JP2006117099A - Pneumatic radial tire for heavy load - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a long life pneumatic radial tire for heavy load considerably improved in durability of a belt by suppressing deterioration of cord coating rubber of the belt after constituting the belt by three cord layers and reducing the weight of the belt and suppressing traveling growth of the tire. <P>SOLUTION: This tire 1 is provided with the belt 5 constituted of the three rubber coating cord layers 6, 7 and 8. After an inclined angle of a cord of each cord layer 6, 7 and 8 is made a prescribed range, a rubber composition made by blending 1.0 to 5.0 pts.mass of transpolybutadiene rubber, 0.3 to 3.0 pts.mass of HTS, 0.3 to 1.5 pts.mass of vulcanization accelerator CZ or vulcanization accelerator DZ exceeding 1.0 pts.mass and having ≤2.5 pts.mass in 100 pts.mass of rubber component containing a total of 50 to 100 mass% of at least one of natural rubber and polyisoprene rubber is applied to cord coating rubber 6b, 7b and 8b of each cord layer 6, 7 and 8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heavy-duty pneumatic radial tire, and more particularly to a tire for heavy vehicles such as trucks and buses, and more particularly to a tire in which a belt is composed of three rubber-coated cord layers for weight reduction. The present invention relates to a long-life heavy-duty pneumatic radial tire in which the durability of the belt is enhanced by suppressing the deterioration of the cord-coated rubber of the rubber-coated cord layer.

  In general, in heavy-duty pneumatic radial tires used for heavy vehicles such as trucks and buses, the tread belt is composed of four rubber-coated cord layers, and the cord of the first cord layer located closest to the carcass is treaded. An arrangement in which the cords of the second cord layer and the third cord layer intersect with each other across the plane with respect to a plane including the circumference of the portion (that is, a plane parallel to the tire equator plane) (For this reason, the second cord layer and the third cord are called cord intersection layers), and the cords of the fourth cord layer are arranged in the same direction as the cords of the third cord layer, and the inclination angle is also the third cord layer. The inclination angle is almost the same as that of the cord.

  When a tire having a belt composed of the above four rubber-coated cord layers rolls under a load on a rough road, for example, a rough road where crushed stones and small rocks are scattered, the tread portion is crushed stone and small rocks. Stepping on the sharp corners of the belt often leads to cut wounds that reach the belt. Therefore, the main role of the fourth cord layer is protected so that the belt's cut injury is stopped at the fourth cord layer, which is the outermost cord layer, with the aim of avoiding even the slightest possible belt damage due to the cut. Layered configurations have been proposed.

  On the other hand, as with pneumatic radial tires for passenger cars, there is an increasing demand for weight reduction for heavy duty pneumatic radial tires, and belts that occupy a large proportion of the weight of the tire are changed from four cord layers to three cord layers. Has been proposed. For example, a belt composed of a three-layer cord layer described in Japanese Patent Laid-Open No. 2000-85312 (Patent Document 1) has a cord of a third cord layer (outer cord layer) farthest from the carcass relatively to the tire equatorial plane. The first cord layer (innermost cord layer) and the second cord layer (intermediate cord layer) closest to the carcass are arranged as a cord crossing layer, and each cord of the cord crossing layer is arranged on the tire equator plane. Compared to conventional tires with four-layer belts, the belts are applied to tires to reduce the weight of the tires and reduce the separation resistance and cornering performance of the belts. However, it is said that the cut resistance of the belt and the fatigue resistance of the outermost cord layer cord can be significantly improved on a rough road.

JP 2000-85312 A

  However, when a tire including a belt including the three cord layers is actually verified, the cord crossing layer is located on the inner side (carcass side) of the tire than the conventional tire including the belt including the four cord layers. Therefore, it was confirmed that oxygen in the filling air reaches the cord crossing layer faster, accelerates the deterioration of the cord-covered rubber, and decreases the durability against the belt failure. Further, it was found that the reduction in the cord layer by one increases the tire circumferential length after running, increases the strain input at the belt end, and accelerates the crack extension.

  Accordingly, an object of the present invention is to solve the above-described problems of the prior art, and to reduce the weight of the cord-coated rubber of the belt while presupposing that the belt is composed of three cord layers to reduce the weight. An object of the present invention is to provide a long-life pneumatic radial tire for heavy loads, which suppresses running growth and greatly improves the durability of the belt.

  As a result of intensive investigations to achieve the above object, the present inventor, in a heavy-duty pneumatic radial tire provided with a belt consisting of three cord layers, has a rubber composition having a specific composition in the cord-coated rubber of the cord layer. It has been found that the durability of the belt is improved and the life of the heavy-duty pneumatic radial tire can be significantly improved by applying the object, and the present invention has been completed.

That is, the heavy duty pneumatic radial tire of the present invention has a radial carcass that reinforces a pair of sidewall portions and a tread portion between bead cores embedded in a pair of bead portions, and a tread portion is reinforced at the outer periphery of the carcass. The belt has three rubber-coated cord layers, and among the cord layers, the innermost cord layer and the intermediate cord layer cross each other across a plane in which the cord of each layer includes the tread circumference. In heavy duty pneumatic radial tires that become cord crossing layers,
Each cord of the innermost cord layer and the intermediate cord layer has an inclination angle within a range of 10 to 25 degrees with respect to the plane, and the cord of the outermost cord layer is from the plane of the cord of the middle cord layer The inclination angle of the rubber-coated cord layer is a steel cord having an inclination angle within a range of 45 to 115 ° with respect to the plane as measured in the same direction as the inclination angle of the rubber-coated cord layer. To 100 parts by mass of a rubber component containing a total of 50 to 100% by mass of at least one of natural rubber and polyisoprene rubber in the cord-coated rubber, 1.0 to 5.0 parts by mass of transpolybutadiene rubber and 0.3 to 3.0 parts by mass of 1, A rubber composition comprising 6-hexamethylenedithiosulfate sodium dihydrate and 0.3 to 1.5 parts by mass of N-cyclohexyl-2-benzothiazylsulfenamide is applied.

Another heavy-duty pneumatic radial tire of the present invention includes a radial carcass for reinforcing a pair of sidewall portions and a tread portion between bead cores embedded in a pair of bead portions, and a tread portion on the outer periphery of the carcass. The belt has three rubber-coated cord layers, and the innermost cord layer and the intermediate cord layer of these cord layers sandwich the plane in which the cord of each layer includes the tread portion circumference. In heavy duty pneumatic radial tires that become cord crossing layers that cross each other,
Each cord of the innermost cord layer and the intermediate cord layer has an inclination angle within a range of 10 to 25 degrees with respect to the plane, and the cord of the outermost cord layer is from the plane of the cord of the middle cord layer The inclination angle of the rubber-coated cord layer is a steel cord having an inclination angle within a range of 45 to 115 ° with respect to the plane as measured in the same direction as the inclination angle of the rubber-coated cord layer. To 100 parts by mass of a rubber component containing a total of 50 to 100% by mass of at least one of natural rubber and polyisoprene rubber in the cord-coated rubber, 1.0 to 5.0 parts by mass of transpolybutadiene rubber and 0.3 to 3.0 parts by mass of 1, A rubber composition comprising 6-hexamethylenedithiosulfate sodium dihydrate and N, N′-dicyclohexyl-2-benzothiazolylsulfenamide exceeding 1.0 part by mass and not more than 2.5 parts by mass Applied It is characterized by.

  In a preferred example of the heavy-duty pneumatic radial tire of the present invention, the rubber composition applied to the cord-coated rubber is 0.3 to 2.5 parts by mass of an adhesion promoter and 4.0 to 6.5 parts by mass with respect to 100 parts by mass of the rubber component. Contains part by weight of sulfur. In this case, the adhesiveness between the cord covering rubber and the steel cord can be improved while sufficiently securing the aging characteristics of the cord covering rubber while preventing the cord covering rubber from being overvulcanized.

In another preferred embodiment of the heavy-duty pneumatic radial tire of the present invention, the rubber composition applied to the cord-coated rubber has a nitrogen adsorption specific surface area (N ₂ SA) of 70 with respect to 100 parts by mass of the rubber component. It contains 40-80 parts by mass of carbon black having a viscosity of ˜90 m ² / g and a dibutyl phthalate (DBP) oil absorption of 70-110 mL / 100 g. In this case, it is possible to improve the reinforcing property, heat generation property and anti-destructive property of the cord-coated rubber.

  In another preferred embodiment of the heavy-duty pneumatic radial tire of the present invention, the total content of natural rubber and polyisoprene rubber in the rubber component of the rubber composition applied to the cord-coated rubber is 95 to 100% by mass. .

  In the heavy duty pneumatic radial tire of the present invention, the trans polybutadiene rubber preferably has a trans bond content of 82 to 98 mol% and a weight average molecular weight of 30,000 to 200,000. In this case, the effect of promoting the stretched crystallinity of the natural rubber and isoprene rubber can be sufficiently obtained, and the rubber composition has a good balance between the processability when not vulcanized and the physical properties when vulcanized. Note that trans polybutadiene rubber having a trans bond content exceeding 98 mol% is difficult to synthesize.

  In the heavy duty pneumatic radial tire of the present invention, the rubber composition applied to the cord-coated rubber has a tensile stress of 4.5 MPa or more at 100% elongation after vulcanization and 2% at 25 ° C. It is preferable that the loss tangent at the time of strain (tan δ) is 0.26 or less. In this case, the rigidity of the cord-covered rubber is high, the tire can be sufficiently prevented from expanding in the radial direction, the amount of heat generated by the cord-covered rubber is small, and the heat resistance of the cord-covered rubber is sufficiently high.

  Furthermore, in the heavy duty pneumatic radial tire of the present invention, the rubber composition applied to the cord-coated rubber preferably has a 90% vulcanization time of 12 to 25 minutes at 145 ° C. In this case, it is possible to prevent the cord coating rubber from being overvulcanized, and to suppress the deterioration of the anti-destructive property and heat generation of the cord coating rubber, and it is not necessary to lengthen the vulcanization time. It is possible to prevent the deterioration resistance of the rubber from being lowered.

  According to the present invention, the belt is composed of three cord layers to reduce the weight of the tire, and the cord composition of the belt is applied by applying a rubber composition having a specific composition to the cord coating rubber of the cord layer. It is possible to provide a heavy-duty pneumatic radial tire for a long life that suppresses deterioration of rubber and suppresses the growth of the tire to greatly improve the durability of the belt.

  The heavy duty pneumatic radial tire of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a perspective view in which a part of a tread portion of a heavy-duty pneumatic radial tire according to the present invention is taken out, a part of the tread rubber is cut out, and a belt and a carcass are exposed, and FIG. 2 is shown in FIG. It is explanatory drawing which shows the front development of a part of tread part of a tire, combines the belt development view which cut off the tread rubber, and gave the step-down cut, and the tread pattern development view.

  In FIG. 1, a heavy-duty pneumatic radial tire 1 has a pair of bead portions (not shown), a pair of sidewall portions (not shown), and a tread portion 2 connected to both sidewall portions. Has tread rubber 3 on the tread side. Further, the tire 1 has one or more plies (in the illustrated example, one ply) that reinforce the pair of bead portions, the pair of sidewall portions, and the tread portion 2 between bead cores (not shown) embedded in the pair of bead portions. A radial carcass 4 having a rubber-coated radial arrangement code, and a belt 5 for reinforcing the tread portion 2 on the outer periphery of the carcass 4.

  1 and 2, the belt 5 is composed of three rubber-coated cord layers 6, 7, and 8, and the cords 6 a and 7 a of the innermost cord layer 6 and the intermediate cord layer 7 closest to the carcass 4 are tread portions. The innermost cord layer 6 and the intermediate cord layer 7 form a cord intersection layer 9. The innermost cord layer 6 and the intermediate cord layer 7 are arranged so as to cross each other across a plane P including the circumference of 2 (the tire equatorial plane in the illustrated example). The cord 6a of the innermost cord layer 6 and the cord 7a of the intermediate cord layer 7 are inclined with respect to the plane P within a range of 10 to 25 °, preferably within a range of 15 to 22 °. The measurement direction of the inclination angle δ with respect to the plane P of the cord 6a is indicated by an arrow, and the measurement direction of the inclination angle α with respect to the plane P of the cord 7a is indicated by an arrow. Although the plane P shown in FIGS. 1 and 2 exists on the tire equatorial plane, the plane P may be located on any of the tread portions 2.

  In the lower view of FIG. 2, the cord 8a of the outermost cord layer 8 has the same direction (the direction of the arrow in the drawing) as the direction of measuring the inclination angle α from the plane P of the cord 7a of the intermediate cord layer 7 (the direction of the arrow in the drawing). The angle of inclination β in the range of 45 to 115 ° with respect to the plane P, preferably in the range of 50 to 100 °, is measured.

  In the development view of the tread pattern shown in the upper part of FIG. 2, the tread pattern of the tire includes four circumferential grooves 10 and 11 formed in the tread rubber 3 (see FIG. 1) and extending in a straight line in the circumferential direction. Each of the blocks 15, 16, 17 defined by the circumferential grooves 10, 10 adjacent to each other and a large number of lateral grooves 12, 13, 14 opening in the circumferential grooves between the circumferential grooves 10, 11. A block row is provided in the central region of the tread portion 2, and both side regions of the tread portion are provided with a block row of blocks 19 defined by the circumferential grooves 11 and a plurality of lateral grooves 18 opened to the circumferential grooves 11.

  The example shown in FIG. 2 is an example of a block pattern in which the entire region of the tread portion 2 is formed of blocks, but the central region is a land portion such as a rib other than the block, and the both side regions of the tread portion 2 are the same. In other words, the tread portion 2 may be entirely a rib pattern or a combination pattern of ribs and blocks.

  In the tire of the present invention, the cord 6a of the innermost cord layer 6 and the cord 7a of the intermediate cord layer 7 are inclined with respect to the plane P within a range of 10 to 25 °, preferably within a range of 15 to 22 °. On the other hand, the cord 8a of the outermost code layer 8 is measured in the same direction as the direction in which the inclination angle α of the cord 7a of the intermediate cord layer 7 from the plane P is measured, and within the range of 45 to 115 ° with respect to the plane P In the circumferential direction of the tread portion 2 generated in the belt 5 when the tire 1 is filled with the internal pressure, as indicated by an arrow Fx below the FIG. 2, preferably by setting the inclination angle β within a range of 50 to 100 °. The tension Fx is mainly borne by the cords 6a and 7a of the innermost cord layer 6 and the intermediate cord layer 7 that form the cord crossing layer 9 having a small inclination angle with respect to the plane P, and the tension that the outermost cord layer 8 should bear. Can be greatly reduced. Therefore, even when the tread portion 2 of the tire 1 that rolls under a load load rides on a foreign object such as crushed stone or small rock having sharp corner edges, the corner edges penetrate the tread rubber 3 and reach the belt 5. The cord 8a of the outermost cord layer 8 is difficult to cut, and the durability of the tire 1 based on cut resistance is improved.

  In FIG. 2, the belt 5 has a tendency to protrude in the radial direction of the tire 1 due to the tension Fx generated in the belt 5 when the tire 1 is filled with the internal pressure. As a result, the belt 5 as a whole has a width direction. Shrinking inward, the cords 6a, 7a, 8a of the layers 6, 7, 8 of the belt 5 tend to change in the direction in which the inclination angles δ, α, β decrease. However, under the configuration of the belt 5, the cord 8 a of the outermost cord layer 8 has an inclination angle β that is significantly larger than the inclination angles δ and α of the cords 6 a and 7 a of the innermost cord layer 6 and the intermediate cord layer 7. Since it is large, the degree of decrease in the inclination angle is extremely small compared to the cords 6a and 7a. As a result, the outermost cord layer 8 is difficult to contract in the width direction. For this reason, the cord 8 a of the outermost cord layer 8 acts on the cord intersection layer 9 as a so-called stick rod, and the outermost cord layer 8 acts to suppress the shrinkage in the width direction of the cord intersection layer 9. . In the cord crossing layer 9 in which the shrinkage in the width direction is suppressed, the circumferential rigidity of the tread portion 2 is increased, and as a result, the cornering power (hereinafter referred to as CP) is improved even in the tire 1 including the belt 5 having the three-layer configuration. Cornering performance equal to or better than that of a tire including a conventional belt having a four-layer structure can be exhibited. Further, the increase in the circumferential rigidity of the cord crossing layer 9 greatly contributes to suppressing the tire diameter growth when the tire 1 is filled with the internal pressure.

  In addition, it is preferable that the inclination angles δ and α of the cords 6a and 7a of the innermost cord layer 6 and the intermediate cord layer 7 with respect to the plane P are substantially equal to each other from the viewpoint of equally applying tension to the cords 6a and 7a. . Note that the inclination angles δ and α of the cords 6a and 7a are set within the range of 10 to 25 ° because the end portions of the innermost cord layer 6 and the intermediate cord layer 7 when the inclination angles δ and α are less than 10 °. The interlaminar shear strain generated in the tire becomes too large, and a separation failure is likely to occur at the end portion. The effect of suppressing the shrinkage in the width direction of the outer cord layer 8 is not sufficiently exerted, the rigidity in the circumferential direction of the cord crossing layer 9 is remarkably lowered, the CP characteristics are deteriorated, and the tire diameter growth can be sufficiently suppressed. Because it disappears. Furthermore, the inclination angle β of the cord 8a of the outermost cord layer 8 is set within the range of 45 to 115 °, even if the inclination angle β is less than 45 ° or the inclination angle β exceeds 115 °, compared to the conventional tire. This is because the CP characteristics deteriorate.

The covering rubber 8b of the cord 8a of the outermost cord layer 8 preferably has a compression elastic modulus of 200 kgf / cm ² or more. Here, the compression elastic modulus is obtained by filling a rubber test piece into a cavity of a metal, for example, steel jig, having a cylindrical cavity having a diameter d of 14 mm and a height h of 28 mm without any gaps. Set the tool on the compression tester and apply a load w at a speed of 0.6 mm / min to the upper and lower surfaces of the rubber test piece. At this time, measure the displacement of the rubber test piece with a laser displacement meter. It is a value calculated from the relationship. When the tire 1 rolls on a road surface on which foreign objects such as relatively large crushed stones and rocks are scattered and rides on these large foreign objects, the outermost cord layer 8 of the belt 5 is forced to bend and deform with a large curvature. A rubber having a compressive elastic modulus of 200 kgf / cm ² or more is applied to the covering rubber 8b of the cord 8a of the outermost cord layer 8 when a large compressive force acts locally and the cord 8a of the outermost cord layer 8 is buckled. By applying the above, it becomes possible to increase the compression resistance of the cord covering rubber 8b and to prevent the buckling deformation of the cord 8a of the outermost cord layer 8. As a result, even if the tire 1 often rides on foreign matters such as relatively large crushed stones and rocks, the occurrence of cord breakage due to buckling fatigue of the cord 8a of the outermost cord layer 8 can be prevented. Note that this effect is insufficient when the compression elastic modulus of the cord-coated rubber 8b is less than 200 kgf / cm ² .

  In the heavy-duty pneumatic radial tire of the present invention, the cords 6a, 7a, 8a of the rubber-coated cord layers 6, 7, 8 constituting the belt 5 are steel cords, and the rubber-coated cord layers 6, 7, 8 1.0 to 5.0 parts by mass of trans polybutadiene rubber and 0.3 to 0.3 parts by mass of 100 parts by mass of rubber component containing a total of 50 to 100% by mass of at least one of natural rubber and polyisoprene rubber 3.0 parts by weight of sodium 1,6-hexamethylenedithiosulfate dihydrate (HTS) and 0.3 to 1.5 parts by weight of N-cyclohexyl-2-benzothiazylsulfenamide or more than 1.0 part by weight and 2.5 parts by weight A rubber composition obtained by blending the following N, N′-dicyclohexyl-2-benzothiazolylsulfenamide is applied.

  The rubber composition for cord-covered rubber uses a vulcanization accelerator having a strong vulcanization-accelerating action because the amount of the vulcanization accelerator is larger than that of the conventional rubber composition for cord-coated rubber. Therefore, 90% vulcanization time is short, but the adhesiveness with steel cord is sufficiently high. The reason for this is that HTS contained in the rubber composition is a cross-linking agent and reacts with a polymer such as a rubber component, and also reacts with copper during plating of the steel cord, so that the cord-coated rubbers 6b, 7b, 8b and It can be considered that it effectively worked to improve the adhesiveness with the steel cord. This effect of improving adhesiveness is manifested when the rubber composition contains the above vulcanization accelerator in an amount specified in the present invention.

  Further, the rubber composition for cord-coated rubber has a 90% vulcanization time that is short, that is, the vulcanization speed is fast, so that it becomes sufficiently elastic even in a short time vulcanization, while shortening the vulcanization time. Deterioration resistance is remarkably improved. Further, since the rubber composition contains specific amounts of HTS and transpolybutadiene rubber, the creep resistance is also improved.

  Rubber components used in the rubber composition for cord-coated rubber include natural rubber (NR), polyisoprene rubber (IR), styrene / butadiene copolymer rubber (SBR), and trans-polybutadiene rubber (trans-BR). And polybutadiene rubber (BR). Here, the rubber component contains a total of 50 to 100% by mass, preferably 95 to 100% by mass of natural rubber and polyisoprene rubber. When the total content of the natural rubber and the polyisoprene rubber in the rubber component is less than 50% by mass, the anti-destructive property of the rubber composition is lowered.

  The rubber composition for cord-coated rubber contains 1.0 to 5.0 parts by mass of transpolybutadiene rubber with respect to 100 parts by mass of the rubber component. If the blending amount of trans polybutadiene rubber is less than 1.0 part by mass, the adhesion and creep resistance with the steel cord will decrease, and if it exceeds 5.0 parts by mass, the effect of improving the adhesion and creep resistance with the steel cord will be saturated. Cannot be further improved.

  The trans polybutadiene rubber preferably has a trans bond content of 82 to 98 mol%, more preferably 86 to 98 mol%. The higher the trans bond content of the trans polybutadiene rubber, the higher the effect of promoting the stretch crystallinity of natural rubber and isoprene rubber. Here, when the trans bond content of the trans polybutadiene rubber is less than 82 mol%, the effect of promoting the stretched crystallinity of the natural rubber and isoprene rubber cannot be sufficiently obtained. On the other hand, a trans polybutadiene rubber having a trans bond content exceeding 98 mol% is difficult to synthesize.

The trans polybutadiene rubber preferably has a weight average molecular weight (Mw) of 3 × 10 ^{4 to} 20 × 10 ⁴ , and more preferably 5 × 10 ⁴ to 15 × 10 ⁴ . When the weight average molecular weight is within this range, the rubber composition has a good balance between processability when not vulcanized and physical properties when vulcanized. Here, if the weight average molecular weight of the transpolybutadiene rubber is less than 3 × 10 ⁴ , the elastic modulus of the rubber composition after vulcanization tends to decrease, and if it exceeds 20 × 10 ⁴ , workability during unvulcanized Tends to decrease.

The rubber composition for cord-coated rubber has the following formula (I):
NaO ₃ S—S— (CH ₂ ) ₆ —S—SO ₃ Na.2H ₂ O (I)
1-6-hexamethylenedithiosulfate dihydrate (HTS) represented by the formula: 0.3 to 3.0 parts by mass with respect to 100 parts by mass of the rubber component. If the blending amount of HTS is less than 0.3 parts by mass, the reaction between the rubber component and the copper in the steel cord plating does not proceed sufficiently, and the effect of improving the adhesion between the cord-coated rubber 6b, 7b, 8b and the steel cord is obtained. In addition, the creep resistance of the tire cannot be sufficiently improved. On the other hand, if the blending amount of HTS exceeds 3.0 parts by mass, the effect of improving the adhesiveness and creep resistance with the steel cord reaches saturation and cannot be further improved.

  The rubber composition for cord-coated rubber may be abbreviated as N-cyclohexyl-2-benzothiazylsulfenamide (hereinafter referred to as vulcanization accelerator CZ) as a vulcanization accelerator with respect to 100 parts by mass of the rubber component. 0.3 to 1.5 parts by mass of N), or N, N′-dicyclohexyl-2-benzothiazolylsulfenamide (hereinafter sometimes abbreviated as vulcanization accelerator DZ) in excess of 1.0 part by mass and 2.5 Including parts by mass or less. In conventional rubber compositions for cord-coated rubber, a retarding vulcanization accelerator DZ is compounded in an amount of 1.0 part by mass or less, and 90% vulcanization time is 25 minutes or more to ensure adhesion to steel cords. However, the rubber composition used for the cord-coated rubber 6b, 7b, 8b of the belt of the heavy duty tire of the present invention has sufficient adhesiveness to the steel cord by containing a predetermined amount of the above-mentioned transpolybutadiene rubber and HTS. Has been. Therefore, in the rubber composition for cord-coated rubber, the amount of vulcanization accelerator DZ can be increased to increase the vulcanization speed of the rubber composition. Moreover, it can replace with the vulcanization accelerator DZ and can also raise a vulcanization | cure speed | velocity using the vulcanization accelerator CZ. By increasing the vulcanization speed of the rubber composition, a sufficient elastic modulus can be ensured even in a short time, and by shortening the vulcanization time, the cord-coated rubber 6b, 7b, 8b Deterioration resistance can be improved. When the blending amount of the vulcanization accelerator CZ is less than 0.3 parts by mass and the blending amount of the vulcanization accelerator DZ is 1.0 parts by mass or less, the vulcanization rate cannot be sufficiently increased, and the above-mentioned HTS code- The effect of improving rubber adhesion is not sufficiently exhibited. On the other hand, when the compounding amount of the vulcanization accelerator CZ exceeds 1.5 parts by mass and the compounding amount of the vulcanization accelerator DZ exceeds 2.5 parts by mass, the anti-destructive property of the rubber composition is lowered and steel Adhesion with the cord is also reduced.

  The rubber composition used for the cord-coated rubber 6b, 7b, 8b of the belt 5 of the heavy duty tire of the present invention comprises 0.3 to 2.5 parts by mass of an adhesion promoter and 4.0 to 6.5 parts by mass with respect to 100 parts by mass of the rubber component. It is preferable to contain sulfur. When the blending amount of the adhesion promoter is less than 0.3 parts by mass, the adhesiveness with the steel cord is lowered, and when it exceeds 2.5 parts by mass, the aging characteristics of the rubber composition are excessively deteriorated. Further, if the amount of sulfur is less than 4.0 parts by mass, the adhesiveness with the steel cord is insufficient, and if it exceeds 6.5 parts by mass, the rubber composition becomes overvulcanized and the adhesiveness with the steel cord decreases. Here, examples of the adhesion promoter include cobalt naphthenate, cobalt stearate, cobalt neodecanoate, cobalt rosinate, cobalt versatate, and cobalt cobaltate. The adhesion promoter may be a complex salt in which a part of the organic acid is replaced with boric acid or the like.

The rubber composition for cord-coated rubber has a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 90 m ² / g and a dibutyl phthalate (DBP) oil absorption of 70 to 110 mL / g with respect to 100 parts by mass of the rubber component. It is preferable to contain 40 to 80 parts by mass of 100 g of carbon black. If the N ₂ SA of the carbon black is less than 70 m ² / g, the reinforcing property of the rubber composition is lowered, and if it exceeds 90 m ² / g, the exothermic property of the rubber composition is lowered. Further, when the DBP oil absorption of carbon black is less than 70 mL / 100 g, the reinforcing property of the rubber composition is lowered, and when it exceeds 110 mL / 100 g, the dispersion of carbon black is poor and the anti-destructive property of the rubber composition is lowered. come. Furthermore, if the compounding amount of carbon black having such physical properties is less than 40 parts by mass, the reinforcing property of the rubber composition is insufficient, and if it exceeds 80 parts by mass, the exothermic property of the rubber composition decreases.

  The rubber composition for cord-coated rubber preferably has a tensile stress at 100% elongation after vulcanization of 4.5 MPa or more and a loss tangent (tan δ) at 2% strain at 25 ° C. of 0.26 or less. . As the physical properties after vulcanization, if the tensile stress at 100% elongation is less than 4.5 MPa, the elasticity of the rubber is low, and the tire cannot be sufficiently prevented from expanding in the radial direction, and the tire shape is sufficient. It cannot be secured. Further, as physical properties after vulcanization, when tan δ at 2% strain at 25 ° C. exceeds 0.26, the calorific value increases, and the heat resistance of the cord-coated rubbers 6b, 7b, 8b decreases.

  The rubber composition for cord-coated rubber preferably has a 90% vulcanization time of 12 to 25 minutes at 145 ° C. Here, the 90% vulcanization time is the time (minutes) until the torque reaches {(Fmax−Fmin) × 0.9 + Fmin}, where Fmax is the maximum value of torque in the vulcanization curve and Fmin is the minimum value. It is generally used as an index of vulcanization rate. If the 90% vulcanization time at 145 ° C is less than 12 minutes, the tire will be overvulcanized and the anti-destructive properties and heat build-up of the rubber in the tire will be reduced. In order to sufficiently increase the elasticity and creep resistance of the rubber, it is necessary to lengthen the vulcanization time. As a result, the deterioration resistance of the vulcanized rubber decreases.

  The above-mentioned rubber composition for cord-coated rubber includes the above-mentioned rubber component, transpolybutadiene rubber, HTS, vulcanization accelerator, sulfur, adhesion promoter, carbon black, other fillers, vulcanizers, and vulcanizations. Accelerators, further anti-aging agents, scorch inhibitors, softeners, zinc oxide, stearic acid, silane coupling agents, and other commonly used compounding agents within the range that does not impair the purpose of the present invention. It can select suitably and can mix | blend. As these compounding agents, commercially available products can be suitably used. The above rubber composition is produced by kneading, heat-injecting, extruding, etc., a rubber component with trans polybutadiene rubber, HTS, a vulcanization accelerator, and various compounding agents appropriately selected as necessary. Can do.

  In the heavy-duty pneumatic radial tire of the present invention, the cords 6a, 7a, 8a of the rubber-coated cord layers 6, 7, 8 are steel cords, and the steel cords are cord-coated rubbers 6b, 7b, 8b. In order to improve the adhesiveness, it is preferable that plating is performed with brass, zinc, or a metal containing nickel or cobalt, and brass plating is particularly preferable. Further, the size, the number of twists, the twisting conditions and the like of the cord are appropriately selected according to the required performance of the tire.

  The heavy-duty pneumatic radial tire of the present invention is manufactured by an ordinary method using the belt 5 having the three-layer structure. In addition, as gas with which the heavy-duty pneumatic radial tire of the present invention is filled, inert gas such as nitrogen, argon, helium, etc. can be used in addition to normal or air with adjusted oxygen partial pressure.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

  Each compounding component shown in Table 1 was kneaded and mixed to prepare an unvulcanized rubber composition, and tensile stress and deterioration resistance, loss tangent, creep resistance, and adhesion durability were evaluated by the following methods. These results are shown in Table 1.

(1) Tensile stress and deterioration resistance For each rubber composition, a sample vulcanized under conditions of 145 ° C x 45 minutes was prepared, a tensile test was conducted in accordance with JIS K 6301-1995, and 100% elongation was observed. Tensile stress (100% Mod) was measured. Further, in accordance with JIS K 6301-1995, the elongation at break (EB) of the above sample and the elongation at break of a sample thermally deteriorated at 80 ° C. × 24 hours after vulcanization were measured, and the ratio was calculated. Thus, the index was displayed as an index of the conventional example as 100, and used as an index of deterioration resistance. It shows that deterioration resistance is so favorable that an index value is large.

(2) Loss tangent (tan δ)
Using a viscoelasticity measuring machine manufactured by Toyo Seiki Co., Ltd., with a test piece (length 4.9 mm x width 1.0 mm x thickness 1.0 mm) vulcanized under the condition of 145 ° C x 45 minutes statically stretched 4.5% The loss tangent (tan δ) was measured under the conditions of dynamic strain 2.0%, frequency 52 Hz, and measurement temperature 25 ° C. It shows that it is so favorable that tan-delta is small.

(3) Creep resistance Constant stress amplitude strain of test piece (length 4.9mm x width 1.0mm x thickness 1.0mm) vulcanized under the condition of 145 ° C x 45 minutes using Shimadzu dynamic creep tester The creep amount at the time of input was measured, and the creep amount of the conventional example was set to 100 and displayed as an index. The larger the index value, the smaller the creep amount and the better.

(4) Durability of adhesion Coated steel cord (1 × 5 structure, strand diameter 0.25 mm) plated with brass (Cu: 63 mass%, Zn: 37 mass%) with the above unvulcanized rubber composition A rubber composite was prepared, and the composite was vulcanized under conditions of 145 ° C. × 45 minutes, and then deteriorated at 80 ° C. × 80% RH for 10 days. The steel cord was pulled out from the cord-rubber composite after deterioration, the rubber coverage of the steel cord was measured, and the rubber coverage of the cord-rubber composite using the rubber composition of the conventional example was expressed as an index. The larger the index value, the higher the rubber coverage and the higher the adhesion between the steel cord and the cord-coated rubber.

  Next, radial tires for trucks and buses having the structure shown in FIGS. 1 and 2 and having a size of 11R22.5 are used for the cord-coated rubbers 6b, 7b, and 8b of the rubber-coated cord layers of the belt 5. Prototyped. In the table, the cord inclination angle is shown as the cord inclination angle of the code layer given the reference numerals 1B, 2B, 3B, 4B in order from the carcass 4 side (however, 4B does not exist except for the conventional example). In addition, the code | symbol R attached | subjected before the numerical value of an inclination angle represents a code | cord | chord which goes up to the right, and the code | symbol L represents a code | cord | chord which goes up to the left. The cords of each cord layer are all steel cords of 1 × 0.34 + 6 × 0.34, and the number of cords to be driven is 18.0 pieces / 50 mm. Further, the carcass 4 is one ply, and the ply is obtained by rubber-coating a radial arrangement of (3 + 9 + 15) × 0.175 steel cords. Other configurations were in accordance with convention. Next, the test tire obtained was subjected to a durability test, an elongation measurement at the time of cutting the cord-coated rubber between the cord-crossing layers after deterioration, and a running growth test by the following methods. The results are shown in Table 1.

(5) Durability test Drum tests were performed on the test tires in an environment with an internal pressure of 700 kPa, a load of 28.6 kN, a speed of 60 km / h, and a temperature of 40 ° C., and the distance traveled until the tire failed was measured. The index is shown with the mileage of the example tire as 100. The larger the index value, the longer the distance traveled until failure, and the better the durability.

(6) Measurement of elongation at break of cord-covered rubber between cord-crossing layers after deterioration After the test tire was deteriorated under conditions of filling oxygen 800kPa and 40 ° C for 30 days, the tire was dissected and the cord-crossing layer 9 ( The cord-coated rubber between the innermost cord layer 6 and the intermediate cord layer 7) is taken out, and the elongation at break (EB) is measured in accordance with JIS K 6301-1995. The index was displayed. The larger the index value, the greater the elongation at the time of cutting the cord-coated rubber, and the smaller the degradation of the cord-coated rubber, which is better.

(7) Running growth test Drum test was performed for 48 hours under the conditions of load 28.6kN, speed 60km / h, temperature 40 ° C on the test tire filled with internal pressure 800kPa. From the tire radius before and after the test, The growth rate (%) was calculated and indicated as an index with the radius growth rate of the conventional tire as 100. The smaller the index value, the smaller the diameter growth after running, which is better.

* 1 Trans polybutadiene rubber synthesized according to the method described in Examples of JP-A-2002-362107 was used. That is, after adding 300 g of cyclohexane, 50 g of 1,3-butadiene, 0.3 mmol of lanthanum tris (nonylphenoxide), and subsequently adding 0.9 mmol of n-butyllithium to an 800 mL pressure-resistant glass container that has been dried and purged with nitrogen, Polymerization was carried out at 50 ° C. for 2 hours. After the completion of the polymerization reaction, 0.5 mL of a 5 mass% solution of 2,6-di-t-butyl-p-cresol in 5% by weight of isopropanol was added to the polymerization system to stop the reaction, followed by drying by a conventional method to obtain a transpolybutadiene rubber. . The resulting trans polybutadiene rubber has a 1,4-trans bond content of 92 mol%, a 1,2-vinyl bond content of 5 mol%, a weight average molecular weight (Mw) of 6.4 × 10 ⁴ , and a molecular weight. The distribution (Mw / Mn) was 1.3.
* 2 N326.
* 3 N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, "NOCRACK 6C" manufactured by Ouchi Shinsei Chemical Industry.
* 4 Manobond, manufactured by Rhodia.
* 5 N-Cyclohexyl-2-benzothiazylsulfenamide, “Noxeller CZ” manufactured by Ouchi Shinsei Chemical Industry.

  As is clear from Comparative Example 1, if the belt is changed from a four-layer structure to a three-layer structure, the diameter growth of the tire due to running cannot be suppressed, and the durability is greatly reduced as compared with the conventional tire. . Further, as apparent from Comparative Example 2, the belt has a three-layer structure, and even if the angle of the cord in each layer is an angle defined in the present invention, the diameter growth of the tire due to running cannot be sufficiently suppressed, The durability is lower than that of the conventional tire.

  On the other hand, as is clear from the results of the examples, the belt has a three-layer structure, and the angle of the cord in each layer is set to an angle defined by the present invention, and the cord-coated rubber of each layer is defined by the present invention. By applying the compounded rubber composition, it is possible to suppress the deterioration of the cord-covered rubber and to suppress the tire diameter growth due to running, and as a result, the durability of the tire can be greatly improved.

  On the other hand, in the tires of Comparative Examples 3 to 5, since the rubber composition applied to the cord-coated rubber does not contain HTS, the adhesion durability between the cord-coated rubber and the steel cord is low, and the tire diameter growth due to running is suppressed. This was not possible and the durability was lower than that of the tire of the example.

  Further, the tire of Comparative Example 6 in which the rubber composition having a compounded amount of HTS exceeding 3.0 parts by mass was applied to the cord-coated rubber had a smaller improvement in durability than the tire of Example 3, and as a result, HTS It can be seen that a blending amount of 3.0 is not more than 3.0 parts by mass.

1 is a perspective view of a part of a tread portion of an example of a heavy-duty pneumatic radial tire of the present invention. It is explanatory drawing which expand | deployed the one part front of the tread part of the tire shown in FIG.

Explanation of symbols

1 Heavy load pneumatic radial tire 2 Tread portion 3 Tread rubber 4 Carcass 5 Belt 6 Inner cord layer 6a Cord of innermost cord layer 6b Cord covering rubber of innermost cord layer 7 Intermediate cord layer 7a Cord of intermediate cord layer 7b Intermediate Cord coating rubber 8 Outer cord layer 8a Outer cord cord 8b Outer cord cord coating rubber 9 Cord cross layer 10, 11 Circumferential groove 12, 13, 14, 18 Lateral groove 15, 16 , 17, 19 Block P Plane including tread circumference δ Cord inclination angle of innermost cord layer α Cord inclination angle of intermediate cord layer β Cord inclination angle of outermost cord layer Fx Tension

Claims (8)

A radial carcass that reinforces a pair of sidewall portions and a tread portion between bead cores embedded in a pair of bead portions, and a belt that reinforces the tread portion on the outer periphery of the carcass, and the belt has three layers of rubber In a heavy-duty pneumatic radial tire having a coated cord layer, the innermost cord layer and the intermediate cord layer of these cord layers are cord intersecting layers in which the cords of each layer cross each other across a plane including the tread circumference. ,
Each cord of the innermost cord layer and the intermediate cord layer has an inclination angle within a range of 10 to 25 degrees with respect to the plane, and the cord of the outermost cord layer is from the plane of the cord of the middle cord layer Having an inclination angle in the range of 45 to 115 ° with respect to the plane, measured in the same direction as the direction of measuring the inclination angle of
The cord of the rubber-coated cord layer is a steel cord,
1.0 to 5.0 parts by mass of transpolybutadiene rubber and 100 to 300 parts by mass of a rubber component containing a total of 50 to 100% by mass of at least one of natural rubber and polyisoprene rubber in the cord-coated rubber of the rubber-coated cord layer; A rubber composition comprising 3.0 parts by mass of sodium 1,6-hexamethylenedithiosulfate dihydrate and 0.3 to 1.5 parts by mass of N-cyclohexyl-2-benzothiazylsulfenamide was applied. Heavy duty pneumatic radial tire characterized by that. A radial carcass that reinforces a pair of sidewall portions and a tread portion between bead cores embedded in a pair of bead portions, and a belt that reinforces the tread portion on the outer periphery of the carcass, and the belt has three layers of rubber In a heavy-duty pneumatic radial tire having a coated cord layer, the innermost cord layer and the intermediate cord layer of these cord layers are cord intersecting layers in which the cords of each layer cross each other across a plane including the tread circumference. ,
Each cord of the innermost cord layer and the intermediate cord layer has an inclination angle within a range of 10 to 25 degrees with respect to the plane, and the cord of the outermost cord layer is from the plane of the cord of the middle cord layer Having an inclination angle in the range of 45 to 115 ° with respect to the plane, measured in the same direction as the direction of measuring the inclination angle of
The cord of the rubber-coated cord layer is a steel cord,
1.0 to 5.0 parts by mass of transpolybutadiene rubber and 100 to 300 parts by mass of a rubber component containing a total of 50 to 100% by mass of at least one of natural rubber and polyisoprene rubber in the cord-coated rubber of the rubber-coated cord layer; A blend of 3.0 parts by weight of sodium 1,6-hexamethylenedithiosulfate dihydrate and more than 1.0 part by weight and not more than 2.5 parts by weight of N, N′-dicyclohexyl-2-benzothiazolylsulfenamide A heavy-duty pneumatic radial tire characterized by applying a rubber composition comprising:   The rubber composition applied to the cord-coated rubber contains 0.3 to 2.5 parts by mass of an adhesion promoter and 4.0 to 6.5 parts by mass of sulfur with respect to 100 parts by mass of the rubber component. A heavy-duty pneumatic radial tire according to 1 or 2. The rubber composition applied to the cord-coated rubber has a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 90 m ² / g and a dibutyl phthalate (DBP) oil absorption of 70 to 100 parts by mass of the rubber component. The heavy-duty pneumatic radial tire according to any one of claims 1 to 3, comprising 40 to 80 parts by mass of carbon black of 110 mL / 100 g.   3. The heavy load according to claim 1, wherein the rubber composition applied to the cord-coated rubber has a total content of natural rubber and polyisoprene rubber in the rubber component of 95 to 100% by mass. Pneumatic radial tire.   3. The heavy duty pneumatic radial tire according to claim 1, wherein the trans polybutadiene rubber has a trans bond content of 82 to 98 mol% and a weight average molecular weight of 30,000 to 200,000.   The rubber composition applied to the cord-coated rubber has a tensile stress at 100% elongation after vulcanization of 4.5 MPa or more and a loss tangent (tanδ) at 2% strain at 25 ° C. of 0.26 or less. A heavy-duty pneumatic radial tire according to claim 1 or 2.   3. The heavy-duty pneumatic radial tire according to claim 1, wherein the rubber composition applied to the cord-coated rubber has a 90% vulcanization time of 12 to 25 minutes at 145 ° C. 3.

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