JP2008001163A - Pneumatic radial tire - Google Patents

Abstract

The present invention provides a pneumatic radial tire that has excellent handling stability, ride comfort, and wear resistance, and improved durability.
In a pneumatic radial tire T having a carcass composed of at least two carcass plies 2 using a polyester cord and at least two belt plies 4 using a steel cord, the polyester cord has been bonded. Cord strength is 4.5 cN / dtex or more, bending hardness is 15 to 50 cN, and the steel cord is formed by twisting a plurality of steel filaments having a diameter of 0.20 to 0.30 mm. Has a strength of 450 to 850 N and a bending hardness of 180 to 300 cN.
[Selection] Figure 1

Description

  The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire suitable for a passenger car that has excellent handling stability and ride comfort and improved durability.

  The performance required for radial tires for passenger cars includes steering stability, ride comfort, low fuel consumption, durability, and the like. For carcass of radial tires for passenger cars, polyester (polyethylene terephthalate fiber, PET) cords are widely used instead of conventional rayon cords, which are easy to manage cost, supply capacity, tire manufacturing process, etc. .

  The steering stability and ride comfort are influenced by the rigidity of the side wall portion mainly composed of the carcass ply and the side wall rubber, and the rigidity of the carcass ply itself contributes greatly. In addition, the belt ply that reinforces the tread part controls the tread stiffness, affects the tire contact pressure distribution and the contact shape, and also affects the steering stability, ride comfort, and wear resistance. The selection of steel cords that make up

  By the way, the polyester cord has a lower modulus than the rayon cord, and the tire performance such as steering stability and ride comfort is not as good as the tire using the rayon cord, and the polyester is more adhesive to rubber than the rayon or nylon. It is said that the heat resistance and durability are not sufficient because the adhesive strength and cord strength are lowered due to the action of moisture and amine in the rubber compounding, particularly due to heat.

  With the recent high performance and high grade of vehicles, there is a demand for further improvement of tire performance. For this reason, polyethylene 2, 6 naphthalate fiber cord is used for the carcass cord, the cord thickness, the number of twists, the initial It has been proposed to specify the modulus and loss tangent to improve driving stability and reduce rolling resistance while maintaining high ride comfort (for example, Patent Document 1).

  Further, in recent years, from the viewpoint of energy saving and resource saving, there is a strong demand for reduction in fuel consumption of automobiles, and it is known that weight reduction of tires greatly contributes to this reduction in fuel consumption. To reduce the weight of the tire, it is effective to reduce the amount of the tire constituent material used, and in particular, it is particularly effective to reduce the weight of the belt ply formed of a steel cord having a large proportion of the total tire weight.

Therefore, so-called high-strength wire rods with increased carbon content in steel materials to increase the strength of steel cords than ever before have been put into practical use, and the use of steel cords in belt plies has been reduced to reduce tire weight. ing. (Patent Document 2).
JP 2003-237308 A JP 2000-335206 A

  However, those described in the above-mentioned document 1 are considered to adversely affect the ride comfort because the rigidity of the sidewall portion is high, and durability due to high heat generation and heat accumulation during high-speed driving. There is no description about the improvement of the decrease, and the supply amount of polyethylene 2,6 naphthalate fiber is not enough to be used for a general-purpose tire cord, and there is a problem of cost.

  In addition, to reduce the weight, the steel cord of the belt ply is simply increased in strength to reduce its usage, but even if the belt strength is secured, the volume ratio of the steel cord itself is reduced, and the tread stiffness changes and tagging. The effect is reduced, and the ride comfort, handling stability, wear resistance and the like are impaired.

  Accordingly, an object of the present invention is to use a steel cord used for a belt ply and a polyester cord which is easy to obtain and is advantageous in terms of cost, is used for a carcass of a radial tire with improved modulus and heat resistance. The object is to provide a pneumatic radial tire that optimizes belt rigidity by selecting, has excellent handling stability, ride comfort, and wear resistance, and has improved durability.

  As a result of diligent study on the modulus and side rigidity of the carcass cord, the present inventor has optimized the bending rigidity of the cord within the appropriate range in addition to the tensile modulus conventionally evaluated as the modulus of the tire cord. As a result, the steering stability and ride comfort are balanced and excellent, and the heat resistance improved adhesion treatment is applied to improve tire durability and secure the strength of the steel cord for the belt. It has been found that the overall tire performance can be obtained by optimizing the bending rigidity and applying it to the tire combined with the carcass cord.

  That is, the pneumatic radial tire of the present invention uses a carcass made of at least one carcass ply using a polyester cord disposed between the left and right bead portions, and a steel cord on the outer side in the tire radial direction of the carcass in the tread portion. In a pneumatic radial tire having a belt on which at least two belt plies are arranged, the polyester cord has a cord strength of 4.5 cN / dtex or more after adhesion treatment, and a bending hardness per cord of 15 to 50 cN And the steel cord is formed by twisting a plurality of steel filaments having a diameter of 0.20 to 0.30 mm, the strength of the steel cord is 450 to 850 N, and the bending hardness per cord is 180 to 300 cN.

  In the present invention, the rubber adhesion rate in the peel adhesion test at room temperature of the polyester cord is 90% or more at 140 ° C. for 40 minutes, 80% or more at 170 ° C. for 60 minutes, and 180 ° C. at 170 ° C. The cord strength retention after partial vulcanization is particularly preferably 80% or more.

  Further, in the present invention, the cord occupancy ratio of the carcass ply is preferably 38 to 68%, particularly 38 to 56% for a cord having a cord diameter of less than 0.6 mm, and 44 for a cord having a cord diameter of 0.6 mm or more. It is desirable to be -66%.

  Furthermore, it is preferable that the display fineness of the polyester cord is 2000 to 3500 dtex.

  According to the pneumatic radial tire of the present invention, by properly selecting and using the strength and rigidity of the carcass polyester cord and the steel cord of the belt, the tire strength and the tire rigidity are ensured, and the steering stability and the ride comfort are ensured. By applying the heat resistance improving adhesion treatment to the polyester cord in a well-balanced manner, it is possible to improve the tire durability performance by suppressing adhesion deterioration and strength reduction of the carcass cord due to high heat generation and heat accumulation during high-speed running.

  FIG. 1 is a schematic half-sectional view of a pneumatic radial tire (hereinafter referred to as a radial tire) T according to an embodiment of the present invention.

  The radial tire T includes a pair of bead portions 7 and sidewall portions 6, and a tread portion 5 that is continuous with both sidewall portions 6. A pair of bead cores 1 embedded in a bead portion 7, a carcass 2 composed of a single carcass ply disposed between the two, and two pieces using steel cords provided on the outer side in the tire radial direction of the carcass 2 in the tread portion And a cap ply 3 made of a nylon cord wound around the outer periphery of the belt 4.

  The carcass 2 uses a polyester cord as a reinforcing material. A ply stretched in parallel and rubberized at a predetermined driving density is arranged in the radial direction of the tire so that the bead core 1 and the bead filler 8 are disposed from the inside of the tire. The cord end is locked on the outside of the entraining tire.

  The belt 4 is composed of two belt plies in which steel cords formed by twisting a plurality of steel filaments having a filament diameter of 0.20 to 0.30 mm are arranged in parallel and rubberized, and the steel cord is in the tire circumferential direction. The steel cords are arranged so as to be inclined at about 15 to 30 °, and the steel cords are arranged so as to cross each other between the plies.

  The cap ply 3 is formed by covering both belt edge portions on the outer periphery of the belt 2 and winding a nylon cord, for example, nylon 66, 940 dtex / 2 cord in a spiral shape at an angle of approximately 0 ° with respect to the tire circumferential direction. The belt 4 is tightened in the circumferential direction to obtain a tagging effect that increases the rigidity and belt restraining force in the circumferential direction and radial direction of the tire. To suppress durability and to improve durability and handling stability at high speed. Further, an edge ply (not shown) that covers the edge portion of the belt 4 may be provided, or a structure having no cap ply or edge ply may be used.

  As the above-mentioned carcass polyester cord used for the radial tire T of the present invention, cords conventionally used for tire cords can be used as raw yarns, and commercially available products are “Ester”, Toray Industries, Inc., Toray Industries, Inc. "Tetron" from the company can be used.

  The cord strength of the polyester cord after the adhesion treatment is 4.5 cN / dtex or more, preferably 5.0 cN / dtex or more, more preferably 5.5 cN / dtex or more. If the cord strength is less than 4.5 cN / dtex, the tire strength, which is a basic performance for ensuring tire durability, will be insufficient. To compensate for this, an increase in the number of cords driven into the carcass ply and the number of plies This increases the cost and leads to an increase in tire weight.

  The cord strength can be obtained by selecting the intrinsic viscosity of the raw yarn, the spinning temperature and speed, and the draw ratio, and further selecting an adhesive treatment agent and treatment conditions.

  In addition, the cord subjected to the bonding process has a cord bending hardness of 15 to 50 cN when one cord is bent. Here, the cord bending hardness is a value defined by the maximum load when one tire cord that has been subjected to bonding treatment is bent at the center portion at a distance between fulcrums of 25 mm.

  The inventor obtained the knowledge that the bending modulus (bending rigidity) of the cord and the above-mentioned cord bending hardness have a good correlation, and within the range of the cord occupancy rate described later, the above-mentioned bending hardness is within the range. By using a certain cord, it is possible to optimize the rigidity of the side portion and to achieve both steering stability and ride comfort.

  If the cord bending hardness is less than 15 cN, the side portion rigidity is insufficient and the steering stability is difficult to satisfy. If the number of cords to be driven and the number of plies are increased in order to ensure the side portion rigidity, the tire weight increases and the running speed increases. It may cause a failure such as separation due to heat generation inside. Also, if the cord bending hardness exceeds 50 cN, the cord becomes too stiff and it becomes difficult to improve ride comfort, fatigue resistance is reduced and durability performance is affected, and the difference in modulus from rubber It makes it easy to cause a separation failure from the adhesive failure based on it.

  The means for setting the bending hardness of the polyester cord in the range of 15 to 50 cN is not particularly limited. Examples thereof include spinning and drawing conditions, constituent filament thickness, twisting coefficient, adhesion treatment liquid and treatment conditions, resin adhesion rate, and softening treatment conditions. These two or more means can be combined and adjusted.

  From the viewpoint of maintaining the properties such as strength, dimensional stability, and fatigue resistance of the polyester cord, it is preferable to use means such as the resin adhesion rate during the bonding treatment and the softening treatment conditions that have little influence on the basic properties of the cord.

  The amount of cord used in the carcass ply of the polyester cord is 38 to 68% in terms of cord occupancy per ply. In particular, it is preferable that the cord diameter is 38 to 56% when the cord diameter is less than 0.6 mm, and 44 to 66% when the cord diameter is 0.6 mm or more. 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. Code occupancy (%) = (Cord diameter (mm) × Number of cords driven (lines / 25 mm)) × 100/25 (mm).

  When the cord occupancy rate falls below the lower limit value, even if a cord in the cord bending hardness range is used, side portion rigidity is insufficient and steering stability tends to decrease. Also, if the cord occupancy rate exceeds the upper limit, the side part rigidity becomes too high and the ride comfort decreases, the adjacent cords come close to each other and it is disadvantageous for separation, and furthermore the cord arrangement at the time of ply expansion in tire molding Disturbance is likely to occur, causing a decrease in uniformity.

  Here, the reason why the code occupancy is lower as the cord diameter is smaller includes the reason for the tire molding accuracy that the cord is more likely to be disturbed when the ply is expanded because the thinner the cord, the thinner the topping.

  The thickness of the polyester cord is not particularly limited, but the total fineness is preferably 2000 to 3500 dtex, and the fineness per filament is about 4 to 10 dtex, preferably 5 to 8 dtex. Two twists or three twists may be used, and the number of twists may be different between the upper twist and the lower twist.

  If the total display fineness is less than 2000 dtex, the cord is thin, so even if the above means are combined, the bending hardness is insufficient, and if a small number of thick filaments are used to increase the bending hardness, the fatigue resistance decreases. Moreover, the thing exceeding 3500 dtex is not preferable because the cord diameter becomes too large and the thickness of the carcass ply increases, which is disadvantageous for weight reduction and heat generation.

Further, the number of twists of the polyester cord is not particularly limited, but those having a twist coefficient of 2100 to 2400 are preferable from the viewpoint of maintaining the properties of the carcass cord such as strength, dimensional stability, and fatigue resistance. If the twist coefficient is less than 2100, the fatigue resistance is lowered, and if it exceeds 2400, the dimensional stability and strength are affected, and the cost is increased. The twist coefficient is a value obtained by the following equation. K = T · D ^1/2 (K = twisting coefficient, T = average value of the number of upper twists and the number of lower twists (times / 10 cm), D = total displayed fineness (dtex)).

  The radial tire of the present invention is composed of a carcass ply having one or two plies of a carcass. In the case of two plies, the above-described polyester cord may be used for at least one carcass ply. Conventional polyester cords and nylon cords can be used for the other plies within a range that does not impair.

  In the present invention, the polyester cord has a rubber adhesion rate in a peel adhesion test at room temperature of 90% or more at 140 ° C. for 40 minutes (initial vulcanization conditions) and vulcanized at 170 ° C. for 60 minutes (over vulcanization conditions). The cord strength retention after vulcanization at 170 ° C. for 180 minutes is desirably 80% or more, and these characteristics can be obtained by an adhesive treatment.

  These improvements in adhesion and strength reduction suppress degradation of the polyester cord due to hydrolysis and amine decomposition due to moisture contained in the compounded rubber. Adhesion degradation and cord due to high heat generation and heat accumulation during high speed running The reduction in strength can be improved and the tire durability can be improved.

  The adhesive treatment method for improving heat resistance in the present invention is not particularly limited, and a heat-resistant agent such as an epoxy compound or a polyisocyanate compound can be added to a conventionally known adhesive formulation. Moreover, it can implement according to the method of Unexamined-Japanese-Patent No. 2006-2327, for example.

  The above-mentioned cord bending hardness can be adjusted by adjusting processing conditions such as the composition of the treatment liquid at the time of adhesion treatment, the solid content concentration, the number of treatments and the stretching ratio, the heat treatment temperature, and the time. Changing the adhesion rate and adjusting the cord bending hardness can be easily performed with little influence of other cord characteristics.

  Conventionally known polyester fiber adhesion treatment includes a method in which polyester fiber is treated with a known epoxy compound in advance and then treated with resorcin / formalin / rubber latex (RFL), which is widely used as an adhesive with rubber. As disclosed in JP-A-54-82492, there is a method of treating with a mixed solution of a polyepoxide compound, a vinyl pyridine latex and a blocked isocyanate compound and then treating with RFL.

  Further, the effect of improving the heat resistance by the treatment method described in JP-A-2006-2327 is that the use of water-soluble blocked isocyanate makes the infiltration and diffusion of isocyanate into the fiber more uniform by the carrier. Acts more effectively as a scavenger for amines in rubber compounds that cause a decrease in heat resistance, and the polyfunctional isocyanate increases the resin cross-linking density and improves the barrier properties against the penetration of amine into the fiber. This is a preferable processing method because the deterioration of the polyester is suppressed by the synergistic effect, and the heat-resistant adhesiveness and cord strength retention are remarkably improved.

  When adjusting the cord bending hardness by the resin adhesion rate, the resin adhesion rate to the polyester cord is not particularly limited, but is preferably 5 to 10% by weight. If the amount is less than 5% by weight, sufficient cord bending hardness, initial adhesion and heat-resistant adhesion cannot be obtained, and if it exceeds 10% by weight, the adhesiveness may be lowered due to blistering or the like, and the cord becomes hard. This is not preferable from the viewpoint of quality, such as excessive reduction in strength and fatigue resistance, and increased occurrence of dip wrinkles.

  For the above-mentioned adhesion treatment, a dip machine that is normally used in the rubber industry can be used, and the number of treatments may be repeated two or more times depending on the desired cord characteristics.

  The steel cord used for the belt of the radial tire of the present invention is formed by twisting a plurality of steel filaments having a diameter of 0.20 to 0.30 mm, the strength of the steel cord is 450 to 850 N, and the bending hardness per cord. Is 180 to 300 cN.

  The steel cord can be manufactured by a conventionally known manufacturing method using a predetermined number of filaments using a buncher type twisting machine or a tubular type twisting machine.

  The filament constituting the steel cord has a diameter in the range of 0.20 to 0.30 mm, preferably 0.22 to 0.28 mm. Filaments thinner than 0.20 mm need to use a large number of filaments in order to ensure cord strength and bending hardness, which is contrary to the weight reduction of tires due to the increase in the unit weight of the cord itself and the amount used for the belt ply. Also, the filament productivity is poor and the steel cord for the belt is not worth the cost. In addition, the cord exceeding 0.30 mm becomes stiff and easily causes a decrease in ride comfort and uneven wear, and also adversely affects fatigue resistance and belt edge separation.

The steel filament is made of high carbon steel having a carbon content of about 0.70 to 0.95% by weight (for example, a piano wire specified in JIS G3502), and has a tensile strength of about 2500 to 3300 N / mm ^2. From the viewpoint of weight reduction, the tensile strength is preferably 2700 N / mm ² or more, more preferably 2900 N / mm ² or more. However, if the tensile strength exceeds 3300 N / mm ² , fatigue resistance deteriorates due to deterioration of wire drawing workability such as breakage during wire drawing and generation of surface flaws, and embrittlement of steel, which is not preferable.

  Furthermore, the surface of the filament is coated with brass plating having a copper ratio of 63 to 67% with an adhesion amount of about 4 to 6 g / Kg in order to improve the adhesion to rubber.

  Such a steel cord can adopt a conventionally known cord structure if the strength of the cord is 450 to 850 N and the bending hardness per cord is 180 to 300 cN, and the filament diameter, the number of filaments, The cord characteristics can be designed by combining a twist structure, a twist pitch, and the like.

  As a cord structure, for example, a single twist structure such as 1 × 2, 1 × 3, 1 × 4, and 1 × 5, two-layer twist such as 1 + 2, 1 + 3, 2 + 1, 2 + 2, 2 + 3, 2 + 4, 2 + 5, 2 + 6, and 2 + 7 Examples of the structure (the core may be untwisted or twisted) include double twist structures such as 1 × 2 × 2, 1 × 2 × 3, 1 × 3 × 3, and 1 × 4 × 4.

  In addition, the steel cord is preferably an open type cord structure with good rubber penetration from the viewpoint of improving corrosion fatigue resistance due to trauma of the tread portion, and in a single twist structure such as 1 × 4, 1 × 5 Loose open twist is mentioned, and cords of tight open twist such as 2 + 1, 2 + 2, 2 + 3, etc., which are indicated by an M + N structure, are preferable.

  In the present invention, if the cord strength of the steel cord is less than 450N, the strength as a cord for the belt is insufficient, and if the number of cords to be driven is increased in order to ensure tire strength, the belt stiffness increases and the ride comfort and separation resistance deteriorate. However, it goes against weight reduction. Also, if the strength exceeds 850N, the belt strength will increase even if the number of driving becomes rough in order to design an appropriate belt strength, resulting in deterioration of ride comfort and wear resistance, nails and sharp stones, etc. The cut penetration resistance when stepping on is reduced.

  Also, if the bending hardness per steel cord is less than 180 cN, the cord becomes too flexible and the belt rigidity in the tire circumferential direction is lowered, thereby promoting a reduction in cornering power and uneven wear, and a tagging effect that restrains the tread. Decreases and the high-speed durability decreases. When the bending hardness exceeds 300 cN, the cord becomes stiff and not only deteriorates the ride comfort but also causes a decrease in edge separation and wear resistance.

  The bending hardness of the steel cord is a value defined by the maximum load when one steel cord is bent at the center portion at a distance between fulcrums of 25 mm, as in the case of the polyester cord.

  The radial tire of the present invention uses a specific polyester cord for the carcass, and the belt cord steel cord has the belt rigidity defined by the above-mentioned strength and bending hardness. Further, by optimizing the belt ply rigidity, both the handling stability and the ride comfort can be improved, and the wear resistance and durability can be improved.

  Examples of the present invention will be described below, but the present invention is not limited to these examples without departing from the gist of the present invention.

  Table 1 shows polyester cords of 1100 dtex / 2 (twisting factor 2200), and the polyester cords of 1670 dtex / 2 (twisting factor 2200), in which the resin adhesion rate is changed by the adhesive treatment used in each example and comparative example. Show. Table 3 shows an example in which the polyester cord of 1100 dtex / 2 (twisting coefficient 2200, resin adhesion rate 7.8%) is commonly used for the carcass and the steel cord of the belt ply is changed. The characteristics of each code are shown in Tables 1-3.

[Polyester cord for carcass]
The polyester cord adhesion treatment in the examples and comparative examples is performed twice using treatment liquids similar to the treatment liquid A and treatment liquid B disclosed in JP-A-2006-2327, and the solid content of the treatment liquid B is as follows. The resin adhesion rate of the cord was adjusted by changing the concentration. Further, in the conventional example, the first treatment was performed twice by DuPont IPD22 formulation (solid content 12.2%), and the second treatment was performed with an RFL treatment liquid (solid content 20%). The cord diameter, strength, fineness, bending hardness, peel adhesion and cord strength retention were measured by the following methods.

<Cord diameter, strength, fineness>
In accordance with JIS L1017, after standing for 24 hours or more under constant temperature conditions of 20 ° C. and 65% RH, the cord diameter, fineness, and tensile strength were measured with a tensile tester (Shimadzu Corporation Autograph).

<Bending hardness>
The maximum bending load (cN) was determined by a three-point bending test method using a tensile tester with a span of 25 mm and a cord bending speed at the center of the span of 300 mm / min, and this value was defined as bending hardness.

<Peel adhesion>
Adhesion treatment codes are arranged in the number of stakes listed in the table, and rubber for carcass (100 parts by weight of natural rubber (RSS # 3), 30 parts by weight of carbon black (SRF), 3 parts by weight of zinc, 1 part by weight of stearic acid, naphthene A test piece in which the topping coating coated on both sides with 4 parts by weight of oil, 1 part by weight of anti-aging agent (6C), 2 parts by weight of sulfur, and 1 part by weight of vulcanization accelerator (MBT) is laminated with the same cord direction. (Rubber thickness 0.7 mm, width 25 mm between cords and cords) and vulcanized at 140 ° C. for 40 minutes (initial adhesion) or 170 ° C. for 60 minutes (over-vulcanization adhesion), and then using a tensile tester Then, a peeling test was conducted by a T-shaped method at a normal temperature and a tensile speed of 50 mm / min, and an average peeling force was measured. After the test, the rubber adhesion rate (%) of the release surface cord was visually evaluated on a 100-point scale.

<Strong code retention>
The treated cord is embedded in the above-mentioned carcass rubber in a tensioned state with an initial load, vulcanized at 170 ° C. for 180 minutes, then the cord is taken out from the vulcanized rubber, and the cord strength after vulcanization is in accordance with JIS L1017. Measured and expressed as the retention rate (%) with the cord strength before vulcanization.

[Steel cord for belt]
The steel cord is dry-drawn to an intermediate wire of a predetermined diameter from a 5.5 mm rod of the piano wire SWRS82A material specified in JIS G3502, and this intermediate wire is brass-plated (copper ratio 64%) After applying a plating adhesion amount of 4.5 g / Kg), a filament obtained by final drawing to a predetermined diameter using an ordinary wet wire drawing machine is used in accordance with a conventional method using an ordinary tubular twisting machine. It is manufactured by twisting at the following twist pitch. The cord strength and bending hardness were measured by the following methods. The two-layer structure cord is indicated by (−) when the core is untwisted.

<Strong code>
It measured according to JIS G3510.

<Bending hardness>
The maximum bending load (cN) was determined by a three-point bending test method using a tensile tester at a span of 25 mm and a cord bending speed of 300 mm / min at the center of the span, and this value was defined as the bending hardness.

[Steel cord]
・ 2 + 2 × 0.25: Twist pitch = − / S10 mm
・ 2 + 1 × 0.27: Twist pitch = − / S11mm
・ 2 + 3 × 0.25: Twist pitch = − / S10 mm
・ 2 + 7 × 0.175: Twist pitch = S5 / S10mm
・ 2 + 7 × 0.22: Twist pitch = S6 / S12mm
・ 2 + 7 × 0.25: Twist pitch = S7 / S14mm

[Manufacture of radial tires]
Next, test radial tires were produced in two tire sizes using the polyester cord of the carcass ply and the steel cord of the belt ply according to the specifications shown in the table.

  The radial tires listed in Table 1 have a 1100 dtex / 2 polyester cord (twisting factor 2200) with 2 plies in the carcass and 2 plies with a tire size of 205 / 70R15. The radial tires in Table 2 have a polyester cord with 1670 dtex / 2 The tire size was 205 / 65R15 with a (ply factor) of 1 ply and a belt of 2 plies. The steel cords of the belts were all 2 + 2 × 0.25 (20 pieces / 25 mm driven), and the inclination angles of the cords were 22 ° with respect to the tire circumferential direction.

  The radial tires listed in Table 3 are commonly used for 2 plies of 1100 dtex / 2 (twisting coefficient 2200, resin adhesion rate 7.8%) polyester cord (24 driven / 25 mm) in the carcass, and the steel cord of the belt By changing to the above structure, the number of cords to be driven was adjusted so that the belt strength was substantially the same as that of the tire of Conventional Example 1. The belt strength and belt rigidity in Table 3 are values obtained by multiplying the number of driven wires by cord strength and cord bending hardness, respectively.

  Each tire has a 1-cap ply structure using 940 dtex / 2 of nylon 66 at a driving number of 34 pieces / 25 mm. High speed durability, steering stability, riding comfort and uneven wear resistance were evaluated by the following methods. The results are shown in Tables 1-3.

<High speed durability>
A drum test was conducted according to FMVSS109 (UTQG conditions). JIS standard rim was used, tire internal pressure was 220KPa, load was 88% of the maximum load specified by JATMA, running at 80Km / h for 60 minutes, allowed to cool, and after adjusting internal pressure again, the main run was performed. . The main run started at 120 km / h, the speed was increased stepwise by 8 km / h every 30 minutes, and the drum was run until a failure occurred. The travel distance up to the time of failure occurrence is shown as an index with the conventional example being 100. It shows that high-speed durability is so favorable that a numerical value is large.

<Steering stability>
Each tire is adjusted to an internal pressure of 200 kPa using JIS standard rims, and four similar tires are mounted on a 2000cc domestic passenger car. Steering response by three test drivers on a test course for steering stability evaluation. Comprehensive sensory evaluation of steering stability such as feeling of rigidity, grip, etc., with the conventional example being 6 points, relative comparison was made with a maximum of 100 points, and the average score of 3 people was shown as an index with the conventional example being 100 . The larger the value, the better the steering stability.

<Ride comfort>
Each tire is adjusted to an internal pressure of 200 kPa using a JIS standard standard rim, and four similar tires are mounted on a 2000cc domestic passenger car. Riding comfort is provided by three test drivers on a test course on good and bad roads. Sensory evaluation was performed, and conventional examples were evaluated as a reference. “△” indicates the same as the conventional example, “X” indicates inferior, and “◯” indicates superior.

<Uneven wear resistance>
Each tire is adjusted to an internal pressure of 200 kPa using a JIS standard rim, and four similar tires are mounted on a 2000 cc domestic passenger car, running on a regular road for 50,000 km, and then the wear condition of the appearance of the tread Visual evaluation was performed as follows. Normal wear: “◯”, slight uneven wear occurs: “Δ”, uneven wear state: “x”.

  As is apparent from the results shown in Tables 1 and 2, the radial tires of Examples 1 to 6 according to the present invention have high-speed durability by improving the heat resistance of the carcass polyester cord compared to the conventional tires. Improves and limits the cord bending hardness and cord occupancy, limits the steel cord of the belt, optimizes tire rigidity, improves steering stability and riding comfort in a balanced manner, and prevents uneven wear it can.

  In contrast, Comparative Examples 1, 4, 6, and 9 in which the cord bending hardness is less than 15 cN or the cord occupancy rate is less than 23% have poor steering stability due to insufficient side portion rigidity, and the cord bending hardness is 50 cN. In comparative examples 2 and 7 that exceed, the durability is lowered due to a decrease in fatigue resistance of the cord, and the ride comfort is also deteriorated. In addition, Comparative Examples 3 and 8 have low cord strength and insufficient durability, and Comparative Examples 5 and 10 having large cord occupancy ratios are deteriorated in durability due to adhesion failure of the sidewall, and riding comfort and uneven wear are also deteriorated. To do.

  In addition, as shown in Table 3, the embodiment in which the steel cord according to the present invention is used for the belt ply improves durability, handling stability, and riding comfort in a well-balanced manner by combining it with a carcass polyester cord, Excellent uneven wear. The comparative example 11 with low belt cord bending hardness is inferior in durability and ride comfort, and the comparative example 12 with high steel cord strength is reduced in durability and ride comfort due to a decrease in the number of driving, and also improved uneven wear resistance. Not. Comparative Example 13 using a steel cord having both high cord strength and hardness shows that the tire performance tends to decrease overall, and this strength level steel cord is not suitable for a tire for a passenger car.

  As described above, the pneumatic radial tire of the present invention improves steering durability and comfort while preventing durability while improving durability, and is particularly suitable for passenger car tires.

1 is a half sectional view of a pneumatic radial tire according to an embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Bead core 2 ... Carcass 3 ... Cap ply 4 ... Belt 5 ... Tread part 6 ... Side wall part 7 ... Bead part 8 ... Bead filler T ... Pneumatic radial tire

Claims (5)

A belt in which a carcass made of at least one carcass ply using a polyester cord arranged between the left and right bead portions and at least two belt plies using a steel cord on the outer side in the tire radial direction of the carcass in the tread portion are arranged. In a pneumatic radial tire having
The polyester cord has an adhesive-treated cord strength of 4.5 cN / dtex or more, a bending hardness per cord of 15 to 50 cN, and
The steel cord is formed by twisting a plurality of steel filaments having a diameter of 0.20 to 0.30 mm, the strength of the steel cord is 450 to 850 N, and the bending hardness per cord is 180 to 300 cN. A featured pneumatic radial tire. The polyester cord has a rubber adhesion rate in a peel adhesion test at room temperature of 90% or higher at 140 ° C. for 40 minutes and 80% or higher at 170 ° C. for 60 minutes,
The pneumatic radial tire according to claim 1, wherein the cord strength retention after vulcanization at 170 ° C for 180 minutes is 80% or more. The pneumatic radial tire according to claim 1, wherein a cord occupancy ratio of the carcass ply is 38 to 68%. 4. The air according to claim 3, wherein a cord occupation ratio of the carcass ply is 38 to 56% for a cord having a cord diameter of less than 0.6 mm, and 44 to 66% for a cord having a cord diameter of 0.6 mm or more. Entering radial tire. The pneumatic radial tire according to any one of claims 1 to 4, wherein a display fineness of the polyester cord is 2000 to 3500 dtex.

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