JP2009248658A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire suitable for use for a heavy load with improved uneven wear of a tread part and improved belt durability. <P>SOLUTION: This pneumatic radial tire comprises main belts 11, 13 extending to cross each other, and a 0° belt having a steel cord extended at an angle of 0° relative to a tire peripheral direction. The pneumatic radial tire has a ply twist structure using strands S having a 1×n structure (n=2 to 5) in which element wires F are twisted so that each element wire F has spiral continuous waves in the longitudinal direction, a corrugated height H of the continuous waves and an element wire diameter d satisfy the relation of 1.1≤H/d≤1.5, and a corrugated pitch L and a strand twist pitch P1 satisfy the relation of 0.25≤L/P1≤0.55, and the strands S are further twisted together. The 0° belt 12 is composed of the steel cord C in which a cord twist pitch P2 and a cord outer diameter D satisfy the relation of 7≤P2/D≤14. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire.

  In recent years, the development of trucks for the purpose of improving the efficiency of truck transportation has been actively promoted, and accordingly, the development of heavy-duty pneumatic radial tires with excellent durability and flatness of 70% or less has been requested. Yes.

  In pneumatic radial tires with a small flatness ratio called super single tires, in order to reduce tire durability due to insufficient rigidity of the belt and to improve uneven wear resistance of the tread, together with the working belt (main belt) It has been proposed to provide a layer (0 ° belt) in which steel cords are arranged at an angle of substantially 0 ° with respect to the tire circumferential direction. According to such a tire, it is possible to effectively prevent the tread from bulging outward in the radial direction when the tire is filled with internal pressure and when the tire is rolling with a load, compared to a tire provided with only a working belt. Thus, it is considered that the durability of the belt can be improved.

  However, when a rigid cord such as a normal steel cord is disposed at a substantially 0 ° angle in the tire circumferential direction, it is difficult to expand at the time of tire vulcanization. Therefore, as these steel cords, so-called high elongation cords are used in which the slope of the SS curve of the cord is gentle up to 1 to 2% and suddenly increases beyond that. Easy expansion.

  As such a high elongation cord, a cord having a double twist structure such as a 3 × 7, 4 × 4 structure is generally used. However, in a conventional double twist cord, rubber penetrates into the cord during vulcanization. As a result, many filaments are restrained inside the cord. As a result, the cord cannot be sufficiently stretched in the low load region, and there is a problem in that the cord during running of the tire is excessively strained and durability is reduced due to stress concentration.

  In order to solve such a problem, the following Patent Document 1 discloses that a steel cord constituting a 0 ° belt is made of 1 × N (N = 3 to 5) with an element wire diameter D of 0.3 to 0.4 mm. ) In which each strand has a continuous spiral wave in the longitudinal direction, and the undulation height H and strand diameter D of the continuous wave are 1.1 ≦ H / D ≦ 1. .5 has been proposed that satisfies the relationship .5. By comprising in this way, sufficient low load elongation characteristic is securable also in the state with rubber | gum after vulcanization. However, since the steel cord of the same document has a single twist structure, the slope after the inflection point does not always rise sufficiently large in the above SS curve. There is a problem that it is inferior in restraint.

  By the way, in the following Patent Document 2, in a steel cord having a 1 × n structure, each element wire is provided with a corrugation having a pitch smaller than the twist pitch of the cord, thereby increasing elongation at break and It is disclosed that a gap is formed between the lines to improve rubber permeability. However, the steel cord of this document has a single twist structure, is not a double twist structure, and does not disclose anything about the arrangement on the 0 ° belt.

Further, in Patent Document 3 below, in a steel cord having a three-layer double twist structure, the core is composed of three filaments arranged substantially in parallel, and the core is composed of at least one strand typed out of the filaments. Is disclosed. However, in this document, the mold is formed on the filament simply to facilitate the penetration of rubber inside the cord. Therefore, only the one molded on one filament is disclosed in the embodiments, and the present invention is disclosed. It does not suggest anything.
JP 2007-055389 A Japanese Patent Application Laid-Open No. 07-331587 JP 09-228270 A

  The present invention has been made in view of the above-described problems, and it ensures tire durability by improving belt rigidity and restraint in the tire circumferential direction while ensuring elongation in a low load region in a state with rubber after vulcanization. An object of the present invention is to provide a pneumatic radial tire capable of improving the performance and uneven wear resistance.

A pneumatic radial tire according to the present invention includes a carcass whose both ends are locked by a pair of left and right bead cores, and at least two layers of steel cords that cross each other and extend on the outer peripheral side of the carcass in a tread portion. A pneumatic radial tire including a main belt of the tire and a 0 ° belt in which a steel cord extends substantially at an angle of 0 ° with respect to the tire circumferential direction, and a strand of steel cord constituting the 0 ° belt Is a 1 × n structure (n = 2 to 5), and each strand of the strand has a spiral continuous wave in the longitudinal direction, the corrugation height H of the continuous wave and the strand diameter d Satisfies the relationship of 1.1 ≦ H / d ≦ 1.5, and the corrugation pitch L of the continuous wave and the strand twist pitch P1 satisfy the relationship of 0.25 ≦ L / P1 ≦ 0.55. Before being twisted together The steel cord of the 0 ° belt has a double twist structure in which a plurality of strands are twisted together, and the ratio of the cord twist pitch P2 and the cord outer diameter D satisfies the relationship of 7 ≦ P2 / D ≦ 14. Is.

  According to the present invention, a steel cord having a double twist structure in which strands of a 1 × n structure formed by twisting strands after being subjected to continuous waves are applied to a strand, so that even in a state with rubber after vulcanization Elongation in low load range can be secured and rubber penetration is excellent. By using this as a 0 ° belt cord, the expansion behavior at the time of tire vulcanization can be facilitated, and even in the tire, the cord elongation in the low load region is maintained and the stress concentration during running is dispersed. be able to. Moreover, it is possible to improve the belt rigidity and restraint property in the tire circumferential direction at the time of filling the tire with internal pressure or rolling the tire while securing the elongation in such a low load region. Therefore, the durability of the tire can be improved and the occurrence of uneven wear can be suppressed.

  Hereinafter, a pneumatic radial tire according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a half sectional view of a tire T showing an example of a heavy-duty pneumatic radial tire. Reference numeral 1 denotes a belt composed of four belt layers, reference numeral 2 denotes a carcass, reference numeral 3 denotes a tread portion, reference numeral 4 Indicates a bead portion, and reference numeral 5 indicates a sidewall portion.

  The tire T has a single carcass 2 in which steel cords extending in the tire width direction are arranged at predetermined intervals in the tire circumferential direction between a pair of left and right bead portions 4. The carcass 2 is folded and locked from the inside to the outside of the tire so that the bead filler 7 is sandwiched around the bead core 6 embedded in the bead portion 3 at both ends. A belt 1 composed of four belt layers is disposed on the outer peripheral side of the carcass 2 in the tread portion 3.

  FIG. 2 schematically illustrates a cross-section of the tread portion 3 of the tire T according to the embodiment, and illustrates a belt configuration. In FIG. 2, the belt 1 includes four layers of a first belt 11, a second belt 12, a third belt 13, and a fourth belt 14 in order from the inner side in the tire radial direction (all belts are broken lines). Show).

  The first belt 11 and the third belt 13 are belt layers forming a main belt (working belt) of a tire, and conventional steel cords for belts are arranged at a predetermined angle with respect to the tire circumferential direction at predetermined intervals. The cords are arranged to cross each other.

  The fourth belt 14 is a so-called top belt, which is a protective belt arranged at a constant angle in the tire circumferential direction made of a steel cord excellent in cut resistance and rubber penetration, and improves the resistance to damage and renewability. .

  The second belt 12 is a 0 ° belt according to the present invention in which steel cords are arranged and extended at predetermined intervals in the tire width direction at an angle of substantially 0 ° with respect to the tire circumferential direction.

  As shown in FIG. 3, an example of the steel cord C constituting the 0 ° belt 12 is a double twist structure in which a plurality of strands S formed by twisting a plurality of strands (filaments) F are further twisted. This is the code.

  The strand S has a 1 × n structure (n = 2 to 5). Here, when the number n of strands is 6 or more, the arrangement of the strands becomes unstable at the time of stranded wires, and the cord shape is not stable.

  As shown in FIG. 4, each strand F constituting the strand S is provided by processing a spiral continuous wave in the longitudinal direction. Such a spiral continuous wave can be corrugated by a known mold apparatus in which mold pins and rollers are arranged in a staggered manner.

  The continuous wave corrugation height H and the wire diameter d are provided so as to satisfy the relationship 1.1 ≦ H / d ≦ 1.5. Further, the strand S is formed by twisting the continuous wave corrugation pitch L and the strand twist pitch P1 so as to satisfy the relationship of 0.25 ≦ L / P1 ≦ 0.55.

  If the above H / d is less than 1.1, sufficient elongation in a low load region cannot be obtained with rubber after vulcanization, and conversely if H / d exceeds 1.5, the shape of the cord May become unstable and impair processability. Further, if L / P1 is less than 0.25, it is effective for improving elongation, but the shape becomes non-uniform. Conversely, if L / P1 exceeds 0.55, a low load is applied during rubber vulcanization. When the tension is applied, the gap between the strands tends to be narrowed, so that the rubber penetration is reduced. In addition, since the strand diameter d can be appropriately set according to the number of strands of the strands S and the like, it is not particularly limited, but is preferably 0.1 to 0.3 mm.

  The steel cord C constituting the 0 ° belt 12 is a cord having a double twist structure in which the strand S formed by twisting the strands F as described above is further twisted, and the cord twist pitch P2 and the cord outer diameter D The ratio satisfies the relationship of 7 ≦ P2 / D ≦ 14. The steel cord C has an m × n structure in which the number of strands is n = 2 to 5 and the number of strands S is m. Here, the number of strands m of the strand S is not particularly limited, and can be appropriately set according to the cord outer diameter D and the strand diameter d. As will be described later, the cord outer diameter D is preferably smaller than the cord outer diameter of the main belt. In general, the cord outer diameter D varies depending on the strand diameter d, so that the cord outer diameter D is smaller than the cord outer diameter of the main belt. What is necessary is just to set the twist number m of the strand S according to the strand diameter d within the range which can be done. Preferably, m = 2 to 5.

  When the P2 / D is less than 7, the twist strain increases, the cord strength decreases, and the twist becomes nonuniform. Moreover, when P2 / D exceeds 14, the elongation in a sufficiently low load region cannot be obtained.

  The steel cord C formed as described above has gaps G formed randomly between the strands F in the longitudinal direction of the cord as shown in FIG. 3 (when m = 3 and n = 5). Rubber penetration into the cord can be improved.

Further, the steel cord C has a low load as shown in FIG. 5 in an SS curve in which the vertical axis indicates load (N) and the horizontal axis indicates elongation (%) with rubber after vulcanization attached. It shows a behavior as a semi-elastic cord having an inflection point Z with a gentle slope in the region and a slope that suddenly increases as the load increases. Specifically, the tensile elastic modulus in a low load region is preferably 5000 N / mm ² or less, more preferably 4000 to 5000 N / mm ² .

  This is because, in the low load region of the SS curve, when a tensile force is applied in the cord axis direction, each strand shows a gentle inclination due to rubber elasticity by gradually tightening the rubber that has entered the cord inside. This is due to the sudden change to the large inclination of pulling the steel filament when the tightening allowance due to the line is lost, and therefore an inflection point Z is provided between both inclinations.

  In particular, according to the present embodiment, since the steel cord C has the unique double twist structure, the inclination of the low load region is gentler than that of the steel cord having the single twist structure as in the conventional Patent Document 1 described above. In addition, the inflection point Z can be emphasized by increasing the inclination after the inflection point Z more rapidly, and the restraint can be improved. FIG. 6 shows a S × 3 × 5 × 0.18 steel cord and a 1 × 5 × 0.18 single layer steel cord (each wire is corrugated) according to Example 1 described later. It is the graph which showed each -S curve. As is apparent from the graph, the inflection points are more emphasized in the present embodiment.

  In this embodiment, the elongation A (%) (see FIG. 5) of the intersection of the tangent line X of the slope in the low load region and the tangent line Y of the slope after the inflection point is 0.5 ≦ A <2. 0.0 is preferred. If the elongation at the intersection A is less than 0.5%, the stress distribution during running tends to be insufficient, and if it is 2.0% or more, the 0 ° belt restraint force is insufficient and the durability is low. It tends to decrease.

  The positional relationship of the 0 ° belt 12 within the belt 1 is not particularly limited, but it is preferable that at least one main belt is disposed outside the 0 ° belt in the tire radial direction. More specifically, the 0 ° belt 12 is preferably disposed between the main belts 11 and 13 or between the main belt 11 and the carcass 2 on the inner side in the tire radial direction. The width of the 0 ° belt 12 is preferably 90% or less of the width of the belt layer 13 on the outer side in the tire radial direction, whereby the stress concentration on the 0 ° belt edge portion can be reduced, and the stress concentration It is possible to prevent the edge portion from being deteriorated in durability due to distortion.

  The 0 ° belt 12 may be disposed between the main belt 13 and the top belt 14, but generally, the top belt 14 has a width of 90% or less of the main belts 11 and 13; If the 0 ° belt 12 is disposed in this portion with a width of 90% or less with respect to the outer belt layer, the width of the 0 ° belt 12 becomes too narrow and it is difficult to obtain a sufficient restraining force at the shoulder portion. Therefore, the 0 ° belt 12 is preferably disposed between the main belts 11 and 13 or between the main belt 11 and the carcass 2 as described above.

  On the other hand, when the 0 ° belt is disposed between the main belt or between the main belt and the carcass as described above, if the 0 ° belt layer 12 is thicker than the main belt layers 11 and 13, the distortion inside the belt is zero. ° Concentration on the belt 12 may cause deterioration of separation resistance. Therefore, it is preferable that the cord outer diameter D of the steel cord C of the 0 ° belt 12 is smaller than the cord outer diameter of the steel cord constituting the main belts 11 and 13, thereby separating the belt edge portion. The progress of the tire can be delayed to improve the tire durability.

  The 0 ° belt 12 can be provided by winding the steel cord C in a spiral shape continuously in the circumferential direction of the tire T. The cord angle of the steel cord C is substantially 0 ° with respect to the tire circumferential direction. For example, one cord C is wound in a spiral shape while being shifted in the width direction of the tire T. Further, a ribbon-like belt-like member in which several cords C are aligned and covered with rubber is wound by spirally winding the ribbon-like side ends for each circumference of the molding drum during tire molding. Is called. Thus, by winding the steel cord C continuously in a spiral shape, sufficient belt rigidity can be obtained without being affected by the joint or the like.

  With the pneumatic radial tire of the present embodiment configured as described above, the durability and uneven wear resistance of the tire can be improved by providing the 0 ° belt having the above-described configuration, and particularly heavy-duty vehicles for trucks. It is suitable for a tire having a flatness ratio (ratio of tire height / total tire width) of 60% or less.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples.

  A radial tire having a tire size of 385 / 55R22.5 having the belt configuration shown in FIG. 2 was prototyped. The 0 ° belt was placed on the second belt 12 and each steel cord shown in Tables 1 and 2 was used. The configurations of the first to fourth belts are shown in Table 3 for the examples and comparative examples, and Table 4 for the conventional examples. A common member was used for each part other than the belt. In the angle column in the table, the right and left indicate the belt cord inclination direction.

  The conventional example is an example in which the 0 ° belt shown in FIG. 7 is not used. The tire T1 according to the conventional example includes an air having a belt 100 including four belt layers of first to third belts (main belts) 111, 112, 113 having an angle and a fourth belt (top belt) 114. This is a radial tire.

  The following evaluation was performed on each of the tires. The results are shown in Tables 1 and 2.

[Tensile test]
Each steel cord is subjected to a tensile test with vulcanized rubber (based on JIS G3510). From the SS curve shown in FIG. 5, the tangent line X of the slope in the low load range and the tangent line of the slope after the inflection point. The elongation A (%) at the intersection with Y was determined. The tensile elastic modulus in the low load region was calculated as the strength when it was assumed that the elongation was 100% obtained from the tangent line of the maximum gradient portion near the origin of the SS curve.

[Rubber penetration]
After the steel cord was embedded in rubber and vulcanized, the strand was divided into two parts, the wire surface inside the cord was visually observed, and the area covered with rubber was expressed as a percentage.

[Cord shape stability]
Regarding the shape stability of the cord, the appearance of the twisted cord was visually observed. ○: good, Δ: slightly out of shape but no problem in use, x: out of shape.

[Tire durability]
Increased by 8 km / h every 12 hours from a speed of 56 km / h with a drum tester having a steel rotating drum with a smooth surface of 1700 mm in diameter, constant at an ambient temperature of 38 ± 3 ° C., a tire internal pressure of 900 kPa, and a load of 4500 kg. And let it run until a failure occurred. The distance traveled until the failure occurred is shown in Table 1 as an index with the conventional example being 100. The larger the index, the better the durability.

[Uneven wear resistance]
Attached to the driving wheel of a large truck, the tread contact surface after traveling 50,000 km with an actual vehicle was observed, and the occurrence of uneven wear was judged as good to equivalent to bad based on the conventional example.

  As shown in the table, in Examples 1 to 5, sufficient low load elongation characteristics were secured in a state with rubber after vulcanization, and rubber penetration was excellent. Moreover, both tire durability and uneven wear resistance were excellent.

  On the other hand, since the cord structure of Comparative Example 1 is 3 × 6 (strand structure is 1 × 6), the cord stability is improved such that one strand partially enters the inside of the cord during twisting. As a result, the cord durability was lowered and the tire durability was lowered.

  In Comparative Example 2 with a small H / d, the low load range elongation with rubber after vulcanization was insufficient, and the stress concentration due to strain during running could not be dispersed, resulting in a decrease in tire durability. On the contrary, in Comparative Example 3 where H / d is large, the elongation in the low load region becomes too large, the belt restraint force during running is insufficient, and the uneven wear is not improved.

  In Comparative Example 4 having a small L / P1, the cord shape was not stable. As a result, the cord durability was lowered and the tire durability was lowered. Conversely, in Comparative Example 5 with a large L / P1, when a low load tension was applied during tire vulcanization, the spacing between the strands was narrowed, the rubber penetration was reduced, and the tire durability was poor.

  In Comparative Example 6 having a small P2 / D, the twist strain was increased, the cord durability was lowered, and the twist was not uniform, so the tire durability was lowered. On the contrary, in Comparative Example 7 where P2 / D is large, the low load region elongation A in the rubberized state after vulcanization is small, the stress concentration due to strain during running cannot be dispersed, and the tire durability is inferior.

  As described above, the pneumatic radial tire according to the present invention is excellent in belt durability and uneven wear resistance, and therefore can be used for heavy duty truck and bus tires. Particularly, the flatness is 60%. It is suitable for the following radial tires.

1 is a half sectional view of a pneumatic radial tire according to an embodiment. It is sectional drawing which shows the belt structure of embodiment typically. It is sectional drawing of the steel cord of embodiment. It is explanatory drawing of the corrugation of a strand continuous wave. It is a graph which shows an example of the SS curve of a cord with rubber. It is a graph which shows the SS curve of the steel cord of Example 1, and the steel cord of a comparative example. It is sectional drawing which shows the belt structure of a prior art example typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Belt 2 ... Carcass 6 ... Bead core 11, 13 ... Main belt 12 ... 0 degree belt C ... Steel cord S ... Strand F ... Strand

Claims (3)

A carcass whose both ends are locked by a pair of left and right bead cores, at least two main belts made of steel cords that cross each other and extend on the outer periphery side of the carcass in the tread portion, and the tire circumferential direction A pneumatic radial tire having a 0 ° belt with a steel cord extending substantially at an angle of 0 °,
The strand of the steel cord constituting the 0 ° belt has a 1 × n structure (n = 2 to 5), and each strand of the strand has a continuous wave spiral in the longitudinal direction, and the continuous wave The corrugation height H and the wire diameter d satisfy the relationship of 1.1 ≦ H / d ≦ 1.5, and the corrugation pitch L of the continuous wave and the strand twist pitch P1 are 0.25 ≦ L. Twisted so as to satisfy the relationship of /P1≦0.55,
The steel cord of the 0 ° belt has a double twist structure formed by twisting a plurality of strands, and the ratio of the cord twist pitch P2 and the cord outer diameter D satisfies the relationship of 7 ≦ P2 / D ≦ 14. ,
A pneumatic radial tire characterized by that. The steel cord of the 0 ° belt has a gentle slope in the low load region in the SS curve with the load (N) on the vertical axis and the elongation (%) on the horizontal axis with rubber after vulcanization. And an inflection point where the inclination increases when the load increases, and the elongation A (%) of the intersection of the tangent of the inclination in the low load region and the tangent of the inclination after the inflection point is 0.5 ≦ The pneumatic radial tire according to claim 1, wherein A <2.0. The main belt of at least one layer is arranged outside the 0 ° belt in the tire radial direction, the width of the 0 ° belt is 90% or less of the width of the main belt outside the tire radial direction, and The pneumatic radial tire according to claim 1 or 2, wherein a cord outer diameter of the steel cord is smaller than a cord outer diameter of a steel cord constituting the main belt on the outer side in the tire radial direction.

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