pneumatic tires

Abstract

Pneumatic tires, including: a tread section (1) extending in a circumferential direction of the tire and having a ring shape; a pair of sidewall sections (2) which are arranged on both sides of the running surface section (1); a pair of bead sections (3) which are each arranged on an inner side of the pair of sidewall sections (2) in the tire radial direction; a carcass layer (4) arranged between the pair of bead sections (3); a plurality of belt layers (7) arranged on an outer circumferential side of the carcass layer (4) in the tread section (1); and a belt cover layer (8) arranged on an outer circumferential side of the belt layers (7), wherein the belt cover layer (7) is formed by spirally winding an organic fiber cord thread coated with coating rubber along the circumferential direction of the tire, wherein the organic fiber cord thread is a polyethylene terephthalate cord thread, in which an elastic modulus at a load of 2.0 cN / dtex at 100 °C is in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%), wherein the coating rubber contains as a rubber component one or more rubbers selected from natural rubber, styrene-butadiene rubber and butadiene rubber, and wherein the coating rubber is formed from a rubber composition in which a proportion of natural rubber in the rubber component is 50% by mass or more and 5.0 parts by mass to 9.0 parts by mass of zinc oxide are mixed in per 100 parts by mass of the rubber component.

Description

Technical field

[0001] The present invention relates to an air tire which uses polyethylene terephthalate (PET) fiber cord threads in a belt cover layer. State of the art

[0002] Pneumatic tires for passenger cars or light trucks typically include a structure in which a carcass ply is mounted between a pair of bead sections, multiple belt plies arranged on an outer circumferential side of the carcass ply within a tread section, and a belt cover ply arranged on an outer circumferential side of the belt ply, the belt cover ply comprising multiple organic fiber cord threads wound helically along a circumference of the tire. In this structure, the belt cover ply contributes to improved durability at high speeds and a reduction in mid-frequency road noise.

[0003] In the prior art, nylon fiber cord threads are mainly applied to the organic fiber cord threads used in the belt's outer layer; however, it has been proposed to use polyethylene terephthalate fiber cord threads (hereinafter referred to as PET fiber cord threads), which are very elastic and inexpensive compared to nylon fiber cord threads (see, for example, JP 2001-63312 A). However, PET fiber cord thread tends to generate heat more readily than conventional nylon fiber cord thread, and in particular, the problem is that the lower the tension applied to the cord thread, the easier it is to generate heat. Therefore, there is a need for measures to improve durability at high speeds and in warm, humid conditions, as well as to reduce rolling noise, while simultaneously controlling the tension applied to the cord thread to suppress heat generation.

[0004] DE 11 2020 000 334 T5 discloses a radial pneumatic tire with a belt cover layer formed from organic fiber cord threads. A plurality of belt layers, arranged on an outer circumferential side of a carcass layer in a tread section, are formed from steel cords, each having a 1 × M structure formed from a number M of wire strands. The tensile modulus of elasticity of the steel cords is 130 GPa or more under a load of 5 N to 50 N. The steel cords are arranged inclined with respect to a tire circumferential direction to intersect each other in layers of the belt layers. The belt cover layer, arranged on an outer circumferential side of the belt layers, is formed from organic fiber cord threads with an elongation of 2.0% to 4.0% under a load of 2.0 cN / dtex. The organic fiber cord threads are wound helically along the tire circumferential direction. Brief description of the invention: Technical problem

[0005] The present invention provides a pneumatic tire which has improved resistance at high speeds and under humid warm conditions in order to reduce driving noise by using a PET fiber cord thread for a belt cover layer. Solution to the problem

[0006] A pneumatic tire according to the present invention for fulfilling the above-described problem is a pneumatic tire comprising: a tread section extending in a tire circumferential direction and having a ring shape; a pair of sidewall sections arranged on both sides of the tread section; a pair of bead sections arranged on an inner side of the pair of sidewall sections in the tire radial direction; a carcass layer arranged between the pair of bead sections; a plurality of belt layers arranged on an outer circumferential side of the carcass layer in the tread section;and a belt cover layer arranged on an outer circumferential side of the belt layers, wherein the belt cover layer is formed by spiral winding of an organic fiber cord yarn coated with coating rubber along the tire circumferential direction, wherein the organic fiber cord yarn is a polyethylene terephthalate fiber cord yarn whose modulus of elasticity at a load of 2.0 cN / dtex at 100°C is in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%), wherein the coating rubber contains one or more components selected from natural rubber, styrene-butadiene rubber and butadiene rubber as the rubber component, and the coating rubber is formed from a rubber composition in which a mixed amount of natural rubber in the rubber component is 50 wt% or more and 5.0 wt% to 9.0 wt% zinc oxide per 100 wt% of the The rubber component is mixed. Advantageous effects of the invention

[0007] The present invention is the result of careful investigations of a pneumatic tire with a belt cover layer made of PET fiber cord threads, in which the inventor found that the fatigue resistance and tire effect of the cord thread suitable for the belt cover layer can be achieved by optimizing the dip treatment of the PET fiber cord thread and by adjusting the modulus of elasticity under a load of 2.0 cN / dtex at 100 °C within a predetermined range. That is to say, in one embodiment of the present invention, a PET fiber cord thread whose modulus of elasticity under a load of 2.0 cN / dtex at 100 °C is in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%) is used as the organic fiber cord thread forming the belt cover layer. Thus, the road noise can be effectively reduced while the durability of the pneumatic tire is satisfactorily maintained.

[0008] Furthermore, a coating rubber containing one or more selected components from natural rubber, styrene-butadiene rubber, and butadiene rubber as the rubber component, and formed from a rubber composition in which the mixed amount of natural rubber in the rubber component is 50% by mass or more, and 5.0 to 9.0 parts by mass of zinc oxide per 100 parts by mass of the rubber component are mixed in, is used as a coating rubber covering the PET fiber cord thread. Thus, the physical properties of the coating rubber can be improved at high temperatures by providing the coating rubber with physical properties suitable for combination with the PET fiber cord thread described above, and the durability (damp heat resistance, high-speed resistance) of the tire can be improved.

[0009] In one embodiment of the present invention, the internal tension of the organic fiber cord threads in the tire is preferably 0.9 cN / dtex or more. This has the advantage of suppressing heat generation and improving the tire's durability.

[0010] In one embodiment of the present invention, the tensile strength of the coating rubber at 100 °C is preferably 10.0 MPa or more, and the elongation at break of the coating rubber at 100 °C is 280% or more. This has the advantage of improving the durability of the tire.

[0011] In one embodiment of the present invention, the storage modulus E1 (100°C) of the coating rubber, measured under conditions of a static strain of 10%, a dynamic strain of ±2%, a frequency of 20 Hz, and a temperature of 100°C, is preferably 3.0 MPa ≤ E1 (100°C) ≤ 6.0 MPa. This has the advantage of improving the durability of the tire.

[0012] In one embodiment of the present invention, the proportion of free sulfur in the coating rubber is preferably 0.2% or less. This has the advantage of improving the tire's durability. Brief description of the drawings Fig. Figure 1 is a meridian cross-sectional view illustrating a radial pneumatic tire according to an embodiment of the present invention. Description of embodiments

[0013] Configurations of embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0014] As in Fig. As illustrated in Figure 1, a pneumatic tire of an embodiment of the present invention comprises a tread section 1, a pair of sidewall sections 2 arranged on both sides of the tread section 1, and a pair of bead sections 3 arranged on the inner side of the sidewall sections 2 in a radial direction of the tire. It should be noted that “CL” in Fig. 1. A tire equator. Although in Fig. 1 not illustrated, since Fig.In Figure 1, a meridian cross-sectional view is shown. The tread section 1, the sidewall sections 2, and the bead sections 3 each extend in the tire's circumferential direction and have a ring shape. This configures a torus-shaped basic structure of the pneumatic tire. Although the description uses Fig. 1. Essentially based on the illustrated meridian cross-section, all tire components extend in the direction of the tire's circumference and have a ring shape.

[0015] In the illustrated example, a plurality of main grooves (four main grooves in the illustrated example), extending in the circumferential direction of the tire, are formed in the outer surface of tread section 1; however, the number of main grooves is not subject to any specific restrictions. Furthermore, in addition to the main grooves, various grooves and sipes can be formed, including lug grooves, which extend in the width direction of the tire.

[0016] A carcass layer 4, enclosing a plurality of reinforcing cord threads extending radially in the tire, is mounted between a pair of left and right bead sections 3. A bead core 5 is embedded in each of the bead sections, and a bead filler 6 with an approximately triangular cross-sectional shape is arranged on an outer circumference of the bead core 5. The carcass layer 4 is folded back around the bead core 5 from an inside to an outside in the tire width direction. Accordingly, the bead core 5 and the bead filler 6 are enclosed by a body section (a section extending from the tread section 1 through the respective sidewall sections 2 to each of the bead sections 3) and a folded-back section (a section folded back around the bead core 5 of each bead section 3 and extending toward the respective sidewall section 2) of the carcass layer 4.For example, polyester cord threads are preferably used as the reinforcing cord threads of carcass layer 4.

[0017] On the other hand, a plurality (in the illustrated example, two layers) of belt layers 7 are embedded on an outer circumferential side of the carcass layer 4 in the tread section 1. Each belt layer 7 encloses a plurality of reinforcing cord threads inclined with respect to the tire's circumferential direction and is arranged such that the reinforcing cords of the different layers intersect. In these belt layers 7, the angle of inclination of the reinforcing cord threads with respect to the tire's circumferential direction is set within a range of, for example, 10° to 40°. For example, steel cords are preferably used as the reinforcing cord threads of the belt layers 7.

[0018] A belt cover layer 8 is provided on an outer circumferential side of the belt layers 7 to improve high-speed durability and reduce road noise. The belt reinforcement layer 8 includes organic fiber cord threads oriented in the tire's circumferential direction. In the belt reinforcement layer 8, the angle of the organic fiber cord threads with respect to the tire's circumferential direction is, for example, set to 0° to 5°. In one embodiment of the present invention, the belt cover layer 8 always includes a full cover layer 8a that covers the entire area of ​​the belt layers 7 and can optionally be configured to include a pair of edge cover layers 8b that locally cover both end sections of the belt layers 7 (in the illustrated example, both the full cover layer 8a and the edge cover layers 8b).The belt cover layer 8 is preferably configured such that a strip material made of at least one single organic fiber cord thread, which is bundled and covered with coating rubber, is wound spirally in the circumferential direction of the tire and preferably has a seamless structure.

[0019] In one embodiment of the present invention, a polyethylene terephthalate fiber cord (PET fiber cord) is used as the organic fiber cord thread of which the belt cover layer 8 consists. The modulus of elasticity of this PET fiber cord thread, under a load of 2.0 cN / dtex at 100°C, is in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%). By using a specific PET fiber cord thread as the organic fiber cord thread forming the belt cover layer 8, it is possible to effectively reduce road noise while simultaneously maintaining the durability of the pneumatic tire. If the modulus of elasticity of this PET fiber cord thread is less than 3.5 cN / (tex·%) under a load of 2.0 cN / dtex at 100°C, the road noise in the mid-frequency range cannot be sufficiently reduced.If the modulus of elasticity of the PET fiber cord exceeds 5.5 cN / (tex·%) at a load of 2.0 cN / dtex at 100 °C, the fatigue resistance of the cord decreases and the durability of the tire diminishes. In one embodiment of the present invention, the modulus of elasticity [N / (tex·%)] at a load of 2.0 cN / dtex at 100 °C is calculated by performing a tensile test under the conditions of a gripping interval of 250 mm and a tensile speed of 300 ± 20 mm / min according to the "Test methods for tire cords made of synthetic fibers" of JIS-L1017 and converting the slope of the tangent at the point corresponding to the load of 2.0 cN / dtex of the load-strain curve into the value per tex.

[0020] When this organic fiber cord thread (PET fiber cord thread) is used as the belt cover layer 8, the internal tension of the cord thread within the tire can preferably be 0.9 cN / dtex or more, more preferably 1.5 cN / dtex to 2.0 cN / dtex. By adjusting the tension of the cord thread within the tire, heat generation can be suppressed and the tire's durability improved. If the cord thread tension of this organic fiber cord thread (PET fiber cord thread) within the tire is less than 0.9 cN / dtex, the peak value of tanδ increases, and the improvement in tire durability cannot be sufficiently achieved. The cord thread tension of the organic fiber cord thread (PET fiber cord thread) within the tire, forming the belt cover layer 8, is measured at two or more turns on the inside in the tire's width direction from the end of the strip material forming the belt cover layer.

[0021] In the event that PET fiber cord threads are used as organic fiber cord threads forming the belt cover layer 8, the PET fiber cord threads preferably have a heat shrinkage stress of 0.6 cN / tex or more at 100 °C. The heat shrinkage stress at 100 °C is set as described above, and thus road noise can be effectively reduced while more successfully maintaining the durability of the pneumatic tire. If the heat shrinkage stress of the PET fiber cord threads at 100 °C is less than 0.6 cN / tex, the tire's performance during driving cannot be sufficiently improved, and it is difficult to maintain adequate durability at high speeds. The upper limit of the heat shrinkage stress of the PET fiber cord threads at 100 °C is not subject to any specific restrictions, but is preferably, for example, 2.0 cN / tex.It should be noted that in one embodiment of the present invention, the heat shrink tension (cN / tex) at 100 °C is the heat shrink tension of a cord thread as measured according to the “Test methods for man-made fiber tire cord threads” of JIS-L1017 and when heated under the conditions of a sample length of 500 mm and a heating condition of 100 °C for 5 minutes.

[0022] To obtain PET fiber cord threads with the aforementioned physical properties, for example, it is preferred to optimize the dip treatment. In other words, an immersion treatment with adhesive is carried out on the PET fiber cord threads before a calendering process; however, in a normalization process following a two-bath treatment, it is preferred that an ambient temperature in the range of 210 °C to 250 °C is set and the cord tension in the range of 2.2 × 10 -2 N / tex up to 6.7×10 7 2N / tex is set. Accordingly, the PET fiber cord threads can be given the desired physical properties, as described above. If the cord thread tension in the normalization process is less than 2.2 × 10 -2 If the N / tex value is low, the cord thread elasticity modulus is low, and therefore the medium-frequency road noise cannot be sufficiently reduced. However, if the cord thread tension is greater than 6.7 × 10 -2 If N / tex is high, the cord thread elasticity modulus is high, and therefore the fatigue resistance of the cord threads decreases.

[0023] In the tread section 1, a tread rubber layer 10 is arranged on the outer circumferential side of the aforementioned tire components (the carcass layer 4, the belt layer 7, and the belt cover layer 8). In particular, in one embodiment of the present invention, the tread rubber layer 10 has a structure in which two types of rubber layers with different physical properties (an upper tread layer 11 and an under tread layer 12) are layered in the radial direction of the tire. A sidewall rubber layer 20 is arranged on the outer circumferential side (the outside in the tire width direction) of the carcass layer 4 in the sidewall section 2, and a rim cushion rubber layer 30 is arranged on the outer circumferential side (the outside in the tire width direction) of the carcass layer 4 in the bead section 3.

[0024] The organic fiber cord yarn (PET fiber cord yarn) from which the belt cover layer 8 is made is coated with coating rubber (hereinafter referred to as the coating rubber of the belt cover layer). The rubber composition of the coating rubber always contains natural rubber as a rubber component, optionally including styrene-butadiene rubber and / or butadiene rubber in combination. The natural rubber is present in the rubber component in an amount of 50% by weight or more, preferably 60% by weight or more. Preferably, two types of natural rubber and styrene-butadiene rubber are used together, or three types of natural rubber, styrene-butadiene rubber, and butadiene rubber are used. In the first case, the proportion of natural rubber in the mixture can be 60% to 80% by mass, and the proportion of styrene-butadiene rubber in the mixture can be 20% to 40% by mass.In the latter case, the proportion of natural rubber in the mixture can be 50% to 70% by mass, the proportion of styrene-butadiene rubber can be 10% to 40% by mass, and the proportion of butadiene rubber can be 5% to 20% by mass. In any case, the desired effect of the present invention cannot be sufficiently achieved if the proportion of natural rubber in the mixture is less than 50% by mass. The natural rubber, styrene-butadiene rubber, and butadiene rubber used can be those normally used for pneumatic tires (in particular, the lining rubber of the belt).

[0025] In one embodiment of the present invention, zinc oxide is always added to the rubber composition of which the belt coating rubber is made. The proportion of zinc oxide in the mixture is 5.0 to 9.0 parts by mass, preferably 6.5 to 8.5 parts by mass per 100 parts by mass of the rubber component. This zinc oxide mixture improves the physical properties of the belt coating rubber, which has a beneficial effect on the tire's durability. If the proportion of zinc oxide in the mixture is less than 5.0 parts by mass, it becomes difficult to ensure sufficient hardness of the belt coating rubber. If the proportion of zinc oxide in the mixture exceeds 9.0 parts by mass, the fatigue resistance may decrease.

[0026] In one embodiment of the present invention, carbon black can further be added to the rubber composition that forms the belt coating rubber. The proportion of carbon black in the mixture is preferably 35 to 65 parts by mass, and more preferably 40 to 60 parts by mass per 100 parts by mass of the rubber component. By mixing carbon black in this way, hardness and strength can be increased, and it becomes possible to use it for belt coating rubber. If the proportion of carbon black in the mixture is less than 35 parts by mass, it becomes difficult to ensure sufficient hardness and strength of the belt coating rubber. If the proportion of carbon black in the mixture exceeds 65 parts by mass, the rolling resistance may deteriorate.

[0027] When soot is mixed as described above, the specific nitrogen adsorption surface area N2SA of soot is preferably 35 m². 2 / g up to 120 m 2 / g, and preferably more than 40 m2 / g up to 90 m 2 / g. By using specific carbon black, the hardness and strength of the belt coating rubber can be increased accordingly. If the specific nitrogen adsorption surface area (N₂SA) of the carbon black is less than 35 m² 2 If the specific nitrogen adsorption surface area (N2SA) of the carbon black exceeds 120 m² / g, it becomes difficult to adequately ensure the hardness and strength of the belt coating rubber. 2 / g, the rolling resistance can worsen. In one embodiment of the present invention, the specific nitrogen adsorption surface area N2SA of the carbon black is measured according to JIS K6217-7.

[0028] In one embodiment of the present invention, sulfur can be added to the rubber composition forming the belt coating rubber. The proportion of sulfur in the mixture is preferably 2.0 to 3.5 parts by mass, and more preferably 2.3 to 3.2 parts by mass, based on 100 parts by mass of the rubber component. This sulfur mixture can correspondingly increase the hardness of the belt coating rubber. If the proportion of sulfur in the mixture is less than 2.0 parts by mass, it becomes difficult to ensure sufficient hardness of the belt coating rubber. If the proportion of sulfur in the mixture exceeds 3.5 parts by mass, the elongation of the belt coating rubber may decrease.

[0029] In one embodiment of the present invention, a vulcanization accelerator can be added to the rubber composition forming the belt coating rubber. The proportion of the vulcanization accelerator is preferably 0.5 to 2.0 parts by mass, and more preferably 0.7 to 1.5 parts by mass per 100 parts by mass of the rubber component. This addition of the vulcanization accelerator increases the hardness of the belt coating rubber accordingly. If the proportion of the vulcanization accelerator is less than 0.5 parts by mass, it becomes difficult to ensure sufficient hardness of the belt coating rubber. If the proportion of the vulcanization accelerator exceeds 2.0 parts by mass, the elongation of the belt coating rubber may decrease.

[0030] The belt coating rubber has the composition mentioned above, and its tensile strength at 100 °C is preferably 10.0 MPa or more, more preferably 11 MPa or more, and even more preferably 12 MPa or more. The elongation at break of the belt coating rubber at 100 °C is preferably 280% or more, more preferably 300% or more, and even more preferably 330% or more. Additionally, the modulus at 100% elongation (M100) is preferably 1.5 MPa to 3.5 MPa, and more preferably 1.8 MPa to 3.2 MPa. By adjusting the physical properties, the belt coating rubber exhibits a physical characteristic suitable for use in combination with the aforementioned organic fiber cord (PET fiber cord), which is advantageous in improving the tire's durability. If the tensile strength is less than 10.0 MPa, it will be difficult to adequately ensure durability.If the elongation at break is less than 280%, it becomes difficult to ensure sufficient strength. If the modulus at 100% elongation (M100) is less than 1.5 MPa, steering stability decreases. If the modulus at 100% elongation (M100) exceeds 3.5 MPa, adhesion may decrease and high-speed strength may deteriorate. In one embodiment of the present invention, the tensile strength, elongation at break, and modulus at 100% elongation (M100) are measured according to JIS K6251 using a No. 3 barbell at a tensile speed of 500 mm / min and a temperature of 100 °C.

[0031] The storage modulus E1 (100 °C) range of the belt coating rubber, measured under conditions of static strain of 10%, dynamic strain of ±2%, a frequency of 20 Hz, and a temperature of 100 °C according to JIS K6394:2007, can preferably be 3.0 MPa or more and 6.0 MPa or less, preferably 3.5 MPa to 5.5 MPa. Adjusting the storage modulus in this way can improve high-speed durability. If the storage modulus E1 (100 °C) deviates from the above range, it will be difficult to achieve satisfactory high-speed strength.

[0032] In one embodiment of the present invention, the modulus of elasticity for each of the organic fiber cord threads (PET fiber cord thread) and the belt coating rubber forming the belt cover layer 8 is determined as described above. However, if the modulus of elasticity (modulus of elasticity at a load of 2.0 cN / dtex at 100 °C) of the organic fiber cord thread (PET fiber cord thread) forming the belt cover layer 8 is A and the modulus of elasticity (the storage modulus E1 (100 °C), measured under conditions of a static strain of 10%, a dynamic strain of ±2%, a frequency of 20 Hz, and a temperature of 100 °C) of the belt coating rubber is B, the ratio A / B can preferably be 0.6 to 1.6 and more preferably 0.7 to 1.5. By determining the ratio of the modulus of elasticity in this way, the resistance at high speeds can be effectively improved.If the A / B ratio deviates from the range mentioned above, it will be difficult to achieve satisfactory high-speed stability.

[0033] In the vulcanized belt coating rubber, the proportion of free sulfur (sulfur atoms that remain in a free state without participating in crosslinking after vulcanization) in the rubber can preferably be 0.2% or less, more preferably 0.15% or less, and even more preferably 0.08% or less. By keeping the proportion of free sulfur low in this way, high-speed durability can be effectively improved. If the proportion of free sulfur exceeds 0.2%, the improvement in high-speed durability cannot be sufficiently achieved. In one embodiment of the present invention, the proportion of free sulfur is measured according to JIS K6234. Examples

[0034] Tires of the conventional example 1, comparison examples 1 to 5 and examples 1 to 13 with a tire size of 225 / 60R18 were manufactured, which meet the requirements of the test described in the following example: Fig. The basic structure is illustrated in Figure 1. The elastic modulus [cN / (tex·%)] at a load of 2.0 cN / dtex at 100 °C and the internal cord tension [cN / dtex] were specified for the organic fiber cord thread (PET fiber cord thread) forming the belt cover layer, as shown in Tables 1 and 2, and for the rubber composition mixture forming the coating rubber, a tensile strength TB (100 °C) [MPa] at 100 °C, an elongation at break EB (100 °C) [%] at 100 °C, the storage modulus E1 (100 °C) [MPa] at 100 °C, and the free sulfur content [%] were specified for the coating rubber (belt coating rubber) covering the organic fiber cord thread (PET fiber cord thread), as shown in Tables 1 and 2.

[0035] In these examples, the belt cover layer has a seamless structure in which a strip formed by bundling an organic fiber cord thread (PET fiber cord thread) and its coating rubber is wound spirally in the tire's circumferential direction. The cord thread density in the strip is 50 cord threads / 50 mm. Furthermore, each organic fiber cord thread (PET fiber cord thread) has a structure of 1100 dtex / 2.

[0036] In each example, the modulus of elasticity [N / (tex·%)] at a load of 2.0 cN / dtex at 100 °C was calculated by performing a tensile test under conditions of a gripping interval of 250 mm and a tensile speed of 300 ± 20 mm / min according to the "Test methods for man-made fiber tire cord threads" of JIS-L1017. The slope of the tangent at the point corresponding to the load of 2.0 cN / dtex on the load-strain curve was then converted into the value per tex. Furthermore, the tire-internal cord thread tension [cN / dtex] was determined by removing the tread rubber from the tread section to expose the belt cover, peeling the fiber cord thread from a predetermined length range of the belt cover, measuring the length after removal, and determining the amount of contraction relative to the length before removal.Specifically, the average contraction value was determined for five cord threads positioned in the middle of the belt layer on the outermost side. Subsequently, the load (%) corresponding to the degree of contraction was calculated from the SS curve and measured by converting it to the value per dtex.

[0037] In each example, the tensile strength TB (100 °C) [MPa] of the belt coating rubber at 100°C, the elongation at break EB (100°C) [%] at 100°C and the storage modulus E1 (100°C) at 100°C [MPa] were measured by vulcanizing the rubber composition of each example for 5 minutes at 180°C, using a pre-shaped mold to produce 2 mm thick, sheet-shaped, vulcanized rubber test pieces and performing the measurement using these pieces according to the following procedures. TB (100°C) and EB (100°C)

[0038] Using the vulcanized rubber test pieces of each example, dumbbell-shaped test pieces of type JIS No. 3 according to JIS K6251 were produced, a tensile test was carried out under the conditions of a tensile speed of 500 mm / min and a temperature of 100°C using a fully automatic tensile testing machine with a thermal chamber, Strograph AR-T (available from Toyo Seiki Seisaku-sho, Ltd.), and the tensile stress (tensile strength TB (100 °C) [MPa] at 100 °C) and the elongation at break (elongation at break EB (100 °C) [%] at 100 °C) were measured. E1 (100 °C)

[0039] Using the rubber test pieces of each example, the storage modulus E1 (100°C) [MPa] at 100°C was measured under the conditions of a strain deformation of 10 % ±2 %, a vibration frequency of 20 Hz and a temperature of 100°C according to JIS K6394: 2007 using a viscoelastic spectrometer (available from Toyo Seiki Seisaku-sho, Ltd.).

[0040] The percentage of free sulfur [%] was measured using the sodium sulfite method described in JIS K6234.

[0041] Road noise, resistance to damp heat, and resistance to high speeds were evaluated for these test tires using the following procedures, and the results are also shown in Tables 1 and 2. street noise

[0042] Each test tire was mounted on a wheel with a rim size of 18×7J, as the front and rear wheels of a passenger car (front-wheel drive vehicle) with a 2.5 L engine, and inflated to a pressure of 230 kPa. A sound-collecting microphone was placed on the inside of the driver's seat window. A sound pressure level at or near the frequency of 315 Hz was measured when the vehicle was driven at an average speed of 50 km / h on a test track with an asphalt road surface. The evaluation results were based on a state-of-the-art example as a reference and indicated the magnitude of change (dB) of the reference. Resistance to humid heat

[0043] Each test tire was mounted on wheels with a rim size of 18×7J, inflated with oxygen to an internal pressure of 230 kPa, and kept for 30 days in a chamber maintained at a temperature of 70 °C and a humidity of 95%. The pre-treated test tires were then mounted on a drum testing machine with a smooth steel drum measuring 1707 mm in diameter, and the ambient temperature was controlled to 38 ± 3 °C. The speed was increased every 24 hours from 120 km / h in 10 km / h increments, and the mileage until tire failure was measured. The evaluation results are expressed as index values ​​using measured distances, with an index value of 100 assigned to the prior art example 1. Higher index values ​​indicate a greater distance traveled before failure and better resistance in humid heat. Durability at high speed

[0044] Each test tire was mounted on a wheel with a rim size of 18×7J, inflated to a pressure of 230 kPa, mounted on an indoor drum testing machine (drum diameter 1707 mm), and subjected to a high-speed durability test according to JIS D4230. The speed was then increased by 8 km / h every hour, and the distance traveled until tire failure was measured. The evaluation results are expressed as index values ​​using the measured distances, with an index value of 100 assigned to the state-of-the-art example 1. Higher index values ​​indicate a longer distance traveled before failure and better resistance in humid heat. Resistance to dry heat

[0045] Each test tire was mounted on a wheel with a rim size of 18×7J, inflated to an oxygen pressure of 350 kPa, and stored in a Geer oven at a temperature of 80 °C for 5 days. These dry-heat pre-treated tires were then inflated to a pressure of 230 kPa, mounted on an indoor drum testing machine (drum diameter 1707 mm), and subjected to a high-speed durability test according to JIS D4230. Subsequently, the speed was increased by 8 km / h every hour, and the distance traveled until tire failure was measured. The evaluation results are expressed as index values ​​using measured distances, with an index value of 100 assigned to the prior art example 1. Higher index values ​​indicate a greater distance traveled before failure and better dry-heat durability. [Table 1-I] State of the art example 1 Comparative example 1 Comparative example 2 Comparative example 3 Organic fiber cord thread modulus of elasticity cN / (tex·%) 2,0 5,8 3,2 4,5 Cord thread tension in the tire cN / dtex 0,7 0,7 0,7 0,7 Coating rubber NR Mass parts 45 45 45 45 SBR Mass parts 55 55 55 55 CB1 Mass parts 40 40 40 40 CB2 Mass parts CB3 Mass parts Aroma oil Mass parts 5 5 5 5 Age-delaying agents Mass parts 0,5 0,5 0,5 0,5 Stearic acid Mass parts 1,2 1,2 1,2 1,2 Zinc dioxide Mass parts 4,5 4,5 4,5 4,5 Vulcanization accelerator Mass parts 1,2 1,2 1,2 1,2 Insoluble sulfur Mass parts 2,8 2,8 2,8 2,8 TB (100 °C) MPa 11,2 11,2 11,2 11,2 EB (100°C) % 350 350 350 350 E1 (100°C) MPa 4,1 4,1 4,1 4,1 Free sulfur % 0,05 0,05 0,05 0,05 road noise level dB 0 -2,8 -0,5 -1,8 Resistance to humid heat Resistance to humid heat Index value 100 95 90 88 Durability at high speed Index value 100 98 103 103 Resistance to dry heat Index value 100 96 101 101 [Table 1-II] Comparative example 4 Example 1 Example 2 Example 3 Example 4 Organic fiber cord thread modulus of elasticity cN / (tex·%) 4,5 3,8 4,5 5,0 5,3 Cord thread tension in the tire cN / dtex 0,7 0,7 0,7 0,7 0,7 Coating rubber NR Mass parts 45 70 70 70 70 SBR Mass parts 55 30 30 30 30 CB1 Mass parts 40 40 40 40 40 CB2 Mass parts CB3 Mass parts Aroma oil Mass parts 5 5 5 5 5 Age-delaying agents Mass parts 0,5 0,5 0,5 0,5 0,5 Stearic acid Mass parts 1,2 1,2 1,2 1,2 1,2 Zinc dioxide Mass parts 6,5 6,5 6,5 6,5 6,5 Vulcanization accelerator Mass parts 1,2 1,2 1,2 1,2 1,2 Insoluble sulfur Mass parts 2,8 2,8 2,8 2,8 2,8 TB (100°C) MPa 11,2 12,8 12,8 12,8 12,8 EB (100°C) % 350 410 410 410 410 E1 (100°C) MPa 4,1 4,6 4,6 4,6 4,6 Free sulfur % 0,05 0,05 0,05 0,05 0,05 [Table 2-I] Example 5 Example 6 Comparative example 5 Example 7 Example 8 Organic fiber cord thread modulus of elasticity cN / (tex·%) 4,5 4,5 4,5 4,5 4,5 Cord thread tension in the tire cN / dtex 0,7 0,7 0,7 0,7 0,7 Coating rubber NR Mass parts 70 70 70 70 80 SBR Mass parts 30 30 30 30 20 CB1 Mass parts 40 40 40 20 CB2 Mass parts 40 CB3 Mass parts 20 Aroma oil Mass parts 5 5 5 5 5 Age-delaying agents Mass parts 0,5 0,5 0,5 0,5 0,5 Stearic acid Mass parts 1,2 1,2 1,2 1,2 1,2 zinc oxide Mass parts 7,5 8,5 9,5 7,5 7,5 Vulcanization accelerator Mass parts 1,2 1,2 1,2 1,2 1,2 Insoluble sulfur Mass parts 2,8 2,8 2,8 3,5 3,5 TB (100°C) MPa 13 12,5 12,0 9,8 13,9 EB (100°C) % 400 380 340 270 420 E1 (100°C) MPa 4,5 4,3 4,1 4,1 4,9 Free sulfur % 0,05 0,05 0,05 0,05 0,05 road noise level dB -2,8 -2,8 -2,8 -2,8 -2,8 Resistance to humid heat Index value 117 116 97 108 119 Durability at high speed Index value 118 115 94 106 120 Resistance to dry heat Index value 115 118 99 103 123 [Table 2-II] Example 9 Example 10 Example 11 Example 12 Example 13 Organic fiber cord thread modulus of elasticity cN / (tex·%) 4,5 4,5 4,5 4,5 4,5 Cord thread tension in the tire cN / dtex 0,7 0,7 0,7 0,7 0,7 Coating rubber NR Mass parts 60 70 70 70 70 SBR Mass parts 40 30 30 30 30 CB1 Mass parts 45 50 40 40 CB2 Mass parts 40 CB3 Mass parts Aroma oil Mass parts 15 5 2 5 5 Age-delaying agents Mass parts 0,5 0,5 0,5 0,5 0,5 Stearic acid Mass parts 1,2 1,2 1,2 1,2 1,2 zinc oxide Mass parts 7,5 7,5 7,5 7,5 7,5 Vulcanization accelerator Mass parts 1,2 1,2 1,2 1,0 0,6 Insoluble sulfur Mass parts 2,8 2,8 2,8 2,8 2,8 TB (100°C) MPa 9,5 12,8 12,8 13,0 10,9 EB (100°C) % 520 350 290 420 520 E1 (100°C) MPa 2,8 5,0 6,1 4,4 3,5 Free sulfur % 0,05 0,05 0,05 0,12 0,3 road noise level dB -2,7 -2,8 -2,9 -2,8 -2,8 Resistance to humid heat Index value 105 116 106 117 104 Durability at high speed Index value 106 114 106 117 103 Resistance to dry heat Index value 105 112 107 116 107

[0046] The types of starting materials used in Tables 1 and 2 are described below. • NR: Natural rubber, STR 20 • SBK: Styrene-butadiene rubber, SBR 1502, available from ZEON CORPORATION • CB1: Carbon black (HAF), Show Black N330, available from Cabot Japan KK • CB2: Carbon black (GPF), Niteron #NG, available from Nippon Stahl Chemical Carbon Co. Ltd. • CB3: Carbon black (ISAF), Show Black N234, available from Cabot Japan KK • Aroma oil: Extract No. 4S, available from Showa Shell Sekiyu KK • Aging retardant: NOCRAC 224, available from Ouchi Shinko Chemical Industrial Co., Ltd. • Stearic acid: Stearic acid spheres NY, available from Nippon Oil & Fats Co., Ltd. • Zinc oxide: Zinc oxide III, available from Seido Chemical Industry Co., Ltd. • Vulcanization accelerator: NS-G, available from Sanshin Chemical Industry Co., Ltd. • Insoluble sulfur: MUCRON OT-20 (sulfur content: 80 wt%), available from Shikoku Chemicals Corporation

[0047] As shown in Tables 1 and 2, the tires in Examples 1 to 13 exhibited reduced road noise and improved resistance to damp heat, dry heat, and high speed compared to the conventional tires in Example 1 as a reference. On the other hand, in the tire from Comparison Example 1, the elastic modulus of the polyethylene terephthalate cord forming the belt ply was high at a stress of 2.0 cN / dtex at 100 °C, and the proportions of natural rubber and zinc oxide in the coating rubber were low. Therefore, resistance to damp heat, dry heat, and high speed were impaired.In the tire from comparison example 2, the elastic modulus of the polyethylene terephthalate cord thread forming the belt cover layer was low at a load of 2.0 cN / dtex at 100 °C, and the proportions of natural rubber and zinc oxide in the coating rubber were low. Therefore, road noise could not be sufficiently reduced, and resistance to humid heat was impaired. In the tire from comparison example 3, resistance to humid heat was impaired due to the low proportions of natural rubber and zinc oxide in the coating rubber. In the tire from comparison example 4, resistance to humid heat and resistance to high speed were impaired due to the low proportion of natural rubber in the coating rubber.In the tire from comparison example 5, the resistance to humid heat and the resistance to high speed were worsened because the proportion of zinc oxide in the coating rubber was high. List of reference symbols 1 tread section 2 Side wall section 3 bead section 4 Carcass layer 5 bead core 6 bead fillers 7th belt layer 8 Belt cover layer 8a Full top layer 8b Edge cover layer 10 Tread rubber layer 11 Protector tread layer 12 Base tread layer 20 side rubber layer 30 Rim pad rubber layer CL tire equator

Claims

[1] Pneumatic tires, including: a tread section (1) extending in a circumferential direction of the tire and having a ring shape; a pair of sidewall sections (2) which are arranged on both sides of the running surface section (1); a pair of bead sections (3) which are each arranged on an inner side of the pair of sidewall sections (2) in the tire radial direction; a carcass layer (4) arranged between the pair of bead sections (3); a plurality of belt layers (7) arranged on an outer circumferential side of the carcass layer (4) in the tread section (1); and a belt cover layer (8) arranged on an outer circumferential side of the belt layers (7), wherein the belt cover layer (7) is formed by spirally winding an organic fiber cord thread coated with coating rubber along the circumferential direction of the tire, wherein the organic fiber cord thread is a polyethylene terephthalate cord thread, in which an elastic modulus at a load of 2.0 cN / dtex at 100 °C is in the range of 3.5 cN / (tex·%) to 5.5 cN / (tex·%), wherein the coating rubber contains as a rubber component one or more rubbers selected from natural rubber, styrene-butadiene rubber and butadiene rubber, and wherein the coating rubber is formed from a rubber composition in which a proportion of natural rubber in the rubber component is 50% by mass or more and 5.0 parts by mass to 9.0 parts by mass of zinc oxide are mixed in per 100 parts by mass of the rubber component. [2] Pneumatic tire according to claim 1, wherein the internal tire cord tension of the organic fiber cord thread is 0.9 cN / dtex or more. [3] Pneumatic tires according to claim 1 or 2, wherein a tensile strength of the coating rubber at 100 °C is 10.0 MPa or more, and the elongation at break of the coating rubber at 100 °C is 280% or more. [4] Pneumatic tire according to any one of claims 1 to 3, wherein a storage modulus E1 (100 °C) of the coating rubber, measured under conditions of a static strain of 10%, a dynamic strain of ±2%, a frequency of 20 Hz and a temperature of 100°C, is 3.0 MPa ≤ E1 (100°C) ≤ 6.0 MPa. [5] Pneumatic tires according to any one of claims 1 to 4, wherein the proportion of free sulfur in the coating rubber is 0.2% or less.

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