On the other hand, in the tires of Comparative Examples 1 and 2, the elastic modulus of the polyethylene terephthalate fiber cord constituting the belt cover layer under a 2.0 cN / dtex load at 100 ° C. was high, so that the wet and heat durability was deteriorated. In the tire of Comparative Example 3, the elastic modulus of the polyethylene terephthalate fiber cord constituting the belt cover layer under a 2.0 cN / dtex load at 100 ° C. is low, so that the road noise cannot be sufficiently reduced, and the road noise cannot be sufficiently reduced. Wet and heat durability deteriorated. Since the tires of Comparative Examples 4 and 5 had a large tan δ (60 ° C.) of the coated rubber, the wet and heat durability was deteriorated. In addition, the belt cover separation occurred in each of Comparative Examples 1 to 5.

1 tread part 2 sidewall part 3 bead part 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt cover layer 8a full cover layer 8b edge cover layer 10 tread rubber layer 11 cap tread layer 12 under tread layer 20 side rubber layer 30 rim Cushion rubber layer CL Tire equatorial line E Ground edge A Center area B Shoulder area

Claims (4)

A tread portion extending in the tire circumferential direction to form 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 these sidewall portions. A 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 belt cover arranged on the outer peripheral side of the belt layer. In pneumatic tires with layers
The belt cover layer is formed by spirally winding an organic fiber cord coated with coated rubber along the tire circumferential direction, and the organic fiber cord has an elastic modulus at 100 ° C. under a 2.0 cN / dtex load. A polyethylene terephthalate fiber cord in the range of 3.5 cN / (tex ·%) to 5.5 cN / (tex ·%), measured under the conditions of initial strain 10%, amplitude ± 2%, frequency 20 Hz, and temperature 60 ° C. A pneumatic tire having a tan δ of the coated rubber of 0.03 or more and less than 0.15. The rubber composition constituting the coated rubber contains at least one selected from natural rubber, styrene-butadiene rubber, and butadiene rubber as the rubber component, and the blending amount of the natural rubber in the rubber component is 20% by mass to 65% by mass. There, said the nitrogen adsorption specific surface area N ₂ SA with respect to 100 parts by mass of the rubber component is one that carbon black is 25m ² / g~50m ² / g is 30 parts by mass to 80 parts by mass The pneumatic tire according to claim 1. The pneumatic tire according to claim 1 or 2, wherein the cord tension in the tire of the organic fiber cord is 0.9 cN / dtex or more. When 70% of the contact width centered on the tire equator is the center region and the region outside the tire width direction is the shoulder region, the cord tension in the tire of the organic fiber cord arranged in the center region. Any of claims 1 to 3, wherein the ratio Ce / Sh of Ce and the cord tension Sh in the tire of the organic fiber cord arranged in the shoulder region is 1.0 or more and 2.0 or less. Pneumatic tires described in.

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