JP2012106570A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain excellent steering stability, ride comfort and durability and to attain lightness in weight, in a pneumatic radial tire using a steel cord 1 as a belt ply.SOLUTION: Two to six main filaments 2 having the same diameter are arranged side by side to form a single layer without twisting them and one non-shaped lapping filament 3 having a diameter smaller than that of the main filament 2 is wound around the main filaments. Each of the main filaments 2 has a diameter (D) of 0.15-0.30 mm, and a specified composition in which a carbon (C) content is 0.95-1.20 mass% or the like, and tensile strength TS (Mpa) satisfying following formula (I): -2000×D+4400≤TS (Mpa)≤-2000×D+5400.

Description

  The present invention relates to a pneumatic radial tire using a steel cord as a reinforcing material such as a belt layer. In particular, the present invention relates to a pneumatic radial tire that is excellent in handling stability and durability in high-speed driving and can achieve weight reduction.

  Pneumatic radial tires generally have a belt section in which a plurality of belt plies are crossed and laminated between the outer surface of the carcass ply and the tread rubber. This belt ply has excellent tensile strength and tensile elasticity. A steel cord with

  Conventionally, steel cords used for belt plies of passenger car tires are generally 1 × n structure (n = 3 to 5), but from tread damage and cracks in 1 × n structure steel cords. In order to prevent belt failure due to moisture intrusion, a 1 × n structure in which the filament is excessively molded and twisted loosely, or an m + n structure in which the filament is wound spirally around the aligned filament bundle, for example, Many steel cords having improved rubber penetration such as 2 + 2, 2 + 1 structures have been disclosed to improve tire durability.

  On the other hand, in recent years, there has been a strong demand for lower fuel consumption of vehicles due to the problem of global environmental pollution. As part of this, weight reduction of pneumatic radial tires has attracted attention as one of the major technical issues. . However, the steel cord used for the belt portion has a large specific gravity and a large amount of use, and therefore is an obstacle to weight reduction. Therefore, various ideas have been made on the structure of the steel cord described above, but it is not easy to achieve weight reduction while maintaining high durability of the tire and driving stability when mounted on an automobile. .

  For example, in the following Patent Document 1, it is disclosed that a belt ply is formed with steel filaments that are arranged separately, instead of using a steel cord composed of a plurality of steel filaments (single wire, steel strand). ing. Since the cross-sectional area can be reduced as compared with the steel cord, the diameter of the steel wire can be made compact, and the thickness and the rubber amount of the belt ply can be reduced. Patent Document 1 uses a high-strength steel wire having a relatively high carbon content (0.96% in the example) and chromium content (0.2% or 0.5% in the example), and durability by not using a steel cord. In order to cover this drop, it has been proposed to corrugate each steel filament in two dimensions along the longitudinal direction. However, with the structure described in Patent Document 1, since the corrugated steel filament easily stretches during the tire molding process, it is difficult to ensure accuracy and the tire uniformity is reduced. There was a problem of impairing the ride comfort.

  Therefore, in the following Patent Documents 2 to 3, a plurality of steel filaments are arranged adjacent to each other so as to form a single layer or two layers, and a thinner “straight” wrapping is provided around this. Winding a filament, ie a wrapping filament that is not waved or otherwise shaped. In this way, by bundling the main filaments in parallel in one or two layers, the flat steel cord is reduced in weight and the accuracy is prevented from being lowered due to elongation at low load.

  Specifically, according to Patent Document 2, in order to align the three corrugated main filaments in parallel, the main filaments are “aligned so as to have different waveform directions and / or phases”. (0035 paragraph). In this way, it is said that “extension when an external force is applied to the steel cord is suppressed”, and accuracy can be improved by this action. However, with such a steel cord structure, the bundled shape is easily broken, so that rolling resistance increases and steering stability may be impaired.

  Therefore, in Patent Document 3, by making the cross-sectional shape of the main filament a regular hexagon, the side surfaces of the main filament are brought into contact with each other to “hold the bundle shape reliably”, thereby reducing the rolling resistance. It is disclosed to ensure steering stability. However, in the steel cord structure described in Patent Document 3, the production of the main filament and the process of aligning it become complicated.

  On the other hand, in Patent Document 4 below, in order to cope with improvement in tire durability and weight reduction, “a high-strength ultra-fine steel with a high tensile strength of 4000 MPa or more and excellent ductility with a drawing value of 40% or more. A method of stably obtaining a line is disclosed. That is, it is described that the content of additive elements such as carbon is optimized and the conditions for patenting and wire drawing are optimized. However, when the tensile strength is 4000 MPa or more, avoidance of brittleness is not always sufficient, and durability may be reduced.

On the other hand, in Patent Document 5 below, the carbon content (C amount) is set to 0.7% or more and the silicon content (Si amount) is set to 0.6% or more in order to increase the strength of the bridge wire or PC steel wire. It is disclosed that a solid solution boron (B) corresponding to the amount and the amount of Si coexists before the patenting treatment. However, “In this embodiment, by setting the diameter of the wire in the range of 5.5 to 18 mm, excellent wire drawing characteristics and high strength can be stably obtained” (0042 paragraph), “φ5 It is described that when a steel wire for PWS of .2 mm was prototyped, the tensile strength TS was 1910-1932 MPa (paragraph 0058). However, simple comparison is difficult because the wire diameter and the conditions of rolling and patenting at the time of wire drawing differ greatly from the steel wire for tires.
JP-A-5-345503 JP-A-8-120578 JP 2004-060128 A Japanese Patent Laid-Open No. 2007-262496 JP 2007-039800 A

  The present invention has been made in view of the above-mentioned problems of the prior art, and in a pneumatic radial tire using a steel cord as a belt ply, it is excellent in handling stability, riding comfort, durability and light weight. An object of the present invention is to provide a pneumatic radial tire that can be used.

  In view of the above problems, the present inventor has intensively studied the structure of the steel cord and the characteristics of the steel filament, and by chance, by adopting certain conditions, a very excellent effect can be obtained. As a result, the present invention has been completed.

  That is, in the pneumatic radial tire according to the present invention, 2 to 6 main filaments having the same diameter are juxtaposed so as to form a single layer without being twisted, and the circumference thereof is smaller than the main filament. A steel cord (n + 1 structure: n = 2 to 6) wound with one unshaped (straight) steel filament as a wrapping filament is provided as a reinforcing cord for the tread, and the diameter (D) is 0.15 0.30 mm, carbon (C) content is 0.95-1.20 mass%, silicon (Si) content is 0.1-1.5 mass%, manganese (Mn) content is 0.1 -1.0 mass%, both aluminum (Al) content and titanium (Ti) content are 0.01 mass% or less, nitrogen (N) content and oxygen (O) content are any 20-40ppm (mass basis, any of the following "pp The same applies to “m”, and the tensile strength TS (Mpa) satisfies the following formula (I). In the following formula (I), D is a numerical value indicating the diameter of the main filament in mm.

−2000 × D + 4400 ≦ TS (Mpa) ≦ −2000 × D + 5400 (I)
Moreover, the steel filament used for the wrapping filament is not particularly limited. For example, a carbon steel wire having a carbon content of 0.60 to 1.02% by mass can be used. From the piano wire defined in JIS G 3502 Various carbon steels such as SWRS72A and SWRS82A can be used.

  In the embodiment of the present invention, the main filament may be used that has been molded or corrugated. As a preferred embodiment at that time, the main filament is wave-shaped (corrugated), and the corrugated two-dimensional surface and the parallel two-dimensional surface are arranged in parallel to the tread surface. The corrugation height and pitch are the same, the corrugation height (wave height) is 0.03 to 0.11 mm, and the corrugation pitch (wavelength) is 3.0 mm to 30.0 mm.

  According to the present invention, a specific ultra-high strength steel filament is used as a main filament, and a structure (n + 1 structure) in which a single layer is arranged in parallel without being twisted and bundled with a wrapping filament is used. As a result, it is possible to achieve light weight while being excellent in handling stability, ride comfort and durability.

1 is a schematic plan view showing a configuration of a steel cord as an essential part in an embodiment of a pneumatic radial tire of the present invention. It is the figure seen from the direction perpendicular | vertical to a tread surface, ie, a tire radial direction. It is sectional drawing along the II-II line of FIG. It is typical sectional drawing of the belt ply in embodiment shown to FIGS. It is sectional drawing corresponding to FIG. 2 which shows the structure of the steel cord in a modification.

  Each steel cord for belt ply, which is a main part of the pneumatic radial tire of the present invention, consists of only steel filaments, 2 to 6 main filaments having the same diameter, and one wrapping filament for bundling them. Consists of. The diameter of the main filament is 0.15 to 0.30 mm, preferably 0.15 to 0.25 mm. When the diameter of the main filament is less than 0.15 mm, the rigidity of the steel cord becomes too low, and the steering stability when the tire is mounted is lowered. If it exceeds 0.30 mm, it becomes too rigid, and the surface strain accompanying compression deformation increases, so the fatigue resistance of the belt ply deteriorates and the durability of the tire decreases. The wrapping filament has a bending rigidity smaller than that of the main filament, for example, 10 to 40% of the main filament. The diameter of the wrapping filament is smaller than the diameter of the main filament, for example, 0.4 to 0.6 times the diameter of the main filament. When the diameter of the wrapping filament is larger than this range, the diameter of the steel cord increases, which is not preferable. On the other hand, when the diameter is smaller than this range, the binding force may be insufficient.

  These main filaments are juxtaposed so as to form one layer along one plane. In other words, the steel cords are aligned in a row in a cross section perpendicular to the steel cord. Therefore, each steel cord is flat, and the ratio of major axis / minor axis is, for example, 1.5 to 5 times, preferably 2 to 4 times. When the number of main filaments exceeds six, it becomes difficult to align the main filaments in a row, and the shape as a bundle becomes uneven. The number of main filaments arranged in parallel in one cord is preferably 4-6, more preferably 5-6. With such a number, the flatness of the cord can be increased and the thickness of the belt layer and the like can be reduced while keeping the shape as a bundle stable.

  On the other hand, as the wrapping filament, a so-called “straight” one is used which is not corrugated. This is because it is preferable for facilitating winding and for uniformly increasing the binding force of winding. In addition, due to the restraining force of the wrapping filament, the aligned main filament can have a sense of unity as a steel cord, and high rigidity is obtained against in-plane deformation of the belt material when changing the route while driving or turning a curve. It is done. The main filament does not necessarily have a circular cross section. For example, if a flat filament is used as the main filament, the steel cord can be further flattened.

  Moreover, the main filament may use what gave a shaping | molding or corrugation, and when corrugating, all are corrugated only to the major axis direction of a steel cord. That is, the wave is two-dimensionally waved in a plane along the major axis direction and the length direction. In particular, the plurality of main filaments forming the steel cord have the same corrugation height (wave height) and the same corrugation pitch (wavelength). Thus, by performing the same corrugation for all the main filaments, when a tensile load is applied to the steel cord, substantially the same elongation behavior is performed between the parallel main filaments. That is, since the stress acts evenly without concentration, the tensile strength of each steel filament can be utilized to the maximum, and the tensile strength of the steel cord increases.

  When forming the belt ply, the long diameter of the steel cord is always arranged so as to be parallel to the belt surface at any part. Therefore, the direction in which the main filament of the steel cord is waved two-dimensionally is parallel to the tread surface. Therefore, the thickness of the belt ply can be reduced, and the corrugated waveform can be smoothly spread in the circumferential direction along the tread surface when the vehicle is in contact with the ground.

  In a preferred embodiment, the corrugation height of the main filament is 0.03 to 0.11 mm, preferably 0.05 to 0.10 mm. The corrugated pitch is 3.0 mm to 30.0 mm, preferably 3.0 mm to 5.0 mm. On the other hand, the pitch for winding the wrapping filament (winding pitch) is 3.0 mm to 30.0 mm, preferably 3.0 mm to 5.0 mm, which is 1.0 to 2.0 times the corrugated pitch.

  In a preferred embodiment, the plurality of main filaments forming each steel cord are not operated so as to be out of phase with respect to the corrugation. That is, they have basically the same phase, and in the major axis direction of the steel cord, the mountain portions and the valley portions overlap each other, so that the gap between them is relatively small. Therefore, each steel cord has a structure that is advantageous in that the bundle of the main filaments is strongly bound by the wrapping filaments with little variation in the dimension in the major axis direction of the bundle of the main filaments for each part along the length direction. Therefore, high fatigue resistance and corrosion resistance can be maintained without facilitating rubber penetration into the steel cord.

  The main filament is a moderately high strength steel filament as described below. First, carbon (C) content is 0.95-1.20 mass%, silicon (Si) content is 0.1-1.5 mass%, manganese (Mn) content is 0.1-1.0. The mass% and the nitrogen (N) content are 20 to 40 ppm. The aluminum (Al) content and the titanium (Ti) content are preferably 0.01% by mass or less, and the oxygen (O) content is preferably 20 to 40 ppm. Preferably, the boron (B) content is 4 to 30 ppm, of which the solid solution boron (B) content is 3 ppm or more. Further, the tensile strength TS satisfies the following formula (I). In the following formula (I), D is a numerical value of the diameter in mm.

−2000 × D + 4400 ≦ TS (Mpa) ≦ −2000 × D + 5400 (I)
In the above formula (I), the term −2000 × D is a correction term for canceling the strength diameter dependence, and it is experimental that the influence of the filament diameter can be almost eliminated in the range of the filament diameter of 0.15 to 0.30 mm. Has been confirmed. When the filament diameter is 0.20 mm, the numerical value of the correction term is −400, and the above formula (I) is 4000 ≦ TS (Mpa) ≦ 5000.

  If the carbon (C) content is less than 0.95% by weight, the desired tensile strength cannot be stably obtained. If it exceeds 1.20% by weight, proeutectoid cementite is formed and the wire drawing is performed. This deteriorates the property and causes not only wire breakage during wire drawing, but also deteriorates the toughness of the steel filament. If the Si content is less than 0.1% by mass, the action as a deoxidizing agent and the strength improvement at the time of patenting may be insufficient. By promoting precipitation of precipitated ferrite and forming bainite, the limit working degree in wire drawing decreases. If the Mn content is less than 0.1% by mass, the action as a deoxidizer may be insufficient. If it exceeds 1.0% by mass, segregation of Mn is likely to occur, and the center portion of the wire By segregating, martensite and bainite are generated and wire drawing workability is lowered. When the N content is less than 20 ppm, the effect of preventing the coarsening of the austenite grain size can be insufficient by generating a small amount of Al, B or Ti and nitride, so that the strength or durability is low. May deteriorate. On the other hand, if it exceeds 40 ppm, the aging during wire drawing is promoted, which may cause a decrease in strength. On the other hand, if the oxygen (O) content is less than 20 ppm, the effect of promoting the formation of crystal grains is insufficient, and if it exceeds 40 ppm, the toughness of the steel filament is reduced due to oxide formation.

  Furthermore, both aluminum (Al) content and titanium (Ti) content are 0.01 mass% (100 ppm) or less. When Al content exceeds 0.01 mass%, a hard alumina inclusion will be produced | generated and wire drawing workability will fall. When Ti content exceeds 0.01 mass%, the oxide of Ti will be produced | generated and wire drawing workability will fall. Al or Ti of less than 0.01% by mass can contribute as a deoxidizing agent in the same manner as Mn.

In a preferred embodiment, the boron (B) content is 4 to 30 ppm, of which the solid solution B content is 3 ppm or more. Boron (B) suppresses the precipitation of a non-pearlite structure if it exists in a solid solution state before the patenting treatment. If the solute B content is less than 3 ppm, this effect is insufficient. Moreover, when the total content of boron (B) is less than 4 mass ppm, it is difficult to make the solid solution B content 3 ppm or more. On the other hand, if the boron (B) content exceeds 30 ppm, coarse Fe ₃ (CB) ₆ carbide is produced, and the wire drawing workability may be reduced. A boron (B) content of 4 to 30 ppm and a nitrogen (N) content of 20 to 40 ppm are also preferable for producing the nitride appropriately.

  In a preferred embodiment, chromium (Cr) content, nickel (Ni) content, cobalt (Co) content, and vanadium (V) content are all 0.5% by mass or less (not including 0%) It is. Moreover, copper (Cu) content, molybdenum (Mo) content, tungsten (W) content, and niobium (Nb) content are all 0.2 mass% or less (excluding 0%). Chromium (Cr) has the effect of improving the wire drawing workability by refining the lamellar spacing of pearlite, particularly when added in an amount of 0.01% by mass or more. When the content exceeds 0.5% by mass, pearlite is effective. It takes a long time to complete the transformation, and it becomes easy to generate supercooled structures such as martensite and bainite. Nickel (Ni) has an effect of increasing the toughness of the steel wire particularly when added in an amount of 0.01% by mass or more, but when the content exceeds 0.5% by mass, the time until the pearlite transformation is completed becomes long. . Cobalt (Co) has the effect of suppressing the precipitation of pro-eutectoid cementite particularly when added in an amount of 0.01% by mass or more, and vanadium (V) particularly increases the austenite grain size by adding 0.01% by mass or more. This has the effect of preventing and increasing the strength of the steel filament. However, in any case, when the content exceeds 0.5% by mass, the effect of addition is already saturated, so that the excessive content is wasted and the production cost is increased. Copper (Cu) has the effect of improving the corrosion resistance of steel filaments, but when it exceeds 0.2% by mass, it reacts with sulfur (S) to produce CuS, so it is scratched on steel ingots and wires during the wire manufacturing process. (疵) may occur. Molybdenum (Mo) has the effect of refining the pearlite structure, especially when added in an amount of 0.01% by mass or more, but when it exceeds 0.2% by mass, coarse carbide Mo2C is generated and the wire drawing workability is lowered. Let Tungsten (W) and niobium (Nb) both have an effect of improving corrosion resistance, particularly when added in an amount of 0.01% by mass or more, but when any of these exceeds 0.2% by mass, the pearlite transformation is completed. The time to do becomes longer.

  If the strength of the steel filament used as the main filament is smaller than the range of the above formula (I), the number of steel cords to be driven becomes too dense in order to obtain the belt material strength. For this reason, the distance between adjacent steel cords is narrowed, so that cord separation is likely to occur, and the durability of the tire is reduced. Further, if it exceeds the range of the above formula (I), the ductility becomes extremely poor, and early failure due to embrittlement is induced, so that the tire durability is also lowered.

  In the pneumatic radial tire of the present invention, the steel cord occupancy (“cord occupancy”) in the width dimension of each belt ply is preferably 50 to 75%. If the steel cord occupancy is less than 50%, the distance between the steel cords is too wide, which leads to a decrease in bending rigidity and a decrease in steering stability. On the other hand, if it exceeds 75%, the belt ply becomes too rigid, so the ride comfort is impaired, especially the smoothness when entering and exiting the saddle (Wadachi), and The handle is removed due to repulsion from the bag. In addition, since the distance between steel cords becomes excessively small, stresses between the steel cords may not be sufficiently absorbed by the rubber layer, causing separation and peeling between the steel cords, referred to as “code separation”. It becomes easy. As a result, the durability of the tire decreases. Here, the code occupancy (%) uses a value calculated by the following formula in a so-called topping reaction in which the cords are arranged at a predetermined driving density and are covered with rubber. Cord occupation ratio (%) = Cord diameter (mm) × Number of cords driven (pieces / 25.4 mm) × 100 / 25.4 (mm).

  The structure of the steel cord and the belt ply in each example (Examples 1 and 2) of the present invention will be briefly described with reference to FIGS. In this embodiment, each steel cord 1 is composed of five main filaments 2-1, 2-2, 2-3, 2-4, and 2-5 having a circular cross section. The phases of the sinusoidal corrugations are almost equal to each other. In the specific form shown in FIG. 1, the corrugated pitch of the main filament 2 and the pitch of winding the wrapping filament 3 are both the same pitch P. Then, a concave portion having a bay shape is formed by corrugation on the side surface of the bundle formed by the main filament 2, but the wrapping filament 3 is wound around the portion of the concave portion so that the steel cord 1 is directed to the left and right. Make a conversion. As shown in FIG. 3, the thickness of the belt ply 4 is slightly larger than the short diameter (thickness) T of the steel cord 1.

  Other configurations and conditions used in each example are as shown in Tables 1 to 4 below.

  Two types of steel filaments having different diameters were used as the main filament 2 and the wrapping filament 3. First, a steel filament having a diameter of 0.20 mm was subjected to predetermined corrugation in a sinusoidal and two-dimensional manner to obtain a main filament 2. Then, the five main filaments 2 were arranged in parallel in the waving direction without being twisted, and a flat bundle was formed such that peaks and valleys overlap each other. Thereafter, a lapping filament 3 having a diameter of 0.15 mm without being waved or the like was wound around the bundle of main filaments 2 at a predetermined pitch. During the winding, the bundle of main filaments 2 was not twisted.

  The upper half part of Tables 1-2 shows the carbon content of the main filament and other alloy element compositions in each example. As shown in Tables 1 and 2, in Examples 1 to 4, the carbon content was changed in the range of 0.97 to 1.12% (mass%, the same applies hereinafter), and other conditions were almost the same, so that the carbon content was Saw the effect of quantity. Further, in Examples 5 to 10, while changing the carbon content of the main filament to 1.07%, other alloy element compositions of the main filament were changed and the effect was observed. In Tables 1-2, Al and Ti are less than 0.001% when there is no description, and Ni, Cu, V, Co, and Nb are less than 0.01% when there is no description. That is, in any of Examples and Comparative Examples, the Al content and the Ti content were 0.001% or less, and Cu, V, Co, and Nb were 0.01% or less. In any of the examples, the same wrapping filament was used in any of the comparative examples. A wrapping filament having a diameter of 0.15 mm was used. For the main filament, the content of each alloy element was measured in accordance with each JIS standard as follows. C: JIS G 1211 "High-frequency floating heating combustion-infrared absorption method". Si, Mn, P, Al, Ti, Mo, Cr. Ni, Cu, V, Co: JIS G 1258-1 “Thermal decomposition / potassium disulfate melting method”, where Cr is hydrochloric acid: nitric acid: water (mass The steel material was dissolved in an aqueous solution having a ratio of 1: 1: 2) to perform IPC analysis. S: JIS G 1215 “Combustion-High Frequency Induction Heating Infrared Absorption Method”. B: JIS G 1258-6 “pyrolysis and sodium carbonate melting method”. N: JIS G 1228 “Inert gas melting-thermal conductivity method”. O: JIS Z 2613 "Inert gas melting-thermal conductivity method". Nb: JIS G 1258-4 "Thermal decomposition and potassium disulfate melting method".

  The diameters of the main filament 2 and the wrapping filament 3 were measured according to JIS G3510. Further, the corrugated height and pitch of the main filament 2 after corrugation were measured by the following method. For the corrugated main filament 2, the corrugated main filament 2 was measured by measuring the distance in the amplitude direction of the corrugation from one peak to the next trough at five locations, and taking the average. For the corrugated main filament 2, the corrugated pitch P was measured by measuring the distance in the continuous direction (cord axis direction) from one peak to the next peak at five locations, and taking the average. Moreover, about the obtained steel cord 1, while measuring a major axis (width) W and a minor axis (thickness) T according to JIS G3510, tensile strength was measured with a tensile tester (Shimadzu Corporation Autograph). It was measured. Furthermore, the cross-sectional shape of the steel cord 1 was observed, and it was determined whether or not the main filaments 2 were arranged on the same plane in one layer.

  On the other hand, in the conventional example used as a reference for comparison, a steel filament having a circular cross section of 0.27 mm diameter is used as a core filament and a sheath filament, and around two untwisted (non-twisted) core filaments. In addition, two sheath filaments are wound. The winding (twisting) pitch is 14.0 mm.

  Next, each steel cord is topped using a calendar device at a counter width of 300 mm with a constant rubber coating thickness at the top and bottom of the cord at a driving rate of 13.3 / 25.4 mm (inch) to 14.9 / inch. Anti made. After that, the topping was applied to the belt ply (cutting angle 23 °, 2 ply). In Table 1, after converting the weight to the weight per tire in Table 1, the weight is displayed as an index with the conventional example being 100. The weight ratio of the belt layer to the entire tire is about 12.5%.

  On the other hand, the carcass ply was made of polyester cord 1100 dtex / 2 and the number of driving 24 pieces / 25 mm was two plies. Thus, a passenger car tire of size 205 / 55R16 common to each tire was manufactured, and the following evaluation was performed.

・ Tire durability: The test tire is assembled to a standard rim specified by JIS at an internal pressure of 110 kPa (1.1 kgf / cm ² ), and the tire is pressed against the drum with a load that deflects by 62% of the maximum load specified by JATMA. It was over. This travel was performed at 420 rpm for 720 hours. However, if a clear abnormality was observed, the driving test was terminated at that time. Then, the tire after the running test was disassembled, the length of the edge separation at the belt end was measured, and the presence or absence of cord breakage was observed. The edge separation was determined as follows. 0 mm: None. 1-3mm: Minute. 4-6mm: Small. 7-9mm: Medium. 10mm or more: Large.

Actual vehicle handling stability: Each tire was adjusted to an internal pressure of 200 kPa using a JIS standard rim and mounted on a passenger car with a displacement of 2000 cc. Then, in the test course for evaluating steering stability, three trained test drivers performed a comprehensive sensory evaluation of steering stability such as steering response, rigidity, and grip. At this time, the conventional example was set to 6 points and relative comparison was performed with a maximum of 10 points. The larger the value, the better the steering stability.

・ Waddle ride-over: Test tires are mounted on the front wheels of the test vehicle under the same conditions as in actual vehicle handling stability, and the ride-over performance is sensual by three test drivers on the test course for pass-by evaluation evaluated. The ones that can be carried over smoothly are marked with “○”, and those that are difficult to get over are marked with “x”.

  As shown in the results of Tables 1 and 2, in Examples 1 to 10, while maintaining the weight of the belt layer small, tire durability equivalent to the conventional example and actual vehicle handling stability significantly superior to the conventional example were obtained. . Moreover, the same result as the conventional example was obtained also in the overpass performance of the kite. In Examples 3 to 5 and 8 to 10, the tensile strength of the filament and the tensile strength of the cord were higher than those of the other examples, and thus the actual vehicle handling stability was excellent. Examples 1-2 have a slightly lower carbon content than the other examples, Example 6 has a Cr content of less than 0.01% and a boron (B) content of less than 1 ppm, and Example 7 The boron (B) content was excessive. These were considered to be the reasons why Examples 1-2 and 6-7 had relatively low strength and low steering stability. In Examples 8 to 9, the filament strength was the highest, which is probably because the boron (B) content was the most appropriate, and the content of molybdenum (Mo) and the like was also appropriate.

  In Comparative Example 1, since the carbon content was low and the boron (B) content was too low, the filament strength and cord strength were low, and it was necessary to increase the number of cords to be driven. For this reason, after the durability test, peeling at the belt end of 7 to 9 mm was observed. In Comparative Example 2, since the carbon content was excessive, the weight of the belt layer could be considerably reduced, but the toughness of the cord was insufficient, and the cord was broken after the durability test. In Comparative Example 3, since the filament diameter was too small, it was necessary to increase the number of cords to be driven. Therefore, the belt edge separation was large and the cords were broken.

  In Comparative Example 4, when the diameter of the main filament 2 was increased to 0.32 mm, the same weight reduction effect as that of the example was obtained, but cord breakage was observed after the durability test. The cause is considered to be that the main filament diameter is excessive, the durability of the tire cord is lowered, and as a result, the durability of the tire is lowered.

  In Comparative Example 5, since the number of main filaments per cord is 1, the number of cords to be driven needs to be very large, and the cord occupation ratio exceeds 100%. In Comparative Example 5, it was clear that performance such as durability could not be obtained, so performance test was not performed. In Comparative Example 6, since the number of the main filaments 2 arranged in parallel was set to 7, when the wrapping filament 3 was wound, the shape in which the main filaments 2 were aligned in one layer collapsed and a stable cord shape could not be obtained. Therefore, cord breakage was observed after the durability test.

  Next, Table 3 shows examples and comparative examples in which the wave height and wave pitch of the corrugation are changed. As shown in Table 3, Example 11 and Example 5 differ only in the wave height of the corrugation. In Example 11 in which the wave height was increased, no cord breakage was observed, and the belt end peeling was at a minute level as in Example 5, but the amount of peeling was slightly smaller than in Example 5. This is because, in the case of Example 11, there is a large room for the waveform to be expanded in the tire circumferential direction at the time of ground contact, so that the stress is more dispersed and the tire failure is less likely to occur, and deformation occurs. It is considered that the handling stability has decreased due to the ease.

The pneumatic radial tires of Comparative Examples 7 to 9 are the same as the tires of Example 5 except for the configurations mentioned below. The tire of Comparative Example 7 had an excessive wave height of 0.15 mm. As a result, although the degree of weight reduction of the belt layer was the same as that of the example, the steering stability was lowered. In Comparative Example 8, as a result of making the corrugation pitch as small as 2.0 mm, although the degree of weight reduction of the belt layer was the same as that of the example, the steering stability was lowered. Comparative Example 9 was inferior in tire durability as a result of making the wave height of the corrugation 0.01mm too small. However, the handling stability was high.

Table 4 below summarizes 49 types of test examples of the belt cord including the Examples and Comparative Examples of Tables 1 and 2 above.

  In Table 4, for those corresponding to the above-mentioned Examples or Comparative Examples, this is described in the column outside the left of Test Example No. In each test example in Table 4, the same steel filament with a diameter of 0.15 mm is used for the wrapping film, and when multiple main filaments are used, they are juxtaposed to form a single layer without twisting. ing. In any test example, each main filament has the same corrugation to have a corrugation height of 0.06 mm and a corrugation pitch of 4.5 mm as described in Tables 1 and 2 above. Was given.

  In Test Example 2 in Table 4, the filament made of the same steel material as in Example 1 (Test Example 3) was used as the main filament, but the cord filament strength was as small as 0.15 mm. Is getting smaller. In addition, when a tire using this cord as a belt ply is attached to an actual vehicle, the stability of the cord is somewhat disadvantageous because the stiffness of the cord is small, or it is somewhat disadvantageous in terms of tire durability because of the need to increase the number of driving. is there. On the other hand, in Test Example 4 (shown between Test Example 6 and Test Example 7) in Table 4, a filament made of the same steel material as in Example 1 (Test Example 3) was used as the main filament. However, the filament strength was a little smaller, but the major and minor diameters of the cords increased and the cord strength increased. In this case, the rigidity of the cord becomes relatively large, which is somewhat disadvantageous in terms of tire durability.

  For the cords of Test Examples 23 and 26, a steel material having a higher carbon content than that of Example 5 (Test Example 16) was used. Other conditions were the same as those of Example 5, and the cord tensile strength was carried out. It is a little larger than in the case of Example 5. However, the rigidity of the cord becomes relatively large, which is somewhat disadvantageous in terms of tire durability. On the other hand, the cord of Test Example 25 uses the same steel material as Test Example 26 and the diameter of the main filament is 0.15 mm, the cord strength is small, and when the tire used for the belt ply is attached, Since the rigidity of the cord is small, the steering stability is slightly low, or the tire durability is low because it is necessary to increase the number of driving. In the cord of Test Example 27, the same steel material as in Test Examples 25 and 26 is used, and the diameter of the main filament is increased to 0.30 mm. Therefore, the rigidity of the cord becomes relatively large, which is somewhat disadvantageous in terms of tire durability.

  The cord of Test Example 28 is a comparative example in which the same steel material as in Test Examples 25 to 27 was used and the diameter of the main filament was excessively increased to 0.32 mm. Since the long and short diameters of the cord are excessive and the rigidity is excessive, the tire durability is inferior. On the other hand, the cord of Test Example 24 is a comparative example in which the same steel material as in Test Examples 25 to 28 is used and the diameter of the main filament is made as small as 0.14 mm. The filament strength is outside the scope of the present invention, and the rigidity of the cord is small.

  Finally, a modified example of the structure of the steel cord will be described with reference to FIG. In the modified steel cord 1 ′, the cross section of the main filament 2 is not circular but flat. The ratio of the thickness DT to the diameter D in each main filament 2 is, for example, 0.6 to 0.8 times. According to the modification, the thickness of the steel cord can be further reduced. However, the number of main filaments arranged in parallel is, for example, 5 or less or 4 or less.

  As described above, the pneumatic radial tire of the present invention is excellent in handling stability, ride comfort, and durability and realizes weight reduction, and is particularly suitable for various types of passenger car tires.

DESCRIPTION OF SYMBOLS 1 Steel cord 2 Main filament 3 Wrapping filament 4 Belt ply 5 Belt binding rubber material D Diameter of main filament DT Thickness of main filament in modified example H Corrugated height
P Corrugation and winding pitch T Steel cord minor diameter (thickness)
W Long diameter of steel cord (width)

Claims (7)

By mass-based content, C: 0.95 to 1.20%, Si: 0.1 to 1.5%, Mn: 0.1 to 1.0%, Al: 0.01% or less, Ti: 0.01% or less, N: 20 to 40 ppm, O: 20 to 40 ppm, diameter (D) is 0.15 to 0.30 mm, and tensile strength TS (Mpa) satisfies the following formula (I) Using steel filament as the main filament,
Two to six main filaments of the same diameter are juxtaposed to form a single layer without twisting together to form a main filament bundle, and one steel filament smaller in diameter and straight than the main filament is a wrapping filament A pneumatic radial tire using a steel cord (n + 1 structure: n = 2 to 6) wound around the main filament bundle as a tire belt layer.
−2000 × D + 4400 ≦ TS (Mpa) ≦ −2000 × D + 5400 (I)
However, D is a numerical value indicating the diameter of the main filament in mm.   The steel filament constituting the main filament has a boron (B) content of 4 to 30 ppm by mass, and a solid solution boron (B) content of 3 ppm by mass or more. Pneumatic radial tire described in 2.   The steel filament constituting the main filament is in mass%, Cr, Ni and Co are all 0.5% or less, V, Cu, Mo and W are all 0.2% or less, and Nb is 0.1% or less. And containing at least 0.01% or more selected from the group consisting of Cr, Ni, Co, V, Cu, Mo, W and Nb. The described pneumatic radial tire.   The pneumatic radial tire according to any one of claims 1 to 3, wherein the steel filament constituting the main filament is formed or corrugated.   The steel filaments constituting the main filament have the same corrugation height and pitch, the corrugation height (wave height) is 0.03 to 0.11 mm, and the corrugation pitch (wavelength) is 3.0 mm to 30.30 mm. The pneumatic radial tire according to claim 1, wherein the pneumatic radial tire is 0 mm.   The pneumatic radial tire according to any one of claims 1 to 5, wherein the occupation ratio of the steel cord in the width dimension of each belt ply is 50 to 75%.   The pneumatic radial tire according to any one of claims 1 to 6, wherein at least two belt plies are provided.

Images