JP6062817B2 - Pneumatic radial tire for passenger cars - Google Patents

Description

  The present invention relates to a pneumatic radial tire for passenger cars.

  The performance required for radial tires for passenger cars includes handling stability, riding comfort, low fuel consumption, durability, and the like. For the carcass of radial tires for passenger cars, polyester (polyethylene terephthalate fiber, PET) cords that are easy to manage, such as cost, supply capability, and tire manufacturing process, are widely used instead of the conventional rayon cords. Yes. 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 reduction in tire mass greatly contributes to this reduction in fuel consumption.

  Conventionally, a carcass ply mainly uses an organic fiber cord having a double twist structure in which a plurality of strands (so-called strands) of organic fibers subjected to a lower twist are further twisted by an upper twist (for example, Patent Documents 1 and 2). However, in the double twist structure, since the twist directions of the lower twist and the upper twist are opposite to each other, the shape retention is good, but there are many twist processes and the manufacturing cost is high. In addition, the cord mass increases due to an increase in the cord diameter and causes an increase in tire mass such as an increase in ply thickness. Therefore, in order to reduce the weight of the tire, it is known to use a single twisted cord for the carcass ply to reduce the thickness of the carcass ply (for example, see Patent Documents 3 and 4).

JP 2008-1164 A JP 2008-1163 A JP2011-11594A JP 2011-235864 A

  As described above, it is preferable to use a single twisted cord to reduce the weight of the tire. In that case, in order to obtain excellent steering stability, riding comfort and durability as a radial tire for a passenger car, a carcass ply and a belt ply are used. The problem is how to set the rigidity. That is, the steering stability and the ride comfort are influenced by the rigidity of the sidewall portion, and the rigidity of the carcass ply itself contributes greatly. In addition, since the belt ply that reinforces the tread dominates the tread rigidity and affects the handling stability and the ride comfort, the selection of the steel cord constituting the belt ply is important.

  The present invention has been made in view of the above points, and is a pneumatic radial tire for a passenger car that can balance the steering stability and the riding comfort in a well-balanced manner and achieve weight reduction while improving tire durability. The purpose is to provide.

  The present inventor has been intensively studying in view of the above problems, and while using a single-twisted polyester cord for the carcass ply, by appropriately setting the rigidity of the steel cord of the polyester cord and the belt ply, the tire It has been found that the rigidity is secured, the steering stability and the ride comfort are balanced and the tire durability is improved while achieving weight reduction, and the present invention has been completed.

  That is, a pneumatic radial tire for a passenger car according to the present invention includes a carcass made of at least one carcass ply using a polyester cord disposed between left and right bead portions, and a steel tread portion on the outer side in the tire radial direction of the carcass. In a pneumatic radial tire for a passenger car having a belt on which at least two belt plies using a cord are arranged, the polyester cord is a single twist cord, and a bending hardness per cord is 4 to 14 cN The cord occupancy ratio of the carcass ply is 38 to 68%, and the steel cord is formed by twisting a plurality of steel filaments having a diameter of 0.20 to 0.30 mm. The bending hardness per one is 180 to 380 cN. Is shall.

  According to the present invention, by appropriately selecting and using the rigidity of the polyester cord of the carcass ply and the steel cord of the belt ply, it is possible to ensure the tire rigidity and balance the steering stability and the ride comfort in a balanced manner. The tire durability can be improved while achieving weight reduction.

It is a half sectional view of the pneumatic tire of an embodiment. It is drawing explaining the measuring method of cord bending hardness.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 is a half sectional view of a pneumatic radial tire (1) for a passenger car according to an embodiment. The tire (1) includes a tread portion (2) constituting a ground contact surface, a pair of left and right bead portions (3), and a pair of left and right sides interposed between the tread portion (2) and the bead portion (3). And a wall portion (4). A carcass (5) is embedded in the radially inner portion of the tread portion (2), and the carcass (5) is disposed between the left and right bead portions (3). That is, the carcass (5) is locked by the bead portion (3) from the tread portion (2) through the side wall portions (4) on both sides, and both end portions (5A) of the carcass (5) are bead portions. It is locked by being rolled up from the inside of the bead core (6) embedded in (3). In addition, a belt (7) composed of two belt plies is arranged on the outer side in the radial direction of the carcass (5) in the tread portion (2), and further, on the outer periphery of the belt (7) with respect to the tire circumferential direction. A belt reinforcing layer (8) made of an organic fiber cord wound spirally at an angle of 0 to 5 degrees is provided.

  The carcass (5) is composed of at least one carcass ply (one in the example shown in the figure) formed by arranging polyester cords as reinforcing materials in parallel with a predetermined number of driving and covering with a covering rubber. The carcass ply is arranged so as to be substantially perpendicular to the circumferential direction.

  The belt (7) is formed by inclining steel cords as a reinforcing material at a predetermined angle (for example, 15 to 35 degrees) with respect to the tire circumferential direction, and arranging in parallel at a predetermined number of driving and covering with a covering rubber The steel cord is composed of two belt plies (two in the illustrated example), and the steel cord is disposed so as to cross each other between the two belt plies.

  The polyester cord constituting the carcass (hereinafter sometimes referred to as PET cord) is a cord having a single twisted structure in which a yarn formed by bundling a large number of polyester filaments is unidirectionally twisted (that is, a single twisted cord). Is used.

  The fineness of the polyester cord (also referred to as nominal fineness or display fineness) is preferably 500 to 1500 dtex. Conventionally, it has not been known to use such a low-fineness PET cord as a single twisted structure for a carcass ply. By using such a low-fineness PET cord, the tire can be reduced in weight and the ply thickness can be reduced. By being able to do so, heat generation can be reduced and the durability of the tire can be improved. When the fineness is 500 dtex or more, it is possible to prevent an excessive number of cords from being driven in order to ensure rigidity. Moreover, when the fineness is 1500 dtex or less, the weight reduction effect of the tire can be enhanced. The fineness of the PET cord is more preferably 900 to 1300 dtex.

  As the polyester cord, one having a bending hardness per cord (hereinafter sometimes referred to as cord bending hardness) of 4 to 14 cN is used. Here, the cord bending hardness is a value defined by the maximum load when one polyester cord is bent at the center part at a distance between fulcrums of 25.4 mm. If the cord bending hardness is less than 4 cN, the sidewall portion rigidity is insufficient and the steering stability is difficult to satisfy. If the number of cords driven and the number of plies are increased in order to ensure the sidewall portion rigidity, the tire mass increases. This may cause a malfunction such as separation due to heat generation during driving. Also, if the cord bending hardness exceeds 14 cN, the cord becomes too stiff, making it difficult to improve the ride comfort, lowering fatigue resistance and affecting durability, and the difference in modulus from rubber It is easy to cause a separation failure from the adhesive failure based on the above. The cord bending hardness is more preferably 5 to 12 cN, and further preferably 6 to 10 cN.

  The means for setting the bending hardness of the polyester cord in the range of 4 to 14 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.

  The cord usage amount of the polyester cord in the carcass ply is 38 to 68% in terms of the cord occupancy per ply. Here, the code occupancy (%) is a value calculated by the following equation in the so-called topping reaction in which the cords are arranged in a predetermined number of driven lines and are covered with rubber. Code occupancy (%) = (Cord diameter (mm) × Number of cords driven (lines / 25 mm)) × 100/25 (mm).

  When the cord occupancy falls below the lower limit, the side wall rigidity is insufficient even when a cord in the cord bending hardness range is used, and the steering stability tends to decrease. If the cord occupancy exceeds the upper limit, the rigidity of the sidewall will be too high and the ride comfort will be lowered, the adjacent cords will approach each other and will be disadvantageous for separation, and the cord will be expanded when the ply is expanded in tire molding. This is likely to cause a disorder in the arrangement of the particles and cause a decrease in uniformity. The code occupancy is more preferably 40 to 60%, still more preferably 45 to 58%.

The number of twists of the polyester cord is not particularly limited, and the twist coefficient K may be set so that the bending hardness is within the above range. In one embodiment, the twist coefficient K may be 500 to 2000. Here, the twist coefficient K is defined as K = T × (D / 1.39) ^1/2 where T is the number of twists per 10 cm of the cord length (times / 10 cm) and the fineness is D (dtex). Is the value to be

  The polyester cord may be subjected to resin treatment such as heat resistance or adhesion treatment. Such a resin treatment may be performed on a polyester cord woven in a sled shape, or may be performed at the stage of a single cord before weaving. As one embodiment, the polyester cord is woven in a sled shape with a predetermined number of driving, then dipped with a known treatment liquid such as RFL (resorcin-formalin-latex) adhesive, and then dried, and then, A carcass material for producing an unvulcanized tire (green tire) can be obtained by covering the both sides with a coated rubber made of a rubber composition and processing it in a topping process.

  As the steel cord constituting the belt, a plurality of steel filaments having a diameter of 0.20 to 0.30 mm are twisted, and the bending hardness per cord (hereinafter sometimes referred to as cord bending hardness). In which 180 is 380 cN.

  The filament constituting the steel cord has a diameter in the range of 0.20 to 0.30 mm, and a filament thinner than 0.20 mm needs to use a large number of filaments in order to ensure the cord bending hardness. The unit weight of the cord itself and the amount used for the belt ply increase, which is contrary to the weight reduction of the tire. On the other hand, if it exceeds 0.30 mm, the cord becomes rigid and the riding comfort is lowered, and the fatigue resistance and separation of the belt edge are also adversely affected. The diameter of the steel filament is more preferably 0.22 to 0.28 mm.

  The cord bending hardness of the steel cord is 180 to 380 cN. If the cord bending hardness is less than 180 cN, the cord becomes too flexible, the belt rigidity in the tire circumferential direction is lowered, the cornering power is lowered, and the steering stability is lowered. . On the other hand, if the cord bending hardness exceeds 380 cN, the cord becomes stiff and the ride comfort deteriorates. The cord bending hardness is more preferably 190 to 250 cN, and further preferably 200 to 230 cN. The cord bending hardness is a value defined by the maximum load when one steel cord is bent at the center portion at a distance between fulcrums of 25.4 mm, as in the case of the polyester cord.

  The cord structure of the steel cord is not particularly limited as long as the cord bending hardness can be within the above range, and a known cord structure can be adopted. Filament diameter, number of filaments, twisted structure The cord characteristics can be designed by combining the twist pitch and the like. As the cord structure, for example, a single twist structure such as 1 × 2, 1 × 3, 1 × 4, and 1 × 5, a two-layer twist structure such as 1 + 2, 1 + 3, 2 + 1, 2 + 2, 2 + 3, 2 + 4, and 2 + 5 (m + n structure) [Preferably, m = 1 or 2, n = 1 to 4. Note that the core may be untwisted or twisted.) A double twist structure such as 1 × 2 × 2, 1 × 2 × 3, etc. Can be mentioned.

  Such a steel cord can be manufactured using, for example, a known twisting machine such as a buncher twisting machine or a tubular twisting machine. The steel filament surface may be coated with, for example, 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.

  After the steel cords are arranged in parallel with a predetermined number of driving, a belt ply material for producing an unvulcanized tire (green tire) can be obtained by coating a coated rubber made of a rubber composition on both sides. .

  The number of steel cords to be driven into the belt ply can be appropriately set according to the cord tensile strength and the like, and is not particularly limited, but is preferably 10 to 25 / 25.4 mm, more preferably 15 to 25. Book / 25.4 mm.

  The radial tire according to the present embodiment uses a polyester cord having a single twist structure having the specific cord bending hardness for the carcass, and the belt steel cord has a belt rigidity defined by the cord bending hardness. By setting, tire strength and tire rigidity can be ensured, steering stability and riding comfort can be balanced, and the durability of the tire can be improved while achieving weight reduction.

  In the radial tire according to the present embodiment, the carcass can be constituted by one-ply or two-ply carcass plies, and in the case of two plies, the above polyester cord may be used for at least one carcass ply, Conventional polyester cords and nylon cords may be used for other carcass plies as long as the above effects are not impaired.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

  A pneumatic radial tire having a tire size of 195 / 65R15 was prototyped. The configurations of the carcass and the belt are as shown in Tables 1 and 2 below for the tires of the example and the comparative example, and the configurations other than the carcass and the belt are all common configurations. The number of belt plies constituting the belt was two, and the inclination angles of the cords were 22 ° (+ 22 ° / −22 °) with respect to the tire circumferential direction.

  “PET” in the carcass cord materials in Tables 1 and 2 means polyethylene terephthalate, and “1100 dtex / 2” is a twisted structure obtained by twisting two twisted yarns made of PET filaments with a fineness of 1100 dtex. “1100 dtex / 1” means a single twist structure composed of a PET filament bundle having a fineness of 1100 dtex. For the dip treatment for each PET cord, a known treatment solution can be used. In this example, the polyester cord is first treated once with the first treatment solution shown in Table 3 below, and then resorcin, formalin, By the method of processing once with the 2nd process liquid which consists of rubber latex (RFL), in Examples 1-3, it performed so that the resin adhesion rate might be about 4%. In addition, the difference in the fineness of the PET cord and the cord bending hardness in Examples 1 to 3 is due to the variation in the resin adhesion rate. In Example 4 and Comparative Examples 2 and 3, the cord bending hardness in the table was obtained by changing the resin adhesion rate.

As a steel cord for the belt, a piano wire rod SWRS82A material specified in JIS G3502 is subjected to dry drawing to an intermediate wire having a predetermined diameter by repeating patenting and wire drawing, and this intermediate wire is brass-plated (copper copper) After applying a ratio of 64% and an amount of plating of 4.5 g / kg), a filament obtained by final drawing to a predetermined diameter using a normal wet wire drawing machine is used using a normal tubular twisting machine. According to a conventional method, it is manufactured by twisting at the following twist pitch. The two-layer structure cord is indicated by (−) when the core is untwisted.
・ 2 + 2 × 0.25: Twist pitch = − / S14 mm
・ 2 + 1 × 0.27: Twist pitch = − / S15mm
・ 2 + 3 × 0.24: Twist pitch = − / S10 mm
・ 2 + 7 × 0.175: Twist pitch = S5 / S10mm
・ 2 + 7 × 0.20: Twist pitch = S6 / S12mm
・ 2 + 7 × 0.25: Twist pitch = S7 / S14mm
・ 1 × 3 × 0.28: Twist pitch = S11mm
・ 1 × 2 × 0.32: Twist pitch = S15mm

  Each measurement / evaluation method for each physical property and tire performance in Tables 1 and 2 is as follows.

-Carcass cord fineness, cord diameter, strength, strength: According to JIS L1017, after standing at a constant temperature of 20 ° C. and 65% RH for 24 hours or more, the cord diameter, fineness, and tensile tester (manufactured by Shimadzu Corporation) The strength and elongation were measured with an autograph.

Carcass cord bending hardness: Maximum load when a cord is bent using a tensile tester (manufactured by Shimadzu Corporation), and was measured as follows. That is, the support tool in a state in which the cord (10) having a length of 50 to 80 mm is hung at a position spaced by 25.4 mm with the both ends being free as shown in FIG. (12) and support the middle point (10M) so that it intersects the straight upper side (14A) of the inverted U-shaped fixed jig (14) perpendicularly from below. Hit it. Here, the upper side portion (14A) has a rod shape with a circular cross section (diameter = 3.0 mm). From this state, the support (12) is pulled upward at a tensile speed of 300 mm / min, and the load applied to the support (12) is measured while the cord (10) is bent by the jig (14). The maximum load at that time is the maximum bending load (cN) of the cord (10), and the average value of n = 5 is the cord bending hardness.

Carcass total cord bending hardness: Bending hardness per 25 mm width calculated by driving the cord bending hardness into the number of cords.

-Number of plies: The number of carcass plies that make up the carcass of the tire.

Carcass ply thickness: The thickness of a carcass ply formed by covering a polyester cord with a coated rubber, and measured with a dial gauge (leg diameter: 9.5 mm, load: 1670 mN).

Carcass total ply strength: Tensile strength per 25 mm width of carcass calculated by multiplying cord strength by the number of cords driven and the number of plies.

Carcass cord occupancy rate: Cord occupancy rate (%) = (Cord diameter (mm) × Number of cords driven (lines / 25 mm)) × 100/25 (mm)

-Belt cord diameter, strength: measured according to JIS G3510.

Belt cord bending hardness: Measured by the same method as carcass cord bending hardness.

Belt strength: Tensile strength per 25.4 mm width calculated by multiplying the cord strength by the number of cords to be driven.

Belt bending stiffness: Bending hardness per 25.4 mm width calculated by driving the cord bending hardness and the number of cords.

Belt ply thickness: This is the thickness of a belt ply formed by coating a steel cord with coated rubber, and was measured with a dial gauge (leg diameter 9.5 mm, load 1670 mN).

Carcass ply mass (index): The carcass ply mass per tire is indicated by an index with Comparative Example 1 being 100, and the smaller the index, the lighter the weight.

Tire mass (index): The mass per tire is indicated by an index with Comparative Example 1 being 100, and the smaller the index, the lighter the weight.

-Tire load durability: Based on FMVSS109 (UTQG), measurement was performed as follows using a drum tester having a 1700 mm diameter rotating drum made of steel with a smooth surface. The tire internal pressure was 200 kPa, and the test speed was constant at 80 km / h. After running at 85% of the maximum load specified by JATMA for 4 hours, then at 90% of the maximum load for 6 hours, and further at 100% of the maximum load for 24 hours, it is run at 120% of the maximum load for 24 hours. At this time, if there is no abnormality on the appearance and the inner surface, the vehicle is further driven at 140% of the maximum load until a failure occurs. The distance traveled until the failure occurred was indexed with the tire of Comparative Example 1 as 100. The larger the index, the better the load durability.

-Actual vehicle handling stability: A test tire incorporated with an internal pressure of 200 kPa was mounted on a test vehicle with a displacement of 2000 cc, and a test course was run by three trained test drivers to evaluate the feeling. The scoring was based on a 10-point evaluation, and a relative comparison was performed with the tire of Comparative Example 1 being 6 points. The larger the index, the better the steering stability.

・ Ride comfort: Adjust each tire to 200 kPa using JIS standard rims, install 4 similar tires on a 2000cc domestic passenger car, and use three test drivers on the good and bad test courses The ride comfort was sensorially evaluated and evaluated based on Comparative Example 1. The equivalent to Comparative Example 1 is indicated by “Δ”, the inferior is indicated by “X”, and the excellent is indicated by “◯”.

  The results are as shown in Tables 1 and 2. Compared to Comparative Example 1 using a double twisted PET cord made of 1100 dtex / 2 for the carcass ply, Comparative Example 2 using a single twisted PET cord made of 1100 dtex / 1 is effective in reducing the weight of the tire. Although the carcass cord bending hardness was as low as 3 cN, the steering stability was inferior due to insufficient rigidity of the sidewall portion. In Comparative Example 3 in which a single-twisted PET cord made of 1100 dtex / 1 was used, but the cord bending hardness was too large at 17 cN, the carcass cord was too stiff, making it difficult to improve ride comfort and resistance. The tire's load durability decreased due to a decrease in fatigue. Although a single twist PET cord made of 1100 dtex / 1 was used, in Comparative Example 4 having a low cord occupancy rate of 37%, the steering stability was inferior due to insufficient rigidity of the sidewall portion. Although a single twist PET cord made of 1100 dtex / 1 was used, in Comparative Example 5 having a high cord occupancy ratio of 69%, the rigidity of the sidewall portion was increased and the riding comfort was deteriorated. Durability decreased due to adhesion failure, and the adjacent cords were close to each other, resulting in separation and decreased durability. In Comparative Example 6 using a single twisted PET cord made of 1670 dtex / 1, the cord bending hardness was too large at 16 cN, so that the carcass cord became too rigid, making it difficult to improve ride comfort and fatigue resistance. As a result, the load durability of the tire decreased.

  As the carcass ply, a single twisted PET cord satisfying both cord bending hardness and cord occupancy was used, but the belt cord was flexible in Comparative Example 7 where the bending hardness of the steel cord constituting the belt ply was too small at 125 cN. As a result, the stability of the belt in the circumferential direction of the tire decreased and the steering stability decreased. Moreover, in Comparative Example 8 in which the bending hardness of the steel cord constituting the belt ply was too large at 515 cN, the riding comfort deteriorated. In Comparative Example 9 in which the filament diameter of the steel cord constituting the belt ply was too large at 0.32 mm, the riding comfort was deteriorated, the cord fatigue was lowered, and the load durability was lowered.

  On the other hand, Examples 1 to 8 in which the carcass ply is set to a predetermined cord occupancy using a single twist PET cord having a predetermined cord bending hardness and set to a predetermined bending hardness as a steel cord of the belt. As a result, the load durability was improved as compared with Comparative Example 1, and the steering stability and the ride comfort were improved in a well-balanced manner by optimizing the tire rigidity, and the tire weight reduction effect was also great.

DESCRIPTION OF SYMBOLS 1 ... Pneumatic radial tire, 2 ... Tread part, 3 ... Bead part, 4 ... Side wall part, 5 ... Carcass, 7 ... Belt, 8 ... Belt reinforcement layer

Claims (2)

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 for a passenger car having
The polyester cord is a single twist cord, the bending hardness per cord is 4 to 14 cN, and the cord occupancy of the carcass ply is 38 to 68%,
The steel cord is formed by twisting a plurality of steel filaments having a diameter of 0.20 to 0.30 mm, and the bending hardness per cord of the steel cord is 180 to 380 cN. Pneumatic radial tire.   The pneumatic radial tire for a passenger car according to claim 1, wherein the fineness of the polyester cord is 500 to 1500 dtex.

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